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Towards a neurocomputational and dynamical understanding of rumination
No full textSelena Singh PhD thesis, supervised by Dr. Suzanna Becker.Ruminative brooding, the maladaptive repetitive dwelling on abstract, self-referential thoughts, is a transdiagnostic feature of many psychiatric disorders, yet its neurocognitive mechanisms remain poorly understood. Brooding is both repetitive and perseverative, implicating deficits in cognitive control and maladaptive emotion regulation. We investigated these properties using experimental psychology, computational modeling, network neuroscience, and dynamical systems approaches. First, we reported brooding-associated inhibitory control deficits that were exacerbated by emotional cues, as reflected by performance on Stroop interference tasks. Numerically fitting parallel distributed processing models to participant Stroop data revealed a set of brooding-associated parameters that reflected network sensitivity to changing task demands and activity persistence of emotional processes, but not cognitive control processes. Next, we analyzed relationships between self-regulatory processes and brooding, and their corresponding EEG functional connectivity patterns. We found evidence of internal resistance to emotions and thoughts in brooding. Furthermore, functional connectivity patterns indicated that brooding and emotion dysregulation co-varied with aberrant top-down modulation from prefrontal regions to emotion and interoceptive systems, potentially reflecting compensatory regulation of internal emotional states. Finally, we proposed that brooding is an emergent property of an attractor state within the brain’s default mode network (DMN). Here, we hypothesised that brooding-related attractor dynamics would produce stable, recurrent neural dynamics that resist perturbation. Supporting this, DMN regions demonstrated persistent activity when switching from a cued rumination to a working memory task, consistent with resistance of ruminative thought to perturbation. In addition, nonlinear analyses of the recurrence properties of EEG demonstrated a positive association between brooding and neural recurrence, further supporting this attractor state hypothesis. Together, these studies advance a mechanistic understanding of brooding from neurocomputational, network, and dynamical perspectives
Colorful photovoltaics using thickness-modulated thin film optical filters
No full textColorful photovoltaics have long been appealing to consumers for applications such as rooftop, building-integrated, and electric vehicle-integrated solar cells, among others. Achieving vibrant colors involves reflecting specific wavelengths of visible light. But energy capture in the visible range is crucial, as it often provides optimal external quantum efficiency. Therefore, it is essential to enhance the reflection of solar irradiance to achieve color while minimizing photocurrent loss. Researchers have explored various bottom-up approaches, such as modulating the thickness of single or dual-layer antireflective coatings (ARCs) or adding layers to existing standard ARCs. However, this often leads to broader reflection peaks and substantial photocurrent loss. While photonic crystal structures and metasurfaces show promise for color rendering, they require significant development before mass production. We explored various design strategies to develop two innovative methods for optical filter design that enhance both aesthetic appeal and photovoltaic efficiency while using fewer layers.
Our first method employs a top-down strategy utilizing OptiLayer and MATLAB to design optical filters consisting of 2-6 layers. This approach results in narrower reflection peaks and achieves optimal colors (blue, green, red) while maintaining a photocurrent loss of only 5-10%, a notable improvement over previously proposed solutions. We investigated various combinations of materials to identify the optimal range of material pairs for this specific application. Our designs were validated through fabrication with three material pairs and two deposition techniques (CVD and PVD), and feedback from our experimental understanding was incorporated into our design method to make it robust.
