Moscow University Physics Bulletin最新文献

Using first-principles methods for calculating crystal energy, the atomic mechanism of the transformation between the BCC ((beta)) and HCP ((alpha)) phases of zirconium at low temperature has been investigated. An accurate two-parameter geometric approach has been developed to describe the lattice transformation via the Burgers mechanism. The proposed description method accounts for changes in atomic volume and the shape of the crystal lattice during the transformation. Using the proposed transformation description, potential energy surfaces of zirconium during the BCC–HCP transformation were constructed in the pressure range from 0 to 25 GPa with a step of 5 GPa. The gradient descent method was used to determine the minimum energy paths along the potential energy surfaces. Analysis of the results revealed a strong dependence of the shape of the energy surfaces and the minimum energy path on pressure. As the pressure increases to 25 GPa, the shape of the potential energy surface of zirconium undergoes a critical change, and a structure appears on the surface with an energy 10.5 meV lower than that of the HCP phase. Comparison of the calculated results obtained using the developed two-parameter transformation description method with one-parameter analogues from the literature demonstrated the inconsistency of the latter as a tool for studying atomic mechanisms of phase transitions.

Semiconducting mesoporous films with a large specific surface area are of interest for the development of gaseous medium sensors. In this study, such sensors were fabricated using a material synthesized on bulk substrates via a chemical reaction between gaseous H({}_{2})S and Mo vapour obtained by thermal evaporation. X-ray photoelectron spectroscopy confirmed that the obtained layers consist of MoS({}_{2}). Scanning electron microscopy (SEM) revealed that the films deposited on different substrates are an array of crystallites with thicknesses of a few nanometers and transversal dimensions of several hundred nanometers. The MoS({}_{2}) crystallites are predominantly oriented perpendicular to the substrate surface and are spaced by distances of several tens of nanometers. The surface electrical resistance of the mesoporous MoS({}_{2}) layers was measured as a function of water vapour and ammonia vapour concentrations in the surrounding medium. It was discovered that the electrical resistance of MoS({}_{2}) decreases with increasing relative humidity and ammonia vapour concentration. The current response profile to changes in the concentration of these components in air exhibits an exponential time dependence with two characteristic time constants. For NH({}_{3}) vapour, the characteristic rise times are 0.9 and 17 s, while the fall times are 1.2 and 29 s. In the case of H({}_{2})O vapour, the characteristic rise times are 4 and 45 s, and the fall times are 1.25 and 42 s. The mechanisms underlying the increase in electrical conductivity of MoS({}_{2}) films with increasing humidity and ammonia vapour concentration are discussed.

The electromagnetic form factors of the deuteron have been calculated within the dibaryon model for nuclear forces, which is based on the resonance mechanism of six-quark bag (dibaryon) formation in (NN) collisions. The calculations take into account both single-nucleon currents (impulse approximation) and additional contributions induced by the formation of an intermediate dibaryon. Two versions of the dibaryon model, from 2002 and 2022, have been used for the form factor calculations. It is shown that both versions of the model reproduce the experimental data well for all three deuteron form factors in the momentum transfer region (Q<0.8) GeV/(c). At higher (Q), the predictions of the different versions of the model diverge, with one version (2002) providing a better description of the magnetic form factor and the other (2022) better describing the charge form factor. Possible reasons for the observed discrepancy between theoretical calculations and experimental data for large momentum transfers are discussed.

The paper presents a review of numerical algorithms developed at the Laboratory of Medical and Industrial Ultrasound at Lomonosov Moscow State University, which are used to solve the evolution equations of nonlinear acoustics, such as the Burgers equation, the Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation, and the one-way Westervelt equation. The main results obtained using these numerical models in studying the propagation of intense acoustic waves in various media are presented. In particular, examples of solving problems in medical ultrasound, nonlinear aeroacoustics, and nonlinear underwater acoustics are considered. The generalization of one-way models to account for medium inhomogeneities is discussed, employing wide-angle parabolic approximation methods in three-dimensional problems.

This study is aimed at solving the problem of experimental implementation and investigation of single-electron reservoir networks with As impurity atoms in a quasi-two-dimensional near-surface layer of a solid-state matrix based on silicon-on-insulator (SOI) material. The study of electron transport in the fabricated experimental structures revealed the presence of horizontal Coulomb blockade sections in the current–voltage characteristics (CVC) typical of single-electron transport. The shape of the recorded CVC between a pair of selected control electrodes of the reservoir network significantly depended on the potentials of the remaining surrounding electrodes, which modified the structure of the conductive channels passing through the impurity centers. By adjusting the control voltages and utilizing the intrinsic nonlinearity of the system of disordered single As impurity atoms, which possesses an enormous state space, it was possible to demonstrate the feasibility of implementing a tunable nanoscale current switch and the logical functions ‘‘NOT,’’ ‘‘AND,’’ and ‘‘OR’’ in the single-electron reservoir network. A vector tuning method was employed to determine the required configuration of the reservoir network for the implementation of functional elements.

