The requirements for future DVB-T/H networks demand that broadcasters design and deploy networks that provide ubiquitous reception in challenging indoors and other obstructed situations. It is essential that such networks are designed cost-effectively and with minimized environmental impact. The use of transmit diversity techniques with multiple antennas have long been proposed to improve the performance and capacity of wireless systems. Transmit diversity exploits the scattering effect inherent in the channel by means of transmitting multiple signals in a controlled manner from spatially separated antennas, allowing independently faded signals to arrive at the receiver and improves the chances of decoding a signal of acceptable quality. Transmit diversity can complement receive diversity by adding an additional diversity gain and in situations where receiver diversity is not practical, transmit diversity alone delivers a comparable amount of diversity gain. Transmit Delay Diversity (DD) can be applied to systems employing the DVB standard without receiver equipment modifications. Although transmit DD can provide a gain in NLOS situations, it can introduce degradation in LOS situation. The aim of this thesis is to investigate the effectiveness in real-word applications of novel diversity techniques for broadcast transmitter networks. Tests involved laboratory experiments using a wireless MIMO channel emulator and the deployment of a field measurement campaign dedicated to driving, indoor and rooftop reception. The relationship between the diversity gain, the propagation environment and several parameters such as the transmit antenna separation, the receiver speed and the Forward Error Correction Codes (FEC) configuration are investigated. Results includes the effect of real-word parameter usually not modeled in the software simulation analysis, such as antenna radiation patterns and mutual coupling, scattering vegetation impact, non-Gaussian noise sources and receiver implementation. Moreover, a practical analysis of the effectiveness of experimental techniques to mitigate the loss due to transmit DD loss in rooftop reception is presented. The results of this thesis confirmed, completed and extended the existing predictions with real word measurement results.

Accuracy of the measurement data used for the decision making process or for shipboard operations and control is very important to ensure the reliability and survivability. The uncertainties present in measurement data need to be minimized for reliable system operation. In this work, a fuzzy logic based model is developed to deal with uncertainty in the meter data. Operational and historical parameters of the meters were used to determine a ‘trust’ value of individual meter. A fuzzy correction system for measurement data was used to generate an input dataset for a genetic algorithm based reconfiguration system. Additionally, with the goal of optimizing the performance of power system operator, the effects of Decision Support System (DSS) on the quality of decisions taken by the operator were examined. Unaided and aided interface prototypes were developed and usability tests were carried out on interface prototypes with users having knowledge of power systems.

Doctor of Philosophy / Department of Physics / Kristan L. Corwin / The focus of this research is improving the pulse output energy of a mid-IR pulsed acetylene-filled Hollow-core Optical Fiber Gas LASer (HOFGLAS) system. Pump pulses and acetylene molecules interact with each other inside hollow-core photonic crystal fiber that effectively confines light and allows for strong gain. This results in lasing at 3.11 μm and 3.17 μm lines based on population inversion of acetylene molecules, which are optically pumped at rotational-vibrational overtones near 1.5 μm using 1 ns pulse duration from an optical parametric amplifier (OPA). This acetylene laser operates with no cavity mirrors because of a high gain in a single pass configuration. There are few laser sources in the mid-IR region while there are many applications for having a laser source in this range such as remote sensing, hazardous chemical