title: In vivo assessment of the relation between trabecular bone structure in the radius and gender, aging, mechanical loading and fracture

contributor:
Webber, Colin E.
Medical Sciences

subject:
Medical Sciences
Medical Sciences

abstract: Bone structure is compromised in individuals with osteoporosis. Indices of trabecular bone structure which reflect the connectivity (CI), the average dimensions of the marrow holes (HA ) and the area of the largest hole (HM ) at the distal radius can determined in vivo . This work evaluates whether these structural indices (1) are influenced by gender, aging and mechanical loading and (2) aid in the discrimination of individuals with low bone mass most at risk for fracture. Gender and age-related patterns of bone structure in the nondominant distal radius measured using peripheral quantitative computed tomography (pQCT) demonstrate the expected trends in a cross-sectional study of 145 healthy adults. Men have a better connected, less porous trabecular network. The age-related decrease in CI in men (-0.8%/yr, p < 0.05) is less pronounced than in women (-2.2%/yr, p < 0.001). Similarly, there are significant age-related increases in HA (+2.2%/yr, p < 0.01) and H M (+1.1%/yr, p < 0.01) in women but not in men. To investigate the impact of mechanical loading associated with hand dominance on indices of bone structure, bilateral images for 106 healthy adults were acquired. For all subjects, HM is significantly smaller in the dominant radius (p < 0.01). Right handed subjects (n = 96) have greater CI (p < 0.05) and smaller HM (p < 0.01) in the dominant limb. The effect of altered mechanical loading on bone structure was assessed by immobilizing the nondominant limb of 10 healthy volunteers in a plaster cast for 6 weeks followed by a remobilization period of 1 year. HM increases (p = 0.04) during immobilization and recovers within 3 months of remobilization. The ability of indices of trabecular structure to discriminate individuals with recent wrist fracture (n = 22) from controls matched for bone density (n = 22) was evaluated. The fracture group has a larger mean HA than the group without fractures (p < 0.05). The relative odds of wrist fracture is 6.9 (95% CI: 1.3 to 37.3) for individuals with a HA ≥ 6 mm2 . These data show that indices of trabecular bone structure, derived from pQCT images, reflect the expected patterns with respect to gender, age and mechanical loading. Preliminary results suggest that measuring HA at the distal radius may aid in the identification of individuals with low bone mass who will sustain a fracture.

abstract: Doctor of Philosophy (PhD)


title: The experiences of people who use alternative therapies: A symbolic interactionist analysis

contributor:
Shaffir, William
Sociology

subject: Sociology Sociology

abstract: This thesis focuses on Canadians who use alternative therapies. Using a symbolic interactionist perspective, which emphasizes individuals' own understandings of reality as a basis for their actions and in-depth, qualitative interviews, I explored how and why people come to use alternative medicine, the ideology that informs the alternative models of health and healing they espouse, and the impact this ideology has on them. I found that the twenty-one people who participated in this research sought out alternative therapies in order to solve problems for which they found little or no redress in allopathic medicine. They began using alternative therapies through a variety of different points of entrée including encounters with friends, family members, and the media, among others. Once involved in using these therapies they developed ever-expanding networks of alternative health care composed of alternative practitioners and others who use alternative therapies. In participating in alternative health care, and in interaction with others who use it, these people began to take on alternative ideologies of health and healing. These ideologies can impact on individual identity in two important ways. Some of the people who took part in this research became so enamoured with alternative approaches to health care that they began the process of becoming alternative healers themselves. For others the impact was more pervasive. For these informants, the ideology contained within the alternative model of health and healing became a mechanism through which they transformed themselves, creating a sense of themselves as healthy. This thesis contributes to knowledge by adding to the relatively sparse literature on individuals who use alternative approaches to health and health care, as well as the hitherto under-developed area of the impact use of these therapies has on individuals' subjective perceptions of self.

abstract: Doctor of Philosophy (PhD)


title: Changes in Electromyographic Activity in Human Muscle Fatigue

contributor:
McComas, Alan
Medical Sciences

subject:
Medical Sciences
Medical Sciences

abstract: The purpose of this research was to determine the physiological mechanism(s) underlying the reduction in voluntary electromyographic (EMG) activity with maximal contractions during fatigue. The specific hypothesis was that this reduction in EMG activity results from reflex inhibition of homonymous motoneurons by afferents from the fatigued muscles. The experiments were conducted on the human ankle dorsiflexor and plantarflexor muscles, with the use of eschemia to accelerate the fatigue process. In the first part of the study it was shown that, within 3-4 minutes, repetitive indirect stimulation of the dorsiflexor muscles via the peroneal nerve, at either 15 Hz or 30 Hz, could abolish dorsiflexion torque elicited by single shocks and trains of stimuli. During the 15 Hz fatiguing frequency the relative loss of dorsiflexion torque was greater than the decline in the amplitude of the evoked muscle compound action potentials (M-waves). Tus 15 Hz was the rate of fatiguing stimulation used in the remainder of the study. In the second part of the study, fatiguing indirect stimulation at 15 Hz caused significant reduction in both the dorsiflexion torque and EMG activity associated with subsequent maximal voluntary contractions (MVCs) of 66.1 ± 16.4% and 50.3 ± 27% respectively. The relative preservation of M-wave amplitudes in the fatigued muscle (reduction of 13.1 ± 22.9%) indicated that most of the loss of EMG activity was not due to inexcitability of the neuromuscular junctions or muscle fibre membranes. Nor could the reduction in voluntary EMG activity have been due primarily to failure of subjects to exert maximal voluntary effort since supraspinal motor pathways had not been involved in the fatigue process. Furthermore, during the MVC, no additional force was evident with a supramaximal interpolated stimulus. Hence, reflex inhibition appeared to be the most likely mechanism. The third part of the study explored the possibility that the reduction in voluntary EMG activity during fatigue was due to a lower level of alpha motoneuron excitability; for these experiments recordings were made of the electrically-induced homonymous response (H-reflex) of the soleus muscle. It was shown that the H-reflex excitability was depressed by 44.4 ± 25.1% during fatigue of the right soleus muscle using 15 Hz stimulation under ischemic conditions; the H-reflex excitability in the nonfatigued left soleus did not change significantly. The maximum M-wave amplitudes demonstrated a mean decline of only 8.8 ± 11.9% indicating good peripheral excitability of the muscle fibre membranes. Control experiments performed under ischemic conditions alone (without induced fatigue) or with electrical stimulation alone (without ischemia and hence without fatigue) failed to demonstrate any significant changes in reflex excitability. Thus, in the absence of fatigue, the depression could not be accounted for on the basis of either ischemia or electrical stimulation; instead the findings were consistent with the presence of an inhibitory reflex from the fatigued muscle onto the homonymous alpha motoneurons. In the final part of the study it was demonstrated, by means of pressure-induced impulse blockade of large myelinated afferents in the sciatic nerve prior to fatigue, that the mean plantarflexor torque produced during MVCs decreased by 38.0 ± 18.6% from the postblock value compared to a decrease of 5.2 ± 7.0% in the ischemia control; the mean EMG activity decreased from postblock values by 43.4 ± 15.6% following fatigue and by only 6.6 ± 5.5% following ischemia alone. These results were very similar to those demonstrated without any blockade of large diameter afferents. This suggested that the afferents involved in the putative reflex inhibition of the alpha motoneuron pool with fatigue were likely to have been those with small diameters (Group III and IV). This research provided evidence suggestive that the reduction in voluntary EMG during fatigue, in both tibialis anterior and soleus muscles, resulted from reflex inhibition of the motoneuron pool.

abstract: Doctor of Philosophy (PhD)


title: Three Dimensional Tracking of Four Point Planar Patterns Using Corner

contributor:
Kitai, R.
Capson, David
Electrical and Computer Engineering

subject:
Electrical and Computer Engineering
Electrical and Computer Engineering

abstract:
This thesis concerns tracking of planar shapes using a single camera view. Two dimensional silhouette projections of planar shapes randomly oriented and positioned and rotational orientation with respect to the camera. This information can then be provided to robots or automated guided vehicles for automated assembly, docking, shape identification and retrieval.

Silhouettes are initially encoded in the system as a linked list of vertex points representing changes in the direction of the contour. This contour is employed to get an initial estimate of the shape's position. Corner feature points of the shape are then more accurately located using a fast corner location algorithm. A photogrammetric solution is then applied to the projection points of the corners to determine the three dimensional position of the shape. The photogrammetric technique employed does not require a least squares fit as does the traditional photogrammetric approach. This new approach is contrasted with the traditional method in terms of accuracy and computational complexity.

abstract: Doctor of Philosophy (PhD)


title: Workers' Attitudes and Bourgeois Hegemony: Investigations of the Political Consciousness of Canadian Workers in the 1980s

contributor:
Archibald, Peter W.
Sociology

subject: Sociology Sociology

abstract: The principal objectives of this thesis are to deepen our understanding of the character of working class consent to capitalist domination in contemporary Canada, and to assess the possibilities for the development of an alternative hegemonic movement. The following four points are among the important findings of my research. (1) Canadian workers are generally to the Left of other classes on economic issues, and are far more libertarian on social issues than sociologists have commonly thought. (2) The social experiences which have an important influence on a wide range of workers' political attitudes are class background, manual nor nonmanual work, age, education, and residency in Quebec. (3) Many members of the Hamilton local of the Canadian Union of Postal Workers (CUPW) did not continue to struggle in the weeks after the government legislated an end to their 1987 strike. They passively consented to management domination on the shopfloor and government domination of the negotiation process because they believed that nothing could be done to change the situation. In many cases these alienated workers' individual identities and priorities had taken precedence over their identification with the collective cause. This indicates that the mere presence of individual opportunities to do something else, even if they are not taken up, is often sufficient to deflect workers' dissatisfaction and build up a certain amount of active consent to the status quo in Canadian society. (4) In 1097-88 the national leadership of CUPW attempted to organize a broad cross-section of groups around its vision of a "worker- and service-oriented postal system." My assessment of the problems which plagued this political campaign suggests that a labour union will only be able to carry through a counter-hegemonic project in Canada if it has a strong service record and has nurtured grassroots activism over an extended period.

