Ion-Sensing Systems Based on Mesoporous Carbon: from Bulk Electrodes to Paper-Based Ion Sensors

Hu, Jinbo ProQuest Dissertations & Theses University of Minn 2017 해외박사(DDOD)

Potentiometric sensors, comprising ion-selective electrodes (ISEs) and reference electrodes, are a large subgroup of electrochemical ion sensors. In view of affordable and portable analytical devices, all-solid-state ISEs and reference electrodes, in which a solid contact is used as an ion-to-electron transducer, are highly desirable. Compared with conventional ISEs, all-solid-state ISEs offer comparable electrochemical performance with the distinct advantages of simple maintenance and miniaturization.This dissertation focuses on the development of robust all-solid-state potentiometric ion-sensing systems. It starts with the investigation of colloid-imprinted mesoporous (CIM) carbon as a novel solid contact material. CIM carbon exhibits desirable properties as a solid contact material, including a low content of redox-active impurities and a high double layer capacitance. Therefore, sensors based on CIM carbon can be constructed with superior electrochemical performance, including excellent ionic response, reproducibility, signal stability, and resistance to common interfering agents. These outstanding characteristics make CIM carbon-based potentiometric sensors promising candidates for the next generation of commercial ion sensors.To develop low-cost and simple ion sensors for point-of-care applications, this dissertation also involves the development of disposable ion-sensing platforms based on paper. The use of ISEs can be significantly simplified by embedding a conventional potentiometric cell into paper. Paper-based Cl- and K+ sensors are fabricated with highly reproducible and linear responses towards different concentrations of analyte ions in aqueous and biological samples. To further simplify the use of these paper-based ion sensors, CIM carbon-based ISEs and reference electrodes can be integrated into the paper substrate, thus constructing all-solid-state paper-based ion-sensing platforms.Finally, the dissertation explores the possibility of constructing robust calibration-free ion sensors by covalently attaching a redox buffer to CIM carbon. Click chemistry and amide coupling reactions are evaluated for the attachment, and the cobalt-based redox buffer can be attached to CIM carbon. It is found that the open circuit potential of modified CIM carbon films can be affected by the oxidation states of the redox buffer, but a higher redox buffer loading is required to achieve high electrode-to-electrode reproducibility. Possible approaches to achieving such high redox buffer loading are discussed at the end of this dissertation.

Financing Public Higher Education: The Impact of Responsibility Center Management on a Public Research University

Pappone, David J ProQuest Dissertations & Theses University of Minn 2016 해외박사(DDOD)

To explore the impacts on public universities of implementing an incentive-based budgeting system, this dissertation focuses on one university's extensive experience with Responsibility Center Management. The financial and non-financial impacts of Responsibility Center Management will be considered by examining the extent to which commonly held beliefs about Responsibility Center Management are supported by empirical data. Interviews with twenty-one key leaders at the University of Minnesota are the primary data source for understanding the extent to which actual experience supports common beliefs about Responsibility Center Management. Review of financial and other quantitative data, as well as internal documents, also inform the investigation. Responsibility Center Management is found to have a multitude of impacts on the finances and culture of an institution, and interpretation of these impacts is often dependent on one's philosophical views on public higher education. By understanding the actual outcomes and potential pitfalls associated with Responsibility Center Management, university leaders are better informed as they navigate the challenging road ahead for public higher education.

The Association Between Out-Of-Home Placement Characteristics and Crossover from the Foster Care System to the Juvenile Justice System: Risk and Protective Factors

VanMeter, Faith ProQuest Dissertations & Theses University of Minn 2022 해외박사(DDOD)

Youth within the out-of-home care system are at increased risk for a variety of negative developmental outcomes, including increased risk for juvenile delinquency and later criminality as adults. However, little is known about which characteristics of out-of-home placements increase versus reduce risk for delinquency. The current study used data from the Minn-LInK Project (Minnesota-Linking Information for Kids), which is housed in the University of Minnesota’s Center for Advanced Studies in Child Welfare (CASCW), to establish a link between foster care placement characteristics and the likelihood and timing of initial contact with the juvenile justice system. Further, a Latent Class Analysis was conducted to explore profiles of placement characteristics. The sample followed 981 Minnesotan youth who were born in 2000 or 2001 from birth until age 18. The study integrated state administrative data from out-of-home care, child protection, the education system, and the juvenile court system to predict crossover into the juvenile justice system. The current study also utilized a multiverse approach, in which researchers systematically conduct analyses that answer the same research question, but differ in decisions leading up to that answer, such as decisions about coding, data transformations, or analytic techniques, resulting in three unique datasets. Results indicated that removal for a child or parent reason and being identified as male, American Indian/Alaska Native, or receiving special education services robustly predicted the overall risk and/or timing of crossover. Study findings provide significant insight that can aid child welfare practitioners and researchers, and inform policies and practices related to the structure of the child welfare system.

