arXiv subjects

Artem Petrosyan

Publications and source records attributed to Artem Petrosyan.

7 recordsLinked to original sources

arXiv2011

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.

cond-mat.stat-mech↗

arXiv2010

Fluctuations in out of equilibrium systems: from theory to experiment

We introduce from an experimental point of view the main concepts of fluctuation theorems for work, heat and entropy production in out of equilibrium systems. We will discuss the important difference between the applications of these concepts to stochastic systems and to a second class of systems (chaotic systems) where the fluctuations are induced either by chaotic flows or by fluctuating driving forces. We will mainly analyze the stochastic systems using the measurements performed in two experiments : a) a harmonic oscillator driven out of equilibrium by an external force b) a colloidal particle trapped in a time dependent double well potential. We will rapidly describe some consequences of fluctuation theorems and some useful applications to the analysis of experimental data. As an example the case of a molecular motor will be analyzed in some details. Finally we will discuss the problems related to the applications of fluctuation theorems to chaotic systems.

cond-mat.stat-mech↗

arXiv2009

Aging and effective temperatures near a critical point

The orientation fluctuations of the director of a liquid crystal(LC) are measured after a quench near the Fréedericksz transition, which is a second order transition driven by an electric field. We report experimental evidence that, because of the critical slowing down, the LC presents, after the quench, several properties of an aging system, such as power law scaling versus time of correlation and response functions. During this slow relaxation, a well defined effective temperature, much larger than the heat bath temperature, can be measured using the fluctuation dissipation relation.

cond-mat.stat-mech↗

arXiv2008

Work and dissipation fluctuations near the stochastic resonance of a colloidal particle

We study experimentally the fluctuations of the injected and dissipated energy in a system of a colloidal particle trapped in a double well potential periodically modulated by an external perturbation. The work done by the external force and the dissipated energy are measured close to the stochastic resonance where the injected power is maximum. We show that the steady state fluctuation theorem holds in this system.

cond-mat.soft↗

arXiv2007

Experimental study of work fluctuations in a harmonic oscillator

The work fluctuations of a harmonic oscillator in contact with a thermostat and driven out of equilibrium by an external force are studied experimentally. For the work both the transient and stationary state fluctuation theorems hold. The finite time corrections are very different from those of a first order Langevin equation. The heat and work fluctuations are studied when a periodic forcing is applied to the oscillator. The importance of the choice of the ''good work'' to compute the free energy from the Jarzinsky equality is discussed.

cond-mat.stat-mech↗

arXiv2006

Work fluctuation theorems for harmonic oscillators

The work fluctuations of an oscillator in contact with a thermostat and driven out of equilibrium by an external force are studied experimentally and theoretically within the context of Fluctuation Theorems (FTs). The oscillator dynamics is modeled by a second order Langevin equation. Both the transient and stationary state fluctuation theorems hold and the finite time corrections are very different from those of a first order Langevin equation. The periodic forcing of the oscillator is also studied; it presents new and unexpected short time convergences. Analytical expressions are given in all cases.

cond-mat.stat-mech↗

arXiv2005

Estimate of the free energy difference in mechanical systems from work fluctuations: experiments and models

The work fluctuations of an oscillator in contact with a heat reservoir and driven out of equilibrium by an external force are studied experimentally. The oscillator dynamics is modeled by a Langevin equation. We find both experimentally and theoretically that, if the driving force does not change the equilibrium properties of the thermal fluctuations of this mechanical system, the free energy difference $ΔF$ between two equilibrium states can be exactly computed using the Jarzynski equality (JE) and the Crooks relation (CR) \cite{jarzynski1, crooks1, jarzynski2}, independently of the time scale and amplitude of the driving force. The applicability limits for the JE and CR at very large driving forces are discussed. Finally, when the work fluctuations are Gaussian, we propose an alternative empirical method to compute $ΔF$ which can be safely applied, even in cases where the JE and CR might not hold. The results of this paper are useful to compute $ΔF$ in complex systems such as the biological ones.

cond-mat.stat-mech↗