text
string | predicted_class
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|---|---|---|
The monopole antenna was inserted into the structure until the tip of the antenna reaches the center of the structural height in the y- direction. Keeping in mind that the monopole antenna should be parallel to the polarization axis of the injected electric field, the fact that the electric field is localized mostly between the rods that are perpendicular to the polarization axis inhibits the monopole antenna to be inserted parallel to the polarization axis. Therefore, as shown in Fig. 8(a) the monopole antenna was inserted from the neighboring layer inside and was tilted towards the region of interest with an angle of 16°. The measured electric field intensity was then normalized by the intensity measured with the same tilt angle at the center of the aperture of the transmitter horn antenna.
|
study
| 99.94 |
Dental caries is a public health problem in Belo Horizonte, state capital of Minas Gerais (southeastern Brazil) [1, 2], as well as in other Brazilian cities , and in many countries . In 2010, untreated caries in permanent teeth was the most prevalent health condition worldwide, affecting 2.4 billion people, and untreated caries in deciduous teeth was the 10th most prevalent health condition, affecting 621 million children worldwide . In Brazilian children, data from the 2010 Oral Health Project reveal that 56.5% of 12-year-olds have at least one permanent tooth with dental caries experience. This represents approximately 1.7 million children . Brazilian children also have a high prevalence of malocclusion (38.8%) and traumatic dental injury (20.5%) up to the age of 12 years .
|
study
| 99.5 |
In recent years, these conditions have been associated with a negative impact on children’s quality of life [8, 9, 10, 11]. Cross-sectional studies [12, 13, 14] demonstrated that dental caries have been associated with a negative impact on the quality of life of children from different age groups [15, 16, 17] So far, only one study, including 3- to 5 year-old children had used a case-control design to evaluate the association between dental caries and negative impact on oral health-related quality of life (OHRQoL). A case-control study provides adequate statistical power. This power depends not only on the number of cases and controls, but also on the distribution of the exposure of the population at risk and on the relative risk of disease the study aims to detect . Instead of measuring relative risk of disease based on exposure, a retrospective case-control study allows us measure the odds of exposure based on disease.
|
review
| 99.56 |
Given the paucity of case-control studies on the impact of oral conditions on OHRQoL, the objective of this study was to assess the negative impact of dental caries on the OHRQoL of 8- to 10-year-old Brazilian children, controlled by the other two main oral conditions in children (malocclusion and traumatic dental injury), using a design that offers greater strength of evidence.
|
study
| 99.94 |
A population-based case-control survey was carried out with a representative sample (546 male and female children aged 8 to 10 years, attending public and private elementary schools) in the city of Belo Horizonte, Brazil. Belo Horizonte is divided into nine regional areas of local administration. This case-control study was nested in a cross-sectional study .
|
study
| 99.94 |
A multistage sampling technique was adopted to select children. The first stage was comprised of randomly selected public and private elementary schools in each administrative district of Belo Horizonte. In the second stage, classes were randomly chosen from the selected schools.
|
other
| 90.56 |
The sample size was calculated to give a power of 80.0% and a standard error of 5.0%. Two controls were individually matched for each case. The odds ratio (OR) used was set at 2.0 and the probability of dental caries experience among cases was set at 63.7% . The probability of traumatic dental injuries among cases was set at 16.0% and the probability of malocclusion among cases was set at 57.2% . The sample size was calculated for each oral condition. The probability of traumatic dental injuries among cases was used due to their lower prevalence, indicating the need for a larger sample. The minimum sample size to satisfy the requirements was 182 cases and 364 controls.
|
study
| 100.0 |
Oral health-related quality of life (OHRQoL) was the dependent variable. The Brazilian version of the Child Perceptions Questionnaire for ages 8 to 10 years (CPQ8-10) was used to assess the impact of oral conditions on OHRQoL. The CPQ8-10 is an OHRQoL instrument designed exclusively for this age group. This instrument has been proven to be valid and reliable for use in Brazilian children . This instrument is made up of 25 items distributed into four subscales: oral symptoms (5 items), functional limitations (5 items), emotional well-being (5 items), and social well-being (10 items). The items address the frequency of events in the four previous weeks. A five-point rating scale is used, with the following options: never = 0; once/twice = 1; sometimes = 2; often = 3, and every day/almost every day = 4. CPQ8-10 scores are calculated by summing all the item scores, with the total score ranging from 0 (no impact of oral condition on OHRQoL) to 100 (maximum negative impact of oral condition on OHRQoL).
|
study
| 100.0 |
In order to define cases and controls, the CPQ8-10 scores were analyzed using the two-step cluster method. The log-likelihood distance measure was used. Two-step cluster analysis considered the 25 items of the Brazilian version of the CPQ8-10 separately and compared the mean of one item within each cluster to the overall mean of the same item in the total sample . The case group included those children who experienced a higher negative impact on OHRQoL whereas controls showed a lower negative impact on OHRQoL. Cases and controls were individually matched by school and gender.
|
study
| 100.0 |
Dental examinations were carried out at schools during daytime hours, in a private room. The examiners were seated in front of the children, who remained seating. The examiners used appropriate equipment to protect against individual cross-infection, with all instruments sterilized. The CPQ8-10 was applied by interviews before the clinical exams.
|
other
| 98.9 |
During the calibration process, 70 children (5.8% of the sample and not part of the study population) from a convenience sample were examined by two dentists. The examiners assessed the three conditions (dental caries experience, malocclusion, and TDI) and obtained inter-examiners agreement (kappa = 0.78–1.00). They re-examined the children after two weeks to assess intra-examiners agreement (kappa = 0.93–1.00).
|
study
| 100.0 |
The Statistical Package for Social Sciences, version 19.0 (SPSS Inc., Chicago, IL, USA), was used for the statistical analysis. Data analysis involved descriptive statistics. Bivariate logistic regression analysis was conducted to measure the association between independent variables and the negative impact on OHRQoL. Multiple conditional logistic regression was used for the matched case–control study. All the three clinical conditions were included in the logistic model based on their clinical epidemiological importance. The significance level was set at 5%.
|
study
| 100.0 |
The research was ethically conducted in accordance with the Declaration of Helsinki. The study was approved by the Human Research Ethics Committee of the Federal University of Minas Gerais (protocol 04.65.0.203.000–09). Parents/guardians and children read and signed an informed consent form prior to their participation in the study.
|
other
| 99.94 |
This population-based case-control study involved 546 children, 182 cases with a high negative impact on OHRQoL and 364 controls with a low negative impact on OHRQoL. The mean age was 9,08 (29.7%- 8 years old; 32.6%- 9 years old and 37.7%- 10 years old). The controls were individually matched with cases for gender and school using a 2:1 ratio. Table 1 demonstrates the frequency distribution of independent variables for matched cases and controls. There was no significant difference in traumatic dental injuries and malocclusion between the case and control groups (p>0.05). There was a statistically significant difference in dental caries experience between the case and control groups (p<0.05).
|
study
| 100.0 |
Table 2 displays the multiple conditional logistic regression and the influence of dental caries experience on children’s OHRQoL. Although traumatic dental injuries and malocclusion did not achieve statistical significance, these variables were maintained in the model to control for potential confounding factors. The results indicate that children with DMFT/dmft 1 or 2 had a 1.61-fold (95%CI = 1.05–2.49, p = 0.029) and children with DMFT/dmft ≥ 3 had a 2.06-fold (95%CI = 1.28–3.31, p = 0.003) greater chance of experiencing a high negative impact on OHRQoL than those with DMFT/dmft = 0.
|
study
| 100.0 |
Dental caries can influence children’s quality of life in activities such as eating, sleeping and talking, as well as their general health [15, 27]. The results of this study demonstrate that children with dental experience (DMFT/dmft 1 to 10) are more likely to suffer a high negative impact on their OHRQoL than those without dental caries experience (DMFT/dmft = 0). This finding is important because it proves that public health policies should be directed towards the most vulnerable groups. In Brazil, 20% of the school population concentrates about 60% of the disease burden .
|
study
| 99.94 |
Despite the overall reduction in the DMFT index and an increase in the prevalence of caries frees among Brazilian adolescents, there were increases in both income and education-related inequalities among caries-active individuals . This indicates inequality, i.e., the different prevalence of dental caries among individuals can be explained not only by inevitable biological changes, but also by differences in the social environment in which these individuals live, which is expressed through the health-disease process . More severe oral changes are found in a small percentage of the population, which requires greater attention. The damage and unequal distribution of dental caries can be minimized by comprehensive dental care, including prevention, oral health promotion, and treatment .
|
study
| 99.94 |
The Brazilian version of CPQ8-10 was used in this study to assess the impact of oral conditions on quality of life. This OHRQoL instrument was designed exclusively for this age group. This instrument has been proven valid and reliable for use in Brazilian children . In order to define cases and controls, the CPQ8-10 scores were analyzed using the two-step cluster method. Cases and controls were individually matched by school because a previous study showed that dental caries experience and severity of dental caries in primary and permanent teeth are influenced by the type of school . In Brazil, economically underprivileged children are enrolled public schools, had a higher prevalence of dental caries and the greatest impact thereof on their quality of life . Cases and controls were individually matched by gender to control the perception of negative impact on quality of life in this age group between sexes, since most studies demonstrated such association [12, 16, 31]. Even though the literature shows that there is no significant difference between boys and girls as to caries increment in the mixed dentition .
|
study
| 99.94 |
There was no significant difference in traumatic dental injuries between the case and control groups, probably because most of the children had mild dental trauma (e.g., enamel fractures). At this age, only severe trauma is associated with a negative impact on quality of life .
|
study
| 100.0 |
There was no significant difference in malocclusion between the case and control groups, contradicting a study with same-age children, which found that schoolchildren with malocclusion were 1.30-fold more likely to experience a negative impact on OHRQoL than those without malocclusion . This can be due to the cutoff point of the DAI. Malocclusion was dichotomized as either absent/mild (DAI ≤ 25) or present (DAI > 25). Thus, moderate malocclusions (DAI 26 to 30) could not have an impact on OHRQoL.
|
study
| 100.0 |
The present study has limitations. The sample selection used multistage sampling method rather than random sampling. This sampling method provides a cluster with children similar to each other and different from children in other clusters. For correct the similarity within the same cluster (school), a design factor of 1.2 was applied in the sample size calculation for the cross-sectional study in which this present case-control study was nested .
