A congestion aware ant colony optimisation-based routing and wavelength assignment algorithm for transparent flexi-grid optical burst switched networks
- Authors: Oladipo, Joshua Femi
- Date: 2018
- Subjects: Ants -- Behavior -- Mathematical models , Distributed algorithms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/34733 , vital:33432
- Description: Optical Burst Switching (OBS) over transparent exi-grid optical networks, is considered a potential solution to the increasing pressure on backbone networks due to the increase in internet use and widespread adoption of various high bandwidth applications. Both technologies allow for more e cient usage of a networks resources. However, transmissions over exi-grid networks are more susceptible to optical impairments than transmissions made over xed-grid networks, and OBS suers from high burst loss due to contention. These issues need to be solved in order to reap the full benets of both technologies. An open issue for OBS whose solution would mitigate both issues is the Routing and Wavelength Assignment (RWA) algorithm. Ant Colony Optimisation (ACO) is a method of interest for solving the RWA problem on OBS networks. This study aims to improve on current dynamic ACO-based solutions to the Routing and Wavelength Assignment problem on transparent exi-grid Optical Burst Switched networks.
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- Date Issued: 2018
Petrophysical analysis of thermo-tectonic effects linked to Lower Jurassic dolerite intrusions in sedimentary rocks of the Main Karoo Basin, with implications for shale gas development in South Africa
- Authors: Nengovhela, Vhuhwavhohau
- Date: 2018
- Subjects: Sedimentary rocks -- South Africa -- Research , Sedimentation and deposition Geology, Structural -- South Africa Geology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/33802 , vital:33034
- Description: Prevalent dolerite sills and dikes emplaced in the sedimentary rocks of the main Karoo Basin are associated with contact metamorphism and devolatilization of carbon-rich shales of the Lower Ecca Formation. These thermal effects may have significant bearings on the potential of shale gas development in the Karoo. This research aims to study and quantify the effects of dolerite intrusions on the Karoo sedimentary rocks along contact aureoles in shales and sandstones of the Ecca Group based on drill core samples collected from deep SOEKOR boreholes, and field samples from the Lower Beaufort Group of the Eastern Cape Province. Variations in host rock minerals, chemistry, and porosity are determined using analytical techniques including: petrography, scanning electron microscopy (SEM), X-ray diffraction (XRD) on samples collected along the thermal aureoles at various distances away from the intrusions. Using the determined mineral phase equilibria, geochemistry and thermal modelling, the pressure-temperature (P/T) conditions that prevailed during contact metamorphism are evaluated to constrain the thickness of the contact aureoles in deep boreholes, and to further evaluate potential loss of shale gas. The mineral composition of the samples generally consists of quartz, feldspar, illite/smectite, calcite, muscovite, and pyrite. Metamorphic minerals close to contacts with the sills include andalusite-chiastolite, biotite, muscovite, illite, forsterite, and diopside. SEM imaging confirms that the hornfels samples are compact and that the metamorphic minerals reduce and limit porosity to grain boundaries, and in few cases intra-mineral porosity occurs within individual crystals. The porosities are in the range of mesopores (2-50 nm) and micropores (< 2 nm). The data also suggests that the thermal alteration of the Ecca shales were short lived (e.g. 10-100 years). Disequilibrium metamorphic textures such as irregular grain boundaries, and inclusions in andalusite and cordierite confirm that the elevated temperatures did not last long enough to accomplish (re)crystallization and create equilibrium textures. To test the effect of geothermal gradients on the initial host rock temperatures prior to intrusive activity, and how these temperature differences affect the contact aureole thickness, thermal models were simulated for the deep boreholes using three geothermal gradients: 30 ◦C/km, 35 ◦C/km, and 40 ◦C/km. In addition, the depths were re-calculated based on post-emplacement erosion of the overlying host rocks (2000-3000 m). Heat flow away from dolerite sills through the host shales were modelled using convection and conduction heat flow mechanism separately, to assess differences and/or similarities in cooling trends. The models show that a 10 ◦C increase in geothermal gradient (from 30 ◦C /km to 40 ◦C/km) significantly affects the initial temperature of the host rocks and in turn decreases the rate at which the dolerite sills cool. Thermal modeling data is coherent with the mineralogy of the contact zones. Andalusitechiastolite and cordierite porphyroblasts occur within 10-20 m of the contact aureole, together with biotite and authigenic muscovite. Literature data shows that crystallization of this mineral assemblage in pelitic hornfels occurs at temperatures ranging between 450 ◦C and 600 ◦C. Thermal modelling results indicate maximum temperatures of shales at the contact with dolerite sills range between 650 ◦C to 700 ◦C. Temperatures decrease rapidly to approximately 400 ◦C within 10-20 m away from the contacts. The data also shows that thermal perturbation flanking the sills were short-lived, with maximum temperatures reached within the first 100 years of cooling depending on the thickness of dolerite sills and the combined effect of multiple sill intrusions. Data acquired from the thermal models and literature was used to evaluate gas loss estimations. The calculations conducted around a 45 m thick sill, suggests that at least 4- 6 TCF of gas was liberated from the Whitehill Formation during Karoo sill emplacement. These values are significantly less than previously calculated losses (22 TCF), and thus have a significant bearing on further predictions of shale gas potential of the Karoo Basin.
