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Articles 1 - 30 of 36
Full-Text Articles in Physical Sciences and Mathematics
Correspondence Between Environmental Gradients And The Assemblage Structure Of Littoral Fishes In The Tidal Portion Of Three Virginia Coastal Plain Rivers, Clifford Michael Wagner
Correspondence Between Environmental Gradients And The Assemblage Structure Of Littoral Fishes In The Tidal Portion Of Three Virginia Coastal Plain Rivers, Clifford Michael Wagner
Dissertations, Theses, and Masters Projects
No abstract provided.
On The Circulation Of The Northern North Sea And The Patagonian Shelf, Pablo D. Glorioso
On The Circulation Of The Northern North Sea And The Patagonian Shelf, Pablo D. Glorioso
Dissertations, Theses, and Masters Projects
The Northern North Sea and the Patagonian Shelf have similar characteristics, and their circulation is determined by strong tidal regimes, significant wind-driven flow, and by density gradients to a lesser degree. The influence of oceanic currents is notable in the Patagonian Shelf, where the Falkland Current flows along the shelf edge, but less important in the North Sea. While the North Sea is perhaps the most studied body of water in the world, the circulation of the Patagonian Shelf have remained fairly unknown. This study presents evidence of near-inertial oscillations in the Northern North Sea, not reported previously, derived from …
Correlation Of Dynamic Dielectric Properties To Reaction Kinetics And Changing Mechanical Properties Of Epoxy Resins During Cure, Yunfei Wang
Dissertations, Theses, and Masters Projects
The principal objective of this paper is to describe how complex impedance, obtained from frequency dependent dielectric sensing technique, can be used as an effective diagnostic tool for in situ real-time investigation in the fabrication of thermoset structures.;Two epoxy systems (Pr500 from 3M and My720 from Ciba Geigy) with different functionality are characterized in terms of their dielectric, thermal, and rheological behavior. It is observed that there is a one to one relationship between Tg and conversion which is independent of cure temperature. The chemical kinetics of the reaction is satisfactorily described by an autocatalyzed reaction mechanism. The chemical rate …
Development Of Supercritical Fluid Extraction (Sfe) For The Determination Of Polychlorinated Biphenyls In Tissues Of Aquatic Biota, Michael O. Gaylor
Development Of Supercritical Fluid Extraction (Sfe) For The Determination Of Polychlorinated Biphenyls In Tissues Of Aquatic Biota, Michael O. Gaylor
Dissertations, Theses, and Masters Projects
No abstract provided.
The Promotion Of Poly(Methyl Methacrylate) Depolymerization By Metal-Based Initiators, Jason Andrew Macko
The Promotion Of Poly(Methyl Methacrylate) Depolymerization By Metal-Based Initiators, Jason Andrew Macko
Dissertations, Theses, and Masters Projects
No abstract provided.
Small Mammal Habitat Uses Of Two Natural And Created Wetlands In Southeastern Virginia, Amanda Mckenney Mueller
Small Mammal Habitat Uses Of Two Natural And Created Wetlands In Southeastern Virginia, Amanda Mckenney Mueller
Dissertations, Theses, and Masters Projects
No abstract provided.
