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Articles 121 - 150 of 204
Full-Text Articles in Astrophysics and Astronomy
Impact Of A Finite-Temperature Equation Of State On Neutron Stars, Christian D. Draper
Impact Of A Finite-Temperature Equation Of State On Neutron Stars, Christian D. Draper
Theses and Dissertations
In this research, we study how a finite-temperature nuclear equation of state suitable for astrophysical simulations impacts the oscillation modes of neutron stars. We chose the Shen equation of state (EOS) because it accurately describes both stable and unstable nuclei as well as nuclear incompressibilities. I modified the existing MHD code at BYU, the HAD code, to call a lookup table for the Shen EOS for use at run time, and added a Newton-Raphson method algorithm to convert conserved variables to primitive variables. The algorithm was tested and verified by evolving a stable neutron star for several dynamical times and …
High-Quality Broadband Bvri Photometry Of Benchmark Open Clusters, Michael Deloss Joner
High-Quality Broadband Bvri Photometry Of Benchmark Open Clusters, Michael Deloss Joner
Theses and Dissertations
Photometric techniques are often used to observe stars and it can be demonstrated that fundamental stellar properties can be observationally determined using calibrated sets of photometric data. Many of the most powerful techniques utilized to calibrate stellar photometry employ the use of stars in clusters since the individual stars are believed to have many common properties such as age, composition, and approximate distance. Broadband photometric Johnson/Cousins BVRI observations are presented for several nearby open clusters. The new photometry has been tested for consistency relative to archival work and shown to be both accurate and precise. The careful use of a …
Three Channel Polarimetric Based Data Deconvolution, Kurtis G. Engelson
Three Channel Polarimetric Based Data Deconvolution, Kurtis G. Engelson
Theses and Dissertations
A three channel polarimetric deconvolution algorithm was developed to mitigate the degrading effects of atmospheric turbulence in astronomical imagery. Tests were executed using both simulation and laboratory data. The resulting efficacy of the three channel algorithm was compared to a recently developed two channel approach under identical conditions ensuring a fair comparison amongst both algorithms. Two types of simulations were performed. The first was a binary star simulation to compare resulting resolutions between the three and two channel algorithms. The second simulation measured how effective both algorithms could deconvolve a blurred satellite image. The simulation environment assumed the key parameters …
Time-Series Observations Of The High Mass X-Ray Binary 4u 2206+54 To Monitor Light Variation, Jessica Lynn Bugno
Time-Series Observations Of The High Mass X-Ray Binary 4u 2206+54 To Monitor Light Variation, Jessica Lynn Bugno
Theses and Dissertations
The high mass X-ray binary 4U 2206+54 has been a very controversial system due to variability in spectral data as well as photometric data. We, at Brigham Young University, have been observing this system in multiple filters with several telescopes. This thesis presents our methods of observations, reductions, and results. It also compares what we have been detecting to other groups looking at the same target in different wavelengths. Furthermore, this thesis discusses some of the peculiarities of 4U 2206+54 and possible theories to explain these phenomena. Based on our photometric observations for the past three years, we believe the …
Comparison Of H-Alpha And H-Beta Temperature Indices In The Hyades And Coma Star Clusters And Selected H-Beta Standard Stars, Miriam Anne West
Comparison Of H-Alpha And H-Beta Temperature Indices In The Hyades And Coma Star Clusters And Selected H-Beta Standard Stars, Miriam Anne West
Theses and Dissertations
Using the Dominion Astrophysical Observatory's 1.2-m McKellar Telescope, we have obtained spectra on 81 stars from the Hyades Cluster, the Coma Cluster, and selected H-beta standard stars. These spectra cover from 4500 Å to 6900 Å which includes both the H-β and H-α absorption lines. The H-β absorption line has a long history of being used as a temperature index and more recently, calibration of an H-α index has been established for photometric observations. Through spectrophotometric comparison of temperature indices from the H-α and H-β absorption lines we find the expected strong correlation between photometric indices based on the strength …
Generalized Acoustic Energy Density And Its Applications, Buye Xu
Generalized Acoustic Energy Density And Its Applications, Buye Xu
Theses and Dissertations
The properties of acoustic kinetic energy density and total energy density of sound fields in lightly damped enclosures have been explored thoroughly in the literature. Their increased spatial uniformity makes them more favorable measurement quantities for various applications than acoustic potential energy density (or squared pressure), which is most often used. In this dissertation, a new acoustic energy quantity, the generalized acoustic energy density (GED), will be introduced. It is defined by introducing weighting factors, α and 1 − α, in the formulation of total acoustic energy density. With the additional degree of freedom, the GED can conform to the …
Acoustical Analysis Of A Horn-Loaded Compression Drivers Using Numerical Analysis, Daniel Ross Tengelsen
Acoustical Analysis Of A Horn-Loaded Compression Drivers Using Numerical Analysis, Daniel Ross Tengelsen
Theses and Dissertations
Two numerical techniques, the boundary-element method (BEM) and the finite-difference method (FDM), are used for simulating the radiation from horn-loaded compression drivers and from an infinitely-baffled, finite-length pipe. While computations of the horn-loaded compression driver are in steady state, transient analysis of the finite-length pipe is studied as a precursor to transient analysis within the horn-loaded compression driver. BEM numerical simulations show promise for the development of new designs. Numerical simulations serve as a good tool for time and cost-effective prototyping as poor designs are detected before they are built.
