559 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

### 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

### Derivation of fluid dynamics from kinetic theory with the 14--moment approximation

We review the traditional derivation of the fluid-dynamical equations from
kinetic theory according to Israel and Stewart. We show that their procedure to
close the fluid-dynamical equations of motion is not unique. Their approach
contains two approximations, the first being the so-called 14-moment
approximation to truncate the single-particle distribution function. The second
consists in the choice of equations of motion for the dissipative currents.
Israel and Stewart used the second moment of the Boltzmann equation, but this
is not the only possible choice. In fact, there are infinitely many moments of
the Boltzmann equation which can serve as equations of motion for the
dissipative currents. All resulting equations of motion have the same form, but
the transport coefficients are different in each case.Comment: 15 pages, 3 figures, typos fixed and discussions added; EPJA: Topical
issue on "Relativistic Hydro- and Thermodynamics

### Design of a novel flow-and-shoot microbeam

Presented here is a novel microbeam technology—the Flow-And-ShooT (FAST) microbeam—under development at RARAF. In this system, cells undergo controlled fluidic transport along a microfluidic channel intersecting the microbeam path. They are imaged and tracked in real-time, using a high-speed camera and dynamically targeted, using a magnetic Point and Shoot system. With the proposed FAST system, RARAF expects to reach a throughput of 100 000 cells per hour, which will allow increasing the throughput of experiments by at least one order of magnitude. The implementation of FAST will also allow the irradiation of non-adherent cells (e.g. lymphocytes), which is of great interest to many of the RARAF users. This study presents the design of a FAST microbeam and results of first tests of imaging and tracking as well as a discussion of the achievable throughput

### Some thoughts about nonequilibrium temperature

The main objective of this paper is to show that, within the present
framework of the kinetic theoretical approach to irreversible thermodynamics,
there is no evidence that provides a basis to modify the ordinary Fourier
equation relating the heat flux in a non-equilibrium steady state to the
gradient of the local equilibrium temperature. This fact is supported, among
other arguments, through the kinetic foundations of generalized hydrodynamics.
Some attempts have been recently proposed asserting that, in the presence of
non-linearities of the state variables, such a temperature should be replaced
by the non-equilibrium temperature as defined in Extended Irreversible
Thermodynamics. In the approximations used for such a temperature there is so
far no evidence that sustains this proposal.Comment: 13 pages, TeX, no figures, to appear in Mol. Phy

### Phase space reduction of the one-dimensional Fokker-Planck (Kramers) equation

A pointlike particle of finite mass m, moving in a one-dimensional viscous
environment and biased by a spatially dependent force, is considered. We
present a rigorous mapping of the Fokker-Planck equation, which determines
evolution of the particle density in phase space, onto the spatial coordinate
x. The result is the Smoluchowski equation, valid in the overdamped limit,
m->0, with a series of corrections expanded in powers of m. They are determined
unambiguously within the recurrence mapping procedure. The method and the
results are interpreted on the simplest model with no field and on the damped
harmonic oscillator.Comment: 13 pages, 1 figur

### Second Order Dissipative Fluid Dynamics for Ultra-Relativistic Nuclear Collisions

The M\"uller-Israel-Stewart second order theory of relativistic imperfect
fluids based on Grad's moment method is used to study the expansion of hot
matter produced in ultra-relativistic heavy ion collisions. The temperature
evolution is investigated in the framework of the Bjorken boost-invariant
scaling limit. The results of these second-order theories are compared to those
of first-order theories due to Eckart and to Landau and Lifshitz and those of
zeroth order (perfect fluid) due to Euler.Comment: 5 pages, 4 figures, size of y-axis tick marks for Figs. 3 and 4 fixe

### An interpretative phenomenological analysis of posttraumatic growth in adults bereaved by suicide

This study explored experiences of posttraumatic growth in adults bereaved by suicide. Six participants were interviewed using a semi-structured interview schedule. Transcribed interviews were analyzed from an interpretative phenomenological framework. Two superordinate themes, with three ordinate themes in each, were identified: (a) positive growth (“life view,” “knowledge of self,” and “relation to others”) and (b) social context (“gaze of others,” “public guise,” and “solace of other survivors”). Suicide survivors gain extra insights due to their experiences, but are reluctant to acknowledge that they do. This requires consideration in theoretical and clinical setting

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