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Defining Fidelity for Tradespace Application
Get PDFThis research proposes a definition of tradespace fidelity and presents a study on its effectiveness in the tradespace. Tradespace exploration helps evaluate various design options, allowing engineers to make informed decisions in early design stages. Fidelity generally refers to how closely a model approximates reality. However, the definition of fidelity has been inconsistently defined and interpreted in various contexts concerning particular problems. In some cases, it is a measure of accuracy; in others, information; in another, uncertainty; and in others, computational complexity. Fidelity is poorly and inconsistently defined in the literature. In general, higher fidelity models tend to be more accurate with respect to reality but can be computationally expensive to evaluate and less robust under different evaluation scenarios. Conversely, lower fidelity models are quicker and more flexible but may lack accuracy. The study provides a comprehensive literature review to understand the attributes used by various researchers to define fidelity over time. It also introduces a methodology for a novel approach to defining and quantifying tradespace fidelity using vectors and norms, which allow for a more objective comparison of relatively similar models. This definition allows for trade-offs between model uncertainty and computational complexity to be evaluated to determine the relative fidelity of different models within the tradespace. Effectively, this method evaluates fidelity as a relative metric between models rather than an absolute measure. The study aims to bridge the gap between subjective assessments and objective measurements by quantifying tradespace fidelity, enabling more consistent and reliable trade-offs in tradespace
Growth, Cladding, and Characterization of Single Crystal Optical Fiber: The Next Evolution in Directed Energy Systems
Get PDFHigh-power fiber lasers are steadily increasing in maximum power and rapidly approaching theoretical maximum power output from a single fiber aperture. The low thermal conductivity of silica fibers is an inherent limitation to the dissipation of heat from the fiber core, and the buildup of heat within the laser gain media is the principal driver of transverse mode instability within fiber systems. This limitation necessitates the exploration of alternate fiber host materials. Due to their high thermal conductivity, excellent transmission range, ability to host most of the optically active rare earth ions, and success as bulk laser materials, single-crystalline YAG and Lu2O3 are excellent candidates as high-power fiber lasers. Lu2O3 is especially promising due to its ability to maintain high thermal conductivity upon Yb-doping. Here, we grow Yb:YAG single-crystal fibers to demonstrate the effective commissioning of the LHPG system at Clemson University, and the system is used to grow the first reported sub-200 mm, Yb:Lu2O3 single-crystal fibers via the LHPG technique. Moreover, the Yb:Lu2O3 fiber cores are clad with single crystalline Lu2O3 for the first time via the hydrothermal synthesis technique. The crystallinity of the clad fiber system is confirmed through single-crystal X-ray diffraction, SEM imaging, and Raman spectroscopy, and the core-cladding interface properties are specifically addressed. Spectroscopic properties of the unclad Yb:Lu2O3 fibers are measured for various dopant concentrations, and amplification is demonstrated within the unclad system. Parallel thermal conductivity measurements along the fiber axis of a YAG-clad, Yb:YAG fiber core are modeled to probe the phonon properties across the core-cladding interface. The results reported in this study suggest that single crystal fibers show great potential for high-power laser systems, although further development is needed before high power levels can be achieved
3D Bioprinting of Hydrogel Scaffold Skin Equivalents for Cosmetic and Drug Testing
Get PDFTissue engineering scaffolds are a crucial element of generating larger 3D tissue equivalents for modeling and clinical grafting. Currently, much of scaffold technology has not been significantly updated since the introduction of manually pipetted hydrogels and electrospun fiber scaffolds. Both of these approaches have their advantages and disadvantages, but neither utilize emerging biofabrication techniques such as advanced 3D bioprinting and plotting. In addition to more precision in the outer geometries of the scaffold, the use of bioprinting also introduces the ability to shape hydrogels into very intricate porous inner patterns within the outer geometries. This allows for the design of a highly intricate and advanced network of ECM like material that is