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Moment stability of strongly nonlinear structural systems under random excitations
(2026) Ghaedi, Maral; Deng, Jian; Wiebe, Richard; Siddiqui, Sultan; Gong, Yanglin
Many structures in civil engineering are subjected to dynamic loadings. Examples include wind-induced vibrations of cables and tall buildings, wave loading on offshore structures, and seismic excitations acting on civil infrastructure. These dynamic excitations can often be described satisfactorily in probabilistic terms. Current research trends in structural dynamics are evolving from deterministic to stochastic analysis, from linear to nonlinear systems, from elastic to viscoelastic behavior, and from external excitation alone to incorporating parametric excitation. This thesis investigates the stochastic stability of strongly nonlinear structural systems subjected to random parametric excitations, with stochastic stability referring to the long-term probabilistic growth or decay of the system response. The principal stability measure employed in this study is the Moment Lyapunov Exponent (MLE), which characterizes the exponential growth or decay rate of the statistical moments of the system response. Knowledge of the MLE gives the almost-sure asymptotic stability of a stochastic dynamical system through the corresponding Lyapunov exponent. The MLE is the ideal avenue and the ultimate characteristic number for the study of the dynamic stability of stochastic dynamical systems. A unified analytical and numerical methodology is developed for the evaluation of MLEs of nonlinear oscillatory systems. The analysis is primarily based on the stochastic averaging method, which allows the original nonlinear stochastic differential equations to be reduced to averaged equations governing the slow evolution of key response variables. Particular emphasis is placed on transformations based on the system Hamiltonian or total mechanical energy, through which the response of strongly nonlinear oscillators can be represented by an energy envelope. This formulation enables the derivation of analytical expressions for the drift and diffusion coefficients governing the stochastic evolution of the system energy and provides a tractable framework for moment stability analysis. In addition to the analytical formulation, a modified Monte Carlo simulation framework is developed for the numerical estimation of MLEs. In contrast with conventional algorithms that rely on the Euclidean norm of the state vector, the proposed approach employs the square root of the system energy as the generalized amplitude used in periodic normalization procedures. This energy-based formulation offers improved numerical robustness and provides a physically meaningful measure for the response of strongly nonlinear systems, allowing reliable estimation of the MLE through long-term stochastic simulations. Using the developed framework, the stochastic stability characteristics of nonlinear systems are investigated under three representative classes of stochastic excitation: Gaussian white noise, real noise modeled by the Ornstein–Uhlenbeck process, and bounded noise with phase modulation generated by a Wiener process. These excitation models represent different spectral and amplitude characteristics and physical realism commonly encountered in engineering applications. For each case, analytical expressions or approximate eigenvalue formulations for the MLE are derived, and the corresponding stability regions are evaluated. The analytical MLE predictions are compared against independent Monte Carlo estimates obtained directly from simulations of the original stochastic equations, demonstrating strong agreement between theoretical and numerical results. Furthermore, the thesis examines the influence of viscoelastic behavior, represented by a Maxwell-type model, on the stochastic stability of nonlinear systems. Viscoelastic effects introduce additional energy dissipation mechanisms and memory-dependent dynamics that may significantly alter the stability characteristics of the system. The results demonstrate that viscoelastic parameters, including relaxation amplitude and decay rate, can modify the effective damping properties of the system and thereby shift the moment stability boundaries under stochastic excitation. Overall, this thesis provides a comprehensive investigation of stochastic stability of strongly nonlinear structural systems and extends the MLE framework to include realistic stochastic excitation models and viscoelastic material behavior. The analytical formulations and numerical methodologies developed herein contribute to a deeper understanding of stochastic parametric instability in nonlinear structures and provide practical tools for assessing the probabilistic stability and reliability of engineering systems subjected to uncertain dynamic environments.
