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Members of our group working in this topic: R. Brito
Granular matter, because of lack of energy conservation, are systems out of equilibirum. Then usual approaches based on Thermodynamics of Statistical mechanics are not applicable a priori. Phenomenology in these systems is very rich. Patterns, oscillations, segregation, avalanches, etc, at the macroscopic level, and long range correlations, lack of gaussianity in velocity distributions, violation of Fluctuation-Dissipation, etc at the miscroscopic level, are examples of some of the phenomenology in these systems.
Our group has worked on some topics mentioned above. Currently is involved is aspects related with segregation. One is the appearance of segregation under gravity due to different inelasticities of the constituent particles. We have found that the more inelastic the particles are, the most tendency to sink down in the container . This effect can compete with the usual Brazil nut effect and even reverse it. In systems where the gravity is not relevant, like horizontally vibrated ones, we have found segregation effects as well .
Recently we turned our interest into the development of a theory to describe structure factors in granular systems, and test how the usual structure factors have to be modified in order to include the features of the inelastic fluids.
 R. Brito, H. Enríques, S. Godoy and R. Soto, Segregation-Induced by inelasticity in a vibrofluidized granular mixture, Physical Review E 77, 061301 (2008). R. Brito and R. Soto, Competition of Brazil nut effect, buoyancy, and inelasticity induced segregation in a granular mixture, Eur. Phys. J. Special Topics 179, 207 (2009)
 T. Schnautz, R. Brito, C.A. Kruelle and I. Rehberg A Horizontal Brazil-Nut Effect and Its Reverse Physical Review Letters, 95, 028001 (2005). Read our Web Page about segregation including a Comment in Science Magazine