Phenomenological Study of Hydrodynamic Fluctuations and Quark Gluon Plasma at Non Zero Baryon Densities

De, Aritra ProQuest Dissertations & Theses University of Minn 2022 해외박사(DDOD)

The main focus in this thesis is on the phenomenology of heavy-ion collisions, especially hydrodynamic fluctuations and quark-gluon plasma at finite baryon densities. Atoms consist of electrons bound to a nucleus. Inside the nucleus are the subatomic particles - protons and neutrons which are themselves bound state of quarks and gluons. If the energy density and the temperature of the nucleus is made high enough, the quarks are no longer bound in these protons and neutrons. Instead, quarks, antiquarks and gluons become deconfined and form a thermal state called quark-gluon plasma (QGP). Such deconfinement happens in the early universe after the Big Bang. As the universe expands, it cools and quarks get confined into hadrons (protons, neutrons). There are experimental facilities which produce QGP, such as the LHC (Large Hadron Collider) at CERN (Geneva) and the RHIC (Relativistic Heavy Ion Collider) at Brookhaven National Laboratory (New York). Relativistic hydrodynamic simulations have been very successful in explaining the collective behaviour observed in QGP formed in the heavy-ion collision experiments. There are thermal fluctuations in any hydrodynamic system. Study of these fluctuations can be used to extract transport properties of QGP like shear viscosity, bulk viscosity, thermal conductivity etc. Fluctuations are also important in order to detect the presence of the postulated critical point in the QCD (Quantum Chromodynamics) phase diagram. Systematic quantification of these fluctuations in the heavy ion collision simulations is essential to detect the QCD critical point if there is one and that is what has been studied in this thesis. In addition, a new 3D initial state has been proposed for finite baryon densities and, out-of-equilibrium distribution functions have been calculated for finite baryon densities. They have been utilized to perform realistic heavy ion collisions for low energies in anticipation of Beam Energy Scan program at RHIC. Lastly, the stochastic machinery developed was put to work in the context of cosmological inflation to arrive at some novel results.

Observer Design for Non-Monotonic Nonlinear Systems and Interesting Contemporary Applications

Movahedi, Hamidreza ProQuest Dissertations & Theses University of Minn 2022 해외박사(DDOD)

This dissertation analyzes observer design for non-monotonic nonlinear systems and develops globally stable observer design techniques for such systems. Non-monotonic nonlinear systems are frequently encountered in many practical applications, including vehicle tracking, magnetic position estimation, robotics, state of charge (SoC) estimation in Li-ion batteries, and infectious disease spread dynamics. Very few papers in literature have recognized the challenge that existing nonlinear observer design methods do not work for non-monotonic systems. This dissertation demonstrates that current LMI-based observer design methods do not have feasible solutions for many non-monotonic systems. This motivates the need for new observer design techniques. Such techniques are used in three major applications in this thesis: state of charge estimation in Li-ion batteries, magnetic position estimations, and infectious disease spread dynamics estimation.First, a class of systems in which the process dynamics and output equations contain nonlinear functions of only scalar arguments are considered. A Lyapunov approach is utilized to develop an LMI-based observer design method for this class of nonlinear systems. Then, the failure of LMI-based methods to provide constant observer gains for non-monotonic systems is rigorously analyzed, and it is demonstrated that, no matter how small the Lipschitz constant or the Jacobian bounds of the involved nonlinear functions, these methods cannot provide a stabilizing constant observer gain if all the functions of the system are non-monotonic. Based on this theoretical result, a technique to extend the design method to include switched gain observers is presented and its global asymptotic stability is rigorously proven.The developed observer design methodology is utilized to estimate the SoC in a lithium-ion battery, using measurements of terminal voltage and bulk force. The challenge in this application is that the bulk force applied to the casing of the battery, as a result of Lithium-ion intercalation and deintercalation, is a non-monotonic function of the SoC. Hence, a switched gain observer is devised and applied. Using detailed simulations of possible mismatches in the battery model, the robustness of the observer is compared with that of the extended Kalman filter, and the observer is showed to be less susceptible to these model errors. Experimental results corroborate this finding.Position estimation in electro-hydraulic actuators using non-contacting magnetic sensors is another subject that is considered. Magnetic measurements in this application are all non-monotonic, hence based on the theoretical findings of this dissertation it is clear that more than one magnetic sensor is needed for this estimation problem. Subsequently, the minimum singular values of the observability matrix are utilized as a metric for minimizing the number of sensors and optimizing sensor locations. Extensive experimental results are provided to demonstrate the optimality of the sensor locations and the accuracy of the switched gain observer designed for this application.Next, the hysteresis in Li-ion batteries is analyzed. A nonlinear double capacitor model is used for this problem that contains a measurement equation with two nonlinear functions, one of them being significant hysteresis in voltage of the battery as a function of the SoC. Previously, researchers in this field used a differential equation to model the hysteresis. In this dissertation, it is shown that this popular method loses observability and a modified Preisach method is suggested as an alternative. Then a nonlinear Lipschitz observer is designed for this application, and it is shown that the observer provides accurate SoC estimates based on experimental data in the presence of hysteresis.Another research application explored in this dissertation is centered around infectious disease spread dynamics and the real-time estimation problem of variables characterizing disease spread. The COVID-19 epidemic is studied for this purpose, and a new nonlinear dynamic model is developed to enhance the traditional SEIR epidemic model to include additional variables. Subsequently, a cascaded observer is developed to estimate the real-time values of the infection rate, and the basic reproduction number of COVID-19 spread in Minnesota.Finally, the use of the nonlinear observer design techniques for handling sensor noise and disturbance rejection is considered. A H∞-based globally stable nonlinear observer design technique was explored to provide design flexibility equivalent to the popular locally stable extended Kalman filter which is based on linearization of plant dynamics. Furthermore, comparing with the performance of the extended and unscented Kalman filters in the presence of non-Gaussian pulse disturbances and through detailed simulations, it is shown that the H∞ nonlinear observer performs better and can provide a guaranteed upper bound on the estimation error.