highly similar to the real porous environment of tissues, allowing for gas and nutrient exchange similar to that which occurs due to microvasculature of tissues. Additionally, advanced temperature-controlled extrusion bioprinters with UV cure capabilities allow for utilizing very advanced hydrogel materials. These materials can be designed and tailored to maximize their mechanical properties, adhesion, similarity to the natural ECM/basement membrane, and have the ability to be UV cured into very intricate, high resolution, and detailed prints. The unique shapes and materials that can be utilized with advanced 3D extrusion bioprinters significantly improves the adhesion, proliferation, and viability of cells within scaffolds. The use of common tissue engineering hydrogels modified for use as UV cure bioinks allows for precise printing and simple seeding and growth for a robust and advanced scaffold for generation of 3D tissue equivalents. In this dissertation, these technology advancements will be applied to the advancement of 3D skin equivalents for modeling skin for cosmetic and drug testing. Demonstrating both the general efficacy of 3D printing of scaffolds for tissue engineering, and more specifically, the advantages when designing for a specific tissue model, in this case skin equivalents, and how materials, outer geometry, and inner geometry can all be customized to produce an excellent 3D model very similar to the native tissue
Stromal Cells in the Small Intestine: Physiology, Localization, Function, and Alterations Induced by Chronic Arsenic Exposure
Get PDFArsenic is a prevalent toxicant found to affect around 94 to 240 million individuals in over fifty countries who are exposed to levels above the EPA and WHO standard of 10 ppb. As one of WHO’s top ten chemicals of public health concern, it is linked to several chronic diseases including diabetes, obesity, cancers, and inflammatory bowel diseases. Arsenic increases inflammation and disrupts the intestinal barrier in the small intestine and colon. Further, previous studies found that arsenic decreased secretory cell lineage and stromal cell gene expression markers in the small intestine. Thus, our goal was to investigate arsenic’s effect on Pdgfrα stromal cell numbers, localization and signaling, while also observing how stromal cells change between the duodenum, jejunum, and ileum.
First, thirty-six Sox9 tm2Crm-EGFP (strain B6:129S4-Sox9/J) mice were exposed to 0, 33, and 100 ppb arsenic for 13 weeks, which are environmentally relevant concentrations. Sox9 fluorescence was used as a marker for enteroendocrine cells (EECs; secretory cell lineage), transit amplifying cells (TA; immature absorptive and secretory cells), and intestinal stem cells (ISCs). A fluorescein isothiocyanate-dextran 4000 (FD-4) gavage was also conducted to assess intestinal barrier damage. From this study, duodenal tissue was collected for flow cytometry, immunohistochemistry, and RT qPCR. Flow cytometry analysis revealed an overall population decrease in Sox9 expressing cells (EECs, TA cells, and ISCs), while no changes in barrier function were observed (FD-4). qPCR revealed a significant decrease in the trophocyte marker Cd81 by 10- and 9.0-fold in males and females, respectively. IHC data discovered sex-dependent differences in response to arsenic toxicity (at 100 ppb) with telocytes (PdgfrαHi) increasing in female mice. Trophocytes (PdgfrαLo) and Igfbp5+ fibroblasts (PdgfrαLo), with their signaling protein Grem1, increased in males. PCA validated these sex-dependent changes, which also revealed sex differences may also be present between male and female controls.
The results of this study led to a second exposure with thirty-eight (B6129SF2/J) mice exposed to 0, 100, and 500 ppb for 13 weeks. The goal of this study was to expand our tissue collection to include all three regions of the small intestine - the duodenum, jejunum, and ileum. We also examined expression of Igfbp5+ and Fgfr2+ fibroblasts, which are recently discovered stromal cell types that were not analyzed in the first exposure. Tissue was collected and processed for RT-qPCR, IHC, and immunoblotting from the duodenum, jejunum, and ileum. Markers used to assess changes between small intestinal regions and arsenic exposure were Pdgfrα, Cd201, Bmp4, Bmp5, Cd81, Grem1, Igfbp5+, Fgfr2+, and Olfm4. Physiologically, telocyte (PdgfrαHi expressing) numbers and Cd201 levels in males and females were reduced in the ileum compared to the duodenum; meanwhile, only male Bmp4, a telocyte signaling protein, was reduced. Gene expression of Igfbp5+ markers decreased from the duodenum to jejunum, while Fgfr2+ fibroblasts increased. Finally, IHC revealed Igfbp5 fibroblast numbers were higher in male mice in all three regions of the small intestine.
