Search results

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.
Show less

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.
Show less

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.
Show less

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.
Show less

Title: LATE-GESTATION METABOLIC STRESS IN DAIRY CATTLE : ASSOCIATION WITH COLOSTRUM YIELD AND IMMUNOGLOBULIN CONTENT
Creator: May Rossi, Renato
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Despite improvements made in the dairy industry and advances on heifer management, calf morbidity and mortality are still high. Calves rely on colostrum ingestion for acquisition of passive immunity, and provision of insufficient quantity of colostrum may lead these animals to failure of transfer passive immunity, hence leading to higher risks of morbidity and mortality. Many farms do not have sufficient colostrum available at times to feed their calves. Synthesis of colostrum starts few...
Show moreDespite improvements made in the dairy industry and advances on heifer management, calf morbidity and mortality are still high. Calves rely on colostrum ingestion for acquisition of passive immunity, and provision of insufficient quantity of colostrum may lead these animals to failure of transfer passive immunity, hence leading to higher risks of morbidity and mortality. Many farms do not have sufficient colostrum available at times to feed their calves. Synthesis of colostrum starts few weeks before calving and it is at the time when cows are experiencing augmented metabolic adaptations due to increasing nutrient demands for fetal growth, colostrogenesis, and preparation for the onset of lactogenesis. The study described in Chapter 2 aimed to compare the metabolic status of dairy cows during the last 6 wk of gestation based on colostrum volume and Ig content across seasons during a year. The results in the latter study suggest that greater availability of antioxidants might support the production of higher volumes of colostrum. Therefore, the study reported in Chapter 3, aimed to evaluate whether administering a dietary antioxidant supplement during the last 3 weeks of gestation improves colostrum volume and immunoglobulin content. Our results showed that DATS increased colostrum volume. However, despite finding higher volume of colostrum in treatment group with statistical differences compared to control, the distribution of colostrum volume between groups are relatively the same, as well for IgG, IgM, and IgA.
Show less

Title: MODELING THE JOINT IMPACTS OF SOCIAL NETWORK AND BUILT ENVIRONMENT ON ADOLESCENTS’ PHYSICAL ACTIVITY
Creator: Liu, Wei
Date: 2021
Collection: Electronic Theses & Dissertations
Description: This research stems from the worldwide public health problem of childhood obesity and insufficient physical activity (PA) among adolescents. Studies have shown that both social networks and the built environment could affect PA, but how do they jointly exert influence? Understanding the scale and mechanism of this joint impact could shed light on developing an effective intervention to promote PA. The goal of this dissertation is to try to disentangle the joint influence of social networks...
Show moreThis research stems from the worldwide public health problem of childhood obesity and insufficient physical activity (PA) among adolescents. Studies have shown that both social networks and the built environment could affect PA, but how do they jointly exert influence? Understanding the scale and mechanism of this joint impact could shed light on developing an effective intervention to promote PA. The goal of this dissertation is to try to disentangle the joint influence of social networks and the built environment on changes in PA through social network analysis and test a novel intervention based on the findings from the social network models. This study uses two waves of Add Health data from two sample schools. Chapter Two investigates how school-based friendship networks could influence Physical Education (PE) class enrollment. Chapter Three examines the influence of home location, neighborhood characteristics, as well as the demographic characteristics and change in PA of peers who were nominated as friends in the Add Health social survey on high school student’s friend selection and PA dynamics between two academic years. Chapter Four presents a spatial agent-based model that was derived from the social network model and integrates a location-based mobile game similar to Pokémon Go as a PA-promoting intervention to test different intervention scenarios. Through this research, I demonstrate that friends’ PE enrollment status has a weak influence on the change of individual’s PE enrollment in two consecutive years. Another observation is that student’s total PA change can affect their PA behaviors. Contrarily, the built environment of the neighborhood did not prove to exert significant influence. Due to social influence, students participating in an intervention program may cause a change in PA of non-participants, i.e., we can observe a spillover effect of the intervention program. This dissertation enriches the field of health geography by integrating social network analysis and spatial thinking to jointly investigate the influence of environmental and social spaces and to facilitate a more comprehensive understanding of the complex system of childhood obesity. It also extends existing models and provides a spatial agent-based model as an intervention exploration tool that can be calibrated for research and education by other scholars.
Show less

Title: THE COMMODIFICATION OF INTIMACY AND GENDER INEQUALITY WITHIN SOUTH KOREAN DATING RITUALS
Creator: Glayzer, Edward James
Date: 2021
Collection: Electronic Theses & Dissertations
Description: The economic boom of the 90’s promised increased gender equity for South Korean women through their new ability to “find employment off the land and outside of the family economy,” gaining some level of autonomy from their families. However, South Korea now has the widest gender income gap among OCED nations. I argue that, while women have gained the power to choose their own marriage partners, the hyper-commodification of dating rituals has left them as unequal partners in the negotiation of...
Show moreThe economic boom of the 90’s promised increased gender equity for South Korean women through their new ability to “find employment off the land and outside of the family economy,” gaining some level of autonomy from their families. However, South Korea now has the widest gender income gap among OCED nations. I argue that, while women have gained the power to choose their own marriage partners, the hyper-commodification of dating rituals has left them as unequal partners in the negotiation of romantic courtship. Additionally, the commodification of intimacy has also increased inequality between men and women within the South Korean sexual field, hardening class hierarchies. This has had negative effects on men’s ability to materially express their feelings of interest, love, and intimacy with their dating partners during a time of slow economic growth, concentration of wealth among elites, and high unemployment among South Korean youth. I found that a reversion to a reliance on South Korean singles’ parents class status and economic clout in the competitive South Korean sexual field has taken place despite tremendous economic development, and advances in women’s rights and education. While the democratizing effects of capitalism that have allowed South Korean women to choose their own marriage partners would seem to have increased gender equality, my study calls this assumption into question and asks how this shift instead creates new inequalities. I investigate how the development of a consumer economy has affected gender inequality through the commodification of intimate relationships within dating and marriage rituals. I use dating and courtship rituals in South Korea as a lens through which to examine how the commodification of intimacy has affected gender and class inequality. Unequal access to income between genders and classes unevenly effects the expression of intimate relationships that are heavily mediated by the hyper-consumption of commodities. I argue that inequity in the economic market creates analogous inequity in dating, marriage, and intimate markets with especially negative repercussions for those who do not fit what that market has deemed ideal feminine or masculine actors. Class inequalities within the sexual field are most apparent between men whose evaluations are based on breadwinner masculinity; strongly correlated with their incomes and the class background of their parents. Women too ascend or descend the hierarchy of the South Korean sexual field through their adherence to marketable ideals of femininity and a “good wife,” namely their education, docility, and erotica capital. The emancipatory power of new technologies of intimate consumption such as the internet are interrupted by both commodification and the threat of abuse by South Korean singles with the ability to weaponize their higher incomes within their intimate relationships. Online matchmaking agencies who perform such screening services are expensive and reintroduce economic inequalities and hegemonic male power back into intimate relationships. South Koreans exploit the internet to discover new social groups and extend the reach of their existing social networks through meetup groups and hobbies rather than deploying dating applications more directly to find a dating partner. However, I argue that the rise of online dating in South Korea and its intensive commodification has actually led to the retrenchment of existing gender norms and ideals rather than their subversion.
Show less

