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Control of Dynamical Systems with Temporal Logic Specifications
Get PDFThis thesis is motivated by safety-critical applications involving autonomous air, ground, and space vehicles carrying out complex tasks in uncertain and adversarial environments. We use temporal logic as a language to formally specify complex tasks and system properties. Temporal logic specifications generalize the classical notions of stability and reachability that are studied in the control and hybrid systems communities. Given a system model and a formal task specification, the goal is to automatically synthesize a control policy for the system that ensures that the system satisfies the specification. This thesis presents novel control policy synthesis algorithms for optimal and robust control of dynamical systems with temporal logic specifications. Furthermore, it introduces algorithms that are efficient and extend to high-dimensional dynamical systems.
The first contribution of this thesis is the generalization of a classical linear temporal logic (LTL) control synthesis approach to optimal and robust control. We show how we can extend automata-based synthesis techniques for discrete abstractions of dynamical systems to create optimal and robust controllers that are guaranteed to satisfy an LTL specification. Such optimal and robust controllers can be computed at little extra computational cost compared to computing a feasible controller.
The second contribution of this thesis addresses the scalability of control synthesis with LTL specifications. A major limitation of the standard automaton-based approach for control with LTL specifications is that the automaton might be doubly-exponential in the size of the LTL specification. We introduce a fragment of LTL for which one can compute feasible control policies in time polynomial in the size of the system and specification. Additionally, we show how to compute optimal control policies for a variety of cost functions, and identify interesting cases when this can be done in polynomial time. These techniques are particularly relevant for online control, as one can guarantee that a feasible solution can be found quickly, and then iteratively improve on the quality as time permits.
The final contribution of this thesis is a set of algorithms for computing feasible trajectories for high-dimensional, nonlinear systems with LTL specifications. These algorithms avoid a potentially computationally-expensive process of computing a discrete abstraction, and instead compute directly on the system's continuous state space. The first method uses an automaton representing the specification to directly encode a series of constrained-reachability subproblems, which can be solved in a modular fashion by using standard techniques. The second method encodes an LTL formula as mixed-integer linear programming constraints on the dynamical system. We demonstrate these approaches with numerical experiments on temporal logic motion planning problems with high-dimensional (10+ states) continuous systems.</p
Extractive Institutions in Colonial Africa
Get PDFA common explanation for African current underdevelopment is the extractive character of institutions established during the colonial period. Yet, since colonial extraction is hard to quantify and its exact mechanisms are not well understood, we still do not know precisely how colonial institutions affect economic growth today. In this project, I study this issue by focusing on the peculiar structure of trade and labor policies employed by the French colonizers.
First, I analyze how trade monopsonies and coercive labor institutions reduced African gains from trade during the colonial period. By using new data on prices to agricultural producers and labor institutions in French Africa, I show that (1) the monopsonistic character of colonial trade implied a reduction in prices to producers far below world market prices; (2) coercive labor institutions allowed the colonizers to reduce prices even further; (3) as a consequence, colonial extraction cut African gains from trade by over 60%.
Given the importance of labor institutions, I then focus on their origin by analyzing the colonial governments' incentives to choose between coerced and free labor. I argue that the choice of institutions was affected more by the properties of exported commodities, such as prices and economies of scale, than by the characteristics of colonies, such indigenous population density and ease of settlement for the colonizers.