|
study
| 100.0 |
In general, there is a paucity of studies on dental caries with children in the mixed dentition phase [12, 20, 31]. In Brazil, a study using the same instrument was developed with 112 poor 8- to 10-year-old children. This previous study demonstrated that children with untreated dental caries have a greater prevalence ratio of having a negative perception of their oral health status than those without dental caries . The present study has a clear advantage over this previous study because of its case-control design. It provides stronger evidence than cross-sectional studies. There is a case-control study on dental caries and quality of life; however, it evaluated 415 children aged 3–5 years enrolled in public and private preschools. This previous study showed that caries severity impacted the OHRQoL of preschool children . The present study demonstrated that higher caries experience was associated with a greater negative impact on quality of life. In this way, children in the mixed dentition stage with high caries experience must be one of the priorities in the planning and implementation of public health policies for the prevention, control, and treatment of this disease.
|
study
| 99.8 |
Transparent amorphous oxide semiconductors have received much attention for such applications as thin film transistor (TFT) devices in liquid crystal displays (LCD), organic light emitting diodes (OLED), and transparent displays. In 2004, Hosono et al. made a breakthrough in replacing hydrogenated amorphous silicon (a-Si:H) and low-temperature polysilicon (LTPS) devices with amorphous oxide semiconductor in the fabrication of thin film transistors which were widely used in various display panels . More recently, a-Si:H semiconductor has been excluded by most manufacturers because of its poor mobility, degradation under electrical bias stress, and instability under illumination . In particular, LTPS is mostly used in active-matrix organic light emitting diode (AMOLED) displays with field effect mobility value of up to 100 cm2/Vs. However, despite its high mobility characteristics, LTPS usually showed relatively large threshold voltage variation . In contrast, TFTs based on metal oxide channel layer created a whole new area to explore with such advantages as simpler manufacturing process with good characteristics including high on-current and low off-current .
|
review
| 99.75 |
A lot of amorphous semiconductors have been studied for possible TFT applications, e.g., zinc oxide (ZnO) , indium zinc oxide (IZO) , zinc tin oxide (ZTO) and indium gallium zinc oxide (IGZO) . Since Arai reported the amorphous indium zinc tin oxide (a-IZTO) with good field effect mobility in the range of ~30 cm2/Vs, it has attracted some attention to see if there exists the possibility of an alternative to a-IGZO . IZTO is a ternary oxide semiconductor which is known to exhibit good electrical conductivity, high transparency, and high mobility, making it a promising candidate for further enhancement of the performance of display technologies . In the IZTO system, both indium and tin have similar electron configurations with about the same conduction bands, which then allows electrons to move easier and faster, even in amorphous state .
|
study
| 99.94 |
In this study, the electrical and optical properties of IZTO thin films were examined for the films deposited from a ceramic target with the nominal chemical composition corresponding to 40 at % indium, 50 at % zinc, and 10 at % tin on the metallic component basis. The deposition of IZTO thin films was conducted using radio frequency (RF) magnetron sputtering as reported earlier by our group . The variation of the electrical properties and TFT performance with annealing treatment was investigated in detail.
|
study
| 100.0 |
Zinc-rich IZTO ceramic target with the metal ratio of In:Zn:Sn = 40:50:10 at % was prepared using the conventional mixed-oxide process. IZTO thin films were then sputter-deposited onto 15 mm × 15 mm-square commercial glass in order to observe the transparency and morphology of the films. Top-contact bottom-gate TFTs were fabricated where an IZTO active layer was deposited onto n++ heavily-doped silicon wafer with 200 nm-thick SiO2 gate insulating layer. Deposition of IZTO films was conducted using RF magnetron sputtering at room temperature with RF power of 125 W and working pressure of 5 × 10−3 Torr. Prior to deposition, the vacuum chamber was evacuated to a base pressure of 2 × 10−5 Torr or below. The deposition time was kept for 3 min to obtain the channel layer thickness of around 50 nm. During deposition, oxygen acted as ambient gas where O2:Ar ratio was 5%:95% while the gas flow rate was fixed at 20 sccm. After deposition, the films were annealed at temperature in the range of 150–350 °C for 30 min in air inside of the tube furnace. Titanium and copper bilayer metallic films were subsequently deposited as source and drain contacts using an e-beam evaporator through shadow mask with width and length dimensions of 350 μm and 150 μm, respectively. The structural and surface topography were characterized and confirmed by X-ray diffraction (XRD, Rigaku D-500) and atomic force microscopy (AFM, Nanoscope IIIA). The X-ray photoelectron spectroscopy (XPS) study was performed using an XPS system (Thermo Fisher Scientific K-Alpha, Waltham, MA, USA) with monochromated Al Kα X-ray source (hν = 1486.6 eV) at a spot size of 400 μm in diameter with charge compensation. Survey spectra were obtained at pass energy of 200 eV and a resolution of 1 eV, and high-resolution spectra were acquired at pass energy of 30 eV and a resolution of 0.1 eV. All of the obtained binding energies (BEs) were compensated with that of adventitious carbon (C 1s) core level peak at 284.6 eV as a reference . The Avantage software provided by the manufacturer was used for controlling the spectrometer, analyzing the spectra, and the deconvolution of O 1s core level spectra.
|
study
| 100.0 |
The electrical properties of the IZTO films and TFTs were characterized using Hall effect measurement (Ecopia HMS-5000, Anyang, Republic of Korea) and I–V measurement (Keithley 4200-SCS, Beaverton, OR, USA). The optical transmittance of the films across visible spectrum was observed using ultraviolet-visible spectrophotometer (UV/Vis/NIR spectrophotometer, Cary 5000, Agilent, Santa Clara, CA, USA).
|
study
| 99.94 |
X-ray diffraction patterns of the IZTO films deposited onto glass substrates at room temperature by RF magnetron sputtering are shown in Figure 1. The amorphous nature is clearly seen in all samples. This commonly happens in many multicomponent complex mixed oxide films where the crystallization energy is considerably higher than the thermal energy available at room temperature. Similar results were reported elsewhere , where IZTO films with low zinc content deposited at room temperature remained in amorphous state . The crystallinity of the films is known to be affected by the processing variables, such as gas ambient, deposition temperature, working pressure, annealing temperature, and chemical composition . However, even after annealing with temperature of up to 350 °C, no particular diffraction peaks corresponding to crystalline phases were observed from all IZTO films we had prepared. Furthermore, the surface topography observed using AFM revealed that subsequently, all films showed very smooth and uniform surface, which is very important for TFT application to minimize defects at the interlayers . There was no prominent change in root-mean-square surface roughness values (Rq), which increased from about 0.2 nm to 0.3 nm for all IZTO films as the annealing temperature increased, as summarized in Table 1.
|
study
| 100.0 |
The optical transmittance was determined by taking the average value in the visible light region ranging between 400 nm and 700 nm in wavelength. Figure 2 illustrates the optical transmittance of the IZTO films deposited on glass substrate. Among all films, as-deposited IZTO film showed the lowest average transmittance of about 84%. The band gap energy value of IZTO films was estimated from the inset in Figure 2, which was done by extrapolating the linear part of hν versus (αhν)2 graph to the x axis according to Tauc equation . The average optical band gap energy value was estimated at 3.25 eV, while there was no significant difference, even after annealing treatment. An optical band gap value of about 3 eV was reported from IZTO with composition of 50 at % zinc and 30 at % indium , as increasing indium and zinc deteriorated the optical transmittance and decreased the optical band gap energy of IZTO thin films . Nevertheless, a shift in band gap energy and average transmittance values was reported elsewhere by composition variation of IZTO . This is why an annealing treatment did not alter the band gap value of the IZTO film. Overall, the optical properties of all IZTO films exhibited high average transmittance above 80% and relatively high band gap energy, which is desirable for transparent display application.
|
study
| 100.0 |
Table 2 summarizes the typical electrical property data (i.e., carrier concentration and resistivity) of IZTO films. The carrier concentration value increased, while resistivity value decreased with the increase of annealing temperature. Lower values of resistivity led to an active layer with more electrons, resulting in the threshold voltage shift to the negative direction .
|
study
| 100.0 |
Table 3 shows relative peak area ratio and binding energy of the IZTO thin films deposited by RF magnetron sputtering on silicon substrates at various annealing temperatures in the range of 150–350 °C. The related binding energies existed in metal-oxide (In-O, Zn-O, and Sn-O), oxygen vacancy (Oxy. Vac), and impurities such as hydroxides (O-OH) known as trapping sites on the interface of the TFT . Based on the detailed O 1s XPS spectra of IZTO films shown in Figure 3a, the oxygen vacancy peak existed at the binding energy of 530.4 eV. It was seen that the oxygen vacancy tended to increase slightly with the increase of annealing temperature. This rather unusual result could only be explained by the rearrangement of oxygen ions in the film to thermodynamically more stable positions, thereby yielding slightly more oxygen vacancies. However, as shown in Table 2, the increase of electron concentration is much higher than the increase of oxygen vacancy, and thereby is not just because of the increase of oxygen vacancy concentration but rather because of the increase of singly- or doubly-ionized oxygen vacancy concentration yielding mobile electrons. As-deposited films should have a greater number of neutral oxygen vacancies with the two electrons trapped at or near the vacancy and does not contribute to mobile carriers . In turn, this electron concentration increase brought the negative shift of the threshold voltage to be further explained below.
|
study
| 100.0 |
To investigate TFT device performance based on IZTO semiconductor channel layer, the transistor prepared using heavily-doped silicon wafer substrate was examined in n-channel mode. Figure 4 depicts the transfer characteristic of IZTO TFT device deposited by RF magnetron sputtering with annealing temperature variation. It is seen that field effect mobility (μFE), on/off current ratio (Ion/off), and subthreshold swing (SS) values improved as annealing temperature increased from 150 °C to 350 °C, as shown in Table 4. Threshold voltage (VT) value tended to shift to zero voltage by controlling the carrier concentration of IZTO channel layer with the increasing annealing temperature. As the carrier concentration increased, the threshold voltage and subthreshold swing values shifted to more desirable values . The enhancement of TFT performance was noticed by lowering resistivity and reducing SS values of IZTO channel layer with increasing annealing temperature, which might be mainly due to oxygen diffusion from IZTO layer and rearrangement of molecular bonding during annealing process, thus inducing the acceleration of electrons to pass through channel region between source and drain .
