LD2668 .T4 1940 A9 / Master of Science

LD2668 .T4 1954 H9 / Master of Science

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The absorption lines found in the spectra of distant quasars provide a unique method of probing the physical conditions in the universe at early epochs. This thesis describes a study of the Lyman alpha forest absorption systems seen in the spectra of high redshift QSOs. The Anglo-Australian Telescope has been used to obtain high resolution spectra of several bright QSOs. Considerable effort has gone into developing statistical techniques for profile fitting to the data to objectively and reliably extract the parameters associated with each absorbing cloud. The distribution functions for these are given and discussed. Particular attention has been paid to the clustering properties of the Lyman alpha clouds and it is found that they are weakly (but significantly) clustered on small velocity scales. Possible interpretations of this result are discussed. One especially interesting aspect of QSO absorption systems concerns the potential for measuring, or obtaining limits on, the deuterium to hydrogen abundance at high redshifts. A knowledge of this quantity is important for constraining cosmological models and can also help us to understand the chemical evolution of light elements in galaxies. A series of numerical simulations has been carried out to explore the potential for such measurements and an absorption system has been analysed to obtain an upper limit to D/H at z = 3.

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Significant advances in the understanding of chemical interactions at the solid-liquid interface have been made in this research through the use of diagnostic separations as a surface analysis technique. Diagnostic liquid chromatography has been employed in a detailed investigation of the thermodynamic and kinetic quantities which describe the interactions associated with a temperature induced conformational change in the octadecyldimethylsilane moieties of two different bonded silica materials. As a result of this study the nature of the structure and interactions of the ∼20Å thick interfacial region which acts as the stationary phase in reversed-phase liquid chromatography (RPLC) has been elucidated. The location and orientation of the average intermolecular interactions in the solvated layer stationary phase for solutes of differing hydrogen bonding ability and geometry has been determined as affected by bonded surface coverage, solvent hydrogen bonding competition and the structure of the solvated layer. These refinements in the model of the stationary phase solvated layer provide a much more detailed and accurate description of the intermolecular interactions responsible for retention and selectivity in RPLC than was previously available. A new modification of the method of measuring column mobile phase volume in RPLC employing retention linearization of an homologous series of compounds has been described from fundamental themodynamic principles and a statistically valid data reduction approach. The added advantage of providing thermodynamic information about the chromatographic system under study is inherent in this new technique. The experimental and theoretical bases for the new separation technique of magnetic field-flow fractionation (magnetic FFF) have been demonstrated. It has been shown that FFF techniques can be used in a diagnostic mode to study the dynamic stability of particle suspensions. The application of an external magnetic field to non-aqueous suspensions of sub-micron sized γFe₂O₃ particles, whose surface character has been modified by the adsorption of water, has been shown to enhance the suspension stability with respect to sedimentation. With the choice of proper operational conditions, magnetic FFF has also been demonstrated to be useful in monitoring particle flocculation as a result of its ability to separate particle flocculates on the basis of size.

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No description available.