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https://en.wikipedia.org/wiki/Augmented%20pentagonal%20prism
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In geometry, the augmented pentagonal prism is one of the Johnson solids (). As the name suggests, it can be constructed by augmenting a pentagonal prism by attaching a square pyramid () to one of its equatorial faces.
External links
Johnson solids
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https://en.wikipedia.org/wiki/Biaugmented%20pentagonal%20prism
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In geometry, the biaugmented pentagonal prism is one of the Johnson solids (). As the name suggests, it can be constructed by doubly augmenting a pentagonal prism by attaching square pyramids () to two of its nonadjacent equatorial faces. (The solid obtained by attaching pyramids to adjacent equatorial faces is not convex, and thus not a Johnson solid.)
External links
Johnson solids
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https://en.wikipedia.org/wiki/Augmented%20hexagonal%20prism
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In geometry, the augmented hexagonal prism is one of the Johnson solids (). As the name suggests, it can be constructed by augmenting a hexagonal prism by attaching a square pyramid () to one of its equatorial faces. When two or three such pyramids are attached, the result may be a parabiaugmented hexagonal prism (), a metabiaugmented hexagonal prism (), or a triaugmented hexagonal prism ().
External links
Johnson solids
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https://en.wikipedia.org/wiki/Parabiaugmented%20hexagonal%20prism
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In geometry, the parabiaugmented hexagonal prism is one of the Johnson solids (). As the name suggests, it can be constructed by doubly augmenting a hexagonal prism by attaching square pyramids () to two of its nonadjacent, parallel (opposite) equatorial faces. Attaching the pyramids to nonadjacent, nonparallel equatorial faces yields a metabiaugmented hexagonal prism (). (The solid obtained by attaching pyramids to adjacent equatorial faces is not convex, and thus not a Johnson solid.)
External links
Johnson solids
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https://en.wikipedia.org/wiki/Metabiaugmented%20hexagonal%20prism
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In geometry, the metabiaugmented hexagonal prism is one of the Johnson solids (). As the name suggests, it can be constructed by doubly augmenting a hexagonal prism by attaching square pyramids () to two of its nonadjacent, nonparallel equatorial faces. Attaching the pyramids to opposite equatorial faces yields a parabiaugmented hexagonal prism. (The solid obtained by attaching pyramids to adjacent equatorial faces is not convex, and thus not a Johnson solid.)
See also
Hexagonal prism
External links
Johnson solids
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https://en.wikipedia.org/wiki/Triaugmented%20hexagonal%20prism
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In geometry, the triaugmented hexagonal prism is one of the Johnson solids (). As the name suggests, it can be constructed by triply augmenting a hexagonal prism by attaching square pyramids () to three of its nonadjacent equatorial faces.
See also
Hexagonal prism
References
External links
Johnson solids
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https://en.wikipedia.org/wiki/Augmented%20dodecahedron
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In geometry, the augmented dodecahedron is one of the Johnson solids (), consisting of a dodecahedron with a pentagonal pyramid () attached to one of the faces. When two or three such pyramids are attached, the result may be a parabiaugmented dodecahedron (), a metabiaugmented dodecahedron (), or a triaugmented dodecahedron ().
External links
Johnson solids
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https://en.wikipedia.org/wiki/Parabiaugmented%20dodecahedron
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In geometry, the parabiaugmented dodecahedron is one of the Johnson solids (). It can be seen as a dodecahedron with two pentagonal pyramids () attached to opposite faces. When pyramids are attached to a dodecahedron in other ways, they may result in an augmented dodecahedron (), a metabiaugmented dodecahedron (), a triaugmented dodecahedron (), or even a pentakis dodecahedron if the faces are made to be irregular.
The dual of this solid is the Gyroelongated pentagonal bifrustum.
External links
Johnson solids
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https://en.wikipedia.org/wiki/Metabiaugmented%20dodecahedron
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In geometry, the metabiaugmented dodecahedron is one of the Johnson solids (). It can be viewed as a dodecahedron with two pentagonal pyramids () attached to two faces that are separated by one face. (The two faces are not opposite, but not adjacent either.) When pyramids are attached to a dodecahedron in other ways, they may result in an augmented dodecahedron (), a parabiaugmented dodecahedron (), a triaugmented dodecahedron (), or even a pentakis dodecahedron if the faces are made to be irregular.
External links
Johnson solids
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https://en.wikipedia.org/wiki/Triaugmented%20dodecahedron
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In geometry, the triaugmented dodecahedron is one of the Johnson solids (). It can be seen as a dodecahedron with three pentagonal pyramids () attached to nonadjacent faces. When pyramids are attached to a dodecahedron in other ways, they may result in an augmented dodecahedron (), a parabiaugmented dodecahedron (), a metabiaugmented dodecahedron (), or even a pentakis dodecahedron if the faces are made to be irregular.
External links
Johnson solids
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https://en.wikipedia.org/wiki/Parabigyrate%20rhombicosidodecahedron
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In geometry, the parabigyrate rhombicosidodecahedron is one of the Johnson solids (). It can be constructed as a rhombicosidodecahedron with two opposing pentagonal cupolae rotated through 36 degrees. It is also a canonical polyhedron.
Alternative Johnson solids, constructed by rotating different cupolae of a rhombicosidodecahedron, are:
The gyrate rhombicosidodecahedron () where only one cupola is rotated;
The metabigyrate rhombicosidodecahedron () where two non-opposing cupolae are rotated;
And the trigyrate rhombicosidodecahedron () where three cupolae are rotated.
External links
Johnson solids
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https://en.wikipedia.org/wiki/Paragyrate%20diminished%20rhombicosidodecahedron
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In geometry, the paragyrate diminished rhombicosidodecahedron is one of the Johnson solids (). It can be constructed as a rhombicosidodecahedron with one pentagonal cupola rotated through 36 degrees, and the opposing pentagonal cupola removed.
External links
Johnson solids
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https://en.wikipedia.org/wiki/Metagyrate%20diminished%20rhombicosidodecahedron
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In geometry, the metagyrate diminished rhombicosidodecahedron is one of the Johnson solids (). It can be constructed as a rhombicosidodecahedron with one pentagonal cupola () rotated through 36 degrees, and a non-opposing pentagonal cupola removed. (The cupolae cannot be adjacent.)
External links
Johnson solids
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https://en.wikipedia.org/wiki/Bigyrate%20diminished%20rhombicosidodecahedron
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In geometry, the bigyrate diminished rhombicosidodecahedron is one of the Johnson solids (). It can be constructed as a rhombicosidodecahedron with two pentagonal cupolae rotated through 36 degrees, and a third pentagonal cupola removed. (None of the cupolae can be adjacent.)
External links
Johnson solids
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https://en.wikipedia.org/wiki/Gyrate%20bidiminished%20rhombicosidodecahedron
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In geometry, the gyrate bidiminished rhombicosidodecahedron is one of the Johnson solids ().
It can be constructed as a rhombicosidodecahedron with two non-opposing pentagonal cupolae () removed and a third is rotated 36 degrees. Related Johnson solids are:
The diminished rhombicosidodecahedron () where one cupola is removed,
The parabidiminished rhombicosidodecahedron () where two opposing cupolae are removed,
The metabidiminished rhombicosidodecahedron () where two non-opposing cupolae are removed,
And the tridiminished rhombicosidodecahedron () where three cupolae are removed.
External links
Johnson solids
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https://en.wikipedia.org/wiki/Metabigyrate%20rhombicosidodecahedron
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In geometry, the metabigyrate rhombicosidodecahedron is one of the Johnson solids (). It can be constructed as a rhombicosidodecahedron with two non-opposing pentagonal cupolae rotated through 36 degrees. It is also a canonical polyhedron.
Alternative Johnson solids, constructed by rotating different cupolae of a rhombicosidodecahedron, are:
The gyrate rhombicosidodecahedron () where only one cupola is rotated;
The parabigyrate rhombicosidodecahedron () where two opposing cupolae are rotated;
And the trigyrate rhombicosidodecahedron () where three cupolae are rotated.
External links
World of Polyhedra - metabigyrate rhombicosidodecahedron (interactive rotatable wireframe applet)
Johnson solids
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https://en.wikipedia.org/wiki/Gyroelongated%20pentagonal%20bicupola
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In geometry, the gyroelongated pentagonal bicupola is one of the Johnson solids (). As the name suggests, it can be constructed by gyroelongating a pentagonal bicupola ( or ) by inserting a decagonal antiprism between its congruent halves.
The gyroelongated pentagonal bicupola is one of five Johnson solids which are chiral, meaning that they have a "left-handed" and a "right-handed" form. In the illustration to the right, each square face on the bottom half of the figure is connected by a path of two triangular faces to a square face above it and to the right. In the figure of opposite chirality (the mirror image of the illustrated figure), each bottom square would be connected to a square face above it and to the left. The two chiral forms of are not considered different Johnson solids.
Area and Volume
With edge length a, the surface area is
and the volume is
External links
Johnson solids
Chiral polyhedra
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https://en.wikipedia.org/wiki/Flickr
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Flickr ( ; ) is an image hosting and video hosting service, as well as an online community, founded in Canada and headquartered in the United States. It was created by Ludicorp in 2004 and was previously a common way for amateur and professional photographers to host high-resolution photos. It has changed ownership several times and has been owned by SmugMug since April 20, 2018.
Flickr had a total of 112 million registered members and more than 3.5 million new images uploaded daily. On August 5, 2011, the site reported that it was hosting more than 6 billion images. Photos and videos can be accessed from Flickr without the need to register an account, but an account must be made to upload content to the site. Registering an account also allows users to create a profile page containing photos and videos that the user has uploaded and also grants the ability to add another Flickr user as a contact. For mobile users, Flickr has official mobile apps for iOS, Android, and an optimized mobile site.
History
Flickr was launched on February 10, 2004 by Ludicorp, a Vancouver-based company founded by Stewart Butterfield and Caterina Fake. The service emerged from tools originally created for Ludicorp's Game Neverending, a web-based massively multiplayer online game. Flickr proved a more feasible project, and ultimately Game Neverending was shelved, Butterfield later launched a similar online game, Glitch, which was shut down on November 14, 2012.
Early versions of Flickr focused on a chat room called FlickrLive, with real-time photo exchange capabilities. The successive evolutions focused more on the uploading and filing back-end for individual users and the chat room was buried in the site map. It was eventually dropped as Flickr's back-end systems evolved away from Game Neverendings codebase. Key features of Flickr not initially present are tags, marking photos as favorites, group photo pools and interestingness, for which a patent was granted.
In addition to being a p
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https://en.wikipedia.org/wiki/Bill%20English%20%28computer%20engineer%29
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William Kirk English (January 27, 1929July 26, 2020) was an American computer engineer who contributed to the development of the computer mouse while working for Douglas Engelbart at SRI International's Augmentation Research Center. He would later work for Xerox PARC and Sun Microsystems.
Early life
English was born on January 27, 1929, in Lexington, Kentucky. The only son of Harry English and Caroline (Gray) English, he had two half-brothers from his father's previous marriage. Harry English was an electrical engineer who managed coal mines and Caroline was a homemaker. William, or Bill as he was known, attended a boarding school in Arizona and then studied electrical engineering at the University of Kentucky.
Career
English served in the US Navy until the late 1950s, including postings in northern California and Japan. He then joined the Stanford Research Institute in the 1960s to work on magnets, and built one of the first all-magnetic arithmetic units with Hewitt Crane. In 1964, he was the first person to join Douglas Engelbart's lab, the Augmentation Research Center.
He and Douglas Engelbart share credit for creating the first computer mouse in 1963; English built the initial prototype, and was its first user, based on Engelbart's notes. English led a 1965 project, sponsored by NASA, which evaluated the best way to select a point on a computer display; the mouse was the winner. English was also instrumental at The Mother of All Demos in 1968, which showcased the mouse and other technologies developed as part of their NLS (oN-Line System). In particular, English figured out how to connect a terminal in the San Francisco Civic Auditorium to the host computer at SRI away, and also transmitted audio and video between the locations.
He left SRI in 1971 and went to Xerox PARC, where he managed the Office Systems Research Group. While working at PARC, English developed a ball mouse, in which a ball replaced the original set of wheels. It worked similarly to a mov
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https://en.wikipedia.org/wiki/Index%20of%20construction%20articles
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This page is a list of construction topics.
A
Abated
- Abrasive blasting
- AC power plugs and sockets
- Access mat
- Accrington brick
- Accropode
- Acid brick
- Acoustic plaster
- Active daylighting
- Adaptive reuse
- Aerial crane
- Aerosol paint
- Aggregate base
- Agile construction
- Akmon
- Alternative natural materials
- Anchorage in reinforced concrete
- Angle grinder
- Arc welding
- Artificial stone
- Asbestos cement
- Asbestos insulating board
- Asbestos shingle
- Asphalt concrete
- Asphalt roll roofing
- Autoclaved aerated concrete
- Autonomous building
- Azulejo
- Australian Construction Contracts
- Axe
B
Backhoe
- Balloon framing
- Bamboo construction
- Bamboo-mud wall
- Bandsaw
- Banksman
- Barrel roof
- Baseboard
- Basement waterproofing
- Batten
- Batter board
- Belt sander
- Bill of quantities
- Bioasphalt
- Biocidal natural building material
- Bituminous waterproofing
- Block paving
- Blowtorch
- Board roof
- Bochka roof
- Bond beam
- Boulder wall
- Bowen Construction
- Box crib
- Breaker
- Brettstapel
- Brick
- Brick clamp
- Brick hod
- Bricklayer
- Brickwork
- Bughole
- Builder's risk insurance
- Builders hardware
- Builders' rites
- Building
- Building automation
- Building code
- Building construction
- Building control body
- Building cooperative
- Building design
- Building diagnostics
- Building engineer
- Building envelope
- Building estimator
- Building implosion
- Building information modeling
- Building information modeling in green building
- Building insulation
- Building insulation materials
- Building-integrated photovoltaics
- Building life cycle
- Building maintenance unit
- Building material
- Building officials
- Building performance
- Building performance simulation
- Building regulations approval
- Building regulations in the United Kingdom
- Building science
- Building services engineering
- Building typology
- Bull's eye level
- Bulldozer
- Bundwerk
- Bush hammer
- Butterfly roof
C
Calcium aluminate cements
- Camber beam
-
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https://en.wikipedia.org/wiki/OpenSolaris
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OpenSolaris () is a discontinued open-source computer operating system based on Solaris and created by Sun Microsystems. It was also, perhaps confusingly, the name of a project initiated by Sun to build a developer and user community around the eponymous operating system software.
OpenSolaris is a descendant of the UNIX System V Release 4 (SVR4) code base developed by Sun and AT&T in the late 1980s and is the only version of the System V variant of UNIX available as open source. OpenSolaris was developed as a combination of several software consolidations that were open sourced starting with Solaris 10. It includes a variety of free software, including popular desktop and server software.
After Oracle’s acquisition of Sun Microsystems in 2010, Oracle discontinued development of OpenSolaris in house, pivoting to focus exclusively on the development of the proprietary Solaris Express (now Oracle Solaris).
Prior to Oracle's close-sourcing Solaris, a group of former OpenSolaris developers began efforts to fork the core software under the name OpenIndiana. The illumos Foundation, founded in the wake of the discontinuation of OpenSolaris, continues to develop and maintain the kernel and userland of OpenIndiana (together renamed “illumos”), while the OpenIndiana Project (now under the auspices of the illumos Foundation) continues to maintain and develop the illumos-based OpenIndiana distribution (including its installer and build system) as the direct descendant of OpenIndiana. Since then additional illumos distributions, both commercial and non-commercial, have appeared and are under active development, combining the illumos kernel and userland with custom installers, packaging and build systems, and other distribution-specific utilities and tooling.
History
OpenSolaris was based on Solaris, which was originally released by Sun in 1991. Solaris is a version of UNIX System V Release 4 (SVR4), jointly developed by Sun and AT&T to merge features from several existi
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https://en.wikipedia.org/wiki/Homo%20Ludens
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Homo Ludens is a book originally published in Dutch in 1938 by Dutch historian and cultural theorist Johan Huizinga.
It discusses the importance of the play element of culture and society. Huizinga suggests that play is primary to and a necessary (though not sufficient) condition of the generation of culture. The Latin word is the present active participle of the verb , which itself is cognate with the noun . has no direct equivalent in English, as it simultaneously refers to sport, play, school, and practice.
Reception
Homo Ludens is an important part of the history of game studies. It influenced later scholars of play, like Roger Caillois. The concept of the magic circle was inspired by Homo Ludens.
