Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 196-200).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1983. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.A.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Proefschrift--Groningen. / "Samenvattend overzicht": p. [55]-57. "Stellingen" (2 leaves) laid in. Bibliographical foot-notes.

Thesis (doctoral)--Lund University, 1994. / Added t.p. with thesis statement inserted.

Quantitative studies of global radiation damage are presented for two different types of experiments in structural biology: macromolecular crystallography (MX) and small angle X-ray scattering (SAXS) MX is the most common technique to elucidate the atomic resolution structures of biological macromolecules. However, these molecules undergo radiation induced changes during the experiment that undesirably affect the data. Global radiation damage, which is characterised by an overall loss in the diffracted intensity of Bragg reflections, limits the amount of useful data that can be collected from a single crystal in an experiment. Furthermore, for experimental phasing experiments, the radiation induced intensity changes can be so significant that the phasing signal becomes undetectable, thereby hindering successful structure determination. This thesis investigates methods to track and correct the diffraction data that are affected as a result of global radiation damage. First, extensions to the diffraction weighted dose (DWD) metric are investigated for the ability of DWD to track the overall intensity decay of reflections. This metric then is combined with a new mathematical model of intensity decay to perform zero-dose extrapolation. An additional probabilistic extrapolation approach is incorporated into the traditional regression based approach to allow extrapolation of low multiplicity reflections. As an alternative approach, a new hidden Markov model representation of the data collection experiment is developed that allows the time-resolved calculation of structure factor amplitudes, with error estimates calculated explicitly. This method gives comparable refinement statistics to that obtained from data processed with the current data reduction pipeline, and improvements to the algorithm are proposed. SAXS, on the other hand, is a complementary structural technique that results in low resolution information about macromolecules. However it still requires the probing of the macromolecules with ionising radiation, so radiation induced changes are still a problem. Unfortunately the tools for assessing radiation damage in SAXS experiments are not mature enough for them to be used routinely. This thesis presents extensions to RADDOSE-3D to perform dose calculations for SAXS samples. Additionally, a free, open source Python library has been developed to allow the exploration and visualisation of the results of a similarity analysis of frames within a dataset. These tools are then used to determine the efficacy of various radioprotectant compounds at different concentrations to mitigate radiation damage effects.

