School of Chemistry and Physics

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A detailed kinetic and mechanistic investigation into the rate of chloride substitution from chloro terpyridine platinum (II) and analogous complexes by a series of azole nucleophiles.
(2010) Gillham, Kate J.; Reddy, Desigan.; Jaganyi, Deogratius.
Structural and synthetic studies of sesquiterpenoids and flavonoids isolated from Helichrysum species
(2008) Lourens, Anna C. U.
The genus Helichrysum (Asteraceae) consists of approximately 500 species worldwide, with 245 indigenous to South Africa. As a result of the large number of species, the chemistry and biological activity of several species have not yet been investigated. The aim of this project was to investigate the phytochemistry of three species and propose a synthetic route to one of the antibacterial compounds isolated. An extensive literature review regarding the widespread traditional uses, biological activity and phytochemistry of the South African Helichrysum species is provided. From Helichrysum splendidum, a plant used traditionally to treat rheumatism, two monomeric guaianolides and a dimeric guaianolide, helisplendidilactone, were isolated. The stereochemistry of these known compounds was confirmed and the NMR assignments for certain peaks of helisplendidilactone were corrected. An X-ray structure for helisplendidilactone was obtained for the first time. The phytochemistry of Helichrysum montanum was investigated for the first time and new diastereoisomers of known guaianolides were isolated. The phytochemistry of H. splendidum and H. montanum is remarkably similar and supports their morphological classification in the same taxonomic group. The chloroform:methanol extract of H. montanum yielded a new dimeric guaianolide, 13’-epihelisplendidilactone, which is related to helisplendidilactone, as well as three monomeric guaianolides (of which one is a new diastereomer of a known compound). The extract also yielded spathulenol (a sesquiterpene), umbelliferone (a coumarin) and 4’,5,7-trihydroxy-3,3’,8-trimethoxyflavone (a flavonoid). Thirty-five Helichrysum species were screened for antimicrobial activity against six microorganisms and a preliminary cytotoxic assay, which included the use of “normal” and cancer cell lines, was performed. H. excisum was selected for further study based on the fact that it exhibited promising antimicrobial activity and relative low toxicity. Furthermore, with the exception of the essential oil, the phytochemistry of this species has not been investigated. From the aerial parts of H. excisum, five flavonoids, identified as pinocembrin, gnaphaliin, lepidissipyrone, 5-hydroxy-7,8-dimethoxyflavone and isoscutellarein 7-O-b-glucoside were isolated. Four of these flavonoids have an unsubstituted B-ring, a phenomenon often observed in flavonoids isolated from Helichrysum species. The active antimicrobial component of H. excisum has been identified as lepidissipyrone. Owing to the interesting biological activities reported for phloroglucinol a-pyrones and the synthetic challenges associated with these molecules, lepidissipyrone was selected for a synthetic study. Both the flavanone and pyrone moieties present in lepidissipyrone have been successfully synthesised. A successful strategy towards the CH2 linker between the two units has been illustrated. The strategy could be used to synthesise similar phloroglucinol-derived pyrones.
Progress towards the synthesis of Indolizidine alkaloid 223AB
(2008) Janse van Rensburg, Caryl Kerith Alice.
It has been shown that alkaloids from various sources are vital as lead compounds in medicinal research and thus also the efficient synthesis of these. With the goal of developing a general synthetic route that can potentially access pyrrolizidine, indolizidine, quinolizidine and possibly lehmizidine alkaloid skeletons, a modified route that has been shown to produce pyrrolizidines was employed towards the synthesis of indolizidine alkaloid 223AB. Within this synthesis, a 6-endo-dig hydroamination-cyclization step was attempted for construction of the bicyclic system. For this purpose, a selection of titanium-based catalysts were synthesized in order to determine their regiochemical outcome. For the purpose of investigating ab initio the mechanism of regioselective hydroamination, the skills and methods involved in computational chemistry were acquired through a study into amide rotational barriers: A range of novel 2-oxo-2H-chromen-7-yl dimethylcarbamates were synthesised containing either an oxygen or sulphur in the α-position to the carbonyl or thiocarbonyl group of the amide moiety. Microwave synthesis was essential for the successful synthesis of some of the sulphur containing carbamates. The barriers to internal rotation of each of these compounds were investigated as follows. Variable Temperature and Exchange Spectroscopy NMR was performed on these compounds and the barrier to free amide rotation was calculated. Each of these compounds were also modeled ab initio and the gas phase barrier to rotation calculated. These three sets of data were compared and the influence of the α-heteroatom on rotation for amides and thioamides evaluated.
