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Determining the Effect of Structural Differences on the Degree of Conversion at the Gel Point of Rapid Cure Epoxy Thermoset Resins
No full textThe degree of conversion at the critical gel point of a polymer system has been calculated, measured, or modeled using a variety of mathematical and experimental techniques for nearly 90 years. In this research, a new method is presented to determine the degree of conversion at the gel point, or α_gel, of rapid cure thermoset epoxy novolac resins cured by dihydrazide curing agents. These data are then used to correlate the effects of different structure/property relationships on the value of α_gel for use in formulating rapid cure thermoset epoxy prepreg resins applicable to the hydrogen storage pressure vessel industry. The data obtained in this new research method is contrasted with the α_gel predictions created by the Carothers theory and the Flory-Stockmayer theory. It was found that when intramolecular reactions are expected to occur, based on the functional chemistry of the formulation, the Flory-Stockmayer theory underestimated the value of α_gel and the Carothers theory overestimated the value of α_gel. When structural effects were conducive to the creation of a high level of molecular sterics, due to high resin functionality and molecule size, the Flory-Stockmayer theory prediction matched the experimentally measured values. When the governing cure reaction was understood to be etherification rather than stepwise addition, based on formulation chemistry and referencing similar chemistry cited in the literature, both the Carothers and Flory-Stockmayer theory underestimated the value of α_gel, however, the prediction by the Carothers theory was more accurate than the Flory-Stockmayer theory for this specific circumstance. This research used isothermal gel data collected by a rheometer, which measures physical effects, to identify the crossover point between three different frequencies of the tan delta curve at four different temperatures to obtain the chemical gel point, following the method of Winter et al. By following the method of Hoffman and Boll, these four gel temperatures were used to create a derived mathematical model with resin formulation specific kinetic constants capable of modeling the chemical gel point under dynamic and isothermal cure conditions. Differential scanning calorimetry, which measures kinetic processes, is used to determine the degree of total chemical conversion, or α. In a novel method to determine the degree of conversion at the chemical gel point, the derived resin system specific kinetic constants are used to mathematically model and convert physical rheology data to kinetically modeled data that are used to interpolate within the range of α, as measured by calorimetric techniques.
In this research, three different functionalities of novolac resin are presented and evaluated for the value of α_gel. Each of these novolac resins were evaluated in formulations with varied structural substitutions which were optimized to contain identical epoxide content and 1:1 stoichiometry balance to a dihydrazide curing agent. Each formulation also contained a urone accelerator to effectively lower the onset point of the dihydrazide curing agent and further facilitate rapid cure behavior at lower temperatures. To identify the contributing structure/property effects to the rate of cure, each formulation was compared with a control or reference formulation, with a total of 15 different epoxy formulations being evaluated in this study. In these 15 formulations, the most common contributing effect to the change in the value α_gel was the change in resin functionality. A change in the physical structure of the accelerator was found to not significantly affect the value of α_gel, regardless of the resin functionality evaluated. For many formulations, an increase in the functionality of the novolac resin decreased the value of α_gel in reference to the lower functionality resins, and the value of α_gel remained constant for the higher functionality formulations cured by adipic dihydrazide, an aliphatic dihydrazide curing agent. However, as the functionality of the novolac resin increased in formulations cured with isophthalic dihydrazide, an aromatic curing agent, the value of α_gel was found to increase significantly with simultaneous reduction in the overall cure time. These differences were attributed to the governing curing reaction proceeding by epoxy etherification versus stepwise addition for the aromatic versus aliphatic dihydrazide chemistries, respectively.
