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Title: FIELD AND EXPERIMENTAL STUDIES FIND VARIATION IN LEVELS OF LARVAL LAKE STURGEON PREDATION IS ASSOCIATED WITH BEHAVIOR AND ENVIRONMENTAL CONDITIONS
Creator: Riedy, Joseph Jerry
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Species are vulnerable to predation during early in life stages, especially those who provide little or no parental care. Predation risk is further elevated during periods of migration when individuals are exposed to a greater abundance and diversity of predators. Levels of predation during migration are often variable and can be heavily influenced by environmental conditions and changes in behavior. It is important to understand how these factors influence predation rates of threatened and...
Show moreSpecies are vulnerable to predation during early in life stages, especially those who provide little or no parental care. Predation risk is further elevated during periods of migration when individuals are exposed to a greater abundance and diversity of predators. Levels of predation during migration are often variable and can be heavily influenced by environmental conditions and changes in behavior. It is important to understand how these factors influence predation rates of threatened and endangered species. Lake sturgeon are an imperiled species native to the Great Lakes, Mississippi River, and Hudson Bay drainages that undergo a downstream from spawning grounds to nursery habitat at the beginning of the larval stage. This migration begins at night and larvae are exposed to several known predator species as they migrate the length of the spawning river in event. In this dissertation, I examine influences of ecological factors and behavior on levels of predation during the downstream migration. In Chapters 1 and 2, I used mesocosm experiments to determine the effects of night light level, rearing temperature, and prey abundance on survival during migration. Survival is highest during the environmental conditions present early in the season: new moon light levels, colder rearing conditions, and when prey abundance is high. In Chapters 3 and 4, I returned to the mesocosms to examine the survival implications of the behavioral responses to alarm cues during the larval stage. Lake sturgeon larvae exposed to a predator species odor and lake sturgeon alarm cue have higher survival rates when later exposed to the predator species. Additionally, lake sturgeon can use alarm cues from unrelated allopatric and sympatric species as kairomones similarly to conspecific alarm cues. In Chapter 5, I collected lake sturgeon larvae and predator diets from a natural lake sturgeon spawning stream to estimate nightly mortality rates, identify the predatory species that consumed, and determine the environmental factors that influence lake sturgeon mortality in a wild population. Survival rates varied greatly, but on average, approximately one third of lake sturgeon larvae survived the section of the river sampled. Additionally, roughly one third of all potential predator diets sampled contained lake sturgeon. Similar to previous chapters, light level and the abundance of prey had the greatest influence on the survival rates of lake sturgeon and the probability of detecting lake sturgeon in the diets of potential predators. Results indicate the timing of lake sturgeon spawning influences larval survival by determining the ecological conditions present during offspring development and downstream migration. Work presented here identifies the factors with the strongest influence on larval lake sturgeon survival. Though variation in larval lake sturgeon mortality is high, managers may begin to use these factors to forecast larval lake sturgeon survival rates in populations. It will be important to monitor changes to these ecological variables, such as fluctuations in co-distributed fish and invertebrate populations, and variation in water temperatures during development, because these factors have strong and predictable influences lake sturgeon recruitment rates.
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Title: THE EFFECT OF SALES TAXES ON LOCATION DECISIONS AND CAPITAL MARKET OUTCOMES : EVIDENCE FROM WAYFAIR
Creator: Shaw, Joanna
Date: 2022
Collection: Electronic Theses & Dissertations
Description: This study examines how investors, analysts, and firms respond to changes in sales tax obligations for e-commerce firms. Previous research finds that e-retailers have a competitive advantage over their brick-and-mortar counterparts due to their ability to avoid collecting sales taxes. Using the Supreme Court of the United States (The Court) decision in South Dakota v. Wayfair, Inc., 585 U.S.__ (2011) (Wayfair) as a setting, I examine investor and analyst reactions to, and corporate location...
Show moreThis study examines how investors, analysts, and firms respond to changes in sales tax obligations for e-commerce firms. Previous research finds that e-retailers have a competitive advantage over their brick-and-mortar counterparts due to their ability to avoid collecting sales taxes. Using the Supreme Court of the United States (The Court) decision in South Dakota v. Wayfair, Inc., 585 U.S.__ (2011) (Wayfair) as a setting, I examine investor and analyst reactions to, and corporate location decisions following, the broadening of state nexus rules for interstate commerce. I find that investors and analysts responded negatively to the announcement that The Court would hear the Wayfair case and to the release of the ruling, as evidenced by negative mean cumulative abnormal returns and downward revenue forecast revisions, respectively. These results are consistent with capital market participants perceiving increased sales tax obligations as being detrimental to e-commerce firms. Next, I investigate how e-commerce firms respond to increased sales tax obligations by examining their location decision-making in the wake of Wayfair. I find that e-commerce firms are more likely to establish locations in new states with sales taxes after Wayfair. In cross-sectional analysis, I find that my results are primarily driven by retail, wholesale, and service firms. I also find evidence that e-commerce firms are more likely to establish locations in states with high populations after Wayfair.
