Volume 64, Nº 10 (2019)

Existence of the soliton solution to the generalized sine–Gordon equation (also known as the Kryuchkov–Kukhar’ equation) is numerically studied. The equation can be used to describe propagation of electromagnetic waves in a graphene-based superlattice. Calculation errors related to implicit representation of the kink solution to the equation under study are estimated. Variations in the shapes of kinks that move in opposite directions are studied prior to and after collision. The results show that the kink solution is not a soliton.

We consider general properties of kernels of the inverse collision integral, as well as kernels of integral operators appearing in the expansion of the collision integral in spherical harmonics. The recurrent relations between kernels obtained earlier are generalized to the case of interaction of particles with different masses. It is shown that the obtained properties ensure additive invariance of the number of particles, energy, and momentum.

We have numerically investigated nonlinear nonstationary velocity and pressure fields in a viscous incompressible fluid near an oscillating absolutely rigid plate of an infinitely small thickness and a limited length in the direction of oscillations. It is shown that the limitation imposed on the plate size along the direction of its oscillations leads to nonlinearity of the problem even for a small amplitude of surface oscillations of the plate. We have analyzed the velocity and pressure fields for large amplitudes of plate oscillations. The emergence of displacement flows during oscillations of an infinitely thin plate of a finite length is explained. The mechanism of formation of instantaneous vortex motions in the viscous fluid is investigated.

The interaction of a 3D supersonic turbulent gas flow with a transverse sonic jet injected from the wall has been studied in detail both numerically and experimentally. However, the main drawback of such studies is the lack of detailed description of formation and propagation of vortex structures for moderate and large parameters n (ratio of pressure in the jet to pressure in the flow). Analysis performed in this study is aimed at revelation and detailed explanation of mechanisms of formation of vortices behind the injected sonic jet in a supersonic oncoming flow depending on n for improving the effectiveness of mixing of the jet with the flow. As initial equations, we have used 3D Favre-averaged Navier–Stokes equations closed by the k–ω model of turbulence; these equations are solved using the algorithm based on the essentially nonoscillatory scheme of the third approximation order. We have demonstrated the presence of the following vortex structures known from a number of theoretical publications: two oppositely rotating vortices in front of the jet, a horseshoe vortex; and two pairs formed in the mixing zone between the jet and the flow (one in the wake behind the jet and the other on the lateral line of the jet). We have determined the pressure ratios for which extra pairs of vortices appear (one pair emerges at the Mach disk edge as a result of interaction of a retarded flow of the jet behind the Mach disk with a high-velocity ascending flow behind the barrel and the other pair is formed due to the interaction of the ascending jet flow with the incoming main gas flow). As a result of comparative analysis, the pressure ratios for which a clear pattern of additional horn vortices is observed near the wall in the region behind the jet, have been determined. The dependence of the slope of the bow shock on the pressure ratio has been plotted. It is found that the pressure distribution at the wall in front of the jet in the symmetry plane is in satisfactory agreement with experimental data.

The results of experimental studies of combustion of propane–air gaseous mixture when it was ignited by a microwave discharge have been described. The mixture with different propane content fills a sealed radio-transparent tube placed along the axis of a focused linearly polarized quasi-optical microwave beam at atmospheric pressure. Multi-point ignition of the mixture is carried out near one end of the tube by a pulsed microwave discharge with a surface-developed streamer structure. The growth of gas pressure in the tube as propane burned was recorded in the experiments. The microwave pulse energy being invested in high-temperature discharge plasma has been estimated in them. The minimum percentage of propane in the mixture at which the microwave discharge ignites it has been determined in experiments. The time dependence of the pressure increase in the tube as the propane burns determines the combustion process dynamics.

We investigate the structure of the wall sheath of a gas discharge near a flat surface at a negative potential for high mean electron energy. It is shown that in the conditions where the mean energy of ions in the plasma is much lower than the mean electron energy, the parameters of the wall sheath weakly depend on the mutual orientation of the normal to the surface and the electric field in the plasma for an arbitrary ratio of the Debye radius to the ion mean free path relative to the resonant charge exchange process. It is found that for inert gases (He, Ar) for ratio E/P of the electric field to pressure exceeding 10 V/(cm Torr) in the plasma, the disregard of ionization in the perturbed wall sheath can lead to substantial errors in the calculation of its parameters. It is shown that the ionization leads to an increase in the electric field in the wall sheath and, as a consequence, to an increase in the mean velocity of ions at the boundary between the quasi-neutral presheath and the part of the perturbed wall sheath in which quasi-neutrality is substantially violated. The parameters of the wall sheath where quasi-neutrality is significantly violated depend on the ionization rate much less strongly than the corresponding parameters of the quasi-neutral presheath. We have determined the relation for concentration of charged particles in the unperturbed plasma from the ion saturation current considering the actual ion energy distribution function in the plasma as well as ionization in the presheath and the part of the perturbed wall sheath in which quasi-neutrality is violated significantly.

