Efficient non-linear 3D electrical tomography reconstruction

Non-linear electrical tomography imaging can be performed efficiently if certain optimisations are applied to the computational reconstruction process. We present a 3D non-linear reconstruction algorithm based on a regularized conjugate gradient solver and discuss the optimisations which we incorporated to allow for an efficient and accurate reconstruction. In particular, the application of image smoothness constraints or other regularization techniques and auto-adaptive mesh refinement are highly relevant. We demonstrate the results of applying this algorithm to the reconstruction of a simulated material distribution in a cubic volume

Optimal finite element modelling and efficient reconstruction in non-linear 3D electrical resistance tomography

Electrical Impedance Tomography can provide images with well-defined characteristics using a fully non-linear reconstruction process when appropriate constraints are imposed on the solution to allow the ill-posed inverse problem to be solved. Using appropriate finite element discretizations for forward solution and inverse problem offers additional advantages in the image reconstruction process, such as (a) inclusion of prior knowledge, (b) generic model templating to adapt to, for example, individual head shapes, and (c) obtaining accurate results without unnecessary computational overhead. We have developed an efficient 3D non-linear reconstruction algorithm based on a regularized inverse conjugate gradient solver which incorporates (a) local image smoothness constraints, and (b) a number of optimisations which reduce the computing power required to obtain an accurate solution. We show results from applying this to various problems which arise in medical resistivity reconstruction given only surface potential measurements and demonstrate the importance of the FE discretization. Keywords: 3D non-linear electrical impedance tomography, FE template modelling, optimal finite element meshes, 3D visualization, FE discretization

An Approach to Overloading With Polymorphism

One of the principal characterising features of a programming language is its type system. Many recent functional programming languages adopt a Hindley-Milner style type system facilitating parametric polymorphism. One of the forms of polymorphism found most commonly in programming languages is overloading. Whereas one may consider the Hindley-Milner system an off-the-shelf package for parametric polymorphism, there is no similar uniformity in the approaches taken to overloading. This thesis extends the standard Hindley-Milner system. A type system incorporating parametric polymorphism and overloading is presented both formally and informally, and it is shown to satisfy a principal type theorem. The Hindley-Milner type inference algorithm is extended for the new system. This algorithm is shown to be sound and complete. The characteristic feature of parametric polymorphism is that the same code can be used at many different types. The corresponding characterisation rule for overloading is that different code is used at different types. As such, meaning is assigned to terms on the basis of their typing. The semantics of the form of overloading described herein is assigned by means of a derivation to derivation translation scheme. This scheme is shown to be sound and, under certain well-defined conditions, coherent. This approach to overloading is closely related to the lazy functional programming language Haskell's type class mechanism. Some discussion of matters related to the current system, and arising through that project, is given

Essays in Labor Economics

The three chapters of this dissertation are closely related to one another and pertain to work flexibility. The first chapter uses an occupational choice model to estimate how workers value schedule flexibility in terms of other on the job characteristics. The second chapter also estimates how workers value flexibility using a hedonic wage approach. This method provides an estimate of how workers value schedule flexibility in terms of real wages. In the third chapter I estimate the impact of family structure on the probability that men choose a flexible job. Flexible work schedules are becoming an increasingly important characteristic for one\u27s occupational choice. I examine the effect of flexible work schedules on college graduates\u27 occupational choice. Over the past 30 years flexible work schedules have become more prevalent in the work place to help employees balance work and family lives. The United States\u27 government is advocating flexible work schedules in order to promote gender equality for men and women\u27s occupational distribution. I estimate an occupational choice model with over 200 occupations using Census data for 1980, 1990, and 2000. Both men and women college graduates are attracted to jobs with flexible work hours, but in terms of marginal rate of substitution men are willing to sacrifice increasingly more safety on the job to obtain flexible schedules relative to women. Further, married individuals have become increasingly attracted to flexible work hours in terms of MRS; however, single mothers now value flexible work hours relative to safety less compared to 1980. The hedonic wage model finds similar results to the occupational choice model. The results suggest that men and women value schedule flexibility differently and that workers in high and low skilled occupations value flexibility differently. Looking at men and women aggregated by occupational skill level there is little difference between the value men and women place on flexibility due the relatively large size of the standard errors on the estimated marginal willingness to pay. Women are willing to sacrifice approximately 1% of wages to obtain flexibility and men are willing to sacrifice 2% of wages. The difference between men and women becomes starker when examining differences in occupational skill level. There is the peculiar result that men in low skilled occupations must be compensated to take on flexible schedules. In theory workers need not be compensated for schedule flexibility because if it is undesired characteristics workers do not to utilize the flexibility and thus would be unwilling to sacrifice wages. Men in high skilled occupations value schedule flexibility more than women. These results are consistent with the results from the occupational choice model which also showed that men were more willing to sacrifice physical safety on the job to obtain flexibility. Lastly, in the occupational choice model I find that married value flexibility relatively more compared to other demographic groups. On an intuitive level it makes sense that men with working spouses would be more likely to choose jobs with flexible schedules. Families may wish to be able to coordinate their schedules in order to better balance their work and personal lives. It also provides an opportunity for individuals to take off from work if something unexpected arises. Family structure is an important determinant in the occupational choice model and how individuals value flexible schedules. I find that having a working spouse increases the probability of choosing a job with schedule flexibility by 1-6 percentage points depending on the specification