Title: A nitrogen-responsive small peptide signaling mechanism modulates plant root system architecture
Creator: Lay-Pruitt, Katerina Sibala
Date: 2021
Collection: Electronic Theses & Dissertations
Description: The plant root system changes dynamically in response to environmental cues. Plants utilize their root system for uptake of essential mineral nutrients that are heterogeneously distributed in the soil environment. Nutrient-dependent modulation of root system architecture (RSA) traits such as primary root growth, lateral root emergence, and the angles at which these roots grow allows for optimization of nutrient acquisition. Among signaling pathways by which plants may sense the availability...
Show moreThe plant root system changes dynamically in response to environmental cues. Plants utilize their root system for uptake of essential mineral nutrients that are heterogeneously distributed in the soil environment. Nutrient-dependent modulation of root system architecture (RSA) traits such as primary root growth, lateral root emergence, and the angles at which these roots grow allows for optimization of nutrient acquisition. Among signaling pathways by which plants may sense the availability of nutrients from the environment, small signaling peptide (SSP) pathways play important roles in optimizing root functions. These SSP pathways may further regulate molecular processes underlying RSA, such as the biosynthesis and transport of the major plant growth hormone, auxin. Characterization of these nutrient-responsive SSP pathways is thus of great importance and critical for understanding plant development in nutrient-poor environments. For my dissertation, I have identified and characterized a nitrogen (N)-responsive SSP pathway modulating root gravitropic response and lateral root development. Co-regulation of these RSA components by this module is proposed to prevent root outgrowth into N-poor regions and drive deeper root growth towards mobile nitrate (NO3-) resources stratified deeper in the soil profile. First, I show that a signaling pathway involving the CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) family of peptides and the CLAVATA1 (CLV1) receptor kinase, which is involved in N-dependent repression of lateral root emergence, also enhances root gravitropic response under N-limited conditions. Transcriptomic profiling of a clv1 mutant and CLE3 overexpressing lines identified Arabidopsis thaliana CENTRORADIALIS (ATC), a mobile protein previously characterized for its role in flowering regulation, as a downstream target of CLE-CLV1 signaling. Loss of ATC function significantly weakens root gravitropic response and has a moderate impact on lateral root emergence under low NO3- availability. ATC promoter activity and protein localization are also detected throughout the phloem and in the root columella cells, which are major centers for gravity sensing. Second, I demonstrate the relevance of ATC function on the molecular processes underlying root gravitropic response. While mutation in ATC does not impact gravity sensing via amyloplast sedimentation, it does inhibit the asymmetric transport of auxin needed for gravitropic bending. I determine that this occurs via the significant reduction of the PIN3 auxin efflux transporter in the vasculature and root tip of atc mutant lines. Lastly, I examine how the known roles of ATC in floral development could be implicated in root developmental processes. ATC binds to phosphatidic acid and phosphatidylserine, which is contrary to the binding capacity of its homolog FLOWERING LOCUS T (FT) to phosphatidylcholine and may contribute to its activity in N-limited environments. I also investigate the interaction of ATC and the transcription factor FD in the transcriptional regulation of PIN3. Although FD appears to have an impact on root gravitropic response, FD inhibits the expression of PIN3, suggesting potentially complex control of this gene via floral regulatory components. Taken together, the results presented in this dissertation contribute greatly to our understanding of how plant root architecture alters in response to N. These results can be further utilized in plant engineering strategies to regulate root growth in nutrient-limited soils.
Show less

