Despite the high prevalence and global burden of low back pain (LBP), the pathogenesis is poorly understood. Without a better understanding of what structures are involved in the development and chronicity of LBP, the value and efficacy of clinical assessments and physical therapy interventions are limited. Although there is a clear link between the lumbar spine, pelvis and hip extensors during movement in both LBP and healthy subjects, there is limited evidence regarding whether it is passive or active components that are influenced. There is a need for improved prognostic evaluation of patients with LBP, including whether altered hip biomechanics are the result of structural, passive elements, or neuromuscular, active components of movement. Such evaluations will be beneficial for researchers, clinicians and physical therapists. The purpose of the present investigation is initially to demonstrate how a handheld measuring device can be adapted for use in measuring passive hip moments during supine leg raising. Comparisons are then made between subjects with LBP and healthy controls. A validated dynamic biomechanical model is used to calculate passive hip moments at a variety of knee angles, from which a predictive equation is derived, which is specific to each subject. Following a gait analysis protocol, the predictive equation is used to calculate passive hip extensor moments during the hip flexion component of gait. Comparisons are made between passive hip extensor moments, total hip moments, power and work done, in subjects with and without LBP. The present investigation demonstrated the high accuracy of a handheld force transducer for the measurement of passive hip moments. There were no statistically significant differences in passive hip extensor biomechanical properties between subjects with LBP and healthy controls. However, assessment during walking demonstrated significant differences in passive hip extensor moments between subjects with LBP and controls. Further differences were identified in total hip moments, power and work done, despite no differences in gait parameters. It is plausible that the passive and active components of movement interact, although further research is required to determine whether such interactions are consistent and predictable. It was observed that the passive contribution to hip biomechanics during the swing phase of gait is considerable, and should be incorporated into dynamic modelling. Differentiating between passive and active components may be particularly useful for researchers, clinicians and physical therapists, for evaluating which components are influenced by LBP and for assessing the efficacy of component-specific interventions. Future research should expand on this research to include a wider range of LBP patients, with different severity and disability of LBP, to develop a more complete range of data on how passive and active components are influenced and the range of interactions during common movements. Other research should attempt to determine which interventions are most appropriate for targeting changes to passive and active components independently, and in accordance with patient adaptations to LBP. The modelling, experimental procedures and customised equipment used in the present investigation are appropriate for use in assessing passive contributions to joint biomechanics during movement.

Increasing the level of semiconductor devices' quality, reliability, and associated system safety is important as a fundamental contributor to overall technical advancement in the electronics sector. However, the growing requirements of optimizing device design for the broadest application areas need an enhanced level of understanding of thermal behaviour, and self-heating in particular, of semiconductor devices under harsh thermal operation conditions. The aim of the research presented in this thesis is to develop and verify a numerical tool to assist in the understanding and the prediction of phenomena that contribute to the ageing and stressing of semiconductor devices. An aged semiconductor device can substantially adversely affect a system's electromagnetic compatibility (EMC) performance and reduce the desired functionality. The chosen method is a co-simulation approach for a linked electrical and thermal model, using the Transmission Line Matrix (TLM) method. This selection is based on having a single method that can simulate both domains, that is intuitive and flexible. The method is enhanced by including electromigration and thermomigration mechanisms as an influential element in the calculation of material properties inside the hybrid solver. The proposed model was subjected to a customized Thermal Cycling Test (TCT) in order to observe device behaviour and comprehend the degradation phenomenon that Abstract appears after accelerated ageing test in RF LDMOS device. The research is a generic step forward, showing that a single TLM 'engine' can be used to model the linked factors in ageing and its effects, namely electrical, and thermal behaviour, that also allows for probabilistic events such as electro/thermo-migration. Further, the method developed in this thesis is applied to two problem areas: • Silicon nanowires, where the thermal radiation effects are addressed by adding an additional shunt conductance to a one-dimensional TLM node structure. The results demonstrate good agreement with previously published results and provide an appropriate tool to solve the internal heating problems and, hence, the degradation caused by thermal factors for future semiconductor devices. • Silicon Carbide Metal-Semiconductor Field Effect Transistor (MESFET) and RF Laterally Diffused Metal Oxide Semiconductor (LDMOS) devices, which are approached as 2D structures, where the probability of occurring electromigration and thermomigration phenomenon in MESFET devices is investigated and the MTTF is shown when the model is subjected to thermal stress. The TCT is applied as a thermal acceleration factor in a MOS device, where the impact on the device IV (current-voltage) characteristic is studied. The results demonstrated good agreement with previous published results.

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A commercial unsaturated polyester resin has been used in combination with commercial multiwalled carbon nanotubes (MWNTs) to study the effects of this nanofiller on the electrical properties of the mix in the liquid state, during the cure and in the solid state. The level of addition of the nanotubes ranged from 0.05 to 0.3 wt%. The dispersion of the filler particles in the matrix was carried out combining triple roll milling, horn sonication and high shear mixing. Qualitative optical and electronic microscopy characterisation supports the development of novel techniques for real-time quantitative assessments of dispersion quality. Fitting of shear dependent viscosity, measured between 0.1 and 100 s-1, to Carreau's model has been shown to provide an indicator of the state of nanotube dispersion in the mixture. Additionally, liquid electrical conductivity measurements offer the option of on-line monitoring, providing a promising tool for process optimisation. The formation of an effective conductive network of nanotubes during the cure was investigated by combining impedance spectroscopy measurements and equivalent circuit modelling with two parallel RC circuit in series with each other. This allows in-situ observation of the key phenomenon responsible for the electrical conductivity of the nanocomposite, namely the filler re-aggregation during cure. Optimisation of dispersion and cure parameters results in a nanocomposite showing conductive behaviour in the solid state, achieving DC conductivity of 0.13 S/m at 0.30 wt% loading. The percolation threshold was estimated to occur at 0.026 wt% filler loading. The conductivity achieved is comparable to state-ofthe-art epoxy thermosetting nanocomposites based on use of carbon nanotubes of equivalent quality. Successful laboratory scale trials demonstrated the suitability of the materials in copper electroplating and resistance heating. An industrial scale up trial of a 40 kg batch was carried out, using the dispersion and the monitoring techniques developed in the study.

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