UC Irvine

Digital markets are built on data, low-friction access, and user trust. This dissertation studies what happens when each of these pillars is disrupted. Across three essays, it shows that privacy regulation, registration-based access barriers, and public revelations of workplace misconduct can materially alter consumer purchasing, attention allocation, and platform choice. The first essay examines the unintended consequences of the California Consumer Privacy Act (CCPA) for consumer commerce. Using the CCPA as a natural experiment and combining billions of payment transactions with browsing data and firm-level measures of advertising technologies, the essay shows that Californians purchased less, returned more, and spent more time browsing after the law took effect. Firms subject to the regulation also reduced their use of ad-related technologies. These findings suggest that stronger privacy protections may unintentionally weaken personalization and product-consumer matching, reducing commercial activity even as they expand consumers' control over personal data. The second essay studies the New York Times' introduction of a registration wall as a first-party data collection strategy. Using web browsing data together with a regional measure of privacy salience based on cumulative exposure to data breaches, the essay finds that registration walls generate heterogeneous responses across user segments. News-singlehomers reduce engagement after the wall is introduced, whereas news-multihomers slightly increase engagement. Higher privacy salience attenuates the decline among singlehomers and strengthens the positive response among multihomers. When users disengage, their attention shifts primarily toward search engines and video-sharing platforms, revealing broader ecosystem consequences of registration-based access barriers for news consumption. The third essay investigates how public whistleblowing about workplace sexual harassment and discrimination affects consumer demand in platform competition. Exploiting a blog post by a former Uber employee describing sexual harassment, discrimination, and the company’s response—an account that quickly went viral on social media—as an exogenous reputational shock, the essay shows that Uber usage declines while Lyft usage rises among riders most able to switch between the two platforms. These effects are strongest in markets with greater local attention to the event and among riders predicted to be female, highlighting how misconduct toward minorities can translate into meaningful demand-side consequences in consumer markets. Taken together, the three essays demonstrate that consumer behavior in digital markets is shaped not only by prices and product attributes, but also by data governance, access design, and corporate legitimacy. The dissertation contributes to research on privacy regulation, digital media monetization, and platform competition, while offering practical implications for firms and policymakers seeking to balance personalization, access, and accountability in the digital economy.

The distributed training of machine learning models via gradient descent is generally conducted by iteratively computing the local gradients of a loss function and aggregating them across all processors. Communicating these gradients during aggregation is often a major cost but sparsification techniques can greatly improve efficiency. One such technique, Top-k gradient compression, ensures that only the k largest components of each local gradient are sent. However, effectively scaling this method can be challenging. The standard ring AllReduce algorithm, which is frequently used to aggregate dense gradients, lacks a counterpart that is optimized for sparse data. Notably, ring algorithms are contention-free, which generally make them easier to scale than other collective communication algorithms. Thus, in practice, the ring AllGather algorithm, which can be trivially adapted for sparse data, may be used instead, even though its bandwidth costs are proportional to the number of utilized processors (unlike ring AllReduce). To provide a more scalable contention-free alternative, we present a variant of ring AllReduce that has been better optimized for sparse data. We compare it to the standard dense ring AllReduce and ring AllGather algorithms, and we evaluate it empirically using gradients sampled from fine-tuning Llama 2 7b.

English academic writing is a critical yet challenging skill for learners in English as a Foreign Language (EFL) contexts. The rapid integration of digital tools, accelerated by the COVID-19 pandemic, has transformed writing instruction; however, evidence of its pedagogical effectiveness remains fragmented and often overlooks teacher perceptions and genre-specific impacts. This three-study dissertation addresses these gaps by investigating the role of digital tools in EFL writing instruction within the EFL higher education context, employing a multi-method approach to triangulate evidence from student outcomes, meta-analytic synthesis, and teacher experiences.Study 1 conducted a classroom experiment with 111 Chinese undergraduates, comparing infographic-based pre-writing to traditional outlining. Results showed that infographic creation significantly improved summary-writing quality, source use, and self-efficacy, but not opinion writing, highlighting the genre-sensitive nature of tool effectiveness.Study 2 synthesized 17 experimental and quasi-experimental studies (N = 1,085) through a meta-analysis. It found a statistically significant, moderate overall effect favoring web-based collaborative writing (WBCW) over non-technological collaboration on writing quality (Hedges’ *g* = 0.51). Moderator analyses indicated that training was a significant factor enhancing outcomes.Study 3 explored the perceptions of seven Chinese university writing instructors through qualitative interviews. Grounded in the TPACK framework, the findings revealed that while digital tools are deeply embedded in instruction, their use is shaped by teachers' knowledge, institutional support, and access. Teachers exhibited cautious and limited integration of emerging Generative Artificial Intelligence (GenAI) tools due to concerns over academic integrity and a lack of institutional guidance.Collectively, the findings demonstrate that technology enhances EFL academic writing most effectively when tools are aligned with genre demands, collaboration is scaffolded by design and training, and implementation is supported by teacher knowledge and institutional context. The dissertation concludes by advocating for a situated, tool-genre-task alignment perspective in future research and practice, moving beyond technocentric adoption to support equitable and effective writing instruction in diverse EFL settings.

