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Articles 931 - 960 of 1876
Full-Text Articles in Physical Sciences and Mathematics
Organic Matter Composition Of Sediments And The History Of Eutrophication And Anoxia In The Mesohaline Chesapeake Bay, Andrew R. Zimmerman
Organic Matter Composition Of Sediments And The History Of Eutrophication And Anoxia In The Mesohaline Chesapeake Bay, Andrew R. Zimmerman
Dissertations, Theses, and Masters Projects
To evaluate the effects of anthropogenic alteration of the Chesapeake Bay (CB) watershed since European settlement, the historical progression of eutrophication and anoxia in the mesohaline region of CB was reconstructed. Lipid biomarker and carbon and nitrogen stable isotopic and elemental composition of CB surficial sediments were examined seasonally in order to identify the present sources of organic matter to CB sediments and the processes controlling their distribution. Temporal variability in surficial sediment composition could be linked to seasonal changes in phytoplankton community composition and biomass while spatial variation was dominated by the delivery of alloclithonous versus autochthonous sources of …
Field Measurement Of Mixed Grain Size Suspension In The Nearshore Under Waves, Grace M. Battisto
Field Measurement Of Mixed Grain Size Suspension In The Nearshore Under Waves, Grace M. Battisto
Dissertations, Theses, and Masters Projects
The Sensor Insertion System (SIS) located at the US Army Corps Field Research Facility (FRF) in Duck, NC, allows closely spaced measurements of along-shore velocity and suspended sediment concentration to be collected across the entire surf zone during storms. The SIS infers suspended sand concentration from backscatter off of suspended material using optical backscatter (OBS) sensors. Unfortunately, OBS response is highly sensitive to grain size, including both differences between sand and mud and variations in size within the sand range. As part of this study, ground-truthing measurements were added to the SIS during a storm in October 1997, including measurements …
Routing And Wavelength Assignment In Wdm Optical Networks, Guangzhi Li
Routing And Wavelength Assignment In Wdm Optical Networks, Guangzhi Li
Dissertations, Theses, and Masters Projects
In this thesis, we focus on the routing and wavelength assignment problems in WDM all-optical networks. Since the general problem is difficult (NP-complete), we classify the problem into several models with different formulations. Our objectives are to analyze some subclasses of routing and wavelength assignment problems; to understand their special properties; to estimate algorithm bounds and performance; and, to design efficient heuristic algorithms. These goals are important because results that follow can help engineers design efficient network topologies and protocols, and eventually provide end-users with cost-effective high bandwidth.;We first study the off-line wavelength assignment problem in single fiber ring and …
In-Situ Frequency-Dependent Electromagnetic Sensing For Monitoring Physical And Chemical Attributes During Chemical Processing, Jeffrey David Rogozinski
In-Situ Frequency-Dependent Electromagnetic Sensing For Monitoring Physical And Chemical Attributes During Chemical Processing, Jeffrey David Rogozinski
Dissertations, Theses, and Masters Projects
The objective of this research was to develop an in-situ sensing technique that monitors the molecular-level response of ions and dipoles to an applied electric field in order to characterize the changes in state of a polymer resin during chemical processing. This technique needs to be capable of monitoring the reaction progress not only in the laboratory setting but also in-situ in the processing tool or reaction environment. Frequency Dependent Electromagnetic Sensing (FDEMS) was selected for this task.;This dissertation investigates the applicability of FDEMS to monitoring two types of processing methods: reactive and batch reactor. The reactive processing system examined …
An Interactive Simulation Environment For End-To-End Digital Imaging System Design And Fidelity Analysis, Moira Joyce Turner
An Interactive Simulation Environment For End-To-End Digital Imaging System Design And Fidelity Analysis, Moira Joyce Turner
Dissertations, Theses, and Masters Projects
The detailed specification, implementation, and documentation of an interactive software environment based on a continuous/discrete/continuous imaging system model is presented. The purpose of the interactive environment is to support the design and performance analysis of end-to-end digital imaging systems. Development of the environment is based on the objectives of acceptable response time, large sampling grid capability, good graphical user interface design, independence from proprietary applications and portability among UNIX workstations. While one-dimensional variations of interactive design environments have been developed by the commercial active filter design community, there is little or no evidence that the increased complexity associated with the …
Bioremediation Of Tributyltin Contaminated Sediment Using Spartina Alterniflora In A Created Tidal Wetland, Britt-Anne Anderson
Bioremediation Of Tributyltin Contaminated Sediment Using Spartina Alterniflora In A Created Tidal Wetland, Britt-Anne Anderson
Dissertations, Theses, and Masters Projects
No abstract provided.
