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Articles 1 - 30 of 35
Full-Text Articles in Physical Sciences and Mathematics
Distribution, Fluxes, And Bacterial Utilization Of Different Molecular Weight Fractions Of Dissolved Organic Matter In The York River Estuary, Carol J. Pollard
Distribution, Fluxes, And Bacterial Utilization Of Different Molecular Weight Fractions Of Dissolved Organic Matter In The York River Estuary, Carol J. Pollard
Dissertations, Theses, and Masters Projects
No abstract provided.
Use Of Remote Sensing To Identify Essential Habitat For Aeschynomene Virginica (L) Bsp, A Threatened Tidal Freshwater Wetland Plant, Elizabeth M. Mountz
Use Of Remote Sensing To Identify Essential Habitat For Aeschynomene Virginica (L) Bsp, A Threatened Tidal Freshwater Wetland Plant, Elizabeth M. Mountz
Dissertations, Theses, and Masters Projects
No abstract provided.
Estuarine Suspended Aggregate Dynamics And Characteristics, David C. Fugate
Estuarine Suspended Aggregate Dynamics And Characteristics, David C. Fugate
Dissertations, Theses, and Masters Projects
The research presented in this study is motivated by the need to improve prediction of sediment transport in estuaries. A novel application of the Acoustic Doppler Velocimeter (ADV) in the lower Chesapeake Bay is shown to estimate in-situ particle fall velocity at a single point without affecting the ambient turbulence. Acoustic backscatter from the ADV proved to be the best estimator of mass concentrations due to its apparent insensitivity to the size or density of muddy aggregates. Fall velocities are estimated analytically from a balance of settling and diffusive flux gradients using two methods, one employing Reynolds concentration flux, and …
Software And Hardware Methods For Memory Access Latency Reduction On Ilp Processors, Zhao Zhang
Software And Hardware Methods For Memory Access Latency Reduction On Ilp Processors, Zhao Zhang
Dissertations, Theses, and Masters Projects
While microprocessors have doubled their speed every 18 months, performance improvement of memory systems has continued to lag behind. to address the speed gap between CPU and memory, a standard multi-level caching organization has been built for fast data accesses before the data have to be accessed in DRAM core. The existence of these caches in a computer system, such as L1, L2, L3, and DRAM row buffers, does not mean that data locality will be automatically exploited. The effective use of the memory hierarchy mainly depends on how data are allocated and how memory accesses are scheduled. In this …
First-Principles Calculations Of Piezoelectricity And Polarization Rotation In Lead Zirconate Titanate, Zhigang Wu
First-Principles Calculations Of Piezoelectricity And Polarization Rotation In Lead Zirconate Titanate, Zhigang Wu
Dissertations, Theses, and Masters Projects
Recent experimental and theoretical work indicates that polarization rotation via a monoclinic phase at the morphotropic phase boundary in PZT is responsible for its large piezoelectric response. We performed Linearized augmented plane wave with the local orbital extension (LAPW+LO) method within local density approximation (LDA) on B-site [001]1:1 ordered Pb(Zr 0.5Ti0.5)O3 (PZT 50/50). We use a tetragonal super-cell and constrain it with monoclinic Cm space group. Atomic forces following the formulation of Yu et al. are calculated, and the conjugate gradient method is implemented to optimize the internal coordinates. Both the tetragonal (P4mm) and monoclinic (Cm) phases are reproduced, when …
Organism -Sediment Interactions: The Role Of Seabed Dynamics In Structuring The Mesohaline York River Macrobenthic Community, Elizabeth K. Hinchey
Organism -Sediment Interactions: The Role Of Seabed Dynamics In Structuring The Mesohaline York River Macrobenthic Community, Elizabeth K. Hinchey
Dissertations, Theses, and Masters Projects
