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<p>Void growth and coalescence in a single layer model material with holes were visualized by the environmental electron scanning microscope coupled with in situ tensile test. Single sheet model materials were manufactured with a line of laser drilled holes through thickness. In order to investigate the effect of shear localization, the line of holes were oriented with the misorientation angle <em>θ </em>= 0°, 15°, 30°, and 45°. The α-brass samples were studied to introduce the work hardening effect in comparison with the pure copper samples.</p> <p>By taking images at intervals with small strain increments, the void growth behaviors were visualized during the interrupted tensile testing. The void coalescence (defined consistent with Hosokawa et al (2011), as the point at which the voids stopped shrinking laterally) was successfully captured for the first time in the two dimensional studies. The evolutions of void shape change and void rotation during deformation were also studied quantitatively. The results showed that the higher work hardening behaviors can suppress the void coalescence. It also showed that the effect of local volume fraction dominated the coalescence event rather than the void spacing and shear localization. A comparison of the classic models with the experimental results were also made.</p> / Master of Science in Materials Science and Engineering (MSMSE)

<p>Ships, including those in the US Navy, collect oily wastewater in their bilge due to onboard cleaning and mechanical operations. Oil-in-water emulsions (O/W) are present in bilgewater, and their filtration is difficult due to surfactants provided by cleaning products. Despite cleaning efforts, over 457,000 tons of oil are discharged into the ocean every year. An often overlooked aspect of bilgewater emulsions is their evolution, as the ship's movement at sea provides extra energy that can further emulsify the collected oil. This work aims to understand the effects of motion on model bilgewater emulsions by tracking their evolution in dynamic (rocking motion) and static conditions. The model bilgewater emulsion comprises mineral oil, deionized water with 0.42 M NaCl to mimic the salinity of seawater and sodium lauryl ether sulfate and Triton X-100, as commonly found anionic and nonionic surfactants, respectively. A rocker is used to simulate a ship motion; 15 mL of emulsion were placed in 50 mL centrifuge tubes to mimic partially filled bilgewater tanks. Emulsions were characterized via laser diffraction and optical microscopy. Model bilgewater emulsions with either SLES or Triton X-100 at concentrations above 100 ppm and 500 ppm, respectively, show long-term stability in static (no-rocking) conditions up to 20 days of observation. These concentrations represent the minimum surfactant concentration needed to obtain stable emulsions under static conditions. Under dynamic conditions, the minimum surfactant concentration to obtain stable emulsions increases to 500 ppm and 1000 ppm for SLES and Triton X-100, respectively. These results mean that the ship motion can induce drop coalescence in unstable emulsions with lower surfactant concentrations. However, the drop size distributions for stable emulsions under dynamic conditions show further emulsification as the average drop size decreases. The ship motion can help further reduce the size of the emulsion drops to diameters < 2.8 µm, which are significantly harder to filter out using current methods. A bilgewater tank partially filled will likely show a higher amount of sloshing than a filled one. To understand the effects of bilgewater storage volume on emulsification, a series of dynamic experiments were carried out with samples that contained up to 100% of the centrifuge tube volume occupied by the model bilge water emulsion. Even when 100% of the centrifuge volume is occupied and sloshing is eliminated, the oil moves due to density differences, and the shear stress between fluids can induce the generation of drops < 2.8 µm. In summary, this work shows that the ship motion provides enough energy for emulsification once a minimum surfactant concentration is reached regardless of the volume of emulsion stored in the tanks. The data suggests that the best way to mitigate stable bilgewater emulsion formation is by reducing surfactant concentration.</p>

Cette thèse se concentre sur certains sujets en génétique des populations. Dans la première partie, nous donnons des formules y compris l'espérance et la variance de la hauteur et celles de la longueur du graphe de recombinaison ancestral (ARG) et l'espérance et la variance du nombre de recombinaison et nous montrons que l'espérance de la longueur de l'ARG est une combinaison linéaire de l'espérance de la longueur de la coalescence de Kingman et l'espérance de la hauteur de l'ARG. En outre, nous avons obtenu une relation entre l'espérance la longueur de l'ARG et l'espérance du nombre de recombinaisons. À la fin de cette partie, nous montrons que l'ARG descend de l'infini de telle sorte que X_0 =∞, alors que X_t < ∞ ; pour tout t et on trouve la vitesse à laquelle l'ARG descend de l'infini. Dans la deuxième partie on généralise la formule d'échantillonnage d'Ewens (GESF) en présence de la recombinaison pour les échantillons de taille n = 2 et n = 3. Dans la troisième partie de la thèse, nous étudions l'ARG le long du génome et nous avons trouvé la distribution du nombre de mutations dans le cas avec une seule recombinaison dans la généalogie de l'échantillon. / This thesis is concentrated on some sub jects on population genetics. In the first part we give formulae including the expectation and variance of the height and the length of the ancestral recombination graph (ARG) and the expectation and variance of the number of recombination events and we show that the expectation of the length of the ARG is a linear combination of the expectation of the length of Kingman's coalescent and the expectation of the height of the ARG. Also we show give a relation between the expectation of the ARG and the expectation of the number of recombination events. At the end of this part we show that the ARG comes down from infinity in the sense that we can dfine it with X_0 = ∞, while X_t <∞ ; for all t and we find the speed that the ARG comes down from infinity. In the second part wfind a generalization of the the Ewens sampling formula (GESF) in the presence of recombination for sample of sizes n = 2 and n = 3. In the third part of the thesis we study the ARG along the genome and we we find the distribution of the number of mutations when we have one recombination event in the genealogy of the sample.

