With the advances in microprocessor technology, control systems are widely seen not only in industry but now also in household appliances and consumer electronics. Among all control schemes developed so far, Proportional plus Integral plus Derivative (PID) control is the most widely adopted in practice. Today, more than 90% of industrial controllers have a built-in PID function. Their wide applications have stimulated and sustained the research and development of PID tuning techniques, patents, software packages and hardware modules. Due to parameter interaction and format variation, tuning a PID controller is not as straightforward as one would have anticipated. Therefore, designing speedy tuning rules should greatly reduce the burden on new installation and ‘time-to-market’ and should also enhance the competitive advantages of the PID system under offer. A multi-objective evolutionary algorithm (MOEA) would be an ideal candidate to conduct the learning and search for multi-objective PID tuning rules. A simple to implement MOEA, termed s-MOEA, is devised and compared with MOEAs developed elsewhere. Extensive study and analysis are performed on metrics for evaluating MOEA performance, so as to help with this comparison and development. As a result, a novel visualisation technique, termed “Distance and Distribution” (DD)” chart, is developed to overcome some of the limitations of existing metrics and visualisation techniques. The DD chart allows a user to view the comparison of multiple sets of high order non-dominated solutions in a two-dimensional space. The capability of DD chart is shown in the comparison process and it is shown to be a useful tool for gathering more in-depth information of an MOEA which is not possible in existing empirical studies. Truly multi-objective global PID tuning rules are then evolved as a result of interfacing the s-MOEA with closed-loop simulations under practical constraints. It takes into account multiple, and often conflicting, objectives such as steady-state accuracy and transient responsiveness against stability and overshoots, as well as tracking performance against load disturbance rejection. These evolved rules are compared against other tuning rules both offline on a set of well-recognised PID benchmark test systems and online on three laboratory systems of different dynamics and transport delays. The results show that the rules significantly outperform all existing tuning rules, with multi-criterion optimality. This is made possible as the evolved rules can cover a delay to time constant ratio from zero to infinity based on first-order plus delay plant models. For second-order plus delay plant models, they can also cover all possible dynamics found in practice.

The rise of photonic integration makes optical code division multiple access (OCDMA) worth revisiting due to its promising role in future all-optical networks. OCDMA has the potential to exploit the surplus bandwidth of optical fibres and to carry over to the optical domain the benefits seen CDMA radio communication systems, such as the effective sharing of the spectrum for multiple network subscribers, and resistance to jamming and eavesdropping. One of the major requirements for the deployment of OCDMA in networks is integration. This thesis presents a research study of integrated OCDMA systems using the AlGaInAs/InP semiconductor material system. This material is considered due to its useful intrinsic properties such as thermal stability, strong electron confinement, and low threshold, making it suitable for fabricating optoelectronic devices. Two bespoke OCDMA systems are considered for integration: coherent temporal phase coding (TPC), and incoherent wavelength-hopping time-spreading (WHTS) OCDMA systems. TPC systems are excellent for high speed communications due to their static en/decoding enabling features. In this research, a 2×2 asymmetric Mach Zehnder interferometer (AMZI) is used to generate a 2-bit phase code, allowing multiplexing for up to four users. A semiconductor mode-locked ring laser is also embedded in the circuit, and using a synchronous mode-locking method, adequate signal en/decoding is achieved. WHTS systems on the other hand fully exploit the spectral and temporal space available in networks by assigning each user with a unique wavelength-time hop sequence for en/decoding data signals. Here, a mode-locked laser array is used with intracavity distributed Bragg reflectors (DBRs) for spectrally tuning each laser, and a 4:1 multimode interference coupler is used to combine the laser signals into a single channel for amplification, modulation and transmission. The integrated system is fully characterised and synchronisation experiments are performed to show the potential for its use in high speed multi-user networks. Mode-locked lasers play an important role in many OCDMA implementations due to their wide spectrum and discrete temporal properties, which can be easily exploited during data en/decoding. Various mode-locked laser devices have been studied during this research with additional embedded components such as intracavity DBRs and phase controllers for precise tuning of the wavelength and pulse repetition frequency. However, the noisy nature of passively operating mode-locked lasers make them prone to high jitter, which can result in high bit error rates. Synchronisation schemes are thereby explored in order to temporally stabilise the pulse oscillations to make them suitable for use in long haul transmission systems. This includes synchronous and hybrid mode-locking, as well as a passive technique using an optical fibre loop to provide phase feedback, which is shown to promote ultralow RF linewidths in mode-locked lasers.

