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Algorithms For Safe And Robust Motion Control Of Autonomous Ground Robots And Vehicles
Get PDFThis dissertation explores, investigates, develops and experimentally validates algorithms for safe and robust motion control of ground robots and vehicles. The emphasis is on design of controllers for ground autonomy with safety either embedded by design or enforced by appropriately wrapping a safety net around an existing nominal controller.
Ground robots have been considered for their importance in compensating for labour or personnel shortage for material handling in the manufacturing, logistics and healthcare sectors. On the other hand, ground vehicles have been considered for the existing potential of making driver assistance systems safer and more intelligent, particularly in at-the-limit driving scenarios. For ground robots, safety is considered in the context of obstacle-avoidance. For ground vehicles, safety and robustness is considered in the context of retaining tire-road traction in safety-necessitated aggressive maneuvers, despite the presence of modeling errors.
Throughout this dissertation, the control architectures and schemes developed are minim\-ally invasive, that is, the control effort of an existing nominal controller is modified only if safety is expected to be compromised. This has promoted adaptability, modularity and compactness in the design of the control architectures.
Where considered appropriate, the control design in this dissertation is accompanied by theory and analyses for provable safety and stability. This enables their implementation on real-world robots in the near-term. For the long-term, the theory and analyses provided lay the foundation for developing data-driven controllers that are embedded, by design, with stability and safety guarantees.
The main contributions of this dissertation are,
1. provision of a control architecture that decouples kinematic and dynamic control of ground robots in a loop-within-a-loop fashion for trajectory-tracking and obstacle-avoidance. At the kinematic level, a self-adaptive barrier function-based safe steering envelope provides safe commands for translational velocity and heading. At the dynamic level, the innermost wheel velocity control loop comprises a compensator for actuator-level time-delays that allows timely steering for obstacle avoidance,
2. formulation of a minimally invasive auxiliary control that avoids undesirable local equilibria in control Lyapunov function and control barrier function based quadratic programs designed for trajectory-tracking and obstacle avoidance in ground robots. The auxiliary control is accompanied with specific QP constraints designed based on the theoretical investigations that provide the mathematical conditions for occurrence of the undesirable equilibria, 3. development of an accurate and robust input-to-state stable nonlinear observer for ground vehicles that can estimate, online and in real-time, errors in modeling lateral and longitudinal vehicle dynamics, and translate these errors into improved estimates of ground-truth tire-road forces. Experimental validation on a one-tenth scale and full-scale cars opens up opportunities to improve vehicle-tire modeling and robustness of vehicle control to ultimately improve vehicle safety,
4. construction of an observer robustified control barrier function filter that wraps around a nominal vehicle controller to retain traction and motion control in a vehicle driven at the limits of handling, despite the presence of modeling errors in the nominal controller. Experimental validation on a full-scale vehicle showed improvement in vehicle safety by preventing loss of tire-road traction and consequent vehicle understeer and oversteer
First-Principles Investigation Of Interfacial Chemistries In Room Temperature Sodium-Sulfur Batteries
No full textThe widespread integration of Lithium-ion (Li-ion) batteries into grid systems underscores the critical need for further reductions in energy storage costs, particularly to support renewable energy sources such as wind and solar power. However, the limitations of current Li-ion technology, notably resource constraints, particularly concerning metals like lithium (Li) and cobalt (Co), are increasingly evident. With the escalating demand for lower costs and higher energy density, alongside growing concerns regarding natural resource depletion, research into beyond Li-ion technologies has garnered significant attention. Metal-sulfur (M-S) batteries are emerging as promising successors to Li-ion batteries due to their superior energy density, specific capacity, cost-effectiveness of S, and environmental friendliness. Among these, LiS batteries have demonstrated remarkable advancements in high capacity, rate capability, and extended cycle life, positioning them closer to market readiness. However, constraints related to the cost and availability of Li resources presently impede their suitability for large-scale applications. From sustainability and economic standpoints, sodium (Na) emerges as a superior choice over Li for pairing with S cathodes owing to their analogous chemical properties and significantly greater natural abundance.
Room temperature sodium-sulfur batteries (RT Na-S) hold promise as potential replacements forLi-ion batteries, yet their development faces significant hurdles, including issues such as poor reversible capacity, rapid capacity fade, and inadequate Coulombic efficiency. The limited accessible capacity stems from S\u27s insulating nature and its sluggish reactivity with Na, resulting in incomplete reduction rather than complete Na2S formation. Moreover, the dissolution of polysulfides into the electrolyte during cycling, known as the shuttle effect, stands as the primary cause behind rapid capacity degradation. Through meticulous investigation, our aim is to mitigate the shuttle effect and improve electrochemical reaction kinetics. Conventional methods of addressing the shuttle effect and enhancing performance in RT Na-S batteries, predominantly relying on physical and chemical adsorption, face challenges in overcoming poor reaction kinetics and limited capacity. Traditional materials tailored for Li-S batteries may not adequately meet the demands of RT Na-S batteries due to heightened shuttle effects and sluggish reaction kinetics. Consequently, there is a pressing need for innovative approaches to overcome these obstacles.
