9,247 research outputs found
Towards a Landau-Ginzburg-type Theory for Granular Fluids
In this paper we show how, under certain restrictions, the hydrodynamic
equations for the freely evolving granular fluid fit within the framework of
the time dependent Landau-Ginzburg (LG) models for critical and unstable fluids
(e.g. spinodal decomposition). The granular fluid, which is usually modeled as
a fluid of inelastic hard spheres (IHS), exhibits two instabilities: the
spontaneous formation of vortices and of high density clusters. We suppress the
clustering instability by imposing constraints on the system sizes, in order to
illustrate how LG-equations can be derived for the order parameter, being the
rate of deformation or shear rate tensor, which controls the formation of
vortex patterns. From the shape of the energy functional we obtain the
stationary patterns in the flow field. Quantitative predictions of this theory
for the stationary states agree well with molecular dynamics simulations of a
fluid of inelastic hard disks.Comment: 19 pages, LaTeX, 8 figure
Self-Diffusion in Simple Models: Systems with Long-Range Jumps
We review some exact results for the motion of a tagged particle in simple
models. Then, we study the density dependence of the self diffusion
coefficient, , in lattice systems with simple symmetric exclusion in
which the particles can jump, with equal rates, to a set of neighboring
sites. We obtain positive upper and lower bounds on
for .
Computer simulations for the square, triangular and one dimensional lattice
suggest that becomes effectively independent of for .Comment: 24 pages, in TeX, 1 figure, e-mail addresses: [email protected],
[email protected], [email protected]
The prediction and measurement of sound radiated by structures
Theories regarding the radiation of sound are reviewed and the implementation in strategies for explaining or measuring the sound produced by practical strucutres are discussed. Particular attention is given to those aspects that relate to the determination of the relative amounts of sound generated by various parts of a machine or structure, which can be very useful information for noise reduction efforts
Renormalized Equilibria of a Schloegl Model Lattice Gas
A lattice gas model for Schloegl's second chemical reaction is described and
analyzed. Because the lattice gas does not obey a semi-detailed-balance
condition, the equilibria are non-Gibbsian. In spite of this, a self-consistent
set of equations for the exact homogeneous equilibria are described, using a
generalized cluster-expansion scheme. These equations are solved in the
two-particle BBGKY approximation, and the results are compared to numerical
experiment. It is found that this approximation describes the equilibria far
more accurately than the Boltzmann approximation. It is also found, however,
that spurious solutions to the equilibrium equations appear which can only be
removed by including effects due to three-particle correlations.Comment: 21 pages, REVTe
Efficiency of Brownian Motors
The efficiency of different types of Brownian motors is calculated
analytically and numerically. We find that motors based on flashing ratchets
present a low efficiency and an unavoidable entropy production. On the other
hand, a certain class of motors based on adiabatically changing potentials,
named reversible ratchets, exhibit a higher efficiency and the entropy
production can be arbitrarily reduced.Comment: LaTeX 209, 6 pages, 7 postscript figures, uses psfi
Programas de controle das mastites causadas por microrganismos contagiosos e do ambiente
Este trabalho foi elaborado com o objetivo de apresentar os conceitos em que se baseiam os programas de controle da mastite, em uso na maioria das indústrias leiteiras desenvolvidas. Foram abordados os fundamentos dos programas de controle, as características dos patógenos mais comuns, os fatores relacionados à ocorrência da doença e a síntese do programa de controle. Destina-se prioritariamente a médicos veterinários e estudantes, embora outros profissionais e produtores interessados no tema possam também usá-lo.bitstream/item/81916/1/Programas-de-controle-das-mastites.pd
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