detection, and breath analysis. This adds to the importance of the acetylene-filled HOFGLAS system. Some of the applications like remote sensing require high power. So, we moved toward power scaling this laser system by optimizing the laser operation through maximizing the OPA alignment to improve its modal content using longer length of fiber to increase the interaction length and improving the beam quality of the mid-IR emissions. The highest pulse energy ever obtained in the 3 µm mid-IR region from the acetylene-filled HOFGLAS after applying the improvements is reported here (1.4 μJ). Higher mid-IR pulse energies can be achieved by improving the pulse energy achievable from the OPA pump source and working with longer pulse duration to decrease the bandwidth of the OPA. This operation demonstrates many novel properties of acetylene-filled pulsed mid-IR hollow-core fiber lasers. The excellent spatial beam quality at highest power and phenomenological scaling of saturation power and efficiency with pressure that we observe point to the promise of power scaling and motivate further development of numerical models of the laser for deeper insight into these effects. M² measurement method was used to examine spatial beam quality and it was found to be fiber-dependent. For the improved setup, M² was investigated at several input pump powers in addition to the reproducibility checks. M² of 1.14 at the maximum output power motivates for beam combining to scale to higher power. The independence of efficiency on pressure is an evidence for reaching higher mid-IR power at a pressure where saturation behavior does not exist. achieving the highest mid-IR power to date, 1.4 μJ, encourages for building higher power OPA to produce high power mid-IR emissions. Taken as a whole, this laser exhibits novel behavior that motivates both numerical/theoretical investigation and further efforts to scale to higher powers.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The compound sharp-crested weir, which consists of two or more notches at different elevations, is the most common type of flow gauging structure found in South Africa. The Department of Water Affairs and Forestry (DWAF) is responsible for the operation of these weirs. They are currently experiencing the following problems regarding flow measurement with compound sharp-crested weirs: 1. During free-flow conditions, also known as modular flows, there is uncertainty about the accuracy of the discharge formulas. Although reliable formulas exist for single notch weirs, it is not clear how they should be modified for compound weirs. Whilst methods have already been developed to deal with compound weirs their accuracy needs to be investigated further. 2. When the weirs become submerged during floods, the upstream water head is affected by downstream water levels and the original formulas are not applicable. It has so far been impossible to calculate discharge accurately under these so-called non-modular flow conditions. This report summarises the findings of an extensive study which addressed the issues mentioned above. A comprehensive test programme was completed during which variations of compound sharp-crested weirs were tested under both modular and non-modular flow conditions. In the development of new methods care was taken to adhere to internationally accepted standards. This should make South African practice acceptable to others. One important characteristic of compound weirs is the presence of end contractions. It was found that they have a significant effect on discharge measurement. Generally, the more a weir is contracted, the lower its coefficient of discharge becomes. It was also established that end contractions can ensure excellent aeration for compound weirs. For modular flow conditions it was possible to develop a discharge formula based on the IMFf equation, which is included in the ISO standards. This new method was found to produce the smallest errors when compared to other existing formulas (average error 0.6%). During non-modular flow conditions it was noted that end contractions also play an important role, at least during the early stages of submergence. In