Andrea Puglisi (CNR-ISC, Italy)

Fluctuations and response in dense vibro-fluidized granular experiments

I will discuss a series of recent experimental results obtained within the same setup in different conditions of vibro-fluidization, density and applied external forcing. After reviewing older results obtained in the dilute limit, I will focus on the effect of increasing density and reducing temperature, when the gas first becomes a liquid: collisions become correlated and typical cage effects appear with subdiffusive transient. Surprisingly, at very low "granular temperatures", some new collective phenomena emerges inducing in the probe a pronounced superdiffusive behavior. Another important aspect of a granular media is its response properties. The application of a torque to the probe, by means of an external motor, allows us to verify linear response theory - with its non-equilibrium effects which become important at increasing density. In the non-linear regime, we enter the domain of granular rheology, where we have discovered a discontinuous transition from thinning to thickening regime. At very low intensity of the forcing, we also found (as a function of the vibration frequency) a reentrant transition from jammed to fluidized to jammed, interpreted as a kind of "viscosity recovery", whose frequency threshold depends upon inelasticity.

A Gnoli, L. de Arcangelis, F. Giacco, E. Lippiello, M. Pica Ciamarra, A. Puglisi, and A. Sarracino, Phys. Rev. Lett. 120, 138001 (2018)
A Gnoli, A Lasanta, A Sarracino, A Puglisi, Scientific Reports 6, 38604 (2016)
C Scalliet, A Gnoli, A Puglisi, A Vulpiani, Physical Review Letters 114, 198001 (2015)
A Gnoli, A Puglisi, A Sarracino, A Vulpiani, PloS one 9, e93720 (2014)
A Gnoli, A Petri, F Dalton, G Pontuale, G Gradenigo, A Sarracino, A. Puglisi, Physical Review Letters 110, 120601 (2013)