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2004

All Physics Faculty Publications

Articles 1 - 19 of 19

Full-Text Articles in Physics

Tidal Perturbations And Variability In Mesopause Region Over Fort Collins, Co(41n, 105w): Continuous Multi-Day Temperature And Wind Lidar Observations, C. Y. She, T. Li, R. L. Collins, Tao Yuan, B. P. Williams, T. Kawahara, J. D. Vance, P. Acott, D. A. Krueger, H. L. Liu, M. E. Hagan Dec 2004

Tidal Perturbations And Variability In Mesopause Region Over Fort Collins, Co(41n, 105w): Continuous Multi-Day Temperature And Wind Lidar Observations, C. Y. She, T. Li, R. L. Collins, Tao Yuan, B. P. Williams, T. Kawahara, J. D. Vance, P. Acott, D. A. Krueger, H. L. Liu, M. E. Hagan

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An unusually long data set was acquired at the sodium lidar facility at Colorado State University (41N, 105W), between Sep 18 and Oct 01, 2003, including a 9-day continuous observation. This time is long enough to average out the perturbations of gravity waves and short-period planetary waves. As such, it can be used to define tidal-period perturbations in temperature and horizontal wind. Assuming the sodium mixing ratio is a constant of motion, the observed tidal-period oscillation in sodium density follows that of vertical wind. Thus, the data set defines tidal-period perturbations of temperature and wind vector. The observed amplitudes and …

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Seasonal Variations Of The Gravity Wave Momentum Flux In The Antarctic Mesosphere And Lower Thermosphere, P. J. Espy, G. O.L. Jones, G. R. Swenson, J. Tang, Michael J. Taylor Dec 2004

Seasonal Variations Of The Gravity Wave Momentum Flux In The Antarctic Mesosphere And Lower Thermosphere, P. J. Espy, G. O.L. Jones, G. R. Swenson, J. Tang, Michael J. Taylor

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Airglow imager and dynasonde/imaging Doppler interferometer (IDI) radar wind measurements at Halley Station, Antarctica (75.6S, 26.6W) have been used to estimate the seasonal variation of the vertical fluxes of horizontal momentum carried by highfrequency atmospheric gravity waves. The cross-correlation coefficients between the vertical and horizontal wind perturbations were calculated from sodium (Na) airglow imager data collected during the austral winter seasons of 2000 and 2001. These were combined with wind velocity variances from coincident radar measurements to estimate the daily averaged upper limit of the vertical flux of horizontal momentum due to gravity waves. The resulting momentum flux at the …

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Concurrent Oh Imager And Sodiumtemperature/Wind Lidar Observation Of A Mesopause Region Undular Bore Event Over Fort Collins/Platteville, Co, C. Y. She, T. Li, B. P. Williams, Tao Yuan, R. H. Picard Nov 2004

Concurrent Oh Imager And Sodiumtemperature/Wind Lidar Observation Of A Mesopause Region Undular Bore Event Over Fort Collins/Platteville, Co, C. Y. She, T. Li, B. P. Williams, Tao Yuan, R. H. Picard

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We reported the observation of a mesospheric front with the properties of an undular bore by an OH imager, over the Fort Collins/Platteville area on 6/7 October 2002. Unlike the earlier bore observations, a Na lidar capable of measuring mesopause region temperature, zonal, and meridional winds was in operation concurrently. The lidar data confirm, for the first time, the existence of a collocated temperature inversion layer to serve as the ducting region for bore propagation, as required by the simple theory proposed by Dewan and Picard 6 years ago. In addition, the lidar data in principle provide sufficient information for …

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The Effect Of Low Energy Electron And Uv/Vis Radiation Aging On The Electron Emission Properties And Breakdown Of Thin-Film Dielectrics, John R. Dennison, C. D. Thomson, Alec Sim Nov 2004

The Effect Of Low Energy Electron And Uv/Vis Radiation Aging On The Electron Emission Properties And Breakdown Of Thin-Film Dielectrics, John R. Dennison, C. D. Thomson, Alec Sim