Theoretical and experimental investigations of the Kerr Effect and Cotton-Mouton Effect.
(2008) Janse Van Rensburg, Angela Louise.; Couling, Vincent William.
Mr T. J. Sono, an MSc student during the period January 2001 to January 2003, developed an apparatus to measure the pressure and temperature dependence of the electric-field induced birefringence (or electro-optic Kerr effect) in gases. Mr Sono obtained experimental results for dimethyl ether at a wavelength of 632.8 nm resulting in polarizability tensor components, first and second Kerr hyperpolarizabilities, and second Kerr-effect virial coefficients for this particular molecular species. One of the primary concerns of this thesis has been to obtain new measured Kerr-effect data for dimethyl ether and for trifluoromethane over a range of temperature. The cell has been calibrated using hydrogen as a primary standard, and has been carefully aligned to avoid multiple reflections of the incident laser beam off the closely-spaced electrode surfaces. The data has been analyzed to extract values of the polarizability anisotropy and the second Kerr hyperpolarizability for these molecules. In addition, precise values for the second Kerr-effect virial coefficients have been obtained from measurements of the Kerr effect a function of pressure. The molecular-tensor theory of the second Kerr-effect virial coefficient BK is reviewed. This theory describes the effects of intermolecular interactions on the molar Kerr constant, and it has been used to compute BK for dimethyl ether and trifluoromethane over the experimental temperature range. Agreement between experiment and theory is generally good. BK for ammonia has also been calculated, and compared to recent measured data found in the literature. The theory of the Cotton-Mouton effect (the magnetic analogue of the Kerr-effect) in a dilute gas is reviewed, and a new molecular-tensor theory describing the effects of molecular pair-interactions is developed. Calculations for a test molecule, namely chloromethane, indicate that density-dependent effects for this molecule are extremely tiny (of the order of 1% for typical experimental pressures). This new theory could be profitably used in selecting molecules which might demonstrate a larger effect which might be more readily measured in the laboratory.
Structural and Physical Studies of Co(III) Salen Derivatives.
(2007) Govender, Santham.
A number of ligands that belong to the salen-type family were synthesized in this thesis. These ligands were synthesized from salicylaldehyde and 1,2-phenylenediamine, 1,3- diamino-2-hydroxypropane, 1,2-diamino-ethane, N-(3-aminopropyl)-1,3-propanediamine, diethylenetriamine, diaminomaleonitrile, 2,2-dimethyl-1,3-propanediamine and 1,3- diaminopropane. From this range of ligands, H2salophen was chosen as the ligand for further studies. This work is aimed primarily at elucidating the structures and spectroscopic properties of [Co(salophen)(amine)2](OAc) derivatives, where salophen is N,N’-disalicylidene-1,2- phenylenediamine and the amines used were butylamine, benzylamine, a- methylbenzylamine, dibutylamine, N-methylpiperazine and piperidine. Three novel crystal structures of [CoIII(salophen)L2]Cl derivatives, where L = butylamine, benzylamine, and piperidine, with Co-N distances that range from 1.901 Å to 2.024 Å, have been reported in this thesis. The novel crystal structure of [Co(salophen)(N-MePipz)(OAc)] is also reported in this thesis. These cobalt complexes have been analysed by 1H, 13C and 59Co NMR as well as electronic and IR spectroscopy. A 59Co NMR spectrum was obtained for the [Co(salophen)(BuNH2)2]CH2Cl2×Cl complex. The spectrum exhibits a single line at 8504 ppm. The binding constants of all [Co(salophen)(amine)2](OAc) complexes, where amine = butylamine, benzylamine, a-methylbenzylamine, dibutylamine, N-methylpiperazine and piperidine, were determined by spectroscopic titrations. The titrations were carried out at various concentrations of the amine and at temperatures ranging from 25°C to 45°C. It was found that the primary amines had much larger values of K1 and K2 compared to the secondary amines. Typical values of K1 and K2 were 8000 M-1 and 63.6 M-1 respectively at 25°C, for a-methylbenzylamine. Of the primary amines, it was found that a- methylbenzylamine had the largest value of K1 and K2 compared to the other two amines. For the secondary amines, it was found that N-methylpiperazine had the bigger value of K1 compared to that of dibutylamine.
