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Context: ##ctonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s snake called jormungandr. the norse creation account preserved in gylfaginning ( viii ) states that during the creation of the earth, an impassable sea was placed around it : and jafnharr said : " of the blood, which ran and welled forth freely out of his wounds, they made the sea, when they had formed and made firm the earth together, and laid the sea in a ring round. about her ; and it may well seem a hard thing to most men to cross over it. " the late norse konungs skuggsja, on the other hand, explains earth ' s shape as a sphere : if you take a lighted candle and set it in a room, you may expect it to light up the entire interior, unless something should hinder, though the room be quite large. but if you take an apple and hang it close to the flame, so near that it is heated, the apple will darken nearly half the room or even more. however, if you hang the apple near the wall, it will not get hot ; the candle will light up the whole house ; and the shadow on the wall where the apple hangs will be scarcely half as large as the apple itself. from this you may infer that the earth - circle is round like a ball and not equally near the sun at every point. but where the curved surface lies nearest the sun ' s path, there will the greatest heat be ; and some of the lands that lie continuously under the unbroken rays cannot be inhabited. = = = = east asia = = = = in ancient china, the prevailing belief was that the earth was flat and square, while the heavens were round, an assumption virtually unquestioned until the introduction of european astronomy in the 17th century. the english sinologist cullen emphasizes the point that there was no concept of a round earth in ancient chinese astronomy : chinese thought on the form of the earth remained almost unchanged from early times until the first contacts with modern science through the medium of jesuit missionaries in the seventeenth century. while the heavens were variously described as being like an umbrella covering the earth ( the kai tian theory ), or like a sphere surrounding it ( the hun tian theory ), or as being without substance while the heavenly bodies float freely ( the hsuan yeh theory ), the earth was at all times flat, although perhaps bulging up slightly. the model of an egg was often used by chinese astronomers such as zhang heng ( 78 – 139 ad ) to ##morphology studies the origin of landscapes. structural geology studies the deformation of rocks to produce mountains and lowlands. resource geology studies how energy resources can be obtained from minerals. environmental geology studies how pollution and contaminants affect soil and rock. mineralogy is the study of minerals and includes the study of mineral formation, crystal structure, hazards associated with minerals, and the physical and chemical properties of minerals. petrology is the study of rocks, including the formation and composition of rocks. petrography is a branch of petrology that studies the typology and classification of rocks. = = earth ' s interior = = plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make it available as drinking water. the earliest exploitation of groundwater resources dates back to 3000 bc, and hydrogeology as a science was developed by hydrologists beginning in the 17th century. ecohydrology is the study of ecological systems in the hydrosphere. it can be divided into the physical study of aquatic ecosystems and the , crystal structure, hazards associated with minerals, and the physical and chemical properties of minerals. petrology is the study of rocks, including the formation and composition of rocks. petrography is a branch of petrology that studies the typology and classification of rocks. = = earth ' s interior = = plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest ##sphere ( or lithosphere ). earth science can be considered to be a branch of planetary science but with a much older history. = = geology = = geology is broadly the study of earth ' s structure, substance, and processes. geology is largely the study of the lithosphere, or earth ' s surface, including the crust and rocks. it includes the physical characteristics and processes that occur in the lithosphere as well as how they are affected by geothermal energy. it incorporates aspects of chemistry, physics, and biology as elements of geology interact. historical geology is the application of geology to interpret earth history and how it has changed over time. geochemistry studies the chemical components and processes of the earth. geophysics studies the physical properties of the earth. paleontology studies fossilized biological material in the lithosphere. planetary geology studies geoscience as it pertains to extraterrestrial bodies. geomorphology studies the origin of landscapes. structural geology studies the deformation of rocks to produce mountains and lowlands. resource geology studies how energy resources can be obtained from minerals. environmental geology studies how pollution and contaminants affect soil and rock. mineralogy is the study of minerals and includes the study of mineral formation, crystal structure, hazards associated with minerals, and the physical and chemical properties of minerals. petrology is the study of rocks, including the formation and composition of rocks. petrography is a branch of petrology that studies the typology and classification of rocks. = = earth ' s interior = = plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as all christian authors held that the earth was round. athenagoras, an eastern christian writing around the year 175 ad, said that the earth was spherical. methodius ( c. 290 ad ), an eastern christian writing against " the theory of the chaldeans and the egyptians " said : " let us first lay bare... the theory of the chaldeans and the egyptians. they say that the circumference of the universe is likened to the turnings of a well - rounded globe, the earth being a central point. they say that since its outline is spherical,... the earth should be the center of the universe, around which the heaven is whirling. " arnobius, another eastern christian writing sometime around 305 ad, described the round earth : " in the first place, indeed, the world itself is neither right nor left. it has neither upper nor lower regions, nor front nor back. for whatever is round and bounded on every side by the circumference of a solid sphere, has no beginning or end... " other advocates of a round earth included eusebius, hilary of poitiers, irenaeus, hippolytus of rome, firmicus maternus, ambrose, jerome, prudentius, favonius eulogius, and others. the only exceptions to this consensus up until the mid - fourth century were theophilus of antioch and lactantius, both of whom held anti - hellenistic views and associated the round - earth view with pagan cosmology. lactantius, a western christian writer and advisor to the first christian roman emperor, constantine, writing sometime between 304 and 313 ad, ridiculed the notion of antipodes and the philosophers who fancied that " the universe is round like a ball. they also thought that heaven revolves in accordance with the motion of the heavenly bodies.... for that reason, they constructed brass globes, as though after the figure of the universe. " the influential theologian and philosopher saint augustine, one of the four great church fathers of the western church, similarly objected to the " fable " of antipodes : but as to the fable that there are antipodes, that is to say, men on the opposite side of the earth, where the sun rises when it sets to us, men who walk with their feet opposite ours that is on no ground credible. and, indeed, it is not affirmed that this has been learned by historical knowledge, but by scientific conjecture antipodes, that is to say, men on the opposite side of the earth, where the sun rises when it sets to us, men who walk with their feet opposite ours that is on no ground credible. and, indeed, it is not affirmed that this has been learned by historical knowledge, but by scientific conjecture, on the ground that the earth is suspended within the concavity of the sky, and that it has as much room on the one side of it as on the other : hence they say that the part that is beneath must also be inhabited. but they do not remark that, although it be supposed or scientifically demonstrated that the world is of a round and spherical form, yet it does not follow that the other side of the earth is bare of water ; nor even, though it be bare, does it immediately follow that it is peopled. for scripture, which proves the truth of its historical statements by the accomplishment of its prophecies, gives no false information ; and it is too absurd to say, that some men might have taken ship and traversed the whole wide ocean, and crossed from this side of the world to the other, and that thus even the inhabitants of that distant region are descended from that one first man. some historians do not view augustine ' s scriptural commentaries as endorsing any particular cosmological model, endorsing instead the view that augustine shared the common view of his contemporaries that the earth is spherical, in line with his endorsement of science in de genesi ad litteram. c. p. e. nothaft, responding to writers like leo ferrari who described augustine as endorsing a flat earth, says that "... other recent writers on the subject treat augustine ' s acceptance of the earth ' s spherical shape as a well - established fact ". while it always remained a minority view, from the mid - fourth to the seventh centuries ad, the flat - earth view experienced a revival, around the time when diodorus of tarsus founded the exegetical school known as the school of antioch, which sought to counter what he saw as the pagan cosmology of the greeks with a return to the traditional cosmology. the writings of diodorus did not survive, but are reconstructed from later criticism. this revival primarily took place in the east syriac world ( with little influence on the latin west ) where it gained proponents such as ephrem the syrian and in the popular hexaemeral homilies of jacob of serugh. chrys earth science or geoscience includes all fields of natural science related to the planet earth. this is a branch of science dealing with the physical, chemical, and biological complex constitutions and synergistic linkages of earth ' s four spheres : the biosphere, hydrosphere / cryosphere, atmosphere, and geosphere ( or lithosphere ). earth science can be considered to be a branch of planetary science but with a much older history. = = geology = = geology is broadly the study of earth ' s structure, substance, and processes. geology is largely the study of the lithosphere, or earth ' s surface, including the crust and rocks. it includes the physical characteristics and processes that occur in the lithosphere as well as how they are affected by geothermal energy. it incorporates aspects of chemistry, physics, and biology as elements of geology interact. historical geology is the application of geology to interpret earth history and how it has changed over time. geochemistry studies the chemical components and processes of the earth. geophysics studies the physical properties of the earth. paleontology studies fossilized biological material in the lithosphere. planetary geology studies geoscience as it pertains to extraterrestrial bodies. geomorphology studies the origin of landscapes. structural geology studies the deformation of rocks to produce mountains and lowlands. resource geology studies how energy resources can be obtained from minerals. environmental geology studies how pollution and contaminants affect soil and rock. mineralogy is the study of minerals and includes the study of mineral formation, crystal structure, hazards associated with minerals, and the physical and chemical properties of minerals. petrology is the study of rocks, including the formation and composition of rocks. petrography is a branch of petrology that studies the typology and classification of rocks. = = earth ' s interior = = plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and Question: What do you call the heat below earth’s surface that can be used to produce electricity? A) renewable energy B) inert energy C) geothermal energy D) natural energy	C) geothermal energy
Context: eat them. plants and other photosynthetic organisms are at the base of most food chains because they use the energy from the sun and nutrients from the soil and atmosphere, converting them into a form that can be used by animals. this is what ecologists call the first trophic level. the modern forms of the major staple foods, such as hemp, teff, maize, rice, wheat and other cereal grasses, pulses, bananas and plantains, as well as hemp, flax and cotton grown for their fibres, are the outcome of prehistoric selection over thousands of years from among wild ancestral plants with the most desirable characteristics. botanists study how plants produce food and how to increase yields, for example through plant breeding, making their work important to humanity ' s ability to feed the world and provide food security for future generations. botanists also study weeds, which are a considerable problem in agriculture, and the biology and control of plant pathogens in agriculture and natural ecosystems. ethnobotany is the study of the relationships between plants and people. when applied to the investigation of historical plant – people relationships ethnobotany may be referred to as archaeobotany or palaeoethnobotany. some of the earliest plant - people relationships arose between the indigenous people of canada in identifying edible plants from inedible plants. this relationship the indigenous people had with plants was recorded by ethnobotanists. = = plant biochemistry = = plant biochemistry is the study of the chemical processes used by plants. some of these processes are used in their primary metabolism like the photosynthetic calvin cycle and crassulacean acid metabolism. others make specialised materials like the cellulose and lignin used to build their bodies, and secondary products like resins and aroma compounds. plants and various other groups of photosynthetic eukaryotes collectively known as " algae " have unique organelles known as chloroplasts. chloroplasts are thought to be descended from cyanobacteria that formed endosymbiotic relationships with ancient plant and algal ancestors. chloroplasts and cyanobacteria contain the blue - green pigment chlorophyll a. chlorophyll a ( as well as its plant and green algal - specific cousin chlorophyll b ) absorbs light in the blue - violet and orange / red parts of the spectrum while reflecting and transmitting the green light that we see as the characteristic colour unspecialised cells ) that can grow into a new plant. in vascular plants, the xylem and phloem are the conductive tissues that transport resources between shoots and roots. roots are often adapted to store food such as sugars or starch, as in sugar beets and carrots. stems mainly provide support to the leaves and reproductive structures, but can store water in succulent plants such as cacti, food as in potato tubers, or reproduce vegetatively as in the stolons of strawberry plants or in the process of layering. leaves gather sunlight and carry out photosynthesis. large, flat, flexible, green leaves are called foliage leaves. gymnosperms, such as conifers, cycads, ginkgo, and gnetophytes are seed - producing plants with open seeds. angiosperms are seed - producing plants that produce flowers and have enclosed seeds. woody plants, such as azaleas and oaks, undergo a secondary growth phase resulting in two additional types of tissues : wood ( secondary xylem ) and bark ( secondary phloem and cork ). all gymnosperms and many angiosperms are woody plants. some plants reproduce sexually, some asexually, and some via both means. although reference to major morphological categories such as root, stem, leaf, and trichome are useful, one has to keep in mind that these categories are linked through intermediate forms so that a continuum between the categories results. furthermore, structures can be seen as processes, that is, process combinations. = = systematic botany = = systematic botany is part of systematic biology, which is concerned with the range and diversity of organisms and their relationships, particularly as determined by their evolutionary history. it involves, or is related to, biological classification, scientific taxonomy and phylogenetics. biological classification is the method by which botanists group organisms into categories such as genera or species. biological classification is a form of scientific taxonomy. modern taxonomy is rooted in the work of carl linnaeus, who grouped species according to shared physical characteristics. these groupings have since been revised to align better with the darwinian principle of common descent – grouping organisms by ancestry rather than superficial characteristics. while scientists do not always agree on how to classify organisms, molecular phylogenetics, which uses dna sequences as data, has driven many recent revisions along evolutionary lines and is likely to continue to do so. the dominant classification system is called linnaean taxonomy. it includes ranks and binomi the best - suited crops ( e. g., those with the highest yields ) to produce enough food to support a growing population. as crops and fields became increasingly large and difficult to maintain, it was discovered that specific organisms and their by - products could effectively fertilize, restore nitrogen, and control pests. throughout the history of agriculture, farmers have inadvertently altered the genetics of their crops through introducing them to new environments and breeding them with other plants — one of the first forms of biotechnology. these processes also were included in early fermentation of beer. these processes were introduced in early mesopotamia, egypt, china and india, and still use the same basic biological methods. in brewing, malted grains ( containing enzymes ) convert starch from grains into sugar and then adding specific yeasts to produce beer. in this process, carbohydrates in the grains broke down into alcohols, such as ethanol. later, other cultures produced the process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united kingdom desperately needed to manufacture explosives during world war i. biotechnology has also led to the development of antibiotics. in 1928, alexander fleming discovered the mold penicillium. his work led to the purification of the antibiotic formed by the mold by howard florey, ernst boris chain and norman heatley – to form stems mainly provide support to the leaves and reproductive structures, but can store water in succulent plants such as cacti, food as in potato tubers, or reproduce vegetatively as in the stolons of strawberry plants or in the process of layering. leaves gather sunlight and carry out photosynthesis. large, flat, flexible, green leaves are called foliage leaves. gymnosperms, such as conifers, cycads, ginkgo, and gnetophytes are seed - producing plants with open seeds. angiosperms are seed - producing plants that produce flowers and have enclosed seeds. woody plants, such as azaleas and oaks, undergo a secondary growth phase resulting in two additional types of tissues : wood ( secondary xylem ) and bark ( secondary phloem and cork ). all gymnosperms and many angiosperms are woody plants. some plants reproduce sexually, some asexually, and some via both means. although reference to major morphological categories such as root, stem, leaf, and trichome are useful, one has to keep in mind that these categories are linked through intermediate forms so that a continuum between the categories results. furthermore, structures can be seen as processes, that is, process combinations. = = systematic botany = = systematic botany is part of systematic biology, which is concerned with the range and diversity of organisms and their relationships, particularly as determined by their evolutionary history. it involves, or is related to, biological classification, scientific taxonomy and phylogenetics. biological classification is the method by which botanists group organisms into categories such as genera or species. biological classification is a form of scientific taxonomy. modern taxonomy is rooted in the work of carl linnaeus, who grouped species according to shared physical characteristics. these groupings have since been revised to align better with the darwinian principle of common descent – grouping organisms by ancestry rather than superficial characteristics. while scientists do not always agree on how to classify organisms, molecular phylogenetics, which uses dna sequences as data, has driven many recent revisions along evolutionary lines and is likely to continue to do so. the dominant classification system is called linnaean taxonomy. it includes ranks and binomial nomenclature. the nomenclature of botanical organisms is codified in the international code of nomenclature for algae, fungi, and plants ( icn ) and administered by the international botanical congress. kingdom plantae belongs to domain eukaryota and is broken down recursively until each species is separately classified. the order is : best - known and controversial applications of genetic engineering is the creation and use of genetically modified crops or genetically modified livestock to produce genetically modified food. crops have been developed to increase production, increase tolerance to abiotic stresses, alter the composition of the food, or to produce novel products. the first crops to be released commercially on a large scale provided protection from insect pests or tolerance to herbicides. fungal and virus resistant crops have also been developed or are in development. this makes the insect and weed management of crops easier and can indirectly increase crop yield. gm crops that directly improve yield by accelerating growth or making the plant more hardy ( by improving salt, cold or drought tolerance ) are also under development. in 2016 salmon have been genetically modified with growth hormones to reach normal adult size much faster. gmos have been developed that modify the quality of produce by increasing the nutritional value or providing more industrially useful qualities or quantities. the amflora potato produces a more industrially useful blend of starches. soybeans and canola have been genetically modified to produce more healthy oils. the first commercialised gm food was a tomato that had delayed ripening, increasing its shelf life. plants and animals have been engineered to produce materials they do not normally make. pharming uses crops and animals as bioreactors to produce vaccines, drug intermediates, or the drugs themselves ; the useful product is purified from the harvest and then used in the standard pharmaceutical production process. cows and goats have been engineered to express drugs and other proteins in their milk, and in 2009 the fda approved a drug produced in goat milk. = = = other applications = = = genetic engineering has potential applications in conservation and natural area management. gene transfer through viral vectors has been proposed as a means of controlling invasive species as well as vaccinating threatened fauna from disease. transgenic trees have been suggested as a way to confer resistance to pathogens in wild populations. with the increasing risks of maladaptation in organisms as a result of climate change and other perturbations, facilitated adaptation through gene tweaking could be one solution to reducing extinction risks. applications of genetic engineering in conservation are thus far mostly theoretical and have yet to be put into practice. genetic engineering is also being used to create microbial art. some bacteria have been genetically engineered to create black and white photographs. novelty items such as lavender - colored carnations, blue roses, and glowing fish, have also been produced through genetic engineering. = = regulation = = the regulation of genetic engineering ##ch which is stored in the chloroplast. starch is the characteristic energy store of most land plants and algae, while inulin, a polymer of fructose is used for the same purpose in the sunflower family asteraceae. some of the glucose is converted to sucrose ( common table sugar ) for export to the rest of the plant. unlike in animals ( which lack chloroplasts ), plants and their eukaryote relatives have delegated many biochemical roles to their chloroplasts, including synthesising all their fatty acids, and most amino acids. the fatty acids that chloroplasts make are used for many things, such as providing material to build cell membranes out of and making the polymer cutin which is found in the plant cuticle that protects land plants from drying out. plants synthesise a number of unique polymers like the polysaccharide molecules cellulose, pectin and xyloglucan from which the land plant cell wall is constructed. vascular land plants make lignin, a polymer used to strengthen the secondary cell walls of xylem tracheids and vessels to keep them from collapsing when a plant sucks water through them under water stress. lignin is also used in other cell types like sclerenchyma fibres that provide structural support for a plant and is a major constituent of wood. sporopollenin is a chemically resistant polymer found in the outer cell walls of spores and pollen of land plants responsible for the survival of early land plant spores and the pollen of seed plants in the fossil record. it is widely regarded as a marker for the start of land plant evolution during the ordovician period. the concentration of carbon dioxide in the atmosphere today is much lower than it was when plants emerged onto land during the ordovician and silurian periods. many monocots like maize and the pineapple and some dicots like the asteraceae have since independently evolved pathways like crassulacean acid metabolism and the c4 carbon fixation pathway for photosynthesis which avoid the losses resulting from photorespiration in the more common c3 carbon fixation pathway. these biochemical strategies are unique to land plants. = = = medicine and materials = = = phytochemistry is a branch of plant biochemistry primarily concerned with the chemical substances produced by plants during secondary metabolism. some of these compounds are toxins such as the alkaloid coniine from hemlock. the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the sugar ) for export to the rest of the plant. unlike in animals ( which lack chloroplasts ), plants and their eukaryote relatives have delegated many biochemical roles to their chloroplasts, including synthesising all their fatty acids, and most amino acids. the fatty acids that chloroplasts make are used for many things, such as providing material to build cell membranes out of and making the polymer cutin which is found in the plant cuticle that protects land plants from drying out. plants synthesise a number of unique polymers like the polysaccharide molecules cellulose, pectin and xyloglucan from which the land plant cell wall is constructed. vascular land plants make lignin, a polymer used to strengthen the secondary cell walls of xylem tracheids and vessels to keep them from collapsing when a plant sucks water through them under water stress. lignin is also used in other cell types like sclerenchyma fibres that provide structural support for a plant and is a major constituent of wood. sporopollenin is a chemically resistant polymer found in the outer cell walls of spores and pollen of land plants responsible for the survival of early land plant spores and the pollen of seed plants in the fossil record. it is widely regarded as a marker for the start of land plant evolution during the ordovician period. the concentration of carbon dioxide in the atmosphere today is much lower than it was when plants emerged onto land during the ordovician and silurian periods. many monocots like maize and the pineapple and some dicots like the asteraceae have since independently evolved pathways like crassulacean acid metabolism and the c4 carbon fixation pathway for photosynthesis which avoid the losses resulting from photorespiration in the more common c3 carbon fixation pathway. these biochemical strategies are unique to land plants. = = = medicine and materials = = = phytochemistry is a branch of plant biochemistry primarily concerned with the chemical substances produced by plants during secondary metabolism. some of these compounds are toxins such as the alkaloid coniine from hemlock. others, such as the essential oils peppermint oil and lemon oil are useful for their aroma, as flavourings and spices ( e. g., capsaicin ), and in medicine as pharmaceuticals as in opium from opium poppies. many medicinal and recreational drugs, such as tetrahydrocannabino 3 - carbon sugar glyceraldehyde 3 - phosphate ( g3p ). glyceraldehyde 3 - phosphate is the first product of photosynthesis and the raw material from which glucose and almost all other organic molecules of biological origin are synthesised. some of the glucose is converted to starch which is stored in the chloroplast. starch is the characteristic energy store of most land plants and algae, while inulin, a polymer of fructose is used for the same purpose in the sunflower family asteraceae. some of the glucose is converted to sucrose ( common table sugar ) for export to the rest of the plant. unlike in animals ( which lack chloroplasts ), plants and their eukaryote relatives have delegated many biochemical roles to their chloroplasts, including synthesising all their fatty acids, and most amino acids. the fatty acids that chloroplasts make are used for many things, such as providing material to build cell membranes out of and making the polymer cutin which is found in the plant cuticle that protects land plants from drying out. plants synthesise a number of unique polymers like the polysaccharide molecules cellulose, pectin and xyloglucan from which the land plant cell wall is constructed. vascular land plants make lignin, a polymer used to strengthen the secondary cell walls of xylem tracheids and vessels to keep them from collapsing when a plant sucks water through them under water stress. lignin is also used in other cell types like sclerenchyma fibres that provide structural support for a plant and is a major constituent of wood. sporopollenin is a chemically resistant polymer found in the outer cell walls of spores and pollen of land plants responsible for the survival of early land plant spores and the pollen of seed plants in the fossil record. it is widely regarded as a marker for the start of land plant evolution during the ordovician period. the concentration of carbon dioxide in the atmosphere today is much lower than it was when plants emerged onto land during the ordovician and silurian periods. many monocots like maize and the pineapple and some dicots like the asteraceae have since independently evolved pathways like crassulacean acid metabolism and the c4 carbon fixation pathway for photosynthesis which avoid the losses resulting from photorespiration in the more common c3 carbon fixation pathway herbicides. the people ' s republic of china was the first country to commercialise transgenic plants, introducing a virus - resistant tobacco in 1992. in 1994 calgene attained approval to commercially release the first genetically modified food, the flavr savr, a tomato engineered to have a longer shelf life. in 1994, the european union approved tobacco engineered to be resistant to the herbicide bromoxynil, making it the first genetically engineered crop commercialised in europe. in 1995, bt potato was approved safe by the environmental protection agency, after having been approved by the fda, making it the first pesticide producing crop to be approved in the us. in 2009 11 transgenic crops were grown commercially in 25 countries, the largest of which by area grown were the us, brazil, argentina, india, canada, china, paraguay and south africa. in 2010, scientists at the j. craig venter institute created the first synthetic genome and inserted it into an empty bacterial cell. the resulting bacterium, named mycoplasma laboratorium, could replicate and produce proteins. four years later this was taken a step further when a bacterium was developed that replicated a plasmid containing a unique base pair, creating the first organism engineered to use an expanded genetic alphabet. in 2012, jennifer doudna and emmanuelle charpentier collaborated to develop the crispr / cas9 system, a technique which can be used to easily and specifically alter the genome of almost any organism. = = process = = creating a gmo is a multi - step process. genetic engineers must first choose what gene they wish to insert into the organism. this is driven by what the aim is for the resultant organism and is built on earlier research. genetic screens can be carried out to determine potential genes and further tests then used to identify the best candidates. the development of microarrays, transcriptomics and genome sequencing has made it much easier to find suitable genes. luck also plays its part ; the roundup ready gene was discovered after scientists noticed a bacterium thriving in the presence of the herbicide. = = = gene isolation and cloning = = = the next step is to isolate the candidate gene. the cell containing the gene is opened and the dna is purified. the gene is separated by using restriction enzymes to cut the dna into fragments or polymerase chain reaction ( pcr ) to amplify up the gene segment. these segments can then be extracted through gel electrophoresis. if the chosen gene or the donor organism ' s Question: How do most plants create food? A) glycolysis B) electrolysis C) photosynthesis D) atherosclerosis	C) photosynthesis
Context: single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids are polymers of nucleotides. their function is to store, transmit, and express hereditary information. = = cells = = cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids are polymers of nucleotides. their function is to store, transmit, and express hereditary information. = = cells = = cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division. most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids are polymers of nucleotides. their function is to store, transmit, and express hereditary information. = = cells = = cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division. most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed the skin without applying strain. conformal contact and proper adhesion enable the device to bend and stretch without delaminating, deforming or failing, thereby eliminating the challenges with conventional, bulky wearables, including measurement artifacts, hysteresis, and motion - induced irritation to the skin. with this inherent ability to take the shape of skin, epidermal electronics can accurately acquire data without altering the natural motion or behavior of skin. the thin, soft, flexible design of epidermal electronics resembles that of temporary tattoos laminated on the skin. essentially, these devices are " mechanically invisible " to the wearer. epidermal electronics devices may adhere to the skin via van der waals forces or elastomeric substrates. with only van der waals forces, an epidermal device has the same thermal mass per unit area ( 150 mj / cm2k ) as skin, when the skin ' s thickness is < 500 nm. along with van der waals forces, the low values of e and thickness are effective in maximizing adhesion because they prevent deformation - induced detachment due to tension or compression. introducing an elastomeric substrate can improve adhesion but will raise the thermal mass per unit area slightly. several materials have been studied to produce these skin - like properties, including photolithography patterned serpentine gold nanofilm and patterned doping of silicon nanomembranes. = = = foot - worn = = = smart shoes are an example of wearable technology that incorporate smart features into shoes. smart shoes often work with smartphone applications to support tasks cannot be done with standard footwear. the uses include vibrating of the smart phone to tell users when and where to turn to reach their destination via google maps or self - lacing. self - lacing sneaker technology, similar to the nike mag in back to the future part ii, is another use of the smart shoe. in 2019 german footwear company puma was recognized as one of the " 100 best inventions of 2019 " by time for its fi laceless shoe that uses micro - motors to adjust the fit from an iphone. nike also introduced a smart shoe in 2019 known as adapt bb. the shoe featured buttons on the side to loosen or tighten the fit with a custom motor and gear, which could also be controlled by a smartphone. = = modern technologies = = on april 16, 2013, google invited " glass explorers " who had pre - ordered its wearable glasses at the 2012 google i / o conference to pick up their devices. the topic of using nuclear power sources for generating energy. organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. an organic compound is defined as any compound based on a carbon skeleton. organic compounds can be classified, organized and understood in reactions by their functional groups, unit atoms or molecules that show characteristic chemical properties in a compound. physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. in particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, spectroscopy, and more recently, astrochemistry. physical chemistry has large overlap with molecular physics. physical chemistry involves the use of infinitesimal calculus in deriving equations. it is usually associated with quantum chemistry and theoretical chemistry. physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap. theoretical chemistry is the study of chemistry via fundamental theoretical reasoning ( usually within mathematics or physics ). in particular the application of quantum mechanics to chemistry is called quantum chemistry. since the end of the second world war, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. theoretical chemistry has large overlap with ( theoretical and experimental ) condensed matter physics and molecular physics. other subdivisions include electrochemistry, femtochemistry, flavor chemistry, flow chemistry, immunohistochemistry, hydrogenation chemistry, mathematical chemistry, molecular mechanics, natural product chemistry, organometallic chemistry, petrochemistry, photochemistry, physical organic chemistry, polymer chemistry, radiochemistry, sonochemistry, supramolecular chemistry, synthetic chemistry, and many others. = = = interdisciplinary = = = interdisciplinary fields include agrochemistry, astrochemistry ( and cosmochemistry ), atmospheric chemistry, chemical engineering, chemical biology, chemo - informatics, environmental chemistry, geochemistry, green chemistry, immunochemistry, marine chemistry, materials science, mechanochemistry, medicinal chemistry, molecular biology, nanotechnology, oenology, pharmacology, phytochemistry, solid - state chemistry, surface science, thermochemistry, and many others. = = = industry = = = the chemical industry represents an important economic activity worldwide. the global top 50 chemical producers in 2013 had sales the crystals of potassium hydrogen carbonate ( khco3 ) and the kdco3 analogue are isomorphous. they are composed of hydrogen or deuterium bonded centrosymmetric dimers ( hco3 - ) ( 2 ) or ( dco3 - ) ( 2 ). the space group symmetry of khpd1 - pco3 ( p approximate to 0. 75 ) determined with neutron diffraction is identical to those of khco3 and kdco3. this is at variance with a random distribution of h and d nuclei. these crystals are macroscopic quantum systems in which protons or / and deuterons merge into macroscopic states. a variation of sneutrino inflation based on chi ^ 2 potential is considered where the inflaton and the late - decaying field are sneutrinos of different generations. the lighter, late - decaying sneutrino dilutes the gravitinos over - produced after inflaton decay and generates the matter asymmetry. it can also significantly contribute to the curvature perturbation, realizing the mixed inflaton - curvaton case. the cosmic microwave background ( cmb ) observables can distinguish this case from inflation with chi ^ 2 potential, provided that the initial value of the late - decaying sneutrino is either an order of magnitude smaller or larger than the reduced planck scale. ##idermal electronics mirror those of skin to allow them to perform in this same way. like skin, epidermal electronics are ultrathin ( h < 100 μm ), low - modulus ( e ≈70 kpa ), and lightweight ( < 10 mg / cm2 ), enabling them to conform to the skin without applying strain. conformal contact and proper adhesion enable the device to bend and stretch without delaminating, deforming or failing, thereby eliminating the challenges with conventional, bulky wearables, including measurement artifacts, hysteresis, and motion - induced irritation to the skin. with this inherent ability to take the shape of skin, epidermal electronics can accurately acquire data without altering the natural motion or behavior of skin. the thin, soft, flexible design of epidermal electronics resembles that of temporary tattoos laminated on the skin. essentially, these devices are " mechanically invisible " to the wearer. epidermal electronics devices may adhere to the skin via van der waals forces or elastomeric substrates. with only van der waals forces, an epidermal device has the same thermal mass per unit area ( 150 mj / cm2k ) as skin, when the skin ' s thickness is < 500 nm. along with van der waals forces, the low values of e and thickness are effective in maximizing adhesion because they prevent deformation - induced detachment due to tension or compression. introducing an elastomeric substrate can improve adhesion but will raise the thermal mass per unit area slightly. several materials have been studied to produce these skin - like properties, including photolithography patterned serpentine gold nanofilm and patterned doping of silicon nanomembranes. = = = foot - worn = = = smart shoes are an example of wearable technology that incorporate smart features into shoes. smart shoes often work with smartphone applications to support tasks cannot be done with standard footwear. the uses include vibrating of the smart phone to tell users when and where to turn to reach their destination via google maps or self - lacing. self - lacing sneaker technology, similar to the nike mag in back to the future part ii, is another use of the smart shoe. in 2019 german footwear company puma was recognized as one of the " 100 best inventions of 2019 " by time for its fi laceless shoe that uses micro - motors to adjust the fit from an iphone. nike also introduced a smart shoe in 2019 known as adapt bb. the shoe featured buttons on the computations in the cohomology of finite groups. the mechanism leading to an auger transition is based on the residual coulomb interaction between the valence electron and the core electrons. on the assumption that the wave field is switched on adiabatically, the probability of the auger effect of the inner electrons of the atom is determined. Question: In a ketone, two of which kind of groups are attached to the carbonyl carbon atom? A) ions B) carbon groups C) nitrogen groups D) oxygen groups	B) carbon groups
Context: the thickness of freshly made soap films is usually in the micron range, and interference colors make thickness fluctuations easily visible. circular patterns of constant thickness are commonly observed, either a thin film disc in a thicker film or the reverse. in this letter, we evidence the line tension at the origin of these circular patterns. using a well controlled soap film preparation, we produce a piece of thin film surrounded by a thicker film. the thickness profile, measured with a spectral camera, leads to a line tension of the order of 0. 1 nn which drives the relaxation of the thin film shape, initially very elongated, toward a circular shape. a balance between line tension and air friction leads to a quantitative prediction of the relaxation process. such a line tension is expected to play a role in the production of marginal regeneration patches, involved in soap film drainage and stability. three of what is called the six simple machines, from which all machines are based. these machines are the inclined plane, the wedge, and the lever, which allowed the ancient egyptians to move millions of limestone blocks which weighed approximately 3. 5 tons ( 7, 000 lbs. ) each into place to create structures like the great pyramid of giza, which is 481 feet ( 147 meters ) high. they also made writing medium similar to paper from papyrus, which joshua mark states is the foundation for modern paper. papyrus is a plant ( cyperus papyrus ) which grew in plentiful amounts in the egyptian delta and throughout the nile river valley during ancient times. the papyrus was harvested by field workers and brought to processing centers where it was cut into thin strips. the strips were then laid - out side by side and covered in plant resin. the second layer of strips was laid on perpendicularly, then both pressed together until the sheet was dry. the sheets were then joined to form a roll and later used for writing. egyptian society made several significant advances during dynastic periods in many areas of technology. according to hossam elanzeery, they were the first civilization to use timekeeping devices such as sundials, shadow clocks, and obelisks and successfully leveraged their knowledge of astronomy to create a calendar model that society still uses today. they developed shipbuilding technology that saw them progress from papyrus reed vessels to cedar wood ships while also pioneering the use of rope trusses and stem - mounted rudders. the egyptians also used their knowledge of anatomy to lay the foundation for many modern medical techniques and practiced the earliest known version of neuroscience. elanzeery also states that they used and furthered mathematical science, as evidenced in the building of the pyramids. ancient egyptians also invented and pioneered many food technologies that have become the basis of modern food technology processes. based on paintings and reliefs found in tombs, as well as archaeological artifacts, scholars like paul t nicholson believe that the ancient egyptians established systematic farming practices, engaged in cereal processing, brewed beer and baked bread, processed meat, practiced viticulture and created the basis for modern wine production, and created condiments to complement, preserve and mask the flavors of their food. = = = = indus valley = = = = the indus valley civilization, situated in a resource - rich area ( in modern pakistan and northwestern india ), is notable for its early application of city planning, sanitation technologies, and plumbing. indus valley construction and architecture, called ' vaastu river valley during ancient times. the papyrus was harvested by field workers and brought to processing centers where it was cut into thin strips. the strips were then laid - out side by side and covered in plant resin. the second layer of strips was laid on perpendicularly, then both pressed together until the sheet was dry. the sheets were then joined to form a roll and later used for writing. egyptian society made several significant advances during dynastic periods in many areas of technology. according to hossam elanzeery, they were the first civilization to use timekeeping devices such as sundials, shadow clocks, and obelisks and successfully leveraged their knowledge of astronomy to create a calendar model that society still uses today. they developed shipbuilding technology that saw them progress from papyrus reed vessels to cedar wood ships while also pioneering the use of rope trusses and stem - mounted rudders. the egyptians also used their knowledge of anatomy to lay the foundation for many modern medical techniques and practiced the earliest known version of neuroscience. elanzeery also states that they used and furthered mathematical science, as evidenced in the building of the pyramids. ancient egyptians also invented and pioneered many food technologies that have become the basis of modern food technology processes. based on paintings and reliefs found in tombs, as well as archaeological artifacts, scholars like paul t nicholson believe that the ancient egyptians established systematic farming practices, engaged in cereal processing, brewed beer and baked bread, processed meat, practiced viticulture and created the basis for modern wine production, and created condiments to complement, preserve and mask the flavors of their food. = = = = indus valley = = = = the indus valley civilization, situated in a resource - rich area ( in modern pakistan and northwestern india ), is notable for its early application of city planning, sanitation technologies, and plumbing. indus valley construction and architecture, called ' vaastu shastra ', suggests a thorough understanding of materials engineering, hydrology, and sanitation. = = = = china = = = = the chinese made many first - known discoveries and developments. major technological contributions from china include the earliest known form of the binary code and epigenetic sequencing, early seismological detectors, matches, paper, helicopter rotor, raised - relief map, the double - action piston pump, cast iron, water powered blast furnace bellows, the iron plough, the multi - tube seed drill, the wheelbarrow, the parachute, the compass, the rudder, the crossbow, the south pointing chariot and gunpowder ##ization. the fouling is usually induced faster at higher driving forces. membrane fouling and particle retention in a feed solution also builds up a concentration gradients and particle backflow ( concentration polarization ). the tangential flow devices are more cost and labor - intensive, but they are less susceptible to fouling due to the sweeping effects and high shear rates of the passing flow. the most commonly used synthetic membrane devices ( modules ) are flat sheets / plates, spiral wounds, and hollow fibers. flat membranes used in filtration and separation processes can be enhanced with surface patterning, where microscopic structures are introduced to improve performance. these patterns increase surface area, optimize water flow, and reduce fouling, leading to higher permeability and longer membrane lifespan. research has shown that such modifications can significantly enhance efficiency in water purification, energy applications, and industrial separations. flat plates are usually constructed as circular thin flat membrane surfaces to be used in dead - end geometry modules. spiral wounds are constructed from similar flat membranes but in the form of a " pocket " containing two membrane sheets separated by a highly porous support plate. several such pockets are then wound around a tube to create a tangential flow geometry and to reduce membrane fouling. hollow fiber modules consist of an assembly of self - supporting fibers with dense skin separation layers, and a more open matrix helping to withstand pressure gradients and maintain structural integrity. the hollow fiber modules can contain up to 10, 000 fibers ranging from 200 to 2500 μm in diameter ; the main advantage of hollow fiber modules is the very large surface area within an enclosed volume, increasing the efficiency of the separation process. the disc tube module uses a cross - flow geometry and consists of a pressure tube and hydraulic discs, which are held by a central tension rod, and membrane cushions that lie between two discs. = = membrane performance and governing equations = = the selection of synthetic membranes for a targeted separation process is usually based on few requirements. membranes have to provide enough mass transfer area to process large amounts of feed stream. the selected membrane has to have high selectivity ( rejection ) properties for certain particles ; it has to resist fouling and to have high mechanical stability. it also needs to be reproducible and to have low manufacturing costs. the main modeling equation for the dead - end filtration at constant pressure drop is represented by darcy ' s law : d v p d t = q = δ p μ a ( 1 r m + r ) { \ displaystyle { \ frac { dv _ earliest record of a ship under sail is that of a nile boat dating to around 7, 000 bce. from prehistoric times, egyptians likely used the power of the annual flooding of the nile to irrigate their lands, gradually learning to regulate much of it through purposely built irrigation channels and " catch " basins. the ancient sumerians in mesopotamia used a complex system of canals and levees to divert water from the tigris and euphrates rivers for irrigation. archaeologists estimate that the wheel was invented independently and concurrently in mesopotamia ( in present - day iraq ), the northern caucasus ( maykop culture ), and central europe. time estimates range from 5, 500 to 3, 000 bce with most experts putting it closer to 4, 000 bce. the oldest artifacts with drawings depicting wheeled carts date from about 3, 500 bce. more recently, the oldest - known wooden wheel in the world as of 2024 was found in the ljubljana marsh of slovenia ; austrian experts have established that the wheel is between 5, 100 and 5, 350 years old. the invention of the wheel revolutionized trade and war. it did not take long to discover that wheeled wagons could be used to carry heavy loads. the ancient sumerians used a potter ' s wheel and may have invented it. a stone pottery wheel found in the city - state of ur dates to around 3, 429 bce, and even older fragments of wheel - thrown pottery have been found in the same area. fast ( rotary ) potters ' wheels enabled early mass production of pottery, but it was the use of the wheel as a transformer of energy ( through water wheels, windmills, and even treadmills ) that revolutionized the application of nonhuman power sources. the first two - wheeled carts were derived from travois and were first used in mesopotamia and iran in around 3, 000 bce. the oldest known constructed roadways are the stone - paved streets of the city - state of ur, dating to c. 4, 000 bce, and timber roads leading through the swamps of glastonbury, england, dating to around the same period. the first long - distance road, which came into use around 3, 500 bce, spanned 2, 400 km from the persian gulf to the mediterranean sea, but was not paved and was only partially maintained. in around 2, 000 bce, the minoans on the greek island of crete built a 50 km road leading from the palace of gortyn on the south side of the island, through the mountains, an essay on horndeski gravity, how it was formulated in the early 1970s and how it was ' re - discovered ' and widely adopted by cosmologists more than thirty years later. ##lling, pipe jacking and other operations. a caisson is sunk by self - weight, concrete or water ballast placed on top, or by hydraulic jacks. the leading edge ( or cutting shoe ) of the caisson is sloped out at a sharp angle to aid sinking in a vertical manner ; it is usually made of steel. the shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. an open caisson may fill with water during sinking. the material is excavated by clamshell excavator bucket on crane. the formation level subsoil may still not be suitable for excavation or bearing capacity. the water in the caisson ( due to a high water table ) balances the upthrust forces of the soft soils underneath. if dewatered, the base may " pipe " or " boil ", causing the caisson to sink. to combat this problem, piles may be driven from the surface to act as : load - bearing walls, in that they transmit loads to deeper soils. anchors, in that they resist flotation because of the friction at the interface between their surfaces and the surrounding earth into which they have been driven. h - beam sections ( typical column sections, due to resistance to bending in all axis ) may be driven at angles " raked " to rock or other firmer soils ; the h - beams are left extended above the base. a reinforced concrete plug may be placed under the water, a process known as tremie concrete placement. when the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. = = = monolithic = = = a monolithic caisson ( or simply a monolith ) is larger than the other types of caisson, but similar to open caissons. such caissons are often found in quay walls, where resistance to impact from ships is required. = = = pneumatic = = = shallow caissons may be open to the air, whereas pneumatic caissons ( sometimes called pressurized caissons ), which penetrate soft mud, are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. an airlock allows access to the chamber. workers, called sandhogs in american english, move mud and rock debris ( called the hun tian theory ), or as being without substance while the heavenly bodies float freely ( the hsuan yeh theory ), the earth was at all times flat, although perhaps bulging up slightly. the model of an egg was often used by chinese astronomers such as zhang heng ( 78 – 139 ad ) to describe the heavens as spherical : the heavens are like a hen ' s egg and as round as a crossbow bullet ; the earth is like the yolk of the egg, and lies in the centre. this analogy with a curved egg led some modern historians, notably joseph needham, to conjecture that chinese astronomers were, after all, aware of the earth ' s sphericity. the egg reference, however, was rather meant to clarify the relative position of the flat earth to the heavens : in a passage of zhang heng ' s cosmogony not translated by needham, zhang himself says : " heaven takes its body from the yang, so it is round and in motion. earth takes its body from the yin, so it is flat and quiescent ". the point of the egg analogy is simply to stress that the earth is completely enclosed by heaven, rather than merely covered from above as the kai tian describes. chinese astronomers, many of them brilliant men by any standards, continued to think in flat - earth terms until the seventeenth century ; this surprising fact might be the starting - point for a re - examination of the apparent facility with which the idea of a spherical earth found acceptance in fifth - century bc greece. further examples cited by needham supposed to demonstrate dissenting voices from the ancient chinese consensus actually refer without exception to the earth being square, not to it being flat. accordingly, the 13th - century scholar li ye, who argued that the movements of the round heaven would be hindered by a square earth, did not advocate a spherical earth, but rather that its edge should be rounded off so as to be circular. however, needham disagrees, affirming that li ye believed the earth to be spherical, similar in shape to the heavens but much smaller. this was preconceived by the 4th - century scholar yu xi, who argued for the infinity of outer space surrounding the earth and that the latter could be either square or round, in accordance to the shape of the heavens. when chinese geographers of the 17th century, influenced by european cartography and astronomy, showed the earth as a sphere that could be circumnavigated by sailing around the globe, they any two generating systems of the fundamental group of a closed surface are nielsen equivalent. , and carpentry. the trade of the ship - wright. the trade of the wheel - wright. the trade of the wainwright : making wagons. ( the latin word for a two - wheeled wagon is carpentum, the maker of which was a carpenter. ) ( wright is the agent form of the word wrought, which itself is the original past passive participle of the word work, now superseded by the weak verb forms worker and worked respectively. ) blacksmithing and the various related smithing and metal - crafts. folk music played on acoustic instruments. mathematics ( particularly, pure mathematics ) organic farming and animal husbandry ( i. e. ; agriculture as practiced by all american farmers prior to world war ii ). milling in the sense of operating hand - constructed equipment with the intent to either grind grain, or the reduction of timber to lumber as practiced in a saw - mill. fulling, felting, drop spindle spinning, hand knitting, crochet, & similar textile preparation. the production of charcoal by the collier, for use in home heating, foundry operations, smelting, the various smithing trades, and for brushing ones teeth as in colonial america. glass - blowing. various subskills of food preservation : smoking salting pickling drying note : home canning is a counter example of a low technology since some of the supplies needed to pursue this skill rely on a global trade network and an existing manufacturing infrastructure. the production of various alcoholic beverages : wine : poorly preserved fruit juice. beer : a way to preserve the calories of grain products from decay. whiskey : an improved ( distilled ) form of beer. flint - knapping masonry as used in castles, cathedrals, and root cellars. = = = domestic or consumer = = = ( non exhaustive ) list of low - tech in a westerner ' s everyday life : getting around by bike, and repairing it with second - hand materials using a cargo bike to carry loads ( rather than a gasoline vehicle ) drying clothes on a clothesline or on a drying rack washing clothes by hand, or in a human - powered washing machine cooling one ' s home with a fan or an air expander ( rather than electrical appliances such as air conditioners ) using a bell as door bell a cellar, " desert fridge ", or icebox ( rather than a fridge or freezer ) long - distance travel by sailing boat ( rather than by plane ) a wicker bag or a tote bag ( rather than a plastic bag ) to Question: Tapeworms are what type of flatworms? A) single-celled B) parasitic C) symbiotic D) endogenous	B) parasitic
Context: a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' ##ctonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s polymer diodes require cathodes that do not corrode the polymer but do have low work function to minimize the electron injection barrier. first - principles calculations demonstrate that the work function of the ( 1000 ) surface of the compound ca2n is half an ev lower than that of the elemental metal ca ( 2. 35 vs. 2. 87 ev ). moreover its reactivity is expected to be smaller. this makes ca2n an interesting candidate to replace calcium as cathode material for polymer light emitting diode devices. , crystal structure, hazards associated with minerals, and the physical and chemical properties of minerals. petrology is the study of rocks, including the formation and composition of rocks. petrography is a branch of petrology that studies the typology and classification of rocks. = = earth ' s interior = = plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest are dreidels fair? in other words, does the average dreidel have an equal chance of turning up any one of its four sides? to explore this hypothesis, three different dreidels were each spun hundreds of times with the number of occurrences of each side recorded. it was found that all three dreidels tested - - a cheap plastic dreidel, an old wooden dreidel, and a dreidel that came embossed with a picture of santa claus - - were not fair. statistically, for each dreidel, some sides came up significantly more often than others. although an unfair dreidel does not necessarily make the game itself unfair, it is conjectured that hundreds of pounds of chocolate have been distributed during chanukah under false pretenses. symbiotic and syntrophic communities, for example. = = = eukaryotes = = = eukaryotes are hypothesized to have split from archaea, which was followed by their endosymbioses with bacteria ( or symbiogenesis ) that gave rise to mitochondria and chloroplasts, both of which are now part of modern - day eukaryotic cells. the major lineages of eukaryotes diversified in the precambrian about 1. 5 billion years ago and can be classified into eight major clades : alveolates, excavates, stramenopiles, plants, rhizarians, amoebozoans, fungi, and animals. five of these clades are collectively known as protists, which are mostly microscopic eukaryotic organisms that are not plants, fungi, or animals. while it is likely that protists share a common ancestor ( the last eukaryotic common ancestor ), protists by themselves do not constitute a separate clade as some protists may be more closely related to plants, fungi, or animals than they are to other protists. like groupings such as algae, invertebrates, or protozoans, the protist grouping is not a formal taxonomic group but is used for convenience. most protists are unicellular ; these are called microbial eukaryotes. plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom plantae, which would exclude fungi and some algae. plant cells were derived by endosymbiosis of a cyanobacterium into an early eukaryote about one billion years ago, which gave rise to chloroplasts. the first several clades that emerged following primary endosymbiosis were aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related. algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of plantae. unlike glaucophytes, the other algal clades such as red and green algae are multicellular. green algae comprise three major clades : chlorophytes, coleochaetophytes, and stoneworts. fungi are eukaryotes that the luminescence of 3 speleothem samples from the acquafredda karst system and 1 from the novella cave ( gessi bolognesi natural park, italy ) has been recorded using excitation by impulse xe - lamp. all these carbonate speleothems are believed to be formed only from active co2 from the air, because the bedrock of the cave consist of gypsum and does not contain carbonates. the obtained photos of luminescence record the climate changes during the speleothem growth. u / th and 14c dating proved that studied speleothems started to grow since about 5, 000 years ago. the detailed analyses of the luminescence records is still in progress. some references for the breaking strength of fused silica fibers compiled in 1999. building block. ceramics – not to be confused with raw, unfired clay – are usually seen in crystalline form. the vast majority of commercial glasses contain a metal oxide fused with silica. at the high temperatures used to prepare glass, the material is a viscous liquid which solidifies into a disordered state upon cooling. windowpanes and eyeglasses are important examples. fibers of glass are also used for long - range telecommunication and optical transmission. scratch resistant corning gorilla glass is a well - known example of the application of materials science to drastically improve the properties of common components. engineering ceramics are known for their stiffness and stability under high temperatures, compression and electrical stress. alumina, silicon carbide, and tungsten carbide are made from a fine powder of their constituents in a process of sintering with a binder. hot pressing provides higher density material. chemical vapor deposition can place a film of a ceramic on another material. cermets are ceramic particles containing some metals. the wear resistance of tools is derived from cemented carbides with the metal phase of cobalt and nickel typically added to modify properties. ceramics can be significantly strengthened for engineering applications using the principle of crack deflection. this process involves the strategic addition of second - phase particles within a ceramic matrix, optimizing their shape, size, and distribution to direct and control crack propagation. this approach enhances fracture toughness, paving the way for the creation of advanced, high - performance ceramics in various industries. = = = composites = = = another application of materials science in industry is making composite materials. these are structured materials composed of two or more macroscopic phases. applications range from structural elements such as steel - reinforced concrete, to the thermal insulating tiles, which play a key and integral role in nasa ' s space shuttle thermal protection system, which is used to protect the surface of the shuttle from the heat of re - entry into the earth ' s atmosphere. one example is reinforced carbon - carbon ( rcc ), the light gray material, which withstands re - entry temperatures up to 1, 510 °c ( 2, 750 °f ) and protects the space shuttle ' s wing leading edges and nose cap. rcc is a laminated composite material made from graphite rayon cloth and impregnated with a phenolic resin. after curing at high temperature in an autoclave, the laminate is pyrolized to convert the resin to carbon, impregnated with furfuryl alcohol in a onset of electro - chemical corrosion. similar problems are encountered in coastal and offshore structures. = = = anti - fouling = = = anti - fouling is the process of eliminating obstructive organisms from essential components of seawater systems. depending on the nature and location of marine growth, this process is performed in a number of different ways : marine organisms may grow and attach to the surfaces of the outboard suction inlets used to obtain water for cooling systems. electro - chlorination involves running high electrical current through sea water, altering the water ' s chemical composition to create sodium hypochlorite, purging any bio - matter. an electrolytic method of anti - fouling involves running electrical current through two anodes ( scardino, 2009 ). these anodes typically consist of copper and aluminum ( or alternatively, iron ). the first metal, copper anode, releases its ion into the water, creating an environment that is too toxic for bio - matter. the second metal, aluminum, coats the inside of the pipes to prevent corrosion. other forms of marine growth such as mussels and algae may attach themselves to the bottom of a ship ' s hull. this growth interferes with the smoothness and uniformity of the ship ' s hull, causing the ship to have a less hydrodynamic shape that causes it to be slower and less fuel - efficient. marine growth on the hull can be remedied by using special paint that prevents the growth of such organisms. = = = pollution control = = = = = = = sulfur emission = = = = the burning of marine fuels releases harmful pollutants into the atmosphere. ships burn marine diesel in addition to heavy fuel oil. heavy fuel oil, being the heaviest of refined oils, releases sulfur dioxide when burned. sulfur dioxide emissions have the potential to raise atmospheric and ocean acidity causing harm to marine life. however, heavy fuel oil may only be burned in international waters due to the pollution created. it is commercially advantageous due to the cost effectiveness compared to other marine fuels. it is prospected that heavy fuel oil will be phased out of commercial use by the year 2020 ( smith, 2018 ). = = = = oil and water discharge = = = = water, oil, and other substances collect at the bottom of the ship in what is known as the bilge. bilge water is pumped overboard, but must pass a pollution threshold test of 15 ppm ( parts per million ) of oil to be discharged. water is tested Question: In most crustaceans, what two structures fuse to form a cephalothorax? A) body and shoulders B) foot and toes C) wing and legs D) head and thorax	D) head and thorax
Context: sciences are the clinical diagnostic services that apply laboratory techniques to diagnosis and management of patients. in the united states, these services are supervised by a pathologist. the personnel that work in these medical laboratory departments are technically trained staff who do not hold medical degrees, but who usually hold an undergraduate medical technology degree, who actually perform the tests, assays, and procedures needed for providing the specific services. subspecialties include transfusion medicine, cellular pathology, clinical chemistry, hematology, clinical microbiology and clinical immunology. clinical neurophysiology is concerned with testing the physiology or function of the central and peripheral aspects of the nervous system. these kinds of tests can be divided into recordings of : ( 1 ) spontaneous or continuously running electrical activity, or ( 2 ) stimulus evoked responses. subspecialties include electroencephalography, electromyography, evoked potential, nerve conduction study and polysomnography. sometimes these tests are performed by techs without a medical degree, but the interpretation of these tests is done by a medical professional. diagnostic radiology is concerned with imaging of the body, e. g. by x - rays, x - ray computed tomography, ultrasonography, and nuclear magnetic resonance tomography. interventional radiologists can access areas in the body under imaging for an intervention or diagnostic sampling. nuclear medicine is concerned with studying human organ systems by administering radiolabelled substances ( radiopharmaceuticals ) to the body, which can then be imaged outside the body by a gamma camera or a pet scanner. each radiopharmaceutical consists of two parts : a tracer that is specific for the function under study ( e. g., neurotransmitter pathway, metabolic pathway, blood flow, or other ), and a radionuclide ( usually either a gamma - emitter or a positron emitter ). there is a degree of overlap between nuclear medicine and radiology, as evidenced by the emergence of combined devices such as the pet / ct scanner. pathology as a medical specialty is the branch of medicine that deals with the study of diseases and the morphologic, physiologic changes produced by them. as a diagnostic specialty, pathology can be considered the basis of modern scientific medical knowledge and plays a large role in evidence - based medicine. many modern molecular tests such as flow cytometry, polymerase chain reaction ( pcr ), immunohistochemistry, cytogenetic , 400 km from the persian gulf to the mediterranean sea, but was not paved and was only partially maintained. in around 2, 000 bce, the minoans on the greek island of crete built a 50 km road leading from the palace of gortyn on the south side of the island, through the mountains, to the palace of knossos on the north side of the island. unlike the earlier road, the minoan road was completely paved. ancient minoan private homes had running water. a bathtub virtually identical to modern ones was unearthed at the palace of knossos. several minoan private homes also had toilets, which could be flushed by pouring water down the drain. the ancient romans had many public flush toilets, which emptied into an extensive sewage system. the primary sewer in rome was the cloaca maxima ; construction began on it in the sixth century bce and it is still in use today. the ancient romans also had a complex system of aqueducts, which were used to transport water across long distances. the first roman aqueduct was built in 312 bce. the eleventh and final ancient roman aqueduct was built in 226 ce. put together, the roman aqueducts extended over 450 km, but less than 70 km of this was above ground and supported by arches. = = = pre - modern = = = innovations continued through the middle ages with the introduction of silk production ( in asia and later europe ), the horse collar, and horseshoes. simple machines ( such as the lever, the screw, and the pulley ) were combined into more complicated tools, such as the wheelbarrow, windmills, and clocks. a system of universities developed and spread scientific ideas and practices, including oxford and cambridge. the renaissance era produced many innovations, including the introduction of the movable type printing press to europe, which facilitated the communication of knowledge. technology became increasingly influenced by science, beginning a cycle of mutual advancement. = = = modern = = = starting in the united kingdom in the 18th century, the discovery of steam power set off the industrial revolution, which saw wide - ranging technological discoveries, particularly in the areas of agriculture, manufacturing, mining, metallurgy, and transport, and the widespread application of the factory system. this was followed a century later by the second industrial revolution which led to rapid scientific discovery, standardization, and mass production. new technologies were developed, including sewage systems, electricity, light bulbs, electric motors, railroads, automobiles, and airplanes. these technological advances led to significant developments in medicine and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids are polymers of nucleotides. their function is to store, transmit, and express hereditary information. = = cells = = cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division. most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell interaction between tannin and bovine serum albumin ( bsa ) was examined by the fluorescent quenching. the process of elimination between bsa and tannin was the one of a stationary state, and the coupling coefficient was one. the working strength between the tannin and the beef serum was hydrophobic one. also launched missions to mercury in 2004, with the messenger probe demonstrating as the first use of a solar sail. nasa also launched probes to the outer solar system starting in the 1960s. pioneer 10 was the first probe to the outer planets, flying by jupiter, while pioneer 11 provided the first close up view of the planet. both probes became the first objects to leave the solar system. the voyager program launched in 1977, conducting flybys of jupiter and saturn, neptune, and uranus on a trajectory to leave the solar system. the galileo spacecraft, deployed from the space shuttle flight sts - 34, was the first spacecraft to orbit jupiter, discovering evidence of subsurface oceans on the europa and observed that the moon may hold ice or liquid water. a joint nasa - european space agency - italian space agency mission, cassini – huygens, was sent to saturn ' s moon titan, which, along with mars and europa, are the only celestial bodies in the solar system suspected of being capable of harboring life. cassini discovered three new moons of saturn and the huygens probe entered titan ' s atmosphere. the mission discovered evidence of liquid hydrocarbon lakes on titan and subsurface water oceans on the moon of enceladus, which could harbor life. finally launched in 2006, the new horizons mission was the first spacecraft to visit pluto and the kuiper belt. beyond interplanetary probes, nasa has launched many space telescopes. launched in the 1960s, the orbiting astronomical observatory were nasa ' s first orbital telescopes, providing ultraviolet, gamma - ray, x - ray, and infrared observations. nasa launched the orbiting geophysical observatory in the 1960s and 1970s to look down at earth and observe its interactions with the sun. the uhuru satellite was the first dedicated x - ray telescope, mapping 85 % of the sky and discovering a large number of black holes. launched in the 1990s and early 2000s, the great observatories program are among nasa ' s most powerful telescopes. the hubble space telescope was launched in 1990 on sts - 31 from the discovery and could view galaxies 15 billion light years away. a major defect in the telescope ' s mirror could have crippled the program, had nasa not used computer enhancement to compensate for the imperfection and launched five space shuttle servicing flights to replace the damaged components. the compton gamma ray observatory was launched from the atlantis on sts - 37 in 1991, discovering a possible source of antimatter at the center of the milky way and observing that the majority of gamma - ray bursts three of what is called the six simple machines, from which all machines are based. these machines are the inclined plane, the wedge, and the lever, which allowed the ancient egyptians to move millions of limestone blocks which weighed approximately 3. 5 tons ( 7, 000 lbs. ) each into place to create structures like the great pyramid of giza, which is 481 feet ( 147 meters ) high. they also made writing medium similar to paper from papyrus, which joshua mark states is the foundation for modern paper. papyrus is a plant ( cyperus papyrus ) which grew in plentiful amounts in the egyptian delta and throughout the nile river valley during ancient times. the papyrus was harvested by field workers and brought to processing centers where it was cut into thin strips. the strips were then laid - out side by side and covered in plant resin. the second layer of strips was laid on perpendicularly, then both pressed together until the sheet was dry. the sheets were then joined to form a roll and later used for writing. egyptian society made several significant advances during dynastic periods in many areas of technology. according to hossam elanzeery, they were the first civilization to use timekeeping devices such as sundials, shadow clocks, and obelisks and successfully leveraged their knowledge of astronomy to create a calendar model that society still uses today. they developed shipbuilding technology that saw them progress from papyrus reed vessels to cedar wood ships while also pioneering the use of rope trusses and stem - mounted rudders. the egyptians also used their knowledge of anatomy to lay the foundation for many modern medical techniques and practiced the earliest known version of neuroscience. elanzeery also states that they used and furthered mathematical science, as evidenced in the building of the pyramids. ancient egyptians also invented and pioneered many food technologies that have become the basis of modern food technology processes. based on paintings and reliefs found in tombs, as well as archaeological artifacts, scholars like paul t nicholson believe that the ancient egyptians established systematic farming practices, engaged in cereal processing, brewed beer and baked bread, processed meat, practiced viticulture and created the basis for modern wine production, and created condiments to complement, preserve and mask the flavors of their food. = = = = indus valley = = = = the indus valley civilization, situated in a resource - rich area ( in modern pakistan and northwestern india ), is notable for its early application of city planning, sanitation technologies, and plumbing. indus valley construction and architecture, called ' vaastu the gas giant planets in the solar system have a retinue of icy moons, and we expect giant exoplanets to have similar satellite systems. if a jupiter - like planet were to migrate toward its parent star the icy moons orbiting it would evaporate, creating atmospheres and possible habitable surface oceans. here, we examine how long the surface ice and possible oceans would last before being hydrodynamically lost to space. the hydrodynamic loss rate from the moons is determined, in large part, by the stellar flux available for absorption, which increases as the giant planet and icy moons migrate closer to the star. at some planet - star distance the stellar flux incident on the icy moons becomes so great that they enter a runaway greenhouse state. this runaway greenhouse state rapidly transfers all available surface water to the atmosphere as vapor, where it is easily lost from the small moons. however, for icy moons of ganymede ' s size around a sun - like star we found that surface water ( either ice or liquid ) can persist indefinitely outside the runaway greenhouse orbital distance. in contrast, the surface water on smaller moons of europa ' s size will only persist on timescales greater than 1 gyr at distances ranging 1. 49 to 0. 74 au around a sun - like star for bond albedos of 0. 2 and 0. 8, where the lower albedo becomes relevant if ice melts. consequently, small moons can lose their icy shells, which would create a torus of h atoms around their host planet that might be detectable in future observations. classes according to pore size : the form and shape of the membrane pores are highly dependent on the manufacturing process and are often difficult to specify. therefore, for characterization, test filtrations are carried out and the pore diameter refers to the diameter of the smallest particles which could not pass through the membrane. the rejection can be determined in various ways and provides an indirect measurement of the pore size. one possibility is the filtration of macromolecules ( often dextran, polyethylene glycol or albumin ), another is measurement of the cut - off by gel permeation chromatography. these methods are used mainly to measure membranes for ultrafiltration applications. another testing method is the filtration of particles with defined size and their measurement with a particle sizer or by laser induced breakdown spectroscopy ( libs ). a vivid characterization is to measure the rejection of dextran blue or other colored molecules. the retention of bacteriophage and bacteria, the so - called " bacteria challenge test ", can also provide information about the pore size. to determine the pore diameter, physical methods such as porosimeter ( mercury, liquid - liquid porosimeter and bubble point test ) are also used, but a certain form of the pores ( such as cylindrical or concatenated spherical holes ) is assumed. such methods are used for membranes whose pore geometry does not match the ideal, and we get " nominal " pore diameter, which characterizes the membrane, but does not necessarily reflect its actual filtration behavior and selectivity. the selectivity is highly dependent on the separation process, the composition of the membrane and its electrochemical properties in addition to the pore size. with high selectivity, isotopes can be enriched ( uranium enrichment ) in nuclear engineering or industrial gases like nitrogen can be recovered ( gas separation ). ideally, even racemics can be enriched with a suitable membrane. when choosing membranes selectivity has priority over a high permeability, as low flows can easily be offset by increasing the filter surface with a modular structure. in gas phase filtration different deposition mechanisms are operative, so that particles having sizes below the pore size of the membrane can be retained as well. = = membrane classification = = bio - membrane is classified in two categories, synthetic membrane and natural membrane. synthetic membranes further classified in organic and inorganic membranes. organic membrane sub classified polymeric membranes and inorganic membrane sub classified ceramic polymers. = = synthesis of biomass membrane basics of neutrino oscillations is discussed. importance of time - energy uncertainty relation is stressed. neutrino oscillations in the leading approximation and evidence for neutrino oscillations are briefly summarized. strangelets ( stable lumps of quark matter ) can have masses and charges much higher than those of nuclei, but have very low charge - to - mass ratios. this is confirmed in a relativistic thomas - fermi model. the high charge allows astrophysical strangelet acceleration to energies orders of magnitude higher than for protons. in addition, strangelets are much less susceptible to the interactions with the cosmic microwave background that suppress the flux of cosmic ray protons and nuclei above energies of $ 10 ^ { 19 } $ - - $ 10 ^ { 20 } $ ev ( the gzk - cutoff ). this makes strangelets an interesting possibility for explaining ultra - high energy cosmic rays. Question: What class of animal, including hydras and jellies, is considered the simplest to contain a nervous system? A) prokaryotes B) cnidarians C) sponges D) fish	B) cnidarians
Context: high quality thread. the power loom was invented by edmund cartwright in 1787. in the mid - 1750s, the steam engine was applied to the water power - constrained iron, copper and lead industries for powering blast bellows. these industries were located near the mines, some of which were using steam engines for mine pumping. steam engines were too powerful for leather bellows, so cast iron blowing cylinders were developed in 1768. steam powered blast furnaces achieved higher temperatures, allowing the use of more lime in iron blast furnace feed. ( lime rich slag was not free - flowing at the previously used temperatures. ) with a sufficient lime ratio, sulfur from coal or coke fuel reacts with the slag so that the sulfur does not contaminate the iron. coal and coke were cheaper and more abundant fuel. as a result, iron production rose significantly during the last decades of the 18th century. coal converted to coke fueled higher temperature blast furnaces and produced cast iron in much larger amounts than before, allowing the creation of a range of structures such as the iron bridge. cheap coal meant that industry was no longer constrained by water resources driving the mills, although it continued as a valuable source of power. the steam engine helped drain the mines, so more coal reserves could be accessed, and the output of coal increased. the development of the high - pressure steam engine made locomotives possible, and a transport revolution followed. the steam engine which had existed since the early 18th century, was practically applied to both steamboat and railway transportation. the liverpool and manchester railway, the first purpose - built railway line, opened in 1830, the rocket locomotive of robert stephenson being one of its first working locomotives used. manufacture of ships ' pulley blocks by all - metal machines at the portsmouth block mills in 1803 instigated the age of sustained mass production. machine tools used by engineers to manufacture parts began in the first decade of the century, notably by richard roberts and joseph whitworth. the development of interchangeable parts through what is now called the american system of manufacturing began in the firearms industry at the u. s. federal arsenals in the early 19th century, and became widely used by the end of the century. until the enlightenment era, little progress was made in water supply and sanitation and the engineering skills of the romans were largely neglected throughout europe. the first documented use of sand filters to purify the water supply dates to 1804, when the owner of a bleachery in paisley, scotland, john gibb, installed an experimental filter, selling his unwanted joints. = = = metal alloys = = = the alloys of iron ( steel, stainless steel, cast iron, tool steel, alloy steels ) make up the largest proportion of metals today both by quantity and commercial value. iron alloyed with various proportions of carbon gives low, mid and high carbon steels. an iron - carbon alloy is only considered steel if the carbon level is between 0. 01 % and 2. 00 % by weight. for steels, the hardness and tensile strength of the steel is related to the amount of carbon present, with increasing carbon levels also leading to lower ductility and toughness. heat treatment processes such as quenching and tempering can significantly change these properties, however. in contrast, certain metal alloys exhibit unique properties where their size and density remain unchanged across a range of temperatures. cast iron is defined as an iron – carbon alloy with more than 2. 00 %, but less than 6. 67 % carbon. stainless steel is defined as a regular steel alloy with greater than 10 % by weight alloying content of chromium. nickel and molybdenum are typically also added in stainless steels. other significant metallic alloys are those of aluminium, titanium, copper and magnesium. copper alloys have been known for a long time ( since the bronze age ), while the alloys of the other three metals have been relatively recently developed. due to the chemical reactivity of these metals, the electrolytic extraction processes required were only developed relatively recently. the alloys of aluminium, titanium and magnesium are also known and valued for their high strength to weight ratios and, in the case of magnesium, their ability to provide electromagnetic shielding. these materials are ideal for situations where high strength to weight ratios are more important than bulk cost, such as in the aerospace industry and certain automotive engineering applications. = = = semiconductors = = = a semiconductor is a material that has a resistivity between a conductor and insulator. modern day electronics run on semiconductors, and the industry had an estimated us $ 530 billion market in 2021. its electronic properties can be greatly altered through intentionally introducing impurities in a process referred to as doping. semiconductor materials are used to build diodes, transistors, light - emitting diodes ( leds ), and analog and digital electric circuits, among their many uses. semiconductor devices have replaced thermionic devices like vacuum tubes in most applications. semiconductor devices are manufactured both as single discrete devices and as integrated circuits ( ics ), which consist of a number — from a . historically, metallurgy has predominately focused on the production of metals. metal production begins with the processing of ores to extract the metal, and includes the mixture of metals to make alloys. metal alloys are often a blend of at least two different metallic elements. however, non - metallic elements are often added to alloys in order to achieve properties suitable for an application. the study of metal production is subdivided into ferrous metallurgy ( also known as black metallurgy ) and non - ferrous metallurgy, also known as colored metallurgy. ferrous metallurgy involves processes and alloys based on iron, while non - ferrous metallurgy involves processes and alloys based on other metals. the production of ferrous metals accounts for 95 % of world metal production. modern metallurgists work in both emerging and traditional areas as part of an interdisciplinary team alongside material scientists and other engineers. some traditional areas include mineral processing, metal production, heat treatment, failure analysis, and the joining of metals ( including welding, brazing, and soldering ). emerging areas for metallurgists include nanotechnology, superconductors, composites, biomedical materials, electronic materials ( semiconductors ) and surface engineering. = = etymology and pronunciation = = metallurgy derives from the ancient greek μεταλλουργος, metallourgos, " worker in metal ", from μεταλλον, metallon, " mine, metal " + εργον, ergon, " work " the word was originally an alchemist ' s term for the extraction of metals from minerals, the ending - urgy signifying a process, especially manufacturing : it was discussed in this sense in the 1797 encyclopædia britannica. in the late 19th century, metallurgy ' s definition was extended to the more general scientific study of metals, alloys, and related processes. in english, the pronunciation is the more common one in the united kingdom. the pronunciation is the more common one in the us and is the first - listed variant in various american dictionaries, including merriam - webster collegiate and american heritage. = = history = = the earliest metal employed by humans appears to be gold, which can be found " native ". small amounts of natural gold, dating to the late paleolithic period, 40, 000 bc, have been found in spanish caves. silver, copper, tin and meteoric iron iron - peroxide intermediates are central in the reaction cycle of many iron - containing biomolecules. we trapped iron ( iii ) - ( hydro ) peroxo species in crystals of superoxide reductase ( sor ), a nonheme mononuclear iron enzyme that scavenges superoxide radicals. x - ray diffraction data at 1. 95 angstrom resolution and raman spectra recorded in crystallo revealed iron - ( hydro ) peroxo intermediates with the ( hydro ) peroxo group bound end - on. the dynamic sor active site promotes the formation of transient hydrogen bond networks, which presumably assist the cleavage of the iron - oxygen bond in order to release the reaction product, hydrogen peroxide. pumping. steam engines were too powerful for leather bellows, so cast iron blowing cylinders were developed in 1768. steam powered blast furnaces achieved higher temperatures, allowing the use of more lime in iron blast furnace feed. ( lime rich slag was not free - flowing at the previously used temperatures. ) with a sufficient lime ratio, sulfur from coal or coke fuel reacts with the slag so that the sulfur does not contaminate the iron. coal and coke were cheaper and more abundant fuel. as a result, iron production rose significantly during the last decades of the 18th century. coal converted to coke fueled higher temperature blast furnaces and produced cast iron in much larger amounts than before, allowing the creation of a range of structures such as the iron bridge. cheap coal meant that industry was no longer constrained by water resources driving the mills, although it continued as a valuable source of power. the steam engine helped drain the mines, so more coal reserves could be accessed, and the output of coal increased. the development of the high - pressure steam engine made locomotives possible, and a transport revolution followed. the steam engine which had existed since the early 18th century, was practically applied to both steamboat and railway transportation. the liverpool and manchester railway, the first purpose - built railway line, opened in 1830, the rocket locomotive of robert stephenson being one of its first working locomotives used. manufacture of ships ' pulley blocks by all - metal machines at the portsmouth block mills in 1803 instigated the age of sustained mass production. machine tools used by engineers to manufacture parts began in the first decade of the century, notably by richard roberts and joseph whitworth. the development of interchangeable parts through what is now called the american system of manufacturing began in the firearms industry at the u. s. federal arsenals in the early 19th century, and became widely used by the end of the century. until the enlightenment era, little progress was made in water supply and sanitation and the engineering skills of the romans were largely neglected throughout europe. the first documented use of sand filters to purify the water supply dates to 1804, when the owner of a bleachery in paisley, scotland, john gibb, installed an experimental filter, selling his unwanted surplus to the public. the first treated public water supply in the world was installed by engineer james simpson for the chelsea waterworks company in london in 1829. the first screw - down water tap was patented in 1845 by guest and chrimes, a brass foundry in rotherham. the practice of water treatment soon became mainstream, ratio, sulfur from coal or coke fuel reacts with the slag so that the sulfur does not contaminate the iron. coal and coke were cheaper and more abundant fuel. as a result, iron production rose significantly during the last decades of the 18th century. coal converted to coke fueled higher temperature blast furnaces and produced cast iron in much larger amounts than before, allowing the creation of a range of structures such as the iron bridge. cheap coal meant that industry was no longer constrained by water resources driving the mills, although it continued as a valuable source of power. the steam engine helped drain the mines, so more coal reserves could be accessed, and the output of coal increased. the development of the high - pressure steam engine made locomotives possible, and a transport revolution followed. the steam engine which had existed since the early 18th century, was practically applied to both steamboat and railway transportation. the liverpool and manchester railway, the first purpose - built railway line, opened in 1830, the rocket locomotive of robert stephenson being one of its first working locomotives used. manufacture of ships ' pulley blocks by all - metal machines at the portsmouth block mills in 1803 instigated the age of sustained mass production. machine tools used by engineers to manufacture parts began in the first decade of the century, notably by richard roberts and joseph whitworth. the development of interchangeable parts through what is now called the american system of manufacturing began in the firearms industry at the u. s. federal arsenals in the early 19th century, and became widely used by the end of the century. until the enlightenment era, little progress was made in water supply and sanitation and the engineering skills of the romans were largely neglected throughout europe. the first documented use of sand filters to purify the water supply dates to 1804, when the owner of a bleachery in paisley, scotland, john gibb, installed an experimental filter, selling his unwanted surplus to the public. the first treated public water supply in the world was installed by engineer james simpson for the chelsea waterworks company in london in 1829. the first screw - down water tap was patented in 1845 by guest and chrimes, a brass foundry in rotherham. the practice of water treatment soon became mainstream, and the virtues of the system were made starkly apparent after the investigations of the physician john snow during the 1854 broad street cholera outbreak demonstrated the role of the water supply in spreading the cholera epidemic. = = = second industrial revolution ( 1860s – 1914 ) = = = the 19th century saw astonishing developments in transportation, construction, is collected and processed to extract valuable metals. ore bodies often contain more than one valuable metal. tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. additionally, a concentrate may contain more than one valuable metal. that concentrate would then be processed to separate the valuable metals into individual constituents. = = metal and its alloys = = much effort has been placed on understanding iron – carbon alloy system, which includes steels and cast irons. plain carbon steels ( those that contain essentially only carbon as an alloying element ) are used in low - cost, high - strength applications, where neither weight nor corrosion are a major concern. cast irons, including ductile iron, are also part of the iron - carbon system. iron - manganese - chromium alloys ( hadfield - type steels ) are also used in non - magnetic applications such as directional drilling. other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. these metals are most often used as alloys with the noted exception of silicon, which is not a metal. other forms include : stainless steel, particularly austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important. aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications. copper - nickel alloys ( such as monel ) are used in highly corrosive environments and for non - magnetic applications. nickel - based superalloys like inconel are used in high - temperature applications such as gas turbines, turbochargers, pressure vessels, and heat exchangers. for extremely high temperatures, single crystal alloys are used to minimize creep. in modern electronics, high purity single crystal silicon is essential for metal - oxide - silicon transistors ( mos ) and integrated circuits. = = production = = in production engineering, metallurgy is concerned with the production of metallic components for use in consumer or engineering products. this involves production of alloys, shaping, heat treatment and surface treatment of product. the task of the metallurgist is to achieve balance between material properties, such as cost, weight, strength, toughness, hardness, corrosion, fatigue resistance and performance in temperature extremes. to achieve this goal, the operating environment must be carefully considered. determining the hardness of the metal using the rockwell, vickers, and brinell hardness scales ". = = extraction = = extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted raw metals into a purer form. in order to convert a metal oxide or sulphide to a purer metal, the ore must be reduced physically, chemically, or electrolytically. extractive metallurgists are interested in three primary streams : feed, concentrate ( metal oxide / sulphide ) and tailings ( waste ). after mining, large pieces of the ore feed are broken through crushing or grinding in order to obtain particles small enough, where each particle is either mostly valuable or mostly waste. concentrating the particles of value in a form supporting separation enables the desired metal to be removed from waste products. mining may not be necessary, if the ore body and physical environment are conducive to leaching. leaching dissolves minerals in an ore body and results in an enriched solution. the solution is collected and processed to extract valuable metals. ore bodies often contain more than one valuable metal. tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. additionally, a concentrate may contain more than one valuable metal. that concentrate would then be processed to separate the valuable metals into individual constituents. = = metal and its alloys = = much effort has been placed on understanding iron – carbon alloy system, which includes steels and cast irons. plain carbon steels ( those that contain essentially only carbon as an alloying element ) are used in low - cost, high - strength applications, where neither weight nor corrosion are a major concern. cast irons, including ductile iron, are also part of the iron - carbon system. iron - manganese - chromium alloys ( hadfield - type steels ) are also used in non - magnetic applications such as directional drilling. other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. these metals are most often used as alloys with the noted exception of silicon, which is not a metal. other forms include : stainless steel, particularly austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important. aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications. copper - nickel alloys ( such as monel ) are used in highly corrosive environments and for non - magnetic applications ##chemistry, and chemical degradation ( corrosion ). in contrast, physical metallurgy focuses on the mechanical properties of metals, the physical properties of metals, and the physical performance of metals. topics studied in physical metallurgy include crystallography, material characterization, mechanical metallurgy, phase transformations, and failure mechanisms. historically, metallurgy has predominately focused on the production of metals. metal production begins with the processing of ores to extract the metal, and includes the mixture of metals to make alloys. metal alloys are often a blend of at least two different metallic elements. however, non - metallic elements are often added to alloys in order to achieve properties suitable for an application. the study of metal production is subdivided into ferrous metallurgy ( also known as black metallurgy ) and non - ferrous metallurgy, also known as colored metallurgy. ferrous metallurgy involves processes and alloys based on iron, while non - ferrous metallurgy involves processes and alloys based on other metals. the production of ferrous metals accounts for 95 % of world metal production. modern metallurgists work in both emerging and traditional areas as part of an interdisciplinary team alongside material scientists and other engineers. some traditional areas include mineral processing, metal production, heat treatment, failure analysis, and the joining of metals ( including welding, brazing, and soldering ). emerging areas for metallurgists include nanotechnology, superconductors, composites, biomedical materials, electronic materials ( semiconductors ) and surface engineering. = = etymology and pronunciation = = metallurgy derives from the ancient greek μεταλλουργος, metallourgos, " worker in metal ", from μεταλλον, metallon, " mine, metal " + εργον, ergon, " work " the word was originally an alchemist ' s term for the extraction of metals from minerals, the ending - urgy signifying a process, especially manufacturing : it was discussed in this sense in the 1797 encyclopædia britannica. in the late 19th century, metallurgy ' s definition was extended to the more general scientific study of metals, alloys, and related processes. in english, the pronunciation is the more common one in the united kingdom. the pronunciation is the more common one in the us and is the first - listed variant in various american dictionaries, including merriam - webster collegiate iron - carbon alloy is only considered steel if the carbon level is between 0. 01 % and 2. 00 % by weight. for steels, the hardness and tensile strength of the steel is related to the amount of carbon present, with increasing carbon levels also leading to lower ductility and toughness. heat treatment processes such as quenching and tempering can significantly change these properties, however. in contrast, certain metal alloys exhibit unique properties where their size and density remain unchanged across a range of temperatures. cast iron is defined as an iron – carbon alloy with more than 2. 00 %, but less than 6. 67 % carbon. stainless steel is defined as a regular steel alloy with greater than 10 % by weight alloying content of chromium. nickel and molybdenum are typically also added in stainless steels. other significant metallic alloys are those of aluminium, titanium, copper and magnesium. copper alloys have been known for a long time ( since the bronze age ), while the alloys of the other three metals have been relatively recently developed. due to the chemical reactivity of these metals, the electrolytic extraction processes required were only developed relatively recently. the alloys of aluminium, titanium and magnesium are also known and valued for their high strength to weight ratios and, in the case of magnesium, their ability to provide electromagnetic shielding. these materials are ideal for situations where high strength to weight ratios are more important than bulk cost, such as in the aerospace industry and certain automotive engineering applications. = = = semiconductors = = = a semiconductor is a material that has a resistivity between a conductor and insulator. modern day electronics run on semiconductors, and the industry had an estimated us $ 530 billion market in 2021. its electronic properties can be greatly altered through intentionally introducing impurities in a process referred to as doping. semiconductor materials are used to build diodes, transistors, light - emitting diodes ( leds ), and analog and digital electric circuits, among their many uses. semiconductor devices have replaced thermionic devices like vacuum tubes in most applications. semiconductor devices are manufactured both as single discrete devices and as integrated circuits ( ics ), which consist of a number — from a few to millions — of devices manufactured and interconnected on a single semiconductor substrate. of all the semiconductors in use today, silicon makes up the largest portion both by quantity and commercial value. monocrystalline silicon is used to produce wafers used in the semiconductor and electronics industry. gallium arsenide ( Question: When iron and sulfur are mixed together in a certain ratio and heated, what do they become? A) iron oxide B) sulfuric acid C) rust D) iron sulfide	D) iron sulfide
Context: , tertiary, and quaternary ). the similarities among all known present - day species indicate that they have diverged through the process of evolution from their common ancestor. biologists regard the ubiquity of the genetic code as evidence of universal common descent for all bacteria, archaea, and eukaryotes. microbial mats of coexisting bacteria and archaea were the dominant form of life in the early archean eon and many of the major steps in early evolution are thought to have taken place in this environment. the earliest evidence of eukaryotes dates from 1. 85 billion years ago, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. later, around 1. 7 billion years ago, multicellular organisms began to appear, with differentiated cells performing specialised functions. algae - like multicellular land plants are dated back to about 1 billion years ago, although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2. 7 billion years ago. microorganisms are thought to have paved the way for the inception of land plants in the ordovician period. land plants were so successful that they are thought to have contributed to the late devonian extinction event. ediacara biota appear during the ediacaran period, while vertebrates, along with most other modern phyla originated about 525 million years ago during the cambrian explosion. during the permian period, synapsids, including the ancestors of mammals, dominated the land, but most of this group became extinct in the permian – triassic extinction event 252 million years ago. during the recovery from this catastrophe, archosaurs became the most abundant land vertebrates ; one archosaur group, the dinosaurs, dominated the jurassic and cretaceous periods. after the cretaceous – paleogene extinction event 66 million years ago killed off the non - avian dinosaurs, mammals increased rapidly in size and diversity. such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. = = diversity = = = = = bacteria and archaea = = = bacteria are a type of cell that constitute a large domain of prokaryotic microorganisms. typically a few micrometers in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. bacteria were among the first life forms to appear on earth, and are present in most of its habitats. bacteria inhabit soil, water, acidic hot springs, radioactive have evolved from the earliest emergence of life to present day. earth formed about 4. 5 billion years ago and all life on earth, both living and extinct, descended from a last universal common ancestor that lived about 3. 5 billion years ago. geologists have developed a geologic time scale that divides the history of the earth into major divisions, starting with four eons ( hadean, archean, proterozoic, and phanerozoic ), the first three of which are collectively known as the precambrian, which lasted approximately 4 billion years. each eon can be divided into eras, with the phanerozoic eon that began 539 million years ago being subdivided into paleozoic, mesozoic, and cenozoic eras. these three eras together comprise eleven periods ( cambrian, ordovician, silurian, devonian, carboniferous, permian, triassic, jurassic, cretaceous, tertiary, and quaternary ). the similarities among all known present - day species indicate that they have diverged through the process of evolution from their common ancestor. biologists regard the ubiquity of the genetic code as evidence of universal common descent for all bacteria, archaea, and eukaryotes. microbial mats of coexisting bacteria and archaea were the dominant form of life in the early archean eon and many of the major steps in early evolution are thought to have taken place in this environment. the earliest evidence of eukaryotes dates from 1. 85 billion years ago, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. later, around 1. 7 billion years ago, multicellular organisms began to appear, with differentiated cells performing specialised functions. algae - like multicellular land plants are dated back to about 1 billion years ago, although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2. 7 billion years ago. microorganisms are thought to have paved the way for the inception of land plants in the ordovician period. land plants were so successful that they are thought to have contributed to the late devonian extinction event. ediacara biota appear during the ediacaran period, while vertebrates, along with most other modern phyla originated about 525 million years ago during the cambrian explosion. during the permian period, synapsids, including the ancestors of mammals, dominated the land, but most of this group became . microbial mats of coexisting bacteria and archaea were the dominant form of life in the early archean eon and many of the major steps in early evolution are thought to have taken place in this environment. the earliest evidence of eukaryotes dates from 1. 85 billion years ago, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. later, around 1. 7 billion years ago, multicellular organisms began to appear, with differentiated cells performing specialised functions. algae - like multicellular land plants are dated back to about 1 billion years ago, although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2. 7 billion years ago. microorganisms are thought to have paved the way for the inception of land plants in the ordovician period. land plants were so successful that they are thought to have contributed to the late devonian extinction event. ediacara biota appear during the ediacaran period, while vertebrates, along with most other modern phyla originated about 525 million years ago during the cambrian explosion. during the permian period, synapsids, including the ancestors of mammals, dominated the land, but most of this group became extinct in the permian – triassic extinction event 252 million years ago. during the recovery from this catastrophe, archosaurs became the most abundant land vertebrates ; one archosaur group, the dinosaurs, dominated the jurassic and cretaceous periods. after the cretaceous – paleogene extinction event 66 million years ago killed off the non - avian dinosaurs, mammals increased rapidly in size and diversity. such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. = = diversity = = = = = bacteria and archaea = = = bacteria are a type of cell that constitute a large domain of prokaryotic microorganisms. typically a few micrometers in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. bacteria were among the first life forms to appear on earth, and are present in most of its habitats. bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of the earth ' s crust. bacteria also live in symbiotic and parasitic relationships with plants and animals. most bacteria have not been characterised, and only about 27 percent of the bacterial phyla have species that can be grown in the laboratory. archaea constitute the other domain of into major divisions, starting with four eons ( hadean, archean, proterozoic, and phanerozoic ), the first three of which are collectively known as the precambrian, which lasted approximately 4 billion years. each eon can be divided into eras, with the phanerozoic eon that began 539 million years ago being subdivided into paleozoic, mesozoic, and cenozoic eras. these three eras together comprise eleven periods ( cambrian, ordovician, silurian, devonian, carboniferous, permian, triassic, jurassic, cretaceous, tertiary, and quaternary ). the similarities among all known present - day species indicate that they have diverged through the process of evolution from their common ancestor. biologists regard the ubiquity of the genetic code as evidence of universal common descent for all bacteria, archaea, and eukaryotes. microbial mats of coexisting bacteria and archaea were the dominant form of life in the early archean eon and many of the major steps in early evolution are thought to have taken place in this environment. the earliest evidence of eukaryotes dates from 1. 85 billion years ago, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. later, around 1. 7 billion years ago, multicellular organisms began to appear, with differentiated cells performing specialised functions. algae - like multicellular land plants are dated back to about 1 billion years ago, although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2. 7 billion years ago. microorganisms are thought to have paved the way for the inception of land plants in the ordovician period. land plants were so successful that they are thought to have contributed to the late devonian extinction event. ediacara biota appear during the ediacaran period, while vertebrates, along with most other modern phyla originated about 525 million years ago during the cambrian explosion. during the permian period, synapsids, including the ancestors of mammals, dominated the land, but most of this group became extinct in the permian – triassic extinction event 252 million years ago. during the recovery from this catastrophe, archosaurs became the most abundant land vertebrates ; one archosaur group, the dinosaurs, dominated the jurassic and cretaceous periods. after the cretaceous – paleogene extinction event 66 million years ago killed off ##rozoic eon that began 539 million years ago being subdivided into paleozoic, mesozoic, and cenozoic eras. these three eras together comprise eleven periods ( cambrian, ordovician, silurian, devonian, carboniferous, permian, triassic, jurassic, cretaceous, tertiary, and quaternary ). the similarities among all known present - day species indicate that they have diverged through the process of evolution from their common ancestor. biologists regard the ubiquity of the genetic code as evidence of universal common descent for all bacteria, archaea, and eukaryotes. microbial mats of coexisting bacteria and archaea were the dominant form of life in the early archean eon and many of the major steps in early evolution are thought to have taken place in this environment. the earliest evidence of eukaryotes dates from 1. 85 billion years ago, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. later, around 1. 7 billion years ago, multicellular organisms began to appear, with differentiated cells performing specialised functions. algae - like multicellular land plants are dated back to about 1 billion years ago, although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2. 7 billion years ago. microorganisms are thought to have paved the way for the inception of land plants in the ordovician period. land plants were so successful that they are thought to have contributed to the late devonian extinction event. ediacara biota appear during the ediacaran period, while vertebrates, along with most other modern phyla originated about 525 million years ago during the cambrian explosion. during the permian period, synapsids, including the ancestors of mammals, dominated the land, but most of this group became extinct in the permian – triassic extinction event 252 million years ago. during the recovery from this catastrophe, archosaurs became the most abundant land vertebrates ; one archosaur group, the dinosaurs, dominated the jurassic and cretaceous periods. after the cretaceous – paleogene extinction event 66 million years ago killed off the non - avian dinosaurs, mammals increased rapidly in size and diversity. such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. = = diversity = = = = = bacteria and archaea = = = bacteria are a type of cell that constitute a large domain of prokar ##ochondria and chloroplasts, both of which are now part of modern - day eukaryotic cells. the major lineages of eukaryotes diversified in the precambrian about 1. 5 billion years ago and can be classified into eight major clades : alveolates, excavates, stramenopiles, plants, rhizarians, amoebozoans, fungi, and animals. five of these clades are collectively known as protists, which are mostly microscopic eukaryotic organisms that are not plants, fungi, or animals. while it is likely that protists share a common ancestor ( the last eukaryotic common ancestor ), protists by themselves do not constitute a separate clade as some protists may be more closely related to plants, fungi, or animals than they are to other protists. like groupings such as algae, invertebrates, or protozoans, the protist grouping is not a formal taxonomic group but is used for convenience. most protists are unicellular ; these are called microbial eukaryotes. plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom plantae, which would exclude fungi and some algae. plant cells were derived by endosymbiosis of a cyanobacterium into an early eukaryote about one billion years ago, which gave rise to chloroplasts. the first several clades that emerged following primary endosymbiosis were aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related. algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of plantae. unlike glaucophytes, the other algal clades such as red and green algae are multicellular. green algae comprise three major clades : chlorophytes, coleochaetophytes, and stoneworts. fungi are eukaryotes that digest foods outside their bodies, secreting digestive enzymes that break down large food molecules before absorbing them through their cell membranes. many fungi are also saprobes, feeding on dead organic matter, making them important decomposers in ecological systems. animals are multicellular eukaryotes. with few exceptions, animals prehistory. the oldest gold treasure in the world, dating from 4, 600 bc to 4, 200 bc, was discovered at the site. the gold piece dating from 4, 500 bc, found in 2019 in durankulak, near varna is another important example. other signs of early metals are found from the third millennium bc in palmela, portugal, los millares, spain, and stonehenge, united kingdom. the precise beginnings, however, have not be clearly ascertained and new discoveries are both continuous and ongoing. in approximately 1900 bc, ancient iron smelting sites existed in tamil nadu. in the near east, about 3, 500 bc, it was discovered that by combining copper and tin, a superior metal could be made, an alloy called bronze. this represented a major technological shift known as the bronze age. the extraction of iron from its ore into a workable metal is much more difficult than for copper or tin. the process appears to have been invented by the hittites in about 1200 bc, beginning the iron age. the secret of extracting and working iron was a key factor in the success of the philistines. historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. this includes the ancient and medieval kingdoms and empires of the middle east and near east, ancient iran, ancient egypt, ancient nubia, and anatolia in present - day turkey, ancient nok, carthage, the celts, greeks and romans of ancient europe, medieval europe, ancient and medieval china, ancient and medieval india, ancient and medieval japan, amongst others. a 16th century book by georg agricola, de re metallica, describes the highly developed and complex processes of mining metal ores, metal extraction, and metallurgy of the time. agricola has been described as the " father of metallurgy ". = = extraction = = extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted raw metals into a purer form. in order to convert a metal oxide or sulphide to a purer metal, the ore must be reduced physically, chemically, or electrolytically. extractive metallurgists are interested in three primary streams : feed, concentrate ( metal oxide / sulphide ) and tailings ( waste ). after mining, large pieces of the ore feed are broken through crushing or grinding in order to obtain particles small enough, where each particle is either mostly valuable or likely that protists share a common ancestor ( the last eukaryotic common ancestor ), protists by themselves do not constitute a separate clade as some protists may be more closely related to plants, fungi, or animals than they are to other protists. like groupings such as algae, invertebrates, or protozoans, the protist grouping is not a formal taxonomic group but is used for convenience. most protists are unicellular ; these are called microbial eukaryotes. plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom plantae, which would exclude fungi and some algae. plant cells were derived by endosymbiosis of a cyanobacterium into an early eukaryote about one billion years ago, which gave rise to chloroplasts. the first several clades that emerged following primary endosymbiosis were aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related. algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of plantae. unlike glaucophytes, the other algal clades such as red and green algae are multicellular. green algae comprise three major clades : chlorophytes, coleochaetophytes, and stoneworts. fungi are eukaryotes that digest foods outside their bodies, secreting digestive enzymes that break down large food molecules before absorbing them through their cell membranes. many fungi are also saprobes, feeding on dead organic matter, making them important decomposers in ecological systems. animals are multicellular eukaryotes. with few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. over 1. 5 million living animal species have been described — of which around 1 million are insects — but it has been estimated there are over 7 million animal species in total. they have complex interactions with each other and their environments, forming intricate food webs. = = = viruses = = = viruses are submicroscopic infectious agents that replicate inside the cells of organisms. viruses infect all types of life forms, from animals and plants to microorganisms, diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the ancestor of plants by entering into an endosymbiotic relationship with an early eukaryote, ultimately becoming the chloroplasts in plant cells. the new photosynthetic plants ( along with their algal relatives ) accelerated the rise in atmospheric oxygen started by the cyanobacteria, changing the ancient oxygen - free, reducing, atmosphere to one in which free oxygen has been abundant for more than 2 billion years. among the important botanical questions of the 21st century are the role of plants as primary producers in the global cycling of life ' s basic ingredients : energy, carbon, oxygen, nitrogen and water, and ways that our plant stewardship can help address the global environmental issues of resource management, conservation, human food security, biologically invasive organisms, carbon sequestration, climate change, and sustainability. = = = human nutrition = = = virtually all staple foods come either directly from primary production by plants, or indirectly from animals that eat them. plants and other photosynthetic organisms are at the base of most food chains because they use the energy from the sun and nutrients from the soil and atmosphere, converting them into a form that can be used by animals. this is what ecologists call the first trophic level. the modern forms of the major staple foods, such as hemp, teff, maize, rice, wheat and other cereal grasses, pulses, bananas and plantains, as well as hemp, flax and cotton grown for their fibres, are the outcome of prehistoric selection over thousands of years from among wild ancestral plants with the most , fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the ancestor of plants by entering into an endosymbiotic relationship with an early eukaryote, ultimately becoming the chloroplasts in plant cells. the new photosynthetic plants ( along with their algal relatives ) accelerated the rise in atmospheric oxygen started by the cyanobacteria, changing the ancient oxygen - free, reducing, atmosphere to one in which free oxygen has been abundant for more than 2 billion years. among the important botanical questions of the 21st century are the role of plants as primary producers in the global cycling of life ' s basic ingredients : energy, carbon, oxygen, nitrogen and water, and ways that our plant stewardship can help address the global environmental issues of resource management, conservation, human food security, biologically invasive organisms, carbon sequestration, climate change, and sustainability. = = = human nutrition = = = virtually all staple foods come either directly from primary production by plants, or indirectly from animals that eat them. plants and other photosynthetic organisms are at the base of most food chains because they use the energy from the sun and nutrients from the soil and atmosphere, converting them into a form that can be used by animals. this is what ecologists call the first trophic level. the modern forms of the major staple foods, such as hemp, teff, maize, rice, wheat and other cereal grasses, pulses, bananas and plantains, as well as hemp, flax and cotton grown for their fibres, are the outcome of prehistoric selection over thousands of years from among wild ancestral plants with the most desirable characteristics. botanists study how plants produce food and how to increase yields, for example through plant breeding, making their work important to humanity ' s ability to feed the world and provide food security for future generations. botanists also study weeds, which are a considerable problem in agriculture, and the biology and control of plant Question: What do many scientists think are the oldest eukaryotes? A) plants B) protists C) prokaryotes D) arthropods	B) protists
Context: covid - 19, also known as novel coronavirus disease, is a highly contagious disease that first surfaced in china in late 2019. sars - cov - 2 is a coronavirus that belongs to the vast family of coronaviruses that causes this disease. the sickness originally appeared in wuhan, china in december 2019 and quickly spread to over 213 nations, becoming a global pandemic. fever, dry cough, and tiredness are the most typical covid - 19 symptoms. aches, pains, and difficulty breathing are some of the other symptoms that patients may face. the majority of these symptoms are indicators of respiratory infections and lung abnormalities, which radiologists can identify. chest x - rays of covid - 19 patients seem similar, with patchy and hazy lungs rather than clear and healthy lungs. on x - rays, however, pneumonia and other chronic lung disorders can resemble covid - 19. trained radiologists must be able to distinguish between covid - 19 and an illness that is less contagious. our ai algorithm seeks to give doctors a quantitative estimate of the risk of deterioration. so that patients at high risk of deterioration can be triaged and treated efficiently. the method could be particularly useful in pandemic hotspots when screening upon admission is important for allocating limited resources like hospital beds. urinary tract infection ( utis ) is referred as one of the most common infection in medical sectors worldwide and antimicrobial resistance ( amr ) is also a global threat to human that is related with many diseases. as antibiotics used for the treatment of infectious diseases, the rate of resistance is increasing day by day. gram positive pathogens are commonly found in urine sample collected from different age groups of people, associated with uti. the study was conducted in a diagnostic center in dhaka, bangladesh with total 1308 urine samples from november 2021 to april 2022. gram positive pathogens were isolated and antimicrobial susceptibility tests were done. from total 121 samples of gram positive bacteria the highest prevalence rate of utis was found in age group of 21 - 30 year. mostly enterococcus spp. ( 33. 05 % ) staphylococcus aureus ( 27. 27 % ), streptococcus spp. ( 20. 66 % ), beta - hemolytic streptococci ( 19. 00 % ) were found as causative agents of uti compared to others. the majority of isolates have been detected as multi - drug resistant ( mdr ). the higher percentage of antibiotic resistance were found against azithromycin ( 75 % ), and cefixime ( 64. 46 % ). this research focused on the regular basis of surveillance for the gram - positive bacteria antibiotic susceptibility to increase awareness about the use of proper antibiotic thus minimize the drug resistance. consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. over 1. 5 million living animal species have been described — of which around 1 million are insects — but it has been estimated there are over 7 million animal species in total. they have complex interactions with each other and their environments, forming intricate food webs. = = = viruses = = = viruses are submicroscopic infectious agents that replicate inside the cells of organisms. viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. more than 6, 000 virus species have been described in detail. viruses are found in almost every ecosystem on earth and are the most numerous type of biological entity. the origins of viruses in the evolutionary history of life are unclear : some may have evolved from plasmids — pieces of dna that can move between cells — while others may have evolved from bacteria. in evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogous to sexual reproduction. because viruses possess some but not all characteristics of life, they have been described as " organisms at the edge of life ", and as self - replicators. = = ecology = = ecology is the study of the distribution and abundance of life, the interaction between organisms and their environment. = = = ecosystems = = = the community of living ( biotic ) organisms in conjunction with the nonliving ( abiotic ) components ( e. g., water, light, radiation, temperature, humidity, atmosphere, acidity, and soil ) of their environment is called an ecosystem. these biotic and abiotic components are linked together through nutrient cycles and energy flows. energy from the sun enters the system through photosynthesis and is incorporated into plant tissue. by feeding on plants and on one another, animals move matter and energy through the system. they also influence the quantity of plant and microbial biomass present. by breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes. = = = populations = = = a population is the group of organisms of the same species that occupies an area and reproduce from generation to generation. population size can be estimated by multiplying population density by the area or volume. the carrying capacity of an environment agents are represented by nodes on a random graph ( e. g., small world or truncated power law ). each agent is endowed with a zero - mean random value that may be either positive or negative. all agents attempt to find relief, i. e., to reduce the magnitude of that initial value, to zero if possible, through exchanges. the exchange occurs only between agents that are linked, a constraint that turns out to dominate the results. the exchange process continues until a pareto equilibrium is achieved. only 40 % - 90 % of the agents achieved relief on small world graphs with mean degree between 2 and 40. even fewer agents achieved relief on scale - free like graphs with a truncated power law degree distribution. the rate at which relief grew with increasing degree was slow, only at most logarithmic for all of the graphs considered ; viewed in reverse, relief is resilient to the removal of links. technology developed, medicine became more reliant upon medications. throughout history and in europe right until the late 18th century, not only plant products were used as medicine, but also animal ( including human ) body parts and fluids. pharmacology developed in part from herbalism and some drugs are still derived from plants ( atropine, ephedrine, warfarin, aspirin, digoxin, vinca alkaloids, taxol, hyoscine, etc. ). vaccines were discovered by edward jenner and louis pasteur. the first antibiotic was arsphenamine ( salvarsan ) discovered by paul ehrlich in 1908 after he observed that bacteria took up toxic dyes that human cells did not. the first major class of antibiotics was the sulfa drugs, derived by german chemists originally from azo dyes. pharmacology has become increasingly sophisticated ; modern biotechnology allows drugs targeted towards specific physiological processes to be developed, sometimes designed for compatibility with the body to reduce side - effects. genomics and knowledge of human genetics and human evolution is having increasingly significant influence on medicine, as the causative genes of most monogenic genetic disorders have now been identified, and the development of techniques in molecular biology, evolution, and genetics are influencing medical technology, practice and decision - making. evidence - based medicine is a contemporary movement to establish the most effective algorithms of practice ( ways of doing things ) through the use of systematic reviews and meta - analysis. the movement is facilitated by modern global information science, which allows as much of the available evidence as possible to be collected and analyzed according to standard protocols that are then disseminated to healthcare providers. the cochrane collaboration leads this movement. a 2001 review of 160 cochrane systematic reviews revealed that, according to two readers, 21. 3 % of the reviews concluded insufficient evidence, 20 % concluded evidence of no effect, and 22. 5 % concluded positive effect. = = quality, efficiency, and access = = evidence - based medicine, prevention of medical error ( and other " iatrogenesis " ), and avoidance of unnecessary health care are a priority in modern medical systems. these topics generate significant political and public policy attention, particularly in the united states where healthcare is regarded as excessively costly but population health metrics lag similar nations. globally, many developing countries lack access to care and access to medicines. as of 2015, most wealthy developed countries provide health care to all citizens, with a few exceptions such as the united states where lack of health insurance a binary 1 - error - correcting code can always be embedded in a 1 - perfect code of some larger length index chemical substances. in this scheme each chemical substance is identifiable by a number known as its cas registry number. = = = = molecule = = = = a molecule is the smallest indivisible portion of a pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. however, this definition only works well for substances that are composed of molecules, which is not true of many substances ( see below ). molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs. thus, molecules exist as electrically neutral units, unlike ions. when this rule is broken, giving the " molecule " a charge, the result is sometimes named a molecular ion or a polyatomic ion. however, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry medical history comprises hpi and pmh. medications ( rx ) : what drugs the patient takes including prescribed, over - the - counter, and home remedies, as well as alternative and herbal medicines or remedies. allergies are also recorded. past medical history ( pmh / pmhx ) : concurrent medical problems, past hospitalizations and operations, injuries, past infectious diseases or vaccinations, history of known allergies. review of systems ( ros ) or systems inquiry : a set of additional questions to ask, which may be missed on hpi : a general enquiry ( have you noticed any weight loss, change in sleep quality, fevers, lumps and bumps? etc. ), followed by questions on the body ' s main organ systems ( heart, lungs, digestive tract, urinary tract, etc. ). social history ( sh ) : birthplace, residences, marital history, social and economic status, habits ( including diet, medications, tobacco, alcohol ). the physical examination is the examination of the patient for medical signs of disease that are objective and observable, in contrast to symptoms that are volunteered by the patient and are not necessarily objectively observable. the healthcare provider uses sight, hearing, touch, and sometimes smell ( e. g., in infection, uremia, diabetic ketoacidosis ). four actions are the basis of physical examination : inspection, palpation ( feel ), percussion ( tap to determine resonance characteristics ), and auscultation ( listen ), generally in that order, although auscultation occurs prior to percussion and palpation for abdominal assessments. the clinical examination involves the study of : abdomen and rectum cardiovascular ( heart and blood vessels ) general appearance of the patient and specific indicators of disease ( nutritional status, presence of jaundice, pallor or clubbing ) genitalia ( and pregnancy if the patient is or could be pregnant ) head, eye, ear, nose, and throat ( heent ) musculoskeletal ( including spine and extremities ) neurological ( consciousness, awareness, brain, vision, cranial nerves, spinal cord and peripheral nerves ) psychiatric ( orientation, mental state, mood, evidence of abnormal perception or thought ). respiratory ( large airways and lungs ) skin vital signs including height, weight, body temperature, blood pressure, pulse, respiration rate, and hemoglobin oxygen saturation it is to likely focus on under 50, 000 by 2009. the church is known for its newspaper, the christian science monitor, which won seven pulitzer prizes between 1950 and 2002, and for its public reading rooms around the world. christian science ' s religious tenets differ considerably from many other christian denominations, including key concepts such as the trinity, the divinity of jesus, atonement, the resurrection, and the eucharist. eddy, for her part, described christian science as a return to " primitive christianity and its lost element of healing ". adherents subscribe to a radical form of philosophical idealism, believing that reality is purely spiritual and the material world an illusion. this includes the view that disease is a mental error rather than physical disorder, and that the sick should be treated not by medicine but by a form of prayer that seeks to correct the beliefs responsible for the illusion of ill health. the church does not require that christian scientists avoid medical care — many adherents use dentists, optometrists, obstetricians, physicians for broken bones, and vaccination when required by law — but maintains that christian science prayer is most effective when not combined with medicine. the reliance on prayer and avoidance of medical treatment has been blamed for the deaths of adherents and their children. between the 1880s and 1990s, several parents and others were prosecuted for, and in a few cases convicted of, manslaughter or neglect. = = overview = = = = = metaphysical family = = = several periods of protestant christian revival nurtured a proliferation of new religious movements in the united states. in the latter half of the 19th century, these included what came to be known as the metaphysical family : groups such as christian science, divine science, the unity school of christianity, and ( later ) the united church of religious science. from the 1890s, the liberal section of the movement became known as new thought, in part to distinguish it from the more authoritarian christian science. the term metaphysical referred to the movement ' s philosophical idealism, a belief in the primacy of the mental world. adherents believed that material phenomena were the result of mental states, a view expressed as " life is consciousness " and " god is mind. " the supreme cause was referred to as divine mind, truth, god, love, life, spirit, principle or father – mother, reflecting elements of plato, hinduism, berkeley, hegel, swedenborg, and transcendentalism. the metaphysical groups became known as the mind - cure movement because of their strong focus on healing. medical practice was in the non - avian dinosaurs, mammals increased rapidly in size and diversity. such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. = = diversity = = = = = bacteria and archaea = = = bacteria are a type of cell that constitute a large domain of prokaryotic microorganisms. typically a few micrometers in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. bacteria were among the first life forms to appear on earth, and are present in most of its habitats. bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of the earth ' s crust. bacteria also live in symbiotic and parasitic relationships with plants and animals. most bacteria have not been characterised, and only about 27 percent of the bacterial phyla have species that can be grown in the laboratory. archaea constitute the other domain of prokaryotic cells and were initially classified as bacteria, receiving the name archaebacteria ( in the archaebacteria kingdom ), a term that has fallen out of use. archaeal cells have unique properties separating them from the other two domains, bacteria and eukaryota. archaea are further divided into multiple recognized phyla. archaea and bacteria are generally similar in size and shape, although a few archaea have very different shapes, such as the flat and square cells of haloquadratum walsbyi. despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably for the enzymes involved in transcription and translation. other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, including archaeols. archaea use more energy sources than eukaryotes : these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. salt - tolerant archaea ( the haloarchaea ) use sunlight as an energy source, and other species of archaea fix carbon, but unlike plants and cyanobacteria, no known species of archaea does both. archaea reproduce asexually by binary fission, fragmentation, or budding ; unlike bacteria, no known species of archaea form endospores. the first observed archaea were extremophiles, living in extreme environments, such as hot springs and salt lakes with no other organisms. improved molecular detection Question: Culprits in the common cold and aids, what infectious agents are far smaller and simpler than bacteria? A) parasites B) pathogens C) viruses D) poisons	C) viruses
Context: becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under current in passing over from one concave bank to the next on the opposite side. the lowering of such a shoal by dredging merely effects a temporary deepening, for it soon forms again from the causes which produced it. the removal, moreover, of the rocky obstructions at rapids, though increasing the depth and equalizing the flow at these places, produces a lowering of the river above the rapids by facilitating the efflux, which may result in the appearance of fresh shoals at the low stage of the river. where, however, narrow rocky reefs or other hard shoals stretch across the bottom of a river and present obstacles to the erosion by the current of the soft materials forming the bed of the river above and below, their removal may result in permanent improvement by enabling the river to deepen its bed by natural scour. the capability of a river to provide a waterway for navigation during the summer or throughout the dry season depends on the depth that can be secured in the channel at the lowest stage. the problem in the dry season is the small discharge and deficiency in scour during this period. a typical solution is to restrict the width of the low - water channel, concentrate all of the flow in it, and also to fix its position so that it is scoured out every year by the floods which follow the deepest part of the bed along the line of the strongest current. this can be effected by closing subsidiary low - water channels with dikes across them, and narrowing the channel at the low stage by low - dipping cross dikes extending from the river banks down the slope and pointing slightly up - stream so as to direct the water flowing over them into a central channel. = = estuarine works = = the needs of navigation may also require that a stable, continuous, navigable channel is prolonged from the navigable river to deep water at the mouth of the estuary. the interaction of river flow and tide needs to be modeled by computer or using scale models, moulded to the configuration of the estuary under consideration and reproducing in miniature the tidal ebb and flow and fresh - water discharge over a bed of fine sand, in which various lines of training walls can be successively inserted. the models should be capable of furnishing valuable indications of the respective effects and comparative merits of the different schemes proposed for works. = = see also = = bridge scour flood control = = references = = = = external links = = u. s. army corps of engineers – civil works program river morphology and stream restoration references ##ediment to up - stream navigation, and there are generally variations in water level, and when the discharge becomes small in the dry season. it is impossible to maintain a sufficient depth of water in the low - water channel. the possibility to secure uniformity of depth in a river by lowering the shoals obstructing the channel depends on the nature of the shoals. a soft shoal in the bed of a river is due to deposit from a diminution in velocity of flow, produced by a reduction in fall and by a widening of the channel, or to a loss in concentration of the scour of the main current in passing over from one concave bank to the next on the opposite side. the lowering of such a shoal by dredging merely effects a temporary deepening, for it soon forms again from the causes which produced it. the removal, moreover, of the rocky obstructions at rapids, though increasing the depth and equalizing the flow at these places, produces a lowering of the river above the rapids by facilitating the efflux, which may result in the appearance of fresh shoals at the low stage of the river. where, however, narrow rocky reefs or other hard shoals stretch across the bottom of a river and present obstacles to the erosion by the current of the soft materials forming the bed of the river above and below, their removal may result in permanent improvement by enabling the river to deepen its bed by natural scour. the capability of a river to provide a waterway for navigation during the summer or throughout the dry season depends on the depth that can be secured in the channel at the lowest stage. the problem in the dry season is the small discharge and deficiency in scour during this period. a typical solution is to restrict the width of the low - water channel, concentrate all of the flow in it, and also to fix its position so that it is scoured out every year by the floods which follow the deepest part of the bed along the line of the strongest current. this can be effected by closing subsidiary low - water channels with dikes across them, and narrowing the channel at the low stage by low - dipping cross dikes extending from the river banks down the slope and pointing slightly up - stream so as to direct the water flowing over them into a central channel. = = estuarine works = = the needs of navigation may also require that a stable, continuous, navigable channel is prolonged from the navigable river to deep water at the mouth of the estuary. the interaction of river equalizing the flow at these places, produces a lowering of the river above the rapids by facilitating the efflux, which may result in the appearance of fresh shoals at the low stage of the river. where, however, narrow rocky reefs or other hard shoals stretch across the bottom of a river and present obstacles to the erosion by the current of the soft materials forming the bed of the river above and below, their removal may result in permanent improvement by enabling the river to deepen its bed by natural scour. the capability of a river to provide a waterway for navigation during the summer or throughout the dry season depends on the depth that can be secured in the channel at the lowest stage. the problem in the dry season is the small discharge and deficiency in scour during this period. a typical solution is to restrict the width of the low - water channel, concentrate all of the flow in it, and also to fix its position so that it is scoured out every year by the floods which follow the deepest part of the bed along the line of the strongest current. this can be effected by closing subsidiary low - water channels with dikes across them, and narrowing the channel at the low stage by low - dipping cross dikes extending from the river banks down the slope and pointing slightly up - stream so as to direct the water flowing over them into a central channel. = = estuarine works = = the needs of navigation may also require that a stable, continuous, navigable channel is prolonged from the navigable river to deep water at the mouth of the estuary. the interaction of river flow and tide needs to be modeled by computer or using scale models, moulded to the configuration of the estuary under consideration and reproducing in miniature the tidal ebb and flow and fresh - water discharge over a bed of fine sand, in which various lines of training walls can be successively inserted. the models should be capable of furnishing valuable indications of the respective effects and comparative merits of the different schemes proposed for works. = = see also = = bridge scour flood control = = references = = = = external links = = u. s. army corps of engineers – civil works program river morphology and stream restoration references - wildland hydrology at the library of congress web archives ( archived 2002 - 08 - 13 ) also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in ##ructing the channel depends on the nature of the shoals. a soft shoal in the bed of a river is due to deposit from a diminution in velocity of flow, produced by a reduction in fall and by a widening of the channel, or to a loss in concentration of the scour of the main current in passing over from one concave bank to the next on the opposite side. the lowering of such a shoal by dredging merely effects a temporary deepening, for it soon forms again from the causes which produced it. the removal, moreover, of the rocky obstructions at rapids, though increasing the depth and equalizing the flow at these places, produces a lowering of the river above the rapids by facilitating the efflux, which may result in the appearance of fresh shoals at the low stage of the river. where, however, narrow rocky reefs or other hard shoals stretch across the bottom of a river and present obstacles to the erosion by the current of the soft materials forming the bed of the river above and below, their removal may result in permanent improvement by enabling the river to deepen its bed by natural scour. the capability of a river to provide a waterway for navigation during the summer or throughout the dry season depends on the depth that can be secured in the channel at the lowest stage. the problem in the dry season is the small discharge and deficiency in scour during this period. a typical solution is to restrict the width of the low - water channel, concentrate all of the flow in it, and also to fix its position so that it is scoured out every year by the floods which follow the deepest part of the bed along the line of the strongest current. this can be effected by closing subsidiary low - water channels with dikes across them, and narrowing the channel at the low stage by low - dipping cross dikes extending from the river banks down the slope and pointing slightly up - stream so as to direct the water flowing over them into a central channel. = = estuarine works = = the needs of navigation may also require that a stable, continuous, navigable channel is prolonged from the navigable river to deep water at the mouth of the estuary. the interaction of river flow and tide needs to be modeled by computer or using scale models, moulded to the configuration of the estuary under consideration and reproducing in miniature the tidal ebb and flow and fresh - water discharge over a bed of fine sand, in which various lines of training walls can be successively inserted. the models approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform the injuries of the inundations they have been designed to prevent, as the escape of floods from the raised river must occur sooner or later. inadequate planning controls which have permitted development on floodplains have been blamed for the flooding of domestic properties. channelization was done under the auspices or overall direction of engineers employed by the local authority or the national government. one of the most heavily channelized areas in the united states is west tennessee, where every major stream with one exception ( the hatchie river ) has been partially or completely channelized. channelization of a stream may be undertaken for several reasons. one is to make a stream more suitable for navigation or for navigation by larger vessels with deep draughts. another is to restrict water to a certain area of a stream ' s natural bottom lands so that the bulk of such lands can be made available for agriculture. a third reason is flood control, with the idea of giving a stream a sufficiently large and deep channel so that flooding beyond those limits will be minimal or nonexistent, at least on a routine basis. one major reason is to reduce natural erosion ; as a natural waterway curves back and forth, it usually deposits sand and gravel on the inside of the corners where the water flows slowly, and cuts sand, gravel, subsoil, and precious topsoil from the outside corners where it flows rapidly due to a change in direction. unlike sand and gravel, the topsoil that is eroded does not get deposited on the inside of the next corner of the river. it simply washes away. = = loss of wetlands = = channelization has several predictable and negative effects. one of them is loss of wetlands. wetlands are an excellent habitat for multiple forms of wildlife, and additionally serve as a " filter " for much of the world ' s surface fresh water. another is the fact that channelized streams are almost invariably straightened. for example, the channelization of florida ' s kissimmee river has been cited as a cause contributing to the loss of wetlands. this straightening causes the streams to flow more rapidly, which can, in some instances, vastly increase soil erosion. it can also increase flooding downstream from the channelized area, as larger volumes of water traveling more rapidly than normal can reach choke points over a shorter period of time than they otherwise would, with a net effect of flood control in one area coming at the expense of aggravated flooding in another. in addition, studies have shown that stream channelization results in declines of river fish populations. : 3 - 1ff a a watershed ( called a " divide " in north america ) over which rainfall flows down towards the river traversing the lowest part of the valley, whereas the rain falling on the far slope of the watershed flows away to another river draining an adjacent basin. river basins vary in extent according to the configuration of the country, ranging from the insignificant drainage areas of streams rising on high ground near the coast and flowing straight down into the sea, up to immense tracts of continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching the ocean. the size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern Question: What triangular feature is formed when a river empties into a large body of still water? A) region B) flow C) confluence D) delta	D) delta
Context: for the treatment of diabetes, was previously extracted from the pancreas of abattoir animals ( cattle or pigs ). the genetically engineered bacteria are able to produce large quantities of synthetic human insulin at relatively low cost. biotechnology has also enabled emerging therapeutics like gene therapy. the application of biotechnology to basic science ( for example through the human genome project ) has also dramatically improved our understanding of biology and as our scientific knowledge of normal and disease biology has increased, our ability to develop new medicines to treat previously untreatable diseases has increased as well. genetic testing allows the genetic diagnosis of vulnerabilities to inherited diseases, and can also be used to determine a child ' s parentage ( genetic mother and father ) or in general a person ' s ancestry. in addition to studying chromosomes to the level of individual genes, genetic testing in a broader sense includes biochemical tests for the possible presence of genetic diseases, or mutant forms of genes associated with increased risk of developing genetic disorders. genetic testing identifies changes in chromosomes, genes, or proteins. most of the time, testing is used to find changes that are associated with inherited disorders. the results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person ' s chance of developing or passing on a genetic disorder. as of 2011 several hundred genetic tests were in use. since genetic testing may open up ethical or psychological problems, genetic testing is often accompanied by genetic counseling. = = = agriculture = = = genetically modified crops ( " gm crops ", or " biotech crops " ) are plants used in agriculture, the dna of which has been modified with genetic engineering techniques. in most cases, the main aim is to introduce a new trait that does not occur naturally in the species. biotechnology firms can contribute to future food security by improving the nutrition and viability of urban agriculture. furthermore, the protection of intellectual property rights encourages private sector investment in agrobiotechnology. examples in food crops include resistance to certain pests, diseases, stressful environmental conditions, resistance to chemical treatments ( e. g. resistance to a herbicide ), reduction of spoilage, or improving the nutrient profile of the crop. examples in non - food crops include production of pharmaceutical agents, biofuels, and other industrially useful goods, as well as for bioremediation. farmers have widely adopted gm technology. between 1996 and 2011, the total surface area of land cultivated with gm crops had increased by a factor of 94, from 17, 000 to 1, 600, 000 square genetic engineering takes the gene directly from one organism and delivers it to the other. this is much faster, can be used to insert any genes from any organism ( even ones from different domains ) and prevents other undesirable genes from also being added. genetic engineering could potentially fix severe genetic disorders in humans by replacing the defective gene with a functioning one. it is an important tool in research that allows the function of specific genes to be studied. drugs, vaccines and other products have been harvested from organisms engineered to produce them. crops have been developed that aid food security by increasing yield, nutritional value and tolerance to environmental stresses. the dna can be introduced directly into the host organism or into a cell that is then fused or hybridised with the host. this relies on recombinant nucleic acid techniques to form new combinations of heritable genetic material followed by the incorporation of that material either indirectly through a vector system or directly through micro - injection, macro - injection or micro - encapsulation. genetic engineering does not normally include traditional breeding, in vitro fertilisation, induction of polyploidy, mutagenesis and cell fusion techniques that do not use recombinant nucleic acids or a genetically modified organism in the process. however, some broad definitions of genetic engineering include selective breeding. cloning and stem cell research, although not considered genetic engineering, are closely related and genetic engineering can be used within them. synthetic biology is an emerging discipline that takes genetic engineering a step further by introducing artificially synthesised material into an organism. plants, animals or microorganisms that have been changed through genetic engineering are termed genetically modified organisms or gmos. if genetic material from another species is added to the host, the resulting organism is called transgenic. if genetic material from the same species or a species that can naturally breed with the host is used the resulting organism is called cisgenic. if genetic engineering is used to remove genetic material from the target organism the resulting organism is termed a knockout organism. in europe genetic modification is synonymous with genetic engineering while within the united states of america and canada genetic modification can also be used to refer to more conventional breeding methods. = = history = = humans have altered the genomes of species for thousands of years through selective breeding, or artificial selection : 1 : 1 as contrasted with natural selection. more recently, mutation breeding has used exposure to chemicals or radiation to produce a high frequency of random mutations, for selective breeding purposes. genetic engineering as the direct manipulation of dna by humans outside breeding and ##tes, i. e., genes are unlinked. an exception to this rule would include traits that are sex - linked. test crosses can be performed to experimentally determine the underlying genotype of an organism with a dominant phenotype. a punnett square can be used to predict the results of a test cross. the chromosome theory of inheritance, which states that genes are found on chromosomes, was supported by thomas morgans ' s experiments with fruit flies, which established the sex linkage between eye color and sex in these insects. = = = genes and dna = = = a gene is a unit of heredity that corresponds to a region of deoxyribonucleic acid ( dna ) that carries genetic information that controls form or function of an organism. dna is composed of two polynucleotide chains that coil around each other to form a double helix. it is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. the set of chromosomes in a cell is collectively known as its genome. in eukaryotes, dna is mainly in the cell nucleus. in prokaryotes, the dna is held within the nucleoid. the genetic information is held within genes, and the complete assemblage in an organism is called its genotype. dna replication is a semiconservative process whereby each strand serves as a template for a new strand of dna. mutations are heritable changes in dna. they can arise spontaneously as a result of replication errors that were not corrected by proofreading or can be induced by an environmental mutagen such as a chemical ( e. g., nitrous acid, benzopyrene ) or radiation ( e. g., x - ray, gamma ray, ultraviolet radiation, particles emitted by unstable isotopes ). mutations can lead to phenotypic effects such as loss - of - function, gain - of - function, and conditional mutations. some mutations are beneficial, as they are a source of genetic variation for evolution. others are harmful if they were to result in a loss of function of genes needed for survival. = = = gene expression = = = gene expression is the molecular process by which a genotype encoded in dna gives rise to an observable phenotype in the proteins of an organism ' s body. this process is summarized by the central dogma of molecular biology, which was formulated by francis crick in 1958. according to the central dogma, genetic information flows from dna for natural scientists, with the creation of transgenic organisms one of the most important tools for analysis of gene function. genes and other genetic information from a wide range of organisms can be inserted into bacteria for storage and modification, creating genetically modified bacteria in the process. bacteria are cheap, easy to grow, clonal, multiply quickly, relatively easy to transform and can be stored at - 80 °c almost indefinitely. once a gene is isolated it can be stored inside the bacteria providing an unlimited supply for research. organisms are genetically engineered to discover the functions of certain genes. this could be the effect on the phenotype of the organism, where the gene is expressed or what other genes it interacts with. these experiments generally involve loss of function, gain of function, tracking and expression. loss of function experiments, such as in a gene knockout experiment, in which an organism is engineered to lack the activity of one or more genes. in a simple knockout a copy of the desired gene has been altered to make it non - functional. embryonic stem cells incorporate the altered gene, which replaces the already present functional copy. these stem cells are injected into blastocysts, which are implanted into surrogate mothers. this allows the experimenter to analyse the defects caused by this mutation and thereby determine the role of particular genes. it is used especially frequently in developmental biology. when this is done by creating a library of genes with point mutations at every position in the area of interest, or even every position in the whole gene, this is called " scanning mutagenesis ". the simplest method, and the first to be used, is " alanine scanning ", where every position in turn is mutated to the unreactive amino acid alanine. gain of function experiments, the logical counterpart of knockouts. these are sometimes performed in conjunction with knockout experiments to more finely establish the function of the desired gene. the process is much the same as that in knockout engineering, except that the construct is designed to increase the function of the gene, usually by providing extra copies of the gene or inducing synthesis of the protein more frequently. gain of function is used to tell whether or not a protein is sufficient for a function, but does not always mean it is required, especially when dealing with genetic or functional redundancy. tracking experiments, which seek to gain information about the localisation and interaction of the desired protein. one way to do this is to replace the wild - type gene with a ' fusion ' gene, which is a juxtaposition used to manufacture existing medicines relatively easily and cheaply. the first genetically engineered products were medicines designed to treat human diseases. to cite one example, in 1978 genentech developed synthetic humanized insulin by joining its gene with a plasmid vector inserted into the bacterium escherichia coli. insulin, widely used for the treatment of diabetes, was previously extracted from the pancreas of abattoir animals ( cattle or pigs ). the genetically engineered bacteria are able to produce large quantities of synthetic human insulin at relatively low cost. biotechnology has also enabled emerging therapeutics like gene therapy. the application of biotechnology to basic science ( for example through the human genome project ) has also dramatically improved our understanding of biology and as our scientific knowledge of normal and disease biology has increased, our ability to develop new medicines to treat previously untreatable diseases has increased as well. genetic testing allows the genetic diagnosis of vulnerabilities to inherited diseases, and can also be used to determine a child ' s parentage ( genetic mother and father ) or in general a person ' s ancestry. in addition to studying chromosomes to the level of individual genes, genetic testing in a broader sense includes biochemical tests for the possible presence of genetic diseases, or mutant forms of genes associated with increased risk of developing genetic disorders. genetic testing identifies changes in chromosomes, genes, or proteins. most of the time, testing is used to find changes that are associated with inherited disorders. the results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person ' s chance of developing or passing on a genetic disorder. as of 2011 several hundred genetic tests were in use. since genetic testing may open up ethical or psychological problems, genetic testing is often accompanied by genetic counseling. = = = agriculture = = = genetically modified crops ( " gm crops ", or " biotech crops " ) are plants used in agriculture, the dna of which has been modified with genetic engineering techniques. in most cases, the main aim is to introduce a new trait that does not occur naturally in the species. biotechnology firms can contribute to future food security by improving the nutrition and viability of urban agriculture. furthermore, the protection of intellectual property rights encourages private sector investment in agrobiotechnology. examples in food crops include resistance to certain pests, diseases, stressful environmental conditions, resistance to chemical treatments ( e. g. resistance to a herbicide ), reduction of spoilage, or improving the nutrient profile of the crop. examples in non - food crops include production of and the creation of genetically modified crops. = = = epigenetics = = = epigenetics is the study of heritable changes in gene function that cannot be explained by changes in the underlying dna sequence but cause the organism ' s genes to behave ( or " express themselves " ) differently. one example of epigenetic change is the marking of the genes by dna methylation which determines whether they will be expressed or not. gene expression can also be controlled by repressor proteins that attach to silencer regions of the dna and prevent that region of the dna code from being expressed. epigenetic marks may be added or removed from the dna during programmed stages of development of the plant, and are responsible, for example, for the differences between anthers, petals and normal leaves, despite the fact that they all have the same underlying genetic code. epigenetic changes may be temporary or may remain through successive cell divisions for the remainder of the cell ' s life. some epigenetic changes have been shown to be heritable, while others are reset in the germ cells. epigenetic changes in eukaryotic biology serve to regulate the process of cellular differentiation. during morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, defective gene with a functioning one. it is an important tool in research that allows the function of specific genes to be studied. drugs, vaccines and other products have been harvested from organisms engineered to produce them. crops have been developed that aid food security by increasing yield, nutritional value and tolerance to environmental stresses. the dna can be introduced directly into the host organism or into a cell that is then fused or hybridised with the host. this relies on recombinant nucleic acid techniques to form new combinations of heritable genetic material followed by the incorporation of that material either indirectly through a vector system or directly through micro - injection, macro - injection or micro - encapsulation. genetic engineering does not normally include traditional breeding, in vitro fertilisation, induction of polyploidy, mutagenesis and cell fusion techniques that do not use recombinant nucleic acids or a genetically modified organism in the process. however, some broad definitions of genetic engineering include selective breeding. cloning and stem cell research, although not considered genetic engineering, are closely related and genetic engineering can be used within them. synthetic biology is an emerging discipline that takes genetic engineering a step further by introducing artificially synthesised material into an organism. plants, animals or microorganisms that have been changed through genetic engineering are termed genetically modified organisms or gmos. if genetic material from another species is added to the host, the resulting organism is called transgenic. if genetic material from the same species or a species that can naturally breed with the host is used the resulting organism is called cisgenic. if genetic engineering is used to remove genetic material from the target organism the resulting organism is termed a knockout organism. in europe genetic modification is synonymous with genetic engineering while within the united states of america and canada genetic modification can also be used to refer to more conventional breeding methods. = = history = = humans have altered the genomes of species for thousands of years through selective breeding, or artificial selection : 1 : 1 as contrasted with natural selection. more recently, mutation breeding has used exposure to chemicals or radiation to produce a high frequency of random mutations, for selective breeding purposes. genetic engineering as the direct manipulation of dna by humans outside breeding and mutations has only existed since the 1970s. the term " genetic engineering " was coined by the russian - born geneticist nikolay timofeev - ressovsky in his 1934 paper " the experimental production of mutations ", published in the british journal biological reviews. jack williamson used the term in his science fiction novel dragon ' cross. the chromosome theory of inheritance, which states that genes are found on chromosomes, was supported by thomas morgans ' s experiments with fruit flies, which established the sex linkage between eye color and sex in these insects. = = = genes and dna = = = a gene is a unit of heredity that corresponds to a region of deoxyribonucleic acid ( dna ) that carries genetic information that controls form or function of an organism. dna is composed of two polynucleotide chains that coil around each other to form a double helix. it is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. the set of chromosomes in a cell is collectively known as its genome. in eukaryotes, dna is mainly in the cell nucleus. in prokaryotes, the dna is held within the nucleoid. the genetic information is held within genes, and the complete assemblage in an organism is called its genotype. dna replication is a semiconservative process whereby each strand serves as a template for a new strand of dna. mutations are heritable changes in dna. they can arise spontaneously as a result of replication errors that were not corrected by proofreading or can be induced by an environmental mutagen such as a chemical ( e. g., nitrous acid, benzopyrene ) or radiation ( e. g., x - ray, gamma ray, ultraviolet radiation, particles emitted by unstable isotopes ). mutations can lead to phenotypic effects such as loss - of - function, gain - of - function, and conditional mutations. some mutations are beneficial, as they are a source of genetic variation for evolution. others are harmful if they were to result in a loss of function of genes needed for survival. = = = gene expression = = = gene expression is the molecular process by which a genotype encoded in dna gives rise to an observable phenotype in the proteins of an organism ' s body. this process is summarized by the central dogma of molecular biology, which was formulated by francis crick in 1958. according to the central dogma, genetic information flows from dna to rna to protein. there are two gene expression processes : transcription ( dna to rna ) and translation ( rna to protein ). = = = gene regulation = = = the regulation of gene expression by environmental factors and during different stages of development can occur at each step of the process such as transcription, rna splicing , and includes, but is not limited to, the study of epidemics. genetics is the study of genes, and their role in biological inheritance. gynecology is the study of female reproductive system. histology is the study of the structures of biological tissues by light microscopy, electron microscopy and immunohistochemistry. immunology is the study of the immune system, which includes the innate and adaptive immune system in humans, for example. lifestyle medicine is the study of the chronic conditions, and how to prevent, treat and reverse them. medical physics is the study of the applications of physics principles in medicine. microbiology is the study of microorganisms, including protozoa, bacteria, fungi, and viruses. molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic material. neuroscience includes those disciplines of science that are related to the study of the nervous system. a main focus of neuroscience is the biology and physiology of the human brain and spinal cord. some related clinical specialties include neurology, neurosurgery and psychiatry. nutrition science ( theoretical focus ) and dietetics ( practical focus ) is the study of the relationship of food and drink to health and disease, especially in determining an optimal diet. medical nutrition therapy is done by dietitians and is prescribed for diabetes, cardiovascular diseases, weight and eating disorders, allergies, malnutrition, and neoplastic diseases. pathology as a science is the study of disease – the causes, course, progression and resolution thereof. pharmacology is the study of drugs and their actions. photobiology is the study of the interactions between non - ionizing radiation and living organisms. physiology is the study of the normal functioning of the body and the underlying regulatory mechanisms. radiobiology is the study of the interactions between ionizing radiation and living organisms. toxicology is the study of hazardous effects of drugs and poisons. = = = specialties = = = in the broadest meaning of " medicine ", there are many different specialties. in the uk, most specialities have their own body or college, which has its own entrance examination. these are collectively known as the royal colleges, although not all currently use the term " royal ". the development of a speciality is often driven by new technology ( such as the development of effective anaesthetics ) or ways of working ( such as emergency departments ) ; the new specialty leads to the formation of a unifying body of is opened and the dna is purified. the gene is separated by using restriction enzymes to cut the dna into fragments or polymerase chain reaction ( pcr ) to amplify up the gene segment. these segments can then be extracted through gel electrophoresis. if the chosen gene or the donor organism ' s genome has been well studied it may already be accessible from a genetic library. if the dna sequence is known, but no copies of the gene are available, it can also be artificially synthesised. once isolated the gene is ligated into a plasmid that is then inserted into a bacterium. the plasmid is replicated when the bacteria divide, ensuring unlimited copies of the gene are available. the rk2 plasmid is notable for its ability to replicate in a wide variety of single - celled organisms, which makes it suitable as a genetic engineering tool. before the gene is inserted into the target organism it must be combined with other genetic elements. these include a promoter and terminator region, which initiate and end transcription. a selectable marker gene is added, which in most cases confers antibiotic resistance, so researchers can easily determine which cells have been successfully transformed. the gene can also be modified at this stage for better expression or effectiveness. these manipulations are carried out using recombinant dna techniques, such as restriction digests, ligations and molecular cloning. = = = inserting dna into the host genome = = = there are a number of techniques used to insert genetic material into the host genome. some bacteria can naturally take up foreign dna. this ability can be induced in other bacteria via stress ( e. g. thermal or electric shock ), which increases the cell membrane ' s permeability to dna ; up - taken dna can either integrate with the genome or exist as extrachromosomal dna. dna is generally inserted into animal cells using microinjection, where it can be injected through the cell ' s nuclear envelope directly into the nucleus, or through the use of viral vectors. plant genomes can be engineered by physical methods or by use of agrobacterium for the delivery of sequences hosted in t - dna binary vectors. in plants the dna is often inserted using agrobacterium - mediated transformation, taking advantage of the agrobacteriums t - dna sequence that allows natural insertion of genetic material into plant cells. other methods include biolistics, where particles of gold or tungsten are coated with dna and then shot into Question: Professionals known as genetic counselors can help them understand the risks of? A) contagion B) infection C) disease D) children being affected	D) children being affected
Context: becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding sea approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding seawards, so that in the po river in italy, for instance, pebbles and gravel are found for about 140 miles below turin, sand along the next 100 miles, and silt and mud in the last 110 miles ( 176 km ). = = channelization = = the removal of obstructions, natural or artificial there are a few different mechanisms that can cause white dwarf stars to vary in brightness, providing opportunities to probe the physics, structures, and formation of these compact stellar remnants. the observational characteristics of the three most common types of white dwarf variability are summarized : stellar pulsations, rotation, and ellipsoidal variations from tidal distortion in binary systems. stellar pulsations are emphasized as the most complex type of variability, which also has the greatest potential to reveal the conditions of white dwarf interiors. variation in total solar irradiance is thought to have little effect on the earth ' s surface temperature because of the thermal time constant - - the characteristic response time of the earth ' s global surface temperature to changes in forcing. this time constant is large enough to smooth annual variations but not necessarily variations having a longer period such as those due to solar inertial motion ; the magnitude of these surface temperature variations is estimated. also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding seawards, so that in the po river in italy, for instance, pebbles and gravel are found for about 140 miles below turin, sand along the next 100 miles, and silt and mud in the last 110 miles ( 176 km ). = = channelization = = the removal of obstructions, natural or artificial ( e. g., trunks of trees, boulders and accumulations of gravel ) from a river bed furnishes a simple and efficient means of increasing the discharging capacity of its channel. such removals will consequently lower the height of floods upstream. every impediment to the flow, in proportion to discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding seawards, so that in the po river in italy, for instance, pebbles and gravel are found for about 140 miles below turin, sand along the next 100 miles, and silt and mud in the last 110 miles ( 176 km ). = = channelization = = the removal of obstructions, natural or artificial ( e. g., trunks of trees, boulders and accumulations of gravel ) from a river bed furnishes a simple and efficient means of increasing the discharging capacity of its channel. such removals will consequently lower the height of floods upstream. every impediment to the flow, in proportion to its extent, raises the level of the river above it so as to produce the additional artificial fall necessary to convey the flow through the restricted channel, thereby reducing the total available fall. reducing the length of the channel by substituting straight cuts for a winding course is the only way in which the effective fall can be increased. this involves some loss of capacity in the channel as a whole, and in the case of a large river with a considerable flow it is difficult to maintain a straight cut owing to the tendency of the current to erode the banks and form again a sinuous channel. even if the cut is preserved by protecting the banks, when fast radio burst ( frb ) waves propagate through the local ( < 1 pc ) environment of the frb source, electrons in the plasma undergo large - amplitude oscillations. the finite - amplitude effects cause the effective plasma frequency and cyclotron frequency to be dependent on the wave strength. the dispersion measure and rotation measure should therefore vary slightly from burst to burst for a repeating source, depending on the luminosity and frequency of the individual burst. furthermore, free - free absorption of strong waves is suppressed due to the accelerated electrons ' reduced energy exchange in coulomb collisions. this allows bright low - frequency bursts to propagate through an environment that would be optically thick to low - amplitude waves. given a large sample of bursts from a repeating source, it would be possible to use the deficit of low - frequency and low - luminosity bursts to infer the emission measure of the local intervening plasma and its distance from the source. information about the local environment will shed light on the nature of frb sources. Question: What type of fronts often bring sudden changes in the weather, including different types of precipitation, depending on the season? A) warm fronts B) stationary fronts C) cold fronts D) occluded fronts	C) cold fronts
Context: as subjects perceive the sensory world, different stimuli elicit a number of neural representations. here, a subjective distance between stimuli is defined, measuring the degree of similarity between the underlying representations. as an example, the subjective distance between different locations in space is calculated from the activity of rodent hippocampal place cells, and lateral septal cells. such a distance is compared to the real distance, between locations. as the number of sampled neurons increases, the subjective distance shows a tendency to resemble the metrics of real space. - people relationships arose between the indigenous people of canada in identifying edible plants from inedible plants. this relationship the indigenous people had with plants was recorded by ethnobotanists. = = plant biochemistry = = plant biochemistry is the study of the chemical processes used by plants. some of these processes are used in their primary metabolism like the photosynthetic calvin cycle and crassulacean acid metabolism. others make specialised materials like the cellulose and lignin used to build their bodies, and secondary products like resins and aroma compounds. plants and various other groups of photosynthetic eukaryotes collectively known as " algae " have unique organelles known as chloroplasts. chloroplasts are thought to be descended from cyanobacteria that formed endosymbiotic relationships with ancient plant and algal ancestors. chloroplasts and cyanobacteria contain the blue - green pigment chlorophyll a. chlorophyll a ( as well as its plant and green algal - specific cousin chlorophyll b ) absorbs light in the blue - violet and orange / red parts of the spectrum while reflecting and transmitting the green light that we see as the characteristic colour of these organisms. the energy in the red and blue light that these pigments absorb is used by chloroplasts to make energy - rich carbon compounds from carbon dioxide and water by oxygenic photosynthesis, a process that generates molecular oxygen ( o2 ) as a by - product. the light energy captured by chlorophyll a is initially in the form of electrons ( and later a proton gradient ) that is used to make molecules of atp and nadph which temporarily store and transport energy. their energy is used in the light - independent reactions of the calvin cycle by the enzyme rubisco to produce molecules of the 3 - carbon sugar glyceraldehyde 3 - phosphate ( g3p ). glyceraldehyde 3 - phosphate is the first product of photosynthesis and the raw material from which glucose and almost all other organic molecules of biological origin are synthesised. some of the glucose is converted to starch which is stored in the chloroplast. starch is the characteristic energy store of most land plants and algae, while inulin, a polymer of fructose is used for the same purpose in the sunflower family asteraceae. some of the glucose is converted to sucrose ( common table the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the are further divided into multiple recognized phyla. archaea and bacteria are generally similar in size and shape, although a few archaea have very different shapes, such as the flat and square cells of haloquadratum walsbyi. despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably for the enzymes involved in transcription and translation. other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, including archaeols. archaea use more energy sources than eukaryotes : these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. salt - tolerant archaea ( the haloarchaea ) use sunlight as an energy source, and other species of archaea fix carbon, but unlike plants and cyanobacteria, no known species of archaea does both. archaea reproduce asexually by binary fission, fragmentation, or budding ; unlike bacteria, no known species of archaea form endospores. the first observed archaea were extremophiles, living in extreme environments, such as hot springs and salt lakes with no other organisms. improved molecular detection tools led to the discovery of archaea in almost every habitat, including soil, oceans, and marshlands. archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. archaea are a major part of earth ' s life. they are part of the microbiota of all organisms. in the human microbiome, they are important in the gut, mouth, and on the skin. their morphological, metabolic, and geographical diversity permits them to play multiple ecological roles : carbon fixation ; nitrogen cycling ; organic compound turnover ; and maintaining microbial symbiotic and syntrophic communities, for example. = = = eukaryotes = = = eukaryotes are hypothesized to have split from archaea, which was followed by their endosymbioses with bacteria ( or symbiogenesis ) that gave rise to mitochondria and chloroplasts, both of which are now part of modern - day eukaryotic cells. the major lineages of eukaryotes diversified in the precambrian about 1. 5 billion years ago and can be classified into eight major clades : alveolates, other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ) of the mass of all organisms, with calcium, phosphorus, sulfur, sodium, chlorine, and magnesium constituting essentially all the remainder. different elements can combine to form compounds such as water, which is fundamental to life. biochemistry is the study of chemical processes within and relating to living organisms. molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including molecular synthesis, modification, mechanisms, and interactions. = = = water = = = life arose from the earth ' s first ocean, which formed some 3. 8 billion years ago. since then, water continues to be the most abundant molecule in every organism. water is important to life because it is an effective solvent, capable of dissolving solutes such as sodium and chloride ions or other small molecules to form an aqueous solution. once dissolved in water, these solutes are more likely to come in contact with one another and therefore take part in chemical reactions that sustain life. in terms of its molecular structure, water is a small polar molecule with a bent shape formed by the polar covalent bonds of two hydrogen ( h ) atoms to one oxygen ( o ) atom ( h2o ). because the o – h bonds are polar, the oxygen atom has a slight negative charge and the two hydrogen atoms have a slight positive charge. this polar property of water allows it to attract other water molecules via hydrogen bonds, which makes water cohesive. surface tension results from the cohesive force due to the attraction between molecules at the surface of the liquid. water is also adhesive as it is able to adhere to the surface of any polar or charged non - water molecules. water is denser as a liquid than it is as a solid ( or ice ). this unique property of water allows ice to float above liquid water such as ponds, lakes, and oceans, thereby insulating the liquid below from the cold air above. water has the capacity to absorb energy, giving it a higher specific heat capacity than other solvents such as ethanol. thus, a large amount of energy is needed to break the hydrogen bonds between water molecules to convert liquid water into water vapor. as a molecule, water is not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again. in pure water, the number of hydrogen ions balances ( or equals ) the number of hydroxyl ions, resulting in a ph that is neutral. = = = organic compounds = = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then oxidized into acetyl - coa by the pyruvate dehydrogenase complex, which also generates nadh and carbon dioxide. acetyl - coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. at the end of the cycle, the total yield from 1 glucose ( or 2 pyruvates ) is 6 nadh, 2 fadh2, and 2 atp molecules. finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from nadh and fadh2 that is coupled to the pumping of protons ( hydrogen ions ) across the inner mitochondrial membrane ( chemiosmosis ), which generates a proton motive force. energy from the proton motive force drives the enzyme atp synthase to synthesize more atps by phosphorylating adps. the transfer of electrons terminates with molecular oxygen being the final electron acceptor. if oxygen were not present, pyruvate would not be metabolized by cellular respiration but undergoes , tertiary, and quaternary ). the similarities among all known present - day species indicate that they have diverged through the process of evolution from their common ancestor. biologists regard the ubiquity of the genetic code as evidence of universal common descent for all bacteria, archaea, and eukaryotes. microbial mats of coexisting bacteria and archaea were the dominant form of life in the early archean eon and many of the major steps in early evolution are thought to have taken place in this environment. the earliest evidence of eukaryotes dates from 1. 85 billion years ago, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. later, around 1. 7 billion years ago, multicellular organisms began to appear, with differentiated cells performing specialised functions. algae - like multicellular land plants are dated back to about 1 billion years ago, although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2. 7 billion years ago. microorganisms are thought to have paved the way for the inception of land plants in the ordovician period. land plants were so successful that they are thought to have contributed to the late devonian extinction event. ediacara biota appear during the ediacaran period, while vertebrates, along with most other modern phyla originated about 525 million years ago during the cambrian explosion. during the permian period, synapsids, including the ancestors of mammals, dominated the land, but most of this group became extinct in the permian – triassic extinction event 252 million years ago. during the recovery from this catastrophe, archosaurs became the most abundant land vertebrates ; one archosaur group, the dinosaurs, dominated the jurassic and cretaceous periods. after the cretaceous – paleogene extinction event 66 million years ago killed off the non - avian dinosaurs, mammals increased rapidly in size and diversity. such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. = = diversity = = = = = bacteria and archaea = = = bacteria are a type of cell that constitute a large domain of prokaryotic microorganisms. typically a few micrometers in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. bacteria were among the first life forms to appear on earth, and are present in most of its habitats. bacteria inhabit soil, water, acidic hot springs, radioactive reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then oxidized into acetyl - coa by the pyruvate dehydrogenase complex, which also generates nadh and carbon dioxide. acetyl - coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. at the end of the cycle, the total yield from 1 glucose ( or 2 pyruvates ) is 6 nadh, 2 fadh2, and 2 atp molecules. finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from nadh and fadh2 that is coupled to the pumping of protons ( hydrogen ions ) across the inner mitochondrial membrane ( chemiosmosis ), which generates a proton motive force. energy Question: Similarity in biochemicals, like the glucose used by virtually all living things for energy, provides evidence of what? A) gravity B) evolution C) DNA D) variation	B) evolution
