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All-solid-state batteries (ASSBs) are considered promising candidates for next-generation batteries due to their excellent safety performance guaranteed by inorganic solid electrolytes (SEs) with the non-flammability nature, as well as the greatly increased energy density enabled by the adoption of lithium metal anode. Unlike conventional lithium-ion batteries (LIBs) using liquid electrolytes, all the components within the ASSBs system, including the composite cathode, lithium anode, and solid electrolyte, are solid-state. Solid-solid interfacial contacts within ASSBs, such as the dendrite-electrolyte interface and electrode-electrolyte interface, are the origin of interfacial instability issues. The interfacial instability problems mainly exhibit in the form of lithium dendrite growth-induced short circuits and interfacial debonding failure inside composite cathode, which are the major hurdles on the road towards the large-scale commercialization of ASSBs. Experimental characterizations are limited by the coupling of the solid nature of SE (vision overlap), and ultrasmall length scale. Therefore, versatile and physics-based models to describe the electrochemical behaviors of the ASSBs are in pressing need.
Herein, considering the highly multiphysics nature of ASSB behaviors, fully coupled electrochemo-mechanics models at different scales are developed to investigate the underlying mechanism of dendrite growth and interfacial failure. From the energy conservation perspective, the electrochemical-mechanical phase-field model at the electrolyte scale is firstly established to explore the dendrite growth behavior in polycrystalline SE. The newly formed crack and the grain boundary are found to be the preferential dendrite growth paths, and stacking pressure affects the driving force for both dendrite growth and crack propagation. Next, the cell-scale multiphysics modeling framework integrating the battery model, mechanical model, phase-field model, and short-circuit model is developed to study the entire process from battery charging to dendrite growth and to the final short circuit. The governing effects from various dominant factors are comprehensively discussed. Further on, inspired by the “brick-and-mortar” structure, the strategy of inserting heterogeneous blocks into SEs is proposed to mitigate dendrite penetration-induced short circuit risk, and the overall dendrite mitigation mechanism map is given. Finally, the three-dimensional fully coupled electrochemical-mechanical model is developed to investigate the interfacial failure phenomena, taking into account the electrochemical reaction kinetics, Li diffusion within the particle, mechanical deformation, and interfacial debonding. The randomly distributed LiNi1/3Co1/3Mn1/3O2 primary particles result in the anisotropic Li diffusion and volume variation inside the secondary particle, leading to significant nonuniformity of the Li concentration, strain, and stress distributions. This also serves as a root cause for the internal cracks or particle pulverization. The particle volume shrinkage under the constraint of the surrounding SE triggers the interfacial debonding with increased interfacial impedance to degrade cell capacity. This study explores the dendritic issue and mechanical instability inside ASSBs from the multiphysics perspective at different scales, obtaining an in-depth understanding of the electrochemical-mechanical coupling nature as well as providing insightful mechanistic design guidance maps for robust and safe ASSB cells.
This dissertation explores Black/African American students’ perceptions of college readiness through student demographic questionnaires, semi-structured interviews, and focus group data. One objective of this study was to explore how advanced coursework contributed to the college readiness of Black students. Another objective was to examine academic writing readiness for Black students, which is an under-researched aspect of college readiness. The findings indicated that having a fostered college mindset, collegiate academic exposure, and being provided foundational skills and knowledge were aspects of advanced course participation that contributed to postsecondary success for the participants. In terms of writing readiness, writing opportunities and writing skill enhancement contributed to the participants’ college writing readiness and success. However, misalignment between high school and college expectations, mismatch of collegiate level writing expectations, and lack of citation knowledge were other areas related to college readiness that also emerged from the data. This study provides implications for policy, teachers, school personnel, and teacher educators.
Stance detection in social media data has received attention in recent years as an approach to determine the standpoint of users towards a target of interest, such as a person or a topic included in Twitter data. Although interviewing, surveying, and polling representative populations have long proven reliable methods for analyzing public opinion, these methods suffer from various limitations, including high costs and an inability to be collected retrospectively. On the other hand, detecting and analyzing social media trends through natural language processing approaches, such as text classification, offers a valuable alternative or complementary approach to gathering, analyzing, monitoring, and understanding public opinion on emerging issues.
