A thesis presented in partial fulfilment of the requirements for the degree of Doctor of Medicine at the University of the Witwatersrand, Johannesburg. / The quantity of iron in the body is regulated largely by the amount absorbed from the gut as the body's capacity to excrete it seems to be very limited. However three conditions have been described in which enormous amounts of iron may accumulate. Such a finding is characteristic of idiopathic haemochromatosis, it is present in a proportion of malnourished South African and is seen also in cases of refractory anaemia treated over long periods with blood transfusions. / IT2018

Tsui Shu Ki. / Bibliography: leaves 110-112 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1985

Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 83-84.

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Tse Wang Kong = 單泡聲致發光的熱輻射 / 謝宏岡. / Thesis submitted in: July 2003. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 110-114). / Text in English; abstracts in English and Chinese. / Tse Wang Kong = Dan pao sheng zhi fa guang de re fu she / Xie Honggang. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- General review of sonoluminescence --- p.1 / Chapter 1.2 --- Thermal light emission models --- p.3 / Chapter 1.3 --- Motivation and structure of this thesis --- p.7 / Chapter 2 --- "Bubble-wall Dynamics, Hydrodynamics and Ionization" --- p.9 / Chapter 2.1 --- Uniform bubble model --- p.9 / Chapter 2.1.1 --- Bubble-wall dynamics --- p.9 / Chapter 2.1.2 --- Equation of state of the gas --- p.10 / Chapter 2.1.3 --- Temperature dynamics --- p.11 / Chapter 2.1.4 --- Ionization --- p.12 / Chapter 2.2 --- Computational fluid mechanics model --- p.13 / Chapter 2.2.1 --- Bubble-wall dynamics --- p.13 / Chapter 2.2.2 --- Hydrodynamics of the gas --- p.15 / Chapter 2.2.3 --- Equation of State of the gas --- p.16 / Chapter 2.2.4 --- Energy equation in the liquid --- p.17 / Chapter 3 --- Thermal Radiation --- p.18 / Chapter 3.1 --- Thermal electromagnetic fields --- p.20 / Chapter 3.2 --- Generalized Kirchhoff's law --- p.22 / Chapter 3.3 --- Thermal radiation from an absorbing object --- p.24 / Chapter 3.4 --- Application to a slab --- p.26 / Chapter 3.5 --- Application to a multilayered configuration --- p.29 / Chapter 4 --- Absorption in a Multilayered Dielectric Sphere --- p.31 / Chapter 4.1 --- Absorption cross-section for weakly absorbing sphere --- p.31 / Chapter 4.2 --- Absorption cross-section for strongly absorbing sphere --- p.33 / Chapter 4.3 --- Transfer matrix method --- p.33 / Chapter 4.4 --- Calculation of the absorption cross-section --- p.39 / Chapter 5 --- Collision Processes in a SL Bubble --- p.40 / Chapter 5.1 --- Electron-ion Bremsstrahlung --- p.41 / Chapter 5.2 --- Electron-ion Recombination --- p.43 / Chapter 5.3 --- Electron-atom Bremsstrahlung --- p.43 / Chapter 5.4 --- Effective Collision Frequency for a Maxwellian Plasma --- p.44 / Chapter 6 --- Light Emission Models for a Sonoluminescing Bubble --- p.47 / Chapter 6.1 --- The geometric optics model --- p.47 / Chapter 6.2 --- The wave optics model --- p.48 / Chapter 7 --- Thermal radiation from sonoluminescing bubbles --- p.50 / Chapter 8 --- Effect of the light emission model --- p.53 / Chapter 9 --- A more sophisticated model for collision processes --- p.58 / Chapter 10 --- Effect of bubble temperature and water temperature --- p.65 / Chapter 10.1 --- Effect of bubble temperature --- p.65 / Chapter 10.2 --- Effect of water temperature --- p.68 / Chapter 11 --- A more sophisticated hydro dynamic model --- p.70 / Chapter 12 --- Degree of Strong Coupling and Summary --- p.94 / Chapter 13 --- Conclusion --- p.98 / Chapter 13.1 --- Summary --- p.98 / Chapter 13.2 --- Suggestions for future work --- p.101 / Chapter A --- Proof of the Reciprocity Theorem --- p.103 / Chapter B --- Vector Spherical Harmonics --- p.105 / Chapter C --- Collision frequencies and absorption coefficients --- p.107 / Bibliography --- p.110

