A brief review of three-dimensional turbulent boundary layer mean velocity profile models was presented, with emphasis on the applicability of these to predict cross flow profiles when skewing existed in any single profile. A recurving or s-shaped rectangular channel was used to experimentally investigate the possible existence of such a turbulent boundary layer flow. The time average velocity profiles along the centerline of this channel were obtained with a hot film anemometer. The resultant profiles indicated that a turbulent boundary layer can exist with cross flow in two lateral directions simultaneously in the same profile and this phenomenon can occur over a relatively long flow distance. Several attempts were made to fit the models of Eichelbrenner and Shanebrook to the measured cross flow profiles, but with only limited success. A test of the three-dimensional wall-wake formulation proposed by Coles was made for each profile. A shear velocity was inferred by a modification of the two-dimensional Ludwieg and Tillman skin friction equation, and by a modified form of the two-dimensional Clauser skin friction chart. A linear semi-logarithmic region was judged distinguishable for profiles with skewing in one lateral direction and with the limiting wall streamline angle less than approximately 30 degrees. Additionally in some instances a linear semi-logarithmic region was judged to exist when when simultaneous lateral skewing occurred in two directions. Generally, the constructed wake profiles did not resemble the universal form tentatively proposed by Coles, but rather resembled the characteristic preasymptotic form as discussed by Pierce. / Master of Science

The problem with which this investigation was concerned was the determination of group perception profiles of selected higher education faculties. These group perception profiles were based upon faculty perceptions of the ten most important criteria considered in evaluating faculty members for purposes of rank, promotion, salary, and tenure. Also, the study determined whether or not cluster profiles existed at three levels or types of institutions-- university, liberal arts, and junior college--and how such profiles differed between levels. This study had several purposes. The first was to determine how group perception profiles of higher education faculties clustered in response to perceptions of criteria considered in evaluating faculty members. The second was to determine if similar clusters existed at three types of institutions. A third was to determine differences in the proportion of teachers belonging to each identifiable cluster at each level of institution. The fourth was to determine differences in profiles according to proportions of teachers across common clusters. And finally, the fifth was to determine differences in profiles among faculty members in identified clusters at each institutional level according to biographical characteristics: age, rank, teaching experience, seniority, and highest degree held.