Understanding How Participants Become Champions and Succeed in Adopting Healthy Lifestyles: A storytelling of a community health and nutrition program at a Land-Grant University

Keo, Phalla Duong ProQuest Dissertations & Theses University of Minn 2016 해외박사(DDOD)

The purpose of this study was to investigate and understand the experiences of participants who become champions and succeed in adopting healthy lifestyles. The setting was a health and nutrition educational program at University of Minnesota Extension. The main research questions were: How do participants in the Community Health Education Program become champions of the program and succeed in adopting healthy lifestyles? What can we learn about their success?. A storytelling, narrative analysis design was conducted, including interviews with program participants in 10-13 person settings. This study is important as the organization strategically supports the outreach mission of the university. Findings included emergent themes which were organized into domains. Personal characteristics included being outgoing and passionate about what they do. The program learner domain describes their participation and engagement. This included learners' attitudes and facilitators' mindfulness that changes occur in small steps for learners. The program content domain discusses the content, including its connection to key nutrition messages based on the program implementation guidelines, the need to adapt content to fit culturally diverse learners' backgrounds, and learners' immediate needs and interests. The program context domain suggests that context matters, including how low income families face barriers to change that are multi layered. These barriers include but are not limited to financial, health, and social exclusion; this affects the health and well being of participants. Based on these findings, there are practical and theoretical implications for Human Resource Development (HRD).

Complicating International Education: Intersections of Internationalization and Indigenization

Heath, Theresa ProQuest Dissertations & Theses University of Minn 2019 해외박사(DDOD)

Internationalization of higher education is no longer a peripheral strategy for most universities and colleges, now positioned to influence multiple layers of institutions. Intercultural learning as a positive and necessary outcome has bolstered the importance of internationalization; in Canada, intercultural learning has increasingly been institutionalized as an organizational strategy. More recently, Indigenization, or the engagement with Indigenous knowledge and peoples, has been taken up by higher education institutions in Canada. These strategies are grounded in differing educational philosophies, values, and motivations but are implemented simultaneously.This dissertation examines one Canadian higher education institution and the intersections of its strategic priorities of internationalization, interculturalization, and Indigenization. Utilizing case study methodology with interviews, document review, and observation as data collection methods, I examine the following research questions: 1) How do faculty and staff conceptualize the university’s international and intercultural efforts and motivations? 2) How does the institutional priority of increasing intercultural understanding engage with the internationalization and Indigenization organizational strategies of the university? 3) How do staff and faculty across the university understand the intersection of Indigenization and internationalization?Through this dissertation, I make two primary arguments. First, internationalization’s implementation through a business framework has motivated a movement toward interculturalization to further academic learning on campus and temper more the neoliberal outcomes of internationalization. This relationship has established a lasting link between the two strategies. Second, the growing engagement of higher education in Indigenization efforts has brought about intersecting strategic priorities and a hope that interculturalization can support and further Indigenization. However, the Indigenization project is supported and motivated by Indigenous autonomy and sovereignty, not by Western organizational frameworks. Further possibilities of engagement require an uncoupling of business and economic motivations for internationalization and interculturalization to open both to the possibility of transformation.