abstract: Doctor of Philosophy (PhD)


title: Analysis and monitoring of a CANDU nuclear power plant using multivariate statistical process control methods

contributor:
Garland, Wm. J.
Engineering Physics

subject:
Engineering Physics
Engineering Physics

abstract: In the nuclear power industry, the ability to efficiently analyse historical data, and to detect and diagnose process faults in a timely manner are critical tasks in operating and maintaining a nuclear power plant. The objectives of this research were to prove that established Statistical Process Control (SPC) techniques could be used to analyse nuclear power plant data and to develop a hierarchical process monitoring methodology which could deliver relevant information to different functional groups within a plant. The use of established Multivariate SPC techniques to analyse nuclear power plant data was successfully proven in several areas and is considered a significant contribution to the development of data analysis tools for the nuclear energy industry. By analysing actual data from an operational nuclear power plant, the techniques were able to provide key insights into the process. Process tests and different plant configurations were easily identified. The multivariate techniques could relate the different plant configurations to sensor calibrations and process changes. Also, the techniques were able to identify two anomalies in the data which were not previously detected using the existing analysis tools. In order to produce a hierarchical process monitoring methodology, a multi-block, multi-level Principal Component Analysis algorithm, and associated prediction code, was developed and tested. This algorithm is an extension of existing multi-block, two-level algorithms and represents a contribution to the current state of Multivariate SPC techniques. It was found that the algorithm was very useful for analysis but marginal for delivering relevant information in a process monitoring capacity. This finding resulted in the third major contribution of this research work. The Multivariate SPC techniques are very useful for analysing nuclear power plant data but not as feasible for monitoring the process in an on-line manner. This was attributed to the goals defined for the monitoring methodology, the scaling method used for the data, and the numerous normal plant operating states.

abstract: Doctor of Philosophy (PhD)


title: Aggregate Surface Texture Influences on Asphaltic Concrete Skid Resistance

contributor:
Emery, J. J.
Civil Engineering

subject:
Civil Engineering
Civil Engineering

abstract:
For asphaltic concrete surface courses, the surface texture of the exposed coarse aggregate in the key factor influencing the skid resistance performance of the pavement. With time, this surface texture is altered by the dynamic, interactive processes of polishing, wear or abrasion and weathering. In this study, four types of aggregate which are available in Ontario - traprock, limestone, steel slag and blast furnace slag - were subjected to these processes in order to evaluate their surface texture characteristics. The study was completed in terms of both quantitative analyses of laboratory samples and qualitative analyses of field and laboratory samples. Two major aspects were surface texture evaluation using the scanning electron microscopy, and the simulation of weathering influences on skid resistance. Both chemical and x-ray diffraction analyses were completed to support the evaluation.

From the study, two new concepts - positive and negative rejuvenating processes and Potential Rejuvenating Value (PRV) - were developed. Steel slag, with a relatively high PSV, low AAV and potential negative rejuvenation was found to be the most desirable aggregate in terms of skid resistance performance.

abstract: Master of Engineering (ME)


title: Intrinsic electrophysiological properties of interstitial cells of Cajal and smooth muscle cells

contributor:
Huizinga, Jan D.
Medical Sciences

subject:
Medical Sciences
Medical Sciences

abstract: The gastrointestinal (GI) tract is a hollow tubular organ that runs through the length of the central body. To move, mix, and compartmentalize ingesta through this tract, different patterns of motility are needed. This thesis is concerned with the myogenic control of motility through the pacemaker network of interstitial cells of Cajal (ICC) and the smooth muscle cells (SMC). Using patch clamp techniques, the electrophysiological properties of single ICC and SMC were examined. Previous research suggested the possibility of a specialized cell type generating the pacemaker slow wave potentials: the network of ICC that resides in the Auerbach's plexus region of the small intestine. An isolation procedure was developed and optimized to harvest single ICC that can survive short term culture and allow examination by patch clamp. Single cell patch clamp recordings demonstrated the presence of slow wave-like voltage oscillations driven by active current oscillations that match all properties seen in whole intestinal tissue slow waves. With different recording modes, whole cell currents, voltage and current oscillations were recorded from the same cell, showing that ICC are electrophysiologically unique and that the active inward current driving the slow wave-like oscillations are not voltage dependent. The isolated single ICC were demonstrated to have a specific tyrosine receptor marker protein for ICC, Kit , by selective RT-PCR amplification. The slow wave-like oscillations had a reversal potential consistent with a non-specific cation conductance. Although previous research had been done on single smooth muscle cells, there is currently no consensus on the cellular ionic currents present. In this thesis, analysis of different recordings demonstrated that there are at least four main groups of SMCs with different whole cell current profiles. Different cellular ionic currents were found specifically in different groups, and can be confirmed by reconstructing single channel recordings. One cellular outward current was chosen for further investigation-a fast activating and inactivating transient outward current. This current was characterized by common protocols and with a novel ramp analysis. Characterization revealed two distinct transient outward currents with different kinetic properties. Finally, spontaneous transient outward currents (STOCs) have been recorded in 25% of smooth muscle cells, reflecting quantal Ca2+ release from the intracellular stores to the plasmalemma calcium dependent potassium channels. Therefore, the study of STOCs gives direct information not only on the activities of intracellular Ca2+ stores, but also on the kinetics of Ca2+ release and reuptake in the microenvironment where STOCs originate. From these results, a simple model for GI motility was developed to account for the cellular interactions between nerve, ICC, and smooth muscle.

abstract: Doctor of Philosophy (PhD)


title: Back-mixing Studies in the Presence of an Unstable Density Gradient in a Reciprocating Plate Extraction Column

contributor:
Baird, Malcolm H.I.
Chemical Engineering

subject:
Chemical Engineering
Chemical Engineering

abstract: The efficient design of extraction columns calIs for the accounting of flow non idealities, collectively termed axial mixing, in the phases involved. Axial mixing occurs mainly through back-mixing caused by circulation, wake transport with dispersed drops and induced turbulence due to mechanical agitation. Non uniform velocity profiles and forward mixing due to drops of different sizes are the other factors. A new factor identified to significantly enhance back-mixing, is the increase in the density of the continuous phase with column height termed as the unstable density gradient. In this thesis, attention was focussed on this factor using a 5 cm reciprocating plate extraction column (RPC). A new approach based on the Kohnogoroff isotropic turbulence theory was developed to model the continuous phase back-mixing under two phase flow conditions. The contribution due to mechanical agitation, dispersed phase flow and the unstable density gradient were accounted in the model in terms of their respective energy dissipation rates and mixing lengths. The parameters were estimated by fitting the model to the experimental data obtained through the steady state tracer injection technique under non mass transfer conditions. The results showed that the unstable density gradient played an important role in enhancing the back-mixing even though its energy dissipation rate was very small relative to the other two contributing factors. This was due to the large mixing length associated with the unstable density gradient effect. At high mechanical agitations, the contributions of the dispersed phase and the density gradient declined. A preliminary study was also performed to investigate the unstable density gradient effect under mass transfer condition. Water was used as the solvent to extract i-propanol from lsopar M drops in the extractor. As increasing amount of alcohol was extracted, the density of water decreased leading to an unstable density gradient. To ensure the reliability of the estimation of the back-mixing coefficient (Ec), a non transferring tracer dye was also injected steadily into the continuous phase. Ec values were determined simultaneously from the concentration profiles of the tracer and the solute, thereby providing two independent estimates for each experiment. The results were comparable under most operating conditions thereby validating the tracer technique. The dispersed phase hold-up, drop size and the mass transfer coefficient were also estimated and compared critically with the models available in literature. The hydrodynamics in the column were significantly altered by the interfacial effects associated with the transfer of solute from the dispersed phase to the continuous phase. In particular coalescence was promoted leading to large drops. Under these conditions the Kolmogoroff model could not isolate the influence of the density gradient from other contributing factors. However the experimental results clearly showed an enhancement in the back-mixing relative to the non mass transfer case. Based on these observations it is concluded that care must be taken to avoid the unstable density gradient created either inadvertently during tracer measurements involving ionic compounds or during mass transfer.

abstract: Doctor of Philosophy (PhD)


title: Short and Long Term Capacities of Slender Concrete Block Walls

contributor:
Drysdale, Robert G.
Civil Engineering

subject:
Civil Engineering
Civil Engineering

abstract:
Short and long term capacities of slender concrete block masonry walls subject to eccentric axial loads were investigated. A finite element model was developed to include both the geometric and the material nonlinearities. To analyze large members, a combined macro-micro finite element model for the masonry assemblage was also developed by which the advantages of the micro material analysis, using the theory of plasticity, as well as the interaction among the different constituent materials were accounted for within the macro finite element model.

Utilizing the finite element model, parametric studies were conducted to cover wide ranges of the parameters which affect behaviour. The geometric, loading, and the material parameters as well as their interactions were involved in this study.

Three simplified methods were developed to provide some rational design approaches. The first method, called "Lumped Area Method", provides a closed form solution for the wall capacity. In the second method, Moment Magnifier Method, a rational method for determining the modulus of rigidity was empirically developed to be used in the calculation of the moment magnification factor. In the third method, Deflection method, the theory of structural mechanics was used to determine the secondary moments using a secant modulus of rigidity which was numerically developed.

Experimental creep tests were carried out on ungrouted and grouted masonry prisms built with normal weight blocks, and ungrouted prisms built with light weight blocks. Creep data were collected for almost 400 days under two levels of sustained stresses. Creep functions were statistically developed and were incorporated in the finite element-creep analysis.