Title: THE ORIGINS OF SUPEROXIDE AND HYDROGEN PEROXIDE PRODUCTION BY THE MAMMALIAN MITOCHONDRIAL ELECTRON TRANSPORT CHAIN : A COMPUTATIONAL AND EXPERIMENTAL APPROACH
Creator: Duong, Quynh Van
Date: 2021
Collection: Electronic Theses & Dissertations
Description: The mitochondrial electron transport chain (ETC) produces reactive oxygen species (ROS) as by-products of cellular respiration. Certain pathological conditions including ischemia-reperfusion (IR) injury disrupts mitochondrial ROS homeostasis, causing oxidative stress which can lead to cell death. Despite research efforts in the past few decades, an incomplete understanding of how mitochondria orchestrate ROS production and elimination prevails and hinders the development of efficacious...
Show moreThe mitochondrial electron transport chain (ETC) produces reactive oxygen species (ROS) as by-products of cellular respiration. Certain pathological conditions including ischemia-reperfusion (IR) injury disrupts mitochondrial ROS homeostasis, causing oxidative stress which can lead to cell death. Despite research efforts in the past few decades, an incomplete understanding of how mitochondria orchestrate ROS production and elimination prevails and hinders the development of efficacious therapeutic measures against oxidative stress. A major impediment is the lack of a quantitative framework capable of identifying site-specific sources of mitochondrial ROS production. Many mathematical models of mitochondria have been developed to tackle this challenge. Unfortunately, none is comprehensive and able to quantitatively reproduce a variety of bioenergetic data.The work presented in this dissertation culminates in a mathematical model of ROS production by the ETC complexes coupled with substrate metabolism. First, a variety of bioenergetic data are generated in-house using isolated mitochondria. Generating in-house data permits precise control over experimental conditions, which minimizes hidden variables in model simulations. Second, a biophysically detailed model of the ETC complex II is developed. Finally, the complex II model is integrated with the models developed by Beard and colleagues. These include the bioenergetic model, the kinetic model of complex I and the functional bc1 dimer model. The integrated model is biophysically detailed, mass-and-charge balanced and thermodynamically consistent. The modelling process involves an iterative process of model calibration and validation to ensure the quality of model predictions. Using this model, the flavin mononucleotide of complex I is identified as the primary source of superoxide and hydrogen peroxide in forward electron transport. The model predicts that, under conditions that favor highly reduced quinol and NADH pools in uninhibited mitochondria, both sites IF and IQ produce significant amounts of ROS. The model also reveals that hydrogen peroxide (H2O2) production by site IF underlies the substrate-specific monotonic dependence between net ROS production and oxygen concentrations. When electron flux is perturbed such as in the presence of an inhibitor, the topology of ROS production is altered. Thus, the model can be used to quantify the effects of changes to mitochondrial environment on ROS production, an application that, today, is experimentally limited. The model also highlights the importance of furthering our understanding of the scavenging system under different conditions to establish a complete picture of mitochondrial ROS homeostasis.
Show less

Title: THEORETICAL MODELING OF ULTRAFAST OPTICAL-FIELD INDUCED PHOTOELECTRON EMISSION FROM BIASED METAL SURFACES
Creator: Luo, Yi
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Laser-induced electron emission from nanostructures offers a platform to coherently control electron dynamics in ultrashort spatiotemporal scales, making it important to both fundamental research and a broad range of applications, such as to ultrafast electron microscopy, diffraction, attosecond electronics, strong-field nano-optics, tabletop particle accelerators, free electron lasers, and novel nanoscale vacuum devices. This thesis analytically studies nonlinear ultrafast photoelectron...
Show moreLaser-induced electron emission from nanostructures offers a platform to coherently control electron dynamics in ultrashort spatiotemporal scales, making it important to both fundamental research and a broad range of applications, such as to ultrafast electron microscopy, diffraction, attosecond electronics, strong-field nano-optics, tabletop particle accelerators, free electron lasers, and novel nanoscale vacuum devices. This thesis analytically studies nonlinear ultrafast photoelectron emission from biased metal surfaces, by solving the time-dependent Schrödinger equation exactly. Our study provides better understanding of the ultrafast control of electrons and offers useful guidance for the future design of ultrafast nanoelectronics. First, we present an analytical model for photoemission driven by two-color laser fields. We study the electron energy spectra and emission current modulation under various laser intensities, frequencies, and relative phase between the two lasers. We find strong modulation for both the energy spectra and emission current (with a modulation depth up to 99%) due to the interference effect of the two-color lasers. Using the same input parameter, our theoretical prediction for the photoemission current modulation depth (93.9%) is almost identical to the experimental measurement (94%). Next, to investigate the role of dc field, we construct an analytical model for two-color laser induced photoemission from dc biased metal surfaces. We systematically examine the combined effects of a dc electric field and two-color laser fields. We find the strong modulation in two-color photoemission persists even with a strong dc electric field. In addition, the dc field opens up more tunneling emission channels and thus increases the total emission current. Application of our model to time-resolved photoelectron spectroscopy is also demonstrated, showing the dynamics of the n-photon excited states depends strongly on the applied dc field. We then propose to utilize two lasers of the same frequency to achieve the interference modulation of photoemission by their relative phase. This is motivated by the easier access to single-frequency laser pairs than two-color lasers in experiments. We find a strong current modulation (> 90%) can be achieved with a moderate ratio of the laser fields (< 0.4) even under a strong dc bias. Our study demonstrates the capability of measuring the time-resolved photoelectron energy spectra using single-frequency laser pairs. We further extend our exact analytic model to photoelectron emission induced by few-cycle laser pulses. The single formulation is valid from photon-driven electron emission in low intensity optical fields to field-driven emission in high intensity optical fields, and is valid for arbitrary pulse length from sub-cycle to CW excitation, and for arbitrary pulse repetition rate. We find the emitted charge per pulse oscillatorily increases with pulse repetition rate, due to varying coherent interaction of neighboring laser pulses. For a well-separated single pulse, our results recover the experimentally observed vanishing carrier-envelope phase sensitivity in the optical-field regime. We also find that applying a large dc field to the photoemitter is able to greatly enhance the photoemission current and in the meantime substantially shorten the current pulse. Finally, we construct analytical models for nonlinear photoelectron emission in a nanoscale metal-vacuum-metal gap. Our results reveal the energy redistribution of photoelectrons across the two interfaces between the gap and the metals. Additionally, we find that decreasing the gap distance tends to extend the multiphoton regime to higher laser intensity. The effect of dc bias is also studied in detail.
Show less