Estuaries are dynamic physical environments. The stability of the sediment-water interface is influenced by sources and rates of sediment delivery and physical reworking of sediments by currents, tides, waves and biology, but effects of disruption of this interface on benthic biology are poorly resolved. For this study, I investigated effects of prevalent gradients in seabed disturbance processes and associated seabed characteristics on estuarine benthic community structure and function in the mesohaline York River, a tributary of Chesapeake Bay, USA. I used a variety of approaches to characterize the seabed, including sediment grain size, sediment water content, maximum depth of 7Be, …
Predicting Metal Interactions With A Novel Quantitative Ion Character -Activity Relationship (Qicar) Approach, David R. Ownby
Predicting Metal Interactions With A Novel Quantitative Ion Character -Activity Relationship (Qicar) Approach, David R. Ownby
Dissertations, Theses, and Masters Projects
Environmental toxicologists adopted QSARs from pharmacology fairly early on to predict organic contaminant toxicity. In contrast, models relating metal ion characteristics to their bioactivity remain poorly explored and underutillized. Quantitative Ion Character-Activity Relationships (QICARs) have recently been developed to predict metal toxicity. The QICAR approach based on metal-ligand binding tendencies has been applied to a wide range of effects, species, and media on a single metal basis. In previous single metal studies, a softness parameter and the ; log of KOH ; were the ion qualities with the highest predictive value for toxicity. Here, QICAR modeling was brought a step …
The Fusion And Integration Of Virtual Sensors, Thomas F. Litant
The Fusion And Integration Of Virtual Sensors, Thomas F. Litant
Dissertations, Theses, and Masters Projects
There are numerous sensors from which to choose when designing a mobile robot: ultrasonic, infrared, radar, or laser range finders, video, collision detectors, or beacon based systems such as the Global Positioning System. In order to meet the need for reliability, accuracy, and fault tolerance, mobile robot designers often place multiple sensors on the same platform, or combine sensor data from multiple platforms. The combination of the data from multiple sensors to improve reliability, accuracy, and fault tolerance is termed Sensor Fusion.;The types of robotic sensors are as varied as the properties of the environment that need to be sensed. …
Fate Of Organic Compounds Associated With Extractable And Bound Phases Of Estuarine Sediments Deposited Under Varying Depositional Regimes, Krisa Murray Arzayus
Fate Of Organic Compounds Associated With Extractable And Bound Phases Of Estuarine Sediments Deposited Under Varying Depositional Regimes, Krisa Murray Arzayus
Dissertations, Theses, and Masters Projects
Surficial sediments and sediment cores were collected from two distinct depositional regimes of the York River subestuary of Chesapeake Bay to document seasonal inputs, spatial variability, and longer-term (>40 years) fate of total organic carbon (TOC), lipid biomarker compounds and polycyclic aromatic hydrocarbons (PAHs). These regimes included biological mixing in the lower York and episodic mixing at the mid river site. Compounds were selected to represent a range of chemical reactivities, biological and anthropogenic sources, and modes of entry to the environment. The depositional environments were characterized with a suite of analytical tools: x-radiographs, Eh, 210Pb and 137Cs, total …
Development Of A Watershed And Stream-Reach Spawning Habitat Model For River Herring Alosa Pseudoharengus And Alosa Aestivalis, Rebecca A. Boger
Development Of A Watershed And Stream-Reach Spawning Habitat Model For River Herring Alosa Pseudoharengus And Alosa Aestivalis, Rebecca A. Boger
Dissertations, Theses, and Masters Projects
