Theses

Permanent URI for this collectionhttps://uwspace.uwaterloo.ca/handle/10012/6

The theses in UWSpace are publicly accessible unless restricted due to publication or patent pending.

This collection includes a subset of theses submitted by graduates of the University of Waterloo as a partial requirement of a degree program at the Master's or PhD level. It includes all electronically submitted theses. (Electronic submission was optional from 1996 through 2006. Electronic submission became the default submission format in October 2006.)

This collection also includes a subset of UW theses that were scanned through the Theses Canada program. (The subset includes UW PhD theses from 1998 - 2002.)

Browse

Now showing 1 - 20 of 16178

Carbon Emissions and Evaporation Dynamics at Peatlands Under Active Extraction in Alberta and Quebec, Canada
(University of Waterloo, 2024-11-20) Hunter, Miranda
The extraction of peatlands for horticultural peat use is a small but important source of peatland drainage in Canada, converting these long-term net sinks of carbon (C) into net sources. With demand for peat expected to grow over the coming decades, there is a need to understand how C emissions and water exchange vary with environmental and site management conditions. Extraction operations alter the site hydrology, peat physical and thermal properties, and peat substrate quality, which in turn alter the C cycling and water budget; however, few studies have quantified this. As part of site preparation for extraction, the surface vegetation is removed and a series of drainage ditches are installed to lower the water table, allowing machinery to access the sites. Exterior ditches surround the perimeter of the sites, while interior ditches run the length of the sites, dividing them into 30 m wide fields of peat bounded by ditches. Sites will be extracted for 15 to 40 plus years using the vacuum harvesting method. As part of this, companies repeatedly disturb the surface by harrowing (tilling) the top ~ 5 cm layer to cut it off hydrologically from the peat below. A portion of this newly dry layer is then harvested, processed and sold for use as a horticultural growing medium. This study conducted plot and ecosystem scale measurements of carbon dioxide (CO2), methane (CH4) and evaporation (E) at multiple actively extracted peatlands of varying extraction durations at sites in both Alberta (AB) and Quebec (QC). Specifically, the research objectives were to: i) investigate spatial distribution and seasonal and interannual patterns of C emissions (Chapters 2 and 3); ii) understand the impact of site management, including drainage, harrowing and drainage ditch maintenance, on C fluxes (Chapters 2 and 3) and E (Chapter 4) and iii) assess the environmental drivers of C emissions and E (Chapters 2, 3 and 4). Plot scale C emissions at AB, and ecosystem scale C and E measurements at AB and QC, were conducted for multiple years between 2019 and 2022, with a focus on the March to October period. A peat incubation experiment and a lysimeter experiment were conducted during summer 2022 at AB to understand the impact of substrate quality on C emissions, and the impact of harrowing on E rates, respectively. Water table depth (WTD), volumetric water content (VWC), soil temperature, and a range of atmospheric variables were also measured throughout the study period. We found that while C emissions did not vary spatially across fields, drainage ditches were hotspots of C loss, emitting around double, and ten times the CO2 and CH4 emissions, respectively, of the fields across a range of VWC. Carbon dioxide emission varied by up to 50% seasonally and interannually, with differences driven by the interaction between soil temperature and moisture conditions. Our results demonstrated the importance of characterizing hydrological conditions at drained sites, as the temperature dependence of CO2 emissions increased with increasing moisture content, and CO2 emissions were significantly higher under heavily drained (WTD > 60 cm) conditions. A non-linear relationship between WTD and E demonstrated the strong upward capillary water movement in these heavily compacted sites, and how adequate surface moisture conditions for E can be maintained across a range of WTDs. Site specific WTD thresholds aided in classifying the relative importance of surface and atmospheric variables on E rates. The impact of harrowing on E rates varied with time, which highlighted the importance of considering the length of time between harrowing and harvesting for management operations. This work will have implications for national greenhouse gas reporting, providing data to support updating C emission factors for Canada. The research can be used by industry partners to inform management practices that balance harvesting yields with C emissions. Additionally, due to the absence of vegetation, these study sites provide a unique opportunity to understand environmental controls of heterotrophic respiration and peatland E, without having to partition out the impact of vegetation.
Creation of a Custom Language Model for Pediatric Occupational Therapy Documentation
(University of Waterloo, 2024-11-20) DiMaio, Rachel
KidsAbility is a pediatric rehabilitation center that offers services including occupational therapy (OT) to youth. Documentation, including writing progress notes for each treatment appointment, is essential to OT treatment but can also be time-consuming and tedious. If the time spent on writing progress notes was reduced, KidsAbility believes that their capacity for treatment would increase. This thesis explores the creation of a custom large language model that is intended to decrease the amount of time that clinicians spend writing progress notes by transforming point-form scratch notes from pediatric OT treatment appointments into draft full-form documentation in SOAP format for the clinicians to edit. A dataset of thousands of historical progress notes, with personal health information redacted, was used in the model training paradigm for which different training techniques were explored including domain-adaptive pre-training and LoRA fine-tuning. As there were no corresponding scratch notes in the dataset, few-shot prompting with a human-in-the-loop evaluation process was used to generate matching scratch notes. The historical progress notes and generated point-form notes were used to fine-tune Llama 2 and 3 models on the desired task. Different models’ outputs were evaluated and compared before the final model, a fully fine-tuned Llama 3 8B Instruct model, was selected for a pilot study at KidsAbility in which the custom model was compared against the proprietary Microsoft Co-Pilot model. Ten OT’s participated in the study, using Co-Pilot and then the custom model to write their progress notes for three weeks each. It was found that providing training on how to most effectively use the custom model is important in reducing the amount of time spent on the process. After training, the average time taken to write a note was 7.6 minutes compared to an average of 13.8 minutes before training, both of which are based on subjective reporting. The progress notes written during the pilot study were also used in a quality assessment, in which four OTs scored the custom model notes, Co-Pilot notes, and manually written notes on multiple criteria. Results for this evaluation demonstrated that the notes written with the custom model were of high quality, receiving the highest score for three criteria and the second highest score for the remaining two. For all criteria, the custom model notes scored higher than the manually written notes. Objective timing data collection for determining the impact of using the custom model compared to not using any model was limited by the availability of clinicians.mac
Time trends in abundance and composition of microplastic particles deposited in profundal sediment of two headwater reservoirs within the Grand River Watershed (Ontario, Canada)
(University of Waterloo, 2024-11-20) Watson, Meredith
Plastic pollution has become pervasive in the environment, raising concern for degradation of aquatic ecosystems by microplastics (MPs). Studies on the supply and abundance of MPs in Canadian freshwaters are rapidly emerging, however temporal trends spanning several decades remain sparse. In this study, we report multidecadal records of MP abundance and composition in dated sediment cores from two headwater reservoirs (Belwood Lake and Conestogo Lake) located within an agricultural region of the rapidly urbanizing Grand River Watershed (GRW; southern Ontario, Canada), a major tributary of Lake Erie. Extracted MPs from contiguous 1-cm thick intervals of sediment cores were enumerated and categorized by shape (fragment, fiber). A subset of samples at approximately decadal intervals were chemically characterized using Laser Direct Infrared (LDIR) Spectroscopy. Results reveal that MP concentrations in both reservoirs varied within a similar range (~50-550 particles g/dw) with no observed increasing trend since the start of each record (1957 for Belwood Lake, 1985 for Conestogo Lake). MP flux in Conestogo Lake increased from ~50 particles/cm^2/year in the mid-1980s to ~100 particles/cm^2/year in recently deposited sediment, whereas MP flux varied without a trend between ~5-60 particles/cm^2/year in Belwood Lake since 1957, apart from a peak in the uppermost sample (~150 particles/cm^2/year). More rapid sediment deposition at Conestogo Lake accounts for the difference in MP flux between the reservoirs, suggesting reduction of sediment transport could reduce the supply of MPs to aquatic ecosystems in the GRW. Analysis by LDIR revealed that polyamide, rubber, and polyethylene were the most abundant polymer types in both reservoirs. The relative abundance of rubber particles has increased since the 1990s, indicating an increase of paved road surface and vehicle traffic as a potential source. The findings suggest MP accumulation in these upstream rural reservoirs of the GRW may be primarily driven by local, regional, and hydrologic factors instead of the rise in global plastic production.
