PRISM | Institutional Repository
Communities in PRISM
Select a community to browse its collections.
Recent Submissions
Item type: Item , Access status: Embargo , Evaluating the Effect of Transcranial Ultrasound Stimulation (TUS) as an Emerging Neuromodulation Tool(2026-04-15) Khosroshahizadeh, Ali; Monchi, Oury; Pichardo, Samuel; Martino, Davide; Pike, G. BruceeTranscranial ultrasound stimulation (TUS) is an emerging non-invasive neuromodulation technique with the potential to target cortical and subcortical circuits with millimeter-scale precision. Realizing this potential in human neuroscience requires accurate acoustic targeting, principled selection of stimulation parameters, and evidence that modulation generalizes beyond motor measures to clinically relevant sensory systems. This thesis advances TUS across these methodological and physiological dimensions through four linked studies. Study 1 validates radiation-free stimulation planning by comparing MRI-derived skull models to CT-based simulations, demonstrating that MRI-only workflows can provide sufficiently accurate estimates of focal location and intracranial pressure for many stimulation sites while delineating locations where errors are larger. Study 2 investigates the role of pulse repetition frequency (PRF) in inducing aftereffects: in a double-blind, sham-controlled motor cortex experiment with matched dose, low PRFs (10 and 100 Hz) produced sustained inhibition of corticospinal excitability, whereas 1000 Hz did not. Study 3 examines spatial determinants of efficacy by contrasting broad (250 kHz), narrow (825 kHz), and multi-focal stimulation; broader or spatially distributed strategies yielded more reliable modulation than a highly focal unifocal beam. Study 4 applies TUS to probe the human pain system by stimulating primary somatosensory cortex (S1) and the ventral posterolateral thalamus (VPL) and quantifying sensory function with quantitative sensory testing (QST). TUS at these nodes produced shifts in thermal detection and pain thresholds, supporting a causal role of the S1-VPL circuit in regulating somatosensory gain. Collectively, this work improves practical TUS deployment in humans and demonstrates mechanistic effects in sensory circuits relevant to pain.Item type: Item , Access status: Open Access , Algorithmic Detection of Dwarf Galaxies in NGC 5128 with Image Processing and Deep Learning(2026-04-17) Leahy, Cameron; Taylor, Matthew; Plume, Rene; Friesen, Tim; Moradi, Shahpoor; Barclay, PaulDwarf galaxies are important objects to study, as their dark matter content and numerical abundance makes them excellent probes of large-scale structure formation in the Lambda Cold Dark Matter (ΛCDM) cosmological model. However, many dwarf galaxies are faint and hard to detect, resulting in fragmented knowledge of dwarf galaxy populations in distant environments. While significant improvements in telescope imaging capabilities have facilitated the discovery of many faint dwarf galaxies in the last two decades, standard methods for detecting dwarf galaxies in imaging data can be inefficient, both in terms of speed and recovery rate. Detection is often done by eye because standard source detection software frequently misses the faint profiles of dwarfs in imaging; however, by-eye detection has significant drawbacks. In this thesis, we describe a novel algorithm that detects dwarf galaxies in optical Dark Energy Camera (DECam) imaging data of the giant elliptical galaxy NGC 5128 (also known as Centaurus A). The imaging comes from the Survey of Centaurus A's Baryonic Structures (SCABS), a 72-square-degree, DECam survey centered on NGC 5128. The dwarf detection algorithm uses image processing techniques and a custom-designed Convolutional Neural Network (CNN), trained on synthetic data of dwarf galaxies and non-dwarf objects, to pinpoint dwarf galaxy candidates in the SCABS imaging. The user reviews the final candidates in the last stage of the algorithm, rendering the detection process semi-automatic. Excluding the manual segment, the algorithm takes 10 minutes to process a very large 570-megapixel image, speeding up the process of finding faint dwarf candidates in the DECam imaging by more than 10 times. Using the algorithm, we find 155 promising candidates across the SCABS survey, 19 of which are detected in previous studies. A spatial analysis is conducted on the candidates, putting our findings in the context of previous work on NGC 5128. Future analyses will help determine which of our detections represent true, newly-discovered dwarf satellites of the NGC 5128 system.Item type: Item , Access status: Open Access , An Explanatory Mixed-Methods Study of the Determinants of Happiness and Well-Being Among Women in Senior Leadership at a Canadian Communications Company(2026-04-17) Sumner Keogh, Laura Janine; Steel, Piers; Grandy, Gina; Bourdage, JoshDespite increasing scholarly attention to