Context: cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions ##logous in nature, and can be used in a myriad of ways, from helping repair skeletal tissue to replenishing beta cells in diabetic patients. allogenic : cells are obtained from the body of a donor of the same species as the recipient. while there are some ethical constraints to the use of human cells for in vitro studies ( i. e. human brain tissue chimera development ), the employment of dermal fibroblasts from human foreskin demonstrates an immunologically safe and thus a viable choice for allogenic tissue engineering of the skin. xenogenic : these cells are derived isolated cells from alternate species from the recipient. a notable example of xenogeneic tissue utilization is cardiovascular implant construction via animal cells. chimeric human - animal farming raises ethical concerns around the potential for improved consciousness from implanting human organs in animals. syngeneic or isogenic : these cells describe those borne from identical genetic code. this imparts an immunologic benefit similar to autologous cell lines ( see above ). autologous cells can be considered syngenic, but the classification also extends to non - autologously derived cells such as those from an identical twin, from genetically identical ( cloned ) research models, or induced stem cells ( isc ) as related to the donor. = = = stem cells = = = stem cells are undifferentiated cells with the ability to divide in culture and give rise to different forms of specialized cells. stem cells are divided into " adult " and " embryonic " stem cells according to their source. while there is still a large ethical debate related to the use of embryonic stem cells, it is thought that another alternative source – induced pluripotent stem cells – may be useful for the repair of diseased or damaged tissues, or may be used to grow new organs. totipotent cells are stem cells which can divide into further stem cells or differentiate into any cell type in the body, including extra - embryonic tissue. pluripotent cells are stem cells which can differentiate into any cell type in the body except extra - embryonic tissue. induced pluripotent stem cells ( ipscs ) are subclass of pluripotent stem cells resembling embryonic stem cells ( escs ) that have been derived from adult differentiated cells. ipscs are created by altering the expression of transcriptional factors in adult cells until they become like embryonic stem cells. multipotent stem cells can be differentiated into any cell , depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in of cells = = = autologous : the donor and the recipient of the cells are the same individual. cells are harvested, cultured or stored, and then reintroduced to the host. as a result of the host ' s own cells being reintroduced, an antigenic response is not elicited. the body ' s immune system recognizes these re - implanted cells as its own, and does not target them for attack. autologous cell dependence on host cell health and donor site morbidity may be deterrents to their use. adipose - derived and bone marrow - derived mesenchymal stem cells are commonly autologous in nature, and can be used in a myriad of ways, from helping repair skeletal tissue to replenishing beta cells in diabetic patients. allogenic : cells are obtained from the body of a donor of the same species as the recipient. while there are some ethical constraints to the use of human cells for in vitro studies ( i. e. human brain tissue chimera development ), the employment of dermal fibroblasts from human foreskin demonstrates an immunologically safe and thus a viable choice for allogenic tissue engineering of the skin. xenogenic : these cells are derived isolated cells from alternate species from the recipient. a notable example of xenogeneic tissue utilization is cardiovascular implant construction via animal cells. chimeric human - animal farming raises ethical concerns around the potential for improved consciousness from implanting human organs in animals. syngeneic or isogenic : these cells describe those borne from identical genetic code. this imparts an immunologic benefit similar to autologous cell lines ( see above ). autologous cells can be considered syngenic, but the classification also extends to non - autologously derived cells such as those from an identical twin, from genetically identical ( cloned ) research models, or induced stem cells ( isc ) as related to the donor. = = = stem cells = = = stem cells are undifferentiated cells with the ability to divide in culture and give rise to different forms of specialized cells. stem cells are divided into " adult " and " embryonic " stem cells according to their source. while there is still a large ethical debate related to the use of embryonic stem cells, it is thought that another alternative source – induced pluripotent stem cells – may be useful for the repair of diseased or damaged tissues, or may be used to grow new organs. totipotent cells capable elad would temporarily function as an individual ' s liver, thus avoiding transplantation and allowing regeneration of their own liver. artificial pancreas : research involves using islet cells to regulate the body ' s blood sugar, particularly in cases of diabetes. biochemical factors may be used to cause human pluripotent stem cells to differentiate ( turn into ) cells that function similarly to beta cells, which are in an islet cell in charge of producing insulin. artificial bladders : anthony atala ( wake forest university ) has successfully implanted artificial bladders, constructed of cultured cells seeded onto a bladder - shaped scaffold, into seven out of approximately 20 human test subjects as part of a long - term experiment. cartilage : lab - grown cartilage, cultured in vitro on a scaffold, was successfully used as an autologous transplant to repair patients ' knees. scaffold - free cartilage : cartilage generated without the use of exogenous scaffold material. in this methodology, all material in the construct is cellular produced directly by the cells. bioartificial heart : doris taylor ' s lab constructed a biocompatible rat heart by re - cellularising a de - cellularised rat heart. this scaffold and cells were placed in a bioreactor, where it matured to become a partially or fully transplantable organ. the work was called a " landmark ". the lab first stripped the cells away from a rat heart ( a process called " decellularization " ) and then injected rat stem cells into the decellularized rat heart. tissue - engineered blood vessels : blood vessels that have been grown in a lab and can be used to repair damaged blood vessels without eliciting an immune response. tissue engineered blood vessels have been developed by many different approaches. they could be implanted as pre - seeded cellularized blood vessels, as acellular vascular grafts made with decellularized vessels or synthetic vascular grafts. artificial skin constructed from human skin cells embedded in a hydrogel, such as in the case of bio - printed constructs for battlefield burn repairs. artificial bone marrow : bone marrow cultured in vitro to be transplanted serves as a " just cells " approach to tissue engineering. tissue engineered bone : a structural matrix can be composed of metals such as titanium, polymers of varying degradation rates, or certain types of ceramics. materials are often chosen to recruit osteoblasts to aid in reforming the bone and returning biological function ##artificial liver device, " temporary liver ", extracorporeal liver assist device ( elad ) : the human hepatocyte cell line ( c3a line ) in a hollow fiber bioreactor can mimic the hepatic function of the liver for acute instances of liver failure. a fully capable elad would temporarily function as an individual ' s liver, thus avoiding transplantation and allowing regeneration of their own liver. artificial pancreas : research involves using islet cells to regulate the body ' s blood sugar, particularly in cases of diabetes. biochemical factors may be used to cause human pluripotent stem cells to differentiate ( turn into ) cells that function similarly to beta cells, which are in an islet cell in charge of producing insulin. artificial bladders : anthony atala ( wake forest university ) has successfully implanted artificial bladders, constructed of cultured cells seeded onto a bladder - shaped scaffold, into seven out of approximately 20 human test subjects as part of a long - term experiment. cartilage : lab - grown cartilage, cultured in vitro on a scaffold, was successfully used as an autologous transplant to repair patients ' knees. scaffold - free cartilage : cartilage generated without the use of exogenous scaffold material. in this methodology, all material in the construct is cellular produced directly by the cells. bioartificial heart : doris taylor ' s lab constructed a biocompatible rat heart by re - cellularising a de - cellularised rat heart. this scaffold and cells were placed in a bioreactor, where it matured to become a partially or fully transplantable organ. the work was called a " landmark ". the lab first stripped the cells away from a rat heart ( a process called " decellularization " ) and then injected rat stem cells into the decellularized rat heart. tissue - engineered blood vessels : blood vessels that have been grown in a lab and can be used to repair damaged blood vessels without eliciting an immune response. tissue engineered blood vessels have been developed by many different approaches. they could be implanted as pre - seeded cellularized blood vessels, as acellular vascular grafts made with decellularized vessels or synthetic vascular grafts. artificial skin constructed from human skin cells embedded in a hydrogel, such as in the case of bio - printed constructs for battlefield burn repairs. artificial bone marrow : bone marrow cultured in vitro to electrons to drive the synthesis of glucose by fixing atmospheric carbon dioxide into existing organic carbon compounds, such as ribulose bisphosphate ( rubp ) in a sequence of light - independent ( or dark ) reactions called the calvin cycle. = = = cell signaling = = = cell signaling ( or communication ) is the ability of cells to receive, process, and transmit signals with its environment and with itself. signals can be non - chemical such as light, electrical impulses, and heat, or chemical signals ( or ligands ) that interact with receptors, which can be found embedded in the cell membrane of another cell or located deep inside a cell. there are generally four types of chemical signals : autocrine, paracrine, juxtacrine, and hormones. in autocrine signaling, the ligand affects the same cell that releases it. tumor cells, for example, can reproduce uncontrollably because they release signals that initiate their own self - division. in paracrine signaling, the ligand diffuses to nearby cells and affects them. for example, brain cells called neurons release ligands called neurotransmitters that diffuse across a synaptic cleft to bind with a receptor on an adjacent cell such as another neuron or muscle cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and s immune system recognizes these re - implanted cells as its own, and does not target them for attack. autologous cell dependence on host cell health and donor site morbidity may be deterrents to their use. adipose - derived and bone marrow - derived mesenchymal stem cells are commonly autologous in nature, and can be used in a myriad of ways, from helping repair skeletal tissue to replenishing beta cells in diabetic patients. allogenic : cells are obtained from the body of a donor of the same species as the recipient. while there are some ethical constraints to the use of human cells for in vitro studies ( i. e. human brain tissue chimera development ), the employment of dermal fibroblasts from human foreskin demonstrates an immunologically safe and thus a viable choice for allogenic tissue engineering of the skin. xenogenic : these cells are derived isolated cells from alternate species from the recipient. a notable example of xenogeneic tissue utilization is cardiovascular implant construction via animal cells. chimeric human - animal farming raises ethical concerns around the potential for improved consciousness from implanting human organs in animals. syngeneic or isogenic : these cells describe those borne from identical genetic code. this imparts an immunologic benefit similar to autologous cell lines ( see above ). autologous cells can be considered syngenic, but the classification also extends to non - autologously derived cells such as those from an identical twin, from genetically identical ( cloned ) research models, or induced stem cells ( isc ) as related to the donor. = = = stem cells = = = stem cells are undifferentiated cells with the ability to divide in culture and give rise to different forms of specialized cells. stem cells are divided into " adult " and " embryonic " stem cells according to their source. while there is still a large ethical debate related to the use of embryonic stem cells, it is thought that another alternative source – induced pluripotent stem cells – may be useful for the repair of diseased or damaged tissues, or may be used to grow new organs. totipotent cells are stem cells which can divide into further stem cells or differentiate into any cell type in the body, including extra - embryonic tissue. pluripotent cells are stem cells which can differentiate into any cell type in the body except extra - embryonic tissue. induced pluripotent stem cells ( ipscs ) founded in 1976 and started the production of human proteins. genetically engineered human insulin was produced in 1978 and insulin - producing bacteria were commercialised in 1982. genetically modified food has been sold since 1994, with the release of the flavr savr tomato. the flavr savr was engineered to have a longer shelf life, but most current gm crops are modified to increase resistance to insects and herbicides. glofish, the first gmo designed as a pet, was sold in the united states in december 2003. in 2016 salmon modified with a growth hormone were sold. genetic engineering has been applied in numerous fields including research, medicine, industrial biotechnology and agriculture. in research, gmos are used to study gene function and expression through loss of function, gain of function, tracking and expression experiments. by knocking out genes responsible for certain conditions it is possible to create animal model organisms of human diseases. as well as producing hormones, vaccines and other drugs, genetic engineering has the potential to cure genetic diseases through gene therapy. chinese hamster ovary ( cho ) cells are used in industrial genetic engineering. additionally mrna vaccines are made through genetic engineering to prevent infections by viruses such as covid - 19. the same techniques that are used to produce drugs can also have industrial applications such as producing enzymes for laundry detergent, cheeses and other products. the rise of commercialised genetically modified crops has provided economic benefit to farmers in many different countries, but has also been the source of most of the controversy surrounding the technology. this has been present since its early use ; the first field trials were destroyed by anti - gm activists. although there is a scientific consensus that currently available food derived from gm crops poses no greater risk to human health than conventional food, critics consider gm food safety a leading concern. gene flow, impact on non - target organisms, control of the food supply and intellectual property rights have also been raised as potential issues. these concerns have led to the development of a regulatory framework, which started in 1975. it has led to an international treaty, the cartagena protocol on biosafety, that was adopted in 2000. individual countries have developed their own regulatory systems regarding gmos, with the most marked differences occurring between the united states and europe. = = overview = = genetic engineering is a process that alters the genetic structure of an organism by either removing or introducing dna, or modifying existing genetic material in situ. unlike traditional animal and plant breeding, which involves doing multiple crosses and then selecting for the organism with the desired phenotype, stem cells to differentiate ( turn into ) cells that function similarly to beta cells, which are in an islet cell in charge of producing insulin. artificial bladders : anthony atala ( wake forest university ) has successfully implanted artificial bladders, constructed of cultured cells seeded onto a bladder - shaped scaffold, into seven out of approximately 20 human test subjects as part of a long - term experiment. cartilage : lab - grown cartilage, cultured in vitro on a scaffold, was successfully used as an autologous transplant to repair patients ' knees. scaffold - free cartilage : cartilage generated without the use of exogenous scaffold material. in this methodology, all material in the construct is cellular produced directly by the cells. bioartificial heart : doris taylor ' s lab constructed a biocompatible rat heart by re - cellularising a de - cellularised rat heart. this scaffold and cells were placed in a bioreactor, where it matured to become a partially or fully transplantable organ. the work was called a " landmark ". the lab first stripped the cells away from a rat heart ( a process called " decellularization " ) and then injected rat stem cells into the decellularized rat heart. tissue - engineered blood vessels : blood vessels that have been grown in a lab and can be used to repair damaged blood vessels without eliciting an immune response. tissue engineered blood vessels have been developed by many different approaches. they could be implanted as pre - seeded cellularized blood vessels, as acellular vascular grafts made with decellularized vessels or synthetic vascular grafts. artificial skin constructed from human skin cells embedded in a hydrogel, such as in the case of bio - printed constructs for battlefield burn repairs. artificial bone marrow : bone marrow cultured in vitro to be transplanted serves as a " just cells " approach to tissue engineering. tissue engineered bone : a structural matrix can be composed of metals such as titanium, polymers of varying degradation rates, or certain types of ceramics. materials are often chosen to recruit osteoblasts to aid in reforming the bone and returning biological function. various types of cells can be added directly into the matrix to expedite the process. laboratory - grown penis : decellularized scaffolds of rabbit penises were recellularised with smooth muscle and endothelial cells. the organ was then transplanted to live rabbits and functioned comparably Question: In type 2 diabetes, body cells do not respond to normal amounts of what hormone? A) insulin B) estrogen C) hemoglobin D) glucose	A) insulin
Context: electromagnetic induction. the transmission speed ranges from 2 mbit / s to 10 gbit / s. twisted pair cabling comes in two forms : unshielded twisted pair ( utp ) and shielded twisted - pair ( stp ). each form comes in several category ratings, designed for use in various scenarios. an optical fiber is a glass fiber. it carries pulses of light that represent data via lasers and optical amplifiers. some advantages of optical fibers over metal wires are very low transmission loss and immunity to electrical interference. using dense wave division multiplexing, optical fibers can simultaneously carry multiple streams of data on different wavelengths of light, which greatly increases the rate that data can be sent to up to trillions of bits per second. optic fibers can be used for long runs of cable carrying very high data rates, and are used for undersea communications cables to interconnect continents. there are two basic types of fiber optics, single - mode optical fiber ( smf ) and multi - mode optical fiber ( mmf ). single - mode fiber has the advantage of being able to sustain a coherent signal for dozens or even a hundred kilometers. multimode fiber is cheaper to terminate but is limited to a few hundred or even only a few dozens of meters, depending on the data rate and cable grade. = = = wireless = = = network connections can be established wirelessly using radio or other electromagnetic means of communication. terrestrial microwave – terrestrial microwave communication uses earth - based transmitters and receivers resembling satellite dishes. terrestrial microwaves are in the low gigahertz range, which limits all communications to line - of - sight. relay stations are spaced approximately 40 miles ( 64 km ) apart. communications satellites – satellites also communicate via microwave. the satellites are stationed in space, typically in geosynchronous orbit 35, 400 km ( 22, 000 mi ) above the equator. these earth - orbiting systems are capable of receiving and relaying voice, data, and tv signals. cellular networks use several radio communications technologies. the systems divide the region covered into multiple geographic areas. each area is served by a low - power transceiver. radio and spread spectrum technologies – wireless lans use a high - frequency radio technology similar to digital cellular. wireless lans use spread spectrum technology to enable communication between multiple devices in a limited area. ieee 802. 11 defines a common flavor of open - standards wireless radio - wave technology known as wi - fi. free - space optical communication uses visible or invisible light for communications. in most cases, line - of unitary recordings in freely - moving pulse weakly electric fish suggest spike timing encoding of electrosensory signals blood vessels. mechanical stimuli, such as pressure pulses seem to be beneficial to all kind of cardiovascular tissue such as heart valves, blood vessels or pericardium. = = = bioreactors = = = in tissue engineering, a bioreactor is a device that attempts to simulate a physiological environment in order to promote cell or tissue growth in vitro. a physiological environment can consist of many different parameters such as temperature, pressure, oxygen or carbon dioxide concentration, or osmolality of fluid environment, and it can extend to all kinds of biological, chemical or mechanical stimuli. therefore, there are systems that may include the application of forces such as electromagnetic forces, mechanical pressures, or fluid pressures to the tissue. these systems can be two - or three - dimensional setups. bioreactors can be used in both academic and industry applications. general - use and application - specific bioreactors are also commercially available, which may provide static chemical stimulation or a combination of chemical and mechanical stimulation. cell proliferation and differentiation are largely influenced by mechanical and biochemical cues in the surrounding extracellular matrix environment. bioreactors are typically developed to replicate the specific physiological environment of the tissue being grown ( e. g., flex and fluid shearing for heart tissue growth ). this can allow specialized cell lines to thrive in cultures replicating their native environments, but it also makes bioreactors attractive tools for culturing stem cells. a successful stem - cell - based bioreactor is effective at expanding stem cells with uniform properties and / or promoting controlled, reproducible differentiation into selected mature cell types. there are a variety of bioreactors designed for 3d cell cultures. there are small plastic cylindrical chambers, as well as glass chambers, with regulated internal humidity and moisture specifically engineered for the purpose of growing cells in three dimensions. the bioreactor uses bioactive synthetic materials such as polyethylene terephthalate membranes to surround the spheroid cells in an environment that maintains high levels of nutrients. they are easy to open and close, so that cell spheroids can be removed for testing, yet the chamber is able to maintain 100 % humidity throughout. this humidity is important to achieve maximum cell growth and function. the bioreactor chamber is part of a larger device that rotates to ensure equal cell growth in each direction across three dimensions. quinxell technologies now under quintech life sciences from singapore has developed a bioreactor known as the tisxell biaxial bioreactor which is specially designed for the purpose of fluid dynamics video demonstrating the evolution of dynamic stall on a wind turbine blade. , phone lines and power lines ) to create a high - speed local area network. twisted pair cabling is used for wired ethernet and other standards. it typically consists of 4 pairs of copper cabling that can be utilized for both voice and data transmission. the use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. the transmission speed ranges from 2 mbit / s to 10 gbit / s. twisted pair cabling comes in two forms : unshielded twisted pair ( utp ) and shielded twisted - pair ( stp ). each form comes in several category ratings, designed for use in various scenarios. an optical fiber is a glass fiber. it carries pulses of light that represent data via lasers and optical amplifiers. some advantages of optical fibers over metal wires are very low transmission loss and immunity to electrical interference. using dense wave division multiplexing, optical fibers can simultaneously carry multiple streams of data on different wavelengths of light, which greatly increases the rate that data can be sent to up to trillions of bits per second. optic fibers can be used for long runs of cable carrying very high data rates, and are used for undersea communications cables to interconnect continents. there are two basic types of fiber optics, single - mode optical fiber ( smf ) and multi - mode optical fiber ( mmf ). single - mode fiber has the advantage of being able to sustain a coherent signal for dozens or even a hundred kilometers. multimode fiber is cheaper to terminate but is limited to a few hundred or even only a few dozens of meters, depending on the data rate and cable grade. = = = wireless = = = network connections can be established wirelessly using radio or other electromagnetic means of communication. terrestrial microwave – terrestrial microwave communication uses earth - based transmitters and receivers resembling satellite dishes. terrestrial microwaves are in the low gigahertz range, which limits all communications to line - of - sight. relay stations are spaced approximately 40 miles ( 64 km ) apart. communications satellites – satellites also communicate via microwave. the satellites are stationed in space, typically in geosynchronous orbit 35, 400 km ( 22, 000 mi ) above the equator. these earth - orbiting systems are capable of receiving and relaying voice, data, and tv signals. cellular networks use several radio communications technologies. the systems divide the region covered into multiple geographic areas. each area is served by a low - power transceiver. radio and spread spectrum technologies – wireless lans use a high - frequency radio technology similar to a review of mhd dynamos and turbulence. if a fintie group g acts topologically and faithfully on r ^ 3, then g is a subgroup of o ( 3 ) some references for the breaking strength of fused silica fibers compiled in 1999. computer networking. coaxial cable is widely used for cable television systems, office buildings, and other work - sites for local area networks. transmission speed ranges from 200 million bits per second to more than 500 million bits per second. itu - t g. hn technology uses existing home wiring ( coaxial cable, phone lines and power lines ) to create a high - speed local area network. twisted pair cabling is used for wired ethernet and other standards. it typically consists of 4 pairs of copper cabling that can be utilized for both voice and data transmission. the use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. the transmission speed ranges from 2 mbit / s to 10 gbit / s. twisted pair cabling comes in two forms : unshielded twisted pair ( utp ) and shielded twisted - pair ( stp ). each form comes in several category ratings, designed for use in various scenarios. an optical fiber is a glass fiber. it carries pulses of light that represent data via lasers and optical amplifiers. some advantages of optical fibers over metal wires are very low transmission loss and immunity to electrical interference. using dense wave division multiplexing, optical fibers can simultaneously carry multiple streams of data on different wavelengths of light, which greatly increases the rate that data can be sent to up to trillions of bits per second. optic fibers can be used for long runs of cable carrying very high data rates, and are used for undersea communications cables to interconnect continents. there are two basic types of fiber optics, single - mode optical fiber ( smf ) and multi - mode optical fiber ( mmf ). single - mode fiber has the advantage of being able to sustain a coherent signal for dozens or even a hundred kilometers. multimode fiber is cheaper to terminate but is limited to a few hundred or even only a few dozens of meters, depending on the data rate and cable grade. = = = wireless = = = network connections can be established wirelessly using radio or other electromagnetic means of communication. terrestrial microwave – terrestrial microwave communication uses earth - based transmitters and receivers resembling satellite dishes. terrestrial microwaves are in the low gigahertz range, which limits all communications to line - of - sight. relay stations are spaced approximately 40 miles ( 64 km ) apart. communications satellites – satellites also communicate via microwave. the satellites are stationed in space, typically in geosynchronous orbit 35, 400 km ( 22, 000 mi ) above the equator. these earth - orbiting systems are an oscillation with a period of around 500 kb in guanine and cytosine content ( gc % ) is observed in the dna sequence of human chromosome 21. this oscillation is localized in the rightmost one - eighth region of the chromosome, from 43. 5 mb to 46. 5 mb. five cycles of oscillation are observed in this region with six gc - rich peaks and five gc - poor valleys. the gc - poor valleys comprise regions with low density of cpg islands and, alternating between the two dna strands, low gene density regions. consequently, the long - range oscillation of gc % result in spacing patterns of both cpg island density, and to a lesser extent, gene densities. Question: What fibres are seen in some vertebrates that twitch at rates far faster than any human muscle? A) slow twitch fibres B) skeletal muscle fibers C) fast glycolytic fibres D) fast oxidative fibres	B) skeletal muscle fibers
Context: it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a spindle apparatus on the cell. before binary fission, dna in the bacterium is tightly coiled. after it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. growth of a new cell wall begins to separate the bacterium ( triggered by ft ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a spindle apparatus on the cell. before binary fission, dna in the bacterium is tightly coiled. after it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. growth of a new cell wall begins to separate the bacterium ( triggered by ftsz polymerization and " z - ring " formation ). the new cell wall ( septum ) fully develops, resulting in the complete split of the bacterium. the new daughter cells have tightly coiled dna rods, ribosomes, and plasmids. = = = sexual reproduction and meiosis = = = meiosis is a central feature of sexual reproduction in eukaryotes, and the most fundamental function of meiosis appears to be conservation of the integrity of the genome that is passed on to progeny by parents. two aspects of sexual reproduction, meiotic recombination and outcrossing, are likely maintained respectively by the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a spindle apparatus on the cell. before binary fission, dna in the bacterium is tightly coiled. after it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. growth of a new cell wall begins to separate the bacterium ( triggered by ftsz polymerization and " z - ring " formation ). the new cell wall ( septum ) fully develops, resulting in the complete split of the bacterium. the new daughter cells have tightly coiled dna rods, ribosomes, and plasmids. = = = sexual reproduction and meiosis = = = meiosis is a central feature of sexual reproduction in eukaryotes, and the most fundamental function of meiosis appears to be conservation of the integrity of the genome that is passed on to progeny by parents. two aspects of sexual reproduction, meiotic recombination and outcrossing, are likely maintained respectively by the adaptive advantages of recombinational repair of genomic dna damage and genetic complementation which masks the expression of deleterious recessive mutations. the beneficial effect of genetic complementation, derived from outcrossing ( cross - fertilization ) is also referred to as hybrid vigor or heterosis. charles darwin in his 1878 book the effects of cross and self - fertilization in the vegetable kingdom at the start of chapter xii noted “ the first and most important of the conclusions which may be drawn from the observations given in this volume, is that generally cross - fertilisation is beneficial and self - fertilis protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a spindle apparatus on the cell. before binary fission, dna in the bacterium is tightly coiled. after it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. growth of a new cell wall begins to separate the bacterium ( triggered by ftsz polymerization and " z - ring " formation ). the new cell wall ( septum ) fully develops, resulting in the complete split of the bacterium. the new daughter cells have tightly coiled dna rods, ribosomes, and plasmids. = = = sexual reproduction and meiosis = = = mei of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a spindle apparatus on the cell. before binary fission, dna in the bacterium is tightly coiled. after it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. growth of a new cell wall begins to separate the bacterium ( triggered by ftsz polymerization and " z - ring " formation ). the new cell wall ( septum ) fully develops, resulting in the complete split of the bacterium. the new daughter cells have tightly coiled dna rods, ribosomes, and plasmids. = = = sexual reproduction and meiosis = = = meiosis is a central feature of sexual reproduction in eukaryotes, and the most fundamental function of meiosis appears to be conservation of the integrity of the genome that is passed on to progeny by parents. two aspects of sexual reproduction, meiotic recombination and outcrossing, are likely maintained respectively by the adaptive advantages of recombinational repair of genomic dna damage and genetic complementation which masks the expression of deleterious recessive mutations. the beneficial effect of genetic complementation, derived from outcrossing ( cross - fertilization ) is also referred to as hybrid vigor or heterosis. charles activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a cytokinesis ). the natural cytokinin zeatin was discovered in corn, zea mays, and is a derivative of the purine adenine. zeatin is produced in roots and transported to shoots in the xylem where it promotes cell division, bud development, and the greening of chloroplasts. the gibberelins, such as gibberelic acid are diterpenes synthesised from acetyl coa via the mevalonate pathway. they are involved in the promotion of germination and dormancy - breaking in seeds, in regulation of plant height by controlling stem elongation and the control of flowering. abscisic acid ( aba ) occurs in all land plants except liverworts, and is synthesised from carotenoids in the chloroplasts and other plastids. it inhibits cell division, promotes seed maturation, and dormancy, and promotes stomatal closure. it was so named because it was originally thought to control abscission. ethylene is a gaseous hormone that is produced in all higher plant tissues from methionine. it is now known to be the hormone that stimulates or regulates fruit ripening and abscission, and it, or the synthetic growth regulator ethephon which is rapidly metabolised to produce ethylene, are used on industrial scale to promote ripening of cotton, pineapples and other climacteric crops. another class of phytohormones is the jasmonates, first isolated from the oil of jasminum grandiflorum which regulates wound responses in plants by unblocking the expression of genes required in the systemic acquired resistance response to pathogen attack. in addition to being the primary energy source for plants, light functions as a signalling device, providing information to the plant, such as how much sunlight the plant receives each day. this can result in adaptive changes in a process known as photomorphogenesis. phytochromes are the photoreceptors in a plant that are sensitive to light. = = plant anatomy and morphology = = plant anatomy is the study of the structure of plant cells and tissues, whereas plant morphology is the study of their external form. all plants are multicellular eukaryotes, their dna stored in nuclei. the characteristic features of plant cells that distinguish them from those of animals and fungi include a primary cell wall composed of the polysaccharides cellulose, could be maintained in culture containing iaa, followed by the observation in 1947 that it could be induced to form roots and shoots by controlling the concentration of growth hormones were key steps in the development of plant biotechnology and genetic modification. cytokinins are a class of plant hormones named for their control of cell division ( especially cytokinesis ). the natural cytokinin zeatin was discovered in corn, zea mays, and is a derivative of the purine adenine. zeatin is produced in roots and transported to shoots in the xylem where it promotes cell division, bud development, and the greening of chloroplasts. the gibberelins, such as gibberelic acid are diterpenes synthesised from acetyl coa via the mevalonate pathway. they are involved in the promotion of germination and dormancy - breaking in seeds, in regulation of plant height by controlling stem elongation and the control of flowering. abscisic acid ( aba ) occurs in all land plants except liverworts, and is synthesised from carotenoids in the chloroplasts and other plastids. it inhibits cell division, promotes seed maturation, and dormancy, and promotes stomatal closure. it was so named because it was originally thought to control abscission. ethylene is a gaseous hormone that is produced in all higher plant tissues from methionine. it is now known to be the hormone that stimulates or regulates fruit ripening and abscission, and it, or the synthetic growth regulator ethephon which is rapidly metabolised to produce ethylene, are used on industrial scale to promote ripening of cotton, pineapples and other climacteric crops. another class of phytohormones is the jasmonates, first isolated from the oil of jasminum grandiflorum which regulates wound responses in plants by unblocking the expression of genes required in the systemic acquired resistance response to pathogen attack. in addition to being the primary energy source for plants, light functions as a signalling device, providing information to the plant, such as how much sunlight the plant receives each day. this can result in adaptive changes in a process known as photomorphogenesis. phytochromes are the photoreceptors in a plant that are sensitive to light. = = plant anatomy and morphology = = plant anatomy is the study of the structure of , depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a Question: The cytoplasm divides during what process? A) osmosis B) genesys C) cytokinesis D) metamorphosis	C) cytokinesis
Context: ##tion, and pasteurization in order to become products that can be sold. there are three levels of food processing : primary, secondary, and tertiary. primary food processing involves turning agricultural products into other products that can be turned into food, secondary food processing is the making of food from readily available ingredients, and tertiary food processing is commercial production of ready - to eat or heat - and - serve foods. drying, pickling, salting, and fermenting foods were some of the oldest food processing techniques used to preserve food by preventing yeasts, molds, and bacteria to cause spoiling. methods for preserving food have evolved to meet current standards of food safety but still use the same processes as the past. biochemical engineers also work to improve the nutritional value of food products, such as in golden rice, which was developed to prevent vitamin a deficiency in certain areas where this was an issue. efforts to advance preserving technologies can also ensure lasting retention of nutrients as foods are stored. packaging plays a key role in preserving as well as ensuring the safety of the food by protecting the product from contamination, physical damage, and tampering. packaging can also make it easier to transport and serve food. a common job for biochemical engineers working in the food industry is to design ways to perform all these processes on a large scale in order to meet the demands of the population. responsibilities for this career path include designing and performing experiments, optimizing processes, consulting with groups to develop new technologies, and preparing project plans for equipment and facilities. = = = pharmaceuticals = = = in the pharmaceutical industry, bioprocess engineering plays a crucial role in the large - scale production of biopharmaceuticals, such as monoclonal antibodies, vaccines, and therapeutic proteins. the development and optimization of bioreactors and fermentation systems are essential for the mass production of these products, ensuring consistent quality and high yields. for example, recombinant proteins like insulin and erythropoietin are produced through cell culture systems using genetically modified cells. the bioprocess engineer ’ s role is to optimize variables like temperature, ph, nutrient availability, and oxygen levels to maximize the efficiency of these systems. the growing field of gene therapy also relies on bioprocessing techniques to produce viral vectors, which are used to deliver therapeutic genes to patients. this involves scaling up processes from laboratory to industrial scale while maintaining safety and regulatory compliance. as the demand for biopharmaceutical products increases, advancements ; however, a successful large - scale industrial application of the process was the development of continuous freeze drying of coffee. high - temperature short time processing – these processes, for the most part, are characterized by rapid heating and cooling, holding for a short time at a relatively high temperature and filling aseptically into sterile containers. decaffeination of coffee and tea – decaffeinated coffee and tea was first developed on a commercial basis in europe around 1900. the process is described in u. s. patent 897, 763. green coffee beans are treated with water, heat and solvents to remove the caffeine from the beans. process optimization – food technology now allows production of foods to be more efficient, oil saving technologies are now available on different forms. production methods and methodology have also become increasingly sophisticated. aseptic packaging – the process of filling a commercially sterile product into a sterile container and hermetically sealing the containers so that re - infection is prevented. thus, this results into a shelf stable product at ambient conditions. food irradiation – the process of exposing food and food packaging to ionizing radiation can effectively destroy organisms responsible for spoilage and foodborne illness and inhibit sprouting, extending shelf life. commercial fruit ripening rooms using ethylene as a plant hormone. food delivery – an order is typically made either through a restaurant or grocer ' s website or mobile app, or through a food ordering company. the ordered food is typically delivered in boxes or bags to the customer ' s doorsteps. = = categories = = technology has innovated these categories from the food industry : agricultural technology – or agtech, it is the use of technology in agriculture, horticulture, and aquaculture with the aim of improving yield, efficiency, and profitability. agricultural technology can be products, services or applications derived from agriculture that improve various input / output processes. food science – technology in this sector focuses on the development of new functional ingredients and alternative proteins. foodservice – technology innovated the way establishments prepare, supply, and serve food outside the home. there ' s a tendency to create the conditions for the restaurant of the future with robotics and cloudkitchens. consumer tech – technology allows what we call consumer electronics, which is the equipment of consumers with devices that facilitates the cooking process. food delivery – as the food delivery market is growing, companies and startups are rapidly revolutionizing the communication process between consumers and food establishments, with platform - to - consumer delivery as the new crop traits as well as a far greater control over a food ' s genetic structure than previously afforded by methods such as selective breeding and mutation breeding. commercial sale of genetically modified foods began in 1994, when calgene first marketed its flavr savr delayed ripening tomato. to date most genetic modification of foods have primarily focused on cash crops in high demand by farmers such as soybean, corn, canola, and cotton seed oil. these have been engineered for resistance to pathogens and herbicides and better nutrient profiles. gm livestock have also been experimentally developed ; in november 2013 none were available on the market, but in 2015 the fda approved the first gm salmon for commercial production and consumption. there is a scientific consensus that currently available food derived from gm crops poses no greater risk to human health than conventional food, but that each gm food needs to be tested on a case - by - case basis before introduction. nonetheless, members of the public are much less likely than scientists to perceive gm foods as safe. the legal and regulatory status of gm foods varies by country, with some nations banning or restricting them, and others permitting them with widely differing degrees of regulation. gm crops also provide a number of ecological benefits, if not used in excess. insect - resistant crops have proven to lower pesticide usage, therefore reducing the environmental impact of pesticides as a whole. however, opponents have objected to gm crops per se on several grounds, including environmental concerns, whether food produced from gm crops is safe, whether gm crops are needed to address the world ' s food needs, and economic concerns raised by the fact these organisms are subject to intellectual property law. biotechnology has several applications in the realm of food security. crops like golden rice are engineered to have higher nutritional content, and there is potential for food products with longer shelf lives. though not a form of agricultural biotechnology, vaccines can help prevent diseases found in animal agriculture. additionally, agricultural biotechnology can expedite breeding processes in order to yield faster results and provide greater quantities of food. transgenic biofortification in cereals has been considered as a promising method to combat malnutrition in india and other countries. = = = industrial = = = industrial biotechnology ( known mainly in europe as white biotechnology ) is the application of biotechnology for industrial purposes, including industrial fermentation. it includes the practice of using cells such as microorganisms, or components of cells like enzymes, to generate industrially useful products in sectors such as chemicals, food and feed, detergents, paper earth. each satellite has an onboard atomic clock and transmits a continuous radio signal containing a precise time signal as well as its current position. two frequencies are used, 1. 2276 and 1. 57542 ghz. since the velocity of radio waves is virtually constant, the delay of the radio signal from a satellite is proportional to the distance of the receiver from the satellite. by receiving the signals from at least four satellites a gps receiver can calculate its position on earth by comparing the arrival time of the radio signals. since each satellite ' s position is known precisely at any given time, from the delay the position of the receiver can be calculated by a microprocessor in the receiver. the position can be displayed as latitude and longitude, or as a marker on an electronic map. gps receivers are incorporated in almost all cellphones and in vehicles such as automobiles, aircraft, and ships, and are used to guide drones, missiles, cruise missiles, and even artillery shells to their target, and handheld gps receivers are produced for hikers and the military. radio beacon – a fixed location terrestrial radio transmitter which transmits a continuous radio signal used by aircraft and ships for navigation. the locations of beacons are plotted on navigational maps used by aircraft and ships. vhf omnidirectional range ( vor ) – a worldwide aircraft radio navigation system consisting of fixed ground radio beacons transmitting between 108. 00 and 117. 95 mhz in the very high frequency ( vhf ) band. an automated navigational instrument on the aircraft displays a bearing to a nearby vor transmitter. a vor beacon transmits two signals simultaneously on different frequencies. a directional antenna transmits a beam of radio waves that rotates like a lighthouse at a fixed rate, 30 times per second. when the directional beam is facing north, an omnidirectional antenna transmits a pulse. by measuring the difference in phase of these two signals, an aircraft can determine its bearing ( or " radial " ) from the station accurately. by taking a bearing on two vor beacons an aircraft can determine its position ( called a " fix " ) to an accuracy of about 90 metres ( 300 ft ). most vor beacons also have a distance measuring capability, called distance measuring equipment ( dme ) ; these are called vor / dme ' s. the aircraft transmits a radio signal to the vor / dme beacon and a transponder transmits a return signal. from the propagation delay between the transmitted and received signal the aircraft can calculate . the first major technologies were tied to survival, hunting, and food preparation. stone tools and weapons, fire, and clothing were technological developments of major importance during this period. human ancestors have been using stone and other tools since long before the emergence of homo sapiens approximately 300, 000 years ago. the earliest direct evidence of tool usage was found in ethiopia within the great rift valley, dating back to 2. 5 million years ago. the earliest methods of stone tool making, known as the oldowan " industry ", date back to at least 2. 3 million years ago. this era of stone tool use is called the paleolithic, or " old stone age ", and spans all of human history up to the development of agriculture approximately 12, 000 years ago. to make a stone tool, a " core " of hard stone with specific flaking properties ( such as flint ) was struck with a hammerstone. this flaking produced sharp edges which could be used as tools, primarily in the form of choppers or scrapers. these tools greatly aided the early humans in their hunter - gatherer lifestyle to perform a variety of tasks including butchering carcasses ( and breaking bones to get at the marrow ) ; chopping wood ; cracking open nuts ; skinning an animal for its hide, and even forming other tools out of softer materials such as bone and wood. the earliest stone tools were irrelevant, being little more than a fractured rock. in the acheulian era, beginning approximately 1. 65 million years ago, methods of working these stones into specific shapes, such as hand axes emerged. this early stone age is described as the lower paleolithic. the middle paleolithic, approximately 300, 000 years ago, saw the introduction of the prepared - core technique, where multiple blades could be rapidly formed from a single core stone. the upper paleolithic, beginning approximately 40, 000 years ago, saw the introduction of pressure flaking, where a wood, bone, or antler punch could be used to shape a stone very finely. the end of the last ice age about 10, 000 years ago is taken as the end point of the upper paleolithic and the beginning of the epipaleolithic / mesolithic. the mesolithic technology included the use of microliths as composite stone tools, along with wood, bone, and antler tools. the later stone age, during which the rudiments of agricultural technology were developed, is called the neolithic period. during this period, the european union ' s galileo. global positioning system ( gps ) – the most widely used satellite navigation system, maintained by the us air force, which uses a constellation of 31 satellites in low earth orbit. the orbits of the satellites are distributed so at any time at least four satellites are above the horizon over each point on earth. each satellite has an onboard atomic clock and transmits a continuous radio signal containing a precise time signal as well as its current position. two frequencies are used, 1. 2276 and 1. 57542 ghz. since the velocity of radio waves is virtually constant, the delay of the radio signal from a satellite is proportional to the distance of the receiver from the satellite. by receiving the signals from at least four satellites a gps receiver can calculate its position on earth by comparing the arrival time of the radio signals. since each satellite ' s position is known precisely at any given time, from the delay the position of the receiver can be calculated by a microprocessor in the receiver. the position can be displayed as latitude and longitude, or as a marker on an electronic map. gps receivers are incorporated in almost all cellphones and in vehicles such as automobiles, aircraft, and ships, and are used to guide drones, missiles, cruise missiles, and even artillery shells to their target, and handheld gps receivers are produced for hikers and the military. radio beacon – a fixed location terrestrial radio transmitter which transmits a continuous radio signal used by aircraft and ships for navigation. the locations of beacons are plotted on navigational maps used by aircraft and ships. vhf omnidirectional range ( vor ) – a worldwide aircraft radio navigation system consisting of fixed ground radio beacons transmitting between 108. 00 and 117. 95 mhz in the very high frequency ( vhf ) band. an automated navigational instrument on the aircraft displays a bearing to a nearby vor transmitter. a vor beacon transmits two signals simultaneously on different frequencies. a directional antenna transmits a beam of radio waves that rotates like a lighthouse at a fixed rate, 30 times per second. when the directional beam is facing north, an omnidirectional antenna transmits a pulse. by measuring the difference in phase of these two signals, an aircraft can determine its bearing ( or " radial " ) from the station accurately. by taking a bearing on two vor beacons an aircraft can determine its position ( called a " fix " ) to an accuracy of about 90 metres ( 300 ft ). most vor beacons also have a have primarily focused on cash crops in high demand by farmers such as soybean, corn, canola, and cotton seed oil. these have been engineered for resistance to pathogens and herbicides and better nutrient profiles. gm livestock have also been experimentally developed ; in november 2013 none were available on the market, but in 2015 the fda approved the first gm salmon for commercial production and consumption. there is a scientific consensus that currently available food derived from gm crops poses no greater risk to human health than conventional food, but that each gm food needs to be tested on a case - by - case basis before introduction. nonetheless, members of the public are much less likely than scientists to perceive gm foods as safe. the legal and regulatory status of gm foods varies by country, with some nations banning or restricting them, and others permitting them with widely differing degrees of regulation. gm crops also provide a number of ecological benefits, if not used in excess. insect - resistant crops have proven to lower pesticide usage, therefore reducing the environmental impact of pesticides as a whole. however, opponents have objected to gm crops per se on several grounds, including environmental concerns, whether food produced from gm crops is safe, whether gm crops are needed to address the world ' s food needs, and economic concerns raised by the fact these organisms are subject to intellectual property law. biotechnology has several applications in the realm of food security. crops like golden rice are engineered to have higher nutritional content, and there is potential for food products with longer shelf lives. though not a form of agricultural biotechnology, vaccines can help prevent diseases found in animal agriculture. additionally, agricultural biotechnology can expedite breeding processes in order to yield faster results and provide greater quantities of food. transgenic biofortification in cereals has been considered as a promising method to combat malnutrition in india and other countries. = = = industrial = = = industrial biotechnology ( known mainly in europe as white biotechnology ) is the application of biotechnology for industrial purposes, including industrial fermentation. it includes the practice of using cells such as microorganisms, or components of cells like enzymes, to generate industrially useful products in sectors such as chemicals, food and feed, detergents, paper and pulp, textiles and biofuels. in the current decades, significant progress has been done in creating genetically modified organisms ( gmos ) that enhance the diversity of applications and economical viability of industrial biotechnology. by using renewable raw materials to produce a variety of chemicals and fuels, industrial biotechnology is actively advancing towards lowering greenhouse beam reveals the object ' s location. since radio waves travel at a constant speed close to the speed of light, by measuring the brief time delay between the outgoing pulse and the received " echo ", the range to the target can be calculated. the targets are often displayed graphically on a map display called a radar screen. doppler radar can measure a moving object ' s velocity, by measuring the change in frequency of the return radio waves due to the doppler effect. radar sets mainly use high frequencies in the microwave bands, because these frequencies create strong reflections from objects the size of vehicles and can be focused into narrow beams with compact antennas. parabolic ( dish ) antennas are widely used. in most radars the transmitting antenna also serves as the receiving antenna ; this is called a monostatic radar. a radar which uses separate transmitting and receiving antennas is called a bistatic radar. airport surveillance radar – in aviation, radar is the main tool of air traffic control. a rotating dish antenna sweeps a vertical fan - shaped beam of microwaves around the airspace and the radar set shows the location of aircraft as " blips " of light on a display called a radar screen. airport radar operates at 2. 7 – 2. 9 ghz in the microwave s band. in large airports the radar image is displayed on multiple screens in an operations room called the tracon ( terminal radar approach control ), where air traffic controllers direct the aircraft by radio to maintain safe aircraft separation. secondary surveillance radar – aircraft carry radar transponders, transceivers which when triggered by the incoming radar signal transmit a return microwave signal. this causes the aircraft to show up more strongly on the radar screen. the radar which triggers the transponder and receives the return beam, usually mounted on top of the primary radar dish, is called the secondary surveillance radar. since radar cannot measure an aircraft ' s altitude with any accuracy, the transponder also transmits back the aircraft ' s altitude measured by its altimeter, and an id number identifying the aircraft, which is displayed on the radar screen. electronic countermeasures ( ecm ) – military defensive electronic systems designed to degrade enemy radar effectiveness, or deceive it with false information, to prevent enemies from locating local forces. it often consists of powerful microwave transmitters that can mimic enemy radar signals to create false target indications on the enemy radar screens. marine radar – an s or x band radar on ships used to detect nearby ships and obstructions like bridges. a rotating antenna sweeps a vertical process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united kingdom desperately needed to manufacture explosives during world war i. biotechnology has also led to the development of antibiotics. in 1928, alexander fleming discovered the mold penicillium. his work led to the purification of the antibiotic formed by the mold by howard florey, ernst boris chain and norman heatley – to form what we today know as penicillin. in 1940, penicillin became available for medicinal use to treat bacterial infections in humans. the field of modern biotechnology is generally thought of as having been born in 1971 when paul berg ' s ( stanford ) experiments in gene splicing had early success. herbert w. boyer ( univ. calif. at san francisco ) and stanley n. cohen ( stanford ) significantly advanced the new technology in 1972 by transferring genetic material into a bacterium, such that the imported material would be reproduced. the commercial viability of a biotechnology industry was significantly expanded on june 16, 1980, when the united states supreme court ruled that a genetically modified microorganism could be patented in the case of diamond v. chakrabarty. indian - born ananda chakrabarty, working for general electric, had modified a bacterium ( of the genus pseudomonas ) capable of breaking down crude oil, which he proposed to pharmaceutical agents, biofuels, and other industrially useful goods, as well as for bioremediation. farmers have widely adopted gm technology. between 1996 and 2011, the total surface area of land cultivated with gm crops had increased by a factor of 94, from 17, 000 to 1, 600, 000 square kilometers ( 4, 200, 000 to 395, 400, 000 acres ). 10 % of the world ' s crop lands were planted with gm crops in 2010. as of 2011, 11 different transgenic crops were grown commercially on 395 million acres ( 160 million hectares ) in 29 countries such as the us, brazil, argentina, india, canada, china, paraguay, pakistan, south africa, uruguay, bolivia, australia, philippines, myanmar, burkina faso, mexico and spain. genetically modified foods are foods produced from organisms that have had specific changes introduced into their dna with the methods of genetic engineering. these techniques have allowed for the introduction of new crop traits as well as a far greater control over a food ' s genetic structure than previously afforded by methods such as selective breeding and mutation breeding. commercial sale of genetically modified foods began in 1994, when calgene first marketed its flavr savr delayed ripening tomato. to date most genetic modification of foods have primarily focused on cash crops in high demand by farmers such as soybean, corn, canola, and cotton seed oil. these have been engineered for resistance to pathogens and herbicides and better nutrient profiles. gm livestock have also been experimentally developed ; in november 2013 none were available on the market, but in 2015 the fda approved the first gm salmon for commercial production and consumption. there is a scientific consensus that currently available food derived from gm crops poses no greater risk to human health than conventional food, but that each gm food needs to be tested on a case - by - case basis before introduction. nonetheless, members of the public are much less likely than scientists to perceive gm foods as safe. the legal and regulatory status of gm foods varies by country, with some nations banning or restricting them, and others permitting them with widely differing degrees of regulation. gm crops also provide a number of ecological benefits, if not used in excess. insect - resistant crops have proven to lower pesticide usage, therefore reducing the environmental impact of pesticides as a whole. however, opponents have objected to gm crops per se on several grounds, including environmental concerns, whether food produced from gm crops is safe, whether gm crops are needed to address the world ' s food needs, and economic Question: Where do birds store and moisten food that is waiting to be digested? A) crop B) nest C) tree D) gullet	A) crop
Context: navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding sea becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make it available as drinking water. the earliest exploitation of groundwater resources dates back to 3000 bc, and hydrogeology as a science was developed by hydrologists beginning in the 17th century. ecohydrology is the study of ecological systems in the hydrosphere. it can be divided into the physical study of aquatic ecosystems and the approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with and their competitive or mutualistic interactions with other species. some ecologists even rely on empirical data from indigenous people that is gathered by ethnobotanists. this information can relay a great deal of information on how the land once was thousands of years ago and how it has changed over that time. the goals of plant ecology are to understand the causes of their distribution patterns, productivity, environmental impact, evolution, and responses to environmental change. plants depend on certain edaphic ( soil ) and climatic factors in their environment but can modify these factors too. for example, they can change their environment ' s albedo, increase runoff interception, stabilise mineral soils and develop their organic content, and affect local temperature. plants compete with other organisms in their ecosystem for resources. they interact with their neighbours at a variety of spatial scales in groups, populations and communities that collectively constitute vegetation. regions with characteristic vegetation types and dominant plants as well as similar abiotic and biotic factors, climate, and geography make up biomes like tundra or tropical rainforest. herbivores eat plants, but plants can defend themselves and some species are parasitic or even carnivorous. other organisms form mutually beneficial relationships with plants. for example, mycorrhizal fungi and rhizobia provide plants with nutrients in exchange for food, ants are recruited by ant plants to provide protection, honey bees, bats and other animals pollinate flowers and humans and other animals act as dispersal vectors to spread spores and seeds. = = = plants, climate and environmental change = = = plant responses to climate and other environmental changes can inform our understanding of how these changes affect ecosystem function and productivity. for example, plant phenology can be a useful proxy for temperature in historical climatology, and the biological impact of climate change and global warming. palynology, the analysis of fossil pollen deposits in sediments from thousands or millions of years ago allows the reconstruction of past climates. estimates of atmospheric co2 concentrations since the palaeozoic have been obtained from stomatal densities and the leaf shapes and sizes of ancient land plants. ozone depletion can expose plants to higher levels of ultraviolet radiation - b ( uv - b ), resulting in lower growth rates. moreover, information from studies of community ecology, plant systematics, and taxonomy is essential to understanding vegetation change, habitat destruction and species extinction. = = genetics = = inheritance in plants follows the same fundamental principles of genetics as in other multicellular organisms. gregor mendel discovered the genetic laws of inheritance by studying higher concentrations of atmospheric nitrous oxide ( n2o ) are expected to slightly warm earth ' s surface because of increases in radiative forcing. radiative forcing is the difference in the net upward thermal radiation flux from the earth through a transparent atmosphere and radiation through an otherwise identical atmosphere with greenhouse gases. radiative forcing, normally measured in w / m ^ 2, depends on latitude, longitude and altitude, but it is often quoted for the tropopause, about 11 km of altitude for temperate latitudes, or for the top of the atmosphere at around 90 km. for current concentrations of greenhouse gases, the radiative forcing per added n2o molecule is about 230 times larger than the forcing per added carbon dioxide ( co2 ) molecule. this is due to the heavy saturation of the absorption band of the relatively abundant greenhouse gas, co2, compared to the much smaller saturation of the absorption bands of the trace greenhouse gas n2o. but the rate of increase of co2 molecules, about 2. 5 ppm / year ( ppm = part per million by mole ), is about 3000 times larger than the rate of increase of n2o molecules, which has held steady at around 0. 00085 ppm / year since 1985. so, the contribution of nitrous oxide to the annual increase in forcing is 230 / 3000 or about 1 / 13 that of co2. if the main greenhouse gases, co2, ch4 and n2o have contributed about 0. 1 c / decade of the warming observed over the past few decades, this would correspond to about 0. 00064 k per year or 0. 064 k per century of warming from n2o. proposals to place harsh restrictions on nitrous oxide emissions because of warming fears are not justified by these facts. restrictions would cause serious harm ; for example, by jeopardizing world food supplies. weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding seawards, so that in the po river in italy, for instance, pebbles and gravel are found for about 140 miles below turin, sand along the next 100 miles, and silt and mud in the last 110 miles ( 176 km ). = = channelization = = the removal of obstructions, natural or artificial the experimental study of spiral - 2 high intensity radiofrequency cooler prototype ( shirac ) is the goal of this paper. a box model of the inter - hemispheric atlantic meridional overturning circulation is developed, including a variable pycnocline depth for the tropical and subtropical regions. the circulation is forced by winds over a periodic channel in the south and by freshwater forcing at the surface. the model is aimed at investigating the ocean feedbacks related to perturbations in freshwater forcing from the atmosphere, and to changes in freshwater transport in the ocean. these feedbacks are closely connected with the stability properties of the meridional overturning circulation, in particular in response to freshwater perturbations. acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make it available as drinking water. the earliest exploitation of groundwater resources dates back to 3000 bc, and hydrogeology as a science was developed by hydrologists beginning in the 17th century. ecohydrology is the study of ecological systems in the hydrosphere. it can be divided into the physical study of aquatic ecosystems and the biological study of aquatic organisms. ecohydrology includes the effects that organisms and aquatic ecosystems have on one another as well as how these ecoystems are affected by humans. glaciology is the study of the cryosphere, including glaciers and coverage of the earth by ice and snow. concerns of gla Question: Where can you find humid subtropical climates? A) between 20 and 40 degrees latitude B) between 20 and 40 degrees longitude C) between 40 and 60 degrees longitude D) between 40 and 60 degrees latitude	A) between 20 and 40 degrees latitude
Context: in gravitational lensing, the concept of optical depth assumes the lens is dark. several microlensing detections have now been made where the lens may be bright. relations are developed between apparent and absolute optical depth in the regime of the apparent and absolute brightness of the lens. an apparent optical depth through bright lenses is always less than the true, absolute optical depth. the greater the intrinsic brightness of the lens, the more likely it will be found nearer the source. it is hard for us humans to recognize things in nature until we have invented them ourselves. for image - forming optics, nature has made virtually every kind of lens humans have devised. but what about lensless " imaging "? recently, we showed that a bare array of sensors on a curved substrate could achieve resolution not limited by diffraction - without any lens at all provided that the objects imaged conform to our a priori assumptions. is it possible that somewhere in nature we will find this kind of vision system? we think so and provide examples that seem to make no sense whatever unless they are using something like our lensless imaging work. use virtual retinal display to enhance the experience of the oculus rift. some augmented reality devices fall under the category of wearables. augmented reality glasses are currently in development by several corporations. snap inc. ' s spectacles are sunglasses that record video from the user ' s point of view and pair with a phone to post videos on snapchat. microsoft has also delved into this business, releasing augmented reality glasses, hololens, in 2017. the device explores using digital holography, or holograms, to give the user a first hand experience of augmented reality. these wearable headsets are used in many different fields including the military. wearable technology has also expanded from small pieces of technology on the wrist to apparel all over the body. there is a shoe made by the company shiftwear that uses a smartphone application to periodically change the design display on the shoe. the shoe is designed using normal fabric but utilizes a display along the midsection and back that shows a design of your choice. the application was up by 2016 and a prototype for the shoes was created in 2017. another example of this can be seen with atari ' s headphone speakers. atari and audiowear are developing a face cap with built in speakers. the cap will feature speakers built into the underside of the brim, and will have bluetooth capabilities. jabra has released earbuds, in 2018, that cancel the noise around the user and can toggle a setting called " hearthrough. " this setting takes the sound around the user through the microphone and sends it to the user. this gives the user an augmented sound while they commute so they will be able to hear their surroundings while listening to their favorite music. many other devices can be considered entertainment wearables and need only be devices worn by the user to experience media. = = = gaming = = = the gaming industry has always incorporated new technology. the first technology used for electronic gaming was a controller for pong. the way users game has continuously evolved through each decade. currently, the two most common forms of gaming is either using a controller for video game consoles or a mouse and keyboard for pc games. in 2012, virtual reality headphones were reintroduced to the public. vr headsets were first conceptualized in the 1950s and officially created in the 1960s. the creation of the first virtual reality headset can be credited to cinematographer morton heilig. he created a device known as the sensorama in 1962. the sensorama was a videogame like device that as possible in order to avoid frustration or injury. there are two main types of human errors which are categorized as slips and mistakes. slips are a very common kind of error involving automatic behaviors ( i. e. typos, hitting the wrong menu item ). when we experience slips, we have the correct goal in mind, but execute the wrong action. mistakes on the other hand involve conscious deliberation that result in the incorrect conclusion. when we experience mistakes, we have the wrong goal in mind and thereby execute the wrong action. even though slips are the more common type of error, they are no less dangerous. a certain type of slip error, a mode error, can be especially dangerous if a user is executing a high - risk task. for instance, if a user is operating a vehicle and does not realize they are in the wrong mode ( i. e. reverse ), they might step on the gas intending to drive, but instead accelerate into a garage wall or another car. in order to avoid modal errors, designers often employ modeless states in which users do not have to choose a mode at all, or they must execute a continuous action while intending to execute a certain mode ( i. e. pressing a key continuously in order to activate " lasso " mode in photoshop ). = = evaluation methods = = usability engineers conduct usability evaluations of existing or proposed interfaces and their findings are fed back to the designer for use in design or redesign. common usability evaluation methods include : card sorting cognitive task analysis cognitive walkthroughs contextual inquiry focus groups heuristic evaluations interviews questionnaires rite method surveys think aloud protocol usability testing = = software applications and development tools = = there are a variety of online resources that make the job of a usability engineer a little easier. online tools are only a useful tool, and do not substitute for a complete usability engineering analysis. some examples of these include : = = = the web metrics tool suite = = = this is a product of the national institute of standards and technology. this toolkit is focused on evaluating the html of a website versus a wide range of usability guidelines and includes : web static analyzer tool ( websat ) – checks web page html against typical usability guidelines web category analysis tool ( webcat ) – lets the usability engineer construct and conduct a web category analysis web variable instrumenter program ( webvip ) – instruments a website to capture a log of user interaction framework for logging usability data ( flu ##itive material by selective exposure to a radiation source such as light. a photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source. if a photosensitive material is selectively exposed to radiation ( e. g. by masking some of the radiation ) the pattern of the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differs. this exposed region can then be removed or treated providing a mask for the underlying substrate. photolithography is typically used with metal or other thin film deposition, wet and dry etching. sometimes, photolithography is used to create structure without any kind of post etching. one example is su8 based lens where su8 based square blocks are generated. then the photoresist is melted to form a semi - sphere which acts as a lens. electron beam lithography ( often abbreviated as e - beam lithography ) is the practice of scanning a beam of electrons in a patterned fashion across a surface covered with a film ( called the resist ), ( " exposing " the resist ) and of selectively removing either exposed or non - exposed regions of the resist ( " developing " ). the purpose, as with photolithography, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching. it was developed for manufacturing integrated circuits, and is also used for creating nanotechnology architectures. the primary advantage of electron beam lithography is that it is one of the ways to beat the diffraction limit of light and make features in the nanometer range. this form of maskless lithography has found wide usage in photomask - making used in photolithography, low - volume production of semiconductor components, and research & development. the key limitation of electron beam lithography is throughput, i. e., the very long time it takes to expose an entire silicon wafer or glass substrate. a long exposure time leaves the user vulnerable to beam drift or instability which may occur during the exposure. also, the turn - around time for reworking or re - design is lengthened unnecessarily if the pattern is not being changed the second time. it is known that focused - ion beam lithography has the capability of writing extremely fine lines ( less than 50 nm line and space has been achieved ) without proximity effect. however, because the writing field in ion - beam lit ##tronics, the science of using mechanical devices with human muscular, musculoskeletal, and nervous systems to assist or enhance motor control lost by trauma, disease, or defect. prostheses are typically used to replace parts lost by injury ( traumatic ) or missing from birth ( congenital ) or to supplement defective body parts. inside the body, artificial heart valves are in common use with artificial hearts and lungs seeing less common use but under active technology development. other medical devices and aids that can be considered prosthetics include hearing aids, artificial eyes, palatal obturator, gastric bands, and dentures. prostheses are specifically not orthoses, although given certain circumstances a prosthesis might end up performing some or all of the same functionary benefits as an orthosis. prostheses are technically the complete finished item. for instance, a c - leg knee alone is not a prosthesis, but only a prosthetic component. the complete prosthesis would consist of the attachment system to the residual limb – usually a " socket ", and all the attachment hardware components all the way down to and including the terminal device. despite the technical difference, the terms are often used interchangeably. the terms " prosthetic " and " orthotic " are adjectives used to describe devices such as a prosthetic knee. the terms " prosthetics " and " orthotics " are used to describe the respective allied health fields. an occupational therapist ' s role in prosthetics include therapy, training and evaluations. prosthetic training includes orientation to prosthetics components and terminology, donning and doffing, wearing schedule, and how to care for residual limb and the prosthesis. = = = exoskeletons = = = a powered exoskeleton is a wearable mobile machine that is powered by a system of electric motors, pneumatics, levers, hydraulics, or a combination of technologies that allow for limb movement with increased strength and endurance. its design aims to provide back support, sense the user ' s motion, and send a signal to motors which manage the gears. the exoskeleton supports the shoulder, waist and thigh, and assists movement for lifting and holding heavy items, while lowering back stress. = = = adaptive seating and positioning = = = people with balance and motor function challenges often need specialized equipment to sit or stand safely and securely. this equipment is frequently in mathematics, a reflection ( also spelled reflexion ) is a mapping from a euclidean space to itself that is an isometry with a hyperplane as the set of fixed points ; this set is called the axis ( in dimension 2 ) or plane ( in dimension 3 ) of reflection. the image of a figure by a reflection is its mirror image in the axis or plane of reflection. for example the mirror image of the small latin letter p for a reflection with respect to a vertical axis ( a vertical reflection ) would look like q. its image by reflection in a horizontal axis ( a horizontal reflection ) would look like b. a reflection is an involution : when applied twice in succession, every point returns to its original location, and every geometrical object is restored to its original state. the term reflection is sometimes used for a larger class of mappings from a euclidean space to itself, namely the non - identity isometries that are involutions. the set of fixed points ( the " mirror " ) of such an isometry is an affine subspace, but is possibly smaller than a hyperplane. for instance a reflection through a point is an involutive isometry with just one fixed point ; the image of the letter p under it would look like a d. this operation is also known as a central inversion ( coxeter 1969, § 7. 2 ), and exhibits euclidean space as a symmetric space. in a euclidean vector space, the reflection in the point situated at the origin is the same as vector negation. other examples include reflections in a line in three - dimensional space. typically, however, unqualified use of the term " reflection " means reflection in a hyperplane. some mathematicians use " flip " as a synonym for " reflection ". = = construction = = in a plane ( or, respectively, 3 - dimensional ) geometry, to find the reflection of a point drop a perpendicular from the point to the line ( plane ) used for reflection, and extend it the same distance on the other side. to find the reflection of a figure, reflect each point in the figure. to reflect point p through the line ab using compass and straightedge, proceed as follows ( see figure ) : step 1 ( red ) : construct a circle with center at p and some fixed radius r to create points a ′ and b ′ on the line ab, which will be equidistant from p. step 2 ( green ) : construct circles centered at a ′ and b ′ having radius r usability engineering, it ' s important target and identify human errors when interacting with the product of interest because if a user is expected to engage with a product, interface, or service in some way, the very introduction of a human in that engagement increases the potential of encountering human error. error should be reduced as much as possible in order to avoid frustration or injury. there are two main types of human errors which are categorized as slips and mistakes. slips are a very common kind of error involving automatic behaviors ( i. e. typos, hitting the wrong menu item ). when we experience slips, we have the correct goal in mind, but execute the wrong action. mistakes on the other hand involve conscious deliberation that result in the incorrect conclusion. when we experience mistakes, we have the wrong goal in mind and thereby execute the wrong action. even though slips are the more common type of error, they are no less dangerous. a certain type of slip error, a mode error, can be especially dangerous if a user is executing a high - risk task. for instance, if a user is operating a vehicle and does not realize they are in the wrong mode ( i. e. reverse ), they might step on the gas intending to drive, but instead accelerate into a garage wall or another car. in order to avoid modal errors, designers often employ modeless states in which users do not have to choose a mode at all, or they must execute a continuous action while intending to execute a certain mode ( i. e. pressing a key continuously in order to activate " lasso " mode in photoshop ). = = evaluation methods = = usability engineers conduct usability evaluations of existing or proposed interfaces and their findings are fed back to the designer for use in design or redesign. common usability evaluation methods include : card sorting cognitive task analysis cognitive walkthroughs contextual inquiry focus groups heuristic evaluations interviews questionnaires rite method surveys think aloud protocol usability testing = = software applications and development tools = = there are a variety of online resources that make the job of a usability engineer a little easier. online tools are only a useful tool, and do not substitute for a complete usability engineering analysis. some examples of these include : = = = the web metrics tool suite = = = this is a product of the national institute of standards and technology. this toolkit is focused on evaluating the html of a website versus a wide range of usability guidelines and includes : web static analyzer tool which may not be as reliable as previously assumed ( see also : ' counterintuitive ' concepts in such as quantum nonlocality, and action at a distance ). another issue is that one numeral system may not necessarily be applicable to problem solving. subjects such as complex numbers or imaginary numbers require specific changes to more commonly used axioms of mathematics ; otherwise they cannot be adequately understood. alternatively, computer programmers may use hexadecimal for its ' human - friendly ' representation of binary - coded values, rather than decimal ( convenient for counting because humans have ten fingers ). the axioms or logical rules behind mathematics also vary through time ( such as the adaption and invention of zero ). as perceptions from the human brain are subject to illusions, assumptions, deceptions, ( induced ) hallucinations, cognitive errors or assumptions in a general context, it can be questioned whether they are accurate or strictly indicative of truth ( see also : philosophy of being ), and the nature of empiricism itself in relation to the universe and whether it is independent to the senses and the universe. the human mind has no special claim on reality or approaches to it built out of math. if such constructs as euler ' s identity are true then they are true as a map of the human mind and cognition. embodied mind theorists thus explain the effectiveness of mathematics — mathematics was constructed by the brain in order to be effective in this universe. the most accessible, famous, and infamous treatment of this perspective is where mathematics comes from, by george lakoff and rafael e. nunez. in addition, mathematician keith devlin has investigated similar concepts with his book the math instinct, as has neuroscientist stanislas dehaene with his book the number sense. for more on the philosophical ideas that inspired this perspective, see cognitive science of mathematics. = = = = aristotelian realism = = = = aristotelian realism holds that mathematics studies properties such as symmetry, continuity and order that can be literally realized in the physical world ( or in any other world there might be ). it contrasts with platonism in holding that the objects of mathematics, such as numbers, do not exist in an " abstract " world but can be physically realized. for example, the number 4 is realized in the relation between a heap of parrots and the universal " being a parrot " that divides the heap into so many parrots. aristotelian realism is defended by james franklin and the sydney school in the philosophy of mathematics and is english ) ) are concerned respectively with childbirth and the female reproductive and associated organs. reproductive medicine and fertility medicine are generally practiced by gynecological specialists. pediatrics ( ae ) or paediatrics ( be ) is devoted to the care of infants, children, and adolescents. like internal medicine, there are many pediatric subspecialties for specific age ranges, organ systems, disease classes, and sites of care delivery. pharmaceutical medicine is the medical scientific discipline concerned with the discovery, development, evaluation, registration, monitoring and medical aspects of marketing of medicines for the benefit of patients and public health. physical medicine and rehabilitation ( or physiatry ) is concerned with functional improvement after injury, illness, or congenital disorders. podiatric medicine is the study of, diagnosis, and medical and surgical treatment of disorders of the foot, ankle, lower limb, hip and lower back. preventive medicine is the branch of medicine concerned with preventing disease. community health or public health is an aspect of health services concerned with threats to the overall health of a community based on population health analysis. psychiatry is the branch of medicine concerned with the bio - psycho - social study of the etiology, diagnosis, treatment and prevention of cognitive, perceptual, emotional and behavioral disorders. related fields include psychotherapy and clinical psychology. = = = interdisciplinary fields = = = some interdisciplinary sub - specialties of medicine include : addiction medicine deals with the treatment of addiction. aerospace medicine deals with medical problems related to flying and space travel. biomedical engineering is a field dealing with the application of engineering principles to medical practice. clinical pharmacology is concerned with how systems of therapeutics interact with patients. conservation medicine studies the relationship between human and non - human animal health, and environmental conditions. also known as ecological medicine, environmental medicine, or medical geology. disaster medicine deals with medical aspects of emergency preparedness, disaster mitigation and management. diving medicine ( or hyperbaric medicine ) is the prevention and treatment of diving - related problems. evolutionary medicine is a perspective on medicine derived through applying evolutionary theory. forensic medicine deals with medical questions in legal context, such as determination of the time and cause of death, type of weapon used to inflict trauma, reconstruction of the facial features using remains of deceased ( skull ) thus aiding identification. gender - based medicine studies the biological and physiological differences between the human sexes and how that affects differences in disease. health informatics is a relatively recent field that deal with the application of computers and information technology to medicine. hospice and pal Question: What type of lenses can correct myopia? A) concave lenses B) polarized lenses C) diffusion lenses D) convex lenses	A) concave lenses
Context: their primary metabolism like the photosynthetic calvin cycle and crassulacean acid metabolism. others make specialised materials like the cellulose and lignin used to build their bodies, and secondary products like resins and aroma compounds. plants and various other groups of photosynthetic eukaryotes collectively known as " algae " have unique organelles known as chloroplasts. chloroplasts are thought to be descended from cyanobacteria that formed endosymbiotic relationships with ancient plant and algal ancestors. chloroplasts and cyanobacteria contain the blue - green pigment chlorophyll a. chlorophyll a ( as well as its plant and green algal - specific cousin chlorophyll b ) absorbs light in the blue - violet and orange / red parts of the spectrum while reflecting and transmitting the green light that we see as the characteristic colour of these organisms. the energy in the red and blue light that these pigments absorb is used by chloroplasts to make energy - rich carbon compounds from carbon dioxide and water by oxygenic photosynthesis, a process that generates molecular oxygen ( o2 ) as a by - product. the light energy captured by chlorophyll a is initially in the form of electrons ( and later a proton gradient ) that is used to make molecules of atp and nadph which temporarily store and transport energy. their energy is used in the light - independent reactions of the calvin cycle by the enzyme rubisco to produce molecules of the 3 - carbon sugar glyceraldehyde 3 - phosphate ( g3p ). glyceraldehyde 3 - phosphate is the first product of photosynthesis and the raw material from which glucose and almost all other organic molecules of biological origin are synthesised. some of the glucose is converted to starch which is stored in the chloroplast. starch is the characteristic energy store of most land plants and algae, while inulin, a polymer of fructose is used for the same purpose in the sunflower family asteraceae. some of the glucose is converted to sucrose ( common table sugar ) for export to the rest of the plant. unlike in animals ( which lack chloroplasts ), plants and their eukaryote relatives have delegated many biochemical roles to their chloroplasts, including synthesising all their fatty acids, and most amino acids. the fatty acids that with one allele inducing a change on the other. = = plant evolution = = the chloroplasts of plants have a number of biochemical, structural and genetic similarities to cyanobacteria, ( commonly but incorrectly known as " blue - green algae " ) and are thought to be derived from an ancient endosymbiotic relationship between an ancestral eukaryotic cell and a cyanobacterial resident. the algae are a polyphyletic group and are placed in various divisions, some more closely related to plants than others. there are many differences between them in features such as cell wall composition, biochemistry, pigmentation, chloroplast structure and nutrient reserves. the algal division charophyta, sister to the green algal division chlorophyta, is considered to contain the ancestor of true plants. the charophyte class charophyceae and the land plant sub - kingdom embryophyta together form the monophyletic group or clade streptophytina. nonvascular land plants are embryophytes that lack the vascular tissues xylem and phloem. they include mosses, liverworts and hornworts. pteridophytic vascular plants with true xylem and phloem that reproduced by spores germinating into free - living gametophytes evolved during the silurian period and diversified into several lineages during the late silurian and early devonian. representatives of the lycopods have survived to the present day. by the end of the devonian period, several groups, including the lycopods, sphenophylls and progymnosperms, had independently evolved " megaspory " – their spores were of two distinct sizes, larger megaspores and smaller microspores. their reduced gametophytes developed from megaspores retained within the spore - producing organs ( megasporangia ) of the sporophyte, a condition known as endospory. seeds consist of an endosporic megasporangium surrounded by one or two sheathing layers ( integuments ). the young sporophyte develops within the seed, which on germination splits to release it. the earliest known seed plants date from the latest devonian famennian stage. following the evolution of the seed habit, seed plants diversified, giving rise to a number of now - extinct groups, including seed ferns, as well as the modern gym known as " algae " have unique organelles known as chloroplasts. chloroplasts are thought to be descended from cyanobacteria that formed endosymbiotic relationships with ancient plant and algal ancestors. chloroplasts and cyanobacteria contain the blue - green pigment chlorophyll a. chlorophyll a ( as well as its plant and green algal - specific cousin chlorophyll b ) absorbs light in the blue - violet and orange / red parts of the spectrum while reflecting and transmitting the green light that we see as the characteristic colour of these organisms. the energy in the red and blue light that these pigments absorb is used by chloroplasts to make energy - rich carbon compounds from carbon dioxide and water by oxygenic photosynthesis, a process that generates molecular oxygen ( o2 ) as a by - product. the light energy captured by chlorophyll a is initially in the form of electrons ( and later a proton gradient ) that is used to make molecules of atp and nadph which temporarily store and transport energy. their energy is used in the light - independent reactions of the calvin cycle by the enzyme rubisco to produce molecules of the 3 - carbon sugar glyceraldehyde 3 - phosphate ( g3p ). glyceraldehyde 3 - phosphate is the first product of photosynthesis and the raw material from which glucose and almost all other organic molecules of biological origin are synthesised. some of the glucose is converted to starch which is stored in the chloroplast. starch is the characteristic energy store of most land plants and algae, while inulin, a polymer of fructose is used for the same purpose in the sunflower family asteraceae. some of the glucose is converted to sucrose ( common table sugar ) for export to the rest of the plant. unlike in animals ( which lack chloroplasts ), plants and their eukaryote relatives have delegated many biochemical roles to their chloroplasts, including synthesising all their fatty acids, and most amino acids. the fatty acids that chloroplasts make are used for many things, such as providing material to build cell membranes out of and making the polymer cutin which is found in the plant cuticle that protects land plants from drying out. plants synthesise a number of unique polymers like the polysaccharide molecules cellulose, , fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the ancestor of plants by entering into an endosymbiotic relationship with an early eukaryote, ultimately becoming the chloroplasts in plant cells. the new photosynthetic plants ( along with their algal relatives ) accelerated the rise in atmospheric oxygen started by the cyanobacteria, changing the ancient oxygen - free, reducing, atmosphere to one in which free oxygen has been abundant for more than 2 billion years. among the important botanical questions of the 21st century are the role of plants as primary producers in the global cycling of life ' s basic ingredients : energy, carbon, oxygen, nitrogen and water, and ways that our plant stewardship can help address the global environmental issues of resource management, conservation, human food security, biologically invasive organisms, carbon sequestration, climate change, and sustainability. = = = human nutrition = = = virtually all staple foods come either directly from primary production by plants, or indirectly from animals that eat them. plants and other photosynthetic organisms are at the base of most food chains because they use the energy from the sun and nutrients from the soil and atmosphere, converting them into a form that can be used by animals. this is what ecologists call the first trophic level. the modern forms of the major staple foods, such as hemp, teff, maize, rice, wheat and other cereal grasses, pulses, bananas and plantains, as well as hemp, flax and cotton grown for their fibres, are the outcome of prehistoric selection over thousands of years from among wild ancestral plants with the most desirable characteristics. botanists study how plants produce food and how to increase yields, for example through plant breeding, making their work important to humanity ' s ability to feed the world and provide food security for future generations. botanists also study weeds, which are a considerable problem in agriculture, and the biology and control of plant substrate - level phosphorylation, which does not require oxygen. = = = photosynthesis = = = photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organism ' s metabolic activities via cellular respiration. this chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water. in most cases, oxygen is released as a waste product. most plants, algae, and cyanobacteria perform photosynthesis, which is largely responsible for producing and maintaining the oxygen content of the earth ' s atmosphere, and supplies most of the energy necessary for life on earth. photosynthesis has four stages : light absorption, electron transport, atp synthesis, and carbon fixation. light absorption is the initial step of photosynthesis whereby light energy is absorbed by chlorophyll pigments attached to proteins in the thylakoid membranes. the absorbed light energy is used to remove electrons from a donor ( water ) to a primary electron acceptor, a quinone designated as q. in the second stage, electrons move from the quinone primary electron acceptor through a series of electron carriers until they reach a final electron acceptor, which is usually the oxidized form of nadp +, which is reduced to nadph, a process that takes place in a protein complex called photosystem i ( psi ). the transport of electrons is coupled to the movement of protons ( or hydrogen ) from the stroma to the thylakoid membrane, which forms a ph gradient across the membrane as hydrogen becomes more concentrated in the lumen than in the stroma. this is analogous to the proton - motive force generated across the inner mitochondrial membrane in aerobic respiration. during the third stage of photosynthesis, the movement of protons down their concentration gradients from the thylakoid lumen to the stroma through the atp synthase is coupled to the synthesis of atp by that same atp synthase. the nadph and atps generated by the light - dependent reactions in the second and third stages, respectively, provide the energy and electrons to drive the synthesis of glucose by fixing atmospheric carbon dioxide into existing organic carbon compounds, such as ribulose bisphosphate ( rubp ) in a sequence of light - independent ( or dark ) reactions called the calvin cycle. = = = cell signaling = = = cell signaling ( or communication ) is the ##nosperms and angiosperms. gymnosperms produce " naked seeds " not fully enclosed in an ovary ; modern representatives include conifers, cycads, ginkgo, and gnetales. angiosperms produce seeds enclosed in a structure such as a carpel or an ovary. ongoing research on the molecular phylogenetics of living plants appears to show that the angiosperms are a sister clade to the gymnosperms. = = plant physiology = = plant physiology encompasses all the internal chemical and physical activities of plants associated with life. chemicals obtained from the air, soil and water form the basis of all plant metabolism. the energy of sunlight, captured by oxygenic photosynthesis and released by cellular respiration, is the basis of almost all life. photoautotrophs, including all green plants, algae and cyanobacteria gather energy directly from sunlight by photosynthesis. heterotrophs including all animals, all fungi, all completely parasitic plants, and non - photosynthetic bacteria take in organic molecules produced by photoautotrophs and respire them or use them in the construction of cells and tissues. respiration is the oxidation of carbon compounds by breaking them down into simpler structures to release the energy they contain, essentially the opposite of photosynthesis. molecules are moved within plants by transport processes that operate at a variety of spatial scales. subcellular transport of ions, electrons and molecules such as water and enzymes occurs across cell membranes. minerals and water are transported from roots to other parts of the plant in the transpiration stream. diffusion, osmosis, and active transport and mass flow are all different ways transport can occur. examples of elements that plants need to transport are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. in vascular plants, these elements are extracted from the soil as soluble ions by the roots and transported throughout the plant in the xylem. most of the elements required for plant nutrition come from the chemical breakdown of soil minerals. sucrose produced by photosynthesis is transported from the leaves to other parts of the plant in the phloem and plant hormones are transported by a variety of processes. = = = plant hormones = = = plants are not passive, but respond to external signals such as light, touch, and injury by moving or growing towards or away from the stimulus, as appropriate. tangible evidence of touch sensitivity is the almost instantaneous collapse of leaflets of mimosa pudica, the insect traps of ##vary. ongoing research on the molecular phylogenetics of living plants appears to show that the angiosperms are a sister clade to the gymnosperms. = = plant physiology = = plant physiology encompasses all the internal chemical and physical activities of plants associated with life. chemicals obtained from the air, soil and water form the basis of all plant metabolism. the energy of sunlight, captured by oxygenic photosynthesis and released by cellular respiration, is the basis of almost all life. photoautotrophs, including all green plants, algae and cyanobacteria gather energy directly from sunlight by photosynthesis. heterotrophs including all animals, all fungi, all completely parasitic plants, and non - photosynthetic bacteria take in organic molecules produced by photoautotrophs and respire them or use them in the construction of cells and tissues. respiration is the oxidation of carbon compounds by breaking them down into simpler structures to release the energy they contain, essentially the opposite of photosynthesis. molecules are moved within plants by transport processes that operate at a variety of spatial scales. subcellular transport of ions, electrons and molecules such as water and enzymes occurs across cell membranes. minerals and water are transported from roots to other parts of the plant in the transpiration stream. diffusion, osmosis, and active transport and mass flow are all different ways transport can occur. examples of elements that plants need to transport are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. in vascular plants, these elements are extracted from the soil as soluble ions by the roots and transported throughout the plant in the xylem. most of the elements required for plant nutrition come from the chemical breakdown of soil minerals. sucrose produced by photosynthesis is transported from the leaves to other parts of the plant in the phloem and plant hormones are transported by a variety of processes. = = = plant hormones = = = plants are not passive, but respond to external signals such as light, touch, and injury by moving or growing towards or away from the stimulus, as appropriate. tangible evidence of touch sensitivity is the almost instantaneous collapse of leaflets of mimosa pudica, the insect traps of venus flytrap and bladderworts, and the pollinia of orchids. the hypothesis that plant growth and development is coordinated by plant hormones or plant growth regulators first emerged in the late 19th century. darwin experimented on the movements of plant shoots and roots towards light and gravity, and concluded " it is hardly an ex - people relationships arose between the indigenous people of canada in identifying edible plants from inedible plants. this relationship the indigenous people had with plants was recorded by ethnobotanists. = = plant biochemistry = = plant biochemistry is the study of the chemical processes used by plants. some of these processes are used in their primary metabolism like the photosynthetic calvin cycle and crassulacean acid metabolism. others make specialised materials like the cellulose and lignin used to build their bodies, and secondary products like resins and aroma compounds. plants and various other groups of photosynthetic eukaryotes collectively known as " algae " have unique organelles known as chloroplasts. chloroplasts are thought to be descended from cyanobacteria that formed endosymbiotic relationships with ancient plant and algal ancestors. chloroplasts and cyanobacteria contain the blue - green pigment chlorophyll a. chlorophyll a ( as well as its plant and green algal - specific cousin chlorophyll b ) absorbs light in the blue - violet and orange / red parts of the spectrum while reflecting and transmitting the green light that we see as the characteristic colour of these organisms. the energy in the red and blue light that these pigments absorb is used by chloroplasts to make energy - rich carbon compounds from carbon dioxide and water by oxygenic photosynthesis, a process that generates molecular oxygen ( o2 ) as a by - product. the light energy captured by chlorophyll a is initially in the form of electrons ( and later a proton gradient ) that is used to make molecules of atp and nadph which temporarily store and transport energy. their energy is used in the light - independent reactions of the calvin cycle by the enzyme rubisco to produce molecules of the 3 - carbon sugar glyceraldehyde 3 - phosphate ( g3p ). glyceraldehyde 3 - phosphate is the first product of photosynthesis and the raw material from which glucose and almost all other organic molecules of biological origin are synthesised. some of the glucose is converted to starch which is stored in the chloroplast. starch is the characteristic energy store of most land plants and algae, while inulin, a polymer of fructose is used for the same purpose in the sunflower family asteraceae. some of the glucose is converted to sucrose ( common table horticultural botany, phytopathology, and phytopharmacology. = = scope and importance = = the study of plants is vital because they underpin almost all animal life on earth by generating a large proportion of the oxygen and food that provide humans and other organisms with aerobic respiration with the chemical energy they need to exist. plants, algae and cyanobacteria are the major groups of organisms that carry out photosynthesis, a process that uses the energy of sunlight to convert water and carbon dioxide into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ) pathogens in agriculture and natural ecosystems. ethnobotany is the study of the relationships between plants and people. when applied to the investigation of historical plant – people relationships ethnobotany may be referred to as archaeobotany or palaeoethnobotany. some of the earliest plant - people relationships arose between the indigenous people of canada in identifying edible plants from inedible plants. this relationship the indigenous people had with plants was recorded by ethnobotanists. = = plant biochemistry = = plant biochemistry is the study of the chemical processes used by plants. some of these processes are used in their primary metabolism like the photosynthetic calvin cycle and crassulacean acid metabolism. others make specialised materials like the cellulose and lignin used to build their bodies, and secondary products like resins and aroma compounds. plants and various other groups of photosynthetic eukaryotes collectively known as " algae " have unique organelles known as chloroplasts. chloroplasts are thought to be descended from cyanobacteria that formed endosymbiotic relationships with ancient plant and algal ancestors. chloroplasts and cyanobacteria contain the blue - green pigment chlorophyll a. chlorophyll a ( as well as its plant and green algal - specific cousin chlorophyll b ) absorbs light in the blue - violet and orange / red parts of the spectrum while reflecting and transmitting the green light that we see as the characteristic colour of these organisms. the energy in the red and blue light that these pigments absorb is used by chloroplasts to make energy - rich carbon compounds from carbon dioxide and water by oxygenic photosynthesis, a process that generates molecular oxygen ( o2 ) as a by - product. the light energy captured by chlorophyll a is initially in the form of electrons ( and later a proton gradient ) that is used to make molecules of atp and nadph which temporarily store and transport energy. their energy is used in the light - independent reactions of the calvin cycle by the enzyme rubisco to produce molecules of the 3 - carbon sugar glyceraldehyde 3 - phosphate ( g3p ). glyceraldehyde 3 - phosphate is the first product of photosynthesis and the raw material from which glucose and almost all other organic molecules of biological origin are synthesised. some of the glucose is converted to star Question: Photoautotrophs including (a) plants, (b) algae, and (c) cyanobacteria synthesize their organic compounds via photosynthesis using sunlight as this? A) light source4 B) fuel source C) energy source D) heating source	C) energy source
Context: and their competitive or mutualistic interactions with other species. some ecologists even rely on empirical data from indigenous people that is gathered by ethnobotanists. this information can relay a great deal of information on how the land once was thousands of years ago and how it has changed over that time. the goals of plant ecology are to understand the causes of their distribution patterns, productivity, environmental impact, evolution, and responses to environmental change. plants depend on certain edaphic ( soil ) and climatic factors in their environment but can modify these factors too. for example, they can change their environment ' s albedo, increase runoff interception, stabilise mineral soils and develop their organic content, and affect local temperature. plants compete with other organisms in their ecosystem for resources. they interact with their neighbours at a variety of spatial scales in groups, populations and communities that collectively constitute vegetation. regions with characteristic vegetation types and dominant plants as well as similar abiotic and biotic factors, climate, and geography make up biomes like tundra or tropical rainforest. herbivores eat plants, but plants can defend themselves and some species are parasitic or even carnivorous. other organisms form mutually beneficial relationships with plants. for example, mycorrhizal fungi and rhizobia provide plants with nutrients in exchange for food, ants are recruited by ant plants to provide protection, honey bees, bats and other animals pollinate flowers and humans and other animals act as dispersal vectors to spread spores and seeds. = = = plants, climate and environmental change = = = plant responses to climate and other environmental changes can inform our understanding of how these changes affect ecosystem function and productivity. for example, plant phenology can be a useful proxy for temperature in historical climatology, and the biological impact of climate change and global warming. palynology, the analysis of fossil pollen deposits in sediments from thousands or millions of years ago allows the reconstruction of past climates. estimates of atmospheric co2 concentrations since the palaeozoic have been obtained from stomatal densities and the leaf shapes and sizes of ancient land plants. ozone depletion can expose plants to higher levels of ultraviolet radiation - b ( uv - b ), resulting in lower growth rates. moreover, information from studies of community ecology, plant systematics, and taxonomy is essential to understanding vegetation change, habitat destruction and species extinction. = = genetics = = inheritance in plants follows the same fundamental principles of genetics as in other multicellular organisms. gregor mendel discovered the genetic laws of inheritance by studying a watershed ( called a " divide " in north america ) over which rainfall flows down towards the river traversing the lowest part of the valley, whereas the rain falling on the far slope of the watershed flows away to another river draining an adjacent basin. river basins vary in extent according to the configuration of the country, ranging from the insignificant drainage areas of streams rising on high ground near the coast and flowing straight down into the sea, up to immense tracts of continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching the ocean. the size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern made of steel. the shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. an open caisson may fill with water during sinking. the material is excavated by clamshell excavator bucket on crane. the formation level subsoil may still not be suitable for excavation or bearing capacity. the water in the caisson ( due to a high water table ) balances the upthrust forces of the soft soils underneath. if dewatered, the base may " pipe " or " boil ", causing the caisson to sink. to combat this problem, piles may be driven from the surface to act as : load - bearing walls, in that they transmit loads to deeper soils. anchors, in that they resist flotation because of the friction at the interface between their surfaces and the surrounding earth into which they have been driven. h - beam sections ( typical column sections, due to resistance to bending in all axis ) may be driven at angles " raked " to rock or other firmer soils ; the h - beams are left extended above the base. a reinforced concrete plug may be placed under the water, a process known as tremie concrete placement. when the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. = = = monolithic = = = a monolithic caisson ( or simply a monolith ) is larger than the other types of caisson, but similar to open caissons. such caissons are often found in quay walls, where resistance to impact from ships is required. = = = pneumatic = = = shallow caissons may be open to the air, whereas pneumatic caissons ( sometimes called pressurized caissons ), which penetrate soft mud, are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. an airlock allows access to the chamber. workers, called sandhogs in american english, move mud and rock debris ( called muck ) from the edge of the workspace to a water - filled pit, connected by a tube ( called the muck tube ) to the surface. a crane at the surface removes the soil with a clamshell bucket. the water pressure in the tube balances the air pressure, with excess air escaping up depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform from the insignificant drainage areas of streams rising on high ground near the coast and flowing straight down into the sea, up to immense tracts of continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching the ocean. the size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding sea approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding seawards, so that in the po river in italy, for instance, pebbles and gravel are found for about 140 miles below turin, sand along the next 100 miles, and silt and mud in the last 110 miles ( 176 km ). = = channelization = = the removal of obstructions, natural or artificial becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in Question: Glaciers modify the landscape by what? A) sediment B) truncation C) silt D) erosion	D) erosion
Context: various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial differences in gene expression. a small fraction of the genes in an organism ' s genome called the developmental - genetic toolkit control the development of that organism. these toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. among the most important toolkit genes are the hox genes. hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva. = = evolution = = = = = evolutionary processes = = = evolution is a central organizing concept in biology. it is the change in heritable characteristics of populations over successive generations. in artificial selection, animals were selectively bred for specific traits. given that traits are inherited, populations contain a varied mix of traits, and reproduction is able to increase any population, darwin argued that in the natural world, it was nature that played the role of humans in selecting for specific traits. darwin inferred that individuals who possessed heritable traits better adapted to their environments are more likely to survive and produce more offspring than other individuals. he further inferred that this would lead to the accumulation of favorable traits over successive generations, thereby increasing the match between the organisms and their environment. = = = speciation = = = a species is a group of organisms that mate with one another and speciation is the process by which one lineage splits into two lineages as a result of having evolved independently from each other the cell ' s life. some epigenetic changes have been shown to be heritable, while others are reset in the germ cells. epigenetic changes in eukaryotic biology serve to regulate the process of cellular differentiation. during morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, with one allele inducing a change on the other. = = plant evolution = = the chloroplasts of plants have a number of biochemical, structural and genetic similarities to cyanobacteria, ( commonly but incorrectly known as " blue - green algae " ) and are thought to be derived from an ancient endosymbiotic relationship between an ancestral eukaryotic cell and a cyanobacterial resident. the algae are a polyphyletic group and are placed in various divisions, some more closely related to plants than others. there are many differences between them in features such as cell wall composition, biochemistry, pigmentation, chloroplast structure and nutrient reserves. the algal division charophyta, sister to the green algal division chlorophyta, is considered to contain the ancestor of true plants. the charophyte class charophyceae and the land plant sub - kingdom embryophy to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial differences in gene expression. a small fraction of the genes in an organism ' s genome called the developmental - genetic toolkit control the development of that organism. these toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. among the most important toolkit genes are the hox genes. hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva. = = evolution = = = = = evolutionary processes = = = evolution is a central organizing concept in biology. it is the change in heritable characteristics of populations over successive generations. in artificial selection, animals were selectively bred for specific traits. given that traits are inherited, populations contain a varied mix of traits, and reproduction is able to increase any population, darwin argued that in the natural world, it was nature that played the role of humans in selecting for specific traits. darwin inferred that individuals who possessed heritable traits better adapted to their environments are more likely to survive and produce more offspring than other individuals. he further inferred that this would lead to the or removed from the dna during programmed stages of development of the plant, and are responsible, for example, for the differences between anthers, petals and normal leaves, despite the fact that they all have the same underlying genetic code. epigenetic changes may be temporary or may remain through successive cell divisions for the remainder of the cell ' s life. some epigenetic changes have been shown to be heritable, while others are reset in the germ cells. epigenetic changes in eukaryotic biology serve to regulate the process of cellular differentiation. during morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, with one allele inducing a change on the other. = = plant evolution = = the chloroplasts of plants have a number of biochemical, structural and genetic similarities to cyanobacteria, ( commonly but incorrectly known as " blue - green algae " ) and are thought to be derived from an ancient endosymbiotic relationship between an ancestral eukaryotic cell and a cyanobacterial resident. the algae are a polyphyletic group and are placed in various divisions, some more closely related to plants than others. there are many differences between them in features such as cell wall composition, biochemistry, the gene is expressed or what other genes it interacts with. these experiments generally involve loss of function, gain of function, tracking and expression. loss of function experiments, such as in a gene knockout experiment, in which an organism is engineered to lack the activity of one or more genes. in a simple knockout a copy of the desired gene has been altered to make it non - functional. embryonic stem cells incorporate the altered gene, which replaces the already present functional copy. these stem cells are injected into blastocysts, which are implanted into surrogate mothers. this allows the experimenter to analyse the defects caused by this mutation and thereby determine the role of particular genes. it is used especially frequently in developmental biology. when this is done by creating a library of genes with point mutations at every position in the area of interest, or even every position in the whole gene, this is called " scanning mutagenesis ". the simplest method, and the first to be used, is " alanine scanning ", where every position in turn is mutated to the unreactive amino acid alanine. gain of function experiments, the logical counterpart of knockouts. these are sometimes performed in conjunction with knockout experiments to more finely establish the function of the desired gene. the process is much the same as that in knockout engineering, except that the construct is designed to increase the function of the gene, usually by providing extra copies of the gene or inducing synthesis of the protein more frequently. gain of function is used to tell whether or not a protein is sufficient for a function, but does not always mean it is required, especially when dealing with genetic or functional redundancy. tracking experiments, which seek to gain information about the localisation and interaction of the desired protein. one way to do this is to replace the wild - type gene with a ' fusion ' gene, which is a juxtaposition of the wild - type gene with a reporting element such as green fluorescent protein ( gfp ) that will allow easy visualisation of the products of the genetic modification. while this is a useful technique, the manipulation can destroy the function of the gene, creating secondary effects and possibly calling into question the results of the experiment. more sophisticated techniques are now in development that can track protein products without mitigating their function, such as the addition of small sequences that will serve as binding motifs to monoclonal antibodies. expression studies aim to discover where and when specific proteins are produced. in these experiments, the dna sequence before the dna that codes for much sunlight the plant receives each day. this can result in adaptive changes in a process known as photomorphogenesis. phytochromes are the photoreceptors in a plant that are sensitive to light. = = plant anatomy and morphology = = plant anatomy is the study of the structure of plant cells and tissues, whereas plant morphology is the study of their external form. all plants are multicellular eukaryotes, their dna stored in nuclei. the characteristic features of plant cells that distinguish them from those of animals and fungi include a primary cell wall composed of the polysaccharides cellulose, hemicellulose and pectin, larger vacuoles than in animal cells and the presence of plastids with unique photosynthetic and biosynthetic functions as in the chloroplasts. other plastids contain storage products such as starch ( amyloplasts ) or lipids ( elaioplasts ). uniquely, streptophyte cells and those of the green algal order trentepohliales divide by construction of a phragmoplast as a template for building a cell plate late in cell division. the bodies of vascular plants including clubmosses, ferns and seed plants ( gymnosperms and angiosperms ) generally have aerial and subterranean subsystems. the shoots consist of stems bearing green photosynthesising leaves and reproductive structures. the underground vascularised roots bear root hairs at their tips and generally lack chlorophyll. non - vascular plants, the liverworts, hornworts and mosses do not produce ground - penetrating vascular roots and most of the plant participates in photosynthesis. the sporophyte generation is nonphotosynthetic in liverworts but may be able to contribute part of its energy needs by photosynthesis in mosses and hornworts. the root system and the shoot system are interdependent – the usually nonphotosynthetic root system depends on the shoot system for food, and the usually photosynthetic shoot system depends on water and minerals from the root system. cells in each system are capable of creating cells of the other and producing adventitious shoots or roots. stolons and tubers are examples of shoots that can grow roots. roots that spread out close to the surface, such as those of willows, can produce shoots and ultimately new plants. in the event that one of the systems is lost young plant cells, and electroporation, which involves using an electric shock to make the cell membrane permeable to plasmid dna. as only a single cell is transformed with genetic material, the organism must be regenerated from that single cell. in plants this is accomplished through the use of tissue culture. in animals it is necessary to ensure that the inserted dna is present in the embryonic stem cells. bacteria consist of a single cell and reproduce clonally so regeneration is not necessary. selectable markers are used to easily differentiate transformed from untransformed cells. these markers are usually present in the transgenic organism, although a number of strategies have been developed that can remove the selectable marker from the mature transgenic plant. further testing using pcr, southern hybridization, and dna sequencing is conducted to confirm that an organism contains the new gene. these tests can also confirm the chromosomal location and copy number of the inserted gene. the presence of the gene does not guarantee it will be expressed at appropriate levels in the target tissue so methods that look for and measure the gene products ( rna and protein ) are also used. these include northern hybridisation, quantitative rt - pcr, western blot, immunofluorescence, elisa and phenotypic analysis. the new genetic material can be inserted randomly within the host genome or targeted to a specific location. the technique of gene targeting uses homologous recombination to make desired changes to a specific endogenous gene. this tends to occur at a relatively low frequency in plants and animals and generally requires the use of selectable markers. the frequency of gene targeting can be greatly enhanced through genome editing. genome editing uses artificially engineered nucleases that create specific double - stranded breaks at desired locations in the genome, and use the cell ' s endogenous mechanisms to repair the induced break by the natural processes of homologous recombination and nonhomologous end - joining. there are four families of engineered nucleases : meganucleases, zinc finger nucleases, transcription activator - like effector nucleases ( talens ), and the cas9 - guiderna system ( adapted from crispr ). talen and crispr are the two most commonly used and each has its own advantages. talens have greater target specificity, while crispr is easier to design and more efficient. in addition to enhancing gene targeting, engineered nucleases can be used to introduce mutations from the oil of jasminum grandiflorum which regulates wound responses in plants by unblocking the expression of genes required in the systemic acquired resistance response to pathogen attack. in addition to being the primary energy source for plants, light functions as a signalling device, providing information to the plant, such as how much sunlight the plant receives each day. this can result in adaptive changes in a process known as photomorphogenesis. phytochromes are the photoreceptors in a plant that are sensitive to light. = = plant anatomy and morphology = = plant anatomy is the study of the structure of plant cells and tissues, whereas plant morphology is the study of their external form. all plants are multicellular eukaryotes, their dna stored in nuclei. the characteristic features of plant cells that distinguish them from those of animals and fungi include a primary cell wall composed of the polysaccharides cellulose, hemicellulose and pectin, larger vacuoles than in animal cells and the presence of plastids with unique photosynthetic and biosynthetic functions as in the chloroplasts. other plastids contain storage products such as starch ( amyloplasts ) or lipids ( elaioplasts ). uniquely, streptophyte cells and those of the green algal order trentepohliales divide by construction of a phragmoplast as a template for building a cell plate late in cell division. the bodies of vascular plants including clubmosses, ferns and seed plants ( gymnosperms and angiosperms ) generally have aerial and subterranean subsystems. the shoots consist of stems bearing green photosynthesising leaves and reproductive structures. the underground vascularised roots bear root hairs at their tips and generally lack chlorophyll. non - vascular plants, the liverworts, hornworts and mosses do not produce ground - penetrating vascular roots and most of the plant participates in photosynthesis. the sporophyte generation is nonphotosynthetic in liverworts but may be able to contribute part of its energy needs by photosynthesis in mosses and hornworts. the root system and the shoot system are interdependent – the usually nonphotosynthetic root system depends on the shoot system for food, and the usually photosynthetic shoot system depends on water and minerals from the root system. cells in each system are capable pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, with one allele inducing a change on the other. = = plant evolution = = the chloroplasts of plants have a number of biochemical, structural and genetic similarities to cyanobacteria, ( commonly but incorrectly known as " blue - green algae " ) and are thought to be derived from an ancient endosymbiotic relationship between an ancestral eukaryotic cell and a cyanobacterial resident. the algae are a polyphyletic group and are placed in various divisions, some more closely related to plants than others. there are many differences between them in features such as cell wall composition, biochemistry, pigmentation, chloroplast structure and nutrient reserves. the algal division charophyta, sister to the green algal division chlorophyta, is considered to contain the ancestor of true plants. the charophyte class charophyceae and the land plant sub - kingdom embryophyta together form the monophyletic group or clade streptophytina. nonvascular land plants are embryophytes that lack the vascular tissues xylem and phloem. they include mosses, liverworts and hornworts. pteridophytic vascular plants with true xyle ##ply quickly, relatively easy to transform and can be stored at - 80 °c almost indefinitely. once a gene is isolated it can be stored inside the bacteria providing an unlimited supply for research. organisms are genetically engineered to discover the functions of certain genes. this could be the effect on the phenotype of the organism, where the gene is expressed or what other genes it interacts with. these experiments generally involve loss of function, gain of function, tracking and expression. loss of function experiments, such as in a gene knockout experiment, in which an organism is engineered to lack the activity of one or more genes. in a simple knockout a copy of the desired gene has been altered to make it non - functional. embryonic stem cells incorporate the altered gene, which replaces the already present functional copy. these stem cells are injected into blastocysts, which are implanted into surrogate mothers. this allows the experimenter to analyse the defects caused by this mutation and thereby determine the role of particular genes. it is used especially frequently in developmental biology. when this is done by creating a library of genes with point mutations at every position in the area of interest, or even every position in the whole gene, this is called " scanning mutagenesis ". the simplest method, and the first to be used, is " alanine scanning ", where every position in turn is mutated to the unreactive amino acid alanine. gain of function experiments, the logical counterpart of knockouts. these are sometimes performed in conjunction with knockout experiments to more finely establish the function of the desired gene. the process is much the same as that in knockout engineering, except that the construct is designed to increase the function of the gene, usually by providing extra copies of the gene or inducing synthesis of the protein more frequently. gain of function is used to tell whether or not a protein is sufficient for a function, but does not always mean it is required, especially when dealing with genetic or functional redundancy. tracking experiments, which seek to gain information about the localisation and interaction of the desired protein. one way to do this is to replace the wild - type gene with a ' fusion ' gene, which is a juxtaposition of the wild - type gene with a reporting element such as green fluorescent protein ( gfp ) that will allow easy visualisation of the products of the genetic modification. while this is a useful technique, the manipulation can destroy the function of the gene, creating secondary effects and possibly calling into question the results of the experiment. Question: The cells in the follicle undergo physical changes and produce a structure called a what? A) secondary ovum B) primordial follicle C) corpus luteum D) liberated ovum	C) corpus luteum
Context: some references for the breaking strength of fused silica fibers compiled in 1999. what kind of new physics, if any, we expect to discover at the lhc? i will try to address this formidable question by re - formulating it as follows : is the breaking of the electroweak symmetry strong or weak? which could be used as tools, primarily in the form of choppers or scrapers. these tools greatly aided the early humans in their hunter - gatherer lifestyle to perform a variety of tasks including butchering carcasses ( and breaking bones to get at the marrow ) ; chopping wood ; cracking open nuts ; skinning an animal for its hide, and even forming other tools out of softer materials such as bone and wood. the earliest stone tools were irrelevant, being little more than a fractured rock. in the acheulian era, beginning approximately 1. 65 million years ago, methods of working these stones into specific shapes, such as hand axes emerged. this early stone age is described as the lower paleolithic. the middle paleolithic, approximately 300, 000 years ago, saw the introduction of the prepared - core technique, where multiple blades could be rapidly formed from a single core stone. the upper paleolithic, beginning approximately 40, 000 years ago, saw the introduction of pressure flaking, where a wood, bone, or antler punch could be used to shape a stone very finely. the end of the last ice age about 10, 000 years ago is taken as the end point of the upper paleolithic and the beginning of the epipaleolithic / mesolithic. the mesolithic technology included the use of microliths as composite stone tools, along with wood, bone, and antler tools. the later stone age, during which the rudiments of agricultural technology were developed, is called the neolithic period. during this period, polished stone tools were made from a variety of hard rocks such as flint, jade, jadeite, and greenstone, largely by working exposures as quarries, but later the valuable rocks were pursued by tunneling underground, the first steps in mining technology. the polished axes were used for forest clearance and the establishment of crop farming and were so effective as to remain in use when bronze and iron appeared. these stone axes were used alongside a continued use of stone tools such as a range of projectiles, knives, and scrapers, as well as tools, made from organic materials such as wood, bone, and antler. stone age cultures developed music and engaged in organized warfare. stone age humans developed ocean - worthy outrigger canoe technology, leading to migration across the malay archipelago, across the indian ocean to madagascar and also across the pacific ocean, which required knowledge of the ocean currents, weather patterns, sailing, and celestial navigation. although paleolithic cultures ##morphology studies the origin of landscapes. structural geology studies the deformation of rocks to produce mountains and lowlands. resource geology studies how energy resources can be obtained from minerals. environmental geology studies how pollution and contaminants affect soil and rock. mineralogy is the study of minerals and includes the study of mineral formation, crystal structure, hazards associated with minerals, and the physical and chemical properties of minerals. petrology is the study of rocks, including the formation and composition of rocks. petrography is a branch of petrology that studies the typology and classification of rocks. = = earth ' s interior = = plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to ##simal cube of material relative to a reference configuration. mechanical strains are caused by mechanical stress, see stress - strain curve. the relationship between stress and strain is generally linear and reversible up until the yield point and the deformation is elastic. elasticity in materials occurs when applied stress does not surpass the energy required to break molecular bonds, allowing the material to deform reversibly and return to its original shape once the stress is removed. the linear relationship for a material is known as young ' s modulus. above the yield point, some degree of permanent distortion remains after unloading and is termed plastic deformation. the determination of the stress and strain throughout a solid object is given by the field of strength of materials and for a structure by structural analysis. in the above figure, it can be seen that the compressive loading ( indicated by the arrow ) has caused deformation in the cylinder so that the original shape ( dashed lines ) has changed ( deformed ) into one with bulging sides. the sides bulge because the material, although strong enough to not crack or otherwise fail, is not strong enough to support the load without change. as a result, the material is forced out laterally. internal forces ( in this case at right angles to the deformation ) resist the applied load. = = types of deformation = = depending on the type of material, size and geometry of the object, and the forces applied, various types of deformation may result. the image to the right shows the engineering stress vs. strain diagram for a typical ductile material such as steel. different deformation modes may occur under different conditions, as can be depicted using a deformation mechanism map. permanent deformation is irreversible ; the deformation stays even after removal of the applied forces, while the temporary deformation is recoverable as it disappears after the removal of applied forces. temporary deformation is also called elastic deformation, while the permanent deformation is called plastic deformation. = = = elastic deformation = = = the study of temporary or elastic deformation in the case of engineering strain is applied to materials used in mechanical and structural engineering, such as concrete and steel, which are subjected to very small deformations. engineering strain is modeled by infinitesimal strain theory, also called small strain theory, small deformation theory, small displacement theory, or small displacement - gradient theory where strains and rotations are both small. for some materials, e. g. elastomers and polymers, subjected to large deformations, the engineering definition of strain is not applicable, e. g. typical engineering strains , crystal structure, hazards associated with minerals, and the physical and chemical properties of minerals. petrology is the study of rocks, including the formation and composition of rocks. petrography is a branch of petrology that studies the typology and classification of rocks. = = earth ' s interior = = plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest of tool usage was found in ethiopia within the great rift valley, dating back to 2. 5 million years ago. the earliest methods of stone tool making, known as the oldowan " industry ", date back to at least 2. 3 million years ago. this era of stone tool use is called the paleolithic, or " old stone age ", and spans all of human history up to the development of agriculture approximately 12, 000 years ago. to make a stone tool, a " core " of hard stone with specific flaking properties ( such as flint ) was struck with a hammerstone. this flaking produced sharp edges which could be used as tools, primarily in the form of choppers or scrapers. these tools greatly aided the early humans in their hunter - gatherer lifestyle to perform a variety of tasks including butchering carcasses ( and breaking bones to get at the marrow ) ; chopping wood ; cracking open nuts ; skinning an animal for its hide, and even forming other tools out of softer materials such as bone and wood. the earliest stone tools were irrelevant, being little more than a fractured rock. in the acheulian era, beginning approximately 1. 65 million years ago, methods of working these stones into specific shapes, such as hand axes emerged. this early stone age is described as the lower paleolithic. the middle paleolithic, approximately 300, 000 years ago, saw the introduction of the prepared - core technique, where multiple blades could be rapidly formed from a single core stone. the upper paleolithic, beginning approximately 40, 000 years ago, saw the introduction of pressure flaking, where a wood, bone, or antler punch could be used to shape a stone very finely. the end of the last ice age about 10, 000 years ago is taken as the end point of the upper paleolithic and the beginning of the epipaleolithic / mesolithic. the mesolithic technology included the use of microliths as composite stone tools, along with wood, bone, and antler tools. the later stone age, during which the rudiments of agricultural technology were developed, is called the neolithic period. during this period, polished stone tools were made from a variety of hard rocks such as flint, jade, jadeite, and greenstone, largely by working exposures as quarries, but later the valuable rocks were pursued by tunneling underground, the first steps in mining technology. the polished axes were used for forest clearance and the establishment of crop the monocrystalline silicon neutron beam window is one of the key components of neutron spectrometers and thin circular plate. monocrystalline silicon is a brittle material and its strength is not constant but is consistent with the weibull distribution. the window is designed not simply through the average strength, but according to the survival rate. bending deformation is the main form of the window, so dangerous parts of the neutron beam window is stress - linearized to the combination of membrane stress and bending stress. according to the weibull distribution of bending strength of monocrystalline silicon based on a large number of experimental data, finally the optimized neutron beam window is 1. 5mm thick. its survival rate is 0. 9994 and its transmittance is 0. 98447 ; it meets both physical requirements and the mechanical strength. ##ctonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s to that of a flat crack through the plain matrix. the magnitude of the toughening is determined by the mismatch strain caused by thermal contraction incompatibility and the microfracture resistance of the particle / matrix interface. the toughening becomes noticeable with a narrow size distribution of appropriately sized particles, and researchers typically accept that deflection effects in materials with roughly equiaxial grains may increase the fracture toughness by about twice the grain boundary value. the model reveals that the increase in toughness is dependent on particle shape and the volume fraction of the second phase, with the most effective morphology being the rod of high aspect ratio, which can account for a fourfold increase in fracture toughness. the toughening arises primarily from the twist of the crack front between particles, as indicated by deflection profiles. disc - shaped particles and spheres are less effective in toughening. fracture toughness, regardless of morphology, is determined by the twist of the crack front at its most severe configuration, rather than the initial tilt of the crack front. only for disc - shaped particles does the initial tilting of the crack front provide significant toughening ; however, the twist component still overrides the tilt - derived toughening. additional important features of the deflection analysis include the appearance of asymptotic toughening for the three morphologies at volume fractions in excess of 0. 2. it is also noted that a significant influence on the toughening by spherical particles is exerted by the interparticle spacing distribution ; greater toughening is afforded when spheres are nearly contacting such that twist angles approach π / 2. these predictions provide the basis for the design of high - toughness two - phase ceramic materials. the ideal second phase, in addition to maintaining chemical compatibility, should be present in amounts of 10 to 20 volume percent. greater amounts may diminish the toughness increase due to overlapping particles. particles with high aspect ratios, especially those with rod - shaped morphologies, are most suitable for maximum toughening. this model is often used to determine the factors that contribute to the increase in fracture toughness in ceramics which is ultimately useful in the development of advanced ceramic materials with improved performance. = = theory of chemical processing = = = = = microstructural uniformity = = = in the processing of fine ceramics, the irregular particle sizes and shapes in a typical powder often lead to non - uniform packing morphologies that result in packing density variations in the powder compact. uncontrolled aggl Question: Scientists can use what tool to determine an earthquake's strength? A) kilocalorie B) telescope C) geiger counter D) seismogram	D) seismogram
Context: the gas giant planets in the solar system have a retinue of icy moons, and we expect giant exoplanets to have similar satellite systems. if a jupiter - like planet were to migrate toward its parent star the icy moons orbiting it would evaporate, creating atmospheres and possible habitable surface oceans. here, we examine how long the surface ice and possible oceans would last before being hydrodynamically lost to space. the hydrodynamic loss rate from the moons is determined, in large part, by the stellar flux available for absorption, which increases as the giant planet and icy moons migrate closer to the star. at some planet - star distance the stellar flux incident on the icy moons becomes so great that they enter a runaway greenhouse state. this runaway greenhouse state rapidly transfers all available surface water to the atmosphere as vapor, where it is easily lost from the small moons. however, for icy moons of ganymede ' s size around a sun - like star we found that surface water ( either ice or liquid ) can persist indefinitely outside the runaway greenhouse orbital distance. in contrast, the surface water on smaller moons of europa ' s size will only persist on timescales greater than 1 gyr at distances ranging 1. 49 to 0. 74 au around a sun - like star for bond albedos of 0. 2 and 0. 8, where the lower albedo becomes relevant if ice melts. consequently, small moons can lose their icy shells, which would create a torus of h atoms around their host planet that might be detectable in future observations. the origin of the martian moons deimos and phobos is controversial. one hypothesis for their origin is that they are captured asteroids, but the mechanism requires an extremely dense martian atmosphere, and the mechanism by which an asteroid in solar orbit could shed sufficient orbital energy to be captured into mars orbit has not been well elucidated. since the discovery by the space probe galileo that the asteroid ida has a moon " dactyl ", a significant number of asteroids have been discovered to have smaller asteroids in orbit about them. the existence of asteroid moons provides a mechanism for the capture of the martian moons ( and the small moons of the outer planets ). when a binary asteroid makes a close approach to a planet, tidal forces can strip the moon from the asteroid. depending on the phasing, the asteroid can then be captured. clearly, the same process can be used to explain the origin of any of the small moons in the solar system. also launched missions to mercury in 2004, with the messenger probe demonstrating as the first use of a solar sail. nasa also launched probes to the outer solar system starting in the 1960s. pioneer 10 was the first probe to the outer planets, flying by jupiter, while pioneer 11 provided the first close up view of the planet. both probes became the first objects to leave the solar system. the voyager program launched in 1977, conducting flybys of jupiter and saturn, neptune, and uranus on a trajectory to leave the solar system. the galileo spacecraft, deployed from the space shuttle flight sts - 34, was the first spacecraft to orbit jupiter, discovering evidence of subsurface oceans on the europa and observed that the moon may hold ice or liquid water. a joint nasa - european space agency - italian space agency mission, cassini – huygens, was sent to saturn ' s moon titan, which, along with mars and europa, are the only celestial bodies in the solar system suspected of being capable of harboring life. cassini discovered three new moons of saturn and the huygens probe entered titan ' s atmosphere. the mission discovered evidence of liquid hydrocarbon lakes on titan and subsurface water oceans on the moon of enceladus, which could harbor life. finally launched in 2006, the new horizons mission was the first spacecraft to visit pluto and the kuiper belt. beyond interplanetary probes, nasa has launched many space telescopes. launched in the 1960s, the orbiting astronomical observatory were nasa ' s first orbital telescopes, providing ultraviolet, gamma - ray, x - ray, and infrared observations. nasa launched the orbiting geophysical observatory in the 1960s and 1970s to look down at earth and observe its interactions with the sun. the uhuru satellite was the first dedicated x - ray telescope, mapping 85 % of the sky and discovering a large number of black holes. launched in the 1990s and early 2000s, the great observatories program are among nasa ' s most powerful telescopes. the hubble space telescope was launched in 1990 on sts - 31 from the discovery and could view galaxies 15 billion light years away. a major defect in the telescope ' s mirror could have crippled the program, had nasa not used computer enhancement to compensate for the imperfection and launched five space shuttle servicing flights to replace the damaged components. the compton gamma ray observatory was launched from the atlantis on sts - 37 in 1991, discovering a possible source of antimatter at the center of the milky way and observing that the majority of gamma - ray bursts three planets with minimum masses less than 10 earth masses orbit the star hd 40307, suggesting these planets may be rocky. however, with only radial velocity data, it is impossible to determine if these planets are rocky or gaseous. here we exploit various dynamical features of the system in order to assess the physical properties of the planets. observations allow for circular orbits, but a numerical integration shows that the eccentricities must be at least 0. 0001. also, planets b and c are so close to the star that tidal effects are significant. if planet b has tidal parameters similar to the terrestrial planets in the solar system and a remnant eccentricity larger than 0. 001, then, going back in time, the system would have been unstable within the lifetime of the star ( which we estimate to be 6. 1 + / - 1. 6 gyr ). moreover, if the eccentricities are that large and the inner planet is rocky, then its tidal heating may be an order of magnitude greater than extremely volcanic io, on a per unit surface area basis. if planet b is not terrestrial, e. g. neptune - like, these physical constraints would not apply. this analysis suggests the planets are not terrestrial - like, and are more like our giant planets. in either case, we find that the planets probably formed at larger radii and migrated early - on ( via disk interactions ) into their current orbits. this study demonstrates how the orbital and dynamical properties of exoplanet systems may be used to constrain the planets ' physical properties. three major planets, venus, earth, and mercury formed out of the solar nebula. a fourth planetesimal, theia, also formed near earth where it collided in a giant impact, rebounding as the planet mars. during this impact earth lost $ { \ approx } 4 $ \ % of its crust and mantle that is now is found on mars and the moon. at the antipode of the giant impact, $ \ approx $ 60 \ % of earth ' s crust, atmosphere, and a large amount of mantle were ejected into space forming the moon. the lost crust never reformed and became the earth ' s ocean basins. the theia impact site corresponds to indian ocean gravitational anomaly on earth and the hellas basin on mars. the dynamics of the giant impact are consistent with the rotational rates and axial tilts of both earth and mars. the giant impact removed sufficient co $ _ 2 $ from earth ' s atmosphere to avoid a runaway greenhouse effect, initiated plate tectonics, and gave life time to form near geothermal vents at the continental margins. mercury formed near venus where on a close approach it was slingshot into the sun ' s convective zone losing 94 \ % of its mass, much of which remains there today. black carbon, from co $ _ 2 $ decomposed by the intense heat, is still found on the surface of mercury. arriving at 616 km / s, mercury dramatically altered the sun ' s rotational energy, explaining both its anomalously slow rotation rate and axial tilt. these results are quantitatively supported by mass balances, the current locations of the terrestrial planets, and the orientations of their major orbital axes. and measuring radiation levels. the surveyor program conducted uncrewed lunar landings and takeoffs, as well as taking surface and regolith observations. despite the setback caused by the apollo 1 fire, which killed three astronauts, the program proceeded. apollo 8 was the first crewed spacecraft to leave low earth orbit and the first human spaceflight to reach the moon. the crew orbited the moon ten times on december 24 and 25, 1968, and then traveled safely back to earth. the three apollo 8 astronauts — frank borman, james lovell, and william anders — were the first humans to see the earth as a globe in space, the first to witness an earthrise, and the first to see and manually photograph the far side of the moon. the first lunar landing was conducted by apollo 11. commanded by neil armstrong with astronauts buzz aldrin and michael collins, apollo 11 was one of the most significant missions in nasa ' s history, marking the end of the space race when the soviet union gave up its lunar ambitions. as the first human to step on the surface of the moon, neil armstrong uttered the now famous words : that ' s one small step for man, one giant leap for mankind. nasa would conduct six total lunar landings as part of the apollo program, with apollo 17 concluding the program in 1972. = = = = end of apollo = = = = wernher von braun had advocated for nasa to develop a space station since the agency was created. in 1973, following the end of the apollo lunar missions, nasa launched its first space station, skylab, on the final launch of the saturn v. skylab reused a significant amount of apollo and saturn hardware, with a repurposed saturn v third stage serving as the primary module for the space station. damage to skylab during its launch required spacewalks to be performed by the first crew to make it habitable and operational. skylab hosted nine missions and was decommissioned in 1974 and deorbited in 1979, two years prior to the first launch of the space shuttle and any possibility of boosting its orbit. in 1975, the apollo – soyuz mission was the first ever international spaceflight and a major diplomatic accomplishment between the cold war rivals, which also marked the last flight of the apollo capsule. flown in 1975, a us apollo spacecraft docked with a soviet soyuz capsule. = = = interplanetary exploration and space science = = = during the 1960s, nasa started its space science and interplanetary probe program. the mariner program was its flagship . both probes became the first objects to leave the solar system. the voyager program launched in 1977, conducting flybys of jupiter and saturn, neptune, and uranus on a trajectory to leave the solar system. the galileo spacecraft, deployed from the space shuttle flight sts - 34, was the first spacecraft to orbit jupiter, discovering evidence of subsurface oceans on the europa and observed that the moon may hold ice or liquid water. a joint nasa - european space agency - italian space agency mission, cassini – huygens, was sent to saturn ' s moon titan, which, along with mars and europa, are the only celestial bodies in the solar system suspected of being capable of harboring life. cassini discovered three new moons of saturn and the huygens probe entered titan ' s atmosphere. the mission discovered evidence of liquid hydrocarbon lakes on titan and subsurface water oceans on the moon of enceladus, which could harbor life. finally launched in 2006, the new horizons mission was the first spacecraft to visit pluto and the kuiper belt. beyond interplanetary probes, nasa has launched many space telescopes. launched in the 1960s, the orbiting astronomical observatory were nasa ' s first orbital telescopes, providing ultraviolet, gamma - ray, x - ray, and infrared observations. nasa launched the orbiting geophysical observatory in the 1960s and 1970s to look down at earth and observe its interactions with the sun. the uhuru satellite was the first dedicated x - ray telescope, mapping 85 % of the sky and discovering a large number of black holes. launched in the 1990s and early 2000s, the great observatories program are among nasa ' s most powerful telescopes. the hubble space telescope was launched in 1990 on sts - 31 from the discovery and could view galaxies 15 billion light years away. a major defect in the telescope ' s mirror could have crippled the program, had nasa not used computer enhancement to compensate for the imperfection and launched five space shuttle servicing flights to replace the damaged components. the compton gamma ray observatory was launched from the atlantis on sts - 37 in 1991, discovering a possible source of antimatter at the center of the milky way and observing that the majority of gamma - ray bursts occur outside of the milky way galaxy. the chandra x - ray observatory was launched from the columbia on sts - 93 in 1999, observing black holes, quasars, supernova, and dark matter. it provided critical observations on the sagittarius a * black hole at the center of the milky way galaxy and fuel cells instead of batteries, and conducted the first american spacewalks and rendezvous operations. the ranger program was started in the 1950s as a response to soviet lunar exploration, however most missions ended in failure. the lunar orbiter program had greater success, mapping the surface in preparation for apollo landings, conducting meteoroid detection, and measuring radiation levels. the surveyor program conducted uncrewed lunar landings and takeoffs, as well as taking surface and regolith observations. despite the setback caused by the apollo 1 fire, which killed three astronauts, the program proceeded. apollo 8 was the first crewed spacecraft to leave low earth orbit and the first human spaceflight to reach the moon. the crew orbited the moon ten times on december 24 and 25, 1968, and then traveled safely back to earth. the three apollo 8 astronauts — frank borman, james lovell, and william anders — were the first humans to see the earth as a globe in space, the first to witness an earthrise, and the first to see and manually photograph the far side of the moon. the first lunar landing was conducted by apollo 11. commanded by neil armstrong with astronauts buzz aldrin and michael collins, apollo 11 was one of the most significant missions in nasa ' s history, marking the end of the space race when the soviet union gave up its lunar ambitions. as the first human to step on the surface of the moon, neil armstrong uttered the now famous words : that ' s one small step for man, one giant leap for mankind. nasa would conduct six total lunar landings as part of the apollo program, with apollo 17 concluding the program in 1972. = = = = end of apollo = = = = wernher von braun had advocated for nasa to develop a space station since the agency was created. in 1973, following the end of the apollo lunar missions, nasa launched its first space station, skylab, on the final launch of the saturn v. skylab reused a significant amount of apollo and saturn hardware, with a repurposed saturn v third stage serving as the primary module for the space station. damage to skylab during its launch required spacewalks to be performed by the first crew to make it habitable and operational. skylab hosted nine missions and was decommissioned in 1974 and deorbited in 1979, two years prior to the first launch of the space shuttle and any possibility of boosting its orbit. in 1975, the apollo – soyuz mission was the first ever international spaceflight and a major diplomatic accomplishment between the cold war two planetary nebulae are shown to belong to the sagittarius dwarf galaxy, on the basis of their radial velocities. this is only the second dwarf spheroidal galaxy, after fornax, found to contain planetary nebulae. their existence confirms that this galaxy is at least as massive as the fornax dwarf spheroidal which has a single planetary nebula, and suggests a mass of a few times 10 * * 7 solar masses. the two planetary nebulae are located along the major axis of the galaxy, near the base of the tidal tail. there is a further candidate, situated at a very large distance along the direction of the tidal tail, for which no velocity measurement is available. the location of the planetary nebulae and globular clusters of the sagittarius dwarf galaxy suggests that a significant fraction of its mass is contained within the tidal tail. a 4mj planet with a 15. 8day orbital period has been detected from very precise radial velocity measurements with the coralie echelle spectrograph. a second remote and more massive companion has also been detected. all the planetary companions so far detected in orbit closer than 0. 08 au have a parent star with a statistically higher metal content compared to the metallicity distribution of other stars with planets. different processes occuring during their formation may provide a possible explanation for this observation. Question: How many moons does pluto have? A) three B) four C) six D) two	A) three
Context: lift caissons : the word caisson is also used as a synonym for the moving trough part of caisson locks, canal lifts and inclines in which boats and ships rest while being lifted from one canal elevation to another ; the water is retained on the inside of the caisson, or excluded from the caisson, according to the respective operating principle. structural caissons : caisson is also sometimes used as a colloquial term for a reinforced concrete structure formed by pouring into a hollow cylindrical form, typically by placing a caisson form below grade in an open excavation and pouring once backfill is complete, or by drilling at grade, although this can be problematic with deep caissons, as unsupported excavations can collapse before the caisson form can be inserted. in this manner, the earth placed around the empty caisson form provides stability and strength, allowing concrete to be poured with fewer complications and with less risk of a form blowout. while, technically, only the form itself is actually a caisson, it is not uncommon for any below - grade cast concrete pillar to be referred to as, simply, a caisson. ventilation filtration systems : the word caisson is also used as a name for an airtight housing for ventilation filters in facilities that handle hazardous materials. the housing usually has an upstream compartment for a pre - filter element and a downstream compartment for a high - efficiency filter element. it may have multiple sets of compartments. the housing has gasketed access doors to allow for the change out of the filter elements. the housing is usually equipped with connection points used to test the efficiency of the filters and monitor changes in the differential pressure across the filter media. = = see also = = suction caisson – open bottomed tube anchor embedded and released by pressure differential air lock diving - bell plant – underwater work support barge used at gibraltar, a mobile barge - mounted engineering caisson used in the port of gibraltar cofferdam – barrier allowing liquid to be pumped out of an enclosed area, a temporary water - excluding structure built in place, sometimes surrounding a working area as does an open caisson. offshore geotechnical engineering – sub - field of engineering concerned with human - made structures in the sea, for information on geotechnical considerations. = = patents = = u. s. patent 123, 002 – improvement in construction of sub - aqueous foundations = = references = = = = external links = = works related to caisson at wikisource made of steel. the shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. an open caisson may fill with water during sinking. the material is excavated by clamshell excavator bucket on crane. the formation level subsoil may still not be suitable for excavation or bearing capacity. the water in the caisson ( due to a high water table ) balances the upthrust forces of the soft soils underneath. if dewatered, the base may " pipe " or " boil ", causing the caisson to sink. to combat this problem, piles may be driven from the surface to act as : load - bearing walls, in that they transmit loads to deeper soils. anchors, in that they resist flotation because of the friction at the interface between their surfaces and the surrounding earth into which they have been driven. h - beam sections ( typical column sections, due to resistance to bending in all axis ) may be driven at angles " raked " to rock or other firmer soils ; the h - beams are left extended above the base. a reinforced concrete plug may be placed under the water, a process known as tremie concrete placement. when the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. = = = monolithic = = = a monolithic caisson ( or simply a monolith ) is larger than the other types of caisson, but similar to open caissons. such caissons are often found in quay walls, where resistance to impact from ships is required. = = = pneumatic = = = shallow caissons may be open to the air, whereas pneumatic caissons ( sometimes called pressurized caissons ), which penetrate soft mud, are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. an airlock allows access to the chamber. workers, called sandhogs in american english, move mud and rock debris ( called muck ) from the edge of the workspace to a water - filled pit, connected by a tube ( called the muck tube ) to the surface. a crane at the surface removes the soil with a clamshell bucket. the water pressure in the tube balances the air pressure, with excess air escaping up river - beds ), but not for where there may be large obstructions in the ground. an open caisson that is used in soft grounds or high water tables, where open trench excavations are impractical, can also be used to install deep manholes, pump stations and reception / launch pits for microtunnelling, pipe jacking and other operations. a caisson is sunk by self - weight, concrete or water ballast placed on top, or by hydraulic jacks. the leading edge ( or cutting shoe ) of the caisson is sloped out at a sharp angle to aid sinking in a vertical manner ; it is usually made of steel. the shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. an open caisson may fill with water during sinking. the material is excavated by clamshell excavator bucket on crane. the formation level subsoil may still not be suitable for excavation or bearing capacity. the water in the caisson ( due to a high water table ) balances the upthrust forces of the soft soils underneath. if dewatered, the base may " pipe " or " boil ", causing the caisson to sink. to combat this problem, piles may be driven from the surface to act as : load - bearing walls, in that they transmit loads to deeper soils. anchors, in that they resist flotation because of the friction at the interface between their surfaces and the surrounding earth into which they have been driven. h - beam sections ( typical column sections, due to resistance to bending in all axis ) may be driven at angles " raked " to rock or other firmer soils ; the h - beams are left extended above the base. a reinforced concrete plug may be placed under the water, a process known as tremie concrete placement. when the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. = = = monolithic = = = a monolithic caisson ( or simply a monolith ) is larger than the other types of caisson, but similar to open caissons. such caissons are often found in quay walls, where resistance to impact from ships is required. = = = pneumatic = = = shallow caissons may be open to the air, whereas pneumatic caisson ##morphology studies the origin of landscapes. structural geology studies the deformation of rocks to produce mountains and lowlands. resource geology studies how energy resources can be obtained from minerals. environmental geology studies how pollution and contaminants affect soil and rock. mineralogy is the study of minerals and includes the study of mineral formation, crystal structure, hazards associated with minerals, and the physical and chemical properties of minerals. petrology is the study of rocks, including the formation and composition of rocks. petrography is a branch of petrology that studies the typology and classification of rocks. = = earth ' s interior = = plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to a watershed ( called a " divide " in north america ) over which rainfall flows down towards the river traversing the lowest part of the valley, whereas the rain falling on the far slope of the watershed flows away to another river draining an adjacent basin. river basins vary in extent according to the configuration of the country, ranging from the insignificant drainage areas of streams rising on high ground near the coast and flowing straight down into the sea, up to immense tracts of continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching the ocean. the size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern ##lling, pipe jacking and other operations. a caisson is sunk by self - weight, concrete or water ballast placed on top, or by hydraulic jacks. the leading edge ( or cutting shoe ) of the caisson is sloped out at a sharp angle to aid sinking in a vertical manner ; it is usually made of steel. the shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. an open caisson may fill with water during sinking. the material is excavated by clamshell excavator bucket on crane. the formation level subsoil may still not be suitable for excavation or bearing capacity. the water in the caisson ( due to a high water table ) balances the upthrust forces of the soft soils underneath. if dewatered, the base may " pipe " or " boil ", causing the caisson to sink. to combat this problem, piles may be driven from the surface to act as : load - bearing walls, in that they transmit loads to deeper soils. anchors, in that they resist flotation because of the friction at the interface between their surfaces and the surrounding earth into which they have been driven. h - beam sections ( typical column sections, due to resistance to bending in all axis ) may be driven at angles " raked " to rock or other firmer soils ; the h - beams are left extended above the base. a reinforced concrete plug may be placed under the water, a process known as tremie concrete placement. when the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. = = = monolithic = = = a monolithic caisson ( or simply a monolith ) is larger than the other types of caisson, but similar to open caissons. such caissons are often found in quay walls, where resistance to impact from ships is required. = = = pneumatic = = = shallow caissons may be open to the air, whereas pneumatic caissons ( sometimes called pressurized caissons ), which penetrate soft mud, are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. an airlock allows access to the chamber. workers, called sandhogs in american english, move mud and rock debris ( called ##ctonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s muck ) from the edge of the workspace to a water - filled pit, connected by a tube ( called the muck tube ) to the surface. a crane at the surface removes the soil with a clamshell bucket. the water pressure in the tube balances the air pressure, with excess air escaping up the muck tube. the pressurized air flow must be constant to ensure regular air changes for the workers and prevent excessive inflow of mud or water at the base of the caisson. when the caisson hits bedrock, the sandhogs exit through the airlock and fill the box with concrete, forming a solid foundation pier. a pneumatic ( compressed - air ) caisson has the advantage of providing dry working conditions, which is better for placing concrete. it is also well suited for foundations for which other methods might cause settlement of adjacent structures. construction workers who leave the pressurized environment of the caisson must decompress at a rate that allows symptom - free release of inert gases dissolved in the body tissues if they are to avoid decompression sickness, a condition first identified in caisson workers, and originally named " caisson disease " in recognition of the occupational hazard. construction of the brooklyn bridge, which was built with the help of pressurised caissons, resulted in numerous workers being either killed or permanently injured by caisson disease during its construction. barotrauma of the ears, sinus cavities and lungs and dysbaric osteonecrosis are other risks. = = other uses = = caissons have also been used in the installation of hydraulic elevators where a single - stage ram is installed below the ground level. caissons, codenamed phoenix, were an integral part of the mulberry harbours used during the world war ii allied invasion of normandy. = = other meanings = = boat lift caissons : the word caisson is also used as a synonym for the moving trough part of caisson locks, canal lifts and inclines in which boats and ships rest while being lifted from one canal elevation to another ; the water is retained on the inside of the caisson, or excluded from the caisson, according to the respective operating principle. structural caissons : caisson is also sometimes used as a colloquial term for a reinforced concrete structure formed by pouring into a hollow cylindrical form, typically by placing a caisson form below grade in an open excavation and pouring once backfill is complete, or by from the insignificant drainage areas of streams rising on high ground near the coast and flowing straight down into the sea, up to immense tracts of continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching the ocean. the size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their ##s ( sometimes called pressurized caissons ), which penetrate soft mud, are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. an airlock allows access to the chamber. workers, called sandhogs in american english, move mud and rock debris ( called muck ) from the edge of the workspace to a water - filled pit, connected by a tube ( called the muck tube ) to the surface. a crane at the surface removes the soil with a clamshell bucket. the water pressure in the tube balances the air pressure, with excess air escaping up the muck tube. the pressurized air flow must be constant to ensure regular air changes for the workers and prevent excessive inflow of mud or water at the base of the caisson. when the caisson hits bedrock, the sandhogs exit through the airlock and fill the box with concrete, forming a solid foundation pier. a pneumatic ( compressed - air ) caisson has the advantage of providing dry working conditions, which is better for placing concrete. it is also well suited for foundations for which other methods might cause settlement of adjacent structures. construction workers who leave the pressurized environment of the caisson must decompress at a rate that allows symptom - free release of inert gases dissolved in the body tissues if they are to avoid decompression sickness, a condition first identified in caisson workers, and originally named " caisson disease " in recognition of the occupational hazard. construction of the brooklyn bridge, which was built with the help of pressurised caissons, resulted in numerous workers being either killed or permanently injured by caisson disease during its construction. barotrauma of the ears, sinus cavities and lungs and dysbaric osteonecrosis are other risks. = = other uses = = caissons have also been used in the installation of hydraulic elevators where a single - stage ram is installed below the ground level. caissons, codenamed phoenix, were an integral part of the mulberry harbours used during the world war ii allied invasion of normandy. = = other meanings = = boat lift caissons : the word caisson is also used as a synonym for the moving trough part of caisson locks, canal lifts and inclines in which boats and ships rest while being lifted from one canal elevation to another ; the water is retained on the inside of the caisson, or excluded from the caisson Question: Huge calderas form when the mountain above an empty chamber of what collapses? A) coal B) gas C) mercury D) magma	D) magma
Context: charges in the nuclei and the negative charges oscillating about them. more than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom. the chemical bond can be a covalent bond, an ionic bond, a hydrogen bond or just because of van der waals force. each of these kinds of bonds is ascribed to some potential. these potentials create the interactions which hold atoms together in molecules or crystals. in many simple compounds, valence bond theory, the valence shell electron pair repulsion model ( vsepr ), and the concept of oxidation number can be used to explain molecular structure and composition. an ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non - metal atom, becoming a negatively charged anion. the two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them. for example, sodium ( na ), a metal, loses one electron to become an na + cation while chlorine ( cl ), a non - metal, gains this electron to become cl−. the ions are held together due to electrostatic attraction, and that compound sodium chloride ( nacl ), or common table salt, is formed. in a covalent bond, one or more pairs of valence electrons are shared by two atoms : the resulting electrically neutral group of bonded atoms is termed a molecule. atoms will share valence electrons in such a way as to create a noble gas electron configuration ( eight electrons in their outermost shell ) for each atom. atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. however, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration ; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium, which has two electrons in its outer shell. similarly, theories from classical physics can be used to predict many ionic structures. with more complicated compounds, such as metal complexes, valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. = = = energy = = = in the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. since a chemical transformation is accompanied by a change ##als force. each of these kinds of bonds is ascribed to some potential. these potentials create the interactions which hold atoms together in molecules or crystals. in many simple compounds, valence bond theory, the valence shell electron pair repulsion model ( vsepr ), and the concept of oxidation number can be used to explain molecular structure and composition. an ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non - metal atom, becoming a negatively charged anion. the two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them. for example, sodium ( na ), a metal, loses one electron to become an na + cation while chlorine ( cl ), a non - metal, gains this electron to become cl−. the ions are held together due to electrostatic attraction, and that compound sodium chloride ( nacl ), or common table salt, is formed. in a covalent bond, one or more pairs of valence electrons are shared by two atoms : the resulting electrically neutral group of bonded atoms is termed a molecule. atoms will share valence electrons in such a way as to create a noble gas electron configuration ( eight electrons in their outermost shell ) for each atom. atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. however, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration ; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium, which has two electrons in its outer shell. similarly, theories from classical physics can be used to predict many ionic structures. with more complicated compounds, such as metal complexes, valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. = = = energy = = = in the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants is the electrostatic force of attraction between them. for example, sodium ( na ), a metal, loses one electron to become an na + cation while chlorine ( cl ), a non - metal, gains this electron to become cl−. the ions are held together due to electrostatic attraction, and that compound sodium chloride ( nacl ), or common table salt, is formed. in a covalent bond, one or more pairs of valence electrons are shared by two atoms : the resulting electrically neutral group of bonded atoms is termed a molecule. atoms will share valence electrons in such a way as to create a noble gas electron configuration ( eight electrons in their outermost shell ) for each atom. atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. however, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration ; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium, which has two electrons in its outer shell. similarly, theories from classical physics can be used to predict many ionic structures. with more complicated compounds, such as metal complexes, valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. = = = energy = = = in the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population it is also possible to define analogs in two - dimensional systems, which has received attention for its relevance to systems in biology. = = = bonding = = = atoms sticking together in molecules or crystals are said to be bonded with one another. a chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them. more than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom. the chemical bond can be a covalent bond, an ionic bond, a hydrogen bond or just because of van der waals force. each of these kinds of bonds is ascribed to some potential. these potentials create the interactions which hold atoms together in molecules or crystals. in many simple compounds, valence bond theory, the valence shell electron pair repulsion model ( vsepr ), and the concept of oxidation number can be used to explain molecular structure and composition. an ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non - metal atom, becoming a negatively charged anion. the two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them. for example, sodium ( na ), a metal, loses one electron to become an na + cation while chlorine ( cl ), a non - metal, gains this electron to become cl−. the ions are held together due to electrostatic attraction, and that compound sodium chloride ( nacl ), or common table salt, is formed. in a covalent bond, one or more pairs of valence electrons are shared by two atoms : the resulting electrically neutral group of bonded atoms is termed a molecule. atoms will share valence electrons in such a way as to create a noble gas electron configuration ( eight electrons in their outermost shell ) for each atom. atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. however, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration ; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium, which has two electrons in its outer shell. similarly, theories from classical physics can be used to predict many ionic structures. with more complicated compounds, such as metal complexes to explain molecular structure and composition. an ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non - metal atom, becoming a negatively charged anion. the two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them. for example, sodium ( na ), a metal, loses one electron to become an na + cation while chlorine ( cl ), a non - metal, gains this electron to become cl−. the ions are held together due to electrostatic attraction, and that compound sodium chloride ( nacl ), or common table salt, is formed. in a covalent bond, one or more pairs of valence electrons are shared by two atoms : the resulting electrically neutral group of bonded atoms is termed a molecule. atoms will share valence electrons in such a way as to create a noble gas electron configuration ( eight electrons in their outermost shell ) for each atom. atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. however, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration ; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium, which has two electrons in its outer shell. similarly, theories from classical physics can be used to predict many ionic structures. with more complicated compounds, such as metal complexes, valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. = = = energy = = = in the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of set of chemical reactions with other substances. however, this definition only works well for substances that are composed of molecules, which is not true of many substances ( see below ). molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs. thus, molecules exist as electrically neutral units, unlike ions. when this rule is broken, giving the " molecule " a charge, the result is sometimes named a molecular ion or a polyatomic ion. however, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. the united rest mass and charge of a particle correspond to the two forms of the same regularity of the unified nature of its ultimate structure. each of them contains the electric, weak, strong and the gravitational contributions. as a consequence, the force of an attraction among the two neutrinos and force of their repulsion must be defined from the point of view of any of the existing types of the actions. therefore, to understand the nature of the micro world interaction at the fundamental level, one must use the fact that each of the four types of well known forces includes both a kind of the newton and a kind of the coulomb components. the opinion has been spoken that the existence of the gravitational parts of the united rest mass and charge would imply the availability of such a fifth force which come forwards in the system as a unified whole. of substances dissolved in aqueous solution ( that is, in water ). less familiar phases include plasmas, bose – einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. while most familiar phases deal with three - dimensional systems, it is also possible to define analogs in two - dimensional systems, which has received attention for its relevance to systems in biology. = = = bonding = = = atoms sticking together in molecules or crystals are said to be bonded with one another. a chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them. more than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom. the chemical bond can be a covalent bond, an ionic bond, a hydrogen bond or just because of van der waals force. each of these kinds of bonds is ascribed to some potential. these potentials create the interactions which hold atoms together in molecules or crystals. in many simple compounds, valence bond theory, the valence shell electron pair repulsion model ( vsepr ), and the concept of oxidation number can be used to explain molecular structure and composition. an ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non - metal atom, becoming a negatively charged anion. the two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them. for example, sodium ( na ), a metal, loses one electron to become an na + cation while chlorine ( cl ), a non - metal, gains this electron to become cl−. the ions are held together due to electrostatic attraction, and that compound sodium chloride ( nacl ), or common table salt, is formed. in a covalent bond, one or more pairs of valence electrons are shared by two atoms : the resulting electrically neutral group of bonded atoms is termed a molecule. atoms will share valence electrons in such a way as to create a noble gas electron configuration ( eight electrons in their outermost shell ) for each atom. atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. however, some elements like hydrogen and lithium need only two electrons in their outermost shell to examples are given of the usefulness of electrons in interaction with nuclei for probing fundamental interactions and structure , the oxygen atom has a slight negative charge and the two hydrogen atoms have a slight positive charge. this polar property of water allows it to attract other water molecules via hydrogen bonds, which makes water cohesive. surface tension results from the cohesive force due to the attraction between molecules at the surface of the liquid. water is also adhesive as it is able to adhere to the surface of any polar or charged non - water molecules. water is denser as a liquid than it is as a solid ( or ice ). this unique property of water allows ice to float above liquid water such as ponds, lakes, and oceans, thereby insulating the liquid below from the cold air above. water has the capacity to absorb energy, giving it a higher specific heat capacity than other solvents such as ethanol. thus, a large amount of energy is needed to break the hydrogen bonds between water molecules to convert liquid water into water vapor. as a molecule, water is not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again. in pure water, the number of hydrogen ions balances ( or equals ) the number of hydroxyl ions, resulting in a ph that is neutral. = = = organic compounds = = = organic compounds are molecules that contain carbon bonded to another element such as hydrogen. with the exception of water, nearly all the molecules that make up each organism contain carbon. carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules. for example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six Question: What type of bonds are the attractive forces between the positively charged nuclei of the bonded atoms and one or more pairs of electrons that are located between the atoms? A) covalent B) active C) reactive D) gravitational	A) covalent
