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Title: WE DON’T NEED TO KNOW WHAT WE SEE : MODEST MEDIATION OF BISTABLE PERCEPTION BY KNOWLEDGE
Creator: Zhang, Bobicheng
Date: 2022
Collection: Electronic Theses & Dissertations
Description: When faced with ambiguous visual input, an observer may have various perceptual interpre- tations even when the input remains unchanged. Indeed, such ambiguous displays can cause the observer to experience distinct perceptual interpretations in turn, unpredictably switching between them over time. Theories of such so-called multistable perception broadly fall into two categories: top-down theories that hold that perception in these cases depends strongly on higher-level cogni- tive factors...
Show moreWhen faced with ambiguous visual input, an observer may have various perceptual interpre- tations even when the input remains unchanged. Indeed, such ambiguous displays can cause the observer to experience distinct perceptual interpretations in turn, unpredictably switching between them over time. Theories of such so-called multistable perception broadly fall into two categories: top-down theories that hold that perception in these cases depends strongly on higher-level cogni- tive factors such as knowledge, and bottom-up theories which suggests more vital involvement of aspects of lower-order information processing such as local adaptation in the visual system. We evaluated whether the occurrence of perceptual reversals in the face of ambiguous input is related to the observer’s knowledge that the input is, indeed, ambiguous. We used an ambiguous animation that was designed such that subjects could report perceptual reversals without realizing the ambigu- ity. Subjects observed the animation, reported their perception, and filled out a questionnaire that assessed their knowledge of the animation’s ambiguity. We found that informed subjects reported slightly more perceptual switches than the other subjects, but that this between-group difference was very small compared to the lack of variability within each group between subjects who were aware of the ambiguity and those who were not. These findings suggests that knowledge of ambiguity can influence perception of ambiguous stimuli, but that this influence is relatively minor. This discrepancy between current findings and past work is discussed.
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Title: MEMBRANE-LOCALIZED TRANSCRIPTION REGULATORS : UNDERSTANDING POST-TRANSLATIONAL REGULATION AND SINGLE-MOLECULE DYNAMICS OF TCPP IN VIBRIO CHOLERAE
Creator: Demey, Lucas Maurice
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Vibrio cholerae is a Gram-negative gastrointestinal pathogen that has evolved an elegant regulatory system to precisely time production of essential virulence factors. A key step in this regulatory system is the transcription of a soluble AraC-like transcription factor, ToxT. ToxR and TcpP, two membrane-localized transcription regulators (MLTRs), positively regulate toxT. Much work has contributed to our understanding of TcpP and ToxR regulation, yet major gaps remain in our knowledge of...
Show moreVibrio cholerae is a Gram-negative gastrointestinal pathogen that has evolved an elegant regulatory system to precisely time production of essential virulence factors. A key step in this regulatory system is the transcription of a soluble AraC-like transcription factor, ToxT. ToxR and TcpP, two membrane-localized transcription regulators (MLTRs), positively regulate toxT. Much work has contributed to our understanding of TcpP and ToxR regulation, yet major gaps remain in our knowledge of these MLTRs. MLTRs are unique one-component signal transduction systems because they respond to extracellular stimuli by influencing gene transcription from their location in the cytoplasmic membrane. In Chapter 2, I explore the prevalence and diversity of MLTRs within prokaryotes to enhance our understanding of TcpP and ToxR. I show that MLTRs are far more common among prokaryotes than previously anticipated and that MLTRs are an understudied class of transcription regulators. In Chapter 3, I describe the use of super-resolution single-molecule tracking to investigate how TcpP, a model MLTR, identifies the toxT promoter. I provide evidence that TcpP binds to the toxT promoter independent of ToxR, and TcpP transitions to a specific diffusion state. The data support the first biophysical model for how TcpP-like MLTRs locate their target promoters. TcpP is subject to a form of post-translational regulation known as regulated intramembrane proteolysis (RIP). RIP of TcpP results in its complete inactivation, resulting in loss of virulence factor production. TcpH inhibits RIP of TcpP under certain pH and temperature conditions. In Chapter 4, I describe the mechanism TcpH employs to inhibit TcpP RIP while V. cholerae is present in the mouse gastrointestinal tract. I demonstrate that the dietary fatty acid α-linolenic acid enhances inhibition. I also show that α-linolenic acid promotes TcpH-mediated inhibition of TcpP RIP by increasing association of both proteins with detergent-resistant membrane (DRM) domains. My work provides the first evidence that DRMs influence virulence factor transcription in V. cholerae and that a dietary fatty acid promotes V. cholerae pathogenesis.
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Title: BLAME JUDGEMENTS FOR PAST ACTIONS OF GROUPS
Creator: Vallabha, Shree
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Historically, groups have committed innumerable atrocities, including genocide and slavery. I tested if people blame current groups for the actions of their past members and what underlies this blame. Current models of blame overlook the dimension of time and therefore have difficulty explaining this phenomenon. I hypothesized that perceiving higher (a) connectedness between past and present perpetrator groups, (b) unfulfilled obligations of perpetrator groups, (c) continued privilege of...
Show moreHistorically, groups have committed innumerable atrocities, including genocide and slavery. I tested if people blame current groups for the actions of their past members and what underlies this blame. Current models of blame overlook the dimension of time and therefore have difficulty explaining this phenomenon. I hypothesized that perceiving higher (a) connectedness between past and present perpetrator groups, (b) unfulfilled obligations of perpetrator groups, (c) continued privilege of perpetrator groups, and (d) continued harm of victim groups would facilitate higher blame judgements against current groups for the past. In a survey (N=518) using real events, I find results consistent with all the four hypotheses and some preliminary evidence for group differences in these relationships. I find that factors that link the present group to the past explain why groups are blamed for their past actions. These findings bring to light the deficiencies in existing theories of blame – calling into question its assumptions and incomplete criterion of judgement.
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Title: Evaluation of Operational Performance and Environmental Impact of a Commercial Scale Anaerobic Digester Utilizing Multiple Feedstocks
Creator: Dwilaksono, Fahmi
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Food waste and livestock manure become some of major sources that contribute to greenhouse gas (GHG) emissions in the U.S. Utilizing manure and food wastes as biogas feedstocks through anaerobic digestion (AD) process can improve renewable energy production while reducing the impact of climate change due to GHG emission from untreated organic wastes. This study evaluated the operational performance of Michigan State University’s commercial South Campus Anaerobic Digester (SCAD) as well as the...
