4,113 research outputs found
Turing pattern formation in the Brusselator system with nonlinear diffusion
In this work we investigate the effect of density dependent nonlinear
diffusion on pattern formation in the Brusselator system. Through linear
stability analysis of the basic solution we determine the Turing and the
oscillatory instability boundaries. A comparison with the classical linear
diffusion shows how nonlinear diffusion favors the occurrence of Turing pattern
formation. We study the process of pattern formation both in 1D and 2D spatial
domains. Through a weakly nonlinear multiple scales analysis we derive the
equations for the amplitude of the stationary patterns. The analysis of the
amplitude equations shows the occurrence of a number of different phenomena,
including stable supercritical and subcritical Turing patterns with multiple
branches of stable solutions leading to hysteresis. Moreover we consider
traveling patterning waves: when the domain size is large, the pattern forms
sequentially and traveling wavefronts are the precursors to patterning. We
derive the Ginzburg-Landau equation and describe the traveling front enveloping
a pattern which invades the domain. We show the emergence of radially symmetric
target patterns, and through a matching procedure we construct the outer
amplitude equation and the inner core solution.Comment: Physical Review E, 201
Preliminary analysis of the potential of LANDSAT imagery to study desertification
The use of LANDSAT imagery to define and delimit areas under process of desertification was investigated. Imagery for two different years (1973 and 1978) and two different seasons (dry and rainy seasons in 1976), were used to identify terrain morphology and vegetation cover. The analysis of LANDSAT interpretation, combined with geological and soil information obtained from published literature, allowed the identification of eleven ecological units which were classified corresponding to the degree of the Xique Xique region of Rio Sao Francisco
On the spin-isospin decomposition of nuclear symmetry energy
The decomposition of nuclear symmetry energy into spin and isospin components
is discussed to elucidate the underlying properties of the NN bare interaction.
This investigation was carried out in the framework of the
Brueckner-Hartree-Fock theory of asymmetric nuclear matter with consistent two
and three body forces. It is shown the interplay among the various two body
channels in terms of isospin singlet and triplet components as well as spin
singlet and triplet ones. The broad range of baryon densities enables to study
the effects of three body force moving from low to high densities.Comment: 8 pages, 4 figure
Model of separated form factors for unilamellar vesicles
New model of separated form factors is proposed for the evaluation of
small-angle neutron scattering curves from large unilamellar vesicles. The
validity of the model was checked by comparison to the model of hollow sphere.
The model of separated form factors and hollow sphere model give reasonable
agreement in the evaluation of vesicle parameters.Comment: LaTeX: 3 pages, 1 figure, 14 references; submitted to Applied Physics
Effect of Hund's exchange on the spectral function of a triply orbital degenerate correlated metal
We present an approach based on the dynamical mean field theory which is able
to give the excitation spectrum of a triply degenerate Hubbard model with a
Hund's exchange invariant under spin rotation. The lattice problem can be
mapped onto a local Anderson model containing 64 local eigenstates. This local
problem is solved by a generalized non-crossing approximation. The influence of
Hund's coupling J is examined in detail for metallic states close to the metal
insulator transition. The band-filling is shown to play a crucial role
concerning the effect of J on the low energy dynamics.Comment: Phys. Rev. B (In Press
In medium T-matrix for nuclear matter with three-body forces - binding energy and single particle properties
We present spectral calculations of nuclear matter properties including
three-body forces. Within the in-medium T-matrix approach, implemented with the
CD-Bonn and Nijmegen potentials plus the three-nucleon Urbana interaction, we
compute the energy per particle in symmetric and neutron matter. The three-body
forces are included via an effective density dependent two-body force in the
in-medium T-matrix equations. After fine tuning the parameters of the
three-body force to reproduce the phenomenological saturation point in
symmetric nuclear matter, we calculate the incompressibility and the energy per
particle in neutron matter. We find a soft equation of state in symmetric
nuclear matter but a relatively large value of the symmetry energy. We study
the the influence of the three-body forces on the single-particle properties.
For symmetric matter the spectral function is broadened at all momenta and all
densities, while an opposite effect is found for the case of neutrons only.
Noticeable modification of the spectral functions are realized only for
densities above the saturation density. The modifications of the self-energy
and the effective mass are not very large and appear to be strongly suppressed
above the Fermi momentum.Comment: 20 pages, 11 figure
Casimir energy between media-separated cylinders: the scalar case
We derive exact expressions for the Casimir scalar interaction energy between
media-separated eccentric dielectric cylinders and for the media-separated
cylinder-plane geometry using a mode-summation approach. Similarly to the
electromagnetic Casimir-Lifshitz interaction energy between fluid-separated
planar plates, the force between cylinders is attractive or repulsive depending
on the relative values of the permittivities of the three intervening media.Comment: New figure and discussion about the integration contour in the
complex plan
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