Title: AN INTEGRATED OF CONTROL AND PROTECTION SCHEME FOR AC MICROGRIDS
Creator: AlZahrani, Saad Atitullah
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Numerous advances have occurred in the area of microgrids (MGs) in the last two decades. Protection is one of the most significant challenges facing the deployment of MGs. With the utilization of renewable energy resources (RES) to reduce emissions and costs, short circuit levels have drooped in comparison to those produced by conventional generating sources. Therefore, traditional protection schemes that apply to distribution system are no longer effective in protecting the microgrid against...
Show moreNumerous advances have occurred in the area of microgrids (MGs) in the last two decades. Protection is one of the most significant challenges facing the deployment of MGs. With the utilization of renewable energy resources (RES) to reduce emissions and costs, short circuit levels have drooped in comparison to those produced by conventional generating sources. Therefore, traditional protection schemes that apply to distribution system are no longer effective in protecting the microgrid against fault currents, either in grid–connected or islanded mode. In microgrid framework, distributed generation (DG) based RES require an interface of power electronic converters to regulate their output voltage, current, and frequency as well as to share the generated power properly. Mitigation the impacts of fault currents in microgrid system is an important aspect of restricting the output current of converters from exceeding their rated value, preventing power discontinuity, enhancing reliability of protection system and improving the stability of the network.For microgrid control and protection challenges, several approaches have been proposed in the last decade. However, the need for efficient and reliable protection schemes of islanded microgrid system still exists. This research thesis develops and synthesizes an adaptive integration of control and protection framework for MGs. The proposed strategy is based on detecting the faults and limiting the fault currents for short periods until the protection devices make a proper decision. A single state observer has been developed to detect the faults that occur within protection zones. Moreover, fault current limiter (FCL) devices have been utilized to achieve rapid switching with instant reduction of fault current contribution. The adaptive integrated protection proposed in this research is achievable using either centralized or decentralized control in MGs. The proposed framework has been applied to islanded microgrid configuration and is demonstrated to be an effective means to protect the system and maintain the voltage and frequency within acceptable range with the capability of power continuity during both transient and persistent faults.
Show less

Title: Insurgent Stratego : How Rebels Influence the Public During Civil Conflict
Creator: Lucas, Caleb
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Rebel groups rely on civilians to achieve victory in civil conflict. The public's attitudes determine their ability to realize key aims, such as extracting vital information, coercing support, and mobilizing new fighters. However, numerous strategic considerations encourage rebels to use violence against civilians. More so, rebel groups also face battlefield losses and political setbacks that can damage their reputation among non-combatants. I explore how rebels navigate the tension that...
Show moreRebel groups rely on civilians to achieve victory in civil conflict. The public's attitudes determine their ability to realize key aims, such as extracting vital information, coercing support, and mobilizing new fighters. However, numerous strategic considerations encourage rebels to use violence against civilians. More so, rebel groups also face battlefield losses and political setbacks that can damage their reputation among non-combatants. I explore how rebels navigate the tension that results from these dynamics in this dissertation. Overall, I argue that rebels influence the public's attitudes using intentional messaging and violence. My theory suggests rebel media can effectively shape how the public perceives an organization and be used to distract from bad behavior or losses to the government. It can also justify and contextualize attacks that might otherwise be considered offensive. However, I argue that tactical considerations still restrain rebel behavior and that they generally attempt to conduct violence when the payoffs are high and the costs are relatively low. I argue in the first empirical chapter that civilians partly rely on rebel propaganda to inform their beliefs about a conflict. This is because credible information about a conflict's warring parties and their attributes is difficult for civilians to obtain, as misinformation, rumors, and selective news coverage are common in civil conflicts. Rebels understand this and provide ostensible evidence that indicates their organization is strong relative to the government in their media outlets. I expect civilians to update their beliefs partly based on this information due to their information disadvantage. I estimate a difference-in-differences model that exploits the sudden introduction of a rebel group's radio station between two representative survey waves and demonstrate that exposure to rebel media can increase perceptions of a group's strength. I explore the functional use of propaganda in the second empirical chapter. Specifically, I argue that rebels use media to distract their supporters from tactical setbacks and to refute narratives of the conflict that are unfavorable to them. By deploying messaging approximate to events that could cause reputational harm, rebels attempt to reshape public perceptions of their organization. Consistent with this, I show that rebel groups in Syria respond to battlefield losses by publishing more propaganda. Additionally, I demonstrate through two case studies that rebels provide evidence of military strength while losing territory to the government and information about their governance activities when targeting civilians. The third empirical chapter examines the logic that rebel groups employ when deciding whether to conduct violence. I specifically examine the use of terrorism during religious holidays. I argue multiple incentives exist that encourage violence on these days. For example, attacks on holy days allow terrorists to signal their religiosity and impose extra terror on their targets. Rebels can decrease possible blowback from their own supporters for violating these days by framing their violence as divinely inspired in official propaganda. Governments understand these days are triggers for violence though and increase security surrounding them. However, their ability to do this is limited by the length of the holiday due to resource constraints and practical concerns. I demonstrate that the probability of an attack occurring on holidays that last a few days or less is lower than on non-holidays and provide evidence this is because state security is at its peak. I also show that holidays that last weeks have a higher likelihood of witnessing a terror attack than non-holidays, which I argue is because they are more difficult to protect and still provide payoffs to terror groups. This dissertation consequently broadly investigates how rebel groups attempt to influence the public during civil conflict through both propaganda and violence. I argue throughout that rebels are calculating actors that seek to maximize their ability to use violence while minimizing possible sanctions for that behavior. In doing so, I demonstrate propaganda meaningfully affects civilian attitudes. More so, I provide evidence that rebels understand the benefits of propaganda and attempt to use it to their advantage. However, I also show that tactical choices made by the government can limit the behavior of rebel groups, influencing their ability to benefit from propaganda.
Show less

