Thesis (Ph. D.)--University of Virginia, 2001. / Includes bibliographical references (leaf 239). Also available online through Digital Dissertations.

Th. doct.-ing.--Sci des matér.--Nancy--I.N.P.L., 1984.

Th. 3e cycle--Phys. nucl.--Grenoble 1, 1978. N°: ISN 78. / 26.

Samples of pure nickel have been implanted with 500keV helium ions, at a dose of 10[17]ions/cm[2], followed by annealing in vacuo at 750°C (≈0.6T[m]) for various time periods to allow bubble nucleation and growth to occur. A transverse sectioning technique has been developed to allow TEM studies of the complete depth distribution of cavities, hence allowing the mechanisms for bubble growth at 750°C in nickel to be identified. It was found that after 2 hours annealing, a fine layer of cavities developed, corresponding well with the gas deposition profile calculated using the E-DEP-1 code. Subsequent annealing resulted in cavity growth on the periphery of the layer by vacancy collection, the principal vacancy sources being the irradiated surface and grain boundaries in the bulk of the material. Cavity growth in the peak implanted region was found to be suppressed due to the lack of vacancies and with bubble migration being hindered as a result of high bubble pressures, hence migration and coalescence did not occur until cavities approached their equilibrium pressure. The same bubble growth mechanisms were found to prevail after implantation of 5x10[16]ions/cm[2] and also after 250keV He implantation. The growth of helium bubbles has been compared to neon bubbles after implantation with 500keV Ne ions at two doses: 7.8x10[16]ions/cm[2] to obtain the same peak gas concentration and 2.9x10[15]ions/cm[2] to achieve the same peak displacement damage, followed by annealing. The cavity density was found to be established by the gas concentration, the displacement damage apparently having little or no effect, even after an approximately 27-fold increase. The growth mechanisms observed after Ne implantation appeared to be the same as those for He, although the bubbles after low dose Ne implantation achieved equilibrium conditions more rapidly, due to the lack of implanted gas. He and Ne have been compared after high energy implantation at 500°C, in the Variable Energy Cyclotron at Harwell to a peak gas concentration of 250ppm. For 4MeV He, an inhomogeneous cavity distribution was observed, compared to a relatively uniform cavity layer after 17MeV Ne implantation. However, the observed cavity sizes and number densities were found to be similar. Finally, nickel has been irradiated at 500°C with a mixed beam of 51MeVNi[6+]/17MeVNe[2+] ions, to 250ppm Ne together with 30dpa displacement damage, and compared to an irradiation with 51MeVNi[6+] ions without inert gas, as well as with 17MeVNe[2+] ions. The void number density profile resulting from the single heavy ion irradiation was similar to the computed damage profile, although the peak was ≈10% deeper than that predicted. A depression in the swelling profile was observed in this peak region resulting from a reduction in cavity size, a bimodal distribution being observed. The effect of simultaneous gas deposition was to increase the cavity nucleation and reduce cavity size. This phenomenon was found to be dominant in the region corresponding to the implanted gas layer, however the gas appeared to influence cavities produced at greater depths, with an overall reduction in swelling.

Neste trabalho são apresentadas medidas das secções de choque de fusão nuclear para o sistema ANTPOT 27 Al + ANTPOT. 16 0,nas energias de bombardeio do feixe de ANTPOT 16 O de 45.6 MeV e 49 MeV. Também foram calculadas através do estudo do espalhamento elástico de ANTPOT 16 O por ANTPOT. 27 Al (modelo Óptico), as secções de choque de reação na faixa de energia de bombardeio de 30 MeV a 45.6 MeV. Na energia de bombardeio de 45.6 MeV, foi feito um estudo da contribuição de outros tipos de reações para a secção de choque total de reação. Neste esquema foi detetada experimentalmente a reação ANTPOT. 27 Al (ANTPOT. 16 O, C). Os dados da secção de choque de fusão nuclear foram comparados com o modelo de Glas e Mosel e foram obtidos valores do momento angular critico (l IND. Cr ). Contribuições de processos como emissão de pré-equilíbrio e fissão nuclear foram calculadas com o uso do código de evaporação Alice. / In this work we present cross-section measurements for nuclear fusion in the 27 Al + 16 O system, at 16 O bombarding energies of 45.6 MeV and 49 MeV. With the aid of the optical model the elastic scattering of 16 O by 27 Al was used to calculate reaction cross-section from 30 MeV to 45.6 MeV. At 45.6 MeV contributions by reaction mechanisms other than fusion were studied. The nuclear fusion cross-sections were compared with the model of Glas and Mosel and values of the critical angular momentum (l cr ) extracted at the above cited energies. Contributions by fusion and pre-equilibrium emission were calculated with the code \"Alice\".

