Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 121-125). Also available via the Internet.

In this thesis, an analysis of solar energetic particle (SEP) data from multiple instruments onboard the ACE, SOHO and STEREO spacecraft is presented. The temporal variation and the dependence of heavy ion abundances on solar longitude were studied and quantitatively characterised during SEP events between 2006 and 2016. Ionic abundances vary over the duration of SEP events, e.g. Fe/O often shows a decrease over time. This behaviour was identified as a common characteristic within the data. The time variation of 36 different ionic pairs was studied for a number of SEP events. The fit constant describing time evolution was found to show ordering by the value of S, given e.g. for Fe/O by SFe/O = (M/Q)Fe/(M/Q)O, where M is the mass number and Q the charge number. The ionic ratios with S > 1 decreased over time and those with S < 1 showed increases, while ratios with a large S decayed at a higher rate. Anomalous behaviour of ratios involving protons was identified in several events. The longitudinal dependence of Fe/O simultaneously observed by multiple spacecraft at 1 AU was studied in 12 SEP events. The event-averaged Fe/O values observed by spacecraft at different longitudes varied within a single event, but this variation was less significant than the event-to-event variation. Although the longitudinal dependence was a complicated one, in some events the Fe/O values were higher at a remote observer. The temporal evolution of heavy ion ratios, which was studied quantitatively for a number of ionic pairs, is consistent with an MQ-dependent interplanetary transport mechanism. The observed longitudinal dependence of event-averaged Fe/O, where higher Fe/O values are observed at a spacecraft that is not well magnetically connected to the source region, cannot be fully explained by the two-class paradigm for classification of SEP events.

The effects of the application of increasing concentrations of the growth retardant paclobutrazol (PBZ) to in vitro cultures of Populus and Betula species was studied, with a view to translating the effect into the field, and ultimately to control undesired tree growth commercially. Plant growth and associated regulatory effects were studied under controlled conditions over an eight to twelve week culture period, after which explants were harvested. At harvest, explants of both species were removed from their culture universals after growing on hard agarose gel media containing a range of PBZ concentrations. Explant fresh weight, height and dry weight was recorded. Spent culture medium was frozen, thawed and centrifuged for analysis, by High Performance Liquid Chromatography (HPLC), of PBZ uptake. Other investigation carried out included the influence of PBZ on explants' response to directional light, and the phytosterol content of explant leaves. It was shown that treatments of PBZ, irrespective of concentration, had a regulatory effect on the growth of explants of both species. Recorded height, fresh weight and dry weight of explants showed a reduced growth proportional with increased PBZ concentration. Explant response to the higher concentrations was different for each species, with Betula showing a higher degree of retardation at lower concentration than Populus. Uptake of PBZ also appeared to be species dependent, the average uptake of the available PBZ being 70% and 51% for Populus and Betula, respectively. Even though there was very little growth at high concentration, explants appeared reasonably healthy; no symptoms associated with tree decline, chlorosis, die back and or death, were observed on explants treated with PBZ, however a failure to leaf and severe stunting indicated potential over regulation at 5 pM in Betula explants. This investigation has shown that a dose-dependant response can be obtained from tissuecultured tree species and that the response appears to be species specific.

It is widely recognized that topographically-driven groundwater flow can perturb conductive thermal regimes. High-relief topography amplifies the impact of factors controlling groundwater flow and advective heat transfer. A finite element method is developed to model the influence of geology, climate, surface topography and regional heat flux on steady groundwater flow and heat transfer. Because fluid viscosity (hence fluid flux) depends upon temperature, groundwater flow is influenced by the regional heat flux. As a consequence, isothermal approaches to modeling deep groundwater flow in mountains may be inappropriate. Using a free-surface approach, the water table is represented as an internal characteristic of the groundwater flow system, rather than the upper boundary for fluid flow. Thick unsaturated zones are expected in high-permeability terrain (greater than 10⁻¹⁵ m²) with arid climate, or where groundwater recharge is restricted by extensive alpine glaciers. Only vertical fluid flow is assumed to occur in the unsaturated zone, therefore, heat transfer above the water table is represented by one-dimensional advection and two-dimensional conduction. Simulation results indicate that water table elevations are highly sensitive to changes in the controlling factors, but have little impact on the thermal regime. Conductive thermal regimes are predicted in low-permeability terrain (less than 10⁻¹⁸ m²) or in high-permeability terrain with arid climate (recharge rates less than 10⁻¹¹ m/sec). Strong advective heat transfer masks the regional heat flux when permeability exceeds 10⁻¹⁶ m² in terrain with relief of 2 km over a horizontal distance of 6 km. Less than one percent of typical mean annual precipitation is transmitted through deep groundwater flow systems under these conditions. Asymmetric surface topography complicates efforts to interpret chemical and thermal data collected near the valley floor. Fracture zones outcropping at the valley floor can capture a large percentage of groundwater flowing through the system and a significant percentage of the basal heat flux. Maximum spring temperatures are indicated when bulk permeability is between 10⁻¹⁷ m² and 10⁻¹⁵ m². Outside this range, spring temperatures approach ambient air temperature. Topographically driven groundwater flow can distort and obliterate free-convection cells that might otherwise develop within a mountain massif. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

