Includes bibliographical references. / This thesis reports the research done into a relatively unknown modulation scheme called VPSK (Variable Phase Shift Keying) and the use of DSSS (Direct Sequence Spread Spectrum) techniques to achieve carrier synchronization and hence coherent demodulation in the receiver. VPSK is a new and relatively unknown modulation scheme in which data bits are encoded using patented algorithms designed by Millerand Walker. VPSK modulation is a SSBSC (Single Sideband Suppressed Carrier) modulation scheme with good bandwidth efficiency. Data is coherently demodulated in the receiver. In existing VPSK systems, the locally generated carrier in the receiver is synchronized to an integer multiple of the symbol clock frequency to allow coherent demodulation. This coherent method of demodulation is not optimum if the channel over which information must be transmitted is a non-Gaussian channel, or has multi-path characteristics.

Power sector reforms around the world have been driven by various factors ranging from economic and financial to technological reasons. The reforms in the power sector are frequently undertaken under conditionality agreements linked to broader macro economic reforms. The main objective of this thesis is to find out whether power sector reforms advance social benefits to the poor, specifically increase their affordable access and use of electricity in Zambia. The rationale behind power sector reforms in Zambia include the increase of access to electricity by the majority of the Zambian population through expansion of the national electricity network to cover areas that have production potential. The promotion of private sector participation in the electricity industry by ensuring that market rules are attractive to private investors is another objective of reforms. The reforms also aim to improve efficiency in the electricity industry. To achieve the rationale of power sector reforms, the government's focus is on macro electrification projects. These electrification projects exclude poor household electrification owing to its unprofitable nature. Furthermore, the expected economic benefits arising from the macro electrification projects could result in further marginalization of poor household electrification. In short, the proposed approach to restructure the electricity industry in Zambia does not contain specific initiatives for increasing affordable access to electricity by the poor households. This thesis draws out the point that without considerable attention to affordable access to electricity by the poor at the inception of the reforms, addressing them at a later stage could difficult. To be effective, social concerns need to be included into the reform design early and backed by strong political commitment.

Includes bibliographical references. / Since the emergence of the digital computer in the 1940s, computer architecture has been largely dictated by the requirements of mathematicians and scientists. Trends have thus been towards processing data as quickly and as accurately as possible. Even now, in the age of large scale integration culminating in the microprocessor, internal structures remain committed to these ideals. This is not surprising since the main users of computers are involved with data processing and scientific computing. The process control engineer, who turned to the digital computer to provide the support he required in his ever increasing strive towards automation, has had therefore to use these generalized computing structures. His basic requirements however, are somewhat different to those of the data processing manager or the scientific user. He has to contend with an inherent problem of synchronizing the computer to the real-world timing of his plants. He is far more interested in the response time of the computer to an external occurrence than he is to sheer 'number-crunching' power. Despite the trends in process control towards distributed computing, even the most advanced systems require a relatively large central processor. This processor is called upon to carry out a wide variety of different tasks most of which are 'requested' by external events. Multiprogramming facilities are therefore essential and are normally effected by means of a real-time operating system. One of the prime objectives of such a real time operating system is to permit the various programs to be run at the required time on some priority basis. In many cases these routines can be large - thus requiring access to backing storage. Traditionally the backing store, implemented by a moving-head disc for example is under the control of the real-time operating system. This can have serious consequences. If real-time requirements are to be met, transfer to and from the disc must be made as rapidly as possible. Also, in initiating and controlling such transfer, the computer is using time which otherwise could be avai1ab1e for useful, process-orientated work. With the rapid advancement of digital technology, the time is c1ear1y right to examine our present computer architecture. This dissertation explores the problem area previously discussed - the control over the bulk storage device in a real-time process-control computer system. It is proposed that a possible solution lies in the development of an intelligent backing-store controller. This essentially combines the conventional low-level backing store interface with a special purpose processor which handles all file routines. This dissertation demonstrates how such a structure can be implemented using current technology, and will evaluate its inherent advantages.

Bibliography: pages 104-118. / The need for accurate, synoptic, up to date information, concerning the quality of South African impoundments, prompted a study into the relationship between Landsat reflectance data and chlorophyll ~ and turbidity in Roodeplaat Dam. Surface and integrated chlorophyll a as well as surface and integrated turbidity were collected simultaneously with the satellite's overpass, from 32 sampling sites on the impoundment. Six days, between 81.10 .14 and 82 .11.16, were cloud free and the data were analysed in order to establish the relationship between the specific water quality conditions and the satellite reflectance data. Prior to the analysis certain factors required attention. Firstly, it was important to accurately align the sampling sites with their corresponding Landsat pixels. Secondly, the satellite reflectance data were corrected for influences of haze and the angle of the sun. Thirdly, the requirement that the water quality surface reference data be representative of the range of conditions in the impoundment was recognised. Lastly, the interrelationship between chlorophyll a and turbidity and the multicollinearity evident between the four reflectance bands, demanded that a multi-variate statistical technique be implemented, in order to adequately analyse the available data.

