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Title: ANALYSIS OF EJECTOR-STYLE MICROBUBBLE GENERATORS : MASS-TRANSFER PROPERTIES, MATHEMATICAL MODELING, AND DESIGN ALGORITHM
Creator: Wang, Ziwei
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Gas-to-liquid mass transfer is a rate-limiting step for many commercial-scale operations in the chemical, biochemical, pharmaceutical, and wastewater-treatment industries. The use of microbubbles with a diameter on the100 μm scale has been shown to provide high volumetric mass-transfer rates due to its high gas contact area per volume. However, the use of microbubbles in commercial processes has been hampered by the lack of design algorithms with which to fabricate high-performance,...
Show moreGas-to-liquid mass transfer is a rate-limiting step for many commercial-scale operations in the chemical, biochemical, pharmaceutical, and wastewater-treatment industries. The use of microbubbles with a diameter on the100 μm scale has been shown to provide high volumetric mass-transfer rates due to its high gas contact area per volume. However, the use of microbubbles in commercial processes has been hampered by the lack of design algorithms with which to fabricate high-performance, microbubble-sparged gas-liquid contacting equipment. The goals of this study were to identify the type of microbubble generator best suited to provide high volumetric mass transfer rates in commercial-scale equipment, characterize the mass-transfer properties, develop models able to predict the mass-transfer rate as a function of the key independent variables, and use the models to develop a design algorithm suitable to use microbubble sparging in industrial processes. The study began with a literature review of microbubble generators that considered factors including the mechanism, safety, cost, and scalability, with the goal of identifying generators suited to cost-effectively provide extremely high mass transfer in commercial-scale equipment. Microbubble generators that used liquid turbulence were found to have the best combination of properties for such applications. In collaboration with the Michigan Biotechnology Institute, a 300-L bioreactor was customized for use with either a RiverForest microbubble ejector and a conventional ring sparger. E.coli batch growth experiments were conducted to compare the growth rates using the two aeration methods. The E.coli growth rate observed during microbubble aeration was about twice that observed with the traditional ring sparger. Mathematical models describing the performance properties of both a microbubble ejector and a Modified Jameson Cell were developed. The models included energy requirements, mass transfer rates, gas and liquid flow patterns, and clearance of spent bubbles. The models predicted that the ejector would be more energy-efficient for applications requiring higher mass-transfer rates and lower gas volume fractions, whereas the Modified Jameson Cell would be more energy-efficient for applications requiring lower mass-transfer rates and higher gas void fractions. Moreover, the ejector generator was considered to have operational advantages over the modified Jameson Cell in terms of surfactant requirement and scalability. Based on these advantages, ejector generators were used for subsequent studies. A novel flow system was developed to measure the mass-transfer rate of microbubble produced by an ejector generator. A mathematical model was developed to reproduce experimental trends and estimate the effective microbubble diameter generated as a function of the gas and liquid flow rates. New axial mixing and two-phase friction factor correlations were developed for the model fidelity. The mathematical model was used to determine the effective microbubble diameter that best reproduced the dissolved oxygen profile for various combinations of gas and liquid velocities. The results were used to develop a correlation to predict the effective microbubble size as a function of system properties. The predictive power of this correlation has utility for industrial process design and scale-up applications. The friction factor and microbubble diameter correlations developed in this study were used to develop additional models to simulate the microbubble mass-transfer in large reactors that are sparged with arrays of microbubble ejectors. The models simulated flow from each ejector using an entrainment model for jet cones. They also simulated arrangement of ejectors into triangular arrays to estimate insufficiently aerated volume and optimize ejector spacing. Collectively, the models developed in this study provide powerful new design tools that enable rational design, optimization, and scale-up of ejector microbubble sparger arrays for commercial-scale reactors that require extremely high volumetric mass-transfer rates.
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Title: SEX DIFFERENCES IN HYPERTENSION AND THE ROLE OF ENDOTHELIAL TRPV4 CHANNELS IN CEREBROVASCULAR AND COGNITIVE FUNCTION
Creator: Chambers, Laura Christine
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Vascular cognitive impairment and dementia (VCID) describes a spectrum of cognitive disorders that have a cerebrovascular origin. VCID can range from mild cognitive impairment to frank vascular dementia. The mechanisms behind VCID development are not fully understood and there are no effective treatments available. VCID arises from functional impairment in the small arteries and arterioles in the brain. Hypertension, which affects nearly half of all American adults, is the leading modifiable...
Show moreVascular cognitive impairment and dementia (VCID) describes a spectrum of cognitive disorders that have a cerebrovascular origin. VCID can range from mild cognitive impairment to frank vascular dementia. The mechanisms behind VCID development are not fully understood and there are no effective treatments available. VCID arises from functional impairment in the small arteries and arterioles in the brain. Hypertension, which affects nearly half of all American adults, is the leading modifiable risk factor for VCID. Hypertension impairs cerebrovascular function that can starve neurons of necessary nutrients, increasing risk of cognitive impairment. My studies focus on cerebral parenchymal arterioles (PAs), which direct blood flow from the pial circulation to the capillaries. Because they lack collateral connections, PAs are considered the weak link in the cerebral perfusion. The occlusion of a single PA creates a discrete column of ischemic tissue that can produce cognitive impairment. PAs are dependent on TRPV4 channels for endothelium-dependent dilation, and there is a strong link between TRPV4 and cognitive function. Previous studies in male rodents showed that hypertension impairs TRPV4-mediated dilation in PAs, and this was associated with memory impairments. When mineralocorticoid receptor (MR) antagonists are administered alongside developing hypertension, these impairments are prevented. However, it is thus far unknown whether MR antagonist treatment can reverse cerebrovascular and cognitive impairments after they have developed. My first aim tests the hypothesis that rats with established hypertension will have impaired TRPV4 function in PAs that is associated with cognitive impairment, and that treatment with the MR antagonist eplerenone can reverse this damage after its development. My second aim focuses on sex differences in hypertension, as this is a major gap in the literature. Thus far, all studies linking TRPV4 function to cognition have been conducted in male mice. Given that estrogen is vasoprotective in other vascular beds, I hypothesize that hypertensive female mice would be protected against impaired TRPV4 function in PAs, and from the associated cognitive deficits observed in male mice. Lastly, my third aim addresses the importance of TRPV4 channels specifically in the endothelium. There is a consistent link between TRPV4 impairment and cognitive dysfunction, but due to the channel’s ubiquitous expression, its role in endothelial cells is unknown. Here, I test the hypothesis that male and female mice with endothelial TRPV4 channel deletion will have cognitive impairment. My studies show that MR antagonism reverses cerebrovascular and cognitive damage in hypertension, and that female sex protects against the development of these impairments. Further, I show that endothelial TRPV4 channel deletion results in cognitive dysfunction and increased inflammation in both male and female mice. My studies show for the first time that young female mice have preserved TRPV4 channel function in PAs that is associated with preserved cognitive function. Further, my data suggest the MR is a promising therapeutic target in hypertensive patients because it not only protects against neurovascular damage but can reverse it after it has developed.
