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

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Геннадий Семенович

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Теперь показываю 1 - 10 из 34

Только метаданные
3D Simulation of Anisotropic Heat Transfer in Outer Layers of Magnetized Neutron Stars
(2020) Kondratyev, I. A.; Moiseenko, S. G.; Bisnovatyi-Kogan, G. S.; Glushikhina, M. V.; Бисноватый-Коган, Геннадий Семенович
The results of three-dimensional numerical simulation of heat transfer in the outer layers of magnetized neutron stars are presented. Determining the structure of the magnetic field on a neutron star surface is an important task of modern astrophysics. In the presence of strong magnetic fields, the medium becomes anisotropic, and the laws of heat conduction change. The tensor coefficient of thermal conductivity for magnetized degenerate plasma was obtained by Bisnovatyi-Kogan and Glushikhina by solving the Boltzmann equation with the Chapman-Enskog method. In this paper, the temperature distribution on the surface of a magnetized neutron star is obtained for magnetic fields of the dipolar and quadrupolar type, as well as for their superposition. To numerically solve the stationary temperature distribution problem in the outer layers of a magnetized neutron star, the basic (support) operator numerical method was extended to a three-dimensional case. The problem was solved on the grid which consists of tetrahedra.
Только метаданные
Strong Shock in the Uniformly Expanding Universe with a Spherical Void
(2020) Panafidina, S. A.; Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
© 2020, Pleiades Publishing, Ltd.Abstract: Propagation of a strong shock wave in the expanding universe is studied using approximate analytic and exact numerical solution of self-similar equations. Both solutions have similar properties, which change qualitatively, depending on the adiabatic powers γ. In the interval 1 < γ < γcr ~ 1.16 analytic and numeric solutions fill all the space without any voids and they are rather close to each other. At larger γ > γcr a pressure becomes zero at finite radius, and a spherical void appears around the origin in both solutions. All matter is collected in thin layer behind the shock wave front. The structure of this layer qualitatively depends on γ. At the inner edge of the layer the pressure is always zero, but the density at this edge is jumping from zero to infinity at γ=14 in both solutions.
Только метаданные
First analytical calculation of black hole shadow in McVittie metric
(2020) Tsupko, O. Y.; Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
Cosmic expansion influences the angular size of black hole shadow. The most general way to describe a black hole embedded into an expanding universe is to use the McVittie metric. So far, the exact analytical solution for the shadow size in the McVittie metric, valid for arbitrary law of expansion and arbitrary position of the observer, has not been found. In this paper, we present the first analytical solution for angular size of black hole shadow in McVittie metric as seen by observer comoving with the cosmic expansion. We use a method of matched asymptotic expansions to find approximate solution valid within the entire range of possible positions of observer. As two particular examples, we consider black hole in de Sitter and matter-dominated universe.
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
Two-body problem in presence of cosmological constant
(2019) Merafina, M.; Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
© 2019 World Scientific Publishing Company.We consider the Kepler two-body problem in presence of the cosmological constant . Contrary to the classical case, where finite solutions exist for any angular momentum of the system L, in presence of finite solutions exist only in the interval 0 < L < Llim(). The qualitative picture of the two-body motion is described, and critical parameters of the problem are found. Application is made to the relative motion of the Local Group and Virgo cluster.
Только метаданные
Spectral Distortions in CMB by the Bulk Comptonization Due to Zeldovich Pancakes
(2019) Bisnovatyi-Kogan, G. S.; Бисноватый-Коган, Геннадий Семенович
If the large scale structure of the Universe was created, even partially, via Zeldovich pancakes, than the fluctuations of the CMB radiation should be formed due to bulk comptonization of black body spectrum on the contracting pancake. Approximate formulae for the CMB energy spectrum after bulk comptonization are obtained. The difference between comptonized energy spectra of the CMB due to thermal and bulk comptonozation may be estimated by comparison of the plots for the spectra in these two cases.
Только метаданные
Four tensors determining the heat and electro-conductivities of degenerate electrons in the dense magnetized matter
(2019) 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).A solution is obtained for the Boltzmann equation for a plasma in a magnetic field with strongly degenerate electrons and non-degenerate nuclei. In the Lorentz approximation, the components of the diffusion, thermal diffusion, and diffusion thermoeffect tensors in a non-quantizing magnetic field are calculated. This approximation, in which electron-electron collisions are neglected, is asymptotically accurate for a plasma with highly degenerate electrons. These formulas have a much more complex dependence on the magnetic field than similar dependences in previous publications on this topic.
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
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.
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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.