full-width weirs the upstream water level tends to drop first (due to de-aeration) before it rises again with increasing submergence. Weirs with end contractions do not suffer from this problem. It was further established that the effect of submergence could be described in terms of an energy loss occurring at the drowned weir. This energy loss is a function of the velocities at the so-called vena contracta of the weir and at the downstream river cross section. As the difference between these velocities increases, the energy loss increases as well. Two methods were tested to estimate the discharge under submerged conditions. The Villemonte formula works well if the energy losses at the weir are relatively high, while the Wessels method is reliable if the energy losses become smaller. A procedure was developed which indicates when each method is applicable. The test data indicated that the maximum error is up to ±10% at high submergence ratios (S> 0.80) if this procedure is followed. / AFRIKAANSE OPSOMMING: Multikeep-skerpkruinmeetstrukture bestaande uit twee of meer kepe op verskillende vlakke word meestal gebruik om vloeie in Suid-Afrikaanse riviere te meet. Die Departement van Waterwese en Bosbou (DWAF) is verantwoordelik vir die instandhouding van sulke meetstrukture. Hulle ervaar tans die volgende probleme met vloeimeting by multikeepskerpkruine: 1. Gedurende modulêre (onversuipte) toestande bestaan daar nog onsekerheid oor die akkuraatheid van die formules wat gebruik word om vloeitempo's te bereken. Alhoewel betroubare formules ontwikkel is vir enkelkepe, is dit nie duidelik hoe hulle aangepas kan word sodat hulle ook vir multikepe gebruik kan word nie. Die akkuraatheid van sommige bestaande metodes vir multikepe moet ook ondersoek word. 2. Onder versuipte toestande word die stroom-op watervlak beïnvloed deur die stroom-af watervlak en die formules vir vry-vloei toestande is nie geldig nie. Dit was tot nou toe nie moontlik om vloeitempo ' s akkuraat te bereken onder hierdie nie-modulêre toestande nie. Hierdie verslag bied 'n opsomming van die bevindinge van 'n navorsingsprojek wat bogenoemde probleme aangespreek het. 'n Toetsprogram is uitgevoer wat moontlike konfigurasies van multikepe ingesluit het. Die modelle van die meetstrukture is onder beide vry-vloei en versuipte toestande bestudeer. Gedurende die ontwikkeling van nuwe formules vir die berekening van vloeie is daarna gestreef om so veel as moontlik gebruik te maak van internasionale standaarde. Dit behoort Suid-Afrikaanse praktyke vir andere aanvaarbaar te maak. 'n Belangrike eienskap van multikepe is die voorkoms van end-kontraksies. Hulle het 'n groot invloed op vloeimeting en oor die algemeen het 'n keep met groot end-kontraksies 'n laer vloei koëffisient as 'n vol-wydte keep. End-kontraksies is ook baie effektief om skerpkruine te belug. Vir vry-vloei toestande is gevind dat 'n metode gebaseer op die IMFT vergelyking (ingesluit in ISO standaarde) baie goeie resultate lewer. In vergelyking met ander bestaande metodes gee dié metode die kleinste foute met 'n gemiddelde fout van 0.6%. Onder versuipte toestande speel end-kontraksies ook 'n belangrike rol, ten minste by beperkte versuiping. As vol-wydte kepe beskou word, kan gesien word dat die stroom-op watervlak eers daal voordat dit weer styg (weens ontlugting). Kepe met end-kontraksies ly nie aan hierdie probleem nie. Dit is verder bevestig dat versuipte toestande beskryf kan word in terme van 'n energie verlies wat by die versuipte meetstruktuur voorkom. Hierdie energie verlies is 'n funksie van die snelhede by die vena contraeta van die keep en by die stroom-af rivier snit. As die verskil tussen die twee snelhede groot is, is die energie velies ook groot. Twee bestaande metodes vir versuipte toestande is getoets. Villemonte se vergelyking werk goed as die energie verliese groot is, terwyl Wessels se metode beter werk as die verliese klein raak. 'n Prosedure is ontwikkel wat dit moontlik maak om die regte metode te kies vir 'n spesifieke toestand. Vanaf die toetsdata is bepaal dat die maksimum fout ±10% is by hoë grade van versuiping (S> 0.80) wanneer bogenoemde prosedure gevolg word.

