Plastics glazing materials have properties which allow their widespread use in construction, for example as rootlights. However, they are more susceptible than is glass to degradation by weathering, notably the combined effects of ultraviolet light, heat and moisture. Examples of unacceptable durability have been seen in practice, particularly when high operating temperatures occur in sunlight. Artificial weathering tests are used to assess plastics glazing materials in a reasonably short time, two main types being utilised in this study. The applicability of ultra-fast methods of accelerated degradation has been shown to depend on the extent to which the mechanisms of degradation simulate practical weathering, since different procedures were found to promote different mechanisms in the materials tested. Misleading information was obtained when the full spectrum of solar UV and much of the visible was not adequately reproduced in the accelerated tests. In particular an established grade of PVC-U performed unexpectedly poorly under fluorescent lamps. Procedures based on xenon arc sources were found to be the most generally applicable because they better reproduce the full solar spectrum range and, hence, the typical effects observed in plastics materials in practice. Several analytical techniques were used to characterise the virgin polymers and to assess the weathered materials. Two commercial grades of each polymer type (poly[vinylchloride], polycarbonate and poly[methylmethacrylate]) were studied, and measured changes explained in terms of initial polymer properties. Profiling of chemical (e.g. carbonyl index measured by photo-acoustic fourier transform infrared), physical (e.g. molecular weight, surface gloss/roughness), optical (e.g. colour, light transmission) and mechanical properties (e.g. impact resistance) as a function of exposure period and environmental conditions enabled degradation rates and mechanisms to be established for each material. In conducting these tests particular attention was given to the control and effects of sample temperature during weathering, and to the wavelength range of the light source used. Poly(vinylchloride) was affected much more by weathering at higher temperatures, and by exposure to short wavelength radiation, than was polycarbonate, with acrylic being the most durable overall. Practical applications of this work are through Standards committees primarily. in particular with plastics rootlights (B/542/8 and CEN/TCI28/SC9).

No description available.

Dematiaceous hyphomycetes are a taxonomically diverse artificial assemblage of conidial fungi that have dark pigments known as melanins in their walls. Select dematiaceous hyphomycetes from the Coniochaetales, Pleosporales, and Helotiales obtained from arctic and alpine bryophytes and vascular plant roots were chosen for further study. Eight isolates, all from roots of Saxifraga oppositifolia, represented a new species of Monodictys, M. arctica. This species, characterised by large, darkly pigmented, multicelled, often branching conidia, was most closely related to members of the Leptosphaeria, making M. arctica potentially the first non-pycnidial anamorph associated with that genus. In alpine glacial forefields, the primary colonisers are bryophytes, which form an organic grout between the rocks. These mosses trap organic particles. Three pleosporalean fungi were isolated from this grout and examined to see if they could degrade moss. All three removed the outer, cellulose rich layer of the cells, but not the inner, polyphenol rich layer. I propose that the mosses disarticulate after degradation and the fragments are trapped in the grout, increasing soil organic matter and aiding pedogenesis. This first soil ostensibly facilitates colonisation by vascular plants, the roots of which are colonised by dark septate endophytes (DSE), a group known for asymptomatically colonising vascular plant roots and thought to be quasi-mycorrhizal. Cadophora luteo-olivacea, Cadophora melinii, Leptodontidium orchidicola, Phialocephala fortinii and Coniochaeta nepalica were examined for their abilities to degrade moss. All showed that colonisation patterns varied along with the formation of conidia and sclerotic structures, which could serve as inocula for establishing species of vascular plants. Cadophora and Phialocephala are delineated by phialide complexity, so I decided traced the origin and evolutionary history of that character on a phylogenetic framework. Based on this reconstruction, phialide complexity is a good character for separating the two genera. I propose that the sclerotium of the outgroup taxon, which develops phialides that produce spermatia, evolved into the phialidic heads of Phialocephala, which resemble sclerotia, and then into the solitary phialides of Cadophora. Traits in the sexual fungi associated with these asexual taxa support the phylogenetic placement of the asexual fungi. / Ecology

Thesis (Ph.D.)--York University, 2006. Graduate Programme in Environmental Studies. / Typescript. Includes bibliographical references (leaves 305-321). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR19807

Diss. Univ. Bern, 1999.

Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 174-192).

Thesis (M.A.)--University of Delaware, 2009. / Principal faculty advisor: Yda Schreuder, Dept. of Geography. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains vi, 181 p. : col. maps. Includes abstract. Includes bibliographical references (p. 100-106).

Thesis (M.S.)--Montana State University--Bozeman, 2005. / Typescript. Chairperson, Graduate Committee: John Antle. Includes bibliographical references (leaves 115-124).

Universiẗat, Diss., 2006--Würzburg. / Erscheinungsjahr an der Haupttitelstelle: 2005. Dateien im PDF-Format.