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Studies of secondary and backscattered electron yield curves of thin-film dielectrics have recently been made using pulsed, low current electron beam methods to minimize insulator charging. These capabilities have allowed us to investigate the evolution of surface and internal charge profiles as a function of low energy electron (keV) pulsed-electron fluence to determine how quickly insulators charge, and how this can affect subsequent electron emission properties. We have also studied critical incident electron energies that result in electrical breakdown of insulator materials and the effect of breakdown on subsequent emission, charging and conduction. The qualitative physics of such processes in …

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Event Rate Estimates For Lisa Extreme Mass Ratio Capture Sources, J. Gair, L. Barack, T. Creighton, C. Cutler, Shane L. Larson, E. S. Phinney, M. Vallisneri Oct 2004

Event Rate Estimates For Lisa Extreme Mass Ratio Capture Sources, J. Gair, L. Barack, T. Creighton, C. Cutler, Shane L. Larson, E. S. Phinney, M. Vallisneri

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One of the most exciting prospects for the LISA gravitational wave observatory is the detection of gravitational radiation from the inspiral of a compact object into a supermassive black hole. The large inspiral parameter space and low amplitude of the signal make detection of these sources computationally challenging. We outline here a first-cut data analysis scheme that assumes realistic computational resources. In the context of this scheme, we estimate the signal-to-noise ratio that a source requires to pass our thresholds and be detected. Combining this with an estimate of the population of sources in the universe, we estimate the number …

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First Nearglobal Retrievals Of Oh Rotational Temperatures From Satellite-Based Meinel Band Emission Measurements, C. Von Savigny, C. U. Eichmann, E. J. Llewellyn, H. Bovensmann, J. P. Burrows, M. Bittner, K. Hoppner, D. Offermann, Michael J. Taylor, Y. Zhao, W. Steinbrecht, P. Winkler Aug 2004

First Nearglobal Retrievals Of Oh Rotational Temperatures From Satellite-Based Meinel Band Emission Measurements, C. Von Savigny, C. U. Eichmann, E. J. Llewellyn, H. Bovensmann, J. P. Burrows, M. Bittner, K. Hoppner, D. Offermann, Michael J. Taylor, Y. Zhao, W. Steinbrecht, P. Winkler

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For the first time near-global retrievals of mesopause OH rotational temperatures from satellite-borne Meinel band emission measurements are presented. The measurements of the OH (3-1) Meinel band near 1.5 micron were performed with the SCIAMACHY instrument on the European Space Agency’s environmental satellite Envisat. The derived OH (3-1) rotational temperatures are shown to be in reasonable agreement with the CIRA (1986) atmosphere temperatures for the seasons and latitudes considered. The derived temperatures are in good agreement with groundbased measurements of the OH rotational temperature performed with a CEDAR Mesospheric Temperature Mapper (MTM) at Maui, Hawaii (21N/204E), with the GRound based …

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Thunderstorm And Lightning Characteristics Associated With Sprites In Brazil, O. Pinto Jr., M. M.F. Saba, I. R.C.A. Pinto, F. S.S. Tavares, K. P. Naccarato, N. N. Solorzano, Michael J. Taylor, P. D. Pautet, R. H. Holzworth Jul 2004

Thunderstorm And Lightning Characteristics Associated With Sprites In Brazil, O. Pinto Jr., M. M.F. Saba, I. R.C.A. Pinto, F. S.S. Tavares, K. P. Naccarato, N. N. Solorzano, Michael J. Taylor, P. D. Pautet, R. H. Holzworth

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A study of the thunderstorm and cloud-ground lightning characteristics associated with sprite events observed in Brazil is presented. The study is based on ground and aircraft sprite observations with high sensitivity intensified CCD cameras of six different thunderstorms, GOES satellite infrared images, radar and lightning network data. A total of eighteen transient optical events were recorded at three different days in 2002 and 2003, sixteen of which exhibited vertical structures typically associated with sprites. Four thunderstorms were associated with two different cold fronts, one with a Mesoscale Convective System, and one was a local isolated thunderstorm. The sprites occurred during …