Finally, I study the long-term effects of colonial trade monopsonies and coercive labor institutions. By combining archival data on prices in the French colonies with maps of crop suitability, I show that the extent to which prices to agricultural producers were reduced with respect to world market prices is strongly negatively correlated with current regional development, as proxied by luminosity data from satellite images. The evidence suggests that colonial extraction affected subsequent growth by reducing development in rural areas in favor of a urban elite. The differential impact in rural and urban areas can be the reason why trade monopsonies and extractive institutions persisted long after independence.</p
Eavan Boland and Paula Meehan : Irish Voices of the Past
Get PDFHistory, myth, exile, identity—for generations those have been the themes of Irish poetry, an Irish poetry written almost exclusively by male poets. As women moved in to claim a voice the themes were often the same, though reworked in essential ways. The key to that reworking, the pivot for an Irish women’s poetry, was the development of a female poetic identity. Eavan Boland led the way. In particular, Boland’s struggles as the first prominent female poet of modern Irish Literature emphasize a search for self-identity. At the forefront of this movement and a precedent for those around her, she establishes themes that pave the way for Irish women writers. With Boland, comes a hopeful recovery of the contemporary female literary experience, with the perspective and approach towards self-identity endlessly evolving over time with each new poet. Inspired by Boland, but a generation younger, Paula Meehan explores similar themes of female constraint, yet raises her own distinctive concerns, in particular the division of male and female roles and generational conflict, exploring what is real and ordinary
On the Local Tamagawa Number Conjecture for Tate Motives
Get PDFThere is a wonderful conjecture of Bloch and Kato that generalizes both the analytic Class Number Formula and the Birch and Swinnerton-Dyer conjecture. The conjecture itself was generalized by Fukaya and Kato to an equivariant formulation. In this thesis, I provide a new proof for the equivariant local Tamagawa number conjecture in the case of Tate motives for unramified fields, using Iwasawa theory and (φ,Γ)-modules, and provide some work towards extending the proof to tamely ramified fields
A Multi-Scale Approach to Shaping Carbon Nanotube Structures for Hollow Microneedles
Get PDFThe concept of a carbon nanotube microneedle array is explored in this thesis from multiple perspectives including microneedle fabrication, physical aspects of transdermal delivery, and in vivo transdermal drug delivery experiments. Starting with standard techniques in carbon nanotube (CNT) fabrication, including catalyst patterning and chemical vapor deposition, vertically-aligned carbon nanotubes are utilized as a scaffold to define the shape of the hollow microneedle. Passive, scalable techniques based on capillary action and unique photolithographic methods are utilized to produce a CNT-polymer composite microneedle. Specific examples of CNT-polyimide and CNT-epoxy microneedles are investigated. Further analysis of the transport properties of polymer resins reveals general requirements for applying arbitrary polymers to the fabrication process.
The bottom-up fabrication approach embodied by vertically-aligned carbon nanotubes allows for more direct construction of complex high-aspect ratio features than standard top-down fabrication approaches, making microneedles an ideal application for CNTs. However, current vertically-aligned CNT fabrication techniques only allow for the production of extruded geometries with a constant cross-sectional area, such as cylinders. To rectify this limitation, isotropic oxygen etching is introduced as a novel fabrication technique to create true 3D CNT geometry. Oxygen etching is utilized to create a conical geometry from a cylindrical CNT structure as well as create complex shape transformations in other CNT geometries.
CNT-polymer composite microneedles are anchored onto a common polymer base less than 50 µm thick, which allows for the microneedles to be incorporated into multiple drug delivery platforms, including modified hypodermic syringes and silicone skin patches. Cylindrical microneedles are fabricated with 100 µm outer diameter and height of 200-250 µm with a central cavity, or lumen, diameter of 30 µm to facilitate liquid drug flow. In vitro delivery experiments in swine skin demonstrate the ability of the microneedles to successfully penetrate the skin and deliver aqueous solutions.
An in vivo study was performed to assess the ability of the CNT-polymer microneedles to deliver drugs transdermally. CNT-polymer microneedles are attached to a hand actuated silicone skin patch that holds a liquid reservoir of drugs. Fentanyl, a potent analgesic, was administered to New Zealand White Rabbits through 3 routes of delivery: topical patch, CNT-polymer microneedles, and subcutaneous hypodermic injection. Results demonstrate that the CNT-polymer microneedles have a similar onset of action as the topical patch. CNT-polymer microneedles were also vetted as a painless delivery approach compared to hypodermic injection. Comparative analysis with contemporary microneedle designs demonstrates that the delivery achieved through CNT-polymer microneedles is akin to current hollow microneedle architectures. The inherent advantage of applying a bottom-up fabrication approach alongside similar delivery performance to contemporary microneedle designs demonstrates that the CNT-polymer composite microneedle is a viable architecture in the emerging field of painless transdermal delivery.</p
Microfabricated Tools and Engineering Methods for Sensing Bioanalytes
Get PDFThere is a convergence between the needs of the medical community and the capabilities of the engineering community. For example, the scale of biomedical devices and sensors allow for finer, more cost-effective quantification of biological and chemical targets. By using micro-fabrication techniques, we design and demonstrate a variety of microfluidic sensors and actuators that allow us to interact with a biochemical environment. We demonstrate the performance of microfluidic blood-filtrations chips, immune-diagnostic assays, and evaporative coolers. Furthermore, we show how micro-fabricated platinum filaments can be used for highly localized heating and temperature measurement. We demonstrate that these filaments can be used as miniature IR spectroscopic sources. Finally, we describe and demonstrate novel combinatorial coding methods for increasing the information extracted from biochemical reactions. We show proof-principle of these techniques in the context of Taqman PCR as well as persistence length PCR
The Development of a Synthetic Strategy Toward Dihydrooxepine-Containing Epipolythiodiketopiperazines: Enantioselective Total Synthesis of (-)-Acetylaranotin and Related Investigations
Get PDFTo the chemist, the epipolythiodiketopiperazine (ETP) fungal metabolites represent a fascinating family of natural products, not only for their unique structural elements, but also for the unusual modes by which they are hypothesized to exert their biological activities. Though efforts at the total synthesis of these molecules have led to an evolution of innovative synthetic methodologies and strategies, challenges remain—particularly with respect to acid-sensitive and highly oxygenated ETP structures, such as those containing one or more dihydrooxepine ring. As part of a broad research program targeting ETP natural products, we have developed a synthetic strategy towards dihydrooxepine-containing ETPs.
