Jeans instability of interstellar gas clouds in the background of weakly interacting massive particles

Criterion of the Jeans instability of interstellar gas clouds which are gravitationally coupled with weakly interacting massive particles is revisited. It is established that presence of the dark matter always reduces the Jeans length, and in turn, Jeans mass of the interstellar gas clouds. Astrophysical implications of this effect are discussed.Comment: version accepted in ApJ, Nov. 1, 1998 issue, vol. 50

On the gravitational stability of a compressed slab of gas in the background of weakly interacting massive particles

Linear stability of an isothermal, pressure-bounded, self-gravitating gas slab which is gravitationally coupled with the background weakly interacting massive particles (WIMPs) is investigated. Analytic dispersion relations describing such a configuration are derived. Two novel, distinct oscillatory modes are found. Astrophysical implications of the results are discussed.Comment: 6 pages, AASTEX aaspp4 style, no figures; submitted to Ap

Phenomenological model of propagation of the elastic waves in a fluid-saturated porous solid with non-zero boundary slip velocity

Zhu & Granick [Phys. Rev. Lett. 87, 096105 (2001)] have recently experimentally established existence of a boundary slip in a Newtonian liquid. They reported typical values of the slip length of the order of few micro-meters. In this light, the effect of introduction of the boundary slip into the theory of propagation of elastic waves in a fluid-saturated porous medium formulated by Biot is investigated. The new model should allow to fit the experimental seismic data in circumstances when Biot's theory fails, as the introduction of phenomenological dependence of the slip velocity upon frequency, which is based on robust physical arguments, adds an additional degree of freedom to the model. If fact, it predicts higher than the Biot's theory values of attenuation coefficients of the both rotational and dilatational waves in the intermediate frequency domain, which is in qualitative agreement with the experimental data. Therefore, the introduction of the boundary slip yields three-fold benefits: (A) Better agreement of theory with an experimental data since the parametric space of the model is larger (includes effects of boundary slip); (B) Possibility to identify types of porous medium and physical situations where boundary slip is important; (C) Constrain model parameters that are related to the boundary slip.Comment: numerical error corrected; J. Acoust. Soc. Am. (accepted

Kinetic model of three component, weakly ionized, collisional plasma with a beam of neutral particles

Kinetic model of three component, weakly ionized, collisional plasma with a beam of neutral particles is developed. New dispersion relations for linear perturbations are derived and analyzed in various limiting cases.Comment: 5 pages, RevTex style, no figure

On the conical refraction of hydromagnetic waves in plasma with anisotropic thermal pressure

A phenomenon analogous to the conical refraction widely known in the crystalooptics and crystaloacoustics is discovered for the magnetohydrodynamical waves in the collisionless plasma with anisotropic thermal pressure. Angle of the conical refraction is calculated for the medium under study which is predicted to be $18^{\circ}26^{\prime}$. Possible experimental corroborating of the discovered phenomenon is discussed.Comment: 6 pages, REVTeX, Accepted in Physics of Plasma

Missing bits of the solar jigsaw puzzle: small-scale, kinetic effects in coronal studies

The solar corona, anomalously hot outer atmosphere of the Sun, is traditionally described by magnetohydrodynamic, fluid-like approach. Here we review some recent developments when, instead, a full kinetic description is used. It is shown that some of the main unsolved problems of solar physics, such as coronal heating and solar flare particle acceleration can be viewed in a new light when the small-scale, kinetic plasma description methods are used.Comment: 10 pages, 6 figure

Dark matter concentration in the galactic center

It is shown that the matter concentration observed through stellar motion at the galactic center (Eckart & Genzel, 1997, MNRAS, 284, 576 and Genzel et al., 1996, ApJ, 472, 153) is consistent with a supermassive object of $2.5 \times 10^6$ solar masses composed of self-gravitating, degenerate heavy neutrinos, as an alternative to the black hole interpretation. According to the observational data, the lower bounds on possible neutrino masses are $m_\nu \geq 12.0$ keV$/c^2$ for $g=2$ or $m_\nu \geq 14.3$ keV$/c^2$ for $g=1$, where $g$ is the spin degeneracy factor. The advantage of this scenario is that it could naturally explain the low X-ray and gamma ray activity of Sgr A$^*$, i.e. the so called "blackness problem" of the galactic center.Comment: ApJ, 500, 591 (1998), AASTEX, aasms4.sty, v2 reference adde

Non-Newtonian effects in the peristaltic flow of a Maxwell fluid

We analyzed the effect of viscoelasticity on the dynamics of fluids in porous media by studying the flow of a Maxwell fluid in a circular tube, in which the flow is induced by a wave traveling on the tube wall. The present study investigates novelties brought about into the classic peristaltic mechanism by inclusion of non-Newtonian effects that are important, for example, for hydrocarbons. This problem has numerous applications in various branches of science, including stimulation of fluid flow in porous media under the effect of elastic waves. We have found that in the extreme non-Newtonian regime there is a possibility of a fluid flow in the direction {\it opposite} to the propagation of the wave traveling on the tube wall.Comment: to Appear in Phys. Rev. E., 01 September 2001 issu