R e g u l a r p a p e r s

Theoretical and mathematical physics

Moscow University Physics Bulletin 2023. N 4.

In this work, a model of a symmetric tensor $C^*$-category with conjugation is constructed for the dimension of the object $d=3$. It is proved that the constructed conjugate object of the category satisfies the conjugation equations. The classes of morphisms between objects of the modeled category are considered and studied, and the algebra of observables in the presence of such an conjugate object is introduced. As an application of the model, we consider the theory of quantum information transfer, where it is necessary to take into account the constraints associated with the superselection rules.

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The statistical theory based on the two-parameter Sharma-Mittal functional is a generalization of the statistics of Gibbs, Renyi and Tsallis. In this paper, the formalism of statistical mechanics based on the Sharma-Mittal entropy functional is considered, and the theorem on the equidistribution of energy for classical statistical systems by degrees of freedom is proved. A generalized Maxwell distribution for the corresponding statistics is obtained and the characteristics of statistical systems described by the distribution are calculated: the average velocity modulus, the root-mean-square and the most probable velocities of gas particles. A generalized Sakura-Tetrode formula is also obtained.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

Ferromagnets, multiferroics and other magnetically ordered materials are described by various models of the evolution of the magnetization of the medium. In this paper, we develop the method of many-particle quantum hydrodynamics for such media. We use the Heisenberg Hamiltonian and derive an equation for the evolution of macroscopic magnetization, corresponding to the non-dissipative version of the Landau-Lifshitz equation for particles with spin 1/2. It is shown that the well-known form of the contribution of the exchange interaction to the Landau-Lifshitz equation arises in the third order in terms of the interaction radius. The possibilities of the systematic generalization of the result obtained are discussed when considering the fifth order in the interaction radius or when considering particles with a large spin.

Show AbstractPhysics of nuclei and elementary particles

Moscow University Physics Bulletin 2023. N 4.

The paper considers some kinematic conditions for the back Compton scattering of photons by relativistic electrons and the polarizations of colliding particles, which affect the value of the differential cross section of the process. A significant influence of the electron and photon helicity on the value of the cross section was found. In the ultrarelativistic case, a surprising effect of an almost twofold increase in the cross section of scattering in the direction of the initial electron momentum was also discovered, when the initial photon momentum is perpendicular to that of the initial electron.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

The paper presents the results of test measurements to determine the possibilities of studying the cluster structure of highly excited states of the 6Li nucleus in the 6Li(n,3He n)3H reaction on the RADEX neutron channel of the Institute for Nuclear Research of the Russian Academy of Sciences. In the experiment, scattered neutrons were detected in coincidence with the decay products of highly excited states (helium-3). The first experimental data on the excitation energy of the 6Li nucleus have been obtained.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

The authors offer works using the MMF INR RAS neutron channel to study the cluster structures in light nuclei, in particular, α-4n-α and 8Be-4n in the highly excited state 12Be*. This needs the registration of charged particles from the 12Be* β-decay during its formation in the n + 13C reaction in the intervals between cascade neutron pulses. The paper presents the first results of an experiment on measuring the spectra and time distributions of gamma-quanta and neutrons using a proton beam of 50 Hz and a duration of 0.3 μs.

Show AbstractRadiophysics, electronics, acoustics

Moscow University Physics Bulletin 2023. N 4.

The paper proposes a theoretical and numerical study of the quality criteria of radar absorbing layer. Simple analytical expressions for the minimum of the reflection coefficient of a homogeneous absorbing layer are obtained. It is shown that this quantity is not a correct characteristic of absorption. To describe the quality of an absorber, other quality criteria are needed, such as relative bandwidth of operating waveband or the ratio of the operating waveband to the layer thickness. The first of these values may be useful in obtaining a broadband absorber, and the second, in obtaining a small thickness of an absorber.

Show AbstractOptics and spectroscopy. Laser physics

Moscow University Physics Bulletin 2023. N 4.

We present a method of creation of photonic structures whose optical spectrum of the reflection coefficient has an arbitrary shape and has predetermined features. We develop an algorithm for the construction of a photonic crystal structure, perform numerical simulation of its reflection spectra, and create an experimental sample of a photonic crystal that has a spectral response corresponding to a given shape.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

This paper demonstrates an example of optical information encoding using the spectral response of a photonic crystal. The spectral dependence of the reflection coefficient of a one-dimensional photonic crystal reproduces the sequence of the EAN-13 standard barcode. An algorithm for building the structure of a photonic crystal based on a given encoded sequence of 12 digits was developed. This structure was experimentally implemented, its spectral response allows to decode the original encoded sequence.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

