Physical Sciences and Mathematics Commons^™

Vector Operations In Superscalar Architectures, Nathan Daniel Flinn

Electrical & Computer Engineering Theses & Dissertations

Vector calculations are very prevalent today. Though the vector-processing computer is quite an old concept, superscalar processors lack hardware support for vector operations. This thesis investigates whether an ordinary superscalar computer architecture can be designed to include hardware support for improved vector operations without drastically changing the existing superscalar design and behavior. A computer architecture design was created and implemented that included the vector multiply (dot product) operation. The design includes a Vector Operations Unit that captures incoming vector operations and generates the necessary set of machine instructions to complete the vector operation internally. It then delivers these instructions to …

Modeling And Simulation Of Photonic Crystal Fibers Using Finite Difference Frequency Domain Method, Md. Khalid Ikram

Electrical & Computer Engineering Theses & Dissertations

Photonic crystal fibers (PCFs) allow guiding light in low-index core. These fibers exhibit properties such as single-mode operation in broad wavelength region. The mode shape and group velocity dispersion can be controlled by designing the microstructures of the cladding. In order to study these properties, a fast, efficient, and highly accurate numerical modeling method is required.

A full-vectorial finite-difference frequency-domain (FDFD) method is implemented. The modal properties of conventional step index fiber and index-guiding PCF are analyzed using this modeling technique. Compared to plane wave expansion and biorthogonal basis methods, FDFD is found to be simple, reliable, and efficient. PCFs …

Bottleneck Analysis Of Cports, Sreekalyana Chakravarthy Kajuluri

Electrical & Computer Engineering Theses & Dissertations

CPortS is a transportation logistics simulation that models the flow of military cargo through a seaport and the interaction of the cargo with the port resources and infrastructure. It provides information about the seaport's capabilities, how the cargo has been handled, how many days the cargo took to clear a particular port area, and the overall throughput of the seaport. The model is highly data intensive since it models the huge traffic in a real seaport.

Bottlenecks reduce system performance. Systems that are traffic intensive or simulations of systems, which are data intensive, encounter bottlenecks, which reduce their performance. In …

Hierarchical Hybrid Multicast An End System Multicast Algorithm Approach, Guillermo Loaisiga

Electrical & Computer Engineering Theses & Dissertations

Due to the rapid development in the computer and communication technologies, the Internet is experiencing an increasing demand of high-speed, real-time distributed applications, such as live streaming multimedia, videoconferencing, distributed simulations, and multiparty games. Multicast is an efficient transmission mechanism to support these applications. Historically, IP Multicast (IPM) has provided multicast support with well-known benefits, especially in bandwidth savings. However, it has experienced little deployment due to economic and architectural limitations.

Overlay multicast holds promise for the implementation of large scale Internet multicast services. An overlay network is a virtual topology constructed on top of the Internet infrastructure. This concept …

Huffman Approach To Opcode Compression, Jason B. Shreve

Electrical & Computer Engineering Theses & Dissertations

Instructions are the building blocks of computer programs. They are composed of opcodes, which uniquely identify each instruction, and the operands or data. In most architectures, the instruction length is a set multiple of the word size. The size and number of operands vary by instruction. Due to programmer usage, program need, or compiler design, opcodes do not occur with a constant distribution. Likely, some opcodes occur very frequently, whereas others occur very infrequently or not at all. If the length of an opcode were representative of its frequency, compression in program size might be achieved.

This thesis is an …

The Effect Of Submarine Canyon Width And Stratification On Coastal Circulation And Across Shelf Exchange, Kyung-Hoon Hyun

OES Theses and Dissertations

A 3-D ocean circulation model is used to investigate the effect of the width of a submarine canyon and stratification on adjacent coastal circulation and across shelf exchange. Upwelling winds for 20 d drive circulation over six canyons of varying widths (8–60 km), two escarpments to represent infinitely wide canyons, and a generic shelf-slope without a canyon. Also six stratifications whose first internal Rossby radii (a) range over 2–18 km were applied to two canyons (20 and 40 km) to see the effect of stratification. All simulations adjust to the canyon after 5 days spinup and reach an …