Efficiency Of Pound-Net Cull Panels: A Comparison Of Size Selectivity And Relative Release For Weakfish (Cynoscion Regalis) And Summer Flounder (Paralichthys Dentatus), Christian Harding Hager
Efficiency Of Pound-Net Cull Panels: A Comparison Of Size Selectivity And Relative Release For Weakfish (Cynoscion Regalis) And Summer Flounder (Paralichthys Dentatus), Christian Harding Hager
Dissertations, Theses, and Masters Projects
No abstract provided.
Application Of Genetic Markers To Provide Species Identification And Define Stock Structure: Analyses Of Selected Marine Fishes Of The Mid -Atlantic Bight, Jan F. Cordes
Dissertations, Theses, and Masters Projects
Molecular markers and techniques were employed to develop a genetic key for the forensic identification of 16 species of Chesapeake Bay sportfishes and to investigate the stock structure of one of those species, the weakfish Cynoscion regalis. Regions within the ATP synthetase 6 (ATPase 6), Cytochrome b , cytochrome c oxidase I, NADH dehydrogenase 4 (ND4), and 12S/16S ribosomal RNA mitochondrial genes were amplified using the polymerase chain reaction (PCR) and digested with a bank of restriction endonucleases to find a genetic marker that exhibited complete interspecific differentiation and low intraspecific variation. Complete separation of all sixteen species was accomplished …
Ecological Interactions Between Benthic Oyster Reef Fishes And Oysters, Juliana Maria Harding
Ecological Interactions Between Benthic Oyster Reef Fishes And Oysters, Juliana Maria Harding
Dissertations, Theses, and Masters Projects
Restoration of oyster reef structures rehabilitates habitats and the multi-level ecological communities built on eastern oysters (Crassostrea virginica), the keystone species. Quantitative descriptions of ecological interactions within a habitat are required to delineate essential fish habitats for management and protection. Parallel development of primary (oysters) and secondary trophic levels (benthic fishes) offer an ecological metric of restoration progress over time. The interaction between larval oysters and larval fishes (e.g., Gobiosoma bosc, Chasmodes bosquianus) is quantitatively examined. Oyster settlement estimates for Palace Bar reef, Piankatank River, Virginia are of the same order of magnitude as field densities of recently settled oysters. …
Across-Shelf Sediment Transport Modeling And Its Application To Storms At Duck, North Carolina, Guan-Hong. Lee
Across-Shelf Sediment Transport Modeling And Its Application To Storms At Duck, North Carolina, Guan-Hong. Lee
Dissertations, Theses, and Masters Projects
To understand the morphodynamics of the inner shelf, a benthic boundary layer tripod supporting 6 point-measuring current meters, an acoustic Doppler current profiler, and three near-bed profiling acoustic backscatter sensors documented storm and swell conditions during October, 1996, at a depth 13 in on the inner shelf off Duck, North Carolina. The relationship between eddy viscosity and eddy diffusivity during storm and swell conditions was examined using data collected in October 1996 on the inner shelf off Duck, NC. Sediment suspension models, including Rouse-type diffusion models, combined advection and diffusion models, and a Rouse model with a thickened wave boundary …
Carbon Dynamics In A Tidal Freshwater Marsh, Scott C. Neubauer
Carbon Dynamics In A Tidal Freshwater Marsh, Scott C. Neubauer
Dissertations, Theses, and Masters Projects
The sources and fates of carbon in a tidal freshwater marsh (Sweet Hall marsh; Pamunkey River, Virginia) were determined to understand the role that these marshes play with respect to estuarine carbon cycling. A carbon gas flux model, based on measured carbon dioxide and methane fluxes, was developed to calculate annual rates of macrophyte and microalgal photosynthesis and community and belowground respiration. Because carbon fluxes out of marsh sediments may underestimate true belowground respiration if sediment-produced gases are transported through plant tissues, gross nitrogen mineralization was used as a proxy for belowground carbon respiration. Annual community respiration exceeded gross photosynthesis, …
Assessment Of Spawning And Nursery Habitat Suitability For American Shad (Alosa Sapidissima) In The Mattaponi And Pamunkey Rivers, Donna Marie Bilkovic
Assessment Of Spawning And Nursery Habitat Suitability For American Shad (Alosa Sapidissima) In The Mattaponi And Pamunkey Rivers, Donna Marie Bilkovic
