1,622 research outputs found
Hydrodynamic Modes in a Trapped Strongly Interacting Fermi Gases of Atoms
The zero-temperature properties of a dilute two-component Fermi gas in the
BCS-BEC crossover are investigated. On the basis of a generalization of the
variational Schwinger method, we construct approximate semi-analytical formulae
for collective frequencies of the radial and the axial breathing modes of the
Fermi gas under harmonic confinement in the framework of the hydrodynamic
theory. It is shown that the method gives nearly exact solutions.Comment: 11 page
Dynamics of the Free Surface of a Conducting Liquid in a Near-Critical Electric Field
Near-critical behavior of the free surface of an ideally conducting liquid in
an external electric field is considered. Based on an analysis of three-wave
processes using the method of integral estimations, sufficient criteria for
hard instability of a planar surface are formulated. It is shown that the
higher-order nonlinearities do not saturate the instability, for which reason
the growth of disturbances has an explosive character.Comment: 19 page
Calculation of shear viscosity using Green-Kubo relations within a parton cascade
The shear viscosity of a gluon gas is calculated using the Green-Kubo
relation. Time correlations of the energy-momentum tensor in thermal
equilibrium are extracted from microscopic simulations using a parton cascade
solving various Boltzmann collision processes. We find that the pQCD based
gluon bremsstrahlung described by Gunion-Bertsch processes significantly lowers
the shear viscosity by a factor of 3-8 compared to elastic scatterings. The
shear viscosity scales with the coupling as 1/(alpha_s^2\log(1/alpha_s)). For a
constant coupling constant the shear viscosity to entropy density ratio has no
dependence on temperature. Replacing the pQCD-based collision angle
distribution of binary scatterings by an isotropic form decreases the shear
viscosity by a factor of 3.Comment: 17 pages, 5 figure
Imaginary-time formulation of steady-state nonequilibrium in quantum dot models
We examine the recently proposed imaginary-time formulation for strongly
correlated steady-state nonequilibrium for its range of validity and discuss
significant improvements in the analytic continuation of the Matsubara voltage
as well as the fermionic Matsubara frequency. The discretization error in the
conventional Hirsch-Fye algorithm has been compensated in the Fourier
transformation with reliable small frequency behavior of self-energy. Here we
give detailed discussions for generalized spectral representation ansatz by
including high order vertex corrections and its numerical analytic continuation
procedures. The differential conductance calculations agree accurately with
existing data from other nonequilibrium transport theories. It is verified
that, at finite source-drain voltage, the Kondo resonance is destroyed at bias
comparable to the Kondo temperature. Calculated coefficients in the scaling
relation of the zero bias anomaly fall within the range of experimental
estimates.Comment: 16 pages, 10 figures, Comparison to other theories adde
Anomalous Hall effect for the phonon heat conductivity in paramagnetic dielectric
The theory of anomalous Hall effect for the heat transfer in a paramagnetic
dielectric, discovered experimentally in [1], is developed. The appearance of
the phonon heat flux normal to both the temperature gradient and the magnetic
field is connected with the interaction of magnetic ions with the crystal field
oscillations. In crystals with an arbitrary phonon spectrum this interaction
creates the elliptical polarization of phonons. The kinetics related to phonon
scattering induced by the spin-phonon interaction determines an origin of the
off-diagonal phonon density matrix. The combination of the both factors is
decisive for the phenomenon under consideration.Comment: 5 pages; typos and abstract correcte
Research of the possibility of self-excited vibrations amplitude reducing when turning by the variation of the cutting speed
In this paper the results of research of the possibilities of self-excited vibrations suppression in turning by the cutting speed modulation are presented. The experimental approach to conduct the variative control of lathe main drive is described. The possibilities of main drive working in continuous rotation speed mode are researched.В статье приведены результаты исследования возможности подавления автоколебаний при точении модулированием скоростью резания. Описан экспериментальный подход осуществления вариативного управления приводом главного движения токарного станка. Исследованы возможности привода главного движения работы в режиме постоянного варьирования скоростью вращения
Self-consistent theory of turbulence
A new approach to the stochastic theory of turbulence is suggested. The
coloured noise that is present in the stochastic Navier-Stokes equation is
generated from the delta-correlated noise allowing us to avoid the nonlocal
field theory as it is the case in the conventional theory. A feed-back
mechanism is introduced in order to control the noise intensity.Comment: submitted to J.Tech. Phys.Letters (St. Petersburg
- …