The quantum-mechanical problem of the motion of a charged particle in a magnetic field is considered. The properties of the Wiener measure under transformations of the functional integration variable of a specific type are investigated. It is shown that the functional integrals for a particle in a uniform magnetic field are equivalent to those for a free particle.
This paper presents the results of sequential irradiation of the YBa _2 Cu _3 O _7-δ superconducting layer of a 2G HTS tape using atomic and cluster argon ions. It is shown that two-stage irradiation with monomers at a grazing incidence angle of 85 ^∘ made it possible to remove a-orientated crystallite protrusions, significantly reducing the root-mean-square (RMS) roughness. Subsequent surface processing with cluster ions at normal ion incidence results in smoothing of the surface topography in the range of spatial frequencies from 0.5 to 10 μ m ^-1 . It is worth noting that, within the framework of this method, the depth of the modified layer does not exceed 10–20 nm, which indicates that no structural damage is introduced into the bulk of the superconducting film.
Single crystals of the overdoped iron pnictide Ba _0.45 K _0.55 Fe _2 As _2 with T_c≈ 29 K have been studied. The current–voltage characteristics of planar mechanically controlled break junctions at various temperatures have been obtained and analysed. The temperature dependence of the self-field bulk critical supercurrent in zero magnetic field is successfully described within a two-band model, which made it possible to estimate the values of the large and small superconducting gaps, their characteristic ratios, and the partial contributions of the two effective bands to the conductivity.
This review focuses on methods for the production of promising medical radionuclides using photoproton nuclear reactions. Primary attention is paid to theranostic isotopes, such as lutetium isotopes ^177 Lu and rhenium isotopes ^186,188,189 Re, which can be obtained with high radionuclide purity. Of particular note is an innovative scheme for producing the diagnostic positron-emitting radioisotope zirconium ^89 Zr via photoproton reactions on molybdenum, which ensures high radionuclidic purity of the preparation and enables production organized according to the principle of a generator system. The leading role of the Skobeltsyn Institute of Nuclear Physics at Lomonosov Moscow State University in the development of this field in Russia is highlighted, which involves fundamental research on the photonuclear fission, obtaining reliable cross sections for photonuclear reactions and their subsequent application in medical technologies and clinical practice.
Using wave phenomena initiated in Kuril Lake (Kamchatka Peninsula, Russia) by the 8.8 Mw Kamchatka earthquake as an example, the formation of seismogenic seiches in enclosed bodies of water on land is analyzed. Within the framework of linear potential wave theory, it is shown that the primary contribution to the amplitude of seiche oscillations comes from the first few eigenmodes, which can be considered long-wavelength. The contribution of higher eigenmodes decreases inversely proportional to the square of the frequency. Seiches generated by the 8.8 Mw Kamchatka earthquake in Kuril Lake were numerically simulated using linear shallow-water equations. It was shown that in narrow bays and straits, lake level fluctuations could reach 5 m, and current velocities could reach 2 m/s. The numerical results for the ‘‘Kordon Ozerny’’ point (2.3 m, 1.1 m/s) are consistent with eyewitness accounts.
A method of bolus shape calculation in ion-beam therapy for a large set of ions and for various bolus materials is presented. Currently, it is possible to use any ion in the range H–Ca, and a list of bolus materials can include polystyrene, PLA, and aluminium. The list of ions and materials can be expanded. This method is implemented as a component of the planning system for the ion-beam therapy centre being developed at the NRC ‘‘Kurchatov Institute’’—IHEP. An example of bolus calculation for a real patient and the results of verification using detailed modelling in GEANT4 are presented.
Within the framework of the DFT and DFT + U methods, the electronic structure and density of states of solid solutions CsPb _1-x Mn _x Cl _3 with the perovskite structure ( x=0 , 0.125, 0.25) were calculated. The crystals were characterised as direct bandgap dielectrics. With an increase in the manganese concentration in the compound ( x ), the following trends were revealed: a decrease in the perovskite lattice constant, an increase in the bandgap of the solid solution, and also an enhancement of the influence of Mn states on the formation of the valence-band top and the conduction-band bottom. The Mn 3 d states form defect subbands, forming an additional emission channel for the recombination of excited carriers. The calculation results agree with the experimental data from the literature.
The problem of optimal control of a dynamic system in the presence of inaccurate information about its parameters is considered. A continuous real-time parameter calibration approach is proposed, involving the accumulation of calibration information of a special kind for model predictive control. This approach does not require storage of the complete data history and allows the calibration information to be updated and the parameters to be recomputed at each control step. The algorithm developed in the paper is illustrated using the example of the problem of the motion of an object in a viscous medium. The numerical simulation results demonstrated a significant improvement in the control quality after parameter calibration: elimination of oscillations, reduction in overshoot and a decrease in the objective function values. An important feature of the proposed approach is the possibility of refining the model parameters without interrupting the normal operation of the system. A modification of the algorithm that ensures gradual forgetting of calibration information, making it applicable in the presence of parameter drift, is also considered.
