Physical Sciences and Mathematics Commons^™

Investigation Of Low-Stress Silicon Nitride As A Replacement Material For Beryllium X-Ray Windows, David B. Brough

Theses and Dissertations

The material properties of low stress silicon nitride make it a possible replacement material for beryllium in X-ray windows. In this study, X-ray windows made of LPCVD deposited low stress silicon nitride are fabricated and characterized. The Young's modulus of the LPCVD low stress silicon nitride are characterized and found to be 226±23 GPa. The residual stress is characterized using two different methods and is found to be 127±25 MPa and 141±0.28 MPa. Two support structure geometries for the low stress silicon nitride X-ray windows are used. X-ray windows with thicknesses of 100 nm and 200 nm are suspended on …

Thin Films Of Carbon Nanotubes And Nanotube/Polymer Composites, Anthony D. Willey

Theses and Dissertations

A method is described for ultrasonically spraying thin films of carbon nanotubes that have been suspended in organic solvents. Nanotubes were sonicated in N-Methyl-2-pyrrolidone or N-Cyclohexyl-2-pyrrolidone and then sprayed onto a heated substrate using an ultrasonic spray nozzle. The solvent quickly evaporated, leaving a thin film of randomly oriented nanotubes. Film thickness was controlled by the spray time and ranged between 200-500 nm, with RMS roughness of about 40 nm. Also described is a method for creating thin (300 nm) conductive freestanding nanotube/polymer composite films by infiltrating sprayed nanotube films with polyimide.

Comparing Theory And Experiment For Analyte Transport In The First Vacuum Stage Of The Inductively Coupled Plasma Mass Spectrometer, Matthew R. Zachreson

Theses and Dissertations

The Direct Simulation Monte Carlo algorithm as coded in FENIX is used to model the transport of trace ions in the first vacuum stage of the inductively coupled plasma mass spectrometer. Haibin Ma of the Farnsworth group at Brigham Young University measured two radial trace density profiles: one 0.7 mm upstream of the sampling cone and the other 10 mm downstream. We compare simulation results from FENIX with the experimental results. We find that gas dynamic convection and diffusion are unable to account for the experimentally-measured profile changes from upstream to downstream. Including discharge quenching and ambipolar electric fields, however, …

Advanced Numerical Methods In General Relativistic Magnetohydrodynamics, Michael J. Besselman

Theses and Dissertations

We show our work to refine the process of evolutions in general relativistic magnetohydrodynamics. We investigate several areas in order to improve the overall accuracy of our results. We test several versions of conversion methodologies between different sets of variables. We compare both single equation and two equations solvers to do the conversion. We find no significant improvement for multiple equation conversion solvers when compared to single equation solvers. We also investigate the construction of initial data and the conversion of coordinate systems between initial data code and evolution code. In addition to the conversion work, we have improved some …

Modeling Radial Bernstein Modes In A Finite-Length Axisymmetric Non-Neutral Plasma, Mark Andrew Hutchison

Theses and Dissertations

Axisymmetric radial Bernstein modes are known to exist in non-neutral plasmas and have been studied theoretically and computationally in 1D, but detection of these modes has still proven to be difficult due to self-shielding. To help advance the work on this front we created a 2D particle-in-cell (PIC) code that simulates a non-neutral plasma in a Malmberg-Penning trap. A detailed description of the PIC code itself has been included that highlights the benefits of using an $r^2$--$z$ grid and how it can be tested. The focus of the PIC simulation was to discover how best to drive and detect these …

Researching Effective Methods For Teaching The Phases Of The Moon, Heather Patti Jones

Theses and Dissertations

This study investigated the effectiveness of commonly used instructional methods for teaching the phases of the Moon to fifth and sixth grade students. The instructional methods investigated were the use of diagrams, animations, and models. The effectiveness of each method was tested by measuring students' understanding of Moon phases with a pre and post-assessment after receiving instruction with a specific method or combination of methods. These methods were then evaluated for their ability to help students learn essential concepts, reinforce relevant vocabulary and discourage misconceptions. Results showed that students had better scores with less prevalence of misconception when they were …

