UCLA

Supported Pd-Au bimetallic nanoparticles are a promising class of catalysts used for hydrogenation and oxidation reactions. Recently, the role of dynamic restructuring of Pd regions at and near the nanoparticle surface in response to modulating gas (H2 and O2) concentration was highlighted for controlling the surface Pd oxide stoichiometry. Here we investigate the mechanism of formation and decomposition of Pd hydride (PdHx) at and near the bimetallic nanoparticle surfaces, a key species for controlling the activity, selectivity, and stability of Pd catalysts in many hydrogenation reactions. Density functional theory (DFT) calculations provide additional insights into the stability and energetics of PdHx formation under varying H fractions and Pd sub-structures. Our results reveal a complex interplay between Pd ensemble size, surface structure, and hydrogen environment in determining the kinetics and thermodynamics of PdHx formation. By elucidating the mechanisms underlying surface PdHx formation and decomposition, the rational design of dynamic catalysts with controlled Pd hydride stoichiometries becomes possible. Hydrogen dissociation is an essential step in hydrogenation catalysis and critical to catalyst performance. Recently, Au–Pd core-shell nanoparticle catalysts have emerged as a highly promising class of materials for hydrogenation catalysis. Yet, fundamental understanding of the origin of bimetallic synergy in these core-shell catalysts and their interaction with hydrogen remains largely unknown. Here, we investigate the kinetics of hydrogen dissociation and recombination over Au–Pd core-shell catalysts using the hydrogen-deuterium (HD) exchange reaction. Density functional theory calculations indicate that subsurface hydrogen plays a major role in accelerating the hydrogen-deuterium exchange reaction by providing a lower-energy pathway for recombinative desorption of hydrogen and deuterium, which is the rate-limiting step. Altogether, our combined experiment-theory approach revealed that lattice strain and hydride formation can significantly influence the hydrogenation behavior of Au–Pd core-shell nanoparticles and are relevant to further advance the design of core-shell materials for hydrogenation catalysis. The ethanol oxidation reaction (EOR) has attracted considerable attention because of the high energy density of ethanol and its low-cost, renewable production from biomass. However, EOR suffers from sluggish kinetics and generally does not proceed to complete oxidation. In this study, we employed first-principles calculations to investigate the stability of Ptn clusters on various graphite surfaces, determine the optimal hydroxyl coverages, and explore potential-dependent EOR pathways. Our results show that the formation of Ptn clusters on defective graphite is highly favorable, particularly when the initial kinetic energy imparted to the clusters during hard-landing experiments is taken into account. The calculations further indicate that complete ethanol oxidation requires low-to-intermediate potentials and may involve changes in cluster configuration. At low potentials, the EOR exhibits low reactivity but high selectivity, whereas at high potentials, its reactivity increases at the expense of selectivity. In addition, our DFT calculations reveal CO poisoning of the cluster catalysts, in agreement with experimental observations.

This dissertation examines how Latino Republicans make sense of their partisan alignment in a political environment in which such alignment is widely treated as incompatible with Latino and immigrant belonging. Existing scholarship often explains Latino Republicanism as the product of weakened ethnoracial identity or attenuated ties to the immigrant experience, offering insight into movement away from the Democratic Party but less into how Latinos come to align with the contemporary Republican Party. Drawing on (N = 85) in-depth interviews conducted in five majority-Latino counties in South Texas—Cameron, Hidalgo, Starr, Willacy, and Zapata—this study examines how participants interpret their political commitments within a polarized party system. Participants describe arriving at Republican affiliation by relating longstanding commitments—especially around religion, family, and national belonging—to perceived differences between the parties. In these accounts, partisan alignment does not appear as a single decision, but as a process through which prior commitments and party identification come to fit together. This alignment is reinforced through participants’ everyday social environments, particularly within religious communities and understandings of American national identity, where Republican affiliation is experienced as fitting and appropriate. At the same time, participants confront claims that their partisan affiliation conflicts with Latino identity. Rather than abandoning those attachments, they describe when and how Latino identity and immigrant experience should matter for political judgment, allowing those ties to remain meaningful without leading them to reconsider their partisan alignment. By examining these patterns, this dissertation shows that Latino Republicanism is not best understood as the loss of identity-based ties, but as part of a broader shift in how people relate their values, identities, and party affiliation in a polarized political environment. Latino Republican alignment, in this sense, reflects how individuals come to see their political commitments as fitting together within their everyday lives.

