Moscow University Physics Bulletin最新文献

The gravitational interaction of a classical moving charge with an infinite straight cosmic string with linear energy density (mu) is considered. The string generates a gravitational conical background with a small relative angular deficit (beta^{prime}=4Gmu). The geodesic of the charge lies in a plane transverse to the string. The scattering is described by the Lorentz factor (gamma) and the impact parameter (b). In the leading order in (gamma), the gravitational perturbation of the charge and the string is computed within the perturbation theory. In the second perturbation order, the total energy radiated in the form of electromagnetic waves is calculated, as well as the spectral–angular and polarization characteristics of the bremsstrahlung. The radiation is characterized by a concentration in a cone with opening angle of the order of (1/gamma), with the dominant contribution to the emission coming from frequencies of the order of (gamma/b).

The formation of superconducting pair correlations between like nucleons in the ground state of spherical even–even nuclei is considered within a special Bogoliubov transformation. The influence of the monopole pairing interaction on the energy of single-particle states is taken into account. It is shown that the appearance of pair correlations depends on the particle number and shell structure. In open subshell nuclei the correlations exist for arbitrarily weak attractive monopole interaction and nucleon pairs are distributed over all subshells involved in the pairing interaction. It is confirmed that the superconducting pair correlations arise if the coupling constant exceeds a certain threshold value. Rough upper and lower estimates are obtained for the threshold value.

The properties of the symmetry of the phase diagram of dense quark matter composed of (u) and (d) three-color quarks are investigated within the framework of massless (3+1)-dimensional Nambu–Jona–Lasinio and quantum chromodynamics models. It turns out that in the presence of baryon (mu_{B}), isospin (mu_{I}), chiral (mu_{5}), and chiral isospin (mu_{I5}) chemical potentials, the Lagrangians of these models are invariant under the so-called dual transformation. Consequently, the full thermodynamic potentials of these models exhibit dual symmetry. This means that, on the complete ((mu_{B},mu_{I},mu_{5},mu_{I5})) phase portraits of these models, the phases with spontaneous chiral symmetry breaking and charged pion condensation are dually conjugate (symmetric) to each other.

This publication presents the latest experimental data on the physics of relativistic heavy-ion collisions obtained using the Compact Muon Solenoid (CMS) facility at the Large Hadron Collider (LHC) at CERN.

The phenomenon of isothermal supersaturation of solutions in a porous medium during ion exchange is studied using mathematical modelling. The phenomenon consists in the formation of a solution with a concentration significantly exceeding the maximum solubility of the substance under ordinary conditions, and no precipitation occurs within the pores of the ion exchanger. In the works of several authors, the general nature of the phenomenon has been noted, and an explanation has been provided for the stability of the supersaturated solution in micropores. The question of why precipitation does not occur in larger pores remains open. In the present work, a model for the variation in the number of particles of the condensed phase in pores is proposed, and estimations are obtained that make it possible to determine the possible supersaturation depending on the process parameters. It is shown that the phenomenon under consideration can be explained not by a change in the thermodynamic conditions in the porous medium relative to ordinary conditions, but by the effect of dynamic equilibrium between the aggregation of condensed phase particles in the interior of the pores, their diffusion, and their decomposition near the surface of the ion exchanger grains. The proposed hypothesis is supported by quantitative analysis and comparison with available experimental data.

The applicability of the values of the strength (H_{textrm{irr}}) of the irreversibility field and the strength (H_{c2}) of the upper critical field in pinning mechanism determination in a sample of the family of iron pnictides of the class 111, NaFe({}_{1-x})Co({}_{x})As, was analyzed in this work. Methods for calculating (H_{textrm{irr}}) and (H_{c2}) were also considered. The first method for determining the strength (H_{textrm{irr}}) of the irreversibility field is based on extrapolation of the zeros of the graph (J_{c}(H)). The second method, considered exclusively from a theoretical perspective, is Kramer’s method. It is based on extrapolation of the zeros of the graph (J_{c}^{1/2}B^{1/4}(B)). Each of the methods requires qualitative identification of the graph zeros in order to obtain the most accurate result. The strength of the upper critical field is determined by extrapolating the points obtained at the intersection of the graph (M(T)) with the line at the level (M=0). Due to the limited operating range of the measuring device, the values of (H_{textrm{irr}}) for the NaFe({}_{1-x})Co({}_{x})As sample were obtained by approximating data from previously acquired results. When using (H_{textrm{irr}}), a volume pinning type was identified. The values of (H_{c2}) were also calculated based on already obtained data and allowed the surface pinning mechanism to be determined, which is consistent with earlier studies. This indicates that the pinning mechanism determined using (H_{textrm{irr}}) was established incorrectly. It was found that the use of irreversibility field strength values for the NaFe({}_{1-x})Co({}_{x})As sample may lead to incorrect identification of the pinning type.

Light input/output devices are essential for coupling between bulk and fiber optics devices and photonic integrated circuits (PICs). In this work, broadband couplers for optical waveguides lifted from the surface were fabricated using two-photon laser lithography, and comparison with numerical modelling was carried out. It was demonstrated experimentally that the ellipsoid-based coupler is optimal for coupling light into the waveguide. The average transmittance of a system comprising two adapters in the spectral range 700–1000 nm for (s)-polarized radiation amounted to at least 27(%).

Within the framework of the self-consistent Hartree–Fock method based on a Skyrme-type energy density functional, the contributions of various terms to the nucleon effective mass have been studied. Additional terms of the EDF affecting the nucleon effective mass at the nuclear surface have been introduced, and their influence on the ground-state properties (nuclear charge radius, binding energy, and single-particle spectrum) of the doubly closed shell nuclei ({}^{16})O, ({}^{40,48})Ca, ({}^{56,78})Ni, ({}^{100,132})Sn, and ({}^{208})Pb has been analyzed. It has been found that the radial dependence of the effective mass of nucleons affects both the density diffuseness and the single-particle level scheme near the Fermi surface. Two new parameter sets of the energy density functional are proposed.

Using the method of perturbation theory, the problem of light scattering by particles of arbitrary axisymmetric shape has been solved. The proposed approach makes it possible to consider substantial deformations by decomposing the total deformation into smaller ones. The issues of convergence, applicability limits and conditions are discussed; a comparison with an alternative computational method is presented.

Hafnium oxide, possessing a high permittivity, is of interest for use as memristors in electronics. In this paper, a comparative analysis of the type and main characteristics of paramagnetic centers has, for the first time, been performed on a series of samples that underwent successive synthesis stages: from the initial target sample to the film on a substrate It has been established that the primary type of defects in the studied materials are oxygen vacancies with an unpaired electron (F({}^{+}) centers). It has been found that during the deposition of the target (crystalline hafnium oxide), the concentration of F({}^{+}) centers decreases, probably as a result of recharging. It has been established that in the deposited hafnium oxide film, the concentration of F({}^{+}) defects increases by an order of magnitude. The observed experimental fact is explained by the disordered (amorphous) structure of the film.