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First principles investigations of structures and properties of ternary ABC compounds in hexagonal and Half-Heusler configurations
No full textIn this work, I present a number of different aspects of first principles studies of ternary ABC compounds. I address the reproducibility of results for ABC ferroelectric structures presented in the literature, concluding that results can be closely, but not exactly, reproduced. I designed and began the construction of a database of ABC ternary compounds with first-principles data for the energies and bandstructures for each composition in the most common hexagonal crystal structures. Using this database, I compared the energy for the Pnma structure with that of the structure, and investigated the energy barrier separating these two structures along the linear interpolation path. Identification of insulating ABC hexagonal crystals is of particular interest in the search for new ferroelectrics. I present the example of LaAuGe, which is a polar system and, because it is metallic, cannot be used as a ferroelectric. However, with an increase of the buckling of the honeycomb lattice, the band edge states shift, opening a band gap and suggesting that some metallic ABC compounds could be stabilized as insulators under appropriate conditions, such as epitaxial strain. Another example of competing phases for ABC crystals is that of LiZnSb, on which I worked with the experimental group of Jason Kawasaki at the University of Wisconsin. While the ground state of this compound is half Heusler, they succeeded in synthesizing LiZnSb in the metastable hexagonal phase. Half-Heusler ABC crystals have been considered as candidates for topological materials. In our experimental-theoretical collaboration, I calculated the band structures for GdPtSb with and without f orbitals and for GdPtBi. The results were compared to previous work on GdPtBi, where it was hypothesized that GdPtBi was a Weyl semimetal. Finally, I discuss the computation of the effects of bending strain on polar systems, previously suggested as a way to switch polar metals. I present an efficient method to find the second derivative of the force constant matrix using only seven q points near Γ. I also present an alternative approach to calculate the minimum bending needed to switch a system from one polar variant to the other.Ph.D.Includes bibliographical reference
Intergranular fracture and toughening of heterogeneous, brittle polycrystals
No full textIn the field of structural materials, a repeated issue is the trade-off between strength and toughness. Many ceramics tend to have a high strength but poor toughness due to their poor crack resistance. Ceramics, due to their chemical nature, do not have access to the same intrinsic toughening mechanisms that metals or polymers have. Therefore, the predominant approach to toughen ceramics has been through introducing extrinsic toughening mechanisms through the introduction of secondary phases. The most remarkable case of this strategy of toughening comes from nature in the form of nacre which has a brick-and-mortar type structure which combines the strength of ceramics with the high toughness of a biopolymer to create a material which has a higher strength and toughness than either phase. However, replication of this success with different materials in a lab is expensive and difficult due to delamination issues between the polymer and the ceramic, and the toughening results do not display an efficient use of the polymer phase.
In this paper, crack propagation behavior is modeled for a similar heterogeneous system with a high strength low toughness phase and low strength high toughness phases. The models were analyzed using a finite-element analysis approach in Abaqus 2019 using cohesive surface definitions to observe how failure will occur with a stochastic distribution of the two phases at the grain level. The salient parameters that were varied were the modified fraction of grains, the strength ratio between the modified grains and the unmodified grains, and the toughness ratio between the modified grains and the unmodified grains. The mechanisms of toughening in these simulations were identified as crack deflection, crack branching, and crack jumping. An analytical method is proposed which decomposes the total toughness of the system into the individual contributions of the toughening mechanisms. From this, deviations from Vegardian behavior are identified for variations in strength ratio and toughness ratio.
The main findings from this paper are that the highest amounts of toughening occur at low strength ratios and high toughness ratios. Rising R-curve behavior for these systems was only observed for low strength ratio simulations. The decomposition analysis showed that both variations in toughness ratio and strength ratio yielded deviations from Vegardian behavior.M.S.Includes bibliographical reference
The role of post-transcriptional control of CD40L on the development of autoimmune disorders
No full textControl of expression of immunostimulatory molecules is vital to the prevention of a break in central or peripheral tolerance that can lead to the development of autoimmune disorders. Among the many signals involved in the activation of adaptive immunity, CD40L on CD4+ T cells binding to CD40 on antigen-presenting cells (APCs) and B cells in particular has been identified as a key interaction and point of control for fine-tuning immune responses. Ligation of CD40L by B cells is critical for the formation of germinal centers, affinity maturation, and terminal differentiation into plasma or memory B cells, all processes that have been found to be pathogenically enhanced in systemic lupus erythematosus (SLE). Thus, regulation of CD40L expression is critical to ensure stimulation of B cell activation pathways when appropriate and makes CD40L an attractive therapeutic target for treating autoimmune disorders.