This research presents a more complete flexible model for the Motorised Momentum Exchange Tether (MMET) concept. In order to analyse the vibration aspect of the problem the tether is modelled as a string governed by partial differential equations of motion, with specific static and dynamic boundary conditions and the tether sub-span is flexible and elastic, thereby allowing three dimensional displacements of the motorised tether. The boundary conditions lead to a specific frequency equation and the Eigenvalues from this provide the natural frequencies of the orbiting flexible motorised tether when static, accelerating in spin, and at terminal angular velocity. The rotation matrix is utilized to get the position vectors of the system’s components in an inertial frame. The spatio-temporal coordinates u(x,t), v(x,t) and w(x,t) are transformed to modal coordinates before applying Lagrange’s equations and the pre-selected linear modes are included in generating the equations of motion. The equations of motion contain inertial nonlinearities of cubic order, and these show the potential for intricate intermodal coupling effects. The study of planar and non-planar motions has been carried out and the differences in the modal responses in both motions between the rigid body and flexible model are highlighted and discussed. The dynamics and stability of the flexible MMET is investigated using the dynamical analysis tools for representing the behaviour of the tether system. The study is also includes the engineering side of the MMET by investigating the power requirements of an electric motor located in the central facility of the Motorised Momentum Exchange Tether (MMET). A simulation was run using a specially written computer program to obtain the required minimum power for a typical duty cycle, and also to study the responses for three different operating conditions; before payload release, torque-off and reverse torques conditions for both the propulsion and outrigger system on both circular and elliptical orbits. The differences in the responses when using rigid body and flexible models of MMET are highlighted and discussed in order to look at the sensitivity of the model to the power budget calculations. The study then continues with a comparative study between the MMET and conventional propulsion systems in terms of the energy used specifically for an Earth-Moon return mission for circular and elliptical orbits.

The increasing density offered by Field Programmable Gate Arrays(FPGA), coupled with their short design cycle, has made them a popular choice for implementing a wide range of algorithms and complete systems. In this thesis the implementation of video compression algorithms on FPGAs is studied. Two areas are specifically focused on; the integration of a video encoder into a complete system and the power consumption of FPGA based video encoders. Two FPGA based video compression systems are described, one which targets surveillance applications and one which targets video conferencing applications. The FPGA video surveillance system makes use of a novel memory format to improve the efficiency with which input video sequences can be loaded over the system bus. The power consumption of a FPGA video encoder is analyzed. The results indicating that the motion estimation encoder stage requires the most power consumption. An algorithm, which reuses the intra prediction results generated during the encoding process, is then proposed to reduce the power consumed on an FPGA video encoder’s external memory bus. Finally, the power reduction algorithm is implemented within an FPGA video encoder. Results are given showing that, in addition to reducing power on the external memory bus, the algorithm also reduces power in the motion estimation stage of a FPGA based video encoder.

Corrosion within the oil and gas sector is an ongoing concern for operators. The challenging nature of extraction and processing fluids is an unavoidable cause of severe metallic corrosion. With modern emphasis on health, safety and the environment, the case for managing corrosion has become an imperative agenda. Whilst new and more effective methods of mitigation are key, an interim solution is improving the value of current methods. A literature survey carried out within this project has revealed CO2 corrosion as contributing to most corrosion related failures within the industry. The corrosion behaviour in CO2 containing environments is complex partly due to the wide range of prevailing conditions such as temperature, CO2 concentration and flow conditions. For oil and gas transportation pipelines, internal corrosion mitigation can be achieved by the use of chemical inhibitors. Inhibitors have been established to be effective but are by no means a complete solution. Issues such as their effectiveness in high velocity and high shear flow are a main consideration for their function. The hydrodynamic nature of the flowing fluids can affect inhibitor efficiency by either slowing the rate of formation of the inhibitive layer or causing degradation of well-formed inhibitive layers. A combined effect may also be active. The corrosion behaviour of carbon steel in simulated oilfield conditions is investigated in this project with emphasis on conditions of varying velocity, impinging flow and consequently shear stress. Since inhibition is the main mitigation technique for fluid related corrosion, the efficiency of a commercially used inhibitor is, in this case assessed in the abovementioned conditions. To simulate both impingement and flow, a jet impingement apparatus is used in conjunction with a segmented-electrode specimen set up to separately study the erosion-corrosion behaviour of different hydrodynamic zones under the jet. Corrosion rates are measured by gravimetric analysis and results are also evaluated with electrochemistry. Additionally, galvanic interactions between the different hydrodynamic zones have been investigated. Visual and light-optical microscopic examinations are also used to assess variable effects within the zones. Under such conditions, the corrosion rates have been found to be significantly higher in impingement zones. Aerated conditions have shown a significant variation in corrosion behaviour between impingement and non-impingement zones. The results in CO2 saturated brines are consistent but with evidence of different relations between hydrodynamics and the corrosion rate. The inhibitor has been shown to be effective in CO2 saturated brines and significantly influenced by both inhibitor concentration and hydrodynamic conditions. Inhibitor efficiency has also shown a complex dependence on concentration and establishes a need to evaluate optimum inhibitor concentrations before field application. Evaluation of the mass loss results against electrochemistry has shown a large discrepancy between the two methods. This rather surprising result suggests solid-free flow is not entirely free of erosion and synergistic effects. This comprehensive study has not only improved current knowledge on the relation between hydrodynamics and inhibitor efficiency but also indicates a critical need to evaluate suitability of current monitoring methods. Electrochemical methods are increasingly used as a method of choice and while they contribute significant monitoring data, they are observed to be unable, alone, to monitor erosion and synergy. An industry review on their suitability to monitor solid-free flow corrosion is recommended.