This research develops a model to identify indicators of potential suitable spawning habitat for river herring, Alosa pseudoharengus and A. aestivalis, using watershed and stream-reach metrics. The results of icthyoplankton samples collected from thirty-four streams feeding into the Rappahannock River below the Embree Dam at Fredericksburg indicate where river herring spawning occurred. Watershed and stream-reach metrics were either measured in the field or derived from digital data in a GIS. Benthic macroinvertebrate analysis was used to compare habitat quality among sites. Streams were classified as either absence or presence of herring eggs or larvae based on the results of the …
Effects Of Urbanization And Land Use On Pah Accumulation In Wetland Sediments, Kimani L. Kimbrough
Effects Of Urbanization And Land Use On Pah Accumulation In Wetland Sediments, Kimani L. Kimbrough
Dissertations, Theses, and Masters Projects
The relationship between wetland polycyclic aromatic hydrocarbon (PAH) concentrations and adjacent land use was assessed using surface sediments, sediment cores and global information systems (GIS) in the Elizabeth River, Virginia, an urbanized subestuary of the Chesapeake Bay. Wetlands adjacent to parking lots and petroleum industrial sites exhibited the highest PAH concentrations of all land uses in surfaces sediment and historically. Automobile and coal are the dominant sources of PAHs in wetland sediments historically as determined by relative concentration, fingerprinting and source specific compounds. An analysis of variance (ANOVA) test used to compare sixteen surface sediment sites based on land use …
Effects Of Habitat Fragmentation On The Utilization Of Eelgrass (Zostera Marina) By Mobile Epifauna And Macrofauna, Scott R. Marion
Effects Of Habitat Fragmentation On The Utilization Of Eelgrass (Zostera Marina) By Mobile Epifauna And Macrofauna, Scott R. Marion
Dissertations, Theses, and Masters Projects
The threat to biodiversity posed by increasing rates of anthropogenic habitat fragmentation necessitates an understanding of the consequences of spatial pattern for natural communities. Reduction of patch size, loss of habitat, changes in the quantity and proportion of habitat edge, and reduced connectivity among habitats can all shape ecological processes and faunal behavior. Seagrass habitats provide a natural model system for examining spatial inf1uences on marine fauna, but separating the effects of habitat structure, environmental conditions, and spatial pattern is difficult because shoot density, percent cover, and hydrodynamic regime often co-vary with patch size. This study used experimentally manipulated seagrass …
Comparison Of The Fate Of Dissolved Organic Matter In Two Coastal Systems: Hog Island Bay, Va (Usa) And Plum Island Sound, Ma (Usa), Tami L. Lunsford
Comparison Of The Fate Of Dissolved Organic Matter In Two Coastal Systems: Hog Island Bay, Va (Usa) And Plum Island Sound, Ma (Usa), Tami L. Lunsford
Dissertations, Theses, and Masters Projects
No abstract provided.
The Development Of A Water Quality Model In Baltimore Harbor, Back River, And The Adjacent Upper Chesapeake Bay, Hui Liu
Dissertations, Theses, and Masters Projects
No abstract provided.
Meta-Analysis And Modeling Of Benthic Oxygen And Nutrient Fluxes, Tyler Christensen
Meta-Analysis And Modeling Of Benthic Oxygen And Nutrient Fluxes, Tyler Christensen
Dissertations, Theses, and Masters Projects
No abstract provided.
Temporal And Spatial Variation In Reproductive Output Of The Veined Rapa Whelk (Rapana Venosa) In The Chesapeake Bay, Catherine C. Ware
Temporal And Spatial Variation In Reproductive Output Of The Veined Rapa Whelk (Rapana Venosa) In The Chesapeake Bay, Catherine C. Ware
Dissertations, Theses, and Masters Projects
No abstract provided.
Estimating Commercial Scallop Dredge Efficiency Through Vessel Tracking, Catch Data, And Depletion Models, Todd Gedamke
Estimating Commercial Scallop Dredge Efficiency Through Vessel Tracking, Catch Data, And Depletion Models, Todd Gedamke
Dissertations, Theses, and Masters Projects
No abstract provided.
Nekton Utilization Of Intertidal Fringing Salt Marsh And Revetment Hardened Shorelines, Robert A. Carroll
Nekton Utilization Of Intertidal Fringing Salt Marsh And Revetment Hardened Shorelines, Robert A. Carroll
Dissertations, Theses, and Masters Projects
No abstract provided.