Qos Provisioning For Multi-Class Traffic In Wireless Networks, Mona El-Kadi Rizvi

Computer Science Theses & Dissertations

Physical constraints, bandwidth constraints and host mobility all contribute to the difficulty of providing Quality of Service (QoS) guarantees in wireless networks. There is a growing demand for wireless networks to support all the services that are available on wired networks. These diverse services, such as email, instant messaging, web browsing, video conferencing, telephony and paging all place different demands on the network, making QoS provisioning for wireless networks that carry multiple classes of traffic a complex problem. We have developed a set of admission control and resource reservation schemes for QoS provisioning in multi-class wireless networks.

We present three …

Anthropogenic Lead Deposition And Four National Parks In Poland As Determined By Lead Isotope Ratios, Shannon Simcoe

OES Theses and Dissertations

Polluted soils are recognized by having high concentrations of heavy metals, including Pb. Partitioning of metals in geochemical fractions, by sequential chemical extractions, may indicate whether a metal has been recently deposited in the soil. While concentration levels alone cannot distinguish between natural and anthropogenic Pb, studies have demonstrated that anthropogenic pollution is accurately recorded by specific Pb isotope signatures, which differ from natural Pb isotopes. The objective of this project was to use ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁶Pb/²⁰⁴Pb isotope ratios to differentiate between the anthropogenic Pb input and the naturally occurring Pb in four national …

Interactive Land Use Vrml Application Using Servlet Assist, Suresh Chitithoti

Electrical & Computer Engineering Theses & Dissertations

The integration of VRML and Servlet technologies has the potential to revolutionize web-based simulation visualization. The Interactive Land Use VRML Application (ILUVA) uses Java Servlets enabling one to perform urban planning by taking a virtual land area and add buildings, roadways, landscaping, and other features. The Virtual Reality Modeling Language (VRML) is a web-based technology for specifying and delivering interactive three-dimensional visualizations over a browser. The Java Servlet technology offers several powerful capabilities such as user authentication, session management, database connectivity for maintaining several possibly simultaneous user sessions, and dynamically generated VRML. Save and restore capabilities for any applications are …

Fuzzy Modeling Of Electromagnetic Emissions From Portable Electronic Devices Onboard Commercial Aircraft, Madiha Jamil Jafri

Electrical & Computer Engineering Theses & Dissertations

The use of Portable Electronic Devices (PEDs) is prohibited during take-off and landing of an aircraft because PEDs may emit signals that can interfere with the aircraft's navigation and communication systems. The electromagnetic interference (EMI) on the aircraft's electronics due to PEDs emissions is examined for Boeing 737 and 747 aircraft. This work, funded by the NASA Graduate Researchers Program, uses Interference Path Loss (IPL) data, collected by researchers from NASA Langley Research Center, Eagles Wings Inc. and United Airlines on several out-of-service United B737 and B747 airplanes.

B737 and B747 IPL data has been analyzed using a graphical analysis …

Dynamical Studies Of Model Membrane And Cellular Response To Nanosecond, High-Intensity Pulsed Electric Fields, Qin Hu

Electrical & Computer Engineering Theses & Dissertations

The dynamics of electroporation of biological cells subjected to nanosecond, high intensity pulses are studied based on a coupled scheme involving the current continuity and Smoluchowski equations. The improved pore formation energy model includes a dependence on pore population and density. It also allows for variable surface tension and incorporates the effects of finite conductivity on the electrostatic correction term, which was not considered by the simple energy models in the literature. It is shown that E(r) becomes self-adjusting with variations in its magnitude and profile. The whole scheme is self-consistent and dynamic.

