title: Characterization of arsenic and antimony minerals in Yellowknife Bay sediments

contributor:
Jamieson, Heather
Environmental Studies

subject:
Arsenic
Antimony
Mineral characterization
Environmental geochemistry
Yellowknife Bay

abstract: Yellowknife Bay, Northwest Territories, Canada, is a waterbody valued by surrounding communities for its subsistence, recreational, and cultural use. Located adjacent to the former Giant and Con Mines, Yellowknife Bay has received inputs from mine waste streams enriched in arsenic (As), antimony (Sb), and metals since the late 1930s. Lake sediments in Yellowknife Bay provided a record of metal(loid) contamination from aerially deposited roaster stack emissions, mine effluent, and direct disposal of Giant Mine tailings. A sediment sampling program was conducted in Yellowknife Bay to characterize both As and Sb mineralogy by scanning electron microscopy-mineral liberation analysis (SEM-MLA). Results from nine sediment cores collected in summer (August 2018, July 2019) and winter (March 2019) confirmed that As was mobile relative to layers of enrichment associated with peak mining emissions both downwards, where it precipitated as authigenic sulfides (interpreted to be realgar), and upwards where it was attenuated by Fe-oxyhydroxides and possibly roaster-generated Fe-oxides near the sediment water interface. Antimony minerals appeared to be stable in Yellowknife Bay sediments with no distinct evidence of post-depositional mobility identified. The observed prevalence of arsenic trioxide (As2O3) in near surface sediments proximal to Giant Mine suggested that As and Sb contamination is ongoing, likely from terrestrial weathering of contaminated soils and shoreline outcrops. Arsenic bearing oxide minerals were prevalent in near-surface sediments and may become unstable should redox conditions in the hypolimnion change; prolonged anoxia would destabilize the As phases and release As to bottom waters. Therefore, continual monitoring of hypolimnion conditions in Yellowknife Bay is necessary.

abstract: M.E.S.


title: The New Moon in Black Space: The Poetics of Ummah

contributor:
McKittrick, Katherine
Cultural Studies

rights: Queen's University's Thesis/Dissertation Non-Exclusive License for Deposit to QSpace and Library and Archives Canada

rights: ProQuest PhD and Master's Theses International Dissemination Agreement

rights: Intellectual Property Guidelines at Queen's University

rights: This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.

rights: Attribution-NonCommercial-NoDerivs 3.0 United States

subject:
Muslim
Black Diaspora
Hip Hop
Caribbean
Canada
United States
Indentureship
Cultural Geography
Ethnography
Anti-Blackness
Afro-Asian
Visual Art
South Asian Diaspora
Ummah

abstract: This work examines how diasporic Black and South Asian Muslims in Toronto and New York practice ummah (Muslim brotherhood and sisterhood, global Muslim unity). Through online surveys, in-person interviews, and ethnographies of mosques, it becomes clear that the ummah illuminates interracial connections and collaborations. My work shows that interracial ummah is not in plain sight but, if read alongside Édouard Glissant’s “Poetics of Relation” and Khal Torabully’s “Coolitude,” it can be illuminated. In addition to qualitative research, this dissertation analyzes poetics (through hip hop and soca music), poetry, film, and the visual  arts as well as conversations about carnival, Pride (Toronto), and cultural appropriation. I look to concepts such as Orientalism, coolitude, homonationalism, and indentured labour, to address Islam in relation to modernity, racial attachments, and spatial resistances. These different analytical sites and concepts allow me to theorize different practices of inclusion, exclusion, belonging, and unbelonging to think through the complexities of Caribbean (Black and South Asian) Muslim identifications; the focus on poetics, which is touched on throughout, shows how ummah exists as a form of sonic transnationalism. Ultimately, in highlighting diasporic, transnational, narrative (interview), and creative expressions of ummah, this project reconceptualizes the figure of the Muslim, moving it away from a problematic geographically fixed location toward a more robust, shifting, and relational category of belonging.

abstract: PhD


title: Behavioral Modelling of the Transient and CdV/dt Induced Turn-on of a Hybrid High Power Switch Unit

contributor:
Jain, Praveen
Electrical and Computer Engineering

subject:
Power Electronics
Hybrid Switching
Modelling

abstract: The use of hybrid power switches is a practical and effective method of improving the performance of high power switching devices. An emerging strategy is to combine high power Si IGBTs with SiC MOSFETs to take advantage of the SiC MOSFETs superior switching speed and lower switching losses. While this approach has a number of advantages, when it is used in a half bridge arrangement the possibility of false turn becomes a concern. The SiC MOSFETs improved transient characteristics leads to higher dv/dt during switching, which can induce a spike in the gate voltage of the low side Si IGBT through the parasitic capacitances. This behavior poses a serious risk of lowering efficiencies in operation as well as safety concerns. In this study, a set of behavior models were developed for both the SiC MOSFET and Si IGBT, with the specific target of modelling the transient behavior. These models were then integrated together into a half bridge capable of performing hybrid switching. Lastly, a model was developed to assess the risk of false turn on in the low side IGBT, based on the developed hybrid switching models. The models were limited to only parameters which are readily available on device datasheets, allowing the system to be useful and accessible to designers without the need to perform parameter extraction. The individual switch models accuracy were assessed against a set Spice models, covering a range of power conditions. The induced gate voltage in a synchronous buck converter with two hybrid SiC MOSFET Si IGBT switches was measured and used to verify the validity of the induced voltage model. The design approach for the development of a behavioral transient model and the limitations of the model were explored and discussed.

abstract: M.A.Sc.


title: On the Transient Response of Rotors and Autorotating Seeds in Gusty Flows

contributor:
Rival, David
Mechanical and Materials Engineering

subject:
Gust Flow
Low-Inertia Rotor
Samara-Inspired Rotor
Samaras
Small Wind Turbines
Tidal Turbines
Leading-Edge Vortices

abstract: Low-inertia rotors are present in quadrotors, micro aerial vehicles, and small wind and tidal turbines, to name but a few examples. The common practice of modelling the unsteady behaviour of low-inertia rotors using quasi-steady assumptions typically means poor rotor performance in unsteady (turbulent) flow environments. This thesis explores the behaviour of low-inertia rotors (and associated flow physics) so as to improve the unsteady performance of generic low-inertia rotor systems. Furthermore, lessons from the robust autorotation of samaras (e.g. maple seeds) in unsteady wind environments are extracted with the potential of applying such lessons in the design of efficient rotor systems. The four studies in this thesis experimentally characterize the unsteady response of low-inertia rotors and autorotating samaras experiencing a sudden change in flow, i.e. an axial gust. Low-inertia rotors are found to produce higher power output during the gust than for quasi-steady operation. To better describe the unsteady response of low-inertia rotors, a new dimensionless group, defining the influence of the rotor moment of inertia relative to the flow inertia, is introduced. Additionally, the kinematics of samaras experiencing canonical gusts, and related aerodynamic mechanisms, are explored experimentally using natural samaras as well as a samara-abstracted rotor. It is shown that natural samaras, and the samara-abstracted rotor, exhibit robust rotation under a variety of gust conditions.

abstract: PhD


title: On the extraction of path-dependent dynamics from recirculating pulsatile flows using optical and ultrasound imaging

contributor:
Rival, David E.
Mechanical and Materials Engineering

subject:
Pulsatile flow
Recirculation
Particle Residence Time
Ultrasound imaging
Stenosis

abstract: Recirculation is present in nearly every fluid system, and often jeopardizes the system's primary function. This thesis is motivated by recirculation in the cardiovascular system and how it impacts disease. Developing methods of both measuring and analyzing path-dependent dynamics of recirculating flows is critical to influence diagnostics and therapeutics. The studies in this thesis encompass both state-of-the-art measurement science and recirculating fluid dynamics using both steady and pulsatile flows, and are abstracted to apply generally to recirculation in many systems. A Lagrangian measurement technique, capable of extracting path-dependent quantities, is developed and utilized throughout the four major works to plot the trajectories of hundreds of thousands of unique fluid parcels as they flow through an idealized stenosis geometry. As a step towards in vivo investigations, a novel technique called echo-Lagrangian particle tracking is introduced, which couples the Lagrangian tool with ultrasound imaging. Recirculating-fluid entrainment and depletion mechanics are revealed and suggest that mixing is enhanced by periodic vortex formation in pulsatile flows. Finally, depletion efficiency is compared for flow in a pure-liquid, as well as dilute and dense suspensions. Together, these results begin to expose the complex vortex dynamics that contribute to elevated transit times in pulsatile, two-phase flows.

abstract: PhD


title: TRANSITION METAL CATALYZED CROSS-COUPLINGS OF ALKYL SULFONE ELECTROPHILES

contributor:
Crudden, Cathleen
Chemistry

subject: Cross-coupling Sulfone Nickel

abstract: Sulfones are an important class of organic molecules that can participate in a wide variety of synthetic transformations. For this reason, they have been described as chemical chameleons. While their use as Csp2 electrophiles in cross-coupling dates to the early 1970’s, their potential as competent Csp3 electrophiles has not been recognized until recently. Our group has made significant contributions to the development of new cross-coupling methodologies utilizing alkyl sulfones as electrophiles. This thesis describes the use of alkyl sulfones as electrophiles in both nickel and palladium catalyzed cross-coupling reactions. First, we developed a nickel-catalyzed Suzuki–Miyaura cross-coupling of π-extended tertiary benzylic and allylic sulfones with arylboroxines. A variety of tertiary sulfones were reacted to afford quaternary products in good yields and we identified a unique phosphine ligand capable of promoting the challenging cross-coupling reaction. The method enabled the concise synthesis of a biologically active molecule. We then adapted and extended the nickel-catalyzed system to the cross-coupling of simple tertiary benzylic sulfones using olefins as removable directing groups. Several dialkydiarylmethanes were prepared in good yields and we revealed that the mechanism likely involves an η2-nickel coordination complex with the olefin, which facilitates oxidative addition. Following cross-coupling, the olefin could be cleaved to introduce new functionalities. Next, we developed a nickel-catalyzed Kumada cross-coupling of cyclic alkyl sulfones with aryl Grignard nucleophiles. Uniquely, the sulfinate leaving group was retained following ring-opening cross-coupling and it served as a handle for further functionalization. Overall, the methodology provided access to doubly functionalized products in a one-pot procedure. Finally, we developed a palladium-catalyzed Suzuki-Miyaura cross-coupling of α-fluorinated benzylic triflones with arylboronic acids. The method afforded a variety of mono- and difluorinated diarylmethanes and we demonstrated that both mono- and difluorinated benzylic triflones could be desulfonylated to afford the corresponding α-fluoromethylarenes. Because α-fluoromethylarenes are important substructures in pharmaceuticals and agrochemicals, we utilized our methodology to prepare several fluorinated analogues and derivatives of biologically active compounds.