Existing stance detection and analysis studies use multiple methodologies and strategies to determine and analyze the standpoint of Twitter users toward a target. These techniques feature strengths and weaknesses, and the literature lacks studies investigating the broad implications of using such methods for public stance measurements. Understanding these implications is crucial to the validity, interpretation, and replicability of research findings.
In this dissertation, we first introduce the concept of user-based stance analysis and highlight the difference between user-based and tweet-based stance analyses. We describe the relevance of user-based stance analysis to the measurement of public opinion. We suggest that the stance of Twitter users, instead of a stance presented in a tweet's content, must be the core aspect of stance analysis for measuring public opinion. Therefore, we claim that a user-based stance analysis is more aligned with the concept of public opinion than a tweet-based stance analysis. Second, we compare the results of measuring public opinion with tweet- and user-based stance analyses from Twitter data and demonstrate that each produces statistically different results. Third, we present findings that while a tweet-based stance analysis is sensitive to the presence of social bots, a user-based stance analysis provides a more robust measure of public opinion with minimal impact from social bots. Fourth, we describe the design and evaluation of StanceDash, a web-based dashboard that assists end users measure, analyze, and monitor public opinion through a user-based stance analysis of Twitter data.
While the landmark Brown v. Board of Education decision may have overturned the legal practice of race-based segregation in public schools on the basis of separate being “inherently unequal”, the promise of equality for Black students in the United States has yet to materialize (Noguera et al., 2015). Sixty-seven years removed from the Brown decision and 50 years after Swann v. CMS, African American students are still faring worse than their white counterparts by nearly every conceivable metric and the composition of many schools throughout the nation have actually moved rapidly in the direction of resegregation (Charlotte-Mecklenburg Schools, 2018). Despite the dominant narrative of segregated Black schools as wholly inadequate, there are counternarratives of them producing educational excellence, racial pride and serving as pillars in the African American community. Second Ward High School was the first Black public secondary school in Charlotte, North Carolina, and located in the historic Black neighborhood called “Brooklyn”. It was closed in the wake of desegregation. This investigation of Second Ward High School utilizes a historical case study method through the theoretical framework of Community Cultural Wealth to better understand the institutional assets segregated Black schools in the urban South endowed to their student populations during the period of 1960-1969.
Beginning teachers are more likely to secure jobs in diverse school districts (Gagnon & Mattingly, 2012; (Holme et al., 2018). Unfortunately, beginning teachers are also more likely to leave diverse school districts and urban schools due to a number of challenges (Doran, 2020; Howard & Milner, 2021). Because these schools consist of predominately students of color, the high turnover affects students’ academic success (Ladson-Billings, 2022). Additionally, beginning teachers in these specific school settings have been historically non-proficient in providing students of color with a culturally relevant education (Ladson-Billings, 1995) which has caused the educational system to be centered around a Eurocentric perspective and not reflective of students’ racial diversity (Davis et al., 2022). Using a critical lens, this study explores three beginning teachers’ perceptions of preparedness in teaching racially diverse students and the influences it has on their teaching practices.
Keywords: beginning teachers, perceptions, racial diversity
Solid tumor metastasis is the leading cause of cancer-related mortality. Cancer invasion through the confining basement membrane (BM) is the initial step in tumor dissemination and metastasis, and it represents a key diagnostic feature of cancer. Thus, identifying the mechanisms involved in the breaching of cancer cells through the BM is potentially important for developing novel therapeutic approaches. BM is a dense sheet of specialized extracellular matrix proteins that separates tissue compartments. It is also a nanoporous structure, and since the average width of a cell is ~10 µm, invasion requires extensive widening of the BM nanopores. Previous research provided evidence that this expansion of BM nanopores involves protease degradation. However, protease inhibitors have failed to prevent cell invasion and metastasis in clinical trials, suggesting that cells may also breach the BM barrier using physical and mechanical mechanisms. Currently, it is unknown what mechanical mechanisms human tumor cells use to breach the BM. This is in part due to the difficulty of visualizing interactions at the cell-BM interface during cell invasion. Here, we designed and published a 3-dimensional in vitro organoid model of cancer spheroids encapsulated by a basement membrane and embedded in 3D collagen gels to visualize the early events of cancer invasion by confocal microscopy and live-cell imaging.
