1,575 research outputs found
Scaling relation for determining the critical threshold for continuum percolation of overlapping discs of two sizes
We study continuum percolation of overlapping circular discs of two sizes. We
propose a phenomenological scaling equation for the increase in the effective
size of the larger discs due to the presence of the smaller discs. The critical
percolation threshold as a function of the ratio of sizes of discs, for
different values of the relative areal densities of two discs, can be described
in terms of a scaling function of only one variable. The recent accurate Monte
Carlo estimates of critical threshold by Quintanilla and Ziff [Phys. Rev. E, 76
051115 (2007)] are in very good agreement with the proposed scaling relation.Comment: 4 pages, 3 figure
Roughening Transition in a One-Dimensional Growth Process
A class of nonequilibrium models with short-range interactions and sequential
updates is presented. The models describe one dimensional growth processes
which display a roughening transition between a smooth and a rough phase. This
transition is accompanied by spontaneous symmetry breaking, which is described
by an order parameter whose dynamics is non-conserving. Some aspects of models
in this class are related to directed percolation in 1+1 dimensions, although
unlike directed percolation the models have no absorbing states. Scaling
relations are derived and compared with Monte Carlo simulations.Comment: 4 pages, 3 Postscript figures, 1 Postscript formula, uses RevTe
Herding model and 1/f noise
We provide evidence that for some values of the parameters a simple agent
based model, describing herding behavior, yields signals with 1/f power
spectral density. We derive a non-linear stochastic differential equation for
the ratio of number of agents and show, that it has the form proposed earlier
for modeling of 1/f^beta noise with different exponents beta. The non-linear
terms in the transition probabilities, quantifying the herding behavior, are
crucial to the appearance of 1/f noise. Thus, the herding dynamics can be seen
as a microscopic explanation of the proposed non-linear stochastic differential
equations generating signals with 1/f^beta spectrum. We also consider the
possible feedback of macroscopic state on microscopic transition probabilities
strengthening the non-linearity of equations and providing more opportunities
in the modeling of processes exhibiting power-law statistics
Change in physical activity after smoking cessation: the Coronary Artery Risk Development in Young Adults (CARDIA) study.
AIMS: To estimate physical activity trajectories for people who quit smoking, and compare them to what would have been expected had smoking continued.
DESIGN, SETTING AND PARTICIPANTS: A total of 5115 participants in the Coronary Artery Risk Development in Young Adults Study (CARDIA) study, a population-based study of African American and European American people recruited at age 18-30 years in 1985/6 and followed over 25 years.
MEASUREMENTS: Physical activity was self-reported during clinical examinations at baseline (1985/6) and at years 2, 5, 7, 10, 15, 20 and 25 (2010/11); smoking status was reported each year (at examinations or by telephone, and imputed where missing). We used mixed linear models to estimate trajectories of physical activity under varying smoking conditions, with adjustment for participant characteristics and secular trends.
FINDINGS: We found significant interactions by race/sex (Pâ=â0.02 for the interaction with cumulative years of smoking), hence we investigated the subgroups separately. Increasing years of smoking were associated with a decline in physical activity in black and white women and black men [e.g. coefficient for 10 years of smoking: -0.14; 95% confidence interval (CI)â=â-0.20 to -0.07, Pâ<â0.001 for white women]. An increase in physical activity was associated with years since smoking cessation in white men (coefficient 0.06; 95% CIâ=â0 to 0.13, Pâ=â0.05). The physical activity trajectory for people who quit diverged progressively towards higher physical activity from the expected trajectory had smoking continued. For example, physical activity was 34% higher (95% CIâ=â18 to 52%; Pâ<â0.001) for white women 10 years after stopping compared with continuing smoking for those 10 years (Pâ=â0.21 for race/sex differences).
CONCLUSIONS: Smokers who quit have progressively higher levels of physical activity in the years after quitting compared with continuing smokers
Roughness of Crack Interfaces in Two-Dimensional Beam Lattices
The roughness of crack interfaces is reported in quasistatic fracture, using
an elastic network of beams with random breaking thresholds. For strong
disorders we obtain 0.86(3) for the roughness exponent, a result which is very
different from the minimum energy surface exponent, i.e., the value 2/3. A
cross-over to lower values is observed as the disorder is reduced, the exponent
in these cases being strongly dependent on the disorder.Comment: 9 pages, RevTeX, 3 figure
Detecting modules in dense weighted networks with the Potts method
We address the problem of multiresolution module detection in dense weighted
networks, where the modular structure is encoded in the weights rather than
topology. We discuss a weighted version of the q-state Potts method, which was
originally introduced by Reichardt and Bornholdt. This weighted method can be
directly applied to dense networks. We discuss the dependence of the resolution
of the method on its tuning parameter and network properties, using sparse and
dense weighted networks with built-in modules as example cases. Finally, we
apply the method to data on stock price correlations, and show that the
resulting modules correspond well to known structural properties of this
correlation network.Comment: 14 pages, 6 figures. v2: 1 figure added, 1 reference added, minor
changes. v3: 3 references added, minor change
miRvestigator: web application to identify miRNAs responsible for co-regulated gene expression patterns discovered through transcriptome profiling
Transcriptome profiling studies have produced staggering numbers of gene co-expression signatures for a variety of biological systems. A significant fraction of these signatures will be partially or fully explained by miRNA-mediated targeted transcript degradation. miRvestigator takes as input lists of co-expressed genes from Caenorhabditis elegans, Drosophila melanogaster, G. gallus, Homo sapiens, Mus musculus or Rattus norvegicus and identifies the specific miRNAs that are likely to bind to 3âČ un-translated region (UTR) sequences to mediate the observed co-regulation. The novelty of our approach is the miRvestigator hidden Markov model (HMM) algorithm which systematically computes a similarity P-value for each unique miRNA seed sequence from the miRNA database miRBase to an overrepresented sequence motif identified within the 3âČ-UTR of the query genes. We have made this miRNA discovery tool accessible to the community by integrating our HMM algorithm with a proven algorithm for de novo discovery of miRNA seed sequences and wrapping these algorithms into a user-friendly interface. Additionally, the miRvestigator web server also produces a list of putative miRNA binding sites within 3âČ-UTRs of the query transcripts to facilitate the design of validation experiments. The miRvestigator is freely available at http://mirvestigator.systemsbiology.net
Fracture in Three-Dimensional Fuse Networks
We report on large scale numerical simulations of fracture surfaces using
random fuse networks for two very different disorders. There are some
properties and exponents that are different for the two distributions, but
others, notably the roughness exponents, seem universal. For the universal
roughness exponent we found a value of zeta = 0.62 +/- 0.05. In contrast to
what is observed in two dimensions, this value is lower than that reported in
experimental studies of brittle fractures, and rules out the minimal energy
surface exponent, 0.41 +/- 0.01.Comment: 4 pages, RevTeX, 5 figures, Postscrip
First Order Phase Transition in Intermediate Energy Heavy Ion Collisions
We model the disassembly of an excited nuclear system formed as a result of a
heavy ion collision. We find that, as the beam energy in central collisions in
varied, the dissociating system crosses a liquid-gas coexistence curve,
resulting in a first-order phase transition. Accessible experimental signatures
are identified: a peak in specific heat, a power-law yield for composites, and
a maximum in the second moment of the yield distribution
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