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Articles 1 - 15 of 15
Full-Text Articles in Physics
Hemispherical Shifted Symmetry In Polar Cap Patch Occurrence: A Survey Of Gps Tec Maps From 2015–2018, Michael David, Jan Josef Sojka, Robert W. Schunk, Anthea J. Coster
Hemispherical Shifted Symmetry In Polar Cap Patch Occurrence: A Survey Of Gps Tec Maps From 2015–2018, Michael David, Jan Josef Sojka, Robert W. Schunk, Anthea J. Coster
All Physics Faculty Presentations
Much theoretical and observational work has been devoted to studying the occurrence of F region polar cap patches in the Northern Hemisphere; considerably less work has been applied to the Southern Hemisphere. In recent years, the Madrigal database of mappings of total electron content (TEC) has improved in Southern Hemisphere coverage, to the point that we can now carry out a study of patch frequency and occurrence. We find that Southern Hemisphere patch occurrence is very similar to that of the Northern Hemisphere with a half‐year offset, plus an offset in universal time of approximately 12 hr. This is further …
A Near Horizon Extreme Binary Black Hole Geometry, Jacob Ciafre, Maria J. Rodriguez
A Near Horizon Extreme Binary Black Hole Geometry, Jacob Ciafre, Maria J. Rodriguez
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A new solution of four-dimensional vacuum General Relativity is presented. It describes the near horizon region of the extreme (maximally spinning) binary black hole system with two identical extreme Kerr black holes held in equilibrium by a massless strut. This is the first example of a non-supersymmetric, near horizon extreme binary black hole geometry of two uncharged black holes. The black holes are co-rotating, their relative distance is fixed, and the solution is uniquely specified by the mass. Asymptotically, the geometry corresponds to the near horizon extreme Kerr (NHEK) black hole. The binary extreme system has finite entropy.
Blandford-Znajek Process In Vacuo And Its Holographic Dual, Ted Jacobson, Maria J. Rodriguez
Blandford-Znajek Process In Vacuo And Its Holographic Dual, Ted Jacobson, Maria J. Rodriguez
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Blandford and Znajek discovered a process by which a spinning black hole can transfer rotational energy to a plasma, offering a mechanism for energy and jet emissions from quasars. Here we describe a version of this mechanism that operates with only vacuum electromagnetic fields outside the black hole. The setting, which is not astrophysically realistic, involves either a cylindrical black hole or one that lives in 2+1 spacetime dimensions, and the field is given in simple, closed form for a wide class of metrics. For asymptotically anti–de Sitter black holes in 2+1 dimensions, the holographic dual of this mechanism is …
Electron Parallel Transport For Arbitrary Collisionality, Jeong-Young Ji, Gunsu S. Yun, Yong-Su Na, Eric D. Held
Electron Parallel Transport For Arbitrary Collisionality, Jeong-Young Ji, Gunsu S. Yun, Yong-Su Na, Eric D. Held
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Integral (nonlocal) closures [J.-Y. Ji and E. D. Held, Phys. Plasmas 21, 122116 (2014)] are combined with the momentum balance equation to derive electron parallel transport relations. For a single harmonic fluctuation, the relations take the same form as the classical Spitzer theory (with possible additional terms): The electric current and heat flux densities are connected to the modified electric field and temperature gradient by transport coefficients. In contrast to the classical theory, the dimensionless coefficients depend on the collisionality quantified by a Knudsen number, the ratio of the collision length to the angular wavelength. The key difference comes from …
Comparison Of Coincident Rayleigh-Scatter And Sodium Resonance Lidar Temperature Measurements From The Mesosphere-Lower-Thermosphere Region, Leda Sox, Vincent B. Wickwar, Neal R. Criddle, Tao Yuan
Comparison Of Coincident Rayleigh-Scatter And Sodium Resonance Lidar Temperature Measurements From The Mesosphere-Lower-Thermosphere Region, Leda Sox, Vincent B. Wickwar, Neal R. Criddle, Tao Yuan
All Physics Faculty Presentations
There are relatively few instruments that have the capabilities to make near continuous measurements of the mesosphere-lower-thermosphere (MLT) region. Rayleigh scatter and resonance lidars, particularly sodium resonance lidar, have been the two dominant ground-based techniques for acquiring mesosphere and MLT vertical temperature profiles, respectively, for more than two decades. With these measurements, the dynamics (gravity waves, tides) and long-term temperature trends (upper atmosphere cooling) of the MLT region can be studied. The Utah State University (USU; 41.7º N, 111.8º W) campus hosts a unique upper atmospheric observatory which houses both a high-power, large-aperture Rayleigh lidar and a sodium resonance Doppler …
The Upgraded Rayleigh Lidar At Usu’S Atmospheric Lidar Observatory, Vincent B. Wickwar, Leda Sox, Joshua P. Herron
The Upgraded Rayleigh Lidar At Usu’S Atmospheric Lidar Observatory, Vincent B. Wickwar, Leda Sox, Joshua P. Herron
All Physics Faculty Presentations
No abstract provided.
