215 research outputs found
An exact solution of the inelastic Boltzmann equation for the Couette flow with uniform heat flux
In the steady Couette flow of a granular gas the sign of the heat flux
gradient is governed by the competition between viscous heating and inelastic
cooling. We show from the Boltzmann equation for inelastic Maxwell particles
that a special class of states exists where the viscous heating and the
inelastic cooling exactly compensate each other at every point, resulting in a
uniform heat flux. In this state the (reduced) shear rate is enslaved to the
coefficient of restitution , so that the only free parameter is the
(reduced) thermal gradient . It turns out that the reduced moments of
order are polynomials of degree in , with coefficients that
are nonlinear functions of . In particular, the rheological properties
() are independent of and coincide exactly with those of the
simple shear flow. The heat flux () is linear in the thermal gradient
(generalized Fourier's law), but with an effective thermal conductivity
differing from the Navier--Stokes one. In addition, a heat flux component
parallel to the flow velocity and normal to the thermal gradient exists. The
theoretical predictions are validated by comparison with direct Monte Carlo
simulations for the same model.Comment: 16 pages, 4 figures,1 table; v2: minor change
Effect of breed on meat quality and global acceptance of native lambs and their crosses
International projections point to the growth in global production of sheep meat, mainly from developing countries. However, the exigencies of consumers on characterization of production systems, nutritional information, and sensorial analysis to target the preferences must be answered. The aim of this study was to characterize the meat quality and the global acceptance of Brazilian native ovine breeds and their crosses, and discuss these aspects on the current basis of human health and wellbeing. Three native breeds (Morada Nova, Rabo Largo, and Santa Inês) that were managed in semi-intensive systems and raised in semi-arid Brazilian regions were used. Chemical composition and fatty acid analysis, sensory evaluation and health indices were accessed. The combined effects of breed, sex and breed by sex interaction produced differentiation in meat fatty acid (FA) profiles. The cholesterol contents ranged between 51 and 59.1 mg/100 g. The Morada Nova lambs showed the lowest lipid content (1.93%). The Morada Nova x Rabo Largo crossbreed breed has the potential to increase the content of conjugated linoleic acid. The high content of α-linolenic acid, which is considered hypocholesterolemic, was responsible for better health indices. The moderate acceptability obtained in sensory traits is compatible with the requirements of the consumer market. The combination of nutritional and sensory traits associated with human health and wellbeing that is presented by these native ovine breeds qualifies them as a good choice of red meat to be included in a larger proportion in human food.
Keywords: fatty acids, healthier meat, semi-arid region, shee
Worldsheet Instantons and a Null String Limit of Born-Infeld Theory
For a superstring theory in four spacetime dimensions, we propose a
modification of the Born-Infeld action that possesses a well-defined
tensionless limit. We interpret this as describing the effective target space
dynamics of null strings on a D3-brane. We argue that such a modification can
be induced by nonperturbative contributions from instantons in the worldsheet
sigma-model describing string propagation on the brane.Comment: 11 pages; Comments and references adde
Baxter Q-operator and Separation of Variables for the open SL(2,R) spin chain
We construct the Baxter Q-operator and the representation of the Separated
Variables (SoV) for the homogeneous open SL(2,R) spin chain. Applying the
diagrammatical approach, we calculate Sklyanin's integration measure in the
separated variables and obtain the solution to the spectral problem for the
model in terms of the eigenvalues of the Q-operator. We show that the
transition kernel to the SoV representation is factorized into the product of
certain operators each depending on a single separated variable. As a
consequence, it has a universal pyramid-like form that has been already
observed for various quantum integrable models such as periodic Toda chain,
closed SL(2,R) and SL(2,C) spin chains.Comment: 29 pages, 9 figures, Latex styl
First and second order optimality conditions for optimal control problems of state constrained integral equations
This paper deals with optimal control problems of integral equations, with
initial-final and running state constraints. The order of a running state
constraint is defined in the setting of integral dynamics, and we work here
with constraints of arbitrary high orders. First and second-order necessary
conditions of optimality are obtained, as well as second-order sufficient
conditions
Quantum Group and Magnetic Translations. Bethe-Ansatz Solution for Azbel-Hofstadter Problem
We present a new approach to the problem of Bloch electrons in magnetic (
sometimes called Azbel-Hofstadter problem) field, by making explicit a natural
relation between the group of magnetic translations and the quantum group
. The approach allows us to express the "mid" band spectrum of the
model and the Bloch wave function as solutions of the Bethe-Ansatz equations
typical for completely integrable quantum systems. The zero mode wave functions
are found explicitly in terms of -deformed classical orthogonal
polynomials.In this paper we present solution for the isotropic problem. We
also present a class of solvable quasiperiodic equations related to
.Comment: 19 pages, Revte
Hadrons in AdS/QCD models
We discuss applications of gauge/gravity duality to describe the spectrum of
light hadrons. We compare two particular 5-dimensional approaches: a model with
an infrared deformed Anti-de Sitter metric and another one based on a dynamical
AdS/QCD framework with back-reacted geometry in a dilaton/gravity background.
The models break softly the scale invariance in the infrared region and allow
mass gap for the field excitations in the gravity description, while keeping
the conformal property of the metric close to the four-dimensional boundary.
The models provide linear Regge trajectories for light mesons, associated with
specially designed infrared gravity properties. We also review the results for
the decay widths of the f0's into two pions, as overlap integrals between
mesonic string amplitudes, which are in qualitative agreement with data
Exact resolution of the Baxter equation for reggeized gluon interactions
The interaction of reggeized gluons in multi-colour QCD is considered in the
Baxter-Sklyanin representation, where the wave function is expressed as a
product of Baxter functions Q(lambda) and a pseudo-vacuum state. We find n
solutions of the Baxter equation for a composite state of n gluons with poles
of rank r in the upper lambda semi-plane and of rank n-1-r in the lower lambda
semi-plane (0 leq r leq n-1). These solutions are related by n-2 linear
equations with coefficients depending on coth (pi lambda). The poles cancel in
the wave function, bilinear combination of holomorphic and anti-holomorphic
Baxter functions, guaranteeing its normalizability. The quantization of the
intercepts of the corresponding Regge singularities appears as a result of the
physical requirements that the holomorphic energies for all solutions of the
Baxter equation are the same and the total energies, calculated around two
singularities lambda, lambda^* --> + i or -i, coincide. It results in simple
properties of the zeroes of the Baxter functions. For illustration we calculate
the parameters of the reggeon states constructed from three and four gluons.
For the Odderon the ground state has conformal spin |m -m | = 1 and its
intercept equals unity. The ground state of four reggeized gluons possesses
conformal spin 2 and its intercept turns out to be higher than that for the
BFKL Pomeron. We calculate the anomalous dimensions of the corresponding
operators for arbitrary alpha_s/omega.Comment: LaTex, 42 pages, 8 .ps figures. Expanded and improved versio
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