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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Stratigraphic Distribution, Taphonomy, and Isotope Paleoecology of the Dinosaurian Fauna in the latest Campanian lower Horseshoe Canyon Formation, Alberta, Canada

Straight, William Herbert 02 June 2003 (has links)
Vertebrate fossils in the lower Horseshoe Canyon Formation are remains of dinosaurs, crocodilians, champsosaurs, turtles, and fish supported during the last ~2 m.y. of the Campanian by a coastal lake-strewn wetland occupying what is now south-central Alberta, Canada. Bones accumulated on the floodplain through attritional mortality and are preserved unweathered except for surface polish, scratches, and mottling characteristic of bioturbation during rapid burial in fine-grained sediment. Fossil-bearing sites cluster stratigraphically in laterally extensive horizons between thicker less fossil-rich intervals of similar fluvial strata. These horizons, formed by a long-term balance between bone supply, accommodation, and depositional rate, result from a newly recognized ?floodplain fill? mode of preservation for vertebrate fossils and are analogous to marine condensed sections. Like condensed sections, these fossiliferous horizons lie adjacent to lithostratigraphic surfaces created by stillstands in base-level. Together, hiatal surfaces and fossiliferous horizons reveal repeating rhythms in the facies distribution and fluvial architecture. These rhythms, ?packages? of strata bounded by hiatal surfaces, arose through two scales of variation in base-level: a grand-scale base-level cycle reflecting tectonic control during the construction of the clastic wedge, and a smaller ?package?-scale cycle reflecting Milankovitch control over local climate and precipitation. Both the fluvial architecture and the accumulations of fossils are a consequence of this change in accommodation and sediment supply through time. Fossil evidence does not indicate a faunal change through time, but changes in climate through time resulted in a reduction in organic-rich mudrocks and coal, an increase in soil development, and changes in the dominant configuration for fossil preservation from sparse bonebeds to microsites. Climate change was also investigated through stable oxygen isotopes in tyrannosaur tooth enamel phosphate, which daily recorded the response of surface (drinking) water to changes in humidity and temperature. The enamel isotopic record shows a transition from highly variable, seasonal climate to relatively constant conditions, consistent with the interpretation of change in the stratigraphy and taphonomy. This combined application of architectural stratigraphy, vertebrate taphonomy, and stable isotope paleoecology represents a new approach for paleontologists interested in evaluating changes through geologic time in paleoenvironment and animal communities in a fluvial succession.
12

Internal Tides and Internal Solitary Waves in the Northern South China Sea

Kim, Sungphil 20 July 2009 (has links)
Large-amplitude internal solitary waves (ISWs) are frequently observed in the northern South China Sea (SCS). In a project sponsored by the US Office of Naval Research, four moorings were deployed between the Luzon Strait and the Chinese continental shelf by Steve Ramp of the Naval Postgraduate School and David Tang of National Taiwan University from late April 2005 to May 2006. Several CTD sections were taken during April and July in 2005. Satellite pictures were also collected during that period. In this study, these data were used to examine the characteristics, generation, and propagation of ISWs. In the satellite images, monthly change in stratification may cause northward shift of the propagation path, and ISWs are more frequently observed in July than in April and May. Speed estimation shows that ISWs propagate faster in the deep basin than over the continental margin and near the ridge. The generation of internal tides correlates with the eastward tidal flow over the ridge, while ISWs are produced by northwestward tidal currents over the ridges in the Luzon Strait.
13

