Made available in DSpace on 2014-10-09T12:54:34Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:26Z (GMT). No. of bitstreams: 0 / Este trabalho apresenta uma solução analítica obtida pelo método de expansão para cinética espacial usando o modelo de difusão e considerando meios homogêneos multiplicativos subcríticos acionados por fonte externa. Em particular, partindo de modelos mais simples e aumentando a complexidade do sistema, resultados foram obtidos para diferentes tipos de transientes. Inicialmente, uma solução analítica foi obtida considerando um grupo de energia sem nêutrons atrasados, em seguida considerou-se um sistema de um grupo de energia e uma família de precursores. A solução para o caso G grupos de energia e R famílias de precursores em forma fechada é obtida, apesar do fato que não possa ser resolvido analiticamente, uma vez que não existe forma explícita para os autovalores e métodos numéricos devem ser utilizados para resolver tal problema. Para ilustrar a solução geral um problema de multigrupo (três grupos de energia) dependente do tempo sem precursores é apresentada e os resultados numéricos obtidos usando um código de diferenças finitas são comparados com os resultados exatos para diferentes tipos de transientes. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN/CNEN-SP

The transient temperature fields induced by welding processes largely determine the size of the fusion and heat-affected zones, the microstructures, residual stresses and distortion both in the vicinity of the weld and in the final component as a whole. An accurate prediction of these fields relies heavily on the representation of the welding heat source, both in space and in time. The double-ellipsoidal heat source model proposed by Goldak and co-workers has been widely used to simulate the heat transferred from an electric arc to a component and to compute the induced transient temperature fields. This double-ellipsoidal distribution has worked well for many welding applications, but it is less appropriate when representing the heat transfer at the base of a groove whose width is narrow in relation to its depth. Similarly the conical heat source models used to represent the electron beam welding process, when applied in keyhole mode, are less appropriate when the keyhole terminates within the component, such as in the case of a partial penetration weld. In this work, the double-ellipsoidal heat source model is extended, and alternatives presented, to account for a wider set of welding scenarios, including narrow weld groove geometries and keyhole welding scenarios. A series of mathematically robust novel heat source models is presented and the models are validated against experimental data obtained during the application of various welding processes to an important grade of pressure vessel steel, namely SA508 Grade 3 class 1 steel. The calculation of the transient temperature fields during welding is extremely computationally expensive using numerical methods. Where available, and appropriate, analytical solutions are presented for these novel welding heat source models, coupled with analytical methods for accounting for time dependent heat input rates, to not only reduce computational cost but also to achieve precise predictions of the temperature fields. This, in turn, has the potential to contribute to improvements in safety assessments on critical welded infrastructure through improved predictions for the evolution of microstructure, mechanical properties and the levels of residual stress and distortion in welded joints.

M.Sc. (Computer Science) / As the world enters the new millennium, we are experiencing one of the most important changes since the industrial revolution - the move to an Internet-based society. Traditional business channels are moving to a new platform of interaction that is called Electronic Business (EB). Electronic Business is becoming a significant business tool, provided that businesses understand the benefits, the application areas and impacts of EB, and can apply these concepts optimally. The problem with many businesses, especially SMMEs (Small Medium and Micro Enterprises), is that they are ignorant to many EB-related concepts, how EB can assist their business needs, and how to apply EB into their business components. Various solutions for EB exist in the industry, which are very comprehensive and complex. However, with the constant wave of mergers, acquisitions and new IT-companies forming, as well as the myriad of new solutions being developed, many businesses are not sure which solution would suit their business best, and which solution provider would be the best to approach. What businesses need is an understanding of EB and guidelines on how to start becoming EB focused. The principle aim of the Enterprise-Wide Electronic Business (EWEB) Framework developed is to form the bridge between a traditional business and an electronic business. This is achieved by defining many EB-related concepts and providing guidelines on how to streamline business processes with technology in moving to an EB platform. The EWEB Framework targets this from three perspectives. Firstly, the EWEB Framework follows a top-down approach to EB, targeting business processes across the enterprise as well as business issues from strategic, architectural and infrastructural levels. This allows EWEB to be applicable to all types of business processes and businesses needs. Secondly, the EWEB Framework also consists of business processes that are common across all industries. This allows EWEB to be applicable to all types of businesses...

