Effective temperatures and activated dynamics for a two-dimensional air-driven granular system on two approaches to jamming

TL;DR

This study investigates various effective temperatures in a 2D air-driven granular system across different densities and driving rates, finding consistent temperature measures and Arrhenius behavior indicating activated dynamics near jamming.

Contribution

It introduces multiple methods to measure effective temperatures in granular systems and demonstrates their agreement, providing insights into activated dynamics approaching jamming.

Findings

All effective temperature measurements agree across methods.

Mobility data collapse onto a single curve when plotted against effective temperature.

System exhibits Arrhenius behavior with a common energy barrier.

Abstract

We present experiments on several distinct effective temperatures in a granular system at a sequence of increasing packing densities and at a sequence of decreasing driving rates. This includes single-grain measurements based on the mechanical energies of both the grains and an embedded oscillator, as well as a collective measurement based on the Einstein relation between diffusivity and mobility, which all probe different time scales. Remarkably, all effective temperatures agree. Furthermore, mobility data along the two trajectories collapse when plotted vs effective temperature and exhibit an Arrhenius form with the same energy barrier as the microscopic relaxation time.