Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 158-166). Also available on the Internet.

Thesis (Ph. D.)--University of Oregon, 1999. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 100-105). Also available for download via the World Wide Web; free to University of Oregon users. Address: http://wwwlib.umi.com/cr/uoregon/fullcit?p9947982.

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Released for public view from 10 November 2008. Includes bibliographical references: leaf 136-146.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 126-132).

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (leaves 106-116).

Arctic clouds are poorly represented in numerical models due to the complex, small-scale interactions which occur within them. Modelled cloud fractions are often significantly less than observed in this region; therefore, the radiative budget is not accurately simulated and forecasts of the melting cryosphere are fraught with uncertainty. Our ability to accurately model Arctic clouds can be improved through observational studies. Recent in situ airborne measurements from the springtime Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign are presented in this thesis to improve our understanding of the cloud microphysical interactions unique to this region. Aerosol-cloud interactions - where aerosol particles act as ice nucleating particles (INPs) or cloud condensation nuclei (CCN) - are integral to the understanding of clouds on a global scale. In the Arctic, uncertainties caused by our poor understanding of these interactions are enhanced by strong feedbacks between clouds, the boundary layer, and the sea ice. In the Arctic spring, aerosol-cloud interactions are affected by the Arctic haze, where a stable boundary layer allows aerosol particles to remain in the atmosphere for long periods of time. This leads to a heightened state of mixing in the aerosol population, which affects the ability of particles to act as INPs or CCN. Aerosol particle compositional data are presented to indicate which particles are present during the ACCACIA campaign, and infer how they may participate in aerosol-cloud interactions. Mineral dusts (known INPs) are identified in all flights considered, and the dominating particle classes in each case vary with changing air mass history. Mixed particles, and an enhanced aerosol loading, are identified in the final case. Evidence is presented which suggests these characteristics may be attributed to biomass burning activities in Siberia and Scandinavia. Additionally, in situ airborne observations are presented to investigate the relationship between the Arctic atmosphere and the mixed-phase clouds - containing both liquid cloud droplets and ice crystals - common to this region. Cloud microphysical structure responds strongly to changing surface conditions, as strong heat and moisture fluxes from the comparatively-warm ocean promote more turbulent motion in the boundary layer than the minimal heat fluxes from the frozen sea ice. Observations over the transition from sea ice to ocean show that the cloud liquid water content increases four-fold, whilst ice crystal number concentrations, N_ice, remain consistent at ~0.5/L. Following from this study, large eddy simulations are used to illustrate the sensitivity of cloud structure, evolution, and lifetime to N_ice. To accurately model mixed-phase conditions over sea ice, marginal ice, and ocean, ice nucleation must occur under water-saturated conditions. Ocean-based clouds are found to be particularly sensitive to N_ice, as small decreases in N_ice allow glaciating clouds to be sustained, with mixed-phase conditions, for longer. Modelled N_ice also influences precipitation development over the ocean, with either snow or rain depleting the liquid phase of the simulated cloud.

