Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This thesis investigates questions surrounding the role that iron-rich colloids (nominally sized between 0.02 μm and 0.2 μm) and particulates (>0.2-0.45 μm) play in the context of the greater iron biogeochemical cycle. To this end, this study complements a review of reported size-fractionated iron (Fe) measurements with chemical and mineralogical data derived from synchrotron-based xray measurements. From an extensive literature review, the global surface ocean colloidal iron (cFe) pool is found to be highly dynamic, frequently exhibiting seasonal trends and nutrient-like behaviour. Spatial variability in surface ocean colloidal iron concentration is primarily a function of total iron supply, although the concentration and strength of iron-binding ligands, and inorganic thermodynamic constraints are additional influential factors. The size-fractionated study of colloidal Fe has rendered considerable evidence pointing towards direct or indirect biological utilization of this cFe pool; however, a more complete understanding of cFe-biological interaction necessarily requires better knowledge of cFe chemistry and mineralogy. To address these issues, this thesis documents the development of a novel x-ray microscopy and spectroscopy technique for determining the Fe speciation of individual Fe-rich particles under environmental conditions. Variations in the peak splitting in iron L3-edge XANES (X-ray Absorption Near-Edge Structure) spectra reflect changes in the local coordination environment surrounding the metal centre. Specifically, the energy splitting ( ΔeV) and intensity ratio of the split peaks at the L3-edge vary as a function of the Fe valence state, the number and chemistry of coordinating ligands and polyhedral distortion effects; and combinations of the two parameters are found to be characteristic of individual Fe minerals. To understand Fe speciation, the Δ eV versus intensity ratio plot was successfully applied to a variety of environmental Fe particles (greater than 20 nm diameter) collected from two ocean basins; the Southern Ocean and the south western Pacific Ocean. Speciation differences in Fe particles collected from the Southern Ocean show distinct compositional trends between the coasts of South Africa and Antarctica, with different Fe pools associated with the different oceanographic frontal zones. Despite the oxygenated nature of the seawater sampled, the presence of significant particle-hosted Fe(II) was observed in both the Southern Ocean at high latitudes, and at sampling sites proximal to the Kermadec Ridge in the Pacific Ocean. Ferrous iron particles at the latter study area were shown to be strongly associated with carbon functional groups, notably alcohol and carboxamine moieties. These findings, relating to particle chemical differences and associations with organic matter, have significant implications for our understanding of particle behaviour, their surface interactions and the role that they play in primary productivity and global elemental cycles. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek kwessies met betrekking tot die rol wat ysterryke kolloïede (van nominale groottes tussen 0.02 μm en 0.2 μm) en partikels (>0.2-0.45 μm) in die konteks van die groter ysterbiogeochemiese siklus speel. Vir hierdie doel bou die studie voort op ’n oorsig van aangemelde grootte-gefraksioneerde yster- (Fe-)metings met behulp van chemiese en mineralogiese data wat uit sinchrotrongebaseerde x-straalmetings verkry is. Na aanleiding van ’n uitvoerige literatuurstudie, blyk die globale poel kolloïdale yster (cFe) op die see-oppervlak hoogs dinamies te wees en toon dit dikwels seisoenale tendense en voedingstofagtige gedrag. Ruimtelike veranderlikheid in die cFekonsentrasie op die see-oppervlak is hoofsaaklik ’n funksie van totale ystervoorsiening, hoewel die konsentrasie en sterkte van ysterbindende ligande sowel as anorganiese termodinamiese beperkings ook ’n invloed kan hê. Die grootte-gefraksioneerde studie van kolloïdale Fe het beduidende bewyse opgelewer wat op die direkte of indirekte biologiese benutting van hierdie cFe-poel dui. Tog verg ’n vollediger begrip van cFe- biologiese interaksie noodwendig meer kennis van die chemie en mineralogie van cFe. Om hierdie kwessies te ondersoek, dokumenteer hierdie tesis die ontwikkeling van ’n innoverende X-straalmikroskopie- en X-straalspektroskopietegniek om die Fe-soortvorming van individuele Feryke partikels in omgewingsomstandighede te bepaal. Variasies in die pieksplitsing van yster-L3 rand-XANES- (“X-ray absorption near-edge structure”-)spektra weerspieël veranderlikheid in die lokale koördinasie-omgewing rondom die metaalkern. In die besonder wissel die energiesplitsing ( eV) en intensiteitsverhouding van die splitsingspieke by die L3-rand na gelang van die Fevalensietoestand, die getal en chemie van koördinasie-ligande, en poliëdriese distorsie-effekte, en kombinasies van die twee parameters blyk kenmerkend van individuele Fe-minerale te wees. Om Fe-soortvorming te verstaan, is die stipping van Δ eV versus intensiteitsverhouding suksesvol toegepas op ’n verskeidenheid Fe-omgewingspartikels (groter as 20 nm in deursnee) wat uit twee oseaankomme – die Suidelike Yssee en die suidwestelike Stille Oseaan – bekom is. Soortverskille in Fe-partikels wat uit die Suidelike Yssee bekom is, toon kenmerkende samestellingspatrone tussen die kus van Suid-Afrika en Antarktika, en verskillende Fe-poele word met die verskillende oseanografiese frontsones verbind. Ondanks die suurstofhoudende aard van die seewatermonsters, is beduidende Fe(II) in partikels opgemerk in die Suidelike Yssee by hoë breedteliggings sowel as op studieterreine naby die Kermadec-rif in die Stille Oseaan. Ysterhoudende partikels van laasgenoemde studieterrein het ’n sterk verband met koolstof- funksionele groepe, veral alkohol en karboksamien, getoon. Hierdie bevindinge met betrekking tot die chemiese verskille tussen partikels en die verband met organiese materie het beduidende implikasies vir ons begrip van partikelgedrag, die oppervlak-interaksies van partikels, en die rol wat dit in primêre produktiwiteit en globale elementsiklusse speel.

