2,055 research outputs found
Maxillary nerve blocks in horses: an experimental comparison of surface landmark and ultrasound-guided techniques
A new model of binary opinion dynamics: coarsening and effect of disorder
We propose a model of binary opinion in which the opinion of the individuals
change according to the state of their neighbouring domains. If the
neighbouring domains have opposite opinions, then the opinion of the domain
with the larger size is followed. Starting from a random configuration, the
system evolves to a homogeneous state. The dynamical evolution show novel
scaling behaviour with the persistence exponent and
dynamic exponent . Introducing disorder through a
parameter called rigidity coefficient (probability that people are
completely rigid and never change their opinion), the transition to a
heterogeneous society at is obtained. Close to , the
equilibrium values of the dynamic variables show power law scaling behaviour
with . We also discuss the effect of having both quenched and annealed
disorder in the system.Comment: 4 pages, 6 figures, Final version of PR
On Spatial Consensus Formation: Is the Sznajd Model Different from a Voter Model?
In this paper, we investigate the so-called ``Sznajd Model'' (SM) in one
dimension, which is a simple cellular automata approach to consensus formation
among two opposite opinions (described by spin up or down). To elucidate the SM
dynamics, we first provide results of computer simulations for the
spatio-temporal evolution of the opinion distribution , the evolution of
magnetization , the distribution of decision times and
relaxation times . In the main part of the paper, it is shown that the
SM can be completely reformulated in terms of a linear VM, where the transition
rates towards a given opinion are directly proportional to frequency of the
respective opinion of the second-nearest neighbors (no matter what the nearest
neighbors are). So, the SM dynamics can be reduced to one rule, ``Just follow
your second-nearest neighbor''. The equivalence is demonstrated by extensive
computer simulations that show the same behavior between SM and VM in terms of
, , , , and the final attractor statistics. The
reformulation of the SM in terms of a VM involves a new parameter , to
bias between anti- and ferromagnetic decisions in the case of frustration. We
show that plays a crucial role in explaining the phase transition
observed in SM. We further explore the role of synchronous versus asynchronous
update rules on the intermediate dynamics and the final attractors. Compared to
the original SM, we find three additional attractors, two of them related to an
asymmetric coexistence between the opposite opinions.Comment: 22 pages, 20 figures. For related publications see
http://www.ais.fraunhofer.de/~fran
Absorbing-state phase transitions on percolating lattices
We study nonequilibrium phase transitions of reaction-diffusion systems
defined on randomly diluted lattices, focusing on the transition across the
lattice percolation threshold. To develop a theory for this transition, we
combine classical percolation theory with the properties of the supercritical
nonequilibrium system on a finite-size cluster. In the case of the contact
process, the interplay between geometric criticality due to percolation and
dynamical fluctuations of the nonequilibrium system leads to a new universality
class. The critical point is characterized by ultraslow activated dynamical
scaling and accompanied by strong Griffiths singularities. To confirm the
universality of this exotic scaling scenario we also study the generalized
contact process with several (symmetric) absorbing states, and we support our
theory by extensive Monte-Carlo simulations.Comment: 11 pages, 10 eps figures included, final version as publishe
Nonequilibrium phase transition on a randomly diluted lattice
We show that the interplay between geometric criticality and dynamical
fluctuations leads to a novel universality class of the contact process on a
randomly diluted lattice. The nonequilibrium phase transition across the
percolation threshold of the lattice is characterized by unconventional
activated (exponential) dynamical scaling and strong Griffiths effects. We
calculate the critical behavior in two and three space dimensions, and we also
relate our results to the recently found infinite-randomness fixed point in the
disordered one-dimensional contact process.Comment: 4 pages, 1 eps figure, final version as publishe
Expansion for -Core Percolation
The physics of -core percolation pertains to those systems whose
constituents require a minimum number of connections to each other in order
to participate in any clustering phenomenon. Examples of such a phenomenon
range from orientational ordering in solid ortho-para mixtures to
the onset of rigidity in bar-joint networks to dynamical arrest in
glass-forming liquids. Unlike ordinary () and biconnected ()
percolation, the mean field -core percolation transition is both
continuous and discontinuous, i.e. there is a jump in the order parameter
accompanied with a diverging length scale. To determine whether or not this
hybrid transition survives in finite dimensions, we present a expansion
for -core percolation on the -dimensional hypercubic lattice. We show
that to order the singularity in the order parameter and in the
susceptibility occur at the same value of the occupation probability. This
result suggests that the unusual hybrid nature of the mean field -core
transition survives in high dimensions.Comment: 47 pages, 26 figures, revtex
Holocene carbon-cycle dynamics based on CO2 trapped in ice at Taylor Dome, Antarctica
A high-resolution ice-core record of atmospheric CO2 concentration over the Holocene epoch shows that the global carbon cycle has not been in steady state during the past 11,000 years. Analysis of the CO2 concentration and carbon stable-isotope records, using a one-dimensional carbon-cycle model,uggests that changes in terrestrial biomass and sea surface temperature were largely responsible for the observed millennial-scale changes of atmospheric CO2 concentrations
Solution of the tunneling-percolation problem in the nanocomposite regime
We noted that the tunneling-percolation framework is quite well understood at
the extreme cases of percolation-like and hopping-like behaviors but that the
intermediate regime has not been previously discussed, in spite of its
relevance to the intensively studied electrical properties of nanocomposites.
Following that we study here the conductivity of dispersions of particle
fillers inside an insulating matrix by taking into account explicitly the
filler particle shapes and the inter-particle electron tunneling process. We
show that the main features of the filler dependencies of the nanocomposite
conductivity can be reproduced without introducing any \textit{a priori}
imposed cut-off in the inter-particle conductances, as usually done in the
percolation-like interpretation of these systems. Furthermore, we demonstrate
that our numerical results are fully reproduced by the critical path method,
which is generalized here in order to include the particle filler shapes. By
exploiting this method, we provide simple analytical formulas for the composite
conductivity valid for many regimes of interest. The validity of our
formulation is assessed by reinterpreting existing experimental results on
nanotube, nanofiber, nanosheet and nanosphere composites and by extracting the
characteristic tunneling decay length, which is found to be within the expected
range of its values. These results are concluded then to be not only useful for
the understanding of the intermediate regime but also for tailoring the
electrical properties of nanocomposites.Comment: 13 pages with 8 figures + 10 pages with 9 figures of supplementary
material (Appendix B
Connected component identification and cluster update on GPU
Cluster identification tasks occur in a multitude of contexts in physics and
engineering such as, for instance, cluster algorithms for simulating spin
models, percolation simulations, segmentation problems in image processing, or
network analysis. While it has been shown that graphics processing units (GPUs)
can result in speedups of two to three orders of magnitude as compared to
serial codes on CPUs for the case of local and thus naturally parallelized
problems such as single-spin flip update simulations of spin models, the
situation is considerably more complicated for the non-local problem of cluster
or connected component identification. I discuss the suitability of different
approaches of parallelization of cluster labeling and cluster update algorithms
for calculations on GPU and compare to the performance of serial
implementations.Comment: 15 pages, 14 figures, one table, submitted to PR
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