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<p>Successful navigation requires an accurate mental spatial representation of the environment that can be updated during movement. Experiments with animals and humans have demonstrated the existence of two forms of spatial representation: egocentric (observer-centered) and allocentric (environment-centered). Unfortunately, specifically how humans use these two systems is not well understood. The current dissertation was focused on providing evidence differentiating human use of egocentric and allocentric spatial reference frames, specifically examining the characteristics and contributions from body-based sources. Two empirical chapters are presented that include experiments involving two common spatial tasks. In Chapter 2, updating of feature relations within a room-sized environment was examined by having observers provide directional judgments to learned features with respect to an imagined orientation that was either congruent or incongruent with their physical orientation. The information available for updating the physical orientation was manipulated across experiments. Performance differences between congruent and incongruent conditions demonstrated the reliance on egocentric representations for updating, and differentiated body- and knowledge-based components of the egocentric updating process. The specificity of the body-based component was examined in Chapter 3 by having observers detect changes made to a tabletop spatial scene following a viewpoint shift resulting from their movement, scene rotation or both. The relation between the extent of observer movement and the magnitude of the experienced viewpoint shift was manipulated. Change detection performance was best when the extent of observer movement most closely matched the viewpoint shift, and declined as the match declined. Thus, body-based cues contributed specific information for updating self-to-feature relations that facilitated scene recognition. Throughout the course of the research program it has become clear that humans rely on egocentric representations to complete these tasks, and sensory and motor modalities involved in self-motion are integrated for updating spatial relations of novel environments.</p> / Doctor of Philosophy (PhD)

<p> In this thesis we mainly give a characterization of dual frames of Gabor subspace frames. We give necessary and sufficient conditions for the existence and the uniqueness of a function h (called window) in the closed linear span of a Gabor subspace frame {EmbTnak}m,n∈Z such that the Bessel collection {EmbTnah}m,n∈Z serves as the dual frame of the original frame {EmbTnag}m,n∈Z. We solve the problem for three cases, first ab = 1, second ab = p ∈ N, and third ab = p/q, gcd(p, q) = 1. In each case, we first find the conditions for upper frame bound (known as Bessel collection). Secondly, we characterize the functions which are orthogonal to {EmbTnag}m,n∈Z in terms of the Zak transform, and then obtain necessary and sufficient conditions for lower frame bound. Here we state obtained conditions for normalized tight frame as a corollary. Finally, using all this information we solve the duality problem.</p> / Thesis / Master of Science (MSc)

Resource withdrawal from unnecessary medical services is an important issue as the cost of health care continues to rise. In many countries, resource withdrawal is primarily determined by government policies that remove, restrict, reduce, or limit the availability of publically insured medical services. Ideally, resource withdrawal is the result of a careful assessment of clinical and economic evidence regarding a service’s safety and effectiveness in order to ensure that it is the most efficient use of resources. Despite advocacy for a routinized and systematic approach to the withdrawal of resources from medical services, research has indicated that political and social factors often influence government, resulting in decisions that are neither consistent nor transparent. In this dissertation I seek to understand factors that may influence resource withdrawal decisions in an attempt to promote a more routinized and systematic approach. In order to understand the resource withdrawal landscape and provide greater conceptual clarity, the first study in this dissertation identifies and explores its characteristics (antecedents, attributes, and outcomes). Definitions of two prominent terms, disinvestment, and rationing are proposed. In the second study, a qualitative analysis of two examples of resource withdrawal reveals how the characteristics of problem frames affect the shape and timing of government resource withdrawal policies. Findings support the proposition that the complexity of the story told within the problem frame affects the shape of the policy; while visibility affects the timing. In the third study, I analyzed the perspectives of key informants about the Choosing Wisely Canada (CWC) campaign, which has the aim of reducing unnecessary services by encouraging a discussion between physician and patient. Findings reveal that CWC was designed to address pressures from government, patients, and the public. However, CWC was not designed in a way that is expected to address the underlying reasons unnecessary services are provided, including limited time in the clinical encounter, patient demands, uncertainty in the care pathway, and physician fear of litigation. Results from all three studies help establish a common language, identify influences on government led resource withdrawal and reasons why CWC is unlikely to reduce unnecessary services. Together this thesis provides insights into some of the factors affecting resource withdrawal from medical services, and findings may be used to help assess ways to improve the formulation of resource withdrawal policies. / Dissertation / Doctor of Philosophy (PhD) / Currently several governments pay for unnecessary medical services, leading to suboptimal patient health outcomes and a waste of public resources. Several researchers and organizations have proposed methods to identify and assess medical services to determine if they are unnecessary; however, governments have been slow to adopt such methods on a routine basis. It is clear that evidence is rarely sufficient to motivate governments to withdraw resources from unnecessary medical services. Instead, governments are often influenced by social and political factors when they make such decisions. Through a better understanding of these factors, we may be able to find ways to incorporate evidence into governments’ decisions to withdraw resources from medical services. Qualitative methods were used to investigate how resource withdrawal is defined, factors influencing government resource withdrawal decisions in Ontario, and the effectiveness of Choosing Wisely Canada, an initiative led by the medical community to reduce unnecessary services.

