Vol 61, No 9 (2019)

The most crucial feature of excitation transfer in low-temperature plasma forming the physical basis for operation of contemporary lighting devices is participation of resonant photons in the process. The widely used approximation of complete frequency redistribution assumes independence of the emitted photon frequency from frequency of the absorbed one. Averaged over frequency distribution in a resonance line, the natural transfer equation with the exponential kernel becomes the equation with an inverse power kernel, which in case of an infinite homogeneous medium is asymptotically equivalent to the Laplace equation of non-integer (fractional) order, considered in this article.

Interaction of four counterpropagating waves in a cubic medium being “left” for the signal wave is considered in the constant-intensity approximation. Analytical expression for the signal wave intensity is derived for the general case of four-wave interaction in a metamaterial. The influence of different parameters on the signal wave amplification coefficient, efficiency of conversion into the signal wave, and the reflection coefficient of the mirror whose role is played by the metamaterial is analyzed. It has been obtained for the first time that the determining role in the backward signal wave amplification is played by the total length of the metamaterial and the intensities of all three forward waves. An analysis has shown that the optimal thickness of the metamaterial depends not only on the phase mismatch and the strong coherent pump field intensity, as in the constant-field approximation, but also on the intensity of the weak wave at the frequency ω₂. It has been demonstrated for the first time that the efficiency of frequency conversion in metamaterials depends on the total metamaterial length, input intensities of all four interacting waves, phase mismatch, and losses in the medium. It is established that the maxima of the reflection coefficient of the metamaterial depend on the total metamaterial length and the intensities of all three forward waves.

Systematic information on the application of the extinction formalization of different types for solving the equation of radiative transfer in a crystal cloud is presented. The basic laws of visible and infrared radiation extinction are illustrated that provide the basis for the assessment of the extent with which the special features of the energy and polarization extinction characteristics formed by crystals with different microphysical, optical, and orientational parameters must be taken into account. It is shown that large plates with preferred orientation stand out among crystals of all types in the degree and stability of manifestation of the polarization extinction characteristics and their spectral dependence. For such particles, the polarization extinction effect can be higher by several orders of magnitude and constitute more than 50% of the energy characteristic of the extinction.

Using perturbation theory methods and a variational method, we have calculated the energy of a twodimensional helium atom in its lower excited states, this energy showing itself to be practically independent of the specific characteristics of these excited states; this, together with the known value of the energy in the ground state, found earlier by one of the authors, presents the fundamental possibility of determining the frequencies of the main spectral lines of such an atom, which can be checked experimentally.

Within the framework of the modified potential cluster model, results of a description of available experimental data in terms of the astrophysical S-factor for the reaction of p¹⁴N capture to the third excited state of the 15O nucleus at 6.17 MeV with J = 3/2– for proton energies up to 1 MeV are presented. Under the assumption that this excited state is a P_3/2 level and the two resonances at 260 and 987 keV are D scattering waves, we have on the whole successfully reproduced the experimental data for the astrophysical S-factor.

An anisotropic cosmological model with expansion and rotation and the Bianchi type VIII metric has been constructed within the framework of general relativity theory. The first inflation stage of the Universe filled with a scalar field and an anisotropic fluid is considered. The model describes the Friedman stage of cosmological evolution with subsequent transition to accelerated exponential expansion observed in the present epoch. In the approach realized in the model, the anisotropic fluid describes the rotating dark energy.

Approximate analytical and numerical solutions of the three-dimensional Logunov–Tavkhelidze equation are found for the spherically symmetric case. Solutions are obtained in momentum and relativistic configuration representations. The wave functions in the relativistic configuration representation have additional zeroes compared to the wave functions of the nonrelativistic harmonic oscillator in the coordinate representation.

The dependences of the kinetic coefficients, namely, the Hall coefficient, electrical conductivity, and charge carrier mobility on the temperature, electric field strength, and doping with rare-earth elements are investigated in single crystals of p-type gallium selenide. It has been established that in the low-temperature region, these dependences have a peculiarity caused by the presence of random macroscopic defects in the samples under study. At a small level of doping of p-GaSe single crystals with Gd and Er, a non-monotonic dependence of the mobility and electrical conductivity on the content of the introduced impurity is observed.

