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<p><strong> </strong></p> <p><strong> </strong></p> <p>Considerable attention has been paid to the reaction between molten iron oxide containing slag and iron droplets or solid carbon due to the critical roles it plays in various metallurgical processes. However, during the last two decades, most of the studies have been carried out on iron droplets, for which the size remains constant. Another important phenomenon, that the droplet will swell has not been paid the same attention. Knowledge of the extent of droplet swelling is essential in predicting residence times in BOF steelmaking. The objective of this study is to develop the understanding for droplet swelling and produce a predictive model that predicts droplet swelling over the range of oxygen steelmaking conditions.</p> <p>Several workers have observed swelling of high carbon droplets when exposed to oxidizing slags. In the present work, the measurements on swelling rates were made using X-ray fluoroscopy. Comparing the swelling rate with the total volume of gas evolved during the reaction, it is shown that only a small percentage of the gas generated is retained in the droplet to contribute to swelling. The gas generation rate is shown to be controlled by the rate of nucleation of CO bubbles inside the droplet. The critical supersaturation pressure for nucleation is found to be two orders of magnitude less than predicted from theory, which is in keeping with many other studies on nucleation of gases in liquids. However, the effect of surface tension, temperature and saturation pressure shows quantitative agreement with theory.</p> <p>In order to predict the droplet swelling rate, CO bubble escape rate has to be known. In this research, the escape mechanism has been proposed; it is the film rupture around the iron droplet surface. The rupture rate is mainly influenced by viscosity, surface tension and bubble size. For a given experimental condition, the calculated film thickness is 1.5 μm at the maximum drop diameter, assuming the bubble radius is 0.3 mm. The CO escape rate is 2.51 cm³/s, it agrees well with 1 to 12 cm³/s when gas escapes from steelmaking slags considering the differences of surface tensions and viscosities between metal and slag.</p> / Doctor of Philosophy (PhD)

<p> When a polymer system is strained below its glass transition temperature, T9 , deformed regions called crazes may be formed that have a characteristic extension ratio, λ. Examining the regions of deformed material, which are almost visible to the naked eye, and measuring λ with the use of atomic force microscopy gives information about the space between entanglements along a polymer chain, which is a truly molecular quantity. In this work we present the results of experiments in which entanglements in high molecular weight polystyrene (PS) samples have effectively been swelled by diluting the network with low molecular weight PS. We find that these experiments not only tell us how the molecular weight of a polymer can affect its contribution to the polymer network, but also give an entirely new method of determining the entanglement molecular weight, Me, of a polymer system. </p> / Thesis / Master of Science (MSc)

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Expansive or swelling soils, exist in many part of the world, show excessive volume changes with increasing water content. As a result of this volume increase, expansive soils apply vertical and lateral pressures to the structures located or buried in these regions. Many researchs have been carried out on vertical swelling pressures helping to the engineers to design structures withstanding on these stresses. However, lateral swell behaviour of swelling soils have not been fully understood yet. Structures such as / basement walls, water tanks, canals, tunnels, underground conduits and swimming pools which will be built in expansive soils have to be designed to overcome the lateral swelling pressures as well as the other lateral pressures exerted by the soil. For this aim accurate and reliable methods are needed to predict the magnitude of lateral swelling pressures of expansive soils and to understand the lateral swelling behaviour of expansive soils. In this experimental study, the lateral swelling behaviour of an highly expansive clay is investigated using a modified thin wall oedometer which was developed in the METU Civil Engineering Department Soil Mechanics Laboratory earlier. Statically compacted samples were used in constant volume swell (CVS) tests to measure the magnitude of the lateral and vertical swelling pressures. To study the relationship between the lateral and vertical sweeling pressures, they were measured simultaneously. The samples having different initial water contents and different initial dry densities were used to study the effects of these variables on the vertical and the lateral swelling pressures. It is observed that both lateral and vertical pressures increases with increasing initial dry density and they decrease with increasing initial water content. Swell pressure ratio, the ratio of lateral swelling pressure to the vertical one, is increasing with increasing initial water content. Time needed to obtain the magnitude of maximum lateral and vertical pressures decreases with increasing initial water content and increases with increasing initial dry density.

Diese Arbeit befasst sich mit der Lichttransmission im retinalen Gewebe. Aufgrund der inversen Konfiguration der Wirbeltiernetzhaut muss das ins Auge eintretende Licht zahlreiche Zellschichten durchdringen, bevor es von den Photorezeptoren detektiert wird. Die Autorin geht davon aus, dass die morphologische Heterogenität dieser Zellschichten mit einer optischen Heterogenität einhergeht, welche den Lichttransport zu den Photorezeptoren beeinflusst. In den Versuchsbeschreibungen wird erläutert, wie das native Netzhautgewebe von Meerschweinen verschiedenen osmotischen Stimuli ausgesetzt wurde, um morphologische Veränderungen zu provozieren. Durch die parallele Beobachtung der Durchmesser ausgewählter Zellen der äußeren und inneren Netzhaut, sowie der quantitativen Lichtdurchlässigkeit des Gewebes, konnte die Autorin die morphologischen Veränderungen zur retinalen Lichtdurchlässigkeit in Beziehung setzen. Die Ergebnisse zeigen, dass Zellschwellungen zu einer Erhöhung der quantitativen Lichtdurchlässigkeit und Zellschrumpfungen zu einer Verringerung dieser führen. Es werden folgende Schlüsse gezogen: Die osmotischen Stimuli bewirken Volumenregulationsprozesse, infolge derer sich lokale Brechungsindizes und Extinktionskoeffizienten ändern und die retinale Lichtdurchlässigkeit beeinflussen. Zudem konnte die Autorin durch Versuche mit nativen Primatennetzhäuten nachweisen, dass die Abbildungsqualität im Zentrum der Fovea centralis am besten ist, weil die inneren Netzhautschichten dort nicht vorhanden sind und das Licht direkt auf die Photorezeptoren trifft. Diese Arbeit zeigt, dass die Wirbeltiernetzhaut ein optisch aktives Medium ist, dessen Morphologie die Lichttransmission durch das Gewebe beeinflusst.