Physical Sciences and Mathematics Commons^™

Changes In Thermospheric Temperature Induced By High-Speed Solar Wind Streams, Larry Gardner, Jan Josef Sojka, Robert W. Schunk, Rod Heelis

All Physics Faculty Publications

During high-speed stream (HSS) events the solar wind speed increases, and the cross polar cap potential increases, leading to increased Joule heating at high latitudes. The heat input at high latitudes heats the polar regions, which then conducts to lower latitudes, producing global heating. The heating occurs during the risetime of the cross polar cap potential and throughout the period of high cross polar cap potential as seen in our simulation. These simulations are performed using the Utah State University global thermosphere model driven by Joule heating rates that are consistent with electric fields observed by DMSP-15 observations of HSS …

Velocity Plateaus In Traveling-Wave Electrophoresis, R. Correll, Boyd F. Edwards

All Physics Faculty Publications

One-dimensional models are used to study traveling-wave electrophoresis, a tunable method for separating charged analytes. A traveling-electrode model reveals the mechanism for longitudinal oscillations. A stationary-electrode model explains the origin of mode-locked plateaus in the average velocity, predicts devil's staircases with nested Farey sequences, and reduces to a continuum sinusoidal model in the high electrode-density limit. © 2012 American Physical Society.

Cedar Electrodynamics Thermosphere Ionosphere (Eti) Challenge For Systematic Assessment Of Ionosphere/Thermosphere Models: Electron Density, Neutral Density, Nmf2, And Hmf2 Using Space Based Observations, J. S. Shim, M. Kuznetsova, L. Rastätter, D. Bilitza, L. Butala, M. Emery, B. Foster, T. J. Fuller-Rowell, J. Huba, A. J. Mannucci, X. Pi, A. Ridley, Ludger Scherliess, Jan Josef Sojka, P. Stephens, D. C. Thompson, D. Weimer, Lie Zhu, E. Sutton

All Physics Faculty Publications

In an effort to quantitatively assess the current capabilities of Ionosphere/Thermosphere (IT) models, an IT model validation study using metrics was performed. This study is a main part of the CEDAR Electrodynamics Thermosphere Ionosphere (ETI) Challenge, which was initiated at the CEDAR workshop in 2009 to better comprehend strengths and weaknesses of models in predicting the IT system, and to trace improvements in ionospheric/thermospheric specification and forecast. For the challenge, two strong geomagnetic storms, four moderate storms, and three quiet time intervals were selected. For the selected events, we obtained four scores (i.e., RMS error, prediction efficiency, ratio of the …

Electron Beam Induced Luminescence Of Sio2 Optical Coatings, John R. Dennison, Amberly Evans, Gregory Wilson, Charles W. Bowers, Robert Meloy

All Physics Faculty Publications

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 …

An Embedded-Atom-Method Model For Alkali-Metal Vibrations, D. Mark Riffe, Richard B. Wilson

All Physics Faculty Publications

We present an embedded-atom-method (EAM) model that accurately describes vibrational dynamics in the alkali metals Li, Na, K, Rb, and Cs. Bulk dispersion curves, frequency-moment Debye temperatures, and temperature-dependent entropy Debye temperatures are all in excellent agreement with experimental results. The model is also well suited for studying surface vibrational dynamics in these materials, as illustrated by calculations for the Na(110) surface.

Estimation And Testing For Spatially Indexed Curves With Application To Ionospheric And Magnetic Field Trends, Oleksandr Gromenko, Piotr Kokoszka, Lie Zhu, Jan Josef Sojka

All Physics Faculty Publications

We develop methodology for the estimation of the functional mean and the functional principal components when the functions form a spatial process. The data consist of curves X(sk;t), t∈[0, T], observed at spatial locations s1,s2, . . . ,sN. We propose several methods, and evaluate them by means of a simulation study. Next, we develop a significance test for the correlation of two such functional spatial fields. After validating the finite sample performance of this test by means of a simulation study, we apply it to determine if there is correlation between long-term trends in the so-called critical ionospheric frequency …

Assessment Of Gravity Wave Momentum Flux Measurement Capabilities By Meteor Radars Having Different Transmitter Power And Antenna Configurations, D. C. Fritts, D. Janches, W. K. Hocking, Michael J. Taylor

All Physics Faculty Publications

Measurement capabilities of five meteor radars are assessed and compared to determine how well radars having different transmitted power and antenna configurations perform in defining mean winds, tidal amplitudes, and gravity wave (GW) momentum fluxes. The five radars include two new-generation meteor radars on Tierra del Fuego, Argentina (53.8°S) and on King George Island in the Antarctic (62.1°S) and conventional meteor radars at Socorro, New Mexico (34.1°N, 106.9°W), Bear Lake Observatory, Utah (∼41.9°N, 111.4°W), and Yellowknife, Canada (62.5°N, 114.3°W). Our assessment employs observed meteor distributions for June of 2009, 2010, or 2011 for each radar and a set of seven …

All Homogeneous Pure Radiation Spacetimes Satisfy The Einstein–Maxwell Equations, Charles G. Torre

All Physics Faculty Publications

It is shown that all homogeneous pure radiation solutions to the Einstein equations admit electromagnetic sources. This corrects an error in the literature.

