title: INVESTIGATING THE IMMUNOBIOLOGY OF IgE+ B CELLS AND REGULATORY B CELLS IN ALLERGIC ASTHMA

title: B CELL RESPONSES IN ALLERGIC ASTHMA

contributor:
Gauvreau, Gail M
Medical Sciences

subject:
IgE
B cells
Bregs
regulatory B cells
sputum
asthma
allergy
allergen challenge

abstract:
Global prevalence of allergic diseases has been on the rise for the last 30 years. In Canada, this upward trend in allergic diseases has resulted in over 3 million Canadians being affected by allergic asthma. Allergic asthma is triggered by inhalation of environmental allergens resulting in bronchial constriction and inflammation, which leads to clinical symptoms such as wheezing, coughing and difficulty breathing. Asthmatic airway inflammation is initiated by the release of inflammatory mediators (-eg- histamine) released by granulocytic cells (-eg- mast cells and basophils). However, immunoglobulin E (IgE) antibody is also necessary for the initiation of the allergic cascade, and IgE is produced and released exclusively by memory B cells and plasma cells. Allergen crosslinking of IgE:FcεRI complexes on the surface of mast cells and basophils causes degranulation of pro-inflammatory mediators. Acute allergen exposure has also been shown to increase IgE levels in the airways of patients diagnosed with allergic asthma; however, more studies are needed to better understand local airway inflammation. Our group's work, in accordance with the literature, has shown an increase of IgE in the airways of subjects with mild allergic asthma following allergen inhalation challenge. Although regulatory B cells (Bregs) have been shown to modulate IgE-mediated inflammatory processes in allergic asthma pathogenesis, particularly in mouse models of allergic airway disease, the levels and function of these IgE+ B cells and Bregs remain to be elucidated in human models of asthma. The overall objective for this dissertation was to investigate the biology of B cells in allergic asthma pathogenesis, specifically investigating the frequency of IgE+ B cells and Bregs in allergic asthma, and the kinetics of these cells after allergen exposure.
	First, we characterized IgE+ B cells in the blood and sputum of allergic asthmatics and healthy controls with and without allergies (Chapter 2). We showed that IgE+ B cell levels were higher in sputum, but not blood, of allergic asthmatics compared to controls. We further demonstrated that these findings were consistent across airway IgE+ B cell subsets, which include IgE+ memory B cells and IgE+ plasma cells. Additionally, IgE+ B cells in sputum positively correlated with sputum eosinophils, total IgE and B cell activating factor (BAFF) measured in sputum fluid phase. These findings highlight the association of airway IgE+ B cells with allergic asthma, and suggest that local IgE+ B cell functions contribute to the pathogenesis of asthma.
	Second, we measured the trafficking of IgE+ B cells in periphery (blood, bone marrow and tonsil) and locally (sputum) in allergic asthmatics following whole lung allergen challenge (Chapter 3). IgE+ B cells only increased in the airways of allergic asthmatics following allergen inhalation challenge; there were no allergen-induced changes in IgE+ B cell levels in blood, bone marrow and tonsil. In addition, we showed allergen-induced increases in BAFF and total IgE, but not allergen-specific IgE in sputum fluid phase. Taken together, chapters 2 and 3 show that allergic asthmatics have elevated levels of IgE+ B cells in the airways, that can be further increased after allergen exposure. Therefore, local B cell production of IgE in the lungs may be an important source of IgE for initiation of acute inflammatory responses in allergic airways.
	Third, we evaluated the levels of Bregs in allergic asthmatics compared to controls, and examined the kinetics, function and distribution (bone marrow, blood and sputum) of Bregs following allergen inhalation challenge (Chapter 4). We showed that Bregs were 2-fold lower in the blood of allergic asthmatics compared to controls, highlighting a possible dysregulation of this regulatory cell type in allergic asthmatics, which may contribute to disease pathology. Furthermore, after whole lung allergen challenge Bregs decreased in the bone marrow with a co-incident increase in the blood and sputum of allergic asthmatics. This pattern reflects potential trafficking of these cells from bone marrow to the airways after exposure to allergic stimuli. Lastly, we stimulated CD19+ B cells purified from blood of allergic asthmatic with IL-4 in vitro. IL-4 is a type 2 cytokine known to isotype-switch B cells to IgE+ B cells, as well as differentiates naïve T cells into Th2 cells, thus propagating the allergic cascade. We found that IL-4 promoted higher proportions of IL-10+ and FoxP3+ Bregs, which demonstrates that Bregs may have a role in dampening IgE-mediated inflammation in a type 2 environment. However, further functional studies are warranted.
	Taken together, the findings of this dissertation highlight the local compartmental changes in IgE+ B cells and Bregs following allergen challenge of allergic airways. Better understanding the temporal and compartmental shifts in B cell subpopulations, particularly IgE+ B cells and Bregs, may aid in future development of therapeutics.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: Variational Information-Theoretic Atoms-in-Molecules

contributor:
Ayers, Paul Woodson
Bultinck, Patrick
Verstraelen, Toon
Chemistry

subject:
Atoms in Molecules
Stockholder Partitioning
Additive Variational Hirshfeld
Information-theory measures
Kullback-Liebler divergence

abstract:
It is common to use the electron density to partition a molecular system into atomic regions. The necessity for such a partitioning scheme is rooted in the unquestionable role of atoms in chemistry. Nevertheless, atomic properties are not well- defined concepts within the domain of quantum mechanics, as they are not observable. This has resulted in a proliferation of different approaches to retrieve the concept of atoms in molecules (AIM) within the domain of quantum mechanics and in silico experiments based on various flavors of model theories.
One of the most popular families of models is the Hirshfeld, or stockholder, partitioning methods. Hirshfeld methods do not produce sharp atomic boundaries, but instead distribute the molecular electron density at each point between all the nuclear centers constituting the molecule. The various flavors of the Hirshfeld scheme differ mainly in how the atomic shares are computed from a reference promolecular density and how the reference promolecular density is defined.
We first establish the pervasiveness of the Hirshfeld portioning by extending its information-theoretic framework. This characterizes the family of f-divergence measures as necessary and sufficient for deriving Hirshfeld scheme. Then, we developed a variational version of Hirshfeld partitioning method, called Additive Variational Hirshfeld (AVH). The key idea is finding the promolecular density, expanded as a linear combination of charged and neutral spherically-averaged isolated atomic densities in their ground and/or excited states, that resembles the molecular density as much as possible. Using Kullback-Liebler divergence measure, this automatically guarantees that each atom and proatom have the same number of electrons, and that the partitioning is size consistent. The robustness of this method is confirmed by testing it on various datasets. Considering the mathematical properties and our numerical results, we believe that AVH has the potential to supplant other Hirshfeld partitioning schemes in future.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: The neuropsychiatric sequelae of concussion: towards an understanding of the neurobiology

contributor:
Mazurek, Michael
Neuroscience

subject: Concussion Neurogenesis

abstract:
Concussion/mild traumatic brain injury (mTBI) is a significant public health concern, particularly for young individuals and athletes. While the vast majority recover quickly and without lasting consequences, some will suffer from potentially long-term neuropsychiatric sequelae. These sequelae have been investigated in mTBI samples consisting largely of motor vehicle-related injuries, but very few have examined these following sport-related concussion (SRC). Further, new evidence indicates that participation in contact sports alone can result in similar problems with cognition and mood/anxiety. This thesis investigates neuropsychiatric sequelae in youth and young adults with concussion and who participate in contact sports.
The hippocampus is known to be vulnerable to head injury, and animal models indicate that mTBI impairs hippocampal neurogenesis — the process of the growth, maturation, and integration of adult-born neurons. Hippocampal neurogenesis is well-recognized for its importance to cognition, and has more recently been linked to mood and anxiety. Accumulating evidence indicates that a test involving a component of high memory interference, the mnemonic similarity test (MST), is sensitive to neurogenesis-dependent conditions in humans. To the best of our knowledge, this thesis is the first to investigate whether the MST is sensitive to concussion, contact sport participation, and athletic anxiety.
This thesis describes: (1) a critical review of the literature regarding the psychiatric sequelae of concussion, followed by (2) clinical profiles derived from retrospective data which document the new onset of immediate psychiatric problems in youth, and delayed psychiatric problems in youth with persistent concussion symptomology; that (3) anxiety is the most common and persistent psychiatric symptom in youth with concussion; that (4) concussion and contact sport participation negatively affect performance on the MST; that (5) a reprieve from contact sport participation is associated with an improvement in MST performance; that (6) these negative effects on the MST are not seen with other injuries; that (7) athletic anxiety impairs performance on the MST. Taken together, this thesis provides evidence that psychiatric problems can present immediately after concussion in persons without identifiable risk factors, and that concussion, contact sport participation, and athletic anxiety affect performance on a putatively neurogenesis-linked test. These results may implicate impaired hippocampal neurogenesis in postconcussion sequelae.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: Hegel's Conception of the History of Philosophy

contributor:
Lapointe, Sandra
Philosophy

subject:
Hegel
History of Philosophy
Historiography
Philosophy of History
German Idealism
Concept of Progress

abstract: The main aim of this thesis is to present an account of Hegel's conception of the history of philosophy and to demonstrate its relevance to contemporary issues in the methodology of the history of philosophy both insofar as Hegel still has interesting things to say to contemporary historians, and insofar as an understanding of Hegel's views helps us understand later developments in the historiography of philosophy. In the first chapter, I present the conceptual scaffolding which enables us to compare Hegel's conception of the history of philosophy with contemporary approaches to the history of philosophy. I also criticize some of the myths that have developed around Hegel's conception of the history of philosophy. In the second chapter, I present the principles that constitute Hegel's evaluative framework: coherence or non-contradiction (in relation to the concept of Aufhebung), concreteness, systematicity, autonomy, and the use of clear conceptual language in philosophical discourse. Aside from these formal principles, I also identify a substantive philosophical thesis which Hegel seems to use in order to evaluate development in the history of philosophy, namely, the identity of thought and being. In the third chapter I attempt to attenuate the tension that exists between Hegel's methodological prescriptions, especially the claim that we should be on guard against anachronistic readings and that critique should be internal, with the manner in which he seems to consistently read past philosophers through his own system. I suggest two perspectives which can help attenuate this tension. First, I emphasize that Hegel is trying to write an anti-individualistic history of philosophy, where philosophical systems are presented as public culture achievements and the individual idiosyncrasies of philosophers are suppressed. Second, I show how Hegel's semantic and epistemic holism helps us make sense of the way that he approaches the history of philosophy. In the fourth and final chapter I discuss Hegel's conception of the relationship between philosophy and its socio-cultural milieu, and based on this discussion, I show that Hegel did not think that there is continuity in the kinds of problems that philosophers have been interested in, and that he thought that the main purpose of the history of philosophy is to provide metaphilosophical reconstructions and justifications of shifts in the kinds of problems that philosophers have been interested in.

