# Structure factors in granular experiments with homogeneous fluidization

### A. Puglisi 1, A. Gnoli 2, 3, G. Gradenigo 4, A. Sarracino 5, D. Villamaina 6

#### Journal of Chemical Physics 136 (2012) 014704

Velocity and density structure factors are measured over a hydrodynamic range of scales in a horizontal quasi-2d fluidized granular experiment, with packing fractions $\phi\in[10%,40%]$. 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

• 1. Dipartimento di Fisica,
Università La Sapienza
• 2. Dipartimento di Fisica,
Università degli studi di Roma "La Sapienza"
• 3. Istituto dei Sistemi Complessi,
CNR - Consiglio Nationale delle Ricerche
• 4. Dipartimento di Fisica,
CNR - Consiglio Nationale delle Ricerche
• 5. Dipartimento di Fisica,
CNR - Consiglio Nationale delle Ricerche
• 6. Laboratoire de Physique Théorique et Modèles Statistiques (LPTMS),
CNRS : UMR8626 – Université Paris XI - Paris Sud