abstract: PhD


title: Response of cladocerans to native and invasive invertebrate predators in Lake Simcoe, Canada

contributor:
Arnott, Shelley
Biology

subject:
zooplankton
invasive species

abstract:
How populations respond to changing environmental conditions is critical to their
survival. Organisms can respond adaptively to new environmental conditions, for example an
invasive predator, by the expression of phenotypic plasticity, or evolution through selection for
certain phenotypes. Lake Simcoe, one of the largest inland lakes in Ontario, has been invaded by
several non-native species, including the zooplanktivore Bythotrephes cederstroemii, which is
native to north-central Europe and Asia. To investigate whether the arrival of Bythotrephes
and/or increase of Epischura abundance contributed to the zooplankton shifts observed in Lake
Simcoe in the mid-1990s, we conducted two laboratory experiments. Firstly i) a live predation
experiment to assess prey vulnerability and consumptive effects of each predator and ii) a
phototactic response experiment to assess differences in phototactic behaviour when prey
encounter the presence or absence of each predator cue. We found that bosminids were more
vulnerable than daphniids to Bythotrephes and Epischura predation and that all prey responded
to specific predator cue by altering their phototactic behaviour. Our predation results aligned
with the observed abundance changes in Lake Simcoe for some species, however they were
opposite to the abundance changes for others. Our phototactic results demonstrated that all
species are capable of changing their behaviour in response to predators, but in Lake Simcoe
other factors could be contributing to the observed changes. Although these results only explain
some of the observed changes in Lake Simcoe, they provide predictive insight into how future
invasion sites may respond to an invasive predator.

abstract: M.Sc.


title: Using fluorescence spectroscopy to measure the biodegradation of naphtha in Athabasca oil sands tailings ponds

contributor:
Brown, Stephen
Environmental Studies

subject:
Athabasca oil sands
naphtha
Fluorescence spectroscopy

abstract:
This study used fluorescence spectroscopy and solid phase microextraction (SPME) to develop a time-efficient and cost-effective method to measure naphtha biodegradation in Athabasca Oil Sands Region mature fine tailings (MFT) samples. Diverse microbial communities in tailings ponds can readily utilize certain fractions of the available naphtha and support methanogenesis (Holowenko et al. 2000). This has negative implications for the environment as it results in the release of methane, a potent greenhouse gas (Holowenko et al. 2000). As such, there is a need to better track this biodegradation to determine the amount of naphtha within the ponds and the rate at which methane is released.
	Direct fluorescence analysis by extracting all hydrocarbons could not track changes in naphtha concentrations (ranging from 0-1%) because of high background from bitumen hydrocarbons. When using SPME, with the addition of a silicone polymer to the MFT suspension, there was a multiphase equilibrium of the naphtha hydrocarbons, and less extraction of the bitumen background hydrocarbons. After equilibration in the MFT sample, the polymer was transferred to ethanol, and the hydrocarbons were extracted into the pure solvent phase to be analyzed. Results indicated that while SPME does help reduce the background bitumen signal, samples must still be diluted. This makes it more difficult to track small changes in naphtha over time. However, results do support the use of the polymer providing linear results, good repeatability, and high desorption in the 270-290 nm naphtha region. Thus, SPME can be used to detect naphtha degradation when it ranges from >25-100%.
	The values generated from the SPME fluorescence calibration were used in a multiphase equilibrium model to estimate the volume of bitumen in a sample as well as the amount of naphtha in the water and bitumen phases. Results indicated that the %volume bitumen for MFT was 1.01±0.26% which is within the literature range for the % bitumen in MFT by volume, and that the % naphtha in the water phase was ~10%. These estimates can be used in future remediation studies that require an understanding of bitumen-diluent volumes in MFT such as those looking to track biodegradation over time.

abstract: M.E.S.


title: Inversion of Muon Tomography and Gravity Gradiometry for Reservoir Monitoring

contributor: Geological Sciences and Geological Engineering

subject:
inversion
inverse modelling
muon tomography
gravity
gradiometry
SAGD
geophysics

abstract: Steam-assisted gravity drainage (SAGD) reservoirs utilize enhanced oil recovery methods, namely steam injection, to mobilize bitumen in-situ.  High-resolution continuous monitoring is required to make informed decisions on steam injection, which affect the economic and environmental impact of the operation. Muon tomography uses 2D transmission radiographs of muon intensity to produce 3D volume imaging of the subsurface. Muon sensors placed below the target record the deviation of particle intensity from the expected value at a certain density and depth from all directions within the field-of-view, to reconstruct the relative density in the subsurface. Muon sensors are simulated below a realistic steam-assisted gravity drainage reservoir and muon intensity data is forward modeled using various sensor arrays. Synthesized intensity data is used to calculate the inferred opacity (density-length) along discrete directions from sensor to surface which is subsequently inverted to yield 3D density distributions across the reservoir. Results are presented to assess the feasibility of using muon tomography to monitor SAGD reservoirs during production, and demonstrate possible solutions to mitigate limitations, including lack of vertical resolution and inter-well noise. Muon tomography is demonstrated to be a feasible approach for passive monitoring which can be achieved in high spatial resolution on short observation times of weeks to months. By placing muon sensors below the well pairs, resolution on the order of meters can be achieved, but resolution is limited in the vertical direction when all sensors are placed at a single depth. Vertical gravity and vertical gravity gradient data are simulated at the surface and are jointly inverted with muon data to reduce the vertical smearing in the inverse models by ~12% and 6% for reservoir depths of 100m and 200m, respectively. The addition of gravity data reduces the model uncertainty for shallow reservoirs and demonstrates the advantages of joining multiple data types for improved modeling solutions.

abstract: M.Sc.


title: Stable Leader-Follower Systems: A Passivity Perspective for Telerobotics and Vehicle Platooning

contributor:
Hashtrudi-Zaad, Keyvan
Electrical and Computer Engineering

subject:
Stability Analysis
Passivity
Leader-follower systems
Vehicle Platoons
Teleoperation
Absolute Stability
String Stability
Two-port network

abstract:
Advances in computing, more affordable hardware electronics, and reliable communications have led to development of cutting-edge robotic applications where two or more subsystems interact in a leader-follower arrangement to perform tasks. The major sources of instability and performance degradation in leader-follower systems are time delays and dynamic uncertainties, therefore, stability analysis tools and control architectures are developed to guarantee robust stability amid these uncertainties. In this thesis, the focus is on telerobotic and vehicle platooning examples of leader-follower systems.

Telerobotic systems extend the manipulation capability of humans at different scales to remote, virtual, or dangerous environments. A strategy is developed to resolve the problems encountered in telerobotic applications with significant disparity between leader and follower workspace. Utilizing proximity of the follower from the environment, a hybrid strategy that transitions from rate to position mode is designed. Passivity theory is employed to guarantee stability, while experiments are conducted to determine the viability of the hybrid system.

Energy-based methods like absolute stability are typically model-based, therefore, their outcome is heavily dependent on the accuracy of the teleoperator model. Depending on the degree of uncertainty in the dynamic model of the teleoperator and existing noise, the system may behave as potentially unstable when the model-based analysis predicts otherwise. A methodology to experimentally verify the absolute stability of leader-follower teleoperation systems is developed by utilizing data obtained from three experiments often experienced in teleoperation. The proposed method is examined against the benchmark Llewellyn's absolute stability criterion.

String stability is a property of vehicle platoons which ensure the system states are not amplified downstream along the string of vehicles, causing multi-vehicle accidents. In platoons that employ constant distant spacing, linear controllers and distance from the preceding vehicle only, string stability cannot be guaranteed. A visual tool to assess string stability is presented, and a passivity-based sufficient condition for string stability in the frequency domain is developed. The control strategy, accounting for uncertainties and time delays is validated using numerical simulations.