Defect-Driven Dynamic Model Of Electrostatic Discharge And Endurance Time Measurements Of Polymeric Spacecraft Materials, Alec Sim, John R. Dennison, Matthew Stormo
Defect-Driven Dynamic Model Of Electrostatic Discharge And Endurance Time Measurements Of Polymeric Spacecraft Materials, Alec Sim, John R. Dennison, Matthew Stormo
All Physics Faculty Presentations
Charge buildup on insulating materials in the space environment can produce long exposure to electric fields, which can lead to Electrostatic Discharge (ESD). Charge buildup is the leading cause of spacecraft failure due to space environment interactions. ESD can be thought of as the point at which the buildup of charge in localized defects, found in polymeric insulating materials, leads to a catastrophic change in electrical conductivity, which can cause the materials to structurally breakdown. Defects produced by radiation, or prolonged exposure to electric fields, significantly alter the endurance time, the time it takes to produce enough defects to generate …
Electron Beam Induced Luminescence Of Sio2 Optical Coatings, John R. Dennison, Amberly Evans, Gregory Wilson, Charles W. Bowers, Robert Meloy
Electron Beam Induced Luminescence Of Sio2 Optical Coatings, John R. Dennison, Amberly Evans, Gregory Wilson, Charles W. Bowers, Robert Meloy
All Physics Faculty Presentations
Optical coatings of disordered thin film SiO2/SiOx dielectric samples on reflective metal substrates exhibited cathodoluminescence under electron beam irradiation. Measurements of the absolute radiance and emission spectra as functions of incident electron energy, flux and power over a range of sample temperatures are reported. Radiance reached a saturation plateau at high incident electron power. Well below saturation radiance scaled with deposited power, that is linearly with incident power for lower-energy non-penetrating electrons and decreasing with increasing energy for penetrating radiation. Four bands were observed in spectral measurements from 300 nm to 1000 nm. Changes in peak intensity and shifts in …
Electron Induced Charging And Arcing Of Multilayered Dielectric Materials, John R. Dennison, Gregory Wilson, Amberly Evans
Electron Induced Charging And Arcing Of Multilayered Dielectric Materials, John R. Dennison, Gregory Wilson, Amberly Evans
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Measurements of the charge distribution in electron-bombarded, thin-film, multilayered dielectric samples showed that charging of multilayered materials evolves with time and is highly dependent on incident energy; this is driven by electron penetration depth, electron emission and material conductivity. Based on the net surface potential’s dependence on beam current, electron range, electron emission and conductivity, measurements of the surface potential, displacement current and beam energy allow the charge distribution to be inferred. To take these measurements, a thin-film disordered SiO2 structure with a conductive middle layer was charged using 200 eV and 5 keV electron beams with regular 15 s …
Micrometeoroids From Misse Examined To Understand The Effects Of The Space Environment On Space Suit Materials, John R. Dennison
Micrometeoroids From Misse Examined To Understand The Effects Of The Space Environment On Space Suit Materials, John R. Dennison
All Physics Faculty Presentations
Samples that were part of the Materials International Space Station Experiment (MISSE) experienced varying effects whilst exposed to the space environment; perhaps the most intriguing effect was the crater created by a micrometeoroid impact into a thin film of Vapor Deposited Aluminum (VDA) coated Mylar. Approximately 180 samples of various materials used in space-component design were flown on MISSE-6 and spent 18 months suspended off the side of the International Space Station. The Utah State University SUSpECS project was a unique student experiment that allowed for pre- and post-flight analysis of these material samples which were returned in pristine condition …
