Electricity sector decarbonisation is widely seen as a fundamental step in the global fight against climate change. The need to secure this transition is compounded by the prospective use of electrification to deliver economy-wide carbon reductions, especially in harder to address sectors like heat and transport. No agreement has yet been reached on the best decarbonisation approach. Empirical evidence is required to guide a transition that not only succeeds in delivering a ‘truly’ low carbon electricity source, but also prevents wider environmental issues being exacerbated. This research portfolio examines the low carbon transition of electricity systems in a UK context. The energy and environmental implications in response to different decarbonisation approaches were evaluated using Life Cycle Assessment (LCA) and related methods. Potential UK low carbon electricity systems were investigated via three socio-technical energy scenarios, known as the Transition Pathways. Key factors were identified, which may impact the future environmental performance of UK electricity, such as supply chain dynamics, policy shifts, and new entrant technologies, were investigated to assess their consequences on decarbonisation targets. This research exemplifies the guiding principles of LCA as a valuable proactive tool in shaping superior future decarbonisation and wider environmental policies. A key finding of this thesis was the importance of whole life cycle accounting of power sector GHG emissions, including upstream impacts which are often overlooked by governmental bodies. Hence, current decarbonisation policies may lead to a shift in practices and the adoption of production routes with unintended negative effects upstream. In this work, the upstream gas emissions for future supplies increase significantly (rising 2.7 to 3.4 times current mix per MJ supplied) and are foreseen to be highly influential on the future electricity systems analysed. Increased influx of biomethane leads to a substantial reduction in direct fossil emissions (up to 10.6 million tonnes of CO2eq), and is found to be critical in offsetting rising upstream emissions. The roll-out of carbon capture and storage was also found to be instrumental in the success of the pathways. The electricity system transitions assessed achieved differing, yet significant, levels of decarbonisation (between 75-85% reductions on 1990 levels on a lifecycle basis). Nevertheless, these were often achieved at the expense of wider environmental impacts, suggesting trade-offs were unavoidable. The civic-led energy transition resulted in the greatest associated environmental benefits, realising the greatest reduction in 13 of 18 environmental categories assessed, compared to the 2008 levels. It was also the only pathway to decouple electricity supply from fossil fuel use. Reliance on metal resources was seen to steadily increase in response to a developing renewable energy sector, rising 23-75% from the 2008 baseline system. The presented results, models and data are transparently presented for others in the field to build upon, and scrutinise their implications for wider decarbonisation strategies within and outside of the electricity sector.

The conventional fixed supply pressure valve-controlled (FPVC) hydraulic actuation method is a simple way to obtain motion control of a multi-axis system. The energy dissipated by the relief valve and the control valves is the main cause of the low energy-efficiency (and consequent oil heating) in the system. To overcome this problem, some approaches have been investigated such as load sensing, separate meter-in-and-meter-out, switching control and electro-hydrostatic actuation. In this thesis, a load-prediction based energy-efficient electrohydraulic actuation system – variable supply pressure valve-controlled (VPVC) actuation is described and implemented. A two-axis robotic arm is used as an example plant. In this research, the VPVC hydraulic actuation system is implemented by a fixed capacity pump driven by a brushless servo-motor. The feed forward part of the VPVC controller predicts the minimum required supply pressure for the demanded motion to each joint of the robotic arm by assuming its control valve is fully open. It is based on the prediction of the required piston force for a given motion demand, by applying Lagrange's equations of the-second-kind. The supply pressure for the whole system is the higher one of the two load branches; the other one is controlled by the common valve throttling. The supply flow is varied by controlling the speed of the servomotor. The feedback control of the VPVC is simple PI control for the valves and P control for the motor speed. Although the VPVC method is demonstrated for a two axis system, it is applicable to systems with any number of axes. By using the variable minimum required supply pressure together with the maximum valve opening (and hence minimum throttling losses), the hydraulic energy-efficiency is improved compared with a fixed supply pressure valve-controlled (FPVC) system. Moreover, due to the feed forward control, the response has much less phase lag hence the dynamic error is much smaller than a conventional FPVC system with proportional integral position feedback control. Applied to a known plant, especially enough load information, VPVC provides a higher energy-efficiency and a higher accuracy of motion control. The simulation and experimental results have validated the advantages of the VPVC over the FPVC. The hydraulic power consumption comparison between VPVC and FPVC with the same sine wave motion demand showed that up to 70% saving was achieved by VPVC experimentally. If the energy loss via relief valve in FPVC is taken into account, the saving can be increased greatly. The experiment also showed that the VPVC brought a very quiet operating due to the minimum flow throttling and variable motor speed, whereas serious flow throttling and constant high speed of motor in FPVC. Very low noise is another significant benefit of VPVC over FPVC. All the dynamic errors in VPVC tests were smaller than in FPVC. They were within 6% of the total motion range, compared to 14% for FPVC. And the average dynamic errors of VPVC tests were within 1.5% of the total motion range.

