11,446 research outputs found
Model for erosion-deposition patterns
We investigate through computational simulations with a pore network model
the formation of patterns caused by erosion-deposition mechanisms. In this
model, the geometry of the pore space changes dynamically as a consequence of
the coupling between the fluid flow and the movement of particles due to local
drag forces. Our results for this irreversible process show that the model is
capable to reproduce typical natural patterns caused by well known erosion
processes. Moreover, we observe that, within a certain range of porosity
values, the grains form clusters that are tilted with respect to the horizontal
with a characteristic angle. We compare our results to recent experiments for
granular material in flowing water and show that they present a satisfactory
agreement.Comment: 8 pages, 12 figures, submitted to Phys. Rev.
Situação atual e perspectivas da caprinocultura no Vale do São Francisco.
Caracterização física e agro-sócio-econômico da zona caprinícola do Vale do São Francisco; Limitações da Caprinocultura regional; Potencialidades da Caprinocultura regional; O mercado para os produtos caprinos e ovinos; O potencial de interação com as áreas irrigadas e com outras atividades agrrícolas e não agrícolas; Infraestrutura agroindustrial; O expressivo dispositivo institucional da região; Proposta de um programa de desenvolvimento
Decoherence and the quantum-classical limit in the presence of chaos
We investigate how decoherence affects the short-time separation between
quantum and classical dynamics for classically chaotic systems, within the
framework of a specific model. For a wide range of parameters, the distance
between the corresponding phase-space distributions depends on a single
parameter that relates an effective Planck constant ,
the Lyapunov coeffficient, and the diffusion constant. This distance peaks at a
time that depends logarithmically on , in agreement with
previous estimations of the separation time for Hamiltonian systems. However,
for , the separation remains small, going down with , so the concept of separation time loses its meaning.Comment: 5 pages, 4 figures (in 6 postscript files) two of them are color
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3-3-1 exotic quark search at CERN LEPII-LHC
The 3-3-1 electroweak model is the simplest chiral extension of the standard
model which predicts single and double charged bileptons and exotic quarks
carrying -4/3 and 5/3 units of the positron charge. In this paper we study the
possibilities of the production and decay of one of these exotic quarks at CERN
LEPII-LHC collider. For typical vector bilepton, exotic quark masses and mixing
angles we obtained between 20 and 750 events per year. Angular distributions
are also presented.Comment: 5 pages, RevTex 3.1, 9 eps figures, to appear in Phys. Rev.
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