As the feature sizes in VLSI technology shrink to less than 100 nm the effects due to the quantisation of electronic charge begin to emerge. There are a small number of carriers and impurities and the statistical variation in their number have significant effects on the threshold characteristics of the devices that hamper their large scale integration into future ULSI.The complex potential landscape arising from the Coulomb force, with its sharp localised peaks and troughs, faces problems due to band limiting in meshes and places heavy burdens on the integration techniques. A computationally efficient solution to the problem of band-limiting is presented and is shown to provide an accurate description of the electrostatics. This work also introduces a highly efficient and numerically stable multigrid solver, for Poisson's equation, that can cope with the complex potential distributions on large meshes. The study of ionised impurity scattering is used to validate these molecular dynamics simulations. Results have shown that the Brownian method - despite precluding the use of adaptive integration schemes - gives a good approximation to the standard results and has the advantage of smoothing away errors that can build up during the integration of motion and drives the system towards thermal equilibrium. The greatest hurdle to be cleared before these three-dimensional simulations can be practicable is the sheer computational effort that is required. The implementation of the problem on parallel architectures has been explored and discussed. The methods developed in this work are demonstrated through the simulation of an 80 nm dual-gate MESFET. The results were verified by comparing them with those from a commercial drift-diffusion simulator. The threshold behaviour of devices has been investigated through the study of the formation of conduction channels in blocks. The percolation threshold gives the point when conductive paths form across the gate barrier. The results from the FET simulation were found to be in agreement with the earlier studies on the blocks.

This thesis investigates analogy as a paradigm for retrieving, understanding and customising reusable specifications during requirements engineering. Cooperation between software engineers and support tools is necessary for effective analogical reuse. Retrieval uses a computational implementation of analogical reasoning to search and match many reusable specifications. On the other hand understanding, transferring and adapting specifications requires cooperation between the tool and software engineer. Cooperative support was designed for less-experienced software engineers with most to gain from successful specification reuse. Deliverables from this research have implications for software engineering, artificial intelligence, cognitive science and human-computer interaction. Specification retrieval is founded on a framework of software engineering analogies. This framework includes a set of domain abstractions describing key facts about software engineering domains. A computational model of analogical reasoning which matches domain descriptions to these abstractions was designed, implemented and evaluated during user studies with a prototype reuse advisor. An intelligent dialogue acts as a front-end to this retrieval mechanism by acquiring key domain facts prior to retrieving domain abstractions. This dialogue was designed from empirical studies of software engineering behaviour during requirements capture and modelling. Design of support tools for specification understanding and transfer was based on cognitive task and reasoning models of software engineering behaviour during analogical reuse and mental models of analogical understanding. Two empirical studies of inexperienced software engineers identified problematic mental laziness manifest as specification copying. A third study of expert software engineers who successfully reused specifications identified strategies for effective reuse. Detailed findings from all three studies informed the design of tool-based support for specification understanding and transfer. Findings also have implications for the design of tools to support other requirements engineering activities.

The development of a statistical compact model strategy for nano-scale CMOS transistors is presented in this thesis. Statistical variability which arises from the discreteness of charge and granularity of matter plays an important role in scaling of nano CMOS transistors especially in sub 50nm technology nodes. In order to achieve reasonable performance and yield in contemporary CMOS designs, the statistical variability that affects the circuit/system performance and yield must be accurately represented by the industry standard compact models. As a starting point, predictive 3D simulation of an ensemble of 1000 microscopically different 35nm gate length transistors is carried out to characterize the impact of statistical variability on the device characteristics. PSP, an advanced surface potential compact model that is selected as the next generation industry standard compact model, is targeted in this study. There are two challenges in development of a statistical compact model strategy. The first challenge is related to the selection of a small subset of statistical compact model parameters from the large number of compact model parameters. We propose a strategy to select 7 parameters from PSP to capture the impact of statistical variability on current-voltage characteristics. These 7 parameters are used in statistical parameter extraction with an average RMS error of less than 2.5% crossing the whole operation region of the simulated transistors. Moreover, the accuracy of statistical compact model extraction strategy in reproducing the MOSFET electrical figures of merit is studied in detail. The results of the statistical compact model extraction are used for statistical circuit simulation of a CMOS inverter under different input-output conditions and different number of statistical parameters. The second challenge in the development of statistical compact model strategy is associated with statistical generation of parameters preserving the distribution and correlation of the directly extracted parameters. By using advanced statistical methods such as principal component analysis and nonlinear power method, the accuracy of parameter generation is evaluated and compared to directly extracted parameter sets. Finally, an extension of the PSP statistical compact model strategy to different channel width/length devices is presented. The statistical trends of parameters and figures of merit versus channel width/length are characterized.