Context: remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the infestation of insects and rodents, contributing to the spread of diseases. some of the most common types of solid waste management include ; landfills, vermicomposting, composting, recycling, and incineration. however, a major barrier for solid waste management practices is the high costs associated with recycling and the risks of creating more pollution. = = = e - waste recycling = = = the recycling of electronic waste ( e - waste ) has seen significant technological advancements due to increasing environmental concerns and the growing volume of electronic product disposals. traditional e - waste recycling methods, which often involve manual disassemb = = = = = = environmental remediation = = = environmental remediation is the process through which contaminants or pollutants in soil, water and other media are removed to improve environmental quality. the main focus is the reduction of hazardous substances within the environment. some of the areas involved in environmental remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the infestation of insects and rodents, contributing to the spread of diseases. some of the most common types of solid waste management include ; landfills, vermicomposting, composting, recycling, and incineration. however, a major barrier for solid waste management practices is the high costs associated with recycling ##nts from the air to reduce the potential adverse effects on humans and the environment. the process of air purification may be performed using methods such as mechanical filtration, ionization, activated carbon adsorption, photocatalytic oxidation, and ultraviolet light germicidal irradiation. = = = sewage treatment = = = = = = environmental remediation = = = environmental remediation is the process through which contaminants or pollutants in soil, water and other media are removed to improve environmental quality. the main focus is the reduction of hazardous substances within the environment. some of the areas involved in environmental remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the ) of the mass of all organisms, with calcium, phosphorus, sulfur, sodium, chlorine, and magnesium constituting essentially all the remainder. different elements can combine to form compounds such as water, which is fundamental to life. biochemistry is the study of chemical processes within and relating to living organisms. molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including molecular synthesis, modification, mechanisms, and interactions. = = = water = = = life arose from the earth ' s first ocean, which formed some 3. 8 billion years ago. since then, water continues to be the most abundant molecule in every organism. water is important to life because it is an effective solvent, capable of dissolving solutes such as sodium and chloride ions or other small molecules to form an aqueous solution. once dissolved in water, these solutes are more likely to come in contact with one another and therefore take part in chemical reactions that sustain life. in terms of its molecular structure, water is a small polar molecule with a bent shape formed by the polar covalent bonds of two hydrogen ( h ) atoms to one oxygen ( o ) atom ( h2o ). because the o – h bonds are polar, the oxygen atom has a slight negative charge and the two hydrogen atoms have a slight positive charge. this polar property of water allows it to attract other water molecules via hydrogen bonds, which makes water cohesive. surface tension results from the cohesive force due to the attraction between molecules at the surface of the liquid. water is also adhesive as it is able to adhere to the surface of any polar or charged non - water molecules. water is denser as a liquid than it is as a solid ( or ice ). this unique property of water allows ice to float above liquid water such as ponds, lakes, and oceans, thereby insulating the liquid below from the cold air above. water has the capacity to absorb energy, giving it a higher specific heat capacity than other solvents such as ethanol. thus, a large amount of energy is needed to break the hydrogen bonds between water molecules to convert liquid water into water vapor. as a molecule, water is not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again. in pure water, the number of hydrogen ions balances ( or equals ) the number of hydroxyl ions, resulting in a ph that is neutral. = = = organic compounds = ". = = extraction = = extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted raw metals into a purer form. in order to convert a metal oxide or sulphide to a purer metal, the ore must be reduced physically, chemically, or electrolytically. extractive metallurgists are interested in three primary streams : feed, concentrate ( metal oxide / sulphide ) and tailings ( waste ). after mining, large pieces of the ore feed are broken through crushing or grinding in order to obtain particles small enough, where each particle is either mostly valuable or mostly waste. concentrating the particles of value in a form supporting separation enables the desired metal to be removed from waste products. mining may not be necessary, if the ore body and physical environment are conducive to leaching. leaching dissolves minerals in an ore body and results in an enriched solution. the solution is collected and processed to extract valuable metals. ore bodies often contain more than one valuable metal. tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. additionally, a concentrate may contain more than one valuable metal. that concentrate would then be processed to separate the valuable metals into individual constituents. = = metal and its alloys = = much effort has been placed on understanding iron – carbon alloy system, which includes steels and cast irons. plain carbon steels ( those that contain essentially only carbon as an alloying element ) are used in low - cost, high - strength applications, where neither weight nor corrosion are a major concern. cast irons, including ductile iron, are also part of the iron - carbon system. iron - manganese - chromium alloys ( hadfield - type steels ) are also used in non - magnetic applications such as directional drilling. other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. these metals are most often used as alloys with the noted exception of silicon, which is not a metal. other forms include : stainless steel, particularly austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important. aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications. copper - nickel alloys ( such as monel ) are used in highly corrosive environments and for non - magnetic applications chemistry is the scientific study of the properties and behavior of matter. it is a physical science within the natural sciences that studies the chemical elements that make up matter and compounds made of atoms, molecules and ions : their composition, structure, properties, behavior and the changes they undergo during reactions with other substances. chemistry also addresses the nature of chemical bonds in chemical compounds. in the scope of its subject, chemistry occupies an intermediate position between physics and biology. it is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. for example, chemistry explains aspects of plant growth ( botany ), the formation of igneous rocks ( geology ), how atmospheric ozone is formed and how environmental pollutants are degraded ( ecology ), the properties of the soil on the moon ( cosmochemistry ), how medications work ( pharmacology ), and how to collect dna evidence at a crime scene ( forensics ). chemistry has existed under various names since ancient times. it has evolved, and now chemistry encompasses various areas of specialisation, or subdisciplines, that continue to increase in number and interrelate to create further interdisciplinary fields of study. the applications of various fields of chemistry are used frequently for economic purposes in the chemical industry. = = etymology = = the word chemistry comes from a modification during the renaissance of the word alchemy, which referred to an earlier set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism, and medicine. alchemy is often associated with the quest to turn lead or other base metals into gold, though alchemists were also interested in many of the questions of modern chemistry. the modern word alchemy in turn is derived from the arabic word al - kimia ( الكیمیاء ). this may have egyptian origins since al - kimia is derived from the ancient greek χημια, which is in turn derived from the word kemet, which is the ancient name of egypt in the egyptian language. alternately, al - kimia may derive from χημεια ' cast together '. = = modern principles = = the current model of atomic structure is the quantum mechanical model. traditional chemistry starts with the study of elementary particles, atoms, molecules, substances, metals, crystals and other aggregates of matter. matter can be studied in solid, liquid, gas and plasma states, in isolation or in combination. the interactions, reactions and transformations that . oxidation, reduction, dissociation, acid – base neutralization and molecular rearrangement are some examples of common chemical reactions. a chemical reaction can be symbolically depicted through a chemical equation. while in a non - nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons. the sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. a chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. several empirical rules, like the woodward – hoffmann rules often come in handy while proposing a mechanism for a chemical reaction. according to the iupac gold book, a chemical reaction is " a process that results in the interconversion of chemical species. " accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction. an additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities ( i. e. ' microscopic chemical events ' ). = = = ions and salts = = = an ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. when an atom loses an electron and thus has more protons than electrons, the atom is a positively charged ion or cation. when an atom gains an electron and thus has more electrons than protons, the atom is a negatively charged ion or anion. cations and anions can form a crystalline lattice of neutral salts, such as the na + and cl− ions forming sodium chloride, or nacl. examples of polyatomic ions that do not split up during acid – base reactions are hydroxide ( oh− ) and phosphate ( po43− ). plasma is composed of gaseous matter that has been completely ionized, usually through high temperature. = = = acidity and basicity = = = a substance can often be onset of electro - chemical corrosion. similar problems are encountered in coastal and offshore structures. = = = anti - fouling = = = anti - fouling is the process of eliminating obstructive organisms from essential components of seawater systems. depending on the nature and location of marine growth, this process is performed in a number of different ways : marine organisms may grow and attach to the surfaces of the outboard suction inlets used to obtain water for cooling systems. electro - chlorination involves running high electrical current through sea water, altering the water ' s chemical composition to create sodium hypochlorite, purging any bio - matter. an electrolytic method of anti - fouling involves running electrical current through two anodes ( scardino, 2009 ). these anodes typically consist of copper and aluminum ( or alternatively, iron ). the first metal, copper anode, releases its ion into the water, creating an environment that is too toxic for bio - matter. the second metal, aluminum, coats the inside of the pipes to prevent corrosion. other forms of marine growth such as mussels and algae may attach themselves to the bottom of a ship ' s hull. this growth interferes with the smoothness and uniformity of the ship ' s hull, causing the ship to have a less hydrodynamic shape that causes it to be slower and less fuel - efficient. marine growth on the hull can be remedied by using special paint that prevents the growth of such organisms. = = = pollution control = = = = = = = sulfur emission = = = = the burning of marine fuels releases harmful pollutants into the atmosphere. ships burn marine diesel in addition to heavy fuel oil. heavy fuel oil, being the heaviest of refined oils, releases sulfur dioxide when burned. sulfur dioxide emissions have the potential to raise atmospheric and ocean acidity causing harm to marine life. however, heavy fuel oil may only be burned in international waters due to the pollution created. it is commercially advantageous due to the cost effectiveness compared to other marine fuels. it is prospected that heavy fuel oil will be phased out of commercial use by the year 2020 ( smith, 2018 ). = = = = oil and water discharge = = = = water, oil, and other substances collect at the bottom of the ship in what is known as the bilge. bilge water is pumped overboard, but must pass a pollution threshold test of 15 ppm ( parts per million ) of oil to be discharged. water is tested the article describes what constitutes chemical engineering and its branches are in plain language. it outlines what to expect when one enrolls in a chemical engineering program as an undergraduate or graduate student. this may include core subjects to take, skillset to master, and other essential expertise that might be useful in the workplace. the discussion continues with career options for enthusiastic chemical engineers and how these young and early careers graduates could discover their reason for well - being and life purpose as aspiring chemical engineers. energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. different kinds of spectra are often used in chemical spectroscopy, e. g. ir, microwave, nmr, esr, etc. spectroscopy is also used to identify the composition of remote objects – like stars and distant galaxies – by analyzing their radiation spectra. the term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. = = = reaction = = = when a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. a chemical reaction is therefore a concept related to the " reaction " of a substance when it comes in close contact with another, whether as a mixture or a solution ; exposure to some form of energy, or both. it results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels — often laboratory glassware. chemical reactions can result in the formation or dissociation of molecules, that is, molecules breaking apart to form two or more molecules or rearrangement of atoms within or across molecules. chemical reactions usually involve the making or breaking of chemical bonds. oxidation, reduction, dissociation, acid – base neutralization and molecular rearrangement are some examples of common chemical reactions. a chemical reaction can be symbolically depicted through a chemical equation. while in a non - nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons. the sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. a chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. several empirical rules, like the woodward – hoffmann rules often come in handy while proposing a mechanism for a chemical reaction. according to the iupac gold book, a chemical reaction is " a process that results in the interconversion of chemical species. " accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction. Question: Chemical elements and water are constantly recycled in the ecosystem through what? A) greenhouse gases B) inorganic cycles C) geothermal cycles D) biogeochemical cycles	D) biogeochemical cycles
Context: the operating room, the anesthesiology physician also serves the same function in the labor and delivery ward, and some are specialized in critical medicine. emergency medicine is concerned with the diagnosis and treatment of acute or life - threatening conditions, including trauma, surgical, medical, pediatric, and psychiatric emergencies. family medicine, family practice, general practice or primary care is, in many countries, the first port - of - call for patients with non - emergency medical problems. family physicians often provide services across a broad range of settings including office based practices, emergency department coverage, inpatient care, and nursing home care. medical genetics is concerned with the diagnosis and management of hereditary disorders. neurology is concerned with diseases of the nervous system. in the uk, neurology is a subspecialty of general medicine. obstetrics and gynecology ( often abbreviated as ob / gyn ( american english ) or obs & gynae ( british english ) ) are concerned respectively with childbirth and the female reproductive and associated organs. reproductive medicine and fertility medicine are generally practiced by gynecological specialists. pediatrics ( ae ) or paediatrics ( be ) is devoted to the care of infants, children, and adolescents. like internal medicine, there are many pediatric subspecialties for specific age ranges, organ systems, disease classes, and sites of care delivery. pharmaceutical medicine is the medical scientific discipline concerned with the discovery, development, evaluation, registration, monitoring and medical aspects of marketing of medicines for the benefit of patients and public health. physical medicine and rehabilitation ( or physiatry ) is concerned with functional improvement after injury, illness, or congenital disorders. podiatric medicine is the study of, diagnosis, and medical and surgical treatment of disorders of the foot, ankle, lower limb, hip and lower back. preventive medicine is the branch of medicine concerned with preventing disease. community health or public health is an aspect of health services concerned with threats to the overall health of a community based on population health analysis. psychiatry is the branch of medicine concerned with the bio - psycho - social study of the etiology, diagnosis, treatment and prevention of cognitive, perceptual, emotional and behavioral disorders. related fields include psychotherapy and clinical psychology. = = = interdisciplinary fields = = = some interdisciplinary sub - specialties of medicine include : addiction medicine deals with the treatment of addiction. aerospace medicine deals with medical problems related to flying and space travel. biomedical engineering is a field dealing with the application of engineering principles to medical practice listing of diseases in the family that may impact the patient. a family tree is sometimes used. history of present illness ( hpi ) : the chronological order of events of symptoms and further clarification of each symptom. distinguishable from history of previous illness, often called past medical history ( pmh ). medical history comprises hpi and pmh. medications ( rx ) : what drugs the patient takes including prescribed, over - the - counter, and home remedies, as well as alternative and herbal medicines or remedies. allergies are also recorded. past medical history ( pmh / pmhx ) : concurrent medical problems, past hospitalizations and operations, injuries, past infectious diseases or vaccinations, history of known allergies. review of systems ( ros ) or systems inquiry : a set of additional questions to ask, which may be missed on hpi : a general enquiry ( have you noticed any weight loss, change in sleep quality, fevers, lumps and bumps? etc. ), followed by questions on the body ' s main organ systems ( heart, lungs, digestive tract, urinary tract, etc. ). social history ( sh ) : birthplace, residences, marital history, social and economic status, habits ( including diet, medications, tobacco, alcohol ). the physical examination is the examination of the patient for medical signs of disease that are objective and observable, in contrast to symptoms that are volunteered by the patient and are not necessarily objectively observable. the healthcare provider uses sight, hearing, touch, and sometimes smell ( e. g., in infection, uremia, diabetic ketoacidosis ). four actions are the basis of physical examination : inspection, palpation ( feel ), percussion ( tap to determine resonance characteristics ), and auscultation ( listen ), generally in that order, although auscultation occurs prior to percussion and palpation for abdominal assessments. the clinical examination involves the study of : abdomen and rectum cardiovascular ( heart and blood vessels ) general appearance of the patient and specific indicators of disease ( nutritional status, presence of jaundice, pallor or clubbing ) genitalia ( and pregnancy if the patient is or could be pregnant ) head, eye, ear, nose, and throat ( heent ) musculoskeletal ( including spine and extremities ) neurological ( consciousness, awareness, brain, vision, cranial nerves, ##ry. immunology is the study of the immune system, which includes the innate and adaptive immune system in humans, for example. lifestyle medicine is the study of the chronic conditions, and how to prevent, treat and reverse them. medical physics is the study of the applications of physics principles in medicine. microbiology is the study of microorganisms, including protozoa, bacteria, fungi, and viruses. molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic material. neuroscience includes those disciplines of science that are related to the study of the nervous system. a main focus of neuroscience is the biology and physiology of the human brain and spinal cord. some related clinical specialties include neurology, neurosurgery and psychiatry. nutrition science ( theoretical focus ) and dietetics ( practical focus ) is the study of the relationship of food and drink to health and disease, especially in determining an optimal diet. medical nutrition therapy is done by dietitians and is prescribed for diabetes, cardiovascular diseases, weight and eating disorders, allergies, malnutrition, and neoplastic diseases. pathology as a science is the study of disease – the causes, course, progression and resolution thereof. pharmacology is the study of drugs and their actions. photobiology is the study of the interactions between non - ionizing radiation and living organisms. physiology is the study of the normal functioning of the body and the underlying regulatory mechanisms. radiobiology is the study of the interactions between ionizing radiation and living organisms. toxicology is the study of hazardous effects of drugs and poisons. = = = specialties = = = in the broadest meaning of " medicine ", there are many different specialties. in the uk, most specialities have their own body or college, which has its own entrance examination. these are collectively known as the royal colleges, although not all currently use the term " royal ". the development of a speciality is often driven by new technology ( such as the development of effective anaesthetics ) or ways of working ( such as emergency departments ) ; the new specialty leads to the formation of a unifying body of doctors and the prestige of administering their own examination. within medical circles, specialities usually fit into one of two broad categories : " medicine " and " surgery ". " medicine " refers to the practice of non - operative medicine, and most of its subspecialties require preliminary training in internal medicine. in the uk any two generating systems of the fundamental group of a closed surface are nielsen equivalent. ( or underlined when italics are not available ). the evolutionary relationships and heredity of a group of organisms is called its phylogeny. phylogenetic studies attempt to discover phylogenies. the basic approach is to use similarities based on shared inheritance to determine relationships. as an example, species of pereskia are trees or bushes with prominent leaves. they do not obviously resemble a typical leafless cactus such as an echinocactus. however, both pereskia and echinocactus have spines produced from areoles ( highly specialised pad - like structures ) suggesting that the two genera are indeed related. judging relationships based on shared characters requires care, since plants may resemble one another through convergent evolution in which characters have arisen independently. some euphorbias have leafless, rounded bodies adapted to water conservation similar to those of globular cacti, but characters such as the structure of their flowers make it clear that the two groups are not closely related. the cladistic method takes a systematic approach to characters, distinguishing between those that carry no information about shared evolutionary history – such as those evolved separately in different groups ( homoplasies ) or those left over from ancestors ( plesiomorphies ) – and derived characters, which have been passed down from innovations in a shared ancestor ( apomorphies ). only derived characters, such as the spine - producing areoles of cacti, provide evidence for descent from a common ancestor. the results of cladistic analyses are expressed as cladograms : tree - like diagrams showing the pattern of evolutionary branching and descent. from the 1990s onwards, the predominant approach to constructing phylogenies for living plants has been molecular phylogenetics, which uses molecular characters, particularly dna sequences, rather than morphological characters like the presence or absence of spines and areoles. the difference is that the genetic code itself is used to decide evolutionary relationships, instead of being used indirectly via the characters it gives rise to. clive stace describes this as having " direct access to the genetic basis of evolution. " as a simple example, prior to the use of genetic evidence, fungi were thought either to be plants or to be more closely related to plants than animals. genetic evidence suggests that the true evolutionary relationship of multicelled organisms is as shown in the cladogram below – fungi are more closely related to animals than to plants. in 1998, the angiosperm phylogeny group published a phylogeny for flowering plants based on an analysis of we reply to david ' s comment ( hep - lat / 9504017 ) on our paper phys. rev. lett. 74 ( 1995 ) 1920. this is erratum of the paper [ phys. rev. lett. { \ bf 84 }, 4260 ( 2000 ) ] the thickness of freshly made soap films is usually in the micron range, and interference colors make thickness fluctuations easily visible. circular patterns of constant thickness are commonly observed, either a thin film disc in a thicker film or the reverse. in this letter, we evidence the line tension at the origin of these circular patterns. using a well controlled soap film preparation, we produce a piece of thin film surrounded by a thicker film. the thickness profile, measured with a spectral camera, leads to a line tension of the order of 0. 1 nn which drives the relaxation of the thin film shape, initially very elongated, toward a circular shape. a balance between line tension and air friction leads to a quantitative prediction of the relaxation process. such a line tension is expected to play a role in the production of marginal regeneration patches, involved in soap film drainage and stability. and management. diving medicine ( or hyperbaric medicine ) is the prevention and treatment of diving - related problems. evolutionary medicine is a perspective on medicine derived through applying evolutionary theory. forensic medicine deals with medical questions in legal context, such as determination of the time and cause of death, type of weapon used to inflict trauma, reconstruction of the facial features using remains of deceased ( skull ) thus aiding identification. gender - based medicine studies the biological and physiological differences between the human sexes and how that affects differences in disease. health informatics is a relatively recent field that deal with the application of computers and information technology to medicine. hospice and palliative medicine is a relatively modern branch of clinical medicine that deals with pain and symptom relief and emotional support in patients with terminal illnesses including cancer and heart failure. hospital medicine is the general medical care of hospitalized patients. physicians whose primary professional focus is hospital medicine are called hospitalists in the united states and canada. the term most responsible physician ( mrp ) or attending physician is also used interchangeably to describe this role. laser medicine involves the use of lasers in the diagnostics or treatment of various conditions. many other health science fields, e. g. dietetics medical ethics deals with ethical and moral principles that apply values and judgments to the practice of medicine. medical humanities includes the humanities ( literature, philosophy, ethics, history and religion ), social science ( anthropology, cultural studies, psychology, sociology ), and the arts ( literature, theater, film, and visual arts ) and their application to medical education and practice. nosokinetics is the science / subject of measuring and modelling the process of care in health and social care systems. nosology is the classification of diseases for various purposes. occupational medicine is the provision of health advice to organizations and individuals to ensure that the highest standards of health and safety at work can be achieved and maintained. pain management ( also called pain medicine, or algiatry ) is the medical discipline concerned with the relief of pain. pharmacogenomics is a form of individualized medicine. podiatric medicine is the study of, diagnosis, and medical treatment of disorders of the foot, ankle, lower limb, hip and lower back. sexual medicine is concerned with diagnosing, assessing and treating all disorders related to sexuality. sports medicine deals with the treatment and prevention and rehabilitation of sports / exercise injuries such as muscle spasms, muscle tears, injuries to ligaments ( ligament tears or ruptures ) and their repair in athletes, amateur and professional. be used at high latitudes because of terrestrial interference. cordless phone – a landline telephone in which the handset is portable and communicates with the rest of the phone by a short - range full duplex radio link, instead of being attached by a cord. both the handset and the base station have low - power radio transceivers that handle the short - range bidirectional radio link. as of 2022, cordless phones in most nations use the dect transmission standard. land mobile radio system – short - range mobile or portable half - duplex radio transceivers operating in the vhf or uhf band that can be used without a license. they are often installed in vehicles, with the mobile units communicating with a dispatcher at a fixed base station. special systems with reserved frequencies are used by first responder services ; police, fire, ambulance, and emergency services, and other government services. other systems are made for use by commercial firms such as taxi and delivery services. vhf systems use channels in the range 30 – 50 mhz and 150 – 172 mhz. uhf systems use the 450 – 470 mhz band and in some areas the 470 – 512 mhz range. in general, vhf systems have a longer range than uhf but require longer antennas. am or fm modulation is mainly used, but digital systems such as dmr are being introduced. the radiated power is typically limited to 4 watts. these systems have a fairly limited range, usually 3 to 20 miles ( 4. 8 to 32 km ) depending on terrain. repeaters installed on tall buildings, hills, or mountain peaks are often used to increase the range when it is desired to cover a larger area than line - of - sight. examples of land mobile systems are cb, frs, gmrs, and murs. modern digital systems, called trunked radio systems, have a digital channel management system using a control channel that automatically assigns frequency channels to user groups. walkie - talkie – a battery - powered portable handheld half - duplex two - way radio, used in land mobile radio systems. airband – half - duplex radio system used by aircraft pilots to talk to other aircraft and ground - based air traffic controllers. this vital system is the main communication channel for air traffic control. for most communication in overland flights in air corridors a vhf - am system using channels between 108 and 137 mhz in the vhf band is used. this system has a typical transmission range of 200 miles ( 320 km ) for aircraft flying at cruising altitude. for flights in more Question: What system is the spinal cord related to? A) nervous system B) circulatory system C) digestive system D) lymphatic system	A) nervous system
Context: oscillations of the sun have been used to understand its interior structure. the extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the international community over the past decades. the corot ( convection rotation and planetary transits ) satellite, launched in december 2006, has now measured oscillations and the stellar granulation signature in three main sequence stars that are noticeably hotter than the sun. the oscillation amplitudes are about 1. 5 times as large as those in the sun ; the stellar granulation is up to three times as high. the stellar amplitudes are about 25 % below the theoretic values, providing a measurement of the nonadiabaticity of the process ruling the oscillations in the outer layers of the stars. a rail gun launching at 9 mj of energy would need roughly 32 mj worth of energy from capacitors. current advances in energy storage allow for energy densities as high as 2. 5 mj / dm3, which means that a battery delivering 32 mj of energy would require a volume of 12. 8 dm3 per shot ; this is not a viable volume for use in a modern main battle tank, especially one designed to be lighter than existing models. there has even been discussion about eliminating the necessity for an outside electrical source in etc ignition by initiating the plasma cartridge through a small explosive force. furthermore, etc technology is not only applicable to solid propellants. to increase muzzle velocity even further electrothermal - chemical ignition can work with liquid propellants, although this would require further research into plasma ignition. etc technology is also compatible with existing projects to reduce the amount of recoil delivered to the vehicle while firing. understandably, recoil of a gun firing a projectile at 17 mj or more will increase directly with the increase in muzzle energy in accordance to newton ' s third law of motion and successful implementation of recoil reduction mechanisms will be vital to the installation of an etc powered gun in an existing vehicle design. for example, oto melara ' s new lightweight 120 mm l / 45 gun has achieved a recoil force of 25 t by using a longer recoil mechanism ( 550 mm ) and a pepperpot muzzle brake. reduction in recoil can also be achieved through mass attenuation of the thermal sleeve. the ability of etc technology to be applied to existing gun designs means that for future gun upgrades there ' s no longer the necessity to redesign the turret to include a larger breech or caliber gun barrel. several countries have already determined that etc technology is viable for the future and have funded indigenous projects considerably. these include the united states, germany and the united kingdom, amongst others. the united states ' xm360, which was planned to equip the future combat systems mounted combat system light tank and may be the m1 abrams ' next gun upgrade, is reportedly based on the xm291 and may include etc technology, or portions of etc technology. tests of this gun have been performed using " precision ignition " technology, which may refer to etc ignition. = = notes = = = = bibliography = = = = external links = = electromagnetic launch symposium http : / / www. powerlabs. org / electrothermal. htm observed solar neutrino fluxes are employed to constrain the interior composition of the sun. including the effects of neutrino flavor mixing, the results from homestake, sudbury, and gallium experiments constrain the mg, si, and fe abundances in the solar interior to be within a factor 0. 89 to 1. 34 of the surface values with 68 % confidence. if the o and / or ne abundances are increased in the interior to resolve helioseismic discrepancies with recent standard solar models, then the nominal interior mg, si, and fe abundances are constrained to a range of 0. 83 to 1. 24 relative to the surface. additional research is needed to determine whether the sun ' s interior is metal poor relative to its surface. excess lightweight products of slow neutron capture in the photosphere, over the mass range of 25 to 207 amu, confirm the solar mass separation recorded by excess lightweight isotopes in the solar wind, over the mass range of 3 to 136 amu [ solar abundance of the elements, meteoritics, volume 18, 1983, pages 209 to 222 ]. both measurements show that major elements inside the sun are fe, o, ni, si and s, like those in rocky planets. etc technology is viable it does offer an example that it is possible. etc requires much less energy input from outside sources, like a battery, than a railgun or a coilgun would. tests have shown that energy output by the propellant is higher than energy input from outside sources on etc guns. in comparison, a railgun currently cannot achieve a higher muzzle velocity than the amount of energy input. even at 50 % efficiency a rail gun launching a projectile with a kinetic energy of 20 mj would require an energy input into the rails of 40 mj, and 50 % efficiency has not yet been achieved. to put this into perspective, a rail gun launching at 9 mj of energy would need roughly 32 mj worth of energy from capacitors. current advances in energy storage allow for energy densities as high as 2. 5 mj / dm3, which means that a battery delivering 32 mj of energy would require a volume of 12. 8 dm3 per shot ; this is not a viable volume for use in a modern main battle tank, especially one designed to be lighter than existing models. there has even been discussion about eliminating the necessity for an outside electrical source in etc ignition by initiating the plasma cartridge through a small explosive force. furthermore, etc technology is not only applicable to solid propellants. to increase muzzle velocity even further electrothermal - chemical ignition can work with liquid propellants, although this would require further research into plasma ignition. etc technology is also compatible with existing projects to reduce the amount of recoil delivered to the vehicle while firing. understandably, recoil of a gun firing a projectile at 17 mj or more will increase directly with the increase in muzzle energy in accordance to newton ' s third law of motion and successful implementation of recoil reduction mechanisms will be vital to the installation of an etc powered gun in an existing vehicle design. for example, oto melara ' s new lightweight 120 mm l / 45 gun has achieved a recoil force of 25 t by using a longer recoil mechanism ( 550 mm ) and a pepperpot muzzle brake. reduction in recoil can also be achieved through mass attenuation of the thermal sleeve. the ability of etc technology to be applied to existing gun designs means that for future gun upgrades there ' s no longer the necessity to redesign the turret to include a larger breech or caliber gun barrel. several countries have already determined that etc technology is viable for the future and have funded indigenous projects considerably. these include the united states, germany and the united kingdom, amongst others. the united the magnetic field of the sun is the underlying cause of the many diverse phenomena combined under the heading of solar activity. here we describe the magnetic field as it threads its way from the bottom of the convection zone, where it is built up by the solar dynamo, to the solar surface, where it manifests itself in the form of sunspots and faculae, and beyond into the outer solar atmosphere and, finally, into the heliosphere. on the way it, transports energy from the surface and the subsurface layers into the solar corona, where it heats the gas and accelerates the solar wind. 5 to 20 meters. north america and japan use a frequency of 315 mhz, while europe uses 433. 92 and 868 mhz. some models can also remotely start the engine, to warm up the car. a security concern with all keyless entry systems is a replay attack, in which a thief uses a special receiver ( " code grabber " ) to record the radio signal during opening, which can later be replayed to open the door. to prevent this, keyless systems use a rolling code system in which a pseudorandom number generator in the remote control generates a different random key each time it is used. to prevent thieves from simulating the pseudorandom generator to calculate the next key, the radio signal is also encrypted. garage door opener – a short - range handheld transmitter which can open or close a building ' s electrically operated garage door from outside, so the owner can open the door upon arrival, and close it after departure. when a button is pressed the control transmits a coded fsk radio signal to a receiver in the opener, raising or lowering the door. modern openers use 310, 315 or 390 mhz. to prevent a thief using a replay attack, modern openers use a rolling code system. radio - controlled models – a popular hobby is playing with radio - controlled model boats, cars, airplanes, and helicopters ( quadcopters ) which are controlled by radio signals from a handheld console with a joystick. most recent transmitters use the 2. 4 ghz ism band with multiple control channels modulated with pwm, pcm or fsk. wireless doorbell – a residential doorbell that uses wireless technology to eliminate the need to run wires through the building walls. it consists of a doorbell button beside the door containing a small battery powered transmitter. when the doorbell is pressed it sends a signal to a receiver inside the house with a speaker that sounds chimes to indicate someone is at the door. they usually use the 2. 4 ghz ism band. the frequency channel used can usually be changed by the owner in case another nearby doorbell is using the same channel. = = = = scientific research = = = = radio astronomy is the scientific study of radio waves emitted by astronomical objects. radio astronomers use radio telescopes, large radio antennas and receivers, to receive and study the radio waves from astronomical radio sources. since astronomical radio sources are so far away, the radio waves from them are extremely weak, requiring extremely sensitive receivers, and radio telescopes are the most sensitive radio receivers in existence. they use - power radio transceivers that handle the short - range bidirectional radio link. as of 2022, cordless phones in most nations use the dect transmission standard. land mobile radio system – short - range mobile or portable half - duplex radio transceivers operating in the vhf or uhf band that can be used without a license. they are often installed in vehicles, with the mobile units communicating with a dispatcher at a fixed base station. special systems with reserved frequencies are used by first responder services ; police, fire, ambulance, and emergency services, and other government services. other systems are made for use by commercial firms such as taxi and delivery services. vhf systems use channels in the range 30 – 50 mhz and 150 – 172 mhz. uhf systems use the 450 – 470 mhz band and in some areas the 470 – 512 mhz range. in general, vhf systems have a longer range than uhf but require longer antennas. am or fm modulation is mainly used, but digital systems such as dmr are being introduced. the radiated power is typically limited to 4 watts. these systems have a fairly limited range, usually 3 to 20 miles ( 4. 8 to 32 km ) depending on terrain. repeaters installed on tall buildings, hills, or mountain peaks are often used to increase the range when it is desired to cover a larger area than line - of - sight. examples of land mobile systems are cb, frs, gmrs, and murs. modern digital systems, called trunked radio systems, have a digital channel management system using a control channel that automatically assigns frequency channels to user groups. walkie - talkie – a battery - powered portable handheld half - duplex two - way radio, used in land mobile radio systems. airband – half - duplex radio system used by aircraft pilots to talk to other aircraft and ground - based air traffic controllers. this vital system is the main communication channel for air traffic control. for most communication in overland flights in air corridors a vhf - am system using channels between 108 and 137 mhz in the vhf band is used. this system has a typical transmission range of 200 miles ( 320 km ) for aircraft flying at cruising altitude. for flights in more remote areas, such as transoceanic airline flights, aircraft use the hf band or channels on the inmarsat or iridium satphone satellites. military aircraft also use a dedicated uhf - am band from 225. 0 to 399. 95 mhz. marine radio – medium - range transceivers on - parabolic antenna ( 15 db gain ) with a similarly equipped receiver at the far end might have a range over 32 km. higher gain rating ( dbi ) indicates further deviation ( generally toward the horizontal ) from a theoretical, perfect isotropic radiator, and therefore the antenna can project or accept a usable signal further in particular directions, as compared to a similar output power on a more isotropic antenna. for example, an 8 dbi antenna used with a 100 mw driver has a similar horizontal range to a 6 dbi antenna being driven at 500 mw. this assumes that radiation in the vertical is lost ; this may not be the case in some situations, especially in large buildings or within a waveguide. in the above example, a directional waveguide could cause the low - power 6 dbi antenna to project much further in a single direction than the 8 dbi antenna, which is not in a waveguide, even if they are both driven at 100 mw. on wireless routers with detachable antennas, it is possible to improve range by fitting upgraded antennas that provide a higher gain in particular directions. outdoor ranges can be improved to many kilometres through the use of high gain directional antennas at the router and remote device ( s ). = = = mimo ( multiple - input and multiple - output ) = = = wi - fi 4 and higher standards allow devices to have multiple antennas on transmitters and receivers. multiple antennas enable the equipment to exploit multipath propagation on the same frequency bands giving much higher speeds and longer range. wi - fi 4 can more than double the range over previous standards. the wi - fi 5 standard uses the 5 ghz band exclusively, and is capable of multi - station wlan throughput of at least 1 gigabit per second, and a single station throughput of at least 500 mbit / s. as of the first quarter of 2016, the wi - fi alliance certifies devices compliant with the 802. 11ac standard as " wi - fi certified ac ". this standard uses several signal processing techniques such as multi - user mimo and 4x4 spatial multiplexing streams, and wide channel bandwidth ( 160 mhz ) to achieve its gigabit throughput. according to a study by ihs technology, 70 % of all access point sales revenue in the first quarter of 2016 came from 802. 11ac devices. = = = radio propagation = = = with wi - fi signals line - of - sight usually works best, but signals can transmit, absorb, reflect, ref railgun currently cannot achieve a higher muzzle velocity than the amount of energy input. even at 50 % efficiency a rail gun launching a projectile with a kinetic energy of 20 mj would require an energy input into the rails of 40 mj, and 50 % efficiency has not yet been achieved. to put this into perspective, a rail gun launching at 9 mj of energy would need roughly 32 mj worth of energy from capacitors. current advances in energy storage allow for energy densities as high as 2. 5 mj / dm3, which means that a battery delivering 32 mj of energy would require a volume of 12. 8 dm3 per shot ; this is not a viable volume for use in a modern main battle tank, especially one designed to be lighter than existing models. there has even been discussion about eliminating the necessity for an outside electrical source in etc ignition by initiating the plasma cartridge through a small explosive force. furthermore, etc technology is not only applicable to solid propellants. to increase muzzle velocity even further electrothermal - chemical ignition can work with liquid propellants, although this would require further research into plasma ignition. etc technology is also compatible with existing projects to reduce the amount of recoil delivered to the vehicle while firing. understandably, recoil of a gun firing a projectile at 17 mj or more will increase directly with the increase in muzzle energy in accordance to newton ' s third law of motion and successful implementation of recoil reduction mechanisms will be vital to the installation of an etc powered gun in an existing vehicle design. for example, oto melara ' s new lightweight 120 mm l / 45 gun has achieved a recoil force of 25 t by using a longer recoil mechanism ( 550 mm ) and a pepperpot muzzle brake. reduction in recoil can also be achieved through mass attenuation of the thermal sleeve. the ability of etc technology to be applied to existing gun designs means that for future gun upgrades there ' s no longer the necessity to redesign the turret to include a larger breech or caliber gun barrel. several countries have already determined that etc technology is viable for the future and have funded indigenous projects considerably. these include the united states, germany and the united kingdom, amongst others. the united states ' xm360, which was planned to equip the future combat systems mounted combat system light tank and may be the m1 abrams ' next gun upgrade, is reportedly based on the xm291 and may include etc technology, or portions of etc technology. tests of this gun have been performed using " Question: What is the total range of the energy from the sun called? A) measured spectrum B) molecular spectrum C) solar spectrum D) electromagnetic spectrum	D) electromagnetic spectrum
Context: stems mainly provide support to the leaves and reproductive structures, but can store water in succulent plants such as cacti, food as in potato tubers, or reproduce vegetatively as in the stolons of strawberry plants or in the process of layering. leaves gather sunlight and carry out photosynthesis. large, flat, flexible, green leaves are called foliage leaves. gymnosperms, such as conifers, cycads, ginkgo, and gnetophytes are seed - producing plants with open seeds. angiosperms are seed - producing plants that produce flowers and have enclosed seeds. woody plants, such as azaleas and oaks, undergo a secondary growth phase resulting in two additional types of tissues : wood ( secondary xylem ) and bark ( secondary phloem and cork ). all gymnosperms and many angiosperms are woody plants. some plants reproduce sexually, some asexually, and some via both means. although reference to major morphological categories such as root, stem, leaf, and trichome are useful, one has to keep in mind that these categories are linked through intermediate forms so that a continuum between the categories results. furthermore, structures can be seen as processes, that is, process combinations. = = systematic botany = = systematic botany is part of systematic biology, which is concerned with the range and diversity of organisms and their relationships, particularly as determined by their evolutionary history. it involves, or is related to, biological classification, scientific taxonomy and phylogenetics. biological classification is the method by which botanists group organisms into categories such as genera or species. biological classification is a form of scientific taxonomy. modern taxonomy is rooted in the work of carl linnaeus, who grouped species according to shared physical characteristics. these groupings have since been revised to align better with the darwinian principle of common descent – grouping organisms by ancestry rather than superficial characteristics. while scientists do not always agree on how to classify organisms, molecular phylogenetics, which uses dna sequences as data, has driven many recent revisions along evolutionary lines and is likely to continue to do so. the dominant classification system is called linnaean taxonomy. it includes ranks and binomial nomenclature. the nomenclature of botanical organisms is codified in the international code of nomenclature for algae, fungi, and plants ( icn ) and administered by the international botanical congress. kingdom plantae belongs to domain eukaryota and is broken down recursively until each species is separately classified. the order is : and their competitive or mutualistic interactions with other species. some ecologists even rely on empirical data from indigenous people that is gathered by ethnobotanists. this information can relay a great deal of information on how the land once was thousands of years ago and how it has changed over that time. the goals of plant ecology are to understand the causes of their distribution patterns, productivity, environmental impact, evolution, and responses to environmental change. plants depend on certain edaphic ( soil ) and climatic factors in their environment but can modify these factors too. for example, they can change their environment ' s albedo, increase runoff interception, stabilise mineral soils and develop their organic content, and affect local temperature. plants compete with other organisms in their ecosystem for resources. they interact with their neighbours at a variety of spatial scales in groups, populations and communities that collectively constitute vegetation. regions with characteristic vegetation types and dominant plants as well as similar abiotic and biotic factors, climate, and geography make up biomes like tundra or tropical rainforest. herbivores eat plants, but plants can defend themselves and some species are parasitic or even carnivorous. other organisms form mutually beneficial relationships with plants. for example, mycorrhizal fungi and rhizobia provide plants with nutrients in exchange for food, ants are recruited by ant plants to provide protection, honey bees, bats and other animals pollinate flowers and humans and other animals act as dispersal vectors to spread spores and seeds. = = = plants, climate and environmental change = = = plant responses to climate and other environmental changes can inform our understanding of how these changes affect ecosystem function and productivity. for example, plant phenology can be a useful proxy for temperature in historical climatology, and the biological impact of climate change and global warming. palynology, the analysis of fossil pollen deposits in sediments from thousands or millions of years ago allows the reconstruction of past climates. estimates of atmospheric co2 concentrations since the palaeozoic have been obtained from stomatal densities and the leaf shapes and sizes of ancient land plants. ozone depletion can expose plants to higher levels of ultraviolet radiation - b ( uv - b ), resulting in lower growth rates. moreover, information from studies of community ecology, plant systematics, and taxonomy is essential to understanding vegetation change, habitat destruction and species extinction. = = genetics = = inheritance in plants follows the same fundamental principles of genetics as in other multicellular organisms. gregor mendel discovered the genetic laws of inheritance by studying inherited traits such as shape in pisum sativum ( peas ). what mendel learned from studying plants has had far - reaching benefits outside of botany. similarly, " jumping genes " were discovered by barbara mcclintock while she was studying maize. nevertheless, there are some distinctive genetic differences between plants and other organisms. species boundaries in plants may be weaker than in animals, and cross species hybrids are often possible. a familiar example is peppermint, mentha × piperita, a sterile hybrid between mentha aquatica and spearmint, mentha spicata. the many cultivated varieties of wheat are the result of multiple inter - and intra - specific crosses between wild species and their hybrids. angiosperms with monoecious flowers often have self - incompatibility mechanisms that operate between the pollen and stigma so that the pollen either fails to reach the stigma or fails to germinate and produce male gametes. this is one of several methods used by plants to promote outcrossing. in many land plants the male and female gametes are produced by separate individuals. these species are said to be dioecious when referring to vascular plant sporophytes and dioicous when referring to bryophyte gametophytes. charles darwin in his 1878 book the effects of cross and self - fertilization in the vegetable kingdom at the start of chapter xii noted " the first and most important of the conclusions which may be drawn from the observations given in this volume, is that generally cross - fertilisation is beneficial and self - fertilisation often injurious, at least with the plants on which i experimented. " an important adaptive benefit of outcrossing is that it allows the masking of deleterious mutations in the genome of progeny. this beneficial effect is also known as hybrid vigor or heterosis. once outcrossing is established, subsequent switching to inbreeding becomes disadvantageous since it allows expression of the previously masked deleterious recessive mutations, commonly referred to as inbreeding depression. unlike in higher animals, where parthenogenesis is rare, asexual reproduction may occur in plants by several different mechanisms. the formation of stem tubers in potato is one example. particularly in arctic or alpine habitats, where opportunities for fertilisation of flowers by animals are rare, plantlets or bulbs, may develop instead of flowers, replacing sexual reproduction with asexual reproduction and giving rise to clonal populations genetically identical to the parent. this is one plants, the liverworts, hornworts and mosses do not produce ground - penetrating vascular roots and most of the plant participates in photosynthesis. the sporophyte generation is nonphotosynthetic in liverworts but may be able to contribute part of its energy needs by photosynthesis in mosses and hornworts. the root system and the shoot system are interdependent – the usually nonphotosynthetic root system depends on the shoot system for food, and the usually photosynthetic shoot system depends on water and minerals from the root system. cells in each system are capable of creating cells of the other and producing adventitious shoots or roots. stolons and tubers are examples of shoots that can grow roots. roots that spread out close to the surface, such as those of willows, can produce shoots and ultimately new plants. in the event that one of the systems is lost, the other can often regrow it. in fact it is possible to grow an entire plant from a single leaf, as is the case with plants in streptocarpus sect. saintpaulia, or even a single cell – which can dedifferentiate into a callus ( a mass of unspecialised cells ) that can grow into a new plant. in vascular plants, the xylem and phloem are the conductive tissues that transport resources between shoots and roots. roots are often adapted to store food such as sugars or starch, as in sugar beets and carrots. stems mainly provide support to the leaves and reproductive structures, but can store water in succulent plants such as cacti, food as in potato tubers, or reproduce vegetatively as in the stolons of strawberry plants or in the process of layering. leaves gather sunlight and carry out photosynthesis. large, flat, flexible, green leaves are called foliage leaves. gymnosperms, such as conifers, cycads, ginkgo, and gnetophytes are seed - producing plants with open seeds. angiosperms are seed - producing plants that produce flowers and have enclosed seeds. woody plants, such as azaleas and oaks, undergo a secondary growth phase resulting in two additional types of tissues : wood ( secondary xylem ) and bark ( secondary phloem and cork ). all gymnosperms and many angiosperms are woody plants. some plants reproduce sexually, unspecialised cells ) that can grow into a new plant. in vascular plants, the xylem and phloem are the conductive tissues that transport resources between shoots and roots. roots are often adapted to store food such as sugars or starch, as in sugar beets and carrots. stems mainly provide support to the leaves and reproductive structures, but can store water in succulent plants such as cacti, food as in potato tubers, or reproduce vegetatively as in the stolons of strawberry plants or in the process of layering. leaves gather sunlight and carry out photosynthesis. large, flat, flexible, green leaves are called foliage leaves. gymnosperms, such as conifers, cycads, ginkgo, and gnetophytes are seed - producing plants with open seeds. angiosperms are seed - producing plants that produce flowers and have enclosed seeds. woody plants, such as azaleas and oaks, undergo a secondary growth phase resulting in two additional types of tissues : wood ( secondary xylem ) and bark ( secondary phloem and cork ). all gymnosperms and many angiosperms are woody plants. some plants reproduce sexually, some asexually, and some via both means. although reference to major morphological categories such as root, stem, leaf, and trichome are useful, one has to keep in mind that these categories are linked through intermediate forms so that a continuum between the categories results. furthermore, structures can be seen as processes, that is, process combinations. = = systematic botany = = systematic botany is part of systematic biology, which is concerned with the range and diversity of organisms and their relationships, particularly as determined by their evolutionary history. it involves, or is related to, biological classification, scientific taxonomy and phylogenetics. biological classification is the method by which botanists group organisms into categories such as genera or species. biological classification is a form of scientific taxonomy. modern taxonomy is rooted in the work of carl linnaeus, who grouped species according to shared physical characteristics. these groupings have since been revised to align better with the darwinian principle of common descent – grouping organisms by ancestry rather than superficial characteristics. while scientists do not always agree on how to classify organisms, molecular phylogenetics, which uses dna sequences as data, has driven many recent revisions along evolutionary lines and is likely to continue to do so. the dominant classification system is called linnaean taxonomy. it includes ranks and binomi , the other can often regrow it. in fact it is possible to grow an entire plant from a single leaf, as is the case with plants in streptocarpus sect. saintpaulia, or even a single cell – which can dedifferentiate into a callus ( a mass of unspecialised cells ) that can grow into a new plant. in vascular plants, the xylem and phloem are the conductive tissues that transport resources between shoots and roots. roots are often adapted to store food such as sugars or starch, as in sugar beets and carrots. stems mainly provide support to the leaves and reproductive structures, but can store water in succulent plants such as cacti, food as in potato tubers, or reproduce vegetatively as in the stolons of strawberry plants or in the process of layering. leaves gather sunlight and carry out photosynthesis. large, flat, flexible, green leaves are called foliage leaves. gymnosperms, such as conifers, cycads, ginkgo, and gnetophytes are seed - producing plants with open seeds. angiosperms are seed - producing plants that produce flowers and have enclosed seeds. woody plants, such as azaleas and oaks, undergo a secondary growth phase resulting in two additional types of tissues : wood ( secondary xylem ) and bark ( secondary phloem and cork ). all gymnosperms and many angiosperms are woody plants. some plants reproduce sexually, some asexually, and some via both means. although reference to major morphological categories such as root, stem, leaf, and trichome are useful, one has to keep in mind that these categories are linked through intermediate forms so that a continuum between the categories results. furthermore, structures can be seen as processes, that is, process combinations. = = systematic botany = = systematic botany is part of systematic biology, which is concerned with the range and diversity of organisms and their relationships, particularly as determined by their evolutionary history. it involves, or is related to, biological classification, scientific taxonomy and phylogenetics. biological classification is the method by which botanists group organisms into categories such as genera or species. biological classification is a form of scientific taxonomy. modern taxonomy is rooted in the work of carl linnaeus, who grouped species according to shared physical characteristics. these groupings have since been revised to align better with the darwinian principle of common descent – grouping organisms . species boundaries in plants may be weaker than in animals, and cross species hybrids are often possible. a familiar example is peppermint, mentha × piperita, a sterile hybrid between mentha aquatica and spearmint, mentha spicata. the many cultivated varieties of wheat are the result of multiple inter - and intra - specific crosses between wild species and their hybrids. angiosperms with monoecious flowers often have self - incompatibility mechanisms that operate between the pollen and stigma so that the pollen either fails to reach the stigma or fails to germinate and produce male gametes. this is one of several methods used by plants to promote outcrossing. in many land plants the male and female gametes are produced by separate individuals. these species are said to be dioecious when referring to vascular plant sporophytes and dioicous when referring to bryophyte gametophytes. charles darwin in his 1878 book the effects of cross and self - fertilization in the vegetable kingdom at the start of chapter xii noted " the first and most important of the conclusions which may be drawn from the observations given in this volume, is that generally cross - fertilisation is beneficial and self - fertilisation often injurious, at least with the plants on which i experimented. " an important adaptive benefit of outcrossing is that it allows the masking of deleterious mutations in the genome of progeny. this beneficial effect is also known as hybrid vigor or heterosis. once outcrossing is established, subsequent switching to inbreeding becomes disadvantageous since it allows expression of the previously masked deleterious recessive mutations, commonly referred to as inbreeding depression. unlike in higher animals, where parthenogenesis is rare, asexual reproduction may occur in plants by several different mechanisms. the formation of stem tubers in potato is one example. particularly in arctic or alpine habitats, where opportunities for fertilisation of flowers by animals are rare, plantlets or bulbs, may develop instead of flowers, replacing sexual reproduction with asexual reproduction and giving rise to clonal populations genetically identical to the parent. this is one of several types of apomixis that occur in plants. apomixis can also happen in a seed, producing a seed that contains an embryo genetically identical to the parent. most sexually reproducing organisms are diploid, with paired chromosomes, but doubling of their chromosome number may occur due to errors in of creating cells of the other and producing adventitious shoots or roots. stolons and tubers are examples of shoots that can grow roots. roots that spread out close to the surface, such as those of willows, can produce shoots and ultimately new plants. in the event that one of the systems is lost, the other can often regrow it. in fact it is possible to grow an entire plant from a single leaf, as is the case with plants in streptocarpus sect. saintpaulia, or even a single cell – which can dedifferentiate into a callus ( a mass of unspecialised cells ) that can grow into a new plant. in vascular plants, the xylem and phloem are the conductive tissues that transport resources between shoots and roots. roots are often adapted to store food such as sugars or starch, as in sugar beets and carrots. stems mainly provide support to the leaves and reproductive structures, but can store water in succulent plants such as cacti, food as in potato tubers, or reproduce vegetatively as in the stolons of strawberry plants or in the process of layering. leaves gather sunlight and carry out photosynthesis. large, flat, flexible, green leaves are called foliage leaves. gymnosperms, such as conifers, cycads, ginkgo, and gnetophytes are seed - producing plants with open seeds. angiosperms are seed - producing plants that produce flowers and have enclosed seeds. woody plants, such as azaleas and oaks, undergo a secondary growth phase resulting in two additional types of tissues : wood ( secondary xylem ) and bark ( secondary phloem and cork ). all gymnosperms and many angiosperms are woody plants. some plants reproduce sexually, some asexually, and some via both means. although reference to major morphological categories such as root, stem, leaf, and trichome are useful, one has to keep in mind that these categories are linked through intermediate forms so that a continuum between the categories results. furthermore, structures can be seen as processes, that is, process combinations. = = systematic botany = = systematic botany is part of systematic biology, which is concerned with the range and diversity of organisms and their relationships, particularly as determined by their evolutionary history. it involves, or is related to, biological classification, scientific taxonomy and phylogenetics. biological classification is the method plant cells and tissues, whereas plant morphology is the study of their external form. all plants are multicellular eukaryotes, their dna stored in nuclei. the characteristic features of plant cells that distinguish them from those of animals and fungi include a primary cell wall composed of the polysaccharides cellulose, hemicellulose and pectin, larger vacuoles than in animal cells and the presence of plastids with unique photosynthetic and biosynthetic functions as in the chloroplasts. other plastids contain storage products such as starch ( amyloplasts ) or lipids ( elaioplasts ). uniquely, streptophyte cells and those of the green algal order trentepohliales divide by construction of a phragmoplast as a template for building a cell plate late in cell division. the bodies of vascular plants including clubmosses, ferns and seed plants ( gymnosperms and angiosperms ) generally have aerial and subterranean subsystems. the shoots consist of stems bearing green photosynthesising leaves and reproductive structures. the underground vascularised roots bear root hairs at their tips and generally lack chlorophyll. non - vascular plants, the liverworts, hornworts and mosses do not produce ground - penetrating vascular roots and most of the plant participates in photosynthesis. the sporophyte generation is nonphotosynthetic in liverworts but may be able to contribute part of its energy needs by photosynthesis in mosses and hornworts. the root system and the shoot system are interdependent – the usually nonphotosynthetic root system depends on the shoot system for food, and the usually photosynthetic shoot system depends on water and minerals from the root system. cells in each system are capable of creating cells of the other and producing adventitious shoots or roots. stolons and tubers are examples of shoots that can grow roots. roots that spread out close to the surface, such as those of willows, can produce shoots and ultimately new plants. in the event that one of the systems is lost, the other can often regrow it. in fact it is possible to grow an entire plant from a single leaf, as is the case with plants in streptocarpus sect. saintpaulia, or even a single cell – which can dedifferentiate into a callus ( a mass of in mosses and hornworts. the root system and the shoot system are interdependent – the usually nonphotosynthetic root system depends on the shoot system for food, and the usually photosynthetic shoot system depends on water and minerals from the root system. cells in each system are capable of creating cells of the other and producing adventitious shoots or roots. stolons and tubers are examples of shoots that can grow roots. roots that spread out close to the surface, such as those of willows, can produce shoots and ultimately new plants. in the event that one of the systems is lost, the other can often regrow it. in fact it is possible to grow an entire plant from a single leaf, as is the case with plants in streptocarpus sect. saintpaulia, or even a single cell – which can dedifferentiate into a callus ( a mass of unspecialised cells ) that can grow into a new plant. in vascular plants, the xylem and phloem are the conductive tissues that transport resources between shoots and roots. roots are often adapted to store food such as sugars or starch, as in sugar beets and carrots. stems mainly provide support to the leaves and reproductive structures, but can store water in succulent plants such as cacti, food as in potato tubers, or reproduce vegetatively as in the stolons of strawberry plants or in the process of layering. leaves gather sunlight and carry out photosynthesis. large, flat, flexible, green leaves are called foliage leaves. gymnosperms, such as conifers, cycads, ginkgo, and gnetophytes are seed - producing plants with open seeds. angiosperms are seed - producing plants that produce flowers and have enclosed seeds. woody plants, such as azaleas and oaks, undergo a secondary growth phase resulting in two additional types of tissues : wood ( secondary xylem ) and bark ( secondary phloem and cork ). all gymnosperms and many angiosperms are woody plants. some plants reproduce sexually, some asexually, and some via both means. although reference to major morphological categories such as root, stem, leaf, and trichome are useful, one has to keep in mind that these categories are linked through intermediate forms so that a continuum between the categories results. furthermore, structures can be seen as processes, Question: Plants have specialized organs that help them survive and reproduce in a great diversity of habitats. major organs of most plants include roots, stems, and what? A) clusters B) lungs C) leaves D) sacs	C) leaves
Context: the following purposes : allowing cell attachment and migration, delivering and retaining cells and biochemical factors, enabling diffusion of vital cell nutrients and expressed products, and exerting certain mechanical and biological influences to modify the behaviour of the cell phase. in 2009, an interdisciplinary team led by the thoracic surgeon thorsten walles implanted the first bioartificial transplant that provides an innate vascular network for post - transplant graft supply successfully into a patient awaiting tracheal reconstruction. to achieve the goal of tissue reconstruction, scaffolds must meet some specific requirements. high porosity and adequate pore size are necessary to facilitate cell seeding and diffusion throughout the whole structure of both cells and nutrients. biodegradability is often an essential factor since scaffolds should preferably be absorbed by the surrounding tissues without the necessity of surgical removal. the rate at which degradation occurs has to coincide as much as possible with the rate of tissue formation : this means that while cells are fabricating their own natural matrix structure around themselves, the scaffold is able to provide structural integrity within the body and eventually it will break down leaving the newly formed tissue which will take over the mechanical load. injectability is also important for clinical uses. recent research on organ printing is showing how crucial a good control of the 3d environment is to ensure reproducibility of experiments and offer better results. = = = materials = = = material selection is an essential aspect of producing a scaffold. the materials utilized can be natural or synthetic and can be biodegradable or non - biodegradable. additionally, they must be biocompatible, meaning that they do not cause any adverse effects to cells. silicone, for example, is a synthetic, non - biodegradable material commonly used as a drug delivery material, while gelatin is a biodegradable, natural material commonly used in cell - culture scaffolds the material needed for each application is different, and dependent on the desired mechanical properties of the material. tissue engineering of long bone defects for example, will require a rigid scaffold with a compressive strength similar to that of cortical bone ( 100 - 150 mpa ), which is much higher compared to a scaffold for skin regeneration. there are a few versatile synthetic materials used for many different scaffold applications. one of these commonly used materials is polylactic acid ( pla ), a synthetic polymer. pla – polylactic acid. this is a polyester which medical purposes. cells are often ' seeded ' into these structures capable of supporting three - dimensional tissue formation. scaffolds mimic the extracellular matrix of the native tissue, recapitulating the in vivo milieu and allowing cells to influence their own microenvironments. they usually serve at least one of the following purposes : allowing cell attachment and migration, delivering and retaining cells and biochemical factors, enabling diffusion of vital cell nutrients and expressed products, and exerting certain mechanical and biological influences to modify the behaviour of the cell phase. in 2009, an interdisciplinary team led by the thoracic surgeon thorsten walles implanted the first bioartificial transplant that provides an innate vascular network for post - transplant graft supply successfully into a patient awaiting tracheal reconstruction. to achieve the goal of tissue reconstruction, scaffolds must meet some specific requirements. high porosity and adequate pore size are necessary to facilitate cell seeding and diffusion throughout the whole structure of both cells and nutrients. biodegradability is often an essential factor since scaffolds should preferably be absorbed by the surrounding tissues without the necessity of surgical removal. the rate at which degradation occurs has to coincide as much as possible with the rate of tissue formation : this means that while cells are fabricating their own natural matrix structure around themselves, the scaffold is able to provide structural integrity within the body and eventually it will break down leaving the newly formed tissue which will take over the mechanical load. injectability is also important for clinical uses. recent research on organ printing is showing how crucial a good control of the 3d environment is to ensure reproducibility of experiments and offer better results. = = = materials = = = material selection is an essential aspect of producing a scaffold. the materials utilized can be natural or synthetic and can be biodegradable or non - biodegradable. additionally, they must be biocompatible, meaning that they do not cause any adverse effects to cells. silicone, for example, is a synthetic, non - biodegradable material commonly used as a drug delivery material, while gelatin is a biodegradable, natural material commonly used in cell - culture scaffolds the material needed for each application is different, and dependent on the desired mechanical properties of the material. tissue engineering of long bone defects for example, will require a rigid scaffold with a compressive strength similar to that of cortical bone ( 100 - 150 mpa ), listen ), generally in that order, although auscultation occurs prior to percussion and palpation for abdominal assessments. the clinical examination involves the study of : abdomen and rectum cardiovascular ( heart and blood vessels ) general appearance of the patient and specific indicators of disease ( nutritional status, presence of jaundice, pallor or clubbing ) genitalia ( and pregnancy if the patient is or could be pregnant ) head, eye, ear, nose, and throat ( heent ) musculoskeletal ( including spine and extremities ) neurological ( consciousness, awareness, brain, vision, cranial nerves, spinal cord and peripheral nerves ) psychiatric ( orientation, mental state, mood, evidence of abnormal perception or thought ). respiratory ( large airways and lungs ) skin vital signs including height, weight, body temperature, blood pressure, pulse, respiration rate, and hemoglobin oxygen saturation it is to likely focus on areas of interest highlighted in the medical history and may not include everything listed above. the treatment plan may include ordering additional medical laboratory tests and medical imaging studies, starting therapy, referral to a specialist, or watchful observation. a follow - up may be advised. depending upon the health insurance plan and the managed care system, various forms of " utilization review ", such as prior authorization of tests, may place barriers on accessing expensive services. the medical decision - making ( mdm ) process includes the analysis and synthesis of all the above data to come up with a list of possible diagnoses ( the differential diagnoses ), along with an idea of what needs to be done to obtain a definitive diagnosis that would explain the patient ' s problem. on subsequent visits, the process may be repeated in an abbreviated manner to obtain any new history, symptoms, physical findings, lab or imaging results, or specialist consultations. = = institutions = = contemporary medicine is, in general, conducted within health care systems. legal, credentialing, and financing frameworks are established by individual governments, augmented on occasion by international organizations, such as churches. the characteristics of any given health care system have a significant impact on the way medical care is provided. from ancient times, christian emphasis on practical charity gave rise to the development of systematic nursing and hospitals, and the catholic church today remains the largest non - government provider of medical services in the world. advanced industrial countries ( with the exception of the united states ) and many developing countries provide medical services through a system of universal health care that aims to the boron buckyball avoids the high symmetry icosahedral cage structure. the previously reported ih symmetric structure is not an energy minimum in the potential energy surface and exhibits a spontaneous symmetry breaking to yield a puckered cage with a rare th symmetry. the homo - lumo gap is twice as large as the reported value and amounts to 1. 94 ev at b3lyp / 6 - 31g ( d ) level. the valence orbital structure of boron buckyball is identical to the one in the carbon analogue. it is shown that von neumann uniqueness theorem doesn ' t hold in hyperbolic quantum mechanics the clinical symptoms of pulmonary embolism ( pe ) are very diverse and non - specific, which makes it difficult to diagnose. in addition, pulmonary embolism has multiple triggers and is one of the major causes of vascular death. therefore, if it can be detected and treated quickly, it can significantly reduce the risk of death in hospitalized patients. in the detection process, the cost of computed tomography pulmonary angiography ( ctpa ) is high, and angiography requires the injection of contrast agents, which increase the risk of damage to the patient. therefore, this study will use a deep learning approach to detect pulmonary embolism in all patients who take a ct image of the chest using a convolutional neural network. with the proposed pulmonary embolism detection system, we can detect the possibility of pulmonary embolism at the same time as the patient ' s first ct image, and schedule the ctpa test immediately, saving more than a week of ct image screening time and providing timely diagnosis and treatment to the patient. the experimental study of spiral - 2 high intensity radiofrequency cooler prototype ( shirac ) is the goal of this paper. some properties of the nuclear matter as revealed by cherenkov gluons are discussed. the flow of a gas through porous medium is considered in the case of pressure dependent permeability. approximate self - similar solutions of the boundary - value problems are found. the muck tube. the pressurized air flow must be constant to ensure regular air changes for the workers and prevent excessive inflow of mud or water at the base of the caisson. when the caisson hits bedrock, the sandhogs exit through the airlock and fill the box with concrete, forming a solid foundation pier. a pneumatic ( compressed - air ) caisson has the advantage of providing dry working conditions, which is better for placing concrete. it is also well suited for foundations for which other methods might cause settlement of adjacent structures. construction workers who leave the pressurized environment of the caisson must decompress at a rate that allows symptom - free release of inert gases dissolved in the body tissues if they are to avoid decompression sickness, a condition first identified in caisson workers, and originally named " caisson disease " in recognition of the occupational hazard. construction of the brooklyn bridge, which was built with the help of pressurised caissons, resulted in numerous workers being either killed or permanently injured by caisson disease during its construction. barotrauma of the ears, sinus cavities and lungs and dysbaric osteonecrosis are other risks. = = other uses = = caissons have also been used in the installation of hydraulic elevators where a single - stage ram is installed below the ground level. caissons, codenamed phoenix, were an integral part of the mulberry harbours used during the world war ii allied invasion of normandy. = = other meanings = = boat lift caissons : the word caisson is also used as a synonym for the moving trough part of caisson locks, canal lifts and inclines in which boats and ships rest while being lifted from one canal elevation to another ; the water is retained on the inside of the caisson, or excluded from the caisson, according to the respective operating principle. structural caissons : caisson is also sometimes used as a colloquial term for a reinforced concrete structure formed by pouring into a hollow cylindrical form, typically by placing a caisson form below grade in an open excavation and pouring once backfill is complete, or by drilling at grade, although this can be problematic with deep caissons, as unsupported excavations can collapse before the caisson form can be inserted. in this manner, the earth placed around the empty caisson form provides stability and strength, allowing concrete to be poured with fewer complications and with less risk of a Question: The lungs of mammals are unique in having what? A) alveoli B) alveolar C) glands D) acini	A) alveoli
Context: english ) ) are concerned respectively with childbirth and the female reproductive and associated organs. reproductive medicine and fertility medicine are generally practiced by gynecological specialists. pediatrics ( ae ) or paediatrics ( be ) is devoted to the care of infants, children, and adolescents. like internal medicine, there are many pediatric subspecialties for specific age ranges, organ systems, disease classes, and sites of care delivery. pharmaceutical medicine is the medical scientific discipline concerned with the discovery, development, evaluation, registration, monitoring and medical aspects of marketing of medicines for the benefit of patients and public health. physical medicine and rehabilitation ( or physiatry ) is concerned with functional improvement after injury, illness, or congenital disorders. podiatric medicine is the study of, diagnosis, and medical and surgical treatment of disorders of the foot, ankle, lower limb, hip and lower back. preventive medicine is the branch of medicine concerned with preventing disease. community health or public health is an aspect of health services concerned with threats to the overall health of a community based on population health analysis. psychiatry is the branch of medicine concerned with the bio - psycho - social study of the etiology, diagnosis, treatment and prevention of cognitive, perceptual, emotional and behavioral disorders. related fields include psychotherapy and clinical psychology. = = = interdisciplinary fields = = = some interdisciplinary sub - specialties of medicine include : addiction medicine deals with the treatment of addiction. aerospace medicine deals with medical problems related to flying and space travel. biomedical engineering is a field dealing with the application of engineering principles to medical practice. clinical pharmacology is concerned with how systems of therapeutics interact with patients. conservation medicine studies the relationship between human and non - human animal health, and environmental conditions. also known as ecological medicine, environmental medicine, or medical geology. disaster medicine deals with medical aspects of emergency preparedness, disaster mitigation and management. diving medicine ( or hyperbaric medicine ) is the prevention and treatment of diving - related problems. evolutionary medicine is a perspective on medicine derived through applying evolutionary theory. forensic medicine deals with medical questions in legal context, such as determination of the time and cause of death, type of weapon used to inflict trauma, reconstruction of the facial features using remains of deceased ( skull ) thus aiding identification. gender - based medicine studies the biological and physiological differences between the human sexes and how that affects differences in disease. health informatics is a relatively recent field that deal with the application of computers and information technology to medicine. hospice and pal ##tase, human chorionic gonadotrophin, α - fetoprotein and others are organ - associated antigens and the production of monoclonal antibodies against these antigens helps in determining the nature of a primary tumor. monoclonal antibodies are especially useful in distinguishing morphologically similar lesions, like pleural and peritoneal mesothelioma, adenocarcinoma, and in the determination of the organ or tissue origin of undifferentiated metastases. selected monoclonal antibodies help in the detection of occult metastases ( cancer of unknown primary origin ) by immuno - cytological analysis of bone marrow, other tissue aspirates, as well as lymph nodes and other tissues and can have increased sensitivity over normal histopathological staining. one study performed a sensitive immuno - histochemical assay on bone marrow aspirates of 20 patients with localized prostate cancer. three monoclonal antibodies ( t16, c26, and ae - 1 ), capable of recognizing membrane and cytoskeletal antigens expressed by epithelial cells to detect tumour cells, were used in the assay. bone marrow aspirates of 22 % of patients with localized prostate cancer ( stage b, 0 / 5 ; stage c, 2 / 4 ), and 36 % patients with metastatic prostate cancer ( stage d1, 0 / 7 patients ; stage d2, 4 / 4 patients ) had antigen - positive cells in their bone marrow. it was concluded that immuno - histochemical staining of bone marrow aspirates are very useful to detect occult bone marrow metastases in patients with apparently localized prostate cancer. although immuno - cytochemistry using tumor - associated monoclonal antibodies has led to an improved ability to detect occult breast cancer cells in bone marrow aspirates and peripheral blood, further development of this method is necessary before it can be used routinely. one major drawback of immuno - cytochemistry is that only tumor - associated and not tumor - specific monoclonal antibodies are used, and as a result, some cross - reaction with normal cells can occur. in order to effectively stage breast cancer and assess the efficacy of purging regimens prior to autologous stem cell infusion, it is important to detect even small quantities of breast cancer cells. immuno - histochemical methods are ideal for this purpose because they are simple, sensitive, and quite specific the hun tian theory ), or as being without substance while the heavenly bodies float freely ( the hsuan yeh theory ), the earth was at all times flat, although perhaps bulging up slightly. the model of an egg was often used by chinese astronomers such as zhang heng ( 78 – 139 ad ) to describe the heavens as spherical : the heavens are like a hen ' s egg and as round as a crossbow bullet ; the earth is like the yolk of the egg, and lies in the centre. this analogy with a curved egg led some modern historians, notably joseph needham, to conjecture that chinese astronomers were, after all, aware of the earth ' s sphericity. the egg reference, however, was rather meant to clarify the relative position of the flat earth to the heavens : in a passage of zhang heng ' s cosmogony not translated by needham, zhang himself says : " heaven takes its body from the yang, so it is round and in motion. earth takes its body from the yin, so it is flat and quiescent ". the point of the egg analogy is simply to stress that the earth is completely enclosed by heaven, rather than merely covered from above as the kai tian describes. chinese astronomers, many of them brilliant men by any standards, continued to think in flat - earth terms until the seventeenth century ; this surprising fact might be the starting - point for a re - examination of the apparent facility with which the idea of a spherical earth found acceptance in fifth - century bc greece. further examples cited by needham supposed to demonstrate dissenting voices from the ancient chinese consensus actually refer without exception to the earth being square, not to it being flat. accordingly, the 13th - century scholar li ye, who argued that the movements of the round heaven would be hindered by a square earth, did not advocate a spherical earth, but rather that its edge should be rounded off so as to be circular. however, needham disagrees, affirming that li ye believed the earth to be spherical, similar in shape to the heavens but much smaller. this was preconceived by the 4th - century scholar yu xi, who argued for the infinity of outer space surrounding the earth and that the latter could be either square or round, in accordance to the shape of the heavens. when chinese geographers of the 17th century, influenced by european cartography and astronomy, showed the earth as a sphere that could be circumnavigated by sailing around the globe, they describe the heavens as spherical : the heavens are like a hen ' s egg and as round as a crossbow bullet ; the earth is like the yolk of the egg, and lies in the centre. this analogy with a curved egg led some modern historians, notably joseph needham, to conjecture that chinese astronomers were, after all, aware of the earth ' s sphericity. the egg reference, however, was rather meant to clarify the relative position of the flat earth to the heavens : in a passage of zhang heng ' s cosmogony not translated by needham, zhang himself says : " heaven takes its body from the yang, so it is round and in motion. earth takes its body from the yin, so it is flat and quiescent ". the point of the egg analogy is simply to stress that the earth is completely enclosed by heaven, rather than merely covered from above as the kai tian describes. chinese astronomers, many of them brilliant men by any standards, continued to think in flat - earth terms until the seventeenth century ; this surprising fact might be the starting - point for a re - examination of the apparent facility with which the idea of a spherical earth found acceptance in fifth - century bc greece. further examples cited by needham supposed to demonstrate dissenting voices from the ancient chinese consensus actually refer without exception to the earth being square, not to it being flat. accordingly, the 13th - century scholar li ye, who argued that the movements of the round heaven would be hindered by a square earth, did not advocate a spherical earth, but rather that its edge should be rounded off so as to be circular. however, needham disagrees, affirming that li ye believed the earth to be spherical, similar in shape to the heavens but much smaller. this was preconceived by the 4th - century scholar yu xi, who argued for the infinity of outer space surrounding the earth and that the latter could be either square or round, in accordance to the shape of the heavens. when chinese geographers of the 17th century, influenced by european cartography and astronomy, showed the earth as a sphere that could be circumnavigated by sailing around the globe, they did so with formulaic terminology previously used by zhang heng to describe the spherical shape of the sun and moon ( i. e. that they were as round as a crossbow bullet ). as noted in the book huainanzi, in the 2nd century bc, chinese astronomers effectively inverted eratosthenes ' calculation the specific isolation of particular types of cells. = = = in diagnostic histopathology = = = with the help of monoclonal antibodies, tissues and organs can be classified based on their expression of certain defined markers, which reflect tissue or cellular genesis. prostate specific antigen, placental alkaline phosphatase, human chorionic gonadotrophin, α - fetoprotein and others are organ - associated antigens and the production of monoclonal antibodies against these antigens helps in determining the nature of a primary tumor. monoclonal antibodies are especially useful in distinguishing morphologically similar lesions, like pleural and peritoneal mesothelioma, adenocarcinoma, and in the determination of the organ or tissue origin of undifferentiated metastases. selected monoclonal antibodies help in the detection of occult metastases ( cancer of unknown primary origin ) by immuno - cytological analysis of bone marrow, other tissue aspirates, as well as lymph nodes and other tissues and can have increased sensitivity over normal histopathological staining. one study performed a sensitive immuno - histochemical assay on bone marrow aspirates of 20 patients with localized prostate cancer. three monoclonal antibodies ( t16, c26, and ae - 1 ), capable of recognizing membrane and cytoskeletal antigens expressed by epithelial cells to detect tumour cells, were used in the assay. bone marrow aspirates of 22 % of patients with localized prostate cancer ( stage b, 0 / 5 ; stage c, 2 / 4 ), and 36 % patients with metastatic prostate cancer ( stage d1, 0 / 7 patients ; stage d2, 4 / 4 patients ) had antigen - positive cells in their bone marrow. it was concluded that immuno - histochemical staining of bone marrow aspirates are very useful to detect occult bone marrow metastases in patients with apparently localized prostate cancer. although immuno - cytochemistry using tumor - associated monoclonal antibodies has led to an improved ability to detect occult breast cancer cells in bone marrow aspirates and peripheral blood, further development of this method is necessary before it can be used routinely. one major drawback of immuno - cytochemistry is that only tumor - associated and not tumor - specific monoclonal antibodies are used, and as a result, some cross - reaction with normal cells can occur unitary recordings in freely - moving pulse weakly electric fish suggest spike timing encoding of electrosensory signals offended athenian audiences ; in this play, he speculated that the titular sorceress medea killed her own children, as opposed to their being killed by other corinthians after her departure. in historiography, what is now called speculative fiction has previously been termed historical invention, historical fiction, and similar names. these terms have been extensively applied in literary criticism to the works of william shakespeare. for example, in a midsummer night ' s dream, he places several characters from different locations and times into the fairyland of the fictional merovingian germanic sovereign oberon ; these characters include the athenian duke theseus, the amazonian queen hippolyta, the english fairy puck, and the roman god cupid. in mythography, the concept of speculative fiction has been termed mythopoesis or mythopoeia. this process involves the creative design and development of lore and mythology for works of fiction. the term ' s definition comes from use by j. r. r. tolkien ; his series of novels, the lord of the rings, shows an application of the process. themes common in mythopoeia, such as the supernatural, alternate history, and sexuality, continue to be explored in works produced in modern speculative fiction. speculative fiction in the general sense of hypothetical history, explanation, or ahistorical storytelling has been attributed to authors in ostensibly non - fiction modes since herodotus of halicarnassus ( fl. 5th century bce ) with his histories ; it was already both created and edited out by early encyclopedic writers such sima qian ( c. 145 or 135 bce – 86 bce ), author of shiji. these examples highlight a caveat — many works that are now viewed as speculative fiction long predated the labelling of the genre. in the broadest sense, the genre ' s concept does two things : it captures both conscious and unconscious aspects of human psychology in making sense of the world, and it responds to the world by creating imaginative, inventive, and artistic expressions. such expressions can contribute to practical societal progress through interpersonal influences ; social and cultural movements ; scientific research and advances ; and the philosophy of science. in english - language usage in arts and literature since the mid 20th century, the term speculative fiction has often been attributed to robert a. heinlein, who first used it in an editorial in the saturday evening post ( on 8 february 1947 ). in the article, heinlein used speculative fiction as a synonym for science fiction ; in ##fer the validity of a general statement from a number of specific instances or infer the truth of a theory from a series of successful tests. for example, a chicken observes that each morning the farmer comes and gives it food, for hundreds of days in a row. the chicken may therefore use inductive reasoning to infer that the farmer will bring food every morning. however, one morning, the farmer comes and kills the chicken. how is scientific reasoning more trustworthy than the chicken ' s reasoning? one approach is to acknowledge that induction cannot achieve certainty, but observing more instances of a general statement can at least make the general statement more probable. so the chicken would be right to conclude from all those mornings that it is likely the farmer will come with food again the next morning, even if it cannot be certain. however, there remain difficult questions about the process of interpreting any given evidence into a probability that the general statement is true. one way out of these particular difficulties is to declare that all beliefs about scientific theories are subjective, or personal, and correct reasoning is merely about how evidence should change one ' s subjective beliefs over time. some argue that what scientists do is not inductive reasoning at all but rather abductive reasoning, or inference to the best explanation. in this account, science is not about generalizing specific instances but rather about hypothesizing explanations for what is observed. as discussed in the previous section, it is not always clear what is meant by the " best explanation ". ockham ' s razor, which counsels choosing the simplest available explanation, thus plays an important role in some versions of this approach. to return to the example of the chicken, would it be simpler to suppose that the farmer cares about it and will continue taking care of it indefinitely or that the farmer is fattening it up for slaughter? philosophers have tried to make this heuristic principle more precise regarding theoretical parsimony or other measures. yet, although various measures of simplicity have been brought forward as potential candidates, it is generally accepted that there is no such thing as a theory - independent measure of simplicity. in other words, there appear to be as many different measures of simplicity as there are theories themselves, and the task of choosing between measures of simplicity appears to be every bit as problematic as the job of choosing between theories. nicholas maxwell has argued for some decades that unity rather than simplicity is the key non - empirical factor in influencing the choice of theory in science, persistent preference for unified theories in effect committing science to the the resulting entity is a genetically modified organism ( gmo ). the first gmo was a bacterium generated by herbert boyer and stanley cohen in 1973. rudolf jaenisch created the first gm animal when he inserted foreign dna into a mouse in 1974. the first company to focus on genetic engineering, genentech, was founded in 1976 and started the production of human proteins. genetically engineered human insulin was produced in 1978 and insulin - producing bacteria were commercialised in 1982. genetically modified food has been sold since 1994, with the release of the flavr savr tomato. the flavr savr was engineered to have a longer shelf life, but most current gm crops are modified to increase resistance to insects and herbicides. glofish, the first gmo designed as a pet, was sold in the united states in december 2003. in 2016 salmon modified with a growth hormone were sold. genetic engineering has been applied in numerous fields including research, medicine, industrial biotechnology and agriculture. in research, gmos are used to study gene function and expression through loss of function, gain of function, tracking and expression experiments. by knocking out genes responsible for certain conditions it is possible to create animal model organisms of human diseases. as well as producing hormones, vaccines and other drugs, genetic engineering has the potential to cure genetic diseases through gene therapy. chinese hamster ovary ( cho ) cells are used in industrial genetic engineering. additionally mrna vaccines are made through genetic engineering to prevent infections by viruses such as covid - 19. the same techniques that are used to produce drugs can also have industrial applications such as producing enzymes for laundry detergent, cheeses and other products. the rise of commercialised genetically modified crops has provided economic benefit to farmers in many different countries, but has also been the source of most of the controversy surrounding the technology. this has been present since its early use ; the first field trials were destroyed by anti - gm activists. although there is a scientific consensus that currently available food derived from gm crops poses no greater risk to human health than conventional food, critics consider gm food safety a leading concern. gene flow, impact on non - target organisms, control of the food supply and intellectual property rights have also been raised as potential issues. these concerns have led to the development of a regulatory framework, which started in 1975. it has led to an international treaty, the cartagena protocol on biosafety, that was adopted in 2000. individual countries have developed their own regulatory systems regarding gmos, with the most marked differences occurring between the been used for research, model animals and the production of agricultural or pharmaceutical products. the genetically modified animals include animals with genes knocked out, increased susceptibility to disease, hormones for extra growth and the ability to express proteins in their milk. = = = medicine = = = genetic engineering has many applications to medicine that include the manufacturing of drugs, creation of model animals that mimic human conditions and gene therapy. one of the earliest uses of genetic engineering was to mass - produce human insulin in bacteria. this application has now been applied to human growth hormones, follicle stimulating hormones ( for treating infertility ), human albumin, monoclonal antibodies, antihemophilic factors, vaccines and many other drugs. mouse hybridomas, cells fused together to create monoclonal antibodies, have been adapted through genetic engineering to create human monoclonal antibodies. genetically engineered viruses are being developed that can still confer immunity, but lack the infectious sequences. genetic engineering is also used to create animal models of human diseases. genetically modified mice are the most common genetically engineered animal model. they have been used to study and model cancer ( the oncomouse ), obesity, heart disease, diabetes, arthritis, substance abuse, anxiety, aging and parkinson disease. potential cures can be tested against these mouse models. gene therapy is the genetic engineering of humans, generally by replacing defective genes with effective ones. clinical research using somatic gene therapy has been conducted with several diseases, including x - linked scid, chronic lymphocytic leukemia ( cll ), and parkinson ' s disease. in 2012, alipogene tiparvovec became the first gene therapy treatment to be approved for clinical use. in 2015 a virus was used to insert a healthy gene into the skin cells of a boy suffering from a rare skin disease, epidermolysis bullosa, in order to grow, and then graft healthy skin onto 80 percent of the boy ' s body which was affected by the illness. germline gene therapy would result in any change being inheritable, which has raised concerns within the scientific community. in 2015, crispr was used to edit the dna of non - viable human embryos, leading scientists of major world academies to call for a moratorium on inheritable human genome edits. there are also concerns that the technology could be used not just for treatment, but for enhancement, modification or alteration of a human beings ' appearance, adaptability, intelligence, character or behavior. the distinction between cure and enhancement Question: The organs of female mammals that that produce eggs are called what? A) ovaries B) fallopian tubes C) testes D) Uterus	A) ovaries
Context: parts of australia have been privileged to see dazzling lights in the night sky as the aurora australis ( known as the southern lights ) puts on a show this year. aurorae are significant in australian indigenous astronomical traditions. aboriginal people associate aurorae with fire, death, blood, and omens, sharing many similarities with native american communities. observations of an ancient stellar stream provide the first evidence of a vanished population of extremely metal - poor stellar clusters. their remnants might reveal how the early assembly of the milky way proceeded. i give a brief history of astronomical observatories as an institution. this includes : 1 ) observatories in islam ; 2 ) china and india ; 3 ) early european observatories ; 4 ) the rise of national observatories ; 5 ) private ( amateur ) observatories ; 6 ) mountaintop observatories and the modern era. additional references, to material not cited in the version that will be published in the encyclopedia, are also given. star clusters can be found in galaxy mergers, not only in central regions, but also in the tidal debris. in both the eastern and western tidal tails of ngc 3256 there are dozens of young star clusters, confirmed by their blue colors and larger concentration index as compared to sources off of the tail. tidal tails of other galaxy pairs do not have such widespread cluster formation, indicating environmental influences on the process of star formation or the packaging of the stars. winds from agn and quasars will form large amounts of dust, as the cool gas in these winds passes through the ( pressure, temperature ) region where dust is formed in agb stars. conditions in the gas are benign to dust at these radii. as a result quasar winds may be a major source of dust at high redshifts, obviating a difficulty with current observations, and requiring far less dust to exist at early epochs. v735 sgr was known as an enigmatic star with rapid brightness variations. long - term ogle photometry, brightness measurements in infrared bands, and recently obtained moderate resolution spectrum from the 6. 5 - m magellan telescope show that this star is an active young stellar object of herbig ae / be type. i will discuss the presence of massive star clusters in starburst galaxies with an emphasis on low mass galaxies outside the local group. i will show that such galaxies, with respect to their mass and luminosity, may be very rich in young luminous clusters. there are a few different mechanisms that can cause white dwarf stars to vary in brightness, providing opportunities to probe the physics, structures, and formation of these compact stellar remnants. the observational characteristics of the three most common types of white dwarf variability are summarized : stellar pulsations, rotation, and ellipsoidal variations from tidal distortion in binary systems. stellar pulsations are emphasized as the most complex type of variability, which also has the greatest potential to reveal the conditions of white dwarf interiors. in the year 1598 philipp uffenbach published a printed diptych sundial, which is a forerunner of franz ritters horizantal sundial. uffenbach ' s sundial contains apart from the usual information on a sundial ascending signs of the zodiac, several brigthest stars, an almucantar and most important the oldest gnomonic world map known so far. the sundial is constructed for the polar height of 50 1 / 6 degrees, the height of frankfurt / main the town of his citizenship. planetary nebulae retain the signature of the nucleosynthesis and mixing events that occurred during the previous agb phase. observational signatures complement observations of agb and post - agb stars and their binary companions. the abundances of the elements heavier than iron such as kr and xe in planetary nebulae can be used to complement abundances of sr / y / zr and ba / la / ce in agb stars, respectively, to determine the operation of the slow neutron - capture process ( the s process ) in agb stars. additionally, observations of the rb abundance in type i planetary nebulae may allow us to infer the initial mass of the central star. several noble gas components present in meteoritic stardust silicon carbide ( sic ) grains are associated with implantation into the dust grains in the high - energy environment connected to the fast winds from the central stars during the planetary nebulae phase. Question: What do you call the patterns and groups of stars in the sky that ancient people observed and made stories about? A) asteroid fields B) constellations C) meteors D) planets	B) constellations
Context: factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. for example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. the existence of characteristic reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then oxidized into acetyl - coa by the pyruvate dehydrogenase complex, which also generates nadh and carbon dioxide. acetyl - coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. at the end of the cycle, the total yield from 1 glucose ( or 2 pyruvates ) is 6 nadh, 2 fadh2, and 2 atp molecules. finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from nadh and fadh2 that is coupled to the pumping of protons ( hydrogen ions ) across the inner mitochondrial membrane ( chemiosmosis ), which generates a proton motive force. energy . a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer , valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. = = = energy = = = in the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive not only is the bekenstein expression for the entropy of a black hole a convex function of the energy, rather than being a concave function as it must be, it predicts a final equilibrium temperature given by the harmonic mean. this violates the third law, and the principle of maximum work. the property that means are monotonically increasing functions of their argument underscores the error of transferring from temperature means to means in the internal energy when the energy is not a monotonically increasing function of temperature. whereas the former leads to an increase in entropy, the latter lead to a decrease in entropy thereby violating the second law. the internal energy cannot increase at a slower rate than the temperature itself. the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then it was the best of times ; it was the worst of times is the way dickens begins the tale of two cities. the line is appropriate to our time in particle physics. it is the best of times because we are in the midst of a revolution in understanding, the third to occur during my career. it is the worst of times because accelerator facilities are shutting down before new ones are opening, restricting the opportunity for experiments, and because of great uncertainty about future funding. my task today is to give you a view of the most important opportunities for our field under a scenario that is constrained by a tight budget. it is a time when we cannot afford the merely good, but must give first priority to the really important. Question: Each enzyme has an optimal what at which its reaction rate is greatest? A) temperature B) size C) precipitation D) weight	A) temperature
Context: . most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support ##yotic microorganisms. typically a few micrometers in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. bacteria were among the first life forms to appear on earth, and are present in most of its habitats. bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of the earth ' s crust. bacteria also live in symbiotic and parasitic relationships with plants and animals. most bacteria have not been characterised, and only about 27 percent of the bacterial phyla have species that can be grown in the laboratory. archaea constitute the other domain of prokaryotic cells and were initially classified as bacteria, receiving the name archaebacteria ( in the archaebacteria kingdom ), a term that has fallen out of use. archaeal cells have unique properties separating them from the other two domains, bacteria and eukaryota. archaea are further divided into multiple recognized phyla. archaea and bacteria are generally similar in size and shape, although a few archaea have very different shapes, such as the flat and square cells of haloquadratum walsbyi. despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably for the enzymes involved in transcription and translation. other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, including archaeols. archaea use more energy sources than eukaryotes : these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. salt - tolerant archaea ( the haloarchaea ) use sunlight as an energy source, and other species of archaea fix carbon, but unlike plants and cyanobacteria, no known species of archaea does both. archaea reproduce asexually by binary fission, fragmentation, or budding ; unlike bacteria, no known species of archaea form endospores. the first observed archaea were extremophiles, living in extreme environments, such as hot springs and salt lakes with no other organisms. improved molecular detection tools led to the discovery of archaea in almost every habitat, including soil, oceans, and marshlands. archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. archaea are a major part of earth ' s life. excavates, stramenopiles, plants, rhizarians, amoebozoans, fungi, and animals. five of these clades are collectively known as protists, which are mostly microscopic eukaryotic organisms that are not plants, fungi, or animals. while it is likely that protists share a common ancestor ( the last eukaryotic common ancestor ), protists by themselves do not constitute a separate clade as some protists may be more closely related to plants, fungi, or animals than they are to other protists. like groupings such as algae, invertebrates, or protozoans, the protist grouping is not a formal taxonomic group but is used for convenience. most protists are unicellular ; these are called microbial eukaryotes. plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom plantae, which would exclude fungi and some algae. plant cells were derived by endosymbiosis of a cyanobacterium into an early eukaryote about one billion years ago, which gave rise to chloroplasts. the first several clades that emerged following primary endosymbiosis were aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related. algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of plantae. unlike glaucophytes, the other algal clades such as red and green algae are multicellular. green algae comprise three major clades : chlorophytes, coleochaetophytes, and stoneworts. fungi are eukaryotes that digest foods outside their bodies, secreting digestive enzymes that break down large food molecules before absorbing them through their cell membranes. many fungi are also saprobes, feeding on dead organic matter, making them important decomposers in ecological systems. animals are multicellular eukaryotes. with few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. over 1. 5 million living animal species have been described — of which around 1 million are insects — but it has been estimated there are over 7 million waste, and the deep biosphere of the earth ' s crust. bacteria also live in symbiotic and parasitic relationships with plants and animals. most bacteria have not been characterised, and only about 27 percent of the bacterial phyla have species that can be grown in the laboratory. archaea constitute the other domain of prokaryotic cells and were initially classified as bacteria, receiving the name archaebacteria ( in the archaebacteria kingdom ), a term that has fallen out of use. archaeal cells have unique properties separating them from the other two domains, bacteria and eukaryota. archaea are further divided into multiple recognized phyla. archaea and bacteria are generally similar in size and shape, although a few archaea have very different shapes, such as the flat and square cells of haloquadratum walsbyi. despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably for the enzymes involved in transcription and translation. other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, including archaeols. archaea use more energy sources than eukaryotes : these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. salt - tolerant archaea ( the haloarchaea ) use sunlight as an energy source, and other species of archaea fix carbon, but unlike plants and cyanobacteria, no known species of archaea does both. archaea reproduce asexually by binary fission, fragmentation, or budding ; unlike bacteria, no known species of archaea form endospores. the first observed archaea were extremophiles, living in extreme environments, such as hot springs and salt lakes with no other organisms. improved molecular detection tools led to the discovery of archaea in almost every habitat, including soil, oceans, and marshlands. archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. archaea are a major part of earth ' s life. they are part of the microbiota of all organisms. in the human microbiome, they are important in the gut, mouth, and on the skin. their morphological, metabolic, and geographical diversity permits them to play multiple ecological roles : carbon fixation ; nitrogen cycling ; organic compound turnover ; and maintaining microbial likely that protists share a common ancestor ( the last eukaryotic common ancestor ), protists by themselves do not constitute a separate clade as some protists may be more closely related to plants, fungi, or animals than they are to other protists. like groupings such as algae, invertebrates, or protozoans, the protist grouping is not a formal taxonomic group but is used for convenience. most protists are unicellular ; these are called microbial eukaryotes. plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom plantae, which would exclude fungi and some algae. plant cells were derived by endosymbiosis of a cyanobacterium into an early eukaryote about one billion years ago, which gave rise to chloroplasts. the first several clades that emerged following primary endosymbiosis were aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related. algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of plantae. unlike glaucophytes, the other algal clades such as red and green algae are multicellular. green algae comprise three major clades : chlorophytes, coleochaetophytes, and stoneworts. fungi are eukaryotes that digest foods outside their bodies, secreting digestive enzymes that break down large food molecules before absorbing them through their cell membranes. many fungi are also saprobes, feeding on dead organic matter, making them important decomposers in ecological systems. animals are multicellular eukaryotes. with few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. over 1. 5 million living animal species have been described — of which around 1 million are insects — but it has been estimated there are over 7 million animal species in total. they have complex interactions with each other and their environments, forming intricate food webs. = = = viruses = = = viruses are submicroscopic infectious agents that replicate inside the cells of organisms. viruses infect all types of life forms, from animals and plants to microorganisms, ##ochondria and chloroplasts, both of which are now part of modern - day eukaryotic cells. the major lineages of eukaryotes diversified in the precambrian about 1. 5 billion years ago and can be classified into eight major clades : alveolates, excavates, stramenopiles, plants, rhizarians, amoebozoans, fungi, and animals. five of these clades are collectively known as protists, which are mostly microscopic eukaryotic organisms that are not plants, fungi, or animals. while it is likely that protists share a common ancestor ( the last eukaryotic common ancestor ), protists by themselves do not constitute a separate clade as some protists may be more closely related to plants, fungi, or animals than they are to other protists. like groupings such as algae, invertebrates, or protozoans, the protist grouping is not a formal taxonomic group but is used for convenience. most protists are unicellular ; these are called microbial eukaryotes. plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom plantae, which would exclude fungi and some algae. plant cells were derived by endosymbiosis of a cyanobacterium into an early eukaryote about one billion years ago, which gave rise to chloroplasts. the first several clades that emerged following primary endosymbiosis were aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related. algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of plantae. unlike glaucophytes, the other algal clades such as red and green algae are multicellular. green algae comprise three major clades : chlorophytes, coleochaetophytes, and stoneworts. fungi are eukaryotes that digest foods outside their bodies, secreting digestive enzymes that break down large food molecules before absorbing them through their cell membranes. many fungi are also saprobes, feeding on dead organic matter, making them important decomposers in ecological systems. animals are multicellular eukaryotes. with few exceptions, animals in this article i explain in detail a method for making small amounts of liquid oxygen in the classroom if there is no access to a cylinder of compressed oxygen gas. i also discuss two methods for identifying the fact that it is liquid oxygen as opposed to liquid nitrogen. symbiotic and syntrophic communities, for example. = = = eukaryotes = = = eukaryotes are hypothesized to have split from archaea, which was followed by their endosymbioses with bacteria ( or symbiogenesis ) that gave rise to mitochondria and chloroplasts, both of which are now part of modern - day eukaryotic cells. the major lineages of eukaryotes diversified in the precambrian about 1. 5 billion years ago and can be classified into eight major clades : alveolates, excavates, stramenopiles, plants, rhizarians, amoebozoans, fungi, and animals. five of these clades are collectively known as protists, which are mostly microscopic eukaryotic organisms that are not plants, fungi, or animals. while it is likely that protists share a common ancestor ( the last eukaryotic common ancestor ), protists by themselves do not constitute a separate clade as some protists may be more closely related to plants, fungi, or animals than they are to other protists. like groupings such as algae, invertebrates, or protozoans, the protist grouping is not a formal taxonomic group but is used for convenience. most protists are unicellular ; these are called microbial eukaryotes. plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom plantae, which would exclude fungi and some algae. plant cells were derived by endosymbiosis of a cyanobacterium into an early eukaryote about one billion years ago, which gave rise to chloroplasts. the first several clades that emerged following primary endosymbiosis were aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related. algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of plantae. unlike glaucophytes, the other algal clades such as red and green algae are multicellular. green algae comprise three major clades : chlorophytes, coleochaetophytes, and stoneworts. fungi are eukaryotes that the non - avian dinosaurs, mammals increased rapidly in size and diversity. such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. = = diversity = = = = = bacteria and archaea = = = bacteria are a type of cell that constitute a large domain of prokaryotic microorganisms. typically a few micrometers in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. bacteria were among the first life forms to appear on earth, and are present in most of its habitats. bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep biosphere of the earth ' s crust. bacteria also live in symbiotic and parasitic relationships with plants and animals. most bacteria have not been characterised, and only about 27 percent of the bacterial phyla have species that can be grown in the laboratory. archaea constitute the other domain of prokaryotic cells and were initially classified as bacteria, receiving the name archaebacteria ( in the archaebacteria kingdom ), a term that has fallen out of use. archaeal cells have unique properties separating them from the other two domains, bacteria and eukaryota. archaea are further divided into multiple recognized phyla. archaea and bacteria are generally similar in size and shape, although a few archaea have very different shapes, such as the flat and square cells of haloquadratum walsbyi. despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably for the enzymes involved in transcription and translation. other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, including archaeols. archaea use more energy sources than eukaryotes : these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. salt - tolerant archaea ( the haloarchaea ) use sunlight as an energy source, and other species of archaea fix carbon, but unlike plants and cyanobacteria, no known species of archaea does both. archaea reproduce asexually by binary fission, fragmentation, or budding ; unlike bacteria, no known species of archaea form endospores. the first observed archaea were extremophiles, living in extreme environments, such as hot springs and salt lakes with no other organisms. improved molecular detection invertebrates, or protozoans, the protist grouping is not a formal taxonomic group but is used for convenience. most protists are unicellular ; these are called microbial eukaryotes. plants are mainly multicellular organisms, predominantly photosynthetic eukaryotes of the kingdom plantae, which would exclude fungi and some algae. plant cells were derived by endosymbiosis of a cyanobacterium into an early eukaryote about one billion years ago, which gave rise to chloroplasts. the first several clades that emerged following primary endosymbiosis were aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related. algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of plantae. unlike glaucophytes, the other algal clades such as red and green algae are multicellular. green algae comprise three major clades : chlorophytes, coleochaetophytes, and stoneworts. fungi are eukaryotes that digest foods outside their bodies, secreting digestive enzymes that break down large food molecules before absorbing them through their cell membranes. many fungi are also saprobes, feeding on dead organic matter, making them important decomposers in ecological systems. animals are multicellular eukaryotes. with few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. over 1. 5 million living animal species have been described — of which around 1 million are insects — but it has been estimated there are over 7 million animal species in total. they have complex interactions with each other and their environments, forming intricate food webs. = = = viruses = = = viruses are submicroscopic infectious agents that replicate inside the cells of organisms. viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. more than 6, 000 virus species have been described in detail. viruses are found in almost every ecosystem on earth and are the most numerous type of biological entity. the origins of viruses in the evolutionary history of life are unclear : some may have evolved from plasmids — pieces of dna Question: What type of prokaryotes live in habitats without oxygen? A) enzymatic B) phosphoric C) aerobic D) anaerobic	D) anaerobic
Context: ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. for example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. the existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. different kinds of spectra are often used in chemical spectroscopy, e. g. ir, microwave, nmr, esr, etc. spectroscopy is also used to identify the composition of remote objects – like stars and distant galaxies – by analyzing their radiation spectra. the term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. = = = reaction = = = when a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. a chemical reaction is therefore a concept related to the " reaction " of a substance when it comes in close contact with another, whether as a mixture or a solution ; exposure to some form of energy, or both. it results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels — often laboratory glassware. chemical reactions can result in the formation or dissociation of molecules, that is, molecules breaking apart to form two or more molecules or rearrangement of atoms within or across molecules. chemical reactions usually involve the making or breaking of chemical bonds or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. for example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. the existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. different kinds of spectra are often used in chemical spectroscopy, e. g. ir, microwave, nmr, esr, etc. spectroscopy is also used to identify the composition of remote objects – like stars and distant galaxies – by analyzing their radiation spectra. the term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. = = = reaction = = = when a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. a chemical reaction is therefore a concept related to the " reaction " of a substance when it comes in close contact with another, whether as a mixture or a solution ; exposure to some form of energy, or both. it results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels — often laboratory glassware. chemical reactions can result in the formation or dissociation of molecules, that is, molecules breaking apart to form two or more molecules or rearrangement of atoms within or across molecules. chemical reactions usually involve the making or breaking of chemical bonds. oxidation, reduction, dissociation, acid – base neutralization and molecular rearrangement are some examples of common chemical reactions. a chemical reaction can be symbolically depicted through a chemical equation. while in a non - nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for the valuable metals into individual constituents. = = metal and its alloys = = much effort has been placed on understanding iron – carbon alloy system, which includes steels and cast irons. plain carbon steels ( those that contain essentially only carbon as an alloying element ) are used in low - cost, high - strength applications, where neither weight nor corrosion are a major concern. cast irons, including ductile iron, are also part of the iron - carbon system. iron - manganese - chromium alloys ( hadfield - type steels ) are also used in non - magnetic applications such as directional drilling. other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. these metals are most often used as alloys with the noted exception of silicon, which is not a metal. other forms include : stainless steel, particularly austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important. aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications. copper - nickel alloys ( such as monel ) are used in highly corrosive environments and for non - magnetic applications. nickel - based superalloys like inconel are used in high - temperature applications such as gas turbines, turbochargers, pressure vessels, and heat exchangers. for extremely high temperatures, single crystal alloys are used to minimize creep. in modern electronics, high purity single crystal silicon is essential for metal - oxide - silicon transistors ( mos ) and integrated circuits. = = production = = in production engineering, metallurgy is concerned with the production of metallic components for use in consumer or engineering products. this involves production of alloys, shaping, heat treatment and surface treatment of product. the task of the metallurgist is to achieve balance between material properties, such as cost, weight, strength, toughness, hardness, corrosion, fatigue resistance and performance in temperature extremes. to achieve this goal, the operating environment must be carefully considered. determining the hardness of the metal using the rockwell, vickers, and brinell hardness scales is a commonly used practice that helps better understand the metal ' s elasticity and plasticity for different applications and production processes. in a saltwater environment, most ferrous metals and some non - ferrous alloys corrode quickly. metals exposed to cold or cryogenic conditions may undergo a ductile to brittle iron - carbon alloy is only considered steel if the carbon level is between 0. 01 % and 2. 00 % by weight. for steels, the hardness and tensile strength of the steel is related to the amount of carbon present, with increasing carbon levels also leading to lower ductility and toughness. heat treatment processes such as quenching and tempering can significantly change these properties, however. in contrast, certain metal alloys exhibit unique properties where their size and density remain unchanged across a range of temperatures. cast iron is defined as an iron – carbon alloy with more than 2. 00 %, but less than 6. 67 % carbon. stainless steel is defined as a regular steel alloy with greater than 10 % by weight alloying content of chromium. nickel and molybdenum are typically also added in stainless steels. other significant metallic alloys are those of aluminium, titanium, copper and magnesium. copper alloys have been known for a long time ( since the bronze age ), while the alloys of the other three metals have been relatively recently developed. due to the chemical reactivity of these metals, the electrolytic extraction processes required were only developed relatively recently. the alloys of aluminium, titanium and magnesium are also known and valued for their high strength to weight ratios and, in the case of magnesium, their ability to provide electromagnetic shielding. these materials are ideal for situations where high strength to weight ratios are more important than bulk cost, such as in the aerospace industry and certain automotive engineering applications. = = = semiconductors = = = a semiconductor is a material that has a resistivity between a conductor and insulator. modern day electronics run on semiconductors, and the industry had an estimated us $ 530 billion market in 2021. its electronic properties can be greatly altered through intentionally introducing impurities in a process referred to as doping. semiconductor materials are used to build diodes, transistors, light - emitting diodes ( leds ), and analog and digital electric circuits, among their many uses. semiconductor devices have replaced thermionic devices like vacuum tubes in most applications. semiconductor devices are manufactured both as single discrete devices and as integrated circuits ( ics ), which consist of a number — from a few to millions — of devices manufactured and interconnected on a single semiconductor substrate. of all the semiconductors in use today, silicon makes up the largest portion both by quantity and commercial value. monocrystalline silicon is used to produce wafers used in the semiconductor and electronics industry. gallium arsenide ( based on 1 / 10 and 1 / 100 weight percentages of the carbon and other alloying elements they contain. thus, the extracting and purifying methods used to extract iron in a blast furnace can affect the quality of steel that is produced. solid materials are generally grouped into three basic classifications : ceramics, metals, and polymers. this broad classification is based on the empirical makeup and atomic structure of the solid materials, and most solids fall into one of these broad categories. an item that is often made from each of these materials types is the beverage container. the material types used for beverage containers accordingly provide different advantages and disadvantages, depending on the material used. ceramic ( glass ) containers are optically transparent, impervious to the passage of carbon dioxide, relatively inexpensive, and are easily recycled, but are also heavy and fracture easily. metal ( aluminum alloy ) is relatively strong, is a good barrier to the diffusion of carbon dioxide, and is easily recycled. however, the cans are opaque, expensive to produce, and are easily dented and punctured. polymers ( polyethylene plastic ) are relatively strong, can be optically transparent, are inexpensive and lightweight, and can be recyclable, but are not as impervious to the passage of carbon dioxide as aluminum and glass. = = = ceramics and glasses = = = another application of materials science is the study of ceramics and glasses, typically the most brittle materials with industrial relevance. many ceramics and glasses exhibit covalent or ionic - covalent bonding with sio2 ( silica ) as a fundamental building block. ceramics – not to be confused with raw, unfired clay – are usually seen in crystalline form. the vast majority of commercial glasses contain a metal oxide fused with silica. at the high temperatures used to prepare glass, the material is a viscous liquid which solidifies into a disordered state upon cooling. windowpanes and eyeglasses are important examples. fibers of glass are also used for long - range telecommunication and optical transmission. scratch resistant corning gorilla glass is a well - known example of the application of materials science to drastically improve the properties of common components. engineering ceramics are known for their stiffness and stability under high temperatures, compression and electrical stress. alumina, silicon carbide, and tungsten carbide are made from a fine powder of their constituents in a process of sintering with a binder. hot pressing provides higher density material. chemical vapor deposition can place a film of a ceramic on another applications, where neither weight nor corrosion are a major concern. cast irons, including ductile iron, are also part of the iron - carbon system. iron - manganese - chromium alloys ( hadfield - type steels ) are also used in non - magnetic applications such as directional drilling. other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. these metals are most often used as alloys with the noted exception of silicon, which is not a metal. other forms include : stainless steel, particularly austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important. aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications. copper - nickel alloys ( such as monel ) are used in highly corrosive environments and for non - magnetic applications. nickel - based superalloys like inconel are used in high - temperature applications such as gas turbines, turbochargers, pressure vessels, and heat exchangers. for extremely high temperatures, single crystal alloys are used to minimize creep. in modern electronics, high purity single crystal silicon is essential for metal - oxide - silicon transistors ( mos ) and integrated circuits. = = production = = in production engineering, metallurgy is concerned with the production of metallic components for use in consumer or engineering products. this involves production of alloys, shaping, heat treatment and surface treatment of product. the task of the metallurgist is to achieve balance between material properties, such as cost, weight, strength, toughness, hardness, corrosion, fatigue resistance and performance in temperature extremes. to achieve this goal, the operating environment must be carefully considered. determining the hardness of the metal using the rockwell, vickers, and brinell hardness scales is a commonly used practice that helps better understand the metal ' s elasticity and plasticity for different applications and production processes. in a saltwater environment, most ferrous metals and some non - ferrous alloys corrode quickly. metals exposed to cold or cryogenic conditions may undergo a ductile to brittle transition and lose their toughness, becoming more brittle and prone to cracking. metals under continual cyclic loading can suffer from metal fatigue. metals under constant stress at elevated temperatures can creep. = = = metalworking processes = = = casting – molten metal is poured into a shaped mold. variants of casting include sand casting, investment building block. ceramics – not to be confused with raw, unfired clay – are usually seen in crystalline form. the vast majority of commercial glasses contain a metal oxide fused with silica. at the high temperatures used to prepare glass, the material is a viscous liquid which solidifies into a disordered state upon cooling. windowpanes and eyeglasses are important examples. fibers of glass are also used for long - range telecommunication and optical transmission. scratch resistant corning gorilla glass is a well - known example of the application of materials science to drastically improve the properties of common components. engineering ceramics are known for their stiffness and stability under high temperatures, compression and electrical stress. alumina, silicon carbide, and tungsten carbide are made from a fine powder of their constituents in a process of sintering with a binder. hot pressing provides higher density material. chemical vapor deposition can place a film of a ceramic on another material. cermets are ceramic particles containing some metals. the wear resistance of tools is derived from cemented carbides with the metal phase of cobalt and nickel typically added to modify properties. ceramics can be significantly strengthened for engineering applications using the principle of crack deflection. this process involves the strategic addition of second - phase particles within a ceramic matrix, optimizing their shape, size, and distribution to direct and control crack propagation. this approach enhances fracture toughness, paving the way for the creation of advanced, high - performance ceramics in various industries. = = = composites = = = another application of materials science in industry is making composite materials. these are structured materials composed of two or more macroscopic phases. applications range from structural elements such as steel - reinforced concrete, to the thermal insulating tiles, which play a key and integral role in nasa ' s space shuttle thermal protection system, which is used to protect the surface of the shuttle from the heat of re - entry into the earth ' s atmosphere. one example is reinforced carbon - carbon ( rcc ), the light gray material, which withstands re - entry temperatures up to 1, 510 °c ( 2, 750 °f ) and protects the space shuttle ' s wing leading edges and nose cap. rcc is a laminated composite material made from graphite rayon cloth and impregnated with a phenolic resin. after curing at high temperature in an autoclave, the laminate is pyrolized to convert the resin to carbon, impregnated with furfuryl alcohol in a still a complex and relatively expensive material to produce. polymers on the other hand can be produced in huge volumes, with a great variety of material characteristics. mems devices can be made from polymers by processes such as injection molding, embossing or stereolithography and are especially well suited to microfluidic applications such as disposable blood testing cartridges. metals metals can also be used to create mems elements. while metals do not have some of the advantages displayed by silicon in terms of mechanical properties, when used within their limitations, metals can exhibit very high degrees of reliability. metals can be deposited by electroplating, evaporation, and sputtering processes. commonly used metals include gold, nickel, aluminium, copper, chromium, titanium, tungsten, platinum, and silver. ceramics the nitrides of silicon, aluminium and titanium as well as silicon carbide and other ceramics are increasingly applied in mems fabrication due to advantageous combinations of material properties. aln crystallizes in the wurtzite structure and thus shows pyroelectric and piezoelectric properties enabling sensors, for instance, with sensitivity to normal and shear forces. tin, on the other hand, exhibits a high electrical conductivity and large elastic modulus, making it possible to implement electrostatic mems actuation schemes with ultrathin beams. moreover, the high resistance of tin against biocorrosion qualifies the material for applications in biogenic environments. the figure shows an electron - microscopic picture of a mems biosensor with a 50 nm thin bendable tin beam above a tin ground plate. both can be driven as opposite electrodes of a capacitor, since the beam is fixed in electrically isolating side walls. when a fluid is suspended in the cavity its viscosity may be derived from bending the beam by electrical attraction to the ground plate and measuring the bending velocity. = = basic processes = = = = = deposition processes = = = one of the basic building blocks in mems processing is the ability to deposit thin films of material with a thickness anywhere from one micrometre to about 100 micrometres. the nems process is the same, although the measurement of film deposition ranges from a few nanometres to one micrometre. there are two types of deposition processes, as follows. = = = = physical deposition = = = = physical vapor deposition ( " pvd " ) consists of a process in which a material is removed from a target, and joints. = = = metal alloys = = = the alloys of iron ( steel, stainless steel, cast iron, tool steel, alloy steels ) make up the largest proportion of metals today both by quantity and commercial value. iron alloyed with various proportions of carbon gives low, mid and high carbon steels. an iron - carbon alloy is only considered steel if the carbon level is between 0. 01 % and 2. 00 % by weight. for steels, the hardness and tensile strength of the steel is related to the amount of carbon present, with increasing carbon levels also leading to lower ductility and toughness. heat treatment processes such as quenching and tempering can significantly change these properties, however. in contrast, certain metal alloys exhibit unique properties where their size and density remain unchanged across a range of temperatures. cast iron is defined as an iron – carbon alloy with more than 2. 00 %, but less than 6. 67 % carbon. stainless steel is defined as a regular steel alloy with greater than 10 % by weight alloying content of chromium. nickel and molybdenum are typically also added in stainless steels. other significant metallic alloys are those of aluminium, titanium, copper and magnesium. copper alloys have been known for a long time ( since the bronze age ), while the alloys of the other three metals have been relatively recently developed. due to the chemical reactivity of these metals, the electrolytic extraction processes required were only developed relatively recently. the alloys of aluminium, titanium and magnesium are also known and valued for their high strength to weight ratios and, in the case of magnesium, their ability to provide electromagnetic shielding. these materials are ideal for situations where high strength to weight ratios are more important than bulk cost, such as in the aerospace industry and certain automotive engineering applications. = = = semiconductors = = = a semiconductor is a material that has a resistivity between a conductor and insulator. modern day electronics run on semiconductors, and the industry had an estimated us $ 530 billion market in 2021. its electronic properties can be greatly altered through intentionally introducing impurities in a process referred to as doping. semiconductor materials are used to build diodes, transistors, light - emitting diodes ( leds ), and analog and digital electric circuits, among their many uses. semiconductor devices have replaced thermionic devices like vacuum tubes in most applications. semiconductor devices are manufactured both as single discrete devices and as integrated circuits ( ics ), which consist of a number — from a is further subdivided into two broad categories : chemical metallurgy and physical metallurgy. chemical metallurgy is chiefly concerned with the reduction and oxidation of metals, and the chemical performance of metals. subjects of study in chemical metallurgy include mineral processing, the extraction of metals, thermodynamics, electrochemistry, and chemical degradation ( corrosion ). in contrast, physical metallurgy focuses on the mechanical properties of metals, the physical properties of metals, and the physical performance of metals. topics studied in physical metallurgy include crystallography, material characterization, mechanical metallurgy, phase transformations, and failure mechanisms. historically, metallurgy has predominately focused on the production of metals. metal production begins with the processing of ores to extract the metal, and includes the mixture of metals to make alloys. metal alloys are often a blend of at least two different metallic elements. however, non - metallic elements are often added to alloys in order to achieve properties suitable for an application. the study of metal production is subdivided into ferrous metallurgy ( also known as black metallurgy ) and non - ferrous metallurgy, also known as colored metallurgy. ferrous metallurgy involves processes and alloys based on iron, while non - ferrous metallurgy involves processes and alloys based on other metals. the production of ferrous metals accounts for 95 % of world metal production. modern metallurgists work in both emerging and traditional areas as part of an interdisciplinary team alongside material scientists and other engineers. some traditional areas include mineral processing, metal production, heat treatment, failure analysis, and the joining of metals ( including welding, brazing, and soldering ). emerging areas for metallurgists include nanotechnology, superconductors, composites, biomedical materials, electronic materials ( semiconductors ) and surface engineering. = = etymology and pronunciation = = metallurgy derives from the ancient greek μεταλλουργος, metallourgos, " worker in metal ", from μεταλλον, metallon, " mine, metal " + εργον, ergon, " work " the word was originally an alchemist ' s term for the extraction of metals from minerals, the ending - urgy signifying a process, especially manufacturing : it was discussed in this sense in the 1797 encyclopædia britannica. in the late 19th century, metallurgy ' Question: What is the only metal that is liquid at room temperature? A) hydrogen B) mercury C) gas D) water	B) mercury
Context: ( potassium hydroxide ), where si < 111 > planes etch approximately 100 times slower than other planes ( crystallographic orientations ). therefore, etching a rectangular hole in a ( 100 ) - si wafer results in a pyramid shaped etch pit with 54. 7° walls, instead of a hole with curved sidewalls as with isotropic etching. hydrofluoric acid is commonly used as an aqueous etchant for silicon dioxide ( sio2, also known as box for soi ), usually in 49 % concentrated form, 5 : 1, 10 : 1 or 20 : 1 boe ( buffered oxide etchant ) or bhf ( buffered hf ). they were first used in medieval times for glass etching. it was used in ic fabrication for patterning the gate oxide until the process step was replaced by rie. hydrofluoric acid is considered one of the more dangerous acids in the cleanroom. electrochemical etching ( ece ) for dopant - selective removal of silicon is a common method to automate and to selectively control etching. an active p – n diode junction is required, and either type of dopant can be the etch - resistant ( " etch - stop " ) material. boron is the most common etch - stop dopant. in combination with wet anisotropic etching as described above, ece has been used successfully for controlling silicon diaphragm thickness in commercial piezoresistive silicon pressure sensors. selectively doped regions can be created either by implantation, diffusion, or epitaxial deposition of silicon. = = = = dry etching = = = = xenon difluoride ( xef2 ) is a dry vapor phase isotropic etch for silicon originally applied for mems in 1995 at university of california, los angeles. primarily used for releasing metal and dielectric structures by undercutting silicon, xef2 has the advantage of a stiction - free release unlike wet etchants. its etch selectivity to silicon is very high, allowing it to work with photoresist, sio2, silicon nitride, and various metals for masking. its reaction to silicon is " plasmaless ", is purely chemical and spontaneous and is often operated in pulsed mode. models of the etching action are available, and university laboratories and various commercial tools offer solutions using this approach. modern to investigate the affinity of acetylated wood for organic liquids, yezo spruce wood specimens were acetylated with acetic anhydride, and their swelling in various liquids were compared to those of untreated specimens. the acetylated wood was rapidly and remarkably swollen in aprotic organic liquids such as benzene and toluene in which the untreated wood was swollen only slightly and / or very slowly. on the other hand, the swelling of wood in water, ethylene glycol and alcohols remained unchanged or decreased by the acetylation. consequently the maximum volume of wood swollen in organic liquids was always larger than that in water. the effect of acetylation on the maximum swollen volume of wood was greater in liquids having smaller solubility parameters. the easier penetration of aprotic organic liquids into the acetylated wood was considered to be due to the scission of hydrogen bonds among the amorphous wood constituents by the substitution of hydroxyl groups with hydrophobic acetyl groups. with curved sidewalls as with isotropic etching. hydrofluoric acid is commonly used as an aqueous etchant for silicon dioxide ( sio2, also known as box for soi ), usually in 49 % concentrated form, 5 : 1, 10 : 1 or 20 : 1 boe ( buffered oxide etchant ) or bhf ( buffered hf ). they were first used in medieval times for glass etching. it was used in ic fabrication for patterning the gate oxide until the process step was replaced by rie. hydrofluoric acid is considered one of the more dangerous acids in the cleanroom. electrochemical etching ( ece ) for dopant - selective removal of silicon is a common method to automate and to selectively control etching. an active p – n diode junction is required, and either type of dopant can be the etch - resistant ( " etch - stop " ) material. boron is the most common etch - stop dopant. in combination with wet anisotropic etching as described above, ece has been used successfully for controlling silicon diaphragm thickness in commercial piezoresistive silicon pressure sensors. selectively doped regions can be created either by implantation, diffusion, or epitaxial deposition of silicon. = = = = dry etching = = = = xenon difluoride ( xef2 ) is a dry vapor phase isotropic etch for silicon originally applied for mems in 1995 at university of california, los angeles. primarily used for releasing metal and dielectric structures by undercutting silicon, xef2 has the advantage of a stiction - free release unlike wet etchants. its etch selectivity to silicon is very high, allowing it to work with photoresist, sio2, silicon nitride, and various metals for masking. its reaction to silicon is " plasmaless ", is purely chemical and spontaneous and is often operated in pulsed mode. models of the etching action are available, and university laboratories and various commercial tools offer solutions using this approach. modern vlsi processes avoid wet etching, and use plasma etching instead. plasma etchers can operate in several modes by adjusting the parameters of the plasma. ordinary plasma etching operates between 0. 1 and 5 torr. ( this unit of pressure, commonly used in vacuum engineering, equals approximately 133. 3 pascal others, such as the essential oils peppermint oil and lemon oil are useful for their aroma, as flavourings and spices ( e. g., capsaicin ), and in medicine as pharmaceuticals as in opium from opium poppies. many medicinal and recreational drugs, such as tetrahydrocannabinol ( active ingredient in cannabis ), caffeine, morphine and nicotine come directly from plants. others are simple derivatives of botanical natural products. for example, the pain killer aspirin is the acetyl ester of salicylic acid, originally isolated from the bark of willow trees, and a wide range of opiate painkillers like heroin are obtained by chemical modification of morphine obtained from the opium poppy. popular stimulants come from plants, such as caffeine from coffee, tea and chocolate, and nicotine from tobacco. most alcoholic beverages come from fermentation of carbohydrate - rich plant products such as barley ( beer ), rice ( sake ) and grapes ( wine ). native americans have used various plants as ways of treating illness or disease for thousands of years. this knowledge native americans have on plants has been recorded by enthnobotanists and then in turn has been used by pharmaceutical companies as a way of drug discovery. plants can synthesise coloured dyes and pigments such as the anthocyanins responsible for the red colour of red wine, yellow weld and blue woad used together to produce lincoln green, indoxyl, source of the blue dye indigo traditionally used to dye denim and the artist ' s pigments gamboge and rose madder. sugar, starch, cotton, linen, hemp, some types of rope, wood and particle boards, papyrus and paper, vegetable oils, wax, and natural rubber are examples of commercially important materials made from plant tissues or their secondary products. charcoal, a pure form of carbon made by pyrolysis of wood, has a long history as a metal - smelting fuel, as a filter material and adsorbent and as an artist ' s material and is one of the three ingredients of gunpowder. cellulose, the world ' s most abundant organic polymer, can be converted into energy, fuels, materials and chemical feedstock. products made from cellulose include rayon and cellophane, wallpaper paste, biobutanol and gun cotton. sugarcane, rapeseed and soy are some of the plants with a highly ferment carried out correctly, with dimensions and angles being extremely accurate. some single crystal materials, such as silicon, will have different etching rates depending on the crystallographic orientation of the substrate. this is known as anisotropic etching and one of the most common examples is the etching of silicon in koh ( potassium hydroxide ), where si < 111 > planes etch approximately 100 times slower than other planes ( crystallographic orientations ). therefore, etching a rectangular hole in a ( 100 ) - si wafer results in a pyramid shaped etch pit with 54. 7° walls, instead of a hole with curved sidewalls as with isotropic etching. hydrofluoric acid is commonly used as an aqueous etchant for silicon dioxide ( sio2, also known as box for soi ), usually in 49 % concentrated form, 5 : 1, 10 : 1 or 20 : 1 boe ( buffered oxide etchant ) or bhf ( buffered hf ). they were first used in medieval times for glass etching. it was used in ic fabrication for patterning the gate oxide until the process step was replaced by rie. hydrofluoric acid is considered one of the more dangerous acids in the cleanroom. electrochemical etching ( ece ) for dopant - selective removal of silicon is a common method to automate and to selectively control etching. an active p – n diode junction is required, and either type of dopant can be the etch - resistant ( " etch - stop " ) material. boron is the most common etch - stop dopant. in combination with wet anisotropic etching as described above, ece has been used successfully for controlling silicon diaphragm thickness in commercial piezoresistive silicon pressure sensors. selectively doped regions can be created either by implantation, diffusion, or epitaxial deposition of silicon. = = = = dry etching = = = = xenon difluoride ( xef2 ) is a dry vapor phase isotropic etch for silicon originally applied for mems in 1995 at university of california, los angeles. primarily used for releasing metal and dielectric structures by undercutting silicon, xef2 has the advantage of a stiction - free release unlike wet etchants. its etch selectivity to silicon is very high, allowing it to work with photores new crop traits as well as a far greater control over a food ' s genetic structure than previously afforded by methods such as selective breeding and mutation breeding. commercial sale of genetically modified foods began in 1994, when calgene first marketed its flavr savr delayed ripening tomato. to date most genetic modification of foods have primarily focused on cash crops in high demand by farmers such as soybean, corn, canola, and cotton seed oil. these have been engineered for resistance to pathogens and herbicides and better nutrient profiles. gm livestock have also been experimentally developed ; in november 2013 none were available on the market, but in 2015 the fda approved the first gm salmon for commercial production and consumption. there is a scientific consensus that currently available food derived from gm crops poses no greater risk to human health than conventional food, but that each gm food needs to be tested on a case - by - case basis before introduction. nonetheless, members of the public are much less likely than scientists to perceive gm foods as safe. the legal and regulatory status of gm foods varies by country, with some nations banning or restricting them, and others permitting them with widely differing degrees of regulation. gm crops also provide a number of ecological benefits, if not used in excess. insect - resistant crops have proven to lower pesticide usage, therefore reducing the environmental impact of pesticides as a whole. however, opponents have objected to gm crops per se on several grounds, including environmental concerns, whether food produced from gm crops is safe, whether gm crops are needed to address the world ' s food needs, and economic concerns raised by the fact these organisms are subject to intellectual property law. biotechnology has several applications in the realm of food security. crops like golden rice are engineered to have higher nutritional content, and there is potential for food products with longer shelf lives. though not a form of agricultural biotechnology, vaccines can help prevent diseases found in animal agriculture. additionally, agricultural biotechnology can expedite breeding processes in order to yield faster results and provide greater quantities of food. transgenic biofortification in cereals has been considered as a promising method to combat malnutrition in india and other countries. = = = industrial = = = industrial biotechnology ( known mainly in europe as white biotechnology ) is the application of biotechnology for industrial purposes, including industrial fermentation. it includes the practice of using cells such as microorganisms, or components of cells like enzymes, to generate industrially useful products in sectors such as chemicals, food and feed, detergents, paper the graphane with chemically bonded alkali metals ( li, na, k ) was considered as potential material for hydrogen storage. the ab initio calculations show that such material can adsorb as many as 4 hydrogen molecules per li, na and k metal atoms. these values correspond to 12. 20 wt %, 10. 33 wt % and 8. 56 wt % of hydrogen, respectively and exceed the doe requirements. the thermodynamic analysis shows that li - graphane complex is the most promising for hydrogen storage with ability to adsorb 3 hydrogen molecules per metal atom at 300 k and pressure in the range from 5 to 250 atm. cortisol, corticosterone and aldosterone activate full - length glucocorticoid receptor ( gr ) from elephant shark, a cartilaginous fish belonging to the oldest group of jawed vertebrates. activation by aldosterone a mineralocorticoid, indicates partial divergence of elephant shark gr from the mr. progesterone activates elephant shark mr, but not elephant shark gr. progesterone inhibits steroid binding to elephant shark gr, but not to human gr. deletion of the n - terminal domain ( ntd ) from elephant shark gr ( truncated gr ) reduced the response to corticosteroids, while truncated and full - length elephant shark mr had similar responses to corticosteroids. chimeras of elephant shark gr ntd fused to mr dbd + lbd had increased activation by corticosteroids and progesterone compared to full - length elephant shark mr. elephant shark mr ntd fused to gr dbd + lbd had similar activation as full - length elephant shark mr, indicating that activation of human gr by the ntd evolved early in gr divergence from the mr. while co - coculturing epithelial and adipocyte cells. the hystem kit is another 3 - d platform containing ecm components and hyaluronic acid that has been used for cancer research. additionally, hydrogel constituents can be chemically modified to assist in crosslinking and enhance their mechanical properties. = = tissue culture = = in many cases, creation of functional tissues and biological structures in vitro requires extensive culturing to promote survival, growth and inducement of functionality. in general, the basic requirements of cells must be maintained in culture, which include oxygen, ph, humidity, temperature, nutrients and osmotic pressure maintenance. tissue engineered cultures also present additional problems in maintaining culture conditions. in standard cell culture, diffusion is often the sole means of nutrient and metabolite transport. however, as a culture becomes larger and more complex, such as the case with engineered organs and whole tissues, other mechanisms must be employed to maintain the culture, such as the creation of capillary networks within the tissue. another issue with tissue culture is introducing the proper factors or stimuli required to induce functionality. in many cases, simple maintenance culture is not sufficient. growth factors, hormones, specific metabolites or nutrients, chemical and physical stimuli are sometimes required. for example, certain cells respond to changes in oxygen tension as part of their normal development, such as chondrocytes, which must adapt to low oxygen conditions or hypoxia during skeletal development. others, such as endothelial cells, respond to shear stress from fluid flow, which is encountered in blood vessels. mechanical stimuli, such as pressure pulses seem to be beneficial to all kind of cardiovascular tissue such as heart valves, blood vessels or pericardium. = = = bioreactors = = = in tissue engineering, a bioreactor is a device that attempts to simulate a physiological environment in order to promote cell or tissue growth in vitro. a physiological environment can consist of many different parameters such as temperature, pressure, oxygen or carbon dioxide concentration, or osmolality of fluid environment, and it can extend to all kinds of biological, chemical or mechanical stimuli. therefore, there are systems that may include the application of forces such as electromagnetic forces, mechanical pressures, or fluid pressures to the tissue. these systems can be two - or three - dimensional setups. bioreactors can be used in both academic and industry applications. general - use and application - specific bioreactors are also commercially available, which may provide static chemical stimulation or a or a base, as is evident in the history of this concept. acid strength is commonly measured by two methods. one measurement, based on the arrhenius definition of acidity, is ph, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale. thus, solutions that have a low ph have a high hydronium ion concentration and can be said to be more acidic. the other measurement, based on the brønsted – lowry definition, is the acid dissociation constant ( ka ), which measures the relative ability of a substance to act as an acid under the brønsted – lowry definition of an acid. that is, substances with a higher ka are more likely to donate hydrogen ions in chemical reactions than those with lower ka values. = = = redox = = = redox ( reduction - oxidation ) reactions include all chemical reactions in which atoms have their oxidation state changed by either gaining electrons ( reduction ) or losing electrons ( oxidation ). substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. an oxidant removes electrons from another substance. similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers. a reductant transfers electrons to another substance and is thus oxidized itself. and because it " donates " electrons it is also called an electron donor. oxidation and reduction properly refer to a change in oxidation number — the actual transfer of electrons may never occur. thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number. = = = equilibrium = = = although the concept of equilibrium is widely used across sciences, in the context of chemistry, it arises whenever a number of different states of the chemical composition are possible, as for example, in a mixture of several chemical compounds that can react with one another, or when a substance can be present in more than one kind of phase. a system of chemical substances at equilibrium, even though having an unchanging composition, is most often not static ; molecules of the substances continue to react with one another thus giving rise to a dynamic equilibrium. thus the concept describes the state in which the parameters such as chemical composition remain unchanged over time. = = = chemical laws = = = chemical reactions are governed by certain laws Question: What do animals store with the help of saturated fatty acids? A) protein B) energy C) sugar D) oxygen	B) energy
Context: and measuring radiation levels. the surveyor program conducted uncrewed lunar landings and takeoffs, as well as taking surface and regolith observations. despite the setback caused by the apollo 1 fire, which killed three astronauts, the program proceeded. apollo 8 was the first crewed spacecraft to leave low earth orbit and the first human spaceflight to reach the moon. the crew orbited the moon ten times on december 24 and 25, 1968, and then traveled safely back to earth. the three apollo 8 astronauts — frank borman, james lovell, and william anders — were the first humans to see the earth as a globe in space, the first to witness an earthrise, and the first to see and manually photograph the far side of the moon. the first lunar landing was conducted by apollo 11. commanded by neil armstrong with astronauts buzz aldrin and michael collins, apollo 11 was one of the most significant missions in nasa ' s history, marking the end of the space race when the soviet union gave up its lunar ambitions. as the first human to step on the surface of the moon, neil armstrong uttered the now famous words : that ' s one small step for man, one giant leap for mankind. nasa would conduct six total lunar landings as part of the apollo program, with apollo 17 concluding the program in 1972. = = = = end of apollo = = = = wernher von braun had advocated for nasa to develop a space station since the agency was created. in 1973, following the end of the apollo lunar missions, nasa launched its first space station, skylab, on the final launch of the saturn v. skylab reused a significant amount of apollo and saturn hardware, with a repurposed saturn v third stage serving as the primary module for the space station. damage to skylab during its launch required spacewalks to be performed by the first crew to make it habitable and operational. skylab hosted nine missions and was decommissioned in 1974 and deorbited in 1979, two years prior to the first launch of the space shuttle and any possibility of boosting its orbit. in 1975, the apollo – soyuz mission was the first ever international spaceflight and a major diplomatic accomplishment between the cold war rivals, which also marked the last flight of the apollo capsule. flown in 1975, a us apollo spacecraft docked with a soviet soyuz capsule. = = = interplanetary exploration and space science = = = during the 1960s, nasa started its space science and interplanetary probe program. the mariner program was its flagship and taken up by the brain. by observing which areas of the brain take up the radioactive isotope, we can see which areas of the brain are more active than other areas. pet has similar spatial resolution to fmri, but it has extremely poor temporal resolution. electroencephalography. eeg measures the electrical fields generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. this technique has an extremely high temporal resolution, but a relatively poor spatial resolution. functional magnetic resonance imaging. fmri measures the relative amount of oxygenated blood flowing to different parts of the brain. more oxygenated blood in a particular region is assumed to correlate with an increase in neural activity in that part of the brain. this allows us to localize particular functions within different brain regions. fmri has moderate spatial and temporal resolution. optical imaging. this technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active ( i. e., those that have more oxygenated blood ). optical imaging has moderate temporal resolution, but poor spatial resolution. it also has the advantage that it is extremely safe and can be used to study infants ' brains. magnetoencephalography. meg measures magnetic fields resulting from cortical activity. it is similar to eeg, except that it has improved spatial resolution since the magnetic fields it measures are not as blurred or attenuated by the scalp, meninges and so forth as the electrical activity measured in eeg is. meg uses squid sensors to detect tiny magnetic fields. = = = computational modeling = = = computational models require a mathematically and logically formal representation of a problem. computer models are used in the simulation and experimental verification of different specific and general properties of intelligence. computational modeling can help us understand the functional organization of a particular cognitive phenomenon. approaches to cognitive modeling can be categorized as : ( 1 ) symbolic, on abstract mental functions of an intelligent mind by means of symbols ; ( 2 ) subsymbolic, on the neural and associative properties of the human brain ; and ( 3 ) across the symbolic – subsymbolic border, including hybrid. symbolic modeling evolved from the computer science paradigms using the technologies of knowledge - based systems, as well as a philosophical perspective ( e. g. " good old - fashioned artificial intelligence " ( gofa fuel cells instead of batteries, and conducted the first american spacewalks and rendezvous operations. the ranger program was started in the 1950s as a response to soviet lunar exploration, however most missions ended in failure. the lunar orbiter program had greater success, mapping the surface in preparation for apollo landings, conducting meteoroid detection, and measuring radiation levels. the surveyor program conducted uncrewed lunar landings and takeoffs, as well as taking surface and regolith observations. despite the setback caused by the apollo 1 fire, which killed three astronauts, the program proceeded. apollo 8 was the first crewed spacecraft to leave low earth orbit and the first human spaceflight to reach the moon. the crew orbited the moon ten times on december 24 and 25, 1968, and then traveled safely back to earth. the three apollo 8 astronauts — frank borman, james lovell, and william anders — were the first humans to see the earth as a globe in space, the first to witness an earthrise, and the first to see and manually photograph the far side of the moon. the first lunar landing was conducted by apollo 11. commanded by neil armstrong with astronauts buzz aldrin and michael collins, apollo 11 was one of the most significant missions in nasa ' s history, marking the end of the space race when the soviet union gave up its lunar ambitions. as the first human to step on the surface of the moon, neil armstrong uttered the now famous words : that ' s one small step for man, one giant leap for mankind. nasa would conduct six total lunar landings as part of the apollo program, with apollo 17 concluding the program in 1972. = = = = end of apollo = = = = wernher von braun had advocated for nasa to develop a space station since the agency was created. in 1973, following the end of the apollo lunar missions, nasa launched its first space station, skylab, on the final launch of the saturn v. skylab reused a significant amount of apollo and saturn hardware, with a repurposed saturn v third stage serving as the primary module for the space station. damage to skylab during its launch required spacewalks to be performed by the first crew to make it habitable and operational. skylab hosted nine missions and was decommissioned in 1974 and deorbited in 1979, two years prior to the first launch of the space shuttle and any possibility of boosting its orbit. in 1975, the apollo – soyuz mission was the first ever international spaceflight and a major diplomatic accomplishment between the cold war the lunar university network for astrophysics research ( lunar ) is a team of researchers and students at leading universities, nasa centers, and federal research laboratories undertaking investigations aimed at using the moon as a platform for space science. lunar research includes lunar interior physics & gravitation using lunar laser ranging ( llr ), low frequency cosmology and astrophysics ( lfca ), planetary science and the lunar ionosphere, radio heliophysics, and exploration science. the lunar team is exploring technologies that are likely to have a dual purpose, serving both exploration and science. there is a certain degree of commonality in much of lunar ' s research. specifically, the technology development for a lunar radio telescope involves elements from lfca, heliophysics, exploration science, and planetary science ; similarly the drilling technology developed for llr applies broadly to both exploration and lunar science. aviation, while the apollo lunar module was designed and built by grumman. to develop the spaceflight skills and equipment required for a lunar mission, nasa initiated project gemini. using a modified air force titan ii launch vehicle, the gemini capsule could hold two astronauts for flights of over two weeks. gemini pioneered the use of fuel cells instead of batteries, and conducted the first american spacewalks and rendezvous operations. the ranger program was started in the 1950s as a response to soviet lunar exploration, however most missions ended in failure. the lunar orbiter program had greater success, mapping the surface in preparation for apollo landings, conducting meteoroid detection, and measuring radiation levels. the surveyor program conducted uncrewed lunar landings and takeoffs, as well as taking surface and regolith observations. despite the setback caused by the apollo 1 fire, which killed three astronauts, the program proceeded. apollo 8 was the first crewed spacecraft to leave low earth orbit and the first human spaceflight to reach the moon. the crew orbited the moon ten times on december 24 and 25, 1968, and then traveled safely back to earth. the three apollo 8 astronauts — frank borman, james lovell, and william anders — were the first humans to see the earth as a globe in space, the first to witness an earthrise, and the first to see and manually photograph the far side of the moon. the first lunar landing was conducted by apollo 11. commanded by neil armstrong with astronauts buzz aldrin and michael collins, apollo 11 was one of the most significant missions in nasa ' s history, marking the end of the space race when the soviet union gave up its lunar ambitions. as the first human to step on the surface of the moon, neil armstrong uttered the now famous words : that ' s one small step for man, one giant leap for mankind. nasa would conduct six total lunar landings as part of the apollo program, with apollo 17 concluding the program in 1972. = = = = end of apollo = = = = wernher von braun had advocated for nasa to develop a space station since the agency was created. in 1973, following the end of the apollo lunar missions, nasa launched its first space station, skylab, on the final launch of the saturn v. skylab reused a significant amount of apollo and saturn hardware, with a repurposed saturn v third stage serving as the primary module for the space station. damage to skylab during its launch required spacewalks to be performed by the first crew to make it habitable and of imaging techniques vary in their temporal ( time - based ) and spatial ( location - based ) resolution. brain imaging is often used in cognitive neuroscience. single - photon emission computed tomography and positron emission tomography. spect and pet use radioactive isotopes, which are injected into the subject ' s bloodstream and taken up by the brain. by observing which areas of the brain take up the radioactive isotope, we can see which areas of the brain are more active than other areas. pet has similar spatial resolution to fmri, but it has extremely poor temporal resolution. electroencephalography. eeg measures the electrical fields generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. this technique has an extremely high temporal resolution, but a relatively poor spatial resolution. functional magnetic resonance imaging. fmri measures the relative amount of oxygenated blood flowing to different parts of the brain. more oxygenated blood in a particular region is assumed to correlate with an increase in neural activity in that part of the brain. this allows us to localize particular functions within different brain regions. fmri has moderate spatial and temporal resolution. optical imaging. this technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active ( i. e., those that have more oxygenated blood ). optical imaging has moderate temporal resolution, but poor spatial resolution. it also has the advantage that it is extremely safe and can be used to study infants ' brains. magnetoencephalography. meg measures magnetic fields resulting from cortical activity. it is similar to eeg, except that it has improved spatial resolution since the magnetic fields it measures are not as blurred or attenuated by the scalp, meninges and so forth as the electrical activity measured in eeg is. meg uses squid sensors to detect tiny magnetic fields. = = = computational modeling = = = computational models require a mathematically and logically formal representation of a problem. computer models are used in the simulation and experimental verification of different specific and general properties of intelligence. computational modeling can help us understand the functional organization of a particular cognitive phenomenon. approaches to cognitive modeling can be categorized as : ( 1 ) symbolic, on abstract mental functions of an intelligent mind by means of symbols ; ( 2 ) subsymbolic, on the neural and associa the origin of the martian moons deimos and phobos is controversial. one hypothesis for their origin is that they are captured asteroids, but the mechanism requires an extremely dense martian atmosphere, and the mechanism by which an asteroid in solar orbit could shed sufficient orbital energy to be captured into mars orbit has not been well elucidated. since the discovery by the space probe galileo that the asteroid ida has a moon " dactyl ", a significant number of asteroids have been discovered to have smaller asteroids in orbit about them. the existence of asteroid moons provides a mechanism for the capture of the martian moons ( and the small moons of the outer planets ). when a binary asteroid makes a close approach to a planet, tidal forces can strip the moon from the asteroid. depending on the phasing, the asteroid can then be captured. clearly, the same process can be used to explain the origin of any of the small moons in the solar system. hand axes emerged. this early stone age is described as the lower paleolithic. the middle paleolithic, approximately 300, 000 years ago, saw the introduction of the prepared - core technique, where multiple blades could be rapidly formed from a single core stone. the upper paleolithic, beginning approximately 40, 000 years ago, saw the introduction of pressure flaking, where a wood, bone, or antler punch could be used to shape a stone very finely. the end of the last ice age about 10, 000 years ago is taken as the end point of the upper paleolithic and the beginning of the epipaleolithic / mesolithic. the mesolithic technology included the use of microliths as composite stone tools, along with wood, bone, and antler tools. the later stone age, during which the rudiments of agricultural technology were developed, is called the neolithic period. during this period, polished stone tools were made from a variety of hard rocks such as flint, jade, jadeite, and greenstone, largely by working exposures as quarries, but later the valuable rocks were pursued by tunneling underground, the first steps in mining technology. the polished axes were used for forest clearance and the establishment of crop farming and were so effective as to remain in use when bronze and iron appeared. these stone axes were used alongside a continued use of stone tools such as a range of projectiles, knives, and scrapers, as well as tools, made from organic materials such as wood, bone, and antler. stone age cultures developed music and engaged in organized warfare. stone age humans developed ocean - worthy outrigger canoe technology, leading to migration across the malay archipelago, across the indian ocean to madagascar and also across the pacific ocean, which required knowledge of the ocean currents, weather patterns, sailing, and celestial navigation. although paleolithic cultures left no written records, the shift from nomadic life to settlement and agriculture can be inferred from a range of archaeological evidence. such evidence includes ancient tools, cave paintings, and other prehistoric art, such as the venus of willendorf. human remains also provide direct evidence, both through the examination of bones, and the study of mummies. scientists and historians have been able to form significant inferences about the lifestyle and culture of various prehistoric peoples, and especially their technology. = = = ancient = = = = = = = copper and bronze ages = = = = metallic copper occurs on the surface of weathered copper ore deposits and copper are the stone - paved streets of the city - state of ur, dating to c. 4, 000 bce, and timber roads leading through the swamps of glastonbury, england, dating to around the same period. the first long - distance road, which came into use around 3, 500 bce, spanned 2, 400 km from the persian gulf to the mediterranean sea, but was not paved and was only partially maintained. in around 2, 000 bce, the minoans on the greek island of crete built a 50 km road leading from the palace of gortyn on the south side of the island, through the mountains, to the palace of knossos on the north side of the island. unlike the earlier road, the minoan road was completely paved. ancient minoan private homes had running water. a bathtub virtually identical to modern ones was unearthed at the palace of knossos. several minoan private homes also had toilets, which could be flushed by pouring water down the drain. the ancient romans had many public flush toilets, which emptied into an extensive sewage system. the primary sewer in rome was the cloaca maxima ; construction began on it in the sixth century bce and it is still in use today. the ancient romans also had a complex system of aqueducts, which were used to transport water across long distances. the first roman aqueduct was built in 312 bce. the eleventh and final ancient roman aqueduct was built in 226 ce. put together, the roman aqueducts extended over 450 km, but less than 70 km of this was above ground and supported by arches. = = = pre - modern = = = innovations continued through the middle ages with the introduction of silk production ( in asia and later europe ), the horse collar, and horseshoes. simple machines ( such as the lever, the screw, and the pulley ) were combined into more complicated tools, such as the wheelbarrow, windmills, and clocks. a system of universities developed and spread scientific ideas and practices, including oxford and cambridge. the renaissance era produced many innovations, including the introduction of the movable type printing press to europe, which facilitated the communication of knowledge. technology became increasingly influenced by science, beginning a cycle of mutual advancement. = = = modern = = = starting in the united kingdom in the 18th century, the discovery of steam power set off the industrial revolution, which saw wide - ranging technological discoveries, particularly in the areas of agriculture, manufacturing, mining, metallurgy, and transport, and the generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. this technique has an extremely high temporal resolution, but a relatively poor spatial resolution. functional magnetic resonance imaging. fmri measures the relative amount of oxygenated blood flowing to different parts of the brain. more oxygenated blood in a particular region is assumed to correlate with an increase in neural activity in that part of the brain. this allows us to localize particular functions within different brain regions. fmri has moderate spatial and temporal resolution. optical imaging. this technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active ( i. e., those that have more oxygenated blood ). optical imaging has moderate temporal resolution, but poor spatial resolution. it also has the advantage that it is extremely safe and can be used to study infants ' brains. magnetoencephalography. meg measures magnetic fields resulting from cortical activity. it is similar to eeg, except that it has improved spatial resolution since the magnetic fields it measures are not as blurred or attenuated by the scalp, meninges and so forth as the electrical activity measured in eeg is. meg uses squid sensors to detect tiny magnetic fields. = = = computational modeling = = = computational models require a mathematically and logically formal representation of a problem. computer models are used in the simulation and experimental verification of different specific and general properties of intelligence. computational modeling can help us understand the functional organization of a particular cognitive phenomenon. approaches to cognitive modeling can be categorized as : ( 1 ) symbolic, on abstract mental functions of an intelligent mind by means of symbols ; ( 2 ) subsymbolic, on the neural and associative properties of the human brain ; and ( 3 ) across the symbolic – subsymbolic border, including hybrid. symbolic modeling evolved from the computer science paradigms using the technologies of knowledge - based systems, as well as a philosophical perspective ( e. g. " good old - fashioned artificial intelligence " ( gofai ) ). they were developed by the first cognitive researchers and later used in information engineering for expert systems. since the early 1990s it was generalized in systemics for the investigation of functional human - like intelligence models, such as personoids, and, in parallel, developed as the soar environment. recently, especially in Question: What are the dark areas of the moon called? A) craters B) laura C) hollow space D) maria	D) maria
