VictorJuiz/thesis huggingface dataset:
On the acceleration, dynamics, and propagation of cosmic rays [electronic resource]

The complete story of the origin, acceleration, and propagation of cosmic rays has remained a mystery for over a century. No conclusive evidence exists for how supernova remnants, the known sources of at least a large fraction of galactic cosmic rays, can accelerate cosmic rays up to the required energies. The origin of extragalactic cosmic rays is still completely unknown, with active galactic nuclei, gamma-ray bursts, certain types of neutron stars, and large scale shocks being the most popular candidates. This dissertation focuses on three separate but related topics: the interaction of anisotropic plasmas and cosmic rays, the propagation of cosmic rays in the presence of dense gas clouds, and the acceleration of extragalactic cosmic rays by strong accretion shocks around clusters and filaments of galaxies. The first major topic relaxes the common assumption that astrophysical plasmas have an isotropic pressure distribution caused by the presence of a magnetic field. We derive the dispersion relation for such a plasma with anisotropic magnetohydrodynamics as well as instabilities that are likely to amplify the magnetic field. This amplification may help to explain how shock fronts amplify the ambient magnetic field and accelerate cosmic rays to higher energies. The second major section examines the effect of dense gas clouds on the magnetic field and consequently on the propagation and emission of cosmic rays. This chapter is an attempt to gain insight on the gamma-ray spectrum of supernova remnants in such environments, where the spatial distribution and the spectral index of cosmic rays remains unexplained. The third topic uses new observations and simulations to modify a model of ultra-high-energy cosmic rays from strong accretion shocks. New evidence suggests that shocks around the large-scale structure of the universe --- not only shocks around galaxy clusters --- are adequate for accelerating cosmic rays up to the highest energies. Though the composition of these particles remains unknown, we propose two potential composition models, one with only protons and one with protons and heavy nuclei. Though the applications and environments discussed in each chapter varies, the underlying principles are similar. The full story of cosmic rays is not a simple one, and we hope that additions we have added to the standard theory provide useful tools for understanding other aspects of cosmic rays and perhaps other areas of astrophysics.

Keywords: Physics.
Advisor: Blandford Roger D. primary advisor. Thesis advisor
Abel Tom G.
Funk Stefan
On using data to design policy when agents search or are not fully rational [electronic resource]

This dissertation contains three papers that use novel data to shed light on the impact of policy on economic outcomes. In Essay 1, I use new data on search and communication behavior from a large online marketplace to study what market characteristics determine the matching rate. I show that informational frictions significantly lower the matching rate and surplus in the marketplace. I the use the data to design ranking algorithms that improve outcomes in the online marketplace. In Essay 2, we study the effect of unemployment insurance of job search effort. We first demonstrate the validity of a new proxy for job search effort based on Google searches for the term "jobs". We use the proxy to show that job search exhibits a small and temporary response to unemployment insurance. Lastly, we show that the drop in job search explain little of the increase in unemployment during the recession of 2007 - 2009. In Essay 3, we study how the default contribution to a savings plan should be set. We estimate a model in which savings decisions in the presence of defaults are affected by behavioral considerations such as time-inconsistency, inattention, and anchoring. We show how the optimal default, the magnitude of the welfare effects, and the degree of normative ambiguity depend on the behavioral model, the scope of the choice domain deemed welfare-relevant, the use of penalties for passive choice, and other 401(k) plan features.

Keywords: Economics.
Advisor: Levin Jonathan
Einav Liran advisor. Thesis advisor
Hoxby Caroline Minter advisor. Thesis advisor
Pistaferri Luigi advisor. Thesis advisor
On-chip buck-boost switched-capacitor DC-DC converter [electronic resource]

The increasing integration level of CMOS integrated circuits (ICs) poses significant challenges for the power delivery network. Multiple independent power domains, each of them individually adjustable, are desirable for complex ICs to optimize the tradeoff between performance and energy consumption. A two-stage power management system, in which a first-stage global converter with a large down conversion ratio is followed by multiple second-stage local regulators for different power domains, fits well in modern power delivery networks. The first stage can be built with conventional, fully optimized DC-DC converters, while the second stage requires flexible, high-density, and high-efficiency on-chip DC-DC converters. With the enhanced fabrication capability of high-density on-chip capacitors, the switched-capacitor (SC) DC-DC converter becomes a perfect candidate for these second-stage on-chip regulators. This dissertation presents the architecture, modeling and design techniques for the development of fully integrated on-chip SC DC-DC converters for the purpose of local regulation. The proposed converter can step up or down the voltage based on the output requirement and circuit performance. Using the unit cell array approach, conversion ratios of n/(n+1) with buck configurations and (n+1)/n with boost configurations are achievable when n cells are grouped as a single converter. Thus, adequate topologies exist to provide a large range of output voltage with high efficiency. A prototype chip with 204 unit cells and nine different finely spaced buck and boost topologies was designed and fabricated in a 45nm bulk CMOS technology. The input is 1V, and the output ranges from 0.58V to 1.3V. The SC converter achieves a peak efficiency of 82.2% at a maximum power density of 0.16W/mm2. Furthermore, the efficiency varies by only 4.2% over the output voltage range. A digital algorithm for closed loop control was implemented in a field-programmable gate array (FPGA) to demonstrate that performance regulation using this type of converter can match circuit performance requirements and compensate for operating conditions or process variations. This dissertation also projects the potential improvements in SC converters with more advanced technology nodes as well as capacitor density scaling, such as using special on-chip capacitor processes like Metal-Insulator-Metal (MIM) capacitors and deep trench capacitors.

