Том 63, № 3 (2018)

The spatial potential of a homogeneous gravitating (or statically charged) circular torus is expanded in terms of geometrical parameter q. The first term of the expansion (coefficient of zero-power parameter q) coincides with the potential of a thin ring the mass of which is equal to the mass of torus and the radius of which is equal to the radius of the axial line. It is shown that the coefficients of terms with odd powers are zeros. Even terms of the expansion of the potential are analytically represented in terms of standard complete elliptic integrals. The corresponding series describes the potential of torus in entire space including internal region. The proposed method for representation of the potential makes it possible to obtain gravitational energy of a homogeneous circular torus. The method is used to calculate masses of two rings of the Chariklo asteroid. The mass of the internal ring is M_r1 ≈ 9.8 × 10¹⁸ g and the ratio of such a mass to the mass of asteroid is \(\frac{{{M_{r1}}}}{{{M_0}}}\)≈ 0.001. The results for the external ring are M_r2 ≈ 10¹⁸ g and \(\frac{{{M_{r1}}}}{{{M_0}}}\)≈ 10_–4.

The results of the theoretical and experimental studies of the electric wind velocity and efficiency are considered. The experiments are carried out in air at atmospheric pressure using the electrode system as a flat multispike electrode–two parallel tube.

The velocity distribution in the vicinity of the surface of an axisymmetric body rotating in a viscous medium at frequency ω directed along its axis is determined. The dissipative function has been calculated and used for deriving the equation of motion, from which an analytic expression for the stopping time of the body (until its complete stoppage) is obtained. The time of entrainment of an external stationary cylinder coaxial with the body is calculated by solving the time-dependent Navier–Stokes equation.

The results of an experimental study of the impact of the focused pulsed-periodic radiation from a CO₂ laser on a gas-dynamic structure in a supersonic jet are presented. The radiation of the CO₂ laser is propagated across the stream and focused by a lens on the axis of the supersonic jet. To register the flow structure, a shadow scheme with a slit and a flat knife located along the flow is used. The image is fixed by a speed camera with an exposure time of 1.5 μs and a frame rate of 1000 1/s. In the flow, the plasma initiated by the pulsedperiodic laser is visualized in order to identify and determine the period of plasma development, as well as the motion of the initial front of the shock wave. It is shown that at the transverse input of laser radiation into the stream the periodic structure of the thermal trace is created with the formation of an unsteady shock wave from the energy release zone. At small repetition rates of laser radiation pulses, the thermal spot interacts with the flow in the pulsed mode. It is shown that elliptic nonstationary shock waves are formed only at low subsonic flow velocities and in a stationary atmosphere. The process of nonstationary ignition by an optical discharge of a methane–air mixture during a subsonic outflow into a motionless atmosphere is shown experimentally. The results of optical visualization indicate burning in the trace behind the optical discharge region.

Two self-similar modes of evolution of charged particles’ high-current beam are described analytically. The situation being considered falls within the field of nonneutral plasma electrodynamics. The process is considered in terms of the nonlinear 1D evolution of the charge density w(x, t) in the channel of a longdistance transmission line with nonlinearly distributed resistance R, capacitance C, and inductance L: R = R(w), C = C(w), and L = 0. It is shown that initially the front of w(x, t) accelerates and then slows down. The description of the process in the channel is based on the charge conservation law. An idealized “kinematic” approach is used according to which an equation in two unknowns (charge density and current density in the channel) can be reduced to an equation in one unknown w(x, t). A strongly nonlinear wave process is studied. A discontinuous solution w(x, t) is constructed with a zero boundary condition at infinity. Such a model description can apply only for revealing the main qualitative features of a complex process. Analytical expressions for the variation in the evolution of the front velocity and perturbed area length are derived. An interrelation between the nonlinearity parameter of the process and the amount of charge in the interelectrode gap is suggested based on the experimental data for the evolution of streamers.

Based on the registration and analysis of the full wave profiles, the Hugoniot elastic limit and spall strength of ceramics based on tungsten carbide with different cobalt content are measured. We also study the influence of the cobalt content on the mechanical characteristics of tungsten carbide such as hardness, fracture strength, Young’s modulus, shear modulus, and sound velocity. It is shown that in the process of spalling, the failure stresses grow and the dynamic elastic limit decreases almost linearly within the scatter of their values with growing cobalt content; moreover, the value of the Hugoniot elastic limit is abruptly practically halved as the cobalt content grows from 0 to 2 wt %.

