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The set of compositions with Fe2+ in the system NaxFex/2Ti2–x/2O4 has been prepared by solid-state reactions in the inert atmosphere at 1050 °С. The oxidation state of iron was confirmed using the XANES method. Na0.88Fe0.44Ti1.56O4 is the new four-element compound in Na2O–“FeO”–TiO2 system. According to the X-ray powder data, it is orthorhombic, Pnma, a = 9.3624(1), b = 2.96718(4), c = 11.3435(1) A and has the same structure as Na0.9Fe0.9Ti1.1O4 with Fe3+. The structure was refined by the Rietveld method. The 3D-framework of (Fe, Ti)O6 octahedra contains quadruple rutile-like chains and sodium ions in double tunnels. Fe/Ti partial ordering in the framework and sodium distribution in the tunnels were studied additionally using the method of bond valence sums and Voronoi tessellation. The structure and composition of Na0.88Fe0.44Ti1.56O4 make it a promising material for cathode application.

В работе рассмотрены вопросы разработки и анализа математической модели динамики круглой сэндвич-пластины, установленной на инерционном упругом основании. Пластина является стенкой канала, в котором находится тонкий слой вязкой жидкости. Давление в слое жидкости изменяется за счет заданной пульсации давления на контуре канала и ее сдавливания колеблющейся сэндвич-пластиной. Сформулирована и решена задача гидроупругости, состоящая из уравнений Навье-Стокса, уравнения неразрывности, динамических уравнений круговой сэндвич-пластины, дополненных граничными условиями. В рамках предложенной модели движение вязкой жидкости изучалось как ползучее. Модель разработана для стационарных осесимметричных изгибных и продольных колебаний сэндвич пластины в условиях гармонического изменения давления жидкости по времени. Для описания кинематика сэндвич-пластин использована гипотеза ломаной нормали, предложенная в работах Э.И. Старовойтова и Д.В. Леоненко. Найдены гидродинамические параметры слоя жидкости, в том числе его напряжения. Разработанная математическая модель представляет собой систему уравнений дляисследования радиальных и изгибных колебаний трехслойной пластины. Ее решение осуществлено методом Фурье в виде рядов. Исследованы гидроупругие колебания пластины на основной моде. В частности, построены и исследованы амплитудно-частотные характеристики круглой сэндвич-пластины.

The calculation of the fluid flow in the interscapular channel of a centrifugal impeller with a finite number of blades, the construction of the energy characteristics of the impeller and its optimization by the number of vanes are considered. The calculation consists of two parts: firstly, the determination of the theoretical pump head taking into account the effect of a finite number of vanes based on the analysis of the force interaction, and, secondly, the determination of hydraulic losses in the impeller by integrating the friction stresses over the limiting surfaces. The results from both parts are used to optimize the number of vanes in the pump impeller.

The photoluminescence of a nonequilibrium polariton condensate in cylindrical and rectangular micropillars etched on the surface of a high-Q GaAs microcavity is investigated in magnetic fields of up to 12 T. The measurements are carried out under different levels of nonresonant optical pumping with nanosecond laser pulses for a wide range of cavity detuning. As far as nonresonant excitation produces a high density of excitons in a reservoir, it should be expected that the exciton–polariton interaction, which depends on the pump level, has a considerable effect on the Zeeman splitting and polarization of the condensate. However, measurements of the Zeeman splitting and polarization in high magnetic fields demonstrate that only minor changes take place up to the highest available pump levels. This means that, in the case under study, the effect of exciton–polariton interaction on the polariton system is insignificant. At the same time, the data obtained provide an estimate for the exciton density in the reservoir. In contrast to cylindrical micropillars, the photoluminescence of the condensate in rectangular micropillars consists of two perpendicularly linearly polarized lines which retain a high degree of linear polarization even in a field as high as 12 T. The Zeeman splitting in this case is nearly independent of the pump power. The degrees of both circular and linear polarization change with pump power, but these changes are noticeably smaller than the ones predicted theoretically. This indicates that the system of polaritons in micropillars deviates considerably from thermodynamic equilibrium.