Temperature And Variability Of Three Ionian Volcanoes, Daniel R. Allen
Temperature And Variability Of Three Ionian Volcanoes, Daniel R. Allen
Theses and Dissertations
Cassini spacecraft images of Io obtained during its flyby of Jupiter in late 2000 and early 2001 were used to determine the lava composition and eruption style of three faint hotspots, Pillan, Wayland, and Loki. We found a maximum color temperature of 1130+/-289 K for Pillan and maximum color temperatures of 1297+/-289 K and 1387+/-287 K for Wayland and Loki, respectively. These temperatures are suggestive of basaltic lava. The temperatures with the best signal-to-noise ratios also suggested basaltic lava and were found to be 780+/-189 K, 1116+/-250 K, and 1017+/-177 K for Pillan, Wayland, and Loki, respectively. Pillan showed increased …
Prediction And Study Of Binary Alloys Using First-Principles Methods, Richard Hansen Taylor Ii
Prediction And Study Of Binary Alloys Using First-Principles Methods, Richard Hansen Taylor Ii
Theses and Dissertations
The utility of first-principles methods in the study and prediction of binary alloys is showcased by three detailed studies. In particular, the T = 0K cluster expansion methodology in conjunction with finite temperature statistical modeling by a Monte Carlo method is used to study two systems of practical interest, Mg-Li (magnesium-lithium) and Rh-W (rhodium-tungsten). Also, an empirically-informed, high-throughput approach to crystal structure prediction is shown by a study of the Pt$_8$Ti (the Pietrokowsky phase) phase and a broad and detailed analysis of binary Mg-X phases in 39 systems (X=Ag, Al, Au, Ca, Cd, Cu, Fe, Ga, Ge, Hf, Hg, In, …
Charged, Rotating Black Holes In Higher Dimensions, Christopher Bruce Verhaaren
Charged, Rotating Black Holes In Higher Dimensions, Christopher Bruce Verhaaren
Theses and Dissertations
We present a method for solving the Einstein-Maxwell equations in a five dimensional, asymptotically flat, black hole spacetime with three commuting Killing vector fields. In particular, we show that by reducing the dimension of the Einstein-Maxwell equations in a Kaluza-Klein like manner we can determine the components of the metric and vector potential which lie in the direction of the Killing vector fields. These components are determined by nine scalar fields each of which satisfy a partial differential equation in two variables. These equations take the form of an elliptic operator set equal to a nonlinear source. We find evidence …
Real-Space Approach To Time Dependent Current Density Functional Theory, Daniel S. Jensen
Real-Space Approach To Time Dependent Current Density Functional Theory, Daniel S. Jensen
Theses and Dissertations
A real-space time-domain calculation of the frequency-dependent dielectric constant of nonmetallic crystals is outlined and the integrals required for this calculation are computed. The outline is based on time dependent current density functional theory and is partially implemented in the ab initio density functional theory FIREBALL program. The addition of a vector potential to the Hamiltonian of the system is discussed as well as the need to include the current density in addition to the particle density. The derivation of gradient integrals within a localized atomic-like orbital basis is presented for use in constructing the current density. Due to the …
In Search Of Empty Places: Voids In The Distribution Of Galaxies, Brian K. Bucklein
In Search Of Empty Places: Voids In The Distribution Of Galaxies, Brian K. Bucklein
Theses and Dissertations
We investigate several techniques to identify voids in the galaxy distribution of matter in the universe. We utilize galaxy number counts as a function of apparent magnitude and Wolf plots to search a two- or three-dimensional data set in a pencil-beam fashion to locate voids within the field of view. The technique is able to distinguish between voids that represent simply a decrease in density as well as those that show a build up of galaxies on the front or back side of the void. This method turns out to be primarily useable only at relatively short range (out to …
Oh Megamasers In Merging Galaxies: A Multi-Frequency Study Of Iizw096, Kirstin Marie Cooprider
Oh Megamasers In Merging Galaxies: A Multi-Frequency Study Of Iizw096, Kirstin Marie Cooprider
Theses and Dissertations
