Vol 62, No 3 (2019)

Results of experimental studies of channel optical waveguide structures with spatially-modulated parameters obtained by point-by-point inducing of refractive index perturbations upon exposure to laser radiation of visible range in Y-cut LiNbO₃ samples with photorefractive surface layer are presented.

Results of studying the structural-phase state and mechanical properties of Al–Si–N coatings fabricated by pulsed magnetron sputtering on a K-208 glass substrate are presented. By the method of X-ray diffraction analysis it has been found that the Al–Si–N coatings with a thickness of 6 μm contain nanoscale hexagonal close-packed (HCP) AlN crystallites. Sputtering of the Al–Si–N coatings allows the nanohardness of the surface layer of the K-208 glass samples to be increased up to 30 GPa and a high level of elastic properties (W_e ≈ 70%) to be maintained. For the examined samples, laboratory tests on the impact of high-speed flows of iron microparticles on the Al–Si–N protective coatings fabricated by the method of pulsed magnetron sputtering have been performed. It is established that sputtering of the Al–Si–N protective coatings with a thickness of 6 μm allows the resistance of the K-208 glass samples to the impact of iron particles accelerated up to 8 km/s to be increased by a factor of 2.8.

Quantum chemical calculations of phosphorescence lifetime are performed for the first time by ab initio CC2 and TD-DFT methods for hetero[8]circulenes bearing Si and Ge atoms. According to the results of calculations, a lower value of τ_phos for tetragermatetrathia[8]circulene (II) originates from two factors: almost 29 times more distorted main macrocycle II and almost four times larger spin-orbit coupling matrix element between T₁ and S₀ by virtue of heavier Ge atoms as compared to Si. The τ_phos values calculated by CC2 ideally agree with its experimental value; the difference is less than 2 and 0.3 s for tetrasilatetrathia[8]circulene (I) and tetragermatetrathia[8]circulene (II) molecules, respectively. The agreement of the lifetimes calculated by TD-DFT is only within an order of magnitude. The main intramolecular decay channel of the T1 state is internal conversion between T₁ and S₀ owing to simultaneous spin-orbit and nonadiabatic interaction of their wavefunctions.

General expressions for the dependence of the entropy of a degenerate neutron gas in a magnetic field on the magnetic field magnitude and the neutron concentration with allowance for the anomalous magnetic moment (AMM) of the neutrons have been obtained in implicit form, and the dependence of the so-called reduced entropy on the field is represented in graphical form for the neutron concentration C = 10³⁸ cm^–3, which is typical of neutron stars. Analytical estimates have been made for a field magnitude of ~10¹⁹ G, which is possible in neutron stars, and this neutron concentration ~ 10³⁸ cm^–3 including when the neutron gas is close to its saturation state with preferred orientation of the AMM of the neutrons in the direction of the field. It is shown that the entropy decreases with increasing field as the neutron gas approaches its saturation state, when the AMM of all the neutrons is oriented in the direction of the field. This is consistent with the second law of thermodynamics, so that the evolution of neutron stars (magnetars), accompanied by an increase in the field, is therefore unlikely, regardless of the reasons for the appearance of the magnetic field. The heat capacity of the degenerate neutron gas is also found, and turns out to be formally equal to the entropy in the absence of a magnetic field.

On the basis of a qualitative and numerical analysis of a cosmological model based on an asymmetric scalar doublet of nonlinear, minimally interacting scalar fields – one classical and one phantom, peculiarities of the behavior of the model near zero energy hypersurfaces have been revealed. Numerical models have been constructed, in which the dynamical system has limit cycles on the zero-energy hypersurfaces. Three types of behavior of the cosmological model have been distinguished, configured by the fundamental constants of the scalar fields and the initial conditions. It is shown that over a wide sector of values of the fundamental constants and initial conditions, the cosmological models have a tendency to adhere to the zero-energy hypersurfaces corresponding to 4-dimensional Euclidean space.

In this paper we consider the joint influence of secular resonances and light pressure on the long-term orbital evolution of objects with reverse motion in the near-Earth space with semimajor axes of orbits from 15000 to 45000 km. The orbital evolution of each object is considered for three values of the area-to-mass ratio of the object: 0.001, 1, and 10 m²/kg.

The electrical conductivity (σ) and the coefficients of thermal e.m.f. (α), Holl (R_H), and thermal conductivity (χ) of extruded n-Вi₂Te_2.7Se_0.3 samples with various grain sizes are studied in the temperature range 77–300 K after extrusion and upon subsequent annealing. It is shown that annealing substantially increases σ and χ and has a little effect on α at 77 K. This indicates that at 77 K, the structural imperfections of grains play the main role in the electron and phonon scattering. There is a correlation between the degree of texture and thermoelectric properties.

