Thesis (Ph. D.)--University of Illinois, 1919. / Vita. Bibliography: p. 45-46.

Thesis (Ph. D.)--University of Illinois, 1919. / Vita. Bibliography: p. 45-46.

No description available.

The overall aim of this research project has been to develop a reference dataset of 19 Holocene silicic Icelandic tephra layers sourced from the Torfajökull, Askja, Katla, Öræfajökull and Hekla volcanic systems. The dataset comprises geochemical data (including major, trace and rare earth element data for bulk and glass phases collected by XRF, electron microprobe, ion probe and laser ablation ICP-MS) and physical data (including sedimentary logs, field photographs, distribution maps and GPS localities of reference sections). Results indicate that Icelandic volcanic systems show unique geochemical signatures which result from the systems proximity to the active rifting zone and the proposed upwelling mantle plume that underlies the island. Within individual volcanic systems, eruptions produce tephra with distinct geochemical characteristics, which allow for the independent confirmation of tephra identity. The identification and discrimination of tephra layers can in some cases be achieved using major element chemistry (e.g. Hekla, H1104 – H5) while other tephra layers can only be discriminated using trace element chemistry (e.g. Torfajökull, Landnám and Gràkolla). Certain tephra layers however show near-identical geochemistry and therefore discrimination is not possible (e.g. Hekla, HA, HB, HC, HM, HN, HX, HY, HZ) without the incorporation of other proxy data. Icelandic micro-tephra horizons are identified in soil, lacustrine and marine sedimentary sequences and are used for dating and correlation in Quaternary studies. Data collected for this project will facilitate reliable data comparison and tephra identification between proximal and distal localities across the North Atlantic region. The data may also contribute to the debate regarding the formation of silicic rocks within Iceland, particularly with regard to the Hekla central volcano. The geochemical data collected for this thesis shows distinct age-dependant geochemical sub-groups suggesting temporal sub-surface relocation of the Hekla magma source.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 175-194).

Thesis (Ph.D.) - University of St Andrews, September 2009. / Electronic version restricted until 21st September 2010.

Magmas experiencing pressure changes can follow equilibrium or nonequilibrium degassing paths that determine the rate of gas exsolution and the composition of gases exsolved. Many variables influence timescales of equilibration between vapor and melt after a perturbation in pressure, temperature, or other factors, and the magnitude of this equilibration time determines whether the system experiences equilibrium degassing or not. In order to create a simplified framework for assessing degassing regime, we constructed a numerical diffusion model to test the sensitivity of equilibration time to variables such as bubble size, spacing, melt temperature, initial and final system pressures, and water content. We then determined the degassing regime for a range of bubble-spacing and decompression rates as an initial simplified framework to build on. We also attempted the first mixed-volatile continuous decompression experiments in order validate our model and further improve analyses and interpretations of volatile gradients in natural samples.

In biotechnology and drug delivery silica materials are of interest but the controlled generation of silicic acid is difficult. To get more insight into the molecular mechanisms that control biosilification, it is important to study the proteins involved in this process. The sponge protein silicatein α synthesises part of the axial filament in the spicules which in situ polymerises silicic acid. It has been demonstrated that the polymerisation of siloxanes such as for example tetraethoxysilane (TEOS) can be carried out by both wild type and recombinant silicatein α. Unfortunately, it has not been possible yet to get reasonable amounts of wild type or recombinant silicatein α to perform biophysical studies. The human cysteine protease cathepsin L has almost 50 % identical residues with silicatein α. To get more insight into the mechanism of silica polymerisation, cathepsin L mutants were generated by our collaborators. Those mutants show sequence features and activity specific for silicatein α. The X-ray structure of one of those mutants (mutant 4SER) to 1.5 Å has allowed us to propose a new chemical mechanism for the catalysis of silicic acid polymerisation. ADP-β-D-glycero-D-mannoheptose and ADP-β-L-glycero-D-mannoheptose are interconverted by the SDR-enzyme ADP-β-L-glycero-D-mannoheptose 6-epimerase (AGME). This epimerisation reaction is the final reaction in the biosynthetic route of the precursor of heptose. Heptose is a part of the inner core of the lipopolysaccharide in Gram-negative bacteria. In mutants which do not have heptose, nonpolar compounds can penetrate more easily through the outer membrane. These mutants also show less pathogenicity. As a consequence the lipopolysaccharide biosynthetic pathway represents an interesting target for antimicrobial compounds. The crystal structure of AGME in complex with ADP-α-glucose has already been solved. From this structure a catalytic mechanism for this enzyme has been proposed with Tyr140 and Lys178 operating as acid/base residues. The disordered nature of the nucleotide sugar’s glucose moiety in the previous structure due to the wrong configuration of the sugar has hindered assignment of a mechanism. The determination of the X-ray structure of AGME Y140F in complex with a substrate in the β-manno configuration (ADP-β-mannose) to 2.4 Å resolution has given new insight into the mechanism of this SDR enzyme. A mechanism is proposed with only Tyr140 operating as catalytic acid/base. Initially it was thought that MMP-3 participates in the synovitis cascade. Glycoproteins, several parts of the ECM such as fibronectin and laminin and also collagens and procollagens are targets of this matrixin. Furthermore MMP-3 can undergo autocatalysis and is also able to cleave a range of other members of the matrixin family. Matrixins also play an important role in diseases such as cancer, rheumatoid arthritis and osteoporosis. This makes them targets for inhibitor design. Many structures of matrix metalloproteinases, such as stromelysin-1, in complex with various inhibitors have already been solved. The structures of the catalytic domain of MMP-3 in complex with two nonpeptide inhibitors are discussed.

In this project the author has attempted to determine the specific conductance of a gel of known composition; the changes, if any, of conductance in a gel as it sets; and the changes in conductance due to the diffusing of an electrolyte through the gel.

Observation of crystal growths resulting from the chemical interaction of stannous chloride and sodium arsenate in silicic acid gels revealed the following very interesting fact. Gels identical in every respect except acidity, contained crystal growths varying greatly in appearance. The purpose of this investigation was, therefore, to allow stannous and arsenate ion to combine in a series of accurately prepared gels, identical in all respects except the acid content, and to observe the effect upon crystal growth of: (1) varying the acid concentration; and (2) varying the kind of acid