Context: river - beds ), but not for where there may be large obstructions in the ground. an open caisson that is used in soft grounds or high water tables, where open trench excavations are impractical, can also be used to install deep manholes, pump stations and reception / launch pits for microtunnelling, pipe jacking and other operations. a caisson is sunk by self - weight, concrete or water ballast placed on top, or by hydraulic jacks. the leading edge ( or cutting shoe ) of the caisson is sloped out at a sharp angle to aid sinking in a vertical manner ; it is usually made of steel. the shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. an open caisson may fill with water during sinking. the material is excavated by clamshell excavator bucket on crane. the formation level subsoil may still not be suitable for excavation or bearing capacity. the water in the caisson ( due to a high water table ) balances the upthrust forces of the soft soils underneath. if dewatered, the base may " pipe " or " boil ", causing the caisson to sink. to combat this problem, piles may be driven from the surface to act as : load - bearing walls, in that they transmit loads to deeper soils. anchors, in that they resist flotation because of the friction at the interface between their surfaces and the surrounding earth into which they have been driven. h - beam sections ( typical column sections, due to resistance to bending in all axis ) may be driven at angles " raked " to rock or other firmer soils ; the h - beams are left extended above the base. a reinforced concrete plug may be placed under the water, a process known as tremie concrete placement. when the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. = = = monolithic = = = a monolithic caisson ( or simply a monolith ) is larger than the other types of caisson, but similar to open caissons. such caissons are often found in quay walls, where resistance to impact from ships is required. = = = pneumatic = = = shallow caissons may be open to the air, whereas pneumatic caisson ##lling, pipe jacking and other operations. a caisson is sunk by self - weight, concrete or water ballast placed on top, or by hydraulic jacks. the leading edge ( or cutting shoe ) of the caisson is sloped out at a sharp angle to aid sinking in a vertical manner ; it is usually made of steel. the shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. an open caisson may fill with water during sinking. the material is excavated by clamshell excavator bucket on crane. the formation level subsoil may still not be suitable for excavation or bearing capacity. the water in the caisson ( due to a high water table ) balances the upthrust forces of the soft soils underneath. if dewatered, the base may " pipe " or " boil ", causing the caisson to sink. to combat this problem, piles may be driven from the surface to act as : load - bearing walls, in that they transmit loads to deeper soils. anchors, in that they resist flotation because of the friction at the interface between their surfaces and the surrounding earth into which they have been driven. h - beam sections ( typical column sections, due to resistance to bending in all axis ) may be driven at angles " raked " to rock or other firmer soils ; the h - beams are left extended above the base. a reinforced concrete plug may be placed under the water, a process known as tremie concrete placement. when the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. = = = monolithic = = = a monolithic caisson ( or simply a monolith ) is larger than the other types of caisson, but similar to open caissons. such caissons are often found in quay walls, where resistance to impact from ships is required. = = = pneumatic = = = shallow caissons may be open to the air, whereas pneumatic caissons ( sometimes called pressurized caissons ), which penetrate soft mud, are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. an airlock allows access to the chamber. workers, called sandhogs in american english, move mud and rock debris ( called made of steel. the shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. an open caisson may fill with water during sinking. the material is excavated by clamshell excavator bucket on crane. the formation level subsoil may still not be suitable for excavation or bearing capacity. the water in the caisson ( due to a high water table ) balances the upthrust forces of the soft soils underneath. if dewatered, the base may " pipe " or " boil ", causing the caisson to sink. to combat this problem, piles may be driven from the surface to act as : load - bearing walls, in that they transmit loads to deeper soils. anchors, in that they resist flotation because of the friction at the interface between their surfaces and the surrounding earth into which they have been driven. h - beam sections ( typical column sections, due to resistance to bending in all axis ) may be driven at angles " raked " to rock or other firmer soils ; the h - beams are left extended above the base. a reinforced concrete plug may be placed under the water, a process known as tremie concrete placement. when the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. = = = monolithic = = = a monolithic caisson ( or simply a monolith ) is larger than the other types of caisson, but similar to open caissons. such caissons are often found in quay walls, where resistance to impact from ships is required. = = = pneumatic = = = shallow caissons may be open to the air, whereas pneumatic caissons ( sometimes called pressurized caissons ), which penetrate soft mud, are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. an airlock allows access to the chamber. workers, called sandhogs in american english, move mud and rock debris ( called muck ) from the edge of the workspace to a water - filled pit, connected by a tube ( called the muck tube ) to the surface. a crane at the surface removes the soil with a clamshell bucket. the water pressure in the tube balances the air pressure, with excess air escaping up ##s ( sometimes called pressurized caissons ), which penetrate soft mud, are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. an airlock allows access to the chamber. workers, called sandhogs in american english, move mud and rock debris ( called muck ) from the edge of the workspace to a water - filled pit, connected by a tube ( called the muck tube ) to the surface. a crane at the surface removes the soil with a clamshell bucket. the water pressure in the tube balances the air pressure, with excess air escaping up the muck tube. the pressurized air flow must be constant to ensure regular air changes for the workers and prevent excessive inflow of mud or water at the base of the caisson. when the caisson hits bedrock, the sandhogs exit through the airlock and fill the box with concrete, forming a solid foundation pier. a pneumatic ( compressed - air ) caisson has the advantage of providing dry working conditions, which is better for placing concrete. it is also well suited for foundations for which other methods might cause settlement of adjacent structures. construction workers who leave the pressurized environment of the caisson must decompress at a rate that allows symptom - free release of inert gases dissolved in the body tissues if they are to avoid decompression sickness, a condition first identified in caisson workers, and originally named " caisson disease " in recognition of the occupational hazard. construction of the brooklyn bridge, which was built with the help of pressurised caissons, resulted in numerous workers being either killed or permanently injured by caisson disease during its construction. barotrauma of the ears, sinus cavities and lungs and dysbaric osteonecrosis are other risks. = = other uses = = caissons have also been used in the installation of hydraulic elevators where a single - stage ram is installed below the ground level. caissons, codenamed phoenix, were an integral part of the mulberry harbours used during the world war ii allied invasion of normandy. = = other meanings = = boat lift caissons : the word caisson is also used as a synonym for the moving trough part of caisson locks, canal lifts and inclines in which boats and ships rest while being lifted from one canal elevation to another ; the water is retained on the inside of the caisson, or excluded from the caisson are the stone - paved streets of the city - state of ur, dating to c. 4, 000 bce, and timber roads leading through the swamps of glastonbury, england, dating to around the same period. the first long - distance road, which came into use around 3, 500 bce, spanned 2, 400 km from the persian gulf to the mediterranean sea, but was not paved and was only partially maintained. in around 2, 000 bce, the minoans on the greek island of crete built a 50 km road leading from the palace of gortyn on the south side of the island, through the mountains, to the palace of knossos on the north side of the island. unlike the earlier road, the minoan road was completely paved. ancient minoan private homes had running water. a bathtub virtually identical to modern ones was unearthed at the palace of knossos. several minoan private homes also had toilets, which could be flushed by pouring water down the drain. the ancient romans had many public flush toilets, which emptied into an extensive sewage system. the primary sewer in rome was the cloaca maxima ; construction began on it in the sixth century bce and it is still in use today. the ancient romans also had a complex system of aqueducts, which were used to transport water across long distances. the first roman aqueduct was built in 312 bce. the eleventh and final ancient roman aqueduct was built in 226 ce. put together, the roman aqueducts extended over 450 km, but less than 70 km of this was above ground and supported by arches. = = = pre - modern = = = innovations continued through the middle ages with the introduction of silk production ( in asia and later europe ), the horse collar, and horseshoes. simple machines ( such as the lever, the screw, and the pulley ) were combined into more complicated tools, such as the wheelbarrow, windmills, and clocks. a system of universities developed and spread scientific ideas and practices, including oxford and cambridge. the renaissance era produced many innovations, including the introduction of the movable type printing press to europe, which facilitated the communication of knowledge. technology became increasingly influenced by science, beginning a cycle of mutual advancement. = = = modern = = = starting in the united kingdom in the 18th century, the discovery of steam power set off the industrial revolution, which saw wide - ranging technological discoveries, particularly in the areas of agriculture, manufacturing, mining, metallurgy, and transport, and the becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under muck ) from the edge of the workspace to a water - filled pit, connected by a tube ( called the muck tube ) to the surface. a crane at the surface removes the soil with a clamshell bucket. the water pressure in the tube balances the air pressure, with excess air escaping up the muck tube. the pressurized air flow must be constant to ensure regular air changes for the workers and prevent excessive inflow of mud or water at the base of the caisson. when the caisson hits bedrock, the sandhogs exit through the airlock and fill the box with concrete, forming a solid foundation pier. a pneumatic ( compressed - air ) caisson has the advantage of providing dry working conditions, which is better for placing concrete. it is also well suited for foundations for which other methods might cause settlement of adjacent structures. construction workers who leave the pressurized environment of the caisson must decompress at a rate that allows symptom - free release of inert gases dissolved in the body tissues if they are to avoid decompression sickness, a condition first identified in caisson workers, and originally named " caisson disease " in recognition of the occupational hazard. construction of the brooklyn bridge, which was built with the help of pressurised caissons, resulted in numerous workers being either killed or permanently injured by caisson disease during its construction. barotrauma of the ears, sinus cavities and lungs and dysbaric osteonecrosis are other risks. = = other uses = = caissons have also been used in the installation of hydraulic elevators where a single - stage ram is installed below the ground level. caissons, codenamed phoenix, were an integral part of the mulberry harbours used during the world war ii allied invasion of normandy. = = other meanings = = boat lift caissons : the word caisson is also used as a synonym for the moving trough part of caisson locks, canal lifts and inclines in which boats and ships rest while being lifted from one canal elevation to another ; the water is retained on the inside of the caisson, or excluded from the caisson, according to the respective operating principle. structural caissons : caisson is also sometimes used as a colloquial term for a reinforced concrete structure formed by pouring into a hollow cylindrical form, typically by placing a caisson form below grade in an open excavation and pouring once backfill is complete, or by , 400 km from the persian gulf to the mediterranean sea, but was not paved and was only partially maintained. in around 2, 000 bce, the minoans on the greek island of crete built a 50 km road leading from the palace of gortyn on the south side of the island, through the mountains, to the palace of knossos on the north side of the island. unlike the earlier road, the minoan road was completely paved. ancient minoan private homes had running water. a bathtub virtually identical to modern ones was unearthed at the palace of knossos. several minoan private homes also had toilets, which could be flushed by pouring water down the drain. the ancient romans had many public flush toilets, which emptied into an extensive sewage system. the primary sewer in rome was the cloaca maxima ; construction began on it in the sixth century bce and it is still in use today. the ancient romans also had a complex system of aqueducts, which were used to transport water across long distances. the first roman aqueduct was built in 312 bce. the eleventh and final ancient roman aqueduct was built in 226 ce. put together, the roman aqueducts extended over 450 km, but less than 70 km of this was above ground and supported by arches. = = = pre - modern = = = innovations continued through the middle ages with the introduction of silk production ( in asia and later europe ), the horse collar, and horseshoes. simple machines ( such as the lever, the screw, and the pulley ) were combined into more complicated tools, such as the wheelbarrow, windmills, and clocks. a system of universities developed and spread scientific ideas and practices, including oxford and cambridge. the renaissance era produced many innovations, including the introduction of the movable type printing press to europe, which facilitated the communication of knowledge. technology became increasingly influenced by science, beginning a cycle of mutual advancement. = = = modern = = = starting in the united kingdom in the 18th century, the discovery of steam power set off the industrial revolution, which saw wide - ranging technological discoveries, particularly in the areas of agriculture, manufacturing, mining, metallurgy, and transport, and the widespread application of the factory system. this was followed a century later by the second industrial revolution which led to rapid scientific discovery, standardization, and mass production. new technologies were developed, including sewage systems, electricity, light bulbs, electric motors, railroads, automobiles, and airplanes. these technological advances led to significant developments in medicine and irrigation in the alluvial south, and catchment systems stretching for tens of kilometers in the hilly north. their palaces had sophisticated drainage systems. writing was invented in mesopotamia, using the cuneiform script. many records on clay tablets and stone inscriptions have survived. these civilizations were early adopters of bronze technologies which they used for tools, weapons and monumental statuary. by 1200 bc they could cast objects 5 m long in a single piece. several of the six classic simple machines were invented in mesopotamia. mesopotamians have been credited with the invention of the wheel. the wheel and axle mechanism first appeared with the potter ' s wheel, invented in mesopotamia ( modern iraq ) during the 5th millennium bc. this led to the invention of the wheeled vehicle in mesopotamia during the early 4th millennium bc. depictions of wheeled wagons found on clay tablet pictographs at the eanna district of uruk are dated between 3700 and 3500 bc. the lever was used in the shadoof water - lifting device, the first crane machine, which appeared in mesopotamia circa 3000 bc, and then in ancient egyptian technology circa 2000 bc. the earliest evidence of pulleys date back to mesopotamia in the early 2nd millennium bc. the screw, the last of the simple machines to be invented, first appeared in mesopotamia during the neo - assyrian period ( 911 – 609 ) bc. the assyrian king sennacherib ( 704 – 681 bc ) claims to have invented automatic sluices and to have been the first to use water screw pumps, of up to 30 tons weight, which were cast using two - part clay molds rather than by the ' lost wax ' process. the jerwan aqueduct ( c. 688 bc ) is made with stone arches and lined with waterproof concrete. the babylonian astronomical diaries spanned 800 years. they enabled meticulous astronomers to plot the motions of the planets and to predict eclipses. the earliest evidence of water wheels and watermills date back to the ancient near east in the 4th century bc, specifically in the persian empire before 350 bc, in the regions of mesopotamia ( iraq ) and persia ( iran ). this pioneering use of water power constituted the first human - devised motive force not to rely on muscle power ( besides the sail ). = = = = egypt = = = = the egyptians, known for building pyramids centuries before the creation of modern tools, invented and used many simple machines, such as the ramp to aid construction processes. historians and archaeologists have found evidence that the pyramids were built using navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding sea Question: What do people use from aquifers from springs or wells? A) fresh water B) oxygen C) soil D) salt	A) fresh water
Context: remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the infestation of insects and rodents, contributing to the spread of diseases. some of the most common types of solid waste management include ; landfills, vermicomposting, composting, recycling, and incineration. however, a major barrier for solid waste management practices is the high costs associated with recycling and the risks of creating more pollution. = = = e - waste recycling = = = the recycling of electronic waste ( e - waste ) has seen significant technological advancements due to increasing environmental concerns and the growing volume of electronic product disposals. traditional e - waste recycling methods, which often involve manual disassemb = = = = = = environmental remediation = = = environmental remediation is the process through which contaminants or pollutants in soil, water and other media are removed to improve environmental quality. the main focus is the reduction of hazardous substances within the environment. some of the areas involved in environmental remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the infestation of insects and rodents, contributing to the spread of diseases. some of the most common types of solid waste management include ; landfills, vermicomposting, composting, recycling, and incineration. however, a major barrier for solid waste management practices is the high costs associated with recycling assertions made in a document recently deposited in the arxiv are refuted. based on 1 / 10 and 1 / 100 weight percentages of the carbon and other alloying elements they contain. thus, the extracting and purifying methods used to extract iron in a blast furnace can affect the quality of steel that is produced. solid materials are generally grouped into three basic classifications : ceramics, metals, and polymers. this broad classification is based on the empirical makeup and atomic structure of the solid materials, and most solids fall into one of these broad categories. an item that is often made from each of these materials types is the beverage container. the material types used for beverage containers accordingly provide different advantages and disadvantages, depending on the material used. ceramic ( glass ) containers are optically transparent, impervious to the passage of carbon dioxide, relatively inexpensive, and are easily recycled, but are also heavy and fracture easily. metal ( aluminum alloy ) is relatively strong, is a good barrier to the diffusion of carbon dioxide, and is easily recycled. however, the cans are opaque, expensive to produce, and are easily dented and punctured. polymers ( polyethylene plastic ) are relatively strong, can be optically transparent, are inexpensive and lightweight, and can be recyclable, but are not as impervious to the passage of carbon dioxide as aluminum and glass. = = = ceramics and glasses = = = another application of materials science is the study of ceramics and glasses, typically the most brittle materials with industrial relevance. many ceramics and glasses exhibit covalent or ionic - covalent bonding with sio2 ( silica ) as a fundamental building block. ceramics – not to be confused with raw, unfired clay – are usually seen in crystalline form. the vast majority of commercial glasses contain a metal oxide fused with silica. at the high temperatures used to prepare glass, the material is a viscous liquid which solidifies into a disordered state upon cooling. windowpanes and eyeglasses are important examples. fibers of glass are also used for long - range telecommunication and optical transmission. scratch resistant corning gorilla glass is a well - known example of the application of materials science to drastically improve the properties of common components. engineering ceramics are known for their stiffness and stability under high temperatures, compression and electrical stress. alumina, silicon carbide, and tungsten carbide are made from a fine powder of their constituents in a process of sintering with a binder. hot pressing provides higher density material. chemical vapor deposition can place a film of a ceramic on another molecular diffusion processes give rise to significant changes in the primary microstructural features. this includes the gradual elimination of porosity, which is typically accompanied by a net shrinkage and overall densification of the component. thus, the pores in the object may close up, resulting in a denser product of significantly greater strength and fracture toughness. another major change in the body during the firing or sintering process will be the establishment of the polycrystalline nature of the solid. significant grain growth tends to occur during sintering, with this growth depending on temperature and duration of the sintering process. the growth of grains will result in some form of grain size distribution, which will have a significant impact on the ultimate physical properties of the material. in particular, abnormal grain growth in which certain grains grow very large in a matrix of finer grains will significantly alter the physical and mechanical properties of the obtained ceramic. in the sintered body, grain sizes are a product of the thermal processing parameters as well as the initial particle size, or possibly the sizes of aggregates or particle clusters which arise during the initial stages of processing. the ultimate microstructure ( and thus the physical properties ) of the final product will be limited by and subject to the form of the structural template or precursor which is created in the initial stages of chemical synthesis and physical forming. hence the importance of chemical powder and polymer processing as it pertains to the synthesis of industrial ceramics, glasses and glass - ceramics. there are numerous possible refinements of the sintering process. some of the most common involve pressing the green body to give the densification a head start and reduce the sintering time needed. sometimes organic binders such as polyvinyl alcohol are added to hold the green body together ; these burn out during the firing ( at 200 – 350 °c ). sometimes organic lubricants are added during pressing to increase densification. it is common to combine these, and add binders and lubricants to a powder, then press. ( the formulation of these organic chemical additives is an art in itself. this is particularly important in the manufacture of high performance ceramics such as those used by the billions for electronics, in capacitors, inductors, sensors, etc. ) a slurry can be used in place of a powder, and then cast into a desired shape, dried and then sintered. indeed, traditional pottery is done with this type of method, using a plastic mixture worked with the hands. ". = = extraction = = extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted raw metals into a purer form. in order to convert a metal oxide or sulphide to a purer metal, the ore must be reduced physically, chemically, or electrolytically. extractive metallurgists are interested in three primary streams : feed, concentrate ( metal oxide / sulphide ) and tailings ( waste ). after mining, large pieces of the ore feed are broken through crushing or grinding in order to obtain particles small enough, where each particle is either mostly valuable or mostly waste. concentrating the particles of value in a form supporting separation enables the desired metal to be removed from waste products. mining may not be necessary, if the ore body and physical environment are conducive to leaching. leaching dissolves minerals in an ore body and results in an enriched solution. the solution is collected and processed to extract valuable metals. ore bodies often contain more than one valuable metal. tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. additionally, a concentrate may contain more than one valuable metal. that concentrate would then be processed to separate the valuable metals into individual constituents. = = metal and its alloys = = much effort has been placed on understanding iron – carbon alloy system, which includes steels and cast irons. plain carbon steels ( those that contain essentially only carbon as an alloying element ) are used in low - cost, high - strength applications, where neither weight nor corrosion are a major concern. cast irons, including ductile iron, are also part of the iron - carbon system. iron - manganese - chromium alloys ( hadfield - type steels ) are also used in non - magnetic applications such as directional drilling. other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. these metals are most often used as alloys with the noted exception of silicon, which is not a metal. other forms include : stainless steel, particularly austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important. aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications. copper - nickel alloys ( such as monel ) are used in highly corrosive environments and for non - magnetic applications the surface of the membrane, retentate is removed from the same side further downstream, whereas the permeate flow is tracked on the other side. in dead - end filtration, the direction of the fluid flow is normal to the membrane surface. both flow geometries offer some advantages and disadvantages. generally, dead - end filtration is used for feasibility studies on a laboratory scale. the dead - end membranes are relatively easy to fabricate which reduces the cost of the separation process. the dead - end membrane separation process is easy to implement and the process is usually cheaper than cross - flow membrane filtration. the dead - end filtration process is usually a batch - type process, where the filtering solution is loaded ( or slowly fed ) into the membrane device, which then allows passage of some particles subject to the driving force. the main disadvantage of dead - end filtration is the extensive membrane fouling and concentration polarization. the fouling is usually induced faster at higher driving forces. membrane fouling and particle retention in a feed solution also builds up a concentration gradients and particle backflow ( concentration polarization ). the tangential flow devices are more cost and labor - intensive, but they are less susceptible to fouling due to the sweeping effects and high shear rates of the passing flow. the most commonly used synthetic membrane devices ( modules ) are flat sheets / plates, spiral wounds, and hollow fibers. flat membranes used in filtration and separation processes can be enhanced with surface patterning, where microscopic structures are introduced to improve performance. these patterns increase surface area, optimize water flow, and reduce fouling, leading to higher permeability and longer membrane lifespan. research has shown that such modifications can significantly enhance efficiency in water purification, energy applications, and industrial separations. flat plates are usually constructed as circular thin flat membrane surfaces to be used in dead - end geometry modules. spiral wounds are constructed from similar flat membranes but in the form of a " pocket " containing two membrane sheets separated by a highly porous support plate. several such pockets are then wound around a tube to create a tangential flow geometry and to reduce membrane fouling. hollow fiber modules consist of an assembly of self - supporting fibers with dense skin separation layers, and a more open matrix helping to withstand pressure gradients and maintain structural integrity. the hollow fiber modules can contain up to 10, 000 fibers ranging from 200 to 2500 μm in diameter ; the main advantage of hollow fiber modules is the very large surface area within delay of ripening, increase of juice yield, and improvement of re - hydration. irradiation is a more general term of deliberate exposure of materials to radiation to achieve a technical goal ( in this context ' ionizing radiation ' is implied ). as such it is also used on non - food items, such as medical hardware, plastics, tubes for gas - pipelines, hoses for floor - heating, shrink - foils for food packaging, automobile parts, wires and cables ( isolation ), tires, and even gemstones. compared to the amount of food irradiated, the volume of those every - day applications is huge but not noticed by the consumer. the genuine effect of processing food by ionizing radiation relates to damages to the dna, the basic genetic information for life. microorganisms can no longer proliferate and continue their malignant or pathogenic activities. spoilage causing micro - organisms cannot continue their activities. insects do not survive or become incapable of procreation. plants cannot continue the natural ripening or aging process. all these effects are beneficial to the consumer and the food industry, likewise. the amount of energy imparted for effective food irradiation is low compared to cooking the same ; even at a typical dose of 10 kgy most food, which is ( with regard to warming ) physically equivalent to water, would warm by only about 2. 5 °c ( 4. 5 °f ). the specialty of processing food by ionizing radiation is the fact, that the energy density per atomic transition is very high, it can cleave molecules and induce ionization ( hence the name ) which cannot be achieved by mere heating. this is the reason for new beneficial effects, however at the same time, for new concerns. the treatment of solid food by ionizing radiation can provide an effect similar to heat pasteurization of liquids, such as milk. however, the use of the term, cold pasteurization, to describe irradiated foods is controversial, because pasteurization and irradiation are fundamentally different processes, although the intended end results can in some cases be similar. detractors of food irradiation have concerns about the health hazards of induced radioactivity. a report for the industry advocacy group american council on science and health entitled " irradiated foods " states : " the types of radiation sources approved for the treatment of foods have specific energy levels well below that which would cause any element in food to become radioactive. food undergoing irradiation does not become any more do not survive or become incapable of procreation. plants cannot continue the natural ripening or aging process. all these effects are beneficial to the consumer and the food industry, likewise. the amount of energy imparted for effective food irradiation is low compared to cooking the same ; even at a typical dose of 10 kgy most food, which is ( with regard to warming ) physically equivalent to water, would warm by only about 2. 5 °c ( 4. 5 °f ). the specialty of processing food by ionizing radiation is the fact, that the energy density per atomic transition is very high, it can cleave molecules and induce ionization ( hence the name ) which cannot be achieved by mere heating. this is the reason for new beneficial effects, however at the same time, for new concerns. the treatment of solid food by ionizing radiation can provide an effect similar to heat pasteurization of liquids, such as milk. however, the use of the term, cold pasteurization, to describe irradiated foods is controversial, because pasteurization and irradiation are fundamentally different processes, although the intended end results can in some cases be similar. detractors of food irradiation have concerns about the health hazards of induced radioactivity. a report for the industry advocacy group american council on science and health entitled " irradiated foods " states : " the types of radiation sources approved for the treatment of foods have specific energy levels well below that which would cause any element in food to become radioactive. food undergoing irradiation does not become any more radioactive than luggage passing through an airport x - ray scanner or teeth that have been x - rayed. " food irradiation is currently permitted by over 40 countries and volumes are estimated to exceed 500, 000 metric tons ( 490, 000 long tons ; 550, 000 short tons ) annually worldwide. food irradiation is essentially a non - nuclear technology ; it relies on the use of ionizing radiation which may be generated by accelerators for electrons and conversion into bremsstrahlung, but which may use also gamma - rays from nuclear decay. there is a worldwide industry for processing by ionizing radiation, the majority by number and by processing power using accelerators. food irradiation is only a niche application compared to medical supplies, plastic materials, raw materials, gemstones, cables and wires, etc. = = accidents = = nuclear accidents, because of the powerful forces involved, are often very dangerous. historically, the first incidents involved fatal usability engineering, it ' s important target and identify human errors when interacting with the product of interest because if a user is expected to engage with a product, interface, or service in some way, the very introduction of a human in that engagement increases the potential of encountering human error. error should be reduced as much as possible in order to avoid frustration or injury. there are two main types of human errors which are categorized as slips and mistakes. slips are a very common kind of error involving automatic behaviors ( i. e. typos, hitting the wrong menu item ). when we experience slips, we have the correct goal in mind, but execute the wrong action. mistakes on the other hand involve conscious deliberation that result in the incorrect conclusion. when we experience mistakes, we have the wrong goal in mind and thereby execute the wrong action. even though slips are the more common type of error, they are no less dangerous. a certain type of slip error, a mode error, can be especially dangerous if a user is executing a high - risk task. for instance, if a user is operating a vehicle and does not realize they are in the wrong mode ( i. e. reverse ), they might step on the gas intending to drive, but instead accelerate into a garage wall or another car. in order to avoid modal errors, designers often employ modeless states in which users do not have to choose a mode at all, or they must execute a continuous action while intending to execute a certain mode ( i. e. pressing a key continuously in order to activate " lasso " mode in photoshop ). = = evaluation methods = = usability engineers conduct usability evaluations of existing or proposed interfaces and their findings are fed back to the designer for use in design or redesign. common usability evaluation methods include : card sorting cognitive task analysis cognitive walkthroughs contextual inquiry focus groups heuristic evaluations interviews questionnaires rite method surveys think aloud protocol usability testing = = software applications and development tools = = there are a variety of online resources that make the job of a usability engineer a little easier. online tools are only a useful tool, and do not substitute for a complete usability engineering analysis. some examples of these include : = = = the web metrics tool suite = = = this is a product of the national institute of standards and technology. this toolkit is focused on evaluating the html of a website versus a wide range of usability guidelines and includes : web static analyzer tool Question: What item lost by diffusion and in the urine are replenished by eating? A) salt B) sugar C) protein D) yeast	A) salt
Context: enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make it available as drinking water. the earliest exploitation of groundwater resources dates back to 3000 bc, and hydrogeology as a science was developed by hydrologists beginning in the 17th century. ecohydrology is the study of ecological systems in the hydrosphere. it can be divided into the physical study of aquatic ecosystems and the a minimum atmospheric temperature, or tropopause, occurs at a pressure of around 0. 1 bar in the atmospheres of earth, titan, jupiter, saturn, uranus and neptune, despite great differences in atmospheric composition, gravity, internal heat and sunlight. in all these bodies, the tropopause separates a stratosphere with a temperature profile that is controlled by the absorption of shortwave solar radiation, from a region below characterised by convection, weather, and clouds. however, it is not obvious why the tropopause occurs at the specific pressure near 0. 1 bar. here we use a physically - based model to demonstrate that, at atmospheric pressures lower than 0. 1 bar, transparency to thermal radiation allows shortwave heating to dominate, creating a stratosphere. at higher pressures, atmospheres become opaque to thermal radiation, causing temperatures to increase with depth and convection to ensue. a common dependence of infrared opacity on pressure, arising from the shared physics of molecular absorption, sets the 0. 1 bar tropopause. we hypothesize that a tropopause at a pressure of approximately 0. 1 bar is characteristic of many thick atmospheres, including exoplanets and exomoons in our galaxy and beyond. judicious use of this rule could help constrain the atmospheric structure, and thus the surface environments and habitability, of exoplanets. cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make higher concentrations of atmospheric nitrous oxide ( n2o ) are expected to slightly warm earth ' s surface because of increases in radiative forcing. radiative forcing is the difference in the net upward thermal radiation flux from the earth through a transparent atmosphere and radiation through an otherwise identical atmosphere with greenhouse gases. radiative forcing, normally measured in w / m ^ 2, depends on latitude, longitude and altitude, but it is often quoted for the tropopause, about 11 km of altitude for temperate latitudes, or for the top of the atmosphere at around 90 km. for current concentrations of greenhouse gases, the radiative forcing per added n2o molecule is about 230 times larger than the forcing per added carbon dioxide ( co2 ) molecule. this is due to the heavy saturation of the absorption band of the relatively abundant greenhouse gas, co2, compared to the much smaller saturation of the absorption bands of the trace greenhouse gas n2o. but the rate of increase of co2 molecules, about 2. 5 ppm / year ( ppm = part per million by mole ), is about 3000 times larger than the rate of increase of n2o molecules, which has held steady at around 0. 00085 ppm / year since 1985. so, the contribution of nitrous oxide to the annual increase in forcing is 230 / 3000 or about 1 / 13 that of co2. if the main greenhouse gases, co2, ch4 and n2o have contributed about 0. 1 c / decade of the warming observed over the past few decades, this would correspond to about 0. 00064 k per year or 0. 064 k per century of warming from n2o. proposals to place harsh restrictions on nitrous oxide emissions because of warming fears are not justified by these facts. restrictions would cause serious harm ; for example, by jeopardizing world food supplies. the project consists to determine, mathematically, the trajectory that will take an artificial satellite to fight against the air resistance. during our work, we had to consider that our satellite will crash to the surface of our planet. we started our study by understanding the system of forces that are acting between our satellite and the earth. in this work, we had to study the second law of newton by taking knowledge of the air friction, the speed of the satellite which helped us to find the equation that relates the trajectory of the satellite itself, its speed and the density of the air depending on the altitude. finally, we had to find a mathematic relation that links the density with the altitude and then we had to put it into our movement equation. in order to verify our model, we ' ll see what happens if we give a zero velocity to the satellite. the purpose of the given work is detailed research of toroidal shock wave movement process to the center of symmetry in air by normal atmosphere pressure. the wave is generated by plazma which is generated by a ring discharger. the paper erroneously assumed that the normal carriers giving rise to the backflow could be either electrons or holes. development and interaction of starting vortices initiated by dielectric barrier discharge ( dbd ) plasma actuators in quiescent air are illustrated in the attached fluid dynamics videos. these include a series of smoke flow visualisations, showing the starting vortices moving parallel or normal to the wall at several different actuator configurations. the origins of the series of european cosmic - ray symposia are briefly described. the first meeting in the series, on hadronic interactions and extensive air showers, held in lodz, poland in 1968, was attended by the author : some memories are recounted. acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make it available as drinking water. the earliest exploitation of groundwater resources dates back to 3000 bc, and hydrogeology as a science was developed by hydrologists beginning in the 17th century. ecohydrology is the study of ecological systems in the hydrosphere. it can be divided into the physical study of aquatic ecosystems and the biological study of aquatic organisms. ecohydrology includes the effects that organisms and aquatic ecosystems have on one another as well as how these ecoystems are affected by humans. glaciology is the study of the cryosphere, including glaciers and coverage of the earth by ice and snow. concerns of gla Question: What is the primary cause of air movement in the troposphere? A) solar winds B) asteroids C) the ozone layer D) differences in heating	D) differences in heating
Context: = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then oxidized into acetyl - coa by the pyruvate dehydrogenase complex, which also generates nadh and carbon dioxide. acetyl - coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. at the end of the cycle, the total yield from 1 glucose ( or 2 pyruvates ) is 6 nadh, 2 fadh2, and 2 atp molecules. finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from nadh and fadh2 that is coupled to the pumping of protons ( hydrogen ions ) across the inner mitochondrial membrane ( chemiosmosis ), which generates a proton motive force. energy from the proton motive force drives the enzyme atp synthase to synthesize more atps by phosphorylating adps. the transfer of electrons terminates with molecular oxygen being the final electron acceptor. if oxygen were not present, pyruvate would not be metabolized by cellular respiration but undergoes reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then oxidized into acetyl - coa by the pyruvate dehydrogenase complex, which also generates nadh and carbon dioxide. acetyl - coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. at the end of the cycle, the total yield from 1 glucose ( or 2 pyruvates ) is 6 nadh, 2 fadh2, and 2 atp molecules. finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from nadh and fadh2 that is coupled to the pumping of protons ( hydrogen ions ) across the inner mitochondrial membrane ( chemiosmosis ), which generates a proton motive force. energy . respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then oxidized into acetyl - coa by the pyruvate dehydrogenase complex, which also generates nadh and carbon dioxide. acetyl - coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. at the end of the cycle, the total yield from 1 glucose ( or 2 pyruvates ) is 6 nadh, 2 fadh2, and 2 atp molecules. finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from nadh and fadh2 that is coupled to the pumping of protons ( hydrogen ions ) across the inner mitochondrial membrane ( chemiosmosis ), which generates a proton motive force. energy from the proton motive force drives the enzyme atp synthase to synthesize more atps by phosphorylating adps. the transfer of electrons terminates with molecular oxygen being the final electron acceptor. if oxygen were not present, pyruvate would not be metabolized by cellular respiration but undergoes a process of fermentation. the pyruvate is not transported into the mitochondrion but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell. this serves the purpose of oxidizing the electron carriers so that they can perform glycol slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then oxidized into acetyl - coa by the pyruvate dehydrogenase complex, which also generates nadh and carbon dioxide. acetyl - coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. at the end of the cycle, the total yield from 1 glucose ( or 2 pyruvates ) is 6 nadh, 2 fadh2, and 2 atp molecules. finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from nadh and fadh2 that is coupled to the pumping of protons ( hydrogen ions ) across the inner mitochondrial membrane ( chemiosmosis ), which generates a proton motive force. energy from the proton motive force drives the enzyme atp synthase to synthesize more atps by phosphorylating adps. the transfer of electrons terminates with molecular oxygen being the final electron acceptor. if oxygen were not present, pyruvate would not be metabolized by cellular respiration but undergoes a process of fermentation. the pyruvate is not transported into the mitochondrion but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell. this serves the purpose of oxidizing the electron carriers so that they can perform glycolysis again and removing the excess pyruvate. fermentation oxidizes nadh to nad + so it can be re - used in glycolysis. in the absence of oxygen, fermentation prevents the buildup of nadh in the cytoplasm and provides nad + for gly liver glycogen. during recovery, when oxygen becomes available, nad + attaches to hydrogen from lactate to form atp. in yeast, the waste products are ethanol and carbon dioxide. this type of fermentation is known as alcoholic or ethanol fermentation. the atp generated in this process is made by substrate - level phosphorylation, which does not require oxygen. = = = photosynthesis = = = photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organism ' s metabolic activities via cellular respiration. this chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water. in most cases, oxygen is released as a waste product. most plants, algae, and cyanobacteria perform photosynthesis, which is largely responsible for producing and maintaining the oxygen content of the earth ' s atmosphere, and supplies most of the energy necessary for life on earth. photosynthesis has four stages : light absorption, electron transport, atp synthesis, and carbon fixation. light absorption is the initial step of photosynthesis whereby light energy is absorbed by chlorophyll pigments attached to proteins in the thylakoid membranes. the absorbed light energy is used to remove electrons from a donor ( water ) to a primary electron acceptor, a quinone designated as q. in the second stage, electrons move from the quinone primary electron acceptor through a series of electron carriers until they reach a final electron acceptor, which is usually the oxidized form of nadp +, which is reduced to nadph, a process that takes place in a protein complex called photosystem i ( psi ). the transport of electrons is coupled to the movement of protons ( or hydrogen ) from the stroma to the thylakoid membrane, which forms a ph gradient across the membrane as hydrogen becomes more concentrated in the lumen than in the stroma. this is analogous to the proton - motive force generated across the inner mitochondrial membrane in aerobic respiration. during the third stage of photosynthesis, the movement of protons down their concentration gradients from the thylakoid lumen to the stroma through the atp synthase is coupled to the synthesis of atp by that same atp synthase. the nadph and atps generated by the light - dependent reactions in the second and third stages, respectively, provide the energy and 3 - carbon sugar glyceraldehyde 3 - phosphate ( g3p ). glyceraldehyde 3 - phosphate is the first product of photosynthesis and the raw material from which glucose and almost all other organic molecules of biological origin are synthesised. some of the glucose is converted to starch which is stored in the chloroplast. starch is the characteristic energy store of most land plants and algae, while inulin, a polymer of fructose is used for the same purpose in the sunflower family asteraceae. some of the glucose is converted to sucrose ( common table sugar ) for export to the rest of the plant. unlike in animals ( which lack chloroplasts ), plants and their eukaryote relatives have delegated many biochemical roles to their chloroplasts, including synthesising all their fatty acids, and most amino acids. the fatty acids that chloroplasts make are used for many things, such as providing material to build cell membranes out of and making the polymer cutin which is found in the plant cuticle that protects land plants from drying out. plants synthesise a number of unique polymers like the polysaccharide molecules cellulose, pectin and xyloglucan from which the land plant cell wall is constructed. vascular land plants make lignin, a polymer used to strengthen the secondary cell walls of xylem tracheids and vessels to keep them from collapsing when a plant sucks water through them under water stress. lignin is also used in other cell types like sclerenchyma fibres that provide structural support for a plant and is a major constituent of wood. sporopollenin is a chemically resistant polymer found in the outer cell walls of spores and pollen of land plants responsible for the survival of early land plant spores and the pollen of seed plants in the fossil record. it is widely regarded as a marker for the start of land plant evolution during the ordovician period. the concentration of carbon dioxide in the atmosphere today is much lower than it was when plants emerged onto land during the ordovician and silurian periods. many monocots like maize and the pineapple and some dicots like the asteraceae have since independently evolved pathways like crassulacean acid metabolism and the c4 carbon fixation pathway for photosynthesis which avoid the losses resulting from photorespiration in the more common c3 carbon fixation pathway the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the from the proton motive force drives the enzyme atp synthase to synthesize more atps by phosphorylating adps. the transfer of electrons terminates with molecular oxygen being the final electron acceptor. if oxygen were not present, pyruvate would not be metabolized by cellular respiration but undergoes a process of fermentation. the pyruvate is not transported into the mitochondrion but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell. this serves the purpose of oxidizing the electron carriers so that they can perform glycolysis again and removing the excess pyruvate. fermentation oxidizes nadh to nad + so it can be re - used in glycolysis. in the absence of oxygen, fermentation prevents the buildup of nadh in the cytoplasm and provides nad + for glycolysis. this waste product varies depending on the organism. in skeletal muscles, the waste product is lactic acid. this type of fermentation is called lactic acid fermentation. in strenuous exercise, when energy demands exceed energy supply, the respiratory chain cannot process all of the hydrogen atoms joined by nadh. during anaerobic glycolysis, nad + regenerates when pairs of hydrogen combine with pyruvate to form lactate. lactate formation is catalyzed by lactate dehydrogenase in a reversible reaction. lactate can also be used as an indirect precursor for liver glycogen. during recovery, when oxygen becomes available, nad + attaches to hydrogen from lactate to form atp. in yeast, the waste products are ethanol and carbon dioxide. this type of fermentation is known as alcoholic or ethanol fermentation. the atp generated in this process is made by substrate - level phosphorylation, which does not require oxygen. = = = photosynthesis = = = photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organism ' s metabolic activities via cellular respiration. this chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water. in most cases, oxygen is released as a waste product. most plants, algae, and cyanobacteria perform photosynthesis, which is largely responsible for producing and maintaining the oxygen content of ##ysis again and removing the excess pyruvate. fermentation oxidizes nadh to nad + so it can be re - used in glycolysis. in the absence of oxygen, fermentation prevents the buildup of nadh in the cytoplasm and provides nad + for glycolysis. this waste product varies depending on the organism. in skeletal muscles, the waste product is lactic acid. this type of fermentation is called lactic acid fermentation. in strenuous exercise, when energy demands exceed energy supply, the respiratory chain cannot process all of the hydrogen atoms joined by nadh. during anaerobic glycolysis, nad + regenerates when pairs of hydrogen combine with pyruvate to form lactate. lactate formation is catalyzed by lactate dehydrogenase in a reversible reaction. lactate can also be used as an indirect precursor for liver glycogen. during recovery, when oxygen becomes available, nad + attaches to hydrogen from lactate to form atp. in yeast, the waste products are ethanol and carbon dioxide. this type of fermentation is known as alcoholic or ethanol fermentation. the atp generated in this process is made by substrate - level phosphorylation, which does not require oxygen. = = = photosynthesis = = = photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organism ' s metabolic activities via cellular respiration. this chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water. in most cases, oxygen is released as a waste product. most plants, algae, and cyanobacteria perform photosynthesis, which is largely responsible for producing and maintaining the oxygen content of the earth ' s atmosphere, and supplies most of the energy necessary for life on earth. photosynthesis has four stages : light absorption, electron transport, atp synthesis, and carbon fixation. light absorption is the initial step of photosynthesis whereby light energy is absorbed by chlorophyll pigments attached to proteins in the thylakoid membranes. the absorbed light energy is used to remove electrons from a donor ( water ) to a primary electron acceptor, a quinone designated as q. in the second stage, electrons move from the quinone primary electron acceptor through a series of electron carriers until they reach a Question: In cellular respiration, glucose is broken down and what is made? A) atp B) simple sugars C) chlorophyll D) rna	A) atp
Context: it is also possible to define analogs in two - dimensional systems, which has received attention for its relevance to systems in biology. = = = bonding = = = atoms sticking together in molecules or crystals are said to be bonded with one another. a chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them. more than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom. the chemical bond can be a covalent bond, an ionic bond, a hydrogen bond or just because of van der waals force. each of these kinds of bonds is ascribed to some potential. these potentials create the interactions which hold atoms together in molecules or crystals. in many simple compounds, valence bond theory, the valence shell electron pair repulsion model ( vsepr ), and the concept of oxidation number can be used to explain molecular structure and composition. an ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non - metal atom, becoming a negatively charged anion. the two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them. for example, sodium ( na ), a metal, loses one electron to become an na + cation while chlorine ( cl ), a non - metal, gains this electron to become cl−. the ions are held together due to electrostatic attraction, and that compound sodium chloride ( nacl ), or common table salt, is formed. in a covalent bond, one or more pairs of valence electrons are shared by two atoms : the resulting electrically neutral group of bonded atoms is termed a molecule. atoms will share valence electrons in such a way as to create a noble gas electron configuration ( eight electrons in their outermost shell ) for each atom. atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. however, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration ; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium, which has two electrons in its outer shell. similarly, theories from classical physics can be used to predict many ionic structures. with more complicated compounds, such as metal complexes factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. for example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. the existence of characteristic or molecules that show characteristic chemical properties in a compound. physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. in particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, spectroscopy, and more recently, astrochemistry. physical chemistry has large overlap with molecular physics. physical chemistry involves the use of infinitesimal calculus in deriving equations. it is usually associated with quantum chemistry and theoretical chemistry. physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap. theoretical chemistry is the study of chemistry via fundamental theoretical reasoning ( usually within mathematics or physics ). in particular the application of quantum mechanics to chemistry is called quantum chemistry. since the end of the second world war, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. theoretical chemistry has large overlap with ( theoretical and experimental ) condensed matter physics and molecular physics. other subdivisions include electrochemistry, femtochemistry, flavor chemistry, flow chemistry, immunohistochemistry, hydrogenation chemistry, mathematical chemistry, molecular mechanics, natural product chemistry, organometallic chemistry, petrochemistry, photochemistry, physical organic chemistry, polymer chemistry, radiochemistry, sonochemistry, supramolecular chemistry, synthetic chemistry, and many others. = = = interdisciplinary = = = interdisciplinary fields include agrochemistry, astrochemistry ( and cosmochemistry ), atmospheric chemistry, chemical engineering, chemical biology, chemo - informatics, environmental chemistry, geochemistry, green chemistry, immunochemistry, marine chemistry, materials science, mechanochemistry, medicinal chemistry, molecular biology, nanotechnology, oenology, pharmacology, phytochemistry, solid - state chemistry, surface science, thermochemistry, and many others. = = = industry = = = the chemical industry represents an important economic activity worldwide. the global top 50 chemical producers in 2013 had sales of us $ 980. 5 billion with a profit margin of 10. 3 %. = = = professional societies = = = = = see also = = = = references = = = = bibliography = = = = further reading = = popular reading atkins, p. w. galileo ' s finger ( oxford university press ) in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. for example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. the existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. different kinds of spectra are often used in chemical spectroscopy, e. g. ir, microwave, nmr, esr, etc. spectroscopy is also used to identify the composition of remote objects – like stars and distant galaxies – by analyzing their radiation spectra. the term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. = = = reaction = = = when a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction the topic of using nuclear power sources for generating energy. organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. an organic compound is defined as any compound based on a carbon skeleton. organic compounds can be classified, organized and understood in reactions by their functional groups, unit atoms or molecules that show characteristic chemical properties in a compound. physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. in particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, spectroscopy, and more recently, astrochemistry. physical chemistry has large overlap with molecular physics. physical chemistry involves the use of infinitesimal calculus in deriving equations. it is usually associated with quantum chemistry and theoretical chemistry. physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap. theoretical chemistry is the study of chemistry via fundamental theoretical reasoning ( usually within mathematics or physics ). in particular the application of quantum mechanics to chemistry is called quantum chemistry. since the end of the second world war, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. theoretical chemistry has large overlap with ( theoretical and experimental ) condensed matter physics and molecular physics. other subdivisions include electrochemistry, femtochemistry, flavor chemistry, flow chemistry, immunohistochemistry, hydrogenation chemistry, mathematical chemistry, molecular mechanics, natural product chemistry, organometallic chemistry, petrochemistry, photochemistry, physical organic chemistry, polymer chemistry, radiochemistry, sonochemistry, supramolecular chemistry, synthetic chemistry, and many others. = = = interdisciplinary = = = interdisciplinary fields include agrochemistry, astrochemistry ( and cosmochemistry ), atmospheric chemistry, chemical engineering, chemical biology, chemo - informatics, environmental chemistry, geochemistry, green chemistry, immunochemistry, marine chemistry, materials science, mechanochemistry, medicinal chemistry, molecular biology, nanotechnology, oenology, pharmacology, phytochemistry, solid - state chemistry, surface science, thermochemistry, and many others. = = = industry = = = the chemical industry represents an important economic activity worldwide. the global top 50 chemical producers in 2013 had sales analyzing their radiation spectra. the term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. = = = reaction = = = when a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. a chemical reaction is therefore a concept related to the " reaction " of a substance when it comes in close contact with another, whether as a mixture or a solution ; exposure to some form of energy, or both. it results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels — often laboratory glassware. chemical reactions can result in the formation or dissociation of molecules, that is, molecules breaking apart to form two or more molecules or rearrangement of atoms within or across molecules. chemical reactions usually involve the making or breaking of chemical bonds. oxidation, reduction, dissociation, acid – base neutralization and molecular rearrangement are some examples of common chemical reactions. a chemical reaction can be symbolically depicted through a chemical equation. while in a non - nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons. the sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. a chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. several empirical rules, like the woodward – hoffmann rules often come in handy while proposing a mechanism for a chemical reaction. according to the iupac gold book, a chemical reaction is " a process that results in the interconversion of chemical species. " accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction. an additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities ( set of chemical reactions with other substances. however, this definition only works well for substances that are composed of molecules, which is not true of many substances ( see below ). molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs. thus, molecules exist as electrically neutral units, unlike ions. when this rule is broken, giving the " molecule " a charge, the result is sometimes named a molecular ion or a polyatomic ion. however, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. affect static bodies dynamics, the study of how forces affect moving bodies. dynamics includes kinematics ( about movement, velocity, and acceleration ) and kinetics ( about forces and resulting accelerations ). mechanics of materials, the study of how different materials deform under various types of stress fluid mechanics, the study of how fluids react to forces kinematics, the study of the motion of bodies ( objects ) and systems ( groups of objects ), while ignoring the forces that cause the motion. kinematics is often used in the design and analysis of mechanisms. continuum mechanics, a method of applying mechanics that assumes that objects are continuous ( rather than discrete ) mechanical engineers typically use mechanics in the design or analysis phases of engineering. if the engineering project were the design of a vehicle, statics might be employed to design the frame of the vehicle, in order to evaluate where the stresses will be most intense. dynamics might be used when designing the car ' s engine, to evaluate the forces in the pistons and cams as the engine cycles. mechanics of materials might be used to choose appropriate materials for the frame and engine. fluid mechanics might be used to design a ventilation system for the vehicle ( see hvac ), or to design the intake system for the engine. = = = mechatronics and robotics = = = mechatronics is a combination of mechanics and electronics. it is an interdisciplinary branch of mechanical engineering, electrical engineering and software engineering that is concerned with integrating electrical and mechanical engineering to create hybrid automation systems. in this way, machines can be automated through the use of electric motors, servo - mechanisms, and other electrical systems in conjunction with special software. a common example of a mechatronics system is a cd - rom drive. mechanical systems open and close the drive, spin the cd and move the laser, while an optical system reads the data on the cd and converts it to bits. integrated software controls the process and communicates the contents of the cd to the computer. robotics is the application of mechatronics to create robots, which are often used in industry to perform tasks that are dangerous, unpleasant, or repetitive. these robots may be of any shape and size, but all are preprogrammed and interact physically with the world. to create a robot, an engineer typically employs kinematics ( to determine the robot ' s range of motion ) and mechanics ( to determine the stresses within the robot ). robots are used extensively in industrial automation engineering. they allow businesses to save money on labor, , valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. = = = energy = = = in the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. for example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. the existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. different kinds of spectra are often used in chemical spectroscopy, e. g. ir, microwave, nmr, esr, etc. spectroscopy is also used to identify the composition of remote objects – like stars and distant galaxies – by Question: The sum of the kinetic and potential energies of a system’s atoms and molecules is called what? A) internal energy B) stored energy C) mechanical energy D) used energy	A) internal energy
Context: a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons. the sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. a chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. several empirical rules, like the woodward – hoffmann rules often come in handy while proposing a mechanism for a chemical reaction. according to the iupac gold book, a chemical reaction is " a process that results in the interconversion of chemical species. " accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction. an additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities ( i. e. ' microscopic chemical events ' ). = = = ions and salts = = = an ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. when an atom loses an electron and thus has more protons than electrons, the atom is a positively charged ion or cation. when an atom gains an electron and thus has more electrons than protons, the atom is a negatively charged ion or anion. cations and anions can form a crystalline lattice of neutral salts, such as the na + and cl− ions forming sodium chloride, or nacl. examples of polyatomic ions that do not split up during acid – base reactions are hydroxide ( oh− ) and phosphate ( po43− ). plasma is composed of gaseous matter that has been completely ionized, usually through high temperature. = = = acidity and basicity = = = a substance can often be classified as an acid or a base. there are several different theories which explain acid – base behavior. the simplest is arrhenius theory, which states that an acid is a substance that produces hydronium ions when it is dissolved in water, and a base is one that produces hydroxide ions when dissolved in water. in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid . oxidation, reduction, dissociation, acid – base neutralization and molecular rearrangement are some examples of common chemical reactions. a chemical reaction can be symbolically depicted through a chemical equation. while in a non - nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons. the sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. a chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. several empirical rules, like the woodward – hoffmann rules often come in handy while proposing a mechanism for a chemical reaction. according to the iupac gold book, a chemical reaction is " a process that results in the interconversion of chemical species. " accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction. an additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities ( i. e. ' microscopic chemical events ' ). = = = ions and salts = = = an ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. when an atom loses an electron and thus has more protons than electrons, the atom is a positively charged ion or cation. when an atom gains an electron and thus has more electrons than protons, the atom is a negatively charged ion or anion. cations and anions can form a crystalline lattice of neutral salts, such as the na + and cl− ions forming sodium chloride, or nacl. examples of polyatomic ions that do not split up during acid – base reactions are hydroxide ( oh− ) and phosphate ( po43− ). plasma is composed of gaseous matter that has been completely ionized, usually through high temperature. = = = acidity and basicity = = = a substance can often be of measurement that denotes an amount of substance ( also called chemical amount ). one mole is defined to contain exactly 6. 02214076×1023 particles ( atoms, molecules, ions, or electrons ), where the number of particles per mole is known as the avogadro constant. molar concentration is the amount of a particular substance per volume of solution, and is commonly reported in mol / dm3. = = = phase = = = in addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. for the most part, the chemical classifications are independent of these bulk phase classifications ; however, some more exotic phases are incompatible with certain chemical properties. a phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature. physical properties, such as density and refractive index tend to fall within values characteristic of the phase. the phase of matter is defined by the phase transition, which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions. sometimes the distinction between phases can be continuous instead of having a discrete boundary ; in this case the matter is considered to be in a supercritical state. when three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions. the most familiar examples of phases are solids, liquids, and gases. many substances exhibit multiple solid phases. for example, there are three phases of solid iron ( alpha, gamma, and delta ) that vary based on temperature and pressure. a principal difference between solid phases is the crystal structure, or arrangement, of the atoms. another phase commonly encountered in the study of chemistry is the aqueous phase, which is the state of substances dissolved in aqueous solution ( that is, in water ). less familiar phases include plasmas, bose – einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. while most familiar phases deal with three - dimensional systems, it is also possible to define analogs in two - dimensional systems, which has received attention for its relevance to systems in biology. = = = bonding = = = atoms sticking together in molecules or crystals are said to be bonded with one another. a chemical bond may be visualized as the multipole balance between the positive final version. to appear in discrete and continuous dynamical systems - a. the top flavour - changing neutral couplings can be large in extended models with vector - like quarks. in the next decade ( s ) the cern large hadron collider will allow to measure ( bound ) them with a precision of few per cent. , they can fission as well, leading to a chain reaction. the average number of neutrons released per nucleus that go on to fission another nucleus is referred to as k. values of k larger than 1 mean that the fission reaction is releasing more neutrons than it absorbs, and therefore is referred to as a self - sustaining chain reaction. a mass of fissile material large enough ( and in a suitable configuration ) to induce a self - sustaining chain reaction is called a critical mass. when a neutron is captured by a suitable nucleus, fission may occur immediately, or the nucleus may persist in an unstable state for a short time. if there are enough immediate decays to carry on the chain reaction, the mass is said to be prompt critical, and the energy release will grow rapidly and uncontrollably, usually leading to an explosion. when discovered on the eve of world war ii, this insight led multiple countries to begin programs investigating the possibility of constructing an atomic bomb — a weapon which utilized fission reactions to generate far more energy than could be created with chemical explosives. the manhattan project, run by the united states with the help of the united kingdom and canada, developed multiple fission weapons which were used against japan in 1945 at hiroshima and nagasaki. during the project, the first fission reactors were developed as well, though they were primarily for weapons manufacture and did not generate electricity. in 1951, the first nuclear fission power plant was the first to produce electricity at the experimental breeder reactor no. 1 ( ebr - 1 ), in arco, idaho, ushering in the " atomic age " of more intensive human energy use. however, if the mass is critical only when the delayed neutrons are included, then the reaction can be controlled, for example by the introduction or removal of neutron absorbers. this is what allows nuclear reactors to be built. fast neutrons are not easily captured by nuclei ; they must be slowed ( slow neutrons ), generally by collision with the nuclei of a neutron moderator, before they can be easily captured. today, this type of fission is commonly used to generate electricity. = = = nuclear fusion = = = if nuclei are forced to collide, they can undergo nuclear fusion. this process may release or absorb energy. when the resulting nucleus is lighter than that of iron, energy is normally released ; when the nucleus is heavier than that of iron, energy is generally absorbed. this process of fusion occurs in stars, which derive their energy from hydrogen and helium. they form, through stellar nucleos - sustaining chain reaction. a mass of fissile material large enough ( and in a suitable configuration ) to induce a self - sustaining chain reaction is called a critical mass. when a neutron is captured by a suitable nucleus, fission may occur immediately, or the nucleus may persist in an unstable state for a short time. if there are enough immediate decays to carry on the chain reaction, the mass is said to be prompt critical, and the energy release will grow rapidly and uncontrollably, usually leading to an explosion. when discovered on the eve of world war ii, this insight led multiple countries to begin programs investigating the possibility of constructing an atomic bomb — a weapon which utilized fission reactions to generate far more energy than could be created with chemical explosives. the manhattan project, run by the united states with the help of the united kingdom and canada, developed multiple fission weapons which were used against japan in 1945 at hiroshima and nagasaki. during the project, the first fission reactors were developed as well, though they were primarily for weapons manufacture and did not generate electricity. in 1951, the first nuclear fission power plant was the first to produce electricity at the experimental breeder reactor no. 1 ( ebr - 1 ), in arco, idaho, ushering in the " atomic age " of more intensive human energy use. however, if the mass is critical only when the delayed neutrons are included, then the reaction can be controlled, for example by the introduction or removal of neutron absorbers. this is what allows nuclear reactors to be built. fast neutrons are not easily captured by nuclei ; they must be slowed ( slow neutrons ), generally by collision with the nuclei of a neutron moderator, before they can be easily captured. today, this type of fission is commonly used to generate electricity. = = = nuclear fusion = = = if nuclei are forced to collide, they can undergo nuclear fusion. this process may release or absorb energy. when the resulting nucleus is lighter than that of iron, energy is normally released ; when the nucleus is heavier than that of iron, energy is generally absorbed. this process of fusion occurs in stars, which derive their energy from hydrogen and helium. they form, through stellar nucleosynthesis, the light elements ( lithium to calcium ) as well as some of the heavy elements ( beyond iron and nickel, via the s - process ). the remaining abundance of heavy elements, from nickel to uranium and beyond, is due to supernova nucleosynthesis, the r - process. of course the amount of a particular substance per volume of solution, and is commonly reported in mol / dm3. = = = phase = = = in addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. for the most part, the chemical classifications are independent of these bulk phase classifications ; however, some more exotic phases are incompatible with certain chemical properties. a phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature. physical properties, such as density and refractive index tend to fall within values characteristic of the phase. the phase of matter is defined by the phase transition, which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions. sometimes the distinction between phases can be continuous instead of having a discrete boundary ; in this case the matter is considered to be in a supercritical state. when three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions. the most familiar examples of phases are solids, liquids, and gases. many substances exhibit multiple solid phases. for example, there are three phases of solid iron ( alpha, gamma, and delta ) that vary based on temperature and pressure. a principal difference between solid phases is the crystal structure, or arrangement, of the atoms. another phase commonly encountered in the study of chemistry is the aqueous phase, which is the state of substances dissolved in aqueous solution ( that is, in water ). less familiar phases include plasmas, bose – einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. while most familiar phases deal with three - dimensional systems, it is also possible to define analogs in two - dimensional systems, which has received attention for its relevance to systems in biology. = = = bonding = = = atoms sticking together in molecules or crystals are said to be bonded with one another. a chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them. more than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom. the chemical bond can be a covalent bond, an ionic bond, a hydrogen bond or just because of van der wa al - kimia is derived from the ancient greek χημια, which is in turn derived from the word kemet, which is the ancient name of egypt in the egyptian language. alternately, al - kimia may derive from χημεια ' cast together '. = = modern principles = = the current model of atomic structure is the quantum mechanical model. traditional chemistry starts with the study of elementary particles, atoms, molecules, substances, metals, crystals and other aggregates of matter. matter can be studied in solid, liquid, gas and plasma states, in isolation or in combination. the interactions, reactions and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together. such behaviors are studied in a chemistry laboratory. the chemistry laboratory stereotypically uses various forms of laboratory glassware. however glassware is not central to chemistry, and a great deal of experimental ( as well as applied / industrial ) chemistry is done without it. a chemical reaction is a transformation of some substances into one or more different substances. the basis of such a chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. it can be symbolically depicted through a chemical equation, which usually involves atoms as subjects. the number of atoms on the left and the right in the equation for a chemical transformation is equal. ( when the number of atoms on either side is unequal, the transformation is referred to as a nuclear reaction or radioactive decay. ) the type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws. energy and entropy considerations are invariably important in almost all chemical studies. chemical substances are classified in terms of their structure, phase, as well as their chemical compositions. they can be analyzed using the tools of chemical analysis, e. g. spectroscopy and chromatography. scientists engaged in chemical research are known as chemists. most chemists specialize in one or more sub - disciplines. several concepts are essential for the study of chemistry ; some of them are : = = = matter = = = in chemistry, matter is defined as anything that has rest mass and volume ( it takes up space ) and is made up of particles. the particles that make up matter have rest mass as well – not all particles have rest mass, such as the photon. matter can be a pure chemical substance or a mixture of substances. = = = = atom = = = = Question: After what state is reached, the concentrations of all reaction components remain constant unless a change is made to the system? A) equality B) homeostasis C) equilibrium D) level	C) equilibrium
Context: the best - suited crops ( e. g., those with the highest yields ) to produce enough food to support a growing population. as crops and fields became increasingly large and difficult to maintain, it was discovered that specific organisms and their by - products could effectively fertilize, restore nitrogen, and control pests. throughout the history of agriculture, farmers have inadvertently altered the genetics of their crops through introducing them to new environments and breeding them with other plants — one of the first forms of biotechnology. these processes also were included in early fermentation of beer. these processes were introduced in early mesopotamia, egypt, china and india, and still use the same basic biological methods. in brewing, malted grains ( containing enzymes ) convert starch from grains into sugar and then adding specific yeasts to produce beer. in this process, carbohydrates in the grains broke down into alcohols, such as ethanol. later, other cultures produced the process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united kingdom desperately needed to manufacture explosives during world war i. biotechnology has also led to the development of antibiotics. in 1928, alexander fleming discovered the mold penicillium. his work led to the purification of the antibiotic formed by the mold by howard florey, ernst boris chain and norman heatley – to form . throughout the history of agriculture, farmers have inadvertently altered the genetics of their crops through introducing them to new environments and breeding them with other plants — one of the first forms of biotechnology. these processes also were included in early fermentation of beer. these processes were introduced in early mesopotamia, egypt, china and india, and still use the same basic biological methods. in brewing, malted grains ( containing enzymes ) convert starch from grains into sugar and then adding specific yeasts to produce beer. in this process, carbohydrates in the grains broke down into alcohols, such as ethanol. later, other cultures produced the process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united kingdom desperately needed to manufacture explosives during world war i. biotechnology has also led to the development of antibiotics. in 1928, alexander fleming discovered the mold penicillium. his work led to the purification of the antibiotic formed by the mold by howard florey, ernst boris chain and norman heatley – to form what we today know as penicillin. in 1940, penicillin became available for medicinal use to treat bacterial infections in humans. the field of modern biotechnology is generally thought of as having been born in 1971 when paul berg ' s ( stanford ) experiments in gene splicing had early success. herbert w. boyer and still use the same basic biological methods. in brewing, malted grains ( containing enzymes ) convert starch from grains into sugar and then adding specific yeasts to produce beer. in this process, carbohydrates in the grains broke down into alcohols, such as ethanol. later, other cultures produced the process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united kingdom desperately needed to manufacture explosives during world war i. biotechnology has also led to the development of antibiotics. in 1928, alexander fleming discovered the mold penicillium. his work led to the purification of the antibiotic formed by the mold by howard florey, ernst boris chain and norman heatley – to form what we today know as penicillin. in 1940, penicillin became available for medicinal use to treat bacterial infections in humans. the field of modern biotechnology is generally thought of as having been born in 1971 when paul berg ' s ( stanford ) experiments in gene splicing had early success. herbert w. boyer ( univ. calif. at san francisco ) and stanley n. cohen ( stanford ) significantly advanced the new technology in 1972 by transferring genetic material into a bacterium, such that the imported material would be reproduced. the commercial viability of a biotechnology industry was significantly expanded on june 16, 1980, when the united states there are a few different mechanisms that can cause white dwarf stars to vary in brightness, providing opportunities to probe the physics, structures, and formation of these compact stellar remnants. the observational characteristics of the three most common types of white dwarf variability are summarized : stellar pulsations, rotation, and ellipsoidal variations from tidal distortion in binary systems. stellar pulsations are emphasized as the most complex type of variability, which also has the greatest potential to reveal the conditions of white dwarf interiors. two types of stars are known to have strong, large scale magnetic fields : the main sequence ap stars and the magnetic white dwarfs. this suggest that the former might be the progenitors of the latter. in order to test this idea, i have carried out a search for large scale magnetic fields in stars with evolutionary states which are intermediate, i. e. in horizontal branch stars and in hot subdwarfs. the broad definition of " utilizing a biotechnological system to make products ". indeed, the cultivation of plants may be viewed as the earliest biotechnological enterprise. agriculture has been theorized to have become the dominant way of producing food since the neolithic revolution. through early biotechnology, the earliest farmers selected and bred the best - suited crops ( e. g., those with the highest yields ) to produce enough food to support a growing population. as crops and fields became increasingly large and difficult to maintain, it was discovered that specific organisms and their by - products could effectively fertilize, restore nitrogen, and control pests. throughout the history of agriculture, farmers have inadvertently altered the genetics of their crops through introducing them to new environments and breeding them with other plants — one of the first forms of biotechnology. these processes also were included in early fermentation of beer. these processes were introduced in early mesopotamia, egypt, china and india, and still use the same basic biological methods. in brewing, malted grains ( containing enzymes ) convert starch from grains into sugar and then adding specific yeasts to produce beer. in this process, carbohydrates in the grains broke down into alcohols, such as ethanol. later, other cultures produced the process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united this is a popular article about the work of maryna viazovska, 2022 fields medalist. process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united kingdom desperately needed to manufacture explosives during world war i. biotechnology has also led to the development of antibiotics. in 1928, alexander fleming discovered the mold penicillium. his work led to the purification of the antibiotic formed by the mold by howard florey, ernst boris chain and norman heatley – to form what we today know as penicillin. in 1940, penicillin became available for medicinal use to treat bacterial infections in humans. the field of modern biotechnology is generally thought of as having been born in 1971 when paul berg ' s ( stanford ) experiments in gene splicing had early success. herbert w. boyer ( univ. calif. at san francisco ) and stanley n. cohen ( stanford ) significantly advanced the new technology in 1972 by transferring genetic material into a bacterium, such that the imported material would be reproduced. the commercial viability of a biotechnology industry was significantly expanded on june 16, 1980, when the united states supreme court ruled that a genetically modified microorganism could be patented in the case of diamond v. chakrabarty. indian - born ananda chakrabarty, working for general electric, had modified a bacterium ( of the genus pseudomonas ) capable of breaking down crude oil, which he proposed to ultramagnetized neutron stars or magnetars are magnetically powered neutron stars. their strong magnetic fields dominate the physical processes in their crusts and their surroundings. the past few years have seen several advances in our theoretical and observational understanding of these objects. in spite of a surfeit of observations, their spectra are still poorly understood. i will discuss the emission from strongly magnetized condensed matter surfaces of neutron stars, recent advances in our expectations of the surface composition of magnetars and a model for the non - thermal emission from these objects. various versions of club are shown to be different. a question of soukup, fuchino and juhasz, is it consistent to have a stick without club, is answered as a consequence. the more detailed version of the paper, which is coming up, also answers a question of galvin. Question: What type of reproduction is exemplified by starfish and yeasts? A) bacteria reproduction B) sexual reproduction C) asexual reproduction D) microscopic reproduction	C) asexual reproduction
Context: grasping an object is a matter of first moving a prehensile organ at some position in the world, and then managing the contact relationship between the prehensile organ and the object. once the contact relationship has been established and made stable, the object is part of the body and it can move in the world. as any action, the action of grasping is ontologically anchored in the physical space while the correlative movement originates in the space of the body. evolution has found amazing solutions that allow organisms to rapidly and efficiently manage the relationship between their body and the world. it is then natural that roboticists consider taking inspiration of these natural solutions, while contributing to better understand their origin. of a point on the object, including whole - body translations and rotations ( rigid transformations ). deformation are changes in the relative position between internals points on the object, excluding rigid transformations, causing the body to change shape or size. strain is the relative internal deformation, the dimensionless change in shape of an infinitesimal cube of material relative to a reference configuration. mechanical strains are caused by mechanical stress, see stress - strain curve. the relationship between stress and strain is generally linear and reversible up until the yield point and the deformation is elastic. elasticity in materials occurs when applied stress does not surpass the energy required to break molecular bonds, allowing the material to deform reversibly and return to its original shape once the stress is removed. the linear relationship for a material is known as young ' s modulus. above the yield point, some degree of permanent distortion remains after unloading and is termed plastic deformation. the determination of the stress and strain throughout a solid object is given by the field of strength of materials and for a structure by structural analysis. in the above figure, it can be seen that the compressive loading ( indicated by the arrow ) has caused deformation in the cylinder so that the original shape ( dashed lines ) has changed ( deformed ) into one with bulging sides. the sides bulge because the material, although strong enough to not crack or otherwise fail, is not strong enough to support the load without change. as a result, the material is forced out laterally. internal forces ( in this case at right angles to the deformation ) resist the applied load. = = types of deformation = = depending on the type of material, size and geometry of the object, and the forces applied, various types of deformation may result. the image to the right shows the engineering stress vs. strain diagram for a typical ductile material such as steel. different deformation modes may occur under different conditions, as can be depicted using a deformation mechanism map. permanent deformation is irreversible ; the deformation stays even after removal of the applied forces, while the temporary deformation is recoverable as it disappears after the removal of applied forces. temporary deformation is also called elastic deformation, while the permanent deformation is called plastic deformation. = = = elastic deformation = = = the study of temporary or elastic deformation in the case of engineering strain is applied to materials used in mechanical and structural engineering, such as concrete and steel, which are subjected to very small deformations. engineering strain is modeled by infinitesimal strain theory, also called casting, also called the lost wax process, die casting, centrifugal casting, both vertical and horizontal, and continuous castings. each of these forms has advantages for certain metals and applications considering factors like magnetism and corrosion. forging – a red - hot billet is hammered into shape. rolling – a billet is passed through successively narrower rollers to create a sheet. extrusion – a hot and malleable metal is forced under pressure through a die, which shapes it before it cools. machining – lathes, milling machines and drills cut the cold metal to shape. sintering – a powdered metal is heated in a non - oxidizing environment after being compressed into a die. fabrication – sheets of metal are cut with guillotines or gas cutters and bent and welded into structural shape. laser cladding – metallic powder is blown through a movable laser beam ( e. g. mounted on a nc 5 - axis machine ). the resulting melted metal reaches a substrate to form a melt pool. by moving the laser head, it is possible to stack the tracks and build up a three - dimensional piece. 3d printing – sintering or melting amorphous powder metal in a 3d space to make any object to shape. cold - working processes, in which the product ' s shape is altered by rolling, fabrication or other processes, while the product is cold, can increase the strength of the product by a process called work hardening. work hardening creates microscopic defects in the metal, which resist further changes of shape. = = = heat treatment = = = metals can be heat - treated to alter the properties of strength, ductility, toughness, hardness and resistance to corrosion. common heat treatment processes include annealing, precipitation strengthening, quenching, and tempering : annealing process softens the metal by heating it and then allowing it to cool very slowly, which gets rid of stresses in the metal and makes the grain structure large and soft - edged so that, when the metal is hit or stressed it dents or perhaps bends, rather than breaking ; it is also easier to sand, grind, or cut annealed metal. quenching is the process of cooling metal very quickly after heating, thus " freezing " the metal ' s molecules in the very hard martensite form, which makes the metal harder. tempering relieves stresses in the metal that were caused by the hardening process ; tempering makes the metal less hard while making it better able to sustain necessary and sufficient conditions for a term to apply to an object. for example : " a platonic solid is a convex, regular polyhedron in three - dimensional euclidean space. " an extensional definition instead lists all objects where the term applies. for example : " a platonic solid is one of the following : tetrahedron, cube, octahedron, dodecahedron, or icosahedron. " in logic, the extension of a predicate is the set of all objects for which the predicate is true. further, the logical principle of extensionality judges two objects to objects to be equal if they satisfy the same external properties. since, by the axiom, two sets are defined to be equal if they satisfy membership, sets are extentional. jose ferreiros credits richard dedekind for being the first to explicitly state the principle, although he does not assert it as a definition : it very frequently happens that different things a, b, c... considered for any reason under a common point of view, are collected together in the mind, and one then says that they form a system s ; one calls the things a, b, c... the elements of the system s, they are contained in s ; conversely, s consists of these elements. such a system s ( or a collection, a manifold, a totality ), as an object of our thought, is likewise a thing ; it is completely determined when, for every thing, it is determined whether it is an element of s or not. = = = background = = = around the turn of the 20th century, mathematics faced several paradoxes and counter - intuitive results. for example, russell ' s paradox showed a contradiction of naive set theory, it was shown that the parallel postulate cannot be proved, the existence of mathematical objects that cannot be computed or explicitly described, and the existence of theorems of arithmetic that cannot be proved with peano arithmetic. the result was a foundational crisis of mathematics. the resolution of this crisis involved the rise of a new mathematical discipline called mathematical logic, which studies formal logic within mathematics. subsequent discoveries in the 20th century then stabilized the foundations of mathematics into a coherent framework valid for all mathematics. this framework is based on a systematic use of axiomatic method and on set theory, specifically zermelo – fraenkel set theory, developed by ernst zermelo and abraham fraenkel. this set theory ( and set theory in general ) is now considered the most common foundation of mathematics needed are stored in containers that are still in use. if methods for a non - existent object are called, a null pointer exception is thrown. one of the ideas behind java ' s automatic memory management model is that programmers can be spared the burden of having to perform manual memory management. in some languages, memory for the creation of objects is implicitly allocated on the stack or explicitly allocated and deallocated from the heap. in the latter case, the responsibility of managing memory resides with the programmer. if the program does not deallocate an object, a memory leak occurs. if the program attempts to access or deallocate memory that has already been deallocated, the result is undefined and difficult to predict, and the program is likely to become unstable or crash. this can be partially remedied by the use of smart pointers, but these add overhead and complexity. garbage collection does not prevent logical memory leaks, i. e. those where the memory is still referenced but never used. garbage collection may happen at any time. ideally, it will occur when a program is idle. it is guaranteed to be triggered if there is insufficient free memory on the heap to allocate a new object ; this can cause a program to stall momentarily. explicit memory management is not possible in java. java does not support c / c + + style pointer arithmetic, where object addresses can be arithmetically manipulated ( e. g. by adding or subtracting an offset ). this allows the garbage collector to relocate referenced objects and ensures type safety and security. as in c + + and some other object - oriented languages, variables of java ' s primitive data types are either stored directly in fields ( for objects ) or on the stack ( for methods ) rather than on the heap, as is commonly true for non - primitive data types ( but see escape analysis ). this was a conscious decision by java ' s designers for performance reasons. java contains multiple types of garbage collectors. since java 9, hotspot uses the garbage first garbage collector ( g1gc ) as the default. however, there are also several other garbage collectors that can be used to manage the heap, such as the z garbage collector ( zgc ) introduced in java 11, and shenandoah gc, introduced in java 12 but unavailable in oracle - produced openjdk builds. shenandoah is instead available in third - party builds of openjdk, such as eclipse temurin. for most applications in java, g1gc is sufficient. ; however, a successful large - scale industrial application of the process was the development of continuous freeze drying of coffee. high - temperature short time processing – these processes, for the most part, are characterized by rapid heating and cooling, holding for a short time at a relatively high temperature and filling aseptically into sterile containers. decaffeination of coffee and tea – decaffeinated coffee and tea was first developed on a commercial basis in europe around 1900. the process is described in u. s. patent 897, 763. green coffee beans are treated with water, heat and solvents to remove the caffeine from the beans. process optimization – food technology now allows production of foods to be more efficient, oil saving technologies are now available on different forms. production methods and methodology have also become increasingly sophisticated. aseptic packaging – the process of filling a commercially sterile product into a sterile container and hermetically sealing the containers so that re - infection is prevented. thus, this results into a shelf stable product at ambient conditions. food irradiation – the process of exposing food and food packaging to ionizing radiation can effectively destroy organisms responsible for spoilage and foodborne illness and inhibit sprouting, extending shelf life. commercial fruit ripening rooms using ethylene as a plant hormone. food delivery – an order is typically made either through a restaurant or grocer ' s website or mobile app, or through a food ordering company. the ordered food is typically delivered in boxes or bags to the customer ' s doorsteps. = = categories = = technology has innovated these categories from the food industry : agricultural technology – or agtech, it is the use of technology in agriculture, horticulture, and aquaculture with the aim of improving yield, efficiency, and profitability. agricultural technology can be products, services or applications derived from agriculture that improve various input / output processes. food science – technology in this sector focuses on the development of new functional ingredients and alternative proteins. foodservice – technology innovated the way establishments prepare, supply, and serve food outside the home. there ' s a tendency to create the conditions for the restaurant of the future with robotics and cloudkitchens. consumer tech – technology allows what we call consumer electronics, which is the equipment of consumers with devices that facilitates the cooking process. food delivery – as the food delivery market is growing, companies and startups are rapidly revolutionizing the communication process between consumers and food establishments, with platform - to - consumer delivery as the no longer in use. once no references to an object remain, the unreachable memory becomes eligible to be freed automatically by the garbage collector. something similar to a memory leak may still occur if a programmer ' s code holds a reference to an object that is no longer needed, typically when objects that are no longer needed are stored in containers that are still in use. if methods for a non - existent object are called, a null pointer exception is thrown. one of the ideas behind java ' s automatic memory management model is that programmers can be spared the burden of having to perform manual memory management. in some languages, memory for the creation of objects is implicitly allocated on the stack or explicitly allocated and deallocated from the heap. in the latter case, the responsibility of managing memory resides with the programmer. if the program does not deallocate an object, a memory leak occurs. if the program attempts to access or deallocate memory that has already been deallocated, the result is undefined and difficult to predict, and the program is likely to become unstable or crash. this can be partially remedied by the use of smart pointers, but these add overhead and complexity. garbage collection does not prevent logical memory leaks, i. e. those where the memory is still referenced but never used. garbage collection may happen at any time. ideally, it will occur when a program is idle. it is guaranteed to be triggered if there is insufficient free memory on the heap to allocate a new object ; this can cause a program to stall momentarily. explicit memory management is not possible in java. java does not support c / c + + style pointer arithmetic, where object addresses can be arithmetically manipulated ( e. g. by adding or subtracting an offset ). this allows the garbage collector to relocate referenced objects and ensures type safety and security. as in c + + and some other object - oriented languages, variables of java ' s primitive data types are either stored directly in fields ( for objects ) or on the stack ( for methods ) rather than on the heap, as is commonly true for non - primitive data types ( but see escape analysis ). this was a conscious decision by java ' s designers for performance reasons. java contains multiple types of garbage collectors. since java 9, hotspot uses the garbage first garbage collector ( g1gc ) as the default. however, there are also several other garbage collectors that can be used to manage the heap, such as the z garbage collector ( zgc ) the hun tian theory ), or as being without substance while the heavenly bodies float freely ( the hsuan yeh theory ), the earth was at all times flat, although perhaps bulging up slightly. the model of an egg was often used by chinese astronomers such as zhang heng ( 78 – 139 ad ) to describe the heavens as spherical : the heavens are like a hen ' s egg and as round as a crossbow bullet ; the earth is like the yolk of the egg, and lies in the centre. this analogy with a curved egg led some modern historians, notably joseph needham, to conjecture that chinese astronomers were, after all, aware of the earth ' s sphericity. the egg reference, however, was rather meant to clarify the relative position of the flat earth to the heavens : in a passage of zhang heng ' s cosmogony not translated by needham, zhang himself says : " heaven takes its body from the yang, so it is round and in motion. earth takes its body from the yin, so it is flat and quiescent ". the point of the egg analogy is simply to stress that the earth is completely enclosed by heaven, rather than merely covered from above as the kai tian describes. chinese astronomers, many of them brilliant men by any standards, continued to think in flat - earth terms until the seventeenth century ; this surprising fact might be the starting - point for a re - examination of the apparent facility with which the idea of a spherical earth found acceptance in fifth - century bc greece. further examples cited by needham supposed to demonstrate dissenting voices from the ancient chinese consensus actually refer without exception to the earth being square, not to it being flat. accordingly, the 13th - century scholar li ye, who argued that the movements of the round heaven would be hindered by a square earth, did not advocate a spherical earth, but rather that its edge should be rounded off so as to be circular. however, needham disagrees, affirming that li ye believed the earth to be spherical, similar in shape to the heavens but much smaller. this was preconceived by the 4th - century scholar yu xi, who argued for the infinity of outer space surrounding the earth and that the latter could be either square or round, in accordance to the shape of the heavens. when chinese geographers of the 17th century, influenced by european cartography and astronomy, showed the earth as a sphere that could be circumnavigated by sailing around the globe, they energy is no doubt an intuitive concept. following a previous analysis on the nature of elementary particles and associated elementary quantum fields, the peculiar status and role of energy is scrutinised further at elementary and larger scales. energy physical characterisation shows that it is a primordial component of reality highlighting the quantum fields natural tendencies to interact, the elementary particles natural tendency to constitute complex bodies and every material thing natural tendency to actualise and be active. energy therefore is a primordial notion in need of a proper assessment. creation of objects is implicitly allocated on the stack or explicitly allocated and deallocated from the heap. in the latter case, the responsibility of managing memory resides with the programmer. if the program does not deallocate an object, a memory leak occurs. if the program attempts to access or deallocate memory that has already been deallocated, the result is undefined and difficult to predict, and the program is likely to become unstable or crash. this can be partially remedied by the use of smart pointers, but these add overhead and complexity. garbage collection does not prevent logical memory leaks, i. e. those where the memory is still referenced but never used. garbage collection may happen at any time. ideally, it will occur when a program is idle. it is guaranteed to be triggered if there is insufficient free memory on the heap to allocate a new object ; this can cause a program to stall momentarily. explicit memory management is not possible in java. java does not support c / c + + style pointer arithmetic, where object addresses can be arithmetically manipulated ( e. g. by adding or subtracting an offset ). this allows the garbage collector to relocate referenced objects and ensures type safety and security. as in c + + and some other object - oriented languages, variables of java ' s primitive data types are either stored directly in fields ( for objects ) or on the stack ( for methods ) rather than on the heap, as is commonly true for non - primitive data types ( but see escape analysis ). this was a conscious decision by java ' s designers for performance reasons. java contains multiple types of garbage collectors. since java 9, hotspot uses the garbage first garbage collector ( g1gc ) as the default. however, there are also several other garbage collectors that can be used to manage the heap, such as the z garbage collector ( zgc ) introduced in java 11, and shenandoah gc, introduced in java 12 but unavailable in oracle - produced openjdk builds. shenandoah is instead available in third - party builds of openjdk, such as eclipse temurin. for most applications in java, g1gc is sufficient. in prior versions of java, such as java 8, the parallel garbage collector was used as the default garbage collector. having solved the memory management problem does not relieve the programmer of the burden of handling properly other kinds of resources, like network or database connections, file handles, etc., especially in the presence of exceptions. Question: What is the scientific term for stored energy an object has due to its position or shape? A) potential energy B) repeat energy C) new energy D) mechanical energy	A) potential energy
Context: also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in in a voltaic cell, positive ( negative ) ions flow from the low ( high ) potential electrode to the high ( low ) potential electrode, driven by an ` electromotive force ' which points in opposite direction and overcomes the electric force. similarly in a superconductor charge flows in direction opposite to that dictated by the faraday electric field as the magnetic field is expelled in the meissner effect. the puzzle is the same in both cases : what drives electric charges against electromagnetic forces? i propose that the answer is also the same in both cases : kinetic energy lowering, or ` quantum pressure '. in steady state, the fuel cycle of a fusion plasma requires inward particle fluxes of fuel ions. these particle flows are also accompanied by heating. in the case of classical transport in a rotating cylindrical plasma, this heating can proceed through several distinct channels depending on the physical mechanisms involved. some channels directly heat the fuel ions themselves, whereas others heat electrons. which channel dominates depends, in general, on the details of the temperature, density, and rotation profiles of the plasma constituents. however, remarkably, under relatively few assumptions concerning these profiles, if the alpha particles, the byproducts of the fusion reaction, can be removed directly by other means, a hot - ion mode tends to emerge naturally. becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform a review of mhd dynamos and turbulence. from the insignificant drainage areas of streams rising on high ground near the coast and flowing straight down into the sea, up to immense tracts of continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching the ocean. the size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their the surface of the membrane, retentate is removed from the same side further downstream, whereas the permeate flow is tracked on the other side. in dead - end filtration, the direction of the fluid flow is normal to the membrane surface. both flow geometries offer some advantages and disadvantages. generally, dead - end filtration is used for feasibility studies on a laboratory scale. the dead - end membranes are relatively easy to fabricate which reduces the cost of the separation process. the dead - end membrane separation process is easy to implement and the process is usually cheaper than cross - flow membrane filtration. the dead - end filtration process is usually a batch - type process, where the filtering solution is loaded ( or slowly fed ) into the membrane device, which then allows passage of some particles subject to the driving force. the main disadvantage of dead - end filtration is the extensive membrane fouling and concentration polarization. the fouling is usually induced faster at higher driving forces. membrane fouling and particle retention in a feed solution also builds up a concentration gradients and particle backflow ( concentration polarization ). the tangential flow devices are more cost and labor - intensive, but they are less susceptible to fouling due to the sweeping effects and high shear rates of the passing flow. the most commonly used synthetic membrane devices ( modules ) are flat sheets / plates, spiral wounds, and hollow fibers. flat membranes used in filtration and separation processes can be enhanced with surface patterning, where microscopic structures are introduced to improve performance. these patterns increase surface area, optimize water flow, and reduce fouling, leading to higher permeability and longer membrane lifespan. research has shown that such modifications can significantly enhance efficiency in water purification, energy applications, and industrial separations. flat plates are usually constructed as circular thin flat membrane surfaces to be used in dead - end geometry modules. spiral wounds are constructed from similar flat membranes but in the form of a " pocket " containing two membrane sheets separated by a highly porous support plate. several such pockets are then wound around a tube to create a tangential flow geometry and to reduce membrane fouling. hollow fiber modules consist of an assembly of self - supporting fibers with dense skin separation layers, and a more open matrix helping to withstand pressure gradients and maintain structural integrity. the hollow fiber modules can contain up to 10, 000 fibers ranging from 200 to 2500 μm in diameter ; the main advantage of hollow fiber modules is the very large surface area within fluid dynamics video demonstrating the evolution of dynamic stall on a wind turbine blade. approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with Question: What kind of current flows in just one direction? A) slow current B) physical current C) Alternating current D) direct current	D) direct current
Context: these are the preparatory notes for a science & music essay, " playing by numbers ", appeared in nature 453 ( 2008 ) 988 - 989. lines are dimension lines and are used for dimensioning, projecting, extending, or leaders. a harder pencil should be used, such as a 2h pencil. type c lines are used for breaks when the whole object is not shown. these are freehand drawn and only for short breaks. 2h pencil type d lines are similar to type c, except these are zigzagged and only for longer breaks. 2h pencil type e lines indicate hidden outlines of internal features of an object. these are dotted lines. 2h pencil type f lines are type e lines, except these are used for drawings in electrotechnology. 2h pencil type g lines are used for centre lines. these are dotted lines, but a long line of 10 – 20 mm, then a 1 mm gap, then a small line of 2 mm. 2h pencil type h lines are the same as type g, except that every second long line is thicker. these indicate the cutting plane of an object. 2h pencil type k lines indicate the alternate positions of an object and the line taken by that object. these are drawn with a long line of 10 – 20 mm, then a small gap, then a small line of 2 mm, then a gap, then another small line. 2h pencil. = = = multiple views and projections = = = in most cases, a single view is not sufficient to show all necessary features, and several views are used. types of views include the following : = = = = multiview projection = = = = a multiview projection is a type of orthographic projection that shows the object as it looks from the front, right, left, top, bottom, or back ( e. g. the primary views ), and is typically positioned relative to each other according to the rules of either first - angle or third - angle projection. the origin and vector direction of the projectors ( also called projection lines ) differs, as explained below. in first - angle projection, the parallel projectors originate as if radiated from behind the viewer and pass through the 3d object to project a 2d image onto the orthogonal plane behind it. the 3d object is projected into 2d " paper " space as if you were looking at a radiograph of the object : the top view is under the front view, the right view is at the left of the front view. first - angle projection is the iso standard and is primarily used in europe. in third - angle projection, the parallel projectors originate as if radiated from the far side of the object the classical and the quantum motion of a massive body in the rotating tube is considered. photon is included. the spin motion described by the bargmann - michel - telegdi equation is considered in the rotation tube and rotating system. are commonly referred to as " cross - hatching ". phantom – ( not shown ) are alternately long - and double short - dashed thin lines used to represent a feature or component that is not part of the specified part or assembly. e. g. billet ends that may be used for testing, or the machined product that is the focus of a tooling drawing. lines can also be classified by a letter classification in which each line is given a letter. type a lines show the outline of the feature of an object. they are the thickest lines on a drawing and done with a pencil softer than hb. type b lines are dimension lines and are used for dimensioning, projecting, extending, or leaders. a harder pencil should be used, such as a 2h pencil. type c lines are used for breaks when the whole object is not shown. these are freehand drawn and only for short breaks. 2h pencil type d lines are similar to type c, except these are zigzagged and only for longer breaks. 2h pencil type e lines indicate hidden outlines of internal features of an object. these are dotted lines. 2h pencil type f lines are type e lines, except these are used for drawings in electrotechnology. 2h pencil type g lines are used for centre lines. these are dotted lines, but a long line of 10 – 20 mm, then a 1 mm gap, then a small line of 2 mm. 2h pencil type h lines are the same as type g, except that every second long line is thicker. these indicate the cutting plane of an object. 2h pencil type k lines indicate the alternate positions of an object and the line taken by that object. these are drawn with a long line of 10 – 20 mm, then a small gap, then a small line of 2 mm, then a gap, then another small line. 2h pencil. = = = multiple views and projections = = = in most cases, a single view is not sufficient to show all necessary features, and several views are used. types of views include the following : = = = = multiview projection = = = = a multiview projection is a type of orthographic projection that shows the object as it looks from the front, right, left, top, bottom, or back ( e. g. the primary views ), and is typically positioned relative to each other according to the rules of either first - angle or third - angle projection. the origin and vector direction of the projectors ( on biological causation and the diversity of life. he made countless observations of nature, especially the habits and attributes of plants and animals on lesbos, classified more than 540 animal species, and dissected at least 50. aristotle ' s writings profoundly influenced subsequent islamic and european scholarship, though they were eventually superseded in the scientific revolution. aristotle also contributed to theories of the elements and the cosmos. he believed that the celestial bodies ( such as the planets and the sun ) had something called an unmoved mover that put the celestial bodies in motion. aristotle tried to explain everything through mathematics and physics, but sometimes explained things such as the motion of celestial bodies through a higher power such as god. aristotle did not have the technological advancements that would have explained the motion of celestial bodies. in addition, aristotle had many views on the elements. he believed that everything was derived of the elements earth, water, air, fire, and lastly the aether. the aether was a celestial element, and therefore made up the matter of the celestial bodies. the elements of earth, water, air and fire were derived of a combination of two of the characteristics of hot, wet, cold, and dry, and all had their inevitable place and motion. the motion of these elements begins with earth being the closest to " the earth, " then water, air, fire, and finally aether. in addition to the makeup of all things, aristotle came up with theories as to why things did not return to their natural motion. he understood that water sits above earth, air above water, and fire above air in their natural state. he explained that although all elements must return to their natural state, the human body and other living things have a constraint on the elements – thus not allowing the elements making one who they are to return to their natural state. the important legacy of this period included substantial advances in factual knowledge, especially in anatomy, zoology, botany, mineralogy, geography, mathematics and astronomy ; an awareness of the importance of certain scientific problems, especially those related to the problem of change and its causes ; and a recognition of the methodological importance of applying mathematics to natural phenomena and of undertaking empirical research. in the hellenistic age scholars frequently employed the principles developed in earlier greek thought : the application of mathematics and deliberate empirical research, in their scientific investigations. thus, clear unbroken lines of influence lead from ancient greek and hellenistic philosophers, to medieval muslim philosophers and scientists, to the european renaissance and enlightenment, to the secular sciences of the modern day. neither reason ##d product that is the focus of a tooling drawing. lines can also be classified by a letter classification in which each line is given a letter. type a lines show the outline of the feature of an object. they are the thickest lines on a drawing and done with a pencil softer than hb. type b lines are dimension lines and are used for dimensioning, projecting, extending, or leaders. a harder pencil should be used, such as a 2h pencil. type c lines are used for breaks when the whole object is not shown. these are freehand drawn and only for short breaks. 2h pencil type d lines are similar to type c, except these are zigzagged and only for longer breaks. 2h pencil type e lines indicate hidden outlines of internal features of an object. these are dotted lines. 2h pencil type f lines are type e lines, except these are used for drawings in electrotechnology. 2h pencil type g lines are used for centre lines. these are dotted lines, but a long line of 10 – 20 mm, then a 1 mm gap, then a small line of 2 mm. 2h pencil type h lines are the same as type g, except that every second long line is thicker. these indicate the cutting plane of an object. 2h pencil type k lines indicate the alternate positions of an object and the line taken by that object. these are drawn with a long line of 10 – 20 mm, then a small gap, then a small line of 2 mm, then a gap, then another small line. 2h pencil. = = = multiple views and projections = = = in most cases, a single view is not sufficient to show all necessary features, and several views are used. types of views include the following : = = = = multiview projection = = = = a multiview projection is a type of orthographic projection that shows the object as it looks from the front, right, left, top, bottom, or back ( e. g. the primary views ), and is typically positioned relative to each other according to the rules of either first - angle or third - angle projection. the origin and vector direction of the projectors ( also called projection lines ) differs, as explained below. in first - angle projection, the parallel projectors originate as if radiated from behind the viewer and pass through the 3d object to project a 2d image onto the orthogonal plane behind it. the 3d object is projected into 2d " paper " space as if you were looking at the motion of celestial bodies through a higher power such as god. aristotle did not have the technological advancements that would have explained the motion of celestial bodies. in addition, aristotle had many views on the elements. he believed that everything was derived of the elements earth, water, air, fire, and lastly the aether. the aether was a celestial element, and therefore made up the matter of the celestial bodies. the elements of earth, water, air and fire were derived of a combination of two of the characteristics of hot, wet, cold, and dry, and all had their inevitable place and motion. the motion of these elements begins with earth being the closest to " the earth, " then water, air, fire, and finally aether. in addition to the makeup of all things, aristotle came up with theories as to why things did not return to their natural motion. he understood that water sits above earth, air above water, and fire above air in their natural state. he explained that although all elements must return to their natural state, the human body and other living things have a constraint on the elements – thus not allowing the elements making one who they are to return to their natural state. the important legacy of this period included substantial advances in factual knowledge, especially in anatomy, zoology, botany, mineralogy, geography, mathematics and astronomy ; an awareness of the importance of certain scientific problems, especially those related to the problem of change and its causes ; and a recognition of the methodological importance of applying mathematics to natural phenomena and of undertaking empirical research. in the hellenistic age scholars frequently employed the principles developed in earlier greek thought : the application of mathematics and deliberate empirical research, in their scientific investigations. thus, clear unbroken lines of influence lead from ancient greek and hellenistic philosophers, to medieval muslim philosophers and scientists, to the european renaissance and enlightenment, to the secular sciences of the modern day. neither reason nor inquiry began with the ancient greeks, but the socratic method did, along with the idea of forms, give great advances in geometry, logic, and the natural sciences. according to benjamin farrington, former professor of classics at swansea university : " men were weighing for thousands of years before archimedes worked out the laws of equilibrium ; they must have had practical and intuitional knowledge of the principals involved. what archimedes did was to sort out the theoretical implications of this practical knowledge and present the resulting body of knowledge as a logically coherent system. " and again : " with astonishment we find ourselves on the threshold of modern science are continuous lines used to depict edges directly visible from a particular angle. hidden – are short - dashed lines that may be used to represent edges that are not directly visible. center – are alternately long - and short - dashed lines that may be used to represent the axes of circular features. cutting plane – are thin, medium - dashed lines, or thick alternately long - and double short - dashed that may be used to define sections for section views. section – are thin lines in a pattern ( pattern determined by the material being " cut " or " sectioned " ) used to indicate surfaces in section views resulting from " cutting ". section lines are commonly referred to as " cross - hatching ". phantom – ( not shown ) are alternately long - and double short - dashed thin lines used to represent a feature or component that is not part of the specified part or assembly. e. g. billet ends that may be used for testing, or the machined product that is the focus of a tooling drawing. lines can also be classified by a letter classification in which each line is given a letter. type a lines show the outline of the feature of an object. they are the thickest lines on a drawing and done with a pencil softer than hb. type b lines are dimension lines and are used for dimensioning, projecting, extending, or leaders. a harder pencil should be used, such as a 2h pencil. type c lines are used for breaks when the whole object is not shown. these are freehand drawn and only for short breaks. 2h pencil type d lines are similar to type c, except these are zigzagged and only for longer breaks. 2h pencil type e lines indicate hidden outlines of internal features of an object. these are dotted lines. 2h pencil type f lines are type e lines, except these are used for drawings in electrotechnology. 2h pencil type g lines are used for centre lines. these are dotted lines, but a long line of 10 – 20 mm, then a 1 mm gap, then a small line of 2 mm. 2h pencil type h lines are the same as type g, except that every second long line is thicker. these indicate the cutting plane of an object. 2h pencil type k lines indicate the alternate positions of an object and the line taken by that object. these are drawn with a long line of 10 – 20 mm, then a small gap, then a small line of 2 mm, then a gap, then another small line. 2h - dashed lines, or thick alternately long - and double short - dashed that may be used to define sections for section views. section – are thin lines in a pattern ( pattern determined by the material being " cut " or " sectioned " ) used to indicate surfaces in section views resulting from " cutting ". section lines are commonly referred to as " cross - hatching ". phantom – ( not shown ) are alternately long - and double short - dashed thin lines used to represent a feature or component that is not part of the specified part or assembly. e. g. billet ends that may be used for testing, or the machined product that is the focus of a tooling drawing. lines can also be classified by a letter classification in which each line is given a letter. type a lines show the outline of the feature of an object. they are the thickest lines on a drawing and done with a pencil softer than hb. type b lines are dimension lines and are used for dimensioning, projecting, extending, or leaders. a harder pencil should be used, such as a 2h pencil. type c lines are used for breaks when the whole object is not shown. these are freehand drawn and only for short breaks. 2h pencil type d lines are similar to type c, except these are zigzagged and only for longer breaks. 2h pencil type e lines indicate hidden outlines of internal features of an object. these are dotted lines. 2h pencil type f lines are type e lines, except these are used for drawings in electrotechnology. 2h pencil type g lines are used for centre lines. these are dotted lines, but a long line of 10 – 20 mm, then a 1 mm gap, then a small line of 2 mm. 2h pencil type h lines are the same as type g, except that every second long line is thicker. these indicate the cutting plane of an object. 2h pencil type k lines indicate the alternate positions of an object and the line taken by that object. these are drawn with a long line of 10 – 20 mm, then a small gap, then a small line of 2 mm, then a gap, then another small line. 2h pencil. = = = multiple views and projections = = = in most cases, a single view is not sufficient to show all necessary features, and several views are used. types of views include the following : = = = = multiview projection = = = = a multiview projection is a type of orthographic projection a suitable choice of the four components of the metric tensor which are at our discretion allows to represent geodesically also the non - gravitational motions. Question: Most motions in nature follow ________ rather than straight lines? A) vertical paths B) curved paths C) sharp paths D) horizontal paths	B) curved paths
Context: energy is no doubt an intuitive concept. following a previous analysis on the nature of elementary particles and associated elementary quantum fields, the peculiar status and role of energy is scrutinised further at elementary and larger scales. energy physical characterisation shows that it is a primordial component of reality highlighting the quantum fields natural tendencies to interact, the elementary particles natural tendency to constitute complex bodies and every material thing natural tendency to actualise and be active. energy therefore is a primordial notion in need of a proper assessment. einstein, when he began working on the general theory of relativity, believed that energy of any kind is the source of the gravitational field. therefore, the energy of gravity, like any energy, must be the source of the field. it was previously discovered that the energy - momentum tensor of the gravitational field is already contained in the ricci tensor. this hypothesis is used to construct a new equation of the gravitational field. the gravitational poynting vector provides a mechanism for the transfer of gravitational energy to a system of falling objects. in the following we will show that the gravitational poynting vector together with the gravitational larmor theorem also provides a mechanism to explain how massive bodies acquire rotational kinetic energy when external mechanical forces are applied on them. factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. for example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. the existence of characteristic ##physical processes which take place in human beings as they make sense of information received through the visual system. the subject of the image. when developing an imaging system, designers must consider the observables associated with the subjects which will be imaged. these observables generally take the form of emitted or reflected energy, such as electromagnetic energy or mechanical energy. the capture device. once the observables associated with the subject are characterized, designers can then identify and integrate the technologies needed to capture those observables. for example, in the case of consumer digital cameras, those technologies include optics for collecting energy in the visible portion of the electromagnetic spectrum, and electronic detectors for converting the electromagnetic energy into an electronic signal. the processor. for all digital imaging systems, the electronic signals produced by the capture device must be manipulated by an algorithm which formats the signals so they can be displayed as an image. in practice, there are often multiple processors involved in the creation of a digital image. the display. the display takes the electronic signals which have been manipulated by the processor and renders them on some visual medium. examples include paper ( for printed, or " hard copy " images ), television, computer monitor, or projector. note that some imaging scientists will include additional " links " in their description of the imaging chain. for example, some will include the " source " of the energy which " illuminates " or interacts with the subject of the image. others will include storage and / or transmission systems. = = subfields = = subfields within imaging science include : image processing, computer vision, 3d computer graphics, animations, atmospheric optics, astronomical imaging, biological imaging, digital image restoration, digital imaging, color science, digital photography, holography, magnetic resonance imaging, medical imaging, microdensitometry, optics, photography, remote sensing, radar imaging, radiometry, silver halide, ultrasound imaging, photoacoustic imaging, thermal imaging, visual perception, and various printing technologies. = = methodologies = = acoustic imaging coherent imaging uses an active coherent illumination source, such as in radar, synthetic aperture radar ( sar ), medical ultrasound and optical coherence tomography ; non - coherent imaging systems include fluorescent microscopes, optical microscopes, and telescopes. chemical imaging, the simultaneous measurement of spectra and pictures digital imaging, creating digital images, generally by scanning or through digital photography disk image, a file which contains the exact content of a data storage medium document imaging, replicating documents commonly affect static bodies dynamics, the study of how forces affect moving bodies. dynamics includes kinematics ( about movement, velocity, and acceleration ) and kinetics ( about forces and resulting accelerations ). mechanics of materials, the study of how different materials deform under various types of stress fluid mechanics, the study of how fluids react to forces kinematics, the study of the motion of bodies ( objects ) and systems ( groups of objects ), while ignoring the forces that cause the motion. kinematics is often used in the design and analysis of mechanisms. continuum mechanics, a method of applying mechanics that assumes that objects are continuous ( rather than discrete ) mechanical engineers typically use mechanics in the design or analysis phases of engineering. if the engineering project were the design of a vehicle, statics might be employed to design the frame of the vehicle, in order to evaluate where the stresses will be most intense. dynamics might be used when designing the car ' s engine, to evaluate the forces in the pistons and cams as the engine cycles. mechanics of materials might be used to choose appropriate materials for the frame and engine. fluid mechanics might be used to design a ventilation system for the vehicle ( see hvac ), or to design the intake system for the engine. = = = mechatronics and robotics = = = mechatronics is a combination of mechanics and electronics. it is an interdisciplinary branch of mechanical engineering, electrical engineering and software engineering that is concerned with integrating electrical and mechanical engineering to create hybrid automation systems. in this way, machines can be automated through the use of electric motors, servo - mechanisms, and other electrical systems in conjunction with special software. a common example of a mechatronics system is a cd - rom drive. mechanical systems open and close the drive, spin the cd and move the laser, while an optical system reads the data on the cd and converts it to bits. integrated software controls the process and communicates the contents of the cd to the computer. robotics is the application of mechatronics to create robots, which are often used in industry to perform tasks that are dangerous, unpleasant, or repetitive. these robots may be of any shape and size, but all are preprogrammed and interact physically with the world. to create a robot, an engineer typically employs kinematics ( to determine the robot ' s range of motion ) and mechanics ( to determine the stresses within the robot ). robots are used extensively in industrial automation engineering. they allow businesses to save money on labor, forces and their effect upon matter. typically, engineering mechanics is used to analyze and predict the acceleration and deformation ( both elastic and plastic ) of objects under known forces ( also called loads ) or stresses. subdisciplines of mechanics include statics, the study of non - moving bodies under known loads, how forces affect static bodies dynamics, the study of how forces affect moving bodies. dynamics includes kinematics ( about movement, velocity, and acceleration ) and kinetics ( about forces and resulting accelerations ). mechanics of materials, the study of how different materials deform under various types of stress fluid mechanics, the study of how fluids react to forces kinematics, the study of the motion of bodies ( objects ) and systems ( groups of objects ), while ignoring the forces that cause the motion. kinematics is often used in the design and analysis of mechanisms. continuum mechanics, a method of applying mechanics that assumes that objects are continuous ( rather than discrete ) mechanical engineers typically use mechanics in the design or analysis phases of engineering. if the engineering project were the design of a vehicle, statics might be employed to design the frame of the vehicle, in order to evaluate where the stresses will be most intense. dynamics might be used when designing the car ' s engine, to evaluate the forces in the pistons and cams as the engine cycles. mechanics of materials might be used to choose appropriate materials for the frame and engine. fluid mechanics might be used to design a ventilation system for the vehicle ( see hvac ), or to design the intake system for the engine. = = = mechatronics and robotics = = = mechatronics is a combination of mechanics and electronics. it is an interdisciplinary branch of mechanical engineering, electrical engineering and software engineering that is concerned with integrating electrical and mechanical engineering to create hybrid automation systems. in this way, machines can be automated through the use of electric motors, servo - mechanisms, and other electrical systems in conjunction with special software. a common example of a mechatronics system is a cd - rom drive. mechanical systems open and close the drive, spin the cd and move the laser, while an optical system reads the data on the cd and converts it to bits. integrated software controls the process and communicates the contents of the cd to the computer. robotics is the application of mechatronics to create robots, which are often used in industry to perform tasks that are dangerous, unpleasant, or repetitive. these robots may be of any shape and size, but all are endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer education, science, in fact the whole society, extensively use images. between us and the world are the visual displays. screens, small and large, individual or not, are everywhere. images are increasingly the 2d substrate of our virtual interaction with reality. however images will never support a complete representation of the reality. three - dimensional representations will not change that. images are primarily a spatial representation of our world dedicated to our sight. key aspects such as energy and the associated forces are not spatially materialized. in classical physics, interaction description is based on newton equations with trajectory and force as the dual central concepts. images can in real time show all aspects of trajectories but not the associated dynamical aspects described by forces and energies. contrary to the real world, the world of images opposes no constrain, nor resistance to our actions. only the physical quantities, that do not contain mass in their dimension can be satisfactory represented by images. often symbols such as arrows are introduced to visualize the force vectors. energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. different kinds of spectra are often used in chemical spectroscopy, e. g. ir, microwave, nmr, esr, etc. spectroscopy is also used to identify the composition of remote objects – like stars and distant galaxies – by analyzing their radiation spectra. the term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. = = = reaction = = = when a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. a chemical reaction is therefore a concept related to the " reaction " of a substance when it comes in close contact with another, whether as a mixture or a solution ; exposure to some form of energy, or both. it results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels — often laboratory glassware. chemical reactions can result in the formation or dissociation of molecules, that is, molecules breaking apart to form two or more molecules or rearrangement of atoms within or across molecules. chemical reactions usually involve the making or breaking of chemical bonds. oxidation, reduction, dissociation, acid – base neutralization and molecular rearrangement are some examples of common chemical reactions. a chemical reaction can be symbolically depicted through a chemical equation. while in a non - nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons. the sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. a chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. several empirical rules, like the woodward – hoffmann rules often come in handy while proposing a mechanism for a chemical reaction. according to the iupac gold book, a chemical reaction is " a process that results in the interconversion of chemical species. " accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction. Question: An object's energy due to motion is known as? A) residual energy B) inertia C) thermodynamic energy D) kinetic energy	D) kinetic energy
Context: approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with the carbon - based biosphere has generated a system ( humans ) capable of creating technology that will result in a comparable evolutionary transition. the digital information created by humans has reached a similar magnitude to biological information in the biosphere. since the 1980s, the quantity of digital information stored has doubled about every 2. 5 years, reaching about 5 zettabytes in 2014 ( 5×1021 bytes ). in biological terms, there are 7. 2 billion humans on the planet, each having a genome of 6. 2 billion nucleotides. since one byte can encode four nucleotide pairs, the individual genomes of every human on the planet could be encoded by approximately 1×1019 bytes. the digital realm stored 500 times more information than this in 2014 ( see figure ). the total amount of dna contained in all of the cells on earth is estimated to be about 5. 3×1037 base pairs, equivalent to 1. 325×1037 bytes of information. if growth in digital storage continues at its current rate of 30 – 38 % compound annual growth per year, it will rival the total information content contained in all of the dna in all of the cells on earth in about 110 years. this would represent a doubling of the amount of information stored in the biosphere across a total time period of just 150 years ". = = = implications for human society = = = in february 2009, under the auspices of the association for the advancement of artificial intelligence ( aaai ), eric horvitz chaired a meeting of leading computer scientists, artificial intelligence researchers and roboticists at the asilomar conference center in pacific grove, california. the goal was to discuss the potential impact of the hypothetical possibility that robots could become self - sufficient and able to make their own decisions. they discussed the extent to which computers and robots might be able to acquire autonomy, and to what degree they could use such abilities to pose threats or hazards. some machines are programmed with various forms of semi - autonomy, including the ability to locate their own power sources and choose targets to attack with weapons. also, some computer viruses can evade elimination and, according to scientists in attendance, could therefore be said to have reached a " cockroach " stage of machine intelligence. the conference attendees noted that self - awareness as depicted in science - fiction is probably unlikely, but that other potential hazards and pitfalls exist. frank s. robinson predicts that once humans achieve a machine with the intelligence of a human, scientific and technological problems will be tackled and solved with above any tidal limit and their average freshwater discharge are proportionate to the extent of their basins and the amount of rain which, after falling over these basins, reaches the river channels in the bottom of the valleys, by which it is conveyed to the sea. the drainage basin of a river is the expanse of country bounded by a watershed ( called a " divide " in north america ) over which rainfall flows down towards the river traversing the lowest part of the valley, whereas the rain falling on the far slope of the watershed flows away to another river draining an adjacent basin. river basins vary in extent according to the configuration of the country, ranging from the insignificant drainage areas of streams rising on high ground near the coast and flowing straight down into the sea, up to immense tracts of continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching the ocean. the size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer to increase as far as practicable the navigable depth at the lowest stage of the water level. engineering works to increase the navigability of rivers can only be advantageously undertaken in large rivers with a moderate fall and a fair discharge at their lowest stage, for with a large fall the current presents a great impediment to up - stream navigation, and there are generally variations in water level, and when the discharge becomes small in the dry season. it is impossible to maintain a sufficient depth of water in the low - water channel. the possibility to secure uniformity of depth in a river by lowering the shoals obstructing the channel depends on the nature of the shoals. a soft shoal in the bed of a river is due to deposit from a diminution in velocity of flow, produced by a reduction in fall and by a widening of the channel, or to a loss in concentration of the scour of the main current in passing over from one concave bank to the next on the opposite side. the lowering of such a shoal by dredging merely effects a temporary deepening, for it soon forms again from the causes which produced it. the removal, moreover, of the rocky obstructions at rapids, though increasing the depth and equalizing the flow at these places, produces a lowering of the river above the rapids by facilitating the efflux, which may result in the appearance of fresh shoals at the low stage of the river. where, however, narrow rocky reefs or other hard shoals stretch across the bottom of a river and present obstacles to the erosion by the current of the soft materials forming the bed of the river above and below, their removal may result in permanent improvement by enabling the river to deepen its bed by natural scour. the capability of a river to provide a waterway for navigation during the summer or throughout the dry season depends on the depth that can be secured in the channel at the lowest stage. the problem in the dry season is the small discharge and deficiency in scour during this period. a typical solution is to restrict the width of the low - water channel, concentrate all of the flow in it, and also to fix its position so that it is scoured out every year by the floods which follow the deepest part of the bed along the line of the strongest current. this can be effected by closing subsidiary low - water channels with dikes across them, and narrowing the channel at the low stage by low - dipping cross dikes extending from the river banks down the for inland navigation in the lower portion of their course, as, for instance, the rhine, the danube and the mississippi. river engineering works are only required to prevent changes in the course of the stream, to regulate its depth, and especially to fix the low - water channel and concentrate the flow in it, so as to increase as far as practicable the navigable depth at the lowest stage of the water level. engineering works to increase the navigability of rivers can only be advantageously undertaken in large rivers with a moderate fall and a fair discharge at their lowest stage, for with a large fall the current presents a great impediment to up - stream navigation, and there are generally variations in water level, and when the discharge becomes small in the dry season. it is impossible to maintain a sufficient depth of water in the low - water channel. the possibility to secure uniformity of depth in a river by lowering the shoals obstructing the channel depends on the nature of the shoals. a soft shoal in the bed of a river is due to deposit from a diminution in velocity of flow, produced by a reduction in fall and by a widening of the channel, or to a loss in concentration of the scour of the main current in passing over from one concave bank to the next on the opposite side. the lowering of such a shoal by dredging merely effects a temporary deepening, for it soon forms again from the causes which produced it. the removal, moreover, of the rocky obstructions at rapids, though increasing the depth and equalizing the flow at these places, produces a lowering of the river above the rapids by facilitating the efflux, which may result in the appearance of fresh shoals at the low stage of the river. where, however, narrow rocky reefs or other hard shoals stretch across the bottom of a river and present obstacles to the erosion by the current of the soft materials forming the bed of the river above and below, their removal may result in permanent improvement by enabling the river to deepen its bed by natural scour. the capability of a river to provide a waterway for navigation during the summer or throughout the dry season depends on the depth that can be secured in the channel at the lowest stage. the problem in the dry season is the small discharge and deficiency in scour during this period. a typical solution is to restrict the width of the low - water channel, concentrate all of the flow in it, and also to fix its position so that it is " thrashing ". this frequently leads to high, runaway cpu utilization that can grind the system to a halt. in modern computers, thrashing may occur in the paging system ( if there is not sufficient physical memory or the disk access time is overly long ), or in the i / o communications subsystem ( especially in conflicts over internal bus access ), etc. depending on the configuration and algorithms involved, the throughput and latency of a system may degrade by multiple orders of magnitude. thrashing is when the cpu performs ' productive ' work less and ' swapping ' work more. the overall memory access time may increase since the higher level memory is only as fast as the next lower level in the memory hierarchy. the cpu is busy swapping pages so much that it cannot respond to users ' programs and interrupts as much as required. thrashing occurs when there are too many pages in memory, and each page refers to another page. real memory reduces its capacity to contain all the pages, so it uses ' virtual memory '. when each page in execution demands that page that is not currently in real memory ( ram ) it places some pages on virtual memory and adjusts the required page on ram. if the cpu is too busy doing this task, thrashing occurs. = = = causes = = = in virtual memory systems, thrashing may be caused by programs or workloads that present insufficient locality of reference : if the working set of a program or a workload cannot be effectively held within physical memory, then constant data swapping, i. e., thrashing, may occur. the term was first used during the tape operating system days to describe the sound the tapes made when data was being rapidly written to and read. a worst case might occur on vax processors. a single movl crossing a page boundary could have a source operand using a displacement deferred addressing mode, where the longword containing the operand address crosses a page boundary, and a destination operand using a displacement deferred addressing mode, where the longword containing the operand address crosses a page boundary, and the source and destination could both cross page boundaries. this single instruction references ten pages ; if not all are in ram, each will cause a page fault. the total number of pages thus involved in this particular instruction is ten, and all ten pages must be simultaneously present in memory. if any one of the ten pages cannot be swapped in ( for example to make room for any of the other pages ) : it is limitless as that space which it finds too narrow for its aspirations ; its possibilities are as infinite as the worlds which are forever crowding in and multiplying upon the astronomer ' s gaze ; it is as incapable of being restricted within assigned boundaries or being reduced to definitions of permanent validity, as the consciousness of life, which seems to slumber in each monad, in every atom of matter, in each leaf and bud cell, and is forever ready to burst forth into new forms of vegetable and animal existence. james joseph sylvester what is mathematics? what is it for? what are mathematicians doing nowadays? wasn ' t it all finished long ago? how many new numbers can you invent anyway? is today ' s mathematics just a matter of huge calculations, with the mathematician as a kind of zookeeper, making sure the precious computers are fed and watered? if it ' s not, what is it other than the incomprehensible outpourings of superpowered brainboxes with their heads in the clouds and their feet dangling from the lofty balconies of their ivory towers? mathematics is all of these, and none. mostly, it ' s just different. it ' s not what you expect it to be, you turn your back for a moment and it ' s changed. it ' s certainly not just a fixed body of knowledge, its growth is not confined to inventing new numbers, and its hidden tendrils pervade every aspect of modern life. ian stewart = = see also = = philosophy of mathematics foundations of mathematics = = references = = = = further reading = = courant, richard ; robbins, herbert ( 1996 ), what is mathematics? ( 2nd ed. ), oxford university press, isbn 978 - 0 - 19 - 510519 - 3 gowers, timothy ; barrow - green, june ; leader, imre, eds. ( 2008 ), the princeton companion to mathematics, princeton university press, isbn 978 - 0 - 691 - 11880 - 2 hersh, reuben ( 1999 ), what is mathematics, really?, oxford university press, isbn 978 - 0 - 19 - 513087 - 4 paulos, john allen ( 1991 ), " beyond numeracy ", nature, 359 ( 6394 ), viking : 463 – 464, bibcode : 1992natur. 359.. 463b, doi : 10. 1038 / 359463b0, isbn 978 - 0 - navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding sea becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under . a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of Question: While populations with unlimited resources grow exponentially, the population of a species will level off when what limit of its environment is reached? A) extinction B) niche C) carrying capacity D) reproduction	C) carrying capacity
Context: prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids are polymers of nucleotides. their function is to store, transmit, and express hereditary information. = = cells = = cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division. most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as it is the purpose of this note to classify connected quandles up to order 14, and in particular to show that there is no connected quandle of order 14. if a fintie group g acts topologically and faithfully on r ^ 3, then g is a subgroup of o ( 3 ) ##ian period, several groups, including the lycopods, sphenophylls and progymnosperms, had independently evolved " megaspory " – their spores were of two distinct sizes, larger megaspores and smaller microspores. their reduced gametophytes developed from megaspores retained within the spore - producing organs ( megasporangia ) of the sporophyte, a condition known as endospory. seeds consist of an endosporic megasporangium surrounded by one or two sheathing layers ( integuments ). the young sporophyte develops within the seed, which on germination splits to release it. the earliest known seed plants date from the latest devonian famennian stage. following the evolution of the seed habit, seed plants diversified, giving rise to a number of now - extinct groups, including seed ferns, as well as the modern gymnosperms and angiosperms. gymnosperms produce " naked seeds " not fully enclosed in an ovary ; modern representatives include conifers, cycads, ginkgo, and gnetales. angiosperms produce seeds enclosed in a structure such as a carpel or an ovary. ongoing research on the molecular phylogenetics of living plants appears to show that the angiosperms are a sister clade to the gymnosperms. = = plant physiology = = plant physiology encompasses all the internal chemical and physical activities of plants associated with life. chemicals obtained from the air, soil and water form the basis of all plant metabolism. the energy of sunlight, captured by oxygenic photosynthesis and released by cellular respiration, is the basis of almost all life. photoautotrophs, including all green plants, algae and cyanobacteria gather energy directly from sunlight by photosynthesis. heterotrophs including all animals, all fungi, all completely parasitic plants, and non - photosynthetic bacteria take in organic molecules produced by photoautotrophs and respire them or use them in the construction of cells and tissues. respiration is the oxidation of carbon compounds by breaking them down into simpler structures to release the energy they contain, essentially the opposite of photosynthesis. molecules are moved within plants by transport processes that operate at a variety of spatial scales. subcellular transport of ions, electrons and molecules such as water and enzymes occurs across cell membranes. minerals and water are transported from roots to other parts of the plant in set theory, an arbitrary permutation of the elements of a set x is an automorphism. the automorphism group of x is also called the symmetric group on x. in elementary arithmetic, the set of integers, z, considered as a group under addition, has a unique nontrivial automorphism : negation. considered as a ring, however, it has only the trivial automorphism. generally speaking, negation is an automorphism of any abelian group, but not of a ring or field. a group automorphism is a group isomorphism from a group to itself. informally, it is a permutation of the group elements such that the structure remains unchanged. for every group g there is a natural group homomorphism g → aut ( g ) whose image is the group inn ( g ) of inner automorphisms and whose kernel is the center of g. thus, if g has trivial center it can be embedded into its own automorphism group. in linear algebra, an endomorphism of a vector space v is a linear operator v → v. an automorphism is an invertible linear operator on v. when the vector space is finite - dimensional, the automorphism group of v is the same as the general linear group, gl ( v ). a field automorphism is a bijective ring homomorphism from a field to itself. in the cases of the rational numbers ( q ) and the real numbers ( r ) there are no nontrivial field automorphisms. some subfields of r have nontrivial field automorphisms, which however do not extend to all of r ( because they cannot preserve the property of a number having a square root in r ). in the case of the complex numbers, c, there is a unique nontrivial automorphism that sends r into r : complex conjugation, but there are infinitely ( uncountably ) many " wild " automorphisms ( assuming the axiom of choice ). field automorphisms are important to the theory of field extensions, in particular galois extensions. in the case of a galois extension l / k the subgroup of all automorphisms of l fixing k pointwise is called the galois group of the extension. = = symmetry in representation theory = = = = = symmetry in quantum mechanics : bosons and fermions = = = in quantum mechanics, bosons have representatives that are symmetric under permutation operators, and fermions have antisymmetric representatives. this implies ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids are polymers of nucleotides. their function is to store, transmit, and express hereditary information. = = cells = = cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division. most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed language is a method by which individuals express their thoughts. each language has its own set of alphabetic and numeric characters. people can communicate with one another through either oral or written communication. however, each language has a sign language counterpart. individuals who are deaf and / or mute communicate through sign language. the bangla language also has a sign language, which is called bdsl. the dataset is about bangla hand sign images. the collection contains 49 individual bangla alphabet images in sign language. bdsl49 is a dataset that consists of 29, 490 images with 49 labels. images of 14 different adult individuals, each with a distinct background and appearance, have been recorded during data collection. several strategies have been used to eliminate noise from datasets during preparation. this dataset is available to researchers for free. they can develop automated systems using machine learning, computer vision, and deep learning techniques. in addition, two models were used in this dataset. the first is for detection, while the second is for recognition. may ask which points x are unchanged, " invariant " under the group action, or under an element g of the group. frequently one will have a group acting on a set x, which leaves one to determine which objects in an associated set f ( x ) are invariant. for example, rotation in the plane about a point leaves the point about which it rotates invariant, while translation in the plane does not leave any points invariant, but does leave all lines parallel to the direction of translation invariant as lines. formally, define the set of lines in the plane p as l ( p ) ; then a rigid motion of the plane takes lines to lines – the group of rigid motions acts on the set of lines – and one may ask which lines are unchanged by an action. more importantly, one may define a function on a set, such as " radius of a circle in the plane ", and then ask if this function is invariant under a group action, such as rigid motions. dual to the notion of invariants are coinvariants, also known as orbits, which formalizes the notion of congruence : objects which can be taken to each other by a group action. for example, under the group of rigid motions of the plane, the perimeter of a triangle is an invariant, while the set of triangles congruent to a given triangle is a coinvariant. these are connected as follows : invariants are constant on coinvariants ( for example, congruent triangles have the same perimeter ), while two objects which agree in the value of one invariant may or may not be congruent ( for example, two triangles with the same perimeter need not be congruent ). in classification problems, one might seek to find a complete set of invariants, such that if two objects have the same values for this set of invariants, then they are congruent. for example, triangles such that all three sides are equal are congruent under rigid motions, via sss congruence, and thus the lengths of all three sides form a complete set of invariants for triangles. the three angle measures of a triangle are also invariant under rigid motions, but do not form a complete set as incongruent triangles can share the same angle measures. however, if one allows scaling in addition to rigid motions, then the aaa similarity criterion shows that this is a complete set of invariants. = = = independent of presentation = = = secondly, a function may be defined in terms of some presentation or ##olithic / mesolithic. the mesolithic technology included the use of microliths as composite stone tools, along with wood, bone, and antler tools. the later stone age, during which the rudiments of agricultural technology were developed, is called the neolithic period. during this period, polished stone tools were made from a variety of hard rocks such as flint, jade, jadeite, and greenstone, largely by working exposures as quarries, but later the valuable rocks were pursued by tunneling underground, the first steps in mining technology. the polished axes were used for forest clearance and the establishment of crop farming and were so effective as to remain in use when bronze and iron appeared. these stone axes were used alongside a continued use of stone tools such as a range of projectiles, knives, and scrapers, as well as tools, made from organic materials such as wood, bone, and antler. stone age cultures developed music and engaged in organized warfare. stone age humans developed ocean - worthy outrigger canoe technology, leading to migration across the malay archipelago, across the indian ocean to madagascar and also across the pacific ocean, which required knowledge of the ocean currents, weather patterns, sailing, and celestial navigation. although paleolithic cultures left no written records, the shift from nomadic life to settlement and agriculture can be inferred from a range of archaeological evidence. such evidence includes ancient tools, cave paintings, and other prehistoric art, such as the venus of willendorf. human remains also provide direct evidence, both through the examination of bones, and the study of mummies. scientists and historians have been able to form significant inferences about the lifestyle and culture of various prehistoric peoples, and especially their technology. = = = ancient = = = = = = = copper and bronze ages = = = = metallic copper occurs on the surface of weathered copper ore deposits and copper was used before copper smelting was known. copper smelting is believed to have originated when the technology of pottery kilns allowed sufficiently high temperatures. the concentration of various elements such as arsenic increase with depth in copper ore deposits and smelting of these ores yields arsenical bronze, which can be sufficiently work hardened to be suitable for making tools. bronze is an alloy of copper with tin ; the latter being found in relatively few deposits globally caused a long time to elapse before true tin bronze became widespread. ( see : tin sources and trade in ancient times ) bronze was a major advancement over stone as a material for the paper has been withdrawn by the author since the protocol is not new. it is just the oldest version of bb84. Question: Group 16 is called what? A) the acid group B) metalloids C) noble gases D) the oxygen group	D) the oxygen group
Context: , lightning strikes, tornadoes, building fires, wildfires, and mass shootings disabling most of the system if not the entirety of it. geographic redundancy locations can be more than 621 miles ( 999 km ) continental, more than 62 miles apart and less than 93 miles ( 150 km ) apart, less than 62 miles apart, but not on the same campus, or different buildings that are more than 300 feet ( 91 m ) apart on the same campus. the following methods can reduce the risks of damage by a fire conflagration : large buildings at least 80 feet ( 24 m ) to 110 feet ( 34 m ) apart, but sometimes a minimum of 210 feet ( 64 m ) apart. : 9 high - rise buildings at least 82 feet ( 25 m ) apart : 12 open spaces clear of flammable vegetation within 200 feet ( 61 m ) on each side of objects different wings on the same building, in rooms that are separated by more than 300 feet ( 91 m ) different floors on the same wing of a building in rooms that are horizontally offset by a minimum of 70 feet ( 21 m ) with fire walls between the rooms that are on different floors two rooms separated by another room, leaving at least a 70 - foot gap between the two rooms there should be a minimum of two separated fire walls and on opposite sides of a corridor geographic redundancy is used by amazon web services ( aws ), google cloud platform ( gcp ), microsoft azure, netflix, dropbox, salesforce, linkedin, paypal, twitter, facebook, apple icloud, cisco meraki, and many others to provide geographic redundancy, high availability, fault tolerance and to ensure availability and reliability for their cloud services. as another example, to minimize risk of damage from severe windstorms or water damage, buildings can be located at least 2 miles ( 3. 2 km ) away from the shore, with an elevation of at least 5 feet ( 1. 5 m ) above sea level. for additional protection, they can be located at least 100 feet ( 30 m ) away from flood plain areas. = = functions of redundancy = = the two functions of redundancy are passive redundancy and active redundancy. both functions prevent performance decline from exceeding specification limits without human intervention using extra capacity. passive redundancy uses excess capacity to reduce the impact of component failures. one common form of passive redundancy is the extra strength of cabling and struts used in bridges. higher concentrations of atmospheric nitrous oxide ( n2o ) are expected to slightly warm earth ' s surface because of increases in radiative forcing. radiative forcing is the difference in the net upward thermal radiation flux from the earth through a transparent atmosphere and radiation through an otherwise identical atmosphere with greenhouse gases. radiative forcing, normally measured in w / m ^ 2, depends on latitude, longitude and altitude, but it is often quoted for the tropopause, about 11 km of altitude for temperate latitudes, or for the top of the atmosphere at around 90 km. for current concentrations of greenhouse gases, the radiative forcing per added n2o molecule is about 230 times larger than the forcing per added carbon dioxide ( co2 ) molecule. this is due to the heavy saturation of the absorption band of the relatively abundant greenhouse gas, co2, compared to the much smaller saturation of the absorption bands of the trace greenhouse gas n2o. but the rate of increase of co2 molecules, about 2. 5 ppm / year ( ppm = part per million by mole ), is about 3000 times larger than the rate of increase of n2o molecules, which has held steady at around 0. 00085 ppm / year since 1985. so, the contribution of nitrous oxide to the annual increase in forcing is 230 / 3000 or about 1 / 13 that of co2. if the main greenhouse gases, co2, ch4 and n2o have contributed about 0. 1 c / decade of the warming observed over the past few decades, this would correspond to about 0. 00064 k per year or 0. 064 k per century of warming from n2o. proposals to place harsh restrictions on nitrous oxide emissions because of warming fears are not justified by these facts. restrictions would cause serious harm ; for example, by jeopardizing world food supplies. ##tering - based methods are simple ( " sinter " has roots in the english " cinder " ). the firing is done at a temperature below the melting point of the ceramic. once a roughly - held - together object called a " green body " is made, it is fired in a kiln, where atomic and molecular diffusion processes give rise to significant changes in the primary microstructural features. this includes the gradual elimination of porosity, which is typically accompanied by a net shrinkage and overall densification of the component. thus, the pores in the object may close up, resulting in a denser product of significantly greater strength and fracture toughness. another major change in the body during the firing or sintering process will be the establishment of the polycrystalline nature of the solid. significant grain growth tends to occur during sintering, with this growth depending on temperature and duration of the sintering process. the growth of grains will result in some form of grain size distribution, which will have a significant impact on the ultimate physical properties of the material. in particular, abnormal grain growth in which certain grains grow very large in a matrix of finer grains will significantly alter the physical and mechanical properties of the obtained ceramic. in the sintered body, grain sizes are a product of the thermal processing parameters as well as the initial particle size, or possibly the sizes of aggregates or particle clusters which arise during the initial stages of processing. the ultimate microstructure ( and thus the physical properties ) of the final product will be limited by and subject to the form of the structural template or precursor which is created in the initial stages of chemical synthesis and physical forming. hence the importance of chemical powder and polymer processing as it pertains to the synthesis of industrial ceramics, glasses and glass - ceramics. there are numerous possible refinements of the sintering process. some of the most common involve pressing the green body to give the densification a head start and reduce the sintering time needed. sometimes organic binders such as polyvinyl alcohol are added to hold the green body together ; these burn out during the firing ( at 200 – 350 °c ). sometimes organic lubricants are added during pressing to increase densification. it is common to combine these, and add binders and lubricants to a powder, then press. ( the formulation of these organic chemical additives is an art in itself. this is particularly important in the manufacture of high performance ceramics such as those used by the billions for significantly greater strength and fracture toughness. another major change in the body during the firing or sintering process will be the establishment of the polycrystalline nature of the solid. significant grain growth tends to occur during sintering, with this growth depending on temperature and duration of the sintering process. the growth of grains will result in some form of grain size distribution, which will have a significant impact on the ultimate physical properties of the material. in particular, abnormal grain growth in which certain grains grow very large in a matrix of finer grains will significantly alter the physical and mechanical properties of the obtained ceramic. in the sintered body, grain sizes are a product of the thermal processing parameters as well as the initial particle size, or possibly the sizes of aggregates or particle clusters which arise during the initial stages of processing. the ultimate microstructure ( and thus the physical properties ) of the final product will be limited by and subject to the form of the structural template or precursor which is created in the initial stages of chemical synthesis and physical forming. hence the importance of chemical powder and polymer processing as it pertains to the synthesis of industrial ceramics, glasses and glass - ceramics. there are numerous possible refinements of the sintering process. some of the most common involve pressing the green body to give the densification a head start and reduce the sintering time needed. sometimes organic binders such as polyvinyl alcohol are added to hold the green body together ; these burn out during the firing ( at 200 – 350 °c ). sometimes organic lubricants are added during pressing to increase densification. it is common to combine these, and add binders and lubricants to a powder, then press. ( the formulation of these organic chemical additives is an art in itself. this is particularly important in the manufacture of high performance ceramics such as those used by the billions for electronics, in capacitors, inductors, sensors, etc. ) a slurry can be used in place of a powder, and then cast into a desired shape, dried and then sintered. indeed, traditional pottery is done with this type of method, using a plastic mixture worked with the hands. if a mixture of different materials is used together in a ceramic, the sintering temperature is sometimes above the melting point of one minor component – a liquid phase sintering. this results in shorter sintering times compared to solid state sintering. such liquid phase sintering involves in faster diffusion processes and may result in abnormal grain ambient air ( see lockheed f - 117 nighthawk, rectangular nozzles on the lockheed martin f - 22 raptor, and serrated nozzle flaps on the lockheed martin f - 35 lightning ). often, cool air is deliberately injected into the exhaust flow to boost this process ( see ryan aqm - 91 firefly and northrop b - 2 spirit ). the stefan – boltzmann law shows how this results in less energy ( thermal radiation in infrared spectrum ) being released and thus reduces the heat signature. in some aircraft, the jet exhaust is vented above the wing surface to shield it from observers below, as in the lockheed f - 117 nighthawk, and the unstealthy fairchild republic a - 10 thunderbolt ii. to achieve infrared stealth, the exhaust gas is cooled to the temperatures where the brightest wavelengths it radiates are absorbed by atmospheric carbon dioxide and water vapor, greatly reducing the infrared visibility of the exhaust plume. another way to reduce the exhaust temperature is to circulate coolant fluids such as fuel inside the exhaust pipe, where the fuel tanks serve as heat sinks cooled by the flow of air along the wings. ground combat includes the use of both active and passive infrared sensors. thus, the united states marine corps ( usmc ) ground combat uniform requirements document specifies infrared reflective quality standards. = = reducing radio frequency ( rf ) emissions = = in addition to reducing infrared and acoustic emissions, a stealth vehicle must avoid radiating any other detectable energy, such as from onboard radars, communications systems, or rf leakage from electronics enclosures. the f - 117 uses passive infrared and low light level television sensor systems to aim its weapons and the f - 22 raptor has an advanced lpi radar which can illuminate enemy aircraft without triggering a radar warning receiver response. = = measuring = = the size of a target ' s image on radar is measured by the rcs, often represented by the symbol σ and expressed in square meters. this does not equal geometric area. a perfectly conducting sphere of projected cross sectional area 1 m2 ( i. e. a diameter of 1. 13 m ) will have an rcs of 1 m2. note that for radar wavelengths much less than the diameter of the sphere, rcs is independent of frequency. conversely, a square flat plate of area 1 m2 will have an rcs of σ = 4π a2 / λ2 ( where a = area, λ = wavelength ), or 13, 982 m2 at 10 ghz if the radar is perpendicular to the flat is also higher at high temperature, as shown by carnot ' s theorem. in a conventional metallic engine, much of the energy released from the fuel must be dissipated as waste heat in order to prevent a meltdown of the metallic parts. despite all of these desirable properties, such engines are not in production because the manufacturing of ceramic parts in the requisite precision and durability is difficult. imperfection in the ceramic leads to cracks, which can lead to potentially dangerous equipment failure. such engines are possible in laboratory settings, but mass - production is not feasible with current technology. work is being done in developing ceramic parts for gas turbine engines. currently, even blades made of advanced metal alloys used in the engines ' hot section require cooling and careful limiting of operating temperatures. turbine engines made with ceramics could operate more efficiently, giving aircraft greater range and payload for a set amount of fuel. recently, there have been advances in ceramics which include bio - ceramics, such as dental implants and synthetic bones. hydroxyapatite, the natural mineral component of bone, has been made synthetically from a number of biological and chemical sources and can be formed into ceramic materials. orthopedic implants made from these materials bond readily to bone and other tissues in the body without rejection or inflammatory reactions. because of this, they are of great interest for gene delivery and tissue engineering scaffolds. most hydroxyapatite ceramics are very porous and lack mechanical strength and are used to coat metal orthopedic devices to aid in forming a bond to bone or as bone fillers. they are also used as fillers for orthopedic plastic screws to aid in reducing the inflammation and increase absorption of these plastic materials. work is being done to make strong, fully dense nano crystalline hydroxyapatite ceramic materials for orthopedic weight bearing devices, replacing foreign metal and plastic orthopedic materials with a synthetic, but naturally occurring, bone mineral. ultimately these ceramic materials may be used as bone replacements or with the incorporation of protein collagens, synthetic bones. durable actinide - containing ceramic materials have many applications such as in nuclear fuels for burning excess pu and in chemically - inert sources of alpha irradiation for power supply of unmanned space vehicles or to produce electricity for microelectronic devices. both use and disposal of radioactive actinides require their immobilization in a durable host material. nuclear waste long - lived radionuclides such as actinides are immobilized using chemical navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding sea not only is the bekenstein expression for the entropy of a black hole a convex function of the energy, rather than being a concave function as it must be, it predicts a final equilibrium temperature given by the harmonic mean. this violates the third law, and the principle of maximum work. the property that means are monotonically increasing functions of their argument underscores the error of transferring from temperature means to means in the internal energy when the energy is not a monotonically increasing function of temperature. whereas the former leads to an increase in entropy, the latter lead to a decrease in entropy thereby violating the second law. the internal energy cannot increase at a slower rate than the temperature itself. pumping. steam engines were too powerful for leather bellows, so cast iron blowing cylinders were developed in 1768. steam powered blast furnaces achieved higher temperatures, allowing the use of more lime in iron blast furnace feed. ( lime rich slag was not free - flowing at the previously used temperatures. ) with a sufficient lime ratio, sulfur from coal or coke fuel reacts with the slag so that the sulfur does not contaminate the iron. coal and coke were cheaper and more abundant fuel. as a result, iron production rose significantly during the last decades of the 18th century. coal converted to coke fueled higher temperature blast furnaces and produced cast iron in much larger amounts than before, allowing the creation of a range of structures such as the iron bridge. cheap coal meant that industry was no longer constrained by water resources driving the mills, although it continued as a valuable source of power. the steam engine helped drain the mines, so more coal reserves could be accessed, and the output of coal increased. the development of the high - pressure steam engine made locomotives possible, and a transport revolution followed. the steam engine which had existed since the early 18th century, was practically applied to both steamboat and railway transportation. the liverpool and manchester railway, the first purpose - built railway line, opened in 1830, the rocket locomotive of robert stephenson being one of its first working locomotives used. manufacture of ships ' pulley blocks by all - metal machines at the portsmouth block mills in 1803 instigated the age of sustained mass production. machine tools used by engineers to manufacture parts began in the first decade of the century, notably by richard roberts and joseph whitworth. the development of interchangeable parts through what is now called the american system of manufacturing began in the firearms industry at the u. s. federal arsenals in the early 19th century, and became widely used by the end of the century. until the enlightenment era, little progress was made in water supply and sanitation and the engineering skills of the romans were largely neglected throughout europe. the first documented use of sand filters to purify the water supply dates to 1804, when the owner of a bleachery in paisley, scotland, john gibb, installed an experimental filter, selling his unwanted surplus to the public. the first treated public water supply in the world was installed by engineer james simpson for the chelsea waterworks company in london in 1829. the first screw - down water tap was patented in 1845 by guest and chrimes, a brass foundry in rotherham. the practice of water treatment soon became mainstream, radiation exposure. marie curie died from aplastic anemia which resulted from her high levels of exposure. two scientists, an american and canadian respectively, harry daghlian and louis slotin, died after mishandling the same plutonium mass. unlike conventional weapons, the intense light, heat, and explosive force is not the only deadly component to a nuclear weapon. approximately half of the deaths from hiroshima and nagasaki died two to five years afterward from radiation exposure. civilian nuclear and radiological accidents primarily involve nuclear power plants. most common are nuclear leaks that expose workers to hazardous material. a nuclear meltdown refers to the more serious hazard of releasing nuclear material into the surrounding environment. the most significant meltdowns occurred at three mile island in pennsylvania and chernobyl in the soviet ukraine. the earthquake and tsunami on march 11, 2011 caused serious damage to three nuclear reactors and a spent fuel storage pond at the fukushima daiichi nuclear power plant in japan. military reactors that experienced similar accidents were windscale in the united kingdom and sl - 1 in the united states. military accidents usually involve the loss or unexpected detonation of nuclear weapons. the castle bravo test in 1954 produced a larger yield than expected, which contaminated nearby islands, a japanese fishing boat ( with one fatality ), and raised concerns about contaminated fish in japan. in the 1950s through 1970s, several nuclear bombs were lost from submarines and aircraft, some of which have never been recovered. the last twenty years have seen a marked decline in such accidents. = = examples of environmental benefits = = proponents of nuclear energy note that annually, nuclear - generated electricity reduces 470 million metric tons of carbon dioxide emissions that would otherwise come from fossil fuels. additionally, the amount of comparatively low waste that nuclear energy does create is safely disposed of by the large scale nuclear energy production facilities or it is repurposed / recycled for other energy uses. proponents of nuclear energy also bring to attention the opportunity cost of utilizing other forms of electricity. for example, the environmental protection agency estimates that coal kills 30, 000 people a year, as a result of its environmental impact, while 60 people died in the chernobyl disaster. a real world example of impact provided by proponents of nuclear energy is the 650, 000 ton increase in carbon emissions in the two months following the closure of the vermont yankee nuclear plant. = = see also = = atomic age lists of nuclear disasters and radioactive incidents nuclear power debate outline of nuclear technology radiology = = references = = = = external links = = nuclear energy institute – beneficial uses Question: What type of temperatures increase the likelihood of fires? A) lower B) freezing C) reduced D) higher	D) higher
Context: a watershed ( called a " divide " in north america ) over which rainfall flows down towards the river traversing the lowest part of the valley, whereas the rain falling on the far slope of the watershed flows away to another river draining an adjacent basin. river basins vary in extent according to the configuration of the country, ranging from the insignificant drainage areas of streams rising on high ground near the coast and flowing straight down into the sea, up to immense tracts of continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching the ocean. the size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform onset of electro - chemical corrosion. similar problems are encountered in coastal and offshore structures. = = = anti - fouling = = = anti - fouling is the process of eliminating obstructive organisms from essential components of seawater systems. depending on the nature and location of marine growth, this process is performed in a number of different ways : marine organisms may grow and attach to the surfaces of the outboard suction inlets used to obtain water for cooling systems. electro - chlorination involves running high electrical current through sea water, altering the water ' s chemical composition to create sodium hypochlorite, purging any bio - matter. an electrolytic method of anti - fouling involves running electrical current through two anodes ( scardino, 2009 ). these anodes typically consist of copper and aluminum ( or alternatively, iron ). the first metal, copper anode, releases its ion into the water, creating an environment that is too toxic for bio - matter. the second metal, aluminum, coats the inside of the pipes to prevent corrosion. other forms of marine growth such as mussels and algae may attach themselves to the bottom of a ship ' s hull. this growth interferes with the smoothness and uniformity of the ship ' s hull, causing the ship to have a less hydrodynamic shape that causes it to be slower and less fuel - efficient. marine growth on the hull can be remedied by using special paint that prevents the growth of such organisms. = = = pollution control = = = = = = = sulfur emission = = = = the burning of marine fuels releases harmful pollutants into the atmosphere. ships burn marine diesel in addition to heavy fuel oil. heavy fuel oil, being the heaviest of refined oils, releases sulfur dioxide when burned. sulfur dioxide emissions have the potential to raise atmospheric and ocean acidity causing harm to marine life. however, heavy fuel oil may only be burned in international waters due to the pollution created. it is commercially advantageous due to the cost effectiveness compared to other marine fuels. it is prospected that heavy fuel oil will be phased out of commercial use by the year 2020 ( smith, 2018 ). = = = = oil and water discharge = = = = water, oil, and other substances collect at the bottom of the ship in what is known as the bilge. bilge water is pumped overboard, but must pass a pollution threshold test of 15 ppm ( parts per million ) of oil to be discharged. water is tested above any tidal limit and their average freshwater discharge are proportionate to the extent of their basins and the amount of rain which, after falling over these basins, reaches the river channels in the bottom of the valleys, by which it is conveyed to the sea. the drainage basin of a river is the expanse of country bounded by a watershed ( called a " divide " in north america ) over which rainfall flows down towards the river traversing the lowest part of the valley, whereas the rain falling on the far slope of the watershed flows away to another river draining an adjacent basin. river basins vary in extent according to the configuration of the country, ranging from the insignificant drainage areas of streams rising on high ground near the coast and flowing straight down into the sea, up to immense tracts of continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching the ocean. the size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer from the insignificant drainage areas of streams rising on high ground near the coast and flowing straight down into the sea, up to immense tracts of continents, where rivers rising on the slopes of mountain ranges far inland have to traverse vast stretches of valleys and plains before reaching the ocean. the size of the largest river basin of any country depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with = = = = = = environmental remediation = = = environmental remediation is the process through which contaminants or pollutants in soil, water and other media are removed to improve environmental quality. the main focus is the reduction of hazardous substances within the environment. some of the areas involved in environmental remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the infestation of insects and rodents, contributing to the spread of diseases. some of the most common types of solid waste management include ; landfills, vermicomposting, composting, recycling, and incineration. however, a major barrier for solid waste management practices is the high costs associated with recycling becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding sea Question: Fertilizer runoff can create what type of zones in the ocean? A) barren zones B) dead zones C) hot zones D) fresh zones	B) dead zones
