LD2668 .T4 1966 T262 / Master of Science

The aim of this study was to investigate the effect of frequent operational changes on the repairs and maintenance of public lighting in the Energy and Electricity Division of the City of Tshwane Metropolitan Municipality as a result of management decisions. The results of the study showed contrasting opinions and perceptions amongst all participants on the repairs and maintenance activities of public lighting. Both employees working in the maintenance operations and public lighting sections agreed that their sections were performing the repairs and maintenance of public lighting satisfactory. Customers and community leaders on the other hand agreed that the maintenance operations sections are performing the repairs and maintenance of public lighting satisfactory as compared to public lighting section. All employees were in favour and support of decisions taken respectively since these decisions were beneficial to their respective sections, but however they were concerned on the frequency of decisions taken by top management and changes implemented within their respective sections as these decisions and changes created confusion and conflict amongst employees. All sections involved in the repairs and maintenance of public lighting were faced with numerous similar challenges that created deficiencies and ineffectiveness on the maintenance activities of public lighting and that contributed to enormous complaints from customers and community leaders on the service rendered by the division.

I have investigated the influence of an ultra-thin Au interface layer on the magnetic anisotropy of Co-Pd and Co-Cu structures. Sandwich structures of the form X/Co/Y/Cu/Si(111), with (X, Y) = (Pd, Pd), (Au, Pd), (Pd, Au), (Cu, Cu), (Au, Cu), and (Cu, Au) were studied. For each structure, a Au layer of systematically varied thickness (t(Au)) was inserted at one Co interface. I also investigated Co/Pd and Co/Cu multilayer systems. For each Co-Pd sandwich structures a maximum is observed in the magnetic anisotropy for t(Au) = 1 to 1.5 atomic monolayer (ML). For the Co/Pd multilayer system, a maximum in coercivity occurs with tAu = 0.5 ML. For each Co-Cu sandwich structure except (X, Y) = (Cu, Au), a minimum in magnetic anisotropy is observed at t(Au) = 1 ML. For the Co/Cu multilayer system, a decrease in magnetoresistance was seen with increased tAu except in multilayers with a relatively thin Co layer thickness (∼3 ML) which display a peak in magnetoresistance is seen at tAu = 1 ML. I have also investigated the strain, surface alloying, and surface (interface) roughness of these systems using RHEED, XPS, and LAXD. Analysis of these measurements reveals some correlation between magnetic anisotropy and both strain and surface roughness. Based on my investigations, I conclude that the most likely cause for the non-monotonic changes seen in anisotropy is changes in the surface magnetocrystalline anisotropy. While strain and surface roughness may also play a role, I believe that the influence of the ultra-thin Au interlayer on the orbital hybridization and electronic environment at the interface is dominant.