Investigation of Aerosol Single Scattering Albedo in the Ultraviolet Spectrum

Petters, Jonathan Leonard 02 July 2002 (has links)
Single scattering albedo (omega), the ratio of scattering coefficient to total extinction coefficient, at UV wavelengths is an important aerosol radiative parameter in determining surface UV irradiance. Surface measurements of total and diffuse UV irradiance in the summer and fall of 1999 at the seven narrowband wavelength channels of an UV multifilter rotating shadowband radiometer (UVMFR-SR) at Black Mountain, NC were coupled with a tropospheric ultraviolet radiative transfer model to produce values of omega. Its value ranged from 0.53 ? 0.94 at 300 nm to 0.55 ? 1.00 at 368 nm. Error in this procedure decreases with increasing aerosol optical depth (AOD), from +/-0.19 at AOD = 0.05 to +/-0.02 at AOD=1.0. Values of omega were not found to be correlated with air mass origin. The current values of omega have a wider variation than values reported from a previous study at the same site, possibly attributable to changes in aerosol chemical composition over time. The value of omega was found to be quadratically correlated with wavelength. Little research has been conducted in the scattering and absorption properties of aerosols in the UV wavelengths, but what has been done suggests such a correlation is possible. More values of omega in the UV spectrum will allow for better estimation of this parameter for UV radiative transfer modeling and will lessen error in estimation of surface UV irradiances.
14

Population dynamics and stock assessment of the blue crab in North Carolina

Johnson, Eric Gordon 07 June 2004 (has links)
The blue crab (Callinectes sapidus) is an ecologically important estuarine predator and represents North Carolina?s most important commercial fishery. Recent fishery-dependent and ?independent data suggest the population is declining. The goal of this study was to increase our understanding of the status and population dynamics of the blue crab in NC by addressing the following objectives: (1) estimate population demographics of blue crabs in salt marsh creeks, (2) construct a discontinuous model of blue crab growth in NC using growth rates estimated from free-ranging blue crabs, and (3) provide a comprehensive stock assessment for the blue crab in NC. A series of complimentary laboratory and field studies assessed the nursery role of salt marsh habitats for the blue crab (Callinectes sapidus). Population demographics and movement patterns of juvenile and adult blue crabs were quantified in two tidal salt marsh creeks near Beaufort, North Carolina, USA during June ? October 2001. While there are many studies that report estimates of population density, mortality rates, or movement rates for blue crabs, this study represents one of the first attempts to estimate all quantities concurrently. Juvenile crabs were mobile within the interstices of the vegetated marsh surface during flood tide, and were equally distributed buried in intertidal marsh and adjacent mud areas during ebb tide. Juvenile crabs may experience a spatial refuge from cannibalism in the marsh surface since adult conspecifics are physically impeded by dense vegetation and rarely move far into marsh habitats. This spatial refuge in the vegetated marsh surface may be significant, since cannibalism represents a large source of mortality for this species. The relatively high use of the marsh surface by juvenile blue crabs, combined with a general lack of sampling these complex habitats, suggest that crab densities may be even higher in salt marsh systems than previously thought. Growth models commonly used in fisheries and ecological modeling assume growth is a continuous function of age. While this approach is appropriate for finfish, the validity of these models for crustacean species, which grow discontinuously, has been questioned. There is a critical need to compare the predictions of discontinuous and continuous models simultaneously to identify if potential biases are introduced by the assumption of continuous growth for the blue crab. The blue crab stock in North Carolina currently sustains heavy exploitation by the commercial fishery, and information on the recreational fishery is generally lacking. There has been a systematic increase in commercial landings from 1987-1999, followed by a period of reduced landings from 2000-2002. During this period fishery-independent indices of abundance have remained stable, or have shown a significant decline. In no case have any indices of abundance shown an increasing trend. Moreover, adult and spawning stock abundance (SSB) during 2000-2001 were at the lowest levels recorded since 1987, and the mean size of mature females has declined significantly during 1987-2003. Increases in the index of relative SSB in 2002-2003, however, may indicate a recovery. We detected a significant stock-recruit relationship for the blue crab in North Carolina using certain estimates of recruit abundance and recommend an urgent need for conservation of the spawning stock. We encourage decision makers to use the information and recommendations in this dissertation as soon as possible to manage the blue crab fishery in NC in a sustainable manner.
15

