Context. In recent years, high spatial resolution techniques have given valuable insights into the complex atmospheres of AGB stars and their wind-forming regions. They make it possible to trace the ...dynamics of molecular layers and shock waves, to estimate dust condensation distances, and to obtain information on the chemical composition and size of dust grains close to the star. These are essential constraints for understanding the mass loss mechanism, which presumably involves a combination of atmospheric levitation by pulsation-induced shock waves and radiation pressure on dust, forming in the cool upper layers of the atmospheres. Aims. Spectro-interferometric observations indicate that Al2O3 condenses at distances of about 2 stellar radii or less, prior to the formation of silicates. Al2O3 grains are therefore prime candidates for producing the scattered light observed in the close vicinity of several M-type AGB stars, and they may be seed particles for the condensation of silicates at lower temperatures. The purpose of this paper is to study the necessary conditions for the formation of Al2O3 and the potential effects on mass loss, using detailed atmosphere and wind models. Methods. We have constructed a new generation of Dynamic Atmosphere and Radiation-driven Wind models based on Implicit Numerics (DARWIN), including a time-dependent treatment of grain growth and evaporation for both Al2O3 and Fe-free silicates (Mg2SiO4). The equations describing these dust species are solved in the framework of a frequency-dependent radiation-hydrodynamical model for the atmosphere and wind structure, taking pulsation-induced shock waves and periodic luminosity variations into account. Results. Condensation of Al2O3 at the close distances and in the high concentrations implied by observations requires high transparency of the grains in the visual and near-IR region to avoid destruction by radiative heating. We derive an upper limit for the imaginary part of the refractive index k around 10-3 at these wavelengths. For solar abundances, radiation pressure due to Al2O3 is too low to drive a wind. Nevertheless, this dust species may have indirect effects on mass loss. The formation of composite grains with an Al2O3 core and a silicate mantle can give grain growth a head start, increasing both mass loss rates and wind velocities. Furthermore, our experimental core-mantle grain models lead to variations of visual and near-IR colors during a pulsation cycle which are in excellent agreement with observations. Conclusions. Al2O3 grains are promising candidates for explaining the presence of gravitationally bound dust shells close to M-type AGB stars, as implied by both scattered light observations and mid-IR spectro-interferometry. The required level of transparency at near-IR wavelengths is compatible with impurities due to a few percent of transition metals (e.g., Cr), consistent with cosmic abundances. Grains consisting of an Al2O3 core and an Fe-free silicate mantle with total grain radii of about 0.1−1 micron may be more efficient at driving winds by the scattering of stellar photons than pure Fe-free silicate grains.
Migration from rural areas of India contributes to urbanisation and may increase the risk of obesity and diabetes. We tested the hypotheses that rural-to-urban migrants have a higher prevalence of ...obesity and diabetes than rural nonmigrants, that migrants would have an intermediate prevalence of obesity and diabetes compared with life-long urban and rural dwellers, and that longer time since migration would be associated with a higher prevalence of obesity and of diabetes.
The place of origin of people working in factories in north, central, and south India was identified. Migrants of rural origin, their rural dwelling sibs, and those of urban origin together with their urban dwelling sibs were assessed by interview, examination, and fasting blood samples. Obesity, diabetes, and other cardiovascular risk factors were compared. A total of 6,510 participants (42% women) were recruited. Among urban, migrant, and rural men the age- and factory-adjusted percentages classified as obese (body mass index BMI >25 kg/m(2)) were 41.9% (95% confidence interval CI 39.1-44.7), 37.8% (95% CI 35.0-40.6), and 19.0% (95% CI 17.0-21.0), respectively, and as diabetic were 13.5% (95% CI 11.6-15.4), 14.3% (95% CI 12.2-16.4), and 6.2% (95% CI 5.0-7.4), respectively. Findings for women showed similar patterns. Rural men had lower blood pressure, lipids, and fasting blood glucose than urban and migrant men, whereas no differences were seen in women. Among migrant men, but not women, there was weak evidence for a lower prevalence of both diabetes and obesity among more recent (</=10 y) migrants.
Migration into urban areas is associated with increases in obesity, which drive other risk factor changes. Migrants have adopted modes of life that put them at similar risk to the urban population. Gender differences in some risk factors by place of origin are unexpected and require further exploration. Please see later in the article for the Editors' Summary.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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•Computational design of nanosensor for common pollutants based on Green Phosphorene (GreenP) Monolayer.•Improved sensitivity and selectivity towards toxic NO2 by means of foreign ...atom substitution.•Appropriate binding energies and measurable changes in the band gaps.•In addition to DFT, employment of statistical thermodynamic, and the non-equilibrium Green’s function approach.
