Open Access. Powered by Scholars. Published by Universities.®
- Discipline
- Keyword
-
- Stars (14)
- Abundances (10)
- EUV (10)
- Acoustics (9)
- Active noise control (9)
-
- Photoluminescence (9)
- Absorption (7)
- Astronomy (7)
- Atomic data (7)
- Energy density (7)
- Non-neutral plasma (7)
- Temperature (7)
- Acoustic (6)
- Calcium (6)
- Carbon nanotubes (6)
- Extreme ultraviolet (6)
- Optical constants (6)
- Plasma (6)
- Alloys (5)
- Atomic physics (5)
- Band gap (5)
- Energy (5)
- Etching (5)
- ISM (5)
- Thin films (5)
- Ultraviolet (5)
- West Mountain Observatory (5)
- ANC (4)
- Acoustic intensity (4)
- Algorithm (4)
- Publication Year
- Publication
- Publication Type
- File Type
Articles 121 - 150 of 378
Full-Text Articles in Astrophysics and Astronomy
Development Of A Strontium-87 Ion Interferometer, Christopher Joseph Erickson
Development Of A Strontium-87 Ion Interferometer, Christopher Joseph Erickson
Theses and Dissertations
I present the construction of a low-velocity intense source (LVIS) of laser-cooled neutral strontium using permanent ring magnets. The LVIS consists of a magneto-optical trap from which cold strontium is extracted in a well-collimated beam. I also present the development and implementation of a full suite of low-noise, high-bandwidth laser control electronics including a microcontroller unit. This microcontroller remotely controls and monitors the current driver, temperature controller, and PID lock circuit for each diode laser simultaneously. The current driver output is accurate to within 2 micro-amps and repeatable to with a few nano-amps. The noise spectral density of the current …
Electron Screening And Disorder-Induced Heating In Ultracold Neutral Plasmas, Mary Elizabeth Lyon
Electron Screening And Disorder-Induced Heating In Ultracold Neutral Plasmas, Mary Elizabeth Lyon
Theses and Dissertations
Disorder-induced heating (DIH) is a nonequilibrium, ultrafast relaxation process that occurs when laser-cooled atoms are photoionized to make an ultracold plasma. Its effects dominate the ion motion during the first 100 ns of the plasma evolution. Using tools of atomic physics we study DIH with ns time resolution for different plasma densities and temperatures. By changing the frequency of the laser beam we use to probe the ions, we map out the time evolution of the velocity distribution. We can compare this to a fluorescence simulation in order to more clearly determine the relationship between the fluorescence signal and the …
A Search For And Characterization Of Young Stellar Objects In N206, An H Ii Complex In The Large Magellanic Cloud, Tabitha Christi Buehler
A Search For And Characterization Of Young Stellar Objects In N206, An H Ii Complex In The Large Magellanic Cloud, Tabitha Christi Buehler
Theses and Dissertations
I have identified 51 young stellar object candidates in N206, an H II complex in the nearby Large Magellanic Cloud galaxy. Using archival images from the Spitzer Space Telescope, supplemented with other infrared and optical images, I located point sources in this region. I distinguished possible young stellar objects based on their spectral energy distributions, morphologies, and locations in color-magnitude space. I classified the young stellar object candidates based on their likelihood of being young stellar objects and based on their apparent evolutionary stages. The spatial distribution of these candidates in N206 indicates that star formation is being triggered …
Fabrication And Application Of Vertically Aligned Carbon Nanotube Templated Silicon Nanomaterials, Jun Song
Fabrication And Application Of Vertically Aligned Carbon Nanotube Templated Silicon Nanomaterials, Jun Song
Theses and Dissertations
A process, called carbon nanotube templated microfabrication (CNT-M) makes high aspect ratio microstructures out of a wide variety of materials by growing patterned vertically aligned carbon nanotubes (VACNTs) as a framework and then infiltrating various materials into the frameworks by chemical vapor deposition (CVD). By using the CNT-M procedure, a partial Si infiltration of carbon nanotube frameworks results in porous three dimensional microscale shapes consisting of silicon-carbon nanotube composites. The addition of thin silicon shells to the vertically aligned CNTs (VACNTs) enables the fabrication of robust silicon nanostructures with edibility to design a wide range of geometries. Nanoscale dimensions are …
Guiding The Experimental Discovery Of Magnesium Alloys, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo
Guiding The Experimental Discovery Of Magnesium Alloys, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo
Faculty Publications
Magnesium alloys are among the lightest structural materials known and are of considerable technological interest. To develop superior magnesium alloys, experimentalists must have a thorough understanding of the concentration-dependent precipitates that form in a given system, and hence, the thermodynamic stability of crystal phases must be determined. This information is often lacking but can be supplied by first-principles methods. Within the high-throughput framework, AFLOW, T = 0 K ground-state predictions are made by scanning a large set of known candidate structures for thermodynamic (formation energy) minima. The following 34 systems are investigated: AlMg, AuMg, CaMg, CdMg, CuMg, FeMg , GeMg, …
