292 research outputs found
Stacking tunable interlayer magnetism in bilayer CrI3
Diverse interlayer tunability of physical properties of two-dimensional
layers mostly lies in the covalent-like quasi-bonding that is significant in
electronic structures but rather weak for energetics. Such characteristics
result in various stacking orders that are energetically comparable but may
significantly differ in terms of electronic structures, e.g. magnetism.
Inspired by several recent experiments showing interlayer
anti-ferromagnetically coupled CrI3 bilayers, we carried out first-principles
calculations for CrI3 bilayers. We found that the anti-ferromagnetic coupling
results from a new stacking order with the C2/m space group symmetry, rather
than the graphene-like one with R3 as previously believed. Moreover, we
demonstrated that the intra- and inter-layer couplings in CrI3 bilayer are
governed by two different mechanisms, namely ferromagnetic super-exchange and
direct-exchange interactions, which are largely decoupled because of their
significant difference in strength at the strong- and weak-interaction limits.
This allows the much weaker interlayer magnetic coupling to be more feasibly
tuned by stacking orders solely. Given the fact that interlayer magnetic
properties can be altered by changing crystal structure with different stacking
orders, our work opens a new paradigm for tuning interlayer magnetic properties
with the freedom of stacking order in two dimensional layered materials
Critical charge and spin instabilities in superconducting LaNiO
Motivated by the recent discovery of superconductivity in LaNiO
under high pressure, we explore its potential charge and spin instabilities
through combined model analysis and first-principles calculations. Taking into
account the negative charge-transfer nature of high valence nickel, a fully
correlated two-cluster model identifies a lattice-coupled rocksalt-type charge
instability characterized by substantial fluctuations of oxygen holes. This
instability is corroborated by density-functional-theory plus calculations
that also reveal a strong tendency towards concurrent antiferromagnetic
ordering. The charge, spin, and associated lattice instabilities are
significantly suppressed with increasing external pressure, contributing to the
emergence of superconductivity in pressurized LaNiO. Carrier doping
is found to effectively suppress these instabilities, suggesting a viable
strategy to stabilize a superconducting phase under ambient pressure
Structure and tanning properties of dialdehyde carboxymethyl cellulose: Effect of degree of substitution
Content:
Developing novel tanning agents from renewable biomass is regarded as an effective strategy for sustainable leather industry. In this study, a series of dialdehyde carboxymethyl cellulose (DCMC) were
prepared by periodate oxidation of carboxymethyl cellulose (CMC) with varying degrees of substitution (DS: 0.7, 0.9 and 1.2). The structural properties of DCMC were characterized. Size Exclusive
Chromatography measurements showed that CMC underwent severe degradation during periodate oxidation, resulting in the decline of weight-average molecular weight from 250,000 g/mol to around
13,000 g/mol. FT-IR analysis illustrated that aldehyde group was successfully introduced into DCMC. The aldehyde group content of DCMC decreased from 8.38 mmol/g to 2.95 mmol/g as the DS rose from 0.7 to 1.2. Interestingly, formaldehyde was found to be produced in DCMC, and its content was 159.4, 151.7 and 38.4 mg/L, respectively when the DS of CMC was 0.7, 0.9 and 1.2, respectively. Further analysis by HPLC found that fructose was formed during oxidative degradation, and was subsequently oxidized to generate formaldehyde. This was in accordance with the fact that higher DS resulted in lower formaldehyde content in DCMC. The whole reaction mechanism is still under investigation at the moment. Tanning trials showed that the shrinkage temperature and thickening rate of DCMC tanned leather decreased as the DS increased. This should be due to the difference in aldehyde content of DCMC. Leather tanned by DCMC-0.7 (DS of CMC was 0.7) had the highest shrinkage temperature of 81°C and thickening rate of 76%. It was noteworthy that the formaldehyde content in DCMC tanned leather was only 0.11-0.40 mg/kg even though DCMC contained a small amount of formaldehyde. In general, we hope the work on dialdehyde tanning agent derived from CMC could provide some essential data for the development of sustainable tanning material and process.
