Regular graphs with four eigenvalues

AbstractWe study the connected regular graphs with four distinct eigenvalues. Properties and feasibility conditions of the eigenvalues are found. Several examples, constructions and characterizations are given, as well as some uniqueness and nonexistence results

Sequencing Interval Situations and Related Games

In this paper we consider one-machine sequencing situations with interval data. We present different possible scenarioes and extend classical results on well known rules and on sequencing games to the interval setting

Transcriptional Control of the Human Aggrecan Gene

Osteoarthritis (OA) is a degenerative joint disease and is the leading cause of physical disability in industrialised nations. Cartilage has received the most attention in the study of OA due to articular chondrocytes acting as potential instigators of disease. These cells are responsible for the anabolic-catabolic balance required for matrix maintenance due to their ability to synthesise the structural components of the extra-cellular matrix along with matrix-degrading proteases. In order to better understand the mechanism by which this balance is shifted in OA, it would be useful to investigate the roles of the genes that are expressed in these cells. One of the most powerful tools to do this would be an inducible and chondrocyte-specific system that utilises a cartilage-specific promoter, such as the aggrecan promoter. Aggrecan, one of the major structural components of cartilage, is a large aggregating chondroitin sulphate proteoglycan. This PhD set out to further our understanding of the transcriptional regulatory mechanisms that govern the chondrocyte-specific expression of the gene. A series of constructs containing various combinations of non-coding aggrecan DNA (mostly upstream of the transcriptional start site and including the first untranslated exon) were used to generate transgenic mouse embryos and an adult line in which the cartilage-specific expression of the transgene indicated the presence of cis-regulatory elements. These studies have identified three putatively important regions. One serves as a basal/core promoter at and around the transcriptional start site (TSS) (containing what could possibly be a non-essential 92bp sequence depending on the developmental stage of the mouse). Another located 10kb upstream of the TSS can serve as an enhancer, and finally another located within a 7kb region further upstream. One or more of these elements seem to respond to injury as indicated by increased promoter activity in the OA-induced knees of the adult line containing all three regulatory regions. Using a combination of our data alongside published work (Han and Lefebvre, 2008), a cartilage-specific Cre recombinase line was generated and tested for specificity and continual gene expression under the induction of OA. The work presented in this thesis can now be used to contribute to knowledge on the pathogenesis of OA

Radiation exposure in X-ray-based imaging techniques used in osteoporosis

Recent advances in medical X-ray imaging have enabled the development of new techniques capable of assessing not only bone quantity but also structure. This article provides (a) a brief review of the current X-ray methods used for quantitative assessment of the skeleton, (b) data on the levels of radiation exposure associated with these methods and (c) information about radiation safety issues. Radiation doses associated with dual-energy X-ray absorptiometry are very low. However, as with any X-ray imaging technique, each particular examination must always be clinically justified. When an examination is justified, the emphasis must be on dose optimisation of imaging protocols. Dose optimisation is more important for paediatric examinations because children are more vulnerable to radiation than adults. Methods based on multi-detector CT (MDCT) are associated with higher radiation doses. New 3D volumetric hip and spine quantitative computed tomography (QCT) techniques and high-resolution MDCT for evaluation of bone structure deliver doses to patients from 1 to 3 mSv. Low-dose protocols are needed to reduce radiation exposure from these methods and minimise associated health risks

SUMS OF SQUARES, MOMENT MATRICES AND OPTIMIZATION OVER POLYNOMIALS

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Analyticity: an unfinished business in possible-world semantics

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Essays on partial retirement

The five essays in this dissertation address a range of topics in the micro-economic literature on partial retirement. The focus is on the labor market behavior of older age groups. The essays examine the economic and non-economic determinants of partial retirement behavior, the effect of partial retirement on retirement income and health, and the factors that could limit workers to participate in partial retirement. The analysis is mainly empirical and makes use of survey data on actual retirement opportunities and retirement decisions, but also on stated preferences concerning abrupt and partial retirement scenarios. The data are collected in the United States and the Netherlands through national surveys and through a web-based questionnaire specifically designed for the stated preference analysis. The empirical analysis relies on micro-econometric methods of discrete choice to estimate the empirical relationships between the variables of interest. In the analysis throughout the dissertation, while the main interest lies in partial retirement, the alternative abrupt full retirement scenario is also examined. Other alternative exit routes such as unemployment or disability are not analyzed in this dissertation

Marginal models for categorical data

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An Iterative Procedure for Evaluating Digraph Competitions

A competition which is based on the results of (partial) pairwise comparisons can be modelled by means of a directed graph. Given initial weights on the nodes in such digraph competitions, we view the measurement of the importance (i.e., the cardinal ranking) of the nodes as an allocation problem where we redistribute the initial weights on the basis of insights from cooperative game theory. After describing the resulting procedure of redistributing the initial weights, we describe an iterative process is described which repeats this procedure: at each step the allocation obtained in the previous step determines the new input weights. Existence and uniqueness of the limit is established for arbitrary digraphs. Applications to the evaluation of e.g. sport competitions and paired comparison experiments are discussed

1Bounds on Metamaterials — Experimental Results

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