118,403 research outputs found
Statistical region based active contour using a fractional entropy descriptor: Application to nuclei cell segmentation in confocal microscopy images
We propose an unsupervised statistical region based active contour approach integrating an original fractional entropy measure for image segmentation with a particular application to single channel actin tagged fluorescence confocal microscopy image segmentation. Following description of statistical based active contour segmentation and the mathematical definition of the proposed fractional entropy descriptor, we demonstrate comparative segmentation results between the proposed approach and standard Shannon’s entropy on synthetic and natural images. We also show that the proposed unsupervised
statistical based approach, integrating the fractional entropy measure, leads to very satisfactory segmentation of the cell nuclei from which shape characterization can be calculated
Fractional Entropy Based Active Contour Segmentation of Cell Nuclei in Actin-Tagged Confocal Microscopy Images
In the framework of cell structure characterization for predictive oncology, we propose in this paper an unsupervised statistical region based active contour approach integrating an original fractional entropy measure for single channel actin tagged fluorescence confocal microscopy image segmentation. Following description of statistical based active contour segmentation and the mathematical definition of the proposed fractional entropy descriptor, we demonstrate comparative segmentation results between the proposed approach and standard Shannon’s entropy obtained for nuclei segmentation. We show that the unsupervised proposed statistical based approach integrating the fractional entropy measure leads to very satisfactory segmentation of the cell nuclei from which shape characterization can be subsequently used for the therapy progress assessment
Vlasov-Poisson in 1D for initially cold systems: post-collapse Lagrangian perturbation theory
We study analytically the collapse of an initially smooth, cold,
self-gravitating collisionless system in one dimension. The system is described
as a central "S" shape in phase-space surrounded by a nearly stationary halo
acting locally like a harmonic background on the S. To resolve the dynamics of
the S under its self-gravity and under the influence of the halo, we introduce
a novel approach using post-collapse Lagrangian perturbation theory. This
approach allows us to follow the evolution of the system between successive
crossing times and to describe in an iterative way the interplay between the
central S and the halo. Our theoretical predictions are checked against
measurements in entropy conserving numerical simulations based on the waterbag
method. While our post-collapse Lagrangian approach does not allow us to
compute rigorously the long term behavior of the system, i.e. after many
crossing times, it explains the close to power-law behavior of the projected
density observed in numerical simulations. Pushing the model at late time
suggests that the system could build at some point a very small flat core, but
this is very speculative. This analysis shows that understanding the dynamics
of initially cold systems requires a fine grained approach for a correct
description of their very central part. The analyses performed here can
certainly be extended to spherical symmetry.Comment: 20 pages, 9 figures, accepted for publication in MNRA
Quantum Chaos and Thermalization in Isolated Systems of Interacting Particles
This review is devoted to the problem of thermalization in a small isolated
conglomerate of interacting constituents. A variety of physically important
systems of intensive current interest belong to this category: complex atoms,
molecules (including biological molecules), nuclei, small devices of condensed
matter and quantum optics on nano- and micro-scale, cold atoms in optical
lattices, ion traps. Physical implementations of quantum computers, where there
are many interacting qubits, also fall into this group. Statistical
regularities come into play through inter-particle interactions, which have two
fundamental components: mean field, that along with external conditions, forms
the regular component of the dynamics, and residual interactions responsible
for the complex structure of the actual stationary states. At sufficiently high
level density, the stationary states become exceedingly complicated
superpositions of simple quasiparticle excitations. At this stage, regularities
typical of quantum chaos emerge and bring in signatures of thermalization. We
describe all the stages and the results of the processes leading to
thermalization, using analytical and massive numerical examples for realistic
atomic, nuclear, and spin systems, as well as for models with random
parameters. The structure of stationary states, strength functions of simple
configurations, and concepts of entropy and temperature in application to
isolated mesoscopic systems are discussed in detail. We conclude with a
schematic discussion of the time evolution of such systems to equilibrium.Comment: 69 pages, 31 figure
Statistical Theory of Finite Fermi-Systems Based on the Structure of Chaotic Eigenstates
The approach is developed for the description of isolated Fermi-systems with
finite number of particles, such as complex atoms, nuclei, atomic clusters etc.
It is based on statistical properties of chaotic excited states which are
formed by the interaction between particles. New type of ``microcanonical''
partition function is introduced and expressed in terms of the average shape of
eigenstates where is the total energy of the system. This
partition function plays the same role as the canonical expression
for open systems in thermal bath. The approach allows to
calculate mean values and non-diagonal matrix elements of different operators.
In particular, the following problems have been considered: distribution of
occupation numbers and its relevance to the canonical and Fermi-Dirac
distributions; criteria of equilibrium and thermalization; thermodynamical
equation of state and the meaning of temperature, entropy and heat capacity,
increase of effective temperature due to the interaction. The problems of
spreading widths and shape of the eigenstates are also studied.Comment: 17 pages in RevTex and 5 Postscript figures. Changes are RevTex
format (instead of plain LaTeX), minor misprint corrections plus additional
references. To appear in Phys. Rev.
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