Alkali metal \(\beta\)/\(\beta^{\prime\prime}\) aluminas are among the fastest ionic conductors, yet little is understood about the role of defects in the ion transport mechanism. Here, we use ...density functional theory (DFT) to investigate the crystal structures of \(\beta\) and \(\beta^{\prime\prime}\) phases, and vacancy and interstitial defects in these materials. We find that charge transport is likely to be dominated by alkali metal interstitials in \(\beta\)-aluminas and by vacancies in \(\beta^{\prime\prime}\) aluminas. Lower bounds for the activation energy for diffusion are found by determining the minimum energy paths for defect migration. The resulting migration barriers are lower than the experimental activation energies for conduction in Na \(\beta\) and \(\beta^{\prime\prime}\) aluminas, suggesting a latent potential for optimization. The lowest activation energy of about 20 meV is predicted for correlated vacancy migration in K \(\beta^{\prime\prime}\) alumina.
The excitonic spectra of single layer GeS and GeSe are predicted by ab initio GW-Bethe Salpeter equation calculations. G 0 W 0 calculations for the band structures find a fundamental band gap of 2.85 ...eV for GeS and 1.70 eV for GeSe monolayer. However, excitons are tightly bound, specially in GeS at the {\Gamma} point, where the quasi-particle interactions are so strong that they shift the {\Gamma} exciton peak energy into the visible range and below the off-{\Gamma} exciton peak. The lowest energy excitons in both materials are excited by light along the zigzag direction and have exciton binding energies of 1.05 eV and 0.4 eV, respectively, but despite the strong binding, the calculated binding energies are in agreement with a Mott-Wannier model.
Phosphorene nanoribbons Carvalho, A; Rodin, A S; Castro Neto, A H
arXiv.org,
08/2014
Paper, Journal Article
Open access
Edge-induced gap states in finite phosphorene layers are examined using analytical models and density functional theory. The nature of such gap states depends on the direction of the cut. Armchair ...nanoribbons are insulating, whereas nanoribbons cut in the perpendicular direction (with zigzag and cliff-type edges) are metallic, unless they undergo a reconstruction or distortion with cell doubling, which opens a gap. All stable nanoribbons with unsaturated edges have gap states that can be removed by hydrogen passivation. Armchair nanoribbon edge states decay exponentially with the distance to the edge and can be described by a nearly-free electron model.
The scattering of two-dimensional massless Dirac fermions from local spin-orbit interactions with an origin in dilute concentrations of physisorbed atomic species on graphene is theoretically ...investigated. The hybridization between graphene and the adatoms' orbitals lifts spin and valley degeneracies of the pristine host material, giving rise to rich spin-orbit coupling mechanisms with features determined by the exact adsorption position on the honeycomb lattice - bridge, hollow or top position - and the adatoms' outer-shell orbital type. Effective graphene-only Hamiltonians are derived from symmetry considerations, while a microscopic tight-binding approach connects effective low-energy couplings and graphene-adatom hybridization parameters. Within the \(T\)-matrix formalism, a theory for (spin-dependent) scattering events involving graphene's charge carriers, and the spin-orbit active adatoms is developed. Spin currents associated with intravalley and intervalley scattering are found to tend to oppose each other. We establish that under certain conditions, hollow-position adatoms give rise to the spin Hall effect, through skew scattering, while top-position adatoms induce transverse charge currents via trigonal potential scattering. We also identify the critical Fermi energy range where the spin Hall effect is dramatically enhanced, and the associated transverse spin currents can be reversed.
Strongly bound excitons confined in two-dimensional (2D) semiconductors are dipoles with a perfect in-plane orientation. In a vertical stack of semiconducting 2D crystals, such in-plane excitonic ...dipoles are expected to efficiently couple across van der Waals gap due to strong interlayer Coulomb interaction and exchange their energy. However, previous studies on heterobilayers of group 6 transition metal dichalcogenides (TMDs) found that the exciton decay dynamics is dominated by interlayer charge transfer (CT) processes. Here, we report an experimental observation of fast interlayer energy transfer (ET) in MoSe2/WS2 heterostructures using photoluminescence excitation (PLE) spectroscopy. The temperature dependence of the transfer rates suggests that the ET is F\"orster-type involving excitons in the WS2 layer resonantly exciting higher-order excitons in the MoSe2 layer. The estimated ET time of the order of 1 ps is among the fastest compared to those reported for other nanostructure hybrid systems such as carbon nanotube bundles. Efficient ET in these systems offers prospects for optical amplification and energy harvesting through intelligent layer engineering.