What Would Grace Hopper Do? Reclaiming Women's Place in Computer Science

Isaacson, Kris ProQuest Dissertations & Theses University of Minn 2019 해외박사(DDOD)

This dissertation investigated the experiences of college women pursuing computer science degrees at a mid-size university in the upper Midwest. Between the 1940s and 1960s computer programming was considered "women's work," but by the 1980s women were being systematically phased out as men recognized the importance (not to mention financial gain) of software development (Brewer, 2017). The percentage of undergraduate degrees in computer science awarded to women and employment in the field reflects the gendered attitudes towards computing. Undergraduate degrees awarded to women and the ratio of women employed in computing-related fields have been in decline in recent decades and are currently at 19 and 25 percent respectively ("Digest of Education Statistics," 2018; Funk & Parker, 2018). The number of men entering computer science since the early 2000s has outpaced that of women, meaning that as an overall, the ratio of women in the field has gone down (Trapiani & Hale, 2019). Moreover, women tend to leave computer science degree programs at nearly twice the rate of their male counterparts (Chen, 2013; White & Massiha, 2016) and there does not appear to be any one definitive reason why women are leaving. Some suggested reasons include the dominant male hegemony, preconceived notions about what it means to “be technical,” stereotype threat, low confidence, and a lack of female peers and role models.The underrepresentation of women in computing is rooted in larger cultural issues; therefore, sociocultural theory and sense of belonging were the conceptual frameworks used to guide this dissertation. A case study design was selected for its ability to gain a deeper understanding of the women’s lived experiences within a specific context and how those experiences shaped their identity, self-efficacy, sense of belonging, and decisions to persist. Five women, studying software development and/or game development at North Central University participated in this research. The data used in this research included transcripts from two in-depth interviews with each of the participants, transcripts from interviews with the academic program directors, classroom observation field notes, and university enrollment numbers.Seven themes and eight sub-themes were derived from the data analysis, were deeply interconnected, and illustrated multiple aspects of the women's experiences as students. The concept of duality, where the women were caught up in a continuous cycle of divergent cultural demands, was determined to be the most pivotal theme insomuch that it interacted with the remaining themes and shaped the women's overall experiences. Five of the themes manifested out of the dichotomous value and belief systems between broader society and the computing micro-culture. The final theme demonstrated the necessity for academic support and mentorship.The findings of this dissertation indicate that there is hope, that there are women who persist in computing degrees, and that concerted efforts to make the computing micro-culture more inclusive show promise for bringing about gender equity. Universities can bring about change and improve women's sense of belonging in the traditionally male-dominated micro-culture by deliberately building communities of women, providing support, demonstrating empathy, and ensuring women have role models. The findings also indicate that additional research and much more work is still needed to bring about gender parity in the field of computer science.

Spintronic Device Physics and Device Applications for Novel and Future Electronic Information Processing and Storage

Lv, Yang ProQuest Dissertations & Theses University of Minn 2018 해외박사(DDOD)

Current complementary metal–oxide–semiconductor (CMOS) technologies have been facing great challenges for decades. Spintronics, a field that addresses transport phenomena, coupled with magnetism, has already found successful solutions for applications in hard disk drives, and recently in embedded memories. It offers a vision of solutions that is still electrical, but also more energy efficient, faster and non-volatile. Among various spintronic devices, the magnetic tunnel junction (MTJ) switched by spin transfer torque (STT) shows immense potential for memory applications. Electric field-induced magnetic anisotropy (EMA) promises more energy-efficient ways to switch MTJ. In this dissertation, EMA is studied by the technique of spin torque-ferromagnetic resonance (ST-FMR) in the in-plane hard-axis transverse direction. Modeling and numerical simulations indicate two distinct FMR spectral line shapes Experimental results confirm the contribution of EMA in FMR process. Spin-orbit torque (SOT) is another promising candidate to switch magnetization. In devices that employ SOT switching, the newly discovered unidirectional spin Hall magnetoresistance (USMR) could sense magnetization change without requiring any additional structures or electrical terminals. To further understand and improve the USMR, ferromagnet (FM)-topological insulator (TI) material systems are studied in this dissertation. The unidirectional spin-Hall and Rashba-Edelstein magnetoresistance (USRMR) is observed in such new material systems and is found to be larger than the USMR in Co/Ta systems. Then the USRMR is studied in magnetic insulator (MI)-TI systems in this dissertation. The USRMR is experimentally observed in this system and its amplitude is further improved. With the large USRMR, a memory prototype of current-induced magnetization switching and USRMR read out is experimentally demonstrated. The MTJ, being a type of more mature spintronic device, has been developed to be integrated into CMOS systems for memory applications. From a different angle, MTJ’s unique properties are being exploited to tackle challenges in specific circuit applications in this dissertation. A true random number generator (TRNG) based on MTJ and utilizing its probabilistic nature of switching is demonstrated experimentally. Two proposals for an analog-to-digital converter (ADC) based on MTJ are also studied by either experiments or simulations. Stochastic computing was proposed decades ago but has not been widely used due to difficulty in employing appropriate devices. Further along this line of effort, a stochastic computing unit based on a single MTJ is proposed and experimentally demonstrated in this dissertation. The unit takes physical conditions, such as field, bias current, pulse amplitude and pulse width, as input and output random bit streams, which in a stochastic manner carry the result of scaled addition and multiplication.

