This thesis carefully investigates some of the limitations of existing methods for atomic spectroscopic determination of mercury, selenium and arsenic in biological and environmental materials. In particular the need for adequate sample preparation to ensure reliable atomic spectroscopic determination of these metalloids was demonstrated extensively. The thesis evaluates four most commonly used wet digestion methods for the accurate determination of mercury in biological and environmental materials by cold vapour atomic absorption spectroscopy. Excellent recovery efficiencies were obtained with this digestion mixture in fish homogenate, horse kidney, soil, canned fish and hair samples for inorganic and organic mercury. The suitability of the digestion method for the reliable determination of mercury in soil, hair and canned fish samples was also demonstrated. Mercury levels in these samples were found within normal acceptable range. The thesis outlines a new simple procedure for overcoming the loss of mercury due to sample charring. It also described a new sample ultrasound low temperature wet digestion method for biological and environmental materials. The main advantage of this approach over other conventional methods is its ability to release all mercury in inorganic form from biological and environmental samples at much lower temperatures than reported earlier / Doctor of Philosophy (PhD)

The current research work investigates the behaviour of steel and composite beams as well as beam-to-column connections at elevated temperatures. Significant attention is needed to identify the main issues, as the behaviour is profoundly different from that at ambient temperature. Local buckling of the beam flange outstands has been found to be highly significant in accelerating the development of catenary action in fire, since this action is reliant on hinges forming which may result from local buckling. Local buckling of the beam web, which experiences a non-uniform temperature variation, is also important because the mechanical properties of the steel are degraded non-uniformly from their ambient values. Current formulations for web buckling at ambient temperature therefore need substantial revision at elevated temperatures. Very large compressive forces are developed within the beams initially and these induce large stresses in the column web; hitherto this has not been considered. Developing a formulation representing the mechanics of this potential failure zone in the column web in the compression region of the connection is a useful and needed addition to research in the topic. Predicting the critical temperature in a connection that causes failure of the bolts, end plate and column flange in the tension zone of the connection is considered in this research work. An elastic analysis of a panel zone in a rigid or semi-rigid joint in a steel frame, which is based on simple equilibrium considerations that takes into account the shear and flexural deformations of the panel zone, is developed at elevated temperatures. In order to model the structural response of a composite beam restrained by cooler members in a steel compartment fire in a frame structure at elevated temperature, recourse is needed to a geometric nonlinear formulation, since the beam transverse deflections are not negligible and the axial compressive force in the member is also substantial at the early stages of the fire. This thesis presents such a formulation, which incorporates partial interaction between the concrete slab and steel component, as well as the degradation of the stiffnesses of the components of the composite beam prior to yield at elevated temperature.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Self-propagating high-temperature synthesis (SHS) is a new method of producing advanced ceramic materials and offers an attractive alternative to conventional methods of materials processing. An experimental investigation was carried out to determine the SHS reaction wave propagation speed in a vertical cylindrical compact made from a mixture of titanium and graphite powders. Ignition was accomplished by radiatively heating the top surface of the cylinder by resistively heated tungsten heating coils. Syntheses were carried out in inert argon environment and under atmospheric pressure. Propagation speeds were determined by analyzing the temperature distribution with time at two locations at known axial distance. Effects of various system parameters, such as, density and diameter of the initial compact, different mixing ratios of the reactants and dilution with product, on reaction propagation speed were determined. A numerical model was also developed to predict the propagation speed. A two-dimensional formulation was adopted with both radiative and natural convective heat loss from the periphery of the cylindrical compact using constant values of properties and kinetic parameters. Two different kinetic models describing the reactions involving solids are employed to calculate the wave speed using a finite difference scheme. The calculated results were compared with the experimental data. Trends of the results with Kanury kinetic model were found to be in better agreement with the experiments. Results showed no significant effect of heat loss on the propagation speed within a practical range of compact diameter. Quenching conditions of the reaction for titanium rich and carbon rich cases and also for the case of dilution with the product were identified. Variation of propagation speed with sample initial density showed a maximum value at densities between 2.1 gm/cm³ and 2.2 gm/cm³. During the synthesis, the samples were found to expand axially. Hence the final product obtained was highly porous with densities below 50% of the density of TiC. / Graduation date: 1991

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 184-189).

Thesis (Ph.D.)--University of Texas at Arlington, 2008.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 119-128).

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