Penetration Forces For Subsurface Regolith Probes, Ahmed Elshafie

Graduate Theses and Dissertations

Investigating planetary bodies using penetrometers can provide detailed information about its history and evolution. An estimation of subsurface density and porosity can be made from the shape of the penetration curve. Using penetrometers mounted on planetary platforms could be challenging due to the uncertainty of the subsurface composition and since the maximum allowed force for penetration is the weight of the lander or rover on the surface. Estimation of penetration forces can provide a reliable constraint on the maximum reachable depth without endangering the whole mission. Therefore, knowledge of the required penetration force to specific depths can be helpful in …

Topics In Galaxy Formation: Pairwise Velocities Of Dark Matter Halos And Molecular Hydrogen Regulated Star Formation In Cosmological Simulations, Robert Jo Thompson

UNLV Theses, Dissertations, Professional Papers, and Capstones

In this dissertation we investigate two distinct challenges within the concordance LCDM model and an unrelated project.

The first is a discrepancy between theory and observation. A massive galaxy sub-cluster known as the `bullet' has fallen through a more massive parent galaxy cluster at a redshift of z=0.296.

Theory finds that in order to reproduce the observational quantities of this cluster, an unusually high relative velocity of v12=3000 km/s between the two cluster's parent halos is required.

We quantify the statistical probability of producing a `bullet-like' halo pair within large N-body simulations, and

conclude that either the LCDM model is …

On The Spherical Symmetry Of Perfect-Fluid Stellar Models In General Relativity, Joshua M Brewer

Masters Theses

It is well known in Newtonian theory that static self-gravitating perfect fluids in a vacuum are necessarily spherically symmetric. The necessity of spherical symmetry of perfect-fluid static spacetimes with constant density in general relativity is shown.

Exploring The Surface Liquid And Lake Regions Of Titan With Laboratory Experimentation And Cassini Spacecraft Data, Felix Casimir Wasiak

Graduate Theses and Dissertations

The surface liquids and lake regions of Titan are studied utilizing three unique techniques, the results of which are reported in this dissertation. The development of a facility to simulate the surface conditions of Titan, and to conduct experiments on samples within that facility, brings an understanding of Titan's surface not possible through observation and modeling alone. The properties of this facility are presented, including conceptual methodology, design, implementation, performance, and experimental results. The facility, the main component of which is a simulation chamber, allows for Titan temperatures of 90 - 94 K and a 1.5 bar N2 atmosphere. The …

Planet Formation In Transition Disks: Modeling, Spectroscopy, And Theory, Joseph Liskowsky

All Dissertations

An important field of modern astronomy is the study of planets. Literally for millennia, careful observers of the night sky have tracked these 'wanderers', with their peculiar motions initiating avenues of inquiry not able to elucidated by a study of the stars alone: we have discovered that the planets (as well as Earth) orbit the sun and that the stars are so far away, even their relative positions do not seem to shift perceptibly when Earth's position moves hundreds of millions of miles. With the advent of the telescope, and subsequent improvements upon it over the course of centuries, accelerating …

Molecular Processes In Astrophysics: Calculations Of H + H2 Excitation, De-Excitation, And Cooling, Matthew Kelley

UNLV Theses, Dissertations, Professional Papers, and Capstones

The implications of H+H2 cooling in astrophysics is important to several applications. One of the most significant and pure applications is its role in cooling in the early universe. Other applications would include molecular dynamics in nebulae and their collapse into stars and astrophysical shocks. Shortly after the big bang, the universe was a hot primordial gas of photons, electrons, and nuclei among other ingredients. By far the most dominant nuclei in the early universe was hydrogen. In fact, in the early universe the matter density was 90 percent hydrogen and only 10 percent helium with small amounts of lithium …

Determining Stellar Velocity Dispersion In Active Galaxies: Is The [Oiii] Width A Valid Surrogate?, Kelsi Flatland