Show moreFood waste and livestock manure become some of major sources that contribute to greenhouse gas (GHG) emissions in the U.S. Utilizing manure and food wastes as biogas feedstocks through anaerobic digestion (AD) process can improve renewable energy production while reducing the impact of climate change due to GHG emission from untreated organic wastes. This study evaluated the operational performance of Michigan State University’s commercial South Campus Anaerobic Digester (SCAD) as well as the environmental impact during its operation in 2014-2020. Evaluation of feedstock supplies quantity and output parameters of SCAD was conducted to understand the operational performance of the digester. A life cycle assessment (LCA) was done to know the environmental impact of SCAD by comparing it to the conventional waste management methods. Technoeconomic analysis was conducted to know the financial feasibility of SCAD as a commercial digester. The result shows that during its operation from 2014 to 2020, SCAD has processed 159,145 metric tons of feedstock from 18 different organic wastes to produce 15,165,156 kWh of electricity for MSU community. LCA results show that AD system possesses fewer environmental burdens in both global warming potential (GWP) and water eutrophication potential (WEP) compared to the conventional system. Technoeconomic analysis reveals that SCAD needs 21.5 years to accomplish its payback time, which is considered quite economically competitive.
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Title: THE RELATIONSHIP BETWEEN REASONS FOR PARTICIPATION AND ACHIEVEMENT
Creator: Arnold, Brian J.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Asynchronous Online Discussions (AODs) are often used to encourage online learner participation as they are believed to approximate the verbal interactions of face-to-face (F2F) learning environments while facilitating learners' metacognitive and critical thinking skills (Deng and Tavares, 2013). Despite mixed and somewhat context dependent research on the relationship between AOD participation and achievement, there appears to be a tendency among teachers and instructional designers to...
Show moreAsynchronous Online Discussions (AODs) are often used to encourage online learner participation as they are believed to approximate the verbal interactions of face-to-face (F2F) learning environments while facilitating learners' metacognitive and critical thinking skills (Deng and Tavares, 2013). Despite mixed and somewhat context dependent research on the relationship between AOD participation and achievement, there appears to be a tendency among teachers and instructional designers to encourage greater participation as it is believed that greater participation promotes greater achievement. Additionally, the act of online participation itself is often measured using visible artifacts like discussion and assignment posts submitted by students and evaluated by instructors and/or peers. This can lead educators to infer that the learners who participate more will earn higher grades than those who participate less.To explore this tendency, this quantitative descriptive study examined students enrolled in an introductory college English course (n = 76) using Learning Management System (LMS) activity reports and survey results. This was done to better understand the relationship between (what may appear to be limited) participation and course achievement. Similarly, the study sought to better understand the relationship between the learners' reasons for participation and their actual achievement. The primary results contribute to a wide range of studies that examine the relationship between participation and achievement. The results share a finding with two other studies in particular; Graff, (2005) and Wikle and West (2019), namely that this study showed no statistically significant correlation between participation and achievement for students who finished the course. Meaning that students who completed the course saw no statistically significant change in achievement for over or under participating. An unexpected finding of this study was that reasons for not participating contributed more to student behavior than reasons for posting.This study also showed that learners’ primary self-identified reasons for participating favored performance, information seeking, UX and interest; however, empirical performance data suggests that the relationship between learners' reasons for participation and their actual level of achievement is strongest when those reasons revolve around topic complexity, UX, time management and social risk. The gap between learners’ metacognitive perception of participation reasons and their data-driven demonstrable reasons is explored in this paper.
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Title: CONSTRAIN NEUTRON STAR PROPERTIES WITH SpiRIT EXPERIMENT
Creator: Tsang, Chun Yuen
Date: 2022
Collection: Electronic Theses & Dissertations
Description: The study of nuclear matter is an interdisciplinary endeavor that is relevant to both astrophysics and nuclear physics. Astrophysicists need to understand the properties of nuclear matter as some astrophysical objects are made of nuclear material. Nuclear physicists also need to understand the properties of nuclear matter as they are fundamental to the understanding of the existence of nuclei, their composition and the dynamics of nuclear collisions.Recent measurements of gravitational waves...
Show moreThe study of nuclear matter is an interdisciplinary endeavor that is relevant to both astrophysics and nuclear physics. Astrophysicists need to understand the properties of nuclear matter as some astrophysical objects are made of nuclear material. Nuclear physicists also need to understand the properties of nuclear matter as they are fundamental to the understanding of the existence of nuclei, their composition and the dynamics of nuclear collisions.Recent measurements of gravitational waves from binary neutron star mergers and precise neutron star radii from X-ray data of pulsars open a new channel for physicists to study nuclear matter. Such astronomical observations of neutron stars are sensitive to nuclear matter at high density that is usually inaccessible on earth. One of the ways physicists are able to reach such high density in laboratory is through heavy-ion collision. Transport model calculations that simulate nuclear collisions show that head-on collisions of heavy nuclei at high beam energy compress the overlapping region momentarily to densities comparable to that of the interior of neutron stars. To study neutron star where number of neutrons far exceeds that of protons, the dependence of nuclear properties on neutron-to-proton ratio (N/Z) needs to be understood. This dependence is quantified by the symmetry energy, which describes the difference in binding energy between pure neutron matter and matter with equal amount of protons and neutrons. The latter is also known as symmetric nuclear matter (SNM) which has been fairly well constrained. The amount of internal neutron star pressure that supports itself from gravitational collapse depends on the value of symmetry energy. Most of the existing heavy-ion collision data comes from collisions of stable isotopes. This limits the range of available N/Z in nuclear experiments. Extending results to a wider range of N/Z is one of the goals of SpiRIT experiment using projectiles provided by the cutting-edge Radioactive Isotope Beam Factory in RIKEN, Japan. SpiRIT time projection chamber (TPC) is constructed to measure charged pions spectra from the collision of neutron-rich system (132Sn + 124Sn), neutron-poor system (108Sn + 112Sn) and intermediate system (112Sn + 124Sn) at 270 MeV/u. By comparing fragmentation patterns for reactions with different number of neutrons, symmetry energy effects can be isolated. Some results from the analysis of pion spectra have been published and will be briefly reviewed in this work before we focus on light fragment observables that are also available from the TPC data. The data analysis software, with highlights on correction of some major detector aberrations, is discussed in details. Monte Carlo simulation of the SpiRIT TPC is then performed to understand the behavior of SpiRIT data and validate our data analysis procedure. Finally, Bayesian analysis is performed to compare transport model simulations with selected light fragment measurements using Markov-Chain Monte Carlo and Gaussian emulators. The observables are chosen to minimize systematic uncertainties from both the experiment and model. The posterior provides a comprehensive constraint on the symmetry energy parameters. Although previous analyses of pion spectra have already constrained the slope of symmetry energy at saturation density (L), its uncertainty can be reduced by 39% if pion results are combined with our new Bayesian posterior. The implications of symmetry energy constraint for neutron star will be discussed to demonstrate the importance of data from rare isotope heavy-ion collisions.
