This paper presents a theoretical study of the electronic and dynamic properties of silicon vacancies and self-interstitials in 4H–SiC using hybrid density functional methods. Several pending issues, ...mostly related to the thermal stability of this defect, are addressed. The silicon site vacancy and the carbon-related antisite-vacancy (CAV) pair are interpreted as a unique and bistable defect. It possesses a metastable negative-U neutral state, which “disproportionates” into VSi+ or VSi−, depending on the location of the Fermi level. The vacancy introduces a (−/+) transition, calculated at Ec−1.25 eV, which determines a temperature threshold for the annealing of VSi into CAV in n-type material due to a Fermi level crossing effect. Analysis of a configuration coordinate diagram allows us to conclude that VSi anneals out in two stages—at low temperatures (T≲600 °C) via capture of a mobile species (e.g., self-interstitials) and at higher temperatures (T≳1200 °C) via dissociation into VC and CSi defects. The Si interstitial (Sii) is also a negative-U defect, with metastable q=+1 and q=+3 states. These are the only paramagnetic states of the defect, and maybe that explains why it escaped detection, even in p-type material where the migration barriers are at least 2.7 eV high.
Hydroxyapatite (HAp) is a widely used biomaterial for the preparation of bone and dental implants. Despite the relevance of HAp in medicine, exciting applications involving this material as a ...biocompatible photocatalyst depend on how well we understand its fundamental properties. Experimental evidence suggests that oxygen vacancies play a critical role in the production of surface radicals upon exposure of HAp to ultraviolet (UV) light. However, very little is known about the underlying physical and chemical details. We present a hybrid density functional study of the structural and electronic properties of oxygen vacancies in large HAp supercells within the plane-wave formalism. We find that under equilibrium conditions, vacancies occur either as a simple vacant oxygen site (in the neutral charge state) or as extended structures replacing several crystalline moieties (in the double plus charge state). Large atomic relaxations upon ionization make the oxygen vacancy a negative-U defect, where the single plus charge state is metastable, being only accessible under UV excitation. From inspection of the transition levels, we find that electron promotion from the valence band top to the donor state of the vacancy involves a zero-phonon transition of 3.6–3.9 eV. This mechanism is the most likely explanation to the 3.4–4.0 eV absorption onset for the observation of photocatalysis using HAp under persistent UV illumination.
This study investigates the remnants and dynamics of religious beliefs and practices among religiously unaffiliated youth in Europe, comparing them with the older unaffiliated as well as with the ...religiously affiliated. Using EVS 2017–2021 data to test contrasting hypotheses of diffused religion and cohort replacement, the study draws three main conclusions. First, youth believe more on average and older age groups believe less when it comes to eschatological beliefs among both the unaffiliated and the affiliated. Second, youth practice less and older age groups practice more on average among both the unaffiliated and the affiliated. Third, the gaps in levels of religious beliefs and practices remain between the religiously unaffiliated and the religiously affiliated among younger populations, but this gap is now narrower for religious practices. Results confirm both hypotheses (diffused religion and cohort replacement) depending on the dimensions of religiosity at study.
Portugal has been a good example of sociocultural changes during the last decades which have influenced the levels of religiosity, namely among young people. In this context, this article studies ...Portuguese youth religiosity in a comparative perspective. First, it compares Portuguese youth religiosity with the other Portuguese age groups’ religiosity. Second, it compares Portuguese youth religiosity over time. A supplementary analysis compares Portugal with Catholic Europe in both aspects. Portuguese youth are less religious than the other age groups, mainly the older group, and are becoming less religious over time. Comparing Portugal with Catholic Europe, differences in young people have decreased in the last two decades, reaching similar values in 2020. Quantitative analyses based on four religiosity dimensions (community, practice, belief, and norm), using the European Values Study, were applied. These data confirm secularization, including the theories of individualization and cohort replacement, in line with other studies.
Visceral leishmaniasis (VL) is a vector borne zoonotic disease endemic in humans and dogs in Brazil. Due to the increased risk of human infection secondary to the presence of infected dogs, public ...health measures in Brazil mandate testing and culling of infected dogs. Despite this important relationship between human and canine infection, little is known about what makes the dog reservoir progress to clinical illness, significantly tied to infectiousness to sand flies. Dogs in endemic areas of Brazil are exposed to many tick-borne pathogens, which are likely to alter the immune environment and thus control of L. infantum.
