Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Data volumes produced by the next generation of earth observation sensors have increased greatly in recent years. Sensors are generating more data than can be easily stored onboard satellites and transmitted to the ground-stations. There are two strategies for solving this problem. The first is to process all images onboard the satellite, and only extract the useful or valuable information. The second is to use a compression algorithm to reduce the data volume. This thesis looks at both strategies and then focusses on an evaluation of the Embedded Zerotree Wavelet (EZW) algorithm, a wavelet-based lossy image compression algorithm, as a solution to reduce the data volumes. Possible hardware implementation strategies for this algorithm are also explored. Finally, a suggested implementation of the EZW algorithm is compared with the FlexWave-II system and with JPEG2000. / AFRIKAANSE OPSOMMING: Die data volumes wat deur die nuwe generasie van aardobservasiesensore geproduseer word, het dramaties vergroot in die laaste paar jaar. Daar word nou meer data geproduseer as wat aanboord van die satelliet gestoor kan word en meer as wat in die beperkte kommunikasietyd aan die grondstasie gestuur kan word. Daar is twee strategiee om hierdie probleem aan te spreek. Eerstens kan beelde aanboord die satelliet verwerk word om die belangrikste of waardevolste inligting uit te haal en die res van die data word dan geskrap. Die alternatief is om 'n beeldkompressie-algoritme te gebruik om die data te verminder. Hierdie tesis ondersoek hierdie strategieë en fokus dan op 'n evaluasie van die "Embedded Zerotree Wavelet" -algoritme. Die EZW-algoritme is 'n verlieserige, golfie-gebaseerde beeldkompressie-algoritme. Moontlike hardeware-implementeringsopsies word ondersoek en die resultate van een voorgestelde opsie word vergelyk met die FlexWave-II stelsel asook die nuwe JPEG2000-standaard.

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: We investigate object detection against cluttered backgrounds, based on the MINACE (Minimum Noise and Correlation Energy) filter. Application of the filter is followed by a suitable segmentation algorithm, and the standard techniques of global and local thresholding are compared to watershed-based segmentation. The aim of this approach is to provide a custom region-based object detection algorithm with a concise set of regions of interest. Two industrial case studies are examined: diamond detection in X-ray images, and the reading of a dynamic, and ink stamped, 2D barcode on packaging clutter. We demonstrate the robustness of our approach on these two diverse applications, and develop a complete algorithmic prototype for an automatic stamped code reader. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die herkenning van voorwerpe teen onduidelike agtergronde. Ons benadering maak staat op die MINACE (" Minimum Noise and Correlation Energy") korrelasiefilter. Die filter word aangewend saam met 'n gepaste segmenteringsalgoritme, en die standaard tegnieke van globale en lokale drumpelingsalgoritmes word vergelyk met 'n waterskeidingsgebaseerde segmenteringsalgoritme. Die doel van hierdie deteksiebenadering is om 'n klein stel moontlike voorwerpe te kan verskaf aan enige klassifikasie-algoritme wat fokus op die voorwerpe self. Twee industriële toepassings word ondersoek: die opsporing van diamante in X-straal beelde, en die lees van 'n dinamiese, inkgedrukte, 2D balkieskode op verpakkingsmateriaal. Ons demonstreer die robuustheid van ons benadering met hierdie twee uiteenlopende voorbeelde, en ontwikkel 'n volledige algoritmiese prototipe vir 'n outomatiese stempelkode leser.

