Physical Sciences and Mathematics Commons^™

Acoustic Measurements Of Cohesive Sediment Transport: Suspension To Consolidation, Ho Kyung Ha

Dissertations, Theses, and Masters Projects

This dissertation aims at utilizing the acoustic approach to measure cohesive sediment behaviors including (1) suspension, (2) settling, (3) deposition and (4) consolidation. The first two processes were attempted to interpret by means of backscattered signal analysis, while the last two processes were done by echo signal analysis. The acoustic instruments used in this study include Acoustic Doppler Velocimeter (ADV), Pulse Coherent Acoustic Doppler Profiler (PC-ADP) and Micro-Chirp system. Used sediments are pure kaolinite and in-situ sediments collected from Mai Po and Clay Bank. 5-MHz ADV was used to estimate the suspended sediment concentration (SSC) and settling velocity (ws). For …

Natural Mortality Of Blue Crab: Estimation And Influence On Population Dynamics, David A. Hewitt

Dissertations, Theses, and Masters Projects

The blue crab Callinectes sapidus supports one of the most important fisheries in the Chesapeake Bay and is the leading contributor to blue crab landings in the United States. Assessment and management of blue crab stocks has been hampered by a lack of estimates of natural mortality rates, a key parameter in assessment models. In Chapter 2, we demonstrate that the approach used for estimating natural mortality that had been used in past assessments was flawed, and provide justification for a superior alternative. In Chapter 3, we synthesize our current understanding of natural mortality rates in adult blue crab and …

Nearshore Morphology And Lithology: Links To Framework Geology And Shoreline Change, Jennifer L. Miselis

Dissertations, Theses, and Masters Projects

Despite evidence of the geologic and morphologic complexity of inner shelves worldwide, there is a paucity of observations from the nearshore, inhibiting direct comparison of these factors to coastal change. Using geophysical instruments to characterize the geology of the nearshore, this research focuses on the relationships between nearshore stratigraphy, sediment heterogeneity, shoreface morphology and shoreline behavior. While generally not considered in engineering models of shoreline evolution, these factors influence nearshore processes. Overall, the findings presented highlight the importance of nearshore geology, both at the seafloor and underlying it, in contributing to modem sediment transport processes affecting beaches. Shallow, sub-seafloor geology …

Bottom-Up And Top-Down Controls On Sedimentary Ecosystem Functioning In A Seagrass Habitat, Amanda C. Spivak

Dissertations, Theses, and Masters Projects

Coastal seagrass ecosystems are complex habitats that are increasingly influenced by human perturbations. Disturbances that affect the strength of bottom-up (i.e. resource availability) and top-down (i.e. consumer) controls may also influence biomass distribution between trophic levels, sediment biogeochemistry, and seagrass ecosystem metabolism. Here, I experimentally tested how top-down and bottom-up perturbations interact with community structure (diversity, food chain length of epibenthic consumers) to alter sediment biogeochemistry and ecosystem metabolism in an experimental eelgrass (Zostera marina ) system. My data indicated that resource availability influenced SOM composition and ecosystem metabolism. Light availability tended to be a stronger determinant of SOM composition …

Synthesis And Field Emission Properties Of Carbon Nanostructures, Kun Hou

Dissertations, Theses, and Masters Projects

This dissertation focuses on developing carbon nanostructures for application as the electron emissive material in novel back-gated triode field emission devices. The synthesis, characterization, and field emission properties of carbon nanostructures, including 1-D carbon nanofibers (CNF), 2-D carbon nanosheets (CNS), and chromium oxide coated carbon nanosheets (CrOx-CNS), are presented in this work.;First, we have fabricated aligned carbon nanofiber based back-gated triode field emission devices and confirmed the operation of these devices. 1-D carbon nanofibers were directly synthesized on blank TiW substrates using direct current plasma enhanced chemical vapor deposition. It was found that the morphology of carbon nanofibers could be …

Methods For Stabilizing High Reynolds Number Lattice Boltzmann Simulations, Brian Robert Keating

Dissertations, Theses, and Masters Projects

The Lattice Boltzmann Method (LBM) is a simple and highly efficient method for computing nearly incompressible fluid flow. However, it is well known to suffer from numerical instabilities for low values of the transport coefficients. This dissertation examines a number of methods for increasing the stability of the LBM over a wide range of parameters. First, we consider a simple transformation that renders the standard LB equation implicit. It is found that the stability is largely unchanged. Next, we consider a stabilization method based on introducing a Lyapunov function which is essentially a discrete-time H-function. The uniqueness of an H-function …

