ScholarWorks@UMassAmherst
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Recent Submissions
Publication Tropicalizing the Graph Profiles of Some Collections of Trees(2024-09)Many important problems in extremal graph theory can be stated as certifying polynomial inequalities in graph homomorphism numbers, and in particular, many ask to certify pure binomial inequalities. For a fixed collection of graphs U, the tropicalization of the graph profile of U essentially records all valid pure binomial inequalities involving graph ho- momorphism numbers for graphs in U. Building upon ideas and techniques described by Blekherman and Raymond in 2022, we compute the tropicalization of the graph profile for K1 and S2,1k -trees for 0 ≤ k ≤ m−1, that is, stars with k+1 branches, one of which is subdi- vided. We call these almost-stars. This allows pure binomial inequalities in homomorphism numbers (or densities) for these graphs to be verified through a linear program in m + 1 variables and m + 5 constraints. We give a conjecture for the f-vector of this tropicalization. We also present a conjecture for the tropicalization of the graph profile for K1, stars, and almost-stars.Publication Synthesis and Characterization of Novel Anisotropic Foams(2024-09)This dissertation pertains to the investigation of innovative technologies to generate high performance anisotropic microcellular materials with unusual morphologies to understand the mechanisms of anisotropic formation and systems to control the structure and ultimate properties. First, a convenient and energy efficient method to produce anisotropic high performance polymeric foams via radically initiated cationic frontal polymerization (RICFP) coupled with chemical blowing agents (CBA) is presented. The results illustrate the development of anisotropy within frontal polymerization (FP) foam formation results from the propagating front working in concert with foam volume expansion. This can be controlled through changes in boundary conditions and front initiation position, which affect the microcellular structure and the physical and mechanical properties. Formulation changes, through the addition of nanoparticles, also affect the properties, microcellular characteristics, and kinetics of the FP process. Additionally, a similar method was developed where the microcellular structure and anisotropy is dictated by the directionality of the propagating front during RICFP from a free-standing gel and not by external confinement. This is DocuSign Envelope ID: 0570F892-1B1E-4799-9F90-7FDB4E1F15C3 viii achieved by first creating a gel where the crosslink density can be tuned by UV intensity and cure time, after which can be foamed while simultaneously creating a second network via RICFP. In this case, the microcellular morphology and ultimate properties are dictated and can be tuned through manipulating the crosslink density of the gel precursor or the formulation. Moreover, by patterning the crosslink density of the initial gel through controlled UV exposure, complex microcellular structures can be formed that are not possible in conventional foaming processes. Solid-state foaming was performed via supercritical-CO2 and superheated-water as green solvents, on an anisotropic media (e.g., fiber) to investigate how molecular orientation affects the resulting anisotropic microcellular structure. Further investigation into the use of this strategy to generate complex microcellular hierarchical constructs by templating assemblies of helically biased fibers was performed to understand their effect on the corresponding deformation. It was found that the anisotropic microcellular structure follows the direction of molecular orientation, resulting in a complex deformational response imposed by the template. That is, foams generated to create a helical bias are shown to undergo torsional deformation commensurate with uniaxial deformation when compressed uniaxially.Publication Mooring Systems for Floating Offshore Wind: Mooring Design, Biocolonisation, and Shared Anchors(2024-09)Offshore wind plays a crucial role in the green transition, with floating offshore wind (FOW) allowing access to deeper waters and expanding installation potential. However, further research is required to make FOW cost-competitive in these environments. This thesis addresses key challenges in mooring systems for FOW, utilizing the IEA 15 MW reference turbine on the UMaine VolturnUS semisubmersible platform [1] to match industry trends. The first chapter provides an overview of mooring systems and the research design process used throughout this thesis, including configurations, system components, modeling methodologies, design considerations, and evaluation methods. It also presents examples of mooring systems for existing FOW platforms. The second chapter investigates the impact of marine growth on mooring line behavior to inform structural health monitoring methods. Line tensions and positions are found to be sensitive to marine growth, with these sensitivities varying by mooring system type (catenary or taut) and environmental conditions. Dynamic simulations reveal variations in fairlead tension, node depths, and node velocities, suggesting a multi-parameter monitoring methodology tailored to each mooring system. Subsequent chapters focus on shared anchor systems. Chapter 4 characterizes cyclic loading for 3-line shared anchors, examining factors affecting cyclic capacity. Wave-driven cycles vary by site, providing insights for multiline anchor design. Chapter 5 compares modeling methodologies for farms with shared anchors, evaluating an uncoupled approach versus a coupled farm-level simulation tool. General agreement is observed between the methodologies, with differences noted due to wave coherence and wake effects. Chapter 6 compares 