VLF waves propagate in the Earth-ionosphere waveguide (EIW). The EIW is bounded below by the surface of the Earth and above by the ionospheric D-region (50–90 km altitude). The conditions for wave propagation in the EIW are studied and derived specifically for VLF propagation. The D-region is maintained by shortwave solar radiation that ionises the neutral atmosphere. The Wait parameters, H′ (reflection height) and (sharpness), describe the lower boundary of the D-region. Any enhancement in solar X-rays modifies these parameters, leading to a change in the propagation conditions for VLF signals. The effect of the terminator is presented where, it is found to narrow the depression of the monthly averaged diurnal amplitude profile from summer to winter. A series of solar flares were identified of which two case studies are presented. H′ and are calculated from the VLF signals by the Long Wave Propagation Code (LWPC). It is found that H′ decreased and increased at the time of flare. Once H′ and are obtained, the electron density profile can be constructed which is of crucial importance for VLF waves propagating in the EIW. The gradient of the electron density profile is found to increase as increases. It’s found that all the modal interference minima are moved towards the transmitter at the time of the flare. For flares of great magnitude, extrapolation is required to classify the flare in a magnitude class using VLF data. The change in the phase of the VLF signal is found to be linearly proportional to the change in the X-ray flux. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.

This dissertation consists of four sections, with the focus on near- and mid-infrared lasers using Yttrium Lithium Fluoride (YLF) crystals doped with various rare-earth ions as a gain medium. As introduction a general overview of the concepts pertaining to end-pumped solid- state lasers are presented. The basic principles, components and operation of lasers are discussed. Stimulated emission, laser gain media, pump sources and pump geometries are elaborated upon. Three-, four-, quasi-three- and quasi-four-level laser schemes are described. Finally, the advantages and disadvantages of end-pumping as opposed to side-pumping schemes for solid-state lasers are discussed. Thereafter, the design and results of a high-powered diode-end-pumped Nd:YLF laser is presented. In conjunction with previously demonstrated methods, the thermal fracture issues of Nd:YLF were addressed by utilizing the natural doping gradient along the boule of the crystal. This, in addition to a novel crystal mounting technique, resulted in the highest reported output power from a diode-end-pumped Nd:YLF laser as well as record pumping powers. In the third section, a compact Ho:YLF oscillator-ampli er system is reported. The novel setup utilised the unpolarised pump power from a bre-laser e ciently by using the pump light transmitted by the oscillator crystal to pump the ampli er crystal, which produced 21.3mJ at 1 kHz, with an M2 better than 1.1. Lastly, the conclusion is drawn that YLF as a host material can be used in a highly successful manner for high-power applications. Additionally, the novel pumping scheme implemented in the Ho:YLF oscillator-amplifier has been shown to be scalable by a subsequent system which delivered record performance. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2010.

Quantum key distribution (QKD) aims at the creation of a secret key in the two locations of partners, traditionally Alice and Bob, wishing to communicate in private. A generic QKD protocol utilises a quantum channel and an authenticated classical channel for exchanges between partners in Phases 1 and 2 of the protocol, respectively. Phase 1 can be described as a prepareand- measure (P&M) or equivalently as an entanglement-based (EB) phase. Bob performs the same measurement in both descriptions. Subsequent to measurement, Phase 2 is commenced, the aim of which is to distill a secret key from the measurement outcomes resulting from Phase 1. A necessary condition for the security of a QKD protocol is that the measurement performed by Bob in Phase 1 must be described by non-commuting POVM elements. One method of proving the unconditional security of a QKD protocol is to show that the complete protocol (including Phases 1 and 2) is equivalent to an entanglement distillation protocol. A rst step towards showing such an equivalence for a given P&M QKD protocol is to describe an EB translation of Phase 1, where the condition on Bob's measurement is met. Di erential-phase-shift (DPS) QKD is a member of the class of distributedphase- reference QKD protocols. Unconditional security proofs for this class of protocols do not yet exist. Phase 1 of DPSQKD is here described and formalised as both a P&M and an EB phase, and Bob's measurement is shown to be described by non-commuting POVM elements. This description of an equivalent EB translation of DPSQKD where the condition on Bob's measurement is met, is a fi rst step towards a potential unconditional security proof for the protocol based on entanglement distillation. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.

