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Title
I. Determination of Absolute Configuration of Chiral 1,2-Diols. II. Progress Towards the Total Synthesis of Napyradiomycin A1.
Creator
Torabi Kohlbouni, Saeedeh
Date
2022
Collection
Electronic Theses & Dissertations
Description
This dissertation focuses on two parts. The first part introduces an operationally simple and microscale method for the absolute stereochemical determination of 1,2-diols. In situ derivatization of 1,2-diols with dinaphthyl borinic acid generates the induced helicity of the two naphthyl groups, which leads to an observable ECCD spectrum. The observed P or M helicity follows a predictable trend for S and R chiral 1,2-diols, respectively.The Second chapter is the progress towards the asymmetric...
Show moreThis dissertation focuses on two parts. The first part introduces an operationally simple and microscale method for the absolute stereochemical determination of 1,2-diols. In situ derivatization of 1,2-diols with dinaphthyl borinic acid generates the induced helicity of the two naphthyl groups, which leads to an observable ECCD spectrum. The observed P or M helicity follows a predictable trend for S and R chiral 1,2-diols, respectively.The Second chapter is the progress towards the asymmetric catalytic synthesis of napyardiomycin A1. The chapter is divided to three sections. The first section is installation of chlorine chiral center at C3. This goal is achieved using cinchona chiral catalyst, and DCDMH as chloronium source. The second section is the synthesis of the -lapachone core of napyradiomycin A1, was accomplished using Diels-Alder/aromatization cascade reaction. The last section shows our effort toward the attachment of geranyl side chain.
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Title
DEVELOPING LIGNIN-BASED EPOXY AND POLYURETHANE RESINS
Creator
Nikafshar, Saeid
Date
2022
Collection
Electronic Theses & Dissertations
Description
Lignin, the most abundant natural aromatic polymer, is currently produced as by-product during biorefinery and chemical pulping processes. Lignin is rich in hydroxyl functional groups (both phenolic and aliphatic OH), making it an excellent raw material for synthesizing epoxy and polyurethane resins. However, there are several challenges in utilizing unmodified lignins as feedstock for product development, including high polydispersity/heterogeneity, low reactivity, poor accessibility of...
Show moreLignin, the most abundant natural aromatic polymer, is currently produced as by-product during biorefinery and chemical pulping processes. Lignin is rich in hydroxyl functional groups (both phenolic and aliphatic OH), making it an excellent raw material for synthesizing epoxy and polyurethane resins. However, there are several challenges in utilizing unmodified lignins as feedstock for product development, including high polydispersity/heterogeneity, low reactivity, poor accessibility of hydroxyl groups for reaction with co-monomers low solubility in common organic solvents, and dark color. There are significant variations in lignin characteristics, depending on the source of biomass and isolation methods. Therefore, in-depth lignin characterization is needed to provide the basic knowledge of the structural, chemical, and thermal properties to facilitate lignin valorization.This study was focused on lignin characterization and development of lignin-based epoxy and polyurethane resins. First, a wide range of lignin samples was fully characterized by measuring their ash contents, elemental analyses, hydroxyl contents, chemical structures, molar mass distributions, and thermal properties. Next, a novel method was developed to measure the reactivity of thirteen different unmodified lignins toward biobased epichlorohydrin (ECH). A partial least square regression (PLS-R) model (with 92 % fitting accuracy and 90 % prediction ability) was created to study the correlation between lignin properties and epoxy content. The results showed that lignins with higher phenolic hydroxyl contents and lower molecular weights were more suitable for replacing 100 % of toxic bisphenol A (BPA) in the formulation of resin precursors. Additionally, two epoxidized lignin samples (with the highest epoxy contents) were cured using a biobased hardener (Cardolite from cashew nutshell), showed comparable thermomechanical performances and thermal stabilities to a petroleum-based epoxy system. Biobased waterborne polyurethane resins (PUDs) were also developed by entirely replacing the petroleum-based polyol and the internal emulsifier with either alkaline pre-extraction lignins or enzymatic hydrolysis lignins as well as tartaric acid (a biobased diacid). The formulated resins had zero VOC (volatile organic compound), which was achieved by replacing toxic n-methyl-2-pyrrolidone (NMP) with cyrene (a biobased solvent). To further improve the mechanical properties of our biobased PUD resins, 20 wt.% of lignin was substituted with low hydroxyl value soy-polyol, which increased their tensile strength and elongation at break to 87% and 68% of a commercial PUD resin. The results of this study demonstrated that it is imperative to fully characterize lignin and choose the right lignin for each specific application. This approach enabled us to entirely replace petroleum-based raw materials (BPA and polyol) with lignin and formulate biobased epoxy and polyurethane resins.
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Title
THE ORIGINATION AND IMPLEMENTATION OF THE NATIONAL WETLANDS POLICY OF UGANDA : ENVIRONMENT, KNOWLEDGE, AND POWER FROM THE LATE NINETEENTH CENTURY TO PRESENT
Creator
Doyle-Raso, John
Date
2022
Collection
Electronic Theses & Dissertations
Description
In the 1980s, following widespread environmental and intellectual changes associated with “swamp reclamation” that in Uganda had started in the early twentieth century, proponents of the emerging science of “wetland conservation” sought to influence the practices and thinking of people across the country. To do so, they created a national wetlands policy based on decentralized “community-based” projects. Yet, farmers’ and investors’ engagements with reclamation have continued. Meanwhile, the...