abstract: Thesis

abstract: Master of Arts (MA)

abstract: In this thesis I attempt to fill in a gap in Anglophone scholarship on Hegel by presenting an account of a much neglected aspect of Hegel's system, namely, Hegel's account and conception of the history of philosophy. I begin by attempting to dispel some misunderstandings that have distorted the Anglophone reception of this aspect of Hegel's thought, and by emphasizing the importance of understanding Hegel's views on the history of philosophy if one wishes to understand later developments in the historiography of philosophy. I then present the principles by which Hegel evaluates development in the history of philosophy, and I attempt to attenuate some of the tension which seems to exist between Hegel's methodological prescriptions and his actual practice as a historian of philosophy. I conclude with an account of Hegel's views on continuity in the history of philosophy, and their relation to contemporary views on continuity in the history of philosophy.


title: Colloidal Fabrication of Advanced Oxide Composite Materials for Supercapacitors

contributor:
Zhitomirsky, Igor
Materials Science and Engineering

subject:
Supercapacitor
Oxide
Carbon nanotubes

abstract: With a unique blend of power and energy densities, as well as long cycling lives, electrochemical supercapacitors are finding greater application in energy storage solutions. Among candidate materials for supercapacitors, MnO2 has garnered a great deal of attention. However, its low intrinsic electrical conductivity has proven to be a serious hindrance on performance when used in supercapacitor electrodes. Efficient use of conductive additives is a demonstrated, effective method to combat this problem, however there is still a great need for improvement. Two new colloidal processing techniques have been developed to mix chemically synthesized MnO2 and conductive multi-walled carbon nanotubes (MWCNT). The first strategy involved the linking of MnO2 and MWCNT through the formation of a Schiff base. 3,4-dihydroxybenzaldehyde (DB) was used to modify MnO2, while MWCNT were dispersed with the dye New Fuchsin (NF). These compounds were selected due to the presence of molecular features previously identified as conducive to strong adsorption and good colloidal dispersion, as well as the necessary functional groups required to form a Schiff base. The second involved the use of liquid-liquid extraction, primarily in an attempt to prevent post synthesis MnO2 particle agglomeration. Lauryl gallate (LG) was used as an extracting and dispersing agent for MnO2 synthesized via the reaction between aqueous potassium permanganate (KMnO4) and 1-butanol. LG facilitated the co-dispersion and mixing of both MnO2 and MWCNT in the 1-butanol phase. V2O3 was also investigated as a replacement for MnO2, as its high intrinsic electrical conductivity gives it a potential advantage over MnO2. In each of these three projects, electrodes were produced with exceptionally high areal normalized capacitances at high active mass loadings. The MnO2-MWCNT composites were used to fabricate full asymmetric supercapacitor devices that were able to deliver a useable amount of energy.

abstract: Thesis

abstract: Master of Applied Science (MASc)

abstract: The modern world has an insatiable appetite for energy and must have access to it for stationary and mobile applications. To meet this demand, it is of paramount importance to develop new, high performance energy storage technologies. The energy requirements for different applications, however, necessitate storage devices that have suitable properties. The energy stored in a large pool of hot water is not in a suitable form to power a cellphone. The key goal of this work was to further develop one particular energy storage technology, called electrochemical supercapacitors. Novel processing techniques were developed and new materials investigated with the aim of producing supercapacitor electrodes that would exceed the performance of what is already available today. The materials that were produced exhibited very high performance and offered new insight and direction for further research in this exciting field.


title: A DIRECT STEAM GENERATION CONCENTRATED SOLAR POWER PLANT WITH A DECALIN/NAPHTHALENE THERMOCHEMICAL STORAGE SYSTEM

contributor:
Adams, Thomas Jr
Chemical Engineering

abstract: This study presents the design and analysis of a new integrated direct steam generation (DSG) concentrated solar power (CSP) plant with a decalin/naphthalene thermochemical storage system. Model simulations were performed in accordance to historical hourly solar radiation data over a year, using a combination of Aspen Plus v10, MATLAB 2016b, and Microsoft Excel VBA. It was found that the proposed plant feasibly stored and discharged energy, based on the solar radiation and chemical storage availability, to maintain base-load power productions (250 MW or 120 MW) with an overall efficiency of 14.6%. The effectiveness of the designed storage system was found to be comparable to a molten salt storage system which is currently used in existing CSP plants. The proposed integrated DSG CSP plant with a decalin/naphthalene thermochemical storage system shows promise for being an alternative to existing CSP plants.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Multi-Rate Control Architectures for Network-Based Multi-User Haptics Interaction

contributor:
Sirouspour, Shahin
Capson, David
Electrical and Computer Engineering

subject: multi-rate, control architectures, network, multi-user, haptics interaction, local area networks, metropolitan area networks, UDP protocol

abstract:
 Cooperative haptics enables multiple users to manipulate computer simulated objects in a shared virtual environment and to feel the presence of other users. Prior research in the literature has mainly addressed single user haptic interaction. This thesis is concerned with haptic simulation in multi-user virtual environments in which the users can interact in a shared virtual world from separate workstations over Ethernet-based Local Area Networks (LANs) or Metropolitan Area Networks (MANs). In practice, the achievable real-time communication rate using a typical implementation of network protocols such as the UDP and TCP/IP can be well below the 1kHz update rate that is suggested in the literature for high fidelity haptic rendering. However by adopting a multi-rate control strategy as proposed in this work, the local control loops can be executed at 1kHz while the data packet transmission between the user workstations occur at a lower rate. Within such a framework, two control architectures, namely centralized and distributed are presented. In the centralized controller a central workstation simulates the virtual environment, whereas in the distributed controller each user workstation simulates its own copy of the virtual environment. Two different approaches have been proposed for mathematical modeling of the controllers and have been used in a comparative analysis of their stability and performance. The results of such analysis
demonstrate that the distributed control architecture has greater stability margins and outperforms the centralized controller. They also reveal that the limited network transmission rate can degrade the haptic fidelity by introducing viscous damping into the virtual object perceived impedance. This extra damping is compensated by active control based on the damping values obtained from the analytical results. Experimental results conducted with a dual-user/dual-finger haptic platform are presented for each of the proposed controller under various scenarios in which the user workstations communicate with UDP protocol subjected to a limited transmission rate. The results demonstrate the effectiveness of the proposed distributed architecture in providing a stable and transparent haptic simulation in free motion and in contact with rigid environments.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Tracking the Operational Mode of Multi-Function Radar

contributor:
Haykin, Simon
Kirubarajan, Thia
Electrical and Computer Engineering

subject: operational mode, multi-function, radar, Recurrent Neural Network, dynamic time warping algorithm, perceptron

abstract: This thesis presents a novel hybrid methodology using Recurrent Neural Network and Dynamic Time Warping to solve the mode estimation problem of a radar warning receiver (RWR). The RWR is an electronic support (ES) system with the primary objective to estimate the threat posed by an unfriendly (hostile) radar in an electronic warfare (EW) environment. One such radar is the multi-function radar (MFR), which employs complex signal architecture to perform multiple tasks. As the threat posed by the radar directly depends on its current mode of operation, it is vital to estimate and track the mode of the radar. The proposed method uses a recurrent neural network (echo state network and recurrent multi-layer perceptron) trained in a supervised manner, with the dynamic time warping algorithm as the post processor to estimate the mode of operation. A grid filter in Bayesian framework is then applied to the dynamic time warp estimate to provide an accurate posterior estimate of the operational mode of the MFR. This novel approach is tested on an EW scenario via simulation by employing a hypothetical MFR. Based on the simulation results, we conclude that the hybrid echo state network is more suitable than its recurrent multi-layer perceptron counterpart for the mode estimation problem of a RWR.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Adaptive Bandwidth Reservation and Scheduling for Efficient Telemedicine Traffic Transmission Over Wireless Cellular Networks

contributor:
Koutsakis, Polychronis
Electrical and Computer Engineering

subject: adaptive bandwidth reservation, scheduling, telemedicine, traffic transmission, wireless cellular networks, multimedia

abstract:
 Telemedicine traffic transmission over wireless cellular networks has gained in importance during the last few years. Most of the current research in the field has focused on software and hardware implementations for telemedicine transmission, without discussing the case of simultaneous transmission of both urgent telemedicine traffic and regular multimedia traffic over the network.