Computational studies of bond-site percolation.
(2007) Nduwayo, Léonard.; Chetty, Nithaya.; Lindebaum, Robert James.
Percolation theory enters in various areas of research including critical phenomena and phase transitions. Bond-site percolation is a generalization of pure percolation motivated by the fact that bond-site is close to many physical realities. This work relies on a numerical study of percolation in lattices. A lattice is a regular pattern of sites also known as nodes or vertices connected by bonds also known as links or edges. Sites may be occupied or unoccupied, where the concentration ps is the fraction of occupied sites. The quantity pb is the fraction of open bonds. A cluster is a set of occupied sites connected by opened bonds. The bond-site percolation problem is formulated as follows: we consider an infinite lattice whose sites and bonds are at random or correlated and either allowed or forbidden with probabilities ps and pb that any site and any bond are occupied and open respectively. If those probabilities are small, there appears a sprinkling of isolated clusters each consisting of occupied sites connected by open bonds surrounded by numerous unoccupied sites. As the probabilities increase, reaching critical values above which there is an infinitely large cluster, then percolation is taking place. This means that one can cross the entire lattice by going successively from one occupied site connected by a opened bond to a neighbouring occupied site. The sudden onset of a spanning cluster happens at particular values of ps and pb, called the critical concentrations. Quantities related to cluster configuration (mean cluster and correlation length) and individual cluster structure (size and gyration radius of clusters ) are determined and compared for different models. In our studies, the Monte Carlo approach is applied while some authors used series expansion and renormalization group methods. The contribution of this work is the application of models in which the probability of opening a bond depends on the occupancy of sites. Compared with models in which probabilities of opening bonds are uncorrelated with the occupancy of sites, in the suppressed bond-site percolation, the higher site occupancy is needed to reach percolation. The approach of suppressed bond-site percolation is extended by considering direction of percolation along bonds (directed suppressed bond-site percolation). Fundamental results for models of suppressed bond-site percolation and directed suppressed bond-site percolation are the numerical determination of phase boundary between the percolating and non-percolating regions. Also, it appears that the spanning cluster around critical concentration is independent on models. This is an intrinsic property of a system.
The effect of the f-component of the pseudopotential on selected properties of 5d transition metal systems
(2008) Cunnama, Daniel
Cohesive energies, bulk moduli, and equilibrium lattice constants have been calculated for the 5d transition atoms (Hf, Ta, W, Re, Os, Ir and Pt) in face–centred cubic crystal lattices. We have used the ab initio pseudopotential method for the total energy calculations within the local density approximation. Two calculations have been performed for each element, one using only the s, p and d angular momentum components and another including the s, p and d components as well as the unoccupied 5f orbital in the ionic pseudopotentials. The pseudo–wave functions and charge densities of the valence electrons have been represented by a basis of plane waves. For the 5d metals the changes in the electronic structure of the solid are small and they produce small changes in the bulk properties.
Measurement of the temperature dependence of the Buckingham effect (electric-field-gradient-induced birefringence) in gases
(2009) Chetty, Naven.
The aim of this research project was to assemble an apparatus to measure the electric quadrupole moments of gas molecules using the technique of electricfield- gradient-induced birefringence, or the Buckingham effect. Comprehensive research by various workers in the field has shown that this technique provides the only direct means of obtaining the quadrupole moment of a molecule. Theory has shown that the most accurate determination of the electric quadrupole moment is through a study of the temperature dependence of the effect. This not only allows for the quadrupole moment to be obtained but also enables the temperature-independent quadrupole hyperpolarisability term to be extracted. Both the quadrupole moment and the hyperpolarisabilty provide valuable information in a variety of applications, including intermolecular forces, electrostatic potentials and non-linear optical phenomena. This thesis fully describes the apparatus used in these measurements, including a description of the custom built oven that allowed for measurements to be performed over a temperature range spanning from 25"C up to 200"C. Results for the quadrupole moments and quadrupole hyperpolarisabilities of carbon dioxide, carbon monoxide, nitrous oxide and hydrogen are presented, together with a quadrupole moment for carbonyl sulphide from room-temperature measurements. Wherever possible, the results of this work are compared to previously published experimental and theoretical data.