Another set of parametric studies was conducted to investigate the long term capacities of masonry walls. Also, the Lumped Area Method was extended to account for the creep effect in predicting the long term capacity.

abstract: Doctor of Philosophy (PhD)


title: Polymer melt formation and densification in rotational molding

contributor:
Vlachopoulos, J.
Chemical Engineering

abstract: The creation of a homogeneous polymer melt from powder particles, which involves particle coalescence followed by the formation and dissolution of bubbles, is a situation encountered in processes such as rotational molding and powder coating. The present work focuses on the study of the transformation of a loosely packed, low density powder compact, to a fully densified polymer part, when processed at temperatures above the melting (or glass transition) point of the polymer. The purpose of this work is to study the appearance of air pockets, or bubbles, which are trapped during the melting-sintering of the polymer particles, to elucidate the mechanisms involved in their formation and subsequent dissolution and to propose models which are suitable for the description of the overall densification of the powder compact. A comparative study of the processing characteristics and properties offered by various polymers has been undertaken. During this work, the problem of the presence of excessive bubbles has been encountered mainly in polymers with high amorphous contents and low crystallinities. Rheological characterization suggested that these types of polymers typically exhibit weak viscosity dependence on temperature and higher melt elasticities. The formation of bubbles and their subsequent dissolution have been studied experimentally. Various types of polymers have been examined, in an effort to identify the important material parameters affecting bubble formation and to elucidate the mechanisms involved. The evolution of density as a function of time during sinter-melting was measured experimentally, using a heating oven. The results revealed that the overall process consists of two stages: Particle coalescence, which depends on viscosity, surface tension and powder properties, occurs during the first stage, during which air pockets, which eventually become bubbles, are entrapped inside the melt. The second stage involves the shrinkage and eventual disappearance of the bubbles. The experimental results were compared to models commonly used in the ceramics, glass and metals processing literature for the densification of particulate compacts. Application of models based solely on viscosity and surface tension phenomena, can describe satisfactorily the process until the point where closed pores (bubbles) form. The latter stage of bubble dissolution has been addressed by modeling the dissolution of a single spherical bubble in an infinite polymer melt under isothermal conditions. The bubble dissolution model has been successfully applied to provide predictions of density as a function of time for the late stages of densification.

abstract: Doctor of Philosophy (PhD)


title: Crosslinking Kinetics in Free-Radical Copolymerization

contributor:
Hamielec, A.E.
Chemical Engineering

abstract:
A new kinetic theory for free radical copolymerization with long chain branching and crosslinking is proposed. This kinetic theory accounts for the history of the generated network structure as well as for all of the important elementary reactions in free radical polymerization. The present theory can be used to make calculations of various important properties such as onset of gelation, weight fraction of sol and gel, number- and weight-average chain length of sol fractions, crosslinking density in sol and gel fractions, etc. Since free radical polymerization is kinetically controlled, each primary polymer molecule experiences a different history of crosslinking and cyclization. The present theory proves the existence and permits the calculation of the crosslinking density distribution, although all statistical models which assume an equilibrium system inevitably employ the assumption that the crosslinking density is the same for all chains. The existence of a crosslinking density distribution with a significant variance is an important feature of the present kinetic theory stating that polymer networks synthesized by free radical polymerization are inherently inhomogeneous on a microscopic scale. This theory reduces to the Flory/Stockmayer theory under Flory's simplifying assumptions and may therefore be considered a general mean-field theory.

The present theory was successfully applied to the copolymerization of methyl methacrylate/ethylene glycol dimethacrylate, and acrylamide/N,N'-methylene-bis-acrylamide. In real systems it was found that the effect of cyclization (intramolecular reactions) and the decreased reactivity of pendant double bonds relative to the monomeric double bonds are important.

This new kinetic theory should assist one to design superior quality network polymer systems and it can also be used to control various polymerization processes. It was found that if branches are formed by chain transfer to polymer the crosslinking density is always higher in continuous stirred tank reactors (CSTR) than in batch reactors, however, this is not true in general for vinyl/divinyl copolymerizations. The variance of the crosslinking density distribution in CSTR's is large due to their broad residence time distributions.

abstract: Doctor of Philosophy (PhD)


title: Adolescent cultural identity and self-esteem in a multicultural society

contributor:
Parisi, L.
Nursing

subject: Nursing Nursing

abstract: This study examined the relationship between cultural identity and self-esteem of adolescents living in a multicultural context. The sample of 550 respondents participating in the study came from four secondary schools in the Hamilton-Wentworth Region, located in the Province of Ontario. The study had a cross-sectional design and used the survey method. Multiple instruments were used in the measurement of cultural identity and self-esteem levels. The Current Self-Esteem scale was introduced as an instrument to measure current self-esteem levels and, through its open-ended items, to identify the promoters and challengers of self-esteem, as defined by the respondents. The relationship between cultural identity and self-esteem was found to evolve out of a context that was influenced by the adolescents' individual (age, gender) and environmental (cultural background, acculturating group, family circumstances, perception of support) attributes. In addition, the emerging complex relationship between cultural identity and self-esteem levels was concluded to be influenced by the contextual nature of cultural identity, the multiple influences on self-esteem, and, possibly, the contextual nature of self-esteem as well. The concepts of neighbourhood concordance and global valuation were introduced among the explanations for the emerging patterns of cultural identification. The findings reinforced the thesis' conception of cultural identity as a dynamic, context-dependent process, which, as an aspect of identity, manifests itself in the presence of culturally-different other(s). The use of the term multiculturation was proposed in future conceptual and empirical work on adolescent cultural identity and self-esteem in Canada. As a concept, the term multiculturation recognizes that the development of cultural identity in a multicultural context can follow many paths, which are not limited to specific cultural and migrant groups, thus contributing toward a society which embraces cultural differences and recognizes such differences as a normal part of human development.

abstract: Doctor of Philosophy (PhD)


title: The influence of extracellular pH on human skeletal muscle metabolism

contributor:
Heigenhauser, G.J.F.
Medical Sciences

subject:
Medical Sciences
Medical Sciences

abstract: Moderate to high intensity exercise generates lactate and hydrogen ions which accumulate in both blood and muscle and are thought to contribute to the development of fatigue. Alteration in the extracellular pH has been shown to influence the appearance of lactate in plasma, acidosis decreasing and alkalosis increasing blood lactate concentration. The present research was designed to explore the potential mechanisms by which acid-base alterations influence lactate production and the associated metabolic changes in exercise. Normal subjects took part in two studies. Acidosis induced by ingestion of ammonium chloride and alkalosis via ingestion of sodium bicarbonate were compared to control during rest and exercise. Needle biopsies of the vastus lateralis muscle, blood flow and arterial and femoral venous blood samples were taken. Acidosis resulted in decreased lactate production and efflux, secondary to decreased glycogenolysis from reduced transformation of glycogen phosphorylase to its active form and the lack of accumulation of positive allosteric modulators. Lower glycogen utilization resulted and was associated with an increase in free fatty acid (FFA) utilization from intramuscular stores. Pyruvate dehydrogenase activity was lower. Alkalosis had opposite effects: greater lactate production, efflux, glycogenolysis, pyruvate dehydrogenase activity and glycogen utilization, with lower FFA utilization. However, the increased glycogenolysis resulted from allosteric activation of glycogen phosphorylase through increases in the concentration of its positive modulators adenosine monophosphate and substrate free inorganic phosphate. These studies conclude that alterations in lactate production result entirely from a mismatch in the catalytic rates of glycogen phosphorylase and pyruvate dehydrogenase. Additionally, these studies identified for the first time the mechanisms responsible for the complex interplay of regulatory enzyme activity, fuel utilization and the importance of acid-base homeostasis in its control.

abstract: Doctor of Philosophy (PhD)


title: Trends in policing: A case study of the Hamilton police, 1900--1973

contributor:
Fox, J.
Sociology

subject: Sociology Sociology

abstract: While there are numerous studies of the police, few have addressed the changes in policing that have occurred since the turn of century. Prior studies address issues such as police effectiveness, social control, the military model of police organization, police socialization, and the relationship between crime rates and the size of police forces. Although these studies have provided insight into different aspects of policing, they have not established a comprehensive understanding of the police as an institution. In other words, we have little understanding of what has caused the police to change. Further, we know little about the substance and consequences of change. My goal is to conduct an exploratory study of changes in policing by examining the main trends in the Hamilton, Ontario, Police Department between 1900 and 1973. Trends in economics, organization and work are considered. The study provides significant findings, which can be understood in relation to the existing literature, and can provide new questions to serve as the basis for future research. I explain trends in policing in relation to larger social and historical factors including population growth, the changing distribution of crime, and the role of the automobile. Change was pluralistic; different factors contributed to major changes in policing. Often, change was the result of external circumstances--the larger social context provided both the motivation for change and the possible range of alternatives that could be implemented. In Hamilton, the twentieth century was a period of considerable population growth. At the same time, the city was being transformed by the automobile, a revolution that redefined urban space, patterns of social interaction and the mobility of citizens. Over the course of the century, there was a substantial shift in the distribution of criminal offences. It is within this context that significant changes to policing occurred. The police responded to the changing times by changing themselves. The growth of the Department paralleled that of the city. The police adopted cars and motorcycles for patrols to cope with traffic problems and to provide a quick response to citizens in need. The Department was completely reorganized and became more professional. At the same time, the costs of policing were rising. Police chiefs continually struggled to find ways to cope with rising wages and declining work weeks. Citizens would be hired, technology employed, patrol strategies changed to cope with declining productivity. The findings of my research suggest that changes to the Hamilton Police can be understood in terms of diffusion theory. The larger social milieu provided not only the motivation for change: it limited the range of possible solutions at any given point in time. I argue that changes to the Police Department were a direct result of their ability to adopt innovations. Ultimately, to understand the police we must view them as social and historical products.

abstract: Doctor of Philosophy (PhD)


title: Holder's Inequality in Spaces of Measurable Functions

contributor:
Bennett, C.
Mathematics

subject: Mathematics Mathematics

abstract:
This thesis gives a historical account of the development of the theory of spaces of measurable functions. The study will be mainly centred around Holder's inequality and its many generalizations.

