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Decoding Solar System Volatile Compositions: Laboratory Investigations of Ice Entrapment and Deuterium Fractionation
No full textStars and planets form within dense molecular clouds composed of gas and microscopic dust grains. On the cold surfaces of these grains, volatile molecules such as H2O, CO2, CH4, and N2 condense to form icy mantles that serve as active chemical reactors. Within these ices, physical trapping, isotopic exchange, and radical chemistry govern how volatile elements are stored, transformed, and ultimately delivered to planets. Understanding these processes is key to tracing the molecular history that connects interstellar clouds to comets, protoplanetary disks, and potentially habitable worlds.
In protoplanetary disks, and in planet formation more broadly, the distribution of volatiles between gas and ice is critical for setting the compositions of the solids that become incorporated into planets, moons, and comets. If ices were pure, this distribution could be described by a sequence of snowlines. In reality, astrophysical ices are complex mixtures, and their compositions at different disk temperatures depend on how different volatiles interact within the ice matrix. Physical trapping, or entrapment, of hyper-volatile molecules such as CO, CH4, N2, and Ar within less volatile ices like H2O or CO2 can delay sublimation to temperatures above their pure desorption points, altering the inventory of gases released into the disk and of the solids incorporated into planetary bodies. Laboratory desorption experiments conducted under astrophysically relevant conditions show that entrapment efficiency is primarily governed by the physical structure of the ice rather than by chemical interactions between species, indicating that entrapment is a mechanical trapping process. These results provide quantitative constraints on how hyper-volatiles are retained or released, influencing the volatile distribution inherited by disks and icy bodies.
Icy grains are not simply passive reservoirs of interstellar species; photochemical processing actively introduces new chemical and isotopic complexity. In the second part of this thesis, ultraviolet irradiation of mixed H2O:CD4 and D2O:CH4 ices was used to investigate solid-state hydrogen–deuterium exchange. These experiments reveal that photodissociation of both water and methane produces reactive OH and OD radicals that drive abstraction and recombination reactions, leading to the formation of HDO and CD3H/CH3D. The efficiency and directionality of this exchange differ between the two isotopic systems, indicating that isotopic equilibration is incomplete. The results suggest that local irradiation conditions can partially reshape primordial D/H ratios, providing a mechanism to explain the diversity of isotopic signatures measured in cometary volatiles and interstellar ices.
The final part of this work explores oxygen-atom insertion as a pathway to form methanol and its deuterated analogs under cold, barrierless conditions. Experiments using mixed CH4 and CD4 ices with 18O2 demonstrate that excited O(1D) atoms readily insert into C–H and C–D bonds to form CH3OH and CD3OD. A subtle isotopic bias toward the formation of deuterated methanol indicates that zero-point energy differences and bond energetics influence the insertion outcome. These findings identify oxygen insertion as a new solid-state pathway for deuterium fractionation in interstellar organics, offering an explanation for otherwise puzzling isotopic enrichments observed in methanol and related molecules.
Together, these studies provide a unified view of how the physical structure and photochemistry of ices regulate volatile retention, isotopic fractionation, and the emergence of molecular complexity in star- and planet-forming regions. By combining systematic laboratory experiments on entrapment, H/D exchange, and oxygen insertion, this thesis connects the chemical evolution of interstellar ices to the processes shaping planetary compositions. The results reveal how cold solid-state chemistry governs the inheritance of volatiles from molecular clouds to planetary systems, bringing us closer to understanding the molecular origins of habitability.Astronom
Incentive Design in the Machine Learning Age
No full textThis dissertation investigates the design of incentives in multi-agent systems where traditional assumptions -- such as fully rational agents and omniscient principals -- do not hold. As real-world systems increasingly involve learning-based decision-makers, either human or algorithmic, this work explores how learning alters the landscape of incentive design. The dissertation is organized into three parts.