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Title: ANTI-DEFICIT FRAMING TYC TRANSFER STUDENTS’ SELF-EFFICACY AS CONTEXTUALLY IMPACTED BY EDUCATION ENVIRONMENTS
Creator: Wood, Laura
Date: 2022
Collection: Electronic Theses & Dissertations
Description: The work in this dissertation aims to support a more equitable science education culture that better supports students who have historically and continue to be inequitably pushed out of science. Our equity-oriented and anti-deficit research agenda led us to study community college and transfer students as well as their self-efficacy and self-efficacy experiences. This dissertation opens by overviewing the state of STEM education and explaining how research approaches often frame students in...
Show moreThe work in this dissertation aims to support a more equitable science education culture that better supports students who have historically and continue to be inequitably pushed out of science. Our equity-oriented and anti-deficit research agenda led us to study community college and transfer students as well as their self-efficacy and self-efficacy experiences. This dissertation opens by overviewing the state of STEM education and explaining how research approaches often frame students in deficit ways. Chapter 1 introduces the author's researcher positionality and relevant literature to her research approaches. The author's research agenda prioritizes supporting marginalized students in STEM through studying the construct of self-efficacy. After reviewing the research framing, Chapter 2 introduces relevant literature about self-efficacy and two-year college (TYC) transfer student experiences. Chapter 2 ends by addressing how the author's research positionality aligns with and impacts the ways she researches self-efficacy and TYC transfer students. Afterwards, each body chapter (Chapters 3, 4, and 5) opens with a transition situating it in the broader story of the dissertation. Chapter 3 opens by reminding readers of the reasons for our qualitative approach to studying self-efficacy. Then, it describes the development of a qualitative codebook for self-efficacy. Chapter 4 opens by explaining our shift to a narrative analysis case study of a single transfer student. This chapter ultimately diverged from self-efficacy, and Chapter 4 will discuss the reasons and the results of that narrative analysis, stating that supporting characters were instrumental in a transfer student’s success story. The chapter ends with implications for universities to learn from TYCs. The dissertation transitions to Chapter 5 by broadening out from a single student’s case study to a positively impactful course experience at a TYC for STEM students intending to transfer. This chapter describes design considerations learned from the course as well as opportunities the course provided for student self-efficacy experiences. Chapter 6 discusses the story across all three body chapters as situated in the research framing and concludes the dissertation.
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Title: NEAR INFRARED (NIR) SURFACE-ENHANCED RAMAN SPECTROSCOPY AND FLUORESCENCE MICROSCOPY FOR MOLECULAR-GUIDED SURGERY
Creator: Yao, Cheng-You
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Molecular imaging has become an emerging technology to assess tumor margins. As the imaging contrast agents are functionalized with multiple ligands that can bind to different biomarkers – multiplexed molecular imaging, this technique can achieve high sensitivity and specificity for tumor margin detection. Optical-based molecular imaging modalities provide non-hazardous optical radiation, multiplexing wavelengths, and higher spatial resolution than ionizing radiation tomography techniques....
Show moreMolecular imaging has become an emerging technology to assess tumor margins. As the imaging contrast agents are functionalized with multiple ligands that can bind to different biomarkers – multiplexed molecular imaging, this technique can achieve high sensitivity and specificity for tumor margin detection. Optical-based molecular imaging modalities provide non-hazardous optical radiation, multiplexing wavelengths, and higher spatial resolution than ionizing radiation tomography techniques. Two categories of optical contrast agents, fluorescent dyes and Surface-Enhanced Raman Spectroscopy (SERS) nanoparticles are introduced and mainly applied in this dissertation. However, because of the tissue-photon interactions, the imaging contrast and penetration depths are limited by the visible wavelengths. The light in the NIR regime (700~1700 nm) has shown a deeper imaging penetration and better contrast with lower autofluorescence background. Thus, in this dissertation, NIR fluorescent dyes and SERS NPs excited by 785 nm are used for ex vivo and in vivo imaging for biological studies.This work aims to develop a variety of optical instruments for NIR ex vivo and in vivo biomedical imaging applications with deeper penetration, better contrast, and higher sensitivity. The optical instruments include a spectrometric system for SERS Raman detection, a VO2 MEMS scanner for SERS imaging, portable confocal microscopes, and a PZT MEMS scanner-based macroscope for wide-field fluorescence imaging. Chapter 1 briefly introduced the research background, pros and cons of existing techniques, and motivations of this study. In Chapter 2, the spectrometric SERS Raman system and ratiometric analysis have been applied to the detection of Alzheimer's Disease biomarkers and breast cancer image-guided surgery, using different SERS NPs conjugated with ligands. The Raman results were confirmed with histological analysis. In Chapter 3, a VO2 MEMS scanner has been designed, fabricated, and characterized for the Lissajous scanning SERS imaging application. In Chapter 4, two variants of the portable confocal microscopes, the point-scan and line-scan systems were designed with reflective parabolic mirrors for broadband wavelengths from the visible to NIR ranges. Ex vivo and in vivo confocal imaging results have been demonstrated using tumor-bearing mouse tissues. In Chapter 5, a thin-film PZT MEMS scanner has been reported, characterized, and integrated into a wide-field macroscope for fluorescence imaging. In Chapter 6, a novel photodetector - SNSPD has been integrated into the point-scan portable confocal microscope and PZT MEMS scanner-based wide-field macroscope to increase the efficiency and contrast of fluorescent imaging in the NIR range. In the last chapter, the future applications of the advanced VO2 MEMS scanners and fluorescence lifetime imaging microscopy using SNSPD were discussed in detail.
