Faculty of Graduate Studies Online Theses

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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
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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.
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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.
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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.
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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.
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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.
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Extreme Water Level Predictions on the Nova Scotian Coastline using a Bayesian Hierarchical Model
(2026-04-29) Sarhan, Fatma; Not Applicable; Master of Science; Department of Mathematics & Statistics - Statistics Division; Not Applicable; n/a; Not Applicable; Dr. Bruce Smith; Dr. Edward Susko; Dr. Orla Murphy; Dr. Jonathan Jalbert
The modelling of extreme coastal water levels is crucial when it comes to flood risk preparations, management, and defense design in Nova Scotia. Given the increasing frequency of flooding events in this region, it is essential to estimate their potential magnitude to mitigate their potentially devastating consequences. In extreme value analysis, return levels are quantifications of risk and represent the level that is expected to be exceeded once on average in a given time period. The challenge is that these extreme events are rare, and the data are limited and often incomplete. To address this challenge, a Bayesian hierarchical extreme value model is developed where information on extreme events is shared spatially across locations. By incorporating atmospheric covariates as physical drivers of extreme water levels, this research aims to establish a well informed Bayesian Hierarchical Model that enhances estimation precision and enables return level predictions for ungauged locations across the Nova Scotian coastline.
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Improving Lifetime of Lithium-Ion Cells with Electrolyte Additives
(2026-04-30) Azam, Saad; Not Applicable; Doctor of Philosophy; Department of Chemistry; Not Applicable; Betar Gallant; Not Applicable; Michael Metzger; Alex Speed; Michael Freund; Jeff Dahn
Lithium-ion batteries are the dominant technology for electric vehicles and grid energy storage, yet improvements in lifetime across wide voltage and temperature ranges remain essential for next-generation applications. Electrolyte additives improve cell lifetime by modifying the electrode–electrolyte interphases, which govern degradation processes including lithium inventory loss, transition metal dissolution, impedance growth, and electrolyte decomposition. In this work, nearly 25 novel additives and more than 100 additive combinations were evaluated in lithium-ion pouch cells containing layered oxide cathodes (LiNixMnyCozO2 or NMC) and olivine cathodes (LiFePO4 or LFP). Cells were tested under demanding conditions including high voltage operation up to 4.4 V and elevated temperatures up to 70 °C. For LFP/graphite cells cycled at 70 °C, 4% vinylene carbonate (VC) emerged as an effective additive formulation. The improved performance is attributed to residual VC in the electrolyte, which suppresses the formation of lithium alkoxide species that promote Fe dissolution from the LFP positive electrode and accelerate solid electrolyte interphase growth and lithium inventory loss. While cells containing 4% VC achieved about 1500 cycles at 70 °C, they failed at room temperature due to the formation of a highly resistive negative electrode surface impedance. To overcome this limitation, a novel additive, bis(1,3,2-dioxathiolane-2,2-dioxide) (bis-DTD), was synthesized by the author and investigated as a co-additive with lower VC concentrations. In LFP/graphite cells, the combination of 2% VC + 2% bis-DTD delivered a lifetime at 70 °C comparable to that obtained with 4% VC, while maintaining stable cycling at room temperature due to lower charge transfer resistance. This formulation enables LFP/graphite cells to operate over a wider temperature range. Bis-DTD also dramatically improved lifetime of LiNi0.65Mn0.3Co0.05O2/graphite pouch cells cycled to 4.4 V, where electrolytes containing 2% bis-DTD retained more than 80% capacity after over 2500 cycles at 40 °C and over 5000 cycles at 20 °C. In sodium-ion cells using layered oxide cathodes paired with hard carbon, bis-DTD improved capacity retention to more than 92% after about 1100 cycles at 40 °C. This single electrolyte additive has demonstrated significant lifetime improvements across diverse lithium-ion and sodium-ion chemistries, highlighting the potential of rational electrolyte additive design for next-generation energy storage systems.
