390 research outputs found
The law of action and reaction for the effective force in a nonequilibrium colloidal system
We study a nonequilibrium Langevin many-body system containing two 'test'
particles and many 'background' particles. The test particles are spatially
confined by a harmonic potential, and the background particles are driven by an
external driving force. Employing numerical simulations of the model, we
formulate an effective description of the two test particles in a
nonequilibrium steady state. In particular, we investigate several different
definitions of the effective force acting between the test particles. We find
that the law of action and reaction does not hold for the total mechanical
force exerted by the background particles, but that it does hold for the
thermodynamic force defined operationally on the basis of an idea used to
extend the first law of thermodynamics to nonequilibrium steady states.Comment: 13 page
Exact transformation of a Langevin equation to a fluctuating response equation
We demonstrate that a Langevin equation that describes the motion of a
Brownian particle under non-equilibrium conditions can be exactly transformed
to a special equation that explicitly exhibits the response of the velocity to
a time dependent perturbation. This transformation is constructed on the basis
of an operator formulation originally used in nonlinear perturbation theory for
differential equations by extending it to stochastic analysis. We find that the
obtained expression is useful for the calculation of fundamental quantities of
the system, and that it provides a physical basis for the decomposition of the
forces in the Langevin description into effective driving, dissipative, and
random forces in a large-scale description.Comment: 14 pages, to appear in J. Phys. A: Math. Ge
A perturbation theory for large deviation functionals in fluctuating hydrodynamics
We study a large deviation functional of density fluctuation by analyzing
stochastic non-linear diffusion equations driven by the difference between the
densities fixed at the boundaries. By using a fundamental equality that yields
the fluctuation theorem, we first relate the large deviation functional with a
minimization problem. We then develop a perturbation method for solving the
problem. In particular, by performing an expansion with respect to the average
current, we derive the lowest order expression for the deviation from the local
equilibrium part. This expression implies that the deviation is written as the
space-time integration of the excess entropy production rate during the most
probable process of generating the fluctuation that corresponds to the argument
of the large deviation functional.Comment: 12page
Energy dissipation and violation of the fluctuation-response relation in non-equilibrium Langevin systems
The fluctuation-response relation is a fundamental relation that is
applicable to systems near equilibrium. On the other hand, when a system is
driven far from equilibrium, this relation is violated in general because the
detailed-balance condition is not satisfied in nonequilibrium systems. Even in
this case, it has been found that for a class of Langevin equations, there
exists an equality between the extent of violation of the fluctuation-response
relation in the nonequilibrium steady state and the rate of energy dissipation
from the system into the environment [T. Harada and S. -i. Sasa, Phys. Rev.
Lett. 95, 130602 (2005)]. Since this equality involves only experimentally
measurable quantities, it serves as a proposition to determine experimentally
whether the system can be described by a Langevin equation. Furthermore, the
contribution of each degree of freedom to the rate of energy dissipation can be
determined based on this equality. In this paper, we present a comprehensive
description on this equality, and provide a detailed derivation for various
types of models including many-body systems, Brownian motor models,
time-dependent systems, and systems with multiple heat reservoirs.Comment: 18 pages, submitted to Phys. Rev.
Theoretical analysis for critical fluctuations of relaxation trajectory near a saddle-node bifurcation
A Langevin equation whose deterministic part undergoes a saddle-node
bifurcation is investigated theoretically. It is found that statistical
properties of relaxation trajectories in this system exhibit divergent
behaviors near a saddle-node bifurcation point in the weak-noise limit, while
the final value of the deterministic solution changes discontinuously at the
point. A systematic formulation for analyzing a path probability measure is
constructed on the basis of a singular perturbation method. In this
formulation, the critical nature turns out to originate from the neutrality of
exiting time from a saddle-point. The theoretical calculation explains results
of numerical simulations.Comment: 18pages, 17figures.The version 2, in which minor errors have been
fixed, will be published in Phys. Rev.
Energy Spectra of Quantum Turbulence: Large-scale Simulation and Modeling
In simulation of quantum turbulence within the Gross-Pitaevskii
equation we demonstrate that the large scale motions have a classical
Kolmogorov-1941 energy spectrum E(k) ~ k^{-5/3}, followed by an energy
accumulation with E(k) ~ const at k about the reciprocal mean intervortex
distance. This behavior was predicted by the L'vov-Nazarenko-Rudenko bottleneck
model of gradual eddy-wave crossover [J. Low Temp. Phys. 153, 140-161 (2008)],
further developed in the paper.Comment: (re)submitted to PRB: 5.5 pages, 4 figure
Content of Trace Metals in Medicinal Plants and their Extracts
The heavy metals (Fe, Cu, Zn and Mn) contents of selected plant species, grown in Southeast region of Serbia, that are traditionally used in alternative medicine were determined. Among the considered metals, iron content was the highest one and varied from 137.53 up to 423.32 mg/kg, while the contents of Cu, Zn and Mn were remarkably lower, and ranged from 8.91 to 62.20 mg/kg. In addition, an analysis of plants extracts showed a significant transfer of heavy metals during extraction procedure; therefore, the corresponding extraction coefficients reached values up to 88.8%. Those were especially high in the ethanol based extracts. Moreover, it is was established that such coefficients mostly depend on the solvent nature and also on the treated plant species. The obtained results impose that medicinal plants from Southeast region of Serbia due to rather low content of heavy metals are appropriate for preparation of teas and medicinal extracts
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