workplace well-being, comparatively little research has examined the conditions that shape the happiness of women in senior leadership roles or the broader well-being systems that support it. Interest in this issue is also reflected in managerial discourse. Surveys of U.S. executives suggest that although a large majority of leaders view well-being as important for organizational success, only a small minority report having a clear organizational strategy for supporting it in practice (Deloitte, 2018, as cited in Bellet et al., 2023). This gap between recognition and implementation highlights the need for research that clarifies the conditions under which happiness can be sustained within demanding organizational contexts, particularly among those responsible for leading others. Leadership scholarship has traditionally emphasized leaders’ influence on followers and organizational outcomes, while comparatively less attention has been given to leaders’ own psychological functioning and well-being (Arnold, 2017; Nielsen & Taris, 2019). Within the literature on women in leadership, research has similarly focused on structural barriers and challenges, including gender bias, the glass ceiling, and unequal advancement opportunities (Eagly & Karau, 2002; Ely et al., 2011). Although this work has provided important insight into the obstacles women leaders encounter, it has devoted less attention to understanding the conditions under which women who remain in senior leadership roles are able to sustain their happiness. More recent scholarship has begun to examine women leaders’ happiness and well-being more directly; however, this emerging body of work remains relatively small and fragmented. Existing studies frequently examine isolated well-being conditions or specific workplace experiences rather than developing integrated explanations of leadership happiness. As a result, relatively few studies simultaneously consider workplace conditions and broader holistic well-being factors or integrate multiple theoretical perspectives to explain how these influences jointly shape leaders’ happiness over time (Azila-Gbettor et al., 2024; Hu et al., 2023; Lutz et al., 2023; Ortiz-Meillón et al., 2024; ; Rojas, 2025; Sudarji et al., 2025;Slemp et al., 2021). This study addresses this gap by examining the determinants of happiness among senior women leaders and the broader well-being conditions that support it. Drawing on Self-Determination Theory (SDT), Conservation of Resources (COR) theory, and Person–Organization Fit (P–O Fit), the study conceptualizes happiness as a relatively stable evaluative set point reflecting leaders’ overall assessment of their happiness with their current lives, while well-being represents the psychological, relational, and contextual conditions that support and sustain that state over time (Cummins, 2010; Hobfoll, 1989; Kristof-Brown et al., 1996; Ryan & Deci, 2017). Using a sequential explanatory mixed-methods design, Study 1 analyzed cross-sectional survey data from women leaders in a large Canadian communications organization using multivariate regression and variance-partitioning techniques. The results identified clusters of conditions associated with higher leadership happiness, including values alignment, vitality and coping capacity, autonomy-supportive work conditions, and supportive relational resources. Study 2 involved semi-structured interviews with a purposive sample of highly happy leaders to explore how these conditions are experienced and sustained in practice. Integrated findings indicate that leadership happiness is grounded in a combination of holistic and workplace well-being conditions, including psychological need satisfaction, resource sufficiency, and alignment between leaders and their organizational environments. Building on these findings, the study develops and proposes an integrated theoretical framework explaining how leadership happiness is sustained among senior women leaders through the interaction of these psychological, resource, and contextual systems. The findings also provide practical insight for organizations seeking to design leadership environments that better support senior women leaders’ happiness and the well-being conditions that sustain it across work and life domains. Keywords: Leadership happiness, women in leadership, leadership well-being, women leaders, workplace well-being, mixed-methods researchItem type: Item , Access status: Embargo , Enhanced Depression Phenotyping in Inpatient Settings Using Machine Learning and Electronic Medical Records(2026-04-08) Lin, Na; Li, Na; Clement, Fiona; Eastwood, Catherine A.; Dahal, Kamala AdhikariDepression is a leading cause of disability worldwide and contributes substantially to morbidity, mortality, and healthcare burden. In inpatient settings, depression often appears as a secondary comorbidity that complicates clinical care, prolongs hospital