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Title: BUSINESS RESPONSES TO SUPPLY CHAIN DYNAMICS : IMPLICATIONS FOR SOURCING AND PUBLIC POLICY
Creator: Yan, Zhenzhen
Date: 2022
Collection: Electronic Theses & Dissertations
Description: This dissertation studies drivers and consequences of firms' policy decisions from a supply chain perspective. Policy decisions can be both internal and external to the firms and carry substantial implications for firms’ performance outcomes. Both internal and external aspects of policy engagement are critical since they help further disciplinary understanding of not only how policy decisions influence the performance of products firms manufacture, but also the fact that firms can reshape...
Show moreThis dissertation studies drivers and consequences of firms' policy decisions from a supply chain perspective. Policy decisions can be both internal and external to the firms and carry substantial implications for firms’ performance outcomes. Both internal and external aspects of policy engagement are critical since they help further disciplinary understanding of not only how policy decisions influence the performance of products firms manufacture, but also the fact that firms can reshape their environmental conditions through adopting policy decisions to engage with regulators and impact their own business practices. Specifically, I investigate firms' sourcing policies and their product performance implications – an internal policy set by firms. Within the context of external policy engagement, my research investigates firms' policy responses to external conditions, such as climate change public policies.The first essay focuses on manufacturing localization, an internal policy set by automakers to relocate manufacturing activities closer to their target market. I apply a causal estimation method to 23-year panel data of the automotive industry complied from diverse data sources including Wards, National Highway and Traffic Safety Authority (NHTSA) recall data to investigate the quality implications of manufacturing localization. The results show an immediate quality decline for localized vehicles, indicated by an increase of 68.203% in the number of recalls (equivalent to 0.552 more recall campaigns) and an increase of customer complaints by 56.831% (equivalent to 9.997 more complaints) in the three years after the manufacturing localization. The increased number of recalls can lead to an extra expense of $2.76 million for a localized vehicle based on conservative estimations. A cautionary note is thus issued for automakers to adjust their planned budgets to account for warranty claims before the localization. This study provides guidance for firms considering the relocation of their manufacturing activities and for regulators that seek to reduce vehicle recalls. The second and third essays of my dissertation investigate firms’ engagement in influencing climate change policies (EICCP), which refers to firms’ strategic actions to influence climate change policymaking processes, aiming at reshaping policies or promoting policy changes in favor of their interests. In the second essay, I conceptualize EICCP and propose a taxonomy for EICCP strategies considering firms’ perceptions of external conditions and internal resources. I also create measures for EICCP to empirically validate this taxonomy by performing text analytics with machine-learning techniques on firms’ self-disclosure in CDP Climate Change data. Building on the second essay, I undertake a large-scale empirical analysis to investigate antecedents of EICCP in the third essay. Specifically, I examine the regulatory risks associated with climate change and firms’ supply network complexity as critical and interrelated factors for firms’ EICCP. The latter two essays contribute to the growing literature on climate change and firm responses. Overall, my thesis responds to the call for policy-related studies in the supply chain field and provides insights for policy decision-makers.
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Title: Evaluation of Operational and Safety Impacts of Part-Time Use of The Inside Shoulder
Creator: Cai, Qiuqi
Date: 2022
Collection: Electronic Theses & Dissertations
Description: The Michigan Department of Transportation (MDOT) introduced its first application of dynamic part-time shoulder use (D-PTSU) on the US-23 corridor in November 2017 to mitigate recurring congestion. This project referred to as the Flex route involved widening the left shoulder, which now serves as a temporary travel lane during between M-14 and M-36 during periods of heavy congestion. As the application of D-PTSU is relatively novel in the United States, especially the use of the left shoulder...