OH Megamasers (OHMs) generally appear in luminous infrared regions i.e. merging galaxies. In this study we assume that OHMs may not be represented by their association with star formation solely, because of the possibility of a compact AGN source in the merging galaxies. In fact, previously classified starburst galaxies where OHMs are found are now optically observed as AGN. OHMs may also serve as a reasonable criterion for the evolutionary stage of the merger. This project focuses on observations from a multi-frequency analysis of merging regions with known OHMs. Optically, Hα and BVRI filters provided an environmental perspective of the …
Inhomogeneity-Induced Spin Current In Atomic And Condensed Matter Systems, Bailey Hsu
Inhomogeneity-Induced Spin Current In Atomic And Condensed Matter Systems, Bailey Hsu
Theses and Dissertations
I derive and apply quantum propagator techniques to atomic and condensed matter systems. I observe many interesting features by following the evolution of a wavepacket. In atomic systems, I revisit the Stern-Gerlach effect and study the spin dynamics inside an inhomogeneous magnetic field. The results I obtained are not exactly the same as the textbook description of the effect which is usually a manifestation of a perfect space and spin entanglement. This discovery can provide insight on more reliable quantum computation device designs. In condensed matter systems, the doping concentration inhomogeneity leads to the Rashba spin-orbit interaction. This makes it …
Development And Demonstration Of A Field-Deployable Fast Chromotomographic Imager, Daniel C. O'Dell
Development And Demonstration Of A Field-Deployable Fast Chromotomographic Imager, Daniel C. O'Dell
Theses and Dissertations
A field deployable hyperspectral imager utilizing chromotomography (CT), with a direct vision prism (DVP) as the dispersive element, has been constructed at AFIT. This research is focused on the development and demonstration of the CT imager. An overview of hyperspectral imaging, chromotomography, a synopsis of reconstruction algorithms, and other CT instruments are given. The importance of component alignment, instrument calibration, and exact prism angular position data are discussed. A simplistic \shift and add" reconstruction algorithm was utilized for this research. Although limited in its ability to reconstruct a spatially and spectrally diverse scene, the algorithm was adequate for the testing …
Evaluation Of Interplanetary Magnetic Field Tracing Models Using Impulsive Seps, Brian P. Elliott
Evaluation Of Interplanetary Magnetic Field Tracing Models Using Impulsive Seps, Brian P. Elliott
Theses and Dissertations
Current Interplanetary Magnetic Field (IMF) models are evaluated in this study to determine which model(s) perform an accurate representation of this magnetic structure. These IMF models include the Parker Spiral model, the Potential Field Source Surface (PFSS) model, the Wang-Sheeley-Arge (WSA) model and the ENLIL model. Impulsive Solar Energetic Particles (SEPs) are used as tracers to determine the magnetic structure of the IMF and provide source locations for model comparisons. Each individual model is analyzed, compared to the identified solar source region and a longitude/latitude offset of these traces assigned. The model connection of the PFSS and Parker models is …
Simulating The Fticr-Ms Signal Of A Decaying Beryllium-7 Ion Plasma In A 2d Electrostatic Pic Code, Michael Takeshi Nakata
Simulating The Fticr-Ms Signal Of A Decaying Beryllium-7 Ion Plasma In A 2d Electrostatic Pic Code, Michael Takeshi Nakata
Theses and Dissertations
Beryllium-7 (Be-7) only decays by electron capture into lithium-7 (Li-7) with a half life of 53 days. We study the effect of ionization on this decay rate. We do so by trapping a Be-7 ion plasma in a cylindrical Malmberg-Penning trap and measuring Be-7 and Li-7 concentrations as functions of time by using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). We have simulated these signals in a 2-dimensional electrostatic particle-in-cell (PIC) code. The two spectrum peaks merge at high ion densities whereas at low ion densities they can be resolved. The merged peak shifts linearly according to the relative …
Equalization Of Loudspeakers And Enclosed Sound Fields, Xi Chen
Equalization Of Loudspeakers And Enclosed Sound Fields, Xi Chen
Theses and Dissertations
