<p>The effects of pressurization on the properties of metals has long been of interest to scientists. Bridgman found that in general, the ductility (ability of the metal to deform without fracture) increased with superimposed hydrostatic pressure. Pugh et al. confirmed similar findings.</p> <p>The effects of hydrostatistic pressure on the mechanical properties of thin anisotropic zinc, heat treated and non heat treated zinc alloy sheets subjected to biaxial tension (via the circular bulge test) is investigated in this project.</p> <p>A brief look is taken into the generalized conditions for the onset of tensile plastic instability in a thin circular diaphragm bulged under superimposed hydrostatic pressure. The material is assumed to obey Hill's theory of yielding for anisotropic materials. These predictions are verified by conducting bulge tests using back pressures up to 10,000 psi. It is concluded that within the pressure range of investigation there is no detectable changes in the properties of the materials tested.</p> <p>In the appendix section a brief look is taken into the microstructure of the materials tested.</p> / Master of Engineering (ME)

<p>The project described in this thesis was to establish the instrumentation and technique for analysing stability of machine-tools against chatter by harmonic excitation. To test out the technique, two sets of experiments were performed on centre lathes:</p> <p>1) comparison of cutting stability with tour different types of boring bars, and</p> <p>2) comparison of cutting stability of a tool oriented in seven orientations in a single plane perpendicular to the spindle axis.</p> <p>The electro-dynamic exciter was used in 1) while an electro-magnetic exciter was used in 2) Data of the excitation tests were used to compute and plot the cross-receptances which indicate the limit width of cut together with the chatter frequency and the modal shapes which identify the main masses and springs of the structure. The contribution of the individual modes to the resulting degree of stability can also be obtained. Cutting tests were conducted to provide some means of checking the reliability of the excitation test results. In this report also included are the theory of vibration, theory of chatter and specification of various parts of instrumentation.</p> / Master of Engineering (ME)

<p>The Internet provides opportunity for knowledge sharing among people with similar interests (i.e., buddies). Common methods available for people to identify buddies for knowledge sharing include emails, mailing lists, chat rooms, electronic bulletin boards, and newsgroups. However, these manual buddy finding methods are time consuming and inefficient. In this thesis, we propose an agent-based buddy finding methodology based on a combination of case-based reasoning methodology and fuzzy logic technique. We performed two experiments to assess the effectiveness of our proposed methodology. The first experiment was comprised of a stock market portfolio knowledge sharing environment in which a conventional cluster analysis was used as a benchmark to assess the technical goodness of the proposed methodology in identifying the clusters of buddies. Statistical analysis showed that there was no significant ranking difference between conventional cluster analysis and the proposed buddy-finding methodology in identifying buddies. Cluster analysis requires centralized database to form buddies (clusters) with similar properties. The unique advantage of our proposed agent-based buddy finding methodology is that it can identify similar buddies in distributed as well as centralized database environments. A second experiment, in the context of sharing musical-knowledge among human subjects, was used to find out whether selection of the buddies by the proposed methodology is as good as those done by human subjects. The findings from this latter empirical test showed that the buddies found by agents are as good as the buddies found manually by humans.</p> / Doctor of Philosophy (PhD)

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The aetiology and pathogenesis of primary open angle glaucoma (POAG), the second most common cause of irreversible visual loss in the United Kingdom, remains a conundrum for contemporary ophthalmology. Evidence suggests that glaucoma is a complex disorder, where multiple genes interact with each other and with factors in the environment. However, the aetiological heterogeneity of glaucoma coupled with its varied clinical presentation and course has made the study of glaucoma genes problematic. We established the Orcades Eye Study, a cross sectional family based genetic study, to explore the inheritance of primary open angle glaucoma (POAG). As POAG is a disease of late onset and low prevalence, rather than study disease per se we chose to study quantitative traits (QTs) related to POAG, in an isolated population in the northern Scottish archipelago of Orkney. A number of factors in this population, including reduced genetic heterogeneity and more homogenous environmental effects, confer certain advantages over more admixed urban populations in complex disease gene mapping. Preliminary analysis of the procured quantitative trait data (n=256) has demonstrated that the values obtained for the POAG related QTs of intraocular pressure (IOP), central corneal thickness and a number of optic disc parameters including optic cup area, disc area, retinal nerve fiber thickness, vertical cup to disc ratio and peripapillary atrophy are not dissimilar to other published White Caucasian populations. We also found that intraocular pressure shows an increase with age and is influenced by central corneal thickness but found no relationship between IOP and gender or IOP and other ocular biometric variables including optic nerve head parameters and refractive components. Neither central corneal thickness nor optic nerve head parameters had a statistically significant relationship to age, gender or other tested ocular biometric parameters. These findings are clinically important as these factors should be taken into consideration when evaluating intraocular pressure and other ocular biometric traits in the investigation of glaucoma and other ocular diseases in the population of Orkney. Data collection is ongoing, and with time, an increased sample size and a meaningful genetic analysis, the Orcades Eye Study will hopefully identify genes and regions of the genome associated with primary open angle glaucoma susceptibility in the Scottish Population Isolate of Orkney. To our knowledge, the only other population based study which has investigated as large a number of glaucoma related QTs is the Beijing Eye Study.