Our second approach uses a custom MATLAB code to design an optimal filter based on selected layer numbers and materials, specified by the manufacturers. The thesis includes details on design methods, deposition and characterization techniques, comparisons of spectral responses, and images of the colors produced by the fabricated filters
Does employee’s diversity help innovation?: Evidence from Canadian firms
No full textThis study examines how ethnic diversity among employees influences innovation within firms. Drawing on organizational behavior theories, it highlights how diversity can both enrich idea generation and create behavioral challenges. Using Canadian Workplace and Employee Survey (WES) data and a mixed logit model, the study finds robust evidence that ethnic diversity positively impacts both product and process innovation, even after addressing endogeneity. Importantly, diverse employees are most effective in firms with strong organizational capital and training programs. Manufacturing, transportation, and selected service sectors benefit the most, underscoring diversity’s role as a driver of knowledge creation and competitive advantage
CHEMICAL FUNCTIONALIZATION OF CELLULOSIC MATERIALS VIA AZETIDINIUM CHEMISTRY
No full textThis proposed work explores the potential of azetidinium chemistry as a versatile platform for grafting functionalities including alkyl, alkyne, azide, and diallyl, as well as amino silicone — onto a wide range of cellulosic materials within different scales. The developed strategies enable either the functionalization of cellulosic materials to tailor their surface properties or the crosslinking of cellulosic materials to form three-dimensional hydrogels and aerogels. This thesis includes four main research as presented:
First, a bifunctional azetidinium coupler was employed to graft functionalities onto carboxylate cellulosic materials. Carboxymethyl cellulose was utilized as a bridge between pulp fibres and functional groups by irreversible adsorption on the surface of pulp fibers and efficient reaction with azetidinium derivatives. Hydrophobicity was introduced through alkyl chains (C12 and C18), while bio-orthogonal reactivity was imparted via alkyne and azide functionalities, enabling further modification of paper sheets.
Second, a versatile fluorescent labeling approach was developed using azetidinium–azide linkers, which allowed efficient conjugation with commercially available dyes such as FAM-alkyne and Cy5-alkyne. This method enabled labeling across all scales of cellulosic materials — including CNCs, CNFs, BC, and pulp fibers — without altering their morphology, providing a powerful tool for cellulose imaging and distribution studies.
Third, a three-dimensional biomaterials ink was formulated by modifying CMC and CNCs with azetidinium–diallylamine. The resulting inks exhibited excellent shear-thinning and rapid thixotropic recovery, enabling high-fidelity extrusion printing. Incorporation of azetidinium–alkyne-modified CMC further enabled selective functionalization of specific regions within printed hydrogels, opening new possibilities for spatially controlled bioprinting applications.
Finally, a water-soluble azetidinium-functionalized amino silicone was synthesized and applied in the fabrication of hydrophobic CNC/silicone aerogels through a water-based process. These aerogels demonstrated tunable mechanical properties, remarkable shape recovery (>90%) under repeated compression, and outstanding performance in solvent absorption, solvent–water separation, and thermal insulation.ThesisDoctor of Philosophy (PhD)Cellulose, the main building block of plant fibers, is one of the most abundant and sustainable materials on Earth. By breaking it down into very small structures such as nanocrystals and nanofibrils, researchers can create lightweight, strong, and biodegradable materials for applications ranging from packaging and water purification to biomedical devices. However, to fulfill more requirements in applications, cellulose often needs to be modified to add new properties. In this work, we developed a simple, water-based chemical tools using azetidinium chemistry to attach useful functions to cellulose. These functions include making cellulose surfaces water-repellent, adding fluorescent tags for imaging, or allowing the material to form three-dimensional structures like hydrogels and aerogels. This research demonstrates environmentally friendly ways to expand how cellulose can be used in new fields
Beyond the binary and linearity: A continuum model of modality and nonlinear approaches to musical emotion
No full textMode and emotion are central to the expressive power of music, yet both present challenges for empirical study. This thesis advances understanding in two complementary ways. The first study reconsiders mode, a foundational property of tonal music traditionally treated as a binary distinction between “major” and “minor.” Using a corpus of 72 piano preludes by Bach, Chopin, and Shostakovich, we conceptualise relative mode as a spectrum and evaluate it across three approaches: perceptual, analytical, and computational. Results show moderate-to-strong alignment between the approaches, with even untrained listeners demonstrating sensitivity to granular modality. Further findings indicate that expert analyses are the most discriminating, however, computational estimates provide a scalable alternative with alignment to other approaches. Together, these results establish relative mode as a perceptually valid and computationally accessible construct for music cognition, theory, and information retrieval.