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Tidal Modulation Of The Gravitywave Momentum Flux In The Antarctic Mesosphere, P. J. Espy, G. O.L. Jones, G. R. Swenson, J. Tang, Michael J. Taylor Jun 2004

Tidal Modulation Of The Gravitywave Momentum Flux In The Antarctic Mesosphere, P. J. Espy, G. O.L. Jones, G. R. Swenson, J. Tang, Michael J. Taylor

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Airglow imager and dynasonde/IDI radar wind measurements at Halley Station, Antarctica (76S, 27W) have been used to estimate the diurnal variation of the vertical fluxes of horizontal momentum carried by highfrequency atmospheric gravity waves. The cross-correlation coefficients between the vertical and horizontal wind perturbations were calculated from the sodium airglow imager data collected during four consecutive nights of near total darkness during July of 2000. These were combined with wind-velocity variances from coincident radar measurements to estimate the upper limit of the vertical flux of horizontal momentum during three-hour intervals throughout the period. The resulting momentum flux showed a marked …

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Plasma Blobs Observed By Ground-Based Optical And Radio Techniques In The Brazilian Tropical Sector, A. A. Pimenta, Y. Sahai, J. A. Bittencourt, M. A. Abdu, H. Takahashi, Michael J. Taylor Jun 2004

Plasma Blobs Observed By Ground-Based Optical And Radio Techniques In The Brazilian Tropical Sector, A. A. Pimenta, Y. Sahai, J. A. Bittencourt, M. A. Abdu, H. Takahashi, Michael J. Taylor

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Ground-based optical and radio observations were carried out in the tropical region in Brazil, during the period from October 1998 to September 2000, and on several occasions we detected F-region plasma blob (localized discrete plasma density enhancement) events. These are the first observations of blobs in the tropical F-region using combined ground-based optical and radio techniques. Allsky images were used to map the spatial extension and temporal location of plasma blobs and ionosonde and photometer measurements were used to measure the plasma densities. Interesting cases of plasma blob events were observed on October 07, 1999 and March 04, 2000 over …

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Biconformal Supergravity And The Ads/Cftconjecture, L. B. Anderson, James Thomas Wheeler May 2004

Biconformal Supergravity And The Ads/Cftconjecture, L. B. Anderson, James Thomas Wheeler

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Biconformal supergravity models provide a new gauging of the superconformal group relevant to the Maldacena conjecture. Using the group quotient method to biconformally gauge SU(2,2|N), we generate a 16-dim superspace. We write the most general even- and odd-parity actions linear in the curvatures, the bosonic sector of which is known to descend to general relativity on a 4-dim manifold.

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Extended Beg Model Of Monhalogenated Methanes Physisorbed On Ionic Crystals, T. E. Burns, John R. Dennison, Jason Kite Apr 2004

Extended Beg Model Of Monhalogenated Methanes Physisorbed On Ionic Crystals, T. E. Burns, John R. Dennison, Jason Kite

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The 2D dielectric phases and phase transitions of adsorbed dipolar molecules are modeled using a dilute spin-one Ising model. This model is studied in the Blume–Emery–Griffiths formalism, using a mean-field approximation, where the interaction parameters are uniquely determined from the system interaction energies using an averaging procedure. The model is applied to four monhalogenated methane species physisorbed on MgO(1 0 0) and NaCl(1 0 0) surfaces using previous experimental and theoretical studies to estimate the interaction energy parameters. We find that temperature- and coverage-dependent antiferroelectric to ferroelectric, coverage-dependent ferroelectric up to ferroelectric down, reentrant ferroelectric to ferrielectric, and order-disorder dipole …

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Lisa Time-Delay Interferometry Zero-Signal Solution: Geometrical Properties, Massimo Tinto, Shane L. Larson Jan 2004