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Title: Perinatal HIV Exposure and Infection and its Association with Caregiver Depression Symptoms and Child Executive Function
Creator: Brewer, Sarah Kathleen
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Survival is possible for children perinatally exposed to or infected by Human Immunodeficiency Virus (HIV) in the post-combined antiretroviral therapy era, but the long-term effects of HIV exposure on children and their caregivers are still being explored. Identifying factors affecting children’s ability to thrive within an HIV context has great public health significance, particularly within a sub-Saharan context where the burden of HIV is felt disproportionately by women and children....
Show moreSurvival is possible for children perinatally exposed to or infected by Human Immunodeficiency Virus (HIV) in the post-combined antiretroviral therapy era, but the long-term effects of HIV exposure on children and their caregivers are still being explored. Identifying factors affecting children’s ability to thrive within an HIV context has great public health significance, particularly within a sub-Saharan context where the burden of HIV is felt disproportionately by women and children. Additionally, caregiver mental health is an important focus given its bidirectional relationship with child behavior. Previous studies on these topics have not included a full complement of HIV exposure or infection groups, considered how caregivers’ mental health may depend on child serostatus, and or are investigated in HIV endemic areas. The three aims presented in this dissertation will explore how perinatal HIV infection and exposure can affect caregivers and school-aged children. In Aim one, we compare depressive symptoms among caregivers of 3 groups of 6-10 year old children in Uganda with known HIV exposure status: children HIV-infected perinatally (CPHIV, n=102), children born to HIV-infected mothers, but HIV negative (CPHEU, n=101), and HIV-unexposed, uninfected community controls (CHUU, n=103). Caregiver depression symptoms were assessed using the Hopkins Symptom Checklist. In Aims two and three, child executive functioning (EF) assessed by caregiver report was compared across the three HIV exposure groups; effect modification of these associations by social support and wealth was also explored. We used random effects general linear models to estimate mean differences among the three HIV exposure groups. Adjusted models included caregiver age, education, social support, lifetime trauma, and wealth as covariates. In aim one, we observed that perinatal HIV exposure status was associated with mean caregiver depression symptoms. Specifically, in unadjusted analyses, depression symptoms were higher among CPHEU compared to CPHIV caregivers (unstandardized beta coefficient [B]=-3.5, 95% confidence interval [CI] -5.3, -1.8). We also observed that caregiver social support modified the findings above (p < 0.10) with CPHEU caregivers with lower social support and lower wealth reporting higher caregiver depressive symptoms compared to CPHIV caregivers. We repeated all analyses within the subsample of biological mothers to examine whether their own diagnostic status drove any findings we observed; our pattern of results remained unchanged. For Aim two, in our unadjusted analyses, perinatal HIV exposure was not associated with the Global Executive Composite (GEC) and Metacognition Index (MCI) scores of EF. However, for the Behavioral Regulation Index (BRI), the CPHIV group had lower levels of problems relative to the CHUU and CPHEU groups (B= -0.40, 95% CI -0.77, -0.03, B=-0.40, 95%CI -0.76, -0.02 respectively). For Aim three, we observed that the child’s sex and caregiver depression symptoms modified the association between HIV status and specific subscales of EF. Future directions for this work should include investigation into what drives the difference in caregiver depression symptoms between exposure groups. Additionally, collecting longitudinal measures of child EF and caregiver depression would help further interrogate time order between caregiver and child functioning among families affected by HIV. Lastly, continued investigation on how our findings relate to outcomes linked to EF such as academic achievement and behavioral problems would help to establish the importance of EF as a potential intervention target to improve school readiness.
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Title: Understanding Student Experiences in Informal Physics Programs Using the Communities of Practice Framework
Creator: Prefontaine, Brean Elizabeth
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Studies on physics identity have shown that it is one of the main factors that can predict a person’s persistence in the field; therefore, studying physics identity is critical to increase diversity within the field of physics and to understand what changes can allow more women and people of color to identify with the field. Informal physics spaces are not only made up of youth participants, but also facilitators who can be undergraduate or graduate student volunteers. In this work, the...
Show moreStudies on physics identity have shown that it is one of the main factors that can predict a person’s persistence in the field; therefore, studying physics identity is critical to increase diversity within the field of physics and to understand what changes can allow more women and people of color to identify with the field. Informal physics spaces are not only made up of youth participants, but also facilitators who can be undergraduate or graduate student volunteers. In this work, the experiences of facilitators within informal physics programs are investigated as spaces for physics identity development. Thus, the driving question for all of this work is: In what ways can participating as a facilitator within an informal physics program affect identity development? The data for these studies were collected through observations, written artifacts, and semi-structured interviews with those who facilitated the informal physics programs. In order to understand more about the experiences of the facilitators, the informal physics programs were viewed as Communities of Practice (CoP), and the CoP framework was operationalized within the context of these spaces. First, stories from two physics graduate students out of the interview sample are presented to provide a context for testing the feasibility of the extended framework and to identify how experiences within an informal physics program can shape physics identity development. Then, the operationalized CoP framework is used to study three distinct informal physics programs to understand the structures that support physics identity development. Finally, informal programs that combine physics and music/art are examined with the operationalized CoP framework to understand how these blended spaces can form communities of practice and support identity development. Analysis showed that the CoP framework is an effective tool for analyzing informal physics programs and highlights the structures that lead to identity development. These findings indicate that informal physics programs that operate with a CoP structure can provide valuable experiences to undergraduate and graduate facilitators that lead to physics identity growth.
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Title: The Construct Development and Measurement of Contributive Justice
Creator: Scott, William Campbell
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Organizational justice has long since been considered multi-dimensional. However, the dimensionality of organizational justice has been stagnant in recent years, consisting primarily of distributive, procedural, interpersonal, and informational justice. When further examining the meaning of justice and fairness in organizations, it becomes apparent that these organizational justice dimensions are not capturing an important element of justice, that being the equality of opportunity. This is an...
