Doklady Physics最新文献

With the help of wire arc additive manufacturing, a high-entropy alloy of AlCrFeCoNi was prepared: of a non-equiatomic composition, on which a B + Cr film with a thickness of ~1 μm was deposited by plasma-assisted RF sputtering. Subsequent processing consisted in electron-beam irradiation of the surface with the following parameters: energy density 20–40 J/cm², pulse duration 200 μs, frequency 0.3 s^–1, and number of pulses 3. A quasi-periodic distribution of chemical elements (at %) 33.4 Al, 8.3 Cr, 17.1 Fe, 5.4 Co, and 35.7 Ni is established. It is shown that, at the energy density of the electron beam E_s = 20 J/cm², the microhardness increases by a factor of two and the wear resistance by a factor of five, and the friction coefficient decreases by a factor of 1.3. High-speed crystallization of the surface layer leads to the formation of a subgrain structure with subgrain sizes (150–200 nm). The increase in strength and tribological properties during electron-beam processing is interpreted taking into account the reduction in grain size, the formation of chromium and aluminum oxyborides, and the formation of a solid solution of boron incorporation into the HEA crystal lattice.

The chemical vapor deposition synthesis of periodic structures in the form of single-crystal diamond–SiO₂ nanosphere composites, which exhibit the properties of photonic crystals in the visible spectral range, are reported.

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.