 Due to the fact that telemedicine traffic carries critical information regarding the patients' condition, it is vitally important that this traffic has highest transmission priority in comparison to all other types of traffic in the cellular network. However, the need for expedited and correct transmission of telemedicine traffic calls for a guaranteed bandwidth to telemedicine users. This creates a tradeoff between the satisfaction of the very strict Quality of Service (QoS) requirements of telemedicine traffic and the loss of the guaranteed bandwidth in the numerous cases when it is left unused, due to the infrequent nature of telemedicine traffic. This waste of the bandwidth may lead to a lack of sufficient bandwidth for regular traffic, hence degrading its QoS.

 To resolve this complex problem, in this thesis, we propose a) an adaptive bandwidth reservation scheme based on road map information and on users' mobility, and b) a fair scheduling scheme for video traffic transmission over wireless cellular networks. The proposed combination of the two schemes, which is evaluated over a hexagonal cellular structure, is shown to achieve high channel bandwidth utilization while offering full priority to telemedicine traffic.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Investigation of Saturable Optical Receiver (SOR) for Fiber to the Home Network

contributor:
Li, Xun
Electrical and Computer Engineering

subject: saturable optical receiver, fiber, home network, FTTH network, low pass filter

abstract:
 Due to the high cost, telephone and cable television companies can only justify installing fiber optical networks to remote sites which serve up to a few hundred customers. For customers located at variable distances from the transmitting station, they will receive signals at different strengths. The signal stability and system reliability of FTTH network affected largely by the distance. We propose an effective solution for the enhancement of signal stability of FTTH network, which uses a semiconductor optical amplifier (SOA) coupled with an optical receiver.

 Before the signal reaches the optical receiver at the user end, signal strength is automatically adjusted through a semiconductor optical amplifier (SOA). Due to the special saturation property of SOA, the output optical signal will have very small
fluctuation regardless the input optical signal power, the signal stability of FTTH network will be improved significantly. A set of simplified governing equations of SOA has been proposed and the corresponding numerical solver has been implemented. Although the main focus is primarily the SOA, a simplified optical receiver is also simulated, which comprises a PIN photodetector and a low pass filter (LPF). All simulations have been carried out in the time-domain with the frequency domain low pass filter modeled by a digital filter.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: The Role of MMP9 and WNT Signaling in Peritoneal Angiogenesis

contributor:
Margetts, Peter
Medical Sciences

subject: Peritoneal Dialysis, Angiogenesis, Fibrosis, Matrix Metalloproteinase 9, WNT/b-catenin signaling, TGFB, Epithelial to Mesenchymal Transition, WNT5A, Ror2, VEGF, Ultrafiltration

abstract:
Patients on peritoneal dialysis (PD) are reliant on the peritoneum to provide a semi-permeable barrier to allow for dialysis (solute clearance), salt and water removal (ultrafiltration). PD patients are at risk of developing peritoneal fibrosis and angiogenesis which can lead to a decline in peritoneal membrane function. Specifically, PD patients develop increased solute transport and decreased osmotic conductance leading to ultrafiltration failure. Peritoneal angiogenesis is the leading factor that results in augmented peritoneal membrane solute transport which is associated with worse outcomes – increased risk of mortality and PD technique failure. Transforming growth factor beta (TGFB) is one of the primary cytokines involved in inducing epithelial to mesenchymal transition (EMT) and fibrosis. We hypothesize that PD leads to injury of the epithelial lining of the peritoneum – the mesothelial cells. These cells undergo a transition process and transitioned mesothelium are a source for angiogenic and fibrogenic growth factors.
Matrix Metalloproteinase (MMP) 9 is an angiogeneic factor and has been observed to correlate with increased expression of vascular endothelial growth factor (VEGF). MMP9 has the ability to cleave and activate membrane bound factors such as E-cadherin and b-catenin respectively. There is substantial evidence that the canonical WNT/b-catenin pathway is active during fibrosis, and angiogenesis in different biological contexts. Thus, we investigated the role of MMP9 and WNT signaling in peritoneal angiogenesis. Limited evidence exists describing the role of noncanonical WNT signaling but some reports suggest that non-canonical WNT signaling inhibits WNT/b-catenin signaling. Non-canonical WNT5A has differential effects based on receptor context and has been shown to block WNT/b-catenin signaling in the presence of Receptor Tyrosine Kinase Like Orphan Receptor 2 (Ror2). The overall hypothesis of this PhD thesis is that MMP9 and WNT signaling play a key role in inducing peritoneal angiogenesis and are associated with changes in peritoneal membrane function. We expect WNT5A and Ror2 to protect against peritoneal membrane injury.
From the overnight effluent of stable PD patients, we cultured mesothelial cells and assayed these for expression of MMP and WNT related genes. MMP9 and WNT1 gene expression were observed to be strongly correlated with peritoneal membrane solute transport in patients on PD. WNT2 mRNA was also positively correlated with peritoneal solute transport. We overexpressed MMP9 in the mouse peritoneum to demonstrate its role in angiogenesis and confirmed these findings using MMP9 -/- mice. In addition to this, we have shown a novel mechanism by which MMP9 induces angiogenesis by E-cadherin cleavage and b-catenin mediated signaling. The observed cross-talk between MMP9 and b-catenin prompted investigation of the activation of canonical WNT/b-catenin signaling in development of peritoneal membrane injury. In an experimental model of TGFB induced pertioneal injury, we confirmed the activation of WNT/b-catenin signaling. In addition to this we, we blocked the WNT pathway and observed that WNT/b-catenin signaling is required to induce peritoneal angiogenesis. WNT5A mRNA was downregulated during TGFB induced injury suggesting a more protective role. Furthermore, several studies have demonstrated its ability to antagonize the WNT/b-catenin signaling pathway. We demonstrated that WNT5A protected against angiogenesis by blocking the canonical WNT pathway. WNT5A is thought to antagonize the WNT/b-catenin signaling pathway by signaling through receptor Ror2. In cell culture, we overexpressed TGFB and blocked Ror2. This resulted in elevated levels of VEGF and fibronectin suggesting that Ror2 is involved in mediating protection. Therefore, Ror2 possesses the ability to regulate VEGF and may be a potential candidate by which WNT5A mediates its protective effects.
In conclusion, our findings identified MMP9 and WNT1 as potential biomarkers of increased peritoneal solute transport in patients that are on PD. We have also found a novel mechanism by which MMP9 interacts with b-catenin to induce peritoneal angiogenesis and have provided a first look at WNT/b-catenin signaling in peritoneal angiogenesis. Lastly, we have shown WNT5A to protect against peritoneal angiogenesis. Taken together, our findings are not only significant to the realm of PD research but hold wide applicability to research in the biomedical sciences.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: Three Essays in Pricing Asset Characteristics

title: Social Screens and Investor Boycott Risk

title: Asset Characteristics and Multi-Factor Efficiency

title: Distinguishing Factors and Characteristics with Characteristic-Mimicking Portfolios

contributor:
Balvers, Ronald
Business

subject: Asset Pricing, Systematic Risks, Characteristics, Multi-Factor Efficiency, Non-pecuniary Preference, Socially Responsible Investment, Sin Stocks

abstract:
This dissertation contains three essays on the non-pecuniary preferences pertaining to financial asset characteristics and their implications for asset pricing. The first essay considers the pricing implications of screens adopted by socially responsible investors. A model including such investors reconciles the empirically observed risk-adjusted sin-stock abnormal return with a systematic “boycott risk premium” which has a substantial financial impact that is, however, not limited to the targeted firms. The boycott effect cannot be displaced by litigation risk, a neglect effect, and liquidity considerations, or by industry momentum and concentration. The boycott risk factor is valuable in explaining cross-sectional differences in mean returns across industries and its premium varies directly with the relative wealth of socially responsible investors and with the business cycle.
	The second essay generalizes Fama (1996)’s concept of Multi-Factor Efficiency without being limited by additional random state variables that must affect future investment opportunities. Incorporating non-pecuniary preferences into a representative investor’s utility function generates multi-factor pricing implications. A representative investor chooses among expected returns, variances, and levels of characteristics according to their taste, which gives rise to an N-fund separation theorem with static characteristics. If a portfolio is built to maximize the exposure to the asset characteristics, the covariance between asset returns and this portfolio returns will be identical to the underlying characteristics. Such identity makes obsolete any attempts to distinguish between characteristics and risk exposures as the driving forces behind the cross-sectional variation in stock returns.
	The third essay   develops a procedure for deriving systematic factors from characteristics, based on maximizing each factor’s exposure to a characteristic subject to a given level of factor variance.  The resulting characteristic-mimicking portfolios (CMP) price mean asset returns identically as the original characteristics, irrespective of the underlying model. Accordingly, differences in the performance of mimicking factors and characteristics in explaining mean returns should be interpreted as an artifact of arbitrary procedural choices for generating mimicking factors.  Factors and characteristics may be distinguished usefully only by determining if CMPs have significant explanatory power for the time series of returns.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: Blind Unique Channel Identification of Alamouti Space-Time Coded Channel via a Signalling Scheme

contributor:
Wong, Kon Max
Electrical and Computer Engineering

subject: blind unique channel, identification, Alamouti, space-time, coded channel, signalling scheme, MISO, STBC

abstract:
 In this thesis, we present a novel signalling scheme for blind channel identification of
Alamouti space-time coded (STBC) channel and a space-time coded multiple-input single-output (MISO) system under flat fading environment. By using p-ary and q-ary PSK signals (where p and q are co-prime integers), we prove that a) under a noise-free environment, only two distinct pairs of symbols are needed to uniquely decode the signal and identify the channel, and b) under complex Gaussian noise, if the pth and qth order statistics of the received signals are available, the channel coefficients can also be uniquely determined. In both cases, simple closed-form solutions are derived by exploiting specific properties of the Alamouti STBC code and linear Diophantine equation theory.

