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Recent Submissions

Access status: Embargo ,
DESIGN, DEVELOPMENT, AND EVALUATION OF A NOVEL HYDRAULIC SPRAY SYSTEM FOR MACHINE VISION-BASED REAL-TIME TARGET APPLICATION OF PESTICIDES ON BOOM SPRAYERS
(2026-04-30) Maambo, Humphrey; Not Applicable; Doctor of Philosophy; Faculty of Agriculture; Not Applicable; Mohamed Khelifi; Not Applicable; Travis J. Esau; Yves Leclerc; Madan Avulapati; Ahmad Al-Mallahi
A novel spraying mechanism assembly designed for machine vision–based, real time target application of pesticides on self propelled boom sprayers was developed and evaluated. The research addressed key limitations in modern precision spraying – such as nozzle valve actuation latency, boom pressure instability, and spray accuracy at higher ground speeds. The study investigates how 3D spray nozzles and a controller area network (CAN)–based feed forward pressure stabilization system can enhance timing accuracy and spraying at prescribed application rate. A comprehensive experimental investigation was conducted to characterize and optimize spray atomization parameters, including droplet size, velocity, breakup behaviour, spray coverage, and collision outcomes, across system pressures ranging from 275 to 482 kPa. Results show that 3D nozzles generate backward inclined spray patterns that effectively compensate for mechanical nozzle valve latency during real-time operation. A system pressure of 275 kPa emerged as the optimal pressure due to coarser droplets, minimized drift risk, favourable droplet coalescence, and reduced pumping power requirements. A CAN compatible feed forward pressure stabilization technique was developed to regulate boom pressure in anticipation of nozzle activation events, outperforming conventional feedback based systems by reducing pressure deviations by up to 63% and shortening pressure settling times by up to 5.7 fold. The system was prototyped on a 60 nozzle target spraying boom as an add-on system and validated through laboratory and field experiments, including tests on artificial and real Colorado potato beetle (CPB) targets. Field results demonstrated accurate real time actuation, consistent droplet placement, and practical integration of machine vision detection with hydraulic and electronic control subsystems. Overall, the research establishes an effective, scalable framework for deploying real time, target specific pesticide application technology that reduces chemical use, improves timing accuracy, and advances the feasibility of precision pest management in commercial agriculture
Access status: Embargo ,
Testing Implicit Safety Science Assumptions in Maritime Waterway Risk Control Options: An Empirical Analysis of PAWSA Reports
(2026-04-29) Adeli, Mehdi; Not Applicable; Master of Science; Department of Industrial Engineering; Not Applicable; n/a; Not Applicable; Dr. Jakub Montewka; Dr. Ron Pelot; Dr. Floris Goerlandt
Maritime waterway safety remains a critical concern due to the severe human, environmental, and economic consequences of shipping accidents. The Ports and Waterways Safety Assessment (PAWSA) method relies on expert judgment to propose and evaluate Risk Control Options (RCOs), including their perceived Risk Reduction Effectiveness (RRE). This thesis analyzes an empirical dataset of 50 unique RCOs extracted from 21 PAWSA reports (2016–2023) using content analysis and a tailored Strength-of-Evidence (SoE) framework. Results show substantial variation in RRE and SoE, with many RCOs lacking strong empirical support and only a small subset demonstrating both high effectiveness and strong evidence. Further analyses examine RCOs across actor groups, hierarchy of controls, and risk management phases. Findings indicate that expert judgments only partially align with common safety science assumptions. This study contributes to understanding how expert judgment reflects underlying safety concepts and supports more evidence-informed decision-making in maritime risk management.
Access status: Embargo ,
DRINKING WATER TREATMENT ADAPTATION FOR LEAD CORROSION CONTROL UNDER CLIMATE-DRIVEN WATER QUALITY CHANGE
(2026-04-30) Hood, Kalli; Not Applicable; Doctor of Philosophy; Department of Civil and Resource Engineering; Not Applicable; Dr. Kelsey Pieper; Yes; Dr. Heather Murphy; Dr. Amina Stoddart; Dr. Graham Gagnon
Lead in drinking water remains a public health concern worth mitigating. Drinking water treatment and distributed water chemistry are key determinants of lead release. Gradual and acute climate-driven changes in source water quality, treatment technology and regulatory targets create new challenges for corrosion control related to natural organic matter, coagulant selection, inorganic compounds, and excess product in wastewater. The goal of this work was to investigate how drinking water treatment adaptation influences lead corrosion control with an emphasis on organic matter and treatment strategies for enhanced removal, orthophosphate-based corrosion inhibitors, trade-offs with sequestration, and the feasibility of zinc-reduction. Pilot- and bench-scale studies in combination with time-series modelling and screening-level exposure projections were used to evaluate lead response to environmental events and experimental treatments. Following an extreme precipitation event, natural organic matter increased in source water and was associated with a prolonged elevation in total lead in a model distribution system and projected increases to short-term exposure risk. Enhanced organic matter removal via granular activated carbon improved lead control in a bench-scale reactor of galvanic lead solder. Equivalent total organic carbon removal was achieved at lower product doses of a chloride-based (polyaluminum chloride) coagulant relative to sulfate- based (alum), but was linked with increased galvanic lead corrosion. Orthophosphate- silicate may be an alternative to blended phosphate for systems needing to manage discolouration due to high iron/manganese, though risks of increased dissolved lead must be considered. In low-alkalinity water, reducing zinc in orthophosphate inhibitors may be feasible without compromising lead or cement corrosion, but may result in small increases in copper. These reductions could offer a more sustainable option with lower burden for wastewater treatment. This work demonstrated shifts in source water quality and treatment processes like coagulation, filtration, corrosion inhibitors and sequestrants can be protective or destabilizing for lead control and infrastructure maintenance. Utilities should consider whole-system trade-offs in lead control, treatment performance, and downstream sustainability during process adaptation or redesign.