Show moreThe Michigan Department of Transportation (MDOT) introduced its first application of dynamic part-time shoulder use (D-PTSU) on the US-23 corridor in November 2017 to mitigate recurring congestion. This project referred to as the Flex route involved widening the left shoulder, which now serves as a temporary travel lane during between M-14 and M-36 during periods of heavy congestion. As the application of D-PTSU is relatively novel in the United States, especially the use of the left shoulder, this study evaluates the operational and safety performance of the US-23 Flex route and provides guidance for future implementation of similar facilities in Michigan and elsewhere. The evaluation assessed various metrics, including average travel time, travel time reliability, driver compliance, and incident clearance times. The findings show that operations of the US-23 Flex route have improved significantly, especially in the southbound direction. While the northbound direction also showed better performance after the Flex lane opened in general, some of the prior congestion has shifted to the end of the Flex route in the northbound direction due to a bottleneck that was introduced at the end terminal. Fortunately, this problem is expected to be alleviated by the planned extension of the Flex lane to I-96 in 2024. The operational analyses also showed improved operations when special events occurred, such as football games and holidays. Incident clearance times largely decreased after the Flex route was opened. Part-time shoulder running also provided an additional travel lane during peak periods, such as University of Michigan home football games, reducing such non-recurrent congestion. Crash data were compared for a period of five years (i.e., 2012 to 2016) before the construction of the Flex route, and two years (i.e., 2018 and 2019) after its completion. After considering increases in traffic volume, crashes were reduced by 17 percent when considering all times of day, including 34 percent in the southbound direction. During the peak operational periods, reductions of approximately 50 percent were experienced in the southbound direction. In contrast, total crashes were comparable in the northbound direction and actually increased by approximately 24 percent during the peak traffic periods. However, much of this increase is attributable to the lane drop that occurs at the northern terminus of the Flex route. The planned extension to I-96 should remedy the existing safety issues.
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Title: A SEPARATION : WATERWAYS, LOGISTICS, AND THE MAKING OF THE USSR’S NORTHEAST ASIAN BORDERLANDS, 1920S-1940S
Creator: ZHANG, LIAO
Date: 2022
Collection: Electronic Theses & Dissertations
Description: This dissertation examines the socioeconomic transformation of the middle and lower Amur River Basin in the first half of the 20th century. Through the lenses of social, spatial, and biographical history, this project addresses the following questions: how the Amur River Basin, once a coherent geographic unit, was socioeconomically carved up along national lines; and how the left bank of the middle Amur River became an inward-looking Soviet borderland that resembled many other Soviet...
Show moreThis dissertation examines the socioeconomic transformation of the middle and lower Amur River Basin in the first half of the 20th century. Through the lenses of social, spatial, and biographical history, this project addresses the following questions: how the Amur River Basin, once a coherent geographic unit, was socioeconomically carved up along national lines; and how the left bank of the middle Amur River became an inward-looking Soviet borderland that resembled many other Soviet heartlands. I discuss this process, by which the Amur River became a hardened, highly politicized international border, through reconstructing biographies of five middle Amur River-centered, interconnected social and economic institutions: an inland shipping company, a cohort of hydrological scientists and engineers, a trans-border brewery, the local establishment of the Soviet customs service, and the state agency for social welfare. This dissertation reveals that the history of everyday socioeconomic institutions was central to understanding the Soviet state and local communities’ participation in distinctively transforming the built environment, the mode of logistics, supply chains, and consequently the human-environment relationship of the left bank in the name of realizing local and All-Union economic self-sufficiency. Underlying the state-led pursuit of socioeconomic self-sufficiency is the Soviet Union’s fascination with legibility in statecraft and socioeconomic reorientation, substantiating the socialist regime’s very modern nature.
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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: Analyzing Synergistic Effects of Combined Aging Environments on Polymer Degradation : Micro-mechanical Modeling of Loss of Performance
Creator: Mohammadi, Hamid
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Materials’ properties play a crucial role in the selection of processes or design for manufacturingsystem components. These components should have high resistance to multiple stress factors such as mechanical and environmental stresses in which the component is being used. For this reason, engineers should analyze all possible scenarios and try to model for combined environment conditions before introducing a product to the market.Polymers are specific materials with significantly high...