Polycyclic Aromatic Hydrocarbon (Pah) Distributions Within Urban Estuarine Sediments, Siddhartha Mitra
Polycyclic Aromatic Hydrocarbon (Pah) Distributions Within Urban Estuarine Sediments, Siddhartha Mitra
Dissertations, Theses, and Masters Projects
Sediments and pore waters from two urban estuaries ranging in sediment mixing energy were studied to evaluate the potential release of contaminants from particles during sediment diagenesis. Two sites in Elizabeth River, VA and two tributaries in the Hudson River Watershed were sampled for polycyclic aromatic hydrocarbons (PAHs). Sediment age, total sediment organic carbon (TOC), carbon to nitrogen (C/N) ratios, and particle surface area (SA) were also sampled at these sites. In the Elizabeth River, both sites sampled (Site 1 and Site 2) have been non-depositional for the past 70 y or are comprised of old dredge spoil. PAH K&\sp\prime\sb{lcub}\rm …
On-Line System Identification For Control System Applications In Particle Accelerators, Mahesh Chowdhary
On-Line System Identification For Control System Applications In Particle Accelerators, Mahesh Chowdhary
Dissertations, Theses, and Masters Projects
Particle accelerators require a number of feedback systems in order to stabilize a variety of parameters. The Continuous Electron Beam Accelerator at Thomas Jefferson National Accelerator Facility presents a unique set of control and identification problems. This accelerator produces a continuous electron beam with energies between 0.5 and 4.0 GeV to be delivered to the experimental halls. In order to meet stringent beam quality requirements specified by the experimental halls, the position and the energy of the electron beam needs to stabilized at various locations in the accelerator.;A number of noise measurement tests were conducted at various locations in the …
The Synthesis Of Reflective And Electrically Conductive Polyimide Films Via An In Situ Self-Metallization Procedure Using Silver(I) Complexes, Robin Elaine Southward
The Synthesis Of Reflective And Electrically Conductive Polyimide Films Via An In Situ Self-Metallization Procedure Using Silver(I) Complexes, Robin Elaine Southward
Dissertations, Theses, and Masters Projects
Optically reflective polyimide films have been prepared by the incorporation of silver(I) acetate and a {dollar}\beta{dollar}-diketone solubilizing agent, hexafluoroacetylacetone (HFAH), into a dimethylacetamide solution of the poly(amic acid) formed from {dollar}3,3\sp\prime,4,4\sp\prime{dollar}-benzophenonetetracarboxylic acid dianhydride (BTDA) and {dollar}4,4\sp\prime{dollar}-oxydianiline {dollar}(4,4\sp\prime{dollar}-ODA). Optically reflective and conductive polyimide films have been prepared by replacing the {dollar}\beta{dollar}-diketone (HFAH), with the less substituted {dollar}\beta{dollar}-diketone, trifluoroacetylacetone (TFAH). The former system has been both cast directly from the poly(amic acid) resin and cast from the poly(amic acid) resin onto a fully imidized {dollar}\rm BTDA/4,4\sp\prime{dollar}-ODA base (forming a metallized topcoat). Thermal curing of the silver(I)-containing poly(amic acid) leads to imidization with …
The Synthesis Of 6a,6b-Dideoxy-6 A,6b-(9,10-Dicyanoanthracenyl-2,3-Dimethylene)-Beta-Cyclodextrin, Jonathan D. Tan
The Synthesis Of 6a,6b-Dideoxy-6 A,6b-(9,10-Dicyanoanthracenyl-2,3-Dimethylene)-Beta-Cyclodextrin, Jonathan D. Tan
Dissertations, Theses, and Masters Projects
No abstract provided.
Collision-Induced Secondary Electron And Negative Ion Emission From Metallic Surfaces, John Christopher Tucek
Collision-Induced Secondary Electron And Negative Ion Emission From Metallic Surfaces, John Christopher Tucek
Dissertations, Theses, and Masters Projects
Absolute yields of negative ions and secondary electrons resulting from collisions of positive sodium ions (Na{dollar}\sp{lcub}+{rcub}){dollar} with polycrystalline aluminum (Al) and molybdenum (Mo) surfaces and the Mo (100) surface have been measured as a function of the oxygen (O) coverage, from none up to several monolayers, for impact energies, E {dollar}<{dollar} 500 eV. Negative oxygen ions (O{dollar}\sp{lcub}-{rcub}){dollar} are found to be the dominant sputtered negative ions and for the three surfaces at all O coverages and Na{dollar}\sp{lcub}+{rcub}{dollar} impact energies. The O{dollar}\sp{lcub}-{rcub}{dollar} and secondary electron yields share a common impact energy threshold at {dollar}\rm E\sb{lcub}th{rcub}\approx 50{dollar} eV, and both have a strong dependence on the oxygen coverage of the surface.;The kinetic energy distributions of the secondary electrons and sputtered O{dollar}\sp{lcub}-{rcub}{dollar} were determined as functions of O coverages and impact energies. The O{dollar}\sp{lcub}-{rcub}{dollar} distributions are characterized by a narrow, low energy peak (at {dollar}\sim{dollar}1-2 eV) followed by a low level, high energy tail. The secondary electrons have a narrow (FWHM {dollar}\sim{dollar} 1-2 eV) kinetic energy distribution, centered essentially at the same most probable kinetic energy as the ions. The shapes of the respective distributions and the most probable kinetic energies are essentially invariant with the impact energy, O coverage and the metal surface.;The results were analyzed in terms of conventional collision cascade model, but the calculation could not be fitted to the experimental results. An electronic excitation mechanism is proposed to augment the collision cascade and to provide a mechanism for secondary electron emission. In the model, adsorbed O, which resides on the surface essentially as O{dollar}\sp{lcub}-{rcub},{dollar} is collisionally excited into an (MO{dollar}\sp{lcub}-{rcub})\sp*{dollar} repulsive state, and as the O{dollar}\sp{lcub}-{rcub}{dollar} exits the surface along the surface potential energy curve, it can decay by emission of an electron to the metal or to the vacuum, or it can survive as an ion. The parameters of this model can be adjusted such that the calculated kinetic energy distribution, together with that of the collision cascade, can reasonably reproduce the experimental observations for the ions and provide a reasonable fit to the corresponding electron kinetic energy distributions as well.