Investigating and Optimizing Charge Balance and Its Effect on Efficiency and Lifetime of QLEDs
(University of Waterloo, 2024-11-19) Azadinia, Mohsen
Colloidal quantum dot light-emitting devices (QLEDs) have gained significant attention as next-generation display and solid-state lighting technologies, offering exceptional color purity, tunable emission wavelengths, high photoluminescence quantum yield (PLQY), and solution-processable fabrication techniques. The ability of quantum dots (QDs) to exhibit size-dependent optical properties through quantum confinement effects enables highly saturated red, green, and blue (RGB) emissions. Since their first demonstration in 1994, QLEDs have shown tremendous improvements in performance, achieving external quantum efficiencies (EQE) close to theoretical limits (~20%) and operational lifetimes (T95@100 cd/m²) exceeding 300,000 hours. Despite significant advancements, several unresolved challenges continue to limit the full commercial potential of QLEDs, particularly blue QLEDs (B-QLEDs), which exhibit notably lower electroluminescence (EL) stability compared to their red and green counterparts. A key factor impacting both device efficiency and lifetime is charge imbalance, which can lead to significant reduction in both performance metrics. This imbalance not only reduces the immediate efficiency of the device but also accelerates its long-term operational instability. Additionally, while many developments have focused on red or single-color QLEDs, less attention has been given to conducting comparative studies that evaluate the performance differences among red, green, and blue QLEDs. This leaves gaps in understanding how charge dynamics and performance vary across these colors, particularly in B-QLEDs where the charge dynamics may differ due to changes in the QDs' bandgap. As a result, the exact mechanisms by which charge imbalance affects both efficiency and lifetime, especially in B-QLEDs, remain unclear. Therefore, further research is necessary to better understand these mechanisms and address the remaining challenges. The primary goal of this thesis is to investigate and optimize charge balance in inverted QLEDs, with a focus on studying charge dynamics to better understand the electron and hole supply properties in red, green, and blue QDs. Additionally, this work explores the interactions between excitons and excess charges, examining how excess carriers, either electrons or holes, impact the EL performance of QLEDs. Based on the findings, new charge transport layers (CTLs) are explored to improve the device's charge balance. This research also investigates the EL loss mechanisms in upright B-QLEDs, which remain a major challenge for the commercialization of QLED technology. Finally, new material systems are tested to enhance the EL stability of upright B-QLEDs. To investigate whether commonly used HTLs in highly efficient upright structures can improve charge balance in inverted QLEDs, polymeric HTLs are employed in these devices. To address the challenge of HTL solvent erosion, a suitable recipe is developed for depositing polymeric HTLs on the QDs-EML. The fabricated inverted R-QLEDs exhibit relatively low efficiency, attributed to a poor interface between the QDs-EML and HTL, though not due to damage to the QDs-EML. However, the introduction of a wide bandgap interlayer between the QDs-EML and the HTL results in significant improvements in both efficiency and lifetime, primarily due to enhanced hole supply. Then, electron/hole supply properties of R, G, and B-QDs are investigated in single carrier devices. Results show that widening the bandgap of QDs increases hole supply efficiency but decreases electron efficiency. To investigate their respective electron and hole supply efficiencies, a comparative study is conducted on inverted R, G, and B-QLEDs to explore charge injection characteristics. The findings reveal that in R-QLEDs, the e/h ratio in the QDs-EML is greater than 1, whereas in G- and B-QLEDs, the e/h ratio is less than 1, with charge balance conditions being significantly worse in the case of B-QLEDs. Additionally, photophysical measurements show that, compared to electrons, holes lead to a stronger Auger quenching effect, which is proposed as one possible reason for the poor efficiency and lifetime of B-QLEDs. Finally, by studying spontaneous electron transfer effect at the ETL/QDs-EML interface, it is observed that injecting electrons into the QDs-EML first, rather than holes, is more favorable for efficiency enhancement, suggesting that efficient electron supply is a prerequisite for achieving efficient QLEDs. Based on the findings regarding the charge supply properties of each color, new CTLs are implemented to develop an inverted QLED structure with improved charge balance. The results from this structure show that employing a double ZnMgO ETL approach, where each ETL is annealed at different temperatures to enhance electron supply, along with an HTL featuring a relatively shallow lowest unoccupied molecular orbital (LUMO), leads to EQEs exceeding 23% for inverted R- and G-QLEDs. Additionally, doping the ZnMgO ETL with graphene QDs is proposed as another method to further enhance electron supply in inverted G-QLEDs, leading to improved device efficiency and extended lifetime due to enhanced charge balance. Next, the EL loss mechanism in upright B-QLEDs is systematically studied using non-invasive marking layers at both HTL and ETL to detect charge leakage. The results indicate that electron injection is stronger than hole injection in upright B-QLEDs. Additionally, findings from EL and PL measurements confirm that, aside from some partially reversible deterioration in the PLQY of the QDs-EML, the rapid EL loss in upright B-QLEDs is primarily due to increased electron leakage across the HTL. This leakage causes damage to the hole injection layer (HIL) and diverts holes away from the QDs-EML, leading to a deterioration in hole supply to the QDs-EML. Ultimately, the functional layers in upright B-QLEDs are modified to reduce electron supply and enhance hole supply. The results show that replacing the Al cathode with an Ag/Al electrode, featuring a deeper work function to limit electron injection, results in a 30X improvement in the device's EL stability. Additionally, introducing an insulating polymer layer between two ZnMgO layers to limit electron supply significantly extends the device lifetime by 12X. Furthermore, utilizing a new HTL to block electron leakage and improve hole supply leads to an 8X improvement in EL stability.
