Density fluctuations in granular piles traversing the glass transition…

Density fluctuations in granular piles traversing the glass transition: A grain-scale characterization via the internal energy

Stefan Boettcher, in collaboration with Paula Gago from Imperial College of London, used simulations of a cylindrical granular pile with 60000 spheres to achieve a grain-level understanding of the compaction dynamics. Its static configurations are rearranged via brief “taps” of precisely tuned intensity. In their Science Advances paper, they show that the pile transitions from a liquid-like into a “glassy” amorphous state for a protocol of taps of decreasing intensity that, however, is reached at a different intensity for different layers due to gravity. Defining effective kinetic energy that characterizes the dynamic process for each layer separately, they find a distinct, critical value at which a layer undergoes that transition, irrespective of its height in the pile or the overall tap intensity. By connecting the kinetic properties of grains with the resulting ensemble of static configurations, this study opens the prospect for a general kinetic theory of grains, especially at the transition into an increasingly dense, “glassy” state.

P.A. Gago and S. Boettcher, Sci. Adv. 8, eabl6304 (2022); DOI: 10.1126/sciadv.abl6304

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