|
study
| 100.0 |
Our TFT devices made from a zinc-rich IZTO channel layer demonstrated excellent performance with a field effect mobility value of 34 cm2/Vs, which is higher than the values reported by other research groups . It is also noticed that interface defect concentration (NT) value, which was estimated from SS value, was reduced with increasing annealing temperature. It is obvious the mobility of charge carriers would then be improved as electrons travel from source to drain through the a-IZTO channel layer .
|
study
| 100.0 |
The stability of the a-IZTO thin film transistor annealed at 350 °C was explored under both positive bias stress (PBS) and negative bias stress (NBS). The tests were performed at drain voltage (VDS) of ±10 V with stress time of up to 1200 s. As shown in Figure 5, the transfer characteristics curve shifted to the positive direction, and thus threshold voltage also changed to the positive direction with the increase of bias stress time. This voltage shift of transfer characteristics was attributed to electron trapping at the gate/insulator interface in n-type TFTs . The threshold voltage shift under PBS is about +1.9 V while the NBS is about +3.1 V. Higher bias instability of a-IZTO thin film transistor would be expected to decrease further by applying passivation layer to prevent humidity .
|
study
| 100.0 |
Room-temperature-deposited IZTO films remained uniform amorphous phase even after annealing at temperatures of up to 350 °C, indicating that the enhancement of TFT performance was not due to the crystallization of the IZTO layer. IZTO films deposited by RF magnetron sputtering showed transparency values higher than 84%, regardless of the annealing treatment across the visible light range, which is desirable for transparent electronic device applications. It was found that annealing treatment affected TFT parameters in such a way as to increase the carrier mobility and on/off current ratio, and to decrease the sub-threshold swing value. The threshold voltage value also shifted to the negative direction, and the carrier concentration value increased upon annealing. Interface defect concentration also reduced, resulting in the movement of more electrons without being trapped between the active layer and the source or drain electrode. However, stability improvement under bias stress still remains as an issue to enhance the performance of a-IZTO thin film transistors in the near future.
|
study
| 100.0 |
Upper gastrointestinal bleeding is a life threatening condition in children. Common sources of upper gastrointestinal bleeding in children include mucosal lesions and variceal hemorrhage [1, 2]. Incidence of upper GI bleeding was observed in 6.4-10% of pediatric ICU admissions [3, 4]. Helicobacter pylori (H. pylori) is a Gram negative spiral-shaped bacterium that is found in the gastric mucous layer or adherent to the epithelial lining of the stomach. H. pylori infection is related to more than 90% of duodenal ulcers and up to 70-80% of gastric ulcers . In adults, the presence of H. pylori confers a six fold increased risk of gastric adenocarcinoma, accounts for half of all gastric cancers and strongly implicated in the development of gastric B cell mucosa associated lymphoid tissue (MALT) lymphomas . Many studies investigated the relationship between H. pylori and upper GIT bleeding in adults , but no enough studies in children.
|
review
| 99.9 |
This is a prospective study included 70 children presented with upper GIT bleeding indicated for upper gastrointestinal endoscopy admitted in pediatric department, Minia university hospital, Egypt during the period from February 2010 to December 2012. Thirty healthy children were included as a control group with age and sex matched. The study was approved by pediatric department council, Minia University and informed consents from parents or caretakers were taken. Children receiving any medications (NSAIDS, anticoagulants, corticosteroids) and those with known history of coagulopathy, bleeding disorders, diabetes mellitus or chronic illness were excluded from the study. All children after history taking and physical examination were exposed to laboratory investigations. Upper G.I.T endoscopy performed within 24 hours of admission for patients group only.
|
study
| 99.94 |
Blood samples were taken by sterile venipuncture: Two mls of venous blood on EDTA containing tube were aspirated for CBC. Another two mls were aspirated on sodium citrate containing tube for prothrombin time and concentration by thrombrel-s (human thromboplastin containing calcium) from (Behring diagnostic Inc. USA). Five mls of venous blood were aspirated on a plain plastic tube and left to be clotted in the incubator and centrifuged to be separated for assessment of liver function tests (using Integra 400 auto analyzer). Hepatitis B surface antigen was measured by Enzyme Linked Immunosorbent Assay (Sanofi Diagnostic Pasture, Marne-La-Coquette. France).Hepatitis C antibody was measured by a third generation ELISA (BIOELISA HCV Kit, BIOKIT, S. A Barcelona). Blood urea and serum creatinine were measured (by fully automated clinical chemistry auto-analyzer system Konelab 20i.). A fresh stool sample was collected and stored at -20 °C for analysis for H. pylori stool antigen test (Premier Platinum HpSA, Meridian Diagnostics, Cincinnati, OH) [13, 14]. Abdominal Ultrasound: done using a real time equipment (Fukuda Denshi - 4500) linear machine. Upper endoscopy was done for patients only. Olympus pediatric gastroscope (GIFP3) was used for the procedure .
|
study
| 99.9 |
Data were analyzed using Statistical Package for the Social Science (SPSS for windows version 13.0). The continuous variables were expressed as mean ± SD which compared using chi-square test. Statistical significance was defined as a probability level of P ≤ 0.05. For calculation and comparison between weights and BMIs centiles we used Z-score. WHO centile charts were used for weight, height and BMI cantle measurements .
|
study
| 99.9 |
Helicobacter pylori infection was significantly higher in children with non-variceal bleeding than controls (P = 0.02) and variceal bleeding (P = 0.03) with no significant differences between children with variceal bleeding and controls (P = 0.9). All patients were negative for both hepatitis B and C markers. No significant differences between cases and controls as regards urea or creatinine levels were present. A laboratory triad of increased ALT (> 45 U/L), decreased albumin levels (< 4 g/dL) and negative H. pylori infection was a significant triad in predicting variceal bleeding as a cause in children presented with upper GIT bleeding. It was positive in 8 cases of 18 children presented with variceal bleeding (44.4%) versus only one case of 52 children presented with non-variceal bleeding (1.9 %) (P = 0.002). Non-Variceal group included: gastritis (38 patients), duodenitis (9 patients), esophagitis (2 patients), multiple duodenal polyps (1 patient) and Mallory Weiss tear (2 patients), (Table 1-3).
|
study
| 99.94 |
H. pylori was shown to be associated with peptic ulcer disease in 1985. Since then, the detection of spiral bacterium in the gastric mucosa has become a principal aspect of the diagnosis of patients with upper gastrointestinal symptoms suggestive of peptic ulcer disease [6, 8].
|
review
| 99.6 |
It is now generally accepted that H. pylori infections are acquired during childhood or adolescence in developing as well as developed countries with prevalence in children ranged from less than 10% to greater than 80% dependening upon age, socioeconomic class and geographic distribution [17, 18].
|
other
| 73.5 |
In this study, H. pylori infection was significantly higher in children with non-variceal bleeding than control group (65.4% vs. 36.7% P = 0.02) and variceal group (65.4% vs. 33.3% P = 0.03) with no significant difference between children with variceal bleeding and control group (33.3% vs. 36.7% P = 0.9). This is partly in agreement with the previous as well as other studies [10, 17, 18].
|
study
| 100.0 |
In this study no significant difference between males and females was present and these results were in agreement with other reports , while Leandro et al, 2005 reported a significant association between H. pylori infection and male gender (without explanation).
|
study
| 99.94 |
Both weights and BMIs centile were significantly lower in variceal and non-variceal groups than controls (P = 0.01 & 0.001 and 0.01 & 0.001 respectively). These results reflected the bad nutritional aspect of those children either due to chronic liver disease or helicobacter-pylori infection. These results were comparable to other studies .
|
study
| 100.0 |
Abnormal liver function tests in the form of elevated ALT and AST, decreased prothrombin concentration, prolonged prothrombin time, elevated bilirubin levels, decreased albumin and total protein levels in children of variceal bleeding may be due to presence of chronic liver disease or due to hepatic hypo perfusion secondary to upper GIT bleeding.
|
other
| 99.9 |
In this study hemoglobin levels were lower -as expected- in cases (variceal and non-variceal) than controls, since our cases presented by upper GI bleeding and most of them were H. pylori positive and this is in agreement with other studies reported association between H. pylori infection and presence of anemia .
|
study
| 100.0 |
H. pylori infection may cause iron deficiency anemia through sequestration of iron by antral H. pylori infection, malabsorption of iron, folic acid, vitamin B6 and vitamin B12 [23, 24] and\or by an autoimmune process triggered by antigenic mimicry between H. pylori epitopes and major autoantigens of the gastric mucosa .
|
study
| 96.9 |
An etiology scoring system was published by Pongprasobchai et al, in March 2009 in the world journal of gastroenterology for predicting the etiology of upper GI bleeding in adults depending upon both clinical and laboratory data , but no scoring system developed in children yet.
|
other
| 69.5 |
The results of this study revealed that a laboratory triad of increased ALT levels (> 45 U/L), decreased albumin levels (< 4 g/dL) and negative H. pylori infection was a significant triad in predicting variceal bleeding as a cause in children presented with upper GIT bleeding as this triad was positive in 9 children, 8 of them (88.8%) were variceal bleeding in origin.
|
study
| 99.94 |
This laboratory triad reflected the un-compensated condition of the liver for those children having variceal bleeding, this is not in accordance with a study reported that 76.5% of children with gastrointestinal bleeding in north India were patients of extrahepatic portal vein obstruction. This difference may be attributed to the high incidence of Bilharsiasis and its complications in Egypt responsible for liver affection and portal hypertension.
|
study
| 99.9 |
No significant differences were found as regards demographic data between H. pylori-positive and H. pylori-negative children except for age where older children had a higher rate of infection. This indicates that the prevalence curve of acquisition of H. pylori infections rises with age, which may be due to outdoor activities and exposure to potential external sources. These results were in agreement with other studies [19, 20].
|
study
| 100.0 |
No significant difference between cases (variceal and non variceal groups) and controls was present as regards platelets count and this is not in agreement with other studies reported association between H. pylori infection and idiopathic thrombocytopenic purpura [28, 29].This difference is attributed to our exclusion criteria as we excluded children with known history of coagulapathy or bleeding disorder from this study.