We present a formal axiomatization of the theory including a general form of Holder's inequality. Then we consider various families of spaces of measurable functions, namely the Orlicz spaces and the Lorentz spaces, both of which include the familiar LP-species. In each of these special cases, Holder's inequality is interesting in its own right. As a particular example, the space Llog⁺L and its conjugate, the exponential space, are studied in detail as they are examples of both an Orlicz space and a Lorentz space.

abstract: Master of Science (MS)


title: Two Essays On the Economics of Marriage and Fertility

subject: Economics Economics

abstract:
The first essay discusses some economic implications of marriages of children. Of particular interest is the strategic behaviour of the parents of the children. A simple two-period model with very general assumptions is developed and some interesting results are obtained. These results are summarized in eight propositions. This essay consists of four parts.

It is first shown that a symmetric Nash equilibrium does not exist unless constraints are imposed. We find that such an equilibrium does exist if bequests are non-negative, if bequests to sons and daughters are equal, and if preferences are heterogeneous. The second part of the essay looks at how one set of parents will react to the actions of another set by adjusting the level of bequests to sons and daughters. The theoretical model yields reasonable predictions of parental behaviour.

The third part examines the efficiency of a Nash equilibrium when it exists and proves that a Nash equilibrium is Pareto-inefficient. Corrective policies are suggested. Finally, the results of the theoretical analysis are found to be independent of whether fertility is exogenous or endogenous. Furthermore, a conjecture by Edgeworth is confirmed by the model: individual decision makers are likely to ignore the impact of their fertility choices on population growth, and when this occurs underpopulation is inevitable.

The second essay investigates socioeconomic determinants of individual fertility in China, utilizing a valuable micro-data set (China's 1985 In-Depth Fertility Survey). The Chicago Model, Easterlin's Theories and Leibenstein's Model are used to develop an econometric model of fertility for China. The model incorporates some special features of Chinese societies that are relevant to fertility behaviour. Ordinary least squares, Tobit maximum likelihood and sequential logit procedures are applied to estimate the model. Several theoretic and statistical problems are discussed and appropriate ways are used to take them into account whenever possible.

It is found that marriage duration, child mortality, sex preference, education of woman, occupation of husband, family structure, and durable ownership are significant factors in determining individual fertility. Marriage duration, replacement effect of child deaths and male preference for children all appear to be positively related to fertility. The relationship between level of education of woman and fertility is not linear. Furthermore, it is found that fertility falls as occupational status of husband rises, that women living in extended families have higher fertility, and that owning a durable has a negative effect on fertility.

abstract: Doctor of Philosophy (PhD)


title: The Structure and Fluxionality of Cobalt-Based Tetrahedral Organometallic Clusters

contributor:
McGlinchey, M.J.
Chemistry

subject: Chemistry Chemistry

abstract:
A series of trimetal tetrahedra were synthesized with the goal of studying their structures and the mechanistic processes which occur during fluxionality of their ligands. The basic skeleton utilized was a CO₃C tetrahedron, varied to include Mo or W on occasion, but always maintaining the four-vertex core.

The bidentate ligands DIPHOS (bis-diphenylphosphinoethane) and ARPHOS (1-diphenylphosphino-2-diphenylarsinoethane) coordinate to tricobalt and mixed-metal clusters, bonding only at the cobalt vertices. The DIPHOS chelate remains tightly bound to the cluster while the carbonyl ligands migrate about the vertices. The ARPHOS ligand cleaves at the As-Co linkage and can move between Co vertices. This process, as well as the concomitant CO migration, is slowed on the NMR timescale at reduced temperature.

In a system with a carbonyl ligand bridging two cobalt vertices of a tricobalt cluster, CO₃(CO)₄(C₅H₅)₂C-C₆H₅, the ¹³C NMR spectrum was observed to determine if the EHMO-predicted favoured orientation of the phenyl ring could be frozen out in solution in the NMR experiment. A xylyl ring was incorporated into the system as a probe for loss of mirror symmetry. At a range of temperatures, the clusters did not show cessation of the rotation. The tetrahedral cluster CO₃(CO)₄(C₅H₅)₂C-C₆H₅ crystallizes in the monoclinic space group P2₁2₁2₁, and the phenyl ring was found to be oriented parallel to the bridging CO unit, corresponding to the proposed structure as predicted by EHMO theory.

The bulky dinaphthyl fragment CH(4-CIC₁₀H₆)₂ was incorporated into a tricobalt nonacarbonyl cluster as the capping ligand to investigate possible hindrance to exchange of the CO ligands. Cessation of carbonyl exchange was observed on the DDT derivative and other analogues, but the relatively unstable dinaphthyl cluster showed no evidence of this behaviour, attributed to the inability of the naphthyl rings to rotate because of steric restrictions. The crystal structure of CO₃(CO)₉C-CH-(4-CIC₁₀H₆)₂ was solved.

The molecules M(CP)(CO)₂Co₂(CO)₆C-CO₂CH(CH₃)₂, (M=Mo, W; CP = (C₅H₅), (C₅H₄CH₃), [C₅(CH₃)₅]) adopt two conformations at reduced temperatures in the NMR experiment, dependent on the position of the cyclopentadienyl ring: one involves the ring in a conventional axial position (accompanying CO ligands equatorial), while in the second isomer, the ring centroid is above the trimetal plane, with the two carbonyl ligands semi-bridged. Isomer interchange occurs rapidly at room temperature. The favoured isomer in the C₅H₅ and C₅H₄CH₃ clusters has the ring below the basal plane, while the larger C₅(CH₃)₅ rings prefer the "up" position, allowing distribution of excess electron density to the remaining vertices via the carbonyl ligands. [C₅(CH₃)₅]Mo(CO)₂CO₂(CO)₆C-CO₂CH(CH₃)₂ crystallizes in the space group P2₁/n, and displays the large C₅(CH₃)₅ ring in the area of least unfavourable interaction with the bulk of the cluster.

abstract: Doctor of Philosophy (PhD)


title: Radar Clutter Classification

contributor:
Haykin, Simon
Electrical Engineering

subject:
Electrical and Electronics
Electrical and Electronics

abstract:
The problem of classifying radar clutter as found on air traffic control radar systems is studied, and an algorithm is developed to carry out this classification automatically. The basis for the algorithm is Bayes decision theory and the parametric maximum a posteriori probability (MAP) classifier. This classifier employs a quadratic discriminant function and is optimum for feature vectors that are distributed according to the multivariate normal density. Separable clutter classes are most likely to arise from the analysis of the Doppler spectrum. Specifically, a feature set based on the complex reflection coefficients of the lattice prediction error filter (PEP) is proposed. These coefficients are also used in the maximum entropy method (MEM) of spectral estimation, and this link establishes many of their characteristics. A number of transformations are necessary, however, before they can be used as features.

The classifier is thoroughly tested using data recorded from two L-band air traffic control radars at different sites. The collected data base contains extensive bird, rain, and ground clutter, as well as thunderstorms, aircraft and ground-based moving vehicle echoes. Their Doppler spectra are examined; and the properties of the feature set, computed using these data, are studied in terms of both the marginal and multivariate statistics. Several strategies involving different numbers of features, class assignments, and data set pretesting according to Doppler frequency and signal-to-noise ratio, were evaluated before settling on a workable algorithm. Final results are presented in terms of experimental misclassification rates and simulated and classified PPI displays.

abstract: Doctor of Philosophy (PhD)


title: The modulation of protein kinase C by hydration and membrane spontaneous curvature

contributor:
Epand, Richard
Biochemistry

subject: Biochemistry Biochemistry

abstract: It has been shown previously that the biophysical properties of the membrane influence the ability of protein kinase C (PKC) to bind to it and become activated. The mechanism by which this occurs has not been firmly established. The following studies were undertaken to elucidate the roles of membrane structure in modulating PKC. This was accomplished by determining the effects that a defined change in membrane structure had on the binding and catalysis of PKC, by addition of phospholipids or other compounds to lamellar phase membranes, or through the use of non-lamellar phases. Also, the role of hydration in binding and catalysis was studied. Unsaturated phosphatidylethanolamines (PEs) were found to be activators of the enzyme, when added to large unilamellar vesicles (LUVs). Relative activation caused by different PEs correlated with their bilayer to hexagonal phase transition temperatures (TH S), but the extent of activation was not always proportional to the effect on TH since two PEs which caused similar levels of activation did not cause a similar change in TH . Activation was found to correlate best with the interfacial polarity of LUVs containing the PEs. Other properties of the phospholipid, such as its intrinsic radius of curvature, and its bending modulus, as well as the actual curvature strain it imposes on the LUVs did not correlate with the activation seen. Cubic phases were found to activate membrane-bound PKC to a greater extent than LUVs of similar composition which possessed a higher level of curvature strain. Hexagonal phases, containing the lowest level of curvature strain, supported levels of activation similar to that of lamellar phases. Lipophosphoglycan from Leishmania donovani , was a potent inhibitor of membrane-bound PKC, which could exert its effects from the opposite monolayer of the bilayer to which the enzyme binds. Polyethylene-glycol linked PEs were also found to inhibit the membrane-bound form of the enzyme.

abstract: Doctor of Philosophy (PhD)


title: High Speed Interdigital MSM Photodiodes

contributor:
Garside, B.K.
Physics

subject: Physics Physics

abstract: A fast, simple photodetector which is compatible with optical integration techniques can be produced using a design consisting of an interdigital metal -- semiconductor -- metal (MSM) photodiode. The general operation of these devices is discussed with emphasis placed on basic device characteristics such as IV, CV, and steady state and pulsed light response. Ideas and models are presented to allow predictions of generic device performance as well as design and optimization of specific devices. These theoretical aspects are validated through comparison with experimental results.

abstract: Doctor of Philosophy (PhD)


title: Three-Photon Absorption Spectroscopy of Diatomic Molecules

contributor:
King, G.W.
Chemistry

subject: Chemistry Chemistry

abstract:
Multiphoton absorption spectroscopy has been used to study the isotopically-pure bromine (⁷⁹Br₂) and iodine monochlorides (I³⁵Cl), as well as the respective natural-abundance molecules.