This thesis investigates the fundamental performance of Hierarchical Non-Terrestrial Networks for the 6th generation (6G). 6G communication research is currently focus- ing on non-terrestrial networks (NTNs) to promote ubiquitous and ultra-high-capacity global connectivity. Specifically, multi-layered hierarchical networks, i.e., the orches- tration among different aerial/space platforms, including Unmanned Aerial Vehicles (UAVs), High Altitude Platforms (HAPs), and satellites co-operating at different al- titudes, currently represents one the most attractive technological options to solve coverage and latency constraints associated with the NTN paradigm. However, there are still several issues to be resolved for proper network design. In this thesis, we in- vestigate the propagation model in air/space links and then evaluate the performance of different multi-layered non-terrestrial configurations, and then provide guidelines on the optimal working point(s) for which it is possible to achieve a good compro- mise between improved system flexibility and network performance, with respect to a baseline standalone deployment.

Metabolites of DDT were detected in five out of six major organs of blue crabs, Callinectes sapidus, taken from estuarine populations. Residue concentrations were highest in the hepatopancreas and below the limit of detection in the heart. Concentrations in pooled gonad samples (ovaries + testes) depended on the stage of development of the ovaries. Residue levels were low in claw and backfin muscles. Adult blue crabs were exposed for 12 hours to 0.01, 0.1, and 1.0 ppm DDT in water. No significant mortality was recorded. DDT was absorbed through the gills and transported to the hepatopancreas via the hemolymph. Biotransformation and distribution of DDT and its metabolites was regulated by the hepatopancreas. Induction of metabolic transformation of DDT to DDD and DDE occurred immediately. Storage of residues was greatest in the hepatopancreas and developing ovaries . Rates of loss of DDT residues from organs was subject to considerable variation. This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.

Zooplankton composition, distribution, biomass and biochemical constituents were determined monthly in the lower Chesapeake Bay for two years beginning in August 1971. Settled volume, dry weight, and ash-free dry weight estimates of total biomass were generally consistent in showing summer and late winter peaks. A mean dry weight peak of 258 mg/m3 in August 1971 decreased precipitously to a December low of 9 mg/m3, then increased to a March 1972 peak of 199 mg/m3. The second year mirrored this pattern, except that the passage of Tropical Storm Agnes in June 1972 lowered the summer peak values for July and August considerably. In August 1971 and again in August 1972, a total of 53 species, from four dominant major groups, were used to characterize four distinct geographical cluster zones. The summer zooplankton was dominated by cladocerans, largely Penilia avirostris and Evadne tergestina, and the copepod Acartia tonsa. Decapod larvae proved to be the most diverse summer group studied, containing 30 species in August 1971 and 33 species in August of 1972. Dominant species included Upogebia affinis, Callinectes sapidus, and Uca sp. Chaetognath peaks in September of each year consisted almost entirely of Sagitta tenuis. Winter populations contained less than half the number of taxa as summer zooplankton and were dominated by Acartia clausi. This species almost completely replaced Acartia tonsa by April of each year. The most notable effects of the lowered salinities caused by Tropical Storm Agnes in the summer of 1972 were a drastic reduction in cladoceran abundance and a compression of chaetognath distribution to the higher salinity areas near the bay mouth. Protein, the largest organic fraction of the zooplankton, usually accounted for 40-60% of the total dry weight. Mean monthly lipid values ranged from 1.9 to 9.5% of the dry weight, and carbohydrate appeared only as a minor organic fraction. This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.

