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Articles 1 - 23 of 23
Full-Text Articles in Physics
Coherent Excitation Of The Optic Phonon In Si: Transiently Stimulated Raman Scattering With Afinite-Lifetime Electronic Excitation, D. Mark Riffe, A. J. Sabbah
Coherent Excitation Of The Optic Phonon In Si: Transiently Stimulated Raman Scattering With Afinite-Lifetime Electronic Excitation, D. Mark Riffe, A. J. Sabbah
All Physics Faculty Publications
Using 28-fs, 800-nm laser pulses we have coherently excited and subsequently probed, with time-dependent reflectivity, the Si zone-center optic phonon. The phonon-induced reflectivity change ΔR∕R is well described by the response of an underdamped oscillator: ΔR∕R∝ exp(−t∕τph) cos(2πt∕Tph+ϕ). The measured phase ϕ indicates that transiently stimulated Raman scattering (TSRS) is responsible for the coherent-phonon generation: our results are in good agreement with a recent theory of TSRS for opaque materials [ T. E. Stevens et al. Phys. Rev. B 65 144304 (2002)] when we extend the theory to include the finite lifetime of the excited charge …
Characteristics Of Short-Period Wavelike Features Near 87 Km Altitude From Airglow And Lidar Observations Over Maui, J. H. Hecht, A. Z. Liu, R. L. Walterscheid, S. J. Franke, R. J. Rudy, Michael J. Taylor, Pierre-Dominique Pautet
Characteristics Of Short-Period Wavelike Features Near 87 Km Altitude From Airglow And Lidar Observations Over Maui, J. H. Hecht, A. Z. Liu, R. L. Walterscheid, S. J. Franke, R. J. Rudy, Michael J. Taylor, Pierre-Dominique Pautet
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Small-scale (less than 15 km horizontal wavelength) wavelike structures known as ripples are a common occurrence in OH airglow images. Recent case studies attribute their origin to the presence of either convective or dynamical instabilities. However, little is known about their frequency of occurrence and period. The Maui-MALT Observatory, located at Mt. Haleakala, is instrumented with a Na wind/temperature lidar, which allows the determination of whether the atmosphere is dynamically or convectively unstable, and a fast OH airglow camera which takes images every 3 s with a sensitivity high enough to see the ripples. This study reports on 2 months …
Gravitational Wave Bursts From The Galactic Massive Black Hole, Clovis Hopman, Marc Freitag, Shane L. Larson
Gravitational Wave Bursts From The Galactic Massive Black Hole, Clovis Hopman, Marc Freitag, Shane L. Larson
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The Galactic massive black hole (MBH), with a mass of M•= 3.6 × 106 M⊙, is the closest known MBH, at a distance of only 8 kpc. The proximity of this MBH makes it possible to observe gravitational waves (GWs) from stars with periapse in the observational frequency window of the Laser Interferometer Space Antenna (LISA). This is possible even if the orbit of the star is very eccentric, so that the orbital frequency is many orders of magnitude below the LISA frequency window, as suggested by Rubbo, Holley-Bockelmann & Finn (2006). …
Gauging Newton’S Law, James Thomas Wheeler
Gauging Newton’S Law, James Thomas Wheeler
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We derive both Lagrangian and Hamiltonian mechanics as gauge theories of Newtonian mechanics. Systematic development of the distinct symmetries of dynamics and measurement suggest that gauge theory may be motivated as a reconciliation of dynamics with measurement. Applying this principle to Newton's law with the simplest measurement theory leads to Lagrangian mechanics, while use of conformal measurement theory leads to Hamiltonian mechanics.PACS Nos.: 45.20.Jj, 11.25.Hf, 45.10.–b [ABSTRACT FROM AUTHOR]
Doppler Ducting Of Short-Period Waves By Mid-Latitude Tidal Wind Structure, J. B. Snively, V. P. Pasko, Michael J. Taylor, W. K. Hocking
Doppler Ducting Of Short-Period Waves By Mid-Latitude Tidal Wind Structure, J. B. Snively, V. P. Pasko, Michael J. Taylor, W. K. Hocking
