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All Physics Faculty Publications

Series

1999

Articles 1 - 11 of 11

Full-Text Articles in Physical Sciences and Mathematics

Video And Photometric Observations Of A Sprite In Coincidence With A Meteor-Triggered Jet Event, D. M. Suszcynsky, R. Strabley, R. Roussel-Dupre, E. M.D. Symbalisty, R. A. Armstrong, W. A. Lyons, Michael J. Taylor Dec 1999

Video And Photometric Observations Of A Sprite In Coincidence With A Meteor-Triggered Jet Event, D. M. Suszcynsky, R. Strabley, R. Roussel-Dupre, E. M.D. Symbalisty, R. A. Armstrong, W. A. Lyons, Michael J. Taylor

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Video and photometric observations of a meteor-triggered “jet” event in association with the occurrence of a sprite were collected during the SPRITES '98 campaign. The event raises interest in the question of possible meteoric triggering of upper atmospheric transients as originally suggested by Muller [1995]. The event consisted of three stages: (1) the observation of a moderately bright meteor, (2) the development of a sprite in the immediate vicinity of the meteor as the meteor reached no lower than ∼70 km altitude, and (3) a slower-forming jet of luminosity that appeared during the late stages of the sprite and propagated …

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Conformal Actions In Any Dimension, Andre Wehner, James Thomas Wheeler Sep 1999

Conformal Actions In Any Dimension, Andre Wehner, James Thomas Wheeler

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Biconformal gauging of the conformal group gives a scale-invariant volume form, permitting a single form of the action to be invariant in any dimension. We display several 2n-dimensional scale-invariant polynomial actions and a dual action. We solve the field equations for the most general action linear in the curvatures for a minimal torsion geometry. In any dimension n > 2, the solution is foliated by equivalent n-dimensional Ricci-flat Riemannian space-times, and the full 2n-dimensional space is symplectic. Two fields defined entirely on the Riemannian submanifolds completely determine the solution: a metric eμα, and …

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Criteria For Elves And Sprites On Schumann Resonance Observations, E. W. Huang, E. R. Williams, R. Boldi, S. Heckman, W. Lyons, Michael J. Taylor, C. Wong, T. Nelson Jul 1999

Criteria For Elves And Sprites On Schumann Resonance Observations, E. W. Huang, E. R. Williams, R. Boldi, S. Heckman, W. Lyons, Michael J. Taylor, C. Wong, T. Nelson

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Ground flashes with positive polarity associated with both sprites and elves excite the Earth's Schumann resonances to amplitudes several times greater than the background resonances. Theoretical predictions for dielectric breakdown in the mesosphere are tested using ELF methods to evaluate vertical charge moments of positive ground flashes. Comparisons of the measured time constants for lightning charge transfer with the electrostatic relaxation time at altitudes of nighttime sprite initiation (50–70 km) generally validate the electrostatic assumption in predictions made initially by Wilson [1925]. The measured charge moments (Q dS = 200–2000 C-km) are large in comparison with ordinary negative lightning but …

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Effects Of Spacecraft Potential On Secondary Electron Yields In Geosynchronous Orbit, Neal E. Nickles Jan 1999

Effects Of Spacecraft Potential On Secondary Electron Yields In Geosynchronous Orbit, Neal E. Nickles

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Surface charging due to interactions with the earth=s plasma is a hazard for orbiting spacecraft. Secondary electron (SE) emission is an important physical process in spacecraft charging. Current spacecraft charging models do not consider the SE energy or angular distributions and their implications for estimating the return of SE to the spacecraft. Comprehensive work on the application of SE energy and angular distributions to spacecraft charging has been published [Nickles et al., 1999] and part of that work is summarized here. The application of SE energy distributions to the case of positive charging in geosynchronous orbit is discussed and shown …

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The Conductor-Dielectric Junctions In A Low Density Plasma, B. V. Vayner, J. T. Galofaro, D. C. Ferguson, Win De Groot, Clint Thomson, John R. Dennison, Robert Davies Jan 1999

The Conductor-Dielectric Junctions In A Low Density Plasma, B. V. Vayner, J. T. Galofaro, D. C. Ferguson, Win De Groot, Clint Thomson, John R. Dennison, Robert Davies

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A conductor-dielectric junction exposed to the space environment is a frequent spacecraft design feature. Due to spacecraft charging and/or solar array operation, the conductor can acquire a high potential with respect to the surrounding plasma. If this potential is positive the insulators adjacent to exposed conductors can collect current as if they were conductors themselves. This phenomenon, called snapover, results in a substantial increase in current collection, and may even result in a glow discharge if the potential is high enough. If a conductor has a negative potential, arcing can occur at the site of a junction. Both of these …