We first found that human breast cancer cells generated large numbers of basement membrane perforations, or holes, of varying sizes that expanded over time during cell invasion. We used a wide variety of small molecule inhibitors to probe the mechanisms of basement membrane perforation and hole expansion. Protease inhibitor treatment (BB94), led to a 63% decrease in perforation size. After myosin II inhibition (blebbistatin), the basement membrane perforation area decreased by only 15%. These treatments produced correspondingly decreased cellular breaching events. Interestingly, inhibition of actin polymerization dramatically decreased basement membrane perforation by 80% and blocked invasion. Our findings suggest that human cancer cells can primarily use proteolysis and actin polymerization to perforate the BM and to expand perforations for basement membrane breaching with a relatively small contribution from myosin II contractility.
We also found by using live timelapse imaging that cancer cells can send out long, actin-based prehensile protrusions (~30-100 microns in length) through the BM that subsequently grip and pull on the surrounding collagenous matrix to help cells pull themselves through the BM for invasion. These long protrusions are supported by microtubules and pull on the surrounding collagen using actomyosin contractility. We quantified this pulling exerted on collagen by generating kymographs for control and treatment groups and measuring collagen displacement over time. We found that by specifically inhibiting actin polymerization, microtubule formation, or actomyosin contractility, tumor organoids are unable to form these protrusions and fail to pull on the surrounding collagen matrix to enable invasion. Furthermore, by inhibiting the cell surface receptor for collagen, integrin ⍺2ß1, organoids could not form protrusions nor pull on the surrounding matrix, indicating that protrusions use integrin ⍺2ß1 to attach to and pull on the collagen matrix during the initial stages of invasion through the BM. In conclusion, some cancer cells extend long actin-based protrusions to bind to collagen via integrin ⍺2ß1 and use pulling forces driven by actomyosin contractility exerted on the surrounding extracellular matrix to squeeze through perforations in the basement membrane for translocating their cell body across this major tissue barrier to cancer invasion.
APRIL DENIECE THOMAS: Do you see yourself in multicultural literature? Seeking self-reflections from Black students
(Under the Supervision of Dr. ERIK BYKER)
In the United States, Muhammad (2020) explains how Black students who attend schools have a greater potential success when they see themselves represented in the curriculum and when their cultural, gender, and racial identities are affirmed. This dissertation study examined the ways in which third grade Black girls and boys (n=5) see themselves when they read African American multicultural literature. The study also investigated the literary elements in African American multicultural text that encourage self-reflection. The study’s methodology was based on a qualitative phenomenological research design, which included a pilot study (n=4) of the interview protocol. The interview protocol was revised for suitability based on the findings from the pilot study. Both the pilot study and the main dissertation research study were conducted using semi-structured interviews. The participants chose a text from a collection of African American multicultural literature and shared their responses to that text based on the interview protocol. The following research questions guided the study: 1) How do Black children respond to African American multicultural literature?; 2) How do Black children describe their cultural and racial identity within multicultural literature?; and 3) What literary features facilitate Black children’s ability to self-reflect? The findings of the study were organized based on these research questions. The study utilized two frameworks, Reader Response Theory (Rosenblatt, 2004) and Black Identity Theory (Jackson III, 2012), to unpack and discuss the findings. A new theory emerged from the study’s findings, which is called Multicultural Self-Reflection Theory. This theory explains and provides insights into how Black children self-reflect when reading African American multicultural literature. Multicultural Self-Reflection Theory provides a lens for understanding how Black children engage in what the dissertation coins, “multicultural self-reflection" when responding to African American multicultural text.
