Doklady Physics最新文献

A vector method for recording phase-dynamic radio images is proposed by forming and numerically analyzing the S-parametric scattering matrix of multidisciplinary signatures of material media and objects. The key advantages of aperture capture of signal radio images by the method of a frequency-synthesized power spectral density function of a scattered wave radio profile are determined. On the basis of a vector analyzer of microwave circuits and broadband antennas of the Vivaldi type, an experimental laboratory installation for signal registration of time-scale radio images in the spectral region of 0.03–6.0 GHz has been built. The dependences of the influence of the angular characteristics of the object on the spectral-temporal structure of the formation of phase-dynamic radio images have been experimentally established. As the time-scale postprocessing of radio images, a method of cepstral transformation of S-parametric characteristics with convolution of basic signatures in the radiogenic part of the irradiated object is proposed. A series of cepstral convolutions of phase-dynamic radio images was obtained, establishing a functional relationship between the change of the signature of an object in time with its radio genome.

In the expanding Universe, the evolution of quantum black holes with modified Schwarzschild and Reissner–Nordström geometries is considered. All quantum black holes at definite moments of the cosmological time lose event horizons and are transformed to gravitating objects with masses M.

The structure and orientational relationships of the α' and γ-phases in medium-carbon steels during rotational friction welding were studied using orientation (EBSD) and transmission electron microscopy methods. It is shown that, as a result of phase recrystallization, martensite with interlayers of the γ-phase is formed in the structure of the weld. Based on the type of spectrum of angular deviations of interphase boundaries, the formation of secondary (reverted) austenite was established. It is shown that in this case an orientation relationship close to Bain’s is realized between the α- and γ-phase crystals.

We carry out a numerical modeling of plasma injection with hot electrons into a thin layer of cold plasma in the presence of an external magnetic field. We show that the latter can significantly affect the emerging small-scale current filaments and sheets, even if it does not magnetize the particles and does not change the overall dynamics of the redistribution of the total plasma density in the process of injection. The effect observed depends on the orientation of the external magnetic field that is parallel to the plane that bounds the cold plasma layer, if the injection occurs from a narrow strip lying in this plane. In this situation, which corresponds to the ablation of a flat target by a femtosecond laser beam using cylindrical focusing, we study the evolution of the characteristic structures of the formed small-scale magnetic field. It is established that its generation is associated with instabilities of the anisotropic velocity distribution of electrons and that its value can be many times greater than the value of the external magnetic field.

The interaction of a shock wave in a combustible gas mixture with an ellipsoidal region of an inert gas of increased density is numerically simulated using the Euler equations in the two-dimensional plane and axisymmetric formulations. Four qualitatively different regimes of indirect initiation of detonation have been found: upon reflection of a wave from the gas interface, upon focusing of secondary transverse shock waves on the axis/plane of symmetry, upon amplification of a transverse wave converging to the axis of symmetry, and upon secondary focusing of waves in front of the bubble. It is shown that the mode of detonation initiation depends significantly on both the intensity of the shock wave and the shape of the bubble. Based on a series of simulations, the dependence of the threshold Mach numbers of the incident wave on the shape of the bubble is determined. In the plane flow, a moderate elongation of the bubble leads to a significant decrease in the threshold Mach number. In an axisymmetric flow, the lower threshold Mach number is less sensitive to the shape of the bubble, and the most effective detonation initiation is carried out using a spherical bubble. The effect of shock wave focusing makes it possible to achieve successful initiation of detonation at a fundamentally lower intensity of the incident wave compared to direct initiation.

In this paper, we study experimentally the forced longitudinal oscillations of gas and aerosol in an open tube with a cross-sectional jump. An intensification of gas oscillations in a tube with a cross-sectional jump in comparison with a homogeneous tube, while the pressure waveform remains close to harmonic and continuous, is observed. A nonmonotonic dependence of the aerosol deposition time on the oscillation frequency with a minimal value at the resonant frequency was discovered.

The features of the bi- and multistability effects in the semiconductor Bragg microcavity with a chiral photonic crystal slab on the upper mirror are investigated theoretically. It is shown that the response of such a chiral structure under a linearly polarized coherent resonant pump demonstrates sharp multistable transitions with abrupt jumps of the exciton intensity and degree of circular polarization. It is shown that the thresholds of bistable transitions in the system with a different sense of circular polarization differ slightly; i.e., in the case of a nonoptimized structure, we can expect to obtain even a larger amplitude of jumps of the degree of circular polarization of the excitonic response due to the multistability than in a specially optimized chiral structure with a high degree of circular polarization at a low pump intensity.

Within the framework of the theory of thermodynamics, a method for determining the electro-optical coefficients is proposed. It is shown that for all ferroelectrics the symmetry of which admits a diagonal susceptibility, the ratio of some electro-optical coefficients is expressed in terms of the ratio of susceptibilities. For barium titanate, the dependence of the electrooptical coefficients on the electric field has been revealed and studied. It is shown that large values of the electro-optical coefficients of barium titanate are associated with a nonlinear dependence of the dielectric susceptibility on the electric field.

A numerical simulation of a turbulent boundary layer on a permeable plate with helium injection into a supersonic xenon flow in the presence of a positive longitudinal pressure gradient has been carried out. The injection regimes in which the temperature of the injected gas is lower than the temperature of the adiabatic impermeable wall and the stagnation temperature of the oncoming flow are considered. The existence of a minimum temperature of the permeable wall is confirmed, at which the wall temperature is lower than the temperature of the injected gas, while there are two sections along the length of the permeable plate in which the adiabatic conditions are satisfied. The results of calculations of a supersonic flow with a longitudinal pressure gradient differ significantly from the results obtained for a gradientless flow around a plate, for both subcritical and critical injection.

Experiments on the propagation of powerful high-voltage pulses with a duration on the order of a nanosecond or less in large-scale transmission lines in an atmosphere of various gases make it possible to solve a wide range of fundamental and applied problems, from modeling the passage of electromagnetic pulses (EMPs) through the atmosphere to estimating the electrical strength of elements of pulsed high-voltage gas-filled systems. At the Institute of Applied Physics, Russian Academy of Sciences, experiments with strip lines with a length of up to 5 m were conducted using the Krot and Sprait setups. When EMP propagates with an electric field strength level of up to 100 kV/m in a rarefied gas, effects such as the formation of inhomogeneous and significantly nonstationary glow structures, nonlinear absorption, and dispersive transformation of the shape of high-power pulses caused by gas ionization in the EMP field are studied.