Show moreIn the 1980s, following widespread environmental and intellectual changes associated with “swamp reclamation” that in Uganda had started in the early twentieth century, proponents of the emerging science of “wetland conservation” sought to influence the practices and thinking of people across the country. To do so, they created a national wetlands policy based on decentralized “community-based” projects. Yet, farmers’ and investors’ engagements with reclamation have continued. Meanwhile, the Ugandan wetlands policy became internationally influential for its groundbreaking approach to interdisciplinary questions about governance, emphasizing economic analyses based on concepts such as “ecosystem services” and “Environmental Economic Valuation.” Ugandan wetland conservationists have had more influence abroad than domestically, as in Uganda neoliberalization and recentralization have limited the power of the community-based groups who have worked through the national policy. Using a range of sources including but not limited to archives and interviews with conservationists, this dissertation historicizes the Ugandan wetlands conservation policy. It comprises two parts addressing overlapping time periods. The first three chapters consider the origination of this policy by analyzing environmental and intellectual changes in southeastern and southwestern Uganda, leading to the creation in the late-twentieth century of environmental regulations. The latter three chapters examine how conservationists have tried implementing the policy in rural and urban places, and in relation to the national emblem of Uganda – the Grey Crowned Crane. They have focused their efforts on community-based projects outside Protected Areas promoting indigenous knowledges and practices to obtain economic benefits from wetlands that conservationists. This approach was an early manifestation of connected trends in international developmentalist networks. Furthermore, the limitations on its implementation have become pivotal in the global histories of neoliberalization, decentralization, and recentralization. Historicizing Ugandan wetland conservationism contributes to four scholarly literatures. 1) Analyzing community-based projects outside “Protected Areas” advances the historiographies of conservation and watershed management in Africa by considering the significances of neoliberalization, decentralization, and recentralization beyond extraordinary legal cases. 2) Examining intellectual changes in this history – including an emphasis on community-based projects, use of the concept of ecosystem services, and the promotion of indigenous knowledges and sciences – reveals connections between changes in environmental science and global trends in developmentalism. 3) Focusing on these changes in Uganda builds on analyses of environmental management in political power there by identifying the importance of an underexamined resource in entrenched land conflicts, and by uncovering early institutional bases of recentralization. 4) Because Ugandan wetland conservationists were global leaders in policy creation, citizen science, and more changes in scientific thinking, researching their work reveals how African scientists have navigated tensions between their local, national, and international interlocutors to become internationally influential. Studying the history of Ugandan wetland conservationism reveals how different people’s engagements with changes in environmental thinking have reshaped environments and livelihoods, as well as influenced international scientific networks.
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Title
Development and application of hierarchical models for monitoring avian soundscapes, populations, and communities
Creator
Doser, Jeffrey W.
Date
2022
Collection
Electronic Theses & Dissertations
Description
Climate change, land use change, and other anthropogenic pressures are increasing species extinctions, phenology shifts, and drastic population declines. Avian populations and communities are particularly vulnerable to global change given their mobile and migratory life history strategies. Avian abundance has drastically declined throughout North America over several decades, which is compounded by phenological shifts in breeding periods and migratory patterns. Informed management and...
Show moreClimate change, land use change, and other anthropogenic pressures are increasing species extinctions, phenology shifts, and drastic population declines. Avian populations and communities are particularly vulnerable to global change given their mobile and migratory life history strategies. Avian abundance has drastically declined throughout North America over several decades, which is compounded by phenological shifts in breeding periods and migratory patterns. Informed management and conservation of avian populations and communities requires large-scale monitoring programs, as well as associated inferential tools to provide statistically robust inference using multiple data sources. In this dissertation, I develop a suite of hierarchical modeling approaches to understand avian soundscapes, populations, and communities. I leverage a hierarchical Bayesian modeling framework, which is ideally suited for complex wildlife data with numerous types of observation error and dependencies among data points. In Chapter 1, I provide a brief overview of avian monitoring approaches and their associated statistical analysis frameworks. In Chapters 2 and 3, I develop hierarchical models for the analysis of complex avian soundscape data, and apply these approaches to two case studies. In Chapter 2, I apply a two-stage hierarchical beta regression model to quantify the relationship between anthropogenic and biological sounds in avian soundscapes in western New York. In Chapter 3, I use a multivariate linear mixed model to assess disturbance impacts of a shelterwood logging on avian soundscapes in northern Michigan. In Chapter 4, I develop a multi-region, multi-species abundance model to quantify trends of avian species and communities using point count data across a network of National Parks in the northeastern US. In Chapters 5 and 6, I use a model-based data integration approach to yield improved inference on avian population and communities. In Chapter 5, I integrate automated acoustic recording data with point count data to estimate avian abundance, which I apply to a case study on the Eastern Wood Pewee (Contopus virens) in a National Historical Park in Vermont. In Chapter 6, I develop an integrated community occupancy model that combines multiple types of detection-nondetection data for inference on species-specific and community level occurrence dynamics, which I use to assess occurrence dynamics of a foliage-gleaning bird community in New Hampshire. These results exhibit the value of hierarchical models to partition ecological data into distinct observation and ecological components for improved inference on avian population and community dynamics. Future work should continue to leverage complex data sources within hierarchical modeling frameworks to address pressing conservation and management questions on avian populations, communities, and the ecosystem services they provide.
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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
Molecular epidemiology, pangenomic diversity, and comparative genomics of Campylobacter jejuni
Creator
Rodrigues, Jose Alexandre
Date
2022
Collection
Electronic Theses & Dissertations
Description
Campylobacter jejuni, the leading cause of bacterial gastroenteritis in the United States, is often resistant to commonly used antibiotics and has been classified as a serious threat to public health. Through this work, we sought to evaluate infection trends, quantify resistance frequencies, identify epidemiological factors associated with infection, and use whole-genome sequencing (WGS) as well as comparative phylogenomic and pangenomic approaches to understand circulating C. jejuni...
Show moreCampylobacter jejuni, the leading cause of bacterial gastroenteritis in the United States, is often resistant to commonly used antibiotics and has been classified as a serious threat to public health. Through this work, we sought to evaluate infection trends, quantify resistance frequencies, identify epidemiological factors associated with infection, and use whole-genome sequencing (WGS) as well as comparative phylogenomic and pangenomic approaches to understand circulating C. jejuni populations in Michigan. C. jejuni isolates (n=214) were collected from patients via an active surveillance system at four metropolitan hospitals in Michigan between 2011 and 2014. Among the 214 C. jejuni isolates, 135 (63.1%) were resistant to at least one antibiotic. Resistance was observed for all nine antibiotics tested yielding 11 distinct resistance phenotypes. Tetracycline resistance predominated (n=120; 56.1%) followed by resistance to ciprofloxacin (n= 49; 22.9%), which increased from 15.6% in 2011 to 25.0% in 2014. Notably, patients with ciprofloxacin resistant infections were more likely to report traveling in the past month (Odds Ratio (OR): 3.0; 95% confidence interval (CI): 1.37, 6.68) and international travel (OR: 9.8; 95% CI: 3.69, 26.09). To further characterize these strains, we used WGS to examine the pangenome and investigate the genomic epidemiology of this set of C. jejuni strains recovered from Michigan patients. Among the 214 strains evaluated, 83 unique multilocus sequence types (STs) were identified that were classified as belonging to 19 previously defined clonal complexes (CCs). Core-gene phylogenetic reconstruction based on 615 genes identified three clades, with Clade I comprising six subclades (IA-IF) and predominating (83.2%) among the strains. Because specific cattle-associated STs, such as ST-982, predominated among strains from Michigan patients, we also examined a collection of 72 C. jejuni strains from cattle recovered during an overlapping time period by WGS. Several phylogenetic analyses demonstrated that most cattle strains clustered separately within the phylogeny, but a subset clustered together with human strains. Hence, we used high quality single nucleotide polymorphism (hqSNP) profiling to more comprehensively examine those cattle and human strains that clustered together to evaluate the likelihood of interspecies transmission. Notably, this method distinguished highly related strains and identified clusters comprising strains from both humans and cattle. For instance, 88 SNPs separated a cattle and human strain that were previously classified as ST-8, while the human and cattle derived ST-982 strains differed by >200 SNP differences. These findings demonstrate that highly similar strains were circulating among Michigan patients and cattle during the same time period and highlight the potential for interspecies transmission and diversification within each host. In all, the data presented illustrate that WGS and pangenomic analyses are important tools for enhancing our understanding of the distribution, dissemination, and evolution of specific pathogen populations. Combined with more traditional phenotypic and genotypic approaches, these tools can guide the development of public health prevention and mitigation strategies for C. jejuni and other foodborne pathogens.