Context: world made wide use of hydropower, along with early uses of tidal power, wind power, fossil fuels such as petroleum, and large factory complexes ( tiraz in arabic ). a variety of industrial mills were employed in the islamic world, including fulling mills, gristmills, hullers, sawmills, ship mills, stamp mills, steel mills, and tide mills. by the 11th century, every province throughout the islamic world had these industrial mills in operation. muslim engineers also employed water turbines and gears in mills and water - raising machines, and pioneered the use of dams as a source of water power, used to provide additional power to watermills and water - raising machines. many of these technologies were transferred to medieval europe. wind - powered machines used to grind grain and pump water, the windmill and wind pump, first appeared in what are now iran, afghanistan and pakistan by the 9th century. they were used to grind grains and draw up water, and used in the gristmilling and sugarcane industries. sugar mills first appeared in the medieval islamic world. they were first driven by watermills, and then windmills from the 9th and 10th centuries in what are today afghanistan, pakistan and iran. crops such as almonds and citrus fruit were brought to europe through al - andalus, and sugar cultivation was gradually adopted across europe. arab merchants dominated trade in the indian ocean until the arrival of the portuguese in the 16th century. the muslim world adopted papermaking from china. the earliest paper mills appeared in abbasid - era baghdad during 794 – 795. the knowledge of gunpowder was also transmitted from china via predominantly islamic countries, where formulas for pure potassium nitrate were developed. the spinning wheel was invented in the islamic world by the early 11th century. it was later widely adopted in europe, where it was adapted into the spinning jenny, a key device during the industrial revolution. the crankshaft was invented by al - jazari in 1206, and is central to modern machinery such as the steam engine, internal combustion engine and automatic controls. the camshaft was also first described by al - jazari in 1206. early programmable machines were also invented in the muslim world. the first music sequencer, a programmable musical instrument, was an automated flute player invented by the banu musa brothers, described in their book of ingenious devices, in the 9th century. in 1206, al - jazari invented programmable automata / robots. he described four automaton musicians, including two fluid dynamics video demonstrating the evolution of dynamic stall on a wind turbine blade. in 1738. the spinning jenny, invented in 1764, was a machine that used multiple spinning wheels ; however, it produced low quality thread. the water frame patented by richard arkwright in 1767, produced a better quality thread than the spinning jenny. the spinning mule, patented in 1779 by samuel crompton, produced a high quality thread. the power loom was invented by edmund cartwright in 1787. in the mid - 1750s, the steam engine was applied to the water power - constrained iron, copper and lead industries for powering blast bellows. these industries were located near the mines, some of which were using steam engines for mine pumping. steam engines were too powerful for leather bellows, so cast iron blowing cylinders were developed in 1768. steam powered blast furnaces achieved higher temperatures, allowing the use of more lime in iron blast furnace feed. ( lime rich slag was not free - flowing at the previously used temperatures. ) with a sufficient lime ratio, sulfur from coal or coke fuel reacts with the slag so that the sulfur does not contaminate the iron. coal and coke were cheaper and more abundant fuel. as a result, iron production rose significantly during the last decades of the 18th century. coal converted to coke fueled higher temperature blast furnaces and produced cast iron in much larger amounts than before, allowing the creation of a range of structures such as the iron bridge. cheap coal meant that industry was no longer constrained by water resources driving the mills, although it continued as a valuable source of power. the steam engine helped drain the mines, so more coal reserves could be accessed, and the output of coal increased. the development of the high - pressure steam engine made locomotives possible, and a transport revolution followed. the steam engine which had existed since the early 18th century, was practically applied to both steamboat and railway transportation. the liverpool and manchester railway, the first purpose - built railway line, opened in 1830, the rocket locomotive of robert stephenson being one of its first working locomotives used. manufacture of ships ' pulley blocks by all - metal machines at the portsmouth block mills in 1803 instigated the age of sustained mass production. machine tools used by engineers to manufacture parts began in the first decade of the century, notably by richard roberts and joseph whitworth. the development of interchangeable parts through what is now called the american system of manufacturing began in the firearms industry at the u. s. federal arsenals in the early 19th century, and became widely used by the end of the century. until the enlightenment era, little progress becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under in a voltaic cell, positive ( negative ) ions flow from the low ( high ) potential electrode to the high ( low ) potential electrode, driven by an ` electromotive force ' which points in opposite direction and overcomes the electric force. similarly in a superconductor charge flows in direction opposite to that dictated by the faraday electric field as the magnetic field is expelled in the meissner effect. the puzzle is the same in both cases : what drives electric charges against electromagnetic forces? i propose that the answer is also the same in both cases : kinetic energy lowering, or ` quantum pressure '. high quality thread. the power loom was invented by edmund cartwright in 1787. in the mid - 1750s, the steam engine was applied to the water power - constrained iron, copper and lead industries for powering blast bellows. these industries were located near the mines, some of which were using steam engines for mine pumping. steam engines were too powerful for leather bellows, so cast iron blowing cylinders were developed in 1768. steam powered blast furnaces achieved higher temperatures, allowing the use of more lime in iron blast furnace feed. ( lime rich slag was not free - flowing at the previously used temperatures. ) with a sufficient lime ratio, sulfur from coal or coke fuel reacts with the slag so that the sulfur does not contaminate the iron. coal and coke were cheaper and more abundant fuel. as a result, iron production rose significantly during the last decades of the 18th century. coal converted to coke fueled higher temperature blast furnaces and produced cast iron in much larger amounts than before, allowing the creation of a range of structures such as the iron bridge. cheap coal meant that industry was no longer constrained by water resources driving the mills, although it continued as a valuable source of power. the steam engine helped drain the mines, so more coal reserves could be accessed, and the output of coal increased. the development of the high - pressure steam engine made locomotives possible, and a transport revolution followed. the steam engine which had existed since the early 18th century, was practically applied to both steamboat and railway transportation. the liverpool and manchester railway, the first purpose - built railway line, opened in 1830, the rocket locomotive of robert stephenson being one of its first working locomotives used. manufacture of ships ' pulley blocks by all - metal machines at the portsmouth block mills in 1803 instigated the age of sustained mass production. machine tools used by engineers to manufacture parts began in the first decade of the century, notably by richard roberts and joseph whitworth. the development of interchangeable parts through what is now called the american system of manufacturing began in the firearms industry at the u. s. federal arsenals in the early 19th century, and became widely used by the end of the century. until the enlightenment era, little progress was made in water supply and sanitation and the engineering skills of the romans were largely neglected throughout europe. the first documented use of sand filters to purify the water supply dates to 1804, when the owner of a bleachery in paisley, scotland, john gibb, installed an experimental filter, selling his unwanted neo - assyrian period ( 911 – 609 ) bc. the egyptian pyramids were built using three of the six simple machines, the inclined plane, the wedge, and the lever, to create structures like the great pyramid of giza. the earliest civil engineer known by name is imhotep. as one of the officials of the pharaoh, djoser, he probably designed and supervised the construction of the pyramid of djoser ( the step pyramid ) at saqqara in egypt around 2630 – 2611 bc. the earliest practical water - powered machines, the water wheel and watermill, first appeared in the persian empire, in what are now iraq and iran, by the early 4th century bc. kush developed the sakia during the 4th century bc, which relied on animal power instead of human energy. hafirs were developed as a type of reservoir in kush to store and contain water as well as boost irrigation. sappers were employed to build causeways during military campaigns. kushite ancestors built speos during the bronze age between 3700 and 3250 bc. bloomeries and blast furnaces were also created during the 7th centuries bc in kush. ancient greece developed machines in both civilian and military domains. the antikythera mechanism, an early known mechanical analog computer, and the mechanical inventions of archimedes, are examples of greek mechanical engineering. some of archimedes ' inventions, as well as the antikythera mechanism, required sophisticated knowledge of differential gearing or epicyclic gearing, two key principles in machine theory that helped design the gear trains of the industrial revolution, and are widely used in fields such as robotics and automotive engineering. ancient chinese, greek, roman and hunnic armies employed military machines and inventions such as artillery which was developed by the greeks around the 4th century bc, the trireme, the ballista and the catapult, the trebuchet by chinese circa 6th - 5th century bce. = = = middle ages = = = the earliest practical wind - powered machines, the windmill and wind pump, first appeared in the muslim world during the islamic golden age, in what are now iran, afghanistan, and pakistan, by the 9th century ad. the earliest practical steam - powered machine was a steam jack driven by a steam turbine, described in 1551 by taqi al - din muhammad ibn ma ' ruf in ottoman egypt. the cotton gin was invented in india by the 6th century ad, and the spinning wheel was invented in the islamic a transformer of energy ( through water wheels, windmills, and even treadmills ) that revolutionized the application of nonhuman power sources. the first two - wheeled carts were derived from travois and were first used in mesopotamia and iran in around 3, 000 bce. the oldest known constructed roadways are the stone - paved streets of the city - state of ur, dating to c. 4, 000 bce, and timber roads leading through the swamps of glastonbury, england, dating to around the same period. the first long - distance road, which came into use around 3, 500 bce, spanned 2, 400 km from the persian gulf to the mediterranean sea, but was not paved and was only partially maintained. in around 2, 000 bce, the minoans on the greek island of crete built a 50 km road leading from the palace of gortyn on the south side of the island, through the mountains, to the palace of knossos on the north side of the island. unlike the earlier road, the minoan road was completely paved. ancient minoan private homes had running water. a bathtub virtually identical to modern ones was unearthed at the palace of knossos. several minoan private homes also had toilets, which could be flushed by pouring water down the drain. the ancient romans had many public flush toilets, which emptied into an extensive sewage system. the primary sewer in rome was the cloaca maxima ; construction began on it in the sixth century bce and it is still in use today. the ancient romans also had a complex system of aqueducts, which were used to transport water across long distances. the first roman aqueduct was built in 312 bce. the eleventh and final ancient roman aqueduct was built in 226 ce. put together, the roman aqueducts extended over 450 km, but less than 70 km of this was above ground and supported by arches. = = = pre - modern = = = innovations continued through the middle ages with the introduction of silk production ( in asia and later europe ), the horse collar, and horseshoes. simple machines ( such as the lever, the screw, and the pulley ) were combined into more complicated tools, such as the wheelbarrow, windmills, and clocks. a system of universities developed and spread scientific ideas and practices, including oxford and cambridge. the renaissance era produced many innovations, including the introduction of the movable type printing press to europe, which facilitated the communication of knowledge. technology became increasingly influenced by science ##ediment to up - stream navigation, and there are generally variations in water level, and when the discharge becomes small in the dry season. it is impossible to maintain a sufficient depth of water in the low - water channel. the possibility to secure uniformity of depth in a river by lowering the shoals obstructing the channel depends on the nature of the shoals. a soft shoal in the bed of a river is due to deposit from a diminution in velocity of flow, produced by a reduction in fall and by a widening of the channel, or to a loss in concentration of the scour of the main current in passing over from one concave bank to the next on the opposite side. the lowering of such a shoal by dredging merely effects a temporary deepening, for it soon forms again from the causes which produced it. the removal, moreover, of the rocky obstructions at rapids, though increasing the depth and equalizing the flow at these places, produces a lowering of the river above the rapids by facilitating the efflux, which may result in the appearance of fresh shoals at the low stage of the river. where, however, narrow rocky reefs or other hard shoals stretch across the bottom of a river and present obstacles to the erosion by the current of the soft materials forming the bed of the river above and below, their removal may result in permanent improvement by enabling the river to deepen its bed by natural scour. the capability of a river to provide a waterway for navigation during the summer or throughout the dry season depends on the depth that can be secured in the channel at the lowest stage. the problem in the dry season is the small discharge and deficiency in scour during this period. a typical solution is to restrict the width of the low - water channel, concentrate all of the flow in it, and also to fix its position so that it is scoured out every year by the floods which follow the deepest part of the bed along the line of the strongest current. this can be effected by closing subsidiary low - water channels with dikes across them, and narrowing the channel at the low stage by low - dipping cross dikes extending from the river banks down the slope and pointing slightly up - stream so as to direct the water flowing over them into a central channel. = = estuarine works = = the needs of navigation may also require that a stable, continuous, navigable channel is prolonged from the navigable river to deep water at the mouth of the estuary. the interaction of river earliest record of a ship under sail is that of a nile boat dating to around 7, 000 bce. from prehistoric times, egyptians likely used the power of the annual flooding of the nile to irrigate their lands, gradually learning to regulate much of it through purposely built irrigation channels and " catch " basins. the ancient sumerians in mesopotamia used a complex system of canals and levees to divert water from the tigris and euphrates rivers for irrigation. archaeologists estimate that the wheel was invented independently and concurrently in mesopotamia ( in present - day iraq ), the northern caucasus ( maykop culture ), and central europe. time estimates range from 5, 500 to 3, 000 bce with most experts putting it closer to 4, 000 bce. the oldest artifacts with drawings depicting wheeled carts date from about 3, 500 bce. more recently, the oldest - known wooden wheel in the world as of 2024 was found in the ljubljana marsh of slovenia ; austrian experts have established that the wheel is between 5, 100 and 5, 350 years old. the invention of the wheel revolutionized trade and war. it did not take long to discover that wheeled wagons could be used to carry heavy loads. the ancient sumerians used a potter ' s wheel and may have invented it. a stone pottery wheel found in the city - state of ur dates to around 3, 429 bce, and even older fragments of wheel - thrown pottery have been found in the same area. fast ( rotary ) potters ' wheels enabled early mass production of pottery, but it was the use of the wheel as a transformer of energy ( through water wheels, windmills, and even treadmills ) that revolutionized the application of nonhuman power sources. the first two - wheeled carts were derived from travois and were first used in mesopotamia and iran in around 3, 000 bce. the oldest known constructed roadways are the stone - paved streets of the city - state of ur, dating to c. 4, 000 bce, and timber roads leading through the swamps of glastonbury, england, dating to around the same period. the first long - distance road, which came into use around 3, 500 bce, spanned 2, 400 km from the persian gulf to the mediterranean sea, but was not paved and was only partially maintained. in around 2, 000 bce, the minoans on the greek island of crete built a 50 km road leading from the palace of gortyn on the south side of the island, through the mountains, Question: What kind of electricity can you generate with the energy found in flowing water? A) hydroelectric power B) wind energy C) electrical power D) transient power	A) hydroelectric power
Context: generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. this technique has an extremely high temporal resolution, but a relatively poor spatial resolution. functional magnetic resonance imaging. fmri measures the relative amount of oxygenated blood flowing to different parts of the brain. more oxygenated blood in a particular region is assumed to correlate with an increase in neural activity in that part of the brain. this allows us to localize particular functions within different brain regions. fmri has moderate spatial and temporal resolution. optical imaging. this technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active ( i. e., those that have more oxygenated blood ). optical imaging has moderate temporal resolution, but poor spatial resolution. it also has the advantage that it is extremely safe and can be used to study infants ' brains. magnetoencephalography. meg measures magnetic fields resulting from cortical activity. it is similar to eeg, except that it has improved spatial resolution since the magnetic fields it measures are not as blurred or attenuated by the scalp, meninges and so forth as the electrical activity measured in eeg is. meg uses squid sensors to detect tiny magnetic fields. = = = computational modeling = = = computational models require a mathematically and logically formal representation of a problem. computer models are used in the simulation and experimental verification of different specific and general properties of intelligence. computational modeling can help us understand the functional organization of a particular cognitive phenomenon. approaches to cognitive modeling can be categorized as : ( 1 ) symbolic, on abstract mental functions of an intelligent mind by means of symbols ; ( 2 ) subsymbolic, on the neural and associative properties of the human brain ; and ( 3 ) across the symbolic – subsymbolic border, including hybrid. symbolic modeling evolved from the computer science paradigms using the technologies of knowledge - based systems, as well as a philosophical perspective ( e. g. " good old - fashioned artificial intelligence " ( gofai ) ). they were developed by the first cognitive researchers and later used in information engineering for expert systems. since the early 1990s it was generalized in systemics for the investigation of functional human - like intelligence models, such as personoids, and, in parallel, developed as the soar environment. recently, especially in and taken up by the brain. by observing which areas of the brain take up the radioactive isotope, we can see which areas of the brain are more active than other areas. pet has similar spatial resolution to fmri, but it has extremely poor temporal resolution. electroencephalography. eeg measures the electrical fields generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. this technique has an extremely high temporal resolution, but a relatively poor spatial resolution. functional magnetic resonance imaging. fmri measures the relative amount of oxygenated blood flowing to different parts of the brain. more oxygenated blood in a particular region is assumed to correlate with an increase in neural activity in that part of the brain. this allows us to localize particular functions within different brain regions. fmri has moderate spatial and temporal resolution. optical imaging. this technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active ( i. e., those that have more oxygenated blood ). optical imaging has moderate temporal resolution, but poor spatial resolution. it also has the advantage that it is extremely safe and can be used to study infants ' brains. magnetoencephalography. meg measures magnetic fields resulting from cortical activity. it is similar to eeg, except that it has improved spatial resolution since the magnetic fields it measures are not as blurred or attenuated by the scalp, meninges and so forth as the electrical activity measured in eeg is. meg uses squid sensors to detect tiny magnetic fields. = = = computational modeling = = = computational models require a mathematically and logically formal representation of a problem. computer models are used in the simulation and experimental verification of different specific and general properties of intelligence. computational modeling can help us understand the functional organization of a particular cognitive phenomenon. approaches to cognitive modeling can be categorized as : ( 1 ) symbolic, on abstract mental functions of an intelligent mind by means of symbols ; ( 2 ) subsymbolic, on the neural and associative properties of the human brain ; and ( 3 ) across the symbolic – subsymbolic border, including hybrid. symbolic modeling evolved from the computer science paradigms using the technologies of knowledge - based systems, as well as a philosophical perspective ( e. g. " good old - fashioned artificial intelligence " ( gofa of imaging techniques vary in their temporal ( time - based ) and spatial ( location - based ) resolution. brain imaging is often used in cognitive neuroscience. single - photon emission computed tomography and positron emission tomography. spect and pet use radioactive isotopes, which are injected into the subject ' s bloodstream and taken up by the brain. by observing which areas of the brain take up the radioactive isotope, we can see which areas of the brain are more active than other areas. pet has similar spatial resolution to fmri, but it has extremely poor temporal resolution. electroencephalography. eeg measures the electrical fields generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. this technique has an extremely high temporal resolution, but a relatively poor spatial resolution. functional magnetic resonance imaging. fmri measures the relative amount of oxygenated blood flowing to different parts of the brain. more oxygenated blood in a particular region is assumed to correlate with an increase in neural activity in that part of the brain. this allows us to localize particular functions within different brain regions. fmri has moderate spatial and temporal resolution. optical imaging. this technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active ( i. e., those that have more oxygenated blood ). optical imaging has moderate temporal resolution, but poor spatial resolution. it also has the advantage that it is extremely safe and can be used to study infants ' brains. magnetoencephalography. meg measures magnetic fields resulting from cortical activity. it is similar to eeg, except that it has improved spatial resolution since the magnetic fields it measures are not as blurred or attenuated by the scalp, meninges and so forth as the electrical activity measured in eeg is. meg uses squid sensors to detect tiny magnetic fields. = = = computational modeling = = = computational models require a mathematically and logically formal representation of a problem. computer models are used in the simulation and experimental verification of different specific and general properties of intelligence. computational modeling can help us understand the functional organization of a particular cognitive phenomenon. approaches to cognitive modeling can be categorized as : ( 1 ) symbolic, on abstract mental functions of an intelligent mind by means of symbols ; ( 2 ) subsymbolic, on the neural and associa this scaffold and cells were placed in a bioreactor, where it matured to become a partially or fully transplantable organ. the work was called a " landmark ". the lab first stripped the cells away from a rat heart ( a process called " decellularization " ) and then injected rat stem cells into the decellularized rat heart. tissue - engineered blood vessels : blood vessels that have been grown in a lab and can be used to repair damaged blood vessels without eliciting an immune response. tissue engineered blood vessels have been developed by many different approaches. they could be implanted as pre - seeded cellularized blood vessels, as acellular vascular grafts made with decellularized vessels or synthetic vascular grafts. artificial skin constructed from human skin cells embedded in a hydrogel, such as in the case of bio - printed constructs for battlefield burn repairs. artificial bone marrow : bone marrow cultured in vitro to be transplanted serves as a " just cells " approach to tissue engineering. tissue engineered bone : a structural matrix can be composed of metals such as titanium, polymers of varying degradation rates, or certain types of ceramics. materials are often chosen to recruit osteoblasts to aid in reforming the bone and returning biological function. various types of cells can be added directly into the matrix to expedite the process. laboratory - grown penis : decellularized scaffolds of rabbit penises were recellularised with smooth muscle and endothelial cells. the organ was then transplanted to live rabbits and functioned comparably to the native organ, suggesting potential as treatment for genital trauma. oral mucosa tissue engineering uses a cells and scaffold approach to replicate the 3 dimensional structure and function of oral mucosa. = = cells as building blocks = = cells are one of the main components for the success of tissue engineering approaches. tissue engineering uses cells as strategies for creation / replacement of new tissue. examples include fibroblasts used for skin repair or renewal, chondrocytes used for cartilage repair ( maci – fda approved product ), and hepatocytes used in liver support systems cells can be used alone or with support matrices for tissue engineering applications. an adequate environment for promoting cell growth, differentiation, and integration with the existing tissue is a critical factor for cell - based building blocks. manipulation of any of these cell processes create alternative avenues for the development of new tissue ( e. g., cell reprogramming - somatic ##logous in nature, and can be used in a myriad of ways, from helping repair skeletal tissue to replenishing beta cells in diabetic patients. allogenic : cells are obtained from the body of a donor of the same species as the recipient. while there are some ethical constraints to the use of human cells for in vitro studies ( i. e. human brain tissue chimera development ), the employment of dermal fibroblasts from human foreskin demonstrates an immunologically safe and thus a viable choice for allogenic tissue engineering of the skin. xenogenic : these cells are derived isolated cells from alternate species from the recipient. a notable example of xenogeneic tissue utilization is cardiovascular implant construction via animal cells. chimeric human - animal farming raises ethical concerns around the potential for improved consciousness from implanting human organs in animals. syngeneic or isogenic : these cells describe those borne from identical genetic code. this imparts an immunologic benefit similar to autologous cell lines ( see above ). autologous cells can be considered syngenic, but the classification also extends to non - autologously derived cells such as those from an identical twin, from genetically identical ( cloned ) research models, or induced stem cells ( isc ) as related to the donor. = = = stem cells = = = stem cells are undifferentiated cells with the ability to divide in culture and give rise to different forms of specialized cells. stem cells are divided into " adult " and " embryonic " stem cells according to their source. while there is still a large ethical debate related to the use of embryonic stem cells, it is thought that another alternative source – induced pluripotent stem cells – may be useful for the repair of diseased or damaged tissues, or may be used to grow new organs. totipotent cells are stem cells which can divide into further stem cells or differentiate into any cell type in the body, including extra - embryonic tissue. pluripotent cells are stem cells which can differentiate into any cell type in the body except extra - embryonic tissue. induced pluripotent stem cells ( ipscs ) are subclass of pluripotent stem cells resembling embryonic stem cells ( escs ) that have been derived from adult differentiated cells. ipscs are created by altering the expression of transcriptional factors in adult cells until they become like embryonic stem cells. multipotent stem cells can be differentiated into any cell . currently, even blades made of advanced metal alloys used in the engines ' hot section require cooling and careful limiting of operating temperatures. turbine engines made with ceramics could operate more efficiently, giving aircraft greater range and payload for a set amount of fuel. recently, there have been advances in ceramics which include bio - ceramics, such as dental implants and synthetic bones. hydroxyapatite, the natural mineral component of bone, has been made synthetically from a number of biological and chemical sources and can be formed into ceramic materials. orthopedic implants made from these materials bond readily to bone and other tissues in the body without rejection or inflammatory reactions. because of this, they are of great interest for gene delivery and tissue engineering scaffolds. most hydroxyapatite ceramics are very porous and lack mechanical strength and are used to coat metal orthopedic devices to aid in forming a bond to bone or as bone fillers. they are also used as fillers for orthopedic plastic screws to aid in reducing the inflammation and increase absorption of these plastic materials. work is being done to make strong, fully dense nano crystalline hydroxyapatite ceramic materials for orthopedic weight bearing devices, replacing foreign metal and plastic orthopedic materials with a synthetic, but naturally occurring, bone mineral. ultimately these ceramic materials may be used as bone replacements or with the incorporation of protein collagens, synthetic bones. durable actinide - containing ceramic materials have many applications such as in nuclear fuels for burning excess pu and in chemically - inert sources of alpha irradiation for power supply of unmanned space vehicles or to produce electricity for microelectronic devices. both use and disposal of radioactive actinides require their immobilization in a durable host material. nuclear waste long - lived radionuclides such as actinides are immobilized using chemically - durable crystalline materials based on polycrystalline ceramics and large single crystals. alumina ceramics are widely utilized in the chemical industry due to their excellent chemical stability and high resistance to corrosion. it is used as acid - resistant pump impellers and pump bodies, ensuring long - lasting performance in transferring aggressive fluids. they are also used in acid - carrying pipe linings to prevent contamination and maintain fluid purity, which is crucial in industries like pharmaceuticals and food processing. valves made from alumina ceramics demonstrate exceptional durability and resistance to chemical attack, making them reliable for controlling the flow of corrosive liquids. = , biomedical research, genetics, and medical technology to diagnose, treat, and prevent injury and disease, typically through pharmaceuticals or surgery, but also through therapies as diverse as psychotherapy, external splints and traction, medical devices, biologics, and ionizing radiation, amongst others. medicine has been practiced since prehistoric times, and for most of this time it was an art ( an area of creativity and skill ), frequently having connections to the religious and philosophical beliefs of local culture. for example, a medicine man would apply herbs and say prayers for healing, or an ancient philosopher and physician would apply bloodletting according to the theories of humorism. in recent centuries, since the advent of modern science, most medicine has become a combination of art and science ( both basic and applied, under the umbrella of medical science ). for example, while stitching technique for sutures is an art learned through practice, knowledge of what happens at the cellular and molecular level in the tissues being stitched arises through science. prescientific forms of medicine, now known as traditional medicine or folk medicine, remain commonly used in the absence of scientific medicine and are thus called alternative medicine. alternative treatments outside of scientific medicine with ethical, safety and efficacy concerns are termed quackery. = = etymology = = medicine ( uk :, us : ) is the science and practice of the diagnosis, prognosis, treatment, and prevention of disease. the word " medicine " is derived from latin medicus, meaning " a physician ". the word " physic " itself, from which " physician " derives, was the old word for what is now called a medicine, and also the field of medicine. = = clinical practice = = medical availability and clinical practice vary across the world due to regional differences in culture and technology. modern scientific medicine is highly developed in the western world, while in developing countries such as parts of africa or asia, the population may rely more heavily on traditional medicine with limited evidence and efficacy and no required formal training for practitioners. in the developed world, evidence - based medicine is not universally used in clinical practice ; for example, a 2007 survey of literature reviews found that about 49 % of the interventions lacked sufficient evidence to support either benefit or harm. in modern clinical practice, physicians and physician assistants personally assess patients to diagnose, prognose, treat, and prevent disease using clinical judgment. the doctor - patient relationship typically begins with an interaction with an examination of the patient ' s medical history and medical record decision making during a task, and they provide us with some insight into the ways in which those decisions may be processed. = = = brain imaging = = = brain imaging involves analyzing activity within the brain while performing various tasks. this allows us to link behavior and brain function to help understand how information is processed. different types of imaging techniques vary in their temporal ( time - based ) and spatial ( location - based ) resolution. brain imaging is often used in cognitive neuroscience. single - photon emission computed tomography and positron emission tomography. spect and pet use radioactive isotopes, which are injected into the subject ' s bloodstream and taken up by the brain. by observing which areas of the brain take up the radioactive isotope, we can see which areas of the brain are more active than other areas. pet has similar spatial resolution to fmri, but it has extremely poor temporal resolution. electroencephalography. eeg measures the electrical fields generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. this technique has an extremely high temporal resolution, but a relatively poor spatial resolution. functional magnetic resonance imaging. fmri measures the relative amount of oxygenated blood flowing to different parts of the brain. more oxygenated blood in a particular region is assumed to correlate with an increase in neural activity in that part of the brain. this allows us to localize particular functions within different brain regions. fmri has moderate spatial and temporal resolution. optical imaging. this technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active ( i. e., those that have more oxygenated blood ). optical imaging has moderate temporal resolution, but poor spatial resolution. it also has the advantage that it is extremely safe and can be used to study infants ' brains. magnetoencephalography. meg measures magnetic fields resulting from cortical activity. it is similar to eeg, except that it has improved spatial resolution since the magnetic fields it measures are not as blurred or attenuated by the scalp, meninges and so forth as the electrical activity measured in eeg is. meg uses squid sensors to detect tiny magnetic fields. = = = computational modeling = = = computational models require a mathematically and logically formal representation of a problem. computer models are used in the simulation and experimental verification of different ##thic, or " old stone age ", and spans all of human history up to the development of agriculture approximately 12, 000 years ago. to make a stone tool, a " core " of hard stone with specific flaking properties ( such as flint ) was struck with a hammerstone. this flaking produced sharp edges which could be used as tools, primarily in the form of choppers or scrapers. these tools greatly aided the early humans in their hunter - gatherer lifestyle to perform a variety of tasks including butchering carcasses ( and breaking bones to get at the marrow ) ; chopping wood ; cracking open nuts ; skinning an animal for its hide, and even forming other tools out of softer materials such as bone and wood. the earliest stone tools were irrelevant, being little more than a fractured rock. in the acheulian era, beginning approximately 1. 65 million years ago, methods of working these stones into specific shapes, such as hand axes emerged. this early stone age is described as the lower paleolithic. the middle paleolithic, approximately 300, 000 years ago, saw the introduction of the prepared - core technique, where multiple blades could be rapidly formed from a single core stone. the upper paleolithic, beginning approximately 40, 000 years ago, saw the introduction of pressure flaking, where a wood, bone, or antler punch could be used to shape a stone very finely. the end of the last ice age about 10, 000 years ago is taken as the end point of the upper paleolithic and the beginning of the epipaleolithic / mesolithic. the mesolithic technology included the use of microliths as composite stone tools, along with wood, bone, and antler tools. the later stone age, during which the rudiments of agricultural technology were developed, is called the neolithic period. during this period, polished stone tools were made from a variety of hard rocks such as flint, jade, jadeite, and greenstone, largely by working exposures as quarries, but later the valuable rocks were pursued by tunneling underground, the first steps in mining technology. the polished axes were used for forest clearance and the establishment of crop farming and were so effective as to remain in use when bronze and iron appeared. these stone axes were used alongside a continued use of stone tools such as a range of projectiles, knives, and scrapers, as well as tools, made from organic materials such as wood, bone, and antler. stone age cultures medical purposes. cells are often ' seeded ' into these structures capable of supporting three - dimensional tissue formation. scaffolds mimic the extracellular matrix of the native tissue, recapitulating the in vivo milieu and allowing cells to influence their own microenvironments. they usually serve at least one of the following purposes : allowing cell attachment and migration, delivering and retaining cells and biochemical factors, enabling diffusion of vital cell nutrients and expressed products, and exerting certain mechanical and biological influences to modify the behaviour of the cell phase. in 2009, an interdisciplinary team led by the thoracic surgeon thorsten walles implanted the first bioartificial transplant that provides an innate vascular network for post - transplant graft supply successfully into a patient awaiting tracheal reconstruction. to achieve the goal of tissue reconstruction, scaffolds must meet some specific requirements. high porosity and adequate pore size are necessary to facilitate cell seeding and diffusion throughout the whole structure of both cells and nutrients. biodegradability is often an essential factor since scaffolds should preferably be absorbed by the surrounding tissues without the necessity of surgical removal. the rate at which degradation occurs has to coincide as much as possible with the rate of tissue formation : this means that while cells are fabricating their own natural matrix structure around themselves, the scaffold is able to provide structural integrity within the body and eventually it will break down leaving the newly formed tissue which will take over the mechanical load. injectability is also important for clinical uses. recent research on organ printing is showing how crucial a good control of the 3d environment is to ensure reproducibility of experiments and offer better results. = = = materials = = = material selection is an essential aspect of producing a scaffold. the materials utilized can be natural or synthetic and can be biodegradable or non - biodegradable. additionally, they must be biocompatible, meaning that they do not cause any adverse effects to cells. silicone, for example, is a synthetic, non - biodegradable material commonly used as a drug delivery material, while gelatin is a biodegradable, natural material commonly used in cell - culture scaffolds the material needed for each application is different, and dependent on the desired mechanical properties of the material. tissue engineering of long bone defects for example, will require a rigid scaffold with a compressive strength similar to that of cortical bone ( 100 - 150 mpa ), Question: At the time of birth, bones of the brain case are separated by what wide areas of fibrous connective tissue, which later become sutures? A) fluctuations B) sporozoans C) cerebellum D) fontanelles	D) fontanelles
Context: , but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. = = = = substance and mixture = = = = a chemical substance is a kind of matter with a definite composition and set of properties. a collection of substances is called a mixture. examples of mixtures are air and alloys. = = = = mole and amount of substance = = = = the mole is a unit of measurement that denotes an amount of substance ( also called chemical amount ). one mole is defined to contain exactly 6. 02214076×1023 particles ( atoms, molecules, ions, or electrons ), where the number of particles per mole is known as the avogadro constant. molar concentration is the amount of a particular substance per volume of solution, and is commonly reported in mol / dm3. = = = phase = = = in addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. for the most part, the chemical classifications are independent of these bulk phase classifications ; however, some more exotic phases are incompatible with certain chemical properties. a phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature. physical properties, such as density and refractive index tend to fall within values characteristic of the phase electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. = = = = substance and mixture = = = = a chemical substance is a kind of matter with a definite composition and set of properties. a collection of substances is called a mixture. examples of mixtures are air and alloys. = = = = mole and amount of substance = = = = the mole is a unit of measurement that denotes an amount of substance ( also called chemical amount ). one mole is defined to contain exactly 6. 02214076×1023 particles ( atoms, molecules, ions, or electrons ), where the number of particles per mole is known as the avogadro constant. molar concentration is the amount of a particular substance per volume of solution, and is commonly reported in mol / dm3. = = = phase = = = in addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. for the most part, the chemical classifications are independent of these bulk phase that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. = = = = substance and mixture = = = = a chemical substance is a kind of matter with a definite composition and set of properties. a collection of substances is called a mixture. examples of mixtures are air and alloys. = = = = mole and amount of substance = = = = the mole is a unit of measurement that denotes an amount of substance ( also called chemical amount ). one mole is defined to contain exactly 6. 02214076×1023 particles ( atoms, molecules, ions, or electrons ), where the number of particles per mole is known as the avogadro constant. molar concentration is other electrons either in bonds or in lone pairs. thus, molecules exist as electrically neutral units, unlike ions. when this rule is broken, giving the " molecule " a charge, the result is sometimes named a molecular ion or a polyatomic ion. however, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. = = = = substance and mixture = = = = a chemical substance is a kind of matter with a definite composition and set of properties. a collection of substances is called a mixture. examples of mixtures are air and alloys. = = = = mole and amount of substance = = = = the mole is a unit set of chemical reactions with other substances. however, this definition only works well for substances that are composed of molecules, which is not true of many substances ( see below ). molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs. thus, molecules exist as electrically neutral units, unlike ions. when this rule is broken, giving the " molecule " a charge, the result is sometimes named a molecular ion or a polyatomic ion. however, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. = = organic compounds are molecules that contain carbon bonded to another element such as hydrogen. with the exception of water, nearly all the molecules that make up each organism contain carbon. carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules. for example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids index chemical substances. in this scheme each chemical substance is identifiable by a number known as its cas registry number. = = = = molecule = = = = a molecule is the smallest indivisible portion of a pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. however, this definition only works well for substances that are composed of molecules, which is not true of many substances ( see below ). molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs. thus, molecules exist as electrically neutral units, unlike ions. when this rule is broken, giving the " molecule " a charge, the result is sometimes named a molecular ion or a polyatomic ion. however, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry used by pharmaceutical companies as a way of drug discovery. plants can synthesise coloured dyes and pigments such as the anthocyanins responsible for the red colour of red wine, yellow weld and blue woad used together to produce lincoln green, indoxyl, source of the blue dye indigo traditionally used to dye denim and the artist ' s pigments gamboge and rose madder. sugar, starch, cotton, linen, hemp, some types of rope, wood and particle boards, papyrus and paper, vegetable oils, wax, and natural rubber are examples of commercially important materials made from plant tissues or their secondary products. charcoal, a pure form of carbon made by pyrolysis of wood, has a long history as a metal - smelting fuel, as a filter material and adsorbent and as an artist ' s material and is one of the three ingredients of gunpowder. cellulose, the world ' s most abundant organic polymer, can be converted into energy, fuels, materials and chemical feedstock. products made from cellulose include rayon and cellophane, wallpaper paste, biobutanol and gun cotton. sugarcane, rapeseed and soy are some of the plants with a highly fermentable sugar or oil content that are used as sources of biofuels, important alternatives to fossil fuels, such as biodiesel. sweetgrass was used by native americans to ward off bugs like mosquitoes. these bug repelling properties of sweetgrass were later found by the american chemical society in the molecules phytol and coumarin. = = plant ecology = = plant ecology is the science of the functional relationships between plants and their habitats – the environments where they complete their life cycles. plant ecologists study the composition of local and regional floras, their biodiversity, genetic diversity and fitness, the adaptation of plants to their environment, and their competitive or mutualistic interactions with other species. some ecologists even rely on empirical data from indigenous people that is gathered by ethnobotanists. this information can relay a great deal of information on how the land once was thousands of years ago and how it has changed over that time. the goals of plant ecology are to understand the causes of their distribution patterns, productivity, environmental impact, evolution, and responses to environmental change. plants depend on certain edaphic ( soil ) and climatic factors in their environment but can modify these factors too. for example, they can change their environment ' s albedo, increase runoff interception not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again. in pure water, the number of hydrogen ions balances ( or equals ) the number of hydroxyl ions, resulting in a ph that is neutral. = = = organic compounds = = = organic compounds are molecules that contain carbon bonded to another element such as hydrogen. with the exception of water, nearly all the molecules that make up each organism contain carbon. carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules. for example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids are polymers of nucleotides. their function is to store, transmit, and express hereditary information. = = cells = = cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division Question: What are inorganic compounds that take the form of discrete molecules called? A) ionic compounds B) functional compounds C) molecular compounds D) magnetic compounds	C) molecular compounds
Context: ammonium hydrosulphide has long since been postulated to exist at least in certain layers of the giant planets. its radiation products may be the reason for the red colour seen on jupiter. several ammonium salts, the products of nh3 and an acid, have previously been detected at comet 67p / churyumov - gerasimenko. the acid h2s is the fifth most abundant molecule in the coma of 67p followed by nh3. in order to look for the salt nh4 + sh -, we analysed in situ measurements from the rosetta / rosina double focusing mass spectrometer during the rosetta mission. nh3 and h2s appear to be independent of each other when sublimating directly from the nucleus. however, we observe a strong correlation between the two species during dust impacts, clearly pointing to the salt. we find that nh4 + sh - is by far the most abundant salt, more abundant in the dust impacts than even water. we also find all previously detected ammonium salts and for the first time ammonium fluoride. the amount of ammonia and acids balance each other, confirming that ammonia is mostly in the form of salt embedded into dust grains. allotropes s2 and s3 are strongly enhanced in the impacts, while h2s2 and its fragment hs2 are not detected, which is most probably the result of radiolysis of nh4 + sh -. this makes a prestellar origin of the salt likely. our findings may explain the apparent depletion of nitrogen in comets and maybe help to solve the riddle of the missing sulphur in star forming regions. molecular nitrogen is the most commonly assumed background gas that supports habitability on rocky planets. despite its chemical inertness, nitrogen molecule is broken by lightning, hot volcanic vents, and bolide impacts, and can be converted into soluble nitrogen compounds and then sequestered in the ocean. the very stability of nitrogen, and that of nitrogen - based habitability, is thus called into question. here we determine the lifetime of molecular nitrogen vis - a - vis aqueous sequestration, by developing a novel model that couples atmospheric photochemistry and oceanic chemistry. we find that hno, the dominant nitrogen compounds produced in anoxic atmospheres, is converted to n2o in the ocean, rather than oxidized to nitrites or nitrates as previously assumed. this n2o is then released back into the atmosphere and quickly converted to n2. we also find that the deposition rate of no is severely limited by the kinetics of the aqueous - phase reaction that converts no to nitrites in the ocean. putting these insights together, we conclude that the atmosphere must produce nitrogen species at least as oxidized as no2 and hno2 to enable aqueous sequestration. the lifetime of molecular nitrogen in anoxic atmospheres is determined to be > 1 billion years on temperate planets of both sun - like and m dwarf stars. this result upholds the validity of molecular nitrogen as a universal background gas on rocky planets. plasma etching should not be conflated with the use of the same term when referring to orientation - dependent etching. the source gas for the plasma usually contains small molecules rich in chlorine or fluorine. for instance, carbon tetrachloride ( ccl4 ) etches silicon and aluminium, and trifluoromethane etches silicon dioxide and silicon nitride. a plasma containing oxygen is used to oxidize ( " ash " ) photoresist and facilitate its removal. ion milling, or sputter etching, uses lower pressures, often as low as 10−4 torr ( 10 mpa ). it bombards the wafer with energetic ions of noble gases, often ar +, which knock atoms from the substrate by transferring momentum. because the etching is performed by ions, which approach the wafer approximately from one direction, this process is highly anisotropic. on the other hand, it tends to display poor selectivity. reactive - ion etching ( rie ) operates under conditions intermediate between sputter and plasma etching ( between 10−3 and 10−1 torr ). deep reactive - ion etching ( drie ) modifies the rie technique to produce deep, narrow features. in reactive - ion etching ( rie ), the substrate is placed inside a reactor, and several gases are introduced. a plasma is struck in the gas mixture using an rf power source, which breaks the gas molecules into ions. the ions accelerate towards, and react with, the surface of the material being etched, forming another gaseous material. this is known as the chemical part of reactive ion etching. there is also a physical part, which is similar to the sputtering deposition process. if the ions have high enough energy, they can knock atoms out of the material to be etched without a chemical reaction. it is a very complex task to develop dry etch processes that balance chemical and physical etching, since there are many parameters to adjust. by changing the balance it is possible to influence the anisotropy of the etching, since the chemical part is isotropic and the physical part highly anisotropic the combination can form sidewalls that have shapes from rounded to vertical. deep reactive ion etching ( drie ) is a special subclass of rie that is growing in popularity. in this process, etch depths of hundreds of micrometers are achieved with almost vertical sidewalls. the primary technology is based on the , and trifluoromethane etches silicon dioxide and silicon nitride. a plasma containing oxygen is used to oxidize ( " ash " ) photoresist and facilitate its removal. ion milling, or sputter etching, uses lower pressures, often as low as 10−4 torr ( 10 mpa ). it bombards the wafer with energetic ions of noble gases, often ar +, which knock atoms from the substrate by transferring momentum. because the etching is performed by ions, which approach the wafer approximately from one direction, this process is highly anisotropic. on the other hand, it tends to display poor selectivity. reactive - ion etching ( rie ) operates under conditions intermediate between sputter and plasma etching ( between 10−3 and 10−1 torr ). deep reactive - ion etching ( drie ) modifies the rie technique to produce deep, narrow features. in reactive - ion etching ( rie ), the substrate is placed inside a reactor, and several gases are introduced. a plasma is struck in the gas mixture using an rf power source, which breaks the gas molecules into ions. the ions accelerate towards, and react with, the surface of the material being etched, forming another gaseous material. this is known as the chemical part of reactive ion etching. there is also a physical part, which is similar to the sputtering deposition process. if the ions have high enough energy, they can knock atoms out of the material to be etched without a chemical reaction. it is a very complex task to develop dry etch processes that balance chemical and physical etching, since there are many parameters to adjust. by changing the balance it is possible to influence the anisotropy of the etching, since the chemical part is isotropic and the physical part highly anisotropic the combination can form sidewalls that have shapes from rounded to vertical. deep reactive ion etching ( drie ) is a special subclass of rie that is growing in popularity. in this process, etch depths of hundreds of micrometers are achieved with almost vertical sidewalls. the primary technology is based on the so - called " bosch process ", named after the german company robert bosch, which filed the original patent, where two different gas compositions alternate in the reactor. currently, there are two variations of the drie. the first variation consists of three distinct steps ( the original bosch process ) while the second variation only consists of jwst / nircam obtained high angular - resolution ( 0. 05 - 0. 1 ' ' ), deep near - infrared 1 - - 5 micron imaging of supernova ( sn ) 1987a taken 35 years after the explosion. in the nircam images, we identify : 1 ) faint h2 crescents, which are emissions located between the ejecta and the equatorial ring, 2 ) a bar, which is a substructure of the ejecta, and 3 ) the bright 3 - 5 micron continuum emission exterior to the equatorial ring. the emission of the remnant in the nircam 1 - 2. 3 micron images is mostly due to line emission, which is mostly emitted in the ejecta and in the hot spots within the equatorial ring. in contrast, the nircam 3 - 5 micron images are dominated by continuum emission. in the ejecta, the continuum is due to dust, obscuring the centre of the ejecta. in contrast, in the ring and exterior to the ring, synchrotron emission contributes a substantial fraction to the continuum. dust emission contributes to the continuum at outer spots and diffuse emission exterior to the ring, but little within the ring. this shows that dust cooling and destruction time scales are shorter than the synchrotron cooling time scale, and the time scale of hydrogen recombination in the ring is even longer than the synchrotron cooling time scale. with the advent of high sensitivity and high angular resolution images provided by jwst / nircam, our observations of sn 1987a demonstrate that nircam opens up a window to study particle - acceleration and shock physics in unprecedented details, probed by near - infrared synchrotron emission, building a precise picture of how a sn evolves. ##nts from the air to reduce the potential adverse effects on humans and the environment. the process of air purification may be performed using methods such as mechanical filtration, ionization, activated carbon adsorption, photocatalytic oxidation, and ultraviolet light germicidal irradiation. = = = sewage treatment = = = = = = environmental remediation = = = environmental remediation is the process through which contaminants or pollutants in soil, water and other media are removed to improve environmental quality. the main focus is the reduction of hazardous substances within the environment. some of the areas involved in environmental remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the this paper has been withdrawn by the authors until some changes are made. other electrons either in bonds or in lone pairs. thus, molecules exist as electrically neutral units, unlike ions. when this rule is broken, giving the " molecule " a charge, the result is sometimes named a molecular ion or a polyatomic ion. however, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. = = = = substance and mixture = = = = a chemical substance is a kind of matter with a definite composition and set of properties. a collection of substances is called a mixture. examples of mixtures are air and alloys. = = = = mole and amount of substance = = = = the mole is a unit also used as fillers for orthopedic plastic screws to aid in reducing the inflammation and increase absorption of these plastic materials. work is being done to make strong, fully dense nano crystalline hydroxyapatite ceramic materials for orthopedic weight bearing devices, replacing foreign metal and plastic orthopedic materials with a synthetic, but naturally occurring, bone mineral. ultimately these ceramic materials may be used as bone replacements or with the incorporation of protein collagens, synthetic bones. durable actinide - containing ceramic materials have many applications such as in nuclear fuels for burning excess pu and in chemically - inert sources of alpha irradiation for power supply of unmanned space vehicles or to produce electricity for microelectronic devices. both use and disposal of radioactive actinides require their immobilization in a durable host material. nuclear waste long - lived radionuclides such as actinides are immobilized using chemically - durable crystalline materials based on polycrystalline ceramics and large single crystals. alumina ceramics are widely utilized in the chemical industry due to their excellent chemical stability and high resistance to corrosion. it is used as acid - resistant pump impellers and pump bodies, ensuring long - lasting performance in transferring aggressive fluids. they are also used in acid - carrying pipe linings to prevent contamination and maintain fluid purity, which is crucial in industries like pharmaceuticals and food processing. valves made from alumina ceramics demonstrate exceptional durability and resistance to chemical attack, making them reliable for controlling the flow of corrosive liquids. = = glass - ceramics = = glass - ceramic materials share many properties with both glasses and ceramics. glass - ceramics have an amorphous phase and one or more crystalline phases and are produced by a so - called " controlled crystallization ", which is typically avoided in glass manufacturing. glass - ceramics often contain a crystalline phase which constitutes anywhere from 30 % [ m / m ] to 90 % [ m / m ] of its composition by volume, yielding an array of materials with interesting thermomechanical properties. in the processing of glass - ceramics, molten glass is cooled down gradually before reheating and annealing. in this heat treatment the glass partly crystallizes. in many cases, so - called ' nucleation agents ' are added in order to regulate and control the crystallization process. because there is usually no pressing and sintering, glass - ceramics do not contain the volume fraction of porosity typically present in sintered ceramics. the nubia technology is a chinese smartphone manufacturer headquartered in shenzhen, guangdong. originally established as a wholly owned subsidiary of zte in 2012, it became an independent company in 2015 and received a significant investment from suning holdings group and suning commerce group in 2016. zte reduced its stake in nubia to 49. 9 % in 2017, officially meaning nubia was no longer considered a subsidiary of zte, but more of an associate company. in february 2016 nubia became a sponsor of jiangsu suning f. c. for a reported cn¥150 million. the company hired footballer cristiano ronaldo to promote the mobile phone of the company in may 2016. in 2017, china daily reported that nubia would build a factory in nanchang, jiangxi province. in april 2018, nubia technology launched a gaming sub - brand, named redmagic ( [UNK] [UNK] ). redmagic announced its new 5g compatible device redmagic 5g on march 12, 2020, in shanghai. redmagic is known for being the first smartphone brand to put cooling fans inside their phones. the company also unveiled a partnership with chinese esport team royal never give up, to further expand its brand among esport enthusiasts. on 13 april 2020, the company unveiled a brand new logo as well as its new brand vision. in march 2022, nubia unveiled the first gaming phone featuring an under - display camera technology, the redmagic 7 pro. in 2023, nubia released the red magic 8s pro, touted as the strongest gaming phone to date. in 2024, nubia released the red magic 9s pro + with the highest antutu smartphone score to date. in july 2024, redmagic announced its entry in the computer category with its first gaming laptop, the titan 16 pro, available in china and global markets, while in september, they launched their first gaming tablet, the nova gaming pad. = = products = = = = = smartphone = = = = = = = redmagic sub - brand = = = = = = = = nubia = = = = 2024 — nubia neo 2 2025 — nubia z70s ( also pro, ultra and ultra photographer edition ) = = references = = = = external links = = official website Question: The other ammonium ions are changed into nitrogen gas by what? A) fungi B) fluctuations bacteria C) accompanying bacteria D) denitrifying bacteria	D) denitrifying bacteria
Context: weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding seawards, so that in the po river in italy, for instance, pebbles and gravel are found for about 140 miles below turin, sand along the next 100 miles, and silt and mud in the last 110 miles ( 176 km ). = = channelization = = the removal of obstructions, natural or artificial navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding sea becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under this article has been withdrown by the author. hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding seawards, so that in the po river in italy, for instance, pebbles and gravel are found for about 140 miles below turin, sand along the next 100 miles, and silt and mud in the last 110 miles ( 176 km ). = = channelization = = the removal of obstructions, natural or artificial ( e. g., trunks of trees, boulders and accumulations of gravel ) from a river bed furnishes a simple and efficient means of increasing the discharging capacity of its channel. such removals will consequently lower the height of floods upstream. every impediment to the flow, in proportion to floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding seawards, so that in the po river in italy, for instance, pebbles and gravel are found for about 140 miles below turin, sand along the next 100 miles, and silt and mud in the last 110 miles ( 176 km ). = = channelization = = the removal of obstructions, natural or artificial ( e. g., trunks of trees, boulders and accumulations of gravel ) from a river bed furnishes a simple and efficient means of increasing the discharging capacity of its channel. such removals will consequently lower the height of floods upstream. every impediment to the flow, in proportion to its extent, raises the level of the river above it so as to produce the additional artificial fall necessary to convey the flow through the restricted channel, thereby reducing the total available fall. reducing the length of the channel by substituting straight cuts for a winding course is the only way in which the effective fall can be increased. approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make this is the introductory part of my ph. d thesis, defended at the faculty of science and technology, ntnu on december 10, 2012. enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make it available as drinking water. the earliest exploitation of groundwater resources dates back to 3000 bc, and hydrogeology as a science was developed by hydrologists beginning in the 17th century. ecohydrology is the study of ecological systems in the hydrosphere. it can be divided into the physical study of aquatic ecosystems and the Question: What is typical weather for chicago in winter? A) rain and wind B) dry and windy C) ice and humidity D) cold & snow	D) cold & snow
Context: reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then oxidized into acetyl - coa by the pyruvate dehydrogenase complex, which also generates nadh and carbon dioxide. acetyl - coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. at the end of the cycle, the total yield from 1 glucose ( or 2 pyruvates ) is 6 nadh, 2 fadh2, and 2 atp molecules. finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from nadh and fadh2 that is coupled to the pumping of protons ( hydrogen ions ) across the inner mitochondrial membrane ( chemiosmosis ), which generates a proton motive force. energy in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle . oxidation, reduction, dissociation, acid – base neutralization and molecular rearrangement are some examples of common chemical reactions. a chemical reaction can be symbolically depicted through a chemical equation. while in a non - nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons. the sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. a chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. several empirical rules, like the woodward – hoffmann rules often come in handy while proposing a mechanism for a chemical reaction. according to the iupac gold book, a chemical reaction is " a process that results in the interconversion of chemical species. " accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction. an additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities ( i. e. ' microscopic chemical events ' ). = = = ions and salts = = = an ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. when an atom loses an electron and thus has more protons than electrons, the atom is a positively charged ion or cation. when an atom gains an electron and thus has more electrons than protons, the atom is a negatively charged ion or anion. cations and anions can form a crystalline lattice of neutral salts, such as the na + and cl− ions forming sodium chloride, or nacl. examples of polyatomic ions that do not split up during acid – base reactions are hydroxide ( oh− ) and phosphate ( po43− ). plasma is composed of gaseous matter that has been completely ionized, usually through high temperature. = = = acidity and basicity = = = a substance can often be , valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. = = = energy = = = in the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer . a reaction is said to be exergonic if the final state is lower on the energy scale than the initial state ; in the case of endergonic reactions the situation is the reverse. a reaction is said to be exothermic if the reaction releases heat to the surroundings ; in the case of endothermic reactions, the reaction absorbs heat from the surroundings. chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. the speed of a chemical reaction ( at given temperature t ) is related to the activation energy e, by the boltzmann ' s population factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then factor e − e / k t { \ displaystyle e ^ { - e / kt } } – that is the probability of a molecule to have energy greater than or equal to e at the given temperature t. this exponential dependence of a reaction rate on temperature is known as the arrhenius equation. the activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound. a related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. a reaction is feasible only if the total change in the gibbs free energy is negative, δ g ≤ 0 { \ displaystyle \ delta g \ leq 0 \, } ; if it is equal to zero the chemical reaction is said to be at equilibrium. there exist only limited possible states of energy for electrons, atoms and molecules. these are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. the atoms / molecules in a higher energy state are said to be excited. the molecules / atoms of substance in an excited energy state are often much more reactive ; that is, more amenable to chemical reactions. the phase of a substance is invariably determined by its energy and the energy of its surroundings. when the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water ( h2o ) ; a liquid at room temperature because its molecules are bound by hydrogen bonds. whereas hydrogen sulfide ( h2s ) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole – dipole interactions. the transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. however, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. for example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. the existence of characteristic Question: What works by providing a lower energy pathway from reactants to products? A) hormones B) magnetism C) catalyst D) thermodynamics	C) catalyst
Context: electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. = = = = substance and mixture = = = = a chemical substance is a kind of matter with a definite composition and set of properties. a collection of substances is called a mixture. examples of mixtures are air and alloys. = = = = mole and amount of substance = = = = the mole is a unit of measurement that denotes an amount of substance ( also called chemical amount ). one mole is defined to contain exactly 6. 02214076×1023 particles ( atoms, molecules, ions, or electrons ), where the number of particles per mole is known as the avogadro constant. molar concentration is the amount of a particular substance per volume of solution, and is commonly reported in mol / dm3. = = = phase = = = in addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. for the most part, the chemical classifications are independent of these bulk phase , but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. = = = = substance and mixture = = = = a chemical substance is a kind of matter with a definite composition and set of properties. a collection of substances is called a mixture. examples of mixtures are air and alloys. = = = = mole and amount of substance = = = = the mole is a unit of measurement that denotes an amount of substance ( also called chemical amount ). one mole is defined to contain exactly 6. 02214076×1023 particles ( atoms, molecules, ions, or electrons ), where the number of particles per mole is known as the avogadro constant. molar concentration is the amount of a particular substance per volume of solution, and is commonly reported in mol / dm3. = = = phase = = = in addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. for the most part, the chemical classifications are independent of these bulk phase classifications ; however, some more exotic phases are incompatible with certain chemical properties. a phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature. physical properties, such as density and refractive index tend to fall within values characteristic of the phase that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. = = = = substance and mixture = = = = a chemical substance is a kind of matter with a definite composition and set of properties. a collection of substances is called a mixture. examples of mixtures are air and alloys. = = = = mole and amount of substance = = = = the mole is a unit of measurement that denotes an amount of substance ( also called chemical amount ). one mole is defined to contain exactly 6. 02214076×1023 particles ( atoms, molecules, ions, or electrons ), where the number of particles per mole is known as the avogadro constant. molar concentration is = = organic compounds are molecules that contain carbon bonded to another element such as hydrogen. with the exception of water, nearly all the molecules that make up each organism contain carbon. carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules. for example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids other electrons either in bonds or in lone pairs. thus, molecules exist as electrically neutral units, unlike ions. when this rule is broken, giving the " molecule " a charge, the result is sometimes named a molecular ion or a polyatomic ion. however, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. = = = = substance and mixture = = = = a chemical substance is a kind of matter with a definite composition and set of properties. a collection of substances is called a mixture. examples of mixtures are air and alloys. = = = = mole and amount of substance = = = = the mole is a unit grain sizes are a product of the thermal processing parameters as well as the initial particle size, or possibly the sizes of aggregates or particle clusters which arise during the initial stages of processing. the ultimate microstructure ( and thus the physical properties ) of the final product will be limited by and subject to the form of the structural template or precursor which is created in the initial stages of chemical synthesis and physical forming. hence the importance of chemical powder and polymer processing as it pertains to the synthesis of industrial ceramics, glasses and glass - ceramics. there are numerous possible refinements of the sintering process. some of the most common involve pressing the green body to give the densification a head start and reduce the sintering time needed. sometimes organic binders such as polyvinyl alcohol are added to hold the green body together ; these burn out during the firing ( at 200 – 350 °c ). sometimes organic lubricants are added during pressing to increase densification. it is common to combine these, and add binders and lubricants to a powder, then press. ( the formulation of these organic chemical additives is an art in itself. this is particularly important in the manufacture of high performance ceramics such as those used by the billions for electronics, in capacitors, inductors, sensors, etc. ) a slurry can be used in place of a powder, and then cast into a desired shape, dried and then sintered. indeed, traditional pottery is done with this type of method, using a plastic mixture worked with the hands. if a mixture of different materials is used together in a ceramic, the sintering temperature is sometimes above the melting point of one minor component – a liquid phase sintering. this results in shorter sintering times compared to solid state sintering. such liquid phase sintering involves in faster diffusion processes and may result in abnormal grain growth. = = strength of ceramics = = a material ' s strength is dependent on its microstructure. the engineering processes to which a material is subjected can alter its microstructure. the variety of strengthening mechanisms that alter the strength of a material include the mechanism of grain boundary strengthening. thus, although yield strength is maximized with decreasing grain size, ultimately, very small grain sizes make the material brittle. considered in tandem with the fact that the yield strength is the parameter that predicts plastic deformation in the material, one can make informed decisions on how to increase the strength of a material depending on its microstructural set of chemical reactions with other substances. however, this definition only works well for substances that are composed of molecules, which is not true of many substances ( see below ). molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs. thus, molecules exist as electrically neutral units, unlike ions. when this rule is broken, giving the " molecule " a charge, the result is sometimes named a molecular ion or a polyatomic ion. however, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well - separated form, such as a directed beam in a vacuum in a mass spectrometer. charged polyatomic collections residing in solids ( for example, common sulfate or nitrate ions ) are generally not considered " molecules " in chemistry. some molecules contain one or more unpaired electrons, creating radicals. most radicals are comparatively reactive, but some, such as nitric oxide ( no ) can be stable. the " inert " or noble gas elements ( helium, neon, argon, krypton, xenon and radon ) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. however, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the earth are chemical compounds without molecules. these other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. examples of such substances are mineral salts ( such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. one of the main characteristics of a molecule is its geometry often called its structure. while the structure of diatomic, triatomic or tetra - atomic molecules may be trivial, ( linear, angular pyramidal etc. ) the structure of polyatomic molecules, that are constituted of more than six atoms ( of several elements ) can be crucial for its chemical nature. smallest genomes among flowering plants. arabidopsis was the first plant to have its genome sequenced, in 2000. the sequencing of some other relatively small genomes, of rice ( oryza sativa ) and brachypodium distachyon, has made them important model species for understanding the genetics, cellular and molecular biology of cereals, grasses and monocots generally. model plants such as arabidopsis thaliana are used for studying the molecular biology of plant cells and the chloroplast. ideally, these organisms have small genomes that are well known or completely sequenced, small stature and short generation times. corn has been used to study mechanisms of photosynthesis and phloem loading of sugar in c4 plants. the single celled green alga chlamydomonas reinhardtii, while not an embryophyte itself, contains a green - pigmented chloroplast related to that of land plants, making it useful for study. a red alga cyanidioschyzon merolae has also been used to study some basic chloroplast functions. spinach, peas, soybeans and a moss physcomitrella patens are commonly used to study plant cell biology. agrobacterium tumefaciens, a soil rhizosphere bacterium, can attach to plant cells and infect them with a callus - inducing ti plasmid by horizontal gene transfer, causing a callus infection called crown gall disease. schell and van montagu ( 1977 ) hypothesised that the ti plasmid could be a natural vector for introducing the nif gene responsible for nitrogen fixation in the root nodules of legumes and other plant species. today, genetic modification of the ti plasmid is one of the main techniques for introduction of transgenes to plants and the creation of genetically modified crops. = = = epigenetics = = = epigenetics is the study of heritable changes in gene function that cannot be explained by changes in the underlying dna sequence but cause the organism ' s genes to behave ( or " express themselves " ) differently. one example of epigenetic change is the marking of the genes by dna methylation which determines whether they will be expressed or not. gene expression can also be controlled by repressor proteins that attach to silencer regions of the dna and prevent that region of the dna code from being expressed. epigenetic marks may be added mwco, molecular weight cut off, with units in dalton ). it is defined as the minimum molecular weight of a globular molecule that is retained to 90 % by the membrane. the cut - off, depending on the method, can by converted to so - called d90, which is then expressed in a metric unit. in practice the mwco of the membrane should be at least 20 % lower than the molecular weight of the molecule that is to be separated. using track etched mica membranes beck and schultz demonstrated that hindered diffusion of molecules in pores can be described by the rankin equation. filter membranes are divided into four classes according to pore size : the form and shape of the membrane pores are highly dependent on the manufacturing process and are often difficult to specify. therefore, for characterization, test filtrations are carried out and the pore diameter refers to the diameter of the smallest particles which could not pass through the membrane. the rejection can be determined in various ways and provides an indirect measurement of the pore size. one possibility is the filtration of macromolecules ( often dextran, polyethylene glycol or albumin ), another is measurement of the cut - off by gel permeation chromatography. these methods are used mainly to measure membranes for ultrafiltration applications. another testing method is the filtration of particles with defined size and their measurement with a particle sizer or by laser induced breakdown spectroscopy ( libs ). a vivid characterization is to measure the rejection of dextran blue or other colored molecules. the retention of bacteriophage and bacteria, the so - called " bacteria challenge test ", can also provide information about the pore size. to determine the pore diameter, physical methods such as porosimeter ( mercury, liquid - liquid porosimeter and bubble point test ) are also used, but a certain form of the pores ( such as cylindrical or concatenated spherical holes ) is assumed. such methods are used for membranes whose pore geometry does not match the ideal, and we get " nominal " pore diameter, which characterizes the membrane, but does not necessarily reflect its actual filtration behavior and selectivity. the selectivity is highly dependent on the separation process, the composition of the membrane and its electrochemical properties in addition to the pore size. with high selectivity, isotopes can be enriched ( uranium enrichment ) in nuclear engineering or industrial gases like nitrogen can be recovered ( gas separation ) the chemistry of condensed phases ( solids, liquids, polymers ) and interfaces between different phases. neurochemistry is the study of neurochemicals ; including transmitters, peptides, proteins, lipids, sugars, and nucleic acids ; their interactions, and the roles they play in forming, maintaining, and modifying the nervous system. nuclear chemistry is the study of how subatomic particles come together and make nuclei. modern transmutation is a large component of nuclear chemistry, and the table of nuclides is an important result and tool for this field. in addition to medical applications, nuclear chemistry encompasses nuclear engineering which explores the topic of using nuclear power sources for generating energy. organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. an organic compound is defined as any compound based on a carbon skeleton. organic compounds can be classified, organized and understood in reactions by their functional groups, unit atoms or molecules that show characteristic chemical properties in a compound. physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. in particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, spectroscopy, and more recently, astrochemistry. physical chemistry has large overlap with molecular physics. physical chemistry involves the use of infinitesimal calculus in deriving equations. it is usually associated with quantum chemistry and theoretical chemistry. physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap. theoretical chemistry is the study of chemistry via fundamental theoretical reasoning ( usually within mathematics or physics ). in particular the application of quantum mechanics to chemistry is called quantum chemistry. since the end of the second world war, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. theoretical chemistry has large overlap with ( theoretical and experimental ) condensed matter physics and molecular physics. other subdivisions include electrochemistry, femtochemistry, flavor chemistry, flow chemistry, immunohistochemistry, hydrogenation chemistry, mathematical chemistry, molecular mechanics, natural product chemistry, organometallic chemistry, petrochemistry, photochemistry, physical organic chemistry, polymer chemistry, radiochemistry, sonochemistry, supramolecular chemistry, synthetic chemistry, and many others. = = = interdisciplinary = = = interdisciplinary fields include ag Question: What is the smallest part of a compound? A) dna B) electron C) nucleus D) molecule	D) molecule
Context: ##idermal electronics mirror those of skin to allow them to perform in this same way. like skin, epidermal electronics are ultrathin ( h < 100 μm ), low - modulus ( e ≈70 kpa ), and lightweight ( < 10 mg / cm2 ), enabling them to conform to the skin without applying strain. conformal contact and proper adhesion enable the device to bend and stretch without delaminating, deforming or failing, thereby eliminating the challenges with conventional, bulky wearables, including measurement artifacts, hysteresis, and motion - induced irritation to the skin. with this inherent ability to take the shape of skin, epidermal electronics can accurately acquire data without altering the natural motion or behavior of skin. the thin, soft, flexible design of epidermal electronics resembles that of temporary tattoos laminated on the skin. essentially, these devices are " mechanically invisible " to the wearer. epidermal electronics devices may adhere to the skin via van der waals forces or elastomeric substrates. with only van der waals forces, an epidermal device has the same thermal mass per unit area ( 150 mj / cm2k ) as skin, when the skin ' s thickness is < 500 nm. along with van der waals forces, the low values of e and thickness are effective in maximizing adhesion because they prevent deformation - induced detachment due to tension or compression. introducing an elastomeric substrate can improve adhesion but will raise the thermal mass per unit area slightly. several materials have been studied to produce these skin - like properties, including photolithography patterned serpentine gold nanofilm and patterned doping of silicon nanomembranes. = = = foot - worn = = = smart shoes are an example of wearable technology that incorporate smart features into shoes. smart shoes often work with smartphone applications to support tasks cannot be done with standard footwear. the uses include vibrating of the smart phone to tell users when and where to turn to reach their destination via google maps or self - lacing. self - lacing sneaker technology, similar to the nike mag in back to the future part ii, is another use of the smart shoe. in 2019 german footwear company puma was recognized as one of the " 100 best inventions of 2019 " by time for its fi laceless shoe that uses micro - motors to adjust the fit from an iphone. nike also introduced a smart shoe in 2019 known as adapt bb. the shoe featured buttons on the directly on the skin is currently available as a sole study source. the significance of epidermal electronics involves their mechanical properties, which resemble those of skin. the skin can be modeled as bilayer, composed of an epidermis having young ' s modulus ( e ) of 2 - 80 kpa and thickness of 0. 3 – 3 mm and a dermis having e of 140 - 600 kpa and thickness of 0. 05 - 1. 5 mm. together this bilayer responds plastically to tensile strains ≥ 30 %, below which the skin ' s surface stretches and wrinkles without deforming. properties of epidermal electronics mirror those of skin to allow them to perform in this same way. like skin, epidermal electronics are ultrathin ( h < 100 μm ), low - modulus ( e ≈70 kpa ), and lightweight ( < 10 mg / cm2 ), enabling them to conform to the skin without applying strain. conformal contact and proper adhesion enable the device to bend and stretch without delaminating, deforming or failing, thereby eliminating the challenges with conventional, bulky wearables, including measurement artifacts, hysteresis, and motion - induced irritation to the skin. with this inherent ability to take the shape of skin, epidermal electronics can accurately acquire data without altering the natural motion or behavior of skin. the thin, soft, flexible design of epidermal electronics resembles that of temporary tattoos laminated on the skin. essentially, these devices are " mechanically invisible " to the wearer. epidermal electronics devices may adhere to the skin via van der waals forces or elastomeric substrates. with only van der waals forces, an epidermal device has the same thermal mass per unit area ( 150 mj / cm2k ) as skin, when the skin ' s thickness is < 500 nm. along with van der waals forces, the low values of e and thickness are effective in maximizing adhesion because they prevent deformation - induced detachment due to tension or compression. introducing an elastomeric substrate can improve adhesion but will raise the thermal mass per unit area slightly. several materials have been studied to produce these skin - like properties, including photolithography patterned serpentine gold nanofilm and patterned doping of silicon nanomembranes. = = = foot - worn = = = smart shoes are an example of wearable technology that incorporate smart features into shoes. smart shoes often work with smartphone applications to support the skin without applying strain. conformal contact and proper adhesion enable the device to bend and stretch without delaminating, deforming or failing, thereby eliminating the challenges with conventional, bulky wearables, including measurement artifacts, hysteresis, and motion - induced irritation to the skin. with this inherent ability to take the shape of skin, epidermal electronics can accurately acquire data without altering the natural motion or behavior of skin. the thin, soft, flexible design of epidermal electronics resembles that of temporary tattoos laminated on the skin. essentially, these devices are " mechanically invisible " to the wearer. epidermal electronics devices may adhere to the skin via van der waals forces or elastomeric substrates. with only van der waals forces, an epidermal device has the same thermal mass per unit area ( 150 mj / cm2k ) as skin, when the skin ' s thickness is < 500 nm. along with van der waals forces, the low values of e and thickness are effective in maximizing adhesion because they prevent deformation - induced detachment due to tension or compression. introducing an elastomeric substrate can improve adhesion but will raise the thermal mass per unit area slightly. several materials have been studied to produce these skin - like properties, including photolithography patterned serpentine gold nanofilm and patterned doping of silicon nanomembranes. = = = foot - worn = = = smart shoes are an example of wearable technology that incorporate smart features into shoes. smart shoes often work with smartphone applications to support tasks cannot be done with standard footwear. the uses include vibrating of the smart phone to tell users when and where to turn to reach their destination via google maps or self - lacing. self - lacing sneaker technology, similar to the nike mag in back to the future part ii, is another use of the smart shoe. in 2019 german footwear company puma was recognized as one of the " 100 best inventions of 2019 " by time for its fi laceless shoe that uses micro - motors to adjust the fit from an iphone. nike also introduced a smart shoe in 2019 known as adapt bb. the shoe featured buttons on the side to loosen or tighten the fit with a custom motor and gear, which could also be controlled by a smartphone. = = modern technologies = = on april 16, 2013, google invited " glass explorers " who had pre - ordered its wearable glasses at the 2012 google i / o conference to pick up their devices. layer of the skin. these wearables are mounted directly onto the skin to continuously monitor physiological and metabolic processes, both dermal and subdermal. wireless capability is typically achieved through battery, bluetooth or nfc, making these devices convenient and portable as a type of wearable technology. currently, epidermal electronics are being developed in the fields of fitness and medical monitoring. current usage of epidermal technology is limited by existing fabrication processes. its current application relies on various sophisticated fabrication techniques such as by lithography or by directly printing on a carrier substrate before attaching directly to the body. research into printing epidermal electronics directly on the skin is currently available as a sole study source. the significance of epidermal electronics involves their mechanical properties, which resemble those of skin. the skin can be modeled as bilayer, composed of an epidermis having young ' s modulus ( e ) of 2 - 80 kpa and thickness of 0. 3 – 3 mm and a dermis having e of 140 - 600 kpa and thickness of 0. 05 - 1. 5 mm. together this bilayer responds plastically to tensile strains ≥ 30 %, below which the skin ' s surface stretches and wrinkles without deforming. properties of epidermal electronics mirror those of skin to allow them to perform in this same way. like skin, epidermal electronics are ultrathin ( h < 100 μm ), low - modulus ( e ≈70 kpa ), and lightweight ( < 10 mg / cm2 ), enabling them to conform to the skin without applying strain. conformal contact and proper adhesion enable the device to bend and stretch without delaminating, deforming or failing, thereby eliminating the challenges with conventional, bulky wearables, including measurement artifacts, hysteresis, and motion - induced irritation to the skin. with this inherent ability to take the shape of skin, epidermal electronics can accurately acquire data without altering the natural motion or behavior of skin. the thin, soft, flexible design of epidermal electronics resembles that of temporary tattoos laminated on the skin. essentially, these devices are " mechanically invisible " to the wearer. epidermal electronics devices may adhere to the skin via van der waals forces or elastomeric substrates. with only van der waals forces, an epidermal device has the same thermal mass per unit area ( 150 mj / cm2k ) as skin, when the skin ' s thickness is < 500 0. 3 – 3 mm and a dermis having e of 140 - 600 kpa and thickness of 0. 05 - 1. 5 mm. together this bilayer responds plastically to tensile strains ≥ 30 %, below which the skin ' s surface stretches and wrinkles without deforming. properties of epidermal electronics mirror those of skin to allow them to perform in this same way. like skin, epidermal electronics are ultrathin ( h < 100 μm ), low - modulus ( e ≈70 kpa ), and lightweight ( < 10 mg / cm2 ), enabling them to conform to the skin without applying strain. conformal contact and proper adhesion enable the device to bend and stretch without delaminating, deforming or failing, thereby eliminating the challenges with conventional, bulky wearables, including measurement artifacts, hysteresis, and motion - induced irritation to the skin. with this inherent ability to take the shape of skin, epidermal electronics can accurately acquire data without altering the natural motion or behavior of skin. the thin, soft, flexible design of epidermal electronics resembles that of temporary tattoos laminated on the skin. essentially, these devices are " mechanically invisible " to the wearer. epidermal electronics devices may adhere to the skin via van der waals forces or elastomeric substrates. with only van der waals forces, an epidermal device has the same thermal mass per unit area ( 150 mj / cm2k ) as skin, when the skin ' s thickness is < 500 nm. along with van der waals forces, the low values of e and thickness are effective in maximizing adhesion because they prevent deformation - induced detachment due to tension or compression. introducing an elastomeric substrate can improve adhesion but will raise the thermal mass per unit area slightly. several materials have been studied to produce these skin - like properties, including photolithography patterned serpentine gold nanofilm and patterned doping of silicon nanomembranes. = = = foot - worn = = = smart shoes are an example of wearable technology that incorporate smart features into shoes. smart shoes often work with smartphone applications to support tasks cannot be done with standard footwear. the uses include vibrating of the smart phone to tell users when and where to turn to reach their destination via google maps or self - lacing. self - lacing sneaker technology, similar to the nike mag in back to the future part ii, is another use of the ##fts. autografted skin comes from a patient ' s own skin, which allows the dermis to have a faster healing rate, and the donor site can be re - harvested a few times. allograft skin often comes from cadaver skin and is mostly used to treat burn victims. lastly, xenografted skin comes from animals and provides a temporary healing structure for the skin. they assist in dermal regeneration, but cannot become part of the host skin. tissue - engineered skin is now available in commercial products. integra, originally used to only treat burns, consists of a collagen matrix and chondroitin sulfate that can be used as a skin replacement. the chondroitin sulfate functions as a component of proteoglycans, which helps to form the extracellular matrix. integra can be repopulated and revascularized while maintaining its dermal collagen architecture, making it a bioartificial organ dermagraft, another commercial - made tissue - engineered skin product, is made out of living fibroblasts. these fibroblasts proliferate and produce growth factors, collagen, and ecm proteins, that help build granulation tissue. = = = = heart = = = = since the number of patients awaiting a heart transplant is continuously increasing over time, and the number of patients on the waiting list surpasses the organ availability, artificial organs used as replacement therapy for terminal heart failure would help alleviate this difficulty. artificial hearts are usually used to bridge the heart transplantation or can be applied as replacement therapy for terminal heart malfunction. the total artificial heart ( tah ), first introduced by dr. vladimir p. demikhov in 1937, emerged as an ideal alternative. since then it has been developed and improved as a mechanical pump that provides long - term circulatory support and replaces diseased or damaged heart ventricles that cannot properly pump the blood, restoring thus the pulmonary and systemic flow. some of the current tahs include abiocor, an fda - approved device that comprises two artificial ventricles and their valves, and does not require subcutaneous connections, and is indicated for patients with biventricular heart failure. in 2010 syncardia released the portable freedom driver that allows patients to have a portable device without being confined to the hospital. = = = = kidney = = = = while kidney transplants are possible, renal failure is more often treated using an artificial kidney. the first artificial 1975. skin tissue - engineered skin is a type of bioartificial organ that is often used to treat burns, diabetic foot ulcers, or other large wounds that cannot heal well on their own. artificial skin can be made from autografts, allografts, and xenografts. autografted skin comes from a patient ' s own skin, which allows the dermis to have a faster healing rate, and the donor site can be re - harvested a few times. allograft skin often comes from cadaver skin and is mostly used to treat burn victims. lastly, xenografted skin comes from animals and provides a temporary healing structure for the skin. they assist in dermal regeneration, but cannot become part of the host skin. tissue - engineered skin is now available in commercial products. integra, originally used to only treat burns, consists of a collagen matrix and chondroitin sulfate that can be used as a skin replacement. the chondroitin sulfate functions as a component of proteoglycans, which helps to form the extracellular matrix. integra can be repopulated and revascularized while maintaining its dermal collagen architecture, making it a bioartificial organ dermagraft, another commercial - made tissue - engineered skin product, is made out of living fibroblasts. these fibroblasts proliferate and produce growth factors, collagen, and ecm proteins, that help build granulation tissue. = = = = heart = = = = since the number of patients awaiting a heart transplant is continuously increasing over time, and the number of patients on the waiting list surpasses the organ availability, artificial organs used as replacement therapy for terminal heart failure would help alleviate this difficulty. artificial hearts are usually used to bridge the heart transplantation or can be applied as replacement therapy for terminal heart malfunction. the total artificial heart ( tah ), first introduced by dr. vladimir p. demikhov in 1937, emerged as an ideal alternative. since then it has been developed and improved as a mechanical pump that provides long - term circulatory support and replaces diseased or damaged heart ventricles that cannot properly pump the blood, restoring thus the pulmonary and systemic flow. some of the current tahs include abiocor, an fda - approved device that comprises two artificial ventricles and their valves, and does not require subcutaneous connections, and is indicated for the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differs. this exposed region can then be removed or treated providing a mask for the underlying substrate. photolithography is typically used with metal or other thin film deposition, wet and dry etching. sometimes, photolithography is used to create structure without any kind of post etching. one example is su8 based lens where su8 based square blocks are generated. then the photoresist is melted to form a semi - sphere which acts as a lens. electron beam lithography ( often abbreviated as e - beam lithography ) is the practice of scanning a beam of electrons in a patterned fashion across a surface covered with a film ( called the resist ), ( " exposing " the resist ) and of selectively removing either exposed or non - exposed regions of the resist ( " developing " ). the purpose, as with photolithography, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching. it was developed for manufacturing integrated circuits, and is also used for creating nanotechnology architectures. the primary advantage of electron beam lithography is that it is one of the ways to beat the diffraction limit of light and make features in the nanometer range. this form of maskless lithography has found wide usage in photomask - making used in photolithography, low - volume production of semiconductor components, and research & development. the key limitation of electron beam lithography is throughput, i. e., the very long time it takes to expose an entire silicon wafer or glass substrate. a long exposure time leaves the user vulnerable to beam drift or instability which may occur during the exposure. also, the turn - around time for reworking or re - design is lengthened unnecessarily if the pattern is not being changed the second time. it is known that focused - ion beam lithography has the capability of writing extremely fine lines ( less than 50 nm line and space has been achieved ) without proximity effect. however, because the writing field in ion - beam lithography is quite small, large area patterns must be created by stitching together the small fields. ion track technology is a deep cutting tool with a resolution limit around 8 nm applicable to radiation resistant minerals, glasses and polymers. it is capable of generating holes in thin films without any development process. structural depth can be defined techniques that provide heart and lung support. it is used primarily to support the lungs for a prolonged but still temporary timeframe ( 1 – 30 days ) and allow for recovery from reversible diseases. robert bartlett is known as the father of ecmo and performed the first treatment of a newborn using an ecmo machine in 1975. skin tissue - engineered skin is a type of bioartificial organ that is often used to treat burns, diabetic foot ulcers, or other large wounds that cannot heal well on their own. artificial skin can be made from autografts, allografts, and xenografts. autografted skin comes from a patient ' s own skin, which allows the dermis to have a faster healing rate, and the donor site can be re - harvested a few times. allograft skin often comes from cadaver skin and is mostly used to treat burn victims. lastly, xenografted skin comes from animals and provides a temporary healing structure for the skin. they assist in dermal regeneration, but cannot become part of the host skin. tissue - engineered skin is now available in commercial products. integra, originally used to only treat burns, consists of a collagen matrix and chondroitin sulfate that can be used as a skin replacement. the chondroitin sulfate functions as a component of proteoglycans, which helps to form the extracellular matrix. integra can be repopulated and revascularized while maintaining its dermal collagen architecture, making it a bioartificial organ dermagraft, another commercial - made tissue - engineered skin product, is made out of living fibroblasts. these fibroblasts proliferate and produce growth factors, collagen, and ecm proteins, that help build granulation tissue. = = = = heart = = = = since the number of patients awaiting a heart transplant is continuously increasing over time, and the number of patients on the waiting list surpasses the organ availability, artificial organs used as replacement therapy for terminal heart failure would help alleviate this difficulty. artificial hearts are usually used to bridge the heart transplantation or can be applied as replacement therapy for terminal heart malfunction. the total artificial heart ( tah ), first introduced by dr. vladimir p. demikhov in 1937, emerged as an ideal alternative. since then it has been developed and improved as a mechanical pump that provides long - term circulatory support and ##itive material by selective exposure to a radiation source such as light. a photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source. if a photosensitive material is selectively exposed to radiation ( e. g. by masking some of the radiation ) the pattern of the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differs. this exposed region can then be removed or treated providing a mask for the underlying substrate. photolithography is typically used with metal or other thin film deposition, wet and dry etching. sometimes, photolithography is used to create structure without any kind of post etching. one example is su8 based lens where su8 based square blocks are generated. then the photoresist is melted to form a semi - sphere which acts as a lens. electron beam lithography ( often abbreviated as e - beam lithography ) is the practice of scanning a beam of electrons in a patterned fashion across a surface covered with a film ( called the resist ), ( " exposing " the resist ) and of selectively removing either exposed or non - exposed regions of the resist ( " developing " ). the purpose, as with photolithography, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching. it was developed for manufacturing integrated circuits, and is also used for creating nanotechnology architectures. the primary advantage of electron beam lithography is that it is one of the ways to beat the diffraction limit of light and make features in the nanometer range. this form of maskless lithography has found wide usage in photomask - making used in photolithography, low - volume production of semiconductor components, and research & development. the key limitation of electron beam lithography is throughput, i. e., the very long time it takes to expose an entire silicon wafer or glass substrate. a long exposure time leaves the user vulnerable to beam drift or instability which may occur during the exposure. also, the turn - around time for reworking or re - design is lengthened unnecessarily if the pattern is not being changed the second time. it is known that focused - ion beam lithography has the capability of writing extremely fine lines ( less than 50 nm line and space has been achieved ) without proximity effect. however, because the writing field in ion - beam lit Question: What layer of skin is located right beneath the epidermis? A) scars B) dermis C) humus D) cusps	B) dermis
Context: ##ta together form the monophyletic group or clade streptophytina. nonvascular land plants are embryophytes that lack the vascular tissues xylem and phloem. they include mosses, liverworts and hornworts. pteridophytic vascular plants with true xylem and phloem that reproduced by spores germinating into free - living gametophytes evolved during the silurian period and diversified into several lineages during the late silurian and early devonian. representatives of the lycopods have survived to the present day. by the end of the devonian period, several groups, including the lycopods, sphenophylls and progymnosperms, had independently evolved " megaspory " – their spores were of two distinct sizes, larger megaspores and smaller microspores. their reduced gametophytes developed from megaspores retained within the spore - producing organs ( megasporangia ) of the sporophyte, a condition known as endospory. seeds consist of an endosporic megasporangium surrounded by one or two sheathing layers ( integuments ). the young sporophyte develops within the seed, which on germination splits to release it. the earliest known seed plants date from the latest devonian famennian stage. following the evolution of the seed habit, seed plants diversified, giving rise to a number of now - extinct groups, including seed ferns, as well as the modern gymnosperms and angiosperms. gymnosperms produce " naked seeds " not fully enclosed in an ovary ; modern representatives include conifers, cycads, ginkgo, and gnetales. angiosperms produce seeds enclosed in a structure such as a carpel or an ovary. ongoing research on the molecular phylogenetics of living plants appears to show that the angiosperms are a sister clade to the gymnosperms. = = plant physiology = = plant physiology encompasses all the internal chemical and physical activities of plants associated with life. chemicals obtained from the air, soil and water form the basis of all plant metabolism. the energy of sunlight, captured by oxygenic photosynthesis and released by cellular respiration, is the basis of almost all life. photoautotrophs, including all green plants, algae and cyanobacteria gather energy directly from sunlight by photosynthesis. hetero his sickle to one location. ( he realized it was a sickle by testing various blades on an animal carcass and comparing the wounds. ) flies, attracted by the smell of blood, eventually gathered on a single sickle. in light of this, the owner of that sickle confessed to the murder. the book also described how to distinguish between a drowning ( water in the lungs ) and strangulation ( broken neck cartilage ), and described evidence from examining corpses to determine if a death was caused by murder, suicide or accident. methods from around the world involved saliva and examination of the mouth and tongue to determine innocence or guilt, as a precursor to the polygraph test. in ancient india, some suspects were made to fill their mouths with dried rice and spit it back out. similarly, in ancient china, those accused of a crime would have rice powder placed in their mouths. in ancient middle - eastern cultures, the accused were made to lick hot metal rods briefly. it is thought that these tests had some validity since a guilty person would produce less saliva and thus have a drier mouth ; the accused would be considered guilty if rice was sticking to their mouths in abundance or if their tongues were severely burned due to lack of shielding from saliva. = = education and training = = initial glance, forensic intelligence may appear as a nascent facet of forensic science facilitated by advancements in information technologies such as computers, databases, and data - flow management software. however, a more profound examination reveals that forensic intelligence represents a genuine and emerging inclination among forensic practitioners to actively participate in investigative and policing strategies. in doing so, it elucidates existing practices within scientific literature, advocating for a paradigm shift from the prevailing conception of forensic science as a conglomerate of disciplines merely aiding the criminal justice system. instead, it urges a perspective that views forensic science as a discipline studying the informative potential of traces — remnants of criminal activity. embracing this transformative shift poses a significant challenge for education, necessitating a shift in learners ' mindset to accept concepts and methodologies in forensic intelligence. recent calls advocating for the integration of forensic scientists into the criminal justice system, as well as policing and intelligence missions, underscore the necessity for the establishment of educational and training initiatives in the field of forensic intelligence. this article contends that a discernible gap exists between the perceived and actual comprehension of forensic intelligence among law enforcement and forensic science managers, positing that this asymmetry can be rectified only through educational interventions. required. for example, certain cells respond to changes in oxygen tension as part of their normal development, such as chondrocytes, which must adapt to low oxygen conditions or hypoxia during skeletal development. others, such as endothelial cells, respond to shear stress from fluid flow, which is encountered in blood vessels. mechanical stimuli, such as pressure pulses seem to be beneficial to all kind of cardiovascular tissue such as heart valves, blood vessels or pericardium. = = = bioreactors = = = in tissue engineering, a bioreactor is a device that attempts to simulate a physiological environment in order to promote cell or tissue growth in vitro. a physiological environment can consist of many different parameters such as temperature, pressure, oxygen or carbon dioxide concentration, or osmolality of fluid environment, and it can extend to all kinds of biological, chemical or mechanical stimuli. therefore, there are systems that may include the application of forces such as electromagnetic forces, mechanical pressures, or fluid pressures to the tissue. these systems can be two - or three - dimensional setups. bioreactors can be used in both academic and industry applications. general - use and application - specific bioreactors are also commercially available, which may provide static chemical stimulation or a combination of chemical and mechanical stimulation. cell proliferation and differentiation are largely influenced by mechanical and biochemical cues in the surrounding extracellular matrix environment. bioreactors are typically developed to replicate the specific physiological environment of the tissue being grown ( e. g., flex and fluid shearing for heart tissue growth ). this can allow specialized cell lines to thrive in cultures replicating their native environments, but it also makes bioreactors attractive tools for culturing stem cells. a successful stem - cell - based bioreactor is effective at expanding stem cells with uniform properties and / or promoting controlled, reproducible differentiation into selected mature cell types. there are a variety of bioreactors designed for 3d cell cultures. there are small plastic cylindrical chambers, as well as glass chambers, with regulated internal humidity and moisture specifically engineered for the purpose of growing cells in three dimensions. the bioreactor uses bioactive synthetic materials such as polyethylene terephthalate membranes to surround the spheroid cells in an environment that maintains high levels of nutrients. they are easy to open and close, so that cell spheroids can be removed for testing, yet the chamber is able to maintain 100 % humidity throughout. this humidity is important to achieve maximum cell growth and function. the ##icellular ancestor of plantae. unlike glaucophytes, the other algal clades such as red and green algae are multicellular. green algae comprise three major clades : chlorophytes, coleochaetophytes, and stoneworts. fungi are eukaryotes that digest foods outside their bodies, secreting digestive enzymes that break down large food molecules before absorbing them through their cell membranes. many fungi are also saprobes, feeding on dead organic matter, making them important decomposers in ecological systems. animals are multicellular eukaryotes. with few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. over 1. 5 million living animal species have been described — of which around 1 million are insects — but it has been estimated there are over 7 million animal species in total. they have complex interactions with each other and their environments, forming intricate food webs. = = = viruses = = = viruses are submicroscopic infectious agents that replicate inside the cells of organisms. viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. more than 6, 000 virus species have been described in detail. viruses are found in almost every ecosystem on earth and are the most numerous type of biological entity. the origins of viruses in the evolutionary history of life are unclear : some may have evolved from plasmids — pieces of dna that can move between cells — while others may have evolved from bacteria. in evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogous to sexual reproduction. because viruses possess some but not all characteristics of life, they have been described as " organisms at the edge of life ", and as self - replicators. = = ecology = = ecology is the study of the distribution and abundance of life, the interaction between organisms and their environment. = = = ecosystems = = = the community of living ( biotic ) organisms in conjunction with the nonliving ( abiotic ) components ( e. g., water, light, radiation, temperature, humidity, atmosphere, acidity, and soil ) of their environment is called an ecosystem. these biotic and abiotic components are linked together through nutrient cycles and energy flows. energy from the sun enters the system through photosynthesis and is incorporated into plant tissue horticultural botany, phytopathology, and phytopharmacology. = = scope and importance = = the study of plants is vital because they underpin almost all animal life on earth by generating a large proportion of the oxygen and food that provide humans and other organisms with aerobic respiration with the chemical energy they need to exist. plants, algae and cyanobacteria are the major groups of organisms that carry out photosynthesis, a process that uses the energy of sunlight to convert water and carbon dioxide into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ) pigmentation, chloroplast structure and nutrient reserves. the algal division charophyta, sister to the green algal division chlorophyta, is considered to contain the ancestor of true plants. the charophyte class charophyceae and the land plant sub - kingdom embryophyta together form the monophyletic group or clade streptophytina. nonvascular land plants are embryophytes that lack the vascular tissues xylem and phloem. they include mosses, liverworts and hornworts. pteridophytic vascular plants with true xylem and phloem that reproduced by spores germinating into free - living gametophytes evolved during the silurian period and diversified into several lineages during the late silurian and early devonian. representatives of the lycopods have survived to the present day. by the end of the devonian period, several groups, including the lycopods, sphenophylls and progymnosperms, had independently evolved " megaspory " – their spores were of two distinct sizes, larger megaspores and smaller microspores. their reduced gametophytes developed from megaspores retained within the spore - producing organs ( megasporangia ) of the sporophyte, a condition known as endospory. seeds consist of an endosporic megasporangium surrounded by one or two sheathing layers ( integuments ). the young sporophyte develops within the seed, which on germination splits to release it. the earliest known seed plants date from the latest devonian famennian stage. following the evolution of the seed habit, seed plants diversified, giving rise to a number of now - extinct groups, including seed ferns, as well as the modern gymnosperms and angiosperms. gymnosperms produce " naked seeds " not fully enclosed in an ovary ; modern representatives include conifers, cycads, ginkgo, and gnetales. angiosperms produce seeds enclosed in a structure such as a carpel or an ovary. ongoing research on the molecular phylogenetics of living plants appears to show that the angiosperms are a sister clade to the gymnosperms. = = plant physiology = = plant physiology encompasses all the internal chemical and physical activities of plants associated with life. chemicals obtained from the air, soil and water form occur outside of the milky way galaxy. the chandra x - ray observatory was launched from the columbia on sts - 93 in 1999, observing black holes, quasars, supernova, and dark matter. it provided critical observations on the sagittarius a * black hole at the center of the milky way galaxy and the separation of dark and regular matter during galactic collisions. finally, the spitzer space telescope is an infrared telescope launched in 2003 from a delta ii rocket. it is in a trailing orbit around the sun, following the earth and discovered the existence of brown dwarf stars. other telescopes, such as the cosmic background explorer and the wilkinson microwave anisotropy probe, provided evidence to support the big bang. the james webb space telescope, named after the nasa administrator who lead the apollo program, is an infrared observatory launched in 2021. the james webb space telescope is a direct successor to the hubble space telescope, intended to observe the formation of the first galaxies. other space telescopes include the kepler space telescope, launched in 2009 to identify planets orbiting extrasolar stars that may be terran and possibly harbor life. the first exoplanet that the kepler space telescope confirmed was kepler - 22b, orbiting within the habitable zone of its star. nasa also launched a number of different satellites to study earth, such as television infrared observation satellite ( tiros ) in 1960, which was the first weather satellite. nasa and the united states weather bureau cooperated on future tiros and the second generation nimbus program of weather satellites. it also worked with the environmental science services administration on a series of weather satellites and the agency launched its experimental applications technology satellites into geosynchronous orbit. nasa ' s first dedicated earth observation satellite, landsat, was launched in 1972. this led to nasa and the national oceanic and atmospheric administration jointly developing the geostationary operational environmental satellite and discovering ozone depletion. = = = space shuttle = = = nasa had been pursuing spaceplane development since the 1960s, blending the administration ' s dual aeronautics and space missions. nasa viewed a spaceplane as part of a larger program, providing routine and economical logistical support to a space station in earth orbit that would be used as a hub for lunar and mars missions. a reusable launch vehicle would then have ended the need for expensive and expendable boosters like the saturn v. in 1969, nasa designated the johnson space center as the lead center for the design, development, and manufacturing of the space shuttle orbiter, while the marshall space flight center blood vessels. mechanical stimuli, such as pressure pulses seem to be beneficial to all kind of cardiovascular tissue such as heart valves, blood vessels or pericardium. = = = bioreactors = = = in tissue engineering, a bioreactor is a device that attempts to simulate a physiological environment in order to promote cell or tissue growth in vitro. a physiological environment can consist of many different parameters such as temperature, pressure, oxygen or carbon dioxide concentration, or osmolality of fluid environment, and it can extend to all kinds of biological, chemical or mechanical stimuli. therefore, there are systems that may include the application of forces such as electromagnetic forces, mechanical pressures, or fluid pressures to the tissue. these systems can be two - or three - dimensional setups. bioreactors can be used in both academic and industry applications. general - use and application - specific bioreactors are also commercially available, which may provide static chemical stimulation or a combination of chemical and mechanical stimulation. cell proliferation and differentiation are largely influenced by mechanical and biochemical cues in the surrounding extracellular matrix environment. bioreactors are typically developed to replicate the specific physiological environment of the tissue being grown ( e. g., flex and fluid shearing for heart tissue growth ). this can allow specialized cell lines to thrive in cultures replicating their native environments, but it also makes bioreactors attractive tools for culturing stem cells. a successful stem - cell - based bioreactor is effective at expanding stem cells with uniform properties and / or promoting controlled, reproducible differentiation into selected mature cell types. there are a variety of bioreactors designed for 3d cell cultures. there are small plastic cylindrical chambers, as well as glass chambers, with regulated internal humidity and moisture specifically engineered for the purpose of growing cells in three dimensions. the bioreactor uses bioactive synthetic materials such as polyethylene terephthalate membranes to surround the spheroid cells in an environment that maintains high levels of nutrients. they are easy to open and close, so that cell spheroids can be removed for testing, yet the chamber is able to maintain 100 % humidity throughout. this humidity is important to achieve maximum cell growth and function. the bioreactor chamber is part of a larger device that rotates to ensure equal cell growth in each direction across three dimensions. quinxell technologies now under quintech life sciences from singapore has developed a bioreactor known as the tisxell biaxial bioreactor which is specially designed for the purpose of consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. over 1. 5 million living animal species have been described — of which around 1 million are insects — but it has been estimated there are over 7 million animal species in total. they have complex interactions with each other and their environments, forming intricate food webs. = = = viruses = = = viruses are submicroscopic infectious agents that replicate inside the cells of organisms. viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. more than 6, 000 virus species have been described in detail. viruses are found in almost every ecosystem on earth and are the most numerous type of biological entity. the origins of viruses in the evolutionary history of life are unclear : some may have evolved from plasmids — pieces of dna that can move between cells — while others may have evolved from bacteria. in evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogous to sexual reproduction. because viruses possess some but not all characteristics of life, they have been described as " organisms at the edge of life ", and as self - replicators. = = ecology = = ecology is the study of the distribution and abundance of life, the interaction between organisms and their environment. = = = ecosystems = = = the community of living ( biotic ) organisms in conjunction with the nonliving ( abiotic ) components ( e. g., water, light, radiation, temperature, humidity, atmosphere, acidity, and soil ) of their environment is called an ecosystem. these biotic and abiotic components are linked together through nutrient cycles and energy flows. energy from the sun enters the system through photosynthesis and is incorporated into plant tissue. by feeding on plants and on one another, animals move matter and energy through the system. they also influence the quantity of plant and microbial biomass present. by breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes. = = = populations = = = a population is the group of organisms of the same species that occupies an area and reproduce from generation to generation. population size can be estimated by multiplying population density by the area or volume. the carrying capacity of an environment results of an experiment are presented whose aim is to explore the relationship between respiration and cerebral oxygenation. measurements of end tidal co2 ( etco2 ) were taken simultaneously with cerebral oxygen saturation ( rso2 ) using the invos cerebral oximeter of somanetics. due to the device limitations we could explore only subjects who could perform with a breathing rate of around 2 / min or less. six subjects were used who were experienced in yoga breathing techniques. they performed an identical periodic breathing exercise including periodicity of about 2 / min. the results of all six subjects clearly show a periodic change of cerebral oxygenation with the same period as the breathing exercises. similar periodic changes in blood volume index were observed as well. Question: Some terrestrial species breathe through their skin and oral cavity because they lack what? A) mouth B) windpipe C) nose D) lungs	D) lungs
Context: . most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support , depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions a cell. there are generally four types of chemical signals : autocrine, paracrine, juxtacrine, and hormones. in autocrine signaling, the ligand affects the same cell that releases it. tumor cells, for example, can reproduce uncontrollably because they release signals that initiate their own self - division. in paracrine signaling, the ligand diffuses to nearby cells and affects them. for example, brain cells called neurons release ligands called neurotransmitters that diffuse across a synaptic cleft to bind with a receptor on an adjacent cell such as another neuron or muscle cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares notes of the lectures delivered in les houches during the summer school on complex systems ( july 2006 ). ability of cells to receive, process, and transmit signals with its environment and with itself. signals can be non - chemical such as light, electrical impulses, and heat, or chemical signals ( or ligands ) that interact with receptors, which can be found embedded in the cell membrane of another cell or located deep inside a cell. there are generally four types of chemical signals : autocrine, paracrine, juxtacrine, and hormones. in autocrine signaling, the ligand affects the same cell that releases it. tumor cells, for example, can reproduce uncontrollably because they release signals that initiate their own self - division. in paracrine signaling, the ligand diffuses to nearby cells and affects them. for example, brain cells called neurons release ligands called neurotransmitters that diffuse across a synaptic cleft to bind with a receptor on an adjacent cell such as another neuron or muscle cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis the tests, assays, and procedures needed for providing the specific services. subspecialties include transfusion medicine, cellular pathology, clinical chemistry, hematology, clinical microbiology and clinical immunology. clinical neurophysiology is concerned with testing the physiology or function of the central and peripheral aspects of the nervous system. these kinds of tests can be divided into recordings of : ( 1 ) spontaneous or continuously running electrical activity, or ( 2 ) stimulus evoked responses. subspecialties include electroencephalography, electromyography, evoked potential, nerve conduction study and polysomnography. sometimes these tests are performed by techs without a medical degree, but the interpretation of these tests is done by a medical professional. diagnostic radiology is concerned with imaging of the body, e. g. by x - rays, x - ray computed tomography, ultrasonography, and nuclear magnetic resonance tomography. interventional radiologists can access areas in the body under imaging for an intervention or diagnostic sampling. nuclear medicine is concerned with studying human organ systems by administering radiolabelled substances ( radiopharmaceuticals ) to the body, which can then be imaged outside the body by a gamma camera or a pet scanner. each radiopharmaceutical consists of two parts : a tracer that is specific for the function under study ( e. g., neurotransmitter pathway, metabolic pathway, blood flow, or other ), and a radionuclide ( usually either a gamma - emitter or a positron emitter ). there is a degree of overlap between nuclear medicine and radiology, as evidenced by the emergence of combined devices such as the pet / ct scanner. pathology as a medical specialty is the branch of medicine that deals with the study of diseases and the morphologic, physiologic changes produced by them. as a diagnostic specialty, pathology can be considered the basis of modern scientific medical knowledge and plays a large role in evidence - based medicine. many modern molecular tests such as flow cytometry, polymerase chain reaction ( pcr ), immunohistochemistry, cytogenetics, gene rearrangements studies and fluorescent in situ hybridization ( fish ) fall within the territory of pathology. = = = = other major specialties = = = = the following are some major medical specialties that do not directly fit into any of the above - mentioned groups : anesthesiology ( also cross - fertilization that takes place among the various fields. psychology differs from biology and neuroscience in that it is primarily concerned with the interaction of mental processes and behaviour, and of the overall processes of a system, and not simply the biological or neural processes themselves, though the subfield of neuropsychology combines the study of the actual neural processes with the study of the mental effects they have subjectively produced. many people associate psychology with clinical psychology, which focuses on assessment and treatment of problems in living and psychopathology. in reality, psychology has myriad specialties including social psychology, developmental psychology, cognitive psychology, educational psychology, industrial - organizational psychology, mathematical psychology, neuropsychology, and quantitative analysis of behaviour. psychology is a very broad science that is rarely tackled as a whole, major block. although some subfields encompass a natural science base and a social science application, others can be clearly distinguished as having little to do with the social sciences or having a lot to do with the social sciences. for example, biological psychology is considered a natural science with a social scientific application ( as is clinical medicine ), social and occupational psychology are, generally speaking, purely social sciences, whereas neuropsychology is a natural science that lacks application out of the scientific tradition entirely. in british universities, emphasis on what tenet of psychology a student has studied and / or concentrated is communicated through the degree conferred : bpsy indicates a balance between natural and social sciences, bsc indicates a strong ( or entire ) scientific concentration, whereas a ba underlines a majority of social science credits. this is not always necessarily the case however, and in many uk institutions students studying the bpsy, bsc, and ba follow the same curriculum as outlined by the british psychological society and have the same options of specialism open to them regardless of whether they choose a balance, a heavy science basis, or heavy social science basis to their degree. if they applied to read the ba. for example, but specialized in heavily science - based modules, then they will still generally be awarded the ba. = = = sociology = = = sociology is the systematic study of society, individuals ' relationship to their societies, the consequences of difference, and other aspects of human social action. the meaning of the word comes from the suffix - logy, which means " study of ", derived from ancient greek, and the stem soci -, which is from the latin word socius, meaning " companion ", or society in general. auguste comte ( 1798 – 1857 ) coined three of what is called the six simple machines, from which all machines are based. these machines are the inclined plane, the wedge, and the lever, which allowed the ancient egyptians to move millions of limestone blocks which weighed approximately 3. 5 tons ( 7, 000 lbs. ) each into place to create structures like the great pyramid of giza, which is 481 feet ( 147 meters ) high. they also made writing medium similar to paper from papyrus, which joshua mark states is the foundation for modern paper. papyrus is a plant ( cyperus papyrus ) which grew in plentiful amounts in the egyptian delta and throughout the nile river valley during ancient times. the papyrus was harvested by field workers and brought to processing centers where it was cut into thin strips. the strips were then laid - out side by side and covered in plant resin. the second layer of strips was laid on perpendicularly, then both pressed together until the sheet was dry. the sheets were then joined to form a roll and later used for writing. egyptian society made several significant advances during dynastic periods in many areas of technology. according to hossam elanzeery, they were the first civilization to use timekeeping devices such as sundials, shadow clocks, and obelisks and successfully leveraged their knowledge of astronomy to create a calendar model that society still uses today. they developed shipbuilding technology that saw them progress from papyrus reed vessels to cedar wood ships while also pioneering the use of rope trusses and stem - mounted rudders. the egyptians also used their knowledge of anatomy to lay the foundation for many modern medical techniques and practiced the earliest known version of neuroscience. elanzeery also states that they used and furthered mathematical science, as evidenced in the building of the pyramids. ancient egyptians also invented and pioneered many food technologies that have become the basis of modern food technology processes. based on paintings and reliefs found in tombs, as well as archaeological artifacts, scholars like paul t nicholson believe that the ancient egyptians established systematic farming practices, engaged in cereal processing, brewed beer and baked bread, processed meat, practiced viticulture and created the basis for modern wine production, and created condiments to complement, preserve and mask the flavors of their food. = = = = indus valley = = = = the indus valley civilization, situated in a resource - rich area ( in modern pakistan and northwestern india ), is notable for its early application of city planning, sanitation technologies, and plumbing. indus valley construction and architecture, called ' vaastu frequent itemsets form a polytope and can be found and analyzed with linear programming. Question: What is the main type of cell in the nervous system called? A) sensory B) neuron C) axon D) conduction	B) neuron
Context: not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again. in pure water, the number of hydrogen ions balances ( or equals ) the number of hydroxyl ions, resulting in a ph that is neutral. = = = organic compounds = = = organic compounds are molecules that contain carbon bonded to another element such as hydrogen. with the exception of water, nearly all the molecules that make up each organism contain carbon. carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules. for example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( ##ulating the liquid below from the cold air above. water has the capacity to absorb energy, giving it a higher specific heat capacity than other solvents such as ethanol. thus, a large amount of energy is needed to break the hydrogen bonds between water molecules to convert liquid water into water vapor. as a molecule, water is not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again. in pure water, the number of hydrogen ions balances ( or equals ) the number of hydroxyl ions, resulting in a ph that is neutral. = = = organic compounds = = = organic compounds are molecules that contain carbon bonded to another element such as hydrogen. with the exception of water, nearly all the molecules that make up each organism contain carbon. carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules. for example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, use less energy than conventional thermal separation processes such as distillation, sublimation or crystallization. the separation process is purely physical and both fractions ( permeate and retentate ) can be obtained as useful products. cold separation using membrane technology is widely used in the food technology, biotechnology and pharmaceutical industries. furthermore, using membranes enables separations to take place that would be impossible using thermal separation methods. for example, it is impossible to separate the constituents of azeotropic liquids or solutes which form isomorphic crystals by distillation or recrystallization but such separations can be achieved using membrane technology. depending on the type of membrane, the selective separation of certain individual substances or substance mixtures is possible. important technical applications include the production of drinking water by reverse osmosis. in waste water treatment, membrane technology is becoming increasingly important. ultra / microfiltration can be very effective in removing colloids and macromolecules from wastewater. this is needed if wastewater is discharged into sensitive waters especially those designated for contact water sports and recreation. about half of the market is in medical applications such as artificial kidneys to remove toxic substances by hemodialysis and as artificial lung for bubble - free supply of oxygen in the blood. the importance of membrane technology is growing in the field of environmental protection ( nano - mem - pro ippc database ). even in modern energy recovery techniques, membranes are increasingly used, for example in fuel cells and in osmotic power plants. = = mass transfer = = two basic models can be distinguished for mass transfer through the membrane : the solution - diffusion model and the hydrodynamic model. in real membranes, these two transport mechanisms certainly occur side by side, especially during ultra - filtration. = = = solution - diffusion model = = = in the solution - diffusion model, transport occurs only by diffusion. the component that needs to be transported must first be dissolved in the membrane. the general approach of the solution - diffusion model is to assume that the chemical potential of the feed and permeate fluids are in equilibrium with the adjacent membrane surfaces such that appropriate expressions for the chemical potential in the fluid and membrane phases can be equated at the solution - membrane interface. this principle is more important for dense membranes without natural pores such as those used for reverse osmosis and in fuel cells. during the filtration process a boundary layer forms on the membrane. this concentration gradient is created by molecules which cannot pass through the membrane. the = = organic compounds are molecules that contain carbon bonded to another element such as hydrogen. with the exception of water, nearly all the molecules that make up each organism contain carbon. carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules. for example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids the most abundant molecule in every organism. water is important to life because it is an effective solvent, capable of dissolving solutes such as sodium and chloride ions or other small molecules to form an aqueous solution. once dissolved in water, these solutes are more likely to come in contact with one another and therefore take part in chemical reactions that sustain life. in terms of its molecular structure, water is a small polar molecule with a bent shape formed by the polar covalent bonds of two hydrogen ( h ) atoms to one oxygen ( o ) atom ( h2o ). because the o – h bonds are polar, the oxygen atom has a slight negative charge and the two hydrogen atoms have a slight positive charge. this polar property of water allows it to attract other water molecules via hydrogen bonds, which makes water cohesive. surface tension results from the cohesive force due to the attraction between molecules at the surface of the liquid. water is also adhesive as it is able to adhere to the surface of any polar or charged non - water molecules. water is denser as a liquid than it is as a solid ( or ice ). this unique property of water allows ice to float above liquid water such as ponds, lakes, and oceans, thereby insulating the liquid below from the cold air above. water has the capacity to absorb energy, giving it a higher specific heat capacity than other solvents such as ethanol. thus, a large amount of energy is needed to break the hydrogen bonds between water molecules to convert liquid water into water vapor. as a molecule, water is not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again. in pure water, the number of hydrogen ions balances ( or equals ) the number of hydroxyl ions, resulting in a ph that is neutral. = = = organic compounds = = = organic compounds are molecules that contain carbon bonded to another element such as hydrogen. with the exception of water, nearly all the molecules that make up each organism contain carbon. carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules. for example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such ) of the mass of all organisms, with calcium, phosphorus, sulfur, sodium, chlorine, and magnesium constituting essentially all the remainder. different elements can combine to form compounds such as water, which is fundamental to life. biochemistry is the study of chemical processes within and relating to living organisms. molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including molecular synthesis, modification, mechanisms, and interactions. = = = water = = = life arose from the earth ' s first ocean, which formed some 3. 8 billion years ago. since then, water continues to be the most abundant molecule in every organism. water is important to life because it is an effective solvent, capable of dissolving solutes such as sodium and chloride ions or other small molecules to form an aqueous solution. once dissolved in water, these solutes are more likely to come in contact with one another and therefore take part in chemical reactions that sustain life. in terms of its molecular structure, water is a small polar molecule with a bent shape formed by the polar covalent bonds of two hydrogen ( h ) atoms to one oxygen ( o ) atom ( h2o ). because the o – h bonds are polar, the oxygen atom has a slight negative charge and the two hydrogen atoms have a slight positive charge. this polar property of water allows it to attract other water molecules via hydrogen bonds, which makes water cohesive. surface tension results from the cohesive force due to the attraction between molecules at the surface of the liquid. water is also adhesive as it is able to adhere to the surface of any polar or charged non - water molecules. water is denser as a liquid than it is as a solid ( or ice ). this unique property of water allows ice to float above liquid water such as ponds, lakes, and oceans, thereby insulating the liquid below from the cold air above. water has the capacity to absorb energy, giving it a higher specific heat capacity than other solvents such as ethanol. thus, a large amount of energy is needed to break the hydrogen bonds between water molecules to convert liquid water into water vapor. as a molecule, water is not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again. in pure water, the number of hydrogen ions balances ( or equals ) the number of hydroxyl ions, resulting in a ph that is neutral. = = = organic compounds = navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding sea becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids are polymers of nucleotides. their function is to store, transmit, and express hereditary information. = = cells = = cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division air, organic vapor removal from air or a nitrogen stream ) and sometimes in membrane distillation. the later process helps in the separation of azeotropic compositions reducing the costs of distillation processes. = = pore size and selectivity = = the pore sizes of technical membranes are specified differently depending on the manufacturer. one common distinction is by nominal pore size. it describes the maximum pore size distribution and gives only vague information about the retention capacity of a membrane. the exclusion limit or " cut - off " of the membrane is usually specified in the form of nmwc ( nominal molecular weight cut - off, or mwco, molecular weight cut off, with units in dalton ). it is defined as the minimum molecular weight of a globular molecule that is retained to 90 % by the membrane. the cut - off, depending on the method, can by converted to so - called d90, which is then expressed in a metric unit. in practice the mwco of the membrane should be at least 20 % lower than the molecular weight of the molecule that is to be separated. using track etched mica membranes beck and schultz demonstrated that hindered diffusion of molecules in pores can be described by the rankin equation. filter membranes are divided into four classes according to pore size : the form and shape of the membrane pores are highly dependent on the manufacturing process and are often difficult to specify. therefore, for characterization, test filtrations are carried out and the pore diameter refers to the diameter of the smallest particles which could not pass through the membrane. the rejection can be determined in various ways and provides an indirect measurement of the pore size. one possibility is the filtration of macromolecules ( often dextran, polyethylene glycol or albumin ), another is measurement of the cut - off by gel permeation chromatography. these methods are used mainly to measure membranes for ultrafiltration applications. another testing method is the filtration of particles with defined size and their measurement with a particle sizer or by laser induced breakdown spectroscopy ( libs ). a vivid characterization is to measure the rejection of dextran blue or other colored molecules. the retention of bacteriophage and bacteria, the so - called " bacteria challenge test ", can also provide information about the pore size. to determine the pore diameter, physical methods such as porosimeter ( mercury, liquid - liquid porosimeter and bubble point test ) are also used Question: Many ionic compounds occur as hydrates, compounds that contain specific ratios of loosely bound water molecules, called waters of hydration. waters of hydration can often be removed simply by doing this? A) melting B) cooling C) observing D) heating	D) heating
Context: generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. this technique has an extremely high temporal resolution, but a relatively poor spatial resolution. functional magnetic resonance imaging. fmri measures the relative amount of oxygenated blood flowing to different parts of the brain. more oxygenated blood in a particular region is assumed to correlate with an increase in neural activity in that part of the brain. this allows us to localize particular functions within different brain regions. fmri has moderate spatial and temporal resolution. optical imaging. this technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active ( i. e., those that have more oxygenated blood ). optical imaging has moderate temporal resolution, but poor spatial resolution. it also has the advantage that it is extremely safe and can be used to study infants ' brains. magnetoencephalography. meg measures magnetic fields resulting from cortical activity. it is similar to eeg, except that it has improved spatial resolution since the magnetic fields it measures are not as blurred or attenuated by the scalp, meninges and so forth as the electrical activity measured in eeg is. meg uses squid sensors to detect tiny magnetic fields. = = = computational modeling = = = computational models require a mathematically and logically formal representation of a problem. computer models are used in the simulation and experimental verification of different specific and general properties of intelligence. computational modeling can help us understand the functional organization of a particular cognitive phenomenon. approaches to cognitive modeling can be categorized as : ( 1 ) symbolic, on abstract mental functions of an intelligent mind by means of symbols ; ( 2 ) subsymbolic, on the neural and associative properties of the human brain ; and ( 3 ) across the symbolic – subsymbolic border, including hybrid. symbolic modeling evolved from the computer science paradigms using the technologies of knowledge - based systems, as well as a philosophical perspective ( e. g. " good old - fashioned artificial intelligence " ( gofai ) ). they were developed by the first cognitive researchers and later used in information engineering for expert systems. since the early 1990s it was generalized in systemics for the investigation of functional human - like intelligence models, such as personoids, and, in parallel, developed as the soar environment. recently, especially in also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under and taken up by the brain. by observing which areas of the brain take up the radioactive isotope, we can see which areas of the brain are more active than other areas. pet has similar spatial resolution to fmri, but it has extremely poor temporal resolution. electroencephalography. eeg measures the electrical fields generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. this technique has an extremely high temporal resolution, but a relatively poor spatial resolution. functional magnetic resonance imaging. fmri measures the relative amount of oxygenated blood flowing to different parts of the brain. more oxygenated blood in a particular region is assumed to correlate with an increase in neural activity in that part of the brain. this allows us to localize particular functions within different brain regions. fmri has moderate spatial and temporal resolution. optical imaging. this technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active ( i. e., those that have more oxygenated blood ). optical imaging has moderate temporal resolution, but poor spatial resolution. it also has the advantage that it is extremely safe and can be used to study infants ' brains. magnetoencephalography. meg measures magnetic fields resulting from cortical activity. it is similar to eeg, except that it has improved spatial resolution since the magnetic fields it measures are not as blurred or attenuated by the scalp, meninges and so forth as the electrical activity measured in eeg is. meg uses squid sensors to detect tiny magnetic fields. = = = computational modeling = = = computational models require a mathematically and logically formal representation of a problem. computer models are used in the simulation and experimental verification of different specific and general properties of intelligence. computational modeling can help us understand the functional organization of a particular cognitive phenomenon. approaches to cognitive modeling can be categorized as : ( 1 ) symbolic, on abstract mental functions of an intelligent mind by means of symbols ; ( 2 ) subsymbolic, on the neural and associative properties of the human brain ; and ( 3 ) across the symbolic – subsymbolic border, including hybrid. symbolic modeling evolved from the computer science paradigms using the technologies of knowledge - based systems, as well as a philosophical perspective ( e. g. " good old - fashioned artificial intelligence " ( gofa of imaging techniques vary in their temporal ( time - based ) and spatial ( location - based ) resolution. brain imaging is often used in cognitive neuroscience. single - photon emission computed tomography and positron emission tomography. spect and pet use radioactive isotopes, which are injected into the subject ' s bloodstream and taken up by the brain. by observing which areas of the brain take up the radioactive isotope, we can see which areas of the brain are more active than other areas. pet has similar spatial resolution to fmri, but it has extremely poor temporal resolution. electroencephalography. eeg measures the electrical fields generated by large populations of neurons in the cortex by placing a series of electrodes on the scalp of the subject. this technique has an extremely high temporal resolution, but a relatively poor spatial resolution. functional magnetic resonance imaging. fmri measures the relative amount of oxygenated blood flowing to different parts of the brain. more oxygenated blood in a particular region is assumed to correlate with an increase in neural activity in that part of the brain. this allows us to localize particular functions within different brain regions. fmri has moderate spatial and temporal resolution. optical imaging. this technique uses infrared transmitters and receivers to measure the amount of light reflectance by blood near different areas of the brain. since oxygenated and deoxygenated blood reflects light by different amounts, we can study which areas are more active ( i. e., those that have more oxygenated blood ). optical imaging has moderate temporal resolution, but poor spatial resolution. it also has the advantage that it is extremely safe and can be used to study infants ' brains. magnetoencephalography. meg measures magnetic fields resulting from cortical activity. it is similar to eeg, except that it has improved spatial resolution since the magnetic fields it measures are not as blurred or attenuated by the scalp, meninges and so forth as the electrical activity measured in eeg is. meg uses squid sensors to detect tiny magnetic fields. = = = computational modeling = = = computational models require a mathematically and logically formal representation of a problem. computer models are used in the simulation and experimental verification of different specific and general properties of intelligence. computational modeling can help us understand the functional organization of a particular cognitive phenomenon. approaches to cognitive modeling can be categorized as : ( 1 ) symbolic, on abstract mental functions of an intelligent mind by means of symbols ; ( 2 ) subsymbolic, on the neural and associa , characterizing organs as predominantly yin or yang, and understood the relationship between the pulse, the heart, and the flow of blood in the body centuries before it became accepted in the west. little evidence survives of how ancient indian cultures around the indus river understood nature, but some of their perspectives may be reflected in the vedas, a set of sacred hindu texts. they reveal a conception of the universe as ever - expanding and constantly being recycled and reformed. surgeons in the ayurvedic tradition saw health and illness as a combination of three humors : wind, bile and phlegm. a healthy life resulted from a balance among these humors. in ayurvedic thought, the body consisted of five elements : earth, water, fire, wind, and space. ayurvedic surgeons performed complex surgeries and developed a detailed understanding of human anatomy. pre - socratic philosophers in ancient greek culture brought natural philosophy a step closer to direct inquiry about cause and effect in nature between 600 and 400 bc. however, an element of magic and mythology remained. natural phenomena such as earthquakes and eclipses were explained increasingly in the context of nature itself instead of being attributed to angry gods. thales of miletus, an early philosopher who lived from 625 to 546 bc, explained earthquakes by theorizing that the world floated on water and that water was the fundamental element in nature. in the 5th century bc, leucippus was an early exponent of atomism, the idea that the world is made up of fundamental indivisible particles. pythagoras applied greek innovations in mathematics to astronomy and suggested that the earth was spherical. = = = aristotelian natural philosophy ( 400 bc – 1100 ad ) = = = later socratic and platonic thought focused on ethics, morals, and art and did not attempt an investigation of the physical world ; plato criticized pre - socratic thinkers as materialists and anti - religionists. aristotle, however, a student of plato who lived from 384 to 322 bc, paid closer attention to the natural world in his philosophy. in his history of animals, he described the inner workings of 110 species, including the stingray, catfish and bee. he investigated chick embryos by breaking open eggs and observing them at various stages of development. aristotle ' s works were influential through the 16th century, and he is considered to be the father of biology for his pioneering work in that science. he also presented philosophies about physics, nature, and astronomy using every riordan array has what we call a horizontal half and a vertical half. these halves of a riordan array have been studied separately before. here, we place them in a common context, showing that one may be obtained from the other. we also ask and answer the question : given a riordan array, when is it the half ( either horizontal of vertical ) of a riordan array? depends on the extent of the continent in which it is situated, its position in relation to the hilly regions in which rivers generally arise and the sea into which they flow, and the distance between the source and the outlet into the sea of the river draining it. the rate of flow of rivers depends mainly upon their fall, also known as the gradient or slope. when two rivers of different sizes have the same fall, the larger river has the quicker flow, as its retardation by friction against its bed and banks is less in proportion to its volume than is the case with the smaller river. the fall available in a section of a river approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with a rapid fall near the sources of rivers can carry down rocks, boulders and large stones, which are by degrees ground by attrition in their onward course into slate, gravel, sand and silt, simultaneously with the gradual reduction in fall, and, consequently, in the transporting force of the current. accordingly, under ordinary conditions, most of the materials brought down from the high lands by torrential water courses are carried forward by the main river to the sea, or partially strewn over flat alluvial plains during floods ; the size of the materials forming the bed of the river or borne along by the stream is gradually reduced on proceeding sea approximately corresponds to the slope of the country it traverses ; as rivers rise close to the highest part of their basins, generally in hilly regions, their fall is rapid near their source and gradually diminishes, with occasional irregularities, until, in traversing plains along the latter part of their course, their fall usually becomes quite gentle. accordingly, in large basins, rivers in most cases begin as torrents with a variable flow, and end as gently flowing rivers with a comparatively regular discharge. the irregular flow of rivers throughout their course forms one of the main difficulties in devising works for mitigating inundations or for increasing the navigable capabilities of rivers. in tropical countries subject to periodical rains, the rivers are in flood during the rainy season and have hardly any flow during the rest of the year, while in temperate regions, where the rainfall is more evenly distributed throughout the year, evaporation causes the available rainfall to be much less in hot summer weather than in the winter months, so that the rivers fall to their low stage in the summer and are liable to be in flood in the winter. in fact, with a temperate climate, the year may be divided into a warm and a cold season, extending from may to october and from november to april in the northern hemisphere respectively ; the rivers are low and moderate floods are of rare occurrence during the warm period, and the rivers are high and subject to occasional heavy floods after a considerable rainfall during the cold period in most years. the only exceptions are rivers which have their sources amongst mountains clad with perpetual snow and are fed by glaciers ; their floods occur in the summer from the melting of snow and ice, as exemplified by the rhone above the lake of geneva, and the arve which joins it below. but even these rivers are liable to have their flow modified by the influx of tributaries subject to different conditions, so that the rhone below lyon has a more uniform discharge than most rivers, as the summer floods of the arve are counteracted to a great extent by the low stage of the saone flowing into the rhone at lyon, which has its floods in the winter when the arve, on the contrary, is low. another serious obstacle encountered in river engineering consists in the large quantity of detritus they bring down in flood - time, derived mainly from the disintegration of the surface layers of the hills and slopes in the upper parts of the valleys by glaciers, frost and rain. the power of a current to transport materials varies with its velocity, so that torrents with Question: When blood vessels in the head dilate, what kind of severe headache can occur? A) tension headache B) chronic headache C) malignant D) migraine	D) migraine
Context: 1975. skin tissue - engineered skin is a type of bioartificial organ that is often used to treat burns, diabetic foot ulcers, or other large wounds that cannot heal well on their own. artificial skin can be made from autografts, allografts, and xenografts. autografted skin comes from a patient ' s own skin, which allows the dermis to have a faster healing rate, and the donor site can be re - harvested a few times. allograft skin often comes from cadaver skin and is mostly used to treat burn victims. lastly, xenografted skin comes from animals and provides a temporary healing structure for the skin. they assist in dermal regeneration, but cannot become part of the host skin. tissue - engineered skin is now available in commercial products. integra, originally used to only treat burns, consists of a collagen matrix and chondroitin sulfate that can be used as a skin replacement. the chondroitin sulfate functions as a component of proteoglycans, which helps to form the extracellular matrix. integra can be repopulated and revascularized while maintaining its dermal collagen architecture, making it a bioartificial organ dermagraft, another commercial - made tissue - engineered skin product, is made out of living fibroblasts. these fibroblasts proliferate and produce growth factors, collagen, and ecm proteins, that help build granulation tissue. = = = = heart = = = = since the number of patients awaiting a heart transplant is continuously increasing over time, and the number of patients on the waiting list surpasses the organ availability, artificial organs used as replacement therapy for terminal heart failure would help alleviate this difficulty. artificial hearts are usually used to bridge the heart transplantation or can be applied as replacement therapy for terminal heart malfunction. the total artificial heart ( tah ), first introduced by dr. vladimir p. demikhov in 1937, emerged as an ideal alternative. since then it has been developed and improved as a mechanical pump that provides long - term circulatory support and replaces diseased or damaged heart ventricles that cannot properly pump the blood, restoring thus the pulmonary and systemic flow. some of the current tahs include abiocor, an fda - approved device that comprises two artificial ventricles and their valves, and does not require subcutaneous connections, and is indicated for types may be unsigned ( capable of representing only non - negative integers ) or signed ( capable of representing negative integers as well ). an integer value is typically specified in the source code of a program as a sequence of digits optionally prefixed with + or −. some programming languages allow other notations, such as hexadecimal ( base 16 ) or octal ( base 8 ). some programming languages also permit digit group separators. the internal representation of this datum is the way the value is stored in the computer ' s memory. unlike mathematical integers, a typical datum in a computer has some minimal and maximum possible value. the most common representation of a positive integer is a string of bits, using the binary numeral system. the order of the memory bytes storing the bits varies ; see endianness. the width, precision, or bitness of an integral type is the number of bits in its representation. an integral type with n bits can encode 2n numbers ; for example an unsigned type typically represents the non - negative values 0 through 2n − 1. other encodings of integer values to bit patterns are sometimes used, for example binary - coded decimal or gray code, or as printed character codes such as ascii. there are four well - known ways to represent signed numbers in a binary computing system. the most common is two ' s complement, which allows a signed integral type with n bits to represent numbers from −2 ( n−1 ) through 2 ( n−1 ) − 1. two ' s complement arithmetic is convenient because there is a perfect one - to - one correspondence between representations and values ( in particular, no separate + 0 and −0 ), and because addition, subtraction and multiplication do not need to distinguish between signed and unsigned types. other possibilities include offset binary, sign - magnitude, and ones ' complement. some computer languages define integer sizes in a machine - independent way ; others have varying definitions depending on the underlying processor word size. not all language implementations define variables of all integer sizes, and defined sizes may not even be distinct in a particular implementation. an integer in one programming language may be a different size in a different language, on a different processor, or in an execution context of different bitness ; see § words. some older computer architectures used decimal representations of integers, stored in binary - coded decimal ( bcd ) or other format. these values generally require data sizes of 4 bits per decimal digit ( sometimes called a nibble ), usually with additional bits size of the grouping varies so the set of integer sizes available varies between different types of computers. computer hardware nearly always provides a way to represent a processor register or memory address as an integer. = = value and representation = = the value of an item with an integral type is the mathematical integer that it corresponds to. integral types may be unsigned ( capable of representing only non - negative integers ) or signed ( capable of representing negative integers as well ). an integer value is typically specified in the source code of a program as a sequence of digits optionally prefixed with + or −. some programming languages allow other notations, such as hexadecimal ( base 16 ) or octal ( base 8 ). some programming languages also permit digit group separators. the internal representation of this datum is the way the value is stored in the computer ' s memory. unlike mathematical integers, a typical datum in a computer has some minimal and maximum possible value. the most common representation of a positive integer is a string of bits, using the binary numeral system. the order of the memory bytes storing the bits varies ; see endianness. the width, precision, or bitness of an integral type is the number of bits in its representation. an integral type with n bits can encode 2n numbers ; for example an unsigned type typically represents the non - negative values 0 through 2n − 1. other encodings of integer values to bit patterns are sometimes used, for example binary - coded decimal or gray code, or as printed character codes such as ascii. there are four well - known ways to represent signed numbers in a binary computing system. the most common is two ' s complement, which allows a signed integral type with n bits to represent numbers from −2 ( n−1 ) through 2 ( n−1 ) − 1. two ' s complement arithmetic is convenient because there is a perfect one - to - one correspondence between representations and values ( in particular, no separate + 0 and −0 ), and because addition, subtraction and multiplication do not need to distinguish between signed and unsigned types. other possibilities include offset binary, sign - magnitude, and ones ' complement. some computer languages define integer sizes in a machine - independent way ; others have varying definitions depending on the underlying processor word size. not all language implementations define variables of all integer sizes, and defined sizes may not even be distinct in a particular implementation. an integer in one programming language may be a different size in a different language, on a different processor transmitters is their power consumption as this is closely related to their signal strength. if the signal strength of a transmitter is insufficient the signal ' s information will be corrupted by noise. aviation - electronics engineering and aviation - telecommunications engineering, are concerned with aerospace applications. aviation - telecommunication engineers include specialists who work on airborne avionics in the aircraft or ground equipment. specialists in this field mainly need knowledge of computer, networking, it, and sensors. these courses are offered at such as civil aviation technology colleges. control engineering has a wide range of electronic applications from the flight and propulsion systems of commercial airplanes to the cruise control present in many modern cars. it also plays an important role in industrial automation. control engineers often use feedback when designing control systems. instrumentation engineering deals with the design of devices to measure physical quantities such as pressure, flow, and temperature. the design of such instrumentation requires a good understanding of electronics engineering and physics ; for example, radar guns use the doppler effect to measure the speed of oncoming vehicles. similarly, thermocouples use the peltier – seebeck effect to measure the temperature difference between two points. often instrumentation is not used by itself, but instead as the sensors of larger electrical systems. for example, a thermocouple might be used to help ensure a furnace ' s temperature remains constant. for this reason, instrumentation engineering is often viewed as the counterpart of control engineering. computer engineering deals with the design of computers and computer systems. this may involve the design of new computer hardware, the design of pdas or the use of computers to control an industrial plant. development of embedded systems — systems made for specific tasks ( e. g., mobile phones ) — is also included in this field. this field includes the microcontroller and its applications. computer engineers may also work on a system ' s software. however, the design of complex software systems is often the domain of software engineering which falls under computer science, which is usually considered a separate discipline. vlsi design engineering vlsi stands for very large - scale integration. it deals with fabrication of ics and various electronic components. in designing an integrated circuit, electronics engineers first construct circuit schematics that specify the electrical components and describe the interconnections between them. when completed, vlsi engineers convert the schematics into actual layouts, which map the layers of various conductor and semiconductor materials needed to construct the circuit. = = education and training = = electronics is a subfield within the wider electrical engineering academic the dual - caliber approach. it uses a breech that is large enough to accept 140 mm ammunition and be mounted with both a 120 mm barrel and a 135 mm or 140 mm barrel. the xm291 also mounts a larger gun tube and a larger ignition chamber than the existing m256 l / 44 main gun. through the application of electrothermal - chemical technology the xm291 has been able to achieve muzzle energy outputs that equate that to a low - level 140 mm gun, while achieving muzzle velocities greater than those of the larger 140 mm gun. although the xm291 does not mean that etc technology is viable it does offer an example that it is possible. etc requires much less energy input from outside sources, like a battery, than a railgun or a coilgun would. tests have shown that energy output by the propellant is higher than energy input from outside sources on etc guns. in comparison, a railgun currently cannot achieve a higher muzzle velocity than the amount of energy input. even at 50 % efficiency a rail gun launching a projectile with a kinetic energy of 20 mj would require an energy input into the rails of 40 mj, and 50 % efficiency has not yet been achieved. to put this into perspective, a rail gun launching at 9 mj of energy would need roughly 32 mj worth of energy from capacitors. current advances in energy storage allow for energy densities as high as 2. 5 mj / dm3, which means that a battery delivering 32 mj of energy would require a volume of 12. 8 dm3 per shot ; this is not a viable volume for use in a modern main battle tank, especially one designed to be lighter than existing models. there has even been discussion about eliminating the necessity for an outside electrical source in etc ignition by initiating the plasma cartridge through a small explosive force. furthermore, etc technology is not only applicable to solid propellants. to increase muzzle velocity even further electrothermal - chemical ignition can work with liquid propellants, although this would require further research into plasma ignition. etc technology is also compatible with existing projects to reduce the amount of recoil delivered to the vehicle while firing. understandably, recoil of a gun firing a projectile at 17 mj or more will increase directly with the increase in muzzle energy in accordance to newton ' s third law of motion and successful implementation of recoil reduction mechanisms will be vital to the installation of an etc powered gun in an existing vehicle design. for example, oto melara ' ##xadecimal ( base 16 ) or octal ( base 8 ). some programming languages also permit digit group separators. the internal representation of this datum is the way the value is stored in the computer ' s memory. unlike mathematical integers, a typical datum in a computer has some minimal and maximum possible value. the most common representation of a positive integer is a string of bits, using the binary numeral system. the order of the memory bytes storing the bits varies ; see endianness. the width, precision, or bitness of an integral type is the number of bits in its representation. an integral type with n bits can encode 2n numbers ; for example an unsigned type typically represents the non - negative values 0 through 2n − 1. other encodings of integer values to bit patterns are sometimes used, for example binary - coded decimal or gray code, or as printed character codes such as ascii. there are four well - known ways to represent signed numbers in a binary computing system. the most common is two ' s complement, which allows a signed integral type with n bits to represent numbers from −2 ( n−1 ) through 2 ( n−1 ) − 1. two ' s complement arithmetic is convenient because there is a perfect one - to - one correspondence between representations and values ( in particular, no separate + 0 and −0 ), and because addition, subtraction and multiplication do not need to distinguish between signed and unsigned types. other possibilities include offset binary, sign - magnitude, and ones ' complement. some computer languages define integer sizes in a machine - independent way ; others have varying definitions depending on the underlying processor word size. not all language implementations define variables of all integer sizes, and defined sizes may not even be distinct in a particular implementation. an integer in one programming language may be a different size in a different language, on a different processor, or in an execution context of different bitness ; see § words. some older computer architectures used decimal representations of integers, stored in binary - coded decimal ( bcd ) or other format. these values generally require data sizes of 4 bits per decimal digit ( sometimes called a nibble ), usually with additional bits for a sign. many modern cpus provide limited support for decimal integers as an extended datatype, providing instructions for converting such values to and from binary values. depending on the architecture, decimal integers may have fixed sizes ( e. g., 7 decimal digits plus a sign fit into a 32 - bit word ), possible value. the most common representation of a positive integer is a string of bits, using the binary numeral system. the order of the memory bytes storing the bits varies ; see endianness. the width, precision, or bitness of an integral type is the number of bits in its representation. an integral type with n bits can encode 2n numbers ; for example an unsigned type typically represents the non - negative values 0 through 2n − 1. other encodings of integer values to bit patterns are sometimes used, for example binary - coded decimal or gray code, or as printed character codes such as ascii. there are four well - known ways to represent signed numbers in a binary computing system. the most common is two ' s complement, which allows a signed integral type with n bits to represent numbers from −2 ( n−1 ) through 2 ( n−1 ) − 1. two ' s complement arithmetic is convenient because there is a perfect one - to - one correspondence between representations and values ( in particular, no separate + 0 and −0 ), and because addition, subtraction and multiplication do not need to distinguish between signed and unsigned types. other possibilities include offset binary, sign - magnitude, and ones ' complement. some computer languages define integer sizes in a machine - independent way ; others have varying definitions depending on the underlying processor word size. not all language implementations define variables of all integer sizes, and defined sizes may not even be distinct in a particular implementation. an integer in one programming language may be a different size in a different language, on a different processor, or in an execution context of different bitness ; see § words. some older computer architectures used decimal representations of integers, stored in binary - coded decimal ( bcd ) or other format. these values generally require data sizes of 4 bits per decimal digit ( sometimes called a nibble ), usually with additional bits for a sign. many modern cpus provide limited support for decimal integers as an extended datatype, providing instructions for converting such values to and from binary values. depending on the architecture, decimal integers may have fixed sizes ( e. g., 7 decimal digits plus a sign fit into a 32 - bit word ), or may be variable - length ( up to some maximum digit size ), typically occupying two digits per byte ( octet ). = = common integral data types = = different cpus support different integral data types. typically, hardware will support both signed and unsigned types, but only a small, fixed set of widths intended for just one destination. stations typically ignore information not addressed to them. the use of the same channel also means that the data bandwidth is shared, so for example, available throughput to each device is halved when two stations are actively transmitting. as with other ieee 802 lans, stations come programmed with a globally unique 48 - bit mac address. the mac addresses are used to specify both the destination and the source of each data packet. on the reception of a transmission, the receiver uses the destination address to determine whether the transmission is relevant to the station or should be ignored. a scheme known as carrier - sense multiple access with collision avoidance ( csma / ca ) governs the way stations share channels. with csma / ca stations attempt to avoid collisions by beginning transmission only after the channel is sensed to be idle, but then transmit their packet data in its entirety. csma / ca cannot completely prevent collisions, as two stations may sense the channel to be idle at the same time and thus begin transmission simultaneously. a collision happens when a station receives signals from multiple stations on a channel at the same time. this corrupts the transmitted data and can require stations to re - transmit. the lost data and re - transmission reduces throughput, in some cases severely. = = = waveband = = = the 802. 11 standard provides several distinct radio frequency ranges for use in wi - fi communications : 900 mhz, 2. 4 ghz, 3. 6 ghz, 4. 9 ghz, 5 ghz, 6 ghz and 60 ghz bands. each range is divided into a multitude of channels. in the standards, channels are numbered at 5 mhz spacing within a band ( except in the 60 ghz band, where they are 2. 16 ghz apart ), and the number refers to the centre frequency of the channel. although channels are numbered at 5 mhz spacing, transmitters generally occupy at least 20 mhz, and standards allow for neighbouring channels to be bonded together to form a wider channel for higher throughput. countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges. 802. 11b / g / n can use the 2. 4 ghz band, operating in the united states under fcc part 15 rules and regulations. in this frequency band, equipment may occasionally suffer interference from microwave ovens, cordless telephones, usb 3. 0 hubs, bluetooth and other devices. spectrum assignments and operational limitations are not consistent worldwide : australia and europe allow for an additional two channels ( 12, 13 ) the information being sent, and the spectral efficiency of the modulation method used ; how much data it can transmit in each unit of bandwidth. different types of information signals carried by radio have different data rates. for example, a television signal has a greater data rate than an audio signal. the radio spectrum, the total range of radio frequencies that can be used for communication in a given area, is a limited resource. each radio transmission occupies a portion of the total bandwidth available. radio bandwidth is regarded as an economic good which has a monetary cost and is in increasing demand. in some parts of the radio spectrum, the right to use a frequency band or even a single radio channel is bought and sold for millions of dollars. so there is an incentive to employ technology to minimize the bandwidth used by radio services. a slow transition from analog to digital radio transmission technologies began in the late 1990s. part of the reason for this is that digital modulation can often transmit more information ( a greater data rate ) in a given bandwidth than analog modulation, by using data compression algorithms, which reduce redundancy in the data to be sent, and more efficient modulation. other reasons for the transition is that digital modulation has greater noise immunity than analog, digital signal processing chips have more power and flexibility than analog circuits, and a wide variety of types of information can be transmitted using the same digital modulation. because it is a fixed resource which is in demand by an increasing number of users, the radio spectrum has become increasingly congested in recent decades, and the need to use it more effectively is driving many additional radio innovations such as trunked radio systems, spread spectrum ( ultra - wideband ) transmission, frequency reuse, dynamic spectrum management, frequency pooling, and cognitive radio. = = = itu frequency bands = = = the itu arbitrarily divides the radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten ( 10n ) metres, with corresponding frequency of 3 times a power of ten, and each covering a decade of frequency or wavelength. each of these bands has a traditional name : it can be seen that the bandwidth, the range of frequencies, contained in each band is not equal but increases exponentially as the frequency increases ; each band contains ten times the bandwidth of the preceding band. the term " tremendously low frequency " ( tlf ) has been used for wavelengths from 1 – 3 hz ( 300, 000 – 100, 000 km ), though the term has not been defined by the itu. = = regulation = the top flavour - changing neutral couplings can be large in extended models with vector - like quarks. in the next decade ( s ) the cern large hadron collider will allow to measure ( bound ) them with a precision of few per cent. Question: Acne and different types of cancer can affect what large organ? A) brain B) lungs C) liver D) skin	D) skin
Context: , translation, and post - translational modification of a protein. gene expression can be influenced by positive or negative regulation, depending on which of the two types of regulatory proteins called transcription factors bind to the dna sequence close to or at a promoter. a cluster of genes that share the same promoter is called an operon, found mainly in prokaryotes and some lower eukaryotes ( e. g., caenorhabditis elegans ). in positive regulation of gene expression, the activator is the transcription factor that stimulates transcription when it binds to the sequence near or at the promoter. negative regulation occurs when another transcription factor called a repressor binds to a dna sequence called an operator, which is part of an operon, to prevent transcription. repressors can be inhibited by compounds called inducers ( e. g., allolactose ), thereby allowing transcription to occur. specific genes that can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial to rna to protein. there are two gene expression processes : transcription ( dna to rna ) and translation ( rna to protein ). = = = gene regulation = = = the regulation of gene expression by environmental factors and during different stages of development can occur at each step of the process such as transcription, rna splicing, translation, and post - translational modification of a protein. gene expression can be influenced by positive or negative regulation, depending on which of the two types of regulatory proteins called transcription factors bind to the dna sequence close to or at a promoter. a cluster of genes that share the same promoter is called an operon, found mainly in prokaryotes and some lower eukaryotes ( e. g., caenorhabditis elegans ). in positive regulation of gene expression, the activator is the transcription factor that stimulates transcription when it binds to the sequence near or at the promoter. negative regulation occurs when another transcription factor called a repressor binds to a dna sequence called an operator, which is part of an operon, to prevent transcription. repressors can be inhibited by compounds called inducers ( e. g., allolactose ), thereby allowing transcription to occur. specific genes that can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial differences in gene expression. a small fraction of the genes in an organism ' s genome called the developmental - genetic toolkit control the development of that organism. these toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. among the most important toolkit genes are the hox genes. hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva. = = evolution = = = = = evolutionary processes = = = evolution is a central organizing concept in biology. it is the change in heritable characteristics of populations over successive generations. in artificial selection, animals were selectively bred for specific traits. given that traits are inherited, populations contain a varied mix of traits, and reproduction is able to increase any population, occurs when another transcription factor called a repressor binds to a dna sequence called an operator, which is part of an operon, to prevent transcription. repressors can be inhibited by compounds called inducers ( e. g., allolactose ), thereby allowing transcription to occur. specific genes that can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial differences in gene expression. a small fraction of the genes in an organism ' s genome called the developmental - genetic toolkit control the development of that organism. these toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. among the most important toolkit genes are the hox genes. hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva. = = evolution = = = = = evolutionary and the creation of genetically modified crops. = = = epigenetics = = = epigenetics is the study of heritable changes in gene function that cannot be explained by changes in the underlying dna sequence but cause the organism ' s genes to behave ( or " express themselves " ) differently. one example of epigenetic change is the marking of the genes by dna methylation which determines whether they will be expressed or not. gene expression can also be controlled by repressor proteins that attach to silencer regions of the dna and prevent that region of the dna code from being expressed. epigenetic marks may be added or removed from the dna during programmed stages of development of the plant, and are responsible, for example, for the differences between anthers, petals and normal leaves, despite the fact that they all have the same underlying genetic code. epigenetic changes may be temporary or may remain through successive cell divisions for the remainder of the cell ' s life. some epigenetic changes have been shown to be heritable, while others are reset in the germ cells. epigenetic changes in eukaryotic biology serve to regulate the process of cellular differentiation. during morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, of epigenetic change is the marking of the genes by dna methylation which determines whether they will be expressed or not. gene expression can also be controlled by repressor proteins that attach to silencer regions of the dna and prevent that region of the dna code from being expressed. epigenetic marks may be added or removed from the dna during programmed stages of development of the plant, and are responsible, for example, for the differences between anthers, petals and normal leaves, despite the fact that they all have the same underlying genetic code. epigenetic changes may be temporary or may remain through successive cell divisions for the remainder of the cell ' s life. some epigenetic changes have been shown to be heritable, while others are reset in the germ cells. epigenetic changes in eukaryotic biology serve to regulate the process of cellular differentiation. during morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, with one allele inducing a change on the other. = = plant evolution = = the chloroplasts of plants have a number of biochemical, structural and genetic similarities to cyanobacteria, ( commonly but incorrectly known as " blue - green algae " ) and are thought to be derived from an process by which a genotype encoded in dna gives rise to an observable phenotype in the proteins of an organism ' s body. this process is summarized by the central dogma of molecular biology, which was formulated by francis crick in 1958. according to the central dogma, genetic information flows from dna to rna to protein. there are two gene expression processes : transcription ( dna to rna ) and translation ( rna to protein ). = = = gene regulation = = = the regulation of gene expression by environmental factors and during different stages of development can occur at each step of the process such as transcription, rna splicing, translation, and post - translational modification of a protein. gene expression can be influenced by positive or negative regulation, depending on which of the two types of regulatory proteins called transcription factors bind to the dna sequence close to or at a promoter. a cluster of genes that share the same promoter is called an operon, found mainly in prokaryotes and some lower eukaryotes ( e. g., caenorhabditis elegans ). in positive regulation of gene expression, the activator is the transcription factor that stimulates transcription when it binds to the sequence near or at the promoter. negative regulation occurs when another transcription factor called a repressor binds to a dna sequence called an operator, which is part of an operon, to prevent transcription. repressors can be inhibited by compounds called inducers ( e. g., allolactose ), thereby allowing transcription to occur. specific genes that can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem from the oil of jasminum grandiflorum which regulates wound responses in plants by unblocking the expression of genes required in the systemic acquired resistance response to pathogen attack. in addition to being the primary energy source for plants, light functions as a signalling device, providing information to the plant, such as how much sunlight the plant receives each day. this can result in adaptive changes in a process known as photomorphogenesis. phytochromes are the photoreceptors in a plant that are sensitive to light. = = plant anatomy and morphology = = plant anatomy is the study of the structure of plant cells and tissues, whereas plant morphology is the study of their external form. all plants are multicellular eukaryotes, their dna stored in nuclei. the characteristic features of plant cells that distinguish them from those of animals and fungi include a primary cell wall composed of the polysaccharides cellulose, hemicellulose and pectin, larger vacuoles than in animal cells and the presence of plastids with unique photosynthetic and biosynthetic functions as in the chloroplasts. other plastids contain storage products such as starch ( amyloplasts ) or lipids ( elaioplasts ). uniquely, streptophyte cells and those of the green algal order trentepohliales divide by construction of a phragmoplast as a template for building a cell plate late in cell division. the bodies of vascular plants including clubmosses, ferns and seed plants ( gymnosperms and angiosperms ) generally have aerial and subterranean subsystems. the shoots consist of stems bearing green photosynthesising leaves and reproductive structures. the underground vascularised roots bear root hairs at their tips and generally lack chlorophyll. non - vascular plants, the liverworts, hornworts and mosses do not produce ground - penetrating vascular roots and most of the plant participates in photosynthesis. the sporophyte generation is nonphotosynthetic in liverworts but may be able to contribute part of its energy needs by photosynthesis in mosses and hornworts. the root system and the shoot system are interdependent – the usually nonphotosynthetic root system depends on the shoot system for food, and the usually photosynthetic shoot system depends on water and minerals from the root system. cells in each system are capable . most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support not always mean it is required, especially when dealing with genetic or functional redundancy. tracking experiments, which seek to gain information about the localisation and interaction of the desired protein. one way to do this is to replace the wild - type gene with a ' fusion ' gene, which is a juxtaposition of the wild - type gene with a reporting element such as green fluorescent protein ( gfp ) that will allow easy visualisation of the products of the genetic modification. while this is a useful technique, the manipulation can destroy the function of the gene, creating secondary effects and possibly calling into question the results of the experiment. more sophisticated techniques are now in development that can track protein products without mitigating their function, such as the addition of small sequences that will serve as binding motifs to monoclonal antibodies. expression studies aim to discover where and when specific proteins are produced. in these experiments, the dna sequence before the dna that codes for a protein, known as a gene ' s promoter, is reintroduced into an organism with the protein coding region replaced by a reporter gene such as gfp or an enzyme that catalyses the production of a dye. thus the time and place where a particular protein is produced can be observed. expression studies can be taken a step further by altering the promoter to find which pieces are crucial for the proper expression of the gene and are actually bound by transcription factor proteins ; this process is known as promoter bashing. = = = industrial = = = organisms can have their cells transformed with a gene coding for a useful protein, such as an enzyme, so that they will overexpress the desired protein. mass quantities of the protein can then be manufactured by growing the transformed organism in bioreactor equipment using industrial fermentation, and then purifying the protein. some genes do not work well in bacteria, so yeast, insect cells or mammalian cells can also be used. these techniques are used to produce medicines such as insulin, human growth hormone, and vaccines, supplements such as tryptophan, aid in the production of food ( chymosin in cheese making ) and fuels. other applications with genetically engineered bacteria could involve making them perform tasks outside their natural cycle, such as making biofuels, cleaning up oil spills, carbon and other toxic waste and detecting arsenic in drinking water. certain genetically modified microbes can also be used in biomining and bioremediation, due to their ability to extract heavy metals from their environment and incorporate them into compounds that are more easily recover Question: Prokaryotic cells can only regulate gene expression by controlling the amount of what? A) folding B) translation C) transcription D) RNA processing	C) transcription
