Engineering Physics Commons^™

Perspective: The Physics, Diagnostics, And Applications Of Atmospheric Pressure Low Temperature Plasma Sources Used In Plasma Medicine, M. Laroussi

Electrical & Computer Engineering Faculty Publications

Low temperature plasmas have been used in various plasma processing applications for several decades. But it is only in the last thirty years or so that sources generating such plasmas at atmospheric pressure in reliable and stable ways have become more prevalent. First, in the late 1980s, the dielectric barrier discharge was used to generate relatively large volume diffuse plasmas at atmospheric pressure. Then, in the early 2000s, plasma jets that can launch cold plasma plumes in ambient air were developed. Extensive experimental and modeling work was carried out on both methods and much of the physics governing such sources …

Relaxation Of Microwave Nonlinearity In A Cuprate Superconducting Resonator, Richard A. Huizen, Sean L. Hamilton, Geoffrey T. Lenters, Stephen K. Remillard

Faculty Publications

The second- and third-order nonlinear microwave response of a superconducting YBa2Cu3O7 thin-film resonator was synchronously measured using three input tones. This technique permits the local measurement, and hence mapping, of intermodulation distortion inside the resonator. Second- and third-order IMD measured with a fixed probe relaxed in remarkably different ways after the removal of a static magnetic field. The second-order IMD relaxed by two different magnetic processes, a fast process that appears related to bulk remanent magnetization and a slow process that fits the description of Bean and Livingston. The third-order IMD relaxes by only one process that is distinct from …

The Magnetic, Electrical And Structural Properties Of Copper-Permalloy Alloys, Makram A. Qader, A. Vishina, Lei Yu, Cougar Garcia, Rakesh K. Singh, Nicholas D. Rizzo, Mengchu Huang, Ralph Chamberlin, Kirill Belashchenko, Mark Van Schilfgaarde, N. Newman

Kirill Belashchenko Publications

Copper-permalloy [Cu_1–x(Ni₈₀Fe₂₀)_x] alloy films were deposited by co-sputtering and their chemical, structural, magnetic, and electrical properties were characterized. These films are found to have favorable weak ferromagnetic properties for low temperature magnetoelectronic applications. Our results show that by varying the composition, the saturation magnetization (M_s) can be tuned from 700 emu/cm³ to 0 and the Curie temperature (T_c), can be adjusted from 900 K to 0 K. The M_s and T_c are found to scale linearly between x = 25% and 100%. Electronic structure calculations …

Operating Temperature Of A Solar Thermal Stirling Engine, Spencer Beck

Senior Theses

This paper explores the relationship between the operating temperature and electricity production of a simple heat engine. A Stirling engine was designed and constructed which runs on solar thermal energy collected by a Fresnel lens. The surface area of the solar collector was varied. This manipulated the operating temperature of the Stirling engine in order to measure power output. The mechanical energy from the engine was converted to electricity using a DC motor running in reverse, acting like a generator, in conjunction with an Arduino for data collection. Although adjustments must be made in order to improve the efficiency of …

Are Solar Panels A Viable Power Source For A Green Energy Vehicle?, Mason C. Adams

Senior Theses

A solar cell powered go-kart has been built and tested. The result shows using solar energy alone cannot meet the requirement of running a regular passenger car. This is due to the limited surface area of the passenger car. This thesis also discusses the operating principles of solar panels, the physics of P type and N type semiconductors, and the formation of the PN junction, as well as the solar current. Modifications of an existing go-kart are described in detail in this thesis. Suggestions for making green vehicles are discussed as well.

Gallium Vacancies In Β-Ga2O3 Crystals, Brant E. Kananen, Larry E. Halliburton, K. T. Stevens, G. K. Foundos

Faculty Publications

The gallium vacancy, an intrinsic acceptor, is identified in β-Ga₂O₃ using electron paramagnetic resonance (EPR). Spectra from doubly ionized (V²⁻_Ga) and singly ionized (V⁻_Ga) gallium vacancies are observed at room temperature, without photoexcitation, after an irradiation with high-energy neutrons. The V²⁻_Ga centers (with S = 1/2) have a slight angular variation due to a small anisotropy in the g matrix (principal values are 2.0034, 2.0097, and 2.0322). The V²⁻_Ga centers also exhibit a resolved hyperfine structure due to equal and nearly isotropic interactions with the …

Time-Resolved Thz Conductivity Of An Intermediate Band Semiconductor, Elliot Weiss

Macalester Journal of Physics and Astronomy

Intermediate band materials have promising applications as affordable, highly efficient solar materials. However, intermediate band solar cells exhibit low efficiency to date. Carrier recombination is a critical process that limits efficiency. If electrons relax to the valence band before they can be collected, their energy is lost. To help understand the recombination dynamics and physical properties of intermediate band semiconductors, we obtain time-resolved THz conductivity measurements of the intermediate band semiconductor, GaPAsN, at various temperatures. From our results, we build a model that provides insight to the recombination dynamics of GaPAsN.

