Vol 107, No 7 (2018)

Processes of explosion and expansion of laser targets, experiments with which could clarify the reason for the observed asymmetric distribution of matter in a remnant cloud of some supernovae (e.g., the Cassiopeia A supernova), have been simulated. By analyzing criteria of hydrodynamic similarity of conditions characteristic of an astrophysical object and experiment, targets for absorbed laser energies in the range of 1–100 kJ have been proposed. This work continues a series of previous studies of supernovae and the possibility of simulating a number of processes observed at the explosion of supernovae such as the motion of a shock wave in matter, development of hydrodynamic instabilities at interfaces between shells with different densities, and largescale mixing of layers of the central region of a star with elements initially located at the periphery of the remnant cloud under laboratory conditions with high-power lasers. The studies are based on the numerical simulation of the explosion and explosion of targets using one- and two-dimensional hydrodynamic programs.

It has been found that the third harmonic generated under the tight focusing of a near-infrared (1.24-μm) femtosecond laser pulse indicates the energy deposition into the bulk transparent dielectric and can be used as a feedback system in the process of microstructuring. A third harmonic signal is sensitive to a change in both the size of a laser-induced microplasma and the free-electron density, which allows the detection of the microplasma with submicron longitudinal sizes. It has been shown that the method based on the third harmonic is universal and can be applied in both single-pulse and two-color microstructuring.

A classical problem of the dynamics of the free surface of an ideal incompressible fluid with infinite depth has been considered. It has been found that the regime of motion of the fluid where the pressure is a quadratic function of the velocity components is possible in the absence of external forces and capillarity. It has been shown that equations of plane potential flow for this situation are linearized in conformal variables and are then easily solved analytically. The found solution includes an arbitrary function specifying the initial shape of the surface of the fluid. The developed approach makes it possible for the first time to locally describe the formation of various singularities on the surface of the fluid—bubbles, drops, and cusps.

The comparison of the temperature anomalies of the charge carrier density in high-temperature cuprate superconductor Bi_1.6(Pb_0.4)Sr₂Ca₂Cu₃O_{10 + x} and features of the parameters of the crystal lattice has demonstrated that the concept of pairing of single-particle hole excitations on the Fermi surface into singlet pairs is realistic. Anomalies of the thermal conductivity correlated with the presence of paired quasiparticle states have been revealed. Both types of anomalies indicate the existence of three stages of the temperature evolution of a pseudogap.

The superconducting and magnetic properties of the (Fe/Cr/Fe)/V/Fe layered system with variable thickness of the chromium layer have been experimentally and theoretically studied. The magnetic properties of the system have been studied by the ferromagnetic resonance method, and the superconducting transition temperature has been measured from the jump in the magnetic susceptibility. A wide variety of magnetic states are observed in the system; in particular, the structure of small domains can arise in the iron layer placed between vanadium and chromium. It has been shown experimentally that the critical temperature T_c of the superconducting transition undergoes nonmonotonic oscillations with a noticeable amplitude in the given system with the change in the thickness of the Cr layer. The proposed model based on the proximity effect theory makes it possible to relate these T_c oscillations to the features of the magnetic structure of the samples.

The problem of controlling the quantum dynamics of localized plasmons has been considered in the model of a four-particle spaser composed of metallic nanoparticles and semiconductor quantum dots. Conditions for the observation of stable steady-state regimes of the formation of surface plasmons in this model have been determined in the mean-field approximation. It has been shown that the presence of strong dipole–dipole interactions between metallic nanoparticles of the spaser system leads to a considerable change in the quantum statistics of plasmons generated on the nanoparticles.

The principles and mechanisms of information processing in the brain are among key fundamental problems of modern science. Neurons being the main signal cells of the brain provide the transmission and transformation of sequences of electrical pulses in a neural network. Signal networks include not only neurons but also glial cells called astrocytes executing regulatory functions, as is accepted in neurobiology. In this work, a morphofunctional (compartment) model of an astrocyte has been proposed. It has been shown that the astrocyte can serve as a detector of synchronous events of different points of the neural network, generating a calcium response signal. In turn, this signal induces the synchronous ejection of neuroactive substances to the corresponding points of the network, which can enhance the spatial synchronization of neurons or the synchronous modulation of different neural paths.

Ni–Cr–C materials with a high hardness determined by the presence of regions consisting of Cr₃C₂ microrods with a record microhardness reaching 3200 kg/mm² have been obtained. Their self-organization in a powder consisting of Ni, Cr, and carbon microparticles with a high weight percentage occurs in the process of its sintering at a temperature of 1300°C and the subsequent sharp cooling of the resulting alloy. A model has been proposed for the process of formation of such crystal microrods whose characteristics have been determined by hardness measurement, electron microscopy, and microchemical and X-ray diffraction analyses.