ABSTRACT
Dynamics near jamming (glassy phase, aging, memory, intermittency) shows amazing analogies among a variety of very different systems (colloids, dense suspensions, foams, granular materials). Recently, several proposals have emerged with the aim of describing in a general and unified way this common behavior (Liu & Nagel 1998). With the idea of testing experimentally these, several studies have concentrated on granular materials under vibration. It was proposed that dense granular assemblies could be interesting models where a new kind of fluctuation-dissipation relations is likely to extend the classical notion of thermal temperature (Makse & Kurchan 2002). It was also suggested that a “structural temperature” could be a relevant concept that governs the granular reorganization dynamics around a local steady state in the jammed regime (Metha & Edwards 1989; Fierro & Coniglio 2002). Experimentally, the dynamics of granular assemblies have been studied under different modes of excitation either under sinusoidal vibration or under sequences of taps. For granular assemblies under tap, density was shown to exhibit slow compaction regime and striking memory effects that resemble the phenomenology of spin glasses or ferro electric glasses (Nowak & Nagel 1998). Experimental determination of fluctuationdissipation relation was also proposed, but it is not clear then, that in the weak agitation limit, the perturbing action of the probe can be decoupled from the intrinsic dynamics of the medium (G. D’Anna & Nori 2003). Moreover, in a regime where agitation is of the order or much larger than the acceleration of
gravity, a granular assembly experiences two strongly distinct phases: an impact phase where grains reorganize and a launch phase where the average confining pressure is almost zero (free fall). In this last phase the resistance to external drag is almost inexistent and thus governs the mobility of an externally driven intruder (Zik & Rabin 1992). Furthermore, in all these situations, several studies have sown that boundaries generate convection effects that may couple strongly to the reorganization dynamics (Caballero & Clement 2004; Philippe & Bideau 2003).
