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Title: Three essays on the causes and consequences of youth migration in Tanzania
Creator: Moskaleva, Evgeniya Alekseevna
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Migration of youth is a prominent phenomenon in Sub-Saharan Africa and in East Africa in particular. International and rural-to-urban migration gained a lot of attention in the older literature, yet internal rural-to-rural migration is the most frequent type. This work revolves around several issues of internal migration of youth in rural Tanzania. First, I determine which factors are associated with destination decisions made by young people. I look at four to six destination types on the...
Show moreMigration of youth is a prominent phenomenon in Sub-Saharan Africa and in East Africa in particular. International and rural-to-urban migration gained a lot of attention in the older literature, yet internal rural-to-rural migration is the most frequent type. This work revolves around several issues of internal migration of youth in rural Tanzania. First, I determine which factors are associated with destination decisions made by young people. I look at four to six destination types on the rural-urban spectrum and consider various individual, household, and community factors that could affect migration decision. Second, I test how does migration to various destination areas on the rural-urban spectrum contribute to structural transformation through the shifts in main occupation. Although focusing on the shifts from agricultural work to self-employment and wage job, I also consider other employment categories like students, those working mainly in household maintenance, and unemployed people. Third, I estimate the impacts of youth outmigration on the livelihood of non-migrant household members. I consider changes to the labor supplied to the household farm, attraction of new household members, and adjustments to household participation in labor and land markets.I make contribution to the literature on internal migration of youth in Sub-Saharan Africa, and Tanzania in particular, in four ways. First, I distinguish several migration destinations across the rural-urban spectrum, from low-density rural areas to cities, broadening the conceptualization of migration decision instead of focusing on a specific flow of migrants. I test three categorizations of location types to account for different interpretations of results and to verify that the main results are not an artifact of the choice of the definition of “rural”. Second, I stress the importance of rural-to-rural migration, which is prevalent in Tanzania, although understudied. I show that even migration to low-density rural areas is associated with a shift towards non-agricultural employment. Third, while looking at occupational shifts, I consider people who are usually excluded from the analysis: students and those employed in household maintenance. I also look at women who state marriage as their main reason for migration. It allows to broaden the view on migration flows and discover employment difficulties for certain groups of people, for example, female rural-to-rural migrants involved mainly in household maintenance and students transitioning into employment. Fourth, I explore the labor adjustment strategies of the households left behind after a young adult migrates, which has rarely been studied in the context of the countries of Sub-Saharan Africa.
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Title: SYNTHESIS OF 3-HYDROXYPROPIONIC ACID FROM ACETYLENECARBOXYLIC ACID
Creator: Mathes Hewage, Amaya Nethmini Sirinimal
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Throughout the past several decades, the petroleum industry has remained a dominant player in the production of fuels, chemicals, and consumer products. However, rising global temperatures and declining fossil fuel reserves demand the need for sustainable processes that can compete with the existing crude oil-based economy. Employing microbes such as E. coli for the chemical production using renewable starch-derived feedstocks such as glucose has been identified as a preferred alternative....
Show moreThroughout the past several decades, the petroleum industry has remained a dominant player in the production of fuels, chemicals, and consumer products. However, rising global temperatures and declining fossil fuel reserves demand the need for sustainable processes that can compete with the existing crude oil-based economy. Employing microbes such as E. coli for the chemical production using renewable starch-derived feedstocks such as glucose has been identified as a preferred alternative. Although lignocellulosic feedstocks have been explored as an alternative to renewable sugars, these processes are yet to be successfully implemented in an industrial setting. Despite more recent research efforts to incorporate C1 feedstocks such as methane, methanol and carbon dioxide in microbial catalysis, development of efficient bacterial metabolic pathways using these feedstocks have proven to be challenging. Herein, acetylenecarboxylic acid (ACA) is proposed as a unique feedstock for microbial catalysis. ACA can be derived from dehydrodimerization of methane to acetylene and subsequent carboxylation of acetylene. Cg10062 was previously identified as an enzyme capable of hydrating ACA to form a mixture of malonate semialdehyde (MSA) and acetaldehyde. In this study, novel variant Cg10062(E114N)) that forms exclusively MSA from ACA was discovered using rational mutagenesis. Cg10062(E114N) was coupled with NADPH-dependent dehydrogenase YdfG to develop a unique biocatalytic route to building block chemical 3-hydroxypropionic acid (3-HP). In vitro synthesis of 3-HP from ACA was demonstrated using catalytic amounts of NADP(H) where cofactor regeneration was achieved using NADP+-dependent phosphite dehydrogenase PTDH.
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Title: Action-Oriented Studies in Green Criminology and a Harmful Trade in Pet Wildlife in Trinidad and Tobago
Creator: Gibson, Mark Charles
Date: 2022
Collection: Electronic Theses & Dissertations
Description: This dissertation presents five chapters, inclusive of three manuscripts styled as draft publications, to advance the contested paradigm of green criminology—or the study of crimes and harms that involve the natural world, non-human species, and the human communities that depend on them—and to support the emerging professional practice of non-governmental wildlife trade reduction. Two of the presented manuscripts meet the requirements for submission to scientific journals in criminology,...