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Additives in solid-solutions: Understanding structural properties of alloys from electron & phonon dynamics
No full textThe overarching goal of this dissertation is to explore and examine the effect of adding specific elements to an alloy on its properties. By mixing additives into pure metals and alloys, one can modify the structural properties, thermal stability, and electronic characteristics of the resulting solid-solutions. These modifications are primarily driven by changes in electron behavior and phonon dynamics, which in turn affect the overall structural and functional response of the material. The body of this dissertation is sequentially organized into four chapters, each focusing on a unique solid solution and shedding light on the complex interplay between composition, electronic and phononic behavior, and structural properties. First, we scrutinize the effects of aluminum and zinc on the elastic properties and lattice dynamics of a commercial lightweight AZ80 magneisum alloy. Despite its low concentration, aluminum significantly enhances the mechanical strength of the ensuing solid-solution by modulating the Fermi surface. Zinc, on the other hand, has minimal impact on the orbital-resolved band structure but affects lattice dynamics. Our findings highlight that charge sharing between magnesium and aluminum contributes to the anisotropy in the elastic properties of the solid-solution. Next, we extend the analyses to refractory alloys, albeit dilute solid-solutions, where hafnium plays a crucial role in influencing mechanical properties and phase transformations. At lower concentrations, Hf enhances strength through solid solution strengthening but destabilizes the structure at higher concentrations. Then, we interrogate the impact of rhenium additives to tungsten for enhancing ductility in dilute refractory solid-solutions. On one hand, this investigation uncovers an alloy with an optimal rhenium atomic percent exhibiting preferential elastic softening, driven by both electronic and phonon characteristics. A newly developed probabilistic theory further substantiates this phenomenon, highlighting the subtle interplay between charge localization, phonon softening, and slip systems. Finally, we employ the insights gained towards understanding the role of lattice dynamics in concentrated solid-solutions, such as medium- and high-entropy alloys, and the generation of mechanical and thermal properties in such compositionally complex metallic mixtures.In gestalt, our findings underscore the critical role of lattice dynamics, electronic structure, phonon softening and broadening on the structural properties and crystallographic phase of solid-solutions, and how to tailor such properties of complex metallic mixtures through additives. The analyses of phase equilibrium between competing lattice structures offers recommendations on the suitability of an alloy for extreme temperature applications. In particular, phonon calculations help us understand phase stability, addressing a crucial gap in the current literature. Introducing additives significantly alters dispersion relations and the resulting density of states, creating an opportunity for improving and altering properties of both commercially produced alloys and designer solid-solutions for assuming tailored thermal, electronic, and mechanical properties. This research paves the way for the development of advanced alloys with enhanced performance in catalysis, energy conversion, and most significantly for high-temperature applications such in propulsion and nuclear systems.</p
Evaluating Child, Parent, and Family Predictors and Moderators of School Readiness for Young Children with Asthma
No full textPrior research demonstrated a relationship between an asthma diagnosis and children\u27s early academic and social-emotional skills at school entry. Children\u27s contextual factors (i.e., individual, parent, and family factors) are associated with both asthma management and school readiness. Few studies in the past two decades have evaluated this relationship in young children, although research demonstrates that children under age four have the greatest asthma-related healthcare use compared to children aged 5 through 17. The current study evaluated the relationship between the diagnosis of asthma and school readiness for young children in a nationally representative sample of U.S. children, and explored child, parent, and family factors as moderators of this relationship. The sample included 6,984 parents of young children (i.e., aged 3 to 5 years) with asthma (with/without comorbid medical conditions) and healthy children who completed the 2016 National Survey of Children\u27s Health. Results demonstrated, child ethnicity, parent marital status, parent nativity, and parent stress were associated with scores of school readiness and demonstrated large effect sizes. Parent education level and family income, as measured by Federal Poverty Level, were also associated with school readiness and demonstrated small effect sizes. Similar to prior research, child health status (i.e., healthy children or children with asthma or asthma and a comorbid medical condition) was associated with school readiness and this finding demonstrated a small effect size. Family income was a