On The Measurement Of Angular Dependent Sound Transmission Through Airborne Supercritical Plates, Matthew D. Shaw
On The Measurement Of Angular Dependent Sound Transmission Through Airborne Supercritical Plates, Matthew D. Shaw
Theses and Dissertations
A method of measuring angular dependence of acoustic transmission through supercritical plates in air is discussed. The coincidence effect occurs in a supercritical plate when the component of the acoustic wave number parallel to the plate matches the bending wave number in the plate. The transmission of sound is a maximum at the angle where this trace wave number matching occurs. The theory of the coincidence effect is well-defined for unbounded thin plates using plane-wave excitation. However, experimental results for finite plates are known to diverge from theory, especially near grazing angles. An experimental setup has been developed in order …
Scaling Carbon Nanotube Localization By Floating Potential Dielectrophoresis: An Enabling Geometry, Brian S. Davis
Scaling Carbon Nanotube Localization By Floating Potential Dielectrophoresis: An Enabling Geometry, Brian S. Davis
Theses and Dissertations
Dielectrophoresis has been used as a technique for the parallel localization and alignment of both semiconducting and metallic carbon nanotubes (CNTs) at junctions between electrodes. A variation of this technique known as Floating Potential Dielectrophoresis (FPD) allows for a self-limiting number of CNTs to be localized at each junction, on a massively parallel scale. However, the smallest FPD geometries to date are restricted to conductive substrates and have a lower limit on floating electrode size. We present a geometry which eliminates this lower limit and enables FPD to be performed on non-conducting substrates. We also discuss experiments clarifying the self-limiting …
Photoemission By Large Electron Wave Packets Emitted Out The Side Of A Relativistic Laser Focus, Eric Flint Cunningham
Photoemission By Large Electron Wave Packets Emitted Out The Side Of A Relativistic Laser Focus, Eric Flint Cunningham
Theses and Dissertations
There are at least two common models for calculating the photoemission of accelerated electrons. The 'extended-charge-distribution' method uses the quantum probability current (multiplied by the electron charge) as a source current for Maxwell's equations. The 'point-like-emitter' method treats the electron like a point particle instead of like a diffuse body of charge. Our goal is to differentiate between these two viewpoints empirically. To do this, we consider a large electron wave packet in a high-intensity laser field, in which case the two viewpoints predict measurable photoemission rates that differ by orders of magnitude. Under the treatment of the 'extended-charge-distribution' model, …
Photoemission From A Laser-Driven Electron Wave Packet, John Purvis Corson
Photoemission From A Laser-Driven Electron Wave Packet, John Purvis Corson
Theses and Dissertations
We use quantum electrodynamics (QED) to investigate the possibility of radiative interference from a single laser-driven electron wave packet. Intuition gleaned from classical electrodynamics suggests that radiation from a large electron wave packet might interfere destructively when different regions of the packet oscillate out of phase with each other. We show that when the incident light is represented with a multi-mode coherent state, the relative phases of the electron's constituent momenta have no influence of the amount of scattered light. Hence, the radiation does not depend on the amount of free-particle spreading experienced by the electron before the interaction. This …
Polymer Molded Templates For Nanostructured Amorphous Silicon Photovoltaics, Lei Pei, Amy Balls, Cary Tippets, Jonathan Abbott, Matthew R. Linford, David D. Allred, Richard R. Vanfleet, Robert C. Davis, Jian Hu, Arun Madan
Polymer Molded Templates For Nanostructured Amorphous Silicon Photovoltaics, Lei Pei, Amy Balls, Cary Tippets, Jonathan Abbott, Matthew R. Linford, David D. Allred, Richard R. Vanfleet, Robert C. Davis, Jian Hu, Arun Madan
Faculty Publications
Here, the authors report the fabrication of transparent polymer templates for nanostructured amorphous silicon photovoltaics using low-cost nanoimprint lithography of polydimethylsiloxane. The template contains a square two-dimensional array of high-aspect-ratio nanoholes (300 nm diameter by 1 µm deep holes) on a 500X500 nm^2 pitch. A 100 nm thick layer of a-Si:H was deposited on the template surface resulting in a periodically nanostructured film. The optical characterization of the nanopatterned film showed lower light transmission at 600-850 nm wavelengths and lower light reflection at 400-650 nm wavelengths, resulting in 20% higher optical absorbance at AM 1.5 spectral irradiance versus a nonpatterned …
