Approximation Algorithms for Geometric Networks

The main contribution of this thesis is approximation algorithms for several computational geometry problems. The underlying structure for most of the problems studied is a geometric network. A geometric network is, in its abstract form, a set of vertices, pairwise connected with an edge, such that the weight of this connecting edge is the Euclidean distance between the pair of points connected. Such a network may be used to represent a multitude of real-life structures, such as, for example, a set of cities connected with roads. Considering the case that a specific network is given, we study three separate problems. In the first problem we consider the case of interconnected `islands' of well-connected networks, in which shortest paths are computed. In the second problem the input network is a triangulation. We efficiently simplify this triangulation using edge contractions. Finally, we consider individual movement trajectories representing, for example, wild animals where we compute leadership individuals. Next, we consider the case that only a set of vertices is given, and the aim is to actually construct a network. We consider two such problems. In the first one we compute a partition of the vertices into several subsets where, considering the minimum spanning tree (MST) for each subset, we aim to minimize the largest MST. The other problem is to construct a $t$-spanner of low weight fast and simple. We do this by first extending the so-called gap theorem. In addition to the above geometric network problems we also study a problem where we aim to place a set of different sized rectangles, such that the area of their corresponding bounding box is minimized, and such that a grid may be placed over the rectangles. The grid should not intersect any rectangle, and each cell of the grid should contain at most one rectangle. All studied problems are such that they do not easily allow computation of optimal solutions in a feasible time. Instead we consider approximation algorithms, where near-optimal solutions are produced in polynomial time. In addition to the above geometric network problems we also study a problem where we aim to place a set of different sized rectangles, such that the area of their corresponding bounding box is minimized, and such that a grid may be placed over the rectangles. The grid should not intersect any rectangle, and each cell of the grid should contain at most one rectangle. All studied problems are such that they do not easily allow computation of optimal solutions in a feasible time. Instead we consider approximation algorithms, where near-optimal solutions are produced in polynomial time

Search for the electroweak production of supersymmetric particles in three-lepton events at the ATLAS detector with focus on compressed mass spectra

This thesis presents a search for the electroweak production of supersymmetry using the dataset taken by the ATLAS detector at the Large Hadron Collider with √8 = 8 TeV during 2012. Events with three leptons are selected and required to satisfy additional kinematic criteria that define optimised signal regions. In these signal regions, Standard Model processes are discriminated against, whilst retaining a large fraction of events produced by specified compressed supersymmetry scenarios. Compressed refers to near massdegeneracy between the decaying gauginos and the final state gauginos. The expected number of Standard Model events are estimated using a combination of Monte Carlo and data-driven methods, where the predictions are tested against data in specifically designed validation regions. Exclusion limits are then set at 95% confidence level (CL) on via ℓ`L- and via WZ-decay scenarios for the decaying charginos and neutralinos. With the ℓ`L halfway between the decaying charginos and neutralinos and the final state neutralinos, there is a new sensitivity up to 250 GeV. In scenarios with large mass splitting, the decaying chargino and neutralino masses are excluded up to 740 GeV. Looking forward to the 13 TeV data-taking, a search for the electroweak production of supersymmetry with threelepton final states is presented, with a first look at an optimisation strategy to improve sensitivity to charginos and neutralinos

Development, validation and implementation of a novel dietary salt monitor in type 2 diabetes in UK