Numerical simulation methods are used to study the spectral transformation of a femtosecond wave packet during filamentation in fused silica under conditions of normal, zero, and anomalous group velocity dispersion. It is shown that during plasma generation that causes phase modulation of the light field, a rapid anti-Stokes broadening of the spectrum occurs. It was established that the short-wavelength shift of the broadband supercontinuum spectrum is much larger in case of anomalous group velocity dispersion than in case of normal and zero dispersion. The influence of the wave packet energy on the spectrum broadening dynamics is considered. Estimates of the numerical scheme parameters are obtained based on the dispersion analysis of the process of broadband supercontinuum propagation in a medium.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

For efficient operation of many organic electronic devices, organic semiconductors with high charge carrier mobility are required. However, in most of the known organic semiconductors, the charge mobility is low, since it is limited by the strong local electron-phonon interaction. In the present work, using the example of thiophene-phenylene co-oligomers, a class of organic semiconductors that combine a sufficiently high charge mobility with light emission and therefore promising for light-emitting transistors and electrically pumped lasers, the mechanism of suppression of the electron-phonon interaction by introducing electronegative atoms or an additional thiophene ring is studied. It was found that such structural changes alter the contribution of various vibrational modes to the local electron-phonon interaction, in particular, to the suppression of the contribution of the low-frequency torsion mode. In addition, it is shown that for the two modes that make the largest contribution to the local electron-phonon interaction in an unsubstituted oligomer, this change correlates with their intensity of Raman scattering, and this confirms the promise of studying the electron-phonon interaction using Raman spectroscopy. The results obtained improve the understanding of the relationship between the local electron-phonon interaction and the molecular structure of organic semiconductors, which is extremely important for the directed design of such materials with high charge mobility.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

Organic light-emitting transistors are a new type of optoelectronic devices that combine the functionality of OLED and a transistor that controls it. The working layer of these devices requires organic semiconductors that combine high charge mobility with a high photoluminescence quantum yield. One of the promising classes of such materials are thiophene-phenylene co-oligomers, the properties of which can be tuned over a wide range by adding various substituents. In this work, we address the effect of fluorination on the properties of two model thiophene-phenylene co-oligomers with an annulated central fragment, P-TTA-P and P-BTBT-P. It is shown that fluorination of both molecules lowers their frontier orbitals energy levels, and this should enable electron transport in their crystals and films. At the same time, fluorination has a qualitatively different effect on the delocalization of frontier orbitals, the width of the optical gap, the oscillator strength, the exciton binding energy, and the Raman spectrum, which is explained by the difference in the equilibrium geometry of fluorinated molecules. It is expected that the revealed relationships between the structure and properties of the studied compounds will contribute to the rational design of organic semiconductors for efficient light emitting devices.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

The features of the Fourier spectra of fractal-like systems are studied. On the basis of theoretical studies, the features of the scaling invariants of the objects under consideration in light fields are determined, which manifest themselves in the form of stable local formations - patterns. Particular attention is paid to the problem of stability of the ratios of the scaling characteristics of the analyzed systems and their Fourier transforms. The possibility of identifying and systematizing various fractal systems based on the estimation of their scaling parameters is considered. An analysis of the stability of the scaling parameters of the probing radiation to changes in the parameters of the systems under study indicates that the pattern approach to improving the methods of optical diagnostics is promising.

Show AbstractCondensed matter physics

Moscow University Physics Bulletin 2023. N 4.

Using tunneling spectroscopy, we measured current-voltage characteristics (CVC) and dynamic conductance spectra dI(V)/dV of SnS tunneling contacts in single crystals of slightly overdoped superconducting ferro-pnictide of nominal composition BaFe$_{1.88}$Ni$_{0.12}$As$_{2}$ with bulk critical temperature $T_c = 18$ K. Besides the Andreev structure, a strong nonlinearity is observed in the obtained curves both in the superconducting and normal state. For the temperature range $4.3-26.4$ K we determined the positions and temperature dependences of the observed dI(V)/dV-features irrelated to the superconducting state. Additionally, we discuss the possible origins for the appearance of the observed features.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

The paper presents the results of investigations of the magnetic properties of glasses of the composition K2O•Al2O3•B2O3 (KAB) with the addition of Fe2O3 2.0 and 3.0 wt.%, subjected to radiation treatment in 60Co gamma field at dose rate of 236 R/s for 2 hours at room temperature and when samples are heated to 423 K. Both under radiation and thermoradiation exposure, the magnetic susceptibility of glasses follows the Curie–Weiss law at 4.2–200 K and slightly deviates from this dependence at 200–340 K. The weakly pronounced magnetic hysteresis with low coercive force was detected at low temperatures against the background of magnetization that depends almost linearly on the field. An analysis of data on the temperature and field dependences of magnetization in weak and strong fields, combined with data on structural and optical properties, indicates that mainly Fe2O3 nanoparticles in the uncompensated antiferromagnetic state are formed in glasses, as well as an insignificant amount of dissociated Fe and Fe3O4 ions.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

