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Dept of Physics

Statistical Mechanics of Granular Materials

With their ability to act as solids, liquids, or gases, the behavior of granular materials begs analogy with much of what we first learned about conventional molecules, but there are imporant differences. One goal of our research is to understand the solid-liquid ("jamming") transition for dense granular materials. In particular, the dynamics of granular materials depend strongly on whether they are loosely or closely packed. In this movie we show the diffusion and braiding of trajectories in a 2D granular system.

Additionally, we examined the fluctuations of the local volume fraction in dense driven granular systems. We found the fluctuations decrease as the system approaches the jamming transition independent of boundary condition (Constant pressure / Constant Volume) and inter-particle friction. To explore the universality of the relationship between local volume fraction and its fluctuations, we extended the recent granocentric model by including the separation distribution. Through the granocentric model, we observe that diverse functional forms of the separation distribution all produce the trend of decreasing fluctuations, but only the experimentally observed separation distribution provides quantitative agreement with the measured local volume fluctuations. Therefore, both the volume fraction and separation distribution encode similar information about the ensemble and are connected with the granocentric model.


  • Dapeng Bi, Silke Henkes, Karen E. Daniels, Bulbul Chakraborty. The Statistical Physics of Athermal Materials. (Annual Review of Condensed Matter Physics) [arXiV]

  • James G. Puckett and Karen E. Daniels. Equilibrating temperaturelike variables in jammed granular subsystems [Link] [PDF] [APS Synopsis] Physical Review Letters 110: 058001 (2013)

  • Kiri Nichol and Karen E. Daniels. Equipartition of rotational and translational energy in a dense granular gas. Physical Review Letters 108, 018001 (2012) [Link]

  • James G. Puckett, Frederic Lechenault, Karen E. Daniels. Local origins of volume fraction fluctuations in dense granular materials. Physical Review E 83, 041301 (2011) [Link]

  • Frederic Lechenault and Karen E. Daniels. Equilibration in Granular Subsystems. Soft Matter. 6: 3074 (2010) [Link]

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