 When only a limited number of received data are available, under Gaussian noise environment, we suggest the use of the semi-definite relaxation method and/or the sphere decoding method to implement blind ML detection so that the joint estimation of the channel and the transmitted symbols can be efficiently facilitated. Simulation results show that blind ML detection methods with our signalling scheme provide superior normalized mean square error in channel estimation compared to the method using only one constellation and that the average symbol error rate is close to that of the coherent detector (which necessitates perfect channel knowledge at the receiver), particularly when the SNR is high.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Sensitivity to Predator Response Functions in the Chemostat

contributor:
Wolkowicz, Gail
Mathematics

subject:
chemostat
predator-prey
Holling Type 2

abstract:
Biological models of predator-prey interaction have been shown to have high
sensitivity to the functional form of the predator response (see [3]). Chemo-
stat models with competition have been shown to be robust under various
forms of response function (see [15]). The fcus here is restricted to a simple
chemostat model with predator-prey dynamics. Several functional responses
of Holling Type II form are considered. The sensitivity of dynamics to our
choice of functional form is demonstrated by way of bifurcation theory. These
results should be a warning to modelers, since by data collection and curve-
fitting alone it is impossible to determine the exact functional form of the
predator response function.

abstract: Thesis

abstract: Master of Science (MSc)


title: Transitioning to Practice in Long-term Care: From New Graduate Nurse to Nurse Leader

contributor:
Baxter, Pamela
Kaasalainen, Sharon
Ploeg, Jenny
Nursing

subject:
New Graduate Nurse
Transition to Practice
Long-term Care
Nursing

abstract: This project, which used a qualitative, explanatory case-study design explored the transition to practice of new graduate Registered Nurses (RNs) and Registered Practical Nurses (RPNs) in long-term care (LTC). Specifically, this study focused on the self-described transition to practice experience of the new graduate nurse (NGN), the contextual factors present in LTC that influenced this transition to practice, and how the transition experience was similar and different for the new graduate RN and RPN. Both NGNs and LTC directors were included in the study. In total, 7 NGNs and 2 LTC directors participated in semi-structured interviews. The NGN participants were employed as a nurse in one of the two LTC sites and had been working as a nurse for less than one year. Data were collected through Key Informants (NGNs and LTC directors), and Key Documents (LTC policies and orientation material). Results of this study introduced six contextual factors present in LTC that influence the transition to practice of NGNs and five processes that, as a result of the contextual factors, accelerate the transition to practice experience. This described accelerated transition to practice refutes the previously universally applied transition to practice theory and contributes new knowledge and understanding to the transition to practice experience of the NGN in LTC and more specifically how the new graduate RPN experiences transitioning. The findings also described the many similarities and some differences between the transition to practice experience of the new graduate RN and RPN in LTC. With increasing demands on the long-term care sector, these findings will be of interest to a broad audience including policy makers, educators, LTC directors and administrators, as well as nursing students and NGNs. It is anticipated that these results will direct further research on this topic, and inform policy, practice, and educational programs.

abstract: Thesis

abstract: Master of Science (MSc)


title: Implementation of MOSFET High-Frequency Noise for RF ICs

contributor:
Chen, C. H.
Electrical and Computer Engineering

subject: MOSFET, high-frequency, noise, circuit simulators

abstract:
 This thesis focuses on the noise model verification at both device and circuit levels using circuit simulators. The techniques and procedures developed in this thesis are general and can be applied to any proposed RF noise model equations. To fulfil the two tasks, three main topics have been accomplished. First, a general noise source implementation method has been presented in detail in this thesis and is verified with measurements for both long and short-channel MOSFETs. This method provides a simple and effective way to implement the enhanced channel noise and induced gate noise of MOSFETs without increasing the simulation complexity for the simulators.

 Second, a systematic procedure to refine the model parameters used in noise calculation is presented. For a model to accurately predict the HF noise characteristics, the accuracy in the prediction of both DC and AC characteristics has to be ensured. The procedure proposed in this thesis provides both DC and AC model parameter verification and optimization for RF noise simulation purpose.

 Third, as for benchmark circuits to verify noise model at the circuit level, two LNA designs are proposed in the thesis. The first design gives the emphasis on the noise reduction technique and the LNA design procedure. The proposed noise reduction technique gives circuit designers more control on noise figure minimization through noise matching. The second design is used to experimentally verify the noise model at the circuit level.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: THE SOCIOECONOMIC GRADIENT IN THE DEVELOPMENTAL HEALTH OF CANADIAN CHILDREN WITH DISABILITIES

contributor:
Janus, Magdalena
Health Research Methodology

subject:
health research methodology
child development
special needs
psychometrics
socioeconomic status

abstract:
Background: Compared with typically developing children, children with special needs often struggle with academic and social aspects of school, though certain factors can improve their academic and social developmental trajectory. The objective of this investigation was to explore the association between the developmental health of children with special needs at school-entry, as measured by the Early Development Instrument (EDI), and neighborhood-level SES. To date, the EDI has only been validated for use in typically developing children. Hence, a secondary objective of this investigation was to explore the psychometric properties of the EDI for children with special needs.
Methods: The data for this investigation were from the Pan-Canadian database of children’s developmental health at school entry. The psychometric properties of the EDI, including item and domain characteristics, factor structure, and construct validity, were tested for children with special needs. Hierarchical generalized linear models was used to model the association between EDI domain scores and a custom neighborhood SES index.
Results: A total of 29,841 (69.8% male) and 29,520 (69.7% male) children with special needs were available for the investigation on the psychometric properties of the EDI and the relationship between EDI outcomes and SES, respectively. The psychometric performance of the EDI in children with special needs was similar to its performance in typically developing children. The EDI was subsequently used to explore the association between developmental outcomes and neighborhood socioeconomic status (SES). All EDI domains were positively correlated with SES, indicating that children in high SES neighborhoods have better developmental outcomes at school entry than those in lower SES neighborhoods.
Conclusions: The results of this investigation draw attention to the potential impact of contextual factors on children’s health and have implications for policy development and service planning. These results also indicate that the EDI performs similarly in children with special needs and typically developing children, thus enabling its more extensive use for this population.

abstract: Thesis

abstract: Master of Science (MSc)


title: Computational determination of the largest lattice polytope diameter

contributor:
Deza, Antoine
Computing and Software

abstract:
A lattice (d, k)-polytope is the convex hull of a set of points in dimension d whose
coordinates are integers between 0 and k. Let δ(d, k) be the largest diameter over all
lattice (d, k)-polytopes. We develop a computational framework to determine δ(d, k)
for small instances. We show that δ(3, 4) = 7 and δ(3, 5) = 9; that is, we verify for
(d, k) = (3, 4) and (3, 5) the conjecture whereby δ(d, k) is at most (k + 1)d/2 and is
achieved, up to translation, by a Minkowski sum of lattice vectors.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Connecting the Chemical Composition of Planetary Atmospheres with Planet Formation

contributor:
Pudritz, Ralph
Physics and Astronomy

subject:
Planet formation
Astrochemistry
Accretion disk physics
Dust physics
Planetary atmospheres

abstract:
What sets the observable chemical composition of exoplanetary atmospheres? The available chemical abundance of the planet's natal protoplanetary disk gas will have a deciding role in the bulk abundance of the atmosphere very early in the planet's life. While late accretion of ices and inter-atmosphere physical processing can change the observable chemical abundances. We have developed a theoretical model which connects the chemical and physical evolution of an accretion disk with the growth of a young planet to predict the bulk chemical abundance of the planetary atmosphere that is inherited from the disk.

We assess what variation in atmospheric chemical abundances are attributed to different planet formation histories. We find differences in the relative abundances of primary nitrogen carriers NH$_3$ and N$_2$ depending on {\it when} the planet accreted its gas. Early ($t<1$ Myr) accreters predominately accreted warmer gas which tend to have its nitrogen in NH$_3$, while later protoplanets accrete colder, more N$_2$ dominated gas.

Furthermore we compute the carbon-to-oxygen ratio (C/O) for each planets, which is used to infer {\it where} a planet forms in its accretion disk. We find that each of our planets accrete their gas very close to the water ice line, thereby accreting `pristine' gas with C/O$_{planet}$ exactly matching its host star.
We extend our results by tuning our initial disk parameters to reproduce the properties of the HL Tau disk. We produce three models that span the range of measured gas masses, and one model which studies a UV quiet system. We generally find that planet formation is efficient enough to produce a Jupiter-massed planet within the predicted 1 Myr age of the disk. We find a correspondence between the radial locations of ice lines within our astrochemical model and the set of observed dust gaps in the HL Tau system.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: Application of the Wavelet Transform for EMG M-Wave Pattern Recognition

contributor:
de Bruin, H.
Electrical Engineering

subject: wavelet transform, EMG M-Wave pattern recognition, application, power spectral coefficients, Euclidean distances

abstract:
 An investigation as to the appropriateness of the wavelet transform for surface
electromyography (EMG) M-wave pattern recognition is described. The M-waves are obtained by stimulating the median nerve at the wrist to activate the motor units. Surface electrodes and a graded stimulus amplitude are used. The resulting M-waves are classified using both wavelet vectors and the traditional power spectral coefficients as features sets in the pattern recognition scheme. A novel system was developed to obtain M-wave collections from subjects in the laboratory and to perform both real-time and offline analysis.

 The results obtained from the left and right thenar muscles of 4 healthy females and 2 healthy males are presented. These results are further analyzed offline to determine the effects of a changing discriminatory threshold for both wavelet and power spectral pattern recognition techniques. In addition, intra-class and inter-class Euclidean distances are shown for the set of unique M-waves derived from using the different feature sets. A time-invariant wavelet transform is implemented to improve classification by eliminating errors due to latency shifts.