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Multiwavelength airglow image data depicting a short-period (4.9 min) atmospheric gravity wave characterized by a sharp leading front have been analyzed together with synoptic meteor radar wind data recorded simultaneously from Bear Lake Observatory, Utah (41.6N, 111.6W). The wind data suggest the presence of a semidiurnal tide with horizontal winds peaking at around 60 m/s along the SSE direction of motion (170 from north) of this short-period wave. It was found that the gravity wave was most probably ducted because of the Doppler shift imposed by this wind structure. A marked 180 phase shift was observed between the near-infrared OH …
On The Use Of Simultaneous Measurements Of Oh And O2 Emissions To Investigate Wave Growth And Dissipation, A. Taori, A. Guharay, Michael J. Taylor
On The Use Of Simultaneous Measurements Of Oh And O2 Emissions To Investigate Wave Growth And Dissipation, A. Taori, A. Guharay, Michael J. Taylor
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Simultaneous measurements of mesospheric OH (6–2) Meinel and O2 (0–1) Atmospheric band emissions from a low-latitude station, Maui, Hawaii (20.8 N, 156.2 W) are utilized to study the wave characteristics and associated processes. Deduced temperatures show large variability in both OH and O2 data. The seasonal variability in the temperature shows a well-defined, semiannual type of oscillation, which are comparable to the ground-based rocket sounding data. The “Wave Growth Factor”, a ratio of normalized perturbation amplitude in O2 to the OH temperature variability, is estimated for principal as well as residual smaller period components of the nocturnal variability. It is …
A Very Active Sprite-Producing Storm Observed Over Argentina, J. N. Thomas, Michael J. Taylor, Pierre-Dominique Pautet, T. Berkey, N. N. Solorzano, R. H. Holzworth, M. P. Mccarthy, M. Kokorowski, F. Sao Sabbas, O. Pinto Jr., S. A. Cummer, N. Jaugey, J. Li, N. J. Schuch
A Very Active Sprite-Producing Storm Observed Over Argentina, J. N. Thomas, Michael J. Taylor, Pierre-Dominique Pautet, T. Berkey, N. N. Solorzano, R. H. Holzworth, M. P. Mccarthy, M. Kokorowski, F. Sao Sabbas, O. Pinto Jr., S. A. Cummer, N. Jaugey, J. Li, N. J. Schuch
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During the night of 22–23 February 2006, more than 400 middle- atmospheric optical discharges were observed above one large thunderstorm system over northeastern Argentina. These transient luminous events (TLEs) were imaged during the Southern Brazil Sprite Campaign, the first campaign to focus on TLEs over southern Brazil, northeastern Argentina, and Uruguay. All of the TLEs were imaged from the Brazilian Southern Space Observatory (SSO) near Santa Maria, which is nearly in the center of the southernmost Brazilian state of Rio Grande do Sul. Although the fields of view of the imaging cameras were too narrow to view the entire storm, …
Investigation Of A "Wall" Wave Event, F. Li, G. R. Swenson, A. Z. Liu, Michael J. Taylor, Y. Zhao
Investigation Of A "Wall" Wave Event, F. Li, G. R. Swenson, A. Z. Liu, Michael J. Taylor, Y. Zhao
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A bright airglow event was observed at Maui, Hawaii, on the night of 11–12 August 2004 with multiple instruments including a Na wind/temperature lidar, an airglow imager, and a mesospheric temperature mapper. The characteristics of this event were investigated with measurements from these instruments. Analysis showed that this event was caused by a large-amplitude, upward-propagating gravity wave with a period of about 4–5 hours and a vertical wavelength of about 20 km, i.e., a ‘‘wall’’ wave. This wall wave induced dramatic changes in temperature (60 K), airglow intensity (doubled in the OH and tripled in the O2 emissions), and Na …
Electron-Induced Electron Yields Of Uncharged Insulating Materials, Ryan Carl Hoffmann, John R. Dennison, Jennifer Albretsen
Electron-Induced Electron Yields Of Uncharged Insulating Materials, Ryan Carl Hoffmann, John R. Dennison, Jennifer Albretsen
