Most contemporary modems provide a bit-oriented service at the physical layer of the OSI reference model. They do not provide any specific support for packet data transmission. A novel Hop-Aligned Slow Frequency Hopping (HA-SFH) concept is proposed to provide a packet traffic service in a Partial Band Jamming (PBJ) environment. Frequently, SFH is used together with deep interleaving and powerful Forward Error Correction (FEC) to combat PBJ. The proposed HA-SFH exploits the error control mechanism of the link layer packet protocol and reduces the data redundancy by using a low gain FEC, it results in a more bandwidth efficient system. The HA-SFH and deep interleaving SFH (DI-SFH) performance were analysed and compared by using a series of simulations and experiments employing a network simulator and hardware such as Viterbi decoders and a channel noise simulator, etc. The results are presented in terms of throughput and average frame delay, which are more meaningful qualities than BER for packet traffic. It shows concrete results that HA-SFH performs 2 times better than DI-SFH in terms of throughput under PBJ. This thesis also discusses a wide range of technical issues involving the implementation of HA-SFH such as the coding level required, protocol enhancement, networking traffic, adaptive FEC, channel state estimation, etc. It also explores an adaptive code rate system called the Smart Codec (SmCodec), which can be integrated into HA-SFH. The further development of the SmCodec also makes it a suitable system for use in commercial PSK modems to combat the effect of channel fading (eg. from rain). A new channel state estimation technique is also proposed. It estimates the channel state from the block error rate and the required estimation time is as low as 2 seconds for the most required range of E_b/N_o at a 64 kbps link (the estimation time decreases when the link speed increases).

This thesis proposes a novel consolidated approach for substantial compaction of HVDC lines that includes both new tower geometries as well as novel control concepts. This is based on a thorough discussion on the basic overhead line design parameters and their impact on the right of way width and tower height. Then the electrical aspects of the new approach such as dc overvoltage assessment and lightning performance are investigated. The required horizontal clearances between pole conductors and tower members, as a component of the right of way width, depend on the maximum expected overvoltages. Detailed electromagnetic transient models for the point to point MMC HVDC with different transmission configurations, all including the proposed dc overhead line, are developed for this thesis. The models are used to assess fault contingencies that result in the most significant overvoltage stresses on the HVDC transmission line for finding minimum air clearances and for the design of overvoltage limiting devices, such as surge arresters. New control approaches are proposed that significantly reduce the dc side overvoltage and consequently minimize the required air clearances for maximum compaction of the HVDC overhead lines and also reduce the required surge arrester size for line insulation. Because power transmission lines are the most exposed component within a power system, they are subject to lightning strikes which, in turn, are the main cause of disruption to power flows. This thesis will include an analysis of lightning occurrence on the proposed compact transmission line in order to assess the risk of pole faults. The focus of this analysis is mainly on evaluation of the critical lightning currents that cause fast front overvoltage stresses that may result in insulation failure. / May 2017

In an infectious disease with a long infectious period (which can be the entire life for some diseases), the infectivity of individuals may change due to different reasons. For example, infected individuals may receive treatment and their level of infectivity can reduce depending on the efficacy of the treatment. Or, infected individuals may change their behaviour and reduce their activity once the disease is diagnosed, leading to a reduction of their infectivity. Treated individuals may stop getting treatment, and return to the infective class at a rate depending on how long they have been receiving treatment. In this thesis, a compartmental model consisting of three compartments (susceptibles, infectives and treated infectives) is formulated to study the effect of treatment on the transmission dynamics of a disease. Continuous and discrete treatment-age-structured models are derived and the asymptotic behaviour of the system is studied and the basic reproduction number is determined. / October 2016

In the world of networked system, average consensus is an important dimension of co-ordinate control and cooperation. Since the communication medium is digital, real value cannot be transmitted and we need to perform quantization before data transmission. But for the quantization, error is introduced in exact value and initial average is lost. Based on this limitation, my 16 bit quantization method (sending MSB in 1-4 cycle and MSB+LSB in 5th cycle) reduces error significantly and preserves initial average. Besides, it works on all types of graphs (star, complete, ring, random geometric graph). My other algorithm, distributing averaging algorithm (PQDA) with probabilistic quantization also works on random geometric graph, star, ring and slow co-herency graph. It shows significant reduced error and attain strict consensus.