The energy demands by the industrial world are continuing to rise, while the rate of new oil discoveries is falling. Within the next 30 years, available petroleum supplies are likely to fail to meet the demand, and oil will no longer be able to serve as the world’s major energy source. Coal, being relatively abundant worldwide and potentially adaptable for use in existing plants that have been engineered for petroleum use, can serve as an inexpensive substitute for, or successor to, the more expensive oil fuels in use today. Graphitisable carbon is one of the high-value products from petroleum as its value lies partly in the nuclear industry. Making graphitisable isotropic carbon from well-purified coal is therefore a primary motivation for this study. However, its purity is far too low. Substantial purification is obtained by dissolving the organic part of coal in dimethylformamide with the addition of a little alkali. Results indicated that more than 90% of the organic part of a 10% ash flotation product dissolved in N, N dimethylformamide on addition of 10% NaOH. The bulk of the impurities are removed by centrifugation and the dissolved organic material is recovered by water precipitation. Subsequently, the ash level is lowered from 10% in the coal to < 1.60% in the coal extracts at a washing efficiency of 33 %. The addition of Na2S (the molar ratio of NaOH to Na2S was 1:1) lowered the ash level further to 0.70%. The coal extract solution obtained showed an absorbance of 1.00 with an organic content of 8%. However, addition of sodium sulphide to the extraction medium at 25 ± 1oC lowered the organic content to 5.6%. At high temperature of 90 ± 2oC, the organic content was further lowered to 2.6% with subsequent loss in colour. The coal extract obtained by water precipitation showed low C/H atomic ratio on the addition of S-2. Nucleophiles such as cyanide, thiosulphate made no substantial change to the hydrogen content nor the degree of extraction. On coking by step heating under nitrogen to 480oC at a rate of 10oC min-1 for 1h, then to 900oC with a soaking period of 2h, the coal extracts melt, then reorganise into a liquid crystal phase around 500oC, which then solidifies into a semi-coke on further heat treatment. The heat-treatment of the coal extracts produced 75% carbon yield. When polished specimens of the cokes were observed by reflectance microscopy, flow textures with domain sizes of a few to many microns were observed. Isotropic, poorly graphitising cokes showed little or no structure. Anisotropic cokes were produced when these domains of liquid crystal grew and coalesced. The cokes were found to be highly graphitisable. However, in the heat treated coal extracts prepared at high temperature, the liquid crystal domains were graphitisable but appeared not to have coalesced. Nevertheless, the random orientation of the domains allowed isotropic blocks to be formed with extremely low crystallinity. The precursors that form these liquid crystals are generally materials known to have a high aromatic carbon content. The precursors that form these liquid crystals are generally materials with a high purity and aromatic carbon content, and low in heteroatoms. Optical microscopy of the polished samples prepared at 90  2oC revealed surfaces with much less ordered coke, having smaller crystalline domains than the heat–treated coal extracts derived at room temperature. Essentially, isotropic graphites were obtained. Addition of S-2 produced an extensive flowing texture, and a highly crystalline domain cokes. The carbon yield lowered. The graphitisability of the carbon improved. The X-ray diffraction data on the graphitised carbon showed that the degree of graphitisation decreased in the following order: high S-2 coal extracts derived at room temperature (GSF-25RT) > high S-2 coal extracts derived at high temperature (GSF-25HT) and no S-2 coal extracts derived at room temperature (GSF-0RT) > no S-2 coal extracts derived at high temperature (GSF-0HT), corresponding to 79 > 75% and 67 > 25% respectively. The interlayer spacing (d002 -value) of the graphites follows the order GSF-25RT (3.37Å) < GSF- 25HT (3.38 Å) and GSF-0RT (3.38 Å) < GSF-0HT (3.42 Å). Subsequently, the Raman spectroscopy, consistent with the X-ray diffraction data, showed the ratio of the d-peak (degenerate) to g-peak (graphitic) in the order: GSF-0HT < GSF-0RT and GSF-25HT < GSF-25RT, corresponding to 1.26 <1.75 < and 6.7 < 7.0 respectively. Because the quality of the coke depends on the nature and quality of the starting material, addition of the carbon additives in the starting material prior heat-treatment affected the flow texture of the coke. The carbon black, which has a spherical shape, forms aggregates that disperse much more easily than the flat chains of aggregates of acetylene black. The difficulty in dispersing the carbon additives was, however, overcome by using a high-shear mixer. Analysis of the coal extracts revealed that the hydrogen content in the coal extracts decreased linearly on addition of the carbon additives, favoring dehydrogenative polymerisation. The addition of carbon additives in the coal extract solution produced an isotropic carbon on heat treatment. Optical microscopy of the resin-mounted cokes revealed decreasing size of the crystalline domain with increasing dosage of the carbon additives. The optimum amount of carbon additives required was found no to exceed 0.44%. Beyond this threshold, the anisotropy of the cokes could not be observed through the resolution of the optical microscope. In addition, the amounts of volatiles released were found to decrease with increasing dosage of the carbon additives. At low dosage of the carbon additives, the heat-treated coal extracts produced graphitisable isotropic carbon with low level of crystallinity. However, at high dosage of the carbon additives, the cokes did not graphitise. The temperature of graphitisation decreased from 2976 to 2952oC with increasing dosage of the carbon additives. The decreasing order of graphitisation was 69 > 61 > 62%, corresponding to 0.44 > 0.88 > 1.60 acetylene black. With the addition of carbon black, the decreasing order of graphitisation was 57.7 > 56.5 > 51.5%, corresponding to 0.44 > 0.88 > 1.60 wt % respectively. The interlayer spacing d002, increased in the same order, suggesting a shift towards a turbostratic and formation of a poorly graphitised, and turbostratic carbon. Raman spectroscopy revealed that the intensity ratio R of the g to the d peak decreased with increasing dosage of the carbon additive. Cokes produced from the coal extracts prepared at 25oC but without S-2 showed also a remarkable degree of flow texture. Its crystalline domain units were relatively small. The resin-mounted coke samples observed under an optical microscope (objective x 25) showed reduced flow texture with the addition of carbon black. The graphitisability of the resultant cokes also decreased on addition of carbon black. The optimum dosage observed for reducing the flow texture without reducing the crystallinity was found to be < 0.22%. Improved degree of graphitisation of the carbon was studied on addition of iron (lll) compounds. Iron (lll) compounds showed a promising improvement in the graphitisability of the carbon when added in small amounts. The intracellular hard carbon is converted to soft carbon, thereby improving the degree of graphitisation. The overall effect was a more isotropic graphitic carbon but the degree of graphitisation obtained was far too low: on addition of 1% and 3% (by wt) of iron (lll), the compounds were 21% and 27% respectively. Oxygen intrusion into the precursor’s coal material prior to heat treatment is thought to have inhibited the degree of graphitisation. Increasing the amounts of the iron (lll) compound and prohibiting the intrusion of oxygen during mixing could improve the graphitisability of carbon. However, the optimum amount to be used remains an important subject to be explored in future. / Thesis (PhD (Chemistry))--University of Pretoria, 2007. / Chemistry / unrestricted