Foreword controversy
Huizinga makes it clear in the foreword of his book that he means the play element of culture, and not the play element in culture. He writes that he titled the initial lecture on which the book is based, "The Play Element of Culture". This title was repeatedly corrected to "in" Culture, a revision he objected to.
The English version modified the subtitle of the book to "A Study of the Play-Element in Culture", contradicting Huizinga's stated intention. The translator explains in a footnote in the Foreword, "Logically, of course, Huizinga is correct; but as English prepositions are not governed by logic I have retained the more euphonious ablative in this sub-title."
Contents
I. Nature and significance of play as a cultural phenomenon
Play is older than culture, for culture, however inadequately defined, always presupposes human society, and animals have not waited for man to teach them their playing.
Huizinga begins by making it clear that animals played before humans. One of the most significant (human and cultural) aspects of play is that it is fun.
Huizinga identifies 5 characteristics that play must have:
Play is free, is in fact freedom.
Play is not "ordinary" or "real" life.
Play is distinct from "ordinary" life both as to localit
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https://en.wikipedia.org/wiki/Fagan%20inspection
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A Fagan inspection is a process of trying to find defects in documents (such as source code or formal specifications) during various phases of the software development process. It is named after Michael Fagan, who is credited with the invention of formal software inspections.
Fagan inspection defines a process as a certain activity with pre-specified entry and exit criteria. In every process for which entry and exit criteria are specified, Fagan inspections can be used to validate if the output of the process complies with the exit criteria specified for the process. Fagan inspection uses a group review method to evaluate the output of a given process.
Examples
Examples of activities for which Fagan inspection can be used are:
Requirement specification
Software/Information System architecture (for example DYA)
Programming (for example for iterations in XP or DSDM)
Software testing (for example when creating test scripts)
Usage
The software development process is a typical application of Fagan inspection. As the costs to remedy a defect are up to 10 to 100 times less in the early operations compared to fixing a defect in the maintenance phase, it is essential to find defects as close to the point of insertion as possible. This is done by inspecting the output of each operation and comparing that to the output requirements, or exit criteria, of that operation.
Criteria
Entry criteria are the criteria or requirements which must be met to enter a specific process. For example, for Fagan inspections the high- and low-level documents must comply with specific entry criteria before they can be used for a formal inspection process.
Exit criteria are the criteria or requirements which must be met to complete a specific process. For example, for Fagan inspections the low-level document must comply with specific exit criteria (as specified in the high-level document) before the development process can be taken to the next phase.
The exit criteria are specified in
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https://en.wikipedia.org/wiki/RS-485
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RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, defining the electrical characteristics of drivers and receivers for use in serial communications systems. Electrical signaling is balanced, and multipoint systems are supported. The standard is jointly published by the Telecommunications Industry Association and Electronic Industries Alliance (TIA/EIA). Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. Multiple receivers may be connected to such a network in a linear, multidrop bus. These characteristics make RS-485 useful in industrial control systems and similar applications.
Overview
RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422. It is generally accepted that RS-485 can be used with data rates up to 10 Mbit/s or, at lower speeds, distances up to . As a rule of thumb, the speed in bit/s multiplied by the length in metres should not exceed 108. Thus a cable should not signal faster than .
In contrast to RS-422, which has a driver circuit which cannot be switched off, RS-485 drivers use three-state logic allowing individual transmitters to be deactivated. This allows RS-485 to implement linear bus topologies using only two wires. The equipment located along a set of RS-485 wires are interchangeably called nodes, stations or devices. The recommended arrangement of the wires is as a connected series of point-to-point (multidropped) nodes, i.e. a line or bus, not a star, ring, or multiply connected network. Star and ring topologies are not recommended because of signal reflections or excessively low or high termination impedance. If a star configuration is unavoidable, special RS-485 repeaters are available which bidirectionally listen for data on each span and then retransmit the data onto all other spans.
Ideally, the two ends of the
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https://en.wikipedia.org/wiki/Overdominance
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Overdominance is a rare condition in genetics where the phenotype of the heterozygote lies outside the phenotypical range of both homozygous parents. Overdominance can also be described as heterozygote advantage regulated by a single genomic locus, wherein heterozygous individuals have a higher fitness than homozygous individuals. However, not all cases of the heterozygote advantage are considered overdominance, as they may be regulated by multiple genomic regions. Overdominance has been hypothesized as an underlying cause for heterosis (increased fitness of hybrid offspring).
Examples
Sickle cell anemia
An example of overdominance in humans is that of the sickle cell anemia. This condition is determined by a single polymorphism. Possessors of the deleterious allele have lower life expectancy, with homozygotes rarely reaching 50 years of age. However, this allele also yields some resistance to malaria. Thus in regions where malaria exerts or has exerted a strong selective pressure, sickle cell anemia has been selected for its conferred partial resistance to the disease. While homozygotes will have either no protection from malaria or a dramatic propensity to sickle cell anemia, heterozygotes have fewer physiological effects and a partial resistance to malaria.
Salmonoid major histocompatibility complex
Major histocompatibility complex (MHC) genes exhibit extensive variation, generally attributed to the notion of heterozygous individuals identifying a wider range of peptides than homozygous individuals. In arctic char population in Finland, fish heterozygous for MHC alleles had fewer cysts, grew larger, and had a better chance at survival, all indicating a higher fitness of the heterozygotes.
Gymnadenia rhellicani colour polymorphism
In Gymnadenia rhellicani, flower pigmentation is controlled by changes to amino acids 612 and 663 in GrMYB1, which plays a role in anthocyanin pigment production. Red flowers, heterozygous with black and white alleles, maintain a
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https://en.wikipedia.org/wiki/Change%20of%20basis
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In mathematics, an ordered basis of a vector space of finite dimension allows representing uniquely any element of the vector space by a coordinate vector, which is a sequence of scalars called coordinates. If two different bases are considered, the coordinate vector that represents a vector on one basis is, in general, different from the coordinate vector that represents on the other basis. A change of basis consists of converting every assertion expressed in terms of coordinates relative to one basis into an assertion expressed in terms of coordinates relative to the other basis.
Such a conversion results from the change-of-basis formula which expresses the coordinates relative to one basis in terms of coordinates relative to the other basis. Using matrices, this formula can be written
where "old" and "new" refer respectively to the firstly defined basis and the other basis, and are the column vectors of the coordinates of the same vector on the two bases, and is the change-of-basis matrix (also called transition matrix), which is the matrix whose columns are the coordinate vectors of the new basis vectors on the old basis.
This article deals mainly with finite-dimensional vector spaces. However, many of the principles are also valid for infinite-dimensional vector spaces.
Change of basis formula
Let be a basis of a finite-dimensional vector space over a field .
For , one can define a vector by its coordinates over
Let
be the matrix whose th column is formed by the coordinates of . (Here and in what follows, the index refers always to the rows of and the while the index refers always to the columns of and the such a convention is useful for avoiding errors in explicit computations.)
Setting one has that is a basis of if and only if the matrix is invertible, or equivalently if it has a nonzero determinant. In this case, is said to be the change-of-basis matrix from the basis to the basis
Given a vector let be the coordinates of
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https://en.wikipedia.org/wiki/ELAN%20%28programming%20language%29
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ELAN is an interpreted educational programming language for learning and teaching systematic programming.
It was developed in 1974 by C.H.A. Koster and a group at the Technical University of Berlin as an alternative to BASIC in teaching, and approved for use in secondary schools in Germany by the "Arbeitskreis Schulsprache". It was in use until the late 1980s in a number of schools in Germany, Belgium, the Netherlands, and Hungary for informatics teaching in secondary education, and used at the Radboud University Nijmegen in the Netherlands for teaching systematic programming to students from various disciplines and in teacher courses.
The language design focuses strongly on structured programming, and has a special construction for stepwise refinement, allowing students to focus on top-down design, and bottom-up coding.
The microkernel operating system Eumel began as a runtime system (environment) for ELAN.
See also
ALGOL 68
External links
ELAN implementation built by the Radboud University Nijmegen
ELAN implementation download site
Dresden uni on ELAN
Educational programming languages
Algol programming language family
Computer-related introductions in 1974
Procedural programming languages
Programming languages created in 1974
Programming languages
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https://en.wikipedia.org/wiki/Stream%20cipher%20attacks
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Stream ciphers, where plaintext bits are combined with a cipher bit stream by an exclusive-or operation (xor), can be very secure if used properly. However, they are vulnerable to attacks if certain precautions are not followed:
keys must never be used twice
valid decryption should never be relied on to indicate authenticity
Reused key attack
Stream ciphers are vulnerable to attack if the same key is used twice (depth of two) or more.
Say we send messages A and B of the same length, both encrypted using same key, K. The stream cipher produces a string of bits C(K) the same length as the messages. The encrypted versions of the messages then are:
E(A) = A xor C
E(B) = B xor C
where xor is performed bit by bit.
Say an adversary has intercepted E(A) and E(B). They can easily compute:
E(A) xor E(B)
However, xor is commutative and has the property that X xor X = 0 (self-inverse) so:
E(A) xor E(B) = (A xor C) xor (B xor C) = A xor B xor C xor C = A xor B
If one message is longer than the other, our adversary just truncates the longer message to the size of the shorter and their attack will only reveal that portion of the longer message. In other words, if anyone intercepts two messages encrypted with the same key, they can recover A xor B, which is a form of running key cipher. Even if neither message is known, as long as both messages are in a natural language, such a cipher can often be broken by paper-and-pencil methods. During World War II, British cryptanalyst John Tiltman accomplished this with the Lorenz cipher (dubbed "Tunny"). With an average personal computer, such ciphers can usually be broken in a matter of minutes. If one message is known, the solution is trivial.
Another situation where recovery is trivial is if traffic-flow security measures have each station sending a continuous stream of cipher bits, with null characters (e.g. LTRS in Baudot) being sent when there is no real traffic. This is common in military communications. In that case
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https://en.wikipedia.org/wiki/Surrogate%20endpoint
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In clinical trials, a surrogate endpoint (or surrogate marker) is a measure of effect of a specific treatment that may correlate with a real clinical endpoint but does not necessarily have a guaranteed relationship. The National Institutes of Health (USA) defines surrogate endpoint as "a biomarker intended to substitute for a clinical endpoint".
Surrogate markers are used when the primary endpoint is undesired (e.g., death), or when the number of events is very small, thus making it impractical to conduct a clinical trial to gather a statistically significant number of endpoints. The FDA and other regulatory agencies will often accept evidence from clinical trials that show a direct clinical benefit to surrogate markers.
Surrogate endpoints can be obtained from different modalities, such as, behavioural or cognitive scores, or biomarkers from Electroencephalography (qEEG), MRI, PET, or biochemical biomarkers.
A correlate does not make a surrogate. It is a common misconception that if an outcome is a correlate (that is, correlated with the true clinical outcome) it can be used as a valid surrogate endpoint (that is, a replacement for the true clinical outcome). However, proper justification for such replacement requires that the effect of the intervention on the surrogate endpoint predicts the effect on the clinical outcome: a much stronger condition than correlation. In this context, the term Prentice criteria is used.
The term "surrogate" should not be used in describing endpoints. Instead, descriptions of results and interpretations should be formulated in terms that designate the specific nature and category of variable assessed.
A surrogate endpoint of a clinical trial is a laboratory measurement or a physical sign used as a substitute for a clinically meaningful endpoint that measures directly how a patient feels, functions or survives. Changes induced by a therapy on a surrogate endpoint are expected to reflect changes in a clinically meaningful endpoint.
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https://en.wikipedia.org/wiki/Stunt%20Car%20Racer
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Stunt Car Racer (published as Stunt Track Racer in the United States) is a racing video game developed by Geoff Crammond. It was published in 1989 by MicroProse, under their MicroStyle and MicroPlay labels in the United Kingdom and in the United States, respectively. The game pits two racers on an elevated track on which they race in a head-to-head competition, with ramps they must correctly drive off as the main obstacle.
The game was released to critical acclaim. The Commodore 64 version's use of 3D vector graphics was met with critical enthusiasm, which was unusual for a game for that platform. It is considered one of the better racing games and games for Amiga, with many calling it one of the best such games.
Gameplay
The game differs from other racing games in that the races take place on an elevated race track, with nothing to stop the player from accidentally driving off the side. Most race tracks in the game have gaps in them, which players can fall into. If this occurs then the player's vehicle is hoisted back onto the track (by a nearby crane), costing valuable time. Turbo can be used to make a car go faster, but it can only be used for a limited amount of time in each race.
The single-player game consists of a league table which is split into four divisions of three drivers each, making a total of twelve racers including the human player. There are two racing tracks in each division making it a total of eight tracks in the game. The tracks in division four (the first division) are easy, but the tracks get progressively more difficult and dangerous with each division. The player's objective is to reach, and subsequently win, division one. There are four races in a season, and each driver will race the other two drivers in both of the tracks in the division. Each race is run over three laps. Two points are awarded to the winner of each race and one point is awarded to the racer with the fastest lap time. At the end of each season, the top racer of each
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https://en.wikipedia.org/wiki/Data%20control%20language
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A data control language (DCL) is a syntax similar to a computer programming language used to control access to data stored in a database (authorization). In particular, it is a component of Structured Query Language (SQL). Data Control Language is one of the logical group in SQL Commands. SQL is the standard language for relational database management systems. SQL statements are used to perform tasks such as insert data to a database, delete or update data in a database, or retrieve data from a database.
Though database systems use SQL, they also have their own additional proprietary extensions that are usually only used on their system. For Example Microsoft SQL server uses Transact-SQL (T-SQL) which is an extension of SQL. Similarly Oracle uses PL-SQL which is their proprietary extension for them only. However, the standard SQL commands such as "Select", "Insert", "Update", "Delete", "Create", and "Drop" can be used to accomplish almost everything that one needs to do with a database.
Examples of DCL commands include:
GRANT to allow specified users to perform specified tasks.
REVOKE to remove the user accessibility to database object.
The operations for which privileges may be granted to or revoked from a user or role apply to both the Data definition language (DDL) and the Data manipulation language (DML), and may include CONNECT, SELECT, INSERT, UPDATE, DELETE, EXECUTE, and USAGE.
Microsoft SQL Server
As per Microsoft SQL Server there are four groups of SQL Commands.
Data Manipulation Language (DML)
Data Definition Language (DDL)
Data Control Language (DCL)
Transaction Control Language (TCL)
DCL commands are used for access control and permission management for users in the database. With them we can easily allow or deny some actions for users on the tables or records (row level security).
DCL commands are:
GRANT We can give certain permissions for the table (and other objects) for specified groups/users of a database.
DENY bans certain permissio
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https://en.wikipedia.org/wiki/Expensive%20Typewriter
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Expensive Typewriter was a pioneering text editor program that ran on the DEC PDP-1 computer which had been delivered to MIT in the early 1960s.
Description
Since the program could drive an IBM Selectric typewriter (a letter-quality printer), it may be considered the first word processing software. It was written and improved between 1961 and 1962 by Steve Piner and L. Peter Deutsch. In the spirit of an earlier editor program, named "Colossal Typewriter", it was called "Expensive Typewriter" because at that time the PDP-1 cost a lot of money (approximately ) as compared to a conventional manual typewriter.
References
See also
PDP-1
Expensive Desk Calculator
Expensive Planetarium
Expensive Tape Recorder
Text Editor and Corrector
RUNOFF
TJ-2
Word processors
History of software
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https://en.wikipedia.org/wiki/Frontlight
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A frontlight is a means of illuminating a display device, usually a liquid crystal display (LCD), which would otherwise be viewed in ambient light. This improves its performance in poor lighting conditions.
An LCD presents an image by absorbing some light passing through it. When an electric field is applied across the crystal, it changes the passing light so it will not pass through a polarization filter. This allows LCDs to operate at low power, as no energy needs to be spent generating light. Many battery-operated electronic devices, including most calculators and other devices use unilluminated LCDs.
An unilluminated LCD must be lit from the front. To use ambient light, the liquid crystal itself is sandwiched between a polarization filter and a reflective surface. The mirror makes the display opaque so it cannot be illuminated from the back. Most often a light source is placed around the perimeter of the LCD.
Frontlights are relatively uncommon. Electroluminescent lights present a reflective surface when turned off. This allows for a backlit display which can also be used with ambient light. Such backlights are popular in digital watches. The monochromatic light from an electroluminescent source does not work well with color displays, however. An incandescent frontlight was therefore a popular accessory for the Nintendo Game Boy Color.