 The results show that the number of unique M-waves obtained usmg wavelet
features is less sensitive to a variation in discriminatory threshold. It may be concluded that a wavelet based feature set shows slight improvement in M-wave pattern classification. The time-invariant wavelet offers further accuracy.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Fast Screening Algorithm for Template Matching

contributor:
Wu, Xiaolin
Electrical and Computer Engineering

subject:
computer vision
image processing

abstract:
This paper presents a generic pre-processor for expediting
conventional template matching techniques. Instead of locating the
best matched patch in the reference image to a query template via
exhaustive search, the proposed algorithm rules out regions with no
possible matches with minimum computational efforts. While working
on simple patch features, such as mean, variance and gradient, the
fast pre-screening is highly discriminative. Its computational
efficiency is gained by using a novel octagonal-star-shaped template
and the inclusion-exclusion principle to extract and compare patch
features. Moreover, it can handle arbitrary rotation and scaling of
reference images effectively, and also be robust to uniform
illumination changes. GPU-aided implementation shows great efficiency
of parallel computing in the algorithm design, and extensive
experiments demonstrate that the proposed algorithm greatly reduces
the search space while never missing the best match.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Supply, Secrecy, and Surveillance: Experiences of Women who use Cannabis for Pleasure

contributor:
Greene, Saara
Social Work

subject: Cannabis Women Surveillance Legal

abstract:
The purpose of this thesis is to examine the nature of the relationships that exist between women and their use of cannabis. Currently, women’s use of cannabis is legally permitted within a federal, medical system of access; however, cannabis’ consumption outside of that framework is categorized as a criminal act. As a result, women are subjected to differing forms of cannabis stigmatization and surveillance across many socio-political contexts, often resultant in women’s losses of power and position. As Canada prepares to enact a legal cannabis framework, it is crucial that society and institutions understand the relationships which women have developed through cannabis use. Otherwise, the legalization of cannabis use will not -- in and of itself -- alleviate the systemic forms of stigmatization and oppression which continue to impact the lives of certain women because of their use of cannabis.
A review of existing literature demonstrated that there is limited research which discusses the nature of women’s use of cannabis outside of a medical context. Using postmodern feminist and intersectional analysis, I conducted qualitative, semi-structured interviews with six women to gain insights into their experiences of using cannabis. Contrary to the medical and/or criminal cannabis discourse, the women’s stories reveal examples of unique and overlapping instances of cannabis use which differed from the traditional cannabis dichotomy. The findings of the women’s interviews create an alternative cannabis discourse, in which women’s use of cannabis is experienced as a fluid, multi-functional act with effects that satisfy experiences differently across diverse
iv
contexts, which extends our existing knowledge base.
In relation to existing social work policies and practices, the finding implications are discussed. Ultimately, the thesis identifies opportunities for collaboration between social work and women, many of which could serve to disrupt the perpetuation of women’s stigmatization and surveillance in a legal cannabis framework.

abstract: Thesis

abstract: Master of Social Work (MSW)


title: DESIGN AND CONSTRUCTION OF A SILICON SCHOTTKY DIODE DETECTOR FOR SINGLE PROTON COUNTING AT THE MCMASTER MICROBEAM LABORATORY

contributor: Radiation Sciences (Medical Physics/Radiation Biology)

subject:
Schotty
Microbeam
Transmission Detector

abstract:
Microbeams have been used for radiation biology research since their introduction in the 1950s. A goal since their inception has been to irradiate individual cells and sub-cellular components with individual charged particles. These two criteria have been simultaneously achievable only within the last decade thanks to new technologies capable of producing very thin materials.
The McMaster Microbeam Laboratory wishes to conduct such experiments using a proton beam. However, there are presently no commercially available detectors for this application, which necessitates the need for a new detector. Following literature research, a 10 μm thin Schottky diode detector was selected as the most appropriate type of detector for the setup at McMaster. The design of the detector and detection system geometries were optimized to reduce beam scattering and broadening with the aid of TRIM and MCNP simulations.
Two detectors were fully constructed. However, a stable response to radiation was not achieved. One of the detectors appeared to function as a radiation detector very briefly but this result was not reproducible. The I-V curve of the detectors proved that they functioned as expected as diodes. However, without a radiation response no further characterization could be completed. Although problem solving efforts to overcome this issue were unsuccessful, a large silicon dopant concentration is suspected to be a possible cause.

abstract: Thesis

abstract: Master of Science (MSc)


title: Practical Temporal Psychovisual Modulation with Liquid Crystal Devices

abstract:
Temporal Psychovisual Modulation (TPVM) is a new paradigm of computational display, which can concurrently exhibit many different views on a common display. These views are decomposed into a set of atom frames, and the atom frames are modulated by users' liquid crystal (LC) light modulation glasses. Due to the limited refresh rate of LC glasses, a practical TPVM multiview display system can only support two to three atom frames. Such a small number of atom frames are not sufficient to a multiview application with a high image quality. Therefore, the main technical challenge before TPVM is how to support as many viewers as possible while maintaining an acceptable perceptual quality, using only a small number of atom frames. In this thesis, we develop two approaches to meet the challenge.

The first approach is to exploit the sparsity of multiview images to be displayed. One example is the sequence of depth of field (DOF) images. Those images not only provide a strong depth cue, but also have a sparsity structure. That structure allows the DOF images to be reconstructed from a small number of atom frames. We prove that property theoretically. Experimental results also agree well with the proof.

The second approach is to exploit the well-known property of rapidly decreasing visual acuity from fovea to peripheral vision. The strategy is to exhibit different concurrent views at highest quality in viewers' focused regions, while allowing graceful image quality degradation in regions of peripheral vision. This is achieved by a novel fovea weighting algorithm that optimizes for subjective quality. We find the proposed algorithm improves viewers' perceptual quality significantly, especially when the TPVM multiview display system only has a small number of atom frames.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: Silicon micro-ring resonator modulator for inter/intra-data centre applications

contributor:
Knights, Andrew
Cassidy, Daniel
Engineering Physics

subject:
Silicon Photonics
modulator

abstract: The recent and rapid growth of silicon photonics is driven by the ever-increasing demand for bandwidth inside and between data centres. Silicon photonics can offer an unparalleled performance in terms of scalability and power consumption with low-cost fabrication through the leveraging of CMOS fabrication techniques. This thesis describes research on the silicon micro-ring resonator modulator, a device which combines energy-efficiency with a compact footprint that is ideal for data centre applications. Both theoretical and experimental work is described in the context of improving the reachability, capacity and stability of the silicon micro-ring resonator modulator for inter/intra-data centre communication. Chapter 2 presents modeling work using MATLAB® that provides predictive results for both device-level and system-level performance. Chapter 3 studies the chirp characteristic of an over-coupled silicon micro-ring resonator modulator and its capability of generating a negative-chirp modulation. The resulting chirp-induced power penalty is measured to be as low as 2.5 dB after 100 km transmission. Chapter 4 focuses on the advanced modulation techniques that can be efficiently exploited for increasing the spectral efficiency in the typically band-limited system. A record single-polarization 104 Gb/s data rate per wavelength (direct-detect) was achieved by using digital signal processing to alleviate the modulation deficiencies that are specific to the silicon micro-ring resonator modulator. In Chapter 5, a generic resonance control method using intrinsic defect-mediated photocurrent is described and experimentally demonstrated to provide stability for the silicon micro-ring resonator modulator during high-speed operation. This control method can also lead to an “all-silicon” system without the need for power detection using germanium.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: The New Sponsor States: Economic Nationalism & Venture Capital in Quebec and Scotland, 1990-2017

contributor:
Graefe, Peter
Political Science

subject: Quebec; Scotland; minority nationalism; economic nationalism; venture capital; development capital; policy asymmetry; public funds; sponsor state; economic development

abstract: Given the importance that entrepreneurship and start-up businesses operating in technology-intensive sectors (biotechnologies, life sciences, renewable energy, artificial intelligence, information & communication technologies, software, etc.) have come to play as part of the processes of economic development and jobs creation, the access of such entrepreneurs and businesses to appropriate levels of corporate finance has become a major focus of policymakers in recent decades. Yet, this gave way to a wide variety of policy models across nation-states and even within nation-states, as levels of government and market actors adapted to those new challenges by refining or transforming pre-existing policies and institutions as well as by crafting new policy tools to address specific needs or interests. This thesis investigates the roots of such policy diversity within countries, offering in-depth accounts of the evolution of Quebec’s and Scotland’s policy strategies in the sector of development capital and sub-sector of venture capital since 1990.                                                     As compared to other regions’ or provinces’ in the United Kingdom (such as South East England) or Canada (such as Ontario), Quebec and Scottish regional venture capital ecosystems rely on a high degree of state intervention, either direct (through public investment funds) or indirect (through government-backed, hybrid or tax-advantaged funds). Hence the description of these two regions as “sponsor states,” heavily involved in the strategic backing of innovative businesses. Whereas most of the literature on venture capital has focused on economic variables to explain variations in such public sector involvement across polities however, this thesis seeks to explain policy divergence in Quebec and Scotland through a political and ideological lens. Its main argument is that the development of the venture capital ecosystems in these regions was underpinned by Québécois and Scottish nationalisms, which induced perceived imperatives and ideological preferences for policy autonomy, policy divergence, and state intervention.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)

abstract: This thesis investigates the impacts of political ideas on economic policymaking. More specifically, it is a study into the effects of Québécois and Scottish nationalisms on regional policies in the sector of corporate finance, and subsector of venture capital. The question it was devised to answer is as follows: why is it that Quebec and Scotland developed particularly dynamic regional venture capital ecosystems, in which the state (through public investment funds) or state-backed investors (such as hybrid or tax-advantaged funds) play a leading role as compared with other Canadian or British regions? Through an in-depth process-tracing effort aimed at the uncovering of rationales underpinning major policy initiatives in this sector since 1990 and beyond, this thesis shows that minority nationalism contributed to the development of such ecosystems in key ways, notably by inducing perceived imperatives and preferences for policy autonomy, policy asymmetry, and state intervention.


title: The First Passage Time of Degradation Processes

contributor:
Balakrishnan, Narayanaswamy
Mathematics and Statistics

abstract:
The thesis gives perspectives for the first passage time (FPT) of degradation processes from both the parametric and nonparametric aspects. As an important reliability index of the manufactured products, 100pth percentile of the FPT distribution is always required to provide by the market. If the assumed underlying process is misspecified and fails to fit the degradation data, the estimate of the reliability index will lose efficiency. The typically used degradation processes include the Wiener process, the gamma process, and the inverse Gaussian process because all of them are closed under convolution. This property can help us to obtain the FPT in analytic forms. However, it is difficult to accurately fit the actual data with limited model selections, then it is important to discuss how to achieve the flexible selections of the underlying model.

