title: Structure factors in granular experiments with homogeneous fluidization.
abstract: Velocity and density structure factors are measured over a hydrodynamic range of scales in a horizontal quasi-2D fluidized granular experiment, with packing fractions φ ∈ [10%, 40%]. The fluidization is realized by vertically vibrating a rough plate, on top of which particles perform a Brownian-like horizontal motion in addition to inelastic collisions. On one hand, the density structure factor is equal to that of elastic hard spheres, except in the limit of large length-scales, as it occurs in the presence of an effective interaction. On the other hand, the velocity field shows a more complex structure which is a genuine expression of a non-equilibrium steady state and which can be compared to a recent fluctuating hydrodynamic theory with non-equilibrium noise. The temporal decay of velocity modes autocorrelations is compatible with linear hydrodynamic equations with rates dictated by viscous momentum diffusion, corrected by a typical interaction time with the thermostat. Equal-time velocity structure factors display a peculiar shape with a plateau at large length-scales and another one at small scales, marking two different temperatures: the "bath" temperature T(b), depending on shaking parameters, and the "granular" temperature T(g) < T(b), which is affected by collisions. The two ranges of scales are separated by a correlation length which grows with φ, after proper rescaling with the mean free path.
authors.affiliation: Istituto dei Sistemi Complessi-CNR and Dipartimento di Fisica, Università Sapienza, p.le A. Moro 2, 00185 Rome, Italy. andrea.puglisi@roma1.infn.it
authors.forename: Andrea
authors.initials: A
authors.lastname: Puglisi
authors.forename: Andrea
authors.initials: A
authors.lastname: Gnoli
authors.forename: Giacomo
authors.initials: G
authors.lastname: Gradenigo
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sarracino
authors.forename: Dario
authors.initials: D
authors.lastname: Villamaina