One of the major limiting factors of the CMOS device, circuit and system simulation in sub 100nm regimes is the statistical variability introduced by the discreteness of charge and granularity of matter. The statistical variability cannot be eliminated by tuning the layout or by tightening fabrication process control. Since the compact models are the key bridge between technology and design, it is necessary to transfer reliably the MOSFET statistical variability information into compact models to facilitate variability aware design practice. The aim of this project is the development of a statistical extraction methodology essential to capture statistical variability with optimum set of parameters particularly in industry standard compact model BSIM. This task is accomplished by using a detailed study on the sensitivity analysis of the transistor current in respect to key parameters in compact model in combination with error analysis of the fitted Id-Vg characteristics. The key point in the developed direct statistical compact model strategy is that the impacts of statistical variability can be captured in device characteristics by tuning a limited number of parameters and keeping the values for remaining major set equal to their default values obtained from the “uniform” MOSFET compact model extraction. However, the statistical compact model extraction strategies will accurately represent the distribution and correlation of the electrical MOSFET figures of merit. Statistical compact model parameters are generated using statistical parameter generation techniques such as uncorrelated parameter distributions, principal component analysis and nonlinear power method. The accuracy of these methods is evaluated in comparison with the results obtained from ‘atomistic’ simulations. The impact of the correlations in the compact model parameters has been analyzed along with the corresponding transistor figures of merit. The accuracy of the circuit simulations with different statistical compact model libraries has been studied. Moreover, the impact of the MOSFET width/length on the statistical trend of the optimum set of statistical compact model parameters and electrical figures of merit has been analyzed with two methods to capture geometry dependencies in proposed statistical models.

This thesis is concerned with the design, fabrication and investigation of InAs/InP quantum dot mode-locked lasers operating at ~1.55 μm with multi-gigahertz repetition rates. Devices with dual contact configuration operating at ~35 GHz were fabricated and mode-locking characteristics were investigated as a function of the saturable absorber length. The deposition of HR and AR coatings on the two cleaved facets provided an increase in the quantum efficiency and shifted the optimum mode-locking region to a higher injection current. This simple technological step increased the peak power of the emitted pulses by nearly a factor of 2. Furthermore, the appearance of two distinct lobes in the optical spectrum, which is a typical feature of quantum dot material systems, was also investigated. The sonogram technique confirmed the presence of two pulse trains under moderate values of current injection and stable locking of only one lobe at high injection currents. Finally, techniques for high repetition rate mode locking such as colliding pulse, asymmetric colliding pulse and double interval mode-locking were evaluated. Harmonic mode-locking at repetitions rates of ~71 GHz, ~107 GHz and ~238 GHz was demonstrated by placing the absorbers on cavity locations corresponding to the 2nd, 3rd and 7th harmonic, respectively. A monolithically integrated coupled cavity device was also explored, in which an FIB-milled intra-cavity reflector provided mode-locking at a repetition rate of ~107 GHz.