To reduce the misspecification effects for the FPT density, the most straightforward way is to observe the failure times directly. For a good summary and set of references, see Prentice and Kalbfleisch (1979) and Kalbfleisch and Prentice (2002). However, to guarantee the sample size of failure time observation is large enough to make the statistical inference, a large number of experiments are required which are too costly. That is the reason why people choose to reduce the experimental cost by alternatively observing the increments then the FPT density can be estimated based on the mathematical properties of the selected underlying process. Hence, the current methods cannot simultaneously realize the low experimental cost and model robustness.

In this thesis, we firstly propose a novel parametric approach which can generalize the degradation processes only if the corresponding Laplace transforms exist. Then the Laplace transform of the FPT density function can be obtained in closed-form and the survival probability can be computed through Laplace inversion. For many stochastic processes, their likelihood functions are intractable so the maximum likelihood estimate (MLE) of the parameters are unavailable to obtain. We estimate the parameters by generalized method of moments (GMM) which is a distance-based method. Specifically, the weighted convolution of two independent gamma processes incorporated with random effects is exemplified as the parametric underlying model, and it is motivated by the scenario of multiple sensors used for monitoring the degradation of the same critical component. Although the degradation processes generated from these sensors reflect the same degradation path, the corresponding scales and noise are significantly different. To find the unified degradation path, Hua et al. (2013) used the weight-averaged unified approach which determined the weights by the defined leadership scores. Then we develop the parametric model into a distribution-free model which can eliminate the misspecification effects caused by wrong process-type assumption. The theoretical Laplace transform of degradation process can be replaced by the empirical Laplace transform composed by the observed increments and the 100pth percentile of the FPT distribution can be approximated by the empirical saddlepoint method. As one of the important applications in reliability engineering, the optimal design for degradation test is studied under both the parametric and nonparametric scenarios. To optimize the degradation test subject to the experimental cost not exceed the pre-specified budget, the design factors in the experiment such as the number of test units, the number of measurements, the inspection frequency and the termination time are considered.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: The Effect of Strain Ageing on Plastic Deformation in High Strength Steel

contributor:
Zurob, Hatem
Materials Science and Engineering

abstract: The influence of strain ageing on the mechanical properties, plasticity and fracture of quenched and tempered martensitic 300M steel is investigated. Tensile testing with variable strain rate identified the presence of negative strain rate sensitivity at room temperature. The existence of dynamic strain ageing at room temperature was also confirmed for strain rates between 0.00133-0266 s-1 using digital image correlation (DIC). Strain ageing resulted in significant strengthening at room temperature, which masks the presence of dynamic strain ageing upon re-loading. Fracture analysis conducted using scanning electron microscopy (SEM) revealed only minor differences in the failure mechanisms and fracture morphology caused by deformation and ageing. A model by Brown and Embury is used to link inclusion size and distribution to failure strain, and the failure mechanism of 300M was determined to be the formation of micro-voids on transition carbides and inclusion particles. Models for dislocation evolution and locking based on fundamental theories were also produced and successfully used to model the transient strengthening of 300M following ageing at room temperature using differential dislocation evolution equations.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: A BI-DIRECTIONAL ACTIVE CELL BALANCING OPTIMIZATION BASED ON STATE-OF-CHARGE ESTIMATION

contributor:
Yan, Fengjun
Mechanical Engineering

subject:
Cell balancing
Optimization
State-of-Charge estimation
Lithium-ion battery

abstract: Recently, Electric Vehicles (EVs) have received extensive consideration since they offer a more sustainable and greener transportation alternative compared to fossil-fuel propelled vehicles. Lithium-ion batteries are increasingly being considered in EVs due to their high energy density, slow loss of charge when not in use, and for lack of hysteresis effect. Conventionally, the batteries are connected in series to achieve the load voltage requirements. However, for the batteries with intrinsic discrepancies or different initial states, cell balancing is a concern because it is the weakest cell that determines the empty point for the battery and an undercharged series cell will shorten the lifetime of the entire pack. The imbalance potential of the battery behaves as the way of State-of-Charge (SOC) mismatch and it’s also temperature dependent. Therefore, in this thesis, an active cell balancing optimization was proposed and conducted in MATLAB to optimize battery unused capacity and thermal effect simultaneously based on bi-directional balancing system and pre-estimated SOC. The bi-directional balancing system was physically built based on “Fly-back” converter to compare balancing performance in discharging, idle, and plug-in charging mode. Moreover, a battery combined model worked collaboratively with robust state and parameter estimation strategies, namely Extended Kalman Filter (EKF) and Smooth Variable Structure Filter (SVSF) in order to estimate SOC for cell balancing. As a result, the proposed method can effectively optimize SOC mismatch around 2.5%. Meanwhile, more uniform temperature was achieved and the maximum temperature can be reduced about 7 ℃.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: The use of copulas in cost-effectiveness analysis

contributor:
Thabane, Lehana
Health Research Methodology

subject: cost-effectiveness, copulas

abstract:
Background: Copula methods have been proposed as a way of modeling dependence between random variables because it lies in the flexibility of the assumption on marginals. As previous authors stated, "A copula is a function which joins or “couples” a multivariate distribution function to its one-dimensional marginal distribution functions. Given that cost and effectiveness are often related to each other and therefore they show statistical dependence, the use of copulas to handle uncertainty caused by sampling variation could be potentially useful when cost-effectiveness analyses (CEA) are performed using patient-level data.
The objective of this study was to empirically compare various copula distributions with two traditional methods, namely, the bootstrapping approach and the Bayesian approach assuming that incremental cost and LYs gained are bivariate normally distributed.
Methods: The patient-level data from a previously published observational study were analyzed using four copula distributions: independent, Farlie-Gumbel-Morgenstern (FGM), Frank and Clayton copulas. Using the results from the traditional methods previously published, models were compared in terms of incremental cost, incremental life years (LYs) gained and the cost-effectiveness acceptability curves (CEACs) based on the net monetary benefit (NMB).
Results: Using the traditional methods provided similar results. The most pronounced impact was the improvement in precision given that the confidence intervals were so much narrower for the copulas methods in comparison to the traditional methods. Consequently, the probability of being optimal derived from the Frank and Clayton copulas were close to 1.0 at a willingness to pay (𝜆) of CA$20,000. By contrast, the traditional methods were optimal for a 𝜆 of $100,000 CAD.
Conclusions: The results of this study demonstreate the potential impact and importance of copulas in patient-level cost-effectiveness analysis. This approach could be particularly important in those situations where the data suggests some kind of dependence and some restrictions on the marginals, as observed in our case study.

abstract: Thesis

abstract: Master of Science (MSc)


title: Energy-Aware Multiserver Queueing Systems with Setup Times: Structural Properties, Exact Analysis, and Asymptotic Performance

contributor:
Down, Douglas
Software Engineering

abstract: Energy consumption of today's data-centers is a constant concern from the standpoints of monetary and environmental costs. An intuitive solution to address these immense energy demands is to turn servers off to incur less costs. As such, many different authors have modeled this problem as an M/M/C queue where each server can be turned on, with an exponentially distributed setup time, or turned off instantaneously. What policy the model should employ, or rather when each server should be turned on and off is far from a trivial question. A specific policy is often examined, but determining which policy to study can be a difficult process and is often a product of intuition.  Moreover, while a specific policy may do comparatively well against another, in general it may be far from optimal. This problem is further accentuated when one considers the case that a policy may do well or even be optimal under a specific cost function, but far from optimal under another. To address this issue this thesis studies the structural properties of the optimal policy under a wide range of cost functions, allowing for a significant reduction in the search space; then leverages these structural properties to intelligently select three families of policies to study further. An exact analysis of these policies is given, alongside offering insights, observations, and implications for how these systems behave. In particular, results are found which grant insight into the question of the number of servers that should remain on at all times under a general cost function. The model is then analysed under a fixed-load, many-server asymptotic regime, i.e. C approaches infinity, while the load remains fixed, where it is shown that not only are many of the policies in the literature equivalent under this regime, but they are also optimal under any cost function which is non-decreasing in the expected energy cost and response time.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: Carotid artery longitudinal wall motion: Regulatory factors and implications for arterial health

contributor:
MacDonald, Maureen J
Kinesiology

subject:
arterial health
ultrasound
arterial stiffness
exercise training
left ventricular mechanics