Designing and simulating a micro-robot for transporting filamentous cargos in Newtonian and viscoelastic fluids
(University of Waterloo, 2024-11-18) Ghadami, Sepehr
In recent years, there has been a notable surge in interest within the medical field towards minimally invasive procedures, with magnetic micro-robots emerging as a promising avenue. These micro-robots exhibit the capability to traverse various mediums, including viscoelastic and non-Newtonian fluids, facilitating targeted drug delivery and medical interventions. Many current designs, drawing inspiration from micro-swimmers found in biological systems such as bacteria and sperm, utilize a contact-based approach for transporting payloads. However, adhesion between the cargo and the carrier can complicate release at the intended site. In this thesis, our primary aim was to investigate the potential of a helical micro-robot for non-contact delivery of drugs or cargo. We conducted an extensive examination of the shape and geometrical parameters of the helical micro-robot, with a specific focus on its ability to transport passive filaments. Based on our analysis, we propose a novel design comprising three sections with alternating handedness, incorporating two pulling and one pushing microhelices, to improve the capture and transportation of passive filaments in Newtonian fluids using a non-contact approach. Subsequently, we simulated the process of capturing and transporting the passive filament and evaluated the functionality of the newly designed micro-robot. Initially concentrating on naturally straight filaments, we also demonstrated the micro-robot’s capability to capture filaments with intrinsic curvature and those with a spherical payload attached at one end. Our findings provide valuable insights into the mechanics of helical micro-robots and their potential applications in medical procedures and drug delivery. Furthermore, the proposed non-contact delivery method for filamentous cargo could pave the way for the development of more efficient and effective micro-robots for medical purposes. In the second phase of our project, recognizing that most biological fluids exhibit viscoelastic properties due to the presence of protein fibers, we proposed a viscoelastic model. Inspired by the viscoelastic structure of bovine vaginal fluid, we developed and initially characterized this model using creep and strain tests. Subsequently, in the proposed viscoelastic model, we investigated the functionality of the designed micro-robot in the viscoelastic fluid and compared its performance with that of the conventional single-handed helical micro-robot. It was observed that although the designed micro-robot is highly effective in transporting filamentous microcargo without contact in Newtonian fluid, its unique structure presents challenges when moving in viscoelastic fluid.
The Viability of using a Gleeble for Physical Simulation of High Frequency Induction Welded TRIP 690 AHSS
(University of Waterloo, 2024-11-18) Al Hussain, Syed Faique
High Frequency Induction Welding (HFIW) is the predominant process for high volume production of small diameter tubes and pipes for hydroformed automotive and oil and gas applications. This process is well-established due to its high throughput and continuous nature which makes it ideal for industrial use. However, the HFIW process is also complicated, involving several physical phenomena occurring simultaneously such as mechanical deformation during the squeeze-out, phase transformations, large temperature gradients, high heating rates, and electromagnetic induction. These phenomena are difficult to decouple from one another, leading to gaps in the present understanding regarding how each individual phenomenon affects the formation of certain weld defects, such as oxide inclusions trapped within the bond line of the weld joint. With advances in automotive design, new high-Al TRIP steels are being used for automotive hydroforming applications, due to their capability to be used in high strength/light-weight designs. However, HFIW of these materials, such as TRIP 690, is susceptible to the formation of entrapped oxides containing aluminum (Al), manganese (Mn), and silicon (Si) within the bond line, reducing the operation window compared to other steels. In welds containing oxide inclusions, strength and ductility of the weld joint will be significantly decreased. During production, it is difficult to determine the formation of these oxides due to the dynamic and continuous nature of the HFIW process. Conducting mill trials for experimentation is not practical due to economic constraints as there are high operational costs to run a tube mill and trials result in high material usage. Thus, there is a need to be able to physically simulate the HFIW process at a laboratory scale to understand the effect of each of the individual process parameters on the formation of bond line oxide inclusions and weld quality. This study physically simulates the HFIW process in thin sheets of TRIP 690 AHSS using a Gleeble 3500 thermomechanical simulator. The results of this work demonstrated that the Gleeble could reproduce the microstructure across the bond line and heat affected zone of the HFIW produced welds. Mechanical characterization of the welds revealed a similar hardness distribution across both the Gleeble and HFIW welds. Notably, samples containing bond line oxide inclusions such as those found in HFIW welds were also recreated, and the effects of these inclusions on the tensile properties and fracture mechanism were determined. Through this study, the ideal conditions for producing oxide-free welds to ensure superior weld mechanical properties were determined.
RNA-seq exploration of host responses and viral genomic diversity in SARS-CoV-2 infection
(University of Waterloo, 2024-11-18) Luc, Jessica
Since the discovery of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), there have been over 700 million cases and over 7 million deaths worldwide. Although some patients develop severe symptoms such as multiple system organ failure, others can be asymptomatic. This reflects the role of the immune system in disease progression. Although there exist standard PCR and antigen-based tests for SARS-CoV-2 detection and diagnostics, an important research goal is the identification of predictive biomarkers that are indicative of COVID-19 severity. In this thesis, I performed bioinformatic analyses of two original RNA-seq datasets generated by collaborators to gain insights into the mechanisms and host responses of SARS-CoV-2 infection. The first dataset consisted of transcriptomic data from SARS-CoV-2 infected human lung cells as well as bat (Eptesicus fuscus) derived cells, providing insights into host responses of multiple mammalian species. The second dataset consisted of transcriptomic data from nasopharyngeal swabs collected from COVID-19 patients. A bioinformatic approach was used in both datasets to identify host genes that were up-regulated and down-regulated by SARS-CoV-2 infection as well as to identify biologically relevant viral mutations. The analysis resulted in the discovery of a novel R685P mutation in the SARS-CoV-2 spike glycoprotein, that had increased frequency in the Eptesicus fuscus derived cell line. Variant analysis from the clinical nasopharyngeal swab RNA-seq dataset also revealed the existence of a SARS-CoV-2 quasispecies containing multiple distinct viral genotypes with a unique population structure in each patient. Despite each dataset being distinct, a similar bioinformatic analysis was applied to both datasets to reveal host response patterns and visualize the evolution and mutational spectrum of SARS-CoV-2. Although COVID-19 is no longer considered a global emergency, furthering our knowledge of the SARS-CoV-2 infection can aid in the development in new therapeutics and diagnostic tools.
A Parameterized Vibronic Spin-Orbit Coupling Model Protocol Suitable for Spectroscopy
(University of Waterloo, 2024-11-14) Chen, Benny
A diabatization protocol constructing vibronic model Hamiltonians with inclusion of spin-orbit coupling was implemented in Python. This protocol has been extended to include spectroscopic applications. GAMESS package GMC-QDPT level of theory calculations carries out a proposed diabatization scheme to automatically compute a grid of diabatic states in expansions of displaced nuclear coordinates. Diabatic potential energy surfaces can subsequently be constructed through fitting parameters. Generated vibronic models can be used for input to quantum dynamical simulation approaches such as MCTDH and VECC alike, where auto and cross-correlation functions can be obtained after propagation. Simulated gas-phase photoelectron spectra were reproduced for H2O, NH3, and PH3, with excellent agreement to experimentally recorded spectra. Absorption spectra of transition metal trifluorides CoF3 and RhF3, along with iron pentacarbonyl Fe(CO)5, were studied with a triple zeta polarized Sapporo basis set. Both CoF3 and RhF3 showed pronounced splitting originating from spin-orbit coupling effect, whereas Fe(CO)5 only displayed minimal change due to spin-orbit coupling limited to its truncated constant-order spectrum. It is predicted that the Jahn-Teller effect plays a more dominant role over spin-orbit coupling in our Fe(CO)5 model simulated spectra. Streamlining of the protocol has increased its accuracy and robustness, in the interest of supporting future vibronic spin-orbit coupling model research.