The object of this thesis is to present certain matrix techniques which may be employed in the analysis and synthesis or binary combinational logic circuits. These techniques are readily implemented on the digital computer. In developing these methods care has been taken to avoid heuristic algorithms so that each technique has a firm mathematical foundation. The first chapter of the thesis considers a Boolean matrix approach to logic analysis and synthesis. These matrices allow the rigorous and formalised representation of logic circuits. An important property of these matrices is that they embody multiple-output circuit representation and that, together with certain matrix operations, they may be used in the synthesis of multiple output circuits on an iterative basis. The second chapter of the thesis describes a matrix transformation technique which has properties directly applicable to logic synthesis. This technique may be employed not only in the field of conventional logic design but also in the design of circuits using threshold gates. Certain transform-domain operations are used to synthesise logic circuits directly from the transformed truth-table representation of Boolean functions. These operations may also be used in the classification of Boolean functions. They may also be employed in the synthesis of multiple-output circuits and pattern recognition. The third section of the thesis concerns itself with other research work initiated by the topics discussed in chapters one and two. Of special interest is the description of a universal threshold logic gate and its role in logic synthesis.

Sensitivity Analysis for a time-delay system is extended to Adaptive Control of systems with parametric and temporal mismatch. An adaptive control system based on the Smith predictor is investigated analytically and by hybrid and digital simulation. Systematic procedures for choice of adaptive loop gains is given, and the close relationship between linearity of sensitivity coefficients and constancy of adaptive loop gains is discussed in depth. The importance of non-commutativity of time varying elements in an adaptive control scheme is considered. Delay-free optimal control methods are extended to the delay case both for LQP and parametric optimisation. Iso-cost functionals are investigated with respect to temporal and parametric mismatch. Sub-optimality of certain optimal schemes is exposed, and it is shown that in the cases considered optimal performance may be improved by deliberate mismatch of plant and model.

The action of the transmitter, or coding section, of a communication system can be viewed as transformation of a set of variables (derived from the signal to be communicated) into a function of both the variables and time. The characteristics of the channel used to convey the transmitted signal are described by a set of transition probabilities. The receiver operates on part or all of the received signal to produce a representation of the original set of variables. It minimises the mean square error when it selects the mean of the posterior probability distribution. This system model is analysed, using unspecified functions to describe the code and channel characteristics, and a formula for the mean square error is found. An error formula for additive Guassian noise is derived from the general formula by substituting the appropriate channel characteristics. This is used to study the overall properties of codes. It is also used to calculate the performance of a number of practical coding schemes. A difficult integration is involved and approximations had to be used. These result in an error of something less than 1 dB in the threshold signal to noise ratio. Above the threshold the approximation is very close. The results show that there is little to choose between continuous and discrete codes. The best performances are obtained from codes having wide bandwidths, though these are closely approached at much lower bandwidths. The threshold signal to noise ratio can be lowered somewhat through the use of codes with memories, but this is a less significant factor than the bandwidth.

