$1/f^{\alpha}$ fluctuations in a ricepile model
  The temporal fluctuation of the average slope of a ricepile model is investigated. It is found that the power spectrum $S(f)$ scales as $1/f^{\alpha}$ with $\alpha\approx 1.3$ when grains of rice are added only to one end of the pile. If grains are randomly added to the pile, the power spectrum exhibits $1/f^2$ behaviour. The profile fluctuations of the pile under different driving mechanisms are also discussed. 
Shu-dong Zhang (Inst. Low Ener. Nucl. Phys., Beijing Normal   University)