923 research outputs found
Strong Shock Waves and Nonequilibrium Response in a One-dimensional Gas: a Boltzmann Equation Approach
We investigate the nonequilibrium behavior of a one-dimensional binary fluid
on the basis of Boltzmann equation, using an infinitely strong shock wave as
probe. Density, velocity and temperature profiles are obtained as a function of
the mixture mass ratio \mu. We show that temperature overshoots near the shock
layer, and that heavy particles are denser, slower and cooler than light
particles in the strong nonequilibrium region around the shock. The shock width
w(\mu), which characterizes the size of this region, decreases as w(\mu) ~
\mu^{1/3} for \mu-->0. In this limit, two very different length scales control
the fluid structure, with heavy particles equilibrating much faster than light
ones. Hydrodynamic fields relax exponentially toward equilibrium, \phi(x) ~
exp[-x/\lambda]. The scale separation is also apparent here, with two typical
scales, \lambda_1 and \lambda_2, such that \lambda_1 ~ \mu^{1/2} as \mu-->0$,
while \lambda_2, which is the slow scale controlling the fluid's asymptotic
relaxation, increases to a constant value in this limit. These results are
discussed at the light of recent numerical studies on the nonequilibrium
behavior of similar 1d binary fluids.Comment: 9 pages, 8 figs, published versio
A causal statistical family of dissipative divergence type fluids
In this paper we investigate some properties, including causality, of a
particular class of relativistic dissipative fluid theories of divergence type.
This set is defined as those theories coming from a statistical description of
matter, in the sense that the three tensor fields appearing in the theory can
be expressed as the three first momenta of a suitable distribution function. In
this set of theories the causality condition for the resulting system of
hyperbolic partial differential equations is very simple and allow to identify
a subclass of manifestly causal theories, which are so for all states outside
equilibrium for which the theory preserves this statistical interpretation
condition. This subclass includes the usual equilibrium distributions, namely
Boltzmann, Bose or Fermi distributions, according to the statistics used,
suitably generalized outside equilibrium. Therefore this gives a simple proof
that they are causal in a neighborhood of equilibrium. We also find a bigger
set of dissipative divergence type theories which are only pseudo-statistical,
in the sense that the third rank tensor of the fluid theory has the symmetry
and trace properties of a third momentum of an statistical distribution, but
the energy-momentum tensor, while having the form of a second momentum
distribution, it is so for a different distribution function. This set also
contains a subclass (including the one already mentioned) of manifestly causal
theories.Comment: LaTex, documentstyle{article
Entropic force, noncommutative gravity and ungravity
After recalling the basic concepts of gravity as an emergent phenomenon, we
analyze the recent derivation of Newton's law in terms of entropic force
proposed by Verlinde. By reviewing some points of the procedure, we extend it
to the case of a generic quantum gravity entropic correction to get compelling
deviations to the Newton's law. More specifically, we study: (1) noncommutative
geometry deviations and (2) ungraviton corrections. As a special result in the
noncommutative case, we find that the noncommutative character of the manifold
would be equivalent to the temperature of a thermodynamic system. Therefore, in
analogy to the zero temperature configuration, the description of spacetime in
terms of a differential manifold could be obtained only asymptotically.
Finally, we extend the Verlinde's derivation to a general case, which includes
all possible effects, noncommutativity, ungravity, asymptotically safe gravity,
electrostatic energy, and extra dimensions, showing that the procedure is solid
versus such modifications.Comment: 8 pages, final version published on Physical Review
Study of the characteristic parameters of the normal voices of Argentinian speakers
The voice laboratory permits to study the human voices using a method that is objective and noninvasive. In this work, we have studied the parameters of the human voice such as pitch, formant, jitter, shimmer and harmonic-noise ratio of a group of young people. This statistical information of parameters is obtained from Argentinian speakers.publishedVersionFil: Bonzi, Edgardo Venusto. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Bonzi, Edgardo Venusto. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Grad, G. B. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Maggi, A. M. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Escuela de Fonoaudiología; Argentina.Fil: Muñóz, M. R. Universidad Nacional de Córdoba. Facultad de Ciencias Médicas. Escuela de Fonoaudiología; Argentina.Otras Ciencias Física
Real time plasma equilibrium reconstruction in a Tokamak
The problem of equilibrium of a plasma in a Tokamak is a free boundary
problemdescribed by the Grad-Shafranov equation in axisymmetric configurations.