A cross-sectional study of 223 dogs from an area of Natal, in the Rio Grande do Norte, Brazil, were studied to determine the association between comorbid tick-borne disease and Leishmania infection in this endemic area. The risk of Leishmania seropositivity was 1.68× greater in dogs with tick-borne disease seropositivity compared to those without (Adjusted RR: 1.68, 95% CI: 1.09-2.61, P = 0.019). A longitudinal study of 214 hunting dogs in the USA was conducted to determine the causal relationship between infection with tick-borne diseases and progression of VL. Hunting dogs were evaluated three times across a full tick season to detect incident infection with tick-borne diseases. A logistic regression model with generalized estimating equations to estimate the parameters was used to determine how exposure to tick-borne disease altered VL progression over these three time points when controlling for other variables. Dogs infected with three or more tick-borne diseases were 11× more likely to be associated with progression to clinical VL than dogs with no tick-borne disease (Adjusted RR: 11.64, 95% CI: 1.22-110.99, P = 0.03). Dogs with exposure to both Leishmania spp. and tick-borne diseases were five times more likely to die during the study period (RR: 4.85, 95% CI: 1.65-14.24, P = 0.0051).
Comorbid tick-borne diseases dramatically increased the likelihood that a dog had clinical L. infantum infection, making them more likely to transmit infection to sand flies and people. As an important consequence, reduction of tick-borne disease exposure through topical or oral insecticides may be an important way to reduce progression and transmissibility of Leishmania infection from the canine reservoir to people.
Visceral leishmaniasis (VL) is a neglected tropical disease that is globally distributed and has the potential to cause very serious illness. Prior literature highlights the emergence and spread of ...VL is influenced by multiple factors, such as socioeconomic status, sanitation levels or animal and human reservoirs. The study aimed to retrospectively investigate the presence and infectiousness of VL in Rio Grande do Norte (RN), Brazil between 2007 and 2020. We applied a hierarchical Bayesian approach to estimate municipality-specific relative risk of VL across space and time. The results show evidence that lower socioeconomic status is connected to higher municipality-specific VL risk. Overall, estimates reveal spatially heterogeneous VL risks in RN, with a high probability that VL risk for municipalities within the West Potiguar mesoregion are more than double the expected VL risk. Additionally, given the data available, results indicate there is a high probability of increasing VL risk in the municipalities of Natal, Patu and Pau dos Ferros. These findings demonstrate opportunities for municipality-specific public health policy interventions and warrant future research on identifying epidemiological drivers in at-risk regions.
Although there is a rich body of research on religious transmission, relatively little attention has been given to studying this within specific religious traditions such as Catholicism, especially ...in Europe. Using data from the 2018 round of the International Social Survey Programme (ISSP), this study uses regression analysis to investigate individual‐level determinants of religious transmission in 12 European countries with a Catholic tradition. We find support for the idea that parental religious socialization impacts adults' religiosity. More specifically, we find that childhood religiosity has explanatory effects separate from the impact of parental religiosity and that the religiosity of the father has a greater impact on offspring religiosity than the religiosity of the mother. We also find that childhood church attendance has a stronger effect in former communist countries than in western European countries. Overall, this study suggests the religious socialization perspective should be considered more in religious group‐specific terms.
Silicon carbide diodes for neutron detection Coutinho, José; Torres, Vitor J.B.; Capan, Ivana ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2021, Letnik:
986
Journal Article
Recenzirano
In the last two decades we have assisted to a rush towards finding a 3He-replacing technology capable of detecting neutrons emitted from fissile isotopes. The demand stems from applications like ...nuclear war-head screening or preventing illicit traffic of radiological materials. Semiconductor detectors stand among the strongest contenders, particularly those based on materials possessing a wide band gap like silicon carbide (SiC). We review the workings of SiC-based neutron detectors, along with several issues related to material properties, device fabrication and testing. The paper summarizes the experimental and theoretical work carried out within the E-SiCure project (Engineering Silicon Carbide for Border and Port Security), co-funded by the NATO Science for Peace and Security Programme. The main goal was the development of technologies to support the fabrication of radiation-hard silicon carbide detectors of special nuclear materials. Among the achievements, we have the development of successful Schottky barrier based detectors and the identification of the main carrier life-time-limiting defects in the SiC active areas, either already present in pristine devices or introduced upon exposure to radiation fields. The physical processes involved in neutron detection are described. Material properties as well as issues related to epitaxial growth and device fabrication are addressed. The presence of defects in as-grown material, as well as those introduced by ionizing radiation are reported. We finally describe several experiments carried out at the Jozef Stefan Institute TRIGA Mark II reactor (Ljubljana, Slovenia), where a set of SiC-based neutron detectors were tested, some of which being equipped with a thermal neutron converter layer. We show that despite the existence of large room for improvement, Schottky barrier diodes based on state-of-the-art 4H-SiC are closing the gap between gas- and semiconductor-based detectors regarding their sensitivity.
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