Commuting, Spatial Allocations, and Inequalities
(University of Waterloo, 2024-11-14) Yu, Aidi
This thesis examines the complex relationships between commuting times, wage disparities, gender differences, and urban spatial distribution, through the lens of three interconnected studies. The first chapter investigates the relationship between commuting times, wages, and the gender wage gap, with a focus on controlling for occupational choice endogeneity. Using data from the American Community Survey (ACS) and the Occupational Information Network (O*Net), the study highlights how gender differences significantly influence the positive correlation between commuting time and wages, especially among full-time working homeowners in U.S. cities. Through quantile regression analysis, it reveals that while men's returns on commuting diminish as income rises, the commuting gender gap remains relatively constant across the wage distribution. The second chapter delves deeper into the gendered impacts of commuting on wage disparities, addressing the endogeneity of commuting times. By constructing instrumental variables based on exogenous city characteristics from the 2016 ACS, the study isolates the causal effects of commuting on wages. The findings suggest that marital status drives the gender difference in commuting premiums, with married women and single men demanding higher wages to compensate for longer commutes. This chapter contributes to a broader understanding of wage-commute trade-offs and the socio-economic consequences of commuting time. The third chapter explores the interplay between job flexibility, residential location sorting, and wage determination through a monocentric city model. The model incorporates both high- and low-skilled workers and employs a bid-rent framework to determine housing prices and the spatial distribution of labour. The study finds that high-skilled workers' job flexibility significantly impacts their commuting decisions and urban spatial sorting patterns. In low-flexibility settings, high-skilled workers tend to live near the central business district, earning higher wages to offset the high cost of central real estate and commuting. Conversely, increased job flexibility enables these workers to relocate to more distant, affordable areas, thereby reducing the equilibrium skill premium. Together, these chapters provide a comprehensive analysis of how commuting, gender, and job flexibility interact to shape wage patterns and urban spatial structures in contemporary cities.
Ocular Effects of Scleral Lens Wear on Dry Eye Patients
(University of Waterloo, 2024-11-14) Otchere, Heinz
Purpose: Dry eye disease (DED) is among the most complex ocular surface diseases to treat. Complaints of ocular discomfort and dryness are common in DED patients and in contact lens wearers. The use of SL to restore the integrity of the ocular surface in a more severe DED has become increasingly accepted among eye care practitioners. However, little is known about this treatment regimen and its impact on ocular surface in mild to moderate DED. Also, the potential impact of coated SL designs incorporating Hydra-PEG (polyethylene glycol) technology on ocular surface health has not yet been fully investigated. This thesis aimed to address this gap in knowledge and determine whether SL (uncoated or Hydra-PEG) could be used as a viable option for patients who are experiencing milder forms of DED. Over the course of the study, participants were asked to complete DE questionnaires; lens settling and vision, corneal thickness, osmolarity and matrix metalloproteinase 9 (MMP-9) in the pre-corneal tear film were investigated. The study also examined the relationship between the respective parameters and compared the two lens pairs. Methods and Materials: The study was a prospective, double-masked, randomized, dispensing, crossover clinical trial involving five visits, where 20 subjects with mild to moderate dry eye disease (DED) were enrolled. Eligibility of the participants was confirmed following the Tear Film and Ocular Society (TFOS) Diagnostic Report in the first visit: presence of symptoms using the Ocular Surface Disease Index (OSDI) and Standardized Patient Evaluation of Eye Dryness (SPEED) questionnaires (OSDI ≥ 13, SPEED ≥ 4), plus osmolarity values (> 308 mOsmol/L in either eye or interocular difference of > 8 mOsmol/L) and or a positive MMP-9 result (using InflammaDry® test kit) or both. The second visit involved randomization and dispensing of customized hydra-PEG coated or uncoated SL, where each pair of lenses were worn on a daily wear basis for four weeks. Prior to dispensing the lenses, high contrast (HCVA) and low contrast acuities (LCVA) were recorded. The central corneal clearance (CCC) was measured with VisanteTM OCT to determine lens settling over time. Two standard clinical questionnaires (contact lens impact on quality of life (CLIQ) and contact lens dry eye questionnaire 8 (CLDEQ-8)) and an internally developed wearing habit and subjective rating questionnaire were provided to subjects and completed. The third visit (after 4 weeks) involved follow-up of the first randomized SL, where the lenses were evaluated, and clinical measurements repeated. A wash-out period of at least 48 hours was allowed before dispensing (visit 4) and follow-up (visit 5) of the other pair of SL, using the same procedures, measurement protocols and visit schedule. The SL used in the study were Zen™ RC (Alden Optical, Bausch & Lomb, Lancaster, NY, USA) available in only two diameters (14.80 and 15.40 mm), with a central thickness of 250 µm. Results: Eighteen females and two males, mean age 29.10 ± 7.48 years, participated in the study. The overall OSDI and SPEED scores were 36.45 ± 17.08 and 12.50 ± 4.03 respectively. There was no significant difference in the CLIQ and CLDEQ-8 scores between uncoated and coated SL. In terms of wearing habit and subjective ratings, no statistically significant differences were observed in any of the parameters (wear time, dryness, burning, vision, and comfort). This suggests that the use of hydra-PEG coated SL did not show greater performance compared to the uncoated SL. The central corneal clearance (CCC) at the dispensing visit was 260 ± 40 (range: 200 - 300 µm) for both lens pairs. This significantly reduced to 190 ± 40 µm (lens settling: 70 ± 42 µm) for the uncoated SL and 200 ± 30 µm (lens settling: 70 ± 43 µm) for the coated SL at the follow-up visits, (all, p < 0.001). Comparing the CCC for the two lens pairs at the follow-up visits, no significant difference was observed, thus, the lens pairs settled at similar rates. In terms of HCVA and LCVA between the two lens pairs at both the dispensing and follow-up visits, there were no significant differences between them. Also, no significant correlations were found comparing the CCC with HCVA and LCVA of each lens pair at both visits. The CCT at the baseline and follow-up visits were: baseline: 560.55 ± 32.28 µm, post wear of uncoated SL: 557.65 ± 32.10 µm, and post wear of coated SL: 560.50 ± 34.02 µm. There were no significant differences for either lens type for central corneal thickness (CCT) at the baseline and follow-up visits (all, p > 0.05). Also, no significant correlations between CCC and CCT were observed at baseline or follow-up visits. These results demonstrated there were minimal corneal hypoxic effects when these SL were worn on a daily wear basis. For osmolarity measures, there was a statistically significant difference between the baseline and follow-up visit for the coated lenses (311.00 ± 14.86 vs 302.85 ± 7.96 mOsmol/L; p = 0.04). While this is statistically significant, the clinical relevance of this small difference remains questionable. Comparing the two lens pairs, no significant difference was