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- Title
- Experimental and numerical investigation of confined premixed flame
- Creator
- Najim, Younis Mahal
- Date
- 2017
- Collection
- Electronic Theses & Dissertations
- Description
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Understanding the dynamics of premixed flames propagating during constant volume combustion is key to enhancing the performance of existing combustion devices, which provide 80% of the world’s energy supply, and reducing the impact of pollution on the environment. This work experimentally and numerically investigates confined premixed flame propagation in an initially quiescent mixture. Three combustion chambers are used; a curved wave disc engine channel and rectilinear channels of aspect...
Show moreUnderstanding the dynamics of premixed flames propagating during constant volume combustion is key to enhancing the performance of existing combustion devices, which provide 80% of the world’s energy supply, and reducing the impact of pollution on the environment. This work experimentally and numerically investigates confined premixed flame propagation in an initially quiescent mixture. Three combustion chambers are used; a curved wave disc engine channel and rectilinear channels of aspect ratio 7 and 10. The mixture is methane/air and syngas (H2/CO)/air initially at atmospheric pressure and room temperature. The channel walls are assumed to be isothermal to incorporate the effect of heat transfer. For two-dimensional analysis, the reaction rate is modeled using both detailed and reduced kinetic mechanisms. The mass diffusion is investigated using three different diffusion models with different levels of approximation; the multicomponent diffusion model of Chapman-Enskog including the Soret effect; the mixture-averaged model; and constant Lewis number. For three-dimensional analysis, a large eddy simulation coupled with the transport equation of the reaction progress variable is used. In this work, the reaction rate predicted using the Boger model of algebraic flame surface density is modified by incorporating a transient flame speed that accounts for the variation in the temperature and pressure of the unburned gases. The experimental measurements include schlieren photography to track the flame structure and propagation speed, and the pressure-time history during the combustion process is measured by a pressure sensor mounted in the channel wall. The experimental measurements validate the numerical simulation results and provide further understanding of the flame and pressure dynamics. Unlike behavior previously reported in straight or 90◦ bend channels, premixed flame propagation in the wave disc engine channel exhibits different features: the convex tulip flame converts back into a concave flame and thus reveals the influence of channel geometry on flame evolution. The experiments show that the rate of pressure change eventually becomes negative mainly due to heat losses that engender a correspondingly slower flame propagation during the final stage of burning. The analysis of the numerical results reveals the effect of the interaction between the flame front, pressure field, and flame-induced flow on flame evolution during all stages of flame structure development. The results also demonstrate that both multicomponent diffusion with the Soret effect and the mixture-averaged model produce slightly different results in flame speed, structure, peak temperature, and average pressure for the methane/air mixture, while the deviation is more pronounced for syngas flames. The methane/air flame produced by the unity Lewis number model, however, lags behind its counterparts during early stages and dramatically accelerates, at which time the values of peak temperature and average pressure show unrealistic behavior. Furthermore, unity Lewis number flames develop an artificial second tulip flame after the first tulip flame is annihilated. This second tulip flame is neither observed in the Chapman-Enskog and mixture-average simulations, nor in the experiments. This reveals the role of the Lewis number in the intrinsic thermodiffusive flame instabilities and tulip flame formation. The three-dimensional simulation uncovers an interesting behavior for the flame structure that is introduced here as a “transverse tulip” flame, which has not been previously reported. The “transverse tulip” flame evolves in the direction perpendicular to that of the initial tulip flame after the latter undergoes the transition from cusped convex back to the concave finger shape. The commonly used Zimont model produces an unrealistically diffused flame front. The large eddy simulation coupled with the here-modified algebraic flame surface density overcomes this issue and reproduces the experimental observations of the flame structure, pressure-time history, and burning time with good agreement.
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- Title
- Fluid animation on deforming surface meshes
- Creator
- Wang, Xiaojun (Graduate of Michigan State University)
- Date
- 2017
- Collection
- Electronic Theses & Dissertations
- Description
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"We explore methods for visually plausible fluid simulation on deforming surfaces with inhomogeneous diffusion properties. While there are methods for fluid simulation on surfaces, not much research effort focused on the influence of the motion of underlying surface, in particular when it is not a rigid surface, such as knitted or woven textiles in motion. The complexity involved makes the simulation challenging to account for the non-inertial local frames typically used to describe the...
Show more"We explore methods for visually plausible fluid simulation on deforming surfaces with inhomogeneous diffusion properties. While there are methods for fluid simulation on surfaces, not much research effort focused on the influence of the motion of underlying surface, in particular when it is not a rigid surface, such as knitted or woven textiles in motion. The complexity involved makes the simulation challenging to account for the non-inertial local frames typically used to describe the motion and the anisotropic effects in diffusion, absorption, adsorption. Thus, our primary goal is to enable fast and stable method for such scenarios. First, in preparation of the material properties for the surface domain, we describe textiles with salient feature direction by bulk material property tensors in order to reduce the complexity, by employing 2D homogenization technique, which effectively turns microscale inhomogeneous properties into homogeneous properties in macroscale descriptions. We then use standard texture mapping techniques to map these tensors to triangles in the curved surface mesh, taking into account the alignment of each local tangent space with correct feature directions of the macroscale tensor. We show that this homogenization tool is intuitive, flexible and easily adjusted. Second, for efficient description of the deforming surface, we offer a new geometry representation for the surface with solely angles instead of vertex coordinates, to reduce storage for the motion of underlying surface. Since our simulation tool relies heavily on long sequences of 3D curved triangular meshes, it is worthwhile exploring such efficient representations to make our tool practical by reducing the memory access during real-time simulations as well as reducing the file sizes. Inspired by angle-based representations for tetrahedral meshes, we use spectral method to restore curved surface using both angles of the triangles and dihedral angles between adjacent triangles in the mesh. Moreover, in many surface deformation sequences, it is often sufficient to update the dihedral angles while keeping the triangle interior angles fixed. Third, we propose a framework for simulating various effects of fluid flowing on deforming surfaces. We directly applied our simulator on curved surface meshes instead of in parameter domains, whereas many existing simulation methods require a parameterization on the surface. We further demonstrate that fictitious forces induced by the surface motion can be added to the surface-based simulation at a small additional cost. These fictitious forces can be decomposed into different components. Only the rectilinear and Coriolis components are relevant to our choice of local frames. Other effects, such as diffusion, adsorption, absorption, and evaporation are also incorporated for realistic stain simulation. Finally, we explore the extraction of Lagrangian Coherent Structure (LCS), which is often referred to as the skeleton of fluid motion. The LCS structures are often described by ridges of the finite time Lyapunov exponent (FTLE) fields, which describe the extremal stretching of fluid parcels following the flow. We proposed a novel improvement to the ridge marching algorithm, which extract such ridges robustly for the typically noisy FTLE estimates even in well-defined fluid flows. Our results are potentially applicable to visualizing and controlling fluid trajectory patterns. In contrast to current methods for LCS calculation, which are only applicable to flat 2D or 3D domains and sensitive to noise, our ridge extraction is readily applicable to curved surfaces even when they are deforming. The collection of these computational tools will facilitate generation of realistic and easy to adjust surface fluid animation with various physically plausible effects on surface."--Pages ii-iii.