In the coastal meromictic Lakes Kislo-Sladkoe and Trekhtzvetnoe (the White Sea, Kandalaksha Bay), the temperature regime was studied using the generalised one-dimensional model of thermodynamic, hydrodynamic, and biogeochemical processes LAKE. Particular attention was paid to the process of formation of the middepth temperature maximum (TeM). The model demonstrated the ability to realistically reproduce various physical phenomena in the annual cycle of the water body’s life, including the TeM, autumn cooling, and the winter temperature maximum. For the first time, the following factors have been assumed to have a key influence on the characteristics of the TeM and its presence: the salinity of the lake layers relative to one another, the salinity gradient exceeding 10–13 PPT/m, and the location of the salinity-gradient maximum relative to the reservoir surface. The data obtained from the modeling have been compared with field measurements.
The paper presents the results of a comprehensive study of the geodynamic features of the Eastern Segment of the Greater Caucasus, based on original long-term quasi-continuous satellite-geodetic observations at 28 regional Global Navigation Satellite System (GNSS) stations. The GNSS measurements were processed using the GAMIT/GLOBK software package, designed for high-precision geodetic determinations from radio-navigation satellite signals. As a result of the processing, time series of coordinate increments and displacement velocities of the GNSS stations were obtained in two reference frames, the global ITRF2020 and a regional frame, relative to stable Eurasia. To study the relative displacements of regional tectonic structures, the method of velocity profiling was applied. A 500 km-long profile was selected, extending from south to north with an azimuth of 6.58 ^∘ . The profiling results revealed relative motions of the main regional tectonic structures. Interpretation of the obtained results in the context of regional seismotectonics provides a detailed picture of the present-day geodynamic situation of the Eastern Segment of the Greater Caucasus.
The radiation dosimetry quantities are used to calculate the operational and protection quantities by ICRU and ICRP. In the fields of radiation protection and medical physics, accurately differentiating between kerma and absorbed dose is fundamental, especially in interface regions where electronic equilibrium is disrupted. This study investigates the impact of increasing incident photon energy on the relationship between these two quantities within a water phantom, providing a high-precision quantitative analysis. A simulation approach DOSRZnrc code was employed to compute absorbed dose and kerma for mono-energetic photons at energies 0.5, 1, 10, 25, and 30 MeV and spectrum Co-60 and Cs-137 with the number of histories optimized to ensure a relative statistical uncertainty of less than 0.5 % . While the qualitative behavior of these quantities is established in classical physics, this research offers significant added value by providing updated reference datasets that bridge the gap between theoretical textbook models and modern clinical practice. The difference between absorbed dose and kerma are increases with increasing energy. The ratio between absorbed dose and kerma at the medium surface is equal to 0.99, 0.12 at energies 0.5 and 30 MeV. Whereas the ratio between absorbed dose and kerma at maximum dose is equal to 0.99, 0.88 at energies 0.5 and 30 MeV. The study’s significance lies in its precise determination of Transient Charged Particle Equilibrium (TCPE) distances, ensuring higher accuracy in absorbed dose estimations for biological media and radiotherapy treatment planning.
The influence of point defects of the vacancy type on the thermodynamic properties of the two-dimensional Ising model is investigated in the paper. The main attention is paid to the comparison of two approaches to the description of the system: the traditional analysis of the internal energy E and a more complete analysis of the Helmholtz free energy F and entropy S . Using Monte Carlo methods—the Metropolis algorithm and the Wang–Landau algorithm—the temperature dependences of the changes in the indicated quantities upon the introduction of defects are calculated. It is established that the interaction of defects has the character of attraction with an effective radius of d≈ 3 . It is shown that in the phase transition region, the free energy behaves as a continuous monotonically decreasing function of temperature, whereas the internal energy exhibits a singularity caused by the behaviour of the entropy. The possible dynamics of defects is investigated by comparing the energy of different configurations; a tendency towards defect clustering at temperatures above the critical one is observed. A comparative analysis of the accuracy and computational efficiency of both approaches is carried out.
The article presents a review of the greenhouse effect on Earth, as well as on various planets and moons of the Solar System. The history of the study of this phenomenon is described. Various types of the greenhouse effect are considered. References to key scientific works on all the listed issues are given. The comparative analysis provided may give an idea of possible atmospheric processes and conditions on the surface of terrestrial-type exoplanets.
A local modal analysis of the magnetorotational instability (MRI) in the midplane of a thin Keplerian accretion disc with polytropic vertical density stratification has been carried out. To obtain an analytic solution, the approximation ∂/∂ r=0 for all perturbations is adopted and planar adiabatic perturbations in an incompressible fluid with u_z=0 are considered. An analytic closed-form dimensionless dispersion relation has been derived, the unstable intervals of the vertical wavenumber k_z are determined, and the MRI-unstable branch is identified. It is shown how the unstable wavenumber ranges and the extremal values of the dispersion curve depend on the strength of the background magnetic field.