The three application examples show how stability robustness against uncertainties can be tackled employing "energy-based" methods, while meeting the systems performance objectives.

abstract: PhD


title: Detecting Lagrangian Coherent Structures in Realistic Experimental FLuid-Flow Data Sets

subject:
Lagrangian Particle Tracking
Particle clustering analysis
Coherent-Structure Colouring
Coherent-structure detection

abstract: Detection of coherence in sparse Lagrangian particle tracking (LPT) data is a crucial step towards increasing our understanding in a vast number of biological, engineering and geophysical flows. This thesis explores two Lagrangian-invariant approaches for coherent-structures detection in fluid flows using LPT data. The first tested technique is the Coherent-Structure Colouring (CSC) algorithm (Schlueter, 2017). The performance of this Lagrangian approach is assessed by comparing CSC-coloured tracks with baseline vorticity fields of tracks past an Ahmed reference body and in a swirling jet. The effects of two normalized parameters on the identification of vortical structures were defined and studied: the mean track length; and the mean inter-particle distance. It was found that the CSC algorithm yielded accurate detection of coherent structures when mean inter-particle distances were smaller than 15% of the characteristic length scale of the flow, whereas results quickly deteriorate for sparser Lagrangian data. In the second study, a robust coherent-structure detection framework based on Voronoi tessellation and techniques from spectral graph clustering was developed. In this novel approach, the neighbouring times of two particles, defined as the period of time Voronoi cells of two particles remain connected by a Voronoi edge, is adopted as a metric for coherence. Particles for which Voronoi cells share a common Voronoi edge for longer periods of time present a smaller distance in the higher-dimensional eigenspace, hence presenting coherent motion. The proposed approach was shown to be successful at identifying coherence with realistic, sparse LPT data from large wind tunnel experiments. Specifically, coherent structures are identified for the first time with inter-particle distances on the order of 100% of the characteristic length scale of the flow.

abstract: M.Sc.


title: The Application of Structure from Motion Photogrammetry to the Ontario Rockfall Hazard Rating System (RHRON)

subject:
Photogrammetry
Geotechnical Engineering
Risk
Hazard Rating

abstract:
Roadways are considered critical infrastructure in North America, however, many pass-through hazardous terrains, such as rock slopes. To better manage and prioritize rockfall mitigation measures on rock slopes, the Ontario Rockfall Hazard Rating System (RHRON) was developed (Franklin et al., 2015). The RHRON prioritizes slopes into three Classes A, B, and C, with Class A being the most hazardous and warranting a further detailed investigation. The RHRON’s detailed investigation is more time-consuming and potentially hazardous as it subjects inspectors to roadway and rockfall hazards while making subjective slope assessments. This study aims to assess the integration of analysis of 3D point cloud data derived from Structure from Motion (SfM) photogrammetry from both terrestrial and mobile sources into the RHRON assessment procedure.
The first part of the thesis investigates the applicability of SfM photogrammetry using cameras mounted on a vehicle. Several tests are conducted on camera settings, camera lenses, camera orientation, and image exposures. These tests are carried out on sites near Kingston, Ontario, with the objective of determining the possible bounds of quality of imagery to be input into SfM photogrammetry software, such as Agisoft Metashape.
The second part of this thesis investigates the components of the RHRON rating system that can be derived from photogrammetry point cloud models. A repeatable and robust methodology of working with the data is presented using the open-source software CloudCompare. This methodology establishes best practices for the assessment of the RHRON parameters in a 3D virtual environment. Finally, a sensitivity analysis is conducted on the previously presented methodology by analyzing six photogrammetry models and one terrestrial laser scan model to determine the sensitivity of the RHRON method to poor-quality 3D models. The contributions in this thesis (i) enhance current rockfall hazard analysis practices by introducing a more objective methodology for RHRON assessments, (ii) provides a repeatable methodology to assess rock slopes from 3D models, and (iii) provides a recording mechanism for RHRON assessments as seen by the inspector.

abstract: M.A.Sc.


title: Exploring Irish Women's Experiences of Social Climate Around Abortion After the Repeal of the Eighth Amendment

contributor:
Adams, Mary Louise
Kinesiology and Health Studies

subject:
Abortion
Reproductive Justice
Ireland
Repeal

abstract: This study explores abortion activists’ experience of the shift in social climate around abortion in the context of the campaign to Repeal the Eighth Amendment, which previously prohibited abortion in Ireland. Abortion was previously an extremely taboo and stigmatized issue in Ireland, but in the year leading up to the national referendum, there was a highly visible campaign for, and public discussion around, legalized abortion. The purpose of this research was to explore whether the campaign for Repeal, and the ensuing shift in abortion discourses, changed the social climate around abortion in Ireland. I conducted interviews with seven activists involved in a range of organizations, to discuss their experiences of the social climate around abortion before and after the campaign, and of organizing within the campaign for Repeal. Four themes emerged from the data: silence, speaking out, frameworks of abortion in the Repeal campaign, and representation in the Repeal campaign. The interviews revealed a consensus among the participants that there was a clear shift in the social climate around abortion through the campaign, from one of silence and shame, to one of solidarity and compassion. This study demonstrated the crucial role that storytelling played within the campaign, as it rooted the campaign and public discussion of abortion in women’s lived experiences. An unexpected result of this study was the participants’ critique of the mainstream campaign for its failure to situate abortion within a framework that centered the needs of marginalized groups. The participants argued that there was a missed opportunity to root discourses around abortion in intersectional understandings of reproductive justice. This research provides important insight on the successes and failures of the Repeal campaign that can be of use to future reproductive justice activist efforts, both in Ireland and transnationally.

abstract: M.A.


title: CONTEMPORARY MEASURES OF MENTAL HEALTH STATUS AND SCHOOL-BASED RELATIVE AGE EFFECTS IN CANADIAN ADOLESCENTS

contributor:
Pickett, William
Davison, Colleen
Public Health Sciences

subject:
Mental Health
Adolescent
Canada
Relative Age Effects
Dual-factor Model

abstract:
This thesis is on the epidemiology of relative age effects and how they relate to the mental health status of young people. Contemporary measures of mental health are developed, and the association between school-based relative age and mental health is investigated. It consists of four manuscripts, a proposed conceptual model, and a literature review. The analyses used data from the 2014 Canadian Health Behaviour in School-aged Children study.
The first manuscript (BMJ Open) developed a categorical measure of mental health status inspired by the Dual-factor Model, by combining information on subjective well-being and psychopathology. Mental health status was significantly associated with indicators of social and academic functioning, and mental health. Findings support construct validity.
The second manuscript (SSM–Population Health) developed and tested a novel continuous measure of mental health, based on our adaptation of the Dual-factor Model. The continuous version has conceptual and statistical advantages over the categorical form, and evidence supports it as construct valid.
A supplementary chapter provides background information on relative age effects, a review of studies on school-based relative age and adolescent mental health, and a conceptual model linking relative age at school entry to adolescent mental health.
The third manuscript examined the association between school-based relative age and mental health in Canadian adolescents. Analyses were stratified by sex, and effect modification by grade group was considered. Younger students were at increased risk of poor mental health, but effect sizes were modest, and inconsistent depending on the indicator examined.
The fourth manuscript examined effect modification in the association between relative age and suboptimal mental health by levels of family affluence and social supports. There was minimal evidence of statistically significant effect modification, but the effects of relative age were less pronounced in groups of students reporting lower levels of support and lower relative family affluence.
Following this manuscript is a review of potential strategies that have been suggested for addressing school-based relative age effects. There is a need for studies assessing their effectiveness.

abstract: PhD


title: ARTIFICIAL NEURAL NETWORK BASED TRANSFER LEARNING FOR ROBOT KINEMATIC MODELLING

contributor:
Notash, Leila
Mechanical and Materials Engineering

subject:
Neual Network
Robotics
Inverse Kinematics
Transfer Leraning
Machine Learning
Serial Manipulator

abstract:
This thesis discusses the feasibility of applying the transfer learning for modelling robot manipulators. Artificial neural network (ANN) is selected as the tool to conduct transfer learning. For data generation, two types of datasets based on a SCARA-type robot are generated: workspace dataset and path dataset. The ANNs with random initialization are trained using the source dataset, and then the trained initialization (weights and biases) is transferred for transfer learning implementation.
The investigation starts with generating workspace datasets. Transfer learning is conducted first between different robot configurations and then between manipulators with different geometric layouts. The entire trained initial weights and biases from the source neural networks are transferred as the initialization of the target neural network. Because entire pretrained neural network model is transferred to the target ANN, this method is named as fully pretrained ANN. The positive effect of improved final training performance can be observed in most ANN configurations.
To verify the positive impact on data fitting for the same nonlinear relations. Two different spiral paths are used for dataset generation of target dataset and source dataset. Besides the practice of fully pretrained ANN, other three transfer learning methods are proposed and simulated on the path datasets. As the second method, partial initial parameters are transferred from the trained ANN, when the remaining initial parameters are randomly generated. The third method is to freeze partial ANN and initialize the rest weights and biases randomly, which indicates the frozen weights and biases cannot be adjusted during training. To combine two methods of initialization: initial guess and frozen initialization, the ANN with frozen and pretrained initialization is proposed as the fourth method. For an extensive investigation, diverse ANN configurations are tested for the transfer process. The training is performed on both the ANNs with pretrained initial parameters and the ANNs with random initialization. To compare rate of data convergence, different values of performance targets are defined. The training results of ANNs with random initialization and transferred initialization are compared.
It is concluded that, depending on ANNs configurations, the proposed transfer learning methods can improve their final performance differently. Additionally, higher computing efficiency can be observed reaching the specific performance value in most ANNs with transfer learning. Training time can also be shortened by applying transfer learning methods containing frozen initialization.

abstract: M.A.Sc.


title: Characterization of the Biomechanical and Situational Aspects of High Magnitude Subconcussive Impacts in Canadian University Football

contributor:
Cook, Douglas James
Neuroscience Studies

subject:
subconcussive impacts
Canadian football
helmet accelerometers
impact biomechanics

abstract:
Background: Subconcussive impacts are asymptomatic head impacts that induce alterations in the brain after repetitive exposure. Understanding factors that lead to higher magnitude or frequency of subconcussive head impacts in Canadian football is crucial for the development of harm reduction and prevention strategies.
Purpose: The objective of this study was to characterize high magnitude subconcussive impacts in Canadian football to identify injurious relationships between player and game-based characteristics, impact magnitude, and frequency.
Methods: Eighty-one male university-level football players were equipped with helmet accelerometers to capture linear acceleration (LA), impact frequency, and helmet impact location. Impacts with LA ≥60g were included in the analysis. Video footage from 15 games over three seasons was analyzed to characterize aspects of play including play type, position, closing distance, player technique, tackling versus blocking, and impact type (helmet-to-helmet/body/ground) during these high magnitude impacts.
Results: A total of 570 impacts were included in the analysis with a mean LA of 83.44 ± 23.60g. Impacts with a closing distance of ≥10 yards resulted in higher LA compared to <10 yards and occurred most frequently in run plays. Small skill players experienced significantly higher LA than linemen. Helmet-to-body impacts generated significantly higher LA compared to helmet-to-helmet, though helmet-to-helmet occurred more often. Impacts with poor technique had higher LA and occurred more frequently in tackling versus blocking impacts.
Conclusion: The results of this work suggest that rules regarding offensive backfield running starts could be adjusted to decrease the risk of impact after a larger closing distance. Behavioral modifications and coaching approaches aimed at improving tackling technique could decrease exposure to high magnitude impacts at the level of the individual player.

abstract: M.Sc.


title: Liver Transplant Wait-list Trends in Young American Adults

contributor:
Flemming, Dr. Jennifer
Richardson, Dr. Harriet
Hookey, Dr. Lawrence
Translational Medicine

subject: Liver Transplant, Cirrhosis, Chronic Liver Disease, Epidemiology, Health Services Research, Translational Medicine, Population Health, Public Health

abstract:
Background: Cirrhosis refers to end stage liver disease and it is the final common pathway for all chronic liver diseases (CLDs). Recent data illustrates that mortality secondary to cirrhosis is increasing in the United States (US) and is highest among young adults. Whether these trends are also occurring in Liver Transplant (LT) wait-list candidates however has not been well established. This study aimed to describe the epidemiology of LT wait-listing trends in the US over the past two decades stratified by age at listing, cirrhosis etiology, and sex.

