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1998

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Articles 331 - 337 of 337

Full-Text Articles in Physics

Effects Of The Evolution Of Spacecraft Surfaces On Secondary Electron Emission Andspacecraft Charging, R. E. Davies, John R. Dennison Jan 1998

Effects Of The Evolution Of Spacecraft Surfaces On Secondary Electron Emission Andspacecraft Charging, R. E. Davies, John R. Dennison

All Physics Faculty Publications

Spacecraft charging due to the natural plasma environment found in all orbits is known to produce many of the observed spacecraft anomalies and failures. A primary factor in adverse spacecraft charging is the secondary electron emission of differing materials on the spacecraft. Precipitating electrons and ions from the plasma to spacecraft surfaces can result in varying amounts of charge being released, depending on the secondary electron yield of the materials; this can lead to arcing between surfaces. NASA's Space and Environments Effects (SEE) program has recognized the need to improve their current materials database for modeling spacecraft charging and have …

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New Conformal Gauging And The Electromagnetic Theory Of Weyl, James Thomas Wheeler Jan 1998

New Conformal Gauging And The Electromagnetic Theory Of Weyl, James Thomas Wheeler

All Physics Faculty Publications

A new eight-dimensional conformal gauging solves the auxiliary field problem and eliminates unphysical size change from Weyl’s electromagnetic theory. We derive the Maurer–Cartan structure equations and find the zero curvature solutions for the conformal connection. By showing that every one-particle Hamiltonian generates the structure equations we establish a correspondence between phase space and the eight-dimensional base space, and between the action and the integral of the Weyl vector. Applying the correspondence to generic flat solutions yields the Lorentz force law, the form and gauge dependence of the electromagnetic vector potential and minimal coupling. The dynamics found for these flat solutions …

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Evolution Of Secondary Electron Emission Characteristics Of Spacecraft Surfaces: Importance To Spacecraft Charging, R. E. Davies, John R. Dennison Jan 1998

Evolution Of Secondary Electron Emission Characteristics Of Spacecraft Surfaces: Importance To Spacecraft Charging, R. E. Davies, John R. Dennison

All Physics Faculty Publications

Secondary electron emission (SEE) plays a key role in spacecraft charging [Garrett, 1981; Frooninckx and Sojka, 1992] . As a result, spacecraft charging codes require knowledge of the SEE characteristics of various materials in order to predict vehicle potentials in various orbital environments [Katz, et. al., 1986]. Because SEE is a surface phenomenon, occurring in the first few atomic layers of a material, the SEE characteristics of a given surface are extremely sensitive to changes in surface condition—e.g., the addition or removal of surface contaminants, or changes in surface morphology. That spacecraft surfaces can and generally do undergo significant evolution …

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Surface Morphology Of Laser-Superheated Pb(111) And Pb(100), Z. H. Zhang, Bo Lin, X. L. Zeng, H. E. Elsayed-Ali Jan 1998

Surface Morphology Of Laser-Superheated Pb(111) And Pb(100), Z. H. Zhang, Bo Lin, X. L. Zeng, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The surface step density on the vicinal Pb(111) and the surface vacancy density on Pb(100) after laser superheating and melting are investigated using reflection high-energy electron diffraction. With ∼100-ps laser pulses, Pb(111) surface superheating does not significantly change the density of the steps and step-edge roughness. However, after laser surface melting, the average terrace width and the string length at the step edge become as large as those at room temperature. The average terrace width at 573 K changes from 38±15 to 64±19 Å after laser surface melting, while the average string length at the step edge changes from 90±14 …

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Higher Order Isotropic Velocity Grids In Lattice Methods, Pavol Pavlo, George Vahala, Linda L. Vahala Jan 1998

Higher Order Isotropic Velocity Grids In Lattice Methods, Pavol Pavlo, George Vahala, Linda L. Vahala

Electrical & Computer Engineering Faculty Publications

Kinetic lattice methods are a very attractive representation of nonlinear macroscopic systems because of their inherent parallelizability on multiple processors and their avoidance of the nonlinear convective terms. By uncoupling the velocity lattice from the spatial grid, one can employ higher order (non-space-filling) isotropic lattices-lattices which greatly enhance the stable parameter regions, particularly in thermal problems. In particular, the superiority of the octagonal lattice over previous models used in 2D (hexagonal or square) and 3D (projected face-centered hypercube) is shown.

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Utah State University Ground-Based Test Facility For Study Ofelectronic Properties Of Spacecraft Materials, W. Y. Chang, John R. Dennison, Neal Nickles, R. E. Davies Jan 1998

Utah State University Ground-Based Test Facility For Study Ofelectronic Properties Of Spacecraft Materials, W. Y. Chang, John R. Dennison, Neal Nickles, R. E. Davies

All Physics Faculty Publications

No abstract provided.

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A Compact Rotating-Mirror Autocorrelator Design For Femtosecond And Picosecond Laserpulses, D. Mark Riffe, A. J. Sabbah Jan 1998

A Compact Rotating-Mirror Autocorrelator Design For Femtosecond And Picosecond Laserpulses, D. Mark Riffe, A. J. Sabbah

All Physics Faculty Publications

An interferometric rapid-scanning autocorrelator employing two antiparallel rotating mirrors in a variable arm is optimized for maximum optical path difference as a function of the separation of the two rotating mirrors. A very compact design (mirror separation≈mirror diameter) is possible without a reduction in the maximum pulse width that can be measured.

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