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 …
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 …
Diode Properties Of Nanotube Networks, David D. Allred, Bryan Hicks, Stephanie Getty
Diode Properties Of Nanotube Networks, David D. Allred, Bryan Hicks, Stephanie Getty
Faculty Publications
Single-walled carbon nanotubes (SWCNT) were prepared using iron catalysts deposited by indirect evaporation on silicon substrate covered with 500 nm-thick thermal oxide. Diode SWCNT devices have been fabricated using Au and Al, as the asymmetric metal contacts, and a random network of metallic and semiconducting nanotubes as the device channel. No effort was made to align the SWCNTs or to eliminate metallic nanotubes in our devices. Asymmetric voltage-current behavior was seen. Current rectification was observed in the source-drain bias range of -3 V to +3 V. Rectification was somewhat surprising since, although metallic tubes are in the minority (~ 1/3), …
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 …
Structure Maps For Hcp Metals From First-Principles Calculations, Gus L. W. Hart, Ohad Levy, Stefano Curtarolo
Structure Maps For Hcp Metals From First-Principles Calculations, Gus L. W. Hart, Ohad Levy, Stefano Curtarolo
Faculty Publications
The ability to predict the existence and crystal type of ordered structures of materials from their components is a major challenge of current materials research. Empirical methods use experimental data to construct structure maps and make predictions based on clustering of simple physical parameters. Their usefulness depends on the availability of reliable data over the entire parameter space. Recent development of high-throughput methods opens the possibility to enhance these empirical structure maps by ab initio calculations in regions of the parameter space where the experimental evidence is lacking or not well characterized. In this paper we construct enhanced maps for …
Structure-Property Maps And Optimal Inversion In Configurational Thermodynamics, Gus L. W. Hart, Björn Arnold, Alejandro Díaz Ortiz, Helmut Dosch
Structure-Property Maps And Optimal Inversion In Configurational Thermodynamics, Gus L. W. Hart, Björn Arnold, Alejandro Díaz Ortiz, Helmut Dosch
Faculty Publications
Cluster expansions of first-principles density-functional databases in multicomponent systems are now used as a routine tool for the prediction of zero- and finite-temperature physical properties. The ability of producing large databases of various degrees of accuracy, i.e., high-throughput calculations, makes pertinent the analysis of error propagation during the inversion process. This is a very demanding task as both data and numerical noise have to be treated on equal footing. We have addressed this problem by using an analysis that combines the variational and evolutionary approaches to cluster expansions. Simulated databases were constructed ex professo to sample the configurational space in …
Characterization Of Optical Constants For Uranium From 10 To 47 Nm, Nicole Brimhall, Nicholas Herrick, David D. Allred, R. Steven Turley, Michael Ware, Justin Peatross
Characterization Of Optical Constants For Uranium From 10 To 47 Nm, Nicole Brimhall, Nicholas Herrick, David D. Allred, R. Steven Turley, Michael Ware, Justin Peatross
Faculty Publications
We use a laser high-harmonics-based extreme-ultraviolet (EUV) polarimeter to determine the optical constants of elemental uranium in the wavelength range from 10 to 47 nm. The constants are extracted from the measure ratio of p-polarized to s-polarized reflectance from a thin uranium film deposited in situ. The film thickness is inferred from a spectroscopic ellipsometry measurement of the sample after complete oxidation in room air. Uranium has been used as a high-reflectance material in the EUV. However, difficulties with oxidation prevented its careful characterization previous to this study. We find that measured optical constants for uranium vary significantly from previous …
Ordered Magnesium-Lithium Alloys: First-Principles Predictions, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo
Ordered Magnesium-Lithium Alloys: First-Principles Predictions, Richard H. Taylor, Gus L. W. Hart, Stefano Curtarolo
Faculty Publications
Magnesium-lithium (Mg-Li) alloys are among the lightest structural materials. Although considerable work has been done on the Mg-Li system, little is known regarding potential ordered phases. A first and rapid analysis of the system with the high-throughput method reveals an unexpected wealth of potentially stable low-temperature phases. Subsequent cluster expansions constructed for bcc and hcp superstructures extend the analysis and verify our high-throughput results. Of particular interest are those structures with greater than 13 at. % lithium, as they exhibit either partial or complete formation as a cubic structure. Order-disorder transition temperatures are predicted by Monte Carlo simulations to be …
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 …