Herein, the enantioselective total synthesis of (–)-acetylaranotin is described. This represents the first total synthesis of any dihydrooxepine-containing ETP natural product. The key steps of the synthesis include an enantioselective azomethine ylide (1,3)-dipolar cycloaddition reaction to set the absolute and relative stereochemistry, a rhodium-catalyzed cycloisomerization/chloride elimination sequence to generate the dihydrooxepine moiety, and a stereoretentive diketopiperazine sulfenylation to install the epidisulfide.
Our strategy was extended to the synthesis of a small panel of epitetrathiodiketopiperazines, including the natural products SCH64877 and emethallicin C as well as analogs, which are currently being evaluated for biological activity. Furthermore, preliminary investigations into the synthesis of dihydrooxepine-containing macrocycles have been conducted, with a particular focus on the preparation of bis(ortho-methoxyaryl) ethers.
Finally, as part of our efforts to further explore interesting side reactions observed during synthetic studies toward acetylaranotin, a catalytic asymmetric double (1,3)-dipolar cycloaddition reaction was developed. This reaction provides access to highly substituted, enantioenriched pyrrolidizines from inexpensive, commercially available starting materials. Furthermore, the reactivity of diketopiperazine intermediates prepared en route to acetylaranotin toward aerobic oxidation was briefly explored.</p
Superprotonic Solid Acids: Thermochemistry, Structure, and Conductivity
Get PDFIn this work, in order to investigate the thermochemistry and property of the superprotonic solid acid compounds, the measurement methods were established for in situ observation, because superprotonic phases are neither stable at room temperature nor freezable to room temperature. A humidity-controlled TG, DSC and AC impedance measurement system, and high temperature stage for XRD were built for thermal analysis and characterization of the solid acid compounds.
The thermodynamic and kinetics of the dehydration and hydration of CsH2PO4 is investigated by TG, DSC, and XRD analysis. By making use of the enhanced kinetics afforded by SiO2, the phase boundary between CsH2PO4, CsPO3, and dehydrated liquid was precisely determined. The stability of CsH2PO4 and the liquid dehydrate, CsH2(1-x)PO4-x(l), were confirmed by the complete reversal of dehydration to recover these phases in the appropriate temperature and water partial pressure ranges. Rehydration and conversion of CsPO3(s) to CsH2PO4(s) occurs over a period of several hours, depending on temperature, water partial pressure, and morphology of the metaphosphate. High and small particles favor rapid dehydration, whereas the temperature dependence of the rehydration kinetics is nonmonotonic, reaching its fastest rate in the vicinity of the superprotonic transition.