Show moreThis dissertation presents five chapters, inclusive of three manuscripts styled as draft publications, to advance the contested paradigm of green criminology—or the study of crimes and harms that involve the natural world, non-human species, and the human communities that depend on them—and to support the emerging professional practice of non-governmental wildlife trade reduction. Two of the presented manuscripts meet the requirements for submission to scientific journals in criminology, while another is a long-form text modeled on contemporary non-governmental ‘wildlife trade assessment’ reports. The specific wildlife trade under study is a harmful trade in pet wildlife occurring in Trinidad and Tobago and the wider world. This trade was particularly under-studied prior to this dissertation research project and broader initiative. The dissertation is action-oriented in that it seeks to support the green criminology paradigm's empirical, theoretical, and technical development. The resulting manuscript-style chapters have been designed using a best-practice ‘Open Standards’ planning approach now popular in wildlife trade reduction projects. The underlying research activities were also action-oriented in that they were and continue to be conducted in partnership with local activists and scientists as part of a non-governmental project to reduce the harmful trade in pet wildlife trade in Trinidad and Tobago (see www.nurturenaturett.org). The underlying research included focus group discussions with wild animal keepers (n=75), key informant interviews (n=172) with seven stakeholder groups, more than two years of participant observation of physical sites and social media, a national household survey on animal keeping (n=2004), and a taxonomic legal inventory of wildlife laws in Trinidad and Tobago and its trade partners. The first chapter, “Introduction,” provides essential background information on the dissertation research, encompassing project, and implementing researcher. In this way, the chapter describes the developmental context of this dissertation thesis and the strategies employed to produce the dissertation chapters. The second chapter, “The illegal keeping of pet wildlife in Trinidad and Tobago: Diversity, prevalence, populations, and harms,” is designed for submission to a criminological journal on global crime issues and provides insights into the nature of an illegal wildlife trade in a Caribbean country. The third chapter, “‘We all know it’s inhumane’: The awareness and justification of green crimes and harms among Trinidadian songbird keepers,” is designed for submission to a criminological journal on social deviance and provides insights for the development of Neutralization Theory to reduce green crimes and harms. The fourth chapter, “An assessment of the harmful trade in songbirds in Trinidad and Tobago and the wider world,” is designed as a gray-literature ‘wildlife trade assessment’ to educate and empower activists, donors, and policymakers in Trinidad and Tobago and the wider world. A final chapter, “Conclusion and Reflections,” considers the researcher’s experience in relation to action, green criminology, project-based intervention, and science-based activism. The researcher’s concluding reflections include the identification of several next steps to advance green criminology for the continuing and future reduction of harmful wildlife trades and other green crimes and harms.
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Title: MEASUREMENT OF ATMOSPHERIC MUON NEUTRINO DISAPPEARANCE WITH ICECUBE USING CONVOLUTIONAL NEURAL NETWORK RECONSTRUCTIONS
Creator: Micallef, Jessie
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Neutrinos are neutral, fundamental particles that oscillate, or change flavor, while they travel. This phenomenon means that neutrinos deviate from the Standard Model prediction that they are massless, creating an exciting window into physics exploration beyond the Standard Model. Understanding neutrino oscillation and constraining their behavior is crucial to furthering the understanding of these particles and how they fit, or do not fit, into the Standard Model. The IceCube Neutrino...
Show moreNeutrinos are neutral, fundamental particles that oscillate, or change flavor, while they travel. This phenomenon means that neutrinos deviate from the Standard Model prediction that they are massless, creating an exciting window into physics exploration beyond the Standard Model. Understanding neutrino oscillation and constraining their behavior is crucial to furthering the understanding of these particles and how they fit, or do not fit, into the Standard Model. The IceCube Neutrino Observatory has been detecting neutrinos for more than 10 years, leading to a large sample of atmospheric neutrino data available for studying neutrino oscillations. Reconstructing the neutrino interactions, such as the neutrino’s energy and direction, are key to constraining neutrino oscillation. A fast and robust reconstruction method was developed using convolutional neural networks (CNNs) and optimized to reconstruct parameters necessary to both reconstruct and isolate a pure atmospheric neutrino sample using the IceCube detector. This work compares the performance of this reconstruction to the current likelihood-based reconstruction currently used in IceCube. An analysis of the muon neutrino disappearance is then pursued using 9.28 years of neutrino data. The analysis shows competitive projected sensitivity, the ability to account for numerous systematics, and robust recovery of the physics parameters under statistical and systematic variations. While the 9.28 year sample is still under collaboration review, one year of the total data is used to perform a confirmatory study on the CNN reconstruction and sample. The oscillation parameter constraints from this one year analysis are in alignment with past IceCube analyses and other neutrino experiments within one sigma. This opens the pathway to use the CNN reconstruction for future analyses studying low energy neutrinos on IceCube.
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Title: PARENTAL FACTOR INFLUENCES ON RACIAL SOCIALIZATION COMPETENCY AND CHILD BEHAVIOR IN BLACK FAMILIES : A STRUCTURAL EQUATION MODELING INQUIRY
Creator: Crossing, Adrianna E.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Critical theories and analyses of history suggest that white supremacy and anti-Black racism have long shaped U.S. society and that they will likely persist long into the future. The lived effects of racism for Black people span psychological injury, family stress, and stress-related physiological consequences. Given this context, psychologists must dedicate resources to better understanding protective factors against these harmful social forces for those who are negatively affected. Racial...
Show moreCritical theories and analyses of history suggest that white supremacy and anti-Black racism have long shaped U.S. society and that they will likely persist long into the future. The lived effects of racism for Black people span psychological injury, family stress, and stress-related physiological consequences. Given this context, psychologists must dedicate resources to better understanding protective factors against these harmful social forces for those who are negatively affected. Racial socialization (RS) has been found to be a promising means of supporting Black family dynamics and serve as a protective factor for Black children and adolescents. Notably, many Black families enact some version of RS, but the literature suggests that racial socialization competency is a measurable skill and protective factor. Thus, in recent years, there has been a scholarship push toward characterizing, measuring, quantifying, and theorizing RS competency. This paper seeks to illuminate several factors operating within Black families (i.e., general life stress, parental racial discrimination stress, parental racial worry, child behavior problems) alongside several sub-types of RS Competency: Confidence, Skills, General Stress, and “Call to Action” Stress. Rating scales completed by 360 Black parents provided the data for this study. Prior to statistical modeling, several rating scales were examined for psychometric properties to inform which items would serve as indicators for latent variables in an SEM. Prior to understanding the relationships between constructs, a theoretically driven structural equation model was proposed, developed, and statistically tested. A simplified version of the hypothesized model was identified as the best fitting model and was used to test hypotheses concerning the identified familial constructs. Many literature-based hypothesized relationships bore out in the data, with some notable exceptions. Racism-based distress for parents has a stronger predictive relationship to parental racial worry than does general life stress. Parental racial worry may serve as a motivating factor for RS Competency (RSC), rather than a hindrance. RSC Confidence is a stronger protective factor against child behavior problems than is RSC “Call to Action” Stress, but the difference is minor. Further, though stress-related subtypes of racial socialization competency do stem from some distress, they perform more similarly to strengths-focused racial socialization competency subtypes (i.e., confidence). This result supports the findings from previous research that find these subtypes of RSC to be distinct from one another while still strongly representing the overarching construct of racial socialization competency. The information gleaned in this study can be used in many ways. First, several racism-related rating scales were examined for their underlying psychometric properties. Strengths and weaknesses were detected with this sample, suggesting some potential adjustments of these instruments. Further, the results from operating the full SEM could guide the development or revision of RSC interventions. Lastly, future researchers may consider that fostering positive racial socialization in settings outside the home may serve the dual purpose of reinforcing this protective factor for Black youth while reducing the stress or strain of engaging in RS at home for Black parents. Additional interpretations, implications, limitations, and future directions for research are discussed.