abstract: The carotid artery wall moves longitudinally along the length of the vessel, although little is known about what causes this motion, or what health information it represents. The overarching purpose of this dissertation was to investigate the regulation of carotid artery longitudinal wall motion (CALM) in humans, as well as how CALM can be used to infer information about arterial health. Through observational and experimental designs, we tested evidence for a structural ventricular-vascular coupling effect, which postulates that systolic anterograde CALM is influenced by the forward blood shear rate while systolic retrograde CALM is influenced by left ventricular rotation, although the data suggests a moderate influence of left ventricular rotation, and minimal influence of shear rate. In cross-sectional analyses, we demonstrated that diastolic CALM variables are better related to age and health status compared to systolic CALM displacement and that this relationship was independent of traditional measures of arterial stiffness. These experimental and observational results directed the use of diastolic CALM as a potential indicator of arterial health in subsequent studies, due to the relative independence from systolic events. While there was no effect of 12-weeks of exercise training in healthy men on diastolic CALM variables, we observed increased systolic retrograde CALM and diastolic CALM acceleration in men with a history of resistance exercise training compared to sedentary men, suggesting an effect of habitual exercise training. Our novel findings suggest that CALM is regulated by a complex system, in part related to both arterial wall structure and ventricular-vascular coupling, and may have clinical value in complimenting measures of traditional arterial stiffness in humans. Future studies should examine whether local changes to arterial wall structure or indirect changes in regulatory control dictate differences in CALM with aging and with chronic exercise training, before integrating CALM into routine measurement of arterial health.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)

abstract: We have known for a long time that arteries expand in order to absorb pressure; however, only recently have we identified that arteries also move longitudinally along the length of the arterial wall. The overarching purpose of this dissertation was to study what causes carotid artery longitudinal wall motion (CALM), and how we can use this information to understand arterial health. We demonstrated that CALM is partly controlled through the forward blood velocity wave and left ventricular rotation of the heart, and that diastolic CALM is uniquely related to aging and health status, but is not impacted by exercise training in healthy men. There are many aspects of CALM that need to be examined before wide-spread use, though our results indicate that CALM represents a new way of studying arterial health, which has the potential to complement traditional measures of cardiovascular disease risk in humans.


title: THE SUCCESS OF THE NATIONAL NUTRITION STRATEGY OF CAMBODIA OF 2009 IN REDUCING CHILDHOOD UNDERNUTRITION, EVALUATED USING ECONOMETRIC REGRESSION MODELS

contributor:
Guindon, G. Emmanuel
Global Health

abstract: Although both the causes and effects of childhood malnutrition are well studied, Cambodia continues to have high rates of childhood undernutrition. The National Nutrition Strategy (NNS) was implemented in 2009 by the National Nutrition Program (NNP) to address these challenges. The success of one of the key goals of the policy was evaluated through cross-sectional data across four time points (2000, 2005/2006, 2010, and 2014). The results of economic regression models were applied to discuss the effectiveness of the implementation of the NNS. Six nutritional status indicators, three that described size and weight at birth, and three that described WHO anthropometric indicators, were analyzed. The descriptive data suggested the objectives of the policy goal were achieved, however, in comparison to neighboring Vietnam, the achievement in reducing childhood malnutrition in Cambodia became less clear. Differences in descriptive statistics suggested Vietnam was having a greater impact on its nutrition indicators during the period the policy was in effect in Cambodia. Linear and logistic regressions were performed, and demonstrated the complex relationship between nutrition status indicators and covariates, and informed the more complex estimators. The doubly robust (DR) estimator, inverse probability weighted regression adjustment (IPWRA), suggested the implementation of the policy had an overarching negative impact on anthropometric measures and weight at birth (p<0.05). A nearest-neighbour matching (NNM) model found similar results as the IPWRA analysis, confirming that the treatment had a significant negative effect on most of the nutritional indicators of interest. The negative impact of the policy was probably due to lack of staffing and experience managing large-scale programs of the NNP at time of implementation. The nutritional status of children in Cambodia is progressing, despite the NNS of 2009.

abstract: Thesis

abstract: Master of Science (MSc)


title: Noise Characterization and Modeling of Nanoscale MOSFETs

contributor:
Chen, Chih-Hung
Electrical and Computer Engineering

subject: Microelectronics MOSFET Noise

abstract:
High-frequency noise modeling and characterization of nanoscale MOSFETs are essential driving forces for highly scaled CMOS technology to be used in radio-frequency applications. Continuous downscaling increases the operating frequency of the MOSFETs, reduces the power supply voltage but does not scale noise accordingly. This makes the noise issue of future low-power technology more prominent and therefore accurate noise modeling more important.
In this thesis, several important issues regarding noise modeling and characterization for nanoscale MOSFETs are studied. First, a new noise factor deembedding algorithm is proposed for on-wafer noise measurements. It solves the problem of noise factor deembedding in which the active two-port device is surrounded by a four-port parasitic network. Based on it, a new deembedding-first and optimization-last noise parameter deembedding approach is proposed and its performance is evaluated using experimental data.
Second, the noise performance of modern sub-100-nm MOSFETs are evaluated using the noise sheet resistance as a figure of merit. It shows that future technologies generally have degraded noise performance. In addition, two accuracy issues regarding the calibration of noise receiver for high-frequency noise measurements are investigated and methods to mitigate these issues are discussed.
Third, a novel Z-parameter based approach to extract the gate resistance is proposed for MOSFET characterization. It is evaluated against other published methods using experimental data. In addition, the extraction of the resistance of the lightly-doped-drain region and the gate contact is also performed and discussed.
Finally, a new perspective to interpret the MSOFET channel noise as suppressed shot noise is presented. An easy-to-use analytical expression for the suppression factor is derived and it only relies on two process parameters – threshold voltage and effective oxide thickness – to predict the level of suppression for the channel noise of MOSFETs. It is evaluated using published experimental data on various CMOS technology nodes.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: Designing Meaning: An Aesthetic Theory of Value

contributor:
Allen, Barry
Philosophy

abstract: An aesthetic theory of value based off the writings of Friedrich Nietzsche, Albert Camus, and Emil Cioran.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: SOLVENT-FREE EXTRUSION EMULSIFICATION INSIDE TWIN SCREW EXTRUDER

contributor:
Thompson, Michael
Chemical Engineering

subject:
Emelsification
Twin Screw Extruder
Mixing

abstract:
Solvent-free extrusion emulsification (SFEE) is new top-down technique specially suited to high viscosity polymers (100-1000 Pa.s) for producing sub-micron (100-500 nm) particles inside a twin screw extruder (TSE) without the use of hazardous solvents. SFEE has been difficult to implement in industry due to process sensitivities and a lack of mechanistic knowledge on how the polymer-water morphology must develop prior to inversion. To devise a mechanistic explanation of the critical stages of the process, an inline orifice-plate type viscometer was developed to monitor rheological changes previously witnessed in early batch studies. The general variables of study throughout the thesis included the manner by which sodium hydroxide (NaOH) can be added as well as the NaOH content necessary, resin-to-water (R/W) ratio, and surfactant content. The last study in the thesis explores the influence of matrix viscosity, which was accomplished by crosslinking the polyester. The striated lamellae morphology of the polyester-water system, critically controlling the final particle size, depended on two factors, specifically surface energy (determined by endgroup conversion and added surfactant) and matrix viscosity. Analysis of the rheological response indicated that a higher polar surface energy contribution had the greatest influence on the morphological state, demonstrating a steeper viscosity transition due to more favourable and more rapid incorporation of water within the polyester matrix. A strong correlation was repeatedly found between particle size and this viscosity transition, which has been related to the thickness of striated lamellae through a theory of lamellae coarsening (or thinning as is more relevant to the current process). The reported lamellae coarsening model in the literature, which shows the predominant effects of interfacial energy and viscosity on lamellae thickness in a mixed phase system showed excellent correspondence to the results in this thesis.
Among the variables of study in this thesis, the dissolution of the sodium hydroxide species (when added as a solid particle) and the kinetics of end-groups conversion proved to be rate-limiting phenomena to generating thinner striated lamellae. The ionic strength of the system was notably important to the viscosity change occurring in the process as water was added for the first time and subsequently influenced the particle size produced, particularly when additional surfactant was not added and the system relied exclusively on the carboxylate endgroups present. Finally, with mounting evidence that SFEE showed significant sensitivity to the matrix viscosity, a final study examined the effectiveness of SFEE in the face of ever increasing viscous force by blending a crosslinked polyester into the neat resin at different weight fractions. With higher viscosity there was a corresponding decrease in interfacial area growth between the polyester and water, resulting in increased particle size but even with a viscosity near 800 Pa.s, far above a traditional oil-in-water system, it was still found possible in this study to create nano-sized particles by SFEE.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: The Effect of Sex, Menstrual Cycle Phase, and Monophasic Oral Contraceptive Pill Use on Local and Central Arterial Stiffness in Young Adults

contributor:
MacDonald, Maureen
Kinesiology

abstract: Arterial stiffness is a predictor of cardiovascular disease (CVD), and can be measured locally by carotid artery β-stiffness index and centrally by carotid-femoral pulse wave velocity (cfPWV). Previous investigations examining sex differences in these measures have resulted in inconsistent findings, and despite the prior evidence for an influence of sex hormones on the vasculature, have not controlled for menstrual cycle phase in women. Arterial stiffness is also understudied across the menstrual cycle and in women who use oral contraceptive pills (OCPs), despite current use of OCPs by more than 100 million women worldwide. The objectives of this thesis were 1) to examine potential sex differences in local and central arterial stiffness, 2) to explore potential differences in arterial stiffness between a natural menstrual cycle (NAT) and an OCP cycle (OCP), 3) to determine the relationship between duration of OCP use and arterial stiffness, and 4) to examine the repeatability of local and central arterial stiffness across three weeks in men, and across a natural menstrual cycle and an OCP cycle in women. Fifty-three healthy participants (22±3 years) were recruited into three groups (20 men, 15 NAT, 18 OCP). Men attended one visit, NAT attended three visits across the duration of one menstrual cycle (menstrual, follicular, and luteal phases), and OCP attended three visits at the same relative days as NAT across one pill cycle (placebo pill phase, and active pill phase: 2 visits). At each visit, a blood sample was collected to identify serum sex hormone concentrations, and β-stiffness index and cfPWV were also assessed. Men had a higher β-stiffness index than NAT and OCP (p<0.01), whereas cfPWV was not different between groups (p=0.22). There was no difference between NAT and OCP at any timepoint across a cycle for β-stiffness index (p=0.26) or cfPWV (p=0.41), and no association between duration of OCP use and β-stiffness index (r=0.003, p=0.99) or cfPWV (r =-0.261, p=0.30). These results indicate that while men have elevated local arterial stiffness, there are no sex differences in central arterial stiffness. There were also no arterial stiffness differences across a cycle between women who experience natural menstrual cycles or women who use OCPs, despite fluctuations in sex hormone concentrations, and no relationship between duration of OCP use and arterial stiffness. The findings from this study highlight the importance of assessing both local and central arterial stiffness when considering sex differences. Furthermore, future studies related to arterial stiffness may not have to control for menstrual cycle phase, OCP phase, or duration of OCP use in women.

