Physical Sciences and Mathematics Commons^™

New Multiwavelength Variability And Optical Microvariability Investigations Of X-Ray And Radio Selected Blazars, Margaret Angela Osterman

Physics and Astronomy Dissertations

The extreme AGN known as blazars can be classified based on their spectral properties into X-ray and radio selected objects, known as XBLs and RBLs, respectively. In this work, the results of new multiwavelength campaigns are presented for two XBLs and two RBLs. Each campaign contains simultaneous observations in the radio, optical, and X-ray regimes. A campaign on a third RBL was completed using near-simultaneous archival radio, optical/IR, and gamma-ray data. The simultaneous multiwavelength behavior exhibited in each campaign was analyzed by examining the multiwavelength variability and using spectral analysis. Observations of prominent optical microvariability were quantitatively analyzed. Previously published …

Intrinsic Absorption With The Far Ultraviolet Spectroscopic Explorer, Jay Patrick Dunn

Physics and Astronomy Dissertations

We present a survey of 72 Seyfert galaxies and quasars observed by the Far Ultraviolet Spectroscopic Explorer (FUSE). Our survey is the largest to date searching for intrinsic UV absorption with high spectral resolution, and is the first step toward a more comprehensive study of intrinsic absorption in low-redshift AGN. We have determined that 72 of 253 available active galactic nuclei (AGN) are viable targets for detection of intrinsic absorption lines. We examined these spectra for signs of intrinsic absorption in the O VI doublet (lambda lamdba 1031.9, 1037.6) and Lyman beta (lambda 1025.7). The fraction of Seyfert 1 galaxies …

Inspection And Characterization Of Exoplanet Using The Chara Array, Ellyn K. Baines

Physics and Astronomy Dissertations

Until the last decade or so, our entire knowledge of planets around Sun-like stars consisted of those in our own Solar System. This is no longer the case. Over 200 planets have been discovered through radial velocity surveys and photometric studies, both of which depend on observing the planet's effects on its host star. Much of our knowledge of the planets orbiting these stars is uncertain, based on assumptions about the stars' masses and the planets' orbital inclinations. This dissertation is comprised of two main sections. The first involves measuring the angular diameters for a sample of exoplanet host stars …

Hot Stars With Disks, Erika Dawn Grundstrom

Physics and Astronomy Dissertations

The evolutionary paths of the massive O and B type stars are often defined by angular momentum transformations that involve circumstellar gas disks. This circumstellar gas is revealed in several kinds of observations, and here I describe a series of investigations of the hydrogen line emission from such disk using detailed studies of five massive binaries and a survey of 128 Be stars. By examining three sets of spectra of the active mass-transfer binary system RY Scuti, I determined masses of 7.1 +/- 1.2 M_sun for the bright supergiant and 30.0 +/- 2.1 M_sun for the massive companion that is …

Dust Within The Central Regions Of Seyfert Galaxies, Rajesh Deo

Physics and Astronomy Dissertations

We present a detailed study of mid-infrared spectroscopy and optical imaging of Seyfert galaxies with the goal of understanding the properties of astronomical dust around the central supermassive black hole and the accretion disk. Specifically, we have studied Spitzer Space Telescope mid-infrared spectra of 12 Seyfert 1.8-1.9s and 58 Seyfert 1s and 2s available in the Spitzer public archive, and the nuclear dust morphology in the central 500 pc of 91 narrow and broad-line Seyfert 1s using optical images from the Hubble Space Telescope. We have also developed visualization software to aid the understanding of the geometry of the central …

Semiconductor Quantum Structures For Ultraviolet-To-Infrared Multi-Band Radiation Detection, Gamini Ariyawansa

Physics and Astronomy Dissertations

In this work, multi-band (multi-color) detector structures considering different semiconductor device concepts and architectures are presented. Results on detectors operating in ultraviolet-to-infrared regions (UV-to-IR) are discussed. Multi-band detectors are based on quantum dot (QD) structures; which include quantum-dots-in-a-well (DWELL), tunneling quantum dot infrared photodetectors (T-QDIPs), and bi-layer quantum dot infrared photodetectors (Bi-QDIPs); and homo-/heterojunction interfacial workfunction internal photoemission (HIWIP/HEIWIP) structures. QD-based detectors show multi-color characteristics in mid- and far-infrared (MIR/FIR) regions, where as HIWIP/HEIWIP detectors show responses in UV or near-infrared (NIR) regions, and MIR-to-FIR regions. In DWELL structures, InAs QDs are placed in an InGaAs/GaAs quantum well (QW) to …

White Dwarfs In The Solar Neighborhood, John P. Subasavage, Jr.