The Enhanced Actinide Removal Plant (EARP), located on the Sellafield site, is one of the UK's most crucial radioactive effluent treatment plants. EARP removes actinides and select fission products from routine reprocessing effluents by association with a ferric iron oxyhydroxide floc, which is precipitated from acidic effluent streams by the addition of NaOH. The effluent compositions that EARP receives will change in character as the Sellafield site transitions from its current routine reprocessing operations to post-operational clean-out and accelerated decommissioning activities over the next few years. An enhanced understanding of the iron oxyhydroxide formation processes occurring in EARP would help underpin optimisation of current plant efficiency and allow better prediction of changes in efficiency as effluent composition varies. In this study, iron oxyhydroxide formation, properties and evolution with time under EARP-relevant conditions were characterized. These processes were investigated in a pure ferric nitrate system and systems with added sulfate, phosphate and boric acid using a range of techniques including SAXS, TEM and FTIR. In all the experimental systems the iron oxyhydroxide floc was composed of nanoparticulate ferrihydrite aggregated into extensive mass fractal structures. In situ SAXS experiments showed that formation proceeded via a precursor cluster pathway whereby Fe(III) clusters ~ 0.45 nm in radius form rapidly at pH 0.12 - pH 1.5 upon dropwise addition of strong NaOH to the acidic effluent simulants. Further analysis indicates these clusters are Fe13 Keggin clusters, which have previously been shown to be an important structural motif in the ferrihydrite structure. With further pH increase, cluster aggregation occurs along with precipitation of low molecular weight Fe(III) species (mostly monomers), leading to formation of ferrihydrite nanoparticles which preserve the Keggin cluster in the core. Phosphate, sulfate and boric acid exhibit varying interactions with the solid phase throughout the formation process, with both inner and outer sphere adsorption observed for different species. Ageing experiments show that the ferrihydrite floc readily undergoes transformation leading to predominantly hematite formation, except in the presence of phosphate (concentrations > 10 ppm) where transformation is entirely inhibited due to phosphate adsorption to the floc. These results progress the fundamental understanding of the iron oxyhydroxide formation and ageing processes occurring in EARP.

Crystallising large, flexible molecules, which are becoming more common in pharmaceutical development, often presents significant challenges for chemists and particle scientists. These difficulties are sometimes attributed to the flexibility of the molecule, and the existence of multiple conformers in solution. Structurally related impurities, frequently present when crystallising these materials, can also impact on growth and habit, and both these aspects are considered in this thesis. This work considers two pharmaceutical compounds, a relatively small but nonetheless flexible molecule, ethenzamide, and a precursor of Amprenavir, a much larger molecule. Both compounds typically grow as thin needles in a wide variety of solvents, and effort was required to grow suitable crystals for structure determination. Ethenzamide has an unusual structure, the amide group being out-of-plane relative to the ring, while in all known co-crystals of the compound, including three new co-crystal structures determined in this work, it has a planar structure with an intramolecular hydrogen bond not seen in the single component crystal. Theoretical structure generation calculations suggest a second polymorph with a planar conformation may exist, though a screen has not found any further solid phases. ab initio work suggests the planar conformation is the stable arrangement in vacuo. Several structures for the Amprenavir intermediate have been determined, as an ethanol solvate, a methanol solvate and a hydrate. A phase diagram has been measured in the industrial solvent mix, and the nucleation and growth properties of this molecule, both pure and in the presence of several structurally related impurities, have been measured. The Cambridge Structural Database has been searched for similar structures, and conformational searches have been carried out for both molecules, using vacuum phase ab initio energy calculations. Infrared spectroscopy has been used to investigate solution phase structure. These theoretical and practical studies will try to relate conformational properties to crystallisation behaviour.