Take-Away:
1. Higher degree of substitution (DS) of CMC resulted in lower aldehyde group content of DCMC.
2. The formaldehyde content of DCMC was negatively correlated with DS.
3. The tanning performance of DCMC with lower DS was better
Risk of infection and transmission of SARS-CoV-2 among children and adolescents in households, communities and educational settings: A systematic review and meta-analysis
Background: There is uncertainty with respect to SARS-CoV-2 transmission in children (0-19 years) with controversy on effectiveness of school-closures in controlling the pandemic. It is of equal importance to evaluate the risk of transmission in children who are often asymptomatic or mildly symptomatic carriers that may incidentally transmit SARS-CoV-2 in different settings. We conducted this review to assess transmission and risks for SARS-CoV-2 in children (by age-groups or grades) in community and educational-settings compared to adults.Methods: Data for the review were retrieved from PubMed, EMBASE, Cochrane Library, WHO COVID-19 Database, China National Knowledge Infrastructure (CNKI) Database, WanFang Database, Latin American and Caribbean Health Sciences Literature (LILACS), Google Scholar, and preprints from medRixv and bioRixv) covering a timeline from December 1, 2019 to April 1, 2021. Population-screening, contact-tracing and cohort studies reporting prevalence and transmission of SARS-CoV-2 in children were included. Data were extracted according to PRISMA guidelines. Meta-analyses were performed using Review Manager 5.3.Results: Ninety studies were included. Compared to adults, children showed comparable national (risk ratio (RR) = 0.87, 95% confidence interval (CI) = 0.71-1.060 and subnational (RR = 0.81, 95% CI = 0.66-1.01) prevalence in population-screening studies, and lower odds of infection in community/household contact-tracing studies (odds ratio (OR) = 0.62, 95% CI = 0.46-0.84). On disaggregation, adolescents observed comparable risk (OR = 1.22, 95% CI = 0.74-2.04) with adults. In educational-settings, children attending daycare/preschools (OR = 0.53, 95% CI = 0.38-0.72) were observed to be at lower-risk when compared to adults, with odds of infection among primary (OR = 0.85, 95% CI = 0.55-1.31) and high-schoolers (OR = 1.30, 95% CI = 0.71-2.38) comparable to adults. Overall, children and adolescents had lower odds of infection in educational-settings compared to community and household clusters.Conclusions: Children (\u3c10 years) showed lower susceptibility to COVID-19 compared to adults, whereas adolescents in communities and high-schoolers had comparable risk. Risks of infection among children in educational-settings was lower than in communities. Evidence from school-based studies demonstrate it is largely safe for children (\u3c10 years) to be at schools, however older children (10-19 years) might facilitate transmission. Despite this evidence, studies focusing on the effectiveness of mitigation measures in educational settings are urgently needed to support both public health and educational policy-making for school reopening
Biomass derived oligosaccharides for potential leather tanning
The global demand for renewable and affordable feedstocks, combined with the worldwide targets for reducing carbon emissions, is the driving force behind a breakthrough in resource revolution and GreenTech innovations..
Zero-Point Quantum Diffusion of Proton in Hydrogen-rich Superconductor
, as a member of hydrogen-rich superconductors, has a
superconducting critical temperature of 250 K at high pressures, which exhibits
the possibility of solving the long-term goal of room temperature
superconductivity. Considering the extreme pressure and low mass of hydrogen,
the nuclear quantum effects in should be significant and have an
impact on its various physical properties. Here, we adopt the method combines
deep-potential (DP) and quantum thermal bath (QTB), which was verified to be
able to account for quantum effects in high-accuracy large-scale molecular
dynamics simulations. Our method can actually reproduce pressure-temperature
phase diagrams of consistent with experimental and theoretical
results. After incorporating quantum effects, the quantum fluctuation driven
diffusion of proton is found even in the absence of thermal fluctuation near 0
K. The high mobility of proton is found to be compared to liquid, yet the
structure of is still rigid. These results would greatly enrich our
vision to study quantum behavior of hydrogen-rich superconductors.Comment: 7 pages, 6 figure
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