Our lab has previously described a locus on the 3’ UTR of CD40L mRNA that is responsible for extended stability of the message during CD4+ T cell activation by binding of a complex nucleated by the polypyrimidine tract binding protein, PTBP1. Removal of this stability element in CD40LΔ5 mice leads to decreased CD40L on CD4+ T cells and causes significant disruption to a normal T-dependent response by basis of disrupted germinal center formation, decrease in germinal center B cell survival, terminal differentiation down plasma and memory fates, and decreases in antibody affinity and overall titers of switched antibodies. We decided to investigate the effect that the CD40LΔ5 mutation could have in mouse models of SLE, given the importance of autoreactive B cell maturation and autoantibody formation in the pathogenesis of disease. For this, we implemented two well characterized models of human SLE in mice. The first, pristane-induced lupus (PIL), is initiated by injection of the powerful hydrocarbon adjuvant pristane that over the course of six months generates a state of chronic inflammation that allows a break in tolerance and furthers autoreactive B cell activation and enrichment, resulting in high titers of anti-self antibodies and deposition of immunocomplexes in the kidney glomeruli. The second model is an inducible chronic graft-versus-host disease (cGVHD) that resembles SLE by the production of anti-dsDNA antibodies due to the alloactivation of host B cells following adoptive transfer of histoincompatible CD4+ T cells from bm12 mice. bm12 mice harbor a small mutation in the antigen-presenting major histocompatibility complex class II (MHC-II) that results in allorecognition between CD4+ T cells from bm12 donor mice and the non-bm12 recipient’s APCs.
Using our CD40LΔ5 mice, we hypothesized that a reduction in CD40L would result in an ameliorated disease by preventing proper development of autoreactive B cells. Surprisingly, in both of these models, we observed a consistent sex-dependent increase in B cell activation and differentiation as well as increased autoantibody titers in female CD40LΔ5, while mutant males had little to no protection from disease. With the PIL model, we closely assessed the resultant disease through observation of increased immunocomplex deposition of IgG in the glomeruli and found increased deposition in CD40LΔ5 female mice over WT. The bm12 cGVHD model, with a significantly shorter induction time, allowed us to more effectively control the effect of the CD40LΔ5 mutation in a strictly follicular helper T cell driven autoimmune response. With this model, we were further able to identify differences in the cytokine profile of donor and host CD4+ T cells and observed significant skewing between Th1 and Th2 subsets, as well as increased cells expressing the pro-inflammatory cytokines IL-17a and IL-21. Overall, our results advocate for a more nuanced role for CD40L in autoimmunity than has been previously described, particularly in the context of differential cytokine expression and sex, and suggest a boundary threshold of CD40L-CD40 signaling between protection and augmentation of disease.Ph.D.Includes bibliographical reference
Understanding and improving tandem solar cells and modeling agrivoltaics array performance
No full textSolar power, in the form of photovoltaic modules, has been the subject of scientific and engineering research for many years, and it forms an important component of our global power generation as we transition to more renewable and cleaner sources. However, solar technology still needs to improve in several ways in order to see more widespread adoption. Improving the overall efficiency is constantly sought after, but this is no simple task; silicon solar cells, the most popular and commercially available variety, are edging closer to the theoretical limit of what they are able to provide. In order to make strides toward a solar-powered world, it is necessary to look beyond marginal gains in a single type of cell and begin to explore the creation of new solar materials and innovative implementations of existing materials.
In this work, modelling was used to identify new materials to use in conjunction with silicon to create new tandem solar modules that exceed the efficiency of either constituent material alone. A photon-counting simulation is used to evaluate hypothetical stack tandem photovoltaic devices using silicon paired with a thin film wide bandgap material. It examined the impact of film quality on the performance of the device. With the limitations of film quality and voltage ratio in mind, thin-film materials with bandgaps between 1.6 and 2.0 eV were identified as candidate materials for producing realistic and economical tandem devices. Further work was done to synthesize thin films of cadmium selenide (CdSe), a material shown to have favorable properties.