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This study presents electron-induced electron yield measurements from high-resistivity, high-yield materials to validate a model for the yield of uncharged insulators. These measurements are accomplished by using a low-fluence, pulsed incident electron beam and charge neutralization to minimize charge accumulation. Our measurements show large changes in total yield curves and yield decay curves, even for incident electron fluences of/mm2. We model the evolution of the yield as charge accumulates in the material in terms of electron re-capture based on the extended Chung-Everhart model of the electron emission spectrum. This model is used to explain anomalies measured in high yield ceramics, …
Dependence Of Resistivity In Low-Density Polyethylene On Space Environment Parameters, John R. Dennison, Jerilyn Brunson
Dependence Of Resistivity In Low-Density Polyethylene On Space Environment Parameters, John R. Dennison, Jerilyn Brunson
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The conductivity of high-resistivity polymer films is dependent on the magnitude of applied electric field, repeated electric field exposure, and sample temperature. A traditional constant voltage method was used, maintained under vacuum to more closely resemble the space environment. Both the strength of the applied voltage and the thickness of low-density polyethylene (LDPE) samples were varied to determine the electric field dependence of internal polarization and the leakage current most appropriate in calculating the resistivity. Repetition of same field strength measurements determined the influence of sample history and charging memory. Measuring the resistivity from cryogenic temperatures to well above the …
Low Temperature Measurements Of Resistivity In Low-Density Polyethylene, John R. Dennison, J. Brunson
Low Temperature Measurements Of Resistivity In Low-Density Polyethylene, John R. Dennison, J. Brunson
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Measurements of resistivity of low density polyethylene (LDPE) have been made using the standard constant voltage method to determine the temperature dependence of resistivity. Where electrons are assumed to serve as the primary charge carriers, their mobility is believed to be dependent on their probability of hopping between trapping sites treated as potential wells. We consider our measurements of this relatively simple polymeric material using temperature-dependant models of conduction mechanisms developed for amorphous solids and semi-conductors.
Triggering Threshold Spacecraft Charging With Changes In Electron Emission From Materials, John R. Dennison, R. C. Hoffmann, J. Abbott
Triggering Threshold Spacecraft Charging With Changes In Electron Emission From Materials, John R. Dennison, R. C. Hoffmann, J. Abbott
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Modest changes in spacecraft charging conditions can lead to abrupt changes in the spacecraft equilibrium, from small positive potentials to large negative potentials relative to the space plasma; this phenomenon is referred to as threshold charging. It is well known that temporal changes of the space plasma environment (electron plasma temperature or density) can cause threshold charging. Threshold charging can also result from by temporal changes in the juxtaposition of the spacecraft to the environment, including spacecraft orbit, orientation, and geometry. This study focuses on the effects of possible changes in electron emission properties of representative spacecraft materials. It is …
Ionospheric Challenges Of The International Polar Year, Jan Josef Sojka, Robert W. Schunk, Tony Van Eyken, John Kelly, Craig Heinselman, Mary Mccready
Ionospheric Challenges Of The International Polar Year, Jan Josef Sojka, Robert W. Schunk, Tony Van Eyken, John Kelly, Craig Heinselman, Mary Mccready
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Fifty years ago, the first International Geophysical Year (lGY) generated a huge step function increase in observations of ionospheric variability associated with the almost continuous geomagnetic activity experienced during the largest solar maximum of the past 100 years. In turn, these observations fueled more than a decade of theoretical advancement of magnetospheric-ionospheric electrodynamics and geomagnetic storm physics.