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H. pylori infection is significantly higher in children with non-variceal bleeding than controls. No significant difference between children with variceal bleeding and controls. Triad of increased ALT, decreased albumin levels and negative H. pylori infection could be a significant triad in predicting variceal bleeding as a cause of upper GIT bleeding in children.
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Pinning-controlled permanent magnets operating at elevated temperatures boost device performances of magnet-based industrial applications1–9. These include microwave tubes, gyroscopes and accelerometers, reaction and momentum wheels to control and stabilize satellites, magnetic bearings, sensors and actuators. Sm2(Co,Fe,Cu,Zr)17 is an important industrially used material system, since it has both a high Curie temperature and a high magnetocrystalline anisotropy10–14. Unlike nucleation-controlled Nd-Fe-B-based permanent magnets, the Sm2Co17-type maintains its excellent magnetic properties at elevated temperatures15. In order to precisely control the synthesis parameters to obtain such high magnetic performances, it is necessary to thoroughly understand the atomic-scale structure and behavior of the involved phases. This is not a straightforward task and although the relationship of microstructure and chemistry with the magnetic properties has been widely studied by local techniques such as electron microscopy, the number of atomic-scale investigations is still limited1–3, 16–20.
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The iron content has a significant effect on the magnetic properties of Sm2(Co,Fe,Cu,Zr)17 permanent magnets21–26. It was shown by Hadjipanayis et al.4 that an optimum coercivity is reached for an iron content between 15 and 20 wt%. With increasing Fe content, the cellular structure changes from an inhomogeneous to a larger, but uniform cell size (~120 nm), and finally to a coarse and inhomogeneous microstructure27. Iron preferentially replaces cobalt in the 2:17 phase and is responsible for the saturation magnetization. Since the domain wall energy is largest in the cell boundary phase (later referred as SmCo5 or 1:5 phase), this phase acts as a main pinning center for magnetic domain walls21, 28. According to Skomski et al.21 Zr-rich (Z-phase) platelets contribute to the formation of the cell boundaries and do not yield any dominating contribution to the coercivity, but might still act as pinning centers. Skomski et al.21 as well as Katter et al.29, 30 predicted that the domain walls are heavily bowed until they reach an interface between the 2:17 and the 1:5 phase. However, the pinning forces at such straight interfaces are much higher than the observed coercivities. Therefore, the coercivity is determined by the depinning of the domain walls at certain weak points31. These weak points are the edges of the 2:17 cells and the intersection lines of the 1:5 phase with the Z-phase. The domain walls are strongly pinned at the plane interfaces between the 2:17 cell and the 1:5 boundary phase.
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In the following, we present a detailed investigation on the atomic scale of the Z-phase and its contribution to the domain wall-pinning behavior. We demonstrate that it is much favorable from an energetic point of view to move a short section of the domain wall at these weak points from the 2:17 or Z-phase into the 1:5 phase than to press a long section of it into the plane interface. This implies that the domain walls are not only pinned at the plane 1:5 to 2:17 interface, but are also firstly depinned at the edges of the cells and later at the intersection lines of the 1:5 and the Z-phase. In order to clarify the atomic structure of the Z-phase and its contribution to the magnetization process, we investigated in detail the microstructure by combined atomic-structure investigations, microstructure-based micromagnetic simulations and density functional theory calculations.
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Figure 1 shows bright-field transmission electron microscopy (TEM) images and selected area electron diffraction (SAED) patterns of two different samples. Figure 1a is a bright-field TEM image of sample 1 (lower iron content, see Table 1) oriented close to the pole in two-beam condition. The diamond-shaped cellular structure of the 1:5 boundary phase and the Z-phase, therefore show strong diffraction contrast. A detailed energy-dispersive X-ray microanalysis (EDX) of the single phases is presented in Supplementary Fig. 1 and Supplementary Table 1. The diamond-shaped cellular structure has a uniform size ~200 nm and is very well aligned. The Z-phase platelets are ~4 nm in height and are densely distributed. They intersect the 10-nm-thick diamond-shaped 1:5 boundary phase. Figure 1b shows a SAED pattern along the zone-axis (red part) with a oriented twin (blue part). The inset shows a line profile along the [00l] direction. The additional reflections marked by the triangles as well as the slight streaking originate from the Z-phase platelets forming an ordered superstructure along the c-axis direction (see the {0,0,3/2} type of reflections revealed by the line profile). Figure 1c is a bright-field TEM image of sample 2 (higher iron content, see Table 1) oriented close to the pole in two-beam condition. The Z-phase shows here diffraction contrast, however, the striking difference compared to sample 1 is that there is no diamond-shaped cellular structure in the 1:5 boundary phase present. Only single, isolated facets of 1:5 cells are found. Figure 1d shows a SAED along the zone-axis. The different zone-axis orientation makes no difference to the visibility of the 1:5 cellular structure in the two-beam condition obtained bright-field TEM images. The strong streaking being present in the SAED along the [00l] direction originates from the presence of the Z-phase platelets. The inset shows a line profile along the [00l] direction with additional reflections marked by triangles. These additional reflections do not lie on the center between two regular spots of the Sm2Co17 (2:17) phase as it is the case for sample 1 indicating together with the stronger streaking a larger Z-phase disorder for sample 2 as compared to sample 1. Therefore, it is obvious that the structure of sample 2 strongly deviates from that of sample 1: There is no diamond-shaped cellular structure of the 1:5 phase visible at all. However, still isolated unequally distributed 1:5-type lamellas occur. Some of them seem to act as bridges perpendicularly connecting to the Z-phase platelets. Those bridges may be boundaries between two phases, as the Z-phase platelets should only grow in one direction. A few of the Z-phase platelets also suddenly end somewhere in the 2:17 matrix, especially in sample 2.Fig. 1Nanoscale phase distribution. a Bright-field TEM image of sample 1. b Corresponding selected area electron diffraction pattern along the zone axis (red text labels) with additional reflections from a oriented twin (blue text labels). The superstructure reflections of type {0,0,3/2} along the hexagonal c-axis are denoted in the line profile shown in the inset of b. c Bright-field TEM image of sample 2. d Corresponding selected area diffraction pattern along the zone-axis. Note the difference in ordering in the line profile inset in d compared to the line profile shown in the inset in b. The scales bars in the TEM images correspond to 50 nm. The scale bars in the electron diffraction patterns correspond to 5 nm−1 Table 1Iron content and magnetic properties of the samplesSampleNominal Fe content (wt%) B r (T) H cB (kA m−1) H cJ (kA m−1)(BH)max (kJ m−3)1191.28702,3802622230.9250280100The data were extracted from demagnetization curves obtained at T = 20 °C. The determined quantities are remanence (Br), coercive field strength at polarization equals zero (H cB), coercive field strength at flux density equals zero (H cJ) and energy density ((BH)max). These values can be compared to the values provided by Maybury et al.15
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Nanoscale phase distribution. a Bright-field TEM image of sample 1. b Corresponding selected area electron diffraction pattern along the zone axis (red text labels) with additional reflections from a oriented twin (blue text labels). The superstructure reflections of type {0,0,3/2} along the hexagonal c-axis are denoted in the line profile shown in the inset of b. c Bright-field TEM image of sample 2. d Corresponding selected area diffraction pattern along the zone-axis. Note the difference in ordering in the line profile inset in d compared to the line profile shown in the inset in b. The scales bars in the TEM images correspond to 50 nm. The scale bars in the electron diffraction patterns correspond to 5 nm−1
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The data were extracted from demagnetization curves obtained at T = 20 °C. The determined quantities are remanence (Br), coercive field strength at polarization equals zero (H cB), coercive field strength at flux density equals zero (H cJ) and energy density ((BH)max). These values can be compared to the values provided by Maybury et al.15
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An ultra-high resolution scanning TEM high-angle annular dark-field (STEM-HAADF) Z-contrast image is shown in Fig. 2a to reveal the atomic structure of the Z-phase. We implemented two models, SmCo3 and Zr2SmCo9 for the QSTEM simulations as shown in Fig. 2b 32. The later one is a modification of the first one, where the Sm at the Sm1 (6c) atomic position was replaced by Zr. The models were chosen since it was not clear from the beginning which atomic position the Zr would occupy and if there is only a partial or a full replacement of Sm by Zr on the Sm1 (6c) position. A simulated STEM-HAADF Z-contrast image of pure SmCo3 is shown in Fig. 2c together with an atomic model inside the Z-phase. The same is shown for the Zr-modified structure in Fig. 2d. One directly recognizes that the intensity of the Sm1 (6c) position in Fig. 2c is too bright in the simulation compared to the experiment (Fig. 2a), because Sm (Z = 62) is heavier than Zr (Z = 40). Therefore, a simulation with the modified model was carried out yielding the results presented in Fig. 2d. By comparing the simulated image with the experimental one, a perfect match was found regarding the atomic intensities within both images showing that only the Sm1 (6c) position is replaced by Zr. Indications of this behavior were suggested by X-ray measurements before33, 34. The Sm2 (3a) position is still occupied by a Sm atom. By estimating the site-preference energy via first principle calculations (Supplementary Fig. 5), we found that when one or all Sm (6c or 3a) sites are occupied with Zr atoms, the Sm1 (6c) site has a stronger preference to be occupied by Zr, since it is energetically favorable.Fig. 2Atomic-resolution HAADF-STEM images of the Z-phase. a Experimental (left), b atomic models (center) and simulated (right) atomic resolution STEM-HAADF Z-contrast images for c SmCo3 and d Zr2SmCo9. All images are viewed along the zone axis. The experimental image was filtered by principal component analysis to reduce the effect of noise. Scale bar, 5 Å
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Atomic-resolution HAADF-STEM images of the Z-phase. a Experimental (left), b atomic models (center) and simulated (right) atomic resolution STEM-HAADF Z-contrast images for c SmCo3 and d Zr2SmCo9. All images are viewed along the zone axis. The experimental image was filtered by principal component analysis to reduce the effect of noise. Scale bar, 5 Å
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The Z-phase itself has a layered structure (Z-phase stacks) and is in some cases inhomogeneous, that is, contains for example stacking faults, as shown in Supplementary Fig. 2. Supplementary Fig. 2 shows STEM-HAADF Z-contrast images of different Z-phase stacks oriented along the zone axis. The 2:17 matrix is oriented along the or zone axis. Supplementary Fig. 2a and b shows defect-free Z-phase stacks as indicated by numbered yellow arrows with two and four stacks, respectively. These defect-free Z-phase stacks are more likely being observed in the low iron content sample. Supplementary Fig. 2c and d is quadruple and sextuple Z-phase stacks containing stacking faults. These stacking faults consist of one or more Sm/Co-Co layers. The defective Z-phase stacks are more likely found in the high iron content sample. This structural feature has not been reported before and shows that the diffusion of elements like Cu and Fe during the annealing step is suppressed for the high iron content sample.
