Dynamic synchrotron X-ray imaging study of effective temperature in a vibrated granular medium

摘要

We present a dynamic synchrotron X-ray imaging study of the effectivetemperature $T_{eff}$ in a vibrated granular medium. By tracking the directedmotion and the fluctuation dynamics of the tracers inside, we obtained$T_{eff}$ of the system using Einstein relation. We found that as the systemunjams with increasing vibration intensities $\Gamma$, the structuralrelaxation time $\tau$ increases substantially which can be fitted by anArrhenius law using $T_{eff}$. And the characteristic energy scale ofstructural relaxation yielded by the Arrhenius fitting is $E = 0.21 \pm 0.02$$pd^3$, where $p$ is the pressure and $d$ is the background particle diameter,which is consistent with those from hard sphere simulations in which thestructural relaxation happens via the opening up of free volume againstpressure.