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Title: An Experimental Study of the Steadily Plunging Airfoil in Uniform-Shear Flow
Creator: Albrecht, Mitchell Baxter
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Freestream shear may be found in many unsteady aerodynamic situations, such as the fighter jet landing through the air wake of an aircraft carrier and the micro air vehicle (MAV) navigating wind currents around buildings in urban environments. Despite the prevalence of shear in aeronautics, literature concerning its effects on unsteady airfoils is scarce. To address the need to understand the fundamental, complex aerodynamics of moving airfoils coupled with freestream shear, a novel...
Show moreFreestream shear may be found in many unsteady aerodynamic situations, such as the fighter jet landing through the air wake of an aircraft carrier and the micro air vehicle (MAV) navigating wind currents around buildings in urban environments. Despite the prevalence of shear in aeronautics, literature concerning its effects on unsteady airfoils is scarce. To address the need to understand the fundamental, complex aerodynamics of moving airfoils coupled with freestream shear, a novel experimental setup was implemented to investigate the case of the airfoil steadily plunging across a canonical uniform-shear approach flow in a water tunnel. The effect of unsteadiness on the NACA 0012 airfoil in shear is examined by using a servo motion system to plunge the airfoil from the high- to low-speed extremes of the shear zone and varying the steady plunge speed. The aerodynamic load (lift and drag coefficients), streamwise velocity component of the flow, separation and reattachment locations, and boundary layer thickness are characterized such that the flow measurements are correlated to the observed behavior of the load measurements. First, uniform flow measurements are performed that confirm the unique experimental setup reproduces the expected Galilean transformation between the stationary and steadily plunging airfoils. It is confirmed that minimal blockage, confinement, or other artifacts result from the airfoil traversing over a large fraction of the test section's width. Molecular tagging velocimetry is uniquely implemented such that tag lines are created over the entire airfoil surface, image pairs are formed with the entire airfoil in view, and flow measurements are enabled for the moving airfoil. The airfoil aerodynamics are characterized in uniform flow at the same Reynolds numbers of the shear flow at three primary cross-stream locations of interest to provide baselines for the measurements in shear. For Reynolds numbers 13,500 and 16,500, a multi-region behavior is observed in the slope of the lift coefficient curve where the observed rapid rise in lift is related to the flow switching from an open separation to a closed separation bubble. By contrast, a steady rise in lift is observed at Reynolds number 9,800 which correlates to only open separation being observed.Next, the basic effect of shear on the stationary airfoil is studied by placing the airfoil at the three primary cross-stream locations in the shear flow, which also provides baseline measurements for the plunging airfoil in shear. It is observed that the current study reproduces the negative lift at zero angle of attack that is opposite of inviscid theory but consistent with recent computational and experimental literature from our group. A common observation in the lift and drag coefficient curves for the stationary airfoil in shear is asymmetry, as exemplified by the different stall behavior between positive and negative angles of attack. A multi-region behavior is observed among the lift curves which is connected to the airfoil switching from open separation to a closed separation bubble, like for uniform flow. Except for the Reynolds number 13,500 case, there is no observed difference in the angle of attack at which the flow switches from open separation to a closed separation bubble in shear compared to uniform flow. For the highest shear, lowest Reynolds number case, only open separation is observed at positive angles of attack, like the corresponding results in uniform flow.Finally, the effect of the steadily plunging airfoil motion in shear is studied in comparison with its stationary airfoil counterpart. For the range of dimensionless shear rates (0.40-0.69) and chord Reynolds numbers (9,800-16,500) in this study, it is observed that the slope of the lift coefficient curve for the plunging airfoil begins to rapidly increase at lower effective angle of attack than for the stationary airfoil, which is found to be a result of the flow reattaching at a lower effective angle of attack for the former than for the latter. Near stall, the magnitude of the lift coefficient on the plunging airfoil is typically greater than that on the stationary airfoil, which is found to be related to the reattachment point occurring farther upstream for the former than for the latter. It is found that the airfoil must plunge as slowly as 1% of the freestream speed for the load on the plunging airfoil to be well-approximated by that on the stationary airfoil for the same effective angle of attack and freestream conditions.
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Title: Abstract homomorphisms of algebraic groups : rigidity and group actions
Creator: Ruiter, Joshua
Date: 2022
Collection: Electronic Theses & Dissertations
Description: We investigate two related problems involving abstract homomorphisms between the groups of rational points of algebraic groups. First, we show that under appropriate assumptions, abstract representations of quasi-split special unitary groups associated with quadratic extensions of the field of definition have standard descriptions, i.e. can be factored as a group homomorphism induced by a morphism of algebras, followed by a homomorphism arising from a morphism of algebraic groups. This...
Show moreWe investigate two related problems involving abstract homomorphisms between the groups of rational points of algebraic groups. First, we show that under appropriate assumptions, abstract representations of quasi-split special unitary groups associated with quadratic extensions of the field of definition have standard descriptions, i.e. can be factored as a group homomorphism induced by a morphism of algebras, followed by a homomorphism arising from a morphism of algebraic groups. This establishes a new case of a longstanding conjecture of Borel and Tits. In the second part, we apply existing results on standard descriptions for abstract representations of Chevalley groups to study some rigidity properties of actions of elementary subgroups on algebraic varieties.The thesis is organized as follows. To provide context for the study of abstract homomorphisms, in section 1 we give a historical overview of key developments going back to Cartan's work on homomorphisms of Lie groups. In section 2, we prove our rigidity result for special unitary groups, using a strategy inspired by work of Igor Rapinchuk which depends crucially on the construction of certain algebraic rings associated to abstract representations. In section 3, we apply existing rigidity statements for representations of elementary subgroups of Chevalley groups to study rigidity properties of these groups acting on affine algebraic varieties and projective surfaces. We discuss some open questions and plans for future work in section 4. In the appendices, we collect some relevant background material on algebraic rings, and also provide details on the computations of commutator relations needed for the constructions in section 2.