Les processus pétrologiques profonds, qui précèdent ou accompagnent la décompression du manteau sous les dorsales océaniques, tendent à être oblitérés par la fusion partielle. Les régions de dorsales à vitesse d'expansion très lente et/ou anormalement froides exposent des domaines mantelliques qui ont subi un degré de fusion extrêmement faible et donc permettent d'accéder à ces processus. La zone de fracture de Andrew Bain, située à la limite des plaques Africaine et Antarctique, en est un exemple remarquable. Son massif d'intersection avec la dorsale sud-ouest indienne a été exploré au cours de l'expédition océanographique italo-russe S23-AB06. Les échantillons qui ont été prélevés sont principalement des péridotites mantelliques à spinelle ± plagioclase, contenant des plages et des veinules enrichies en pyroxènes ± plagioclase, et montrant des textures de réquilibrages minéralogiques. Les concentrations en éléments majeurs et en traces des pyroxènes, mesurés in situ par EMPA et LA-ICP-MS, montrent une grande variabilité de compositions, identique à toutes les échelles, du massif à la lame mince. La modélisation des compositions des pyroxènes des péridotites indique (1) une cristallisation à partir de liquides de fusion de lithologies enrichies en éléments incompatibles, générés dans un large intervalle de pression débutant dans le faciès à grenat, (2) un rééquilibrage progressif à des conditions de P-T décroissantes, par interaction péridotite - liquide et diffusion à l'état solide. Le modèle est celui d'une refertilisation d'un manteau lithosphérique épais, similaire à celui qui caractérise les domaines de transition continent-océan. / Andrew Bain Fracture Zone represents one of the largest transform faults in the ridge system. Located on the South West Indian Ridge, it constitutes part of the plate margin between Africa and Antarctica. In this area, the lithosphere is thick and mainly constituted by ultramafic rocks; the system is characterized by a negative thermal anomaly. During the Italian-Russian expedition S23-AB06, the seafloor in the Southern Ridge Transform Intersection has been sampled and almost only ultramafic material has been recovered. The sampled spinel and plagioclase peridotites show hybrid textures and are characterized by deep spinel-field impregnation assemblages and by plagioclase-field equilibrated patches and mineral trails marked by crystallization of newly formed plagioclase-field equilibrated trails and formation of plagioclase coronas around pristine spinel. Major and trace element data composition have been collected. Both spinel- and plagioclase-peridotite pyroxenes and spinels follow a main melting trend accompanied by a progressive re-equilibration to lower P/T facies. Thin section-scale variability matches inter-site compositional variability. Progressive re-equilibration to lower P/T conditions can be accounted for by the presence of percolating melts and solid diffusion. Major and trace element shows that percolating melts are generated over a wide pressure range and modeling suggests melting started in garnet stability field but stopped early due to the lithospheric cooling. Thus, this mantle seems to be a thermically “normal” mantle cooled down from above by the anomalous thickness of the old lithosphere, similar to those characterizing continent-ocean transition.