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Analyzing Supplementary Fig. 3 in detail demonstrates that three twinning structures can occur in Sm2Co17-based permanent magnets. Feng et al.3 proposed structural models regarding the 2:17 matrix and the 1:5 boundary phase suggesting how the twinning should look like on the atomic scale by systematically evaluating electron diffraction patterns. Their findings are confirmed also on the atomic scale in this contribution, since we observe a coherent nature of the twinning structures; including the 1:5 boundary phase and the Z-phase. This was predicted by the theory proposed by Maury et al.35, that is, that the Z-phase lamellas prefer to grow from twin boundaries in the 2:17 phase. However, this is not always necessarily the case, since the processing parameters play a fundamental role for the twin formation. For example, when fast cooling is applied35 micro-twinning occurs, that is, resulting in 5–10-nm-thick twins inside the 2:17 matrix. This has also been reported by Hiraga et al.16 and Yang et al.19 but was not observed in our samples. Maury et al.35 also postulate that in multicomponent phases, Fe and Cu atoms substitute for Co atoms without strong change of the dimensions, which is not true for Zr, because its atomic size is between Sm and Co. Nevertheless, Zr was predicted to be located on specific substitution sites which is indeed confirmed directly by our atomically resolved STEM-HAADF Z-contrast images, that is, specific substitution namely on the Sm1 (6c) lattice site of the SmCo3 phase, as clearly shown by comparing Figs 2a,b. Maury et al.35 predicted that the Z-phase platelet formation along the basal plane is due to a significant local Zr supersaturation acting as a driving force for the nucleation.
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After obtaining the microstructural information by (S)TEM, we measured the macroscopic magnetic properties which are extracted from hysteresis loops for both samples, as shown in Table 1. The coercive field strength (H cB) is drastically decreased from 870 kA mˉ1 for sample 1 (lower iron content) to 250 kA mˉ1 for sample 2 (high iron content). This results in a relatively low remanence and energy density for sample 2. For sample 1 attractive magnetic properties were achieved: B r = 1.2 T, (BH)max = 262 kJ mˉ3, H cB = 870 kA mˉ1. We attribute the difference in the magnetic properties of these two samples to their distinguished microstructures. Since Sm2Co17 is a typical pinning-controlled magnet, we used microstructure-based micromagnetic simulations to qualitatively elucidate the domain pinning in these two samples. In order to reduce the computation cost, half of the TEM images shown in Figs 1a,c were adopted to construct the micromagnetic models with a size of 440 × 440 × 220 nm3, as shown in Supplementary Fig. 4. The initial domain wall lies in the plane parallel to the easy axis and separates two antiparallel magnetic domains (Supplementary Fig. 4). With this initial condition, micromagnetic simulations are carried out to calculate the demagnetization curves (Fig. 3a) and capture the magnetization reversal process (Fig. 3b,c). The plateaus in Fig. 3a are a result of domain wall pinning. The zigzag domain walls in Fig. 3b and c indicate the 1:5 phase and the Z-phase as pinning sites. It is obvious that sample 1 exhibits much more plateaus, thus, much more pining sites as compared to sample 2. This is in agreement with the experimental results (sample 1 has higher coercivity). It should be noted that the micromagnetic model is only an extremely small part of the real sample. So the simulated reversal curves cannot be directly compared with the experimental curves. Nevertheless, we analyzed the detailed reversal process to reveal the underlying microstructure-related mechanism. In Figs 3b,c, P1- and P2-type sites show representative pinning sites where the 1:5 phase intersects with the Z-phase, and P1′- and P2′-type sites show representative sites only with the Z-phase. It should be mentioned that unlike the P1- and P2-type pinning sites, P1′- and P2′-type sites are not fixed to particular positions. They move intermittently and their actual position is determined by the interplay between the cost of domain wall energy and the gain of magnetostatic energy (Supplementary Movies 1 and 2). As shown in 1i–1v of Fig. 3b, P1-type sites in sample 1 are strongly pinned until the external field reaches ~1,200 kA mˉ1. But intermittent movements of domain walls occur in the P1′-type sites, resulting in lots of plateaus between 0 to ~1,000 kA mˉ1 in the reversal curve of sample 1 (Fig. 3a). In contrast, in sample 2 domain walls intermittently move much faster in P2′-type sites and rapidly sweep through most of the sample at a low external field of ~400 kA mˉ1 (2iii in Fig. 3c). But P2-type sites in 2i of Fig. 3c are still strongly pinned. Furthermore, the domain wall cannot be pinned by Z-phase any more when it is depinned in 1:5 phase. As shown in Fig. 3b(1v–1vi), the domain wall in 1v contains a long segment in the Z-phase, but this segment collapses immediately after it is not stabilized by the 1:5 phase (1vi). This indicates that in both samples, 1:5 phase related, P1- and P2-type sites have larger pinning strength than Z-phase related P1′- and P2′-type sites. The diamond-shaped cellular structure with a continuous 1:5 phase, i.e. more P1- and P2-type sites, is responsible for the increased number and pinning strength of the pinning sites, which are favorable for an enhanced coercivity. The Z-phase can act as pinning sites, but contributes little to the coercivity. Since the domain wall energy in the Z-phase is lower compared to the 2:17 and the 1:5 phase, the Z-phase acts as a weak attractive pinning site. In contrast, the 1:5 phase act as repulsive pinning site because of its much higher domain wall energy.Fig. 3Simulation results on domain wall pinning. a Demagnetization curves with the red and green lines corresponding to samples 1 and 2, respectively. The magnetization reversal process of b sample 1 and c sample 2 at different values of applied external magnetic field marked in a. m c denotes the magnetization component along the easy axis. P1 and P2 show typical pinning sites, where 1:5 phase intersects with the Z-phase. P1′ and P2′ denote typical sites containing only the Z-phase. The yellow arrows denote the positions
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Simulation results on domain wall pinning. a Demagnetization curves with the red and green lines corresponding to samples 1 and 2, respectively. The magnetization reversal process of b sample 1 and c sample 2 at different values of applied external magnetic field marked in a. m c denotes the magnetization component along the easy axis. P1 and P2 show typical pinning sites, where 1:5 phase intersects with the Z-phase. P1′ and P2′ denote typical sites containing only the Z-phase. The yellow arrows denote the positions
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This contribution presents a detailed microstructural and chemical investigation of Sm2(Co,Fe,Cu,Zr)17 sintered permanent magnets with different iron content. A major objective was to use atomically resolved STEM-HAADF Z-contrast imaging in combination with micromagnetic simulations to directly determine the atomic structure of the pinning relevant phases (1:5 and Z-phase) and their magnetic behavior. Low iron content leads to superstructure type ordering of the Zr-rich platelets, which contribute to the formation of a well-developed 1:5 phase and thus a diamond-shaped cellular structure. The coercivity is dominated by the density and strength of the pinning sites in the 1:5 phase while modified by the Z-phase. Via direct atomic scale observations we demonstrate that Zr preferably replaces the Sm atoms located at the Sm1 (6c) site in the SmCo3 structure yielding a modified structure with the following sum formula: Zr2SmCo9. This enables a comprehensive way of tailoring the magnetic properties, for example, coercivities since Zr favors Z-phase nucleation and controls diffusion along the Zr-rich platelets stabilizing the diamond-shaped cellular 1:5 phase. An enhanced understanding of the pinning mechanisms in Sm2Co17 yields a viable route to apply these thermal and chemical protocols for improved magnetic performances also to other systems than Sm2Co17. Further studies in this material system focusing on nanoscale spin dynamics and on the redistribution of elements like Cu and Zr on the nanoscale during different annealing programs as well as structural and chemical changes after doping by other rare-earth elements will be carried out in the near future and are beyond the scope of the present contribution.
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Several SmZrCoFeCu 2:17 master-alloys were melted in a vacuum furnace, crushed to coarse powders and jet milled in an AFG100 down to a particle size of ~6 µm. The compositions of these fine powders were verified by chemical analysis. The fine powders were blended in order to meet the composition (wt%) Sm25Zr3Co49Fe19Cu5 and Sm25Zr3Co45Fe23Cu5. The fine powders were oriented in a magnetic field of 13 kA cmˉ1 and pressed isostatically at 250 MPa. The green compacts were sintered at 1190 °C, homogenized at 1,160 °C and quenched to room temperature. The samples were annealed at 870 °C and cooled slowly with a cooling rate of about 1 °C minˉ1 to 400 °C.
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A 200 kV Jeol JEM 2100 F STEM equipped with an Oxford X-max80 EDX detector was used to determine the microstructure and chemistry on the nanometer scale. For the TEM studies, the samples were demagnetized, thinned via conventional grinding and polishing plane to a thickness of ~20 µm with the hexagonal c-axis of Sm2Co17 lying perpendicular to the polishing direction and finally mounted on Mo grids. Ion thinning was done in a Gatan Dual Ion Mill Model 600 using Ar+ ions with an incidence angle of 15° at 5 keV. The previous milling step was followed by two 10 min polishing steps at 13° ion incidence using 3 keV and a final step at 1.5 keV. A plasma cleaning step was performed for 2 h in a Gatan Solarus plasma cleaning system before introducing the specimen in the microscope. Annular dark-field (ADF) scanning transmission electron microscope (STEM) images and energy-dispersive X-ray (EDX) spectra were obtained using a 0.7 nm spot size, this being a compromise between spatial resolution and EDX signal (detector dead time around 10%). Quantification of EDX spectra was carried out standardless using the Cliff-Lorimer k-factor method (Supplementary Note 1). Atomic resolution images were acquired using a Jeol Atomic Resolution Microscope (ARM) 200 F equipped with a Schottky emitter and a C s-probe corrector (see also Supplementary Note 1). An electron energy of 120 keV was used to reduce magnetization effects of the sample. High-angle annular dark-field (HAADF) images were acquired using the 8 C spot size setting. A 30 µm condenser aperture was inserted yielding a convergence angle of 24.6 mrad. 6 cm camera length was used for HAADF imaging corresponding to a 90 mrad inner and a 370 mrad outer HAADF detector angle. The specimen thickness according to electron energy-loss spectroscopy (EELS) was estimated to 0.4–0.7 mean free path (mfp) for sample 1 and 0.7–1.0 mfp for sample 2.
