Moscow University Physics Bulletin最新文献

In this work, a phase diagram of the neighbourhood of the triple point of a one-component system in the van der Waals approximation is constructed. It is shown that this approximation makes it possible to describe the triple point corresponding to the coexistence of three aggregate states of matter—solid, liquid, and gaseous. The possibility of using this approximation for triple points of other types is discussed.

The paper investigates a model of the motion of a Brownian particle on (mathbb{C}^{2}). A six-dimensional random process is considered, whose states are described by the coordinates of the particle and the complex analog of the area swept out by the radius vector of the point as it moves along the trajectories of a four-dimensional Brownian bridge. Using the methods of integration over the conditional Wiener measure, an expression for the transition probability density of a random process from an arbitrary state to a subsequent one is obtained. A connection is revealed between the trajectories of the process under consideration and the Heisenberg group constructed over the field of complex numbers (H_{3}(mathbb{C})). The continuity in time and Hölder property with order (alpha<1/2) of the oriented area function (S(t)) are proven, as well as the Heisenberg Markov property of the process. The heat equation describing the system’s evolution and the corresponding sub-Laplacian are derived. The solution to the equation is obtained in the form of a functional integral. Performing a Wick rotation allows for drawing an analogy between the considered process and the motion of an electron in a magnetic field.

A system for monitoring the operation of a laser interferometer in a reactive ion etching setup has been developed. For the precise calibration of the etching rate of the top silicon layer in silicon-on-insulator materials, a series of chips with identical structures were fabricated. The thickness of the structure on each chip varied depending on the etching time. The heights of the resulting steps were measured using the tapping mode of an atomic force microscope. For the etching mode in a plasma of CF({}_{4}) and O({}_{2}) gases (flow ratio (20:5), pressure 4 Pa, power 40 W), the silicon etching rate was determined to be (0.31pm 0.1) nm/s. The adduce parameters allow stopping silicon etching at a depth of ({sim}5) to (120) nm with an accuracy of no worse than 2 nm. The obtained results make it possible to address a number of tasks in the fabrication of various silicon nanoelectronic devices. In particular, the process of forming silicon channel nanowires for field-effect transistors requires high-precision control of the silicon layer thickness during reactive ion etching.

We theoretically studied and observed the photoionization rates of the alkali and noble atoms driven by an elliptically polarized Ti:sapphire laser for the barrier suppression ionization scheme. We extended the barrier suppression ionization formula developed by Posthumus and coworkers by considering the inclusion of the initial momentum of the ejected photoelectrons and the ponderomotive potential and Stark shift in unperturbed ionization potential. The extended formula is applied to both groups of atoms and the obtained results are compared with those obtained by the initial formula with the aim to determine the influence of all mentioned effects. Additionally, we explored the influence of the field’s ellipticity on the barrier suppression ionization rate. We found that it is sensitive to the change of the field ellipticity and the inclusion of all mentioned effects as well.

The paper provides a review of publications on the study of the natural phenomenon of the thermal bar. Results of field observations of this phenomenon in lakes in spring and autumn, offering insights into thermo-hydrodynamic processes in water bodies during these periods, are presented. In laboratory modeling studies of the thermal bar, instability mechanisms leading to its occurence and features of its movement are discussed. Theoretical works are considered, where various approaches to modeling the thermal bar are discussed, including modern hydrodynamic models. Special attention is paid to research on this phenomenon conducted at the Department of Physics of the Sea and Inland Water of the Faculty of Physics, Lomonosov Moscow State University.

The results of studying the systematic errors of the ionospheric model NeQuick 2, verified using electron concentration data of satellite measurements from the Swarm mission for 2014, are presented. The study utilized measurements obtained by Langmuir probes installed on the spacecraft of the mission during the period of solar activity maximum. The research allowed for determining the mean modeling errors in different latitude zones and geomagnetic conditions and obtaining spatial distributions of systematic deviations of the model from the measurement data. The characteristic deviation values amount to 80(%), with the error increasing up to 300(%) in certain geographic regions under geomagnetic disturbance conditions. Zones of elevated deviations are observed at high latitudes in the southern hemisphere. The results of the study will be useful for refining the operational conditions of radio facilities and various applications, including improving navigation and communication systems and enhancing ionospheric models.

This paper discusses the potential of deep learning in solving the inverse problem of computational ghost polarimetry. For the first time, it is demonstrated that the spatial distribution of the polarization properties of objects with linear amplitude anisotropy can be restored using a neural network trained on model data. The spatial distribution of the parameters of linear amplitude anisotropy is determined with an accuracy of 7.8(%) and 15.6(%) for the azimuth and the value of anisotropy, respectively.

The study of the first-order magnetic phase transition mechanisms is one of the key challenges in modern physics. The difficulty in identifying these mechanisms arises from the multitude of factors that play a significant role during the phase transition. FeRh-based alloys are among the most typical systems exhibiting a first-order phase transition from the antiferromagnetic to the ferromagnetic state. Despite the fact that the iron–rhodium alloy possesses a relatively simple crystal structure and does not change the symmetry of its crystal lattice during the phase transition, a number of features in the behavior of its physical properties are observed. This review presents present-day information on the influence of various external factors, the effects of crystalline defects, and dimensional characteristics on the static and dynamic properties of FeRh-based alloys.

The solar flare SOL2015-10-01 was observed at the Astronomical Institute of the Czech Academy of Sciences using the HSFA-2 horizontal solar research setup. After processing the spectra, the integral radiation fluxes were determined for the H(alpha), H(beta), and H(varepsilon) lines of hydrogen, the D3 line of helium, as well as the resonance (lambda=3968) Å and infrared (lambda=8542) Ålines of the CaII ion. The analyzed flare exhibited two characteristic cores, and during processing, the fluxes from each core were determined. Within the framework of the heated gas model, theoretical calculations of plasma parameters were performed, taking into account the physical conditions in the chromosphere, including self-absorption in the spectral lines. The simultaneous analysis of six lines from three atomic systems made it possible to reconstruct the temperature, density, and spatial structure of the emitting gas with high confidence. A strong temperature inhomogeneity in the emitting gas was revealed. The reconstructed theoretical gas concentration values exceed those for prominences by at least an order of magnitude, suggesting the chromospheric nature of the emitting gas.

The (vrightarrow v^{prime}) rate coefficients for the vibrationally inelastic collisions of O atoms with O({}_{2}) molecules are presented for vibrational quantum numbers (v) from 0 to 8 and temperatures from 100 K to 1000 K. The rate coefficients were computed theoretically using an ab initio (mathrm{O}+mathrm{O}_{2}) interaction potential for the ground state of O({}_{3}). The rate constants obtained are compared with available results of quasi-classical calculations. The coefficients calculated are required in the modelling of many industrial processes such as plasma etching, surface treatment, plasma sterilization, and medicine.