moderator of the relationship between the diagnosis of asthma and school readiness for young children in the U.S., which was also consistent with prior research. This finding yielded a small effect size. Findings from the current study extend the line of research on school readiness for children with asthma by demonstrating significant interactions between child, parent, and family factors with school readiness on a national level in the U.S. School psychologists are poised within the school and healthcare settings to directly support caregivers of children with asthma. Additionally, school psychologists can provide consultation to physicians and school staff who also interact with and support this unique population. Limitations, practical implications for clinicians, and directions for future research are discussed. </p
Calabi Hyperkahler Manifold and Singularity Models of U(3)-Invariant Ricci Flow
No full textWe follow the technique in \cite{Appleton2023} and show the occurrence of singularities in a eight-dimensional Ricci flow, which is isometric to the Calabi\u27s hyperk\"ahler space. Specifically, we establish that when started with a set of asymptotically cylindrical -invariant metrics on \tcp^2, a Type II singularity, isometric to the Calabi\u27s hyperk\"ahler space, occurs within a finite time. Additionally, we prove that the only possible outcomes of these Ricci flows at the point of blow-up are (i) the Calabi\u27s hyperk\"ahler space, (ii) the flat , (iii) , where or .</p
Integration of AI-Powered Speech Analysis Tools in Speech Therapy - Project Summary
No full textIntegrating AI-powered tools in diagnostics and treatment of Speech Sound Disorders, improving accessibility and reducing Speech-Language Pathologist workload.I utilized AI-powered speech analysis tools into speech therapy to enhance the diagnosis of Speech Sound Disorders (SSD). Given the limited access to Speech-Language Pathologists (SLPs) and the large number of people with the need for Speech Therapy in the United States, there is a large caseload for SLP\u27s in America. My work aims to bridge this gap by utilizing AI technologies such as automatic speech recognition and large language models. These tools can streamline diagnostics, create individualized therapy materials, and reduce SLP workloads, thereby addressing burnout and improving accessibility to care. Focusing on preschool-aged children due to its relevance in SSD disorder diagnosis, my approach involves reviewing existing diagnostic tools, collaborating with AI and programming experts, developing a coding framework, and planning for validation and replication of the AI system.</p
Evaluating the carbon footprint of the integrated DBD‐plasma bi‐reforming unit via laboratory scale experiments and scaled‐up process modeling
No full textCatalytic dielectric barrier discharge (DBD) plasma reactor experiments were performed in a tubular glass reactor with a 2 mm gap at 550°C to facilitate the reaction kinetics of steam added dry reforming or bireforming. The best specific energy input obtained was 11.2 eV/molecule feed at CO 2 :CH 4 :H 2 O of 4.5:1:4.5 ratio and gas hour space velocity (GHSV) = 432 h −1 . This value was used to design a conceptual process and assess the environmental impact of methane steam reforming‐based H 2 production 18.4 kmol/h CO 2 emission processing into H 2 :CO = 2 syngas, with an emphasis on the carbon footprint
Exploring behavioural patterns and their relationships with social annotation outcomes
No full textBackground Social annotation has emerged as a promising educational technology that fosters collaborative reading and discussion of digital resources among learners. While the positive impact of social annotation on students\u27 learning process and performance is widely acknowledged, students\u27 behavioural patterns in social annotation are underexplored. Objectives This study investigated patterns in students\u27 use of annotation and response behaviours in social annotation activities. We also explored how students\u27 performance in the behavioural, cognitive, emotional, and social dimensions varied based on their behavioural patterns. Methods We recruited 93 undergraduates who were enrolled in an elective course at a large North American University. Students were tasked with collaboratively annotating the class readings uploaded to Perusall, a social annotation platform, over 7 weeks. We used metaclustering to determine the optimal number of clusters pertaining to student behaviours. We compared the differences among clusters across multiple performance dimensions. Results and Conclusions Two distinct clusters were identified and defined as initiators and responders. We found that responders had significantly longer active reading time and exhibited greater social annotation effort compared to initiators. However, initiators received more peer acknowledgement, as evidenced by higher upvotes. No significant difference was found in cognitive insight between initiators and responders, but responders demonstrated significantly higher cognitive discrepancy. Additionally, there were no significant differences in positive and negative tones between initiators and responders; however, responders displayed higher levels of prosocial behaviours than initiators. This study has significant practical implications regarding