Methods: We conducted a retrospective population-based study from 2002 – 2018, examining all adult LT wait-listed patients in the US. Patients >= 20 years at the time of LT listing were identified from the Scientific Registry of Transplant Recipients (SRTR) database. Annual standardized incidence proportions were calculated from US census data. Poisson regression was used to assess changes in the annual incidence of LT wait-listing stratified by age, sex, and cirrhosis etiology and described by incidence rate ratios (IRR).

Results: A total of 216,936 unique individuals were included. The median age at LT wait-listing was 57 years (Range: 20-83; IQR: 51 - 62), with 68% being male, and 11,312 individuals (5.2%) were < 40 years at listing. The most common etiologies of cirrhosis were HCV, alcohol-related liver disease (ALD), and non-alcoholic fatty liver disease (NAFLD). The age and sex standardized incidence proportion of LT wait-listing more than doubled in both young and older adults over the study period (<40: 0.16/100,000 in 2002 to 0.28/ 100,000 in 2018; >=40: 2.2/100,000 in 2002 to 4.34/100,000 in 2018). Using poisson regression, the etiologies with the highest annual IRR were ALD (<40: IRR 1.11, 95% CI 1.10 – 1.12,  p<.001; >=40 IRR 1.06, 95% CI 1.06 – 1.07, p<.001) and NAFLD (<40: IRR 1.13, 95% CI 1.10 – 1.15, p<.001; >=40: IRR 1.16, 95% CI 1.15 – 1.16, p<.001). The rate of waitlisting for ALD in young females was higher than males (IRR 1.11, 95% CI 1.10 – 1.12, p< .001) Conversely, the listing rate for NAFLD was lower in young females compared to young males (IRR 0.97, 95% CI 0.97 – 0.98, p< .001).

Conclusion: The incidence of LT wait-listing is increasing in both young and older adults in the US driven primarily by ALD and NAFLD. In young adults, rates of listing are increasing most in young women with ALD and men with NAFLD. These data support ongoing efforts to identify young adults with ALD and NAFLD where public health interventions can prevent the development of cirrhosis and liver-related complications.

abstract: M.Sc.


title: EVOLUTION OF DEVELOPMENT AND GENE EXPRESSION IN DROSOPHILA

contributor:
Chippindale, Adam
Biology

subject: Drosophila Development Genetics Transcriptomics

abstract:
Evolutionary developmental biology (evo-devo) is the study of trait evolution through variation in development. As early as the modern synthesis, it was recognized that to an understanding of the function of genes during development was critical to understanding evolution as a whole. To that end, modern evo-devo leverages advances in next-generation sequencing to study both the molecular changes that produce interspecific differences in development, as well as the molecular changes associated with evolution in life-history.
In this thesis, I use lab-adapted populations selected for early (Fast) and late-life (Slow) fertility to better understand how life-history selection has led to changes in development and gene expression. These replicated selection lines provide a microevolutionary lens of development time and associated changes in gene expression, both at the transcriptome and the individual gene level.
I found development time to be highly diverged between Fast and Slow selection treatments, though the differences are not proportionate throughout ontogeny. Furthermore, development was highly convergent, with replicate Fast/Slow lines exhibiting highly similar development time. Preliminary transcriptome analysis through RNA-seq suggests the difference in development could be at least partially due to differential ecdysone regulation. Overall, differences in the developmental transcriptome between Fast and Slow were driven by trans-regulatory divergence – a result consistent with strong selection on a microevolutionary timescale. Lastly, I found no clear evidence that Fast and Slow flies differ greatly in their molecular response to stress, suggesting the heat-shock stress response does not trade-off with divergent life-history in this system.
In this thesis, I have shown that the developmental transcriptome can change dramatically on a microevolutionary time-scale. Furthermore, I showed some evidence that developmental evolution can be highly convergent at the phenotypic and global transcriptome level. However, this is not necessarily the case when looking at specific pathways. Overall, my research adds to the growing body of literature on gene expression evolution and provides a foundation for further research into the molecular dynamics of evo-devo changes on microevolutionary time-scales.

abstract: PhD


title: The Infrastructure Trade: Built Relations of the Detroit River Border Region

contributor:
Mullings, Beverley
Viswanathan, Leela
Geography and Planning

subject:
Infrastructure
International Trade
Indigenous Planning
Public-private partnerships
Detroit River
Herb Gray Parkway
Detroit River Tunnel Company
Contracts
Trade corridor
Walpole Island First Nation
Marxism

abstract: Infrastructure is a popular unit of analysis among geographers and planners. The broad field of infrastructure studies provides a means of exploring the ways in which we materialize certain aspects of our communities. This study mines the extensive research into infrastructure and contributes new data and analysis in order to theoretically, historically, and empirically explore the social relations of trade infrastructure; here explored as infrastructure intended for the purposes of international trade that is geographically located within border regions. The context in which this study takes place is spatially located at the border of the U.S. state of Michigan and the Canadian province of Ontario. I also consider two different temporal contexts. First, I look to an historic case study of the first infrastructural crossing of the Detroit River between Windsor and Detroit—a period of roughly 40 years between 1870 and 1911—in order to locate historical consistencies in the economic forces that drive trade infrastructure. Second, I explore the contemporary case study of the Herb Gray Parkway in Windsor, Ontario and the eventual construction of the Gordie Howe International Bridge. This contemporary case features the unique involvement of Walpole Island First Nation (WIFN) and the ways that this Indigenous community informed the planning and development of the parkway and international crossing. A key thread running through these case studies is the inherently social nature of infrastructure. Setting infrastructure into motion require a great deal of social planning; the material expenditures of infrastructure could not exist without first laying a social groundwork that the planning process can move through. Ultimately, this social process is organized in a contractual apparatus that favors the distribution of infrastructural value to a financial class, while the local communities surrounding the infrastructure itself are relegated to securing minor contracts in the hopes of speculative economic benefit.

abstract: PhD


title: A LABORATORY STUDY ON THE EFFECTS OF DISSOLVED GAS EXSOLUTION ON THE PERFORMANCE OF IN-SITU THERMAL TREATMENT TECHNOLOGIES

contributor:
Mumford, Kevin
Civil Engineering

subject:
Gas exsolution
In-situ Thermal Treatment
DNAPL
Groundwater

abstract:
In-situ thermal treatment (ISTT) technologies are a set of remediation methods for treating chlorinated volatile organic compound (CVOC) dense non-aqueous liquid (DNAPL) source zones by increasing the temperature of the subsurface. However, the efficiency and effectiveness of the treatment can be greatly reduced by high groundwater flow as a result of convective heat losses. Dissolved gas exsolution can generate gas below the boiling point of water and may potentially reduce the aqueous relative permeability to mitigate cooling from groundwater flow. The effects of using dissolved gas exsolution in ISTT applications were quantified in laboratory scale experiments. Laboratory-scale heating experiments were conducted at temperatures above and below the co-boiling temperature using sand-water-NAPL mixtures with and without
dissolved carbon dioxide-saturated water. Results indicated extraction of NAPL was possible at temperatures below the co-boiling point. However, limited volumes were extracted (1 to 2 mL from 27 mL emplaced initially) using one pore volume of carbon dioxide-saturated water. Estimates indicate more than 30 pore volumes of solution are required to extract the emplaced volume at a temperature near the co-boiling point. Pore volumes required for treatment increased when temperatures decreased. Additional electrical resistance heating (ERH) experiments were conducted in a 2D flow cell supplied by water with and without dissolved carbon dioxide to determine the effects on groundwater flow rate. Results indicated a reduction of flow by three to four orders of magnitude after exsolution. Results also indicated a change in flow regime from advection dominated flow to natural convection dominated flow. Overall, the two studies indicate that dissolved carbon dioxide exsolution has a potential to be used in practice for groundwater flow reduction, but may only see limited effectiveness for removing NAPLs at lower temperatures. Further work is required to determine the effects in field applications.

abstract: M.A.Sc.


title: A BROAD SCALE INVESTIGATION OF DISPERSAL CONSTRAINTS ON THE NORTHERN RANGE LIMIT OF A PACIFIC COASTAL DUNE PLANT

contributor:
Eckert, Chris
Biology

subject:
Ecology
Range Limits
Dispersal
Metapopulation
Landscape Ecology

abstract: Species are expected to occur and persist where environments allow for population self-replacement, and be limited where biotic and abiotic conditions shift outside their recognized niche. However, many species lack the declines in fitness towards their range edges expected under niche limitation, and even show persistence when moved beyond them, which suggests a role of dispersal limitation in maintaining species' ranges. For species that exist within patchy environments, dispersal limitation can occur through increased heterogeneity of suitable habitat, rather than through an absolute barrier to dispersal. Through reductions in habitat patch frequency and size, as well as greater patch isolation, a species’ ability to successfully disperse to new habitat can decrease along a gradient, with a range limit forming where the recolonization of unoccupied patches can no longer match stochastic patch extinction. I examined the predictions of this hypothesis across the northern range of a Pacific coastal dune endemic, Camissoniopsis cheiranthifolia (Onagraceae). This species occurs in patchy dune habitat, and previous studies of beyond-range transplants strongly suggest that dispersal may limit its northern range. By quantifying geographic variation in the distribution of coastal dune habitat across the northern half of the species' range, and measuring habitat suitability and occupancy at > 7000 randomly distributed 5x5 m plots, I investigated the predictions that towards the species northern limit: (1) habitat availability decreases through reduced patch frequency and size, (2) patch isolation increases through greater inter-patch distances, and (3) occupancy and abundance within suitable habitat patches decreases in response. While coastal dune habitat increased and became more continuous towards and beyond the species northern limit, patch frequency decreased and inter-patch distance increased among suitable habitat patches, with no effect in patch size. This gradient of habitat availability resulted in a gradual reduction in patch occupancy towards the range limit, yet remained higher at the range edge than predicted under the hypothesis of constrained patch dispersal dynamics through habitat availability. Further study on the congruent effects of gradients in reduced patch recolonization and/or increased patch extinction towards the northern limit may further reveal whether dispersal is primarily limiting C. cheiranthifolia’s range.

