Персона:
Бисноватый-Коган, Геннадий Семенович

Организационные подразделения

Организационная единица

Институт лазерных и плазменных технологий

Стратегическая цель Института ЛаПлаз – стать ведущей научной школой и ядром развития инноваций по лазерным, плазменным, радиационным и ускорительным технологиям, с уникальными образовательными программами, востребованными на российском и мировом рынке образовательных услуг.

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Бисноватый-Коган

Имя

Геннадий Семенович

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Теперь показываю 1 - 10 из 30

Только метаданные
An examination of geometrical and potential time delays in gravitational lensing
(2020) Tsupko, O. Y.; Bisnovatyi-Kogan, G. S.; Rogers, A.; Er, X. Z.; Бисноватый-Коган, Геннадий Семенович
In this paper we investigate the relation between the potential and geometric time delays in gravitational lensing. In the original paper of Shapiro (1964), it is stated that there is a time delay in the radar signals between Earth and Venus that pass near a massive object (the Sun), compared to the path taken in the absence of any mass. The reason for this delay is connected with the influence of gravity on the coordinate velocity of a light ray in a gravitational potential. The contribution from the change of the path length, which happens to be of second order, is considered as negligible. Nevertheless, in the gravitational lens theory the geometrical delay, related to the change of path length, is routinely taken into account along with the potential term. In this work we explain this apparent discrepancy. We address the contribution of the geometric part of the time delay in different situations, and introduce a unified treatment with two limiting regimes of lensing. One of these limits corresponds to the time delay experiments near the Sun where the geometrical delay is shown to be negligible. The second corresponds to the typical gravitational lens scenario with multiple imaging where the geometrical delay is shown to be significant. We introduce a compact, analytical, and quantitative criteria based on relation between the angular position of source and the Einstein radius. This criterion allows one to find out easily when it is necessary to take the geometrical delay into account. In particular, it is shown that the geometrical delay is non-negligible in the case of good alignment between source, lens and observer, because in such a case it becomes a first order quantity (the same order as the potential term).
Только метаданные
Dynamic Model of a Non-equilibrium Chemical Composition Formation in the Shell of Single Neutron Stars
(2022) Ignatovskiy, A. Y.; Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
© 2022, Pleiades Publishing, Ltd.Abstract: The process of a non-equilibrium chemical composition formation during cooling due to neutrino energy loss in the shells of hot, formed neutron stars is considered. A model constructed is to explain the presence of a large quantity of nuclear energy accumulated, which can maintain the X-ray luminosity of such compact objects for a long period of time. The study of the numerically obtained final chemical composition dependence on various parameters of the medium has been carried out.
Только метаданные
Nonequilibrium Layer in the Crust of Neutron Stars and Nonequilibrium β-Processes in Astrophysics
(2019) Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
© 2019, Pleiades Publishing, Inc.Abstract: The formation of the chemical composition of neutron star envelopes, at densities 1010–1013 g cm–3, is considered. As hot matter is compressed in the process of collapse, which leads to the explosion of a core-collapse supernova, the stage of nuclear equilibrium with free neutrino escape, kinetic equilibrium in β-processes, and, as a result, the establishment of limited nuclear equilibrium with a fixed number of nuclei takes place. Cold matter is compressed at a fixed number of nuclei whose atomic weight initially does not change and subsequently decreases. A pycnonuclear reaction of the fusion of available nuclei and a decrease in their number begin at the end. The compression of cold matter is accompanied by an increase in the mass fraction of free neutrons. In this case, the chemical composition of the envelope differs significantly from the equilibrium one and contains a considerable store of nuclear energy. Nonequilibrium β-reactions proceed at densities exceeding the upper bound for the nonequilibrium layer density, which lead to heating, nuclear energy release, and the possible attainment of a state of complete thermodynamic equilibrium. The thermodynamics of nonequilibrium β-processes, which lead to the heating of matter as neutrinos escape freely, is considered.
Только метаданные
Thermodiffusion Unipolar Electric Generator
(2024) Bisnovatyi-Kogan,G.S.; Glushikhina,M.V.; Бисноватый-Коган, Геннадий Семенович
Только метаданные
3D numerical study of an anisotropic heat transfer in outer layers of magnetized neutron stars