Title: Theoretical and Experimental Investigations of Arterial Pulse Wave Velocity (PWV)
Creator: Yavarimanesh, Mohammad
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Pulse transit time (PTT) is the time delay for the energy wave to travel between two sites in the arteries. (The energy wave can be visualized as acute dilation of the arterial wall and usually moves much faster than blood.) PTT in the form of pulse wave velocity (PWV = D/PTT, where D is the distance between the two sites) has proven to be a marker of arterial stiffness and a major cardiovascular risk factor based on a large body of epidemiological data. The Bramwell-Hill (BH) equation...
Show morePulse transit time (PTT) is the time delay for the energy wave to travel between two sites in the arteries. (The energy wave can be visualized as acute dilation of the arterial wall and usually moves much faster than blood.) PTT in the form of pulse wave velocity (PWV = D/PTT, where D is the distance between the two sites) has proven to be a marker of arterial stiffness and a major cardiovascular risk factor based on a large body of epidemiological data. The Bramwell-Hill (BH) equation relates arterial stiffness and radius to PWV. Arterial stiffness positively relates to blood pressure (BP); thus, many have pursued BP monitoring via PWV. We investigated PWV from theoretical, experimental, and application prospective.In the first theory study, we investigated the 100-year Bramwell-Hill equation, which relates PWV to BP and thus represents a basis for cuff-less BP monitoring. However, it has long been known that this equation underestimates PWV in a BP-dependent manner. We developed a new equation that accounts for spatial changes in arterial cross-sectional area. This new equation largely corrected this well-known underestimation and predicted PWV better based on experimental data in the literature. In the second experimental study, we examined the most popular PTT (finger PTT). We hypothesize that whole body PTT could be better than finger PTT due to less smooth muscle contraction. We collected data from 32 participants in a near supine position. We placed sensors including electrodes on the chest for an ECG waveform, clips on the ear, finger, and toe for photo-plethysmography (PPG) waveforms, and a cuff on the arm for auscultation BP. We recorded the waveforms and referenced BP before and after mental arithmetic, a cold pressor test, slow breathing, and nitroglycerin. Conventional PTTs were assessed as markers of BP in human subjects undergoing a battery of interventions to change BP. This experimental study concludes that PTTs through the whole body rather than the arm show the best BP change tracking ability. Thirdly, we repeated the previous study for seven subjects in three sessions one year apart to see how much PTTs and other PPG waveform feature models change after one year. While it is known that the PTTs calibration models must be updated periodically to account for aging effects, data on the time period required for these “cuff re-calibrations” are scant. Our experimental finding suggests that the PTTs model through the whole body could hold up after one year, and calibration may occur every year, which is reasonably practical. Finally, because of the inverse relation of PWV and arterial radius in the BH equation, we investigated innovative applications for PTT and other physiology-inspired features of carotid and femoral waveform for screening and surveillance of aortic abdominal aneurysm diameter. We hypothesized that arterial waveform features such as PTT constitute a non-imaging solution for the aneurysm size of the aorta. The features detected AAA with 72-80% accuracy. In conclusion, from a theoretical standpoint, we improved the 100-year PWV equation by relaxing its main assumption. From an experimental perspective, we showed the best body location for measuring PWV in the sense of BP prediction and robustness after one year. Lastly, we found that PWV could be used as markers of the abdominal aortic aneurysm from an application standpoint.
Show less

Title: “This story was inside me this whole time, just waiting” : Coming to Blackgirl storying
Creator: Johnson, Lauren Elizabeth Reine
Date: 2021
Collection: Electronic Theses & Dissertations
Description: This dissertation project explores the various ways Blackgirls (Hill, 2016) from across a New Orleans came together in a collective space to engage in discussions of Blackgirlhood, wherein they shared and developed insights into their individual and collective understandings of self and community. Collective members’ multimodal storying, discussions, and reflections, are centered in this dissertation in response to an urgent need for more expansive presentations of Blackgirls. Informed by...
Show moreThis dissertation project explores the various ways Blackgirls (Hill, 2016) from across a New Orleans came together in a collective space to engage in discussions of Blackgirlhood, wherein they shared and developed insights into their individual and collective understandings of self and community. Collective members’ multimodal storying, discussions, and reflections, are centered in this dissertation in response to an urgent need for more expansive presentations of Blackgirls. Informed by theories, methodologies, and pedagogies, including: Black feminisms and Black Girlhood Studies (e.g., Collins, 2000; Dillard, 2016; Hill, 2016; hooks, 1996; Owens et al., 2017), Indigenous storywork (Archibald, 2008), sociocultural perspectives of literacies (e.g., Street, 1984), and culturally responsive/sustaining humanizing pedagogies (e.g., Ladson-Billings, 1995; Paris & Alim, 2017; Paris & Winn, 2014), this study also builds with the works and examples as put forth by other Blackgirls and Black women, such as Toni Cade Bambara’s (1996) “The Education of a Storyteller” to inquire into how centering Blackgirls and their narratives may move us towards what I conceptualize as “Blackgirl storying,” a medium that we used to critically name and honor our lives and the plurality of Blackgirlhood.
Show less

