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High-Efficiency III-V Semiconductor Device and System Optimization for Photovoltaic Applications
No full textThis thesis addresses barriers to adopting high-efficiency photovoltaic devices through innovative structured surfaces, device designs, and epitaxial growth. I demonstrate improvements using these techniques, through a combination of experiments and simulations. First, structured surfaces are investigated to enhance the performance of photovoltaic systems under concentrated sunlight. Second, novel photovoltaic designs are explored to improve the conversion of infrared or monochromatic light into electrical power. Third, the properties of III-V epitaxy on nonplanar surfaces are studied for substrate reuse applications.
Integrating structured surfaces into photovoltaic systems enhances their performance. High-efficiency photovoltaic devices, based on the epitaxial growth of III-V semiconductor materials, are expensive due to the scarcity of these elements. They are integrated into concentrator photovoltaic systems, which focus sunlight onto the photovoltaic cell, making terrestrial III-V solar cells cost-competitive with silicon-based solar cells. These cells are coated with an encapsulant to shield them from environmental damage. This thesis explores a microstructured encapsulant, comparing it with a standard encapsulant for these systems, and finds up to a 3.4\% improvement in optical performance. Additionally, this thesis shows that the new encapsulant could extend the concentrator system's temperature range operating at high efficiencies.
Optimizing devices at the component level enhances photovoltaic performance for infrared to electrical power conversion. Waste heat is an abundant and largely untapped energy source that can be harnessed using high-efficiency photovoltaic devices. Existing photovoltaic devices achieve efficiencies of less than 1.5\% for waste heat applications. This thesis presents a III-V photovoltaic device design optimized for waste heat recovery, predicted to achieve up to 15\% efficiency in converting waste heat at 900\,K into electrical power. A modified version of this optimized device is then fabricated and characterized.
Device-level optimization augments photovoltaic performance for monochromatic to electrical power conversion. Power by light offers an attractive alternative to transmitting power over metallic wires, especially when wires are unfavorable or impractical. These systems generally consist of lasers (at the light source) and photonic power converters. Most commercially available photonic power converters are based on GaAs and require optical wavelengths with short-range transmission through optical fibers. This thesis presents the design and characterization of photonic power converters for optical wavelengths within the transmission window of optical fibers, enabling much longer power transmission capabilities. These optimized devices breach the 50\% efficiency barrier, achieving efficiencies of up to 53.6\%.
Epitaxial growth provides an effective method to planarize faceted surfaces, facilitating the substrate reuse process. Substrate reuse promises significant cost reductions for III-V photovoltaics. A promising method is to fracture the epitaxial layers from the bulk substrate crystal, known as spalling. Spalling GaAs(100) substrates, commonly used for III-V photovoltaics, generates a rough surface of faceted ridges that need to be planarized for reuse. This thesis explores planarizing this surface using metal-organic vapor phase epitaxy. The optimized process planarizes the surface within 8 minutes of growth, using up to 95\% of the nominally deposited material, which is much faster than the hours required to grow high-efficiency devices. Overall, this thesis aims to increase efficiencies and reduce the costs of III-V photovoltaics
Numerical Modelling of Sloshing Tanks and Their Application in Tuned Liquid Dampers
No full textIn this study, we focus on sloshing tanks, particularly Tuned Liquid Dampers (TLDs). When a tank is excited, sloshing waves are generated and TLDs utilize these waves to mitigate the vibrations of the underlying structure. Due to their easy installation and cost-effective maintenance, TLDs are promising damping solutions for tall slender buildings subjected to wind or earthquake forces. Although extensive experimental research exists on TLD-coupled systems, further studies are needed to enhance the understanding of their dynamic characteristics. To address this, our research is divided into two main parts.
The first section of the first part focuses on the linear wave theory of shallow water equations and investigates how various widely used finite difference and finite volume methods introduce numerical diffusion errors in the simulation of sloshing waves from both initial perturbations and forced excitations. A model with low numerical diffusion, integrating physical diffusion, is then employed and coupled with a single degree of freedom (SDOF) system to develop a numerical model for TLD simulation. This facilitates a parametric study that includes the frequency ratio and damping ratio. The second section shifts to the nonlinear wave theory of shallow water equations. This model incorporates bottom topography and enables the simulation of high-gradient free surfaces. It employs the central upwind method and Minmod slope limiter function for flux approximation, along with the fourth-order Runge-Kutta method for time discretization. The model is verified for dam breaks on both horizontal and sloped beds, as well as for runup and rundown in a parabolic tank. Subsequently, the model integrates dissipation and dispersion terms to create asymmetric and steady waves. After verification with experimental box sloshing tanks, the model is coupled with an SDOF system to represent the TLD model. Finally, the TLD with a sloped bed demonstrates higher sloshing waves and greater suppression of the underlying structure vibrations compared to conventional box TLDs.