Lisa Time-Delay Interferometry Zero-Signal Solution: Geometrical Properties, Massimo Tinto, Shane L. Larson

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Time-delay interferometry (TDI) is the data processing technique needed for generating interferometric combinations of data measured by the multiple Doppler readouts available onboard the three Laser Interferometer Space Antenna (LISA) spacecraft. Within the space of all possible interferometric combinations TDI can generate, we have derived a specific combination that has zero response to the gravitational wave signal, and called it the zero-signal solution (ZSS). This is a two-parameter family of linear combinations of the generators of the TDI space, and its response to a gravitational wave becomes null when these two parameters coincide with the values of the angles of …

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Cosmology, Cohomology, And Compactification, Charles G. Torre Jan 2004

Cosmology, Cohomology, And Compactification, Charles G. Torre

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Ashtekar and Samuel have shown that Bianchi cosmological models with compact spatial sections must be of Bianchi class A. Motivated by general results on the symmetry reduction of variational principles, we show how to extend the Ashtekar-Samuel results to the setting of weakly locally homogeneous spaces as defined, e.g., by Singer and Thurston. In particular, it is shown that any m-dimensional homogeneous space G/K admitting a G-invariant volume form will allow a compact discrete quotient only if the Lie algebra cohomology of G relative to K is non-vanishing at degree m.

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Ionospheric Assimilation Techniques For Argos Low-Resolution Airglow And Aurora Spectrograph (Loraas) Tomographically Reconstructed Equatorial Electron Density Profiles, Jan Josef Sojka, J. V. Eccles, Robert W. Schunk, S. Mcdonald, S. Thonnard, K. Dymond, R. P. Mccoy Jan 2004

Ionospheric Assimilation Techniques For Argos Low-Resolution Airglow And Aurora Spectrograph (Loraas) Tomographically Reconstructed Equatorial Electron Density Profiles, Jan Josef Sojka, J. V. Eccles, Robert W. Schunk, S. Mcdonald, S. Thonnard, K. Dymond, R. P. Mccoy

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The LORAAS instrument aboard the ARGOS satellite observes line-of-sight ultraviolet limb intensities from ionosphere and thermosphere airglow. This study uses tomographically reconstructed electron density profiles (EDPs) from the nightside emissions. The ionospheric reconstruction is performed using a two-dimensional O+ 1356Å radiative recombination forward model and discrete inverse theory. The forward model assumes a Chapman layer for the vertical electron density distribution from which h m F 2, N m F 2, and topside scale height are derived for every 90 s limb scan, which is equivalent to 5° resolution in latitude. Since ARGOS is in a near Sun-synchronous orbit, these …

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Global Assimilation Of Ionospheric Measurements (Gaim), Robert W. Schunk, Ludger Scherliess, Jan Josef Sojka, Donald C. Thompson, David N. Anderson, Mihail Codrescu, Cliff Minter, Timothy J. Fuller-Rowell, Roderick A. Heelis, Marc Hairston, Bruce M. Howe Jan 2004

Global Assimilation Of Ionospheric Measurements (Gaim), Robert W. Schunk, Ludger Scherliess, Jan Josef Sojka, Donald C. Thompson, David N. Anderson, Mihail Codrescu, Cliff Minter, Timothy J. Fuller-Rowell, Roderick A. Heelis, Marc Hairston, Bruce M. Howe

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The ionosphere is a highly dynamic medium that exhibits weather disturbances at all latitudes, longitudes, and altitudes, and these disturbances can have detrimental effects on both military and civilian systems. In an effort to mitigate the adverse effects, we are developing a physics-based data assimilation model of the ionosphere and neutral atmosphere called the Global Assimilation of Ionospheric Measurements (GAIM). GAIM will use a physics-based ionosphere-plasmasphere model and a Kalman filter as a basis for assimilating a diverse set of real-time (or near real-time) measurements. Some of the data to be assimilated include in situ density measurements from satellites, ionosonde …