Solar Wind-Magnetosphere Coupling: A Global Perspective Of Reconnection In The Magnetotail, Miles Thomas Bengtson

Doctoral Dissertations and Master's Theses

We present a case study of the 25 December 2015 substorm which occurred between 08:15 and 08:45 Universal Time. During this interval, fast particle flows and field geometry consistent with magnetic reconnection were detected in the mid-tail region. An ejected plasmoid was observed by the lunar-orbiting Acceleration, Reconnection, Turbulence and Electrodynamics of Moon’s Interaction with the Sun (ARTEMIS) probes and corresponding dipolarization signature was observed by the Time History of Events and Macroscale Interactions During Substorms (THEMIS) spacecraft earthward of the reconnection site, which was determined to be approximately -33 RE. Ground signatures indicative of substorm activity were also observed …

Novel Methods For The Time-Dependent Maxwell’S Equations And Their Applications, Sidney Shields

UNLV Theses, Dissertations, Professional Papers, and Capstones

This dissertation investigates three different mathematical models based on the time domain Maxwell's equations using three different numerical methods: a Yee scheme using a non-uniform grid, a nodal discontinuous Galerkin (nDG) method, and a newly developed discontinuous Galerkin method named the weak Galerkin (WG) method. The non-uniform Yee scheme is first applied to an electromagnetic metamaterial model. Stability and superconvergence error results are proved for the method, which are then confirmed through numerical results. Additionally, a numerical simulation of backwards wave propagation through a negative-index metamaterial is given using the presented method. Next, the nDG method is used to simulate …

Aluminum Multicharged Ion Generation From Femtosecond Laser Plasma, Md. Haider A. Shaim, Frederick Guy Wilson, Hani E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Aluminum multicharged ion generation from femtosecond laser ablation is studied. A Ti:sapphire laser (wavelength 800 nm, pulse width ∼100 fs, and maximum laser fluence of 7.6 J/cm²) is used. Ion yield and energy distribution of each charge state are measured. A linear relationship between the ion charge state and the equivalent acceleration energy of the individual ion species is observed and is attributed to the presence of an electric field within the plasma-vacuum boundary that accelerates the ions. The ion energy distribution follows a shifted Coulomb-Boltzmann distribution. For Al¹⁺ and Al²⁺, the ion energy distributions …

Leader-Follower Trajectory Generation And Tracking For Quadrotor Swarms, Michael James Campobasso

Doctoral Dissertations and Master's Theses

Swarm control is an essential step in the progress of robotic technology. The use of multiple agents to perform tasks more effectively and efficiently than a single agent allows for the expansion of robot use in all aspects of life. One of the foundations of this area of research is the concept of Leader-Follower swarm control. A crucial aspect of this idea is the generation of trajectories with respect to the leader’s path and some desired formation. With these trajectories generated, one can use a tracking controller specific to the swarm vehicle of choice to accomplish the desired swarm formation. …

A Feasibility Study For Using The Erau ÉChelle Spectrograph To Improve Orbital Parameters Of Spectroscopic Binary Systems, Stanimir Letchev

Doctoral Dissertations and Master's Theses

Binary stars are critical for establishing knowledge of stellar masses and refining the mass-luminosity relationship when used in conjunction with precise parallax measurements. However, many spectroscopic binaries have poorly defined orbital parameters as they have not been revisited with newer CCD technology since their first observations on photographic plates. This thesis examines the feasibility of using the high-resolution échelle spectrograph at Embry-Riddle Aeronautical University (ERAU) to obtain radial velocities of spectroscopic binary stars, and establishes a software pipeline to obtain their orbital parameters. This was done by looking at the double-lined binaries HD 205539 and Pegasi, as well as the …

Total Electron Count Variability And Stratospheric Ozone Effects On Solar Backscatter And Lwir Emissions, John S. Ross

Theses and Dissertations

The development of an accurate ionospheric Total Electron Content (TEC) model is of critical importance to High Frequency (HF) radio wave propagation. However, the TEC is highly variable and is continuously influenced by geomagnetic storms, extreme Ultraviolet (UV) radiation, diurnal variation, and planetary waves. The ability to capture this variability is essential to improve current TEC models. Analysis of the growing body of data involving ionospheric fluctuations and thermal tides has revealed persistent correlation between increases in stratospheric ozone and variability of the TEC. The spectral properties of ozone show that it is a greenhouse gas that alters longwave emissions …

Rbhe Potential Energy Surface Sensitivity Study, Ethan D. Thorp

Theses and Dissertations

This paper studies how alterations of features of RbHe potential energy surfaces (PES) for a diode pumped alkali laser (DPAL) system effect the collisional cross section. The Split-Operator method is used to propagate a wave function along these PES and because they are radially coupled, the wave function can be transmitted from the starting surface to other energy surfaces. This transmittance is encoded in the correlation function. The full Hamiltonian used for propagation consists of the electronic potential, the nuclear kinetic energy, and the Coriolis coupling. The correlation function is used to generate the Scattering Matrix elements. These elements describe …

