Wave Profile for Current Bearing Antiforce Waves

For fluid dynamical analysis of breakdown waves, we employ a one-dimensional, three-component (electrons, ions and neutral particles) fluid model to describe a steady-state, ionizing wave propagating counter to strong electric fields. The electron gas temperature and therefore the electron fluid pressure is assumed to be large enough to sustain the wave motion down the discharge tube. Such waves are referred to as antiforce waves. The complete set of equations describing such waves consists of the equations of conservation of mass, momentum and energy coupled with Poisson’s equation. Inclusion of current behind the wave front alters the set of electron fluid dynamical equations and also the boundary condition on electron temperature. For a range of experimentally observed current values, using the modified boundary condition on electron temperature, we have been able to integrate our modified set of electron fluid dynamical equations through the Debye layer. Our solutions meet the expected boundary conditions at the trailing edge of the wave. We present the wave profile for electric field, electron velocity, electron number density and electron temperature within the Debye layer of the wave

Electroconvection in a Suspended Fluid Film: A Linear Stability Analysis

A suspended fluid film with two free surfaces convects when a sufficiently large voltage is applied across it. We present a linear stability analysis for this system. The forces driving convection are due to the interaction of the applied electric field with space charge which develops near the free surfaces. Our analysis is similar to that for the two-dimensional B\'enard problem, but with important differences due to coupling between the charge distribution and the field. We find the neutral stability boundary of a dimensionless control parameter ${\cal R}$ as a function of the dimensionless wave number ${\kappa}$. ${\cal R}$, which is proportional to the square of the applied voltage, is analogous to the Rayleigh number. The critical values ${{\cal R}_c}$ and ${\kappa_c}$ are found from the minimum of the stability boundary, and its curvature at the minimum gives the correlation length ${\xi_0}$. The characteristic time scale ${\tau_0}$, which depends on a second dimensionless parameter ${\cal P}$, analogous to the Prandtl number, is determined from the linear growth rate near onset. ${\xi_0}$ and ${\tau_0}$ are coefficients in the Ginzburg-Landau amplitude equation which describes the flow pattern near onset in this system. We compare our results to recent experiments.Comment: 36 pages, 7 included eps figures, submitted to Phys Rev E. For more info, see http://mobydick.physics.utoronto.ca

Spacetime geometry of static fluid spheres

We exhibit a simple and explicit formula for the metric of an arbitrary static spherically symmetric perfect fluid spacetime. This class of metrics depends on one freely specifiable monotone non-increasing generating function. We also investigate various regularity conditions, and the constraints they impose. Because we never make any assumptions as to the nature (or even the existence) of an equation of state, this technique is useful in situations where the equation of state is for whatever reason uncertain or unknown. To illustrate the power of the method we exhibit a new form of the ``Goldman--I'' exact solution and calculate its total mass. This is a three-parameter closed-form exact solution given in terms of algebraic combinations of quadratics. It interpolates between (and thereby unifies) at least six other reasonably well-known exact solutions.Comment: Plain LaTeX 2e -- V2: now 22 pages; minor presentation changes in the first part of the paper -- no physics modifications; major additions to the examples section: the Gold-I solution is shown to be identical to the G-G solution. The interior Schwarzschild, Stewart, Buch5 XIII, de Sitter, anti-de Sitter, and Einstein solutions are all special cases. V3: Reference, footnotes, and acknowledgments added, typos fixed -- no physics modifications. V4: Technical problems with mass formula fixed -- affects discussion of our examples but not the core of the paper. Version to appear in Classical and Quantum Gravit

Weakly Nonlinear Analysis of Electroconvection in a Suspended Fluid Film

It has been experimentally observed that weakly conducting suspended films of smectic liquid crystals undergo electroconvection when subjected to a large enough potential difference. The resulting counter-rotating vortices form a very simple convection pattern and exhibit a variety of interesting nonlinear effects. The linear stability problem for this system has recently been solved. The convection mechanism, which involves charge separation at the free surfaces of the film, is applicable to any sufficiently two-dimensional fluid. In this paper, we derive an amplitude equation which describes the weakly nonlinear regime, by starting from the basic electrohydrodynamic equations. This regime has been the subject of several recent experimental studies. The lowest order amplitude equation we derive is of the Ginzburg-Landau form, and describes a forward bifurcation as is observed experimentally. The coefficients of the amplitude equation are calculated and compared with the values independently deduced from the linear stability calculation.Comment: 26 pages, 2 included eps figures, submitted to Phys Rev E. For more information, see http://mobydick.physics.utoronto.c

