Physics Commons^™

Microstructure, Vacancies And Voids In Hydrogenated Amorphous Silicon, Rajendra Timilsina

Dissertations

This dissertation presents a theoretical and computational study of microstructure, vacancies and voids in hydrogenated amorphous silicon (a-Si:H). The microstructure consists of all possible silicon-hydrogen bonding configurations such as SiH, SiH₂, SiH₃ and SiH₄. However, it is highly dominated (approximately 75% or even more) by monohydride (SiH) configurations. Furthermore, the hydrogen atoms locate in both clustered and diluted phases; as a result, the distribution becomes highly inhomogeneous. Approximately 5% of hydrogen atoms reside in a form of isolated monohydrides at the lower (7 at.%) concentration whereas such configurations do not appear at the higher concentrations …

Reification: A Process To Configure Java Realtime Processors, John Huddleston Heath

Dissertations

Real-time systems require stringent requirements both on the processor and the software application. The primary concern is speed and the predictability of execution times. In all real-time applications the developer must identify and calculate the worst case execution times (WCET) of their software. In almost all cases the processor design complexity impacts the analysis when calculating the WCET. Design features which impact this analysis include cache and instruction pipelining. With both cache and pipelining the time taken for a particular instruction can vary depending on cache and pipeline contents. When calculating the WCET the developer must ignore the speed advantages …

Radiative Double Electron Capture In Collisions Of Fully-Stripped Fluorine Ions With Thin Carbon Foils, Tamer Mohammad Samy Elkafrawy

Dissertations

Radiative double electron capture (RDEC) is a one-step process in ion-atom collisions occurring when two target electrons are captured to a bound state of the projectile simultaneously with the emission of a single photon. The emitted photon has approximately double the energy of the photon emitted due to radiative electron capture (REC), which occurs when a target electron is captured to a projectile bound state with simultaneous emission of a photon. REC and RDEC can be treated as timereversed photoionization (PI) and double photoionization (DPI), respectively, if loosely-bound target electrons are captured. This concept can be formulated with the principle …

The Characterization Of Volatiles Associated With Young Stellar Objects, Kari Anne Wojtkowski

Dissertations

In the first portion of this work, we searched for differences in volatiles within a single star forming region, Rho Ophiuchi. We determined the amount, temperature, and composition of two ice features, the bending modes of CO2 and H2O at 15 μm and 6 μm, respectively, toward 28 Young Stellar Objects (YSOs). We found that more than 50% of the YSOs studied contained a portion of crystalline CO2 ice. We also found that some sources with Flat or borderline Class II Spectral Energy Distributions (SEDs) have a larger abundance of CO2 ice with respect to H2O ice. In addition to …

Modeling Transmission Of Photonic Crystal Waveguide Modes Enhanced By Kerr Nonlinearity, Buddhi M. Rai

Dissertations

Nonlinear modes of electromagnetic fields propagating in photonic crystal systems have been studied by implementing various computer simulation techniques using electromagnetic theory. The fundamentals of simulation of photonic crystals are analyzed using general purpose methodologies such as the FDTD or PWE methods. Information derived from the underlying physical insights into the systems could be utilized to describe the control mechanisms over the propagation of the modes around impurities in the photonic crystal lattice. The impurities trap the resonantly localized electromagnetic modes having a frequency in a stop band of the photonic crystal, suggesting novel optical controls in the photonic crystal …

Study Of The Structure Of 9C Via Single Neutron Transfer, Scott T. Marley

Dissertations

This thesis describes a study of the nucleus ⁹C, produced in the single-neutron transfer reaction d(¹⁰C, t) ⁹C using a radioactive ¹⁰C beam. The structure of the neutron-deficient nucleus ⁹C is poorly known. Only a few excited states have been observed and no information exists of their single-particle characteristics. The measured ground-state magnetic dipole moment of ⁹C is anomalously small and could imply large contributions from sd-shell orbitals in the ground-state wave function. The positions of the ⁹C excited states and their single-particle properties are vital to furthering the …

Evolution Of 3-D Magnetic Topology In Flare-Productive Active Regions, Yixuan Li

Dissertations

Solar eruptive phenomena, such as flares and coronal mass ejections (CMEs), derive their energy from complex magnetic fields and are the principal source of disturbances that affect space weather. Although physical mechanism and dynamic morphology of flares have been a subject of intense research, many aspects of the flaring process still remain unclear. The objective of this dissertation is to advance the understanding of the physics behind solar flares based on observations, simulations and nonlinear force-free (NLFF) field modeling of magnetic fields.

The data used in this study are obtained from several ground-based or space-borne instruments, including BBSO/DVMG, Hinode/SOT/SP, SDO/HMI …

Terahertz Wireless Communication, Ke Su

Dissertations

The goal of this thesis is to explore Terahertz (THz) wireless communication technology. More specifically the objective is to develop and characterize several THz communication systems and study the effect of atmosphere propagation through fog droplets and dust particles on THz communications.

For demonstration, a THz continuous wave (CW) photomixing system is designed. Terahertz signals are phase encoded with both analog ramp signals and pseudorandom binary data, transmitted over a short distance, and detected. The limitation of transmission bandwidth, low single to noise ratio, vibration effects are also analyzed. In order to study and compare propagation features of THz links …