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Title: Gamified Crisis Framework : The development of serious games for improving behaviors and skills when facing major disasters.
Creator: Graciano Velazquez , Luis
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Every day all over the world, social, economic, health, environmental and political movements convulse and revolve with no limit. Out of these events, some may gain status as paradigmatic, events that affect the world, marking a before and after in the territory they affect. There is always a risk of being on the path of a crisis and dealing with the disaster that follows it. To ameliorate the repercussions of these disasters, people need to have a solid grasp of skills and behaviors that can...
Show moreEvery day all over the world, social, economic, health, environmental and political movements convulse and revolve with no limit. Out of these events, some may gain status as paradigmatic, events that affect the world, marking a before and after in the territory they affect. There is always a risk of being on the path of a crisis and dealing with the disaster that follows it. To ameliorate the repercussions of these disasters, people need to have a solid grasp of skills and behaviors that can help them better survive these events, particularly those that become paradigmatic. This study focuses on the potential of video games as a vehicle for the fomentation of Awareness, Empathy, Knowledge & Skills, and Active Behaviors. To this end, this study proposes creating the Gamified Crisis Framework (GCF), a guideline for researchers and creators. The GCF is based on the characteristics of the phenomena from a complete perspective that includes the societal context, the actor’s characteristics, and cultural location, on top of the best practices of risk amelioration, emergency response, and recommendations on how to obtain them. To get an insight into the framework’s effectivity, this study conducted a qualitative study, divided into a play phase and a questionnaire phase. The play phase revolves around a game created through the GCF by the title of Storm Line, based on the 2017 hurricane Maria, nurtured by a combination of existing research and the researcher’s firsthand experience conducting field research. The game, presented as a text adventure, is a rudimentary but functional Twine prototype. 31 people took part in the study, 3 for in-depth interviews for preliminary questionnaire assessment, and 28 respondents of semi-structured queries. The respondents provided insightful answers that culminated in the codification of the most important themes for them. Findings revealed that not only the framework provides an experience that successfully conveys its themes of Awareness and Empathy, but that the game in its current state makes a better job at helping them reconsider and affirm their own practice for Active Behaviors, and Knowledge & Skills. In this study, we also get the insight that for the games developed through the GCF, the production can benefit from more sophisticated games.
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Title: USING MACHINE LEARNING TO UNCOVER POPULATION HETEROGENEITY IN LONGITUDINAL STUDY
Creator: Lee, Youngjun
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Machine learning has been an emerging data analytic tool in the fields of quantitative social and behavioral sciences. Among others, model-based recursive partitioning (MOB) is one of the popular comprehensive approaches incorporating parametric model into tree-based algorithm. It has gained growing interests as a complementary data analytic tool to address population heterogeneity by detecting parameter instability over candidate covariates. Structural equation models using tree algorithm ...
Show moreMachine learning has been an emerging data analytic tool in the fields of quantitative social and behavioral sciences. Among others, model-based recursive partitioning (MOB) is one of the popular comprehensive approaches incorporating parametric model into tree-based algorithm. It has gained growing interests as a complementary data analytic tool to address population heterogeneity by detecting parameter instability over candidate covariates. Structural equation models using tree algorithm (SEM Trees) has particularly shown its benefits for discovering informative covariates and their complex interactions that predict differences in structural parameters with interpretable results, which in turn produces distinct homogeneous subgroups. While all previous studies make important contributions to use this approach, it has been less examined to investigate the performance of SEM Trees where there exist interaction effects of various types of covariates (i.e., categorical, ordinal, and continuous), which is the key motivation of this study. This study has three main purposes. First, it aims to introduce a framework of MOB for educational researchers and guide them when it can be beneficial with an illustrative example using nationally representative longitudinal data (High School Longitudinal Study of 2009). A parametric latent growth curve model (LGCM) is used as a template model along with MOB. Second, a simulation study for a given LGCM is conduced to investigate the performance of MOB, which provides researchers with statistical evidence of how well MOB recovers true subgroups. Simulation conditions include a) effect size (0.2, 0.4, 0.6, 0.8, and 1.0), b) sample size (1,000, 2,000, 5,000, 10,000, and 20,000), c) three different test statistic for ordinal covariate (chi-square, adapted maximum Lagrange multiplier, and a weighted double maximum), d) pre pruning option of limiting the minimum sample size per subgroup (250 vs. none), and e) post pruning option (BIC vs. none). The main evaluation criteria are a) statistical power to recover true subgroups, b) overall classification accuracy and precision, c) accuracy of cut points of ordinal/continuous covariates and labels of categorical covariates, and d) bias and root mean squared error (RMSE) of the parameter estimates per subgroup. Third, the simulation is parallelly conducted with GMM, and the results of it are compared with the ones of MOB. The key findings suggest that medium effect size (0.4 - 0.6) with relatively large sample sizes (5,000, 10,000, and 20,000) and large effect size (0.8 - 1.0) with adequate sample size (1,000 or 2,000) are enough to distinguish the difference in focal parameters, recovering the true number of subgroups. In addition, treating ordinal variables as either ordinal or categorical is not different in terms of recovering the true subgroups. However, the empirical study suggests that using test statistic for the ordinal covariates is desired when there exist association between the outcome and ordinal covariate. Post pruning using BIC and limiting the minimum size per subgroup simultaneously are also desired options. Without the post pruning with BIC, MOB tends to over-extract the subgroups across conditions. With the same simulated datasets, GMM produced neither accurate subgroups nor reliable parameter estimates. This study sheds light on how to uncover subpopulations using MOB algorithm with a popular parametric model for longitudinal study. This approach is beneficial for large-scale data such as more than 10,000 sizes with large number of potential covariates. Limitations and future directions are also discussed. The findings play a critical role to lay the groundwork of extending the application of MOB into various statistical models by investigating its performance regarding complex covariate effects.
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Title: The regulation surrounding the triose phosphate utilization limitation of photosynthesis
Creator: McClain, Alan M.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: The triose phosphate utilization (TPU) limitation of photosynthesis is a paradigm in which the rate at which stromal phosphate is incorporated into the organic phosphate pool can exceed the rate at which inorganic phosphate is released by processing fixed carbon into end products such as starch or sucrose. TPU limitation is unique among the three canon biochemical limitations of photosynthesis in that the plant must regulate photosynthetic rate to a level below what is maximally possible in...