found at all visits. The inflammaDry® test results indicated that 80 % of the participants tested positive for elevated MMP-9 at the baseline visit. There was a reduction in MMP-9 positive test results following the SL wear, however, there were no significant differences between the baseline and follow-up visits for each lens pair. Comparing the two lens pairs, no significant difference was observed. For either lens, no correlation was observed between osmolarity and MMP-9 test results. Conclusion: There is a potential for using SL to manage symptoms in subjects suffering from mild to moderate DED, as the overall wearing habit and subjective ratings showed > 70 % of lens tolerance among the study cohort. SL wear over the month of wear in this cohort induced little change to the cornea or conjunctival tissue. Furthermore, SL may appear to marginally reduce tear film osmolarity, however, further studies are needed to confirm this result and its impact on subjective dryness. The clinical phenomenon of lens settling needs further investigation, especially on its impact on conjunctival morphology. In this cohort of subjects of mild to moderate DED, the hydra-PEG coating technology did not show superior performance over the uncoated lens for any of the factors assessed. Keywords: dry eye disease. scleral contact lens, hydra-PEG, osmolarity, inflammadry, cornea
Safe Memory Reclamation Techniques
(University of Waterloo, 2024-11-14) Singh, Ajay
This dissertation presents three paradigms to address the challenge of concurrent memory reclamation, manifesting as use-after-free errors that arise in concurrent data structures using non-blocking techniques. Each paradigm aligns with one of our three objectives for practical and safe memory reclamation algorithms. Objective 1: Design memory reclamation algorithms that are fast, have a bounded memory footprint, and are easy to use — requiring neither intrusive changes to data structures nor specific architecture or compiler support. These algorithms should also deliver consistent performance across various workloads and be applicable to a wide range of data structures. To achieve this, we introduce the neutralization paradigm with the NBR (Neutralization-Based Reclamation) algorithm and its enhanced version, NBR+ (Optimized Neutralization-Based Reclamation). These algorithms use POSIX signals and a lightweight handshaking mechanism to facilitate safe memory reclamation among threads. By relying solely on atomic reads and writes, they achieve bounded garbage and high performance with minimal overhead compared to existing algorithms. They are straightforward to implement, similar in reasoning and programming effort to two-phased locking, and compatible with numerous data structures. Objective 2: Eliminate the asymmetric synchronization overhead in existing reclamation algorithms, which often incur costly memory fences while eagerly publishing reservations, as seen in algorithms like hazard pointers and hazard eras. We propose the reactive synchronization paradigm, implemented through deferred memory reclamation and POSIX signals. This mechanism enables threads to privately track memory references (or reservations) and share this information on demand, using the publish-on-ping algorithm. This approach serves as a drop-in replacement for hazard pointers and hazard eras and includes a variant (EpochPOP) that combines epochs with the robustness of hazard pointers to approach the performance of epoch-based reclamation. Objective 3: Completely eliminate the batching common in current reclamation algorithms to allow immediate memory reclamation, similar to sequential data structures, while maintaining high performance. We introduce Conditional Access, a hardware-software co-design paradigm implemented in a graphite multi-core simulator. This paradigm leverages cache coherence to enable efficient detection of potential use-after-free errors without explicit shared-memory communication or additional coherence traffic. Conditional Access provides programmers with hardware instructions for immediate memory reclamation with minimal overhead in optimistic data structures. To validate our claims, we designed and conducted extensive benchmark tests to evaluate all proposed algorithms on high-end machines under various scenarios. We paired these algorithms with several real-world concurrent data structures, representing various memory access patterns, and compared their time and space efficiency against numerous state-of-the-art memory reclamation algorithms, demonstrating significant improvements.
Metal Concentrations in an Arctic Wastewater Wetland: Insights and Innovations from Baker Lake, Nunavut, Canada
(University of Waterloo, 2024-11-14) McPhedran, Bronte
The unique climatic conditions and isolated geographies of Arctic communities present distinct challenges for municipal wastewater treatment. Most communities depend on natural wetlands to provide passive treatment of wastewater; however, increased pressure on these systems from prolonged use, climate change, and intensifying human activity has resulted in the recent development of northern-specific standards for wastewater. These standards, among other objectives, aim to maintain healthy fish populations and diverse aquatic ecosystems, while calling for community consultation, integration of traditional knowledge, and adherence to federal and territorial regulations. A passive wastewater treatment system near Baker Lake, NU, served as a case study to address knowledge gaps regarding ecosystem function and trace metal dynamics in abiotic and biotic ecosystem compartments subject to wastewater inputs. Additionally, this research explored a method for time-resolved analysis of contaminant histories, which is particularly valuable in environments lacking baseline data or where regular monitoring is challenging, including in the Arctic. Between the summers of 2019 and 2021, a series of lakes that represented wastewater-affected and reference systems were sampled for water, sediment, and fish. Water from wastewater-affected lakes had elevated concentrations of metals (e.g., Mn, Fe, Cu) and increased primary productivity (as inferred from chlorophyll-a concentrations), with persistent hypereutrophic conditions; extremely low dissolved oxygen levels were recorded in the lake closest to wastewater influent. Although sediment analysis near wastewater sources indicated higher levels of Cu and Zn, overall sediment chemistry was similar across all sites. The influence of wastewater on the trophic ecology of Burbot (Lota lota) was minimal, whereas Arctic grayling (Thymallus arcticus) had more enriched (i.e., less negative) δ13C at wastewater-affected sites, suggesting altered energy pathways in lakes that receive nutrients from wastewater. Analyses of metals in muscle tissue revealed lower, although not significant, concentrations of methylmercury – the toxic, biomagnifying form of mercury - in fish from wastewater-affected sites compared to those from reference sites. These lower concentrations of methylmercury in fish muscle tissue occurred despite higher concentrations in abiotic media, potentially because of somatic growth dilution, but more research is necessary. Analyses of trace metals in otoliths revealed distinct multi-element otolith signatures (i.e., Zn, Mn, Cu, Fe, and Pb) between wastewater-affected and reference lakes, and significantly greater concentrations of Fe in a lake receiving wastewater across two reconstructed periods of growth. Together, findings from this research not only fill knowledge gaps regarding the influence of municipal wastewater on cold, oligotrophic freshwater systems in the subarctic, but also highlight the potential uses and limitations of otoliths as markers of wastewater exposures.
