5,842 research outputs found
Finite sampling effects on generalized fluctuation-dissipation relations for steady states
We study the effects of the finite number of experimental data on the
computation of a generalized fluctuation-dissipation relation around a
nonequilibrium steady state of a Brownian particle in a toroidal optical trap.
We show that the finite sampling has two different effects, which can give rise
to a poor estimate of the linear response function. The first concerns the
accessibility of the generalized fluctuation-dissipation relation due to the
finite number of actual perturbations imposed to the control parameter. The
second concerns the propagation of the error made at the initial sampling of
the external perturbation of the system. This can be highly enhanced by
introducing an estimator which corrects the error of the initial sampled
condition. When these two effects are taken into account in the data analysis,
the generalized fluctuation-dissipation relation is verified experimentally
The Hatano-Sasa equality: transitions between steady states in a granular gas
An experimental study is presented, about transitions between Non-Equilibrium
Steady States (NESS) in a dissipative medium. The core device is a small
rotating blade that imposes cycles of increasing and decreasing forcings to a
granular gas, shaken independently. The velocity of this blade is measured,
subject to the transitions imposed by the periodic torque variation. The
Hatano-Sasa equality, that generalises the second principle of thermodynamics
to NESS, is verified with a high accuracy (a few ), at different
variation rates. Besides, it is observed that the fluctuating velocity at fixed
forcing follows a generalised Gumbel distribution. A rough evaluation of the
mean free path in the granular gas suggests that it might be a correlated
system, at least partially
Coarsening in potential and nonpotential models of oblique stripe patterns
We study the coarsening of two-dimensional oblique stripe patterns by
numerically solving potential and nonpotential anisotropic Swift-Hohenberg
equations. Close to onset, all models exhibit isotropic coarsening with a
single characteristic length scale growing in time as . Further from
onset, the characteristic lengths along the preferred directions and
grow with different exponents, close to 1/3 and 1/2, respectively. In
this regime, one-dimensional dynamical scaling relations hold. We draw an
analogy between this problem and Model A in a stationary, modulated external
field. For deep quenches, nonpotential effects produce a complicated
dislocation dynamics that can lead to either arrested or faster-than-power-law
growth, depending on the model considered. In the arrested case, small isolated
domains shrink down to a finite size and fail to disappear. A comparison with
available experimental results of electroconvection in nematics is presented.Comment: 13 pages, 13 figures. To appear in Phys. Rev.
Steady state fluctuation relations for systems driven by an external random force
We experimentally study the fluctuations of the work done by an external
Gaussian random force on two different stochastic systems coupled to a thermal
bath: a colloidal particle in an optical trap and an atomic force microscopy
cantilever. We determine the corresponding probability density functions for
different random forcing amplitudes ranging from a small fraction to several
times the amplitude of the thermal noise. In both systems for sufficiently weak
forcing amplitudes the work fluctuations satisfy the usual steady state
fluctuation theorem. As the forcing amplitude drives the system far from
equilibrium, deviations of the fluctuation theorem increase monotonically. The
deviations can be recasted to a single master curve which only depends on the
kind of stochastic external force.Comment: 6 pages, submitted to EP
Large deviations of heat flow in harmonic chains
We consider heat transport across a harmonic chain connected at its two ends
to white-noise Langevin reservoirs at different temperatures. In the steady
state of this system the heat flowing from one reservoir into the system in
a finite time has a distribution . We study the large time
form of the corresponding moment generating function . Exact formal expressions, in terms of phonon
Green's functions, are obtained for both and also the lowest
order correction . We point out that, in general a knowledge of
both and is required for finding the large
deviation function associated with . The function is
known to be the largest eigenvector of an appropriate Fokker-Planck type
operator and our method also gives the corresponding eigenvector exactly.Comment: 15 pages; minor modification
Efficiency of Free Energy Transduction in Autonomous Systems
We consider the thermodynamics of chemical coupling from the viewpoint of
free energy transduction efficiency. In contrast to an external
parameter-driven stochastic energetics setup, the dynamic change of the
equilibrium distribution induced by chemical coupling, adopted, for example, in
biological systems, is inevitably an autonomous process. We found that the
efficiency is bounded by the ratio between the non-symmetric and the
symmetrized Kullback-Leibler distance, which is significantly lower than unity.
Consequences of this low efficiency are demonstrated in the simple two-state
case, which serves as an important minimal model for studying the energetics of
biomolecules.Comment: 4 pages, 4 figure
The fluctuation-dissipation relation: how does one compare correlation functions and responses?
We discuss the well known Einstein and the Kubo Fluctuation Dissipation
Relations (FDRs) in the wider framework of a generalized FDR for systems with a
stationary probability distribution. A multi-variate linear Langevin model,
which includes dynamics with memory, is used as a treatable example to show how
the usual relations are recovered only in particular cases. This study brings
to the fore the ambiguities of a check of the FDR done without knowing the
significant degrees of freedom and their coupling. An analogous scenario
emerges in the dynamics of diluted shaken granular media. There, the
correlation between position and velocity of particles, due to spatial
inhomogeneities, induces violation of usual FDRs. The search for the
appropriate correlation function which could restore the FDR, can be more
insightful than a definition of ``non-equilibrium'' or ``effective
temperatures''.Comment: 22 pages, 9 figure
Mode coupling in a hanging-fiber AFM used as a rheological probe
We analyze the advantages and drawbacks of a method which measures the viscosity of liquids at microscales, using a thin glass fiber fixed on the tip of a cantilever of an ultra-low-noise Atomic Force Microscope (AFM). When the fiber is dipped into a liquid, the dissipation of the cantilever-fiber system, which is linked to the liquid viscosity, can be computed from the power spectral density of the thermal fluctuations of the cantilever deflection. The high sensitivity of the AFM allows us to show the existence and to develop a model of the coupling between the dynamics of the fiber and that of the cantilever. This model, which accurately fits the experimental data, gives also more insights into the dynamics of coupled microdevices in a viscous environment. Copyright (C) EPLA, 201
Heat release by controlled continuous-time Markov jump processes
We derive the equations governing the protocols minimizing the heat released
by a continuous-time Markov jump process on a one-dimensional countable state
space during a transition between assigned initial and final probability
distributions in a finite time horizon. In particular, we identify the
hypotheses on the transition rates under which the optimal control strategy and
the probability distribution of the Markov jump problem obey a system of
differential equations of Hamilton-Bellman-Jacobi-type. As the state-space mesh
tends to zero, these equations converge to those satisfied by the diffusion
process minimizing the heat released in the Langevin formulation of the same
problem. We also show that in full analogy with the continuum case, heat
minimization is equivalent to entropy production minimization. Thus, our
results may be interpreted as a refined version of the second law of
thermodynamics.Comment: final version, section 2.1 revised, 26 pages, 3 figure
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