Call number: LD2668 .T4 1950 F85 / Master of Science

M.Ing. (Electrical and Electronic Engineering Science) / This study presents a simple methodology developed to set up and establish a simplex communication system over a power line using load signatures. Traditional concepts such as normalization and matched filtering form the core of these algorithms. The analysis also relies extensively on the voltage and current measurements made over a fixed period of time on a single phase. Furthermore, analyses on the capacity of this kind of system are also presented, taking into consideration various disturbances.

Financial Transmission Rights (FTRs) have been a feature of competitive electricity markets for nearly 20 years. FTRs are financial derivatives sold in periodic auctions. Revenues from the sale of these derivatives are passed through to electricity ratepayers to compensate them for transmission congestion payments they make in the spot energy market. FTR purchasers are effectively swapping their auction payment for an uncertain revenue stream over the life of the FTR. In recent years, industry market monitors have become concerned with the auctions’ performance in adequately compensating ratepayers – FTRs sell, on average, for a price less than the revenue they generate for the purchaser. This dissertation contributes to our understanding of FTR market functioning by studying the Auction Revenue Rights (ARR) management process, which is the predominate mechanism used in U.S. electricity markets to distribute FTR auction revenue to electricity ratepayers. This dissertation is organized into three essays, detailed below. The first essay demonstrates how the ARR process influences fundamental supply conditions in the FTR auction market and show how divergent auction equilibria emerge under different ARR decision-making regimes. Using market data from the PJM Interconnection, this essay finds empirical evidence that variation in ARR management strategies helps explain differences between an FTR’s auction price and its realized ex post value. The second essay studies the interaction of affiliated subsidiaries in auctions for FTRs. The essay documents a setting where a regulated utility routinely sells FTRs (through the ARR process) to an affiliated generation company in an auction where a portion of the revenue is passed through to the regulated utility’s retail customers. It appears that the affiliated generator may be placing strategic bids in the auction to minimize the price they pay for the derivatives, which would also minimize the revenue passed through to the regulated utility’s retail customers. The third essay studies the relationship between the long-term FTR auction market and the annual auction market in terms of ARR prices. Long-term auction clearing prices systematically overvalue FTRs that are along the paths of an ARR, thus providing electricity ratepayers with a biased signal of the potential value of their ARR allocations. Collectively, these three essays demonstrate the role of the ARR process in determining equilibrium FTR auction prices. Not only do ARR management decisions directly affect equilibrium prices, but ARRs constitute the mechanism by which auction revenues are passed through to ratepayers. Thus, any analysis of FTR auction revenue deficiency must include a thorough understanding and empirical incorporation of the ARR process into the analysis. <br><br>

Introduction: Prevention of mother-to-child-transmission of HIV is a priority public health problem in Africa as pregnant women and their children are the most vulnerable. In South Africa, a prevention of mother to child transmission of HIV (PMTCT) programme has been implemented in antenatal clinics to reduce paediatric HIV/AIDS. It is necessary to assess the uptake of this programme by pregnant women. Objectives The purpose of this study was to determine the uptake of the PMTCT programme in the antenatal clinics of Sedibeng district. Using data coming from all the antenatal clinics (ANC) at a primary health care levelin Sedibeng for 2005 and 2006, we determined the proportion of ANC attendees who accepted to be counselled, the proportion of these who accepted to be tested for HIV, the proportion of these who came back for results and the proportion who were HIV positive. Nevirapine (NVP)uptake was determined as well among HIV positive women and babies born to HIV positive women. Methods Data collection was by a record review of PMTCT records from all antenatal clinics in the district. To determine maternal uptake of PMTCT, data were extracted from antenatal clinics monthly collation sheets for 2005 and 2006. Nevirapine uptake for the babies born to HIV positive mothers was determined in one facility: data were v - collected in the midwife obstetric unit of the community health centre from both the Nevirapine register and the mothers’ delivery records. Results A total of 8010 women attended in Sedibeng antenatal clinics in 2005 and 10217 in 2006. In 2005 95 % of attendee women accepted to be counselled among whom 91% accepted to be tested for HIV. In 2006 93% women accepted to be counselled among whom 91% accepted to be tested. Almost all tested women came back for results: 99% came back for results in 2005 and 98% in 2006. The proportion of HIV positive women in the attendees population was 23% in 2005 and 24% in 2006. Nevirapine was dispensed to only 600 per 1000 HIV positive women in 2005 and 539 per 1000 HIV positive women in 2006. From June 2005 to May 2006 only 59% of babies born to an HIV positive mother received NVP. Discussion and conclusion The study showed a good uptake of voluntary counselling and HIV testing in Sedibeng district antenatal clinics. But a low proportion of HIV positive women and HIV-exposed babies received NVP. There was probably a loss of follow up of women between ANC visits and delivery. Nevirapine uptake must be improved in Sedibeng antenatal clinics and further investigations need to be done to understand the factors influencing uptake.