Diet Composition Of Young-Of-The-Year Bluefish, Pomatomus Saltatrix, In The Lower Chesapeake Bay And Virginia's Coastal Ocean, James Gartland
Diet Composition Of Young-Of-The-Year Bluefish, Pomatomus Saltatrix, In The Lower Chesapeake Bay And Virginia's Coastal Ocean, James Gartland
Dissertations, Theses, and Masters Projects
No abstract provided.
An Evaluation Of Closed Area Boundaries Of The Sea Scallop Stock In The Middle Atlantic Bight, John David Lange
An Evaluation Of Closed Area Boundaries Of The Sea Scallop Stock In The Middle Atlantic Bight, John David Lange
Dissertations, Theses, and Masters Projects
No abstract provided.
Effects Of Longitudinal Disorder On The Magnetic Field Distribution In Bismuth Strontium Calcium Copper Oxide, Xuewen Wan
Dissertations, Theses, and Masters Projects
Transverse Field muon spin relaxation (TF-muSR) experiments were performed in external magnetic fields 1.0, 2.7, 3.0, 4.5, 5.5, 6.0 and 7.0 T along the Bi2212 crystalline c-axis. For the first time, the heterodyned fitting analysis technique shows that the field profiles on the ab basal planes of single crystal Bi2212 are symmetric in all experimental fields 1.0--7.0 T and at all experimental temperatures 2.0-90.0 K. The muon spin relaxation rates due to the mixed state of Bi2212 were found to increase linearly from 0 mus-1 at the transition temperature, 90.0 K, to about 1.0 mus -1 at the lowest temperature, …
Organic Matter Cycling In The York River Estuary, Virginia: An Analysis Of Potential Sources And Sinks, Leigh Mccallister
Organic Matter Cycling In The York River Estuary, Virginia: An Analysis Of Potential Sources And Sinks, Leigh Mccallister
Dissertations, Theses, and Masters Projects
A study of the organic matter (OM) sources and biogeochemical and physicochemical sinks was undertaken in the York River estuary, Virginia. The reactivity of dissolved organic carbon (DOC) was enhanced from ∼25--68% by the combined effects of exposure to natural sunlight and bacterial decomposition. In contrast, sunlight exposure decreased the bioreactivity of DOC in the higher salinity lower York by a factor of five. The combined effects of photochemical and bacterial processing were found to modify both the bioavailability and metabolic fate of OM (e.g. respiration vs. biomass). Stable isotopic (delta13C, delta15N) and radiocarbon (Delta14C) values of bacterial nucleic acids …
Genetic Stock Structure Of The Sailfish, Istiophorus Platypterus, Based On Nuclear And Mitochondrial Dna, Jan Renee Mcdowell
Genetic Stock Structure Of The Sailfish, Istiophorus Platypterus, Based On Nuclear And Mitochondrial Dna, Jan Renee Mcdowell
Dissertations, Theses, and Masters Projects
The results of life history studies involving the sailfish, Istiophorus platypterus, from the Atlantic, Pacific, and Indian oceans were reviewed. Results of studies agree on several aspects of sailfish biology; sailfish exhibit opportunistic feeding behavior, follow the 28??C isotherm, spawn in summer mature at approximately age 3, and are the least migratory of the billfishes. However, results are in conflict concerning sex ratio and whether sailfish are single or multiple spawners. Although many researchers have reported that sailfish are sexually dimorphic, their fragile otoliths make them difficult to age, aging studies have not been validated, and sexual dimorphism has not …
Coastal Zone Landscape Classification Using Remote Sensing And Model Development, Kevin R. Slocum
Coastal Zone Landscape Classification Using Remote Sensing And Model Development, Kevin R. Slocum
Dissertations, Theses, and Masters Projects
Coastal zone landscape characterization and empirical model development were evaluated using multi-spectral airborne imagery. Collectively, four projects are described that address monitoring and classification issues common to the resource management community. Chapter 1 discusses opportunities for remote sensing. Chapter 2 examines spectral and spatial image resolution requirements, as well as training sample selection methods required for accurate landscape classification. Classification accuracy derived from 25nm imagery with 4m pixel sizes outperformed 70nm imagery with 1m pixel sizes. Eight natural and five cultural landscape features were tested for classification accuracy. Chapter 3 investigated the ability to characterize 1m multispectral imagery into rank-ordered …
Oyster Reef Restoration In Virginia: Broodstock Addition & Nutrient Exchanges, Laurie Ann Sorabella
Oyster Reef Restoration In Virginia: Broodstock Addition & Nutrient Exchanges, Laurie Ann Sorabella
Dissertations, Theses, and Masters Projects
No abstract provided.
