Issue 4, 2024

A. M. Adelyanov, E. A. Generalov, V. -. Chjen, L. V. Yakovenko

Results of experiments in the field of biophysics are often presented in the form of time series obtained with low resolution and not always of great length. In particular, in studies of effects of various physico-chemical factors on bilayer lipid membranes, transmembrane ion currents and their fluctuations are usually measured. At the same time, the average values and current variances may not differ significantly, and it is difficult to determine the nature and degree of impact from them, therefore, the development of approaches to time series analysis has never stopped. Attempts to use entropy of distributions of random variables in such an analysis have been made for a long time, but in practical work these approaches were difficult to implement, especially due to the requirements for the length of the series and for the absence of noise. Significant changes have taken place in this area in recent decades, and many new methods of time series analysis using various entropy modifications have been proposed. In this regard, there is a need for a summary of methods based on the calculation of entropy with indication of their advantages and disadvantages. This purpose is served by the proposed brief overview of entropy methods for analyzing scalar time series which can be useful in analyzing experimental data. The review considers only some of the basic approaches on which further improvements in calculation algorithms are based. The concept of entropy sometimes causes difficulties for students, so the review can also be useful for pedagogical purposes.

Structural, mechanical, electronic, chemical bonding and optical properties of cubic Cu2O: First-principles calculations

Z. Mu$^1$, H. Y. Jia$^1$, Q. J. Liu$^1$, Z. T. Liu$^2$, Z. X. Bai$^1$

First-principles calculations using the plane-wave ultrasoft pseudopotential technique have been performed to investigate structural parameters, mechanical, electronic, chemical bonding and optical properties of cubic Cu2O. The optimized structure of cubic Cu2O is in good agreement with previous theoretical and experimental work. The calculated independent elastic constants of cubic Cu2O are consistent with previous results. The bulk, shear and Young’s modulus, Poisson coefficient, compressibility, Lamé constants, shear, longitudinal and average sound velocity, Debye temperature of cubic Cu2O are obtained using Voigt–Reuss–Hill method and Debye–Grüneisen model, which are consistent with previous results. Electronic structure and chemical bonding have been calculated and analyzed to describe the electronic properties of cubic Cu2O. Moreover, the complex dielectric function, refractive index and extinction coefficient of cubic Cu2O are gained, which are consistent with previous results.

The structural and electronic properties in monolayer MoS2 with various vacancies: First-principles calculations

Z. Bai$^1$, F. Lu$^1$, Q. Liu$^1$, Z. Liu$^2$

The structural and electronic properties of perfect and defective MoS2 were calculated by first-principles density functional theory. The defect stability has been evaluated using the defect formation energy. The calculated results show that the formation of Mo, S and Mo-S defects requires extra energy. Moreover, the S vacancy is energetically more favorable than the Mo vacancy. After doping, the defect level is introduced into the forbidden band. The defect level in the Mo defect model tends to be the accepter level, while the defect level in the S defect model and Mo-S defect model tends to be the donor level. These three different defect models still maintain the direct band gap characteristics as perfect models. Then, the type of conduction after doping is also analyzed. The projected state density and the charge density of these four models have been further analyzed, showing the positions of defect energy levels and change of chemical bonds.

D. S. Kireev$^1$, K. F. Minnebaev$^2$, V. A. Kiselevskiy$^3$, A. E. Ieshkin$^4$

Additive manufacturing (AM) is a modern, developing group of technologies based not on the removal of material, but on the layer-by-layer growth and synthesis of an object according to a CAD (Computer-Aided Design) model. The main disadvantages of objects manufactured using AM technologies are a high degree of porosity and surface roughness. This work examines the possibility of modifying the surface of additive materials Ti6Al4V and AlSi10Mg using irradiation with Ar+ ions with energies in the range from 2 to 9 keV. Using SEM, the surface topography was obtained before and after irradiation and mechanical polishing. A decrease in surface porosity and roughness, as well as the influence of beam energy on the final surface topography, was demonstrated.

Yu. V. Grats, P. -. Spirin

We consider the vacuum polarization effect near the point delta-like source. The corresponding interaction is introduced within a technique of self-adjoint extension for the Laplace operator. Such a technique was widely discussed within Quantum Mechanics; we propose it for the investigation of vacuum field effects. It allows to compute the renormalized Hadamard function and the renormalized vacuum energy density for massive real scalar field with minimal curvature coupling. The dependence of the vacuum polarization effect upon the fields's mass is analyzed.

Yu. V. Chugreev

For the flat FLRW model of Universe evolution in RTG a new model of Dark Energy is proposed. It is a global scalar field Φ with the quadratic potential. It ensures cosmological acceleration at the present time and a bounce at the latе times. At the contraction stage Kazner-like growing anisotropy of Riemannian metrics will break a mass-of- the-graviton bounce mechanism near the Big Bang in FLRW case. In order to save the cyclic model one probably has to add some exotic fields, like galileons etc. There is also noncyclic option, when small enough graviton-mass-terms are significant only at the end of expansion. After bounce, during next contraction epoch, an anisotropy grows and the matter density finally reaches the Planck one.

D. V. Nakashidze$^1$, A. M. Savchenko$^1$, T. N. Bakiev$^2$

We propose a universal method for performing calculations within the framework of generalized statistics generated by the parametric Tsallis, Renyi, and Sharma–Mittal entropies. The essence of the approach lies in the use of an auxiliary gamma distribution whose parameters correspond to a particular variant of the statistics. Equations are derived that allow the generalised partition function and the mean energy to be expressed in terms of canonical quantities. The effectiveness of the proposed method is demonstrated using the example of Renyi statistics. The Maxwell - Renyi distribution is obtained and its properties are calculated, on the basis of which assumptions about the possible nature of the generalised parameter are formulated.