The right hand side of this equation is a non linear source, which represents
the toroidal component of the plasma current density. This paper deals with the
real time identification of this non linear source from experimental
measurements. The proposed method is based on a fixed point algorithm, a finite
element resolution, a reduced basis method and a least-square optimization
formulation
On the kinetic systems for simple reacting spheres : modeling and linearized equations
Series: Springer Proceedings in Mathematics & Statistics, Vol. 75In this work we present some results on the kinetic theory of chemically
reacting gases, concerning the model of simple reacting spheres (SRS) for a gaseous
mixture undergoing a chemical reaction of type A1 +A2 A3 +A4. Starting from
the approach developed in paper [11], we provide properties of the SRS system
needed in the mathematical and physical analysis of the model. Our main result in
this proceedings provides basic properties of the SRS system linearized around the
equilibrium, including the explicit representations of the kernels of the linearized
SRS operators.Fundação para a Ciência e a Tecnologia (FCT), PEst-C/MAT/UI0013/2011, SFRH/BD/28795/200
Bioreactor mechanically guided 3D mesenchymal stem cell chondrogenesis using a biocompatible novel thermo-reversible methylcellulose-based hydrogel
Autologous chondrocyte implantation for cartilage repair represents a challenge because strongly limited by chondrocytes' poor expansion capacity in vitro. Mesenchymal stem cells (MSCs) can differentiate into chondrocytes, while mechanical loading has been proposed as alternative strategy to induce chondrogenesis excluding the use of exogenous factors. Moreover, MSC supporting material selection is fundamental to allow for an active interaction with cells. Here, we tested a novel thermo-reversible hydrogel composed of 8% w/v methylcellulose (MC) in a 0.05 M Na 2 SO 4 solution. MC hydrogel was obtained by dispersion technique and its thermo-reversibility, mechanical properties, degradation and swelling were investigated, demonstrating a solution-gelation transition between 34 and 37 °C and a low bulk degradation (<20%) after 1 month. The lack of any hydrogel-derived immunoreaction was demonstrated in vivo by mice subcutaneous implantation. To induce in vitro chondrogenesis, MSCs were seeded into MC solution retained within a porous polyurethane (PU) matrix. PU-MC composites were subjected to a combination of compression and shear forces for 21 days in a custom made bioreactor. Mechanical stimulation led to a significant increase in chondrogenic gene expression, while histological analysis detected sulphated glycosaminoglycans and collagen II only in loaded specimens, confirming MC hydrogel suitability to support load induced MSCs chondrogenesis
Bioreactor mechanically guided 3D mesenchymal stem cell chondrogenesis using a biocompatible novel thermo-reversible methylcellulose-based hydrogel
Autologous chondrocyte implantation for cartilage repair represents a challenge because strongly limited by chondrocytes' poor expansion capacity in vitro. Mesenchymal stem cells (MSCs) can differentiate into chondrocytes, while mechanical loading has been proposed as alternative strategy to induce chondrogenesis excluding the use of exogenous factors. Moreover, MSC supporting material selection is fundamental to allow for an active interaction with cells. Here, we tested a novel thermo-reversible hydrogel composed of 8% w/v methylcellulose (MC) in a 0.05 M Na 2 SO 4 solution. MC hydrogel was obtained by dispersion technique and its thermo-reversibility, mechanical properties, degradation and swelling were investigated, demonstrating a solution-gelation transition between 34 and 37 °C and a low bulk degradation (<20%) after 1 month. The lack of any hydrogel-derived immunoreaction was demonstrated in vivo by mice subcutaneous implantation. To induce in vitro chondrogenesis, MSCs were seeded into MC solution retained within a porous polyurethane (PU) matrix. PU-MC composites were subjected to a combination of compression and shear forces for 21 days in a custom made bioreactor. Mechanical stimulation led to a significant increase in chondrogenic gene expression, while histological analysis detected sulphated glycosaminoglycans and collagen II only in loaded specimens, confirming MC hydrogel suitability to support load induced MSCs chondrogenesis
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