Show moreThe triose phosphate utilization (TPU) limitation of photosynthesis is a paradigm in which the rate at which stromal phosphate is incorporated into the organic phosphate pool can exceed the rate at which inorganic phosphate is released by processing fixed carbon into end products such as starch or sucrose. TPU limitation is unique among the three canon biochemical limitations of photosynthesis in that the plant must regulate photosynthetic rate to a level below what is maximally possible in its current environment.I investigated the methods through which the photosynthetic rate is regulated in response to TPU limitation. For the first minute after imposition of TPU limitation by excess light and CO2, the photosynthetic rate is limited by oscillations in availability of NADP+ for photosystem I and availability of inorganic phosphate for the chloroplastic ATP synthase. These oscillations cause variance in the redox state of the electron carrier Qa which primarily controls energy flow during photosynthesis. After a few minutes, slower energy-dependent regulatory mechanisms at photosystem II and the cytochrome b6f complex reduce energy flow, relieving any excess reduction at Qa or photosystem I. After a day of acclimation, photoinhibition and rubisco deactivation prevent the appearance of TPU limitation at elevated CO2 and also prevented the occurrence of oscillations in photosynthetic electron carrier redox status. Oscillations induced by TPU limitation are temporarily able to exceed the steady-state photosynthetic rate. However, the advantage is short-lived, and overall plants assimilate less over the course of oscillations than they would during steady-state photosynthesis. The plants can temporarily exceed the limitation on photosynthesis typically imposed by TPU limitation or the RuBP regeneration limitation, but not the rubisco limitation. This is due to the availability of metabolites caused by a brief period of inactivity. Furthermore, the amplitude of the oscillations depended on how quickly the plant entered TPU limitation and how severe TPU limitation was when imposed.
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Title: Application of nuclear Density Functional Theory to exotic nuclei
Creator: Chen, Mengzhi
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Nuclear density functional theory (DFT) is the method of choice to study the nuclear properties of medium-mass and heavy nuclei.This dissertation employs the Skryme Hartree-Fock-Bogoliubov (HFB) approach to study nuclear reflection-asymmetric deformations and collective rotation.Nuclear ground states with stable reflection-asymmetric shapes, predicted by theory, have been confirmed experimentally.To explore the microscopic origin of reflection-asymmetric nuclear shapes, we applied the density...
Show moreNuclear density functional theory (DFT) is the method of choice to study the nuclear properties of medium-mass and heavy nuclei.This dissertation employs the Skryme Hartree-Fock-Bogoliubov (HFB) approach to study nuclear reflection-asymmetric deformations and collective rotation.Nuclear ground states with stable reflection-asymmetric shapes, predicted by theory, have been confirmed experimentally.To explore the microscopic origin of reflection-asymmetric nuclear shapes, we applied the density expansion method to decompose the total HFB energy into different multipolarities. We demonstrated that the reflection-asymmetric deformation is driven by the isoscalar part of the interaction energy. We also confirmed the importance of high-multipolarity fields for stabilizing reflection-asymmetric deformations.The nucleon localization function (NLF) has been successfully applied to characterize nuclear shell structure and collective motion.In our work, we extended the application of NLF to study the nuclear response to fast rotation. By solving the cranked harmonic-oscillator and comparing it with cranked Hartree-Fock results, we defined the simplified localization measure and demonstrated its usefulness as an indicator of nuclear rotation. The above nuclear DFT calculations were performed using existing HFB solvers.However, the current HFB solvers are deficient in the study of exotic nuclei whose properties are strongly affected by the quasiparticle continuum space. For this purpose, we developed a three-dimensional Skyrme-HFB solver HFBFFT in the coordinate-space representation using the canonical basis approach. We implemented the soft energy cutoff and pairing annealing to solve the problem of pairing collapse; a sub-iteration method to improve the convergence, and an algorithm to restore the Hermiticity of differential operators brought by Fourier-transform-based differentiation. The accuracy and performance of HFBFFT were tested by benchmarking it against other HFB codes, both spherical and deformed, for a set of well-bound and weakly-bound nuclei.
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Title: PROBE EFFECTS DURING CONCENTRATION DETERMINATION IN SCANNING ELECTROCHEMICAL MICROSCOPY
Creator: Mirabal, Alex
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Efficient, sustainable chemical reactions will play a large role in addressing many growing issues, including alternative energy production, greenhouse gas conversion, and pharmaceuticals. Electrochemical reactions are attractive due to their relatively mild reaction conditions and direct use of electricity. The understanding and design of the local liquid-solid interface will guide future progress in electrocatalytic reactions.Over time, nature has evolved many highly efficient reactions...
Show moreEfficient, sustainable chemical reactions will play a large role in addressing many growing issues, including alternative energy production, greenhouse gas conversion, and pharmaceuticals. Electrochemical reactions are attractive due to their relatively mild reaction conditions and direct use of electricity. The understanding and design of the local liquid-solid interface will guide future progress in electrocatalytic reactions.Over time, nature has evolved many highly efficient reactions through enzymatic reactions. These long-studied catalysts provide complex reaction environments that: 1) enhance interaction with reactants, 2) protect intermediates from side reactions, 3) increase the rates of reactions, and 4) selectively react to a specific product. The overarching lesson to be learned is that the local reaction environment plays a large role in the catalyst’s reactivity, selectivity, and efficiency. One way to characterize the local environment is through scanning electrochemical microscopy (SECM), in which a small electrochemical probe is rastered over an interface. A quantitative correlation of the probe response to concentration provides a direct measurement of the local environment. The presence of the SECM probe itself can induce changes in the local environment. Comparing the changed local environment (in situ) to what it would be without the probe present (operando), shows large differences of up to 120% under specific operating conditions. A few physical parameters such as the surface site geometry are shown to have an impact on how significant the probe effects are. Additional parameters such as the tip geometry and tip-surface separation are also to have an impact. A finite element method (FEM) simulation informed by experiments is used to examine the above-mentioned tip effects. It is found that fitting responses to other frequently used electrochemical measurements, such as approach curves and CVs, to parameterize the model appropriately describes experimental SECM results. We first apply this method to study platinum nanoparticles, where a ~50 nm resolution is the highest resolution to our knowledge for AFM-SECM. Through statistical analysis of the surface, an isolated nanoparticle SECM response is correlated with a concentration profile. It is found that the concentration profile has minimal probe effects due to the use of a conical electrode. Applying a similar approach, we also study the probe effects in pH detection during hydrogen evolution and CO2 reduction. Where we match experimental results to parameterize the system. It shown that there is a pH difference of up to ~7 pH units underneath the probe due to hindered diffusion. However, even with these large differences, the probes are still able to reflect the trends seen without the probe present. Moreover, it is shown that the physical parameters have correlated responses, indicating that hindered diffusion is controlled by the insulation radius and tip-surface separation. Finally, the importance of the analyte is discussed with regard to its interaction with the tip. In addition to the concentration impact on the response signal, the compatibility with the tip need be considered. Degradation of the tip and/or the redox couple of choice will detrimentally affect the ability to examine the local interface. We show that, of the redox couples examined, ferrocene-based compounds appear to best satisfy the most crucial factors of stability and mild redox potentials. Overall, this work studies and removes the impact of the probe for local concentration detection using SECM. This work acts as a guide to quantitatively study the local environment of electrocatalyzed reactions. This is realized through a combined experimental-FEM approach in which the simulation is informed by experiments such that it’s representative of the experimental environment.