Die klinische Magnetresonanztomografie (MRT) operiert meist bei einer Magnetfeldstärke von 1,5 Tesla (T). Es halten jedoch immer mehr 3T MRT-Systeme Einzug im klinischen Alltag und seit kurzem auch 7T Ganzkörper-MRT-Systeme in die Grundlagenforschung. Höhere Magnetfeldstärken führen grundsätzlich zum einem verbesserten Signal-zu-Rausch- Verhältnis, welches sich gewinnbringend in eine erhöhte Ortsauflösung oder schnellere Bildaufnahme äußert. Ein Nachteil ist aber die dabei im Patienten deponierte Hochfrequenz-Energie (HF-Energie), welche quadratisch mit ansteigender Feldstärke zusammenhängt. Charakterisiert wird diese durch die spezifische Absorptionsrate (SAR) und ist durch vorgegebene gesetzliche Grenzwerte beschränkt. Moderne, SAR-intensive MRT-Techniken (z.B. Multispinecho-Verfahren) sind bereits bei 1,5T nahe den zulässigen SAR-Grenzwerten und somit nicht unverändert auf Hochfeld-Systeme übertragbar. In dieser Arbeit soll das Potential modularer Hybrid-MRT-Techniken genutzt werden, um das SAR bei besonders SAR-intensiven MRT-Verfahren ohne signifikante Einbußen in der Bildqualität erheblich zu verringern. Die Hybrid-Techniken sollen in Verbindung mit zusätzlichen Methoden der SAR-Reduzierung den breiteren Einsatz SAR-intensiver MRT-Techniken an hohen Magnetfeldern ermöglichen. Ziel dieser Arbeit ist es, routinefähige und SAR-reduzierte MRT-Standard-Protokolle für neuroanatomische Humanuntersuchungen mit räumlicher Höchstauflösung bei Magnetfeldern von 3T und 7T zu etablieren. / Spin echo based MRI sequences builds one of the main priorities in the medical/-morphological MRI imaging. Especially T2-weighted spin-echo sequences and the multi-spin-echo RARE imaging sequence represents one of the basic methods, which allows to minimize measurement times down to minutes or seconds. Modern MRI systems usually have a magnetic field strength beyond 1.5T. In order to acquire high resolution images with acceptable acquisition times, high RF power is needed. In many cases the intrinsic safety limits of the radiated power are already exeeded at field strengths of 3T. This leads often to restrictions for the full performance. In research systems of 7T and more T2-weighted images are only feasible with significant amount of time. Especially in RARE imaging methods, which require a large number of refocusing pulses, this is a significant restriction factor. Therefore, in recent years there were further development of hybrid sequences which combines different acquisition methods together into one, to exploit their fully advantages of the basic methods and to minimize ...

Typewritten Includes bibliographical references.

The chemistry and dynamics of our atmosphere are complex and diverse. A plethora of different chemical reactions are thought to be important, of which only some are known, and even less are well understood. Many of these atmospheric reactions involve highly reactive or unstable trace species, which can be difficult to study experimentally. However, the advancement of computational methods and hardware now make it possible to investigate these chemical species theoretically to an accuracy that is useful for atmospheric chemistry. In this thesis, we have applied modern electronic structure methods to some prototypical hydrogen bonded complexes and sulfonic acid derivatives to better understand the roles of these trace species in the atmosphere. We have calculated fundamental and overtone vibrational spectra, electronic absorption spectra, and reaction energetics with high level ab initio methods. Where possible, we compare our calculated results to experiment and in the absence of experimental data we suggest that our theoretical findings may be of use to atmospheric modelers.