Three-photon excitation spectra have been obtained under low- (ΔV = 1.0 cmˉ¹) and high- (ΔV = 0.2 cmˉ¹) resolution. High-resolution spectra were recorded using either a single tunable dye laser (3P1C) or two independently-tunable dye lasers (3P2C).

For ⁷⁹Br₂, the existence of at least three separate excited electronic states in the 6.7-7.3 eV region were confirmed. Two of these states were spectroscopically identified and shown to have ion-pair bonding. The two-photon transitions from the intermediate B state to these ion-pair states consisted of simple O, Q and S branches. The polarization effect on their transition probability indicated that these states were of O symmetry.

For isotopically-pure I³⁵Cl, an excited state in the 6.0 eV region has been identified.

abstract: Doctor of Philosophy (PhD)


title: Informed survival: Media activism by people with HIV/AIDS

contributor:
Knight, G.
Sociology

subject: Sociology Sociology

abstract: This study looks at print media projects by and for people with HIV/AIDS. Three types of publications are examined: newsletters; treatment publications; and general interest magazines. Each of these media began as part of political organizing by people with HIV in the context of the community-based response to the AIDS epidemic. The argument is made that those involved in contemporary social movements produce their own media as a means of constructing an alternative public sphere. The significance and function of this public realm is twofold. First, it is a social space for people with HIV/AIDS that is independent of forms of institutional influence and control. Second, it invites not only the articulation of opposition to the dominant social order but an alternative to the status quo. This study demonstrates the role of communication media--forums through which people can share their experiences and knowledge--in the struggle for self representation and survival among people with HIV/AIDS.

abstract: Doctor of Philosophy (PhD)


title: Demodulation/Decoding of a DC Free Construction of the Gosset Lattice

contributor:
Buda, R. de
Taylor, D.P.
Carter, C.R.
Yipand, P.
Electrical and Computer Engineering

abstract:
Over the past decade, lattices have been increasingly recognized as an important source of codes for the Gaussian channel. The 8-dimensional Gosset lattice has figured prominently in these new developments because it offers an asymptotic coding gain of 3 dB over conventional pulse amplitude modulation and can be soft decision demodulated/decoded with a reasonable amount of speed. In the present work, we revive a little used definition of the Gosset lattice and show that codes derived from this construction exhibit a null at dc in their baseband spectrum. Such codes are useful as line codes for baseband signalling on channels that do not support a dc spectral component or for bandpass transmission where spectral shaping is required to combat intersymbol interference.

Previous applications of lattice codes have been aimed primarily at voiceband data communications. This thesis was motivated by the need to develop a decoder that would make applications in the multi-megabit range of data transmission possible. To achieve this goal, a two-stage approach to demodulation was developed. The first stage makes a fast estimate of the transmitted vector and has the ability to declare an erasure when it knows its estimate is unreliable. This initial erasure declaring stage controls the throughput of the demodulator. Because it is far simpler than a maximum likelihood demodulator, greater speed is achieved. The second stage is provided to correct the occasional occurrence of an erasure and maintain the error performance of the lattice. To complete the decoder structure, we outline a method of lexicographic ordering the signal set that leads to a compact set of decoder look-up tables used to obtain a binary message sequence from each demodulated vector. Finally, we evaluate the effects of quantization on the probabilities of erasure and error and give results from a Monte-Carlo simulation undertaken to verify the demodulators performance.

abstract: Doctor of Philosophy (PhD)


title: Jane Austen and Her Biographers: The Woman Writer as Literary Icon

contributor:
King, James
English

subject:
English Language and Literature
English Language and Literature

abstract:
This thesis examines the biographies of Jane Austen written between 1817 and the present in an attempt to discover how life writers have shaped the reputation of a woman writer. While Austen's art is often compared to Shakespeare's in its ability to delineate 'real' life and character, biographers have tended to deny her the worldly experience which they deem so necessary to the formation of Shakespeare's art. Both these authors present similar problems for life writers in that so little evidence remains of their lives, but the portrayals of them suggest that in the absence of verifiable 'fact' biographers tend to depict their subjects in terms of gender stereotypes. In this construct, the occupation of author demands worldly experience which is by definition denied the female subject. This tension, between the need for experience and the perception of femininity as necessarily innocent, is apparent in biographies of Austen written well into the twentieth-century.

My investigation reveals that the Austen family's concern to maintain their relative's gentility played a significant role in the way she was depicted. When this coincided with the Victorian impulse to portray authors as virtuous examples to their readers, Austen's reputation became frozen into that of a literary icon. Not only did she become the saintly maiden aunt, but my study suggests that biographers and many critics read the novels solely as drawing-room comedies, and in the process often identified the author with her female characters. From the 1860s onwards some literary critics did challenge this image of sweet perfection, but their views were generally not reflected in the lives of Austen. Biographies written in the twentieth-century have not appreciably altered this situation; only recently, for example, has a biographer chosen to depict Austen as cranky and disillusioned by her lot in life. My conclusion is that the biographers' acceptance of stereotypes of femininity, and their perception that domestic life is impermeable, uneventful, and hence has no influence on the creative process, are particularly detrimental to the portrayal of Austen, both as woman and as artist.

abstract: Doctor of Philosophy (PhD)


title: Evidence, policy and practice in environmental health: An international case study of sun safety

contributor:
Eyles, John D.
Geography

subject: Geography Geography

abstract: The past decade has seen increasing interest in the uncertain and complex problems related to environmental health and global environmental change issues. While this has brought together scientists, policymakers and the public to work towards solutions, relations between the groups are strained due to the differences in how each group recognizes, validates and places limits on evidence and knowledge. This thesis presents a detailed case study of how internationally-accepted information is interpreted, adapted and adopted into specific programs in a single environmental health case study: Sun Safety programs in Australia, Canada and England. Within the broad case study, the project uses a mixed method approach in a series of nested investigations. The first investigation uses critical theory to examine the theoretical relations between scientists, policymakers and the public. It concludes that each group engages in a different form of rationality (scientific, political, and social respectively) that is different yet equally valid. The second investigation uses expert interviews to trace the transfer of evidence and information from an international community of experts (an epistemic community) to national programs in Australia, Canada and England. This investigation concludes that framing and narrative construction are key to how information gets translated and transformed from evidence to policy at the national level. The third nested investigation reports the results of a survey of Public Health Units (PHUs) in Ontario, Canada to show the transfer of evidence and information from national policymakers to local programs for the public. It concludes that the public is playing an increasingly powerful role in defining problems and proposing solutions due, in part, to the rise of information as a commodity in the postmodern world. This thesis concludes that ideology plays a critical role in defining how evidence and knowledge gets translated and transformed in the policymaking process. This work makes substantive and methodological contributions through its use of mixed and complementary methods and through its detailed analysis of an environmental health issue (Sun Safety) in three countries. The thesis' main contributions, however, are theoretical. First, it extends the epistemic community concept to show how international evidence is increasingly influential at the public level through technological advances and greater international flows of information. Second, it develops a framework explicating the different evaluative criteria used by scientists, policymakers and the public in uncertain and complex issues. Both of these contributions will prove useful for future research in complex and uncertain issues such as global environmental change and environmental health problems.

abstract: Doctor of Philosophy (PhD)


title: Metal-Gill Surface Interactions in Rainbow Trout (Oncorhynchus mykiss)

contributor:
McDonald, Gordon D.
Biology

subject: Biology Biology

abstract:
Experiments were conducted on rainbow trout to analyze: 1) the impact on gill function of cadmium (Cd⁺⁺) as compared to the effects of copper (Cu⁺⁺) and low pH (H⁺), 2) the metal binding characteristics of the external gill surface, and 3) modifications in metal binding activity of the gills associated with chronic exposure to low Ca⁺⁺ water or aluminum (Al).

Short-term exposure (24 h) to equimolar (6.5 μmol‧Lˉ¹)Cd⁺⁺, Cu⁺⁺, or H⁺ (pH 4.8) resulted in the disruption of transepithelial ion exchange in trout, confirming the surface activity of Cu⁺⁺ and H⁺, and characterizing the impact of Cd⁺⁺ on gill function. The effects of each metal were different from one another with respect to specific site of action, rapidity of action, and persistence of the disturbance. Furthermore, Cu⁺⁺ and 11⁺ had only minor effects on Ca⁺⁺ balance and major effects on Na⁺ balance whereas the reverse was the case for Cd⁺⁺, with water hardness ([Ca⁺⁺]) having a fundamentally different role to play in the toxicity of Cd⁺⁺ compared to Cu⁺⁺.

Analysis of metal-gill surface interactions, using an in vitro methodology, revealed that metal binding kinetics were related predominantly to the charge of the metal. The gills had the highest affinity for lanthanum (La⁺⁺⁺) and AI, intermediate affinity for Ca⁺⁺ and Cd⁺⁺, and the lowest for Cu⁺⁺ and H⁺. All metals, with the exception of Cu⁺⁺, would inhibit the binding of Ca⁺⁺ to the gills. These metals were ranked, in decreasing ability to act as Ca⁺⁺-antagonists at the gill surface, as follows: AI, La⁺⁺⁺, Cd⁺⁺ and H⁺ then Cu⁺⁺. Although the binding affinity, and, to some extent, the competitiveness of these metals was correlated with charge, metal toxicity was correlated with neither the metal charge nor the affinity of the metal-gill surface interaction.