Self-renewing hematopoietic stem cells (HSCs) produce billions of blood cells a day to maintain peripheral blood and immune cells in circulation. Inflammation can alter the balance of steady-state hematopoiesis, and disrupted hematopoiesis can lead to blood disorders or cancers. Over a lifetime of cell divisions, HSCs may acquire somatic mutations that provide a competitive advantage over their wild-type counterparts. The clonal expansion of a mutant HSC population is termed “clonal hematopoiesis” (CH). CH is linked to an increased overall risk of mortality due to incidences of cardiovascular disease and transformation into hematological malignancy. Tobacco and nicotine use remain the leading preventable drivers of cancer risk, and both direct and secondhand exposure to combustible cigarettes or electronic nicotine devices perturbs immune function and hematopoiesis. The World Health Organization estimates more than 100 million people across the world are using electronic cigarettes, or e-cigarettes, but the health impacts of these “safer” e-cigarette alternative have yet to be fully elucidated. E-cigarettes have been associated with inflammation and oxidative stress, which can provide selective pressures for the outgrowth of CHIP mutant cells.Here, we evaluate the impact of e-cigarette vapor and combustible cigarette smoke on in vitro cell inflammatory responses and in vivo long-term hematopoietic differentiation. The overarching goal of this project was to understand further how an inflammatory lifestyle stressor, such as smoking, contributes to aberrant hematopoiesis in wild-type normal stem cells, Tet2- deficient cells, and JAK2V617F mutant cells. In cell-based studies, cigarette smoke extract (CSE) and e-cigarette vapor extract (EVE) consistently suppress LPS-induced TNF-α secretion across macrophage/monocyte models, including primary mouse and human cells and complementary cell lines, indicating a reproducible immunosuppressive effect on mature myeloid cells. To assess consequences of smoking behavior in vivo, we used a custom nose-cone inhalation system to deliver controlled exposures to combustible cigarette smoke or e-cigarette aerosol to mice. Chronic exposure increased myeloid proliferation, a hallmark of HSC aging. Taken together, these results support a model in which tobacco exposures blunt innate immune responsiveness while simultaneously driving myeloid expansion conditions that accelerate hematopoietic aging and promote the expansion of mutant hematopoietic cells.

One-dimensional (1D) and quasi-1D (q-1D) van der Waals (vdW) materials, which have strong bonding along only one crystallographic axis, have emerged as powerful class of solids that hosts novel electronic, optical, and quantum properties useful for next-generation electronics. These materials can, in theory, be thinned to the angstrom scale due to the ideal vdW surfaces along two axes. In practice, achieving atomically precise single chains of these materials poses a significant challenge, as conventional top-down exfoliation and bottom-up growth techniques consistently retain interchain bonding, especially in q-1D materials with anisotropic interchain bonding motifs. The question then arises: Is there a synthetic approach that would enable the suppression of all inter-chain interactions, leaving only intra-chain covalent bonding in one dimension? Using the model q-1D pnictogen chalcogenides (Pn2Ch3; Pn = Sb, Bi; Ch = S, Se, Te), chosen for the highly anisotropic structural complexity and strong inter-chain bonding combined with distinct photophysical properties, we explore encapsulation within ultranarrow nanotube growth templates to precisely define the growth of the material in sub-nanometer length scales. The deployment of these nanotube templates as encapsulants overcomes the inter-chain interactions in these phases to isolate single q-1D chains by affording physical space that directly matches the size of a single chain. More importantly, we can also probe many chains simultaneously in a collective using conventional spectroscopic techniques used in ensemble samples, allowing us to access nanoscale properties through bulk measurements. Herein, not only do we gain insight into structural and electronic properties of these single chains, but we also further our understanding of anisotropic bonding in the bulk structure by understanding how it affects single chain accessibility. As technological devices advance through shrinking and densification, understanding material properties at the atomic limit becomes increasingly vital. Our results demonstrate a powerful tool for synthesizing and studying precisely defined single inorganic chains that approach the atomic limit.