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STEM-HAADF Z-contrast image simulation was carried out using the QSTEM software32. A C s value of 1 µm, a C c value of 1 mm and an energy spread of 0.7 eV were assumed; higher order aberrations were neglected. For the convergence angle and the HAADF detector the values listed in the previous paragraph were used. Thermal diffuse scattering was not considered. For the simulation two structural modifications were used: pure SmCo3 (space group R-3m) and Zr2SmCo9, which is essentially the same as the pure compound, but with the Sm1 (6c) atomic position (6c, x = 0, y = 0, z = 0.141) replaced with Zr. STEM-HAADF images were Wiener filtered for noise reduction36. Selected STEM-HAADF images were filtered using a 5–15 component principal component analysis for improved noise reduction37.
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In the micromagnetic simulations of the magnetization reversal process of the model sample 1 and 2, microstructure-oriented models were discretized by cubic meshes with a size of 1 nm. The Landau–Lifshitz–Gilbert equation at each node was solved by the 3D NIST OOMMF software. The magnetocrystalline anisotropy values of the 1:5 phase, the 2:17 phase, and the Z-phase are taken from the literature29 as 12.1 MJ mˉ3, 3.9 MJ mˉ3, and 2.1 MJ mˉ3, respectively. The magnitude of the saturation magnetization of 1:5 phase, 2:17 phase and Z-phase are taken from the literature29 as 1.1, 1.23, and 0.39 T, respectively. The exchange constant of the 1:5 phase, the 2:17 phase, and the Z-phase is estimated from the literature29 as 15.1, 19.6, and 0.48 pJ mˉ1, respectively. Supplementary Fig. 4 shows the three-dimensional(3D) micromagnetic model of samples 1 and 2. The models (440 × 440 × 220 nm3) only consider the upper half of the microstructure shown in the TEM images (Fig. 1), in order to lower the computation cost. The stripes denote the 1:5 phase and Z-phase. An initial 180° domain wall along the easy axis is set to study the domain wall pinning effect. The external field is applied antiparallel to the arrows (c-axis) shown in Supplementary Fig. 4. The simulated magnetization reversal process is shown in Supplementary Movies 1 and 2.
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First-principles calculations based on density functional theory were performed by using the Vienna ab initio simulation package. The exchange correlation energy was calculated within the generalized gradient approximation of the Perdew–Burke-Ernzerhof (PBE) form. The cutoff energies for the plane wave basis set to expand the Kohn-Sham orbitals were 500 eV for all calculations. The energies through simulation mentioned in this work are the energies after structural relaxation. Γ centered 9 × 9 × 2 and 15 × 15 × 3 K-point mesh within Monkhorst-Pack scheme was used for the Brillouin zone integration for structural relaxation and energy calculation, respectively. The structural relaxation was done until the forces were smaller than 2 meV Åˉ1. Supplementary Fig. 5 shows the calculated energies of SmCo3 with different Sm sites replaced by Zr atoms.
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Zinc (Zn) is an essential nutrient for living organisms1, however, an excess supply of Zn can lead to toxic effect on plants234 and microorganisms56 in soil. Due to anthropogenic activities (such as industrial activities, sludge application, waste water irrigation, etc.3), Zn can be easily released into soil environment7, which could pose a threat to the health of ecosystems8 and even to human beings910. As free Zn ions are the main species for Zn toxicity15, the immobilization of free Zn ions by some materials would reduce its bioavailability and toxicity in soil. Thus, materials which are effective in Zn immobilization should be developed.
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As an emerging carbonaceous material, biochar has been extensively studied especially in the field of soil remediation11121314151617. The carbonaceous residue and entrained minerals (ash) are two main components of biochar18, they perform different functions in soil remediation. The carbonaceous residue can adsorb and retain water19 and some organic pollutants20212223; the ash can provide nutrient elements and improve soil pH24. In terms of heavy metal immobilization, both of the two components could be involved in the process. Plenty of studies have reported the immobilization behavior of Zn on biochars derived from different biomass (such as hardwood2526, corn straw25, sugarcane straw27, dairy manure28, and meat and bonemeal29), and some of them have proposed the immobilization mechanisms which implied more important role of ash on biochar on Zn immobilization272830. Xu et al. studied the sorption behavior of Zn on biochar derived from dairy manure, and found that large amounts of PO43− and CO32− were released from biochar and reacted with Zn2+ to form Zn phosphate and Zn carbonate28. With the help of P K-edge XANES spectroscopy, Wegner et al. found that hopeite (Zn3(PO4)·2H2O) or a similar Zn-P phase were formed, when biochar was used to immobilize Zn in the sewage field soils30. In addition to forming Zn precipitates, the formation of Zn complexes on biochar surface also led to Zn immobilization29. By using the method of extended X-ray absorption fine structure (EXAFS) spectroscopy, Betts et al.29 found that Zn bound to phosphate groups in meat and bonemeal biochar in a monodentate inner-sphere surface complex.
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Feedstock types and pyrolysis temperature are two main factors influencing biochar property18. As a wide variety of biomasses can be used for biochar production, previous studies on Zn2+ immobilization behavior of limited type of biochars are far from enough. To explore the immobilization mechanisms of Zn2+ on different biochars and provide more basic data for biochar application, studies which are focused on biochars produced by other waste biomasses need to be done. Although many studies have mentioned the effect of pyrolysis temperature on biochar property2031323334, few studies systematically investigated the effect of pyrolysis temperature on immobilization behavior of Zn2+ on biochar and elucidated the internal connection between pyrolysis temperature, biochar property, and immobilization behavior of Zn2+ on biochar. In this study, biochars produced by pine needle (PN) and wheat straw (WS) were chosen for investigation, to our knowledge, there is no published work concentrated on Zn2+ immobilization behavior of biochars derived from these biomasses. Two temperatures were chosen for biochar preparation, and the Zn2+ immobilization behaviors of biochars produced by different temperature were compared through several sorption experiments (i.e. sorption kinetics, sorption isotherms, and the effect of pH). To reveal the importance of the ash on biochars on Zn immobilization, the ash was removed from biochars, and the Zn2+ immobilization behaviors of de-ashed biochars were compared with those of the raw biochars. To explore the immobilization mechanisms, the methods of Zn K-edge EXAFS spectroscopy and X-ray Powder Diffraction (XRD) were used for biochar characterization. Through this study, the Zn species immobilized by PN and WS biochars will be identified, the immobilization mechanisms and the relation between pyrolysis temperature and immobilization behaviors of Zn2+ on studied biochars will be clear.
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The contents of the common elements (i.e. K, Ca, Mg, Al, Fe, Zn, and P) in biochars were determined and listed in Table 1. The contents of most studied elements in biochars produced at 550 °C were higher than those in biochars produced at 350 °C, which suggested that the ash contents of biochars produced at 550 °C were higher than those of biochars produced at 350 °C. The high Ca contents in PN biochars and high K contents in WS biochars implied that, in addition to immobilizing heavy metal, PN and WS biochars could also supply large amounts of nutrient elements to the soil. When raw biochars were washed by HCl/HF solution, the contents of the elements substantially dropped, this means that the factor of ash which may influence the sorption of Zn can be excluded in de-ashed biochars. The pHs of raw biochars and the pHPZC of de-ashed biochars were also listed in Table 1.
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To study the sorption behaviors of Zn2+ on different biochars, a series of sorption experiments were conducted. Figure 1 shows the kinetics and isotherms of Zn2+ sorption on different biochars. From Fig. 1a we find that sorption reactions between Zn2+ and most biochars can reach equilibrium at 48 h, the sorption capacities of Zn2+ on biochars produced at 550 °C were higher than those of Zn2+ on biochars produced at 350 °C. Figure 1c shows that the maximum sorption capacities of Zn2+ on raw biochars decreased in the following order: PN550 (25.9 mg g−1) > WS550 (20.4 mg g−1) > WS350 (16.0 mg g−1) > PN350 (3.0 mg g−1). It seems that biochars with higher ash contents were more effective on Zn immobilization. From Fig. 1c,d we find that, the maximum sorption capacities of Zn2+ on de-ashed biochars were lower than those of Zn2+ on their corresponding raw biochars. Especially for biochars produced at 550 °C, the maximum sorption capacities of Zn2+ on biochars decreased by more than 80% when the ash was removed. These results suggested the important role of ash on Zn immobilization by biochar. Among de-ashed biochars, WS350D had the highest sorption capacity (9.4 mg g−1), which may be due to the more oxygen-containing functional groups WS350D had compared with other biochars. Kinetics experiments show that sorption reactions between Zn2+ and most biochars can reach equilibrium at 48 h, thus the equilibrium time for the following experiments was set to be 48 h. As PN550, WS350, and WS550 had considerable sorption capacities of Zn2+, several kinetics models (pseudo-first and pseudo-second-order models35, Elovich model3637, and intraparticle diffusion model3839) and isotherms models (Langmuir, Frendlich, and Langmuir-Frendlich models40) were performed on kinetics and isotherms data of these biochars, the fitting results were shown in Supplementary Tables S2 and S3.
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The effect of initial pH on sorption capacities of Zn2+ on biochars were shown in Supplementary Fig. S4. As can be seen from Fig. S4, the sorption capacities of PN550, WS350, and WS550 decreased gradually with the decrease of initial pH. Unlike the sorption behaviors of raw biochars, sharp decreases occurred on the sorption capacities of de-ashed biochars, when the initial pH decreased from 9 to 7. This may be caused by the absence of buffer effect of ash. The low sorption capacity of Zn2+ on PN350 under the whole pH range could be due to the low ash content.