Bibliography: p. 108. / This dissertation comprises an investigation into the rate at which reinforced concrete structures deteriorate in the Cape Peninsula due to reinforcement corrosion, the reasons for this deterioration, and the accompanying repair costs. The costing of repair work is calculated per m2 of reinforced concrete and is based on quoted labour rates and material rates of repair materials supplied by four major suppliers in the Western Cape. Formulas are included which enable a person using the data listed in tables and figures to calculate what repair costs will be in future, and also enable the calculation of monthly/annual deposit amounts in order to save sufficient money for future maintenance at a specified date. Life cycle costing and decision models for the maintenance of concrete structures are discussed and guidelines for the establishment of optimal maintenance cycles are included. Based on the results of the life cycle costing exercise the importance of planned preventative maintenance is highlighted. Finally, locally and internationally available maintenance management computer systems are reviewed.

There is a continuous need to locate more targets for coal exploration and evaluation of geological structures in the north-west coalfields in Zimbabwe. Conventional methods of analysing geological structures and field mapping are being hindered by inaccessibility of some areas and thick covers of Recent sediments. Remote sensing has been found to be a valuable method of identifying lithologic units and geological structures in the· area. Integration of the remotely sensed data in a 2D GIS resulted in recognition of spatial relationships between lithologic units, geological structures , coal seams and vegetation patterns. The Hwange area constitutes the western part of the Mid-Zambezi Karoo basin. The area consist of a wide spectrum of rocks ranging from Precambrian gneisses, Proterozoic schists and granulites, Karoo sediments to Tertiary and Recent sands. The area has been affected by a number of faults and shears some of which post date the Karoo sediments. These faults are an expression of the major tectonic events associated with this area. Some of the faults have been attributed to the effects of the Zambezi Rift System. Fault zones in the area, such as the Deka, Entuba and Inyantue Zones have been recognised as part of this system and these divide the Lower Karoo rocks into different coalfields. To try and evaluate the outcrop patterns and geological structures in the Hwange area, all the available geological and structural data were captured in a spatial database. The diversity of data incorporated in the spatial database demanded the need for a structured database design approach. The Entity-Relationship model was used to conceptualise the geological data of the ' Hwange area This model was transformed into the Relational Model that formed the implementation model of the database. Landsat 5 TM data covering the area from the Zimbabwean winter (20 June 1984) path 172, row 73 were also analysed for the information required to locate Karoo rift faults and the distribution of lithologic units associated with coal. The use of directional filters in the E-W and NE-SW directions and vegetation reflection characteristics during the dry season (June 1984) proved very effective in mapping fractures in the Karoo rocks. Landsat TM image enhancement techniques such as principal components analysis, edge enhancement, decorrelation stretching, band ratios; and colour composites made following these techniques, allowed mapping of different lithological units and discrimination between Karoo rocks and the crystalline basement rocks. Lineament analysis defined E-W, ENE-WSW, NE-SW and NW-SE conjugate sets of lineaments. The first three sets are related to the regional fracture zones of the Zambezi rift system The Entuba fault zone was found to be associated with most of the fractures affecting the Hwange coalfields. These have a dominant NE-SW and ENE-WSW trend in the Western Areas, Wankie Concession, Chaba, Entuba and Sinamatella coalfields. The E-W trending fracture set is dominated by joint sets in the Karoo basalt covering the north-west portion of the Hwange Coalfields. These show no relationship with the linear features of the Zambezi Rift system The NW-SE trending lineaments are dominantly developed on tilted bedding planes in the Karoo rocks as well as a few sparse joints in the Karoo basalt. Overlaying enhanced Landsat TM images on mapped faults and lithology data in a GIS revealed a number of features along the Entuba zone which were not previously known. The south-western part of the Entuba inlier was shown to consist of a synformal fold plunging to the south and bound on both sides by strike slip faults. Several kinematic indicators such as displacement of sedimentary strata have shown that the Entuba fault displays right lateral strike-slip coupled with dipslip movement. Proximity analysis using borehole data (depth to top and bottom of a coal seam) showed that most of the lineaments in the area are normal faults which have caused considerable displacements of the main coal seam Comparison of seam depth across most of these faults within coalfields and from one field to another shows that local and regional variations in depths of the main seam is primarily a function of vertical displacements along the faults over and above variations in the morphology of the pre-Karoo floor. The Entuba field was found to have greatest vertical variations over very short distances across faults, with depths varying from 60m to 520m from west to east over distances of less than 500m This part of the field has been partly affected by extensive normal faults, some of which can be traced for more than 10km. In the Hwange area, the Karoo rocks have been down faulted into a rift margin which is in turn divided into smaller fault blocks by intra-rift faulting. The shape of the fault blocks are further controlled by the orientation of the post-Karoo faults which have also down faulted the main coal seam Exploration activity in the area should also seek to establish the locations of these faults to help further decipher variations in depths of coal seams.