Key Words: African American, Black children, Black Identity Theory, interview study, multicultural literature, Multicultural Self-Reflection Theory, phenomenology
Reader Response Theory, self-reflect,
Graphene is a monoatomic thick sheet of sp2-hybridized carbon atoms tightly packed in a honeycomb lattice structure. Since its discovery, it has drawn extensive attention to the science community for its unique 2D structure and has been studied for both basic science and commercial applications due to its extraordinary thermal, optical, and mechanical properties. In this research, we employed molecular dynamics simulations and machine learning methods to study mechanical and fracture properties of graphene-like two-dimensional materials (i.e.; C3N, bicrystalline graphene, and polycrystalline graphene). Molecular dynamics (MD) simulations are used to extract the traction-separation laws (TSLs) of symmetric grain boundaries of bicrystalline graphene. Grain boundaries with realistic atomic structures are constructed using different types of dislocations. The TSLs of grain boundaries are extracted by using cohesive zone volume elements (CZVEs) ahead of the crack tip. The areas under the traction-separation curves are used to calculate the separation energy of the grain boundaries. The results show that as the grain boundary misorientation angle increases the separation energy of the grain boundaries decreases. The impact of temperature on the traction separation laws is studied. The results show that, with an increase of the temperature from 0.1 K to 300 K, the separation energy first increases to reach its peak at around 25 K and then slightly decreases. Finally, a deep convolutional neural network model has been developed to predict the mechanical and grain properties of polycrystalline graphene. The data required for training our machine learning model is generated using molecular dynamics simulations by modeling the behavior of polycrystalline graphene under uniaxial tensile loading. More than 2000 data points are generated for graphene sheets of different grain sizes and grain orientations. The goal is to train the network such that it can predict the Young's modulus and fracture stress of graphene sheets by analyzing an image of the polycrystalline sheet.
Molecular dynamics simulations are also used to study the mechanical and fracture properties of C3N, a graphene-like two-dimensional material. The impact of initial crack orientation on the crack path is studied by applying tensile strain to C3N sheets containing initial cracks in the armchair and zigzag directions. The results show that the cracks grow by creating new surfaces in the zigzag direction. The impact of temperature and strain rate on Young's modulus and fracture stress of C3N are studied. The capability of Griffith theory, and quantized fracture mechanics (QFM) in predicting the fracture strength of C3N is studied. The molecular dynamic results indicate that Griffith theory cannot predict the fracture strength of C3N if the crack length is shorter than 9 nm. The notch effects on the fracture strength of C3N is studied and it is shown that notch effects are important in predicting the fracture strength of C3N. Using the Rivling-Thomas method, the molecular dynamics simulations predict a critical energy release rate of 10.982 Jm-2 for C3N.
The “Urban Stream Syndrome” is a term that refers to a group of predictable negative impacts to stream ecosystems due to the alteration of the natural hydrologic regime associated with urbanization including increases in the volume and intensity of storm water inputs to streams, channel erosion, streambed sedimentation, and nutrient and pollutant concentrations. These negative impacts of urbanization degrade the habitat available to the aquatic biota in streams. The decline in aquatic insect taxa richness due to urbanization has been well documented. However, the impact of the stressors associated with the increased stormwater flashiness to the composition of the aquatic insect assemblages’ taxa and trait richness and diversity is not well known.
For my dissertation, I proposed three research studies designed to improve the understanding of how the increased stormwater from urban areas impacts the aquatic insect assemblages’ taxa and trait richness and diversity. To do this, I first examined a 26-year data set to study the impact of land use changes on biodiversity and ecosystem function in stream ecosystems in watersheds that span a gradient of impervious cover and stream habitat conditions. Next, to better understand the impact of urbanization on biodiversity and ecosystem function, I examined the relationship between aquatic insect taxa and trait richness and diversity and stream habitat diversity at the watershed scale and the importance of microhabitats at the reach scale. Finally, to better understand stormwater impacts on aquatic insect assemblages, I compared macroinvertebrate taxa and trait richness and diversity in 2 adjacent headwater tributaries that received stormwater runoff through different processes (stormwater infrastructure verse natural overland and subsurface processes).
This research investigates beer production in Mecklenburg County and its impact on water demand, and waste production, with a specific focus on how beer production fits into Charlotte’s public strategy of a Circular Economy. Charlotte adopted a Circular Economy to not only provide environmental benefits, by reducing waste and recycling, but also to bridge the wealth divide and create opportunities for upward mobility through innovation and job creation. In this research, three questions are examined in relationship to beer production: investigate the impact of water demand on beer production in Mecklenburg County through 2065, quantify the impact of spent grain waste generated by beer production on the Circular Economy, and assess if and how breweries can support the Circular Economy in Mecklenburg County. The results of this research answers questions to knowledge gaps as to the impact the brewery industry has on water demand and solid waste in Mecklenburg County.