Equalization of loudspeakers and enclosed sound fields has been a topic of considerable interest for decades. Confusion has often arisen among audio professionals regarding the feasibility of simultaneously equalizing a loudspeaker and the enclosed field (i.e., the “room”) it excites. Because of frustrations encountered in such efforts, some have advocated abandoning simultaneous equalization altogether. This dissertation discusses the drawbacks of this approach as well as traditional in situ equalization methods. It demonstrates that many problems with traditional equalization stem from the use of measured acoustic pressure at a discrete point in a sound field as the system output. The dissertation …
Multiwavelength Studies Of Lsi+61°303, Michael E. Fahrenwald
Multiwavelength Studies Of Lsi+61°303, Michael E. Fahrenwald
Theses and Dissertations
LSI+61°303 is a member of a small class of X-ray binary stars that are also sources of strong radio emission. It has been detected as a periodic radio source with the NRAO Very Large Array, a magnitude 10.7 B0 star, a 0.5-5 keV X-ray source by the Einstein X-ray satellite and may be associated with an unidentified 100 MeV γ-ray source discovered by the Compton Gamma Ray Observatory satellite. Theories exist which suggest that binary systems are capable of emitting γ-rays at energies > 100 GeV. A similar system, PSR B1259-63, has been found to emit γ-rays at TeV energies. In …
Carbon Coated Tellurium For Optical Data Storage, Jonathan D. Abbott
Carbon Coated Tellurium For Optical Data Storage, Jonathan D. Abbott
Theses and Dissertations
A highly durable optical disk has been developed for data archiving. This optical disk uses tellurium as the write layer and carbon as a dielectric and oxidation prevention layer. The sandwich style CTeC film was deposited on polycarbonate and silicon substrates by plasma sputtering. These films were then characterized with SEM, TEM, EELS, ellipsometry, ToF-SIMS, etc, and were tested for writability and longevity. Results show the films were uniform in physical structure, are stable, and able to form permanent pits. Data was written to a disk and successfully read back in a commercial DVD drive.
Development And Comparison Of Methods For Measuring Directional Sound Arrivals In Rooms, Brian Trevor Thornock
Development And Comparison Of Methods For Measuring Directional Sound Arrivals In Rooms, Brian Trevor Thornock
Theses and Dissertations
In room acoustics, the directional information of sound arrivals at a listening location can be used to diagnose the origins of problematic reflections so offending surfaces or other features can be properly treated. It can also be used for other purposes, including the study of psychoacoustic indicators. Many methods have been developed in the past to derive directional information, but despite their benefits, each has had significant drawbacks that have necessitated further research into their properties and development of an improved method. This thesis presents a review of past methods, their benefits and shortcomings. It discusses many theoretical and practical …
Scan-Based Near-Field Acoustical Holography On Partially Correlated Sources, Michael D. Gardner
Scan-Based Near-Field Acoustical Holography On Partially Correlated Sources, Michael D. Gardner
Theses and Dissertations
Scan-based near-field acoustical holography (NAH) is applied to partially correlated sources. Partial field decomposition via the virtual coherence method is used to implement the scan-based NAH. The background and theory of these methods are developed. Multiple stationary reference microphones are required for the partial field decomposition. Guidelines for reference microphone placement in the literature thus far have been limited. Improved guidelines for reference microphones are given after the results of two sets of experiments. The first set involves discrete, partially correlated sources, both physical and numerical. The second set of experiments is strictly numerical and involves continuous sources. Fewer microphones …
Massively Parallel Indirect Dielectrophoresis Controlled Placement Of Carbon Nanotubes, Hiram Jacob Conley
Massively Parallel Indirect Dielectrophoresis Controlled Placement Of Carbon Nanotubes, Hiram Jacob Conley
Theses and Dissertations
Placement of single walled carbon nanotubes is demonstrated through massively parallel indirect dielectrophoresis (MPID). MPID is shown to be able to control the placement of carbon tubes as well as the number of tubes placed. Lumped element analysis for AC circuits is used to model MPID. This model allows for predictions of the number of tubes that will be captured in a trap. This model has been consistent with experimental data of numbers of nanotube placed in a junction. Carbon nanotubes placed with MPID are shown to be electrically active.
