9,124 research outputs found
Accidental suppression of Landau damping of the transverse breathing mode in elongated Bose-Einstein condensates
We study transverse radial oscillations of an elongated Bose-Einstein
condensate using finite temperature simulations, in the context of a recent
experiment at ENS. We demonstrate the existence of a mode corresponding to an
in-phase collective oscillation of both the condensate and thermal cloud.
Excitation of this mode accounts for the very small damping rate observed
experimentally, and we find excellent quantitative agreement between experiment
and theory. In contrast to other condensate modes, interatomic collisions are
found to be the dominant damping mechanism in this case.Comment: 4 pages, 3 figure
Electro-diffusion in a plasma with two ion species
Electric field is a thermodynamic force that can drive collisional
inter-ion-species transport in a multicomponent plasma. In an inertial
confinement fusion (ICF) capsule, such transport causes fuel ion separation
even with a target initially prepared to have equal number densities for the
two fuel ion species. Unlike the baro-diffusion driven by ion pressure gradient
and the thermo-diffusion driven by ion and electron temperature gradients,
electro-diffusion has a critical dependence on the charge-to-mass ratio of the
ion species. Specifically, it is shown here that electro-diffusion vanishes if
the ion species have the same charge-to-mass ratio. An explicit expression for
the electro-diffusion ratio is obtained and used to investigate the relative
importance of electro- and baro-diffusion mechanisms. In particular, it is
found that electro-diffusion reinforces baro-diffusion in the deuterium and
tritium mix, but tends to cancel it in the deuterium and helium-3 mix.Comment: Submitted to Phys. Plasmas on 2012-03-06 (revised version 05/13/2012
Dynamics of long-range order in an exciton-polariton condensate
We report on time resolved measurements of the first order spatial coherence
in an exciton polariton Bose-Einstein condensate. Long range spatial coherence
is found to set in right at the onset of stimulated scattering, on a picosecond
time scale. The coherence reaches its maximum value after the population and
decays slower, staying up to a few hundreds of picoseconds. This behavior can
be qualitatively reproduced, using a stochastic classical field model
describing interaction between the polariton condensate and the exciton
reservoir within a disordered potential.Comment: 7 pages, 4 figure
Sound attenuation in the superconducting amorphous alloy ZrTiCuNiBe
The superconducting energy gap and the parameter of the intensity of electron
scattering at two-level systems in amorphous ZrTiCuNiBe are determined from the
results of measurements of sound attenuation. The mechanism of adiabatic
renormalization of the amplitude of coherent tunneling is used for a
quantitative description of the peculiarities of sound absorption in the
vicinity of critical temperature.Comment: 4 pages, LaTeX, 2 Postscript figures corrected, submitted to Low
Temp. Phy
Rayleigh-Taylor instability of crystallization waves at the superfluid-solid 4He interface
At the superfluid-solid 4He interface there exist crystallization waves
having much in common with gravitational-capillary waves at the interface
between two normal fluids. The Rayleigh-Taylor instability is an instability of
the interface which can be realized when the lighter fluid is propelling the
heavier one. We investigate here the analogues of the Rayleigh-Taylor
instability for the superfluid-solid 4He interface. In the case of a uniformly
accelerated interface the instability occurs only for a growing solid phase
when the magnitude of the acceleration exceeds some critical value independent
of the surface stiffness. For the Richtmyer-Meshkov limiting case of an
impulsively accelerated interface, the onset of instability does not depend on
the sign of the interface acceleration. In both cases the effect of
crystallization wave damping is to reduce the perturbation growth-rate of the
Taylor unstable interface.Comment: 8 pages, 2 figures, RevTe
Existence of two-channel Kondo regime for tunneling impurities with resonant scattering
Dynamical tunneling systems have been proposed earlier to display a
two-channel Kondo effect, the orbital index of the particle playing the role of
a pseudospin in the equivalent Kondo problem, and the spin being a silent
channel index. However, as shown recently by Aleiner et al. [Phys. Rev. Lett.
86, 2629 (2001)], the predicted two-channel Kondo behavior can never be
observed in the weak coupling regime, where the tunneling induced splitting of
the levels of the tunneling system always dominates the physics. Here we show
that the above scenario changes completely if the conduction electrons are
scattered by resonant scattering off the tunneling impurity; Then - as a
non-perturbative analysis reveals - the two-channel Kondo regime can easily be
reached.Comment: 10 PRB page
Condensation and vortex formation in Bose-gas upon cooling
The mechanism for the transition of a Bose gas to the superfluid state via
thermal fluctuations is considered. It is shown that in the process of external
cooling some critical fluctuations (instantons) are formed above the critical
temperature. The probability of the instanton formation is calculated in the
three and two-dimensional cases. It is found that this probability increases as
the system approaches the transition temperature. It is shown that the
evolution of an individual instanton is impossible without the formation of
vortices in its superfluid part
Long-Term Clustering, Scaling, and Universality in the Temporal Occurrence of Earthquakes
Scaling analysis reveals striking regularities in earthquake occurrence. The
time between any one earthquake and that following it is random, but it is
described by the same universal-probability distribution for any spatial region
and magnitude range considered. When time is expressed in rescaled units, set
by the averaged seismic activity, the self-similar nature of the process
becomes apparent. The form of the probability distribution reveals that
earthquakes tend to cluster in time, beyond the duration of aftershock
sequences. Furthermore, if aftershock sequences are analysed in an analogous
way, yet taking into account the fact that seismic activity is not constant but
decays in time, the same universal distribution is found for the rescaled time
between events.Comment: short paper, only 2 figure
On the influence of time and space correlations on the next earthquake magnitude
A crucial point in the debate on feasibility of earthquake prediction is the
dependence of an earthquake magnitude from past seismicity. Indeed, whilst
clustering in time and space is widely accepted, much more questionable is the
existence of magnitude correlations. The standard approach generally assumes
that magnitudes are independent and therefore in principle unpredictable. Here
we show the existence of clustering in magnitude: earthquakes occur with higher
probability close in time, space and magnitude to previous events. More
precisely, the next earthquake tends to have a magnitude similar but smaller
than the previous one. A dynamical scaling relation between magnitude, time and
space distances reproduces the complex pattern of magnitude, spatial and
temporal correlations observed in experimental seismic catalogs.Comment: 4 Figure
Cold three-body collisions in hydrogen-hydrogen-alkali atomic system
We have studied hydrogen-hydrogen-alkali three-body systems in the adiabatic
hyperspherical representation. For the spin-stretched case, there exists a
single H molecular state when is one of the bosonic alkali atoms:
Li, Na, K, Rb and Cs. As a result, the {\em
only} recombination process is the one that leads to formation of H
molecules, H+H+H+H, and such molecules will be stable
against vibrational relaxation. We have calculated the collision rates for
recombination and collision induced dissociation as well as the elastic
cross-sections for H+H collisions up to a temperature of 0.5 K, including
the partial wave contributions from = to . We have also found
that there is just one three-body bound state for such systems for
= and no bound states for higher angular momenta.Comment: 10 pages, 5 figures, 4 table
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