The Wigner formalism can be used to provide a representation of quantum dynamics in a classical-like phase space. However, there are many cases, such as when dealing with spin systems in a dissipative environment, in which one can more conveniently resort to a partial Wigner representation. The quantum propagator in the partial Wigner representation is, in general, a very complicated mathematical object. However, using a linear approximation, the propagator can be taken as a basis for describing the dynamics of hybrid quantum-classical systems. Such a hybrid system is composed of a quantum subsystem interacting with a coupled environment subsystem which evolves under classical-like dynamics represented in the Wigner phase space. In studying these hybrid dynamics it becomes apparent that, for a general environment system, there exists a series of quantum correction terms that restore the hybrid equation to exact quantum dynamics. Thus it is these correction terms that influence the existence of quantum effects in the dynamics of the environment subsystem and could therefore provide unique dynamical signatures indicating the existence of quantum effects. With the above motivation, we have derived an analytical expression for the quantum propagator, including correction terms, in the case of position-dependent couplings and polynomial-potential environment systems, and we have studied, numerically, the resulting quantum dynamics in a few relevant cases through comparison of quantum-classical and quantum-corrected evolutions. The type of system chosen for numerical study consisted of a two-level, or pseudo-spin, quantum system coupled to an environment represented by a quartic potential. It was found that the Rabi oscillations of the pseudo-spin are sensitive to the quantum corrections in a certain range of parameter values, either exhibiting stronger damping or stronger oscillations, depending on the tunnelling behaviour introduced by the corrections. If one were to interpret the pseudo-spin as a Cooper-pair box and the polynomial potential as representing the oscillatory behaviour of a buckled nano-rod, then this works suggests that one might be able to witness the transition of a non-linear nano-oscillator from the realm of classical dynamics to the quantum regime by observation of the pseudo-spin Rabi oscillations. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

In this dissertation the formulation of various integration algorithms is studied, with a view to simulate quantum-classical systems in contact with a thermal bath. In particular focus is given to the constant temperature dynamics of the Nos e-Hoover, Nos e-Hoover Chain and Nos e-Hoover Power thermostat schemes. Through the use of the time symmetric Trotter factorisation of the Liouville operator, algorithms are derived that are both time-reversible and measure-preserving. The efficiency of these algorithms is tested via the constant temperature simulation of a low-dimensional harmonic system. In addition The Nos e-Hoover Power thermostat was then extended to the quantum-classical case. The damping of a tunnelling spin coupled to a thermalised harmonic mode was simulated and the results are presented. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.

In this work, we considered and developed a new method to detect and quantify the fluctuations of a laser beam due to thermal turbulence. The new method consisted of a single laser beam propagating in air and passing through a point diffraction interferometer (PDI). Stable interferograms were thus formed by diffraction of light at the PDI pinhole. Such interferograms underwent phase shifts due to the application of simulated thermal turbulence on the propagating laser beam. These phase shifts were then used to obtain atmospheric turbulence parameters such as the atmospheric turbulence strength, temperature near the propagating beam and the scintillation index. Chapter 1 of this thesis is an introduction and discussion of the theory on the propagation of laser beams in air. Gaussian beam propagation, turbulence detectors, Rytov’s theory and Kolmogorov’s theory of turbulence is also discussed in detail. artefact descriptive experimental procedure is then provided. This chapter focuses on the behavior of a laser beam propagating under the conditions of weak turbulence and relates the Rytov weak fluctuations to the Kolmogorov spectrum since the Rytov variance can be exactly equal to the scintillation index under the conditions of weak turbulence. Two unpublished scientific papers were submitted for publication to the Canadian Journal of Physics and Europian Journal of Remote Sensing. Chapter 2 consist of paper 1 which is based on the development of the experiment and it describes the apparatus in detail as well as it explains the experimental procedure. The preliminary results presented in paper 1 showed that a PDI can produce stable interferograms that can be used to extract the atmospheric turbulence parameters and thus, the PDI method can be used for atmospheric detection and ranging. In chapter 3, we discussed and analysed the experimental results, where the phase shifts were used to estimate the temperature that caused the purturbations on the interferograms. In chapter 4, we concluded about the use of a PDI as a remote sensing technique. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