The second study examines whether traditional linear models suffice for explaining emotional responses across both the common-practice period (CPP; ~1650–1900) and later repertoire. We compare linear and nonlinear regression techniques in predicting valence ratings of preludes by Bach and Chopin (CPP) as well as Shostakovich and Debussy (non-CPP), using four well-established musical properties: relative mode, attack rate, pitch height, and amplitude. Results showed that linear and nonlinear models performed similarly for CPP composers. In contrast, nonlinear approaches substantially outperformed linear ones for Shostakovich and especially for Debussy, whose harmonically ambiguous and stylistically innovative preludes served as a case study for the benefits of nonlinear modeling. These findings demonstrate that although linear models are sufficient for CPP repertoire, capturing emotional responses to non-CPP music—particularly Debussy—requires more flexible, nonlinear approaches.ThesisMaster of Science (MSc)Music has a powerful ability to convey emotions but understanding how is far less obvious. Traditional research has relied on simple rules—for example, major keys sound brighter than minor ones, and faster music feels more energetic. This thesis challenges these assumptions in two ways. First, we show that “mode,” usually labelled as major or minor, can instead be understood on a spectrum. This approach better matches how listeners actually hear music and aligns with expert analysis and computer models. Second, we test whether common statistical methods can explain emotional responses to more modern music, using Claude Debussy’s preludes as a case study. We find that although simple models work well for earlier classical composers such as Bach and Chopin, more flexible nonlinear methods are needed for latter composers such as Shostakovich and Debussy. Together, these studies move beyond traditional assumptions of binary modality and linear modeling, offering new tools for understanding how music across history communicates emotion
CRDCN research-policy snapshot digest: Volume 5 Issue 1
No full textEach CRDCN Research-Policy Snapshot Digest, produced twice per year, assembles the individual snapshots prepared in the previous six months.
Chaque d’instantanés recherches-politiques du RCCDR, produit deux fois par an, compile les instantanés préparés au cours des six mois précédents
Three Essays in Health Economics
No full textThis thesis comprises three essays in health economics. Chapter 1, co-authored with Dr. Michel Grignon, examines how minimum wage increases affect access to employer-sponsored prescription drug insurance. Using cross-sectional data linked with provincial minimum wages changes from 2008 to 2019, the study identifies threshold effects: increases of 20–30 cents reduce coverage by about three percent, with the strongest impacts among women, young workers, immigrants, and racial minorities.
Chapter 2 evaluates the impact of the Ontario Health Insurance Plan Plus (OHIP+), introduced in 2018 to provide free prescription drug coverage to residents under 25. Applying event study and Difference-in-differences methods with administrative emergency department data, the analysis finds no overall effect on utilization but reveals significant declines among low-income households. This suggests that improved drug access reduced reliance on emergency departments as a substitute source of medication.
Chapter 3 investigates how a cancer diagnosis influences household spending patterns by linking the Canadian Cancer Registry with household expenditure survey data. The results show an average decline in total spending of about seven percent following a diagnosis, with the largest reductions in food and income tax expenditures. Although budget shares remain broadly stable, heterogeneity analysis reveals meaningful reallocations across families with and without children, single parents, and younger households. In contrast, subsequent diagnoses generate smaller adjustments.DissertationDoctor of Philosophy (PhD)This thesis examines the effects of Canadian public policies on prescription drug access and healthcare utilization, as well as how health shocks influence household spending decisions.
The first chapter asks how raising the minimum wage influences workers' access to drug benefits from their employers. It shows that when the minimum wage rises by a certain amount, some workers—especially women, young people, immigrants, and racial minorities—are less likely to have drug coverage through their jobs.
The second chapter examines whether Ontario’s OHIP+ program, launched in 2018 to provide free coverage for prescription drugs to everyone under the age of 25, had any effect on visits to the emergency department. While the program did not change overall emergency department visits among young people, it did reduce visits for those from low-income families. This suggests that before OHIP+, some youth may have gone to the emergency department to get medicines they could not otherwise afford.