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EXAMINING THE ROLE OF PROFESSIONAL NETWORK SIGNALS IN JOB SEEKERS BIAS AGAINST HIJAB-WEARING RECRUITERS
(2026-04-28) Sharifi, Sara; Not Applicable; Master of Science; Rowe School of Business; Received; N/A; Not Applicable; Anika Cloutier; Colin Conrad; Dana Kabat-Farr
Research on workplace discrimination shows that hijab-wearing Muslim women face disadvantages in hiring, yet is known bias toward in positions of authority. This study examined whether visible religious identity (hijab vs. no hijab) affects evaluations of recruiters and engagement with them in a professional setting. Drawing on the stereotype content model, implicit leadership theory, and selective incivility, we predicted that hijab visibility would lower competence, warmth, and leadership, and reduce engagement, willingness to connect and message tone and length. We also hypothesized mediation by attentional focus and moderation by Islamophobia. One hundred fifty-three participants completed an online experiment involving a simulated LinkedIn recruiter profile, a message-writing task, and a creativity task as a proxy for attention. Results showed no significant differences across conditions, and mediation and moderation were unsupported. However, higher creativity predicted more positive message tone. These findings suggest context shapes bias expression and highlight directions for future research.
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Transforming Waste Materials into Supplementary Cementitious Materials: An Approach to Mitigate the Carbon Footprint of Cementitious Composites
(2026-04-30) Jafari, Alireza; Yes; Doctor of Philosophy; Department of Civil and Resource Engineering; Not Applicable; Rahil Khoshnazar; Yes; Kyle Tousignant; George Jarjoura; Pedram Sadeghian
This doctoral research investigates the transformation of waste materials into cement alternative to reduce the carbon footprint of cementitious composites while maintaining structural and durability performance. The study focuses on recycled gypsum drywall (RGD), untreated and copper-treated biochar, and hydrochar derived from spent coffee grounds as partial replacements for ordinary Portland cement (OPC). A comprehensive experimental program was conducted at both mortar and concrete scales. More than 490 mortar specimens, with a dimension of 50×50×50 mm, and over 360 concrete cylinders, with a diameter of 100 mm and height of 200 mm, were prepared and tested to evaluate compressive strength, bulk density, ultrasonic pulse velocity (UPV), stress–strain behavior, dimensional stability, and microstructural evolution. Cement replacement levels reached up to 50% for fly ash, 30% for recycled gypsum drywall (RGD), and 15% for biochar or hydrochar. Carbonaceous materials were evaluated using both direct cement replacement and additive incorporation approaches. Engineered interface modification using copper-treated biochar was also investigated to enhance interfacial transition zone stability. Results indicate that optimized OPC-RGD–fly ash systems improved long-term compressive performance compared with OPC–RGD blends, while maintaining dimensional stability. Low biochar dosages (≤5%) exhibited filler and internal curing effects, whereas higher replacement levels introduced stiffness-sensitive behavior due to the porous and low-modulus nature of carbonaceous inclusions. Hydrochar performance was governed by interaction mechanisms with other cement alternatives, where synergistic cement alternative systems mitigated long-term deterioration. Structural-scale stress–strain analysis demonstrated that peak broadness, elastic modulus, and post-peak response were sensitive to carbonaceous inclusion content, highlighting the need for dosage optimization in structural applications. Durability was evaluated under drying, marine, and sustained 5% sodium sulfate exposure for up to 6000 hours. Measurements showed bulk density variations remained within approximately ±2.5% of baseline values, with observed transitions from pore-filling densification to stiffness-sensitive disturbance under prolonged sulfate exposure. Environmental assessment revealed that incorporating RGD and high-volume fly ash mixtures reduced carbon dioxide emissions by up to 55% relative to conventional OPC concrete. Overall, this thesis establishes a mechanistic framework for stabilizing sulfate-bearing and carbonaceous waste materials in low-carbon cementitious systems while satisfying structural performance requirements.