The ²⁷AI(n,d)²⁶Mg and ⁵⁶Fe(n,d)⁵⁵Mn reactions have been studied at 22 MeV incident energy. The 6MV Van de Graaff facility at the National Accelerator Centre, Faure was used for the experimental aspects. An (n, charged particle) spectrometer was used to detect the energy and angle of the outgoing deuterons. The spectrometer allows for accumulation of particle discriminated data over an angular range of 80⁰. The intrinsic geometry of the spectrometer limits its' angular resolution to ~ 5⁰ (FWHM). The spectrometer has an energy resolution of ~ 0.7MeV(FWHM). A detailed study of the experimental system has been conducted and the proportional counters in particular were extensively investigated. A review of the relevant nuclear models for the target and residual nuclei is presented, together with a theoretical outline of the reaction mechanism for the (n,d) reaction. The distorted waves method approach is used in the analysis of the reaction cross sections. Optical potentials are used to simulate the incoming and outgoing distorted waves and thus generate the theoretical cross sections for the (n,d) reactions. The shapes of the angular distributions of the reaction cross sections for different orbital angular momentum transfers are compared to obtain a fit. Comparison of experimental and theoretical cross sections produce the spectroscopic factors which reveal the occupancy or vacany of level states and hence the single particle nature of these states. It was concluded from the study that the shell model of the nuclei under investigation gives a very good description of the results obtained for the (n,d) reactions. / Thesis (M.Sc.)-University of Durban-Westville, 1988.

The crystal structure of Ru₃ (C0)₁₀(C₆H₅)₂PN(C₂H₅) P(C₆H₅)₂ (RUC)PNP) has been determined by single crystal X-ray analysis. The crystals are tri-- clinic with space group PĪ. The unit cell of dimensions a = 14,732; b = 12,386; c = 10,982 Å; α = 104,52; β = 100,64; γ = 94,89° contains two formula units. The unit cell and space group were determined by photographic deJong-Bouman and precession techniques using CuKα radiation. A procedure was developed for more accurate alignment of the crystal for rotating crystal techniques. Intensity data were collected on a Philips PW1100 four-circle diffractometer with MoKα radiation. The positions of the Ru atoms were determined from Patterson syntheses and the remaining atoms located using successive Fourier synthesis. The structure was refined by blocked full-matrix least-squares methods to a residual of R = 0,0537 for 3538 independent reflections with I > 5σ(I) with 300 parameters in the final refinement. The phenyl rings and the CH₂ and CH₃ moities were refined as rigid groups with H-atoms included at fixed positions. A difference Fourier synthesis was done and showed no significant peaks. RUCOPNP is derived from Ru₃(CO)₁₂ by substitution of two equatorial carbonyl ligands by the P atoms of a single edge-bridging (C₆H₅)₂PN(C₂H₅)P( C₆H₅)₂ ligand (PNP). In both complexes the Ru atoms are arranged in a triangle and have distorted octahedral geometry. The introduction of the PNP ligand to the symmetrical parent Ru₃(CO)₁₂ has the following effects: (a) It causes a contraction of the ligand-bridged Ru-Ru bond distance to 2,798 Å whereas the other Ru-Ru distances are 2,860 and 2,848 Å which are close to the distances in the parent compound; (b) It causes the adjacent equatorial carbonyl ligands to rotate towards the PNP ligand by 11,4°. (c) It causes considerable deviations of some of the axial carbonyl ligands from the normal to the plane containing the Ru atoms. / Thesis (M.Sc.)-University of Durban-Westville, 1984.