As Particles Collide: Extra Dimensions And Heavy Leptons, Erin Kathleen De Pree

Dissertations, Theses, and Masters Projects

Despite excellent agreement with experiment, the Standard Model leaves several issues unresolved. These issues will be explored and several extensions to the Standard Model introduced: models with extra dimensions and a fourth family of particles.;In extra dimensional models, there are Fourier modes of the Standard Model particles. We study the detection of bound states of one of the modes and its Standard Model particle.;We then explore a particular model of extra dimensions known as Randall-Sundrum or warped extra dimensions. We will see how this model affects top quark measurements at the proposed International Linear Collider.;Finally we will study the detection …

Measurement Of Inclusive Proton Double -Spin Asymmetries And Polarized Structure Functions, Robert G. Fersch

Dissertations, Theses, and Masters Projects

The scattering of polarized electrons from a polarized proton target provides a means for studying the internal spin structure of the proton. The CLAS (CEBAF Large Acceptance Spectrometer) EG1b experiment in Hall-B at Jefferson Laboratory measured double-spin inclusive and exclusive electron-nucleon scattering asymmetries using longitudinally polarized frozen NH3 and ND3 targets and a longitudinally polarized electron beam at 4 different energies (1.6, 2.5, 4.2, 5.6 GeV). Extraction of the virtual photon asymmetry Ap1 (for 0.05 GeV2 < Q2 < 5.0 GeV2) provides precision measurements of the polarized proton spin-structure function gp1 in and above the resonance region. Linear regression of data between the varying energies yields new constraints on the virtual photon asymmetry Ap2 (and thus the structure function gp2 ) in the resonance region (for 0.3 GeV2 < Q2 < 1.0 GeV2). Measurements of these structure functions and their moments allows testing of perturbative Quantum Chromodynamics (pQCD) models and evaluation of moments of the structure functions in the Operator Product Expansion. Testing of Chiral Perturbation Theory (chiPT) at Q2 < 0.2 GeV 2 is enabled by the new data. Other applications of polarized structure functions include measurement of foward-spin polarizability, evaluation of high-order corrections in 1H hyperfine splitting, and testing of quark-hadron duality.

Status, Distribution And Reproductive Rates Of American Oystercatchers In Virginia, Alexandra Lee Wilke

Dissertations, Theses, and Masters Projects

No abstract provided.

Broad Spatial Trends In Osprey Provisioning, Reproductive Success, And Population Growth Within Lower Chesapeake Bay, Kenneth Andrew Glass

Dissertations, Theses, and Masters Projects

No abstract provided.

Mercury Levels In Newly Independent Songbirds, Anne Moire Condon

Dissertations, Theses, and Masters Projects

No abstract provided.

Automatically Generating Random Test Data For Relevant And Implicitly Defined Subdomains, John Alexander Murphy

Dissertations, Theses, and Masters Projects

No abstract provided.

Organotitanium-Aluminum Promoted Carbometalations Of Alkynols: Substituent Effects, Nikola A. Nikolic

Dissertations, Theses, and Masters Projects

No abstract provided.

Time-Resolved Magnetic Flux And Ac-Current Distributions In Superconducting Yttrium Barium Copper Oxide Thin Films And Multifilaments, Ran Yang

Dissertations, Theses, and Masters Projects

Time-resolved magneto-optical imaging (TRMOI) technique allows dynamic ac transport measurements on superconductors. The high time and spatial resolutions of the measurements also offer good quantitative data analysis of the MO images. YBa2Cu 3O7-delta (YBCO) was discovered as a high-temperature superconductor (HTSC) which has wide applications due to its high critical temperature of Tc = 91 K, and high critical current density Jc in the order of 106-7 Acm-2. Many of the applications require high ac current load and a high magnetic field. We study the interaction behavior of YBCO thin films in an ac transport current and a dc magnetic …

Magneto-Optical Imaging Of Superconducting Mgb2 Thin Films, Stephanie Maria Hummert

Dissertations, Theses, and Masters Projects

No abstract provided.