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Advancing eDNA Sampling for Biodiversity Monitoring
(2026-04-30) Ebanks, Tori; Not Applicable; Master of Applied Science; Department of Electrical & Computer Engineering; Not Applicable; N/A; Not Applicable; Dr. Mae Seto; Dr. Colin O'Flynn; Dr. Vincent Sieben
Environmental DNA (eDNA) is an important tool used in marine biodiversity monitoring. eDNA samplers offer a more cost effective and efficient means of the collection and concentration stages in the eDNA pipeline. A review of existing devices was done to compare their performance and features. This thesis describes the theory that determine the eDNA Sampler's effective flow rate, as well as using optics as a feedback mechanisms in eDNA sampling. The relationships between the dimensions of the fluid channel, the pressure source and flow rate were examined, and the physical limitations of flow through a membrane and filter cake buildup were also explored. This theory was supported by bench testing whose experimental results aligned with theoretical calculations. A submersible sampler was designed with this information, and was tested in the Bedford Basin in Halifax, Nova Scotia, Canada. The device captured samples at relatively high flow rates, which were successfully sequenced. The sequencing data from this instrument is presented and compared to samples captured by manual sampling and a previously tested instrument. The use of optics as a feedback mechanism during sampling was explored and showed favorable results. The results from this thesis will hopefully prove informative to the developers of eDNA samplers to refine instrument designs.
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SOCIO-SPATIAL EQUITY AND SOCIAL ENGAGEMENT IN SOLAR PHOTOVOLTAIC (PV) ADOPTION IN HALIFAX, NOVA SCOTIA: A MIXED METHODS STUDY
(2026-04-29) Blagogie, Lewis; Not Applicable; Master of Planning Studies; School of Planning; Received; Dr. Stanley Asah; Not Applicable; Dr. Mikiko Terashima; Dr. Chad Walker
Both globally and in Canada, inequitable access to residential solar photovoltaic (PV) systems has remained a persistent challenge to achieving a just energy transition. Yet limited empirical research has examined how a combination of economic, demographic, social, and spatial factors may interact to shape solar adoption, especially in Canada. To address this gap, I used mixed methods to investigate household solar PV adoption in Halifax, Nova Scotia. The initial quantitative phase analyzed survey data (n=158) from solar adopters to understand [in]equity and socio-spatial patterns of uptake. For example, comparisons between survey data and Halifax census-based community data revealed that solar PV adoption is skewed toward older, married, and highly educated homeowners with higher household incomes. Correlation results, however, indicate that income alone explains an extremely limited share of the variation in PV installations (p >.320), suggesting that other factors may shape adoption patterns. Follow-up interviews (n=16) designed to build on quantitative findings and shaped by the existing literature as well as a spatial analysis of survey respondents provided critical explanatory insight into these findings. Participants emphasized the importance of neighbourhood visibility (i.e., passive peer effects) and interpersonal interactions with friends and peers (i.e., active peer effects) in shaping adoption decisions. Friends frequently acted as trusted information brokers, while visible installations within neighbourhoods signaled technological legitimacy and reduced perceived risk. These findings suggest that efforts to expand solar adoption may benefit from approaches that harness community-level social dynamics.
