No description available.

Recurrent events experienced by individual units or systems occur in many fields. The main target of this thesis is to develop formal tests for certain features of recurrent event processes, and to discuss their properties. In particular, carryover effects and time trends are considered. The former is related to clustering of events together in time, and the latter refers to a tendency for the rate of event occurrence to change over time in some systematic way. Score tests are developed for models incorporating carryover effects or time trends. The tests considered are easily interpreted and based on simple models but have good robustness properties against a range of carryover and trend alternatives. Asymptotic properties of test statistics are discussed when the number of processes approaches infinity as well as when one process is under observation for a long time. In applications involving multiple systems or individuals, heterogeneity is often apparent, and there is a need for tests developed for such cases. Allowance for heterogeneity is, therefore, considered. Methods are applied to data sets from industry and medicine. The results are supported by simulation studies.

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No description available.

In order to clone the DNA repair gene of Aspergillus nidulans, uvsF$ sp-$ pyrG$ sp-$ strains were transformed with a genomic library in a plasmid vector that carried the pyr-4 gene of Neurospora which complements pyrG mutants of Aspergillus. Out of the several transformants obtained, four were like wild type. For rescuing plasmids, transformant DNA was digested with Bg/II and self ligated, and used for transformation of E. coli. Two types of plasmids were obtained; these two had a region in common ($<$1.0 kb) that was not a simple overlap and gave evidence for rearrangements. Surprisingly, only the plasmids with the larger insert of Aspergillus DNA were able to complement uvsF$ sp-$ in the secondary transformation. Northerns of polyA$ sp+$-enriched mRNA, probed with this plasmid, showed three bands. However, its subclone which spans the shared region hybridized to only one of them (1.0 kb). Two cDNA and five genomic clones were identified. The two cDNA clones though not identical, cross-hybridized. Three out of five genomic clones were identical. The cDNA hybridized to a short segment (2.2 kb) of one of the three types of genomic clones, locating the putative uvsF gene sequence.

<p><font face="Times New Roman" size="4"><font face="Times New Roman" size="4"> <p align="left">The aim of this study is to investigate the repair bond strength of composite resin following micromechanical and chemical means of retention in improving the repair of composite resin specimens.</p> </font></font></p>

The activity of Adenosine diphosphoribosyl transferase (ADPRT), the chromatin-bound enzyme which specifically catalyses the cleavage of oxidized NAD⁺ with the concomitant covalent attachment of the ADP-ribose moiety to acceptor proteins, was investigated in Polyoma Virus-Transformed (PyY) and Untransformed BHK21/C13 (BHK) cells. It was shown that ADPRT activity was consistently 2-4 fold higher in PyY cells than in BHK cells. The spectrum of (ADP-ribose)_n residues synthesised by the two cell types was very similar when analysed by hydroxyapatite column chromatography. Poly (ADP-ribose) Glycohydrolase activity in the two cell types was identical with 25-30% degradation of the poly(ADP-ribose) over a period of 90 minutes. DNA damage resulting from incubation with Deoxyribonuclease was reflected by an immediate increase in ADPRT activity and an increase in (ADP-ribose)_n chain length by both cell types. Polyamines which are present at high concentrations in rapidly dividing tissues were able to stimulate ADPRT activity both <i>in vitro</i> and <i>in vivo</i> in BHK and PyY cells. In general the average chain length of ADP-ribose residues synthesised remained unaltered. No significant increase in the level of DNA-strand breakage could be detected in the polyamine-treated cells. Depletion of the cellular polyamine levels resulted in stimulation of ADPRT activity, but there was no significant difference in the spectrum of (ADP-ribose)_n residues synthesised. Again no significant increase in the level of DNA-strand breaks could be detected in the polyamine-depleted cells. These results suggest that DNA-damage may not be the only means of regulating ADPRT activity and that polyamines may have a role to play in this regard <i>in vivo</i>.

Clinical and experimental observations of foetal wound healing have led to a reappraisal of dermal wound repair. Because of the major contribution of collagen to scar tissue, the presence and role of collagen in scarless healing in foetal animal models has been a source of some controversy. The experimental work described in this thesis clearly establishes that foetal animals are able to deposit abundant collagen in traditional wound healing models. The emphasis of speculation subsequently shifted to consider the role of other matrix elements, particularly hyaluronan, which has particularly high levels in foetal wounds. Some investigators have proposed that the more 'fluid' nature of the matrix facilitates the remodelling of the deposited collagen. Experimental evidence presented in this thesis suggests, however, that while the physico-chemical properties of hyaluronan are important in influencing cell and matrix interactions, more specific and controllable interactions may be due to the action of proteins associated with the hyaluronan.

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Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available online.