Sandpile model on a quenched substrate generated by kinetic self-avoiding trails

Abelian deterministic self-organized-criticality model: complex dynamics of avalanche waves

The aim of this study is to investigate a wave dynamics and a size scaling of avalanches which were created by the mathematical model [J. Černák, Phys. Rev. E 65, 046141 (2002)]. Numerical simulations were carried out on a two-dimensional lattice L×L in which two constant thresholds E(c)(I) = 4 and E(c)(II) > E(c)(I) were randomly distributed. The density of sites c of the thresholds E(c)(II) and threshold E(c)(II) are parameters of the model. Autocorrelations of avalanche size waves, Hurst exponents, avalanche structures, and avalanche size moments were determined for several densities c and thresholds E(c)(II). The results show correlated avalanche size waves and multifractal scaling of avalanche sizes not only for specific conditions, densities c = 0.0,1.0 and thresholds 8 ≤ E(c)(II) ≤ 32, in which relaxation rules were precisely balanced, but also for more general conditions, densities 0.0 < c < 1.0 and thresholds 8 ≤ E(c)(II) ≤ 32, in which relaxation rules were unbalanced. The results suggest that the hypothesis of a precise relaxation balance could be a specific case of a more general rule.

Characteristics of deterministic and stochastic sandpile models in a rotational sandpile model

Rotational constraint representing a local external bias generally has a nontrivial effect on the critical behavior of lattice statistical models in equilibrium critical phenomena. In order to study the effect of rotational bias in an out-of-equilibrium situation like self-organized criticality, a two state "quasideterministic" rotational sandpile model is developed here imposing rotational constraint on the flow of sand grains. An extended set of critical exponents are estimated to characterize the avalanche properties at the nonequilibrium steady state of the model. The probability distribution functions are found to obey usual finite size scaling supported by negative time autocorrelation between the toppling waves. The model exhibits characteristics of both deterministic and stochastic sandpile models.

Inhomogeneous sandpile model: Crossover from multifractal scaling to finite-size scaling

We study an inhomogeneous sandpile model in which two different toppling rules are defined. For any site only one rule is applied corresponding to either the Bak, Tang, and Wiesenfeld model [P. Bak, C. Tang, and K. Wiesenfeld, Phys. Rev. Lett. 59, 381 (1987)] or the Manna two-state sandpile model [S. S. Manna, J. Phys. A 24, L363 (1991)]. A parameter c is introduced which describes a density of sites which are randomly deployed and where the stochastic Manna rules are applied. The results show that the avalanche area exponent tau a, avalanche size exponent tau s, and capacity fractal dimension Ds depend on the density c. A crossover from multifractal scaling of the Bak, Tang, and Wiesenfeld model (c = 0) to finite-size scaling was found. The critical density c is found to be in the interval 0 < c < 0.01. These results demonstrate that local dynamical rules are important and can change the global properties of the model.