Microbiology of bentonite clay relevant to a deep geological repository for used nuclear fuel
(University of Waterloo, 2024-11-12) Beaver, Rachel
Nuclear energy is an important source of energy globally, but results in the production of used nuclear fuel. When removed from a nuclear reactor after its useful lifetime, used nuclear fuel is still highly radioactive and must be stored safely for approximately one million years until it returns to the radioactivity level of naturally occurring uranium ore. Canada, along with other countries that have an inventory of used nuclear fuel, is in the process of designing a deep geological repository (DGR) for long-term storage of used nuclear fuel. In this system, used nuclear fuel, itself a stable solid, will be stored in copper-coated steel used fuel containers, and placed in bentonite clay buffer boxes made of highly compacted Wyoming MX-80 bentonite. Buffer boxes would then be stacked in placement rooms approximately 500 m below ground in a suitable host rock with spaces between buffer boxes and host rock filled in with a granulated form of bentonite referred to as gapfill material. To ensure the longevity of a DGR, it is important to consider the role that microorganisms could play, particularly through contributing to corrosion of used fuel containers through a process termed microbiologically influenced corrosion. Expected to dominate occurrences of microbiologically influenced corrosion under anoxic conditions, sulfate-reducing bacteria (SRB) are a primary target of research, but rarely live in isolation, thus necessitating the study of microbial communities that could live in the bentonite clay surrounding used fuel containers on a broader scale. Due to the potentially detrimental role that some microorganisms could play in a DGR, a goal in designing a DGR is to compact bentonite, a type of swelling clay, to a sufficiently high dry density that microbial growth is suppressed upon saturation. The first goal of this thesis was to investigate the bentonite dry density necessary to suppress microbial growth in Wyoming MX-80 bentonite under oxic conditions and gapfill material under both oxic and anoxic conditions. A set of pressure vessel experiments demonstrated suppression of microbial growth under oxic conditions in bentonite compacted to a minimum dry density of 1.4 g/cm3. Under anoxic conditions, growth of heterotrophs was suppressed in pressure vessels with a minimum dry density of 1.45 g/cm3, but culturable SRB persisted in abundances higher than the as-received bentonite starting material in the outer layers of all pressure vessels throughout the full one-year experiment. Additional experiments were conducted to explain the increase in abundance of SRB, which had not previously been observed in other studies. These experiments suggested that the increase in abundance of SRB was likely not inherent to the gapfill material, nor was there evidence for it being a result of differences in SRB medium or in amounts of trace oxygen between studies. In both oxic and anoxic pressure vessels, an initial increase in abundance of culturable heterotrophs was observed prior to complete saturation, presumably as water became available but swelling pressure remained sufficiently low to allow for their growth. Although previously proposed to potentially be associated with a recovery from the viable but not culturable state rather than growth, a follow-up experiment suggested that the initial increase in abundance of culturable heterotrophs was likely a reflection of growth (i.e., cell division). Dry density is an important consideration in DGR design, but it is not the only physical property that could influence microbial growth within a DGR. Temperature is expected to fluctuate from natural subsurface temperatures of <20°C to temperatures as high as 94°C, and little research has been conducted to explore the potential for microbial growth in bentonite at these elevated temperatures. This thesis includes experiments testing the abundance and community composition of microorganisms adapted to a variety of temperatures in as-received and hydrated bentonite. The results showed a low abundance of culturable microorganisms that survived incubation at 60°C, but 16S rRNA gene profiles dominated by presumably unculturable representatives of the thermophilic family Thermoactinomycetaceae. Hydrated bentonite was additionally incubated at temperatures of 75, 90, and 105°C, but DNA sequencing results did not show a shift in community composition from as-received bentonite, suggesting that the natural as-received bentonite microbial community may not include members adapted to these very high temperatures. Lab-scale experiments allow for testing of very specific DGR-relevant conditions (e.g., dry density and temperature) and the effect these have on microbial community abundance and composition. However, a DGR is being designed to exist for upwards of one hundred thousand years, which is not a realistic timescale for any experiment. To circumvent this limitation, one approach is to couple lab-scale experiments to the study of natural analogues, which have naturally existed for DGR-relevant timeframes. This thesis presents a study of the Tsukinuno bentonite deposit in Japan, which can serve as a natural analogue to DGR bentonite. In this study, sequencing of DNA extracted from bentonite revealed microbial communities dominated by sequences associated with Thiobacillus, Hydrogenophaga, Comamonadaceae, and Pseudomonas. Although differences in community composition were observed between samples, microbial communities were relatively similar for all four studied cores and at all depths into the clay bed. A series of geochemical parameters were measured to help identify factors that may influence microbial community composition. The abundance of culturable anaerobic heterotrophs was positively correlated with the concentration of nitrate, which could be used by anaerobes for denitrification, and the abundance of culturable aerobic and anaerobic heterotrophs was negatively correlated with the abundance of the clay mineral montmorillonite, increased concentrations of which would increase the swelling capacity of the bentonite. The results presented throughout this thesis will together be useful for incorporation into future models of microbial activity within a DGR and can ultimately be used to inform DGR design.
Combined Action Observation, Motor Imagery and Steady State Motion Visual Evoked Potential Based Brain Computer Interface System
(University of Waterloo, 2024-11-12) Ravi, Aravind
Stroke is one of the leading causes of long-term acquired disability in adults worldwide. Gait recovery is a major objective in post-stroke rehabilitation programs. Conventional gait therapy encourages patient involvement, but the results can be slow and/or limited, leading to sub-optimal recovery. Active patient involvement, collaboration, and motivation are key factors that promote efficient motor learning. Therefore, there is a need to develop novel rehabilitation strategies to enhance user engagement by utilizing their movement intent. Brain-computer interfaces (BCIs) based on electroencephalography (EEG) offer an attractive approach for rehabilitation as they enable an alternative method for active participation in therapy. Current visual BCIs provide high decoding accuracy but typically do not activate sensorimotor areas critical for motor recovery. Conversely, BCIs based on motor imagery (MI) activate motor areas but suffer from high inter-subject variability and long user training, resulting in poorer movement intent detection accuracy and potentially leading to high cognitive demand. This thesis proposed a novel BCI paradigm called CAMS—Combined Action Observation (AO), Motor Imagery (MI), and Steady-State Motion Visual Evoked Potentials (SSMVEP). The CAMS paradigm aimed to induce acute changes in movement-related areas of the cortex through the observation and imagery of gait movements, activating both motor and visual cortices to elicit SSMVEP-like responses. Furthermore, the responses elicited by the CAMS paradigm were investigated in two distinct applications to detect user movement intent with the aim of actively engaging the participant. The research conducted across three studies investigates the efficacy of CAMS in enhancing cortical excitability, decoding gait phases, and improving asynchronous visual BCI performance. Twenty-five healthy volunteers participated in this study wherein they observed and imagined lower limb movements of gait as part of the CAMS intervention, which was compared with an SSMVEP control condition. Study I aimed to investigate the acute changes in cortical excitability induced by the CAMS intervention. The results demonstrated significant increases in movement-related cortical potential (MRCP) components, indicating enhanced cortical excitability. For instance, the magnitude of BP1 at channel C1 increased from -1.41 ± 0.54 µV pre-intervention to -3.23 ± 0.5 µV post-intervention (p = 0.009), highlighting the potential of CAMS to engage motor- related brain areas and promote neuroplasticity. Study II focused on decoding the phases of gait (swing and stance) from EEG responses elicited by the CAMS paradigm. Using Linear Discriminant Analysis (LDA) and Support Vector Machine (SVM), the study achieved a classification accuracy of 75% and 78%, respectively, in decoding the swing and stance phases of gait. Study III introduced a novel detection algorithm based on Complex Convolutional Neural Networks (C-CNN) for asynchronous offline CAMS BCI. The C-CNN method achieved high F1-scores for asynchronous operation. Median F1-scores for C-CNN were 0.88 (W=1s), 0.92 (W=2s), and 0.96 (W=3s), with corresponding False activation rates (FARs) of 0.34, 0.30, and 0.27. Additionally, larger stimulus frequency differences resulted in stronger visual BCI classification performance, with combinations (7.5 Hz, 12 Hz) and (8.57 Hz, 12 Hz) yielding the highest accuracies of 87% and 78%, respectively. These findings underscore the potential of the CAMS BCI paradigm in enhancing cortical excitability, eliciting responses for decoding gait phases, and improving asynchronous visual BCI performance while simultaneously engaging the movement related areas of the cortex. By providing a comprehensive investigation of the CAMS paradigm, this work contributes to existing knowledge and helps guide future clinical applications in neurorehabilitation.
