26,552 research outputs found
A stochastic evaluation of the contour strength
International audienceIf one considers only local neighborhoods for segmenting an image, one gets contours whose strength is often poorly estimated. A method for reevaluating the contour strength by taking into account non local features is presented: one generates a fixed number of random germs which serve as markers for the watershed segmentation. For each new population of markers, another set of contours is generated. "Important" contours are selected more often. The present paper shows that the probability that a contour is selected can be estimated without performing the effective simulations. Copyright Springer-Verlag 2010. The original publication is available at www.springerlink.com/content/y057x103475301r2
Automatic Selection of Stochastic Watershed Hierarchies
International audienceThe segmentation, seen as the association of a partition with an image, is a difficult task. It can be decomposed in two steps: at first, a family of contours associated with a series of nested partitions (or hierarchy) is created and organized, then pertinent contours are extracted. A coarser partition is obtained by merging adjacent regions of a finer partition. The strength of a contour is then measured by the level of the hierarchy for which its two adjacent regions merge. We present an automatic segmentation strategy using a wide range of stochastic watershed hierarchies. For a given set of homogeneous images, our approach selects automatically the best hierarchy and cut level to perform image simplification given an evaluation score. Experimental results illustrate the advantages of our approach on several real-life images datasets
Evaluation of Self-Intersecting Wilson Loop in the Stochastic Vacuum Model
A Wilson loop is evaluated within the stochastic vacuum model for the case
when the respective contour is self-intersecting and its size does not exceed
the correlation length of the vacuum. The result has the form of a certain
functional of the tensor area. It is similar to that for the
non-self-intersecting loop only when the contour is a plane one. Even for such
a contour, the obtained expression depends on the ratio of two functions
parametrizing the bilocal field strength correlator taken at the origin, which
is not so for the case of non-self-intersecting contour.Comment: 7 pages, LaTeX2e, no figures, minor stylistic corrections of the tex
Analytical probabilistic approach to the ground state of lattice quantum systems: exact results in terms of a cumulant expansion
We present a large deviation analysis of a recently proposed probabilistic
approach to the study of the ground-state properties of lattice quantum
systems. The ground-state energy, as well as the correlation functions in the
ground state, are exactly determined as a series expansion in the cumulants of
the multiplicities of the potential and hopping energies assumed by the system
during its long-time evolution. Once these cumulants are known, even at a
finite order, our approach provides the ground state analytically as a function
of the Hamiltonian parameters. A scenario of possible applications of this
analyticity property is discussed.Comment: 26 pages, 5 figure
DNA-Protein Binding Rates: Bending Fluctuation and Hydrodynamic Coupling Effects
We investigate diffusion-limited reactions between a diffusing particle and a
target site on a semiflexible polymer, a key factor determining the kinetics of
DNA-protein binding and polymerization of cytoskeletal filaments. Our theory
focuses on two competing effects: polymer shape fluctuations, which speed up
association, and the hydrodynamic coupling between the diffusing particle and
the chain, which slows down association. Polymer bending fluctuations are
described using a mean field dynamical theory, while the hydrodynamic coupling
between polymer and particle is incorporated through a simple heuristic
approximation. Both of these we validate through comparison with Brownian
dynamics simulations. Neither of the effects has been fully considered before
in the biophysical context, and we show they are necessary to form accurate
estimates of reaction processes. The association rate depends on the stiffness
of the polymer and the particle size, exhibiting a maximum for intermediate
persistence length and a minimum for intermediate particle radius. In the
parameter range relevant to DNA-protein binding, the rate increase is up to
100% compared to the Smoluchowski result for simple center-of-mass motion. The
quantitative predictions made by the theory can be tested experimentally.Comment: 21 pages, 11 figures, 1 tabl
An Iterative Procedure for the Estimation of Drift and Diffusion Coefficients of Langevin Processes
A general method is proposed which allows one to estimate drift and diffusion
coefficients of a stochastic process governed by a Langevin equation. It
extends a previously devised approach [R. Friedrich et al., Physics Letters A
271, 217 (2000)], which requires sufficiently high sampling rates. The analysis
is based on an iterative procedure minimizing the Kullback-Leibler distance
between measured and estimated two time joint probability distributions of the
process.Comment: 4 pages, 5 figure
Exact c-number Representation of Non-Markovian Quantum Dissipation
The reduced dynamics of a quantum system interacting with a linear heat bath
finds an exact representation in terms of a stochastic Schr{\"o}dinger
equation. All memory effects of the reservoir are transformed into noise
correlations and mean-field friction. The classical limit of the resulting
stochastic dynamics is shown to be a generalized Langevin equation, and
conventional quantum state diffusion is recovered in the Born--Markov
approximation. The non-Markovian exact dynamics, valid at arbitrary temperature
and damping strength, is exemplified by an application to the dissipative
two-state system.Comment: 4 pages, 2 figures. To be published in Phys. Rev. Let
Testing Nonperturbative Ansaetze for the QCD Field Strength Correlator
A test for the Gaussian and exponential Ansaetze for the nonperturbative
parts of the coefficient functions, D^{nonpert.} and D_1^{nonpert.}, which
parametrize the gauge-invariant bilocal correlator of the field strength
tensors in the stochastic vacuum model of QCD, is proposed. It is based on the
evaluation of the heavy-quark condensate within this model by making use of the
world-line formalism and equating the obtained result to the one following
directly from the QCD Lagrangian. This yields a certain relation between
D^{nonpert.}(0) and D_1^{nonpert.}(0), which is further compared with an
analogous relation between these quantities known from the existing lattice
data. Such a comparison leads to the conclusion that at the distances smaller
than the correlation length of the vacuum, Gaussian Ansatz is more suitable
than the exponential one.Comment: 10 pages, LaTeX2e, 1 table, no figure
- …