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Title: NEUTRON SCATTERING AND TRANSPORT STUDIES OF QUANTUM MATERIALS
Creator: Zhang, Heda
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Quantum material is an multi-disciplinary research topic that continues to thrive in recent years. The term \textit{Quantum material} covers all systems which demonstrate physical phenomena beyond the scope of single-particle, semi-classical/quantum theory. Among many sub-fields of quantum materials, topological systems and strongly correlated systems are two topics which have receive growing attention from the scientific community. We begin with a discussion on a van der Waals magnet VI$_3$...
Show moreQuantum material is an multi-disciplinary research topic that continues to thrive in recent years. The term \textit{Quantum material} covers all systems which demonstrate physical phenomena beyond the scope of single-particle, semi-classical/quantum theory. Among many sub-fields of quantum materials, topological systems and strongly correlated systems are two topics which have receive growing attention from the scientific community. We begin with a discussion on a van der Waals magnet VI$_3$ in chapter three. VI$_3$ hosts ferromagnetism on a honeycomb lattice, which was one of the proposed models for topological magnon bands. There have been ample theoretical studies on ferromagnetic honeycomb lattice. However, there has not been any physical realization of such model. In our study, we show that the is a strong anomalous thermal Hall effect in VI$_3$, the underlying mechanism of which is the non-trivial topological nature of the magnon bands.In chapter four, we discuss our transport studies on some magnetic topological metals. The non-zero Berry curvature in the reciprocal space of topological metals can lead to anomalous transverse conductivities ($\kappa^A, \sigma^A, \alpha^A$) in the system. We found large anomalous transverse conductivities in TbMn$_6$Sn$_6$ and verified its intrinsic nature through first-principle calculations. Furthermore, we have found large exchange-bias behavior in TbMn$_6$Sn$_6$, which renders it as a promising system for anomalous Nernst effect based thermoelectric device. We will also discuss the topological Nernst effect observed in Fe$_3$Sn$_2$, which is potentially due to the Skyrmion bubble phase revealed by the Lorentz transmission electron microscopic studies.In chapter five, we discuss our inelastic neutron scattering study on a unique quantum spin chain system in Cu$_2$(OH)$_3$Br. The system hosts alternating ferromagnetic and anti-ferromagnetic spin chains with finite inter-chain couplings. This allows for the coexistence and interactions between magnons and spinons.
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Title: Investigation into the Performance of a Twin-Screw Compressor for Helium Compression
Creator: WILLIAMS, Tasha L.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: The screw compressor is a rotary positive displacement compressor, capable of compressing gas, vapors, and refrigerants. It is commonly used in various applications, including building and architecture, food, chemical process, pharmaceutical, metallurgical industries, refrigeration, air conditioning, vehicle superchargers and in cryogenic helium compression applications. The main characteristics that make the screw compressor attractive include high rotational speed, compactness, ability to...
Show moreThe screw compressor is a rotary positive displacement compressor, capable of compressing gas, vapors, and refrigerants. It is commonly used in various applications, including building and architecture, food, chemical process, pharmaceutical, metallurgical industries, refrigeration, air conditioning, vehicle superchargers and in cryogenic helium compression applications. The main characteristics that make the screw compressor attractive include high rotational speed, compactness, ability to maintain high efficiency over a wide range of operating conditions, long service life, and good reliability.An oil-flooded twin screw compressor is selected for investigation in the present work due to its reliability, large capacity, and capability to handle helium’s high heat of compression. Oil-flooded screw compressors refers to the oil being injected into the compression process and mixed with helium. The benefits of injected oil are cooling the helium, creating sealing between rotors, lubrication, and higher performance. In helium systems, the loss of power within the compression system is roughly two-thirds. With such a high loss in power, it is imperative to understand the need for investigating the design and thermodynamic parameters that impact the overall performance of these machines.Initially, a review of different types of compressors is carried out to determine the best suited compressor for helium compression in this current work. A numerical model was created to simulate the compression process of the screw compressor. The model consists of three segments: rotor curve generation, thermodynamic analysis, and performance prediction. The geometric data are a necessary input for the thermodynamic analysis; however, the thermodynamic analysis segment can be used for any rotor geometry. The thermodynamic analysis outputs the thermodynamic parameters as a function of the male rotation angle of helium and oil. The performance prediction determines characteristics of performance such as the volumetric and isothermal efficiencies. The model was validated using a commercial software, which was developed on the basis of extensive screw compressor data. The model predicted performance with reasonable accuracy varying at extreme case with a maximum of a 13\% difference. Using the numerical model, the oil analysis in this thesis determined that the compressor performance is highly dependent on oil injection parameters. The isothermal efficiency spanned from 49.9\% to 56.5\% when adjusting the mass flow rate and oil injection position of the oil. Experimental results determined that the discharge temperature has the biggest impact on compressor performance.
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Title: Numerical Methods for the Evolution of Fields with Applications to Plasmas
Creator: Sands, William A.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: In this dissertation, we present a collection of algorithms for evolving fields in plasmas with applications to the Vlasov-Maxwell system. Maxwell's equations are reformulated in terms of the Lorenz and Coulomb gauge conditions to obtain systems involving wave equations. These wave equations are solved using the methods developed in this thesis and are combined with a particle-in-cell method to simulate plasmas. The particle-in-cell methods developed in this work treat particles using several...
Show moreIn this dissertation, we present a collection of algorithms for evolving fields in plasmas with applications to the Vlasov-Maxwell system. Maxwell's equations are reformulated in terms of the Lorenz and Coulomb gauge conditions to obtain systems involving wave equations. These wave equations are solved using the methods developed in this thesis and are combined with a particle-in-cell method to simulate plasmas. The particle-in-cell methods developed in this work treat particles using several approaches, including the standard Newton-Lorenz equations, as well as a generalized momentum formulation that eliminates the need to compute time derivatives of the field data. In the first part of this thesis, we develop and extend some earlier methods for scalar wave equations, which are used to update the potentials in these formulations. Our developments are based on a class of algorithms known as the MOL$^T$, which combines a dimensional splitting technique with a one-dimensional integral equation method. This results in methods that are unconditionally stable, can address geometry, and are $\mathcal{O}(N)$, where $N$ is the number of mesh points. Our work contributes methods to construct spatial derivatives of the potentials for this class of dimensionally-split algorithms, which are used to evolve particles.The second part of this thesis considers core algorithms used in the MOL$^T$ and the related class of successive convolution methods in the context of high-performance computing environments. We developed a novel domain decomposition approach that ultimately allows the method to be used on distributed memory computing platforms. Shared memory algorithms were developed using the Kokkos performance portability library, which permits a user to write a single code that can be executed on various computing devices with the architecture-dependent details being managed by the library. We optimized predominant loop structures in the code and developed a blocking pattern that prescribes parallelism at multiple levels and is also more cache-friendly. Moreover, the proposed iteration pattern is flexible enough to work with shared memory features available on GPU systems.The final part of this thesis presents the particle-in-cell method for the Vlasov-Maxwell system, which leverages the methods for fields and derivatives developed in this work. The proposed methods are applied to several test problems involving beams. Our results are generally encouraging and demonstrate the capabilities of the proposed field solvers in simulating basic plasma phenomena. Additionally, our results serve to validate the generalized momentum formulation, which will be the foundation of our future work.