The evolutionary and ecological factors that shape ectoparasite populations and communities at multiple scales
(University of Waterloo, 2024-11-12) Sauk, Alexandra
Although parasites are one of the most prolific and diverse consumer groups on the planet, they are often excluded from biodiversity surveys as they are difficult to detect and identify. This deficit limits our understanding of host-parasite relationships and parasite diversity. The vast diversity of host-parasite relationships means that many ecological and evolutionary forces may be at play, shaping the evolution of host and parasite in different ways and varying between species pairs. Bats and their ectoparasites provide a unique system to study the factors influencing parasite populations and communities. The different ecological niches and social behaviours of bats provide variation in the ectoparasites they encounter, and the selective forces experienced by the ectoparasites. I hypothesised that certain attributes of ectoparasite infections (e.g., ectoparasite diversity and infection level) are influenced by the life history traits of both host and ectoparasite and be the environmental restrictions of individual ectoparasite species. Using a collection of ectoparasites passively collected from bats throughout Atlantic Canada between 1999 and 2017, I quantified the ectoparasite communities of two bat species, Myotis lucifugus and M. septentrionalis, and used model-based inferences to assess the differences in infection of their two most common ectoparasites, the mite Spinturnix americanus and the flea Myodopsylla insignis. I found that both bat species had similar ectoparasite communities while S. americanus and M. insignis showed opposing trends in presence and abundance between the two bat species, in keeping with their different life history strategies. I also used a subset of this collection to compare how life history traits and host-parasite dynamics influence the genetic structure and biogeography of co-infecting ectoparasites. I found limited genetic structure with M. insignis exhibiting some isolation by distance between Labrador and Nova Scotia and S. americanus exhibiting regional differentiation between the island of Newfoundland and the mainland. I also provide a synthesis of the currently described bat ectoparasites in North America and an analysis of how host characteristics and environmental factors influence ectoparasite richness and geographic distribution. I found that estimated ectoparasite richness varies widely between host species but is influenced by sampling effort. Bat ectoparasite diversity appears consistent with the predictions of the latitudinal diversity hypothesis with a 3.4% decrease in species richness for every degree increase in latitude. Overall, my findings add to the evidence that ectoparasite populations and communities are shaped by life history traits of the host and ectoparasite. I suggest multidisciplinary collaborations between bat biologists, parasitologists, and taxonomists are necessary to collect ectoparasites and catalogue bat-ectoparasite associations to better understand the ecological and evolutionary forces that shape these communities and to better be able to conserve them in the face of ongoing threats from climate change and landscape changes.
Attributing Corporate Carbon Mitigation Outcomes to Substantive Decarbonization Actions through Change Analysis
(University of Waterloo, 2024-11-12) Lin, Meijie
Abstract As corporations increasingly disclose their environmental performance and claim to decarbonize their operations, it becomes challenging to distinguish substantive decarbonization actions from symbolic gestures that obscure business-as-usual operations. Despite numerous studies highlighting the prevalence of symbolic corporate carbon management, a clear method for measuring and comparing substantive corporate decarbonization action is still not well established. This study develops an outcome attribution framework using decomposition and decoupling analysis to measure substantive decarbonization actions that effectively reduce emissions. Using secondary panel data from a sample of firms listed on the Hong Kong Stock Exchange from 2018 to 2023, this study aims to: 1) analyze how changes in emissions can be broken down into changes in carbon intensity, energy intensity, and revenue; 2) evaluate the extent of effective corporate carbon mitigation outcomes that can be attributed to substantive corporate decarbonization actions; and 3) examine the correlation between substantive actions and emission reductions. The findings reveal a generally low level of substantive actions, aligning with previous research that suggests corporate climate actions are often more symbolic than substantive. More notably, the weak correlation between substantive actions and emission reductions underscores the limitation of using mitigation outcomes as a proxy for the effectiveness or substantiveness of corporate climate actions. This result emphasizes the influence of unintended external driving factors that may obscure symbolic actions and enable business-as-usual operations to persist under seemingly positive mitigation outcomes. The outcome attribution framework developed in this study offers a novel approach for researchers and decision-makers to measure and compare substantive decarbonization actions at scale, which enhances the decision-usefulness of the commonly disclosed metrics, provides clarity on the effectiveness of corporate decarbonization initiatives, and ultimately guides resources towards meaningful climate actions and advances best practices.
Fatigue of Aluminum Gas Metal Arc Welds in Electric Vehicle Battery Pack
(University of Waterloo, 2024-11-12) Burchat, Thomas
Aluminum extrusions, when strengthened with precipitation hardening, are an ideal material for lightweight structures. The gas metal arc welding (GMAW) process offers a cost effective and high-volume method of joining mating plates for large structural components. As the automotive industry is looking for lightweight structures to offset the increased weight of electric vehicle battery packs, it is crucial to understand the process limitations and resulting fatigue properties of aluminum GMA welds to ensure the structure outlasts the battery chemistry and warranty. High volume manufactured aluminum welds are controlled with weld acceptance criteria, which are in turn predicted with statistical representation of randomly tested samples. This research investigated the aluminum GMAW process window that consistently produces welds within the industry partner acceptance criteria and resulting microstructure. This research performed component level testing of 2.3 mm AA-6061-T6 mating plates in the tee joint and lap configurations under quasi static and cyclic loading conditions. The quasi-static testing revealed the influence of porosity on the maximum load before rupture of lap shear joints, and the failure location of the joint and lap joint geometries. The cyclic test results showed crack initiation behavior through the thickness of the heat affected zone (HAZ) when observed by digital image correlation (DIC) during testing. Fracture surface analysis revealed crack initiation zones along existing defects and preexisting cracks attached to the root area of the weld for both tee joint and lap joint samples. Structural stress methods are employed to correlate far field nodal force and moment derived stresses to the observed failure locations in thin sheet aluminum welds, excluding local effects. Load life data is translated to structural stress life data for 2.3 mm thick tested samples, as well as for additional 4mm and 8 mm thick samples provided by the industry partner. Stress life data is segregated based on a bending stress to total stress bending ratio into two distinct structural stress curves. Power law regression is used to calculate a line of best fit through each curve. Random samples configurations are excluded from a separate regression, which is used to predict the life of the excluded samples within 3 folds (3x) from tested sample life. Mean stress corrections are used to further collapse test data into single membrane and bending curves but applied thickness corrections increased observed scatter amongst test data.
