This work attempts to relate global teleconnections, through physical phenomena such as the El Nino-Southern Oscillation (ENSO), Artic Oscillation (AO), North Atlantic Oscillation (NAO), and the Pacific North American (PNA) pattern to synoptic-scale weather patterns and precipitation in the Roanoke, Virginia region. The first chapter describes the behavior of the El Nino-Southern Oscillation (ENSO) by implementing non-homogeneous and homogeneous Markov Chain models on a monthly time series of the Troup Southern Oscillation Index (SOI), a sea level pressure based index. Meanwhile, in the second chapter the author has related or an attempt has been made to relate global teleconnections (through ENSO and AO) to a synoptic scale, station-centered set of weather types in order to assess trends in precipitation. The final portion of this work describes spatial variability of seasonal precipitation in southwestern Virginia in a context that incorporates global teleconnections (through AO, PNA, NAO, and ENSO) and frontogenesis. It was found that the Markov property can be used to describe and predict the monthly evolution of ENSO. Also evident is an increased probability of a wetter spring in the Roanoke region when El Nino combines with the negative phase of the AO during the previous winter. Meanwhile, Roanoke winters subsequent to a fall season described by this same El Nino-AO condition are predicted to receive more precipitation than average. This work additionally showed possible trends between frontal-precipitation events in the Roanoke region and global teleconnections. / Master of Science

This project addresses two main subjects of moisture-cure polyurethane (PUR) wood adhesives: wood/PUR interactions and structure-property behavior emphasizing on weather durability. For these purposes, one simplified model PUR (MPUR) and three more commercially significant PURs (CPURs) with different hard segment contents were prepared. Separately, an early side project involved the synthesis of a 13C and 15N double-labeled polymeric methylenebis(phenylisocyanate) (pMDI) resin; this was used for the solid-state NMR characterization of isocyanate cure chemistry in wood bondline. MPUR and a CPUR were employed to investigate whether wood/adhesive interactions influence PUR properties. Wood interactions significantly altered PUR hard/soft domain size distribution (atomic force microscopy, AFM), thermal transition temperatures (dynamic mechanical analyses, DMA), and urethane/urea hydrogen bonds (Fourier transform infrared spectroscopy, FTIR). The effects of hard segment content on properties of PUR prepolymers, and cured PURs (films and wood composites) were studied. Hard segment content largely influenced the PURs’ molecular weights, viscosity, penetration, thermal transitions, and hard segment hydrogen bonds, but only slightly altered the dry (unweathered) bondline toughness. Three accelerated weathering procedures were developed to evaluate CPUR bondline weather durability through mode-I fracture testing. Both hard segment content and weathering conditions were found to significantly influence the bondline weather durability. Among these weathering procedures, only one (VPSS) was able to effectively distinguish weather durability of PUR adhesives, and therefore it was selected for detailed structure-weather durability studies. PUR weather durability was found to correlate with its moisture sensitivity and hard segment softening temperature; both were provided by water-submersion DMA. Much attention was directed to the investigation of weather-induced PUR molecular changes. FTIR studies provided evidences of post-cure, hydrolytic degradation, and variation of urethane/urea hydrogen bonds. DMA presented weathering effects on PUR thermal properties. Special efforts have been made to correlate these analytical results with PUR weather durability. A 13C and 15N double-labeled pMDI resin was synthesized and used for solid-state NMR characterization of isocyanate cure chemistry in wood bondline, particularly to detect the evidence of urethane formation. Rotational echo double resonance (REDOR) NMR clearly revealed the formation of urethane linkages, but largely overestimated their content. / Ph. D.

Severe weather events frequently affect important marine fish stocks and fisheries along the United States Atlantic and Gulf of Mexico coasts. However, the effects of these events on fish and fisheries are not well understood. The availability of self-reported data from two fisheries in a region frequently affected by tropical cyclones provided a unique opportunity to investigate short-term responses to past events. This study involved selecting severe weather events, calculating changes in effort and catch-per-unit- effort (CPUE), and analyzing those changes across various temporal, spatial, and species-specific scenarios. Responses in each variable were analyzed within and across scenario factors and explored for correlations and linear multivariate relationships with hypothesized explanatory variables. A negative overall directional change was identified for logbook fishing effort. Based on both correlations and linear models, changes in logbook fishing effort were inversely related to changes in average maximum wind speed. Severe weather events are more likely to affect fishing effort than catch rates of reef-fish species. However, lack of responses in CPUE may also relate to the ability of this study to detect changes. The temporal and spatial scales analyzed in this study may not have been adequate for identifying changes in effort for the headboat fishery, or in CPUE for either fishery. Although there was no region-wide response in CPUE associated with severe weather events, further research on this topic is necessary to determine if storm-induced changes in fishery data are likely strong, long-lasting, or widespread enough to influence the outcome of stock-wide assessments. / Master of Science

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