Approaches to the total synthesis of a novel diarylheptanoid
(2008) Vela, Nomandla Magnificent
The total synthesis of a novel diarylheptanoid isolated from a South African medicinal plant, Siphonochilus aethiopicus, was investigated. S. aethiopicus (Indungulu in Zulu) is the only South African species of the Zingiberaceae plant family and is widely used in traditional medicine. One of the compounds isolated from this plant is a novel diarylheptanoid. Diarylheptanoids constitute a distinct group of natural plant metabolites characterized by two aromatic rings linked by a linear seven-carbon aliphatic chain, with varying functional groups on the aryl and the aliphatic chain. The target molecule for our synthesis contains two highly oxygenated aryl rings linked by an aliphatic chain with two stereogenic centres and a trans-alkene. In this study we present our investigation of different strategies to a viable synthetic method that could provide material to supplement the relatively small quantity of product that can be isolated from the plant extract. The major challenges of this synthesis were to develop procedures for the preparation of the homobenzylic trans-alkene, the stereogenic centres and to attach the electron-rich aromatic rings to the aliphatic chain. In this thesis the following aspects are described: • Various types of olefination reactions (including Wittig, Julia and organometalic-mediated type of olefination reactions) • Various types of alkylation reactions (including Grignard, Friedel-Crafts and organometalic-mediated type of alkylation reactions) • Incorporation of the stereogenic centres (including asymmetric hydroxylation and use of chiral starting materials) The synthesis will not only give a viable synthetic route to the target compound but is also versatile enough to allow the preparation of analogues.
Elemental distribution in selected edible nuts and the impact of soil quality on the chemical characteristics of macadamia (Macadamia integrifolia) nuts
(2007) Moodley, Roshila.
Environmental and nutritional imperatives make it necessary to carry out regular and reliable
Synthesis of novel pentacyclo-undecane chiral ligands for application in asymmetric catalysis
(2008) Naicker, Tricia.
There is enormous interest in the design and development of efficient chiral ligands for asymmetric catalysis, as a result, this field has become one of the most popular areas of research in organic chemistry. This project involved the investigation of the novel chiral pentacyclo-undecane (PCU) diol 54a, PCU bisimine 87 and PCU bis(oxazoline) 100 type ligands. The PCU diol ligand was synthesized, but proved to be difficult to obtain enantiomerically pure which hindered further investigation into this type of ligand. The PCU bisimine ligand 87 was synthesized. However due to its instability it was not further pursued. Synthesis of the PCU bis(oxazoline) ligand 100 was successful. This ligand was complexed to various metal salts and its efficiency as a chiral Lewis acid catalyst was evaluated on the asymmetric Diels-Alder reaction between 3-acryloyloxazolidin- 2-one 52 and cyclopentadiene 33. The anhydrous magnesium perchlorate ligand complex emerged as the best catalyst providing the endo-cycloadduct product 53 in 81 % enantiomeric excess at -40 oC. Optimizations of the possible conformations of the magnesium complex of ligand 100 with the substrate 52 were performed using Density Functional Theory (DFT) calculations. The more energetically favoured complex conformation was established. The Re-face of the dienophile which was less hindered produced the product consistent with the experimentally observed product 16. Based on the calculated bond lengths from the computational model binding of the ether oxygen on the PCU moiety to magnesium was observed. All the novel compounds were fully characterized using NMR, IR and mass spectroscopy as the main tools.
N-butane activation over ruthenium and iron promoted VPO catalysts.
(2009) Masilo, Neoentle.; Friedrich, Holger Bernhard.