A New Packet Filter: Fast Packet Filtering By Exploiting Cisc And Simd Isa, Zhenyu Wu

Dissertations, Theses, and Masters Projects

No abstract provided.

Shelf Sediment Dispersal Mechanisms And Deposition On The Waiapu River Shelf, New Zealand, Tara A. Kniskern

Dissertations, Theses, and Masters Projects

The Waiapu River, located on the North Island of New Zealand, drains a small catchment and has one of the highest sediment yields in the world. The river delivers most of its annual sediment load during floods into energetic coastal waters. These conditions are favorable for producing multiple sediment transport mechanisms, including transport in positively and negatively buoyant freshwater plumes, gravitydriven flows, and resuspension. Analyses of Waiapu River shelf seabed data showed that multiple transport mechanisms influence strata formation. Fluvial sediments are initially deposited at water depths shallower than 80 m before being remobilized and deposited at greater water depths. …

Hypoxia And Macoma Balthica: Ecological Effects On A Key Infaunal Benthic Species, William Christopher Long

Dissertations, Theses, and Masters Projects

Hypoxia, low dissolved oxygen, is an important environmental stressor in estuarine systems. In this dissertation, I examine the effects of hypoxia on the macrobenthic communities of the York and Rappahannock Rivers, Chesapeake Bay, USA, and in particular its effects on the infaunal clam Macoma balthica. A survey of the macrobenthic community was performed using box-coring before and after hypoxia in 2003 and 2004 in both rivers. Hypoxia was associated with a change in the macrobenthic community towards smaller, shorter-lived, opportunistic species; and a substantial decrease in biomass. M. balthica recruited into all areas of the river but suffered local extinction …

The Role Of Bacteria-Particle Interactions In Marine Snow Dynamics, Emily M. Yam

Dissertations, Theses, and Masters Projects

Marine snow aggregates are one of the primary vehicles for deep-sea carbon sequestration. Bacterial activity on marine snow affects both degradation and aggregation processes that determine the flux of carbon to depth, biogeochemical cycling, and microbial food webs. The microscale processes occurring on aggregates depend on specific interactions between bacteria and particles. In this thesis, I describe two such interactions which have larger scale implications on marine snow dynamics: (1) the effects of starvation on bacterial motility and colonization behaviors on marine aggregates and (2) interactions between bacteria and phytoplankton which could contribute to the production of TEP.

Current models …

Inactive Sulfide Mounds Of The Manus Basin: Invertebrate Composition And Potential For A Chemoautotrophic Food Web, Kristin Lynn Erickson

Dissertations, Theses, and Masters Projects

No abstract provided.

Boron Carbide Filled Neutron Shielding Textile Polymers, Derrick Anthony Manzlak

Dissertations, Theses, and Masters Projects

No abstract provided.

Tweakable Blockciphers Secure Against Generic Exponential Attacks, Elizabeth Ann Crump

Dissertations, Theses, and Masters Projects

No abstract provided.

Parallel Three-Dimensional Acoustic And Elastic Wave Simulation Methods With Applications In Nondestructive Evaluation, Kevin Edward Rudd

Dissertations, Theses, and Masters Projects

In this dissertation, we present two parallelized 3D simulation techniques for three-dimensional acoustic and elastic wave propagation based on the finite integration technique. We demonstrate their usefulness in solving real-world problems with examples in the three very different areas of nondestructive evaluation, medical imaging, and security screening. More precisely, these include concealed weapons detection, periodontal ultrasography, and guided wave inspection of complex piping systems. We have employed these simulation methods to study complex wave phenomena and to develop and test a variety of signal processing and hardware configurations. Simulation results are compared to experimental measurements to confirm the accuracy of …

Parity-Violation In Elastic Electron Scattering: A First Measurement Of The Parity-Violating Asymmetry At Q2 = 0.631 (Gev/C)2 At Backward Angle, Stephanie L. Bailey

Dissertations, Theses, and Masters Projects

The goal of Experiment E04-115 (the G0 backward angle measurement) at Jefferson Lab is to investigate the contributions of strange quarks to the fundamental properties of the nucleon. The experiment measures parity-violating asymmetries in elastic electron scattering off hydrogen and quasielastic electron scattering off deuterium at backward angles at Q2 = 0.631 (GeV/c)2 and Q 2 = 0.232 (GeV/c)2. The backward angle measurement represents the second phase of the G0 experiment. The first phase, Experiment E00-006 (the G0 forward angle experiment), measured parity-violating asymmetries in elastic electron scattering off hydrogen at forward angles over a Q 2 range of 0.1-1.0 …

