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    94480 research outputs found

    Structural and mechanistic identification of heterogeneous catalysts

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    Due to their importance and widespread use in the chemical and energy industries, understanding and improving heterogeneous catalysts is essential to advance their development and enable more sustainable processes. Atomically disperse or single atom catalysts have shown particular promise for their ability to exceed nanoparticle catalysts with regards to activity, stability and selectivity for a growing number of chemical reactions. Understanding key properties of these materials, such as structure-property relationships, structural dynamics and reaction-driven restructuring, is, however, often complicated by issues including low weight loadings, strong metal-support interactions and heterogeneity in active component speciations. The following work details how these challenges may be addressed through a review of how a multimodal approach including scanning transmission electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy may be employed to identify the catalytically relevant properties (charge state, electronic structure, atomic configuration, bonding interaction). Furthermore, this approach is demonstrated through its application to Pt-Ni bimetallic nanoparticles on mesoporous silica, single atom Pt on CeO2, nanoparticle Pt on CeO2 and single atom Pt on Gd-doped CeO2.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    Study of Phospholipid/Graphene interfaces and the effect of substrate curvature on lipid morphology and dynamics.

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    Phospholipids are an important class of lipids which are widely used as model platforms to study biological processes and interactions. They have been known to form stable interfaces with solid substrates like graphene, and these interfaces have potential applications in bio-sensing and targeted drug-delivery. In this paper, we perform molecular dynamics simulations of graphene supported lipid monolayers to characterize lipid properties in such interfaces. We observed substantial differences in lipid properties like tail order-parameter, density profile, diffusion rate, etc., between lipids in a supported monolayer and free-standing bilayer. Further, we studied these interfaces on sinusoidally deformed graphene substrates to understand the effect of curvature on the supported lipids. Here, we observed that the nature of substrate curvature—concave, convex or flat—can affect the lipid/substrate adhesion strength as well as induce structural and dynamical changes in the adsorbed lipid monolayer. Together, these results help characterize the properties of lipid/graphene interfaces, as well as understand the effect of substrate curvature on these interfaces, which can enable tuning of lipid properties for various sensor device and drug delivery applications.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    The evaluation of a metacognition education intervention through dialogic teaching for the promotion of self-regulated learning of Deaf and hard of hearing students in Deaf schools

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    A majority of one's education is conducted through informal learning. With the increase in digitization and the use of the Internet, informal learning is becoming a facet of formal learning and adult learning. Learning strategies can be employed to aid students and learners toward a higher degree of achievement in academic or workplace goals. These strategies include metacognition, self-regulated learning, and self-directed learning. These tools are nested entities in that strong metacognitive skills and awareness are important to have strong self-regulated learning skills and effective self-regulated learners are effective self-directed learners. This would imply that in order to have successful lifelong learning, metacognitive strategies are a necessity. Deaf and hard of hearing people have issues employing metacognitive skills due to being passive learners, having too much external regulation, and other executive functioning issues that stem from hearing loss. The literature reveals self-directed learning is important in adult learning including on-the-job training and developing good managerial skills. The implications from the literature suggests that by increasing metacognitive skills in a formal setting, through means of active learning and scaffolding, Deaf and hard of hearing students can increase the use of metacognition in their learning which could have lifelong applications for academic success. This study will address the Deaf and hard of hearing students' deficits in metacognition through an educational intervention of dialogic teaching and evaluate the promotion of self-regulated learning.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    Essays on health economics and innovation