The third chapter looks at how a cancer diagnosis changes family budgetary decisions. It finds that affected households cut their total spending and shift money around—for example, reducing food spending and increasing spending on housing and healthcare
SED Fitting of Globular Cluster Population in Abell 2744 at an Intermediate Redshift
No full textGlobular clusters (GCs) are ancient, compact stellar systems that serve as laboratories for stellar evolution and as fossil records of galaxy assembly, with their ages, metallicites, and spatial distributions constraining star-formation histories and the evolution of halos. This thesis presents SED fitting analysis of unresolved GC candidates in Abell 2744 at z = 0.308 using JWST/NIRCam images in eight filters (F070W-F444W). After PSF-fitting photometry and strict data selection, we retain 67 candidates with detections in all bands. Model magnitudes are generated by convolving E-MILES simple stellar population spectra and fit dirctly to the observed photometry. Age, metallicity, and mass of the GC candidates are estimated in parallel via minimization and MCMC. Both approaches deliver mutually consistent results. The inferred stellar masses of the candidates are mostly around , ages around 6 Gyr and 10 Gyr, and metallicities mostly between . We also explore the limitation of SED fitting of this data such as age-mass degeneracy and LWC dimming
The van der Waerden Simplicial Complex and the Lefschetz Properties
No full textNaveena Ragunathan M.Sc ThesisIn this thesis, we examine the van der Waerden simplicial complexes, defined on two parameters n and k, and the Artinian rings we can form by modding out the squares of the variables from the Stanley-Reisner ring of the van der Waerden complex. We begin by providing a thorough background on all the necessary background, from abstract algebra, graph theory, and linear algebra. The main question investigated in this thesis is when the Artinian rings constructed from the van der Waerden complexes have either the Weak or Strong Lefschetz property. We examine for what values of n and k do these Artinian rings have the Weak, and in some instances Strong, Lefschetz Property. We focus on the smallest possible values of k, namely k = 1 and k = 2; and the largest possible value k can take, which is n − 1. We also focus on the case where k = 3, as the first instance of the failure of the Weak Lefschetz Property occurs here.
We also investigate in what degrees the Artinian ring always has the Weak Lefschetz Property. We then give a characterization of when these simplicial complexes are pseudo- manifolds, which provides some further insight on what degrees the associated Artinian ring has the Weak Lefschetz Property. We conclude by providing some conjectures on both Lefschetz Properties, as well as further areas of possible future research. A Macaulay2 package on the van der Waerden simplicial complexes is also provided
If it ain't Broke, Why Rehabilitate it? Canadian Occupational Therapy in the Rehabilitation Era, 1950-1985
No full textAn increase in healthcare funding as well as the rehabilitation needs of Canadians enabled an expansion of practicing occupational therapists over the Rehabilitation Era, spanning the 1950s-1980s. Canada saw changes to hospital system funding through the transition to public healthcare, advances in medicine allowing more individuals to live with disabilities, and population growth, among many compounding factors resulting in more Canadians wanting or needing occupational therapy. Coined the “Rehabilitation Era” due to the growth of rehabilitation and a remedial focus in care through the use of the medical model, occupational therapists employed a multi-pronged approach to help meet the demand for their services.
The context of the Rehabilitation Era highlighted and contributed to occupational therapists’ challenges in defining what skills lay within, and outside of, their professional boundaries. Occupational therapists’ fragile professional identity entering a period of rapid growth led to a variety of new areas of practice. When Canada transitioned to a publicly funded healthcare system, it created a system disturbance for healthcare professionals to redefine their areas of expertise. Due to a combination of occupational therapy’s relatively small size, a predominantly female composition, and entering this transition as a role subjugated under physicians, occupational therapy had difficulty fully realizing the opportunities available. Further, due to other professions and the healthcare system more broadly shifting in focus to remediation, occupational therapists found themselves frequently uncomfortable and poorly aligned with predominant models of practice.
Over the course of the Rehabilitation Era, occupational therapy diversified drastically. Factors including gender, power structures, perceived and legitimate control over a knowledge base, and the external understanding of the role, each influenced the trajectory of the profession’s evolution. Occupational therapy’s absence of societal understanding of the scope of practice, value to the healthcare system, and professional expertise has consistently limited its ability to meet all criteria of professionalism. These challenges were highlighted particularly strongly during the Rehabilitation Era with the rapid changes to the healthcare and education systems. Given occupational therapy’s challenges in philosophical alignment with the medical model and the expanding areas of practice facilitated through the Rehabilitation Era, if it wasn’t broken, why did occupational therapy choose rehabilitation