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Theses/Dissertations

William & Mary

2002

Articles 31 - 35 of 35

Full-Text Articles in Physical Sciences and Mathematics

Fate Of Organic Compounds Associated With Extractable And Bound Phases Of Estuarine Sediments Deposited Under Varying Depositional Regimes, Krisa Murray Arzayus Jan 2002

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 …

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The Fusion And Integration Of Virtual Sensors, Thomas F. Litant Jan 2002

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. …

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First-Principles Calculations Of Piezoelectricity And Polarization Rotation In Lead Zirconate Titanate, Zhigang Wu Jan 2002

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 …

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Development Of A Watershed And Stream-Reach Spawning Habitat Model For River Herring Alosa Pseudoharengus And Alosa Aestivalis, Rebecca A. Boger Jan 2002

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 …

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Estuarine Suspended Aggregate Dynamics And Characteristics, David C. Fugate Jan 2002

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 …

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