Orientador: Lourenço Correr Sobrinho / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-13T08:17:31Z (GMT). No. of bitstreams: 1 Biscaro_SandroLuis_D.pdf: 1231684 bytes, checksum: 94a704d3aec635c1016ca3eb4b5ced3a (MD5) Previous issue date: 2009 / Resumo: O objetivo neste estudo foi avaliar a influência de diferentes doses de radiação X na resistência de união de restaurações adesivas à dentina, mediadas por sistemas que apresentam diferentes estratégias para união. Foram obtidas superfícies planas de dentina em molares humanos e amostras cilíndricas foram construídas com compósito (Z250, 3M ESPE), para o teste de resistência de união ao microcisalhamento, utilizando três sistemas de união: um adesivo de condicionamento total de dois passos (Single Bond 2 - SB2, 3M ESPE), um autocondicionante de dois passos (Clearfil SE Bond - CSE, Kuraray) e um autocondicionante de passo único (Adper Prompt - ADP, 3M ESPE). As amostras foram separadas em 4 grupos (n= 10), de acordo com a dose de radiação X: 0 (controle), 5, 35 ou 70 Gy. A radiação foi direcionada para a superfície dos cilindros de compósito. O teste de microcisalhamento foi realizado após 24 h, e os modos das falhas classificadas com aumento de 200x. Os dados foram submetidos à Análise de Variância dois fatores e teste de Holm-Sidak's (p < 0,05). Uma análise de regressão não-linear foi conduzida com "resistência de união" como variável dependente. Os resultados de resistência de união (MPa) foram dose e material dependentes. SB2: controle > 5 = 35 > 70; CSE: controle = 5 > 35 = 70; ADP: controle = 5 = 35 = 70. Generalizando, SB2 > CSE > ADP. A análise de regressão não-linear mostrou que, em geral, um aumento na dose de radiação promoveu diminuição na resistência de união (R2 < 0,905). Os modos de falhas foram dependentes do sistema de união, mas, em geral, não houve influência significativa da radiação. Concluindo, a radiação-X apresentou um efeito dosedependente significativamente negativo na adesão à dentina. / Abstract: This study investigated the influence of different x-ray radiation doses on the bond strength of adhesive restorations to dentin mediated by systems presenting distinct bonding strategies. Flat dentin surfaces in human molars were obtained and cylinder-shaped specimens for the microshear bond test were build-up with a composite (Z250, 3M ESPE), using three adhesive systems: a total-etch, two-step (Single Bond 2 - SB2, 3M ESPE), a self-etching, two-step (Clearfil SE Bond - CSE, Kuraray), or a self-etching, single step (Adper Prompt - ADP, 3M ESPE). The specimens were assigned to 4 groups (n = 10), according to the x-ray dose: 0 (control), 5, 35 or 70 Gy. Radiation was directed to the surface of the resin cylinders. Microshear testing was conducted after 24 h, and the failure modes classified under magnification (200x). Data were submitted to two-way ANOVA and Holm-Sidak's test (p<0.05). A non-linear regression analysis was carried out with 'bond strength' as dependent variable. Bond strength results were dose- and material-dependent. SB2: control > 5 = 35 > 70; CSE: control = 5 > 35 = 70; ADP: control = 5 = 35 = 70. Generally, SB2 > CSE > ADP. The non-linear regression plots showed that in general, an increase in radiation dose may predict a decrease in bond strength (R2 = 0.905). Failure modes were dependent on the bonding system, generally with no significant influence of radiation. X-ray radiation presented a significant, dose-dependent detrimental effect on the bond to dentin. / Doutorado / Radiologia Odontologica / Doutor em Radiologia Odontológica

The ultimate aim of this work is to develop a laboratory model of large area, xenon-filled, proportional counter, that has good spatial resolution in conjunction with optimum spectral resolution in the energy range 1 to 10 keV. The results of initial development on a 10cm x 10cm imaging counter are first described. The most important effect established in this work is the dependence of spatial resolution on the quench gas. This effect is also observed to be a function of detector size. The mechanism proposed is that secondary electrons liberated by UV photons from the avalanche cause fluctuations in the centroid position of the induced charge distribution. Space charge effects are also observed at the gains required for imaging, which implies that the detector is semi-proportional. This causes degraded energy resolution at the high gains that are used for imaging. The linearity of a xenon imaging counter is found to be poor in the axis perpendicular to the anode wire direction. The use of a long drift region and different quench gases are investigated together with their effect on linearity and spatial resolution in the axis perpendicular to the anode wire direction. Finally, the construction and evaluation of a large area counter 30cm square is described. It is shown that this device produces excellent results (spatial resolution of 1.2mm FWHM and an energy resolution of 27% at 6 keV). Methods of improving the performance of the instrument are also discussed.

M.Sc. (Chemistry) / In this investigation a monostandard calibration technique was developed for multi-element X-ray fluorescence analysis. A reliable method is described for the calculation of slopes of calibration lines for thin-film and powder samples using monochromatic as well as polichromatic excitation. Theoretically calculated slopes for elements within one serles, e.g. the K-series, were normalised .using one or two known slopes for elements in the series. The mathematical equations used to -. interpolate slopes as a function of atomic number, were based on the fundamental relationship between fluorescent intensity and atomic number, fluorescent yield, detector efficiency, concentration and mass absorption coefficients. Kramer's formula was used to approximate the shape of the" primary radiation spectrum. The method was applied to the analysis of the K-series elements, with the use of thin-film and powder samples. The excitation was achieved by the use of a molybdenum-, gold-, tungsten- and chrome anodes. The method was also applied to the analysis of the L-series powder samples. The monochromatic excitation of the L-series elements, achieved with the use of a molybdenum anode, is also described. The polichromatic excitation of the L-series powder samples was obtained with a molybdenum-, gold-, tungsten- and chrome anode.

No description available.