Also in this work, modelling was used to investigate the viability of agrivoltaic installations in New Jersey, i.e. the dual use of land to operate farms growing crops or raising animals and simultaneously to generate electricity via solar modules. A model was used to track the movement of the sun throughout the year in order to calculate the irradiance reaching the ground and the solar modules in a number of different configurations. This data was used to project the annual energy output of vertical bifacial solar panel arrays on a per-module basis and per-acre basis. Rows of double-high modules in landscape orientation can produce more than 159 MWh/year/acre, when rows are spaced 20 feet apart. Similar results are achieved with modules installed in a portrait orientation.Ph.D.Includes bibliographical reference
In pursuit of representation: a quantitative analysis of flourishing and associated factors for LGBTQ+ graduate students pursuing careers in healthcare
No full textIn pursuit of increased Lesbian, Gay, Bisexual, Transgender, and Queer (LGBTQ+) representation in the healthcare workforce as a means to reduce health disparities, this study examines the well-being of LGBTQ+ health professions graduate students. This research serves a larger aim within graduate health professions education, to grow the LGBTQ+ student body and ultimately increase workforce representation. Using data from the national 2019-2020 Healthy Minds Survey (N=37,624) a series of quantitative analyses was conducted on a sample of all graduate health professions students (n=2785; n=362 LGBTQ+), and two sub-samples, 1) respondents who attend Rutgers Biomedical and Health Sciences (RBHS) (n =1108; n =152 LGBTQ+), and 2) a sub-sample of only LGBTQ+ students (n =362). The analysis found that LGBTQ+ students have lower levels of well-being, as measured by the flourishing scale, in the national and RBHS samples (50% and 36%, respectively, p=0.015). In alignment with past research, LGBTQ+ respondents have higher levels of depression (36%) and anxiety (44%) which were identified in this study as primary drivers of flourishing (p = <0.05). In the LGBTQ+ sample, belonging was significant with LGBTQ+ medical students having a stronger sense of belonging than LGBTQ+ students in other health professions (43% and 30% respectively, p = 0.07). The comparison of outcomes across disciplines is a unique contribution of this study and allows for insights about the supports that may be needed for graduate students in other health professional graduate programs in addition to those already identified in medicine.Dr.P.H.Includes bibliographical reference
Paul Robeson Library Undergraduate Research Award 2024. Owens, Lauren_Night, Allison_Brodsky, Matthew-consent forms
No full textCounting classes of matrices and more using experimental mathematics
No full textThis thesis gives several examples of how finite state machines can be used to count rectangular objects.We associate a matrix with the object, fix the number of rows, and consider the sequence formed by increasing the number of columns. We then construct transfer matrices to count the number of accept strings for each finite state machine, and solve for a generating function. The process is completely automated using the maple computer algebra system. 4 cases are considered: logic puzzles, baxter matrices, voting districts, and seating arrangements that obey social distancing. At the end we provide code that is easily modifiable to handle any variation that the reader may be interested in.Ph.D.Includes bibliographical reference
China’s new philanthropy: resignifying giving and cultivating charitable elites in the post-reform era
No full textEven though the People’s Republic of China has risen to a position of economic might, the nation struggles with drastically diminished socioeconomic equality at home, and a persistent lack of esteem on the global stage. Against a backdrop of trenchant tensions between market economics and socialist ethics, and between aspirations of global leadership versus tenacious Western cultural imperialism, a phenomenon of “new philanthropy” (xin cishan) has emerged. This reinvented form of giving has been encouraged through top-down rhetoric and policies, but also seized upon and reshaped by Chinese social actors. In particular, professionals working at newly founded philanthropy training organizations in Beijing have taken up this nationalist project to cultivate Chinese charitability. Based on fifteen months of ethnographic research alongside individuals both designing and participating in a range of training programs, this dissertation argues that the “new philanthropy” emerging in China challenges existing universalist notions of what philanthropy is, or ought to be, and revisits charitable giving and its social and discursive effects. In contradistinction to much of the recent flood of applied scholarship on philanthropy worldwide, this dissertation refrains from evaluating the activities and “outcomes” of Chinese philanthropy, per se, but instead investigates “philanthropic subjectification”—the process of coming to see oneself as a philanthropist (cishanjia) or a changemaker (chuangbianzhe), for example. Both program organizers and participants with whom I conducted participant observation (those seeking to induce and undergo resubjectification, respectively) undertook an agentive resignifying of the concept of “philanthropy.” By manipulating a web of meanings and associations, intellectuals, politicians, and professionals designing philanthropy training courses (as well as, to a lesser extent, participants in these courses) put forth different paradigms that I have identified and labelled as: philanthropy-as-revolution, philanthropy-as-family-legacy, philanthropy-as-traditional-Chinese-culture, and philanthropy-as-making-change. In doing so, they imagined and transformed into an array of new kinds of nationalist, socialist, elite, “culturally proud,” young, innovative, and/or “effective” moral and economic subjects. It is this resubjectification that stands to potentially mediate the paradox inherent in a marketized socialism, as well as the conundrum of a rising China that fundamentally challenges, yet seeks to be legible to, the West.Ph.D.Includes bibliographical referencesIncludes vit
From childhood to nationhood: memory, media and malevolence
No full textThis talk explicates the entangled relationship between childhood and nationhood in the Indian context through the analysis of two key events in modern Indian history. The current right-wing nationalist discourse in India espouses an ethnonationalist identity that relies on a unitary logic of race, religion, land, and language. This logic is founded upon Savarkar’s slogan of “Hindi, Hindu, Hindustan” that valorizes not only the Hindu religion but also the Aryan race, the Hindi language, and the land beyond the river Indus. Children and young people are perceived to be the crucible of this Hindu nation that (supposedly) rightfully belongs to the Hindu Brahmanical Hindi-speaking Aryan male. This presentation aims to show how history, narrativity and performance have been deployed to center the figure of the child as well as real children (and youth) as critical players of the Neo-Hindutva discourse. Through a combination of field evidence, secondary literature and media sources, this poster shows how stories and memories are instrumental in the production and propagation of nationalist discourses to children and young people. The talk expounds different tactics such as distorting history, maneuvering memory and rewriting myths that are deployed within the private spaces of homes, the public spaces of schools and neighborhoods and mediatized spaces of movies, through which children imbibe as well as disseminate the idea of India as a Hindu nation.This work was accepted to the annual Graduate Research and Creative Works Symposium while the author was a graduate student at Rutgers University-Camden