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    The association between social support and executive function in mid- to late-life within the context of attrition: Results from the Canadian Longitudinal Study on Aging
    (University of Waterloo, 2026-03-04) Rutter, Emily
    Background. As the population over the age of 65 increases, a greater proportion of Canadians will be impacted by the effects of cognitive decline, necessitating research on risk factors that can influence cognitive outcomes. Social support has been identified as a potential area of intervention for the cognitive health of the aging population and may have a particularly strong association with key cognitive domains such as executive function. Executive function is an important cognitive domain in successful aging given its role in the tasks required for daily independent living. While there is largely consistent evidence for a positive cross-sectional association between social support and executive function, longitudinal studies have produced more mixed findings. As both social support and executive function play a role in attrition (i.e., participants dropping out of studies over time), longitudinal studies investigating the association between the two may be at greatest risk of increasingly selective, and possibly biased, samples. Developing a better understanding of how social support impacts executive function within the context of attrition is essential to maximizing public health efforts aimed at supporting the cognitive health of the aging population. Aim. The overall aim of this thesis was to investigate the association between functional social support and executive function in mid- to late-life and to explore how attrition may be impacting our knowledge of this relationship. Methods. Modified Poisson and logistic regression analyses utilized baseline (T1; 2012-2015), first (T2; 2015-2018) and second (T3; 2018-2021) follow-up data from the Comprehensive cohort of the Canadian Longitudinal Study on Aging (CLSA). Attrition was assessed based on participation at baseline only (T1), both T1 and T2, and at all timepoints (T1, T2, T3). As data collection for follow-up 2 (T3) occurred both pre- and post-implementation of COVID-19-related restrictions in Canada, this time point was divided into two cohorts (i.e., those who participated pre vs post COVID-19 restrictions). The 19-item Medical Outcomes Study-Social Support Survey was used to assess perceived availability of social support (overall and subtypes: emotional/informational, tangible, affectionate, positive social interactions). Executive function was calculated by averaging standardized scores across multiple cognitive tests. Final models were adjusted for sociodemographic, health, lifestyle, and additional social variables. Results. Study 1 (Chapter 4) investigated if baseline social support and executive function were associated with attrition and if the association between social support and executive function varied across those participating at one (T1), two (T1, T2), or three (T1, T2, T3) timepoints. After accounting for covariates, those with low social support, low executive function, or those missing data on any of the tests of executive function were significantly more likely to drop out of the study after baseline (T1) assessment and were significantly less likely to complete all three waves (T1, T2, T3) of the study. The cross-sectional association between low social support and low executive function at baseline was statistically significant for those who participated at baseline-only but not for those who participated at both T1 and T2 or at all three timepoints. This suggests that the association between functional social support and executive function at baseline varies in a meaningful way for those lost to attrition vs those who remained in the study, and that those with the strongest association between social support and executive function may be those most likely to be lost to follow-up. Attrition in longitudinal studies can lead to underestimating or overestimating the impact of risk factors given the cognitively healthier and more socially engaged participants who remain in the study over time. Study 2 (Chapter 5) investigated the longitudinal role of functional social support (T1) and its subtypes on executive function (T3) while exploring how attrition and individual characteristics may impact the results and conclusions generated from these analyses. The longitudinal association between low social support and low executive function was not statistically significant. Taken at face value, these results would seem to add to the conflicting, non-significant, findings regarding the long-term association between social support and cognitive function. Yet, when those who completed all assessments were compared cross-sectionally (T1) to those who had dropped out of the study, only those lost after baseline had a significant positive association between low social support and low executive function. These findings indicate that attrition may be introducing bias into our longitudinal results and, if we as researchers are not careful in our interpretation, into our conclusions about the value of functional social support for cognitive health. Study 3 (Chapter 6) investigated how the association between social support and executive function differs pre- vs post-COVID-19 restrictions (T3), with half of the sample completing their assessments in-person, pre-COVID-19, and the latter half via telephone interviews post-COVID-19 restrictions. While the cross-sectional (T3) association between social support and executive function pre-COVID-19 restrictions was only statistically significant for one subtype of support (i.e., emotional/informational), post-COVID-19 restrictions, overall social support, as well as positive social