ABSTRACT
Theoretical models of accretion discs and observational data indicate that the X-ray emission from the inner parts of an accretion disc can irradiate its outer regions and induce a thermal ...wind, which carries away the mass and angular momentum from the disc. Our aim is to investigate the influence of the thermal wind on the outburst light curves of black hole X-ray binary systems. We carry out numerical simulations of a non-stationary disc accretion with wind using upgraded open code freddi. We assume that the wind launches only from the ionized part of the disc and may turn off if the latter shrinks fast enough. Our estimates of the viscosity parameter α are shifted downward compared to a scenario without a wind. Generally, correction of α depends on the spectral hardness of central X-rays and the disc outer radius, but unlikely to exceed a factor of 10 in the case of a black hole low-mass X-ray binary (BH LMXB). We fit 2002 outburst of BH LMXB 4U 1543 − 47 taking into account the thermal wind. The mass-loss in the thermal wind is of order of the accretion rate on the central object at the peak of the outburst. New estimate of the viscosity parameter α for the accretion disc in this system is about two times lower than the previous one. Additionally, we calculate evolution of the number of hydrogen atoms towards 4U 1543 − 47 due to the thermal wind from the hot disc.
High refractive glasses in the La2O3–Nb2O5–B2O3 (LNB) system were synthesized by the melt-quenching technique and correlations between their compositions and structural features were clarified. It ...was found that the refraction index of the LNB glasses is tunable from 1.71 to 1.98 by the variation of the Nb2O5 fraction from 5 to 30 mol%. The infrared spectroscopy analysis implies on the presence of three and four coordinated borate units, as well as six coordinated niobium atoms. The X-ray absorption (La L3-edge and Nb K-edge XANES and EXAFS) spectroscopy and total X-ray scattering results show that niobium atoms maintain octahedral oxygen coordination despite the wide variation of the Nb2O5 content, while average lanthanum coordination number is versatile and changes from ~8 to ~10. The interatomic distance values testify that the niobium octahedra in the glass network are connected only “by corners”. The stability of niobium local atomic structure implies that the main source of the changes in the optical properties of studied glasses is the variation of the Nb2O5 content. The deeper understanding of the local atomic structure of the high refractive index LNB glasses paves ways for the development of new glass wafers for cutting-edge augmented reality devices.
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•High refractive index Nb2O5–La2O3–B2O3 glasses derived by the melt-quenched technique.•Local atomic structure of Nb and La studied by the X-ray synchrotron techniques.•Nb atomic structure weakly depends on the concentration of Nb2O5.•Nb octahedra connected “by corners” in the glass network.•Local atomic structure of La is sensitive to the concentration of Nb2O5.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Local electric field enhancement (LEFE) for NPs aggregate in oxide glass was obtained.•Approach to LEF analysis reproduces Er3+ luminescence enhancement by Ag NPs aggregate.•Optimal parameters of Ag ...NPs aggregate which maximize LEFE were estimated.•LEFE is largest for aggregates of Ag, less for Rb, lowest for aggregates of Au NPs.•Rb containing bimetallic NPs enable to tune LSPR-LEF characteristics in wide ranges.
Local electric field (LEF) distribution near Ag, Au, AgAu NPs synthesized by UV laser or temperature treatments, and near simulated Rb, AgRb, AuRb NPs in oxide glasses, was studied considering aggregates of 10–15 particles - necessary condition for description of optical extinction spectra. For efficient analysis of LEF spatial distributions under different sizes, components, agglomerations of NPs in these aggregates, approach was proposed that enables to obtain dependence of averaged LEF enhancement upon the distance from the nearest particles in aggregate. This approach reproduced enhancement of Er3+ luminescence intensity in zinc-tellurite glass after formation of Ag NPs and showed that average LEF enhancement per hypothetical Rare Earth ion (REI) is largest for aggregates of Ag, less for Rb, lowest for Au NPs. The optimal Ag NPs aggregate was estimated for best LEF enhancement per hypothetical REI. Simulated aggregates of Rb containing NPs demonstrated strong LEF, shifted in a wide range.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Optical extinction spectra calculated via multisphere
T
-matrices for nanoparticles with different concentrations of metals and different architectures (core–shell, inverse core–shell, or alloy) are ...considered. A method is proposed for determination of architecture of nanoparticles (core–shell or alloy) from only data on the position of plasmon resonance and composition of components. The use of an optical spectrum fitting technique to the spectra of monodisperse noninteracting bimetallic nanoparticles with a predetermined structure appeared to be effective for the determination of the internal structure of nanoparticles, except large nanoparticles with a radius of more than 60 nm containing less than ∼25% silver atoms.
The most widely used and applied plasmonic materials, namely silver and gold, has limitations due to their high cost and restriction on the spectral position and shape of the plasmon resonance. This ...remains true for bimetallic silver–gold nanoparticles. Higher flexibility is required, in particular, for the design of broadband absorbers of light, and for this task the metals other than silver and gold are considered. In this paper we study the optical extinction spectra of alloy and composite nanoparticles containing magnesium and gold. The dielectric properties are calculated within the approximation of independent particles (IPA) based on the electronic structure obtained using density functional theory (DFT) with Hubbard correction (DFT+U). The obtained spectra of optical extinction of magnesium–gold alloy nanoparticles demonstrate that the most sensitive to the composition is the region of wavelengths below 500 nm. Simultaneously, the position of the plasmon resonance predicted by Vegard’s law is higher than obtained from accurate DFT+U based calculations. We managed to describe the experimental optical extinction spectra of the glass sample containing gold and magnesium atoms using the calculated spectra. The results points on the formation of composite nanoparticles with core of Au
3
Mg alloy and shell of Au in the considered sample.