Abstract : The industrial partner of this project uses a slurry bubble reactor for the production of biogenic methanol. In the latter syngas is dispersed into the slurry continuous phase containing both liquid and solid phases. The rising bubbles containing a wide spectrum of the bubbles sizes, interact with the continuous phase due to the interface momentum transfer. The latter includes the drag, lift, wall lubrication and turbulent dispersion terms that require average bubble size, which needs to be calculated. One way to predict this average bubble size is by using population balance model (PBM), which can be coupled with the Eulerian framework. PBM also needs closure kernels for the bubble coalescence and bubble breakup. In this study, the influence of bubble coalescence and bubble breakup kernels have been studied in two- and three-phase system using eulerian approach, which solves momentum equation for each phase. The influence of the mesh sizes, number of bubble classes, numerical schemes, wall lubrication force and turbulent dispersion force are also included. In the two-phase system, results show that the Luo coalescence model needs to be tuned when used in combination with the Luo breakup kernel. The combination of the Luo coalescence and the Lehr breakup kernels (Luo-Lehr) show promising time-averaged radial profiles of gas holdup and axial liquid velocity as compared to empirical values. In the three-phase system, the combination of the Luo coalescence and the Lehr breakup kernels (Luo-Lehr) and the Luo coalescence and the Luo breakup kernels (Luo-Luo) predict convincing time-averaged radial profile of axial solid velocity as compared to experiments. However, at an elevated superficial gas velocity, a non-realistic behavior was predicted when compared to empirical observations. The sensitivity analysis results show that the 3 mm mesh size depicts a trend similar to the empirical values of the radial profiles of the gas holdup, axial liquid velocity, and solid axial velocity. The number of bubble classes influence the predicted bubble size distribution in the three-phase system while the numerical discretizing schemes have no influence on the results. The bench simulation results show that the inclusion of the turbulent dispersion term using a single porous tubular sparger influences the hydrodynamic behavior of the bubble column. / Le partenaire industriel de ce projet utilise un réacteur à suspension à trois phases pour la production de méthanol biogénique. Dans celui-ci, le gaz de synthèse est diffusé par barbotement dans la phase à suspension qui contient à la fois les phases liquide et solide. Les bulles en ascension présentent un large spectre de tailles et interagissent avec la phase à suspension en échangeant de la quantité de mouvement via leurs surfaces. Cet échange comprend les forces de trainé, de portance, de lubrification en proche parois et de dispersion par turbulence; lesquelles requièrent notamment le calcul de la taille moyenne des bulles. Une façon de prédire numériquement cette taille moyenne est de recourir à un modèle de bilan de population (PBM, de l’anglais Population Balance Model), qui peut être couplé avec un model multiphasique eulérien. Un tel PBM a requière des modèles de fermetures pour la coalescence et la rupture des bulles. Dans la présente étude, l'influence des modèles noyaux de coalescence et de rupture des bulles a été étudiée pour des systèmes à deux et à trois phases en utilisant l’approche eulérienne. L'influence de la taille du maillage, du nombre de classes de bulles, du schéma numérique, de la force de lubrification en proche parois et de la force de dispersion par turbulence sont également incluses. Dans un système bi-phasique, les résultats montrent que le modèle de coalescence Luo doit être ajusté lorsqu'il est utilisé en combinaison avec le noyau de rupture Luo. La combinaison des noyaux de coalescence Luo et de rupture Lehr (Luo-Lehr) montrent des profils radiaux moyennés dans le temps qui sont valides pour la concentration de gaz et la vitesse axiale du liquide par rapport aux mesures expérimentales. Dans le système triphasé, la combinaison des modèles noyaux de coalescence de Luo et de rupture de Lehr (Luo-Lehr) et de la coalescence de Luo et de rupture de Luo (Luo-Luo) prédisent des profils radiaux moyennés dans le temps qui sont valides pour la vitesse axiale moyenné dans le temps par rapport aux expériences. Cependant, à une vitesse de gaz superficielle élevée, ces profils prédisent un comportement non réaliste par rapport aux observations empiriques. Les résultats de l'analyse de sensibilité du maillage montrent qu’avec des cellules de 3 mm, le model prédit une tendance similaire aux valeurs empiriques pour les profils radiaux de concentration du gaz, de vitesse axiale du liquide et de vitesse axiale solide. Le nombre de classes de bulles influe sur les distributions prédites de taille de bulle dans le système triphasé alors que les schémas de discrétisation numériques n'ont aucune influence sur les résultats. Les résultats des simulations d’un banc d’essai avec diffuseur à bulles poreux montrent que tenir compte du terme de dispersion influence le comportement hydrodynamique de la colonne à bulles.

Heavy haul railway operations permit the transport of huge volumes at lower cost than other modes of transport. The low cost can only be sustained if the maintenance costs associated with such railway operations are minimised. The maintenance costs are mainly driven by wheel and rail damage in the form of wear and rolling contact fatigue (RCF). Low wear rates in the wheel-rail interface have resulted in an increase in the prevalence of rail RCF, thereby increasing rail maintenance costs. The aim of this study is to develop an approach to reduce rail RCF on South Africa’s iron ore export line by managing the worn wheel shape. This approach is developed by evaluating wheel and rail profile shapes that contribute the most to RCF initiation, studying the influence of suspension stiffness and rail profile changes as well as a redesign of the wheel profile. The influence of wheel and rail profile shape features on the initiation of rolling contact fatigue (RCF) cracks was evaluated based on the results of multibody vehicle dynamics simulations. The damage index and surface fatigue index were used as two damage parameters to assess the influence of the different features. The damage parameters showed good agreement to one another and to in-field observations. The wheel and rail profile shape features showed a correlation to the predicted RCF damage. The RCF damage proved to be most sensitive to the position of hollow wear and thus bogie tracking. RCF initiation and crack growth can be reduced by eliminating unwanted shape features through maintenance and design and by improving bogie tracking. Two potential mitigation measures had been adapted from those published in literature to reduce RCF. The mitigation measures involved changes in suspension stiffness to spread wheel wear across the tread and the use of gauge corner relief rail profiles. These mitigation measures were evaluated by means of multibody dynamics and wear maintenance costs. These mitigation measures, however, did not prove to be successful in reducing RCF initiation while maintaining a low wheel wear rate. The current operating conditions on South Africa’s iron ore line, although still not optimal overall, were found to be better in terms of their wear and RCF performance than the two proposed RCF mitigation measures. Based on the finding of the study on two RCF mitigation measures it was recommended that a conformal wheel profile be developed to spread the wheel wear across the tread to reduce the occurrence and propagation of RCF cracks, while still maintaining low wheel wear rates. A comparative study of this new wheel profile design and the current wheel profile design was therefore performed using multibody dynamics simulation together with numerical wheel wear and RCF predictions. The advantages of the conformal wheel profile design were illustrated by evaluating the worn shape and resulting kinematic behaviour of the conformal design. The conformal design had a steadier equivalent conicity progression and a smaller conicity range compared with the current wheel profile design over the wheel’s wear life. The combination of a conformal wheel profile design with 2 mm hollow wear and inadequate adherence to grinding tolerances often result in two-point contact, thereby increasing the probability of RCF initiation. The conformal wheel profile design was shown to have many wear and RCF benefits compared with the current wheel profile design. However, implementation of such a conformal wheel profile must be accompanied by improved rail grinding practices to ensure rail profile compliance. Based on these findings an approach is proposed where the conformal wheel profile design together with improved compliance of the in-service rail profiles to the target rail profile are implemented. This has the potential to reduce RCF initiation on South Africa’s iron ore export line. / Thesis (PhD)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