The last part includes an innovative analytical approach to model the dynamic behavior of a TLD-coupled system, bridging a significant gap in the literature. The separation of variables technique is employed to convert the linear shallow water equations, including the continuity and momentum equations, into a modal coordinate system. These equations are then strongly coupled with the dynamic equation of a single degree of freedom (SDOF) system under free vibration, resulting in a fourth-order characteristic equation. Using this equation, novel and significant concepts such as the stability of the coupled system, natural frequencies of the coupled system, initial boundary conditions, and response of the coupled system are discussed. In the next stage, the model incorporates both structural and fluid dissipations, leading to a different characteristic equation. This allows for the study of new topics, including the influence of dissipations on the natural frequencies and stability of the coupled system. For the first time, an expression for the response of the coupled system, indicating an exponential reduction in vibration, is proposed. Additionally, the analytical model is modified to consider the effect of a sloshing tank equipped with screens on the coupled system response. Finally, contrary to previous cases focusing on free vibration, this stage examines the forced vibration of the coupled system. It presents a characteristic equation and describes the particular, complementary, and total responses in three scenarios: undamped coupled system, structurally damped coupled system, and fluid and structurally damped coupled system. Regarding the particular solution, the model introduces new concepts, including dynamic amplification and phase difference between the force and displacement of the coupled system. For the first time, closed-form analytical solutions for the response of the coupled system in all three scenarios are proposed. Notably, in each scenario, in addition to the general case, two special cases are analytically investigated: resonant excitation of the coupled system and when the excitation frequency approaches the water tank frequency
Development of a Manual Handling Task Recognition and Holistic Fatigue Estimation System
No full textThe overarching goal of this dissertation was to contribute to the body of research on mitigating work-related musculoskeletal disorders (WMSDs) and occupational accident risk by identifying opportunities to leverage machine learning (ML) techniques, then develop an effective intervention strategy. A scoping review on the role of ML in the primary prevention of WMSD was conducted and identified fatigue modelling during physical labour as a notable and novel intervention strategy. Some shortcomings of existing efforts include the dichotomization of fatigue, the over-reliance on self-reported fatigue as a ground truth, and the inability to automatically adapt estimations to various tasks. Thus, this doctoral research aimed to build off these shortcomings and develop the primary components of an automatic system to adapt to the performance of various manual handling tasks using minimal wearable sensors, then estimate holistic fatigue as a continuous variable. To achieve this, four research objectives were formulated:
1) Perform a scoping review to document how ML techniques have been used to improve efforts to mitigate WMSD risk and identify areas for further research and development.
2) Develop human activity recognition (HAR) models that utilized either raw (i.e., linear acceleration, angular velocity, magnetometer) or fused (i.e., orientation and position) IMU data to classify manual handling tasks.
3) Perform a sensitivity analysis of the quantity and placement of IMUs for classification of the manual handling tasks.
4) Develop task-specific ML models to estimate continuous fatigue levels during the performance of the six manual handling tasks, where fatigue was quantified holistically using a composite index.
The scoping review returned 130 English studies published since 1990 regarding the use of ML techniques and were classified as contributions to the six steps of WMSD prevention (van der Beek et al., 2017). ML techniques were found to contribute most commonly to the development of interventions (48 studies; step 4), where a notable intervention approach was fatigue modelling during physical work.
For studies 2 – 4, a simulated, fatiguing manual handling protocol was conducted, where participants performed 5 min manual handling sets of pulling, lifting, carrying, and pushing a crate, followed by walking and standing. Between each set, they performed a fatigue assessment, then continued to perform manual handling sets and fatigue assessment without breaks until a stopping criterion was reached.
In the second study, HAR models were trained to classify the manual handling tasks with strong performances (accuracy ≥ 94.39%). However, HAR models performed significantly (yet marginally) better when using raw versus fused IMU data (p < 0.01). The third study developed 36 HAR models, with 18 sensor combinations and two ML model architectures to provide a sensitivity analysis. A greater number of IMUs lead to greater classification performances, while using one IMU achieved similar classification performance compared to using six (i.e., T8 and 6 IMU accuracy = 93.17% and 94.26%, respectively). Marginally better performances were observed with the deeper neural network (four convolutional and two long short-term memory layers) compared to the shallower neural network (three dense layers) until 3 or more IMUs were involved, after which the shallower neural network was equal or better.