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Title: Advancing Field Emission Technology for High Power Injectors Operating in GHz and Beyond
Creator: Schneider, Mitchell E.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: As the next generation of electron injectors pushes to achieve higher gradient fields than ever before (>300 MV/m), they are driven to operate at higher frequencies (C-band through W-band). This shrinks the fabrication dimensions of these cavities, making field emission cathodes (FECs) an electron source of choice. Photoemission and thermionic sources are increasingly less suited as the complex laser transport schemes and heating source powering these injectors cannot provide the necessary...
Show moreAs the next generation of electron injectors pushes to achieve higher gradient fields than ever before (>300 MV/m), they are driven to operate at higher frequencies (C-band through W-band). This shrinks the fabrication dimensions of these cavities, making field emission cathodes (FECs) an electron source of choice. Photoemission and thermionic sources are increasingly less suited as the complex laser transport schemes and heating source powering these injectors cannot provide the necessary beam quality and may cause damage to the cathode or the injector itself. Carbon-based FECs have dominated the field emission sources R&D portfolio at DOD and DOE for the past 30 years across various high-power vacuum electronic device activities. Compared to traditional metal cathode technology, carbon-based technology cathodes are able to produce higher charge at low electric fields. Small intrinsic electron momentum and simple fabrication means these can become a leading technology, e.g., in the case of carbon nanotubes, nanoscale emitters make them attractive for producing high brightness beams. Specifically, diamond-based cathodes can handle extreme temperature and mechanical stresses that can occur under high gradient conditions.Most promising is a unique form of diamond, ultra-nano-crystalline diamond (UNCD) due to its material and electrical properties, which include being the most conductive form of diamond due to having the largest amount of grain boundaries. This cathode material allows us to explore new frontiers of cathode physics research, revealing a new field emission mechanism that diverges from classical Fowler Nordheim, termed space charge dominated Fowler Nordheim. This form of Fowler Nordheim is space charge dominated but can surpass the 1D Child Langmuir limit and approaches the 2D limit. This is not space charge limited Fowler Nordheim. This ability to decouple the extracted current from the space charge effects allows for the production of extremely xiii bright beams. This can be achieved by expanding the current cathode testing facilities beyond L band into C band so as to access these high fields and explore the temporal dynamics of a field emission source. This will yield the new physics knowledge needed to construct the world’s first custom-built injector specifically designed for field emission sources. Furthermore, exploring other forms of diamond cathode such as Diamond Field Emitter Arrays (DFEA) yields insight into the applications of transversely shaped beams for advanced accelerator applications such as emittance exchange beam lines. DFEA’s allow for the exploration of additional materials effects on the cathode performance such as the ballast resistance. This ultimately allows the derivation of a comprehensive concept map for the field emission dynamic regimes needed for the design of RF injectors. Previously, the theoretical assumption was that everything operated under classical Fowler Nordheim without any additional contributions from other materials properties or beam effects.
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Title: IMPROVING INTERACTIONS BETWEEN SELF-MEDICATING CONSUMERS AND OVER-THE-COUNTER PACKAGING WITH FRONT-OF-PACK AND PERSONALIZED LABELING AS STRATEGIES
Creator: LIU, LANQING
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Interactions between self-medicating consumers and the labeling of Over-the-Counter medications (OTC) influence the quality of information processing and hence the appropriateness of medication decisions. Our previous work on human-package interaction yielded evidence that early stages of processing important regulatory information were necessary to improve OTC packaging labeling and human-package interactions, and thus to inform appropriate decisions.Under the framework of Human-Package...
Show moreInteractions between self-medicating consumers and the labeling of Over-the-Counter medications (OTC) influence the quality of information processing and hence the appropriateness of medication decisions. Our previous work on human-package interaction yielded evidence that early stages of processing important regulatory information were necessary to improve OTC packaging labeling and human-package interactions, and thus to inform appropriate decisions.Under the framework of Human-Package Interaction model (H-PIM) and the types of directiveness of label designs, we proposed two novel labeling strategies: Front-of-Pack (FOP) labeling and personalized FOP labeling. The FOP strategy utilized the concepts of front-of-pack, boxing, grouping, and highlighting (HL), whereas the personalized FOP strategy further combined the concepts of the FOP labeling with augmented user interface and decision-support signals to assist the decision-making process for enhancing human-package interactions. To quantitatively investigate the effectiveness of those FOP labeling strategies, we firstly conducted a change detection test to evaluate the impact of the FOP labeling strategy on consumers’ attention to critical drug information. Additionally, we then developed an absolute judgement test to evaluate the effectiveness of the personalized FOP labeling strategy for assisting decision-making to benchmark the potential benefits of this strategy. The change detection test results indicated that the use of HL was effective and efficient to garner attentions. Specifically, the presence of HL increased change detection accuracy (HL:ME=0.932, SE=0.008; not HL:ME=0.770, SE=0.019; p<0.001)) and shortened the time to correctly detect changes. (HL: ME=3.790, SE=0.200; not HL:ME=5.073, SE=0.268; p<0.001). However, no evidence was found to suggest that the use of FOP labels enhanced the change detection accuracy. Moreover, the presence of FOP labels could prolong the time consumers used to correctly detect changes on the OTC packages than the standard labels. (FOP: ME=4.542, SE=0.238; standard: ME=4.233, SE=0.225; p=<0.001) These results may be caused by factors such as the FOP label location and unbalanced experimental design. Further studies are needed to gain more knowledge of this strategy. The absolute judgement test results supported the effectiveness and efficiency of the personalized FOP strategy on assisting consumer’s decision making. When introduced and educated with the concept of personalized FOP labeling, participants made decisions significantly more accurate (personalized FOP: ME=0.977, SE=0.007; standard: ME=0.933, SE=0.017; p=0.002) and faster (personalized FOP: ME=9.584, SE=0.854; standard: ME=19.052, SE=2.322; p<0.001) with the presence of personalized FOP labels compared to the presence of standard ones. In conclusion, this dissertation extends FOP labeling strategies from non-directive labels to personalized labels. The personalized FOP labeling could act as a very important role in improving the consumer-package interactions in the OTC market. Future studies can explore different designs and presentation modes of personalized labeling to identify the most effective design combination that can assist consumers’ information processing of OTC packaging and medical decision-making. More research is also needed to generalize the effectiveness of personalized labels on medication decision-making to various natural settings, different package types, and other populations.