Physics and Astronomy Dissertations

The study of white dwarfs (WDs) provides insight into understanding WD formation rates, evolution, and space density. Individually, nearby WDs are excellent candidates for astrometric planetary searches because the astrometric signature is greater than for an identical, more distant WD system. As a population, a complete volume-limited sample is necessary to provide unbiased statistics; however, their intrinsic faintness has allowed some to escape detection.

The aim of this dissertation is to identify nearby WDs, accurately characterize them, and target a subset of potentially interesting WDs for follow-up analyses. The most unambiguous method of identifying new WDs is by their proper …

Electrical And Optical Characterization Of Group Iii-V Heterostructures With Emphasis On Terahertz Devices, Aruna Bandara Weerasekara

Physics and Astronomy Dissertations

Electrical and optical characterizations of heterostructures and thin films based on group III-V compound semiconductors are presented. Optical properties of GaMnN thin films grown by Metalorganic Chemical Vapor Deposition (MOCVD) on GaN/Sapphire templates were investigated using IR reflection spectroscopy. Experimental reflection spectra were fitted using a non - linear fitting algorithm, and the high frequency dielectric constant (ε∞), optical phonon frequencies of E1(TO) and E1(LO), and their oscillator strengths (S) and broadening constants (Γ) were obtained for GaMnN thin films with different Mn fraction. The high frequency dielectric constant (ε∞) of InN thin films grown by the high pressure chemical …

Energy Deposition Study Of Low-Energy Cosmic Radiation At Sea Level, Pushpa Indumathie Wijesinghe

Physics and Astronomy Dissertations

In this dissertation work, a computer simulation model based on the Geant4 simulation package has been designed and developed to study the energy deposition and track structures of cosmic muons and their secondary electrons in tissue-like materials. The particle interactions in a cubic water volume were first simulated. To analyze the energy deposition and tracks in small structures, with the intention of studying the energy localization in nanometric structures such as DNA, the chamber was sliced in three dimentions. Validation studies have been performed by comparing the results with experimental, theoretical, and other simulation results to test the accuracy of …

Development Of Cosmic Ray Simulation Program -- Earth Cosmic Ray Shower (Ecrs), Sampath S. Hakmana Witharana

Physics and Astronomy Dissertations

ECRS is a program for the detailed simulation of extensive air shower initiated by high energy cosmic ray particles. In this dissertation work, a Geant4 based ECRS simulation was designed and developed to study secondary cosmic ray particle showers in the full range of Earth's atmosphere. A proper atmospheric air density and geomagnetic field are implemented in order to correctly simulate the charged particles interactions in the Earth's atmosphere. The initial simulation was done for the Atlanta (33.460 N , 84.250 W) region. Four different types of primary proton energies (109, 1010, 1011 and 1012 eV) were considered to determine …

Numerical Hydrodynamics Of Relativistic Extragalactic Jets, Eunwoo Choi

Physics and Astronomy Dissertations

This dissertation describes a multidimensional relativistic hydrodynamic code which solves the special relativistic hydrodynamic equations as a hyperbolic system of conservation laws based on the total variation diminishing (TVD) scheme. Several standard tests and test simulations are presented to demonstrate the accuracy, robustness and flexibility of the code. Using this code we have studied three-dimensional hydrodynamic interactions of relativistic extragalactic jets with two-phase ambient media. The deflection angle of the jet is influenced more by the density contrast of the cloud than by the beam Mach number of the jet, and a relativistic jet with low relativistic beam Mach number …