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- Title
- Intrinsic motivation in a blended learning environment : an exploratory study
- Creator
- Zeller, Angelina N.
- Date
- 2018
- Collection
- Electronic Theses & Dissertations
- Description
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It is estimated that 75% of all K-12 schools in the United States incorporate some form of e-learning within their instructional program offerings (Watson, Pape, Murin, Gemin, & Vashaw, 2014). However, current research relating to the success of virtual learners is providing mixed results at best, with virtual course completion rates hovering around 58% (Freidhoff, 2017) and attrition rates as high as 80% in some e-learning courses (Bawa, 2016; Bonk, 2001; Moshinskie, 2001).The purpose of...
Show moreIt is estimated that 75% of all K-12 schools in the United States incorporate some form of e-learning within their instructional program offerings (Watson, Pape, Murin, Gemin, & Vashaw, 2014). However, current research relating to the success of virtual learners is providing mixed results at best, with virtual course completion rates hovering around 58% (Freidhoff, 2017) and attrition rates as high as 80% in some e-learning courses (Bawa, 2016; Bonk, 2001; Moshinskie, 2001).The purpose of this study was to understand the degree to which students who were new to a blended learning program were motivated toward tasks aimed at developing 1) a sense of community; 2) e-skills, 3) self-regulation, and 4) goal-setting; and to examine whether motivation in these domains is predictive of continued enrollment, progressing in school and academic engagement during their first semester in the program. This study provided an intimate window through which to view students’ sociodemographic characteristics, motivations and outcomes in this cyber school blended learning model, with key findings related to sociodemographic background and motivational characteristic variables statistically significant to important education outcomes.
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- Title
- Affective aesthetics and the social politics of Neoliberalism in New Extremism cinema
- Creator
- Clark, Cameron
- Date
- 2017
- Collection
- Electronic Theses & Dissertations
- Description
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This thesis investigates the aesthetics of transgression in New Extremism cinema for the ways in which they inform, and are mutually informed by, neoliberal affect and social politics. Although negative affect and spectatorial embodiment are often central to critical discourse on New Extremism, this thesis instead attends to the interlocking aesthetic, narrative, and spatio-temporal expressions of affect as they correlate with neoliberal politics of respectability and reproduction. By...
Show moreThis thesis investigates the aesthetics of transgression in New Extremism cinema for the ways in which they inform, and are mutually informed by, neoliberal affect and social politics. Although negative affect and spectatorial embodiment are often central to critical discourse on New Extremism, this thesis instead attends to the interlocking aesthetic, narrative, and spatio-temporal expressions of affect as they correlate with neoliberal politics of respectability and reproduction. By deploying feminism and queer theory, this thesis locates positive, productive potentials within formal expressions of negative affect that mobilize a political critique of the violences within each film. In so doing, the selected film examples--Fabrice Du Welz's Calvaire (2004), Marina de Van's Dans ma peu (2002), Olivier Assayas's Demonlover (2002), Bruno Dumont's Twentynine Palms (2004), François Ozon's Criminal Lovers (2001), Alain Guiraudie's Stranger by the Lake (2014), to name a few--portray the shifting relations between politics, gender, and sexuality in the neoliberal present and offer critical alternatives for how such developments have impacted and impeded sociality.
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- Title
- Effects of dimensions of word knowledge and their accessibility on different levels of reading comprehension in adolescent EFL learners
- Creator
- Choi, Yunjeong
- Date
- 2017
- Collection
- Electronic Theses & Dissertations
- Description
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Researchers have investigated that different dimensions of word knowledge (breadth versus depth) may play distinct roles in second language (L2) reading comprehension. Yet, little research has addressed how learners’ efficiency of accessing those dimensions of knowledge functions in their comprehension (i.e., the issue of knowledge availability versus accessibility in Cremer and Schoonen, 2013), not to mention comprehension at different levels. To fill gaps in previous research and enrich our...
