Variational wave functions for the S=1/2S=1/2 Heisenberg model on the anisotropic triangular lattice: Spin liquids and spiral orders

By using variational wave functions and quantum Monte Carlo techniques, we investigate the complete phase diagram of the Heisenberg model on the anisotropic triangular lattice, where two out of three bonds have super-exchange couplings $J$ and the third one has instead $J^\prime$. This model interpolates between the square lattice and the isotropic triangular one, for $J^\prime/J \le 1$, and between the isotropic triangular lattice and a set of decoupled chains, for $J/J^\prime \le 1$. We consider all the fully-symmetric spin liquids that can be constructed with the fermionic projective-symmetry group classification [Y. Zhou and X.-G. Wen, arXiv:cond-mat/0210662] and we compare them with the spiral magnetic orders that can be accommodated on finite clusters. Our results show that, for $J^\prime/J \le 1$, the phase diagram is dominated by magnetic orderings, even though a spin-liquid state may be possible in a small parameter window, i.e., $0.7 \lesssim J^\prime/J \lesssim 0.8$. In contrast, for $J/J^\prime \le 1$, a large spin-liquid region appears close to the limit of decoupled chains, i.e., for $J/J^\prime \lesssim 0.6$, while magnetically ordered phases with spiral order are stabilized close to the isotropic point.Comment: 11 pages, 11 figure

THE EFFECT OF A VARNISH CONTAINING SELF-CURING RESIN ON THE SOFTNESS OF TWO TYPES OF TISSUE CONDITIONERS

Objectives: One of the limitations of tissue conditioners (TC) is the gradual hardening of the material in a short time after insertion in the mouth. This study aimed to determine the softness of two different tissue conditioners with and without the coating made up of 1,1,1trichloroethan and self-curing acrylic resin.Materials and Methods: In this experimental study, Acrosoft (Marlic, Tehran, Iran) and GC (GC corporation, Tokyo, Japan) tissue conditioners were examined. 28 discs of 20 x 3 mm dimensions were prepared for each tissue conditioner (n=14). Half of the samples in each group were coated with varnish coating made up of 1,1,1trichloroethan and self-curing acrylic resin. The hardness of all samples was measured at five intervals of 1,3,7,14, and28 days by a Shore-A Durometer with a conical indenter. The data were analyzed by descriptive statistics and Friedman analyses. P<0.05 was considered statistically significant.Results: The mean hardness of the GC and Acrosoft tissue conditioners on days 1, 3, 7, 14, and 28 in both varnish-coated and non-varnish-coated groups were statistically different and Acrosoft tissue conditioner was harder than the GC. In the paired mean hardness comparison on days 1, 3, 7, 14, and 28 in the GV and G0 groups: this trend was the same in AV and A0 groups. The comparison of hardness in the GV and G0 groups at each time interval indicated that only on day 3, the control group(G0) was harder than the surface coating group(GV). The comparison of the hardness in the AV and A0 groups showed that on days 3 and 7, the hardness in the control group (A0) was higher than the surface coating group(AV).Conclusions: The varnish containing self-curing resin can soften the Acrosoft and GC tissue conditioner in a short time. Moreover, this varnish can be clinically applied in the borders between the soft liner and acrylic denture, which is usually the starting point for debonding

COVID-19 Infection and Seropositivity in Multiple Sclerosis Patients in Guilan in 2021

Background: Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system. COVID-19 has presented a significant challenge to the care providers of patients with MS. Objectives: The present study aimed to investigate the frequency of COVID-19 infection and its seropositivity in MS patients in Guilan, Iran, in 2021. Materials & Methods: In this analytical-cross-sectional study, all patients with relapsing-remitting MS registered in the Guilan MS Association with an expanded disability status scale of less than 5 who were referred for evaluation participated in the study. Information related to the clinical and serological symptoms of COVID-19 infection, changes in drug use, and the occurrence of new attacks were collected. Serological results of COVID-19 (IgG) among them were registered. Results: In total, 260 patients with MS (78.8% women, and 21.2% men) with a Mean±SD age of 38.7±9.9 years, and a Mean±SD duration of MS of 8.9±4.9 years were investigated. The most commonly used drugs were Dimethyl fumarate, Interferon, and Rituximab, respectively. Thirty-three patients (12.6%) had a clinical COVID-19 infection, of which 32 people had a mild and only one had a critical infection. Eight patients (1.3%) had positive COVID-19 IgG tests. No significant relationship was found between the COVID-19 infection with the type of medication, medication change, clinical attack of MS, and co-morbidities (P>0.05). Conclusion: A few patients had positive COVID-19 IgG tests and clinical COVID-19 infection. The vast majority had mild disease, and the clinical attack was not related to COVID-19 infection