Includes bibliographical references. / The thermal conductivity of titanium aluminide and several ruthenium-aluminium alloys has been studied from room temperature up to 500°C. Ruthenium aluminide is a B2-type intermetallic which is unusual and of special interest because of its toughness, specific strength and stiffness, oxidation resistance and low cost. The possible use of ruthenium aluminide in high temperature industrial applications required an investigation of the thermal properties of this compound. Apparatus, capable of measuring thermal conductivity at elevated temperatures has been designed and constructed. This study represents the first experimental results for the thermal conductivity of ruthenium aluminide alloys. The electrical resistivity of the intermetallic compounds has been measured using apparatus based on the Van der Pauw method. The Weidman-Franz ratio of the ruthenium aluminide alloys has been calculated and this indicates that the primary source of heat conduction in these alloys is by electronic movement and that the lattice contribution is minor. The electrical and thermal properties of ruthenium aluminide are shown to be similar to that of platinum and nickel aluminide. This has important implications for the use of these alloys in high temperature applications.

Includes bibliographical references. / The stress corrosion cracking susceptibility of an experimental high nitrogen Cr-Mn stainless steel, known as Cromanite ™, and conventional AISI 304 stainless steel were investigated in order to compare their stress corrosion performance in solutions where AISI 304 stainless steel is known to be susceptible. Slow strain rate tests (SSRT) were performed on solution treated specimens a t30°C in aerated aqueous sodium chloride (NaCI) solution containing hydrochloric acid (HCI) of varying concentration at open circuit potentials. Static tests in the form of bent-beam tests were performed on both solution treated and aged specimens in 3M NaCI solution containing 0.05 M HCI. Potentiodynamic scans and Tafel plots were used to assess corrosion behaviour and corrosion rate respectively, while the electrochemical potentiokinetic reactivation (EPR) method was used to quantify the degree of sensitisation for the materials. The SSRT revealed poor corrosion behaviour of Cromanite TM in the presence of hydrochloric acid. Whilst AISI 304 could be examined for stress corrosion cracking at HCI concentrations up to 0.5 M HCI, Cromanite ™ exhibited corrosion rates which were too fast to permit assessment of stress corrosion susceptibility at HCI concentrations of 0.15 M or above. SCC started in a salt solution containing 0.05M HCI for AISI 304 while Cromanite TM cracked in both salt solution (3M NaCI) and in 0.05 M HCI +3M NaCI. The bent-beam test performed on solution treated specimens revealed no evidence of cracking for both alloys after 100 days of exposure; however, Cromanite ™ suffered substantial mass loss after this period. While aged Cromanite TM suffered intergranular cracking after only 25 days in the test solution, no cracking was observed for the aged AISI 304 after 75 days.

In the past, network clock synchronization has been sufficient for the needs of traditional distributed systems, for such purposes as maintaining Network File Systems, enabling Internet mail services and supporting other applications that require a degree of clock synchronization. Increasingly real time systems arc requiring high degrees of time synchronization. Where this is required, the common approach up until now has been to distribute the clock to each processor by means of hardware (e.g. GPS and cesium clocks) or to distribute time by means of an additional dedicated timing network. Whilst this has proved successful for real time systems, the use of present day high speed networks with definable quality of service from the protocol layers has lead to the possibility of using the existing data network to distribute the time. This thesis demonstrates that by using system integration and implementation of commercial off the shelf (COTS) products it is possible to distribute and coordinate the time of the computer time clocks to microsecond range. Thus providing close enough synchronization to support real time systems whilst avoiding the additional time, infrastructure and money needed to build and maintain a specialized timing network.

The electrical properties of platinum, gold-palladium and a selection of alloys from the ruthenium-aluminium system have been studied at high temperatures (up to 1000°C). The majority of the ruthenium-aluminium alloy compositions studied lie near or in the ruthenium aluminide phase field. Ruthenium aluminide is a B2 structure intermetallic which is suited to high temperature applications because in addition to a high melting point (2060°C), oxidation resistance to 1200°C and high temperature strength, it is also relatively ductile at room temperature. The possibility of high temperature electrical applications required an investigation of the electrical properties of ruthenium-aluminium alloys as compared to platinum and gold-palladium. Two sets of apparatus, capable of measuring the resistivity and thermo-e.m.f to high temperatures, were constructed and used to obtain the first experimental results for the electrical properties of ruthenium-aluminium alloys. Chemical analysis of these alloys has been performed for the first time, and together with energy dispersive spectroscopy, has revealed a composition at which there is a resistivity minimum and a positive thermo-e.m.f maximum, which appears to be associated with the formation of the ordered ruthenium aluminide phase. The resistivity and the temperature dependence of resistivity of some ruthenium-aluminium alloys are similar to that of platinum, the least resistive of the three materials investigated.