Show moreMaterials’ properties play a crucial role in the selection of processes or design for manufacturingsystem components. These components should have high resistance to multiple stress factors such as mechanical and environmental stresses in which the component is being used. For this reason, engineers should analyze all possible scenarios and try to model for combined environment conditions before introducing a product to the market.Polymers are specific materials with significantly high durability and resilience due to theirloosely cross-linked polymer matrix made by long interconnected polymer chains. Due to these excellent properties, they are among the most frequently used materials in load-transfer applications in adhesives, joints, sealing, bumpers, coatings, and protection shields. Due to the increasing use of composite materials in the industry, polymers’ usage, especially in polymeric adhesive, drastically increased. Since polymeric adhesives are used to join dissimilar material interfaces. However, degradation of polymeric adhesives is a menace to joints.Degradation or aging defined as the loss of properties due to environmental condition. Agingis an irreversible process that changes the network topology of the material. Polymeric adhesives are susceptible to degradation which makes them a critical part with extreme sensitivity to temperature, moisture, and sunlight. Degradation-induced failure occurs due to damage accumulated from mechanical sources and the loss of properties due to aging which cause a premature failure in system. Therefore, reliability of a system can be greatly compromised due to this degradation induced failure. Consequently, polymeric adhesives are a significant challenge for design reliability of multi-material systems. Reliable theoretical models to predict the degradation-induced failure in polymeric adhesives can substantially reduce the cost and enhance the reliability of adhesive bonding.Current approach in Original Equipment Manufacturers (OEM) companies is to use experimentalapproaches to predict the failure. However, laboratory conditions omit many factors that are present in real-time and might not paint a clear picture of the mechanisms of failure. Most importantly, the time and cost needed for these tests are substantially high. To this end, developing a comprehensive software that would be able to model the real-time conditions of aging seems of great value.This dissertation objective is to provide micro-mechanical constitutive models that would beable to model damage accumulation in polymers and polymeric adhesives during combined aging environments. These constitutive models provide the necessary modules to build a platform for creating a Finite Element Method (FEM) based model for a 3D modeling of polymers in combined environmental aging condition under mechanical stresses. To this end, the project followed four main steps namely, (I) performing accelerated aging tests, (II) analyzing the tests result to understand the underlying aging phenomena, (III) developing degradation model, (IV) validating the proposed model versus the experimental data. After successfully finishing these steps, the necessary modules to start creating an FEM platform would be ready which should be the next step for this project.To go in further detail, this project successfully delivered five major tasks that has been definedas the necessary steps for developing the platform. These steps are as follows, (I) providing a model for thermo-oxidative aging of polymers, (II) understanding the effects of decay functions on modeling properties of aging, (III) developing a model for a combined thermo- and photo-oxidative aging, (IV) developing a model that can successfully consider accumulated damage during combined aging, (V) developing a model for cyclic environmental conditions. All of these models are the first ones in the literature that being developed which suggests great novelty and value that this work can bring to the industry. The model proposed in this work can significantly enhance the design process by allowing pre-selection of materials and product geometries with respect to the expected mechanical and environmental loading. Such process will allow agile design evaluation.
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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: NETWORK-WIDE CHARGING INFRASTRUCTURE PLANNING AND MARKET SHARE ANALYSIS FOR ELECTRIC VEHICLES
Creator: Kavianipour, Mohammadreza
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Electric vehicles (EVs) are widely considered a sustainable substitution to conventional vehicles to mitigate fossil fuel dependence and reduce tail-pipe emissions. However, limited ranges, long charging times, and lack of charging infrastructure have hindered EV’s market acceptance. This calls for more investments in building charging stations and advancing battery and charging technologies to obviate issues associated with EVs and increase their market share and improve sustainability. This...
Show moreElectric vehicles (EVs) are widely considered a sustainable substitution to conventional vehicles to mitigate fossil fuel dependence and reduce tail-pipe emissions. However, limited ranges, long charging times, and lack of charging infrastructure have hindered EV’s market acceptance. This calls for more investments in building charging stations and advancing battery and charging technologies to obviate issues associated with EVs and increase their market share and improve sustainability. This study introduces modeling frameworks to optimize fast-charging infrastructure locations at the network level to address the challenges associated with EVs. Furthermore, it investigates the required charging investments for the current and future EV market shares, technology advancements, and seasonal demand variations. First, this study seeks an optimal configuration for plug-in electric vehicle charging infrastructure that supports their long-distance intercity trips at the network level. A mathematical optimization model is proposed which minimizes the total system cost and considers the range anxiety, multiple refueling, maximum capacity, charging delay, and detour time. This study considers the impacts of charging station locations on the traffic assignment problem with a mixed fleet of electric and conventional vehicles considering a user equilibrium framework. This study fills existing gaps in the literature by capturing realistic patterns of travel demand and considering flow-dependent charging delays at charging stations in intercity networks. Then, the study focuses on Michigan and its future needs to support the intercity trips of EVs across the state in two target years of 2020 and 2030, considering monthly traffic demand and battery performance variations, as well as different battery sizes and charger technologies, the main contributing factors in defining the infrastructure needs of EV users, particularly in states with adverse weather conditions. This study incorporates the developed intercity model to suggest the optimal locations of EV fast chargers to be implemented in Michigan. Next, this study introduces an integrated framework for urban fast-charging infrastructure to address the range anxiety issue in urban networks. Unlike intercity trips that start with fully charged batteries, urban trips might start with any state of charge because of home/work chargers' unavailability, being part of a trip chain, and forgetting to charge overnight. A mesoscopic simulation tool is incorporated to generate trip trajectories, and a state-of-the-art tool is developed to simulate charging behavior based on various trip attributes for these trajectories. The resulting temporal charging demand is the key element in finding the optimum charging infrastructure. The solution quality and significant superiority in the computational efficiency of the decomposition approach are confirmed in comparison with the implicit enumeration approach. Finally, this study generates forecasting models to estimate the number of chargers and charging stations to support the EV charging demand for urban areas. These models provide macro-level estimates of the required infrastructure investment in urban areas, which can be easily implemented by policy-makers and city planners. This study incorporates data obtained from applying a disaggregate optimization-based charger placement model, for multiple case studies to generate the required data to calibrate the macro-level models, in the state of Michigan.
