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No description available.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

The free radical addition of saturated polymers and small molecules to unsaturated monomers is used to prepare functional derivatives under solvent-free, reactive extrusion conditions. Of particular interest are the dynamics and yields of conventional peroxide-initiated grafting of vinyltrialkoxysilanes to polyethylene, as well as the mechanisms through which bicumene initiates the process at high temperatures. Knowledge of these commercial processes is applied toward the development of new graft modification technology, including radical initiated polymer addition to alkynes, and a new variation of precipitation polymerization chemistry. The thermolysis of bicumene at temperatures ranging from 220°C to 270°C was used to initiate C-H bond addition from alkanes to vinylsilanes in a high-temperature analogue of conventional grafting practice. The initiation mechanism is shown to involve direct hydrogen atom abstraction by intermediate cumyl radicals, as well as autooxidation processes involving cumyl radicals and available oxygen. Conventional peroxide initiated graft modifications of polyethylene with vinylsilanes are examined from the standpoint of reaction dynamics and yields. The influence of peroxide loading and monomer concentration on these reaction variables can be described using a simple quasi-steady state kinetic analysis, while the unusual insensitivity of reaction yields to temperature requires further investigation. A new chemical modification of saturated polymers involving free radical addition to mono-substituted alkynes is presented and examined in terms of reaction yield, graft structure, and changes to molecular weight. Model compounds are used to characterize alkyne grafting products, and to probe the relationship between reagent properties, reaction yields, and product structures. The discovery of cross-linked particles in the products of polypropylene graft modifications with triallyltrimesate has led to a variation of precipitation polymerization wherein C-H bond addition to an allyl monomer contributes to molecular weight growth, thereby incorporating a significant amount of saturated hydrocarbon into the solid phase. The relationships between reaction conditions and solid-phase composition and morphology are discussed. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2008-12-18 14:35:52.483

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Cytotoxic T lymphocytes play an important role in mediating host immune reactions to viruses and other pathogens. Selective mechanisms operate during V(D)J recombination to enhance the diversity of the T cell repertoire that is generated, particularly in the CDR3 regions of the TCR, which mediate peptide recognition. The influence of V gene 3' sequences on the composition of the CDR3 loop in TCR β chains is analysed; in particular, A/T-rich coding termini are shown to be more susceptible to exonuclease "nibbling" during recombination. The recent development of peptide-MHC tetrameric complexes has enabled us to detect T lymphocytes according to their antigen specificity. Their use in detection and characterisation of EBV-specific CD8⁺ T cells during the primary acute phase of infection is described here. In particular, CTL responses to EBV lytic cycle antigens have only recently been reported and this study reveals unexpectedly high frequencies of activated, circulating CD8⁺ T lymphocytes which are directed towards lytic cycle epitopes, compared to well-characterised latent cycle antigens. In a second cohort of healthy long term asymptomatic donors, the frequency of CD8⁺ T cells recognising EBV lytic and latent cycle antigens was analysed by tetramer staining, ELISpot assays and limiting dilution assays; the tetramers detected antigen-specific CD8⁺ T lymphocytes with greater efficiency than other methods. Lytic cycle antigen-specific T lymphocytes were clearly detectable in all the asymptomatic donors, at higher frequencies than those specific for latent antigens. The final section of this thesis investigates the existence of enriched populations of EBV-specific T lymphocytes found within synovial joint fluid of rheumatoid arthritis patients. Although these cells do not appear to be directly involved in the initiation of disease, their ability to secrete proinflammatory cytokines within joints probably contributes to the maintenance of chronic inflammation in these patients.

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No description available.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 358-379). Also available via the Internet.

No description available.