12,795 research outputs found
Fingerprints of Classical Instability in Open Quantum Dynamics
The dynamics near a hyperbolic point in phase space is modelled by an
inverted harmonic oscillator. We investigate the effect of the classical
instability on the open quantum dynamics of the oscillator, introduced through
the interaction with a thermal bath, using both the survival probability
function and the rate of von Neumann entropy increase, for large times. In this
parameter range we prove, using influence functional techniques, that the
survival probability function decreases exponentially at a rate, K', depending
not only on the measure of instability in the model but also on the strength of
interaction with the environment. We also show that K' determines the rate of
von Neumann entropy increase and that this result is independent of the
temperature of the environment. This generalises earlier results which are
valid in the limit of vanishing dissipation. The validity of inferring similar
rates of survival probability decrease and entropy increase for quantum chaotic
systems is also discussed.Comment: 13 pages, to be published in Physical Review
Measuring the Effects of Artificial Viscosity in SPH Simulations of Rotating Fluid Flows
A commonly cited drawback of SPH is the introduction of spurious shear
viscosity by the artificial viscosity term in situations involving rotation.
Existing approaches for quantifying its effect include approximate analytic
formulae and disc-averaged be- haviour in specific ring-spreading simulations,
based on the kinematic effects produced by the artificial viscosity. These
methods have disadvantages, in that they typically are applicable to a very
small range of physical scenarios, have a large number of simplifying
assumptions, and often are tied to specific SPH formulations which do not
include corrective (e.g., Balsara) or time-dependent viscosity terms. In this
study we have developed a simple, generally applicable and practical technique
for evaluating the local effect of artificial viscosity directly from the
creation of specific entropy for each SPH particle. This local approach is
simple and quick to implement, and it al- lows a detailed characterization of
viscous effects as a function of position. Several advantages of this method
are discussed, including its ease in evaluation, its greater accuracy and its
broad applicability. In order to compare this new method with ex- isting ones,
simple disc flow examples are used. Even in these basic cases, the very roughly
approximate nature of the previous methods is shown. Our local method pro-
vides a detailed description of the effects of the artificial viscosity
throughout the disc, even for extended examples which implement Balsara
corrections. As a further use of this approach, explicit dependencies of the
effective viscosity in terms of SPH and flow parameters are estimated from the
example cases. In an appendix, a method for the initial placement of SPH
particles is discussed which is very effective in reducing numerical
fluctuations.Comment: 15 pages, 9 figures, resubmitted to MNRA
AN ECONOMETRIC ANALYSIS OF THE ECONOMIC CONTRIBUTION OF SUBTHERAPEUTIC ANTIBIOTIC USE IN PORK PRODUCTION
There is growing concern among public health experts regarding the diminishing efficacy of antimicrobial therapy in human and veterinary medicine, and some have called for a ban on subtherapeutic antibiotic use in pork production. This paper develops an econometric analysis to identify the economic contributions of subtherapeutic antibiotic use in swine production.Livestock Production/Industries,
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