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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015., In title on title-page, double underscored characters appear as subscript (Prx̳Ce1̳-̳x̳O2̳-̳[̳d̳e̳l̳t̳a̳]̳) Cataloged from PDF version of thesis., Includes bibliographical references (pages 129-134)., An improved fundamental understanding of oxygen defect equilibria and transport kinetics in oxides is essential for achieving enhanced performance and longevity in many oxide-based practical applications. The ability to diagnose a material's behavior in a thin film structure under operating conditions (in operando), ideally in situ, is therefore of importance. In this dissertation, a novel experimental technique capable of simultaneously performing in situ and in operando optical absorption and electrochemical impedance spectroscopy (EIS) measurements was developed and utilized, for the first time, over a range of temperatures and controlled atmospheres. The technique was applied to the Prx̳Ce1̳-̳x̳O2̳-̳[̳d̳e̳l̳t̳a̳]̳, (PCO) model thin film system. PCO shows mixed ionic and electronic conducting (MIEC) characteristics at relatively high pO2 regimes (e.g. air), which is beneficial for solid oxide fuel cells (SOFCs) cathode performance. The Pr impurity levels in PCO allow for optical transitions (2.0 - 3.3 eV), leading to the red coloration of oxidized samples. A change in the redox state of Pr results in a color change and so serves as a means of investigating the Pr oxidation state and thereby oxygen non-stoichiometry. Pr⁴⁺ concentrations, derived independently from optical and electrochemical measurements, and their corresponding trends, were found to be self-consistent, confirming that the oxygen reduction enthalpy in thin film 10PCO is lower than that in the bulk. The derived extinction coefficient, . . . , can now be utilized to study defect equilibria of PCO or other relevant oxide films by optical means alone. The oxygen surface exchange reaction kinetics, driven by chemical and electrical driving forces, were investigated and correlated to each other, with the aid of the thermodynamic factor. The impact of surface chemistry and metal current collector on the reaction kinetics was discussed. A specially designed cell structure enabled the extension of the oxyg, by Jae Jin Kim., Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015., In title on title-page, double underscored characters appear as subscript (Prx̳Ce1̳-̳x̳O2̳-̳[̳d̳e̳l̳t̳a̳]̳) Cataloged from PDF version of thesis., Includes bibliographical references (pages 129-134)., An improved fundamental understanding of oxygen defect equilibria and transport kinetics in oxides is essential for achieving enhanced performance and longevity in many oxide-based practical applications. The ability to diagnose a material's behavior in a thin film structure under operating conditions (in operando), ideally in situ, is therefore of importance. In this dissertation, a novel experimental technique capable of simultaneously performing in situ and in operando optical absorption and electrochemical impedance spectroscopy (EIS) measurements was developed and utilized, for the first time, over a range of temperatures and controlled atmospheres. The technique was applied to the Prx̳Ce1̳-̳x̳O2̳-̳[̳d̳e̳l̳t̳a̳]̳, (PCO) model thin film system. PCO shows mixed ionic and electronic conducting (MIEC) characteristics at relatively high pO2 regimes (e.g. air), which is beneficial for solid oxide fuel cells (SOFCs) cathode performance. The Pr impurity levels in PCO allow for optical transitions (2.0 - 3.3 eV), leading to the red coloration of oxidized samples. A change in the redox state of Pr results in a color change and so serves as a means of investigating the Pr oxidation state and thereby oxygen non-stoichiometry. Pr⁴⁺ concentrations, derived independently from optical and electrochemical measurements, and their corresponding trends, were found to be self-consistent, confirming that the oxygen reduction enthalpy in thin film 10PCO is lower than that in the bulk. The derived extinction coefficient, . . . , can now be utilized to study defect equilibria of PCO or other relevant oxide films by optical means alone. The oxygen surface exchange reaction kinetics, driven by chemical and electrical driving forces, were investigated and correlated to each other, with the aid of the thermodynamic factor. The impact of surface chemistry and metal current collector on the reaction kinetics was discussed. A specially designed cell structure enabled the extension of the oxyg, by Jae Jin Kim., Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012., In title on title-page, double underscored "L" and "T" appear as subscript. Cataloged from PDF version of thesis., Includes bibliographical references (p. 273-291)., In this thesis I discuss the first measurement of the beam-target double-spin asymmetry ALT for charged pion electroproduction in deep inelastic electron scattering on a transversely polarized 3He target. These data were taken between October 2008 to February 2009 using a 5.9 GeV polarized electron beam at Thomas Jefferson National Accelerator Facility Experimental Hall A. The kinematics focused on the valence quark region, 0.16 < x < 0.35 with 1.4 < Q2 < 2.7 GeV2. The systematic uncertainties in this measurement due to acceptance, detector response drift, target density fluctuations and single spin asymmetries were suppressed to a negligible level by the frequent reversals of both beam helicity and target spin direction. Using the effective polarization approximation, the neutron ALT asymmetries were extracted from the measured 3He asymmetries and proton over 3He cross section ratios. The ALT asymmetries probe the poorly known transverse momentum dependent parton distribution function gq/1T, which describes the longitudinal polarization of quarks in a transversely polarized nucleon. The gq/1T function requires an interference between wave function components differing by one unit of quark OAM, and therefore provide access to quark spin-orbit correlations in the nucleons. While the measured [pi]+ asymmetries are consistent with zero, these data indicate a positive azimuthal asymmetry for [pi]- production on 3He and the neutron, which at leading twist leads to a non-zero gq/1T. This work has laid the foundation for the future high precision mapping of the ALT asymmetries, which is also discussed in this thesis., by Jin Huang., Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012., In title on title-page, double underscored "L" and "T" appear as subscript. Cataloged from PDF version of thesis., Includes bibliographical references (p. 273-291)., In this thesis I discuss the first measurement of the beam-target double-spin asymmetry ALT for charged pion electroproduction in deep inelastic electron scattering on a transversely polarized 3He target. These data were taken between October 2008 to February 2009 using a 5.9 GeV polarized electron beam at Thomas Jefferson National Accelerator Facility Experimental Hall A. The kinematics focused on the valence quark region, 0.16 < x < 0.35 with 1.4 < Q2 < 2.7 GeV2. The systematic uncertainties in this measurement due to acceptance, detector response drift, target density fluctuations and single spin asymmetries were suppressed to a negligible level by the frequent reversals of both beam helicity and target spin direction. Using the effective polarization approximation, the neutron ALT asymmetries were extracted from the measured 3He asymmetries and proton over 3He cross section ratios. The ALT asymmetries probe the poorly known transverse momentum dependent parton distribution function gq/1T, which describes the longitudinal polarization of quarks in a transversely polarized nucleon. The gq/1T function requires an interference between wave function components differing by one unit of quark OAM, and therefore provide access to quark spin-orbit correlations in the nucleons. While the measured [pi]+ asymmetries are consistent with zero, these data indicate a positive azimuthal asymmetry for [pi]- production on 3He and the neutron, which at leading twist leads to a non-zero gq/1T. This work has laid the foundation for the future high precision mapping of the ALT asymmetries, which is also discussed in this thesis., by Jin Huang., Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012., In title on title-page, double underscored "L" and "T" appear as subscript. Cataloged from PDF version of thesis., Includes bibliographical references (p. 273-291)., In this thesis I discuss the first measurement of the beam-target double-spin asymmetry ALT for charged pion electroproduction in deep inelastic electron scattering on a transversely polarized 3He target. These data were taken between October 2008 to February 2009 using a 5.9 GeV polarized electron beam at Thomas Jefferson National Accelerator Facility Experimental Hall A. The kinematics focused on the valence quark region, 0.16 < x < 0.35 with 1.4 < Q2 < 2.7 GeV2. The systematic uncertainties in this measurement due to acceptance, detector response drift, target density fluctuations and single spin asymmetries were suppressed to a negligible level by the frequent reversals of both beam helicity and target spin direction. Using the effective polarization approximation, the neutron ALT asymmetries were extracted from the measured 3He asymmetries and proton over 3He cross section ratios. The ALT asymmetries probe the poorly known transverse momentum dependent parton distribution function gq/1T, which describes the longitudinal polarization of quarks in a transversely polarized nucleon. The gq/1T function requires an interference between wave function components differing by one unit of quark OAM, and therefore provide access to quark spin-orbit correlations in the nucleons. While the measured [pi]+ asymmetries are consistent with zero, these data indicate a positive azimuthal asymmetry for [pi]- production on 3He and the neutron, which at leading twist leads to a non-zero gq/1T. This work has laid the foundation for the future high precision mapping of the ALT asymmetries, which is also discussed in this thesis., by Jin Huang., Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012., Vita. Cataloged from PDF version of thesis., Includes bibliographical references (p. 183-195)., Ti:Sapphire mode-locked lasers are a unique technology that enables a wide variety of applications. Owing to the ultrabroadband nature of the Ti:sapphire crystal and the invention of