Fossil fuel is an important energy source, but is unavoidabiy running out. Since the cellulosic material is the most abundant source of organic matter, the ethanol, which is produced from cellulosic waste materials, is gaining more and more attention. These materials are cheap, renewable and their availability makes them superior compared to other raw materials. The cellulose must be hydrolyzed to glucose before it can be fermented to ethanol. The enzymatic hydrolysis of cellulose using cellulase enzymes is the most widely used method. The production cost of cellulase enzymes is the major cost in ethanol manufacture. To optimize the cost of ethanol production, enzyme stability needs to be improved through maintaining the activity of the enzymes and by optimizing the production of the cellulase. The aim of researchers, engineers and industrials is to get more biomass for the same cost. The filamentous fungus Trichoderma reesei has a long history in the production of the cellulase enzymes. This production can be influenced strongly by varying the growth media and culture conditions (pH, temperature, DO, agitation,... ). At present, it is my opinion that no modelling study has included both the hydrodynamic and kinetic aspects to investigate the effect of shear and mass transfer on the morphology of microorganisms that influence the rheology of the broth and production of cellulase. This thesis presents the development of a mathematical model for cellulase production and the growth of biomass in an airlift bioreactor. The kinetic model is coupled with the methodology of two-phase flow using mathematical models based on the bubble break-up and coalescence to predict mass transfer rate, which is one of the critical factor in the fermentation. A comparison between the results obtained by the developed model and the experimental data is given and discussed. The design proposed for the airlift geometry by Ahamed and Vermette enables us to get a high mass transfer and production rate. The results are very promising with respect to the potential of such a model for industrial use as a prediction tool, and even for design.

We propose a mathematical procedure to derive a stochastic parameterization for the bulk warm cloud micro-physical properties of collision and coalescence. Unlike previous bulk parameterizations, the stochastic parameterization does not assume any particular droplet size distribution, all parameters have physical meanings which are recoverable from data, all equations are independently derived making conservation of mass intrinsic, the auto conversion parameter is finely controllable, and the resultant parameterization has the flexibility to utilize a variety of collision kernels. This new approach to modelling the kinetic collection equation (KCE) decouples the choice of a droplet size distribution and a collision kernel from a cloud microphysical parameterization employed by the governing climate model. In essence, a climate model utilizing this new parameterization of cloud microphysics could have different distributions and different kernels in different climate model cells, yet employ a single parameterization scheme. This stochastic bulk model is validated theoretically and empirically against an existing bulk model that contains a simple enough (toy) collision kernel such that the KCE can be solved analytically. Theoretically, the stochastic model reproduces all the terms of each equation in the existing model and precisely reproduces the power law dependence for all of the evolving cloud properties. Empirically, values of stochastic parameters can be chosen graphically which will precisely reproduce the coefficients of the existing model, save for some ad-hoc non-dimensional time functions. Furthermore values of stochastic parameters are chosen graphically. The values selected for the stochastic parameters effect the conversion rate of mass cloud to rain. This conversion rate is compared against (i) an existing bulk model, and (ii) a detailed solution that is used as a benchmark. The utility of the stochastic bulk model is extended to include hydrodynamic and turbulent collision kernels for both clean and polluted clouds. The validation and extension compares the time required to convert 50\% of cloud mass to rain mass, compares the mean rain radius at that time, and used detailed simulations as benchmarks. Stochastic parameters can be chosen graphically to replicate the 50\% conversion time in all cases. The curves showing the evolution of mass conversion that are generated by the stochastic model with realistic kernels do not match corresponding benchmark curves at all times during the evolution for constant parameter values. The degree to which the benchmark curves represent ground truth, i.e. atmospheric observations, is unknown. Finally, among alternate methods of acquiring parameter values, getting a set of sequential values for a single parameter has a stronger physical foundation than getting one value per parameter, and a stochastic simulation is preferable to a higher order detailed method due to the presence of bias in the latter. / Graduate / 0725 0608 0405 / davidc@uvic.ca

La formation de cristaux dans la phase dispersée d'une émulsion huile-dans-eau fait apparaître des irrégularités ou aspérités aux interfaces pouvant entraîner des modifications rhéologiques spectaculaires comme le passage d'un état fluide à un état solide. Nous montrons que la gélification des émulsions par voie thermique peut être attribuée à deux mécanismes : la coalescence partielle, qui permet grâce aux cristaux interfaciaux deformer des liens irréversibles entre gouttes, et le «jamming » qui est un phénomène de blocage dû aux aspérités empêchant le mouvement relatif des surfaces au contact. Sur des systèmes modèles, nous établissons que les mécanismes et les cinétiques de gélification sont contrôlés par la proportion d'huile cristallisée, le diamètre moyen des gouttes et la composition de l'interface. Nous montrons en particulier que la coalescence partielle peut être décrite comme un processus de percolation nécessitant des contacts de type « solide contre liquide » entre les gouttes. Nous montrons ensuite que la mise en écoulement des émulsions ou des gels peut conduire à deux situations limites : la séparation macroscopique des phases (ou barattage) ou bien la persistance d'un gel de plus faible connectivité. Nous étudions l'influence des paramètres qui sont à l'origine de cette évolution topologique. La variété des états accessibles rend ces matériaux très attractifs pour les secteurs de la cosmétique et l'agroalimentaire.