The goal of this thesis was to design, synthesize and test a chemical switch for control of membrane fusion. Control of the shape of the molecules that comprise a membrane should induce a phase change in the membrane. According to current views of membrane fusion, the phase change should also facilitate formation of fusion intermediates hence should provoke membrane fusion. The design thus focused on synthetic lipid targets that have controllable shape changes. Specifically the incorporation of the hemithioindigo (HT) photochemical switch into the fatty acid chains of phospholipids was deemed a solution to the design problem. The synthesis of four phosphatidylcholine (PC) analogues bearing two hemithioindigo moieties was accomplished. The successful synthesis starts from bromophenols. The bromide is extended to a nitrile via the Heck reaction with acrylonitrile. The thiophenol is converted to a thioindoxyl which is coupled with an aromatic aldehyde to produce the HT core. “Solventless” hydrolysis of the nitrile produces a carboxylic acid that can be coupled to a phosphoglycerol to give the target lipids. The synthetic process is both efficient and modular. All new compounds were characterized by NMR, MS and elemental analysis. The photochemistry of various HT derivatives was studied to confirm the expected photoisomerization in both homogenous solutions and vesicle bilayers. Although the UV-Vis spectra become rather insensitive to the presence of different isomers, there is evidence to confirm the Z-E switching in a range of organic solvents and in vesicles. Apparent bleaching of the HT-Iipid may indicate a photochemical dimerization reaction although isomerization would also be consistent with the data. Fusion was explored by manufacturing PS vesicles with varying concentrations and isomers of HT-lipid, and was monitored with the Terbium/Dipicolinic acid aqueous contents mixing assay (Tb/DPA assay). The sensitivity of this assay was lower than originally expected due to inner filter effects resulting in self-quenching the complex luminescence. The available data suggest that the synthetic HT-lipids disturb the membrane structure. Spontaneous fusion, apposition without metal cations, and contents leakage are some of the observations of the complexity of this system. HT-lipids in one population of vesicles are able to interact with a second population of vesicles, presumeably via membrane mixing. These results confirm that shape is a key factor in the integrity of membranes, and that second generation HT-lipids have the potential to control membrane fusion. / Graduate

Adenovirus (Ad) has been one of the most commonly used vectors in gene therapy for many years. One of the limitations of using Ad for cancer therapy is that Ad does not spread within a tumor well. As such, fusogenic proteins have been incorporated into these vectors in an attempt to improve spread through cell-cell fusion. Fusogenic protein mediated cell fusion is also associated with syncytiosome release and cell death, which promote an immune response and suggests that fusogenic proteins may be effective as a sole therapeutic for cancer treatment. In this study, I examined whether the reptilian reovirus p14 fusion-associated small transmembrane (FAST) protein can improve Ad efficacy in cancer models in vitro and in vivo. Ad-mediated FAST protein expression induced cell-cell fusion in human embryonic kidney 293 cells and in human lung adenocarcinoma A549 cells. Infected cells had decreased membrane integrity, cellular metabolic activity and increased cleaved caspase-3 expression. In an A549 xenograft nude mouse model, AdFAST did not induce tumor cell fusion or promote mouse survival compared to control mice. In murine 4T1 mammary carcinoma cells, FAST protein expression had modest effects on cell fusion and metabolic activity in vitro. When AdFAST was administered intratumorally in a 4T1 syngeneic mouse model, there were no obvious signs of cell fusion or improved mouse survival. As FAST protein expression promotes membrane permeability, whether AdFAST could enhance the bystander effect of cancer therapies or promote uptake of anti-cancer drugs was investigated in vitro. FAST protein expression in combination with thymidine kinase/ganciclovir or etoposide administration did not have an enhanced effect. Addition of Smac-mimetic compound (SMC) was not effective in the SMC resistant A549 cell line, but the combinational therapy was able to decrease metabolic activity in SMC susceptible SNB75 cells. AdFAST and administration of the membrane impermeable chemotherapeutic drug bleomycin decreased metabolic activity and promoted cleaved caspase-3 expression in A549 cells. Overall, my results suggest that FAST protein expression could improve adenovirus efficacy and could be used with other anti-cancer treatments.