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Title
STUDENTS’ TOOL USAGE, JUSTIFICATIONS, AND REPORTED CONFIDENCE WHEN USING DYNAMIC GEOMETRY ENVIRONMENTS
Creator
Wegner, Timothy Scott
Date
2022
Collection
Electronic Theses & Dissertations
Description
Dynamic Geometry Environments (DGEs) are popular tools in the exploration of geometry. This research is designed to explore the confidence of undergraduate mathematics students as they make mathematical statements when completing geometric tasks using DGEs. Students completed two series of tasks in both Euclidean and hyperbolic geometry. The first series of tasks asked students about properties of parallel transports and the second series of tasks asked students about the existence of regular...
Show moreDynamic Geometry Environments (DGEs) are popular tools in the exploration of geometry. This research is designed to explore the confidence of undergraduate mathematics students as they make mathematical statements when completing geometric tasks using DGEs. Students completed two series of tasks in both Euclidean and hyperbolic geometry. The first series of tasks asked students about properties of parallel transports and the second series of tasks asked students about the existence of regular polygons. The ten students in this research used Geometry Explorer, a DGE which they had previous experience using in Euclidean geometry, but minimal experience using in hyperbolic geometry. Hyperbolic geometry tasks were included in this study because features of that geometry (e.g. curved lines and unexpected length measure) were expected to pose challenges for students’ intuitive expectations. Because of this lack of intuition, students may use the features of DGEs (e.g. dragging and measurement) to make various justifications (e.g. authoritative, inductive, and deductive) of the mathematical claims they are making. Both the features of the DGE and students’ justifications affect their confidence in the claims they make. This research explored the interaction between these three factors. Analysis of the data showed that these two series of tasks elicited both dragging and measurement tool usage. During the parallel transport tasks, students used these tools in both in an exploratory mode looking for relationships and a validation mode confirming previous conjectures. During the regular polygon construction tasks, students mainly used the tools in a validation mode. Additionally, many students waited until the hyperbolic portion of the tasks to begin using these tools. The tasks elicited a range of justifications, though students generally used inductive arguments. Deductive justifications, when used, were mainly for familiar tasks that took place within Euclidean geometry. Reported confidence was high across both series of tasks as well as across both Euclidean and hyperbolic geometry when working with the DGE. Reported confidence dropped when working on conjecturing or proof validation prompts that did not use the DGE.This research suggests there is still much work to be done investigating how students use tools, make justifications, and report confidence when using DGEs in both Euclidean and non-Euclidean geometries. The researcher recommends further study including the exploration of additional tools within DGEs, the dynamics of working in partners within DGEs, and how students’ expectations of justification affect their responses.
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Title
DEVELOPMENT OF 3D BIOACTIVE AND ANTIBACTERIAL SILICATE-BASED SCAFFOLDS FOR BONE TISSUE REGENERATION IN LOAD-BEARING APPLICATIONS
Creator
Marsh, Adam Christoph
Date
2022
Collection
Electronic Theses & Dissertations
Description
Current gold-standard approaches to addressing the needs of bone defects in load-bearing applications entail the use of either autographs or allographs. Both solutions, however, are imperfect as both autographs and allographs carry the risk of additional trauma, threat of disease transmission, and potential donor rejection respectively. Porous 3D scaffolds are attractive alternatives, illuminating a potential path towards achieving the ideal scaffold for targeting bone tissue regeneration in...
Show moreCurrent gold-standard approaches to addressing the needs of bone defects in load-bearing applications entail the use of either autographs or allographs. Both solutions, however, are imperfect as both autographs and allographs carry the risk of additional trauma, threat of disease transmission, and potential donor rejection respectively. Porous 3D scaffolds are attractive alternatives, illuminating a potential path towards achieving the ideal scaffold for targeting bone tissue regeneration in load-bearing applications, usurping autographs to become the new gold-standard. To unlock the full healing potential of 3D scaffolds, such scaffolds must be multifunctional such that (1) their mechanical performance meets the requisite requirements as dictated by the mechanical performance characteristics of interest for native bone tissue, (2) they stimulate the necessary biological responses for bone tissue regeneration, and (3) they exhibit antibacterial characteristics to combat the threat of infection. To date, no reports document 3D scaffolds exhibiting all three performance characteristics. The aim of this dissertation, therefore, is to deliver 3D scaffolds that are mechanically competent, possess and exhibit inherent and advanced antibacterial characteristics, and are successful at providing the needed biological characteristics for bone tissue regeneration. To achieve this, this dissertation implements a multidisciplinary approach, utilizing comprehensive structural characterization across a wide range of scales to elucidate process – performance relationships to execute scientifically driven modifications to engineer and deliver a 3D scaffold to successfully target bone tissue regeneration in load-bearing applications. A silver-doped bioactive glass-ceramic (Ag-BG) composition was selected as the material for scaffold synthesis due to its inherent and attractive antibacterial and biological performance characteristics. Two fundamentally different processing approaches were utilized for synthesizing Ag-BG scaffolds: the polymer foam replication technique and fused filament fabrication (FFF). The Ag-BG scaffolds studied herein were found to exhibit advanced antibacterial performance characteristics against methicillin-resistant Staphylococcus aureus (MRSA), a common pathogen implicated in osteomyelitis development, able to combat MRSA both in planktonic and biofilm forms. Ag-BG scaffolds demonstrated the ability to form an apatite-like layer when immersed in simulated body fluid (SBF), an indicator that Ag-BG scaffolds will induce the necessary mineralization for bone tissue regeneration, in addition to exhibiting attractive cell viability, proliferation, and differentiation characteristics when studied in vitro. The mechanical performance of Ag-BG scaffolds reported herein saw progressive improvements in each iteration of Ag-BG scaffold synthesis, achieving desirable mechanical competency and reliability as a result of the multidisciplinary approach formulated. In addition to the exploration of developing 3D antibacterial and biological silicate-based scaffolds capable of targeting bone tissue regeneration in load-bearing applications, foundational work towards the development of class II hybrid scaffolds comprised of gelatin methacryloyl (GelMA) and Ag-BG for targeting softer tissue regeneration. The novel syntheses applied to the successful molecular coupling of GelMA and Ag-BG presents an attractive class II hydrogel showing great promise as a compatible ink for 3D bioprinting cell-laden scaffolds capable of targeting tissue regeneration of more sophisticated systems.
