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Thesis (M.Sc.), Faculty of Engineering (Metallurgy and Materials Engineering), 1996

I studied the occurrence of two sympatric morphs of arctic charr, Salvelinus alpinus (L.) in Vatnshlidarvatn, a small shallow lake in NW Iceland. The arctic charr were subjectively distinguished by colour and appearance as brown morph or silver morph, and measured for morphological and life history characters. The study revealed the presence of two growth forms represented by the two morphs that differed in age and size at sexual maturation, reproductive investment, and time and place of spawning. The morphs differed significantly in gill raker number and morphometric characters related to manoeuvrability and cruising ability. Morphological segregation was established early in life and is most readily explained as developmental heterochrony. Both morphs were benthivorous, but could be segregated as diet specialist and generalist, with diet segregation being important only when food (especially the benthic crustacean Eurycercus spp.) was scarce, The occurrence of one abundant food resource, and lack of interspecific competition (no other fish species are present) may explain the different feeding strategies. The presence of "empty" niche should induce variability and divergence in morphology and life history to occupy available niche space. / Graduation date: 1997

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Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xii, 78 p. : ill. Includes abstract. Includes bibliographical references (p. 76-78).

Research Doctorate - Doctor of Philosophy (PhD) / An increased demand worldwide for the reduction in pollutants emitted from coal-fired power stations has meant that advanced coal utilisation technologies are being sought as alternatives to pulverised fuel (pf) fired plants. The leading systems use coal gasification to produce a fuel gas which is cleaned and used in a combined-cycle gas turbine system. This produces electricity at high efficiencies and with significant reductions in the emissions of CO2, N- and S- gases and particulates. These systems offer the emission levels approaching those of natural gas combined-cycle plants, with the low fuel cost of coal. Modern coal gasification technologies operate with high temperatures and at pressures many times that of pf boilers: the reliability and efficiency of gasification-based systems are strongly influenced by the performance of the coal used under these conditions. The high-intensity nature of these processes means that generating experimental coal performance data for coal assessment and reactor design is time consuming, expensive or even impossible due to the lack of suitable facilities. Using process models based on fundamental gasification phenomena, coal performance can be predicted over a range of conditions. This is beneficial for both the development of new gasification technologies and in the assessment of Australian coals for use in the evolving international market. The slowest stage of the coal gasification process, i.e. the conversion of the char, has been identified as an important parameter for the design and implementation of such models. In particular, the intrinsic reactivity—characterised by data measured under conditions where chemical processes alone control the reaction rates—is extremely important, as intrinsic data can be readily combined with char physical properties to predict the high-temperature reaction rates of coal chars. The lack of intrinsic data generated at pressures relevant to modern gasification systems has meant that kinetic input into process models has been somewhat unreliable. In particular, there are no high-pressure reactivity data—intrinsic or otherwise—available for Australian black coals. To address this need, work in this thesis has used a pressurised thermogravimetric analyser to measure the effects of pressure (up to 30 atm) on the intrinsic reactivities to O2, CO2 and H2O of several Australian black coal chars, at emperatures between 350 and 900°C. These chars were made under a range of pressures and heating rates, and were in the size range 100 μm to 1.0 mm. In particular, the experiments were performed under conditions where chemical processes alone controlled the reaction rates, and where inhibition of the respective reactions by the products was negligible. It was found (using chars made in bulk at atmospheric pressure with slow heating rates) that whilst the reaction rate increased with reactant pressure in all gases, at pressures above approximately 15–20 atm the rates of reaction with CO2 and H2O ceased to increase with pressure. There was no such observation for the char–O2 reaction up to 16 atm. Activation energies of the reactions were unaffected by pressure. Samples made at high pressures and with high heating rates were found to be orders of magnitude more reactive than the chars made at atmospheric pressure under slow heating rates. These differences were found to be largely due to an increased microporous surface area, such that the intrinsic reactivities (calculated using the CO2 adsorption surface area) were similar. The effects of variations in pyrolysis pressure and parent coal petrography (and consequently char morphology) were also largely accounted for by char surface area, such that intrinsic rates were not greatly affected by these variables. These intrinsic reaction rate data were examined to produce a modified version of the nth order rate equation. This incorporated a pressure order that decreased as the reactant pressure increased, based on the physical process of available surface saturation. This model was compared with measured data and it was shown that the predictive capability of the nth order rate equation over a range of pressures was improved. There is scope for further refinement of this model by investigating the effects of reactant pressure on the development of the surface area of the char during conversion, since it was shown in this work that pressure has a strong effect on the such development. Moreover, this effect of pressure was not consistent between reactant and coal char type. This kinetic model was combined with measured char properties such as surface area, pore size, etc. to crudely predict the high temperature reactivity of a sample. This demonstrated the usefulness of reliable intrinsic data in the development of high temperature gasification models, and highlighted the need for experimental data obtained under process conditions of high temperature and pressure that can be used to validate such models.