Physics

The tight empirical relation between the stellar velocity dispersion (sigma) of the bulge and the mass of the supermassive black hole (BH) at its center indicates a close connection between galactic evolution and BH growth. The evolution of this relation with cosmic time provides valuable clues to its origin. While the mass of the BH can be easily estimated using the Doppler broadening of the Hbeta emission line in type I active galactic nuclei (AGNs), measuring sigma simultaneously is challenging, since the nuclear emission outshines the host galaxy. Thus, it is highly desirable to find an alternative way to estimate …

Evaluation Of 26al Method As Star Formation Rate Indicator, Manjeet Singh

All Theses

The aim of this work is to evaluate the '26Al method' used to determine the Galactic Star Formation Rate (SFR) and compare it to other alternative methods. 26Al is a radioactive isotope produced mainly in massive star winds and in the ensuing core collapse supernova explosion. The radioactive 26Al decays with a life time of 106 years by emitting γ- ray photons in 1.808 MeV band. The 26Al method involves using the Galactic 26Al radioactive flux as a tracer. This approach based on the γ- ray line measurements does not suffer from extinction and small number statistics.
To evaluate the …

The Assembly Of Galaxies Over Cosmic Time, Yicheng Guo

Open Access Dissertations

To Understand how galaxies were assembled across the cosmic time remains one of the most outstanding questions in astronomy. The core of this question is how today's Hubble Sequence, namely the differentiation of galaxy morphology and its correlation to galaxy physical properties, is formed. In this thesis, we investigate the origin of the Hubble Sequence through galaxies at z~2, an epoch when the cosmic star formation activity reaches its peak and the properties of galaxies undergo dramatic transitions. Galaxies at z~2 have two important features that are distinct from nearby galaxies: much higher frequency of clumpy morphology in star-forming systems, …

Nanoscale Surface Patterning And Applications: Using Top-Down Patterning Methods To Aid Bottom-Up Fabrication, Anthony Craig Pearson

Theses and Dissertations

Bottom-up self-assembly can be used to create structures with sub-20 nm feature sizes or materials with advanced electrical properties. Here I demonstrate processes to enable such self-assembling systems including block copolymers and DNA origami, to be integrated into nanoelectronic devices. Additionally, I present a method which utilizes the high stability and electrical conductivity of graphene, which is a material formed using a bottom-up growth process, to create archival data storage devices. Specifically, I show a technique using block copolymer micelle lithography to fabricate arrays of 5 nm gold nanoparticles, which are chemically modified with a single-stranded DNA molecule and used …

Curious Growth Of A Buried Sio2 Layer, Thomas O. Mcconkie

Theses and Dissertations

Initial investigation of Moxtek wire grid polarizers composed of Al and coated with SiO2 - SiX - SiO2 (where SiX is used to indicate a Si rich layer whose complete composition is not to be disclosed for proprietary reasons) showed a growth of 3x in the inner (closest to Al) SiO2 layer after baking. Upon removing the X and varying rib composition and layering composition and geometries in 12 sets of before and after samples, no obvious growth was observed. Even baking the original unbaked sample yielded no growth. Our data suggest that the initial conclusion of buried oxide growth …

Quantum Dynamics Using Lie Algebras, With Explorations In The Chaotic Behavior Of Oscillators, Ryan Thomas Sayer

Theses and Dissertations

We study the time evolution of driven quantum systems using analytic, algebraic, and numerical methods. First, we obtain analytic solutions for driven free and oscillator systems by shifting the coordinate and phase of the undriven wave function. We also factorize the quantum evolution operator using the generators of the Lie algebra comprising the Hamiltonian. We obtain coupled ODE's for the time evolution of the Lie algebra parameters. These parameters allow us to find physical properties of oscillator dynamics. In particular we find phase-space trajectories and transition probabilities. We then search for chaotic behavior in the Lie algebra parameters as a …

The Neutron-Star Equation Of State And Gravitational Waves From Compact Binaries, Benjamin David Lackey