An electromechanical analysis based on thin-shell theory …

Circulation, Vol. 11, No. 1, Center For Coastal Physical Oceanography, Old Dominion University, Chris Powell

CCPO Circulation

Spring 2004 issue of CCPO Circulation featuring article "Technical Requirements for a Real-Time Oceanographic Mooring at LEO-15" by Chris Powell

A Framework For Secure Group Key Management, Sahar Mohamed Ghanem

Computer Science Theses & Dissertations

The need for secure group communication is increasingly evident in a wide variety of governmental, commercial, and Internet communities. Secure group key management is concerned with the methods of issuing and distributing group keys, and the management of those keys over a period of time. To provide perfect secrecy, a central group key manager (GKM) has to perform group rekeying for every join or leave request. Fast rekeying is crucial to an application's performance that has large group size, experiences frequent joins and leaves, or where the GKM is hosted by a group member. Examples of such applications are interactive …

Models, Composability, And Validity, Eric Werner Weisel

Computational Modeling & Simulation Engineering Theses & Dissertations

Composability is the capability to select and assemble simulation components in various combinations into simulation systems to satisfy specific user requirements. The defining characteristic of composability is the ability to combine and recombine components into different simulation systems for different purposes. The ability to compose simulation systems from repositories of reusable components has been a highly sought after goal among modeling and simulation developers. The expected benefits of robust, general composability include reduced simulation development cost and time, increased validity and reliability of simulation results, and increased involvement of simulation users in the process. Consequently, composability is an active research …

Relating Water And Otolith Chemistry In Chesapeake Bay, And Their Potential To Identify Essential Seagrass Habitats For Juveniles Of An Estuarine-Dependent Fish, Spotted Seatrout (Cynoscion Nebulosus), Emmanis Dorval

Biological Sciences Theses & Dissertations

A quantitative understanding of habitat use of estuarine-dependent fishes is critical to the conservation of their most essential habitats. Because recruitment and fitness may be influenced by the quality of juvenile habitats, developing methods to quantify habitat-specific survivorship is pivotal to such understanding. An initial step to quantify survivorship is to validate the habitat-specific natural tags contained in otoliths. To this aim I investigated the variability in the chemistry of surface waters and otoliths of juvenile spotted seatrout, Cynoscion nebulosus, in five seagrass habitats of Chesapeake Bay, namely: Potomac, Rappahannock, York, Island, and Eastern Shore. I measured Mg, Ca, …

Role Of Nanophase Oxides In Short-Term Atmospheric Corrosion Of Structural Steels, Rama Balasubramanian

Physics Theses & Dissertations

Systematic studies on the development of nanophase iron oxides in the corrosion products of carbon and weathering steel were performed to understand the role of nanophase oxides in short-term atmospheric corrosion. Similarities and/or differences between short-term and long-term atmospheric corrosion were established by studying carbon steel and weathering steel coupons exposed in mild marine environments for short-term and comparing it with previously established long-term data. Influence of substitutional elements, in particular chromium, in forming nanophase goethite was investigated. Crystallographic, magnetic and morphological properties of nanophase chromium substituted goethite have been characterized in order to understand the protective nature of chromium-substituted …

Spin Structure Functions Of The Deuteron Measured With Clas In And Above The Resonance Region, Kahanawita G. Vipuli G. Dharmawardane

Physics Theses & Dissertations

Spin structure functions of the nucleon in the region of large x and small to moderate Q² continue to be of high current interest. The first moment of the spin structure function g₁, Γ₁, goes through a rapid transition from the photon point (Q² = 0), where it is constrained by the Gerasimov-Drell-Hearn sum rule, to the deep inelastic limit where it is sensitive to the nucleon spin fraction carried by quarks. The interesting behavior in the transition region is dominated by baryon resonance excitations. We concluded an experiment to measure these observables …

Bio-Optical Properties Of The Arctic Waters: Empirical And Theoretical Observations, Jian Wang

OES Theses and Dissertations

Bio-optical observations were made during August 2000 in the Beaufort and Chukchi Seas. Chlorophyll a concentration (Chl) ranged from 0.068 to 18.51 mg chl m⁻³. Both total particulate and phytoplankton absorption at 443 nm were closely correlated with chlorophyll concentration. There is no strong correlation between chlorophyll concentration and absorption by soluble materials or nonpigmented particulates. Absorption, scattering, and attenuation all show strong first-order spectral relationships. Two semianalytical remote sensing reflectance models were evaluated and validated using bio-optical data collected in this region. Both models were proficient at retrieving chlorophyll concentration, phytoplankton absorption coefficients, and particulate backscattering coefficients. …

Parallel Decomposition Procedures For Large-Scale Linear Programming Problems, Yusong Hu

Civil & Environmental Engineering Theses & Dissertations

In practice, many large-scale linear programming problems are too large to be solved effectively due to the computer's speed and/or memory limitation, even though today's computers have many more capabilities than before. Algorithms are exploited to solve such large linear programming problems, either in the sequential or parallel computation environment. This study focuses on two parallel algorithms for solving large-scale linear programming problems efficiently.

