3,783 research outputs found
Sandpile model on a quenched substrate generated by kinetic self-avoiding trails
Kinetic self-avoiding trails are introduced and used to generate a substrate
of randomly quenched flow vectors. Sandpile model is studied on such a
substrate with asymmetric toppling matrices where the precise balance between
the net outflow of grains from a toppling site and the total inflow of grains
to the same site when all its neighbors topple once is maintained at all sites.
Within numerical accuracy this model behaves in the same way as the
multiscaling BTW model.Comment: Four pages, five figure
Stochastic model of transcription factor-regulated gene expression
We consider a stochastic model of transcription factor (TF)-regulated gene
expression. The model describes two genes: Gene A and Gene B which synthesize
the TFs and the target gene proteins respectively. We show through analytic
calculations that the TF fluctuations have a significant effect on the
distribution of the target gene protein levels when the mean TF level falls in
the highest sensitive region of the dose-response curve. We further study the
effect of reducing the copy number of Gene A from two to one. The enhanced TF
fluctuations yield results different from those in the deterministic case. The
probability that the target gene protein level exceeds a threshold value is
calculated with a knowledge of the probability density functions associated
with the TF and target gene protein levels. Numerical simulation results for a
more detailed stochastic model are shown to be in agreement with those obtained
through analytic calculations. The relevance of these results in the context of
the genetic disorder haploinsufficiency is pointed out. Some experimental
observations on the haploinsufficiency of the tumour suppressor gene, Nkx3.1,
are explained with the help of the stochastic model of TF-regulated gene
expression.Comment: 17 pages, 11 figures. Accepted for publication in Physical Biolog
Texture as pixel feature for video object segmentation
As texture represents one of the key perceptual attributes of any object, integrating textural information into existing video object segmentation frameworks affords the potential to achieve semantically improved performance. While object segmentation is fundamentally pixel-based classification, texture is normally defined for the entire image, which raises the question of how best to directly specify and characterise texture as a pixel feature. Introduced is a generic strategy for representing textural information so it can be seamlessly incorporated as a pixel feature into any video object segmentation paradigm. Both numerical and perceptual results upon various test sequences reveal considerable improvement in the object segmentation performance when textural information is embedded
Equilibrium glassy phase in a polydisperse hard sphere system
The phase diagram of a polydisperse hard sphere system is examined by
numerical minimization of a discretized form of the Ramakrishnan-Yussouff free
energy functional. Crystalline and glassy local minima of the free energy are
located and the phase diagram in the density-polydispersity plane is mapped out
by comparing the free energies of different local minima. The crystalline phase
disappears and the glass becomes the equilibrium phase beyond a "terminal"
value of the polydispersity. A crystal to glass transition is also observed as
the density is increased at high polydispersity. The phase diagram obtained in
our study is qualitatively similar to that of hard spheres in a quenched random
potential.Comment: 4 pages, 4 figure
Precise toppling balance, quenched disorder, and universality for sandpiles
A single sandpile model with quenched random toppling matrices captures the
crucial features of different models of self-organized criticality. With
symmetric matrices avalanche statistics falls in the multiscaling BTW
universality class. In the asymmetric case the simple scaling of the Manna
model is observed. The presence or absence of a precise toppling balance
between the amount of sand released by a toppling site and the total quantity
the same site receives when all its neighbors topple once determines the
appropriate universality class.Comment: 5 Revtex pages, 4 figure
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