Employing electrocatalytic concepts presents a promising strategy for addressing these challengesin RT Na-S batteries. By utilizing electrocatalytic materials, we not only reduce the energy barrier of electrochemical reactions but also serve as an anchor for polysulfides, thus containing them to the cathode and minimizing their shuttle effect. In this study, we conducted fundamental mechanistic investigations into the S-electrocatalyst interface to develop an optimized catalytic cathode. We explored polysulfide adsorption and S electrochemical reaction kinetics on various electrocatalytic surfaces, including VS2, single transition metal (TM) atom-doped graphene, and MoS2, focused on understanding the effectiveness of these surfaces in influencing the S reaction kinetics during both discharging and charging processes. We calculate the adsorption energies of solid/liquid polysulfide species onto substrates. This investigation includes a comparative assessment of energetics against commonly employed electrolyte solvents like 1,3- dioxolane (DOL) and 1,2-dimethoxyethane (DME), elucidating the efficacy of our studied cathode electrocatalysts in mitigating the polysulfide shuttle phenomenon. Furthermore, we explore the adsorption mechanisms of various TM-doped substrates, employing d-band theory, and Bader charge analysis. The electronic structure evolution of our studied cathode electrocatalysts, both pre- and post-reaction with Na2Sn, is comprehensively analyzed through density of states (DOS). To address kinetic challenges associated with polysulfide conversion during discharge, we conduct Gibbs free energy analyses for the studied electrocatalysts. This endeavor seeks to elucidate the role of catalysts in enhancing reaction kinetics and facilitating Na2S deposition on cathode surfaces. Moreover, a detailed examination of charging behavior in RT Na-S batteries utilizing our studied electrocatalysts is conducted through nudged elastic band analysis. This endeavor aims to unravel the significance of chosen electrocatalysts in modulating the activation barrier of Na2S decomposition, crucial for facilitating rapid charging phenomena in Na-S batteries. Overall, our study significantly advances the understanding of tailoring polysulfide chemistry at electrocatalyst interfaces, thereby representing a pivotal step towards the systematic design of cathode materials tailored for Na-S batteries. Furthermore, our findings underscore the efficacy of enhancing active sites through the strategic engineering of TMDs and graphene surfaces, offering valuable insights into the precise modulation of electrochemical reactions involving polysulfides. Additionally, this research is poised to catalyze further computational and experimental explorations into a diverse array of 2D anchoring materials, thereby fostering the progressive development of cathodes tailored for Na-S batteries, characterized by diminished reversible capacity loss and improved performance metric
The Drivers Of Perceived Oem-Supplier Relationship Quality And The Influence Of Culture, Alignment & Engagement
No full textABSTRACTTHE DRIVERS OF PERCEIVED OEM-SUPPLIER RELATIONSHIP QUALITY AND THE INFLUENCE OF CULTURE, ALIGNMENT & ENGAGEMENT by ANGELA M. JOHNSON August 2024 Advisor: Dr. Ratna Babu Chinnam Major: Industrial Engineering Degree: Doctor of Philosophy
Through a case study analysis of one U.S. automotive OEM and over 300 direct material supplier relationships, this dissertation examines the drivers of bilateral perceived relationship satisfaction. As the automotive industry undergoes massive technological transformation amid unparalleled global supply chain disruption, OEM relationships with critical suppliers provide a key to delivering cost-effective, first-to-market innovation and to fortify supply chain resilience. Spanning 2020 – 2022, the research uniquely contributes to industry and academia through insights drawing upon an unprecedented repository of externally and internally sourced data. Qualitative coding analyzes 20,000 verbatims spanning 4,000 buying situations. Annual Plante Moran Working Relations Index and internal OEM-issued bilateral relationship surveys, supplemented with demographic, performance, and employee engagement data provide a broad and deep analysis of bilateral relationship satisfaction. Survey analysis findings are subsequently validated through 18 dyadic OEM-supplier interviews. A new concept is introduced, Behaviors Influencing Transactional Efficiency (BITE), as it is distinguished from the relational constructs commonly associated with high-functioning corporate partnerships such as knowledge sharing, collaboration, innovation, and continuity. BITE provides the mechanism through which exchange relationships transform from transactional to relational ties. The role of Corporate Composition is introduced in reference to the fundamental structure, culture, and operating model of the OEM, and how it shapes the boundary conditions between relationship satisfaction and enterprise objectives. Overall, this research demonstrates that trade-offs of enterprise strategic decisions and functional strategy execution compromise transactional efficiency, and thus bi-lateral relationship satisfaction. Adequate transactional efficiency, as each party defines through its own perspective, must be achieved before the relational constructs and benefits that define high-functioning partnerships can be realized. The data demonstrates the moderating effect of cultural similarity, strategic significance, and peer connections to pacify or amplify the effects of transactional inefficiencies. Furthermore, it builds upon extant research that transactional governance and relational governance exist not in isolation but along a spectrum and demonstrates that OEM governance mechanisms must align to Corporate Composition. When misalignment exists, initiatives fail to sustain, and enterprise performance is compromised. Several recommendations are provided as a continuous improvement approach to balance market objectives and key supplier partnerships.