The first parallel decomposition algorithm discussed in this study is from the theory problems in a special block-angular structure. The theory or the decomposition principle is first examined. Since the subproblems of a linear programming problem …

Some Aspects Of Deeply Virtual Compton Scattering, Elena Kuchina

Physics Theses & Dissertations

We consider different aspects of the virtual Compton amplitude in QCD on two examples: small-x physics accessible in the Regge regime and twist-3 approximation in the description of DVCS through the general parton distributions. Using this model, we give an estimate for the cross section of deeply virtual Compton scattering for the kinematics of CEBAF at Jefferson Lab.

Electron Scattering From A High Momentum Neutron In Deuterium, Alexei V. Klimenko

Physics Theses & Dissertations

The deuterium nucleus is a system of two nucleons (proton and neutron) bound together. The configuration of the system is described by a quantum-mechanical wave function and the state of the nucleons at a given time is not known a priori. However, by detecting a backward going proton of moderate momentum in coincidence with a reaction taking place on the neutron in deuterium, the initial state of that neutron can be inferred if we assume that the proton was a spectator to the reaction. This method, known as spectator tagging, was used to study the electron scattering from high-momentum neutrons …

Neutron Star Electromagnetic Field Structure, Hugh O. Thurman Iii

Physics Theses & Dissertations

This dissertation investigates the neutron star magnetic field from generation to radiation production. We have investigated the spontaneous magnetization process to explain the magnetic field generation. This magnetization is then applied to determine the electromagnetic field structure of the neutron star. As an application of these two calculations, we briefly investigate several radiation mechanisms that are closely related to stellar magnetic fields.

Neutron star magnetic field generation is studied through the spontaneous magnetization process. This process was studied in the non-relativistic, ultra-relativistic, and rigorous relativistic dispersion regimes for the neutrons. Both analytical and numerical approaches show that a phase transition …

Experimental Investigation Of A Rubidium-Argon Dual Species Magneto-Optical Trap, Hauke Christian Busch

Physics Theses & Dissertations

The first simultaneous cooling and confinement of two different atomic species from opposite sides of the periodic table in a dual magneto optical trap (DMOT) has been accomplished. The alkali-metal ⁸⁵Rb and the noble gas ⁴⁰Ar* have been simultaneously confined, characterized, and interspecies interaction parameters have been measured. The DMOT confined 1.2 × 10^{6 85}Rb atoms at a density of 1 × 10¹⁰/cm³ and 1.4 × 10^{6 40}Ar* atoms with a density of 1.2 × 10¹⁰/cm³. A collisional loss rate coefficient for Rb-Ar* has been determined to …

Speaker Normalization For Improved Automatic Speech Recognition For Digital Libraries, Wei Wang

Electrical & Computer Engineering Theses & Dissertations

The context of this thesis work is the improvement of automatic speech recognition (ASR) for use with digital libraries. First, commonly used multimedia file formats and codecs are surveyed with the objective of identifying those formats that preserve speech quality while keeping file sizes compact. The main contribution of the work is a new technique for speaker adaptation based on frequency scale modifications. The frequency scale is modified using a minimum mean square error matching of a spectral template for each speaker to a "typical speaker" spectral template. Each spectral template is computed from the average amplitude-normalized spectra of several …

Scaling And Characterization Of Direct Current Glow Discharge Plasma In Atmospheric Air, Abdel-Aleam Hefney Mohamed