The Fe- and Ru-promoted vanadium phosphorus oxide (VPO) catalysts were synthesized via the organic route in iso-butanol to form the VPO precursor, VOHPO4·0.5H2O. The resulting precursor was then activated in a stream of nitrogen to form an amorphous (VO)2P2O7, which crystallized after conditioning in the reactor in the presence of n-butane. The promoted catalysts were synthesized at 0.1%, 0.3% and 1% loading, pelletized and sieved to give a 300-600 μm pellet size. The catalysts were tested in a fixed-bed continuous flow micro-reactor and the products were analyzed by GC’s equipped with a flame ionization detector (FID) to monitor maleic anhydride and n-butane and a thermal conductivity detector (TCD) to monitor the carbon oxides. A range of characterization techniques were employed to determine the influence of the promoting elements on a VPO catalyst and to associate the composition of the catalysts obtained from such techniques with their performance. The characterization techniques used include X-ray diffraction (XRD), BET-surface area, ICP-OES, EDS, 31PNMR, TPR, redox titrations, ATR and SEM to determine the phase composition of the catalysts, the surface area of the promoted catalysts relative to the un-promoted VPO, elemental mole ratios, the reducibility of the catalysts, average vanadium oxidation state, determination of the anions present in the surface of the catalysts and the variations in the morphology of the catalysts, respectively. Optimization of the system involved variation of the GHSV, the reactor temperature and the promoter loading. (Activation of a 0.75% n-butane in air mixture was performed at an optimum temperature of 400oC while varying the gas hourly space velocity to establish a range of feed conversions and subsequently determine the activity of each catalyst with respect to n-butane conversion). The promoted catalysts modified the morphology of the catalysts as evidenced by the scanning electron microscopy and the X-ray diffraction patterns. Furthermore an improved conversion was obtained with these catalysts. However, only the 0.1% iron-promoted catalyst improved maleic anhydride yield leading to ca. 10% maleic anhydride yield increment. Yields of 46% and 55% were obtained at GHSVs of 2573 and 1450 per hour respectively and a temperature of 400oC. Electronic and structural modifications were encountered leading to an improved catalytic performance. The performance of this catalyst is associated with a vanadyl pyrophosphate phase (XRD), and a limited and controlled amount of V5+ species as illustrated in the TPR, and solid state 31P NMR data. Moreover, this modification can be considered both structural and electronic in nature as observed in the SEM images and FTIR spectra of this catalyst. Furthermore, this improved performance is possible at higher conversions 80 to 90% conversion.
Sedimentation and chemical processes on the Lower Mkuze floodplain : implications for wetland structure and function
(2008) Humphries, Marc
The Mkuze Wetland System, situated in northern KwaZulu-Natal, is South Africa’s largest freshwater wetland area. The system plays a vital role in the functioning of the local landscape and has been identified as an important site for the retention of a number of solutes. The mechanisms through which this retention occurs were investigated through analysis of sediment, groundwater and porewater samples collected from the lower floodplain. Sample analysis was achieved through the use of several techniques, including Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), X-ray Diffraction (XRD), X-ray Fluorescence (XRF), electron microscopy and sequential extraction.
An investigation into the antimalarial activity of metal chelators
(2008) Pareskevopoulos, Jason Nicholas.; Maguire, Glenn Eamonn Mitchel.; Kruger, Hendrik Gerhardus.
Malaria remains one of the greatest problems facing developing nations, especially in sub-Saharan Africa. Part of the problem stems from increased resistance to current treatments hence there is a large drive to develop novel antimalarial compounds. Several chelating compounds, including 8-hydroxyquinoline (8-HQ), 1,10- phenanthroline (1,10-phen) and 2,2.6,2-terpyridine (terpy), have disputed activities (8-HQ and 1,10-phen) or are untested (terpy). Furthermore the mechanism(s) by which these ligands and/or their complexes with metal ions exhibit their toxic effect is unknown. In order to resolve these issues, a study of the antimalarial activities of the free ligands, the ligands complexed with metal ions (Au 3+, Cu 2+, Fe 3+, Pd 2+ and Pt 2+), and the ligands with free metals in solution were measured. The ligands, complexes and metals were also tested for their ability to inhibit β-haematin formation, the mode of action ascribed to the most widely used antimalarial, chloroquine. The background toxicity levels of the various metal ions (previously unreported) were also measured and are reported here. None of the ligands were found to have particularly high activity (all approximately 1μM). In general the metals in were found to have no beneficial effect on activity whether complexed or freely available in solution. None of the ligands were found to inhibit β-haematin formation. The complexes however, with the exception of those of Cu 2+, all inhibited β-haematin formation. Upon further investigation it was found that the each of the metal ions with the exception of Cu 2+ had an innate ability to inhibit β-haematin formation. Thus the mode of action of the ligands and the complexes is likely to be via different mechanisms. In an attempt to enhance the activities of the ligands they were modified by covalently linking them to nutrients essential to the malaria parasite (adenosine and pantothenic acid). These six novel compounds however, showed no improvement in action.
Transverse modes in porro prism resonators
(2008) Burger, Liesl.