A psychometric evaluation and application of a measure of food literacy among young adults
(University of Waterloo, 2024-11-11) Holmes, Martin
Background: Food literacy is an emerging study area encompassing the knowledge, skills, and attitudes required to navigate dynamic food systems. Food literacy has been suggested as a potential leverage point for improving diet quality and health outcomes. The emerging adult population, facing unique dietary and life transitions, is highlighted as an important group in public health research. Following calls for standard and well-evaluated measures of food literacy, a collaborative working group of public health nutrition practitioners in Ontario, Canada, led the development of a comprehensive food literacy measure, the FLit50, for use with young adults. To support the broad use of the measure in public health practice, assessment of the construct validity of the FLit50 and the development of a shortened version were desired by the public health nutrition practitioners. Objectives: The objectives of this dissertation were to: (1) evaluate the construct validity of the FLit50 measure among post-secondary students (Chapter 5); (2) analyze the characteristics of the FLit50 items to facilitate the development and evaluation of a shortened measure (Chapter 6); and (3) explore the demographic, income adequacy, studentship, and health correlates of food literacy among post-secondary students (Chapter 7). This work was undertaken in collaboration with the public health nutrition practitioners. Methods and results: The first study (Chapter 5) drew upon data from 457 post-secondary students in Ontario, Canada, to evaluate the measure's construct validity by assessing whether it could differentiate between groups hypothesized to have differences in food literacy. The FLit50 showed adequate construct validity, evidenced by higher median food literacy scores among students in food and nutrition programs (KW χ2) = 108, p < 0.001), women (KW χ2= 49.2, p < 0.001), those with adequate health literacy (KW χ2 = 20.6, p < 0.001), those with higher general health (KW χ2 = 49.5, p < 0.001), those with higher mental health (KW χ2 = 17.4, p < 0.001), and those experiencing food security in the past 12 months (KW χ2 = 21.9, p < 0.001), as hypothesized. No differences were observed by age (KW χ2 = 5.24, p = 0.63) or perceived income adequacy (KW χ2 = 4.21, p = 0.38). Differences in group means were observed as hypothesized for scores on items reflecting the underlying domains of food and nutrition knowledge and self-efficacy and confidence, but not food skills or ecological factors. The second study (Chapter 6) involved the application of the 2-parameter Item Response Theory, using data from postsecondary students (n=457) along with data collected from young adults across Canada during the initial development of the measure (n=351). Item difficulty (mean= -1.72 SD from the sample’s average food literacy ability level, range: -3.64 to 3.05 SD) and item discrimination (mean= 1.78, range: 0.33 to 8.43) characteristics were estimated for items on the FLit50. The parameters informed discussions with the public health nutrition practitioner partners to select sixteen items for inclusion in the shortened measure, the FLit16. The correlation coefficient between scores on the FLit50 and the FLit16 was estimated, and whether the FLit16 could differentiate among groups hypothesized to have different levels of food literacy, as per study 1, was examined. Scores from the two versions of the measure were strongly and positively correlated (Rho = 0.87, p < 0.01) and the short measure was able to differentiate among groups, consistent with the full measure. The third study (Chapter 7) drew upon data from the sample of postsecondary students to explore associations between demographic, income, studentship, and health characteristics, identified a priori based on the emerging food literacy literature, and food literacy scores using multiple linear regression analysis. Data from 413 students were included in these analyses after accounting for missing data on the characteristics of interest. Food literacy was assessed using the FLit50 measure, with a mean score of 42 of 49 points. Adjusting for other characteristics, food literacy was higher among women compared to men (β = 2.509, p < 0.001) and those who reported positive or neutral general health (β = 1.743, p < 0.001). Food literacy was lower among individuals identifying as East/Southeast Asian (β = -2.036, p < 0.001), South Asian (β = -2.409, p < 0.001), and other racial/ethnic identities (β = -1.568, p = 0.005) compared to those identifying as White. Food literacy was also lower among those who lived on-campus (β = -1.457, p = 0.073) and those experiencing food insecurity (β = -1.274, p = 0.004). Food literacy scores did not differ by age, income adequacy, domestic or international studentship, whether students attended college or university, household composition, or self-reported mental health status. The regression analysis yielded an R2 of 0.403, indicating that 40% of the variance in food literacy scores was explained by this model, with an overall significance of F(15, 396 DF) = 17.79, p < 0.001. Conclusions: This dissertation continues the work of the collaboration of public health nutritionists by furthering two of its main aims: establishing the construct validity of the FLit50 and developing a shortened measure that demonstrates construct validity. The availability of two well-evaluated measures presents opportunities to better understand and monitor food literacy in emerging adults and assess associations with factors such as diet quality.
A Test Collection for Offline Evaluation of Recommender Systems
(University of Waterloo, 2024-11-07) Chamani, Houmaan
Recommendation systems have long been evaluated by collecting a large number of individuals' ratings for items, and then dividing these ratings into test and train sets to see how well recommendation algorithms can predict individuals' preferences. A complaint about this approach is that the evaluation measures can only use a small number of known preferences and have no information about the majority of recommended items. Prior research has shown that offline evaluation of recommendation systems using a test/train split methodology may not agree with actual user preferences when all recommended items are judged by the user. To address this issue, we apply traditional information retrieval test collection construction techniques for movie recommendations. An information retrieval test collection is composed of documents, search topics, and relevance judgments that tell us which documents are relevant for each topic. For our test collection, each search topic is an individual who is looking for movies to watch. In other words, while the search topic is always ``Please recommend me movies that I will be interested in watching,'' the context of the search topic changes to be the individual who is requesting the recommendations. When document collections are too large to be completely judged by assessors, the traditional approach is to use pooling. We followed this same approach in the construction of our test collection. For each individual, we used their existing profile of rated movies as input to a wide range of recommendation algorithms to produce recommendations for movies not found in their profile. We then pooled these recommendations separately for each person and asked them to rate the movies. In addition to rating, we also had each individual rate a random sample of movies selected from their ratings profile to measure their consistency in rating. The resulting new test collection consists of 51 individual ratings profiles totaling 123,104 ratings and 31,236 relevance judgments. In this thesis, we detail the creation of the test collection and provide an analysis of the individuals that comprise its search topics, and we analyze the collection's relevance judgments as well as other aspects.
Experimental Characterization of Sample Tubing Dynamics for the Improvement of Droplet Microfluidic Feedback Control Systems
(University of Waterloo, 2024-11-05) Hahn, Dylan
This thesis presents the development of an experimental methodology to characterize pressure transient dynamics across liquid sample tubing in the plant of a pressure-driven droplet microfluidic feedback control system (PDMFCS). To progress the PDMFCS towards being a widely adopted fluidic analysis tool for non-expert end-users in various biochemical fields, i.e. progressing the PDMFCS towards modularity, will require utilization of an accurate plant model to establish informed and robust control system design procedures. Increased accuracy in the plant model can be obtained through development of experimental methods to characterize the dynamics associated with the plant components. Previous PDMFCS implementations have approximated the sample tubing dynamics using a hydrodynamic equivalent circuit model (HECM), but did not experimentally validate this model. As well, pressure transient studies performed for other fluid applications do not model a flow scenario physically similar to that occurring through the sample tubing during PDMFCS operation, further justifying the need for this present study. Pressure transient dynamics across the sample tubing of the PDMFCS plant were found to be characterized as an approximately linear first-order system with transport lag through estimation of a transfer function (TF), with 95% confidence in uncertainty in the estimated parameters, from an experimental frequency response obtained by simultaneously measuring pressure waves at the inlet and outlet of the sample tubing. Decreasing the average inlet pressure, increasing the tubing length to inner diameter ratio, or increasing the fluid viscosity, resulted in a decrease of the corner frequency (an increase in the time constant) of the frequency (step) response of the experimentally estimated TF. Comparing experimentally estimated TF dynamics to those predicted by the HECM showed that, due to the assumption of hydrodynamic steady-state flow inherent to its derivation, the HECM fails to quantitatively approximate the pressure transient dynamics across the sample tubing. The primary conclusion of this study is that the experimentally estimated TF should be used, instead of the HECM, to approximate the sample tubing dynamics within the PDMFCS plant model. Using the experimentally estimated TF to approximate the pressure transient dynamics across the sample tubing should improve the plant model accuracy, such that informed and robust control system design methodologies can be developed for the PDMFCS, which will enhance the modular potential of the system.

Browse

Recent Submissions