Show moreResearchers have investigated that different dimensions of word knowledge (breadth versus depth) may play distinct roles in second language (L2) reading comprehension. Yet, little research has addressed how learners’ efficiency of accessing those dimensions of knowledge functions in their comprehension (i.e., the issue of knowledge availability versus accessibility in Cremer and Schoonen, 2013), not to mention comprehension at different levels. To fill gaps in previous research and enrich our knowledge about the lexical basis of L2 reading comprehension, the present study examined how different dimensions of L2 word knowledge and their respective accessibility function concurrently in explaining different levels of L2 reading comprehension in adolescent English as a Foreign Language (EFL) learners in Korea. To achieve this research goal, the present study defined lexical competence by distinguishing between vocabulary breadth and depth knowledge as well as between knowledge availability and accessibility. A number of tasks were employed to measure participants’ lexical competences: three paper-and-pencil tests for knowledge availability and three researcher-developed, computer-based tests for knowledge accessibility documenting response accuracy as well as latency. Reading comprehension was measured with the Gates-MacGinitie Reading Comprehension Test (MacGinitie & MacGinitie, 1992), which assessed both literal and inferential comprehension. In addition, the participants’ working memory and grammatical knowledge were also measured. The following key research findings were revealed. First, Confirmatory Factor Analysis analyses confirmed that knowledge of individual word meanings (breadth availability) and the ability to activate that knowledge efficiently (breadth accessibility), and knowledge of meaning relations among words (depth availability) and the ability to access that knowledge efficiently (depth accessibility) are distinctive constructs under the conceptualization of lexical competence. Second, availability and accessibility of depth knowledge were the only predictors that made significant contributions to reading comprehension when the impacts of those of breadth knowledge and working memory were controlled for. Within vocabulary depth, availability played a more important role than did accessibility. Availability and accessibility of breadth knowledge made no unique contribution to reading comprehension over and beyond those of depth knowledge. Third, the patterns of predictive roles of each lexical competence in reading comprehension did not seem substantially different between literal and inferential comprehension, confirming a stronger impact of depth knowledge, both availability and accessibility, than of breadth knowledge, and of availability of depth knowledge than of accessibility. However, the involvement of depth knowledge, particularly availability, seemed greater in inferential comprehension than in literal comprehension. These findings enriched our understanding about the lexical basis of L2 reading comprehension, particularly, the importance of efficient access to semantic network knowledge for textual reading and potentially differential involvement of semantic network knowledge in different levels of comprehension. Pedagogically, they suggested that vocabulary instruction should provide a learning environment where new words are provided in a meaningful reading context so that learners can establish a semantic network in their lexicon and continue developing, expanding, and consolidating the lexicon as they learn new words.
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- Title
- Transparent multijunction organic photovoltaics
- Creator
- Young, Margaret (Process engineer)
- Date
- 2017
- Collection
- Electronic Theses & Dissertations
- Description
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"The widespread adoption of conventional solar cells based on inorganic semiconductors has been gaining traction in recent years but is still often hindered by high cost and lack of aesthetic appeal. Transparent organic semiconductor-based solar cells that selectively absorb in the UV and the NIR enable integration into building windows, automobiles, and consumer electronics in ways that traditional solar cells cannot. Moreover, integration onto existing infrastructure reduces the racking and...
Show more"The widespread adoption of conventional solar cells based on inorganic semiconductors has been gaining traction in recent years but is still often hindered by high cost and lack of aesthetic appeal. Transparent organic semiconductor-based solar cells that selectively absorb in the UV and the NIR enable integration into building windows, automobiles, and consumer electronics in ways that traditional solar cells cannot. Moreover, integration onto existing infrastructure reduces the racking and installation cost. In this work, we investigate routes to improve the efficiency of transparent solar cells by utilizing multijunction architectures. A transfer-matrix optical interference model is developed as a framework to optimize the full device stack considering the angle-dependent PV performance that is critical for matching subcell photocurrents in series tandem solar cells. In addition, a new method of fine tuning energy levels of low-bandgap small molecules with infrared selective absorption was demonstrated using a series of organic heptamethine salts. By exchanging the counterion from a small, hard anion to a fluorinated weakly coordinating anion, the frontier energy of the salt is shown to shift without affecting the bandgap, thus enabling simultaneous optimization of photocurrent generation of photovoltage. We further utilize this tunability to develop heptamethine molecules with absorption as deep as 1600 nm, the deepest infrared photo-response demonstrated to date with organic small molecules ideal for multijunction integration. Ultimately, transparent solar cells are an exciting new paradigm for solar deployment enabled by organic and excitonic semiconductors that offer a pathway to integrate solar onto virtually any surface without impacting the view."--Page ii.
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- Title
- Empirical analyses of regional innovation and economic growth in the United States
- Creator
- Aryal, Giri Raj
- Date
- 2018
- Collection
- Electronic Theses & Dissertations
- Description
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Much of the innovation creation literature is focused on urban firms and areas or relies heavily on data based on these; less studied are rural firms or rural areas in this regard. The goal of this dissertation is to explore the drivers of rural-urban innovation gap and the link between regional innovation and economic growth and propose policies to mitigate regional innovation ecosystem deficiencies and impediments that contribute to the gap. In my first essay, I analyze heterogeneity in...
Show moreMuch of the innovation creation literature is focused on urban firms and areas or relies heavily on data based on these; less studied are rural firms or rural areas in this regard. The goal of this dissertation is to explore the drivers of rural-urban innovation gap and the link between regional innovation and economic growth and propose policies to mitigate regional innovation ecosystem deficiencies and impediments that contribute to the gap. In my first essay, I analyze heterogeneity in inventiveness across urban and rural counties is using a spatial autoregressive negative binomial regression model, considering spatial spillover effects, creative class population, industry characteristics, human capital, and other regional factors influencing innovation. Results indicate that drivers of invention, namely a college-educated labor force and diversity of high-tech industries are common across all counties types, but urban inventive advantage persists due to agglomeration economies, higher number of universities, and higher shares of high-tech firms, professional services and immigrants. Consistent with the creative class hypothesis, population share of college graduates in creative disciplines also positively contributes to inventive output in urban counties. However, the effects of spatial spillovers and mobile phone technology penetration are stronger for rural counties, suggesting that policies promoting rural centers of innovation, technological diversity, and communication infrastructure in rural counties could help mitigate the urban-rural innovation gap. My second essay explores the interdependence between regional innovation and economic growth by accounting for possible endogenous relationships among regional innovation, income growth, employment and population. It draws on data for 3,038 counties in the 48 contiguous states of the United States collected from several publicly available sources for 2009-13. Endogeneity tests using instrumental variable regressions show that regional innovation and economic growth have endogenous relationships. Considering the endogeneity and estimating the system of simultaneous equations for regional innovation and economic growth using three stage least squares (3SLS) method, I find that innovation belongs to system of regional growth. Further, reduced form estimates of the 3SLS results suggest that policies promoting regional clusters of high-tech firms and capitalizing on the knowledge potential of the immigrants are likely to reinforce both regional innovation rates and economic growth. My third essay analyzes the characteristics that potentially influence innovation creation across rural and urban firms employing a survey dataset from 2014 National Survey of Business Competitiveness combined with secondary data reflecting the regional business and innovative environments where these firms operate. The number of patent applications filed by these firms measures their innovation creation, and the paper employs a negative binomial regression estimation for analysis. The findings of this essay show that, after controlling for industry, county and state factors, rural and urban firms differ in their innovation creation characteristics and behaviors, suggesting that urban firms capitalize on their resources better than rural firms. Other major findings of the essay provide evidence that (i) for rural firms, the influence of university R&D is relevant to innovation creation, but their perception of university provided information is not significant and (ii) rural firms that are willing to try, but fail, in terms of innovation creation have a slight advantage over other rural firms less willing to take on the risk.
