29,295 research outputs found
Estimation of the shear viscosity at finite net-baryon density from A+A collision data at GeV
Hybrid approaches based on relativistic hydrodynamics and transport theory
have been successfully applied for many years for the dynamical description of
heavy ion collisions at ultrarelativistic energies. In this work a new viscous
hybrid model employing the hadron transport approach UrQMD for the early and
late non-equilibrium stages of the reaction, and 3+1 dimensional viscous
hydrodynamics for the hot and dense quark-gluon plasma stage is introduced.
This approach includes the equation of motion for finite baryon number, and
employs an equation of state with finite net-baryon density to allow for
calculations in a large range of beam energies. The parameter space of the
model is explored, and constrained by comparison with the experimental data for
bulk observables from SPS and the phase I beam energy scan at RHIC. The favored
parameter values depend on energy, but allow to extract the effective value of
the shear viscosity coefficient over entropy density ratio in the
fluid phase for the whole energy region under investigation. The estimated
value of increases with decreasing collision energy, which may
indicate that of the quark-gluon plasma depends on baryochemical
potential .Comment: minor changes in the text, results for constant eta*T/w added.
Version accepted for publication in Phys. Rev.
Baroclinic Vorticity Production in Protoplanetary Disks; Part I: Vortex Formation
The formation of vortices in protoplanetary disks is explored via
pseudo-spectral numerical simulations of an anelastic-gas model. This model is
a coupled set of equations for vorticity and temperature in two dimensions
which includes baroclinic vorticity production and radiative cooling. Vortex
formation is unambiguously shown to be caused by baroclinicity because (1)
these simulations have zero initial perturbation vorticity and a nonzero
initial temperature distribution; and (2) turning off the baroclinic term halts
vortex formation, as shown by an immediate drop in kinetic energy and
vorticity. Vortex strength increases with: larger background temperature
gradients; warmer background temperatures; larger initial temperature
perturbations; higher Reynolds number; and higher resolution. In the
simulations presented here vortices form when the background temperatures are
and vary radially as , the initial vorticity
perturbations are zero, the initial temperature perturbations are 5% of the
background, and the Reynolds number is . A sensitivity study consisting
of 74 simulations showed that as resolution and Reynolds number increase,
vortices can form with smaller initial temperature perturbations, lower
background temperatures, and smaller background temperature gradients. For the
parameter ranges of these simulations, the disk is shown to be convectively
stable by the Solberg-H{\o}iland criteria.Comment: Originally submitted to The Astrophysical Journal April 3, 2006;
resubmitted November 3, 2006; accepted Dec 5, 200
Centrality and Energy Dependence of Proton, Light Fragment and Hyperon Production
Recent results of the NA49 collaboration are discussed. These include the
energy dependence of stopping and the production of the light fragments t and
3He. New data on the system size dependence of hyperon production at 40A and
158AGeV are also presented.Comment: 4 pages, Quark Matter 2006 proceeding
Relation of lineaments to sulfide deposits: Bald Eagle Mountain, Centre County, Pennsylvania
The author has identified the following significant results. Discrete areas of finely-fractured and brecciated sandstone float are present along the crest of Bald Mountain and are commonly sites of sulfide mineralization, as evidenced by the presence of barite and limonite gossans. The frequency distributions of the brecciated float as the negative binomial distribution supports the interpretation of a separate population of intensely fractured material. Such zones of concentrated breccia float have an average width of one kilometer with a range from 0.4 to 1.6 kilometers and were observed in a quarry face to have subvertical dips. Direct spatial correlation of the Landsat-derived lineaments to the fractured areas on the ridge is low; however, the mineralized and fracture zones are commonly assymetrical to the lineament positions. Such a systematic dislocation might result from an inherent bias in the float population or could be the product of the relative erosional resistance of the silicified material in the mineralized areas in relation to the erosionally weak material at the stream gaps
Some triviality results for quasi-Einstein manifolds and Einstein warped products
In this paper we prove a number of triviality results for Einstein warped
products and quasi-Einstein manifolds using different techniques and under
assumptions of various nature. In particular we obtain and exploit gradient
estimates for solutions of weighted Poisson-type equations and adaptations to
the weighted setting of some Liouville-type theorems.Comment: 15 pages, fixed minor mistakes in Section
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