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Global Adjoint Tomography with Source Encoding
No full textWe present our latest results on the tomographic models and method development for adjoint tomography. We start with concluding our decade-long global adjoint tomography project using classical methods. The third-generation model, GLAD-M35, features improved constraints on the P wavespeed and deep mantle structure, thanks to a 50\% increase in the event numbers and a new P-wave category that compensates for the imbalance between P and S measurements in the dataset. From the Broyden-Fletcher-Goldfarb-Shanno (BFGS) update history we are able to approximate the Hessian and its inverse and provide estimates on the resolution and uncertainty of the model through their low-rank representations.
We then explore the application of a new technology called source encoding. It dramatically reduces the number of simulations required for an iteration, which can potentially bring the global tomography to a next level. We demonstrate the effectiveness of source encoding through regional experiments. With a dataset of 786 events and 9,846 stations, we are able to recover the target model well with a computational cost much less than classical methods. We obtain a new regional model SE100 by applying our experiments with actual data and the new features revealed from the inversion are consistent with our existing knowledge and provide new insights to the mantle structure of the region.
Finally, we explore the application of source encoding on a global scale, which is more challenging due to steady state condition and data availability. To increase the ray coverage, we introduce a new trace processing technique that replaces part of observed data with synthetic data, enabling us to utilize some traces that are otherwise not suitable for source-encoded inversion. We show that Laplace domain is the only option for global source encoding, which makes the measurement mainly based on first arrival and surface waves. To compensate for the lack of coverage in the Southern Hemisphere and deep mantle due to this measurement, we explore options like epicentral distance weighting and a mask for regional Fourier domain measurement
Ca-based layered double hydroxides as solids sorbents for CO₂ capture
No full textCalcium based layered double hydroxides (Ca LDHs, Ca₂M(OH)₆A·2H₂O) have emerged as promising materials for carbon capture due to their high density of alkaline adsorption sites and tunable physicochemical properties, which can be modified by altering the trivalent cation, M³⁺, and interlayer anion, A⁻. However, green synthesis of high-purity Ca-LDHs with different chemistries, together with assessment of their carbon capture performance, remains largely unexplored. This thesis investigates the effect of chemical tailoring and relative humidity on the CO₂ sorption performance of Ca LDHs at room temperature, providing new insight on how the molecular design of these sorbents affects their carbon capture potential.The first part focuses on understanding how Ca(OH)₂ thin films (known as portlandene) interact with CO₂ in the absence of water vapor, with results showing a complex adsorption mechanism dependent on film thickness. In thicker films, the interaction is dominated by strong chemisorption via CaCO₃ formation, whereas thinner films form a mixed metal oxide with the substrate that enables weaker chemisorption and even physisorption of CO₂.
Next, the thesis examines the CO₂ sorption performance of two crystalline Ca LDHs: Ca₂Fe(OH)₆Cl·2H₂O and Ca₂Al(OH)₆Cl·2H₂O under humid conditions. Both Ca LDHs demonstrate higher CO₂ uptake and lower desorption temperatures than bulk portlandite, motivating further exploration of these Ca-LDHs.
A novel green synthesis method is developed for high purity Ca LDHs of various chemistries, enabling comparative studies of four compounds, including Ca₂Fe(OH)₆Br·2H₂O, synthesized for the first time. In situ neutron and X ray scattering, along with density functional theory modeling, reveal the atomic structures of Ca LDHs and their transformation into layered double oxides (LDOs) at high temperatures, including the formation of Ca₂AlO₃Cl and Ca₂FeO₃Cl with perovskite like structures.