Electric Field Dependence Of The Time To Electrostatic Breakdown In Insulating Polymers, Alec Sim, John R. Dennison
Electric Field Dependence Of The Time To Electrostatic Breakdown In Insulating Polymers, Alec Sim, John R. Dennison
All Physics Faculty Presentations
Electrostatic breakdown can be thought of as the point at which a buildup of local defects in insulators leads to a catastrophic change in electrical conductivity. Defects can be produced by temperature, radiation, or a prolonged exposure to constant electric fields. The endurance time is the time it takes to generate enough defects to create a conduction path for electric current to flow more readily. The literature for electrostatic breakdown in polymeric highly disordered insulating materials discusses two competing theories for electrostatic breakdown, based on generation of either recoverable defects or irrecoverable defects. Such defects in the polymer chains can …
Simulation Chamber For Space Environment Survivability Testing, Lisa Montierth, Robert H. Johnson, John R. Dennison, James Dyer
Simulation Chamber For Space Environment Survivability Testing, Lisa Montierth, Robert H. Johnson, John R. Dennison, James Dyer
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A vacuum chamber was designed and built that simulates the space environment making possible the testing of material modification due to exposure of solar radiation. Critical environmental components required include an ultra high vacuum (10-9 Torr), a UV/VIS/NIR solar spectrum source, an electron gun and charge plasma, temperature extremes, and long exposure duration. To simulate the solar spectrum, a solar simulator was attached to the chamber with a range of 200nm to 2000nm. The exposure time can be accelerated by scaling the solar intensity up to four suns. A Krypton lamp imitates the 120 nm ultraviolet hydrogen Lymann alpha emission …
Low Temperature Cathodoluminescence In Disordered Sio2, Amberly Evans, Gregory Wilson, John R. Dennison
Low Temperature Cathodoluminescence In Disordered Sio2, Amberly Evans, Gregory Wilson, John R. Dennison
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Disordered SiO2 is commonly used for optical instrumentation and coatings. In space telescope applications, these materials can be exposed to low temperature (particularly for IR telescopes) and simultaneous electron fluxes from the space plasma environment. During recent charging tests of this dielectric material, a discernable glow was detected emanating from the surface of the SiO2, indicating that the incident electron beam induced a luminescent effect, termed cathodoluminescence. As the sample cooled from 300 K to 120 K, a change in the intensity and energy spectrum of the glow was observed between 250 nm and 1700 nm, demonstrating that the SiO2 …
Temperature Dependence Of Sio2 Electron-Induced Cathodoluminescence, Amberly Evans, Gregory Wilson, John R. Dennison
Temperature Dependence Of Sio2 Electron-Induced Cathodoluminescence, Amberly Evans, Gregory Wilson, John R. Dennison
All Physics Faculty Presentations
No abstract provided.
Applications Of Secondary Electron Energy- And Angular-Distributions To Spacecraft Charging, Neal Nickles, R. E. Davies
Applications Of Secondary Electron Energy- And Angular-Distributions To Spacecraft Charging, Neal Nickles, R. E. Davies
All Physics Faculty Presentations
Secondary electron (SE) emission from spacecraft surfaces as a result of energetic electron bombardment is a key process in the electrical charging of spacecraft. It has been suggested that incorporating more complete knowledge of the energy- and angular-distributions of secondary electrons is necessary to fully model how SE emission and spacecraft charging are affected by re-adsorption of low energy electrons in the presence of charge-induced electrostatic fields and ambient magnetic fields in the spacecraft environment. We present data for such energy- and angular-distributions from sputtered, polycrystalline gold surfaces. The data are compared to empirical SE emission models and found to …