Thermal Lattice Boltzmann Simulations Of Variable Prandtl Number Turbulent Flow, Min Soe
Thermal Lattice Boltzmann Simulations Of Variable Prandtl Number Turbulent Flow, Min Soe
Dissertations, Theses, and Masters Projects
With the advent of massively parallel processor machines, thermal lattice Boltzmann equation (TLBE) techniques offer an attractive way of handling turbulence simulations. TLBE is new form of DNS (direct numerical simulation method)--with the important advantages of being ideal for multi-parallel processors as well as being able to handle complicated geometries. Since there are many kinetic models that will reproduce the macroscopic nonlinear (compressible) transport equations, TLBE chooses that subset which can be readily solved on a discrete spatial lattice. The lattice geometry must be so chosen that the discrete phase representation of TLBE will not taint the rotational symmetric continuum …
Targeting Wetland Preservation Areas For Compensatory Mitigation Utilizing A Gis Protocol, Lynn M. Dancy
Targeting Wetland Preservation Areas For Compensatory Mitigation Utilizing A Gis Protocol, Lynn M. Dancy
Dissertations, Theses, and Masters Projects
No abstract provided.
Cp Violation In K-Long Decays, Gregory Dominick Dorata
Cp Violation In K-Long Decays, Gregory Dominick Dorata
Dissertations, Theses, and Masters Projects
The main topic of this dissertation concerns alternative models of CP violation and the rates predicted by these models for the particular decay {dollar}K\sb{lcub}L{rcub}\to\pi\sp0\nu\bar\nu .{dollar} This decay is promising as a probe of the origin of CP violation in the kaon system. It is virtually free of hadronic uncertainties and its branching ratio would (along with a measurement of the CP asymmetry in {dollar}B\sbsp{lcub}d{rcub}{lcub}0{rcub}\to\psi K\sb{lcub}S{rcub}){dollar} allow a determination of all the elements of the CKM matrix (assuming all CP violation arises from the CKM matrix).;The first group of models of CP violation considered consists of three extensions of the Higgs …
Propagation Of Rayleigh Waves In Thin Films, Agus A. Ananda
Propagation Of Rayleigh Waves In Thin Films, Agus A. Ananda
Dissertations, Theses, and Masters Projects
With the advent of thin film technology and more recently its applications in microelectronics and control of surface properties, the interest in mechanical properties of thin films has grown tremendously. Mechanical defects such as creep, fracture and adhesion loss, play a very important role in physical instabilities of thin film materials. An acoustic microscope has been built to study mechanical properties of thin-films. The microscope operates at a nominal frequency of 50 MHz. Rayleigh surface waves velocities on the surface of film-substrate systems were measured from V(z) curves generated by the acoustic microscope. V(z) curves are produced from interference between …
Winter/Spring Steady-State Water Balances For A Palustrine Forested Wetland Located In Southeastern Virginia, Daniel Otis Redgate
Winter/Spring Steady-State Water Balances For A Palustrine Forested Wetland Located In Southeastern Virginia, Daniel Otis Redgate
Dissertations, Theses, and Masters Projects
No abstract provided.