Low affinity Fcγ receptors (FcγR) mediate key immune effector mechanisms through the engagement of the Fc portion of immunoglobulin G (IgG). These receptors are involved in multiple biological processes, including clearance of antigen/antibody immune complexes, enhancement of antigen presentation, antibody-dependent cell-mediated cytotoxicity (ADCC), phagocytosis, regulation of antibody production, and activation of inflammatory cells. FcγR phenotypic variability modulates these processes through altering receptor IgG subclass binding affinity (FcγRIIa-H131R and FcγRIIIa-F158V), subcellular localization (FcγRIIb-I232T), post-translational modification (FcγRIIIb-HNA1a/b/c), expression of an otherwise pseudogene (FcγRIIc), and receptor surface density (gene copy number variability and promoter haplotypes). Accumulating data suggest that FcγR-mediated effector functions play a significant role in HIV-1 protective immunity, which is substantiated by the association of FcγR phenotypic variants with HIV-1 disease outcome. This study set out to characterize FcγR functional variability in the South African population, and to investigate the potential role thereof in HIV-1 transmission and disease progression in South African Black individuals. Since the only known determinant of FcγRIIIa surface density – FCGR3A gene copy number – is rare, this study investigated novel genetic determinants of FcγRIIIa expression by flow cytometry and nucleotide sequencing. FcγRIIIa expression on peripheral blood mononuclear cells was characterized for 32 South African Caucasian individuals and 22 South African Black individuals (Chapter 3). Significant differences in the proportion of FcγRIIIa-positive monocytes and FcγRIIIa expression levels on natural killer (NK) cells were observed between the population groups. A novel four-variant FCGR3A intragenic haplotype that associated with increased surface expression of FcγRIIIa on NK cells was detectable in Caucasian individuals, but not Black individuals and may account for the observed population differences. Further exploration of genetic diversity at the low affinity FCGR gene locus was extended to include all currently known functional variants of FcγRIIa, FcγRIIb, FcγRIIc, FcγRIIIa, and FcγRIIIb using a commercial multiplex ligation-dependent probe amplification assay (Chapter 4). Thirty-two South African Caucasian individuals and 131 South African Black

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering Degree awarded with distinction on 8 December I998 Johannesburg, 1998 / This report discusses high phase order (HPO) technology, i.e. the use of more than the conventional 3 phases for transmission of electric power, its use in the compaction of lines, and power density maximization over existing servitudes. It is structured in four parts. The first part introduces the concepts, establishes the need, and lists the advantages ofHPO. The second part deals with the technology itself and shows that it is possible to analyze HPO systems using symmetrical component analysis, lists common transformer configurations, covers protection, and so on. The third part analyses 5 case studies, the first 3 being analytical, and the last 2 being the first experimental test line, and the world's :first utility application ofHPO lines. The fmal section is a South African case study and compares an HPO line to an existing 400 kV 3-phase line and shows that the former is 87.5% more expensive to implement than the latter. Comparing the 3-phase and 6-phase lines on a more even basis, yielded a breakeven distance of225.86 km, above which the 6-phase option becomes more economical. These results are then explained and discussed in the conclusions section.