In the fourth study, a holistic fatigue composite index (FCI) comprised of 6 fatigue variables was computed for all participants and reflected an increase in fatigue throughout the manual handling protocol. Then, task-specific ML regression models were trained to estimate the FCI using kinematic data from 1 or 3 IMUs (combinations informed by study 3), with and without heart rate. On average, using only the T8 IMU and heart rate data allowed for estimation of the FCI with small errors (RMSE = 0.06, MAE = 0.05) and moderate correlation (r = 0.59) across all tasks and participants.
The contributions of this dissertation include a thorough scoping review, knowledge surrounding the development of HAR models, and a novel approach to estimate task-specific holistic fatigue. This work represents the primary components of an unobtrusive and inexpensive system that can inform workers and employers of near real-time fatigue progression during the performance of manual handling work tasks, to ultimately mitigate WMSD and occupational accident risk
Asserting One's Identity as a French Teacher: An Empirical Study of the Positioning of Prospective French Teachers
No full textThis study explores the development of professional identity among pre-service French language teachers in a large bilingual university in Canada, focusing on challenges related to training and ideologies that shape their self-perception as future French language educators and have direct impact on their teaching approaches, sense of their roles and effectiveness and long- term willingness to pursue a career as French language instructors. Drawing on a mixed-methods case study approach (Duff, 2014), data was collected through questionnaires and semi-formal interviews with future French language teachers. The findings highlight the critical role of hands- on teaching experiences, such as mastery experiences (Bandura, 1997), and the observation of skilled educators in building confidence and self-efficacy. Additionally, positive feedback and encouraging discourse were found to significantly influence identity formation. The research further highlights the importance of addressing nativist ideologies (Shuck, 2006) and promoting linguistic diversity within teacher training programs, validating both native and non-native speakers as legitimate French teachers. Implications focus on the importance of efforts to explicitly counter nativist discourses while also providing pre-service French language teachers with authentic teaching experiences, a stronger emphasis on cultural awareness (Byram, 1997; Kramsch, 1993), and the integration of reflective practices to support identity development. These insights contribute to enhancing teacher training programs, with implications for better preparing and retaining future French educators in diverse classroom contexts
Discipliné et dominé par un ordre social performé : Observation de l'évènement-procès au sein des tribunaux canadiens
No full textCette étude exploratoire, basée sur une observation à « participation involontaire » au sein de deux tribunaux canadiens, vise à mettre en lumière la manière dont l'ordre social y est performé. En analysant ces observations avec l'ethnosémiotique, relatives à l'évènement-procès, ce travail se propose d'utiliser le chercheur comme outil et d'analyser les différents aspects de l'ordre social. Il en ressort que l'ordre social est dominant et disciplinaire envers les acteurs, surtout envers le public. Que ce soit l'agencement, les acteurs non-humains ou encore les ressentis du chercheur, tout converge vers une visualisation de la hiérarchisation, de la domination, de la distance des professionnels du droit envers les membres du public qui, par leur passivité, leur docilité, leur conformisme et leur soumission, légitiment les professionnels et plus généralement l'institution judiciaire
Partnered health research in Canada: a cross-sectional survey of perceptions among researchers and knowledge users involved in funded projects between 2011 and 2019
No full textAbstract Background Engaging knowledge users in health research is accelerating in Canada. Our objective was to examine perceptions of partnered health research among individuals involved in funded Canadian partnered health research projects between 2011 and 2019. Methods We invited 2155 recipients of 1153 funded projects to answer a questionnaire probing project characteristics and perceptions of partnered health research. We described and compared perceived effects of involving knowledge users in the project, team cohesion, capability, opportunity and motivation for working in partnership between two categories of respondents: project role [nominated principal investigators (NPIs), other researchers and knowledge users] and gender. Findings We analysed data from 589 respondents (42% NPIs, 40% other researchers and 18% knowledge users; 56% women). Among the perceived effects variables, the proportion of ratings of significant influence of involving knowledge users in the project ranged between 12% and 63%. Cohesion, capability, opportunity and motivation variables ranged between 58% and 97% agreement. There were no significant differences between respondent groups for most variables. NPIs and women rated the overall influence of involving knowledge users as significant more than other respondent groups (p < 0.001). NPIs also reported higher agreement with feeling sufficiently included in team activities, pressure to engage and partnerships enabling personal goals (all p < 0.001). Conclusions Most respondents held positive perceptions of working in partnership, although ratings of perceived effects indicated limited effects of involving knowledge users in specific research components and on project outcomes. Continued analysis of project outcomes may identify specific contexts and partnership characteristics associated with greater impact
