3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Investigation into the correlation between paper insulation thermal ageing estimation using the arrhenius equation and other methods for generator transformers(2015) Metebe, Michael TebogoMany generator transformers were installed many years ago during the initial commissioning of Eskom’s power stations. Many of these transformers have started showing signs of significant ageing of the paper insulation and hence require regular monitoring. There are two methods that are currently being employed to assess the degree of ageing of the paper insulation in a generator transformer, which are paper sampling and furan level measurement. This dissertation investigates an alternative method of predicting the degree of ageing of the paper insulation instead of what is used currently. This method uses the Arrhenius equation that relates time and temperature to determine the degree of degradation of organic materials. The reliability of the Arrhenius estimation method is assessed by comparing the predicted DP (Degree of polymerisation) values with the measured DP values of the same transformer paper insulation. The results obtained showed that there is reasonable correlation between the DP values estimated from the Arrhenius equation and the DP values estimated from the measured furan levels. The accuracy of the prediction method is reduced when the oil temperature greatly differs from the paper insulation temperature. The application of the Arrhenius equation to estimate the ageing of paper insulation is a great milestone in the quest to predict the remaining life of a transformer. It is the only method available to do this prediction and using online temperature measurement on transformers makes the method more reliable.Item Palladium (II) and iron (II) complexes derived from pyridyl-imine ligands as catalyst precursors for 1-hexene oligomerization and norbornene polymerization(2017) Khuzwayo, Pamela ZanelePyridyl-imine ligands L1-L4 were prepared by condensation of pyridine-2-carboxyaldehyde with an appropriate amine. Characterization by NMR spectroscopy, infrared spectroscopy, mass spectrometry and elemental analysis confirmed successful preparation in yields of 64-88%. These ligands were used to prepare Pd(II) complexes C1-C4, from PdCl2(CH3CN)2 and the corresponding pyridyl-imine ligand. 1H-NMR, 13C-NMR, FT-IR, mass spectrometry and elemental analysis confirmed coordination. Attempts to prepare target Fe(II) complexes C5-C8 by reacting the ligands with anhydrous FeCl2 were unsuccessful. Infrared data suggested coordination of ligands to the Fe centre, however mass spectrometry and elemental analysis data revealed that target complexes were not obtained. Pd(II) complexes C1-C4 were evaluated as catalyst precursors for 1-hexene oligomerization and norbornene polymerization using methylaluminoxane (MAO) as co-catalyst. The oligomerization of 1-hexene was investigated in a neat reaction media at various Al:Pd ratios. All investigated complexes were found to be inactive for the oligomerization of 1-hexene. From 1H-NMR spectroscopy and GC-MS analysis it was observed that the product distribution was mainly a mixture of 2-hexene and 3-hexene isomers. Parameters such as temperature and time did not have any significant influence towards the productivity of 1-hexene oligomers. Norbornene polymerization studies were carried out with Pd(II) complex C4 in toluene at room temperature. This complex was found to exhibit good activity for norbornene polymerization, producing a vinyl bicyclic polymer, confirmed with infrared and solid state 13C-NMR spectroscopy. Increasing the amount of co-catalyst (MAO) and temperature did not have any significant influence on the activity and monomer conversion. However, increasing reaction time was observed to have a significant influence on the activity.Item The molecular evolution of complexity at the origin of life(2016-10-25) Dhar, NishaA widely accepted hypothesis for the origin of life is that it was based on catalytic RNA or ribozymes (the RNA world hypothesis). In this paradigm, one of the earliest and essential functions for an RNA based life to emerge was polymerisation. Although polymerisation activity has been demonstrated in extant and engineered ribozymes, these molecules are large and too complex to have formed spontaneously in the prebiotic world. Furthermore, the evolution and stability of RNA based life would have required a pool of diverse complex ribozymes. An understanding of the basic mechanistic processes implicated in the emergence of a minimal polymerase and diverse complex molecules from small oligomers remains a major gap. This project examined the ligation activity of a polymerase and its smaller derivatives with random oligonucleotide substrates and revealed how the molecular dynamics of ligation would have affected the evolution of complexity in the early stages of an RNA world. The size and structural complexity of a minimal polymerase (called R18 polymerase ribozyme) was reduced in a stepwise fashion. All RNA constructs were examined for self-ligation function with 24 random oligonucleotide substrates (each 35 nucleotides long) in the absence of experimentally designed base pairing. The smallest element (40 nucleotides long) was able to non-specifically ligate substrates to its own end, however, with low efficiency. A gradual increase in specificity for the substrates and overall functional efficiency was observed with an increase in structural complexity of the ribozymes. The most complex R18 polymerase ligated only selected substrate variants to itself, although with much greater efficiency than the smaller constructs. These findings suggest that the complexity in a primitive molecular system increased in a modular fashion via ligases. Furthermore, general compatibility of the ligases with the substrates was a mechanism for increase in the molecular complexity and functionality. The inverse correlation between functional flexibility and efficiency with increase in structural complexity of the catalysts points to a molecular trade-off. In the ecology of the RNA world, this molecular trade-off would have been central to ribozyme population stability and for the development of functional specialisation. The findings in this project point to a form of hypercycle composed of a complementary set of processes stabilised by inherent molecular trade-offs. Such a hypercycle is suggested to facilitate the emergence of a stable molecular network and a replicative unit essential for life to begin.