ABSTRACT Detection of and discrimination between different nanoparticles and biomolecules are vital steps in analytical, biochemical, and diagnostic biomedical procedures used in life sciences. Synthetic micro/nanopores in solid-state membranes form an emerging class of single-molecule detectors capable of detecting and probing the properties of particles and biomolecules with high throughput and resolution: The particles or biomolecules to be analyzed are added to an electrolyte solution in one of the two reservoirs of the detector system separated by a thin membrane containing a single micro/nanopore. An outer electric field induces an open-pore ionic current (Iopen) through the pore, dragging the particles with itself. Transient changes occur when a particle slightly smaller than the pore translocates through the pore. This electrical signal can be analyzed to derive information regarding to the particle or biomolecule size and even its morphology, concentration in the solution, and the affinity for the pore. Many detectors are based on self-assembled, naturally occurring protein pores in lipid bilayer membranes. Most solid-state pore-based detectors reported in literature use artificial pores in silicon nitride or silicon oxide membranes. Applying polymers as a membrane potentially offers advantages over the aforementioned types, including good electrical insulation, improved wettability thanks to higher hydrophilicity, and long-term stable yet low-cost and disposable devices. The present study aims at exploiting such advantages by developing the proof-of-concept for a single-material, all-polymer, nanopore detector allowing the continuous variation of target pore size in the range from micrometers to a few nanometers for best pore size adaption to the biomolecules to be investigated. The research comprises materials selection, system design, development of a fabrication and assembly sequence, device fabrication, and functional device testing. Poly (methyl methacrylate) (PMMA) was selected as it combines advantageous microfluidic properties know from competing materials, such as polyimide, polystyrene, polycarbonate, or polyethylene terephthalate, with outstanding micropatterning capabilities. The membrane thickness is set to be 1 µm, based on a compromise between robustness during fabrication and operation on one side, and electrochemical performance on the other. After spincoating the membrane onto a sacrificial wafer, pores with diameters of typically several hundred nanometers are patterned by electron beam lithography. In combination with thermal post processing leading to polymer reflow, diameters one order of magnitude smaller can be achieved. The present study focuses on 450 nm and 22 nm pores, respectively. Besides these pores fabricated in a top-down approach, self-assembled -hemolysin protein pores of 1.5 nm diameter are integrated in a combined top-down and bottom-up approach so that single digit, double digit, and triple digit nanometer pores are available. Systems integration is achieved by capillary-forced based release from the sacrificial substrate and the application of UV-initiated glue. Test sequences proved and qualified the device functionality: Electrical characterization was performed in aqueous KCl electrolyte solution. The devices exhibit a stable, time-independent ionic current. The current-voltage curves are linear and scale with the electrolyte concentration. System verification was performed using silica nanospheres of 100 nm and 150 nm diameter as known test particles. Translocation through a 450 nm pore induced current blockades for about 1 ms with an amplitude of 30 pA to 55 pA for 100 nm particles and in excess of 70 pA for 150 nm particles. This is in close agreement with results obtained by a mathematical model used in this study. Biomolecules relevant to many life science applications, double-stranded DNA (dsDNA) and bovine serum albumin (BSA) were subsequently analyzed to prove the device concept. Post-processed pores of 22 nm diameter were used at 600 mV driving voltage and 0.1 molar electrolyte in a slightly acidic regime of pH = 6. Typical current blockade amplitudes for complete translocations of dsDNA are Iblock = 22 pA for a translocation time of tD = 0.2 ms, and an almost threefold current blockade (Iblock = 60 pA) for the larger BSA molecules, respectively. The results demonstrate that the PMMA-based nanopores are sensitive enough to not only detect translocating biomolecules, but to also sense them by distinguishing between different biomolecules. The molecule-specific and distinct translocation signals through the pores using both, standardized silica nanoparticles and biomolecules of different dimensions, prove the concept of an all-PMMA electrophoretic flow detector with adjustable pore diameters. Devices with pore diameters covering three orders of magnitude in the nanometer range were successfully built, tested, and characterized. The results suggest such detectors are promising candidates for biomolecule detecting applications.

This thesis considers the structural characteristics of online criminal networks from a technical and an economic perspective. Through large-scale measurements, we empirically describe some salient elements of the online criminal infrastructures, and we derive economic models characterizing the associated monetization paths enabling criminal profitability. This analysis reveals the existence of structural choke points: components of online criminal operations being limited in number, and critical for the operations’ profitability. Consequently, interventions targeting such components can reduce the opportunities and incentives to engage in online crime through an increase in criminal operational costs, and in the risk of apprehension. We define a methodology describing the process of distilling the knowledge gained from the empirical measurements on the criminal infrastructures towards identifying and evaluating appropriate countermeasures. We argue that countermeasures, as defined in the context of situational crime prevention, can be effective for a long-term reduction in the occurrence of online crime.