Extreme Ultraviolet Polarimetry With Laser-Generated High-Order Harmonics: Characterization Of Uranium, Nicole Brimhall
Extreme Ultraviolet Polarimetry With Laser-Generated High-Order Harmonics: Characterization Of Uranium, Nicole Brimhall
Theses and Dissertations
We developed an extreme ultraviolet (EUV) polarimeter, which employs laser-generated high-order harmonics as the light source. This relatively high-flux, directional EUV source has available wavelengths between 10 nm and 47 nm with easily rotatable linear polarization. The polarimeter has allowed us to characterize the optical constants of materials that may be useful for EUV optics. The instrument has a versatile positioning system and a spectral resolution of about 180, and we have demonstrated that reflectance as low as 0.1% can be measured repeatably at EUV wavelengths. We investigate the high harmonic source used for polarimetry measurements by documenting the spatial …
Development Of An Adaptive Equalization Algorithm Using Acoustic Energy Density, Panu Tapani Puikkonen
Development Of An Adaptive Equalization Algorithm Using Acoustic Energy Density, Panu Tapani Puikkonen
Theses and Dissertations
Sound pressure equalization of audio signals using digital signal processors has been a subject of ongoing study for many years. The traditional approach is to equalize sound at a point in a listening environment, but because of its specific dependence on the room frequency response between a source and receiver position, this equalization generally causes the spectral response to worsen significantly at other locations in the room. This work presents both a time-invariant and a time-varying implementation of an adaptive acoustic energy density equalization filter for a one-dimensional sound field. Energy density equalization addresses the aforementioned challenge and others that …
Simulation And Analysis Of Cadmium Sulfide Nanoparticles, Chad Everett Junkermeier
Simulation And Analysis Of Cadmium Sulfide Nanoparticles, Chad Everett Junkermeier
Theses and Dissertations
I used ab initio molecular dynamics calculations to model cadmium sulfide nanoparticles. The nanoparticles were originaly spherical, bulk-like zinc-blende structures. Constant temperature molecular dynamics calculations reveals that CdS nanoparticles that are about 2 nm in diameter and have unpassivated surfaces are in an amorphous structure with short range order. The nearest neighbor distance on the surface of the nanoparticles being near the wurtzite nearest neighbor distance. I wrote the program xyzSTATS and used its results in justifying the amorphous nanoparticles claim. I also estimated the band gap of the CdS nanoparticles with unpassivated dangling bonds.
Testing Direct Simulation Monte Carlo Methods Against The Fluid Equations In The Inductively Coupled Plasma Mass Spectrometer, William R. Somers
Testing Direct Simulation Monte Carlo Methods Against The Fluid Equations In The Inductively Coupled Plasma Mass Spectrometer, William R. Somers
Theses and Dissertations
A Direct Simulation Monte Carlo fluid dynamics code named FENIX has been employed to study gas flow-through properties of the inductively coupled plasma mass spectrometer (ICP-MS). Simulation data have been tested against the Navier-Stokes and heat equations in order to see if FENIX functions properly. The Navier-Stokes and heat equations have been constructed from simulation data and are compared term by term. This comparison shows that FENIX is able to correctly reproduce fluid dynamics throughout the ICP-MS simulation, with an exception immediately behind the ICP-MS sampler cone, where the continuum criterion for the Navier-Stokes equation is not met. Testing the …
Implementation Of Optical Spectra Calculations In Fireball: A Local-Orbital Density Functional Theory Approach, Ivan Grigoryevich Okhrimenko
Implementation Of Optical Spectra Calculations In Fireball: A Local-Orbital Density Functional Theory Approach, Ivan Grigoryevich Okhrimenko
Theses and Dissertations
We have expanded the capabilities of the ab initio tight-binding molecular dynamics package FIREBALL to include calculations of optical properties. Basic zero order approximation is based on transitions between Kohn-Sham states. Corrections for electron-electron interactions are based on time dependant density functional theory (TDDFT). Consistent with the FIREBALL approach, we use precalculated integrals and approximations to make the program faster.
Theory And Estimation Of Acoustic Intensity And Energy Density, Derek C. Thomas
Theory And Estimation Of Acoustic Intensity And Energy Density, Derek C. Thomas
Theses and Dissertations
In order to facilitate the acquisition and accurate interpretation of intensity and energy density data in high-amplitude pressure fields, the expressions for intensity and energy density are examined to ascertain the impact of nonlinear processes on the standard expressions. Measurement techniques for estimating acoustic particle velocity are presented. The finite-difference method is developed in an alternate manner and presented along with bias and confidence estimates. Additionally, two new methods for estimating the local particle velocity are presented. These methods appears to eliminate the errors and bias associated with the finite-difference technique for certain cases.
Early Dynamics Of Ultracold Neutral Plasmas, Adam W. Denning
Early Dynamics Of Ultracold Neutral Plasmas, Adam W. Denning
Theses and Dissertations
We report new studies on the early-time dynamics of ultracold neutral plasmas. We use fluorescence spectroscopy to probe plasma dynamics on the nanosecond time scale. We determine the rms ion velocity during the initial plasma period. The initial ion acceleration is found as the time derivative of the ion velocity. We compare to a theoretical model. The experimental results agree with the model at low plasma densities. However, the ion acceleration is a factor of ten lower than the model at higher densities. The cause of this discrepancy is currently unknown.