A Re-Analysis of the Skull of Acrocanthosaurus atokensis (NCSM 14345): Implications for Allosauroid Morphology, Phylogeny, and Biogeography

Eddy, Drew Richard 08 August 2008 (has links)
Considerable debate has surrounded the phylogenetic position of the large-bodied theropod Acrocanthosaurus atokensis from the Early Cretaceous Antlers Formation of North America. Many phylogenetic analyses place Acrocanthosaurus as the sister taxon to the smaller- bodied Allosaurus, known from formations in North America and Europe, whereas others recover it as a member of Carcharodontosauridae, a derived group of large-bodied allosauroids that inhabited Gondwana. Re-examination of a well-preserved skull of Acrocanthosaurus (NCSM 14345) has provided new information regarding the morphology of the palatal complex and inner surfaces of the skull and mandible, features that were obscured by a sediment matrix during a previous description. From this revised description, twenty-three new characters were identified and added to a data matrix (164 characters; 17 terminals), the analysis of which recovered a single most parsimonious tree placing Acrocanthosaurus as a derived member of Carcharodontosauridae. This hypothesis is supported by several shared cranial characteristics, including: a sinuous medial groove for the maxillary dental lamina; a small accessory process between the quadratojugal prongs of the jugal; and a dorsal curvature of the jugal ramus of the ectopterygoid. The phylogeny recovered by this analysis fit significantly better with the stratigraphic record than previous hypotheses that place Acrocanthosaurus as more closely related to Allosaurus, a finding supported by visual assessment of phylograms and stratigraphic consistency metrics. An analysis of the paleobiogeography of Allosauroidea found Asia to be the most likely ancestral area for the clade, consistent with previous analyses. Distribution of carcharodontosaurid ancestors likely reached both North America and Gondwana during the Valanginian or Barremian stages, with Europe providing a connection between the two continents.
16

Biological and Operational Factors Causing Mortality in North Carolina's Soft-Shell Blue Crab Industry

Chaves, Juan Carlos 07 August 2002 (has links)
Factors causing mortality in North Carolina's soft-shell blue crab industry were quantified and identified at 11 crab shedding systems across the state. Operators of crab shedding systems who shed peeler crabs (pre-molt crabs) that they had caught themselves (self-caught peeler crabs) experienced significantly lower crab mortality rates than operators who shed peelers that they had bought from different sources (purchased-peeler crabs). Molt stage had a significant effect on the mortality rates of self-caught peeler crabs, as early molt stage crabs (white-line peelers) suffered significantly higher mortality rates than late molt stage crabs (red-line peelers). Purchased male crabs experienced significantly higher mortality rates than purchased females crabs. Water quality did not have a significant effect on crab mortality. Male peeler crab mortality was not significantly affected by the presence or absence of female red-line peeler crabs. Male red-line peelers experienced significantly longer times to molt when male crab density was high. Results of this study may lead to improvements in crab shedding technology, increased profits, and better fishery management practices.
17

An Analysis of the Physical Processes and Model Representation of Cold Air Damming Erosion

