EXPERIMENTAL TEST OF TIME SCALES IN FLOWING SAND

We describe dynamic measurements of the stress obtained during a sand flow. The data show a large noise component as seen in power spectra for these data which satisfy P = = P0omega(-alpha) over at least three decades. Values of alpha span 1.3 less-than-or-equal-to alpha less-than-or-equal-to 2.3. A calculation of the Hurst parameter of fractional Brownian motion yields values of H which satisfy alpha = 2H + 1 within statistical errors. A time scale predicted from continuum models of sand flow may be present, but the inherent noise makes this scale difficult to determine.