No description available.

The kinetics of the hydrogen reduction of aqueous cupric perchlorate and sulphate solutions were studied at 160°C and 5 to 10 atm hydrogen pressure. In sulphate solutions the observed rates were consistent with a rate law, derived from previously proposed mechanisms, that has the form [ Equations omitted ] The rate constants of the hydrogen activation steps of the reaction are represented by k₁and k₃ which reflect the activation rates by Cu'' and Cu' respectively and have the values 3.2 X 10¯³M¯¹sec¯¹ and 6.4 X 10¯²M¯¹sec¯¹ at 160°C. The ratios of the back- to net forward-reaction rate constants are k-₁/k₂ for the Cu'' activation step and k-₃/k₄ for the Cu' activation step. These have values of approximately 0.13 and 0.45 respectively at 160°C. In perchlorate solutions the rates were also consistent with the rate law applying to sulphate solutions if a necessary correction due to perchlorate decomposition was taken into account. In this system the second term of this rate law was found to be much smaller and more difficult to resolve. For the first term the value of k₁ was found to be 6.7 X 10¯³M¯¹sec¯¹ at 160°C and the value of k-₁/k₂ was 0.51. Exchange experiments with deuterium in place of hydrogen were also done. These gave rates consistent with previously proposed mechanisms, but in perchlorate solutions much higher exchange rates were observed than in sulphate solutions. The indicated value of k₃ is approximately the same in perchlorate as in sulphate solutions and the indicated value of k-₃/k₄ is much greater in perchlorate solutions. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Purpose: Solution-induced corneal staining (SICS) has been the subject of much debate in the clinical literature. While it has been suggested that this form of staining indicates toxicity of the cornea, microscopy studies have suggested that cells treated with multi-purpose solutions (MPS) known to produce SICS in vivo are undamaged. There is further debate in the literature as to whether or not sodium fluorescein (‘fluorescein’) actually enters epithelial cells or not. The aim of this work was to investigate the cellular mechanisms involved in SICS by developing an in vitro cell culture model to mimic the clinical presentation of this phenomenon. Methods: An in vitro model of SICS was developed using cultured cells that were exposed overnight to ReNu MultiPlus® (Bausch + Lomb) MPS. After addition of fluorescein, cells were imaged using an automated fluorescence microscope. Hyperfluorescent cells were identified using predetermined threshold of intensity in fluorescence microscope, and confocal microscopy was used to investigate where fluorescein was situated within the cells. The extent of cell toxicity was assessed using propidium iodide and Annexin V. In order to examine the contribution of passive and active transport mechanisms in fluorescein uptake and release, levels of hyperfluorescent staining were measured at 37°C and 4°C. In all described experiments, fluorescein staining was expressed by the proportion of hyperfluorescent cells in the total cells. Results: All cultured cells readily took up fluorescein at room temperature, however a sub-population of cells stained more intensely with fluorescein. These cells were termed ‘hyperfluorescent’ cells. Exposure to ReNu MultiPlus® resulted in a significant increase in the proportion of hyperfluorescent cells compared with control cells. In addition, the staining profiles of individual cells showed no correlation between cell death and hyperfluorescence. The data also showed that hyperfluorescence did not occur extensively in deliberately lysed cells.Addition of fluorescein to the cells at 4°C resulted in very low levels of hyperfluorescence compared to high levels at 37°C. Fluorescein was rapidly released from cells at 37°C but not from those at 4°C. Conclusion: In this work, an effective in vitro model of SICS was developed in order to provide a better understanding of the mechanisms involved in fluorescein staining. This work suggests that corneal fluorescein staining may reflect a simple cellular uptake of fluorescein. Levels of staining in the cells appear to be unrelated to cellular toxicity or cell damage. Staining appears to occur in the cytoplasm and the nucleus of the cells. Finally, fluorescein uptake and release are likely to occur through active transports mechanisms.