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    This dissertation consists of three chapters. In chapter 1, we studied the impact of competition on incremental innovation in the pharmaceutical context. Research and development is not a linear process that ends when a patent is granted. Instead, pioneer innovators continue innovating after their product has been patented. We study how competition affects post-patent innovation incentives for pharmaceutical firms that introduce first-in-class drugs. We find that “me-too” competition reduces R&D directed towards finding alternative uses for a safe drug. Our estimates suggest that the entry of a me-too drug reduces the number of post-approval clinical trials by 8.9 percent. In chapter 2, we ask that Does the market punish physicians’ misconducts? We answer this question in the context of California physicians. We assemble a novel dataset that includes a history of disciplinary actions, detailing payments, Medicare information, and physicians’ referral network. About 4.3 percent of physicians in California have at least one prior disciplinary action (DA). For those physicians who remain active after receiving a DA, we show that prior DAs have a negative impact on detailing payments. Physicians with prior DAs receive a less severe punishment from firms that have invested more in them. In chapter 3, we study innovation incentives in the presence of “product hopping,” whereby the incumbent patents a minor modification of a drug (e.g., a new delivery method) and invests in marketing to switch demand towards the minor modification. In our setting, firms compete sequentially to discover two innovative drugs. The winner of the first R&D race (the incumbent) can alter the market structure that follows the second R&D race through product hopping. This can increase investments during the second R&D race when product hopping softens competition or when the incumbent benefits from becoming a multi-product monopolist. The change in expected continuation values can increase or decrease investments during the first R&D race. Thus, the welfare effect of product hopping is ambiguous. We discuss our results in the context of the current policy debate on product hopping, welfare, and antitrust.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    Reliability-based co-design and its applications to wind energy and mobile energy storage systems

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    Autonomous systems, such as autonomous driving vehicles, unmanned aerial vehicles (UAVs), and field robots, received much attentions recently. The performance of autonomous systems relies on both its physical design and the appropriate control strategies, which often takes place at an early stage of design. The plant design and the control design are strongly coupled. Neglecting this coupling effect may cause an imbalance in the feasible design spaces of plant design and control design, such as over-constrained operation conditions, over design, or requirement of skilled operators, which hinders the development of autonomous systems. On the other hand, the products are manufactured goods and usually operate in environments with uncertainty. Reliable operation of such systems ask for balanced physical design and feasible control decisions to address the parametric uncertainty and stochastic environmental disturbances. While integrated physical and control system co-design has been demonstrated successfully on several engineering system design applications, it has been primarily applied in a deterministic manner without considering uncertainties. An opportunity exists to study non-deterministic co-design strategies, taking into account various uncertainties in an integrated co-design framework. While significant advancements have been made in co-design and RBDO separately, little is known about methods where reliability-based dynamic system design and control design optimization are considered jointly. In this research, we investigate optimal design and control of dynamical systems with model parametric uncertainties, which presumably operate in uncertain environments. Techniques in control co-design (CCD) and reliability-based design optimization (RBDO) are adapted and integrated to solve the proposed problem. Since the proposed method adopts the idea of multi-disciplinary design optimization, it can improve the performance of autonomous systems without leveraging the difficulty in design and control for systems with uncertainties. First, the problem formulation and strategies to solve the reliability-based control co-design problem is presented. A comparison of accuracy and efficiency is made using numerical and simple engineering case studies. The method is then applied to a horizontal axis wind turbine. The uncertain wind load and model parameters of a wind turbine are compensated through active control or endured by a reliable design regarding its aerodynamics and structural dynamics. Different strategies of reliability assessment are also compared, which provides insights on their advantages and limits under different cases. In the second application, reliability-based control co-design is applied to Lithium-ion battery. The electrode and charging current are optimized to minimize its charging time while regulating its aging effect for reasonable cycle life. The multi-scale nature of the problem requires first principle model to preserve the coupling effect between electrode design at the micro scale and the charging control at the macro scale. However, it is not feasible to use the first principle model for control optimization. A hybrid physics and machine learning strategy is proposed in this work, which extends the applicability of reliability-based control co-design to multi-scale problems.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    Seeing systems: A rhetorical history of visual media at the Massachusetts Institute of Technology, 1939-1969

