D. Maza, Iker Zuriguel, Luis Pugnialoni,  & Angel Garcimartin
Universidad de Navarra
 

A wide array of systems get jammed: vehicles, people in panic, colloids, compacted granular materials or foams. The question that arises is whether all of them share common features in fundamental way, enabling us to think of a jammed system as a new thermodynamic state. Jamming could then be amenable to be described as a phase transition.

A particular experiment aimed at understanding this will then be presented. It consists of a silo filled with grains, with an orifice at the base. Grains begin to pour freely, then -if the orifice is not much bigger than several grain diameters- the flow stops because an arch is formed: it jams. The probability density function (pdf) of the avalanches, shows a clear exponential tail, so it can be concluded that the system is not critical. It can be rescaled with only two parameters, namely the mean avalanche size and the jamming probability of a single grain. Interestingly, the shape of the pdf can has strong similarities with the force distribution inside the granular matter.