Effect Of Disorder On The Resistivity Of Cofecral Films, Y. Jin, R. Skomski, P. Kharel, S.R. Valloppilly, D. J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

Structural and electron-transport properties of thin films of the ferrimagnetic Heusler compound CoFeCrAl have been investigated to elucidate structure-property relationships. The alloy is, ideally, a spin-gapless semiconductor, but structural disorder destroys the spin-gapless character and drastically alters the transport behavior. Two types of CoFeCrAl films were grown by magnetron sputtering deposition at 973 K, namely polycrystalline films on Si substrates and epitaxial films on MgO (001) substrates. The resistivity decreases with increasing temperature, with relatively small temperature coefficients of –0.19 cm=K for the polycrystalline films and –0.12 cm=K for the epitaxial films. The residual resistivity of the polycrystalline films deposited …

Designing Novel Nanostructured Permanent Magnets, Ali Al Kadhim

UNO Student Research and Creative Activity Fair

Rare earth element based alloys have been the source of high performance magnetic alloys, and have played a paramount role in the development of various technologies, including: memory devices (such as credit cards, random-access memory), sensors, and various biomedical applications. However, there is a tremendous need to replace rare earth metals with material with powerful magnetic properties. Our group recently found CrTe-based materials that show very promising magnetic properties in nanostructured form. The magnetic modeling of such material in nanostructured form prior to their fabrication demonstrates their magnetic properties in bulk form. In this project, we investigate the behavior of …

Formation Of Mound-Like Multiscale Surface Structures On Titanium By Femtosecond Laser Processing, Edwin Peng, Alfred Tsubaki, Craig A. Zuhlke, Ryan Bell, Meiyu Wang, Dennis R. Alexander, George Gogos, Jeffrey E. Shield

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Surface Functionalization Technique • Femtosecond Laser Surface Processing (FLSP) • Utilize high power, femtosecond (10-15 s) laser pulses • Produce self-organized, multiscale surface micro/nanostructures • Diverse range of applicable substrates: semiconductors, metals, polymers, & composites

Why? • What are the different types of FLSP structures on Ti? • Physical evidence needed for FLSP formation models • Optimize FLSP of Ti for biomedical & other applications

How? • Obtain evidence of mound growth processes by examining underlying microstructure • Utilize dual beam Scanning Electron Microscope-Focused Ion Beam instrument to cross section surface structures & fabricate transmission electron microscopy samples

Half-Metallic Magnetism In Ti3co5-Xfexb2, Rohit Pathak, Imran Ahamed, W. Y. Zhang, Shah Vallopilly, D. J. Sellmyer, Ralph Skomski, Arti Kashyap

Nebraska Center for Materials and Nanoscience: Faculty Publications

Bulk alloys and thin films of Fe-substituted Ti₃Co₅B₂ have been investigated by first-principle density-functional calculations. The series, which is of interest in the context of alnico magnetism and spin electronics, has been experimentally realized in nanostructures but not in the bulk. Our bulk calculations predict paramagnetism for Ti₃Co₅B₂, Ti₃Co₄FeB₂ and Ti₃CoFe₄B₂, whereas Ti₃Fe₅B₂ is predicted to be ferromagnetic. The thin films are all ferromagnetic, indicating that moment formation may be facilitated at nanostructural …

Cooperative And Noncooperative Magnetization Reversal In Alnicos, Raplh Skomski, Liqin Ke, Matthew J. Kramer, Iver E. Anderson, C.Z. Wang, W.Y. Zhang, Jeff E. Shield, D. J. Sellmyer

Nebraska Center for Materials and Nanoscience: Faculty Publications

It is investigated how magnetostatic interactions affect the coercivity of alnicotype magnets. Starting from exact micromagnetic relations, we analyze two limits, namely cooperative reversal processes operative on short lengths scales and noncooperative reversal processes on long length scales. In alnicos, intrawire interactions are predominantly cooperative, whereas interwire effects are typically noncooperative. However, the transition between the regimes depends on feature size and hysteresis-loop shape, and interwire cooperative effects are largest for nearly rectangular loops. Our analysis revises the common shape-anisotropy interpretation of alnicos.

Estimation Of Turbulence From Time-Lapse Imagery, Jack E. Mccrae, Santasri Bose-Pillai, Steven T. Fiorino

Faculty Publications

Atmospheric turbulence parameters are estimated for an imaging path based on time-lapse imaging results. Atmospheric turbulence causes frame-to-frame shifts of the entire image as well as parts of the image. The statistics of these shifts encode information about the turbulence strength (as characterized by Cn2, the refractive index structure function constant) along the optical path. The shift variance observed is simply proportional to the variance of the tilt of the optical field averaged over the area being tracked and averaged over the camera aperture. By presuming this turbulence follows the Kolmogorov spectrum, weighting functions, which relate the turbulence strength along …