Thesis (Ph.D.)--Murdoch University, 2003. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 255-267.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xii, 190 p.; also includes graphics (some col.). Includes bibliographical references (p. 181-190). Available online via OhioLINK's ETD Center.

A nova is a cataclysmic variable star consisting of a white dwarf and a main sequence, subgiant or red giant companion. In a nova explosion, the white dwarf undergoes a thermonuclear runaway on its surface, as a result of build-up of accreted material from its companion. This leads to a large expulsion of matter from the WD surface, as well as a dramatic increase in the optical magnitude of the system. In this thesis, 5GHz C-band e-MERLIN observations of two novae (V959 Mon and V339 Del) and one symbiotic star (AG Pegasi) are presented. V959 Mon is a classical nova which was discovered in June 2012 by the Fermi Large Area Telescope as a gamma-ray source. High resolution e-MERLIN images of V959 Mon were made at six epochs following the June 2012 outburst, between 90 and 615 days after the Fermi discovery. The first four e-MERLIN observations revealed a morphology which was aspherical and expanding in the east-west direction. However, in the last two epochs, V959 Mon's ejecta morphology changed from being elongated east-west to being elongated north-south. Constant velocity models fit to measurements of V959 Mon's angular size at each epoch indicated that the expansion rate of the north-south component was significantly slower than that of the east-west component. The e-MERLIN observations of V339 Del and AG Pegasi were not as well resolved as the observations of V959 Mon, and only limited analysis of their ejecta structure was possible. In order to understand the complicated morphology seen in the e-MERLIN observations of V959 Mon, radio emission models of nova ejecta were constructed, and e-MERLIN observations of them were simulated. When constructing the models, two possible explanations for V959 Mon's morphology were explored. Firstly, the possibility was considered that the elongation observed in V959 Mon's ejecta, which changed over time from east- west to north-south, was spurious, resulting from incomplete sampling of the uv plane by e-MERLIN. To investigate this, an expanding spherical shell of ejecta was simulated, the extent to which its shape was distorted in simulated e-MERLIN images of it was investigated. Secondly, emission from an ejecta model featuring two components - one fast-moving component in the east-west direction, and another, more slow-moving component in the north-south direction - was simulated, in order to determine whether such an ejecta structure could result in the morphology seen in the e-MERLIN observations of V959 Mon. It was found that the spherical, Hubble flow model simulations were a reasonably good fit to V959 Mon's light curve, but could not explain the east-west elongation seen in V959 Mon's ejecta at the early epochs. Simulated observations of the two-component model were morphologically similar to V959 Mon, but produced light curves which were much fainter than V959 Mon's, indicating that a more in-depth analysis of two-component models of nova ejecta is necessary.

This thesis is primarily concerned with a description of four types of stochastic algorithms, namely the genetic algorithm, the continuous parameter genetic algorithm, the particle swarm algorithm and the differential evolution algorithm. Each of these techniques is presented in sufficient detail to allow the layman to develop her own program upon examining the text. All four algorithms are applied to the optimization of a certain set of unconstrained problems known as the extended Dixon-Szegö test set. An algorithm's performance at optimizing a set of problems such as these is often used as a benchmark for judging its efficacy. Although the same thing is done here, an argument is presented that shows that no such general benchmarking is possible. Indeed, it is asserted that drawing general comparisons between stochastic algorithms on the basis of any performance criterion is a meaningless pursuit unless the scope of such comparative statements is limited to specific sets of optimization problems. The idea is a result of the no free lunch theorems proposed by Wolpert and Macready. Two methods of presenting the results of an optimization run are discussed. They are used to show that judging an optimizer's performance is largely a subjective undertaking, despite the apparently objective performance measures which are commonly used when results are published. An important theme of this thesis is the observation that a simple paradigm shift can result in a different decision regarding which algorithm is best suited to a certain task. Hence, an effort is made to present the proper interpretation of the results of such tests (from the author's point of view). Additionally, the four abovementioned algorithms are used in a modelling environment designed to determine the structure of a Magnetic Cataclysmic Variable. This 'real world' modelling problem contrasts starkly with the well defined test set and highlights some of the issues that designers must face in the optimization of physical systems. The particle swarm optimizer will be shown to be the algorithm capable of achieving the best results for this modelling problem if an unbiased <font face="symbol">c</font>2 performance measure is used. However, the solution it generates is clearly not physically acceptable. Even though this drawback is not directly attributable to the optimizer, it is at least indicative of the fact that there are practical considerations which complicate the issue of algorithm selection. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21572号 / 理博第4479号 / 新制||理||1643(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 野上 大作, 教授 長田 哲也, 教授 嶺重 慎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (p. 139-145).

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