title: Scaling of avalanche queues in directed dissipative sandpiles
abstract: Using numerical simulations and analytical methods we study a two-dimensional directed sandpile automaton with nonconservative random defects (concentration c) and varying driving rate r. The automaton is driven only at the top row and driving rate is measured by the number of added particles per time step of avalanche evolution. The probability distribution of duration of elementary avalanches at zero driving rate is exactly given by P1(t,c)=t(-3/2) exp[t ln(1-c)]. For driving rates in the interval 0<r</=1 the avalanches are queuing one after another, increasing the periods of noninterrupted activity of the automaton. Recognizing the probability P1 as a distribution of service time of jobs arriving at a server with frequency r, the model represents an example of the class <E,1,GI/infinity,1> server queue in the queue theory. We study scaling properties of the busy period and dissipated energy of sequences of noninterrupted activity. In the limit c-->0 and varying linear system size L<<1/c we find that at driving rates r</=L(-1/2) the distributions of duration and energy of the avalanche queues are characterized by a multifractal scaling and we determine the corresponding spectral functions. For L>>1/c increasing the driving rate somewhat compensates for the energy losses at defects above the line r approximately sqrt[c]. The scaling exponents of the distributions in this region of phase diagram vary approximately linearly with the driving rate. Using properties of recurrent states and the probability theory we determine analytically the exact upper bound of the probability distribution of busy periods. In the case of conservative dynamics c=0 the probability of a continuous flow increases as F(infinity) approximately r(2) for small driving rates.
authors.affiliation: Jozef Stefan Institute, P.O. Box 3000, 1001 Ljubljana, Slovenia.
authors.initials: B
authors.lastname: Tadic
authors.initials: V
authors.lastname: Priezzhev