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Title
Three Essays on Panel Data Models with Interactive and Unobserved Effects
Creator
Brown, Nicholas Lynn
Date
2022
Collection
Electronic Theses & Dissertations
Description
Chapter 1: More Efficient Estimation of Multiplicative Panel Data Models in the Presence of Serial Correlation (with Jeffrey Wooldridge)We provide a systematic approach in obtaining an estimator asymptotically more efficient than the popular fixed effects Poisson (FEP) estimator for panel data models with multiplicative heterogeneity in the conditional mean. In particular, we derive the optimal instrumental variables under appealing `working' second moment assumptions that allow...
Show moreChapter 1: More Efficient Estimation of Multiplicative Panel Data Models in the Presence of Serial Correlation (with Jeffrey Wooldridge)We provide a systematic approach in obtaining an estimator asymptotically more efficient than the popular fixed effects Poisson (FEP) estimator for panel data models with multiplicative heterogeneity in the conditional mean. In particular, we derive the optimal instrumental variables under appealing `working' second moment assumptions that allow underdispersion, overdispersion, and general patterns of serial correlation. Because parameters in the optimal instruments must be estimated, we argue for combining our new moment conditions with those that define the FEP estimator to obtain a generalized method of moments (GMM) estimator no less efficient than the FEP estimator and the estimator using the new instruments. A simulation study shows that the GMM estimator behaves well in terms of bias, and it often delivers nontrivial efficiency gains -- even when the working second-moment assumptions fail.Chapter 2: Information equivalence among transformations of semiparametric nonlinear panel data modelsI consider transformations of nonlinear semiparametric mean functions which yield moment conditions for estimation. Such transformations are said to be information equivalent if they yield the same asymptotic efficiency bound. I first derive a unified theory of algebraic equivalence for moment conditions created by a given linear transformation. The main equivalence result states that under standard regularity conditions, transformations which create conditional moment restrictions in a given empirical setting need only to have an equal rank to reach the same efficiency bound. Example applications are considered, including nonlinear models with multiplicative heterogeneity and linear models with arbitrary unobserved factor structures.Chapter 3: Moment-based Estimation of Linear Panel Data Models with Factor-augmented ErrorsI consider linear panel data models with unobserved factor structures when the number of time periods is small relative to the number of cross-sectional units. I examine two popular methods of estimation: the first eliminates the factors with a parameterized quasi-long-differencing (QLD) transformation. The other, referred to as common correlated effects (CCE), uses the cross-sectional averages of the independent and response variables to project out the space spanned by the factors. I show that the classical CCE assumptions imply unused moment conditions which can be exploited by the QLD transformation to derive new linear estimators which weaken identifying assumptions and have desirable theoretical properties. I prove asymptotic normality of the linear QLD estimators under a heterogeneous slope model which allows for a tradeoff between identifying conditions. These estimators do not require the number of cross-sectional variables to be less than T-1, a strong restriction in fixed-$T$ CCE analysis. Finally, I investigate the effects of per-student expenditure on standardized test performance using data from the state of Michigan.
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Title
HELLGATE TO HIGHWAY : ISLAND MAKING, DREDGING, AND INFRASTRUCTURE IN THE DETROIT RIVER, 1874-1938
Creator
Swayamprakash, Ramya
Date
2022
Collection
Electronic Theses & Dissertations
Description
This dissertation exposes the tensions, trials, and tribulations along the U.S.-Canada border in the Detroit River between 1874 and 1938. I study how dredging—a seemingly inert process of removing river bottom sediment and depositing it elsewhere—helped create landforms across and along the political border, in turn, revealing the myriad social and political tensions that undergird it. By exposing how infrastructure revealed border tensions, especially those related to resource extraction,...