Access status: Open Access ,
Microfluidic Systems for Long-Term and High Spatiotemporal In Situ Total Alkalinity Measurement in Marine Environments
(2026-04-30) Motahari, Shahrooz; Yes; Doctor of Philosophy; Department of Electrical & Computer Engineering; Not Applicable; Dr. Adrian M. Nightingale; Yes; Dr. Michael Freund; Dr. Ghada Koleilat; Dr. Vincent Sieben
Atmospheric carbon dioxide (CO₂) levels continue to rise, altering the global carbon cycle and driving ocean acidification. The ocean absorbs a large fraction of emitted CO₂, making accurate measurement of marine carbonate chemistry essential. Total alkalinity (TA) is a key parameter of the carbonate system because it controls seawater buffering capacity, playing a critical role in carbon uptake and air–sea CO₂ exchange. However, most TA measurements are still performed in laboratories using discrete water samples, limiting sampling frequency and spatial coverage in dynamic marine environments. This thesis presents the first field deployment of a microfluidic Lab-on-Chip (LoC) TA analyzer during an Ocean Alkalinity Enhancement trial in Halifax Harbour. The system performed closed-cell, multi-point spectrophotometric titrations in a stop-flow configuration using integrated syringe pumps, solenoid valves, and on-chip optical absorbance cells. Over 40 days, the analyzer completed 314 TA measurements and 52 onboard certified reference material (CRM) measurements, generating approximately 3,300 optical readings. This autonomous in situ platform demonstrated high-resolution monitoring of alkalinity variability that is difficult to achieve with traditional bottle sampling. To improve performance for long-term autonomous deployment, two design advancements were developed. First, a compact Dean-flow micromixer was designed and experimentally validated to enhance mixing while reducing channel length and internal volume relative to the original ~300 µL stop-flow mixer. The design was modeled using COMSOL Multiphysics and validated through bench-top TA measurements of certified reference materials. Second, the first reported droplet-based LoC TA sensor was developed. The system performs multi-point spectrophotometric titrations in segmented flow, where each droplet represents a titration point. Superhydrophobic surface modification of PMMA channels enabled stable droplet formation. This droplet architecture significantly reduces sample and reagent consumption while increasing sampling frequency, making it well suited for long-term, high-spatiotemporal-resolution carbonate monitoring in marine environments. Overall, this work demonstrates that microfluidic Lab-on-Chip systems provide an efficient and practical solution for autonomous, high spatiotemporal, total alkalinity monitoring in marine environments.
Access status: Open Access ,
Understanding Optimism: Winston Churchill and the Evolution of British Strategic Bombing Warfare Against Germany, 1914-1941
(2026-04-30) Wang, Yufan; Not Applicable; Master of Arts; Department of History; Not Applicable; na; Not Applicable; Paul Doerr; Gregory Hanlon; Denis Kozlov
This thesis examines the origins, evolution and early effectiveness of British strategic bombing warfare against Germany from 1914 to 1941. It traces the intellectual and institutional foundations of air power, from the creation of the Royal Air Force, which included the Independent Force and later Bomber Command. The treatise situates British air policy within the broader framework of interwar grand strategy, highlighting the expectations that bombers could deter enemies and deliver decisive results. Particular emphasis is placed on Winston Churchill, whose support for strategic bombing reflected both strategic calculation and personal inclination towards offensive actions. The work evaluates the limited effectiveness of strategic bombing from both British and German perspectives. Although early results fell short of expectations, British optimism and continued investment were not irrational given contemporary theorical and technological constraints. Ultimately, effective inter-service cooperation is more important than over reliance on single magic weapon in winning a war.
Access status: Embargo ,
CHEMICAL MODIFICATION APPROACHES IN ORGANOMETAL HALIDE PEROVSKITE MATERIALS AND SOLAR CELLS
(2026-04-30) Abdelmageed, Ghada; Yes; Doctor of Philosophy; Department of Process Engineering and Applied Science; Not Applicable; Dr Bryan Koivisto; Yes; Dr Suzanne Budge; Dr Mita Dasog; Dr Ghada Koleilat
Metal halide perovskites are promising for future photovoltaics due to their optical absorption, carrier diffusion, and tunable bandgaps. Despite efficiency gains, instability and defects remain barriers. This thesis explores chemical modifications, additive engineering, and surface passivation to improve their optoelectronic properties and stability. First, the study examined how film formation and surface chemistry affect passivation by linking deposition techniques to the results. Oleic acid was used as a hydrophobic ligand for the surface passivation of MAPbI3 films prepared by different deposition techniques. Our findings showed that the success of surface treatments depends heavily on film morphology, and that customized passivation strategies notably improve resistance to humidity and stability. Next, we explored additive engineering through sulfur-based molecular engineering with thiazoline to boost crystallization, passivate halide vacancies, and enhance interfacial charge extraction. Strong Pb–S bonds lowered trap densities, increased carrier lifetimes, and led to high-performance devices with over 22% efficiency and better stability under humid and illuminated conditions. Finally, we synergistically combined additive engineering and surface passivation techniques by using carbamide-based additives to improve crystallization and reduce defect density in the bulk and 2D capping layer, passivating surface defects. These treatments resulted in significant improvements in charge-carrier lifetimes and recombination dynamics, emphasizing the importance of controlling defect formation during film growth. Overall, this research shows that incorporating specific chemical modifications into both the bulk and interfaces of perovskite films is an effective strategy to reduce recombination losses and improve environmental stability. By elucidating the connections between molecular design, film formation, and device physics, this thesis provides a detailed framework for creating high-efficiency, durable perovskite solar cells and supporting their development toward scalable, practical use.