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Title: Profiles of Student Engagement in Synchronous and Asynchronous Science Instruction
Creator: Schell, Matthew J.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Virtual instruction at the K-12 level is on the rise, yet we know very little about the ways students engage in different types of virtual instruction. The goals of this study were to: 1) describe high school students’ engagement in virtual science courses in terms of behavioral, affective, cognitive-value, and cognitive-self regulatory dimensions; 2) explore whether students’ engagement patterns across these dimensions differed depending on whether science activities were synchronous or...
Show moreVirtual instruction at the K-12 level is on the rise, yet we know very little about the ways students engage in different types of virtual instruction. The goals of this study were to: 1) describe high school students’ engagement in virtual science courses in terms of behavioral, affective, cognitive-value, and cognitive-self regulatory dimensions; 2) explore whether students’ engagement patterns across these dimensions differed depending on whether science activities were synchronous or asynchronous; and 3) examine whether these engagement patterns were associated with students’ final course grades or over-summer retention in a virtual high school. Students enrolled in a range of science courses at virtual high school (n=124) provided multiple reports (n=493) of their engagement during both synchronous and asynchronous learning activities. Latent Profile Analysis (LPA) conducted with these data suggested five distinct situational engagement profiles representing different constellations of the affective, behavioral, cognitive-value, and cognitive-self-regulatory dimensions of engagement. During synchronous instruction, students tended to engage in ways characterized by higher engagement in all dimensions compared with asynchronous instruction. These high engagement profiles were also associated with higher final course grades. There were few differences in the extent to which profiles predicted retention; however, lower self-regulation was associated with higher rates of retention.
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Title: MOLECULAR MECHANISMS INVOLVING PPARY IN THE PLACENTAL PATHOPHYSIOLOGY OF PREECLAMPSIA
Creator: Grimaldi, Brooke A.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Preeclampsia (PE) is a hypertensive disorder of pregnancy that effects 5-7% of all pregnancies and is the main cause of maternal-fetal morbidity and mortality worldwide. Despite significant advancements in obstetric and neonatal care, the prevalence of PE has remained steady over the past thirty years. There is no cure for PE other than placental and fetal delivery. The exact etiology of the PE syndrome remains unclear however, maternal vascular malperfusion and placental ischemia are...
Show morePreeclampsia (PE) is a hypertensive disorder of pregnancy that effects 5-7% of all pregnancies and is the main cause of maternal-fetal morbidity and mortality worldwide. Despite significant advancements in obstetric and neonatal care, the prevalence of PE has remained steady over the past thirty years. There is no cure for PE other than placental and fetal delivery. The exact etiology of the PE syndrome remains unclear however, maternal vascular malperfusion and placental ischemia are prominent features of the PE placenta that cause abnormal trophoblast differentiation and function. PE is considered a two-stage disease due to the ischemic-diseased placenta releasing altered secretion of placental proteins that negatively impact the maternal endothelium causing hypertension and end organ damage. The placental dysfunction is as well characterized by a reduction of the transcription factor, peroxisome proliferator activated receptor γ (PPARγ) which normally promotes trophoblast differentiation and healthy placental function. This dissertation has aimed to understand the link between PPARγ-driven trophoblast dysfunction and the imbalance of secreted proteins in PE. The restoration of these disrupted pathways by PPARγ actions in the placenta could offer potential therapeutic pathways to reverse the disease, extend pregnancy duration, and dampen maternal sequalae. This dissertation has utilized a collection of first trimester and term healthy and preeclamptic placentas in addition to immortalized cell lines to understand the effect of PPARγ activation by the drug, Rosiglitazone, during preeclamptic or in vitro ischemic conditions. These studies revealed several molecules that are regulated by PPARγ in the human placenta, including the anti-angiogenic soluble fms-like tyrosine kinase 1 (sFLT1) and the cytoprotective heme oxygenase (HO1). Both proteins were restored to normal levels in PE by treatment with the PPARγ activating drug, Rosiglitazone. Furthermore, PPARγ activation improved the anti-angiogenic environment in the PE placenta as shown by increasing the pro-angiogenic and growth factor proteins: placental growth factor, fibroblast growth factor 2, follistatin and heparin-binding epidermal growth factor. Placental activation of PPARγ further restored the angiogenic balance in PE through significant reductions in the anti-angiogenic proteins, angiopoietin-2 and soluble endoglin. Using an endothelial cell model representing the maternal response to the placental protein secretion, these works revealed improved angiogenesis in endothelial cells during culture with conditioned medium from Rosiglitazone-treated PE placentas. These studies collectively show the beneficial effects of placental activation of PPARγ to improve placental and vascular function in PE. Future works should aim to understand global changes from PPARγ regulation in the human placenta and focus on compounds that hold promise to be safely used during pregnancy with the goal to improve pregnancy outcomes.
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Title: Hadamard-Babich ansatz and fast Huygens sweeping method for point-source elastic wave equations in an inhomogeneous medium at high frequencies
Creator: Song, Jian
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Asymtotic methods are efficient for solving wave equations in the high frequency regime. In the thesis, we first develop a new asymptotic ansatz for point source elastic wave equations in an inhomogeneous medium. Then, we propose a fast Huygens sweeping method to construct a globally valid Green's functions in the presence of caustics. Finally, an Eulerian partial-differential-equation method is proposed to compute complex-valued eikonals in attenuating media.In Chapter 3, we develop the...
