title: Stationary state volume fluctuations in a granular medium.
abstract: A statistical description of static granular material requires ergodic sampling of the phase space spanned by the different configurations of the particles. We periodically fluidize a column of glass beads and find that the sequence of volume fractions phi of postfluidized states is history independent and Gaussian distributed about a stationary state. The standard deviation of phi exhibits, as a function of phi, a minimum corresponding to a maximum in the number of statistically independent regions. Measurements of the fluctuations enable us to determine the compactivity X , a temperaturelike state variable introduced in the statistical theory of Edwards and Oakeshott [Physica A 157, 1080 (1989)].
authors.affiliation: Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, 78712, USA. schroeter@chaos.utexas.edu
authors.forename: Matthias
authors.initials: M
authors.lastname: Schröter
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Goldman
authors.forename: Harry L
authors.initials: HL
authors.lastname: Swinney