The first part focuses on incentive design by learning principals, specifically in information and mechanism design settings. For information design, this part introduces novel algorithms that allow a principal to learn an agent's non-Bayesian belief updating process, such as a subjective prior or cognitive bias, via strategic interaction with the agent.
For mechanism design, this part examines how a coordinator can learn to compute Bayes correlated equilibria in non-truthful auctions using limited samples of agent types.
The second part studies incentive design for learning agents, who are modeled as boundedly rational learners rather than best responders. This part first presents, for a general class of principal-agent problems, a reduction from no-regret learning agents to approximately best-responding agents, enabling a precise analysis of the principal's performance. It then characterizes the convergence properties of multi-agent learning in first-price auction games, identifying when convergence to equilibrium is possible.
The third part explores incentive issues in deployed machine learning systems, with a case study on recommender systems. It demonstrates that the strategic behaviors by content creators can exacerbate polarization, even under diversity-promoting algorithms, and proposes alternative algorithmic designs that mitigate these effects.
Collectively, this dissertation lays foundational insights for designing systems that are robust to the incentives of learning-based, data-driven participants.Engineering and Applied Sciences - Computer Scienc
Education and Economic Mobility: How Schools Shape Peer Composition and Student Trajectories
No full textThe potentially equalizing role of schools is called into question when lower-income students increasingly attend different schools—and, within schools, different classrooms—than their higher-income peers. My dissertation examines how schools shape lower-income students’ peer composition and the implications for long-term outcomes.
In the first paper, using data from Texas, a large and nationally representative state, I find that the median lower-income student experiences schooling with nearly ten times fewer upper-income classmates than their wealthier peers. To understand why exposure to upper-income peers may matter for long-term outcomes, I isolate peer effects from resource access using within-school, between-cohort variation in the share of upper-income students, controlling for school trends. I find that lower-income students in cohorts with more upper-income peers are marginally more likely to enroll in four-year colleges and earn higher wages. These effects do not appear to operate through changes in access to school resources; the increase in college enrollment seems to be driven by exposure to lower-achieving upper-income peers.
The second paper bridges research on school choice and academic tracking by examining how the addition of advanced courses affects classroom and school peer composition. Public schools may introduce academic tracks to attract or retain upper-income and higher-achieving students. However, tracking can also exacerbate sorting by income and achievement within schools. Exploiting variation in the timing of Advanced Placement (AP) course additions within subjects, I find that adding an AP course increases lower-income students’ exposure to upper-income classmates. This increase is driven by a rise in the overall share of upper-income students at the school following the course addition, offsetting the increase in within-school sorting.
In the third paper, my co-authors and I study the expansion of alternative schools for lower-performing students in Chicago. These schools offer tailored curricula and flexible scheduling, potentially improving graduation rates among students at high risk of dropping out. However, they may also segregate vulnerable students who otherwise may have graduated from traditional public schools. Using variation in the timing and proximity of school openings, we find that alternative schools increase high school persistence and reduce student arrests but reduce the likelihood of college enrollment.Educatio
Revealing the formation of massive quiescent galaxies using various techniques
No full textUnderstanding why and how galaxies stop forming stars (``quenched'') and become quiescent has been a key question in galaxy evolution. This thesis aims to understand the formation of massive quiescent galaxies at various epochs by combining three different approaches: 1) Galaxy formation simulations, 2) Ground- & space-based spectroscopic observations, and 3) Stellar population synthesis models.
In the local Universe (z~0), star-forming activity/quiescence is closely linked to galaxy morphology. To understand how galaxy quenching and morphological transformation are related, I use a high-resolution cosmological galaxy simulation (Illustris-TNG50). I track the evolution of massive quiescent galaxies down to z=0 and show how quenching histories/timescales and mechanisms differ for quiescent galaxies with different morphology.