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Tribological Evaluation Of Additively Manufactured Alumina Ceramics Processed Using Digital Light Processing
(2026-04-29) David, Achilles Marian Sonica; Not Applicable; Doctor of Philosophy; Department of Mechanical Engineering; Not Applicable; Dr Tom Coyle; Yes; Dr John Frampton; Dr Ted Hubbard; Dr Kevin Plucknett
The current thesis aims to address the lack of wear-response data for additively manufactured technical ceramics in literature, by using digital light processing (DLP) technology to additively manufacture alumina (Al2O3). Parts were first modelled using SolidWorks software, fabricated, and with subsequent thermal treatments, produced dense sintered parts even with 49 vol% solids loading. Firstly, the impact of build orientation and layer thickness in controlling the tribological response were evaluated by printing samples parallel (0°) and perpendicular (90°) to the build plate, and it was found that the samples exhibited distinct surface topographies and near-isotropic thermal responses. Wear mechanisms were found to be a combination of two- and three-body abrasion, adhesive material transfer, and fatigue-induced spallation. Nanoscratch analysis confirmed that the surface containing tribolayer offers mechanical protection approaching that of the polished surface. Then, the above study was complemented by printing samples between 0° and 90° with 15° increments. Wear tests indicated that 45° was the worst performing sample which was rectified by adjusting the layer thickness to match the pixel size of the print strategy of DLP (35 µm) thereby eliminating secondary step structures; this strategy saw an improvement in the counter face wear response as well. Furthermore, designing micro-patterns on the surface proved that staggering, chamfering, having a less-sharp angle seen in hexagonal voids (i.e., 120° as compared to squares with 90° edges) reduced wear, as these patterns trap the tribolayer and wear debris better, which then potentially act as a lubricant, influencing the coefficient of friction. Specially designed wave patterns exploited their geometry and alumina’s hardness to substantially reduce wear, despite the absence of tribolayer formation. Finally, a strengthening mechanism was studied by adding liquid phase forming additives and platelets to induce grain alignment and texture development during sintering. It was found that build orientation highly influenced the templated grain growth, thermal expansion behaviour, and surface morphology. All these modifications helped in understanding the wear response, tribolayer formation, wear mechanisms involved, and orientation dependent anisotropic behaviour of additively manufacture alumina. These findings are novel and are useful in advancing the knowledge of the scientific community.
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Development of full-scale machine vision scheme of multi-camera systems on boom sprayer for real-time management of Colorado Potato Beetles
(2026-04-28) Hassan, Imran; Not Applicable; Doctor of Philosophy; Faculty of Agriculture; Not Applicable; Mark Eramian; Not Applicable; Qamar Zaman; Khalil Al-Mughrabi; Ahmad Al-Mallahi
Precision agriculture demands site-specific pest management to reduce chemical inputs and environmental harm, yet real-time detection of small insect pests from mobile platforms re-mains challenging. The Colorado potato beetle (CPB), measuring less than 10 mm in body length, is among the most economically destructive pests in potato production globally and has developed resistance across all major insecticide classes. This research addresses the gap between laboratory-validated detection algorithms and field-deployable systems by developing, integrating, and evaluating a machine vision scheme for real-time CPB detection under commercial operating conditions. A field dataset was constructed from imagery captured using static handheld and moving sprayer-mounted cameras across two growing seasons, with bounding-box annotation under variable lighting, diverse canopy structures, and natural backgrounds. An image-cropping-based pre-processing technique was developed to preserve fine-scale morphological features suppressed by conventional input resizing, directly addressing the tiny object detection challenge in high-resolution agricultural imagery. Three deep learning architecture — YOLOv5, YOLOv7, and Faster R-CNN — were trained and benchmarked; YOLOv5 was selected for deployment on its favorable accuracy–latency trade-off, achieving 78 % accuracy on independent test data while sustaining real-time throughput. A modular software pipeline was engineered for concurrent multi-camera stream processing, combining TensorRT-accelerated inference with deterministic spray command generation and network-based communication with sprayer control systems. End-to-end latency measured approximately 120 milliseconds across four simultaneous camera feeds. Full-scale machine vision scheme deployment was implemented on a Case IH Patriot 3240 boom sprayer with eight machine vision systems across a 30-meter boom, each handling three to four downward-facing cameras. Engineering challenges resolved included distributed power supply, environmental enclosure de-sign, boom folding compatibility, and synchronized multi-unit operation under field vibration. Field validation at a commercial spraying speed of 2.7 m/s confirmed stable real-time operation, with detection accuracy exceeding 80 %, precision near 90 %, and recall approaching 90 %. Furthermore, a novel five-crop dataset expansion technique increased effective training data fivefold while preserving object scale and introducing natural background diversity; benchmarking with state-of-the-art YOLOv11 architecture demonstrated mean average precision exceeding 85 % at standard IoU thresholds. This research establishes a validated framework for insect-specific precision spraying, with contributions in tiny object detection, real-time multi-camera processing, and mobile agricultural system integration.