Deposition modes for thin films of FeSe({}_{0.5})Te({}_{0.5}) on an amorphous substrate made of K-208 glass, containing cerium oxide (CeO({}_{2})), have been found. The transition temperature of the film, (T_{textrm{C}}=9.5) K, to the superconducting state turned out to be higher than that on borosilicate glass from Fischer Scientific, which does not contain CeO({}_{2}), but lower than the superconducting transition temperature of the target, (T_{textrm{C}}(M)=14) K. This behavior contrasts with the well-known properties of thin films in the FeSe and FeSe({}_{x})Te({}_{1-x}) family on crystalline substrates. Based on the measurement results, the vortex activation energy (U), the critical current density ((j_{textrm{C}})), the upper critical field ((H_{C2})), and the irreversibility field ((H_{textrm{irr}})) have been obtained.

We have constructed an approximate analytical solution to the spectral problem for a finite-dimensional matrix of a special form, which proves to be a very simple and sufficiently satisfactory model of the metastable state. This model reproduces most of the characteristic properties of the metastable state, including the line shape, decay dynamics, and density of states. The accuracy of the approximate analytical solution was verified through direct numerical calculations. The proposed model represents a finite-dimensional analog of the Fano formalism.

Reliable forecasting of meteorological, hydrothermodynamic, and ice characteristics in the waters of the Western Arctic Seas of Russia using atmospheric circulation, marine circulation, and sea ice models is currently impossible without observational data assimilation. Data assimilation improves the quality of the initial state of hydrophysical and ice characteristics in models for forecasting simulations, thereby enhancing their accuracy. This study presents a technique for assimilating satellite data on sea surface temperature (SST) and sea ice concentration (SIC) into the INMOM marine circulation model using the Data Assimilation Research Testbed (DART) software, with an assessment of the validity of the employed assimilation algorithm. A comparative analysis of the accuracy of hydrothermodynamic state forecasts with and without satellite SST and SIC data assimilation has been conducted. It is shown that assimilating satellite data reduce the root-mean-square deviation (RMSD) of 24-h forecast results from observational data by approximately 80(%) for SST and by 60–70(%) for SIC compared to the simulation without assimilation. The temporal variability of RMSD in SST and SIC forecasts indicates that the largest errors occur during periods of intense upper sea layer heating and ice melting. The importance of simultaneous assimilation of SST and SIC data is highlighted: more accurate SST reproduction improves the accuracy of heat and salt flux calculations at the ocean-ice boundary, which regulate the thermal accretion/melting processes of ice, consequently enhancing the reproduction of ice area and its edge. In turn, a more accurate SIC calculation directly improves the accuracy of heat flux calculations at the water–air boundary and, consequently, SST.

The results of measuring the power output of an industrial nuclear reactor based on the antineutrino flux from the core are presented. The measurements were conducted using the iDREAM detector at a distance of 19.5 m from the center of the core of the VVER-1000 reactor at Unit 3 of the Kalinin Nuclear Power Plant. Estimates of the sensitivity of the iDREAM detector to changes in reactor power over 2-, 4-, and 6-h intervals of antineutrino interaction statistics collection were obtained.

The results of photometric observations of two supernovae in NGC 4666, SN Ia ASASSN-14lp and SN Ib 2019yvr, as well as spectroscopic observations of SN 2019yvr, are presented. Light curves have been constructed, and their main parameters have been derived. Supernova ASASSN-14lp is a fairly typical Type Ia object with low rate of brightness decline and large interstellar extinction. Using the dependence of the maximum luminosity of SNe Ia on the light curve parameters, an estimate of the distance to the galaxy NGC 4666 has been obtained. The spectrum of SN 2019yvr near maximum light, its peak luminosity, and the shapes of the light curves during the first 90 days after maximum revealed characteristics of a typical Type Ib supernova, with interstellar extinction exceeding that of ASASSN-14lp. A decrease in the rate of brightness decline at a phase of approximately 90 days has been detected. Light curve modeling was performed using the STELLA code, and the physical parameters of the optimal model were determined. It is shown that the agreement between the model and observations breaks down after ({sim})40 days post-maximum; to explain this divergence, a model with an extra energy source due to the spin-down of the magnetar formed in the explosion has been proposed.