Balancing between local capital’s requirement for labor, a shrinking local workforce, and exclusionary notions of national belonging, Taiwan’s migration regime bears similarity to a growing number of analogous migration regimes globally. Often described as ‘guest-worker’ programs, these policies exclude migrants from incorporating socially and culturally, by distinguishing between migrants based on skill. This dissertation explores the reproduction and mediation of guest-worker programs within everyday life through an analysis of migrant soccer leagues in Taiwan. The project focuses on guest-workers from Southeast Asia, but also highlights the experiences of student-workers and highly skilled migrants from Europe, the Americas, Southeast Asia, and East Asia in migrant soccer communities. The empirical evidence collected through semi-structured interviews and ethnographic observation and participation within migrant soccer communities, demonstrates overlapping processes through which Taiwan’s guest-worker program is perpetuated and challenged as migrants confront and overcome barriers to attending soccer games during their limited free time. This dissertation engages with the critical border studies literature to parse the various motivations that animate the exclusion guest-workers experience in Taiwan and analyzes the social capital guest-worker communities rely on to negotiate access to field space and organize soccer games. Finally, the dissertation explores the sense of place that is produced by migrant soccer communities as an analysis of the effects that the guest-worker program has on globalization and multicultural encounters.

As the global demand for energy continues to rise, cost effective and energy dense rechargeable battery systems have become increasingly desirable. This dissertation focuses on the synthesis of high-energy density alloy anode nanomaterials and characterization utilizing synchrotron X-ray sources for lithium- and sodium-ion batteries (LIBs/SIBs). Alloy anodes form atomic-scale mixtures with Li/Na, accompanied by multi-electron redox, providing drastically higher energy densities (phosphorous=2596 mAh/g), compared to commercial graphite anodes (372 mAh/g). Unfortunately, to accommodate so much Li/Na, the primary particles volume must expand, leading to particle pulverization and rapid capacity decay. To mitigate these effects, here, nanoporous architectures and nanocomposites were used to improve high-capacity long-term cycling.This thesis first details the synthesis of nanoporous Sb (NP-Sb) and characterizes the electro-chemo-mechanical behavior when cycled with Li and Na utilizing operando X-ray diffraction (XRD) and transmission X-ray microscopy (TXM). NP-Sb cycled against Li transitions through crystalline phase intermediates, resulting in crack formation; NP-Sb cycled against Na transitions through amorphous phase intermediates, and shows ductile behavior and crack self-healing. To visualize these structure changes, a cost-effective operando single particle nanotomography electrochemical cell was developed to follow volume expansion or crack formation in 3D. Utilizing this cell, operando nanotomographic reconstructions for a variety of battery materials were obtained. For example, NPSb cycled with Na undergoes massive, but reversible, anisotropic expansion. A bimetallic nanoporous SbSn alloy (NP-SbSn) with variable porosity was then examined. Operando XRD and TXM indicate that the nanotruss architectures in highly-porous samples mitigate the formation of cracks and enable reversible long-term, high-capacity cycling as LIBs. TXM tomography using AI-assisted segmentation on optimized NP-SbSn materials allow for quantification of the mechanism responsible for mitigation of volume expansion and strain dissipation.To make more economically-viable high-capacity SIB anodes, laser-scribed phosphorous/graphene oxide (GO) nanocomposites were synthesized. Utilizing synchrotron soft- and tender-X-ray absorption spectroscopy (XAS), the nanocomposites were shown to have a stratified nanoscale architecture, which enhance long-term high-capacity cycling in SIBs. Lastly, the synthesis and electrochemical performance of a phosphorous/GO nanocomposite anode with exceptional electrochemical performance over hundreds of cycles is described. High-capacity full cells were achieved by coupling these anodes to several SIB cathodes.