Devices using a frontlight
GP32 FLU (2002)
Game Boy Advance SP (2003)
Kindle Paperwhite (2013)
See also
LCD
Backlight
Liquid crystal displays
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https://en.wikipedia.org/wiki/Computational%20science
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Computational science, also known as scientific computing, technical computing or scientific computation (SC), is a division of science that uses advanced computing capabilities to understand and solve complex physical problems. This includes
Algorithms (numerical and non-numerical): mathematical models, computational models, and computer simulations developed to solve sciences (e.g, physical, biological, and social), engineering, and humanities problems
Computer hardware that develops and optimizes the advanced system hardware, firmware, networking, and data management components needed to solve computationally demanding problems
The computing infrastructure that supports both the science and engineering problem solving and the developmental computer and information science
In practical use, it is typically the application of computer simulation and other forms of computation from numerical analysis and theoretical computer science to solve problems in various scientific disciplines. The field is different from theory and laboratory experiments, which are the traditional forms of science and engineering. The scientific computing approach is to gain understanding through the analysis of mathematical models implemented on computers. Scientists and engineers develop computer programs and application software that model systems being studied and run these programs with various sets of input parameters. The essence of computational science is the application of numerical algorithms and computational mathematics. In some cases, these models require massive amounts of calculations (usually floating-point) and are often executed on supercomputers or distributed computing platforms.
The computational scientist
The term computational scientist is used to describe someone skilled in scientific computing. Such a person is usually a scientist, an engineer, or an applied mathematician who applies high-performance computing in different ways to advance the state-of-the-ar
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https://en.wikipedia.org/wiki/Design%E2%80%93build
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Design–build (or design/build, and abbreviated D–B or D/B accordingly), also known as alternative delivery, is a project delivery system used in the construction industry. It is a method to deliver a project in which the design and construction services are contracted by a single entity known as the design–builder or design–build contractor. It can be subdivided into architect-led design–build (ALDB, sometimes known as designer-led design–build) and contractor-led design–build.
In contrast to "design–bid–build" (or "design–tender"), design–build relies on a single point of responsibility contract and is used to minimize risks for the project owner and to reduce the delivery schedule by overlapping the design phase and construction phase of a project.
Design–build also has a single point responsibility. The design-build contractor is responsible for all work on the project, so the client can seek legal remedies for any fault from one party.
The traditional approach for construction projects consists of the appointment of a designer on one side, and the appointment of a contractor on the other side. The design–build procurement route changes the traditional sequence of work. It answers the client's wishes for a single point of responsibility in an attempt to reduce risks and overall costs. Although the use of subcontractors to complete more specialized work is common, the design-build contractor remains the primary contact and primary force behind the work. It is now commonly used in many countries and forms of contracts are widely available.
Design–build is sometimes compared to the "master builder" approach, one of the oldest forms of construction procedure. Comparing design–build to the traditional method of procurement, the authors of Design-build Contracting Handbook noted that: "from a historical perspective the so-called traditional approach is actually a very recent concept, only being in use approximately 150 years. In contrast, the design–build concept—a
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https://en.wikipedia.org/wiki/Carmichael%20function
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In number theory, a branch of mathematics, the Carmichael function of a positive integer is the smallest positive integer such that
holds for every integer coprime to . In algebraic terms, is the exponent of the multiplicative group of integers modulo .
The Carmichael function is named after the American mathematician Robert Carmichael who defined it in 1910. It is also known as Carmichael's λ function, the reduced totient function, and the least universal exponent function.
The following table compares the first 36 values of with Euler's totient function (in bold if they are different; the s such that they are different are listed in ).
Numerical examples
Carmichael's function at 5 is 4, , because for any number coprime to 5, i.e. there is with namely, , , and . And this is the smallest exponent with this property, because (and as well.)Moreover, Euler's totient function at 5 is 4, , because there are exactly 4 numbers less than and coprime to 5 (1, 2, 3, and 4). Euler's theorem assures that for all coprime to 5, and 4 is the smallest such exponent.
Carmichael's function at 8 is 2, , because for any number coprime to 8, i.e. it holds that . Namely, , , and .Euler's totient function at 8 is 4, , because there are exactly 4 numbers less than and coprime to 8 (1, 3, 5, and 7). Moreover, Euler's theorem assures that for all coprime to 8, but 4 is not the smallest such exponent.
Computing with Carmichael's theorem
By the unique factorization theorem, any can be written in a unique way as
where are primes and are positive integers. Then is the least common multiple of the of each of its prime power factors:
This can be proved using the Chinese remainder theorem.
Carmichael's theorem explains how to compute of a prime power : for a power of an odd prime and for 2 and 4, is equal to the Euler totient ; for powers of 2 greater than 4 it is equal to half of the Euler totient:
Euler's function for prime powers is given by
Prope
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https://en.wikipedia.org/wiki/CMS-2
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CMS-2 is an embedded systems programming language used by the United States Navy. It was an early attempt to develop a standardized high-level computer programming language intended to improve code portability and reusability. CMS-2 was developed primarily for the US Navy’s tactical data systems (NTDS).
CMS-2 was developed by RAND Corporation in the early 1970s and stands for "Compiler Monitor System". The name "CMS-2" is followed in literature by a letter designating the type of target system. For example, CMS-2M targets Navy 16-bit processors, such as the AN/AYK-14.
History
CMS-2 was developed for FCPCPAC (Fleet Computer Programming Center - Pacific) in San Diego, CA. It was implemented by Computer Sciences Corporation in 1968 with design assistance from Intermetrics. The language continued to be developed, eventually supporting a number of computers including the AN/UYK-7 and AN/UYK-43 and UYK-20 and UYK-44 computers.
Language features
CMS-2 was designed to encourage program modularization, permitting independent compilation of portions of a total system. The language is statement oriented. The source is free-form and may be arranged for programming convenience. Data types include fixed-point, floating-point, boolean, character and status. Direct reference to, and manipulation of character and bit strings is permitted. Symbolic machine code may be included, known as direct code.
Program structure
A CMS-2 program is composed of statements. Statements are made up of symbols separated by delimiters. The categories of symbols include operators, identifiers, and constants. The operators are language primitives assigned by the compiler for specific operations or definitions in a program. Identifiers are unique names assigned by the programmer to data units, program elements and statement labels. Constants are known values that may be numeric, Hollerith strings, status values or Boolean.
CMS-2 statements are free form and terminated by a dollar sign. A statemen
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https://en.wikipedia.org/wiki/Signed-digit%20representation
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In mathematical notation for numbers, a signed-digit representation is a positional numeral system with a set of signed digits used to encode the integers.
Signed-digit representation can be used to accomplish fast addition of integers because it can eliminate chains of dependent carries. In the binary numeral system, a special case signed-digit representation is the non-adjacent form, which can offer speed benefits with minimal space overhead.
History
Challenges in calculation stimulated early authors Colson (1726) and Cauchy (1840) to use signed-digit representation. The further step of replacing negated digits with new ones was suggested by Selling (1887) and Cajori (1928).
In 1928, Florian Cajori noted the recurring theme of signed digits, starting with Colson (1726) and Cauchy (1840). In his book History of Mathematical Notations, Cajori titled the section "Negative numerals". For completeness, Colson uses examples and describes addition (pp. 163–4), multiplication (pp. 165–6) and division (pp. 170–1) using a table of multiples of the divisor. He explains the convenience of approximation by truncation in multiplication. Colson also devised an instrument (Counting Table) that calculated using signed digits.
Eduard Selling advocated inverting the digits 1, 2, 3, 4, and 5 to indicate the negative sign. He also suggested snie, jes, jerd, reff, and niff as names to use vocally. Most of the other early sources used a bar over a digit to indicate a negative sign for it. Another German usage of signed-digits was described in 1902 in Klein's encyclopedia.
Definition and properties
Digit set
Let be a finite set of numerical digits with cardinality (If , then the positional number system is trivial and only represents the trivial ring), with each digit denoted as for is known as the radix or number base. can be used for a signed-digit representation if it's associated with a unique function such that for all
This function, is what rigorously and formally
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https://en.wikipedia.org/wiki/Furnace%20anneal
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Furnace annealing is a process used in semiconductor device fabrication which consist of heating multiple semiconductor wafers in order to affect their electrical properties. Heat treatments are designed for different effects. Wafers can be heated in order to activate dopants, change film to film or film to wafer substrate interfaces, densify deposited films, change states of grown films, repair damage from implants, move dopants or drive dopants from one film into another or from a film into the wafer substrate. During ion implantation process, the crystal substrate is damaged due to bombardment with high energy ions. The damage caused can be repaired by subjecting the crystal to high temperature. This process is called annealing. Furnace anneals may be integrated into other furnace processing steps, such as oxidations, or may be processed on their own.
Furnace anneals are performed by equipment especially built to heat semiconductor wafers. Furnaces are capable of processing many wafers at a time but each process can last between several hours and a day. Increasingly, furnace anneals are being supplanted by Rapid Thermal Anneal (RTA) or Rapid Thermal Processing (RTP). This is due to the relatively long thermal cycles of furnaces that causes the dopants that are being activated, especially boron, to diffuse farther than is intended. RTP or RTA fixes this by having thermal cycles for each wafer that is of the order of minutes rather than hours for furnace anneals.
Equipment
Consolidated Engineering Company Annealing furnaces cover a broad range of Steel and Aluminum applications including tempering, normalizing, and aging, and similar automated loading, unloading and natural or forced cooling is possible with roller hearth, tip-up or batch arrangements.
Koyo Thermo Systems annealing furnaces for semiconductor, solar, display and electronic applications
Tokyo Electron Limited TELFORMULA and TELINDY PLUS
Annealing furnaces - for high or low carbon steel wir
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https://en.wikipedia.org/wiki/Double%20switching
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Double switching, double cutting, or double breaking is the practice of using a multipole switch to close or open both the positive and negative sides of a DC electrical circuit, or both the hot and neutral sides of an AC circuit. This technique is used to prevent shock hazard in electric devices connected with unpolarised AC power plugs and sockets. Double switching is a crucial safety engineering practice in railway signalling, wherein it is used to ensure that a single false feed of current to a relay is unlikely to cause a wrong-side failure. It is an example of using redundancy to increase safety and reduce the likelihood of failure, analogous to double insulation. Double switching increases the cost and complexity of systems in which it is employed, for example by extra relay contacts and extra relays, so the technique is applied selectively where it can provide a cost-effective safety improvement.
Examples
Landslip and Washaway Detectors
A landslip or washaway detector is buried in the earth embankment, and opens a circuit should a landslide occur. It is not possible to guarantee that the wet earth of the embankment will not complete the circuit which is supposed to break. If the circuit is double cut with positive and negative wires, any wet conductive earth is likely to blow a fuse on the one hand, and short the detecting relay on the other hand, either of which is almost certain to apply the correct warning signal.
Accidents
Clapham
The Clapham Junction rail crash of 1988 was caused in part by the lack of double switching (known as "double cutting" in the British railway industry). The signal relay in question was switched only on the hot side, while the return current came back on an unswitched wire. A loose wire bypassed the contacts by which the train detection relays switched the signal, allowing the signal to show green when in fact there was a stationary train ahead. 35 people were killed in the resultant collision.
United Flight 811
A sim
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https://en.wikipedia.org/wiki/Project%20delivery%20method
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Project delivery methods are systems used by a construction manager (also known as agency) or owner to carry-out a construction project while mitigating the risks to the scope of work, time, budget, quality and safety of the project. These risks ranges from cost overruns, time delays and conflict among the various parties.
History
Trends in delivery methods
Though DBB is now used for most private projects and the majority of public projects, it has not historically been the predominant delivery method of choice. The master builders of centuries past acted both as designers and constructors for both public and private clients. In the United States, Zane's Post Road in Ohio and the IRT in New York City were both originally developed under more integrated delivery methods, as were most infrastructure projects until 1933. Integrated Project Delivery offers a new delivery method to remove considerable waste from the construction process while improving quality and a return to more collaborative methods from the past.
In an effort to assist industry professionals with the selection of appropriate project delivery systems, construction management researchers have prepared a Procurement Method and Contract Selection Model, which can be used for high level decision making for construction projects on a case-by-case basis.
Types
Common project delivery methods include:
Design-Bid-Build (DBB) or Design-Award-Build (DAB)
In Design-Bid-Build, owner develops contract documents with an architect or an engineer consisting of a set of blueprints and a detailed specification. Bids are solicited from contractors based on these documents; a contract is then awarded to the lowest responsive and responsible bidder. This is the traditional model for public sector infrastructure projects.
DBB with Construction Management (DBB with CM)
DBB with Construction Management is a modified version of the Design-bid-build approach With partially completed contract documents, an owner
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https://en.wikipedia.org/wiki/Design%E2%80%93bid%E2%80%93build
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Design–bid–build (or design/bid/build, and abbreviated D–B–B or D/B/B accordingly), also known as Design–tender (or "design/tender"), traditional method, or hardbid, is a project delivery method in which the agency or owner contracts with separate entities for the design and construction of a project.
Design–bid–build is the traditional method for project delivery and differs in several substantial aspects from design–build.
There are three main sequential phases to the design–bid–build delivery method:
The design phase
The bidding (or tender) phase
The construction phase
Design phase
In this phase, the owner retains an architect (or consulting engineer for infrastructure works) to design and produce bid documents, including construction drawings and technical specifications, on which various general contractors will in turn bid to construct the project. For building projects, the architect will work with the owner to identify the owner's needs, develop a written program documenting those needs and then produce a conceptual and/or schematic design. This early design is then developed, and the architect will usually bring in other design professionals including a structural engineer, sometimes a civil engineer, mechanical, electrical, and plumbing engineers (MEP engineers), a fire protection engineer and often a landscape architect to help complete the construction drawings and technical specifications. The finished bid documents are coordinated by the architect and owner for issuance to general contractors during the bid phase.
Design fees are typically between 5-10% of the total project cost.
Bid (or tender) phase
Bidding can be "open", in which any qualified bidder may participate, or "select", in which a limited number of pre-selected contractors are invited to bid.
The various general contractors bidding on the project obtain copies of the bid (or tender) documents, and then put them out to multiple subcontractors for bids on sub-components of the proj
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https://en.wikipedia.org/wiki/Design%20engineer
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A design engineer is an engineer focused on the engineering design process in any of the various engineering disciplines (including civil, mechanical, electrical, chemical, textiles, aerospace, nuclear, manufacturing, systems, and structural /building/architectural) and design disciplines like Human-Computer Interaction.
Design engineers tend to work on products and systems that involve adapting and using complex scientific and mathematical techniques. The emphasis tends to be on utilizing engineering physics and other applied sciences to develop solutions for society.
A design engineer usually works with a team of other engineers and other types of designers (e.g. industrial designers), to develop conceptual and detailed designs that ensure a product functions, performs, and is fit for its purpose. They may also work with marketers to develop the product concept and specifications to meet customer needs, and may direct the design effort. In many engineering areas, a distinction is made between the "design engineer" and other engineering roles (e.g. planning engineer, project engineer, test engineer). Analysis tends to play a larger role for the latter areas, while synthesis is more paramount for the former; nevertheless, all such roles are technically part of the overall engineering design process.
When an engineering project involves public safety, design engineers involved are often required to be licensed - for example, as a Professional Engineer (in the U.S and Canada). There is often an "industrial exemption" for engineers working on project only internally to their organization, although the scope and conditions of such exemptions vary widely across jurisdictions.
Design engineer tasks
Design engineers may work in a team along with other designers to create the drawings necessary for prototyping and production, or in the case of buildings, for construction. However, with the advent of CAD and solid modeling software, the design engineers may create the
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https://en.wikipedia.org/wiki/Provable%20security
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Provable security refers to any type or level of computer security that can be proved. It is used in different ways by different fields.
Usually, this refers to mathematical proofs, which are common in cryptography. In such a proof, the capabilities of the attacker are defined by an adversarial model (also referred to as attacker model): the aim of the proof is to show that the attacker must solve the underlying hard problem in order to break the security of the modelled system. Such a proof generally does not consider side-channel attacks or other implementation-specific attacks, because they are usually impossible to model without implementing the system (and thus, the proof only applies to this implementation).
Outside of cryptography, the term is often used in conjunction with secure coding and security by design, both of which can rely on proofs to show the security of a particular approach. As with the cryptographic setting, this involves an attacker model and a model of the system. For example, code can be verified to match the intended functionality, described by a model: this can be done through static checking. These techniques are sometimes used for evaluating products (see Common Criteria): the security here depends not only on the correctness of the attacker model, but also on the model of the code.
Finally, the term provable security is sometimes used by sellers of security software that are attempting to sell security products like firewalls, antivirus software and intrusion detection systems. As these products are typically not subject to scrutiny, many security researchers consider this type of claim to be selling snakeoil.