The effect of severe plastic deformation and the subsequent impact of high hydrostatic pressure on the elastic and microplastic properties of Cu–0.2 wt % Zr alloy has been studied and analyzed. The influence of nanoporosity, which is formed in the process of equal-channel angular pressing and is fixed by applying hydrostatic pressure, has been evaluated.

Al₈₆Ni₄Co₄Yb₆ and Al₈₆Ni₆Co₂Yb₆ metallic ribbons have been obtained by a standard planar flow method. According to X-ray diffraction data, the ribbons are amorphous. Their crystallization kinetics at different heating rates and resistivity has been determined. These alloys remain amorphous in a wide range of compositions, and the crystallization process depends significantly on transition metal concentration.

In this paper, we discuss causes of the multidirectional effect of changes in the concentrations of free charge carriers in silicon crystals of p- and n-type conductivity on the transverse dimensions of pores formed as a result of anodic etching in hydrofluoric acid solutions, as well as the effect of anodic current density on pore size. The observed dependences are explained based on the concepts of electrochemical pore formation in semiconductor crystals as self-organizing cooperative processes accompanied by the injection of electrons from the chemical reaction region at the pore advancement front. Differences in the size of pores forming at the same current density in crystals differing in type and concentration of free charge carriers are associated with the effective temperature of the front of the cooperative chemical reaction at the bottom of germinating pores. This temperature, in turn, correlates with the power density of thermal energy released in the near-surface region of the etching crystal, either due to recombination processes for a p-type semiconductor or direct or indirect energy transfer from hot electrons to lattice vibrations in the case of a n-type semiconductor. The characteristic relaxation times of injected nonequilibrium electrons were calculated depending on the concentrations of the majority charge carriers in silicon crystals of both types of conductivity and the corresponding thicknesses of the regions of relaxation energy release. The revealed patterns of concentration changes in the power density of heat release in the near-frontal region of etching silicon crystals of p- and n-type conductivity are in good agreement with observed changes in the size of germinating pores.

It has been shown that the formation of GaAlAs nanofilms on a GaAs surface leads to an increase in the emission coefficient of true secondary electrons and in the quantum yield of photoelectrons, which can be accounted for by the difference of the escape depth of true secondary electrons for GaAs and GaAlAs.

The capabilities of metalorganic vapor-phase epitaxy (MOVPE) in fabrication of structures with thin (1–2 nm) alternating InAs/GaSb layers on a GaSb substrate are studied. The characteristics of these structures were examined using transmission electron microscopy and methods of photo- and electroluminescence. It was found that two GaInAsSb solid solutions of different compositions were formed in the active regions of structures in the given growth conditions. The fabricated system was characterized by an emission wavelength of 4.96 μm at a temperature of 77 K. The results reveal new opportunities for bandgap engineering of semiconductor structures based on InAs/GaSb, which are designed for optoelectronic devices operating in the infrared range, provided by MOVPE.

Electrodynamic characteristics of an antenna in the form of an infinitesimally thin, perfectly conducting narrow strip located at a plane interface of a uniaxial magnetic metamaterial and an isotropic magnetodielectric medium are studied. The antenna is placed perpendicular to the anisotropy axis of the metamaterial and excited by a time-harmonic external voltage. Singular integral equations for the antenna current are derived for an infinitely long conducting strip. The solutions to such equations are used to find and analyze the current distribution and input impedance of the antenna. Conditions for applicability of an approximate transmission line method for determining the antenna characteristics are established. Within the framework of this method, the obtained results are generalized to the case of a strip antenna with finite length.

Modification of Si(111) surface due to ion bombardment and subsequent annealing has been studied. It has been found that annealing following bombardment with 0.3- to 1.0-keV ions causes a multilayer metal silicide coating to form on the surface. It has also been established that work function φ of Si(111) variously depends on dose at different energies of types of ions.

The emission area is one of the main parameters of field emission systems. A variety of formal determination techniques for the emission area is studied. Using the model hemisphere-on-cylindrical-post constructed with the COMSOL Multiphysics software package, the relation between well-known estimates of the emission area is shown. The corresponding fractions of the emission currents are computed. It is demonstrated that the formal emission area (the ratio of the total current to the current density at the vertex) ensures approximately 75% of the emission current. The effect of abnormal behavior on the effective emission area is obtained (cutoff from the trend line of the current–voltage characteristics) for varying voltage level in standard Fowler–Nordheim coordinates. An experimental assessment of the area with application of modified Fowler–Nordheim coordinates ln(I/U^2–η/6) vs 1/U is proposed. The method is applied for analysis of field emission data of the multipoint nanocomposite emitter with carbon nanotubes.

A novel method of studying mass transfer processes in porous media has been considered. The method allows one to carry out operation monitoring of the diffusivity in thin articles without destruction of them and in the absence of preliminary calibration of the equipment used to measure the diffusant concentration. The method has provided an increase in the accuracy of measuring sought characteristics of the mass-transfer due to the possibility of selecting measured parameters that enter the calculation equation at sections of the static characteristic of a converter with high sensitivity and noise immunity.