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- Title
- EFFECT OF GATE-OXIDE DEGRADATION ON ELECTRICAL PARAMETERS OF SILICON AND SILICON CARBIDE POWER MOSFETS
- Creator
- KARKI, UJJWAL
- Date
- 2019
- Collection
- Electronic Theses & Dissertations
- Description
-
The power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is recognized as a crucial component of many power-electronic systems. The physical structure of both Silicon and Silicon Carbide power MOSFETs require an oxide layer as a dielectric material between their gate terminal and the semiconductor surface. The gate-oxide material, which is predominantly silicon dioxide, slowly degrades under the presence of an electric field. Over time, the degradation process significantly alters...
Show moreThe power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is recognized as a crucial component of many power-electronic systems. The physical structure of both Silicon and Silicon Carbide power MOSFETs require an oxide layer as a dielectric material between their gate terminal and the semiconductor surface. The gate-oxide material, which is predominantly silicon dioxide, slowly degrades under the presence of an electric field. Over time, the degradation process significantly alters the electrical parameters of power MOSFETs, causing a negative impact on performance, reliability, and efficiency of power converters they are used in. In order to monitor this, the electrical parameters are utilized as precursors (or failure indicators) of gate-oxide degradation.Despite extensive investigation of gate-oxide degradation in Silicon (Si) power MOSFETs, the research literature has not attributed a consistent variation pattern to its gate-oxide degradation precursors. This dissertation investigates the variation pattern of existing precursors: a) threshold voltage, b) gate-plateau voltage, and c) on-resistance. While confirming the previously reported dip-and-rebound variation pattern of the threshold voltage and the gate-plateau voltage, a similar dip-and-rebound variation pattern is also identified in the on-resistance of Si power MOSFETs. Furthermore, a new online precursor of gate-oxide degradation— the gate-plateau time, is proposed and demonstrated to exhibit a similar dip-and-rebound variation pattern. The gate-plateau time is also shown to be the most sensitive online precursor for observing the rebound phenomenon. In addition, the analytical expressions are derived to correlate the effect of gate-oxide degradation with simultaneous dip-and-rebound variation pattern in all four precursors. The dip-and-rebound variation pattern is experimentally confirmed by inducing accelerated gate-oxide degradation in two different commercial Si power MOSFETs. While multiple electrical parameters have been identified as precursors for monitoring the gate-oxide degradation in Si MOSFETs, very few precursors have been proposed for Silicon Carbide (SiC) power MOSFETs. This dissertation proposes that in addition to the threshold voltage, the other online precursors identified for Si power MOSFETs: the gate-plateau voltage and the gate-plateau time, are also effective for monitoring the effect of gate-oxide degradation process in SiC power MOSFETs. Though the gate-oxide material is the same in both Si and SiC power MOSFETs, the effect of gate-oxide degradation on the variation pattern of electrical parameters is different. In contrast to the dip-and-rebound variation pattern of precursors in Si MOSFETs, the research literature has attributed a consistent linear-with-log-stress-time variation pattern to the threshold-voltage shift in SiC power MOSFETs. It is shown that both the gate-plateau voltage and the gate-plateau time increase in a linear-with-log-stress-time manner similar to the threshold voltage. The analytical expressions are derived to correlate the effect of gate-oxide degradation with simultaneous linear-with-log-stress-time variation pattern in all three online precursors. The increasing trend of precursors is experimentally confirmed by inducing accelerated gate-oxide degradation in both planar and trench-gate commercial SiC power MOSFETs under high voltage, high temperature, and hard-switching conditions.
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- Title
- Through experiences, from interactions, and by choices over time : how professors at a research university understand and explain the factors that have influenced their teaching
- Creator
- Steele, Gregory John
- Date
- 2019
- Collection
- Electronic Theses & Dissertations
- Description
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The intent of this study was to understand professors at a research university, and how the environments and individuals they interact with influenced them and their teaching. The primary research question for this study was, "How do professors at a research university understand and explain the factors that have influenced their teaching?" The secondary research question was intended to focus on the institutional factors that had the most influence on a professor and their teaching: "What...
Show moreThe intent of this study was to understand professors at a research university, and how the environments and individuals they interact with influenced them and their teaching. The primary research question for this study was, "How do professors at a research university understand and explain the factors that have influenced their teaching?" The secondary research question was intended to focus on the institutional factors that had the most influence on a professor and their teaching: "What are the most influential factors that affect a professor's teaching at a research institution?"I interviewed 15 award-winning professors from Michigan State University (MSU) about how they had been prepared, supported, and recognized for their work as teachers. My analysis showed how little preparation the professors received about teaching at a research university, how they relieved more on experience and trusted peers than any of the available campus resources, and how they tended to find personal student recognition more rewarding than their prestigious teaching awards. My results showed how institutional deficiencies (the lack teaching preparation, applicable resources, and sufficient recognition) created obstacles for the professors to overcome as they progressed and developed as teachers. To lessen or remove the institutional obstacles, I recommend research universities better assess and recognize a professor's teaching, faculty developers localize their available resources to the individual colleges and departments, and professors utilize their peers and self-reflection as a way to meet their needs and expectations as teachers. Professors at research universities are expected to prioritize their teaching and scholarship, but the importance of the former can become complicated when institutions place a greater emphasis on the latter (via the tenure process, promotions, raises, and rewards). This study extends previous scholarship which shows that professors at research universities are not sufficiently prepared, supported, or recognized for their work as teachers. If the individual institutions do not properly prepare their professors as teachers, then there is uncertainty as to how, where, and why the individual professors succeed and develop as teachers.
