Searcharxiv⌕ Search

arXiv subjects

S. A. Trigger

Publications and source records attributed to S. A. Trigger.

52 records · Page 3Linked to original sources
arXiv2009

Anomalous Kinetics in Velocity Space: equations and models

Equation for anomalous diffusion in momentum space, recently obtained in the recent paper (S.A. Trigger, ArXiv 0907.2793 v1, [cond-matt. stat.-mech.], 16 July 2009) is solved for the stationary and non-stationary cases on basis of the appropriate probability transition function (PTF). Consideration of diffusion for heavy particles in a gas of the light particles can be essentially simplified due to small ratio of the masses of the particles. General equation for the distribution of the light particles, shifted in velocity space, is also derived. For the case of anomalous diffusion in momentum space the closed equation is formulated for the Fourier-component of the momentum distribution function. The effective friction and diffusion coefficients are found also for the shifted distribution. If the appropriate integrals are finite the equations derived in the paper are applicable for both cases: the PT-function with the long tails and the short range PT-functions in momentum space. In the last case the results are equivalent to the Fokker-Planck equation. Practically the new results of this paper are applicable to strongly non-equilibrium physical systems.

cond-mat.stat-mech↗
arXiv2009

Anomalous Diffusion in Velocity Space

The problem of anomalous diffusion in the momentum space is considered on the basis of the appropriate probability transition function (PTF). New general equation for description of the diffusion of heavy particles in the gas of the light particles is formulated on basis of the new approach similar to one in coordinate space (S. Trigger et al.). The obtained results permit to describe the various situations when the probability transition function (PTF) has a long tail in the momentum space. The effective friction and diffusion coefficients are found.

cond-mat.stat-mech↗
arXiv2009

The Possibility of Existence of an Energy Gap in the One-Particle Excitation Spectrum of He II

Possibility for coexistence of a phonon and one-particle spectra in ${}^4He$ at all temperatures including temperatures below the $λ$ - point is shown. An approach developed to consider the problem of the weakly imperfect Bose gas results in the existence of a gap in the one-particle (one-atom) excitation spectrum below the transition point. Thus, the microscopic model of He II turns out to differ both from the model initially suggested by Landau and from the Bogolyubov model accepted at present. Analysis of the experimental data obtained by measuring enthalpy and the part of helium atoms condensed in the state with the momentum $p=0$ enabled to estimate the size of the gap. It turned out to be approximately equal to 0.31 K at zero temperature.

cond-mat.supr-con↗
arXiv2007

Non-Planck equilibrium radiation in plasma model of early Universe

Consideration of the adiabatic character of radiation expansion in early Universe leads to the conclusion that equilibrium distribution of the primordial radiation in the presence of charged particles could be different from the Planck distribution in some regions of the spectrum. The equilibrium distribution of electromagnetic radiation (the black body radiation) is generalized for the system containing an extremely dense fully ionized plasma. The conditions of the adiabatic expansion of radiation for the model of the early Universe are found.

cond-mat.stat-mech↗
arXiv2006

Generalized Master Equation with Two Times: Diffusion in External Field

The generalized master equation with two times, introduced in earlier, applies to the problem of diffusion in an time-dependent (in general inhomogeneous) external field. We consider the case of the quasi Fokker-Planck approximation, when the probability transition function for diffusion (PTD-function) does not possess a long tail in coordinate space and can be expanded as the function of instantaneous displacements. The more complicated case of the long tails in PTD will be discussed separately.

cond-mat.soft↗
arXiv2006

Remarks on the Nyquist and Callen-Welton Theorems

The connection of the Callen-Welton and Nyquist fluctuation-dissipation relations is considered for plasma-like classical and quantum systems. The conditions for appearance of the dissipative parameters in the equilibrium current-current correlation function are investigated. The paper presents the arguments for the restrictions of the Nyquist theorem and against violation of the Callen-Welton theorem in the quantum case.

cond-mat.stat-mech↗
arXiv2004

Velocity-Dependent Friction and Diffusion for Grains in Neutral Gases, Dusty Plasmas and Active Systems

A self-consistent and universal description of friction and diffusion for Brownian particles (grains) in different systems, as a gas with Boltzmann collisions, dusty plasma with ion absorption by grains, and for active particles (e.g., cells in biological systems) is suggested on the basis of the appropriate Fokker-Planck equation. Restrictions for application of the Fokker-Planck equation to the problem of velocity-dependent friction and diffusion coefficients are found. General description for this coefficient is formulated on the basis of master equation. Relation of the diffusion coefficient in the coordinate and velocity spaces is found for active (capable to transfer momentum to the ambient media) and passive particles in the framework of the Fokker-Planck equation. The problem of anomalous space diffusion is formulated on the basis of the appropriate probability transition (PT) function. The method of partial differentiation is avoided to construct the correct probability distributions for arbitrary distances, what is important for applications to different stochastic problems. Generale equation for time-dependent PT function is formulated and discussed. Generalized friction in the velocity space is determined and applied to describe the friction force itself as well as the drag force in the case of a non-zero driven ion velocity in plasmas. The negative friction due to ion scattering on grains exists and can be realized for the appropriate experimental conditions.