Machines are commercially available for the automatic recognition of characters hand-printed in accordance with rules of constraint. When the rules of constraint are removed, the number of possible shapes of each character becomes astronomical, and reliable automatic recognition has not yet been accomplished. The general idea of the present work is that to recognise a wider range of shapes of each character it will be necessary to make fewer simplifying assumptions in designing the recognition machine: limitations in performance arise from logical restrictions in the design. Some commonly made restrictive assumptions are analysed, and the problem of working without them is stated in the form of two hypotheses, the first being a preliminary simplification of the second. A detailed formulation of the problem of recognising, say, unconstrained hand-printed characters is necessarily hypothetical: the only way to show that the problem is correctly formulated is to show experimentally that its solution leads to good practical recognition performance. Specifically, it is common to base automatic character recognition on the detection of features, but the problem of automatically determining suitable features is notoriously unsolved. The problems tackled here can be regarded as simplifications of, and no more than early steps towards, the practical feature-choosing problem. In solution to these simplified problems an algebraic technique is introduced, its efficacy being demonstrated experimentally rather than theoretically. Although the cost of this technique is great, and its performance is limited, it achieves its main purpose of working with very much less logical restriction than has hitherto been possible.

This thesis describes an investigation of the perception of the strongly voiced components of speech. The work was related to the perception of speech in very noisy environments since the strongly voiced components are usually the ones least masked by noise. Experiments were performed to measure the intelligibility of a wide range of test materials. When strongly voiced components were heard, about 20% of PB words were correctly repeated and about 45% of words from prose phrases. As semantic and grammatical constraints were removed, the scores fell. When white noise was inserted in the silences between strongly voiced components, the number of words correctly repeated increased. The increase for prose phrases was about 20 percentage points and about 1 percentage point for PB (phonetically balanced) words. The number of PB words repeated rose by 10 percentage points when the words were embedded in a known phrase. Similar results were obtained when noise was added in the silences caused by regular interruption of speech or by removal of the strongly voiced components. No significant increase in the number of words correctly repeated was found when a monotone synthetic vowel was inserted instead of the white noise. A number of hypotheses have been discussed in the text that might provide an explanation for the observed results. The one most consistent with the results, including those of other workers, is based on linguistic association. The basis of this hypothesis is that only auditory signals with special characteristics are perceived in terms of language. Interrupted speech was not sufficiently speech-like to be classed as language but the addition of noise in the silences did allow more complete use to be made of linguistic knowledge. It has not yet been determined-precisely which features of the signal heard control the use of linguistic knowledge.

Advancements in electronic integrated chip technology are slowing down with transistor sizes approaching their theoretical limit in most equipment and devices. As the data transmission rate has benefited from the telecommunication technology through optical fibers, Photonic Integrated Chips (PICs) are expected to fill the gap in the demand for higher transmission rates and faster computational speeds that the electronic chips would fail to fulfill. The research into PICs is in the center of attention in the academic and industrial fields, and the way in front of PICs development and improvement is still long. There are many opportunities including the use of new materials, different designs and architectures, and the use of various physical effects on the macro and micro scales. The main aim of this work is to design a hybrid-multi-layer PIC that allows the integration between an ultra-high-Q micro-resonator made of silica and an optical waveguide of a different material through a MEMS actuated coupler. To date, the ultra-high-Q silica micro-resonators can confine light within for the longest period, which is very beneficial for many applications including revolutionary accurate time measurements, and studying non-linear optical phenomena using modest laser powers. As using silica micro-resonators offers the highest-Q factor, using an optical waveguide of different material can offer the best operation condition based on the required application. For instance, having a silicon waveguide with high refractive index allows the fabrication of dense photonic chips, while using nanocrystalline diamond (NCD) waveguide suits wide-transmission-window applications. To achieve this goal, several studies were required along the way. For example, the hybrid-chip would include a suspended NCD waveguide structure that has not been demonstrated before. So we took the initiative and designed, fabricated and studied its operation. During fabricating the chips in this work, the ablation of NCD films using CO2 laser was observed, which was unexpected. As explanations in the literature was unsatisfactory, we hypothesized a new explanation, and confirmed it using numerical and experimental tests. After designing the hybrid-multi-layer PIC, we took the study a step further and developed the fabrication process. Also, an analytical formula for estimating the scattering loss from asymmetric rough rectangular waveguide surfaces has been formulated to assess the practicality of using specific waveguide designs using certain fabrication techniques. Finally, the design of grating couplers is presented as a starting point for prospective work. The work presented here is believed to be a beneficial milestone in the realisation of practical hybrid multi-layer PICs.