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    The Massachusetts Institute of Technology (MIT) was an epicenter of visual media research and experimentation during the middle of the twentieth century. In the 1930s and 40s, electrical engineer Harold Edgerton developed a high-speed photography system that would be taken up in machine research, art photography, and nuclear weapons testing. In the 1950s, scientists in the Physical Science Study Committee partnered with filmmakers to create educational films that showed physics and physicists to Cold War America. And in the 1960s, architecture professor Gyorgy Kepes formalized collaborations between artists and scientists in order to create visual art “on a civic scale.” These innovations resist neat classification as strictly “media,” “machine,” “visual art,” or “experimental tool.” They were technological configurations and modes of practice that could be any, or all, of these, and they were all part of a larger institutional project at MIT that was deeply invested in the possibilities of visual media as a component of science and technology. This dissertation offers a rhetorical history of media research at MIT from World War II into the Cold War—a time during which MIT became one of the preeminent techno-scientific institutions in the world. I argue that as MIT shifted from functioning as an industrial ancillary to a prominent center of the military-industrial complex, visual media research became crucial to the construction and promotion of its anti-instrumental and networked approach to science and engineering. This approach heavily relied upon a rhetoric of basic and integrated science—framing and promoting scientific and technical research for its potential utility and broad relevance. Rhetorics of vision co-constituted this approach, as visual media had diverse instrumentality and facilitated the collaboration between disparate communities of research and application. This rhetoric allowed MIT to traverse previously rigid boundaries between humanities/sciences, public/private, and theoretical/applied knowledge. In doing so, MIT broadened the purview of academic science and technology, playing a key role in embedding media and technology, as well as media technologies, across ever-wider areas of American life. This project speaks to rhetorical scholars invested in the formation of techno-scientific cultures in the United States, as it illuminates the internal discourses of a crucial site of American science and technology. It also contextualizes scientific and technical rhetorics within a shared organizational context, demonstrating how organizational exigencies and the proximity of researchers can circumscribe scientific and technical discourses and practices. Finally, it adds dimension to histories of Cold War science and technology, giving a local perspective on mid-century conflicts such as the Red Scare, the “Two Cultures” debates, and the postwar politization of America’s scientists and engineers.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste

    Three essays on the effects of health policy on health care financing, demand, and provision