Electrical & Computer Engineering Theses & Dissertations

A microhollow cathode discharge was used as a plasma cathode to sustain a stable direct current glow discharge in atmospheric pressure air. The volumetric scale of glow discharge increased from the millimeter to the centimeter range by extending the plasma in lateral and axial directions. In the axial direction, the length of the glow discharge column was varied from 1 mm to 2 cm, with the sustaining voltage increasing linearly with the glow discharge column length. Extension in the lateral direction was obtained by operating discharges in parallel. The glow discharge plasma of the parallel discharge columns was found to …

Generic Performance Evaluation Tool Implementation For An Imaging Fourier Transform Spectrometer, James M. Mengert

Electrical & Computer Engineering Theses & Dissertations

Evaluation software for analyzing general analytical model applications utilizing MATLAB is presented in this thesis. The focus is to provide an interactive environment for the evaluation of model applications relating to an Imaging Fourier Transform Spectrometer. The Generic Performance Evaluation Tool (GPET) was developed by researchers at Old Dominion University and NASA-Langley Research Center and was a NASA-Langley Research Center sponsored project. GPET is capable of producing a multitude of object-oriented input data for any number of individual model applications. The tool is also capable of creating user-defined input interfaces for the purpose of viewing and/or editing input object data, …

Microdischarge Arrays, Wenhui Shi

Electrical & Computer Engineering Theses & Dissertations

Microhollow cathode discharges (MHCDs) are DC or pulsed gas discharges between two electrodes, separated by a dielectric, and containing a concentric hole. The diameter of the hole, in this hollow cathode configuration, is in the hundred-micrometer range. MHCDs satisfy the two conditions necessary for an efficient excimer radiation sources: (1) high energy electrons which are required to provide a high concentration of excited or ionized rare gas atoms; (2) high pressure operation which favors excimer formation (a three-body process). Flat panel excimer sources require parallel operation of MHCDs. Based on the current-voltage characteristics of MHCD discharges, which have positive slopes …

Spectral Dependence Of Coherent Backscattering Of Light In A Narrow-Resonance Atomic System, D. V. Kupriyanov, I. M. Sokolov, N. V. Larionov, P. Kulatunga, C. I. Sukenik, S. Balik, M. D. Havey

Physics Faculty Publications

We report a combined theoretical and experimental study of the spectral and polarization dependence of near-resonant radiation coherently backscattered from an ultracold gas of 85Rb atoms. Measurements in a 6 MHz range about the 5s 2S1/25p 2P3/2, F=3F'=4 hyperfine transition are compared with simulations based on a realistic model of the experimental atomic density distribution. In the simulations, the influence of heating of the atoms in the vapor, magnetization of the vapor, finite spectral bandwidth, and other nonresonant hyperfine transitions are considered. Good agreement is found between the simulations and measurements.

Astronaut Eva Exposure Estimates From Cad Model Spacesuit Geometry, Giovanni De Angelis, Brooke M. Anderson, William Atwell, John E. Nealy, Gary D. Qualls, John W. Wilson

Mathematics & Statistics Faculty Publications

Ongoing assembly and maintenance activities at the International Space Station (ISS) require much more extravehicular activity (EVA) than did the earlier U.S. Space Shuttle missions. It is thus desirable to determine and analyze, and possibly foresee, as accurately as possible what radiation exposures crew members involved in EVAs will experience in order to minimize risks and to establish exposure limits that must not to be exceeded. A detailed CAD model of the U.S. Space Shuttle EVA Spacesuit, developed at NASA Langley Research Center (LaRC), is used to represent the directional shielding of an astronaut; it has detailed helmet and backpack …

Numerical Study Of The Diapycnal Flow Through A Tidal Front With Passive Tracers, Chingming Dong, Robert Houghton, Hsien-Wang Ou, Dake Chen, Tal Ezer

CCPO Publications

A two-dimensional numerical model is used to study the diapycnal flow through a tidal front with passive tracers. In a basic numerical experiment a passive tracer is released into the bottom water at the offshore edge of a tidal front, and it subsequently moves on-bank with a velocity that decreases with time. This qualitatively agrees with a recent field experiment using a dye tracer on Georges Bank. Additional experiments are performed to investigate the sensitivity of the tracer dispersion to the tidal phase and the location of tracer release within the front. As the release point is moved on-bank across …