arXiv subjects

Sylvain Joubaud

Publications and source records attributed to Sylvain Joubaud.

31 records · Page 2Linked to original sources

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

The effect of finite container size on granular jet formation

When an object is dropped into a bed of fine, loosely packed sand, a surprisingly energetic jet shoots out of the bed. In this work we study the effect that boundaries have on the granular jet formation. We did this by (i) decreasing the depth of the sand bed and (ii) reducing the container diameter to only a few ball diameters. These confinements change the behavior of the ball inside the bed, the void collapse, and the resulting jet height and shape. We map the parameter space of impact with Froude number, ambient pressure, and container dimensions as parameters. From these results we propose a new explanation for the thick-thin structure of the jet reported by several groups [J.R.Royer \textit{et al}., Nature Phys. \textbf{1}, 164 (2005)], [G.Caballero \textit{et al}., Phys. Rev. Lett. \textbf{99}, 018001 (2007)] and [J.O. Marston, \textit{et al}., Physics of Fluids \textbf{20}, 023301 (2008)].

physics.flu-dyn↗

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 fluctuations in a nematic liquid crystal

The orientation fluctuations of the director of a liquid crystal are measured, by a sensitive polarization interferometer, close to the Fréedericksz transition, which is a second order transition driven by an electric field. Using mean field theory, we define the work injected into the system by a change of the electric field and we calibrate it using Fluctuation-Dissipation Theorem. We show that the work fluctuations satisfy the Transient Fluctuation Theorem. An analytical justification of this result is given. The open problems for the out of equilibrium case are finally discussed.

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↗

arXiv2008

Fluctuations of the total entropy production in stochastic systems

Fluctuations of the excess heat in an out of equilibrium steady state are experimentally investigated in two stochastic systems : an electric circuit with an imposed mean current and a harmonic oscillator driven out of equilibrium by a periodic torque. In these two linear systems, we study excess heat that represents the difference between the dissipated heat out of equilibrium and the dissipated heat at equilibrium. Fluctuation theorem holds for the excess heat in the two experimental systems for all observation times and for all fluctuation magnitudes.

cond-mat.stat-mech↗

arXiv2007

Thermodynamic time asymmetry in nonequilibrium fluctuations

We here present the complete analysis of experiments on driven Brownian motion and electric noise in a $RC$ circuit, showing that thermodynamic entropy production can be related to the breaking of time-reversal symmetry in the statistical description of these nonequilibrium systems. The symmetry breaking can be expressed in terms of dynamical entropies per unit time, one for the forward process and the other for the time-reversed process. These entropies per unit time characterize dynamical randomness, i.e., temporal disorder, in time series of the nonequilibrium fluctuations. Their difference gives the well-known thermodynamic entropy production, which thus finds its origin in the time asymmetry of dynamical randomness, alias temporal disorder, in systems driven out of equilibrium.

cond-mat.stat-mech↗

arXiv2007

Entropy production and time asymmetry in nonequilibrium fluctuations

The time-reversal symmetry of nonequilibrium fluctuations is experimentally investigated in two out-of-equilibrium systems namely, a Brownian particle in a trap moving at constant speed and an electric circuit with an imposed mean current. The dynamical randomness of their nonequilibrium fluctuations is characterized in terms of the standard and time-reversed entropies per unit time of dynamical systems theory. We present experimental results showing that their difference equals the thermodynamic entropy production in units of Boltzmann's constant.

cond-mat.stat-mech↗

arXiv2007

Fluctuation theorems for harmonic oscillators

We study experimentally the thermal fluctuations of energy input and dissipation in a harmonic oscillator driven out of equilibrium, and search for Fluctuation Relations. We study transient evolution from the equilibrium state, together with non equilibrium steady states. Fluctuations Relations are obtained experimentally for both the work and the heat, for the stationary and transient evolutions. A Stationary State Fluctuation Theorem is verified for the two time prescriptions of the torque. But a Transient Fluctuation Theorem is satisfied for the work given to the system but not for the heat dissipated by the system in the case of linear forcing. Experimental observations on the statistical and dynamical properties of the fluctuation of the angle, we derive analytical expressions for the probability density function of the work and the heat. We obtain for the first time an analytic expression of the probability density function of the heat. Agreement between experiments and our modeling is excellent.

cond-mat.stat-mech↗

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

Heat fluctuations for harmonic oscillators

Heat fluctuations of a harmonic oscillator in contact with a thermostat and driven out of equilibrium by an external deterministic force are studied experimentally and theoretically within the context of Fluctuation Theorems. We consider the case of a periodic forcing of the oscillator, and we calculate the analytic probability density function of heat fluctuations. The limit of large time is discussed and we show that heat fluctuations satisfy the conventional fluctuation theorem, even if a different fluctuation relation exists for this quantity. Experimental results are also given for a transient state.

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↗

arXiv2006

Wringing out DNA

The chiral nature of DNA plays a crucial role in cellular processes. Here we use magnetic tweezers to explore one of the signatures of this chirality, the coupling between stretch and twist deformations. We show that the extension of a stretched DNA molecule increases linearly by 0.42 nm per excess turn applied to the double helix. This result contradicts the intuition that DNA should lengthen as it is unwound and get shorter with overwinding. We then present numerical results of energy minimizations of torsionally restrained DNA that display a behaviour similar to the experimental data and shed light on the molecular details of this surprising effect.

q-bio.BM↗