Show moreAsymtotic methods are efficient for solving wave equations in the high frequency regime. In the thesis, we first develop a new asymptotic ansatz for point source elastic wave equations in an inhomogeneous medium. Then, we propose a fast Huygens sweeping method to construct a globally valid Green's functions in the presence of caustics. Finally, an Eulerian partial-differential-equation method is proposed to compute complex-valued eikonals in attenuating media.In Chapter 3, we develop the Hadamard-Babich (H-B) ansatz for frequency-domain point source elastic wave equations in an inhomogeneous medium in the high-frequency regime. First, we develop a novel asymptotic series, dubbed Hadamard’s ansatz, to form the fundamental solution of the Cauchy problem for the time-domain point-source (TDPS) elastic wave equations in the region close to the source. Then, the governing equations for the unknown asymptotics of the ansatz are derived including the traveltime functions and dyadic coefficients. A matching condition is proposed to initialize the data of unknowns at the source. To treat singularity of dyadic coefficients at the source, smoother dyadic coefficients are then introduced. Directly taking the Fourier transform of Hadamard’s ansatz in time, we obtain the H-B ansatz for the frequency-domain point-source (FDPS) elastic wave equations. To verify the feasibility of the new ansatz, we truncate the ansatz to keep only the first two terms to compute the resulting asymptotic solutions. Numerical examples demonstrate the accuracy of our method.In Chapter 4, we propose a new truncated Hadamard-Babich ansatz based globally valid asymptotic method, dubbed the fast Huygens sweeping method, for computing Green's functions of FDPS elastic wave equations in inhomogeneous media in the high-frequency regime and in the presence of caustics. The first novelty of the fast Huygens sweeping method is that the Huygens-Kirchhoff secondary-source principle is used to integrate many locally valid asymptotic solutions to yield a globally valid asymptotic solution so that caustics can be treated automatically and implicitly. The precomputed asymptotic ingredients can be used to construct Green's functions of elastic wave equations for many different point sources and for arbitrary frequencies. The second novelty is that a butterfly algorithm is adapted to accelerate matrix-vector products induced by the discretization of the Huygens-Kirchhoff integral. The computational cost of the butterfly algorithm is O(NlogN) which is in nearly optimal complexity in terms of the total number of mesh points N. The prefactor of the complexity depends only on the specified accuracy and is independent of the frequency parameter. Numerical examples are presented to demonstrate the performance and accuracy of the new method. In Chapter 5, we propose a Eulerian partial-differential-equation method to solve complex-valued eikonals in attenuating media. In the regime of high-frequency asymptotics, a complex-valued eikonal is an essential ingredient for describing wave propagation in attenuating media, where the real and imaginary parts of the eikonal function capture dispersion effects and amplitude attenuation of seismic waves, respectively. Therefore, a unified framework to eulerianize several popular approximate real-space ray-tracing methods for complex-valued eikonals is proposed so that the real and imaginary parts of the eikonal function satisfy the classical real-space eikonal equation and a novel real-space advection equation, respectively, and we dub the resulting method the Eulerian partial-differential-equation method. We further develop highly efficient high-order methods to solve these two equations by using the factorization idea and the Lax-Friedrichs weighted essentially non-oscillatory (WENO) schemes. Numerical examples demonstrate that the proposed method yields highly accurate complex-valued eikonals, analogous to those from ray-tracing methods.
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Title: LISTERIA MONOCYTOGENES PLACENTAL COLONZATION AND CONSEQUENCES FOR PREGNANCY OUTCOME
Creator: Conner, Kayla Nicole
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Listeria monocytogenes (Lm) is a Gram-positive bacterium that causes the severe food-borne disease listeriosis. Listeriosis is particularly problematic in pregnant women as Lm colonizes the placenta, resulting in adverse pregnancy outcomes including stillbirth, miscarriage, and preterm labor. Despite numerous studies of placental listeriosis (PL) in various animal models, the mechanisms driving adverse outcomes following PL are largely uncharacterized. This dissertation addresses some of the...
Show moreListeria monocytogenes (Lm) is a Gram-positive bacterium that causes the severe food-borne disease listeriosis. Listeriosis is particularly problematic in pregnant women as Lm colonizes the placenta, resulting in adverse pregnancy outcomes including stillbirth, miscarriage, and preterm labor. Despite numerous studies of placental listeriosis (PL) in various animal models, the mechanisms driving adverse outcomes following PL are largely uncharacterized. This dissertation addresses some of the field’s knowledge gaps by analyzing the changes in placental gene expression and metabolism following infection with Lm and by characterizing a key Lm virulence factor, Internalin P (InlP), which plays a significant role in Lm placental colonization. Chapter 1 gives pertinent background information on the placenta, Lm, and PL and broadly addresses the knowledge gaps to be addressed by the rest of the dissertation. Chapter 2 describes an in vivo study of PL in mice. Infected and control placentas were analyzed for differences in gene expression profiles between the two groups. We identified an enrichment of genes associated with eicosanoid biosynthesis, suggesting perturbations in eicosanoid metabolism in infected tissues. By quantifying placental eicosanoid concentrations through mass spectrometry, we found a significant increase in the concentrations of several eicosanoids with known roles in inflammation and/or labor. This study provides a likely explanation for temporal disruptions of labor following placental infection. Chapters 3 and 4 discuss two studies of the Lm virulence factor InlP, a key player in placental colonization. InlP contributes to Lm’s placental pathogenesis likely by conferring the ability of Lm to transcytose through placental layers. Prior studies reported that no homologs of InlP exist in Listeria species other than Lm. Chapter 3 describes our discovery that at least two other Listeria species, L. ivanovii and L. seeligeri, encode InlP homologs. We characterized the domain architectures and genomic neighborhoods of these homologs and speculated on their implications for Listeria evolution. In chapter 4, I continue discussion of InlP and describe our identification and preliminary characterization of naturally occurring InlP variants. In this study, we used a bioinformatics approach to analyze Lm whole genome sequences (WGS) and identify InlP variants. We uncovered two InlP variants of interest in the Lm population. The first results from a start codon point mutation in the inlP gene, likely resulting in a truncated and potentially nonfunctional InlP protein product. The second is an InlP variant with a PRO to SER substitution in the InlP calcium binding loop, which is hypothesized to play a role in InlP activation or stabilization. These results provide two avenues for further investigation of InlP regulation and function and suggest the potential for InlP-dependent variation in placental colonization potential across Lm isolates. In chapter 5, I summarize this dissertation. This chapter reflects on the results, implications, and challenges of each study outlined in the prior chapters. I discuss the unique challenges faced due to the ongoing COVID-19 pandemic and its effects on my graduate training. Finally, I share concluding remarks and propose future directions for this project and the field of PL. Together, the chapters of this dissertation describe novel findings that contribute to the field by assessing genetic and metabolic changes to the placenta due to listeriosis and further characterizing a known key placental virulence factor.