As a result of arsenic exposure, arsenic seemed to target ileal stromal cells the greatest. Pdgfrα, Cd201, Cd81, Grem1, Igfbp5, and Fgfr2 gene expression changes were observed in female mice; however, these changes were not seen in males. In both males and females, telocyte (PdgfrαHi) markers were significantly increased by 6.3-fold in males and 2.3-fold in females at 500 ppb. Overall, the findings suggest arsenic affects Pdgfrα stromal cells as an attempt to maintain the ISC niche resulting in the preservation of small intestine homeostasis
Exploring the Pedagogical Impact of Software Development Live Streams: Informal Learning Opportunities for Software and Game Developers
Get PDFLive streaming is an increasingly popular medium for throwing back the curtain on software development where streamers and viewers share their knowledge and experiences. Popular platforms like Twitch and YouTube enable developers to stream live coding sessions where people around the world can engage in real-time collaboration, feedback, knowledge sharing, and skill development. This work investigates the pedagogical implications and learning opportunities present in software and game development live streaming while focusing on the role of streaming as a learning environment and collaborative community. We begin by exploring summer camps as an informal learning opportunity for STEM education, highlighting the impact that informal learning has on students. Next, we explore the motivations of software and game development live streamers and how they find accountability, community, and continued education through their streams. Next, we investigate the viewers\u27 perspectives of software live streams, what motivates them to watch, participate or engage, and ultimately, what they receive by being a viewer of this type of stream. Finally, I present a case study on collegiate-level computer science students\u27 live streaming software and game development projects, aiming to understand how they approach and use live streams and where their perceived skill development progresses. The implications of this research extend outside of academia to educators and industry professionals seeking to begin or continue a journey to software development education. Understanding and highlighting the benefits of live streams as a learning platform contributes to democratizing knowledge within the software and game development communities and provide an alternative and digital approach to education for those unable to access or participate in traditional educational settings
Deciphering and Translating Bioinspired Structures for Engineering Materials Design via Computational Modeling and Machine Learning
No full textNature has evolved extraordinary structural materials—such as nacre, bone, and the mantis shrimp’s dactyl club—that achieve remarkable combinations of strength, toughness, and impact resistance. These properties arise from sophisticated synergies between structure and composition. Inspired by these biological systems, this dissertation presents a comprehensive investigation into bioinspired materials, uncovering fundamental mechanisms and providing guidance on designing materials with superior mechanical properties.
This dissertation begins by examining the brick-and-mortar structure of nacre, which informs the design of layered polymer-graphene nanocomposite films. Using coarse-grained molecular dynamics simulations, I elucidate mechanisms of dynamic wave propagation and energy dissipation in these systems, providing critical insights for the development of lightweight, impact-resistant structures. Inspired by the impact-resistant coating on the dactyl club of the mantis shrimp, I propose a novel class of nanoparticle-polymer nanocomposites that overcome the conventional stiffness-damping tradeoff. By introducing dynamic heterogeneity through nanoparticle reinforcement, these composites achieve simultaneous enhancements in stiffness and energy dissipation—offering transformative potential for protective materials and structural applications.
Mammalian tissues are then introduced as a new inspiration for material design. The porous microarchitecture of bone is emulated through freeze-casting to produce biomimetic scaffolds. By integrating 3D printing, finite element modeling, and mechanics theory, I establish predictive relationships linking scaffold architecture to mechanical performance, enabling the rational design of bone-like scaffolds. Additionally, I investigate the tendon-bone insertion, a natural gradient material that seamlessly joins soft tendon and hard bone without leading to stress concentrations. Through analysis of its structure-composition-property relationships, I uncover mechanisms underlying its remarkable load transfer and damage tolerance, which inform the design of robust interfaces for engineering materials with dissimilar mechanical properties.
Having mapped the pathways from structure and composition to mechanical function in biological materials, I then shift focus to inverse design—determining optimal structural and compositional configurations that yield desired mechanical properties. I demonstrate this approach using individual interface fibers at the bone end of the tendon–bone insertion. The mechanical behavior of these fibers depends on three spatial fields: mineralization scale, fibril angular dispersion, and mean fibril orientation. I develop a multiscale continuum model to predict fiber properties based on these inputs, generating a dataset used to train a convolutional neural network (CNN)-based surrogate model. This trained model enables an inverse design framework that integrates predictive modeling with gradient descent optimization. A case study validates the approach, demonstrating its efficacy in identifying optimal design parameters.
