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The minority carrier lifetime is a valuable parameter for determining the electrical properties of semiconductors. It is particularly useful in the fabrication of solar cells as minority carrier lifetime is directly related to device efficiency. Pump-probe techniques, in which a pump laser of photon energy above the bandgap energy of the material is used to excite free carrier populations while a sub-bandgap probe laser is used to monitor the change in excess carrier density have been demonstrated to be an effective, non-contact, method to measure the minority carrier lifetime, particularly well-suited for use as an in-line measurement apparatus for the solar cell manufacturing processes In this thesis a non-contact, optical, pump-probe method has been used to determine the minority carrier lifetime of float zone and Czochralski grown <100> silicon samples through measurements of modulated free carrier absorption. The equivalence between measurements performed using the transmitted part of the probe beam and those made with the reflected part have been demonstrated on bare silicon wafers, as well as measurement of effective minority carrier lifetime of a completed solar cell, demonstrating the ability of this technique to measure the effective minority carrier lifetime at any stage of the solar cell manufacturing process. / Thesis / Master of Applied Science (MASc)

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The general aim of this study was to gain an insight into the nature of gully erosion at Golden Gate Highlands National Park. In order to achieve this the spatial and temporal characteristics of six gullies were investigated by examining their typological and morphological characteristics, the relationship between their morphometric properties and their increase in extent over a 39 year period (1952-1991). Where possible these findings and observed gully forms were related to initiating factors. Extensive field surveys and measurements were carried out to ascertain the typological and morphological characteristics of each gully. The results of the field measurements were then statistically analyzed using linear regression analysis, principal component analysis and canonical variate analysis. These methods of analysis were used to get an indication of the relationships taht exist between the morphometric properties of the gullies as well as to highlight the similarities and differences that exist between them. These results showed that the morphometric varaibles of the gullies are strongly interrelated. Furthermore they revealed that the six gullies could be divided into three broad groups on the basis of their morphometric and sediment properties. The gullies within two of the three groups were found to be similar not only in terms of the above mentioned but they also occur on same facing slopes of similar gradients and appear to have been initiated by similar processes. Differences occurring within and between the gully groups were attributed to varying combinations of initiating factors. Aerial photographs from 1952 and 1984 were used together with surverys to map the extent and development of five of the six gullies - teh remainign gully was only initiated in 1988. The 1952 and 1984 photographs were selected as they represented the earleist and most recent photographs to be taken of the area. The maps show the gullies to have experienced a greater amount of growth during the 1984 - 1991 period than during the 1952 - 1984 period. This finding was attributed to the sporadic nature of gully growth. The spatial location of the gullies in relation to one another appears to have had little influence on their typological and morphological characteristics. However, their spatial location within the landscape has undoubtedly influenced these properties. In general the research described has shown that the spatial and temporal differences of the gullies occurring in the park are the result of various combinations of endogenous and exogenous factors that governed the initiation and development of each gully.

Doctor of Philosophy (PhD) / This thesis primarily details the application of high-level ab initio quantum chemistry techniques in order to understand aspects of free-radical mediated protein oxidation. Traditionally, product analysis and electron paramagnetic resonance (EPR) spectroscopy are the primary means for elucidating the chemistry of protein oxidation. However, in experiments involving relatively small proteins reacting with a controlled radical-flux, a vast array of compounds can be produced, which are often difficult to analyse. Quantum chemical techniques on the other hand, can calculate the properties of any particular species directly, without suffering from the problems associated with experiment, such as side-reactions and chain processes. The results presented in this thesis are aimed at elucidating mechanistic details of protein oxidation, which might otherwise be difficult to probe experimentally. Chapter 1 gives an overview of the free-radical hypothesis of disease and ageing. Protein-derived radicals can undergo a variety of reactions, with the particular reaction that occurs depending on numerous aspects. Many types of reactions have been identified through radiolysis experiments of amino acids, and these are detailed in this chapter. In addition, the key reactive species are characterized and their different chemistries explained. Chapter 2 details the theoretical tools used throughout this thesis. Species with unpaired electrons (radicals) present unique problems for quantum chemistry to handle, thus an appropriate choice of theoretical technique is needed. The approach taken in this thesis is to use high-level compound methods, many of which have been directly formulated to give improved results for radical species, to provide benchmark quality results by which other less demanding techniques can be assessed. During the course of this study, it became apparent there was a void in the armoury of tools that could be used for the theoretical chemistry calculations. Chapter 3 details the formulation of a new tool in an attempt to fill this gap. Historically, the formulation of this new procedure came after much of the work in this thesis had been carried out. Thus, for the study of many of the reactions of this thesis the new method has not been used. However, it is most appropriate to place its formulation after summarizing the current status of techniques in common use today. Chapters 4 and 5 detail computations carried out on models of peptides containing backbone carbon- and nitrogen-centered radicals. A number of different theoretical techniques are used in these chapters, ranging from the highly accurate and computationally intensive to the less reliable and less demanding. The highly accurate techniques are used to gauge the accuracy of the other less demanding theoretical techniques so that the latter can be used with confidence in larger systems. Not only is the choice of theoretical technique important but also the judicious choice of model is essential. With this in mind, models are incrementally built until convergence of the particular property of interest is reached. Chapters 6 and 7 detail the calculations of β-scission reactions of alkoxyl radicals, which are a particular class of reaction known to occur on peptide backbones. Alkoxyl radicals are particularly difficult for theory to describe correctly. Therefore, Chapter 6 extensively assesses and then identifies the theoretical methods needed to portray them. Chapter 7 uses the techniques identified in the previous chapter in order to predict how the preference for a particular type of β-scission reaction changes.

Aims: To identify factors, which were related to being smoke-free and snus-free, respectively, among adolescents in relation to adolescents who were smoking and/or using snus, and de-termine if there were any sex differences. Me- thods: A questionnaire study was performed among students in year two in upper secondary schools (17-years-old) in southern Sweden in 2009. More than 2200 students completed the questionnaire regarding health and living habits anonymously. The variables were tested by χ²-test, before selection into the logistic model. Because of the salutogenic approach in the study, the results of the logistic regression analyses were expressed as Positive Odds Ratio (POR). Results: The prevalence of being smoke- free was 75.6 percent for girls and 70.2 percent for boys, whilst the prevalence of being snus- free was 95.1 percent for girls and 70.2 percent for boys. Having a tobacco-free best friend was the most important factor that correlated with being smoke- and snus-free as an adolescent, for both boys and girls. Good living habits, such as drinking less alcohol, were also central to being smoke-free and snus-free. Conclusions: The results show that a tobacco-free environ-ment has a great influence on whether or not adolescents stay tobacco-free. As the environ-ment has a big impact, the school has a big challenge to work with the school environment and policies but also with family responsibility, norms and attitudes to tobacco.