279 research outputs found
Kadanoff-Baym Equations with Initial Correlations
The Kadanoff-Baym equations (KBE) are usually derived under the assumption of
the weakening of initial correlations (Bogolyubov's condition) and, therefore,
fail to correctly describe the short time behavior. We demonstrate that this
assumption is not necessary. Using functional derivatives techniques, we
present a straightforward generalization of the KBE which allows to include
arbitrary initial correlations and which is more general than previous
derivations. As a result, an additional collision integral is obtained which is
being damped out after a few collisions. Our results are complemented with
numerical investigations showing the effect of initial correlations.Comment: 10 pages, 3 figures, to be published in ``Progress in Nonequilibrium
Green's Functions'', M. Bonitz (Ed.), World Scientific, Singapore 2000, uses
sprocl.st
Fluid Modes of a Spherically Confined Yukawa Plasma
The normal modes of a three-dimensional Yukawa plasma in an isotropic,
harmonic confinement are investigated by solving the linearized cold fluid
equations. The eigenmodes are found analytically and expressed in terms of
hypergeometric functions. It is found that the mode frequencies solely depend
on the dimensionless plasma parameter , where is the plasma
radius and the inverse screening length. The eigenfrequencies increase
monotonically with and saturate in the limit . Compared
with the results in the Coulomb limit~[D. H. E. Dubin, Phys. Rev. Lett.
\textbf{66}, 2076 (1991)], we find a new class of modes characterized by the
number which determines the number of radial nodes in the perturbed
potential. These modes originate from the degenerate bulk modes of the Coulomb
system. Analytical formulas for the eigenfrequencies are derived for limiting
cases
Ferromagnetic behavior in magnetized plasmas
We consider a low-temperature plasma within a newly developed MHD Fluid
model. In addition to the standard terms, the electron spin, quantum particle
dispersion and degeneracy effects are included. It turns out that the electron
spin properties can give rise to Ferromagnetic behavior in certain regimes. If
additional conditions are fulfilled, a homogenous magnetized plasma can even be
unstable. This happen in the low-temperature high-density regime, when the
magnetic properties associated with the spin can overcome the stabilizing
effects of the thermal and Fermi pressure, to cause a Jeans like instability.Comment: 4 pages, 1 figur
Dynamic ion structure factor of warm dense matter
The dynamics of the ion structure in warm dense matter is determined by molecular dynamics simulations using an effective ion-ion potential. This potential is obtained from ab initio simulations and has a strong short-range repulsion added to a screened Coulomb potential. Models based on static or dynamic local field corrections are found to be insufficient to describe the data. An extended Mermin approach, a hydrodynamic model, and the method of moments with local constraints are capable of reproducing the numerical results but have rather limited predictive powers as they all need some numerical data as input. The method of moments is found to be the most promising
Coupled mode effects on energy transfer in weakly coupled, two-temperature plasmas
The effects of collective modes on the temperature relaxation in fully ionized, weakly coupled plasmas are investigated. A coupled mode (CM) formula for the electron-ion energy transfer is derived within the random phase approximation and it is shown how it can be evaluated using standard methods. The CM rates are considerably smaller than rates based on Fermi's golden rule for some parameters and identical for others. It is shown how the CM effects are connected to the occurrence of ion acoustic modes and when they occur. Interestingly, CM effects occur also for plasmas with very high electron temperatures; a regime, where the Landau–Spitzer approach is believed to be accurate
Short time dynamics with initial correlations
The short-time dynamics of correlated systems is strongly influenced by
initial correlations giving rise to an additional collision integral in the
non-Markovian kinetic equation. Exact cancellation of the two integrals is
found if the initial state is thermal equilibrium which is an important
consistency criterion. Analytical results are given for the time evolution of
the correlation energy which are confirmed by comparisons with molecular
dynamics simulations (MD)
Self-diffusion in sheared colloidal suspensions: violation of fluctuation-dissipation relation
Using memory-function formalism we show that in sheared colloidal suspensions
the fluctuation-dissipation theorem for self-diffusion, i.e. Einstein's
relation between self-diffusion and mobility tensors, is violated and propose a
new way to measure this violation in Brownian Dynamics simulations. We derive
mode-coupling expressions for the tagged particle friction tensor and for an
effective, shear-rate dependent temperature
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