In the last 50 years microelectronics have advanced at an exponential rate, causing microelectronic devices to shrink, have very low operating voltages and increased complexities; all this has made circuits more sensitive to various kinds of failures. These trends allowed soft errors, which up until recently was just a concern for space application, to become a major source of system failures of electronic products. The aim of this research paper was to investigate different mitigation techniques that prevent these soft errors in a Video Graphics Array (VGA) controller which is commonly used in projecting images captured by cameras. This controller was implemented on a Flash Based Field Programmable Gate array (FPGA). A test set-up was designed and implemented at NRF iThemba LABS, which was used to conduct the experiments necessary to evaluate the effectiveness of different mitigation techniques. The set-up was capable of handling multiple Device Under Tests (DUT) and had the ability to change the angle of incidence of each DUT. The DUTs were radiated with a 66MeV proton beam while the monitoring equipment observed any errors that had occurred. The results obtained indicated that all the implemented mitigation techniques tested on the VGA system improved the system’s capability of mitigating Single Event Upsets (SEU). The most effective mitigation technique was the OR-AND Multiplexer Single Event Transient (SET) filter technique. It was thus shown that mitigation techniques are viable options to prevent SEU in a VGA controller. The permanent SEU testing set-up which was designed and manufactured and was used to conduct the experiments, proved to be a practical option for further microelectronics testing at iThemba LABS.

This thesis reports a study of the quantization of generally covariant and nonlinear field theories. It begins by reviewing some existing general theories in Chapter 2 and Chapter 3, Chapter 2 deals with general classical theories while Chapter 3 examines various quantization schemes. The model field derived from the Lagrangian density ℓ = 1/4 ℇ[super]lkμλ (A [sub] k,t – A [sub] k,t)(A, {sub{ A[sub]μ,λ – A[sub]λ,μ). is proposed in Chapter 4 especially for the study of general covariance. It is demonstrated that for this field general covariance alone does not appear to bring in anything physically new, a discussion is given on the differences between general covariance and Lorentz covariance. In subsequent chapters a generally covariant and nonlinear model field, a 4-surface of stationary 4-volume embedded in a 5-dimensional Pseudo-Euclidean space, is investigated. Firstly a manifestly covariant quantization programme is carried out. The model field is then examined in a special coordinate frame for the study of its nonlinearity. Various treatments of the intrinsic nonlinearity are examined starting with conventional perturbation theory in Chapter 6. The usual divergence problem in quantum field theory appears, in particular in the self-energy calculation of a one-particle state. A new variational method is proposed in Chapter 8 which is able to lead to finite results for one-particle states. The thesis is concluded with a chapter discussing some general problems involved and a chapter containing suggestions for further work.

The metabolic demands for women hockey players (n=12) were estimated during real match play using heart rate analysis and time-motion analysis. An individual heart rate - oxygen uptake regression equation, established at steady state workloads on the treadmill, was applied to heart rates recorded throughout the match to estimate energy expenditure. A specific energy cost was assigned to each of nine discrete activities to give an energy cost for the whole match. The mean estimated energy cost for a complete match from heart rate analysis was 3873 +/-436 kj and from time-motion analysis, 2846 +/-284 kJ. In order to check the errors in these methodologies expired air was collected continually during 15 minutes intermittent activity on a treadmill (n=16) with the heart rates and work : rest ratios similar to those established in the earlier part of the study. The error in the use of heart rate to estimate energy expenditure was 3.7 +/-5.1% and for time-motion analysis was 16.6 +/-4.8%, when compared with the measured value from the analysis of expired air. It was concluded that heart rate gave a good estimation of energy expenditure during intermittent activity at workloads similar to women's hockey. In order to gain a greater insight into the metabolic demands of women's hockey both heart rate and time-motion analysis need to be applied simultaneously. The heart rate analysis suggested that the estimated energy expenditure was similar during the first and second halves, hi contrast the time-motion analysis established that less time was spent in high intensity activity during the second half. Women's hockey is played at greater intensities than previously reported with no differences in the metabolic demands when related to specific player positions.

Field theory is used to describe the material content of the universe throughout its entire history, and an oscillating cosmological model without a singularity is presented. In our theory, the “cosmological fluid” is described by a classical scalar field that undergoes a series of phase transitions over the lifetime of the universe. Each transition corresponds to a discontinuous change in the equation of state of the field. In general, for an FRW universe and a given equation of state, we show that the field potential V(Φ) may be derived from the solution of Piccati’s equation. The resulting expression for V(Φ) includes parameters whose values are determined from the boundary conditions. In our theory, we employ the standard cosmological model and the fundamental Planck quantities to provide these boundary conditions. We thereby determine the scalar field Lagrangian for the entire history of the universe. The resulting cosmological model is free of any singularities, and includes an early inflationary epoch. Inflation arises in our theory as a consequence of the initial conditions. The theory describes a universe that is very cold at its minimum radius, although it heats rapidly during the initial inflationary era. This increase in the temperature of the scalar field during inflation is a direct consequence of applying classical thermodynamics under the assumed conditions for the early universe, and does not depend on the fine-tuning of free parameters. Inflation continues until a maximum possible physical temperature (the Planck temperature) is attained, at which point a phase transition occurs and the standard model era begins. By relating the temperature of the scalar field in our theory to the radiation temperature in the standard model universe, it is possible to establish a thermodynamic constraint on a more complete theory of matter for the early universe. Although, in principle, inflation occurs for any equation of state where p < -(1/3)p, we find that the initial equation of state must be p ≈ -p if the later epochs of the universe are to resemble the standard model. In particular, we find that Ho = 33 - 44 km sec-1 Mpc-1 is the value of the Hubble parameter a t the current epoch that is least sensitive to the initial equation of state. / Graduate

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The magnetic properties of some rare earth based Heusler alloys have been investigated. Rare earth Heusler alloys of the form Pd2Reln exhibit magnetic behaviour characterised by magnetic moments localised on the rare earth atoms. X-ray and neutron diffraction investigation show that all alloys crystallise in the cubic L21 Heusler structure with space group Fm3m.