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FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
•Effect of B2O3on LNB glasses structure was revealed.•Crystal chemical similarity of La environment in LNB glass and LaB3O6 was determined.•Within this similarity mean RLa-O decreases under narrowing ...PRDF of nearest oxygens.•Ratio of main peaks in La L3-XANES-probe on the number of O atoms around La in glass.
Dependence of lanthanum local atomic structure in borate glasses La2O3-Nb2O5-B2O3 upon component composition was studied combining XANES, computer simulations using crystal chemical similarity (CCS) of a short-range order in glass and crystal, and multidimensional interpolation of spectra as the function of structural parameters. By this approach, the values of La-O bond lengths and angles in chains O-La-O were determined. Comparison of the obtained radial and angle distribution functions of oxygen atoms around La in the studied glasses with the same functions of the reference crystals revealed that within the existing CCS of La local structure in glasses and in B3LaO6, there is a decrease in the average length of La-O bonds by ∼ 0.1 Å and decrease of FWHF by ∼ 0.2 Å in the radial distribution of nearest O atoms, under retaining angle distribution of these atoms. It was shown that the ratio of intensities of the first two peaks in experimental La L3-edge XANES is an effective fingerprint of the number of nearest oxygen neighbors of lanthanum. Using the dependence of this ratio upon the component composition of glasses, the changes in the local structure of La under decreasing of B2O3 fraction from 72.5 to 47.5% were determined.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The effect of temperature conditions on the formation of copper active sites obtained by solid state ion exchange between copper chloride and H-mordenite zeolite using X-ray absorption spectroscopy ...in near-threshold (XANES) and extended (EXAFS) spectral regions behind the copper
K
-edge measured in in-situ conditions of the reaction at temperatures varying from room temperature to 400°C. The analysis of the spectra performed using direct calculations of Cu
K
-XANES and taking into account anharmonic corrections for Cu
K
-EXAFS fitting enables us to establish that there is no ion exchange up to 200°C and copper remains in the CuCl state. An increase in the temperature higher 200°C leads to the incorporation of copper atoms to the zeolite framework.
The formation of a localized surface plasmon resonance (SPR) spectrum of randomly distributed gold nanoparticles in the surface layer of silicate float glass, generated and implanted by UV ...ArF-excimer laser irradiation of a thin gold layer sputter-coated on the glass surface, was studied by the T-matrix method, which enables particle agglomeration to be taken into account. The experimental technique used is promising for the production of submicron patterns of plasmonic nanoparticles (given by laser masks or gratings) without damage to the glass surface. Analysis of the applicability of the multi-spheres T-matrix (MSTM) method to the studied material was performed through calculations of SPR characteristics for differently arranged and structured gold nanoparticles (gold nanoparticles in solution, particles pairs, and core-shell silver-gold nanoparticles) for which either experimental data or results of the modeling by other methods are available. For the studied gold nanoparticles in glass, it was revealed that the theoretical description of their SPR spectrum requires consideration of the plasmon coupling between particles, which can be done effectively by MSTM calculations. The obtained statistical distributions over particle sizes and over interparticle distances demonstrated the saturation behavior with respect to the number of particles under consideration, which enabled us to determine the effective aggregate of particles, sufficient to form the SPR spectrum. The suggested technique for the fitting of an experimental SPR spectrum of gold nanoparticles in glass by varying the geometrical parameters of the particles aggregate in the recurring calculations of spectrum by MSTM method enabled us to determine statistical characteristics of the aggregate: the average distance between particles, average size, and size distribution of the particles. The fitting strategy of the SPR spectrum presented here can be applied to nanoparticles of any nature and in various substances, and, in principle, can be extended for particles with non-spherical shapes, like ellipsoids, rod-like and other T-matrix-solvable shapes.
The structural and physical properties of hydroxyapatite with the substitutions of Sr/Ca were studied by density functional theory calculations using Quantum ESPRESSO. The calculation of the lattice ...constants upon substitution of Sr/Ca in HAP was compared with the experimental data and showed similar increase in these parameters after the Sr/Ca substitutions. The changes in the band gap ΔE
g
and the electron work function Δϕ after Sr/Ca substitutions were estimated. The changes in the polarization and piezoelectric properties upon Sr/Ca substitution were calculated using the new quantum-chemical semi-empirical PM7, PM6-D3H4 (MOPAC) calculations.
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The results are based on DFT calculations of hydroxyapatite (HAp) structures, pristine and defective, determined by various defects formed by oxygen vacancy depending on the charged states. Ordered ...hexagonal and monoclinic HAp phases have polarization, while disordered ones do not. These ferroelectric properties are determined by orientation of OH dipoles and cause the piezoelectric and pyroelectric phenomena in such HAp structures. Optical properties of defected HAp are mainly determined by various types of oxygen vacancy defects and can be manifested in the absorption and photocatalysis under ultraviolet illumination.
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