2,270 research outputs found
Nonlinear Debye-Onsager-Relaxation-Effect
The quantum kinetic equation for charged particles in strong electric fields
is used to derive the nonlinear particle flux. The relaxation field is
calculated quantum mechanically up to any order in the applied field provided a
given Maxwellian plasma. The classical limit is given in analytical form. In
the range of weak fields the deformation of the screening cloud is responsible
for the Debye-Onsager relaxation effect.Comment: Proceeding of the 8. International Workshop on Atomic Physics for
Ion-Driven Fusion, Heidelberg 1997, appear in Laser and Particle beam
Femtosecond formation of collective modes due to meanfield fluctuations
Starting from a quantum kinetic equation including the mean field and a
conserving relaxation-time approximation we derive an analytic formula which
describes the time dependence of the dielectric function in a plasma created by
a short intense laser pulse. This formula reproduces universal features of the
formation of collective modes seen in recent experimental data of femtosecond
spectroscopy. The presented formula offers a tremendous simplification for the
description of the formation of quasiparticle features in interacting systems.
Numerical demanding treatments can now be focused on effects beyond these gross
features found here to be describable analytically.Comment: 4 pages 3 figures, PRB in pres
Formation of correlations in strongly coupled plasmas
The formation of binary correlations in plasma is studied from the quantum
kinetic equation. It is shown that this formation is much faster than
dissipation due to collisions. In a hot (dense) plasma the correlations are
formed on the scale of inverse plasma frequency (Fermi energy). We derive
analytical formulae for the time dependency of the potential energy which
measures the extent of correlations. We discuss the dynamical formation of
screening and compare with the statical screened result. Comparisons are made
with molecular dynamic simulations.Comment: Proceedings of the 8th International Workshop on Atomic Physics for
Ion-Driven Fusion, Heidelberg 1997, appear in Laser and Particle Beam
Debye-Onsager-Relaxation-Effect beyond linear Response and Antiscreening in Plasma Systems
The quantum kinetic equation for charged particles in strong electric fields
is derived and analyzed with respect to the particle flux. It is found that the
applied electric field is screened nonlinearly. The relaxation field is
calculated completely quantum mechanically and up to any order in the applied
field. The classical limit is given in analytical form. In the range of weak
fields the deformation of the screening cloud is responsible for the
Debye-Onsager relaxation effect. The result beyond linear response presented
here allows to investigate a field regime where no screening cloud is present.
The descreening field is determined as a function of thermal energy density of
the plasma. For stronger fields the moving charge is accelerated by accumulated
opposite charges in front of the particle. This can be understood in analogue
to the accoustic Doppler effect. A critical field strength is presented up to
which value a thermalized plasma is possible. The range of applicability of the
treatment is discussed with respect to applied field strength and space
gradients.Comment: text and 2 figures appear in Contrib. to Plasma Physic
Reversed Currents in Charged Liquid Bridges
The velocity profile in a water bridge is reanalyzed. Assuming hypothetically
that the bulk charge has a radial distribution, a surface potential is formed
that is analogous to the Zeta potential. The Navier Stokes equation is solved,
neglecting the convective term; then, analytically and for special field and
potential ranges, a sign change of the total mass flow is reported caused by
the radial charge distribution
Quasiparticle parameterization of meanfields, Galilei invariance and universal conserving response functions
The general possible form of meanfield parameterization in a running frame in
terms of current, energy and density functionals are examined under the
restrictions of Galilean invariance. It is found that only two
density-dependent parameters remain which are usually condensed in a
position-dependent effective mass and the selfenergy formed by current and
mass. The position-dependent mass induces a position-dependent local current
which is identified for different nonlinear frames. In a second step the
response to an external perturbation and relaxation towards a local equilibrium
is investigated. The response function is found to be universal in the sense
that the actual parameterization of the local equilibrium does not matter and
is eliminated from the theory due to the conservation laws. The explicit form
of the response with respect to density, momentum and energy is derived. The
compressibility sum rule as well as the sum rule by first and third-order
frequency moments are proved analytically to be fulfilled simultaneously. The
results are presented for Bose- or Fermi systems in one- two and three
dimensions.Comment: Phys Rev E in pres
Dynamical charge and pseudospin currents in graphene and possible Cooper pair formation
Based on the quantum kinetic equations for systems with SU(2) structure,
regularization-free density and pseudospin currents are calculated in graphene
realized as the infinite mass-limit of electrons with quadratic dispersion and
a proper spin-orbit coupling. Correspondingly the currents possess no
quasiparticle part but only anomalous parts. The intraband and interband
conductivities are discussed with respect to magnetic fields and magnetic
domain puddles. It is found that the magnetic field and meanfield of domains
can be represented by an effective Zeeman field. For large Zeeman fields the
dynamical conductivities become independent of the density and are universal in
this sense. The different limits of vanishing density, relaxation, frequency,
and Zeeman field are not interchangeable. The optical conductivity agrees well
with the experimental values using screened impurity scattering and an
effective Zeeman field. The universal value of Hall conductivity is shown to be
modified due to the Zeeman field. The pseudospin current reveals an anomaly
since a quasiparticle part appears though it vanishes for particle currents.
The density and pseudospin response functions to an external electric field are
calculated and the dielectric function is discussed with respect to collective
excitations. A frequency and wave-vector range is identified where the
dielectric function changes sign and the repulsive Coulomb potential becomes
effectively attractive allowing Cooper pairing.Comment: revisions in tex
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