Theses and Dissertations

The equation of state (EOS) of matter above nuclear density is currently uncertain by almost an order of magnitude. Fortunately, neutron stars (NS) provide an ideal laboratory for studying high density matter. In order to systematize the study of the EOS from NS observations, we introduce a parametrized high-density EOS that accurately fits theoretical candidate EOSs. We then determine the ability of several recent and near-future electromagnetic observations to constrain the parameter space of our EOS. Recent observations include measurements of masses, gravitational redshift, and spin period, and we find that high mass observations are the most useful at constraining …

Subsurface Planetary Investigation Techniques And Their Role For Assessing Subsurface Planetary Composition, Ahmed Elshafie

Graduate Theses and Dissertations

Subsurface planetary investigation techniques are of high interest and importance for the scientific community. Not only they can enhance our knowledge of the history of planetary formation but also can lead to information about its future. Whether the investigation is being conducted remotely using imagers, radars or physically using penetrometers or drills, a pre-existed knowledge of the mechanical and electrical properties of the subsurface regolith should be acquired for better data interpretation and analysis. Therefore, the main objective of this work is to investigate the mechanical and electrical properties of planetary analogs, understand their role for assessing the subsurface structure …

Advancements In Modeling Self-Consistent Core-Collapse Supernovae With Chimera, Merek Austin Chertkow

Doctoral Dissertations

Using a sophisticated program named CHIMERA, we perform numerical simulations of the end of a massive star's life when its core can no longer support itself through electron degeneracy pressure. After a violent collapse to super-nuclear densities, the core releases its binding energy (10^53 ergs) in the form of neutrinos. Simulations have shown that a small fraction of these neutrinos' energy is deposited into the matter above the forming neutron star, which drives a delayed explosion. Throughout this process, the oxygen and lighter elements that had composed the star's outer-core and envelope experience shock-driven explosive nucleosynthesis, forming newly synthesized heavy …

Stability Of Phyllosilicates On Mars, Patricia Gavin

Graduate Theses and Dissertations

This study investigates the stability of phyllosilicates on the surface of Mars through laboratory experiments and analysis of terrestrial analogs. Phyllosilicates are mostly found in the oldest Noachian terrains on Mars and hence hold clues to the planet's earliest aqueous and geologic history. Phyllosilicates relevant to Mars were heated up to ~1100°C for up to 24 hours and impacted with projectile velocities up to ~4.5 km/s. Heated samples were analyzed using x-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy in the near- (NIR, 1.0-2.5 µm) and mid-infrared (MIR, 5.0-15.0 µm) ranges. Impacted samples were also analyzed using Raman spectroscopy …

Orbital Periodicities Reflected In Ancient Surfaces Of Our Solar System And The Implications For A Record Of Early Life, Dixie Lee Androes

Graduate Theses and Dissertations

Uniformitarian processes, governed by invariant physical laws, remain the most reliable source for reconstructing the past. Driving many of the repetitive, predictable processes are the orbital dynamics of the Sun-Planet-Moon systems. Astronomical periodicities range from a few hours (tides) to thousands of years (Milankovitch). These periodicities, combined with geomorphic observations of planetary surfaces, constrain the time-dependent processes and allow for reconstruction of events and conditions favorable for sedimentary accumulations. This research suggests that seasonal sedimentary processes are dominant on Titan and Mars, and have played a significant role in the formation of ancient banded-iron formations (BIF's) on Earth.