abstract: M.Sc.


title: Epistemic Emotions and the Number of Sources Explored

contributor:
Fitneva, Stanka
Psychology

subject:
epistemic emotion
curiosity
surprise
breadth of exploration
information-seeking

abstract: Several theories postulate that epistemic emotions, such as curiosity and surprise, motivate information-seeking. In these theories, information-seeking is treated as a unitary, singular construct, with the motivation assumed to be consistent across the various forms of exploration. However, there have been few empirical studies which actually test the emotion-exploration link, and the question of whether epistemic emotions affect the number of sources individuals explore (i.e., the breadth of search) has not been examined. The goal of the present study was thus to investigate the emotion-exploration link in the context of the breadth of exploration. To examine this question, university students were presented with trivia questions and asked to answer them. Participants were then shown an answer submitted by another participant, asked to rate how surprised and curious they felt in response, and then given the option of exploring up to three more responses submitted by different participants. In line with previous work, we found that the model with best fit to the data consisted of a serial mediation, with certainty predicting surprise, surprise predicting curiosity, and curiosity predicting the number of sources explored. However, in contrast to previous work, we did not consistently find that high-certainty errors resulted in greater epistemic emotions or exploration than low-certainty errors. The current findings support the many theories that argue for a role of emotions in motivating information-seeking behaviours, and demonstrated that this emotion-exploration link extends to the breadth of search as well.

abstract: M.Sc.


title: Concurrent Thickness and Material Optimization

contributor:
Kim, Il Yong
Mechanical and Materials Engineering

subject:
Thickness optimization
Topology optimization
Multi-material
Variable thickness
Shell structures

abstract: There is a gap in the literature for an algorithm capable of concurrent thickness and material optimization (CTMO), utilizing fully analytical sensitivities with prevention of coincident material layers. Such a method is required for the efficient optimization of multi-material, non-laminate shell structures. The algorithm is developed with an adaptive penalization scheme, user selected thickness limits, and two candidate materials; all through a compliance minimization problem statement, subject to a mass fraction constraint. The proposed method is gradient-based, relying upon the method of moving asymptotes (MMA) for optimization and solid isotropic material with penalization (SIMP) for interpolation. Solver behavior is studied with five case studies, three academic and two industry-based. Thorough design sweeps of maximum and minimum allowable thickness, at multiple mass constraints, are conducted for the academic models. Further, select results are shown to illustrate solver behavior for thickness and material distributions. Design studies are performed for the two complex models; an automotive hood and an airplane wing. These design studies culminate in a series of design procedure learnings. To verify the feasibility of the tool within industry projects, two design interpretation analyses are performed on the airplane wing. One simple, the other with full joint design. Overall results show excellent behavior across academic models and useful results for the complex models. The design interpretation study verifies that such an algorithm could be used effectively in industry application.

abstract: M.A.Sc.


title: A Modeling Study of Large-Scale Solute Transport in Fractured Carbonate Rock

contributor:
Novakowski, Kent
Civil Engineering

subject:
Groundwater
Solute Transport
Fractures
Numerical modelling
Tracer experiments
Constant head tests

abstract:
Fractures influence aqueous contaminant transport by allowing for rapid migration over long distances through complex pathways and through diffusion into the adjacent rock matrix. While there have been many studies examining transport at smaller scales, there have been far fewer investigations at larger distances (> 50-100 m) due to the cost and difficulty of such research. This study focused on identifying key properties governing large-scale solute transport in sparsely fractured rock. Numerical models which accommodate flow and transport in fractures were used to simulate the results of two divergent tracer experiments previously conducted at large scale in a fractured dolostone. One of the experiments was conducted in what is believed to be a discrete horizontal fracture, and the other conducted in a fracture network. Both experiments had observation points > 100 m from the injection well. As the numerical analysis required estimates of fracture aperture, an improved method of determining fracture transmissivities from the bulk values obtained in constant head testing was also developed.
The results of fitting the measured data with simulations determined that fracture aperture heterogeneity was likely the key property for simulating the tortuous transport observed in the experiments. Simulation of the discrete fracture experiment identified the errors inherent in the use of scaling parameters (e.g. matrix porosity) to the scale-up of experimental results. This study also highlights the significant issues with non-uniqueness that can arise in the interpretation of large-scale tracer experiments in fractured rock. Aperture heterogeneity and complex interconnections can produce an extensive number of equally plausible networks, the difference between which can have significant impact on transport predictions. The error resulting from this non-uniqueness and the application of scaling parameters needs to be better recognized and can be used to more accurately quantify risk assessment for potable water supplies in the vicinity of contaminated sites.

abstract: PhD


title: Advanced Data Analysis Of In-Situ Bioremediation Site Data Using Dimensionality Reduction Techniques

contributor:
Kevin, Mumford
Civil Engineering

subject:
Data Analysis
Bioremediation
Principal Component Analysis
Self-Organising Map
Groundwater
Machine Learning

abstract:
Chlorinated solvents are one of the most prevalent groundwater contaminants in North America. Many of these contaminants are very difficult to clean up due to their physical properties and can pollute drinking water aquifers for decades to centuries. Tens of billions of dollars have been spent to clean up these sites, and thousands more remain for the foreseeable future. In-situ bioremediation (ISB) has emerged as a popular remediation technology for the treatment of tetrachloroethene (PCE) and trichloroethene (TCE) due to its inexpensiveness and flexibility for low-strength remediation applications. A typical ISB implementation involves the collection of large amounts of data to address the many possible problems and optimization decisions. Currently, rather primitive tools and techniques are used to analyse these data and the large amount being collected limits analyses that can be performed. Computer science algorithms for dimensionality reduction are common in research and certain industries that use “big data”, however these techniques have yet to be adapted for environmental industry needs or performance monitoring of ISB applications in particular. In this study a new method of multivariate spatiotemporal analysis was developed using principal component analysis (PCA), with the purpose of including multiple analytes and multiple intermediate sampling results in a single analysis. The new PCA “state-trajectory” method visualized temporal evolution in PCA space by connecting multiple well samples in two principal components. Three dimensionality reduction techniques were then compared using one TCE-contaminated site and included (1) the PCA state trajectory method, (2) a self-organizing map (SOM) state trajectory method, and (3) a Mann-Kendall (MK) trend analysis method.

The PCA state trajectory method was able to separate monitoring wells into useful categories that generally agreed with practitioner analysis. The main benefits of the PCA state trajectory method were its speed and ease of analysis. When comparing the three dimensionality reduction methods, the PCA state trajectory method had the best results. The results of this research provide the field of practical ISB data interpretation a basis for utilizing computer science algorithms with the purpose of including multiple variables in a single analysis method.

abstract: M.A.Sc.


title: MONOSODIUM GLUTAMATE INCREASES VISCERAL SENSITIVITY IN A PRECLINICAL MODEL OF IRRITABLE BOWEL SYNDROME

contributor:
Vanner, Stephen
Lomax, Alan
Neuroscience Studies

subject:
Monosodium glutamate
Irritable Bowel Syndrome
Pain
Diet

abstract: Patients with irritable bowel syndrome (IBS) have identified that monosodium glutamate (MSG) triggers symptoms of abdominal pain. I sought to use a preclinical model for IBS to study how MSG effects intestinal afferent nerve sensitivity. A preclinical model for IBS was developed in mice using a water-avoidance stress (WAS) protocol. To understand the effects of MSG on visceral sensitivity, ex vivo changes in extrinsic intestinal afferent nerve sensitivity to jejunal distension (0-60 mmHg) were measured. In the preliminary study, mice that were exposed to WAS had increased intestinal afferent nerve sensitivity in the presence of MSG (10 M) at noxious pressures (40-60 mmHg). This effect was mediated by increased activity in high-threshold (HT) units. With this preliminary evidence, I examined the effects of MSG on intestinal afferent nerve sensitivity in mice exposed to WAS and MSG gavage, WAS and saline gavage and sham-WAS and gavage controls. There was a significant increase in distension response in intestinal afferent nerves from mice exposed to WAS and MSG gavage at both physiologic and noxious pressures (10-60 mmHg). The increases in intestinal afferent nerve distension response were mediated by an increase in the activity in wide-dynamic range (WDR) and HT units. Serum glutamate levels were also increased in mice exposed to WAS and MSG gavage in comparison to other treatment groups; however, this did not reach significance. MSG had no significant effect in non-handled or sham-WAS controls. Applying MSG directly to the intestinal afferent nerves from healthy controls resulted in a significant increase in distension response. This effect again mediated by WDR and HT units. Ussing chamber permeability assays demonstrated that jejunal tissue from mice exposed to WAS was significantly more permeable to MSG in comparison to control. WAS exposure did not impact ex vivo FITC dextran permeability. Overall, these findings demonstrate that MSG increases visceral sensitivity in a pre-clinical model for IBS. The increase in visceral sensitivity is mediated by units that detect noxious stimuli and may be a result of increased permeability to MSG.