interactions, emotional/informational and affectionate social support were statistically significantly associated with executive function, such that higher social support was associated with higher executive function. It is unclear whether the significant relationship between social support and executive function post-COVID-19 restrictions reflects the changes in data collection procedures or the greater psychological and cognitive impacts of the COVID-19 pandemic and related changes to daily life. The COVID-19 pandemic will continue to have an undeniable impact on data analyses for the foreseeable future and analyses considering the long-term impact of social exposures on cognitive health should explicitly account for how the COVID-19 pandemic and related restrictions may impact our understanding of this association. Contributions. Understanding how different aspects of social support impact cognitive function—and, by proxy, independence and adaptability— is essential to public health efforts aimed at improving health outcomes for older adults through evidence-based social programs and policies. The results of this dissertation reveal that the longitudinal relationship between social support and executive function is complex and that conclusions in this research area may be influenced by attrition. This dissertation demonstrated that those with the strongest association between social support and executive function were also those most likely to be lost to follow-up. While the long-term impact of social support on cognitive health is best investigated using longitudinal studies, these samples are vulnerable to biases which can lead to generalizations that do not reflect the greater population. Of greatest concern is that those who are lost to these studies over time may be those who would benefit most greatly from cognitive research, given their poorer health. While what is demonstrated in this dissertation discusses the association between social support and executive function, the limitations of the data represented here have wide-spread implications for longitudinal research on aging. Future research considering the long-term impact of exposures on cognitive health over the lifespan should actively investigate how attrition may impact their samples and findings.
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    Engineering giant field-free spin-orbit torque from a topological insulator onto a covalent 2D magnet
    (University of Waterloo, 2026-03-04) Ren, He
    Magnetic random-access memory (MRAM) is a leading candidate for next-generation non-volatile memory due to its fast switching speed, high endurance, and compatibility with CMOS technology. Spin–orbit torque (SOT) provides an efficient and reliable purely electrical means for magnetization switching in MRAM devices; however, deterministic switching of perpendicular magnetic anisotropy (PMA) bits typically requires an external magnetic field, which complicates device integration. Achieving field-free SOT switching through materials and symmetry engineering is therefore a critical challenge for scalable spintronic memory and logic applications. Transition metal dichalcogenides (TMDs) are a versatile class of layered materials whose electronic and magnetic properties can be dramatically modified through intercalation. Among them, self-intercalated chromium tellurides Cr1+δTe2 have attracted increasing attention due to their intrinsic ferromagnetism, structural compatibility with telluride-based materials, and potential for spintronic applications. In parallel, topological insulators such as (Bi0.75Sb0.25)2Te3 host spin–momentum–locked surface states that enable highly efficient charge-to-spin conversion, providing a powerful platform for SOT-based devices. In this thesis, the epitaxial growth of both Cr3Te4 and (Bi0.75Sb0.25)2Te3 thin films is demonstrated. Their high crystalline quality is verified through detailed structural and electronic characterization, establishing a reliable materials platform for subsequent heterostructure fabrication and symmetry-engineered SOT studies. A pronounced Kondo-like resistivity upturn is observed in ultrathin (< 12 monolayers) Cr3Te4 films grown on sapphire substrates. Low-temperature transport measurements are well described by a Kondo model, while the effect is suppressed in thicker films. Scanning tunneling microscopy reveals defect-induced electronic states consistent with Kondo scattering, and cross-sectional transmission electron microscopy shows that structural defects are concentrated at the film–substrate interface, providing localized magnetic disorder responsible for the observed behavior. The self-intercalation induced flatbands further enhance the electron-spin correlations. Moreover, the presence of Kondo scattering enhances current-induced spin accumulation, which is beneficial for SOT efficiency. Finally, deterministic, field-free switching of perpendicular magnetization using SOT is demonstrated in Cr3Te4/(Bi0.75Sb0.25)2Te3 heterostructures. While the topological insulator surface states enable efficient charge-to-spin conversion, deterministic out-of-plane switching requires additional in-plane symmetry breaking. The ordered 2×1 self-intercalation structure of Cr3Te4 introduces the necessary symmetry reduction, resulting in a unidirectional mirror symmetry m (Cs) at the interface. This enables robust field-free switching of a high-coercivity (∼ 1.3 T) perpendicular ferromagnet. Wafer-scale growth produces three equivalent 2 × 1 domains, giving rise to a characteristic three-fold angular dependence in the SOT response. Together, these results establish a novel and practical route to engineering topological insulator heterostructures as a multifunctional platform for studying correlated electron phenomena and engineering efficient, field-free spintronic devices.