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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: THREE ESSAYS ON RISK MANAGEMENT AND IRRIGATION WATER DEMAND IN AGRICULTURE
Creator: Lu, Pin
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Both extensive (share of insured acres in total insurable acres) and intensive (coverage level choice) margin participation rates in the U.S. crop insurance program have increased due to generous subsidies. On a national scale, this program has been well rated to satisfy the actuarial fairness requirement by USDA Risk Management Agency. However, sizeable spatial heterogeneity remains across the Great Plains and Corn Belt regions. If subsidies were to be reduced in the future because of...
Show moreBoth extensive (share of insured acres in total insurable acres) and intensive (coverage level choice) margin participation rates in the U.S. crop insurance program have increased due to generous subsidies. On a national scale, this program has been well rated to satisfy the actuarial fairness requirement by USDA Risk Management Agency. However, sizeable spatial heterogeneity remains across the Great Plains and Corn Belt regions. If subsidies were to be reduced in the future because of financial constraints, such heterogeneity might be detrimental to the sustainability of the crop insurance program. A central theme of this dissertation is to investigate how farmers make participation decisions when risk factors exist. In a separate but related line of work, this dissertation also explores the irrigation water usage in the Great Lakes region because farmers' irrigation behavior reflects their risk preferences and impacts their incentives for enrolling in the program. The dissertation consists of three essays on farmers' decisions regarding premium mispricing, basis risk, and irrigation water usage. The first essay proposes a novel resampling procedure to estimate farm-level actuarially fair premiums. The resampling procedure mainly contains two parts: (i) semi-parametric quantile regression; and (ii) rejection method. Many previous studies explore whether county-level mispricing exists based on the historical loss ratio records. However, we can identify farm-level mispricing by imputing actuarially fair premiums based on historical yield records, consistent with theory. We find that farmers with lower land quality cropland paid fewer premiums than they should, but a contrary case happens for farmers with higher land quality cropland. Empirical evidence shows farmers may be more concerned about mispricing than subsidy transfer. Regression results support a conclusion that such farm-level mispricing deters farmers’ crop insurance demand. Our analysis sheds light on the policy-making that: (i) mispricing may be a substitution of subsidy so mitigating mispricing can maintain high participation while saving subsidies; and (ii) imputation of premiums based on historical yield records can apply. The second essay focuses on the impact of basis risk on participation rates in the U.S. crop insurance program. In recent years, basis risk has been increasingly recognized as an essential driver for deterring insurance uptake. Most research concentrates on index insurance contracts; however, few investigate the effect of mismatch between cash and futures markets on farmers’ insurance decisions. We first build a conceptual model to show farmers’ acreage response to basis risk within the expected utility framework. Next, we apply the Fractional Probit with Control Function for the empirical analysis and find that the effects of basis risk on participation rates are significantly negative for nearly all insurance contracts. Our analysis implies that: (i) to remove basis risk, revision for revenue contract may be considered; (ii) subsidy structure may be adjusted to be consistent with the underlying basis risk. The third essay investigates irrigation water usage in the Great Lakes region. Although the water conservation policy was implemented, there has been an upward trend in irrigation water demand from 2003 to 2018, including irrigated acres and total water usage. We employ firm-level irrigation data to examine what factors impact farmers' response to irrigation water usage. We find that: (i) price elasticities vary significantly according to model specifications and water costs; (ii) demand at both extensive (irrigated acres) and intensive (water application per acre) margins is input price inelastic; and (iii) price elasticities are homogeneous across crops but heterogeneous across states. For the policy-making, if there is a 10% tax on irrigation water cost, total water usage decreases by about 4% for corn and soybean, respectively.