Dissertations, Theses, and Masters Projects
Delineation of essential fish habitat is particularly difficult for migratory fish which utilize large expanses of habitat throughout their life history. This study's main objective was the development and evaluation of habitat assessment tools for the early life stages of American shad (Alosa sapidissima) in two coastal plain rivers. to accomplish this, shad spawning and larval nursery habitats were delineated in the Mattaponi and Pamunkey rivers using presence of eggs and larvae (1997--1999) as evidence of habitat use. A watershed habitat assessment protocol was developed and used to rate habitat based on hydrographic, physical habitat, shoreline and land use parameters. …
Photosynthetic Response And Nutrient Uptake Dynamics Of Phytoplankton In The Ross Sea, Antarctica, Christina Marie Van Hilst
Photosynthetic Response And Nutrient Uptake Dynamics Of Phytoplankton In The Ross Sea, Antarctica, Christina Marie Van Hilst
Dissertations, Theses, and Masters Projects
No abstract provided.
The Human Factor In Size Selectivity In The Sea Scallop, Placopecten Magellanicus Fishery, Arman O. Kaltayev
The Human Factor In Size Selectivity In The Sea Scallop, Placopecten Magellanicus Fishery, Arman O. Kaltayev
Dissertations, Theses, and Masters Projects
No abstract provided.
Characterization Of Iron-Bearing Solids Used By Naturally-Occurring Microbes In The Anaerobic Degradation Of Hydrocarbons, David C. Powell
Characterization Of Iron-Bearing Solids Used By Naturally-Occurring Microbes In The Anaerobic Degradation Of Hydrocarbons, David C. Powell
Dissertations, Theses, and Masters Projects
No abstract provided.
Microgeographic Population Genetic Structure Of The Mummichog (Fundulus Heteroclitus L) Inhabiting An Industrialized Waterway, Luis Felipe Arzayus
Microgeographic Population Genetic Structure Of The Mummichog (Fundulus Heteroclitus L) Inhabiting An Industrialized Waterway, Luis Felipe Arzayus
Dissertations, Theses, and Masters Projects
No abstract provided.
Population Dynamics Of The Smooth Dogfish, Mustelus Canis, In The Northwest Atlantic, Christina L. Conrath
Population Dynamics Of The Smooth Dogfish, Mustelus Canis, In The Northwest Atlantic, Christina L. Conrath
Dissertations, Theses, and Masters Projects
No abstract provided.
Synoptic Scale Climatic Forcing Of Multispecies Fish Recruitment Patterns In Chesapeake Bay, Robert J. Wood
Synoptic Scale Climatic Forcing Of Multispecies Fish Recruitment Patterns In Chesapeake Bay, Robert J. Wood
Dissertations, Theses, and Masters Projects
Five fishery independent data sets were used to investigate multispecies fish recruitment patterns in Chesapeake Bay (1966--1997). Despite differences in sampling gear, sampled habitat, collection methods, and sampling sites, the strongest multispecies recruitment patterns within each data set (revealed by separate principal components analyses) depict a negative relationship between recruitment of spring spawning anadromous fishes and fall-winter continental shelf spawning species. This pattern dominates both low and high frequency components of the multispecies data. Because these two species groups utilize freshwater and oligohaline reaches of the Bay and its tributaries as springtime nursery areas, this Chesapeake Bay Anadromous-Shelf Spawner (CBASS) …
Structural Instabilities In Strontium Titanate From First-Principles Calculations, Christopher A. Lasota
Structural Instabilities In Strontium Titanate From First-Principles Calculations, Christopher A. Lasota
Dissertations, Theses, and Masters Projects
For some time now, first-principles calculation methods have proven to be an effective tool for investigating the physics of condensed matter systems. The additional use of density functional theory (DFT) and the local density approximation (LDA) has permitted even complex materials to be studied on desktop workstations with remarkable success. The incorporation of linear response theory into these methods has extended their power, allowing investigation of important dynamical properties.;Contained within the following pages are the results of a first-principles study of SrTiO3. This transition metal oxide is often grouped with ferroelectric materials, due to its similar composition and perovskite structure. …
Low Damage Processing And Process Characterization, Xianmin Tang