The properties of cubic nitrides grown by molecular beam epitaxy (MBE) on GaAs (001) have been studied using optical and electrical techniques. The aim of these studies was the improvement of the growth techniques in order to improve the quality of grown nitrides intended for bulk substrate and optoelectronic device applications. We have also characterised hexagonal nanocolumn structures incorporating indium. Firstly, bulk films of cubic AlxGa1-xN with aluminium fractions (x) spanning the entire composition range were tested using time-integrated and time-resolved photoluminescence (PL) plus reflectivity measurements. Strong PL emission was recorded from the samples, with improved intensity for higher aluminium concentrations. Temperature dependent and time-resolved PL showed the increasing role of carrier localisation at larger AlN fractions. The reflectivity results showed a near-steady increase in the bandgap energy with increasing AlN content. Alternative interpretations that did and did not involve a transition from direct-gap to indirect-gap behaviour in cubic AlxGa1-xN were considered. We next looked at cubic AlxGa1-xN/GaN/AlxGa1-xN single quantum well (QW) structures with varying AlN content in the barrier regions. The PL studies indicated that carrier escape from the QWs and non-radiative recombination at layer interfaces were limiting factors for strong well emission. Higher AlN concentration in the barriers appeared to exacerbate these problems. The doping of cubic GaN with silicon (n-type) and magnesium (p-type) was also studied. For Mg-doped GaN, a strong blue band emission was noted in the PL spectrum, which became more intense at higher doping levels. The Mg-doped GaN layers had low conductivity and their mobility could not be measured due to strong compensation effects. The cubic film had similar time-resolved PL properties for the blue band emission compared to hexagonal Mg:GaN. These results suggested that the blue band was the result of recombination between a shallow Mg acceptor and deep donor, believed to be a complex including a nitrogen vacancy and an Mg atom. This complex was also associated with the compensation effect seen in the electrical measurements. With the Si-doped cubic GaN, we observed PL spectra that were consistent with other sources. Thicker layers of GaN:Si did not have measurable mobility. This was likely caused by the rough surface structure that was imaged using a scanning electron microscope. The thin layer had a very smooth surface in comparison. The mobility of sub-micron thickness layers with a carrier concentrations of n = 2.0×1018cm-3 and n = 9.0×1017cm-3 were μ = 3.9cm2/Vs and μ = 9.5cm2/Vs respectively. The mobility values and structural issues indicated that growth improvements were needed to reduce scattering defects. In addition to cubic structures, we have considered nanocolumn growth of InGaN and InN. InxGa1-xN nanocolumns were grown on Si (111) by MBE with a nominal indium concentration of x = 0.5. PL emission was obtained from samples grown at higher temperature, but overall intensity was low. A second set of samples, where nanocolumn growth was followed by growth of a continuous coalesced film exhibited much stronger PL emission, which was attributed to the elimination of a phase separated core-shell structure in the nanocolumns. Next, a coalesced InxGa1-xN structure with vertically varying indium fraction was characterised. PL readings showed evidence of successful concentration grading. Finally, the PL spectra of coalesced InN layers were recorded, for which a specialised infrared PL system needed to be used. The results highlighted how increased growth temperature and indium flux can improve PL properties. For the binary alloy however, coalescence growth can decrease PL intensity compared to the nanocolumns stage.

No description available.

This report investigates the effects a demand based tariff would have on private electricity consumers and how it could contribute to a sustainable electrical grid. The fuse tariff that is currently used charges customers for their electricity usage and does not fully reflect the electrical grid load and thereby not the cost for the distribution system operators. A demand based tariff, that charges customers for their power peaks and promotes a change of behaviour better reflects the grid load and could lead to a more even grid distribution and a sustainable development. In light of this issue, two demand based tariffs have been constructed for the energy company Upplands Energi’s private customers’ current electricity consumption. One of the tariffs consists of a higher fixed cost and a lower variable cost and the other consists of a lower fixed cost and a higher variable cost, both leading to the same revenue för Upplands Energi. The two different demand based tariffs have been simulated and analysed, where the one with the lowest fixed cost is recommended since it gives customers higher economic incentives to change their electricity usage behaviour. It is essential that electricity retailers communicate the information of how the demand based tariff works to the customers in order to make them change their electricity behaviour to attain a sustainable grid.

No description available.

published_or_final_version / Electrical Engineering / Master / Master of Science in Engineering

published_or_final_version / Electrical Engineering / Master / Master of Philosophy

This dissertation studies how to characterize strategic behaviors in electricity markets from a transmission-constrained residual demand perspective. This dissertation generalizes the residual demand concept, widely used by economists in general markets, to electricity markets, which are constrained by transmission networks. The transmission-constrained residual demand is characterized by a sensitivity analysis of the optimal power flow program, which is the electricity market clearing engine. Methods are proposed to optimize a generator or generation firm's profit utilizing the residual demand sensitivity information, which has several advantages over existing methods. The transmission-constrained residual demand concept and the methods are helpful for market participants to develop bidding strategies and for market monitors to analyze market power in electricity markets. / text