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Recent Submissions
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.
Web Accessibility baby steps: anyone can conduct audits even with limited resources
(2024-07-17) Cefrin da Silva, Israel Jose; Voichita, Stefaniada; Sivakumaran, Mayuri
In today's digital landscape of academic libraries, web accessibility has become a legal requirement under different legislation. Ensuring equal access to digital scholarship, and online library services of libraries for people, with or without disabilities, is crucial. However, conducting web accessibility audits even on our own websites can seem daunting or too tech savvy, especially for individuals with limited technical expertise and resources to afford expensive monitoring tools. This poster, titled "Web Accessibility baby steps: anyone can conduct audits even with limited resources," aims to show how to run basic but effective accessibility audits in a sustainable manner. The main goal is to demonstrate that, using an easy approach, anyone in the library can perform an initial but comprehensive web accessibility audit. It is focused on manual testing techniques, particularly keyboard-only testing which makes the process accessible to all. The process is structured into 3 critical components as follows: Tabbing Order: how to assess tabbing order to ensure logical navigation. Tab Focus: the importance of visible focus indicators and how to verify their effectiveness using a keyboard. Linking/button elements: We explain how to assess link accessibility and activate links using only a keyboard. For those who would like to dive deeper into the subject, they will be provided with links to valuable accessibility tools, guides, and tutorials.