abstract: Thesis

abstract: Master of Science (MSc)

abstract: Arterial stiffness is associated with increased cardiovascular disease (CVD) risk and all cause mortality. Pre-menopausal women are relatively protected against CVD, and it is speculated that this protection is due to estrogen. However, few studies have examined the effect of sex hormones on arterial stiffness. Previous studies to examine sex differences in arterial stiffness do not have consistent findings, and have not controlled for menstrual cycle phase in women. The effect of oral contraceptive pill (OCP) use on arterial stiffness is also unexplored, despite the high prevalence of women who use OCPs. This project examined arterial stiffness in men, and across a natural menstrual cycle, and an OCP cycle in women. We observed men to have stiffer carotid arteries than women, but no differences in central arterial stiffness. We also found no differences in arterial stiffness between naturally cycling women and women who use OCPs, or across a cycle in women, and no effect of duration of OCP use on arterial stiffness.


title: Investigating Strategies to Modulate Macrophage Function to Prevent the Progression of Fibrotic Lung Disease

title: Investigating the UPR in Fibrotic Lung Disease

contributor:
Ask, Kjetil
Medical Sciences

subject:
Lung
Fibrosis
Macrophages
ER stress
Unfolded Protein Response
GRP78
ER expansion
IL-6

abstract: Tissue fibrosis occurs in the advanced stages of various chronic diseases and can account for 45% of all deaths related to chronic diseases worldwide. The extracellular matrix (ECM) components comprising the fibrotic scar are primarily derived from myofibroblasts, which are contractile fibroblasts arising from the trans-differentiation of several cellular progenitors. Disturbances in immune cell infiltration and function could lead to the uncontrolled production of pro/anti-inflammatory mediators, which may alter the phenotype, state, and function of myofibroblasts progenitors, leading to aberrant wound repair and pathological fibrosis. A great deal of knowledge has implicated macrophages in the pathogenesis and exacerbation of the fibrotic process. Nonetheless, much remains to be elucidated on the potential mechanisms regulating macrophage accumulation and pro-fibrotic polarization, and whether these mechanisms can be further investigated to modulate tissue repair. The Endoplasmic reticulum (ER) stress has recently been implicated as a key mechanism that propagates the pathogenesis of the fibrotic process. How ER stress precisely impacts the fibrotic process is still unclear. This thesis partly explored how modulating the outcome of ER stress – the unfolded protein response (UPR), would affect the severity of lung fibrosis and addressed the role of IL-6 signalling in macrophages during fibrosis. The data demonstrated that UPR activation in pro-fibrotic macrophages and partial deficiency of Grp78, the master regulator of the UPR, abrogated pulmonary fibrotic changes and reduced the accumulation of pro-fibrotic (M2-like) macrophages. These findings were later associated with high TUNEL levels, 7AAD positive cells, Chop and cleaved caspase 3 levels, which are suggestive of GRP78 mediated apoptosis in this population. On the contrary, mice lacking a terminal UPR mediator of apoptosis, called Chop, had increased ECM deposition and greater persistence of non-apoptotic macrophages. These findings suggest that UPR-mediated macrophage polarization and apoptosis may alter lung wound repair processes. As IL-6 synergized the effect of IL-4 to promote a hyper M2 macrophage state, it provided a unique and compelling model to study the dynamics of macrophage alternative programming, which has set the stage to investigate whether the UPR was implicated in the generation of a hyper pro-fibrotic macrophage phenotype. This hyper M2 macrophage model led to the identification of ER expansion program and the IRE1-XBP1 arm of the UPR in pro-fibrotic macrophage polarization, and suggested an unprecedented in vivo role of IL-6 in priming macrophages in the injured lungs to possibly potentiate pathological wound repair. Looking forward, many questions remain to be answered in order to precisely identify the vital UPR axis regulating ER expansion in macrophages during pathological wound repair and to get closer to the understanding of whether the UPR modulates the pro-fibrotic/pro-resolving capacity of macrophages. Insights on these mechanisms may facilitate the development of therapeutics that better manage chronic fibrotic diseases which pose fatal consequences and increase public concern.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)


title: Electrohydrodynamic Solidification of Phase Change Materials

contributor:
Cotton, James
Mechanical Engineering

subject:
Electrohydrodynamics
Thermal Storage
Phase Change Materials

abstract:
In this investigation an electric field was applied to a phase change thermal storage system while it was discharging energy. The phase change material used was octadecane. Octadecane is a high purity dielectric material that has a melting temperature close to room temperature. The material was forced to solidify using a heat exchanger mount below the phase change material, cold water flowed through the heat exchanger to ensure it maintained a constant temperature below the melting temperature of the phase change material. By applying -8kV to 9 electrodes – positioned in the phase change material – and by using the heat exchanger as an electrical ground – an electric field was generated in the phase change material. The electric field caused unbalanced body forces in the fluid which generated electro-convection in the fluid. The system was designed such that electro-convection is the only source of convection in the system to isolate the effects of electro-convection, allowing for the underlying physics of electro-convection to be studied easier.
To understand the effects of applying electro-convection, a case where there is no applied voltage on the electrodes was compared to a case where there was -8 kV applied to the electrodes. Experiments showed that the effect of applying electro-convection depends on the initial temperature; however, it was found that the improvement after two hours was less than 10%. For a wall temperature of 8.5℃ and an initial temperature of 50℃ - the melting temperate of octadecane is 28℃- then the maximum enhancement of the energy extracted is 50%, but two hours after the start of the test the enhancement approached zero. For a wall temperature of 8.5℃ and an initial temperature of 30℃, the maximum enhancement is 10% and similarly fall to zero after a few hours of application.
A simple analytical model was developed. The experimental and numerical results showed that at the early stages of energy discharge the electro-convection case had a large improvement compared to a pure conduction case, however as time progresses this improvement decreases. The explanation for the trend is that adding convection only increases the rate that energy is taken out of the liquid, thus the maximum improvement is bounded by the amount of sensible energy in the liquid phase change material, once this sensible energy is removed applying electrohydrodynamics is no longer beneficial.

abstract: Thesis

abstract: Master of Applied Science (MASc)


title: INVESTIGATION OF MECHANICAL PERFORMANCE AND FORMABILITY OF WELDED AND BRAZED SHEET MATERIALS

contributor:
Jain, Mukesh
Chen, James
Mechanical Engineering

subject:
laser welding
hybrid brazing
CMT brazing
DP steel
steel/aluminum
TWBs
TBBs
double-layer
formability
miniature tensile

abstract:
In the last two decades or so, hybrid structures from dissimilar materials and/or sheet gauges have been developed to achieve weight reduction while maintaining or even improving structural performance such as stiffness, crash and impact behavior. In particular, welded and brazed sheet materials in the form of tailor blanks (TBs) are being increasingly used or considered for future applications in different applications such as automotive, aerospace and marine constructions as they offer attractive combination of strength and performance in applications where weight reduction is desirable. However, technical problems are often encountered during forming of TBs from dissimilar base sheet materials with different thickness and/or strength. These include weld line movement and non-uniform deformation. Additionally, there are premature weld failures due to the presence of softening zone (as in TBs made from advanced high strength steels), and brazed interface failure due to insufficient bonding and wetting (as in TBs made from steel and aluminum). These areas of forming of TBs need to be scientifically studied to advance the use of dissimilar materials.
The current research involves an understanding of deformation and forming behavior of steel-to-steel tailor welded blanks (TWBs) made from advanced high strength steel (AHSS) such as dual phase (DP780) steel. The research also involves a study of deformation behavior of steel-to-aluminum tailor brazed blanks (TBBs). TWBs have been successfully joined using a relatively new welding techniques such as defocused fiber laser welding. TBBs, on the other hand, have been successfully produced by fiber Laser/MIG hybrid brazing and Cold Metal Transfer brazing (CMT).
In addition, the formability of TWBs of different gauges and/or strengths was tested by using a new, simple and reproducible method of formability testing using a double-layer blank method. This method was devised and assessed for testing various steel combinations in different strain paths such that the weld line stayed in position with respect to forming tools and is subjected to the same stress and strain state as the parent material in the weld and its vicinity. Moreover, results from conventional stretch forming tests, single-layer blank, and the double-layer method were compared at the macroscopic level (such as weld line movement, forming limit etc.) as well as at the microscopic level (such as failure location within the weld and failure mode) to isolate the advantages of the proposed double-layer method.
With regard to TBBs made by fiber Laser/MIG and CMT brazing methods, a fundamental knowledge and understanding of the local deformation behavior and material plastic ow in and around the brazed steel-aluminum interfaces were obtained by conducting miniature tensile mechanical tests that focus on continuous observation of the brazed region under a high magnification optical microscope to assess the ductility of the brazed joint and its capacity to carry the load during a material shaping process.

abstract: Thesis

abstract: Doctor of Philosophy (PhD)