Earth, Mars, …

The Power Of Thermonuclear Supernovae After One Year, Ginger Bryngelson

All Dissertations

Type Ia supernovae (SNe Ia), the thermonuclear explosion of a white dwarf, shape our understanding of the expansion of the universe with the use of their uniformity in distance determinations. Powered by radioactivity synthesized in the explosion, they fade slowly over hundreds of days. Sometime after 200 days, the continually expanding ejecta allows γ-rays from 56 Ni and 56 Co decays to escape, and soon any radioactive power contributing to lighting up the SN comes from positrons formed in 19% of 56 Co
decays.
While at first it seemed that positrons escaped through the thinning ejecta, it has become apparent …

Star-Disk Interaction In Herbig Ae/Be Stars, Christa Speights

All Theses

The question of the mechanism of certain types of stars is important. Classical T Tauri (CTTS) stars accrete magnetospherically, and Herbig Ae/Be stars (higher-mass analogs to CTTS) are thought to also accrete magnetospherically, but the source of a kG magnetic field is unknown, since these stars have radiative interiors. For magnetospheric accretion, an equation has been derived (Hartmann, 2001) which relates the truncation radius, stellar radius, stellar mass, mass accretion rate and magnetic field strength.
Currently the magnetic field of Herbig stars is known to be somewhere between 0.1 kG and 10 kG. One goal of this research is to …

Variability Studies Of Multi-Wavelength Data From Gamma-Ray Blazars Mrk 421 And Mrk 501, Brandon Becker

Physics

In this thesis we take astronomical multi-wavelength data from nearby blazars Markarian 421 and Markarian 501 and perform computational analysis and correlative studies to determine any possible time lag across different bands of our targets as well as to measure the statistical significance of this calculated result. The data was taken over the interval of December 2010 to May 2012 from multiple instruments spanning a broad range of wavelengths. We used the Discrete Correlation Function (DCF) to determine the time lag factor across data set pairs, focusing on X-ray and Very-High-Energy (VHE; >100 GeV) data. To establish the significance of …

Array-Based Characterization Of Military Jet Aircraft Noise, David William Krueger

Theses and Dissertations

Since the 1950s the jet aeroacoustics community has been involved in predicting and measuring the noise distribution in jets. In this work, cylindrical and planar Fourier near-field acoustical holography are used to investigate radiation from a full-scale, installed jet engine. Practical problems involving measurement aperture and the highly directional nature of the source are addressed. Insights from numerical simulations reveal usable reconstruction regions. A comparison of cylindrical and planar NAH for the respective measurement apertures shows cylindrical NAH outperforms planar NAH on reconstructions both towards and away from the source.

Analog Feedback Control Of Broadband Fan Noise, Cole Victor Duke

Theses and Dissertations

Active noise control (ANC) has been implemented using analog filters to reduce broadband noise from a small axial cooling fan. Previous work successfully attenuated narrow-band, tonal portions of the noise using a digital controller. The practical performance limits of this system were reached and it was desirable to attenuate the noise further. Additional research, therefore, sought to attenuate broadband noise from the fan using a digital controller, but performance was limited by the group delay inherent in the digital signal processor (DSP). Current research attempts to further attenuate broadband noise and improve performance of the system by combining the tonal …

Active Noise Control Of A Centrifugal Fan Mounted In A Mock Laptop Enclosure, John J. Esplin

Theses and Dissertations

Noise from information technology (IT) equipment is a significant problem in today's modern society. Active Noise Control (ANC) has shown promise in reducing the effect of IT fan noise on users. Though ANC has been applied to axial fans (such as those found in desktop computers), it has not been applied to centrifugal fans, such as those found in laptop computers. This work applies an ANC method to a centrifugal fan mounted in a mock laptop enclosure. This method is applied in four steps. First, secondary sources are placed in the vicinity of the fan. Second, an accurate model of …

A Study Of Rr Lyrae Stars In The Globular Cluster Ic 4499, Anna Paola Mikler

Honors Theses

Observations of the globular cluster IC4499 were taken with the 1m telescope at Cerro Tololo and combined with archival data from multiple telescopes. These data were used to study the variable star population using CCD photometry, with observations in the U, B, V, R and I passbands. The period and the magnitudes have been measured for the RR Lyrae stars. We present light curves in all passbands for all 97 RR Lyrae stars. The magnitudes of the RR Lyrae stars are compared with those measured by Walker and Nemec (1996). The distribution of stars on the horizontal branch is compared …