Show moreThis dissertation exposes the tensions, trials, and tribulations along the U.S.-Canada border in the Detroit River between 1874 and 1938. I study how dredging—a seemingly inert process of removing river bottom sediment and depositing it elsewhere—helped create landforms across and along the political border, in turn, revealing the myriad social and political tensions that undergird it. By exposing how infrastructure revealed border tensions, especially those related to resource extraction, scarcity, and national security—on both sides of the Canada-U.S. border—this dissertation offers a new way to link environmental and border history as well as environmental diplomacy.The lower Detroit River forms the ideal study site for two interrelated reasons. One, its narrow and rocky riverbed along the shipping channel was a dangerous bottleneck, slowing traffic on one of the busiest waterways in the world. Two, dredging the lower part of the river kept this busy waterway running efficiently. The Livingstone Channel fundamentally reordered the Detroit River when it was carved out of the riverbed where hitherto there existed fish spawning grounds and shallow water. Concentrating on the lower Detroit River in general and the Livingstone Channel in particular, this dissertation will show how conflict and cooperation overlapped when it came to international diplomacy in the Great Lakes. Cultural and social historians have analyzed Great Lakes borderlands. Environmental historians though have yet to fully analyze these lakes. The political border between the United States and Canada has often been portrayed as being benign and uncontested. Yet, as this dissertation shows, border infrastructure, such as shipping channels, was seldom uncontested. By focusing on the political border, this dissertation aims to bring attention to the border as a site rather than a liminal space or an end zone of state sovereignty. The border in this reading is the origin of state sovereignty. Studies of the Canada-U.S. borderlands have often explored the role of international environmental diplomacy, especially in the joint management and conservation of binational water bodies like the Great Lakes through policy mechanisms such as the Boundary Waters Treaty (BWT) of 1908 and the International Joint Commission. As my dissertation shows, however, the BWT was an important staging point on which the different intercultural and international misunderstandings were exposed. The Great Lakes have often been cast as being abundant, yet there is little or no work on how that plentitude was not just manufactured in thought, but also embodied in infrastructures. As a transformative process, dredging does not seem monumental. Yet, dredging in the Detroit River has permanently lowered the levels of Lakes Huron and Michigan by at least 25 cm. Dredging thus reveals how environmental transformation lies at the heart of Great Lakes geography as we know it. By exposing dredging in a connecting channel, this dissertation shows that infrastructural creation and imagination undergirds the Great Lakes environment. Infrastructure, as I show, is an important and unseen filter to understand intercultural and international relationships. This is especially true of countries such as the U.S. and Canada which pride themselves in intercultural similarities more than differences. Studying conflict and contestation offers a novel way to understand the cooperative mechanism that drives current borderlands diplomacy. Studying dredging along the lower Detroit River in the nineteenth and twentieth centuries reveals ideas about nature as well as historical challenges and contestations to them.
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Title
IMPROVING YIELD AND QUALITY OF LEAFY GREENS GROWN INDOORS WITH PRECISE RADIATION, TEMPERATURE, AND CARBON DIOXIDE MANAGEMENT
Creator
Tarr, Sean T.
Date
2022
Collection
Electronic Theses & Dissertations
Description
Indoor agriculture systems can allow for precise manipulation of the mean daily temperature (MDT), carbon dioxide (CO2) concentration, and photosynthetic photon flux densities (PPFD). Identifying how these environmental parameters interact to influence crop growth, development, yield, and color can assist growers with selecting their desired growing environment. Therefore, the objectives of Expt. 1 and 2 were to quantify and model how PPFD and CO2 concentrations interact with MDT to influence...
Show moreIndoor agriculture systems can allow for precise manipulation of the mean daily temperature (MDT), carbon dioxide (CO2) concentration, and photosynthetic photon flux densities (PPFD). Identifying how these environmental parameters interact to influence crop growth, development, yield, and color can assist growers with selecting their desired growing environment. Therefore, the objectives of Expt. 1 and 2 were to quantify and model how PPFD and CO2 concentrations interact with MDT to influence the growth, yield, and quality of hydroponically grown green butterhead ‘Rex’ and red oakleaf lettuce ‘Rouxaï RZ’. In Expt. 3 we developed models to predict growth parameters and cardinal temperatures of lettuce, arugula, and kale from 8 to 33 °C. In Expt. 1, lettuce ‘Rex’ and ‘Rouxaï RZ’ were grown in deep-flow hydroponic tanks under a PPFD of 150 or 300 μmol·m‒2·s‒1 for 17 h·d–1 at MDTs of 20, 23, or 26 °C. PPFD and MDT interacted to influence biomass accumulation of both cultivars. In Expt. 2, lettuce ‘Rex’ and ‘Rouxaï RZ’ were grown under a PPFD of 300 μmol·m‒2·s‒1 and at the same MDTs as Expt. 1, but with CO2 concentrations of 500, 800, or 1200 μmol·mol–1. Dry mass of both cultivars was influenced by the interaction of CO2 and MDT; biomass accumulation was greatest at 800 μmol·mol–1 CO2 at MDTs of 23 and 26 °C. In Expt. 3, ‘Rex’ and ‘Rouxaï RZ’, kale ‘Red Russian’, and arugula ‘Astro’ were grown at MDTs of 8, 13, 18, 23, 28, or 33 °C. ‘Rex’ and ‘Rouxaï RZ’ had similar base and optimal temperature estimates of 8 °C and 26 °C, while arugula and kale were lower at 6 °C and 23 °C.
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Title
Evaluation of Operational Performance and Environmental Impact of a Commercial Scale Anaerobic Digester Utilizing Multiple Feedstocks
Creator
Dwilaksono, Fahmi
Date
2022
Collection
Electronic Theses & Dissertations
Description
Food waste and livestock manure become some of major sources that contribute to greenhouse gas (GHG) emissions in the U.S. Utilizing manure and food wastes as biogas feedstocks through anaerobic digestion (AD) process can improve renewable energy production while reducing the impact of climate change due to GHG emission from untreated organic wastes. This study evaluated the operational performance of Michigan State University’s commercial South Campus Anaerobic Digester (SCAD) as well as the...
Show moreFood waste and livestock manure become some of major sources that contribute to greenhouse gas (GHG) emissions in the U.S. Utilizing manure and food wastes as biogas feedstocks through anaerobic digestion (AD) process can improve renewable energy production while reducing the impact of climate change due to GHG emission from untreated organic wastes. This study evaluated the operational performance of Michigan State University’s commercial South Campus Anaerobic Digester (SCAD) as well as the environmental impact during its operation in 2014-2020. Evaluation of feedstock supplies quantity and output parameters of SCAD was conducted to understand the operational performance of the digester. A life cycle assessment (LCA) was done to know the environmental impact of SCAD by comparing it to the conventional waste management methods. Technoeconomic analysis was conducted to know the financial feasibility of SCAD as a commercial digester. The result shows that during its operation from 2014 to 2020, SCAD has processed 159,145 metric tons of feedstock from 18 different organic wastes to produce 15,165,156 kWh of electricity for MSU community. LCA results show that AD system possesses fewer environmental burdens in both global warming potential (GWP) and water eutrophication potential (WEP) compared to the conventional system. Technoeconomic analysis reveals that SCAD needs 21.5 years to accomplish its payback time, which is considered quite economically competitive.
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Title
TECHNOLOGICAL INNOVATION’S IMPACT ON AUDIT QUALITY AND AUDIT FEES : EVIDENCE FROM DISTANT AUDITS
Creator
Fritz, Aaron
Date
2022
Collection
Electronic Theses & Dissertations
Description
This paper examines the impact of advances in communication technology on audit quality and audit fees over the first two decades of the twenty-first century. Using theories on virtual teams from the management literature and distant audits as a setting where auditors and clients are most reliant on communication technology, I hypothesize that advances in communication technology improve audit quality over time for distant audits, specifically, and when compared to local audits. With two...
