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DY: Fachverband Dynamik und Statistische Physik

DY 40: Posters II

DY 40.25: Poster

Thursday, March 17, 2011, 17:00–19:00, P3

Transition from attractive to repulsive Casimir-like forces in granular media — •reza shaebani¹, jalal sarabadani², and dietrich wolf¹ — ¹Department of Theoretical Physics, University of Duisburg-Essen, 47048 Duisburg, Germany — ²Department of Physics, University of Isfahan, Isfahan 81746, Iran

We investigate the effective long-range interactions between intruder particles immersed in a randomly driven granular fluid. The effective force between two intruders, induced by the fluctuations of the hydrodynamic fields, is attractive when the volume fraction of the granular fluid is sufficiently high. However, a crossover from attraction to repulsion occurs as the volume fraction decreases. This behavior can be explained by two competing dynamical effects, resulting in a non-uniform collision distribution around the intruders. We present the phase diagram of the transition with three control parameters: the volume fraction, the distance between the intruders, and the restitution coefficient. Our results reveal that the force is proportional to the steady-state temperature and grows logarithmically with increasing the system size in two dimensions. Moreover, by increasing the number of intruders, we verify that the fluctuation-induced interaction is not derived from a pair-potential. These results shed new light on the mechanisms of segregation in granular media.