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Philosophiae Doctor - PhD / It has been noted by Lin (2013) that studies on multilingual talk, as illustrated by code switching in the classroom, have been repetitive and descriptive, and have for a while not been underpinned by substantially new or different questions (Lin, 2013:15). First, many of the studies in the literature have, for instance, concluded that there is a functional allocation of languages (FAL) in multilingual classroom teacher talk (e.g. Baker, 2012; Martin, 1996; Probyn, 2006, 2014; Jegede, 2012; Modupeola, 2013; Salami, 2008), such that language „a‟ is used for presentational knowledge, and language „b‟ is used for explanatory knowledge, and these claims have not been subjected to sustained scrutiny. Secondly, codeswitching and translanguaging increasingly have been the dominant and exclusive frameworks used, and this has limited the kinds of insights that can be obtained or the kinds of questions that can be posed. Thirdly, where the effects of multilingual teacher talk on students‟ understanding or knowledge are at all captured in studies, such effects have either been based on researcher intuition or have not been the object of sustained empirical demonstration. Fourthly, many studies have assumed merely that it is the configuration of languages that produces claimed effects of multilingual teacher talk, and attention has hardly been paid to repetition of content or to knowledge structure. Fifthly, it is not often the case that studies or findings are presented in a nuanced form that takes into account the possible effect of different subject types, school types or levels of study. Sixthly, and overall, many studies making claims on the effect of teacher‟s code-switching or trans-languaging on students‟ knowledge do not theoretically engage with knowledge, beyond the distinction between presentational and explanatory forms of knowledge, thus illustrating what Maton (2013) regards as “knowledge-blindness” (that is, the paradox of limited engagement with knowledge structures in pedagogical research making knowledge claims). As a result, little is known about how specific units of knowledge are encoded according to categories in a theory of knowledge, how knowledge encodings interface with languages, and how composite knowledge structures-language profiles can be visualised. This study draws on Legitimation Code Theory Semantic and Terminology Theory in order to investigate the interface of language and knowledge in multilingual teacher-talk in science and business studies classrooms in Yola, North-Eastern Nigeria. This focus should make it possible to answer questions such as the following which, though important, have not often been posed on account of the limited engagement in the research on classroom multilingualism with theories of knowledge: a) to what extent is it appropriate to claim that there is a functional allocation of language in multilingual teacher-talk (in which language „a‟ is used for so-called presentational knowledge, and language „b‟ for explanatory knowledge)?; b) what kinds of encodings of knowledge occur in a set of science and business studies lessons?; c) given documented visual patterns of knowledge dynamics emerging from recent research in the sociology of knowledge (e.g. semantic waves, semantic flatlines both high and low, downward shift and upward shift), (Maton: 2013, 2014a, 2014b), what knowledge profiles are observable and how does language use in multilingual teacher-talk map onto these patterns?; d) how are any observed differences in the composite knowledge-language profiles to be explained?; and e) what effects do various language-knowledge profiles have on students‟ understanding of the lesson and on their demonstration of their knowledge? Data for the study was derived from transcripts of audio-recorded multilingual teacher-talk in two subjects (integrated science and business studies) as taught in grades seven and nine in four secondary schools (two private and two public schools) in Yola, North-East Nigeria. Findings show, among others, that it is not always the case that the official classroom language (English) is used for introductory discourses, and the non-official classroom languages are used for explanatory discourses. Findings further reveal that it is not primarily the functional allocation of languages that explains perceptions or empirical claims of enhanced student understanding. We also observed that the number of content iterations, combined with knowledge structures, is an important factor that enhances or explains the performance of students. While this research has paid a lot of attention to teacher talk in the classrooms in two sites in Yola, North-East, Nigeria, where the use of Hausa and Fulfulde languages by the students is mainly in the spoken form, it would be interesting for future research to replicate this type of study in an environment where the non-official language of the classroom is perhaps used more frequently in reading and writing.

