Generalized Manna sandpile model with height restrictions
  Sandpile models with conserved number of particles (also called fixed energy sandpiles) may undergo phase transitions between active and absorbing states. We generalize the Manna sandpile model with fixed number of particles, introducing a parameter $-1 \leq \lambda \leq 1$ related to the toppling of particles from active sites to its first neighbors. In particular, we discuss a model with height restrictions, allowing for at most two particles on a site. Sites with double occupancy are active, and their particles may be transfered to first neighbor sites, if the height restriction do allow the change. For $\lambda=0$ each one of the two particles is independently assigned to one of the two first neighbors and the original stochastic sandpile model is recovered. For $\lambda=1$ exactly one particle will be placed on each first neighbor and thus a deterministic (BTW) sandpile model is obtained. When $\lambda=-1$ two particles are moved to one of the first neighbors, and this implies that the density of active sites is conserved in the evolution of the system, and no phase transition is observed. Through simulations of the stationary state, we estimate the critical density of particles and the critical exponents as functions of $\lambda$. 
W.G.Dantas and J.F.Stilck