1,621 research outputs found
Fluctuation relations for a driven Brownian particle
We consider a driven Brownian particle, subject to both conservative and
non-conservative applied forces, whose probability evolves according to the
Kramers equation. We derive a general fluctuation relation, expressing the
ratio of the probability of a given Brownian path in phase space with that of
the time-reversed path, in terms of the entropy flux to the heat reservoir.
This fluctuation relation implies those of Seifert, Jarzynski and
Gallavotti-Cohen in different special cases
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
Using the de Haas-van Alphen effect to map out the closed three-dimensional Fermi surface of natural graphite
The Fermi surface of graphite has been mapped out using de Haas van Alphen
(dHvA) measurements at low temperature with in-situ rotation. For tilt angles
between the magnetic field and the c-axis, the majority
electron and hole dHvA periods no longer follow the behavior
demonstrating that graphite has a 3 dimensional closed Fermi surface. The Fermi
surface of graphite is accurately described by highly elongated ellipsoids. A
comparison with the calculated Fermi surface suggests that the SWM trigonal
warping parameter is significantly larger than previously thought
Hard colloidal rods near a soft wall: wetting, drying, and symmetry breaking
Within an Onsager-like density functional theory we explore the thermodynamic
and structural properties of an isotropic and nematic fluid of hard needle-like
colloids in contact with a hard substrate coated with a soft short-ranged
attractive or repulsive layer. As a function of the range and the strength of
the soft interactions we find wetting and drying transitions, a pre-drying
line, and a symmetry-breaking transition from uniaxial to biaxial in the
wetting and drying film.Comment: 7 pages, 2 figure
Electroviscous effects of simple electrolytes under shear
On the basis of a hydrodynamical model analogous to that in critical fluids,
we investigate the influences of shear flow upon the electrostatic contribution
to the viscosity of binary electrolyte solutions in the Debye-H\"{u}ckel
approximation. Within the linear-response theory, we reproduce the classical
limiting law that the excess viscosity is proportional to the square root of
the concentration of the electrolyte. We also extend this result for finite
shear. An analytic expression of the anisotropic structure factor of the charge
density under shear is obtained, and its deformation at large shear rates is
discussed. A non-Newtonian effect caused by deformations of the ionic
atmosphere is also elucidated for . This finding
concludes that the maximum shear stress that the ionic atmosphere can support
is proportional to , where , and
are, respectively, the shear rate, the Debye screening
length and the Debye relaxation time with being the relative diffusivity at
the infinite dilution limit of the electrolyte.Comment: 13pages, 2figure
Anomalous magneto-oscillations and spin precession
A semiclassical analysis based on concepts developed in quantum chaos reveals
that anomalous magneto-oscillations in quasi two-dimensional systems with
spin-orbit interaction reflect the non-adiabatic spin precession of a classical
spin vector along the cyclotron orbits.Comment: 4 pages, 2 figure
Fluctuation-dissipation theorem and quantum tunneling with dissipation at finite temperature
A reformulation of the fluctuation-dissipation theorem of Callen and Welton
is presented in such a manner that the basic idea of Feynman-Vernon and
Caldeira -Leggett of using an infinite number of oscillators to simulate the
dissipative medium is realized manifestly without actually introducing
oscillators. If one assumes the existence of a well defined dissipative
coefficient which little depends on the temperature in the energy
region we are interested in, the spontanous and induced emissions as well as
induced absorption of these effective oscillators with correct Bose
distribution automatically appears.
Combined with a dispersion relation, we reproduce the tunneling formula in
the presence of dissipation at finite temperature without referring to an
explicit model Lagrangian. The fluctuation-dissipation theorem of Callen-Welton
is also generalized to the fermionic dissipation (or fluctuation) which allows
a transparent physical interpretation in terms of second quantized fermionic
oscillators. This fermionic version of fluctuation-dissipation theorem may
become relevant in the analyses of, for example, fermion radiation from a black
hole and also supersymmetry at the early universe.Comment: 19 pages. Phys. Rev. E (in press
Nematic-Isotropic Spinodal Decomposition Kinetics of Rod-like Viruses
We investigate spinodal decomposition kinetics of an initially nematic
dispersion of rod-like viruses (fd virus). Quench experiments are performed
from a flow-stabilized homogeneous nematic state at high shear rate into the
two-phase isotropic-nematic coexistence region at zero shear rate. We present
experimental evidence that spinodal decomposition is driven by orientational
diffusion, in accordance with a very recent theory.Comment: 17 pages, 6 figures, accepted in Phys. Rev.
On the calculation of the self-diffusion coefficient of interacting Brownian particles
We consider two ways to calculate the self-diffusion coefficient of interacting Brownian particles. The first approach is based on the calculation of the mean square displacement of a Brownian particle starting from the Smoluchowski equation. In the second approach the self-diffusion
coefficient is obtained as the product of the thermodynamic driving force and the mobility. The advantages and limitations of the two methods are discussed
Entanglement perturbation theory for the quantum ground states in two dimensions
A simple, general and practically exact method, Entanglement Perturbation
Theory (EPT), is formulated to calculate the ground states of 2D macroscopic
quantum systems with translational symmetry. An emphasis will be placed on the
applicability of EPT to fermions. We will discuss some preliminary evidences
which indicate a potential of EPT
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