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    This dissertation evaluates the effects of a rural health insurance program in China and tort reforms in the United States. Rural residents’ health status, health-seeking behaviors, financial burden, physicians’ practices, and total hospitalization charges are discussed in the three chapters respectively. The first chapter estimates the 6–12 year effects of the New Cooperative Medical System (NCMS) on reducing the financial burden of rural residents and improving their health status. The NCMS is a national health insurance system for rural residents in China. The primary goals of this program are to alleviate medical impoverishment and improve health. The implementation of the NCMS can be divided into two stages, a pilot stage, and a full implementation stage. The pilot stage ran from 2003 to 2007. The full implementation stage began in 2008. Insurance coverage rates and reimbursement levels of the two stages are substantially different. Although numerous studies reported the effects of the expanded insurance coverage at the pilot stage, we know little about the longer-term effects of the NCMS program. The time span of my research covers both the pilot stage and the full implementation stage. This study utilizes the panel data from the China Health and Nutrition Survey. It is a nationwide longitudinal survey project and mainly focuses on the health and nutritional status of the population. In the survey years, the coverage rate of the program at the individual level reached 93 percent. I apply the individual fixed-effects strategy and the probit model with the Mundlak device estimation. Different from previous studies’ findings that there is no evidence that the scheme has reduced out-of-pocket spending, the result of this research shows that the NCMS has a significant effect on relieving the financial burden, as measured by out-of-pocket spending among patients. This effect could be explained by the fact that the reimbursement levels in the full implementation stage are substantially higher than those in the pilot stage. This effect is heightened among lower-income, younger, better educated, and married patients. However, there is no evidence that the NCMS changes their health-seeking behaviors or improves residents’ health. The goals of the NCMS program are to reduce the burden of medical expenditure and to improve health. These goals are logically related. Health policy assumes that lack of insurance contributes to poor health. Therefore, reducing medical expenditure can lead to increased access to healthcare and consequently to improved health. This research shows that the NCMS reduces the financial burden of individuals in rural areas. However, it does not affect health-seeking behaviors. These results explain the lack of improvement in health outcomes from the NCMS. The second chapter examines malpractice pressure by evaluating the effects of tort reform on physicians’ choice of procedure. While the World Health Organization suggests the ideal rate for cesarean sections (C-section) to be between 10% and 15%, the C-section rate in the United States has been over 30% since 2005. There is no evidence showing the benefits of unnecessary C-sections. However, C-sections are costly in time, medical care resources, and patient comfort. Like any surgery, C-sections do entail short and long term risks which can extend many years beyond the current delivery, affecting the health of the woman, her child, and future pregnancies. One of the reasons that physicians perform unnecessary C-sections is malpractice pressure. Physicians employ precautionary treatments to avoid legal liability. Tort reforms attempt to change physicians’ practices by relieving their liability pressures. The four most common state-level tort reforms are caps on punitive damages, caps on noneconomic damages, reform of the rule of joint and several liabilities, and reforms of the collateral source rule. A substantial number of states have adopted tort reforms by 2010. Numerous studies have examined malpractice pressure by evaluating the effects of tort reform on physicians’ choice of procedure. Yet the heterogeneous effects of tort reforms based on hospitals’ characteristics such as being in urban or rural areas, and ownership type are not clear. We estimate the heterogeneous effects of tort reforms on physicians’ diagnosis, C-section rates, and total hospitalization charges using the National Inpatient Sample and the Database of State Tort Law Reforms from 2001 to 2010. Taking advantage of a large number of observations and detailed information about hospitals and procedures, we apply the difference-in-differences model with time fixed effects, hospital fixed effects, and both mother and hospital control variables. We find strong evidence to support the claim that relief of malpractice pressure induces physicians to perform fewer C-sections. Physicians in rural or public hospitals face more malpractice pressure than those in urban or private hospitals. The third chapter aims to identify factors from a demand-side affecting patients’ cross-regional mobility decisions to provide recommendations to policymakers to encourage patient mobility. The unbalanced distribution of health resources within countries prevents people from having equal access to good health care. Patient mobility constitutes a way of using health care services effectively and efficiently. The data for this study were drawn from the China Health and Retirement Longitudinal Study. We built our sample based on individuals who had hospitalization experiences in the preceding year. Following the six-step purposeful selection method, we developed a multivariate population average logit regression model. The results indicated that being diagnosed with cancer or malignant tumor plays the most important role in influencing patients’ decisions. Concurrently, a high reimbursement rate of health insurance obviously encourages patient mobility. Different from the positive effect of being diagnosed with cancer or malignant tumor, being diagnosed with arthritis and rheumatism hamper patient mobility. Additionally, medical technology progress promotes patient mobility, and older patients are unlikely to travel long distances to seek hospitalizations. This study is the first to examine the determinants of inter jurisdictional patient mobility in China from the demand side. The policy implications of the findings include improving the screening and diagnosis of malignant diseases such as cancer, raising the reimbursement level of health insurance for urban unemployed residents and rural residents, and encouraging the development and popularization of medical technologies.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste

    Toric mirror symmetry and GIT windows

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    This thesis, partially based on the author's joint work [HZ20], studies mirror symmetry for toric varieties from the perspective of geometric invariant theory. We translate GIT constructions of toric varieties into skeletal terms and study them in the context of wrapped Fukaya categories and wrapped constructible sheaves. We explain how the mirror image of the Halpern-Leistner-Sam "magic window" for quasi-symmetric torus actions computes the category associated to the equivariant semistable skeleton upon stop removal, where the generating cotangent fibers are described by a generic shift of a lattice zonotope in the real character space of the torus. After identifying the "FI parameter space" of the B-model GLSM with the GKZ complex parameter space of the skeletal LG A-model, homological mirror symmetry in the quasi-symmetric case becomes two geometric incarnations of the Špenko-Van den Bergh schober over C^k stratified by a complexified periodic hyperplane arrangement whose complement models both parameter spaces. We obtain a universal deformation of skeletons interpolating variation of parameters.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste

