In antenna array processing it is generally required to enhance the reception or detection of a signal from a particular direction while suppressing noise and interference signals from other directions. An optimisation problem often posed to achieve this result is to minimise the array processor mean output power (or variance) subject to a fixed response in the array look direction. The look direction requirement can be met by imposing a set of linear constraints on the processor weights to yield what is known as the Linearly Constrained Minimum Variance (LCMV) processor. It has been found, however, that LCMV processors are susceptible to errors in the assumed direction of arrival of the desired signal. To achieve robustness against directional mismatch, additional constraints known as derivative constraints can be introduced. These constraints force the first and second order spatial derivatives of the array power response in the look direction to zero. However, constraints corresponding to necessary and sufficient (NS) conditions for these spatial derivatives to be zero are in general quadratic, and the resulting weight vector solution space is non-convex. One approach to this complex problem has been to consider conditions which are only sufficient for the spatial derivatives to be zero. Whilst this results in linear constraints, it exhibits certain anomalous behaviour, for example, dependence on the choice of array phase centre.Recent work in the area of derivative constraints has resulted in a method for efficiently solving the non-convex output power minimisation problem with quadratic derivative constraints. The optimisation problem addressed assumes that the input signal statistics and hence the input signal autocorrelation matrix R are known. In practice, R must be estimated from the receiver data.The main contribution of this thesis is the derivation of a ++ / new adaptive algorithm which implements an adaptive array processor with look direction plus 1st and 2nd order NS derivative constraints. The new algorithm is derived from the well-known Recursive Least Squares (RLS) technique but allows linear and quadratic constraints to be incorporated within the recursive framework. The algorithm offers the high performance characteristics associated with RLS methods, namely, fast convergence and high steady-state accuracy. The work encompasses a study of the characteristics of the algorithm in terms of numerical robustness, convergence properties, tracking and computational complexity.The study of the numerical properties of the algorithm has led to the second important contribution of this thesis: the identification of a parameter which is central to the numerical stability of the algorithm in a practical fixed precision environment. We show that this parameter is bounded during stable operation and can therefore be used to detect the onset of numerical instability within the algorithm. In addition, we show how existing techniques can be used to significantly improve the numerical robustness of the algorithm.Another important contribution of the thesis stems from an investigation into the multimodal nature of the quadratic, equality constrained optimisation problem resulting from the use of second order NS derivative constraints. In particular, we show that for a linear antenna array operating under certain conditions, the complex multimodal optimisation problem can be greatly simplified. This has important implications in both optimum and adaptive array signal processing.

This theoretical thesis investigates the effects of communicative constraints within a second language (L2) classroom with the purpose of developing ways of exploiting and modifying these constraints to improve L2 learning. This investigation incorporates the identification of hierarchical structures, teaching and learning practices which constrain L2 learning within the classroom. The hierarchical structures of institutional power relations and the authority of the teacher guide set goals and assessment. However, L2 learners may have different expectations to those of their teachers. Therefore, in the presentation of an understanding of classroom genre, this thesis analyses the inherent logic or common fallacies of thinking and practice within L2 classrooms and further, the individual experience which each L2 learner brings to the classroom situation. This thesis examines classroom constraints which prevent L2 learners from developing an appropriate range of experiences to enable them to participate in authentic social interaction. Cultural, linguistic and educational disciplinary views are engaged in the description of these substantive problems. L2 learners invariably experience difficulties in communication when they interact socially within their L2 culture, outside the classroom. Learners often lack the experience to express self-purpose within cultural genres because previous classroom learning may have been based upon situation-specific and context-determined patterns of communication and practice. Such patterns and practices are an inherent part of the classroom because the classroom is a specific genre itself and consequently classroom talk is very different from talk in other places. This thesis develops alternative hypotheses which incorporate critical findings pertaining to L2 classroom practices. Further, a project for realistic solutions to L2 learning is offered. These solutions have been developed from the recognition that learning a L2 in a classroom-based situation is a process which lacks the diversity of everyday societal life.

A virtual holonomic constraint (VHC) for an Euler-Lagrange Control System is a smooth relation between the configuration variables that can be made invariant through application of suitable feedback. In this thesis we investigate the role played by VHCs in the synchronization of Euler-Lagrange systems. We focus on two problems. For $N$ underactuated cart-pendulums, we design a smooth feedback that fully synchronizes the cart-pendulums while simultaneously stabilizing a periodic orbit corresponding to a desired oscillation for the pendulums. A by-product of our results is the ability to simultaneously synchronize the pendulums and stabilize the unstable upright equilibrium. The second synchronization problem investigated in this thesis is bilateral teleoperation, whereby a master robot is operated by a human while a slave robot synchronizes to the master. For two identical planar manipulators, we develop a methodology to achieve teleoperation in the presence of a hard surface, with simultaneous force control.

A virtual holonomic constraint (VHC) for an Euler-Lagrange Control System is a smooth relation between the configuration variables that can be made invariant through application of suitable feedback. In this thesis we investigate the role played by VHCs in the synchronization of Euler-Lagrange systems. We focus on two problems. For $N$ underactuated cart-pendulums, we design a smooth feedback that fully synchronizes the cart-pendulums while simultaneously stabilizing a periodic orbit corresponding to a desired oscillation for the pendulums. A by-product of our results is the ability to simultaneously synchronize the pendulums and stabilize the unstable upright equilibrium. The second synchronization problem investigated in this thesis is bilateral teleoperation, whereby a master robot is operated by a human while a slave robot synchronizes to the master. For two identical planar manipulators, we develop a methodology to achieve teleoperation in the presence of a hard surface, with simultaneous force control.

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The purpose of this study was to identify benefits and constraints associated with the use of urban parks by a sample of elderly in Hong Kong. Before studying these topics, self-perception of aging of the elderly in Hong Kong was explored. In-depth interviews were conducted with 13 individuals inside and 12 outside the Tsuen Wan Jockey Club Tak Wah Park. Purposive sampling was used to select the sample. The interviews were semi-structured, based on an interview guide of open-ended questions. Results of the study suggested that although there are some differences in explanations of aging among different countries, some aging models and theories which have been developed in western countries can be employed to interpret the aging phenomenon in Hong Kong. Several constraints and health-related social and psychological benefits of attending a park were reported by the sample. Heterogeneity of leisure constraints among different age cohorts of the elderly was found in the study. Although similarities were found between the benefits reported in this study and those reported in western countries, the magnitude of benefits received from visiting parks may be different because of the different characteristics of elderly in different countries.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 139-149). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 139-149). Also available on the Internet.

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