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- Title
- Microwave Imaging Using a Tunable Reflectarray Antenna and Superradiance in Open Quantum Systems
- Creator
- Tayebi, Amin
- Date
- 2017
- Collection
- Electronic Theses & Dissertations
- Description
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Theory, experiment, and computation are the three paradigms for scientific discoveries. This dissertation includes work in all three areas. The first part is dedicated to the practical design and development of a microwave imaging system, a problem mostly experimental and computational in nature. The second part discusses theoretical foundations of possible future advances in quantum signal transmission. In part one, a new active microwave imaging system is proposed. At the heart of this...
Show moreTheory, experiment, and computation are the three paradigms for scientific discoveries. This dissertation includes work in all three areas. The first part is dedicated to the practical design and development of a microwave imaging system, a problem mostly experimental and computational in nature. The second part discusses theoretical foundations of possible future advances in quantum signal transmission. In part one, a new active microwave imaging system is proposed. At the heart of this novel system lies an electronically reconfigurable beam-scanning reflectarray antenna. The high tuning capability of the reflectarray provides a broad steering range of +\- 60 degrees in two distinct frequency bands: S and F bands. The array, combined with an external source, dynamically steers the incoming beam across this range in order to generate multi-angle projection data for target detection. The collected data is then used for image reconstruction by means of time reversal signal processing technique. Our design significantly reduces cost and operational complexities compared to traditional imaging systems. In conventional systems, the region of interest is enclosed by a costly array of transceiver antennas which additionally requires a complicated switching circuitry. The inclusion of the beam scanning array and the utilization of a single source, eliminates the need for multiple antennas and the involved circuitry. In addition, unlike conventional setups, this system is not constrained by the dimensions of the object under test. Therefore the inspection of large objects, such as extended laminate structures, composite airplane wings and wind turbine blades becomes possible. Experimental results of detection of various dielectric targets as well as detecting anomalies within them, such as defects and metallic impurities, using the imaging prototype are presented.The second part includes the theoretical consideration of three different problems: quantum transport through two different nanostructures, a solid state device suitable for quantum computing and spherical plasmonic nanoantennas and waveguides. These three physically different systems are all investigated within a single quantum theory; the effective non-Hermitian Hamiltonian framework. The non-Hermitian Hamiltonian approach is a convenient mathematical formalism for the description of open quantum systems. This method based on the Feshbach projection formalism provides an alternative to popular methodssuch as the Feynman diagrammatic techniques and the master equation approach that are commonly used for studying open quantum systems. It is formally exact but very flexible and can be adjusted to many specific situations. One bright phenomenon emerging in the situation with a sufficiently strong continuum coupling in the case when the number of open channels is relatively small compared to the number of involved intrinsic states is the so-called superradiance. Being an analog of superradiance in quantum optics, this term stands for the formation in the system of a collective superposition of the intrinsic states coherently coupled to the same decay channel. The footprint of superradiance in each system is investigated in detail. In the quantum transport problem, signal transmission is greatly enhanced at the transition to superradiance. In the proposed solid state based charge qubit, the superradiant states effectively protect the remaining internal states from decaying into the continuum and hence increase the lifetime of the device. Finally, the superradiance phenomenon provides us a tool to manipulate light at the nanoscale. It is responsible for the existence of modes with distinct radiation properties in a system of coupled plasmonic nanoantennas: superradiant states with enhanced and dark modes with extremely damped radiation. Furthermore, similar to the quantum case, energy transport through a plasmonic waveguide is greatly enhanced.
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- Title
- "Take action in the world!" : advocacy and reciprocity as research practices in technical communication
- Creator
- Turner, Heather Noel
- Date
- 2018
- Collection
- Electronic Theses & Dissertations
- Description
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This dissertation examines how scholars in technical and professional communication conduct research related to social justice. I define social justice research, then identify and visualize disciplinary activity related to social justice over a 10 year (2006-2016) time span. Using data visualizations and critical computations as a methodological heuristic, I present the practices of four scholars conducting social justice research to offer thematic data narratives. I found that scholars can...
Show moreThis dissertation examines how scholars in technical and professional communication conduct research related to social justice. I define social justice research, then identify and visualize disciplinary activity related to social justice over a 10 year (2006-2016) time span. Using data visualizations and critical computations as a methodological heuristic, I present the practices of four scholars conducting social justice research to offer thematic data narratives. I found that scholars can enact social justice when they intentionally integrate principles of advocacy and reciprocity across the arcs of their research processes. Advocacy occurs when researchers negotiate, accommodate and facilitate justice across research settings, throughout research processes, and with research partners. Reciprocity occurs when researchers structure opportunities to exchange knowledge, labor, and resources with participants and related peoples, communities, organizations, and nonprofits. The data from 960 conference presentations and four semi-structured interviews with technical communication researchers reveals that technical communication as a field has commitments to inclusion, public action, and increasing individual agency. Social justice researchers enact these commitments through their research processes, across research contexts, and with various research partners.
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- Title
- A detailed study of the gamma-ray nova V1324 Sco
- Creator
- Finzell, Thomas Michael Broen
- Date
- 2017
- Collection
- Electronic Theses & Dissertations
- Description
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It has recently been discovered that some, if not all, classical novae emit GeV gamma-rays, but the mechanisms involved in the production of the gamma-rays are still not well understood. We present here a comprehensive, multi-wavelength dataset---from radio to X-rays---for the most gamma-ray luminous classical nova to-date, V1324 Sco. Using this dataset, we show that V1324 Sco is a canonical dusty Fe-II type nova, with a reddening of E(B-V) = 1.16 +\- 0.12, a distance > 6.5 kpc, a bulk ejecta...