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    Misogyny and Extremism Across Forums, Podcasts, and Manifestos: A Mixed-Methods Study
    (University of Waterloo, 2026-03-03) Padda, Karmvir Kaur
    Over the past decade, gender-based hate, online harassment, and ideologically motivated violent extremism have increased significantly. Digital platforms have played a central role in this shift, facilitating the large-scale circulation of misogynistic grievance and extremist narratives that increasingly translate into offline harm. This dissertation examines misogynistic discourse across three digital infrastructures: incel forums (across both mainstream and alt-tech platforms), manosphere podcasts, and violent extremist manifestos. While existing research on extremism has often treated these sites in isolation, this study examines how they share overlapping narratives that orient and normalize extremist worldviews. Across these infrastructures, misogynistic narratives collectivize grievance, legitimize violence, and inscribe ideological legacy. The dissertation argues that gender-based bigotry and misogyny function as an ideological glue at the center of these dynamics, underpinning and amplifying other forms of harm and hate, including racism, xenophobia, and anti-authority sentiment. The first study (Chapter 2) analyzes over 33 million posts from Reddit (r/Incels, r/Braincels, r/IncelExit) and Incels.is to show how incel discourse transforms experiences of despair and rejection into epistemic “truths.” Using topic modeling (BERTopic) alongside qualitative discourse analysis, this study identifies recurring patterns of biologized rejection, misogynistic dehumanization, and glorified violence. Incel ideology is conceptualized as an affective epistemology: a system in which emotional pain is converted into ideological belief through repetition, shared resonance, and cross-platform circulation. The second study (Chapter 3) examines more than 1,800 podcast episodes produced by Andrew Tate, Nick Fuentes, and Gavin McInnes. Through a combination of topic modeling (BERTopic), text classification (misogyny and emotion detection), and qualitative discourse analysis, the study shows how these influencers mainstream subcultural grievances by embedding them in humour, storytelling, and everyday advice. Podcasts function as affective infrastructures that cultivate parasocial intimacy, naturalize patriarchal dominance, and frame grievance as a core masculine identity, thereby normalizing resentment and positioning violence as a legitimate or restorative masculine response. The third study (Chapter 4) analyzes 100 violent extremist manifestos authored between 1966 and 2025, representing the first largest systematic collection examined to date. The analysis demonstrates that misogyny anchors hybrid or “salad-bar” extremism by providing the emotional and ideological thread linking racism, antisemitism, anti-government sentiment, and anti-LGBTQ+ hostility. Suicidality emerges as a structural feature of gender-motivated attacks, with perpetrators framing self-annihilation as an integral component of their violent performance. Lastly, this chapter argues that manifestos function as batons, where perpetrators cite prior attackers and legitimize violence for future actors. Overall, this dissertation demonstrates how misogynistic discourse operates across different digital spaces by integrating computational text analysis with qualitative discourse analysis. In doing so, it shows that ideologically motivated violent extremism cannot be fully understood without attending to its gendered foundations. By positioning misogyny as a central force that sustains grievance and connects otherwise distinct extremist ideologies, this research provides an integrated account of gender-based extremism with implications for prevention, policy, and scholarship.