Proprioception is the body’s sense of relative position and force in space. It is crucial for human movement planning and execution, as well as advanced control of robotic devices. In this dissertation, I explore this importance to both the myoelectric control of supernumerary robotic devices, as well as the impact of limiting ankle range of motion during walking on gait adaptation. First, I present an experiment on the impact of proprioception on myoelectric referred control performance, finding that individuals performed virtual and physical robotic tasks better when they were freely able to move their body and receiving position-based proprioception while controlling the referred devices. Then, I present a study on the impact of control mapping on referred control, showing that while using antagonist muscle pairs to control virtual degrees of freedom is important, not all antagonist pairings are equally as easy to use as others. In addition, I describe a study conducted on the feasibility of achieving differential activation of typically synergistic muscle compartments by leveraging proprioceptive feedback, finding that free space proprioceptive feedback enabled individuals to volitionally activate one side of their biceps brachii and not the other. Finally, I present a biomechanics experiment where participants walked on a treadmill at two level-ground speeds, up and down incline and decline settings, and up and down a staircase while wearing a passive exoskeleton that restricted ankle range of motion to discrete, predetermined values. Across different walking and range of motion conditions, it was consistently observed that individuals did not change their gait parameters to avoid contacting end-range hard stops, but that that ranges of motion at the ankle as small as ±10° are sufficient in preserving natural, uninhibited gait biomechanics.

Chemically-doped conjugated polymers are a class of emerging semiconducting materials with unique and advantageous properties distinct from inorganic semiconductors, including solution processability, mechanical flexibility, highly tunable electronic behavior, and intrinsically low thermal conductivity. These properties make them promising candidates for thermoelectric applications, where temperature gradients are converted into electrical energy or vice versa. Such devices are relevant for applications ranging from industrial waste heat recovery to wearable electronics powered by body heat. Research on chemically-doped conjugated polymers has historically focused on maximizing the thermoelectric power factor, which depends on the electrical conductivity and the Seebeck coefficient. However, full quantification of thermoelectric performance also requires knowledge of the thermal conductivity to calculate the thermoelectric figure of merit, a measure of the degree of energetic conversion efficiency. Despite the importance of the figure of merit, the thermal conductivity of chemically-doped conjugated polymers remains poorly characterized. Most calculations of the figure of merit incorporate either thermal conductivity values that are representative of the undoped polymer or values from measurements embedded with a multitude of poor assumptions. This lack of thermal conductivity measurements largely arises from experimental challenges. Conjugated polymers exhibit very low thermal conductivities (below 1 W m⁻1 K⁻2), resulting in weak measurement signals. Additionally, these materials are typically studied as thin films (tens to hundreds of nanometers thick), requiring careful modeling of adjacent layers that often have much higher thermal conductivities and thus dominate the thermal response. Many measurement techniques operate in high-frequency regimes, probing thermal diffusivity rather than conductivity directly, which necessitates the accurate knowledge of volumetric heat capacity to extract the thermal conductivity. Because volumetric heat capacity is rarely measured in doped polymer systems due to separate measurement challenges, researchers often unphysically assume it remains unchanged from the undoped polymer. Furthermore, doped conjugated polymers may be both heat-sensitive and chemically reactive when exposed to certain environmental conditions and materials, respectively, during various measurement techniques. This thesis addresses these challenges by focusing on fully understanding the nature of changes in conjugated polymer thermal conductivity upon doping. The focus is on doped poly(3-hexylthiophene-2,5-diyl) (P3HT), a widely studied p-type conjugated polymer. The approach combines experimentally-measured volumetric heat capacities with thermoreflectance techniques that probe thermal diffusivity or effusivity. Structural analysis using X-ray diffraction is used to interpret changes in thermal transport, while electrical conductivity and Seebeck measurements enable a full evaluation of thermoelectric performance. Chapter 2 of this thesis specifically examines how volumetric heat capacity, thermal conductivity, and the thermoelectric figure of merit vary as a function of different amounts of doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Conventional time-domain thermoreflectance (TDTR) is employed to measure cross-plane thermal conductivity. The results show that both the volumetric heat capacity and thermal conductivity vary non-monotonically with doping, contradicting the common assumption that these properties remain unchanged from the undoped state. These variations are linked to doping-induced changes in crystallinity, morphology, and the incorporation of dopant molecules at higher concentrations. Chapter 3 of this thesis introduces a new technique, femtosecond transient thermo reflectance (fs-TTR), which uses a low-repetition-rate, high-pulse-energy amplified ultrafast laser, as well a newly-derived thermal model to interpret fs-TTR data. The new method has improved measurement accuracy compared to conventional TDTR of the cross-plane thermal conductivity, particularly for low-thermal-conductivity polymeric thin-films. For example, the lack of pulse accumulation-induced heat built-up from the low repetition rate allows control over the thermal penetration depth, preventing substrate effects from influencing the thermoreflectance signal. The easy achievability of large pump-probe spot-size ratios allows the measurement to achieve rigorous one-dimensional axial heat transport in materials with thermal anisotropy. The ability to spectrally probe the thermoreflectance signal simultaneously at multiple wavelengths yields an improved signal-to-noise ratio compared to single-wavelength measurements that rely on lock-in amplification. These advantages allow fs-TTR to measure both the thermal conductivity and thermal boundary conductance with an accuracy comparable to or slightly exceeding that of conventional TDTR, making it well suited for chemically-doped polymer thin-film systems. Chapter 4 of this thesis presents preliminary fs-TTR measurements of P3HT films doped with dodecaborane clusters functionalized with 3,5-bis(trifluoromethyl)benzyloxy functional groups (referred to as DDB-F72), a bulkier and much stronger oxidizing dopant than F4TCNQ. The use of DDB-F72 as a dopant not only improves carrier mobility, but also may achieve very low cross-plane thermal conductivity and higher thermoelectric figure of merit values compared to F4TCNQ-doped P3HT. Preliminary results suggest that the cross-plane thermal conductivity of DDB-F72-doped P3HT films monotonically decreases by an order of magnitude by high doping levels under the assumption that the volumetric heat capacity remains the same as the undoped polymer. Preliminary density measurements show that the film density monotonically increases upon doping with DDB-F72, suggesting that the volumetric heat capacity of these composite systems differs from that of the undoped polymer, although specific heat measurements are still needed to confirm this. The thermoreflective decays of DDB-F72-doped P3HT films show a large-amplitude damped oscillation of unknown origin that dominates the signal during the timeframe needed to extract information about heat transfer within the doped polymer film. This means that thermal conductivity values for these doped P3HT systems cannot be defined until the damped oscillation is fully understood, a subject for future work. However, combining our preliminary thermal conductivity results with measured power factors reveal that DDB-F72-doped P3HT may reach zT values of up to 0.18.