Show moreOrganizational justice has long since been considered multi-dimensional. However, the dimensionality of organizational justice has been stagnant in recent years, consisting primarily of distributive, procedural, interpersonal, and informational justice. When further examining the meaning of justice and fairness in organizations, it becomes apparent that these organizational justice dimensions are not capturing an important element of justice, that being the equality of opportunity. This is an important absence because the opportunity to contribute in organizations will likely affect both organizational outcomes and personal outcomes outside of work. Therefore, building upon previous work, the construct of contributive justice in organizations was introduced and defined as the fairness of opportunities to contribute to core work processes. Contributive justice consists of two dimensions, the equal opportunity to engage in complex labor, and the equal opportunity to participate in decision-making processes. A measure was constructed to capture these dimensions, along with specific subdimensions. In a sample of 534 full-time employees, the results suggested that the contributive justice measure was a reliable two-factor measure that was discriminable from the other organizational justice dimensions and was positively correlated with other variables such as meaningful work, instrumental voice, inclusion, empowerment, and self-esteem. Contributive justice was also found to have incremental validity over the other organizational justice dimensions. These results suggest the importance of contributive justice as an aspect of organizational fairness and employee well-being.
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Title: MACHINE LEARNING APPROACHES FOR PROCESSING AND DECODING ATTENTION MODULATION OF SENSORY REPRESENTATIONS FROM EEG
Creator: saba-sadiya, sari
Date: 2023
Collection: Electronic Theses & Dissertations
Description: This thesis presents novel machine learning algorithms that achieve state-of-the-art performance on a variety of electroencephalography (EEG) tasks, including decoding, classification, and unsupervised / semi-supervised artifact detection and correction. These algorithms are then used within the scope of an EEG experiment that explores how attention to multiple items modulates sensory representations. Using a signal detection paradigm, we demonstrate that attending to multiple items impacts...
Show moreThis thesis presents novel machine learning algorithms that achieve state-of-the-art performance on a variety of electroencephalography (EEG) tasks, including decoding, classification, and unsupervised / semi-supervised artifact detection and correction. These algorithms are then used within the scope of an EEG experiment that explores how attention to multiple items modulates sensory representations. Using a signal detection paradigm, we demonstrate that attending to multiple items impacts the sensitivity of our participants, causing a sharp increase in false-alarm rates and only slightly decreasing hit-rate. We conclude that our behavioral and EEG decoding results contradict simultaneous attention guidance by multiple items (the multiple item template hypothesis).
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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: 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: 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: ASSESSING THE DETERMINANTS THAT PARSE THE LYASE AND MUTASE ACTIVITIES OF A PLANT AMINOMUTASE, AND DEVELOPING A REGIOSELECTIVE COUPLING REACTION FOR A TRIALKYL PYRAZINE.
Creator: Attanayake, Gayanthi Kumari
Date: 2021
Collection: Electronic Theses & Dissertations
Description: This dissertation is mainly contributed with two main projects. The first project is based on aminomutase enzyme. Recent discovery of MIO-dependent aminomutases on the biosynthetic pathways of biologically active, medicinal compounds in plants and microorganisms raises interest in further understanding how they catalyze β-amino acid building blocks. A tyrosine aminomutase isolated from Japanese rice, Oryza sativa (OsTAM), converts α-tyrosine to β-tyrosine (75%) and makes an acrylate, p...
Show moreThis dissertation is mainly contributed with two main projects. The first project is based on aminomutase enzyme. Recent discovery of MIO-dependent aminomutases on the biosynthetic pathways of biologically active, medicinal compounds in plants and microorganisms raises interest in further understanding how they catalyze β-amino acid building blocks. A tyrosine aminomutase isolated from Japanese rice, Oryza sativa (OsTAM), converts α-tyrosine to β-tyrosine (75%) and makes an acrylate, p-coumarate (25%), as a by-product. OsTAM is the first TAM to have slight phenylalanine aminomutase (PAM) activity (3%). This may not be surprising since the active sites of OsTAM and TcPAM from Taxus plants differ by only two residues (Y125 and N446 of OsTAM compared to C107 and K427 of TcPAM, respectively) positioned similarly near the aryl ring of their substrates. We anticipated by changing key active site residues of OsTAM to nonpolar side chains found in TcPAM would improve the binding of substituted phenylalanine substrates. Another feature of MIO-aminomutases, highlighted in a previous study,1 is a hinge-gate inner loop that opens and closes the entry to the active site. We changed hydrophilic for more hydrophobic residues within the OsTAM loop like in TcPAM to make it function as a more efficient PAM and expected the mutants to produce a greater proportion of the β-amino acid over acrylate compared to that made by wild-type OsTAM. Our data suggested that a combination of active site mutants and loop mutants generally increased the turnover of OsTAM for para-substituted substrates over the other meta- and ortho- regioisomers to their corresponding cinnamates, and not to the β-amino acids, as the major products. These findings suggest that while active site residues may be involved primarily in creating broad substrate selectivity, their role along with that of the inner loop to parse the reaction toward β-amino acids remains elusive.The second project mainly focused on regioselective synthesis of ethyl dimethyl pyrazine. Alkylpyrazines are important heterocyclic compounds used as flavorants in the food and beverage industries. This study developed a regioselective synthesis of 2-ethyl-3,5-dimethylpyrazine (235-EDMP) over its 3-ethyl-2,5-dimethyl isomer (325-EDMP). Our first attempts explored how steric direct the coupling orientations between diamines to diketones to access 235-EDMP. Also, various physical parameters of the reaction conditions were changed, such as reduced temperature, the order-of-addition of reactants, and supplementation with chiral zeolites (Montmorillonite phyllosilicates) to template the orientation of the coupling partners to direct the regiochemistry of the reaction. Each reaction trial resulted in 50:50 mixtures of the ethyl dimethylpyrazine regioisomers. An alternative approach was explored to direct the regioselectivity of the reactions; acyloins (α-hydroxy ketone) replaced the diketone as the electrophilic coupling reactant used in the previous trial experiments. The hydroxy ketone reactants were made biocatalytically with pyruvate decarboxylase (E.C. 4.1.1.1). The coupling reaction between 2-hydroxypentan-3-one and propane-1,2-diamine resulted in the desired 235-EDMP at >70% (~77 mg total) relative to 30% 325-EDMP in the product mixture. The 3-hydroxypentan-2-one acyloin congener bio catalyzed and reacted with propane-1,2-diamine as proof of principle to make 325-EDMP (~60% relative abundance, ~57 mg) over the 235-EDMP. These results hinted toward a mechanism directed by the hydroxy ketone electrophilicity and the sterics at each nucleophilic center of the diamine.