In cryptography
In cryptography, a system has provable security if its security requirements can be stated formally in an adversarial model, as opposed to heuristically, with clear assumptions that the adversary has access to the system as well as enough computational resources. The proof of security (called a "reduction")
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https://en.wikipedia.org/wiki/Clock%20synchronization
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Clock synchronization is a topic in computer science and engineering that aims to coordinate otherwise independent clocks. Even when initially set accurately, real clocks will differ after some amount of time due to clock drift, caused by clocks counting time at slightly different rates. There are several problems that occur as a result of clock rate differences and several solutions, some being more acceptable than others in certain contexts.
Terminology
In serial communication, clock synchronization can refer to clock recovery which achieves frequency synchronization, as opposed to full phase synchronization. Such clock synchronization is used in synchronization in telecommunications and automatic baud rate detection.
Plesiochronous or isochronous operation refers to a system with frequency synchronization and loose constraints on phase synchronization. Synchronous operation implies a tighter synchronization based on time perhaps in addition to frequency.
Problems
As a result of the difficulties managing time at smaller scales, there are problems associated with clock skew that take on more complexity in distributed computing in which several computers will need to realize the same global time. For instance, in Unix systems the make command is used to compile new or modified code and seeks to avoid recompiling unchanged code. The make command uses the clock of the machine it runs on to determine which source files need to be recompiled. If the sources reside on a separate file server and the two machines have unsynchronized clocks, the make program might not produce the correct results.
Synchronization is required for accurate reproduction of streaming media. Clock synchronization is a significant component of audio over Ethernet systems.
Solutions
In a system with a central server, the synchronization solution is trivial; the server will dictate the system time. Cristian's algorithm and the Berkeley algorithm are potential solutions to the clock synchroniza
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https://en.wikipedia.org/wiki/Hard-core%20predicate
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In cryptography, a hard-core predicate of a one-way function f is a predicate b (i.e., a function whose output is a single bit) which is easy to compute (as a function of x) but is hard to compute given f(x). In formal terms, there is no probabilistic polynomial-time (PPT) algorithm that computes b(x) from f(x) with probability significantly greater than one half over random choice of x. In other words, if x is drawn uniformly at random, then given f(x), any PPT adversary can only distinguish the hard-core bit b(x) and a uniformly random bit with negligible advantage over the length of x.
A hard-core function can be defined similarly. That is, if x is chosen uniformly at random, then given f(x), any PPT algorithm can only distinguish the hard-core function value h(x) and uniformly random bits of length |h(x)| with negligible advantage over the length of x.
A hard-core predicate captures "in a concentrated sense" the hardness of inverting f.
While a one-way function is hard to invert, there are no guarantees about the feasibility of computing partial information about the preimage c from the image f(x). For instance, while RSA is conjectured to be a one-way function, the Jacobi symbol of the preimage can be easily computed from that of the image.
It is clear that if a one-to-one function has a hard-core predicate, then it must be one way. Oded Goldreich and Leonid Levin (1989) showed how every one-way function can be trivially modified to obtain a one-way function that has a specific hard-core predicate. Let f be a one-way function. Define g(x,r) = (f(x), r) where the length of r is the same as that of x. Let xj denote the jth bit of x and rj the jth bit of r. Then
is a hard core predicate of g. Note that b(x, r) = <x, r> where <·, ·> denotes the standard inner product on the vector space (Z2)n. This predicate is hard-core due to computational issues; that is, it is not hard to compute because g(x, r) is information theoretically lossy. Rather, if there e
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https://en.wikipedia.org/wiki/Dual%20basis%20in%20a%20field%20extension
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In mathematics, the linear algebra concept of dual basis can be applied in the context of a finite extension L/K, by using the field trace. This requires the property that the field trace TrL/K provides a non-degenerate quadratic form over K. This can be guaranteed if the extension is separable; it is automatically true if K is a perfect field, and hence in the cases where K is finite, or of characteristic zero.
A dual basis () is not a concrete basis like the polynomial basis or the normal basis; rather it provides a way of using a second basis for computations.
Consider two bases for elements in a finite field, GF(pm):
and
then B2 can be considered a dual basis of B1 provided
Here the trace of a value in GF(pm) can be calculated as follows:
Using a dual basis can provide a way to easily communicate between devices that use different bases, rather than having to explicitly convert between bases using the change of bases formula. Furthermore, if a dual basis is implemented then conversion from an element in the original basis to the dual basis can be accomplished with multiplication by the multiplicative identity (usually 1).
References
, Definition 2.30, p. 54.
Linear algebra
Field extensions
Theory of cryptography
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https://en.wikipedia.org/wiki/Dual%20basis
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In linear algebra, given a vector space with a basis of vectors indexed by an index set (the cardinality of is the dimension of ), the dual set of is a set of vectors in the dual space with the same index set I such that and form a biorthogonal system. The dual set is always linearly independent but does not necessarily span . If it does span , then is called the dual basis or reciprocal basis for the basis .
Denoting the indexed vector sets as and , being biorthogonal means that the elements pair to have an inner product equal to 1 if the indexes are equal, and equal to 0 otherwise. Symbolically, evaluating a dual vector in on a vector in the original space :
where is the Kronecker delta symbol.
Introduction
To perform operations with a vector, we must have a straightforward method of calculating its components. In a Cartesian frame the necessary operation is the dot product of the vector and the base vector. For example,
where is the bases in a Cartesian frame. The components of can be found by
However, in a non-Cartesian frame, we do not necessarily have for all . However, it is always possible to find a vector such that
The equality holds when is the dual base of . Notice the difference in position of the index .
In a Cartesian frame, we have
Existence and uniqueness
The dual set always exists and gives an injection from V into V∗, namely the mapping that sends vi to vi. This says, in particular, that the dual space has dimension greater or equal to that of V.
However, the dual set of an infinite-dimensional V does not span its dual space V∗. For example, consider the map w in V∗ from V into the underlying scalars F given by for all i. This map is clearly nonzero on all vi. If w were a finite linear combination of the dual basis vectors vi, say for a finite subset K of I, then for any j not in K, , contradicting the definition of w. So, this w does not lie in the span of the dual set.
The dual of an infinite-dimensional spa
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https://en.wikipedia.org/wiki/Quadratic%20residuosity%20problem
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The quadratic residuosity problem (QRP) in computational number theory is to decide, given integers and , whether is a quadratic residue modulo or not.
Here for two unknown primes and , and is among the numbers which are not obviously quadratic non-residues (see below).
The problem was first described by Gauss in his Disquisitiones Arithmeticae in 1801.
This problem is believed to be computationally difficult.
Several cryptographic methods rely on its hardness, see .
An efficient algorithm for the quadratic residuosity problem immediately implies efficient algorithms for other number theoretic problems, such as deciding whether a composite of unknown factorization is the product of 2 or 3 primes.
Precise formulation
Given integers and , is said to be a quadratic residue modulo if there exists an integer such that
.
Otherwise we say it is a quadratic non-residue.
When is a prime, it is customary to use the Legendre symbol:
This is a multiplicative character which means for exactly of the values , and it is for the remaining.
It is easy to compute using the law of quadratic reciprocity in a manner akin to the Euclidean algorithm, see Legendre symbol.
Consider now some given where and are two, different unknown primes.
A given is a quadratic residue modulo if and only if is a quadratic residue modulo both and and .
Since we don't know or , we cannot compute and . However, it is easy to compute their product.
This is known as the Jacobi symbol:
This can also be efficiently computed using the law of quadratic reciprocity for Jacobi symbols.
However, can not in all cases tell us whether is a quadratic residue modulo or not!
More precisely, if then is necessarily a quadratic non-residue modulo either or , in which case we are done.
But if then it is either the case that is a quadratic residue modulo both and , or a quadratic non-residue modulo both and .
We cannot distinguish these cases from knowing just that .
This leads
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https://en.wikipedia.org/wiki/Derrick
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A derrick is a lifting device composed at minimum of one guyed mast, as in a gin pole, which may be articulated over a load by adjusting its guys. Most derricks have at least two components, either a guyed mast or self-supporting tower, and a boom hinged at its base to provide articulation, as in a stiffleg derrick. The most basic type of derrick is controlled by three or four lines connected to the top of the mast, which allow it both to move laterally and cant up and down. To lift a load, a separate line runs up and over the mast with a hook on its free end, as with a crane.
Forms of derricks are commonly found aboard ships and at docking facilities. Some large derricks are mounted on dedicated vessels, and known as floating derricks and sheerlegs. The term derrick is also applied to the framework supporting a drilling apparatus in an oil rig. The derrick derives its name from a type of gallows named after Thomas Derrick, an Elizabethan era English executioner.
Types
There are various types of derrick based on how the tower or mast is set up and the use of boom:
A frame
A-frame derrick means a derrick in which the boom is hinged from a cross member between the bottom ends of two upright members spread apart at the lower ends and joined at the top; the boom point secured to the junction of the side members, and the side members are braced or guyed from this junction point..
Basket
A basket derrick is a derrick without a boom that is supported by a rope-and-pole system that forms a basket. The basket is constructed from a group of poles to form a polygon. There are crossbars between the pole members to strengthen their support. The supporting ropes are tied to the top of the basket poles on one end and joined together on the other end at a lower elevation than the top of the basket poles to form the base for the derrick tower. The derrick tower can be a mast or a post with the bottom hinged at the base where all ropes meet. The top of the tower is secured w
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https://en.wikipedia.org/wiki/Total%20internal%20reflection%20fluorescence%20microscope
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A total internal reflection fluorescence microscope (TIRFM) is a type of microscope with which a thin region of a specimen, usually less than 200 nanometers can be observed.
TIRFM is an imaging modality which uses the excitation of fluorescent cells in a thin optical specimen section that is supported on a glass slide. The technique is based on the principle that when excitation light is totally internally reflected in a transparent solid coverglass at its interface with a liquid medium, an electromagnetic field, also known as an evanescent wave, is generated at the solid-liquid interface with the same frequency as the excitation light. The intensity of the evanescent wave exponentially decays with distance from the surface of the solid so that only fluorescent molecules within a few hundred nanometers of the solid are efficiently excited. Two-dimensional images of the fluorescence can then be obtained, although there are also mechanisms in which three-dimensional information on the location of vesicles or structures in cells can be obtained.
History
Widefield Fluorescence was introduced in 1910 which was an optical technique that illuminates the entire sample as seen in Figure 1. Confocal microscopy was then introduced in 1960 which decreased the background and exposure time of the sample by directing light to a pinpoint and illuminating cones of light into the sample. In the 1980s, the introduction of TIRFM further decreased background and exposure time by only illuminating the thin section of the sample being examined.
Background
There are two common methods for producing the evanescent wave for TIRFM. The first is the prism method which uses a prism to direct the laser toward the interface between the coverglass and the media/cells at an incident angle sufficient to cause total internal reflection. This configuration has been applied to cellular microscopy for over 30 years but has never become a mainstream tool due to several limitations. Although there are
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https://en.wikipedia.org/wiki/Dumper
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A dumper or dumper truck (British English) or dump truck (North American English) is a truck designed for carrying bulk material, often on building sites. A dumper has a body which tilts or opens at the back for unloading and is usually an open 4-wheeled vehicle with the load skip in front of the driver. The skip can tip to dump the load; this is where the name "dumper" comes from. They are normally diesel powered. A towing eye is fitted for secondary use as a site tractor. Dumpers with rubber tracks are used in special circumstances and provide a more even distribution of weight compared to tires. Continuous tracks allow the operator to carry heavier payload on slick, snowy, or muddy surfaces, and are popular in some countries.
Background
One of the earliest British dumpers was the Muir-Hill, which was based on the Fordson tractor with 2 cubic yard bucket, driving on the front axle and steered by the back wheels. Devised in 1927, and on sale by 1931, it gained a lot of versatility when in 1933 Dunlop introduced 'tractor-style' pneumatic low pressure tyres. This allowed it to travel on tarmac roads or off road, which was of particular advantage on construction sites. Originally advertised as the "dumping tractor", it soon became known as the Muir-Hill dumper.
Modern dumpers have payloads of up to and usually steer by articulating at the middle of the chassis (pivot steering). They have multi-cylinder diesel engines, some turbocharged, electric start and hydraulics for tipping and steering and are usually four-wheel drive. An A-frame known as a ROPS (Roll-Over Protection) frame, may be fitted over the seat to protect the driver if the dumper rolls over. Some dumpers have FOPS (Falling Object Protection) as well. Lifting skips are available for discharging above ground level. In the 1990s dumpers with swivel skips, which could be rotated to tip sideways, became popular, especially for working in narrow sites such as road works. Dumpers are the most common cause of
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https://en.wikipedia.org/wiki/Scratch%20drive%20actuator
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A scratch drive actuator (SDA) is a microelectromechanical system device that converts electrical energy into one-dimensional motion.
Description
The actuator component can come in many shapes and sizes, depending on the fabrication method used. It can be visualised as an 'L'. The smaller end is called the 'bushing'.
The actuator sits on top of a substrate that has a thin insulating dielectric layer on top. A voltage is applied between the actuator and the substrate, and the resulting potential pulls the body of the actuator downwards. When this occurs, the brush is pushed forwards by a small amount, and energy is stored in the strained actuator. When the voltage is removed, the actuator springs back into shape while the bushing remains in its new position. By applying a pulsed voltage, the SDA can be made to move forward.
The voltage is usually applied to the actuator by means of a 'tether'. This can consist of a rigid connector or a rail which the SDA follows.
The size of an SDA is typically measured on the μm scale.
References
Actuators
Microtechnology
Microelectronic and microelectromechanical systems
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https://en.wikipedia.org/wiki/Protocooperation
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Protocooperation is where two species interact with each other beneficially; they have no need to interact with each other - they interact purely for the gain that they receive from doing this. It is not at all necessary for protocooperation to occur; growth and survival is possible in the absence of the interaction. The interaction that occurs can be between different kingdoms.
The term, initially used for intraspecific interactions, was popularized by Eugene Odum (1953), although other authors prefer to use the terms "cooperation" or "mutualism".
Mutualism
Protocooperation is a form of mutualism, but the cooperating species do not depend on each other for survival. An example of protocooperation happens between soil bacteria or fungi, and the plants that occur growing in the soil. None of the species rely on the relationship for survival, but all of the fungi, bacteria and higher plants take part in shaping soil composition and fertility. Soil bacteria and fungi interrelate with each other, forming nutrients essential to the plants survival. The plants obtain nutrients from root nodules and decomposing organic substance. Plants benefit by getting essential mineral nutrients and carbon dioxide. The plants do not need these mineral nutrients but do help the plant grow even further.
Examples
Ants and aphids
A further example of protocooperation is the connection between ants and aphids. The ant searches for food on trees and shrubs that are hosts to honeydew-secreting species such as aphids, mealybugs, and some scales. The ant gathers the sugary substance and takes it to its nest as food for its offspring. It has been known for the ant to stimulate the aphid to secrete honeydew straight into its mouth. Some ant species even look after the honeydew producers from natural predators. In areas where the ant inhabited the same ecosystem as the aphid, the plants they inhabit normally suffer from a higher presence of aphids which is detrimental to the plant but not to
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https://en.wikipedia.org/wiki/Royal%20Engineers%20Museum
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The Royal Engineers Museum, Library and Archive is a military engineering museum and library in Gillingham, Kent. It tells the story of the Corps of Royal Engineers and British military engineering in general.
History
The 'Ravelin Building', which was designed by Major E.C.S. Moore, Royal Engineers and was completed in 1905 at a cost £40,000, was originally used as electrical engineers' school before becoming the home of the museum in 1987. It was classed as Grade II listed on 5 December 1996. Its collection received 'Designated' status in 1998 (it is recognised as having an outstanding collection of national and international significance). It is one of only three military or regimental museums in the country to hold this status.
Collections
The museum and library hold over 500,000 objects relating to the history of the Corps of Royal Engineers and the development of military engineering. It also has a collection of paintings and a large collection of medals including 25 Victoria Crosses. Other items include a German V-2 rocket used during the Second World War, the map used by the Duke of Wellington during the Battle of Waterloo, a finial from the Mahdi's tomb, weapons used by Lieutenant John Chard during the Anglo-Zulu War, a collection of bridge-laying tanks, a Brennan torpedo and a Harrier jump jet.
See also
Waterbeach Military Heritage Museum
References
External links
Royal Engineers Museum Official Website
Regimental museums in England
Museums in Medway
Gillingham, Kent
Royal Engineers
Military engineering
Military and war museums in England
Technology museums in the United Kingdom
Musical instrument museums
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https://en.wikipedia.org/wiki/Storage%20Resource%20Broker
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Storage Resource Broker (SRB) is data grid management computer software used in computational science research projects. SRB is a logical distributed file system based on a client-server architecture which presents users with a single global logical namespace or file hierarchy. Essentially, the software enables a user to use a single mechanism to work with multiple data sources.