Keywords: Electrical Engineering.
Advisor: Wong S. Simon primary advisor. Thesis advisor
Arbabian Amin advisor. Thesis advisor
Murmann Boris advisor. Thesis advisor
Online motion-plan modification in dynamic environments [electronic resource] : collision-free range of motion approach

The demand and the applications of personal and service robots are continuously growing, and robots have begun complementing instead of replacing humans. As a result, newly emerging applications challenge robots to have the capability of continuously updating their motion plans in dynamically changing situations. This dissertation introduces new efficient methodology for an online motion-plan modification. To generate collision-free motions in dynamic environments, a new approach based on the robot Motion Range is introduced, and an online plan modification layer and a new collision checking algorithm are added to compute continuous motions within the Motion Range online. Even if obstacles suddenly appear in run-time and the plan is not modified yet, the robot is allowed to react to the sudden changes in the free space of the Motion Range by the real-time execution strategy. For the real-time execution, low-level motion controllers are implemented, which enable complex robots to move through their Motion Range while complying with multiple task conditions and constraints. This approach was experimentally validated by various complex robots, which can effectively move in unpredictably changing scenarios by deploying the Motion Range concept, the new collision checking algorithm, and the reactive controllers.

Keywords: Mechanical Engineering.
Advisor: Khatib Oussama primary advisor. Thesis advisor
Cutkosky Mark R. advisor. Thesis advisor
Waldron Kenneth J. advisor. Thesis advisor
Onset of CDK2 activity determines passage through the restriction point in primary cells [electronic resource]

The restriction point (R) is crossed when mammalian cells become refractory to stimulatory or inhibitory signals. While it is fundamental to both development and disease, we currently lack an agreement on the molecular basis of the restriction point. Here, we review our current understanding of commitment in yeast and mammals and perform single-cell studies to determine both the timing and molecular mechanism of the restriction point. We show that three cell lines commit to division in previous cell cycles, while two types of primary cells commit solely in G1. Next, we determine the timing and order of molecular events in primary cells using live cell sensors for CDK2 and APC/CCdh1 activity, antibodies for G1 regulators, and a novel live cell E2F1 transcriptional reporter. Our results suggest that while the timing of the restriction point is variable from cell to cell, the first onset of a relatively low level of CDK2 activity is sufficient to commit cells to division, rather than full activation of the positive feedback loop. We demonstrate that CDK2 activation and the onset of E2F1 promoter activity occur at approximately the same time. Taken together, our results support a positive feedback model of commitment where upstream signals drive CDK activity, thus traversing a threshold where positive feedback becomes self-sustaining. Our studies establish a quantitative framework that defines the molecular foundation for G1 restriction point control and will permit further investigation into altered cellular states, such as cancer.

Keywords: Biology.
Advisor: Skotheim Jan
Ferrell James Ellsworth advisor. Thesis advisor
Morrison Ashby J.
Stearns Tim advisor. Thesis advisor
Optical characterization of time reversal symmetry breaking states in heavy fermion superconductors [electronic resource]

Heavy fermion materials have been of interest for decades because of the numerous ordered phases they exhibit at low temperatures, often resulting in novel bulk properties including various forms of magnetic ordering and unconventional superconductivity. A full understanding of these phases and their associated order parameters requires knowledge of their corresponding symmetries. This thesis examines specifically the role of time-reversal symmetry (TRS), as probed by polar Kerr effect (PKE) measurements, in identifying the order parameter of the canonical heavy fermion superconductors UPt_3 and URu_2Si_2. In UPt_3, the onset of PKE is observed below a temperature T_Kerr that coincides with the low temperature "B phase" superconducting transition temperature T_c- ~ 480 mK. In contrast, no change in Kerr effect is observed through either the high temperature "A phase" superconducting transition at T_c+ ~ 550 mK or the small-moment antiferromagnetic (AF) transition at T_N ~ 5 K. These results indicate that TRS is broken only in the B phase, independently of the higher temperature AF order, thus placing strong restrictions on the theory of superconductivity in this system. The case of URu_2Si_2 is more complex. There is a finite PKE loosely associated with the so-called "hidden order" (HO) transition at T_HO ~ 17.5 K. However, the magnitude of the signal appears to depend on the strength of the magnetic field used to train it, and for high fields the signal clearly onsets at ~25 K -- well above T_HO. At lower temperatures, an additional Kerr signal appears below the superconducting transition T_c ~ 1.5 K, which is independent of impurity concentration and which can be trained independently of the HO signal, all of which is consistent with broken TRS intrinsic to superconductivity in \URS. At the same time, an anomaly in the PKE data at ~0.8-1 K is consistently observed whose origins remain a puzzle; there is still more to be learned about URu_2Si_2 within the superconducting state.