Doping Rb and K into CDP was examined and the stable region of Cs1-xRbxH2PO4 and Cs1-xKxH2PO4 are determined by in situ XRD and DSC measurement. Then the effects of doping to the structure and conductivity are discussed. It was found that Rb has whole-range solubility for both cubic and monoclinic CDP. Ts increases and Td decrease with Rb content. K has 27% solubility for cubic CDP, Ts and Td decrease with K content. The eutectic temperature is 208 ± 2°C. The lattice size of Rb- or K- doped CDP depends on the averaged cation size. Conductivity linearly decreases by dopant concentration. The impact of K doping is deeper than that of Rb for the equivalent averaged cation size.
in situ XRD measurement was carried out using single-crystal CsH2PO4 in order to study the phase transformation mechanism of this compound. A plate-like single crystal with (100) orientation was prepared, and the phase transition was observed by heating and cooling with ramp rate 0.2 K/min. From the obtained XRD profile — the after-first-phase transition (monoclinic-->cubic) — the distribution of the domain orientation was estimated. It was found that (100) is the preferential orientation after phase transition, however, the amount of the domains with other orientation is not ignorable. Therefore, it is considered that the phase transformation in CsH2PO4 is not simple martensitic, but that some other event, such as recrystallization, happens during the transition process.</p
Chemistry of PNP Bis(phosphide) Pincer Ligands and Palladium(II) Dimers as Robust, Versatile Precatalysts for Olefin Isomerization, Oligomerization, and Oxidation
Get PDFThe first half of this thesis details the synthesis and coordination chemistry of a very unusual pyridine-linked bis(secondary phosphine) pincer ligand system. Despite the highly nucleophilic phosphide donors, this dianionic system is an unexpectedly poor pincer ligand. Crystallographic and DFT studies reveal that both phosphide-metal σ- and π-bonding is compromised by long metal-phosphorus bonds, which result in significant distortions to the chelate ring. The neutral ligand coordinates readily κ2 (via phosphines) to late metals, such as palladium(II), affording P-chirogenic diastereomers. Crystallographic and spectroscopic analysis of a series of palladium(II) dihalides stabilized by this bis(phosphine) indicate that one diastereomer is enthalpically favored, while the other more structurally versatile diastereomer is favored entropically. There is also evidence of an interesting phosphine epimerization pathway assisted by the non-coordinated pyridine ring.
Ethylene polymerization and ethylene/1-hexene copolymerization activities of several zirconium(IV) and vanadium(III) polymerization precatalysts supported by heterocycle-linked bis(phenolate) ligands are also discussed. Activities as high as 106 g PE/(mol x h) were observed, but only the vanadium catalyst incorporates comonomer, albeit with low efficiency (<1 mol%).
Finally, catalytic applications of air- and water-tolerant bis(μ-hydroxy) palladium(II) dimers have been investigated. Mechanistic studies show that this precatalyst can oxygenate olefins via a Wacker-type mechanism upon dimer dissociation. In the absence of stoichiometric oxidant, the resulting palladium(II) hydride intermediate can then isomerize and oligomerize olefins with turnover numbers at room temperature as high as 2100/h and 600/h, respectively. We also show that the catalyst is insensitive to water and air, so that olefin isomerization and oligomerization can be carried out on the benchtop in the absence of activators. In the presence of excess tert-butylhydroperoxide, Wacker-type behavior is favored, and neither isomerization nor oligomerization is observed. These dimers can also catalyze the aerobic dehydrogenation of cyclohexene to benzene with relatively low turnover numbers (1/h). Nevertheless, mechanistic studies indicate a C-H activation/β-hydride elimination sequence that does not involve an allylic-activated species.</p
Host Seeking and the Genomic Architecture of Parasitism among Entomopathogenic Nematodes
Get PDFNematodes represent an especially abundant and species-rich phylum, with many free-living and parasitic species. Among the diversity of parasitic species is a guild of specialists known as entomopathogenic nematodes due to their unusual ability to quickly kill their hosts with the aid of pathogenic bacteria. Herein I discuss in detail the hallmarks of entomopathogenic nematodes and how they are different from other insect parasites. Further I explore their host-seeking behaviors, demonstrating their ability to detect insect hosts in complex soil environments and assess their odor preference profiles. I show that CO2 is a major driver of host seeking and that entomopathogenic nematodes detect CO2 using the same pair of conserved neurons that the fruit-dwelling Caenorhabditis elegans uses to detect and respond to CO2. I demonstrate dramatic differences in odor preference profiles and virulence capabilities, even between closely related nematodes. I discuss the role of genomic sequencing generally and more specifically in nematology, including how genomes are sequenced and analyzed and the types of characteristics that are most prominently assessed. This thesis concludes with a discussion of the genomic sequencing of entomopathogenic nematodes in the genus Steinernema and the clues these genomes provide regarding the genomic architecture of parasitism