abstract: M.Sc.


title: The response of Cladocera assemblages and size structure to multiple stressors in three Kawartha lakes (Ontario) over the last 200 years)

contributor:
Cumming, Brian
Wang, Yuxiang
Biology

subject:
Cladocera
Kawartha lake
Paleolimnology
Multiple stressors
Eutrophication
Climate change
Anthropogenic stressors

abstract: The Kawartha lakes region has experienced many impacts from human activities since the European settlement in early 1800s including damming, logging, agricultural activities, fisheries, urbanization, and the introduction of exotic species. The temperature has also increased with regional warming by over a degree Celsius. In this study I used the cores collected from a previous paleolimnological study that sought to understand how primary production changed in these lakes over the last ~200 years in three Kawartha region lakes (Cameron, Pigeon and Stoney lakes) using changes in diatoms and subfossil pigments. The previous study concluded that all three lakes experienced cultural eutrophication, beginning in the early 1800s, with only Cameron Lake potentially experiencing a less nutrient-rich conditions since c. 1940 according to the diatoms. This study assessed the cumulative impact of the multiple stressors on subfossil cladoceran over the last ~200 years by analysing the Cladocera assemblages and the changes in the size structure of Bosmina and Daphnia species. Major restructuring of cladoceran assemblages occurred c. 1830 in all three lakes with increases in the abundance of Chydorus brevilabris, suggesting that damming in c. 1830 was an important factor. Pigeon Lake remained stable in cladoceran assemblages after damming while Cameron and Stoney lakes exhibited increases of ~20-30% abundance of pelagic Daphnia spp. c. 1940-50s. The inconsistency in the timing of Daphnia spp. rising among lakes indicates potential interactions between environmental changes related to climate change, eutrophication, and other anthropogenic stressors. A recent return of Cladocera composition to pre-industrial conditions was seen in Cameron Lake. Changes in size of the dominant Bosmina and Daphnia spp. showed little consistency among lakes. These results support previous findings that nutrient enrichment related to multiple factors has resulted in large and significant changes to Kawartha region lakes. This information provides the context for setting realistic restoration goals.

abstract: M.Sc.


title: Exploring the Lived Experience of Youth Who Have Been Suspended From Secondary School: A Narrative Inquiry

contributor:
Matheson, Ian
Education

subject: Education Suspension Youth

abstract: Despite empirical evidence suggesting that out of school suspensions do more harm than good, they are still commonplace in education system. According to the Ontario Ministry of Education, 33,030 secondary school students were suspended during the 2017-2018 academic year. Students who have been suspended are at an increased risk for future suspensions and are less likely to complete secondary school (Nichols, 2004). The purpose of this study was to document, analyze and interpret the lived experience of youth who have been suspended one or more times from an Ontario secondary school and hear their voices. The data for this narrative inquiry was collected through three in depth semi-structured interviews with each one of the three participants.  The interviews audio-recorded, transcribed and analyzed using constant comparative analysis.  The common themes of aspirations and feeling ignored and excluded spanned all participant narratives.  Findings also identified a third theme. For two participants, this was the theme of childhood adversity, and for one participant, the third theme was parental support and expectations. The narratives were originally intended to be viewed through a self-efficacy lens; however, an inductive framework helped draw more meaning from the participant stories. Therefore, the narratives were also viewed through a temporal- needs threat model of ostracism. This study responds to the gap in the literature by hearing the voices of those often not heard and makes sense of youths’ experiences with suspension. The findings can help to increase educator understanding of youths’ experiences and underscores the need for more research.

abstract: M.Ed.


title: MEMORIES AND FORECASTS IN CLOSE RELATIONSHIPS: A CROSS-CULTURAL INVESTIGATION

contributor:
Ji, Li-Jun
Psychology

subject:
Interpersonal Memories
Interpersonal Forecasts
Focal Thinking
Close relationships
Culture

abstract: Interpersonal memories and forecasts can be influenced (or shaped) by individuals’ current relationship experiences. The present research examined cultural differences in interpersonal memories and forecasts, situated in a current/recent positive or negative interpersonal context. Significant cultural differences were observed in the negative, but not positive, interpersonal context. When a current/recent negative relationship event was made salient, Euro-Canadians brought to mind more negative memories (Studies 1 to 3), and generated more negative forecasts (Study 4), about their close other than Chinese did. This was true regardless of whether the current event was a hypothetical scenario or an actual real-life situation. Furthermore, cultural differences in interpersonal memories and forecasts in the negative condition were mediated by focal thinking, which is the extent to which individuals think about and focus on their current negative interpersonal experience (Studies 3 and 4). These negative relational memories and forecasts were associated with poorer perceived relationship quality, lower willingness to help a close other, and less forgiveness. In particular, when a close other did something that was hurtful or wrong, Euro-Canadians perceived their relationship quality to be poorer than did Chinese, partly due to the negative thoughts that came to their mind. The present findings highlighted the role of focal thinking in the way people recall and forecast interpersonal events in a current negative relational context, and further demonstrated that cultural differences in the accessibility of memories and forecasts were not attributable to potential alternative explanations such as relationship-harmony maintenance or non-linear thinking styles.

abstract: PhD


title: Onboarding support systems into elite sport organizations

contributor:
Martin, Luc
Kinesiology and Health Studies

subject: onboarding programs, support network, transition, socialization, professional athletes

abstract:
Onboarding is a term used to describe the process of socialization for new members into an established group or organization. Across an extensive body of literature from organizational settings, and more recently sport settings, there is relative consensus that effective practices can result in numerous positive outcomes for both the incoming individual and the organization. It is interesting to note, however, that current onboarding frameworks focus predominantly on the individual being integrated and do not describe the onboarding experiences of other relevant people involved in the process. For instance, professional athletes that are transitioning to a new team are often accompanied by a support network (e.g., parents, significant other, siblings), who also experience stressors during transition periods. Despite their salient role in the transition process and evidence that suggests their ability to aid the athlete (Poczwardowski et al., 2014), little is known of how organizations engage them in the onboarding process. This thesis addresses this gap in the literature by exploring onboarding experiences for support network individuals in a professional sport context (i.e., National Basketball Association).
A qualitative study was conducted using semi-structured interviews with individuals who had been involved with/experienced the onboarding of support networks. These participants included organizational representatives (n = 11), athletes (n = 5), and support individuals (n = 6). Findings demonstrated the importance of communicating, valuing, and mentoring for successful onboarding and noted several considerations (e.g., timing, acquisition type) and barriers (e.g., member turnover, status hierarchy). Ultimately, it was evident that although organizations strove to onboard support networks properly, none prioritized the task or had a systematic process in place. These findings will be described in relation to the broader onboarding literature, strengths and limitations will be discussed, and future directions will be proposed.

abstract: M.Sc.


title: Design and Analysis of a Low Q Three-phase Series Resonant Converter

contributor:
Jain, Praveen
Pahlevani, Majid
Electrical and Computer Engineering

subject:
Resonant converter
Photovoltaic application
DC-DC converter
Zero voltage switching
Time-domain analysis
Series resonant

abstract:
Renewable energy applications require highly efficient DC-DC converter stages that can work under a wide range of operating conditions. Resonant DC-DC converters have extensively been used for many applications due to their ability to operate at high switching frequencies with good efficiency. At higher power levels (e.g., greater than 1kW), three-phase resonant converters have significant advantages over single-phase ones due to reduced component stresses, smaller filter size requirements, and higher power density.

 This thesis presents the design and analysis of a three-phase series resonant converter for solar applications. Series resonant converters can operate with high efficiency from full load to part-load conditions but generally require a high quality factor (Q) design to maintain regulation and soft-switching at light load conditions. However, a high Q design leads to increased voltage/current stresses for the resonant components. This thesis focuses on achieving soft-switching and regulation in the entire operating range for a low Q three-phase series resonant converter.

A hybrid modulation technique employing APWM and variable frequency is used to reduce the switching frequency range required for the converter operation. Due to the low Q factor, the resonant circuit waveforms are non-sinusoidal and hence, fundamental harmonic analysis cannot provide accurate results. Multiple harmonics at the input and load sides have to be taken into consideration to ensure accurate results using frequency-domain analysis. However, due to the presence of asymmetric pulse width and discontinuous conduction intervals, the voltage waveforms at the load end cannot be defined. Hence, a precise time-domain analysis technique is introduced to analyze the converter operation for varying duty cycles and switching frequencies.

To maintain regulation as well as soft-switching up to extremely light load conditions, it is further proposed to operate the converter in a variable structure including three-phase, single-phase, and burst modes. The operating regions for the different modes are defined and a control strategy is proposed for the converter operation. The performance of the converter is verified using a 200V/250W experimental prototype operating with an input voltage range of 40-80V.

abstract: M.A.Sc.


title: Experiencing Virtual Reality: The Impact of Motion Parallax and Binocular Disparity on Presence, Cybersickness, and Restoration

contributor:
Troje, Nikolaus
Neuroscience Studies

subject:
Virtual reality
Sense of presence
Cybersickness
Restoration

abstract:
The main goal of virtual reality devices is to provide virtual environments where users experience a high level of presence, less cybersickness and suitable for many applications. One of the main applications that has attracted much attention recently is related to restoration. Experiencing a naturalistic virtual environment provides the opportunity to recover from mental and physical fatigue related to modern lifestyle. Given that virtual reality immersion is predominantly achieved by simulating a visual world, it might not be surprising that most factors that affect presence, cybersickness, and restoration concern the visual quality provided by virtual reality devices.

The illusory nature of being in a virtual environment is highly mediated through simulating two prominent depth cues, binocular disparity and motion parallax. Given the importance of these two depth cues, this thesis aims to investigate the role of motion parallax and binocular disparity in the sense of presence, cybersickness, and restoration.
In Chapter 2, I investigated the contribution of motion parallax and binocular disparity to the sense of presence. The results of Chapter 2 demonstrated a reduction in participants' subjective feeling of presence when motion parallax was compromised. Chapter 3 examined the effect of motion parallax and binocular disparity to the extent of experienced cybersickness in a nauseating virtual environment. Results revealed an equal contribution of both depth cues to the amount of experienced cybersickness. Finally, in Chapter 4, I compared the restoration effects of a virtual environment that contains plenty of nature elements, such as trees and plants, to the pictorial representation of the same environment. The results showed that participants who completed their restoration session in the middle of the virtual nature exhibited a significant improvement in stress and mood.