Stanton, Wendy Marie 11 August 2003 (has links)
The occurrence of Appalachian cold air damming (CAD) is often associated with significant sensible weather impacts throughout the Carolinas and Virginia. CAD sensible weather, defined as below-normal maximum temperatures, overcast skies, fog, and reduced visibility, can often persist in the damming region for days. Furthermore, the confinement of a dome of low-level cold air along the eastern slopes of the Appalachians can create an environment ideal for freezing rain and sleet. Such potentially hazardous conditions necessitate accurate and timely forecasting in order to properly warn the public. Despite this need for reliable CAD prediction, accurate forecasting of the magnitude of sensible weather impacts and the timing of CAD demise are extremely challenging. Furthermore, many operational numerical weather prediction models do not accurately simulate CAD events. One of the more common problems associated with model forecasts is the premature erosion of the CAD cold dome and the underestimation of the duration of CAD sensible weather. A better understanding of the physical processes involved in cold dome erosion would lead to improved erosion forecasting by increasing forecaster awareness of the signs of CAD erosion and by isolating physical processes that may be poorly handled by operational models. <br> <br>One objective of this research is to describe the common synoptic patterns evident during the erosion period of CAD events. These synoptic erosion scenarios are representative of the physical mechanisms contributing to cold dome erosion. To accomplish this objective, 89 classical CAD events detected by the algorithm of Bailey et al. (2003) were grouped according to similarities in sea-level pressure and surface potential temperature fields. Composite maps of each group were created, resulting in five CAD erosion scenarios: (1) Northwestern Low, (2) Cold Frontal Passage, (3) Coastal Low, (4) Residual Cold Pool, and (5) Southwestern Low. High levels of statistical significance were associated with the dominant synoptic features in all scenarios except the Southwestern Low, suggesting that the remaining four scenarios effectively represented distinct erosion patterns. Several potential erosion mechanisms could be inferred from the evolution of dominant synoptic features in each erosion scenario. Multiple erosion mechanisms may be simultaneously contributing to cold dome erosion for any one given scenario. <br> <br>The second objective involved detailed case studies of three CAD events in order to more closely examine erosion mechanisms. The first case was an example of the Coastal Low erosion scenario, the second case was representative of the Northwestern Low erosion scenario, and erosion of the third case was multi-faceted and not clearly classifiable. Detailed examination of observations and EDAS analyses revealed that multiple erosion mechanisms were contributing to the weakening of the capping inversion above the cold dome and promoting the erosion of the CAD event. In the Coastal Low case, cold advection aloft led to a decrease in the potential temperature difference across the inversion, indicating erosion from the top of the cold dome down to the surface. Comparatively, the inland progression of a coastal front, in association with surface divergence, corresponded to an increase in surface temperatures and a weakening of the inversion during the Northwestern Low case study. This development was more indicative of erosion from the surface upwards. <br> <br>The performance of NCEP Eta Model forecasts during the three CAD events was evaluated. Consistent with the findings of previous research, the Eta Model eroded the cold dome prematurely for all three cases, and surface temperature were consistently overestimated. Control run simulations using the PSU/NCAR MM5 Model were performed for the Coastal Low and Northwestern Low cases. The control run simulations showed improved accuracy over the Eta Model forecasts in the representation of CAD erosion. However, erosion was still premature in comparison to observations. For both CAD events, overestimated values of shortwave radiation appeared to correlate with the decrease in model inversion strength. <br> <br>Finally, two sets of sensitivity tests for the Coastal Low case using the MM5 model were designed to test the sensitivity of model performance to alterations in certain physics parameterizations. The first sensitivity test involved altering the model values of cloud albedo, based on speculations that the overestimation of surface temperatures in the Eta Model was a result of the interaction between clouds and shortwave radiation. As hypothesized, the simulation in which cloud albedo was decreased produced the warmest surface temperatures. The second sensitivity test involved altering the PBL schemes used in the MM5 control run. It was found that the simulated vertical structure of the atmosphere did vary according to the PBL scheme, as anticipated. <br> <br>Although some of the alterations made to the MM5 control run for the sensitivity tests did improve the representation of certain features, the model continued to erode the cold dome earlier than observed. Comparisons of the MM5 simulations to the corresponding Eta Model forecasts revealed that none of the alterations to the MM5 control run produced the magnitude of error evident in the Eta Model.
18

An Assessment of Ammonia Emissions from Water-holding Structures for Hog Farms: Lagoon and Spray Technology and Potential Environmentally Superior Technologies