Show moreThis paper examines the impact of advances in communication technology on audit quality and audit fees over the first two decades of the twenty-first century. Using theories on virtual teams from the management literature and distant audits as a setting where auditors and clients are most reliant on communication technology, I hypothesize that advances in communication technology improve audit quality over time for distant audits, specifically, and when compared to local audits. With two measures of audit quality (discretionary accruals and misstatements) and an analysis that identifies three “eras” of communication technology in the 2000s, I find evidence that audit quality has seen statistically significant improvement over time with advances in communication technology for distant audits and that this improvement is statistically significant when compared to local audits as a control group. In an additional test, I find evidence that advances in communication technology also impact audit fees. Specifically, audit fees of distant audits increase over time at a lower rate than local audits suggesting that distant audits benefit more from advances in communication technology. These results are important because they provide evidence that communication technology has benefited audits by increasing quality and reducing fees, particularly for distant audit clients. This is relevant to the current audit environment where firms are considering long-term remote working strategies that will be heavily reliant on these technologies.
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Title
ADVANCING BLUEBERRY POSTHARVEST BIOLOGY : THE EFFECT OF SULFUR DIOXIDE FUMIGATION ON BLUEBERRY PHYSIOLOGY AND RNA-SEQ OF THE BLUEBERRY-COLLETOTRICHUM FIORINIAE PATHOSYSTEM IN ‘ELLIOTT’ FRUIT
Creator
Abeli, Patrick
Date
2022
Collection
Electronic Theses & Dissertations
Description
The physiology and biology of blueberry fruit is the most important consideration for understanding postharvest storage. Fruit physiology is responsive to many stimuli including biotic, genetic, and environmental inputs. The extent to which a blueberry fruit are affected by these factors is largely cultivar dependent. The following studies address two aspects of blueberry fruit postharvest biology as it relates to pest control: In Chapter 2, we explore the effect of SO2 fumigation on five...
Show moreThe physiology and biology of blueberry fruit is the most important consideration for understanding postharvest storage. Fruit physiology is responsive to many stimuli including biotic, genetic, and environmental inputs. The extent to which a blueberry fruit are affected by these factors is largely cultivar dependent. The following studies address two aspects of blueberry fruit postharvest biology as it relates to pest control: In Chapter 2, we explore the effect of SO2 fumigation on five blueberry cultivars: ‘Bluecrop’, ‘Draper’, ‘Elliott’, ‘Jersey’, and ‘Liberty’ and the extent to which SO2 fumigation can be used to disinfest blueberry fruit of blueberry maggot (BBM) Rhagoletis mendax Curran. In Chapter 3, we use RNA sequencing (RNA-seq) to reveal genes differentially expressed (DE) in ‘Elliott’ fruit in response to infection by Colletotrichum fioriniae compared to mock- (water-) inoculated fruit. By filtering out DE genes in mock-inoculated fruit postharvest, as well as DE genes in infected ‘Jersey’ and ‘Draper’ fruit, we discovered 113 genes unique to ‘Elliott’ fruit that are inoculation-responsive. This set of genes include canonical plant resistance genes as well as genes associated with secondary metabolite biosynthesis, cell wall metabolism, reactive oxygen species production and scavenging, and the hypersensitive response. These studies provide important groundwork for future blueberry breeding by identifying cultivars with genetics and physiology amenable to different interventions for reducing postharvest fruit losses.
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Title
EXAMINING THE RELATIONSHIP AMONG PHYSICAL ACTIVITY, STRESS, DEPRESSION, AND ANXIETY IN COLLEGE STUDENTS
Creator
Hayden, Dorian James
Date
2022
Collection
Electronic Theses & Dissertations
Description
Mental health challenges have been steadily increasing around college campuses, with consistent findings pointing to ethnic minorities and low socioeconomic groups adversely affected and needing more support than their counterparts. On the other end, physical activity (PA) has consistently been associated with positive mental health outcomes. Therefore, further understanding the relationship among race, socioeconomic status, and PA, as well as college students personal experiences on campuses...
Show moreMental health challenges have been steadily increasing around college campuses, with consistent findings pointing to ethnic minorities and low socioeconomic groups adversely affected and needing more support than their counterparts. On the other end, physical activity (PA) has consistently been associated with positive mental health outcomes. Therefore, further understanding the relationship among race, socioeconomic status, and PA, as well as college students personal experiences on campuses, is of great importance to improve college student well-being. This two-study dissertation sought to address these relationships. Study 1 evaluated differences in mental health across race, parental education (proxy for SES) and PA. Student obstacles to using on-campus mental health and PA resources were examined in a mixed methods design. Most of the data was collected prior to the establishment of COVID-19 restrictions at a large Midwest university. Mental health levels were anticipated to vary between the variables of race, parental education, and PA, which was partially supported. Results showed that low SES participants had significantly higher levels of depression, while PA was associated with lower levels of anxiety and stress. Study 2 sought to replicate findings of study 1 and test the relationships within the context of a diathesis-stress model that includes PA using an expanded sample of students drawn from a large Midwest university and a smaller East Coast university. In addition to replicating study 1 findings, study 2 yielded several themes that revealed common obstacles of college students and how they overcome those obstacles. The hypothesized relationship among race, SES, PA and mental health was partially supported. Specifically, participants whose parents or guardians had lower levels of education reported higher levels of anxiety, while there were significant differences in mental health across different levels of PA. The other goal of this study was to map the above relationship onto a PA moderating model, including variables of race, parental education, depression, stress, and anxiety, based on an adapted diathesis-stress model. This relationship was not supported by the data. Free response answers revealed interesting themes related to the college student experience and campus resources. Focus groups added to this through discussions on topics like the COVID-19 pandemic, mental health, and advice for future students. Data from study 2 was collected while COVID-19 pandemic restrictions were in place. Overall results expanded knowledge on the experience of COVID-19 on college campus and the interconnection between race, parental education, PA, and mental health. Further social relations were important for student wellbeing. Students’ also shared obstacles they faced with the use of on campus mental health and other resources.
