83 research outputs found
Dynamics of unstable sound waves in a non-equilibrium medium at the nonlinear stage
A new dispersion equation is obtained for a non-equilibrium medium with an
exponential relaxation model of a vibrationally excited gas. We have researched
the dependencies of the pump source and the heat removal on the medium
thermodynamic parameters. The boundaries of sound waves stability regions in a
non-equilibrium gas have been determined. The nonlinear stage of sound waves
instability development in a vibrationally excited gas has been investigated
within CSPH-TVD and MUSCL numerical schemes using parallel technologies
OpenMP-CUDA. We have obtained a good agreement of numerical simulation results
with the linear perturbations dynamics at the initial stage of the sound waves
growth caused by instability. At the nonlinear stage, the sound waves amplitude
reaches the maximum value that leads to the formation of shock waves system.Comment: 11 pages, 5 figure
Instability of high-frequency acoustic waves in accretion disks with turbulent viscosity
Dynamics of linear perturbations in a differentially rotating accretion disk
with non-homogeneous vertical structure is investigated. It has been found that
turbulent viscosity results in instability of both pinching oscillations, and
bending modes. Not only the low-frequency fundamental modes, but also the
high-frequency reflective harmonics appear to be unstable. The question of the
limits of applicability of the thin disk model (MTD) is also investigated. The
insignificant distinctions in the dispersion properties of MTD and
three-dimensional model appear for wave numbers k<(1-3)/h (h is the
half-thickness of a disk). In the long-wavelenght limit, the relative
difference between eigenfrequencies of the unstable acoustic mode in the
3D-model and the MTD is smaller than 5%.Comment: Plain TeX, 9 pages, 3 figures (GIF), uses cp-aa.tex, Submitted to
Astron. Astrophy
Self-consistent gas and stellar dynamics of disk galaxies: A problem of dark mass
We present results of numerical modeling made for the galactic stellar and
stellar-gas disk embedded in the spherical halo and bulge. The stellar disk is
simulated by N-body system, the equations of hydrodynamics are solved by
TVD-method. We used TREEcode-algorithm for calculation of a self-gravity in
stellar and gaseous components. The possibility of bars birth in a hot stellar
disk because of gravitational instability of a cold gas component is
investigated. The conditions of occurrence lopsided-galaxies from a
axisymmetric disk as a result of gravitational instability are explored. The
self-consistent models of double bars are constructed and the dynamical
stability of these structures is discussed.Comment: 7 pages 6 figures, conference: 'Progress in Study of Astrophysical
Disks: Collective and Stochastic Phenomena and Computational Tools
Disorder solutions for the free energy of the Ising-like models
For arbitrary Ising-like models of any dimension and Hamiltonians with a
finite support with all possible multispin interactions and boundary conditions
with a shift, the exact value of the free energy in the thermodynamic limit is
obtained at some parametrically specified set of multispin interaction
coefficients. In this case, half of the multispin interaction coefficients and
the coordinates of the special eigenvector corresponding to the largest
eigenvalue of the elementary transfer matrix are parameters, and the second
half of the multispin coefficients is calculated using simple explicit
formulas. For models with Hamiltonians invariant under the reversal of signs of
all spins, the formulas are simplified. As examples of independent interest,
solutions are written for the cases when the support of the Hamiltonian is a
simplex, a cube, the support of the ANNNI model in spaces of 2, 3 and arbitrary
dimensions.Comment: 35 pages, 3 figure
Interaction between collisionless galactic discs and nonaxissymmetric dark matter haloes
Using -body simulations (), we examine how a
non-axisymmetric dark halo affects the dynamical evolution of the structure in
collisionless (stellar) discs. We demonstrate how the model parameters such as
mass of the halo, initial conditions in the disc and the halo axes ratio affect
morphology and kinematics of the stellar discs. We show that a non-axisymmetric
halo can generate a large-scale spiral density pattern in the embedded stellar
disc. The pattern is observed in the disc for many periods of its revolution,
even if the disc is gravitationally over-stable. The growth of the spiral arms
is not accompanied by significant dynamical heating of the disc, irrelevant to
its initial parameters. We also investigate transformation of the dark halo's
shape driven by the long-lived spiral pattern in the disc . We show that the
analysis of the velocity field in the stellar disc and in the spiral pattern
gives us a possibility to figure out the spatial orientation of the
triaxial-shaped dark halo and to measure the triaxiality.Comment: 11 pages, 13 figures, accepted to MNRA