Cette thèse s’intéresse à la propagation dynamique de fissure dans les membranes élastomères du point de vue expérimental. Elle a pour but d’identifier les paramètres qui gouvernent la cinématique de ces fissures se propageant à grande vitesse, afin d’en prédire la trajectoire. Fondé sur l’utilisation conjointe d’une caméra à haute résolution et d’une caméra rapide, le dispositif expérimental permet de mesurer des champs à partir de la corrélation d’images au cours de la propagation de la fissure. Mis en pratique sur un polyuréthane, ce dispositif permet de retrouver la configuration de référence de l’éprouvette pendant la propagation de fissure, préalable indispensable à l’étude mécanique du problème. En plus des champs cinématiques, la densité d’énergie élastique et les contraintes sont évaluées grâce à une loi de comportement hypérélastique Les résultats de ces essais constituent une large base de données sur la rupture dynamique de membranes élastomères. La méthode permet de réaliser une analyse cinématique et énergétique de la propagation stationnaire et instationnaire, toujours dans la configuration de référence. La propagation supersonique est observée pour les hauts niveaux de déformation de la membrane. Enfin,ces observations permettent une discussion sur l’utilisation de l’approche énergétique de la rupture dynamique et de la pertinence des mesures de champs actuelles pour caractériser ce type de propagation de fissure. / This PhD thesis tackles the issue of dynamic fracture of elastomer membranes from an experimental point of view. It aims at providing some insight to predict the trajectories of high speed cracks under large strain. An experimental procedure involving high resolution and high speed cameras is developed in order to perform full-field measurements based on digital image correlation during crack propagation. Tested with a highly stretchable elastomer (polyurethane), this set-up permits to retrieve the material configurations of the sample all along crack growth, which is a crucial step toward a complete mechanical analysis of the problem. In addition to the kinematic fields,both strain energy density and stress fields are estimated thanks to a hyperelastic model, which is issued from mechanical characterisation of the material. Results of these experiments provide a comprehensive database on dynamic fracture of membranes. The method is designed to perform kinematic and energetic analyses of both steady and unsteady crack propagation in the reference configuration. Supersonic crack growth is observed for large prescribed deformation of the membranes. Finally, these observations lead to a discussion on the energetic approach in dynamic crack growth and the current applicability of full-field measurements to characterise dynamic crack growth in elastomers.

The purpose of the present study was to investigate the construct validity of the Differential Ability Scales (DAS) with a mentally handicapped population. The DAS is an individually administered, standardized test of intelligence. The stated purposes of the DAS are to provide a composite measure of conceptual reasoning abilities for classification and placement decisions and to provide a reliable profile of relative strengths and weaknesses for diagnostic purposes. With these goals in mind, it follows that this cognitive measure would be used often with mentally handicapped students. The DAS was developed using an hierarchical model based upon exploratory and confirmatory factor analyses. The model assumes that ability measures or subtests will load on a general factor g and will form subfactors at a lower level. The model also assumes that as children get older, the number of subfactors will increase because of development and differentiation of abilities. How mentally handicapped children would fit into this model was the subject of the current research.Using a sample of 100 mildly and moderately handicapped children ages 8 years, 0 months to 17 years, 5 months, confirmatory factor analysis was used to explore the factor structure of the DAS with this population. Three separate models were investigated: Model I, in which a one factor solution was proposed, Model II, in which two factors, Verbal Ability and Nonverbal Ability, were proposed, and Model III, in which three factors, Verbal Ability, Nonverbal Reasoning Ability, and Spatial Ability, as proposed by the test's authors, were investigated. Results of the analyses support the use of a one factor interpretation when using the DAS with mentally handicapped students. In practice, only the broadest score, the General Conceptual Ability Score (GCA), can be interpreted with confidence. Further, case study investigation illustrates the inconsistencies encountered in scoring at the lower end of the norms, as well as in using the outof-level procedure proposed by the test's authors. / Department of Educational Psychology