The crux of all modern semiconductor technology is the exciton, the bound electron-hole pair that drives everything from photovoltaics to light emitting diodes to transistors. This dissertation explores how we can develop materials that are able to control the energetics of excitons, by splitting them and combining them. Also explored are the applications allowed by the control of exciton energetics. The topics covered in this thesis are singlet exciton fission, and triplet fusion upconversion. Chapter 1 will introduce these concepts, and provide an overview of these fields. Chapter 2 discusses the singlet fission properties of a fully conjugated tetracene polymer and its derivatives. This chapter includes the synthesis of these materials, their photophysical properties, as well as their incorporation into bilayer semiconducting devices and their properties under an applied magnetic field. Chapter 3 explores the study of an organic-inorganic hybrid singlet fission triplet acceptor complex. A singlet fission capable pentacene dimer was covalently linked to an iron-oxo cluster with an electron affinity appropriate to accept triplets generated from singlet fission. This chapter explores the synthesis and photophysical properties of this hybrid complex, as well as the nature of the triplet pair state generated from intramolecular singlet fission. In Chapter 4, a new design rule for intramolecular singlet fission is studied, the energy sink. A series of pentacene dimers spaced by tetracene bridges are synthesized, and their singlet fission properties are explored via transient absorption spectroscopy and time resolved electron spin resonance spectroscopy. Chapter 5 begins the portion of the thesis focused on triplet fusion upconversion. The lessons learned from previous work in intramolecular singlet fission are applied to synthesize more efficient annihilators for upconversion. A series of tetracene dimers are synthesized, and their upconversion properties are explored. The work demonstrates intramolecular triplet fusion as a method to enhance the performance of existing annihilators. Chapter 6 details the discovery that diketopyrrolopyrroles can be used as upconversion annihilators. The advantages of these materials relative to existing annihilators are explained. Energetic design rules for upconversion annihilators are also discussed. Finally, in Chapter 7 a new application of triplet fusion upconversion is explored: infrared light sensitized photoredox catalysis.

A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, in partial fulfillment of the requirements for the degree of Master of Medicine in the branch of Orthopaedic Surgery Johannesburg, 2017 / Background Unstable Thoracolumbar spinal fractures are conventionally treated by open reduction and internal fixation. This involves extensive mobilization of paraspinal muscles, which in turn leads to long-term disability in the form of chronic backache. One of the reasons fractures are stabilized is to prevent kyphotic deformity. Posterior lumbar stabilization done through a minimally invasive technique can achieve the same result as the open technique at the expense of less mobilization of the paraspinal muscles. Aim of the study The aim of the study was to assess the effectiveness of minimally invasive posterior spinal fixation in unstable Thoraco-lumbar fractures in our setting at Charlotte Maxeke Academic Hospital. Objectives To assess the effectiveness of Minimally Invasive Spine Surgery over a short term of minimum of 12 months regarding: Maintaining the correction of fracture kyphosis, Re-operations and Any serious Adverse Events Methodology This was a prospective interventional pilot study. Fractures were classified according to the AO comprehensive system. AO Comprehensive classification fractures A3, B1, B2, C1 and C2 were considered suitable for this technique. Pre-operative, immediate post-operative and one year follow up Cobb’s angles of fracture kyphosis were measured on plain lateral x-rays. Any Serious Adverse Events (SAE) that may have required re-operations were recorded over the minimum of 12 months follow up. Results Twenty patients met the inclusion criteria for this study. Post-operative follow up ranged between 12 and 22 months. There were 14 males and 6 females. The age ranged between 16 years to 54 years with mean of 33.9 years. L1 was the most commonly fractured vertebra. Eleven out of 20 patients sustained fracture of L1, 6 patients had fracture of L2 whereas 3 patients sustained fracture of T12. The AO classification types included one B1, five B2, seven C1 and seven C2 fractures. The pre-operative Cobb’s angle ranged from 7 degrees to 38 degrees with mean of 21.2 degrees. The immediate post-operative Cobb’s angle ranged between zero degrees to 16 degrees with mean of 8.3 degrees. The last follow up Cobb’s angle ranged between zero degrees to 21 degrees with a mean of 10.7 degrees. The loss of correction of fracture kyphosis ranged between zero degrees to 6 degrees with a mean of 2.4 degrees. The post-operative Cobb’s angle was maintained. There was no deterioration of pre-operative neurological status. There was no serious adverse event requiring a re-operation. Conclusion Minimally Invasive Posterior Spinal stabilization for thoracolumbar fractures had an acceptable outcome in our hands in appropriately selected cases. The average loss of correction of 2.4 degrees was in keeping with that found in open technique as well as MIS at other centers. While the number is less, this procedure can be recommended for well selected patients where skills are available. / MT2017