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Effects Of Magnetospheric Precipitation And Ionospheric Conductivity On The Ground Magnetic Signatures Of Traveling Convection Vortices, Lie Zhu, Robert W. Schunk, Jan Josef Sojka Jan 1999

Effects Of Magnetospheric Precipitation And Ionospheric Conductivity On The Ground Magnetic Signatures Of Traveling Convection Vortices, Lie Zhu, Robert W. Schunk, Jan Josef Sojka

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By using an improved TCV model (Zhu et al., 1997), a quantitative study of the effects of magnetospheric precipitation and ionospheric background conductivity on the ground magnetic signatures of traveling convection vortices (TCVs) has been conducted. In this study the localized conductivity enhancement associated with the TCVs is present and the ratio of the Hall and Pedersen conductances vary both spatially and temporally according to the hardness of the TCV precipitation. It is found that a strong conductivity enhancement associated with hard TCV precipitation can significantly distort the TCV current closure in the ionosphere and lead to ground magnetic disturbance …

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Constructing A Portable Sundial, Michelle B. Larson Jan 1999

Constructing A Portable Sundial, Michelle B. Larson

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Throughout history people have used shadows and sundials to measure the passage of time. This article describes how to construct a personal sundial that can be worn as a necklace or carried as a key chain. The activity is easily adaptable for grade levels elementary through high school. The instructions can be scaled for a schoolyard project. We’ve found sundial construction to be a terrific project that not only encourages students to investigate movement of the Sun in the sky, but also allows them to practice their math skills.

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Synchrotron X-Ray Diffraction Of Layering Transitions Of Multilayer Nitrogen Physisorbed On Graphite, T. E. Burns, John R. Dennison, S. N. Ehrlich Jan 1999

Synchrotron X-Ray Diffraction Of Layering Transitions Of Multilayer Nitrogen Physisorbed On Graphite, T. E. Burns, John R. Dennison, S. N. Ehrlich

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We use synchrotron x-ray diffraction for structural analysis of the behavior of multilayer nitrogen films physisorbed on graphite foam. We provide structural information and concentrations of 2D and 3D solid phases at a coverage of Θ = 8 ML (Θ / 1 ML for a %3 x %3 structure) for temperatures from below the bulk α-ß transition temperature [Tα-ß = 34 " 0.5 K] to above the bulk triple point [Ttp = 63 K]. Our data indicate layering begins near Tα-ß, with subsequent layering occurring as the temperature is raised; all bulk nitrogen forms disordered film …

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Functional Evolution Of Free Quantum Fields, Charles G. Torre, Madhavan Varadarajan Jan 1999

Functional Evolution Of Free Quantum Fields, Charles G. Torre, Madhavan Varadarajan

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We consider the problem of evolving a quantum field between any two (in general, curved) Cauchy surfaces. Classically, this dynamical evolution is represented by a canonical transformation on the phase space for the field theory. We show that this canonical transformation cannot, in general, be unitarily implemented on the Fock space for free quantum fields on flat spacetimes of dimension greater than 2. We do this by considering time evolution of a free Klein-Gordon field on a flat spacetime (with toroidal Cauchy surfaces) starting from a flat initial surface and ending on a generic final surface. The associated Bogolubov transformation …

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Midisuperspace Models Of Canonical Quantum Gravity, Charles G. Torre Jan 1999

Midisuperspace Models Of Canonical Quantum Gravity, Charles G. Torre

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A midisuperspace model is a field theory obtained by symmetry reduction of a parent gravitational theory. Such models have proven useful for exploring the classical and quantum dynamics of the gravitational field. I present three recent classes of results pertinent to canonical quantization of vacuum general relativity in the context of midisuperspace models. (1) I give necessary and sufficient conditions such that a given symmetry reduction can be performed at the level of the Lagrangian or Hamiltonian.(2) I discuss the Hamiltonian formulation of models based upon cylindrical and toroidal symmetry. In particular, I explain how these models can be identified …

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Null Geodesics In The Alcubierre Warp Drive Spacetime: The View From The Bridge, Chad Clark, William A. Hiscock, Shane L. Larson Jan 1999

Null Geodesics In The Alcubierre Warp Drive Spacetime: The View From The Bridge, Chad Clark, William A. Hiscock, Shane L. Larson

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The null geodesic equations in the Alcubierre warp-drive spacetime are numerically integrated to determine the angular deflection and redshift of photons which propagate through the distortion of the `warp-drive' bubble to reach an observer at the origin of the warp effect. We find that for a starship with an effective warp speed exceeding the speed of light, stars in the forward hemisphere will appear closer to the direction of motion than they would to an observer at rest. This aberration is qualitatively similar to that caused by special relativity. Behind the starship, a conical region forms from within which no …

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