London Black Cab Drivers have a rich and documented history of mobile work practices that are geographically distributed and driven by situated choices for everyday work. To date mobile studies researchers have not made a close examination of these mobile working practices, hence there is a gap in mobile studies concerning this type of worker. This dissertation aims to study the evolution of Black Cab drivers' work practices since the introduction of mobile Information and Communication Technology (mICT) in their everyday work. The theoretical framework for the research is based on studies of taxi drivers' work practices, mobility research, computer supported co-operative work and organisational change promoted by IS interventions. The ontology of this research pinpoints the factors influencing the situated and idiosyncratic choice associated with the use of mICTs when carrying out planned and unplanned work. The case study references a 420-year history of "old", established work practices as a comparison framework. When compared with the "new" and situated choice of mICT-supported work, it becomes apparent that there has been a change in the dynamics of how this type of work is actually completed. Embedding and mixing elements of self-referenced work - as discretionary and independent - with working practices in which mutual interdependencies are supported by the use of mICT aids seems to provide the case for a re-negotiation of the working practices model as well as its associated organisational forms, together with a social shift in the definition of the role and skills required to perform this type of mobile work. The empirical data have been sourced from one-to-one interviews and video recordings using a combination of ethnographic methods and interpretative approaches for the data analysis. This dissertation makes a theoretical and practical contribution to mobile studies by understanding the changing of working practices; it further offers methodological insights for studying mICT-supported work. Finally, it provides a formative evaluation of the new organisational forms emerging as mICT has been introduced to everyday Black Cab work.

published_or_final_version / Paediatrics and Adolescent Medicine / Doctoral / Doctor of Philosophy

Influenza A virus infection is a major cause of human morbidity and mortality. T cell immunity is believed to play critical roles for host defenses against influenza A infection. Once intracellular influenza A infection is established, viral clearance is mainly dependent on virus-specific CD8+ T cells. CD4+ T cells are important for adaptive immunity to natural influenza A infection or vaccination by providing help to B cells for antibody production and also providing help to CD8+ T cells for the generation of cytotoxicity. In addition, virusspecific CD4+ and CD8+ T cells are rich sources of effector cytokines, such as IFN-and TNF-, which can promote the function of antigen presenting cells and have direct antiviral activity. Cross-subtype reactive CD4+ and CD8+ memory T cells also affect the clearance of virus infection even in those who lack virus-specific antibodies. Therefore, the aim of our study is to assess the influenza virus-specific T cell responses and define their possible protective role in pandemic H1N1 virus and seasonal influenza infection in human. First we determined whether healthy adults have the cross-reactivity of memory CD4+ and CD8+ T cells against pandemic virus. In April of 2009, 7 pandemic H1N1 infected patients and 17 their healthy contacts who had no pandemic influenza infection were recruited in this study. By using intracellular IFN-staining and flow cytometry, we examined their pandemic H1N1 virus and seasonal influenza H1N1-specific CD4+ and CD8+ T cell responses. Healthy contacts did have measurable but low frequencies of cross-reactive influenza-specific CD4+ and CD8+ T cells, though the frequencies of these T cells specific to pandemic H1N1 virus were slightly lower than that specific to seasonal H1N1 virus. Furthermore, when compared the pandemic H1N1-specific T cell responses between healthy contacts and patients with pandemic H1N1 infection, we can found that the healthy contacts have higher pandemic H1N1 specific-T cell responses than patients, suggesting these pre-existing pandemic H1N1 specific-T cells may have protection from pandemic influenza virus infection. In addition, we conducted a prospective T cell immunity and influenza surveillance study in a cohort of more than 200 healthy volunteers before the influenza season and investigated whether the pre-existing T cell immunity is related to the protection from influenza infection in the next coming influenza season. Using intracellular IFN-staining assay, we examined their pre-existing seasonal influenza H1N1, H3N2, seasonal influenza B virus-specific CD4+ and CD8+ T cell responses. Due to the small number of cases of influenza infection in the coming influenza season, the results only showed a trend that the subjects who have higher frequency of influenza virus strain-specific T cells may have lower chance to suffer from same strain of influenza infection, which to some extent, reflect the pre-exist memory T cells have association with the protection in the coming influenza season. In conclusion, T cells play an important role in defensing against influenza infection. The higher influenza virus specific-T cells response activity in healthy adults may have a protection against influenza virus infection. / published_or_final_version / Paediatrics and Adolescent Medicine / Master / Master of Philosophy

