838 research outputs found
Analysis of the Relaxation Process using Non-Relativistic Kinetic Equation
We study the linearized kinetic equation of relaxation model which was
proposed by Bhatnagar, Gross and Krook (also called BGK model) and solve the
dispersion relation. Using the solution of the dispersion relation, we analyze
the relaxation of the macroscopic mode and kinetic mode. Since BGK model is not
based on the expansion in the mean free path in contrast to the Chapman-Enskog
expansion, the solution can describe accurate relaxation of initial disturbance
with any wavelength. This non-relativistic analysis gives suggestions for our
next work of relativistic analysis of relaxation.Comment: 18 pages, 14 figures, accepted for publication in Prog. Theor. Phys
Evolutionary Conditions in the Dissipative MHD System Revisited
The evolutionary conditions for the dissipative continuous
magnetohydrodynamic (MHD) shocks are studied. We modify Hada's approach in the
stability analysis of the MHD shock waves. The matching conditions between
perturbed shock structure and asymptotic wave modes shows that all types of the
MHD shocks, including the intermediate shocks, are evolutionary and perturbed
solutions are uniquely defined. We also adopt our formalism to the MHD shocks
in the system with resistivity without viscosity, which is often used in
numerical simulation, and show that all types of shocks that are found in the
system satisfy the evolutionary condition and perturbed solutions are uniquely
defined. These results suggest that the intermediate shocks may appear in
reality.Comment: 13 pages, 4 figures, accepted for publication in Prog. Theor. Phy
Self-Sustained Turbulence without Dynamical Forcing: A Two-Dimensional Study of a Bistable Interstellar Medium
In this paper, the nonlinear evolution of a bistable interstellar medium is
investigated using two-dimensional simulations with a realistic cooling rate,
thermal conduction, and physical viscosity. The calculations are performed
using periodic boundary conditions without any external dynamical forcing. As
the initial condition, a spatially uniform unstable gas under thermal
equilibrium is considered. At the initial stage, the unstable gas quickly
segregates into two phases, or cold neutral medium (CNM) and warm neutral
medium (WNM). Then, self-sustained turbulence with velocity dispersion of
is observed in which the CNM moves around in the
WNM. We find that the interfacial medium (IFM) between the CNM and WNM plays an
important role in sustaining the turbulence. The self-sustaining mechanism can
be divided into two steps. First, thermal conduction drives fast flows
streaming into concave CNM surfaces towards the WNM. The kinetic energy of the
fast flows in the IFM is incorporated into that of the CNM through the phase
transition. Second, turbulence inside the CNM deforms interfaces and forms
other concave CNM surfaces, leading to fast flows in the IFM. This drives the
first step again and a cycle is established by which turbulent motions are
self-sustained.Comment: 14 pages, 15 figures, accepted by The Astrophysical Journa
- β¦