13,291 research outputs found
Combustion of hydrogen-air jets in local chemical equilibrium: A guide to the CHARNAL computer program
A guide to a computer program, written in FORTRAN 4, for predicting the flow properties of turbulent mixing with combustion of a circular jet of hydrogen into a co-flowing stream of air is presented. The program, which is based upon the Imperial College group's PASSA series, solves differential equations for diffusion and dissipation of turbulent kinetic energy and also of the R.M.S. fluctuation of hydrogen concentration. The effective turbulent viscosity for use in the shear stress equation is computed. Chemical equilibrium is assumed throughout the flow
Magnetovac Cylinder to Magnetovac Torus
A method for mapping known cylindrical magnetovac solutions to solutions in
torus coordinates is developed. Identification of the cylinder ends changes
topology from R1 x S1 to S1 x S1. An analytic Einstein-Maxwell solution for a
toroidal magnetic field in tori is presented. The toroidal interior is matched
to an asymptotically flat vacuum exterior, connected by an Israel boundary
layer.Comment: to appear in Class. Quant. Gra
Two-dimensional shear modulus of a Langmuir foam
We deform a two-dimensional (2D) foam, created in a Langmuir monolayer, by
applying a mechanical perturbation, and simultaneously image it by Brewster
angle microscopy. We determine the foam stress tensor (through a determination
of the 2D gas-liquid line tension, 2.35 0.4 pJm) and the
statistical strain tensor, by analyzing the images of the deformed structure.
We deduce the 2D shear modulus of the foam, .
The foam effective rigidity is predicted to be , which agrees with the value obtained in an independent mechanical measurement.Comment: submitted May 12, 2003 ; resubmitted Sept 9, 200
Finite Temperature Spectral Densities of Momentum and R-Charge Correlators in Yang Mills Theory
We compute spectral densities of momentum and R-charge correlators in thermal
Yang Mills at strong coupling using the AdS/CFT correspondence. For
and smaller, the spectral density differs markedly from
perturbation theory; there is no kinetic theory peak. For large , the
spectral density oscillates around the zero-temperature result with an
exponentially decreasing amplitude. Contrast this with QCD where the spectral
density of the current-current correlator approaches the zero temperature
result like . Despite these marked differences with perturbation
theory, in Euclidean space-time the correlators differ by only from
the free result. The implications for Lattice QCD measurements of transport are
discussed.Comment: 18 pages, 3 figure
Brayton heat exchanger unit development program (alternate design)
A Brayton Heat Exchanger Unit Alternate Design (BHXU-Alternate) consisting of a recuperator, a heat sink heat exchanger, and a gas ducting system, was designed and fabricated. The design was formulated to provide a high performance unit suitable for use in a long-life Brayton-cycle powerplant. Emphasis was on double containment against external leakage and leakage of the organic coolant into the gas stream. A parametric analysis and design study was performed to establish the optimum component configurations to achieve low weight and size and high reliability, while meeting the requirements of high effectiveness and low pressure drop. Layout studies and detailed mechanical and structural design were performed to obtain a flight-type packaging arrangement, including the close-coupled integration of the BHXU-Alternate with the Brayton Rotating Unit (BRU)
Topological Constraints on the Charge Distributions for the Thomson Problem
The method of Morse theory is used to analyze the distributions of unit
charges interacting through a repulsive force and constrained to move on the
surface of a sphere -- the Thomson problem. We find that, due to topological
reasons, the system may organize itself in the form of pentagonal structures.
This gives a qualitative account for the interesting ``pentagonal buttons''
discovered in recent numerical work.Comment: 10 pages; dedicated to Rafael Sorkin on his 60th birthda
Removal of terrestrial DOC in aquatic ecosystems of a temperate river network
Surface waters play a potentially important role in the global carbon balance. Dissolved organic carbon (DOC) fluxes are a major transfer of terrestrial carbon to river systems, and the fate of DOC in aquatic systems is poorly constrained. We used a unique combination of spatially distributed sampling of three DOC fractions throughout a river network and modeling to quantify the net removal of terrestrial DOC during a summer base flow period. We found that aquatic reactivity of terrestrial DOC leading to net loss is low, closer to conservative chloride than to reactive nitrogen. Net removal occurred mainly from the hydrophobic organic acid fraction, while hydrophilic and transphilic acids showed no net change, indicating that partitioning of bulk DOC into different fractions is critical for understanding terrestrial DOC removal. These findings suggest that river systems may have only a modest ability to alter the amounts of terrestrial DOC delivered to coastal zones
High rate continuous synthesis of nanocrystalline materials in a colliding vapor stream of microdroplets
Progress in nanotechnology is driving the need of large scale synthesis of functional
nanomaterials. The lack of a workforce trained on process control and scale-up of nanomaterials
manufacturing, the gap between laboratories and economically practical nanofabrication and the
funding strain on the survivability of startup companies all contribute to the difficulties in scaling up
nanotechnologies and their commercialization [1,2]. We report here a high rate continuous synthesis of
functional inorganic nanomaterials using colliding vapor stream of reagents microdroplets
Capillary-gravity waves: The effect of viscosity on the wave resistance
The effect of viscosity on the wave resistance experienced by a 2d
perturbation moving at uniform velocity over the free surface of a fluid is
investigated. The analysis is based on Rayleigh's linearized theory of
capillary-gravity waves. It is shown in particular that the wave resistance
remains bounded as the velocity of the perturbation approches the minimun phase
speed, unlike what is predicted by the inviscid theory.Comment: Europhysics Letters, in pres
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