Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Nonequilibrium Phase Transition and Self-Organized Criticality in a
  Sandpile Model with Stochastic Dynamics   We introduce and study numerically a directed two-dimensional sandpile
automaton with probabilistic toppling (probability parameter p) which provides
a good laboratory to study both self-organized criticality and the
far-from-equilibrium phase transition. In the limit p=1 our model reduces to
the critical height model in which the self-organized critical behavior was
found by exact solution [D. Dhar and R. Ramaswamy, Phys. Rev. Lett. 63, 1659
(1989)]. For 0<p<1 metastable columns of sand may be formed, which are relaxed
when one of the local slopes exceeds a critical value sigma _c. By varying the
probability of toppling p we find that a continuous phase transition occurs at
the critical probability p_c, at which the steady states with zero average
slope (above p_c) are replaced by states characterized by a finite average
slope (below p_c). We study this phase transition in detail by introducing an
appropriate order parameter and the order-parameter susceptibility chi. In a
certain range of p<1 we find the self- organized critical behavior which is
characterized by nonuniversal p-dependent scaling exponents for the probability
distributions of size and length of avalanches. We also calculate the
anisotropy exponent zeta and the fractal dimension d_f of relaxation clusters
in the entire range of values of the toppling parameter p. We show that the
relaxation clusters in our model are anisotropic and can be described as
fractals for values of $p$ above the transition point. Below the transition
they are isotropic and compact.

16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
10
The categories of this paper are: q-bio
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
28
The categories of this paper are: alg-geom