Title: ANALYZING FACTORS WHICH AFFECT LEGIONELLA OCCURRENCE IN A FULL-SCALE GREEN BUILDING PREMISE PLUMBING SYSTEM
Creator: Julien, Ryan
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Water consumption in the United States has decreased in recent decades due to improved water efficiency and adoption of water conservation practices. However, plumbing design guidance has not been updated to reflect this change, resulting in increased hydraulic retention time, disinfectant decay, and the proliferation of opportunistic premise plumbing pathogens (OPPPs) such as Legionella pneumophila. Time spent in premise plumbing systems has been shown to impact water quality through such...
Show moreWater consumption in the United States has decreased in recent decades due to improved water efficiency and adoption of water conservation practices. However, plumbing design guidance has not been updated to reflect this change, resulting in increased hydraulic retention time, disinfectant decay, and the proliferation of opportunistic premise plumbing pathogens (OPPPs) such as Legionella pneumophila. Time spent in premise plumbing systems has been shown to impact water quality through such mechanisms as the loss of residual disinfectant, leaching of pipe materials, biofilm formation, and increased concentrations of opportunistic pathogens such as Legionella spp.Quantitative Microbial Risk Assessment (QMRA) is a tool used to evaluate human health risks, and has been used to assess risks associated with Legionella. However, these assessments require data regarding the concentration of Legionella in water. Due to the ubiquity of Legionella in plumbing systems, their growth in biofilms, and the sporadic nature of biofilm detachment, Legionella concentrations are poorly understood, thus limiting the utility of QMRA in this instance. Factors which influence the prevalence of Legionella have been studied at the bench scale, but never in a full-scale building water system. The work presented herein takes a risk factor approach in exploring how to better monitor or predict concentrations of Legionella spp. This dissertation presents research to help better understand factors which best predict Legionella spp. Research objectives of this work were to: (1) identify variables which most effectively predict Legionella spp. concentrations using multiple relevant statistical methods, (2) determine the time water spends stored in building plumbing prior to use using a novel model, and (3) determine whether compliance with common temperature guidelines to limit Legionella proliferation has a significant influence on Legionella spp. concentrations. This research employs a rich data set from a full-scale home, equipped with flowmeters and temperature sensors to assess water conditions. Analytical samples were also collected to determine common water quality variables, as well as enumeration of Legionella spp. Multiple statistical analyses, including Spearman’s rank correlation, principal component analysis, generalized linear modeling, and a Bayesian variable selection technique were used to investigate variable relationships and to evaluate the value of model results in predicting Legionella spp. concentrations. Principal component analysis suggests that water age and biofilm detachment are the primary drivers of changes observed in water quality, accounting for 53% of the total variance in the data. General linear modeling revealed that heterotrophic plate count, total organic carbon, total cell count, maxTSL and meanTSL (metrics describing water use), and modeled water age were each significant predictors of Legionella spp. concentrations at the p < 0.05 level. Bayesian variable selection indicated that the 95th percentile of water age and maxTSL were most predictive of Legionella spp. concentrations. Results from the water age model were evaluated, indicating that modeled water age is indeed a statistically significant (p < 0.05) predictor of Legionella spp. Compliance with common temperature guidelines was found to be significantly correlated (ρ = 0.22, p < 0.001) to Legionella spp Results of this research indicate that water quality and water use have significant implications to Legionella occurrence. These results provide a framework to investigate Legionella spp. using a limited set of variables which are more commonly and cheaply measured than direct measurement, which could encourage more widespread monitoring for Legionella and ultimately reduce the incidence of illness. While water age remains poorly understood, these results show that water age is a critical factor in determining Legionella spp. prevalence. This knowledge should be applied to plumbing design and maintenance to limit water age and thereby Legionella spp. concentrations. Statistical significance between compliance with commonly cited temperature guidelines and Legionella spp. concentrations indicate that these guidelines do provide some level of control, and should be considering in design and operation of premise plumbing systems.
Show less

Title: USING FRAGARIA AS A MODEL SYSTEM FOR THE STUDY OF SUBGENOME DOMINANCE AND ADAPTATION IN CROPS
Creator: Alger, Elizabeth
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Polyploidy, or the presence of three or more complete genomes in a single organism, has occurred frequently in plants, especially in the angiosperm lineage. Allopolyploids, or polyploids resulting from the merging of different genomes in an interspecific hybrid, have often been shown to experience subgenome dominance. Subgenome dominance is the phenomenon where there is bias in the gene loss and expression between the different genomes in a polyploid, known as subgenomes. Despite the...
Show morePolyploidy, or the presence of three or more complete genomes in a single organism, has occurred frequently in plants, especially in the angiosperm lineage. Allopolyploids, or polyploids resulting from the merging of different genomes in an interspecific hybrid, have often been shown to experience subgenome dominance. Subgenome dominance is the phenomenon where there is bias in the gene loss and expression between the different genomes in a polyploid, known as subgenomes. Despite the prevalence of polyploids and subgenome dominance, little is known about the factors and mechanisms that influence this process. Strawberry (Fragaria sp.) is emerging as a powerful model system to investigate polyploid subgenome dominance evolution due to the recent identification of the four extant diploid progenitor species of the cultivated octoploid strawberry (Fragaria x ananassa). Having the diploid progenitors in hand allows us to identify differences between the dominant subgenome, F. vesca, and the other three progenitors that may have an impact of subgenome dominance. One possible factor is transposable element (TE) abundance, as low TE density has been consistently associated with the dominant subgenome in allopolyploids. Epigenetic silencing of TEs by DNA methylation to suppress TE activity has been shown to result in decreased expression of neighboring genes and this lowered gene expression may affect the establishment of subgenome dominance. F. vesca will be used as a diploid model for the study of subgenome dominance in strawberry where I can examine how TE abundance and other factors influence gene expression in a single accession and in hybrid crosses between different accessions. Tracking changes in gene expression in the hybrids will allow us to examine how genomes with difference sizes and genomic factors interact. The results and insights observed from this study can then be applied to subgenome dominance research in octoploid strawberry. In addition to the germplasm and genomic resources, strawberries are also a high value crop and the loss of their production due to (a)biotic stressors results in the loss of millions of United States dollars annually. Using a population of octoploid strawberries segregating for salt tolerance, I will identify candidate genes related to salt tolerance. Together this work will identify factors and mechanisms related to subgenome dominance and use genotypic data in a practical breeding context.
Show less