Cosmic noon (z~2) is the epoch when galaxy growth and feedback are the most active. I focus on young quiescent galaxies at z~2, as they likely still hold the evidence of powerful rapid quenching they underwent recently. I perform Magellan/FIRE spectroscopic observations of young quiescent galaxies at z~2, infer their star formation histories from spectral energy distribution fitting, and analyze their ionized emission lines and their sizes. JWST has enabled us to obtain a larger spectroscopic sample of massive quiescent galaxies at cosmic noon. I study the quenching histories and mechanisms of 14 massive quiescent galaxies at z~2 from deep JWST/NIRSpec observations (JWST Cycle-1 program: the Blue Jay survey). I reconstruct their star formation histories and investigate their neutral and ionized gas properties to understand the physical mechanism behind rapid quenching.
Finally, I develop new self-consistent alpha-enhanced stellar population models, which will be essential in deriving accurate physical properties of high-z galaxies where alpha-enhancement is expected to be common. For future work, I will apply these new alpha-enhanced models to early massive quiescent galaxies (z>3) to reveal their true formation histories. Since these galaxies are likely descendants of the first galaxies and progenitors of the massive quiescent galaxies in the local universe, revealing their accurate formation histories will shed light on how the first galaxies grow into the most massive galaxies we see today.Astronom
Contextualizing the Environmental Crisis through Narrative in Richard Powers’ The Overstory
No full textRichard Powers’ 2018 novel The Overstory confronts an uncertain planetary future in the face of a world ravaged by climate change. While many recent works of environmental-based literature employ elements of science fiction—dystopian settings in a not-so distant future—Powers’ novel mirrors the contemporary United States and rooted in applicable ecology. The following analysis explores how The Overstory and selected precedent works of fiction use narrative to contextualize complex ideas, particularly the climate crisis. While data and science can be instructive, they often fail to grab public attention to the degree necessary to inspire appropriate reactions and behaviors, as underscored by many actions of the American government. Climate crisis skeptics are unlikely to care more about the environment through a bombardment of data, but those nonbelievers might be moved by a well-told story they can connect with. Drawing on the literary field of eco-criticism—particularly the work of Ursula K. Heise and Richard Nixon—this paper explores how fiction can shape the conversation around climate change in ways that account for both the human and natural world.Extension Studie
Can Cities Be Smart? Urban Governance in the Digital Age
No full textAmid the federal government’s policy disarray of the 2010s, scholars from multiple fields called for U.S. cities to take the lead in advancing progressive policy aims. In the same decade, responding to the digital revolution, “smart city” initiatives proliferated throughout the country. These initiatives combined aspirations for unlocking the governance potential of cities with excitement about the power of digitization to enhance public goods provision. But the promise of smart urbanism quickly faded as many projects became mired in controversy. Critical academic scholarship, including in Science and Technology Studies (STS), has detailed many of the ethical and political concerns raised by smart cities, such as surveillance, digital inequality and privatization. Yet little comparative work has been done to understand how and why city residents accepted or problematized local smart city projects in different ways, to different ends. At the same time, smart city controversies have been largely neglected in the literature on city-scale governance.
This dissertation addresses these gaps through a comparative study of smart city controversies in the United States in the 2010s. Specifically, it examines three pairs of smart city projects across three key areas of urban life: self-driving mobility in Phoenix and Columbus; digital connectivity in New York City and San Diego; and economic opportunity in Queens and Northern Virginia through the competition for Amazon’s second headquarters. Working with the STS method of comparative problematization, which calls attention to the site-specific character of problem framings, I find that controversies emerged from local processes of epistemic and normative co-production, whereby the abstract and promissory concept of the smart city was interpreted against more durable forms of local meaning-making and value creation. Smart city projects produced conflicts when they imposed visions of urban futures – often formulated by actors at other sites and scales – that were out of alignment with local imaginaries of social progress. These cases reveal new ways in which urban citizens are confronting the process of digitization by voicing different expectations about their capacity to exercise agency in setting the terms of progress, digital or otherwise. It is this collective capacity for upholding what I call the “urban social compact” that will determine whether, in the face of digital transformation, cities can be smart.Public Polic
A Marketplace for Populism: The Moral Politics of Digitization in India’s Informal Economy
No full textDigital India is a flagship policy of the Government of India to foster “economic growth combined with social inclusion.” Central to Digital India is the Aadhaar card, a biometric identification now distributed to 1.3 billion Indians, and a real time mobile payment technology, Unified Payments Interface (UPI), that has significantly replaced cash transactions. This technological transformation was imagined and implemented against the social backdrop of India's large informal economy. Prior scholarship has shown that technological promises to improve governance and economic opportunities are often not fully realized and create new sources of friction, especially for marginalized communities. Nevertheless, digital technologies have been taken up by actors in the informal economy, such as street vendors in urban areas. In this dissertation, I ask: How has digitization altered informal workers’ economic and political subjectivity, and with what consequences for their agency in the market and political sphere? How do citizens rationalize breakdowns in techno-economic promises, and how has digitization become an instrument of populist politics? I explore these questions through fieldwork across Delhi, Mumbai and Bangalore. While my ethnography is based in the Sarojini Nagar market of New Delhi, my methodology also includes discourse analysis, controversy studies, legal and policy analysis, archival work, and oral histories.