Three-Dimensional Tomographic Reconstruction Of Mesospheric Airglow Structures Using Two-Station Ground-Based Image Measurements, V. P. Hart, T. E. Doyle, Michael J. Taylor, B. L. Carruth, Pierre-Dominique Pautet, Yucheng Zhao

All Physics Faculty Publications

A new methodology is presented to create two-dimensional (2D) and three-dimensional (3D) tomographic reconstructions of mesospheric airglow layer structure using two-station all-sky image measurements. A fanning technique is presented that produces a series of cross-sectional 2D reconstructions, which are combined to create a 3D mapping of the airglow volume. The imaging configuration is discussed and the inherent challenges of using limited-angle data in tomographic reconstructions have been analyzed using artificially generated imaging objects. An iterative reconstruction method, the partially constrained algebraic reconstruction technique (PCART), was used in conjunction with a priori information of the airglow emission profile to constrain the …

Fabrication And Performance Of A Microfluidic Traveling-Wave Electrophoresis System, K. D. Jo, J. E. Schiffbauer, Boyd F. Edwards, R. Lloyd Carroll, A. T. Timperman

All Physics Faculty Publications

A microfluidic traveling-wave electrophoresis (TWE) system is reported that uses a locally defined traveling electric field wave within a microfluidic channel to achieve band transport and separation. Low voltages, over a range of-0.5 to +0.5 V, are used to avoid electrolysis and other detrimental redox reactions while the short distance between electrodes, ∼25 μm, provides high electric fields of ∼200 V cm ^-1. It is expected that the low voltage requirements will simplify the future development of smaller portable devices. The TWE device uses four interdigitated electrode arrays: one interdigitated electrode array pair is on the top of the …

Charge Enhanced Contamination And Environmental Degradation Of Misse-6 Suspecs Materials, John R. Dennison, Amberly Evans, Danielle Fulmer, Joshua L. Hodges

All Physics Faculty Publications

The effects of prolonged exposure to the LEO space environment and charge-enhanced contamination on optical, thermal, and electron emission and transport properties of common spacecraft materials have been investigated by comparing pre- and post-flight characterization measurements. The State of Utah Space Environment and Contamination Study (SUSpECS) deployed in March 2008 on board the Materials International Space Station Experiment (MISSE-6) payload, was exposed for ~18 months on the exterior of the International Space Station (ISS), and was retrieved in September 2009. A total of 165 samples were mounted on three separate SUSpECS panels on the ram and wake sides on the …

Measurement Methods Of Electron Emission Over A Full Range Of Sample Charging, R. Hoffmann, John R. Dennison

All Physics Faculty Publications

Spacecraft charging codes require accurate models of electron yields as a function of accumulated charge to correctly predict the charge build up on spacecraft. The accumulated charge creates equilibrium surface potentials on spacecraft resulting from interactions with the space plasma environment. There is, however, a complex relation between these emission properties and the charge built up in spacecraft insulators.

This paper focuses on different methods appropriate to determine the fundamental electronic material property of total electron yield as the materials accumulate charge. Three methods for determining the uncharged total yield are presented:

(i) The DC Continuous Beam Method is a …

The Dynamic Interplay Between Spacecraft Charging, Space Environment Interactions And Evolving Materials, John R. Dennison

All Physics Faculty Publications

The charge on spacecraft is constantly changing, as a result of the dynamic nature of the space environment, the spacecraft orbit, the interactions between environment and spacecraft, and even the spacecraft materials. While the effects on spacecraft charging from varying environmental conditions and from the selection of different construction materials have been studied extensively, the modification of material properties by the space plasma environment can also have profound effects on spacecraft charging. These same considerations apply to other extreme plasma applications. This presentation focuses on the measurement methods and modeling we use to study electron emission and transport processes, charging, …

Ultrahigh Vacuum Cryostat System For Extended Low Temperature Space Environment Testing, Justin Dekany, Robert H. Johnson, Gregory Wilson, Amberly Evans, John R. Dennison

All Physics Faculty Publications

The range of temperature measurements have been significantly extended for an existing space environment simulation test chamber used in the study of electron emission, sample charging and discharge, electrostatic discharge and arcing, electron transport, and luminescence of spacecraft materials. This was accomplished by incorporating a new twostage, closed-cycle helium cryostat which has an extended sample temperature range from 40 K to 450 K, with long-term controlled stability of 0.5 K. The system was designed to maintain compatibility with an existing ultrahigh vacuum chamber (base pressure 10-7 Pa) that can simulate diverse space environments. These existing capabilities include controllable vacuum and …