Three new reconstruction methods for quantitative phase imaging, including two interrelated two-dimensional methods, called multifilter phase imaging with partially coherent light and phase optical transfer function recovery, which lead to a third three-dimensional method, called tomographic deconvolution phase microscopy, were developed in response to a growing need among biomedical end users for solutions which can be integrated on standard microscope platforms. The performance of these new methods were evaluated using modelling and simulation as well as experimentation with known test cases. In addition to the development of new methods, existing methods for quantitative phase imaging were applied to characterize the effects of manufacturing, cleaving, and fusion splicing in large-mode-area erbium- and ytterbium-doped optical fibers.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The assessment of dehydration is an ever elusive golden standard, even given the plethora of hydration markers that exist to date. Many literature sources acknowledge the need for a portable device that can be used as an indicative tool for hydration. This project sought to find a solution for assessing dehydration on a micro level looking for an indication of hydration by investigating the levels of water concentration in the skin and water compartments of the body using bioelectrical impedance, stratum corneum impedance and infrared spectrometry. Two studies were conducted to evaluate the efficacy of these devices: an infield study to assess the efficacy of the devices for measuring dehydration brought on by exercise in adults and an infant study where the devices where used to assess its ability to measure dehydration in infants who have succumbed to diarrhoea. The studies showed that the devices are not applicable in measuring real time hydration in exercising subjects as sweat was a perturbing factor in the measurements. The infant study provided promising results with regards to the usage of the infrared device. It is believed that these results could spur further investigation into the field of using infrared spectrometry as a dehydration marker. Dehydration still remains to be an ever elusive standard but the importance of finding a solution to quantitatively assess hydration is a field which could benefit the general population and its importance should not be underestimated. / AFRIKAANSE OPSOMMING: Die assessering van dehidrasie is steeds 'n ontwykende goue standaard selfs gegewe die oorvloed van hidrasiemerkers wat bestaan tot op datum. Baie literatuurbronne erken egter die behoefte aan 'n draagbare toestel wat as 'n hulpmiddel kan dien vir die evaluering van die vlakke van dehidrasie. Hierdie projek streef daarna om ondersoek in te stel tot die assessering van dehidrasie op 'n mikrovlak deur die waterkonsentrasies te meet in die vel en die verskeie waterkompartemente in die liggaam via die gebruik van bio-elektriese impedansie analise, stratum corneum impedansie analise en infrarooi-spektrometrie. Twee studies is gedoen om die doeltreffendheid van die toestelle te evalueer: 'n inveldstudie wat die hidrasievlakke van volwassenes meet wat ly aan dehidrasie weens oefening en 'n studie wat dehidrasie meet in neonate wat ly aan dehidrasie weens diarree. Die studies het bewyse gelewer dat die toestelle nie effektief is met betrekking tot die meet van dehidrasie in aktiewe volwassenes nie, weens die rede dat sweet 'n verstorende faktor is. Die neonate studie het belowende resultate verskaf met betrekking tot die gebruik van die infrarooi toestel. Daar word geglo dat hierdie resultate verdere ondersoek in die veld met betrekking tot infrarooi spektrometrie as 'n hidrasie merker kan motiveer. Finale bevindinge wys dat die kwantifisering van dehidrasie steeds 'n ontwykende standaard is, maar die belangrikheid van 'n moontlike oplossing sal voordelig wees vir die wêreld se volke en moet dus nie onderskat word nie.

Malonaldehyde, a very reactive member of the homologous series of dialdehydes, is associated with the autoxidative deterioration of lipids. Its measurement, in autoxidized lipid systems is an expression of the extent of oxidation, in lipids. Malonaldehyde lends itself well to such determinations because of the sensitivity and specificity of its quantification in complex lipid systems. Complete knowledge of the formation of malonaldehyde in autoxidized lipids. is lacking. Such knowledge would undoubtedly promote a better understanding of lipid autoxidation mechanisms. In this investigation, a method for detecting malonaldehyde through the use of its reaction with p-aminobenzoic acid was developed. This was adapted for use in measuring malonaldehyde in lipids and in tissue samples. The reaction between p-aminobenzoic acid and malonaldehyde was partially characterized, and a mechanism for the formation of the reaction product was postulated. The quantification of malonaldehyde in lipid systems by the use of p-aminobenzoic acid involves the use of a mild reducing agent such as stannous chloride to prevent interference from hyd roperoxides present in the system. The p-aminobenzoic acid reaction is highly specific for malonaldehyde and proceeds smoothly and rapidly at room temperature in a non-aqueous chloroform-methanol solvent system to yield a highly colored compound having a maximum absorbance at 406 mμ. and with a molar absorptivity of 73,500. The absorbance value may be converted directly to parts-per-million malonaldehyde through the use of a conversion factor in a simple equation. The limits of detectability of themethod are on the order of one ppm malonaldehyde. The measurement of malonaldehyde in the lipid fraction of tissue samples involves the prior extraction of the lipid with a non-aqueous chloroform-methanol solvent, by an extraction method which was developed for this purpose. The reaction of malonaldehyde with p-aminobenzoic acid involves the condensation of two molecules of p-aminobenzoic acid with one molecule of malonaldehyde. The reaction exhibits a rate maximum at a hydrogen ion concentrations of about 0.1 molar, and also exhibits rate dependencies upon the concentrations of both malonaldehyde and p-aminobenzoic acid. This strongly suggests that the reaction proceeds according to an S [subscript N] 2 mechanism. A postulated mechanism involves nucleophilic 1,4-addition of the amino nitrogen of p-aminobenzoic acid to the enol of malonaldehyde followed by-loss of water to form the enamine. The reaction with a second molecule of p-aminobenzoic acid involves nucleophilic substitution of the amino nitrogen at the carbonyl function of malonaldehyde followed by loss of water to form an imine linkage. / Graduation date: 1968

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