The paper deals with the development and analysis of a mathematical model for a circular sandwich plate resting an inertial elastic foundation and interacting with pulsating viscous liquid layer. The sandwich plate is the bottom wall of a channel containing a thin layer of viscous liquid. The pressure in the viscous liquid layer changes due to a predetermined pressure pulsation law at the channel contour and its squeeze between the upper channel wall and the vibrating circular sandwich plate. The coupled hydroelasticity problem consisting of the Navier-Stokes equations, the continuity equation, and the dynamics equations for the circular sandwich plate with corresponding boundary conditions was formulated and solved. We studied the viscous fluid motion inside the channel as a creeping one. The elastic foundation was considered in the framework of inertial Winkler foundation model. To write the sandwich plate dynamics equations, we used the kinematic hypothesis of the broken normal. The hydrodynamic parameters of the liquid layer, including its stresses acting on the sandwich plate, were found. The final mathematical model is the system of partial differential equations for studying bending and radial hydroelastic oscillations of the sandwich plate. Its investigation was carried out by the Fourier method. We studied plate dynamic behaviour in the main vibration mode. In particular, the frequency response of the circular sandwich plate were constructed and studied.

The paper proposes a mathematical model for predicting the hydroelastic response of a mechanical system consisting of a circular sandwich plate forming the bottom wall of a narrow channel filled with a pulsating viscous liquid. The pressure pulsation in the liquid layer is caused by upper vibrating channel wall represented by a rigid disk. We needed to formulate and solve the hydroelasticity problem for developing the mathematical model. The hydroelasticity problem consisted of the Navier-Stokes equations, the continuity equation, the circular sandwich plate dynamic equations, and the corresponding boundary conditions. The viscous liquid layer movement was assumed as a creeping one. We studied the stationary axisymmetric hydroelastic oscillations problem under harmonic pulsation of liquid pressure, i.e. harmonic vibrations of the upper channel wall. Using the perturbation method, we obtained the system of two integro-differential equations for studying the radial and flexural vibrations of the sandwich plate. Hydroelastic oscillations of the main mode were considered as a special case. The program for calculating the hydroelastic response of circular sandwich plate in various frequency ranges was developed. As an example, we made calculations of the circular sandwich plate amplitude-frequency response. The developed model can be applied in monitoring and decision-making systems for complex mechanical objects.

The electron paramagnetic resonance spectra of KTaO3: Mn nanocrystalline powders in the temperature range from 77 to 620 K have been measured and studied for the first time. The change observed in the spectra has been investigated as a function of the doping level. The doping regions in which Mn2+ ions are individual paramagnetic impurities have been established, as well as the regions where the dipole-dipole and exchange interactions of these ions begin to occur. The spin-Hamiltonian constants for the spectrum of non-interacting individual Mn2+ ions have been determined as follows: g = 2.0022, D = 0.0170 cm−1, and A = 85 × 10−4 cm−1. A significant decrease in the axial constant D in the KTaO3: Mn nanopowder, as compared to the single crystal, has been explained by the remoteness of the charge compensator from the paramagnetic ion and by the influence of the surface of the nanoparticle. It has been assumed that the Mn2+ ions are located near the surface and do not penetrate deep into the crystallites.

Low-temperature (T = 1.6 K) photoluminescence (PL) of individual CdSe/ZnSe/ZnMnSe quantum dots (QDs) with different magnitudes of the sp-d exchange interaction between the magnetic impurity ions and charge carriers has been studied in a magnetic field up to 12 T applied in the Faraday and Voigt geometry. The magnitude of the interaction was controlled by changing the fraction (ηe, h) of the squared wave function of charge carriers in the semimagnetic barrier by means of variation of the nonmagnetic (ZnSe) layer thickness. It is established that the sp-d exchange interaction leads to a change in the sign of the effective hole g factor even for ηe, h ∼ 5%, while further increase in the interaction magnitude is accompanied by a rapid growth in the magnitude of spin splitting for both electrons and holes. The quantum yield of PL exhibits a significant decrease due to nonradiative Auger recombination with the excitation of Mn ions only for ηe, h ∼ 12%, while the rate of the holes spin relaxation starts growing only for still higher ηe, h values. In a strong magnetic field perpendicular to the sample plane, the alignment of Mn spins leads to suppression of the Auger recombination only in the excited spin state. For a small rate of the hole spin relaxation, this leads to a rather unusual result: the emission from an excited trion state predominates in strong magnetic fields.

Self-assembled Cd(Mn)Se/Zn(Mn)Se quantum dots have been investigated by means of spatially and time-resolved magneto-optical spectroscopy. In such quasi zero-dimensional diluted magnetic semiconductors, the exchange interaction couples the spins of optically generated charge carriers with localized magnetic ion spins. We demonstrate that this can be used on the one hand to monitor nanoscale magnetization with a resolution of

This paper reports on the first investigation made of luminescence of Ge/Ge1−xSix heterostructures at liquid-helium temperatures in a magnetic field of up to 14 T. The luminescence lines observed in the spectra are due to both free and impurity bound excitons in Ge layers. The diamagnetic shift of the quasi-two-dimensional exciton has been measured. From the experimental data the size of the exciton has been estimated to be 75–90 A.