The gill micro-environment was found to be capable of responding in an adaptive fashion to environmental stressors (low Ca⁺⁺ water or elevated AI). Modifications of the gill, in response to the reduction of water Ca⁺⁺, resulted in a significant increase in the Ca⁺⁺ binding affinity and capacity of the external gill surface. Furthermore, chronic exposure to elevated AI induced a prophylactic response by the gill micro-environment, resulting in a significant suppression of the surface activity of AI manifested as an enhanced resistance to the ionoregulatory and hematological impact of Al exposure.

abstract: Doctor of Philosophy (PhD)


title: Filamentary molecular clouds and their prolate cores

contributor:
Pudritz, Ralph E.
Physics and Astronomy

subject:
Astrophysics and Astronomy
Physics
Astrophysics and Astronomy

abstract: We develop a model of self-gravitating, pressure truncated, filamentary molecular clouds with a rather general helical magnetic field topology. By comparing with existing observational data, our analysis suggests that the mass per unit length of many filamentary clouds is significantly reduced by the effects of external pressure, and that toroidal fields play a significant role in squeezing clouds. We show that there is an upper limit to the mass per unit length allowed for equilibrium, whose value depends on the strength and character of the magnetic field threading the filament. Clouds that are below this critical mass per unit length are always stable against radial gravitational collapse. Our theoretical models involve 3 parameters; two to describe the mass loading of the poloidal and toroidal fields, and a third to describe the radial concentration of the filament. We find that many of our models with helical fields are in good agreement with the observed ∼r-2 radial density structure of filamentary clouds. Unmagnetized filaments and models with purely poloidal magnetic fields result in steep density gradients that are not allowed by the observations. We consider the stability of our models against axisymmetric modes of fragmentation. Many of our models fragment gravitationally, although some are subject to MHD-driven "sausage" modes of instability. Our main result is that the toroidal magnetic field helps to stabilize long wavelength gravitational instabilities, but short wavelength MHD "sausage" instabilities result when the toroidal field is sufficiently strong. Many of our models lie in a physical regime where the growth rates of gravitational and MHD instabilities are at a minimum. We then go on to develop a model of the helically magnetized cores that might originate from finite segments of our filament models. Only modest toroidal fields are required to produce prolate cores, with mean projected axis ratios in the range 0.3-1. Thus, many of our models are in good agreement with the observed shapes of cores (Myers et al 1991, Ryden 1996), which find axis ratios distributed about a mean value in the range 0.5-0.6. We show that the Bonnor-Ebert critical mass is reduced by about 20%, as a result of the helical field in our models.

abstract: Doctor of Philosophy (PhD)


title: Physiological effects of aluminum on rainbow trout in acidic soft water, with emphasis on the gill micro-environment

contributor:
Wood, C.M.
Biology

subject: Biology Biology

abstract:
This thesis examined the physiological and toxicological effects of Al (-100 μg.Lˉ¹) in acidic soft water (pH 4.0-6.5) on the rainbow trout (Salmo gairdneri = Oncorhynchus mykiss), and the mechanisms of Al deposition on the gills. Cannulated trout exposed for 66 h to Al in synthetic soft water (Ca²⁺ = 45 or 410 μequiv.Lˉ¹) showed highest mortality at pH 5.2, intermediate mortality at pH 4.8, and least mortality at pH 4.4. Aluminum caused losses of Na⁺ and Clˉ from the plasma at pH 5.2 and 4.8, where there were no ion losses in the absence of Al. Respiratory disturbances (decreases in arterial O₂ tension, increases in CO₂ tension) occurred in fish exposed to Al at pH 5.2 and 4.8.

Experiments on trout fitted with ventilation masks and opercular catheters showed that acidic soft water is rendered more basic as it passes over fish gills, and basic inspired water is made more acidic. A model was generated in which these effects were adequately explained by measured ammonia, base, and CO₂ release at the gills.

Exposure to acidic soft water containing Al resulted in hyperventilation during both short (2-3 h) and longer term (44 h) exposures. Alkalinization of the gill micro-environment was modified but not abolished in the presence of Al. This alkalinization was large enough to exceed the theoretical solubility limit for Al, so that Al precipitation from solution onto the gills would occur. The alkalinization also altered the theoretical speciation of Al near the gills, resulting in shifts in the direction Al³⁺ → Al(OH)²⁺ → Al(OH)₂⁺ → Al(OH)₃°.

Aluminum extraction at the gills, and Al accumulation on the gills, was greatest at higher inspired and expired pH, in agreement with an Al precipitation explanation of Al deposition on fish gills. Aluminum precipitation experiments indicated that precipitation of Al from solution was fast enough to occur during the short (<2 s) residence time of water at the gills. Measured accumulation on trout gills was about 10% of the deposition calculated from measurements of ventilation volume and Al extraction; the difference was explained as extensive sloughing of Al from the gills.

A model of Al interactions at fish gills is presented, in which precipitation of Al onto the gills causes the respiratory effects of Al. A smaller proportion of Al deposition is proposed to be positively charged Al species interacting with the negatively charged gill surfaces, causing the ionoregulatory effects of Al.

abstract: Doctor of Philosophy (PhD)


title: Integrating Computational Chemistry and Mass Spectrometry: A Study of Isomerization Reactions of Oxygen-Containing Ions in the Gas Phase

contributor:
Terlouw, Johan K.
Chemistry

subject: Chemistry Chemistry

abstract: The unimolecular chemistry of several organic radical cations has been studied with ab initio molecular orbital calculations and tandem mass spectrometric experiments. The computational chemistry involves. Hartree-Fock (HF), density functional (DFT), Moeller-Plesset perturbation, (MP) and coupled cluster (CC) theories. The tandem mass spectrometry experiments involves metastable ion (MI), collision induced dissociative ionization (CID), and neutralization-reionization mass spectrometry (NRMS) in conjunction with isotopic labeling using ²H, ¹³C and ¹⁸O isotopes. The chemistry has been interpreted by consideration of several fascinating intermediates in the gas-phase which include hydrogen-bridged radical cations, distonic ions and ion-dipole complexes. Two new hydrogen-bridged radical cations have been identified by experiments and were characterized by calculations. The unimolecular chemistry of ionized 1,2-propanediol was re-examined with these methods. It was found that a considerable simplification of a previous mechanistic proposal could be brought about by invoking two different mechanistic concepts, a 1,2-proton shift catalyzed by a dipole and charge (electron) transfer taking place in ion-dipole complexes. This new mechanistic proposal was compared to a more conventional alternative which involves hydrogen atom shifts in distonic ions for both 1,2-propanediol and its lower involves hydrogen atom shifts in distonic ions for both 1,2-propanediol and its lower homologue, 1,2-ethanediol. It was found that a surprisingly large barrier exists for a 1,4-H atom shift in these stable distonic ions. Other low energy dissociation processes in ionized 1,2-propanediol (involving the loss of CH₃･, H₂O, H₂O + CH₃･, H₂O + CH₄) were interpreted by Bohme's 'methyl cation shuttle' mechanism taking place in ion-dipole complexes. Tandem mass spectrometry experiments confirmed previous indirect evidence that commercially available oxalacetic acid, HOOCCH₂C(=O)COOH (OAA) samples do not have the structure of the acid but rather that of its (Z)-enol, hydroxyfumaric acid, HOOCC(H)=C(OH)COOH. It was further established that: (i) the samples contained a minor impurity assigned as a dehydration product of 4-hydroxy-4-methyl-2-ketoglutaric acid; (ii) careful evaporation of OAA yielded mass spectra characteristics of the (Z)-enol form; partial ketonization of the neutral (Z)-enol takes place and these species are either ionized intact or decarboxylane giving a mixture of α-hydroxygen-bridged radical cation, CH₂=O•••H•••O=C-OH･⁺. The long-lived, low internal energy (metastable) ions enolize prior to the loss of C=O yielding an ion-dipole complex of ionized hydroxyketene and water, HOC(H)=C=O･⁺/H₂O. The high energy hydrogen-bridged radical cations also show an intriguing rearrangement ion, CH₂OH₂･⁺, resulting from a decarboxylation process. This reaction likely occurs via communication with ionized glycolic acid and the hydrogen-bridged radical cation CH₂OH₂･⁺•••O=C=O. The methyl ester of β-hydroxypyruvic acid, HOCH₂C(=O)COOCH₃, behaves analogously: upon decarbonylation the high and low internal energy ions are CH₂=O•••H•••O=C-OCH₃･⁺ and HOC(H)=C=O･⁺/CH₃OH respectively. The hydrogen-bridged radical cation formed in the high internal energy process shows an intriguing rearrangement as well. This ion rearranges extensively before dissociation into protonated methylformate, CH₃OC(H)OH⁺ and the formyl radical, HC=O･. This rearrangement occurs via sequential transfers of a proton, electron and another proton within ion-dipole complexes in the gas-phase, akin to that proposed for the diols mentioned above. In the EI mass spectrum of HPA an ion at m/z 59 is observed which was confirmed to have the expected structure HOCH₂-C⁺O. We found the calculated dissociation energy of ionized HPA into HOCH₂-C⁺=O and HOCO･ to be rather different from that derived from an earlier experimental and theoretical study. This observation led us to re-examine the enthalpies of formation for the m/z 59 C₂H₃O₂⁺ system of ions, which includes the methoxycarbonyl ion CH₃-O-C⁺=O, with high level G2 ab initio calculations. A variety of calculated reactions and reconsideration of previous and new experimental measurements resulted in an upwards revisal, by 9 kcal/mol, of the ∆Hf assigned to these ions.