precisely engineered dispersion-compensating mirrors (DCMs), these lasers are now capable of generating stable pulse trains directly with octave-spanning spectrum, few-cycle pulse duration, and a desired repetition rate from a compact system. This paves the way to a new world of emerging applications ranging from the search of exoplanets, high-harmonic generation, to precision measurement Qualitatively, the key to the stable mode-locking of Ti:Sapphire lasers lies in the balance of various spatial and temporal nonlinear effects such as self-amplitude modulation(SAM), self-phase modulation(SPM), saturable absorption, self-focusing, gain-filtering, gain-guiding, and so on. However, since much shorter pulses and much higher intracavity intensities are often reached inside the laser gain medium, the spatiotemporal dynamics in such lasers are even more complicated as non-negligible multi-photon processes also come into play. Due to the strong coupling between these effects, performing a reliable analysis and optimization become extremely challenging. In this thesis we study the spatiotemporal dynamics of pulse evolution in the few-cycle regime and provide guidelines for designing and optimizing these lasers for repetition rate ranging from 85 MHz to 2 GHz. The essential background reviews as well as key concepts in KLM lasers will be given together with a demonstration of octave-spanning Ti:sapphire lasers with record-high repetition rate. A numerical model for simulating the full spatiotemporal dynamics is introduced. For an efficient numerical calculation, GPU accelerated computing techniques are adopted. With this model, many unique features that are observed from the experiments can be simulated for the first time. A novel type of output coupler called gain-matched output coupler is intr, by Li-Jin Chen., Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012., Vita. Cataloged from PDF version of thesis., Includes bibliographical references (p. 183-195)., Ti:Sapphire mode-locked lasers are a unique technology that enables a wide variety of applications. Owing to the ultrabroadband nature of the Ti:sapphire crystal and the invention of precisely engineered dispersion-compensating mirrors (DCMs), these lasers are now capable of generating stable pulse trains directly with octave-spanning spectrum, few-cycle pulse duration, and a desired repetition rate from a compact system. This paves the way to a new world of emerging applications ranging from the search of exoplanets, high-harmonic generation, to precision measurement Qualitatively, the key to the stable mode-locking of Ti:Sapphire lasers lies in the balance of various spatial and temporal nonlinear effects such as self-amplitude modulation(SAM), self-phase modulation(SPM), saturable absorption, self-focusing, gain-filtering, gain-guiding, and so on. However, since much shorter pulses and much higher intracavity intensities are often reached inside the laser gain medium, the spatiotemporal dynamics in such lasers are even more complicated as non-negligible multi-photon processes also come into play. Due to the strong coupling between these effects, performing a reliable analysis and optimization become extremely challenging. In this thesis we study the spatiotemporal dynamics of pulse evolution in the few-cycle regime and provide guidelines for designing and optimizing these lasers for repetition rate ranging from 85 MHz to 2 GHz. The essential background reviews as well as key concepts in KLM lasers will be given together with a demonstration of octave-spanning Ti:sapphire lasers with record-high repetition rate. A numerical model for simulating the full spatiotemporal dynamics is introduced. For an efficient numerical calculation, GPU accelerated computing techniques are adopted. With this model, many unique features that are observed from the experiments can be simulated for the first time. A novel type of output coupler called gain-matched output coupler is intr, by Li-Jin Chen., Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011., This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections., Cataloged from student submitted PDF version of thesis., Includes bibliographical references (p. 169-179)., Probabilistic models commonly assume that variables are independent of each other conditioned on a subset of other variables. Graphical models provide a powerful framework for encoding such conditional independence structure of a large collection of random variables. A special class of graphical models with significant theoretical and practical importance is the class of tree-structured graphical models. Tree models have several advantages: they can be easily learned given data, their structures are often intuitive, and inference in tree models is highly efficient. However, tree models make strong conditional independence assumptions, which limit their modeling power substantially. This thesis exploits the advantages of tree-structured graphical models and considers modifications to overcome their limitations. To improve the modeling accuracy of tree models, we consider latent trees in which variables at some nodes represent the original (observed) variables of interest while others represent the latent variables added during the learning