4,948 research outputs found
Thermal effects on chaotic directed transport
We study a chaotic ratchet system under the influence of a thermal
environment. By direct integration of the Lindblad equation we are able to
analyze its behavior for a wide range of couplings with the environment, and
for different finite temperatures. We observe that the enhancement of the
classical and quantum currents due to temperature depend strongly on the
specific properties of the system. This makes difficult to extract universal
behaviors. We have also found that there is an analogy between the effects of
the classical thermal noise and those of the finite size. These results
open many possibilities for their testing and implementation in kicked BECs and
cold atoms experiments.Comment: 5 pages, 4 figure
Garcia v. San Antonio Metropolitan Transit Authority: The Commerce Clause and the Political Process
Memory-Controlled Diffusion
Memory effects require for their incorporation into random-walk models an
extension of the conventional equations. The linear Fokker-Planck equation for
the probability density is generalized to include non-linear and
non-local spatial-temporal memory effects. The realization of the memory
kernels are restricted due the conservation of the basic quantity . A
general criteria is given for the existence of stationary solutions. In case
the memory kernel depends on polynomially the transport is prevented. Owing
to the delay effects a finite amount of particles remains localized and the
further transport is terminated. For diffusion with non-linear memory effects
we find an exact solution in the long-time limit. Although the mean square
displacement shows diffusive behavior, higher order cumulants exhibits
differences to diffusion and they depend on the memory strength
Non-equilibrium dynamics: Studies of reflection of Bose-Einstein condensates
The study of the non-equilibrium dynamics in Bose-Einstein condensed gases
has been dominated by the zero-temperature, mean field Gross-Pitaevskii
formalism. Motivated by recent experiments on the reflection of condensates
from silicon surfaces, we revisit the so-called {\em classical field}
description of condensate dynamics, which incorporates the effects of quantum
noise and can also be generalized to include thermal effects. The noise is
included in a stochastic manner through the initial conditions. We show that
the inclusion of such noise is important in the quantitative description of the
recent reflection experiments
Quantum Kinetic Theory VI: The Growth of a Bose-Einstein Condensate
A detailed analysis of the growth of a BEC is given, based on quantum kinetic
theory, in which we take account of the evolution of the occupations of lower
trap levels, and of the full Bose-Einstein formula for the occupations of
higher trap levels, as well as the Bose stimulated direct transfer of atoms to
the condensate level introduced by Gardiner et al. We find good agreement with
experiment at higher temperatures, but at lower temperatures the experimentally
observed growth rate is somewhat more rapid. We also confirm the picture of the
``kinetic'' region of evolution, introduced by Kagan et al., for the time up to
the initiation of the condensate. The behavior after initiation essentially
follows our original growth equation, but with a substantially increased rate
coefficient.
Our modelling of growth implicitly gives a model of the spatial shape of the
condensate vapor system as the condensate grows, and thus provides an
alternative to the present phenomenological fitting procedure, based on the sum
of a zero-chemical potential vapor and a Thomas-Fermi shaped condensate. Our
method may give substantially different results for condensate numbers and
temperatures obtained from phenomentological fits, and indicates the need for
more systematic investigation of the growth dynamics of the condensate from a
supersaturated vapor.Comment: TeX source; 29 Pages including 26 PostScript figure
Salmonella in Irish pig farms; prevalence, antibiotic resistance and molecular epidemiology
The objective was to examine the prevalence of Salmonella in manure from 30 Irish pig farms and to characterize any recovered isolates in order to assess potential risks and epidemiological relationships. Salmonella was detected in the manure from finisher pigs in 50% of the herds investigated. S. Typhimurium was the predominant serotype recovered and the most common phage types were DT104 and DT104b. Nineteen of the 29 Salmonella isolates recovered were resistant to one or more antibiotics and 15 of these (all Typhimurium) were multi-resistant
Low Earth Orbit satellite/terrestrial mobile service compatibility
Currently the geostationary type of satellite is the only one used to provide commercial mobile-satellite communication services. Low earth orbit (LEO) satellite systems are now being proposed as a future alternative. By the implementation of LEO satellite systems, predicted at between 5 and 8 years time, mobile space/terrestrial technology will have progressed to the third generation stage of development. This paper considers the system issues that will need to be addressed when developing a dual mode terminal, enabling access to both terrestrial and LEO satellite systems
Failure of the work-Hamiltonian connection for free energy calculations
Extensions of statistical mechanics are routinely being used to infer free
energies from the work performed over single-molecule nonequilibrium
trajectories. A key element of this approach is the ubiquitous expression
dW/dt=\partial H(x,t)/ \partial t which connects the microscopic work W
performed by a time-dependent force on the coordinate x with the corresponding
Hamiltonian H(x,t) at time t. Here we show that this connection, as pivotal as
it is, cannot be used to estimate free energy changes. We discuss the
implications of this result for single-molecule experiments and atomistic
molecular simulations and point out possible avenues to overcome these
limitations
Scaling properties of growing noninfinitesimal perturbations in space-time chaos
We study the spatiotemporal dynamics of random spatially distributed
noninfinitesimal perturbations in one-dimensional chaotic extended systems. We
find that an initial perturbation of finite size grows in time
obeying the tangent space dynamic equations (Lyapunov vectors) up to a
characteristic time , where is the largest Lyapunov exponent and
is a constant. For times perturbations exhibit spatial
correlations up to a typical distance . For times larger than
finite perturbations are no longer described by tangent space
equations, memory of spatial correlations is progressively destroyed and
perturbations become spatiotemporal white noise. We are able to explain these
results by mapping the problem to the Kardar-Parisi-Zhang universality class of
surface growth.Comment: 4.5 pages LaTeX (RevTeX4) format, 3 eps figs included. Submitted to
Phys Rev
Tunable pulse delay and advancement in a coupled nanomechanical resonator-superconducting microwave cavity system
We theoretically study the transmission of a weak probe field under the
influence of a strong pump field in a coupled nanomechanical
resonator-superconducting microwave cavity system. Using the standard
input-output theory, we find that both pulse delay (slow light effect) and
advancement (fast light effect) of the probe field can appear in this coupled
system provided that we choose the suitable detuning of the pump field from
cavity resonance. The magnitude of the delay (advancement) can be tuned
continuously by adjusting the power of the pump field. This technique
demonstrates great potential in applications including microwave phase shifter
and delay line.Comment: 12pages, 3 figure
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