How can developing countries simultaneously participate in global markets and maintain economic sovereignty? I address this question by explaining how Maoist China (1949–1976) implemented “self-reliant” trade with the capitalist West, and especially with West Germany. Like other developing countries in the postwar period, Maoist China pursued a form of import-substitution industrialization (ISI). Unlike most other developing countries, however, China’s ISI experience adhered closely to the Maoist slogan of “self-reliance” and did not result in balance-of-payments problems and debt crises in the 1980s. Thus, China entered the decade with no external obligations, an autonomous policy environment for gradualist market reforms, and an industrial base on which to unleash them. Yet Maoist self-reliance is a puzzle for development theory. Lacking a Weberian economic bureaucracy and facing Cold War geopolitical constraints to accessing global markets, Maoist China’s internal and external conditions appear to have been hostile to successful implementation of ISI. To explain Maoist self-reliance, I reevaluate the internal and external conditions of Maoist development. I argue that the state-formation and state-building processes of the People’s Republic China interacted with the expansionary tendency of capital to enable self-reliant trade. First I trace how intra-elite, intra-state, and state-society relations favored trade bureaucracy capacity over rational domestic economic governance. Second, I show how the capitalist core saw the Chinese market as a spatial-temporal fix for overcapacity—and how the Maoist trade bureaucracy’s semi-withdrawal from global markets leveraged capitalist competition to import technology and other resources on advantageous terms. This dissertation makes three contributions. First, I develop a heuristic framework for analyzing the social foundations of institutional capacity. The framework relaxes the theoretical juxtaposition of developmental states and pockets of efficiency, inviting more comparative-historical work on variation in capacity both within the state and over time. Second, I find that overcapacity and competition can provide opportunities for geopolitically marginalized states and global capital to defy hegemonic trade policies. This finding has implications for the trade conflicts and the resurgence of industrial policy in the present. Third, I show that Maoist China’s socialist development was bound up with the fluctuations of global capitalism.

