Phase diagrams and magnetic behavior of films with amorphization and anisotropy in surfaces

The phase diagrams and magnetic behavior of thin films with two amorphous surfaces are investigated by the use of the effective field theory with correlations. The transition temperature dependence of the exchange integral at surfaces, coupling between surface and nearest-layers, film thickness, and structural fluctuations are studied. Some interesting phenomena can occur as wetting phenomena and compensation point.The phase diagrams and magnetic behavior of thin films with two amorphous surfaces are investigated by the use of the effective field theory with correlations. The transition temperature dependence of the exchange integral at surfaces, coupling between surface and nearest-layers, film thickness, and structural fluctuations are studied. Some interesting phenomena can occur as wetting phenomena and compensation point

Numerical study of rice-pile model

A one-dimensional model of a rice-pile is numerically studied for different driving mechanisms. We found that for a sufficiently large system, there is a sharp transition between the trivial behaviour of a 1D BTW model and self-organized critical (SOC) behaviour. Depending on the driving mechanism, the self-organized critical rice-pile model belongs to two different universality classes.A one-dimensional model of a rice-pile is numerically studied for different driving mechanisms. We found that for a sufficiently large system, there is a sharp transition between the trivial behaviour of a 1D BTW model and self-organized critical (SOC) behaviour. Depending on the driving mechanism, the self-organized critical rice-pile model belongs to two different universality classes

A simulation study of an asymmetric exclusion model with disorder

On the one hand, using numerical simulations, we study the asymmetric exclusion model with open boundaries, particlewise disorder. The phase diagram in the (α , β)   -plane displays high density, low density and maximum current phases, with the first order transition line between high and low density phases shifted away from the line α =β. Within the low density phase a platoon phase transition occurs, many features of which can be explained using exact results for asymmetric exclusion with particlewise disorder on the ring. In a certain region of parameter space the disorder induces a cusp in the current-density relation at maximum flow. Our simulations indicate that this does not affect the topology of the phase diagram, nor the familiar 1/Öx -decay of the density profile in the maximum current phase. On the other hand, we study the effects of defects in the road and of jumping rate ∆t on the phase diagram J−ρ, using asymmetric exclusion model with periodic boundaries. For different level of disorder, the space-time evolution of particles displays «waves» for both phases low density and high density. Besides, there exist two critical values of density, a lower critical value ρc1 and a upper critical value ρc2, in between the current is constant and reaches its maximal value Jmax which increases with increasing the jumping rate ∆t and/or the degree of disorder c. Increasing ∆t and/or c, ρc1 increases and ρc2 decreases.On the one hand, using numerical simulations, we study the asymmetric exclusion model with open boundaries, particlewise disorder. The phase diagram in the (α , β)   -plane displays high density, low density and maximum current phases, with the first order transition line between high and low density phases shifted away from the line α =β. Within the low density phase a platoon phase transition occurs, many features of which can be explained using exact results for asymmetric exclusion with particlewise disorder on the ring. In a certain region of parameter space the disorder induces a cusp in the current-density relation at maximum flow. Our simulations indicate that this does not affect the topology of the phase diagram, nor the familiar 1/Öx -decay of the density profile in the maximum current phase. On the other hand, we study the effects of defects in the road and of jumping rate ∆t on the phase diagram J−ρ, using asymmetric exclusion model with periodic boundaries. For different level of disorder, the space-time evolution of particles displays «waves» for both phases low density and high density. Besides, there exist two critical values of density, a lower critical value ρc1 and a upper critical value ρc2, in between the current is constant and reaches its maximal value Jmax which increases with increasing the jumping rate ∆t and/or the degree of disorder c. Increasing ∆t and/or c, ρc1 increases and ρc2 decreases

Disorder-induced phase transition in a one-dimensional model of rice pile

We propose a one-dimensional rice-pile model which connects the 1D BTW sandpile model (Phys. Rev. A 38, 364 (1988)) and the Oslo rice-pile model (Phys. Rev. lett. 77, 107 (1997)) in a continuous manner. We found that for a sufficiently large system, there is a sharp transition between the trivial critical behaviour of the 1D BTW model and the self-organized critical (SOC) behaviour. When there is SOC, the model belongs to a known universality class with the avalanche exponent $\tau=1.53$.Comment: 10 pages, 7 eps figure

A sharp transition between a trivial 1D BTW model and self-organized critical rice-pile model

PACS. 05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion - 64.60.Ht Dynamic critical phenomena - 05.70.Ln Nonequilibrium and irreversible thermodynamics,