Vol 163, No 2 (2023)

We propose and investigate a precise wavefront correction method for the astronomical observation of exoplanets in the diffraction stellar vicinity. We show the applicability of the method for measuring and correcting the wavefront in the scheme of a telescope and an interferometric coronagraph without applying any Hartmann wavefront sensors. In our laboratory experiment we achieved a correction accuracy ~λ/50 and a coronagraphic contrast better than 105. We outline the prospects for increasing the correction accuracy to a target value of λ/500 to visualize the Earth in the vicinity of the Sun observed from a distance of 10 pc (in the immediate neighborhood of the Solar System) through an additional amplitude correction and the inclusion of non-common-path aberrations.

We consider the motion of atoms in a cell free of a buffer gas with an antirelaxation wall coating on the spectrum and shift of the coherent population trapping resonance. We compare two types of reflection of atoms, viz., elastic (specular) and diffuse reflection, when the velocity of an atom after its reflection is determined by the wall temperature, as well by the quality of the antirelaxation wall coating. It is shown that for both types of reflection, a nonmonotonic dependence of the coherent population trapping resonance shift on the cell size is observed. In the case of diffuse reflection, the shift can change sign, and a complex two-hump structure of the coherent population trapping resonance is observed in a certain range of cell lengths. The dependence of the detected effects on the laser radiation spectral width is analyzed.

The characteristics of point Josephson contacts Pb0.6In0.4/KFe2As2 and KFe2As2/KFe2As2 have been studied. The temperature dependences of characteristic contact voltages VC(T) and the dependences of the first current step amplitudes in I–V characteristics on the power of 7.6-GHz electromagnetic radiation have been measured. It has been found that VC(T) curves for all contacts can be described in terms of the SIS*IS contact model (S, I, and S* stand for superconductor, insulator, and superconductor with a lower critical temperature, respectively) for superconductors with the s-symmetry of order parameter. It has been proved that the current step oscillation period as a function of microwave power can be exactly approximated with the resistive model of contact with IS = ICsin(φ). Obtained data are consistent with the normal s-symmetry of order parameter.

The formation of gas nanobubbles through the merging of individual fission products of uranium is an important process for the evolution of nuclear fuels. The theoretical description of this process is very difficult because both the dynamics of individual atoms in the lattice and the kinetics of evolution of an ensemble of bubbles should be taken into account within a unified model. Such a model is constructed in this work on the basis of molecular dynamics simulations for xenon bubbles in bcc uranium in the case of the excess of interstitial atoms in the crystal matrix. The analysis is based on the molecular dynamics simulation of the nonequilibrium process of formation of xenon nanobubbles from individual Xe atoms dissolved in the crystal matrix. A relation between the size of bubbles and the number of gas atoms in them, as well as the dependence of the diffusion coefficient of bubbles on their radius and the number of interstitial atoms in the γ-U matrix, has been analyzed. A kinetic model of evolution of the ensemble of bubbles has been proposed to describe the molecular dynamics results and to extrapolate them to long times.

The interacting electron and hole in transition metal dichalcogenides are considered. To investigate the interaction the Bethe-Salpeter equation was obtained in the leading order in the interaction potential. It is shown that the behavior of the potential at short distances significantly affects the binding energy of the electron and the hole. We demonstrate that the expansion of the Bethe-Salpeter equation in the small coupling constant does not contain singular operators. Therefore, the binding energy of the electron and the hole does not contain the regularization parameter. Using the perturbation theory in the coupling constant we analytically calculated the energies of the ground and first excited states of the exiton. For arbitrary values of the coupling constant, the energies of the bound states of the electron and the hole are obtained numerically. The critical values of the coupling constant for the Coulomb potential and for the exponentially decreasing potential are also found numerically.

The results of four experiments on studying preliminarily statically compressed gaseous helium and deuterium during their subsequent compression in explosive spherical cascade structures providing quasi-isentropic gas compression are presented. For helium, the following parameters were achieved: in one experiment, the compression pressure is Pmean ≈ 4.9 TPa at a density ρmax ≈ 6.4 g/cm3 and the compression ratio is δ = ρ/ρ0 ≈ 320; in another experiment, Pmean ≈ 10.9 TPa, ρmax ≈ 10.3 g/cm3, and δ ≈ 470. For deuterium, these parameters are Pmean ≈ 3.4 TPa, ρmax ≈ 6.0 g/cm3, and δ ≈ 162 in one experiment and Pmean ≈ 13.3 TPa, ρmax ≈ 11.4 g/cm3, and δ ≈ 520 in another experiment. The gas density was determined by an X-ray method using the position of the boundaries of the steel shells compressing a gas. The experiments are simulated with a one-dimensional gasdynamic software package, in which the Kopyshev–Khrustalev equations of state are used for the gases under study. The pressures are determined using calculations, in which the dynamics of gas compression is satisfactorily simulated for the entire set of experiments.

The evolution of burning modes of a weak-current corona discharge in a diode filled with atmospheric air, having a pointed cathode and a flat anode, has been investigated. A theoretical description is performed in terms of an axisymmetric multifluid plasma model, including the kinetics of 9 types of particles and 25 plasma-chemical reactions. A discharge in a gap 10 mm long, with a needle-like cathode having a tip curvature radius of 100 μm, a source voltage of 8 kV, a ballast capacitance of 100 pF and a circuit ballast resistance of 1 MΩ, is described in detail. It is shown, both experimentally and theoretically, that the discharge has a lifetime of 180 μs and occurs in four clearly different stages under these conditions: (1) dark breakdown delay phase (0–20 μs); (2) Trichel pulse phase with a variable on–off time ratio and quasi-steady-state corona current component (20–80 μs); and (3) intermediate phase of monotonically rising weak current (80–130 μs), which ends with a vibrational transition to the (4) steady-state phase (130–180 μs), having a typical structure of glow discharge. The tendencies to a change in the corona discharge parameters with a variation in the feed voltage are analyzed. The results of theoretical calculations are in good agreement with the experimental data.