Finally, a dual CO₂ adsorption mechanism is uncovered for Ca-LDHs: in dry conditions, CO₂ physisorbs within the interlayer space of Ca LDHs by anionic substitution, forming H bonds with the OH groups, whereas water vapor enables the chemisorption of CO₂ via CaCO₃ formation, leading to structural degradation. In practice, the physisorption kinetics can be controlled by selecting the appropriate M(III), while the rate of chemisorption can likely be minimized by drying the CO₂-rich gas before sorption
Studies of Structured Disorder in Classical Many-Body and Quantum Network Systems
No full textDisorder is ubiquitous in nature, but can be realized in a myriad of ways, each with differing effects on the physical properties of the system under study. In this thesis, we conduct studies of disordered hyperuniform classical systems and open quantum systems modeled after molecular exciton networks. In hyperuniform systems, the long-range density fluctuations asymptotically grow with the same order as a crystal. In Ch. 2, we investigate the Barlow packings, which are the stacking variations of the close-packing of equal spheres. These systems are hyperuniform, but can exhibit stacking disorder. We compute the hyperuniformity order metric of these packings. Despite this metric describing the density fluctuations at large length scales, we find that, for these packings, it is almost-linearly determined by the fraction of hcp-like local clusters. In Ch. 3, we study the nearest-neighbor functions of disordered stealthy hyperuniform many-particle systems in the low-temperature limit. These systems have a gap in their structure factor (or single-scattering intensity), and they undergo a disorder-to-order transition as an increasing gap fixes more degrees of freedom. They can also be shown to have a bounded hole size. Using an accurate approximation for the pair correlation function, we obtain short-range approximations and proposed bounds on the nearest-neighbor functions. We then investigate the behavior near the critical-hole size, and propose accurate expressions across all length scales. Finally, in Ch. 4, we look at the influence of the interaction topology, decoherence, and static disorder on open quantum exciton-like networks. We find that certain interaction graphs and decoherence models, such as the star graph under collective de-excitation, can force the eigenvalues to spread in a symmetric manner with increasing site energy disorder. On the other hand, the susceptibility to disorder found in topologies like the nearest-neighbor graph can help protect the first-excited state population against collective excitation loss. We also investigate disordered all-to-all interactions and topological disorder. These results expand the library of examples in which knowledge of the precise correlations and interactions responsible for disorder is needed to understand the geometric and physical properties of the system
Boundary-induced kinetic effects in low temperature E × B plasmas
No full textElectron beam (e-beam) generated plasmas in applied crossed electric and magnetic (ExB) fields have demonstrated effectiveness for a range of advanced material processing applications, for instance as process reactors for low-damage (`gentle') surface modification and high density ion sources for ion implantation. The rich physics of e-beam generated ExB plasmas, which includes both fluid and kinetic instabilities, can lead to anomalous heating and transport of electrons and ions, altering device performance for material processing. This work addresses the role of an active (biased or floating) axial boundary in controlling the electron kinetics and plasma instability formation in an e-beam generated ExB plasma, with particular outlook for developing improved regimes for material processing
IN CASE OF EMERGENCY BREAK GLASS: HOW CRISES PROPEL WOMEN TO POLITICAL LEADERSHIP AND SHIFT GENDER NORMS
No full textAlthough women’s representation in government continues to increase over time, only five countries have achieved gender parity in their legislatures at the time of this writing. A large body of literature illustrates the many bottlenecks woman face on their path to power, beginning before even deciding to run for office, and continuing after they are elected. This dissertation contributes to this literature by examining one particular event that can serve as another potential chokepoint, but can also provide an opportunity for women to be viewed more favorably: crisis. I develop a theory that during times of economic, political, or other type of crisis, women have a unique set of attributes that make them more favorable to lead than their male counterparts. First, because women face gendered barriers to holding office, they must be on average higher quality candidates in order to win elections at the same rate as men. Second, because women who have achieved office are still usually excluded from the inner circles of male power, they are most likely unassociated with the cause of the predicament. Because of these attributes of hyper-competence and independence, women are preferentially selected or elected to lead during times of crisis.
I demonstrate this theory with observational evidence derived from original interviews with elected officials, journalists, and voters in the United Kingdom and Turks and Caicos, two countries that saw women rise to executive positions following crisis. I then test this theory with an original survey experiment, showing that, conditional on crisis, citizens do prefer female leaders. I provide suggestive evidence that this preference is due to women’s perceived higher level of competence. This preference for female leaders is especially strong among individuals who express greater support for gender equality. I also show preliminary evidence that the relationship between women leaders and gender equality is reciprocal: female authority figures can induce stronger expressions of support for gender equality and women’s rights. Taken together, the theory and empirical analyses advance our understanding of the promise and limitations of crisis to “fast-track” both women’s concrete political representation, and public attitudes towards women’s rights and empowerment
