arXiv subjects

A. D. Rogava

Publications and source records attributed to A. D. Rogava.

6 recordsLinked to original sources

arXiv2004

Is the solar corona nonmodally self-heated?

Recently it was pointed out that nonmodally (transiently and/or adiabatically) pre-amplified waves in shear flows, undergoing subsequent viscous damping, can ultimately heat the ambient flow. The key ingredient of this process is the ability of waves to grow, by extracting energy from the spatially inhomogeneous mean flow. In this paper we examine this mechanism in the context of the solar coronal plasma flows. "Self-heating" (SH) processes are examined when both viscous damping and magnetic resistivity are at work. We show that if the plasma viscosity is in the favorable range of values the asymptotic SH rate in these flows can be quite substantial.

astro-ph↗

arXiv1996

Acoustic perturbations in special-relativistic parallel flows

Acoustic perturbations in a parallel relativistic flow of an inviscid fluid are considered. The general expression for the frequency of the sound waves in a uniformly (with zero shear) moving medium is derived. It is shown that relativity evokes a difference in the frequencies of the sound-type perturbations propagating along and against the current. Besides, it is shown that the perturbations are not purely irrotational as they are in nonrelativistic case. For a non-uniformly (with nonzero shear) moving fluid a general set of equations, describing the evolution of the acoustic perturbations in relativistic sheared flows, is obtained and analysed when the temperature is nonrelativistic. It is shown that, like the nonrelativistic case, in the new system: (a) the excitation of vortical, transiently growing perturbations, and (b) the excitation of sound-type perturbations, extracting the kinetic energy of the background flow, are possible. It is demonstrated that the relativistic character of the motion significantly intensifies the efficiency of both these processes. Finally, the possible relevance of this study to processes in astrophysical shear flows is pointed out.

astro-ph↗

arXiv1996

"Centrifugal force: A gedanken experiment" - new surprises

A recently proposed "gedanken experiment" [G.Z. Machabeli and A.D. Rogava. Phys. Rev. A {\bf 50}, 98 (1994)], exhibiting surprising behavior, is reexamined. A description of this behavior in terms of the laboratory inertial frame is presented, avoiding uncertainties arising due to a definition of a centrifugal force in relativity. The surprising analogy with the radial geodesic motion in Schwarzschild geometry is discovered. The definition of the centrifugal force, suggested by J.C. Miller and M.A. Abramowicz, is discussed.

gr-qc↗

arXiv1996

General-relativistic Model of Magnetically Driven Jet

The general scheme for the construction of the general-relativistic model of the magnetically driven jet is suggested. The method is based on the usage of the 3+1 MHD formalism. It is shown that the critical points of the flow and the explicit radial behavior of the physical variables may be derived through the jet ``profile function."

gr-qc↗

arXiv1996

Special-relativistic model flows of viscous fluid

Two, the most simple cases of special-relativistic flows of a viscous, incompressible fluid are considered: plane Couette flow and plane Poiseuille flow. Considering only the regular motion of the fluid we found the distribution of velocity in the fluid (velocity profiles) and the friction force, acting on immovable wall. The results are expressed through simple analytical functions for the Couette flow, while for the Poiseiulle flow they are expressed by higher transcendental functions (Jacobi's elliptic functions).

plasm-ph↗

arXiv1996

Electrostatic Ion Perturbations in Unmagnetized Plasma Shear Flow

The electrostatic perturbations in an unmagnetized, non-isothermal ($T_i{\ll}T_e$) electron-ion plasma shear flow are considered. New physical effects, arising due to the non-normality of linear dynamics, are described. It is shown that the velocity shear induces the extraction of the mean flow energy by the acoustic perturbations (ion-sound waves). The influence of the medium dispersion, rising due to the violation of quasineutrality for perturbations, is examined. It is shown that in the course of the evolution ion-sound waves turn into ion plasma oscillations. New class of nonperiodic, electrostatic perturbations (with vortical motion of ion component), characterized by the intense energy exchange with the mean flow, is also described.

plasm-ph↗