One of the main interests in the vanadium oxides V2O5 and VO2 is that, when doped with a metal such as Fe, these oxides display semiconductor-to-metal transitions at certain critical temperatures. These transitions are also accompanied with changes in the crystallographic phases of the oxides. This thesis describes the use of hyperfine interactions at dopant sites in the vanadium oxides V2O5 and VO2 to infer information on the phase transitions that take place in these oxides. The hyperfine interaction techniques of Mossbauer Spectroscopy and Time Differential Perturbed Angular Correlation (TDPAC) are used to study the hyperfine parameters in the Fe - V2O5 system and Cd - V2O5 system, respectively. X-ray powder diffraction spectroscopy were also conducted on the samples to establish the phases created. A large part of this project was spent in the design of apparatus. The apparatus constructed were (i) a furnace to perform a solid state reaction in order to introduce Fe into V2O5, the maximum operating temperature of the furnace being 1473 K, (ii) a Mossbauer sample chamber and sample holder which enabled the sample to be heated up to a temperature of 873 K, and (iii) a device constructed to determine the electrical conductivities of powder samples at temperatures ranging from 773 K to room temperature. For the Mossbauer studies, the Fe-V2O5 system was studied as a function of the Fe concentration. Six symmetric doublets, with intensities changing as the Fe concentration changed, were observed. Correlating the Mossbauer components of the individual spectra with the phases identified using powder x-ray diffraction patterns in terms of the reflection intensities, allowed two of the doublets to be assigned to lattice sites in the vanadium oxide bronze system, θ-YOB, a further two doublets to substitutional and interstitial sites in the Fe doped V2O5 system, respectively, and the fifth doublet to the super-paramagnetic Fe2O3 phase. The sixth doublet observed was attributed to an unresolved crystallographic phase observed in the x-ray diffraction spectra at large Fe concentrations. The magnitude of the quadrupole splittings of the doublets assigned to the vanadium oxide bronze and the Fe-V2O5 systems indicate that the electronic environment of the Fe atoms in the bronze phase displays a greater symmetry than those in the V2O5 phase. In order to gain insight on the semiconducting nature of the Fe doped V2O5 and the θ-VOB phases, temperature dependent Mossbauer measurements ranging from 300 K to 573 K, together with electrical conductivity measurements, were performed on a few samples. The temperature dependent Mossbauer spectra displayed the usual second order Doppler shift of the isomer shifts for the various components as a function of temperature, but no significant change in the magnitude of the quadrupole splittings. From this result, on the basis of the Duncan-Golding correlation diagram, the valence state of the Fe ions was inferred to be 3+. No components were observed (with increasing temperature) that could be correlated with the population of Fe2+ states. This therefore suggests that the semiconducting properties of the Fe doped V2O5 phase and the θ-VOB phase are associated with electron hopping between V4+ - V5+ valence sites rather than Fe3+ - Fe2+ valence sites. 111In-TDPAC measurements were made on V2Os and VO2. For V2O5, the measurements yielded one distinct substitutional cation site for the 1llCd ions, with quadrupole coupling constant vQ =88,1(3) MHz, and asymmetry η =0,619(3) In VO2, temperature dependent TDPAC measurements yielded two well defined quadrupole coupling frequencies for the 1llCd probe nuclei, the first, vQ =43,0(7) MHz, observed at room temperature, corresponding to a monoclinic or triclinic phase of VO2, and the second, vQ =89,1(1) MHz, observed at 423 K and above, corresponding to the rutile phase of VO2. / Thesis (Ph.D.)-University of Durban-Westville, 1999.

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. / Thesis (PhD)-University of KwaZulu-Natal, Westville, 2009.