Photochemical aging alters the physical and chemical properties of atmospheric aerosols, influencing their climate and health impacts, yet the underlying mechanisms remain poorly understood. A significant knowledge gap is the role of short-lived free radicals that escape most direct detection methods. This work provides new insights into radical chemistry during photochemical aging of simplified biomass burning organic aerosol (BBOA) systems. Radicals were detected in situ during irradiation using electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping compound. Time-resolved EPR data were incorporated into kinetic models to identify reactions leading to reactive oxygen species (ROS) formation, which drive atmospheric oxidation and influence particle toxicity. We also developed a method to identify organic radicals adducts using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). Their radical nature produced unusual oxidized [M]+ and reduced [M+2H]+ ions that complicated interpretation but using simplified systems we established a framework for using collision induced fragmentation mass spectra to differentiate between adduct types. These methods were applied to examine radical formation during irradiation of solutions containing benzoquinone and levoglucosan, key BBOA tracer molecules. EPR analysis revealed formation of hydroxyl radicals (•OH), known products of the reaction between triplet-state benzoquinone and water, accompanied by organic carbon- and oxygen-centered radicals that became more prominent with increasing levoglucosan content. LC-ESI-MS confirmed semiquinone formation and detected additional radicals derived from benzoquinone and levoglucosan oxidation. We also observed the first experimental evidence of hydrogen radical (H•) formation, likely from semiquinone decomposition. Kinetic modeling reproduced the time evolution of BMPO adducts observed by EPR and predicted the evolution of species in atmospherically relevant systems. These findings indicate that photoirradiation of aerosols containing photosensitizers induces radical formation and secondary radical chemistry that drives BBOA aging in the atmosphere. We next investigated radicals formed during irradiation of secondary organic aerosols from biomass burning precursors (BBSOA). Through a combination of laboratory measurements and kinetic modeling we determined that superoxide generation is driven by photosensitization reactions in aromatic SOA, while the dominant source of superoxide in biogenic SOA is photo-induced decomposition of carbonyls with minor contributions from peroxide decomposition. This was supported by measurements of the radical formation by model compounds including carbonyls and organic peroxides. The superoxide burst serves as a substantial source of reactive oxygen species (ROS) including hydrogen peroxide and hydroxyl radical in cloud droplets and deliquesced particles, competing with traditional sources such as uptake from the gas phase. This work elucidated mechanisms of radical formation during photochemical aging, advancing understanding of oxidant budgets and health impacts of aged atmospheric systems.

Games are more than media for consumption; they are increasingly valuable educational tools and social platforms connecting players around the globe. The known benefits aside, harmful conduct prevails in online play, severely impacting players, gaming communities, and the games industry at large. Players’ understanding of social safety and their coping strategies with harmful conduct are influenced by the design and implementation of the safety infrastructure in online games. Therefore, improving these mechanisms can help reduce harmful behavior, enable proactive coping strategies, and develop healthier gaming environments. Safety infrastructure is a broader concept commonly incorporating policies, technological systems, and trust and safety teams. This work focuses on the technological components that directly shape player experience through structuring and moderating social interactions.In three studies, (1) I assess parental controls and in-game tools of social safety and privacy, (2) examine how players perceive moderation systems, and (3) explore possible future avenues in AI-assisted moderation that move from common retributive approaches towards supportive interventions.I argue that existing retributive moderation systems are insufficient to cultivate thriving communities, and that currently missing proactive and supportive measures are better aligned with player needs and shared expectations.First, I show that retaliating against toxicity or leaving it unchallenged solidifies toxic norms; yet to a lesser extent, victimization and game experience also foster resilience and productive coping. Proactive tools that help players respond with constructive strategies rather than reciprocating harm are, therefore, pertinent. I use the Teens Online Safety Strategies (TOSS) framework to review parental tools and social safety controls in popular multiplayer online games and publishing platforms. I demonstrate that teens’ developmental needs are not well supported, and parental systems both infantilize them and leave them vulnerable. The available social safety and privacy controls are mostly restrictive, and mechanisms supporting active coping and impulse control are scarce, if they exist at all.The recent surge in utilizing AI invites the question of its potential for innovating moderation systems. Thus, I explore players’ attitudes toward real-time AI interventions aiming to reduce toxicity and foster prosocial behavior. I elucidate that the most opportune solutions seamlessly integrate AI-assisted mediation into gameplay and follow strong ethical considerations for transparency, privacy, as well as human agency and control.This dissertation delineates the current state of safety infrastructures and technological moderation in multiplayer online games and specifies viable future directions that may inspire a cascade of work exploring proactive supporting ways of moderation.

