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.Comment: REVTEX4, 20 pages, 2 figure

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.-yComment: 18 page

Interaction of Grains in Dusty Plasmas

Plasma absorption by dust grains results in anisotropy of plasma distribution function. This yields the effective attractive interaction between grains. Here a brief teview of physical properties of this interaction is given. First we demonstrate that there is the attracting force between two grains obeying the inverse square low. Then a set of kinetic equations taking into account both attracting and repulsing forces is proposed. We study a simple model of a dust cloud consisting of finite number of grains. It is shown that even within gaseous approximation a dust cloud is a compact object with a sharp boundary. Finally, we discuss recent experiments aimed to detecting the attractive force between massive bodie

Two viruses competition in the SIR model of epidemic spread: application to COVID-19

The SIR model of the epidemic spread is used for consideration the problem of the competition of two viruses having different contagiousness. It is shown how the more contagious strain replaces over time the less contagious one. In particular the results can be applied to the current situation when the omicron strain appeared in population affected by the delta strain.PACS number(s)02.50.-r, 05.60.-k, 82.39.-k, 87.19.Xx</jats:sec

Strain-stream model of epidemic spread in application to COVID-19

The recently developed model of the epidemic spread of two virus stains in a closed population is generalized for situation typical for the couple of strains delta and omicron, when there is high probability for omicron infection enough soon after recovering from delta infection. This model can be considered as some kind of weave of SIR and SIS models for the case of competition of two strains of the same virus having different contagiousness in a population.PACS number(s)02.50.-r, 05.60.-k, 82.39.-k, 87.19.Xx</jats:sec