Show moreIt has recently been discovered that some, if not all, classical novae emit GeV gamma-rays, but the mechanisms involved in the production of the gamma-rays are still not well understood. We present here a comprehensive, multi-wavelength dataset---from radio to X-rays---for the most gamma-ray luminous classical nova to-date, V1324 Sco. Using this dataset, we show that V1324 Sco is a canonical dusty Fe-II type nova, with a reddening of E(B-V) = 1.16 +\- 0.12, a distance > 6.5 kpc, a bulk ejecta velocity of 1150 +/- 40 km/s and an ejecta mass of 2.0 +\- 0.4 * 10^-5 M_{Solar}. However, despite its seeming normalcy, there is also evidence for complex shock interactions, including the aforementioned gamma-rays and early time high-brightness temperature radio emission. To explain how a nova can be simultaneously ordinary and have the highest gamma-ray luminosity to date, we present a simplified model of the ejecta in which the strength of gamma-ray emission is set by properties of a fast ejecta component that collides with a slower component to produce shocks. We conclude this detailed study of V1324 Sco by showing how it has helped shape our understanding of the role of shocks in novae. Along with the study of V1324 Sco, this work also presents detailed methods for determining the reddening, distance, and filling factor of a classical nova from optical spectroscopy (using V1324 Sco as an example). We also provide detailed derivations for fitting nova radio light curves, to determine ejecta mass and velocity.
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- Title
- Instrument automation and measurement data curation platform for enhancing research reproducibility and knowledge discovery
- Creator
- Gtat, Yousef
- Date
- 2019
- Collection
- Electronic Theses & Dissertations
- Description
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"Many applications demand the continued development of sensing systems that employ smart sensors, instrumentation circuits, and signal processing techniques to extract relevant information from real-world environments. In the engineering efforts to develop new sensors, tasks such as instrument automation, measurement process curation, real-time data acquisition, data analysis, and long-term tracking of inter-related datasets generate a significant volume and variety of information that is...
Show more"Many applications demand the continued development of sensing systems that employ smart sensors, instrumentation circuits, and signal processing techniques to extract relevant information from real-world environments. In the engineering efforts to develop new sensors, tasks such as instrument automation, measurement process curation, real-time data acquisition, data analysis, and long-term tracking of inter-related datasets generate a significant volume and variety of information that is challenging to organize, record, and analyze. Sensor development and characterization experiments can be laborious, prone to human error, difficult to repeat precisely, and can produce data that are challenging to interpret. Such issues highlight a need for a structured, automated approach to curate measurement processes and data acquisition. This thesis presents the first software platform for i) digitally designing measurement recipes, ii) remotely scheduling and monitoring experiment execution, iii) automatic data acquisition, iv) analyzing and storing results datasets, and v) linking the datasets with their prospective meta-datasets for deeper analysis and inspection. The proposed platform is flexible and capable of managing a large set of diverse instruments, measurement recipes and sensor datasets. By employing several design abstractions, it allows users to remotely design, schedule, monitor and execute measurement-based experiments while archiving results along with their information-rich metadata therefore preserving the provenance of the datasets. The platform enable precise timing control of instruments and stimulus signals along with long-term tracking of datasets eliminating manual errors and human omissions thus enhancing research reproducibility and promoting knowledge discovery methodologies."--Page ii.
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- Title
- Prime torsion in the Brauer group of an elliptic curve
- Creator
- Ure, Charlotte
- Date
- 2019
- Collection
- Electronic Theses & Dissertations
- Description
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The Brauer group is an invariant in algebraic geometry and number theory, that can be associated to a field, variety, or scheme. Let k be a field of characteristic different from 2 or 3, and let E be an elliptic curve over k. The Brauer group of E is a torsion abelian group with elements given by Morita equivalence classes of central simple algebras over the function field k(E). The Merkurjev-Suslin theorem implies that any such element can be described by a tensor product of symbol algebras....
Show moreThe Brauer group is an invariant in algebraic geometry and number theory, that can be associated to a field, variety, or scheme. Let k be a field of characteristic different from 2 or 3, and let E be an elliptic curve over k. The Brauer group of E is a torsion abelian group with elements given by Morita equivalence classes of central simple algebras over the function field k(E). The Merkurjev-Suslin theorem implies that any such element can be described by a tensor product of symbol algebras. We give a description of elements in the d-torsion of the Brauer group of E in terms of these tensor products, provided that the d-torsion of E is k-rational and k contains a primitive d-th root of unity. Furthermore, if d = q is a prime, we give an algorithm to compute the q-torsion of the Brauer group over any field k of characteristic different from 2,3, and q containing a primitive q-th root of unity.
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- Title
- The consequences of authenticity and impression management in the context of taboo conversations
- Creator
- Bryant, Courtney M.
- Date
- 2018
- Collection
- Electronic Theses & Dissertations
- Description
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"The current study integrates the construct of taboo into the organizational literature by considering its impact on coworker relationships, particularly in the context of authenticity and impression management. To explore how taboo topics may intrude on positive employee relationships, I consider its potential to impact helping behaviors in the workplace. An online between-subjects experiment manipulates motivation to be authentic or impression manage and a topic of discussion with a...
Show more"The current study integrates the construct of taboo into the organizational literature by considering its impact on coworker relationships, particularly in the context of authenticity and impression management. To explore how taboo topics may intrude on positive employee relationships, I consider its potential to impact helping behaviors in the workplace. An online between-subjects experiment manipulates motivation to be authentic or impression manage and a topic of discussion with a coworker to be taboo (e.g. abortion) or neutral (e.g. fitness). I evaluated participants' perceptions of their own motivation, participant's perceptions of their behavior during the interaction as authentic or impression management, and helping behaviors following the interaction. Results showed that motivation, but not taboo topics, influenced perceptions of behavior during the interaction. Further, taboo topics and the behavior during the interaction did not influence subsequent helping behaviors. However, exploratory results showed that taboo topics did impact affect towards the coworker that brought up the taboo topic. Limitations, implications for theory and practice, and future research directions are discussed."--Abstract.
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- Title
- Flexible hierarchical Bayesian modeling extensions to improve whole genome prediction and genome wide association analyses
- Creator
- Chen, Chunyu (Graduate of Michigan State University)
- Date
- 2017
- Collection
- Electronic Theses & Dissertations
- Description
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"Whole genome prediction (WGP) has been widely implemented in animal and plant breeding for genomic selection of economically important traits, having already accelerated genetic progress for economically important traits in some species especially dairy cattle. Genome wide association (GWA) analysis is used for screening genomic regions that may include important candidate genes segregating for the trait of interest and is being increasingly integrated with WGP analysis. Both WGP and GWA...