Title: INVESTIGATING UGANDA’S HIGH HIV INCIDENCE AMONG YOUNG WOMEN IN AN ERA OF WIDESPREAD GAINS IN HIV PREVENTION AND TREATMENT
Creator: Namanya, Judith
Date: 2021
Collection: Electronic Theses & Dissertations
Description: This dissertation examines the factors driving risky sexual behavior associated with reported high numbers of new HIV infections among young women in Uganda, using Mbarara District as a case study. Using the modified Social Ecological Model for Young Women’s Vulnerability to HIV Infection, the study investigates the contextual and broader structural factors, their interactions within and across multiple levels, and how they influence the sexual behaviors of individual young women in ways that...
Show moreThis dissertation examines the factors driving risky sexual behavior associated with reported high numbers of new HIV infections among young women in Uganda, using Mbarara District as a case study. Using the modified Social Ecological Model for Young Women’s Vulnerability to HIV Infection, the study investigates the contextual and broader structural factors, their interactions within and across multiple levels, and how they influence the sexual behaviors of individual young women in ways that increase their vulnerability to contracting HIV. The objectives of the study are: 1) Evaluate individual-level factors associated with sexual risk-taking behavior, specifically having unprotected sex, among young women ages 15-35 years; 2) Describe contextual and broader structural factors that make young women vulnerable to HIV-related risky sexual behaviors, and assess how these contextual factors interact with individual-level factors in ways that perpetuate high levels of HIV infection; and 3) Re-examine the connection between poverty and other economic factors to risky sexual behavior and vulnerability in the context of high HIV transmission among young women. The study used mixed qualitative and quantitative methods, combining household surveys, focus group discussions, key informant interviews, and in-depth interviews. Household survey results show that risky sexual behavior i.e., having sex without a condom, is still high (over 48%) among the unmarried young women ages 15-35 years. Engagement in unprotected sex increased by age, with young adults reporting more unprotected sex encounters than adolescent girls. Those with primary or some secondary education were at an increased risk of having unprotected sex. Surprisingly, women with tertiary education were at higher risk of engaging in unprotected sex than those who had completed secondary education. Negative binomial regression analyses show that women with no employment and those with part-time employment were at an increased risk for unprotected sex compared to those with low paying but stable employment. These findings on education and HIV risk call for a careful reexamination of the link between higher education and HIV vulnerability to inform policy. Education policies and interventions need to focus on curricula that incorporate entrepreneurial skills at different educational levels from primary to college. Keeping girls in school under the protective eye of parents, guardians and teachers is key in reducing exposure to unprotected sex among young girls. Findings from the qualitative analysis revealed that sociocultural and structural factors, including social norms (premarital sex as taboo, early marriage pressures, subornation of girls and women), youth unfriendly HIV services (e.g., long waiting times, rude and unprofessional clinic staff), high unemployment rates, sexual harassment, exploitation by male employers, and discrimination were key factors perceived to drive risky sexual behavior in relation to HIV contraction among young women. The findings show that while many young women, especially those with children, engaged in risky transactional sexual behavior to meet basic needs, many younger women, including college-level ones, did so to meet materialistic wants and to fit-in with peers. Widespread availability of antiretroviral drugs (ARVs) caused complacency among young people. HIV was no longer perceived as life threatening due to ARVs, which prevent progression into full-blown AIDS, morbidity and death. In fact, some young women were more scared of getting pregnant than contracting HIV. We suggest that efforts to reduce new HIV infections among young women and young men should target individual risk perception, and balance HIV treatment and prevention messages. Findings reveal a complex mix of dynamic and interacting factors operating at different levels that create context specific sexual behavioral risk socioscapes that sustain or accentuate the high rates of new HIV infections among the young women. Using a Social Ecological Model for Young Women’s Vulnerability to HIV as a guiding framework, we contend that efforts for addressing the high HIV infections among young women, including sexual behavioral change interventions, economic empowerment programs, should not only aim at individual women but also target factors operating at the sociocultural and structural levels.
Show less

Title: MECHANISMS UNDERLYING DESICCATION RESISTANCE IN DROSOPHILA SPECIES
Creator: Wang, Zinan
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Adaptation to various and extreme environments is key to long-term species persistence. Reducing water loss is important for organisms adapting to different terrestrial environments. In Drosophila fruit flies and other terrestrial insects, their small body size and large surface areas to volume ratios make them vulnerable to desiccation stress. Their ability to prevent water loss is crucial for their survival. Previous studies have suggested that cuticular water loss accounts for the majority...
Show moreAdaptation to various and extreme environments is key to long-term species persistence. Reducing water loss is important for organisms adapting to different terrestrial environments. In Drosophila fruit flies and other terrestrial insects, their small body size and large surface areas to volume ratios make them vulnerable to desiccation stress. Their ability to prevent water loss is crucial for their survival. Previous studies have suggested that cuticular water loss accounts for the majority of water loss in insects and hypothesized that differences in cuticular hydrocarbon (CHC) content accounted for differences in desiccation resistance between mesic and desert species. However, the specific association between different CHC components and desiccation has not been established, and the genetic mechanisms underlying the evolution of these CHC components that confer high desiccation resistance have not been elucidated. This dissertation investigated how the evolution of CHCs in insects affected desiccation resistance and elucidates the genetic mechanisms underlying their evolution. With a comprehensive association study of desiccation resistance and CHCs in 46 Drosophila species and 4 species in closely-related genera, the analyses showed that mbCHC chain lengths were important predictors of desiccation resistance and longer mbCHCs contributed to higher desiccation resistance. This dissertation further investigated the genetic and molecular mechanisms underlying longer chain mbCHCs and higher desiccation resistance in a desert Drosophila species, Drosophila mojavensis. A fatty acyl-CoA elongase gene, mElo (methyl-branched CHC Elongase), was identified in Drosophila species for the elongation of mbCHCs. Overexpression experiments in D. melanogaster demonstrated that coding changes in mElo from D. mojavensis lead to longer mbCHCs and higher desiccation resistance. Further experiments using CRISPR-Cas9 to knock out mElo from D. mojavensis showed that knockout of this gene decreased the production of the longest mbCHCs and significantly reduced desiccation resistance at their ecological-relevant temperature. Results from this dissertation elucidate the molecular and evolutionary mechanisms that enable species to reduce water loss and maintain water balance as our planet gets warmer and more arid in the next few decades.
Show less

