403 research outputs found
Linear Response for Confined Particles
The dynamics of fluctuations is considered for electrons near a positive ion
or for charges in a confining trap. The stationary nonuniform equilibrium
densities are discussed and contrasted. The linear response function for small
perturbations of this nonuniform state is calculated from a linear Markov
kinetic theory whose generator for the dynamics is exact in the short time
limit. The kinetic equation is solved in terms of an effective mean field
single particle dynamics determined by the local density and dynamical
screening by a dielectric function for the non-uniform system. The
autocorrelation function for the total force on the charges is discussed.Comment: 4 pages, 1 figure. Results presented at the "International Conference
on Strongly Coupled Coulomb Systems", Camerino, Italy, July 2008. Submitted
for publication in the conference proceedings (special issue of Journal of
Physics A
Transport Far From Equilibrium --- Uniform Shear Flow
The BGK model kinetic equation is applied to spatially inhomogeneous states
near steady uniform shear flow. The shear rate of the reference steady state
can be large so the states considered include those very far from equilibrium.
The single particle distribution function is calculated exactly to first order
in the deviations of the hydrodynamic field gradients from their values in the
reference state. The corresponding non-linear hydrodynamic equaitons are
obtained and the set of transport coefficients are identified as explicit
functions of the shear rate. The spectrum of the linear hydrodynamic equation
is studied in detail and qualitative differences from the spectrum for
equilibrium fluctuations are discussed. Conditions for instabilities at long
wavelengths are identified and disccused.Comment: 32 pages, 1 figure, RevTeX, submitted to Phys. Rev.
Nonlinear response of electrons to a positive ion
Electric field dynamics at a positive ion imbedded in an electron gas is
considered using a semiclassical description. The dependence of the field
autocorrelation function on charge number is studied for strong ion-electron
coupling via MD simulation. The qualitative features for larger charge numbers
are a decreasing correlation time followed by an increasing anticorrelation.
Stopping power and related transport coefficients determined by the time
integral of this correlation function result from the competing effects of
increasing initial correlations and decreasing dynamical correlations. An
interpretation of the MD results is obtained from an effective single particle
model showing good agreement with the simulation results.Comment: To be published in the proceedings of the International Workshop on
Strongly Coupled Coulomb Systems, Journal of Physics
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