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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: An exploration of selected relationships between insufficient and poor-quality sleep and dietary intake
Creator: Du, Chen
Date: 2022
Collection: Electronic Theses & Dissertations
Description: One in three adults in the U.S. and globally suffers from insufficient sleep and/or poor sleep quality, which are associated with poor health outcomes, including all top 10 leading causes of death. Sleep affects health outcomes, in part, by directly and indirectly influencing undesirable dietary behaviors, which, in this work, is defined as frequent consumption of foods that are inconsistent with health. For example, insufficient sleep leads to more frequent consumption of sweets, a direct...
Show moreOne in three adults in the U.S. and globally suffers from insufficient sleep and/or poor sleep quality, which are associated with poor health outcomes, including all top 10 leading causes of death. Sleep affects health outcomes, in part, by directly and indirectly influencing undesirable dietary behaviors, which, in this work, is defined as frequent consumption of foods that are inconsistent with health. For example, insufficient sleep leads to more frequent consumption of sweets, a direct effect, and stress negatively influences sleep where insufficient and poor-quality sleep can lead to unhealthy dietary behaviors, and indirect effect. Additionally, sleep influences taste measures, such as sweet taste preference; therefore, sleep may also alter dietary intake through changes in taste preference. Singular relationships between sleep, stress, taste measures, and undesirable dietary behaviors and dietary intake have been investigated; however, more complex relationships between these measures have yet to be explored. Therefore, the overall objective of this research was to explore relationships between sleep and undesirable dietary behaviors in a more holistic manner. This was achieved by investigating the role of sleep in the relationship between stress and dietary behavior as well its influence on taste measures and dietary intake relationships.Chapter 2 characterizes and compares health behaviors of higher education students from seven different countries during the COVID-19 pandemic and investigates the effects of changes in sleep duration and quality on dietary risk, alcohol misuse, physical activity, and sitting time. A total of 2,254 students completed the study. Health behaviors were consistent across countries, and students from all countries reported poor sleep quality. Additionally, students who experienced a decline in sleep quality during the COVID-19 pandemic had higher dietary risk scores than students who did not experience a change in sleep quality (p=0.001). Improved sleep quality was associated with less sitting time (p=0.010). The chapter reveals the pressing concern of poor sleep quality that students in higher education were experiencing, and worsened sleep quality was associated with more frequent engagement in unhealthy dietary behaviors. Therefore, addressing poor sleep quality among higher education student is urgent. After investigating how changes in sleep predicted dietary risk, alcohol misuse, physical activity, and sitting time, chapter 3 considers mental health measures and explores more complex relationships between stress, sleep, resilience, undesirable dietary behaviors, and alcohol misuse. This study investigates whether sleep duration and quality mediated and resilience moderated the relationships between stress and undesirable dietary behaviors and the relationship between stress and alcohol misuse. A total of 2,254 students from seven countries completed the study. Results indicated sleep quality, but not sleep duration, mediated the relationship between perceived stress and undesirable dietary behaviors as well as the relationship between perceived stress and alcohol misuse. Further, increased resilience reduced the strength of the relationship between perceived stress and undesirable dietary behaviors but not alcohol misuse. Therefore, chapter 3 demonstrates that students in higher education are likely to benefit from sleep education and resilience trainings, especially during a stressful period. Chapter 4 presents two studies, one methodological and one experimental. The methodological study examined whether a standardized tool used in evaluating sweet taste preference could be used in determining salt taste preference, and the experimental study used the new tool to investigate the effects of sleep curtailment on salt taste measures and explored the relationship between salt taste measures and dietary intake under the habitual and the curtailed sleep conditions. A total of 59 participants completed the study and slept one curtailed night (33% sleep duration reduction) and one habitual night in random order wearing a single-channel electroencephalograph (EEG). Results illustrated the adapted forced-choice paired-comparison tracking test can serve as a valid tool for determining salt taste preference. No changes in salt taste function (slopes of intensity ratings: p=0.844) and hedonic measures (slopes of liking ratings: p=0.074; preferred NaCl concentrations: p=0.092) were observed after a night of curtailed sleep compared to habitual sleep (study 2). However, the slope of liking was associated with energy-corrected Na intake only under the habitual sleep condition (p<0.001). These results suggest that the adapted forced-choice paired-comparison tracking test can be adopted as a tool to assess salt taste preference, and sleep should be accounted for when performing taste studies. In summary, the work presented in this dissertation explores the relationship between sleep and dietary intake in a complex manner. The results reveal 1) poor sleep quality among higher education students is a pressing concern, especially during the COVID-19 pandemic; 2) decline in sleep quality is associated with higher dietary risk, and improvement in sleep quality is associated with less sitting time; 3) sleep quality, but not sleep duration, mediated the relationship between perceived stress and undesirable dietary behaviors and the relationship between perceived stress and alcohol misuse; 4) acute sleep curtailment does not affect salt taste function or hedonic measures; 5) the slope of salt taste liking was associated with energy-corrected Na intake only under the habitual sleep condition. Overall, the work demonstrates the importance of improving sleep, which could reduce dietary risks, alcohol misuse, and sitting time, and the significance of accounting for sleep in taste studies.