Description
SRB provides a uniform interface to heterogeneous computer data storage resources over a network. As part of this, it implements a logical namespace (distinct from physical file names) and maintains metadata on data-objects (files), users, groups, resources, collections, and other items in an SRB metadata catalog (MCAT) stored in a relational database management system. System and user-defined metadata can be queried to locate files based on attributes as well as by name. SRB runs on various versions of Unix, Linux, and Microsoft Windows.
The SRB system is middleware in the sense that it is built on top of other major software packages (various storage systems, real-time data sources, a relational database management system, etc.) and it has callable library functions that can be utilized by higher level software. However, it is more complete than many middleware software systems as it implements a comprehensive distributed data management environment, including various end-user client applications. It has features to support the management and collaborative (and controlled) sharing, publication, replication, transfer, and preservation of distributed data collections.
SRB is sometimes used in conjunction with computational grid computing systems, such as Globus Alliance, and can utilize the Globus Alliance Grid Security Infrastructure (GSI) authentication system.
SRB can store and retrieve data in archival storage systems such as the High Performance Storage System and SAM-FS, on disk file systems (Unix, Linux, or Windows), as binary large objects or tabular data in relati
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https://en.wikipedia.org/wiki/Central%20European%20Olympiad%20in%20Informatics
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The Central European Olympiad in Informatics (CEOI) is an annual informatics competition for secondary school students. Each of the participating central European countries (plus one or two guest countries, and a local team from the host area) sends a team of up to four contestants, a team leader and a deputy team leader. The contestants compete individually, i.e. a team score is not calculated. Competitors are selected through national competitive programming contests.
The contest consists of two days computer programming, solving problems of an algorithmic nature. The structure of these competition days is described in the article about the International Olympiad in Informatics (IOI), which served as a role model for the more local CEOI.
The first CEOI was held in 1994 in Romania (founder of the CEOI), five years after the first IOI.
List of CEOI websites and locations
CEOI 2021 was supposed to be held in Zagreb, Croatia, was held online instead (1- 5 September 2021).
CEOI 2020 was held in Nagykanizsa, Hungary (23 - 29 August 2020).
CEOI 2019 was held in Bratislava, Slovakia (23 - 29 July 2019).
CEOI 2018 was held in Warsaw, Poland (12 - 18 August 2018).
CEOI 2017 was held in Ljubljana, Slovenia (10 - 15 July 2017). Results
CEOI 2016 was held in Piatra Neamț, Romania (18 - 23 July 2016). Participants: Bulgaria, Croatia, Czech Republic, Georgia, Germany, Hungary, Moldova, Poland, Romania, Slovakia, Slovenia, Switzerland.
CEOI 2015 was held in Brno, Czech Republic (29 June - 4 July 2015). Participants: Croatia, Czech Republic, Georgia, Germany, Hungary, Poland, Romania, Slovakia, Slovenia, Switzerland.
CEOI 2014 was held in Jena, Germany (18 - 24 June 2014).
CEOI 2013 was held in Primošten, Croatia (13 - 19 October 2013). Participants: Croatia, Czech republic, Germany, Hungary, Poland, Romania, Switzerland, Slovakia and Slovenia.
CEOI 2012 was held in Tata, Hungary (7-13 July 2012). Participants: Bulgaria, Croatia, Czech Republic, Germany, Hungary, Pol
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https://en.wikipedia.org/wiki/Penguin%20Adventure
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is a racing platform game released by Konami in 1986, and a sequel to 1983's Antarctic Adventure. The game marks the professional debut of game designer Hideo Kojima, who participated in the planning for this game.
The story follows Penta, a penguin who has to bring home a golden apple in order to cure Penguette, the Penguin Princess.
Gameplay
This title significantly expanded upon the gameplay of Antarctic Adventure by most notably adding a greater variety of stages and enemies and RPG elements: boss fights, purchasable items, and several minigames. Items can be purchased through three different fisherman, in exchange for fish, that give Penta new abilities. One of the items that can be bought is a gun.
Level design and variety have increased from Antarctic Adventure; there are forest levels, ice levels, water-based levels, caves, and even some outer-space bonus levels. There are several shortcuts, usually hidden underneath holes (which are typically harmful hazards) in the game, that allow the player to go on almost completely different paths. The game also featured multiple endings, with the hidden good ending available when the player pauses the game a certain number of times. In the bad ending, the princess dies, while in the good ending, she lives.
Some publications have stated that Kojima reused the idea for multiple endings from this game in Metal Gear Solid and, to an extent, Metal Gear Solid 2: Sons of Liberty, due to it often being cited as his debut game. However, Kojima himself has stated that he only participated in the project for about a month to help plan the game, pitching suggestions such as the slot machine in the shop and how to defeat the bosses. Additionally, his name does not appear in the credits either. Hideo Kojima's first game credit and official directorial debut would be with Metal Gear, released for the MSX2 the next year.
Ports
Zemina, a South Korean video game company, made an unauthorized Master System port with the same titl
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https://en.wikipedia.org/wiki/Schmaltz%20herring
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Schmaltz herring (Yiddish) is herring caught just before spawning, when the fat (schmaltz) in the fish is at a maximum. Colloquially, schmaltz herring refers to this fish pickled in brine: see pickled herring.
References
External links
Herring dishes
Food preservation
Ashkenazi Jewish cuisine
Shabbat food
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https://en.wikipedia.org/wiki/Organogenesis
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Organogenesis is the phase of embryonic development that starts at the end of gastrulation and continues until birth. During organogenesis, the three germ layers formed from gastrulation (the ectoderm, endoderm, and mesoderm) form the internal organs of the organism.
The cells of each of the three germ layers undergo differentiation, a process where less-specialized cells become more-specialized through the expression of a specific set of genes. Cell differentiation is driven by cell signaling cascades. Differentiation is influenced by extracellular signals such as growth factors that are exchanged to adjacent cells which is called juxtracrine signaling or to neighboring cells over short distances which is called paracrine signaling. Intracellular signals - a cell signaling itself (autocrine signaling) - also play a role in organ formation. These signaling pathways allow for cell rearrangement and ensure that organs form at specific sites within the organism. The organogenesis process can be studied using embryos and organoids.
Organs produced by the germ layers
The endoderm is the inner most germ layer of the embryo which gives rise to gastrointestinal and respiratory organs by forming epithelial linings and organs such as the liver, lungs, and pancreas. The mesoderm or middle germ layer of the embryo will form the blood, heart, kidney, muscles, and connective tissues. The ectoderm or outermost germ layer of the developing embryo forms epidermis, the brain, and the nervous system.
Mechanism of organ formation
While each germ layer forms specific organs, in the 1820s, embryologist Heinz Christian Pander discovered that the germ layers cannot form their respective organs without the cellular interactions from other tissues. In humans, internal organs begin to develop within 3–8 weeks after fertilization. The germ layers form organs by three processes: folds, splits, and condensation. Folds form in the germinal sheet of cells and usually form an enclosed tube
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https://en.wikipedia.org/wiki/Segmentation%20and%20reassembly
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Segmentation and reassembly (SAR) is the process used to fragment and reassemble variable length packets into fixed length cells so as to allow them to be transported across Asynchronous Transfer Mode (ATM) networks or other cell based infrastructures. Since ATM's payload is only 48 bytes, nearly every packet from any other protocol has to be processed in this way. Thus, it is an essential process for any ATM node. It is usually handled by a dedicated chip, called the SAR.
The process is conceptually simple: an incoming packet from another protocol to be transmitted across the ATM network is chopped up into segments that fit into 48-byte chunks carried as ATM cell payloads. At the far end, these chunks are fitted back together to reconstitute the original packet.
The process is analogous to the fragmentation of IP packets on reaching an interface with a maximum transmission unit (MTU) less than the packet size and the subsequent reassembly of the original packet once the fragments have reached the original packet's destination.
Since different types of data are encapsulated in different ways, the details of the segmentation process vary according to the type of data being handled. There are several different schemes, referred to as ATM adaptation layers (AAL). The schemes are:
AAL0 – Raw cells with no special format
AAL1 – Constant bitrate, circuit emulation (T1, E1, etc.)
AAL2 – Variable bitrate synchronous traffic, eous traffic, e.g. Frame Relay transport
AAL5 – Used for most data traffic, such as IP
See also
Packet segmentation
Packet aggregation
Network protocols
Networking standards
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https://en.wikipedia.org/wiki/Friend-to-friend
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A friend-to-friend (or F2F) computer network is a type of peer-to-peer network in which users only make direct connections with people they know. Passwords or digital signatures can be used for authentication.
Unlike other kinds of private P2P, users in a friend-to-friend network cannot find out who else is participating beyond their own circle of friends, so F2F networks can grow in size without compromising their users' anonymity. Retroshare, WASTE, GNUnet, Freenet and OneSwarm are examples of software that can be used to build F2F networks, though RetroShare is the only one of these configured for friend-to-friend operation by default.
Many F2F networks support indirect anonymous or pseudonymous communication between users who do not know or trust one another. For example, a node in a friend-to-friend overlay can automatically forward a file (or a request for a file) anonymously between two friends, without telling either of them the other's name or IP address. These friends can in turn automatically forward the same file (or request) to their own friends, and so on.
Dan Bricklin coined the term "friend-to-friend network" in 2000.
Potential applications of F2F
The Bouillon project uses a friend-to-friend network to assign trust ratings to messages.
See also
Darknet
LAN messenger
Private peer-to-peer
Web of trust
References
B.C. Popescu, B. Crispo, and A.S. Tanenbaum. "Safe and Private Data Sharing with Turtle: Friends Team-Up and Beat the System." In 12th International Workshop on Security Protocols, Cambridge, UK, April 2004.
T. Chothia and K. Chatzikokolakis. "A Survey of Anonymous Peer-to-Peer File-Sharing." In Proceedings of the IFIP International Symposium on Network-Centric Ubiquitous Systems (NCUS 2005), Nagasaki, Japan, volume 3823 of Lecture Notes in Computer Science, pages 744–755. Springer, 2005.
J. Li and F. Dabek. "F2F: Reliable Storage in Open Networks." In 5th International Workshop on Peer-to-Peer Systems (IPTPS '06), Santa Barbara, C
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https://en.wikipedia.org/wiki/Fluorescence%20microscope
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A fluorescence microscope is an optical microscope that uses fluorescence instead of, or in addition to, scattering, reflection, and attenuation or absorption, to study the properties of organic or inorganic substances. "Fluorescence microscope" refers to any microscope that uses fluorescence to generate an image, whether it is a simple set up like an epifluorescence microscope or a more complicated design such as a confocal microscope, which uses optical sectioning to get better resolution of the fluorescence image.
Principle
The specimen is illuminated with light of a specific wavelength (or wavelengths) which is absorbed by the fluorophores, causing them to emit light of longer wavelengths (i.e., of a different color than the absorbed light). The illumination light is separated from the much weaker emitted fluorescence through the use of a spectral emission filter. Typical components of a fluorescence microscope are a light source (xenon arc lamp or mercury-vapor lamp are common; more advanced forms are high-power LEDs and lasers), the excitation filter, the dichroic mirror (or dichroic beamsplitter), and the emission filter (see figure below). The filters and the dichroic beamsplitter are chosen to match the spectral excitation and emission characteristics of the fluorophore used to label the specimen. In this manner, the distribution of a single fluorophore (color) is imaged at a time. Multi-color images of several types of fluorophores must be composed by combining several single-color images.
Most fluorescence microscopes in use are epifluorescence microscopes, where excitation of the fluorophore and detection of the fluorescence are done through the same light path (i.e. through the objective). These microscopes are widely used in biology and are the basis for more advanced microscope designs, such as the confocal microscope and the total internal reflection fluorescence microscope (TIRF).
Epifluorescence microscopy
The majority of fluorescence microsco
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https://en.wikipedia.org/wiki/Bottom%20trawling
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Bottom trawling is trawling (towing a trawl, which is a fishing net) along the seafloor. It is also referred to as "dragging". The scientific community divides bottom trawling into benthic trawling and demersal trawling. Benthic trawling is towing a net at the very bottom of the ocean and demersal trawling is towing a net just above the benthic zone. Bottom trawling can be contrasted with midwater trawling (also known as pelagic trawling), where a net is towed higher in the water column. Midwater trawling catches pelagic fish such as anchovies and mackerel, whereas bottom trawling targets both bottom-living fish (groundfish) and semi-pelagic species such as cod, squid, shrimp, and rockfish.
Trawling is done by a trawler, which can be a small open boat with only or a large factory trawler with . Bottom trawling can be carried out by one trawler or by two trawlers fishing cooperatively (pair trawling).
Global catch from bottom trawling has been estimated at over 30 million tonnes per year, an amount larger than any other fishing method. Concerns about the environmental impacts of bottom trawling have led to changes in gear design, such as the addition of turtle excluder devices to reduce bycatch, and limitations on locations where bottom trawling is allowed, such as marine protected areas. Moreover, a 2021 paper estimated that bottom trawling contributed between 600 and 1500 million tons of carbon dioxide a year by disturbing carbon dioxide in the sea floor – emissions approximately equivalent to those of Germany, or the aviation industry. International attempts to limit bottom trawling have been ineffective.
History
An early reference to fishery conservation measures comes from a complaint about a form of trawling dating from the 14th century, during the reign of Edward III. A petition was presented to Parliament in 1376 calling for the prohibition of a "subtlety contrived instrument called the wondyrchoum". This was an early beam trawl with a wooden beam, and c
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https://en.wikipedia.org/wiki/Private%20information%20retrieval
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In cryptography, a private information retrieval (PIR) protocol is a protocol that allows a user to retrieve an item from a server in possession of a database without revealing which item is retrieved. PIR is a weaker version of 1-out-of-n oblivious transfer, where it is also required that the user should not get information about other database items.
One trivial, but very inefficient way to achieve PIR is for the server to send an entire copy of the database to the user. In fact, this is the only possible protocol (in the classical or the quantum setting) that gives the user information theoretic privacy for their query in a single-server setting. There are two ways to address this problem: make the server computationally bounded or assume that there are multiple non-cooperating servers, each having a copy of the database.
The problem was introduced in 1995 by Chor, Goldreich, Kushilevitz and Sudan in the information-theoretic setting and in 1997 by Kushilevitz and Ostrovsky in the computational setting. Since then, very efficient solutions have been discovered. Single database (computationally private) PIR can be achieved with constant (amortized) communication and k-database (information theoretic) PIR can be done with communication.
Advances in computational PIR
The first single-database computational PIR scheme to achieve communication complexity less than was created in 1997 by Kushilevitz and Ostrovsky and achieved communication complexity of for any , where is the number of bits in the database. The security of their scheme was based on the well-studied Quadratic residuosity problem. In 1999, Christian Cachin, Silvio Micali and Markus Stadler achieved poly-logarithmic communication complexity. The security of their system is based on the Phi-hiding assumption. In 2004, Helger Lipmaa achieved log-squared communication complexity , where is the length of the strings and is the security parameter. The security of his system reduces to the semantic se
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https://en.wikipedia.org/wiki/Guard%20%28computer%20science%29
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In computer programming, a guard is a boolean expression that must evaluate to true if the program execution is to continue in the branch in question. Regardless of which programming language is used, a guard clause, guard code, or guard statement, is a check of integrity preconditions used to avoid errors during execution.
Uses
A typical example is checking that a reference about to be processed is not null, which avoids null-pointer failures.
Other uses include using a boolean field for idempotence (so subsequent calls are nops), as in the dispose pattern.public string Foo(string username)
{
if (username == null) {
throw new ArgumentNullException(nameof(username), "Username is null.");
}
// Rest of the method code follows here...
}
Flatter code with less nesting
The guard provides an early exit from a subroutine, and is a commonly used deviation from structured programming, removing one level of nesting and resulting in flatter code: replacing if guard { ... } with if not guard: return; ....
Using guard clauses can be a refactoring technique to improve code. In general, less nesting is good, as it simplifies the code and reduces cognitive burden.