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The sorption experiments showed that some Zn precipitates/minerals may be formed on biochar, thus XRD analysis were performed on these biochars. As PN350 had a relatively low sorption capacity of Zn2+, we just focused on other three biochars (PN550, WS350, and WS550) and biochars loaded with Zn (denoted as PN550 + Zn, WS350 + Zn, and WS550 + Zn). Figure 2 shows the XRD spectra of the samples. The main mineral in PN550 was CaCO3, the peaks of quartz in PN550 were not obvious. The peak intensities of CaCO3 and quartz show that there could be large amount of CO32− and low amount of Si contained in PN550. In WS350 and WS550, two minerals can be detected, they were quartz and sylvine. Compared with PN550, WS350 and WS550 contained larger amount of Si species.
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Compared with the spectra of PN550, two more peaks appeared in the spectra of PN550 + Zn, which may belong to hydrozincite. Thus the formation of hydrozincite could be one of the mechanisms for Zn immobilization on PN550. In WS350 + Zn and WS550 + Zn, as sylvine is soluble, only quartz was maintained on WS350 and WS550. Although WS350 and WS550 had considerable sorption capacities of Zn2+, none of the Zn species could be detected from the two samples by XRD analysis. This may be caused by the poor crystallinity of Zn species formed on WS350 and WS550. As the characterization way of XRD has the requirement on sample crystallinity, the method of XAFS was applied in Zn species identification.
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| 100.0 |
The k3-weighted χ(k) functions of raw biochars and de-ashed biochars are shown in Fig. 3. To obtain the types and fractions of Zn species on these biochars, Principal Component Analysis (PCA) accompanied with Target Transformation (TT) and Linear Combination Fitting (LCF) were performed on χ(k) k3-spectra ranging from 3–11 Å−1 for all the samples. PCA was used to determine the number of primary components which may be present in the spectra of biochars; TT was used to evaluate which species may be contained in these biochars; and LCF was applied to quantitatively analyze the Zn species on biochars. (The details on PCA, TT and LCF were shown in S1 in SI).
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The result of PCA shows that five principal components may be present in the spectra of biochars. After TT by using the χ(k) k3-spectra of a series of standard Zn compounds (Supplementary Fig. S5), we found six Zn species (i.e. Zn(NO3)2 aqueous (Zn(NO3)2 aq), Zn(OH)2, willemite (Zn2SiO4), smithsonite (ZnCO3), hemimorphite (Zn4(H2O)(Si2O7)(OH)2), and hydrozincite (Zn5(CO3)2(OH)6)) may be contained in these biochars. The number of Zn species obtained by TT was higher than that obtained by PCA, this is due to the similarity between the spectra of some standard species414243. The PCA results suggested that the Zn precipitates/minerals could take up a large fraction of Zn species in biochar.
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The LCF was subsequently performed on the samples using the Zn species selected by TT. The main components and their fractions in the samples were obtained and shown in Fig. 3 and Supplementary Table S6. From the fitting results (Fig. 3), we find that Zn precipitates/minerals (i.e. hydrozincite, Zn(OH)2, and hemimorphite) accounted for a large share of Zn species (>70%) in raw biochars, which indicated the indispensable role of ash in biochar on Zn immobilization. High proportions of hydrozincite (>40%) and Zn(OH)2 (>10%) were observed in most of the raw biochars. This result indicated that CO32− and OH− were two common ions for Zn immobilization. It is noteworthy that, unlike other raw biochars, WS550 contained large fraction of hemimorphite (66%). This was probably caused by the large amount of dissolved Si species released from WS550, which implied the crucial role of dissolved Si species in Zn immobilization. The species Zn(NO3)2 aq represents the Zn adsorbed on oxygen-containing functional groups (i.e. carboxyl and hydroxyl) on biochar. In PN350 and WS350, the fractions of Zn(NO3)2 aq were respectively 14% and 26%; while in PN550 and WS550, the two values dropped to 6% and 2%. These changes were due to the increase in ash contents and loss of oxygen-containing functional groups in biochars with pyrolysis temperature. In de-ashed biochars, only two main Zn species, hydrozincite and Zn(NO3)2 aq, existed in de-ashed biochars. Although hydrozincite is Zn mineral, the formation of small amounts of hydrozincite in de-ashed biochars may be caused by the dissolution of CO2 in the air. The pHPZC of de-ashed biochars were 4.3–5.5 (Table 1), thus when the solution pHs were controlled to 7, the de-ashed biochars could easily adsorb few amount of Zn2+.
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According to the analysis of XRD and EXAFS, we have identified the main Zn species formed on biochars. To examine these results, the pHs of the samples withdrawn at 2 h and the concentrations of CO32− and Si species in the samples withdrawn at 120 h in kinetics experiments were determined. For comparison, these determinations were also conducted on their corresponding blank samples (0.1 g of biochar + 25 mL of water). The concentrations of PO43−, Ca2+, and Mg2+ were also determined. The samples in kinetics experiments are denoted as B + Zn, and the blank samples are denoted as B.
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As shown in Table 2, the pHs of B + Zn at the reaction time of 2 h reached 7.0, which were lower than those of B. This indicated that plenty of OH− were consumed during Zn immobilization. For PN350 and WS350, the concentrations of CO32− in B were respectively 0.3 and 1.1 mmol L−1; while the concentrations of CO32− in B + Zn could not be detected (ND) indicating the consumption of CO32− during Zn immobilization. As Ca2+ which released from biochars could also react with CO32−, the amount of CO32− which would react with Zn to form hydrozincite would be underestimated from these results. The released Si species could also influence the determination of CO32−, as they could buffer H+ in the solution44, which lead to the overestimated concentrations of CO32−. Thus the concentrations of CO32− in different samples cannot be used to calculate the real amounts of consumed CO32− in Zn immobilization, they were only for reference. For WS350 and WS550, the Si concentrations in B were respectively 0.9 and 2.0 mmol L−1 (the initial concentration of Zn2+ was 2.3 mmol L−1). Once reacted with Zn2+, the concentrations of Si decreased drastically. From the considerable amounts of released and consumed Si species, we assumed that some Si species in WS biochars may play an important role in Zn immobilization. Fig. S6 shows the ATR-FTIR spectra of the raw biochar filtrates. From Figs S6a and S6b we cannot see any band present in the spectra, while in Figs S6c and S6d there is a broad band in the region 1150–1050 cm−1 in each of the spectrum, which is due to the asymmetric Si–O–Si stretching vibration of long chain polymers45. The ATR-FTIR result suggested that the Si species released from biochar are Si-containing polymers with different chain length. The release and consumption of OH−, CO32− and Si species confirmed the results of XRD and EXAFS.
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The difference on the concentrations of PO43− between B and B + Zn implied the formation of Zn3(PO4)2 on biochars, however the concentrations of PO43− in B were no more than 0.06 mmol L−1, thus the precipitation role of PO43− in the studied biochars can be ignored. The concentrations of Ca2+ and Mg2+ in B + Zn were much higher than those of Ca2+ in B; expect for the condition of PN350, the concentrations of Mg2+ in B + Zn were also higher than those of Mg2+ in B. This may be caused by the competition of Zn2+ for released OH−, CO32−, and some sorption sites. When raw biochar was added into water, plenty of ions such as Ca2+, Mg2+, OH−, and CO32− were released from biochar to bulk solution. With the gradual increase in concentrations of Ca2+, Mg2+, and anions such as OH−, CO32− in the solution close to biochar surface, some of these ions would be over-saturated, Ca, Mg-precipitates would form and deposit on the surface of biochar. In addition to forming precipitates, a portion of Ca2+ and Mg2+ could also be captured by oxygen-containing functional groups of biochar. Thus, in raw biochar-water systems, the newly released Ca2+ and Mg2+ can be immobilized rapidly. When Zn2+ was present in the solution, Zn2+ would diffuse to the area close to biochar surface, they could also react with the newly released anions (i.e. OH− and CO32−) and occupy the sorption sites (i.e. oxygen-containing functional groups of biochar). This process would decrease the concentrations of OH−, CO32−, and PO43− and sorption sites of Ca2+ and Mg2+, which further resulted in the increased amounts of released Ca2+ and Mg2+ in raw biochar-Zn solution systems (B + Zn). The low sorption capacity of Zn2+ on PN350 and inhomogeneous distribution of Mg on biochar may lead to the lower concentration of Mg2+ in B(PN350) + Zn, when compared with those of Mg2+ in B(PN350) + Zn.
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To reveal the immobilization mechanism of Zn on biochars, we first need to know the formation rule of OH−, CO32−, and Si Species. Although few studies can describe the clear evolution processes of ash in biochar, we may obtain the general evolution processes based on the pyrolysis rule of biomass.
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| 99.94 |
In plants, some alkali and alkaline earth metal (AAEM), e.g. K, Ca, and Mg, are associated with organic molecules46. During pyrolysis, with the decomposition of the organic matters and reconstruction of the remaining parts, biomass transformed into char (not the ultimate biochar), and AAEMs were then bonded to the char in the form of C–O–Met+ or C–O–Met2+–O–C (Met+ represents K+, and Met2+ represents Ca2+ and Mg2+)47. Once the bonds between AAEMs and char were attacked by free radicals which were formed in pyrolysis, elemental AAEMs were formed47484950. As these species are not stable, they would be easily oxidized to form metal oxides and react with H2O, which was released from biomass during pyrolysis, to form AAEM hydroxides (see Equation 1, M represents elemental AAEMs, such as K, Ca, or Mg). These AAEM hydroxides could be the source of released OH− in the solution. The decomposition of cellulose and lignin1851 lead to the generation of CO2. CO2 may react with H2O and newly formed AAEM hydroxides to form various carbonates (see Equations 2 and 3). Thus, in addition to the carbonates contained in the raw biomass, the newly formed carbonates during pyrolysis could also be the source of CO32− in the solution. The Si species are much more stable than other inorganic species in biomass1852. It is reported that the main forms of Si in wheat biomass are amorphous silica and silicate esters5354, the forms of these Si species would change when the water in biomass evaporated and the organic matters decomposed during pyrolysis, some of the Si species would transform into quartz (see Fig. 2) and dehydroxylated silicates18, some of them would transformed into alkali silicates (such as K2SiO3)52. Without the protection of organic matters, the exposed Si species can be easily released to the solution. Among the Si species formed on biochar, alkali silicates are soluble compounds, the solutions of which contain a wide variety of polysilicate ions55 (consist with the ATR-FTIR results of raw biochar filtrates). Thus alkali silicates are probably the Si species released into water or Zn solution.