procedure. The appeal of such models is clear: the additional latent variables significantly increase the modeling power, and inference on trees is scalable with or without latent variables. We propose two computationally efficient and statistically consistent algorithms for learning latent trees, and compare the proposed algorithms to other methods by performing extensive numerical experiments on various latent tree models. We exploit the advantages of tree models in the application of modeling contextual information of an image. Object co-occurrences and spatial relationships can be important cues in recognizing and localizing object instances. We develop tree-based context models and demonstrate that its simplicity enables us to integrate many sources of contextual information efficiently. In addition to object recognition, we are interested in using context models to detect objects that are out of their normal context. This tas, by Myung Jin Choi., Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007., Includes bibliographical references (p. 89-93)., In an attempt to explore an alternative to today's robot actuators, a new approach to artificial muscle actuator design and control is presented. The objective of this research is to coordinate the multitude of artificial muscle actuator axes for a large DOF (degree of freedom) robotic system based on dimensionality reduction. An array of SMA actuators is segmented into many independently controlled, spatially discrete volumes, each contributing a small displacement to create a large motion. Segmented Binary Control is proposed where each segment is controlled in an on-off manner, creating a stepper-motor like actuator. This overcomes hysteresis and other nonlinearities of the actuator material. The segmented cellular architecture of SMA wires is extended to a multi-axis actuator array by arranging the segments in a two-dimensional array. The multi-axis control is streamlined and coordinated using a grouping of segments called C-segments in order to activate multiple links of a robot mechanism in a coordinated manner. This allows control of large DOF with a small number of controls. The proposed approach is inspired by the segmented architecture of biological muscles and synergies, a strategy of grouping output variables to simplify the control of large number of muscles. Data from various hand postures are collected using data glove and used in creating the C-segment design that is capable of performing the given postures. A lightweight Robotic Hand with 16 DOF is built using shape memory alloy actuators. This hand weighs less than 1kg including 32 SMA actuators and control circuitry. Eight C-segments that are ON-off controlled are used to create sixteen given postures. In the future, this approach can be applied to applications where the control signal is inherently limited due to limited amount of information that can be extracted or transferred to the robot, such as brain machine interface and tele-operation., by Kyu-Jin Cho., Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2007., Includes bibliographical references., This thesis is a collection of three independent essays that study the implication of learning on labor mobility, labor supply, wage distribution, wage dynamics, and allocations of workers under different assumptions about the nature of employer learning. The first essay develops a model of job mobility and wage dispersion under the assumption that the current employers have superior information about their workers over outside firms. The superior information of the workers does not lead to market collapse. Instead, there is a unique mixed strategy equilibrium which leads to a positive amount of turnover and a nondegenerate wage distribution. This model implies that a skill-biased technology change that also favors general skill can lead to increase both in job mobility and wage dispersion. This sheds light, on the joint evolution of job mobility and wage dispersion in the U.S. in the past 30 years. The second essay studies the wage distribution and wage dynamics under matching and symmetric Pareto learning. I develop a model that contains pure learning and pure matching as limiting cases. In addition, the model generates effects that arise from the interaction of learning and matching. In particular, the model generates an earning profile typically obtained in a Mincerian regression., (cont.) Moreover, the model predicts that the wage residuals are more likely to be serially correlated in younger workers in industries with increasingly convex wage schedules. This helps reconcile the conflicting findings that positive correlations are found in small, homogenous samples but not large, heterogeneous samples. The third essay, jointly with Peter Schnabl, develops a, model that examines the optimal solution to the problem of assigning workers into jobs under adverse selections. Workers differ by their disutility of effort. Jobs differ by their productivity and ease of effort-monitoring. Firms would like to assign hard workers to higher level jobs because efforts on these jobs are harder to monitor. To prevent the lazy workers from mimicking the hard workers, we study the use of two instruments firms may use: requiring