This dissertation describes synthetic investigations aimed to expand the fundamental chemistry of thorium. Chapter 1 describes the radical reactivity of thorium-ligand bonds with the molecular radical 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO). Organothorium bonds are found to be very reactive with TEMPO and reveal previously unobserved reaction pathways for thorium. Chapter 2 discusses the isolation and characterization the first molecular complexes which contain thorium in the formal +2 oxidation state: [K(2.2.2-cryptand)]{[C5H3(SiMe3)2]3Th} and [K(18-crown-6)(THF)2]{[C5H3(SiMe3)2]3Th}. Physical, spectroscopic, and theoretical studies of these new Th2+ ions conclude they the first examples of a [Rn]6d2 electronic ground state in an isolable metal complex of any kind. The 6d2 configuration is what is expected for the radioactive fourth row transition metal ions such as Rf 2+ and Db3+. Chapters 3 and 4 describe the reactivity of the new Th2+ complexes, with comparisons to the analogous Th3+ compounds where appropriate. Substrates investigated include H2, [Et3NH][BPh4], cyclooctatetraene, iodomethane, iodoethane, benzyl bromide, chlorbenzene, fluoropentane, and benzyl isocyanide. Th2+ is shown to affect both one- and two-electron reductions of substrates. The isolation of new Th3+ complexes, including the first mixed-valent thorium complex and first hydride of Th3+, [K(18-crown-6)(Et2O)]{[C5H3(SiMe3)2)2ThH2]}2, is described, as well as evidence for the in situ generation of a transient Th2+ complex with the (C5Me4H)33− ligand set. Chapter 5 involves the synthesis and reactivity of the sterically-crowded Th3+ complex (C5Me5)3Th. Other sterically-crowded Th4+ complexes are also isolated and their reactivity is reported. Substrates examined include iodomethane, diiodide, chlorobenzene, trimethylaluminum, dihydrogen, and carbon monoxide. Investigations with carbon monoxide led to the formation of [(C5Me5)3Th(CO)][BPh4], the first room temperature stable carbonyl complex of thorium. Chapter 6 describes an initial investigation into the reactivity of the Th3+ complexes (C5Me4H)3Th and [C5H3(SiMe3)2]3Th with nitric oxide (NO). Two structurally different bimetallic complexes are isolated, namely [(C5Me4H)2Th]2(μ-ONNO), and {[C5H3(SiMe3)2]2Th(μ-O)}2. Chapter 7 describes the synthesis of the nitrile-solvated [(C5Me5)2Th(NCR)5][BPh4]2 (R = Me, Ph, tBu) complexes, which are the first examples of linear metallocenes of thorium containing cyclopentadienyl ligands. Chapter 8 presents preliminary results on other synthetic attempts to isolate low-valent thorium compounds. Evidence of transient low-valent species is described and factors leading to the instability are discussed.

As the capabilities of robotic systems increase, we move closer to the vision of ubiquitous robotic assistance throughout our everyday lives. In transitioning robots and autonomous systems from traditional factory and industrial settings, it is critical that these systems are able to adapt to uncertain environments and the humans who populate them. In order to better understand and predict the behavior of these humans, Inverse Reinforcement Learning (IRL) uses demonstrations to infer the underlying motivations driving human actions. The information gained from IRL can be used to improve a robot’s understanding of the environment as well as to allow the robot to better interact with or assist humans.

In this dissertation, we address the challenge of incorporating safety into the application of IRL. We first consider safety in the context of using IRL for assisting humans in shared control tasks. Through a user study, we show how incorporating haptic feedback into human assistance can increase humans’ sense of control while improving safety in the presence of imperfect learning. Further, we present our method for using IRL to automatically create such haptic feedback policies from task demonstrations.

We further address safety in IRL by incorporating notions of safety directly into the learning process. Currently, most work on IRL focuses on learning explanatory rewards that humans are modeled as optimizing. However, pure reward optimization can fail to effectively capture hard requirements, such as safety constraints. We draw on the definition of safety from Hamilton-Jacobi reachability analysis to infer human perceptions of safety and to modify robot behavior to respect these learned safety constraints. We also extend this work on learning constraints by adapting the framework of Maximum Entropy IRL in order to learn hard constraints given nominal task rewards, and we show how this technique infers the most likely constraints to align expected behavior with observed demonstrations.

Introduction: The degree to which individual patients use multiple emergency departments (EDs)is not well-characterized. We determined the degree of overlap in ED population between threegeographically proximate hospitals.

Methods: This retrospective cohort study reviewed administrative hospital records from 2003 to2007 for patients registered to receive ED services at an urban academic, urban community, andsuburban community ED located within 10 miles of one another. We determined the proportion whosought care at multiple EDs and secondarily characterized patterns of repeat encounters.

Results: There were 795,176 encounters involving 282,903 patients. There were 89,776 (31%)patients with multiple encounters to a single ED and 39,920 (14%) patients who sought care frommultiple EDs. The 39,920 patients who sought care from multiple EDs generated 185,629 (23%)of all encounters. Patients with repeat encounters involving multiple EDs were more likely to befrequent or highly frequent users (30%) than patients with multiple encounters to a single ED (14%).

Conclusion: While only 14% of patients received care from more than one ED, they wereresponsible for a quarter of ED encounters. Patients who use multiple EDs are more oftenfrequent or highly frequent users than are repeat ED visitors to the same ED. Overlap between ED populations is sufficient to warrant consideration by multiple domains of research, practice, andpolicy. [West J Emerg Med. 2015;16(2):229–233.]

It is clear that Protohistoric Period ceramic jars were necessary for adapting to the harsh conditions of the Lower Colorado River Valley and its adjoining deserts. Although it remains to be conclusively demonstrated whether the Trigo Mountains cache also reflected ritual behavior, such analyses merit further exploration, given the ethnographic insights on this issue. Despite the fact that noneconomic activity is difficult to document archaeologically, ceramic design iconography is a promising and largely untapped avenue for considering this dimension of native survival in the Lower Colorado Desert. Analysis of the Trigo Mountains cache contributes new perspectives on this and related topics.