For example, in Python:
# This function has no guard clause
def f_noguard(x):
if isinstance(x, int):
#code
#code
#code
return x + 1
else:
return None
# Equivalent function with a guard clause. Note that most of the code is less indented, which is good
def f_guard(x):
if not isinstance(x, int):
return None
#code
#code
#code
return x + 1
Another example, written in C:
// This function has no guard clause
int funcNoGuard(int x) {
if (x >= 0) {
//code
//code
//code
return x + 1;
} else {
return 0;
}
}
// Equivalent function with a guard clause
int funcGuard(int x) {
if (x < 0) {
return 0;
}
//code
//code
//code
return x + 1;
}
Terminology
The term is used with specific mean
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https://en.wikipedia.org/wiki/Raoul%20Hausmann
|
Raoul Hausmann (July 12, 1886 – February 1, 1971) was an Austrian artist and writer. One of the key figures in Berlin Dada, his experimental photographic collages, sound poetry, and institutional critiques would have a profound influence on the European Avant-Garde in the aftermath of World War I.
Early biography
Raoul Hausmann was born in Vienna but moved to Berlin with his parents at the age of 14, in 1901. His earliest art training was from his father, a professional conservator and painter. He met Johannes Baader, an eccentric architect and another future member of Dada, in 1905. At around the same time he met Elfride Schaeffer, a violinist, whom he married in 1908, a year after the birth of their daughter, Vera. That same year Hausmann enrolled at a private Art School in Berlin, where he remained until 1911.
After seeing Expressionist paintings in Herwarth Walden's gallery Der Sturm in 1912, Hausmann started to produce Expressionist prints in Erich Heckel's studio, and became a staff writer for Walden's magazine, also called Der Sturm, which provided a platform for his earliest polemical writings against the art establishment. In keeping with his Expressionist colleagues, he initially welcomed the war, believing it to be a necessary cleansing of a calcified society, although being an Austrian citizen living in Germany he was spared the draft.
Hausmann met Hannah Höch in 1915, and embarked upon an extramarital affair that produced an 'artistically productive but turbulent bond' that would last until 1922 when she left him. The relationship's turmoil even reached the point where Hausmann fantasized about killing Höch. He talked down to her about her opinions on everything from politics to art, and only came to her aid when the other artists of the Dada movement tried to exclude her from their art shows. Even after defending her art and arguing for its inclusion in the First International Dada Fair, he went on to say Höch "was never part of the club." Though H
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https://en.wikipedia.org/wiki/Ample%20line%20bundle
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In mathematics, a distinctive feature of algebraic geometry is that some line bundles on a projective variety can be considered "positive", while others are "negative" (or a mixture of the two). The most important notion of positivity is that of an ample line bundle, although there are several related classes of line bundles. Roughly speaking, positivity properties of a line bundle are related to having many global sections. Understanding the ample line bundles on a given variety X amounts to understanding the different ways of mapping X into projective space. In view of the correspondence between line bundles and divisors (built from codimension-1 subvarieties), there is an equivalent notion of an ample divisor.
In more detail, a line bundle is called basepoint-free if it has enough sections to give a morphism to projective space. A line bundle is semi-ample if some positive power of it is basepoint-free; semi-ampleness is a kind of "nonnegativity". More strongly, a line bundle on a complete variety X is very ample if it has enough sections to give a closed immersion (or "embedding") of X into projective space. A line bundle is ample if some positive power is very ample.
An ample line bundle on a projective variety X has positive degree on every curve in X. The converse is not quite true, but there are corrected versions of the converse, the Nakai–Moishezon and Kleiman criteria for ampleness.
Introduction
Pullback of a line bundle and hyperplane divisors
Given a morphism of schemes, a vector bundle E on Y (or more generally a coherent sheaf on Y) has a pullback to X, (see Sheaf of modules#Operations). The pullback of a vector bundle is a vector bundle of the same rank. In particular, the pullback of a line bundle is a line bundle. (Briefly, the fiber of at a point x in X is the fiber of E at f(x).)
The notions described in this article are related to this construction in the case of a morphism to projective space
with E = O(1) the line bundle on projective
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https://en.wikipedia.org/wiki/Confocal%20microscopy
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Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM) or laser scanning confocal microscopy (LSCM), is an optical imaging technique for increasing optical resolution and contrast of a micrograph by means of using a spatial pinhole to block out-of-focus light in image formation. Capturing multiple two-dimensional images at different depths in a sample enables the reconstruction of three-dimensional structures (a process known as optical sectioning) within an object. This technique is used extensively in the scientific and industrial communities and typical applications are in life sciences, semiconductor inspection and materials science.
Light travels through the sample under a conventional microscope as far into the specimen as it can penetrate, while a confocal microscope only focuses a smaller beam of light at one narrow depth level at a time. The CLSM achieves a controlled and highly limited depth of field.
Basic concept
The principle of confocal imaging was patented in 1957 by Marvin Minsky and aims to overcome some limitations of traditional wide-field fluorescence microscopes. In a conventional (i.e., wide-field) fluorescence microscope, the entire specimen is flooded evenly in light from a light source. All parts of the sample can be excited at the same time and the resulting fluorescence is detected by the microscope's photodetector or camera including a large unfocused background part. In contrast, a confocal microscope uses point illumination (see Point Spread Function) and a pinhole in an optically conjugate plane in front of the detector to eliminate out-of-focus signal – the name "confocal" stems from this configuration. As only light produced by fluorescence very close to the focal plane can be detected, the image's optical resolution, particularly in the sample depth direction, is much better than that of wide-field microscopes. However, as much of the light from sample fluorescence is blocked at the pinhole, this increase
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https://en.wikipedia.org/wiki/Fibrinoid%20necrosis
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Fibrinoid necrosis is a specific pattern of irreversible, uncontrolled cell death that occurs when antigen-antibody complexes are deposited in the walls of blood vessels along with fibrin. It is common in the immune-mediated vasculitides which are a result of type III hypersensitivity. When stained with hematoxylin and eosin, they appear brightly eosinophilic and smudged.
Diseases
Fibrinoid necrosis is not limited to the immune-mediated vasculitides; many pathologic processes can lead to areas of fibrinoid necrosis. In systemic lupus erythematosus, the dermis is often affected by fluid accumulation and inflammation around the small vessels in the skin, which may show prominent fibrinoid necrosis. Also it's seen in rheumatoid nodules with similar pathology. Also seen in Serum Sickness(Type III hypersensitivity reaction)
References
Histopathology
Necrosis
Cellular processes
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https://en.wikipedia.org/wiki/Social%20software%20%28research%20field%29
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In philosophy and the social sciences, social software is an interdisciplinary research program that borrows
mathematical tools and techniques from game theory and computer science in order to analyze and design social procedures. The goals of research in this field are modeling social situations, developing theories of correctness, and designing social procedures.
Work under the term social software has been going on since about 1996, and conferences in Copenhagen, London, Utrecht and New York, have been partly or wholly devoted to it. Much of the work is carried out at the City University of New York under the leadership of Rohit Jivanlal Parikh, who was influential in the development of the field.
Goals and tools
Current research in the area of social software include the analysis of social procedures and examination of them for fairness, appropriateness, correctness and efficiency. For example, an election procedure could be a simple majority vote, Borda count, a Single Transferable vote (STV), or Approval voting. All of these procedures can be examined for various properties like monotonicity. Monotonicity has the property that voting for a candidate should not harm that candidate. This may seem obvious, true
under any system, but it is something which can happen in STV. Another question would be the ability to elect a Condorcet winner in case there is one.
Other principles which are considered by researchers in social software include the concept that a procedure for fair division should be Pareto optimal, equitable and envy free. A procedure for auctions should be one which would encourage bidders to bid their actual valuation – a property which holds with the Vickrey auction.
What is new in social software compared to older fields is the use of tools from computer science like program logic, analysis of algorithms and epistemic logic. Like programs, social procedures dovetail into each other. For instance an airport provides runways for planes to l
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https://en.wikipedia.org/wiki/Rational%20agent
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A rational agent or rational being is a person or entity that always aims to perform optimal actions based on given premises and information. A rational agent can be anything that makes decisions, typically a person, firm, machine, or software.
The concept of rational agents can be found in various disciplines such as artificial intelligence, cognitive science, decision theory, economics, ethics, game theory, and the study of practical reason.
Economics
In reference to economics, rational agent refers to hypothetical consumers and how they make decisions in a free market. This concept is one of the assumptions made in neoclassical economic theory. The concept of economic rationality arises from a tradition of marginal analysis used in neoclassical economics. The idea of a rational agent is important to the philosophy of utilitarianism, as detailed by philosopher Jeremy Bentham's theory of the felicific calculus, also known as the hedonistic calculus.
The action a rational agent takes depends on:
the preferences of the agent
the agent's information of its environment, which may come from past experiences
the actions, duties and obligations available to the agent
the estimated or actual benefits and the chances of success of the actions.
In game theory and classical economics, it is often assumed that the actors, people, and firms are rational. However, the extent to which people and firms behave rationally is subject to debate. Economists often assume the models of rational choice theory and bounded rationality to formalize and predict the behavior of individuals and firms. Rational agents sometimes behave in manners that are counter-intuitive to many people, as in the traveler's dilemma.
Criticisms
Many economic theories reject utilitarianism and rational agency, especially those that might be considered heterodox.
For example, Thorstein Veblen, known as the father of institutional economics, rejects the notion of hedonistic calculus and pure rationa
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https://en.wikipedia.org/wiki/ClanLib
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ClanLib is a video game SDK, supporting Microsoft Windows, macOS, and Linux, with partial support for mobile platforms. It has full hardware accelerated graphics support through OpenGL, and also a software renderer. ClanLib also helps in playing sound, using the Vorbis or MikMod libraries, and has classes for collision detection, GUIs, XML, networking, and other things that may be helpful to a game programmer.
The earliest known public release is in 1999 (Version 0.1.18). Introduction to C++ Game Programming, published June 2007, dedicates a chapter to "Learn how to use the ClanLib library to make 2D games". Also Game Programming with Python, Lua, and Ruby, published December 2003, has a chapter about using ClanLib together with Ruby.
See also
Allegro
Raylib
SDL
SFML
References
External links
Application programming interfaces
Audio libraries
C++ libraries
Cross-platform software
Free game engines
Graphics libraries
Linux APIs
MacOS APIs
Software using the zlib license
Video game development software
Windows APIs
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https://en.wikipedia.org/wiki/Eqn%20%28software%29
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Part of the troff suite of Unix document layout tools, eqn is a preprocessor that formats equations for printing. A similar program, neqn, accepted the same input as eqn, but produced output tuned to look better in nroff. The eqn program was created in 1974 by Brian Kernighan and Lorinda Cherry.
It was implemented using yacc compiler-compiler.
The input language used by eqn allows the user to write mathematical expressions in much the same way as they would be spoken aloud. The language is defined by a context-free grammar, together with operator precedence and operator associativity rules. The eqn language is similar to the mathematical component of TeX, which appeared several years later, but is simpler and less complete.
An independent compatible implementation of the eqn preprocessor has been developed by GNU as part of groff, the GNU version of troff. The GNU implementation extends the original language by adding a number of new keywords such as smallover and accent. mandoc, a specialised compiler for UNIX man pages, also contains a standalone eqn parser/formatter.
History
Eqn was done by using yacc parser generator.
Syntax examples
Here is how some examples would be written in eqn (with equivalents in TeX for comparison):
Spaces are important in eqn; tokens are delimited only by whitespace characters, tildes ~, braces {} and double-quotes "". Thus f(pi r sup 2) results in , whereas f( pi r sup 2 ) is needed to give the intended .
References
Bibliography
External links
Typesetting Mathematics, User's Guide (Second Edition)
eqn
Plan 9 commands
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https://en.wikipedia.org/wiki/Jensen%27s%20alpha
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In finance, Jensen's alpha (or Jensen's Performance Index, ex-post alpha) is used to determine the abnormal return of a security or portfolio of securities over the theoretical expected return. It is a version of the standard alpha based on a theoretical performance instead of a market index.
The security could be any asset, such as stocks, bonds, or derivatives. The theoretical return is predicted by a market model, most commonly the capital asset pricing model (CAPM). The market model uses statistical methods to predict the appropriate risk-adjusted return of an asset. The CAPM for instance uses beta as a multiplier.
History
Jensen's alpha was first used as a measure in the evaluation of mutual fund managers by Michael Jensen in 1968. The CAPM return is supposed to be 'risk adjusted', which means it takes account of the relative riskiness of the asset.
This is based on the concept that riskier assets should have higher expected returns than less risky assets. If an asset's return is even higher than the risk adjusted return, that asset is said to have "positive alpha" or "abnormal returns". Investors are constantly seeking investments that have higher alpha.
Since Eugene Fama, many academics believe financial markets are too efficient to allow for repeatedly earning positive Alpha, unless by chance. Nevertheless, Alpha is still widely used to evaluate mutual fund and portfolio manager performance, often in conjunction with the Sharpe ratio and the Treynor ratio.
Calculation
In the context of CAPM, calculating alpha requires the following inputs:
: the realized return (on the portfolio),
: the market return,
: the risk-free rate of return, and
: the beta of the portfolio.
An additional way of understanding the definition can be obtained by rewriting it as:
If we define the excess return of the fund (market) over the risk free return as and then Jensen's alpha can be expressed as:
Use in quantitative finance
Jensen's alpha is a statistic that is co
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https://en.wikipedia.org/wiki/Diaphragm%20%28mechanical%20device%29
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In mechanics, a diaphragm is a sheet of a semi-flexible material anchored at its periphery and most often round in shape. It serves either as a barrier between two chambers, moving slightly up into one chamber or down into the other depending on differences in pressure, or as a device that vibrates when certain frequencies are applied to it.
A diaphragm pump uses a diaphragm to pump a fluid. A typical design is to have air on one side constantly vary in pressure, with fluid on the other side. The increase and decrease in volume caused by the action of the diaphragm alternately forces fluid out the chamber and draws more fluid in from its source. The action of the diaphragm is very similar to the action of a plunger with the exception that a diaphragm responds to changes in pressure rather than the mechanical force of the shaft.
A diaphragm pressure tank is a tank which has pressurant sealed inside on one side of the diaphragm. It is favored in certain applications due to its high durability and reliability. This comes with a downside, as the vessel needs to be replaced in the case of a rupture of the diaphragm.
Diaphragm tanks are used to store hypergolic propellant aboard space probes and various other spacecraft.
Pressure regulators use diaphragms as part of their design. Most uses of compressed gasses, for example, in gas welding and scuba diving rely on regulators to deliver their gas output at appropriate pressures. Automotive fuel systems frequently require fuel-pressure regulators; this is true of many fuel injection systems as well as in vehicles fueled with liquefied petroleum gas (autogas) and compressed natural gas.
See also
Gas engine
Hybrid vehicle
References
Mechanics.
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https://en.wikipedia.org/wiki/List%20of%20undecidable%20problems
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In computability theory, an undecidable problem is a type of computational problem that requires a yes/no answer, but where there cannot possibly be any computer program that always gives the correct answer; that is, any possible program would sometimes give the wrong answer or run forever without giving any answer. More formally, an undecidable problem is a problem whose language is not a recursive set; see the article Decidable language. There are uncountably many undecidable problems, so the list below is necessarily incomplete. Though undecidable languages are not recursive languages, they may be subsets of Turing recognizable languages: i.e., such undecidable languages may be recursively enumerable.
Many, if not most, undecidable problems in mathematics can be posed as word problems: determining when two distinct strings of symbols (encoding some mathematical concept or object) represent the same object or not.
For undecidability in axiomatic mathematics, see List of statements undecidable in ZFC.
Problems in logic
Hilbert's Entscheidungsproblem.
Type inference and type checking for the second-order lambda calculus (or equivalent).
Determining whether a first-order sentence in the logic of graphs can be realized by a finite undirected graph.
Trakhtenbrot's theorem - Finite satisfiability is undecidable.
Satisfiability of first order Horn clauses.
Problems about abstract machines
The halting problem (determining whether a Turing machine halts on a given input) and the mortality problem (determining whether it halts for every starting configuration).
Determining whether a Turing machine is a busy beaver champion (i.e., is the longest-running among halting Turing machines with the same number of states and symbols).
Rice's theorem states that for all nontrivial properties of partial functions, it is undecidable whether a given machine computes a partial function with that property.
The halting problem for a Minsky machine: a finite-state automaton w
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https://en.wikipedia.org/wiki/Pseudo-Hadamard%20transform
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The pseudo-Hadamard transform is a reversible transformation of a bit string that provides cryptographic diffusion. See Hadamard transform.
The bit string must be of even length so that it can be split into two bit strings a and b of equal lengths, each of n bits. To compute the transform for Twofish algorithm, a' and b', from these we use the equations:
To reverse this, clearly:
On the other hand, the transformation for SAFER+ encryption is as follows:
Generalization
The above equations can be expressed in matrix algebra, by considering a and b as two elements of a vector, and the transform itself as multiplication by a matrix of the form:
The inverse can then be derived by inverting the matrix.