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Title: PATTERN AND PROCESS OF TREE REGENERATION AND RECRUITMENT IN MANAGED NORTHERN HARDWOOD FORESTS
Creator: Henry, Catherine Rose
Date: 2022
Collection: Electronic Theses & Dissertations
Description: For managed forests which rely on natural tree regeneration for canopy recruitment, abundance and composition of tree regeneration portend future forest structure and diversity. For northern hardwood forests, a geographically widespread forest type in North America, typical single-tree selection (STS) management relies on natural regeneration to promote new cohorts of canopy trees. Harvesting dispersed, select trees every 15 – 20 years, STS generates low light levels intended to promote sugar...
Show moreFor managed forests which rely on natural tree regeneration for canopy recruitment, abundance and composition of tree regeneration portend future forest structure and diversity. For northern hardwood forests, a geographically widespread forest type in North America, typical single-tree selection (STS) management relies on natural regeneration to promote new cohorts of canopy trees. Harvesting dispersed, select trees every 15 – 20 years, STS generates low light levels intended to promote sugar maple (Acer saccharum) and other shade-tolerant tree species in an uneven-aged system. However, following 60 + years of STS implementation in the Great Lakes region, concerning regeneration trends have emerged, namely low densities of sugar maple and low tree species diversity. Additionally, few studies have analyzed age structure under this system to assess its past efficacy in generating uneven-aged forests. The research presented here characterizes regeneration and recruitment outcomes of STS, analyzing data from a uniquely detailed and geographically widespread research project of 141 northern hardwood stands across northern Michigan. Given the silvicultural focus on regenerating sugar maple, the first two chapters focus on management outcomes for this key species. First, a flexible Bayesian hierarchical model offers insight on patterns of sugar maple regeneration for key size classes as a function of plot and stand level predictors. Our results indicate that sugar maple regeneration is sparse to absent, particularly for size classes actively browsed by deer and recently escaped from the deer browsing zone. The second analysis characterizes age structure for a subset of 51 stands, drawing on 1499 sugar maple trees > 5 cm diameter sampled via basal discs from recently harvested stumps; this analysis provides insight to past patterns of recruitment and establishment. The results suggest little evidence of sugar maple seedling regeneration and canopy ingrowth over the past 60 + years of STS management; instead, stands have highly suppressed saplings plus aging poletimber and sawtimber classes, which are at or quickly approaching economic maturity. Given declines in sugar maple dominance as evidenced by the first two research analyses, the third analysis assesses stand-level tree species diversity and individual species abundance as a function of landscape predictors and size class to shed light on projected future canopy composition. On average, there are approximately three effective common species for seedlings, saplings, and canopy stems at the stand level, and species less desirable for management are occupying growing space in the sapling layer. Together, these results indicate that STS has been unsuccessful in regenerating or recruiting sugar maple over the past 60 + years, and stands are characterized by a paucity of tree species. Our results support several potential alternative management strategies, including decreasing basal area via more intense harvests, prohibiting deer browsing via natural browsing barriers, or introducing greater diversity of tree species via direct seeding or planting. These results should be considered to improve current management of northern hardwood forests in the Great Lakes region.
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Title: ENGINEERING STUDIES IN ADVANCED PLA MATERIALS – STEREOCHEMISTRY, STEREOCOMPLEXATION, AND THERMAL RECYCLING OF PLA
Creator: Alhaj, Mohammed A.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Polylactide (PLA) polymers are the world’s foremost 100% biobased resin with both composting and recycling end-of-life options in harmony with Ellen MacArthur Foundation “Circularity Model.” It is commercially manufactured by converting lactic acid to lactide, which is then polymerized to PLA. These molecules present unique and intriguing stereochemistry that dictate manufacturing, performance properties, and processability. However, it is seldom discussed and not well understood in the role...