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Title: Safe Control Design for Uncertain Systems
Creator: Marvi, Zahra
Date: 2021
Collection: Electronic Theses & Dissertations
Description: This dissertation investigates the problem of safe control design for systems under model and environmental uncertainty. Reinforcement learning (RL) provides an interactive learning framework in which the optimal controller is sequentially derived based on instantaneous reward. Although powerful, safety consideration is a barrier to the wide deployment of RL algorithms in practice. To overcome this problem, we proposed an iterative safe off-policy RL algorithm. The cost function that encodes...
Show moreThis dissertation investigates the problem of safe control design for systems under model and environmental uncertainty. Reinforcement learning (RL) provides an interactive learning framework in which the optimal controller is sequentially derived based on instantaneous reward. Although powerful, safety consideration is a barrier to the wide deployment of RL algorithms in practice. To overcome this problem, we proposed an iterative safe off-policy RL algorithm. The cost function that encodes the designer's objectives is augmented with a control barrier function (CBF) to ensure safety and optimality. The proposed formulation provides a look-ahead and proactive safety planning, in which the safety is planned and optimized along with the performance to minimize the intervention with the optimal controller. Extensive safety and stability analysis is provided and the proposed method is implemented using the off-policy algorithm without requiring complete knowledge about the system dynamics. This line of research is then further extended to have a safety and stability guarantee even during the data collection and exploration phases in which random noisy inputs are applied to the system. However, satisfying the safety of actions when little is known about the system dynamics is a daunting challenge. We present a novel RL scheme that ensures the safety and stability of the linear systems during the exploration and exploitation phases. This is obtained by having a concurrent model learning and control, in which an efficient learning scheme is employed to prescribe the learning behavior. This characteristic is then employed to apply only safe and stabilizing controllers to the system. First, the prescribed errors are employed in a novel adaptive robustified control barrier function (AR-CBF) which guarantees that the states of the system remain in the safe set even when the learning is incomplete. Therefore, the noisy input in the exploratory data collection phase and the optimal controller in the exploitation phase are minimally altered such that the AR-CBF criterion is satisfied and, therefore, safety is guaranteed in both phases. It is shown that under the proposed prescribed RL framework, the model learning error is a vanishing perturbation to the original system. Therefore, a stability guarantee is also provided even in the exploration when noisy random inputs are applied to the system. A learning-enabled barrier-certified safe controllers for systems that operate in a shared and uncertain environment is then presented. A safety-aware loss function is defined and minimized to learn the uncertain and unknown behavior of external agents that affect the safety of the system. The loss function is defined based on safe set error, instead of the system model error, and is minimized for both current samples as well as past samples stored in the memory to assure a fast and generalizable learning algorithm for approximating the safe set. The proposed model learning and CBF are then integrated together to form a learning-enabled zeroing CBF (L-ZCBF), which employs the approximated trajectory information of the external agents provided by the learned model but shrinks the safety boundary in case of an imminent safety violation using instantaneous sensory observations. It is shown that the proposed L-ZCBF assures the safety guarantees during learning and even in the face of inaccurate or simplified approximation of external agents, which is crucial in highly interactive environments. Finally, the cooperative capability of agents in a multi-agent environment is investigated for the sake of safety guarantee. CBFs and information-gap theory are integrated to have robust safe controllers for multi-agent systems with different levels of measurement accuracy. A cooperative framework for the construction of CBFs for every two agents is employed to maximize the horizon of uncertainty under which the safety of the overall system is satisfied. The information-gap theory is leveraged to determine the contribution and share of each agent in the construction of CBFs. This results in the highest possible robustness against measurement uncertainty. By employing the proposed approach in constructing CBF, a higher horizon of uncertainty can be safely tolerated and even the failure of one agent in gathering accurate local data can be compensated by cooperation between agents. The effectiveness of the proposed methods is extensively examined in simulation results.
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Title: CHARACTERIZATION AND APPLICATION OF THE SURFACE CHARGE-INDUCED LONG-RANGE ORGANIZATION IN ROOM TEMPERATURE IONIC LIQUIDS
Creator: Wang, Yufeng
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Room temperature ionic liquids (RTILs) are salts characterized by a melting point below room temperature. RTILs have a wide range of applications, in areas ranging from supercapacitor energy storage to sequestration of toxic gas phase species and use as reusable solvents for selected organic reactions. All these applications stem from their unique physical and chemical properties, which remain understood to a limited extent. Among the issues of greatest importance is the extent to which RTILs...