Access status: Open Access ,
Multimodal Representation Learning for Mental Health: Transfer Learning, PEFT, and Contrastive Learning
(2026-04-28) Naderi Khorshidi, Habibeh; Not Applicable; Doctor of Philosophy; Faculty of Computer Science; Not Applicable; Dr. Diana Inkpen; Not Applicable; Dr. Evangelos Milios; Dr. Sageev Oore; Dr. Stan Matwin; Dr. Frank Rudzicz
This thesis addresses the challenge of learning effective multimodal representations in low-resource clinical settings by leveraging implicit supervision from paired modalities and introducing adaptive fusion mechanisms based on Mixture-of-Experts (MoE). Focusing on mental health assessment, it utilizes clinical audio interviews from parents and children to jointly model speech and language signals for predicting emotion, sentiment, and higher-level psychological and cognitive outcomes under conditions of data scarcity and class imbalance. In collaboration with the Department of Psychiatry at Dalhousie University, we curate a dataset of parent-child clinical interviews annotated at both segment and document levels, including fine-grained labels for emotion recognition, sentiment analysis, and criticism detection, as well as higher-level diagnostic outcomes such as ADHD, depression, and bipolar disorder. The thesis systematically investigates transfer learning, parameter-efficient fine-tuning (PEFT), and contrastive audio-text learning for multimodal representation learning. We first conduct a comprehensive study of transfer learning using 29 pre-trained language models and 22 audio models, evaluating their effectiveness under various adaptation strategies and analyzing the impact of limited and imbalanced data. Building on this, we explore PEFT as a more efficient alternative, applying six techniques, LoRA, AdaLoRA, OFT, LoHa, LoKr, and IA3, across multiple models. PEFT consistently outperforms conventional transfer learning, yielding improvements of +1.41\% and +0.8\% in average AUC on parent and offspring data, respectively. Finally, we propose a three-stage contrastive learning framework for multimodal representation learning. The approach combines unimodal encoding, cross-modal contrastive alignment, and downstream task learning with a MoE architecture that adaptively integrates modality-specific information. Across all evaluated tasks, the proposed frameworks consistently outperform strong unimodal and multimodal baselines, demonstrating the effectiveness of adaptive multimodal learning for mental health assessment in low-resource settings.
Access status: Open Access ,
THE APPLICATION OF PALEOLIMNOLOGY TO INFORM FRESHWATER MANAGEMENT: THE CASE OF URBAN LAKES IN HALIFAX REGIONAL MUNICIPALITY, NOVA SCOTIA, CANADA
(2026-04-28) Hipwell, Kathleen; Not Applicable; Master of Environmental Studies; School for Resource & Environmental Studies; Not Applicable; Dr. Josh Kurek; Yes; Dr. Alana Westwood; Dr. Andrew S. Medeiros
Watershed-scale stress from urbanization can negatively impact ecosystem services communities rely on. Yet, a lack of historical context for individual-lake conditions impedes management planning that promotes evidence-based restoration/remediation targets and the efficient allocation of resources. Halifax Regional Municipality (HRM) Nova Scotia, Canada, has hundreds of lakes that are increasingly influenced by residential development, and most lakes in the urban/suburban core are developed to some degree. Here, I assessed surface sediment subfossil chironomid assemblages (Diptera: Chironomidae) from 40 HRM lakes and used a development index to determine if there is a relationship between assemblage structure and watershed development level. Chironomid assemblages were analyzed to understand the broader context of urban influence and to identify lake-specific environmental stressors that influence assemblage structure with water quality parameters for a subset of 29 lakes. Through the additional biostratigraphic analysis of three lakes we used paleolimnology to fill the gap in long-term monitoring data and to infer the influence of watershed development on urban lakes (Chocolate Lake and Settle Lake lie in residentially developed watersheds, and Spider Lake is in an undeveloped watershed). I found that chironomid assemblages followed a productivity gradient with development level, and that conductivity and ions were the primary drivers explaining variation in surface sediment assemblages. In the two lakes in developed watersheds, shifts in chironomid assemblages over time reflected documented patterns of human disturbance and indicate increased productivity. In contrast, the lake in an undeveloped watershed has remained oligotrophic throughout its history. Our results could facilitate informed decisions related to restoration/remediation targets and assist in the planning and management of freshwater resources.
