Chaotic systems have properties such as ergodicity, sensitivity to initial conditions/parameter mismatches, mixing property, deterministic dynamics, structure complexity, to mention a few, that map nicely with cryptographic requirements such as confusion, diffusion, deterministic pseudorandomness, algorithm complexity. Furthermore, the possibility of chaotic synchronization, where the master system (transmitter) is driving the slave system (receiver) by its output signal, made it probable for the possible utilization of chaotic systems to implement security in the communication systems. Many methods like chaotic masking, chaotic modulation, inclusion, chaotic shift keying (CSK) had been proposed however, many attack methods later showed them to be insecure. Different modifications of these methods also exist in the literature to improve the security, but almost all suffer from the same drawback. Therefore, the implementation of chaotic systems in security still remains a challenge. In this work, different possibilities on how it might be possible to improve the security of the existing methods are explored. The main problem with the existing methods is that the message imprint could be found in the dynamics of the transmitted signal, therefore by some signal processing or pattern classification techniques, etc, allow the exposition of the hidden message. Therefore, the challenge is to remove any pattern or change in dynamics that the message might bring in the transmitted signal.

Harmonic resonance occurs when the network equivalent shunt harmonic capacitive reactance is associated with the network series harmonic inductive reactance. When such resonance occurs, it amplifies harmonic components with frequency close to the resonance point. Solutions used to solve harmonic resonance problems can be divided into two main categories. One is to reduce the content of harmonic components in the network (e.g. by using active or passive harmonic filters, etc.) and the other is to remove the resonance stimulating factor by shifting away the resonance frequency to a non-critical frequency range (e.g. detuning PFC capacitors, redesigning feeder transformers, etc.). Studies show that these techniques are not adequate to solve harmonic resonance problems in power distribution networks which are dynamic by their nature and with complex interconnections. Due to this, solutions in the category one are designed for localised harmonic distortion compensation, while solutions in the category two lack real-time operation feature. Therefore, it was identified that there is a need for real-time harmonic resonance attenuation that is suitable for power distribution networks. In this thesis, a new real-time Harmonic Resonance Attenuation (HRA) technique is proposed. This technique may be used with ordinary shunt harmonic filters to make them behave like a virtual shunt capacitor or inductor. Thus, looking from the harmonic current source side, the filter alters the network harmonic impedance and hence results in harmonic resonance attenuation. In order to implement the HRA technique, fast measurement of system harmonics in real-time is required. Therefore, in this work, a fast individual harmonic extraction (FIHE) technique is developed to enhance the desired real-time operation of the HRA. The proposed FIHE needs only one sixth of the fundamental cycle to extract any individual harmonic component which is faster than other methods currently available. In addition to the speed, the proposed FIHE provides overshoot free, oscillation free and ripple free extraction characteristics. The proposed HRA and FIHE techniques are described in this thesis with detailed analysis to illustrate their operating principles. A series of simulations and experiments are conducted to evaluate their functionality and performance. Results of the evaluation are presented and discussed in this thesis together with details of the experimental HRA model developed to verify the theoretical and simulation results.

This thesis explorers the reasons for power shortage and the level of maintenance implementation in Iraqi power plants, furthermore, it examines the current organisational culture in Iraqi power plants, and its effect on maintenance implementation factors. Currently the active power plant units in Iraq are producing only 54% their designed capacity, which is in turn only supplying 50% of the countries’ demand. Therefore, to try and understand the reasons for this low level of efficiency, this research uses an exploratory sequential mixed method design, starting with semi-structured interviews (qualitative) with nine power plant managers or their representatives, followed by a questionnaire survey (quantitative), receiving 484 responses from the employees of those nine power plants. The reasons for power shortage in Iraq were identified, Furthermore, the level of maintenance implementation in the Iraqi power plants, was examined found to be at a medium level. In terms of organisational culture, not enough attention has been paid in the literature. This lack of research in the area of cultural effect on maintenance implementation was one of the main motivators for this study to answer the following question; to what extent do organizational culture profiles effect maintenance implementation factors in organisations. Structural equation modelling (SEM) technique was used to examine the relationship between organisational culture and maintenance implementation factors. Furthermore, based on the research findings, maintenance improvement framework was developed and detailed plans for implementation were formulated. The framework was built on the basis that improving organisational culture will improve the factors affecting maintenance and these factors will facilitate Total Productive Maintenance (TPM) implementation in Iraqi power plants.