Climatologically Forced Coherence Between Diverse Juvenile Populations In The Virginia Tributaries To The Chesapeake Bay, Thomas C. Mosca Iii
Climatologically Forced Coherence Between Diverse Juvenile Populations In The Virginia Tributaries To The Chesapeake Bay, Thomas C. Mosca Iii
Dissertations, Theses, and Masters Projects
Long term trends in juvenile recruitment of oyster, bluecrab, and 24 species of finfish in a large temperate estuary (lower Chesapeake Bay, USA) are coherent across the three major tributaries (the Virginia rivers James, York, and Rappahannock). The driving force for these long term trends is geographically large in scale. Anomalous winters in the mid 1970's, with the warmest years on record followed immediately by the coldest, caused a severe perturbation in population dynamics. The extreme conditions caused the system to shift, with recruitment patterns following temperatures by a one year lag. Following this anomalous episode, smoothed mean winter water …
Response Modes Of The Lower Chesapeake Bay Wave Field, Katherine L. Farnsworth
Response Modes Of The Lower Chesapeake Bay Wave Field, Katherine L. Farnsworth
Dissertations, Theses, and Masters Projects
An extensive wave monitoring program was conducted in the lower Chesapeake Bay from fall 1989 through spring 1995. From October 23, 1992 - April 20, 1993 the Virginia Institute of Marine Science deployed an aluminum tetrapod containing wave and current sensing and recording equipment in the Thimble Shoal region of the lower Chesapeake Bay. Measurements were made in half hour bursts every three hours to document the area’s dynamic wave characteristics. It was shown previously by Boon et al. (1990 - 1996) that a bimodal frequency distribution of waves in the Thimble Shoal region existed, which was not seen in …
Effects Of Spot (Leisostomus Xanthurus) Induced Bioturbation And Suspension On The Transport And Fate Of Sediments And A Particle-Associated Organic Contaminant, Michele A. Horvath
Effects Of Spot (Leisostomus Xanthurus) Induced Bioturbation And Suspension On The Transport And Fate Of Sediments And A Particle-Associated Organic Contaminant, Michele A. Horvath
Dissertations, Theses, and Masters Projects
No abstract provided.
New Data On Ichthyoplankton Of The Southwestern Pacific, Andrei V. Suntsov
New Data On Ichthyoplankton Of The Southwestern Pacific, Andrei V. Suntsov
Dissertations, Theses, and Masters Projects
No abstract provided.
Analysis Of Mercury Coordination Environments Of Tridentate And Tetradentate Nitrogen Based Ligands By Nmr Spectroscopy And X-Ray Crystallography, Rachel E. Freer
Analysis Of Mercury Coordination Environments Of Tridentate And Tetradentate Nitrogen Based Ligands By Nmr Spectroscopy And X-Ray Crystallography, Rachel E. Freer
Dissertations, Theses, and Masters Projects
No abstract provided.
The Thermal Cure Of Phenylethynyl-Terminated Polyimides And Selected Model Compounds, Karen H. Wood
The Thermal Cure Of Phenylethynyl-Terminated Polyimides And Selected Model Compounds, Karen H. Wood
Dissertations, Theses, and Masters Projects
The ability to process high performance polymers into useful adhesives and high quality composites has been significantly advanced by synthetic techniques in which oligomers terminated with reactive groups cure or crosslink at elevated temperature after the article has been fabricated. Several matrix resin systems of considerable interest to the aerospace community utilize phenylethynyl terminated imide (PETI) technology developed at the Langley Research Center to achieve this advantage. This work addresses the cure chemistry of PETI oligomers.;The thermal cure of selected oligomers and model compounds was studied using a variety of analytical techniques including differential scanning calorimetry, high pressure liquid chromatography, …
Solar Infrared Relative Intensity Data From The Halogen Occultation Experiment, Philip Todd Spickler
Solar Infrared Relative Intensity Data From The Halogen Occultation Experiment, Philip Todd Spickler
Dissertations, Theses, and Masters Projects
Solar data from the Halogen Occultation Experiment (HALOE) were analyzed to determine the center-to-limb relative intensity and the vertical temperature profile for the quiet and active Sun over wavelengths from 2.4 to 10 {dollar}\mu{dollar}m. An algorithm that incorporated a nonlinear least squares procedure was developed that modeled the HALOE instrument during data acquisition. Data obtained from limb-to-limb scans along the solar equator on days of very low activity in May 1994 were analyzed to obtain coefficients of a function describing the relative intensity from center to limb. The relative intensities produced were precise to 0.1% (2{dollar}\sigma{dollar}) from the center to …