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    Thorax Response in Young and Aged Small Females Under Side Impact, Isolated Ribs and Full-Body Computational Studies
    (University of Waterloo, 2026-03-02) Corrales Fabre, Miguel Angel
    Small-stature females and aged individuals face a disproportionate risk of thoracic injury in automotive crashes. Epidemiological studies indicate the heightened susceptibility observed in the aged small statured individuals compared to average statured males through a significantly increased number of rib fractures (NRF), especially in side impacts. The present thesis investigates the biomechanical factors contributing to the increased NRF observed in the aged small statured female individuals, focusing on the age-related changes in thoracic geometry and material properties. Advanced finite element human body models (HBMs) were employed to quantify these effects under side-impact loading conditions, with a specific emphasis on young and aged small female modelling. First, age and sex-specific isolated rib models were developed including a 26-year-old mid-stature male (M5026IR), 26-year-old small female (F0526IR) and a 75-year-old small female (F0575IR) 6th rib. Using morphing techniques, with targets based on regression models, the rib gross geometry, cortical bone thickness, and rib cross-sectional area were enhanced to reflect population-specific characteristics. The Cortical Bone Fracture and Continuum Damage Mechanics Constitutive Model (CFraC) was implemented to enhance the representation of rib cortical bone material behaviour, integrating age-specific mechanical properties. The isolated rib models were loaded in anterior-posterior compression and compared to available population-specific experimental data. The isolated rib models served as a stepping stone for full body model development and as foundational model validation exercise. Subsequently, three novel HBMs were developed by integrating the isolated rib developments and performing full-body morphing: a young adult small female (F0526), an aged adult small female based on statistically derived population data (F0575), and an aged adult small female based on subject-specific imaging data (F0584). These three models, alongside the baseline small female GHBMC model (F05B), were assessed in two environments: a simplified side impact sled using rigid plates, and an Advanced Side Impact System (ASIS) representing a realistic vehicle environment with a deformable seat, seatbelt with pretensioner, thorax airbag, and intruding door. Isolated rib results demonstrated good correlation to the age-, sex- and size-specific experimental data (i.e. young mid-size male, young small female and aged female) predicting the overall rib stiffness, force-displacement to fracture and fracture location. The rib models predicted the expected age and size/sex differences, that is, reduced stiffness and lower force and displacement to fracture with increasing age and decreasing size. Transition zones from thick to thin cortical bone led to stress concentrators that dictated the fracture location in the isolated rib models. The CFraC material model was shown to be a foundational improvement allowing for the prediction of cortical bone fracture. At the full body level, the baseline F05B model demonstrated limited sensitivity to impact severity, underestimating injury outcomes attributed to its simplified cortical bone model. The F0526 demonstrated sensitivity to impact severity. The F0575 model predicted NRF, chest compression maximum magnitude and timing, and AIS injury scores higher than the F0526 with values aligned closely to experimental Post-Mortem Human Subject (PMHS) data for aged small females. The subject-specific model (F0584), experienced higher rib torque owing to increased rib angles associated with this subject specific model, relative to the population average F0575 model. Increased rib torque, led to higher shear stresses in the cortical bone, resulting in the initiation of rib fracture earlier in the impact an increased NRF. These findings quantified and suggested that age-related reductions in cortical bone strain to failure, rib cortical bone thickness, and inter-subject variability can increase NRF. The present thesis demonstrates, for the first time, a methodology to develop predictive thorax models capable of capturing age-, sex-, and size-related differences considering rib fracture and thorax response. The presented results suggest that the development of population-specific tissue-level-predictive HBMs require a combination of appropriate material models coupled with population-specific material properties and geometry. Importantly, the HBMs developed in this work can be used to evaluate existing safety systems and aid in the development of future inclusive safety systems
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    Transient Development of a Laminar Separation Bubble Over a Low Reynolds Number Airfoil
    (American Society of Mechanical Engineers, 2026-02-05) Zilstra, Alison; Johnson, David A.
    Airfoils operating in low Reynolds number (Re) conditions frequently have a laminar separation bubble (LSB) form as a part of the natural boundary layer (BL) transition. A transient analysis of the Kelvin-Helmholtz (K-H) rolls in the LSB uncovered a new pressure feedback process that alters the development of the BL transition. The SD 7037 airfoil at a modest Re of 41,000 is studied using Large Eddy Simulation (LES) where a free-shear flow filter length criterion is applied to capture the K-H roll development. Multiple detailed experimental data sets are used to validate the chordwise positioning of the time averaged LSB and the dominant K-H roll frequency. The K-H rolls are shown to pinch-off from the reverse flow region of the LSB and the lift-off and subsequent touchdown of the K-H rolls are the source of the pressure feedback. The pressure feedback occurs consistently at 1 deg angle of attack (AOA) resulting in a dominance of the K-H roll frequency throughout the transitional BL. The dominant frequency is relevant to the aeroacoustic performance of low Re airfoils, where K-H rolls at a consistent frequency can generate tonal noise. The intermittent feedback at 5 deg AOA provides a clear distinction between the transition structures during a natural BL transition and feedback-initiated transition. The analysis of the K-H rolls and the discovery of a novel feedback mechanism provides invaluable information for the aerodynamic and aeroacoustic performance of low Re airfoils.