A. V. Golda$^1$, A. A. Golubenko$^{1,2}$, M. M. Davydov$^1$, E. L. Isupov$^2$, V. I. Mokeev$^3$, S. A. Savkin$^1$, V. V. Chistyakova$^1$

We report the tool for evaluation of the cross section for K+Λ and K+Σ0 electroproduction channels off proton. Within the framework of this work, we interpolated and extrapolated the structure functions of the K+Λ and K+Σ0 electroproduction channels using various algorithms for predicting the behavior of the studied observables. A set of algorithms for estimating systematic errors in the differential cross section prediction result is implemented. The program has been developed for estimating the differential cross section and structural functions using the C++ and Python libraries. For interactive work with the program, a web site was developed that allows you to visually analyze one-dimensional and two-dimensional distributions of structural functions and differential cross section.

S. E. Strigin

The number of unstable combinations of elastic and Stokes optical modes of the LIGO Voyager gravitational wave detector, frequencies and spatial distributions of displacement vectors of elastic modes of mirrors were calculated. The values of overlap factors for unstable modes up to ninth-order optical modes are calculated, taking into account the azimuthal condition of parametric instability. An analysis of the influence of the temperature dependence of the Young's modulus of the mirror material on the number of unstable modes in the Fabry-Perot resonator was performed.

E. R. Burmistrov$^1$, L. P. Avakyants$^2$

The zone diagrams of LED heterostructures with multiple quantum wells InxGa1-xN/GaN are calculated by numerically self-consistent solution of the system of Schrodinger equations and Poisson electroneutrality. The effect of the electron-phonon interaction, the nonparabolicity of the dispersion law and the hybridization of the wave function on the values of the effective mass of the main charge carriers in InxGa1-xN/GaN quantum wells has been studied. The redshift of 2D plasmon resonances is associated with the temperature renormalization of the effective mass of two-dimensional carriers. To describe the temperature dependence of the effective mass, the function of displacement of the 2D plasmon resonance frequency is used.

A. V. Kharcheva$^1$, K. D. Shmelkov$^1$, Yu. G. Sokolovskaya$^1$, A. V. Ivanov$^2$, N. E. Borisova$^3$, S. V. Patsaeva$^1$

Solutions in acetonitrile of three mixed complexes of rare earth elements (terbium and samarium) with organic ligands with various pyridine substituents were studied in this work. The ratios of ligands and metals in the resulting complexes were determined, and the stability constants of samarium complexes were calculated using the spectrophotometric titration method. Measurements of absorption, emission and excitation spectra of luminescence, luminescence kinetics of solutions of mixed complexes of rare earth elements with an excess of metal relative to the ligand were carried out at various temperatures in the range 298-328 K. An increase of luminescence intensity of a samarium ion in complex upon heating has been discovered for the first time. The dependences of the luminescence quantum yield and lifetime of mixed complexes on temperature were obtained. A thermometric parameter — the ratio of the integral luminescence intensities of samarium and terbium ions — was proposed, and the temperature sensitivity coefficient of this parameter was determined for different complexes.

P. S. Ryzhikov, V. A. Makarov

Using electromagnetic field angular momentum conservation law in a form of balance equation, which relates the angular momentum density, the angular momentum flux density and caused by the anisotropy of the medium torque density in nonabsorbing media, we obtained the formulas for the densities of the orbital and spin parts of the angular momentum and the flux densities of this quantities in case of interaction of monochromatic waves in nonabsorbing medium with spatial dispersion demonstrating n-th order nonlinear optical response to the external light field. In media without spatial and frequency dispersion the obtained expressions coinside with the canonical expressions for the densities and flux densities of the orbital and spin parts of angular momentum. The additional terms to the greatest components among the spin parts of angular momentum and its flux related to nonlinearity of the medium may reach ten percent of their linear parts during self-focusing of the elliptically polarized Gaussian laser beam in isotropic gyrotropic medium near the area of its collapse.

V. A. Kiselev$^1$, A. P. Chernyaev$^2$, Yu. D. Udalov$^1$, M. A. Belikhin$^3$, A. M. Demidova$^1$, S. E. Gritsenko$^1$

The development of proton therapy techniques increases the requirement for the accuracy of proton beam delivery. Existing methods for determining the planning target volume allow one to take into account only the influence of patient positioning errors before the start of irradiation. In this paper, the results of work on taking into account beam delivery errors by a proton therapy system to determine the planning target volume are presented. The technique for measuring the parameters of a proton beam and analyzing the measurement results is described. The calculation of the minimum required deviation from the clinical target volume is carried out to guarantee its irradiation, taking into account the errors in beam delivery by the proton therapy system.

E. N. Lykova$^1$, A. A. Shcherbakov$^{1,2}$, A. P. Strelkovskaya$^1$, F. R. Studenikin$^{1,2}$, S. A. Gavrilova$^3$, A. P. Chernyaev$^{1,2}$

MRI is widely used in planning radiation therapy, in particular in stereotactic radiosurgery of brain metastases. The article discusses the distortion of MR images, which can lead to errors in radiation therapy planning. A series of experiments were carried out with a simple phantom on two MRI scanners with 0.5 T and 1.5 T magnetic fields. Deviations of the position of phantom objects from their real location were observed. Detected that they can reach 5 mm. A theoretical dependence of the magnetic field gradient on the distance to the center of field homogeneity has been calculated. This dependence is in a good agreement with the approximation of experimental data. The dependence of the distortion of center field located object area on their actual sizes was estimated. It was found that the area distorcion can reach 20%.