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Title
Regulation of Chlamydomonas reinhardtii cell cycle during synchronous growth
Creator
Lin, Yang-Tsung
Date
2022
Collection
Electronic Theses & Dissertations
Description
The regulation of the cell cycle in microalgae has long been a central topic in third-generation biofuel studies, as it relates to biomass accumulation and lipid production, the two determining factors of economically feasible biofuel production. The discovery of Compromised Hydrolysis of TAG 7 (CHT7) in the green alga Chlamydomonas reinhardtii has provided valuable insights into the metabolic status-dependent regulation of the cell cycle. CHT7 belongs to the CHC protein family, members of...
Show moreThe regulation of the cell cycle in microalgae has long been a central topic in third-generation biofuel studies, as it relates to biomass accumulation and lipid production, the two determining factors of economically feasible biofuel production. The discovery of Compromised Hydrolysis of TAG 7 (CHT7) in the green alga Chlamydomonas reinhardtii has provided valuable insights into the metabolic status-dependent regulation of the cell cycle. CHT7 belongs to the CHC protein family, members of which include transcriptional regulators programming the initiation of cell division. A similar role of CHT7 in mediating cell cycle progression has been suggested. However, the regulatory mechanism and specific processes regulated by CHT7 have yet to be determined. In this dissertation, I applied bioinformatics approaches to comprehensively study CHT7-mediated gene regulation during the cell cycle using cell cultures synchronously grown in bioreactors. I found that specific pathways such as DNA replication, chromosome condensation, and spindle assembly are affected by the absence of CHT7. Other affected pathways include cell-wall remodeling and previously uncharacterized putative kinase cascades. In addition, I discovered the presence of two potential cis-regulatory elements near the transcription start site of misregulated genes in cht7, which are potentially linked to homeodomain transcription factors. Moreover, I explored the potential relationship between the CHT7-mediated pathway and the gene network governed by the retinoblastoma protein complex. Lastly, I characterized the function of a novel CHC protein in cell cycle progression and compared it with the role of CHT7. Together, these studies facilitate a better understanding of the cell cycle regulation in microalgae.
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Title
Profiles of Student Engagement in Synchronous and Asynchronous Science Instruction
Creator
Schell, Matthew J.
Date
2022
Collection
Electronic Theses & Dissertations
Description
Virtual instruction at the K-12 level is on the rise, yet we know very little about the ways students engage in different types of virtual instruction. The goals of this study were to: 1) describe high school students’ engagement in virtual science courses in terms of behavioral, affective, cognitive-value, and cognitive-self regulatory dimensions; 2) explore whether students’ engagement patterns across these dimensions differed depending on whether science activities were synchronous or...
Show moreVirtual instruction at the K-12 level is on the rise, yet we know very little about the ways students engage in different types of virtual instruction. The goals of this study were to: 1) describe high school students’ engagement in virtual science courses in terms of behavioral, affective, cognitive-value, and cognitive-self regulatory dimensions; 2) explore whether students’ engagement patterns across these dimensions differed depending on whether science activities were synchronous or asynchronous; and 3) examine whether these engagement patterns were associated with students’ final course grades or over-summer retention in a virtual high school. Students enrolled in a range of science courses at virtual high school (n=124) provided multiple reports (n=493) of their engagement during both synchronous and asynchronous learning activities. Latent Profile Analysis (LPA) conducted with these data suggested five distinct situational engagement profiles representing different constellations of the affective, behavioral, cognitive-value, and cognitive-self-regulatory dimensions of engagement. During synchronous instruction, students tended to engage in ways characterized by higher engagement in all dimensions compared with asynchronous instruction. These high engagement profiles were also associated with higher final course grades. There were few differences in the extent to which profiles predicted retention; however, lower self-regulation was associated with higher rates of retention.
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Title
BLENDING OF POLY(LACTIC ACID) AND POLY(3-HYDROXYBUTYRATE-CO-3-HYDROXYVALERATE) – THE EFFECT OF MALEATED PLA AS A REACTIVE COMPATIBILIZER AND BIODEGRADATION STUDY
Creator
Muangmala, Woranit
Date
2022
Collection
Electronic Theses & Dissertations
Description
Poly(lactic acid), PLA was blended with poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, based on a crossed mixture-factorial experimental design with three levels of factorial variable of the type of pre-produced maleated PLA, PLAgMA-type, used as the blend compatibilizer, and three components mixture variable which were the contents of PLA, PHBV, and PLAgMA, included in the polymer blends. The mixture model was based on the constrained level of the weight fraction of each mixture...
Show morePoly(lactic acid), PLA was blended with poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, based on a crossed mixture-factorial experimental design with three levels of factorial variable of the type of pre-produced maleated PLA, PLAgMA-type, used as the blend compatibilizer, and three components mixture variable which were the contents of PLA, PHBV, and PLAgMA, included in the polymer blends. The mixture model was based on the constrained level of the weight fraction of each mixture component as follows: 0.2 ≤ PHBV ≤ 0.7, 0.2 ≤ PLA ≤ 0.7, and 0.05 ≤ PLAgMA ≤ 0.15. The design of experiment yielded 16 runs of compatibilized blends, with 2 runs of non-compatibilized blend and 2 runs of neat polymers, PLA and PHBV, for comparison. The model of relationship between variables was derived based on the multiplication of a linear relationship of one factorial variable with a quadratic Scheffe model of the mixture ingredients. Multiple formulas of the blend compatibilizer, maleated PLA (PLA-g-MA), were pre-produced by a reactive melt blending method to functionalize maleic anhydride, MA, on the PLA backbone in a twin-screw co-rotating extruder. Dicumyl peroxide, DCP, was used as a free radical initiator in the reactive blending. The formulas were designed using response surface experimental design to determine the effect of the contents of MA and DCP on the amount of grafted MA, MA-grafting yield, and the molecular weight properties, Mn, Mw, IV, and dispersity of PLA-g-MA. The model regression indicated a significant effect of DCP with increasing DCP tending to reduce the MA-grafting yield, Mn, Mw, and IV, and increase the dispersity. The optimum point that maximized the desirability of these responses simultaneously was with the content of DCP = 0.1 wt. % and MA = 3.94 wt. % (PLA basis). Blending of PLA and PHBV clearly increased the crystalline fraction of the blends compared to neat PLA, which affects the barrier properties of the materials. Inclusion of PHBV at 25 wt. % in the non-compatiblilized blend and at 45 – 60 wt. % in compatibilized blends resulted in more than 60% reduction of water and O2 permeability compared to PLA. The compatibilized