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Understanding Mid-Latitude Space Weather: Storm Impacts Observed At Blo On 31 March 2001, Jan Josef Sojka, D. Rice, J. V. Eccles, F. T. Berkey, P. Kintner, W. Denig Jan 2004

Understanding Mid-Latitude Space Weather: Storm Impacts Observed At Blo On 31 March 2001, Jan Josef Sojka, D. Rice, J. V. Eccles, F. T. Berkey, P. Kintner, W. Denig

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On 30 March 2001 in the late evening an auroral display was observed over the United States of America. The Bear Lake Observatory (BLO) magnetometer in Utah measured changes of 550 nT in less than 30 min. During the same period, BLO ionosonde measurements showed deep high-frequency radio wave absorption up to 7 MHz. BLO's GPS single-frequency receiver experienced geolocation errors of 20 m for over 3 hours. These storm signatures were also accompanied by L-band scintillation effects which approached an S4 value of 0.2, which is large for midlatitudes. Although such measurements have been have been made at …

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Space Weather Effects On Mid-Latitude Hf Propagation Paths: Observations And A Data-Driven D-Region Model, J. V. Eccles, R. D. Hunsucker, D. Rice, Jan Josef Sojka Jan 2004

Space Weather Effects On Mid-Latitude Hf Propagation Paths: Observations And A Data-Driven D-Region Model, J. V. Eccles, R. D. Hunsucker, D. Rice, Jan Josef Sojka

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A two-pronged study is under way to improve understanding of the D region response to space weather and its effects on HF propagation. One part, the HF Investigation of D region Ionospheric Variation Experiment (HIDIVE), is designed to obtain simultaneous, quantitative propagation and absorption data from an HF signal monitoring network along with solar X-ray flux from the NOAA GOES satellites. Observations have been made continuously since late December 2002 and include the severe disturbances of October–November 2003. GOES satellite X-ray observations and geophysical indices are assimilated into the Data-Driven D Region (DDDR) electron density model developed as the second …

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Development Of A Physics-Based Reduced State Kalman Filter For The Ionosphere, Ludger Scherliess, Robert W. Schunk, Jan Josef Sojka, Donald C. Thompson Jan 2004

Development Of A Physics-Based Reduced State Kalman Filter For The Ionosphere, Ludger Scherliess, Robert W. Schunk, Jan Josef Sojka, Donald C. Thompson

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A physics-based data assimilation model of the ionosphere is under development as the central part of a Department of Defense/Multidisciplinary University Research Initiative (MURI)-funded program called Global Assimilation of Ionospheric Measurements (GAIM). With the significant increase in the number of ionospheric observations that will become available over the next decade, this model will provide a powerful tool toward an improved specification and forecasting of the global ionosphere, with an unprecedented accuracy and reliability. The goal of this effort will be specifications and forecasts on spatial grids that can be global, regional, or local (25 km × 25 km). The specification/forecast …

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Observations Of Atmosphericgravity Waves Using Airglow All-Sky Ccd Imager At Cachoeira Paulista (23° S, 45° W), A. F. Medeiros, H. Takahashi, P. P. Batista, D. Gobbi, Michael J. Taylor Jan 2004

Observations Of Atmosphericgravity Waves Using Airglow All-Sky Ccd Imager At Cachoeira Paulista (23° S, 45° W), A. F. Medeiros, H. Takahashi, P. P. Batista, D. Gobbi, Michael J. Taylor

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An all-sky CCD imager for OH, O2 and OI (557.7 nm) airglow was operated at Cachoeira Paulista (CP), Brazil, (23° S, 45° W), from October 1998 to September 1999, with Utah State University. Dominant gravity wave components are extracted and seasonal variations are investigated. These waves have typically short horizontal wavelengths (5 - 60 km), short periods (5 - 35 minutes), and horizontal phase speeds of 1 - 80 m/s. Band-type waves of horizontal wavelength between 10 and 60 km showed clear seasonal dependence in the horizontal propagation direction to southeast in summer and to northwest in winter. The direction …

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