The results of this thesis shed more light on important contributing factors to the above-mentioned topics. Understanding and Resolving problems related to cybersickness and presence will pave the path for virtual reality applications such as restoration to be more accessible and pleasant for users.

abstract: PhD


title: TIMING AND SOURCE OF MELTING AT THE EASTERN EDGE OF THE GURLA MANDHATA CORE COMPLEX, NW NEPAL HIMALAYA

contributor: Geological Sciences and Geological Engineering

subject:
Himalaya
Nepal
Himalayan granite
Gurla Mandhata core complex
Petrochronology
Monazite
Structural geology and tectonics

abstract: Located at the eastern edge of the Gurla Mandhata core complex in the NW Nepal Himalaya, the Chuwa Khola exposes stromatic metatexite, calc-silicate gneiss, augen orthogneiss, and schlieren structured diatexite, all crosscut by a leucogranitic dyke and sill network that culminates in the peraluminous Chuwa granite at the structurally highest level. Distributed shear sense indicators are consistent with top-to-the-southwest ductile extrusion of the Himalayan metamorphic core as observed elsewhere in the Himalaya. In situ U-Th/Pb monazite petrochronology conducted on the Chuwa granite yields an interpreted mean crystallization age of ca. 18 Ma, with no ages younger than 16.5 ± 0.6 Ma. The dyke and sill network yields an interpreted mean crystallization age of ca. 19.5 Ma, with a minimum age of 15.8 ± 0.6 Ma. The southernmost migmatite samples yield similar mean dates interpreted to be the migmatization age (ca. 18.5 Ma), but also contain monazite ages as young as 12.8 ± 0.5 Ma. Yttrium content of the monazite in the migmatite increases with decreasing age, suggesting garnet breakdown and retrograde metamorphism from ca. 18 Ma to 12 Ma. The dyke and sill network are interpreted as a feeder system to the overlying Chuwa granite, based on their similar (ca. 18 Ma) age and geochemical signature. Migmatization occurred as young as ca. 13 Ma as a result of orogen-parallel extension. It is suggested that the dyke and sill network and the coeval Chuwa granite were emplaced during southward-directed crustal extrusion prior to orogen-parallel extension, whereas the Chuwa Khola migmatite rocks record the transition from orogen perpendicular extrusion of the Himalayan metamorphic core to orogen parallel extensional exhumation at ca. 15 Ma to 13 Ma. The Gurla Mandhata core complex and the Chuwa Khola rocks have been affected by a coeval thermal pulse typical of southward extrusion of the Himalayan metamorphic core from ca. 22 Ma to 16 Ma. Although, the Gurla Mandhata core complex records top-to-the-west/northwest sense of shear at ca. 15 Ma to 13 Ma, the Chuwa Khola exhibits dominant top-to the southwest suggesting the existence of a strain partitioning boundary between the two areas.

abstract: M.Sc.


title: Bulk and triple oxygen isotope geochemistry of marine ferromanganese crusts, nodules, and deposits

subject:
Ferromanganese crust
Manganese nodule
pre-treatment
pre-fluorination
triple oxygen isotope
Mariana arc

abstract:
Ferromanganese (Fe-Mn) crusts, nodules, and deposits are chemical precipitates that are ubiquitous in the global ocean and contain valuable metals and metalloids. The chemical and mineralogical composition of Fe-Mn precipitates from the southern Mariana arc were used to decipher their genetic assemblage, assess their potential as a source of trace metals, and place them into context, globally. Discrimination diagrams indicate that 10 samples are predominantly of hydrothermal origin, nine are mixed-origin (hydrogenetic-hydrothermal), and three are hydrogenetic. Together, the samples form a continuum from the hydrogenetic to hydrothermal endmembers. Average metal contents of Fe-Mn precipitates from the southern Mariana arc are low relative to hydrogenetic Fe-Mn crusts and hydrothermal Fe-Mn deposits from the northern Mariana arc and elsewhere, globally, and are therefore unlikely to be viable exploration targets.
Ferromanganese precipitates can have considerably large fractions of carbonate minerals and non-stoichiometric water which, if unaccounted for, can interfere with oxygen isotope measurements of the oxide-silicate fraction. To ensure consistent results between studies, Fe-Mn precipitates should be acidified using 20 % HCl acid for 3 hours, rinsed, dried completely, and then pre-fluorinated using BrF5 at ambient temperature for 90 minutes, prior to conventional BrF5 extraction of oxygen. Reference materials NOD-A-1 and NOD-P-1 have treated δ18O values of 11.0 ± 1.0 ‰ and 11.1 ± 0.7 ‰, respectively, and each have a complex mineralogy typical of a Mn nodule.
Ferromanganese precipitates have triple oxygen isotope ratios that reflect the various reservoirs of this element, formation conditions, and isotope fractionating processes. The Δ’17O values of layered Fe-Mn precipitates do not appear to reflect equilibrium isotopic fractionation processes. Oxygen isotope ratios were measured in the silicate mineral fraction of select layers, to constrain the isotopic composition of this endmember, and through mass-balance calculation, those of the oxide-oxyhydroxide endmember. Individual layers are characterized mineralogically and geochemically, and although mineralogy and ambient formation conditions appear to control the element contents in Fe-Mn precipitates, these factors exert minimal influence on 17O compared to tropospheric dissolved O2 incorporated during precipitation.

abstract: PhD


title: Computational Studies of Reactions within the Solid State and on Solid Surfaces

contributor:
Mosey, Nicholas
Chemistry

subject:
computational chemistry
solid-state
oxygen evolution reaction
stress-induced transitions
nickel selenides
extended Bell model

abstract:
The growing climate crisis makes it imperative that we reduce our energy consumption through process optimization and that we develop clean renewable sources of energy. This thesis addresses both challenges. The first part investigates the possibility of optimizing mechanically driven processes such as stress-induced phase transitions in the solid state by tuning the applied stresses to reduce reaction barriers. Computational studies can help elucidate the changes in reaction paths caused by the applied stress, but accurate calculations are costly because it is necessary to re-optimize the reaction path for every new stress. Here, we develop a simple model to predict the reaction barrier and enthalpy for any low force from quantum mechanically calculated parameters. These parameters are calculated from stationary point structures on the minimum energy path with no force applied. We show how to use this model to obtain the reaction energetics of a manifold of stresses, thereby allowing the identification of stresses that will most efficiently lower the reaction barrier and reduce energy consumption. The model’s predictions are assessed through molecular dynamics simulations.
The second part examines the energetics and possible reaction pathways on NiSe2, NiSe, and Ni3Se2 surfaces using density functional theory. These materials have been demonstrated experimentally as cheap, efficient catalysts for the oxygen evolution reaction (OER) which is a rate-limiting step in the production of hydrogen from water creating a bottleneck in replacing fossil fuels with hydrogen fuels cells. Our computational investigation of different Miller index surfaces and surface terminations provide insight into these materials’ activities and restructurings under OER conditions. Our results show that the (101) surface of NiSe gives the lowest reaction potential energy; however, owing to the electronic structure of the OER intermediates, SeO desorption may be a competing reaction. Doping these nickel compounds with cobalt has been shown experimentally to improve the material’s catalytic activity. Here, we shall discuss the effects of cobalt levels and surficial symmetry on the stability of NiSe2 and Ni3Se2. We also show how the dopant levels and distribution affect the energetics of the OER and possible SeO desorption on NiSe2 surfaces.

abstract: PhD


title: An efficient process for the copper(0)-mediated controlled radical synthesis of acrylate-methacrylate block copolymers

contributor:
Hutchinson, Robin
Chemical Engineering

subject: p(MA) p(MMA) Copper(0) methacrlates PMDETA Me6TREN

abstract:
Cu(0)-mediated polymerization using tris[2-(dimethylamino)ethyl]amine (Me6TREN) as ligand is a promising method to polymerize acrylates at ambient temperature with fast reaction rates that also maintains the high chain-end functionality needed for the synthesis of block copolymers. However, higher ligand levels are required to successfully control methacrylate chain growth, and the cost of Me6TREN presents a significant barrier to commercialization. Thus, reaction conditions suitable for continuous production of low molecular weight poly(methyl acrylate) (p(MA)) macroinitiator with target chain length of 10 in the continuous copper tubular reactor were developed using the less expensive N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) as ligand by increasing reactor temperature to 70°C and using the initiator ethyl α-bromoisobutyrate. The resulting macroinitiator solution could be stored and chain-extended with MA to high conversion in a semi-batch reactor using either PMDETA or Me6TREN, increasing the versatility of a newly developed process to efficiently produce block copolymers using either ligand, or a combination of the two.
PMDETA ligand also provides a route for semi-batch chain extensions of the p(MA) macroinitiator using methacrylates, as significantly higher ligand levels are required to promote controlled chain growth while achieving high conversions. Successful operating conditions were developed with diethylene glycol methyl ether methacrylate (DEGMEMA), to overcome solubility issues found with poly(methyl methacrylate), p(MMA). It was demonstrated that MA as comonomer is not necessary to achieve high DEGMEMA conversions in the process, but that increased concentrations of both the ligand (by a factor of 10) and the ascorbic acid reducing agent (by a factor of 2) are required for chain extensions using methacrylates compared to the conditions used for acrylate chain extensions. Addition of 5 wt% water as cosolvent increased DEGMEMA conversion to > 90% for room temperature operation in 4 h, as well as improved the initiation efficiency of the macroinitiator. These optimized reaction conditions with PMDETA were successfully applied to chain extensions with butyl methacrylate and MMA, although the conversions achieved were not as high. Polymers containing hydrophobic and hydrophilic blocks were also synthesized from the p(MA) macroinitiator by sequential feeding of DEGMEMA and MMA or MA.  The reaction rates achieved with methacrylates are much faster than reported in literature, and the use of PMDETA as ligand provides an economically favorable and versatile system to produce block copolymers using acrylates or methacrylates.