PLA/PHBV blend with PLA weight fraction of 0.45 achieved 300% increase in the tensile strength compared to the neat PHBV; this level of improvement was equivalent to the non-compatibilized blend containing PLA 75 wt. %. This was attributed to enhanced interfacial adhesion that was evidently supported by increased miscibility between the blend components in compatibilized blends which was exhibited through the shifting of Tg of PLA and the decrease of k constants based on the Gordon-Taylor equation of the compatibilized blends. The factorial-mixture model regression suggested the validity of the mixture variable of PLA, and PHBV in both tensile and barrier properties; the PLAgMA had a significant effect only on the tensile performance of the polymer blends. The overlapped contour plots as well as the desirability functions could be used to optimize the mixture of the PLA/PHBV blend components that provide desirable tensile and barrier properties. A biodegradation study was conducted on neat PLA, PHBV, non-compatibilized blend of 75:25 PLA/PHBV, and compatibilized blend of 65:15:20 PLA/PLA-g-MA/PHBV. PLA/PLA-g-MA/PHBV was the fastest to reach 100% mineralization, followed by PLA and PLA/PHBV samples, according to the CO2 evolution and % mineralization, whereas PHBV reached only 81% mineralization at the end of the test of 180 days. The facilitation of anhydride present in PLA-g-MA on the hydrolysis of PLA was a major cause of the fast biodegradation of PLA/PLA-g-MA/PHBV. A sharp increase in enthalpy of fusion, ΔHf, as well as a rapid reduction of the molecular weight of PLA/PLA-g-MA/PHBV compared to PLA and PLA/PHBV support the occurrence of an elevated rate of hydrolysis. The PHBV sample showed the biodegradation was barely affected by abiotic hydrolytic degradation as the thermal properties did not show any shifting of the melting transition and the ΔHf remained stable until 30 days of the test; the main mechanism was the enzymatic microbial degradation causing an erosion at the surface rather than affecting the bulk properties such as the molecular weight. The scanning electron micrographs also revealed the biodegradation of PHBV that initially occurred was from the surface and later showed the degradation of the crystalline structure. The PLA crystals formed during the biodegradation of PLA/PHBV and PLA/PLA-g-MA/PHBV samples could be seen from SEM photos.
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Title
DESIGNING OUR FREEDOM : A NARRATIVE INQUIRY AND VISUAL RHETORICAL ANALYSIS OF BLACK WOMEN ENTREPRENEURS DIGITAL CONTENT STRATEGY ON SOCIAL NETWORKING SITES
Creator
Wourman, Ja'La Janice
Date
2022
Collection
Electronic Theses & Dissertations
Description
This study explores the role of race and identity in Black women entrepreneurship and how each of these play a part when developing content for online audiences. The purpose of this study was to better understand how our intersecting identities are important to draw upon or consider, when conducting research in work-place studies or entrepreneurship for technical and professional communication scholars. And with the rise of digital platforms, I wanted to better understand if the...
Show moreThis study explores the role of race and identity in Black women entrepreneurship and how each of these play a part when developing content for online audiences. The purpose of this study was to better understand how our intersecting identities are important to draw upon or consider, when conducting research in work-place studies or entrepreneurship for technical and professional communication scholars. And with the rise of digital platforms, I wanted to better understand if the entrepreneurial journey factors into the design process of developing content for online audiences. To answer these questions, I used a narrative inquiry approach to conduct 5 separate interviews for each of my participants. The purpose of the interviews was to amplify the voices of each of my participants drawing from Patricia Hill Collins and the Combahee River Collective’s Black feminist theory. I then conducted a content analysis of 3 images from each of my participants business Instagram profiles, to demonstrate how design and cultural background can play a role in developing content. The results from this study revealed 3 major outcomes from each of the interviews and 4 emerging themes in the images used for all 5 participants content analysis of Instagram. Together, the themes and outcomes show a direct correction of race, culture, and design in content strategy. Using this data, I was able to develop tenets to help scholars and practitioners imagine a culturally centered design framework for developing content for diverse audiences and situations.
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Title
Robust Maxwell Solvers for Large Scale Particle-in-Cell Simulations
Creator
Crawford, Zane Daniel
Date
2022
Collection
Electronic Theses & Dissertations
Description
The design of modern devices is impacted heavily by the use and availability of robust, accurate, and efficient computational tools. This includes modeling devices that exploit plasma physics like particle accelerators, klystrons, ion thrusters, and micro-plasma generators among many other applications. While there are a number of current and emerging applications, the common thread between all is the need to accurately and efficiently capture all the relevant physics in geometrically...
Show moreThe design of modern devices is impacted heavily by the use and availability of robust, accurate, and efficient computational tools. This includes modeling devices that exploit plasma physics like particle accelerators, klystrons, ion thrusters, and micro-plasma generators among many other applications. While there are a number of current and emerging applications, the common thread between all is the need to accurately and efficiently capture all the relevant physics in geometrically intricate structures. The holy grail is to enable topology optimization to explore the design space. But all this requires rigorous translation from the continuous to the discrete world, while capturing all the underlying physics and not adding spurious artifacts due to discretization.A common computational model to perform this analysis is the particle-in-cell (PIC) method. It provides a straightforward paradigm to self-consistently solve for the distribution of the plasma as a collection of particles. The prevailing approach to solve for the fields in PIC is the finite difference time domain method (FDTD), or EM-FDTDPIC. But this effort leaves much to be desired, given the leaps that have been made in the finite element method; indeed, the latter is the method of choice for most commercial tools that that have become the de-facto workhorse in RF design industry. As a result, in the past decade, considerable effort has been expended in developing finite element (FEM) based PIC schemes, EM-FEMPIC. But we are still not there. One major concern of utilizing EM-FEMPIC over EM-FDTDPIC is the computational cost of FEM, which is greater than FDTD, despite the advantages of field and geometry accuracy FEM affords.This dissertation seeks to develop (i) a theoretically rigorous means to translate from the continuous to the discrete world while ensuring that there are no spurious artifacts, (ii) develops a higher order accurate method in both space and time, and (iii) overcomes cost complexity by introducing a linear scaling domain decomposition scheme. In all of these, the methods developed ensure that the necessary conservation properties are satisfied to machine precision. Numerous examples developed demonstrate these claims.
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