This dissertation establishes a unified framework for the bioinspired design of next-generation structural materials. By uncovering the structure–function relationships of natural systems and leveraging data-driven inverse design techniques, I offer actionable pathways to engineer materials for advanced applications in aerospace, protective technologies, and biomedical devices
Exploring Community Change of North American Stream Fish Communities Due to Species Introductions
No full textThe introduction of nonnative species has facilitated global changes in beta diversity, and these changes have been coined biotic homogenization (loss in beta diversity) and differentiation (gain in beta diversity). Homogenization represents a key conservation threat. Therefore it is imperative to understand the processes that allow nonnative species to establish and how these species contribute to beta diversity change. In this dissertation, I assess three key challenges exist in our ability to address these goals. One challenge is that we have inconsistent support among hypotheses of invasion drivers due to context dependency. Context dependency can arise due to differences in methodology and study design (i.e. apparent) or through differing ecological processes (i.e. mechanistic), accounting for both is critical to gain a general understanding of invasion processes. A second challenge is that many beta diversity change studies use taxonomic measures of diversity, which inconsistently relate to ecological processes. Beta diversity can be measured in multiple dimensions that better represent the complexity of community changes on ecosystems. Therefore, a multidimensional approach to beta diversity change is needed to understand ecological consequences of invasions. Finally, nonnative species do not universally cause homogenization to occur. Factors related to nonnative species origins and native community structure can determine trajectory of beta diversity change. Therefore, we need a better understanding of the factors that affect the trajectory of beta diversity change. I addressed these three challenges using fine resolution, continental extent stream fish community data for the United States. Specifically, I (1) demonstrated that both apparent and mechanistic context dependency can confound interpretation of invasion drivers, (2) classified communities into syndromes of multidimensional beta diversity change, demonstrating that taxonomic diversity is not sufficient to understand consequences of nonnative species, and (3) identified multidimensional beta diversity change drivers related to species origin and native community structure. From my findings, I present three recommendations to future invasion studies: make explicit and transparent methodological choices to reduce apparent context dependency, move away from one-dimensional diversity metrics and blanketed definitions of nonnative species, and consider the intersection of regional- and local-scale processes in biological invasions. By considering these recommendations, invasion ecology can benefit from a more general and mechanistic understanding of invasion processes
Preparing Preservice Teachers to Support Culturally and Linguistically Diverse Students Through the Implementation of a High Leverage Practice
No full textThe student population of United States (U.S.) schools is becoming more culturally and linguistically diverse. Similarly, students identifying as culturally and linguistically diverse students represent approximately 54% of students served under the Individuals with Disabilities Act (U.S. Department of Education, 2023). Despite increased ethnic diversity among students, the teacher workforce remains relatively homogenous, with most teachers identifying as White. Consequently, many new teachers feel ill-equipped to implement effective, evidence-based instructional practices to support culturally and linguistically diverse students. To prepare preservice teachers to meet culturally and linguistically diverse students\u27 unique needs, teacher preparation programs must embed culturally relevant pedagogy and high-leverage practices (Aceves & Kennedy, 2024) into their curricula. This dissertation consists of three papers describing effective methods teacher preparation can use (e.g., explicit teaching, field placements, and practice-based opportunities) to equip preservice teachers with evidence-based practices to support culturally and linguistically diverse students. Paper 1 begins with a pilot study describing the use of explicit teaching, mixed-reality simulation, and performance feedback to prepare preservice teachers enrolled in a special education methods class to implement culturally responsive teaching practices to support culturally and linguistically diverse students. Paper 2, a systematic literature review, explores specific methods teacher preparation programs use to prepare culturally relevant preservice teachers. It introduces a culturally relevant pedagogical framework (Gay, 2002; Ladson-Billings, 1995; Paris, 2012), details various methods teacher preparation programs use to embed culturally relevant pedagogy into their curricula, and describes the impacts of teacher preparation curricula on preservice teachers\u27 attitudes towards supporting culturally and linguistically diverse students. Finally, Paper 3 extends the pilot study design and participant pool from Paper 1 and the theoretical framework from Paper 2. Paper 3 also examines how using explicit teaching, mixed-reality simulation, and performance feedback impacts preservice teachers\u27 knowledge of and attitudes about a culturally relevant high-leverage practice. The results of this dissertation indicate how intentionally embedding culturally relevant pedagogy and a high-leverage practice into teacher preparation program curricula positively impacts preservice teachers\u27 knowledge of and attitudes toward evidence-based instructional practices that support culturally and linguistically diverse students. The findings also provide recommendations for future research and teacher preparation programs
The Math Doesn\u27t Add Up: Gender Inequity in Service Responsibilities in Research-Intensive Mathematics Departments
Get PDFAcademic service responsibilities (e.g., committee work, mentoring), in the most informal definition, are those tasks faculty perform that are neither research nor teaching. However, the simplicity of this definition undercuts not only the tremendous impact service can have on faculty efforts but also the well-documented, disproportionately high service burden carried by faculty with marginalized identities. This study, grounded in the existence of gender inequities in service responsibilities, comprises three interconnected papers that collectively address the overarching research question: How do math faculty at research-intensive institutions perceive, describe, and navigate gender inequities in service responsibilities? Utilizing the framing of Intersectional Feminism and a sequential mixed methods study design, this study provides insight and understanding into the ways math faculty describe, navigate, and experience service responsibilities in research-intensive institutions.