Electron Transport Models And Precision Measurements In A Constant Voltage Chamber, Justin Dekany, Alec Sim, Jerilyn Brunson, John R. Dennison

All Physics Faculty Publications

The conductivity of the material is a key transport parameter in spacecraft charging that determines how deposited charge will redistribute throughout the system, how rapidly charge imbalances will dissipate, and what equilibrium potential will be established under given environmental conditions. As the requirements for space missions extend to new regions of space and more stringent requirements are placed on spacecraft performance, it becomes necessary to better understand the underlying conduction mechanisms that determine the dynamic response of insulators to temperature, electric field dose rate, and sample conditioning and history. This study performed detailed measurements of the transient conductivity of representative …

A Systematic Construction Of Curved Phase Space: A Gravitational Gauge Theory With Symplectic Form, Jeffrey S. Hazboun, James Thomas Wheeler

All Physics Faculty Publications

General relativity can be constructed as a gauge theory using the quotient manifold strategy of [1, 2]. We consider a conformal gauging where the geometry is far richer than normal spacetime, including a symplectic form and the necessary emergence of Lorentzian signature. The resulting 2n-dim manifold constitutes a relativistic phase space, and general relativity is recovered when we demand that the momentum space is flat. However, the full geometry allows for curved phase space.

On The Nature Of Short-Period Mesospheric Gravity Wave Propagation Over Halley, Antarctica, K. Nielsen, Michael J. Taylor, R. E. Hibbins, M. J. Jarvis, J. M. Russell

All Physics Faculty Publications

As part of a collaborative program between British Antarctic Survey and Utah State University, measurements were made using an all-sky airglow imager located at the U.K. Halley Station (76°S, 27°W) during the 2000 and 2001 austral winter seasons from April through to early September. A co-located imaging Doppler interferometer was utilized to obtain coincident wind measurements for a total of 171 wave events. This study comprises the first detailed climatological investigation of the propagation nature (freely propagating, Doppler ducted, or evanescent) of individual quasi-monochromatic, short-period wave events at a high southern latitude. Distributions of the derived vertical wavelength exhibit an …

Electron Energy Dependent Charging Effects Of Multilayered Dielectric Materials, Gregory Wilson, John R. Dennison, Amberly Evans, Justin Dekany

All Physics Faculty Publications

Measurements of the charge distribution in electron-bombarded, thin-film, multilayer 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 …

In Situ Surface Voltage Measurements Of Dielectrics Under Electron Beam Irradiation, Joshua L. Hodges, John R. Dennison, Justin Dekany, Gregory Wilson, Amberly Evans, Alec Sim

All Physics Faculty Publications

New instrumentation has been developed for non-contact, in vacuo measurements of the electron beam-induced surface voltage as a function of time and position for non-conductive spacecraft materials in a simulated space environment. Used in conjunction with the capabilities of an existing ultrahigh vacuum electron emission analysis chamber, the new instrumentation facilitates measurements of charge accumulation, bulk resistivity, effects of charge depletion and accumulation on yield measurements, electron induced electrostatic breakdown potentials, radiation induced conductivity effects, and the radial dispersion of surface voltage. The novel system uses two movable capacitive sensor electrodes that can be swept across the sample to measure …

Small Scale Simulation Chamber For Space Environment Survivability Testing, Robert H. Johnson, Lisa D. Montierth, John R. Dennison, James S. Dyer, Ethan Lindstrom, Alex Chanson

All Physics Faculty Publications

A versatile vacuum system for long duration testing of materials modifications due to exposure to simulated space environment conditions has been designed and built. The chamber is particularly well suited for cost-effective tests of multiple small scale materials samples over prolonged exposure. Critical environmental components simulated include neutral gas [ultrahigh vacuum (10-7 Pa) to ambient], FUV/UV/VIS/NIR solar spectrum, electron plasma fluxes, and temperature. The UV/VIS/NIR solar spectrum is simulated using an external, normally incidence and collimated class AAA Solar Simulator source, with standard Air Mass Zero (AM0) filters to shape the incident radiation spectrum. This Xe arc discharge tube source …

An Embedded-Atom-Method Model For Alkali-Metal Vibrations, R. B. Wilson, D. Mark Riffe

All Physics Faculty Publications

We present an embedded-atom-method (EAM) model that accurately describes the vibrational dynamics in the alkali metals Li, Na, K, Rb and Cs. The bulk dispersion curves, frequency-moment Debye temperatures and temperature-dependent entropy Debye temperatures are all in excellent agreement with experimental results. The model is also well suited for studying surface vibrational dynamics in these materials, as illustrated by calculations for the Na(110) surface.