<p>Bainite is a low temperature transformation product of austenite decomposition in steels. Its unique range of microstructures offers promising combinations of strength with ductility. At low transformation temperatures the crystallography of a phase transformation often plays an important role in the overall microstructure and how it develops. Therefore in this study the structures of ferrite/cementite and ferrite/austenite interfaces in bainite were investigated from a crystallographic viewpoint. After describing these interfaces, the idea of interphase boundary nucleation of cementite on a ferrite/austenite interface was investigated.</p> <p>An O-line model (a special case of the O-Lattice) was used to explain the observed experimental results on orientation relationship, habit plane and good matching direction between ferrite and cementite. The calculated orientation relationship was used in an NCS (near coincident site) model to describe several possible edge facets of cementite precipitates. The major observed edge facet in cementite is deviated from the more favored interfaces based on the NCS model. This deviation could imply that the edge facets are non-equilibrium interfaces whose orientations and morphologies are kinetically determined.</p> <p>Focused Ion Beam sectioning, conventional transmission electron and optical microscopy were used to shed more light on the three dimensional nature of a complex cementite-free bainitic microstructure. The faceted interfaces of bainitic ferrite were characterized and it was shown that the habit plane contains edge misfit dislocations. The orientation of the bainitic ferrite lath did not match an O-line model. Transformation time was considered to play an important role on the orientation and morphology of the bainitic laths and interfacial dislocation character.</p> <p>Finally, with the aid of known crystallographic relations and interfaces between the ferrite/cementite, ferrite/austenite and austenite/cementite phases, a model for cementite nucleation was proposed. This interphase boundary nucleus is assumed to form on a coherent ferrite/austenite interface and to possess ferrite/cementite and austenite/cementite calculated habit planes as two main facets surrounding the nucleus. It was shown that cementite nucleation would be viable if interfacial energies of all surrounding facets of a nucleus are in a semi-coherent energy range.</p> / Doctor of Philosophy (PhD)

The intent of this thesis is to investigate student approaches to linearity within a linear algebra context, focusing on definitional, computational, and theoretical skills. Linear algebra’s abstract nature constitutes a major challenge for a significant sector of STEM students, with the course often serving as undergraduates’ first encounter with mathematical proofs and extrapolations. The current student struggle is reflected through the prominent gap in knowledge derived from a lack of a concrete understanding of rudimentary concepts (like linearity), pivotal to student success. As such, this investigation aimed to bridge this gap by considering students’ modes of thinking regarding the elementary notion of linearity to improve the current course delivery and curriculum. Students were given three assessment questions targeting different skills integral to the mastery of linearity. Their responses were categorized using Action, Process, Object, Schema (APOS) and analyzed through Sierpinska’s (2000) proposed modes of thinking. About 26% of the participants responded correctly to question 1, 77% to question 2, and 59% to question 3. The analytic mode proved pivotal, specifically when considering definition application and computational abilities. The synthetic-geometric mode, however, was integral to the practical application of the concept. Further discussion and suggestions regarding the results and their implications on the current structure of linear algebra instruction are provided.

Metal-based nanoparticles (MNPs) are becoming increasingly common in commercial products. Release of these materials into the environment raises concerns about the potential risks they pose to aquatic life. Predicting these risks requires an understanding of MNPs' chemical transformations. In this study, arrays of immobilized MNPs fabricated by nanosphere lithography (NSL) were used to investigate environmental transformations of MNPs. Specifically, sulfidation of silver nanoparticles (Ag NPs) and dissolution of copper-based nanoparticles (Cu NPs) were investigated. Atomic force microscopy (AFM) and transmission electron microscopy were the primary analytical techniques for these investigations. Because the MNPs were immobilized on a solid surface, the samples were field deployable, environmentally relevant metal concentrations were maintained, and the confounding influence of MNP aggregation was eliminated. Ag NP samples were deployed in a full-scale wastewater treatment plant. Sulfidation occurred almost exclusively in anaerobic zones of the WWTP, where the initial sulfidation rate was 11-14 nm of Ag converted to Ag2S per day. Conversion to Ag2S was complete within 7-10 d. Dissolution rates of Cu-based NPs were measured in situ over a range of pH by flow-cell AFM. Based on the measured rates, CuO/Cu(OH)2 NPs dissolve completely within a matter of hours at any pH, metallic Cu NPs persist for a few hours to days, and CuxS NPs do not dissolve significantly over the time scales studied. Field deployment of samples in a freshwater stream confirmed these conclusions for a natural aquatic system. This research demonstrates that environmental transformations of MNPs will be a key factor in determining the ultimate form and concentration of NPs that aquatic organisms will be exposed to. / Ph. D.