Show moreRoom temperature ionic liquids (RTILs) are salts characterized by a melting point below room temperature. RTILs have a wide range of applications, in areas ranging from supercapacitor energy storage to sequestration of toxic gas phase species and use as reusable solvents for selected organic reactions. All these applications stem from their unique physical and chemical properties, which remain understood to a limited extent. Among the issues of greatest importance is the extent to which RTILs exist as dissociated ionic species, and the length scales over the organizations are seen to exist in them. Our group have reported previously on the existence of a surface charge-induced free charge density gradient in RTILs with a characteristic persistence length of ca. 50 μm. The existence of such a long-range organization in fluid medium is unusual. The overall goal of this work is to achieve a deeper understanding of this phenomenon, thereby providing an opportunity to better understand the local and long-range organization in RTILs and broad their potential applications which benefit from gaining such knowledge.The induced free charge density gradient (ρf) is probed by measuring the fluorescence anisotropy decay of a trace-level charged chromophore in the RTIL as a function of distance from the indium-doped tin oxide (ITO) support surface. In chapter 2, we characterize the structure-dependence of this charge-induced organization as a function of the RTIL constituent identity, and use these data to evaluate the magnitude of the induced free charge density gradient. The magnitude of this gradient is found to depend on the chemical structures of the cationic and anionic constituents of the RTIL used. In chapter 3, we characterize ρf in three different pyrrolidinium RTILs and two imidazolium RTILs, which aims to expand on prior results (chapter 2) on the chemical structure-dependence of ρf. Our measurements demonstrate that the magnitude of ρf depend on the alkyl chain length of RTIL cation. ρf is larger in the RTIL with longer cation alkyl chain. This dependence has been revealed in both pyrrolidinium and imidazolium ionic liquids. In chapter 4, we report on the existence of a surface charge-induced gradient in the RTIL refractive index (n) and evaluate the relationship between the gradient in n and ρf. Because ρf is uniaxial, the induced change in n is manifested as an induced birefringence. We characterize the ρf -dependent n of the RTIL with an apparatus that uses the RTIL as a lens. ρf is controlled by the surface charge density (σs) of the RTIL support. The far-field image of light passed through the RTIL lens as a function of σs is used to measure charge-induced changes in n of the RTIL. We demonstrate a significant modulation of the n with modest changes in σs of the RTIL support. This report places the relationship between ρf and RTIL dielectric response on a quantitative footing and suggests the utility of RTILs for electro-optic applications. In chapter 5, We report on the dependence of surface charge-induced birefringence in room temperature ionic liquids (RTILs) with different cation constituents. The induced birefringence is related to ρf in the RTIL. We find that in all cases the induced birefringence is proportional to the σs and, that the change in n nearest the ITO surface can be on the order of 30%. Our findings indicate that the induced birefringence depends more sensitively on the cation aliphatic substituent length than on the identity of the charge-carrying headgroup.
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Title: Life Cycle Monitoring of Reversible Adhesive Bonded Joints using Guided Waves
Creator: Palanisamy, Rajendra Prasath
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Recent advancements in automotive, aerospace, civil and wind-energy industries have resulted in an ever-increasing demand for lightweight, cost-effective, rapidly manufactured and recyclable/reusable of structural components. Adopting composite materials is a popular solution to achieve light-weighting, however it requires complex joining methods compared to traditional mechanical fasteners. Electromagnetic targeted heating of nano-Fe3O4 reinforced thermoplastic adhesives (Reversible-Adhesive...
Show moreRecent advancements in automotive, aerospace, civil and wind-energy industries have resulted in an ever-increasing demand for lightweight, cost-effective, rapidly manufactured and recyclable/reusable of structural components. Adopting composite materials is a popular solution to achieve light-weighting, however it requires complex joining methods compared to traditional mechanical fasteners. Electromagnetic targeted heating of nano-Fe3O4 reinforced thermoplastic adhesives (Reversible-Adhesive) is an emerging technique for rapid assembly, dis-assembly, and re-assembly of bonded composite parts. Alternate magnetic field applied to the dispersed ferromagnetic nanoparticles (FMNP) within a thermoplastic adhesive results in these particles acting as nano-heaters and rapidly heating the surrounding material resulting in melting and flow of the adhesive, which upon cooling forms a structural bond. This process can be repeated and hence termed reversible adhesive. Reversible-adhesive bonded composite structures (RBCS) offer a greater advantage over thermosets or mechanical joints such as rapid processing, easy repair, quick disassembly, and possible re-usability of components. However, it is essential to accurately measure the temperature of the adhesive during processing and repair, since overheating may cause chemical degradation and underheating may introduce improper bonds. Adhesively bonded composite structures provide a more uniform stress distribution in the bond-line than riveted joints resulting in higher fatigue life. However, modeling the physics behind crack initiation and propagation inside bonded regions is challenging especially under fatigue loading. As a result, real-time in-service bond monitoring is required to ensure structural safety. In addition to monitoring the damage state, prediction of damage area and remaining useful life of the component is imperative. Thus, this research work focusses on developing a life cycle monitoring solution for RBCS using the guided wave (GW) technique. Ultrasonic guided waves were made to propagate across the bond-line of the joint by exciting and sensing them using miniature piezoelectric wafers. Analysis of dispersion relations and dynamic wave propagation were performed using finite element modeling (FEM). Fundamental longitudinal mode L_0 at 35 kHz was found optimal for bond process monitoring. Mapping between the FE-simulated transmission coefficient of L_0 and actual temperature of the thermoplastic adhesive was established using the DMA test data. Real-time guided wave measurements were used as feedback in the discrete control of the induction heater so as to provide optimal bonding and prevent adhesive degradation. The developed ultrasonic technique was successfully validated by fiber-optic temperature sensing. Results indicate that the bondlines processed with GW control offer better ultimate strength compared to uncontrolled processing.Guided wave modal and frequency sensitivity analysis for fatigue damage was performed. Based on the analysis, symmetric mode at 85 kHz was found optimal for fatigue damage detection. Further, a damage propagation model based on Paris law was developed to estimate remaining useful life in terms of the GW signal features. Finally, the remaining useful life of the lap-joint was predicted and validated experimentally. One of the major advantages of reversible adhesive is its ability to repair/heal the damage. The controlled processing technique developed earlier was used for controlled healing of fatigue damaged joints. Experimental investigation proves the healed-bond line have returned to its original strength. A holistic approach of a complete lifecycle monitoring of bonded joints was aimed at increasing the confidence in the use of bonded joints relative to mechanical fasteners, and can be easily extended to other structural applications.
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Title: GENOMIC APPLICATIONS TO PLANT BIOLOGY
Creator: Hoopes, Genevieve
Date: 2021
Collection: Electronic Theses & Dissertations
Description: The study of the total nuclear DNA content of an organism, i.e., the genome, is a relatively new field and has evolved as sequencing technology and its output has changed. A shift from model species to ecological and crop species occurred as sequencing costs decreased and the technology became more broadly accessible, enabling new discoveries in genome biology as increasingly diverse species and populations were profiled. Here, a genome assembly and several transcriptional studies in multiple...