Thesis (MScEng)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: This study investigates the theory of precision satellite orbit propagation and satellite lifetime prediction and lead to the development of two necessary software tools for analysis in these fields. Precision propagation was achieved through the implementation of Cowell's method of special perturbations, considering perturbations due to a 70x70 asymmetrical gravity field, atmospheric drag, Luni-Solar attraction and Solar radiation pressure. The satellite's perturbed equations of motion were integrated utilizing a seveneighth order Runge-Kutta-Fehlberg numerical integration procedure, limiting error propagation by employing adaptive step size control. The MSlS-90 atmospheric density model, providing for diurnal and semi-annual variations, was employed to determine atmospheric density. Care was taken in the precision modelling of the motion of the 12000 equator and equinox. Propagation results for this test case proved to be superior to the SGP4 propagator and a commercial package. The long-term effects of Earth oblateness and atmospheric drag on a satellite's orbital elements were investigated and applied to the orbit decay prediction problem. Orbit decay was predicted by integrating the rates of change of the orbital elements due to Earth oblateness and atmospheric drag. A semi-analytical technique involving Runge-Kutta and Gauss-Legendre quadrature was employed in the solution process. Relevant software was developed to implement the decay theory. Optimum drag coefficients, estimated from drag analysis using precision propagation, were used in decay prediction. Two test cases of observed decayed satellites were used to evaluate the theory. Results for both test cases indicated that the theory fitted observational data well within acceptable limits. / AFRIKAANSE OPSOMMING: 'n Ondersoek is gedoen oor die teorie van presiesie satelliet-wentelbaan vooruitskatting en satelliet-wentelbaanleeftyd afskatting en het gelei tot die ontwikkeling van twee analiseprogramme vir gebruik in hierdie vakgebiede. Presiesie vooruitskatting is bereik deur die gebruik van Cowell se metode van spesiale perturbasies, wat die invloed van 'n nie-simmetriese 70x070 gravitasieveld, atmosferiese sleur, Son-Maan aantrekkingskragte en druk van sonradiasie, in ag neem. Die satelliet se versteurde bewegingsvergelykings is numeries ge-ïntegreer deur gebruik te maak van die sewe-agste orde Runge-Kutta- Fehlberg metode wat fout-voortplanting inhibeer deur gebruik te maak van 'n aanpasbare integrasiestaplengte. Die MSIS-90 atmosferies model, wat voorsiening maak vir dag-nag en half-jaarlikse atmosferiese variasies, is gebruik vir die berekening van atmosferiese digtheid. Sorg is gedra by die presiesie modellering van die beweging van die J2000 ekwator en ekwinokse. Resultate vir hierdie toetsgeval toon meer voortreflik te wees as die SPG4 - en 'n kommersieël-beskikbare vooruitskatter. Die langtermyn effekte van aard-afplatting en atmosferiese sleur op wentelbaanleeftyd is ondersoek en toegepas op die wentelbaanverval-afskattingsprobleem. Wentelbaanverval is bereken deur die integrasie van die tydsafgeleides van die wentelbaanelement onder invloed van aard-afplatting en atmosferiese sleur. Vir die doel is 'n semi-analitiese tegniek, wat gebruik maak van Gauss-Legendre kwadratuur en Runge-Kutta numeriese integrasie, gebruik gemaak. Nodige rekenaar programmatuur is ontwi kkeI om die vervalteorie te implimenteer. Optimale sleur-koëffisiënte is afgeskat deur van presiesie wentelbaananalise gebruik te maak. Twee gevallestudies van bekende vervalde satelliete is gebruik om die vervalteorie te evalueer. Resultate vir beide gevallestudies toon aan dat eksperimentele resultate werklike vervaltye binne aanvaarbare limiete navolg.

The trimeric protein known as porin, found in the outer membrane of Escherichia coli, forms ion channels which have been reported to be voltage-gated. The aim of this investigation is to increase the understanding of the function of such channels, particularly with respect to voltage-gating. To achieve this, porin was first extracted from whole cells of E. coli and then it was incorporated into lipid bilayers, made using the Montal-Mueller method, for subsequent investigation. The extraction of porin from E. coli exploited both its tight association with peptidoglycan and its high level of detergent resistance. Porin was extracted from two strains of E. coli, 0111 :B4 and K12 (a rough mutant), with the resulting samples being rich in OmpF and Ompe porins respectively. Measurement of ion flow through the porin channels was made with different transmembrane voltages and with a variety of salts and salt concentrations. Such measurements enabled the selectivity of the channels to specific ions to be determined and estimates of pore diameter to be made. Instantaneous IN characteristics were asymmetrical and non-linear for both porins and were influenced by the salt concentration, pH of the electrolyte and the number of channels in the bilayer. Based on electrostatic models of gramicidin-like channels, coupled with the available structural information on porin, it was concluded that the porinlLPS complex inserts unidirectionally into the bilayer and has a net negative charge at the LPS end. The influence of the number of channels in the bilayer on the IN characteristic, most marked for the 0111 :B4 porin, was interpreted as being due to 'clusters' of channels in close association an idea supported by the results of voltage-gating experiments. Voltage-gating in single channels was shown to occur in three well defined steps, consistent with the known trimeric structure of porin. Multi-channel membranes showed several different types of current relaxation in response to a sustained voltage application. The most common type was composed of two exponential decays, suggesting the presence of two populations of closing channels. The results from voltage-gating experiments were compared with the theoretical behaviour of a simple two-state channel. This model was also extended to include entropy changes and it was concluded that porin followed the general behaviour predicted by a simple twostate model.

