47,326 research outputs found
A Scaling Limit With Many Noncommutativity Parameters
We derive the worldsheet propagator for an open string with different
magnetic fields at the two ends, and use it to compute two distinct
noncommutativity parameters, one at each end of the string. The usual scaling
limit that leads to noncommutative Yang-Mills can be generalized to a scaling
limit in which both noncommutativity parameters enter. This corresponds to
expanding a theory with U(N) Chan-Paton factors around a background U(1)^N
gauge field with different magnetic fields in each U(1).Comment: 14 pages, harvma
HMO Penetration, Ownership Status, and the Rise of Hospital Advertising
We examine the recent increase in hospital advertising expenditures. We first illustrate that the rise in hospital advertising has not been universal. Large, not-for-profit, teaching hospitals have, by far, experienced the largest increase in spending. Adjusting for size, for-profit hospitals over this period have actually decreased their marketing expenses. This increase in advertising spending is best explained by managed care penetration. There is a small and marginally significant relationship between increases in for-profit presence in hospital markets and an increase in advertising spending by the not-for-profit hospitals in those markets.
Structural properties of impact ices accreted on aircraft structures
The structural properties of ice accretions formed on aircraft surfaces are studied. The overall objectives are to measure basic structural properties of impact ices and to develop finite element analytical procedures for use in the design of all deicing systems. The Icing Research Tunnel (IRT) was used to produce simulated natural ice accretion over a wide range of icing conditions. Two different test apparatus were used to measure each of the three basic mechanical properties: tensile, shear, and peeling. Data was obtained on both adhesive shear strength of impact ices and peeling forces for various icing conditions. The influences of various icing parameters such as tunnel air temperature and velocity, icing cloud drop size, material substrate, surface temperature at ice/material interface, and ice thickness were studied. A finite element analysis of the shear test apparatus was developed in order to gain more insight in the evaluation of the test data. A comparison with other investigators was made. The result shows that the adhesive shear strength of impact ice typically varies between 40 and 50 psi, with peak strength reaching 120 psi and is not dependent on the kind of substrate used, the thickness of accreted ice, and tunnel temperature below 4 C
Intrinsic adaptive mesh techniques
An alternating direction adaptive grid movement code was developed and a thesis adaptive angular meshes was directed. The alternating direction code was also established on the NASA Langley computer system and is available for use there. In essence, grid points are moved on an abstract surface above physical space by means of alternating coordinate directions. The abstract surface is formed with the salient solution properties if they can be extracted by a priori physical reasoning; or otherwise, in the absence of such reasoning, by the use of error estimates in some chosen norm. Upon formulation, all important driving properties for adaptive purposes are consolidated into one object - the abstract surface. At a basic level, a uniform distribution of surface points is equivalent to gradient resolution. This arises from a projection back down into physical space. At a higher level, a more accurate view of the abstract surface is obtained when changes in surface direction are also resolved. The appropriate measure for direction changes is normal curvature. It is defined as the rate of change of surface tangent planes as a surface coordinate curve is transversed in uniform increments of arc length
Unified computer codes: Properties data for low cost nozzle materials
The development of the analytic capability to predict the thermal ablation response of promising low cost materials for rocket nozzles is presented
Exhaust cloud rise and diffusion in the atmosphere
Analytical approach develops physical-mathematical model of rocket engine exhaust cloud rise, growth, and diffusion. Analytic derivations and resultant model apply to hot exhaust cloud study or industrial stack plumes, making work results applicable to air pollution. Model formulations apply to all exhaust cloud types and various atmospheric conditions
Pressure-Temperature Phase Diagram of Multiferroic
The pressure-temperature phase diagram of multiferroic is
investigated for hydrostatic pressures up to 2 GPa. The stability range of the
ferroelectric phase associated with the incommensurate helical spin order is
reduced by pressure and ferroelectricity is completely suppressed at the
critical pressure of 1.64 GPa at 6.2 K. Thermal expansion measurements at
ambient pressure show strong step-like anomalies of the lattice parameters
associated with the lock-in transition into the commensurate paraelectric
phase. The expansion anomalies are highly anisotropic, the related volume
change is consistent with the high-pressure phase diagram
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