No description available.

No description available.

Our investigation suggests that Epac, and not the canonical PKA, is the main effector involved in cAMP-mediated axon growth and guidance, and that the MAPK regulator, B-Raf, can be differentially regulated by both Epac and PKA.  Direct activation of Epac induces activation of B-Raf, whereas activation of PKA results in inhibition.  Moreover, in embryonic neurons, Epac-B-Raf signalling was found to be activated by the cAMP-dependent guidance molecule Netrin-1 (attractive to developing axons) and by cAMP activity at all levels tested, whereas in adult neurons, PKA signalling was activated by Netrin-1 (repulsive to adult neurons) and low levels of cAMP activity.  When cAMP was substantially elevated in adult neurons, Epac-B-Raf signalling was induced, and the response of adult axons to Netrin-1 was switched from repulsion to attraction, indicating B-Raf activity is consistent with chemoattractive axon turning.  Furthermore, B-Raf activity was found to localise towards the leading edge of a turning growth cone when visualised with fluorescent microscopy.  Neurons lacking B-Raf protein were unable to respond to cAMP-dependent guidance cues and postnatal neurons no longer responded to artificial cAMP elevation, which usually induces an increase in axon outgrowth.  Calcium influx into growth cones usually induced by axon guidance cues and cAMP activators, were also attenuated in neurons lacking B-Raf.  These data suggest B-Raf is a vital effector for cAMP-mediated axon growth and guidance.

Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 59-62.

archives@tulane.edu / Silicon-based block copolymers have gained prominence because of their inherent ability to self-assemble at the low molecular weight. By utilizing this vital factor, we synthesize poly(vinylmethylsiloxane-block-methyl methacrylate) (PVMS-b-PMMA) intending to create small characteristic features with the potential application for lithography and membrane filtration. The polymer is made by a combination of anionic synthesis of PVMS, ATRP (atom radical transfer polymerization) of PMMA, and then cojoining the end-group functionalized blocks with a “click” reaction. After synthesis, thin films (10-100 nm) were self-assembled to form structures aligned perpendicular to the substrate. The morphology was observed by atomic force microscopy, grazing incidence small-angle X-ray scattering (GISAXS), and transmission electron microscopy (TEM). Additionally, the hydrophobicity of PVMS prompted us to develop a coating on microporous membrane supports for separation of water-in-oil mixtures. The PVMS was used as an effective coating to prevent fouling while maintaining high selectivity for both water-in-toluene and water-in-decane emulsion in gravity-based filtration. Finally, cyclic block copolymers (BCPs) have garnered increased attention because of their unique structure, which differs from linear BCPs due to a lack of end groups. This feature in combination with the high segregation strength of silicon-based polymers is desirable for nanolithography. Thus, we synthesized a new class of silicon-based cyclic polymer, cyclic PVMS-b-PMMA, intending to later understand the impact of topology on phase behavior, domain spacing, and nanoconfinement in thin films. / 1 / Baraka Lwoya

No description available.

Abstract not available

Thesis (Ph. D.)--University of Oregon, 2006. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 336-357). Also available for download via the World Wide Web; free to University of Oregon users.

The behaviour of sands during loading has been studied in great detail. However, little work has been devoted to understanding the response of sands in unloading. Drained triaxial tests indicate that, contrary to the expected elastic behaviour, sand often exhibit contractive behaviour when unloaded. Undrained cyclic simple shear tests show that the increase in pore water pressure generated during the unloading cycle often exceeds that generated during loading. The tendency to contract upon unloading is important in engineering practice as an increase in pore water pressure during earthquake loading could result in liquefaction. This research contributes to filling the gap in our understanding of soil behaviour in unloading and subsequent reloading. The approach followed includes both theoretical investigation and numerical implementation of experimental observations of stress dilatancy in unload-reload loops. The theoretical investigation is done at the micromechanical level. The numerical approach is developed from observations from drained triaxial compression tests. The numerical implementation of yield in unloading uses NorSand — a hardening plasticity model based on the critical state theory, and extends upon previous understanding. The proposed model is calibrated to Erksak sand and then used to predict the load-unload-reload behaviour of Fraser River sand. The trends predicted from the theoretical and numerical approaches match the experimental observations closely. Shear strength is not highly affected by unload-reload loops. Conversely, volumetric changes as a result of unloading-reloading are dramatic. Volumetric strains in unloading depend on the last value of stress ratio (q/p’) in the previous loading. It appears that major changes in particles arrangement occur once peak stress ratio is exceeded. The developed unload-reload model requires three additional input parameters, which were correlated to the monotonic parameters, to represent hardening in unloading and reloading and the effect of induced fabric changes on stress dilatancy. The calibrated model gave accurate predictions for the results of triaxial tests with load-unload-reload cycles on Fraser River sand.

Polyrotaxanes possess a molecular architecture resembling that of a wheel and axle: linear polymer chains are threaded by cyclic molecules with no covalent bonds linking the two species. One of two methods can be employed for the preparation of polyrotaxanes: a template method to guide threading or an in situ polymerization of monomers in the presence of cyclic molecules. The research described in this dissertation was divided into two distinct sections, which were devoted to each method of polyrotaxane preparation. The first step of synthesizing polyrotaxanes via the in situ polymerization method was to prepare a cyclic molecule. α,Ï -Dihydroxy-PDMS was cyclized and then efficiently purified by an anion-exchange resin to remove uncyclized, yet anionically charged, linear PDMS. The second part of this dissertation included examining polyrotaxanes created by the template-directed threading of α-CD onto polyoctene (PO). End-capped PO, which was unthreadable by α-CD, was synthesized from 1,9-decadiene and a monovinyl bulky compound by acyclic diene metathesis. PO and ecPO each were sonicated in aqueous solutions of α -CD; PO formed a white precipitate indicative of a rotaxanated polymer, but no precipitate formed by the addition of ecPO. These results provided evidence that PO had been included within the cavity of α-CD.