Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Qaisar Shafi, Dept. of Physics & Astronomy. Includes bibliographical references.

Thesis (Ph. D.)--Northeastern University, 2009. / Title from title page (viewed June 22, 2009). Graduate School of Arts and Sciences, Dept. of Physics. Includes bibliographical references (p. 163-178).

In this thesis we study classes of static spherically symmetric solutions to the Einstein and Einstein–Maxwell equations that may be used to model the interior of compact stars. We also study the spherical accretion of fluids on to bodies in both general relativity and the Newtonian theory of gravity. The condition for pressure isotropy is obtained upon specifying one of the gravitational potentials and the electric field intensity. A series solution was found after specifying a cubic form for the potential. The pressure and energy density appear to be non–singular and continuous inside the star. This solution admits an explicit equation of state that, in regions close to the stellar centre, may be approximated by a polytrope. Another class of exact solutions to the Einstein–Maxwell solutions was found with charge. These solutions are in the form of hypergeometric functions with two free parameters. For particular parameter values we recovered two previously known exact solutions that are reasonable models for the interior of compact stars. We demonstrated two new solutions for other choices of the parameters. One of these has well behaved pressure, energy density and electric field intensity variables within the star. The other was rejected as unphysical on the grounds that it has a negative energy density. This violates the energy conditions. We obtained the mass accretion rate and critical radius of a polytrope accreting onto a D– dimensional Schwarzschild black hole. The accretion rate, ˙M , is an explicit function of the black hole mass, M, as well as the gas boundary conditions and the dimensionality, D, of the spacetime. We also found the asymptotic compression ratios and temperature profiles below the accretion radius and at the event horizon. This generalises the Newtonian expressions of Giddings and Mangano (2008) which examined the accretion of TeV black holes. We obtained the critical radius and accretion rates of a generalised Chaplygin gas accreting on to body under a Newtonian potential. The accretion rate is about 2 - 4 times greater than that for neutral hydrogen. The Rankine–Hugoniot relations for shocked GCG flow were also found. We found general expressions for the pressure and density compression ratios. Some post shock states imply negative volumes. We suspect that these may be thermodynamically forbidden. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.

Thesis (Ph. D.)--University of California, San Diego, 2009. / Title from first page of PDF file (viewed September 17, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 444-468).

A "Geometrodynamical Analog to Electric Charge" (or "p-charge") is defined (as in the earlier paper by Unruh, [Gen. Rel. and Grav., 2, (1971), pp 27-33 ] to be the period on a p-cycle (p = 1, 2, or 3) of a p-form which is constructed out of only the Riemann tensor or its derivatives. A previously-unpublished proof by Unruh is briefly summarized which proves that no non-zero p-charges can exist on a completely unrestricted metric field. The metric field is then constrained to obey Einstein's equations for empty space, and sets of linearly-independent, purely-gravitational p-forms are analyzed to determine if p-charges can be defined under these conditions. A scheme is developed, based on the spin-tensor representation of the gravitational field, to generate complete sets of such p-forms, arid calculate their derivatives, with a symbolic-manipulation computer program. It is shown that no gravitational p-forms that are linear combinations of less than five Riemann tensors and less than nine derivatives will result in p-charges. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Thesis (Ph. D.)--University of Notre Dame, 2008. / Thesis directed by Don Howard for the Graduate Program in History and Philosophy of Science. "April 2008." Includes bibliographical references (leaves 212-220).

There are several critical success factors suggested for why agile software development projects succeed, including organisational and process factors. Although there are an increasing number of identified critical success factors, IT professionals lack the modelling techniques and the theoretical framework to help them meaningfully understand their influences. To solve this problem, this study developed a model by employing the following theories: Theory of Reasoned Action (TRA), Theory of Planned Behaviour (TPB), and Unified Theory of Acceptance and Use of Technology (UTAUT) to create a fit model for agile software development projects. The research sought to answer the question: What are the critical success factors that influence the success of agile software development projects? The literature review considers the continued failure of agile and traditional software development projects which have led to the consideration of, and dispute over, critical success factors — the aspects most vital to a methodology’s success. Though TRA, TPB and UTAUT have previously been applied to agile methodologies, empirical models have not been completely integrated to develop a fit model. This research sought to fill this gap. Data was collected in South Africa through a web-based survey using structured questionnaires and an interview guide. Face-to-face interviews were done to identify the critical success factors in agile projects. The data was captured and analysed for descriptive statistics, convergent and discriminant validity, composite and internal reliability, and correlation in order to inform the structural equation modelling (SEM). SEM was used to test the research model and hypotheses to answer the research questions. The results informed development of a comprehensive model that could provide guidelines to the agile community. The study contributes towards understanding the critical success factors for agile projects. It examined direct, indirect and moderating effects, and the findings contribute towards developing a framework to be used by agile professionals. These key result shows that organisational factors have a great influence on performance expectancy characteristics. To ensure success of agile projects, managers are advised to focus on the effect of the organisation’s environment, culture and policies on performance and effort expectancy. / School of Computing / Ph. D. (Computer Science)