    Dearomative hydroboration-enabled synthesis of idarubicinone and synthesis of minor cannabinoids and their metabolites

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    Anthracyclines are archetypal representatives of tetracyclic type II polyketide natural products that are widely used in cancer chemotherapy. Although syntheses of this class of compounds have been extensively explored, all known approaches are based on annulations, relying on the union of properly pre-functionalized building blocks. To complement these studies, here we showcase an alternative, non-annulative entry to anthracyclines, starting from a polynuclear arene. Specifically, tetracene was converted to idarubicinone, an aglycone of the FDA approved anthracycline idarubicin, by a judicious orchestration of Co- and Ru-catalyzed arene oxidation and a novel dearomative hydroboration. This global functionalization strategy, a combination of site-selective arene- and dearomative-functionalizations, provided the key anthracycline framework in five operations and enabled rapid and controlled access to idarubicinone. Another class of compound deriving from polyketide synthases are the cannabinoids. Having a long history of use, yet controversial nature Cannabis offers the possibility for the treatment of many diseases. Reports are varied, however, possibly due to the affect of numerous and under-studied minor cannabinoids. A small library of minor cannabinoids were prepared and tested for their anti-inflammatory pain with the goal of discovering a novel lead compound. Specifically, cannabimovone was prepared in biomimetic fashion and displayed a remarkable ability to stimulate the production of cytokines in a BV-2 mouse microglial cell line under inflammatory response.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste

    Reinforcement learning for multi-agent and robust control systems

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    Recent years have witnessed phenomenal accomplishments of reinforcement learning (RL) in many prominent sequential decision-making problems, such as playing the game of Go, playing real-time strategy games, robotic control, and autonomous driving. Motivated by these empirical successes, research toward theoretical understandings of RL algorithms has also re-gained great attention in recent years. In this dissertation, our goal is to contribute to these efforts through new approaches and tools, by developing RL algorithms for multi-agent and robust control systems, which find broad applications in the aforementioned examples and other diverse areas. In this dissertation, we consider specifically two different and fundamental settings that in general fall into the realm of RL for multi-agent and robust control systems: (i) decentralized multi-agent RL (MARL) with networked agents; (ii) H2/H∞-robust control synthesis. We develop new RL algorithms for these settings, supported by theoretical convergence guarantees. In setting i, a team of collaborative MARL agents is connected via a communication network, without the coordination of any central controller. With only neighbor-to-neighbor communications, we introduce decentralized actor-critic algorithms for each agent, and establish their convergence guarantees when linear function approximation is used. Setting ii corresponds to a classical robust control problem, with linear dynamics and robustness concerns in the H∞-norm sense. In contrast to existing solvers, we introduce policy-gradient methods to solve the robust control problem, with global convergence guarantees, despite its nonconvexity. More interestingly, we show that two of these methods enjoy the implicit regularization property: the iterates of the controller automatically preserve a certain level of robustness stability, by following such policy search directions. This robustness-on-the-fly property is crucial for learning in safety-critical robust control systems. We then study the model-free regime, where we develop derivative-free policy gradient methods to solve the finite-horizon version of the problem, with sampled trajectories from the system and sample complexity guarantees. Interestingly, this robust control problem also unifies several other fundamental settings in control theory and game theory, including risk-sensitive linear control, i.e., linear exponential quadratic Gaussian (LEQG) control, and linear quadratic zero-sum dynamic games. The latter can be viewed as a benchmark setting for competitive multi-agent RL. Hence, our results provide policy-search methods for solving these problems unifiedly. Finally, we provide numerical results to demonstrate the computational efficiency of our policy search algorithms, compared to several existing robust control solvers.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste


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