Green phosphorus and its monolayer variant, green phosphorene (GreenP), are the recent members of two-dimensional (2D) phosphorus polymorphs. The new polymorph possesses the high stability, tunable direct bandgap, exceptional electronic transport, and directionally anisotropic properties. All these unique features could reinforce it the new contender in a variety of electronic, optical, and sensing devices. Herein, we present gas-sensing characteristics of pristine and defected GreenP towards major environmental gases (i. e., NH3, NO, NO2, CO, CO2, and H2O) using combination of the density functional theory, statistical thermodynamic modeling, and the non-equilibrium Green’s function approach (NEGF). The calculated adsorption energies, density of states (DOS), charge transfer, and Crystal Orbital Hamiltonian Population (COHP) reveal that NO, NO2, CO, CO2 are adsorbed on GreenP, stronger than both NH3 and H2O, which are weakly physisorbed via van der Waals interactions. Furthermore, substitutional doping by sulfur can selectively intensify the adsorption towards crucial NO2 gas because of the enhanced charge transfer between p orbitals of the dopant and the analyte. The statistical estimation of macroscopic measurable adsorption densities manifests that the significant amount of NO2 molecules can be practically adsorbed at ambient temperature even at the ultra-low concentration of part per billion (ppb). In addition, the current-voltage (I–V) characteristics of S-doped GreenP exhibit a variation upon NO2 exposure, indicating the superior sensitivity in sensing devices. Our work sheds light on the promising application of the novel GreenP as promising chemical gas sensors.
The sensitive nature of molecular hydrogen (H2) interaction with the surfaces of pristine and functionalized nanostructures, especially two-dimensional materials, has been a subject of debate for a ...while now. An accurate approximation of the H2 adsorption mechanism has vital significance for fields such as H2 storage applications. Owing to the importance of this issue, we have performed a comprehensive density functional theory (DFT) study by means of several different approximations to investigate the structural, electronic, charge transfer and energy storage properties of pristine and functionalized graphdiyne (GDY) nanosheets. The dopants considered here include the light metals Li, Na, K, Ca, Sc and Ti, which have a uniform distribution over GDY even at high doping concentration due to their strong binding and charge transfer mechanism. Upon 11% of metal functionalization, GDY changes into a metallic state from being a small band-gap semiconductor. Such situations turn the dopants to a partial positive state, which is favorable for adsorption of H2 molecules. The adsorption mechanism of H2 on GDY has been studied and compared by different methods like generalized gradient approximation, van der Waals density functional and DFT-D3 functionals. It has been established that each functionalized system anchors multiple H2 molecules with adsorption energies that fall into a suitable range regardless of the functional used for approximations. A significantly high H2 storage capacity would guarantee that light metal-doped GDY nanosheets could serve as efficient and reversible H2 storage materials.
During the last decade, Inorganic Halide Double Perovskite materials have attracted widespread interest as a promising eco-friendly and non-toxic alternative to lead based hybrid halide ...organic–inorganic perovskites materials, with outstanding Stability, Structural and electronic properties. In this study, First-Principles density functional theory (DFT) calculations were performed on the structural, stability, electronic and optical properties of the transition metal-based double perovskites materials Cs2InGaX6 (X = Cl, Br, or I). Our results reveal that all these materials exhibit excellent thermodynamic and structural stability owing to their negative formation energies and Goldsmith's factors. It is also observed that Cs2InGaCl6, Cs2InGaBr6, and Cs2InGaI6 materials exhibit band gaps calculated by different functional (GGA-PBE and TB-mpj) in visible-range between 0.89 and 3.24 eV. Furthermore, the computed optical properties reveal strong absorption in UV, visible, and IR range with high optical conductivity and low reflectivity. These obtained results predict that the three transition metal-based double perovskites materials carries promising application in nano-electronic and optoelectronic device applications and can be considered as photovoltaic absorber materials.
Schematic illustration of the halide double perovskite absorption over the whole light spectra. Display omitted
•Electronic and Optical properties of Cs2InGaX6(X: Cl, Br and I) were investigated.•Structural stability was demonstrated.•Semiconductor behavior with indirect and direct bandgaps was shown.•High optical conductivity and low reflectivity were found.•Strong absorption coefficient over the whole light spectra was revealed.
