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Proc Natl Acad Sci U S A. 2005 Feb 15;102(7):2299-304. Epub 2005 Feb 8.

Experimental measurement of an effective temperature for jammed granular materials.

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Levich Institute and Physics Department, City College of New York, New York, NY 10031, USA.


A densely packed granular system is an example of an out-of-equilibrium system in the jammed state. It has been a longstanding problem to determine whether this class of systems can be described by concepts arising from equilibrium statistical mechanics, such as an effective temperature and compactivity. The measurement of the effective temperature is realized in the laboratory by slowly shearing a closely packed ensemble of spherical beads confined by an external pressure in a Couette geometry. All of the probe particles considered in this study, independent of their characteristic features, equilibrate at the same temperature, given by the packing density of the system.

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