3-line and 6-line shared anchor layouts in deep waters, involving a comprehensive loads analysis, suction caisson design, and farm-level mooring cost assessment. While the 6-line system experiences higher loads, it exhibits lower inclinations and less variability, leading to similar suction caisson designs as the 3-line system. Shared anchor farms demonstrate cost reductions compared to baseline designs, with marginal differences between 3- and 6-line layouts. Wake modeling indicates varying impacts on anchor loads, with the baseline design showing the largest reductions in mean anchor loads due to wake effects.Publication Nuance and Complexity of First-generation College Student Success, from College Choice to Retention(2024-09)Higher education serves as an important vehicle for social mobility, particularly for students from disadvantaged socioeconomic backgrounds. However, achieving equitable outcomes in college access and success remains challenging, influenced by various layers of contexts, including personal, institutional, and policy dimensions. Despite increased attention and support for first-generation college students, significant disparities persist in retention and completion rates compared to their continuing-generation peers. Understanding these disparities and the complexities facing first-generation college students requires a close examination of the variation within the population. This dissertation aims to understand the complexities of the college experiences of first-generation students through three interconnected studies. This dissertation not only investigates heterogeneity within the first-generation college student population but also specifically seeks to explore how institutional-level factors affect first-generation students and how the interaction between institutional-level and personal factors shapes college experiences and outcomes. The first study investigates how high school contexts impact college choice for first-generation students, particularly leading to college undermatching. Additionally, this study contributes methodologically significance by demonstrating the inclusion and control of college selectivity when studying college undermatching as an outcome. The second study explores the differential effects of college undermatching on postsecondary outcomes for first-generation and non-first-generation students, including GPA and retention rates. The third study examines how postsecondary outcomes vary between students with and without cognitive disabilities, stratified by first-generation college student status. The findings of this dissertation study challenge the common notion of the first-generation college student population as a homegroups group. Results emphasize the importance of tailored support mechanisms at the institutional level, including secondary and postsecondary settings. By recognizing the diversity within this population, institutions can better address the unique needs of first-generation students and promote equitable outcomes.Publication The Role of the Endocannabinoid System in a Hibernator Model of Disuse Osteoporosis Resistance and the Anabolic Response to PTH Osteoporosis Treatment(2024-09)Osteoporosis is a disease of bone loss that affects 200 million women and results in over 8.9 million fractures annually. Determining an optimal treatment method for patients continues to be problematic because individuals exhibit unique responses to various current osteoporosis treatments. For instance, some individuals are nonresponsive to a specific osteoporosis treatment, such as parathyroid hormone (PTH). There is a strong clinical need for alternative osteoporosis treatments, as well as diagnostic methods that quickly and accurately evaluate an individual’s response to an osteoporosis medication for more effective treatment. Hibernators pose an intriguing model for osteoporosis treatment because they do not experience expected bone loss with age or from extended periods of disuse. However, the mechanism used by hibernators to prevent bone loss remains unknown. One potential mechanism hibernators may use to mitigate bone loss is the endocannabinoid system. Endocannabinoids are signaling molecules found throughout the body and are known to play a critical role in homeostasis of bone metabolism. This dissertation explores the influence of the endocannabinoid system in the regulation of bone metabolism of a hibernator through assessing: 1) Seasonal changes in endocannabinoid concentrations in bone and other metabolically relevant tissues of a hibernator, the yellow-bellied marmot; 2) Neural influence of the endocannabinoid system on bone metabolism though neurectomy in hibernating and active marmots; 3) Contribution of cannabinoid receptor CB2 on preventing bone loss in the hibernator, golden mantled ground squirrel through inverse agonism of CB2. This dissertation also examines the diagnostic efficacy of circulating endocannabinoid concentrations as biomarkers for bone loss during osteoporosis development, and for predicting long-term responsiveness to PTH osteoporosis treatment, longitudinally in vivo in a rat ovariectomy osteoporosis model. Furthermore, CB2 inverse agonism was utilized in this model to better define the role of the endocannabinoid system in PTH osteoanabolism. Endocannabinoid concentrations were quantified using targeted mass spectrometry and bone properties evaluated using micro-computed tomography. Notably, marmots exhibited substantial seasonal changes in the endocannabinoid system that may beneficially influence regulation of energy metabolism and mitigate bone loss with inactivity. Ovariectomized rat findings indicated that endocannabinoids may be efficacious as a biomarker for treatment response.
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