Show moreThe study of the total nuclear DNA content of an organism, i.e., the genome, is a relatively new field and has evolved as sequencing technology and its output has changed. A shift from model species to ecological and crop species occurred as sequencing costs decreased and the technology became more broadly accessible, enabling new discoveries in genome biology as increasingly diverse species and populations were profiled. Here, a genome assembly and several transcriptional studies in multiple non-model plant species provided new knowledge of molecular pathways and gene content. Over 157 Mb of the genome of the medicinal plant species Calotropis gigantea (L.) W.T.Aiton was sequenced, de novo assembled and annotated using Next Generation Sequencing technologies. The resulting assembly represents 92% of the genic space and provides a resource for discovery of the enzymes involved in biosynthesis of the anticancer metabolite, cardenolide. An updated gene expression atlas for 79 developmental maize (Zea mays L., 1753) tissues and five abiotic/biotic stress treatments was developed, revealing 4,154 organ-specific and 7,704 stress-induced differentially expressed (DE) genes. Presence-absence variants (PAVs) were enriched for organ-specific and stress-induced DE genes, tended to be lowly expressed, and had few co-expression network connections, suggesting that PAVs function in environmental adaptation and are on an evolutionary path to pseudogenization. The Maize Genomics Resource (http://maize.plantbiology.msu.edu/) was developed to view and data-mine these resources. Through profiling global gene expression over time in potato (Solanum tuberosum L.) leaf and tuber tissue, the first circadian rhythmic gene expression profiles of the below-ground heterotrophic tuber tissue were generated. The tuber displayed a longer circadian period, a delayed phase, and a lower amplitude compared to leaf tissue. Over 500 genes were differentially phased between the leaf and tuber, and many carbohydrate metabolism enzymes are under both diurnal and circadian regulation, reflecting the importance of the circadian clock for tuber bulking. Most core circadian clock genes do not display circadian rhythmic gene expression in the leaf or tuber, yet robust transcriptional and gene expression circadian rhythms are present.
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Title: DATA DRIVEN BASED ESTIMATION AND CONTROL FOR AUTOMOTIVE SYSTEMS
Creator: Tang, Jian
Date: 2022
Collection: Electronic Theses & Dissertations
Description: This dissertation focuses on predicting the system responses and using them to improve the automotive system performance based on the data-driven based algorithms. Two applications included are multivariable borderline knock prediction and control and tire-road friction coefficient estimation. Internal combustion engines are core components of traditional and hybrid passenger vehicles and also widely used for off road applications. When the combustion is limited by the engine knock, it is...
Show moreThis dissertation focuses on predicting the system responses and using them to improve the automotive system performance based on the data-driven based algorithms. Two applications included are multivariable borderline knock prediction and control and tire-road friction coefficient estimation. Internal combustion engines are core components of traditional and hybrid passenger vehicles and also widely used for off road applications. When the combustion is limited by the engine knock, it is desired to operate it as close to its borderline knock limit as possible to optimize combustion efficiency. Traditionally, this limit is detected by sweeping tests of related control parameters, which is expensive and time-consuming; and also, the detected borderline knock limit often is relatively conservative. When more advanced control parameters (subsystems) are added, these sweeping tests lead to tremendous higher test cost. An intelligent and efficient way to predict borderline knock without detailed knowledge of combustion dynamics is proposed. This supervised-learning based Bayesian optimization method is assisted by a surrogate model trained based on the system statistic properties. A two-control-parameter (spark timing and intake valve timing) case is demonstrated for optimizing two competing objectives (knock intensity (KI) and fuel economy). A complete borderline knock control structure is proposed and divided into three parts. The first part is about offline training with necessary modifications of the Bayesian optimization algorithm. Engine tests are conducted under two different operational conditions to obtain knock borderline limit, indicating the proposed algorithm is able to reduce required experimental budget (cost and time) significantly. The predicted mean Pareto front and its variance can be used to find the optimum control parameters at borderline knock limit for the best fuel economy possible. Smooth response surfaces of surrogate models can also be used as the initial model to be updated in real-time. The second part is an online updating process, based on the offline-trained surrogate model, using modified likelihood ratio controller. Principal component analysis indicated that spark timing is the most sensitive factor affecting the Pareto front. A two-buffer design was proposed to update the surrogate model under different rates so that both short-term compensation for environment changes and long-term for slow engine aging effect are covered. Both simulation and engine test results indicate that the proposed control strategy is able to update the machine-learned surrogate models in real-time, which outperforms the conventional knock control strategy and offline-trained knock limit, and especially reduces the conservativeness of borderline knock control significantly. Finally, to reduce cycle-to-cycle combustion variations, a real-time cycle-wised knock compensation scheme is developed based on the measured exhaust temperature when the engine is operated close to its knock borderline. To make model-based control possible, ?-Markov COVER (COVariance Equivalent Realization) system identification was used to obtain a linearized engine exhaust temperature model from change of spark timing to associated variations of exhaust temperature and knock intensity (KI). Accordingly, a Linear–Quadratic–Gaussian (LQG) controller is designed to minimizing the KI fluctuations based on change (?) of exhaust temperature. For the entire control architecture, results of three test scenarios indicated that the spark timing can be further advanced while maintaining the same knock intensity level due to reduced knock combustion variations. For the vehicle dynamics research, estimation of tire-road friction coefficient is very important due to new active safety control systems, especially for autonomous vehicles that rely on the accurate estimation of road surface conditions to find vehicle operational boundary and achieve the best performance possible. Several cause- and effect-based methods were proposed with their own limitations. A new evaluation criterion associated with slip-ratio is found based on CarSim simulation data on different road conditions; and strong correlation between proposed criterion and tire-road friction under different road surface conditions is observed. Note that the data-driven based method proposed in this dissertation only utilizes the statistic information from existing production vehicle sensors without increasing hardware cost. A computational cheap black-box model of proposed criterion and tire-road friction can be obtained and augmented with the existing dual-Kalman filter estimation algorithm, which improves tire-road friction estimation.