I find that over time the Indian state has evolved into a heterogenous set of actors and institutions with competing politics. Bureaucrats, administrators, lower-level officials, politicians, ministers, and middlemen all represent overlapping components of “the state,” with benevolent, oppressive or ambiguous relationships to street vendors. Digitization of identity and payments alters the political relationship between street vendors, governing authorities, and the nation-state in four salient ways. First, digitization opens the possibility of being seen and potentially recognized by the benevolent arms of the state. Second, digital payments represent a traceable and transparent alternative to the cash-based corruption the state is seeking to eliminate. Third, digital welfare creates a personified state with direct connections between welfare recipients and political leaders rather than state services being mediated through the bureaucracy. Fourth, in political discourse, street vendors are reimagined from being subjects in need of social transformation to agents of nation-building through a digital economy that is accessible and immediate. Simultaneously, there exists resistance to the digital imaginary of the Indian nation-state by street vendors, critiques of being seen without recognition, distribution without redistribution, and duty without rights. In postcolonial India, the bureaucratic-state apparatus was strengthened to facilitate the progress of the nation and its citizens. Politics in contemporary India recasts these mediating institutions as threats to democracy. Digitization represents an effort to diminish the bureaucratic state that is understood by political leaders, tech-entrepreneurs, and street vendors as inhibiting the nation’s and its citizens’ progress.Public Polic
Reading the Epigenome: Applications and Innovations in Chromatin Profiling
No full textThe regulation of cell identity is encoded in the chromatin landscape long before transcriptional programs become apparent. However, our ability to interpret and engineer this code has been limited by gaps in mechanistic understanding, a lack of comprehensive reference maps, and the resolution constraints of current technologies. This dissertation establishes a foundational framework for epigenomics across these three dimensions. First, to uncover the mechanistic barriers to cell engineering, we investigate chromatin remodeling during hepatocyte-to-biliary reprogramming. We demonstrate that this lineage conversion is epigenetically incomplete and identify the histone acetyltransferase HBO1 as a critical barrier to plasticity; its depletion enables full lineage conversion. Second, to decode the regulatory logic of lineage specification, we construct a high-resolution CUT&RUN atlas of the mouse immune system. This resource resolves lineage-specific and shared chromatin programs, providing a "regulatory guidebook" for understanding priming, memory, and bivalency across hematopoietic lineages.
Third, to bridge the gap between tissue context and chromatin state, we introduce Photoselective Sequencing (PSS), a method that links spatial information to local epigenetic patterns within complex tissues. Finally, to push the limits of resolution, we describe a single-cell profiling approach that combines expansion microscopy with scCUT&Tag to achieve high-resolution mapping of histone modifications alongside cellular morphology. Collectively, these studies illustrate how new experimental and computational strategies are reshaping our understanding of chromatin dynamics, moving the field from static observation toward the rational engineering of cell fate.Biological and Biomedical Science