This dissertation consists of two main sections. The first is a review of laser resonators using spherical mirrors, and incorporates a physical optics numerical model of a Fabry-Perot laser resonator without gain. The output of this model, which includes spot sizes, loss, and transverse mode formation, is compared to the parameters calculated using published analytical results. This comparison serves as a verification of the numerical methods used, as well as a frame of reference for the model of a Porro prism resonator which follows in the second section. The second section proposes a new method for analysing Porro prism resonators. The analysis incorporates both geometric as well as physical optics concepts, with the prisms modelled as rotating elements with amplitude and phase distortions. This yields expressions for the orientation of the loss at the apex of each prism, and as well as the number of petals in the “petal-pattern” beam structure commonly observed from Porro prism lasers. These expressions are included in a numerical model, which is first used to verify the development of the characteristic petal-pattern. Next, the numerical model is used to investigate the development of the beam structure, in both time and space, in crossed Porro resonators with a range of Fresnel numbers and stability parameters. This leads to some new insight into the transverse modes of these lasers.
Studies on ozone initiated inactivation of pathogenic bacteria in aqueous systems
(2008) Zuma, Favourite N.
The effect of ozone on the inactivation of two Gram-negative strains (Escherichia coli and Pseudomonas aeruginosa) and one Gram-positive endospore (Bacillus subtilis) bacteria, often present in water and the cause of some waterborne diseases was investigated as a function of ozone concentration and ozonation duration. Ozone was generated in situ using corona discharge methods where the ozone concentration ranged from 0.906 - 4.724 mg/L and the inactivation of the three microbes followed pseudo-first order kinetics with respect to the microbes. Three microbes were cultured and the influence of temperature and pH of the aqueous systems on the ozone initiated inactivation rate of the three microbes was also investigated. This study reports that molecular ozone is more effective than hydroxyl radicals initiated by the ozone chain reactions. Two suggested mechanisms for the antimicrobial effectiveness of ozone in water systems from the literature is discussed. The study also found that ozonation significantly decreased the Biological Oxygen Demand (BOD) value of natural water.
Monte Carlo simulations in open quantum systems.
(2007) Van Ryn, Nicholas.; Petruccione, Francesco.
The motivation for this Masters thesis is to develop numerical algorithms to study the dynamical evolution of non-Markovian open quantum systems. Such systems are of importance if one is interested in modeling solid state systems which are candidates for the qubit - the quantum analog of the binary digit. Such an example may be a trapped spin onto which is encoded a chosen spin state. In reality, such a spin is never completely isolated from the environment, and so from a practical point of view it is of interest to study the dynamics of this interaction between some open system with an environment. The goal here is to create a computer program to simulate this behaviour of all density matrix elements for the open system numerically. Many interesting quantum systems, spin chains as an example, do not behave as a Markovian process, and it is sometimes difficult or perhaps indeed impossible to derive exact analytical solutions. As such, the techniques used in this thesis are aimed at describing non-Markovian processes in a way that approaches the exact solution. The study begins by introducing the reader to important concepts and results in the general study of both closed and open quantum systems. Differences in the treatment of the two types of systems are pointed out, and the necessary standard equations used generally are presented. Additionally, two different techniques are explained for the study of open quantum systems, namely the density matrix approach and the stochastic wavefunction approach. Important results from these two methods are presented and the section ends by convincing the reader of their equivalence. The second chapter begins with an example of an open quantum system which exhibits non-Markovian behaviour. The model of the spin star system is described and important results are given from references. This chapter introduces the reader to the model, conceptually explaining the system, and going on to show its exact analytical behaviour. This basic model, with minor changes, will be used throughout this study and the physics, interactions and symmetries, does not really change. This study then shows how one can use the stochastic wavefunction method to solve the dynamics of the spin star model. This chapter follows with deriving stochastic equations for the same system as the preceding chapter, and using these equations a numerical algorithm is developed, the results of which provide a good comparison between the exact analytical and exact numerical techniques. As a further example, a similar but slightly more complex system is studied in exactly the same manner, with the only important difference being that the open quantum system to be modeled is now a spin-one particle. Important differences in the results are pointed out and explained, and important similarities are highlighted. In presenting the results of this second simulation, shortcomings of the numerical technique and areas of applicability are discussed. In the final chapter the author considers using this numerical technique's ability to completely map the dynamics for a density matrix to investigate a measure of quantumness for an open system. This research has been submitted for publication to a peer reviewed journal.