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Title: The Role of Department Chair and Full-Time Non-Tenure-Track Faculty Policies, Practices, and Work Cultures
Creator: Williams, Shauna
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Change in higher education is inevitable (Wergin, 2007). One prominent change is related to faculty composition. Studies have shown increased hiring of full-time non-tenure-track faculty compared to tenure-track faculty (AAUP, 2018; National Center on Educational Statistics, 2018). The department chair plays a critical role in the lives of non-tenure-track faculty. The chair can foster collaboration, navigate tensions, advance improvements, and directly impact change efforts in an academic...
Show moreChange in higher education is inevitable (Wergin, 2007). One prominent change is related to faculty composition. Studies have shown increased hiring of full-time non-tenure-track faculty compared to tenure-track faculty (AAUP, 2018; National Center on Educational Statistics, 2018). The department chair plays a critical role in the lives of non-tenure-track faculty. The chair can foster collaboration, navigate tensions, advance improvements, and directly impact change efforts in an academic department. The department chair may also influence the work environment and culture for faculty – a culture that may result in non-tenure track faculty feeling marginalized, disconnected, like second-class citizens, devalued, and disenfranchised (Haviland, Alleman, & Allen, 2017). Through qualitative interviews with department chairs and faculty, this study sought to answer the question of, what role does the department chair play regarding full-time non-tenure-track faculty policies, practices, and work cultures? The findings reveal that department chairs play an essential role in leading efforts to revise policies and organizational structures in ways that support and include non-tenure-track faculty. The department chair is positioned to valorize the work of non-tenure-track faculty through a commitment to collegiality, collaborative practices, and caring communities. Department chairs, however, are often unable to act alone and may have limited power to change policies and practices for non-tenure-track faculty. Collective leadership efforts, like working across units and ranks, via task forces, and through the inclusion of unions, may be necessary strategies for bringing needed change to non-tenure-track faculty policies, practices, and cultures.
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Title: Soil invertebrate interactions with microplastic pollution
Creator: Helmberger, Maxwell Summit
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Microplastics are an unfortunate byproduct of human society’s increasing reliance on synthetic plastics for packaging, clothing, and other products. Microplastics have long been known to pollute the world’s oceans, but recent work has shown them to be just as prevalent, if not more so, in soil. Early findings indicate similar potential for harm to soil organisms as has been seen for marine microplastics. Yet aside from microplastics’ direct physical and toxicological effects on soil organisms...
Show moreMicroplastics are an unfortunate byproduct of human society’s increasing reliance on synthetic plastics for packaging, clothing, and other products. Microplastics have long been known to pollute the world’s oceans, but recent work has shown them to be just as prevalent, if not more so, in soil. Early findings indicate similar potential for harm to soil organisms as has been seen for marine microplastics. Yet aside from microplastics’ direct physical and toxicological effects on soil organisms, one must also consider their interactions with these organisms, the ways in which organisms may influence microplastics’ formation, occurrence, and distribution in soil as well as mediate their effects on the rest of the soil community. My research is focused on soil invertebrates’ ability to create microplastics by fragmenting large plastic debris. To advance this goal, I first developed a novel fluorescent counterstaining technique, adding a blend of Calcofluor white and Evans blue to the traditional Nile red staining approach. The counterstain allowed microplastics to be visually distinguished from chitin, cellulose, and other biological materials that may survive chemical digestion along with the plastics, making it possible to detect plastics in samples of soil invertebrate fecal material and biomass. I then investigated four soil invertebrates’ ability to generate microplastic from polystyrene (PS) foam debris. Individuals of the beetle larva Zophobas morio, the cricket Gryllodes sigillatus, the isopod Oniscus asellus, and the snail Cornu aspersum were placed in glass arenas with pieces of pristine or weathered PS foam for 24 h, after which I counted microplastic particles in the invertebrates’ fecal material, cadaver biomass, and the sand substrate of their arenas. Z. morio fragmented all plastics and produced the most detectable microplastic, C. aspersum produced almost none, and G. sigillatus and O. asellus fragmented only the weathered plastics. In a follow-up experiment with O. asellus, identical pieces of pristine PS foam were subjected to ultraviolet light, immersion in a soil suspension, and combination treatments to assess the effects of exposure to the elements on fragmentation by the isopods. Plastics immersed in the soil suspension were fragmented to a significantly greater degree than other treatments. Together, these results suggest that large plastic debris could represent a source of microplastics into soil environments, and that laboratory experiments investigating fragmentation of pristine plastics may risk underestimating the phenomenon. My further investigations focused on fragmentation of weathered PS foam by the isopods O. asellus and Trachelipus rathkii, examining fragmentation over different spans of time and the effects of natural materials as alternate substrates for the isopods. Neither species appreciably fragmented the PS foam until after 48 h, an interesting contrast to the previous experience, and O. asellus produced more fragments than T. rathkii. The presence of wood as an alternate substrate did not significantly affect fragmentation. More broadly, these results indicate that laboratory experiments should be conducted over short timescales and do not necessarily need to include alternate or supplementary food for the study organisms. In summary, the potential of soil invertebrates to affect microplastic dynamics, complicating their effects on other organisms compared to what would be seen in a standard ecotoxicological assay, should be considered when assessing this novel pollutant’s impact on soil ecosystems.