Analysis and prediction of changes in the temperature of the pure freshwater ice column in the Antarctic and the Arctic
This paper investigates the initial boundary value problem for a
non-stationary one-dimensional heat equation that simulates the temperature
distribution in freshwater ice near the Earth's poles. The mathematical model
has been constructed taking into account solid-liquid phase transitions. Data
from meteorological stations were used to determine the model parameters, with
the help of which the necessary physical and thermophysical characteristics of
the computational domain were obtained. For the numerical solution of the
problem, the finite volume method (FVM) was used. For the obtained periodic
regime, the temperature versus depth dependences for each month were plotted,
and the depth of the active layer, as well as the depth of zero annual
amplitudes were found for each meteorological station. A forecast of the ice
temperature regime for 2100 was modeled for three Representative Concentration
Pathway (RCP) scenarios of global warming: moderate RCP2.6, corresponding to
the current emissions of RCP7 and adopted at the Paris Agreement in 2015
RCP1.9. By analyzing the impact of an additional 0,5 degrees Celsius of warming
on other areas, a reduction in the full range of risks to humanity and the
planet as a whole becomes evident with the proper efforts of the global
community. Thus, the conducted modeling has confirmed the need to reduce the
rate of global warming.Comment: 33 pages, 7 figure
Spiral structure of the Milky Way galaxy: observations and theoretical predictions
Using observational data on the kinematical properties and density
distributions of the subsystems of the Milky Way galaxy, we construct a set of
multi-component equilibrium models of its disk. The dynamics of the disk is
studied numerically using collisionless-gaseous numerical simulations. After
approximately one Gyr, a prominent central bar is formed with a semi-axis of
about three kiloparsecs. Outside the central regions, a multi-armed spiral
pattern develops, which can be characterized by the superposition of m=2, 3 and
4-armed spiral patterns. The spiral structure and the bar exist for at least 3
Gyr in our simulations. The presence of the bar in the disk of the MilkyWay
galaxy imposes rather strict limitations on the density distributions in the
subsystems of the MilkyWay galaxy.We find that bar does not form if the radial
scale length of the surface density distribution of the disk is more than 2.6
kpc. Analogously, the formation of bar is suppressed in the Milky Way disk in
models with a massive and compact stellar bulge. If future GAIA observations
confirm the existence of the three-four armed spiral pattern in the disk of the
MilkyWay, this will prove the long-term existence of spiral patterns in
galactic disks.Comment: 6 pages, 3 figures, Conference Modern stellar astronomy-2019, SAO
RAS, October 7-11, 2019 (Submitted: Research in Astronomy and Astrophysics
Formation of Ionization-Cone Structures in Active Galactic Nuclei: II. Nonlinear Hydrodynamic Modelling
In Part I of this paper we described an equilibrium model of a jet in the
gravitational field corresponding to the rigid-rotation region of the galactic
disk. We used linear stability analysis to find the waveguide-resonance
instability of internal gravity waves due to the superreflection of these waves
from the jet boundary. In this part of the paper, we perform nonlinear
numerical 2D and 3D simulations of the development of this instability. We show
that the shocks produced by this instability in the ambient medium of the jet
are localized inside a cone with a large opening angle and are capable of
producing features that are morphologically similar to those observed in
galaxies with active nuclei (NGC 5252 for example).Comment: 10 pages, 9 PS and 4 JPEG figures, published in Astrophysical
Bulleti
The structure and kinematics of AGN with ionization cones
Results of 2D spectral observations for 4 Sy galaxies with ionization cones
are presented. Images in the [OIII] line, velocity fields of the ionized gas,
stellar velocity and velocity dispersion fields were obtained at the SAO RAS 6m
telescope. Non-circular gas motions and Z-shaped emission filaments could be
explained as helical waves located in the ionization cone. This waves are
generated by the hydrodynamical instability due to the velocity break between
galactic ISM and outflowing matter from the AGN engine. The axis of cone lies
close to the direction of a nuclear mini bar.Comment: 9 pages, 4 ps-figures (color), poster was presented at JENAM-2000
(Moscow); Corrected typo
Helical structures in Seyfert galaxies
The Seyfert galaxies with Z-shaped emission filaments in the Narrow Line
Region (NLR) are considered. We assume that observable Z-shaped structures and
velocity pattern of NLR may be explained as tridimensional helical waves in the
ionization cone.Comment: To appear in IAU Colloq. 184, AGN Surveys, ed. R. F. Green, E. Ye.
Khachikian, & D. B. Sanders (San Francisco: ASP), in press. 2 pages, 1 EPS
figur
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