abstract: M.A.Sc.


title: THE IMPACT OF THE CHANGES IN PROVINCIAL LARGE-SCALE ASSESSMENTS ON TEACHERS’ SUMMATIVE ASSESSMENT PRACTICES IN CANADIAN SECONDARY CLASSROOMS

contributor:
Klinger, Don
Christou, Theodore
Education

subject: summative assessment, Canadian, secondary school, provincial large-scale assessment

abstract:
Provincial large-scale assessment (LSA) programs in some Canadian provinces recently have undergone important changes. This study examined the driving forces for changes in provincial LSA programs and explored the impact of these changes on secondary teachers’ summative assessment practices in two Canadian provinces, Prince Edward Island (PEI) and British Columbia (BC). This study answered two research questions: (a) what are the driving forces for the changes in provincial LSAs practices? (b) what is the potential impact of the changes in provincial LSAs practices on teachers’ classroom summative assessment practices at the secondary level?
Documents, interviews, and classroom summative assessment samples from provincial LSA informants and secondary teachers were used to address the research questions. The findings demonstrated that within different contexts, educational authorities depended on a variety of rationale to make the changes in provincial LSA. In PEI, the Department of Education introduced the new provincial LSA with the hope of keeping teachers and schools accountable to fully deliver the curriculum. While in BC, the Ministry of Education phased out the Grade 12 Exams and introduced the new numeracy and literacy assessments, considering the increasing criticism on the consequences of the high-stakes Grade 12 Exams coupled with the learning beliefs embodied in the newly reformed curriculum.
The changes in provincial LSAs in PEI and BC impacted some teachers’ perceived summative assessment practices related to creating and marking their summative assessments. Those teachers who changed their summative assessment practices in response to the new provincial LSAs considered that the new provincial LSAs helped them improve their production of summative assessment items to target curriculum outcomes at appropriate levels and emphasize the core competencies that were featured in the curriculum. BC teachers expressed a feeling of freedom in their summative assessment practices. In addition, teachers expressed several challenges to change their summative assessment practices in relation to the changes in provincial LSA, such as the lack of resources and professional development, the misalignment of the curriculum competencies assessed in classroom summative assessments and those in the new provincial assessments.

abstract: PhD


title: Polymer micelles for the protection and delivery of specialized pro-resolving meditators

contributor:
Amsden, Brian
Chemical Engineering

subject:
specialized pro-resolving mediators
polymer biomaterials
micelles
in vitro release

abstract: Specialized pro-resolving mediators (SPM) play a pivotal role in the resolution of acute inflammation events and have recently gained interest as a treatment for chronic inflammation. Polymer micelles are a promising approach for the delivery of these SPMs as they can protect them from oxidative degradation as well as improve their bioavailability. In this study block copolymers of poly(ethylene glycol) and poly(trimethylene carbonate-5-benzyloxy-trimethylene carbonate) (P(TMC-BTMC)) were produced via ring-opening polymerization. The BTMC units were also modified with sorbic acid in an attempt to introduce additional interactions between the micelle core and the model drug linoleic acid. The block copolymers created formed stable micelles capable of high loading of linoleic acid. In vitro release of linoleic acid was observed over 4 weeks and showed no signs of a burst phase. The polymer micelles also reduced the extent of oxidation of linoleic acid prior to its release compared to a linoleic acid control.

abstract: M.A.Sc.


title: Multitaper Transfer Function Estimates and the Hunt for Coherent Signals Trespassing on Time Series Regression Models

contributor:
Takahara, Glen
Burr, Wesley S.
Mathematics and Statistics

subject:
Time Series
Complex Regression
Multitaper
Spectrum
Transfer Function
Signal Detection
Coherence
Stationary

abstract:
This work provides a test statistic for the detection of coherent harmonic signals underlying time series regression models. Time series regression observes a response series modelled as a function of one or more predictor series, relating predictors and response over time. Unfortunately, standard time-domain regression models don’t account for what temporal factors may be present, operating under assumptions of independence commonly unsatisfied by time series data. Linear filter model coefficients provide an unintuitive alternative, being not necessarily analogous to standard regression coefficients. Analysing the filter model via complex regression in the frequency domain by way of a transfer function, however, provides insight into the frequency structures of the original time series. Identifying the distribution of the transfer function's modulus, phase, and variance allows for further interpretation of the model.

Multitaper spectrum estimation expresses the transfer function in terms of the eigencoefficients of predictor and response signals. Advantages of the multitaper method over alternative estimation procedures include that it controls for broadband bias, is an approximately maximum likelihood estimator of the spectrum, and its eigenspectra form a collection of uncorrelated direct spectrum estimators. The multitaper transfer function is estimated, by frequency, as the coefficient obtained from complex regression on response and predictor eigencoefficients. The limiting distributions of eigencoefficents and transfer functions are known if it's assumed that both series are white noise processes, but less is known about their distributions given harmonic elements embedded in more general, stationary noise.

We wish to relate structural temporal components constituting a time series regression model's coherency, by isolating the frequency bands in which those structural components exist. This work explores the distributional behaviour of the multitaper transfer function estimator in bands featuring common structure between response and predictor, versus bands without. We discuss the joint distributions of complex eigencoefficients, along with the multitaper transfer function estimator, itself. We investigate the transfer function's potential to detect frequency bands containing coherent line components, and develop a statistical test based on its differential distributional properties across frequency.

abstract: M.Sc.


title: Structural Performance of Sandwich Concrete Walls including UHPC and GFRP Reinforcement under Bending and Axial Loads

contributor:
Fam, Amir
Civil Engineering

subject: Concrete Sandwich Walls UHPC SIP GFRP Forms

abstract:
This thesis investigates the structural performance of two sandwich walls; one suited for precast applications while the other for cast-in-situ. The first is an insulated double wythe design using very thin (25 mm) ultra high performance concrete (UHPC) wythes with a layer of extruded polystyrene styrofoam (XPS) core and small diameter (4.2 mm) glass fibre-reinforced polymer (GFRP) bars for reinforcement and ties/connectors. The second wall utilizes GFRP flat plates stiffened by T-shape ribs, as stay-in-place (SIP) structural forms on either side, with a concrete fill in between.  For the first wall type, thirteen 3000 x 600 x (100-200) mm panels were tested under out-of-plane bending (M) with and without axial loading (N) applied to one wythe to simulate both architectural and load-bearing walls. The study compared steel and PVA fibers in the UHPC, and examined GFRP reinforcement ratio in the wythes, insulation thickness, amount and configurations of GFRP connectors, and the level of axial load. The full moment – axial load interaction envelope was developed, including slenderness effects. Panels with GFRP reinforcement achieved 78% higher moment capacity than those with fibers only. As insulation thickness increased by a third, moment capacity increased by 2.4 times. The degree of composite action in panels with transverse ties was 5-15% while that of panels with diagonal ties was 32-78%. The design met serviceability requirements at the highest wind pressure based on the 50-year return period in Canada. Failure was generally governed by fracture of shear connectors.
For the second wall type, six 3000 x 616 x (150-200) mm panels were tested under out-of-plane moment, with and without axial load to establish the moment – axial load envelope, including slenderness effect. Surface treatment of GFRP forms using epoxy-bonded gravel resulted in full composite action, reaching 30% higher moment capacity compared to untreated panels. Concrete shear cracking occurred and propagated into horizontal delamination above the GFRP ribs. A simplified design approach is presented. Additionally, nine  (1060-1945) x 170 x 245 mm panels were tested under in-plane moment, including spliced GFRP panels. Adhesively spliced beams reached 92-96% the moment capacity of their unspliced counterparts. Mechanically fastened specimens reached 86-92% of the moment depending on fastener spacing compared to unspliced specimens. The in-plane moment capacity for a section with a 7.6% GFRP reinforcement ratio was found to be the same as a conventional steel-reinforced section of the same size with a 3% ratio.

abstract: PhD


title: Essays on the Spatial Distribution of Income and Housing in Cities

contributor:
Lloyd-Ellis, Huw
Economics

subject:
Residential Sorting
Monocentric Model
Inequality
Assignment Model
Gentrification
Neighborhood Externalities

abstract:
My dissertation consists of three main chapters on the spatial distribution of income and housing in cities. Chapter 2 studies the potential role of alternative commuting choices in determining the variations in residential patterns within a city. I develop an assignment approach to the monocentric city model that features continuous income distribution, income-dependent commuting costs, and endogenous housing supply. In equilibrium, the relative location of households depends the relative size of the income elasticity of marginal commuting costs and the income elasticity of housing demand. I apply the approach to study the effects of commute mode choice on residential sorting. Having commute mode choice can potentially generate non-monotonic income-location relationships. The existence of such equilibria, however, is not guaranteed in the model with commute mode choice.

Chapter 3 extends the approach developed in Chapter 2 to study the effects of rising income inequality on residential patterns and house prices within a city. The key feature of the model is that the net cost of living further the city centre consists of a common component, and a component that is increasing with income. The model can generate imperfect sorting of income across locations: there is income mixing at non-central locations; households at the top and bottom of the income distribution compete for central locations. When income inequality increases, the changes in equilibrium resemble the gentrification phenomenon. A greenbelt places pressures on house prices and reduces welfare when inequality increases, and the welfare loss is most significant for low-income households.

Chapter 4 studies the role of endogenous neighborhood amenities in driving the concentration of rich households near the city center in a monocentric city model. The two key assumptions of the model are: (i) rich households have higher preference for city-type amenities; (ii) the amenity level depends on the location of high-income households in the city: living closer to the rich provides better access to amenities. I show that within the city, higher density near the city center facilitates provision of amenities, making the central locations more attractive for the rich. Endogenous amenities near the city center drive up unit housing price across the city.

abstract: PhD