The risk of cardiovascular morbidity and mortality increases manyfold in Type 2 diabetes, owing to the higher prevalence rates of hypertension. The role of dietary salt intake has been well established in the prevention and management of high blood pressure. However, there is paucity of research interventions and education programme aimed at lowering dietary salt intake in type 2 diabetic population. The aim of this research study is to develop, validate and implement the use of ‘dietary salt monitor’ for reducing dietary salt intake in participants with Type 2 diabetes. A 24h dietary recall using multiple pass recall method was obtained from the participants with type 2 diabetes and concomitant hypertension (n=50), attending outpatient diabetic foot clinic at NHS hospital in Basildon, Essex. More than a quarter of the participants (28%) consumed salt above the recommended daily limit of <6g. The top ten contributors of salt identified using pivot tables were bread and rolls, processed meats, added salt, ready meals, meat dishes, spreading fats, canned beans, soups, cheese, and sandwiches. An interviewer-administered questionnaire captured the knowledge, attitudes, and practices (KAP) related to dietary salt intake and showed a mean KAP score for the group as 22.6 (SD 6.1) against a maximum achievable score of 40. Poor perception of one’s salt intake; non-practice of reading salt content on nutrition label, frequent addition of salt to food and lack of understanding on daily salt limit and food sources of salt were identified as potential barriers in adherence to the recommended salt intake. The dietary data of these type 2 diabetic participants was further analysed for the development of a novel ‘dietary salt monitor’. It included a short list of 23 food categories that were carefully identified based on its salt density, contribution of salt to the diet, non - achievement of 2017 salt targets, challenges faced by food industry for further salt reduction, foods unrecognised as high in salt by consumers, sustainability, change in cooking practices during COVID-19 and overall nutritional composition of the food category, to fulfil its role as an educational intervention. The dietary salt monitor was validated against 24h urinary excretions and food records gathered from university students. The Bland and Altman method for agreement between dietary salt monitor and urinary sodium excretion method suggested a bias of 1.5g/ d (upper LOA 7.68 and lower LOA -4.72). The results for cross classification between this tool and urinary biomarker suggested a low level of misclassification (n=1, 11%), but it varied at individual level. The effectiveness of this dietary salt monitor was pilot tested in an online nutrition education intervention, where type 2 diabetes participants (n=22) were recruited from various online platforms including the Diabetes UK website. This dietary salt monitor was integrated in a web form and supported by a short educational video highlighting the salt content of the food categories and key strategies as ‘4R’s - Reducing portion, Reducing frequent intake, Reduced salt food, Read nutrition label, for lowering salt intake. This short-term intervention study (6 weeks) resulted in a statistically significant reduction in median salt intake for the group, with baseline of 7.9 g/d shifting to 5.2 g/d post the intervention (p=0.001, effect size = 0.6). This study marked the development of UK’s first dietary salt monitor for use in Type 2 diabetes and is effective for reducing salt intake in this group. The tool is proposed to be further used for monitoring salt intake of these patients in collaboration with their health professionals in NHS, private medical setting and signposted at online platforms as Diabetes UK to reach out to diabetic community, at large

Action in context - context in action: towards a grounded theory of software design

This thesis develops a model and a theory of software design. Thirty-two transcripts of interviews with software designers were analysed using the Grounded Theory method. The first set of sixteen interviews drawn from the field of Digital Interactive Multimedia (Data-set A) was used to develop the model and theory, the second set of sixteen interviews drawn from one source of technical literature (Data-set B) was used to test and enhance the initial outcomes. Final outcomes are then grounded in the general literature on problem solving and design. The model is concerned to capture a rich, holistic picture of software design. It is descriptive rather than prescriptive, concerned to capture how software design is done rather than advocate how it ought to be done. The theory is a development of the model and is presented initially as a theoretical framework and then as a series of propositions. The theoretical framework is a function of the juxtaposition of specific properties or attributes of the "core category", which uniquely explains the phenomenon. Its outcome is four design scenarios. Each scenario is of interest as an explanation of software design practice but two scenarios wherein such practice does not "fit" the design context are of most interest. It is argued that these scenarios can be used to identify and explain design breakdowns. Finally, the thesis purports to explicate the "Meta-process" - the process through which the inductive model and theory was developed. This is an unusual objective for a piece of IS research but valid nonetheless and significant, given the complexity of the research method used and the dearth of good process accounts in the IS literature and elsewhere

Marketing managers : The evocation and structure of socially negotiated meaning.

The thesis begins with a parallel between marketing and personnel management and grows into an investigation of marketing managers as practising professionals. The subsequent methodological inadequacies of a dependence upon oral data lead to additional readings in anthropology and a methodology which attempts the complexities of consumption and the everyday importance of industrial artefacts.Individual consumers are seen accordingly as "bricoleurs" and their "closed world" as the result of a limited choice of physical and cultural possibilities. This commercially regulated exchange is, in turn, a significant determinant of social structure for marketing managers and any other band of workers may now be appreciated as kinship groups and not simply functional or work based gatherings. After establishing these patterns of social and industrial exchange as everyday means of communication, the thesis shows commercially regulated exchange to be a physically located practice and therefore responsible for forms of architecture and spatial understanding which reflect the social asymmetries that derive from a dependence upon mass consumption, mass employment and mass production. The same imbalance arises in an analysis of the Ford Edsel, a redoubtable commercial failure. Here, a considerable part of the thesis is focussed upon practical marketing management and the ways in which an industrial artefact might first symbolise "the power to speak" and then be reinterpreted within the terms of these same asymmetries. This process of evaluation involves coherent unspoken languages yet these "ways of seeing" are necessarily negotiated in accordance with the more commonly observed parameters of everyday reality; speech and the written word. "The power to speak" is thus a combination of these verbal disciplines and the visual aspects of consumption which codify and legitimise commercial exchange as a medium for the structuring of contemporary society. The thesis is therefore able to transcend the normally accepted view of marketing by arguing that mass consumption and commercially regulated exchange are so much a part of the "cultural design of persons and goods" as to undermine the exclusivity which is implied by ideas of marketing as a "professional understanding". This in turn enables a fuller evaluation of marketing management as a socially located practice whilst adding to theories of perception, the social construction of knowledge and the development of an "anthropology of consumption"