Multi-wavelength study of radio sources in the universe.
(2009) El Bouchefry, Khadija.; Rash, Jonathan Paul Stuart.; Moodley, Kavilan.
This thesis presents a detailed multi-wavelength study of radio sources. A major part of the thesis focuses on radio sources in the FIRST survey while the latter part of the thesis studies low redshift radio galaxies in X-ray selected galaxy clusters. In the first part of the thesis a cross correlation analysis of FIRST radio sources with optical data from the NDWFS and infrared data from the FLAMINGOS survey in the Boötes and Cetus fields was performed. Optical counterparts were found for 76% (688/900) of sources in one band or more i.e., Bw, R, I or K. Photometric redshifts for these sources have been computed using the Hyperz code. The red-shifts obtained are fairly consistent with those expected from the K−z relation for brighter radio sources. A total number of 57 counterparts have extremely red colour (R− K > 5). Photometric redshifts derived using Hyperz imply that these Extremely Red Object (ERO) counterparts to FIRST radio sources are mostly located in the range z ∼ 0.7 −2, with the bulk of the population at z ∼ 1. A total of 25 ERO counterparts to FIRST radio sources were identified in R, J and K bands. These objects were separated into passively-evolving and dusty star-forming galaxies using their R, J and K colours. The relatively blue J − K colour of these galaxies suggest that most (72%, 18/25) are elliptical galaxies rather than dusty starburst galaxies. Using data from the Chandra XBoötes survey, a total of 92 (10%) FIRST radio sources were identified above the X-ray flux limit, fX (0.5 − 7) keV = 8 × 10−15 erg s−1 cm−2, and of these 79 optical counterparts are in common to the radio-X-ray matches. The majority (68%) of the radio-X-ray matched population were found to have −1 < log fX/ fopt < +1 indicative of AGNs. There is a significant population (23%) with high X-ray-to-optical flux ratio (log fX/ fopt > 1), suggesting high redshift and/or dust obscured AGN. In addition, there is also a population of sources that are X-ray faint optically bright sources with log fX/ fopt < −1. Spectroscopic identifications were found for 22 of the 79 sources. These optical spectra were dominated by broad line AGNs and also included narrow emission line galaxies. It was found that many classes of objects contribute to the X-ray/radio emission including quasars, BL Lacs, starburst galaxies, normal galaxies and galaxies with both AGN and starburst activity. This thesis also investigated the clustering analysis of FIRST radio sources optically identified in the SDSS DR6 survey using the two point angular correlation function ω(θ). The matched sources were found to have a larger amplitude of clustering compared to the full catalogue of radio sources consistent with similar studies in the literature. The angular correlation function was measured for different magnitude limited and flux limited subsamples. It was found that the angular correlation function scales with the depth of the optical survey as expected, whereas the amplitude of the angular correlation function increases as the radio flux increases. The last part of this thesis is devoted to studying radio galaxies in galaxy clusters at high frequencies to explore their contamination to the Sunyaev-Zel’dovich effect signal in these clusters. A total of 139 galaxies at low redshift (z < 0.25) in X-ray selected clusters were observed at four frequencies, 4.9, 9, 22, and 43 GHz using the NRAO Very Large Array. It was found that more than half of the observed sources have steep microwave spectra with steep spectral index, α < −0.5, as generally expected. However, about 60% of the unresolved or barely resolved sources have flat or inverted spectra. Most of these sources show an upward turn in flux at ν > 22 GHz, implying a higher flux than would be expected from an extrapolation of the lower frequency flux measurements. Our results quantify the need for careful source subtraction in increasingly sensitive measurements of the Sunyaev-Zel’dovich effect in clusters of galaxies.
