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Nature 424, 886-887 (21 August 2003) | doi:10.1038/424886a
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Granular materials: Shaken sand — a granular fluid?
Paul Umbanhowar1
Abstract
The connection between random grain motion and viscosity in shaken sand — a strongly non-equilibrium system — has been probed. Curiously, the link is similar to that found in an ordinary liquid in thermal equilibrium.
By measuring both the free and forced oscillations of a rigid pendulum immersed in an ordinary liquid, the temperature and viscosity of the liquid can be determined1. This is due, in part, to a relation from equilibrium statistical mechanics known as the fluctuation–dissipation theorem2, which, in a precursor to its modern form, was devised by Einstein3 to explain the diffusive Brownian motion of small particles suspended in liquids4.
- Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3112, USA.
Email: umbanhowar@nwu.edu
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