Sound Mode Hydrodynamics from Bulk Scalar Fields

We study the hydrodynamic sound mode using gauge/gravity correspondence by examining a generic black brane background's response to perturbations. We assume that the background is generated by a single scalar field, and then generalize to the case of multiple scalar fields. The relevant differential equations obeyed by the gauge invariant variables are presented in both cases. Finally, we present an analytical solution to these equations in a special case; this solution allows us to determine the speed of sound and bulk viscosity for certain special metrics. These results may be useful in determining sound mode transport coefficients in phenomenologically motivated holographic models of strongly coupled systems.Comment: 17 pages. Corrections made to one of the gauge invariant equations (66). This equation was not used in the other main conclusions of the paper, so the rest of the results are unchange

Numerical simulation of the flow and fuel-air mixing in an axisymmetric piston-cylinder arrangement

The implicit factored method of Beam and Warming was employed to describe the flow and the fuel-air mixing in an axisymmetric piston-cylinder configuration during the intake and compression strokes. The governing equations were established on the basis of laminar flow. The increased mixing due to turbulence was simulated by appropriately chosen effective transport properties. Calculations were performed for single-component gases and for two-component gases and for two-component gas mixtures. The flow field was calculated as functions of time and position for different geometries, piston speeds, intake-charge-to-residual-gas-pressure ratios, and species mass fractions of the intake charge. Results are presented in graphical form which show the formation, growth, and break-up of those vortices which form during the intake stroke and the mixing of fuel and air throughout the intake and compression strokes. It is shown that at bore-to-stroke ratio of less than unity, the vortices may break-up during the intake stroke. It is also shown that vortices which do not break-up during the intake stroke coalesce during the compression stroke. The results generated were compared to existing numerical solutions and to available experimental data

Vortex motion in axisymmetric piston-cylinder configurations

By using the Beam and Warming implicit-factored method of solution of the Navier-Stokes equations, velocities were calculated inside axisymmetric piston cylinder configurations during the intake and compression strokes. Results are presented in graphical form which show the formation, growth and breakup of those vortices which form during the intake stroke by the jet issuing from the valve. It is shown that at bore-to-stroke ratio of less than unity, the vortices may breakup during the intake stroke. It is also shown that vortices which do not breakup during the intake stroke coalesce during the compression stroke

The use of a Salmonella Typhimurium live vaccine to control Salmonella Typhimurium in fattening pigs in field and effects on serological surveillance

This field study was designed to evaluate the use of a live-attenuated Salmonella Typh1murium vaccine in pigs in respect of efficacy agamst S. Typhimurium at time of slaughter and the effect on serological herd monitoring using a commercial mixed LPS-ELISA. About 1289 slaughtered pigs (805 of non vaccinated groups and 484 of vaccinated groups) were investigated by bacteriological and serological examination (1149 pigs). The study showed the efficacy of an oral vaccination with a live-attenuated Salmonella Typhimunum vaccme in reducmg the number of Salmonella carrying pigs at slaughter without a detectable interference with the serological monitoring of Salmonella (using a cut off at 40% OD level)

Shear Transport Coefficients from Gauge/Gravity Correspondence

We study the shear mode in the gauge/gravity correspondence at finite temperature. First, we confirm the general formula for the shear viscosity in an arbitrary background metric which includes a black hole in the fifth dimension. We then derive a general formula for the shear mode relaxation time which appears in the theory of relativistic dissipative fluid dynamics; it agrees with known expressions in the limit of conformal fields. These results may be useful in relativistic viscous fluid descriptions of high energy nuclear collisions at RHIC and LHC.Comment: Modifications based on helpful feedback from colleagues and refere

Second order hydrodynamics for a special class of gravity duals

The sound mode hydrodynamic dispersion relation is computed up to order $q^3$ for a class of gravitational duals which includes both Schwarzschild $AdS$ and Dp-Brane metrics. The implications for second order transport coefficients are examined within the context of Israel-Stewart theory. These sound mode results are compared with previously known results for the shear mode. This comparison allows one to determine the third order hydrodynamic contributions to the shear mode for the class of metrics considered here.Comment: 20 page

The eclipsing post-common envelope binary CSS21055: a white dwarf with a probable brown-dwarf companion

We report photometric observations of the eclipsing close binary CSS21055 (SDSS J141126+200911) that strongly suggest that the companion to the carbon-oxygen white dwarf is a brown dwarf with a mass between 0.030 and 0.074 Msun. The measured orbital period is 121.73min and the totality of the eclipse lasts 125s. If confirmed, CSS21055 would be the first detached eclipsing WD+BD binary. Spectroscopy in the eclipse could provide information about the companion's evolutionary state and atmospheric structure.Comment: 6 pages, 5 figure