Cardanol was obtained by vacuum distillation of ‘‘cashew nut shell liquid’’ (CNSL). Cardanol is a by-product of cashew production and a building block for chemical synthesis; cardanol and its ...derivatives can be used for different types of applications. Three of these compounds are the subject of the present NMR study and theoretical comparison. 1H and 13C NMR signals were assigned using 1D and 2D NMR experiments. The DFT/B3LYP method using the cc-pVTZ basis set was employed for the calculations of the 1H and 13C NMR chemical shifts (δ). The obtained data were used as an auxiliary tool for unequivocal assignment of all 1H and 1³C NMR signals. For these compounds, the adopted theoretical model was sufficient to obtain a good description of the chemical shifts.
Cardanol is a by-product of cashew production and a building block for chemical synthesis; cardanol and its derivatives can be used for different types of applications. Three of these compounds are the subject of the present NMR study and theoretical comparison. Display omitted
•Chemical shift calculations using the DFT/B3LYP method.•Complete NMR assignment for three cardanol derivatives.•Experimental and theoretical approach.
This study aimed to identify the symptoms associated with early stage SARS-CoV-2 (COVID-19) infections in healthcare professionals (HCPs) using both clinical and laboratory data.
A total of 1297 ...patients, admitted between 18 March and 8 April 2020, were stratified according to their risk of developing COVID-19 using their responses to a questionnaire designed to evaluate symptoms and risk conditions.
Anosmia/hyposmia (p<0.0001), fever (p<0.0001), body pain (p<0.0001) and chills (p=0.001) were all independent predictors for COVID-19, with a 72% estimated probability for detecting COVID-19 in nasopharyngeal swab samples. Leucopenia, relative monocytosis, decreased eosinophil values, C reactive protein (CRP) and platelets were also shown to be significant independent predictors for COVID-19.
The significant clinical features for COVID-19 were identified as anosmia, fever, chills and body pain. Elevated CRP, leucocytes under 5400×10
/L and relative monocytosis (>9%) were common among patients with a confirmed COVID-19 diagnosis. These variables may help, in the absence of reverse transcriptase PCR tests, to identify possible COVID-19 infections during pandemic outbreaks.
From 19 March to 8 April 2020, 1297 patients attended the Polyclinic Piquet Carneiro for COVID-19 detection. HCP data were analysed, and significant clinical features were anosmia, fever, chills and body pain. Elevated CRP, leucopenia and monocytosis were common in COVID-19.
Water, sanitation and the COVID-19 in the Amazon Costa, Jamerson Souza da; Rodrigues, Liange De Sousa; Silva, Aline Gabriela Castro da ...
Holos (Natal, RN),
01/2020, Volume:
8, Issue:
8
Journal Article
Peer reviewed
Open access
ABSTRACT Several studies on the pathophysiological and epidemiological characteristics of SARS-CoV-2 indicate the extracorporeal viability of the virus and the possibility of faecal-oral transmission ...through contaminated natural water and wastewater' suggesting a potential risk of spreading in socially vulnerable areas' such as the Brazilian Amazon' where access to sanitation and health services is lacking. ...an attempt we made to outline an overview of sanitation in the Brazilian Amazon and its possible impacts on the most vulnerable populations and on the health system in a pandemic situation' based on bibliographic and documentary review and exploratory analysis of data related to basic sanitation and health. The absence or insufficiency of sanitation services, especially with regard to the promotion of drinking water supply and the collection and adequate treatment of sanitary sewers, directly affects the health of the population, increasing the spread of viral, bacterial and parasitic diseases, especially in urban and periurban areas, where these services are even more precarious or simply non-existent. In addition to being an important indicator of a country's level of development, sanitation is an indispensable aspect of health promotion, especially in reducing hospitalizations and mortality from infectious diseases, notably those related to water and excreta. ...this study aims to analyse the situation of access to drinking water supply and sewage collection in the Amazon region, presenting an overview of basic sanitation in a pandemic scenario of COVID-19 and the possible risk of transmission of the new coronavirus (SARS-CoV-2) through contaminated natural water and wastewater. 2 MATERIAL AND METHODS This study starts initially from a literature review that, according to Gil (2008), makes use of materials already published, mainly scientific articles. With the exponential increase in the number of cases, the World Health Organization declared, on January 30, 2020, the Chinese outbreak as a Public Health Emergency of International Interest, with high risk for countries with vulnerable health systems.
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