Observing brownian motion in vibration-fluidized granular matter

@article{DAnnaNoriNature2003, abstract = {Observation of the rotational brownian motion of a very fine wire immersed in a gas led to one of the most important ideas of equilibrium statistical mechanics. Namely, the many-particle problem of a large number of molecules colliding with the wire can be represented by just two macroscopic parameters: viscosity and temperature. Interest has arisen in the question of whether this idea (mathematically developed in the Langevin model and the fluctuation-dissipation theorem) can also be used to describe systems that are far from equilibrium. Here we report an experimental investigation of an archetypal non-equilibrium system, involving a sensitive torsion oscillator immersed in a granular system of millimetre-size grains that are fluidized by strong external vibrations. The vibro-fluidized granular medium is a driven environment, with continuous injection and dissipa- tion of energy, and the immersed oscillator can be seen as analogous to an elastically bound brownian particle. By measur- ing the noise and the susceptibility, we show that the experiment can be treated (to a first approximation) with the equilibrium formalism. This gives experimental access to a granular viscosity and an effective temperature; however, these quantities are anisotropic and inhomogeneous. Surprisingly, the vibro-fluidized granular matter behaves as a thermal bath satisfying a fluctuation-dissipation relation.}, author = {D'Anna, G. and Mayor, P. and Barrat, A. and Loreto, V. and Nori, F. }, citeulike-article-id = {393128}, journal = {Nature}, keywords = {granular-temperature}, month = {August}, pages = {909--912}, posted-at = {2005-11-15 06:30:38}, priority = {2}, title = {Observing brownian motion in vibration-fluidized granular matter}, volume = {424}, year = {2003} }

TY - JOUR ID - DAnnaNoriNature2003 L3 - citeulike-article-id:393128 TI - Observing brownian motion in vibration-fluidized granular matter JF - Nature VL - 424 SP - 909 EP - 912 N2 - Observation of the rotational brownian motion of a very fine wire immersed in a gas led to one of the most important ideas of equilibrium statistical mechanics. Namely, the many-particle problem of a large number of molecules colliding with the wire can be represented by just two macroscopic parameters: viscosity and temperature. Interest has arisen in the question of whether this idea (mathematically developed in the Langevin model and the fluctuation-dissipation theorem) can also be used to describe systems that are far from equilibrium. Here we report an experimental investigation of an archetypal non-equilibrium system, involving a sensitive torsion oscillator immersed in a granular system of millimetre-size grains that are fluidized by strong external vibrations. The vibro-fluidized granular medium is a driven environment, with continuous injection and dissipa- tion of energy, and the immersed oscillator can be seen as analogous to an elastically bound brownian particle. By measur- ing the noise and the susceptibility, we show that the experiment can be treated (to a first approximation) with the equilibrium formalism. This gives experimental access to a granular viscosity and an effective temperature; however, these quantities are anisotropic and inhomogeneous. Surprisingly, the vibro-fluidized granular matter behaves as a thermal bath satisfying a fluctuation-dissipation relation. KW - granular-temperature AU - D'Anna, G AU - Mayor, P AU - Barrat, A AU - Loreto, V AU - Nori, F PY - 2003/08/21/ ER -