However, the matrix can be generalised to higher dimensions, allowing vectors of any power-of-two size to be transformed, using the following recursive rule:
For example:
See also
SAFER
Twofish
This is the Kronecker product of an Arnold Cat Map matrix with a Hadamard matrix.
References
James Massey, "On the Optimality of SAFER+ Diffusion", 2nd AES Conference, 1999.
Bruce Schneier, John Kelsey, Doug Whiting, David Wagner, Chris Hall, "Twofish: A 128-Bit Block Cipher", 1998.
Helger Lipmaa. On Differential Properties of Pseudo-Hadamard Transform and Related Mappings. INDOCRYPT 2002, LNCS 2551, pp 48-61, 2002.
External links
Fast Pseudo-Hadamard Transforms
Theory of cryptography
Transforms
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https://en.wikipedia.org/wiki/Block%20design
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In combinatorial mathematics, a block design is an incidence structure consisting of a set together with a family of subsets known as blocks, chosen such that frequency of the elements satisfies certain conditions making the collection of blocks exhibit symmetry (balance). Block designs have applications in many areas, including experimental design, finite geometry, physical chemistry, software testing, cryptography, and algebraic geometry.
Without further specifications the term block design usually refers to a balanced incomplete block design (BIBD), specifically (and also synonymously) a 2-design, which has been the most intensely studied type historically due to its application in the design of experiments. Its generalization is known as a t-design.
Overview
A design is said to be balanced (up to t) if all t-subsets of the original set occur in equally many (i.e., λ) blocks. When t is unspecified, it can usually be assumed to be 2, which means that each pair of elements is found in the same number of blocks and the design is pairwise balanced. For t=1, each element occurs in the same number of blocks (the replication number, denoted r) and the design is said to be regular. Any design balanced up to t is also balanced in all lower values of t (though with different λ-values), so for example a pairwise balanced (t=2) design is also regular (t=1). When the balancing requirement fails, a design may still be partially balanced if the t-subsets can be divided into n classes, each with its own (different) λ-value. For t=2 these are known as PBIBD(n) designs, whose classes form an association scheme.
Designs are usually said (or assumed) to be incomplete, meaning that the collection of blocks is not all possible k-subsets, thus ruling out a trivial design.
A block design in which all the blocks have the same size (usually denoted k) is called uniform or proper. The designs discussed in this article are all uniform. Block designs that are not necessarily uniform hav
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https://en.wikipedia.org/wiki/Ripple%20effect
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A ripple effect occurs when an initial disturbance to a system propagates outward to disturb an increasingly larger portion of the system, like ripples expanding across the water when an object is dropped into it.
The ripple effect is often used colloquially to mean a multiplier in macroeconomics. For example, an individual's reduction in spending reduces the incomes of others and their ability to spend. In a broader global context, research has shown how monetary policy decisions, especially by major economies like the US, can create ripple effects impacting economies worldwide, emphasizing the interconnectedness of today's global economy.
In sociology, the ripple effect can be observed in how social interactions can affect situations not directly related to the initial interaction, and in charitable activities where information can be disseminated and passed from the community to broaden its impact.
The concept has been applied in computer science within the field of software metrics as a complexity measure.
Examples
The Weinstein effect and the rise of the Me Too movement
In October 2017, according to The New York Times and The New Yorker, dozens of women have accused American film producer Harvey Weinstein, former founder of Miramax Films and The Weinstein Company, of rape, sexual assault and sexual abuse for over a period of three decades. Shortly after over eighty accusations, Harvey was dismissed from his own company, expelled from the Academy of Motion Picture Arts and Sciences and other professional associations, and even retired from public view. The allegations against him results in the Weinstein effect, a global trend involving a serial number of sexual misconduct allegations towards other famous men in Hollywood, such as Louis CK and Kevin Spacey. The effect led to the formation of the controversial Me Too movement, where people share their experiences of sexual harassment/assault.
Corporate social responsibility
The effects of one company's de
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https://en.wikipedia.org/wiki/Interactive%20kiosk
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An interactive kiosk is a computer terminal featuring specialized hardware and software that provides access to information and applications for communication, commerce, entertainment, or education.
By 2010, the largest bill pay kiosk network is AT&T for the phone customers which allows customers to pay their phone bills. Verizon and Sprint have similar units for their customers.
Early interactive kiosks sometimes resembled telephone booths, but have been embraced by retail, food service, and hospitality to improve customer service and streamline operations. Interactive kiosks are typically placed in the high foot traffic settings such as shops, hotel lobbies, or airports.
The integration of technology allows kiosks to perform a wide range of functions, evolving into self-service kiosks. For example, kiosks may enable users to order from a shop's catalog when items are not in stock, check out a library book, look up information about products, issue a hotel key card, enter a public utility bill account number to perform an online transaction, or collect cash in exchange for merchandise. Customized components such as coin hoppers, bill acceptors, card readers, and thermal printers enable kiosks to meet the owner's specialized needs.
History
The first self-service, interactive kiosk was developed in 1977 at the University of Illinois at Urbana–Champaign by a pre-med student, Murray Lappe. The content was created on the PLATO computer system and accessible by the plasma touch-screen interface. The plasma display panel was invented at the University of Illinois by Donald L. Bitzer. Lappe's kiosk, called The Plato Hotline allowed students and visitors to find movies, maps, directories, bus schedules, extracurricular activities, and courses.
The first successful network of interactive kiosks used for commercial purposes was a project developed by the shoe retailer Florsheim Shoe Co., led by their executive VP, Harry Bock, installed circa 1985. The interactive kiosk
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https://en.wikipedia.org/wiki/Host-based%20intrusion%20detection%20system
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A host-based intrusion detection system (HIDS) is an intrusion detection system that is capable of monitoring and analyzing the internals of a computing system as well as the network packets on its network interfaces, similar to the way a network-based intrusion detection system (NIDS) operates. This was the first type of intrusion detection software to have been designed, with the original target system being the mainframe computer where outside interaction was infrequent.
Overview
A host-based IDS is capable of monitoring all or parts of the dynamic behavior and the state of a computer system, based on how it is configured. Besides such activities as dynamically inspecting network packets targeted at this specific host (optional component with most software solutions commercially available), a HIDS might detect which program accesses what resources and discover that, for example, a word-processor has suddenly and inexplicably started modifying the system password database. Similarly a HIDS might look at the state of a system, its stored information, whether in RAM, in the file system, log files or elsewhere; and check that the contents of these appear as expected, e.g. have not been changed by intruders.
One can think of a HIDS as an agent that monitors whether anything or anyone, whether internal or external, has circumvented the system's security policy.
Monitoring dynamic behavior
Many computer users have encountered tools that monitor dynamic system behavior in the form of anti-virus (AV) packages. While AV programs often also monitor system state, they do spend a lot of their time looking at who is doing what inside a computer – and whether a given program should or should not have access to particular system resources. The lines become blurred here, as many of the tools overlap in functionality.
Some intrusion prevention systems protect against buffer overflow attacks on system memory and can enforce security policy.
Monitoring state
The principle o
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https://en.wikipedia.org/wiki/Path%20%28topology%29
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In mathematics, a path in a topological space is a continuous function from the closed unit interval into
Paths play an important role in the fields of topology and mathematical analysis.
For example, a topological space for which there exists a path connecting any two points is said to be path-connected. Any space may be broken up into path-connected components. The set of path-connected components of a space is often denoted
One can also define paths and loops in pointed spaces, which are important in homotopy theory. If is a topological space with basepoint then a path in is one whose initial point is . Likewise, a loop in is one that is based at .
Definition
A curve in a topological space is a continuous function from a non-empty and non-degenerate interval
A in is a curve whose domain is a compact non-degenerate interval (meaning are real numbers), where is called the of the path and is called its .
A is a path whose initial point is and whose terminal point is
Every non-degenerate compact interval is homeomorphic to which is why a is sometimes, especially in homotopy theory, defined to be a continuous function from the closed unit interval into
An or 0 in is a path in that is also a topological embedding.
Importantly, a path is not just a subset of that "looks like" a curve, it also includes a parameterization. For example, the maps and represent two different paths from 0 to 1 on the real line.
A loop in a space based at is a path from to A loop may be equally well regarded as a map with or as a continuous map from the unit circle to
This is because is the quotient space of when is identified with The set of all loops in forms a space called the loop space of
Homotopy of paths
Paths and loops are central subjects of study in the branch of algebraic topology called homotopy theory. A homotopy of paths makes precise the notion of continuously deforming a path while keeping its endpoints fixed.
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https://en.wikipedia.org/wiki/Loop%20%28topology%29
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In mathematics, a loop in a topological space is a continuous function from the unit interval to such that In other words, it is a path whose initial point is equal to its terminal point.
A loop may also be seen as a continuous map from the pointed unit circle into , because may be regarded as a quotient of under the identification of 0 with 1.
The set of all loops in forms a space called the loop space of .
See also
Free loop
Loop group
Loop space
Loop algebra
Fundamental group
Quasigroup
References
Topology
es:Grupo fundamental#Lazo
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https://en.wikipedia.org/wiki/Korean%20language%20and%20computers
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The writing system of the Korean language is a syllabic alphabet of character parts () organized into character blocks () representing syllables. The character parts cannot be written from left to right on the computer, as in many Western languages. Every possible syllable in Korean would have to be rendered as syllable blocks by a font, or each character part would have to be encoded separately. Unicode has both options; the character parts (h) and (a), and the combined syllable (ha), are encoded.
Character encoding
In RFC 1557, a method known as ISO-2022-KR for seven-bit encoding of Korean characters in email was described. Where eight bits are allowed, EUC-KR encoding is preferred. These two encodings combine US-ASCII (ISO 646) with the Korean standard KS X 1001:1992 (previously named KS C 5601:1987). Another character set, KPS 9566 (similar to KS X 1001), is used in North Korea.
The international Unicode standard contains special characters for the Korean language in the hangul phonetic system. Unicode supports two methods. The method used by Microsoft Windows is to have each of the 11,172 syllable combinations as code and a preformed font character. The other method encodes letters (jamos) and lets the software combine them correctly. The Windows method requires more font memory but allows better shapes, since it is complicated to create stylistically correct combinations (preferable for documents).
Another possibility is stacking a sequence of medial(s) (jungseong) and a sequence of final(s) (jongseong) or a Middle Korean pitch mark (if needed) on top of the sequence of initial(s) (choseong) if the font has medial and final jamos with zero-width spacing inserted to the left of the cursor or caret, thus appearing in the right place below (or to the right of) the initial. If a syllable has a horizontal medial (, , , or ), the initial will probably appear further left in a complete syllable than in preformed syllables due to the space that must be reserv
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https://en.wikipedia.org/wiki/One-time%20password
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A one-time password (OTP), also known as a one-time PIN, one-time authorization code (OTAC) or dynamic password, is a password that is valid for only one login session or transaction, on a computer system or other digital device. OTPs avoid several shortcomings that are associated with traditional (static) password-based authentication; a number of implementations also incorporate two-factor authentication by ensuring that the one-time password requires access to something a person has (such as a small keyring fob device with the OTP calculator built into it, or a smartcard or specific cellphone) as well as something a person knows (such as a PIN).
OTP generation algorithms typically make use of pseudorandomness or randomness to generate a shared key or seed, and cryptographic hash functions, which can be used to derive a value but are hard to reverse and therefore difficult for an attacker to obtain the data that was used for the hash. This is necessary because otherwise, it would be easy to predict future OTPs by observing previous ones.
OTPs have been discussed as a possible replacement for, as well as an enhancer to, traditional passwords. On the downside, OTPs can be intercepted or rerouted, and hard tokens can get lost, damaged, or stolen. Many systems that use OTPs do not securely implement them, and attackers can still learn the password through phishing attacks to impersonate the authorized user.
Characteristics
The most important advantage addressed by OTPs is that, in contrast to static passwords, they are not vulnerable to replay attacks. This means that a potential intruder who manages to record an OTP that was already used to log into a service or to conduct a transaction will not be able to use it, since it will no longer be valid. A second major advantage is that a user who uses the same (or similar) password for multiple systems, is not made vulnerable on all of them, if the password for one of these is gained by an attacker. A number of OTP sy
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https://en.wikipedia.org/wiki/Pl%C3%BCcker%20embedding
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In mathematics, the Plücker map embeds the Grassmannian , whose elements are k-dimensional subspaces of an n-dimensional vector space V, either real or complex, in a projective space, thereby realizing it as a projective algebraic variety. More precisely, the Plücker map embeds into the projectivization of the -th exterior power of . The image is algebraic, consisting of the intersection of a number of quadrics defined by the (see below).
The Plücker embedding was first defined by Julius Plücker in the case as a way of describing the lines in three-dimensional space (which, as projective lines in real projective space, correspond to two-dimensional subspaces of a four-dimensional vector space). The image of that embedding is the Klein quadric in RP5.
Hermann Grassmann generalized Plücker's embedding to arbitrary k and n. The homogeneous coordinates of the image of the Grassmannian under the Plücker embedding, relative to the basis in the exterior space corresponding to the natural basis in (where is the base field) are called Plücker coordinates.
Definition
Denoting by the -dimensional vector space over the field , and by
the Grassmannian of -dimensional subspaces of , the Plücker embedding is the map ι defined by
where is a basis for the element and is the projective equivalence class of the element of the th exterior power of .
This is an embedding of the Grassmannian into the projectivization . The image can be completely characterized as the intersection of a number of quadrics, the Plücker quadrics (see below), which are expressed by homogeneous quadratic relations on the Plücker coordinates (see below) that derive from linear algebra.
The bracket ring appears as the ring of polynomial functions on .
Plücker relations
The image under the Plücker embedding satisfies a simple set of homogeneous quadratic relations, usually called the Plücker relations, or Grassmann–Plücker relations, defining the intersection of a number of quadrics i
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https://en.wikipedia.org/wiki/William%20Heerlein%20Lindley
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Sir William Heerlein Lindley (30 January 1853, in Hamburg – 30 December 1917, in London) was a British civil engineer.
One of three sons of the famous British engineer William Lindley, WH Lindley worked together with his father on a number of projects and was a respected engineer in his own right. Between 1881 and 1889 he oversaw the construction of Warsaw waterworks, designed by his father in 1876–1878. He oversaw the construction of the sewage system in Prague, built between 1895 and 1906, which is still in use today, and Sewage plant in Bubeneč in Prague, which was in use from 1907 until 1967 and currently its building serves as a museum of Prague's sewage system and is highly dedicated to Lindley. Between 1897 and 1898 he worked on the project for a water-supply system for Iași, which he linked, via an underground cast-iron aqueduct, to an aquifer located 103 kilometres away, in Timișești, Neamț County; Lindley's project was materialised in 1911, and the water system is still used. He also coordinated the project for Baku's water supply system, working from 1899 up until his death in 1917. In 1909 he also designed a water and sewerage system for Łódź, Poland, although the expense of the system meant the project was shelved until the 1920s.
Literature
Jaroslav Jásek: William Heerlein Lindley a pražská kanalizace (William Heerlein Lindley and sewage works in Prague), Scriptorium, Prague, 2006, . A Czech language monograph.
Franz Lerner, William Heerlein Lindley (1853–1917). Umriss seines Lebens von Franz Lerner, in: Archiv für Frankfurts Geschichte und Kunst, Heft 49, Frankfurt am Main 1965, s. 123–133.
The Dictionary of National Biography, Oxford University Press, 2004, Vol. 33
Ryszard Żelichowski, Lindleyowie. Dzieje inżynierskiego rodu (The Lindleys. Works of a family of engineers), Warszawa 2002,
Notes
External links
How Baku Got Its Water-The British Link
The Old Prague Sewage Works
1853 births
1917 deaths
British civil engineers
Knights Bachelor
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https://en.wikipedia.org/wiki/Domineering
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Domineering (also called Stop-Gate or Crosscram) is a mathematical game that can be played on any collection of squares on a sheet of graph paper. For example, it can be played on a 6×6 square, a rectangle, an entirely irregular polyomino, or a combination of any number of such components. Two players have a collection of dominoes which they place on the grid in turn, covering up squares. One player places tiles vertically, while the other places them horizontally. (Traditionally, these players are called "Left" and "Right", respectively, or "V" and "H". Both conventions are used in this article.)
As in most games in combinatorial game theory, the first player who cannot move loses.
Domineering is a partisan game, in that players use different pieces: the impartial version of the game is Cram.
Basic examples
Single box
Other than the empty game, where there is no grid, the simplest game is a single box.
In this game, clearly, neither player can move. Since it is a second-player win, it is therefore a zero game.