A expansão natural de vegetação lenhosa sobre pradarias tem sido observada em escala global, mas os regimes de distúrbio influenciam a dinâmica da expansão. Basicamente dois padrões de expansão florestal podem ser considerados em áreas campestres excluídas de manejo: o avanço gradual a partir das bordas florestais e a colonização de indivíduos isolados na matriz campestre. Uma vez estabelecidas, as espécies colonizadoras de campos podem facilitar a dispersão de outras espécies sob suas copas (perch effect), servindo como poleiros naturais; e/ou ainda podem facilitar o estabelecimento dessas espécies, atuando como berçários (nurse plant effect). Neste contexto, Araucaria angustifolia é um exemplo de espécie colonizadora em campos que contribui para o processo de expansão. Além disso, A. angustifolia caracteriza-se pela formação de anéis de crescimento anuais em decorrência de variações climáticas sazonais, permitindo o estudo da dinâmica e estrutura etária das populações com o uso de métodos dendrocronológicos. Com base nisso, avaliamos nesta dissertação a estrutura etária de A. angustifolia em campos excluídos de manejo por 34 anos e a relacionamos com o processo de expansão florestal, bem como averiguamos o seu papel como facilitadora da dispersão e estabelecimento de espécies lenhosas colonizadoras de campos. Os resultados apontam para uma relação inversa entre a estrutura etária e a distância da borda florestal; e indicam que A. angustifolia atua mais como um poleiro para deposição de diásporos, do que propriamente como uma facilitadora do estabelecimento dessas espécies. / The natural expansion of woody vegetation over grassland has been observed worldwide, but the expansion dynamics is influenced by the disturbance regimes. Two patterns of forest expansion are well documented: gradual expansion from the forest borders and by the process of nucleation, which consists in the colonization of the grassland matrix by isolated trees. Once established, these colonizing species can facilitate the dispersion process by acting as perches, and/or as nurse plants by facilitating the recruitment of new colonizers. Araucaria angustifolia is an example of colonizer species in open areas contributing to forest expansion. Besides, A. angustifolia presents tree rings that reflect annual cycles of growth and dormancy, allowing us to study dynamics and population age structures using dendrochronological methods. In this dissertation, we evaluate the age structure of A. angustifolia in grasslands excluded from disturbance for 34 years and relate it to the expansion process. As well, we evaluate the role of A. angustifolia as perch (by facilitating seed dispersal) and as a nurse plant (by facilitating the establishment of other species under the crown). Our results point out to an inverse relationship between age structure and distance from the border and indicate that the role of A. angustifolia is more important as a perch than facilitating the establishment of other species.

A expansão natural de vegetação lenhosa sobre pradarias tem sido observada em escala global, mas os regimes de distúrbio influenciam a dinâmica da expansão. Basicamente dois padrões de expansão florestal podem ser considerados em áreas campestres excluídas de manejo: o avanço gradual a partir das bordas florestais e a colonização de indivíduos isolados na matriz campestre. Uma vez estabelecidas, as espécies colonizadoras de campos podem facilitar a dispersão de outras espécies sob suas copas (perch effect), servindo como poleiros naturais; e/ou ainda podem facilitar o estabelecimento dessas espécies, atuando como berçários (nurse plant effect). Neste contexto, Araucaria angustifolia é um exemplo de espécie colonizadora em campos que contribui para o processo de expansão. Além disso, A. angustifolia caracteriza-se pela formação de anéis de crescimento anuais em decorrência de variações climáticas sazonais, permitindo o estudo da dinâmica e estrutura etária das populações com o uso de métodos dendrocronológicos. Com base nisso, avaliamos nesta dissertação a estrutura etária de A. angustifolia em campos excluídos de manejo por 34 anos e a relacionamos com o processo de expansão florestal, bem como averiguamos o seu papel como facilitadora da dispersão e estabelecimento de espécies lenhosas colonizadoras de campos. Os resultados apontam para uma relação inversa entre a estrutura etária e a distância da borda florestal; e indicam que A. angustifolia atua mais como um poleiro para deposição de diásporos, do que propriamente como uma facilitadora do estabelecimento dessas espécies. / The natural expansion of woody vegetation over grassland has been observed worldwide, but the expansion dynamics is influenced by the disturbance regimes. Two patterns of forest expansion are well documented: gradual expansion from the forest borders and by the process of nucleation, which consists in the colonization of the grassland matrix by isolated trees. Once established, these colonizing species can facilitate the dispersion process by acting as perches, and/or as nurse plants by facilitating the recruitment of new colonizers. Araucaria angustifolia is an example of colonizer species in open areas contributing to forest expansion. Besides, A. angustifolia presents tree rings that reflect annual cycles of growth and dormancy, allowing us to study dynamics and population age structures using dendrochronological methods. In this dissertation, we evaluate the age structure of A. angustifolia in grasslands excluded from disturbance for 34 years and relate it to the expansion process. As well, we evaluate the role of A. angustifolia as perch (by facilitating seed dispersal) and as a nurse plant (by facilitating the establishment of other species under the crown). Our results point out to an inverse relationship between age structure and distance from the border and indicate that the role of A. angustifolia is more important as a perch than facilitating the establishment of other species.