The rise of ubiquitous computing devices has provided the catalyst for the next generation World Wide Web, one that shifts the focus from the desktop computer to mobile devices such as cell phones and PDAs, in an ever increasing range of modalities. Web interaction management in this setting must contend with a plethora of interaction interfaces and a diverse range of content types in addition to helping realize the full potential of multimodality (i.e., supporting flexible and personalized interactions between humans and sites). This thesis presents WS://IM, a new software framework for web interaction management that is capable of supporting multimodal interactions. In addition to presenting a loosely bundled, factorized architecture that supports hyperlink interaction, WS://IM has the unique facilitation for out-of-turn interaction. Out-of-turn interaction is a novel technique that helps realize mixed-initiative interactions between humans and Web sites. Design methodology, implementation details, and exposition through three implemented case studies are provided. / Master of Science

No description available.

Sputtered thin films have the capability of producing a very random distribution of alloying elements within a host element. This study demonstrates the ability of the SQUID (Superconducting Quantum Undulating Interference Device) to measure the Curie temperature of thin films of Pd(1-x)Fe(x). The Curie temperatures of these films were found to be significantly less than bulk samples having the same iron concentration. The Curie temperature, furthermore, showed a systematic shift to higher values as the thickness of the film increased. Magnetic structure below the Curie temperature is revealed in magnetization and a.c. susceptibility curves for x=. 078. For other samples susceptibility data exhibited more sensitivity than magnetization in revealing magnetic detail below the Curie temperature. We attribute some of this magnetic detail to cluster glass behavior. / Ph. D.

No / We report a numerical calculation of the melting point of NaCl. The solid-liquid transition was located by determining the point where the chemical potentials of the solid and liquid phases intersect. To compute these chemical potentials, we made use of free energy calculations. For the solid phase the free energy was determined by thermodynamic integration from the Einstein crystal. For the liquid phase two distinct approaches were employed: one based on particle insertion and growth using the Kirkwood coupling parameter, and the other involving thermodynamic integration of the NaCl liquid to a Lennard-Jones fluid. The latter approach was found to be significantly more accurate. The coexistence point at 1074 K was characterized by a pressure of -30+/-40 MPa and a chemical potential of -97.9+/-0.2kßT. This result is remarkably good as the error bounds on the pressure enclose the expected coexistence pressure of about 0.1 MPa (ambient). Using the Clausius-Clapyron relation, we estimate that dP/dT~3 MPa/K. This yields a melting point of 1064+/-14 K at ambient pressure, which encompasses the quoted range for the experimental melting point (1072.45-1074.4 K). The good agreement with the experimental melting-point data provides additional evidence that the Tosi-Fumi model for NaCl is quite accurate. Our study illustrates that the melting point of an ionic system can be calculated accurately by employing a judicious combination of free energy techniques. The techniques used in this work can be directly extended to more complex, charged systems.

No / Bulk crystallisation of protein therapeutic molecules towards their controlled drug delivery is of interest to the biopharmaceutical industry. The complexity of biotherapeutic molecules is likely to lead to complex material properties of crystals in the solid state and to complex transitions. This complexity is explored using batch crystallised lysozyme as a model. The effects of drying and milling on the solid-state transformations of lysozyme crystals were monitored using differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), FT-Raman, and enzymatic assay. XRPD was used to characterise crystallinity and these data supported those of crystalline lysozyme which gave a distinctive DSC thermogram. The apparent denaturation temperature (Tm) of the amorphous lysozyme was ∼201 °C, while the Tm of the crystalline form was ∼187 °C. Raman spectra supported a more α-helix rich structure of crystalline lysozyme. This structure is consistent with reduced cooperative unit sizes compared to the amorphous lysozyme and is consistent with a reduction in the Tm of the crystalline form. Evidence was obtained that milling also induced denaturation in the solid-state, with the denatured lysozyme showing no thermal transition. The denaturation of the crystalline lysozyme occurred mainly through its amorphous form. Interestingly, the mechanical denaturation of lysozyme did not affect its biological activity on dissolution. Lysozyme crystals on drying did not become amorphous, while milling-time played a crucial role in the crystalline-amorphous-denatured transformations of lysozyme crystals. DSC is shown to be a key tool to monitor quantitatively these transformations.

Yes / Bifractional transformations which lead to quantities that interpolate between other known quantities are considered. They do not form a group, and groupoids are used to describe their mathematical structure. Bifractional coherent states and bifractional Wigner functions are also defined. The properties of the bifractional coherent states are studied. The bifractional Wigner functions are used in generalizations of the Moyal star formalism. A generalized Berezin formalism in this context is also studied.

Tableau d'honneur de la Faculté des études supérieures et postdorales, 2015-2016