Rumsey, Ian Cooper 12 August 2004 (has links)
Globally, the largest source of atmospheric NH3 is domestic animal waste contributing 20-35 Tg of nitrogen per year. In North Carolina, hog waste accounts for 47% of all ammonia emissions in North Carolina. This is the result of a huge increase in hog population since the 1980?s from 3 million to 10 million. Currently swine waste is managed using Lagoon and Spray Technology (LST) also known as ?conventional? technology. A LST uses anaerobic lagoons to store the hog waste, and effluent from lagoons is sprayed on surrounding crops as a source of nutrients. This technology lead to a number sources of ammonia emissions, thus there are a number of environmental problems associated with swine facilities. The need for developing sustainable solutions for managing the hog waste problem is critical for shaping the future of hog farms in North Carolina. As a result of this, an agreement between the North Carolina Attorney General and several farming companies was reached to develop environmentally superior technologies (EST?s) for swine facilities. The objective of this study was to quantitatively compare the emissions from the water-holding structures at the two LST farms (Moore farm and Stokes farm) and the three EST farms, and to evaluate the effectiveness of each technology. The three potential EST?s were (1) EKOKAN: Up-flow Bio-filtration system, located at Brown?s of Carolina # 93, (2) BEST: Solids separation/gasification for energy and ash recovery centralized system, located at Corbett # 1,3,4 farms, and (3) Super Soils: Solids separation/nitrification-denitrification/soluble phosphorus removal/solids processing system, located at Goshen Ridge farm. Measurements of NH3 flux were limited to two, two-week long periods, representing warm and cold seasons. These were obtained by using a dynamic flow-through chamber system interfaced to a mobile laboratory containing the ammonia analyzer and the data acquisition system. During the sampling period, environmental parameters such as lagoon temperature, lagoon pH, and TAN were measured, as well as meteorological parameters such as wind speed, wind direction, air temperature, relative humidity, and solar radiation. In order to make a comparison of LST and EST?s, an adjustment for differing environmental conditions was needed. This was achieved by the development of a conventional observational statistical model, which was developed by multiple linear regression analysis based on continuous flux measurements from two conventional farms during a warm and cold season. Ammonia emissions from both conventional and EST farms were normalized to the nitrogen excretion (E) at the hog farms to express the emissions as % E. Potential reductions in ammonia were evaluated by comparing % EEST at EST farms with %ECONV at conventional farms. Overall, all three EST?s were found to be significant in reducing ammonia emissions. Super Soils was found to be the most effective, with NH3 emission reductions of 94.7% in the warm season, and 99% in the cold season. EKOKAN was found to be the next most effective, with reductions of 71.7 % and 42.7 % for the summer and spring sampling periods, respectively. The two BEST technologies were the least effective. There were large reductions for both Corbett # 1 and Corbett # 3,4 in the fall sampling period, 71.1% and 39.6% respectively. There were through extremely low reductions in the winter sampling period, with reductions of 13.6% for Corbett # 1 and 7.5% for Corbett # 3,4, respectively.
19

The Role of Land-Surface Hydrology on Small Stream Flash Flooding in Central North Carolina

Palmer, Trisha Denise 05 November 2004 (has links)
In order to determine the influence of various factors on flash flooding, six case studies during which flash flooding occurred across central North Carolina are examined: 1) 26 August 2002, 2) 11 October 2002, 3) 9-10 April 2003, 4) 16 June 2003, 5) 29 July 2003, and 6) 9 August 2003. Utilizing stream gage data from the United States Geological Survey combined with radar-estimated precipitation from the Weather Surveillance Radar-1988 Doppler (WSR-88D) KRAX near Clayton, NC, several statistical conclusions are drawn. These conclusions are based on relationships between the inputs ? rain rate and precipitation amount ? to the stream responses: the amount of time between when the stream began its rise and when the maximum stage was reached, the amount of time between the onset of precipitation and the initial response of the stream, the maximum stage reached, the change in height of the stream, and the rate of change of height of the stream. Results indicate that precipitation rate and amount tend to dominate the influence of stream response; however, in many situations, land-surface characteristics play an important role. The notable situations where precipitation rate and amount do not dominate are along the major rivers, in locations with sandy soils where infiltration is high, and in urban areas, where runoff occurs rapidly and streams thus respond quickly regardless of precipitation rate or amount. In addition, rain rate and precipitation amount do not necessarily have similar relationships with the stream response variables; rain rate has a stronger correlation with rate of change of stream rise, while precipitation amount has a stronger correlation with change in stream height. However, it is not enough to study rainfall rates and precipitation amounts if a flash flood warning is to be issued. The results of this research show that there is value and necessity in understanding the role of land-surface characteristics when determining if flash flooding is going to occur.
20