Assessing Models For Ionospheric Weather Specifications Over Australia During The 2004 Climate And Weather Of The Sun-Earth-System (Cawses) Campaign, Jan Josef Sojka, D. C. Thompson, L. Scherliess, Robert W. Schunk, T. J. Harris
Assessing Models For Ionospheric Weather Specifications Over Australia During The 2004 Climate And Weather Of The Sun-Earth-System (Cawses) Campaign, Jan Josef Sojka, D. C. Thompson, L. Scherliess, Robert W. Schunk, T. J. Harris
All Physics Faculty Publications
The Utah State University (USU) Global Assimilation of Ionospheric Measurements (GAIM) program is developing assimilation models to specify ionospheric weather. In this study the Gauss Markov Kalman Filter (GMKF) GAIM model was used. The period 20 March through 19 April 2004, which spanned the Climate and Weather of the Sun-Earth-System (CAWSES) first study period, has been extensively studied to validate the performance of the GAIM model. Although the USU-GAIM model has both regional and global capabilities and can assimilate data from a wide variety of ionospheric observations, for this study the GMKF model was run in a global mode using …
Observations Of A Noctilucent Cloud Above Logan, Utah (41.7°N, 111.8°W) In 1995, Joshua P. Herron, Vincent B. Wickwar, P J. Espy, J W. Merriwether
Observations Of A Noctilucent Cloud Above Logan, Utah (41.7°N, 111.8°W) In 1995, Joshua P. Herron, Vincent B. Wickwar, P J. Espy, J W. Merriwether
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A Rayleigh-scatter lidar has been operated at the Atmospheric Lidar Observatory (ALO) on the Utah State University (USU) campus (41.7°N, 111.8°W) since August 1993. During the morning of 22 June 1995, lidar returns from a noctilucent cloud (NLC) were observed for approximately 1 hr, well away from the twilight periods when NLCs are visible. This detection of an NLC at this latitude shows that the first reported sighting, in 1999 (Wickwar et al., 2002), was not a unique occurrence. This 1995 observation differs from the 1999 one in that temperatures could be deduced. Near the 83-km NLC altitude the temperatures …
Yang-Mills Gravity In Biconformal Space, L. B. Anderson, James Thomas Wheeler
Yang-Mills Gravity In Biconformal Space, L. B. Anderson, James Thomas Wheeler
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We write a gravity theory with Yang–Mills-type action using the biconformal gauging of the conformal group. We show that the resulting biconformal Yang–Mills gravity theories describe 4-dim, scale-invariant general relativity in the case of slowly changing fields. In addition, we systematically extend arbitrary 4-dim Yang–Mills theories to biconformal space, providing a new arena for studying flat-space Yang–Mills theories. By applying the biconformal extension to a 4-dim pure Yang–Mills theory with conformal symmetry, we establish a 1-1, onto mapping between a set of gravitational gauge theories and 4-dim, flat-space gauge theories.
Hopping Conductivity In Low-Density Polyethylene, Jerilyn Brunson, John R. Dennison
Hopping Conductivity In Low-Density Polyethylene, Jerilyn Brunson, John R. Dennison
All Physics Faculty Publications
Measurements of resistivity of low density polyethylene (LDPE) have been made using the standard constant voltage method to determine the temperature dependence of resistivity. Where electrons are assumed to serve as the primary charge carriers, their mobility is believed to be dependent on their probability of hopping between trapping sites treated as potential wells. We consider our measurements of this relatively simple polymeric material using temperature-dependant models of conduction mechanisms developed for amorphous solids and semi-conductors.
