ABSTRACT
H < 0.5) monotonically. In the case of Brownian motion (H = 0.5) V (τ) would have a flat slope. If the behavior changes from persistent below a time scale τ0 to antipersistent above τ0, V (τ) will have a maximum at τ = τ0. Thus, if there is a cyclic behavior, the V analysis would be able to recognize its characteristic time scale. In granular materials fluid and solid-like regimes can exist simultaneously but the transitions between these regimes are not yet fully understood. In avalanches, for example, only a superficial layer moves while the rest of the grains remain static (Quintanilla et al. 2001). We find another example of multiphase behavior in a fluidized bed. In the first part of this paper we apply the Hurst analysis to temporal series of the average angle of slope of cohesive and noncohesive granular materials partially filling a rotating drum. This analysis will provide evidence for a scaling behavior in agreement with results from previous statistical studies (Quintanilla et al. 2001). In the second part of the paper we look for deeper insight into the character of fluidization dynamics from the values of the Hurst exponent exhibited by fluctuations of the solids concentration detected by an optical probe (Valverde et al. 2003).