Context: molecular nitrogen is the most commonly assumed background gas that supports habitability on rocky planets. despite its chemical inertness, nitrogen molecule is broken by lightning, hot volcanic vents, and bolide impacts, and can be converted into soluble nitrogen compounds and then sequestered in the ocean. the very stability of nitrogen, and that of nitrogen - based habitability, is thus called into question. here we determine the lifetime of molecular nitrogen vis - a - vis aqueous sequestration, by developing a novel model that couples atmospheric photochemistry and oceanic chemistry. we find that hno, the dominant nitrogen compounds produced in anoxic atmospheres, is converted to n2o in the ocean, rather than oxidized to nitrites or nitrates as previously assumed. this n2o is then released back into the atmosphere and quickly converted to n2. we also find that the deposition rate of no is severely limited by the kinetics of the aqueous - phase reaction that converts no to nitrites in the ocean. putting these insights together, we conclude that the atmosphere must produce nitrogen species at least as oxidized as no2 and hno2 to enable aqueous sequestration. the lifetime of molecular nitrogen in anoxic atmospheres is determined to be > 1 billion years on temperate planets of both sun - like and m dwarf stars. this result upholds the validity of molecular nitrogen as a universal background gas on rocky planets. enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make it available as drinking water. the earliest exploitation of groundwater resources dates back to 3000 bc, and hydrogeology as a science was developed by hydrologists beginning in the 17th century. ecohydrology is the study of ecological systems in the hydrosphere. it can be divided into the physical study of aquatic ecosystems and the is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water. in most cases, oxygen is released as a waste product. most plants, algae, and cyanobacteria perform photosynthesis, which is largely responsible for producing and maintaining the oxygen content of the earth ' s atmosphere, and supplies most of the energy necessary for life on earth. photosynthesis has four stages : light absorption, electron transport, atp synthesis, and carbon fixation. light absorption is the initial step of photosynthesis whereby light energy is absorbed by chlorophyll pigments attached to proteins in the thylakoid membranes. the absorbed light energy is used to remove electrons from a donor ( water ) to a primary electron acceptor, a quinone designated as q. in the second stage, electrons move from the quinone primary electron acceptor through a series of electron carriers until they reach a final electron acceptor, which is usually the oxidized form of nadp +, which is reduced to nadph, a process that takes place in a protein complex called photosystem i ( psi ). the transport of electrons is coupled to the movement of protons ( or hydrogen ) from the stroma to the thylakoid membrane, which forms a ph gradient across the membrane as hydrogen becomes more concentrated in the lumen than in the stroma. this is analogous to the proton - motive force generated across the inner mitochondrial membrane in aerobic respiration. during the third stage of photosynthesis, the movement of protons down their concentration gradients from the thylakoid lumen to the stroma through the atp synthase is coupled to the synthesis of atp by that same atp synthase. the nadph and atps generated by the light - dependent reactions in the second and third stages, respectively, provide the energy and electrons to drive the synthesis of glucose by fixing atmospheric carbon dioxide into existing organic carbon compounds, such as ribulose bisphosphate ( rubp ) in a sequence of light - independent ( or dark ) reactions called the calvin cycle. = = = cell signaling = = = cell signaling ( or communication ) is the ability of cells to receive, process, and transmit signals with its environment and with itself. signals can be non - chemical such as light, electrical impulses, and heat, or chemical signals ( or ligands ) that interact with receptors, which can be found embedded in the cell membrane of another cell or located deep inside onset of electro - chemical corrosion. similar problems are encountered in coastal and offshore structures. = = = anti - fouling = = = anti - fouling is the process of eliminating obstructive organisms from essential components of seawater systems. depending on the nature and location of marine growth, this process is performed in a number of different ways : marine organisms may grow and attach to the surfaces of the outboard suction inlets used to obtain water for cooling systems. electro - chlorination involves running high electrical current through sea water, altering the water ' s chemical composition to create sodium hypochlorite, purging any bio - matter. an electrolytic method of anti - fouling involves running electrical current through two anodes ( scardino, 2009 ). these anodes typically consist of copper and aluminum ( or alternatively, iron ). the first metal, copper anode, releases its ion into the water, creating an environment that is too toxic for bio - matter. the second metal, aluminum, coats the inside of the pipes to prevent corrosion. other forms of marine growth such as mussels and algae may attach themselves to the bottom of a ship ' s hull. this growth interferes with the smoothness and uniformity of the ship ' s hull, causing the ship to have a less hydrodynamic shape that causes it to be slower and less fuel - efficient. marine growth on the hull can be remedied by using special paint that prevents the growth of such organisms. = = = pollution control = = = = = = = sulfur emission = = = = the burning of marine fuels releases harmful pollutants into the atmosphere. ships burn marine diesel in addition to heavy fuel oil. heavy fuel oil, being the heaviest of refined oils, releases sulfur dioxide when burned. sulfur dioxide emissions have the potential to raise atmospheric and ocean acidity causing harm to marine life. however, heavy fuel oil may only be burned in international waters due to the pollution created. it is commercially advantageous due to the cost effectiveness compared to other marine fuels. it is prospected that heavy fuel oil will be phased out of commercial use by the year 2020 ( smith, 2018 ). = = = = oil and water discharge = = = = water, oil, and other substances collect at the bottom of the ship in what is known as the bilge. bilge water is pumped overboard, but must pass a pollution threshold test of 15 ppm ( parts per million ) of oil to be discharged. water is tested higher concentrations of atmospheric nitrous oxide ( n2o ) are expected to slightly warm earth ' s surface because of increases in radiative forcing. radiative forcing is the difference in the net upward thermal radiation flux from the earth through a transparent atmosphere and radiation through an otherwise identical atmosphere with greenhouse gases. radiative forcing, normally measured in w / m ^ 2, depends on latitude, longitude and altitude, but it is often quoted for the tropopause, about 11 km of altitude for temperate latitudes, or for the top of the atmosphere at around 90 km. for current concentrations of greenhouse gases, the radiative forcing per added n2o molecule is about 230 times larger than the forcing per added carbon dioxide ( co2 ) molecule. this is due to the heavy saturation of the absorption band of the relatively abundant greenhouse gas, co2, compared to the much smaller saturation of the absorption bands of the trace greenhouse gas n2o. but the rate of increase of co2 molecules, about 2. 5 ppm / year ( ppm = part per million by mole ), is about 3000 times larger than the rate of increase of n2o molecules, which has held steady at around 0. 00085 ppm / year since 1985. so, the contribution of nitrous oxide to the annual increase in forcing is 230 / 3000 or about 1 / 13 that of co2. if the main greenhouse gases, co2, ch4 and n2o have contributed about 0. 1 c / decade of the warming observed over the past few decades, this would correspond to about 0. 00064 k per year or 0. 064 k per century of warming from n2o. proposals to place harsh restrictions on nitrous oxide emissions because of warming fears are not justified by these facts. restrictions would cause serious harm ; for example, by jeopardizing world food supplies. subsea engineering and the ability to detect, track and destroy submarines ( anti - submarine warfare ) required the parallel development of a host of marine scientific instrumentation and sensors. visible light is not transferred far underwater, so the medium for transmission of data is primarily acoustic. high - frequency sound is used to measure the depth of the ocean, determine the nature of the seafloor, and detect submerged objects. the higher the frequency, the higher the definition of the data that is returned. sound navigation and ranging or sonar was developed during the first world war to detect submarines, and has been greatly refined through to the present day. submarines similarly use sonar equipment to detect and target other submarines and surface ships, and to detect submerged obstacles such as seamounts that pose a navigational obstacle. simple echo - sounders point straight down and can give an accurate reading of ocean depth ( or look up at the underside of sea - ice ). more advanced echo sounders use a fan - shaped beam or sound, or multiple beams to derive highly detailed images of the ocean floor. high power systems can penetrate the soil and seabed rocks to give information about the geology of the seafloor, and are widely used in geophysics for the discovery of hydrocarbons, or for engineering survey. for close - range underwater communications, optical transmission is possible, mainly using blue lasers. these have a high bandwidth compared with acoustic systems, but the range is usually only a few tens of metres, and ideally at night. as well as acoustic communications and navigation, sensors have been developed to measure ocean parameters such as temperature, salinity, oxygen levels and other properties including nitrate levels, levels of trace chemicals and environmental dna. the industry trend has been towards smaller, more accurate and more affordable systems so that they can be purchased and used by university departments and small companies as well as large corporations, research organisations and governments. the sensors and instruments are fitted to autonomous and remotely - operated systems as well as ships, and are enabling these systems to take on tasks that hitherto required an expensive human - crewed platform. manufacture of marine sensors and instruments mainly takes place in asia, europe and north america. products are advertised in specialist journals, and through trade shows such as oceanology international and ocean business which help raise awareness of the products. = = = environmental engineering = = = in every coastal and offshore project, environmental sustainability is an important consideration for the preservation of ocean ecosystems and natural resources. instances in which marine engineers benefit from knowledge of environmental engineering include creation of fisheries, clean planets less massive than about 10 mearth are expected to have no massive h - he atmosphere and a cometary composition ( 50 % rocks, 50 % water, by mass ) provided they formed beyond the snowline of protoplanetary disks. due to inward migration, such planets could be found at any distance between their formation site and the star. if migration stops within the habitable zone, this will produce a new kind of planets, called ocean - planets. ocean - planets typically consist in a silicate core, surrounded by a thick ice mantle, itself covered by a 100 km deep ocean. the existence of ocean - planets raises important astrobiological questions : can life originate on such body, in the absence of continent and ocean - silicate interfaces? what would be the nature of the atmosphere and the geochemical cycles? in this work, we address the fate of hot ocean - planets produced when migration ends at a closer distance. in this case the liquid / gas interface can disappear, and the hot h2o envelope is made of a supercritical fluid. although we do not expect these bodies to harbor life, their detection and identification as water - rich planets would give us insight as to the abundance of hot and, by extrapolation, cool ocean - planets. the standard theory of ideal gases ignores the interaction of the gas particles with the thermal radiation ( photon gas ) that fills the otherwise vacuum space between them. this is an unphysical feature since every material absorbs and radiates thermal energy. this interaction may be important in gases since the latter, unlike solids and liquids are capable of undergoing conspicuous volume changes. taking it into account makes the behaviour of the ideal gases more realistic and removes gibbs ' paradox. cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make the goal of project gauss is to return samples from the dwarf planet ceres. ceres is the most accessible ocean world candidate and the largest reservoir of water in the inner solar system. it shows active cryovolcanism and hydrothermal activities in recent history that resulted in minerals not found in any other planets to date except for earth ' s upper crust. the possible occurrence of recent subsurface ocean on ceres and the complex geochemistry suggest possible past habitability and even the potential for ongoing habitability. aiming to answer a broad spectrum of questions about the origin and evolution of ceres and its potential habitability, gauss will return samples from this possible ocean world for the first time. the project will address the following top - level scientific questions : 1 ) what is the origin of ceres and the origin and transfer of water and other volatiles in the inner solar system? 2 ) what are the physical properties and internal structure of ceres? what do they tell us about the evolutionary and aqueous alteration history of icy dwarf planets? 3 ) what are the astrobiological implications of ceres? was it habitable in the past and is it still today? 4 ) what are the mineralogical connections between ceres and our current collections of primitive meteorites? gauss will first perform a high - resolution global remote sensing investigation, characterizing the geophysical and geochemical properties of ceres. candidate sampling sites will then be identified, and observation campaigns will be run for an in - depth assessment of the candidate sites. once the sampling site is selected, a lander will be deployed on the surface to collect samples and return them to earth in cryogenic conditions that preserves the volatile and organic composition as well as the original physical status as much as possible. Question: Where do oceans absorb gases from? A) sunlight B) atmosphere C) stratosphere D) wind	B) atmosphere
Context: variation in total solar irradiance is thought to have little effect on the earth ' s surface temperature because of the thermal time constant - - the characteristic response time of the earth ' s global surface temperature to changes in forcing. this time constant is large enough to smooth annual variations but not necessarily variations having a longer period such as those due to solar inertial motion ; the magnitude of these surface temperature variations is estimated. a comparison of the sensitivities of methods which allow us to determine the coordinates of a moving hot body is made. their mechanical properties. = = tissue culture = = in many cases, creation of functional tissues and biological structures in vitro requires extensive culturing to promote survival, growth and inducement of functionality. in general, the basic requirements of cells must be maintained in culture, which include oxygen, ph, humidity, temperature, nutrients and osmotic pressure maintenance. tissue engineered cultures also present additional problems in maintaining culture conditions. in standard cell culture, diffusion is often the sole means of nutrient and metabolite transport. however, as a culture becomes larger and more complex, such as the case with engineered organs and whole tissues, other mechanisms must be employed to maintain the culture, such as the creation of capillary networks within the tissue. another issue with tissue culture is introducing the proper factors or stimuli required to induce functionality. in many cases, simple maintenance culture is not sufficient. growth factors, hormones, specific metabolites or nutrients, chemical and physical stimuli are sometimes required. for example, certain cells respond to changes in oxygen tension as part of their normal development, such as chondrocytes, which must adapt to low oxygen conditions or hypoxia during skeletal development. others, such as endothelial cells, respond to shear stress from fluid flow, which is encountered in blood vessels. mechanical stimuli, such as pressure pulses seem to be beneficial to all kind of cardiovascular tissue such as heart valves, blood vessels or pericardium. = = = bioreactors = = = in tissue engineering, a bioreactor is a device that attempts to simulate a physiological environment in order to promote cell or tissue growth in vitro. a physiological environment can consist of many different parameters such as temperature, pressure, oxygen or carbon dioxide concentration, or osmolality of fluid environment, and it can extend to all kinds of biological, chemical or mechanical stimuli. therefore, there are systems that may include the application of forces such as electromagnetic forces, mechanical pressures, or fluid pressures to the tissue. these systems can be two - or three - dimensional setups. bioreactors can be used in both academic and industry applications. general - use and application - specific bioreactors are also commercially available, which may provide static chemical stimulation or a combination of chemical and mechanical stimulation. cell proliferation and differentiation are largely influenced by mechanical and biochemical cues in the surrounding extracellular matrix environment. bioreactors are typically developed to replicate the specific physiological environment of the tissue being grown ( e. g., flex and fluid shearing for heart tissue growth ). this can 10 kgy most food, which is ( with regard to warming ) physically equivalent to water, would warm by only about 2. 5 °c ( 4. 5 °f ). the specialty of processing food by ionizing radiation is the fact, that the energy density per atomic transition is very high, it can cleave molecules and induce ionization ( hence the name ) which cannot be achieved by mere heating. this is the reason for new beneficial effects, however at the same time, for new concerns. the treatment of solid food by ionizing radiation can provide an effect similar to heat pasteurization of liquids, such as milk. however, the use of the term, cold pasteurization, to describe irradiated foods is controversial, because pasteurization and irradiation are fundamentally different processes, although the intended end results can in some cases be similar. detractors of food irradiation have concerns about the health hazards of induced radioactivity. a report for the industry advocacy group american council on science and health entitled " irradiated foods " states : " the types of radiation sources approved for the treatment of foods have specific energy levels well below that which would cause any element in food to become radioactive. food undergoing irradiation does not become any more radioactive than luggage passing through an airport x - ray scanner or teeth that have been x - rayed. " food irradiation is currently permitted by over 40 countries and volumes are estimated to exceed 500, 000 metric tons ( 490, 000 long tons ; 550, 000 short tons ) annually worldwide. food irradiation is essentially a non - nuclear technology ; it relies on the use of ionizing radiation which may be generated by accelerators for electrons and conversion into bremsstrahlung, but which may use also gamma - rays from nuclear decay. there is a worldwide industry for processing by ionizing radiation, the majority by number and by processing power using accelerators. food irradiation is only a niche application compared to medical supplies, plastic materials, raw materials, gemstones, cables and wires, etc. = = accidents = = nuclear accidents, because of the powerful forces involved, are often very dangerous. historically, the first incidents involved fatal radiation exposure. marie curie died from aplastic anemia which resulted from her high levels of exposure. two scientists, an american and canadian respectively, harry daghlian and louis slotin, died after mishandling the same plutonium mass. unlike conventional weapons, the intense light, heat, and explosive force is and their competitive or mutualistic interactions with other species. some ecologists even rely on empirical data from indigenous people that is gathered by ethnobotanists. this information can relay a great deal of information on how the land once was thousands of years ago and how it has changed over that time. the goals of plant ecology are to understand the causes of their distribution patterns, productivity, environmental impact, evolution, and responses to environmental change. plants depend on certain edaphic ( soil ) and climatic factors in their environment but can modify these factors too. for example, they can change their environment ' s albedo, increase runoff interception, stabilise mineral soils and develop their organic content, and affect local temperature. plants compete with other organisms in their ecosystem for resources. they interact with their neighbours at a variety of spatial scales in groups, populations and communities that collectively constitute vegetation. regions with characteristic vegetation types and dominant plants as well as similar abiotic and biotic factors, climate, and geography make up biomes like tundra or tropical rainforest. herbivores eat plants, but plants can defend themselves and some species are parasitic or even carnivorous. other organisms form mutually beneficial relationships with plants. for example, mycorrhizal fungi and rhizobia provide plants with nutrients in exchange for food, ants are recruited by ant plants to provide protection, honey bees, bats and other animals pollinate flowers and humans and other animals act as dispersal vectors to spread spores and seeds. = = = plants, climate and environmental change = = = plant responses to climate and other environmental changes can inform our understanding of how these changes affect ecosystem function and productivity. for example, plant phenology can be a useful proxy for temperature in historical climatology, and the biological impact of climate change and global warming. palynology, the analysis of fossil pollen deposits in sediments from thousands or millions of years ago allows the reconstruction of past climates. estimates of atmospheric co2 concentrations since the palaeozoic have been obtained from stomatal densities and the leaf shapes and sizes of ancient land plants. ozone depletion can expose plants to higher levels of ultraviolet radiation - b ( uv - b ), resulting in lower growth rates. moreover, information from studies of community ecology, plant systematics, and taxonomy is essential to understanding vegetation change, habitat destruction and species extinction. = = genetics = = inheritance in plants follows the same fundamental principles of genetics as in other multicellular organisms. gregor mendel discovered the genetic laws of inheritance by studying is also higher at high temperature, as shown by carnot ' s theorem. in a conventional metallic engine, much of the energy released from the fuel must be dissipated as waste heat in order to prevent a meltdown of the metallic parts. despite all of these desirable properties, such engines are not in production because the manufacturing of ceramic parts in the requisite precision and durability is difficult. imperfection in the ceramic leads to cracks, which can lead to potentially dangerous equipment failure. such engines are possible in laboratory settings, but mass - production is not feasible with current technology. work is being done in developing ceramic parts for gas turbine engines. currently, even blades made of advanced metal alloys used in the engines ' hot section require cooling and careful limiting of operating temperatures. turbine engines made with ceramics could operate more efficiently, giving aircraft greater range and payload for a set amount of fuel. recently, there have been advances in ceramics which include bio - ceramics, such as dental implants and synthetic bones. hydroxyapatite, the natural mineral component of bone, has been made synthetically from a number of biological and chemical sources and can be formed into ceramic materials. orthopedic implants made from these materials bond readily to bone and other tissues in the body without rejection or inflammatory reactions. because of this, they are of great interest for gene delivery and tissue engineering scaffolds. most hydroxyapatite ceramics are very porous and lack mechanical strength and are used to coat metal orthopedic devices to aid in forming a bond to bone or as bone fillers. they are also used as fillers for orthopedic plastic screws to aid in reducing the inflammation and increase absorption of these plastic materials. work is being done to make strong, fully dense nano crystalline hydroxyapatite ceramic materials for orthopedic weight bearing devices, replacing foreign metal and plastic orthopedic materials with a synthetic, but naturally occurring, bone mineral. ultimately these ceramic materials may be used as bone replacements or with the incorporation of protein collagens, synthetic bones. durable actinide - containing ceramic materials have many applications such as in nuclear fuels for burning excess pu and in chemically - inert sources of alpha irradiation for power supply of unmanned space vehicles or to produce electricity for microelectronic devices. both use and disposal of radioactive actinides require their immobilization in a durable host material. nuclear waste long - lived radionuclides such as actinides are immobilized using chemical ##tering - based methods are simple ( " sinter " has roots in the english " cinder " ). the firing is done at a temperature below the melting point of the ceramic. once a roughly - held - together object called a " green body " is made, it is fired in a kiln, where atomic and molecular diffusion processes give rise to significant changes in the primary microstructural features. this includes the gradual elimination of porosity, which is typically accompanied by a net shrinkage and overall densification of the component. thus, the pores in the object may close up, resulting in a denser product of significantly greater strength and fracture toughness. another major change in the body during the firing or sintering process will be the establishment of the polycrystalline nature of the solid. significant grain growth tends to occur during sintering, with this growth depending on temperature and duration of the sintering process. the growth of grains will result in some form of grain size distribution, which will have a significant impact on the ultimate physical properties of the material. in particular, abnormal grain growth in which certain grains grow very large in a matrix of finer grains will significantly alter the physical and mechanical properties of the obtained ceramic. in the sintered body, grain sizes are a product of the thermal processing parameters as well as the initial particle size, or possibly the sizes of aggregates or particle clusters which arise during the initial stages of processing. the ultimate microstructure ( and thus the physical properties ) of the final product will be limited by and subject to the form of the structural template or precursor which is created in the initial stages of chemical synthesis and physical forming. hence the importance of chemical powder and polymer processing as it pertains to the synthesis of industrial ceramics, glasses and glass - ceramics. there are numerous possible refinements of the sintering process. some of the most common involve pressing the green body to give the densification a head start and reduce the sintering time needed. sometimes organic binders such as polyvinyl alcohol are added to hold the green body together ; these burn out during the firing ( at 200 – 350 °c ). sometimes organic lubricants are added during pressing to increase densification. it is common to combine these, and add binders and lubricants to a powder, then press. ( the formulation of these organic chemical additives is an art in itself. this is particularly important in the manufacture of high performance ceramics such as those used by the billions for behavioral responses to different stimuli, one can understand something about how those stimuli are processed. lewandowski & strohmetz ( 2009 ) reviewed a collection of innovative uses of behavioral measurement in psychology including behavioral traces, behavioral observations, and behavioral choice. behavioral traces are pieces of evidence that indicate behavior occurred, but the actor is not present ( e. g., litter in a parking lot or readings on an electric meter ). behavioral observations involve the direct witnessing of the actor engaging in the behavior ( e. g., watching how close a person sits next to another person ). behavioral choices are when a person selects between two or more options ( e. g., voting behavior, choice of a punishment for another participant ). reaction time. the time between the presentation of a stimulus and an appropriate response can indicate differences between two cognitive processes, and can indicate some things about their nature. for example, if in a search task the reaction times vary proportionally with the number of elements, then it is evident that this cognitive process of searching involves serial instead of parallel processing. psychophysical responses. psychophysical experiments are an old psychological technique, which has been adopted by cognitive psychology. they typically involve making judgments of some physical property, e. g. the loudness of a sound. correlation of subjective scales between individuals can show cognitive or sensory biases as compared to actual physical measurements. some examples include : sameness judgments for colors, tones, textures, etc. threshold differences for colors, tones, textures, etc. eye tracking. this methodology is used to study a variety of cognitive processes, most notably visual perception and language processing. the fixation point of the eyes is linked to an individual ' s focus of attention. thus, by monitoring eye movements, we can study what information is being processed at a given time. eye tracking allows us to study cognitive processes on extremely short time scales. eye movements reflect online decision making during a task, and they provide us with some insight into the ways in which those decisions may be processed. = = = brain imaging = = = brain imaging involves analyzing activity within the brain while performing various tasks. this allows us to link behavior and brain function to help understand how information is processed. different types of imaging techniques vary in their temporal ( time - based ) and spatial ( location - based ) resolution. brain imaging is often used in cognitive neuroscience. single - photon emission computed tomography and positron emission tomography. spect and pet use radioactive isotopes, which are injected into the subject ' s bloodstream while co - coculturing epithelial and adipocyte cells. the hystem kit is another 3 - d platform containing ecm components and hyaluronic acid that has been used for cancer research. additionally, hydrogel constituents can be chemically modified to assist in crosslinking and enhance their mechanical properties. = = tissue culture = = in many cases, creation of functional tissues and biological structures in vitro requires extensive culturing to promote survival, growth and inducement of functionality. in general, the basic requirements of cells must be maintained in culture, which include oxygen, ph, humidity, temperature, nutrients and osmotic pressure maintenance. tissue engineered cultures also present additional problems in maintaining culture conditions. in standard cell culture, diffusion is often the sole means of nutrient and metabolite transport. however, as a culture becomes larger and more complex, such as the case with engineered organs and whole tissues, other mechanisms must be employed to maintain the culture, such as the creation of capillary networks within the tissue. another issue with tissue culture is introducing the proper factors or stimuli required to induce functionality. in many cases, simple maintenance culture is not sufficient. growth factors, hormones, specific metabolites or nutrients, chemical and physical stimuli are sometimes required. for example, certain cells respond to changes in oxygen tension as part of their normal development, such as chondrocytes, which must adapt to low oxygen conditions or hypoxia during skeletal development. others, such as endothelial cells, respond to shear stress from fluid flow, which is encountered in blood vessels. mechanical stimuli, such as pressure pulses seem to be beneficial to all kind of cardiovascular tissue such as heart valves, blood vessels or pericardium. = = = bioreactors = = = in tissue engineering, a bioreactor is a device that attempts to simulate a physiological environment in order to promote cell or tissue growth in vitro. a physiological environment can consist of many different parameters such as temperature, pressure, oxygen or carbon dioxide concentration, or osmolality of fluid environment, and it can extend to all kinds of biological, chemical or mechanical stimuli. therefore, there are systems that may include the application of forces such as electromagnetic forces, mechanical pressures, or fluid pressures to the tissue. these systems can be two - or three - dimensional setups. bioreactors can be used in both academic and industry applications. general - use and application - specific bioreactors are also commercially available, which may provide static chemical stimulation or a material. silicon nitride parts are used in ceramic ball bearings. their higher hardness means that they are much less susceptible to wear and can offer more than triple lifetimes. they also deform less under load meaning they have less contact with the bearing retainer walls and can roll faster. in very high speed applications, heat from friction during rolling can cause problems for metal bearings ; problems which are reduced by the use of ceramics. ceramics are also more chemically resistant and can be used in wet environments where steel bearings would rust. the major drawback to using ceramics is a significantly higher cost. in many cases their electrically insulating properties may also be valuable in bearings. in the early 1980s, toyota researched production of an adiabatic ceramic engine which can run at a temperature of over 6000 °f ( 3300 °c ). ceramic engines do not require a cooling system and hence allow a major weight reduction and therefore greater fuel efficiency. fuel efficiency of the engine is also higher at high temperature, as shown by carnot ' s theorem. in a conventional metallic engine, much of the energy released from the fuel must be dissipated as waste heat in order to prevent a meltdown of the metallic parts. despite all of these desirable properties, such engines are not in production because the manufacturing of ceramic parts in the requisite precision and durability is difficult. imperfection in the ceramic leads to cracks, which can lead to potentially dangerous equipment failure. such engines are possible in laboratory settings, but mass - production is not feasible with current technology. work is being done in developing ceramic parts for gas turbine engines. currently, even blades made of advanced metal alloys used in the engines ' hot section require cooling and careful limiting of operating temperatures. turbine engines made with ceramics could operate more efficiently, giving aircraft greater range and payload for a set amount of fuel. recently, there have been advances in ceramics which include bio - ceramics, such as dental implants and synthetic bones. hydroxyapatite, the natural mineral component of bone, has been made synthetically from a number of biological and chemical sources and can be formed into ceramic materials. orthopedic implants made from these materials bond readily to bone and other tissues in the body without rejection or inflammatory reactions. because of this, they are of great interest for gene delivery and tissue engineering scaffolds. most hydroxyapatite ceramics are very porous and lack mechanical strength and are used to coat metal orthopedic devices to aid in forming a bond to bone or as bone fillers. they are Question: Engaging in relatively simple behaviors helps maintain a nearly constant body temperature for organisms classified as what? A) ectotherms B) placoderms C) photophores D) endotherms	A) ectotherms
Context: are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its the operating room, the anesthesiology physician also serves the same function in the labor and delivery ward, and some are specialized in critical medicine. emergency medicine is concerned with the diagnosis and treatment of acute or life - threatening conditions, including trauma, surgical, medical, pediatric, and psychiatric emergencies. family medicine, family practice, general practice or primary care is, in many countries, the first port - of - call for patients with non - emergency medical problems. family physicians often provide services across a broad range of settings including office based practices, emergency department coverage, inpatient care, and nursing home care. medical genetics is concerned with the diagnosis and management of hereditary disorders. neurology is concerned with diseases of the nervous system. in the uk, neurology is a subspecialty of general medicine. obstetrics and gynecology ( often abbreviated as ob / gyn ( american english ) or obs & gynae ( british english ) ) are concerned respectively with childbirth and the female reproductive and associated organs. reproductive medicine and fertility medicine are generally practiced by gynecological specialists. pediatrics ( ae ) or paediatrics ( be ) is devoted to the care of infants, children, and adolescents. like internal medicine, there are many pediatric subspecialties for specific age ranges, organ systems, disease classes, and sites of care delivery. pharmaceutical medicine is the medical scientific discipline concerned with the discovery, development, evaluation, registration, monitoring and medical aspects of marketing of medicines for the benefit of patients and public health. physical medicine and rehabilitation ( or physiatry ) is concerned with functional improvement after injury, illness, or congenital disorders. podiatric medicine is the study of, diagnosis, and medical and surgical treatment of disorders of the foot, ankle, lower limb, hip and lower back. preventive medicine is the branch of medicine concerned with preventing disease. community health or public health is an aspect of health services concerned with threats to the overall health of a community based on population health analysis. psychiatry is the branch of medicine concerned with the bio - psycho - social study of the etiology, diagnosis, treatment and prevention of cognitive, perceptual, emotional and behavioral disorders. related fields include psychotherapy and clinical psychology. = = = interdisciplinary fields = = = some interdisciplinary sub - specialties of medicine include : addiction medicine deals with the treatment of addiction. aerospace medicine deals with medical problems related to flying and space travel. biomedical engineering is a field dealing with the application of engineering principles to medical practice ##ry. immunology is the study of the immune system, which includes the innate and adaptive immune system in humans, for example. lifestyle medicine is the study of the chronic conditions, and how to prevent, treat and reverse them. medical physics is the study of the applications of physics principles in medicine. microbiology is the study of microorganisms, including protozoa, bacteria, fungi, and viruses. molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic material. neuroscience includes those disciplines of science that are related to the study of the nervous system. a main focus of neuroscience is the biology and physiology of the human brain and spinal cord. some related clinical specialties include neurology, neurosurgery and psychiatry. nutrition science ( theoretical focus ) and dietetics ( practical focus ) is the study of the relationship of food and drink to health and disease, especially in determining an optimal diet. medical nutrition therapy is done by dietitians and is prescribed for diabetes, cardiovascular diseases, weight and eating disorders, allergies, malnutrition, and neoplastic diseases. pathology as a science is the study of disease – the causes, course, progression and resolution thereof. pharmacology is the study of drugs and their actions. photobiology is the study of the interactions between non - ionizing radiation and living organisms. physiology is the study of the normal functioning of the body and the underlying regulatory mechanisms. radiobiology is the study of the interactions between ionizing radiation and living organisms. toxicology is the study of hazardous effects of drugs and poisons. = = = specialties = = = in the broadest meaning of " medicine ", there are many different specialties. in the uk, most specialities have their own body or college, which has its own entrance examination. these are collectively known as the royal colleges, although not all currently use the term " royal ". the development of a speciality is often driven by new technology ( such as the development of effective anaesthetics ) or ways of working ( such as emergency departments ) ; the new specialty leads to the formation of a unifying body of doctors and the prestige of administering their own examination. within medical circles, specialities usually fit into one of two broad categories : " medicine " and " surgery ". " medicine " refers to the practice of non - operative medicine, and most of its subspecialties require preliminary training in internal medicine. in the uk . most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support , and includes, but is not limited to, the study of epidemics. genetics is the study of genes, and their role in biological inheritance. gynecology is the study of female reproductive system. histology is the study of the structures of biological tissues by light microscopy, electron microscopy and immunohistochemistry. immunology is the study of the immune system, which includes the innate and adaptive immune system in humans, for example. lifestyle medicine is the study of the chronic conditions, and how to prevent, treat and reverse them. medical physics is the study of the applications of physics principles in medicine. microbiology is the study of microorganisms, including protozoa, bacteria, fungi, and viruses. molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic material. neuroscience includes those disciplines of science that are related to the study of the nervous system. a main focus of neuroscience is the biology and physiology of the human brain and spinal cord. some related clinical specialties include neurology, neurosurgery and psychiatry. nutrition science ( theoretical focus ) and dietetics ( practical focus ) is the study of the relationship of food and drink to health and disease, especially in determining an optimal diet. medical nutrition therapy is done by dietitians and is prescribed for diabetes, cardiovascular diseases, weight and eating disorders, allergies, malnutrition, and neoplastic diseases. pathology as a science is the study of disease – the causes, course, progression and resolution thereof. pharmacology is the study of drugs and their actions. photobiology is the study of the interactions between non - ionizing radiation and living organisms. physiology is the study of the normal functioning of the body and the underlying regulatory mechanisms. radiobiology is the study of the interactions between ionizing radiation and living organisms. toxicology is the study of hazardous effects of drugs and poisons. = = = specialties = = = in the broadest meaning of " medicine ", there are many different specialties. in the uk, most specialities have their own body or college, which has its own entrance examination. these are collectively known as the royal colleges, although not all currently use the term " royal ". the development of a speciality is often driven by new technology ( such as the development of effective anaesthetics ) or ways of working ( such as emergency departments ) ; the new specialty leads to the formation of a unifying body of the manufacturer. one common distinction is by nominal pore size. it describes the maximum pore size distribution and gives only vague information about the retention capacity of a membrane. the exclusion limit or " cut - off " of the membrane is usually specified in the form of nmwc ( nominal molecular weight cut - off, or mwco, molecular weight cut off, with units in dalton ). it is defined as the minimum molecular weight of a globular molecule that is retained to 90 % by the membrane. the cut - off, depending on the method, can by converted to so - called d90, which is then expressed in a metric unit. in practice the mwco of the membrane should be at least 20 % lower than the molecular weight of the molecule that is to be separated. using track etched mica membranes beck and schultz demonstrated that hindered diffusion of molecules in pores can be described by the rankin equation. filter membranes are divided into four classes according to pore size : the form and shape of the membrane pores are highly dependent on the manufacturing process and are often difficult to specify. therefore, for characterization, test filtrations are carried out and the pore diameter refers to the diameter of the smallest particles which could not pass through the membrane. the rejection can be determined in various ways and provides an indirect measurement of the pore size. one possibility is the filtration of macromolecules ( often dextran, polyethylene glycol or albumin ), another is measurement of the cut - off by gel permeation chromatography. these methods are used mainly to measure membranes for ultrafiltration applications. another testing method is the filtration of particles with defined size and their measurement with a particle sizer or by laser induced breakdown spectroscopy ( libs ). a vivid characterization is to measure the rejection of dextran blue or other colored molecules. the retention of bacteriophage and bacteria, the so - called " bacteria challenge test ", can also provide information about the pore size. to determine the pore diameter, physical methods such as porosimeter ( mercury, liquid - liquid porosimeter and bubble point test ) are also used, but a certain form of the pores ( such as cylindrical or concatenated spherical holes ) is assumed. such methods are used for membranes whose pore geometry does not match the ideal, and we get " nominal " pore diameter, which characterizes the membrane, but does not necessarily reflect its actual filt within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with sciences are the clinical diagnostic services that apply laboratory techniques to diagnosis and management of patients. in the united states, these services are supervised by a pathologist. the personnel that work in these medical laboratory departments are technically trained staff who do not hold medical degrees, but who usually hold an undergraduate medical technology degree, who actually perform the tests, assays, and procedures needed for providing the specific services. subspecialties include transfusion medicine, cellular pathology, clinical chemistry, hematology, clinical microbiology and clinical immunology. clinical neurophysiology is concerned with testing the physiology or function of the central and peripheral aspects of the nervous system. these kinds of tests can be divided into recordings of : ( 1 ) spontaneous or continuously running electrical activity, or ( 2 ) stimulus evoked responses. subspecialties include electroencephalography, electromyography, evoked potential, nerve conduction study and polysomnography. sometimes these tests are performed by techs without a medical degree, but the interpretation of these tests is done by a medical professional. diagnostic radiology is concerned with imaging of the body, e. g. by x - rays, x - ray computed tomography, ultrasonography, and nuclear magnetic resonance tomography. interventional radiologists can access areas in the body under imaging for an intervention or diagnostic sampling. nuclear medicine is concerned with studying human organ systems by administering radiolabelled substances ( radiopharmaceuticals ) to the body, which can then be imaged outside the body by a gamma camera or a pet scanner. each radiopharmaceutical consists of two parts : a tracer that is specific for the function under study ( e. g., neurotransmitter pathway, metabolic pathway, blood flow, or other ), and a radionuclide ( usually either a gamma - emitter or a positron emitter ). there is a degree of overlap between nuclear medicine and radiology, as evidenced by the emergence of combined devices such as the pet / ct scanner. pathology as a medical specialty is the branch of medicine that deals with the study of diseases and the morphologic, physiologic changes produced by them. as a diagnostic specialty, pathology can be considered the basis of modern scientific medical knowledge and plays a large role in evidence - based medicine. many modern molecular tests such as flow cytometry, polymerase chain reaction ( pcr ), immunohistochemistry, cytogenetic cross - fertilization that takes place among the various fields. psychology differs from biology and neuroscience in that it is primarily concerned with the interaction of mental processes and behaviour, and of the overall processes of a system, and not simply the biological or neural processes themselves, though the subfield of neuropsychology combines the study of the actual neural processes with the study of the mental effects they have subjectively produced. many people associate psychology with clinical psychology, which focuses on assessment and treatment of problems in living and psychopathology. in reality, psychology has myriad specialties including social psychology, developmental psychology, cognitive psychology, educational psychology, industrial - organizational psychology, mathematical psychology, neuropsychology, and quantitative analysis of behaviour. psychology is a very broad science that is rarely tackled as a whole, major block. although some subfields encompass a natural science base and a social science application, others can be clearly distinguished as having little to do with the social sciences or having a lot to do with the social sciences. for example, biological psychology is considered a natural science with a social scientific application ( as is clinical medicine ), social and occupational psychology are, generally speaking, purely social sciences, whereas neuropsychology is a natural science that lacks application out of the scientific tradition entirely. in british universities, emphasis on what tenet of psychology a student has studied and / or concentrated is communicated through the degree conferred : bpsy indicates a balance between natural and social sciences, bsc indicates a strong ( or entire ) scientific concentration, whereas a ba underlines a majority of social science credits. this is not always necessarily the case however, and in many uk institutions students studying the bpsy, bsc, and ba follow the same curriculum as outlined by the british psychological society and have the same options of specialism open to them regardless of whether they choose a balance, a heavy science basis, or heavy social science basis to their degree. if they applied to read the ba. for example, but specialized in heavily science - based modules, then they will still generally be awarded the ba. = = = sociology = = = sociology is the systematic study of society, individuals ' relationship to their societies, the consequences of difference, and other aspects of human social action. the meaning of the word comes from the suffix - logy, which means " study of ", derived from ancient greek, and the stem soci -, which is from the latin word socius, meaning " companion ", or society in general. auguste comte ( 1798 – 1857 ) coined the term most responsible physician ( mrp ) or attending physician is also used interchangeably to describe this role. laser medicine involves the use of lasers in the diagnostics or treatment of various conditions. many other health science fields, e. g. dietetics medical ethics deals with ethical and moral principles that apply values and judgments to the practice of medicine. medical humanities includes the humanities ( literature, philosophy, ethics, history and religion ), social science ( anthropology, cultural studies, psychology, sociology ), and the arts ( literature, theater, film, and visual arts ) and their application to medical education and practice. nosokinetics is the science / subject of measuring and modelling the process of care in health and social care systems. nosology is the classification of diseases for various purposes. occupational medicine is the provision of health advice to organizations and individuals to ensure that the highest standards of health and safety at work can be achieved and maintained. pain management ( also called pain medicine, or algiatry ) is the medical discipline concerned with the relief of pain. pharmacogenomics is a form of individualized medicine. podiatric medicine is the study of, diagnosis, and medical treatment of disorders of the foot, ankle, lower limb, hip and lower back. sexual medicine is concerned with diagnosing, assessing and treating all disorders related to sexuality. sports medicine deals with the treatment and prevention and rehabilitation of sports / exercise injuries such as muscle spasms, muscle tears, injuries to ligaments ( ligament tears or ruptures ) and their repair in athletes, amateur and professional. therapeutics is the field, more commonly referenced in earlier periods of history, of the various remedies that can be used to treat disease and promote health. travel medicine or emporiatrics deals with health problems of international travelers or travelers across highly different environments. tropical medicine deals with the prevention and treatment of tropical diseases. it is studied separately in temperate climates where those diseases are quite unfamiliar to medical practitioners and their local clinical needs. urgent care focuses on delivery of unscheduled, walk - in care outside of the hospital emergency department for injuries and illnesses that are not severe enough to require care in an emergency department. in some jurisdictions this function is combined with the emergency department. veterinary medicine ; veterinarians apply similar techniques as physicians to the care of non - human animals. wilderness medicine entails the practice of medicine in the wild, where conventional medical facilities may not be available. = = education and legal controls = = medical education and training varies around Question: Meningitis is an infection of the membranes that cover the brain and what else? A) notochord B) spinal cord C) liver D) umbilical cord	B) spinal cord
Context: generally, dead - end filtration is used for feasibility studies on a laboratory scale. the dead - end membranes are relatively easy to fabricate which reduces the cost of the separation process. the dead - end membrane separation process is easy to implement and the process is usually cheaper than cross - flow membrane filtration. the dead - end filtration process is usually a batch - type process, where the filtering solution is loaded ( or slowly fed ) into the membrane device, which then allows passage of some particles subject to the driving force. the main disadvantage of dead - end filtration is the extensive membrane fouling and concentration polarization. the fouling is usually induced faster at higher driving forces. membrane fouling and particle retention in a feed solution also builds up a concentration gradients and particle backflow ( concentration polarization ). the tangential flow devices are more cost and labor - intensive, but they are less susceptible to fouling due to the sweeping effects and high shear rates of the passing flow. the most commonly used synthetic membrane devices ( modules ) are flat sheets / plates, spiral wounds, and hollow fibers. flat membranes used in filtration and separation processes can be enhanced with surface patterning, where microscopic structures are introduced to improve performance. these patterns increase surface area, optimize water flow, and reduce fouling, leading to higher permeability and longer membrane lifespan. research has shown that such modifications can significantly enhance efficiency in water purification, energy applications, and industrial separations. flat plates are usually constructed as circular thin flat membrane surfaces to be used in dead - end geometry modules. spiral wounds are constructed from similar flat membranes but in the form of a " pocket " containing two membrane sheets separated by a highly porous support plate. several such pockets are then wound around a tube to create a tangential flow geometry and to reduce membrane fouling. hollow fiber modules consist of an assembly of self - supporting fibers with dense skin separation layers, and a more open matrix helping to withstand pressure gradients and maintain structural integrity. the hollow fiber modules can contain up to 10, 000 fibers ranging from 200 to 2500 μm in diameter ; the main advantage of hollow fiber modules is the very large surface area within an enclosed volume, increasing the efficiency of the separation process. the disc tube module uses a cross - flow geometry and consists of a pressure tube and hydraulic discs, which are held by a central tension rod, and membrane cushions that lie between two discs. = = membrane performance and governing equations = = the selection of synthetic membranes oil umbrella ) ; for calculating the time of death ( allowing for weather and insect activity ) ; described how to wash and examine the dead body to ascertain the reason for death. at that time the book had described methods for distinguishing between suicide and faked suicide. he wrote the book on forensics stating that all wounds or dead bodies should be examined, not avoided. the book became the first form of literature to help determine the cause of death. in one of song ci ' s accounts ( washing away of wrongs ), the case of a person murdered with a sickle was solved by an investigator who instructed each suspect to bring his sickle to one location. ( he realized it was a sickle by testing various blades on an animal carcass and comparing the wounds. ) flies, attracted by the smell of blood, eventually gathered on a single sickle. in light of this, the owner of that sickle confessed to the murder. the book also described how to distinguish between a drowning ( water in the lungs ) and strangulation ( broken neck cartilage ), and described evidence from examining corpses to determine if a death was caused by murder, suicide or accident. methods from around the world involved saliva and examination of the mouth and tongue to determine innocence or guilt, as a precursor to the polygraph test. in ancient india, some suspects were made to fill their mouths with dried rice and spit it back out. similarly, in ancient china, those accused of a crime would have rice powder placed in their mouths. in ancient middle - eastern cultures, the accused were made to lick hot metal rods briefly. it is thought that these tests had some validity since a guilty person would produce less saliva and thus have a drier mouth ; the accused would be considered guilty if rice was sticking to their mouths in abundance or if their tongues were severely burned due to lack of shielding from saliva. = = education and training = = initial glance, forensic intelligence may appear as a nascent facet of forensic science facilitated by advancements in information technologies such as computers, databases, and data - flow management software. however, a more profound examination reveals that forensic intelligence represents a genuine and emerging inclination among forensic practitioners to actively participate in investigative and policing strategies. in doing so, it elucidates existing practices within scientific literature, advocating for a paradigm shift from the prevailing conception of forensic science as a conglomerate of disciplines merely aiding the criminal justice system. instead, it urges a perspective that views forensic science as a discipline studying the informative potential of wounds or dead bodies should be examined, not avoided. the book became the first form of literature to help determine the cause of death. in one of song ci ' s accounts ( washing away of wrongs ), the case of a person murdered with a sickle was solved by an investigator who instructed each suspect to bring his sickle to one location. ( he realized it was a sickle by testing various blades on an animal carcass and comparing the wounds. ) flies, attracted by the smell of blood, eventually gathered on a single sickle. in light of this, the owner of that sickle confessed to the murder. the book also described how to distinguish between a drowning ( water in the lungs ) and strangulation ( broken neck cartilage ), and described evidence from examining corpses to determine if a death was caused by murder, suicide or accident. methods from around the world involved saliva and examination of the mouth and tongue to determine innocence or guilt, as a precursor to the polygraph test. in ancient india, some suspects were made to fill their mouths with dried rice and spit it back out. similarly, in ancient china, those accused of a crime would have rice powder placed in their mouths. in ancient middle - eastern cultures, the accused were made to lick hot metal rods briefly. it is thought that these tests had some validity since a guilty person would produce less saliva and thus have a drier mouth ; the accused would be considered guilty if rice was sticking to their mouths in abundance or if their tongues were severely burned due to lack of shielding from saliva. = = education and training = = initial glance, forensic intelligence may appear as a nascent facet of forensic science facilitated by advancements in information technologies such as computers, databases, and data - flow management software. however, a more profound examination reveals that forensic intelligence represents a genuine and emerging inclination among forensic practitioners to actively participate in investigative and policing strategies. in doing so, it elucidates existing practices within scientific literature, advocating for a paradigm shift from the prevailing conception of forensic science as a conglomerate of disciplines merely aiding the criminal justice system. instead, it urges a perspective that views forensic science as a discipline studying the informative potential of traces — remnants of criminal activity. embracing this transformative shift poses a significant challenge for education, necessitating a shift in learners ' mindset to accept concepts and methodologies in forensic intelligence. recent calls advocating for the integration of forensic scientists into the criminal justice system, as well as policing and intelligence missions, undersco the walls of a victim ' s stomach. toxicology, a subfield of forensic chemistry, focuses on detecting and identifying drugs, poisons, and other toxic substances in biological samples. forensic toxicologists work on cases involving drug overdoses, poisoning, and substance abuse. their work is critical in determining whether harmful substances play a role in a person ’ s death or impairment. read more james marsh was the first to apply this new science to the art of forensics. he was called by the prosecution in a murder trial to give evidence as a chemist in 1832. the defendant, john bodle, was accused of poisoning his grandfather with arsenic - laced coffee. marsh performed the standard test by mixing a suspected sample with hydrogen sulfide and hydrochloric acid. while he was able to detect arsenic as yellow arsenic trisulfide, when it was shown to the jury it had deteriorated, allowing the suspect to be acquitted due to reasonable doubt. annoyed by that, marsh developed a much better test. he combined a sample containing arsenic with sulfuric acid and arsenic - free zinc, resulting in arsine gas. the gas was ignited, and it decomposed to pure metallic arsenic, which, when passed to a cold surface, would appear as a silvery - black deposit. so sensitive was the test, known formally as the marsh test, that it could detect as little as one - fiftieth of a milligram of arsenic. he first described this test in the edinburgh philosophical journal in 1836. = = = ballistics and firearms = = = ballistics is " the science of the motion of projectiles in flight ". in forensic science, analysts examine the patterns left on bullets and cartridge casings after being ejected from a weapon. when fired, a bullet is left with indentations and markings that are unique to the barrel and firing pin of the firearm that ejected the bullet. this examination can help scientists identify possible makes and models of weapons connected to a crime. henry goddard at scotland yard pioneered the use of bullet comparison in 1835. he noticed a flaw in the bullet that killed the victim and was able to trace this back to the mold that was used in the manufacturing process. = = = anthropometry = = = the french police officer alphonse bertillon was the first to apply the anthropological technique of anthropometry to law enforcement, thereby creating an identification system based on physical measurements. before that time, criminals could be identified only by name or photograph. dissatisfied with the ad hoc methods used to identify captured reaction to proceed more rapidly without being consumed by it — by reducing the amount of activation energy needed to convert reactants into products. enzymes also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell ' s environment or to signals from other cells. = = = cellular respiration = = = cellular respiration is a set of metabolic reactions and processes that take place in cells to convert chemical energy from nutrients into adenosine triphosphate ( atp ), and then release waste products. the reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. respiration is one of the key ways a cell releases chemical energy to fuel cellular activity. the overall reaction occurs in a series of biochemical steps, some of which are redox reactions. although cellular respiration is technically a combustion reaction, it clearly does not resemble one when it occurs in a cell because of the slow, controlled release of energy from the series of reactions. sugar in the form of glucose is the main nutrient used by animal and plant cells in respiration. cellular respiration involving oxygen is called aerobic respiration, which has four stages : glycolysis, citric acid cycle ( or krebs cycle ), electron transport chain, and oxidative phosphorylation. glycolysis is a metabolic process that occurs in the cytoplasm whereby glucose is converted into two pyruvates, with two net molecules of atp being produced at the same time. each pyruvate is then oxidized into acetyl - coa by the pyruvate dehydrogenase complex, which also generates nadh and carbon dioxide. acetyl - coa enters the citric acid cycle, which takes places inside the mitochondrial matrix. at the end of the cycle, the total yield from 1 glucose ( or 2 pyruvates ) is 6 nadh, 2 fadh2, and 2 atp molecules. finally, the next stage is oxidative phosphorylation, which in eukaryotes, occurs in the mitochondrial cristae. oxidative phosphorylation comprises the electron transport chain, which is a series of four protein complexes that transfer electrons from one complex to another, thereby releasing energy from nadh and fadh2 that is coupled to the pumping of protons ( hydrogen ions ) across the inner mitochondrial membrane ( chemiosmosis ), which generates a proton motive force. energy the surface of the membrane, retentate is removed from the same side further downstream, whereas the permeate flow is tracked on the other side. in dead - end filtration, the direction of the fluid flow is normal to the membrane surface. both flow geometries offer some advantages and disadvantages. generally, dead - end filtration is used for feasibility studies on a laboratory scale. the dead - end membranes are relatively easy to fabricate which reduces the cost of the separation process. the dead - end membrane separation process is easy to implement and the process is usually cheaper than cross - flow membrane filtration. the dead - end filtration process is usually a batch - type process, where the filtering solution is loaded ( or slowly fed ) into the membrane device, which then allows passage of some particles subject to the driving force. the main disadvantage of dead - end filtration is the extensive membrane fouling and concentration polarization. the fouling is usually induced faster at higher driving forces. membrane fouling and particle retention in a feed solution also builds up a concentration gradients and particle backflow ( concentration polarization ). the tangential flow devices are more cost and labor - intensive, but they are less susceptible to fouling due to the sweeping effects and high shear rates of the passing flow. the most commonly used synthetic membrane devices ( modules ) are flat sheets / plates, spiral wounds, and hollow fibers. flat membranes used in filtration and separation processes can be enhanced with surface patterning, where microscopic structures are introduced to improve performance. these patterns increase surface area, optimize water flow, and reduce fouling, leading to higher permeability and longer membrane lifespan. research has shown that such modifications can significantly enhance efficiency in water purification, energy applications, and industrial separations. flat plates are usually constructed as circular thin flat membrane surfaces to be used in dead - end geometry modules. spiral wounds are constructed from similar flat membranes but in the form of a " pocket " containing two membrane sheets separated by a highly porous support plate. several such pockets are then wound around a tube to create a tangential flow geometry and to reduce membrane fouling. hollow fiber modules consist of an assembly of self - supporting fibers with dense skin separation layers, and a more open matrix helping to withstand pressure gradients and maintain structural integrity. the hollow fiber modules can contain up to 10, 000 fibers ranging from 200 to 2500 μm in diameter ; the main advantage of hollow fiber modules is the very large surface area within cell - culture scaffolds the material needed for each application is different, and dependent on the desired mechanical properties of the material. tissue engineering of long bone defects for example, will require a rigid scaffold with a compressive strength similar to that of cortical bone ( 100 - 150 mpa ), which is much higher compared to a scaffold for skin regeneration. there are a few versatile synthetic materials used for many different scaffold applications. one of these commonly used materials is polylactic acid ( pla ), a synthetic polymer. pla – polylactic acid. this is a polyester which degrades within the human body to form lactic acid, a naturally occurring chemical which is easily removed from the body. similar materials are polyglycolic acid ( pga ) and polycaprolactone ( pcl ) : their degradation mechanism is similar to that of pla, but pcl degrades slower and pga degrades faster. pla is commonly combined with pga to create poly - lactic - co - glycolic acid ( plga ). this is especially useful because the degradation of plga can be tailored by altering the weight percentages of pla and pga : more pla – slower degradation, more pga – faster degradation. this tunability, along with its biocompatibility, makes it an extremely useful material for scaffold creation. scaffolds may also be constructed from natural materials : in particular different derivatives of the extracellular matrix have been studied to evaluate their ability to support cell growth. protein based materials – such as collagen, or fibrin, and polysaccharidic materials - like chitosan or glycosaminoglycans ( gags ), have all proved suitable in terms of cell compatibility. among gags, hyaluronic acid, possibly in combination with cross linking agents ( e. g. glutaraldehyde, water - soluble carbodiimide, etc. ), is one of the possible choices as scaffold material. due to the covalent attachment of thiol groups to these polymers, they can crosslink via disulfide bond formation. the use of thiolated polymers ( thiomers ) as scaffold material for tissue engineering was initially introduced at the 4th central european symposium on pharmaceutical technology in vienna 2001. as thiomers are biocompatible, exhibit cellular mimicking properties and efficiently support proliferation and differentiation of various cell types, ##ration fuel cell operations in a temperature gradient membrane distillation = = membrane shapes and flow geometries = = there are two main flow configurations of membrane processes : cross - flow ( or tangential flow ) and dead - end filtrations. in cross - flow filtration the feed flow is tangential to the surface of the membrane, retentate is removed from the same side further downstream, whereas the permeate flow is tracked on the other side. in dead - end filtration, the direction of the fluid flow is normal to the membrane surface. both flow geometries offer some advantages and disadvantages. generally, dead - end filtration is used for feasibility studies on a laboratory scale. the dead - end membranes are relatively easy to fabricate which reduces the cost of the separation process. the dead - end membrane separation process is easy to implement and the process is usually cheaper than cross - flow membrane filtration. the dead - end filtration process is usually a batch - type process, where the filtering solution is loaded ( or slowly fed ) into the membrane device, which then allows passage of some particles subject to the driving force. the main disadvantage of dead - end filtration is the extensive membrane fouling and concentration polarization. the fouling is usually induced faster at higher driving forces. membrane fouling and particle retention in a feed solution also builds up a concentration gradients and particle backflow ( concentration polarization ). the tangential flow devices are more cost and labor - intensive, but they are less susceptible to fouling due to the sweeping effects and high shear rates of the passing flow. the most commonly used synthetic membrane devices ( modules ) are flat sheets / plates, spiral wounds, and hollow fibers. flat membranes used in filtration and separation processes can be enhanced with surface patterning, where microscopic structures are introduced to improve performance. these patterns increase surface area, optimize water flow, and reduce fouling, leading to higher permeability and longer membrane lifespan. research has shown that such modifications can significantly enhance efficiency in water purification, energy applications, and industrial separations. flat plates are usually constructed as circular thin flat membrane surfaces to be used in dead - end geometry modules. spiral wounds are constructed from similar flat membranes but in the form of a " pocket " containing two membrane sheets separated by a highly porous support plate. several such pockets are then wound around a tube to create a tangential flow geometry and to reduce membrane fouling. hollow fiber modules consist of an temperature changes up to 1000 °c. = = processing steps = = the traditional ceramic process generally follows this sequence : milling → batching → mixing → forming → drying → firing → assembly. milling is the process by which materials are reduced from a large size to a smaller size. milling may involve breaking up cemented material ( in which case individual particles retain their shape ) or pulverization ( which involves grinding the particles themselves to a smaller size ). milling is generally done by mechanical means, including attrition ( which is particle - to - particle collision that results in agglomerate break up or particle shearing ), compression ( which applies a forces that results in fracturing ), and impact ( which employs a milling medium or the particles themselves to cause fracturing ). attrition milling equipment includes the wet scrubber ( also called the planetary mill or wet attrition mill ), which has paddles in water creating vortexes in which the material collides and break up. compression mills include the jaw crusher, roller crusher and cone crusher. impact mills include the ball mill, which has media that tumble and fracture the material, or the resonantacoustic mixer. shaft impactors cause particle - to particle attrition and compression. batching is the process of weighing the oxides according to recipes, and preparing them for mixing and drying. mixing occurs after batching and is performed with various machines, such as dry mixing ribbon mixers ( a type of cement mixer ), resonantacoustic mixers, mueller mixers, and pug mills. wet mixing generally involves the same equipment. forming is making the mixed material into shapes, ranging from toilet bowls to spark plug insulators. forming can involve : ( 1 ) extrusion, such as extruding " slugs " to make bricks, ( 2 ) pressing to make shaped parts, ( 3 ) slip casting, as in making toilet bowls, wash basins and ornamentals like ceramic statues. forming produces a " green " part, ready for drying. green parts are soft, pliable, and over time will lose shape. handling the green product will change its shape. for example, a green brick can be " squeezed ", and after squeezing it will stay that way. drying is removing the water or binder from the formed material. spray drying is widely used to prepare powder for pressing operations. other dryers are tunnel dryers and periodic dryers. controlled heat is applied in this two - stage process. first, some references for the breaking strength of fused silica fibers compiled in 1999. Question: What use enzymes to break down foreign matter and dead cells? A) hormones B) lymphocytes C) lysosomes D) lipids	C) lysosomes
Context: or magnitude. magnitudes are always non - negative real numbers, and to any non - zero number there belongs a positive real number, its absolute value. for example, the absolute value of −3 and the absolute value of 3 are both equal to 3. this is written in symbols as \| −3 \| = 3 and \| 3 \| = 3. in general, any arbitrary real value can be specified by its magnitude and its sign. using the standard encoding, any real value is given by the product of the magnitude and the sign in standard encoding. this relation can be generalized to define a sign for complex numbers. since the real and complex numbers both form a field and contain the positive reals, they also contain the reciprocals of the magnitudes of all non - zero numbers. this means that any non - zero number may be multiplied with the reciprocal of its magnitude, that is, divided by its magnitude. it is immediate that the quotient of any non - zero real number by its magnitude yields exactly its sign. by analogy, the sign of a complex number z can be defined as the quotient of z and its magnitude \| z \|. the sign of a complex number is the exponential of the product of its argument with the imaginary unit. represents in some sense its complex argument. this is to be compared to the sign of real numbers, except with e i π = − 1. { \ displaystyle e ^ { i \ pi } = - 1. } for the definition of a complex sign - function. see § complex sign function below. = = = sign functions = = = when dealing with numbers, it is often convenient to have their sign available as a number. this is accomplished by functions that extract the sign of any number, and map it to a predefined value before making it available for further calculations. for example, it might be advantageous to formulate an intricate algorithm for positive values only, and take care of the sign only afterwards. = = = = real sign function = = = = the sign function or signum function extracts the sign of a real number, by mapping the set of real numbers to the set of the three reals { − 1, 0, 1 }. { \ displaystyle \ { - 1, \ ; 0, \ ; 1 \ }. } it can be defined as follows : sgn : r → { − 1, 0, 1 } x ↦ sgn ( x ) = { − 1 if x < 0, 0 if x = 0 to that of a flat crack through the plain matrix. the magnitude of the toughening is determined by the mismatch strain caused by thermal contraction incompatibility and the microfracture resistance of the particle / matrix interface. the toughening becomes noticeable with a narrow size distribution of appropriately sized particles, and researchers typically accept that deflection effects in materials with roughly equiaxial grains may increase the fracture toughness by about twice the grain boundary value. the model reveals that the increase in toughness is dependent on particle shape and the volume fraction of the second phase, with the most effective morphology being the rod of high aspect ratio, which can account for a fourfold increase in fracture toughness. the toughening arises primarily from the twist of the crack front between particles, as indicated by deflection profiles. disc - shaped particles and spheres are less effective in toughening. fracture toughness, regardless of morphology, is determined by the twist of the crack front at its most severe configuration, rather than the initial tilt of the crack front. only for disc - shaped particles does the initial tilting of the crack front provide significant toughening ; however, the twist component still overrides the tilt - derived toughening. additional important features of the deflection analysis include the appearance of asymptotic toughening for the three morphologies at volume fractions in excess of 0. 2. it is also noted that a significant influence on the toughening by spherical particles is exerted by the interparticle spacing distribution ; greater toughening is afforded when spheres are nearly contacting such that twist angles approach π / 2. these predictions provide the basis for the design of high - toughness two - phase ceramic materials. the ideal second phase, in addition to maintaining chemical compatibility, should be present in amounts of 10 to 20 volume percent. greater amounts may diminish the toughness increase due to overlapping particles. particles with high aspect ratios, especially those with rod - shaped morphologies, are most suitable for maximum toughening. this model is often used to determine the factors that contribute to the increase in fracture toughness in ceramics which is ultimately useful in the development of advanced ceramic materials with improved performance. = = theory of chemical processing = = = = = microstructural uniformity = = = in the processing of fine ceramics, the irregular particle sizes and shapes in a typical powder often lead to non - uniform packing morphologies that result in packing density variations in the powder compact. uncontrolled aggl there exists a graph with two vertices x and y such that the ratio of the heat kernels p ( x, x ; t ) / p ( y, y ; t ) does not converge as t goes to infinity. ratio, sulfur from coal or coke fuel reacts with the slag so that the sulfur does not contaminate the iron. coal and coke were cheaper and more abundant fuel. as a result, iron production rose significantly during the last decades of the 18th century. coal converted to coke fueled higher temperature blast furnaces and produced cast iron in much larger amounts than before, allowing the creation of a range of structures such as the iron bridge. cheap coal meant that industry was no longer constrained by water resources driving the mills, although it continued as a valuable source of power. the steam engine helped drain the mines, so more coal reserves could be accessed, and the output of coal increased. the development of the high - pressure steam engine made locomotives possible, and a transport revolution followed. the steam engine which had existed since the early 18th century, was practically applied to both steamboat and railway transportation. the liverpool and manchester railway, the first purpose - built railway line, opened in 1830, the rocket locomotive of robert stephenson being one of its first working locomotives used. manufacture of ships ' pulley blocks by all - metal machines at the portsmouth block mills in 1803 instigated the age of sustained mass production. machine tools used by engineers to manufacture parts began in the first decade of the century, notably by richard roberts and joseph whitworth. the development of interchangeable parts through what is now called the american system of manufacturing began in the firearms industry at the u. s. federal arsenals in the early 19th century, and became widely used by the end of the century. until the enlightenment era, little progress was made in water supply and sanitation and the engineering skills of the romans were largely neglected throughout europe. the first documented use of sand filters to purify the water supply dates to 1804, when the owner of a bleachery in paisley, scotland, john gibb, installed an experimental filter, selling his unwanted surplus to the public. the first treated public water supply in the world was installed by engineer james simpson for the chelsea waterworks company in london in 1829. the first screw - down water tap was patented in 1845 by guest and chrimes, a brass foundry in rotherham. the practice of water treatment soon became mainstream, and the virtues of the system were made starkly apparent after the investigations of the physician john snow during the 1854 broad street cholera outbreak demonstrated the role of the water supply in spreading the cholera epidemic. = = = second industrial revolution ( 1860s – 1914 ) = = = the 19th century saw astonishing developments in transportation, construction, lower limits are found for the disorder resistivity of solid neutron - star matter in the neutron - drip region which is amorphous and heterogeneous in nuclear charge. this temperature - independent resistivity, large compared with that produced by phonon scattering, has direct consequences for theories of neutron - star magnetic field generation and evolution. the kinematic moment of inertia of the rare earth even - even nuclei was calculated using three parametric energy based expression. the plot of kinematic moment of inertia versus nuclear spin shows a better sensitivity to back bending than energy plot. for example an increase in income will shift the demand curve for a normal good outward relative to the origin, as in the figure. all determinants are predominantly taken as constant factors of demand and supply. supply is the relation between the price of a good and the quantity available for sale at that price. it may be represented as a table or graph relating price and quantity supplied. producers, for example business firms, are hypothesised to be profit maximisers, meaning that they attempt to produce and supply the amount of goods that will bring them the highest profit. supply is typically represented as a function relating price and quantity, if other factors are unchanged. that is, the higher the price at which the good can be sold, the more of it producers will supply, as in the figure. the higher price makes it profitable to increase production. just as on the demand side, the position of the supply can shift, say from a change in the price of a productive input or a technical improvement. the " law of supply " states that, in general, a rise in price leads to an expansion in supply and a fall in price leads to a contraction in supply. here as well, the determinants of supply, such as price of substitutes, cost of production, technology applied and various factors inputs of production are all taken to be constant for a specific time period of evaluation of supply. market equilibrium occurs where quantity supplied equals quantity demanded, the intersection of the supply and demand curves in the figure above. at a price below equilibrium, there is a shortage of quantity supplied compared to quantity demanded. this is posited to bid the price up. at a price above equilibrium, there is a surplus of quantity supplied compared to quantity demanded. this pushes the price down. the model of supply and demand predicts that for given supply and demand curves, price and quantity will stabilise at the price that makes quantity supplied equal to quantity demanded. similarly, demand - and - supply theory predicts a new price - quantity combination from a shift in demand ( as to the figure ), or in supply. = = = firms = = = people frequently do not trade directly on markets. instead, on the supply side, they may work in and produce through firms. the most obvious kinds of firms are corporations, partnerships and trusts. according to ronald coase, people begin to organise their production in firms when the costs of doing business becomes lower than doing it on the market. firms combine labour and capital, and can achieve far greater economies of scale ( when in 1712, was not known to have any scientific training. : 32 the application of steam - powered cast iron blowing cylinders for providing pressurized air for blast furnaces lead to a large increase in iron production in the late 18th century. the higher furnace temperatures made possible with steam - powered blast allowed for the use of more lime in blast furnaces, which enabled the transition from charcoal to coke. these innovations lowered the cost of iron, making horse railways and iron bridges practical. the puddling process, patented by henry cort in 1784 produced large scale quantities of wrought iron. hot blast, patented by james beaumont neilson in 1828, greatly lowered the amount of fuel needed to smelt iron. with the development of the high pressure steam engine, the power to weight ratio of steam engines made practical steamboats and locomotives possible. new steel making processes, such as the bessemer process and the open hearth furnace, ushered in an area of heavy engineering in the late 19th century. one of the most famous engineers of the mid - 19th century was isambard kingdom brunel, who built railroads, dockyards and steamships. the industrial revolution created a demand for machinery with metal parts, which led to the development of several machine tools. boring cast iron cylinders with precision was not possible until john wilkinson invented his boring machine, which is considered the first machine tool. other machine tools included the screw cutting lathe, milling machine, turret lathe and the metal planer. precision machining techniques were developed in the first half of the 19th century. these included the use of gigs to guide the machining tool over the work and fixtures to hold the work in the proper position. machine tools and machining techniques capable of producing interchangeable parts lead to large scale factory production by the late 19th century. the united states census of 1850 listed the occupation of " engineer " for the first time with a count of 2, 000. there were fewer than 50 engineering graduates in the u. s. before 1865. the first phd in engineering ( technically, applied science and engineering ) awarded in the united states went to josiah willard gibbs at yale university in 1863 ; it was also the second phd awarded in science in the u. s. in 1870 there were a dozen u. s. mechanical engineering graduates, with that number increasing to 43 per year in 1875. in 1890, there were 6, 000 engineers in civil, mining, mechanical and electrical. there was no chair of applied mechanism and applied mechanics at cambridge until 1875, and no chair of engineering at oxford until at the crack tip when the crack is deflected or the crack plane bows. actual crack tortuosity is obtained through imaging techniques, which allows for the direct input of deflection and bowing angles into the model. the model calculates the average strain energy release rate and compares the resulting increase in fracture toughness to that of a flat crack through the plain matrix. the magnitude of the toughening is determined by the mismatch strain caused by thermal contraction incompatibility and the microfracture resistance of the particle / matrix interface. the toughening becomes noticeable with a narrow size distribution of appropriately sized particles, and researchers typically accept that deflection effects in materials with roughly equiaxial grains may increase the fracture toughness by about twice the grain boundary value. the model reveals that the increase in toughness is dependent on particle shape and the volume fraction of the second phase, with the most effective morphology being the rod of high aspect ratio, which can account for a fourfold increase in fracture toughness. the toughening arises primarily from the twist of the crack front between particles, as indicated by deflection profiles. disc - shaped particles and spheres are less effective in toughening. fracture toughness, regardless of morphology, is determined by the twist of the crack front at its most severe configuration, rather than the initial tilt of the crack front. only for disc - shaped particles does the initial tilting of the crack front provide significant toughening ; however, the twist component still overrides the tilt - derived toughening. additional important features of the deflection analysis include the appearance of asymptotic toughening for the three morphologies at volume fractions in excess of 0. 2. it is also noted that a significant influence on the toughening by spherical particles is exerted by the interparticle spacing distribution ; greater toughening is afforded when spheres are nearly contacting such that twist angles approach π / 2. these predictions provide the basis for the design of high - toughness two - phase ceramic materials. the ideal second phase, in addition to maintaining chemical compatibility, should be present in amounts of 10 to 20 volume percent. greater amounts may diminish the toughness increase due to overlapping particles. particles with high aspect ratios, especially those with rod - shaped morphologies, are most suitable for maximum toughening. this model is often used to determine the factors that contribute to the increase in fracture toughness in ceramics which is ultimately useful in the development of advanced ceramic materials with improved performance. = represent 6. 28 = = = the meaning of the symbol π { \ displaystyle \ pi } was not originally defined as the ratio of circumference to diameter, and at times was used in representations of the 6. 28... constant. early works in circle geometry used the letter π to designate the perimeter ( i. e., circumference ) in different fractional representations of circle constants and in 1697 david gregory used π / ρ ( pi over rho ) to denote the perimeter divided by the radius ( 6. 28... ). subsequently π came to be used as a single symbol to represent the ratios in whole. leonhard euler initially used the single letter π was to denote the constant 6. 28... in his 1727 essay explaining the properties of air. euler would later use the letter π for 3. 14... in his 1736 mechanica and 1748 introductio in analysin infinitorum, though defined as half the circumference of a circle of radius 1 rather than the ratio of circumference to diameter. elsewhere in mechanica, euler instead used the letter π for one - fourth of the circumference of a unit circle, or 1. 57.... usage of the letter π, sometimes for 3. 14... and other times for 6. 28..., became widespread, with the definition varying as late as 1761 ; afterward, π was standardized as being equal to 3. 14.... = = notion using [UNK] = = proponents argue that while use of [UNK] in place of 2π does not change any of the underlying mathematics, it does lead to simpler and more intuitive notation in many areas. michael hartl ' s tau manifesto gives many examples of formulas that are asserted to be clearer where τ is used instead of π. = = = units of angle = = = hartl and robert palais have argued that [UNK] allows radian angles to be expressed more directly and in a way that makes clear the link between the radian measure and rotation around the unit circle. for instance, 3τ / 4 rad can be easily interpreted as 3 / 4 of a turn around the unit circle in contrast with the numerically equal 3π / 2 rad, where the meaning could be obscured, particularly for children and students of mathematics. critics have responded that a full rotation is not necessarily the correct or fundamental reference measure for angles and two other possibilities, the right angle and straight angle Question: What is indicated by the ratio of the output force to the input force in a machine? A) man hours B) magnetic force C) momentum D) mechanical advantage	D) mechanical advantage
Context: cortisol, corticosterone and aldosterone activate full - length glucocorticoid receptor ( gr ) from elephant shark, a cartilaginous fish belonging to the oldest group of jawed vertebrates. activation by aldosterone a mineralocorticoid, indicates partial divergence of elephant shark gr from the mr. progesterone activates elephant shark mr, but not elephant shark gr. progesterone inhibits steroid binding to elephant shark gr, but not to human gr. deletion of the n - terminal domain ( ntd ) from elephant shark gr ( truncated gr ) reduced the response to corticosteroids, while truncated and full - length elephant shark mr had similar responses to corticosteroids. chimeras of elephant shark gr ntd fused to mr dbd + lbd had increased activation by corticosteroids and progesterone compared to full - length elephant shark mr. elephant shark mr ntd fused to gr dbd + lbd had similar activation as full - length elephant shark mr, indicating that activation of human gr by the ntd evolved early in gr divergence from the mr. an oscillation with a period of around 500 kb in guanine and cytosine content ( gc % ) is observed in the dna sequence of human chromosome 21. this oscillation is localized in the rightmost one - eighth region of the chromosome, from 43. 5 mb to 46. 5 mb. five cycles of oscillation are observed in this region with six gc - rich peaks and five gc - poor valleys. the gc - poor valleys comprise regions with low density of cpg islands and, alternating between the two dna strands, low gene density regions. consequently, the long - range oscillation of gc % result in spacing patterns of both cpg island density, and to a lesser extent, gene densities. some properties of the nuclear matter as revealed by cherenkov gluons are discussed. practice, general practice or primary care is, in many countries, the first port - of - call for patients with non - emergency medical problems. family physicians often provide services across a broad range of settings including office based practices, emergency department coverage, inpatient care, and nursing home care. medical genetics is concerned with the diagnosis and management of hereditary disorders. neurology is concerned with diseases of the nervous system. in the uk, neurology is a subspecialty of general medicine. obstetrics and gynecology ( often abbreviated as ob / gyn ( american english ) or obs & gynae ( british english ) ) are concerned respectively with childbirth and the female reproductive and associated organs. reproductive medicine and fertility medicine are generally practiced by gynecological specialists. pediatrics ( ae ) or paediatrics ( be ) is devoted to the care of infants, children, and adolescents. like internal medicine, there are many pediatric subspecialties for specific age ranges, organ systems, disease classes, and sites of care delivery. pharmaceutical medicine is the medical scientific discipline concerned with the discovery, development, evaluation, registration, monitoring and medical aspects of marketing of medicines for the benefit of patients and public health. physical medicine and rehabilitation ( or physiatry ) is concerned with functional improvement after injury, illness, or congenital disorders. podiatric medicine is the study of, diagnosis, and medical and surgical treatment of disorders of the foot, ankle, lower limb, hip and lower back. preventive medicine is the branch of medicine concerned with preventing disease. community health or public health is an aspect of health services concerned with threats to the overall health of a community based on population health analysis. psychiatry is the branch of medicine concerned with the bio - psycho - social study of the etiology, diagnosis, treatment and prevention of cognitive, perceptual, emotional and behavioral disorders. related fields include psychotherapy and clinical psychology. = = = interdisciplinary fields = = = some interdisciplinary sub - specialties of medicine include : addiction medicine deals with the treatment of addiction. aerospace medicine deals with medical problems related to flying and space travel. biomedical engineering is a field dealing with the application of engineering principles to medical practice. clinical pharmacology is concerned with how systems of therapeutics interact with patients. conservation medicine studies the relationship between human and non - human animal health, and environmental conditions. also known as ecological medicine, environmental medicine, or medical geology. disaster medicine deals with medical aspects of emergency preparedness, disaster mitigation also called pain medicine, or algiatry ) is the medical discipline concerned with the relief of pain. pharmacogenomics is a form of individualized medicine. podiatric medicine is the study of, diagnosis, and medical treatment of disorders of the foot, ankle, lower limb, hip and lower back. sexual medicine is concerned with diagnosing, assessing and treating all disorders related to sexuality. sports medicine deals with the treatment and prevention and rehabilitation of sports / exercise injuries such as muscle spasms, muscle tears, injuries to ligaments ( ligament tears or ruptures ) and their repair in athletes, amateur and professional. therapeutics is the field, more commonly referenced in earlier periods of history, of the various remedies that can be used to treat disease and promote health. travel medicine or emporiatrics deals with health problems of international travelers or travelers across highly different environments. tropical medicine deals with the prevention and treatment of tropical diseases. it is studied separately in temperate climates where those diseases are quite unfamiliar to medical practitioners and their local clinical needs. urgent care focuses on delivery of unscheduled, walk - in care outside of the hospital emergency department for injuries and illnesses that are not severe enough to require care in an emergency department. in some jurisdictions this function is combined with the emergency department. veterinary medicine ; veterinarians apply similar techniques as physicians to the care of non - human animals. wilderness medicine entails the practice of medicine in the wild, where conventional medical facilities may not be available. = = education and legal controls = = medical education and training varies around the world. it typically involves entry level education at a university medical school, followed by a period of supervised practice or internship, or residency. this can be followed by postgraduate vocational training. a variety of teaching methods have been employed in medical education, still itself a focus of active research. in canada and the united states of america, a doctor of medicine degree, often abbreviated m. d., or a doctor of osteopathic medicine degree, often abbreviated as d. o. and unique to the united states, must be completed in and delivered from a recognized university. since knowledge, techniques, and medical technology continue to evolve at a rapid rate, many regulatory authorities require continuing medical education. medical practitioners upgrade their knowledge in various ways, including medical journals, seminars, conferences, and online programs. a database of objectives covering medical knowledge, as suggested by national societies across the united states, can be searched at http : / / data. medobjectives diagnosis and management of hereditary disorders. neurology is concerned with diseases of the nervous system. in the uk, neurology is a subspecialty of general medicine. obstetrics and gynecology ( often abbreviated as ob / gyn ( american english ) or obs & gynae ( british english ) ) are concerned respectively with childbirth and the female reproductive and associated organs. reproductive medicine and fertility medicine are generally practiced by gynecological specialists. pediatrics ( ae ) or paediatrics ( be ) is devoted to the care of infants, children, and adolescents. like internal medicine, there are many pediatric subspecialties for specific age ranges, organ systems, disease classes, and sites of care delivery. pharmaceutical medicine is the medical scientific discipline concerned with the discovery, development, evaluation, registration, monitoring and medical aspects of marketing of medicines for the benefit of patients and public health. physical medicine and rehabilitation ( or physiatry ) is concerned with functional improvement after injury, illness, or congenital disorders. podiatric medicine is the study of, diagnosis, and medical and surgical treatment of disorders of the foot, ankle, lower limb, hip and lower back. preventive medicine is the branch of medicine concerned with preventing disease. community health or public health is an aspect of health services concerned with threats to the overall health of a community based on population health analysis. psychiatry is the branch of medicine concerned with the bio - psycho - social study of the etiology, diagnosis, treatment and prevention of cognitive, perceptual, emotional and behavioral disorders. related fields include psychotherapy and clinical psychology. = = = interdisciplinary fields = = = some interdisciplinary sub - specialties of medicine include : addiction medicine deals with the treatment of addiction. aerospace medicine deals with medical problems related to flying and space travel. biomedical engineering is a field dealing with the application of engineering principles to medical practice. clinical pharmacology is concerned with how systems of therapeutics interact with patients. conservation medicine studies the relationship between human and non - human animal health, and environmental conditions. also known as ecological medicine, environmental medicine, or medical geology. disaster medicine deals with medical aspects of emergency preparedness, disaster mitigation and management. diving medicine ( or hyperbaric medicine ) is the prevention and treatment of diving - related problems. evolutionary medicine is a perspective on medicine derived through applying evolutionary theory. forensic medicine deals with medical questions in legal context, such as determination of the time and cause of death, type of weapon used to inflict two types of stars are known to have strong, large scale magnetic fields : the main sequence ap stars and the magnetic white dwarfs. this suggest that the former might be the progenitors of the latter. in order to test this idea, i have carried out a search for large scale magnetic fields in stars with evolutionary states which are intermediate, i. e. in horizontal branch stars and in hot subdwarfs. the influence of a neutrinoless electron to positron conversion on a cooling of strongly magnetized iron white dwarfs is studied. a wide range of opiate painkillers like heroin are obtained by chemical modification of morphine obtained from the opium poppy. popular stimulants come from plants, such as caffeine from coffee, tea and chocolate, and nicotine from tobacco. most alcoholic beverages come from fermentation of carbohydrate - rich plant products such as barley ( beer ), rice ( sake ) and grapes ( wine ). native americans have used various plants as ways of treating illness or disease for thousands of years. this knowledge native americans have on plants has been recorded by enthnobotanists and then in turn has been used by pharmaceutical companies as a way of drug discovery. plants can synthesise coloured dyes and pigments such as the anthocyanins responsible for the red colour of red wine, yellow weld and blue woad used together to produce lincoln green, indoxyl, source of the blue dye indigo traditionally used to dye denim and the artist ' s pigments gamboge and rose madder. sugar, starch, cotton, linen, hemp, some types of rope, wood and particle boards, papyrus and paper, vegetable oils, wax, and natural rubber are examples of commercially important materials made from plant tissues or their secondary products. charcoal, a pure form of carbon made by pyrolysis of wood, has a long history as a metal - smelting fuel, as a filter material and adsorbent and as an artist ' s material and is one of the three ingredients of gunpowder. cellulose, the world ' s most abundant organic polymer, can be converted into energy, fuels, materials and chemical feedstock. products made from cellulose include rayon and cellophane, wallpaper paste, biobutanol and gun cotton. sugarcane, rapeseed and soy are some of the plants with a highly fermentable sugar or oil content that are used as sources of biofuels, important alternatives to fossil fuels, such as biodiesel. sweetgrass was used by native americans to ward off bugs like mosquitoes. these bug repelling properties of sweetgrass were later found by the american chemical society in the molecules phytol and coumarin. = = plant ecology = = plant ecology is the science of the functional relationships between plants and their habitats – the environments where they complete their life cycles. plant ecologists study the composition of local and regional floras, their biodiversity, genetic diversity and fitness, the adaptation of plants to their environment, paper is withdrawn due to errors ( superseded by math. ag / 0604303 ). formula 6. 5 is false. section 6 is false, and the main statement is true only for bundles $ b $ with $ c _ 1 ( b ) $ su ( 2 ) - invariant. Question: Glucocorticoids and mineralocorticoids are the two main types of what in humans? A) corticosteroids B) metabolites C) hormones D) carotenoids	A) corticosteroids
Context: armed with an astrolabe and kepler ' s laws one can arrive at accurate estimates of the orbits of planets. three major planets, venus, earth, and mercury formed out of the solar nebula. a fourth planetesimal, theia, also formed near earth where it collided in a giant impact, rebounding as the planet mars. during this impact earth lost $ { \ approx } 4 $ \ % of its crust and mantle that is now is found on mars and the moon. at the antipode of the giant impact, $ \ approx $ 60 \ % of earth ' s crust, atmosphere, and a large amount of mantle were ejected into space forming the moon. the lost crust never reformed and became the earth ' s ocean basins. the theia impact site corresponds to indian ocean gravitational anomaly on earth and the hellas basin on mars. the dynamics of the giant impact are consistent with the rotational rates and axial tilts of both earth and mars. the giant impact removed sufficient co $ _ 2 $ from earth ' s atmosphere to avoid a runaway greenhouse effect, initiated plate tectonics, and gave life time to form near geothermal vents at the continental margins. mercury formed near venus where on a close approach it was slingshot into the sun ' s convective zone losing 94 \ % of its mass, much of which remains there today. black carbon, from co $ _ 2 $ decomposed by the intense heat, is still found on the surface of mercury. arriving at 616 km / s, mercury dramatically altered the sun ' s rotational energy, explaining both its anomalously slow rotation rate and axial tilt. these results are quantitatively supported by mass balances, the current locations of the terrestrial planets, and the orientations of their major orbital axes. the scientific revolution. aristotle also contributed to theories of the elements and the cosmos. he believed that the celestial bodies ( such as the planets and the sun ) had something called an unmoved mover that put the celestial bodies in motion. aristotle tried to explain everything through mathematics and physics, but sometimes explained things such as the motion of celestial bodies through a higher power such as god. aristotle did not have the technological advancements that would have explained the motion of celestial bodies. in addition, aristotle had many views on the elements. he believed that everything was derived of the elements earth, water, air, fire, and lastly the aether. the aether was a celestial element, and therefore made up the matter of the celestial bodies. the elements of earth, water, air and fire were derived of a combination of two of the characteristics of hot, wet, cold, and dry, and all had their inevitable place and motion. the motion of these elements begins with earth being the closest to " the earth, " then water, air, fire, and finally aether. in addition to the makeup of all things, aristotle came up with theories as to why things did not return to their natural motion. he understood that water sits above earth, air above water, and fire above air in their natural state. he explained that although all elements must return to their natural state, the human body and other living things have a constraint on the elements – thus not allowing the elements making one who they are to return to their natural state. the important legacy of this period included substantial advances in factual knowledge, especially in anatomy, zoology, botany, mineralogy, geography, mathematics and astronomy ; an awareness of the importance of certain scientific problems, especially those related to the problem of change and its causes ; and a recognition of the methodological importance of applying mathematics to natural phenomena and of undertaking empirical research. in the hellenistic age scholars frequently employed the principles developed in earlier greek thought : the application of mathematics and deliberate empirical research, in their scientific investigations. thus, clear unbroken lines of influence lead from ancient greek and hellenistic philosophers, to medieval muslim philosophers and scientists, to the european renaissance and enlightenment, to the secular sciences of the modern day. neither reason nor inquiry began with the ancient greeks, but the socratic method did, along with the idea of forms, give great advances in geometry, logic, and the natural sciences. according to benjamin farrington, former professor of classics at swansea university : " men were weighing for thousands of years before archimedes worked out the the motion of celestial bodies through a higher power such as god. aristotle did not have the technological advancements that would have explained the motion of celestial bodies. in addition, aristotle had many views on the elements. he believed that everything was derived of the elements earth, water, air, fire, and lastly the aether. the aether was a celestial element, and therefore made up the matter of the celestial bodies. the elements of earth, water, air and fire were derived of a combination of two of the characteristics of hot, wet, cold, and dry, and all had their inevitable place and motion. the motion of these elements begins with earth being the closest to " the earth, " then water, air, fire, and finally aether. in addition to the makeup of all things, aristotle came up with theories as to why things did not return to their natural motion. he understood that water sits above earth, air above water, and fire above air in their natural state. he explained that although all elements must return to their natural state, the human body and other living things have a constraint on the elements – thus not allowing the elements making one who they are to return to their natural state. the important legacy of this period included substantial advances in factual knowledge, especially in anatomy, zoology, botany, mineralogy, geography, mathematics and astronomy ; an awareness of the importance of certain scientific problems, especially those related to the problem of change and its causes ; and a recognition of the methodological importance of applying mathematics to natural phenomena and of undertaking empirical research. in the hellenistic age scholars frequently employed the principles developed in earlier greek thought : the application of mathematics and deliberate empirical research, in their scientific investigations. thus, clear unbroken lines of influence lead from ancient greek and hellenistic philosophers, to medieval muslim philosophers and scientists, to the european renaissance and enlightenment, to the secular sciences of the modern day. neither reason nor inquiry began with the ancient greeks, but the socratic method did, along with the idea of forms, give great advances in geometry, logic, and the natural sciences. according to benjamin farrington, former professor of classics at swansea university : " men were weighing for thousands of years before archimedes worked out the laws of equilibrium ; they must have had practical and intuitional knowledge of the principals involved. what archimedes did was to sort out the theoretical implications of this practical knowledge and present the resulting body of knowledge as a logically coherent system. " and again : " with astonishment we find ourselves on the threshold of modern science oscillations of the sun have been used to understand its interior structure. the extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the international community over the past decades. the corot ( convection rotation and planetary transits ) satellite, launched in december 2006, has now measured oscillations and the stellar granulation signature in three main sequence stars that are noticeably hotter than the sun. the oscillation amplitudes are about 1. 5 times as large as those in the sun ; the stellar granulation is up to three times as high. the stellar amplitudes are about 25 % below the theoretic values, providing a measurement of the nonadiabaticity of the process ruling the oscillations in the outer layers of the stars. variation in total solar irradiance is thought to have little effect on the earth ' s surface temperature because of the thermal time constant - - the characteristic response time of the earth ' s global surface temperature to changes in forcing. this time constant is large enough to smooth annual variations but not necessarily variations having a longer period such as those due to solar inertial motion ; the magnitude of these surface temperature variations is estimated. in the year 1598 philipp uffenbach published a printed diptych sundial, which is a forerunner of franz ritters horizantal sundial. uffenbach ' s sundial contains apart from the usual information on a sundial ascending signs of the zodiac, several brigthest stars, an almucantar and most important the oldest gnomonic world map known so far. the sundial is constructed for the polar height of 50 1 / 6 degrees, the height of frankfurt / main the town of his citizenship. mike lockwood and mathew owens discuss how eclipse observations are aiding the development of a climatology of near - earth space observed solar neutrino fluxes are employed to constrain the interior composition of the sun. including the effects of neutrino flavor mixing, the results from homestake, sudbury, and gallium experiments constrain the mg, si, and fe abundances in the solar interior to be within a factor 0. 89 to 1. 34 of the surface values with 68 % confidence. if the o and / or ne abundances are increased in the interior to resolve helioseismic discrepancies with recent standard solar models, then the nominal interior mg, si, and fe abundances are constrained to a range of 0. 83 to 1. 24 relative to the surface. additional research is needed to determine whether the sun ' s interior is metal poor relative to its surface. .... for that reason, they constructed brass globes, as though after the figure of the universe. " the influential theologian and philosopher saint augustine, one of the four great church fathers of the western church, similarly objected to the " fable " of antipodes : but as to the fable that there are antipodes, that is to say, men on the opposite side of the earth, where the sun rises when it sets to us, men who walk with their feet opposite ours that is on no ground credible. and, indeed, it is not affirmed that this has been learned by historical knowledge, but by scientific conjecture, on the ground that the earth is suspended within the concavity of the sky, and that it has as much room on the one side of it as on the other : hence they say that the part that is beneath must also be inhabited. but they do not remark that, although it be supposed or scientifically demonstrated that the world is of a round and spherical form, yet it does not follow that the other side of the earth is bare of water ; nor even, though it be bare, does it immediately follow that it is peopled. for scripture, which proves the truth of its historical statements by the accomplishment of its prophecies, gives no false information ; and it is too absurd to say, that some men might have taken ship and traversed the whole wide ocean, and crossed from this side of the world to the other, and that thus even the inhabitants of that distant region are descended from that one first man. some historians do not view augustine ' s scriptural commentaries as endorsing any particular cosmological model, endorsing instead the view that augustine shared the common view of his contemporaries that the earth is spherical, in line with his endorsement of science in de genesi ad litteram. c. p. e. nothaft, responding to writers like leo ferrari who described augustine as endorsing a flat earth, says that "... other recent writers on the subject treat augustine ' s acceptance of the earth ' s spherical shape as a well - established fact ". while it always remained a minority view, from the mid - fourth to the seventh centuries ad, the flat - earth view experienced a revival, around the time when diodorus of tarsus founded the exegetical school known as the school of antioch, which sought to counter what he saw as the pagan cosmology of the greeks with a return to the traditional cosmology. the writings Question: What keeps the earth orbiting the sun? A) strong nuclear force B) weak nuclear force C) gravity D) magnetic force	C) gravity
Context: beacon transmits two signals simultaneously on different frequencies. a directional antenna transmits a beam of radio waves that rotates like a lighthouse at a fixed rate, 30 times per second. when the directional beam is facing north, an omnidirectional antenna transmits a pulse. by measuring the difference in phase of these two signals, an aircraft can determine its bearing ( or " radial " ) from the station accurately. by taking a bearing on two vor beacons an aircraft can determine its position ( called a " fix " ) to an accuracy of about 90 metres ( 300 ft ). most vor beacons also have a distance measuring capability, called distance measuring equipment ( dme ) ; these are called vor / dme ' s. the aircraft transmits a radio signal to the vor / dme beacon and a transponder transmits a return signal. from the propagation delay between the transmitted and received signal the aircraft can calculate its distance from the beacon. this allows an aircraft to determine its location " fix " from only one vor beacon. since line - of - sight vhf frequencies are used vor beacons have a range of about 200 miles for aircraft at cruising altitude. tacan is a similar military radio beacon system which transmits in 962 – 1213 mhz, and a combined vor and tacan beacon is called a vortac. the number of vor beacons is declining as aviation switches to the rnav system that relies on global positioning system satellite navigation. instrument landing system ( ils ) - a short range radio navigation aid at airports which guides aircraft landing in low visibility conditions. it consists of multiple antennas at the end of each runway that radiate two beams of radio waves along the approach to the runway : the localizer ( 108 to 111. 95 mhz frequency ), which provides horizontal guidance, a heading line to keep the aircraft centered on the runway, and the glideslope ( 329. 15 to 335 mhz ) for vertical guidance, to keep the aircraft descending at the proper rate for a smooth touchdown at the correct point on the runway. each aircraft has a receiver instrument and antenna which receives the beams, with an indicator to tell the pilot whether he is on the correct horizontal and vertical approach. the ils beams are receivable for at least 15 miles, and have a radiated power of 25 watts. ils systems at airports are being replaced by systems that use satellite navigation. non - directional beacon ( ndb ) – legacy fixed radio beacons used before the vo earth. each satellite has an onboard atomic clock and transmits a continuous radio signal containing a precise time signal as well as its current position. two frequencies are used, 1. 2276 and 1. 57542 ghz. since the velocity of radio waves is virtually constant, the delay of the radio signal from a satellite is proportional to the distance of the receiver from the satellite. by receiving the signals from at least four satellites a gps receiver can calculate its position on earth by comparing the arrival time of the radio signals. since each satellite ' s position is known precisely at any given time, from the delay the position of the receiver can be calculated by a microprocessor in the receiver. the position can be displayed as latitude and longitude, or as a marker on an electronic map. gps receivers are incorporated in almost all cellphones and in vehicles such as automobiles, aircraft, and ships, and are used to guide drones, missiles, cruise missiles, and even artillery shells to their target, and handheld gps receivers are produced for hikers and the military. radio beacon – a fixed location terrestrial radio transmitter which transmits a continuous radio signal used by aircraft and ships for navigation. the locations of beacons are plotted on navigational maps used by aircraft and ships. vhf omnidirectional range ( vor ) – a worldwide aircraft radio navigation system consisting of fixed ground radio beacons transmitting between 108. 00 and 117. 95 mhz in the very high frequency ( vhf ) band. an automated navigational instrument on the aircraft displays a bearing to a nearby vor transmitter. a vor beacon transmits two signals simultaneously on different frequencies. a directional antenna transmits a beam of radio waves that rotates like a lighthouse at a fixed rate, 30 times per second. when the directional beam is facing north, an omnidirectional antenna transmits a pulse. by measuring the difference in phase of these two signals, an aircraft can determine its bearing ( or " radial " ) from the station accurately. by taking a bearing on two vor beacons an aircraft can determine its position ( called a " fix " ) to an accuracy of about 90 metres ( 300 ft ). most vor beacons also have a distance measuring capability, called distance measuring equipment ( dme ) ; these are called vor / dme ' s. the aircraft transmits a radio signal to the vor / dme beacon and a transponder transmits a return signal. from the propagation delay between the transmitted and received signal the aircraft can calculate the european union ' s galileo. global positioning system ( gps ) – the most widely used satellite navigation system, maintained by the us air force, which uses a constellation of 31 satellites in low earth orbit. the orbits of the satellites are distributed so at any time at least four satellites are above the horizon over each point on earth. each satellite has an onboard atomic clock and transmits a continuous radio signal containing a precise time signal as well as its current position. two frequencies are used, 1. 2276 and 1. 57542 ghz. since the velocity of radio waves is virtually constant, the delay of the radio signal from a satellite is proportional to the distance of the receiver from the satellite. by receiving the signals from at least four satellites a gps receiver can calculate its position on earth by comparing the arrival time of the radio signals. since each satellite ' s position is known precisely at any given time, from the delay the position of the receiver can be calculated by a microprocessor in the receiver. the position can be displayed as latitude and longitude, or as a marker on an electronic map. gps receivers are incorporated in almost all cellphones and in vehicles such as automobiles, aircraft, and ships, and are used to guide drones, missiles, cruise missiles, and even artillery shells to their target, and handheld gps receivers are produced for hikers and the military. radio beacon – a fixed location terrestrial radio transmitter which transmits a continuous radio signal used by aircraft and ships for navigation. the locations of beacons are plotted on navigational maps used by aircraft and ships. vhf omnidirectional range ( vor ) – a worldwide aircraft radio navigation system consisting of fixed ground radio beacons transmitting between 108. 00 and 117. 95 mhz in the very high frequency ( vhf ) band. an automated navigational instrument on the aircraft displays a bearing to a nearby vor transmitter. a vor beacon transmits two signals simultaneously on different frequencies. a directional antenna transmits a beam of radio waves that rotates like a lighthouse at a fixed rate, 30 times per second. when the directional beam is facing north, an omnidirectional antenna transmits a pulse. by measuring the difference in phase of these two signals, an aircraft can determine its bearing ( or " radial " ) from the station accurately. by taking a bearing on two vor beacons an aircraft can determine its position ( called a " fix " ) to an accuracy of about 90 metres ( 300 ft ). most vor beacons also have a ##directional range ( vor ) – a worldwide aircraft radio navigation system consisting of fixed ground radio beacons transmitting between 108. 00 and 117. 95 mhz in the very high frequency ( vhf ) band. an automated navigational instrument on the aircraft displays a bearing to a nearby vor transmitter. a vor beacon transmits two signals simultaneously on different frequencies. a directional antenna transmits a beam of radio waves that rotates like a lighthouse at a fixed rate, 30 times per second. when the directional beam is facing north, an omnidirectional antenna transmits a pulse. by measuring the difference in phase of these two signals, an aircraft can determine its bearing ( or " radial " ) from the station accurately. by taking a bearing on two vor beacons an aircraft can determine its position ( called a " fix " ) to an accuracy of about 90 metres ( 300 ft ). most vor beacons also have a distance measuring capability, called distance measuring equipment ( dme ) ; these are called vor / dme ' s. the aircraft transmits a radio signal to the vor / dme beacon and a transponder transmits a return signal. from the propagation delay between the transmitted and received signal the aircraft can calculate its distance from the beacon. this allows an aircraft to determine its location " fix " from only one vor beacon. since line - of - sight vhf frequencies are used vor beacons have a range of about 200 miles for aircraft at cruising altitude. tacan is a similar military radio beacon system which transmits in 962 – 1213 mhz, and a combined vor and tacan beacon is called a vortac. the number of vor beacons is declining as aviation switches to the rnav system that relies on global positioning system satellite navigation. instrument landing system ( ils ) - a short range radio navigation aid at airports which guides aircraft landing in low visibility conditions. it consists of multiple antennas at the end of each runway that radiate two beams of radio waves along the approach to the runway : the localizer ( 108 to 111. 95 mhz frequency ), which provides horizontal guidance, a heading line to keep the aircraft centered on the runway, and the glideslope ( 329. 15 to 335 mhz ) for vertical guidance, to keep the aircraft descending at the proper rate for a smooth touchdown at the correct point on the runway. each aircraft has a receiver instrument and antenna which receives the beams, with an indicator to tell the pilot whether he is even artillery shells to their target, and handheld gps receivers are produced for hikers and the military. radio beacon – a fixed location terrestrial radio transmitter which transmits a continuous radio signal used by aircraft and ships for navigation. the locations of beacons are plotted on navigational maps used by aircraft and ships. vhf omnidirectional range ( vor ) – a worldwide aircraft radio navigation system consisting of fixed ground radio beacons transmitting between 108. 00 and 117. 95 mhz in the very high frequency ( vhf ) band. an automated navigational instrument on the aircraft displays a bearing to a nearby vor transmitter. a vor beacon transmits two signals simultaneously on different frequencies. a directional antenna transmits a beam of radio waves that rotates like a lighthouse at a fixed rate, 30 times per second. when the directional beam is facing north, an omnidirectional antenna transmits a pulse. by measuring the difference in phase of these two signals, an aircraft can determine its bearing ( or " radial " ) from the station accurately. by taking a bearing on two vor beacons an aircraft can determine its position ( called a " fix " ) to an accuracy of about 90 metres ( 300 ft ). most vor beacons also have a distance measuring capability, called distance measuring equipment ( dme ) ; these are called vor / dme ' s. the aircraft transmits a radio signal to the vor / dme beacon and a transponder transmits a return signal. from the propagation delay between the transmitted and received signal the aircraft can calculate its distance from the beacon. this allows an aircraft to determine its location " fix " from only one vor beacon. since line - of - sight vhf frequencies are used vor beacons have a range of about 200 miles for aircraft at cruising altitude. tacan is a similar military radio beacon system which transmits in 962 – 1213 mhz, and a combined vor and tacan beacon is called a vortac. the number of vor beacons is declining as aviation switches to the rnav system that relies on global positioning system satellite navigation. instrument landing system ( ils ) - a short range radio navigation aid at airports which guides aircraft landing in low visibility conditions. it consists of multiple antennas at the end of each runway that radiate two beams of radio waves along the approach to the runway : the localizer ( 108 to 111. 95 mhz frequency ), which provides horizontal guidance, a heading line to keep the aircraft centered on kilometers ( 4, 200, 000 to 395, 400, 000 acres ). 10 % of the world ' s crop lands were planted with gm crops in 2010. as of 2011, 11 different transgenic crops were grown commercially on 395 million acres ( 160 million hectares ) in 29 countries such as the us, brazil, argentina, india, canada, china, paraguay, pakistan, south africa, uruguay, bolivia, australia, philippines, myanmar, burkina faso, mexico and spain. genetically modified foods are foods produced from organisms that have had specific changes introduced into their dna with the methods of genetic engineering. these techniques have allowed for the introduction of new crop traits as well as a far greater control over a food ' s genetic structure than previously afforded by methods such as selective breeding and mutation breeding. commercial sale of genetically modified foods began in 1994, when calgene first marketed its flavr savr delayed ripening tomato. to date most genetic modification of foods have primarily focused on cash crops in high demand by farmers such as soybean, corn, canola, and cotton seed oil. these have been engineered for resistance to pathogens and herbicides and better nutrient profiles. gm livestock have also been experimentally developed ; in november 2013 none were available on the market, but in 2015 the fda approved the first gm salmon for commercial production and consumption. there is a scientific consensus that currently available food derived from gm crops poses no greater risk to human health than conventional food, but that each gm food needs to be tested on a case - by - case basis before introduction. nonetheless, members of the public are much less likely than scientists to perceive gm foods as safe. the legal and regulatory status of gm foods varies by country, with some nations banning or restricting them, and others permitting them with widely differing degrees of regulation. gm crops also provide a number of ecological benefits, if not used in excess. insect - resistant crops have proven to lower pesticide usage, therefore reducing the environmental impact of pesticides as a whole. however, opponents have objected to gm crops per se on several grounds, including environmental concerns, whether food produced from gm crops is safe, whether gm crops are needed to address the world ' s food needs, and economic concerns raised by the fact these organisms are subject to intellectual property law. biotechnology has several applications in the realm of food security. crops like golden rice are engineered to have higher nutritional content, and there is potential for food products with longer shelf lives. though not a form of agricultural biotechnology, vaccines can help prevent diseases found in received within a limited distance of its transmitter. systems that broadcast from satellites can generally be received over an entire country or continent. older terrestrial radio and television are paid for by commercial advertising or governments. in subscription systems like satellite television and satellite radio the customer pays a monthly fee. in these systems, the radio signal is encrypted and can only be decrypted by the receiver, which is controlled by the company and can be deactivated if the customer does not pay. broadcasting uses several parts of the radio spectrum, depending on the type of signals transmitted and the desired target audience. longwave and medium wave signals can give reliable coverage of areas several hundred kilometers across, but have a more limited information - carrying capacity and so work best with audio signals ( speech and music ), and the sound quality can be degraded by radio noise from natural and artificial sources. the shortwave bands have a greater potential range but are more subject to interference by distant stations and varying atmospheric conditions that affect reception. in the very high frequency band, greater than 30 megahertz, the earth ' s atmosphere has less of an effect on the range of signals, and line - of - sight propagation becomes the principal mode. these higher frequencies permit the great bandwidth required for television broadcasting. since natural and artificial noise sources are less present at these frequencies, high - quality audio transmission is possible, using frequency modulation. = = = = audio : radio broadcasting = = = = radio broadcasting means transmission of audio ( sound ) to radio receivers belonging to a public audience. analog audio is the earliest form of radio broadcast. am broadcasting began around 1920. fm broadcasting was introduced in the late 1930s with improved fidelity. a broadcast radio receiver is called a radio. most radios can receive both am and fm. am ( amplitude modulation ) – in am, the amplitude ( strength ) of the radio carrier wave is varied by the audio signal. am broadcasting, the oldest broadcasting technology, is allowed in the am broadcast bands, between 148 and 283 khz in the low frequency ( lf ) band for longwave broadcasts and between 526 and 1706 khz in the medium frequency ( mf ) band for medium - wave broadcasts. because waves in these bands travel as ground waves following the terrain, am radio stations can be received beyond the horizon at hundreds of miles distance, but am has lower fidelity than fm. radiated power ( erp ) of am stations in the us is usually limited to a maximum of 10 kw, although a few ( clear - channel stations ) are allowed to transmit at 50 these two signals, an aircraft can determine its bearing ( or " radial " ) from the station accurately. by taking a bearing on two vor beacons an aircraft can determine its position ( called a " fix " ) to an accuracy of about 90 metres ( 300 ft ). most vor beacons also have a distance measuring capability, called distance measuring equipment ( dme ) ; these are called vor / dme ' s. the aircraft transmits a radio signal to the vor / dme beacon and a transponder transmits a return signal. from the propagation delay between the transmitted and received signal the aircraft can calculate its distance from the beacon. this allows an aircraft to determine its location " fix " from only one vor beacon. since line - of - sight vhf frequencies are used vor beacons have a range of about 200 miles for aircraft at cruising altitude. tacan is a similar military radio beacon system which transmits in 962 – 1213 mhz, and a combined vor and tacan beacon is called a vortac. the number of vor beacons is declining as aviation switches to the rnav system that relies on global positioning system satellite navigation. instrument landing system ( ils ) - a short range radio navigation aid at airports which guides aircraft landing in low visibility conditions. it consists of multiple antennas at the end of each runway that radiate two beams of radio waves along the approach to the runway : the localizer ( 108 to 111. 95 mhz frequency ), which provides horizontal guidance, a heading line to keep the aircraft centered on the runway, and the glideslope ( 329. 15 to 335 mhz ) for vertical guidance, to keep the aircraft descending at the proper rate for a smooth touchdown at the correct point on the runway. each aircraft has a receiver instrument and antenna which receives the beams, with an indicator to tell the pilot whether he is on the correct horizontal and vertical approach. the ils beams are receivable for at least 15 miles, and have a radiated power of 25 watts. ils systems at airports are being replaced by systems that use satellite navigation. non - directional beacon ( ndb ) – legacy fixed radio beacons used before the vor system that transmit a simple signal in all directions for aircraft or ships to use for radio direction finding. aircraft use automatic direction finder ( adf ) receivers which use a directional antenna to determine the bearing to the beacon. by taking bearings on two beacons they can determine their position. ndbs use frequencies between is not present ( e. g., litter in a parking lot or readings on an electric meter ). behavioral observations involve the direct witnessing of the actor engaging in the behavior ( e. g., watching how close a person sits next to another person ). behavioral choices are when a person selects between two or more options ( e. g., voting behavior, choice of a punishment for another participant ). reaction time. the time between the presentation of a stimulus and an appropriate response can indicate differences between two cognitive processes, and can indicate some things about their nature. for example, if in a search task the reaction times vary proportionally with the number of elements, then it is evident that this cognitive process of searching involves serial instead of parallel processing. psychophysical responses. psychophysical experiments are an old psychological technique, which has been adopted by cognitive psychology. they typically involve making judgments of some physical property, e. g. the loudness of a sound. correlation of subjective scales between individuals can show cognitive or sensory biases as compared to actual physical measurements. some examples include : sameness judgments for colors, tones, textures, etc. threshold differences for colors, tones, textures, etc. eye tracking. this methodology is used to study a variety of cognitive processes, most notably visual perception and language processing. the fixation point of the eyes is linked to an individual ' s focus of attention. thus, by monitoring eye movements, we can study what information is being processed at a given time. eye tracking allows us to study cognitive processes on extremely short time scales. eye movements reflect online decision making during a task, and they provide us with some insight into the ways in which those decisions may be processed. = = = brain imaging = = = brain imaging involves analyzing activity within the brain while performing various tasks. this allows us to link behavior and brain function to help understand how information is processed. different types of imaging techniques vary in their temporal ( time - based ) and spatial ( location - based ) resolution. brain imaging is often used in cognitive neuroscience. single - photon emission computed tomography and positron emission tomography. spect and pet use radioactive isotopes, which are injected into the subject ' s bloodstream and taken up by the brain. by observing which areas of the brain take up the radioactive isotope, we can see which areas of the brain are more active than other areas. pet has similar spatial resolution to fmri, but it has extremely poor temporal resolution. electroencephalography. eeg measures the electrical fields the realization of karl popper ' s epr - like experiment by shih and kim ( published 1999 ) produced the result that popper hoped for : no ` ` action at a distance ' ' on one photon of an entangled pair when a measurement is made on the other photon. this experimental result is interpretable in local realistic terms : each photon has a definite position and transverse momentum most of the time ; the position measurement on one photon ( localization within a slit ) disturbs the transverse momentum of that photon in a non - predictable way in accordance with the uncertainty principle ; however, there is no effect on the other photon ( the photon that is not in a slit ) no action at a distance. the position measurement ( localization within a slit ) of the one photon destroys the entanglement between the photons ; i. e. decoherence occurs. Question: How do bees communicate to tell other bees where food is located? A) mating dance B) wing flapping C) high pitch noise D) waggle dance	D) waggle dance
Context: techniques that provide heart and lung support. it is used primarily to support the lungs for a prolonged but still temporary timeframe ( 1 – 30 days ) and allow for recovery from reversible diseases. robert bartlett is known as the father of ecmo and performed the first treatment of a newborn using an ecmo machine in 1975. skin tissue - engineered skin is a type of bioartificial organ that is often used to treat burns, diabetic foot ulcers, or other large wounds that cannot heal well on their own. artificial skin can be made from autografts, allografts, and xenografts. autografted skin comes from a patient ' s own skin, which allows the dermis to have a faster healing rate, and the donor site can be re - harvested a few times. allograft skin often comes from cadaver skin and is mostly used to treat burn victims. lastly, xenografted skin comes from animals and provides a temporary healing structure for the skin. they assist in dermal regeneration, but cannot become part of the host skin. tissue - engineered skin is now available in commercial products. integra, originally used to only treat burns, consists of a collagen matrix and chondroitin sulfate that can be used as a skin replacement. the chondroitin sulfate functions as a component of proteoglycans, which helps to form the extracellular matrix. integra can be repopulated and revascularized while maintaining its dermal collagen architecture, making it a bioartificial organ dermagraft, another commercial - made tissue - engineered skin product, is made out of living fibroblasts. these fibroblasts proliferate and produce growth factors, collagen, and ecm proteins, that help build granulation tissue. = = = = heart = = = = since the number of patients awaiting a heart transplant is continuously increasing over time, and the number of patients on the waiting list surpasses the organ availability, artificial organs used as replacement therapy for terminal heart failure would help alleviate this difficulty. artificial hearts are usually used to bridge the heart transplantation or can be applied as replacement therapy for terminal heart malfunction. the total artificial heart ( tah ), first introduced by dr. vladimir p. demikhov in 1937, emerged as an ideal alternative. since then it has been developed and improved as a mechanical pump that provides long - term circulatory support and ##fts. autografted skin comes from a patient ' s own skin, which allows the dermis to have a faster healing rate, and the donor site can be re - harvested a few times. allograft skin often comes from cadaver skin and is mostly used to treat burn victims. lastly, xenografted skin comes from animals and provides a temporary healing structure for the skin. they assist in dermal regeneration, but cannot become part of the host skin. tissue - engineered skin is now available in commercial products. integra, originally used to only treat burns, consists of a collagen matrix and chondroitin sulfate that can be used as a skin replacement. the chondroitin sulfate functions as a component of proteoglycans, which helps to form the extracellular matrix. integra can be repopulated and revascularized while maintaining its dermal collagen architecture, making it a bioartificial organ dermagraft, another commercial - made tissue - engineered skin product, is made out of living fibroblasts. these fibroblasts proliferate and produce growth factors, collagen, and ecm proteins, that help build granulation tissue. = = = = heart = = = = since the number of patients awaiting a heart transplant is continuously increasing over time, and the number of patients on the waiting list surpasses the organ availability, artificial organs used as replacement therapy for terminal heart failure would help alleviate this difficulty. artificial hearts are usually used to bridge the heart transplantation or can be applied as replacement therapy for terminal heart malfunction. the total artificial heart ( tah ), first introduced by dr. vladimir p. demikhov in 1937, emerged as an ideal alternative. since then it has been developed and improved as a mechanical pump that provides long - term circulatory support and replaces diseased or damaged heart ventricles that cannot properly pump the blood, restoring thus the pulmonary and systemic flow. some of the current tahs include abiocor, an fda - approved device that comprises two artificial ventricles and their valves, and does not require subcutaneous connections, and is indicated for patients with biventricular heart failure. in 2010 syncardia released the portable freedom driver that allows patients to have a portable device without being confined to the hospital. = = = = kidney = = = = while kidney transplants are possible, renal failure is more often treated using an artificial kidney. the first artificial 1975. skin tissue - engineered skin is a type of bioartificial organ that is often used to treat burns, diabetic foot ulcers, or other large wounds that cannot heal well on their own. artificial skin can be made from autografts, allografts, and xenografts. autografted skin comes from a patient ' s own skin, which allows the dermis to have a faster healing rate, and the donor site can be re - harvested a few times. allograft skin often comes from cadaver skin and is mostly used to treat burn victims. lastly, xenografted skin comes from animals and provides a temporary healing structure for the skin. they assist in dermal regeneration, but cannot become part of the host skin. tissue - engineered skin is now available in commercial products. integra, originally used to only treat burns, consists of a collagen matrix and chondroitin sulfate that can be used as a skin replacement. the chondroitin sulfate functions as a component of proteoglycans, which helps to form the extracellular matrix. integra can be repopulated and revascularized while maintaining its dermal collagen architecture, making it a bioartificial organ dermagraft, another commercial - made tissue - engineered skin product, is made out of living fibroblasts. these fibroblasts proliferate and produce growth factors, collagen, and ecm proteins, that help build granulation tissue. = = = = heart = = = = since the number of patients awaiting a heart transplant is continuously increasing over time, and the number of patients on the waiting list surpasses the organ availability, artificial organs used as replacement therapy for terminal heart failure would help alleviate this difficulty. artificial hearts are usually used to bridge the heart transplantation or can be applied as replacement therapy for terminal heart malfunction. the total artificial heart ( tah ), first introduced by dr. vladimir p. demikhov in 1937, emerged as an ideal alternative. since then it has been developed and improved as a mechanical pump that provides long - term circulatory support and replaces diseased or damaged heart ventricles that cannot properly pump the blood, restoring thus the pulmonary and systemic flow. some of the current tahs include abiocor, an fda - approved device that comprises two artificial ventricles and their valves, and does not require subcutaneous connections, and is indicated for to dye denim and the artist ' s pigments gamboge and rose madder. sugar, starch, cotton, linen, hemp, some types of rope, wood and particle boards, papyrus and paper, vegetable oils, wax, and natural rubber are examples of commercially important materials made from plant tissues or their secondary products. charcoal, a pure form of carbon made by pyrolysis of wood, has a long history as a metal - smelting fuel, as a filter material and adsorbent and as an artist ' s material and is one of the three ingredients of gunpowder. cellulose, the world ' s most abundant organic polymer, can be converted into energy, fuels, materials and chemical feedstock. products made from cellulose include rayon and cellophane, wallpaper paste, biobutanol and gun cotton. sugarcane, rapeseed and soy are some of the plants with a highly fermentable sugar or oil content that are used as sources of biofuels, important alternatives to fossil fuels, such as biodiesel. sweetgrass was used by native americans to ward off bugs like mosquitoes. these bug repelling properties of sweetgrass were later found by the american chemical society in the molecules phytol and coumarin. = = plant ecology = = plant ecology is the science of the functional relationships between plants and their habitats – the environments where they complete their life cycles. plant ecologists study the composition of local and regional floras, their biodiversity, genetic diversity and fitness, the adaptation of plants to their environment, and their competitive or mutualistic interactions with other species. some ecologists even rely on empirical data from indigenous people that is gathered by ethnobotanists. this information can relay a great deal of information on how the land once was thousands of years ago and how it has changed over that time. the goals of plant ecology are to understand the causes of their distribution patterns, productivity, environmental impact, evolution, and responses to environmental change. plants depend on certain edaphic ( soil ) and climatic factors in their environment but can modify these factors too. for example, they can change their environment ' s albedo, increase runoff interception, stabilise mineral soils and develop their organic content, and affect local temperature. plants compete with other organisms in their ecosystem for resources. they interact with their neighbours at a variety of spatial scales in groups, populations and communities that collectively constitute vegetation. regions with characteristic vegetation types and dominant plants as well as similar abiot others, such as the essential oils peppermint oil and lemon oil are useful for their aroma, as flavourings and spices ( e. g., capsaicin ), and in medicine as pharmaceuticals as in opium from opium poppies. many medicinal and recreational drugs, such as tetrahydrocannabinol ( active ingredient in cannabis ), caffeine, morphine and nicotine come directly from plants. others are simple derivatives of botanical natural products. for example, the pain killer aspirin is the acetyl ester of salicylic acid, originally isolated from the bark of willow trees, and a wide range of opiate painkillers like heroin are obtained by chemical modification of morphine obtained from the opium poppy. popular stimulants come from plants, such as caffeine from coffee, tea and chocolate, and nicotine from tobacco. most alcoholic beverages come from fermentation of carbohydrate - rich plant products such as barley ( beer ), rice ( sake ) and grapes ( wine ). native americans have used various plants as ways of treating illness or disease for thousands of years. this knowledge native americans have on plants has been recorded by enthnobotanists and then in turn has been used by pharmaceutical companies as a way of drug discovery. plants can synthesise coloured dyes and pigments such as the anthocyanins responsible for the red colour of red wine, yellow weld and blue woad used together to produce lincoln green, indoxyl, source of the blue dye indigo traditionally used to dye denim and the artist ' s pigments gamboge and rose madder. sugar, starch, cotton, linen, hemp, some types of rope, wood and particle boards, papyrus and paper, vegetable oils, wax, and natural rubber are examples of commercially important materials made from plant tissues or their secondary products. charcoal, a pure form of carbon made by pyrolysis of wood, has a long history as a metal - smelting fuel, as a filter material and adsorbent and as an artist ' s material and is one of the three ingredients of gunpowder. cellulose, the world ' s most abundant organic polymer, can be converted into energy, fuels, materials and chemical feedstock. products made from cellulose include rayon and cellophane, wallpaper paste, biobutanol and gun cotton. sugarcane, rapeseed and soy are some of the plants with a highly ferment tissue engineering is a biomedical engineering discipline that uses a combination of cells, engineering, materials methods, and suitable biochemical and physicochemical factors to restore, maintain, improve, or replace different types of biological tissues. tissue engineering often involves the use of cells placed on tissue scaffolds in the formation of new viable tissue for a medical purpose, but is not limited to applications involving cells and tissue scaffolds. while it was once categorized as a sub - field of biomaterials, having grown in scope and importance, it can be considered as a field of its own. while most definitions of tissue engineering cover a broad range of applications, in practice, the term is closely associated with applications that repair or replace portions of or whole tissues ( i. e. organs, bone, cartilage, blood vessels, bladder, skin, muscle etc. ). often, the tissues involved require certain mechanical and structural properties for proper functioning. the term has also been applied to efforts to perform specific biochemical functions using cells within an artificially - created support system ( e. g. an artificial pancreas, or a bio artificial liver ). the term regenerative medicine is often used synonymously with tissue engineering, although those involved in regenerative medicine place more emphasis on the use of stem cells or progenitor cells to produce tissues. = = overview = = a commonly applied definition of tissue engineering, as stated by langer and vacanti, is " an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve [ biological tissue ] function or a whole organ ". in addition, langer and vacanti also state that there are three main types of tissue engineering : cells, tissue - inducing substances, and a cells + matrix approach ( often referred to as a scaffold ). tissue engineering has also been defined as " understanding the principles of tissue growth, and applying this to produce functional replacement tissue for clinical use ". a further description goes on to say that an " underlying supposition of tissue engineering is that the employment of natural biology of the system will allow for greater success in developing therapeutic strategies aimed at the replacement, repair, maintenance, or enhancement of tissue function ". developments in the multidisciplinary field of tissue engineering have yielded a novel set of tissue replacement parts and implementation strategies. scientific advances in biomaterials, stem cells, growth and differentiation factors, and biomimetic environments have created unique opportunities to fabric involve pressing the green body to give the densification a head start and reduce the sintering time needed. sometimes organic binders such as polyvinyl alcohol are added to hold the green body together ; these burn out during the firing ( at 200 – 350 °c ). sometimes organic lubricants are added during pressing to increase densification. it is common to combine these, and add binders and lubricants to a powder, then press. ( the formulation of these organic chemical additives is an art in itself. this is particularly important in the manufacture of high performance ceramics such as those used by the billions for electronics, in capacitors, inductors, sensors, etc. ) a slurry can be used in place of a powder, and then cast into a desired shape, dried and then sintered. indeed, traditional pottery is done with this type of method, using a plastic mixture worked with the hands. if a mixture of different materials is used together in a ceramic, the sintering temperature is sometimes above the melting point of one minor component – a liquid phase sintering. this results in shorter sintering times compared to solid state sintering. such liquid phase sintering involves in faster diffusion processes and may result in abnormal grain growth. = = strength of ceramics = = a material ' s strength is dependent on its microstructure. the engineering processes to which a material is subjected can alter its microstructure. the variety of strengthening mechanisms that alter the strength of a material include the mechanism of grain boundary strengthening. thus, although yield strength is maximized with decreasing grain size, ultimately, very small grain sizes make the material brittle. considered in tandem with the fact that the yield strength is the parameter that predicts plastic deformation in the material, one can make informed decisions on how to increase the strength of a material depending on its microstructural properties and the desired end effect. the relation between yield stress and grain size is described mathematically by the hall - petch equation which is σ y = σ 0 + k y d { \ displaystyle \ sigma _ { y } = \ sigma _ { 0 } + { k _ { y } \ over { \ sqrt { d } } } } where ky is the strengthening coefficient ( a constant unique to each material ), σo is a materials constant for the starting stress for dislocation movement ( or the resistance of the lattice to dislocation motion ), d is the grain diameter, and σy is the two planetary nebulae are shown to belong to the sagittarius dwarf galaxy, on the basis of their radial velocities. this is only the second dwarf spheroidal galaxy, after fornax, found to contain planetary nebulae. their existence confirms that this galaxy is at least as massive as the fornax dwarf spheroidal which has a single planetary nebula, and suggests a mass of a few times 10 * * 7 solar masses. the two planetary nebulae are located along the major axis of the galaxy, near the base of the tidal tail. there is a further candidate, situated at a very large distance along the direction of the tidal tail, for which no velocity measurement is available. the location of the planetary nebulae and globular clusters of the sagittarius dwarf galaxy suggests that a significant fraction of its mass is contained within the tidal tail. plant cells and tissues, whereas plant morphology is the study of their external form. all plants are multicellular eukaryotes, their dna stored in nuclei. the characteristic features of plant cells that distinguish them from those of animals and fungi include a primary cell wall composed of the polysaccharides cellulose, hemicellulose and pectin, larger vacuoles than in animal cells and the presence of plastids with unique photosynthetic and biosynthetic functions as in the chloroplasts. other plastids contain storage products such as starch ( amyloplasts ) or lipids ( elaioplasts ). uniquely, streptophyte cells and those of the green algal order trentepohliales divide by construction of a phragmoplast as a template for building a cell plate late in cell division. the bodies of vascular plants including clubmosses, ferns and seed plants ( gymnosperms and angiosperms ) generally have aerial and subterranean subsystems. the shoots consist of stems bearing green photosynthesising leaves and reproductive structures. the underground vascularised roots bear root hairs at their tips and generally lack chlorophyll. non - vascular plants, the liverworts, hornworts and mosses do not produce ground - penetrating vascular roots and most of the plant participates in photosynthesis. the sporophyte generation is nonphotosynthetic in liverworts but may be able to contribute part of its energy needs by photosynthesis in mosses and hornworts. the root system and the shoot system are interdependent – the usually nonphotosynthetic root system depends on the shoot system for food, and the usually photosynthetic shoot system depends on water and minerals from the root system. cells in each system are capable of creating cells of the other and producing adventitious shoots or roots. stolons and tubers are examples of shoots that can grow roots. roots that spread out close to the surface, such as those of willows, can produce shoots and ultimately new plants. in the event that one of the systems is lost, the other can often regrow it. in fact it is possible to grow an entire plant from a single leaf, as is the case with plants in streptocarpus sect. saintpaulia, or even a single cell – which can dedifferentiate into a callus ( a mass of three families of quarks and leptons, one higgs to rule them all, and in the darkness bind them. Question: Along with nerve tissue, what kind of tissue are lecithins and cephalins important constituents of? A) lung tissue B) brain tissue C) heart tissue D) skin tissue	B) brain tissue
Context: is collected and processed to extract valuable metals. ore bodies often contain more than one valuable metal. tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. additionally, a concentrate may contain more than one valuable metal. that concentrate would then be processed to separate the valuable metals into individual constituents. = = metal and its alloys = = much effort has been placed on understanding iron – carbon alloy system, which includes steels and cast irons. plain carbon steels ( those that contain essentially only carbon as an alloying element ) are used in low - cost, high - strength applications, where neither weight nor corrosion are a major concern. cast irons, including ductile iron, are also part of the iron - carbon system. iron - manganese - chromium alloys ( hadfield - type steels ) are also used in non - magnetic applications such as directional drilling. other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. these metals are most often used as alloys with the noted exception of silicon, which is not a metal. other forms include : stainless steel, particularly austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important. aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications. copper - nickel alloys ( such as monel ) are used in highly corrosive environments and for non - magnetic applications. nickel - based superalloys like inconel are used in high - temperature applications such as gas turbines, turbochargers, pressure vessels, and heat exchangers. for extremely high temperatures, single crystal alloys are used to minimize creep. in modern electronics, high purity single crystal silicon is essential for metal - oxide - silicon transistors ( mos ) and integrated circuits. = = production = = in production engineering, metallurgy is concerned with the production of metallic components for use in consumer or engineering products. this involves production of alloys, shaping, heat treatment and surface treatment of product. the task of the metallurgist is to achieve balance between material properties, such as cost, weight, strength, toughness, hardness, corrosion, fatigue resistance and performance in temperature extremes. to achieve this goal, the operating environment must be carefully considered. determining the hardness of the metal using the rockwell, vickers, and brinell hardness scales casting, foundry methods, blast furnace extraction, and electrolytic extraction are all part of the required knowledge of a materials engineer. often the presence, absence, or variation of minute quantities of secondary elements and compounds in a bulk material will greatly affect the final properties of the materials produced. for example, steels are classified based on 1 / 10 and 1 / 100 weight percentages of the carbon and other alloying elements they contain. thus, the extracting and purifying methods used to extract iron in a blast furnace can affect the quality of steel that is produced. solid materials are generally grouped into three basic classifications : ceramics, metals, and polymers. this broad classification is based on the empirical makeup and atomic structure of the solid materials, and most solids fall into one of these broad categories. an item that is often made from each of these materials types is the beverage container. the material types used for beverage containers accordingly provide different advantages and disadvantages, depending on the material used. ceramic ( glass ) containers are optically transparent, impervious to the passage of carbon dioxide, relatively inexpensive, and are easily recycled, but are also heavy and fracture easily. metal ( aluminum alloy ) is relatively strong, is a good barrier to the diffusion of carbon dioxide, and is easily recycled. however, the cans are opaque, expensive to produce, and are easily dented and punctured. polymers ( polyethylene plastic ) are relatively strong, can be optically transparent, are inexpensive and lightweight, and can be recyclable, but are not as impervious to the passage of carbon dioxide as aluminum and glass. = = = ceramics and glasses = = = another application of materials science is the study of ceramics and glasses, typically the most brittle materials with industrial relevance. many ceramics and glasses exhibit covalent or ionic - covalent bonding with sio2 ( silica ) as a fundamental building block. ceramics – not to be confused with raw, unfired clay – are usually seen in crystalline form. the vast majority of commercial glasses contain a metal oxide fused with silica. at the high temperatures used to prepare glass, the material is a viscous liquid which solidifies into a disordered state upon cooling. windowpanes and eyeglasses are important examples. fibers of glass are also used for long - range telecommunication and optical transmission. scratch resistant corning gorilla glass is a well - known example of the application of materials science to drastically improve the properties of common components. engineering ceramics are known for their stiffness and the valuable metals into individual constituents. = = metal and its alloys = = much effort has been placed on understanding iron – carbon alloy system, which includes steels and cast irons. plain carbon steels ( those that contain essentially only carbon as an alloying element ) are used in low - cost, high - strength applications, where neither weight nor corrosion are a major concern. cast irons, including ductile iron, are also part of the iron - carbon system. iron - manganese - chromium alloys ( hadfield - type steels ) are also used in non - magnetic applications such as directional drilling. other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. these metals are most often used as alloys with the noted exception of silicon, which is not a metal. other forms include : stainless steel, particularly austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important. aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications. copper - nickel alloys ( such as monel ) are used in highly corrosive environments and for non - magnetic applications. nickel - based superalloys like inconel are used in high - temperature applications such as gas turbines, turbochargers, pressure vessels, and heat exchangers. for extremely high temperatures, single crystal alloys are used to minimize creep. in modern electronics, high purity single crystal silicon is essential for metal - oxide - silicon transistors ( mos ) and integrated circuits. = = production = = in production engineering, metallurgy is concerned with the production of metallic components for use in consumer or engineering products. this involves production of alloys, shaping, heat treatment and surface treatment of product. the task of the metallurgist is to achieve balance between material properties, such as cost, weight, strength, toughness, hardness, corrosion, fatigue resistance and performance in temperature extremes. to achieve this goal, the operating environment must be carefully considered. determining the hardness of the metal using the rockwell, vickers, and brinell hardness scales is a commonly used practice that helps better understand the metal ' s elasticity and plasticity for different applications and production processes. in a saltwater environment, most ferrous metals and some non - ferrous alloys corrode quickly. metals exposed to cold or cryogenic conditions may undergo a ductile to brittle applications, where neither weight nor corrosion are a major concern. cast irons, including ductile iron, are also part of the iron - carbon system. iron - manganese - chromium alloys ( hadfield - type steels ) are also used in non - magnetic applications such as directional drilling. other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. these metals are most often used as alloys with the noted exception of silicon, which is not a metal. other forms include : stainless steel, particularly austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important. aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications. copper - nickel alloys ( such as monel ) are used in highly corrosive environments and for non - magnetic applications. nickel - based superalloys like inconel are used in high - temperature applications such as gas turbines, turbochargers, pressure vessels, and heat exchangers. for extremely high temperatures, single crystal alloys are used to minimize creep. in modern electronics, high purity single crystal silicon is essential for metal - oxide - silicon transistors ( mos ) and integrated circuits. = = production = = in production engineering, metallurgy is concerned with the production of metallic components for use in consumer or engineering products. this involves production of alloys, shaping, heat treatment and surface treatment of product. the task of the metallurgist is to achieve balance between material properties, such as cost, weight, strength, toughness, hardness, corrosion, fatigue resistance and performance in temperature extremes. to achieve this goal, the operating environment must be carefully considered. determining the hardness of the metal using the rockwell, vickers, and brinell hardness scales is a commonly used practice that helps better understand the metal ' s elasticity and plasticity for different applications and production processes. in a saltwater environment, most ferrous metals and some non - ferrous alloys corrode quickly. metals exposed to cold or cryogenic conditions may undergo a ductile to brittle transition and lose their toughness, becoming more brittle and prone to cracking. metals under continual cyclic loading can suffer from metal fatigue. metals under constant stress at elevated temperatures can creep. = = = metalworking processes = = = casting – molten metal is poured into a shaped mold. variants of casting include sand casting, investment of measuring methods. x - rays and gamma rays are used in industrial radiography to make images of the inside of solid products, as a means of nondestructive testing and inspection. the piece to be radiographed is placed between the source and a photographic film in a cassette. after a certain exposure time, the film is developed and it shows any internal defects of the material. gauges - gauges use the exponential absorption law of gamma rays level indicators : source and detector are placed at opposite sides of a container, indicating the presence or absence of material in the horizontal radiation path. beta or gamma sources are used, depending on the thickness and the density of the material to be measured. the method is used for containers of liquids or of grainy substances thickness gauges : if the material is of constant density, the signal measured by the radiation detector depends on the thickness of the material. this is useful for continuous production, like of paper, rubber, etc. electrostatic control - to avoid the build - up of static electricity in production of paper, plastics, synthetic textiles, etc., a ribbon - shaped source of the alpha emitter 241am can be placed close to the material at the end of the production line. the source ionizes the air to remove electric charges on the material. radioactive tracers - since radioactive isotopes behave, chemically, mostly like the inactive element, the behavior of a certain chemical substance can be followed by tracing the radioactivity. examples : adding a gamma tracer to a gas or liquid in a closed system makes it possible to find a hole in a tube. adding a tracer to the surface of the component of a motor makes it possible to measure wear by measuring the activity of the lubricating oil. oil and gas exploration - nuclear well logging is used to help predict the commercial viability of new or existing wells. the technology involves the use of a neutron or gamma - ray source and a radiation detector which are lowered into boreholes to determine the properties of the surrounding rock such as porosity and lithography. [ 1 ] road construction - nuclear moisture / density gauges are used to determine the density of soils, asphalt, and concrete. typically a cesium - 137 source is used. = = = commercial applications = = = radioluminescence tritium illumination : tritium is used with phosphor in rifle sights to increase nighttime firing accuracy. some runway markers and building exit signs use the same technology, to remain illuminated during blackouts. betavoltaics , calorimetry, nuclear microscopy ( hefib ), rutherford backscattering, neutron diffraction, small - angle x - ray scattering ( saxs ), etc. ). besides material characterization, the material scientist or engineer also deals with extracting materials and converting them into useful forms. thus ingot casting, foundry methods, blast furnace extraction, and electrolytic extraction are all part of the required knowledge of a materials engineer. often the presence, absence, or variation of minute quantities of secondary elements and compounds in a bulk material will greatly affect the final properties of the materials produced. for example, steels are classified based on 1 / 10 and 1 / 100 weight percentages of the carbon and other alloying elements they contain. thus, the extracting and purifying methods used to extract iron in a blast furnace can affect the quality of steel that is produced. solid materials are generally grouped into three basic classifications : ceramics, metals, and polymers. this broad classification is based on the empirical makeup and atomic structure of the solid materials, and most solids fall into one of these broad categories. an item that is often made from each of these materials types is the beverage container. the material types used for beverage containers accordingly provide different advantages and disadvantages, depending on the material used. ceramic ( glass ) containers are optically transparent, impervious to the passage of carbon dioxide, relatively inexpensive, and are easily recycled, but are also heavy and fracture easily. metal ( aluminum alloy ) is relatively strong, is a good barrier to the diffusion of carbon dioxide, and is easily recycled. however, the cans are opaque, expensive to produce, and are easily dented and punctured. polymers ( polyethylene plastic ) are relatively strong, can be optically transparent, are inexpensive and lightweight, and can be recyclable, but are not as impervious to the passage of carbon dioxide as aluminum and glass. = = = ceramics and glasses = = = another application of materials science is the study of ceramics and glasses, typically the most brittle materials with industrial relevance. many ceramics and glasses exhibit covalent or ionic - covalent bonding with sio2 ( silica ) as a fundamental building block. ceramics – not to be confused with raw, unfired clay – are usually seen in crystalline form. the vast majority of commercial glasses contain a metal oxide fused with silica. at the high temperatures used to prepare glass, the material is a viscous liquid which solidifies into a disordered state upon the film is developed and it shows any internal defects of the material. gauges - gauges use the exponential absorption law of gamma rays level indicators : source and detector are placed at opposite sides of a container, indicating the presence or absence of material in the horizontal radiation path. beta or gamma sources are used, depending on the thickness and the density of the material to be measured. the method is used for containers of liquids or of grainy substances thickness gauges : if the material is of constant density, the signal measured by the radiation detector depends on the thickness of the material. this is useful for continuous production, like of paper, rubber, etc. electrostatic control - to avoid the build - up of static electricity in production of paper, plastics, synthetic textiles, etc., a ribbon - shaped source of the alpha emitter 241am can be placed close to the material at the end of the production line. the source ionizes the air to remove electric charges on the material. radioactive tracers - since radioactive isotopes behave, chemically, mostly like the inactive element, the behavior of a certain chemical substance can be followed by tracing the radioactivity. examples : adding a gamma tracer to a gas or liquid in a closed system makes it possible to find a hole in a tube. adding a tracer to the surface of the component of a motor makes it possible to measure wear by measuring the activity of the lubricating oil. oil and gas exploration - nuclear well logging is used to help predict the commercial viability of new or existing wells. the technology involves the use of a neutron or gamma - ray source and a radiation detector which are lowered into boreholes to determine the properties of the surrounding rock such as porosity and lithography. [ 1 ] road construction - nuclear moisture / density gauges are used to determine the density of soils, asphalt, and concrete. typically a cesium - 137 source is used. = = = commercial applications = = = radioluminescence tritium illumination : tritium is used with phosphor in rifle sights to increase nighttime firing accuracy. some runway markers and building exit signs use the same technology, to remain illuminated during blackouts. betavoltaics. smoke detector : an ionization smoke detector includes a tiny mass of radioactive americium - 241, which is a source of alpha radiation. two ionisation chambers are placed next to each other. both contain a small source of 241am that gives rise to a small constant current. one is closed and serves for comparison compact antennas. parabolic ( dish ) antennas are widely used. in most radars the transmitting antenna also serves as the receiving antenna ; this is called a monostatic radar. a radar which uses separate transmitting and receiving antennas is called a bistatic radar. airport surveillance radar – in aviation, radar is the main tool of air traffic control. a rotating dish antenna sweeps a vertical fan - shaped beam of microwaves around the airspace and the radar set shows the location of aircraft as " blips " of light on a display called a radar screen. airport radar operates at 2. 7 – 2. 9 ghz in the microwave s band. in large airports the radar image is displayed on multiple screens in an operations room called the tracon ( terminal radar approach control ), where air traffic controllers direct the aircraft by radio to maintain safe aircraft separation. secondary surveillance radar – aircraft carry radar transponders, transceivers which when triggered by the incoming radar signal transmit a return microwave signal. this causes the aircraft to show up more strongly on the radar screen. the radar which triggers the transponder and receives the return beam, usually mounted on top of the primary radar dish, is called the secondary surveillance radar. since radar cannot measure an aircraft ' s altitude with any accuracy, the transponder also transmits back the aircraft ' s altitude measured by its altimeter, and an id number identifying the aircraft, which is displayed on the radar screen. electronic countermeasures ( ecm ) – military defensive electronic systems designed to degrade enemy radar effectiveness, or deceive it with false information, to prevent enemies from locating local forces. it often consists of powerful microwave transmitters that can mimic enemy radar signals to create false target indications on the enemy radar screens. marine radar – an s or x band radar on ships used to detect nearby ships and obstructions like bridges. a rotating antenna sweeps a vertical fan - shaped beam of microwaves around the water surface surrounding the craft out to the horizon. weather radar – a doppler radar which maps weather precipitation intensities and wind speeds with the echoes returned from raindrops and their radial velocity by their doppler shift. phased - array radar – a radar set that uses a phased array, a computer - controlled antenna that can steer the radar beam quickly to point in different directions without moving the antenna. phased - array radars were developed by the military to track fast - moving missiles and aircraft. they are widely used in military equipment and are now spreading to civilian applications. synthetic aperture based on 1 / 10 and 1 / 100 weight percentages of the carbon and other alloying elements they contain. thus, the extracting and purifying methods used to extract iron in a blast furnace can affect the quality of steel that is produced. solid materials are generally grouped into three basic classifications : ceramics, metals, and polymers. this broad classification is based on the empirical makeup and atomic structure of the solid materials, and most solids fall into one of these broad categories. an item that is often made from each of these materials types is the beverage container. the material types used for beverage containers accordingly provide different advantages and disadvantages, depending on the material used. ceramic ( glass ) containers are optically transparent, impervious to the passage of carbon dioxide, relatively inexpensive, and are easily recycled, but are also heavy and fracture easily. metal ( aluminum alloy ) is relatively strong, is a good barrier to the diffusion of carbon dioxide, and is easily recycled. however, the cans are opaque, expensive to produce, and are easily dented and punctured. polymers ( polyethylene plastic ) are relatively strong, can be optically transparent, are inexpensive and lightweight, and can be recyclable, but are not as impervious to the passage of carbon dioxide as aluminum and glass. = = = ceramics and glasses = = = another application of materials science is the study of ceramics and glasses, typically the most brittle materials with industrial relevance. many ceramics and glasses exhibit covalent or ionic - covalent bonding with sio2 ( silica ) as a fundamental building block. ceramics – not to be confused with raw, unfired clay – are usually seen in crystalline form. the vast majority of commercial glasses contain a metal oxide fused with silica. at the high temperatures used to prepare glass, the material is a viscous liquid which solidifies into a disordered state upon cooling. windowpanes and eyeglasses are important examples. fibers of glass are also used for long - range telecommunication and optical transmission. scratch resistant corning gorilla glass is a well - known example of the application of materials science to drastically improve the properties of common components. engineering ceramics are known for their stiffness and stability under high temperatures, compression and electrical stress. alumina, silicon carbide, and tungsten carbide are made from a fine powder of their constituents in a process of sintering with a binder. hot pressing provides higher density material. chemical vapor deposition can place a film of a ceramic on another the thickness and the density of the material to be measured. the method is used for containers of liquids or of grainy substances thickness gauges : if the material is of constant density, the signal measured by the radiation detector depends on the thickness of the material. this is useful for continuous production, like of paper, rubber, etc. electrostatic control - to avoid the build - up of static electricity in production of paper, plastics, synthetic textiles, etc., a ribbon - shaped source of the alpha emitter 241am can be placed close to the material at the end of the production line. the source ionizes the air to remove electric charges on the material. radioactive tracers - since radioactive isotopes behave, chemically, mostly like the inactive element, the behavior of a certain chemical substance can be followed by tracing the radioactivity. examples : adding a gamma tracer to a gas or liquid in a closed system makes it possible to find a hole in a tube. adding a tracer to the surface of the component of a motor makes it possible to measure wear by measuring the activity of the lubricating oil. oil and gas exploration - nuclear well logging is used to help predict the commercial viability of new or existing wells. the technology involves the use of a neutron or gamma - ray source and a radiation detector which are lowered into boreholes to determine the properties of the surrounding rock such as porosity and lithography. [ 1 ] road construction - nuclear moisture / density gauges are used to determine the density of soils, asphalt, and concrete. typically a cesium - 137 source is used. = = = commercial applications = = = radioluminescence tritium illumination : tritium is used with phosphor in rifle sights to increase nighttime firing accuracy. some runway markers and building exit signs use the same technology, to remain illuminated during blackouts. betavoltaics. smoke detector : an ionization smoke detector includes a tiny mass of radioactive americium - 241, which is a source of alpha radiation. two ionisation chambers are placed next to each other. both contain a small source of 241am that gives rise to a small constant current. one is closed and serves for comparison, the other is open to ambient air ; it has a gridded electrode. when smoke enters the open chamber, the current is disrupted as the smoke particles attach to the charged ions and restore them to a neutral electrical state. this reduces the current in the open chamber. when the current drops below a certain threshold, the Question: Metal detectors used for airport security work on which principle? A) electricity B) inductance C) conductivity D) inertia	B) inductance