Vitality-centred education for adulthood: exploring alumni perspectives on the influences of Springhouse School on subjective adulthood
(2026) Lyngstad, Michael; Berger, Paul; Greenwood, David; Brown, Hilary
As we enter the second quarter of the 21st century, longstanding markers of adulthood in North American society such as marriage, parenthood, educational attainment, career establishment, financial independence, and home ownership are often delayed or are no longer being reached by many people in their twenties (Cannon, 2024a; Dalessandro, 2019; Hemez & Vespa, 2025; Ho et al., 2022). This is framed as a social problem (Cerullo, 2025) and a contributor to a growing mental health crisis among young people (Ladhani et al., 2019). Education is a factor in propagating these qualifiers of adulthood since schooling is said to contribute to adult identity development (A. Dewey, 2021; Sloan, 2005). However, little research has been done regarding correlates between school experiences and conceptions of adulthood (Erentaitė et al., 2018; Rich & Schachter, 2012). I spoke with seven young adult alumni of an alternative day school designed around holistic educational principles. I asked them about how they felt their school experiences influenced their views of what it means to be an adult. The findings reveal participants emphasised developing healthy relationships with themselves and community through practises such as cultivating emotional intelligence, exploring core values, and personal introspection. These qualities are not significantly represented in adulthood research. The findings point to the participants’ novel view of adulthood being influenced by a school environment grounded in relationships built on mutual trust and vulnerability.
Pathway-based multi-omics survival modeling: evaluating weak-modality contributions and robustness across cancer types
(2026) Guo, Jingfeng; Alkhateeb, Abedalrhman; Alsmadi, Malek; Ahmed, Saad B.
Multi-omics survival prediction must distinguish whether a modality enters a model from whether it improves prediction. This thesis evaluated the contributions of copy number variation (CNV) and somatic mutation (MUT) beyond clinical variables and ribonucleic acid (RNA) expression, together with the effects of pathway-based modeling and missing-modality training. Data from The Cancer Genome Atlas (TCGA) covered liver hepatocellular carcinoma (LIHC), breast invasive carcinoma (BRCA), and lower-grade glioma (LGG). Complete-case cohorts comprised 346 and 345 patients for LIHC progression-free interval (PFI) and overall survival (OS), respectively; 778 patients for each BRCA endpoint; and 503 patients for LGG OS. Gene set variation analysis (GSVA) mapped RNA expression to Hallmark pathways, each combined with seven CNV and four MUT summaries. Pathway-grouped composite minimax concave penalty (cMCP) Cox models were compared with Elastic Net using identical features and five frozen train–test splits. A gated residual model tested additional CNV/MUT information beyond a clinical-plus-RNA baseline. Paired bootstrap and permutation controls supported evaluation. Matched ensembles trained with and without modality dropout were tested under synthetic and natural missingness. Elastic Net assigned zero coefficients to at least one molecular block in every cancer–endpoint combination. Relative to same-feature Elastic Net, cMCP improved the mean concordance index (C-index) by 0.0374 for BRCA PFI and 0.0658 for BRCA OS, with both paired confidence intervals above zero. These discrimination gains did not consistently reduce absolute-risk prediction error. Conditional CNV/MUT increment was supported only for LGG OS, with a paired C-index increase of 0.0164 and a 95% confidence interval of [0.0051, 0.0300]; residual corrections were zero in all LIHC and BRCA splits. Modality dropout improved mean discrimination under synthetic missingness for LIHC and LGG but reduced it for BRCA, while natural-incompleteness results varied by endpoint. Exploratory graph ablations did not support a biological-topology advantage, and mediation analysis yielded 11 indirect statistical associations without establishing causality. The results separate penalization benefit, conditional modality information, and robustness to missing inputs. BRCA supported structured penalization, whereas LGG supported conditional weak-modality increment. These internally validated findings define endpoint-specific benefit boundaries without establishing universal model superiority or clinical utility.