Laboratory and environmental studies of striped bass (Morone saxatilis) X white perch (M. americana) and striped bass X white bass (M. chrysops) were used to-determine the feasibility of introducing these hybrids into an estuary as a supplement to natural populations of the parental species. Growth patterns, survival, and general hardiness of the hybrids were used as criteria. Growth of striped bass X white perch hybrids in the laboratory was apparently somewhat less than growth of natural populations of striped bass, but was much greater than growth of natural populations of white perch. Hybrid growth was slower than striped bass growth under the same conditions, but hybrid survival was much better than striped bass survival. The hybrids were able to survive and grow in estuarine salinities. Most hybrids matured at two years of age. Striped bass X white bass hybrids were able to adapt to an estuarine environment (the Rappahannock River, Virginia) and could successfully compete with striped bass and other resident ichthyofauna. Hybrid growth was faster than striped bass growth in the Rappahannock and was considerably faster than growth of various freshwater populations of white bass. Hybrids were caught in salinities as high as 17%. They were mature at two years of age. Both hybrids were described using meristic and morphometric characteristics. They were both found to be generally intermediate to the parental species, but in certain traits they tended to resemble one parent more closely than the other. Striped bass, white perch, and their hybrid all had a diploid chromosome number of 48. Possible karyological differences are discussed. One or both hybrids may be suitable for introduction into an estuary to supplement natural populations of striped bass and white perch, but more comprehensive environmental experiments are needed. This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.

Amazonian freshwaters host the most diverse ichthyofauna in the world but the ecological mechanisms that generate and regulate this diversity are poorly known. I performed the first comparison of spatial and temporal patterns of fish community diversity among the four primary aquatic habitats of the Amazon (major rivers, floodplains, lowland terra firme streams, and upland shield streams) and among the three distinct chemical water types in Amazon river-floodplain systems (low-nutrient blackwaters and clearwaters, and high-nutrient whitewaters). To minimize confounding influences of geographical variation in species ranges, my study targeted one of the few parts of Amazonia (near Santarém, Brazil) where all four habitats and all three river-floodplain water types occur in close proximity. In the first of three chapters, I compare diversity and biomass between blackwater, clearwater, and whitewater rivers and floodplains. My results provide the first support for positive species-energy and biomass-energy relationships across multiple aquatic habitat types from the same biome and region. In Chapter 2 I compare patterns of temporal beta-diversity, and beta-deviations from null model simulations, to demonstrate that species turnover is positively correlated to seasonality and hydrological connectivity among the four Amazonian habitats types but is uninfluenced by water type. In Chapter 3 I compare up-river transects from the common confluence of a blackwater, Clearwater, and whitewater river to infer that abrupt gradient of water chemistry act as major barriers to fish dispersal. My results have important implications for biodiversity monitoring and conservation planning in the increasingly threatened aquatic habitats of the Amazon basin.

Despite an increased global interest in harmful algal bloom (HAB) species and eutrophication, the relationship between nutrient sources and changes in species composition or toxicity remains unclear. Stable isotopes are routinely used to identify and track nitrogen (N) sources to water bodies, as sources can be differentiated based on stable isotope values. While literature is available describing N fractionation by diatoms and coccolithophores, data are greatly lacking regarding isotope fractionation by dinoflagellates. Here we investigate the fractionation of nitrogen isotopes by saxitoxin-producing Alexandrium fundyense, to validate the use of the δ15N of particulate organic matter and identify the nitrogen source fueling a dinoflagellate bloom and its toxicity. The effects of N chemical form on isotope fractionation, toxin content, and toxicity, were investigated using isolates in single-N and mixed-N experiments. Growth on NO3-, NH4+, or urea, resulted in isotope fractionation of 2.761.48‰, 29.019.32‰, or 0.340.19‰, respectively, with the lowest cellular toxicity and toxin quotas reported during urea utilization. Toxin composition and growth rates, however, remained constant across all N treatments, showing no effects of NO3-, NH4+, or urea utilization. Alexandrium fundyense was then preconditioned to either NO3-, NH4+, or urea, and abruptly inoculated into mixed-N medium containing all three chemical forms. All treatments initially utilized NH4+ and urea upon inoculation into mixed medium, suggesting no effect of preconditioning. Cells only began utilizing NO3- after NH4+ decreased below 2-4 M in the medium. During the inhibition of NO3- uptake by NH4+ utilization, the cellular δ15N was at its lowest (-5‰), and through the course of the experiment, the δ15N continuously changed to mimic the isotope value of the most recent N source(s) being utilized. When utilizing multiple sources, the isotope signature of the cells fell between the signal of the two N sources. Together this suggests that in NO3- and urea rich environments, the 15NPOM would reliably look like the source or sources of nitrogen utilized, but that caution should be taken in NH4+ rich environments where the large value could lead to misinterpretation of the signal. Nutrients are only one factor influencing bloom dynamics, but information about the relative importance of natural or anthropogenic nutrients in the development and toxicity of bloom events is necessary to predict future shifts in phytoplankton species composition, density, and toxicity.