Functional Time Evolution, Anomaly Potentials, And The Geometric Phase, Charles G. Torre
Functional Time Evolution, Anomaly Potentials, And The Geometric Phase, Charles G. Torre
All Physics Faculty Publications
A free quantum field in 1+1 dimensions admits unitary Schrödinger picture dynamics along any foliation of spacetime by Cauchy curves. Kuchař showed that the Schrödinger picture state vectors, viewed as functionals of spacelike embeddings, satisfy a functional Schrödinger equation in which the generators of time evolution are the field energy-momentum densities with a particular normal-ordering and with a (nonunique) c-number contribution. The c-number contribution to the Schrödinger equation, called the “anomaly potential,” is needed to make the equation integrable in light of the Schwinger terms present in the commutators of the normal-ordered energy-momentum densities. Here we give a quantum geometric …
Schroedinger Representation For The Polarized Gowdy Model, Charles G. Torre
Schroedinger Representation For The Polarized Gowdy Model, Charles G. Torre
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The polarized T3 Gowdy model is, in a standard gauge, characterized by a point particle degree of freedom and a scalar field degree of freedom obeying a linear field equation on R × S1. The Fock representation of the scalar field has been well studied. We construct the Schrödinger representation for the scalar field at a fixed value of the Gowdy time in terms of square-integrable functions on a space of distributional fields with a Gaussian probability measure. We show that 'typical' field configurations are slightly more singular than square-integrable functions on the circle. For each time the corresponding Schrödinger …
Hands-On Gravitational Wave Astronomy: Extracting Astrophysical Information From Simulated Signals, Louis J. Rubbo, Shane L. Larson, Michelle B. Larson, Dale R. Ingram
Hands-On Gravitational Wave Astronomy: Extracting Astrophysical Information From Simulated Signals, Louis J. Rubbo, Shane L. Larson, Michelle B. Larson, Dale R. Ingram
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In this article we introduce an activity in which introductory astronomy students act as gravitational wave astronomers by extracting information from simulated gravitational wave signals. The process mimics the way real gravitational wave analysis is handled by using plots of a pure gravitational wave signal. The students measure the properties of the simulated signal and use these measurements to evaluate standard relations for astrophysical source parameters. Although the activity described focuses on circular binaries, the techniques described can be applied to other gravitational wave sources as well. A problem based on the discussion in this paper is available for use …
Deep Dielectric Charging Of Spacecraft Polymers By Energetic Protons, Nelson W. Green, John R. Dennison
Deep Dielectric Charging Of Spacecraft Polymers By Energetic Protons, Nelson W. Green, John R. Dennison
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The majority of research in the field of spacecraft charging concentrates on electron charging effects with little discussion of charging by protons. For spacecraft orbiting in the traditional LEO and GEO environments, this emphasis on electrons is appropriate since energetic electrons are the dominant species. But for spacecraft in orbits within the inner radiation belts or for interplanetary and lunar space probes, proton charging effects may also be of concern. To examine bulk spacecraft charging effects in these environments several typical highly insulating spacecraft polymers were exposed to energetic protons with energies from 1 MeV to 10 MeV to simulate …
Recent Progress In Mesospheric Gravity Wave Studies Usingnightglow Imaging Systems, Michael J. Taylor, W. R. Pendleton, Pierre-Dominique Pautet, Y. Zhao, C. Olsen, H. K. Surendra-Babu, A. F. Medeiros, H. Takahashi
Recent Progress In Mesospheric Gravity Wave Studies Usingnightglow Imaging Systems, Michael J. Taylor, W. R. Pendleton, Pierre-Dominique Pautet, Y. Zhao, C. Olsen, H. K. Surendra-Babu, A. F. Medeiros, H. Takahashi
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During the past four decades a variety of optical remote sensing techniques have revealed a rich spectrum of wave activity in the upper atmosphere. Many of these perturbations, with periodicites ranging from ~5 min to several hours and horizontal scales of a few ten's of km to several thousands km, are due to freely propagating acoustic-gravity waves and forced tidal oscillations. Optical observations of the spatial and temporal characteristics of these waves in the mesosphere and lower thermosphere (MLT) region (~80-100 km) are facilitated by several naturally occurring, vertically distinct nightglow layers. This paper describes the use of state-of-the-art ground-based …
Longitudinal Dependence Of Middle And Low Latitude Zonal Plasmadrifts Measured By De-2, J. W. Jensen, B. G. Fejer
Longitudinal Dependence Of Middle And Low Latitude Zonal Plasmadrifts Measured By De-2, J. W. Jensen, B. G. Fejer
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We used ion drift observations from the DE-2 satellite to study for the first time the longitudinal variations of middle and low latitude F region zonal plasma drifts during quiet and disturbed conditions. The quiet-time middle latitude drifts are predominantly westward; the low latitude drifts are westward during the day and eastward at night. The daytime quiet-time drifts do not change much with longitude; the nighttime drifts have strong season dependent longitudinal variations. In the dusk-premidnight period, the equinoctial middle latitude westward drifts are smallest in the European sector and the low latitude eastward drifts are largest in the American-Pacific …