Fluorescence Imaging Study Of Free And Impinging Supersonic Jets: Jet Structure And Turbulent Transition, Jennifer Ann Inman

Dissertations, Theses, and Masters Projects

A series of experiments into the behavior of underexpanded jet flows has been conducted at NASA Langley Research Center. This work was conducted in support of the Return to Flight effort following the loss of the Columbia. The tests involved simulating flow through a hypothetical breach in the leading edge of the Space Shuttle Orbiter along its reentry trajectory, with the goal of generating a data set with which other researchers can test and validate computational modeling tools. Two nozzles supplied with high-pressure gas were used to generate axisymmetric underexpanded jets exhausting into a low-pressure chamber. These nozzles had exit …

Measurement Of The Branching Fraction For The Decay Neutral Kaon(Long) Going To Pion-Antipion-Positron-Electron In The High M(Pi-Pi) Invariant Mass Region, Joshua J. Moss

Dissertations, Theses, and Masters Projects

A measurement of the branching fraction for the rare decay K0L → pi+pi-e +e- was performed using data collected from experiment E871 which ran at the AGS of Brookhaven National Laboratory. Analysis of the data revealed 27.7 +/- 7.4 signal events in the signal region, 0.4905 GeV < Mpipiee < 0.505 GeV together with 13.3 +/- 3.7 background events. The branching fractions of ( 8.5+/-2.3stat +/-1.0sys ) x 10-6 using the phenomenological model acceptance and ( 2.3+/-0.6stat +/-0.3sys ) x 10-6 using the chiral perturbation model represent the first measurements for K0L → pi+pi-e +e- in the dipion invariant mass region 0.475 GeV < Mpipi < 0.497 GeV. These results support the prediction of chiral perturbation theory rather than that of the phenomenological model.

Decoupling Method For Parallel Delaunay Two-Dimensional Mesh Generation, Leonidas Linardakis

Dissertations, Theses, and Masters Projects

Parallel mesh generation procedures that are based on geometric domain decompositions require the permanent separators to be of good quality (in terms of their angles and length), in order to maintain the mesh quality. The Medial Axis Domain Decomposition, an innovative geometric domain decomposition procedure that addresses this problem, is introduced. The Medial Axis domain decomposition is of high quality in terms of the formed angles, and provides separators of small size, and also good work-load balance. It presents for the first time a decomposition method suitable for parallel meshing procedures that are based on geometric domain decompositions.;The Decoupling Method …

Environmental Factors And Typha Spp Dominance In Created Wetlands, Azure E. Bevington

Dissertations, Theses, and Masters Projects

As created wetlands are becoming more common due to compensatory mitigation under section 404 of the Clean Water Act, it has become important to understand how the vegetation community and the soil nutrient availability develop over time. For a created wetland to replace the function of the destroyed natural wetland, the biogeochemical cycling and vegetation community must replicate the natural system. In this study, I sampled the vegetation community as well as the soil and porewater nutrient availability in four created wetlands in southeastern Virginia, constructed and managed by the Virginia Department of Transportation. All the sites used in this …

Assessing The Impacts Of Land Use Change On Hard Clam Aquaculture In Old Plantation Creek, Northampton County, Virginia, Matthew J. Strickler

Dissertations, Theses, and Masters Projects

One of the main threats to water quality in the Chesapeake Bay is contamination by bacterial loading from point and non-point sources. While only very high levels of fecal bacteria (greater than 200 MPN/100ml) indicate the potential of a health threat to humans from contact with water, lower concentrations (14 MPN/100 ml) make the shellfish from contaminated waters unfit for human consumption. Many nearshore areas that are vulnerable to bacterial contamination also are suitable for the propagation of shellfish, including the hard clam (Mercenaria mercenaria). This is especially true on Virginia’s Eastern Shore, where shallow, sheltered waters with optimal salinity …

Feeding Ecology Of Atlantic Menhaden (Brevoortia Tyrannus) In Chesapeake Bay, Patrick D. Lynch

Dissertations, Theses, and Masters Projects

No abstract provided.