Microstructures Of Poly(Vinyl Acetate) Studied By Nuclear Magnetic Resonance Spectroscopy, Hongyang Yao
Microstructures Of Poly(Vinyl Acetate) Studied By Nuclear Magnetic Resonance Spectroscopy, Hongyang Yao
Dissertations, Theses, and Masters Projects
Carbon-13 NMR spectroscopy was used to investigate the microstructures of poly(vinyl acetate) prepared by solution polymerization in benzene. A series of aromatic compounds was synthesized in order to model the structures formed via chain transfer to solvent. The peaks near 126.5 and 128.5 ppm in the spectra of the polymer samples were assigned to a 1-phenyl-(2n + 1)-multi-acetoxyalkane (where n = 1, 2, 3, etc.) microstructure. The concentration of that structure obtained from NMR spectra was correlated with the concentration calculated from reported kinetic data.;Chain transfer to benzene was shown to occur by addition of the macroradical to benzene, followed …
Spatial, Geostatistical, And Fractal Measures Of Seafloor Microtopography Across The Eel River Shelf, Off Northern California, George Randall. Cutter
Spatial, Geostatistical, And Fractal Measures Of Seafloor Microtopography Across The Eel River Shelf, Off Northern California, George Randall. Cutter
Dissertations, Theses, and Masters Projects
No abstract provided.
Distribution Of Freshwater Amphipoda In The Lake Matoaka/College Woods Area, Williamsburg, Virginia, Susan Alexandra Mahon
Distribution Of Freshwater Amphipoda In The Lake Matoaka/College Woods Area, Williamsburg, Virginia, Susan Alexandra Mahon
Dissertations, Theses, and Masters Projects
No abstract provided.
Radiation-Induced Luminescence In Terbium-Doped Silicate Glasses, Michael Stuart West
Radiation-Induced Luminescence In Terbium-Doped Silicate Glasses, Michael Stuart West
Dissertations, Theses, and Masters Projects
The purpose of this study is to characterize radiation-induced luminescence of terbium-doped silicate glasses. Experiments performed investigated the optical properties, isothermal time-evolution, and temperature dependence of the radiation-induced luminescence of two commercially available terbium-doped glasses. A problem common to this type of glass is the persistent luminescence, or afterglow, that occurs following the end of excitation from an external source of radiation. While the processes that govern characteristic luminescence of rare earth ions, including terbium, are well understood, the processes that give rise to afterglow in doped glasses are not. Identifying the source of long-term luminescence is essential for controlling …
The Synthesis Of Benzophenone-3,5-Diacid Chloride For The Double Capping Of Beta-Cyclodextrin, Clyde Wesley Eargle
The Synthesis Of Benzophenone-3,5-Diacid Chloride For The Double Capping Of Beta-Cyclodextrin, Clyde Wesley Eargle
Dissertations, Theses, and Masters Projects
No abstract provided.
The Selective Oxidation Of Beta-Cyclodextrin On The Secondary Face, Christine Evelyn Heath
The Selective Oxidation Of Beta-Cyclodextrin On The Secondary Face, Christine Evelyn Heath
Dissertations, Theses, and Masters Projects
No abstract provided.
Discrete-Time Linear And Nonlinear Aerodynamic Impulse Responses For Efficient Cfd Analyses, Walter A. Silva
Discrete-Time Linear And Nonlinear Aerodynamic Impulse Responses For Efficient Cfd Analyses, Walter A. Silva
Dissertations, Theses, and Masters Projects
This dissertation discusses the mathematical existence and the numerical identification of linear and nonlinear aerodynamic impulse response functions. Differences between continuous-time and discrete-time system theories, which permit the identification and efficient use of these functions, will be detailed. Important input/output definitions and the concept of linear and nonlinear systems with memory will also be discussed. It will be shown that indicial (step or steady) responses (such as Wagner's function), forced harmonic responses (such as Theodorsen's function or those from doublet lattice theory), and responses to random inputs (such as gusts) can all be obtained from an aerodynamic impulse response function. …