School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa August, 2016 / One gram amounts of a commercial iron based catalyst were loaded into three reactors and reduced with syngas, hydrogen and carbon monoxide respectively. Fischer Tropsch experiments on the three reactors in parallel with the same operating conditions, namely 60 mL(NTP)/min, 1 bar gauge and 250 °C, were then conducted for extended periods and the gaseous products analysed. Initially (for about 150 hours) the three catalysts had quite different carbon monoxide conversions. After this until about 1000 hours the conversions were similar. However the distribution of products for the differently reduced catalyst was significantly different. This suggested that permanent changes had been done to the catalysts by the different reducing conditions. To try to understand what the differences during the reduction process might be, a thermodynamic analysis of the solid phases after reduction was done. Unfortunately because all the thermodynamic data for the possible carbides was not available this analysis was of limited value. However it did suggest that hydrogen reduced catalyst might contain more oxides and the carbon monoxide reduced catalyst might contain more carbides. Some electron microscope and XRD experiments supported these ideas and might account for the different selectivities of the differently reduced catalysts. Runs after about 5000 hours were done at different flowrates (60, 30 and 15 mL(NTP)/min) of syngas and again the big effects were on differences between the selectivities, the big effects being when going to the lowest flowrate. After about 12000 hours regeneration of the catalysts was then done by oxidation and then the same syngas reduction on all the catalysts. Runs were then done at different pressures (1, 10 and 20 bar gauge) and again selectivities were the biggest effects that remained, clearly showing the initial reduction had made permanent changes. In the final section some novel plots were used to try to make more sense of the results. It was shown that for all the catalysts the Olefin to Paraffin ratios were tied to each other under all conditions and that they were mainly a function of the conversions with much higher values at low conversions. / MT2017

Thesis advisor: Peter Clote / RNA folding pathways play an important role in various biological processes, such as 1) the conformational switch in spliced leader RNA from Leptomonas collosoma, which controls transsplicing of a portion of the 5’ exon, and 2) riboswitches–portions of the 5’ untranslated region of mRNA that regulate genes by allostery. Since RNA folding pathways are determined by the thermodynamic landscape, we have developed a number of novel algorithms—including FFTbor and FFTbor2D—which efficiently compute the coarse-grained energy landscape for a given RNA sequence. These energy landscapes can then be used to produce a model for RNA folding kinetics that can compute both the mean first passage time (MFPT) and equilibrium time in a deterministic and efficient manner, using a new software package we call Hermes. The speed of the software provided within Hermes—namely FFTmfpt and FFTeq—present what we believe to be the first suite of kinetic analysis tools for RNA sequences that are suitable for high throughput usage, something we believe to be of interest in the field of synthetic design. / Thesis (PhD) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

No description available.

This thesis is devoted to the study of a deformable material interface between two immiscible moving media, both of them being magnetizable. The first part concerns the establishment of a complete set of dynamical equations allowing a complete description of the non equilibrium phenomena including a coupling between the internal angular momentum and the electromagnetic field. The effects of the relaxation processes are also discussed. We show that the deformation of the interface introduces a nonlinear term, proportional to the mean curvature, in the surface dynamical equations of mass momentum and angular momentum. That term intervenes also in the singular magnetic and electric fields inside the interface which lead to the influence of currents and charge densities at the interface. In a second part, we give the expression for the entropy production inside the interface as well as in the bulk phase. Using the general principles of non equilibrium thermodynamics, we compute the different thermodynamical fluxes.

Colloidal macroions are known to interact very strongly with oppositely charged polyionic hydrogels. Sometimes this results in a non-uniform distribution of the macroions within the gel, a phenomenon that is not fully understood. This thesis is a summary of four papers on the development of a theory of the thermodynamics of macroions interacting with hydrogels, aimed at explaining the phenomenon of core/shell separation in spherical gels. It is the first theory of such interactions to use a rigorous approach to whole-gel mechanics, in which the elastic interplay between different parts of the gel is treated explicitly. The thesis shows that conventional theories of elasticity, earlier used on gels in pure solvent, can be generalised to apply also to gels in complex fluids, and that the general features of the phase behaviour are the same if mapped to corresponding system variables. It is found that the emergence of shells is due to attractions between macroions in the gel, mediated by polyions. Since the shell state is unfavourable from the perspective of the shell itself, being deformed from its preferred state, there will be a hysteresis between the uptake and the release of the macroion, like already known to occur with the uptake and release of pure solvent. Due to the elastic interplay, growth of the shell makes further growth progressively more favourable. Thus, unless there is a limited amount of macroions available the system will not reach equilibrium until complete phase transition has taken place. If the amount is limited the core/shell separation can be in equilibrium, so the volume of the solution that the gel is in contact with plays a very important part in determining the thermodynamic resting point of the system. The ability of a macroion/hydrogel to phase separate thus depends on the molecular properties whereas the ultimate fate of such a separation depends on the proportions in number between the ingoing components.

No description available.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 86-92). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemical Engineering, 2003. / Includes bibliographical references.

The application of Lagrange's equations to non-equilibrium reacting compressible thermofluid systems yields a modeling methodology for thermofluid dynamics compatible with the discrete energy methods used extensively in other energy domains; examples include mechanical systems simulations and molecular dynamics modeling. The introduction of internal energies as generalized coordinates leads to a thermomechanical model with a simple but general form. A finite element interpolation is used to formulate the ODE model in an ALE reference frame, without reference to any partial differential equations. The formulation is applied to highly nonlinear problems without the use of any time-splitting or shock-tracking methods. The method is verified via the solution of a set of example problems which incorporate a variety of reference frames, both open and closed control volumes, and moving boundaries. The example simulations include transient detonations with complex chemistry, piston-initiated detonations, canonical unstable overdriven detonations, high-resolution induction-zone species evolution within a pulsating hydrogen-air detonation, and the detonation of a solid explosive due to high-velocity impact. / text

The Best M.Phil Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,1993-1995 / published_or_final_version / Physics / Master / Master of Philosophy