Show more"Whole genome prediction (WGP) has been widely implemented in animal and plant breeding for genomic selection of economically important traits, having already accelerated genetic progress for economically important traits in some species especially dairy cattle. Genome wide association (GWA) analysis is used for screening genomic regions that may include important candidate genes segregating for the trait of interest and is being increasingly integrated with WGP analysis. Both WGP and GWA typically represent m226Bn problems as defined by a large number of single nucleotide polymorphism (SNP) markers (m) and comparably much smaller number of individuals (n). Two broad types of parametric models are typically considered for these analyses: traditional best linear unbiased prediction approaches based on SNP marker effects being normally distributed and Bayesian WGP models that allow more flexible specifications for SNP marker effects based on either heavy-tailed or variable selection specifications. Bayesian WGP models can achieve higher prediction accuracies than traditional approaches in many applications if properly tuned; however, their implementation can be computationally challenging. My dissertation was aimed to address some of these emerging issues in Bayesian WGP models as well as providing software tools for real data applications. In Chapter 2, I developed an expectation maximization (EM) algorithm as a fast alternative to traditional Markov Chain Monte Carlo (MCMC) for Bayesian WGP models. I proposed EM implementations for two models, heavy-tailed BayesA and stochastic search and variable selection (SSVS) adapting the EM algorithm for maximum a posterior (MAP) inference of SNP effects and adapting REML like strategies to estimate key hyperparameters. Using a comprehensive simulation study and real data analysis, I found that these empirical Bayes approaches can be quite sensitive to starting values for SNP effects. However, using a deterministic annealing variant of EM, I obtained hyperparameter estimates and prediction accuracies comparable to their MCMC counterparts. In Chapter 3, I further assessed the possibility using two Bayesian WGP models BayesA and SSVS for GWA studies. I also included a popular GWA analysis (EMMAX) based on the utilization of the linear mixed model. In addition to basing inferences on traditional single SNP tests and fixed genomic window tests, I assessed the merit of tests involving adaptively determined windows based on clustering genome into blocks based on linkage disequilibrium. I found that SSVS and BayesA under MCMC and adaptive window tests led to best receiver operating curve (ROC) properties. In Chapter 4, I extended SSVS to single step SSVS to incorporate phenotypes of non-genotyped individuals and compared its performance with corresponding models ignoring these genotypes for both WGP and GWA. I found single step SSVS to be a promising for WGP and GWA, particularly for genetic architectures characterized by a few genes with large effects. In Chapter 5, I combined much of the developments in Chapter 2 to Chapter 4 and beyond in a unified framework as an open source R package BATools to implement several different Bayesian models for WGP and GWA."--Pages ii-iii.
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- Title
- Three dimensional analysis of the gas flow in piston ring pack
- Creator
- Kharazmi, Ali
- Date
- 2017
- Collection
- Electronic Theses & Dissertations
- Description
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"Cylinder-kit dynamics design in an internal combustion engine is highly relevant for the engine performance characteristics, durability and reliability. Since the middle of the 20th century, researchers have been using numerical models to describe the processes that occur in a ring pack. Because it is difficult and extremely costly to conduct experiments on every series of engines to check for the blow-by and oil consumption, a computational analysis can be performed on the ring pack to...
Show more"Cylinder-kit dynamics design in an internal combustion engine is highly relevant for the engine performance characteristics, durability and reliability. Since the middle of the 20th century, researchers have been using numerical models to describe the processes that occur in a ring pack. Because it is difficult and extremely costly to conduct experiments on every series of engines to check for the blow-by and oil consumption, a computational analysis can be performed on the ring pack to study the blow-by and oil-consumption characteristics. In this dissertation a 3D CFD simulation model is introduced to analyze the flow between the cylinder liner and the piston. This model allows for calculation of the piston assembly with consideration of the ring dynamics, transient boundary conditions for combustion chamber pressure and temperature as well as thermal distortion of the piston and liner. The determination of the complex geometry of the cylinder-kit is established in a STL (STereoLithography) format by considering the complicated geometrical details of the ring pack such as thermal distortion of piston and liner, ring twist and ring/groove conformability. The blow by and blow back is numerically calculated for a small bore cylinder operating at 2000 RPM and verified by the results of commercially available 1D models. The calculated velocity filed shows substantial circumferential flow in the piston ring pack that is dominated by the ring and groove geometry as well as the relative position of the rings end gap. It is found that the amount of gas that flows back to the combustion chamber increases when the in-cylinder pressure trace decreases from its peak value. The knowledge from this study can be used as a basis for further multiphase calculations containing oil flow such as oil consumption, oil evaporation and eventually cylinder-kit wear."--Page ii.
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- Title
- Further investigation of a kinetic model to accurately predict evaporation of gasoline
- Creator
- Eklund, Natasha Kimberley
- Date
- 2019
- Collection
- Electronic Theses & Dissertations
- Description
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In fire debris analysis, analysts compare chromatograms of extracts of fire debris to a database containing chromatograms of ignitable liquid reference standards. Typically, the database will contain chromatograms of experimentally evaporated liquids. Unfortunately, experimentally evaporating ignitable liquids can be a time-consuming process. Previously, a mathematical model was developed with diesel that predicts the evaporation rate constant of compounds as a function of retention index (IT...
Show moreIn fire debris analysis, analysts compare chromatograms of extracts of fire debris to a database containing chromatograms of ignitable liquid reference standards. Typically, the database will contain chromatograms of experimentally evaporated liquids. Unfortunately, experimentally evaporating ignitable liquids can be a time-consuming process. Previously, a mathematical model was developed with diesel that predicts the evaporation rate constant of compounds as a function of retention index (IT). The model can be used to generate predicted chromatograms of evaporated liquids. In comparing predicted to experimental chromatograms, predictive accuracy was high for comparisons using diesel, torch fuel, and marine fuel stabilizer.This research aims to improve the predictive accuracy of the model with respect to gasoline and to test the feasibility of developing correlation coefficient ranges for the classification of an ignitable liquid residue as gasoline. Improvement of the predictive accuracy of the model involved changes to the instrumental parameters and data analysis procedures. The feasibility of development of PPMC coefficient ranges involved comparisons of predicted reference collections of a non-gasoline ignitable liquid to chromatograms of experimentally evaporated gasoline.