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- Date Issued: 2018
The path to adoption: experiences of couples who have transitioned from infertility
- Authors: Brophy, Mandy-Lee
- Date: 2017
- Subjects: Adoption -- South Africa -- Port Elizabeth , Infertility -- South Africa -- Port Elizabeth Family social work -- South Africa -- Port Elizabeth
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/14763 , vital:27844
- Description: Parenthood is a life goal for the majority of individuals and couples who have reached a certain life stage. For many couples parenthood is, however, not a reality through expected means. Statistics gathered, in an unpublished information document, by the Port Elizabeth Infertility and Wellness Clinic, it is estimated that 10 to 15% of all married couples in the region experience infertility. After failed infertility treatment, adoption is considered an option for many couples wishing to have children. The social worker plays an integral role in the assessment and preparation for adoption. However, there is no legislated preparation for the fertility treatment process as there is for adoption in South Africa, yet both processes are intended to result in parenthood shadowed by stressful circumstances for prospective parents. The study explored the experiences of couples who have transitioned from being diagnosed as infertile and have successfully adopted. The study was conducted from a qualitative research perspective and employed the exploratory-descriptive strategy of inquiry. Purposive sampling was applied and eight married couples participated in the study. The participants were sourced from a support and information network for adoptive families as well as referrals from social workers working within the adoption field. Semi-structured interviews were conducted by an independent interviewer with thematic analysis being used for data analysis. Trustworthiness constructs were taken into account to ensure reliability and rigour. The major findings revealed the distinctive experiences regarding fertility treatment, the experiences regarding adoption and suggestions from couples for couples facing similar situations as well as for professionals in practice. The study is viewed as significant in guiding professional services to couples, who are intending to achieve parenthood via adoption, by adding to the body of existing knowledge in adoption and medical social work.
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- Date Issued: 2017
Growth and characterization of ZnO nanorods using chemical bath deposition
- Authors: Urgessa, Zelalem Nigussa
- Date: 2012
- Subjects: Zinc oxide , Photoluminescence , Semiconductor nanocrystals , Semiconductors -- Materials , Chemical reactions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10559 , http://hdl.handle.net/10948/d1021124 , http://hdl.handle.net/10948/d1021119
- Description: Semiconductor devices are commonplace in every household. One application of semiconductors in particular, namely solid state lighting technology, is destined for a bright future. To this end, ZnO nanostructures have gained substantial interest in the research community, in part because of its requisite large direct band gap. Furthermore, the stability of the exciton (binding energy 60 meV) in this material, can lead to lasing action based on exciton recombination and possibly exciton interaction, even above room temperature. Therefore, it is very important to realize controllable growth of ZnO nanostructures and investigate their properties. The main motivation for this thesis is not only to successfully realize the controllable growth of ZnO nanorods, but also to investigate the structure, optical and electrical properties in detail by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy (steady state and time resolved) and X-ray diffraction (XRD). Furthermore, strong rectification in the ZnO/p-Si heterojunction is demonstrated. Nanorods have been successfully synthesized on silicon by a two-step process, involving the pre-coating of the substrate by a seed layer, followed by the chemical bath deposition of the nanorods. ZnO seed layers with particle sizes of about 5 nm are achieved by the thermal decomposition of zinc acetate dihydrate dissolved in ethanol. The effects of the seed layer density on the distribution, alignment and uniformity of subsequently grown nanorods were studied. The aspect ratio, orientation and distribution of nanorods are shown to be well controlled through adjusting the density of the ZnO nanoparticles pre-coated onto the substrates. It is shown that the seed layer is a prerequisite for the growth of well aligned ZnO nanorods on lattice mismatched Si substrate. The influence of various nanorod growth parameters on the morphology, optical and electrical properties of the nanorods were also systematically studied. These include the oxygen to zinc molar ratio, the pH of the growth solution, the concentration of the reactants, the growth temperature and growth time, different hydroxide precursors and the addition of surface passivating agents to the growth solution. By controlling these xii parameters different architectures of nanostructures, like spherical particles, well aligned nanorods, nanoflowers and thin films of different thicknesses are demonstrated. A possible growth mechanism for ZnO nanostructures in solution is proposed. XRD indicated that all the as-grown nanostructures produced above 45 C crystallize in the wurtzite structure and post growth annealing does not significantly enhance the crystalline quality of the material. In material grown at lower temperature, traces of zinc hydroxide were observed. The optical quality of the nanostructures was investigated using both steady-state PL and time-resolved (TR) PL from 4 K to room temperature. In the case of as-grown samples, both UV and defect related emissions have been observed for all nanostructures. The effect of post-growth annealing on the optical quality of the nanostructures was carefully examined. The effect of annealing in different atmospheres was also investigated. Regardless of the annealing environment annealing at a temperature as low as 300 C enhances the UV emission and suppresses defect related deep level emission. However, annealing above 500 C is required to out-diffuse hydrogen, the presence of which is deduced from the I4 line in the low temperature PL spectra of ZnO. TRPL was utilized to investigate lifetime decay profiles of nanorods upon different post growth treatments. The bound exciton lifetime strongly depends on the post-growth annealing temperature: the PL decay time is much faster for as grown rods, confirming the domination of surface assisted recombination. In general, the PL analysis showed that the PL of nanorods have the same characteristics as that of bulk ZnO, except for the stronger contribution from surface related bound excitons in the former case. Surface adsorbed impurities causing depletion and band bending in the near surface region is implied from both time resolved and steady state PL. Finally, although strong rectification in the ZnO/p-Si heterojunction is illustrated, no electroluminescence has been achieved. This is explained in terms of the band offset between ZnO and Si and interfacial states. Different schemes are proposed to improve the performance of ZnO/Si heterojunction light emitting devices.
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- Date Issued: 2012