Within the framework of a dynamical model, an analysis of the energy dependences of the mean spins of fission fragments formed in complete fusion reactions of deformed nuclei has been carried out. The parameters of the dynamical model are determined from the conditions of the best description of experimental data on the mean spins of fission fragments for the reactions ^12 C + ^232 Th, ^16 O + ^209 Bi, ^12 C + ^209 Bi, and ^16 O + ^232 Th. The influence of the reaction entrance channel on the formation of fission fragment spins of the compound nucleus is discussed. The effect of the entrance channel is considered using the example of the ^12 C + ^236 U and ^13 C + ^235 U reactions, leading to the formation of the same compound nucleus ^248 Cf. It is shown that, at sub-barrier collision energies, noticeable differences in the behaviour of the mean spins of fission fragments for different entrance channels of the fusion reaction should be observed.
The main characteristics of the liquid–gas phase transition in argon are calculated in this work on the basis of the correlation cell-cluster expansion. On the saturation curve, the heat capacity at constant pressure is calculated both for the liquid and for the gas. There is a monotonic increase in the heat capacity at constant pressure with increasing temperature. This fundamentally distinguishes the behaviour of the heat capacity on the saturation curve from the behaviour on the crystallisation and melting curves. A comparison of the theoretical data with the experimental data has been carried out, and good agreement has been obtained.
We observed an M1.4-class flare in active region NOAA 12403 using the horizontal spectrograph for solar observations (HSFA-2) at the Ondřejov Observatory in the spectral lines of calcium, helium, and hydrogen, as well as using two radio telescopes. The active region remained unchanged over several days, being located in a region of strong magnetic field. It was a typical bipolar region consisting of a group of spots, pores, and bright flocculi. After processing the spectra, the integral radiation fluxes in the H α , H β , H ε , H CaII, IR CaII ( λ=8542 Å), D3 HeI lines were determined. Then, using the model of heated homogeneous gas layers, a theoretical calculation of the plasma parameters was performed, taking into account the physical conditions in the chromosphere, including self-absorption in the spectral lines. To explain the observed fluxes, three gas layers oriented perpendicular to the line of sight, each with its own individual parameters, had to be considered. One of them is very extended, while the other two are thin, indicating that the flare plasma is highly inhomogeneous. The radio observations carried out at frequencies of 0.8–2.0 GHz revealed drifting pulsating structure with frequency decreasing, which evidences the upward rise of the radio-emission source.
The research focuses on multivariate time series of geophysical parameters. During the study, statistical and machine learning methods were employed to recover missing data. The following results were achieved: for the CO _2 concentration series at a height of 30 m, the ARIMAX model demonstrated the lowest RMSE and MAE metrics, taking only 2.3 s for recovery, which is significantly faster compared to the LSTM (251 s) and GRU (160 s) neural network models. Recovery of air–temperature data was performed most effectively using the recurrent neural network GRU. The results indicate that ARIMA family models are more suitable for data recovery when correlated parameters are present, whereas GRU-based neural networks are preferable in other cases. The conclusions can be used to improve data recovery methods in multivariate time series.
Finite-difference and integral forms of relativistic quasipotential equations in the configuration representation for the wave function of a nucleon in the framework of its quark–diquark model are obtained. In this model, the nucleon is considered as a two-particle composite system in which the quark has spin 1/2 and the diquark has spin 0. Approximate solutions of the scattering problem and the spectral problem for the radial wave function of the s -state of a nucleon in a quark–diquark model with a Coulomb (chromodynamical) potential are found. The condition for quantization of the energy levels of the nucleon corresponding to the Coulomb chromodynamical potential is determined. An expression for the relativistic threshold resummation S factor of a nucleon is obtained and its properties are investigated. The new regularities of behavior for the threshold S factor of the nucleon due to the spins and the difference in the masses of the quarks forming the nucleon are established. The consideration is carried out within the framework of a relativistic quasipotential approach based on the covariant Hamiltonian formulation of quantum field theory, via a transition from the momentum formulation in Lobachevsky space to a three-dimensional relativistic configurational representation for the case of a composite system of two relativistic spin particles of arbitrary masses.
The appearance of hyperons at densities several times exceeding nuclear density, in the interior of massive neutron stars, has a substantial effect on neutron star characteristics. Using various parameterisations of Skyrme forces, the equations of state of neutron star matter are calculated and an analysis of possible correlations between the observed characteristics of neutron stars and the properties of nucleon and hyperon interactions is carried out. The strongest influence on the matter density at the point of appearance of Λ -hyperons and, consequently, on the characteristics of neutron stars is exerted by the Λ N -interaction contracting power—a quantity introduced earlier in the physics of hypernuclei and characterising the ability of the Λ -hyperon to modify the nucleon core of a hypernucleus. The relation between astrophysical quantities and the properties of nucleon interactions weakens when hyperons appear, but in most cases is preserved. The determining factors for the maximum mass of a neutron star are the incompressibility of nuclear matter, quantities reflecting the behaviour of the symmetry energy at high densities, as well as the contracting power of the hyperon interaction.