Show morePolylactide (PLA) polymers are the world’s foremost 100% biobased resin with both composting and recycling end-of-life options in harmony with Ellen MacArthur Foundation “Circularity Model.” It is commercially manufactured by converting lactic acid to lactide, which is then polymerized to PLA. These molecules present unique and intriguing stereochemistry that dictate manufacturing, performance properties, and processability. However, it is seldom discussed and not well understood in the role stereochemistry can play and impact product performance and use. In the current work, we critically review and discuss the stereochemical implications for PLA through studies on different PLA compositions.To-date, it is unclear the origin of D-content present in commercial grade PLA, although it is assumed to originate from D-lactide. In this work, we validate that manufacture of lactide monomer from (L)- lactic acid predominantly results in a mixture of L and meso (DL), not L- and D- lactide. Optical rotation and 1H NMR studies are used to elucidate this stereochemistry. Copolymers of L-lactide and meso-lactide and copolymers of L-lactide and D-lactide are synthesized via bulk polymerization at various compositions. The optical rotation, tacticity, crystallinity, and thermal properties of synthesized copolymers are characterized. The optical rotation of poly(meso-lactide) has also been reported for the first time in this text. Differential scanning calorimetry (DSC) and 1H NMR studies confirm that PLA transitions from a predominantly isotactic, semi-crystalline polymer to a predominantly atactic, amorphous polymer when one copolymerizes greater than 10% meso-lactide with L-lactide. The stereochemical composition, mechanical and rheological properties of commercial grade PLA are measured to elucidate the effect of stereochemistry on the tensile and rheological behavior of PLA. We conclude this section with studies on PLA stereochemistry and its influence on immune cellular response. Hydrolytic degradation of semi-crystalline and amorphous PLA is analyzed via molecular weight characterization and lactic acid abundance. Semi-crystalline and amorphous PLA are then studied as potential carriers for glycolytic inhibitors. The stereochemistry of PLA and its implication on performance properties are further explored in studies on stereocomplex PLA. A pilot-scale continuous manufacturing process of stereocomplex PLA is developed and optimized by melt-blending a 1:1 blend of high molecular weight poly(L-lactide) (PLLA) and high molecular weight poly(D-lactide) (PDLA) in a co-rotating twin screw extruder. Stereocomplexation is first characterized via DSC at different temperatures and times. The optimal reaction temperature and reaction time are found and used to process >95% stereocomplex PLA conversion (melting peak temperature Tpm = 240°C). Stereocomplex PLA is used as an additive to produce 70% PLLA/30% stereocomplex PLA composites. The crystallinity, thermal properties, and tensile properties of composites are then characterized. A study on stereocomplex PLA and its effect on the crystallization kinetics of PLLA is conducted. 5% stereocomplex PLA is blended with 95% PLLA to analyze its use as a nucleating agent. The final section discusses a pilot-scale end-of-life method for PLA via thermal recycling. This study continues previous studies on PLA thermodepolymerization by scaling up the reversible reaction in a pilot-scale batch reactor. PLA is run at various temperatures and times to elucidate the processing conditions that yield the highest lactide conversion. The chemical purity, optical purity, lactide yield and stereoisomeric composition of the final lactide product are characterized by DSC, optical rotation, mass balance, and 1H NMR, respectively.
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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: A Longitudinal Analysis of Black Women's Experiences with a Domestic Violence Housing First (DVHF) Intervention
Creator: Ayeni, Oluwafunmilayo Oyesola
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Black women are at an increased risk for intimate partner violence (IPV). The complex interrelationships among housing instability, risk, and severity of abuse among IPV survivors has been established in the research literature, particularly for Black women who are often standing at the intersection of poverty, race, and gender, which results in having fewer financial resources and options for affordable housing. A promising innovation that is gaining national popularity is the Domestic...
Show moreBlack women are at an increased risk for intimate partner violence (IPV). The complex interrelationships among housing instability, risk, and severity of abuse among IPV survivors has been established in the research literature, particularly for Black women who are often standing at the intersection of poverty, race, and gender, which results in having fewer financial resources and options for affordable housing. A promising innovation that is gaining national popularity is the Domestic Violence Housing First (DVHF) model, which involves providing survivor-driven mobile advocacy and flexible funding to meet the immediate housing needs of survivors. While preliminary evidence suggests the beneficial impacts of DVHF on improving survivors’ safety, housing stability, and well-being, there is little research that rigorously evaluates the impact of DVHF on the outcomes of Black survivors. To address this gap, the current study examined the long-term impact of the DVHF model on the safety, housing stability, and depressive symptoms of 61 homeless or unstably housed Black survivors who had recently sought DV services from one of five agencies located in the Pacific Northwest region of the United States. Results indicate that those who received the DVHF model experienced less revictimization compared to those who received services as usual. These findings are promising and have useful implications for Black survivors, DV agencies, policy makers instituting relevant laws, and grant-making institutions funding survivor-related programs/services.
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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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