(2019) Kondratyev, I. A.; Moiseenko, S. G.; Glushikhina, M. V.; Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).Periodic changes in a thermal soft X-ray flux of a rotating neutron star indicate a non-uniform distribution of the surface temperature. A possible cause of this phenomenon is a suppression of the heat flux across the magnetic field lines in a crust and an envelope of magnetized neutron stars. In this paper we study three-dimensional effects, associated with non-axisymmetric magnetic fields in neutron stars. We calculate the surface temperature distribution by solving numerically a three dimensional heat transfer equation in a magnetized neutron star crust. We adopt an anisotropic (tensorial) electron thermal conductivity coefficient, which is derived as an analytical solution of the Boltzmann equation with a Chapman-Enskog method. To calculate the surface temperature distribution, we construct a local one-dimensional plane-parallel model ("Ts-Tb"-relationship) of a magnetized neutron star envelope. We then use it as an outer boundary condition for the three-dimensional problem in the crust to find the self-consistent solution. To study possible observational manifestations from anisotropic temperature distributions we calculate light curves with a composite black-body model. Our calculations show, that a non-axisymmetric magnetic field distribution can lead to the irregular non-sinusoidal shape of a pulse profile as well as in some cases a significant amplification of pulsations of the thermal flux in comparison to the pure-dipolar magnetic field configurations.
Только метаданные
Approximate Analytic Model of the Boundary Layer Arround a Low Magnetic Field Neutron Star at the Disk Accretion
(2025) Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
Только метаданные
Magnetically arrrested disk around a black hole, and jet formation
(2019) Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).The exact time-dependent solution is obtained for a magnetic field growth during a spherically symmetric accretion into a black hole (BH) with a Schwarzschild metric. Magnetic field is increasing with time, changing from the initially uniform into a quasi-radial field. Equipartition between magnetic and kinetic energies in the falling gas is supposed to be established in the developed stages of the flow. Estimates of the synchrotron radiation intensity are presented for the stationary flow. The two-dimensional stationary self-similar magnetohydrodynamic solution is obtained for the matter accretion into BH, in a presence of a large-scale magnetic field, under assumption, that the magnetic field far from the BH is homogeneous. At the symmetry plane perpendicular to the direction of the distant magnetic field, the dense quasi-stationary disk is formed around BH, which structure is determined by dissipation processes. The radiative efficiency of the magnetized disk is very high, reaching ∼ 0.5 Mc ∙ 2. This model of accretion was called recently as a magnetically arrested disk (MAD). Numerical simulations of MAD, and its appearance during accretion into neutron stars are considered and discussed.
Только метаданные
Stellar Critical Parameters in the Uniform Density Approximation
(2025) Bisnovatyi-Kogan, G. S.; Patraman, E. A.; Бисноватый-Коган, Геннадий Семенович
Только метаданные
Free electron gas and electron-positron pair equilibrium in a magnetic field
(2021) Kondratyev, I. A.; Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
© 2021 Uspekhi Fizicheskikh Nauk. All rights reserved.The thermodynamic properties of electron gas under the extreme conditions of high temperature, high matter density, and/or a strong magnetic field largely determine the beha-vior of matter in upper layers of neutron stars and accretion columns of magnetized neutron stars in binary systems. A strong magnetic field in these objects makes the motion of electrons across the field essentially quantum. The possible electron degeneracy and relativism of electrons are also important. When studying accretion onto a magnetar in a binary system, the intensive generation of electron-positron pairs in the quantizing magnetic field should also be taken into account. We consider in detail the thermody namic properties of a gas of free electrons in strong magnetic fields, taking into account their relativism and degeneracy, as well as the equilibrium creation of electron-positron pairs in a high-temperature plasma in the presence of a quantizing magnetic field.
Только метаданные
Cosmological model with interconnection between dark energy and matter
(2021) Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.It is accepted in the present cosmology model that the scalar field, which is responsible for the inflation stage in the early universe, transforms completely into matter, and the accelerated universe expansion is presently governed by dark energy (DE), whose origin is not connected with the inflationary scalar field. We suppose here that dark matter (DM) has a common origin with a small variable component of dark energy (DEV). We suggest that DE may presently have two components, one of which is the Einstein constant Λ, and another, smaller component DEV (ΛV) comes from the remnants of the scalar field responsible for inflation, which gave birth to the origin of presently existing matter. In this note we consider only the stages of the universe expansion after recombination, z≃1100, when DM was the most abundant component of the matter, therefore we suggest for simplicity that a connection exists between DM and DEV so that the ratio of their densities remains constant over all the stages after recombination, ρDM=αρDEV, with a constant α. One of the problems revealed recently in cosmology is a so-called Hubble tension (HT), which is the difference between values of the present Hubble constant, measured by observation of the universe at redshift z≲1, and by observations of a distant universe with CMB fluctuations originated at z∼1100. In this paper we suggest that this discrepancy may be explained by deviation of the cosmological expansion from a standard Lambda-CDM model of a flat universe, due to the action of an additional variable component DEV. Taking into account the influence of DEV on the universe’s expansion, we find the value of α that could remove the HT problem. In order to maintain the almost constant DEV/DM energy density ratio during the time interval at z<1100, we suggest the existence of a wide mass DM particle distribution.