We have performed first-principles calculations based on density functional theory to investigate the doping characteristics of 31 different adatoms on stanene monolayer, which includes the elements ...of alkali metals (AM), alkaline earth metals (AEM), transition metals (TMs), and groups III–VII. The most stable configurations of all the dopants have been explored by calculating and comparing binding energies of all the possible binding sites. To comment on the uniform distribution of adatoms on stanene, the adsorption energies (E ads) of adatoms have been compared with their experimental cohesive energies (E c) in the bulk phase. A further comparison reveals that the binding energies of most of the studied adatoms on stanene are much stronger than other group IV monolayers. Apart from structural and binding characteristics, bond lengths, adatom–adatom distance, charge-transfer mechanism, electronic properties, and work function have also been explored in pristine and doped monolayers. The strong adsorption of adatoms on stanene, tunable electronic properties, and formation of dumbbell structures in the case of AEM and TM shows that doped stanene sheets are worth further exploration.
A significant improvement in molecular hydrogen uptake properties is revealed by our ab initio calculations for Li-decorated metal-organic framework 5. We have found that two Li atoms are strongly ...adsorbed on the surfaces of the six-carbon rings, one on each side, carrying a charge of +0.9e per Li atom. Each Li can cluster three H₂ molecules around itself with a binding energy of 12 kJ (mol H₂)⁻¹. Furthermore, we show from ab initio molecular dynamics simulations with a hydrogen loading of 18 H₂ per formula unit that a hydrogen uptake of 2.9 wt % at 200 K and 2.0 wt % at 300 K is achievable. To our knowledge, this is the highest hydrogen storage capacity reported for metal-organic framework 5 under such thermodynamic conditions.
•The mixed spin-(3/2, 5/2) Ising nanographene system is investigated.•The Quantum Monte Carlo simulation is used.•Dynamic magnetic properties and the hysteresis behavior of the system are ...studied.•The system exhibits the superparamagnetic phase and multiple hysteresis loops.
Using the Quantum Monte Carlo simulation (QMCS), the dynamic blocking temperature of a nano-graphene bilayer has been investigated within the framework of the Transverse Ising Model (TIM) with mixed spins, under the existence of the time-dependent oscillating longitudinal magnetic field (h(t)=hb+h0cos(ωt)) and the transverse field (Ω). The influence of the time-dependent oscillating longitudinal magnetic field, the period of magnetic field (τ) and the transverse field (Ω) on the thermal behavior of the total longitudinal and transverse dynamic order parameters, the total dynamic magnetic susceptibility and the dynamic hysteresis of the nano-graphene bilayer are also studied. As results, we remark the appearance of multiple hysteresis loops and the system exhibits the superparamagnetic behavior at the dynamic blocking temperature.
Herein, we report the phase stability of the hydrogenated Ti2C MXene monolayer using an evolutionary algorithm based on density functional theory. We predict the existence of hexagonal Ti2CH, Ti2CH2, ...and Ti2CH4. The dynamic and energetic stabilities of the predicted structures are verified through phonon dispersion and formation energy, respectively. The electron–phonon coupling is carefully investigated by employing isotropic Eliashberg theory. The Tc values are 0.2 K, 2.3 K, and 9.0 K for Ti2CH, Ti2CH2, and Ti2CH4, respectively. The translation and libration adopted by stretch and bent vibrations contribute to the increasing Tc of Ti2CH4. The high-frequency hydrogen modes contribute to the critical temperature increase. Briefly, this work not only highlights the effect of H-content on the increments of Tc for Ti2CHx, but also demonstrates the first theoretical evidence of the existence of H-rich MXene in the example of Ti2CH4. Therefore, it potentially provides a guideline for developing hydrogenated 2D superconductive applications.
•The ground-state phase has been studied.•The electronic, magnetic and electrical properties have been determined.•The semi-metallic behavior has been found.•The high critical temperature has been ...deduced.
In this paper, a theoretical study of the electronic, magnetic and electrical properties of double perovskite Mn2FeReO6 with a high Curie temperature so far in magnetic oxides was conducted, using several methods such as Ab-initio and Statistical Physics like Monte-Carlo Simulations (MCS). However, the first principles calculations showed a half-metallic behavior from the density of states and band structures calculation, using PBE + U (apply on the elements Mn, Fe, and Re respectively). The critical temperature obtained by MCS has a great similarity with the experimental results.
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