Xeno-nucleic acids (XNAs) are artificial genetic polymers with unnatural sugar and backbone structures that confer unique physicochemical properties, such as enhanced biostability and improved RNA binding thermodynamics, making them attractive for a wide range of applications. One such XNA is threose nucleic acid (TNA), which features a threose sugar ring with a 2′-3′ phosphodiester backbone linkage that confers high nuclease resistance while still supporting anti-parallel Watson-Crick base-pairing with DNA and RNA. Initially investigated as a plausible RNA progenitor, TNA research has since expanded towards its development as a molecular tool. This dissertation examines TNA across three studies that progress from the characterization of one of TNA’s special properties to the application of TNA towards specific functions. First, to examine the mechanistic rationale behind the chemical resilience of TNA, the degradation kinetics of TNA under acidic, high-temperature conditions was assessed using RP-HPLC, mass spectrometry, and molecular dynamics simulations. TNA exhibited a half-life substantially longer than DNA and RNA, with strand cleavage occurring via β-elimination of the 2′-phosphodiester linkage, a mechanism distinct from natural nucleic acids and attributable to destabilization of the oxocarbenium intermediate responsible for depurination. Second, to demonstrate the utility of TNA in a therapeutic context, TNA was incorporated into the backbone architecture of an RNA-cleaving DNA enzyme (DNAzyme) through chemical evolution. The resulting TNA-modified lead construct exhibited enhanced catalytic performance and achieved allele-specific mRNA and protein knockdown of the oncogenic KRAS G12V mutation by evading RNase H1 activity in cells. Third, to explore the link between dynamism and evolvability in nucleic acid enzymes, RNA-cleaving TNA enzymes (threozymes) were evolved by in vitro selection and compared to the well-characterized 10-23 DNAzyme. Unlike the DNAzyme, which was most active at physiological temperature, the threozymes required elevated temperature to become catalytically active, a finding consistent with TNA's more conformationally restricted backbone that limits access to productive folding states and raises the energetic barrier to catalysis. Together, these findings establish TNA as a chemical tool for engineering nucleic acid enzymes and a model system for probing how backbone architecture governs catalytic evolvability in nucleic acids, carrying significant implications in the development of XNA-based molecular medicine and biotechnologies.