In this paper, the mathematical simulation is used to study the effect from the size of incoherent nanoparticles on thermal strength of heterophase aluminum alloy in materials with the equal volume fraction of the strengthening phase. It is shown that during the deformation process, prismatic dislocation loops and dislocation dipoles contribute to the dislocation density. It is found that the behavior of the flow stress curves of materials with the equal volume fraction of strengthening particles depends on a combination of scale parameters of the strengthening phase at various deformation temperatures. The areas of strong and weak temperature dependence of the flow stress are identified.

The paper presents research into the behavior of high-temperature plastic deformation of titanium alloy Ti–4.74 wt.% Al–5.57 wt.% Mo–5.04 wt.% V alloy (VT22) depending on its structure and phase composition. It is shown that the formation of fine-grain structure in this alloy is not a sufficient condition for realizing superplastic deformation. It is found that the formation of the ultra-fine grain structure in VT22 alloy leads to the temperature decrease down to 823 K at the beginning of plastic deformation. This allows achieving the percent elongation of the alloy specimens over 1300% within the temperature range of 973–1073 K and at a 6.9·10^–3 s^–1 initial tensile rate. The grain boundary sliding is considered to be the main deformation mechanism.

The characteristics of microstructure, deformation and fracture of Zr – 1 wt% Nb and Ti – 45 wt% Nb bioinert alloys in the coarse- and ultrafine-grained states are investigated. It is shown that the ultrafine-grained structure formed in them ensures excellent mechanical properties of the alloys and affects the stages of the stress-strain curves and the behavior of the maximum temperature vs. deformation time plot. The formation of an α-phase in the Ti – 45 wt% Nb ultrafine-grained alloy suppresses the linear stage VI characterized by a constant strain hardening coefficient. In stage VII, the strain hardening coefficient rapidly becomes negative, which indicates the material softening prior to its failure.

Using the methods of SEM, EDS, and optical microscopy, a large number of non-metallic inclusions are revealed on the pore surface of a TiNi-based SHS-alloy. According to the XRD and EDS data, the surface is chemically and structurally inhomogeneous and its composition is close to that of a Ti₄Ni₂(O,N,C) intermetallic oxycarbonitride. An optical microscopy examination demonstrates that the entire surface is coated with a semi-transparent film. The results of XRD analysis allow assuming that in the formation of the surface of the TiNi-based porous material surface a significant role is played by the glassy phase and wollastonite, which imparts special physical-chemical properties and high biocompatibility to the alloy. SEM examination of morphological features of evolution of the mesenchymal cells on the pore surface of the TiNi-based SHS-material within the period 1–28 days shows that on the 7–14-th day the main elements of loose fibrous connective tissue are formed. Dense connective tissue is formed by the 21-st–28-th day.

With the help of our own software package DifEqTools, numerical modeling of the cosmological evolution of a system consisting of an asymmetric scalar doublet of nonlinear, minimally interacting scalar fields, a classical field and a phantom field, has been performed. Peculiarities of the behavior of the model near zeroenergy hypersurfaces have been revealed.

Depending on the sizes of the CdS crystallites and silicon pores, electrical and photoelectrical characteristics of c-Si/porous–Si/CdS heterojunctions prepared by electrochemical deposition and anodization, respectively, are studied. The optimal pore size (10–16 nm) is determined, which provides the maximum photoelectric conversion efficiency (7.71%) of heterojunctions.

Using combined deformation processing, including preliminary mechanical activation followed by consolidation via high-pressure torsion, a multi-layer nanocomposite based on nickel and aluminum is manufactured. The influence of the duration of mechanical activation on its microstructure parameters is investigated by the X-ray diffraction analysis and scanning and transmission electron microscopy. It is found out that nanostructuring of the multi-layer nanocomposite during its manufacture ensures the formation of a high density of phase and grain boundaries. It is shown that this structural transformation is accompanied by an intense strengthening effect.