Ring Diameter And Closed Area Scallop Fisheries: The Performance Of A Dredge With 4" Rings In The Atlantic Sea Scallop (Placopecten Magellanicus) Fishery, In The Context Of An Area Rotation Management Scheme, Kevin D. Goff
Dissertations, Theses, and Masters Projects
No abstract provided.
Preparation And Characterization Of Polyimide/Organoclay Nanocomposites, Donavon Mark Delozier
Preparation And Characterization Of Polyimide/Organoclay Nanocomposites, Donavon Mark Delozier
Dissertations, Theses, and Masters Projects
The purpose of this research was to prepare nanocomposite materials comprised of exfoliated clay particles in a polyimide matrix. Poly(amide acid)/organoclay solutions and polyimide/organoclay films were prepared and the clay dispersion was characterized by visual inspection, XRD, and TEM. Mechanical measurements and certain thermal characterization measurements were also obtained. The research began by attempting to repeat the procedures set forth in the literature. Most of the polyimide/organoclay nanocomposites were being prepared by mixing prepared poly(amide acid) solutions with organoclay solutions. This simple mixing technology was used in the preparation of various polyimide/organoclay hybrid formulations. In-situ polymerization, which involved performing the …
Simulation Techniques In An Artificial Society Model, Barry Glenn Lawson
Simulation Techniques In An Artificial Society Model, Barry Glenn Lawson
Dissertations, Theses, and Masters Projects
"Artificial society" refers to a generic class of agent-based simulation models used to discover global social structures and collective behavior produced by simple local rules and interaction mechanisms. Artificial society models are applicable in a variety of disciplines, including the modeling of chemical and biological processes, natural phenomena, and complex adaptive systems. We focus on the underlying simulation techniques used in artificial society discrete-event simulation models, including model time evolution and computational performance.;Although for some applications synchronous time evolution is the correct modeling approach, many other applications are better represented using asynchronous time evolution. We claim that asynchronous time evolution …
Simulation And Numerical Solution Of Stochastic Petri Nets With Discrete And Continuous Timing, Robert Linzey Jones Iii
Simulation And Numerical Solution Of Stochastic Petri Nets With Discrete And Continuous Timing, Robert Linzey Jones Iii
Dissertations, Theses, and Masters Projects
We introduce a novel stochastic Petri net formalism where discrete and continuous phase-type firing delays can appear in the same model. By capturing deterministic and generally random behavior in discrete or continuous time, as appropriate, the formalism affords higher modeling fidelity and efficiencies to use in practice. We formally specify the underlying stochastic process as a general state space Markov chain and show that it is regenerative, thus amenable to renewal theory techniques to obtain steady-state solutions. We present two steady-state analysis methods depending on the class of problem: one using exact numerical techniques, the other using simulation. Although regenerative …
Aggregate Matrix-Analytic Techniques And Their Applications, Alma Riska
Aggregate Matrix-Analytic Techniques And Their Applications, Alma Riska
Dissertations, Theses, and Masters Projects
The complexity of computer systems affects the complexity of modeling techniques that can be used for their performance analysis. In this dissertation, we develop a set of techniques that are based on tractable analytic models and enable efficient performance analysis of computer systems. Our approach is three pronged: first, we propose new techniques to parameterize measurement data with Markovian-based stochastic processes that can be further used as input into queueing systems; second, we propose new methods to efficiently solve complex queueing models; and third, we use the proposed methods to evaluate the performance of clustered Web servers and propose new …