5,906 research outputs found
The effect of shear and bulk viscosities on elliptic flow
In this work, we examine the effect of shear and bulk viscosities on elliptic
flow by taking a realistic parameterization of the shear and bulk viscous
coefficients, and , and their respective relaxation times,
and . We argue that the behaviors close to ideal fluid
observed at RHIC energies may be related to non-trivial temperature dependence
of these transport coefficients.Comment: 6 pages, 4 figures, to appear in the proceedings of Strange Quark
Matter 2009 (SQM09
Diffusion over a saddle with a Langevin equation
The diffusion problem over a saddle is studied using a multi-dimensional
Langevin equation. An analytical solution is derived for a quadratic potential
and the probability to pass over the barrier deduced. A very simple solution is
given for the one dimension problem and a general scheme is shown for higher
dimensions.Comment: 13 pages, use revTeX, to appear in Phys. Rev. E6
Using the Sound Card as a Timer
Experiments in mechanics can often be timed by the sounds they produce. In
such cases, digital audio recordings provide a simple way of measuring time
intervals with an accuracy comparable to that of photogate timers. We
illustrate this with an experiment in the physics of sports: to measure the
speed of a hard-kicked soccer ball.Comment: 3 pages, 4 figures, Late
Equilibrium and Disorder-induced behavior in Quantum Light-Matter Systems
We analyze equilibrium properties of coupled-doped cavities described by the
Jaynes-Cummings- Hubbard Hamiltonian. In particular, we characterize the
entanglement of the system in relation to the insulating-superfluid phase
transition. We point out the existence of a crossover inside the superfluid
phase of the system when the excitations change from polaritonic to purely
photonic. Using an ensemble statistical approach for small systems and
stochastic-mean-field theory for large systems we analyze static disorder of
the characteristic parameters of the system and explore the ground state
induced statistics. We report on a variety of glassy phases deriving from the
hybrid statistics of the system. On-site strong disorder induces insulating
behavior through two different mechanisms. For disorder in the light-matter
detuning, low energy cavities dominate the statistics allowing the excitations
to localize and bunch in such cavities. In the case of disorder in the light-
matter coupling, sites with strong coupling between light and matter become
very significant, which enhances the Mott-like insulating behavior. Inter-site
(hopping) disorder induces fluidity and the dominant sites are strongly coupled
to each other.Comment: about 10 pages, 12 figure
Imaginary Phases in Two-Level Model with Spontaneous Decay
We study a two-level model coupled to the electromagnetic vacuum and to an
external classic electric field with fixed frequency. The amplitude of the
external electric field is supposed to vary very slow in time. Garrison and
Wright [{\it Phys. Lett.} {\bf A128} (1988) 177] used the non-hermitian
Hamiltonian approach to study the adiabatic limit of this model and obtained
that the probability of this two-level system to be in its upper level has an
imaginary geometric phase. Using the master equation for describing the time
evolution of the two-level system we obtain that the imaginary phase due to
dissipative effects is time dependent, in opposition to Garrison and Wright
result. The present results show that the non-hermitian hamiltonian method
should not be used to discuss the nature of the imaginary phases in open
systems.Comment: 11 pages, new version, to appear in J. Phys.
Casimir Energy For a Massive Dirac Field in One Spatial Dimension: A Direct Approach
In this paper we calculate the Casimir energy for a massive fermionic field
confined between two points in one spatial dimension, with the MIT Bag Model
boundary condition. We compute the Casimir energy directly by summing over the
allowed modes. The method that we use is based on the Boyer's method, and there
will be no need to resort to any analytic continuation techniques. We
explicitly show the graph of the Casimir energy as a function of the distance
between the points and the mass of the fermionic field. We also present a
rigorous derivation of the MIT Bag Model boundary condition.Comment: 8 Pages, 4 Figure
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