La facilité de déploiement et la flexibilité des technologies sans fil ont permis une évolution considérable des normes IEEE 802.11. L'arrivée de la fibre optique à la maison a également motivé des études de recherche pour accroître les débits et la capacité. Dans ce contexte, la dernière norme IEEE 802.11ac ratifiée en 2014 a normalisé de nouvelles technologies pour atteindre des débits maximaux au-dessus de 1Obit/s. En particulier, 802 llac propose le Multiple Input Multiple Output Multi-Utilisateurs (MIMO-MU) et le Transmit Beamforming (TxBF). Ces technologies d'antennes intelligentes supposent un diagramme d'antenne d'émission qui dépend de la position des utilisateurs et des caractéristiques du canal de propagation multi-trajets correspondant. Cependant, les outils d'ingénierie et de planification radio actuels simulent une carte de couverture fixe et indépendante de tout traitement d'antennes adaptatives côté émission. Cette thèse étudie l'impact de ces techniques MIMO-MU et TxBF et propose des solutions adaptées pour l'ingénierie radio et l'optimisation du système ainsi que pour les outils de planification radio. En effet, la première partie de cette thèse consiste à affiner les gains de capacité en identifiant les configurations et les paramètres système optimaux. La deuxième partie aborde les gains de beamforming en termes du gain sur le rapport signal à bruit (SNR) et sur la réduction du niveau d'interférence pour avoir une modélisation réaliste de la couverture radio. / The deployment facility and flexibility of wireless technologies have allowed considerable evolution of IEEE 802 .11 standards. The arrival of the optical fiber to the home has further motivated the research studies to increase data rates and capacity. ln this context, the latest IEEE 802.l lac standard ratified in 2014 proposes new technologies to achieve maximum data rates above 1 Gbit/s. ln particular, 802.l lac includes the Multi-User Multiple Input Multiple Output (MU-MIMO) and Transmit Beamforming (TxBF). These smart antenna technologies assume a variable transmit antenna pattern in function of the users' position and the corresponding multipath propagation channel characteristics. However, the actual radio planning tools give a fixed coverage map in dependent of any adaptive or smart antenna processing. This thesis studies the impact of the MU-MIMO and TxBF techniques on radio engineering, system optimization as well as radio planning tools. Indeed, the first part of this thesis deals with refining the sum rate capacity gains by identifying interesting system configurations and optimal system parameters. The second part addresses the beamforming gains in terms of the Signal-to-Noise Ratio (SNR) gain and interference level to have realistic radio coverage modeling.

PURPOSE: The purpose of the study was to examine the relationships between muscle cross-sectional area (CSA) measured by either ultrasonography or biopsy and measures of isometric peak force (IPF) and rate of force development (RFD). METHODS: Fifteen well-trained males (IPF=4445.467 + 613.690 N) participated in the study. Prior to testing and following an overnight fast, each subject’s vastus lateralis (VL) was measured for anatomical CSA (ACSA) using ultrasonography. A muscle biopsy was also sampled from the VL of each subject immediately after the ACSA measurement and at the same site on the VL. Fiber CSA (FCSA) was assessed using immunofluorescent techniques. IPF and RFD at 0-50ms, 0-100ms, 0-150ms, and 0-200ms were assessed during an isometric mid-thigh pull test on force platforms sampling at 1000Hz. Pearson product-moment correlations were calculated between muscle sizes and performance. Statistical significance was set as p≤0.050. RESULTS: Statistically significant correlations were observed between Type II FCSA and IPF (r=0.774, p<0.001), RFD150 (r=0.661, p=0.007), and RFD200 (r=0.725, p=0.002). ACSA was only significantly associated with IPF (r=0.596, p=0.019). Type I FCSA did not relate to any performance measures. CONCLUSIONS: It is clear from our results and previous literature that ultrasonography and muscle biopsy data provide relevant information regarding muscle size and performance. However, the discrepancies observed in the current study between the two suggest each is providing slightly different information to researchers. Specifically, Type II FCSA might be superior when considering more sensitive performance measurements such as RFD.