The impact of ammonia inhalants on neuromuscular function during fatigued isometric contractions
(2026) Puskas, Liam; Klarner Read, Taryn; Zerpa, Carlos; Sanzo, Paolo
Ammonia inhalants (AIs) are commonly used by athletes to increase arousal and prepare for maximal physical effort; however, evidence supporting their ergogenic effects remains insignificant and/or inconsistent, particularly when exercise is performed under fatigued conditions. The purpose of this study was to determine the effect of ammonia inhalation on neuromuscular function following fatiguing exercise. Fourteen male varsity athletes completed a randomized, counterbalanced crossover design consisting of an AI condition and a control condition separated by one week. During each visit, participants completed a baseline 30-s maximal voluntary isometric contraction (MVIC) of the elbow flexors, followed by a standardized dynamic biceps fatigue protocol and a subsequent 30-s fatigued MVIC. Force and surface electromyography (sEMG) were recorded concurrently. Maximal isometric force, rate of force development to peak force production (RTP), time to maximal force (T2M), biceps sEMG amplitude, rate of force decline (RFDDecline), and mean power frequency (MPF) were assessed. Repeated-measures statistical analyses of variance were used to evaluate differences between treatment conditions and fatigue states. Maximal isometric force significantly decreased following the fatigue protocol (p < .001), with reductions of approximately 20% in both treatment conditions. However, no significant treatment × fatigue state interactions were observed for maximal force, RTP, T2M, biceps sEMG amplitude, or RFDDecline (p > .05). MPF progressively decreased across the 30-s fatigued contraction (p < .001), consistent with the frequency shift phenomenon and the development of myoelectric fatigue; however, neither the treatment effect nor treatment × time interaction was significant (p > .05). Collectively, the results provided evidence that the experimental protocol produced measurable mechanical and myoelectric manifestations of fatigue but did not provide evidence that ammonia inhalation significantly altered the measured indices of neuromuscular function during fatigued sustained isometric contractions in male varsity athletes. These finding suggest that athletes, coaches, and sport practitioners should not rely on AIs to preserve neuromuscular performance during sustained isometric exercise with performed under fatigue. Instead, performance preparation should prioritize evidence-based strategies for managing fatigue and recovery.
Three-dimensional geometric morphometric analysis of the intermediate cuneiform in anthropoids
(2026) Zachariasz, Jessica; Tocheri, Matthew; Varney, Tamara; Knigge, Ryan; Patel, Biren
The primate foot exhibits substantial morphological variation associated with locomotor behaviour, substrate use, and phylogenetic history. Despite its central role in load transmission, stability, and mobility during locomotion, the intermediate cuneiform remains one of the least studied tarsal bones in comparative morphology. This study uses three-dimensional geometric morphometrics (3DGM) to investigate variation in intermediate cuneiform morphology among anthropoids and assess the extent to which shape variation reflects locomotor behaviour, functional adaptation, and/or phylogenetic relationships. The sample for this study consists of 403 intermediate cuneiforms across various anthropoid species and focuses specifically on the facets that articulate with the navicular and second metatarsal bones and their impact on intermediate cuneiform shape. Digital 3D models derived from previously acquired laser scans of primate intermediate cuneiforms were analyzed using 3DGM of landmark and semi-landmark data. Analyses were conducted using generalized Procrustes analysis (GPA), principal component analysis (PCA), and Procrustes analysis of variance (PERMANOVA). Across all analyses, the first few principal components captured a substantial proportion of total shape variation, with the first three components explaining over half of the total variance. The results demonstrated that intermediate cuneiform morphology largely reflects phylogeny rather than any simple relationship with locomotor behaviour alone. Closely related taxa generally clustered together, whereas more distantly related taxa with similar locomotor behaviours frequently occupied different regions of morphospace. Atelids and colobus monkeys, for instance, clustered at opposite ends of the morphospace, despite both being primarily arboreal quadrupeds. The Procrustes analysis of variance further supports the interpretation that variation in the intermediate cuneiform is structured by phylogeny as well as locomotor behaviour, as it indicated that taxonomy and locomotor behaviour both explain a substantial proportion of total shape variation among anthropoids. Atelids, in particular, have short and stout intermediate cuneiforms that are unlike any other anthropoid in this study. Gorillas (and colobus monkeys to a degree) also have distinctive intermediate cuneiforms that are tall and narrow in shape. In addition to strong separation from other taxa, gorillas exhibit unusually high levels of interspecific and intraspecific variation in intermediate cuneiform morphology, suggesting that this variation is likely caused by lineage-specific evolutionary history. Unexpectedly, modern humans and fossil hominins occupied a relatively central position within the morphospace rather than forming a highly distinct cluster and consistently overlapped or clustered near orangutans despite major differences in locomotor behaviour. Overall, humans and most other anthropoids follow a similar structural framework for intermediate cuneiform morphology, with only minor differences occurring in the shape of this bone between species. These results suggest that the intermediate cuneiform is morphologically constrained, with phylogenetic history acting as the primary driver of variation while locomotor behaviour contributes secondarily.