1,072 research outputs found
Statistical Laws and Mechanics of Voronoi Random Lattices
We investigate random lattices where the connectivities are determined by the
Voronoi construction, while the location of the points are the dynamic degrees
of freedom. The Voronoi random lattices with an associated energy are immersed
in a heat bath and investigated using a Monte Carlo simulation algorithm. In
thermodynamic equilibrium we measure coordination number distributions and test
the Aboav-Weaire and Lewis laws.Comment: 14 pages (figures not included), LaTeX, HLRZ-26/9
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
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
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
Nature of yrast excitations near N=40: Level structure of Ni-67
Excited states in Ni-67 were populated in deep-inelastic reactions of a Ni-64
beam at 430 MeV on a thick U-238 target. A level scheme built on the previously
known 13 micro-s isomer has been delineated up to an excitation energy of ~5.3
MeV and a tentative spin and parity of (21/2-). Shell model calculations have
been carried out using two effective interactions in the f5/2pg9/2 model space
with a Ni-56 core. Satisfactory agreement between experiment and theory is
achieved for the measured transition energies and branching ratios. The
calculations indicate that the yrast states are associated with rather complex
configurations, herewith demonstrating the relative weakness of the N=40
subshell gap and the importance of multi particle-hole excitations involving
the g9/2 neutron orbital.Comment: Accepted by Physical Review
Self-organized criticality in a rice-pile model
We present a new model for relaxations in piles of granular material. The
relaxations are determined by a stochastic rule which models the effect of
friction between the grains. We find power-law distributions for avalanche
sizes and lifetimes characterized by the exponents and
, respectively. For the discharge events, we find a
characteristic size that scales with the system size as , with . We also find that the frequency of the discharge events
decrease with the system size as with .Comment: 4 pages, RevTex, multicol, epsf, rotate (sty files provided). To
appear Phys. Rev. E Rapid Communication (Nov or Dec 96
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