An investigation of the influence of reaction- and diffusion-induced interactions in the system of PV-N55Т45 TiNi-based powders and activating Co and Ni additions during sintering on special characteristics of microstructure and structural-phase compositions of porous TiNi-based alloys are investigated aimed at designing porous-monolithic structures. Using the method of liquid-phase sintering of TiNi-based powder, porous specimens with activating Co and Ni additions are manufactured with the concentrations of the latter being 0.5, 1.0, 1.5 and 2.0 at.%. It is found out that the activating action of Co is more moderate compared to that of Ni. A calculation of the heat released in the course of the chemical reaction as a result of introduction of activating additions demonstrates that the values of –∆H for manufacturing porous alloys with additions of Co and Ni are 28 and 52 kJ/mol, respectively. It is established that all specimens under study contain the following phases: austenitic B2, martensitic B19′, Ti₂Ni, ₂(О, N, С) and Ti3Ni4. Moreover, in the material with additions of Ni a TiNi₃ phase is observed. Due to an introduction of a monolithic plate into the sintered powder mixture it is possible to compensate for the heat sink at the concentration of the activating Co addition 1.5 at.%. This allows manufacturing porous-monolithic structures based on the TiNi alloy with a high quality of fusion between the porous and monolithic parts.

It is shown that at high percentage content of primary electrons, plasma is generated due to the retention of ions in a potential well created by electrons and not due to the accumulation of secondary electrons in the region of a potential hump formed by ions.

The paper explores the size and morphology of microparticles of soft magnetic alloys 5BDSR and 82K3HSR and nanoparticles first obtained from these alloys using pulsed laser ablation in gas. The magnetic properties of particles are studied depending on their size, composition and production method.

Based on the equations of macroscopic electrodynamics, the spectral-angular characteristics of electromagnetic radiation are considered, which is generated during the passage of fast, charged particles through a finite-size absorbing medium. The variation in the angular distribution of the radiation overcoming the Cerenkov radiation threshold is investigated, the contribution from the generated transition radiation is analyzed at high particle energies and so are the spectral characteristics of the Cerenkov radiation within the X-ray frequency range.

Realization of a criterion of dimensional quantization in quantum wells of various profiles is considered. It is established that there is the limit number of the discrete state of a free charge carrier in the well, above which the criterion of dimensional quantization is not fulfilled. It is shown that in quantum wells of rectangular and triangular profiles, the number of levels of dimensional quantization cannot exceed two or three. The result obtained is applicable to quantum wells, quantum wires, and quantum dots.

Using the Monte Carlo method, the influence of grain size (model cell dimensions) on the peculiarities of pretransitional, low-stability structural-phase states of NiAl intermetallide in the region of structural-phase transformations is investigated during thermal cycling (heating and cooling). An analysis of the temperature dependences of the long-range order parameters shows that during heating the maximal long-range order is observed in an alloy with the maximal grain size, while the minimal – in the alloy with the smallest grain size. In order to achieve disordering of the alloy by increasing its grain size, it has to be increasingly overheated. Under cooling, long-range order primarily appears in a fine-grained alloy. The larger the grain size, the wider the temperature interval of the structural-phase transformation. The peculiarities of formation of the structural-phase states in the course of cooling as a function of the grain size (model cell dimensions) indicate that the first ordered regions appear in the fine-grained alloy. As the grain size increases, the temperature at which long-range order appears becomes lower, in other words, a still higher overcooling is required for the system's atomically-ordered states to be formed.

The results of investigation of pulsed burning modes of a non-self-sustained arc discharge with a combined hot-and-hollow cathode are presented. The principal discharge characteristics are measured at the currents up to 350 A and discharge burning voltages up to 200 V within the working pressure range 0.2–1 Pa. It is shown that an increase in the working pressure gives rise to an increase in the discharge current as a result of gas amplification, resulting from an improvement in the processes of fast electron energy utilization during gas ionization. The maximum resulting discharge current in a nitrogen atmosphere at a pressure of 0.8 Pa is found to be 550 A at the discharge burning voltage up to 200 V and the maximum pulsed power up to 80 kV. The concentration of plasma in the center of the ≈0.2 m³ chamber is found to be about 4·10¹⁷ m^–3 at the density of the ion current from plasma approximately 6.5 mA/cm² and the discharge pulsed power 18 kW.

The name of the second author should read S. I. Koshoridze instead of S. I. Kosharidze.

The paper presents a mathematical model of a system for physics experimental data processing with the need to reprocess data. This model is a queuing system with an unlimited number of servers with feedbacks and service times of primary and repeated applications having different parameters. An expression for the characteristic probability distribution function of the number of experimental data that require reprocessing during allotted time is derived by the method of Markovian summation. The main probability characteristics of this distribution are obtained.