This thesis records the theoretical analysis and hardware development of a laboratory microwave imaging system which uses holographic principles. The application of an aperture synthesis technique and the electronic commutation of all antennae has resulted in a compact and economic assembly - which requires no moving parts and which, consequently, has a high field mapping speed potential. The relationship of this microwave holographic system to other established techniques is examined theoretically and the performance of the imaging system is demonstrated using conventional optically- and numerically-based reconstruction of the measured holograms. The high mapping speed potential of this system has allowed the exploitation of an imaging mode not usually associated with microwave holography. In particular, a certain antenna array specification leads to a versatile imaging system which corresponds closely in the laboratory scale to the widely used synthetic aperture radar principle. It is envisaged that the microwave holographic implementation of this latter principle be used as laboratory instrumentation in the elucidation of the interaction of hydrodynamic and electromagnetic waves. Some simple demonstrations of this application have been presented, and the concluding chapter also describes a suitable hardware specification. This thesis has also emphasised the hardware details of the imaging system since the development of the microwave and other electronic components represented a substantial part of this research and because the potential applications of the imaging principle have been found to be intimately linked to the tolerances of the various microwave components. Bibliography: pages 122-132.

The efficient use of industrial control computers is recognized as an organizational problem akin to the traffic-switching problem in communications. A systematic approach to this problem is proposed, based on theory developed for the handling of telephone traffic. The application of the approach indicates that it is necessary to re-evaluate traditional hardware/software relationships. A change in these relationships is desirable, since multi-programmed computers spend too much time in handling their own organization. This situation is compounded in time-critical industrial process-control applications. It is proposed that the solution lies in the use of a flexible hardware operating system, working in close relationship with a conventional minicomputer. The unit proposed to implement this function, termed a microcontroller, makes use of the new bipolar microprocessor elements and provides a high-speed, flexible control unit, adaptable to user requirements. To retain a high degree of flexibility the microcontroller is microprogrammable. In essence, the unit executes the principal functions of a real-time operating system, acts as a pre-processor for all incoming requests, and ensures a high rate of task-switching. This system is applied to a series of configurations, each selected to demonstrate, quantitatively, the value of the technique in real applications. Comparisons are made between real-time control configurations based on the software-implemented approach and the identical configurations based on this system. The proposed strategy is shown to result in a better and more economical industrial controller. The wider implication for any aspect of organization is that "bigger" is not necessarily "better". Successful management implies effective use of facilities, rather than a proliferating structure.

<div>Thermoelectric (TE) devices are useful in niche applications that require reliability and durability, including energy harvesters for sensors, cooling electronics, and power generation at high temperatures. Assessing, optimizing, and implementing materials into practical TE devices and systems have been difficult theoretical and engineering problems. The goal of this research is to develop a first-principles informed approach to analyze thermoelectric materials for potential practical applications.</div><div>TE materials and devices are traditionally quantified using a material figure of merit (FOM), zT, and device FOM, ZT. Using full numerical descriptions of band structures and solutions to the Boltzmann transport equation (BTE) in the relaxation time approximation (RTA), we examine how band convergence may or may not increase zT depending on the relative strength of intra- and inter-band scattering. We compute zT vs. a generalized TE quality factor (b-factor) and examine a dozen complex TE materials showing none exceeds the performance of a simple, parabolic energy band. In fact, a plot of zT vs. b-factor appears to be universal. We test this conclusion based on RTA solutions to the BTE using a simple treatment of scattering against more rigorous first-principles approaches. </div><div>In addition, we theoretically assess a low-cost TE oxide (2H-CuAlO₂), which has durability at high temperatures and is earth abundant, making it attractive for applications. Finally, with an eye towards minimizing the $cost/kW-hr of thermoelectric energy generation, we discuss our approach to a few specific high temperature environments and discuss their viability as practical system level applications.</div>

<div>Agricultural machinery is critical in modern farming. With continuous technological advancements in farm machinery, farm machines have evolved from simple mechanical machines to cyberphysical systems that contain rich sources of multimodal sensor data. Effective acquisition and analyses of these data have become essential but challenging tasks in revealing machine-centric and logistical insights to researchers and farmers.</div><div><br></div><div>In this dissertation, theses challenge are addressed in two parts. The first part demonstrates successful development and deployment of two open-source telematic devices for collecting machine network, geospatial, and video data. The first, ISOBlue 2.0, was designed to be a logger of both GPS and CAN data with wireless data streaming capabilities. The second, ISOBlue HD, an extension of ISOBlue 2.0, was configured to behave as a network server that interfaced with external cameras for automatic video recording of machine operation contexts. These devices were deployed in a variety of machines in different farming activities. A total of over 1 TB of multimodal machinery data were collected.<br></div><div><br></div><div>The second part presents three problems that focus on analyzing primarily GPS track data collected from past wheat harvests. The first poses an activity classification problem. It involved clustering a 3D feature set generated from both GPS and CAN data from a combine using the Density-Based Spatial Clustering of Applications with Noise algorithm. The<br>resultant clusters between on-road and in-field data samples as well as normal and anomalous activities. The second problem concentrates on combine unloading event detections using GPS tracks of multiple combines in 16 harvest sessions. The identified events from a novel algorithm that couples Interacting Multiple Models filtering and composite rules were utilized to estimate the total yield for each session. The estimated yields had an overall accuracy of over 90% when comparing to the actual weight ticket records. Lastly, two instantaneous metrics, instantaneous area capacity and swath utilization, were proposed and estimated using GPS tracks of multiple combines in 7 different fields during various harvest years. A novel algorithm was created for estimating instantaneous actual harvested area and swath utilization. This enabled exact computations of instantaneous metrics as oppose to conventional rough estimates of area capacity. Harvest performances were evaluated both temporally and geospatially by machines and years. It was discovered that three contributing factors that lead to high area capacity were wide header attachments, high harvesting speed, and uniform harvesting patterns. Moreover, it was found that the benefit of a wider header might diminish if the harvesting speed was low.<br></div>