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Title: IMPROVED DETECTION AND MANAGEMENT OF PHYTOPHTHORA SOJAE
Creator: McCoy, Austin Glenn
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Phytophthora spp. cause root and stem rots, leaf blights and fruit rots on agricultural and economically important plant species. Symptoms of Phytophthora infected plants, particularly root rots, can be difficult to distinguish from other oomycete and fungal pathogens and often result in devastating losses. Phytophthora spp. can lie dormant for many years in the oospore stage, making long-term management of these diseases difficult. Phytophthora sojae is an important and prevalent pathogen of...
Show morePhytophthora spp. cause root and stem rots, leaf blights and fruit rots on agricultural and economically important plant species. Symptoms of Phytophthora infected plants, particularly root rots, can be difficult to distinguish from other oomycete and fungal pathogens and often result in devastating losses. Phytophthora spp. can lie dormant for many years in the oospore stage, making long-term management of these diseases difficult. Phytophthora sojae is an important and prevalent pathogen of soybean (Glycine max L.) worldwide, causing Phytophthora stem and root rot (PRR). PRR disease management during the growing season relies on an integrated pest management approach using a combination of host resistance, chemical compounds (fungicides; oomicides) and cultural practices for successful management. Therefore, this dissertation research focuses on improving the detection and management recommendations for Phytophthora sojae. In Chapter 1 I provide background and a review of the current literature on Phytophthora sojae management, including genetic resistance, chemical control compounds (fungicides; oomicides) and cultural practices used to mitigate losses to PRR. In my second chapter I validate the sensitivity and specificity of a preformulated Recombinase Polymerase Amplification assay for Phytophthora spp. This assay needs no refrigeration, does not require extensive DNA isolation, can be used in the field, and different qPCR platforms could reliably detect down to 3.3-330.0 pg of Phytophthora spp. DNA within plant tissue in under 30 minutes. Based on the limited reagents needed, ease of use, and reliability, this assay would be of benefit to diagnostic labs and inspectors monitoring regulated and non-regulated Phytophthora spp. Next, I transitioned the Habgood-Gilmour Spreadsheet (‘HaGiS’) from Microsoft Excel format to the subsequent R package ‘hagis’ and improved upon the analyses readily available to compare pathotypes from different populations of P. sojae (Chapter 3; ‘hagis’ beta-diversity). I then implemented the R package ‘hagis’ in my own P. sojae pathotype and fungicide sensitivity survey in the state of Michigan, identifying effective resistance genes and seed treatment compounds for the management of PRR. This study identified a loss of Rps1c and Rps1k, the two most widely plant Phytophthora sojae resistance genes, as viable management tools in Michigan and an increase in pathotype complexity, as compared to a survey conducted twenty years ago in Michigan (Chapter 4). In Chapter 5 I led a multi-state integrated pest management field trial that was performed in Michigan, Indiana, and Minnesota to study the effects of partial resistance and seed treatments with or without ethaboxam and metalaxyl on soybean stand, plant dry weights, and final yields under P. sojae pressure. This study found that oomicide treated seed protects stand across three locations in the Midwest, but the response of soybean varieties based on seed treatment, was variety and year specific. Significant yield benefits from using oomicide treated seed were only observed in one location and year. The effects of partial resistance were inconclusive and highlighted the need for a more informative and reliable rating system for soybean varieties partial resistance to P. sojae. Finally, in Chapter 6 I present conclusions and impacts on the studies presented in this dissertation. Overall, the studies presented provide an improvement to the detection, virulence data analysis, and integrated pest management recommendations for Phytophthora sojae.
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Title: Characterization of the human gut resistome, microbiome, and metabolome during enteric infection
Creator: Hansen, Zoe A.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: The human gut environment is replete with host-microbe and microbe-microbe interactions that shape human health. This system is also a known reservoir for antimicrobial resistance (AMR). The ubiquity of AMR is alarming, as greater than 2.8 million antibiotic-resistant infections and 35,000 deaths occur annually in the United States. Multiple human pathogens have demonstrated reduced susceptibility to various antibiotics, including enteric pathogens such as Campylobacter, Salmonella, Shigella,...
Show moreThe human gut environment is replete with host-microbe and microbe-microbe interactions that shape human health. This system is also a known reservoir for antimicrobial resistance (AMR). The ubiquity of AMR is alarming, as greater than 2.8 million antibiotic-resistant infections and 35,000 deaths occur annually in the United States. Multiple human pathogens have demonstrated reduced susceptibility to various antibiotics, including enteric pathogens such as Campylobacter, Salmonella, Shigella, and STEC, which cause millions of foodborne infections each year. The increasing incidence of antibiotic resistant enteric infections substantiates a need to further characterize these pathogens’ role in the curation and dissemination of AMR across environments. In this dissertation, a total of 223 human stools were assessed using shotgun metagenomics sequencing to investigate gut microbiome changes associated with enteric infection. Sixty-three stools were collected from patients suffering from enteric infection between 2011-2015 by the Michigan Department of Health and Human Services (MDHHS). Sixty-one of these patients submitted a follow-up sample between 1- and 29-weeks post-infection, and 99 healthy household members also submitted stools to serve as controls. In Chapter 2, a subset of patients infected with Campylobacter spp. and their related controls were investigated to assess the gut resistome, or collection of all antimicrobial resistance genes (ARGs) and their genetic precursors, related to infection. This examination revealed significantly higher ARG diversity in infected patients compared to healthy controls. Specifically, levels of multi-drug resistance (MDR) were greatly increased during infection. Three case clusters with distinct resistomes were identified; two of these clusters had unique ARG profiles that differed from those of healthy family members. In Chapter 3, a larger subset of 120 paired samples (60 infected vs. 60 recovered) were investigated to further characterize resistome and microbiome fluctuations related to infection and recovery. Again, infected patients harbored greater resistome diversity; however, recovered individuals displayed higher diversity in their microbiota composition. Despite their lower overall microbial diversity, patients with acute infections showed an increase in the abundance of members of Enterobacteriaceae, with specific expansion of the genus Escherichia. Host-tracking analysis revealed that many Enterobacteriaceae carried ARGs related to MDR and biocide resistance, a finding with broad implications for the ecology of resistance during infection. The fourth chapter explored metabolic capacity of gut microbial communities. In addition to metabolic pathway prediction, untargeted metabolomics was performed via LC/MS for 122 paired samples. Pathway annotation suggested that infected individuals contain greater microbial functional capacity, but metabolomics indicated greater overall metabolite diversity among recovered patients. Infection was associated with enhanced nitrogen and amino acid metabolism pathways. Although many metabolites remain uncharacterized, their presence or absence among individuals suggest their importance during and after infection. Altogether, the findings of this dissertation further characterize ecological consequences related to enteric infection in the human gut. Specifically, this research illustrates the importance of enteric infection in the dissemination and persistence of resistance determinants. Moreover, the expansion of Enterobacteriaceae and the evident increase in nitrogen- and amino acid-related metabolism during infection represent potential targets for future intervention practices.