Context: for the treatment of diabetes, was previously extracted from the pancreas of abattoir animals ( cattle or pigs ). the genetically engineered bacteria are able to produce large quantities of synthetic human insulin at relatively low cost. biotechnology has also enabled emerging therapeutics like gene therapy. the application of biotechnology to basic science ( for example through the human genome project ) has also dramatically improved our understanding of biology and as our scientific knowledge of normal and disease biology has increased, our ability to develop new medicines to treat previously untreatable diseases has increased as well. genetic testing allows the genetic diagnosis of vulnerabilities to inherited diseases, and can also be used to determine a child ' s parentage ( genetic mother and father ) or in general a person ' s ancestry. in addition to studying chromosomes to the level of individual genes, genetic testing in a broader sense includes biochemical tests for the possible presence of genetic diseases, or mutant forms of genes associated with increased risk of developing genetic disorders. genetic testing identifies changes in chromosomes, genes, or proteins. most of the time, testing is used to find changes that are associated with inherited disorders. the results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person ' s chance of developing or passing on a genetic disorder. as of 2011 several hundred genetic tests were in use. since genetic testing may open up ethical or psychological problems, genetic testing is often accompanied by genetic counseling. = = = agriculture = = = genetically modified crops ( " gm crops ", or " biotech crops " ) are plants used in agriculture, the dna of which has been modified with genetic engineering techniques. in most cases, the main aim is to introduce a new trait that does not occur naturally in the species. biotechnology firms can contribute to future food security by improving the nutrition and viability of urban agriculture. furthermore, the protection of intellectual property rights encourages private sector investment in agrobiotechnology. examples in food crops include resistance to certain pests, diseases, stressful environmental conditions, resistance to chemical treatments ( e. g. resistance to a herbicide ), reduction of spoilage, or improving the nutrient profile of the crop. examples in non - food crops include production of pharmaceutical agents, biofuels, and other industrially useful goods, as well as for bioremediation. farmers have widely adopted gm technology. between 1996 and 2011, the total surface area of land cultivated with gm crops had increased by a factor of 94, from 17, 000 to 1, 600, 000 square best - known and controversial applications of genetic engineering is the creation and use of genetically modified crops or genetically modified livestock to produce genetically modified food. crops have been developed to increase production, increase tolerance to abiotic stresses, alter the composition of the food, or to produce novel products. the first crops to be released commercially on a large scale provided protection from insect pests or tolerance to herbicides. fungal and virus resistant crops have also been developed or are in development. this makes the insect and weed management of crops easier and can indirectly increase crop yield. gm crops that directly improve yield by accelerating growth or making the plant more hardy ( by improving salt, cold or drought tolerance ) are also under development. in 2016 salmon have been genetically modified with growth hormones to reach normal adult size much faster. gmos have been developed that modify the quality of produce by increasing the nutritional value or providing more industrially useful qualities or quantities. the amflora potato produces a more industrially useful blend of starches. soybeans and canola have been genetically modified to produce more healthy oils. the first commercialised gm food was a tomato that had delayed ripening, increasing its shelf life. plants and animals have been engineered to produce materials they do not normally make. pharming uses crops and animals as bioreactors to produce vaccines, drug intermediates, or the drugs themselves ; the useful product is purified from the harvest and then used in the standard pharmaceutical production process. cows and goats have been engineered to express drugs and other proteins in their milk, and in 2009 the fda approved a drug produced in goat milk. = = = other applications = = = genetic engineering has potential applications in conservation and natural area management. gene transfer through viral vectors has been proposed as a means of controlling invasive species as well as vaccinating threatened fauna from disease. transgenic trees have been suggested as a way to confer resistance to pathogens in wild populations. with the increasing risks of maladaptation in organisms as a result of climate change and other perturbations, facilitated adaptation through gene tweaking could be one solution to reducing extinction risks. applications of genetic engineering in conservation are thus far mostly theoretical and have yet to be put into practice. genetic engineering is also being used to create microbial art. some bacteria have been genetically engineered to create black and white photographs. novelty items such as lavender - colored carnations, blue roses, and glowing fish, have also been produced through genetic engineering. = = regulation = = the regulation of genetic engineering the best - suited crops ( e. g., those with the highest yields ) to produce enough food to support a growing population. as crops and fields became increasingly large and difficult to maintain, it was discovered that specific organisms and their by - products could effectively fertilize, restore nitrogen, and control pests. throughout the history of agriculture, farmers have inadvertently altered the genetics of their crops through introducing them to new environments and breeding them with other plants — one of the first forms of biotechnology. these processes also were included in early fermentation of beer. these processes were introduced in early mesopotamia, egypt, china and india, and still use the same basic biological methods. in brewing, malted grains ( containing enzymes ) convert starch from grains into sugar and then adding specific yeasts to produce beer. in this process, carbohydrates in the grains broke down into alcohols, such as ethanol. later, other cultures produced the process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united kingdom desperately needed to manufacture explosives during world war i. biotechnology has also led to the development of antibiotics. in 1928, alexander fleming discovered the mold penicillium. his work led to the purification of the antibiotic formed by the mold by howard florey, ernst boris chain and norman heatley – to form . throughout the history of agriculture, farmers have inadvertently altered the genetics of their crops through introducing them to new environments and breeding them with other plants — one of the first forms of biotechnology. these processes also were included in early fermentation of beer. these processes were introduced in early mesopotamia, egypt, china and india, and still use the same basic biological methods. in brewing, malted grains ( containing enzymes ) convert starch from grains into sugar and then adding specific yeasts to produce beer. in this process, carbohydrates in the grains broke down into alcohols, such as ethanol. later, other cultures produced the process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united kingdom desperately needed to manufacture explosives during world war i. biotechnology has also led to the development of antibiotics. in 1928, alexander fleming discovered the mold penicillium. his work led to the purification of the antibiotic formed by the mold by howard florey, ernst boris chain and norman heatley – to form what we today know as penicillin. in 1940, penicillin became available for medicinal use to treat bacterial infections in humans. the field of modern biotechnology is generally thought of as having been born in 1971 when paul berg ' s ( stanford ) experiments in gene splicing had early success. herbert w. boyer and still use the same basic biological methods. in brewing, malted grains ( containing enzymes ) convert starch from grains into sugar and then adding specific yeasts to produce beer. in this process, carbohydrates in the grains broke down into alcohols, such as ethanol. later, other cultures produced the process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united kingdom desperately needed to manufacture explosives during world war i. biotechnology has also led to the development of antibiotics. in 1928, alexander fleming discovered the mold penicillium. his work led to the purification of the antibiotic formed by the mold by howard florey, ernst boris chain and norman heatley – to form what we today know as penicillin. in 1940, penicillin became available for medicinal use to treat bacterial infections in humans. the field of modern biotechnology is generally thought of as having been born in 1971 when paul berg ' s ( stanford ) experiments in gene splicing had early success. herbert w. boyer ( univ. calif. at san francisco ) and stanley n. cohen ( stanford ) significantly advanced the new technology in 1972 by transferring genetic material into a bacterium, such that the imported material would be reproduced. the commercial viability of a biotechnology industry was significantly expanded on june 16, 1980, when the united states used to manufacture existing medicines relatively easily and cheaply. the first genetically engineered products were medicines designed to treat human diseases. to cite one example, in 1978 genentech developed synthetic humanized insulin by joining its gene with a plasmid vector inserted into the bacterium escherichia coli. insulin, widely used for the treatment of diabetes, was previously extracted from the pancreas of abattoir animals ( cattle or pigs ). the genetically engineered bacteria are able to produce large quantities of synthetic human insulin at relatively low cost. biotechnology has also enabled emerging therapeutics like gene therapy. the application of biotechnology to basic science ( for example through the human genome project ) has also dramatically improved our understanding of biology and as our scientific knowledge of normal and disease biology has increased, our ability to develop new medicines to treat previously untreatable diseases has increased as well. genetic testing allows the genetic diagnosis of vulnerabilities to inherited diseases, and can also be used to determine a child ' s parentage ( genetic mother and father ) or in general a person ' s ancestry. in addition to studying chromosomes to the level of individual genes, genetic testing in a broader sense includes biochemical tests for the possible presence of genetic diseases, or mutant forms of genes associated with increased risk of developing genetic disorders. genetic testing identifies changes in chromosomes, genes, or proteins. most of the time, testing is used to find changes that are associated with inherited disorders. the results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person ' s chance of developing or passing on a genetic disorder. as of 2011 several hundred genetic tests were in use. since genetic testing may open up ethical or psychological problems, genetic testing is often accompanied by genetic counseling. = = = agriculture = = = genetically modified crops ( " gm crops ", or " biotech crops " ) are plants used in agriculture, the dna of which has been modified with genetic engineering techniques. in most cases, the main aim is to introduce a new trait that does not occur naturally in the species. biotechnology firms can contribute to future food security by improving the nutrition and viability of urban agriculture. furthermore, the protection of intellectual property rights encourages private sector investment in agrobiotechnology. examples in food crops include resistance to certain pests, diseases, stressful environmental conditions, resistance to chemical treatments ( e. g. resistance to a herbicide ), reduction of spoilage, or improving the nutrient profile of the crop. examples in non - food crops include production of eat them. plants and other photosynthetic organisms are at the base of most food chains because they use the energy from the sun and nutrients from the soil and atmosphere, converting them into a form that can be used by animals. this is what ecologists call the first trophic level. the modern forms of the major staple foods, such as hemp, teff, maize, rice, wheat and other cereal grasses, pulses, bananas and plantains, as well as hemp, flax and cotton grown for their fibres, are the outcome of prehistoric selection over thousands of years from among wild ancestral plants with the most desirable characteristics. botanists study how plants produce food and how to increase yields, for example through plant breeding, making their work important to humanity ' s ability to feed the world and provide food security for future generations. botanists also study weeds, which are a considerable problem in agriculture, and the biology and control of plant pathogens in agriculture and natural ecosystems. ethnobotany is the study of the relationships between plants and people. when applied to the investigation of historical plant – people relationships ethnobotany may be referred to as archaeobotany or palaeoethnobotany. some of the earliest plant - people relationships arose between the indigenous people of canada in identifying edible plants from inedible plants. this relationship the indigenous people had with plants was recorded by ethnobotanists. = = plant biochemistry = = plant biochemistry is the study of the chemical processes used by plants. some of these processes are used in their primary metabolism like the photosynthetic calvin cycle and crassulacean acid metabolism. others make specialised materials like the cellulose and lignin used to build their bodies, and secondary products like resins and aroma compounds. plants and various other groups of photosynthetic eukaryotes collectively known as " algae " have unique organelles known as chloroplasts. chloroplasts are thought to be descended from cyanobacteria that formed endosymbiotic relationships with ancient plant and algal ancestors. chloroplasts and cyanobacteria contain the blue - green pigment chlorophyll a. chlorophyll a ( as well as its plant and green algal - specific cousin chlorophyll b ) absorbs light in the blue - violet and orange / red parts of the spectrum while reflecting and transmitting the green light that we see as the characteristic colour ##tion, and pasteurization in order to become products that can be sold. there are three levels of food processing : primary, secondary, and tertiary. primary food processing involves turning agricultural products into other products that can be turned into food, secondary food processing is the making of food from readily available ingredients, and tertiary food processing is commercial production of ready - to eat or heat - and - serve foods. drying, pickling, salting, and fermenting foods were some of the oldest food processing techniques used to preserve food by preventing yeasts, molds, and bacteria to cause spoiling. methods for preserving food have evolved to meet current standards of food safety but still use the same processes as the past. biochemical engineers also work to improve the nutritional value of food products, such as in golden rice, which was developed to prevent vitamin a deficiency in certain areas where this was an issue. efforts to advance preserving technologies can also ensure lasting retention of nutrients as foods are stored. packaging plays a key role in preserving as well as ensuring the safety of the food by protecting the product from contamination, physical damage, and tampering. packaging can also make it easier to transport and serve food. a common job for biochemical engineers working in the food industry is to design ways to perform all these processes on a large scale in order to meet the demands of the population. responsibilities for this career path include designing and performing experiments, optimizing processes, consulting with groups to develop new technologies, and preparing project plans for equipment and facilities. = = = pharmaceuticals = = = in the pharmaceutical industry, bioprocess engineering plays a crucial role in the large - scale production of biopharmaceuticals, such as monoclonal antibodies, vaccines, and therapeutic proteins. the development and optimization of bioreactors and fermentation systems are essential for the mass production of these products, ensuring consistent quality and high yields. for example, recombinant proteins like insulin and erythropoietin are produced through cell culture systems using genetically modified cells. the bioprocess engineer ’ s role is to optimize variables like temperature, ph, nutrient availability, and oxygen levels to maximize the efficiency of these systems. the growing field of gene therapy also relies on bioprocessing techniques to produce viral vectors, which are used to deliver therapeutic genes to patients. this involves scaling up processes from laboratory to industrial scale while maintaining safety and regulatory compliance. as the demand for biopharmaceutical products increases, advancements process of lactic acid fermentation, which produced other preserved foods, such as soy sauce. fermentation was also used in this time period to produce leavened bread. although the process of fermentation was not fully understood until louis pasteur ' s work in 1857, it is still the first use of biotechnology to convert a food source into another form. before the time of charles darwin ' s work and life, animal and plant scientists had already used selective breeding. darwin added to that body of work with his scientific observations about the ability of science to change species. these accounts contributed to darwin ' s theory of natural selection. for thousands of years, humans have used selective breeding to improve the production of crops and livestock to use them for food. in selective breeding, organisms with desirable characteristics are mated to produce offspring with the same characteristics. for example, this technique was used with corn to produce the largest and sweetest crops. in the early twentieth century scientists gained a greater understanding of microbiology and explored ways of manufacturing specific products. in 1917, chaim weizmann first used a pure microbiological culture in an industrial process, that of manufacturing corn starch using clostridium acetobutylicum, to produce acetone, which the united kingdom desperately needed to manufacture explosives during world war i. biotechnology has also led to the development of antibiotics. in 1928, alexander fleming discovered the mold penicillium. his work led to the purification of the antibiotic formed by the mold by howard florey, ernst boris chain and norman heatley – to form what we today know as penicillin. in 1940, penicillin became available for medicinal use to treat bacterial infections in humans. the field of modern biotechnology is generally thought of as having been born in 1971 when paul berg ' s ( stanford ) experiments in gene splicing had early success. herbert w. boyer ( univ. calif. at san francisco ) and stanley n. cohen ( stanford ) significantly advanced the new technology in 1972 by transferring genetic material into a bacterium, such that the imported material would be reproduced. the commercial viability of a biotechnology industry was significantly expanded on june 16, 1980, when the united states supreme court ruled that a genetically modified microorganism could be patented in the case of diamond v. chakrabarty. indian - born ananda chakrabarty, working for general electric, had modified a bacterium ( of the genus pseudomonas ) capable of breaking down crude oil, which he proposed to include the manufacturing of drugs, creation of model animals that mimic human conditions and gene therapy. one of the earliest uses of genetic engineering was to mass - produce human insulin in bacteria. this application has now been applied to human growth hormones, follicle stimulating hormones ( for treating infertility ), human albumin, monoclonal antibodies, antihemophilic factors, vaccines and many other drugs. mouse hybridomas, cells fused together to create monoclonal antibodies, have been adapted through genetic engineering to create human monoclonal antibodies. genetically engineered viruses are being developed that can still confer immunity, but lack the infectious sequences. genetic engineering is also used to create animal models of human diseases. genetically modified mice are the most common genetically engineered animal model. they have been used to study and model cancer ( the oncomouse ), obesity, heart disease, diabetes, arthritis, substance abuse, anxiety, aging and parkinson disease. potential cures can be tested against these mouse models. gene therapy is the genetic engineering of humans, generally by replacing defective genes with effective ones. clinical research using somatic gene therapy has been conducted with several diseases, including x - linked scid, chronic lymphocytic leukemia ( cll ), and parkinson ' s disease. in 2012, alipogene tiparvovec became the first gene therapy treatment to be approved for clinical use. in 2015 a virus was used to insert a healthy gene into the skin cells of a boy suffering from a rare skin disease, epidermolysis bullosa, in order to grow, and then graft healthy skin onto 80 percent of the boy ' s body which was affected by the illness. germline gene therapy would result in any change being inheritable, which has raised concerns within the scientific community. in 2015, crispr was used to edit the dna of non - viable human embryos, leading scientists of major world academies to call for a moratorium on inheritable human genome edits. there are also concerns that the technology could be used not just for treatment, but for enhancement, modification or alteration of a human beings ' appearance, adaptability, intelligence, character or behavior. the distinction between cure and enhancement can also be difficult to establish. in november 2018, he jiankui announced that he had edited the genomes of two human embryos, to attempt to disable the ccr5 gene, which codes for a receptor that hiv uses to enter cells. the work was widely condemned as unethical, dangerous, Question: Methanogens in their gut enable what process in cows? A) digestion B) regeneration C) absorption D) excretion	A) digestion
Context: to dye denim and the artist ' s pigments gamboge and rose madder. sugar, starch, cotton, linen, hemp, some types of rope, wood and particle boards, papyrus and paper, vegetable oils, wax, and natural rubber are examples of commercially important materials made from plant tissues or their secondary products. charcoal, a pure form of carbon made by pyrolysis of wood, has a long history as a metal - smelting fuel, as a filter material and adsorbent and as an artist ' s material and is one of the three ingredients of gunpowder. cellulose, the world ' s most abundant organic polymer, can be converted into energy, fuels, materials and chemical feedstock. products made from cellulose include rayon and cellophane, wallpaper paste, biobutanol and gun cotton. sugarcane, rapeseed and soy are some of the plants with a highly fermentable sugar or oil content that are used as sources of biofuels, important alternatives to fossil fuels, such as biodiesel. sweetgrass was used by native americans to ward off bugs like mosquitoes. these bug repelling properties of sweetgrass were later found by the american chemical society in the molecules phytol and coumarin. = = plant ecology = = plant ecology is the science of the functional relationships between plants and their habitats – the environments where they complete their life cycles. plant ecologists study the composition of local and regional floras, their biodiversity, genetic diversity and fitness, the adaptation of plants to their environment, and their competitive or mutualistic interactions with other species. some ecologists even rely on empirical data from indigenous people that is gathered by ethnobotanists. this information can relay a great deal of information on how the land once was thousands of years ago and how it has changed over that time. the goals of plant ecology are to understand the causes of their distribution patterns, productivity, environmental impact, evolution, and responses to environmental change. plants depend on certain edaphic ( soil ) and climatic factors in their environment but can modify these factors too. for example, they can change their environment ' s albedo, increase runoff interception, stabilise mineral soils and develop their organic content, and affect local temperature. plants compete with other organisms in their ecosystem for resources. they interact with their neighbours at a variety of spatial scales in groups, populations and communities that collectively constitute vegetation. regions with characteristic vegetation types and dominant plants as well as similar abiot organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. salt - tolerant archaea ( the haloarchaea ) use sunlight as an energy source, and other species of archaea fix carbon, but unlike plants and cyanobacteria, no known species of archaea does both. archaea reproduce asexually by binary fission, fragmentation, or budding ; unlike bacteria, no known species of archaea form endospores. the first observed archaea were extremophiles, living in extreme environments, such as hot springs and salt lakes with no other organisms. improved molecular detection tools led to the discovery of archaea in almost every habitat, including soil, oceans, and marshlands. archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. archaea are a major part of earth ' s life. they are part of the microbiota of all organisms. in the human microbiome, they are important in the gut, mouth, and on the skin. their morphological, metabolic, and geographical diversity permits them to play multiple ecological roles : carbon fixation ; nitrogen cycling ; organic compound turnover ; and maintaining microbial symbiotic and syntrophic communities, for example. = = = eukaryotes = = = eukaryotes are hypothesized to have split from archaea, which was followed by their endosymbioses with bacteria ( or symbiogenesis ) that gave rise to mitochondria and chloroplasts, both of which are now part of modern - day eukaryotic cells. the major lineages of eukaryotes diversified in the precambrian about 1. 5 billion years ago and can be classified into eight major clades : alveolates, excavates, stramenopiles, plants, rhizarians, amoebozoans, fungi, and animals. five of these clades are collectively known as protists, which are mostly microscopic eukaryotic organisms that are not plants, fungi, or animals. while it is likely that protists share a common ancestor ( the last eukaryotic common ancestor ), protists by themselves do not constitute a separate clade as some protists may be more closely related to plants, fungi, or animals than they are to other protists. like groupings such as algae, c. 4000 bc, associated with the maadi culture. this represents the earliest evidence for smelting in africa. the varna necropolis, bulgaria, is a burial site located in the western industrial zone of varna, approximately 4 km from the city centre, internationally considered one of the key archaeological sites in world prehistory. the oldest gold treasure in the world, dating from 4, 600 bc to 4, 200 bc, was discovered at the site. the gold piece dating from 4, 500 bc, found in 2019 in durankulak, near varna is another important example. other signs of early metals are found from the third millennium bc in palmela, portugal, los millares, spain, and stonehenge, united kingdom. the precise beginnings, however, have not be clearly ascertained and new discoveries are both continuous and ongoing. in approximately 1900 bc, ancient iron smelting sites existed in tamil nadu. in the near east, about 3, 500 bc, it was discovered that by combining copper and tin, a superior metal could be made, an alloy called bronze. this represented a major technological shift known as the bronze age. the extraction of iron from its ore into a workable metal is much more difficult than for copper or tin. the process appears to have been invented by the hittites in about 1200 bc, beginning the iron age. the secret of extracting and working iron was a key factor in the success of the philistines. historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. this includes the ancient and medieval kingdoms and empires of the middle east and near east, ancient iran, ancient egypt, ancient nubia, and anatolia in present - day turkey, ancient nok, carthage, the celts, greeks and romans of ancient europe, medieval europe, ancient and medieval china, ancient and medieval india, ancient and medieval japan, amongst others. a 16th century book by georg agricola, de re metallica, describes the highly developed and complex processes of mining metal ores, metal extraction, and metallurgy of the time. agricola has been described as the " father of metallurgy ". = = extraction = = extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted raw metals into a purer form. in order to convert a metal oxide or sulphide to a purer metal, the ore must be reduced physically, chemically, or electroly earliest record of a ship under sail is that of a nile boat dating to around 7, 000 bce. from prehistoric times, egyptians likely used the power of the annual flooding of the nile to irrigate their lands, gradually learning to regulate much of it through purposely built irrigation channels and " catch " basins. the ancient sumerians in mesopotamia used a complex system of canals and levees to divert water from the tigris and euphrates rivers for irrigation. archaeologists estimate that the wheel was invented independently and concurrently in mesopotamia ( in present - day iraq ), the northern caucasus ( maykop culture ), and central europe. time estimates range from 5, 500 to 3, 000 bce with most experts putting it closer to 4, 000 bce. the oldest artifacts with drawings depicting wheeled carts date from about 3, 500 bce. more recently, the oldest - known wooden wheel in the world as of 2024 was found in the ljubljana marsh of slovenia ; austrian experts have established that the wheel is between 5, 100 and 5, 350 years old. the invention of the wheel revolutionized trade and war. it did not take long to discover that wheeled wagons could be used to carry heavy loads. the ancient sumerians used a potter ' s wheel and may have invented it. a stone pottery wheel found in the city - state of ur dates to around 3, 429 bce, and even older fragments of wheel - thrown pottery have been found in the same area. fast ( rotary ) potters ' wheels enabled early mass production of pottery, but it was the use of the wheel as a transformer of energy ( through water wheels, windmills, and even treadmills ) that revolutionized the application of nonhuman power sources. the first two - wheeled carts were derived from travois and were first used in mesopotamia and iran in around 3, 000 bce. the oldest known constructed roadways are the stone - paved streets of the city - state of ur, dating to c. 4, 000 bce, and timber roads leading through the swamps of glastonbury, england, dating to around the same period. the first long - distance road, which came into use around 3, 500 bce, spanned 2, 400 km from the persian gulf to the mediterranean sea, but was not paved and was only partially maintained. in around 2, 000 bce, the minoans on the greek island of crete built a 50 km road leading from the palace of gortyn on the south side of the island, through the mountains, used for tools, weapons and monumental statuary. by 1200 bc they could cast objects 5 m long in a single piece. several of the six classic simple machines were invented in mesopotamia. mesopotamians have been credited with the invention of the wheel. the wheel and axle mechanism first appeared with the potter ' s wheel, invented in mesopotamia ( modern iraq ) during the 5th millennium bc. this led to the invention of the wheeled vehicle in mesopotamia during the early 4th millennium bc. depictions of wheeled wagons found on clay tablet pictographs at the eanna district of uruk are dated between 3700 and 3500 bc. the lever was used in the shadoof water - lifting device, the first crane machine, which appeared in mesopotamia circa 3000 bc, and then in ancient egyptian technology circa 2000 bc. the earliest evidence of pulleys date back to mesopotamia in the early 2nd millennium bc. the screw, the last of the simple machines to be invented, first appeared in mesopotamia during the neo - assyrian period ( 911 – 609 ) bc. the assyrian king sennacherib ( 704 – 681 bc ) claims to have invented automatic sluices and to have been the first to use water screw pumps, of up to 30 tons weight, which were cast using two - part clay molds rather than by the ' lost wax ' process. the jerwan aqueduct ( c. 688 bc ) is made with stone arches and lined with waterproof concrete. the babylonian astronomical diaries spanned 800 years. they enabled meticulous astronomers to plot the motions of the planets and to predict eclipses. the earliest evidence of water wheels and watermills date back to the ancient near east in the 4th century bc, specifically in the persian empire before 350 bc, in the regions of mesopotamia ( iraq ) and persia ( iran ). this pioneering use of water power constituted the first human - devised motive force not to rely on muscle power ( besides the sail ). = = = = egypt = = = = the egyptians, known for building pyramids centuries before the creation of modern tools, invented and used many simple machines, such as the ramp to aid construction processes. historians and archaeologists have found evidence that the pyramids were built using three of what is called the six simple machines, from which all machines are based. these machines are the inclined plane, the wedge, and the lever, which allowed the ancient egyptians to move millions of limestone blocks which weighed approximately 3. 5 tons ( 7, 000 lbs. ) each into place to create structures like the pathogens in agriculture and natural ecosystems. ethnobotany is the study of the relationships between plants and people. when applied to the investigation of historical plant – people relationships ethnobotany may be referred to as archaeobotany or palaeoethnobotany. some of the earliest plant - people relationships arose between the indigenous people of canada in identifying edible plants from inedible plants. this relationship the indigenous people had with plants was recorded by ethnobotanists. = = plant biochemistry = = plant biochemistry is the study of the chemical processes used by plants. some of these processes are used in their primary metabolism like the photosynthetic calvin cycle and crassulacean acid metabolism. others make specialised materials like the cellulose and lignin used to build their bodies, and secondary products like resins and aroma compounds. plants and various other groups of photosynthetic eukaryotes collectively known as " algae " have unique organelles known as chloroplasts. chloroplasts are thought to be descended from cyanobacteria that formed endosymbiotic relationships with ancient plant and algal ancestors. chloroplasts and cyanobacteria contain the blue - green pigment chlorophyll a. chlorophyll a ( as well as its plant and green algal - specific cousin chlorophyll b ) absorbs light in the blue - violet and orange / red parts of the spectrum while reflecting and transmitting the green light that we see as the characteristic colour of these organisms. the energy in the red and blue light that these pigments absorb is used by chloroplasts to make energy - rich carbon compounds from carbon dioxide and water by oxygenic photosynthesis, a process that generates molecular oxygen ( o2 ) as a by - product. the light energy captured by chlorophyll a is initially in the form of electrons ( and later a proton gradient ) that is used to make molecules of atp and nadph which temporarily store and transport energy. their energy is used in the light - independent reactions of the calvin cycle by the enzyme rubisco to produce molecules of the 3 - carbon sugar glyceraldehyde 3 - phosphate ( g3p ). glyceraldehyde 3 - phosphate is the first product of photosynthesis and the raw material from which glucose and almost all other organic molecules of biological origin are synthesised. some of the glucose is converted to star if wood has been with us since time immemorial, being part of our environment, housing and tools, now wood has gain momentum, as it is clear that wood improves our life style. because of the healthiness, resistance, ecology and comfort, wood is important for all of us, no matter what our life style is. woodtouch project aims to open a completely new market for furniture and interior design companies, enabling touch interaction between the user and wooden furniture surfaces. why not switch on or dim the lights touching a wooden table? why not turn on the heating system? why not use wood as a touch sensitive surface for domotic control? the furniture designed with this novel technology, offers a wooden outer image and has different touch sensitive areas over the ones the user is able to control all sorts of electric appliances touching over a wooden surface. ##elting. metallurgy of lead has also been found in the balkans during the same period. copper smelting is documented at sites in anatolia and at the site of tal - i iblis in southeastern iran from c. 5000 bc. copper smelting is first documented in the delta region of northern egypt in c. 4000 bc, associated with the maadi culture. this represents the earliest evidence for smelting in africa. the varna necropolis, bulgaria, is a burial site located in the western industrial zone of varna, approximately 4 km from the city centre, internationally considered one of the key archaeological sites in world prehistory. the oldest gold treasure in the world, dating from 4, 600 bc to 4, 200 bc, was discovered at the site. the gold piece dating from 4, 500 bc, found in 2019 in durankulak, near varna is another important example. other signs of early metals are found from the third millennium bc in palmela, portugal, los millares, spain, and stonehenge, united kingdom. the precise beginnings, however, have not be clearly ascertained and new discoveries are both continuous and ongoing. in approximately 1900 bc, ancient iron smelting sites existed in tamil nadu. in the near east, about 3, 500 bc, it was discovered that by combining copper and tin, a superior metal could be made, an alloy called bronze. this represented a major technological shift known as the bronze age. the extraction of iron from its ore into a workable metal is much more difficult than for copper or tin. the process appears to have been invented by the hittites in about 1200 bc, beginning the iron age. the secret of extracting and working iron was a key factor in the success of the philistines. historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. this includes the ancient and medieval kingdoms and empires of the middle east and near east, ancient iran, ancient egypt, ancient nubia, and anatolia in present - day turkey, ancient nok, carthage, the celts, greeks and romans of ancient europe, medieval europe, ancient and medieval china, ancient and medieval india, ancient and medieval japan, amongst others. a 16th century book by georg agricola, de re metallica, describes the highly developed and complex processes of mining metal ores, metal extraction, and metallurgy of the time. agricola has been described as the " father of metallurgy sumerians in mesopotamia used a complex system of canals and levees to divert water from the tigris and euphrates rivers for irrigation. archaeologists estimate that the wheel was invented independently and concurrently in mesopotamia ( in present - day iraq ), the northern caucasus ( maykop culture ), and central europe. time estimates range from 5, 500 to 3, 000 bce with most experts putting it closer to 4, 000 bce. the oldest artifacts with drawings depicting wheeled carts date from about 3, 500 bce. more recently, the oldest - known wooden wheel in the world as of 2024 was found in the ljubljana marsh of slovenia ; austrian experts have established that the wheel is between 5, 100 and 5, 350 years old. the invention of the wheel revolutionized trade and war. it did not take long to discover that wheeled wagons could be used to carry heavy loads. the ancient sumerians used a potter ' s wheel and may have invented it. a stone pottery wheel found in the city - state of ur dates to around 3, 429 bce, and even older fragments of wheel - thrown pottery have been found in the same area. fast ( rotary ) potters ' wheels enabled early mass production of pottery, but it was the use of the wheel as a transformer of energy ( through water wheels, windmills, and even treadmills ) that revolutionized the application of nonhuman power sources. the first two - wheeled carts were derived from travois and were first used in mesopotamia and iran in around 3, 000 bce. the oldest known constructed roadways are the stone - paved streets of the city - state of ur, dating to c. 4, 000 bce, and timber roads leading through the swamps of glastonbury, england, dating to around the same period. the first long - distance road, which came into use around 3, 500 bce, spanned 2, 400 km from the persian gulf to the mediterranean sea, but was not paved and was only partially maintained. in around 2, 000 bce, the minoans on the greek island of crete built a 50 km road leading from the palace of gortyn on the south side of the island, through the mountains, to the palace of knossos on the north side of the island. unlike the earlier road, the minoan road was completely paved. ancient minoan private homes had running water. a bathtub virtually identical to modern ones was unearthed at the palace of knossos. several minoan private homes also and irrigation in the alluvial south, and catchment systems stretching for tens of kilometers in the hilly north. their palaces had sophisticated drainage systems. writing was invented in mesopotamia, using the cuneiform script. many records on clay tablets and stone inscriptions have survived. these civilizations were early adopters of bronze technologies which they used for tools, weapons and monumental statuary. by 1200 bc they could cast objects 5 m long in a single piece. several of the six classic simple machines were invented in mesopotamia. mesopotamians have been credited with the invention of the wheel. the wheel and axle mechanism first appeared with the potter ' s wheel, invented in mesopotamia ( modern iraq ) during the 5th millennium bc. this led to the invention of the wheeled vehicle in mesopotamia during the early 4th millennium bc. depictions of wheeled wagons found on clay tablet pictographs at the eanna district of uruk are dated between 3700 and 3500 bc. the lever was used in the shadoof water - lifting device, the first crane machine, which appeared in mesopotamia circa 3000 bc, and then in ancient egyptian technology circa 2000 bc. the earliest evidence of pulleys date back to mesopotamia in the early 2nd millennium bc. the screw, the last of the simple machines to be invented, first appeared in mesopotamia during the neo - assyrian period ( 911 – 609 ) bc. the assyrian king sennacherib ( 704 – 681 bc ) claims to have invented automatic sluices and to have been the first to use water screw pumps, of up to 30 tons weight, which were cast using two - part clay molds rather than by the ' lost wax ' process. the jerwan aqueduct ( c. 688 bc ) is made with stone arches and lined with waterproof concrete. the babylonian astronomical diaries spanned 800 years. they enabled meticulous astronomers to plot the motions of the planets and to predict eclipses. the earliest evidence of water wheels and watermills date back to the ancient near east in the 4th century bc, specifically in the persian empire before 350 bc, in the regions of mesopotamia ( iraq ) and persia ( iran ). this pioneering use of water power constituted the first human - devised motive force not to rely on muscle power ( besides the sail ). = = = = egypt = = = = the egyptians, known for building pyramids centuries before the creation of modern tools, invented and used many simple machines, such as the ramp to aid construction processes. historians and archaeologists have found evidence that the pyramids were built using Question: The skeleton of lampreys is made of what? A) collagen B) cartilage C) chitin D) ligament	B) cartilage
Context: tubers in potato is one example. particularly in arctic or alpine habitats, where opportunities for fertilisation of flowers by animals are rare, plantlets or bulbs, may develop instead of flowers, replacing sexual reproduction with asexual reproduction and giving rise to clonal populations genetically identical to the parent. this is one of several types of apomixis that occur in plants. apomixis can also happen in a seed, producing a seed that contains an embryo genetically identical to the parent. most sexually reproducing organisms are diploid, with paired chromosomes, but doubling of their chromosome number may occur due to errors in cytokinesis. this can occur early in development to produce an autopolyploid or partly autopolyploid organism, or during normal processes of cellular differentiation to produce some cell types that are polyploid ( endopolyploidy ), or during gamete formation. an allopolyploid plant may result from a hybridisation event between two different species. both autopolyploid and allopolyploid plants can often reproduce normally, but may be unable to cross - breed successfully with the parent population because there is a mismatch in chromosome numbers. these plants that are reproductively isolated from the parent species but live within the same geographical area, may be sufficiently successful to form a new species. some otherwise sterile plant polyploids can still reproduce vegetatively or by seed apomixis, forming clonal populations of identical individuals. durum wheat is a fertile tetraploid allopolyploid, while bread wheat is a fertile hexaploid. the commercial banana is an example of a sterile, seedless triploid hybrid. common dandelion is a triploid that produces viable seeds by apomictic seed. as in other eukaryotes, the inheritance of endosymbiotic organelles like mitochondria and chloroplasts in plants is non - mendelian. chloroplasts are inherited through the male parent in gymnosperms but often through the female parent in flowering plants. = = = molecular genetics = = = a considerable amount of new knowledge about plant function comes from studies of the molecular genetics of model plants such as the thale cress, arabidopsis thaliana, a weedy species in the mustard family ( brassicaceae ). the genome or hereditary information contained in the genes of this species is encoded by about 135 million base pairs of dna, forming one of the consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. over 1. 5 million living animal species have been described — of which around 1 million are insects — but it has been estimated there are over 7 million animal species in total. they have complex interactions with each other and their environments, forming intricate food webs. = = = viruses = = = viruses are submicroscopic infectious agents that replicate inside the cells of organisms. viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. more than 6, 000 virus species have been described in detail. viruses are found in almost every ecosystem on earth and are the most numerous type of biological entity. the origins of viruses in the evolutionary history of life are unclear : some may have evolved from plasmids — pieces of dna that can move between cells — while others may have evolved from bacteria. in evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogous to sexual reproduction. because viruses possess some but not all characteristics of life, they have been described as " organisms at the edge of life ", and as self - replicators. = = ecology = = ecology is the study of the distribution and abundance of life, the interaction between organisms and their environment. = = = ecosystems = = = the community of living ( biotic ) organisms in conjunction with the nonliving ( abiotic ) components ( e. g., water, light, radiation, temperature, humidity, atmosphere, acidity, and soil ) of their environment is called an ecosystem. these biotic and abiotic components are linked together through nutrient cycles and energy flows. energy from the sun enters the system through photosynthesis and is incorporated into plant tissue. by feeding on plants and on one another, animals move matter and energy through the system. they also influence the quantity of plant and microbial biomass present. by breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes. = = = populations = = = a population is the group of organisms of the same species that occupies an area and reproduce from generation to generation. population size can be estimated by multiplying population density by the area or volume. the carrying capacity of an environment ##ta together form the monophyletic group or clade streptophytina. nonvascular land plants are embryophytes that lack the vascular tissues xylem and phloem. they include mosses, liverworts and hornworts. pteridophytic vascular plants with true xylem and phloem that reproduced by spores germinating into free - living gametophytes evolved during the silurian period and diversified into several lineages during the late silurian and early devonian. representatives of the lycopods have survived to the present day. by the end of the devonian period, several groups, including the lycopods, sphenophylls and progymnosperms, had independently evolved " megaspory " – their spores were of two distinct sizes, larger megaspores and smaller microspores. their reduced gametophytes developed from megaspores retained within the spore - producing organs ( megasporangia ) of the sporophyte, a condition known as endospory. seeds consist of an endosporic megasporangium surrounded by one or two sheathing layers ( integuments ). the young sporophyte develops within the seed, which on germination splits to release it. the earliest known seed plants date from the latest devonian famennian stage. following the evolution of the seed habit, seed plants diversified, giving rise to a number of now - extinct groups, including seed ferns, as well as the modern gymnosperms and angiosperms. gymnosperms produce " naked seeds " not fully enclosed in an ovary ; modern representatives include conifers, cycads, ginkgo, and gnetales. angiosperms produce seeds enclosed in a structure such as a carpel or an ovary. ongoing research on the molecular phylogenetics of living plants appears to show that the angiosperms are a sister clade to the gymnosperms. = = plant physiology = = plant physiology encompasses all the internal chemical and physical activities of plants associated with life. chemicals obtained from the air, soil and water form the basis of all plant metabolism. the energy of sunlight, captured by oxygenic photosynthesis and released by cellular respiration, is the basis of almost all life. photoautotrophs, including all green plants, algae and cyanobacteria gather energy directly from sunlight by photosynthesis. hetero an alternative explanation of 1 / f - noise in manganites is suggested and discussed the work is a study of the geometry of the molecules via molecular mechanics of the main alkaloids found in the seeds of argemone mexicana linn, a prickly poppy, which is considered one of the most important species of plants in traditional mexican and indian medicine system. the seeds have toxic properties as well as bactericide, hallucinogenic, fungicide, insecticide, in isoquinolines and sanguinarine alkaloids such as berberine. a computational study of the molecular geometry of the molecules through molecular mechanics of the main alkaloids compounds present in plant seeds is described in a computer simulation. the plant has active ingredients compounds : allocryptopine, berberine, chelerythrine, copsitine, dihydrosanguinarine, protopine and sanguinarine. the studied alkaloids form two groups having similar charge distribution among themselves, which have dipole moments of these two times higher than in the other group. unitary recordings in freely - moving pulse weakly electric fish suggest spike timing encoding of electrosensory signals is the scientific study of inheritance. mendelian inheritance, specifically, is the process by which genes and traits are passed on from parents to offspring. it has several principles. the first is that genetic characteristics, alleles, are discrete and have alternate forms ( e. g., purple vs. white or tall vs. dwarf ), each inherited from one of two parents. based on the law of dominance and uniformity, which states that some alleles are dominant while others are recessive ; an organism with at least one dominant allele will display the phenotype of that dominant allele. during gamete formation, the alleles for each gene segregate, so that each gamete carries only one allele for each gene. heterozygotic individuals produce gametes with an equal frequency of two alleles. finally, the law of independent assortment, states that genes of different traits can segregate independently during the formation of gametes, i. e., genes are unlinked. an exception to this rule would include traits that are sex - linked. test crosses can be performed to experimentally determine the underlying genotype of an organism with a dominant phenotype. a punnett square can be used to predict the results of a test cross. the chromosome theory of inheritance, which states that genes are found on chromosomes, was supported by thomas morgans ' s experiments with fruit flies, which established the sex linkage between eye color and sex in these insects. = = = genes and dna = = = a gene is a unit of heredity that corresponds to a region of deoxyribonucleic acid ( dna ) that carries genetic information that controls form or function of an organism. dna is composed of two polynucleotide chains that coil around each other to form a double helix. it is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. the set of chromosomes in a cell is collectively known as its genome. in eukaryotes, dna is mainly in the cell nucleus. in prokaryotes, the dna is held within the nucleoid. the genetic information is held within genes, and the complete assemblage in an organism is called its genotype. dna replication is a semiconservative process whereby each strand serves as a template for a new strand of dna. mutations are heritable changes in dna. they can arise spontaneously as a result of replication errors that were not corrected by proofreading or can ##m and phloem that reproduced by spores germinating into free - living gametophytes evolved during the silurian period and diversified into several lineages during the late silurian and early devonian. representatives of the lycopods have survived to the present day. by the end of the devonian period, several groups, including the lycopods, sphenophylls and progymnosperms, had independently evolved " megaspory " – their spores were of two distinct sizes, larger megaspores and smaller microspores. their reduced gametophytes developed from megaspores retained within the spore - producing organs ( megasporangia ) of the sporophyte, a condition known as endospory. seeds consist of an endosporic megasporangium surrounded by one or two sheathing layers ( integuments ). the young sporophyte develops within the seed, which on germination splits to release it. the earliest known seed plants date from the latest devonian famennian stage. following the evolution of the seed habit, seed plants diversified, giving rise to a number of now - extinct groups, including seed ferns, as well as the modern gymnosperms and angiosperms. gymnosperms produce " naked seeds " not fully enclosed in an ovary ; modern representatives include conifers, cycads, ginkgo, and gnetales. angiosperms produce seeds enclosed in a structure such as a carpel or an ovary. ongoing research on the molecular phylogenetics of living plants appears to show that the angiosperms are a sister clade to the gymnosperms. = = plant physiology = = plant physiology encompasses all the internal chemical and physical activities of plants associated with life. chemicals obtained from the air, soil and water form the basis of all plant metabolism. the energy of sunlight, captured by oxygenic photosynthesis and released by cellular respiration, is the basis of almost all life. photoautotrophs, including all green plants, algae and cyanobacteria gather energy directly from sunlight by photosynthesis. heterotrophs including all animals, all fungi, all completely parasitic plants, and non - photosynthetic bacteria take in organic molecules produced by photoautotrophs and respire them or use them in the construction of cells and tissues. respiration is the oxidation of carbon compounds by breaking them down into simpler structures to . in animals it is necessary to ensure that the inserted dna is present in the embryonic stem cells. bacteria consist of a single cell and reproduce clonally so regeneration is not necessary. selectable markers are used to easily differentiate transformed from untransformed cells. these markers are usually present in the transgenic organism, although a number of strategies have been developed that can remove the selectable marker from the mature transgenic plant. further testing using pcr, southern hybridization, and dna sequencing is conducted to confirm that an organism contains the new gene. these tests can also confirm the chromosomal location and copy number of the inserted gene. the presence of the gene does not guarantee it will be expressed at appropriate levels in the target tissue so methods that look for and measure the gene products ( rna and protein ) are also used. these include northern hybridisation, quantitative rt - pcr, western blot, immunofluorescence, elisa and phenotypic analysis. the new genetic material can be inserted randomly within the host genome or targeted to a specific location. the technique of gene targeting uses homologous recombination to make desired changes to a specific endogenous gene. this tends to occur at a relatively low frequency in plants and animals and generally requires the use of selectable markers. the frequency of gene targeting can be greatly enhanced through genome editing. genome editing uses artificially engineered nucleases that create specific double - stranded breaks at desired locations in the genome, and use the cell ' s endogenous mechanisms to repair the induced break by the natural processes of homologous recombination and nonhomologous end - joining. there are four families of engineered nucleases : meganucleases, zinc finger nucleases, transcription activator - like effector nucleases ( talens ), and the cas9 - guiderna system ( adapted from crispr ). talen and crispr are the two most commonly used and each has its own advantages. talens have greater target specificity, while crispr is easier to design and more efficient. in addition to enhancing gene targeting, engineered nucleases can be used to introduce mutations at endogenous genes that generate a gene knockout. = = applications = = genetic engineering has applications in medicine, research, industry and agriculture and can be used on a wide range of plants, animals and microorganisms. bacteria, the first organisms to be genetically modified, can have plasmid dna inserted an extended polya urn model with two colors, black and white, is studied with some slln and clt on the proportion of white balls. Question: How do amphibians reproduce? A) biologically B) sexually C) asexually D) they don't	B) sexually
Context: enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make it available as drinking water. the earliest exploitation of groundwater resources dates back to 3000 bc, and hydrogeology as a science was developed by hydrologists beginning in the 17th century. ecohydrology is the study of ecological systems in the hydrosphere. it can be divided into the physical study of aquatic ecosystems and the ranks varying from family to subgenus have terms for their study, including agrostology ( or graminology ) for the study of grasses, synantherology for the study of composites, and batology for the study of brambles. study can also be divided by guild rather than clade or grade. for example, dendrology is the study of woody plants. many divisions of biology have botanical subfields. these are commonly denoted by prefixing the word plant ( e. g. plant taxonomy, plant ecology, plant anatomy, plant morphology, plant systematics ), or prefixing or substituting the prefix phyto - ( e. g. phytochemistry, phytogeography ). the study of fossil plants is called palaeobotany. other fields are denoted by adding or substituting the word botany ( e. g. systematic botany ). phytosociology is a subfield of plant ecology that classifies and studies communities of plants. the intersection of fields from the above pair of categories gives rise to fields such as bryogeography, the study of the distribution of mosses. different parts of plants also give rise to their own subfields, including xylology, carpology ( or fructology ), and palynology, these being the study of wood, fruit and pollen / spores respectively. botany also overlaps on the one hand with agriculture, horticulture and silviculture, and on the other hand with medicine and pharmacology, giving rise to fields such as agronomy, horticultural botany, phytopathology, and phytopharmacology. = = scope and importance = = the study of plants is vital because they underpin almost all animal life on earth by generating a large proportion of the oxygen and food that provide humans and other organisms with aerobic respiration with the chemical energy they need to exist. plants, algae and cyanobacteria are the major groups of organisms that carry out photosynthesis, a process that uses the energy of sunlight to convert water and carbon dioxide into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing scientists look through telescopes, study images on electronic screens, record meter readings, and so on. generally, on a basic level, they can agree on what they see, e. g., the thermometer shows 37. 9 degrees c. but, if these scientists have different ideas about the theories that have been developed to explain these basic observations, they may disagree about what they are observing. for example, before albert einstein ' s general theory of relativity, observers would have likely interpreted an image of the einstein cross as five different objects in space. in light of that theory, however, astronomers will tell you that there are actually only two objects, one in the center and four different images of a second object around the sides. alternatively, if other scientists suspect that something is wrong with the telescope and only one object is actually being observed, they are operating under yet another theory. observations that cannot be separated from theoretical interpretation are said to be theory - laden. all observation involves both perception and cognition. that is, one does not make an observation passively, but rather is actively engaged in distinguishing the phenomenon being observed from surrounding sensory data. therefore, observations are affected by one ' s underlying understanding of the way in which the world functions, and that understanding may influence what is perceived, noticed, or deemed worthy of consideration. in this sense, it can be argued that all observation is theory - laden. = = = the purpose of science = = = should science aim to determine ultimate truth, or are there questions that science cannot answer? scientific realists claim that science aims at truth and that one ought to regard scientific theories as true, approximately true, or likely true. conversely, scientific anti - realists argue that science does not aim ( or at least does not succeed ) at truth, especially truth about unobservables like electrons or other universes. instrumentalists argue that scientific theories should only be evaluated on whether they are useful. in their view, whether theories are true or not is beside the point, because the purpose of science is to make predictions and enable effective technology. realists often point to the success of recent scientific theories as evidence for the truth ( or near truth ) of current theories. antirealists point to either the many false theories in the history of science, epistemic morals, the success of false modeling assumptions, or widely termed postmodern criticisms of objectivity as evidence against scientific realism. antirealists attempt to explain the success of scientific theories without reference to truth. some antirealists claim that scientific ##hosphere ) and its historic development. major subdisciplines are mineralogy and petrology, geomorphology, paleontology, stratigraphy, structural geology, engineering geology, and sedimentology. physical geography focuses on geography as an earth science. physical geography is the study of earth ' s seasons, climate, atmosphere, soil, streams, landforms, and oceans. physical geography can be divided into several branches or related fields, as follows : geomorphology, biogeography, environmental geography, palaeogeography, climatology, meteorology, coastal geography, hydrology, ecology, glaciology. geophysics and geodesy investigate the shape of the earth, its reaction to forces and its magnetic and gravity fields. geophysicists explore the earth ' s core and mantle as well as the tectonic and seismic activity of the lithosphere. geophysics is commonly used to supplement the work of geologists in developing a comprehensive understanding of crustal geology, particularly in mineral and petroleum exploration. seismologists use geophysics to understand plate tectonic movement, as well as predict seismic activity. geochemistry studies the processes that control the abundance, composition, and distribution of chemical compounds and isotopes in geologic environments. geochemists use the tools and principles of chemistry to study the earth ' s composition, structure, processes, and other physical aspects. major subdisciplines are aqueous geochemistry, cosmochemistry, isotope geochemistry and biogeochemistry. soil science covers the outermost layer of the earth ' s crust that is subject to soil formation processes ( or pedosphere ). major subdivisions in this field of study include edaphology and pedology. ecology covers the interactions between organisms and their environment. this field of study differentiates the study of earth from other planets in the solar system, earth being the only planet teeming with life. hydrology, oceanography and limnology are studies which focus on the movement, distribution, and quality of the water and involve all the components of the hydrologic cycle on the earth and its atmosphere ( or hydrosphere ). " sub - disciplines of hydrology include hydrometeorology, surface water hydrology, hydrogeology, watershed science, forest hydrology, and water chemistry. " glaciology covers the icy parts of the earth ( or cryosphere ). atmospheric sciences cover the gaseous parts of the earth ( or atmosphere s seasons, climate, atmosphere, soil, streams, landforms, and oceans. physical geography can be divided into several branches or related fields, as follows : geomorphology, biogeography, environmental geography, palaeogeography, climatology, meteorology, coastal geography, hydrology, ecology, glaciology. geophysics and geodesy investigate the shape of the earth, its reaction to forces and its magnetic and gravity fields. geophysicists explore the earth ' s core and mantle as well as the tectonic and seismic activity of the lithosphere. geophysics is commonly used to supplement the work of geologists in developing a comprehensive understanding of crustal geology, particularly in mineral and petroleum exploration. seismologists use geophysics to understand plate tectonic movement, as well as predict seismic activity. geochemistry studies the processes that control the abundance, composition, and distribution of chemical compounds and isotopes in geologic environments. geochemists use the tools and principles of chemistry to study the earth ' s composition, structure, processes, and other physical aspects. major subdisciplines are aqueous geochemistry, cosmochemistry, isotope geochemistry and biogeochemistry. soil science covers the outermost layer of the earth ' s crust that is subject to soil formation processes ( or pedosphere ). major subdivisions in this field of study include edaphology and pedology. ecology covers the interactions between organisms and their environment. this field of study differentiates the study of earth from other planets in the solar system, earth being the only planet teeming with life. hydrology, oceanography and limnology are studies which focus on the movement, distribution, and quality of the water and involve all the components of the hydrologic cycle on the earth and its atmosphere ( or hydrosphere ). " sub - disciplines of hydrology include hydrometeorology, surface water hydrology, hydrogeology, watershed science, forest hydrology, and water chemistry. " glaciology covers the icy parts of the earth ( or cryosphere ). atmospheric sciences cover the gaseous parts of the earth ( or atmosphere ) between the surface and the exosphere ( about 1000 km ). major subdisciplines include meteorology, climatology, atmospheric chemistry, and atmospheric physics. = = = earth science breakup = = = = = see also = = = = references = = = = = sources = = = = = earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make it available as drinking water. the earliest exploitation of groundwater resources dates back to 3000 bc, and hydrogeology as a science was developed by hydrologists beginning in the 17th century. ecohydrology is the study of ecological systems in the hydrosphere. it can be divided into the physical study of aquatic ecosystems and the biological study of aquatic organisms. ecohydrology includes the effects that organisms and aquatic ecosystems have on one another as well as how these ecoystems are affected by humans. glaciology is the study of the cryosphere, including glaciers and coverage of the earth by ice and snow. concerns of glaciology include access to glacial freshwater, mitigation of glacial hazards, obtaining resources that exist beneath frozen land, and addressing the effects of climate change on the cryosphere. = = ecology = = ecology is the study of the biosphere. this includes the study of nature and of how living things interact with the earth and one another and the consequences of that. it considers how living things use resources such as oxygen, water, and nutrients from the earth to sustain themselves. it also considers how humans and other living creatures cause changes to nature. = = physical geography = = physical geography is the study of earth ' s systems and how they interact with one another as part of a single self - contained system. it incorporates astronomy, mathematical geography, meteorology, climatology, geology, geomorphology, biology, biogeography, pedology, and soils geography. physical geography is distinct from human geography, which studies the human populations on earth, though it does include human effects on the environment. = = methodology = = methodologies vary depending on the nature of the subjects being studied. studies typically fall into one of three categories : observational, experimental, or theoretical. earth scientists often conduct sophisticated computer analysis or visit an interesting location to study earth phenomena ( cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to acid rain. climatology studies the climate and climate change. the troposphere, stratosphere, mesosphere, thermosphere, and exosphere are the five layers which make up earth ' s atmosphere. 75 % of the mass in the atmosphere is located within the troposphere, the lowest layer. in all, the atmosphere is made up of about 78. 0 % nitrogen, 20. 9 % oxygen, and 0. 92 % argon, and small amounts of other gases including co2 and water vapor. water vapor and co2 cause the earth ' s atmosphere to catch and hold the sun ' s energy through the greenhouse effect. this makes earth ' s surface warm enough for liquid water and life. in addition to trapping heat, the atmosphere also protects living organisms by shielding the earth ' s surface from cosmic rays. the magnetic field — created by the internal motions of the core — produces the magnetosphere which protects earth ' s atmosphere from the solar wind. as the earth is 4. 5 billion years old, it would have lost its atmosphere by now if there were no protective magnetosphere. = = earth ' s magnetic field = = = = hydrology = = hydrology is the study of the hydrosphere and the movement of water on earth. it emphasizes the study of how humans use and interact with freshwater supplies. study of water ' s movement is closely related to geomorphology and other branches of earth science. applied hydrology involves engineering to maintain aquatic environments and distribute water supplies. subdisciplines of hydrology include oceanography, hydrogeology, ecohydrology, and glaciology. oceanography is the study of oceans. hydrogeology is the study of groundwater. it includes the mapping of groundwater supplies and the analysis of groundwater contaminants. applied hydrogeology seeks to prevent contamination of groundwater and mineral springs and make , including objects we can see with our naked eyes. it is one of the oldest sciences. astronomers of early civilizations performed methodical observations of the night sky, and astronomical artifacts have been found from much earlier periods. there are two types of astronomy : observational astronomy and theoretical astronomy. observational astronomy is focused on acquiring and analyzing data, mainly using basic principles of physics. in contrast, theoretical astronomy is oriented towards developing computer or analytical models to describe astronomical objects and phenomena. this discipline is the science of celestial objects and phenomena that originate outside the earth ' s atmosphere. it is concerned with the evolution, physics, chemistry, meteorology, geology, and motion of celestial objects, as well as the formation and development of the universe. astronomy includes examining, studying, and modeling stars, planets, and comets. most of the information used by astronomers is gathered by remote observation. however, some laboratory reproduction of celestial phenomena has been performed ( such as the molecular chemistry of the interstellar medium ). there is considerable overlap with physics and in some areas of earth science. there are also interdisciplinary fields such as astrophysics, planetary sciences, and cosmology, along with allied disciplines such as space physics and astrochemistry. while the study of celestial features and phenomena can be traced back to antiquity, the scientific methodology of this field began to develop in the middle of the 17th century. a key factor was galileo ' s introduction of the telescope to examine the night sky in more detail. the mathematical treatment of astronomy began with newton ' s development of celestial mechanics and the laws of gravitation. however, it was triggered by earlier work of astronomers such as kepler. by the 19th century, astronomy had developed into formal science, with the introduction of instruments such as the spectroscope and photography, along with much - improved telescopes and the creation of professional observatories. = = interdisciplinary studies = = the distinctions between the natural science disciplines are not always sharp, and they share many cross - discipline fields. physics plays a significant role in the other natural sciences, as represented by astrophysics, geophysics, chemical physics and biophysics. likewise chemistry is represented by such fields as biochemistry, physical chemistry, geochemistry and astrochemistry. a particular example of a scientific discipline that draws upon multiple natural sciences is environmental science. this field studies the interactions of physical, chemical, geological, and biological components of the environment, with particular regard to the effect of human activities and the impact on biodiversity and sustainability. this science also draws upon expertise from other fields, such , dendrology is the study of woody plants. many divisions of biology have botanical subfields. these are commonly denoted by prefixing the word plant ( e. g. plant taxonomy, plant ecology, plant anatomy, plant morphology, plant systematics ), or prefixing or substituting the prefix phyto - ( e. g. phytochemistry, phytogeography ). the study of fossil plants is called palaeobotany. other fields are denoted by adding or substituting the word botany ( e. g. systematic botany ). phytosociology is a subfield of plant ecology that classifies and studies communities of plants. the intersection of fields from the above pair of categories gives rise to fields such as bryogeography, the study of the distribution of mosses. different parts of plants also give rise to their own subfields, including xylology, carpology ( or fructology ), and palynology, these being the study of wood, fruit and pollen / spores respectively. botany also overlaps on the one hand with agriculture, horticulture and silviculture, and on the other hand with medicine and pharmacology, giving rise to fields such as agronomy, horticultural botany, phytopathology, and phytopharmacology. = = scope and importance = = the study of plants is vital because they underpin almost all animal life on earth by generating a large proportion of the oxygen and food that provide humans and other organisms with aerobic respiration with the chemical energy they need to exist. plants, algae and cyanobacteria are the major groups of organisms that carry out photosynthesis, a process that uses the energy of sunlight to convert water and carbon dioxide into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both are the cryosphere ( corresponding to ice ) as a distinct portion of the hydrosphere and the pedosphere ( corresponding to soil ) as an active and intermixed sphere. the following fields of science are generally categorized within the earth sciences : geology describes the rocky parts of the earth ' s crust ( or lithosphere ) and its historic development. major subdisciplines are mineralogy and petrology, geomorphology, paleontology, stratigraphy, structural geology, engineering geology, and sedimentology. physical geography focuses on geography as an earth science. physical geography is the study of earth ' s seasons, climate, atmosphere, soil, streams, landforms, and oceans. physical geography can be divided into several branches or related fields, as follows : geomorphology, biogeography, environmental geography, palaeogeography, climatology, meteorology, coastal geography, hydrology, ecology, glaciology. geophysics and geodesy investigate the shape of the earth, its reaction to forces and its magnetic and gravity fields. geophysicists explore the earth ' s core and mantle as well as the tectonic and seismic activity of the lithosphere. geophysics is commonly used to supplement the work of geologists in developing a comprehensive understanding of crustal geology, particularly in mineral and petroleum exploration. seismologists use geophysics to understand plate tectonic movement, as well as predict seismic activity. geochemistry studies the processes that control the abundance, composition, and distribution of chemical compounds and isotopes in geologic environments. geochemists use the tools and principles of chemistry to study the earth ' s composition, structure, processes, and other physical aspects. major subdisciplines are aqueous geochemistry, cosmochemistry, isotope geochemistry and biogeochemistry. soil science covers the outermost layer of the earth ' s crust that is subject to soil formation processes ( or pedosphere ). major subdivisions in this field of study include edaphology and pedology. ecology covers the interactions between organisms and their environment. this field of study differentiates the study of earth from other planets in the solar system, earth being the only planet teeming with life. hydrology, oceanography and limnology are studies which focus on the movement, distribution, and quality of the water and involve all the components of the hydrologic cycle on the earth and its atmosphere ( or hydrosphere ). " Question: What are scientists called who study the weather and give forecasts? A) geologists B) meteorologists C) botanists D) climatologists	B) meteorologists
Context: a cell. there are generally four types of chemical signals : autocrine, paracrine, juxtacrine, and hormones. in autocrine signaling, the ligand affects the same cell that releases it. tumor cells, for example, can reproduce uncontrollably because they release signals that initiate their own self - division. in paracrine signaling, the ligand diffuses to nearby cells and affects them. for example, brain cells called neurons release ligands called neurotransmitters that diffuse across a synaptic cleft to bind with a receptor on an adjacent cell such as another neuron or muscle cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares electrons to drive the synthesis of glucose by fixing atmospheric carbon dioxide into existing organic carbon compounds, such as ribulose bisphosphate ( rubp ) in a sequence of light - independent ( or dark ) reactions called the calvin cycle. = = = cell signaling = = = cell signaling ( or communication ) is the ability of cells to receive, process, and transmit signals with its environment and with itself. signals can be non - chemical such as light, electrical impulses, and heat, or chemical signals ( or ligands ) that interact with receptors, which can be found embedded in the cell membrane of another cell or located deep inside a cell. there are generally four types of chemical signals : autocrine, paracrine, juxtacrine, and hormones. in autocrine signaling, the ligand affects the same cell that releases it. tumor cells, for example, can reproduce uncontrollably because they release signals that initiate their own self - division. in paracrine signaling, the ligand diffuses to nearby cells and affects them. for example, brain cells called neurons release ligands called neurotransmitters that diffuse across a synaptic cleft to bind with a receptor on an adjacent cell such as another neuron or muscle cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and ability of cells to receive, process, and transmit signals with its environment and with itself. signals can be non - chemical such as light, electrical impulses, and heat, or chemical signals ( or ligands ) that interact with receptors, which can be found embedded in the cell membrane of another cell or located deep inside a cell. there are generally four types of chemical signals : autocrine, paracrine, juxtacrine, and hormones. in autocrine signaling, the ligand affects the same cell that releases it. tumor cells, for example, can reproduce uncontrollably because they release signals that initiate their own self - division. in paracrine signaling, the ligand diffuses to nearby cells and affects them. for example, brain cells called neurons release ligands called neurotransmitters that diffuse across a synaptic cleft to bind with a receptor on an adjacent cell such as another neuron or muscle cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis , depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions s immune system recognizes these re - implanted cells as its own, and does not target them for attack. autologous cell dependence on host cell health and donor site morbidity may be deterrents to their use. adipose - derived and bone marrow - derived mesenchymal stem cells are commonly autologous in nature, and can be used in a myriad of ways, from helping repair skeletal tissue to replenishing beta cells in diabetic patients. allogenic : cells are obtained from the body of a donor of the same species as the recipient. while there are some ethical constraints to the use of human cells for in vitro studies ( i. e. human brain tissue chimera development ), the employment of dermal fibroblasts from human foreskin demonstrates an immunologically safe and thus a viable choice for allogenic tissue engineering of the skin. xenogenic : these cells are derived isolated cells from alternate species from the recipient. a notable example of xenogeneic tissue utilization is cardiovascular implant construction via animal cells. chimeric human - animal farming raises ethical concerns around the potential for improved consciousness from implanting human organs in animals. syngeneic or isogenic : these cells describe those borne from identical genetic code. this imparts an immunologic benefit similar to autologous cell lines ( see above ). autologous cells can be considered syngenic, but the classification also extends to non - autologously derived cells such as those from an identical twin, from genetically identical ( cloned ) research models, or induced stem cells ( isc ) as related to the donor. = = = stem cells = = = stem cells are undifferentiated cells with the ability to divide in culture and give rise to different forms of specialized cells. stem cells are divided into " adult " and " embryonic " stem cells according to their source. while there is still a large ethical debate related to the use of embryonic stem cells, it is thought that another alternative source – induced pluripotent stem cells – may be useful for the repair of diseased or damaged tissues, or may be used to grow new organs. totipotent cells are stem cells which can divide into further stem cells or differentiate into any cell type in the body, including extra - embryonic tissue. pluripotent cells are stem cells which can differentiate into any cell type in the body except extra - embryonic tissue. induced pluripotent stem cells ( ipscs ) chloroplasts. the gibberelins, such as gibberelic acid are diterpenes synthesised from acetyl coa via the mevalonate pathway. they are involved in the promotion of germination and dormancy - breaking in seeds, in regulation of plant height by controlling stem elongation and the control of flowering. abscisic acid ( aba ) occurs in all land plants except liverworts, and is synthesised from carotenoids in the chloroplasts and other plastids. it inhibits cell division, promotes seed maturation, and dormancy, and promotes stomatal closure. it was so named because it was originally thought to control abscission. ethylene is a gaseous hormone that is produced in all higher plant tissues from methionine. it is now known to be the hormone that stimulates or regulates fruit ripening and abscission, and it, or the synthetic growth regulator ethephon which is rapidly metabolised to produce ethylene, are used on industrial scale to promote ripening of cotton, pineapples and other climacteric crops. another class of phytohormones is the jasmonates, first isolated from the oil of jasminum grandiflorum which regulates wound responses in plants by unblocking the expression of genes required in the systemic acquired resistance response to pathogen attack. in addition to being the primary energy source for plants, light functions as a signalling device, providing information to the plant, such as how much sunlight the plant receives each day. this can result in adaptive changes in a process known as photomorphogenesis. phytochromes are the photoreceptors in a plant that are sensitive to light. = = plant anatomy and morphology = = plant anatomy is the study of the structure of plant cells and tissues, whereas plant morphology is the study of their external form. all plants are multicellular eukaryotes, their dna stored in nuclei. the characteristic features of plant cells that distinguish them from those of animals and fungi include a primary cell wall composed of the polysaccharides cellulose, hemicellulose and pectin, larger vacuoles than in animal cells and the presence of plastids with unique photosynthetic and biosynthetic functions as in the chloroplasts. other plastids contain storage products such as starch ( amyloplasts ) ##aggeration to say that the tip of the radicle.. acts like the brain of one of the lower animals.. directing the several movements ". about the same time, the role of auxins ( from the greek auxein, to grow ) in control of plant growth was first outlined by the dutch scientist frits went. the first known auxin, indole - 3 - acetic acid ( iaa ), which promotes cell growth, was only isolated from plants about 50 years later. this compound mediates the tropic responses of shoots and roots towards light and gravity. the finding in 1939 that plant callus could be maintained in culture containing iaa, followed by the observation in 1947 that it could be induced to form roots and shoots by controlling the concentration of growth hormones were key steps in the development of plant biotechnology and genetic modification. cytokinins are a class of plant hormones named for their control of cell division ( especially cytokinesis ). the natural cytokinin zeatin was discovered in corn, zea mays, and is a derivative of the purine adenine. zeatin is produced in roots and transported to shoots in the xylem where it promotes cell division, bud development, and the greening of chloroplasts. the gibberelins, such as gibberelic acid are diterpenes synthesised from acetyl coa via the mevalonate pathway. they are involved in the promotion of germination and dormancy - breaking in seeds, in regulation of plant height by controlling stem elongation and the control of flowering. abscisic acid ( aba ) occurs in all land plants except liverworts, and is synthesised from carotenoids in the chloroplasts and other plastids. it inhibits cell division, promotes seed maturation, and dormancy, and promotes stomatal closure. it was so named because it was originally thought to control abscission. ethylene is a gaseous hormone that is produced in all higher plant tissues from methionine. it is now known to be the hormone that stimulates or regulates fruit ripening and abscission, and it, or the synthetic growth regulator ethephon which is rapidly metabolised to produce ethylene, are used on industrial scale to promote ripening of cotton, pineapples and other climacteric crops. another class of phytohormones is the jasmonates, first isolated cytokinesis ). the natural cytokinin zeatin was discovered in corn, zea mays, and is a derivative of the purine adenine. zeatin is produced in roots and transported to shoots in the xylem where it promotes cell division, bud development, and the greening of chloroplasts. the gibberelins, such as gibberelic acid are diterpenes synthesised from acetyl coa via the mevalonate pathway. they are involved in the promotion of germination and dormancy - breaking in seeds, in regulation of plant height by controlling stem elongation and the control of flowering. abscisic acid ( aba ) occurs in all land plants except liverworts, and is synthesised from carotenoids in the chloroplasts and other plastids. it inhibits cell division, promotes seed maturation, and dormancy, and promotes stomatal closure. it was so named because it was originally thought to control abscission. ethylene is a gaseous hormone that is produced in all higher plant tissues from methionine. it is now known to be the hormone that stimulates or regulates fruit ripening and abscission, and it, or the synthetic growth regulator ethephon which is rapidly metabolised to produce ethylene, are used on industrial scale to promote ripening of cotton, pineapples and other climacteric crops. another class of phytohormones is the jasmonates, first isolated from the oil of jasminum grandiflorum which regulates wound responses in plants by unblocking the expression of genes required in the systemic acquired resistance response to pathogen attack. in addition to being the primary energy source for plants, light functions as a signalling device, providing information to the plant, such as how much sunlight the plant receives each day. this can result in adaptive changes in a process known as photomorphogenesis. phytochromes are the photoreceptors in a plant that are sensitive to light. = = plant anatomy and morphology = = plant anatomy is the study of the structure of plant cells and tissues, whereas plant morphology is the study of their external form. all plants are multicellular eukaryotes, their dna stored in nuclei. the characteristic features of plant cells that distinguish them from those of animals and fungi include a primary cell wall composed of the polysaccharides cellulose, Question: Autocrine signaling takes place within the same what? A) organ B) cell C) proteins D) tissue type	B) cell
Context: ##tes, i. e., genes are unlinked. an exception to this rule would include traits that are sex - linked. test crosses can be performed to experimentally determine the underlying genotype of an organism with a dominant phenotype. a punnett square can be used to predict the results of a test cross. the chromosome theory of inheritance, which states that genes are found on chromosomes, was supported by thomas morgans ' s experiments with fruit flies, which established the sex linkage between eye color and sex in these insects. = = = genes and dna = = = a gene is a unit of heredity that corresponds to a region of deoxyribonucleic acid ( dna ) that carries genetic information that controls form or function of an organism. dna is composed of two polynucleotide chains that coil around each other to form a double helix. it is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. the set of chromosomes in a cell is collectively known as its genome. in eukaryotes, dna is mainly in the cell nucleus. in prokaryotes, the dna is held within the nucleoid. the genetic information is held within genes, and the complete assemblage in an organism is called its genotype. dna replication is a semiconservative process whereby each strand serves as a template for a new strand of dna. mutations are heritable changes in dna. they can arise spontaneously as a result of replication errors that were not corrected by proofreading or can be induced by an environmental mutagen such as a chemical ( e. g., nitrous acid, benzopyrene ) or radiation ( e. g., x - ray, gamma ray, ultraviolet radiation, particles emitted by unstable isotopes ). mutations can lead to phenotypic effects such as loss - of - function, gain - of - function, and conditional mutations. some mutations are beneficial, as they are a source of genetic variation for evolution. others are harmful if they were to result in a loss of function of genes needed for survival. = = = gene expression = = = gene expression is the molecular process by which a genotype encoded in dna gives rise to an observable phenotype in the proteins of an organism ' s body. this process is summarized by the central dogma of molecular biology, which was formulated by francis crick in 1958. according to the central dogma, genetic information flows from dna and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids are polymers of nucleotides. their function is to store, transmit, and express hereditary information. = = cells = = cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division. most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell according to brønsted – lowry acid – base theory, acids are substances that donate a positive hydrogen ion to another substance in a chemical reaction ; by extension, a base is the substance which receives that hydrogen ion. a third common theory is lewis acid – base theory, which is based on the formation of new chemical bonds. lewis theory explains that an acid is a substance which is capable of accepting a pair of electrons from another substance during the process of bond formation, while a base is a substance which can provide a pair of electrons to form a new bond. there are several other ways in which a substance may be classified as an acid or a base, as is evident in the history of this concept. acid strength is commonly measured by two methods. one measurement, based on the arrhenius definition of acidity, is ph, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale. thus, solutions that have a low ph have a high hydronium ion concentration and can be said to be more acidic. the other measurement, based on the brønsted – lowry definition, is the acid dissociation constant ( ka ), which measures the relative ability of a substance to act as an acid under the brønsted – lowry definition of an acid. that is, substances with a higher ka are more likely to donate hydrogen ions in chemical reactions than those with lower ka values. = = = redox = = = redox ( reduction - oxidation ) reactions include all chemical reactions in which atoms have their oxidation state changed by either gaining electrons ( reduction ) or losing electrons ( oxidation ). substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. an oxidant removes electrons from another substance. similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers. a reductant transfers electrons to another substance and is thus oxidized itself. and because it " donates " electrons it is also called an electron donor. oxidation and reduction properly refer to a change in oxidation number — the actual transfer of electrons may never occur. thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number. = = = equilibrium = = = although the concept of equilibrium is widely used across sciences, in or a base, as is evident in the history of this concept. acid strength is commonly measured by two methods. one measurement, based on the arrhenius definition of acidity, is ph, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale. thus, solutions that have a low ph have a high hydronium ion concentration and can be said to be more acidic. the other measurement, based on the brønsted – lowry definition, is the acid dissociation constant ( ka ), which measures the relative ability of a substance to act as an acid under the brønsted – lowry definition of an acid. that is, substances with a higher ka are more likely to donate hydrogen ions in chemical reactions than those with lower ka values. = = = redox = = = redox ( reduction - oxidation ) reactions include all chemical reactions in which atoms have their oxidation state changed by either gaining electrons ( reduction ) or losing electrons ( oxidation ). substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. an oxidant removes electrons from another substance. similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers. a reductant transfers electrons to another substance and is thus oxidized itself. and because it " donates " electrons it is also called an electron donor. oxidation and reduction properly refer to a change in oxidation number — the actual transfer of electrons may never occur. thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number. = = = equilibrium = = = although the concept of equilibrium is widely used across sciences, in the context of chemistry, it arises whenever a number of different states of the chemical composition are possible, as for example, in a mixture of several chemical compounds that can react with one another, or when a substance can be present in more than one kind of phase. a system of chemical substances at equilibrium, even though having an unchanging composition, is most often not static ; molecules of the substances continue to react with one another thus giving rise to a dynamic equilibrium. thus the concept describes the state in which the parameters such as chemical composition remain unchanged over time. = = = chemical laws = = = chemical reactions are governed by certain laws to a region of deoxyribonucleic acid ( dna ) that carries genetic information that controls form or function of an organism. dna is composed of two polynucleotide chains that coil around each other to form a double helix. it is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. the set of chromosomes in a cell is collectively known as its genome. in eukaryotes, dna is mainly in the cell nucleus. in prokaryotes, the dna is held within the nucleoid. the genetic information is held within genes, and the complete assemblage in an organism is called its genotype. dna replication is a semiconservative process whereby each strand serves as a template for a new strand of dna. mutations are heritable changes in dna. they can arise spontaneously as a result of replication errors that were not corrected by proofreading or can be induced by an environmental mutagen such as a chemical ( e. g., nitrous acid, benzopyrene ) or radiation ( e. g., x - ray, gamma ray, ultraviolet radiation, particles emitted by unstable isotopes ). mutations can lead to phenotypic effects such as loss - of - function, gain - of - function, and conditional mutations. some mutations are beneficial, as they are a source of genetic variation for evolution. others are harmful if they were to result in a loss of function of genes needed for survival. = = = gene expression = = = gene expression is the molecular process by which a genotype encoded in dna gives rise to an observable phenotype in the proteins of an organism ' s body. this process is summarized by the central dogma of molecular biology, which was formulated by francis crick in 1958. according to the central dogma, genetic information flows from dna to rna to protein. there are two gene expression processes : transcription ( dna to rna ) and translation ( rna to protein ). = = = gene regulation = = = the regulation of gene expression by environmental factors and during different stages of development can occur at each step of the process such as transcription, rna splicing, translation, and post - translational modification of a protein. gene expression can be influenced by positive or negative regulation, depending on which of the two types of regulatory proteins called transcription factors bind to the dna sequence close to or at a promoter. a cluster of genes that share the same promoter is called an operon, cross. the chromosome theory of inheritance, which states that genes are found on chromosomes, was supported by thomas morgans ' s experiments with fruit flies, which established the sex linkage between eye color and sex in these insects. = = = genes and dna = = = a gene is a unit of heredity that corresponds to a region of deoxyribonucleic acid ( dna ) that carries genetic information that controls form or function of an organism. dna is composed of two polynucleotide chains that coil around each other to form a double helix. it is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. the set of chromosomes in a cell is collectively known as its genome. in eukaryotes, dna is mainly in the cell nucleus. in prokaryotes, the dna is held within the nucleoid. the genetic information is held within genes, and the complete assemblage in an organism is called its genotype. dna replication is a semiconservative process whereby each strand serves as a template for a new strand of dna. mutations are heritable changes in dna. they can arise spontaneously as a result of replication errors that were not corrected by proofreading or can be induced by an environmental mutagen such as a chemical ( e. g., nitrous acid, benzopyrene ) or radiation ( e. g., x - ray, gamma ray, ultraviolet radiation, particles emitted by unstable isotopes ). mutations can lead to phenotypic effects such as loss - of - function, gain - of - function, and conditional mutations. some mutations are beneficial, as they are a source of genetic variation for evolution. others are harmful if they were to result in a loss of function of genes needed for survival. = = = gene expression = = = gene expression is the molecular process by which a genotype encoded in dna gives rise to an observable phenotype in the proteins of an organism ' s body. this process is summarized by the central dogma of molecular biology, which was formulated by francis crick in 1958. according to the central dogma, genetic information flows from dna to rna to protein. there are two gene expression processes : transcription ( dna to rna ) and translation ( rna to protein ). = = = gene regulation = = = the regulation of gene expression by environmental factors and during different stages of development can occur at each step of the process such as transcription, rna splicing polyatomic ions that do not split up during acid – base reactions are hydroxide ( oh− ) and phosphate ( po43− ). plasma is composed of gaseous matter that has been completely ionized, usually through high temperature. = = = acidity and basicity = = = a substance can often be classified as an acid or a base. there are several different theories which explain acid – base behavior. the simplest is arrhenius theory, which states that an acid is a substance that produces hydronium ions when it is dissolved in water, and a base is one that produces hydroxide ions when dissolved in water. according to brønsted – lowry acid – base theory, acids are substances that donate a positive hydrogen ion to another substance in a chemical reaction ; by extension, a base is the substance which receives that hydrogen ion. a third common theory is lewis acid – base theory, which is based on the formation of new chemical bonds. lewis theory explains that an acid is a substance which is capable of accepting a pair of electrons from another substance during the process of bond formation, while a base is a substance which can provide a pair of electrons to form a new bond. there are several other ways in which a substance may be classified as an acid or a base, as is evident in the history of this concept. acid strength is commonly measured by two methods. one measurement, based on the arrhenius definition of acidity, is ph, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale. thus, solutions that have a low ph have a high hydronium ion concentration and can be said to be more acidic. the other measurement, based on the brønsted – lowry definition, is the acid dissociation constant ( ka ), which measures the relative ability of a substance to act as an acid under the brønsted – lowry definition of an acid. that is, substances with a higher ka are more likely to donate hydrogen ions in chemical reactions than those with lower ka values. = = = redox = = = redox ( reduction - oxidation ) reactions include all chemical reactions in which atoms have their oxidation state changed by either gaining electrons ( reduction ) or losing electrons ( oxidation ). substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. an oxidant removes electrons from another substance. similarly, process by which a genotype encoded in dna gives rise to an observable phenotype in the proteins of an organism ' s body. this process is summarized by the central dogma of molecular biology, which was formulated by francis crick in 1958. according to the central dogma, genetic information flows from dna to rna to protein. there are two gene expression processes : transcription ( dna to rna ) and translation ( rna to protein ). = = = gene regulation = = = the regulation of gene expression by environmental factors and during different stages of development can occur at each step of the process such as transcription, rna splicing, translation, and post - translational modification of a protein. gene expression can be influenced by positive or negative regulation, depending on which of the two types of regulatory proteins called transcription factors bind to the dna sequence close to or at a promoter. a cluster of genes that share the same promoter is called an operon, found mainly in prokaryotes and some lower eukaryotes ( e. g., caenorhabditis elegans ). in positive regulation of gene expression, the activator is the transcription factor that stimulates transcription when it binds to the sequence near or at the promoter. negative regulation occurs when another transcription factor called a repressor binds to a dna sequence called an operator, which is part of an operon, to prevent transcription. repressors can be inhibited by compounds called inducers ( e. g., allolactose ), thereby allowing transcription to occur. specific genes that can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem language is a method by which individuals express their thoughts. each language has its own set of alphabetic and numeric characters. people can communicate with one another through either oral or written communication. however, each language has a sign language counterpart. individuals who are deaf and / or mute communicate through sign language. the bangla language also has a sign language, which is called bdsl. the dataset is about bangla hand sign images. the collection contains 49 individual bangla alphabet images in sign language. bdsl49 is a dataset that consists of 29, 490 images with 49 labels. images of 14 different adult individuals, each with a distinct background and appearance, have been recorded during data collection. several strategies have been used to eliminate noise from datasets during preparation. this dataset is available to researchers for free. they can develop automated systems using machine learning, computer vision, and deep learning techniques. in addition, two models were used in this dataset. the first is for detection, while the second is for recognition. classified as an acid or a base. there are several different theories which explain acid – base behavior. the simplest is arrhenius theory, which states that an acid is a substance that produces hydronium ions when it is dissolved in water, and a base is one that produces hydroxide ions when dissolved in water. according to brønsted – lowry acid – base theory, acids are substances that donate a positive hydrogen ion to another substance in a chemical reaction ; by extension, a base is the substance which receives that hydrogen ion. a third common theory is lewis acid – base theory, which is based on the formation of new chemical bonds. lewis theory explains that an acid is a substance which is capable of accepting a pair of electrons from another substance during the process of bond formation, while a base is a substance which can provide a pair of electrons to form a new bond. there are several other ways in which a substance may be classified as an acid or a base, as is evident in the history of this concept. acid strength is commonly measured by two methods. one measurement, based on the arrhenius definition of acidity, is ph, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale. thus, solutions that have a low ph have a high hydronium ion concentration and can be said to be more acidic. the other measurement, based on the brønsted – lowry definition, is the acid dissociation constant ( ka ), which measures the relative ability of a substance to act as an acid under the brønsted – lowry definition of an acid. that is, substances with a higher ka are more likely to donate hydrogen ions in chemical reactions than those with lower ka values. = = = redox = = = redox ( reduction - oxidation ) reactions include all chemical reactions in which atoms have their oxidation state changed by either gaining electrons ( reduction ) or losing electrons ( oxidation ). substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. an oxidant removes electrons from another substance. similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers. a reductant transfers electrons to another substance and is thus oxidized itself. and because it " donates " electrons it is also called an electron Question: Both dna and rna are what type of acids? A) nucleic acids B) proteins acids C) synthesize acids D) fatty acids	A) nucleic acids
Context: remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the infestation of insects and rodents, contributing to the spread of diseases. some of the most common types of solid waste management include ; landfills, vermicomposting, composting, recycling, and incineration. however, a major barrier for solid waste management practices is the high costs associated with recycling and the risks of creating more pollution. = = = e - waste recycling = = = the recycling of electronic waste ( e - waste ) has seen significant technological advancements due to increasing environmental concerns and the growing volume of electronic product disposals. traditional e - waste recycling methods, which often involve manual disassemb the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the ancestor of plants by entering into an endosymbiotic relationship with an early eukaryote, ultimately becoming the chloroplasts in plant cells. the new photosynthetic plants ( along with their algal relatives ) accelerated the rise in atmospheric oxygen started by the cyanobacteria, changing the to be separated conceptually from geology and crop production and treated as a whole. as a founding father of soil science, fallou has primacy in time. fallou was working on the origins of soil before dokuchaev was born ; however dokuchaev ' s work was more extensive and is considered to be the more significant to modern soil theory than fallou ' s. previously, soil had been considered a product of chemical transformations of rocks, a dead substrate from which plants derive nutritious elements. soil and bedrock were in fact equated. dokuchaev considers the soil as a natural body having its own genesis and its own history of development, a body with complex and multiform processes taking place within it. the soil is considered as different from bedrock. the latter becomes soil under the influence of a series of soil - formation factors ( climate, vegetation, country, relief and age ). according to him, soil should be called the " daily " or outward horizons of rocks regardless of the type ; they are changed naturally by the common effect of water, air and various kinds of living and dead organisms. a 1914 encyclopedic definition : " the different forms of earth on the surface of the rocks, formed by the breaking down or weathering of rocks ". serves to illustrate the historic view of soil which persisted from the 19th century. dokuchaev ' s late 19th century soil concept developed in the 20th century to one of soil as earthy material that has been altered by living processes. a corollary concept is that soil without a living component is simply a part of earth ' s outer layer. further refinement of the soil concept is occurring in view of an appreciation of energy transport and transformation within soil. the term is popularly applied to the material on the surface of the earth ' s moon and mars, a usage acceptable within a portion of the scientific community. accurate to this modern understanding of soil is nikiforoff ' s 1959 definition of soil as the " excited skin of the sub aerial part of the earth ' s crust ". = = areas of practice = = academically, soil scientists tend to be drawn to one of five areas of specialization : microbiology, pedology, edaphology, physics, or chemistry. yet the work specifics are very much dictated by the challenges facing our civilization ' s desire to sustain the land that supports it, and the distinctions between the sub - disciplines of soil science often blur in the process. soil science professionals commonly stay current be the more significant to modern soil theory than fallou ' s. previously, soil had been considered a product of chemical transformations of rocks, a dead substrate from which plants derive nutritious elements. soil and bedrock were in fact equated. dokuchaev considers the soil as a natural body having its own genesis and its own history of development, a body with complex and multiform processes taking place within it. the soil is considered as different from bedrock. the latter becomes soil under the influence of a series of soil - formation factors ( climate, vegetation, country, relief and age ). according to him, soil should be called the " daily " or outward horizons of rocks regardless of the type ; they are changed naturally by the common effect of water, air and various kinds of living and dead organisms. a 1914 encyclopedic definition : " the different forms of earth on the surface of the rocks, formed by the breaking down or weathering of rocks ". serves to illustrate the historic view of soil which persisted from the 19th century. dokuchaev ' s late 19th century soil concept developed in the 20th century to one of soil as earthy material that has been altered by living processes. a corollary concept is that soil without a living component is simply a part of earth ' s outer layer. further refinement of the soil concept is occurring in view of an appreciation of energy transport and transformation within soil. the term is popularly applied to the material on the surface of the earth ' s moon and mars, a usage acceptable within a portion of the scientific community. accurate to this modern understanding of soil is nikiforoff ' s 1959 definition of soil as the " excited skin of the sub aerial part of the earth ' s crust ". = = areas of practice = = academically, soil scientists tend to be drawn to one of five areas of specialization : microbiology, pedology, edaphology, physics, or chemistry. yet the work specifics are very much dictated by the challenges facing our civilization ' s desire to sustain the land that supports it, and the distinctions between the sub - disciplines of soil science often blur in the process. soil science professionals commonly stay current in soil chemistry, soil physics, soil microbiology, pedology, and applied soil science in related disciplines. one exciting effort drawing in soil scientists in the u. s. as of 2004 is the soil quality initiative. central to the soil quality initiative is developing indices of soil health and then monitoring them in a way made of steel. the shoe is generally wider than the caisson to reduce friction, and the leading edge may be supplied with pressurised bentonite slurry, which swells in water, stabilizing settlement by filling depressions and voids. an open caisson may fill with water during sinking. the material is excavated by clamshell excavator bucket on crane. the formation level subsoil may still not be suitable for excavation or bearing capacity. the water in the caisson ( due to a high water table ) balances the upthrust forces of the soft soils underneath. if dewatered, the base may " pipe " or " boil ", causing the caisson to sink. to combat this problem, piles may be driven from the surface to act as : load - bearing walls, in that they transmit loads to deeper soils. anchors, in that they resist flotation because of the friction at the interface between their surfaces and the surrounding earth into which they have been driven. h - beam sections ( typical column sections, due to resistance to bending in all axis ) may be driven at angles " raked " to rock or other firmer soils ; the h - beams are left extended above the base. a reinforced concrete plug may be placed under the water, a process known as tremie concrete placement. when the caisson is dewatered, this plug acts as a pile cap, resisting the upward forces of the subsoil. = = = monolithic = = = a monolithic caisson ( or simply a monolith ) is larger than the other types of caisson, but similar to open caissons. such caissons are often found in quay walls, where resistance to impact from ships is required. = = = pneumatic = = = shallow caissons may be open to the air, whereas pneumatic caissons ( sometimes called pressurized caissons ), which penetrate soft mud, are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. an airlock allows access to the chamber. workers, called sandhogs in american english, move mud and rock debris ( called muck ) from the edge of the workspace to a water - filled pit, connected by a tube ( called the muck tube ) to the surface. a crane at the surface removes the soil with a clamshell bucket. the water pressure in the tube balances the air pressure, with excess air escaping up energy they need to exist. plants, algae and cyanobacteria are the major groups of organisms that carry out photosynthesis, a process that uses the energy of sunlight to convert water and carbon dioxide into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photos ##morphology studies the origin of landscapes. structural geology studies the deformation of rocks to produce mountains and lowlands. resource geology studies how energy resources can be obtained from minerals. environmental geology studies how pollution and contaminants affect soil and rock. mineralogy is the study of minerals and includes the study of mineral formation, crystal structure, hazards associated with minerals, and the physical and chemical properties of minerals. petrology is the study of rocks, including the formation and composition of rocks. petrography is a branch of petrology that studies the typology and classification of rocks. = = earth ' s interior = = plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of physical and chemical processes in the earth ' s crust. beneath the earth ' s crust lies the mantle which is heated by the radioactive decay of heavy elements. the mantle is not quite solid and consists of magma which is in a state of semi - perpetual convection. this convection process causes the lithospheric plates to move, albeit slowly. the resulting process is known as plate tectonics. areas of the crust where new crust is created are called divergent boundaries, those where it is brought back into the earth are convergent boundaries and those where plates slide past each other, but no new lithospheric material is created or destroyed, are referred to as transform ( or conservative ) boundaries. earthquakes result from the movement of the lithospheric plates, and they often occur near convergent boundaries where parts of the crust are forced into the earth as part of subduction. plate tectonics might be thought of as the process by which the earth is resurfaced. as the result of seafloor spreading, new crust and lithosphere is created by the flow of magma from the mantle to the near surface, through fissures, where it cools and solidifies. through subduction, oceanic crust and lithosphere vehemently returns to the convecting mantle. volcanoes result primarily from the melting of subducted crust material. crust material that is forced into the asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface — giving birth to volcanoes. = = atmospheric science = = atmospheric science initially developed in the late - 19th century as a means to forecast the weather through meteorology, the study of weather. atmospheric chemistry was developed in the 20th century to measure air pollution and expanded in the 1970s in response to = = = = = = environmental remediation = = = environmental remediation is the process through which contaminants or pollutants in soil, water and other media are removed to improve environmental quality. the main focus is the reduction of hazardous substances within the environment. some of the areas involved in environmental remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the infestation of insects and rodents, contributing to the spread of diseases. some of the most common types of solid waste management include ; landfills, vermicomposting, composting, recycling, and incineration. however, a major barrier for solid waste management practices is the high costs associated with recycling genesis and its own history of development, a body with complex and multiform processes taking place within it. the soil is considered as different from bedrock. the latter becomes soil under the influence of a series of soil - formation factors ( climate, vegetation, country, relief and age ). according to him, soil should be called the " daily " or outward horizons of rocks regardless of the type ; they are changed naturally by the common effect of water, air and various kinds of living and dead organisms. a 1914 encyclopedic definition : " the different forms of earth on the surface of the rocks, formed by the breaking down or weathering of rocks ". serves to illustrate the historic view of soil which persisted from the 19th century. dokuchaev ' s late 19th century soil concept developed in the 20th century to one of soil as earthy material that has been altered by living processes. a corollary concept is that soil without a living component is simply a part of earth ' s outer layer. further refinement of the soil concept is occurring in view of an appreciation of energy transport and transformation within soil. the term is popularly applied to the material on the surface of the earth ' s moon and mars, a usage acceptable within a portion of the scientific community. accurate to this modern understanding of soil is nikiforoff ' s 1959 definition of soil as the " excited skin of the sub aerial part of the earth ' s crust ". = = areas of practice = = academically, soil scientists tend to be drawn to one of five areas of specialization : microbiology, pedology, edaphology, physics, or chemistry. yet the work specifics are very much dictated by the challenges facing our civilization ' s desire to sustain the land that supports it, and the distinctions between the sub - disciplines of soil science often blur in the process. soil science professionals commonly stay current in soil chemistry, soil physics, soil microbiology, pedology, and applied soil science in related disciplines. one exciting effort drawing in soil scientists in the u. s. as of 2004 is the soil quality initiative. central to the soil quality initiative is developing indices of soil health and then monitoring them in a way that gives us long - term ( decade - to - decade ) feedback on our performance as stewards of the planet. the effort includes understanding the functions of soil microbiotic crusts and exploring the potential to sequester atmospheric carbon in soil organic matter. relating the concept of agriculture to soil quality, however, has not Question: What kind of a resource is soil, for human purposes? A) emanates resource B) guarana resource C) nonrenewable resource D) renewable resource	C) nonrenewable resource
Context: = = = = = = environmental remediation = = = environmental remediation is the process through which contaminants or pollutants in soil, water and other media are removed to improve environmental quality. the main focus is the reduction of hazardous substances within the environment. some of the areas involved in environmental remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the infestation of insects and rodents, contributing to the spread of diseases. some of the most common types of solid waste management include ; landfills, vermicomposting, composting, recycling, and incineration. however, a major barrier for solid waste management practices is the high costs associated with recycling short - term, like pollination and predation, or long - term ; both often strongly influence the evolution of the species involved. a long - term interaction is called a symbiosis. symbioses range from mutualism, beneficial to both partners, to competition, harmful to both partners. every species participates as a consumer, resource, or both in consumer – resource interactions, which form the core of food chains or food webs. there are different trophic levels within any food web, with the lowest level being the primary producers ( or autotrophs ) such as plants and algae that convert energy and inorganic material into organic compounds, which can then be used by the rest of the community. at the next level are the heterotrophs, which are the species that obtain energy by breaking apart organic compounds from other organisms. heterotrophs that consume plants are primary consumers ( or herbivores ) whereas heterotrophs that consume herbivores are secondary consumers ( or carnivores ). and those that eat secondary consumers are tertiary consumers and so on. omnivorous heterotrophs are able to consume at multiple levels. finally, there are decomposers that feed on the waste products or dead bodies of organisms. on average, the total amount of energy incorporated into the biomass of a trophic level per unit of time is about one - tenth of the energy of the trophic level that it consumes. waste and dead material used by decomposers as well as heat lost from metabolism make up the other ninety percent of energy that is not consumed by the next trophic level. = = = biosphere = = = in the global ecosystem or biosphere, matter exists as different interacting compartments, which can be biotic or abiotic as well as accessible or inaccessible, depending on their forms and locations. for example, matter from terrestrial autotrophs are both biotic and accessible to other organisms whereas the matter in rocks and minerals are abiotic and inaccessible. a biogeochemical cycle is a pathway by which specific elements of matter are turned over or moved through the biotic ( biosphere ) and the abiotic ( lithosphere, atmosphere, and hydrosphere ) compartments of earth. there are biogeochemical cycles for nitrogen, carbon, and water. = = = conservation = = = conservation biology is the study of the conservation of earth ' s biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates eat them. plants and other photosynthetic organisms are at the base of most food chains because they use the energy from the sun and nutrients from the soil and atmosphere, converting them into a form that can be used by animals. this is what ecologists call the first trophic level. the modern forms of the major staple foods, such as hemp, teff, maize, rice, wheat and other cereal grasses, pulses, bananas and plantains, as well as hemp, flax and cotton grown for their fibres, are the outcome of prehistoric selection over thousands of years from among wild ancestral plants with the most desirable characteristics. botanists study how plants produce food and how to increase yields, for example through plant breeding, making their work important to humanity ' s ability to feed the world and provide food security for future generations. botanists also study weeds, which are a considerable problem in agriculture, and the biology and control of plant pathogens in agriculture and natural ecosystems. ethnobotany is the study of the relationships between plants and people. when applied to the investigation of historical plant – people relationships ethnobotany may be referred to as archaeobotany or palaeoethnobotany. some of the earliest plant - people relationships arose between the indigenous people of canada in identifying edible plants from inedible plants. this relationship the indigenous people had with plants was recorded by ethnobotanists. = = plant biochemistry = = plant biochemistry is the study of the chemical processes used by plants. some of these processes are used in their primary metabolism like the photosynthetic calvin cycle and crassulacean acid metabolism. others make specialised materials like the cellulose and lignin used to build their bodies, and secondary products like resins and aroma compounds. plants and various other groups of photosynthetic eukaryotes collectively known as " algae " have unique organelles known as chloroplasts. chloroplasts are thought to be descended from cyanobacteria that formed endosymbiotic relationships with ancient plant and algal ancestors. chloroplasts and cyanobacteria contain the blue - green pigment chlorophyll a. chlorophyll a ( as well as its plant and green algal - specific cousin chlorophyll b ) absorbs light in the blue - violet and orange / red parts of the spectrum while reflecting and transmitting the green light that we see as the characteristic colour ". = = extraction = = extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted raw metals into a purer form. in order to convert a metal oxide or sulphide to a purer metal, the ore must be reduced physically, chemically, or electrolytically. extractive metallurgists are interested in three primary streams : feed, concentrate ( metal oxide / sulphide ) and tailings ( waste ). after mining, large pieces of the ore feed are broken through crushing or grinding in order to obtain particles small enough, where each particle is either mostly valuable or mostly waste. concentrating the particles of value in a form supporting separation enables the desired metal to be removed from waste products. mining may not be necessary, if the ore body and physical environment are conducive to leaching. leaching dissolves minerals in an ore body and results in an enriched solution. the solution is collected and processed to extract valuable metals. ore bodies often contain more than one valuable metal. tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. additionally, a concentrate may contain more than one valuable metal. that concentrate would then be processed to separate the valuable metals into individual constituents. = = metal and its alloys = = much effort has been placed on understanding iron – carbon alloy system, which includes steels and cast irons. plain carbon steels ( those that contain essentially only carbon as an alloying element ) are used in low - cost, high - strength applications, where neither weight nor corrosion are a major concern. cast irons, including ductile iron, are also part of the iron - carbon system. iron - manganese - chromium alloys ( hadfield - type steels ) are also used in non - magnetic applications such as directional drilling. other engineering metals include aluminium, chromium, copper, magnesium, nickel, titanium, zinc, and silicon. these metals are most often used as alloys with the noted exception of silicon, which is not a metal. other forms include : stainless steel, particularly austenitic stainless steels, galvanized steel, nickel alloys, titanium alloys, or occasionally copper alloys are used, where resistance to corrosion is important. aluminium alloys and magnesium alloys are commonly used, when a lightweight strong part is required such as in automotive and aerospace applications. copper - nickel alloys ( such as monel ) are used in highly corrosive environments and for non - magnetic applications remediation include ; soil contamination, hazardous waste, groundwater contamination, oil, gas and chemical spills. there are three most common types of environmental remediation. these include soil, water, and sediment remediation. soil remediation consists of removing contaminants in soil, as these pose great risks to humans and the ecosystem. some examples of this are heavy metals, pesticides, and radioactive materials. depending on the contaminant the remedial processes can be physical, chemical, thermal, or biological. water remediation is one of the most important considering water is an essential natural resource. depending on the source of water there will be different contaminants. surface water contamination mainly consists of agricultural, animal, and industrial waste, as well as acid mine drainage. there has been a rise in the need for water remediation due to the increased discharge of industrial waste, leading to a demand for sustainable water solutions. the market for water remediation is expected to consistently increase to $ 19. 6 billion by 2030. sediment remediation consists of removing contaminated sediments. is it almost similar to soil remediation except it is often more sophisticated as it involves additional contaminants. to reduce the contaminants it is likely to use physical, chemical, and biological processes that help with source control, but if these processes are executed correctly, there ' s a risk of contamination resurfacing. = = = solid waste management = = = solid waste management is the purification, consumption, reuse, disposal, and treatment of solid waste that is undertaken by the government or the ruling bodies of a city / town. it refers to the collection, treatment, and disposal of non - soluble, solid waste material. solid waste is associated with both industrial, institutional, commercial and residential activities. hazardous solid waste, when improperly disposed can encourage the infestation of insects and rodents, contributing to the spread of diseases. some of the most common types of solid waste management include ; landfills, vermicomposting, composting, recycling, and incineration. however, a major barrier for solid waste management practices is the high costs associated with recycling and the risks of creating more pollution. = = = e - waste recycling = = = the recycling of electronic waste ( e - waste ) has seen significant technological advancements due to increasing environmental concerns and the growing volume of electronic product disposals. traditional e - waste recycling methods, which often involve manual disassemb the world is changing at an ever - increasing pace. and it has changed in a much more fundamental way than one would think, primarily because it has become more connected and interdependent than in our entire history. every new product, every new invention can be combined with those that existed before, thereby creating an explosion of complexity : structural complexity, dynamic complexity, functional complexity, and algorithmic complexity. how to respond to this challenge? and what are the costs? is called its bandwidth ( bw ). for any given signal - to - noise ratio, a given bandwidth can carry the same amount of information regardless of where in the radio frequency spectrum it is located ; bandwidth is a measure of information - carrying capacity. the bandwidth required by a radio transmission depends on the data rate of the information being sent, and the spectral efficiency of the modulation method used ; how much data it can transmit in each unit of bandwidth. different types of information signals carried by radio have different data rates. for example, a television signal has a greater data rate than an audio signal. the radio spectrum, the total range of radio frequencies that can be used for communication in a given area, is a limited resource. each radio transmission occupies a portion of the total bandwidth available. radio bandwidth is regarded as an economic good which has a monetary cost and is in increasing demand. in some parts of the radio spectrum, the right to use a frequency band or even a single radio channel is bought and sold for millions of dollars. so there is an incentive to employ technology to minimize the bandwidth used by radio services. a slow transition from analog to digital radio transmission technologies began in the late 1990s. part of the reason for this is that digital modulation can often transmit more information ( a greater data rate ) in a given bandwidth than analog modulation, by using data compression algorithms, which reduce redundancy in the data to be sent, and more efficient modulation. other reasons for the transition is that digital modulation has greater noise immunity than analog, digital signal processing chips have more power and flexibility than analog circuits, and a wide variety of types of information can be transmitted using the same digital modulation. because it is a fixed resource which is in demand by an increasing number of users, the radio spectrum has become increasingly congested in recent decades, and the need to use it more effectively is driving many additional radio innovations such as trunked radio systems, spread spectrum ( ultra - wideband ) transmission, frequency reuse, dynamic spectrum management, frequency pooling, and cognitive radio. = = = itu frequency bands = = = the itu arbitrarily divides the radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten ( 10n ) metres, with corresponding frequency of 3 times a power of ten, and each covering a decade of frequency or wavelength. each of these bands has a traditional name : it can be seen that the bandwidth, the range of frequencies, contained in each band is not equal but increases exponentially as the . the first major technologies were tied to survival, hunting, and food preparation. stone tools and weapons, fire, and clothing were technological developments of major importance during this period. human ancestors have been using stone and other tools since long before the emergence of homo sapiens approximately 300, 000 years ago. the earliest direct evidence of tool usage was found in ethiopia within the great rift valley, dating back to 2. 5 million years ago. the earliest methods of stone tool making, known as the oldowan " industry ", date back to at least 2. 3 million years ago. this era of stone tool use is called the paleolithic, or " old stone age ", and spans all of human history up to the development of agriculture approximately 12, 000 years ago. to make a stone tool, a " core " of hard stone with specific flaking properties ( such as flint ) was struck with a hammerstone. this flaking produced sharp edges which could be used as tools, primarily in the form of choppers or scrapers. these tools greatly aided the early humans in their hunter - gatherer lifestyle to perform a variety of tasks including butchering carcasses ( and breaking bones to get at the marrow ) ; chopping wood ; cracking open nuts ; skinning an animal for its hide, and even forming other tools out of softer materials such as bone and wood. the earliest stone tools were irrelevant, being little more than a fractured rock. in the acheulian era, beginning approximately 1. 65 million years ago, methods of working these stones into specific shapes, such as hand axes emerged. this early stone age is described as the lower paleolithic. the middle paleolithic, approximately 300, 000 years ago, saw the introduction of the prepared - core technique, where multiple blades could be rapidly formed from a single core stone. the upper paleolithic, beginning approximately 40, 000 years ago, saw the introduction of pressure flaking, where a wood, bone, or antler punch could be used to shape a stone very finely. the end of the last ice age about 10, 000 years ago is taken as the end point of the upper paleolithic and the beginning of the epipaleolithic / mesolithic. the mesolithic technology included the use of microliths as composite stone tools, along with wood, bone, and antler tools. the later stone age, during which the rudiments of agricultural technology were developed, is called the neolithic period. during this period, ##tion, and pasteurization in order to become products that can be sold. there are three levels of food processing : primary, secondary, and tertiary. primary food processing involves turning agricultural products into other products that can be turned into food, secondary food processing is the making of food from readily available ingredients, and tertiary food processing is commercial production of ready - to eat or heat - and - serve foods. drying, pickling, salting, and fermenting foods were some of the oldest food processing techniques used to preserve food by preventing yeasts, molds, and bacteria to cause spoiling. methods for preserving food have evolved to meet current standards of food safety but still use the same processes as the past. biochemical engineers also work to improve the nutritional value of food products, such as in golden rice, which was developed to prevent vitamin a deficiency in certain areas where this was an issue. efforts to advance preserving technologies can also ensure lasting retention of nutrients as foods are stored. packaging plays a key role in preserving as well as ensuring the safety of the food by protecting the product from contamination, physical damage, and tampering. packaging can also make it easier to transport and serve food. a common job for biochemical engineers working in the food industry is to design ways to perform all these processes on a large scale in order to meet the demands of the population. responsibilities for this career path include designing and performing experiments, optimizing processes, consulting with groups to develop new technologies, and preparing project plans for equipment and facilities. = = = pharmaceuticals = = = in the pharmaceutical industry, bioprocess engineering plays a crucial role in the large - scale production of biopharmaceuticals, such as monoclonal antibodies, vaccines, and therapeutic proteins. the development and optimization of bioreactors and fermentation systems are essential for the mass production of these products, ensuring consistent quality and high yields. for example, recombinant proteins like insulin and erythropoietin are produced through cell culture systems using genetically modified cells. the bioprocess engineer ’ s role is to optimize variables like temperature, ph, nutrient availability, and oxygen levels to maximize the efficiency of these systems. the growing field of gene therapy also relies on bioprocessing techniques to produce viral vectors, which are used to deliver therapeutic genes to patients. this involves scaling up processes from laboratory to industrial scale while maintaining safety and regulatory compliance. as the demand for biopharmaceutical products increases, advancements no offspring, to reduce the population. in industrial and food applications, radiation is used for sterilization of tools and equipment. an advantage is that the object may be sealed in plastic before sterilization. an emerging use in food production is the sterilization of food using food irradiation. food irradiation is the process of exposing food to ionizing radiation in order to destroy microorganisms, bacteria, viruses, or insects that might be present in the food. the radiation sources used include radioisotope gamma ray sources, x - ray generators and electron accelerators. further applications include sprout inhibition, delay of ripening, increase of juice yield, and improvement of re - hydration. irradiation is a more general term of deliberate exposure of materials to radiation to achieve a technical goal ( in this context ' ionizing radiation ' is implied ). as such it is also used on non - food items, such as medical hardware, plastics, tubes for gas - pipelines, hoses for floor - heating, shrink - foils for food packaging, automobile parts, wires and cables ( isolation ), tires, and even gemstones. compared to the amount of food irradiated, the volume of those every - day applications is huge but not noticed by the consumer. the genuine effect of processing food by ionizing radiation relates to damages to the dna, the basic genetic information for life. microorganisms can no longer proliferate and continue their malignant or pathogenic activities. spoilage causing micro - organisms cannot continue their activities. insects do not survive or become incapable of procreation. plants cannot continue the natural ripening or aging process. all these effects are beneficial to the consumer and the food industry, likewise. the amount of energy imparted for effective food irradiation is low compared to cooking the same ; even at a typical dose of 10 kgy most food, which is ( with regard to warming ) physically equivalent to water, would warm by only about 2. 5 °c ( 4. 5 °f ). the specialty of processing food by ionizing radiation is the fact, that the energy density per atomic transition is very high, it can cleave molecules and induce ionization ( hence the name ) which cannot be achieved by mere heating. this is the reason for new beneficial effects, however at the same time, for new concerns. the treatment of solid food by ionizing radiation can provide an effect similar to heat pasteurization of liquids, such as milk. however Question: A natural resource that is consumed or used up faster than it can be made by nature is termed what? A) fossil fuel B) energy-inefficient C) renewable D) non-renewable	D) non-renewable
Context: in a voltaic cell, positive ( negative ) ions flow from the low ( high ) potential electrode to the high ( low ) potential electrode, driven by an ` electromotive force ' which points in opposite direction and overcomes the electric force. similarly in a superconductor charge flows in direction opposite to that dictated by the faraday electric field as the magnetic field is expelled in the meissner effect. the puzzle is the same in both cases : what drives electric charges against electromagnetic forces? i propose that the answer is also the same in both cases : kinetic energy lowering, or ` quantum pressure '. electric motors, servo - mechanisms, and other electrical systems in conjunction with special software. a common example of a mechatronics system is a cd - rom drive. mechanical systems open and close the drive, spin the cd and move the laser, while an optical system reads the data on the cd and converts it to bits. integrated software controls the process and communicates the contents of the cd to the computer. robotics is the application of mechatronics to create robots, which are often used in industry to perform tasks that are dangerous, unpleasant, or repetitive. these robots may be of any shape and size, but all are preprogrammed and interact physically with the world. to create a robot, an engineer typically employs kinematics ( to determine the robot ' s range of motion ) and mechanics ( to determine the stresses within the robot ). robots are used extensively in industrial automation engineering. they allow businesses to save money on labor, perform tasks that are either too dangerous or too precise for humans to perform them economically, and to ensure better quality. many companies employ assembly lines of robots, especially in automotive industries and some factories are so robotized that they can run by themselves. outside the factory, robots have been employed in bomb disposal, space exploration, and many other fields. robots are also sold for various residential applications, from recreation to domestic applications. = = = structural analysis = = = structural analysis is the branch of mechanical engineering ( and also civil engineering ) devoted to examining why and how objects fail and to fix the objects and their performance. structural failures occur in two general modes : static failure, and fatigue failure. static structural failure occurs when, upon being loaded ( having a force applied ) the object being analyzed either breaks or is deformed plastically, depending on the criterion for failure. fatigue failure occurs when an object fails after a number of repeated loading and unloading cycles. fatigue failure occurs because of imperfections in the object : a microscopic crack on the surface of the object, for instance, will grow slightly with each cycle ( propagation ) until the crack is large enough to cause ultimate failure. failure is not simply defined as when a part breaks, however ; it is defined as when a part does not operate as intended. some systems, such as the perforated top sections of some plastic bags, are designed to break. if these systems do not break, failure analysis might be employed to determine the cause. structural analysis is often used by mechanical engineers after a failure has occurred, or when designing to prevent failure the action potential is widely considered a purely electrical phenomenon. however, one also finds mechanical and thermal changes that can be observed experimentally. in particular, nerve membranes become thicker and axons contract. the spatial length of the action potential can be quite large, ranging from millimeters to many centimeters. this suggests to employ macroscopic thermodynamics methods to understand its properties. the pulse length is several orders of magnitude larger than the synaptic gap, larger than the distance of the nodes of ranvier, and even larger than the size of many neurons such as pyramidal cells or brain stem motor neurons. here, we review the mechanical changes in nerves, theoretical possibilities to explain them, and implications of a mechanical nerve pulse for the neuron and for the brain. in particular, the contraction of nerves gives rise to the possibility of fast mechanical synapses. major in electrical engineering, electronics engineering, electrical engineering technology, or electrical and electronic engineering. the same fundamental principles are taught in all programs, though emphasis may vary according to title. the length of study for such a degree is usually four or five years and the completed degree may be designated as a bachelor of science in electrical / electronics engineering technology, bachelor of engineering, bachelor of science, bachelor of technology, or bachelor of applied science, depending on the university. the bachelor ' s degree generally includes units covering physics, mathematics, computer science, project management, and a variety of topics in electrical engineering. initially such topics cover most, if not all, of the subdisciplines of electrical engineering. at many schools, electronic engineering is included as part of an electrical award, sometimes explicitly, such as a bachelor of engineering ( electrical and electronic ), but in others, electrical and electronic engineering are both considered to be sufficiently broad and complex that separate degrees are offered. some electrical engineers choose to study for a postgraduate degree such as a master of engineering / master of science ( meng / msc ), a master of engineering management, a doctor of philosophy ( phd ) in engineering, an engineering doctorate ( eng. d. ), or an engineer ' s degree. the master ' s and engineer ' s degrees may consist of either research, coursework or a mixture of the two. the doctor of philosophy and engineering doctorate degrees consist of a significant research component and are often viewed as the entry point to academia. in the united kingdom and some other european countries, master of engineering is often considered to be an undergraduate degree of slightly longer duration than the bachelor of engineering rather than a standalone postgraduate degree. = = professional practice = = in most countries, a bachelor ' s degree in engineering represents the first step towards professional certification and the degree program itself is certified by a professional body. after completing a certified degree program the engineer must satisfy a range of requirements ( including work experience requirements ) before being certified. once certified the engineer is designated the title of professional engineer ( in the united states, canada and south africa ), chartered engineer or incorporated engineer ( in india, pakistan, the united kingdom, ireland and zimbabwe ), chartered professional engineer ( in australia and new zealand ) or european engineer ( in much of the european union ). the advantages of licensure vary depending upon location. for example, in the united states and canada " only a licensed engineer may seal engineering work for public and private clients ". this requirement is enforced by state and provincial legislation such as quebec that moved gold leaf through electrical conduction. in 1795, francisco salva campillo proposed an electrostatic telegraph system. between 1803 and 1804, he worked on electrical telegraphy, and in 1804, he presented his report at the royal academy of natural sciences and arts of barcelona. salva ' s electrolyte telegraph system was very innovative though it was greatly influenced by and based upon two discoveries made in europe in 1800 — alessandro volta ' s electric battery for generating an electric current and william nicholson and anthony carlyle ' s electrolysis of water. electrical telegraphy may be considered the first example of electrical engineering. electrical engineering became a profession in the later 19th century. practitioners had created a global electric telegraph network, and the first professional electrical engineering institutions were founded in the uk and the us to support the new discipline. francis ronalds created an electric telegraph system in 1816 and documented his vision of how the world could be transformed by electricity. over 50 years later, he joined the new society of telegraph engineers ( soon to be renamed the institution of electrical engineers ) where he was regarded by other members as the first of their cohort. by the end of the 19th century, the world had been forever changed by the rapid communication made possible by the engineering development of land - lines, submarine cables, and, from about 1890, wireless telegraphy. practical applications and advances in such fields created an increasing need for standardized units of measure. they led to the international standardization of the units volt, ampere, coulomb, ohm, farad, and henry. this was achieved at an international conference in chicago in 1893. the publication of these standards formed the basis of future advances in standardization in various industries, and in many countries, the definitions were immediately recognized in relevant legislation. during these years, the study of electricity was largely considered to be a subfield of physics since early electrical technology was considered electromechanical in nature. the technische universitat darmstadt founded the world ' s first department of electrical engineering in 1882 and introduced the first - degree course in electrical engineering in 1883. the first electrical engineering degree program in the united states was started at massachusetts institute of technology ( mit ) in the physics department under professor charles cross, though it was cornell university to produce the world ' s first electrical engineering graduates in 1885. the first course in electrical engineering was taught in 1883 in cornell ' s sibley college of mechanical engineering and mechanic arts. in about 1885, cornell president andrew dickson white established the first department of electrical engineering in the united joseph henry and edward davy, who invented the electrical relay in 1835 ; of georg ohm, who in 1827 quantified the relationship between the electric current and potential difference in a conductor ; of michael faraday, the discoverer of electromagnetic induction in 1831 ; and of james clerk maxwell, who in 1873 published a unified theory of electricity and magnetism in his treatise electricity and magnetism. in 1782, georges - louis le sage developed and presented in berlin probably the world ' s first form of electric telegraphy, using 24 different wires, one for each letter of the alphabet. this telegraph connected two rooms. it was an electrostatic telegraph that moved gold leaf through electrical conduction. in 1795, francisco salva campillo proposed an electrostatic telegraph system. between 1803 and 1804, he worked on electrical telegraphy, and in 1804, he presented his report at the royal academy of natural sciences and arts of barcelona. salva ' s electrolyte telegraph system was very innovative though it was greatly influenced by and based upon two discoveries made in europe in 1800 — alessandro volta ' s electric battery for generating an electric current and william nicholson and anthony carlyle ' s electrolysis of water. electrical telegraphy may be considered the first example of electrical engineering. electrical engineering became a profession in the later 19th century. practitioners had created a global electric telegraph network, and the first professional electrical engineering institutions were founded in the uk and the us to support the new discipline. francis ronalds created an electric telegraph system in 1816 and documented his vision of how the world could be transformed by electricity. over 50 years later, he joined the new society of telegraph engineers ( soon to be renamed the institution of electrical engineers ) where he was regarded by other members as the first of their cohort. by the end of the 19th century, the world had been forever changed by the rapid communication made possible by the engineering development of land - lines, submarine cables, and, from about 1890, wireless telegraphy. practical applications and advances in such fields created an increasing need for standardized units of measure. they led to the international standardization of the units volt, ampere, coulomb, ohm, farad, and henry. this was achieved at an international conference in chicago in 1893. the publication of these standards formed the basis of future advances in standardization in various industries, and in many countries, the definitions were immediately recognized in relevant legislation. during these years, the study of electricity was largely considered to be a subfield of physics since early electrical technology was considered electromechan exploration of outer space and the ocean. human factors and ergonomics engineering : application of engineering, physiology, and psychology to the optimization of the human - machine relationship. ( ex : physical ergonomics, cognitive ergonomics, human – computer interaction ) biotechnology : the use of living systems and organisms to develop or make products. ( ex : pharmaceuticals, bioinformatics, genetic engineering. ) biomimetics : the imitation of models, systems, and elements of nature to solve complex human problems. ( ex : velcro, designed after george de mestral noticed how easily burs stuck to a dog ' s hair. ) bioelectrical engineering biomechanical engineering : is the application of mechanical engineering principles and biology to determine how these areas relate and how they can be integrated to potentially improve human health. bionics : an integration of biomedical, focused more on the robotics and assisted technologies. ( ex : prosthetics ) bioprinting : utilizing biomaterials to print cells, tissues and organs. biorobotics : utilizing advanced electronics and sensors to make prosthetics or biohybrid robots. systems biology : molecules, cells, organs, and organisms are all investigated in terms of their interactions and behaviors. = = organizations = = accreditation board for engineering and technology ( abet ), the u. s. - based accreditation board for engineering b. s. programs, makes a distinction between biomedical engineering and biological engineering, though there is much overlap ( see above ). american institute for medical and biological engineering ( aimbe ) is made up of 1, 500 members. their main goal is to educate the public about the value biological engineering has in our world, as well as invest in research and other programs to advance the field. they give out awards to those dedicated to innovation in the field, and awards of achievement in the field. ( they do not have a direct contribution to biological engineering ; they recognize those who do and encourage the public to continue that forward movement ). institute of biological engineering ( ibe ) is a non - profit organization that runs on donations alone. they aim to encourage the public to learn and to continue advancements in biological engineering. ( like aimbe, they do not perform research directly ; however, they offer scholarships to students who show promise in the field ). society for biological engineering ( sbe ) is a technological community associated with the american institute of chemical engineers ( aiche ). sbe hosts international conferences, and is a global organization of young plant cells, and electroporation, which involves using an electric shock to make the cell membrane permeable to plasmid dna. as only a single cell is transformed with genetic material, the organism must be regenerated from that single cell. in plants this is accomplished through the use of tissue culture. in animals it is necessary to ensure that the inserted dna is present in the embryonic stem cells. bacteria consist of a single cell and reproduce clonally so regeneration is not necessary. selectable markers are used to easily differentiate transformed from untransformed cells. these markers are usually present in the transgenic organism, although a number of strategies have been developed that can remove the selectable marker from the mature transgenic plant. further testing using pcr, southern hybridization, and dna sequencing is conducted to confirm that an organism contains the new gene. these tests can also confirm the chromosomal location and copy number of the inserted gene. the presence of the gene does not guarantee it will be expressed at appropriate levels in the target tissue so methods that look for and measure the gene products ( rna and protein ) are also used. these include northern hybridisation, quantitative rt - pcr, western blot, immunofluorescence, elisa and phenotypic analysis. the new genetic material can be inserted randomly within the host genome or targeted to a specific location. the technique of gene targeting uses homologous recombination to make desired changes to a specific endogenous gene. this tends to occur at a relatively low frequency in plants and animals and generally requires the use of selectable markers. the frequency of gene targeting can be greatly enhanced through genome editing. genome editing uses artificially engineered nucleases that create specific double - stranded breaks at desired locations in the genome, and use the cell ' s endogenous mechanisms to repair the induced break by the natural processes of homologous recombination and nonhomologous end - joining. there are four families of engineered nucleases : meganucleases, zinc finger nucleases, transcription activator - like effector nucleases ( talens ), and the cas9 - guiderna system ( adapted from crispr ). talen and crispr are the two most commonly used and each has its own advantages. talens have greater target specificity, while crispr is easier to design and more efficient. in addition to enhancing gene targeting, engineered nucleases can be used to introduce mutations - injection or micro - encapsulation. genetic engineering does not normally include traditional breeding, in vitro fertilisation, induction of polyploidy, mutagenesis and cell fusion techniques that do not use recombinant nucleic acids or a genetically modified organism in the process. however, some broad definitions of genetic engineering include selective breeding. cloning and stem cell research, although not considered genetic engineering, are closely related and genetic engineering can be used within them. synthetic biology is an emerging discipline that takes genetic engineering a step further by introducing artificially synthesised material into an organism. plants, animals or microorganisms that have been changed through genetic engineering are termed genetically modified organisms or gmos. if genetic material from another species is added to the host, the resulting organism is called transgenic. if genetic material from the same species or a species that can naturally breed with the host is used the resulting organism is called cisgenic. if genetic engineering is used to remove genetic material from the target organism the resulting organism is termed a knockout organism. in europe genetic modification is synonymous with genetic engineering while within the united states of america and canada genetic modification can also be used to refer to more conventional breeding methods. = = history = = humans have altered the genomes of species for thousands of years through selective breeding, or artificial selection : 1 : 1 as contrasted with natural selection. more recently, mutation breeding has used exposure to chemicals or radiation to produce a high frequency of random mutations, for selective breeding purposes. genetic engineering as the direct manipulation of dna by humans outside breeding and mutations has only existed since the 1970s. the term " genetic engineering " was coined by the russian - born geneticist nikolay timofeev - ressovsky in his 1934 paper " the experimental production of mutations ", published in the british journal biological reviews. jack williamson used the term in his science fiction novel dragon ' s island, published in 1951 – one year before dna ' s role in heredity was confirmed by alfred hershey and martha chase, and two years before james watson and francis crick showed that the dna molecule has a double - helix structure – though the general concept of direct genetic manipulation was explored in rudimentary form in stanley g. weinbaum ' s 1936 science fiction story proteus island. in 1972, paul berg created the first recombinant dna molecules by combining dna from the monkey virus sv40 with that of the lambda virus. in 1973 herbert boyer and stanley cohen created the first transgenic organism by insert unitary recordings in freely - moving pulse weakly electric fish suggest spike timing encoding of electrosensory signals Question: An electrical motor changes electrical energy into what? A) mechanical energy B) solar energy C) chemical energy D) thermal energy	A) mechanical energy
Context: 1975. skin tissue - engineered skin is a type of bioartificial organ that is often used to treat burns, diabetic foot ulcers, or other large wounds that cannot heal well on their own. artificial skin can be made from autografts, allografts, and xenografts. autografted skin comes from a patient ' s own skin, which allows the dermis to have a faster healing rate, and the donor site can be re - harvested a few times. allograft skin often comes from cadaver skin and is mostly used to treat burn victims. lastly, xenografted skin comes from animals and provides a temporary healing structure for the skin. they assist in dermal regeneration, but cannot become part of the host skin. tissue - engineered skin is now available in commercial products. integra, originally used to only treat burns, consists of a collagen matrix and chondroitin sulfate that can be used as a skin replacement. the chondroitin sulfate functions as a component of proteoglycans, which helps to form the extracellular matrix. integra can be repopulated and revascularized while maintaining its dermal collagen architecture, making it a bioartificial organ dermagraft, another commercial - made tissue - engineered skin product, is made out of living fibroblasts. these fibroblasts proliferate and produce growth factors, collagen, and ecm proteins, that help build granulation tissue. = = = = heart = = = = since the number of patients awaiting a heart transplant is continuously increasing over time, and the number of patients on the waiting list surpasses the organ availability, artificial organs used as replacement therapy for terminal heart failure would help alleviate this difficulty. artificial hearts are usually used to bridge the heart transplantation or can be applied as replacement therapy for terminal heart malfunction. the total artificial heart ( tah ), first introduced by dr. vladimir p. demikhov in 1937, emerged as an ideal alternative. since then it has been developed and improved as a mechanical pump that provides long - term circulatory support and replaces diseased or damaged heart ventricles that cannot properly pump the blood, restoring thus the pulmonary and systemic flow. some of the current tahs include abiocor, an fda - approved device that comprises two artificial ventricles and their valves, and does not require subcutaneous connections, and is indicated for ##fts. autografted skin comes from a patient ' s own skin, which allows the dermis to have a faster healing rate, and the donor site can be re - harvested a few times. allograft skin often comes from cadaver skin and is mostly used to treat burn victims. lastly, xenografted skin comes from animals and provides a temporary healing structure for the skin. they assist in dermal regeneration, but cannot become part of the host skin. tissue - engineered skin is now available in commercial products. integra, originally used to only treat burns, consists of a collagen matrix and chondroitin sulfate that can be used as a skin replacement. the chondroitin sulfate functions as a component of proteoglycans, which helps to form the extracellular matrix. integra can be repopulated and revascularized while maintaining its dermal collagen architecture, making it a bioartificial organ dermagraft, another commercial - made tissue - engineered skin product, is made out of living fibroblasts. these fibroblasts proliferate and produce growth factors, collagen, and ecm proteins, that help build granulation tissue. = = = = heart = = = = since the number of patients awaiting a heart transplant is continuously increasing over time, and the number of patients on the waiting list surpasses the organ availability, artificial organs used as replacement therapy for terminal heart failure would help alleviate this difficulty. artificial hearts are usually used to bridge the heart transplantation or can be applied as replacement therapy for terminal heart malfunction. the total artificial heart ( tah ), first introduced by dr. vladimir p. demikhov in 1937, emerged as an ideal alternative. since then it has been developed and improved as a mechanical pump that provides long - term circulatory support and replaces diseased or damaged heart ventricles that cannot properly pump the blood, restoring thus the pulmonary and systemic flow. some of the current tahs include abiocor, an fda - approved device that comprises two artificial ventricles and their valves, and does not require subcutaneous connections, and is indicated for patients with biventricular heart failure. in 2010 syncardia released the portable freedom driver that allows patients to have a portable device without being confined to the hospital. = = = = kidney = = = = while kidney transplants are possible, renal failure is more often treated using an artificial kidney. the first artificial techniques that provide heart and lung support. it is used primarily to support the lungs for a prolonged but still temporary timeframe ( 1 – 30 days ) and allow for recovery from reversible diseases. robert bartlett is known as the father of ecmo and performed the first treatment of a newborn using an ecmo machine in 1975. skin tissue - engineered skin is a type of bioartificial organ that is often used to treat burns, diabetic foot ulcers, or other large wounds that cannot heal well on their own. artificial skin can be made from autografts, allografts, and xenografts. autografted skin comes from a patient ' s own skin, which allows the dermis to have a faster healing rate, and the donor site can be re - harvested a few times. allograft skin often comes from cadaver skin and is mostly used to treat burn victims. lastly, xenografted skin comes from animals and provides a temporary healing structure for the skin. they assist in dermal regeneration, but cannot become part of the host skin. tissue - engineered skin is now available in commercial products. integra, originally used to only treat burns, consists of a collagen matrix and chondroitin sulfate that can be used as a skin replacement. the chondroitin sulfate functions as a component of proteoglycans, which helps to form the extracellular matrix. integra can be repopulated and revascularized while maintaining its dermal collagen architecture, making it a bioartificial organ dermagraft, another commercial - made tissue - engineered skin product, is made out of living fibroblasts. these fibroblasts proliferate and produce growth factors, collagen, and ecm proteins, that help build granulation tissue. = = = = heart = = = = since the number of patients awaiting a heart transplant is continuously increasing over time, and the number of patients on the waiting list surpasses the organ availability, artificial organs used as replacement therapy for terminal heart failure would help alleviate this difficulty. artificial hearts are usually used to bridge the heart transplantation or can be applied as replacement therapy for terminal heart malfunction. the total artificial heart ( tah ), first introduced by dr. vladimir p. demikhov in 1937, emerged as an ideal alternative. since then it has been developed and improved as a mechanical pump that provides long - term circulatory support and this scaffold and cells were placed in a bioreactor, where it matured to become a partially or fully transplantable organ. the work was called a " landmark ". the lab first stripped the cells away from a rat heart ( a process called " decellularization " ) and then injected rat stem cells into the decellularized rat heart. tissue - engineered blood vessels : blood vessels that have been grown in a lab and can be used to repair damaged blood vessels without eliciting an immune response. tissue engineered blood vessels have been developed by many different approaches. they could be implanted as pre - seeded cellularized blood vessels, as acellular vascular grafts made with decellularized vessels or synthetic vascular grafts. artificial skin constructed from human skin cells embedded in a hydrogel, such as in the case of bio - printed constructs for battlefield burn repairs. artificial bone marrow : bone marrow cultured in vitro to be transplanted serves as a " just cells " approach to tissue engineering. tissue engineered bone : a structural matrix can be composed of metals such as titanium, polymers of varying degradation rates, or certain types of ceramics. materials are often chosen to recruit osteoblasts to aid in reforming the bone and returning biological function. various types of cells can be added directly into the matrix to expedite the process. laboratory - grown penis : decellularized scaffolds of rabbit penises were recellularised with smooth muscle and endothelial cells. the organ was then transplanted to live rabbits and functioned comparably to the native organ, suggesting potential as treatment for genital trauma. oral mucosa tissue engineering uses a cells and scaffold approach to replicate the 3 dimensional structure and function of oral mucosa. = = cells as building blocks = = cells are one of the main components for the success of tissue engineering approaches. tissue engineering uses cells as strategies for creation / replacement of new tissue. examples include fibroblasts used for skin repair or renewal, chondrocytes used for cartilage repair ( maci – fda approved product ), and hepatocytes used in liver support systems cells can be used alone or with support matrices for tissue engineering applications. an adequate environment for promoting cell growth, differentiation, and integration with the existing tissue is a critical factor for cell - based building blocks. manipulation of any of these cell processes create alternative avenues for the development of new tissue ( e. g., cell reprogramming - somatic tissue engineering is a biomedical engineering discipline that uses a combination of cells, engineering, materials methods, and suitable biochemical and physicochemical factors to restore, maintain, improve, or replace different types of biological tissues. tissue engineering often involves the use of cells placed on tissue scaffolds in the formation of new viable tissue for a medical purpose, but is not limited to applications involving cells and tissue scaffolds. while it was once categorized as a sub - field of biomaterials, having grown in scope and importance, it can be considered as a field of its own. while most definitions of tissue engineering cover a broad range of applications, in practice, the term is closely associated with applications that repair or replace portions of or whole tissues ( i. e. organs, bone, cartilage, blood vessels, bladder, skin, muscle etc. ). often, the tissues involved require certain mechanical and structural properties for proper functioning. the term has also been applied to efforts to perform specific biochemical functions using cells within an artificially - created support system ( e. g. an artificial pancreas, or a bio artificial liver ). the term regenerative medicine is often used synonymously with tissue engineering, although those involved in regenerative medicine place more emphasis on the use of stem cells or progenitor cells to produce tissues. = = overview = = a commonly applied definition of tissue engineering, as stated by langer and vacanti, is " an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve [ biological tissue ] function or a whole organ ". in addition, langer and vacanti also state that there are three main types of tissue engineering : cells, tissue - inducing substances, and a cells + matrix approach ( often referred to as a scaffold ). tissue engineering has also been defined as " understanding the principles of tissue growth, and applying this to produce functional replacement tissue for clinical use ". a further description goes on to say that an " underlying supposition of tissue engineering is that the employment of natural biology of the system will allow for greater success in developing therapeutic strategies aimed at the replacement, repair, maintenance, or enhancement of tissue function ". developments in the multidisciplinary field of tissue engineering have yielded a novel set of tissue replacement parts and implementation strategies. scientific advances in biomaterials, stem cells, growth and differentiation factors, and biomimetic environments have created unique opportunities to fabric cells into the decellularized rat heart. tissue - engineered blood vessels : blood vessels that have been grown in a lab and can be used to repair damaged blood vessels without eliciting an immune response. tissue engineered blood vessels have been developed by many different approaches. they could be implanted as pre - seeded cellularized blood vessels, as acellular vascular grafts made with decellularized vessels or synthetic vascular grafts. artificial skin constructed from human skin cells embedded in a hydrogel, such as in the case of bio - printed constructs for battlefield burn repairs. artificial bone marrow : bone marrow cultured in vitro to be transplanted serves as a " just cells " approach to tissue engineering. tissue engineered bone : a structural matrix can be composed of metals such as titanium, polymers of varying degradation rates, or certain types of ceramics. materials are often chosen to recruit osteoblasts to aid in reforming the bone and returning biological function. various types of cells can be added directly into the matrix to expedite the process. laboratory - grown penis : decellularized scaffolds of rabbit penises were recellularised with smooth muscle and endothelial cells. the organ was then transplanted to live rabbits and functioned comparably to the native organ, suggesting potential as treatment for genital trauma. oral mucosa tissue engineering uses a cells and scaffold approach to replicate the 3 dimensional structure and function of oral mucosa. = = cells as building blocks = = cells are one of the main components for the success of tissue engineering approaches. tissue engineering uses cells as strategies for creation / replacement of new tissue. examples include fibroblasts used for skin repair or renewal, chondrocytes used for cartilage repair ( maci – fda approved product ), and hepatocytes used in liver support systems cells can be used alone or with support matrices for tissue engineering applications. an adequate environment for promoting cell growth, differentiation, and integration with the existing tissue is a critical factor for cell - based building blocks. manipulation of any of these cell processes create alternative avenues for the development of new tissue ( e. g., cell reprogramming - somatic cells, vascularization ). = = = isolation = = = techniques for cell isolation depend on the cell source. centrifugation and apheresis are techniques used for extracting cells from biofluids ( e. g., blood ). whereas digestion processes, typically using enzymes to remove the extra ##ilage generated without the use of exogenous scaffold material. in this methodology, all material in the construct is cellular produced directly by the cells. bioartificial heart : doris taylor ' s lab constructed a biocompatible rat heart by re - cellularising a de - cellularised rat heart. this scaffold and cells were placed in a bioreactor, where it matured to become a partially or fully transplantable organ. the work was called a " landmark ". the lab first stripped the cells away from a rat heart ( a process called " decellularization " ) and then injected rat stem cells into the decellularized rat heart. tissue - engineered blood vessels : blood vessels that have been grown in a lab and can be used to repair damaged blood vessels without eliciting an immune response. tissue engineered blood vessels have been developed by many different approaches. they could be implanted as pre - seeded cellularized blood vessels, as acellular vascular grafts made with decellularized vessels or synthetic vascular grafts. artificial skin constructed from human skin cells embedded in a hydrogel, such as in the case of bio - printed constructs for battlefield burn repairs. artificial bone marrow : bone marrow cultured in vitro to be transplanted serves as a " just cells " approach to tissue engineering. tissue engineered bone : a structural matrix can be composed of metals such as titanium, polymers of varying degradation rates, or certain types of ceramics. materials are often chosen to recruit osteoblasts to aid in reforming the bone and returning biological function. various types of cells can be added directly into the matrix to expedite the process. laboratory - grown penis : decellularized scaffolds of rabbit penises were recellularised with smooth muscle and endothelial cells. the organ was then transplanted to live rabbits and functioned comparably to the native organ, suggesting potential as treatment for genital trauma. oral mucosa tissue engineering uses a cells and scaffold approach to replicate the 3 dimensional structure and function of oral mucosa. = = cells as building blocks = = cells are one of the main components for the success of tissue engineering approaches. tissue engineering uses cells as strategies for creation / replacement of new tissue. examples include fibroblasts used for skin repair or renewal, chondrocytes used for cartilage repair ( maci – fda approved product ), and hepatocytes used in liver support systems cells can be used alone or with into seven out of approximately 20 human test subjects as part of a long - term experiment. cartilage : lab - grown cartilage, cultured in vitro on a scaffold, was successfully used as an autologous transplant to repair patients ' knees. scaffold - free cartilage : cartilage generated without the use of exogenous scaffold material. in this methodology, all material in the construct is cellular produced directly by the cells. bioartificial heart : doris taylor ' s lab constructed a biocompatible rat heart by re - cellularising a de - cellularised rat heart. this scaffold and cells were placed in a bioreactor, where it matured to become a partially or fully transplantable organ. the work was called a " landmark ". the lab first stripped the cells away from a rat heart ( a process called " decellularization " ) and then injected rat stem cells into the decellularized rat heart. tissue - engineered blood vessels : blood vessels that have been grown in a lab and can be used to repair damaged blood vessels without eliciting an immune response. tissue engineered blood vessels have been developed by many different approaches. they could be implanted as pre - seeded cellularized blood vessels, as acellular vascular grafts made with decellularized vessels or synthetic vascular grafts. artificial skin constructed from human skin cells embedded in a hydrogel, such as in the case of bio - printed constructs for battlefield burn repairs. artificial bone marrow : bone marrow cultured in vitro to be transplanted serves as a " just cells " approach to tissue engineering. tissue engineered bone : a structural matrix can be composed of metals such as titanium, polymers of varying degradation rates, or certain types of ceramics. materials are often chosen to recruit osteoblasts to aid in reforming the bone and returning biological function. various types of cells can be added directly into the matrix to expedite the process. laboratory - grown penis : decellularized scaffolds of rabbit penises were recellularised with smooth muscle and endothelial cells. the organ was then transplanted to live rabbits and functioned comparably to the native organ, suggesting potential as treatment for genital trauma. oral mucosa tissue engineering uses a cells and scaffold approach to replicate the 3 dimensional structure and function of oral mucosa. = = cells as building blocks = = cells are one of the main components for the success of tissue engineering approaches inflammatory reactions. because of this, they are of great interest for gene delivery and tissue engineering scaffolds. most hydroxyapatite ceramics are very porous and lack mechanical strength and are used to coat metal orthopedic devices to aid in forming a bond to bone or as bone fillers. they are also used as fillers for orthopedic plastic screws to aid in reducing the inflammation and increase absorption of these plastic materials. work is being done to make strong, fully dense nano crystalline hydroxyapatite ceramic materials for orthopedic weight bearing devices, replacing foreign metal and plastic orthopedic materials with a synthetic, but naturally occurring, bone mineral. ultimately these ceramic materials may be used as bone replacements or with the incorporation of protein collagens, synthetic bones. durable actinide - containing ceramic materials have many applications such as in nuclear fuels for burning excess pu and in chemically - inert sources of alpha irradiation for power supply of unmanned space vehicles or to produce electricity for microelectronic devices. both use and disposal of radioactive actinides require their immobilization in a durable host material. nuclear waste long - lived radionuclides such as actinides are immobilized using chemically - durable crystalline materials based on polycrystalline ceramics and large single crystals. alumina ceramics are widely utilized in the chemical industry due to their excellent chemical stability and high resistance to corrosion. it is used as acid - resistant pump impellers and pump bodies, ensuring long - lasting performance in transferring aggressive fluids. they are also used in acid - carrying pipe linings to prevent contamination and maintain fluid purity, which is crucial in industries like pharmaceuticals and food processing. valves made from alumina ceramics demonstrate exceptional durability and resistance to chemical attack, making them reliable for controlling the flow of corrosive liquids. = = glass - ceramics = = glass - ceramic materials share many properties with both glasses and ceramics. glass - ceramics have an amorphous phase and one or more crystalline phases and are produced by a so - called " controlled crystallization ", which is typically avoided in glass manufacturing. glass - ceramics often contain a crystalline phase which constitutes anywhere from 30 % [ m / m ] to 90 % [ m / m ] of its composition by volume, yielding an array of materials with interesting thermomechanical properties. in the processing of glass - ceramics, molten glass is cooled down gradually before reheating and annealing. in this heat the following purposes : allowing cell attachment and migration, delivering and retaining cells and biochemical factors, enabling diffusion of vital cell nutrients and expressed products, and exerting certain mechanical and biological influences to modify the behaviour of the cell phase. in 2009, an interdisciplinary team led by the thoracic surgeon thorsten walles implanted the first bioartificial transplant that provides an innate vascular network for post - transplant graft supply successfully into a patient awaiting tracheal reconstruction. to achieve the goal of tissue reconstruction, scaffolds must meet some specific requirements. high porosity and adequate pore size are necessary to facilitate cell seeding and diffusion throughout the whole structure of both cells and nutrients. biodegradability is often an essential factor since scaffolds should preferably be absorbed by the surrounding tissues without the necessity of surgical removal. the rate at which degradation occurs has to coincide as much as possible with the rate of tissue formation : this means that while cells are fabricating their own natural matrix structure around themselves, the scaffold is able to provide structural integrity within the body and eventually it will break down leaving the newly formed tissue which will take over the mechanical load. injectability is also important for clinical uses. recent research on organ printing is showing how crucial a good control of the 3d environment is to ensure reproducibility of experiments and offer better results. = = = materials = = = material selection is an essential aspect of producing a scaffold. the materials utilized can be natural or synthetic and can be biodegradable or non - biodegradable. additionally, they must be biocompatible, meaning that they do not cause any adverse effects to cells. silicone, for example, is a synthetic, non - biodegradable material commonly used as a drug delivery material, while gelatin is a biodegradable, natural material commonly used in cell - culture scaffolds the material needed for each application is different, and dependent on the desired mechanical properties of the material. tissue engineering of long bone defects for example, will require a rigid scaffold with a compressive strength similar to that of cortical bone ( 100 - 150 mpa ), which is much higher compared to a scaffold for skin regeneration. there are a few versatile synthetic materials used for many different scaffold applications. one of these commonly used materials is polylactic acid ( pla ), a synthetic polymer. pla – polylactic acid. this is a polyester which Question: What is name for a piece of collagen-rich skin formed after the process of wound healing that differs from normal skin? A) tissue B) Sore C) size D) scar	D) scar
Context: to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial differences in gene expression. a small fraction of the genes in an organism ' s genome called the developmental - genetic toolkit control the development of that organism. these toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. among the most important toolkit genes are the hox genes. hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva. = = evolution = = = = = evolutionary processes = = = evolution is a central organizing concept in biology. it is the change in heritable characteristics of populations over successive generations. in artificial selection, animals were selectively bred for specific traits. given that traits are inherited, populations contain a varied mix of traits, and reproduction is able to increase any population, darwin argued that in the natural world, it was nature that played the role of humans in selecting for specific traits. darwin inferred that individuals who possessed heritable traits better adapted to their environments are more likely to survive and produce more offspring than other individuals. he further inferred that this would lead to the can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial differences in gene expression. a small fraction of the genes in an organism ' s genome called the developmental - genetic toolkit control the development of that organism. these toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. among the most important toolkit genes are the hox genes. hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva. = = evolution = = = = = evolutionary processes = = = evolution is a central organizing concept in biology. it is the change in heritable characteristics of populations over successive generations. in artificial selection, animals were selectively bred for specific traits. given that traits are inherited, populations contain a varied mix of traits, and reproduction is able to increase any population, or removed from the dna during programmed stages of development of the plant, and are responsible, for example, for the differences between anthers, petals and normal leaves, despite the fact that they all have the same underlying genetic code. epigenetic changes may be temporary or may remain through successive cell divisions for the remainder of the cell ' s life. some epigenetic changes have been shown to be heritable, while others are reset in the germ cells. epigenetic changes in eukaryotic biology serve to regulate the process of cellular differentiation. during morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, with one allele inducing a change on the other. = = plant evolution = = the chloroplasts of plants have a number of biochemical, structural and genetic similarities to cyanobacteria, ( commonly but incorrectly known as " blue - green algae " ) and are thought to be derived from an ancient endosymbiotic relationship between an ancestral eukaryotic cell and a cyanobacterial resident. the algae are a polyphyletic group and are placed in various divisions, some more closely related to plants than others. there are many differences between them in features such as cell wall composition, biochemistry, ##es. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the ancestor of plants by entering into an endosymbiotic relationship with an early eukaryote, ultimately becoming the chloroplasts in plant cells. the new photosynthetic plants ( along with their algal relatives ) accelerated the rise in atmospheric oxygen started by the cyanobacteria, changing the ancient oxygen - free, reducing, atmosphere to one in which free oxygen has been abundant for more than 2 billion years. among the important botanical questions of the 21st century are the role of plants as primary producers in the global cycling of life ' s basic ingredients : energy, carbon, oxygen, nitrogen and water, and ways that our plant stewardship can help address the global environmental issues of resource management, conservation, human food security, biologically invasive organisms, carbon sequestration, climate change, and sustainability. = = = human nutrition = = = virtually all staple foods come either directly from primary production by plants, or indirectly from animals that eat them. plants and other photosynthetic organisms are at the base of most food chains because they use the energy from the sun and nutrients from the soil and atmosphere, converting them into a form that can be used by animals. this is what ecologists call the first trophic level. the modern forms of the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the ancestor of plants by entering into an endosymbiotic relationship with an early eukaryote, ultimately becoming the chloroplasts in plant cells. the new photosynthetic plants ( along with their algal relatives ) accelerated the rise in atmospheric oxygen started by the cyanobacteria, changing the ancient oxygen - free, reducing, atmosphere to one in which free oxygen has been abundant for more than 2 billion years. among the important botanical questions of the 21st century are the role of plants as primary producers in the global cycling of life ' s basic ingredients : energy, carbon, oxygen, nitrogen and water, and ways that our plant stewardship can help address the global environmental issues of resource management, conservation, human food security, biologically invasive organisms, carbon sequestration, climate change, and sustainability. = = = human nutrition = = = virtually all staple foods come either directly from primary production by plants, or indirectly from animals that various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial differences in gene expression. a small fraction of the genes in an organism ' s genome called the developmental - genetic toolkit control the development of that organism. these toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. among the most important toolkit genes are the hox genes. hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva. = = evolution = = = = = evolutionary processes = = = evolution is a central organizing concept in biology. it is the change in heritable characteristics of populations over successive generations. in artificial selection, animals were selectively bred for specific traits. given that traits are inherited, populations contain a varied mix of traits, and reproduction is able to increase any population, darwin argued that in the natural world, it was nature that played the role of humans in selecting for specific traits. darwin inferred that individuals who possessed heritable traits better adapted to their environments are more likely to survive and produce more offspring than other individuals. he further inferred that this would lead to the accumulation of favorable traits over successive generations, thereby increasing the match between the organisms and their environment. = = = speciation = = = a species is a group of organisms that mate with one another and speciation is the process by which one lineage splits into two lineages as a result of having evolved independently from each other pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, with one allele inducing a change on the other. = = plant evolution = = the chloroplasts of plants have a number of biochemical, structural and genetic similarities to cyanobacteria, ( commonly but incorrectly known as " blue - green algae " ) and are thought to be derived from an ancient endosymbiotic relationship between an ancestral eukaryotic cell and a cyanobacterial resident. the algae are a polyphyletic group and are placed in various divisions, some more closely related to plants than others. there are many differences between them in features such as cell wall composition, biochemistry, pigmentation, chloroplast structure and nutrient reserves. the algal division charophyta, sister to the green algal division chlorophyta, is considered to contain the ancestor of true plants. the charophyte class charophyceae and the land plant sub - kingdom embryophyta together form the monophyletic group or clade streptophytina. nonvascular land plants are embryophytes that lack the vascular tissues xylem and phloem. they include mosses, liverworts and hornworts. pteridophytic vascular plants with true xyle ##ta together form the monophyletic group or clade streptophytina. nonvascular land plants are embryophytes that lack the vascular tissues xylem and phloem. they include mosses, liverworts and hornworts. pteridophytic vascular plants with true xylem and phloem that reproduced by spores germinating into free - living gametophytes evolved during the silurian period and diversified into several lineages during the late silurian and early devonian. representatives of the lycopods have survived to the present day. by the end of the devonian period, several groups, including the lycopods, sphenophylls and progymnosperms, had independently evolved " megaspory " – their spores were of two distinct sizes, larger megaspores and smaller microspores. their reduced gametophytes developed from megaspores retained within the spore - producing organs ( megasporangia ) of the sporophyte, a condition known as endospory. seeds consist of an endosporic megasporangium surrounded by one or two sheathing layers ( integuments ). the young sporophyte develops within the seed, which on germination splits to release it. the earliest known seed plants date from the latest devonian famennian stage. following the evolution of the seed habit, seed plants diversified, giving rise to a number of now - extinct groups, including seed ferns, as well as the modern gymnosperms and angiosperms. gymnosperms produce " naked seeds " not fully enclosed in an ovary ; modern representatives include conifers, cycads, ginkgo, and gnetales. angiosperms produce seeds enclosed in a structure such as a carpel or an ovary. ongoing research on the molecular phylogenetics of living plants appears to show that the angiosperms are a sister clade to the gymnosperms. = = plant physiology = = plant physiology encompasses all the internal chemical and physical activities of plants associated with life. chemicals obtained from the air, soil and water form the basis of all plant metabolism. the energy of sunlight, captured by oxygenic photosynthesis and released by cellular respiration, is the basis of almost all life. photoautotrophs, including all green plants, algae and cyanobacteria gather energy directly from sunlight by photosynthesis. hetero induced stem cells ( isc ) as related to the donor. = = = stem cells = = = stem cells are undifferentiated cells with the ability to divide in culture and give rise to different forms of specialized cells. stem cells are divided into " adult " and " embryonic " stem cells according to their source. while there is still a large ethical debate related to the use of embryonic stem cells, it is thought that another alternative source – induced pluripotent stem cells – may be useful for the repair of diseased or damaged tissues, or may be used to grow new organs. totipotent cells are stem cells which can divide into further stem cells or differentiate into any cell type in the body, including extra - embryonic tissue. pluripotent cells are stem cells which can differentiate into any cell type in the body except extra - embryonic tissue. induced pluripotent stem cells ( ipscs ) are subclass of pluripotent stem cells resembling embryonic stem cells ( escs ) that have been derived from adult differentiated cells. ipscs are created by altering the expression of transcriptional factors in adult cells until they become like embryonic stem cells. multipotent stem cells can be differentiated into any cell within the same class, such as blood or bone. a common example of multipotent cells is mesenchymal stem cells ( mscs ). = = scaffolds = = scaffolds are materials that have been engineered to cause desirable cellular interactions to contribute to the formation of new functional tissues for medical purposes. cells are often ' seeded ' into these structures capable of supporting three - dimensional tissue formation. scaffolds mimic the extracellular matrix of the native tissue, recapitulating the in vivo milieu and allowing cells to influence their own microenvironments. they usually serve at least one of the following purposes : allowing cell attachment and migration, delivering and retaining cells and biochemical factors, enabling diffusion of vital cell nutrients and expressed products, and exerting certain mechanical and biological influences to modify the behaviour of the cell phase. in 2009, an interdisciplinary team led by the thoracic surgeon thorsten walles implanted the first bioartificial transplant that provides an innate vascular network for post - transplant graft supply successfully into a patient awaiting tracheal reconstruction. to achieve the goal of tissue reconstruction, scaffolds must meet some specific requirements. high porosity and adequate pore size are necessary to facilitate cell seed the cell ' s life. some epigenetic changes have been shown to be heritable, while others are reset in the germ cells. epigenetic changes in eukaryotic biology serve to regulate the process of cellular differentiation. during morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, with one allele inducing a change on the other. = = plant evolution = = the chloroplasts of plants have a number of biochemical, structural and genetic similarities to cyanobacteria, ( commonly but incorrectly known as " blue - green algae " ) and are thought to be derived from an ancient endosymbiotic relationship between an ancestral eukaryotic cell and a cyanobacterial resident. the algae are a polyphyletic group and are placed in various divisions, some more closely related to plants than others. there are many differences between them in features such as cell wall composition, biochemistry, pigmentation, chloroplast structure and nutrient reserves. the algal division charophyta, sister to the green algal division chlorophyta, is considered to contain the ancestor of true plants. the charophyte class charophyceae and the land plant sub - kingdom embryophy Question: Young eutherians complete their embryonic development within what? A) spores B) pollen grains C) ovaries D) uterus	D) uterus
