6,299 research outputs found
H-Theorems from Autonomous Equations
The H-theorem is an extension of the Second Law to a time-sequence of states
that need not be equilibrium ones. In this paper we review and we rigorously
establish the connection with macroscopic autonomy.
If for a Hamiltonian dynamics for many particles, at all times the present
macrostate determines the future macrostate, then its entropy is non-decreasing
as a consequence of Liouville's theorem. That observation, made since long, is
here rigorously analyzed with special care to reconcile the application of
Liouville's theorem (for a finite number of particles) with the condition of
autonomous macroscopic evolution (sharp only in the limit of infinite scale
separation); and to evaluate the presumed necessity of a Markov property for
the macroscopic evolution.Comment: 13 pages; v1 -> v2: Sec. 1-2 considerably rewritten, minor
corrections in Sec. 3-
WILDCOMS
Disease and contaminants can both pose major risks to wildlife and human populations. Disease is a natural driver regulating the dynamics of wildlife populations, but
some diseases warrant particular attention because they (i) cause major mortalities that lead to population crashes, (eg., VHD in rabbits), (ii) threaten wildlife species of
high conservation concern (for example squirrelpox virus in red squirrels), or (iii) pose a potential threat to Man (eg., rabies, avian influenza). The wildlife Disease &
Contaminant Monoitoring and Surveillance (WILDCOMS) Network is a collaborative project among the major disease and contaminant monitoring schemes for vertebrate
wildlife that operate in the United Kingdom. These schemes are run by various government agencies and laboratories, research centres, institutes, and academia. The overall
aim is to establish a network which will foster and facilitate knowledge exchange, harmonisation towards best practice, and productive collaboration between: (i) partner
organisations; (ii) surveillance schemes and end-users. It will aim to provide end-users with an integrated overview of environmental disease and contaminant risk. The specific
objectives will be to develop the network and use it to address common challenges, specifically maximising dissemination of information to stakeholders and harmonisation towards common operational procedures to facilitate interaction and collaboration
Household fish preparation hygiene and cholera transmission in Monrovia, Liberia.
BACKGROUND: In the 1980s Vibrio cholerae was found to be an autochthonous resident of aquatic environments. As result, ingestion of undercooked, contaminated fish has been associated with cholera transmission. An alternative mechanism of transmission associated with fish was hypothesised by Schürmann et al. in 2002. He described a cholera case that was more likely to have been infected by contamination on the patient's hands rather than by ingestion of contaminated fish. METHODOLOGY: With fish being the main diet in Liberia, we decided to examine fish samples and preparation techniques in Monrovia. Excreta of 15 fish, caught in the estuarine waters of Monrovia, were analysed for V. cholerae. In addition, fish preparation methods were observed in 30 households. RESULTS: Two fish samples were found positive. Observations revealed that hygiene measures during the gutting process of fish were limited; although hands were usually rinsed, in all cases soap was not used. Furthermore, contaminated water was frequently reused during food preparation. CONCLUSIONS: Since the cooking process of fish (and thus elimination of bacteria) in Monrovia usually consists of both frying and boiling, it seems plausible that in this context, the hypothesis by Schürmann et al. could be applicable. Further research is necessary to confirm this association, which could be a starting point for more context-specific health education campaigns addressing food preparation hygiene as risk factor for cholera
Nonequilibrium Linear Response for Markov Dynamics, II: Inertial Dynamics
We continue our study of the linear response of a nonequilibrium system. This
Part II concentrates on models of open and driven inertial dynamics but the
structure and the interpretation of the result remain unchanged: the response
can be expressed as a sum of two temporal correlations in the unperturbed
system, one entropic, the other frenetic. The decomposition arises from the
(anti)symmetry under time-reversal on the level of the nonequilibrium action.
The response formula involves a statistical averaging over explicitly known
observables but, in contrast with the equilibrium situation, they depend on the
model dynamics in terms of an excess in dynamical activity. As an example, the
Einstein relation between mobility and diffusion constant is modified by a
correlation term between the position and the momentum of the particle
A nonequilibrium extension of the Clausius heat theorem
We generalize the Clausius (in)equality to overdamped mesoscopic and
macroscopic diffusions in the presence of nonconservative forces. In contrast
to previous frameworks, we use a decomposition scheme for heat which is based
on an exact variant of the Minimum Entropy Production Principle as obtained
from dynamical fluctuation theory. This new extended heat theorem holds true
for arbitrary driving and does not require assumptions of local or close to
equilibrium. The argument remains exactly intact for diffusing fields where the
fields correspond to macroscopic profiles of interacting particles under
hydrodynamic fluctuations. We also show that the change of Shannon entropy is
related to the antisymmetric part under a modified time-reversal of the
time-integrated entropy flux.Comment: 23 pages; v2: manuscript significantly extende
An extension of the Kac ring model
We introduce a unitary dynamics for quantum spins which is an extension of a
model introduced by Mark Kac to clarify the phenomenon of relaxation to
equilibrium. When the number of spins gets very large, the magnetization
satisfies an autonomous equation as function of time with exponentially fast
relaxation to the equilibrium magnetization as determined by the microcanonical
ensemble. This is proven as a law of large numbers with respect to a class of
initial data. The corresponding Gibbs-von Neumann entropy is also computed and
its monotonicity in time discussed.Comment: 15 pages, v2 -> v3: minor typographic correctio
Amplification of compressional MHD waves in systems with forced entropy oscillations
The propagation of compressional MHD waves is studied for an externally
driven system. It is assumed that the combined action of the external sources
and sinks of the entropy results in the harmonic oscillation of the entropy
(and temperature) in the system. It is found that with the appropriate resonant
conditions fast and slow waves get amplified due to the phenomenon of
parametric resonance. Besides, it is shown that the considered waves are
mutually coupled as a consequence of the nonequilibrium state of the background
medium. The coupling is strongest when the plasma . The
proposed formalism is sufficiently general and can be applied for many
dynamical systems, both under terrestrial and astrophysical conditions.Comment: 14 pages, 4 figures, Accepted to Physical Review
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