The thesis presents a comparison study of the two most established simulation approaches in Operational Research, Discrete-Event Simulation (DES) and System Dynamics (SD). The aim of the research implemented is to provide an empirical view of the differences and similarities between DES and SD, in terms of model building and model use. More specifically, the main objectives of this work are: 1. To determine how different the modelling process followed by DES and SD modellers is. 2. To establish the differences and similarities in the modelling approach taken by DES and SD modellers in each stage of simulation modelling. 3. To assess how different DES and SD models of an equivalent problem are from the users’ point of view. In line with the 3 research objectives, two separate studies are implemented: a model building study based on the first and second research objectives and a model use study, dealing with the third research objective. In the former study, Verbal Protocol Analysis is used, where expert DES and SD modellers are asked to ‘think aloud’ while developing simulation models. In the model use study a questionnaire survey with managers (executive MBA students) is implemented, where participants are requested to provide opinions about two equivalent DES and SD models. The model building study suggests that DES and SD modelling are different regarding the model building process and the stages followed. Considering the approach taken to modelling, some similarities are found in DES and SD modellers’ approach to problem structuring, data inputs, validation & verification. Meanwhile, the modellers’ approach to conceptual modelling, model coding, data inputs and model results is considered different. The model use study does not identify many significant differences in the users’ opinions regarding the specific DES and SD models used, implying that from the user’s point of view the type of simulation approach used makes little difference if any. The work described in this thesis is the first of its kind. It provides an understanding of the DES and SD simulation approaches in terms of the differences and similarities involved. The key contribution of this study is that it provides empirical evidence on the differences and similarities between DES and SD from the model building and model use point of view. Albeit the study does not provide a comprehensive comparison of the two simulation approaches, the findings of the study, provide new insights about the comparison of the two simulation approaches and contribute to the limited existing comparison literature.

Electron paramagnetic resonance (EPR) has been used to study point defects in synthetic single crystal diamond. Newly observed defects are reported in high pressure high temperature (HPHT) and chemical vapour deposition (CVD) diamond. HPHT diamond doped with 15N has been used to investigate the g = 2 region of the EPR spectrum which is obscured when natural isotopic abundances are present. Two previously unreported defects labelled WAR9 and WAR10 are reported. The EPR data has been shown to be consistent with the neutral nitrogen interstitial, N0 I (WAR9), and neutral nitrogen di-interstitial, NI-I001 (WAR10), defects respectively. Two further defects observed in CVD diamond are reported here. The first labelled WAR2 is preferentially aligned with the direction of growth, [001]. The EPR data is consistent with a (V-(CH)-V)0 structure although theoretical studies suggest that this structure is unstable at CVD growth temperatures. Growth mechanisms are suggested that would account for the observed preferential alignment. The second defect labelled WAR5, has been observed exclusively in samples grown using an experimental CVD chemistry containing oxygen. The EPR data is consistent with the OV0 defect, although no confirming 17O hyperfine structure has been observed. 13C hyperfine data is also reported for the KUL1/VnH− defect (n = 1 or 2) but the new data is not sufficient to conclusively discount either the n = 1 or n = 2 models suggested for this defect. Changes in defect concentrations in CVD diamond with thermal and illumination treatments has been investigated. Experimental data has indicated the presence of an unseen trap, common to CVD diamond, with concentrations comparable to that of N0S, and levels in the band-gap 0.5{1.2 eV above the top of the valence band. The difficult quantification of sub part per billion defect concentrations, as observed in electronic grade material, is tackled with the use of rapid passage EPR. It is shown that with this technique it is possible to detect concentrations of single nitrogen in diamond at tens of parts per trillion, close to a factor of 100 improvement on the currently used slow passage EPR.

This thesis considers the design of an autonomous ride-on lawnmower, with particular attention paid to the problem of single frequency Global Navigation Satellite System (GNSS) ambiguity resolution. An overall design is proposed for the modification of an existing ride-on lawnmower for autonomous operation. Ways of sensing obstacles and the vehicle's position are compared. The system's computer-to-vehicle interface, software architecture, path planning and control algorithms are all described. An overview of satellite navigation systems is presented, and it is shown that existing high precision single frequency GNSS receivers often require time-consuming initialisation periods to perform ambiguity resolution. The impact of prior knowledge of the topography is analysed. A new algorithm is proposed, to deal with the situation where different areas of the map have been mapped at different levels of precision. Stationary and kinematic tests with real-world data demonstrate that when the map is sufficiently precise, substantial improvements in initialisation time are possible. Another algorithm is proposed, using a noise-detecting acceptance test taking data from multiple receivers on the same vehicle (a GNSS com- pass configuration). This allows a more demanding threshold to be used when noise levels are high, and a less demanding threshold to be used at other times. Tests of this algorithm reveal only slight performance improvements. A final algorithm is proposed, using Monte Carlo simulation to account for time-correlated noise during ambiguity resolution. The method allows a fixed failure rate configuration with variable time, meaning no ambiguities are left floating. Substantial improvements in initialisation time are demonstrated. The overall performance of the integrated system is summarised, conclusions are drawn, further work is proposed, and limitations of the techniques and tests performed are identified.