abstract: Doctor of Philosophy (PhD)


title: Feasibility of a Bone Mineral Measurement Technique Based on Coherent Scattering of Gamma Rays

contributor:
Webber, C.E.
Physics

subject: Physics Physics

abstract: The investigation of the feasibility of a bone mineral measurement technique based on coherent scattering of gamma rays was performed using a HPGe detector. Considerations of detector efficiency and resolution, absorbed dose to bone, spectral separation between coherent and Compton peaks, variation of differential coherent cross section and scattering volume with scattering angle led to the selection of a photon source energy of 103.2 keV (Sm¹⁵³) and a scattering angle of 40°. Bone phantoms (aqueous solutions of K₂HPO₄) were used to examine how the coherent intensity emanating from a scattering volume at the centre of an object varied with object dimensions and solution effective atomic number. Simulation and experimental measurements with solutions in cylindrical polyethylene containers of varying sizes indicated that the ratio of the coherent count rate to the transmission count rate was independent of container dimensions (at least up to 7 cm diameter). For ease of comparison, all the ratios at different concentrations were normalised to that of water obtained in an identical measurement geometry. The normalised coherent-to-transmission ratios were related to solution effective atomic number by a power function with an exponent of 3.30 ± 0.15. When the rate of change of the normalised ratio with effective atomic number is used as an indicator of the sensitivity of the technique, the coherent-to-transmission method is almost twice as sensitive as a coherent-to-Compton technique. In-vitro bone mineral measurements were made in the calcaneus (heel bone), an easily accessible site in which 90% of bone mineral is trabecular. Prior to the measurements the spatial distribution of mineral was investigated with a Norland 278-A single photon absorptiometry (SPA) machine in slices of several calcanei. Cortical bone was restricted to a thin peripheral region of the calcaneus. Three whole calcanei, one of which had its calcium content deliberately reduced by soaking overnight in hydrochloric acid, were selected for measurement using the coherent-to-transmission technique. For the first measurement each bone was submerged in water only. For the second measurement the trabeculae were filled with corn oil, to simulate marrow fat, and again each bone was submerged in water. The latter measurements were about 50% lower than the first, indicating a large "marrow fat" effect. However, both sets of results can be explained by assuming a power relationship between the normalised coherent-to-transmission ratio and the effective atomic number of the scattering volume contents. Cuboid samples of side approximately 16 mm were cut out of the posterior region of each calcaneus and ashed. A plot of the normalised coherent-to-transmission ratio versus the ashed weight per unit volume (bone mineral density) of the three calcanei yielded a straight line. While this indicates that the normalised coherent-to-transmission ratio is an indicator of bone mineral, a larger number of samples will be required to establish a robust calibration curve.

abstract: Doctor of Philosophy (PhD)


title: Applications and Extension of the Theory of Atoms in Molecules

contributor:
Bader, Richard F. W.
Chemistry

subject: Chemistry Chemistry

abstract:
This thesis applies and extends the theory of atoms in molecules. The charge distributions of diatomic molecules, hydrocarbons, hydrogen-bonded complexes and complexes containing NN bonds are examined.

The theory of atoms in molecules provides a quantum mechanical definition of an atom in a molecule and its properties. The topology of the charge distribution is the observational basis for the elements of molecular structure, structural change and stability.

The theory is reviewed in Chapter 1. Studies of hydrocarbons and diatomic molecules are made and the new concept of atomic valume is introduced. Electronegativity schemes are explored and extended.

The nature of the hydrogen bond is discussed in Chapter 2. The charge redistribution which allows for mutual penetration of the van der Waals envelopes of the base atom and the H-bonded H atom is investigated.

Chapter 3 shows how the Laplacian of the charge density can be used to predict structures and geometries of hydrogen-bonded complexes. Reactivities of activated double bonds to nucleophilic attack are predicted.

Chapter 4 surverys a set of complexes containing NN bonds and proposes a bond order and bond energy scheme for these bonds.

Chapter 5 uses density functional theory to construct correlation energy functionals. The correlation energies of atoms in molecules can then be studied and total energies of molecules calculated.

abstract: Doctor of Philosophy (PhD)


title: Designs on Cubic Multigraphs

contributor:
Rosa, A.
Mathematics

subject: Mathematics Mathematics

abstract: Necessary conditions are found for the existence of graph designs on cubic multigraphs. It is shown that, with a few given exceptions, these conditions are sufficient for all connected cubic multigraphs on six or fewer vertices, and for four of the five disconnected ones. Partial results are obtained for the remaining multigraph, which consists of a K4 and a 3K2 component. Necessary and sufficient conditions for the existence of resolvable designs on all bipartite cubic multigraphs on six or fewer vertices are found. Graceful labellings are given for all cubic graphs on eight or ten vertices, and for all prisms on eighteen or fewer vertices. These are used to find some designs on these graphs, including some infinite classes. In addition, some small designs are found for the 5-prism and the Petersen graph, and some results are given for cubes.

abstract: Doctor of Philosophy (PhD)


title: Almost Selfcomplementary Graphs and Extensions

contributor:
Rosa, Alexander
Mathematics

subject: Mathematics Mathematics

abstract:
In this thesis the concept of selfcomplementary graphs is extended to almost selfcomplementary graphs. We dine a p-vertex graph to be almost selfcomplementary if it is isomorphic to its complement with respect to Kp-e, the complete graph with one edge deleted. An almost selfcomplementary graph with p vertices exists if and only if p=2 or 3 (mod 4), ie., precisely when selfcomplementary graphs do not exist. We investigate various properties of almost selfcomplementary graphs and examine the similarities and differences with those of selfcomplementary graphs.

The concepts of selfcomplementary and almost selfcomplementary graphs are combined to define so-called k-selfcomplementary graphs which include the former two classes as subclasses. Although a k-selfcomplementary graph may contain fewer edges than a selfcomplementary or an almost selfcomplementary graph it is found that the former preserves most of the properties of the latter graphs.

The notion of selfcomplementarity is further extended to combinatorial designs. In particular, we examine whether a Steiner triple system (twofold triple system, and a Steiner system S(2,4,v), respectively) can be partitioned into two isomorphic hypergraphs.

abstract: Doctor of Philosophy (PhD)


title: Nutrient Residence Times in Relation to the Trophic Condition of Lakes

contributor:
Vollenweider, Richard Albert
Biology

subject: Biology Biology

abstract:
This thesis is concerned with defining systematic relationships between nutrient flow rates in aquatic ecosystems and their overall biological productivity. The most significant finding was that phosphorus residence time produced a consistent pattern relative to the trophic condition of freshwater lakes and reservoirs which allows both characterization of trophic state and more precise calculation of the concentration response to loadings as commonly applied in lake management.

Nutrient residence times were examined from the perspective of two data types. The data types included time series information on nine individual lake cases and single year cross-sectional information on 220 waterbodies of the OECD Programme on Eutrophication.

The nine case histories gave insight into the applicability of cross-sectionally derived models. These cases showed that sedimentation rates of phosphorus in a given lake varied tremendously from year to year and therefore models based on the assumption of a constant rate are in most instances insufficient. Case histories also showed that phosphorus relative residence times followed a remarkably consistent pattern of increase with an increase in trophic status regardless of te number of types of underlying mechanisms in control of nutrient flows. This increase is related to an acceleration of phosphorus recycling mechanisms rather than a decline in its gross deposition rate. The net decelleration of phosphorus flow rates creates a shift in the relative importance of elimination pathways, from deposition in the sediments to removal via flushing with increasing eutrophication. Lastly, case histories demonstrated that concentration ratios of lake/inflow gave reasonable estimates of nutrient relative residence times as calculated from budget information. Transposing this, the distinctly different dynamics according to tropic category reflected in the cross-sectional concentration ratio data may be interpreted as a functional pattern.

The cross-sectional data indicated that in the case of phosphorus, relative residence time was best described by a different multiple regression equation for each trophic category whereas there was no difference in nitrogen relative residence time according to trophic category. Practical application of this result is in refinement of the calculation of critical loads when the trophic status of a lake is known.

Nutrient limitation judged on the basis of most rapid flow rate implies that phosphorus limitation is far more common that nitrogen limitation, even in eutrophic waterbodies. The relative flow rates is always greater than 1 in oligotrophic and mesotrophic waterbodies, and may be greater than 1 in eutrophic waterbodies. This ration only drops below 1 in some eutrophic waterbodies. Therefore values less that 1 are not necessarily a consequence of eutrophication.

Phosphorus relative residence time was found to be a simple but highly integrative measure capable of characterizing trophic state and its temporal evolution.

abstract: Doctor of Philosophy (PhD)


title: Free Mobility and the Regional Authority in a Federation

contributor:
Papageorgiou, Y.Y.
Economics / Economic Policy

subject: Economics Economics

abstract:
This dissertation contains four primary chapters. Chapter 1 is an introduction. Chapter 2 examines the efficiency properties of a federation characterized by strategically competing regions and freely mobile homogeneous individuals. Previous analyses of this economy have concluded that achieving a Pareto optimal allocation will require intervention by a national authority. This chapter makes one basic point; the Nash equilibrium of regional authority behavior is Pareto optimal. The implication is that there is no role for a national authority in either providing interregional transfers or correcting for decentralized provision of public goods. Free mobility induces strong incentive equivalence between regional authorities. The Nash equilibrium involves Samuelson public good provision and regions purchasing a preferred population distribution with interregional transfers.

Chapter 3 extends the analysis to generalized specifications for public goods. The new specification allows for an analysis of the spillover of public good literature and consideration of impure public goods. Previous analyses of this economy have concluded that a Pareto optimal allocation will require intervention by a national authority in either taking over the function of public good provider or offering matching grants to subsidize regional public good provision. I prove that in an environment of free mobility the Nash equilibrium is Pareto optimal.

Chapter 4 is an extension to a heterogeneous population. The population is modeled as heterogeneous in both preferences and endowments. Enough similarity in preferences and complementarity between labour types in production is assumed to allow abstraction from sorting equilibria. The conclusion is that when regional authorities are not in conflict on normative value judgments, the Nash equilibrium is Pareto optimal. When regional authorities are in conflict the Nash equilibrium does not exist. Once again, this result means that this literature provides no role for a national authority; such intervention is either unnecessary or unhelpful.