Keywords: Physics.
Advisor: Kapitulnik Aharon primary advisor. Thesis advisor
Fejer Martin M. (Martin Michael) advisor. Thesis advisor
Kivelson Steven advisor. Thesis advisor
Optical control of engineered cytoskeletal motors [electronic resource]

Cytoskeletal motors are involved in a vast array of cellular processes, including motility, cargo transport, and force generation. Molecular engineering stands as a useful tool to interrogate the determinants of motor protein activity. Moreover, in order to harness these molecular machines for nanotechnological functions, as well as to perturb the cellular functions dependent on these motors, I have endeavored to develop novel methods of control over the motion generated by both actin- and microtubule-based motors. I first undertook a dissection of the determinants of directionality in an actin-based motor, myosin VI. Based on these results, we were able to identify a strategy for dynamic control over myosin VI directionality based on reversible transitions between rigid and flexible structural states of a portion of the myosin lever arm. We created a calcium-sensitive bidirectional myosin as an initial demonstration of this strategy by fusing calcium-sensitive calmodulin-binding domains to the lever arm. We subsequently extended lever arm engineering to encompass light control through the incorporation of a light-sensitive protein domain (LOV2) into the lever arm of myosin. Junctional variants and computational design yielded constructs that speed up, slow down, and switch directions in response to blue light. To test the generality of our optically-controlled design, we fused our engineered lever arm to myosin XI to create controllable myosins with high velocities, and to kinesin-14 (Ncd) to create controllable microtubule-based motion. These engineered motors could serve as the basis for components of nanoscale devices or for optogenetic control over cytoskeletal motor function in living cells.

Keywords: Chemistry.
Advisor: Bryant Zev David primary advisor. Thesis advisor
Andersen Hans
Pande Vijay advisor. Thesis advisor
Optical manipulation of quantum dot spin qubits with exciton-polariton resonance [electronic resource]

Experiments to manipulate a handful of quantum bits, based on a variety of underlying physical mechanisms, have been demonstrated. The ultimate goal is to build large systems consisting of billions of qubits and implement fast qubit operations with adequate accuracy, for solving problems that are intractable on classical computers (like factoring large numbers and quantum simulations). We develop and analyze a hardware platform for a scalable quantum computer based on semiconductor quantum dot (QD) electron spin qubits and their interaction with microcavity quantum well (QW) exciton-polaritons. This approach is based on the framework of previously proposed QuDOS architecture for surface code quantum computation. Despite the developments in techniques for implementing quantum non-demolition (QND) measurement and nearest-neighbor gates in QD spin systems, achieving the resource requirements for fault-tolerance still remains a challenge. In order to overcome this, our scheme relies on the indirect optical control of QD spins, resulting from the long-ranged Coulomb exchange interaction between the spin qubits and optically excited, spin-polarized, QW exciton-polaritons. The strength of this scheme is twofold. Firstly, by a careful design of the QW and QD it is possible to separate the optical eld from the QD manifold, thus preventing any unwanted backaction during a measurement event. Secondly, the bosonic nature of polaritons and their weak interaction with the solid-state environment allows the injection of numerous polaritons coherently in a single mode, increasing the nonlinearity in the qubit-polariton coupling, crucial for two-qubit operation. We develop schemes for implementing fast, high- delity, single qubit gate, two-qubit geometric phase gate and single-shot QND measurement. Furthermore, we investigate several issues critical for the robustness of the gate operations such as decoherence mechanisms, polariton-polariton interaction, phonon scattering etc.