Skeletal muscle is a highly regenerative tissue that is responsible for voluntary, contractile movement of the body. Endogenous muscle stem cells are responsible for regenerating skeletal muscle upon injury, although in diseased contexts this regeneration becomes impaired to the deficit of the patient. There remains a pressing need for the discovery of viable, long-lasting therapeutic treatments for patients with genetic congenital neuromuscular diseases as current standard of care fails to improve patient quality of life. Thus, the introduction of induced pluripotent stem cell (iPSC) derived muscle stem cell therapies offers an exciting avenue to introducing an autologous healthy donor stem cell into a diseased patient. While this platform is promising, current research has found that iPSC derivations generate immature skeletal muscle stem cells, transcriptomically on par with embryonic human muscle stem cells. One major limitation of these stem cells is the ineffective retention of the stem cell population upon engraftment, an objective highlighted in this dissertation.We describe the heterogenous myogenic populations generated upon engraftment in vivo, importantly finding distinctly different myofibers that resemble either an immature, regenerative state (marked by fetal cardiac actin, ACTC1) or a mature, developed state that arises through fusion with host mouse myofibers. We found that human PAX7+ muscle stem cells are better retained in regions of regenerating ACTC1+ myofibers rather than the larger, chimeric myofibers. We then harnessed spatial transcriptomic approaches to study the early stages of human myogenic regeneration upon engraftment, discovering niche factors expressed by regenerating myofibers that likely support stem cell retention and self-renewal. In line with these findings, after rapid cell loss upon transplantation, MYOG+ and PAX7+ myogenic populations stabilized upon the formation of myofibers. With an understanding of the importance of regenerative myofiber population in the retention of muscle stem cells upon engraftment, we then applied this workflow to a dystrophic microenvironment. We identified that the dystrophic microenvironment induces a massive change in the interactome of myogenic populations, and these changes are detrimental towards the regenerative program after subsequent injuries.Multiple epidermal growth factor like domains 10 (MEGF10) is a poorly understood stem cell niche receptor that appeared as both a candidate niche factor on regenerative myofibers and downregulated in dystrophic microenvironments. Therefore, we postulated that overexpression of MEGF10 may be sufficient to improve stem cell retention in transplantation models. We leveraged CRISPR genomic engineering to generate a TET-On inducible MEGF10 expression iPSC line which can robustly be differentiated to skeletal muscle and engrafted in vivo. We found that overexpression of MEGF10 during the first ten days following engraftments significantly supported more PAX7+ muscle stem cells and myofiber regeneration. Further, spatial transcriptomic analysis reveals that MEGF10 accelerates myofiber regeneration but stalls further maturation, arresting myofibers in a regenerative ACTC1+ state, marked by potential downstream MEGF10 signaling candidates LRRN1, CDH15, DLK1, and JAM2. Our findings are the first that describe advantageous heterogeneity of iPSC muscle stem cells upon engraftment, how they regenerate in real time and in a dystrophic host environment, and the temporal significance of stem cell niche receptors in their roles of transplanted niche formation. These breakthroughs may shed light on how to effectively generate novel stem cell therapy treatments for patients with neuromuscular disorders.

Nanocrystalline metals achieve strengths far beyond those of their coarse-grained counterparts, but pushing them to even higher performance is complicated by the fact that several chemical and structural strengthening mechanisms operate at once. Solute atoms can strengthen the grain interiors, segregate to grain boundaries, or develop nonuniform intragranular distributions, while nanoscale twins introduce additional internal interfaces, and these pathways are coupled rather than independent. This dissertation uses model nanocrystalline Ni-based thin films, together with nanoindentation, transmission electron microscopy, atomic-resolution scanning transmission electron microscopy and energy dispersive X-ray spectroscopy, and an adapted nanocrystalline solid solution strengthening model, to disentangle how these pathways interact and to identify the variables that ultimately set the achievable strength. First, the combined effects of grain-interior solid solution strengthening and grain boundary segregation are examined in Ni-Cr-Y films, in which Cr strengthens the lattice and Y segregates to the boundaries. Y segregation strengthens the interfaces and suppresses grain-boundary-mediated deformation, extending the range over which Cr remains effective, but it also alters dislocation emission geometry and thereby reduces the efficiency of lattice strengthening; the optimized composition reaches a hardness of 11.0 GPa, among the highest reported for Ni-based alloys. Next, the role of solute spatial distribution is examined in Ni-Re-Y films, where hardness rises from 8.84 GPa without Re to a maximum of 12.14 GPa at 8.7 at.% Re and then falls to 10.48 GPa at 14.0 at.% Re despite continued lattice expansion. High-resolution elemental mapping reveals increasingly heterogeneous intragranular Re distributions at higher Re contents, indicating that nominal concentration alone is an insufficient strengthening descriptor and supporting an effective-solute-availability interpretation. Finally, the influence of nanotwins is studied in a high-throughput Ni-Cr library in which twin thickness varies from 0.8 to 2.2 nm at nearly constant grain size; the strengthening response is captured by a modified model with an effective obstacle spacing of approximately 12 nm set by twin-confined volumes, while the very finest twins instead produce softening. Together, these studies show that solute chemistry, interfacial chemistry, and internal twin structure act through a common length scale, the effective spacing of obstacles to confined dislocation motion, and must be coordinated rather than optimized in isolation when designing high-strength nanocrystalline alloys.