Vol 57, No 1 (2019)

We consider the problem of the choice of “free” particle interaction potential and the calculation of virial corrections for interatomic and ion–atom interaction in chemical models with dissociation reactions. We perform a critical analysis of the potentials given in the available literature, propose simple formulas to calculate virial corrections with allowance for the limitations of the two-particle phase space, and present recommendations to apply these formulas.

The optical energy focused on the nanosize spatial domain in the vicinity of the nanoapex of a metal microtip is studied. This focus occurs under the symmetric convergence of the surface plasmon wave to the nanoapex. The metal microtip surface is approximated by the paraboloid of revolution. The focal field distribution near the nanoapex is studied with scanning of the surface of a multilayer thin-film structure. The numerical method for the obtainment of the focal field distribution is considered, and the application of the presented method to the technologies for the creation of stamps and molds for ultraviolet nanolithography are discussed.

Hafnium diboride nano- and microcrystals are studied by high-temperature X-ray diffraction in the temperature range of 300–1500 K. HfB₂ nanocrystals are found to have a greater thermal expansion coefficient than HfB₂ microcrystals. The thermal expansion of HfB₂ is found to be anisotropic with respect to the unit cell axes.

The optical properties of gadolinium in liquid and solid states have been studied. The optical constants are measured by the Beatty ellipsometry method in the range of 0.48–2.6 μm. The dispersion dependences of light conductivity σ, reflectivity R, the imaginary and real parts of dielectric permittivity ε₁ and ε₂, and the function Im(ε)^-1 of the characteristic electron energy losses are calculated from the measured values of the refractive index and the absorption coefficient. The electronic characteristics of gadolinium in solid and liquid states are calculated on the basis of a two-band conductivity model with measurement results in the infrared spectral region.

Techniques for the simulation of thermodynamic processes in molecular systems are proposed. The results of the calculation of the argon isothermal compressibility by the molecular dynamics method for isobar cooling from 200 to 15 K at a pressure of 40 atm and an adiabatic compressibility in the range of 200–160 K at 40 atm are given. Steps, interpreted as phase transitions, are visible on the temperature dependences of the isothermal compressibility at fast (10¹² K/s) and relatively slow (10⁹ K/s) cooling.

The value of the osmium melting heat, ΔH_m= 57.85 kJ/mol, presented in reference handbooks was obtained about 35 years ago from a wide extrapolation (in temperature) of experimental data on the melting entropy of the FCC and the HCP elements of the Periodic Table. Using the correlation of data on the surface tension (developed by B. D. Summ), the melting heat, and the surface layer structure for osmium, the authors obtain a new estimate, ΔH_m = 30−40 kJ/mol, which is half of the reference value.

Numerical simulation of the influence of the frequency of pulses on heat transfer in a bubbly impinging round jet has been carried out. An axisymmetric system of non-stationary RANS equations is used in the paper, and the two-phase flow is taken into account. The turbulence of the liquid phase is described with the transport model of the components of Reynolds stress tensor, which takes into account the effect of bubbles on the modification of turbulence. The dynamics of air bubbles is simulated by the Eulerian approach. The effect of the change in the frequency of the pulses and the gas volumetric flow rate ratio on the heat transfer in a gas-liquid impinging jet is studied. The pulses causes both the suppression of heat transfer in the vicinity of the stagnation point (up to 20–25%) in the region of low frequencies at f > 20 Hz and the Strouhal number Sr > 0.34 and its intensification (up to 15–20%) at/= 100–200 Hz and Sr= 1.7–3.5 in comparison with the stationary impinging bubble jet at the same time-averaged flow rate.

The effect of components of the thermal conductivity tensor of heat-protection material on heat fluxes from the gas to the body were studied based on the first obtained analytical solution of the problem of heat transfer in anisotropic composite material in conditions of a convective-conductive heat transfer flow around by a high-temperature gasdynamic boundary layer. Such an analysis made it possible to determine a considerable decrease in heat fluxes to the lateral surface of blunted anisotropic body with the use of a heat-protection material with a high degree of longitudinal anisotropy (e.g., pyrolytic graphites, the ratio between the longitudinal and transversal thermal conductivities of which may reach a hundred or more). The main contribution to the decrease in heat fluxes is made by the decrease in the temperature gradient on the gas-body boundary from the gas side at the expense of increased body temperature downstream. In addition, the increased gas temperature on the wall leads to increased dynamic viscosity and decreased density, which decreases the local Reynolds numbers and promotes a decrease in heat fluxes. The numeric results are analyzed.

Numerical analysis of the process of unsteady heat transfer in a composite material under the action of moderate-intensity laser radiation has been carried out based on the thermal model of the destruction of the thermal protection coating of the conical part of the body. Different regimes of thermochemical destruction of the carbon fiber reinforced polymer and V-1 graphite coatings of the conical part of the body have been obtained under repeated pulse action. It has been found that the decisive part in laser radiation shielding by products of body destruction is played by gaseous pyrolysis products, particles of the condensed phase, and vapors of the carbon material.

A method for the simulation of turbulent combustion in the two-dimensional formulation is presented. A distinctive feature of this method is the assignment of the nonstationary profiles of velocity components at the input to the computational domain. The algorithms of artificial turbulence used for this purpose make it possible to set the necessary values of both the fluctuation intensity and the integral length scale of turbulence in the incoming flow. It is shown that this procedure describes with good accuracy the angle of the V-shaped flame front observed in the experiment, as well as the flame front thickening with increasing the distance from the flame stabilization point. The influence of various parameters of the incoming flow on the characteristics of the V-shaped flame was analyzed based on the developed method.

A simple, one-dimensional model of an intermittent flow is developed for interpretation of the previously observed effect of hydrodynamic regime rearrangement in a near wake from two cylinders subject to glow discharge. When the cylinders are not spaced too closely, the wake may be assumed to be formed by two von Karman streets. The model is distinguished by an account for the nonlinear interaction of the von Karman streets in the domain of their generation near cylinders; when, the assumption of weak interaction is not applied. Within the framework of the model, in combination wih one-frequency modes of the wake there exists an asymmetric two-frequency mode in a certain domain of the model parameters. In the turbulent wake, this mode and a symmetric mode are observed in intermittent regime between them.

The propagation of acoustic waves in a viscoelastic bubbly medium has been theoretically studied. A linearized system of differential equations for perturbed motion in such medium is presented; the dispersion relation is deduced. As an example of a viscoelastic bubbly medium, we have calculated the frequency dependences of the phase velocity and attenuation coefficient in polydimethylsiloxane with embedded polydisperse air bubbles and compared the results with the known experimental data.

The authors present the results of an experimental study of the thermal conductivity of silicicated silicon carbide within the temperature range of 1400−2200 K.

The dielectric properties of water-saturated rocks at different oil-to-water ratios in the pore space and the features of their heating in a high-frequency electromagnetic field are studied. The experimental methods are described. The features of the dielectric properties of rocks saturated with a mixture of oil and water in various ratios are considered. The results of experimental studies of the heating of rock samples saturated with a mixture of oil and water in various ratios are given.

Optical imaging of spatial distribution of intensity in the focal spot of the terahertz pulse was developed. The technique is based on the THz electric field-induced second harmonic generation in the nonlinear centrosymmetric crystal (SrTiO₃). The measurements of the spatial distribution of focal spot of terahertz radiation with the electric field strength over 1 MV/cm were conducted.