cond-mat.stat-mech↗
arXiv2003

Surface-active dust in a plasma sheath

The inhomogeneity of the plasma pressure near a conducting electrode is a cause for introducing the surface tension associated with the plasma-electrode interface. We evaluate the dependence of the surface tension on the density of the charged dust immersed in the plasma sheath. In a wide range of parameters, the surface tension turns out to be an increasing function of the dust density.

physics.plasm-ph↗
arXiv2003

Fokker-Planck Equation for Boltzmann-type and Active Particles: transfer probability approach

Fokker-Planck equation with the velocity-dependent coefficients is considered for various isotropic systems on the basis of probability transition (PT) approach. This method provides the self-consistent and universal description of friction and diffusion for Brownian particles. Renormalization of the friction coefficient is shown to occur for two dimensional (2-D) and three dimensional (3-D) cases, due to the tensorial character of diffusion. The specific forms of PT are calculated for the Boltzmann-type of collisions and for the absorption-type of collisions (the later are typical for dusty plasmas and some other systems). Validity of the Einstein's relation for the Boltzmann-type collisions is analyzed for the velocity-dependent friction and diffusion coefficients. For the Boltzmann-type collisions in the region of very high grain velocity as well as it is always for non-Boltzmann collisions, such as, e.g., absorption collisions, the Einstein relation is violated, although some other relations (determined by the structure of PT) can exist. The generalized friction force is investigated in dusty plasma in the framework of the PT approach. The relation between this force, negative collecting friction force and scattering and collecting drag forces is established.+AFwAXA- The concept of probability transition is used to describe motion of active particles in an ambient medium. On basis of the physical arguments the PT for a simple model of the active particle is constructed and the coefficients of the relevant Fokker-Planck equation are found. The stationary solution of this equation is typical for the simplest self-organized molecular machines.+AFwAXA- PACS number(s): 52.27.Lw, 52.20.Hv, 52.25.Fi, 82.70.-y

physics.plasm-ph↗
arXiv2002

Brownian Motion of Grains and Negative Friction in Dusty Plasmas

Within the approximation of dominant charging collisions the explicit microscopic calculations of the Fokker-Planck kinetic coefficients for highly-charged grains moving in plasma are performed. It is shown that due to ion absorption by grain the friction coefficient can be negative and the appropriate threshold value of the grain charge is found. The stationary solutions of the Fokker-Planck equation with the velocity dependent kinetic coefficient are obtained and the considerable deviation of such solutions from the Maxwellian distribution is established.

physics.plasm-ph↗
arXiv2001

Internal energy of high density Hydrogen: Analytical approximations compared with path integral Monte Carlo calculations

The internal energy of high-density hydrogen plasmas in the temperature range $T = 10,000 ... 50,000 K$ is calculated by two different analytical approximation schemes (method of effective ion-ion interaction potential - EIIP and Padé approach within the chemical picture - PACH) and compared with path integral Monte Carlo results. Reasonable agreement between the results obtained from the three independent calculations is found, the reasons for still existing differences is investigated. Interesting high density phenomena such as the formation of clusters and the onset of crystallization are discussed.

physics.plasm-ph↗
arXiv2001

Rotational kinetics of absorbing dust grains in neutral gas

We study the rotational and translational kinetics of massive particulates (dust grains) absorbing the ambient gas. Equations for microscopic phase densities are deduced resulting in the Fokker-Planck equation for the dust component. It is shown that although there is no stationary distribution, the translational and rotational temperatures of dust tend to certain values, which differ from the temperature of the ambient gas. The influence of the inner structure of grains on rotational kinetics is also discussed.

physics.plasm-ph↗
arXiv1999

Stationary Velocity and Charge Distributions of Grains in Dusty Plasmas

Within the kinetic approach velocity and charge distributions of grains in stationary dusty plasmas are calculated and the relations between the effective temperatures of such distributions and plasma parameters are established. It is found that the effective temperature which determines the velocity grain distribution could be anomalously large due to the action of accelerating ionic bombarding force. The possibility to apply the results obtained to the explanation of the increasing grain temperature in the course of the Coulomb-crystal melting by reduction of the gas pressure is discussed. This paper was received by Phys.Rev.Lett. on 11 August 1999. As potential referees the authors offered to Editor the following persons: V.N.Tsytovich, Russia; R.Bingham, UK; D.Resendes, Portugal; G.Morfill, P.Shukla, Y.M.Yu., Germany.

physics.plasm-ph↗
arXiv1999

Inhomogeneity of dusty crystals and plasma diagnostics

Real dusty crystals are inhomogeneous due to the presence of external forces. We suggest approximations for calculations of different types of inhomogeneous DC (chain and DC with a few slabs) in the equilibrium state. The results are in a good agreement with experimental results and can be used as an effective diagnostic method for many dusty systems.

physics.plasm-ph↗