Thesis (Ph. D.)--University of Maryland, 1998. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Michigan, 1968.

Thesis (M.S.)--University of Michigan, 1968.

Thesis (M.S.)--University of Michigan, 1981.

Thesis (M.S.)--University of Michigan, 1964.

Thesis (M.S.)--University of Michigan, 1997. / Includes bibliographical references.

Thesis (Ph. D.)--University of Maryland, 1998. / Includes bibliographical references.

We begin our study of amalgamations by examining some ideas which are well-known for the category of R-modules. In particular we look at such notions as direct limits, pushouts, pullbacks, tensor products and flatness in the category of S-sets. Chapter II introduces the important concept of free extensions and uses this to describe the amalgamated free product. In Chapter III we define the extension property and the notion of purity. We show that many of the important notions in semigroup amalgams are intimately connected to these. In Section 2 we deduce that 'the extension property implies amalgamation' and more surprisingly that a semigroup U is an amalgamation base if and only if it has the extension property in every containing semigroup. Chapter IV revisits the idea of flatness and after some technical results we prove a result, similar to one for rings, on flat amalgams. In Chapter V we show that the results of Hall and Howie on perfect amalgams can be proved using the same techniques as those used in Chapters III and IV. We conclude the thesis with a look at the case of rings. We show that almost all of the results for semi group amalgams examined in the previous chapters, also hold for ring amalgams.

We use profinite Bass-Serre theory (the theory of profinite group actions on profinite trees) to prove that the fundamental groups of finite graphs of free groups which are l-acylindrical and have finitely generated edge groups are conjugacy separable. We apply this theorem to: demonstrate that a generic positive one-relator group is conjugacy separable; produce a variant of the Rips con- struction in which the output group is conjugacy separable; apply this last to exhibit an example of a strong profinite equivalence between two finitely presented groups, one of which is conjugacy separable and the other having unsolvable conjugacy problem. We further use profinite Bass-Serre theory to demonstrate that having one end is an up-weak pro-C property for any extension- closed class C of finite groups. We show by example that it is not a down-weak pro-p property for any prime p. We consider Korenev's definition of pro-p ends for a pro-p group, and show that the number of ends of a finitely generated residually p group cannot be less than the number of pro-p ends of its pro-p completion. We explore possibilities for, but are ultimately unsuc- cessful in giving, a proper analogue of Stallings' theorem for pro-p groups. We ask which other properties might be profinite, and use another variant of the Rips construction to produce examples of patholog- ical groups such that either they are hyperbolic groups which are not residually finite, or neither property (FA) nor property (T) is an up-weak profinite property.

Master of Dental Surgery / The safety of amalgam restorations has been challenged, claims having been made that health risks are associated with the constituent mercury. There are assertions that mercury released from amalgam produces mercury poisoning, and is thus responsible for diverse symptoms of impaired health as well as disease states such as Multiple Sclerosis. This study examines the various forms of mercury and their effects and attempts particularly to delineate the significance of dental amalgam as a factor in hypersensitivity reactions and in the human body burden of mercury. Dental personnel are evaluated as a potentially high-risk group for mercury exposure. Dental amalgam and alternative restorative materials are considered, the removal of amalgam being evaluated as a therapeutic modality. The “anti-amalgam” perspective is scrutinised and the validity of the claims assessed. A review of the scientific literature, and the statements of national and international dental and scientific literature, and the statements of national and international dental and scientific organisations reflect the general support for the safety of dental amalgam. There is no evidence that health risks are associated with the use of dental amalgam other than rare local allergic reactions and oral lichenoid lesions. Notwithstanding the usefulness and safety of dental amalgam certain recommendations and conclusions are made in respect of future approaches to the utilisation of this material and for mercury in general. Further objective scientific research is necessary to determine the effects on human health of chronic exposure to low levels of mercury. There is the need for accurate general population threshold levels to be established for mercury vapour with special consideration for the vulnerable members of the community. The health professions have a significant role to play in providing informed opinion and advice for their patients and the public, in countering the more eccentric claims of the anti-amalgamists and assuaging the anxiety and confusion which accompanies this subject.