Context: difficult. = = nuclear weapons = = a nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. both reactions release vast quantities of energy from relatively small amounts of matter. even small nuclear devices can devastate a city by blast, fire and radiation. nuclear weapons are considered weapons of mass destruction, and their use and control has been a major aspect of international policy since their debut. the design of a nuclear weapon is more complicated than it might seem. such a weapon must hold one or more subcritical fissile masses stable for deployment, then induce criticality ( create a critical mass ) for detonation. it also is quite difficult to ensure that such a chain reaction consumes a significant fraction of the fuel before the device flies apart. the procurement of a nuclear fuel is also more difficult than it might seem, since sufficiently unstable substances for this process do not currently occur naturally on earth in suitable amounts. one isotope of uranium, namely uranium - 235, is naturally occurring and sufficiently unstable, but it is always found mixed with the more stable isotope uranium - 238. the latter accounts for more than 99 % of the weight of natural uranium. therefore, some method of isotope separation based on the weight of three neutrons must be performed to enrich ( isolate ) uranium - 235. alternatively, the element plutonium possesses an isotope that is sufficiently unstable for this process to be usable. terrestrial plutonium does not currently occur naturally in sufficient quantities for such use, so it must be manufactured in a nuclear reactor. ultimately, the manhattan project manufactured nuclear weapons based on each of these elements. they detonated the first nuclear weapon in a test code - named " trinity ", near alamogordo, new mexico, on july 16, 1945. the test was conducted to ensure that the implosion method of detonation would work, which it did. a uranium bomb, little boy, was dropped on the japanese city hiroshima on august 6, 1945, followed three days later by the plutonium - based fat man on nagasaki. in the wake of unprecedented devastation and casualties from a single weapon, the japanese government soon surrendered, ending world war ii. since these bombings, no nuclear weapons have been deployed offensively. nevertheless, they prompted an arms race to develop increasingly destructive bombs to provide a nuclear deterrent. just over four years later, on august 29, 1949, the soviet union detonated its first fission weapon. the united kingdom followed on october 2, 1952 ; france, on february if there are enough immediate decays to carry on the chain reaction, the mass is said to be prompt critical, and the energy release will grow rapidly and uncontrollably, usually leading to an explosion. when discovered on the eve of world war ii, this insight led multiple countries to begin programs investigating the possibility of constructing an atomic bomb — a weapon which utilized fission reactions to generate far more energy than could be created with chemical explosives. the manhattan project, run by the united states with the help of the united kingdom and canada, developed multiple fission weapons which were used against japan in 1945 at hiroshima and nagasaki. during the project, the first fission reactors were developed as well, though they were primarily for weapons manufacture and did not generate electricity. in 1951, the first nuclear fission power plant was the first to produce electricity at the experimental breeder reactor no. 1 ( ebr - 1 ), in arco, idaho, ushering in the " atomic age " of more intensive human energy use. however, if the mass is critical only when the delayed neutrons are included, then the reaction can be controlled, for example by the introduction or removal of neutron absorbers. this is what allows nuclear reactors to be built. fast neutrons are not easily captured by nuclei ; they must be slowed ( slow neutrons ), generally by collision with the nuclei of a neutron moderator, before they can be easily captured. today, this type of fission is commonly used to generate electricity. = = = nuclear fusion = = = if nuclei are forced to collide, they can undergo nuclear fusion. this process may release or absorb energy. when the resulting nucleus is lighter than that of iron, energy is normally released ; when the nucleus is heavier than that of iron, energy is generally absorbed. this process of fusion occurs in stars, which derive their energy from hydrogen and helium. they form, through stellar nucleosynthesis, the light elements ( lithium to calcium ) as well as some of the heavy elements ( beyond iron and nickel, via the s - process ). the remaining abundance of heavy elements, from nickel to uranium and beyond, is due to supernova nucleosynthesis, the r - process. of course, these natural processes of astrophysics are not examples of nuclear " technology ". because of the very strong repulsion of nuclei, fusion is difficult to achieve in a controlled fashion. hydrogen bombs, formally known as thermonuclear weapons, obtain their enormous destructive power from fusion, but their energy cannot be controlled team of physicists who were concerned that nazi germany might also be seeking to build a bomb based on nuclear fission. ( the earliest known nuclear reaction on earth occurred naturally, 1. 7 billion years ago, in oklo, gabon, africa. ) the second artificial nuclear reactor, the x - 10 graphite reactor, was also a part of the manhattan project, as were the plutonium - producing reactors of the hanford engineer works. the first nuclear reactor to generate electricity was experimental breeder reactor i ( ebr - i ), which did so near arco, idaho, in 1951. ebr - i was a standalone facility, not connected to a grid, but a later idaho research reactor in the borax series did briefly supply power to the town of arco in 1955. the first commercial nuclear power plant, built to be connected to an electrical grid, is the obninsk nuclear power plant, which began operation in 1954. the second is the shippingport atomic power station, which produced electricity in 1957. for a chronology, from the discovery of uranium to the current era, see outline history of nuclear energy or history of nuclear power. also see history of nuclear engineering part 1 : radioactivity, part 2 : building the bomb, and part 3 : atoms for peace. see list of commercial nuclear reactors for a comprehensive listing of nuclear power reactors and iaea power reactor information system ( pris ) for worldwide and country - level statistics on nuclear power generation. = = sub - disciplines = = nuclear engineers work in such areas as the following : nuclear reactor design, which has evolved from the generation i, proof - of concept, reactors of the 1950s and 1960s, to generation ii, generation iii, and generation iv concepts thermal hydraulics and heat transfer. in a typical nuclear power plant, heat generates steam that drives a steam turbine and a generator that produces electricity materials science as it relates to nuclear power applications managing the nuclear fuel cycle, in which fissile material is obtained, formed into fuel, removed when depleted, and safely stored or reprocessed nuclear propulsion, mainly for military naval vessels, but there have been concepts for aircraft and missiles. nuclear power has been used in space since the 1960s plasma physics, which is integral to the development of fusion power weapons development and management generation of radionuclides, which have applications in industry, medicine, and many other areas nuclear waste management health physics nuclear medicine and medical physics health and safety instrumentation and control engineering process engineering project management quality engineering reactor operations nuclear security ( detection of - sustaining chain reaction. a mass of fissile material large enough ( and in a suitable configuration ) to induce a self - sustaining chain reaction is called a critical mass. when a neutron is captured by a suitable nucleus, fission may occur immediately, or the nucleus may persist in an unstable state for a short time. if there are enough immediate decays to carry on the chain reaction, the mass is said to be prompt critical, and the energy release will grow rapidly and uncontrollably, usually leading to an explosion. when discovered on the eve of world war ii, this insight led multiple countries to begin programs investigating the possibility of constructing an atomic bomb — a weapon which utilized fission reactions to generate far more energy than could be created with chemical explosives. the manhattan project, run by the united states with the help of the united kingdom and canada, developed multiple fission weapons which were used against japan in 1945 at hiroshima and nagasaki. during the project, the first fission reactors were developed as well, though they were primarily for weapons manufacture and did not generate electricity. in 1951, the first nuclear fission power plant was the first to produce electricity at the experimental breeder reactor no. 1 ( ebr - 1 ), in arco, idaho, ushering in the " atomic age " of more intensive human energy use. however, if the mass is critical only when the delayed neutrons are included, then the reaction can be controlled, for example by the introduction or removal of neutron absorbers. this is what allows nuclear reactors to be built. fast neutrons are not easily captured by nuclei ; they must be slowed ( slow neutrons ), generally by collision with the nuclei of a neutron moderator, before they can be easily captured. today, this type of fission is commonly used to generate electricity. = = = nuclear fusion = = = if nuclei are forced to collide, they can undergo nuclear fusion. this process may release or absorb energy. when the resulting nucleus is lighter than that of iron, energy is normally released ; when the nucleus is heavier than that of iron, energy is generally absorbed. this process of fusion occurs in stars, which derive their energy from hydrogen and helium. they form, through stellar nucleosynthesis, the light elements ( lithium to calcium ) as well as some of the heavy elements ( beyond iron and nickel, via the s - process ). the remaining abundance of heavy elements, from nickel to uranium and beyond, is due to supernova nucleosynthesis, the r - process. of course ( create a critical mass ) for detonation. it also is quite difficult to ensure that such a chain reaction consumes a significant fraction of the fuel before the device flies apart. the procurement of a nuclear fuel is also more difficult than it might seem, since sufficiently unstable substances for this process do not currently occur naturally on earth in suitable amounts. one isotope of uranium, namely uranium - 235, is naturally occurring and sufficiently unstable, but it is always found mixed with the more stable isotope uranium - 238. the latter accounts for more than 99 % of the weight of natural uranium. therefore, some method of isotope separation based on the weight of three neutrons must be performed to enrich ( isolate ) uranium - 235. alternatively, the element plutonium possesses an isotope that is sufficiently unstable for this process to be usable. terrestrial plutonium does not currently occur naturally in sufficient quantities for such use, so it must be manufactured in a nuclear reactor. ultimately, the manhattan project manufactured nuclear weapons based on each of these elements. they detonated the first nuclear weapon in a test code - named " trinity ", near alamogordo, new mexico, on july 16, 1945. the test was conducted to ensure that the implosion method of detonation would work, which it did. a uranium bomb, little boy, was dropped on the japanese city hiroshima on august 6, 1945, followed three days later by the plutonium - based fat man on nagasaki. in the wake of unprecedented devastation and casualties from a single weapon, the japanese government soon surrendered, ending world war ii. since these bombings, no nuclear weapons have been deployed offensively. nevertheless, they prompted an arms race to develop increasingly destructive bombs to provide a nuclear deterrent. just over four years later, on august 29, 1949, the soviet union detonated its first fission weapon. the united kingdom followed on october 2, 1952 ; france, on february 13, 1960 ; and china component to a nuclear weapon. approximately half of the deaths from hiroshima and nagasaki died two to five years afterward from radiation exposure. a radiological weapon is a type of nuclear weapon designed to distribute hazardous nuclear material in enemy areas. such a weapon would not have the explosive capability of a fission or fusion bomb, but would kill many people and contaminate a large area. a radiological weapon has never been deployed. while considered useless by a conventional military, such a weapon raises concerns over nuclear terrorism. there have been over 2, 000 nuclear tests conducted since 1945. in 1963, all nuclear and many non - to block. all three types of radiation occur naturally in certain elements. it has also become clear that the ultimate source of most terrestrial energy is nuclear, either through radiation from the sun caused by stellar thermonuclear reactions or by radioactive decay of uranium within the earth, the principal source of geothermal energy. = = = nuclear fission = = = in natural nuclear radiation, the byproducts are very small compared to the nuclei from which they originate. nuclear fission is the process of splitting a nucleus into roughly equal parts, and releasing energy and neutrons in the process. if these neutrons are captured by another unstable nucleus, they can fission as well, leading to a chain reaction. the average number of neutrons released per nucleus that go on to fission another nucleus is referred to as k. values of k larger than 1 mean that the fission reaction is releasing more neutrons than it absorbs, and therefore is referred to as a self - sustaining chain reaction. a mass of fissile material large enough ( and in a suitable configuration ) to induce a self - sustaining chain reaction is called a critical mass. when a neutron is captured by a suitable nucleus, fission may occur immediately, or the nucleus may persist in an unstable state for a short time. if there are enough immediate decays to carry on the chain reaction, the mass is said to be prompt critical, and the energy release will grow rapidly and uncontrollably, usually leading to an explosion. when discovered on the eve of world war ii, this insight led multiple countries to begin programs investigating the possibility of constructing an atomic bomb — a weapon which utilized fission reactions to generate far more energy than could be created with chemical explosives. the manhattan project, run by the united states with the help of the united kingdom and canada, developed multiple fission weapons which were used against japan in 1945 at hiroshima and nagasaki. during the project, the first fission reactors were developed as well, though they were primarily for weapons manufacture and did not generate electricity. in 1951, the first nuclear fission power plant was the first to produce electricity at the experimental breeder reactor no. 1 ( ebr - 1 ), in arco, idaho, ushering in the " atomic age " of more intensive human energy use. however, if the mass is critical only when the delayed neutrons are included, then the reaction can be controlled, for example by the introduction or removal of neutron absorbers. this is what allows nuclear reactors to be built. fast neutrons are not easily captured by nuclei . nuclear weapons are considered weapons of mass destruction, and their use and control has been a major aspect of international policy since their debut. the design of a nuclear weapon is more complicated than it might seem. such a weapon must hold one or more subcritical fissile masses stable for deployment, then induce criticality ( create a critical mass ) for detonation. it also is quite difficult to ensure that such a chain reaction consumes a significant fraction of the fuel before the device flies apart. the procurement of a nuclear fuel is also more difficult than it might seem, since sufficiently unstable substances for this process do not currently occur naturally on earth in suitable amounts. one isotope of uranium, namely uranium - 235, is naturally occurring and sufficiently unstable, but it is always found mixed with the more stable isotope uranium - 238. the latter accounts for more than 99 % of the weight of natural uranium. therefore, some method of isotope separation based on the weight of three neutrons must be performed to enrich ( isolate ) uranium - 235. alternatively, the element plutonium possesses an isotope that is sufficiently unstable for this process to be usable. terrestrial plutonium does not currently occur naturally in sufficient quantities for such use, so it must be manufactured in a nuclear reactor. ultimately, the manhattan project manufactured nuclear weapons based on each of these elements. they detonated the first nuclear weapon in a test code - named " trinity ", near alamogordo, new mexico, on july 16, 1945. the test was conducted to ensure that the implosion method of detonation would work, which it did. a uranium bomb, little boy, was dropped on the japanese city hiroshima on august 6, 1945, followed three days later by the plutonium - based fat man on nagasaki. in the wake of unprecedented devastation and casualties from a single weapon, the japanese government soon surrendered, ending world war ii. since these bombings, no nuclear weapons have been deployed offensively. nevertheless, they prompted an arms race to develop increasingly destructive bombs to provide a nuclear deterrent. just over four years later, on august 29, 1949, the soviet union detonated its first fission weapon. the united kingdom followed on october 2, 1952 ; france, on february 13, 1960 ; and china component to a nuclear weapon. approximately half of the deaths from hiroshima and nagasaki died two to five years afterward from radiation exposure. a radiological weapon is a type of nuclear weapon designed to distribute hazardous nuclear material in enemy areas. such a weapon would not have the explosive capability of a fission or , they can fission as well, leading to a chain reaction. the average number of neutrons released per nucleus that go on to fission another nucleus is referred to as k. values of k larger than 1 mean that the fission reaction is releasing more neutrons than it absorbs, and therefore is referred to as a self - sustaining chain reaction. a mass of fissile material large enough ( and in a suitable configuration ) to induce a self - sustaining chain reaction is called a critical mass. when a neutron is captured by a suitable nucleus, fission may occur immediately, or the nucleus may persist in an unstable state for a short time. if there are enough immediate decays to carry on the chain reaction, the mass is said to be prompt critical, and the energy release will grow rapidly and uncontrollably, usually leading to an explosion. when discovered on the eve of world war ii, this insight led multiple countries to begin programs investigating the possibility of constructing an atomic bomb — a weapon which utilized fission reactions to generate far more energy than could be created with chemical explosives. the manhattan project, run by the united states with the help of the united kingdom and canada, developed multiple fission weapons which were used against japan in 1945 at hiroshima and nagasaki. during the project, the first fission reactors were developed as well, though they were primarily for weapons manufacture and did not generate electricity. in 1951, the first nuclear fission power plant was the first to produce electricity at the experimental breeder reactor no. 1 ( ebr - 1 ), in arco, idaho, ushering in the " atomic age " of more intensive human energy use. however, if the mass is critical only when the delayed neutrons are included, then the reaction can be controlled, for example by the introduction or removal of neutron absorbers. this is what allows nuclear reactors to be built. fast neutrons are not easily captured by nuclei ; they must be slowed ( slow neutrons ), generally by collision with the nuclei of a neutron moderator, before they can be easily captured. today, this type of fission is commonly used to generate electricity. = = = nuclear fusion = = = if nuclei are forced to collide, they can undergo nuclear fusion. this process may release or absorb energy. when the resulting nucleus is lighter than that of iron, energy is normally released ; when the nucleus is heavier than that of iron, energy is generally absorbed. this process of fusion occurs in stars, which derive their energy from hydrogen and helium. they form, through stellar nucleos , no nuclear weapons have been deployed offensively. nevertheless, they prompted an arms race to develop increasingly destructive bombs to provide a nuclear deterrent. just over four years later, on august 29, 1949, the soviet union detonated its first fission weapon. the united kingdom followed on october 2, 1952 ; france, on february 13, 1960 ; and china component to a nuclear weapon. approximately half of the deaths from hiroshima and nagasaki died two to five years afterward from radiation exposure. a radiological weapon is a type of nuclear weapon designed to distribute hazardous nuclear material in enemy areas. such a weapon would not have the explosive capability of a fission or fusion bomb, but would kill many people and contaminate a large area. a radiological weapon has never been deployed. while considered useless by a conventional military, such a weapon raises concerns over nuclear terrorism. there have been over 2, 000 nuclear tests conducted since 1945. in 1963, all nuclear and many non - nuclear states signed the limited test ban treaty, pledging to refrain from testing nuclear weapons in the atmosphere, underwater, or in outer space. the treaty permitted underground nuclear testing. france continued atmospheric testing until 1974, while china continued up until 1980. the last underground test by the united states was in 1992, the soviet union in 1990, the united kingdom in 1991, and both france and china continued testing until 1996. after signing the comprehensive test ban treaty in 1996 ( which had as of 2011 not entered into force ), all of these states have pledged to discontinue all nuclear testing. non - signatories india and pakistan last tested nuclear weapons in 1998. nuclear weapons are the most destructive weapons known - the archetypal weapons of mass destruction. throughout the cold war, the opposing powers had huge nuclear arsenals, sufficient to kill hundreds of millions of people. generations of people grew up under the shadow of nuclear devastation, portrayed in films such as dr. strangelove and the atomic cafe. however, the tremendous energy release in the detonation of a nuclear weapon also suggested the possibility of a new energy source. = = civilian uses = = = = = nuclear power = = = nuclear power is a type of nuclear technology involving the controlled use of nuclear fission to release energy for work including propulsion, heat, and the generation of electricity. nuclear energy is produced by a controlled nuclear chain reaction which creates heat — and which is used to boil water, produce steam, and drive a steam turbine. the turbine is used to generate electricity and / or to do mechanical work. currently nuclear that it would require a fission reaction to detonate. it took until 1952 for the first full hydrogen bomb to be detonated, so - called because it used reactions between deuterium and tritium. fusion reactions are much more energetic per unit mass of fuel than fission reactions, but starting the fusion chain reaction is much more difficult. = = nuclear weapons = = a nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. both reactions release vast quantities of energy from relatively small amounts of matter. even small nuclear devices can devastate a city by blast, fire and radiation. nuclear weapons are considered weapons of mass destruction, and their use and control has been a major aspect of international policy since their debut. the design of a nuclear weapon is more complicated than it might seem. such a weapon must hold one or more subcritical fissile masses stable for deployment, then induce criticality ( create a critical mass ) for detonation. it also is quite difficult to ensure that such a chain reaction consumes a significant fraction of the fuel before the device flies apart. the procurement of a nuclear fuel is also more difficult than it might seem, since sufficiently unstable substances for this process do not currently occur naturally on earth in suitable amounts. one isotope of uranium, namely uranium - 235, is naturally occurring and sufficiently unstable, but it is always found mixed with the more stable isotope uranium - 238. the latter accounts for more than 99 % of the weight of natural uranium. therefore, some method of isotope separation based on the weight of three neutrons must be performed to enrich ( isolate ) uranium - 235. alternatively, the element plutonium possesses an isotope that is sufficiently unstable for this process to be usable. terrestrial plutonium does not currently occur naturally in sufficient quantities for such use, so it must be manufactured in a nuclear reactor. ultimately, the manhattan project manufactured nuclear weapons based on each of these elements. they detonated the first nuclear weapon in a test code - named " trinity ", near alamogordo, new mexico, on july 16, 1945. the test was conducted to ensure that the implosion method of detonation would work, which it did. a uranium bomb, little boy, was dropped on the japanese city hiroshima on august 6, 1945, followed three days later by the plutonium - based fat man on nagasaki. in the wake of unprecedented devastation and casualties from a single weapon, the japanese government soon surrendered, ending world war ii. since these bombings Question: Nuclear reactors use fission reactions to vaporize water, producing steam to drive a turbine and generate what? A) electricity B) fuel C) light D) oil	A) electricity
Context: the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the energy they need to exist. plants, algae and cyanobacteria are the major groups of organisms that carry out photosynthesis, a process that uses the energy of sunlight to convert water and carbon dioxide into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photos ##trophs including all animals, all fungi, all completely parasitic plants, and non - photosynthetic bacteria take in organic molecules produced by photoautotrophs and respire them or use them in the construction of cells and tissues. respiration is the oxidation of carbon compounds by breaking them down into simpler structures to release the energy they contain, essentially the opposite of photosynthesis. molecules are moved within plants by transport processes that operate at a variety of spatial scales. subcellular transport of ions, electrons and molecules such as water and enzymes occurs across cell membranes. minerals and water are transported from roots to other parts of the plant in the transpiration stream. diffusion, osmosis, and active transport and mass flow are all different ways transport can occur. examples of elements that plants need to transport are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. in vascular plants, these elements are extracted from the soil as soluble ions by the roots and transported throughout the plant in the xylem. most of the elements required for plant nutrition come from the chemical breakdown of soil minerals. sucrose produced by photosynthesis is transported from the leaves to other parts of the plant in the phloem and plant hormones are transported by a variety of processes. = = = plant hormones = = = plants are not passive, but respond to external signals such as light, touch, and injury by moving or growing towards or away from the stimulus, as appropriate. tangible evidence of touch sensitivity is the almost instantaneous collapse of leaflets of mimosa pudica, the insect traps of venus flytrap and bladderworts, and the pollinia of orchids. the hypothesis that plant growth and development is coordinated by plant hormones or plant growth regulators first emerged in the late 19th century. darwin experimented on the movements of plant shoots and roots towards light and gravity, and concluded " it is hardly an exaggeration to say that the tip of the radicle.. acts like the brain of one of the lower animals.. directing the several movements ". about the same time, the role of auxins ( from the greek auxein, to grow ) in control of plant growth was first outlined by the dutch scientist frits went. the first known auxin, indole - 3 - acetic acid ( iaa ), which promotes cell growth, was only isolated from plants about 50 years later. this compound mediates the tropic responses of shoots and roots towards light and gravity. the finding in 1939 that plant callus ##ch which is stored in the chloroplast. starch is the characteristic energy store of most land plants and algae, while inulin, a polymer of fructose is used for the same purpose in the sunflower family asteraceae. some of the glucose is converted to sucrose ( common table sugar ) for export to the rest of the plant. unlike in animals ( which lack chloroplasts ), plants and their eukaryote relatives have delegated many biochemical roles to their chloroplasts, including synthesising all their fatty acids, and most amino acids. the fatty acids that chloroplasts make are used for many things, such as providing material to build cell membranes out of and making the polymer cutin which is found in the plant cuticle that protects land plants from drying out. plants synthesise a number of unique polymers like the polysaccharide molecules cellulose, pectin and xyloglucan from which the land plant cell wall is constructed. vascular land plants make lignin, a polymer used to strengthen the secondary cell walls of xylem tracheids and vessels to keep them from collapsing when a plant sucks water through them under water stress. lignin is also used in other cell types like sclerenchyma fibres that provide structural support for a plant and is a major constituent of wood. sporopollenin is a chemically resistant polymer found in the outer cell walls of spores and pollen of land plants responsible for the survival of early land plant spores and the pollen of seed plants in the fossil record. it is widely regarded as a marker for the start of land plant evolution during the ordovician period. the concentration of carbon dioxide in the atmosphere today is much lower than it was when plants emerged onto land during the ordovician and silurian periods. many monocots like maize and the pineapple and some dicots like the asteraceae have since independently evolved pathways like crassulacean acid metabolism and the c4 carbon fixation pathway for photosynthesis which avoid the losses resulting from photorespiration in the more common c3 carbon fixation pathway. these biochemical strategies are unique to land plants. = = = medicine and materials = = = phytochemistry is a branch of plant biochemistry primarily concerned with the chemical substances produced by plants during secondary metabolism. some of these compounds are toxins such as the alkaloid coniine from hemlock. , the other can often regrow it. in fact it is possible to grow an entire plant from a single leaf, as is the case with plants in streptocarpus sect. saintpaulia, or even a single cell – which can dedifferentiate into a callus ( a mass of unspecialised cells ) that can grow into a new plant. in vascular plants, the xylem and phloem are the conductive tissues that transport resources between shoots and roots. roots are often adapted to store food such as sugars or starch, as in sugar beets and carrots. stems mainly provide support to the leaves and reproductive structures, but can store water in succulent plants such as cacti, food as in potato tubers, or reproduce vegetatively as in the stolons of strawberry plants or in the process of layering. leaves gather sunlight and carry out photosynthesis. large, flat, flexible, green leaves are called foliage leaves. gymnosperms, such as conifers, cycads, ginkgo, and gnetophytes are seed - producing plants with open seeds. angiosperms are seed - producing plants that produce flowers and have enclosed seeds. woody plants, such as azaleas and oaks, undergo a secondary growth phase resulting in two additional types of tissues : wood ( secondary xylem ) and bark ( secondary phloem and cork ). all gymnosperms and many angiosperms are woody plants. some plants reproduce sexually, some asexually, and some via both means. although reference to major morphological categories such as root, stem, leaf, and trichome are useful, one has to keep in mind that these categories are linked through intermediate forms so that a continuum between the categories results. furthermore, structures can be seen as processes, that is, process combinations. = = systematic botany = = systematic botany is part of systematic biology, which is concerned with the range and diversity of organisms and their relationships, particularly as determined by their evolutionary history. it involves, or is related to, biological classification, scientific taxonomy and phylogenetics. biological classification is the method by which botanists group organisms into categories such as genera or species. biological classification is a form of scientific taxonomy. modern taxonomy is rooted in the work of carl linnaeus, who grouped species according to shared physical characteristics. these groupings have since been revised to align better with the darwinian principle of common descent – grouping organisms unspecialised cells ) that can grow into a new plant. in vascular plants, the xylem and phloem are the conductive tissues that transport resources between shoots and roots. roots are often adapted to store food such as sugars or starch, as in sugar beets and carrots. stems mainly provide support to the leaves and reproductive structures, but can store water in succulent plants such as cacti, food as in potato tubers, or reproduce vegetatively as in the stolons of strawberry plants or in the process of layering. leaves gather sunlight and carry out photosynthesis. large, flat, flexible, green leaves are called foliage leaves. gymnosperms, such as conifers, cycads, ginkgo, and gnetophytes are seed - producing plants with open seeds. angiosperms are seed - producing plants that produce flowers and have enclosed seeds. woody plants, such as azaleas and oaks, undergo a secondary growth phase resulting in two additional types of tissues : wood ( secondary xylem ) and bark ( secondary phloem and cork ). all gymnosperms and many angiosperms are woody plants. some plants reproduce sexually, some asexually, and some via both means. although reference to major morphological categories such as root, stem, leaf, and trichome are useful, one has to keep in mind that these categories are linked through intermediate forms so that a continuum between the categories results. furthermore, structures can be seen as processes, that is, process combinations. = = systematic botany = = systematic botany is part of systematic biology, which is concerned with the range and diversity of organisms and their relationships, particularly as determined by their evolutionary history. it involves, or is related to, biological classification, scientific taxonomy and phylogenetics. biological classification is the method by which botanists group organisms into categories such as genera or species. biological classification is a form of scientific taxonomy. modern taxonomy is rooted in the work of carl linnaeus, who grouped species according to shared physical characteristics. these groupings have since been revised to align better with the darwinian principle of common descent – grouping organisms by ancestry rather than superficial characteristics. while scientists do not always agree on how to classify organisms, molecular phylogenetics, which uses dna sequences as data, has driven many recent revisions along evolutionary lines and is likely to continue to do so. the dominant classification system is called linnaean taxonomy. it includes ranks and binomi the basis of all plant metabolism. the energy of sunlight, captured by oxygenic photosynthesis and released by cellular respiration, is the basis of almost all life. photoautotrophs, including all green plants, algae and cyanobacteria gather energy directly from sunlight by photosynthesis. heterotrophs including all animals, all fungi, all completely parasitic plants, and non - photosynthetic bacteria take in organic molecules produced by photoautotrophs and respire them or use them in the construction of cells and tissues. respiration is the oxidation of carbon compounds by breaking them down into simpler structures to release the energy they contain, essentially the opposite of photosynthesis. molecules are moved within plants by transport processes that operate at a variety of spatial scales. subcellular transport of ions, electrons and molecules such as water and enzymes occurs across cell membranes. minerals and water are transported from roots to other parts of the plant in the transpiration stream. diffusion, osmosis, and active transport and mass flow are all different ways transport can occur. examples of elements that plants need to transport are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. in vascular plants, these elements are extracted from the soil as soluble ions by the roots and transported throughout the plant in the xylem. most of the elements required for plant nutrition come from the chemical breakdown of soil minerals. sucrose produced by photosynthesis is transported from the leaves to other parts of the plant in the phloem and plant hormones are transported by a variety of processes. = = = plant hormones = = = plants are not passive, but respond to external signals such as light, touch, and injury by moving or growing towards or away from the stimulus, as appropriate. tangible evidence of touch sensitivity is the almost instantaneous collapse of leaflets of mimosa pudica, the insect traps of venus flytrap and bladderworts, and the pollinia of orchids. the hypothesis that plant growth and development is coordinated by plant hormones or plant growth regulators first emerged in the late 19th century. darwin experimented on the movements of plant shoots and roots towards light and gravity, and concluded " it is hardly an exaggeration to say that the tip of the radicle.. acts like the brain of one of the lower animals.. directing the several movements ". about the same time, the role of auxins ( from the greek auxein, to grow ) in control of plant growth was first outlined by the dutch scientist soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ), fungi ( mycology ) – including lichen - forming fungi ( lichenology ), non - chlorophyte algae ( phycology ), and viruses ( virology ). however, attention is still given to these groups by botanists, and fungi ( including lichens ) and photosynthetic protists are usually covered in introductory botany courses. palaeobotanists study ancient plants in the fossil record to provide information about the evolutionary history of plants. cyanobacteria, the first oxygen - releasing photosynthetic organisms on earth, are thought to have given rise to the ancestor of plants by entering into an endosymbiotic relationship with an early eukaryote, ultimately becoming the chloroplasts in plant cells. the new photosynthetic plants ( along with their algal relatives ) accelerated the rise in atmospheric oxygen started by the cyanobacteria, changing the pectin and xyloglucan from which the land plant cell wall is constructed. vascular land plants make lignin, a polymer used to strengthen the secondary cell walls of xylem tracheids and vessels to keep them from collapsing when a plant sucks water through them under water stress. lignin is also used in other cell types like sclerenchyma fibres that provide structural support for a plant and is a major constituent of wood. sporopollenin is a chemically resistant polymer found in the outer cell walls of spores and pollen of land plants responsible for the survival of early land plant spores and the pollen of seed plants in the fossil record. it is widely regarded as a marker for the start of land plant evolution during the ordovician period. the concentration of carbon dioxide in the atmosphere today is much lower than it was when plants emerged onto land during the ordovician and silurian periods. many monocots like maize and the pineapple and some dicots like the asteraceae have since independently evolved pathways like crassulacean acid metabolism and the c4 carbon fixation pathway for photosynthesis which avoid the losses resulting from photorespiration in the more common c3 carbon fixation pathway. these biochemical strategies are unique to land plants. = = = medicine and materials = = = phytochemistry is a branch of plant biochemistry primarily concerned with the chemical substances produced by plants during secondary metabolism. some of these compounds are toxins such as the alkaloid coniine from hemlock. others, such as the essential oils peppermint oil and lemon oil are useful for their aroma, as flavourings and spices ( e. g., capsaicin ), and in medicine as pharmaceuticals as in opium from opium poppies. many medicinal and recreational drugs, such as tetrahydrocannabinol ( active ingredient in cannabis ), caffeine, morphine and nicotine come directly from plants. others are simple derivatives of botanical natural products. for example, the pain killer aspirin is the acetyl ester of salicylic acid, originally isolated from the bark of willow trees, and a wide range of opiate painkillers like heroin are obtained by chemical modification of morphine obtained from the opium poppy. popular stimulants come from plants, such as caffeine from coffee, tea and chocolate, and nicotine from tobacco. most alcoholic beverages come from fermentation of carbohy horticultural botany, phytopathology, and phytopharmacology. = = scope and importance = = the study of plants is vital because they underpin almost all animal life on earth by generating a large proportion of the oxygen and food that provide humans and other organisms with aerobic respiration with the chemical energy they need to exist. plants, algae and cyanobacteria are the major groups of organisms that carry out photosynthesis, a process that uses the energy of sunlight to convert water and carbon dioxide into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells. as a by - product of photosynthesis, plants release oxygen into the atmosphere, a gas that is required by nearly all living things to carry out cellular respiration. in addition, they are influential in the global carbon and water cycles and plant roots bind and stabilise soils, preventing soil erosion. plants are crucial to the future of human society as they provide food, oxygen, biochemicals, and products for people, as well as creating and preserving soil. historically, all living things were classified as either animals or plants and botany covered the study of all organisms not considered animals. botanists examine both the internal functions and processes within plant organelles, cells, tissues, whole plants, plant populations and plant communities. at each of these levels, a botanist may be concerned with the classification ( taxonomy ), phylogeny and evolution, structure ( anatomy and morphology ), or function ( physiology ) of plant life. the strictest definition of " plant " includes only the " land plants " or embryophytes, which include seed plants ( gymnosperms, including the pines, and flowering plants ) and the free - sporing cryptogams including ferns, clubmosses, liverworts, hornworts and mosses. embryophytes are multicellular eukaryotes descended from an ancestor that obtained its energy from sunlight by photosynthesis. they have life cycles with alternating haploid and diploid phases. the sexual haploid phase of embryophytes, known as the gametophyte, nurtures the developing diploid embryo sporophyte within its tissues for at least part of its life, even in the seed plants, where the gametophyte itself is nurtured by its parent sporophyte. other groups of organisms that were previously studied by botanists include bacteria ( now studied in bacteriology ) Question: What type of air do plants take in and use? A) carbon B) oxygen C) liquid dioxide D) carbon dioxide	D) carbon dioxide
Context: two types of stars are known to have strong, large scale magnetic fields : the main sequence ap stars and the magnetic white dwarfs. this suggest that the former might be the progenitors of the latter. in order to test this idea, i have carried out a search for large scale magnetic fields in stars with evolutionary states which are intermediate, i. e. in horizontal branch stars and in hot subdwarfs. high speed photometry of kuv 01584 - 0939 ( alias cet3 ) shows that is has a period of 620. 26 s. combined with its hydrogen - deficient spectrum, this implies that it is an am cvn star. the optical modulation is probably a superhump, in which case the orbital period will be slightly shorter than what we have observed. while the modern stellar imf shows a rapid decline with increasing mass, theoretical investigations suggest that very massive stars ( > 100 solar masses ) may have been abundant in the early universe. other calculations also indicate that, lacking metals, these same stars reach their late evolutionary stages without appreciable mass loss. after central helium burning, they encounter the electron - positron pair instability, collapse, and burn oxygen and silicon explosively. if sufficient energy is released by the burning, these stars explode as brilliant supernovae with energies up to 100 times that of an ordinary core collapse supernova. they also eject up to 50 solar masses of radioactive ni56. stars less massive than 140 solar masses or more massive than 260 solar masses should collapse into black holes instead of exploding, thus bounding the pair - creation supernovae with regions of stellar mass that are nucleosynthetically sterile. pair - instability supernovae might be detectable in the near infrared out to redshifts of 20 or more and their ashes should leave a distinctive nucleosynthetic pattern. we bring you, as usual, the sun and moon and stars, plus some galaxies and a new section on astrobiology. some highlights are short ( the newly identified class of gamma - ray bursts, and the deep impact on comet 9p / tempel 1 ), some long ( the age of the universe, which will be found to have the earth at its center ), and a few metonymic, for instance the term " down - sizing " to describe the evolution of star formation rates with redshift. there are a few different mechanisms that can cause white dwarf stars to vary in brightness, providing opportunities to probe the physics, structures, and formation of these compact stellar remnants. the observational characteristics of the three most common types of white dwarf variability are summarized : stellar pulsations, rotation, and ellipsoidal variations from tidal distortion in binary systems. stellar pulsations are emphasized as the most complex type of variability, which also has the greatest potential to reveal the conditions of white dwarf interiors. oscillations of the sun have been used to understand its interior structure. the extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the international community over the past decades. the corot ( convection rotation and planetary transits ) satellite, launched in december 2006, has now measured oscillations and the stellar granulation signature in three main sequence stars that are noticeably hotter than the sun. the oscillation amplitudes are about 1. 5 times as large as those in the sun ; the stellar granulation is up to three times as high. the stellar amplitudes are about 25 % below the theoretic values, providing a measurement of the nonadiabaticity of the process ruling the oscillations in the outer layers of the stars. v735 sgr was known as an enigmatic star with rapid brightness variations. long - term ogle photometry, brightness measurements in infrared bands, and recently obtained moderate resolution spectrum from the 6. 5 - m magellan telescope show that this star is an active young stellar object of herbig ae / be type. in the present - day universe, it appears that most, and perhaps all, massive stars are born in star clusters. it also appears that all star clusters contain stars drawn from an approximately universal initial mass function, so that almost all rich young star clusters contain massive stars. in this review i discuss the physical processes associated with both massive star formation and with star cluster formation. first i summarize the observed properties of star - forming gas clumps, then address the following questions. how do these clumps emerge from giant molecular clouds? in these clustered environments, how do individual stars form and gain mass? can a forming star cluster be treated as an equilibrium system or is this process too rapid for equilibrium to be established? how does feedback affect the formation process? a 4mj planet with a 15. 8day orbital period has been detected from very precise radial velocity measurements with the coralie echelle spectrograph. a second remote and more massive companion has also been detected. all the planetary companions so far detected in orbit closer than 0. 08 au have a parent star with a statistically higher metal content compared to the metallicity distribution of other stars with planets. different processes occuring during their formation may provide a possible explanation for this observation. two planetary nebulae are shown to belong to the sagittarius dwarf galaxy, on the basis of their radial velocities. this is only the second dwarf spheroidal galaxy, after fornax, found to contain planetary nebulae. their existence confirms that this galaxy is at least as massive as the fornax dwarf spheroidal which has a single planetary nebula, and suggests a mass of a few times 10 * * 7 solar masses. the two planetary nebulae are located along the major axis of the galaxy, near the base of the tidal tail. there is a further candidate, situated at a very large distance along the direction of the tidal tail, for which no velocity measurement is available. the location of the planetary nebulae and globular clusters of the sagittarius dwarf galaxy suggests that a significant fraction of its mass is contained within the tidal tail. Question: How long can a large star be on the main sequence stage? A) 10 million years B) 60.11 million years C) 200.4 million years D) 3 million years	A) 10 million years
Context: ##hography is quite small, large area patterns must be created by stitching together the small fields. ion track technology is a deep cutting tool with a resolution limit around 8 nm applicable to radiation resistant minerals, glasses and polymers. it is capable of generating holes in thin films without any development process. structural depth can be defined either by ion range or by material thickness. aspect ratios up to several 104 can be reached. the technique can shape and texture materials at a defined inclination angle. random pattern, single - ion track structures and an aimed pattern consisting of individual single tracks can be generated. x - ray lithography is a process used in the electronic industry to selectively remove parts of a thin film. it uses x - rays to transfer a geometric pattern from a mask to a light - sensitive chemical photoresist, or simply " resist ", on the substrate. a series of chemical treatments then engraves the produced pattern into the material underneath the photoresist. diamond patterning is a method of forming diamond mems. it is achieved by the lithographic application of diamond films to a substrate such as silicon. the patterns can be formed by selective deposition through a silicon dioxide mask, or by deposition followed by micromachining or focused ion beam milling. = = = etching processes = = = there are two basic categories of etching processes : wet etching and dry etching. in the former, the material is dissolved when immersed in a chemical solution. in the latter, the material is sputtered or dissolved using reactive ions or a vapor phase etchant. = = = = wet etching = = = = wet chemical etching consists of the selective removal of material by dipping a substrate into a solution that dissolves it. the chemical nature of this etching process provides good selectivity, which means the etching rate of the target material is considerably higher than the mask material if selected carefully. wet etching can be performed using either isotropic wet etchants or anisotropic wet etchants. isotropic wet etchant etch in all directions of the crystalline silicon at approximately equal rates. anisotropic wet etchants preferably etch along certain crystal planes at faster rates than other planes, thereby allowing more complicated 3 - d microstructures to be implemented. wet anisotropic etchants are often used in conjunction with boron etch stops wherein the surface of the silicon is heavily doped with boron resulting in a silicon material layer that is reflect radar waves back to the emitting radar is with orthogonal metal plates, forming a corner reflector consisting of either a dihedral ( two plates ) or a trihedral ( three orthogonal plates ). this configuration occurs in the tail of a conventional aircraft, where the vertical and horizontal components of the tail are set at right angles. stealth aircraft such as the f - 117 use a different arrangement, tilting the tail surfaces to reduce corner reflections formed between them. a more radical method is to omit the tail, as in the b - 2 spirit. the b - 2 ' s clean, low - drag flying wing configuration gives it exceptional range and reduces its radar profile. the flying wing design most closely resembles a so - called infinite flat plate ( as vertical control surfaces dramatically increase rcs ), the perfect stealth shape, as it would have no angles to reflect back radar waves. in addition to altering the tail, stealth design must bury the engines within the wing or fuselage, or in some cases where stealth is applied to an extant aircraft, install baffles in the air intakes, so that the compressor blades are not visible to radar. a stealthy shape must be devoid of complex bumps or protrusions of any kind, meaning that weapons, fuel tanks, and other stores must not be carried externally. any stealthy vehicle becomes un - stealthy when a door or hatch opens. parallel alignment of edges or even surfaces is also often used in stealth designs. the technique involves using a small number of edge orientations in the shape of the structure. for example, on the f - 22a raptor, the leading edges of the wing and the tail planes are set at the same angle. other smaller structures, such as the air intake bypass doors and the air refueling aperture, also use the same angles. the effect of this is to return a narrow radar signal in a very specific direction away from the radar emitter rather than returning a diffuse signal detectable at many angles. the effect is sometimes called " glitter " after the very brief signal seen when the reflected beam passes across a detector. it can be difficult for the radar operator to distinguish between a glitter event and a digital glitch in the processing system. stealth airframes sometimes display distinctive serrations on some exposed edges, such as the engine ports. the yf - 23 has such serrations on the exhaust ports. this is another example in the parallel alignment of features, this time on the external airframe. the shaping requirements detracted greatly from the f - 117 ' are continuous lines used to depict edges directly visible from a particular angle. hidden – are short - dashed lines that may be used to represent edges that are not directly visible. center – are alternately long - and short - dashed lines that may be used to represent the axes of circular features. cutting plane – are thin, medium - dashed lines, or thick alternately long - and double short - dashed that may be used to define sections for section views. section – are thin lines in a pattern ( pattern determined by the material being " cut " or " sectioned " ) used to indicate surfaces in section views resulting from " cutting ". section lines are commonly referred to as " cross - hatching ". phantom – ( not shown ) are alternately long - and double short - dashed thin lines used to represent a feature or component that is not part of the specified part or assembly. e. g. billet ends that may be used for testing, or the machined product that is the focus of a tooling drawing. lines can also be classified by a letter classification in which each line is given a letter. type a lines show the outline of the feature of an object. they are the thickest lines on a drawing and done with a pencil softer than hb. type b lines are dimension lines and are used for dimensioning, projecting, extending, or leaders. a harder pencil should be used, such as a 2h pencil. type c lines are used for breaks when the whole object is not shown. these are freehand drawn and only for short breaks. 2h pencil type d lines are similar to type c, except these are zigzagged and only for longer breaks. 2h pencil type e lines indicate hidden outlines of internal features of an object. these are dotted lines. 2h pencil type f lines are type e lines, except these are used for drawings in electrotechnology. 2h pencil type g lines are used for centre lines. these are dotted lines, but a long line of 10 – 20 mm, then a 1 mm gap, then a small line of 2 mm. 2h pencil type h lines are the same as type g, except that every second long line is thicker. these indicate the cutting plane of an object. 2h pencil type k lines indicate the alternate positions of an object and the line taken by that object. these are drawn with a long line of 10 – 20 mm, then a small gap, then a small line of 2 mm, then a gap, then another small line. 2h missiles, ships, vehicles, and also to map weather patterns and terrain. a radar set consists of a transmitter and receiver. the transmitter emits a narrow beam of radio waves which is swept around the surrounding space. when the beam strikes a target object, radio waves are reflected back to the receiver. the direction of the beam reveals the object ' s location. since radio waves travel at a constant speed close to the speed of light, by measuring the brief time delay between the outgoing pulse and the received " echo ", the range to the target can be calculated. the targets are often displayed graphically on a map display called a radar screen. doppler radar can measure a moving object ' s velocity, by measuring the change in frequency of the return radio waves due to the doppler effect. radar sets mainly use high frequencies in the microwave bands, because these frequencies create strong reflections from objects the size of vehicles and can be focused into narrow beams with compact antennas. parabolic ( dish ) antennas are widely used. in most radars the transmitting antenna also serves as the receiving antenna ; this is called a monostatic radar. a radar which uses separate transmitting and receiving antennas is called a bistatic radar. airport surveillance radar – in aviation, radar is the main tool of air traffic control. a rotating dish antenna sweeps a vertical fan - shaped beam of microwaves around the airspace and the radar set shows the location of aircraft as " blips " of light on a display called a radar screen. airport radar operates at 2. 7 – 2. 9 ghz in the microwave s band. in large airports the radar image is displayed on multiple screens in an operations room called the tracon ( terminal radar approach control ), where air traffic controllers direct the aircraft by radio to maintain safe aircraft separation. secondary surveillance radar – aircraft carry radar transponders, transceivers which when triggered by the incoming radar signal transmit a return microwave signal. this causes the aircraft to show up more strongly on the radar screen. the radar which triggers the transponder and receives the return beam, usually mounted on top of the primary radar dish, is called the secondary surveillance radar. since radar cannot measure an aircraft ' s altitude with any accuracy, the transponder also transmits back the aircraft ' s altitude measured by its altimeter, and an id number identifying the aircraft, which is displayed on the radar screen. electronic countermeasures ( ecm ) – military defensive electronic systems designed to degrade enemy radar effectiveness, or deceive it , behind which are structures termed reentrant triangles. radar waves penetrating the skin get trapped in these structures, reflecting off the internal faces and losing energy. this method was first used on the blackbird series : a - 12, yf - 12a, lockheed sr - 71 blackbird. the most efficient way to reflect radar waves back to the emitting radar is with orthogonal metal plates, forming a corner reflector consisting of either a dihedral ( two plates ) or a trihedral ( three orthogonal plates ). this configuration occurs in the tail of a conventional aircraft, where the vertical and horizontal components of the tail are set at right angles. stealth aircraft such as the f - 117 use a different arrangement, tilting the tail surfaces to reduce corner reflections formed between them. a more radical method is to omit the tail, as in the b - 2 spirit. the b - 2 ' s clean, low - drag flying wing configuration gives it exceptional range and reduces its radar profile. the flying wing design most closely resembles a so - called infinite flat plate ( as vertical control surfaces dramatically increase rcs ), the perfect stealth shape, as it would have no angles to reflect back radar waves. in addition to altering the tail, stealth design must bury the engines within the wing or fuselage, or in some cases where stealth is applied to an extant aircraft, install baffles in the air intakes, so that the compressor blades are not visible to radar. a stealthy shape must be devoid of complex bumps or protrusions of any kind, meaning that weapons, fuel tanks, and other stores must not be carried externally. any stealthy vehicle becomes un - stealthy when a door or hatch opens. parallel alignment of edges or even surfaces is also often used in stealth designs. the technique involves using a small number of edge orientations in the shape of the structure. for example, on the f - 22a raptor, the leading edges of the wing and the tail planes are set at the same angle. other smaller structures, such as the air intake bypass doors and the air refueling aperture, also use the same angles. the effect of this is to return a narrow radar signal in a very specific direction away from the radar emitter rather than returning a diffuse signal detectable at many angles. the effect is sometimes called " glitter " after the very brief signal seen when the reflected beam passes across a detector. it can be difficult for the radar operator to distinguish between a glitter event and a digital glitch in the processing system. stealth air lines are dimension lines and are used for dimensioning, projecting, extending, or leaders. a harder pencil should be used, such as a 2h pencil. type c lines are used for breaks when the whole object is not shown. these are freehand drawn and only for short breaks. 2h pencil type d lines are similar to type c, except these are zigzagged and only for longer breaks. 2h pencil type e lines indicate hidden outlines of internal features of an object. these are dotted lines. 2h pencil type f lines are type e lines, except these are used for drawings in electrotechnology. 2h pencil type g lines are used for centre lines. these are dotted lines, but a long line of 10 – 20 mm, then a 1 mm gap, then a small line of 2 mm. 2h pencil type h lines are the same as type g, except that every second long line is thicker. these indicate the cutting plane of an object. 2h pencil type k lines indicate the alternate positions of an object and the line taken by that object. these are drawn with a long line of 10 – 20 mm, then a small gap, then a small line of 2 mm, then a gap, then another small line. 2h pencil. = = = multiple views and projections = = = in most cases, a single view is not sufficient to show all necessary features, and several views are used. types of views include the following : = = = = multiview projection = = = = a multiview projection is a type of orthographic projection that shows the object as it looks from the front, right, left, top, bottom, or back ( e. g. the primary views ), and is typically positioned relative to each other according to the rules of either first - angle or third - angle projection. the origin and vector direction of the projectors ( also called projection lines ) differs, as explained below. in first - angle projection, the parallel projectors originate as if radiated from behind the viewer and pass through the 3d object to project a 2d image onto the orthogonal plane behind it. the 3d object is projected into 2d " paper " space as if you were looking at a radiograph of the object : the top view is under the front view, the right view is at the left of the front view. first - angle projection is the iso standard and is primarily used in europe. in third - angle projection, the parallel projectors originate as if radiated from the far side of the object - dashed lines, or thick alternately long - and double short - dashed that may be used to define sections for section views. section – are thin lines in a pattern ( pattern determined by the material being " cut " or " sectioned " ) used to indicate surfaces in section views resulting from " cutting ". section lines are commonly referred to as " cross - hatching ". phantom – ( not shown ) are alternately long - and double short - dashed thin lines used to represent a feature or component that is not part of the specified part or assembly. e. g. billet ends that may be used for testing, or the machined product that is the focus of a tooling drawing. lines can also be classified by a letter classification in which each line is given a letter. type a lines show the outline of the feature of an object. they are the thickest lines on a drawing and done with a pencil softer than hb. type b lines are dimension lines and are used for dimensioning, projecting, extending, or leaders. a harder pencil should be used, such as a 2h pencil. type c lines are used for breaks when the whole object is not shown. these are freehand drawn and only for short breaks. 2h pencil type d lines are similar to type c, except these are zigzagged and only for longer breaks. 2h pencil type e lines indicate hidden outlines of internal features of an object. these are dotted lines. 2h pencil type f lines are type e lines, except these are used for drawings in electrotechnology. 2h pencil type g lines are used for centre lines. these are dotted lines, but a long line of 10 – 20 mm, then a 1 mm gap, then a small line of 2 mm. 2h pencil type h lines are the same as type g, except that every second long line is thicker. these indicate the cutting plane of an object. 2h pencil type k lines indicate the alternate positions of an object and the line taken by that object. these are drawn with a long line of 10 – 20 mm, then a small gap, then a small line of 2 mm, then a gap, then another small line. 2h pencil. = = = multiple views and projections = = = in most cases, a single view is not sufficient to show all necessary features, and several views are used. types of views include the following : = = = = multiview projection = = = = a multiview projection is a type of orthographic projection . doppler radar can measure a moving object ' s velocity, by measuring the change in frequency of the return radio waves due to the doppler effect. radar sets mainly use high frequencies in the microwave bands, because these frequencies create strong reflections from objects the size of vehicles and can be focused into narrow beams with compact antennas. parabolic ( dish ) antennas are widely used. in most radars the transmitting antenna also serves as the receiving antenna ; this is called a monostatic radar. a radar which uses separate transmitting and receiving antennas is called a bistatic radar. airport surveillance radar – in aviation, radar is the main tool of air traffic control. a rotating dish antenna sweeps a vertical fan - shaped beam of microwaves around the airspace and the radar set shows the location of aircraft as " blips " of light on a display called a radar screen. airport radar operates at 2. 7 – 2. 9 ghz in the microwave s band. in large airports the radar image is displayed on multiple screens in an operations room called the tracon ( terminal radar approach control ), where air traffic controllers direct the aircraft by radio to maintain safe aircraft separation. secondary surveillance radar – aircraft carry radar transponders, transceivers which when triggered by the incoming radar signal transmit a return microwave signal. this causes the aircraft to show up more strongly on the radar screen. the radar which triggers the transponder and receives the return beam, usually mounted on top of the primary radar dish, is called the secondary surveillance radar. since radar cannot measure an aircraft ' s altitude with any accuracy, the transponder also transmits back the aircraft ' s altitude measured by its altimeter, and an id number identifying the aircraft, which is displayed on the radar screen. electronic countermeasures ( ecm ) – military defensive electronic systems designed to degrade enemy radar effectiveness, or deceive it with false information, to prevent enemies from locating local forces. it often consists of powerful microwave transmitters that can mimic enemy radar signals to create false target indications on the enemy radar screens. marine radar – an s or x band radar on ships used to detect nearby ships and obstructions like bridges. a rotating antenna sweeps a vertical fan - shaped beam of microwaves around the water surface surrounding the craft out to the horizon. weather radar – a doppler radar which maps weather precipitation intensities and wind speeds with the echoes returned from raindrops and their radial velocity by their doppler shift. phased - array radar – a radar set compact antennas. parabolic ( dish ) antennas are widely used. in most radars the transmitting antenna also serves as the receiving antenna ; this is called a monostatic radar. a radar which uses separate transmitting and receiving antennas is called a bistatic radar. airport surveillance radar – in aviation, radar is the main tool of air traffic control. a rotating dish antenna sweeps a vertical fan - shaped beam of microwaves around the airspace and the radar set shows the location of aircraft as " blips " of light on a display called a radar screen. airport radar operates at 2. 7 – 2. 9 ghz in the microwave s band. in large airports the radar image is displayed on multiple screens in an operations room called the tracon ( terminal radar approach control ), where air traffic controllers direct the aircraft by radio to maintain safe aircraft separation. secondary surveillance radar – aircraft carry radar transponders, transceivers which when triggered by the incoming radar signal transmit a return microwave signal. this causes the aircraft to show up more strongly on the radar screen. the radar which triggers the transponder and receives the return beam, usually mounted on top of the primary radar dish, is called the secondary surveillance radar. since radar cannot measure an aircraft ' s altitude with any accuracy, the transponder also transmits back the aircraft ' s altitude measured by its altimeter, and an id number identifying the aircraft, which is displayed on the radar screen. electronic countermeasures ( ecm ) – military defensive electronic systems designed to degrade enemy radar effectiveness, or deceive it with false information, to prevent enemies from locating local forces. it often consists of powerful microwave transmitters that can mimic enemy radar signals to create false target indications on the enemy radar screens. marine radar – an s or x band radar on ships used to detect nearby ships and obstructions like bridges. a rotating antenna sweeps a vertical fan - shaped beam of microwaves around the water surface surrounding the craft out to the horizon. weather radar – a doppler radar which maps weather precipitation intensities and wind speeds with the echoes returned from raindrops and their radial velocity by their doppler shift. phased - array radar – a radar set that uses a phased array, a computer - controlled antenna that can steer the radar beam quickly to point in different directions without moving the antenna. phased - array radars were developed by the military to track fast - moving missiles and aircraft. they are widely used in military equipment and are now spreading to civilian applications. synthetic aperture one phenomenological explanation of superluminal propagation of neutrinos, which may have been observed by opera and minos, is that neutrinos travel faster inside of matter than in vacuum. if so neutrinos exhibit refraction inside matter and should exhibit other manifestations of refraction, such as deflection and reflection. such refraction would be easily detectable through the momentum imparted to appropriately shaped refractive material inserted into the neutrino beam. for numi this could be as large as ~ 10g cm / s. if these effect were found, they would provide new ways of manipulating and detecting neutrinos. reasons why this scenario seems implausible are given, however it is still worthwhile to conduct simple searches for differential refraction of neutrinos. Question: What do you call the pattern of lines formed when light passes through a prism to separate it into the different frequencies of light it contains? A) atomic emission spectrum B) prismatic rainbow C) light emission spectrum D) kaleidoscope effect	A) atomic emission spectrum
Context: within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and . most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support own self - division. in paracrine signaling, the ligand diffuses to nearby cells and affects them. for example, brain cells called neurons release ligands called neurotransmitters that diffuse across a synaptic cleft to bind with a receptor on an adjacent cell such as another neuron or muscle cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as cell. in juxtacrine signaling, there is direct contact between the signaling and responding cells. finally, hormones are ligands that travel through the circulatory systems of animals or vascular systems of plants to reach their target cells. once a ligand binds with a receptor, it can influence the behavior of another cell, depending on the type of receptor. for instance, neurotransmitters that bind with an inotropic receptor can alter the excitability of a target cell. other types of receptors include protein kinase receptors ( e. g., receptor for the hormone insulin ) and g protein - coupled receptors. activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions aquatic and most of the aquatic photosynthetic eukaryotic organisms are collectively described as algae, which is a term of convenience as not all algae are closely related. algae comprise several distinct clades such as glaucophytes, which are microscopic freshwater algae that may have resembled in form to the early unicellular ancestor of plantae. unlike glaucophytes, the other algal clades such as red and green algae are multicellular. green algae comprise three major clades : chlorophytes, coleochaetophytes, and stoneworts. fungi are eukaryotes that digest foods outside their bodies, secreting digestive enzymes that break down large food molecules before absorbing them through their cell membranes. many fungi are also saprobes, feeding on dead organic matter, making them important decomposers in ecological systems. animals are multicellular eukaryotes. with few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. over 1. 5 million living animal species have been described — of which around 1 million are insects — but it has been estimated there are over 7 million animal species in total. they have complex interactions with each other and their environments, forming intricate food webs. = = = viruses = = = viruses are submicroscopic infectious agents that replicate inside the cells of organisms. viruses infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea. more than 6, 000 virus species have been described in detail. viruses are found in almost every ecosystem on earth and are the most numerous type of biological entity. the origins of viruses in the evolutionary history of life are unclear : some may have evolved from plasmids — pieces of dna that can move between cells — while others may have evolved from bacteria. in evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity in a way analogous to sexual reproduction. because viruses possess some but not all characteristics of life, they have been described as " organisms at the edge of life ", and as self - replicators. = = ecology = = ecology is the study of the distribution and abundance of life, the interaction between organisms and their environment. = = = ecosystems = = = the community of living ( biotic ) organisms in conjunction with the nonliving ( abiotic ) components ( e. ##s ( sometimes called pressurized caissons ), which penetrate soft mud, are bottomless boxes sealed at the top and filled with compressed air to keep water and mud out at depth. an airlock allows access to the chamber. workers, called sandhogs in american english, move mud and rock debris ( called muck ) from the edge of the workspace to a water - filled pit, connected by a tube ( called the muck tube ) to the surface. a crane at the surface removes the soil with a clamshell bucket. the water pressure in the tube balances the air pressure, with excess air escaping up the muck tube. the pressurized air flow must be constant to ensure regular air changes for the workers and prevent excessive inflow of mud or water at the base of the caisson. when the caisson hits bedrock, the sandhogs exit through the airlock and fill the box with concrete, forming a solid foundation pier. a pneumatic ( compressed - air ) caisson has the advantage of providing dry working conditions, which is better for placing concrete. it is also well suited for foundations for which other methods might cause settlement of adjacent structures. construction workers who leave the pressurized environment of the caisson must decompress at a rate that allows symptom - free release of inert gases dissolved in the body tissues if they are to avoid decompression sickness, a condition first identified in caisson workers, and originally named " caisson disease " in recognition of the occupational hazard. construction of the brooklyn bridge, which was built with the help of pressurised caissons, resulted in numerous workers being either killed or permanently injured by caisson disease during its construction. barotrauma of the ears, sinus cavities and lungs and dysbaric osteonecrosis are other risks. = = other uses = = caissons have also been used in the installation of hydraulic elevators where a single - stage ram is installed below the ground level. caissons, codenamed phoenix, were an integral part of the mulberry harbours used during the world war ii allied invasion of normandy. = = other meanings = = boat lift caissons : the word caisson is also used as a synonym for the moving trough part of caisson locks, canal lifts and inclines in which boats and ships rest while being lifted from one canal elevation to another ; the water is retained on the inside of the caisson, or excluded from the caisson ancient endosymbiotic relationship between an ancestral eukaryotic cell and a cyanobacterial resident. the algae are a polyphyletic group and are placed in various divisions, some more closely related to plants than others. there are many differences between them in features such as cell wall composition, biochemistry, pigmentation, chloroplast structure and nutrient reserves. the algal division charophyta, sister to the green algal division chlorophyta, is considered to contain the ancestor of true plants. the charophyte class charophyceae and the land plant sub - kingdom embryophyta together form the monophyletic group or clade streptophytina. nonvascular land plants are embryophytes that lack the vascular tissues xylem and phloem. they include mosses, liverworts and hornworts. pteridophytic vascular plants with true xylem and phloem that reproduced by spores germinating into free - living gametophytes evolved during the silurian period and diversified into several lineages during the late silurian and early devonian. representatives of the lycopods have survived to the present day. by the end of the devonian period, several groups, including the lycopods, sphenophylls and progymnosperms, had independently evolved " megaspory " – their spores were of two distinct sizes, larger megaspores and smaller microspores. their reduced gametophytes developed from megaspores retained within the spore - producing organs ( megasporangia ) of the sporophyte, a condition known as endospory. seeds consist of an endosporic megasporangium surrounded by one or two sheathing layers ( integuments ). the young sporophyte develops within the seed, which on germination splits to release it. the earliest known seed plants date from the latest devonian famennian stage. following the evolution of the seed habit, seed plants diversified, giving rise to a number of now - extinct groups, including seed ferns, as well as the modern gymnosperms and angiosperms. gymnosperms produce " naked seeds " not fully enclosed in an ovary ; modern representatives include conifers, cycads, ginkgo, and gnetales. angiosperms produce seeds enclosed in a structure such as a carpel or an o shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration Question: What is the term for a watertight seal between two adjacent animal cells? A) cell wall B) placental barrier C) tight junction D) cell membrane	C) tight junction
Context: shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with . most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support manifold of dimension two ( see § topological surface ). a differentiable surface is a surfaces that is a differentiable manifold ( see § differentiable surface ). every differentiable surface is a topological surface, but the converse is false. a " surface " is often implicitly supposed to be contained in a euclidean space of dimension 3, typically r3. a surface that is contained in a projective space is called a projective surface ( see § projective surface ). a surface that is not supposed to be included in another space is called an abstract surface. = = examples = = the graph of a continuous function of two variables, defined over a connected open subset of r2 is a topological surface. if the function is differentiable, the graph is a differentiable surface. a plane is both an algebraic surface and a differentiable surface. it is also a ruled surface and a surface of revolution. a circular cylinder ( that is, the locus of a line crossing a circle and parallel to a given direction ) is an algebraic surface and a differentiable surface. a circular cone ( locus of a line crossing a circle, and passing through a fixed point, the apex, which is outside the plane of the circle ) is an algebraic surface which is not a differentiable surface. if one removes the apex, the remainder of the cone is the union of two differentiable surfaces. the surface of a polyhedron is a topological surface, which is neither a differentiable surface nor an algebraic surface. a hyperbolic paraboloid ( the graph of the function z = xy ) is a differentiable surface and an algebraic surface. it is also a ruled surface, and, for this reason, is often used in architecture. a two - sheet hyperboloid is an algebraic surface and the union of two non - intersecting differentiable surfaces. = = parametric surface = = a parametric surface is the image of an open subset of the euclidean plane ( typically r 2 { \ displaystyle \ mathbb { r } ^ { 2 } } ) by a continuous function, in a topological space, generally a euclidean space of dimension at least three. usually the function is supposed to be continuously differentiable, and this will be always the case in this article. specifically, a parametric surface in r 3 { \ displaystyle \ mathbb { r } ^ { 3 } } is given by three functions of two variables u and v, called parameters x = f 1 ( u, v ), y = f 2 ( u, v ), z = f 3 as subjects perceive the sensory world, different stimuli elicit a number of neural representations. here, a subjective distance between stimuli is defined, measuring the degree of similarity between the underlying representations. as an example, the subjective distance between different locations in space is calculated from the activity of rodent hippocampal place cells, and lateral septal cells. such a distance is compared to the real distance, between locations. as the number of sampled neurons increases, the subjective distance shows a tendency to resemble the metrics of real space. dimension 3, typically r3. a surface that is contained in a projective space is called a projective surface ( see § projective surface ). a surface that is not supposed to be included in another space is called an abstract surface. = = examples = = the graph of a continuous function of two variables, defined over a connected open subset of r2 is a topological surface. if the function is differentiable, the graph is a differentiable surface. a plane is both an algebraic surface and a differentiable surface. it is also a ruled surface and a surface of revolution. a circular cylinder ( that is, the locus of a line crossing a circle and parallel to a given direction ) is an algebraic surface and a differentiable surface. a circular cone ( locus of a line crossing a circle, and passing through a fixed point, the apex, which is outside the plane of the circle ) is an algebraic surface which is not a differentiable surface. if one removes the apex, the remainder of the cone is the union of two differentiable surfaces. the surface of a polyhedron is a topological surface, which is neither a differentiable surface nor an algebraic surface. a hyperbolic paraboloid ( the graph of the function z = xy ) is a differentiable surface and an algebraic surface. it is also a ruled surface, and, for this reason, is often used in architecture. a two - sheet hyperboloid is an algebraic surface and the union of two non - intersecting differentiable surfaces. = = parametric surface = = a parametric surface is the image of an open subset of the euclidean plane ( typically r 2 { \ displaystyle \ mathbb { r } ^ { 2 } } ) by a continuous function, in a topological space, generally a euclidean space of dimension at least three. usually the function is supposed to be continuously differentiable, and this will be always the case in this article. specifically, a parametric surface in r 3 { \ displaystyle \ mathbb { r } ^ { 3 } } is given by three functions of two variables u and v, called parameters x = f 1 ( u, v ), y = f 2 ( u, v ), z = f 3 ( u, v ). { \ displaystyle { \ begin { aligned } x & = f _ { 1 } ( u, v ), \ \ [ 4pt ] y & = f _ { 2 } ( u, v ), \ \ [ 4pt ] z & = f _ { 3 } there are a variety of bioreactors designed for 3d cell cultures. there are small plastic cylindrical chambers, as well as glass chambers, with regulated internal humidity and moisture specifically engineered for the purpose of growing cells in three dimensions. the bioreactor uses bioactive synthetic materials such as polyethylene terephthalate membranes to surround the spheroid cells in an environment that maintains high levels of nutrients. they are easy to open and close, so that cell spheroids can be removed for testing, yet the chamber is able to maintain 100 % humidity throughout. this humidity is important to achieve maximum cell growth and function. the bioreactor chamber is part of a larger device that rotates to ensure equal cell growth in each direction across three dimensions. quinxell technologies now under quintech life sciences from singapore has developed a bioreactor known as the tisxell biaxial bioreactor which is specially designed for the purpose of tissue engineering. it is the first bioreactor in the world to have a spherical glass chamber with biaxial rotation ; specifically to mimic the rotation of the fetus in the womb ; which provides a conducive environment for the growth of tissues. multiple forms of mechanical stimulation have also been combined into a single bioreactor. using gene expression analysis, one academic study found that applying a combination of cyclic strain and ultrasound stimulation to pre - osteoblast cells in a bioreactor accelerated matrix maturation and differentiation. the technology of this combined stimulation bioreactor could be used to grow bone cells more quickly and effectively in future clinical stem cell therapies. mc2 biotek has also developed a bioreactor known as prototissue that uses gas exchange to maintain high oxygen levels within the cell chamber ; improving upon previous bioreactors, since the higher oxygen levels help the cell grow and undergo normal cell respiration. active areas of research on bioreactors includes increasing production scale and refining the physiological environment, both of which could improve the efficiency and efficacy of bioreactors in research or clinical use. bioreactors are currently used to study, among other things, cell and tissue level therapies, cell and tissue response to specific physiological environment changes, and development of disease and injury. = = = long fiber generation = = = in 2013, a group from the university of tokyo developed cell laden fibers up to a meter in length and on the order of 100 μm in size. these fibers were created using a microfluidic device that forms a combination of chemical and mechanical stimulation. cell proliferation and differentiation are largely influenced by mechanical and biochemical cues in the surrounding extracellular matrix environment. bioreactors are typically developed to replicate the specific physiological environment of the tissue being grown ( e. g., flex and fluid shearing for heart tissue growth ). this can allow specialized cell lines to thrive in cultures replicating their native environments, but it also makes bioreactors attractive tools for culturing stem cells. a successful stem - cell - based bioreactor is effective at expanding stem cells with uniform properties and / or promoting controlled, reproducible differentiation into selected mature cell types. there are a variety of bioreactors designed for 3d cell cultures. there are small plastic cylindrical chambers, as well as glass chambers, with regulated internal humidity and moisture specifically engineered for the purpose of growing cells in three dimensions. the bioreactor uses bioactive synthetic materials such as polyethylene terephthalate membranes to surround the spheroid cells in an environment that maintains high levels of nutrients. they are easy to open and close, so that cell spheroids can be removed for testing, yet the chamber is able to maintain 100 % humidity throughout. this humidity is important to achieve maximum cell growth and function. the bioreactor chamber is part of a larger device that rotates to ensure equal cell growth in each direction across three dimensions. quinxell technologies now under quintech life sciences from singapore has developed a bioreactor known as the tisxell biaxial bioreactor which is specially designed for the purpose of tissue engineering. it is the first bioreactor in the world to have a spherical glass chamber with biaxial rotation ; specifically to mimic the rotation of the fetus in the womb ; which provides a conducive environment for the growth of tissues. multiple forms of mechanical stimulation have also been combined into a single bioreactor. using gene expression analysis, one academic study found that applying a combination of cyclic strain and ultrasound stimulation to pre - osteoblast cells in a bioreactor accelerated matrix maturation and differentiation. the technology of this combined stimulation bioreactor could be used to grow bone cells more quickly and effectively in future clinical stem cell therapies. mc2 biotek has also developed a bioreactor known as prototissue that uses gas exchange to maintain high oxygen levels within the cell chamber ; improving upon previous bioreactors, since the higher oxygen levels help the cell grow and undergo normal cell respiration. active are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its Question: What is at the surface of a cell, arranged in similar bilayer? A) fats B) eukaryotes C) pigments D) phospholipids	D) phospholipids
Context: = = organic compounds are molecules that contain carbon bonded to another element such as hydrogen. with the exception of water, nearly all the molecules that make up each organism contain carbon. carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules. for example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids the chemistry of condensed phases ( solids, liquids, polymers ) and interfaces between different phases. neurochemistry is the study of neurochemicals ; including transmitters, peptides, proteins, lipids, sugars, and nucleic acids ; their interactions, and the roles they play in forming, maintaining, and modifying the nervous system. nuclear chemistry is the study of how subatomic particles come together and make nuclei. modern transmutation is a large component of nuclear chemistry, and the table of nuclides is an important result and tool for this field. in addition to medical applications, nuclear chemistry encompasses nuclear engineering which explores the topic of using nuclear power sources for generating energy. organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. an organic compound is defined as any compound based on a carbon skeleton. organic compounds can be classified, organized and understood in reactions by their functional groups, unit atoms or molecules that show characteristic chemical properties in a compound. physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. in particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, spectroscopy, and more recently, astrochemistry. physical chemistry has large overlap with molecular physics. physical chemistry involves the use of infinitesimal calculus in deriving equations. it is usually associated with quantum chemistry and theoretical chemistry. physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap. theoretical chemistry is the study of chemistry via fundamental theoretical reasoning ( usually within mathematics or physics ). in particular the application of quantum mechanics to chemistry is called quantum chemistry. since the end of the second world war, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. theoretical chemistry has large overlap with ( theoretical and experimental ) condensed matter physics and molecular physics. other subdivisions include electrochemistry, femtochemistry, flavor chemistry, flow chemistry, immunohistochemistry, hydrogenation chemistry, mathematical chemistry, molecular mechanics, natural product chemistry, organometallic chemistry, petrochemistry, photochemistry, physical organic chemistry, polymer chemistry, radiochemistry, sonochemistry, supramolecular chemistry, synthetic chemistry, and many others. = = = interdisciplinary = = = interdisciplinary fields include ag the topic of using nuclear power sources for generating energy. organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. an organic compound is defined as any compound based on a carbon skeleton. organic compounds can be classified, organized and understood in reactions by their functional groups, unit atoms or molecules that show characteristic chemical properties in a compound. physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. in particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, spectroscopy, and more recently, astrochemistry. physical chemistry has large overlap with molecular physics. physical chemistry involves the use of infinitesimal calculus in deriving equations. it is usually associated with quantum chemistry and theoretical chemistry. physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap. theoretical chemistry is the study of chemistry via fundamental theoretical reasoning ( usually within mathematics or physics ). in particular the application of quantum mechanics to chemistry is called quantum chemistry. since the end of the second world war, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. theoretical chemistry has large overlap with ( theoretical and experimental ) condensed matter physics and molecular physics. other subdivisions include electrochemistry, femtochemistry, flavor chemistry, flow chemistry, immunohistochemistry, hydrogenation chemistry, mathematical chemistry, molecular mechanics, natural product chemistry, organometallic chemistry, petrochemistry, photochemistry, physical organic chemistry, polymer chemistry, radiochemistry, sonochemistry, supramolecular chemistry, synthetic chemistry, and many others. = = = interdisciplinary = = = interdisciplinary fields include agrochemistry, astrochemistry ( and cosmochemistry ), atmospheric chemistry, chemical engineering, chemical biology, chemo - informatics, environmental chemistry, geochemistry, green chemistry, immunochemistry, marine chemistry, materials science, mechanochemistry, medicinal chemistry, molecular biology, nanotechnology, oenology, pharmacology, phytochemistry, solid - state chemistry, surface science, thermochemistry, and many others. = = = industry = = = the chemical industry represents an important economic activity worldwide. the global top 50 chemical producers in 2013 had sales their mechanical properties. = = tissue culture = = in many cases, creation of functional tissues and biological structures in vitro requires extensive culturing to promote survival, growth and inducement of functionality. in general, the basic requirements of cells must be maintained in culture, which include oxygen, ph, humidity, temperature, nutrients and osmotic pressure maintenance. tissue engineered cultures also present additional problems in maintaining culture conditions. in standard cell culture, diffusion is often the sole means of nutrient and metabolite transport. however, as a culture becomes larger and more complex, such as the case with engineered organs and whole tissues, other mechanisms must be employed to maintain the culture, such as the creation of capillary networks within the tissue. another issue with tissue culture is introducing the proper factors or stimuli required to induce functionality. in many cases, simple maintenance culture is not sufficient. growth factors, hormones, specific metabolites or nutrients, chemical and physical stimuli are sometimes required. for example, certain cells respond to changes in oxygen tension as part of their normal development, such as chondrocytes, which must adapt to low oxygen conditions or hypoxia during skeletal development. others, such as endothelial cells, respond to shear stress from fluid flow, which is encountered in blood vessels. mechanical stimuli, such as pressure pulses seem to be beneficial to all kind of cardiovascular tissue such as heart valves, blood vessels or pericardium. = = = bioreactors = = = in tissue engineering, a bioreactor is a device that attempts to simulate a physiological environment in order to promote cell or tissue growth in vitro. a physiological environment can consist of many different parameters such as temperature, pressure, oxygen or carbon dioxide concentration, or osmolality of fluid environment, and it can extend to all kinds of biological, chemical or mechanical stimuli. therefore, there are systems that may include the application of forces such as electromagnetic forces, mechanical pressures, or fluid pressures to the tissue. these systems can be two - or three - dimensional setups. bioreactors can be used in both academic and industry applications. general - use and application - specific bioreactors are also commercially available, which may provide static chemical stimulation or a combination of chemical and mechanical stimulation. cell proliferation and differentiation are largely influenced by mechanical and biochemical cues in the surrounding extracellular matrix environment. bioreactors are typically developed to replicate the specific physiological environment of the tissue being grown ( e. g., flex and fluid shearing for heart tissue growth ). this can i reject the following null hypothesis : { h0 : your data are normal }. such drastic decision is motivated by theoretical reasons, and applies to your current data, the past ones, and the future ones. while this situation may appear embarrassing, it does not invalidate any of your results. moreover, it allows to save time and energy that are currently spent in vain by performing the following unnecessary tasks : ( i ) carrying out normality tests ; ( ii ) pretending to do something if normality is rejected ; and ( iii ) arguing about normality with referee # 2. not completely stable as each water molecule continuously dissociates into hydrogen and hydroxyl ions before reforming into a water molecule again. in pure water, the number of hydrogen ions balances ( or equals ) the number of hydroxyl ions, resulting in a ph that is neutral. = = = organic compounds = = = organic compounds are molecules that contain carbon bonded to another element such as hydrogen. with the exception of water, nearly all the molecules that make up each organism contain carbon. carbon can form covalent bonds with up to four other atoms, enabling it to form diverse, large, and complex molecules. for example, a single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( on a large scale provided protection from insect pests or tolerance to herbicides. fungal and virus resistant crops have also been developed or are in development. this makes the insect and weed management of crops easier and can indirectly increase crop yield. gm crops that directly improve yield by accelerating growth or making the plant more hardy ( by improving salt, cold or drought tolerance ) are also under development. in 2016 salmon have been genetically modified with growth hormones to reach normal adult size much faster. gmos have been developed that modify the quality of produce by increasing the nutritional value or providing more industrially useful qualities or quantities. the amflora potato produces a more industrially useful blend of starches. soybeans and canola have been genetically modified to produce more healthy oils. the first commercialised gm food was a tomato that had delayed ripening, increasing its shelf life. plants and animals have been engineered to produce materials they do not normally make. pharming uses crops and animals as bioreactors to produce vaccines, drug intermediates, or the drugs themselves ; the useful product is purified from the harvest and then used in the standard pharmaceutical production process. cows and goats have been engineered to express drugs and other proteins in their milk, and in 2009 the fda approved a drug produced in goat milk. = = = other applications = = = genetic engineering has potential applications in conservation and natural area management. gene transfer through viral vectors has been proposed as a means of controlling invasive species as well as vaccinating threatened fauna from disease. transgenic trees have been suggested as a way to confer resistance to pathogens in wild populations. with the increasing risks of maladaptation in organisms as a result of climate change and other perturbations, facilitated adaptation through gene tweaking could be one solution to reducing extinction risks. applications of genetic engineering in conservation are thus far mostly theoretical and have yet to be put into practice. genetic engineering is also being used to create microbial art. some bacteria have been genetically engineered to create black and white photographs. novelty items such as lavender - colored carnations, blue roses, and glowing fish, have also been produced through genetic engineering. = = regulation = = the regulation of genetic engineering concerns the approaches taken by governments to assess and manage the risks associated with the development and release of gmos. the development of a regulatory framework began in 1975, at asilomar, california. the asilomar meeting recommended a set of voluntary guidelines regarding the use of recombinant technology. as the technology improved solid state components or devices with a useful current or future function. the field is a new breadth of study in graduate programs, and it integrates elements from all classical areas of chemistry like organic chemistry, inorganic chemistry, and crystallography with a focus on fundamental issues that are unique to materials. primary systems of study include the chemistry of condensed phases ( solids, liquids, polymers ) and interfaces between different phases. neurochemistry is the study of neurochemicals ; including transmitters, peptides, proteins, lipids, sugars, and nucleic acids ; their interactions, and the roles they play in forming, maintaining, and modifying the nervous system. nuclear chemistry is the study of how subatomic particles come together and make nuclei. modern transmutation is a large component of nuclear chemistry, and the table of nuclides is an important result and tool for this field. in addition to medical applications, nuclear chemistry encompasses nuclear engineering which explores the topic of using nuclear power sources for generating energy. organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. an organic compound is defined as any compound based on a carbon skeleton. organic compounds can be classified, organized and understood in reactions by their functional groups, unit atoms or molecules that show characteristic chemical properties in a compound. physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. in particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, spectroscopy, and more recently, astrochemistry. physical chemistry has large overlap with molecular physics. physical chemistry involves the use of infinitesimal calculus in deriving equations. it is usually associated with quantum chemistry and theoretical chemistry. physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap. theoretical chemistry is the study of chemistry via fundamental theoretical reasoning ( usually within mathematics or physics ). in particular the application of quantum mechanics to chemistry is called quantum chemistry. since the end of the second world war, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. theoretical chemistry has large overlap with ( theoretical and experimental ) condensed matter physics and molecular physics. other subdivisions include electrochemistry, femtochemistry, flavor chemistry, flow chemistry, immunohistochemistry, hydrogenation chemistry, mathematical chemistry single carbon atom can form four single covalent bonds such as in methane, two double covalent bonds such as in carbon dioxide ( co2 ), or a triple covalent bond such as in carbon monoxide ( co ). moreover, carbon can form very long chains of interconnecting carbon – carbon bonds such as octane or ring - like structures such as glucose. the simplest form of an organic molecule is the hydrocarbon, which is a large family of organic compounds that are composed of hydrogen atoms bonded to a chain of carbon atoms. a hydrocarbon backbone can be substituted by other elements such as oxygen ( o ), hydrogen ( h ), phosphorus ( p ), and sulfur ( s ), which can change the chemical behavior of that compound. groups of atoms that contain these elements ( o -, h -, p -, and s - ) and are bonded to a central carbon atom or skeleton are called functional groups. there are six prominent functional groups that can be found in organisms : amino group, carboxyl group, carbonyl group, hydroxyl group, phosphate group, and sulfhydryl group. in 1953, the miller – urey experiment showed that organic compounds could be synthesized abiotically within a closed system mimicking the conditions of early earth, thus suggesting that complex organic molecules could have arisen spontaneously in early earth ( see abiogenesis ). = = = macromolecules = = = macromolecules are large molecules made up of smaller subunits or monomers. monomers include sugars, amino acids, and nucleotides. carbohydrates include monomers and polymers of sugars. lipids are the only class of macromolecules that are not made up of polymers. they include steroids, phospholipids, and fats, largely nonpolar and hydrophobic ( water - repelling ) substances. proteins are the most diverse of the macromolecules. they include enzymes, transport proteins, large signaling molecules, antibodies, and structural proteins. the basic unit ( or monomer ) of a protein is an amino acid. twenty amino acids are used in proteins. nucleic acids are polymers of nucleotides. their function is to store, transmit, and express hereditary information. = = cells = = cell theory states that cells are the fundamental units of life, that all living things are composed of one or more cells, and that all cells arise from preexisting cells through cell division modifying the nervous system. nuclear chemistry is the study of how subatomic particles come together and make nuclei. modern transmutation is a large component of nuclear chemistry, and the table of nuclides is an important result and tool for this field. in addition to medical applications, nuclear chemistry encompasses nuclear engineering which explores the topic of using nuclear power sources for generating energy. organic chemistry is the study of the structure, properties, composition, mechanisms, and reactions of organic compounds. an organic compound is defined as any compound based on a carbon skeleton. organic compounds can be classified, organized and understood in reactions by their functional groups, unit atoms or molecules that show characteristic chemical properties in a compound. physical chemistry is the study of the physical and fundamental basis of chemical systems and processes. in particular, the energetics and dynamics of such systems and processes are of interest to physical chemists. important areas of study include chemical thermodynamics, chemical kinetics, electrochemistry, statistical mechanics, spectroscopy, and more recently, astrochemistry. physical chemistry has large overlap with molecular physics. physical chemistry involves the use of infinitesimal calculus in deriving equations. it is usually associated with quantum chemistry and theoretical chemistry. physical chemistry is a distinct discipline from chemical physics, but again, there is very strong overlap. theoretical chemistry is the study of chemistry via fundamental theoretical reasoning ( usually within mathematics or physics ). in particular the application of quantum mechanics to chemistry is called quantum chemistry. since the end of the second world war, the development of computers has allowed a systematic development of computational chemistry, which is the art of developing and applying computer programs for solving chemical problems. theoretical chemistry has large overlap with ( theoretical and experimental ) condensed matter physics and molecular physics. other subdivisions include electrochemistry, femtochemistry, flavor chemistry, flow chemistry, immunohistochemistry, hydrogenation chemistry, mathematical chemistry, molecular mechanics, natural product chemistry, organometallic chemistry, petrochemistry, photochemistry, physical organic chemistry, polymer chemistry, radiochemistry, sonochemistry, supramolecular chemistry, synthetic chemistry, and many others. = = = interdisciplinary = = = interdisciplinary fields include agrochemistry, astrochemistry ( and cosmochemistry ), atmospheric chemistry, chemical engineering, chemical biology, chemo - informatics, environmental chemistry, geochemistry, green chemistry, immunochemistry, marine chemistry, materials science, mechanochemistry, medicinal chemistry, molecular biology, Question: Vitamins are organic compounds that are essential in very small amounts for the maintenance of normal what? A) metabolism B) calcium C) pigments D) respiration	A) metabolism
Context: it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a spindle apparatus on the cell. before binary fission, dna in the bacterium is tightly coiled. after it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. growth of a new cell wall begins to separate the bacterium ( triggered by ft the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a spindle apparatus on the cell. before binary fission, dna in the bacterium is tightly coiled. after it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. growth of a new cell wall begins to separate the bacterium ( triggered by ftsz polymerization and " z - ring " formation ). the new cell wall ( septum ) fully develops, resulting in the complete split of the bacterium. the new daughter cells have tightly coiled dna rods, ribosomes, and plasmids. = = = sexual reproduction and meiosis = = = meiosis is a central feature of sexual reproduction in eukaryotes, and the most fundamental function of meiosis appears to be conservation of the integrity of the genome that is passed on to progeny by parents. two aspects of sexual reproduction, meiotic recombination and outcrossing, are likely maintained respectively by the adaptive advantages of recombinational repair of genomic dna damage and genetic complementation which masks the expression of deleterious recessive mutations. the beneficial effect of genetic complementation, derived from outcrossing ( cross - fertilization ) is also referred to as hybrid vigor or heterosis. charles darwin in his 1878 book the effects of cross and self - fertilization in the vegetable kingdom at the start of chapter xii noted “ the first and most important of the conclusions which may be drawn from the observations given in this volume, is that generally cross - fertilisation is beneficial and self - fertilis of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a spindle apparatus on the cell. before binary fission, dna in the bacterium is tightly coiled. after it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. growth of a new cell wall begins to separate the bacterium ( triggered by ftsz polymerization and " z - ring " formation ). the new cell wall ( septum ) fully develops, resulting in the complete split of the bacterium. the new daughter cells have tightly coiled dna rods, ribosomes, and plasmids. = = = sexual reproduction and meiosis = = = meiosis is a central feature of sexual reproduction in eukaryotes, and the most fundamental function of meiosis appears to be conservation of the integrity of the genome that is passed on to progeny by parents. two aspects of sexual reproduction, meiotic recombination and outcrossing, are likely maintained respectively by the adaptive advantages of recombinational repair of genomic dna damage and genetic complementation which masks the expression of deleterious recessive mutations. the beneficial effect of genetic complementation, derived from outcrossing ( cross - fertilization ) is also referred to as hybrid vigor or heterosis. charles ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a spindle apparatus on the cell. before binary fission, dna in the bacterium is tightly coiled. after it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. growth of a new cell wall begins to separate the bacterium ( triggered by ftsz polymerization and " z - ring " formation ). the new cell wall ( septum ) fully develops, resulting in the complete split of the bacterium. the new daughter cells have tightly coiled dna rods, ribosomes, and plasmids. = = = sexual reproduction and meiosis = = = meiosis is a central feature of sexual reproduction in eukaryotes, and the most fundamental function of meiosis appears to be conservation of the integrity of the genome that is passed on to progeny by parents. two aspects of sexual reproduction, meiotic recombination and outcrossing, are likely maintained respectively by protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a spindle apparatus on the cell. before binary fission, dna in the bacterium is tightly coiled. after it has uncoiled and duplicated, it is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. growth of a new cell wall begins to separate the bacterium ( triggered by ftsz polymerization and " z - ring " formation ). the new cell wall ( septum ) fully develops, resulting in the complete split of the bacterium. the new daughter cells have tightly coiled dna rods, ribosomes, and plasmids. = = = sexual reproduction and meiosis = = = mei cross. the chromosome theory of inheritance, which states that genes are found on chromosomes, was supported by thomas morgans ' s experiments with fruit flies, which established the sex linkage between eye color and sex in these insects. = = = genes and dna = = = a gene is a unit of heredity that corresponds to a region of deoxyribonucleic acid ( dna ) that carries genetic information that controls form or function of an organism. dna is composed of two polynucleotide chains that coil around each other to form a double helix. it is found as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. the set of chromosomes in a cell is collectively known as its genome. in eukaryotes, dna is mainly in the cell nucleus. in prokaryotes, the dna is held within the nucleoid. the genetic information is held within genes, and the complete assemblage in an organism is called its genotype. dna replication is a semiconservative process whereby each strand serves as a template for a new strand of dna. mutations are heritable changes in dna. they can arise spontaneously as a result of replication errors that were not corrected by proofreading or can be induced by an environmental mutagen such as a chemical ( e. g., nitrous acid, benzopyrene ) or radiation ( e. g., x - ray, gamma ray, ultraviolet radiation, particles emitted by unstable isotopes ). mutations can lead to phenotypic effects such as loss - of - function, gain - of - function, and conditional mutations. some mutations are beneficial, as they are a source of genetic variation for evolution. others are harmful if they were to result in a loss of function of genes needed for survival. = = = gene expression = = = gene expression is the molecular process by which a genotype encoded in dna gives rise to an observable phenotype in the proteins of an organism ' s body. this process is summarized by the central dogma of molecular biology, which was formulated by francis crick in 1958. according to the central dogma, genetic information flows from dna to rna to protein. there are two gene expression processes : transcription ( dna to rna ) and translation ( rna to protein ). = = = gene regulation = = = the regulation of gene expression by environmental factors and during different stages of development can occur at each step of the process such as transcription, rna splicing . most cells are very small, with diameters ranging from 1 to 100 micrometers and are therefore only visible under a light or electron microscope. there are generally two types of cells : eukaryotic cells, which contain a nucleus, and prokaryotic cells, which do not. prokaryotes are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support into major divisions, starting with four eons ( hadean, archean, proterozoic, and phanerozoic ), the first three of which are collectively known as the precambrian, which lasted approximately 4 billion years. each eon can be divided into eras, with the phanerozoic eon that began 539 million years ago being subdivided into paleozoic, mesozoic, and cenozoic eras. these three eras together comprise eleven periods ( cambrian, ordovician, silurian, devonian, carboniferous, permian, triassic, jurassic, cretaceous, tertiary, and quaternary ). the similarities among all known present - day species indicate that they have diverged through the process of evolution from their common ancestor. biologists regard the ubiquity of the genetic code as evidence of universal common descent for all bacteria, archaea, and eukaryotes. microbial mats of coexisting bacteria and archaea were the dominant form of life in the early archean eon and many of the major steps in early evolution are thought to have taken place in this environment. the earliest evidence of eukaryotes dates from 1. 85 billion years ago, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. later, around 1. 7 billion years ago, multicellular organisms began to appear, with differentiated cells performing specialised functions. algae - like multicellular land plants are dated back to about 1 billion years ago, although evidence suggests that microorganisms formed the earliest terrestrial ecosystems, at least 2. 7 billion years ago. microorganisms are thought to have paved the way for the inception of land plants in the ordovician period. land plants were so successful that they are thought to have contributed to the late devonian extinction event. ediacara biota appear during the ediacaran period, while vertebrates, along with most other modern phyla originated about 525 million years ago during the cambrian explosion. during the permian period, synapsids, including the ancestors of mammals, dominated the land, but most of this group became extinct in the permian – triassic extinction event 252 million years ago. during the recovery from this catastrophe, archosaurs became the most abundant land vertebrates ; one archosaur group, the dinosaurs, dominated the jurassic and cretaceous periods. after the cretaceous – paleogene extinction event 66 million years ago killed off activation of g protein - coupled receptors can initiate second messenger cascades. the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events is called signal transduction. = = = cell cycle = = = the cell cycle is a series of events that take place in a cell that cause it to divide into two daughter cells. these events include the duplication of its dna and some of its organelles, and the subsequent partitioning of its cytoplasm into two daughter cells in a process called cell division. in eukaryotes ( i. e., animal, plant, fungal, and protist cells ), there are two distinct types of cell division : mitosis and meiosis. mitosis is part of the cell cycle, in which replicated chromosomes are separated into two new nuclei. cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. in general, mitosis ( division of the nucleus ) is preceded by the s stage of interphase ( during which the dna is replicated ) and is often followed by telophase and cytokinesis ; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. the different stages of mitosis all together define the mitotic phase of an animal cell cycle — the division of the mother cell into two genetically identical daughter cells. the cell cycle is a vital process by which a single - celled fertilized egg develops into a mature organism, as well as the process by which hair, skin, blood cells, and some internal organs are renewed. after cell division, each of the daughter cells begin the interphase of a new cycle. in contrast to mitosis, meiosis results in four haploid daughter cells by undergoing one round of dna replication followed by two divisions. homologous chromosomes are separated in the first division ( meiosis i ), and sister chromatids are separated in the second division ( meiosis ii ). both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. both are believed to be present in the last eukaryotic common ancestor. prokaryotes ( i. e., archaea and bacteria ) can also undergo cell division ( or binary fission ). unlike the processes of mitosis and meiosis in eukaryotes, binary fission in prokaryotes takes place without the formation of a are single - celled organisms such as bacteria, whereas eukaryotes can be single - celled or multicellular. in multicellular organisms, every cell in the organism ' s body is derived ultimately from a single cell in a fertilized egg. = = = cell structure = = = every cell is enclosed within a cell membrane that separates its cytoplasm from the extracellular space. a cell membrane consists of a lipid bilayer, including cholesterols that sit between phospholipids to maintain their fluidity at various temperatures. cell membranes are semipermeable, allowing small molecules such as oxygen, carbon dioxide, and water to pass through while restricting the movement of larger molecules and charged particles such as ions. cell membranes also contain membrane proteins, including integral membrane proteins that go across the membrane serving as membrane transporters, and peripheral proteins that loosely attach to the outer side of the cell membrane, acting as enzymes shaping the cell. cell membranes are involved in various cellular processes such as cell adhesion, storing electrical energy, and cell signalling and serve as the attachment surface for several extracellular structures such as a cell wall, glycocalyx, and cytoskeleton. within the cytoplasm of a cell, there are many biomolecules such as proteins and nucleic acids. in addition to biomolecules, eukaryotic cells have specialized structures called organelles that have their own lipid bilayers or are spatially units. these organelles include the cell nucleus, which contains most of the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its Question: In eukaryotic cells, what divides before the cell itself divides? A) cell wall B) protons C) electrons D) nucleus	D) nucleus
Context: 28 size spectra of extensive air showers from 7 different experiments are analysed consistently. they are fitted by adjusting either 4 or 5 parameters : knee position, power law exponents above and below the knee, overall intensity and, in addition, a parameter describing the smoothness of the bend. the residuals are then normalized to the same knee position and averaged. when 5 parameters are employed no systematic deviation from a single smooth knee is apparent at the 1 % level up to a factor of 4 above the knee. at larger shower sizes a moderately significant deviation can be seen whose shape and position are compatible with a second knee caused by iron group nuclei. two planetary nebulae are shown to belong to the sagittarius dwarf galaxy, on the basis of their radial velocities. this is only the second dwarf spheroidal galaxy, after fornax, found to contain planetary nebulae. their existence confirms that this galaxy is at least as massive as the fornax dwarf spheroidal which has a single planetary nebula, and suggests a mass of a few times 10 * * 7 solar masses. the two planetary nebulae are located along the major axis of the galaxy, near the base of the tidal tail. there is a further candidate, situated at a very large distance along the direction of the tidal tail, for which no velocity measurement is available. the location of the planetary nebulae and globular clusters of the sagittarius dwarf galaxy suggests that a significant fraction of its mass is contained within the tidal tail. a compact four - dimensional manifold whose metric tensor has a positive determinant ( named the " euclid ball " ) is considered. the euclid ball can be immersed in the minkovskian space ( which has the negative determinant ) and can exist stably through the history of the universe. since the euclid ball has the same solution as the schwarzschild black hole on its three - dimensional surface, an asymptotic observer can not distinguish them. if large fraction of whole energy of the pre - universe was encapsulated in euclid balls, they behave as the dark matter in the current universe. euclid balls already existed at the end of the cosmological inflation, and can have a heavy mass in this model, they can be a seed of supper - massive black - holes, which are necessary to initiate a forming of galaxies in the early universe. the $ \ gamma $ - ray burst at early universe is also a possible signal of the euclidean ball. joints. = = = metal alloys = = = the alloys of iron ( steel, stainless steel, cast iron, tool steel, alloy steels ) make up the largest proportion of metals today both by quantity and commercial value. iron alloyed with various proportions of carbon gives low, mid and high carbon steels. an iron - carbon alloy is only considered steel if the carbon level is between 0. 01 % and 2. 00 % by weight. for steels, the hardness and tensile strength of the steel is related to the amount of carbon present, with increasing carbon levels also leading to lower ductility and toughness. heat treatment processes such as quenching and tempering can significantly change these properties, however. in contrast, certain metal alloys exhibit unique properties where their size and density remain unchanged across a range of temperatures. cast iron is defined as an iron – carbon alloy with more than 2. 00 %, but less than 6. 67 % carbon. stainless steel is defined as a regular steel alloy with greater than 10 % by weight alloying content of chromium. nickel and molybdenum are typically also added in stainless steels. other significant metallic alloys are those of aluminium, titanium, copper and magnesium. copper alloys have been known for a long time ( since the bronze age ), while the alloys of the other three metals have been relatively recently developed. due to the chemical reactivity of these metals, the electrolytic extraction processes required were only developed relatively recently. the alloys of aluminium, titanium and magnesium are also known and valued for their high strength to weight ratios and, in the case of magnesium, their ability to provide electromagnetic shielding. these materials are ideal for situations where high strength to weight ratios are more important than bulk cost, such as in the aerospace industry and certain automotive engineering applications. = = = semiconductors = = = a semiconductor is a material that has a resistivity between a conductor and insulator. modern day electronics run on semiconductors, and the industry had an estimated us $ 530 billion market in 2021. its electronic properties can be greatly altered through intentionally introducing impurities in a process referred to as doping. semiconductor materials are used to build diodes, transistors, light - emitting diodes ( leds ), and analog and digital electric circuits, among their many uses. semiconductor devices have replaced thermionic devices like vacuum tubes in most applications. semiconductor devices are manufactured both as single discrete devices and as integrated circuits ( ics ), which consist of a number — from a c. 4000 bc, associated with the maadi culture. this represents the earliest evidence for smelting in africa. the varna necropolis, bulgaria, is a burial site located in the western industrial zone of varna, approximately 4 km from the city centre, internationally considered one of the key archaeological sites in world prehistory. the oldest gold treasure in the world, dating from 4, 600 bc to 4, 200 bc, was discovered at the site. the gold piece dating from 4, 500 bc, found in 2019 in durankulak, near varna is another important example. other signs of early metals are found from the third millennium bc in palmela, portugal, los millares, spain, and stonehenge, united kingdom. the precise beginnings, however, have not be clearly ascertained and new discoveries are both continuous and ongoing. in approximately 1900 bc, ancient iron smelting sites existed in tamil nadu. in the near east, about 3, 500 bc, it was discovered that by combining copper and tin, a superior metal could be made, an alloy called bronze. this represented a major technological shift known as the bronze age. the extraction of iron from its ore into a workable metal is much more difficult than for copper or tin. the process appears to have been invented by the hittites in about 1200 bc, beginning the iron age. the secret of extracting and working iron was a key factor in the success of the philistines. historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. this includes the ancient and medieval kingdoms and empires of the middle east and near east, ancient iran, ancient egypt, ancient nubia, and anatolia in present - day turkey, ancient nok, carthage, the celts, greeks and romans of ancient europe, medieval europe, ancient and medieval china, ancient and medieval india, ancient and medieval japan, amongst others. a 16th century book by georg agricola, de re metallica, describes the highly developed and complex processes of mining metal ores, metal extraction, and metallurgy of the time. agricola has been described as the " father of metallurgy ". = = extraction = = extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted raw metals into a purer form. in order to convert a metal oxide or sulphide to a purer metal, the ore must be reduced physically, chemically, or electroly jwst / nircam obtained high angular - resolution ( 0. 05 - 0. 1 ' ' ), deep near - infrared 1 - - 5 micron imaging of supernova ( sn ) 1987a taken 35 years after the explosion. in the nircam images, we identify : 1 ) faint h2 crescents, which are emissions located between the ejecta and the equatorial ring, 2 ) a bar, which is a substructure of the ejecta, and 3 ) the bright 3 - 5 micron continuum emission exterior to the equatorial ring. the emission of the remnant in the nircam 1 - 2. 3 micron images is mostly due to line emission, which is mostly emitted in the ejecta and in the hot spots within the equatorial ring. in contrast, the nircam 3 - 5 micron images are dominated by continuum emission. in the ejecta, the continuum is due to dust, obscuring the centre of the ejecta. in contrast, in the ring and exterior to the ring, synchrotron emission contributes a substantial fraction to the continuum. dust emission contributes to the continuum at outer spots and diffuse emission exterior to the ring, but little within the ring. this shows that dust cooling and destruction time scales are shorter than the synchrotron cooling time scale, and the time scale of hydrogen recombination in the ring is even longer than the synchrotron cooling time scale. with the advent of high sensitivity and high angular resolution images provided by jwst / nircam, our observations of sn 1987a demonstrate that nircam opens up a window to study particle - acceleration and shock physics in unprecedented details, probed by near - infrared synchrotron emission, building a precise picture of how a sn evolves. - and right - bounded ; and is said to be unbounded otherwise. intervals that are bounded at only one end are said to be half - bounded. the empty set is bounded, and the set of all reals is the only interval that is unbounded at both ends. bounded intervals are also commonly known as finite intervals. bounded intervals are bounded sets, in the sense that their diameter ( which is equal to the absolute difference between the endpoints ) is finite. the diameter may be called the length, width, measure, range, or size of the interval. the size of unbounded intervals is usually defined as + ∞, and the size of the empty interval may be defined as 0 ( or left undefined ). the centre ( midpoint ) of a bounded interval with endpoints a and b is ( a + b ) / 2, and its radius is the half - length \| a − b \| / 2. these concepts are undefined for empty or unbounded intervals. an interval is said to be left - open if and only if it contains no minimum ( an element that is smaller than all other elements ) ; right - open if it contains no maximum ; and open if it contains neither. the interval [ 0, 1 ) = { x \| 0 ≤ x < 1 }, for example, is left - closed and right - open. the empty set and the set of all reals are both open and closed intervals, while the set of non - negative reals, is a closed interval that is right - open but not left - open. the open intervals are open sets of the real line in its standard topology, and form a base of the open sets. an interval is said to be left - closed if it has a minimum element or is left - unbounded, right - closed if it has a maximum or is right unbounded ; it is simply closed if it is both left - closed and right closed. so, the closed intervals coincide with the closed sets in that topology. the interior of an interval i is the largest open interval that is contained in i ; it is also the set of points in i which are not endpoints of i. the closure of i is the smallest closed interval that contains i ; which is also the set i augmented with its finite endpoints. for any set x of real numbers, the interval enclosure or interval span of x is the unique interval that contains x, and does not properly contain any other interval that also contains x. an interval i is ##elting. metallurgy of lead has also been found in the balkans during the same period. copper smelting is documented at sites in anatolia and at the site of tal - i iblis in southeastern iran from c. 5000 bc. copper smelting is first documented in the delta region of northern egypt in c. 4000 bc, associated with the maadi culture. this represents the earliest evidence for smelting in africa. the varna necropolis, bulgaria, is a burial site located in the western industrial zone of varna, approximately 4 km from the city centre, internationally considered one of the key archaeological sites in world prehistory. the oldest gold treasure in the world, dating from 4, 600 bc to 4, 200 bc, was discovered at the site. the gold piece dating from 4, 500 bc, found in 2019 in durankulak, near varna is another important example. other signs of early metals are found from the third millennium bc in palmela, portugal, los millares, spain, and stonehenge, united kingdom. the precise beginnings, however, have not be clearly ascertained and new discoveries are both continuous and ongoing. in approximately 1900 bc, ancient iron smelting sites existed in tamil nadu. in the near east, about 3, 500 bc, it was discovered that by combining copper and tin, a superior metal could be made, an alloy called bronze. this represented a major technological shift known as the bronze age. the extraction of iron from its ore into a workable metal is much more difficult than for copper or tin. the process appears to have been invented by the hittites in about 1200 bc, beginning the iron age. the secret of extracting and working iron was a key factor in the success of the philistines. historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. this includes the ancient and medieval kingdoms and empires of the middle east and near east, ancient iran, ancient egypt, ancient nubia, and anatolia in present - day turkey, ancient nok, carthage, the celts, greeks and romans of ancient europe, medieval europe, ancient and medieval china, ancient and medieval india, ancient and medieval japan, amongst others. a 16th century book by georg agricola, de re metallica, describes the highly developed and complex processes of mining metal ores, metal extraction, and metallurgy of the time. agricola has been described as the " father of metallurgy bare... the theory of the chaldeans and the egyptians. they say that the circumference of the universe is likened to the turnings of a well - rounded globe, the earth being a central point. they say that since its outline is spherical,... the earth should be the center of the universe, around which the heaven is whirling. " arnobius, another eastern christian writing sometime around 305 ad, described the round earth : " in the first place, indeed, the world itself is neither right nor left. it has neither upper nor lower regions, nor front nor back. for whatever is round and bounded on every side by the circumference of a solid sphere, has no beginning or end... " other advocates of a round earth included eusebius, hilary of poitiers, irenaeus, hippolytus of rome, firmicus maternus, ambrose, jerome, prudentius, favonius eulogius, and others. the only exceptions to this consensus up until the mid - fourth century were theophilus of antioch and lactantius, both of whom held anti - hellenistic views and associated the round - earth view with pagan cosmology. lactantius, a western christian writer and advisor to the first christian roman emperor, constantine, writing sometime between 304 and 313 ad, ridiculed the notion of antipodes and the philosophers who fancied that " the universe is round like a ball. they also thought that heaven revolves in accordance with the motion of the heavenly bodies.... for that reason, they constructed brass globes, as though after the figure of the universe. " the influential theologian and philosopher saint augustine, one of the four great church fathers of the western church, similarly objected to the " fable " of antipodes : but as to the fable that there are antipodes, that is to say, men on the opposite side of the earth, where the sun rises when it sets to us, men who walk with their feet opposite ours that is on no ground credible. and, indeed, it is not affirmed that this has been learned by historical knowledge, but by scientific conjecture, on the ground that the earth is suspended within the concavity of the sky, and that it has as much room on the one side of it as on the other : hence they say that the part that is beneath must also be inhabited. but they do not remark that, although it be supposed or scientifically the cosmos in many ways. one of the earliest indian cosmological texts pictures the earth as one of a stack of flat disks. in the vedic texts, dyaus ( heaven ) and prithvi ( earth ) are compared to wheels on an axle, yielding a flat model. they are also described as bowls or leather bags, yielding a concave model. according to macdonell : " the conception of the earth being a disc surrounded by an ocean does not appear in the samhitas. but it was naturally regarded as circular, being compared with a wheel ( 10. 89 ) and expressly called circular ( parimandala ) in the shatapatha brahmana. " by about the 5th century ad, the siddhanta astronomy texts of south asia, particularly of aryabhata, assume a spherical earth as they develop mathematical methods for quantitative astronomy for calendar and time keeping. the medieval indian texts called the puranas describe the earth as a flat - bottomed, circular disk with concentric oceans and continents. this general scheme is present not only in the hindu cosmologies, but also in buddhist and jain cosmologies of south asia. however, some puranas include other models. the fifth canto of the bhagavata purana, for example, includes sections that describe the earth both as flat and spherical. = = = = early christian church = = = = during the early period of the christian church, the spherical view continued to be widely held, with some notable exceptions. until the mid - fourth century ad, virtually all christian authors held that the earth was round. athenagoras, an eastern christian writing around the year 175 ad, said that the earth was spherical. methodius ( c. 290 ad ), an eastern christian writing against " the theory of the chaldeans and the egyptians " said : " let us first lay bare... the theory of the chaldeans and the egyptians. they say that the circumference of the universe is likened to the turnings of a well - rounded globe, the earth being a central point. they say that since its outline is spherical,... the earth should be the center of the universe, around which the heaven is whirling. " arnobius, another eastern christian writing sometime around 305 ad, described the round earth : " in the first place, indeed, the world itself is neither right nor left. it has neither upper nor lower regions, nor front nor back. for whatever Question: The joint that lies between the radius and the ulna is what kind of joint? A) pivot joint B) shaft joint C) socket joint D) hinge joint	A) pivot joint
Context: and cell phones are a particular challenge because the stream of data can interfere with focusing and learning. although these technologies affect adults too, young people may be more influenced by it as their developing brains can easily become habituated to switching tasks and become unaccustomed to sustaining attention. too much information, coming too rapidly, can overwhelm thinking. technology is " rapidly and profoundly altering our brains. " high exposure levels stimulate brain cell alteration and release neurotransmitters, which causes the strengthening of some neural pathways and the weakening of others. this leads to heightened stress levels on the brain that, at first, boost energy levels, but, over time, actually augment memory, impair cognition, lead to depression, and alter the neural circuitry of the hippocampus, amygdala and prefrontal cortex. these are the brain regions that control mood and thought. if unchecked, the underlying structure of the brain could be altered. overstimulation due to technology may begin too young. when children are exposed before the age of seven, important developmental tasks may be delayed, and bad learning habits might develop, which " deprives children of the exploration and play that they need to develop. " media psychology is an emerging specialty field that embraces electronic devices and the sensory behaviors occurring from the use of educational technology in learning. = = = sociocultural criticism = = = according to lai, " the learning environment is a complex system where the interplay and interactions of many things impact the outcome of learning. " when technology is brought into an educational setting, the pedagogical setting changes in that technology - driven teaching can change the entire meaning of an activity without adequate research validation. if technology monopolizes an activity, students can begin to develop the sense that " life would scarcely be thinkable without technology. " leo marx considered the word " technology " itself as problematic, susceptible to reification and " phantom objectivity ", which conceals its fundamental nature as something that is only valuable insofar as it benefits the human condition. technology ultimately comes down to affecting the relations between people, but this notion is obfuscated when technology is treated as an abstract notion devoid of good and evil. langdon winner makes a similar point by arguing that the underdevelopment of the philosophy of technology leaves us with an overly simplistic reduction in our discourse to the supposedly dichotomous notions of the " making " versus the " uses " of new technologies and that a narrow focus on " use and child health in boston, said of the digital generation, " their brains are rewarded not for staying on task, but for jumping to the next thing. the worry is we ' re raising a generation of kids in front of screens whose brains are going to be wired differently. " students have always faced distractions ; computers and cell phones are a particular challenge because the stream of data can interfere with focusing and learning. although these technologies affect adults too, young people may be more influenced by it as their developing brains can easily become habituated to switching tasks and become unaccustomed to sustaining attention. too much information, coming too rapidly, can overwhelm thinking. technology is " rapidly and profoundly altering our brains. " high exposure levels stimulate brain cell alteration and release neurotransmitters, which causes the strengthening of some neural pathways and the weakening of others. this leads to heightened stress levels on the brain that, at first, boost energy levels, but, over time, actually augment memory, impair cognition, lead to depression, and alter the neural circuitry of the hippocampus, amygdala and prefrontal cortex. these are the brain regions that control mood and thought. if unchecked, the underlying structure of the brain could be altered. overstimulation due to technology may begin too young. when children are exposed before the age of seven, important developmental tasks may be delayed, and bad learning habits might develop, which " deprives children of the exploration and play that they need to develop. " media psychology is an emerging specialty field that embraces electronic devices and the sensory behaviors occurring from the use of educational technology in learning. = = = sociocultural criticism = = = according to lai, " the learning environment is a complex system where the interplay and interactions of many things impact the outcome of learning. " when technology is brought into an educational setting, the pedagogical setting changes in that technology - driven teaching can change the entire meaning of an activity without adequate research validation. if technology monopolizes an activity, students can begin to develop the sense that " life would scarcely be thinkable without technology. " leo marx considered the word " technology " itself as problematic, susceptible to reification and " phantom objectivity ", which conceals its fundamental nature as something that is only valuable insofar as it benefits the human condition. technology ultimately comes down to affecting the relations between people, but this notion is obfuscated when technology is treated as an abstract notion devoid of this extra strength allows some structural components to fail without bridge collapse. the extra strength used in the design is called the margin of safety. eyes and ears provide working examples of passive redundancy. vision loss in one eye does not cause blindness but depth perception is impaired. hearing loss in one ear does not cause deafness but directionality is lost. performance decline is commonly associated with passive redundancy when a limited number of failures occur. active redundancy eliminates performance declines by monitoring the performance of individual devices, and this monitoring is used in voting logic. the voting logic is linked to switching that automatically reconfigures the components. error detection and correction and the global positioning system ( gps ) are two examples of active redundancy. electrical power distribution provides an example of active redundancy. several power lines connect each generation facility with customers. each power line includes monitors that detect overload. each power line also includes circuit breakers. the combination of power lines provides excess capacity. circuit breakers disconnect a power line when monitors detect an overload. power is redistributed across the remaining lines. at the toronto airport, there are 4 redundant electrical lines. each of the 4 lines supply enough power for the entire airport. a spot network substation uses reverse current relays to open breakers to lines that fail, but lets power continue to flow the airport. electrical power systems use power scheduling to reconfigure active redundancy. computing systems adjust the production output of each generating facility when other generating facilities are suddenly lost. this prevents blackout conditions during major events such as an earthquake. = = disadvantages = = charles perrow, author of normal accidents, has said that sometimes redundancies backfire and produce less, not more reliability. this may happen in three ways : first, redundant safety devices result in a more complex system, more prone to errors and accidents. second, redundancy may lead to shirking of responsibility among workers. third, redundancy may lead to increased production pressures, resulting in a system that operates at higher speeds, but less safely. = = voting logic = = voting logic uses performance monitoring to determine how to reconfigure individual components so that operation continues without violating specification limitations of the overall system. voting logic often involves computers, but systems composed of items other than computers may be reconfigured using voting logic. circuit breakers are an example of a form of non - computer voting logic. the simplest voting logic in computing systems involves two components : radiation exposure. marie curie died from aplastic anemia which resulted from her high levels of exposure. two scientists, an american and canadian respectively, harry daghlian and louis slotin, died after mishandling the same plutonium mass. unlike conventional weapons, the intense light, heat, and explosive force is not the only deadly component to a nuclear weapon. approximately half of the deaths from hiroshima and nagasaki died two to five years afterward from radiation exposure. civilian nuclear and radiological accidents primarily involve nuclear power plants. most common are nuclear leaks that expose workers to hazardous material. a nuclear meltdown refers to the more serious hazard of releasing nuclear material into the surrounding environment. the most significant meltdowns occurred at three mile island in pennsylvania and chernobyl in the soviet ukraine. the earthquake and tsunami on march 11, 2011 caused serious damage to three nuclear reactors and a spent fuel storage pond at the fukushima daiichi nuclear power plant in japan. military reactors that experienced similar accidents were windscale in the united kingdom and sl - 1 in the united states. military accidents usually involve the loss or unexpected detonation of nuclear weapons. the castle bravo test in 1954 produced a larger yield than expected, which contaminated nearby islands, a japanese fishing boat ( with one fatality ), and raised concerns about contaminated fish in japan. in the 1950s through 1970s, several nuclear bombs were lost from submarines and aircraft, some of which have never been recovered. the last twenty years have seen a marked decline in such accidents. = = examples of environmental benefits = = proponents of nuclear energy note that annually, nuclear - generated electricity reduces 470 million metric tons of carbon dioxide emissions that would otherwise come from fossil fuels. additionally, the amount of comparatively low waste that nuclear energy does create is safely disposed of by the large scale nuclear energy production facilities or it is repurposed / recycled for other energy uses. proponents of nuclear energy also bring to attention the opportunity cost of utilizing other forms of electricity. for example, the environmental protection agency estimates that coal kills 30, 000 people a year, as a result of its environmental impact, while 60 people died in the chernobyl disaster. a real world example of impact provided by proponents of nuclear energy is the 650, 000 ton increase in carbon emissions in the two months following the closure of the vermont yankee nuclear plant. = = see also = = atomic age lists of nuclear disasters and radioactive incidents nuclear power debate outline of nuclear technology radiology = = references = = = = external links = = nuclear energy institute – beneficial uses and myelomas can be made to fuse by chemical protocols, most often using polyethylene glycol. the myeloma cells are selected beforehand to ensure they are not secreting antibody themselves and that they lack the hypoxanthine - guanine phosphoribosyltransferase ( hgprt ) gene, making them sensitive ( or vulnerable ) to the hat medium ( see below ). fused cells are incubated in hat medium ( hypoxanthine - aminopterin - thymidine medium ) for roughly 10 to 14 days. aminopterin blocks the pathway that allows for nucleotide synthesis. hence, unfused myeloma cells die, as they cannot produce nucleotides by the de novo or salvage pathways because they lack hgprt. removal of the unfused myeloma cells is necessary because they have the potential to outgrow other cells, especially weakly established hybridomas. unfused b cells die as they have a short life span. in this way, only the b cell - myeloma hybrids survive, since the hgprt gene coming from the b cells is functional. these cells produce antibodies ( a property of b cells ) and are immortal ( a property of myeloma cells ). the incubated medium is then diluted into multi - well plates to such an extent that each well contains only one cell. since the antibodies in a well are produced by the same b cell, they will be directed towards the same epitope, and are thus monoclonal antibodies. the next stage is a rapid primary screening process, which identifies and selects only those hybridomas that produce antibodies of appropriate specificity. the first screening technique used is called elisa. the hybridoma culture supernatant, secondary enzyme labeled conjugate, and chromogenic substrate, are then incubated, and the formation of a colored product indicates a positive hybridoma. alternatively, immunocytochemical, western blot, and immunoprecipitation - mass spectrometry. unlike western blot assays, immunoprecipitation - mass spectrometry facilitates screening and ranking of clones which bind to the native ( non - denaturated ) forms of antigen proteins. flow cytometry screening has been used for primary screening of a large number ( ~ 1000 ) of hybridoma clones recognizing the native form of the antigen on the cell surface. in the flow the higher microwave band 3 – 6 ghz, and millimeter wave band, around 28 and 39 ghz. since these frequencies have a shorter range than previous cellphone bands, the cells will be smaller than the cells in previous cellular networks which could be many miles across. millimeter - wave cells will only be a few blocks long, and instead of a cell base station and antenna tower, they will have many small antennas attached to utility poles and buildings. satellite phone ( satphone ) – a portable wireless telephone similar to a cell phone, connected to the telephone network through a radio link to an orbiting communications satellite instead of through cell towers. they are more expensive than cell phones ; but their advantage is that, unlike a cell phone which is limited to areas covered by cell towers, satphones can be used over most or all of the geographical area of the earth. in order for the phone to communicate with a satellite using a small omnidirectional antenna, first - generation systems use satellites in low earth orbit, about 400 – 700 miles ( 640 – 1, 100 km ) above the surface. with an orbital period of about 100 minutes, a satellite can only be in view of a phone for about 4 – 15 minutes, so the call is " handed off " to another satellite when one passes beyond the local horizon. therefore, large numbers of satellites, about 40 to 70, are required to ensure that at least one satellite is in view continuously from each point on earth. other satphone systems use satellites in geostationary orbit in which only a few satellites are needed, but these cannot be used at high latitudes because of terrestrial interference. cordless phone – a landline telephone in which the handset is portable and communicates with the rest of the phone by a short - range full duplex radio link, instead of being attached by a cord. both the handset and the base station have low - power radio transceivers that handle the short - range bidirectional radio link. as of 2022, cordless phones in most nations use the dect transmission standard. land mobile radio system – short - range mobile or portable half - duplex radio transceivers operating in the vhf or uhf band that can be used without a license. they are often installed in vehicles, with the mobile units communicating with a dispatcher at a fixed base station. special systems with reserved frequencies are used by first responder services ; police, fire, ambulance, and emergency services, and other government services. other systems are made for 5g cellular network – next - generation cellular networks which began deployment in 2019. their major advantage is much higher data rates than previous cellular networks, up to 10 gbps ; 100 times faster than the previous cellular technology, 4g lte. the higher data rates are achieved partly by using higher frequency radio waves, in the higher microwave band 3 – 6 ghz, and millimeter wave band, around 28 and 39 ghz. since these frequencies have a shorter range than previous cellphone bands, the cells will be smaller than the cells in previous cellular networks which could be many miles across. millimeter - wave cells will only be a few blocks long, and instead of a cell base station and antenna tower, they will have many small antennas attached to utility poles and buildings. satellite phone ( satphone ) – a portable wireless telephone similar to a cell phone, connected to the telephone network through a radio link to an orbiting communications satellite instead of through cell towers. they are more expensive than cell phones ; but their advantage is that, unlike a cell phone which is limited to areas covered by cell towers, satphones can be used over most or all of the geographical area of the earth. in order for the phone to communicate with a satellite using a small omnidirectional antenna, first - generation systems use satellites in low earth orbit, about 400 – 700 miles ( 640 – 1, 100 km ) above the surface. with an orbital period of about 100 minutes, a satellite can only be in view of a phone for about 4 – 15 minutes, so the call is " handed off " to another satellite when one passes beyond the local horizon. therefore, large numbers of satellites, about 40 to 70, are required to ensure that at least one satellite is in view continuously from each point on earth. other satphone systems use satellites in geostationary orbit in which only a few satellites are needed, but these cannot be used at high latitudes because of terrestrial interference. cordless phone – a landline telephone in which the handset is portable and communicates with the rest of the phone by a short - range full duplex radio link, instead of being attached by a cord. both the handset and the base station have low - power radio transceivers that handle the short - range bidirectional radio link. as of 2022, cordless phones in most nations use the dect transmission standard. land mobile radio system – short - range mobile or portable half - duplex radio transceivers operating in the vhf or uhf when farther away. cell tower channel transmitter power is 50 w. current generation phones, called smartphones, have many functions besides making telephone calls, and therefore have several other radio transmitters and receivers that connect them with other networks : usually a wi - fi modem, a bluetooth modem, and a gps receiver. 5g cellular network – next - generation cellular networks which began deployment in 2019. their major advantage is much higher data rates than previous cellular networks, up to 10 gbps ; 100 times faster than the previous cellular technology, 4g lte. the higher data rates are achieved partly by using higher frequency radio waves, in the higher microwave band 3 – 6 ghz, and millimeter wave band, around 28 and 39 ghz. since these frequencies have a shorter range than previous cellphone bands, the cells will be smaller than the cells in previous cellular networks which could be many miles across. millimeter - wave cells will only be a few blocks long, and instead of a cell base station and antenna tower, they will have many small antennas attached to utility poles and buildings. satellite phone ( satphone ) – a portable wireless telephone similar to a cell phone, connected to the telephone network through a radio link to an orbiting communications satellite instead of through cell towers. they are more expensive than cell phones ; but their advantage is that, unlike a cell phone which is limited to areas covered by cell towers, satphones can be used over most or all of the geographical area of the earth. in order for the phone to communicate with a satellite using a small omnidirectional antenna, first - generation systems use satellites in low earth orbit, about 400 – 700 miles ( 640 – 1, 100 km ) above the surface. with an orbital period of about 100 minutes, a satellite can only be in view of a phone for about 4 – 15 minutes, so the call is " handed off " to another satellite when one passes beyond the local horizon. therefore, large numbers of satellites, about 40 to 70, are required to ensure that at least one satellite is in view continuously from each point on earth. other satphone systems use satellites in geostationary orbit in which only a few satellites are needed, but these cannot be used at high latitudes because of terrestrial interference. cordless phone – a landline telephone in which the handset is portable and communicates with the rest of the phone by a short - range full duplex radio link, instead of being attached by a cord. both the handset and the base station have low s spleen, the b cells are fused with immortalised myeloma cells. the fusion of the b cells with myeloma cells can be done using electrofusion. electrofusion causes the b cells and myeloma cells to align and fuse with the application of an electric field. alternatively, the b - cells and myelomas can be made to fuse by chemical protocols, most often using polyethylene glycol. the myeloma cells are selected beforehand to ensure they are not secreting antibody themselves and that they lack the hypoxanthine - guanine phosphoribosyltransferase ( hgprt ) gene, making them sensitive ( or vulnerable ) to the hat medium ( see below ). fused cells are incubated in hat medium ( hypoxanthine - aminopterin - thymidine medium ) for roughly 10 to 14 days. aminopterin blocks the pathway that allows for nucleotide synthesis. hence, unfused myeloma cells die, as they cannot produce nucleotides by the de novo or salvage pathways because they lack hgprt. removal of the unfused myeloma cells is necessary because they have the potential to outgrow other cells, especially weakly established hybridomas. unfused b cells die as they have a short life span. in this way, only the b cell - myeloma hybrids survive, since the hgprt gene coming from the b cells is functional. these cells produce antibodies ( a property of b cells ) and are immortal ( a property of myeloma cells ). the incubated medium is then diluted into multi - well plates to such an extent that each well contains only one cell. since the antibodies in a well are produced by the same b cell, they will be directed towards the same epitope, and are thus monoclonal antibodies. the next stage is a rapid primary screening process, which identifies and selects only those hybridomas that produce antibodies of appropriate specificity. the first screening technique used is called elisa. the hybridoma culture supernatant, secondary enzyme labeled conjugate, and chromogenic substrate, are then incubated, and the formation of a colored product indicates a positive hybridoma. alternatively, immunocytochemical, western blot, and immunoprecipitation - mass spectrometry. unlike western blot assays, immunoprecipitation - mass spectromet in space, can adversely affect the earth ' s environment. some hypergolic rocket propellants, such as hydrazine, are highly toxic prior to combustion, but decompose into less toxic compounds after burning. rockets using hydrocarbon fuels, such as kerosene, release carbon dioxide and soot in their exhaust. carbon dioxide emissions are insignificant compared to those from other sources ; on average, the united states consumed 803 million us gal ( 3. 0 million m3 ) of liquid fuels per day in 2014, while a single falcon 9 rocket first stage burns around 25, 000 us gallons ( 95 m3 ) of kerosene fuel per launch. even if a falcon 9 were launched every single day, it would only represent 0. 006 % of liquid fuel consumption ( and carbon dioxide emissions ) for that day. additionally, the exhaust from lox - and lh2 - fueled engines, like the ssme, is almost entirely water vapor. nasa addressed environmental concerns with its canceled constellation program in accordance with the national environmental policy act in 2011. in contrast, ion engines use harmless noble gases like xenon for propulsion. an example of nasa ' s environmental efforts is the nasa sustainability base. additionally, the exploration sciences building was awarded the leed gold rating in 2010. on may 8, 2003, the environmental protection agency recognized nasa as the first federal agency to directly use landfill gas to produce energy at one of its facilities — the goddard space flight center, greenbelt, maryland. in 2018, nasa along with other companies including sensor coating systems, pratt & whitney, monitor coating and utrc launched the project caution ( coatings for ultra high temperature detection ). this project aims to enhance the temperature range of the thermal history coating up to 1, 500 °c ( 2, 730 °f ) and beyond. the final goal of this project is improving the safety of jet engines as well as increasing efficiency and reducing co2 emissions. = = = climate change = = = nasa also researches and publishes on climate change. its statements concur with the global scientific consensus that the climate is warming. bob walker, who has advised former us president donald trump on space issues, has advocated that nasa should focus on space exploration and that its climate study operations should be transferred to other agencies such as noaa. former nasa atmospheric scientist j. marshall shepherd countered that earth science study was built into nasa ' s mission at its creation in the 1958 national aeronautics and space act. nasa won the 2020 webby people ' s voice award for green in the category Question: Because it damages hair cells, what is the most cause of hearing loss in adults? A) bacteria B) ear wax C) exposure to noise D) water in the ears	C) exposure to noise
Context: , translation, and post - translational modification of a protein. gene expression can be influenced by positive or negative regulation, depending on which of the two types of regulatory proteins called transcription factors bind to the dna sequence close to or at a promoter. a cluster of genes that share the same promoter is called an operon, found mainly in prokaryotes and some lower eukaryotes ( e. g., caenorhabditis elegans ). in positive regulation of gene expression, the activator is the transcription factor that stimulates transcription when it binds to the sequence near or at the promoter. negative regulation occurs when another transcription factor called a repressor binds to a dna sequence called an operator, which is part of an operon, to prevent transcription. repressors can be inhibited by compounds called inducers ( e. g., allolactose ), thereby allowing transcription to occur. specific genes that can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial to rna to protein. there are two gene expression processes : transcription ( dna to rna ) and translation ( rna to protein ). = = = gene regulation = = = the regulation of gene expression by environmental factors and during different stages of development can occur at each step of the process such as transcription, rna splicing, translation, and post - translational modification of a protein. gene expression can be influenced by positive or negative regulation, depending on which of the two types of regulatory proteins called transcription factors bind to the dna sequence close to or at a promoter. a cluster of genes that share the same promoter is called an operon, found mainly in prokaryotes and some lower eukaryotes ( e. g., caenorhabditis elegans ). in positive regulation of gene expression, the activator is the transcription factor that stimulates transcription when it binds to the sequence near or at the promoter. negative regulation occurs when another transcription factor called a repressor binds to a dna sequence called an operator, which is part of an operon, to prevent transcription. repressors can be inhibited by compounds called inducers ( e. g., allolactose ), thereby allowing transcription to occur. specific genes that can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due not always mean it is required, especially when dealing with genetic or functional redundancy. tracking experiments, which seek to gain information about the localisation and interaction of the desired protein. one way to do this is to replace the wild - type gene with a ' fusion ' gene, which is a juxtaposition of the wild - type gene with a reporting element such as green fluorescent protein ( gfp ) that will allow easy visualisation of the products of the genetic modification. while this is a useful technique, the manipulation can destroy the function of the gene, creating secondary effects and possibly calling into question the results of the experiment. more sophisticated techniques are now in development that can track protein products without mitigating their function, such as the addition of small sequences that will serve as binding motifs to monoclonal antibodies. expression studies aim to discover where and when specific proteins are produced. in these experiments, the dna sequence before the dna that codes for a protein, known as a gene ' s promoter, is reintroduced into an organism with the protein coding region replaced by a reporter gene such as gfp or an enzyme that catalyses the production of a dye. thus the time and place where a particular protein is produced can be observed. expression studies can be taken a step further by altering the promoter to find which pieces are crucial for the proper expression of the gene and are actually bound by transcription factor proteins ; this process is known as promoter bashing. = = = industrial = = = organisms can have their cells transformed with a gene coding for a useful protein, such as an enzyme, so that they will overexpress the desired protein. mass quantities of the protein can then be manufactured by growing the transformed organism in bioreactor equipment using industrial fermentation, and then purifying the protein. some genes do not work well in bacteria, so yeast, insect cells or mammalian cells can also be used. these techniques are used to produce medicines such as insulin, human growth hormone, and vaccines, supplements such as tryptophan, aid in the production of food ( chymosin in cheese making ) and fuels. other applications with genetically engineered bacteria could involve making them perform tasks outside their natural cycle, such as making biofuels, cleaning up oil spills, carbon and other toxic waste and detecting arsenic in drinking water. certain genetically modified microbes can also be used in biomining and bioremediation, due to their ability to extract heavy metals from their environment and incorporate them into compounds that are more easily recover of epigenetic change is the marking of the genes by dna methylation which determines whether they will be expressed or not. gene expression can also be controlled by repressor proteins that attach to silencer regions of the dna and prevent that region of the dna code from being expressed. epigenetic marks may be added or removed from the dna during programmed stages of development of the plant, and are responsible, for example, for the differences between anthers, petals and normal leaves, despite the fact that they all have the same underlying genetic code. epigenetic changes may be temporary or may remain through successive cell divisions for the remainder of the cell ' s life. some epigenetic changes have been shown to be heritable, while others are reset in the germ cells. epigenetic changes in eukaryotic biology serve to regulate the process of cellular differentiation. during morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, with one allele inducing a change on the other. = = plant evolution = = the chloroplasts of plants have a number of biochemical, structural and genetic similarities to cyanobacteria, ( commonly but incorrectly known as " blue - green algae " ) and are thought to be derived from an can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial differences in gene expression. a small fraction of the genes in an organism ' s genome called the developmental - genetic toolkit control the development of that organism. these toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. among the most important toolkit genes are the hox genes. hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva. = = evolution = = = = = evolutionary processes = = = evolution is a central organizing concept in biology. it is the change in heritable characteristics of populations over successive generations. in artificial selection, animals were selectively bred for specific traits. given that traits are inherited, populations contain a varied mix of traits, and reproduction is able to increase any population, founded in 1976 and started the production of human proteins. genetically engineered human insulin was produced in 1978 and insulin - producing bacteria were commercialised in 1982. genetically modified food has been sold since 1994, with the release of the flavr savr tomato. the flavr savr was engineered to have a longer shelf life, but most current gm crops are modified to increase resistance to insects and herbicides. glofish, the first gmo designed as a pet, was sold in the united states in december 2003. in 2016 salmon modified with a growth hormone were sold. genetic engineering has been applied in numerous fields including research, medicine, industrial biotechnology and agriculture. in research, gmos are used to study gene function and expression through loss of function, gain of function, tracking and expression experiments. by knocking out genes responsible for certain conditions it is possible to create animal model organisms of human diseases. as well as producing hormones, vaccines and other drugs, genetic engineering has the potential to cure genetic diseases through gene therapy. chinese hamster ovary ( cho ) cells are used in industrial genetic engineering. additionally mrna vaccines are made through genetic engineering to prevent infections by viruses such as covid - 19. the same techniques that are used to produce drugs can also have industrial applications such as producing enzymes for laundry detergent, cheeses and other products. the rise of commercialised genetically modified crops has provided economic benefit to farmers in many different countries, but has also been the source of most of the controversy surrounding the technology. this has been present since its early use ; the first field trials were destroyed by anti - gm activists. although there is a scientific consensus that currently available food derived from gm crops poses no greater risk to human health than conventional food, critics consider gm food safety a leading concern. gene flow, impact on non - target organisms, control of the food supply and intellectual property rights have also been raised as potential issues. these concerns have led to the development of a regulatory framework, which started in 1975. it has led to an international treaty, the cartagena protocol on biosafety, that was adopted in 2000. individual countries have developed their own regulatory systems regarding gmos, with the most marked differences occurring between the united states and europe. = = overview = = genetic engineering is a process that alters the genetic structure of an organism by either removing or introducing dna, or modifying existing genetic material in situ. unlike traditional animal and plant breeding, which involves doing multiple crosses and then selecting for the organism with the desired phenotype, occurs when another transcription factor called a repressor binds to a dna sequence called an operator, which is part of an operon, to prevent transcription. repressors can be inhibited by compounds called inducers ( e. g., allolactose ), thereby allowing transcription to occur. specific genes that can be activated by inducers are called inducible genes, in contrast to constitutive genes that are almost constantly active. in contrast to both, structural genes encode proteins that are not involved in gene regulation. in addition to regulatory events involving the promoter, gene expression can also be regulated by epigenetic changes to chromatin, which is a complex of dna and protein found in eukaryotic cells. = = = genes, development, and evolution = = = development is the process by which a multicellular organism ( plant or animal ) goes through a series of changes, starting from a single cell, and taking on various forms that are characteristic of its life cycle. there are four key processes that underlie development : determination, differentiation, morphogenesis, and growth. determination sets the developmental fate of a cell, which becomes more restrictive during development. differentiation is the process by which specialized cells arise from less specialized cells such as stem cells. stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. cellular differentiation dramatically changes a cell ' s size, shape, membrane potential, metabolic activity, and responsiveness to signals, which are largely due to highly controlled modifications in gene expression and epigenetics. with a few exceptions, cellular differentiation almost never involves a change in the dna sequence itself. thus, different cells can have very different physical characteristics despite having the same genome. morphogenesis, or the development of body form, is the result of spatial differences in gene expression. a small fraction of the genes in an organism ' s genome called the developmental - genetic toolkit control the development of that organism. these toolkit genes are highly conserved among phyla, meaning that they are ancient and very similar in widely separated groups of animals. differences in deployment of toolkit genes affect the body plan and the number, identity, and pattern of body parts. among the most important toolkit genes are the hox genes. hox genes determine where repeating parts, such as the many vertebrae of snakes, will grow in a developing embryo or larva. = = evolution = = = = = evolutionary for the treatment of diabetes, was previously extracted from the pancreas of abattoir animals ( cattle or pigs ). the genetically engineered bacteria are able to produce large quantities of synthetic human insulin at relatively low cost. biotechnology has also enabled emerging therapeutics like gene therapy. the application of biotechnology to basic science ( for example through the human genome project ) has also dramatically improved our understanding of biology and as our scientific knowledge of normal and disease biology has increased, our ability to develop new medicines to treat previously untreatable diseases has increased as well. genetic testing allows the genetic diagnosis of vulnerabilities to inherited diseases, and can also be used to determine a child ' s parentage ( genetic mother and father ) or in general a person ' s ancestry. in addition to studying chromosomes to the level of individual genes, genetic testing in a broader sense includes biochemical tests for the possible presence of genetic diseases, or mutant forms of genes associated with increased risk of developing genetic disorders. genetic testing identifies changes in chromosomes, genes, or proteins. most of the time, testing is used to find changes that are associated with inherited disorders. the results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person ' s chance of developing or passing on a genetic disorder. as of 2011 several hundred genetic tests were in use. since genetic testing may open up ethical or psychological problems, genetic testing is often accompanied by genetic counseling. = = = agriculture = = = genetically modified crops ( " gm crops ", or " biotech crops " ) are plants used in agriculture, the dna of which has been modified with genetic engineering techniques. in most cases, the main aim is to introduce a new trait that does not occur naturally in the species. biotechnology firms can contribute to future food security by improving the nutrition and viability of urban agriculture. furthermore, the protection of intellectual property rights encourages private sector investment in agrobiotechnology. examples in food crops include resistance to certain pests, diseases, stressful environmental conditions, resistance to chemical treatments ( e. g. resistance to a herbicide ), reduction of spoilage, or improving the nutrient profile of the crop. examples in non - food crops include production of pharmaceutical agents, biofuels, and other industrially useful goods, as well as for bioremediation. farmers have widely adopted gm technology. between 1996 and 2011, the total surface area of land cultivated with gm crops had increased by a factor of 94, from 17, 000 to 1, 600, 000 square and the creation of genetically modified crops. = = = epigenetics = = = epigenetics is the study of heritable changes in gene function that cannot be explained by changes in the underlying dna sequence but cause the organism ' s genes to behave ( or " express themselves " ) differently. one example of epigenetic change is the marking of the genes by dna methylation which determines whether they will be expressed or not. gene expression can also be controlled by repressor proteins that attach to silencer regions of the dna and prevent that region of the dna code from being expressed. epigenetic marks may be added or removed from the dna during programmed stages of development of the plant, and are responsible, for example, for the differences between anthers, petals and normal leaves, despite the fact that they all have the same underlying genetic code. epigenetic changes may be temporary or may remain through successive cell divisions for the remainder of the cell ' s life. some epigenetic changes have been shown to be heritable, while others are reset in the germ cells. epigenetic changes in eukaryotic biology serve to regulate the process of cellular differentiation. during morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. a single fertilised egg cell, the zygote, gives rise to the many different plant cell types including parenchyma, xylem vessel elements, phloem sieve tubes, guard cells of the epidermis, etc. as it continues to divide. the process results from the epigenetic activation of some genes and inhibition of others. unlike animals, many plant cells, particularly those of the parenchyma, do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. exceptions include highly lignified cells, the sclerenchyma and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. while plants use many of the same epigenetic mechanisms as animals, such as chromatin remodelling, an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate. epigenetic changes can lead to paramutations, which do not follow the mendelian heritage rules. these epigenetic marks are carried from one generation to the next, the cell ' s dna, or mitochondria, which generate adenosine triphosphate ( atp ) to power cellular processes. other organelles such as endoplasmic reticulum and golgi apparatus play a role in the synthesis and packaging of proteins, respectively. biomolecules such as proteins can be engulfed by lysosomes, another specialized organelle. plant cells have additional organelles that distinguish them from animal cells such as a cell wall that provides support for the plant cell, chloroplasts that harvest sunlight energy to produce sugar, and vacuoles that provide storage and structural support as well as being involved in reproduction and breakdown of plant seeds. eukaryotic cells also have cytoskeleton that is made up of microtubules, intermediate filaments, and microfilaments, all of which provide support for the cell and are involved in the movement of the cell and its organelles. in terms of their structural composition, the microtubules are made up of tubulin ( e. g., α - tubulin and β - tubulin ) whereas intermediate filaments are made up of fibrous proteins. microfilaments are made up of actin molecules that interact with other strands of proteins. = = = metabolism = = = all cells require energy to sustain cellular processes. metabolism is the set of chemical reactions in an organism. the three main purposes of metabolism are : the conversion of food to energy to run cellular processes ; the conversion of food / fuel to monomer building blocks ; and the elimination of metabolic wastes. these enzyme - catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. metabolic reactions may be categorized as catabolic — the breaking down of compounds ( for example, the breaking down of glucose to pyruvate by cellular respiration ) ; or anabolic — the building up ( synthesis ) of compounds ( such as proteins, carbohydrates, lipids, and nucleic acids ). usually, catabolism releases energy, and anabolism consumes energy. the chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme. enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy that will not occur by themselves, by coupling them to spontaneous reactions that release energy. enzymes act as catalysts — they allow a Question: What is regulated to ensure that the correct proteins are made? A) Fat expression B) gene expression C) acids expression D) variation expression	B) gene expression
Context: in mathematics, a reflection ( also spelled reflexion ) is a mapping from a euclidean space to itself that is an isometry with a hyperplane as the set of fixed points ; this set is called the axis ( in dimension 2 ) or plane ( in dimension 3 ) of reflection. the image of a figure by a reflection is its mirror image in the axis or plane of reflection. for example the mirror image of the small latin letter p for a reflection with respect to a vertical axis ( a vertical reflection ) would look like q. its image by reflection in a horizontal axis ( a horizontal reflection ) would look like b. a reflection is an involution : when applied twice in succession, every point returns to its original location, and every geometrical object is restored to its original state. the term reflection is sometimes used for a larger class of mappings from a euclidean space to itself, namely the non - identity isometries that are involutions. the set of fixed points ( the " mirror " ) of such an isometry is an affine subspace, but is possibly smaller than a hyperplane. for instance a reflection through a point is an involutive isometry with just one fixed point ; the image of the letter p under it would look like a d. this operation is also known as a central inversion ( coxeter 1969, § 7. 2 ), and exhibits euclidean space as a symmetric space. in a euclidean vector space, the reflection in the point situated at the origin is the same as vector negation. other examples include reflections in a line in three - dimensional space. typically, however, unqualified use of the term " reflection " means reflection in a hyperplane. some mathematicians use " flip " as a synonym for " reflection ". = = construction = = in a plane ( or, respectively, 3 - dimensional ) geometry, to find the reflection of a point drop a perpendicular from the point to the line ( plane ) used for reflection, and extend it the same distance on the other side. to find the reflection of a figure, reflect each point in the figure. to reflect point p through the line ab using compass and straightedge, proceed as follows ( see figure ) : step 1 ( red ) : construct a circle with center at p and some fixed radius r to create points a ′ and b ′ on the line ab, which will be equidistant from p. step 2 ( green ) : construct circles centered at a ′ and b ′ having radius r beacon transmits two signals simultaneously on different frequencies. a directional antenna transmits a beam of radio waves that rotates like a lighthouse at a fixed rate, 30 times per second. when the directional beam is facing north, an omnidirectional antenna transmits a pulse. by measuring the difference in phase of these two signals, an aircraft can determine its bearing ( or " radial " ) from the station accurately. by taking a bearing on two vor beacons an aircraft can determine its position ( called a " fix " ) to an accuracy of about 90 metres ( 300 ft ). most vor beacons also have a distance measuring capability, called distance measuring equipment ( dme ) ; these are called vor / dme ' s. the aircraft transmits a radio signal to the vor / dme beacon and a transponder transmits a return signal. from the propagation delay between the transmitted and received signal the aircraft can calculate its distance from the beacon. this allows an aircraft to determine its location " fix " from only one vor beacon. since line - of - sight vhf frequencies are used vor beacons have a range of about 200 miles for aircraft at cruising altitude. tacan is a similar military radio beacon system which transmits in 962 – 1213 mhz, and a combined vor and tacan beacon is called a vortac. the number of vor beacons is declining as aviation switches to the rnav system that relies on global positioning system satellite navigation. instrument landing system ( ils ) - a short range radio navigation aid at airports which guides aircraft landing in low visibility conditions. it consists of multiple antennas at the end of each runway that radiate two beams of radio waves along the approach to the runway : the localizer ( 108 to 111. 95 mhz frequency ), which provides horizontal guidance, a heading line to keep the aircraft centered on the runway, and the glideslope ( 329. 15 to 335 mhz ) for vertical guidance, to keep the aircraft descending at the proper rate for a smooth touchdown at the correct point on the runway. each aircraft has a receiver instrument and antenna which receives the beams, with an indicator to tell the pilot whether he is on the correct horizontal and vertical approach. the ils beams are receivable for at least 15 miles, and have a radiated power of 25 watts. ils systems at airports are being replaced by systems that use satellite navigation. non - directional beacon ( ndb ) – legacy fixed radio beacons used before the vo reflection is its mirror image in the axis or plane of reflection. for example the mirror image of the small latin letter p for a reflection with respect to a vertical axis ( a vertical reflection ) would look like q. its image by reflection in a horizontal axis ( a horizontal reflection ) would look like b. a reflection is an involution : when applied twice in succession, every point returns to its original location, and every geometrical object is restored to its original state. the term reflection is sometimes used for a larger class of mappings from a euclidean space to itself, namely the non - identity isometries that are involutions. the set of fixed points ( the " mirror " ) of such an isometry is an affine subspace, but is possibly smaller than a hyperplane. for instance a reflection through a point is an involutive isometry with just one fixed point ; the image of the letter p under it would look like a d. this operation is also known as a central inversion ( coxeter 1969, § 7. 2 ), and exhibits euclidean space as a symmetric space. in a euclidean vector space, the reflection in the point situated at the origin is the same as vector negation. other examples include reflections in a line in three - dimensional space. typically, however, unqualified use of the term " reflection " means reflection in a hyperplane. some mathematicians use " flip " as a synonym for " reflection ". = = construction = = in a plane ( or, respectively, 3 - dimensional ) geometry, to find the reflection of a point drop a perpendicular from the point to the line ( plane ) used for reflection, and extend it the same distance on the other side. to find the reflection of a figure, reflect each point in the figure. to reflect point p through the line ab using compass and straightedge, proceed as follows ( see figure ) : step 1 ( red ) : construct a circle with center at p and some fixed radius r to create points a ′ and b ′ on the line ab, which will be equidistant from p. step 2 ( green ) : construct circles centered at a ′ and b ′ having radius r. p and q will be the points of intersection of these two circles. point q is then the reflection of point p through line ab. = = properties = = the matrix for a reflection is orthogonal with determinant −1 and eigenvalues −1, 1, 1,..., 1. = = when 0 is said to be neither positive nor negative, the following phrases may refer to the sign of a number : a number is positive if it is greater than zero. a number is negative if it is less than zero. a number is non - negative if it is greater than or equal to zero. a number is non - positive if it is less than or equal to zero. when 0 is said to be both positive and negative, modified phrases are used to refer to the sign of a number : a number is strictly positive if it is greater than zero. a number is strictly negative if it is less than zero. a number is positive if it is greater than or equal to zero. a number is negative if it is less than or equal to zero. for example, the absolute value of a real number is always " non - negative ", but is not necessarily " positive " in the first interpretation, whereas in the second interpretation, it is called " positive " — though not necessarily " strictly positive ". the same terminology is sometimes used for functions that yield real or other signed values. for example, a function would be called a positive function if its values are positive for all arguments of its domain, or a non - negative function if all of its values are non - negative. = = = complex numbers = = = complex numbers are impossible to order, so they cannot carry the structure of an ordered ring, and, accordingly, cannot be partitioned into positive and negative complex numbers. they do, however, share an attribute with the reals, which is called absolute value or magnitude. magnitudes are always non - negative real numbers, and to any non - zero number there belongs a positive real number, its absolute value. for example, the absolute value of −3 and the absolute value of 3 are both equal to 3. this is written in symbols as \| −3 \| = 3 and \| 3 \| = 3. in general, any arbitrary real value can be specified by its magnitude and its sign. using the standard encoding, any real value is given by the product of the magnitude and the sign in standard encoding. this relation can be generalized to define a sign for complex numbers. since the real and complex numbers both form a field and contain the positive reals, they also contain the reciprocals of the magnitudes of all non - zero numbers. this means that any non - zero number may be multiplied with the reciprocal of its magnitude, that is, divided by its magnitude. it is immediate that the quotient one phenomenological explanation of superluminal propagation of neutrinos, which may have been observed by opera and minos, is that neutrinos travel faster inside of matter than in vacuum. if so neutrinos exhibit refraction inside matter and should exhibit other manifestations of refraction, such as deflection and reflection. such refraction would be easily detectable through the momentum imparted to appropriately shaped refractive material inserted into the neutrino beam. for numi this could be as large as ~ 10g cm / s. if these effect were found, they would provide new ways of manipulating and detecting neutrinos. reasons why this scenario seems implausible are given, however it is still worthwhile to conduct simple searches for differential refraction of neutrinos. a graviton laser works, in principle, by the stimulated emission of coherent gravitons from a lasing medium. for significant amplification, we must have a very long path length and / or very high densities. black holes and the existence of weakly interacting sub - ev dark matter particles ( wisps ) solve both of these obstacles. orbiting trajectories for massless particles around black holes are well understood \ cite { mtw } and allow for arbitrarily long graviton path lengths. superradiance from kerr black holes of wisps can provide the sufficiently high density \ cite { abh }. this suggests that black holes can act as efficient graviton lasers. thus directed graviton laser beams have been emitted since the beginning of the universe and give rise to new sources of gravitational wave signals. to be in the path of particularly harmfully amplified graviton death rays will not be pleasant. the attenuation length and refractive index of liquid xenon for intrinsic scintillation light ( 178nm ) have been measured in a single experiment. the value obtained for attenuation length is 364 + - 18 mm. the refractive index is found to be 1. 69 + - 0. 02. both values were measured at a temperature of 170 + - 1 k. reflect radar waves back to the emitting radar is with orthogonal metal plates, forming a corner reflector consisting of either a dihedral ( two plates ) or a trihedral ( three orthogonal plates ). this configuration occurs in the tail of a conventional aircraft, where the vertical and horizontal components of the tail are set at right angles. stealth aircraft such as the f - 117 use a different arrangement, tilting the tail surfaces to reduce corner reflections formed between them. a more radical method is to omit the tail, as in the b - 2 spirit. the b - 2 ' s clean, low - drag flying wing configuration gives it exceptional range and reduces its radar profile. the flying wing design most closely resembles a so - called infinite flat plate ( as vertical control surfaces dramatically increase rcs ), the perfect stealth shape, as it would have no angles to reflect back radar waves. in addition to altering the tail, stealth design must bury the engines within the wing or fuselage, or in some cases where stealth is applied to an extant aircraft, install baffles in the air intakes, so that the compressor blades are not visible to radar. a stealthy shape must be devoid of complex bumps or protrusions of any kind, meaning that weapons, fuel tanks, and other stores must not be carried externally. any stealthy vehicle becomes un - stealthy when a door or hatch opens. parallel alignment of edges or even surfaces is also often used in stealth designs. the technique involves using a small number of edge orientations in the shape of the structure. for example, on the f - 22a raptor, the leading edges of the wing and the tail planes are set at the same angle. other smaller structures, such as the air intake bypass doors and the air refueling aperture, also use the same angles. the effect of this is to return a narrow radar signal in a very specific direction away from the radar emitter rather than returning a diffuse signal detectable at many angles. the effect is sometimes called " glitter " after the very brief signal seen when the reflected beam passes across a detector. it can be difficult for the radar operator to distinguish between a glitter event and a digital glitch in the processing system. stealth airframes sometimes display distinctive serrations on some exposed edges, such as the engine ports. the yf - 23 has such serrations on the exhaust ports. this is another example in the parallel alignment of features, this time on the external airframe. the shaping requirements detracted greatly from the f - 117 ' using the same method we provide negative answers to the following questions : is it possible to find real equations for complex polynomials in two variables up to topological equivalence ( lee rudolph )? can two topologically equivalent polynomials be connected by a continuous family of topologically equivalent polynomials? called the natural logarithm. a real function f is monotonic in an interval if the sign of f ( x ) − f ( y ) x − y { \ displaystyle { \ frac { f ( x ) - f ( y ) } { x - y } } } does not depend of the choice of x and y in the interval. if the function is differentiable in the interval, it is monotonic if the sign of the derivative is constant in the interval. if a real function f is monotonic in an interval i, it has an inverse function, which is a real function with domain f ( i ) and image i. this is how inverse trigonometric functions are defined in terms of trigonometric functions, where the trigonometric functions are monotonic. another example : the natural logarithm is monotonic on the positive real numbers, and its image is the whole real line ; therefore it has an inverse function that is a bijection between the real numbers and the positive real numbers. this inverse is the exponential function. many other real functions are defined either by the implicit function theorem ( the inverse function is a particular instance ) or as solutions of differential equations. for example, the sine and the cosine functions are the solutions of the linear differential equation y ″ + y = 0 { \ displaystyle y ' ' + y = 0 } such that sin 0 = 0, cos 0 = 1, ∂ sin x ∂ x ( 0 ) = 1, ∂ cos x ∂ x ( 0 ) = 0. { \ displaystyle \ sin 0 = 0, \ quad \ cos 0 = 1, \ quad { \ frac { \ partial \ sin x } { \ partial x } } ( 0 ) = 1, \ quad { \ frac { \ partial \ cos x } { \ partial x } } ( 0 ) = 0. } = = = vector - valued function = = = when the elements of the codomain of a function are vectors, the function is said to be a vector - valued function. these functions are particularly useful in applications, for example modeling physical properties. for example, the function that associates to each point of a fluid its velocity vector is a vector - valued function. some vector - valued functions are defined on a subset of r n { \ displaystyle \ mathbb { r } ^ { n } } or other spaces that share geometric or topological properties of r n { \ displaystyle \ mathbb { Question: What mirrors diverge light rays and, thus, have a negative focal length? A) curved B) diffraction C) convex D) concave	C) convex

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