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No description available.

An experiment was conducted to ascertain the effects of irradiation and various concentrations of an aqueous solution of ortho-chlorophenoxyacetic acid on growth rate, abscission layer formation, fruit set, yield, time of maturity, ascorbic acidj dry weight, total nitrogen, total phosphorous, titratable acidity, reducing sugars, total carbohydrates, roughage, ash weight, sodium, potassium, calcium, magnesium, copper, iron, zinc and manganese of tomatoes. Supplementary illumination beyond that of the normal day length resulted in significant increases in weekly growth rate and iron content, with slight increases in fruit set, titratable acidity, total nitrogen, ash weight and magnesium content of tomatoes. The xylem area of the abscission layer was increased as a result of the supplementary illumination. Supplementary illumination also resulted in significant decreases in ascorbic acid, total carbohydrates, sodium and potassium. There were also slight decreases in yield, reducing sugars and calcium of tomatoes. Under normal day length the ortho-chlorophenoxy-acetic acid was more effective in inducing fruit set than where supplementary light was used. The most effective concentration was 75 p.p.m. The trends of the effects of the treatments are discussed, as well as the significant findings. / Science, Faculty of / Botany, Department of / Graduate

Luminescence has been observed from water Irradiated with an intense pulse of high energy electrons. The angular dependence, electron energy dependence, visible spectrum, lifetime and yield of the light emission have been determined. In addition, the effect of additives on the emission was studied. The emission spectrum of water was found to be identical to that of methanol, oyclohexane and benzene. All of these results lead to the conclusion that no light emission other than Cerenkov radiation was present in the visible region of the spectrum. The yield of Cerenkov radiation was found to be GhV(4-5000Å)~6x10-4. / Science, Faculty of / Chemistry, Department of / Graduate

A simple empirical model to calculate solar spectral diffuse and global irradiance under cloudless skies was investigated. This formulation takes into account absorption of radiation by molecules such as O3, H2O and the uniformly-mixed absorbing gases CO2 and O2. Attenuation by Rayleigh-scattering and aerosol extinction are included. Aerosol attenuation is calculated through Angstrom's turbidity parameters α and β. The diffuse radiation is assumed to be composed of three parts: (1) Rayleigh-scattered diffuse irradiance; (2) aerosol-scattered diffuse irradiance; and (3) irradiance arising out of multiple reflections between the atmosphere and the ground. The global irradiance is the sum of these three components of diffuse irradiance plus the direct irradiance. The input parameters include an extraterrestrial spectrum, zenith angle θ, turbidity coefficient β, wavelength exponent α, ground albedo p , water vapor content and ozone content. The model is shown to yield very good results up to air mass two when compared to accurate theoretical calculations. No comparisons with measured spectra are presented because of a lack of accurate specifications of the input parameters. Results are presented to show the effect of variation of certain of the input parameters. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Dans ce travail, nous avons amélioré un modèle de diffusion des défauts ponctuels (lacunes et interstitiels) en introduisant les hétéro-interstitiels. Ce modèle permet ainsi de simuler par Monte Carlo cinétique (MCC) la formation d’amas riches en solutés observés expérimentalement dans des alliages modèles ferritiques irradiés de type Fe – Cu MnNiSiP – C.Des calculs de structure électronique nous ont permis de caractériser les interactions existant entre les interstitiels et les différents atomes de solutés et aussi le carbone. Le P interagit avec les lacunes et très fortement avec l'interstitiel, le Mn interagit également avec l’interstitiel pour former un dumbbell mixte. Le C, en position octaédrique, interagit fortement avec la lacune et plus faiblement avec l'interstitiel. Les énergies de liaison, de migration ainsi que d’autres propriétés à l’échelle atomique, déterminées par calculs ab initio, nous ont conduits à un jeu de paramètres pour le code de MCC. Dans un premier temps, ces paramètres ont été optimisés sur des expériences, de la littérature, de recuits isochrones d’alliages binaires préalablement irradiés aux électrons. Les simulations de recuit isochrone, en reproduisant les tendances observées expérimentalement, nous ont permis d'associer précisément un mécanisme à chacune des évolutions de la résistivité au cours du recuit. Par ailleurs, les limites de solubilité des différents éléments ont été déterminées par Monte Carlo Metropolis. Dans un second temps, nous avons simulé l’évolution à 300 °C de la microstructure sous irradiation dans des alliages de complexité croissante : fer pur, alliages binaires, ternaires, quaternaires, et enfin alliages complexes de compositions proches de celle de l'acier de cuve. L'ensemble des simulations montrent que le modèle reproduit globalement les tendances des résultats expérimentaux, ce qui a permis de proposer des mécanismes pour expliquer les différents comportements observés. / In this work, we have improved a diffusion model for point defects (vacancies and self-interstitials) by introducing hetero-interstitials. The model has been used to simulate by Kinetic Monte Carlo (KMC) the formation of solute rich clusters that are observed experimentally in irradiated ferritic model alloys of type Fe – CuMnNiSiP – C.Electronic structure calculations have been used to characterize the interactions between self-interstitials and all solute atoms, and also carbon. P interacts with vacancies and strongly with self-interstitials. Mn also interacts with self-interstitials to form mixed dumbbells. C, with occupies octahedral sites, interacts strongly with vacancies and less with self-interstitials. Binding and migration energies, as well as others atomic scale properties, obtained by ab initio calculations, have been used as parameters for the KMC code. Firstly, these parameters have been optimized over isochronal annealing experiments, in the literature, of binary alloys that have been electron-irradiated. Isochronal annealing simulations, by reproducing experimental results, have allowed us to link each mechanism to a single evolution of the resistivity during annealing. Moreover, solubility limits of all the elements have been determined by Metropolis Monte Carlo. Secondly, we have simulated the evolution at 300 °C of the microstructure under irradiation of different alloys of increasing complexity: pure Fe, binary alloys, ternaries, quaternaries, and finally complex alloys which compositions are close to those of pressure vessel steels. The results show that the model globally reproduces all the experimental tendencies, what has led us to propose mechanisms to explain the behaviours observed.

No abstract available. / Dissertation (MSc)--University of Pretoria, 2010. / Medical Oncology / unrestricted