No description available.

CCI Valve Technology AB is a company located in Säffle, Sweden, that manufactures and installs bypass valves. Due to requirements outside normal standards on the valve's hardness values, some measurements have had difficulties meeting such requirements. During this thesis work, tests were carried out to determine how to overcome the difficulties. The experiments focused on five different areas that may affect the components hardness, welding method, soaking temperature during post weld heat treatment, measuring procedure, component thickness and number of heat treatment cycles. The Grade 91 steel specimens that were examined consisted of five solid cylinders and three various pipes that were welded together by using shielded metal arc welding (SMAW) or gas tungsten arc welding (GTAW). Each pipe was sawed apart into three equal parts. All specimens were hardness tested and eight of the specimens' microstructure was studied with an optical microscope. The hardness measurement instruments used, LECO V-100-C2 and GE-MIC 10, are Vickers hardness testers, one stationary and the other one portable. The measuring results contain a vast number of different hardness measurement data. From the analyzed data, the conclusions were drawn that the most suitable soaking temperature during post weld heat treatment were 750° C, that the SMAW method creates a more stable hardness profile than the GTAW method, and that one heat treatment cycle is more beneficial than two or more.

Les particularités de climat et les nouveaux avions très gros porteurs, imposent des effets cycliques dangereux sur les couches de roulement. Les simulations en laboratoire de ces phénomènes ont montrées leur influence sur les qualités viscoélastiques du bitume et enrobé, qui sont fonctions des variations de la température. Telles que les déformations permanentes avec perte de résistance et le durcissement du bitume associé au vieillissement accéléré. Les lois de comportement en fatigue sous trafic prouvent que les grandes amplitudes de déformation en tandem endommagent sévèrement l’enrobé. Les informations recueillies permettent de mieux prévoir l’évolution du comportement in situ du bitume et enrobé. / Abstract