Synthesis, structural and magnetic properties of bulk and nanosized (Zn, Cd, Cu)0.5Ni0.5Fe2o4 and NiFe204 ferrites
(2007) Msomi, Justice Zakhele
We present a study of the synthesis, structural and magnetic properties of bulk and nanosized (Zn, Cd, Cu)0:5Ni0:5Fe2O4 and NiFe2O4 compounds. The e®ects of electronic con¯guration and atomic sizes of Zn, Cd, Cu and Ni on the magnetic properties of the ferrites are the primary focus of the study. Di®erent synthesis routes, preparation conditions and how they a®ect single phase formation are explored. The synthesis was undertaken by solid{state reaction, combustion, hydrothermal and glycothermal techniques. The structure determination was by Xray di®raction. The magnetic measurements were performed using MÄossbauer spectroscopy (from 79 K to about 850 K) and a vibrating sample magnetometer (at about 300 K). The bulk densities of the sintered pellets were deduced by Archimedes principle. The bulk oxides were produced by solid{state reaction and combustion techniques. Fine powders with grain sizes of about 10 nm were produced from bulk compounds by a Retsch planetary ball mill and by the hydrothermal and glycothermal processes. The e®ects of the applied pressure used to make pellets (related to green density of the raw pellets) and the sintering temperature on the properties were investigated. An anomalous variation of bulk densities of (Zn, Cd)0:5Ni0:5Fe2O4 oxides with increase in pelletizing pressure was observed which appears to suggest evidence for trapped porosity. Di®erent states of pelletizing the samples appear to be related to a systematic change of the hyper¯ne ¯eld distributions derived from the MÄossbauer spectra. The temperature dependence of the magnetic hyper ¯ne ¯elds at tetrahedral (A) and octahedral (B) sites were observed to vary with temperature according to the equations Bhf (T) = Bhf (0)[1 ¡ (T=TC)n]¯n where n = 1 (based on the Landau{Ginzburg theory) and n = 2 (based on the Stoner theory). The equation Bhf (T) = Bhf (0)[1¡(T=TC)2]¯2 appears to ¯t the hyper¯ne ¯eld data over a wider temperature range. The Zn{ and Cd{based oxides were found to be ferrimagnetic with Curie temperature TC = 548 § 3 K (measured by zero velocity technique). The Cu{based compound exhibited antiferromagnetic behavior with a magnetic transition temperature of 825 § 3 K. The di®erence in behavior between Zn{, Cd{ and Cu{based compounds is due to di®erence in electronic con¯guration and atomic or ionic sizes. The stronger magnetic coupling between spins in the Cu{based sample can be explained by the presence of RKKY interactions in addition to superexchange interactions. The larger ionic size for Cd appears to favour smaller grain sizes in Cd{based oxides. An anomalous increase in TC is obtained in the Zn0:5Ni0:5Fe2O4 compound with reduction in grain size. This increase in TC is attributed to a distribution of Zn ions on both A and B sites. The MÄossbauer spectra of the milled nanosized samples show a combination of ferrimagnetic and paramagnetic behavior. The coercive ¯eld (HC) at room temperature was found to increase with reduction in grain size (G) according to the equation HC = am+bm=G, which is consistent with multidomain particles. With further reduction in grain sizes, the coercive ¯eld reduced according to the equation HC = as ¡bs=G2. This equation is associated with the onset of single domain particles. The samples produced by hydrothermal and glycothermal processes show evidence of transformation from single domain to multidomain structure with increasing sintering temperature. The ease of single{phase formation in the compounds studied is shown to depend on the technique used to prepare the samples. Single phase formation of the spinel structure was easier to achieve in samples prepared by wet chemical methods because lower sintering temperatures (T < 1000 oC) were required.
The fluorescent tube-lamp integrating chamber.
(2008) Durrheim, C. R.
The objective of this project is to design a facility that will characterize the electrical and optical properties of both tubular and the more recent compact fluorescent tubes. The first stage of this project, which is the subject of this dissertation, was to design, build, test, and model a cylindrical light integrating chamber. An integrating chamber capable of measuring 2-metre long fluorescent tubes was built at the University of KwaZulu-Natal, South Africa. To approximate an infinitely long tube, precisely mounted planar mirrors were placed at opposite ends of the cylinder. The reflectance of diffusive reflective paint and mirrors enter into calculations and were investigated experimentally using a Jarrel-Ash optical spectrometer. The light flux was finally measured for various chamber lengths and compared with a mathematical model. Total light power output from the lamp was calculated and compared with the electrical power input, and the lamp efficiency deduced. Accurate calculations required that the light field surrounding a cylindrical diffuse source be modeled mathematically. The reflection coefficients of the mirrors were not unity and the equations had to be modified to include this effect. The mathematical model was solved using a combination of analytical and numerical techniques. The model results were compared with measurements. The final result includes a mathematical description of the integrating chamber, and a flux-density plot of the space surrounding the fluorescent tube.

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