Air Quality, Urban Form, and Environmental Justice

Clark, Lara P ProQuest Dissertations & Theses University of Minn 2018 해외박사(DDOD)

Exposure to urban air pollution is the largest environmental risk factor for public health in the United States (US). Inequity in exposure to air pollution (environmental injustice) has been widely documented and has been linked with pervasive health disparities in the US: people with lower socioeconomic status and people of color are often more exposed to air pollution and more burdened by adverse health impacts related to air pollution exposure. Urban form (the physical design of a city) may influence both air pollution exposures and inequities in air pollution exposures. This dissertation quantifies and explores patterns in air quality, urban form, and environmental justice, on a national basis for the US. The goal of this dissertation is to provide new information on these topics that can inform action to reduce air pollution and to reduce pervasive health disparities related (at least in part) to air pollution exposure.This dissertation consists of four US-national empirical studies of air quality, urban form, and environmental justice (Chapters 2-5), plus an introduction to these topics (Chapter 1) and a summary of findings with potential implications for future research and for policy (Chapter 6).Chapter 1 introduces relevant background on the topics of air pollution, environmental justice, and urban form, and describes the objectives, approach, and structure of this dissertation.Chapter 2 presents a study of relationships between urban form characteristics and criteria air pollutant concentrations (focusing on fine particulate matter and ozone) using linear regression models in a cross-section of 111 US urban areas. Urban form attributes of population distributions are associated with concentrations of criteria air pollutants, with strongest associations for population density (associated with increased concentrations) and population centrality (associated with decreased concentrations). The magnitude of impact for these urban form characteristics on air pollution is comparable to the magnitude of impact for climate characteristics on air pollution.Chapter 3 presents a study of national and within-urban patterns of environmental justice for a transportation-related air pollutant, nitrogen dioxide (NO2), using a national satellite-based land use regression model for NO2, paired with census data at the block group (approximate “neighborhood”) scale. Within urban areas, on average, racial and ethnic minority groups experience higher levels of outdoor NO2, even after controlling for income. Based on a simple health-risk assessment calculation, national levels of environmental injustice for NO2 air pollution (measured as the average exposure disparity between people of color and whites) are associated with a substantial additional public health burden among people of color.Chapter 4 presents a study of changes over time in national and within-urban patterns of environmental justice for NO2, using annual land use regression model for NO2 paired with census data, for years 2000 and 2010. This study finds that environmental injustice decreased substantially on an absolute basis but persisted on a relative basis. Reductions in air pollution concentrations contributed to the absolute reduction in environmental injustice more so than changes in demographics or residential patterns (e.g., suburbs becoming more racially diverse).Chapter 5 presents an exploratory study of relationships between changes in urban characteristics (segregation, urban form, income inequality) and changes in NO2 air pollution environmental justice during 2000 to 2010 across 481 US urban areas. After controlling for urban area population, region, and urban form, changes in residential segregation are associated with changes in NO2 disparities by race, by poverty status, and by linguistic isolation.Chapter 6 summarizes the findings of the studies presented in Chapters 2-5 and discusses implications for future research and policy. Collectively, these studies provide national context for inequities in transportation-related air pollution exposures and suggest that urban form can potentially play a modest role in achieving air quality goals. This dissertation contributes to the literature documenting pervasive racial disparities in environmental risks by, for the first time, quantifying disparities in exposure to transportation-related air pollution in the US on a national basis and over time. Future research could explore in greater detail the public health implications of these inequities in air pollution exposure as well as potential policies, tools, and strategies to address environmental injustice in air pollution exposure.