Keywords: Applied Physics.
Advisor: Yamamoto Yoshihisa primary advisor. Thesis advisor
Mabuchi Hideo advisor. Thesis advisor
Vuckovic Jelena advisor. Thesis advisor
Optimal shape design using an unsteady continuous adjoint approach [electronic resource]

Many practical flows of aerodynamic interest are unsteady in nature, and between increases in computing power and advanced algorithms, accurately predicting and designing for the performance of aerospace systems in an unsteady environment is becoming more tractable. Several examples of engineering applications that could immediately benefit from a truly time-accurate design approach are open rotors, rotorcraft, turbomachinery, wind turbines, maneuvering flight, or flapping flight, to name a few. An unsteady treatment of these flows will also directly enable multidisciplinary design, analysis, and optimization involving other time-dependent physics associated with these systems, such as their structural or acoustic responses. Consequently, new unsteady design methodologies will enable the design of next generation aerospace vehicles with reduced fuel burn, emissions, and noise or rotating machinery for meeting future propulsion and energy challenges. This dissertation presents the development and application of a new, unsteady continuous adjoint formulation for optimal shape design. The arbitrary Lagrangian-Eulerian (ALE) form of the unsteady, compressible Reynolds-averaged Navier-Stokes (RANS) equations with a generic source term is considered, and from these governing flow equations, an adjoint formulation centered around finding surface sensitivities using shape calculus is derived. This surface formulation provides the gradient information necessary for performing gradient-based aerodynamic shape optimization. To analyze the effectiveness of the methodology, gradients provided by the continuous adjoint and finite differencing approaches are compared. Optimal shape design is demonstrated in both two and three dimensions for a range of pitching and rotating applications.

Keywords: Aeronautics and Astronautics.
Advisor: Alonso Juan José
Jameson Antony
MacCormack R. W. (Robert William)
Optimization of spacecraft architectures for earth-orbit satellite projects [electronic resource]

Multiple-payload satellites in Earth orbit can be designed either as consolidated or distributed satellite systems. A consolidated satellite approach aggregates multiple payloads onto individual large satellites. A distributed (or 'disaggregated') satellite system allocates payloads across multiple smaller, heterogeneous satellites. U.S. space agencies have debated whether to move from consolidated to distributed systems for almost two decades. Two of the potential advantages of a distributed system include replacement of failed units more efficiently and insertion of new technologies more quickly and easily. Such a system may also be less vulnerable to adversarial threats. I create an approach to analyze the strategic choice between these satellite system-types. I model the value of a satellite program, and find optimal sequential decisions to choose and operate a particular satellite system. This model enables satellite architectures to be compared on the basis of certain equivalent, given a strategy that best-exploits the characteristics of each system alternative. This research finds that the choice between satellite architectures is highly sensitive to a decision maker's risk preference and the rate of technology advancement for payload instruments. This research is able to show that distributed satellite systems often provide greater value in programs that merit risk-averse decision making. Likewise, in scenarios where technology improves for payloads quickly year-over-year, distributed satellite systems often provide significantly more value than consolidated systems.

Keywords: Management Science and Engineering.
Advisor: Paté-Cornell M. Elisabeth (Marie Elisabeth) primary advisor. Thesis advisor
Close Sigrid
Howard Ronald A. (Ronald Arthur)
Worden Simon P.
Optogenetic methods to control excitation and inhibition of neuromuscular activity [electronic resource]

The goal of this dissertation was to develop new methods for optical inhibition of motor neuron and muscle activity to enable studies of neuromuscular control and provide therapeutic insights into disorders of the peripheral nervous system. Optogenetic methods have been used widely in the central nervous system, and for applications of optogenetics in the peripheral nervous system, the work of this dissertation focused on the development of new technologies for light delivery to peripheral nerves, modulation of peripheral nerve temperature, and control of excitation and inhibition of motor neuron and muscle activity. We developed an optogenetics based method that utilizes the chloride pump halorhodopsin (eNpHR2.0) to achieve precise and rapidly reversible optical inhibition of motor neuron and muscle activity in vivo in transgenic Thy1-eNpHR2.0-EYFP mice by illuminating the nerve with green light. We used this method to demonstrate that eNpHR2.0 is capable of intercepting spikes in the axon, optical inhibition is effective at all amplitudes of electrically evoked twitch force, and light power density modulates the degree of inhibition. This study revealed the potential of eNpHR2.0 as a powerful tool for inhibiting motor neuron and muscle activity in the peripheral nervous system. We developed a second method that utilizes in a new way the cation channel channelrhodopsin-2 (ChR2) to inhibit motor neuron and muscle activity in vivo in the cooled sciatic nerve of Thy1-ChR2-EYFP mice by illuminating the nerve with high frequency blue light pulses or continuous blue light. We identified light pulse frequency and nerve temperature as important variables for achieving inhibition and quantified their effects. This study presents an all-optical, single opsin and single wavelength method to control neuronal excitation and inhibition without requiring co-expression of excitatory and inhibitory opsins. This dissertation contributes new methods for optical inhibition of motor neuron and muscle activity and facilitates studies of neuromuscular control and treatment strategies for disorders of the peripheral nervous system.

Keywords: Mechanical Engineering.
Advisor: Delp Scott primary advisor. Thesis advisor
Anikeeva Polina advisor. Thesis advisor
Deisseroth Karl advisor. Thesis advisor