Chapter 5 discusses two versions of the fiscal externality. The first version is the widely accepted market failure view. It is maintained that the free mobility of individuals between regions involves a market failure and thus is a source of inefficiency in regional economics. The chapter concludes that this view is mistaken. This first version of the fiscal externality is a pecuniary externality and thus simply a reflection of efficiently operating markets. Inefficient outcomes are traced to assumed inappropriate regional authority behavior. The second more recent version of the fiscal externality argues that in an environment of perfect capital mobility, a regional authority taxing capital causes capital flight, which generates an external economy for other authorities by increasing their tax base. This chapter also concludes that this view is mistaken. Capital taxation by an authority involves internal costs (loss of tax base) and is thus not an externality. Inefficient outcomes are traced to authorities with fewer instruments than targets. Chapter 6 provides a conclusion.

abstract: Doctor of Philosophy (PhD)


title: Modeling of Transport Phenomena in Reverse Osmosis Membranes

contributor:
Dickson, James M.
Chemical Engineering

abstract:
The present research investigates, both theoretically and experimentally, transport phenomena in reverse osmosis (RO) membranes.

In order to properly describe and predict RO membrane performance, and to properly design RO units, a good understanding of the fundamentals of the membrane transport is needed; this means that a strong transport model needs to be developed. This research is concerned with the development of such a model. As well, the effects of system pressure, concentration, and temperature on the performance of thin-film composite, aromatic polyamide RO membranes with sodium chloride and some other salts are examined both experimentally and theoretically.

The present research investigates the development of a powerful, novel transport model for reverse osmosis, which does not have the serious shortcomings of the previous models, and an experimental evaluation of this model. As a result, a mechanistic model, called the Modified Surface Force-Pore Flow (MD-SF-PF) model, has been developed. The model assumes that transport through the membrane takes place in very fine pores, and the pores are modeled as perfect cylinders. In this two-dimensional model, a balance of applied and frictional forces acting on the solute in a pore is given as a function of radial and axial positions. The model incorporates a potential field inside the membrane which is responsible for the partitioning effect (at the two sides of the membrane) and, in part, determines the membrane performance. A computer code has been developed, based on the "orthogonal collocation" method of weighted residuals, which has proven to be very efficient and precise to solve the complicated differential equations of the transport models.

Three models have been developed during the present research: i) the Modified Surface Force- Pore Flow (MD-SF-PF) model, briefly described above, which is appropriate for solvent-membrane affinity systems (such as salt-water systems); a temperature-extended version of this model has also been derived; ii) the Extended MD-SF-PF model (a generalized form of the MD-SF-PF model) which can be used to describe or predict any type of RO system, that is, both solvent-membrane affinity systems, such as sodium chloride-water system, and solute-membrane affinity systems, such as toluene-water system; and iii) the Modified Finely Porous Model (MD-FPM) which is a one-dimensional transport model, and can describe simple systems.

Experimental data are used to determine model parameters. Also, experimental data can be compared to model predictions. The following experimental plan was undertaken using aromatic polyamide (FilmTec) FT30 membranes: i) experiments with 2000 ppm aqueous solutions of sodium chloride (brackish water concentration) in the range 350-7000 kPa and 5-60°C (a few experiments at 25°C and 5000, 10000, and 15000 ppm sodium chloride solutions were also performed (Phase I)); ii) experiments with 2000 ppm potassium chloride, lithium chloride, and lithium nitrate at 25°C and 500-4000 kPa (Phase II); and iii) experiments with 35 000 ppm sodium chloride (sea water concentration) at 4000-7000 kPa and 5-60°C (Phase III).

Model parameters were determined from the data of Phase I at 25°C, using a nonlinear optimization routine. The average pore radii for the SW30HR and BW30 types of FT30 membranes were determined at about 1.0 and 1.2 nm, respectively. All the experimental data at other pressures and concentrations are well predicted by the MO-SF-PF model. Somewhat fortuitously, the MO-SF-PF model also predicts well for the other 1-1 electrolytes.

Temperature effects are reasonably predicted by the temperature-extended MD-SF-PF model. The apparent activation energies for pure water permeability for the SW30HR and BW30 membranes are about 25400 and 22500 kJ/kmol at 5-40°C, respectively, and about 18100 and 13 000 kJ/kmol at 40-60°C, respectively. Compaction, which becomes more severe as temperature or pressure is increased, has no effect on predicting the membrane separation or flux ratio (the ratio of total solution flux to pure solvent flux). An empirical model for compaction has also been developed and used to correct the flux ratio to the absolute values of permeation fluxes.

The Extended MD-SF-PF model has been found to well describe the difficult case of strong solute-membrane affinity, in which solute molecules are attracted toward the membrane rather than being rejected. The model implies that once the solute is rapidly sorbed into the membrane the solute molecules creep slowly adjacent to the wall of the membrane pores.

Overall, the family of the MD-SF-PF models has been found to predict RO membrane performance over a wide range of operating conditions. The agreement between the experimental data and model predictions supports, but does not prove, the proposed transport mechanism. In principle, the family of the MD-SF-PF models can be used for different research purposes including membrane development and RO module design.

abstract: Doctor of Philosophy (PhD)


title: Polymer Latexes: Production by Homogeneous Nucleation and Methods for Particle Size Determination

contributor:
MacGregor, J.F.
Hamielec, A.E.
Chemical Engineering

abstract:
In this work which consists of two parts, two important aspects in latex production and in the control of latex reactors were studied: the determination of latex particle size using on-line and off-line measurements and the particle nucleation in emulsion polymerization in the absence of micelles.

In the first part, three particle sizing methods (turbidimetry, dynamic light scattering and packed column chromatography) were evaluated for their capability to provide accurate estimates of the particle size distribution (PSD) and for their potential to be applied for on-line measurements to monitor and control the particle size in latex reactors. Dynamic light scattering was successfully applied on-line to follow particle growth during the emulsion polymerization of vinyl acetate in a pilot scale reactor. A layout for the hardware of an on-line sampling device which can be used with packed column chromatography is also suggested. Electron microscopy was used to corroborate results from these methods. Several interesting features were observed during this study and this motivated an in-depth investigation of some aspects related to these methods.

A detailed theoretical and experimental investigation showed for the first time that turbidimetric methods are not expected to provide an estimate of the full PSD in certain cases, and identified these cases. Based on this analysis a controversy and several inconsistencies in the literature were resolved. It was also shown that the wavelength exponent and the turbidity ratio are not different but equivalent methods.

In electron microscopy shrinkage of the latex particle under the electron beam was investigated. It was shown that the diameter decreases in an exponential manner with the time of exposure to the electron beam, and that the largest reduction occurred within the first minutes of exposure.

For the packed column chromatography method, software was developed for the conversion of the observed chromatogram to PSD. This software allows for a retention volume dependent spreading function, mass or turbidity detector and extinction coefficient calculations by taking into account the refractive index of the particles. A chromatographic apparatus operating with two detectors (turbidity and differential refractometer) connected in series was utilized to monitor particle growth during the reaction.

In the second part a systematic study of the emulsion polymerization of vinyl acetate in the absence of soap micelles in a pilot plant reactor was carried out. The effects of several variables on the particle size and the reaction rate were investigated in a series of designed experiments. These parameters were: initiator and monomer concentration, monomer and water soluble impurities and agitation. Both soap free runs and runs with soap concentrations much below the CMC were included in the design. Even though the objective was a systematic study of the soap free polymerization of vinyl acetate, the experiments with soap levels below the CMC were included to provide additional data in an attempt to reconcile the conclusions derived from experiments carried out with no soap and with soap levels above CMC. To test for the reliability and the reproducibility of the results some of the polymerization runs were repeated. Most of the measurements were duplicated or triplicated and the particle size was determined with 3 different methods.

Accurate and reproducible data were obtained. The results were consistent, at all levels of the parameters, both in the soap free polymerizations and in the runs with soap below CMS. These results help to clarify certain mechanisms, and to link phenomena observed in the soap free cases with those in polymerizations with soap above CMC, and to understand the similarities and differences. This set of data can offer valuable information for the modelling of several mechanisms of the homogeneous nucleation.

abstract: Doctor of Philosophy (PhD)


title: Machining of particulate metal matrix composites

contributor:
Sklad, M.
Mechanical Engineering

subject:
Mechanical Engineering
Mechanical Engineering

abstract: Particulate metal matrix composites (PMMCs) are being widely used in the aerospace and automotive industry due to their favourable properties, mainly high specific strength and wear resistance. However, machining of particulate metal matrix composites presents a great challenge to the industry as the reinforcing particles easily abrade most of the common cutting tool materials. Polycrystalline diamond (PCD) tools appear to be the most practical type of tool material for machining PMMCs. The first part of the presented research concentrates on experimentally identifying the effect of the various cutting parameters on the chip formation mechanism, which in turn influences the tool wear. Increasing the feed rate had a beneficial effect on the tool wear due to abrasion. This is attributed to the reduced contact between the tool and the abrading reinforcing particles in the chip. The experimental work also involved an evaluation of the damage introduced into the workpiece due to machining. This damage is in the form of crushed particles, cracks and voids around the particles. The surface finish of the work-piece is a reflection of the tool's wear state. The second part of the research involved building up numerical models for the cutting tool and workpiece. Computer simulation of the machining process can potentially reduce the number of experimental iterations needed to determine the optimum cutting parameters, which are the ones that produce the minimum tool wear and least workpiece damage with minimum cost. The model stress results were verified through scanning electron microscopic observations as well as transmission electron microscopic analysis. The finite element models revealed that the area beneath the machined surface experiences high tensile stresses, which cause void formation around the reinforcing particles. These voids join up to form cracks, which have serious implications on the fatigue life of the machined part. Further research into the changes introduced in the microstructure of the chip and machined work-piece is recommended, as this could help in fully understanding the stress state beneath the machined surface.

abstract: Doctor of Philosophy (PhD)