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Fluctuations dans les systèmes hors d'équilibre

Abstract : The results reported in this thesis contribute to the understanding of the fluctuations of out of equilibrium systems. They have been obtained in two experimental systems.

The first system is a harmonic oscillator fluctuating because of the thermal noise. This system is driven out of equilibrium by an external forcing. Two case are studied : the transient state and the steady state. We measure in this model system work fluctuations, heat fluctuations and total entropy fluctuations. These fluctuations are studied within the context of Fluctuation Theorem. The results are interpreted by comparing the experimental results with a simple theoretical model.

The second part is dedicated to the study of the Fréedericks transition in a nematic liquid crystal which is a second order phase transition. Our experimental setup for the measurement of the order parameter has a very good resolution at low frequency, of the order of millihertz. We study the statistics of the equilibrium fluctuations when the control parameter is close to its critical value. The distribution is compared to a Generalized Gumbel distribution and the parameter of this modeling is related to the effective number of degrees of freedom. We finally study this system out of equilibrium. We show that after a quench at the critical point the system presents aging properties. Preliminary results are presented.
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Contributor : Sylvain Joubaud <>
Submitted on : Wednesday, September 3, 2008 - 8:51:17 AM
Last modification on : Wednesday, November 20, 2019 - 3:01:08 AM
Long-term archiving on: : Thursday, June 3, 2010 - 7:25:20 PM


  • HAL Id : tel-00316170, version 1


Sylvain Joubaud. Fluctuations dans les systèmes hors d'équilibre. Analyse de données, Statistiques et Probabilités []. Ecole normale supérieure de lyon - ENS LYON, 2008. Français. ⟨tel-00316170⟩



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