47,019 research outputs found
Growth-Driven Percolations: The Dynamics of Community Formation in Neuronal Systems
The quintessential property of neuronal systems is their intensive patterns
of selective synaptic connections. The current work describes a physics-based
approach to neuronal shape modeling and synthesis and its consideration for the
simulation of neuronal development and the formation of neuronal communities.
Starting from images of real neurons, geometrical measurements are obtained and
used to construct probabilistic models which can be subsequently sampled in
order to produce morphologically realistic neuronal cells. Such cells are
progressively grown while monitoring their connections along time, which are
analysed in terms of percolation concepts. However, unlike traditional
percolation, the critical point is verified along the growth stages, not the
density of cells, which remains constant throughout the neuronal growth
dynamics. It is shown, through simulations, that growing beta cells tend to
reach percolation sooner than the alpha counterparts with the same diameter.
Also, the percolation becomes more abrupt for higher densities of cells, being
markedly sharper for the beta cells.Comment: 8 pages, 10 figure
A Fast and Accurate Nonlinear Spectral Method for Image Recognition and Registration
This article addresses the problem of two- and higher dimensional pattern
matching, i.e. the identification of instances of a template within a larger
signal space, which is a form of registration. Unlike traditional correlation,
we aim at obtaining more selective matchings by considering more strict
comparisons of gray-level intensity. In order to achieve fast matching, a
nonlinear thresholded version of the fast Fourier transform is applied to a
gray-level decomposition of the original 2D image. The potential of the method
is substantiated with respect to real data involving the selective
identification of neuronal cell bodies in gray-level images.Comment: 4 pages, 3 figure
Magnetic monopole and string excitations in a two-dimensional spin ice
We study the magnetic excitations of a square lattice spin-ice recently
produced in an artificial form, as an array of nanoscale magnets. Our analysis,
based upon the dipolar interaction between the nanomagnetic islands, correctly
reproduces the ground-state observed experimentally. In addition, we find
magnetic monopole-like excitations effectively interacting by means of the
usual Coulombic plus a linear confining potential, the latter being related to
a string-like excitation binding the monopoles pairs, what indicates that the
fractionalization of magnetic dipoles may not be so easy in two dimensions.
These findings contrast this material with the three-dimensional analogue,
where such monopoles experience only the Coulombic interaction. We discuss,
however, two entropic effects that affect the monopole interactions: firstly,
the string configurational entropy may loose the string tension and then, free
magnetic monopoles should also be found in lower dimensional spin ices;
secondly, in contrast to the string configurational entropy, an entropically
driven Coulomb force, which increases with temperature, has the opposite effect
of confining the magnetic defects.Comment: 8 pages. Accepted by Journal of Applied Physics (2009
Two photon decay of and at finite temperature and density
A comparative study of the anomalous decays , at
finite temperature and at finite density, is performed in the framework of the
three--flavor Nambu--Jona-Lasinio. The similarities and differences between
both scenarios are discussed. In both cases the lifetimes of these mesons
decrease significantly at the critical point, although this might not be
sufficient to observe enhancement of these decays in heavy-ion collisions.Comment: 5 pages, 1 figure. Talk given at Strange Quark Matter 2004, Cape
Town, South Africa, 15-20 September, 200
Leguminosas arbóreas e arbustivas de múltiplo uso em Presidente Médici, Rondônia.
Este trabalho teve como objetivo avaliar o desempenho agronômico de leguminosas com potencial de múltiplos usos para compor sistemas mais apropriados as condições de solo e clima locais, visando a manutenção da potencialidade produtiva das áreas. Foram avaliadas taxa de sobrevivência, diâmetro e altura de plantas, em Latossolo Amarelo no Município de Porto Velho-RO, destacando-se como mais promissoras A. angustissima, I.edulis, C. racemosa, A. samam e A. pavonina.bitstream/item/42536/1/Cot299-leguminosas.pd
Entropy, non-ergodicity and non-Gaussian behaviour in ballistic transport
Ballistic transportation introduces new challenges in the thermodynamic
properties of a gas of particles. For example, violation of mixing, ergodicity
and of the fluctuation-dissipation theorem may occur, since all these processes
are connected. In this work, we obtain results for all ranges of diffusion,
i.e., both for subdiffusion and superdiffusion, where the bath is such that it
gives origin to a colored noise. In this way we obtain the skewness and the
non-Gaussian factor for the probability distribution function of the dynamical
variable. We put particular emphasis on ballistic diffusion, and we demonstrate
that in this case, although the second law of thermodynamics is preserved, the
entropy does not reach a maximum and a non-Gaussian behavior occurs. This
implies the non-applicability of the central limit theorem.Comment: 9 pages, 2 figure
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