Instability of mechanical equilibrium during diffusion in a three-component gas mixture in a vertical cylinder with a circular cross section

The problem of the emergence of instability of mechanical equilibrium of a three-component gas mixture during diffusion in a vertical channel with the wall impenetrable for the mass flux is considered in the case when the channel has a circular cross section. The critical Rayleigh numbers are determined, and the neutral stability lines are found in analytic form. The results are compared with experimental data.     

Block element method for solving integrated equations of contact problems in wedge-shaped domains

This paper describes the block element method for spatial integral equations with a difference kernel in the boundary-value problems of continuum mechanics and mathematical physics. The basis of the proposed method is the Wiener — Hopf method, whose generalization for a spatial case is called integral factorization method. The block element method is applied to solve problems in domains with piecewise smooth boundaries containing corner points. The developed method was used to solve the contact problem for a wedge-shaped stamp occupying the first quadrant. This paper describes in detail the methods of obtaining various characteristics of the solution constructed by reversing the system of one-dimensional linear integral equations typical for dynamics and static contact problems for stamps in the form of a strip.     

Analysis of the Local Atomic Structure of the MIL-88а Metal–Organic Framework by Computer Simulation Using XANES Data

Experimental X-ray absorption spectra near the Fe K edge for as-synthesized MIL-88а metal–organic framework (MIL stands for Materials Institute Lavoisier) before and after activation have been obtained and analyzed for the first time. The theoretical analysis of experimental spectra has revealed changes in the local atomic structure of iron at the desorption of water from pores of the studied material in the process of activation.     

Heating and Cooling Transients in the DyPO<Subscript>4</Subscript> Nanocrystals under Femtosecond Laser Irradiation in the NIR Spectral Range

We compared the heating and cooling theoretical and experimental transient times of DyPO₄ nanoparticles as a result of their heating by themultiphonon relaxation after femtosecond laser excitation in the near IR spectral range into different absorption spectral lines of the Dy³⁺ ion. We have shown that the relaxation of the heat flux to a stationary value occurs according to an exponential law. Depending on the value of the Biot number, two different relaxation mechanisms can be realized, in one of which the relaxation time depends on the thermal conductance of the interface, and in the other on the thermal diffusivity. It is shown that, after averaging over the ensemble of nanoparticles, the kinetics of the relaxation of the heat flux in these limiting cases has a substantially different character. The results might be helpful for assessing the prospects of the dielectric crystalline nanoparticles doped with rare-earth ions in the local hyperthermia treatment of cancer cells.     

The Theory of Block Structures in Problems on the Strength of Galleries and Constructions with Multiple Connections

Doklady Physics - It is shown that the boundary-value problem for a layered medium with parallel multiple cavities is reduced to the Riemann vector problem. To solve it, a factorization method is...     

Rolle des Wassers bei der Adsorption grenzfl?chenaktiver Stoffe auf hydrophilen Oberfl?chen

Ohne Zusammenfassung     

X-ray emission study of the electronic structure of nanocrystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Valence states of metal ions and the phase composition of nanocrystalline Al₂O₃ (of the original oxide and the oxide irradiated by high-energy Fe⁺ ions) are studied by using x-ray emission Al L_{2, 3} and O Kα spectra. It is established that the shape of the Al L_{2, 3} spectra strongly changes as one goes from the original (bulk) Al₂O₃ to nanocrystalline oxide, while the O Kα spectra remain practically unchanged. Moreover, irradiation by high-energy Fe⁺ ions results in slight additional changes in the x-ray spectral characteristics of the aluminum oxides under study. The obtained experimental data are compared with the results of theoretical calculations of the electronic structure of α and γ phases of Al₂O₃ performed using the LDA formalism. Using the results of x-ray spectral studies, electronic structure calculations, and x-ray diffraction analysis, it is shown that the revealed spectral differences between the nanocrystalline state of aluminum oxide and the bulk material can be interpreted as a phase transition from the α phase to the γ phase of Al₂O₃ with an addition of bayerite.     

Optical and electro-optical properties of ZnMgSe single crystals

The optical and electro-optical properties of large-sized (diameter, 20 mm; length, 70 mm) single crystals of Zn_{1 ? x}Mg_xSe (x ～ 0.5) semiconductor solid solutions are investigated. The crystals are grown by the vertical Bridgman-Stockbarger method. It is found that, for ZnMgSe single crystals with a magnesium content up to 25 at. %, the modulus of the difference between the electro-optical coefficients |r₁₃ ? r₃₃| at a wavelength of 0.63 μm is equal to (1.1 ± 0.22) × 10^?12 m/V, which is comparable in order of magnitude to the difference in the electro-optical coefficients for classical hexagonal A^IIB^VI compounds, such as CdS and CdSe. It is shown that single crystals of ZnMgSe solid solutions are promising materials for use in the fabrication of electro-optical modulators, λ/4-and λ/2-wavelength plates, and multifunctional optical elements operating in the range of high-intensity radiation of CO and CO₂ lasers.     

Tunneling of excess electron from free and trapped states

The association of an excess electron with scavengers in nonpolar solvents is considered assuming that the free electron performs the free diffusion during the lifetime between sequential places of temporary localization. The reaction of a free electron during this motion is at first taken into account along with a tunneling of the localized electron. When the mean step length between sequential localizations is short the reaction of the excess electron is diffusional and the free state contribution to the total reaction rate is negligible. In the opposite case, when this reaction becomes essentially hopping, the corresponding rate is significantly accelerated due to a faster diffusion of the free electron.