Placental Abruption: Clinical Indicators, Histological Findings, and its Impact on Neonatal Health
No full textPlacental abruption involves premature placental separation from the uterine wall, resulting in adverse maternal and neonatal outcomes. Using data from 287 confirmed cases at two large Canadian hospitals, we examined clinical, lifestyle, imaging, and postpartum histological measures, alongside neonatal health indicators. Canonical correlation analysis revealed moderate relationships among these variables, suggesting potential markers for earlier detection and timely intervention. Specific clinical indicators and histological features were associated with preterm birth and low birth weight. The analysis highlighted the placenta's role in reflecting maternal conditions and emphasized the need for proactive prenatal care. Although limited by the lack of histological data from healthy pregnancy, these findings support targeted follow-up studies to assess diagnostic and predictive accuracy. Identifying such markers may aid clinicians in refining management strategies, potentially improving maternal and neonatal outcomes while addressing ethical considerations surrounding delivery timing. Further confirmatory research with healthy pregnancies and other complications is needed
Stranger danger or good Samaritan? A cross-sectional study examining correlates of tolerance of risk in outdoor play among Canadian parents
No full textAbstract Background Negative parental perceptions of risk may restrict children’s opportunities for outdoor play. Excessively minimizing children’s exposure to risks in their environment may have a range of developmental consequences. The purpose of this cross-sectional study was to assess correlates of parental tolerance of risk among a large sample of Canadian parents. Methods In this cross-sectional study, a sample of 2,291 parents of 7–12 year olds completed online questionnaires assessing a range of potential individual (e.g., gender), social (e.g., neighbourhood cohesion), and environmental (e.g., walkability) correlates of parental tolerance of risk. Logistic regressions were created to examine associations between these factors and odds of being in the most risk averse quartile. The logistic regression was built in hierarchal steps relying on the Akaike information criterion (AIC) and pseudo R2 for model progression. Results The final model had a pseudo R2 of 0.18. Five out of seventeen correlates were associated with risk aversion in parents. Concerns about stranger danger were associated with a higher odds of risk aversion (OR = 2.33, 95%CI[1.93, 2.82]). A higher number of children in the home was associated with lower odds of risk aversion in parents (OR = 0.80, 95%CI[0.69, 0.92], and parents of children born outside of Canada had higher odds of being risk adverse when compared to parents born in Canada (OR = 2.13, 95%CI[1.54, 2.94]). Finally, being very concerned with COVID-19 increased the odds of risk aversion (OR = 3.07, 95%CI[1.93, 5.04], while having a household income of > 100,000 lowered the odds of risk aversion (OR = 0.56, 95%CI[0.36, 0.87]). Conclusions Tailored interventions that reframe perceptions of risk for parents are needed. Such interventions could reframe concerns about stranger danger which persist despite occurrences of stranger abduction being extremely rare. Interventions could also be targeted to immigrant families and those with fewer children as they appear to be more averse to risk. A complementary focus on examining how cultural background influences risk perceptions is needed in future research
Electro-reforming of Glycerol Over Ni for Hydrogen Production in Alkaline Media
No full textThe commercialising of green H2 from water electrolysis is expected to play an important role in the decarbonisation of the global economy. While its commerciality has steadily been improved over the decades from breakthroughs in electrocatalyst, separator and cell design, it still is uncompetitive against other forms of energy storage such as natural gas. This challenge is primarily related with the intrinsic equilibrium potential needed to initiate the coupled half-cell reactions of water electrolysis in similar pH which represents the majority of it’s electricity consumption. To contour this, coupling the half cell hydrogen evolution reaction (HER) responsible for producing H2 with a more thermodynamically favourable anodic electrochemical reaction has shown promise. Among the possible oxidation reactions, glycerol electrooxidation (GEOR) has shown a great deal of attention due to its surplus, high functionality allowing for a large window of potential products, significantly