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Title: Total synthesis of pyrrole-alkaloid-like natural products and analogues
Creator: Hubbell, Grace E.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: The pyrrole-alkaloid family of natural products represents a wide range of biological activities, making the synthesis of these types of scaffolds a worthy endeavor. Of particular interest to our lab is the inhibitory activity of some of these natural products towards the human 20S proteasome, a validated target for the treatment of specific cancer including multiple myeloma and mantle cell lymphoma. With this in mind, the synthesis of scaffolds which bear structural similarity to these...
Show moreThe pyrrole-alkaloid family of natural products represents a wide range of biological activities, making the synthesis of these types of scaffolds a worthy endeavor. Of particular interest to our lab is the inhibitory activity of some of these natural products towards the human 20S proteasome, a validated target for the treatment of specific cancer including multiple myeloma and mantle cell lymphoma. With this in mind, the synthesis of scaffolds which bear structural similarity to these natural products was endeavored. Herein, the synthesis of pyrrole-alkaloid-like scaffolds is represented in several approaches: small molecule design of bromoindolophakellstatins, methodology development, and total synthesis. The development of a novel Rh(III)-catalyzed C-H activation/annulation between 2-imidazolones and N-pivaloyloxybenzohydroxamates is reported, which facilitates access to urea-fused tetrahydroisoquinolone scaffolds which are reminiscent of members of the pyrrole-alkaloid family. Efforts towards the syntheses of bromoindolophakellstatin small molecules is also described. Lastly, route development towards the total syntheses of nagelamide M and the ugibohlin natural products and the particular challenges associated with these approaches are discussed.
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Title: UNDERSTANDING CAREGIVER PERCEPTIONS ON SCHOOL PARTNERSHIPS
Creator: Rice, Darreth R.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Caregivers play an integral role in a child’s academic development, including their literacy development (Compton-Lilly et al., 2019; Cunningham, 2021; Edwards, 2004; Edwards, 2016; Smith, 2020; Volk, 2021). One way caregivers have supported their children’s literacy development is by assisting them with school activities at home. While some caregivers are willing to assist, schools must recognize that not all caregivers know what specific activities support the development of literacy skills...
Show moreCaregivers play an integral role in a child’s academic development, including their literacy development (Compton-Lilly et al., 2019; Cunningham, 2021; Edwards, 2004; Edwards, 2016; Smith, 2020; Volk, 2021). One way caregivers have supported their children’s literacy development is by assisting them with school activities at home. While some caregivers are willing to assist, schools must recognize that not all caregivers know what specific activities support the development of literacy skills. This partnership between home and school becomes especially important when Michigan schools are in the midst of a state-wide literacy policy aimed at improving students’ achievement levels on the state standardized assessments (Weyer, 2018). This study examined the perspective of the caregiver on this partnership during the implementation of a state-wide literacy policy. Overall, this study sought to understand the degree to which current school outreach to caregivers was aligned to current research on caregiver engagement. The study used the caregivers’ own words (Lumby, 2007), whenever possible. This study further investigated caregivers’ perceptions of the school’s outreach during the 2021-22 school year. Additionally, the study sought to discover caregivers’ desires for future partnerships with schools to continue to support their child in early literacy development. Lastly, this study analyzed the availability of resources, as reported by caregivers and found on school websites, as well as how aligned those resources were to current research on caregiver engagement. To undertake this endeavor, this qualitative study utilized an online survey focused on four distinct areas within a state undergoing a state-wide literacy policy. The four areas were chosen for their diversity in race, ethnicity, location, religions practices, population of immigrants, and population of migrant season farm workers. Following the survey, a subset of the caregivers were interviewed. After the interviews, a review of early literacy materials was conducted using the school’s websites. The review included at least one elementary school from each of the focal areas in the survey and interviews. Additionally, twenty-nine other schools, chosen through random interval sampling, were included in the review. The findings of this study shed light on the partial alignment between the current research and the school outreach to caregivers, specifically in relation to literacy activities focused on student literacy development. Using the frameworks of parental involvement (Epstein et al., 2019), intentionality (Edwards, 2016), and efficacy (Bandura, 1977), this study discovered resources offered to caregivers do not always align with intentionally. Current communication methods do not align with parental involvement framework’s tenet of two-way communication. Lastly, the supports offered to caregivers do not always favor efficacious behavior in caregivers. Implications for this work have wide-reaching opportunities for change in the culture of both policymaking and education. Policymakers can use these findings to understand the importance of including the voice of all policy actors. Teacher educators can view these findings to ensure they teach their teacher candidates how to communicate with caregivers. This includes having difficult conversations. School leadership can support current teachers with stronger engagement with caregivers by using the findings in this study and learning to listen to the caregivers and their concerns. Lastly, caregivers can also learn they are their child’s advocate, and they will have to do their part to work with the child.
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Title: Depression Detection in Social Media via Differential Text Embedding
Creator: alfadhli, Norah
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Deep learning models have shown promising results for depression detection using social media data (i.e., Twitter), but the difficulties of maintaining explainability and few-shot adaptation of models for new problems remain an open challenge. Another challenging aspect of the problem of depression detection in social media is the fact that the number of instances belonging to the depressed class are in a minority when compared to the number of instances belonging to the non-depressed class....
Show moreDeep learning models have shown promising results for depression detection using social media data (i.e., Twitter), but the difficulties of maintaining explainability and few-shot adaptation of models for new problems remain an open challenge. Another challenging aspect of the problem of depression detection in social media is the fact that the number of instances belonging to the depressed class are in a minority when compared to the number of instances belonging to the non-depressed class. This, especially, makes it harder for supervised machine learning algorithms to learn and predict depressed class instances.In this study, we proposed a simple solution to this problem by generating \textit{differential embeddings} using the Sentence BERT transformer architecture. More specifically, we proposed a few-shot model that can leverage state-of-the-art (SOTA) representation learning techniques and used it in supervised and unsupervised tasks. We constructed a small set of dysfunctional thought patterns in the embedding space, i.e., a set of clinically-backed depression symptoms. We then used SBERT embedding vectors to measure the similarities between different tweets and anchor points as a distance in the vector space, or fed them directly into the machine learning model. We assessed the capability of our approach on two different datasets. We trained supervised and unsupervised models using different approaches that were derived from Sentence-BERT and the anchor points. Results show that the proposed solution improved SBERT in both supervised and unsupervised tasks.
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