The research provides academic contributions to the complex field of industrial OEM-supplier exchange relationships, offers actionable insights to OEMs and suppliers, and provides a blueprint for manufacturers with complex global supply chains to understand and strengthen strategic supplier relationships in harmony with enterprise strategy
Improving The Accuracy And Practicality Of Patient-Specific Dosimetry In 177lu Radiopharmaceutical Therapies
Get PDFRadiopharmaceutical therapies (RPTs) have their roots in the initial discoveries of radiation and radiotherapy at the turn of the 20th century, but recent interest in the 177Lu- based RPTs 177Lu-DOTATATE and 177Lu-PSMA-617 have highlighted the need to investigate patient-specific, dosimetry-guided approaches to planning these therapies. These RPTs are currently administered in “one-size-fits-all” regimens of fixed activity injections and current dosimetry methodologies often have large uncertainties and are reliant upon reference values that do not necessarily apply to all patients. In this work, several ways to make patient-specific dosimetry in 177Lu-DOTATATE and 177Lu-PSMA- 617 RPTs more accurate or more accessible are addressed.In the first study, information available prior to the start of 177Lu-DOTATATE peptide receptor radionuclide therapy (PRRT) including quantitative 68Ga-DOTATATE PET/CT imaging and biomarkers from patient’s medical records was used to predict the absorbed dose (AD) delivered to the kidneys following the first cycle of therapy. Kidney AD was able to be predicted with a mean absolute percent error (MAPE) of 18% with a relatively simple regression model of renal uptake on 68Ga-DOTATATE PET/CT. The second study quantified the impact of different SPECT/CT imaging schedules on the time-integrated activity (TIA) used for dosimetry in 177Lu-DOTATAE PRRT via patient data and clinically realistic simulations. TIA estimates with 2 and 3 SPECT/CT time points were within 5%, on average, of the reference 4 time point SPECT/CT TIA if imaging time points were not too close together or too early (all \u3c48 h). Single time point TIA estimates had performance comparable to multi-time point imaging at optimal time points, but systematically underestimate the absorbed dose with large variability if not imaged near the optimal time points. The third study saw the development of a novel dosimetry method for quantifying bone marrow AD in patients treated with 177Lu-PSMA-617 radioligand therapy for metastatic castrate resistant prostate cancer. The novel method incorporated information on patient-specific tumor and marrow distributions by leveraging information from 68Ga- PSMA-11 PET/CT and 99mTc-sulfur colloid SPECT/CT imaging studies, respectively. This informed a micro-scale model of the complex spongiosa structure which was coupled with a MC dosimetry code to apportion AD directly to the active marrow and treating the dose distinctly from the other components of the marrow space. This novel methodology was compared with existing dosimetry methodologies. AD values with the novel methodology were lower than other image-based dosimetry methods and more in agreement with accepted dose limits for bone marrow toxicity. The results additionally indicate that blood- based dosimetry, which is commonly applied to 177Lu-PSMA-617 RLT, is not adequate for predicting hematological toxicity and image-based dosimetry studies are necessary for accurately quantifying absorbed dose to the bone marrow, particularly in patients with a substantial metastatic burden in the bone. The results of these studies all support different aspects of improving the RPT dosimetric workflow and move the field toward patient-specific, dosimetry guided therapy
Identification And Mitigation Of Toxic Communications Among Open Source Software Developers
No full textToxicity occurs during the developers\u27 interaction in Free and Open Source Software (FOSS) projects. Prior studies in the Software Engineering domain reported toxic and unhealthy conversations during the developer\u27s communication. These unhealthy behaviors may reduce the professional harmony and productivity of FOSS projects. For example, toxic code review comments may raise pushback from an author to complete suggested changes. Toxic communication with another person may hamper future communication and collaboration. Research also suggests that toxicity disproportionately impacts newcomers, women, and other participants from marginalized groups in open source communities. Therefore, toxicity is a barrier to promoting diversity, equity, and inclusion in the FOSS community. Since toxic communications are not uncommon among FOSS communities and such communications may have serious repercussions, the primary objective of this dissertation is to automatically identify and mitigate toxicity during developers\u27 textual interactions. On this goal, this dissertation completed three studies, which include i) building an automated toxicity detector for the Software Engineering (SE) domain, ii) developing an explainable toxicity detection tool for SE conversations, iii) an empirical investigation of the impacts of toxicity on the outcomes of FOSS projects
Characterization Of Vibrio Cholerae Colonization Factors In Zebrafish