This thesis addresses the problem of detection of an unknown binary event. In particular, we consider centralized detection, distributed detection, and network security in wireless sensor networks (WSNs). The communication links among SNs are subject to limited SN transmit power, limited bandwidth (BW), and are modeled as orthogonal channels with path loss, flat fading and additive white Gaussian noise (AWGN). We propose algorithms for resource allocations, fusion rules, and network security. In the first part of this thesis, we consider the centralized detection and calculate the optimal transmit power allocation and the optimal number of quantization bits for each SN. The resource allocation is performed at the fusion center (FC) and it is referred as a 'centralized' approach. We also propose a novel fully 'distributed' algorithm to address this resource allocation problem. What makes this scheme attractive is that the SNs share with their neighbors just their individual transmit power at the current states. Finally, the optimal soft fusion rule at the FC is derived. But as this rule requires a-priori knowledge that is difficult to attain in practice, suboptimal fusion rules are proposed that are realizable in practice. The second part considers a fully distributed detection framework and we propose a two-step distributed quantized fusion rule algorithm where in the first step the SNs collaborate with their neighbors through error-free, orthogonal channels. In the second step, local 1-bit decisions generated in the first step are shared among neighbors to yield a consensus. A binary hypothesis testing is performed at any arbitrary SN to optimally declare the global decision. Simulations show that our proposed quantized two-step distributed detection algorithm approaches the performance of the unquantized centralized (with a FC) detector and its power consumption is shown to be 50% less than the existing (unquantized) conventional algorithm. Finally, we analyze the detection performance of under-attack WSNs and derive attacking and defense strategies from both the Attacker and the FC perspective. We re-cast the problem as a minimax game between the FC and Attacker and show that the Nash Equilibrium (NE) exists. We also propose a new non-complex and efficient reputation-based scheme to identify these compromised SNs. Based on this reputation metric, we propose a novel FC weight computation strategy ensuring that the weights for the identified compromised SNs are likely to be decreased. In this way, the FC decides how much a SN should contribute to its final decision. We show that this strategy outperforms the existing schemes.

The research described in this thesis investigates the area of subband coding of high quality digital audio signals. The research into the application of a nonuniform filter bank employing frequency warping to digital audio coding is described. Firstly, some aspects of psychoacoustics, especially masking effects, are studied. Utilising psychoacoustic models, perceptual entropies are calculated for a number of audio excerpts and it is shown that theoretically the bit rate can be reduced to lower than 2 bits per sample. Different types of filter banks are reviewed. To examine the best band splitting scheme, studies are carried out on optimum bit allocations for uniform and nonuniform filter banks, with or without a psychoacoustic model. The concept of perceptual coding gain is proposed and it is shown experimentally that band splitting according to the auditory critical band rate is not recommended for audio compress10n. A new generic nonuniform decomposition algorithm, relying on cascading frequency warping and a uniform filter bank, is developed. Detailed analyses of frequency warped signals are carried out. The effect of truncation of the original signal and the warped signal is investigated. It is shown that the reconstruction is near perfect and coding based on the new nonuniform filter bank is capable of noise shaping. A subband coder based on the nonuniform filter bank is constructed and results are presented. Objective assessment and informal subjective assessment are carried out and they show that the coding reaches high quality at 192 kbps per channel; however, some artefact is perceptable. An efficient implementation of the Koilpillai-Vaidyanathan pseudo-quadrature mirror filter (KVPQMF) bank, which features simplicity in prototype filter design and suitability for audio coding, is developed. The savings in the number of calculations and in the execution time over the direct implementation is significant.

In this thesis the development of a novel descriptor for boundary images represented in a chain code format is reported. This descriptor is based on a truncated series of orthogonal polynomials used to represent a piecewise continuous function derived from a chain code. This piecewise continuous function is generated from a chain code by mapping individual chain links onto real numbers. A variety of alternative mappings of chain links onto real numbers are evaluated, along with two specific orthogonal polynomials; namely Legendre polynomials and Chebychev polynomials. The performance of this series descriptor for chain codes is evaluated initially by applying it to the problem of locating short chains within a long chain; and then extending the application and critically evaluating the descriptor when attempting to match features from pairs of similar images. In addition, a formal algebra is developed that provides the rule base that enables the transformation and manipulation of chain encoded boundary images. The foundation of this algebra is based on the notion that the labelling of the directions of an 8-connected chain code is essentially arbitrary and 7 other, different and consistent labellings can be distinguished.

This thesis presents a novel approach to the manufacture of thin film resistors using a new low resistivity material of copper, aluminium and molybdenum, which under industrially achievable optimised process conditions, is shown to be capable of producing excellent temperature coefficient of resistance (TCR) and long term stability properties. Previous developments in the field of thin film resistors have mainly centred around the well established resistive materials such as nickel-chromium, tantalum-nitride and chromium-silicon-monoxide. However recent market demands for lower value resistors have been difficult to satisfy with these materials due to their inherent high resistivity properties. This work focuses on the development and processing of a thin film resistor material system having lower resistivity and equal performance characteristics to that of the well established materials. An in depth review of thin film resistor materials and manufacturing processes was undertaken before the electrical properties of a binary thin film system of copper and aluminium were assessed. These properties were further enhanced through the incorporation of a third doping element, molybdenum, which was used to reduce the TCR and improve the electrical stability of the film. Once the desired chemical composition was established, the performance of the film was then fine tuned through optimisation of critical manufacturing process stages such as sputter deposition, heat treatment and laser adjustment. The results of these investigations were then analysed and used to generate a set of optimum process conditions, suitable for repeatedly producing thin film resistors in the 1 to 10Ω resistance range, to tolerances of less than ±0.25% and TCR values better than ±15ppm/oC.