Low Damage Processing And Process Characterization, Xianmin Tang
Dissertations, Theses, and Masters Projects
Two novel plasma sources (one neutral source and one pulsed inductively coupled plasma source) and ashing process characterization were investigated. The primary goal was to characterize these source properties and develop corresponding applications. The study includes process damage assessment with these two sources and another continuous wave (13.56MHz) plasma source. A global average simulation of the pulsed discharges was also included.;The transient plasma density and electron temperature from the double probe analysis were compared with single Langmuir probe results with sheath displacement corrections in pulsed discharges (200Hz--10kHz). The equivalent resistance method can be used effectively to analyze these double probe …
Plasma Source Ion Implantation Of High Voltage Electrodes, Thomas Joseph Venhaus
Plasma Source Ion Implantation Of High Voltage Electrodes, Thomas Joseph Venhaus
Dissertations, Theses, and Masters Projects
Field emission and breakdown characteristics of high voltage, large area electrodes determine the performance of many vacuum-based electron sources. A corroborative project with the Thomas Jefferson National Accelerator Facility involves studying the behavior of such electrodes after nitrogen ion implantation. A Plasma Source Ion Implantation (PSII) facility is designed and constructed at William and Mary, and used to treat stainless steel electrodes. PSII is a novel implantation technique developed at the University of Wisconsin-Madison. A workpiece is submerged in a quiescent plasma of the species to be implanted. A series of high, negative voltages (30--100 kV) is applied to the …
Theoretical And Experimental Study Of Generation Mechanisms For Laser Ultrasound In Woven Graphite /Epoxy Composites With Translaminar Stitching, Adam D. Friedman
Theoretical And Experimental Study Of Generation Mechanisms For Laser Ultrasound In Woven Graphite /Epoxy Composites With Translaminar Stitching, Adam D. Friedman
Dissertations, Theses, and Masters Projects
The aerospace industry is beginning to use advanced composite materials for primary load bearing structures and their failure mechanisms must be better understood to predict their behavior in service. The Combined Loads Tests (COLTS) facility is being constructed at the NASA Langley Research Center to characterize these failure mechanisms. Laser based ultrasonic NDE can monitor the samples during dynamic loading without interfering with the structural tests. However, the constraints of implementing laser ultrasound in a structures laboratory reduces the efficiency of the technique. The system has to be "eye-safe" because many people will be present during the structural tests. Consequently, …
Precision Measurements Of The Proton And Deuteron Polarized Structure Functions, Paul Mcconihay King Ii
Precision Measurements Of The Proton And Deuteron Polarized Structure Functions, Paul Mcconihay King Ii
Dissertations, Theses, and Masters Projects
Experiment E155 at the Stanford Linear Accelerator Center measured the longitudinal and transverse polarized deep-inelastic scattering asymmetries for the proton and deuteron using longitudinally-polarized electron beams with energies of 48.3 GeV and 38.8 GeV, respectively. The electron beam polarization was measured by Moller polarimetry to be 0.81 +/- 0.02. Dynamically-polarized solid 15N3 and 6Li2H were used as the target materials. The scattered electrons were detected in three independent spectrometers at 2.75??, 5.5??, and 10.5??, covering a kinematic range of 0.014 ≤ x ≤ 0.9 and 1.0(GeV/ c)2 ≤ Q2 ≤ 40(GeV/ c)2. The 10.5?? spectrometer was constructed for this experiment. …
Data Structures For The Analysis Of Large Structured Markov Models, Andrew S. Miner
Data Structures For The Analysis Of Large Structured Markov Models, Andrew S. Miner
Dissertations, Theses, and Masters Projects
High-level modeling formalisms are increasingly popular tools for studying complex systems. Given a high-level model, we can automatically verify certain system properties or compute performance measures about the system. In the general case, measures must be computed using discrete-event simulations. In certain cases, exact numerical analysis is possible by constructing and analyzing the underlying stochastic process of the system, which is a continuous-time Markov chain (CTMC) in our case. Unfortunately, the number of states in the underlying CTMC can be extremely large, even if the high-level model is "small". In this thesis, we develop data structures and techniques that can …