No full textVibrio cholerae is a gram-negative, aquatic bacterium responsible for the deadly diarrheal disease cholera, which affects millions worldwide each year. The zebrafish (Danio rerio), indigenous to cholera endemic regions, serves as an ideal model organism due to its natural susceptibility to V. cholerae infection. However, the specific genetic factors important for Vibrio cholerae colonization in zebrafish are unknown. Previous studies in the lab utilized transposon sequencing analysis (Tn-Seq) to identify potential colonization factors required by V. cholerae in the zebrafish intestine. Some genes identified in this manner were observed to be associated with transport and transcriptional regulation. A few selected genes were subjected to a complete gene knockout (KO) in the El Tor C6706 wild type (WT) strain. The KO strains were generated using Splicing by Overlap Extension method, followed by chitin-induced natural transformation. Using zebrafish as a model, parallel infections were conducted between the KO and WT strains to determine if the suspected colonization factor is important for colonization. We hypothesize that the mutants created will have significant changes in colonizing the zebrafish intestine compared to the wild type. However, our colonization experiments with Δ TCS sensor histidine kinase and Δ Cation-proton antiporter revealed that the gene deletions have no significant impact on intestinal colonization. Identifying genes important for fish colonization holds immense potential and will contribute to our broader understanding of bacterial pathogenesis
Designing For Reliability: Algorithmic And Applied Perspectives On Trustworthy Artificial Intelligence
No full textThis dissertation advances the field of Trustworthy AI, focusing on enhancing robustness, interpretability, and fairness, especially in designing reliable systems. Chapter 2 introduces AttCAT: Explaining Transformers via Attentive Class Activation Tokens, which proposes a novel method for generating accurate explanations for Transformer models using attentive class activation tokens to assess input token impacts. In Chapter 3, Counterfactual Interpolation Augmentation (CIA): A Unified Approach to Enhance Fairness and Explainability of DNN, a method is presented to improve fairness and explainability in deep neural networks. This is achieved through counterfactual interpolations that de-correlate sensitive attributes, enhancing both fairness and interpretability. Chapter 4 discusses Hijacking Large Language Models via Adversarial In-Context Learning, revealing a new vulnerability in LLMs. It demonstrates how imperceptible adversarial suffixes can manipulate LLM outputs, underscoring the need for more robust defenses. Overall, this work contributes significantly to Trustworthy AI by proposing innovative approaches to address key challenges in AI systems’ explainability, robustness, and fairness
An Exploration Of Medical Mistrust In Urban African American Adolescents With High Risk Asthma
No full textProblem: Little is known about the relationship between medical mistrust and health outcomes in adolescents, particularly minority adolescents with chronic illness. There is also a paucity in knowledge on the relationship between caregivers’ trust or mistrust in a provider and if this is similar or dissimilar in their adolescent’s beliefs. To address this critical gap in research, this study aims to explore medical mistrust in AA adolescents with high-risk asthma and their caregivers. Asthma is currently the leading pediatric chronic respiratory condition in the United States, with a reported 60% had uncontrolled asthma symptoms. Asthma disproportionately affects urban, disadvantaged, minority children. It is 26% more prevalent among African American (AA) children than Caucasian children, and AA children experience more emergency visits, hospitalizations, and fatalities from asthma than Caucasians, even after controlling for socioeconomic variables. Adolescents with asthma are at higher risk than younger children for increased morbidity and mortality, with minority adolescents at highest risk. Purpose: The overarching purpose of this study is to explore medical mistrust among African American adolescents with high-risk asthma and their primary caregivers. The study was guided by three aims that compared medical mistrust between both groups of participants, and explored associations between medical mistrust, asthma knowledge, asthma self-management, asthma related health outcomes and health care utilization. Methods: This study is a cross-sectional descriptive secondary analysis of the parent study, an R01 clinical trial. It enrolled 19 caregiver-adolescent dyads of African American individuals aged 12 years, 0 months to 16 years 11 months, with moderate to severe persistent poorly controlled asthma. Participants completed study questionnaires sent through Qualtrics links. The research questions were tested using statistical analyses such as multiple linear regression analysis, Pearson correlation analysis and independent sample t-test. This study was guided by the Behavioral Model for Vulnerable Populations theoretical framework. Results: As adolescents increased in age, medical mistrust levels increased as well. Male adolescents had higher mistrust scores than female adolescents. Caregivers with lower