Pyroelectric, dielectric properties, and thermodepolarization currents of methylammonium alum crystallohydrate single crystals were studied in temperature range 120–200 K. Temperature dependences of these quantities demonstrated peaks at ~143, ~160, and 176.4 K (Curie point). The behavior, which is typical to many crystals with a network of hydrogen bonds with an O–H...O distance of ~2.7 ± 0.1 Å, is considered from the point of view of a quantum chemical model of a hydrogen bond network containing water clusters in addition to individual H2O molecules. The movement of bridging protons in molecular clusters in electric fields is coherent and correlated, and all bridging protons of the system are involved in it. These displacements are associated with oscillations of the oxygen frame of the compression-tension type. The discreteness of the temperature peaks of the electrophysical properties is associated with the discreteness of the energy levels of the double-well potential, caused by the splitting of the excited levels.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

The influence of the surface type on resonant charge exchange between H- ion with a metal surfaces Cu(111) and Cu(110) covered by adsorbate Li+/Na+ has been studied. A model static problem was considered. For modeling, a three-dimensional realization of the wave-packet propagation method was used. The Cu(110) and Cu(111) surfaces were described by a pseudopotential, derived from a density functional theory (DFT). An occupation of H- ion, an electron density dynamics and an ion level width were analyzed. As a result, we obtained that an electron oscillates more in case of the surface Cu(111). Furthermore, the resonant charge exchange is more efficient for Cu(111) surface.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

The method of molecular dynamics is used to consider many-particle interactions during the motion of an ion in a carbon nanotube, and the importance of taking them into account is substantiated. The effect of an elastic perturbation of the nanotube wall on a particle moving in the nanotube channel has been studied. It has been confirmed that when the interaction of the ion with the perturbation of the carbon nanotube wall is taken into account, the energy losses of the ion decrease by a factor of 1.5–3. It is shown that as the temperature of the nanotube decreases, the effect of the interaction of ions with the perturbation of the wall becomes more deterministic. Within the framework of the model under consideration, the electronic stopping power on the electron subsystem of a carbon nanotube is small compared to the energy loss of an ion in elastic collisions with atoms of the nanotube wall.

Show AbstractBiophysics and medical physics

Moscow University Physics Bulletin 2023. N 4.

A series of experiments have been performed to study the activation of chemical macronutrients in human venous blood throughout radiation treatment with the 20 MeV linac. Some elements in the human blood can be activated as positron-emitting radionuclides by (γ, n)-reaction. We calculated the 11C, 13N, 15O, 30P, 34mCl, and 38K activities in irradiated human venous blood samples for the first time. As a result, we concluded that the main contribution to the internal dose from positron-emitting nuclides activated in human blood provides three nuclides: 15O, 34mCl, and 38K. The 34mCl and 38K contribution to the total dose can be comparable with 15O due to the high boundary energy of positrons, a longer half-life, and the presence of high-energy gamma quanta.

Show AbstractAstronomy, astrophysics, and cosmology

Moscow University Physics Bulletin 2023. N 4.

Using formulae for light propagation, redshift and photometric distance in a Bianchi I anisotropic Universe, we create a picture of the Hubble flow that could be observed by a hypothetical observer in the anisotropic Universe. The algorithm used can be applied (after some modification) for more complicated visualizations of a sky seen by an observer in strong gravitational fields.

Show AbstractPhysics of Earth, atmosphere, and hydrosphere

Moscow University Physics Bulletin 2023. N 4.

This work is devoted to studies of the shallow methane seepages temporal variability in the coastal area of Laspi Bay and high-frequency monitoring of the hydrological parameters daily dynamics in this area. The paper presents results obtained during the summer months of 2016, 2018-2021, and early February 2023. Using the passive acoustic method, it is shown that the intensity and periodicity of bubble gas emission by individual point sources can vary during the day and from season to season. It was obtained that a decreased content of dissolved oxygen and its saturation is observed above the active site of the seepages as compared to the distant (background) site. Moments of sharp decrease in oxygen content not accompanied by changes in temperature and other hydrological parameters were noted.

Show AbstractMoscow University Physics Bulletin 2023. N 4.

The effect of a film of hydrophobic dust particles on the water surface on the development of a drift current under the influence of wind is studied. In a uniform air flow on a flat water surface, the drift current is caused by viscous forces and increases along the fetch. The formation of stationary waves on a drift current is found if the drift velocity is > 0.23 m/s. In a decelerating air flow in the presence of wind waves, the total component of the drift velocity cyclically increases and drops to a viscous component when a steep wind wave breaks up into longer linear waves. As the particle settling time Ts increases, the maximum ratio the wave part of the drift velocity to the total decreases from 0.6 for pure water to 0.3 for Ts = 4 days

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