promoting students\u27 collaborative learning experience in social annotation. , Lay Description What is already known about this topic Annotation and response behaviours are two primary actions in social annotation. Understanding how students navigate through annotations and respond to their peers\u27 contributions is essential for optimizing their learning experience. Social annotation outcomes can be assessed in the behavioural, cognitive, emotional, and social dimensions. What this paper adds This paper revealed students\u27 behavioural patterns in social annotation activities. This study offered a comprehensive understanding of the various dimensions of performance among students with different behavioural tendencies. Implications for practice and/or policy The two student clusters, initiators and responders, revealed distinct engagement patterns in social annotation and informed the design of targeted scaffoldings. Responders were not passive learners since they demonstrated significantly longer active reading time, greater social annotation effort, and higher level of prosocial behaviours. Educators might not need to place significant emphasis on monitoring participants\u27 emotional expressions in social annotation. Social annotation platforms should incorporate features that encourage and reward both initiation and response behaviours
Girls are good at <span style="font-variant
No full textGirls and women face persistent negative stereotyping within STEM (science, technology, engineering, mathematics). This field intervention was designed to improve boys\u27 perceptions of girls\u27 STEM ability. Boys ( N = 667; mostly White and East Asian) aged 9–15 years in Canadian STEM summer camps (2017–2019) had an intervention or control conversation with trained camp staff. The intervention was a multi‐stage persuasive appeal: a values affirmation, an illustration of girls\u27 ability in STEM, a personalized anecdote, and reflection. Control participants discussed general camp experiences. Boys who received the intervention (vs. control) had more positive perceptions of girls\u27 STEM ability, d = 0.23, an effect stronger among younger boys. These findings highlight the importance of engaging elementary‐school‐aged boys to make STEM climates more inclusive
The DECam Ecliptic Exploration Project (DEEP). VI. First Multiyear Observations of Trans-Neptunian Objects
No full textAbstract
We present the first set of trans-Neptunian objects (TNOs) observed on multiple nights in data taken from the DECam Ecliptic Exploration Project. Of these 110 TNOs, 105 do not coincide with previously known TNOs and appear to be new discoveries. Each individual detection for our objects resulted from a digital tracking search at TNO rates of motion, using two-to-four-hour exposure sets, and the detections were subsequently linked across multiple observing seasons. This procedure allows us to find objects with magnitudes m
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≈ 26. The object discovery processing also included a comprehensive population of objects injected into the images, with a recovery and linking rate of at least 94%. The final orbits were obtained using a specialized orbit-fitting procedure that accounts for the positional errors derived from the digital tracking procedure. Our results include robust orbits and magnitudes for classical TNOs with absolute magnitudes H ∼ 10, as well as a dynamically detached object found at 76 au (semimajor axis a ≈ 77 au). We find a disagreement between our population of classical TNOs and the CFEPS-L7 three-component model for the Kuiper Belt.</jats:p
The DECam Ecliptic Exploration Project (DEEP). V. The Absolute Magnitude Distribution of the Cold Classical Kuiper Belt
No full textAbstract
The DECam Ecliptic Exploration Project (DEEP) is a deep survey of the trans-Neptunian solar system being carried out on the 4 m Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile using the Dark Energy Camera (DECam). By using a shift-and-stack technique to achieve a mean limiting magnitude of r ∼ 26.2, DEEP achieves an unprecedented combination of survey area and depth, enabling quantitative leaps forward in our understanding of the Kuiper Belt populations. This work reports results from an analysis of 20, 3 deg2 DECam fields along the invariable plane. We characterize the efficiency and false-positive rates for our moving-object detection pipeline, and use this information to construct a Bayesian signal probability for each detected source. This procedure allows us to treat all of our Kuiper Belt object (KBO) detections statistically, simultaneously accounting for efficiency and false positives. We detect approximately 2300 candidate sources with KBO-like motion with signal-to-noise ratios > 6.5. We use a subset of these objects to compute the luminosity function of the Kuiper Belt as a whole, as well as the cold classical (CC) population. We also investigate the absolute magnitude (H) distribution of the CCs, and find consistency with both an exponentially tapered power law, which is predicted by streaming instability models of planetesimal formation, and a rolling power law. Finally, we provide an updated mass estimate for the CC Kuiper Belt of
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, assuming albedo p = 0.15 and density ρ = 1 g cm−3.</jats:p