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Diabetes Mellitius is a major chronic disease with multi-organ involvement and high-cost implications. Although it has been demonstrated that structured education can control the risk of developing these complications, there is a substantial room for improvement in the educational services for these patients. E-learning can be a good solution to fill this gap. A system dynamics model was developed in this study to highlight the potential return on investment in these systems.

In this thesis various aspects of the electromagnetic effects influencing the commutation of uncompensated single phase universal motors are investigated. An introduction to the subject as well as a review of significant literature on the subject are given. The literature review includes classical text books about commutator motors as well as more recent publications about the mathematical analysis of the commutation of universal motors. Subsequently, the analysis of the most important inductances of the machine is outlined that comprises the analytical and numerical calculation as well as the measurement of the machine inductances using different measurement techniques. Moreover, a brush model for commutation analysis of small commutator motors is presented. Equivalent circuits of the brush are established for the cases of one coil shorted and two coils shorted by one brush, and a strategy to obtain their elements is proposed. This uses a dedicated finite difference program to calculate the effective brush resistance between all pairs of terminals. The treatment of the boundary conditions is critical in this process. The resulting terminal resistances are regarded as combinations of a set of internal resistances and this nonlinear relationship is inverted to obtain the internal resistors using a modified Newton-Raphson method. Results are presented showing the influence of anisotropy and geometry, and a simplified example of commutation analysis using the model established is given. In the next step the arcing phenomenon in analysed mathematically. Equations are given for the pre-arcing phase, the arcing phase and the post-arc oscillation. Equivalent circuits for the different phases are proposed and the equations are derived strictly from a circuit point of view. In the analysis a constant arc voltage (confirmed by experimental data and literature on the subject) and a minimum uncommutated residual current necessary for arc ignition are assumed. Those quantities are adopted from reviewed literature and used in the calculations. The design of a motor test bench is described that allows to measure the motor performance according to the principle of the reaction dynamometer. The load machine is mounted on air bearings to minimize possible torque errors in the measurements. A measured torque speed characteristic of a universal motor is shown as well as the torque as a function of the motor current. These measurements were carried out at reduced motor voltage to keep the shaft speed within reasonable limits. Furthermore, theoretical and experimental investigations are carried out in order to estimate how strongly certain rotor coils undergoing rapid current changes affect each other due to mutual coupling and how the mutual coupling changes in the presence of a damping field winding. Several FEA simulations are performed in order to get an insight into the flux pattern if rotor coils are acting on each other and the field winding is allowed to impose its damping effect on the rotor coils. Simple AC measurements are performed as well as di/dt - tests using a more complex oscillating circuit for measurements of the change of the di/dt of a rotor coil with and without the presence of an active field winding. Additionally, investigations are carried out in order to analyse the influence of power cord and source impedances on the ability of the field winding of an uncompensated universal motor to damp flux variations caused by the commutation process. The motor is regarded as a harmonic generator with the power cord and the source impedance acting as a load. Rotational tests are carried out with different loads connected to the field winding and the Fourier spectrums of the field voltage are evaluated. In the final stage a simulation model is described that uses deductions from the previous chapters and that simulates the electromagnetic behaviour of the machine including the complex problem of brush commutation. Measured and calculated signals suitable for validation of the model were compared in order to evaluate the accuracy of the model with regard to motor performance and commutation analysis.