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Title: Leveraging Angiosperm Pangenomics to Understand Genome Evolution
Creator: Yocca, Alan E.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: My dissertation work focused on species-level comparative genomics and pangenomics to describe patterns of genetic variation. I studied multiple systems and unsurprisingly discovered different patterns of variation. Within a species, individuals are genetically diverse. There are some DNA regions present in every individual (core), while others may be specific to a single individual or lineage (variable). The sum of the genetic sequences found across an entire taxonomic group is called the...
Show moreMy dissertation work focused on species-level comparative genomics and pangenomics to describe patterns of genetic variation. I studied multiple systems and unsurprisingly discovered different patterns of variation. Within a species, individuals are genetically diverse. There are some DNA regions present in every individual (core), while others may be specific to a single individual or lineage (variable). The sum of the genetic sequences found across an entire taxonomic group is called the pangenome. This DNA variation greatly contributes to observed phenotypic differences between individuals. Therefore, to understand genome evolution and the link between genotype and phenotype, we must understand the pangenome. In this work, I compare the core and variable genetic regions both coding and noncoding across different flowering plant lineages. I note many consistent features across lineages as well as ways in which each pangenomic pattern is unique. These consistencies and differences can be leveraged in the future to better understand genome evolution as well as how genotype relates to phenotype. Specifically, my dissertation includes four chapters; (1) Evolution of Conserved Noncoding Sequences in Arabidopsis thaliana, (2) Machine learning identifies differences between core and variable genes in Brachypodium distachyon and Oryza sativa, (3) Current status and future perspectives on the evolution of cis-regulatory elements in plants, and (4) A pangenome for Vaccinium.
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Title: Novel Depth Representations for Depth Completion with Application in 3D Object Detection
Creator: Imran, Saif Muhammad
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Depth completion refers to interpolating a dense, regular depth grid from sparse and irregularly sampled depth values, often guided by high-resolution color imagery. The primary goal of depth completion is to estimate depth. In practice methods are trained by minimizing an error between predicted dense depth and ground-truth depth, and are evaluated by how well they minimize this error. Here we identify a second goal which is to avoid smearing depth across depth discontinuities. This second...
Show moreDepth completion refers to interpolating a dense, regular depth grid from sparse and irregularly sampled depth values, often guided by high-resolution color imagery. The primary goal of depth completion is to estimate depth. In practice methods are trained by minimizing an error between predicted dense depth and ground-truth depth, and are evaluated by how well they minimize this error. Here we identify a second goal which is to avoid smearing depth across depth discontinuities. This second goal is important because it can improve downstream applications of depth completion such as object detection and pose estimation. However, we also show that the goal of minimizing error can conflict with the goal of eliminating depth smearing.In this thesis, we propose two novel representations of depths that can encode depth discontinuity across object surfaces by allowing multiple depth estimation in the spatial domain. In order to learn these new representations, we propose carefully designed loss functions and show their effectiveness in deep neural network learning. We show how our representations can avoid inter-object depth mixing and also beat state of the art metrics for depth completion. The quality of ground-truth depth in real-world depth completion problems is another key challenge for learning and accurate evaluation of methods. Ground truth depth created from semi-automatic methods suffers from sparse sampling and errors at object boundaries. We show that the combination of these errors and the commonly used evaluation measure has promoted solutions that mix depths across boundaries in current methods. The thesis proposes alternate depth completion performance measures that reduce preference for mixed depths and promote sharp boundaries.The thesis also investigates whether additional points from depth completion methods can help in a challenging and high-level perception problem; 3D object detection. It shows the effect of different depth noises originated from depth estimates on detection performances and proposes some effective ways to reduce noise in the estimate and overcome architecture limitations. The method is demonstrated on both real-world and synthetic datasets.
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Title: Richard Hilton Tobitt's Diaspora : Religion, Migration, and Grassroots Organizing, 1865-1945
Creator: Shell, Christopher Michael
Date: 2022
Collection: Electronic Theses & Dissertations
Description: My doctoral dissertation project, titled, Richard Hilton Tobitt’s Diaspora: Religion, Migration, and Grassroots Organizing, 1865-1945, is an early twentieth-century political narrative of Black activism in the eastern Caribbean and New York City. The main argument of my dissertation is that through the lens of Antiguan-born Reverend Richard Hilton Tobitt (1873-1961), we learn about the monumental impact of Leeward Islander migration on Black political organizing in the understudied areas of...
Show moreMy doctoral dissertation project, titled, Richard Hilton Tobitt’s Diaspora: Religion, Migration, and Grassroots Organizing, 1865-1945, is an early twentieth-century political narrative of Black activism in the eastern Caribbean and New York City. The main argument of my dissertation is that through the lens of Antiguan-born Reverend Richard Hilton Tobitt (1873-1961), we learn about the monumental impact of Leeward Islander migration on Black political organizing in the understudied areas of Bermuda and Staten Island, New York. Using the early twentieth-century experiences of Tobitt as a window into much larger phenomenon, my project brings attention to Black political organizing in Bermuda, the roots of Caribbean nationalism, and highlights the understudied Black community in Staten Island.
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Title: Interpreting Gravitational Waves and Developing Relativistic Multiphysics Solvers for Core-collapse Supernova Simulations
Creator: Pajkos, Michael Anton
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Core-collapse supernovae (CCSNe) mark the endpoint for millions of years of massive stellar evolution. After a successful explosion, supernovae increase the metallicity of the interstellar medium, generate intense electromagnetic radiation ionizing their surroundings, generate compact objects such as black holes or neutron stars, and create ripples in spacetime---gravitational waves (GWs). Advances in supernova theory over the past few decades have furthered our understanding of CCSNe....