The Fermi energy as common parameter to describe charge compensation mechanisms: A path to Fermi level engineering of oxide electroceramics

Chemical substitution, which can be iso- or heterovalent, is the primary strategy to tailor material properties. There are various ways how a material can react to substitution. Isovalent substitution changes the density of states while heterovalent substitution, i.e. doping, can induce electronic compensation, ionic compensation, valence changes of cations or anions, or result in the segregation or neutralization of the dopant. While all these can, in principle, occur simultaneously, it is often desirable to select a certain mechanism in order to determine material properties. Being able to predict and control the individual compensation mechanism should therefore be a key target of materials science. This contribution outlines the perspective that this could be achieved by taking the Fermi energy as a common descriptor for the different compensation mechanisms. This generalization becomes possible since the formation enthalpies of the defects involved in the various compensation mechanisms do all depend on the Fermi energy. In order to control material properties, it is then necessary to adjust the formation enthalpies and charge transition levels of the involved defects. Understanding how these depend on material composition will open up a new path for the design of materials by Fermi level engineering

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation

On efficiency of earth-abundant chalcogenide photovoltaic materials buffered with CdS: the limiting effect of band alignment

Earth-abundant and environmentally-friendly Cu₂–II–IV–VI₄ (II = Sr, Ba; IV = Ge, Sn; VI = S,Se) are considered materials for the absorber layers in thin film solar cells. Attempts to understand and improve optoelectronic properties of these newly emerged absorbers resulted in an efficiency of 5.2% in less than two years. However, the energy band alignment at the buffer/absorber interface has not been studied yet; an information which is of crucial importance for designing high performance devices. Therefore, current study focuses on the band offsets between these materials and the CdS buffer. Using first-principles calculations, band discontinuities are calculated at the buffer/absorber interface. The results yield a type-II band alignment between all Cu₂–II–IV–VI₄ absorbers and CdS, hence a negative ΔEc. Adoption of a negative ΔEc (cliff-like conduction band offset) at the buffer/absorber interface, however, gives rise to low open circuit voltage and high interface-related recombinations. Therefore, it is necessary to search for an alternative buffer material that forms a type-I band alignment with these absorbers, where the conduction band minimum and the valence band maximum are both localized on the absorber side

On efficiency of earth-abundant chalcogenide photovoltaic materials buffered with CdS: The limiting effect of band alignment

Earth-abundant and environmentally-friendly Cu2-II-IV-VI4(II = Sr, Ba; IV = Ge, Sn; VI = S,Se) are considered materials the absorber layers in thin-film solar cells. Attempts to understand and improve optoelectronic properties of these newly emerged absorbers resulted in an efficiency of 5.2% in less than 2 years. However, the energy band alignment at the buffer/absorber interface has not been studied yet; an information which is of crucial importance for designing high performance devices. Therefore, current study focuses on the band offsets between these materials and the CdS buffer. Using core level energies, band discontinuities are calculated at the buffer/absorber interface by first-principles calculations. The results yield a type-II band alignment between all Cu2-II-IV-VI4 absorbers and CdS, hence a negative ΔEc. Adoption of a negative ΔEc (cliff-like conduction band offset) at the buffer/absorber interface, however, gives rise to low open circuit voltage and high interface-related recombinations. Therefore, it is necessary to search for an alternative buffer material that forms a type-I band alignment with these absorbers, where the conduction band minimum and the valence band maximum are both localized on the absorber side