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- Title
- Atomic simulation on chemical-mechanical coupled deformations in complex nano structures
- Creator
- Liu, Jialin (Graduate of Michigan State University)
- Date
- 2019
- Collection
- Electronic Theses & Dissertations
- Description
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"Nano-structured materials often exhibit very different mechanical properties comparing with their bulk counterpart and are more sensitive and active to chemical interactions with the environments due to the large surface-to-volume ratio. In this thesis, predictive modeling techniques including density functional theory (DFT) and reactive molecular dynamics method (MD) are designed and applied to understand the deformation mechanisms of complex nano-structured material and describe chemical...
Show more"Nano-structured materials often exhibit very different mechanical properties comparing with their bulk counterpart and are more sensitive and active to chemical interactions with the environments due to the large surface-to-volume ratio. In this thesis, predictive modeling techniques including density functional theory (DFT) and reactive molecular dynamics method (MD) are designed and applied to understand the deformation mechanisms of complex nano-structured material and describe chemical-mechanical coupled interactions. Three technologically important materials are investigated, to understanding the high strain rate toughening mechanism in nacre, predicting the formation and fracture of aluminum oxide bifilms in aluminum castings, and revealing the lithium growth morphology as a function of oxygen partial pressure. For nacre, its hierarchical structure and toughening mechanisms have inspired many materials developments. Recently, a new toughening mechanism, deformation twins was observed in nacre after dynamic loading (103 s--1). The deformation twinning tendency and the competition between fracture and deformation twinning were revealed by DFT calculations. We discovered that the ratio of the unstable and the stable stacking fault energy in aragonite is hitherto the highest in a broad range of metallic and oxide materials and the bonding nature for this high ratio is explained. Both aluminum and lithium have high oxygen affinity. Their interaction with the oxygen environment affects the mechanical properties and vice versa. During casting of aluminum, it has long been proposed that the entrapped alumina "bifilms" are detrimental to the fatigue properties of the cast product. However, its properties have never been measured due to experimental limitations. Therefore, a ReaxFF based MD protocol was designed to simulate aging, folding, and fracture of oxide bifilms. The predicted fracture energy, fracture location, and differences between old and young oxides are explained a series of experimental observations. To illustrate the Li-growth mechanism in a solid-state-battery testing platform, we modeled the morphology of Li nano-structure growth in oxygen environment via ReaxFF-based MD. The simulation revealed that the competition of the Li growth rate and oxidation rate leads to the sphere-nanowire-sphere morphology transition with increasing oxygen partial pressure. Understanding the impact of chemical reaction on Li dendrite growth mechanisms and morphology evolution provided insights on the formation of the solid electrolyte interface (SEI) layer in a Li-ion battery. Finally, a shortcoming of the current charge transfer scheme (qEq) used in the ReaxFF MD simulation is discussed. It is demonstrated that qEq method will lead to overductile ionic materials in the MD simulation. A new Force field method and new parameters are proposed to mitigate this problem."--Pages ii-iii.
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- Title
- MULTIPACTOR DISCHARGE WITH TWO-FREQUENCY RF FIELDS
- Creator
- Iqbal, Asif
- Date
- 2021
- Collection
- Electronic Theses & Dissertations
- Description
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Multipactor is a nonlinear ac discharge in which a high frequency rf field creates an electron avalanche sustained through secondary electron emission from metallic or dielectric surfaces. Multipactor discharge can adversely affect various rf systems, such as telecommunications systems, high power electromagnetic sources, and accelerator structures. The restricted frequency spectrum and the cluttered satellite orbits require a single spacecraft to perform the same or enhanced functions which...
Show moreMultipactor is a nonlinear ac discharge in which a high frequency rf field creates an electron avalanche sustained through secondary electron emission from metallic or dielectric surfaces. Multipactor discharge can adversely affect various rf systems, such as telecommunications systems, high power electromagnetic sources, and accelerator structures. The restricted frequency spectrum and the cluttered satellite orbits require a single spacecraft to perform the same or enhanced functions which previously required several satellites. This necessitates complex multi-frequency operation for a much-enlarged orbital capacity and mission, where the requirement of high power rf payload significantly increases the threat of multipactor. This work provides a comprehensive understanding of multipactor discharge driven by two-frequency rf fields. The study provides important results on single and two-surface multipactor, including multipactor mitigation, migration of electron trajectory, and frequency domain analysis.We use Monte Carlo simulations and analytical calculations to obtain single surface multipactor susceptibility diagrams with two-frequency rf fields. We present a novel multiparticle Monte Carlo simulation model with adaptive time steps to investigate the time dependent physics of the single surface multipactor. The effects of the relative strength and phase of the second carrier mode as well as the frequency separation between the two carrier modes are studied. It is found that two-frequency operation can reduce the multipactor strength compared to single-frequency operation with the same total rf power. Migration of the multipactor trajectory is demonstrated for different configurations of the two-frequency rf fields. Formation of beat waves is observed in the temporal profiles of the surface charging electric field with small frequency separation between the two carrier modes. We study the amplitude spectrum of the surface charging field due to multipactor in the frequency domain. It is found that for the single-frequency rf operation, the normal electric field consists of pronounced even harmonics of the driving rf frequency. For two-frequency rf operation, spectral peaks are observed at various frequencies of intermodulation product of the rf carrier frequencies. Pronounced peaks are observed at the sum and difference frequencies of the carrier frequencies, at multiples of those frequencies, and at multiples of the carrier frequencies. We also study two surface multipactor with single- and two-frequency rf fields using Monte Carlo simulations and CST. The effects of the relative strength and phase of the second carrier mode, and the frequency separation between the two carrier modes on multipactor susceptibility are studied. Regions of single and mixed multipactor modes are observed in the susceptibility chart. The effect of space charge on multipactor susceptibility and the time dependent physics is also studied.
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