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| 99.94 |
From the proposed evolution processes of the anions, we find that the formation of these ions are closely related to the decomposition of biomass, and the higher degree of decomposition (higher pyrolysis temperature) will lead to the higher amounts of OH−, CO32−, and Si species presented on biochar surface. Some previous studies have also found this phenomenon. Yuan et al. reported that the pHs and carbonate contents of biochar derived from different straws increased with pyrolysis temperature56; Xiao et al. found that the dissolved Si species released from biochar prepared by rice straw increased33 when the temperature increased from 250 °C to 700 °C.
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The formation of various ashes on biochars is the premise for Zn immobilization; and the formation of different Zn species is the immobilization mechanism of Zn on PN and WS biochars. The formation processes of the main Zn species (the fractions of which are higher than 10%) on different biochars are proposed and described as follows (Fig. 4).
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For PN350 and WS350, once biochars were added into Zn solution, the OH− and CO32−, which were formed on biochar during pyrolysis56, tend to release into bulk solution. As OH− and CO32− were released from biochar, at the early stage of the diffusion the concentrations of OH− and CO32− in the solution close to biochar surface were much higher than those of bulk solution. Under this condition, when Zn2+ diffused to biochar surface, these ions were easily over-saturated and form hydrozincite and Zn(OH)2 (Fig. 4, Paths 1 and 2), and finally deposited on biochar surface. For biochars produced at low temperature (i.e. 350 °C), there existed a large portion of oxygen-containing functional groups (i.e. carboxyl and hydroxyl)24. When they presented in the solution with high pH, these functional groups will be deprotonated and adsorb Zn2+. During the process of Zn immobilization, the solution pHs were not controlled, they decreased from >9 to 7 with reaction time. From the calculation of Visual MINTEQ 3.1 (Supplementary Fig. S7), we find that two Zn species (i.e. Zn2+ and Zn(OH)+) could be involved in the reaction, and the proportion of Zn2+ was much higher than that of Zn(OH)+. The reactions were shown in Fig. 4, Path 3. Although the sorption mechanisms of PN350 and WS350 are the same, the sorption capacity of Zn on PN350 are much lower than that on WS350, which may be due to the lower amounts of OH−, CO32− and oxygen-containing functional groups formed on PN350 when compared with those formed on WS350. This phenomenon implied that different feedstocks have different degree of decomposition under the same pyrolysis temperature, which would lead to different sorption performances of biochars.
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For PN550 and WS550, with the volatilization of organic matters and completion of thermal decompositions, the ash content increased, which made the fraction of Zn precipitates/minerals close to 100%. Compared with PN350, PN550 contained much more CO32− and OH−, thus the sorption capacity of Zn on PN550 was higher than that of PN350. For WS550, a large fraction of hemimorphite was formed. This was due to a considerable amount of released Si species. The formation of hemimorphite on WS550 can be divided into three steps57 (Fig. 4, Path 4): (1) the formation of colloid of Zn(OH)2 under alkaline condition, (2) the adsorption of dissolved silicates on Zn(OH)2 colloid and co-precipitation of silicate and Zn(OH)2, and (3) the reconstruction of the co-precipitates structure and formation of amorphous hemimorphite. Due to the complexity of the sorption system and short reaction time, the well-crystallized hemimorphite was unlikely to form. Thus, it cannot be detected by the method of XRD. Although there were also some Si species released from WS350, only a small portion of hemimorphite was formed. This may be caused by the low amounts of OH− and Si species released from WS350 biochar.
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The formation of different Zn species on biochars confirmed heterogeneous property of these materials which resulted in the co-existence of various sorption mechanisms during Zn retention by biochars. The consumption of OH−, CO32−, or the sorption sites (oxygen-containing functional groups) on biochars by Zn2+ to form different Zn species led to the release of Ca2+ and Mg2+. When the studied raw biochars were added into the acid solutions, the ions OH− and CO32− in biochar were consumed and even some oxygen-containing functional groups were protonated. This was against the formation of different Zn species, which could lead to the decrease in the sorption capacities of Zn on biochars.
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The ash in PN and WS biochars played important role on Zn immobilization. The higher pyrolysis temperature on the feedstock leads to the higher sorption capacity of Zn2+ and the larger fraction of Zn precipitates/minerals on biochar. Hydrozincite and Zn(OH)2 were the main species formed on PN350, PN550, and WS350; while on WS550, besides hydrozincite, a large fraction of hemimorphite was formed. The formation of OH−, CO32−, and Si species on biochars and the release of these species played predominant role on Zn immobilization.
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Biochars derived from PN and WS were prepared in a patented biochar reactor (NO. ZL2009 2 0232191.9) under oxygen-limited conditions. According to the decomposition rule of the feedstocks obtained from thermal analysis, 350 °C and 550 °C were selected as the pyrolysis temperatures (See Supplementary S2). To remove the ash on biochars, HCl/HF (1.0 M, v/v 1:1) solution was used to wash the raw biochars for several times. The details for biochar preparation were shown in Supplementary S2. The biochar sample derived from PN (WS) at 350 °C and 550 °C were denoted as PN350 (WS350) and PN550 (WS550), respectively. The de-ashed biochar were denoted as PN350D, PN550D, WS350D, and WS550D.
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One hundred milligram of raw biochars or de-ashed biochars were added into 25 mL of Zn(NO3)2 solutions in 50 mL vials. These vials were shaken at 200 rpm at 25 °C. For raw biochars, the Zn2+ concentration in Zn(NO3)2 solution was 150 mg L−1 and the pH of the solution was not adjusted. For the sorption experiments of de-ashed biochars, the Zn2+ concentration was 50 mg L−1 and the pH of the solution was adjusted to 7 buffered by 5 mM MOPs. The samples were withdrawn at appropriate time intervals, then the mixture was filtered with a 0.45 μm membrane, and the Zn2+ concentrations of the filtrates were determined. The sorption capacity of biochar in each time interval was obtained by Supplementary Equation S1. The concentrations of CO32−, Si species, PO43−, Ca2+, and Mg2+ were also determined in the samples withdrawn at 120 h, then concentrations of these five species in the filtrates of blank samples (0.1 g of biochar + 25 mL of water) at 120 h were determined for comparison. The concentrations of Zn2+, Ca2+ and Mg2+ were determined using Atomic Absorption Spectrometer (AAS, Hitachi-Z2000, High-Technologies Corporation, Japan); the concentrations of CO32− were determined using titration method44; the concentrations of Si species were determined using Inductively Coupled Plasma − Atomic Emission Spectrometer (ICP-AES, OPTIMA 8000, PerkinElmer, USA); and the concentrations of PO43− were determined using molybdate-ascorbic acid method. Two parallel samples were applied in sorption samples. Sorption isotherms were performed the same way as sorption kinetics except for the initial concentrations of Zn2+ applied (see Supplementary S6).
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Fifty milligram of raw biochars or de-ashed biochars were added into 23 mL of deionized (DI) water in 50 mL vials. These vials were shaken at 200 rpm at 25 C for 3 day equilibrium. Then the pHs of the mixtures in these vials were adjusted to 2–10. Certain amount of Zn(NO3)2 stock solution was dripped into each vial to make the initial concentration of Zn2+ to be 150 mg L−1 for raw biochar and 50 mg L−1 for de-ashed biochar. DI water was then added into the vial to make the solution volume up to 25 mL. The following procedure was the same as that of isotherms experiments and the sorption capacity of biochar was obtained by Supplementary Equation S6.
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The thermal properties of PN and WS were obtained using a Thermogravimertic Analyzer (TGA, Pyris 1 TGA, PerkinElmer, USA) at 20 °C/min up to the final temperature of 700 °C under a flow of N2. The functional groups of biochar and the Si species in the filtrates of raw biochar were analyzed using Fourier Transform Infrared Spectroscopy (FTIR, Nicolet FTIR IS10, Thermo Scientific, USA). The methods of sample preparation and data analysis are shown in Supplementary S8. The surface of biochar was analyzed with X-ray Photoelectron Spectrometer (XPS, PHI-5000 Versaprobe, ULVAC-PHI, Japan) using an Al Kα excitation radiation. The pHs of raw biochars and pHs of point of zero charge (pHPZC) of de-ashed biochars were obtained by the pH drift method in Supplementary S9 and S10. The contents of K, Ca, Mg, Al, Fe, Zn, and P in biochars were analyzed after the microwave digestion of biochars with HNO3-HF-H2O2 (U.S. EPA 3502)58. The concentrations of K, Al, and Fe in the digestion solution were determined with ICP-AES. The digestion experiments were conducted in duplicate for each biochar.
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The minerals in biochars were analyzed by X-ray Powder Diffraction (XRD). The tests were performed on a Rigaku, Ultima IV Diffractmeter (Rigaku Corporation, Japan), and Cu Kα radiation generated at 40 kV/40 mA, data were collected in the range (2θ) from 0° to 60° with the scan step of 0.02°. The minerals in the samples were identified using the XRD data analysis software (MDI JADE 6.5) and its corresponding powder diffraction file (PDF) database. The Zn species on biochars were analyzed by the method of extended X-ray Absorption Fine Structure (EXAFS) spectroscopy in fluorescence modes. Zn K-edge (9659 eV) measurements were carried out at beamline BL14W at the Shanghai Synchrotron Radiation Facility Center (SSRF). Principal Component Analysis (PCA) accompanied with Linear Combination Fitting (LCF) were used for species identification and quantification. The details of EXAFS spectra collection and data processing were shown in Supplementary S11.
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There is general consensus worldwide that health care organizations have historically struggled to embrace the use of information technology to increase productivity and the quality of care delivered . However, the technological landscape is rapidly being transformed with the emergence of the digital revolution. A number of leading health care organizations worldwide have begun to exploit some of the opportunities for novel health care solutions ; however, there appear to be many further opportunities to be unlocked in this space, in particular in the context of digital mobile technologies.
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