No / This study explores the lateral deflections of diagonal braces in concentrically-braced earthquake-resisting frames. The performance of this widely-used system is often compromised by the flexural buckling of slender braces in compression. In addition to reducing the compressive resistance, buckling may also cause these members to undergo sizeable lateral deflections which could damage surrounding structural components. Different approaches have been used in the past to predict the mid-length lateral deflections of cyclically loaded steel braces based on their theoretical deformed geometry or by using experimental data. Expressions have been proposed relating the mid-length lateral deflection to the axial displacement ductility of the member. Recent experiments were conducted on hollow and concrete-filled circular hollow section (CHS) braces of different lengths under cyclic loading. Very slender, concrete-filled tubular braces exhibited a highly ductile response, undergoing large axial displacements prior to failure. The presence of concrete infill did not influence the magnitude of lateral deflection in relation to the axial displacement, but did increase the number of cycles endured and the maximum axial displacement achieved. The corresponding lateral deflections exceeded the deflections observed in the majority of the previous experiments that were considered. Consequently, predictive expressions from previous research did not accurately predict the mid-height lateral deflections of these CHS members. Mid-length lateral deflections were found to be influenced by the member non-dimensional slenderness ( ) and hence a new expression was proposed for the lateral deflection in terms of member slenderness and axial displacement ductility. / TATA Steel

No / This paper presents the results of a simulation study of 10 fire tests on restrained steel beam–column assemblies using five different types of joints: fin plate, flexible endplate, flush endplate, web cleat and extended endplate. This paper will provide details of the simulation methodology for achieving numerical stability and faithful representation of detailed structural behaviour, and compare the simulation and experimental results, including joint failure modes, measured beam axial forces and beam mid-span deflections. Good agreement between ABAQUS simulations and experimental observations confirms that the finite element models developed through the ABAQUS/Standard solver are suitable for predicting the structural fire behaviour of restrained structural assemblies with realistic steel joints undergoing different phases of behaviour in fire, including restrained thermal expansion and catenary action in the beams. The validated model may be used to conduct numerical parametric studies to generate theoretical data to help develop detailed understanding of steel joint behaviour and their effects on robustness of steel framed structures in fire.

Spatial collaboration refers to collaboration activities involving physical space. It occurs every day as people work together to solve spatial problems, such as rearranging furniture or communicating about an environmental issue. In this work, we investigate how to support spatial collaboration when the collaborators are not colocated. We propose using shared, interactive representations of the space to support distributed, spatial collaboration. Our study examines viewpoint constraint techniques, which determine how the collaborators individually view the representation, and awareness techniques, which enable the collaborators to maintain an understanding of each other's work efforts. Our work consists of four phases, in which we explore a design space for interactive representations and examine the effects of different viewpoint constraint and awareness techniques. We consider situations where the collaborators use the same viewpoints, different viewpoints, and have a choice in viewpoint constraint techniques. In phase 1, we examine current technological support for spatial collaboration and designed two early prototypes. Phase 2 compares various two-dimensional map techniques, with the collaborators using identical techniques. Phase 3 focuses on three-dimensional virtual environment techniques, comparing similar and different frames of reference. The final phase reuses the favorable techniques from the previous studies and presents a novel prototype that combines both two-dimensional and three-dimensional representations. Each phase of this research is limited to synchronous communication activities and non-professional users working together on everyday tasks. Our findings highlight the advantages and disadvantages of the different techniques for spatial collaboration solutions. Also, having conducted multiple evaluations of spatial collaboration prototypes, we offer a common set of lessons with respect to distributed, spatial collaboration activities. This research also highlights the need for continued study to improve on the techniques evaluated and to consider additional spatial collaboration activities. / Ph. D.

A well structured computer program has been developed to implement and compare two models for geometrically nonlinear finite element analysis of plane frames. One model is developed using classical beam-column theory, and the other is formulated using standard finite element techniques. The beam-column model is shown to converge to a more accurate equilibrium path using less elements to model a structure than the second model for frames. The models are also compared on the basis of their limitations and on the basis of the degree of difficulty for their implementation. The modified Riks/Wempner method is used to perform postbuckling analysis and to study the effect of varying the composition of the tangent stiffness matrix on its ability to detect instability. The importance of including all contributions in the incrementation of a model derived using convected coordinates is also studied. / M.S.