Access status: Open Access ,
The Marine Predation, Migration, and Habitat Use of Inner Bay of Fundy Atlantic Salmon (Salmo salar) Kelts
(2026-04-23) Brown, Caliyena; Not Applicable; Master of Science; Department of Biology; Not Applicable; Tommi Linnansaari; Not Applicable; Marc Trudel; Sarah Tuziak; Sarah Fortune; Robert Lennox
Atlantic salmon (Salmo salar) populations have declined across much of their range, and the inner Bay of Fundy (iBoF) population has experienced one of the most severe collapses in North America. Despite supplementation-based recovery efforts restoring juvenile freshwater abundance, the number of adults returning to spawning rivers remains critically low and repeat spawners are largely absent, indicating that poor marine survival is hindering population recovery. Using temperature-sensing acoustic transmitters, this thesis examines the marine predation, migration, and habitat use of captive-reared iBoF Atlantic salmon kelts (post-spawned adults) to better understand the marine ecology of this critical life stage. Chapter 2 evaluates the role of predation in kelt marine mortality. Predation was observed in ~ 37% of iBoF salmon kelts detected in the Bay of Fundy (BoF). Neither fish size (total length; m) nor fish sex significantly influenced predation risk, but distinct spatial and temporal patterns of predation were evident, with events occurring predominantly during late spring and summer in the outer BoF. Thermal signatures indicated that most predation events were attributable to mesothermic predators, with limited evidence of marine mammal predation. Chapter 3 characterizes marine migration and seasonal habitat use of iBoF salmon kelts within the BoF. Seasonal modelling revealed increased kelt presence in the middle and outer BoF during late spring and summer, with spatial use shifting across months and concentrating in regions previously identified as important marine habitat. Kelts exhibited variable movement patterns, including both prolonged residency within the BoF and streamlined exits into the Gulf of Maine. About one third of the kelts exited the Bay at least once, primarily in May and June. Collectively, these findings provide contemporary evidence that predation is a prominent driver of marine mortality for iBoF salmon kelts, and that both survival and marine movements vary across space and time. This work directly informs recovery planning for this endangered population, including improving understanding of factors influencing marine survival, refinement of hatchery release strategies, and progress towards identifying important marine habitat for iBoF salmon kelts.
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Genomic Characterization of Five Isolates of Blastocystis Subtype 7
(2026-04-27) Seaton, Gregory; No; Doctor of Philosophy; Department of Biochemistry & Molecular Biology; Not Applicable; Dr. Laura Wegener Parfrey; No; Dr. Claudio H. Slamovits; Dr. James M. Kramer; Dr. Morgan Langille; Dr. Andrew Roger
Blastocystis spp. are common, genetically diverse anaerobic colonizers of the gastrointestinal tracts of both humans and animals. Although they are traditionally regarded as parasites, their precise role in host health remains unclear, in part because cryptic genetic diversity is masked by morphological similarity among divergent lineages. Subtype 7 (ST7) contains several isolates (C, H, E, G and B) that have been shown to exhibit distinct phenotypic differences in experimental settings, suggesting genetic diversity within the subtype. This thesis presents a comparative genomic analysis of those five ST7 isolates, with a focus on genetic differences between the isolates. Genomes of four of the five isolates presented here are newly sequenced using a long-read-based assembly approach resulting in new genomic assemblies that are >98% complete and range from 19.8 (ST7C) to 20.2 (ST7G) Mbp in size and were found to be highly syntenic. Short-read data suggests these Blastocystis ST7 isolates are haploid. For two of the newly sequenced genomes, ST7C and ST7G, the assembly was complete enough to capture 8 and 9 complete chromosomes respectively. Through comparisons of shared syntenic scaffolds amongst isolates, 16 nuclear chromosomes could be hypothetically reconstructed in ST7C. Comparative analyses revealed clear evidence of genomic rearrangements in ST7G and ST7H relative to ST7C. Manual curation was used to create a high-quality gene annotation for ST7C that was propagated to the other genomes yielding 8625-8896 predicted genes per genome. The predicted gene set for ST7B contained 2593 more genes than a previously published genome analysis for this isolate. A pangenome analysis of the five isolates was conducted and a small (228) accessory genome was identified compared to a far larger core gene set (6198) shared by all the isolates. An abundance of endogenous viral elements belonging to the Midsized Eukaryotic Linear dsDNA (MELD) virus class were found and comparative analyses suggest that the MELD viruses first invaded the common ancestor of ST7 and ST6, and then greatly proliferated in the ST7 genomes. The analyses presented here offers insight into the genomic structure and differences between these Blastocystis ST7 isolates.