This thesis focuses on the manufacturing, indoor characterisation and outdoor monitoring of Perovskite solar cells (PSCs) and Organic photovoltaics (OPVs). In order for emerging PV technologies to become commercially viable it is important that their performance under these conditions is defined. In this thesis, the outdoor performance parameters of PSCs and OPVs monitored over the course of several campaigns are reported and benchmarked against polycrystalline silicon (poly-Si) solar cells. The data has been analysed in detail against solar irradiance dose, climatic conditions and stability. It was discovered that in common with poly-Si PVs, PSCs also exhibits a distinctive negative temperature coefficient across all performance parameters (VOC, ISC, FF and PCE) which decreases with increasing irradiation dose. In all outdoor campaigns the main causes for early-life degradation were noted to be sealant failure leading to oxygen and water ingress, although longer-term degradation has been observed and assigned to photo-oxidation which in some cases was effectively suppressed by the utilisation of UV filtering. The stability of PSCs and active layers was improved by the use of luminescent down-shifting coatings which were applied as a substitute to conventional UV filters. This thesis also demonstrates the benefit of multidirectional orientation of OPVs laminated onto an industrial building prototype for building-integrated applications. It is shown that positioning OPVs to more directions than South improves the overall diurnal yield and can potentially double the energy produced per year, in particular for peak generation hours in the UK. The benefit of unreacted lead iodide as partial filter to the highly damaging UV component of sunlight is shown. The importance of a thin residue lead iodide layer in PSCs shows an improvement in the stability of fabricated devices. One of the most significant findings in this thesis is the first report on the stability of perovskite absorber layers and solar cells conducted with irradiance levels at 1sun or 100sun concentrated natural sunlight. By accelerating the aging process, this method provides invaluable information about the long-term performance of absorber layers and devices which is an immense contribution to the PV community in improving the compositions and structure of PSCs. Abstract vi The stability of 3rd generation PV remains a critical issue preventing the appearance of these new and exciting, flexible and highly efficient PVs on the market. The last part of this thesis shows the second important finding in this thesis which focuses on an in-depth study of the stability of OPVs subjected to a multi-stress accelerated lifetime testing (ALT). This study is conducted indoors which facilitates the most destructive elements to the life of an OPV exposed outdoors to be clearly determined by exposing the modules to well-defined exposure conditions.

Radar altimetry over the ocean is now a well established discipline of satellite remote sensing, providing measurements of mean height, significant waveheight and surface wind speed. In contrast, radar altimetry over non-ocean surfaces, to obtain topography of land and polar ice sheets, is still a new idea. The difference between these two situations is that the ocean surface is essentially flat with a very small vertical extent, so a broad-beam pulse-limited mode radar altimeter having a relatively small antenna is sufficient to give very accurate measurements of the ocean mean height. However for topographic surfaces, variations in the elevation can be much higher, and using a conventional altimeter causes serious problems, such as interpretation error and misregistration of a measured range, which cannot be normally corrected. To avoid these problems, a considerably narrower beam antenna has to be used to localise the surface under observation. This requires very large antenna structures, which would be both complex and costly. This thesis investigates the application of aperture synthesis techniques to narrow-beam altimetry as an alternative to physically large antennas, to achieve high along-track resolution. It considers the analysis of the involved factors and design parameters, errors, data handling and signal processing requirements and methods for fixing the antenna beam accurately with the ultimate goal of providing a dynamic global altimetric database. In the second half of the thesis, an experimental aircraft-borne altimeter is examined. Details of the design, construction and evaluation of a prototype system are described. This radar includes several novel features, such as aperture synthesis with full-deramp range processing, digital chirp generation, bistatic FMCW operation and off-line digital signal processing. Also a series of experiments are arranged for this radar to examine its performance to process the signature of corner reflector targets, and consideration is given to the extension of these ideas to a satellite-borne instrument.