long hours and distorting job assignments. The model has an essentially unique separating equilibrium. In equilibrium, workers are required to exert inefficiently high levels of effort and firms commit to promote only a fraction of qualified workers., by Jin Li., Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2007., Includes bibliographical references., This thesis is a collection of three independent essays that study the implication of learning on labor mobility, labor supply, wage distribution, wage dynamics, and allocations of workers under different assumptions about the nature of employer learning. The first essay develops a model of job mobility and wage dispersion under the assumption that the current employers have superior information about their workers over outside firms. The superior information of the workers does not lead to market collapse. Instead, there is a unique mixed strategy equilibrium which leads to a positive amount of turnover and a nondegenerate wage distribution. This model implies that a skill-biased technology change that also favors general skill can lead to increase both in job mobility and wage dispersion. This sheds light, on the joint evolution of job mobility and wage dispersion in the U.S. in the past 30 years. The second essay studies the wage distribution and wage dynamics under matching and symmetric Pareto learning. I develop a model that contains pure learning and pure matching as limiting cases. In addition, the model generates effects that arise from the interaction of learning and matching. In particular, the model generates an earning profile typically obtained in a Mincerian regression., (cont.) Moreover, the model predicts that the wage residuals are more likely to be serially correlated in younger workers in industries with increasingly convex wage schedules. This helps reconcile the conflicting findings that positive correlations are found in small, homogenous samples but not large, heterogeneous samples. The third essay, jointly with Peter Schnabl, develops a, model that examines the optimal solution to the problem of assigning workers into jobs under adverse selections. Workers differ by their disutility of effort. Jobs differ by their productivity and ease of effort-monitoring. Firms would like to assign hard workers to higher level jobs because efforts on these jobs are harder to monitor. To prevent the lazy workers from mimicking the hard workers, we study the use of two instruments firms may use: requiring long hours and distorting job assignments. The model has an essentially unique separating equilibrium. In equilibrium, workers are required to exert inefficiently high levels of effort and firms commit to promote only a fraction of qualified workers., by Jin Li., Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2007., Includes bibliographical references., This thesis is a collection of three independent essays that study the implication of learning on labor mobility, labor supply, wage distribution, wage dynamics, and allocations of workers under different assumptions about the nature of employer learning. The first essay develops a model of job mobility and wage dispersion under the assumption that the current employers have superior information about their workers over outside firms. The superior information of the workers does not lead to market collapse. Instead, there is a unique mixed strategy equilibrium which leads to a positive amount of turnover and a nondegenerate wage distribution. This model implies that a skill-biased technology change that also favors general skill can lead to increase both in job mobility and wage dispersion. This sheds light, on the joint evolution of job mobility and wage dispersion in the U.S. in the past 30 years. The second essay studies the wage distribution and wage dynamics under matching and symmetric Pareto learning. I develop a model that contains pure learning and pure matching as limiting cases. In addition, the model generates effects that arise from the interaction of learning and matching. In particular, the model generates an earning profile typically obtained in a Mincerian regression., (cont.) Moreover, the model predicts that the wage residuals are more likely to be serially correlated in younger workers in industries with increasingly convex wage schedules. This helps reconcile the conflicting findings that positive correlations are found in small, homogenous samples but not large, heterogeneous samples. The third essay, jointly with Peter Schnabl, develops a, model that examines the optimal solution to the problem of assigning workers into jobs under adverse selections. Workers differ by their disutility of effort. Jobs differ by their productivity and ease of effort-monitoring. Firms would like to assign hard workers to higher level jobs because efforts on these jobs are harder to monitor. To prevent the lazy workers from mimicking the hard workers, we study the use of two instruments firms may use: requiring long hours and distorting job assignments. The model has an essentially unique separating equilibrium. In equilibrium, workers are required to exert inefficiently high levels of effort and firms commit to promote only a fraction of qualified workers., by Jin Li., Ph.D.