Show moreCore-collapse supernovae (CCSNe) mark the endpoint for millions of years of massive stellar evolution. After a successful explosion, supernovae increase the metallicity of the interstellar medium, generate intense electromagnetic radiation ionizing their surroundings, generate compact objects such as black holes or neutron stars, and create ripples in spacetime---gravitational waves (GWs). Advances in supernova theory over the past few decades have furthered our understanding of CCSNe. However, constraints on the physics enshrouded in the supernova center would further illuminate their explosion mechanisms. Advances in high performance computing (HPC) resources and the ever-increasing sensitivities of GW observatories have positioned the field of astrophysics between two recent technological advances. The work presented here leverages HPC to perform CCSN simulations, allowing astronomers to translate between GW signals and internal physics. Using this insight, astronomers are better positioned to constrain the physics driving these explosive events that have such a widespread influence throughout astronomy.Investigating the evolution of 12-, 20-, 40-, and 60 solar mass progenitors, I perform axisymmetric neutrino radiation-hydrodynamic CCSN simulations, to relate the convective activity behind the supernova shock to the expected GW strength. I quantify how the rotational content of the supernova lowers GW frequencies. I present a novel method that combines two features of a single GW event to constrain the mass distribution within the stellar progenitor. By only requiring the two most detectable parts of the GW signal, astronomers can also potentially predict the explosion properties ~days before shock breakout. I present work with my undergraduate research assistant, that considers the impact of viewing angle on detecting GWs from CCSNe. Presented is a novel analysis method to identify the distribution of GW emission over all angles, accompanied with results showing that the preferred direction of GW emission for CCSNe migrates over time. Lastly, I present new numerical solvers targeted at exascale computing platforms that account for magnetized fluid evolution with velocities near the speed of light and in extreme spacetimes. These solvers are accompanied with stringent baseline tests, paired with 1D and 2D supernova simulations making use of these features.
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Title: ESSAYS ON COMMUNITY FOCUSED SUPPLY CHAINS
Creator: Cole, Dustin
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Businesses are increasingly being called upon to improve their Environment, Social and Governance (ESG) performance. The need to tackle a range of concerns, both environmentally and socially, can be seen in the United Nations’ 17 development goals set forth in 2015. Beyond governments and regulators, businesses themselves are increasingly aware of the importance of addressing such issues. Two hundred of the top CEOs of the country have emphasized the importance of the role that businesses...
Show moreBusinesses are increasingly being called upon to improve their Environment, Social and Governance (ESG) performance. The need to tackle a range of concerns, both environmentally and socially, can be seen in the United Nations’ 17 development goals set forth in 2015. Beyond governments and regulators, businesses themselves are increasingly aware of the importance of addressing such issues. Two hundred of the top CEOs of the country have emphasized the importance of the role that businesses play in confronting community-related issues and Diversity, Equity and Inclusion (DEI) (Murray 2019). In a series of three essays, this dissertation focuses on the social and environmental sustainability aspects of ESG, thus contributing substantially to the overall domain of sustainability. The first essay examines the impact of leader-worker disability status similarity on front-line manufacturing worker productivity using micro-data gathered from a real-world organization in Michigan. It contributes to the nascent field of inclusive operations and explores how organizations can both be profitable and inclusive of traditionally marginalized workers. The essay focuses on the moderating influence of direct supervisors with a disability on workgroup productivity as the number of workers with disabilities increases. Results suggest that a direct supervisor with a disability does indeed benefit the productivity of workers with disabilities. This benefit, however, is the mitigation of potential productivity declines as the number of workers with a disability increases in the workgroup. A follow-up qualitative study is performed to understand the mechanisms of the productivity benefit by interviewing 50 workers and supervisors with and without disabilities across three organizations. The second and third essays focus on the issue of water, a resource that is increasingly important as an environmental concern. As a resource shared between communities and firms, water is an essential component of building sustainable cities and communities.The second essay examines trade-offs and synergies experienced by organizations when reducing water use and carbon emissions using secondary panel data of large firms. Previous research has found differing results of organizations trading off carbon emissions and water. Some have found reducing one comes at the expense of the other, while other research has found organizations can reduce these two concerns jointly. This past research, though, has generally been qualitative and at the facility level, without quantitative analysis at the firm level. This research fills this gap by providing a firm-level examination of such potential trade-offs using a combination of Data Envelopment Analysis and econometric methods.The third essay uses a vignette experiment with real-world procurement professionals to examine how buyers weigh the competing environmental concerns of carbon emissions and water use reductions in the supply chain against supplier location (local vs. offshore suppliers). The results show an overwhelming preference for local suppliers with lower carbon emissions, to the extent that a supplier with a superior overall environmental performance may be passed over in pursuit of local suppliers with marginally lower carbon emissions.
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Title: Detecting and Mitigating Bias in Natural Languages
Creator: Liu, Haochen
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Natural language processing (NLP) is an increasingly prominent subfield of artificial intelligence (AI). NLP techniques enable intelligent machines to understand and analyze natural languages and make it possible for humans and machines to communicate through natural languages. However, more and more evidence indicates that NLP applications show human-like discriminatory bias or make unfair decisions. As NLP algorithms play an increasingly irreplaceable role in promoting the automation of...
Show moreNatural language processing (NLP) is an increasingly prominent subfield of artificial intelligence (AI). NLP techniques enable intelligent machines to understand and analyze natural languages and make it possible for humans and machines to communicate through natural languages. However, more and more evidence indicates that NLP applications show human-like discriminatory bias or make unfair decisions. As NLP algorithms play an increasingly irreplaceable role in promoting the automation of people's lives, bias in NLP is closely related to users' vital interests and demands considerable attention.While there are a growing number of studies related to bias in natural languages, the research on this topic is far from complete. In this thesis, we propose several studies to fill up the gaps in the area of bias in NLP in terms of three perspectives. First, existing studies are mainly confined to traditional and relatively mature NLP tasks, but for certain newly emerging tasks such as dialogue generation, the research on how to define, detect, and mitigate the bias in them is still absent. We conduct pioneering studies on bias in dialogue models to answer these questions. Second, previous studies basically focus on explicit bias in NLP algorithms but overlook implicit bias. We investigate the implicit bias in text classification tasks in our studies, where we propose novel methods to detect, explain, and mitigate the implicit bias. Third, existing research on bias in NLP focuses more on in-processing and post-processing bias mitigation strategies, but rarely considers how to avoid bias being produced in the generation process of the training data, especially in the data annotation phase. To this end, we investigate annotator bias in crowdsourced data for NLP tasks and its group effect. We verify the existence of annotator group bias, develop a novel probabilistic graphical framework to capture it, and propose an algorithm to eliminate its negative impact on NLP model learning.
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