The future success of chargeable vehicles will, among other factors, depend on their charging costs and their ability to charge with minimal disturbances to the national, local and household electrical grid. To be able to minimize costs and schedule charging sessions, there has to be knowledge of how the charging power varies with time. This is called charging profile. A number of charging profiles for a Volvo V60 plug‑in hybrid electric vehicle have been recorded. For charging currents above 10 A they prove to be more complex than are assumed in most current research papers.   The charging profiles are used together with historical electricity prices to calculate charging costs for 2013 and 2014. Charging is assumed to take place during the night, between 18:00 and 07:00, with the battery being totally depleted at 18:00. By using a timer to have the charging start at 01:00, instead of immediately at 18:00, annual charging costs are reduced by approximately 7 to 8%. By using dynamic programming to optimize the charging sessions, annual charging costs are reduced by approximately 10 to 11%. An interesting issue regarding dynamic programming was identified, namely when using a limited set of predetermined discrete control signals, interpolation returns unrealizable cost-to-go values. This occurs specifically for instances crossing the zero cost-to-go area boundary.   It is concluded that the mentioned savings are realizable, via implementing timers or optimization algorithms into consumer charging stations. Finally, by using these decentralized charging planning tools and seen from a power usage perspective, at least 30% of the Swedish vehicle fleet could be chargeable and powered by the electrical grid.

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In clinical experiments, the evolution of a product concentration in tissue over time is often under study. Different products and tissues may be considered. For instance, one could analyse the evolution of drug concentration in plasma over time, by performing successive blood sampling from the subjects participating to the clinical study. One could also observe the evolution of radioactivity uptakes in different regions of the brain during a PET scan (Positron Emission Tomography). The global objective of this thesis is the modelling of such evolutions, which will be called, generically, pharmacokinetic curves (PK curves). Some clinical measures of interest are derived from PK curves. For instance, when analysing the evolution of drug concentration in plasma, PK parameters such as the area under the curve (AUC), the maximal concentration (Cmax) and the time at which it occurs (tmax) are usually reported. In a PET study, one could measure Receptor Occupancy (RO) in some regions of the brain, i.e. the percentage of specific receptors to which the drug is bound. Such clinical measures may be badly estimated if the PK curves are noisy. Our objective is to provide statistical tools to get better estimations of the clinical measures of interest from appropriately smoothed PK curves. Plenty of literature addresses the problem of PK curves fitting using parametric models. It usually relies on a compartmental approach to describe the kinetic of the product under study. The use of parametric models to fit PK curves can lead to problems in some specific cases. Firstly, the estimation procedures rely on algorithms which convergence can be hard to attain with sparse and/or noisy data. Secondly, it may be difficult to choose the adequate underlying compartmental model, especially when a new drug is under study and its kinetic is not well known. The method that we advocate to fit such PK curves is based on Bayesian Penalized splines (P-splines): it provides good results both in terms of PK curves fitting and clinical measures estimations. It avoids the difficult choice of a compartmental model and is more robust than parametric models to a small sample size or a low signal to noise ratio. Working in a Bayesian context provides several advantages: prior information can be injected, models can easily be generalized and extended to hierarchical settings, and uncertainty for associated clinical parameters are straightforwardly derived from credible intervals obtained by MCMC methods. These are major advantages over traditional frequentist approaches.

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