1,092 research outputs found
Surface Critical Behavior in Systems with Absorbing States
We present a general scaling theory for the surface critical behavior of
non-equilibrium systems with phase transitions into absorbing states. The
theory allows for two independent surface exponents which satisfy generalized
hyperscaling relations. As an application we study a generalized version of
directed percolation with two absorbing states. We find two distinct surface
universality classes associated with inactive and reflective walls. Our results
indicate that the exponents associated with these two surface universality
classes are closely connected.Comment: latex, 4 pages, to appear in PR
Quenched noise and over-active sites in sandpile dynamics
The dynamics of sandpile models are mapped to discrete interface equations.
We study in detail the Bak-Tang-Wiesenfeld model, a stochastic model with
random thresholds, and the Manna model. These are, respectively,
discretizations of the quenched Edwards-Wilkinson equation with columnar,
point-like and correlated noise, with the constraint that the interface
velocity is either zero or exactly one. The constraint, embedded in the
sandpile rules, gives rise to another noise component. This term has for the
Bak-Tang-Wiesenfeld model long-range on-site correlations and reveals that with
open boundary conditions there is no spatial translational invariance.Comment: 4 pages, 3 figure
Onset of criticality and transport in a driven diffusive system
We study transport properties in a slowly driven diffusive system where the
transport is externally controlled by a parameter . Three types of behavior
are found: For the system is not conducting at all. For intermediate
a finite fraction of the external excitations propagate through the system.
Third, in the regime the system becomes completely conducting. For all
the system exhibits self-organized critical behavior. In the middle of
this regime, at , the system undergoes a continuous phase transition
described by critical exponents.Comment: 4 latex/revtex pages; 4 figure
Novel Quenched Disorder Fixed Point in a Two-Temperature Lattice Gas
We investigate the effects of quenched randomness on the universal properties
of a two-temperature lattice gas. The disorder modifies the dynamical
transition rates of the system in an anisotropic fashion, giving rise to a new
fixed point. We determine the associated scaling form of the structure factor,
quoting critical exponents to two-loop order in an expansion around the upper
critical dimension d. The close relationship with another quenched
disorder fixed point, discovered recently in this model, is discussed.Comment: 11 pages, no figures, RevTe
Active Width at a Slanted Active Boundary in Directed Percolation
The width W of the active region around an active moving wall in a directed
percolation process diverges at the percolation threshold p_c as W \simeq A
\epsilon^{-\nu_\parallel} \ln(\epsilon_0/\epsilon), with \epsilon=p_c-p,
\epsilon_0 a constant, and \nu_\parallel=1.734 the critical exponent of the
characteristic time needed to reach the stationary state \xi_\parallel \sim
\epsilon^{-\nu_\parallel}. The logarithmic factor arises from screening of
statistically independent needle shaped sub clusters in the active region.
Numerical data confirm this scaling behaviour.Comment: 5 pages, 5 figure
Universality classes in directed sandpile models
We perform large scale numerical simulations of a directed version of the
two-state stochastic sandpile model. Numerical results show that this
stochastic model defines a new universality class with respect to the Abelian
directed sandpile. The physical origin of the different critical behavior has
to be ascribed to the presence of multiple topplings in the stochastic model.
These results provide new insights onto the long debated question of
universality in abelian and stochastic sandpiles.Comment: 5 pages, RevTex, includes 9 EPS figures. Minor english corrections.
One reference adde
Sow body condition at weaning and reproduction performance in organic piglet production
The objective was to investigate the variation in backfat at weaning and its relations to reproduction results in organic sow herds in Denmark. The study included eight herds and 573 sows. The average backfat at weaning mean�13 mm; SD�4.2 mm) ranging from 10.5 to 17.3 mm among herds shows that it is possible to avoid poor body condition at weaning even with a lactation length of seven weeks or more. No main effect of backfat at weaning on reproduction performance was found, but the probability of a successful reproduction after weaning tended to decrease with decreasing backfat for first parity sows, whereas the opposite was the case for multiparous sows
Surface Critical Behavior in Systems with Non-Equilibrium Phase Transitions
We study the surface critical behavior of branching-annihilating random walks
with an even number of offspring (BARW) and directed percolation (DP) using a
variety of theoretical techniques. Above the upper critical dimensions d_c,
with d_c=4 (DP) and d_c=2 (BARW), we use mean field theory to analyze the
surface phase diagrams using the standard classification into ordinary,
special, surface, and extraordinary transitions. For the case of BARW, at or
below the upper critical dimension, we use field theoretic methods to study the
effects of fluctuations. As in the bulk, the field theory suffers from
technical difficulties associated with the presence of a second critical
dimension. However, we are still able to analyze the phase diagrams for BARW in
d=1,2, which turn out to be very different from their mean field analog.
Furthermore, for the case of BARW only (and not for DP), we find two
independent surface beta_1 exponents in d=1, arising from two distinct
definitions of the order parameter. Using an exact duality transformation on a
lattice BARW model in d=1, we uncover a relationship between these two surface
beta_1 exponents at the ordinary and special transitions. Many of our
predictions are supported using Monte-Carlo simulations of two different models
belonging to the BARW universality class.Comment: 19 pages, 12 figures, minor additions, 1 reference adde
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