No description available.

Le but de ce travail de thèse est d’obtenir une compréhension des mécanisme d’action des revêtements intumescents à base d’époxy afin de fournir des perspectives pour le développement de nouveaux systèmes de protection contre le feu. La formulation intumescente est un système très complexe. Ce travail se concentre en particulier sur les composants clés dont la compréhension des mécanismes d’action était absente. Tout d’abord, les mécanismes d’action des borates ont été étudiés en incluant des modifications chimiques et thermo-physiques; la combinaison des résultats obtenus sous différents aspects permet de comprendre son mode d’action. D’un côté, les borates en particulier l’acide borique ont été mentionnés comme Cancérogènes, Mutagènes, Reprotoxiques (CMR); la substitution de ces composants est nécessaire. Les résultats soulignent le rôle important et la réactivité élevée du zinc (de borate de zinc), ce qui suggère le développement de nouveaux systèmes en incorporant un composé à base de zinc au lieu du borate du zinc. Deuxièmement, l’effet du CaCO3 sur les propriétés de protection contre le feu et son mécanisme d’action dans le revêtement intumescent ont été examinés. L’ajout de CaCO3 améliore les propriétés de protection au feu et d’adhérence/cohérence du revêtement et son mécanisme d’action était justifié. De plus, plusieurs carbonates (MgCO3, ZnCO3, Na2CO3, K2CO3) en tant qu’ingrédient intumescent ont également été examinés. L’utilisation de MgCO3 comme ingrédient intumescent est favorable pour les propriétés de protection contre le feu du revêtement ainsi que pour l’utilisation de CaCO3. Dans ce travail, les mécanismes d’action des borates et des carbonates ont été étudies. Les résultats suggèrent le développement de nouveaux systèmes utilisant des ingrédients alternatifs tels que le composé à base de zinc ou MgCO3. / The goal of this PhD work is to get an insight into the mechanisms of action of epoxy based intumescent coating to be able to provide the outlooks for the development of novel systems of higher protection against fire. The intumescent formulation is highly complex system. This work focuses particularly on the key components of which the understanding of the mechanisms of action is still lacking. Firstly, the mechanisms of action of borates were investigated in both chemical and thermo-physical modifications; the combination of the results obtained from different aspects allows drawing its mode of action. On the one hand, borates in particular boric acid have been mentioned to be Carcinogenic, Mutagenic, Reprotoxic (CMR); the substitution of these important intumescent components are necessary. The results point out the important role and high reactivity of zinc (i.e. from zinc borate), this suggests the development of novel systems by incorporating zinc based compound instead of zinc borate. Secondly, the effect of CaCO3 on fire protective properties and its mechanism of action in intumescent coating were examined. The addition of CaCO3 improves the fire protective properties and adhesion/cohesion of the coating and its mechanism of action was fully justified. Additionally, various carbonates (i.e. MgCO3, ZnCO3, Na2CO3, K2CO3) as intumescent ingredient were also examined. The use of MgCO3 as intumescent ingredient is beneficial for the fire protective properties of the coating as well as the use of CaCO3. In this work, the mechanisms of action of borates and carbonates were fully examined. The results suggest the development of novel systems with using the alternative ingredients such as zinc-based compound or MgCO3.

Thesis (M.S.)--University of Alaska Fairbanks, 2010. / Title from PDF t.p. (viewed Apr. 22, 2010). Includes bibliographical references (p. 12-17, 62-69, and 83).

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2000. / Includes bibliographical references.