In the first phase of the study (paper 1), I collected and analyzed data (n=75) from the Faculty Service Survey (FSS) aiming to understand how faculty acknowledge and described gender inequities in service responsibilities. The second phase of the study (paper 2) involved multiple rounds of narrative interviews with six cisgender women and genderqueer faculty across academic ranks, exploring their experiences with high service responsibilities and the strategies they use to navigate them. The final propagation effort within this study (paper 3) is a guided reflection oriented around service responsibilities, developed as an evidence-based tool incorporating insights from both previous phases to benefit the community.
Results from this study highlight the critical need to consider intersectional identities when making sense of faculty experiences with service and the need to take action to systemically change how service is assigned and evaluated. Findings from the quantitative analysis of the FSS revealed that faculty across ranks and gender groupings perceived service assignments as being unfair within their departments and saw minimal reward or value from the evaluation of service. Complementing this, the qualitative insights from the narrative interviews revealed that a major impact on the decision-making process was `who’ is asking faculty to do service. Furthermore, interview participants exemplified intersectional identities when discussing their orientation to service as being intertwined with their personal values, research interests, and both academic and social identities. Ultimately, this study aims to bring awareness to the ways in which faculty are perceiving and experiencing their service responsibilities as an effort to foster a more equitable academic environment. In times like these, it is crucial that we as academic community make intentional efforts to support the thriving of cisgender women and genderqueer faculty in mathematics departments
Identification and Characterization of Intermediate Phenotypes to Decipher Genetic Architecture of Stalk Lodging Resistance in Maize (Zea Mays L.)
No full textMaize is a key contributor to global food security and incurs severe yield losses due to stalk lodging, the permanent displacement of plants from an upright growth habit due to mechanical damage to the stem (stalk). Stalk lodging resistance, an indicator of the stalk ability to resist lodging, is a complex trait and determined by several structural, geometric, and material properties of stalks, collectively referred to as intermediate phenotypes, whose identity and genetic framework are poorly understood. Therefore, progress in resolving the genetic architecture of stalk lodging resistance was impeded by a lack of standardized phenotyping methodologies and a poor understanding of the intermediate phenotypes associated with stalk lodging resistance. To this end, my thesis work was focused on increasing the genetic resolution of stalk lodging resistance by unpacking the phenotypes underlying stalk lodging resistance, developing a high-density phenotype resource of the intermediate phenotypes identified, and uncovering the genetic basis of candidate intermediate phenotypes. Firstly, we assessed different phenotypes underlying stalk lodging resistance in a small yet genetically diverse set of maize hybrids and identified flexural stiffness, bending strength, diameter, and moment of inertia of stalks as important phenotypes associated with lodging resistance. Secondly, we generated a high-resolution phenotype dataset consisting of about 1.2 million data points recorded on 11 intermediate phenotypes measured on 31,260 stalks representing a panel of 566 maize inbred lines evaluated in four environments and captured substantial natural variation for these phenotypes. In the last objective, I characterized the phenotype variation of intermediate phenotypes and employed association mapping techniques to integrate the phenotype and whole genome resequencing data to identify several novel candidate loci underlying the intermediate phenotypes associated with stalk lodging resistance