Title: DOMESTIC CORPORATE GROUPS : AN ETHNOGRAPHIC AND ARCHAEOLOGICAL EXAMINATION OF HOUSEHOLDS, NEIGHBORHOODS, AND COMMUNITIES
Creator: Conell, Alexandra Organek
Date: 2021
Collection: Electronic Theses & Dissertations
Description: In many different cultures throughout history, humans have chosen to live and work cooperatively, arranging themselves into domestic corporate groups. However, these domestic corporate groups are not identical in their nature or operation. For instance, the ways in which communities organize their domestic corporate groups, manage access to property and resources, and accomplish daily tasks vary between cultures and over time, as people simultaneously adapt to and shape the world in which...
Show moreIn many different cultures throughout history, humans have chosen to live and work cooperatively, arranging themselves into domestic corporate groups. However, these domestic corporate groups are not identical in their nature or operation. For instance, the ways in which communities organize their domestic corporate groups, manage access to property and resources, and accomplish daily tasks vary between cultures and over time, as people simultaneously adapt to and shape the world in which they live. In this research, I combine ethnographic and archaeological evidence to examine this variation in the nature and operation of domestic corporate groups, as well as how those groups change over time. I first assess cross-cultural variation in the nature and operation of domestic corporate groups, as well as changes in those groups over time by analyzing historical ethnographic data on thirteen different variables related to corporateness. To achieve a broad regional perspective on this variation, I examine villages in five different North American culture areas: members of the multi-tribal affiliation of the Haudenosaunee in the Eastern Woodland Area; several tribal groupings within the North Pacific Coast Area; the exemplar cultures of the Pawnee and the Mandan in the Plains Area; the exemplar culture of the Navajo in the Southwestern Area; and the village residential unit of Tzintzuntzan in the Nahua Area. Ethnographies of the Boasians form the foundation of this component of my research. From the ethnographic data, then, I develop a descriptive model for distinguishing between different organizational types of domestic corporate groups, as well as how they change through time. I also establish archaeological correlates for each of the organizational types in my model. Finally, I conduct a preliminary test of the appropriateness and sufficiency of a selection of these archaeological correlates. I analyze several aspects of village and household organization, including nondomestic community buildings, household clusters, storage facilities, and food preparation and consumption facilities for three Wendat archaeological sites in southern Ontario: the Late Middleport Alexandra Site in Toronto (AkGt-53; A.D. 1390-1420), the Late Protohistoric Molson Site in Barrie (BcGw-27; A.D. 1580-1600), and the Late Protohistoric to Early Historic Mantle Site in Whitchurch-Stouffville (AlGt-334; A.D. 1596-1618). Ultimately, through its combination of ethnographic and archaeological evidence, my research supports the value of and potential for identifying variation in domestic corporate groups using archaeological evidence. It is my hope that my research will provide a useful foundation for future research on further refining our understanding of variation and change in domestic corporate groups and how they may be identified archaeologically.
Show less

Title: Essays in Applied Microeconomics
Creator: Ushakov, Nikolay
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Chapter 1: Are There Incentives to Improve the Search Engines in the Age ofInformation Overload?Information overload on the Internet creates a natural demand for higherquality search engines. In this paper, I compare the current advertising (indirect) model of search engines financing with the hypothetical paid (direct) model. I find that under monopoly in innovation activities indirect monopolist has much lower incentives to improve the quality than the direct monopolist. Explicit modeling...
Show moreChapter 1: Are There Incentives to Improve the Search Engines in the Age ofInformation Overload?Information overload on the Internet creates a natural demand for higherquality search engines. In this paper, I compare the current advertising (indirect) model of search engines financing with the hypothetical paid (direct) model. I find that under monopoly in innovation activities indirect monopolist has much lower incentives to improve the quality than the direct monopolist. Explicit modeling of entry and quality competition in a static framework leads to the conclusion that under the indirect model only one firm could profitably enter producing the minimally acceptable by consumers quality. A dynamic framework predicts more firms entry but only because the firms are colluding against consumers by saving on quality improvement investments. In contrast, under the direct model firms' cooperation leads to higher investment incentives since it permanently raises industry profit flows. I suggest several alternative policy recommendations to improve incentives in this market.Chapter 2: Strategic Control and ExclusivityThis paper extends Hagiu and Lee's (2011) "Exclusivity and control" article bymaking control regime over content in addition to exclusivity as the strategic choice in an industry characterized by a severe platform competition first for content and then for consumers. Under the assumption of homogeneous content valuations, the following results are obtained. First, for low and medium levels of content valuation, there are only affiliation equilibria (both exclusive and multihoming and the latter maximizes industry profit). For the high level of content valuation, there are one exclusive outright sale and multiple affiliation multihoming equilibria with the latter maximizing the industry profits. Finally, there are additional platforms' pessimistic expectations equilibria under affiliation regime that give higher payoffs to content providers. Implications for business strategies are presented.Chapter 3: Long Term Effects of Minimum Drinking Age Laws on Organ FailureOrgan failures are among the leading causes to deaths and the most expensive medical procedures in the United States. Medical literature has established the association between alcoholism and chronic dysfunction of organ systems. This paper provides the first causal evidence of the long-term impacts of increasing the MLDA to 21 in various states in the 1970s-1980s on reducing organ failures. By delaying exposure to alcoholic beverages, the MLDA 21 likely limits adolescents’ exposure to alcohol and reduce the likelihood of alcoholism in adulthood and thus the risk of alcohol-related diseases, including organ failures. We find that cohorts exposed to higher MLDA (=21) had lower probability of having organ failures in later life. The empirical findings show that limited access to spirits and alcohol before the age of 21 reduced the demand for transplants by 86 and 50 per 100,000 population, respectively, after ten years, given that the average transplants demanded by the cohort prior to treatment is approximately 155. These findings have important implications for evaluating the benefits of the MLDA21 legislation. Besides preventing traffic fatalities, the MLDA21 has significantly reduced organ failures in adulthood, therefore might have increased productivity and life quality of the generations who were growing up in the presence of this legislation.
Show less

MSU Libraries

Digital Repository

Enabled Filters

Pages

Pages

MSU Libraries

Digital Repository

You are here

Search results

Pages

Pages