Fermion number fractionization in quantum field theory on a finite interval is studied for a (1 + 1) dimensional fermion-soliton system with explicit charge conjugation symmetry breaking. The effects of boundary conditions on the fractional fermion number and the connection with the corresponding open space problem are investigated. It is argued that the open space fractional charges can be correctly reproduced from the finite interval results only through a careful definition of what is meant by the soliton charge. This definition of the charge distinguishes between the fermionic and boundary induced charges in the system, and isolates the soliton from possibly other charged topological objects in the system. It therefore gives a true measure of the localized fractional fermion number induced on the soliton of interest. It is then rigorously proven that the corresponding charge fluctuations vanish, and hence that the induced fractional charge on the soliton is a quantum observable. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Until such a time that computers are powerful enough to routinely perform ab initio simulation of large biomolecules, there will remain a demand for less expensive computational tools. Classical force field methods are widely used for the simulation of large molecules. However, their low computational cost comes at the price of introducing approximations to the description of the system, for example atomic point charges and Hooke type potentials. The quantum chemical topological force field, QCTFF, removes the classical approximations and uses a machine learning method, kriging, to build models that map ab initio atomic properties to changes in the internal coordinates of a chemical system. The atomic properties come from quantum chemical topology, QCT, and include atomic multipole moments and also energy terms from the interacting quantum atoms (IQA) energy decomposition scheme. By using atomic multipole moments, the electrostatic interactions between atoms is described in a more rigorous fashion than most classical force fields, and polarisation is captured through the use of kriging models. In this thesis, the QCTFF approach has been applied to a selection of test cases including small molecular dimers and amino acids. Kriging models are built using a “training set” of molecular geometries, and an investigation of different approaches for sampling amino acids is provided. The concept of the “atomic horizon sphere” is discussed, where the effect on the multipole moments of an atom in an increasingly large environment is investigated. This is an important investigation required to guide the development of future QCTFF training sets. Investigations into the effect of deprotonation of basic and acidic amino acids side chains is provided, as well as a study of the short range repulsion between atoms.

The anionic tridentate chelating ligands [MeGa(pz)₃]⁻, [MeGa(dmpz)₃]⁻, and [MeGa(mpz)₃]⁻ have been synthesized and their coordinative properties studied. The [MeGa(pz)₃]⁻ ligand acts as a six-electron chelating ligand to divalent transition metal ions giving complexes of the type [MeGa(pz)₃]₂M (M=Mn,Co,Ni,Cu,Zn), believed to possess an octahedral MN₆ core. The ligand also forms numerous carbonyl complexes with Mn, Mo and W. The tridentate chelating nature of this new ligand has been demonstrated through a crystal structure determination of the complex [MeGa(pz)₃]Mo(CO)₂(n³-C₃H₅). The [MeGa(dmpz)₃]⁻ ligand also forms carbonyl complexes of Mn, Mo and W. The ready conversion of this ligand to the less sterically demanding tris-chelating "hydroxy" ligand [MeGa(dmpz)₂(OH)]⁻ occurs in the attempted synthesis of "n³-allyl" complexes [MeGa(dmpz)₃]M(CO)₂ " n³-allyl" (where M=Mo or W, "n³-allyl"=n³-C₅H₅, n³-C₄H₇). The tridentate chelating nature of this "hydroxy" ligand is conclusively demonstrated in the crystal structure determination of the complex [MeGa(dmpz)₂(OH) ]Mo(C0)₂(n³-C₄H₇) . The [MeGa(mpz)₃]⁻ ligand forms transition metal complexes of the type [MeGa(mpz)₃]₂M (M=Co,Ni) and also carbonyl complexes of Mo and W. Less definitive results were obtained with this ligand, as characterization of the resulting complexes was complicated by the inability to separate the isomers possible for each complex The synthesis of the [H₂B(OCH₂CH₂NR₂)(pz)]⁻ (R=H, Me) ligands and their reaction with divalent transition metal ions is also described. In this case, the only products isolated were the previously characterized [H₂B(pz)₂]₂M and [HB(pz)₃]₂M (M=Co,Ni, Cu,Zn) complexes. Finally, details of the synthesis and characterization of the [R₂Ga(CH₃C0₂)] and [R₂Ga(C₄H₈NC0₂)] (R=Me,Et) compounds are given. The crystal structure of the [Me₂Ga(C₄H₈NC0₂)] derivative consisted of monomeric units linked to two others by weak Ga-0 bonds to form a chain-like polymeric structure. The gallium atom in this compound is five-coordinate and has distorted trigonal bipyramidal geometry. / Science, Faculty of / Chemistry, Department of / Graduate