Measurements and Modeling of Emissions, Dispersion and Dry Deposition of Ammonia from Swine Facilities

Bajwa, Kanwardeep Singh 18 August 2006 (has links)
Ammonia has recently gained importance for its increasing atmospheric concentrations and its role in the formation of aerosols. Studies have shown increasing atmospheric concentration levels of NH3 and NH4+, especially in the regions of concentrated animal feeding operations. Atmospheric inputs of reduced nitrogen as ammonia and ammonium by dry and wet deposition may represent a substantial contribution to the acidification of semi natural ecosystems and could also affect sensitive coastal ecosystems and estuaries. The anaerobic lagoon and spray method, commonly used for waste storage and disposal in confined animal feeding operations (CAFO), is a significant source of ammonia emissions. An accurate emission model for ammonia from aqueous surfaces can help in the development of emission factors. Study of dispersion and dry deposition patterns of ammonia downwind of a hog farm will help us to understand how much ammonia gets dry deposited near the farm, and how remaining ammonia gets transported farther away. An experimental and modeling study is conducted of emissions, dispersion and dry deposition of ammonia taking one swine farm as a unit. Measurements of ammonia flux were made at 11 swine facilities in North Carolina using dynamic flow-through chamber system over the anaerobic waste treatment lagoons. Continuous measurements of ammonia flux, meteorological and lagoon parameters were made for 8-10 days at each farm during each of the warm and cold seasons. Ammonia concentrations were continuously measured in the chamber placed over the lagoon using a Thermo Environmental Instrument Incorporated (TECO) Model 17c chemiluminescnce ammonia analyzer. A similar ammonia analyzer was used to measure ammonia concentrations at selected locations on the farm. Barn emissions were measured using open-path Fourier transform infrared (OP-FTIR) spectroscopy. A 10 m meteorological tower was erected at each site to measure wind speed and direction, temperature, relative humidity and solar radiation. Data collected from field measurements made at hog waste lagoons in south eastern North Carolina, using the flow through dynamic chamber technique, were used to evaluate the Coupled Mass Transfer and Chemical Reactions model and Equilibrium model. Sensitivity analysis shows that ammonia flux increases exponentially with lagoon temperature and pH, but a linear increase was observed with an increase in total ammoniacal nitrogen (TAN). Ammonia flux also shows a nonlinear increase with increasing wind speed. Observed ammonia fluxes were generally lower in the cold season than in the warm season when lagoon temperatures are higher. About 41% of the Equilibrium model predictions and 43% of the Coupled model predictions are found to be within a factor of two of the observed fluxes. Several model performance statistics were used to evaluate the performance of the two models against the observed flux data. These indicate that the simpler Equilibrium model does as well as the Coupled model. The possible effects of the ?artificial? environment within the chamber, which is different from that in the ambient atmospheric conditions above the open lagoon surface, on the measured fluxes are also recognized. Actual layout of barns and lagoons on the farms was used to simulate dry deposition downwind of the farm. Dry deposition velocity, dispersion and dry deposition of ammonia were studied over different seasons and under different stability conditions. Dry deposition velocities were underpredicted by AERMOD when compared with observed dry deposition velocities. Dry deposition velocities were the highest under near neutral conditions and lowest under stable conditions. The highest deposition at short range occurs under nighttime stable conditions and the lowest deposition occurs during daytime unstable conditions. Significant differences in model predicted depositions over crop and grass surfaces are found under stable conditions. Wind orientation at the farm can also affect deposition of ammonia downwind of the farm.

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