Experimental data for the thermodynamic properties of titanium on the melting curve in the pressure range from atmospheric value to 90 GPa are analyzed and brought into correspondence. The problems that have been considered are (i) the lack of data for the solid β-phase density near the normal melting point and (ii) the formation probability of a triple point on the melting curve for the coexisting β-, ω-, and liquid phases of titanium. To estimate the change of the volume upon melting 3d elements from Mendeleev’s periodic system, a correlation between the change of the volume, ΔV_m, and the change of the entropy, ΔS_m, on the melting curve at atmospheric pressure is suggested and effectively used.

The mechanical properties of the additive material prepared from acrylonitrile–butadiene–styrene plastic are studied experimentally on a 3D printer in the quasi-static and dynamic regimes. The strength curve describing the nonlinear dependence of the critical stress on the strain rate is constructed using the incubation time. The characteristic incubation time τ is determined by comparing the theoretical curve with the experimental data.

Effect of femtosecond laser processing on mechanical properties of plates made of submicrocrystalline VT1-0 titanium alloy is studied using active deformation and fatigue testing involving cantilever bending.

The electrical properties of dual-phase fluorite-pervoskite oxide systems based on strontium titanate- ferrite (SrTi_0.5Fe_0.5O_3–δ) are studied. We find that the oxygen ionic and ambipolar conductivities of strontium titanate-ferrite can be considerably improved by introducing the fluorite phase Ce_0.8(Sm_0.8Sr_0.2)_0.2O_2–δ. This is advantageous considering the prospects of applying these types of composite materials in different electrochemical devices, e.g., as membrane materials in electrochemical converters for the production of hydrogen and syngas and anode materials in solid oxide fuel cells.

The structure and dielectric characteristics of strontium barium niobate thin films deposited on single-crystalline silicon substrates without buffer layers are studied. It is found that the c axis in these heterostructures runs largely normally to the substrate surface and the a and b axes are randomly oriented in the plane of the substrate. The polarization relaxation in such heterostructures is investigated. It is shown that the film–substrate interface in the heterostructures grown by rf cathode sputtering may contain a low amount of long-lived charged defects.

The thermoluminescence (TL) of deep traps of anion-defective alumina monocrystals irradiated by a high-dose (more than 1 kGy) pulsed electron beam (130 keV) is studied. The deep traps in the studied material are classified according to the TL temperature range. It is demonstrated that the phototransferred thermoluminescence (PTTL) in the temperature range of the main TL peak is induced by optical charge migration from deep traps that are emptied at 400–470 and 470–600°C. An anomalous PTTL enhancement in crystals subjected to stepped annealing in the 350–400°C interval is observed. It is demonstrated that this effect may be caused by competing processes of charge transfer that involve deep traps corresponding to the TL peak at 390°C. The applicability of PTTL in the dosimetry of high-dose (1–50 kGy) pulsed electron beams is established.

Technical development of optimal methods for detection of simple gas-phase molecules using rovibrational or rotational spectra by the simultaneous detection of several spectral lines of a molecular band with the aid of a comb filter is considered. Two variants for implementation of the methods are based on a spectrometer with the echelle grating with a limited number of elements and Fresnel lens (mirror) with specific ring components that serves as a grating. The Fresnel filter can be matched with the parameters of optics of astronomic instrumentation in the absence of a decrease in the effective aperture.

Angular dependence of the electric field of electromagnetic wave generated by a rectangular photoemission source with the given surface density of dipole moment is determined. The dipole emission is initiated by the wave that propagates along the surface at a superluminal phase velocity. The spectral distribution of the radiation is determined, and the angular distribution of the radiation energy is calculated.

Silicon-diamond heterostructure based field emission media with silicon microtip arrays at the heterointerface were proposed and experimentally studied. The architecture of the heterostructures is optimized for the applications as an active medium for the field emission cathodes of mobile power microwave devices.

A new method developed here for studying the thermoemission nonuniformity parameters of cathode materials makes it possible to determine the temperature dependences of the average size of the thermoemission centers on the cathode surface, the average distance between thermoemission centers, the relative area of the emission-active surface of the cathodes, and the true value of the work function for emissionactive centers on the cathode surface by processing the current–voltage characteristics. The method is tested on nickel oxide, agglomerated nickel oxide, and impregnated cathodes.