educational achievement and lower household income had higher medical mistrust scores than caregivers with higher education achievement and higher household incomes. An inverse relationship was noted between adolescent medical mistrust scores and adolescent trust in provider scores. Adolescent trust and caregiver trust were positively correlated, with similar scores noted. Caregiver medical mistrust in their own adult healthcare provider and adolescent mistrust in their pediatric provider were not correlated. A negative correlation was found between caregiver medical mistrust and adolescent trust in their provider. Medical mistrust did not predict asthma knowledge, medication adherence, symptom assessment or environmental control. However, medical mistrust did predict poor asthma control. A negative correlation was found between caregiver medical mistrust levels and emergency visits for asthma. A positive correlation was found between caregiver trust in the adolescent’s pediatrician and emergency department visits for asthma. Note: statistical significance of study findings was nullified due to small sample size. Conclusion: This study is the first documented study of intergenerational medical mistrust and among urban minority adolescents with high risk asthma. Study findings indicate that the phenomenon of medical mistrust is complex in nature and therefore more detailed research study approaches are required in the future. Future research is needed to extend the current study results, including utilizing mixed methods research, replicating findings in a larger more diverse sample size to ensure the generalizability of findings, and investigating change in medical mistrust over time, especially in developing adolescents across various adolescent ages. These future research studies should focus on better understanding how adolescents conceptualize medical mistrust. and also examine adolescent medical mistrust towards non-physician healthcare providers. Nurses should focus on developing targeted interventions to mitigate medical mistrust, improve asthma related health outcomes, and to advance health equity in asthma care. This study has provided novel findings that have the potential to contribute to the frontier of examining the development of and various aspects of medical mistrust in youth with chronic illnesses
“(un)safe In Our Bodies”: Religious Fundamentalism, Purity Culture, And The Upholding Of Patriarchy In Contemporary American Literature
No full textThis dissertation explores patriarchal violence against women not only as a symptom of systemic oppression, but also because of Christian fundamentalist beliefs that furtively pervade societal, political, and personal circles. Across my dissertation chapters that focus on four novels—Octavia Butler’s Parable of the Sower, Margaret Atwood’s The Handmaid’s Tale, Jeffrey Eugenides’ The Virgin Suicides, and Sandra Cisneros’ The House on Mango Street—I argue that biblical literalism is used to positively frame oppression and violence against women, and that white supremacy and American nationalism are protected even in seemingly revolutionary texts. Additionally, I argue that purity culture, an ideology that prizes female virginity, paradoxically results in the fetishization of young girls, infantilization of grown women, and commodification of women’s bodies, especially women of color
Why We Come: Investigating Virtual Clubhouse Engagement
Get PDFOnly a fraction of individuals living with serious mental illness (SMI) receive adequatetreatment. This study investigates members’ experiences of a virtual adaptation of the Clubhouse model, a psychosocial rehabilitation program. During the COVID-19 lockdowns, the virtual Clubhouse, referred to as virtual programming, was established to provide an alternative to the traditional brick-and-mortar Clubhouse. This qualitative inquiry utilizes a phenomenological approach to understand participant experiences of the virtual model, including factors related to motivation, recovery, and impact. Data was collected through semi-structured interviews with 15 members of a Clubhouse located in a large metropolitan city in the U.S. The interviews sought to understand members’ experiences with virtual programming, with special considerations of motivations for participating in virtual programming, the impact of virtual programming on their own sense of recovery, as well as a sense of community and perceived empowerment. Consistent with previous research on in-person motivations, social connection remains a primary motivator for participation in virtual mental health programs. Members reported that virtual programming offered a sense of community and provided critical support they may not 109 otherwise be able to access. The findings also revealed the significance of convenience and accessibility when it comes to virtual options for mental health treatment, which may reduce barriers to engagement for individuals with SMI. This study contributes to the expanding literature on virtual mental health interventions and provides support for the potential of virtual Clubhouse models to provide inclusive, equitable, and empowering care in a digital landscape. Future research should explore the scalability and long-term impact of virtual programming on mental health recovery