stays, and increases readmission risk. Accurate identification of depression in hospital data is therefore essential not only for epidemiological research, but also for mental health surveillance, equitable resource allocation, and evidence-informed health system planning. However, case identification based on International Classification of Diseases (ICD) administrative codes has consistently shown low sensitivity, resulting in systematic under-ascertainment and potentially biased estimates of disease burden. This thesis aimed to develop and validate electronic medical record (EMR)-based phenotyping algorithms using natural language processing (NLP) and machine learning (ML) to improve depression detection among hospitalized adults in a Canadian acute care context. A retrospective cross-sectional design was used, including a derivation cohort of 3032 adult inpatient discharges from January to June 2015 and a temporally-independent external validation cohort of 10659 discharges from 2017 to 2022. Manual chart review served as the reference standard in both cohorts. Three EMR-based approaches were developed and compared with ICD-10-CA administrative coding: a rule-based Keyword Search model, a Concept Model that aggregated standardized clinical concepts extracted from free-text notes using cTAKES and classified patients with XGBoost, and a Document-Concept Model that retained document-level granularity. Model development included feature selection, hyperparameter optimization, and internal validation on a held-out test set, followed by external validation of the best-performing model. In the derivation cohort, the Concept Model achieved 76.4% sensitivity and 76.7% F1 score, outperforming the Keyword Search model, the Document-Concept Model, and ICD-10-CA coding. In the external validation cohort, the Concept Model achieved 92.3% sensitivity and an F1 score of 80.1%, whereas ICD-10-CA coding identified only 6.1% of cases. These findings show that EMR-based phenotyping can substantially improve inpatient depression detection, reduce measurement error in routine health data, and provide a scalable, policy-relevant approach for strengthening mental health surveillance and planning in Canadian acute care systems.Item type: Item , Access status: Open Access , The role of niche cell positioning and morphology on stem cell fate in C. elegans(2026-04-10) Chuk, Lucas; Hansen, David Donald; Ayyaz, Arshad; Cobb, John; Childs, SarahThe development and maintenance of all multicellular organisms rely on the ability of stem cells to proliferate and create identical daughter stem cells or differentiate and create specialized cells. The balance between proliferation and differentiation is crucial for the survival of multicellular organisms and is largely controlled by the interactions between the stem cell niche and the stem cell population. In the germline of the nematode Caenorhabditis elegans, the germline stem cell (GSC) population is maintained by GLP-1/Notch signaling from the somatic distal tip cell (DTC) that acts as the germline niche. We have identified that the protein CUP-2 (DER-1) plays a role in maintaining the position of the DTC. In wild type worms, the DTC is positioned at the distal end of the gonad arm and can become displaced proximally by 1-2 germ cell diameters (GCD) (Kocsisova et al. 2019), ~4-8 microns, as the worms age. In cup-2 mutants, the distance and frequency of DTC displacement increases significantly compared to wildtype worms at the same age. It has also been observed that if the DTC becomes displaced greater than 10 GCD the proliferating stem cell population shifts proximally along with the niche cell indicating that the DTC niche is still functional when displaced. The overall mechanism by which the DTC becomes displaced and how CUP-2 plays a role in niche cell positioning has yet to be identified. In this thesis I have explored multiple factors that could help elucidate the role CUP-2 plays in positioning the DTC at the distal end of the gonad. I first studied the morphology of DTCs from cup-2 mutants and wild type worms. I then compared the morphology of displaced DTCs versus non-displaced DTCs. This analysis compared morphological features to identify any differences that could point towards a biological mechanism that controls the positioning of the DTC and explain the displacement phenotype. I then performed a forward enhancer genetic screen with a cup-2 background to identify any other genes that may play a role alongside cup-2 in positioning the DTC and give us insight into how cup-2 acts to position the DTC. Finally, I performed RNA interference (RNAi) gene suppression experiments that explored where cup-2 expression was required for proper positioning of the DTC. These experiments help us to understand how DTC morphology plays a role in positioning the niche cell and the mechanism by which CUP-2 influences niche cell position.