M.Com. (Economics) / Please refer to full text to view abstract

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Deserted and disintegrating barns, houses, and silos have always perplexed me when driving through the country. I am fascinated by how this leisurely decay reveals their structural integrity in a slow, reverse process of construction. It is as if humanity and nature consciously collaborated to create these gigantic memento mori for a steady stream of highway viewers. These monumental tributes to inevitable decline, along with my own adventures in gardening, childrearing, eldercare, and travels, have led me to explore the universal cycles of life. The dilapidated buildings in my work are rendered in a tight, sharp, close-up viewpoint so that the viewer is forced to engage them. I will often layer images of seeds, leaves, and rocks on top of images of houses to symbolize the different stages of the life cycle. I see seeds and buildings as containers and incubators of potential. Any foliage represents a fulfillment of that potential, while rocks stand for the fossilized remains, or the achievements of one’s life accomplishments.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

M.Comm. / There are many different opinions among economists around the validity and existence of the business cycle. It varies from the total nullification of the existence of a business cycle to the founding of a working definition in this regard. One of the characteristics of the South African economy and similar capitalist systems is an unstable business environment. Periods of economic growth are followed by periods of economic recession when employment, production, prices, profits and general economic welfare are in decline. These phases are known as the business cycle. Economists differ from the early days with relation to the factors that led to changes in total economic activity. Classical economists focussed on the supply side factors as the main cause of the business cycle. John Keynes criticized the early models and presented a model in which change in output is largely dependent on changes in aggregate demand. The latest theory is known as the Real Business Cycle and includes both the supply and demand side factors. The emphasis is, however, on the supply side and argues that changes in the aggregate supply are the main determining factor in economic contraction or expansion. Between 1946 and 1996, 14 complete cycles occurred in the South African economy. The total cycle comprises of the first upward phase, the second upward phase, the first downward phase and the second downward phase. Specific indicators are present during each phase. Car sales are determined by demand. The demand include consumer preference, income, the price of competing or similar goods, expectations of the consumer, availability of credit, consumer confidence as well as the price of the product. The single most important influence on car sales is political stability, economic growth and interest rates. These factors determine the extent of consumer confidence. The occurrence of business cycles in the South African economy and the cyclical tendency of car sales are largely in tandem. Of the 14 upward and onward phases since 1960, 12 phases show positive correlations. This means that car sales represent an adequate barometer with regard to the state of economic activity as a whole in the country. It is also an effective barometer regarding expected future developments on the economic front. The state of the business cycle can be of tremendous value regarding planning in the motor manufacturing industry. The specific phase in which the business cycle is, will provide a sound indication of what kind of success might be anticipated with regard to future sales.

OBJECTIVES: To determine and compare color difference CIEDE2000 (ΔE00) of pressed IPS E.max lithium disilicate ceramic material after repeated firing cycles. To determine and evaluate correlation of CIELAB and CIEDE2000 values analyzed by X-Rite Color i5 Spectrophotometer, VITA EasyShade® Advance 4.0 (VITA Zahnfabrik) and Adobe Photoshop CC. MATERIALS AND METHODS: 36 specimens 8mmX10mm at 1.5mm thickness (12 specimens of pressed IPS e.max® Press Lithium Disilicate MT Monochromatic ingots and 24 specimens pressed IPS e.max® Multi Press Lithium Disilicate Multichromatic ingots. Specimens were exposed to repeated firing cycles up to 7 cycles. Color analysis was performed after 1st,2nd,3rd,5th, and7th firing cycle. CIE L*a*b* values measured by X-Rite Color i5 Spectrophotometer, VITA EasyShade® Advance 4.0 (VITA Zahnfabrik) and Adobe Photoshop CC. CIELAB (Δ*ab) and CIEDE2000 (Δ00) calculated to measure color difference. RESULTS: Linear regression and multiple comparison analysis (Tukey’s HSD test) showed a significant color difference (Δ*ab) and CIEDE2000 (Δ00) with (p-value <0.001), after multiple firing cycles, between instruments used and in different shades groups. Moreover, significant different in interactive effect between different shades tested by different instrument, different shades tested after multiple firing cycles and different instruments after multiple firing cycles. CONCLUSION: IPS E.max lithium disilicate material shows significant color difference after repeated firing cycle tested by three color analysis instruments. Measuring instruments used to evaluate CIE L*a*b* color values showed significant different in color values analysis which may lead to altered level of interpretation, particularly to determine perceptibility and clinical acceptability thresholds. / 2021-08-15T00:00:00Z