The objective of the work described in this thesis was to improve the scientific basis for modelling the migration of U in the sub-surface environment. The project involved: ?? studying the sorption of U on model minerals (Georgia kaolinite and ferrihydrite) in laboratory experiments ?? carrying out experimental studies of U sorption on complex natural substrates ?? studying the mechanisms influencing U retardation in the natural environment, including transformation processes of iron oxides ?? identifying chemical factors which control U sorption on model and natural substrates ?? developing a mechanistic model for U sorption on ferrihydrite and kaolinite using the surface complexation adsorption model , and ?? assessing and modelling the effect of complexing ligands on uranyl adsorption. Uranium (VI) sorption on geological materials is influenced by a large number of factors including: pH, ionic strength, partial pressure of CO2, adsorbent loading, total amount of U present, and the presence of inorganic and organic ligands. The sorption of UO22+ typically increases with increasing pH (the 'low pH sorption edge') up to about pH 7. In systems equilibrated with air, there is a sharp decrease in sorption above this pH value (the 'high pH edge'), due to strong complexation between uranyl and carbonate. The adsorption model being used for ferrihydrite is a surface complexation model with a diffuse double layer, and both strong and weak sites for U sorption. Based on the analysis of EXAFS data, the U surface complexes were modelled as mononuclear bidentate surface complexes of the form (&gtFeO2)UO20. Ternary surface complexes involving carbonate with the form (&gtFeO2)UO2CO32- were also required for the best simulation of U sorption data. There was a slight decrease in U sorption on ferrihydrite in systems that contained sulfate. It was necessary to consider competition between UO22+ and SO42- for surface sites, as well as complexation between UO22+ and SO42- to model the data. The presence of citrate considerably reduced U sorption and caused dissolution of ferrihydrite. Complexation of citrate with both uranyl and ferric ions was taken into account in modelling this system. The model required the optimisation of the formation constant for a postulated mixed metal (U/Fe/citrate) aqueous complex. Humic acid increased U uptake at pH values below 7, with little effect at higher pH values. In terms of the amount of U sorbed per gram of adsorbent, U uptake on kaolinites KGa-1 and KGa-1B was much weaker than U uptake on ferrihydrite under similar experimental conditions. Electron microscope examination showed that titanium-rich impurity phases played a major role in the sorption of U by these standard kaolinites. A relatively simple model for uranyl sorption on the model kaolinites was able to account for U sorption under a wide range of experimental conditions. The model involved only three surface reactions on two sites (&gtTiOH and &gtAlOH), with a non-electrostatic surface complexation model. The relative amounts of the sites were estimated from AEM results. Precipitation was taken into account in modelling the experimental data obtained with high U concentrations. The effects of sulfate and citrate on U sorption by kaolinite were also assessed and modelled. Sulfate had a small effect on U sorption, which may be explained by aqueous complexation. Citrate had a greater effect, and this was not wholly explained by the formation of aqueous U-citrate complexes. The most likely explanation would also involve competition for surface sites between U and citrate. Uranyl uptake on ferrihydrite was greatly increased by the presence of phosphate. This was not due to precipitation, and was attributed to the formation of a ternary surface complex with a proposed structure of (&gtFeO2)UO2PO43-. The log K value for the formation of this complex was optimised using FITEQL. Phosphate also increased uptake of uranyl on kaolinite, and this was also attributed to the formation of ternary uranyl phosphate surface species. Uranium sorption on weathered schist samples from the vicinity of the Koongarra U deposit in northern Australia was generally similar to the model minerals (in terms of the effects of pH, ionic strength, total U, etc). Many experiments with the natural materials were spiked with an artificial U isotope (236U), which allowed adsorption (of 236U) and desorption (of 238U) to be distinguished, and provided a means of estimating the 'labile' or 'accessible' portion of the natural U content. A significant advantage of this method is that (unlike chemical extractions) it does not rely on the assumptions about the phases extracted by 'selective' reagents. Uranium sorption experiments were also carried out with Koongarra samples which had been treated with citrate / dithionite / bicarbonate (CDB) reagent to remove iron oxides. Uranium sorption was greatly decreased by the CDB extraction, which reduced the surface area of the samples by about 30-40%. To further elucidate the impact of iron minerals on U mobility in the natural environment, the transformation of synthetic ferrihydrite containing adsorbed natural uranium was studied. In these experiments, the ferrihydrite was partially converted to crystalline forms such as hematite and goethite. The uptake of an artificial uranium isotope (236U) and the leaching of 238U from the samples were then studied in adsorption / desorption experiments. The transformation of ferrihydrite to crystalline minerals substantially reduced the ability of the samples to adsorb 236U from solution. Some of the previously adsorbed 238U was irreversibly incorporated within the mineral structure during the transformation process. Therefore, transformation of iron minerals from amorphous to crystalline forms provides a possible mechanism for uranium immobilisation in the groundwater environment. In considering the overall effect on U migration, this must be balanced against the reduced ability of the transformed iron oxide to adsorb U. The experiments with the model and natural substrates demonstrated that trace impurities (such as Ti-oxides) and mineral coatings (such as ferrihydrite) can play a dominant role in U adsorption in both environmental and model systems. Although the various substrates had different affinities for adsorbing U, the effects of chemical factors, including pH, ionic strength, and carbonate complexation were similar for the different materials. This suggests that a mechanistic model for U sorption on model minerals may eventually be incorporated in geochemical transport models, and used to describe U sorption in the natural environment.

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