Horizontal rows
This game is a 2-by-1 grid. There is a convention of assigning the game a positive number when Left is winning and a negative one when Right is winning. In this case, Left has no moves, while Right can play a domino to cover the entire board, leaving nothing, which is clearly a zero game. Thus in surreal number notation, this game is {|0} = −1. This makes sense, as this grid is a 1-move advantage for Right.
This game is also {|0} = −1, because a single box is unplayable.
This grid is the first case of a choice. Right could play the left two boxes, leaving −1. The rightmost boxes leave −1 as well. He could also play the middle two boxes, leaving two single boxes. This option leaves 0+0 = 0. Thus this game can be expressed as {|0,−1}. This is −2. If this game is played in conjunction with other games, this is two free moves for Right.
Vertical rows
Vertical columns are evaluated in the same way. If there is a row of 2n or 2n+1 boxes, i
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https://en.wikipedia.org/wiki/Critical%20opalescence
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Critical opalescence is a phenomenon which arises in the region of a continuous, or second-order, phase transition. Originally reported by Charles Cagniard de la Tour in 1823 in mixtures of alcohol and water, its importance was recognised by Thomas Andrews in 1869 following his experiments on the liquid-gas transition in carbon dioxide; many other examples have been discovered since. In 1908 the Polish physicist Marian Smoluchowski became the first to ascribe the phenomenon of critical opalescence to large density fluctuations. In 1910 Albert Einstein showed that the link between critical opalescence and Rayleigh scattering is quantitative.
Examples
Binary fluid mixtures
The phenomenon is most commonly demonstrated in binary fluid mixtures, such as methanol and cyclohexane. As the critical point is approached, the sizes of the gas and liquid region begin to fluctuate over increasingly large length scales (the correlation length of the liquid diverges). As the density fluctuations become of a size comparable to the wavelength of light, the light is scattered and causes the normally transparent liquid to appear cloudy. Tellingly, the opalescence does not diminish as one gets closer to the critical point, where the largest fluctuations can reach even centimetre proportions, confirming the physical relevance of smaller fluctuations.
Approaching the critical point from the opposite direction, in case of liquid-gas transition, the gas phase may contain drops of liquid as mist and spray, and the boiling liquid phase bubbles of gas phase as foam. Far from the critical point the gravity causes liquid drops and gas bubbles to rapidly settle towards the interface and surface tension causes drops and bubbles to rapidly merge to larger ones, which settle even faster. But as critical point is approached, the density difference between liquid and vapour diminishes and so does the surface tension. These effects will slow down settling of drops and bubbles and their merger, such
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https://en.wikipedia.org/wiki/Schnorr%20group
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A Schnorr group, proposed by Claus P. Schnorr, is a large prime-order subgroup of , the multiplicative group of integers modulo for some prime . To generate such a group, generate , , such that
with , prime. Then choose any in the range until you find one such that
.
This value
is a generator of a subgroup of of order .
Schnorr groups are useful in discrete log based cryptosystems including Schnorr signatures and DSA. In such applications, typically is chosen to be large enough to resist index calculus and related methods of solving the discrete-log problem (perhaps 1024 to 3072 bits), while is large enough to resist the birthday attack on discrete log problems, which works in any group (perhaps 160 to 256 bits). Because the Schnorr group is of prime order, it has no non-trivial proper subgroups, thwarting confinement attacks due to small subgroups. Implementations of protocols that use Schnorr groups must verify where appropriate that integers supplied by other parties are in fact members of the Schnorr group; is a member of the group if and . Any member of the group except the element is also a generator of the group.
Asymmetric-key algorithms
Number theory
Group theory
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https://en.wikipedia.org/wiki/EchoLink
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EchoLink is a computer-based Amateur Radio system distributed free of charge that allows radio amateurs to communicate with other amateur radio operators using Voice over IP (VoIP) technology on the Internet for at least part of the path between them. It was designed by Jonathan Taylor, a radio amateur with call sign K1RFD.
The system allows reliable worldwide connections to be made between radio amateurs, greatly enhancing Amateur Radio's communications capabilities. In essence it is the same as other VoIP applications (such as Skype), but with the unique addition of the ability to link to an amateur radio station's transceiver. Thus any low-power handheld amateur radio transceiver which can contact a local EchoLink node (a node is an active EchoLink station with a transceiver attached) can then use the Internet connection of that station to send its transmission via VoIP to any other active EchoLink node, worldwide. No special hardware or software is required to relay a transmission via an EchoLink node.
Before using the system, it is necessary for a prospective user's callsign to be validated. The EchoLink system requires that each new user provide positive proof of license and identity before his or her callsign is added to the list of validated users. There is no cost for this service, and it ensures that this system is used only by licensed amateur radio operators.
The software is written to run on 32-bit and 64-bit versions of Microsoft Windows. Another edition of the software runs on Apple mobile devices (iPhone, iPod touch, and iPad), and is available from the Apple App Store. Qtel is an opensource version of the software available in many Linux repositories. An Android version is available on Google Play and several other Android app repositories.
Uses
Radio amateurs using the EchoLink software can operate it in one of two modes:
Single User Mode. If they have an Internet-connected computer, they can use the computer's microphone and speakers to conne
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https://en.wikipedia.org/wiki/Image%20resolution
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Image resolution is the level of detail an image holds. The term applies to digital images, film images, and other types of images. "Higher resolution" means more image detail.
Image resolution can be measured in various ways. Resolution quantifies how close lines can be to each other and still be visibly resolved. Resolution units can be tied to physical sizes (e.g. lines per mm, lines per inch), to the overall size of a picture (lines per picture height, also known simply as lines, TV lines, or TVL), or to angular subtense. Instead of single lines, line pairs are often used, composed of a dark line and an adjacent light line; for example, a resolution of 10 lines per millimeter means 5 dark lines alternating with 5 light lines, or 5 line pairs per millimeter (5 LP/mm). Photographic lens and are most often quoted in line pairs per millimeter.
Types
The resolution of digital cameras can be described in many different ways.
Pixel count
The term resolution is often considered equivalent to pixel count in digital imaging, though international standards in the digital camera field specify it should instead be called "Number of Total Pixels" in relation to image sensors, and as "Number of Recorded Pixels" for what is fully captured. Hence, CIPA DCG-001 calls for notation such as "Number of Recorded Pixels 1000 × 1500". According to the same standards, the "Number of Effective Pixels" that an image sensor or digital camera has is the count of pixel sensors that contribute to the final image (including pixels not in said image but nevertheless support the image filtering process), as opposed to the number of total pixels, which includes unused or light-shielded pixels around the edges.
An image of N pixels height by M pixels wide can have any resolution less than N lines per picture height, or N TV lines. But when the pixel counts are referred to as "resolution", the convention is to describe the pixel resolution with the set of two positive integer numbers, where the
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https://en.wikipedia.org/wiki/Pairing
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In mathematics, a pairing is an R-bilinear map from the Cartesian product of two R-modules, where the underlying ring R is commutative.
Definition
Let R be a commutative ring with unit, and let M, N and L be R-modules.
A pairing is any R-bilinear map . That is, it satisfies
,
and
for any and any and any . Equivalently, a pairing is an R-linear map
where denotes the tensor product of M and N.
A pairing can also be considered as an R-linear map
, which matches the first definition by setting
.
A pairing is called perfect if the above map is an isomorphism of R-modules.
A pairing is called non-degenerate on the right if for the above map we have that for all implies ; similarly, is called non-degenerate on the left if for all implies .
A pairing is called alternating if and for all m. In particular, this implies , while bilinearity shows . Thus, for an alternating pairing, .
Examples
Any scalar product on a real vector space V is a pairing (set , in the above definitions).
The determinant map (2 × 2 matrices over k) → k can be seen as a pairing .
The Hopf map written as is an example of a pairing. For instance, Hardie et al. present an explicit construction of the map using poset models.
Pairings in cryptography
In cryptography, often the following specialized definition is used:
Let be additive groups and a multiplicative group, all of prime order . Let be generators of and respectively.
A pairing is a map:
for which the following holds:
Bilinearity:
Non-degeneracy:
For practical purposes, has to be computable in an efficient manner
Note that it is also common in cryptographic literature for all groups to be written in multiplicative notation.
In cases when , the pairing is called symmetric. As is cyclic, the map will be commutative; that is, for any , we have . This is because for a generator , there exist integers , such that and . Therefore .
The Weil pairing is an important concept in elliptic curve cryptograp
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https://en.wikipedia.org/wiki/Linux-VServer
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Linux-VServer is a virtual private server implementation that was created by adding operating system-level virtualization capabilities to the Linux kernel. It is developed and distributed as open-source software.
Details
The project was started by Jacques Gélinas. It is now maintained by Herbert Pötzl. It is not related to the Linux Virtual Server project, which implements network load balancing.
Linux-VServer is a jail mechanism in that it can be used to securely partition resources on a computer system (such as the file system, CPU time, network addresses and memory) in such a way that processes cannot mount a denial-of-service attack on anything outside their partition.
Each partition is called a security context, and the virtualized system within it is the virtual private server. A chroot-like utility for descending into security contexts is provided. Booting a virtual private server is then simply a matter of kickstarting init in a new security context; likewise, shutting it down simply entails killing all processes with that security context. The contexts themselves are robust enough to boot many Linux distributions unmodified, including Debian and Fedora.
Virtual private servers are commonly used in web hosting services, where they are useful for segregating customer accounts, pooling resources and containing any potential security breaches. To save space on such installations, each virtual server's file system can be created as a tree of copy-on-write hard links to a "template" file system. The hard link is marked with a special filesystem attribute and when modified, is securely and transparently replaced with a real copy of the file.
Linux-VServer provides two branches, stable (2.2.x), and devel (2.3.x) for 2.6-series kernels and a single stable branch for 2.4-series. A separate stable branch integrating the grsecurity patch set is also available.
Advantages
Virtual servers share the same system call interface and do not have any emulation o
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https://en.wikipedia.org/wiki/Seaman%20%28video%20game%29
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is a virtual pet video game for the Sega Dreamcast. It is one of the few Dreamcast games to take advantage of the microphone attachment. The game developed a cult following for its dark humor, bizarre aesthetics, and innovative gameplay.
Seaman was released multiple times, including a limited edition demo version titled Christmas Seaman that was released in Japan in 1999, alongside a limited edition red Dreamcast and a PlayStation 2 version in 2001, titled Seaman: Kindan no Pet - Gaze Hakushi no Jikken Shima, the first edition of which came with a microphone. A PC version for Microsoft Windows was planned, with the Seaman being able to interact with the user's applications. No release date was specified, and it was later cancelled.
A sequel called Seaman 2 was released in Japan for the PlayStation 2 in 2007.
Gameplay
Seaman is considered a unique video game because it contains limited action. The player's goal is to feed and care for the Seaman while providing him with the company that he needs. The mechanic operates in real time, so the player is required to check on the Seaman every real-time day or he could die. A portion of the Seaman's knowledge is random trivia. When he asks what the player's birthday is (and the player responds via the microphone input), the Seaman will share significant events that happened on that date.
Although the Seaman becomes fairly domesticated, it does not stop insulting the player or making less-than-friendly remarks.
At the beginning of the game, the player is provided with an unhatched Seaman egg and develops and interacts with it through various stages of development. Through various buttons on the Dreamcast controller, the player controls all the machinery and physical contact with the mysterious creature. The player is also provided with multiple Seamen for breeding and interaction purposes. Over the course of the game, the player is required to evolve their Seaman to different stages in its life cycle, eventually transf
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https://en.wikipedia.org/wiki/Green%27s%20relations
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In mathematics, Green's relations are five equivalence relations that characterise the elements of a semigroup in terms of the principal ideals they generate. The relations are named for James Alexander Green, who introduced them in a paper of 1951. John Mackintosh Howie, a prominent semigroup theorist, described this work as "so all-pervading that, on encountering a new semigroup, almost the first question one asks is 'What are the Green relations like?'" (Howie 2002). The relations are useful for understanding the nature of divisibility in a semigroup; they are also valid for groups, but in this case tell us nothing useful, because groups always have divisibility.
Instead of working directly with a semigroup S, it is convenient to define Green's relations over the monoid S1. (S1 is "S with an identity adjoined if necessary"; if S is not already a monoid, a new element is adjoined and defined to be an identity.) This ensures that principal ideals generated by some semigroup element do indeed contain that element. For an element a of S, the relevant ideals are:
The principal left ideal generated by a: . This is the same as , which is .
The principal right ideal generated by a: , or equivalently .
The principal two-sided ideal generated by a: , or .
The L, R, and J relations
For elements a and b of S, Green's relations L, R and J are defined by
a L b if and only if S1 a = S1 b.
a R b if and only if a S1 = b S1.
a J b if and only if S1 a S1 = S1 b S1.
That is, a and b are L-related if they generate the same left ideal; R-related if they generate the same right ideal; and J-related if they generate the same two-sided ideal. These are equivalence relations on S, so each of them yields a partition of S into equivalence classes. The L-class of a is denoted La (and similarly for the other relations). The L-classes and R-classes can be equivalently understood as the strongly connected components of the left and right Cayley graphs of S1. Further, the L, R, and J re
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https://en.wikipedia.org/wiki/Retail%20software
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Retail software is computer software, typically installed on PC-type computers post 2005, delivered via the Internet (also known as cloud-based). Traditionally this software was delivered via physical data storage media sold to end consumer but very few companies still provide their software using physical media. The software is typically sold under restricted licenses (e.g. EULAs) or in the case of cloud-based software sold as a Software-as-a-Service (SaaS) model.
Types
Cloud-based software: this is software that is not installed on a user's device but delivered on-demand via the Internet to the end user's device(s) either through web-based apps or native apps (iOS and Android). Most new software companies provide both or a combination of web, and native apps which may provide different functionality depending on the actual user in a client company.
OEM Pack -HOW This is a licensed copy of software given by the software manufacturer to a computer manufacturer to pre-install on a computer being sold to a customer. A backup copy may or may not be provided on a CD to the end-user along with the computer.
Box Pack - This is a licensed copy of the software that an end-user buys off the shelf from any authorized retail outlet. They may sometimes be more highly-priced than OEM versions as you generally get additional software along with the main software within the pack.
Paper License - This is a scheme provided by the software manufacturer to companies or businesses that require many copies of particular software to be installed on multiple computers within the organization (Volume license key). Say, for example, a company requires installing software on 50 computers in its office. Instead of buying 50 CDs and managing those 50 individually, the company can buy one copy of the software and request the software vendor to issue a paper license authorizing them to use it on 50 computers. The software vendor then charges them accordingly. This method is also much cheap
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https://en.wikipedia.org/wiki/RC%20oscillator
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Linear electronic oscillator circuits, which generate a sinusoidal output signal, are composed of an amplifier and a frequency selective element, a filter. A linear oscillator circuit which uses an RC network, a combination of resistors and capacitors, for its frequency selective part is called an RC oscillator.
Description
RC oscillators are a type of feedback oscillator; they consist of an amplifying device, a transistor, vacuum tube, or op-amp, with some of its output energy fed back into its input through a network of resistors and capacitors, an RC network, to achieve positive feedback, causing it to generate an oscillating sinusoidal voltage. They are used to produce lower frequencies, mostly audio frequencies, in such applications as audio signal generators and electronic musical instruments. At radio frequencies, another type of feedback oscillator, the LC oscillator is used, but at frequencies below 100 kHz the size of the inductors and capacitors needed for the LC oscillator become cumbersome, and RC oscillators are used instead. Their lack of bulky inductors also makes them easier to integrate into microelectronic devices. Since the oscillator's frequency is determined by the value of resistors and capacitors, which vary with temperature, RC oscillators do not have as good frequency stability as crystal oscillators.
The frequency of oscillation is determined by the Barkhausen criterion, which says that the circuit will only oscillate at frequencies for which the phase shift around the feedback loop is equal to 360° (2π radians) or a multiple of 360°, and the loop gain (the amplification around the feedback loop) is equal to one. The purpose of the feedback RC network is to provide the correct phase shift at the desired oscillating frequency so the loop has 360° phase shift, so the sine wave, after passing through the loop will be in phase with the sine wave at the beginning and reinforce it, resulting in positive feedback. The amplifier prov
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https://en.wikipedia.org/wiki/Texture%20memory
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Texture memory is a type of digital storage that makes texture data readily available to video rendering processors (also known as GPUs), typically 3D graphics hardware. It is most often (but not always) implemented as specialized RAM (TRAM) that is designed for rapid reading and writing, enabling the graphics hardware increased performance in rendering 3D imagery.
Larger amounts of texture memory allow for more detailed scenes.
Computer memory
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