Access status: Open Access ,
Seismic Retrofit of Dry Precast Concrete Beam To Column Joint Using Shape Memory Alloy
(2026-04-27) Chen, DeZhen; Not Applicable; Master of Applied Science; Department of Civil and Resource Engineering; Not Applicable; N/A; Not Applicable; Pedram Sadeghian; Zoheir Farhat; Fadi Oudah
Superelastic shape memory alloy (SMA) is regarded as an ideal material for enhancing the seismic capacity of structures due to its superelasticity and self-centering properties. This research introduces and validates a new concept for the structural upgrade of seismically deficient precast concrete structures using SMA. The proposed approach establishes partial moment transfer at the beam-column joint, enabling the frame to partially resist lateral loads alongside the building's shear core. To achieve this, a novel device—termed the SMA Partial Moment Transfer (SMA-PMT) device—is developed and validated through experimental testing and analytical modeling using hybrid simulation. The research was executed in three stages, including model development, the experimental joint design and the experimental test. The discussion summarizes the behavior of the experimental joint specimens, focusing on joint moment capacity (yield moment), energy dissipation capabilities, and joint damage assessments. Recommendations for future research are also provided.
Access status: Open Access ,
Phase Change Materials and Storage Design for Pumped Thermal Energy Storage
(2026-04-24) VanLuxemborg, John; Not Applicable; Master of Applied Science; Department of Mechanical Engineering; Not Applicable; Dr. Michael Pegg; Not Applicable; Dr. Baafour Nyantekyi-Kwakye; Dr. Dominic Groulx
Pumped Thermal Energy Storage (PTES) is an emerging energy storage technology; a key component of the system is the Thermal Energy Storage (TES) unit. This thesis investigates the optimization of a multi-tube shell-and-tube TES unit through both numerical simulation and experimental material characterization to enhance thermal performance. A numerical model was developed to evaluate the performance of nine bare-tube configurations, varying from dual to oct-tube arrangements. The addition of longitudinal fins was explored to improve the charging time, while the impact of the length of the TES was also studied. In parallel to the initial numerical studies, potential Phase Change Materials (PCMs) were identified, and four selected materials, adipic acid, D-mannitol, hydroquinone, and LiNO3-LiOH (81:19 wt%), were characterized experimentally using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The numerical results indicated that the Oct-4F configuration delivered the most efficient charging performance and highest energy storage density. It was found that a system length between 0.50 m and 0.75 m balanced a sustained power output with maximal latent energy utilization. Experimentally, the synthesized LiNO3-LiOH (81:19 wt%) eutectic proved to be the most viable PCM, exhibiting excellent thermal stability with a melting temperature of 176.24 °C and a latent heat of fusion of 385.28 J/g. However, when the Oct-4F geometry was simulated using the LiNO3-LiOH (81:19 wt%) eutectic and Therminol 59 as the Heat Transfer Fluid (HTF), the system was unable to complete charging within the target eight-hour window. This was driven by the combination of the PCMs extremely high latent heat of fusion and the substantially lower specific heat capacity of the HTF, indicating that further geometric or operational optimizations are required to fully harness the material’s storage potential.

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