Acoustically excited heated jets. 3: Mean flow data

This is Part 3 of a report on the excitability of heated jets under the influence of acoustic excitation. The effects of upstream internal acoustic excitation on jet mixing were described in Part 1. Part 2 described the effects of external excitation on flow mixing. Part 3 contains quantitative results from the measurements of mean Mach number and temperature and consists of radial profiles and centerline distributions measured at selected jet operating conditions for internally excited and unexcited jets. The mean flow data are presented in both graphical and tabulated forms. For the sake of completeness, this part contains temperature probe calibration curves also

What Is Bulk Milk Handling?

The bulk-tank cooling system offers so many advatages so many advantages is quality and efficiency that its eventual adoption for market milk appears certain. However, the problem of the small producer still remains unsolved

Acoustically excited heated jets. 1: Internal excitation

The effects of relatively strong upstream acoustic excitation on the mixing of heated jets with the surrounding air are investigated. To determine the extent of the available information on experiments and theories dealing with acoustically excited heated jets, an extensive literature survey was carried out. The experimental program consisted of flow visualization and flowfield velocity and temperature measurements for a broad range of jet operating and flow excitation conditions. A 50.8-mm-diam nozzle was used for this purpose. Parallel to the experimental study, an existing theoretical model of excited jets was refined to include the region downstream of the jet potential core. Excellent agreement was found between theory and experiment in moderately heated jets. However, the theory has not yet been confirmed for highly heated jets. It was found that the sensitivity of heated jets to upstream acoustic excitation varies strongly with the jet operating conditions and that the threshold excitation level increases with increasing jet temperature. Furthermore, the preferential Strouhal number is found not to change significantly with a change of the jet operating conditions. Finally, the effects of the nozzle exit boundary layer thickness appear to be similar for both heated and unheated jets at low Mach numbers

Acoustically excited heated jets. 2: In search of a better understanding

The second part of a three-part report on the effects of acoustic excitation on jet mixing includes the results of an experimental investigation directed at resolving the question of poor excitability of some of the heated jets. The theoretical predictions discussed in Part 1 are examined to find explanations for the observed discrepancies between the measured and the predicted results. Additional testing was performed by studying the self excitation of the shock containing hot jets and also by exciting the jet by sound radiated through source tubes located externally around the periphery of the jet. The effects of nozzle-exit boundary layer conditions on jet excitability was also investigated. It is concluded that high-speed, heated jet mixing rates and consequently also the jet excitability strongly depends on nozzle exit boundary layer conditions

Low Speed Current Bearing Anti-force Waves

For theoretical investigation of electrical breakdown of a gas, we apply a one-dimensional, steady profile, constant velocity, three-component (electrons, ions and neutral particles) fluid model. Our fluid model consists of the equations of conservation of mass, momentum and energy, coupled with the Poison’s equation. The set of equations is referred to as the electron fluid dynamical equations (EFD). This investigation involves breakdown waves with a substantial current behind the wave front, and waves for which the electric field force on electrons is in the opposite direction of the wave propagation (anti-force waves – lightning return stroke). Therefore, the set of electron fluid dynamical equations need to be modified. For a low wave speed, we intend to find current values, and also the maximum current, for which solutions for our set of electron fluid dynamical equations become possible

Wormhole Cosmology and the Horizon Problem

We construct an explicit class of dynamic lorentzian wormholes connecting Friedmann-Robertson-Walker (FRW) spacetimes. These wormholes can allow two-way transmission of signals between spatially separated regions of spacetime and could permit such regions to come into thermal contact. The cosmology of a network of early Universe wormholes is discussed.Comment: 13 pages, in RevTe