Thesis (PhD)--University of Stellenbosch, 2004. / 242 Leaves printed single pages, preliminary pages i-viii and numberd pages. Includes bibliography. Tables and figures. / ENGLISH ABSTRACT:The aim of the proposed study was to develop an electrical utility organisational performance measure indicator that measures electrical network utilisation (U) for the actual maximum demand and total energy transferred. The scope of the study extended itself to include reliability and exogenous considerations. The scope of the research study included three primary variables with secondary variables as the performance measures. The available data was screened and filtered from outliers, and thereafter, multivariate analysis was applied in deriving the overall linear equation for each of the above primary variables. The statistical process included the application of principal component analysis and factor analysis, a comparison between the two, and the derivation of linear equations. The study produced linear equations relating to the former. The primary variables were presented in the form of a 3-Dimensional scatter plot. Each variable was inspected for linearity and clustering to validate the results and include any previously excluded outliers that complied with linear functionality. A practical application of the research findings was included. This included the extremes of linearity and clustering. The research concludes with further research opportunities in this study direction. / AFRIKAANSE OPSOMMING:Die doel van hierdie ondersoek was om 'n maatstaf te ontwikkel wat elektrisiteitsverskaffers in staat stel om die effektiwiteit en benutting van die elektriese transmissienetwerk te meet. Dit sluit die maksimum aanvraag en totale hoeveelheid energie wat deur die transmissienetwerk oorgedra word in. Die omvang van die studie is uitgebrei om ook eksterne faktore en betroubaarheidsoorwegings in te sluit. Die beskikbare inligting is gekeur en gefilter om uitskieters uit te skakel en daarna is multivariate analise gebruik om 'n lineêre vergelyking vir elk van die primêre veranderlikes te ontwikkel. Die statistiese analise het onder andere van hoofkomponente analise en faktor analise gebruik gemaak. 'n Vergelyking tussen die twee metodes is gemaak en liniêre vergelykings is afgelei. Die primere veranderlikes was gesamelik getoon in n’ 3-dimensionele grafik. Die lineariteit en groepering van elke veranderlike is egter ondersoek om die resultate te staaf en enige uitskieters wat voorheen uitgesluit is maar wel aan die lineêre verband voldoen het in te sluit. 'n Praktiese toepassing van die bevindings was uitgevoer en het die uiterstes van lineariteit en groepering ingesluit. Die ondersoek word afgesluit met 'n bespreking van moontlike verdere navorsingsgeleenthede.

Thesis (MScIng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / A bi-directional, direct conversion switch-mode converter is proposed for use in distributed household renewable energy systems. The converter is intended as the central interface between the household energy system’s low voltage Direct Current bus and the high voltage Alternating Current bus. The low voltage DC bus is connected to renewable generation and storage devices, while the high voltage AC bus is connected to the user’s equipment and the mains grid. The converter overcomes the inherent reverse-duty cycle problem associated with bi-directional converters by using a combination step-up / step-down half-bridge converter on the high voltage side of a high frequency transformer. The low voltage side of the transformer is driven by a full bridge inverter that acts as a rectifier during reverse mode. In order to control the flow of power in both directions the converter implements Average Current Mode Control. A method is developed to determine the transfer functions of common switch-mode converters by inspection alone. This method is applied to the proposed converter, and both current and voltage mode control loops are designed with the frequency response method. The control system is implemented using a Digital Signal Processor. A method of simultaneously simulating both the converter hardware and software is developed using VHDL. This method greatly reduced the development effort of the converter. The operation of the proposed converter is verified through this method of simulation. A prototype converter is constructed and successfully tested, thereby proving the viability of the proposed converter topology and control methodology.