Use of diamond grinding wheels with organic and ceramic bonds makes it possible to avoid the phenomenon of wheel glazing during fine grinding of molybdenum single crystals and to obtain a high quality ground surface with the minimum level of structural distortions. The nature of the orientation dependence of surface structural distortions is established by studying {001}, {110}, and {111} molybdenum single crystals. This is connected with features of plastic deformation during grinding.

Luminescence spectra of uniaxially and uniformly strained high-purity germanium crystals at liquid-helium temperatures in a magnetic field of up to 14 T have been investigated. In strongly strained Ge crystals, a new line has been detected on the low-energy side of the excitonline in magnetic fields higher than 4 T. Studies of this line’s characteristics as functions of pressure, temperature, and magnetic field have led us to conclude that its presence is due to recombination of electron-hole pairs in an electron-hole liquid. The experimental data suggest that the metallic electron-hole liquid is stabilized in a strong magnetic field. By approximating the shape of the newly detected line using the model of metallic electron-hole liquid, we have obtained the electron-hole liquid density n EHL(B) and Fermi energies E Fe,h of electrons and holes. The liquid binding energy o as a function of magnetic field has been estimated.

A mathematical model is suggested for heating and igniting of a powder material under frictional action. A simulation is carried out for various thermophysical and geometrical characteristics of the rubbing body, the supporter, and the powder material. Consideration of the results and comparison with those of previous experiments demonstrate the applicability of the model.

It is shown that ignition may occur under light frictional pressure. In the case of friction applied to a powder, there are two limits of ignition in terms of the frictional pressure. A frictional approach permits a high degree of compaction of powder at low frictional pressure (∼10 kg/cm2). The influence of the material of the frictional body on sample heating and ignition is investigated. Activation of chemically active powder under the action of friction is observed. A discussion of the results is presented.

We have experimentally investigated the process of propagation of the burning front along the surface of powders of titanium, magnesium, and mixtures of magnesium with diluents in an air atmosphere. We have determined the dependence of the velocity of propagation of the burning front along the surface of bulk metallic powders on the angle of inclination of the test bed of powder, and also the effect of additives introduced into the powders. We used several types of additives: free-burning in an air atmosphere, inert with high melting point, and low-melting-point inert powdered materials not burning in air but reacting exothermically with the metallic powders. In addition to our purely scientific interest, we also pursued a practical goal: solving problems of reducing fire and explosion hazards for production processes using or manufacturing metallic powders and mixtures based on such powders.

An experimental study of the effect of foreign inclusions of both chemically active materials, capable of burning in an air atmosphere and inert oxide materials on the propagation of a combustion front over the surface of titanium powders was carried out. It has been established how the character and the rate of surface combustion Vc of titanium powders change upon their dilution, depending on diluent concentration, melting temperature, disperse composition, and chemical activity.

Experimental data on degradation of photovoltaic and photoenergetic characteristics of silicon solar cells exposed by high-energy electrons and protons as well as low-energy protons have been obtained. The previously proposed theoretical model that can describe degradation of the solar cell characteristics under the influence of irradiation, including that creating spatially inhomogeneous defect distribution over the structure thickness, has been experimentally confirmed. It was ascertained that in the cases of 1 MeV energy electron and 20 MeV energy proton irradiations, when there is a relatively homogeneous defect distribution over the silicon solar cell thickness, its shortcircuit current degrades faster than the open-circuit voltage. On the contrary, in the case of low-energy 0.1 MeV proton irradiation, when the distribution of defects is spatially inhomogeneous, the open-circuit voltage degrades faster than the short-circuit current.

There has been a considerable progress in the photoluminescence (PL) properties investigations of SiGe/Si and Ge/Si structures of late. The PL investigations of Ge-Ge1-xSix structures with quantum wells in germanium layers have been started recently1,2. This work reports the studies of the exciton and magnetoexciton luminescence of Ge-Ge1-xSix heterostructures grown by CVD method on Ge [111] substrates.

The authors demonstrate efficient hole spin injection from a ferromagnetic metal (Ni) contact in a forward biased light emitting Schottky diode (LESD) fabricated on a GaAs based heterostructure with a quantum well (QW). The spin polarization of the injected holes was detected by measuring the circular polarization of the electroluminescence (EL) from the near surface InGaAs∕GaAs QW. An intermediate gold layer has been used in order to improve the spin injection efficiency. Over 40% degree of circular polarization of the EL has been observed at T=2K for the LESD structure with Au–Ni–Au Schottky contact.