low onset potential, reduced risk both in terms of handling and competitive inhibition of O2 production. Most scientific research in GEOR has been focused on its selectivity, reactivity, and resistance to poisonous species due to its significant revenue generation from its value-added products as opposed to H2. Much has been achieved in terms of designing both reactive and selective platinum group and Ni based catalysts. However, the focus on selectivity and general electrochemical tests within small 3-electrode cells has created an under reporting of relevant electrochemical tests within industrially relevant zero-gap electrolysers. This is of particular importance since reporting the advantage of GEOR without its required coupled cathodic reaction to complete the circuit doesn’t provide information to its advantages or limitations from an engineering perspective. In this thesis, previous electrocatalysts developed by Houache et al. 2020 and Asma Shubair et al. 2022 were examined in a relevant 25 cm2 zero-gap electrochemical cell where polarization curves are produced. Additionally, electrolyser parameters such as temperature, catalyst loading, and concentrations are varied due to the lack of studies investigating the influence of external parameters on GEOR in literature. Due to the absence of O2 production, all electrolyser tests were performed with a filter paper to demonstrate the further possibility to reduce the CAPEX significantly as opposed to an anion exchange membrane water electrolysers. The application of a V membrane-free electrolyser also requires an investigation of the influence of glycerol on the hydrogen evolution reaction. Unexpected discoveries were made along the electrolyser tests which did require further investigation. Scaling GEOR to a larger cell not only demonstrated challenges and opportunity to GEOR in terms of energy consumption for H2 production, but it also detected novel GEOR reactions which have not previously been discovered due to difficulties of measuring such phenomena within small 3-electrode cells. Additionally, upscaled polarization curves also demonstrated the detection of a novel GEOR related deactivation mechanism which differs from literature and suggests that catalyst designs for GEOR should consider downstream electrolyte compositional changes to resist deactivation or changes in GEOR mechanism. Finally, investigation of glycerol on the hydrogen evolution reaction has led to a contradiction to the hypothesis in literature. Electrochemical results suggest glycerol acts as both an inhibitor and promoter for HER depending on the catalyst material and the specific HER mechanism in question. DFT and AIMD simulations are recommended to further investigate. However, the differences in catalyst sensitivities to glycerol suggest catalyst designs can mitigate the inhibitory effects of glycerol on HER or even promote HER. Additionally, impedance spectroscopy measurements strongly correlate glycerol interferes with the Nafion® binder microphase structures, significantly inhibiting electrolyte conduction and H2O replenishment which are critical for the hydrogen evolution reaction, highlighting the need for the GEOR field to investigate other ionomers as suitable binders. Furthermore, evidence points to the influence of glycerol on OH- conduction in liquid phase is nulled due to the novel Grothuss conduction mechanism of OH-, presenting a significant advantage for membrane-free electrolysers. Overall, no symmetrical/asymmetrical Ni cell in this work met the D.O.E. target, with the lowest operating at 42.1 kWh.kgH2-1, due to the required metal oxidation state for GEOR to initiate over Ni is intrinsically elevated. Nonetheless, Pd phase GEOR-HER did manage to operate at 37 kWh.kgH2-1, meeting the D.O.E.. This is due to its lower required potential to oxidise potential to an active GEOR state
Transcriptional Regulation of the Postnatal Cardiac Conduction System Heterogeneity
No full textThe cardiac conduction system (CCS) is a network of specialized cardiomyocytes coordinating electrical impulse propagation for synchronized heart contractions. Although the components of the CCS, including the sinoatrial node, atrioventricular node, His bundle, bundle branches, and Purkinje fibers, were anatomically discovered more than 100 years ago, their molecular constituents as well as regulators remain not fully understood. Here, we demonstrated the transcriptomic landscape of the postnatal mouse CCS at a single-cell resolution with spatial information. Integration of single-cell and spatial transcriptomics uncovered region-specific markers and zonation patterns of gene expression across the CCS, which were histologically validated. Network inference showed heterogeneous gene regulatory networks across the CCS. Notably, CCS region-specific gene regulation was recapitulated in a dish using neonatal mouse atrial and ventricular myocytes overexpressing CCS-specific transcription factors, Tbx3 and/or Irx3. This finding was supported by ATAC-seq of different CCS regions, Tbx3 ChIP-seq, and the identification of Irx motifs. Overall, this study demonstrates comprehensive molecular profiles within the postnatal CCS and provides evidence of the regulatory mechanisms contributing to its heterogeneity