The Absorption Spectrum Of The Hydrogen Atom In Crossed Electric And Magnetic Fields, Dongmei Wang
The Absorption Spectrum Of The Hydrogen Atom In Crossed Electric And Magnetic Fields, Dongmei Wang
Dissertations, Theses, and Masters Projects
This dissertation reports the theoretical interpretation of the measured absorption spectrum of hydrogen atoms in crossed electric and magnetic fields. Closed-orbit theory is modified from two-dimensions to three-dimensions to interpret the large scale structure in the absorption spectrum. A new computational method---a Chirped-Fourier-Transform---is developed to extract the closed orbits from an energy spectrum. A quantitative model is provided to calculate the continuum absorption. We prove that the observed continuum absorption is proportional to the flux of electrons along trajectories which escape within a short time. Einstein-Brillouin-Keller (EBK) quantization theory is applied to obtain an approximate energy spectrum. Our results prove …
Redistribution Of Rydberg States By Terahertz Radiation, Jonathan David Curley
Redistribution Of Rydberg States By Terahertz Radiation, Jonathan David Curley
Dissertations, Theses, and Masters Projects
We present the technique and results of our study of the redistribution of Rydberg states in barium by a half cycle pulse (HCP). A survey of previous research concerning the interaction of half cycle pulses with Rydberg atoms reveals a lack of experimental data in the area of state redistribution. This is primarily due to an inability to identify the redistributed states accurately using the currently available tool: selective field ionization (SFI). We present the limitations of SFI as a state identification tool. We then present a survey of isolated core excitation as a state identification tool, along with its …
Accelerating The Simulation Of Wireless Cellular Systems, Luiz Felipe Perrone
Accelerating The Simulation Of Wireless Cellular Systems, Luiz Felipe Perrone
Dissertations, Theses, and Masters Projects
The simulation of comprehensive models for cellular wireless systems poses a computational burden of great proportions. When a sub-model for transmitter power level control is included in the simulation, a continuous process in discrete-time is introduced, requiring traditional execution to advance in small, regular time-steps. to accelerate these simulations, we propose the use of interval jumping, a novel technique which allows time to progress in adaptive, irregularly-sized jumps in time. The foundations for this mechanism are laid out in the light of the simulation of a complex simulation model which includes teletraffic, radio propagation, channel allocation, transmitter power control, and …
Surface Processing By Rfi Pecvd And Rfi Psii, Lingling Wu
Surface Processing By Rfi Pecvd And Rfi Psii, Lingling Wu
Dissertations, Theses, and Masters Projects
An RFI plasma enhanced chemical vapor deposition (PECVD) system and a large-scale RF plasma source immersion ion implantation (PSII) system were designed and built to study two forms of 3-D surface processing, PECVD and PSII. Using the RFI PECVD system, Ti-6Al-4V substrates were coated with diamond-like carbon films with excellent tribological and optical properties. as an innovation, variable angle spectroscopic ellipsometry (VASE) was successfully applied for non-destructive, 3-D, large-area tribological coatings quality investigation.;Based on the experience with the RFI PECVD system, a large-scale RFICP source was designed and built for the PSIL Langmuir probe and optical emission spectroscopy studies indicated …
The Use Of Long-Lived Tracer Observations To Examine Transport Characteristics In The Lower Stratosphere, Gretchen Scott Lingenfelser
The Use Of Long-Lived Tracer Observations To Examine Transport Characteristics In The Lower Stratosphere, Gretchen Scott Lingenfelser
Dissertations, Theses, and Masters Projects
No abstract provided.
The Dehydrochlorination Mechanism Of The Internal Allylic Chloride Structure In Poly(Vinyl Chloride), Lynda B. Payne
The Dehydrochlorination Mechanism Of The Internal Allylic Chloride Structure In Poly(Vinyl Chloride), Lynda B. Payne
Dissertations, Theses, and Masters Projects
No abstract provided.