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Title: STUDIES ON COMPLEX TASK NETWORKS BASED ON CONTEXTUAL SPECIFICS IN ELECTRONIC MEDICAL RECORDS
Creator: Kim, Inkyu
Date: 2022
Collection: Electronic Theses & Dissertations
Description: As organizational processes have become more interconnected and interdependent, contextual factors have become central to both information systems and process management. Despite the importance of context, few studies investigate the influence of contextual factors on the structure of business processes. Thus, in this dissertation, I examine the role of contextual specifics in the structure of the clinical documentation process using data from electronic health records in outpatient clinics....
Show moreAs organizational processes have become more interconnected and interdependent, contextual factors have become central to both information systems and process management. Despite the importance of context, few studies investigate the influence of contextual factors on the structure of business processes. Thus, in this dissertation, I examine the role of contextual specifics in the structure of the clinical documentation process using data from electronic health records in outpatient clinics. The dissertation includes three essays. In the first essay, I address the influence of internal contextual factors on enacted complexity. The findings of the first essay provide a unique opportunity to theorize on the specialization in enacted complexity of process by examining the effects of: 1) the number of roles and 2) specialization index. Contrary to expectations, I find that complexity decreases when a greater number of roles are involved in the clinical process and the roles are highly specialized. In the second essay, I turn my attention to the effects of exogenous shocks: When routines are disrupted, are some patterns of action more likely to be affected than others? I show that cohesion (defined as the consistency of context between pairs of actions) has a particularly strong influence on the persistence of action patterns. In essay three, I suggest a path prediction model in a process based on action sequence and its contextual specifics. The model uses a recurrent neural network that models both the observed sequence of actions and the contextual factors in the process. As expected, the results show that context can improve predictive models. In the case of outpatient medical clinics, the strongest improvement in accuracy comes from two attributes: 1) the workstation (location) where work is performed and 2) whether or not the system has been upgraded. Together, these essays represent a rigorous framework for analyzing the role of context in organizational processes and routines.
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Title: Evaluation of potential therapeutics for non-small cell lung cancer using 3D tumor spheroid models
Creator: Stoub, Hayden Eric
Date: 2022
Collection: Electronic Theses & Dissertations
Description: The development of novel and improved therapies for cancers requires robust means of investigation that both effectively recapitulate tumor biology while also utilizing resources efficiently. 3D tissue culture methods, namely spheroids and organoids, have emerged as an effective bridge between conventional in vitro methods and in vivo animal models in cancer research. This thesis provides background into lung cancer and the current landscape of 3D in vitro models of cancer, as well as...
Show moreThe development of novel and improved therapies for cancers requires robust means of investigation that both effectively recapitulate tumor biology while also utilizing resources efficiently. 3D tissue culture methods, namely spheroids and organoids, have emerged as an effective bridge between conventional in vitro methods and in vivo animal models in cancer research. This thesis provides background into lung cancer and the current landscape of 3D in vitro models of cancer, as well as detailing two studies in which multicellular tumor spheroids were used to investigate the therapeutic potential of candidate compounds. The first study uses an NCI-H358 multicellular tumor spheroid to investigate three compounds: Apigenin, a plant derived flavonoid; MSU42011, a novel retinoid x receptor (RXR) agonist; and CEP-1347, a mixed lineage kinase (MLK) inhibitor. It was found that Apigenin alone decreased the viability of spheroids, and that the combination of Apigenin and CEP-1347 synergistically decreased viability and increased cell death within the spheroids.The second study uses a murine lung adenocarcinoma tumor spheroid model to investigate the effects of MSU-71, a novel inhibitor of the nuclear factor erythroid 2-related factor (NRF2) pathway, on macrophage-induced invasion and migration. This compound blocked both migration in conventional experiments along with spheroid invasion, indicating its potential efficacy in preventing LUAD progression. This study also adapted the spheroid invasion model for use in multiple human LUAD cell lines and THP-1 conditioned medium. The findings presented herein demonstrate the versatility and value of 3D tumor spheroid models in the cancer drug development field.
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Title: EXAMINING THE RELATIONSHIP AMONG PHYSICAL ACTIVITY, STRESS, DEPRESSION, AND ANXIETY IN COLLEGE STUDENTS
Creator: Hayden, Dorian James
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Mental health challenges have been steadily increasing around college campuses, with consistent findings pointing to ethnic minorities and low socioeconomic groups adversely affected and needing more support than their counterparts. On the other end, physical activity (PA) has consistently been associated with positive mental health outcomes. Therefore, further understanding the relationship among race, socioeconomic status, and PA, as well as college students personal experiences on campuses...
Show moreMental health challenges have been steadily increasing around college campuses, with consistent findings pointing to ethnic minorities and low socioeconomic groups adversely affected and needing more support than their counterparts. On the other end, physical activity (PA) has consistently been associated with positive mental health outcomes. Therefore, further understanding the relationship among race, socioeconomic status, and PA, as well as college students personal experiences on campuses, is of great importance to improve college student well-being. This two-study dissertation sought to address these relationships. Study 1 evaluated differences in mental health across race, parental education (proxy for SES) and PA. Student obstacles to using on-campus mental health and PA resources were examined in a mixed methods design. Most of the data was collected prior to the establishment of COVID-19 restrictions at a large Midwest university. Mental health levels were anticipated to vary between the variables of race, parental education, and PA, which was partially supported. Results showed that low SES participants had significantly higher levels of depression, while PA was associated with lower levels of anxiety and stress. Study 2 sought to replicate findings of study 1 and test the relationships within the context of a diathesis-stress model that includes PA using an expanded sample of students drawn from a large Midwest university and a smaller East Coast university. In addition to replicating study 1 findings, study 2 yielded several themes that revealed common obstacles of college students and how they overcome those obstacles. The hypothesized relationship among race, SES, PA and mental health was partially supported. Specifically, participants whose parents or guardians had lower levels of education reported higher levels of anxiety, while there were significant differences in mental health across different levels of PA. The other goal of this study was to map the above relationship onto a PA moderating model, including variables of race, parental education, depression, stress, and anxiety, based on an adapted diathesis-stress model. This relationship was not supported by the data. Free response answers revealed interesting themes related to the college student experience and campus resources. Focus groups added to this through discussions on topics like the COVID-19 pandemic, mental health, and advice for future students. Data from study 2 was collected while COVID-19 pandemic restrictions were in place. Overall results expanded knowledge on the experience of COVID-19 on college campus and the interconnection between race, parental education, PA, and mental health. Further social relations were important for student wellbeing. Students’ also shared obstacles they faced with the use of on campus mental health and other resources.
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