On the use of clustering and the MeSH controlled vocabulary to improve MEDLINE abstract search

Databases of genomic documents contain substantial amounts of structured information in addition to the texts of titles and abstracts. Unstructured information retrieval techniques fail to take advantage of the structured information available. This paper describes a technique to improve upon traditional retrieval methods by clustering the retrieval result set into two distinct clusters using additional structural information. Our hypothesis is that the relevant documents are to be found in the tightest cluster of the two, as suggested by van Rijsbergen's cluster hypothesis. We present an experimental evaluation of these ideas based on the relevance judgments of the 2004 TREC workshop Genomics track, and the CLUTO software clustering package

Down the garden-path and back again: Factors contributing to successful recovery from ambiguity-related misinterpretations

For most adults, understanding the meaning of words and sentences seems like an easy task. However, misinterpretations are common. More than 80% of common English words have more than one meaning – even the word “abstract” is ambiguous. The pervasiveness of ambiguity means that selecting appropriate word meanings is a fundamental skill for readers. But what happens when the language processing system selects the wrong meaning? Sentences like “The plant had been difficult to build” lead readers down a metaphorical “garden path” in interpretation: because they are likely to initially select the meaning of “plant” that first comes to mind (“botanical organism”), readers need to initiate appropriate reinterpretation processes once they realise that this meaning is not compatible with “build”. This thesis addresses two gaps in the literature on the recovery from such misinterpretations: Are the processing costs that comprehenders experience when they need to reinterpret a sentence consistent across a) tasks or stimulus presentation formats with different processing demands, and b) individuals? Results from the present thesis revealed that readers initiated reinterpretation procedures at an earlier point during processing when an explicit task required them to understand the sentence in detail (Chapter 4). Additionally, reinterpretation costs to brain responses were found to be exaggerated in a visual word-by-word presentation format compared with listening or whole-sentence reading (Chapter 5). Individual differences investigations showed that readers with greater vocabulary knowledge tended to be more sensitive to errors in processing, and able to adapt their reading behaviour on-line (Chapters 2 and 3). These findings support theories that view language experience and the development of robust knowledge structures as central to language processing, and highlight the importance for both theorists and experimentalists to carefully consider the influence of task-related and format-related processing demands on processing behaviour and comprehension

The Influence of the “Memorandum” of the Most Rev. Philip Carrington, Archbishop of Quebec, in Revising the Liturgy of the Book of Common Prayer 1959 Canada

In 1943 the Anglican Church of Canada began to revise its Prayer Book. The central matter, the real reason for the undertaking, was the revision of the Eucharist. In 1952 the revised Eucharistic Rite was presented to the Church, and comments solicited. A year later, in a memorandum sent to all members, The Most Rev. Philip Carrington, Archbishop of the Ecclesiastical Province of Canada and Bishop of the Diocese of Quebec, a prominent member of the General Committee on Revision of the Book of Common Prayer, wrote that the revised Rite had been “very successful in creating public interest and in eliciting criticisms and suggestions.” That was putting as good a face on things as possible. The plain truth was that, after long preparation and careful consideration, the revisers felt that in the 1952 Rite they had done their best. The largely negative reaction to their work left them shaken and uncertain as to what direction they should take next. But one thing was certain in the tense situation created by the 1952 Rite: they must not seem to be responding to one criticism above another, or giving way to pressure from one group or another. Into this dilemma came Carrington’s Memorandum: a policy statement which outlined a purposeful new approach, and which was reinforced by the acceptance of his ideas of rising nationalism and new political alignments emerging out of World War II, the message was to strengthen the unity of the world-wide Anglican Communion by a spiritual bond manifested in a commonly distinguishable pattern of worship. As a result of Carrington’s initiative, the Canadian revisers began to re-work the 1952 Rite, using his suggestions and the related models in other Anglican liturgies. In the end they produced a Rite which took its place as one of the contemporary family of liturgies by which various branches of the Anglican Communion were mutually identifiable in a common pattern of Christian life. But it was Archbishop Carrington’s theory of the nature of the Prayer Book in the Anglican Communion, and his concrete proposals for the Rite, which were fundamental in making their achievement possible