In the last decade, organic photovoltaics (OPV) have gained considerable attention with a rapid improvement of power conversion efficiency (PCE) from 5% to more than 13%. At the origin of the gradual efficiency improvements are (i) the rationalization of material design and (ii) systematic optimization of film processing condition. OPV can have a key role in markets such as building-integrated photovoltaics (BIPV). The main advantages of organic solar cells are semitransparency, low weight, good performance at low light intensity, flexibility and potential low-cost module manufacture through solution processed-based technologies. In solution processed OPV, the active layer that converts photons into electric charges is a composite of two organic compounds, a donor (D) and an acceptor (A) where the best morphology is achieved via the so-called bulk heterojunction (BHJ): an interpenetrating phase-separated D-A network. Historically, research has been focused on polymer donors and guidelines about morphology and film processing have been established. However recent studies have shown that small-molecule (SM) donors can rival their polymer counterparts in performance. The advantages of SM are a defined molecular weight, the ease of purification and a good batch-to-batch reproducibility. Using this class of material the existing guidelines have to be adjusted and refined. In this dissertation, using new SM synthesized in our laboratory, solution-processed organic solar cells are fabricated in which the morphology of the active layer is controlled by thermal annealing, the use of additive or solvent vapor annealing. In-depth analyses of the morphology are correlated to charge generation, recombination and extraction inferred from device physics. In the first part of the dissertation, using a small amount of 1,8-Diiodooctane additive that acts as a plasticizer, it is found that the D-A domains do not necessarily need to be pure and that mixed domains can also result in high performing devices. In the second part of the dissertation, the effect of solvent vapor annealing, particularly effective for SM:PCBM BHJ, is discussed where excellent control of the morphology is achieved. In the last part of the dissertation, efficient organic solar cells with open circuit voltage of >1.05V are made via fine-tuning of the morphology.

The diploma thesis deals with the implementation of a Business Intelligence solution for the endowment fund helping with debt relief for people and thus replaces the current process of manually created reports. The main goal of this solution is to bring to the endowment fund the opportunity to make faster and better decisions, as well as many other benefits associated with Business Intelligence.

New one- and two-dimensional NMR techniques were used to elucidate the solution structures of these complex mixtures. The system, lithium tert-butoxide/tert-butyllithium, was studied as a model system with O/Li ratios varying from 0/1 to 1/1. It was found that at low O/Li ratios, a single mixed tetrameric aggregate was formed. At higher O/Li ratios, mixed hexameric species were formed. Two other systems, lithium isopropoxide/iso-propyllithium and lithium n-propoxide/n-propyllithium were also studied at low O/Li ratios.