Contemporary climate change is expected to outpace the migration of long-lived trees, underscoring the importance of understanding how populations respond to changing environments through standing variation of traits. Intraspecific trait variation is shaped by both local adaptation and phenotypic plasticity, but an adaptive trait must be genetically based, have a clear function, and confer a fitness advantage. To determine how leaf traits and drought response strategies contribute to adaptedness in valley oak (Quercus lobata Née), a California endemic tree spanning a wide climate gradient, we combined common garden and greenhouse experiments. First, using eleven-year-old trees in two common gardens, we tested whether leaf morphological traits are genetically differentiated, associated with maternal climate, related to leaf physiology, and under contemporary selection. We found that leaf morphological traits were genetically differentiated, and that plasticity shaped both leaf morphology and physiology. Leaf thickness emerged as the most prominent trait measured in shaping adaptedness, being genetically differentiated, climate-associated, consistently related to physiology, and under selection favoring thinner leaves in both gardens. Second, to test whether trees from drier regions have evolved trait values related to greater drought tolerance, we compared leaf morphology, foliar nutrients, diurnal gas exchange, and leaf water potential between trees from the wetter northern and drier southern regions of the species’ range. We found that the southern trees produced smaller, thicker, denser leaves and had lower photosynthetic rates and stomatal conductance in both gardens. However, water use efficiency, foliar nutrient content, and leaf water potential did not differ between maternal regions. Lastly, to determine whether stomatal behavior under drought is genetically diverged, we conducted a greenhouse drought experiment on seedlings from both regions across a controlled drought cycle. We found that stomatal closure was the primary drought response in both regions, but that southern seedlings closed their stomata more than northern seedlings, while photosynthetic biochemistry did not differ between regions. Collectively, this work 1) identifies leaf thickness as a key trait shaping adaptedness in valley oak, 2) demonstrates that local adaptation has shaped leaf structure, photosynthetic capacity and diurnal patterns of stomatal conductance, consistent with greater drought tolerance in drier regions, and 3) provides evidence that the degree of stomatal closure in response to drought may be genetically differentiated, showing that selection will act on physiology that can facilitate greater drought tolerance. Overall, this work underscores the importance of distinguishing genetically based and plastic trait variation when considering climate-informed seed sourcing and management of long-lived trees.

Sustainability disclosures are more common than ever. Yet whether they are actually useful remains an open question. This dissertation examines that question across three studies spanning different audiences, methods, and sustainability domains.The first study systematically reviews how business journal articles engage with third-party sustainability measures in sustainability-financial performance linking research. The review identifies two sources of uncertainty that limit confidence in these measures: the quality of underlying data and how data is aggregated. Methodological rigor is bimodal; researchers either scrutinize multiple dimensions of measurement quality or none at all, and choices about data quality and aggregation are shown to be related to reported financial performance relationships. The study offers practical recommendations for improving rigor and transparency in corporate sustainability research. The second study examines how job applicants price corporate sustainability signals as part of their compensation using a choice-based conjoint experiment (N = 249) analyzed via Hierarchical Bayes. Drawing on Herzberg's hygiene-motivator distinction, the study finds two distinct asymmetries. Within domains, penalties for withdrawal exceed rewards for proactive investment. Across domains, climate commitments tied to managerial incentives generate a reliable compensation discount while equivalently structured diversity commitments do not. These patterns are consistent with diversity functioning as hygiene factor and climate functioning as prestige motivators. The third study employs a randomized between-subjects survey experiment with 516 retail investors to examine whether financial or impact framing of corporate sustainability strategies shifts investor sustainability judgments. Despite perceiving financial framing, retail investors showed no meaningful differences in perceived importance ratings or investor materiality assessments across framing conditions. Political ideology emerged as the dominant predictor of sustainability importance judgments and the strongest covariate predictor of investor materiality assessments, replicating across three independent samples. The findings challenge the assumption embedded in global disclosure frameworks that strategic framing shapes how retail investors receive sustainability information. Across three audiences and three methods, the dissertation finds that sustainability information does not operate uniformly. Its usefulness depends on who receives it, how it is disaggregated, and what psychological register it activates. These findings carry direct implications for how sustainability measures are constructed, disclosed, and regulated.

In Closer to Reproductive Freedom, I examine the emergence of a Black-led birth center and the reclamation of traditions of Black Birth work in the context of organized reproductive abandonment. Using participant observations, interviews and auto-ethnography I investigate how Black women who experience pregnancy both inside and outside of a prison context think about and practice care in spite of pervasive threats to their survival. Ultimately, I argue that the quotidian epistemologies and praxes of care I witnessed in this burgeoning space lay the groundwork for reproductive liberation.