Fluctuations in partitioning systems with few degrees of freedom.
We study the behavior of a moving wall in contact with a particle gas and subjected to an external force. We compare the fluctuations of the system observed in the microcanonical and canonical ensembles, by varying the number of particles. Static and dynamic correlations signal significant differences between the two ensembles. Furthermore, velocity-velocity correlations of the moving wall present a complex two-time relaxation that cannot be reproduced by a standard Langevin-like description. Quite remarkably, increasing the number of gas particles in an elongated geometry, we find a typical time scale, related to the interaction between the partitioning wall and the particles, which grows macroscopically.
Dipartimento di Fisica, Università di Roma Sapienza, Piazzale A. Moro 2, 00185 Roma, Italy.
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Cerino
CEA, DSM, CNRS, URA No. 2306, CEA Saclay, F-91191 Gif-sur-Yvette Cedex, France and Université Paris-Sud, CNRS, LPTMS, UMR No. 8626, Orsay 91405, France.
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Gradenigo
ISC-CNR and Dipartimento di Fisica, Università Sapienza, Piazzale A. Moro 2, 00185 Roma, Italy; Kavli Institute for Theoretical Physics China, CAS, Beijing 100190, China; and Laboratoire de Physique Théorique de la Matière Condensée, CNRS UMR No. 7600, Université Paris 6, Case Courrier 121, 4 Place Jussieu, 75255 Paris Cedex.
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Sarracino
Laboratoire de Physique Théorique de l'ENS and Institut de Physique Théorique Philippe Meyer, 24 Rue Lhomond, 75005 Paris, France.
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Villamaina
Dipartimento di Fisica, Università Sapienza and ISC-CNR, Piazzale A. Moro 2, 00185 Roma, Italy and Kavli Institute for Theoretical Physics China, CAS, Beijing 100190, China.
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Vulpiani