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Structural Insights into Mycobacteriales Galactan Biosynthesis
No full textThe order Mycobacteriales includes a number of severe human pathogens, including Mycobacterium tuberculosis, the causative agent of tuberculosis and a leading cause of infectious disease-related mortality worldwide. The unique cell wall structure of these bacteria is essential for their viability, and has been studied as a potential target for novel therapeutics development. A key component of the mycobacterial cell wall is the galactan, a 30-40 residue linear polysaccharide of galactofuranose (Galf) with an alternating β(1,5) and β(1,6) linkage pattern, synthesized by the polymerase Galactofuranosyl Transferase 2 (GlfT2). While GlfT2 has been established as a processive polymerase with intrinsic sequence control, the mechanism underlying this activity remains unclear. In the studies presented here, we provide structural insights into Nocardia brasiliensis GlfT2 (NbrGlfT2) using X-ray crystallography and cryo-electron microscopy. We characterize both the acceptor-bound and membrane-embedded structures of NbrGlfT2 and propose three models for its catalysis: Processive Galactan Sliding, Feedback-Regulated Sequence Control, and Membrane Curvature-Mediated Polymerization. Furthermore, we structurally characterize a previously undescribed GlfT2 paralog from Rhodococcus equi, which we term ReqGlfT3. We confirm its galactofuranosyl transferase activity and identify the production of β(1,3) and β(1,5) linkages. These findings offer new insights into GlfT2 and related polymerizing glycosyltransferases, which will provide insights into enzymatic regioselectivity mechanisms and polysaccharide biosynthesis across the bacterial kingdom.Ph.D
Healthy Behavior: Essays in Health and Behavioral Economics
No full textThese essays examine beliefs and decision-making in health settings, emphasizing the role of attention, information, and technology in shaping behavior. The first essay studies human error in chest x-ray interpretation, a common and consequential medical task. It casts radiologists as facing a classical decision-theory problem, derives a novel martingale test for optimal behavior, and implements this test through a prudent application of machine learning to anonymized health records from the Beth Israel Deaconess Medical Center. I find that 58 percent of radiologists make predictable mistakes when assessing cardiac health on chest x-rays. Roughly two thirds of errors are explainable as individual radiologists making inconsistent decisions, and one third reflect the possibility that algorithms detect novel or complex signals. The second essay studies app-based mindfulness meditation, which has grown popular due to claims about its effects on mental well-being, productivity, and decision making. We assess these claims an experiment with 2,384 US adults, randomizing access and usage incentives for a popular mindfulness app. App access improves an index of anxiety, depression, and stress at two weeks and four weeks, with persistent effects three months later. It also improves earnings on a focused proofreading task by 2 percent. The third essay studies a tradeoff governments face when making recommendations in an evolving crisis. We investigate the effect of taking an early position on how much people believe later recommendations, using an online experiment with 1,900 US respondents in early April 2020. We present participants with CDC projection about coronavirus death counts and randomize exposure to information that highlights how the President previously downplayed the threat. When the President’s inconsistency is salient, participants are less likely to revise their beliefs about death counts from the CDC projection. This aligns with a model of signal extraction from government communication, and has implications for changing guidelines in other settings. JEL Codes: D91, I12, C8Ph.D
Essays in International Macroeconomics
No full textHow do exchange rates and tariffs shape the economy? Their effects both independently and in regard to each other are puzzling with respect to classical economic models. This dissertation focuses on how macroeconomic factors -- sticky prices (Chapter 1), interest rates (Chapter 2), and scale economies (Chapter 3) -- inform the scope of exchange rates and tariffs. Unveiling these factors helps illuminate the nature of these shocks' influence.
Chapter 1: The first chapter revisits the classic relationship between exchange rate pass-through, how exchange rates influence prices, and expenditure-switching, the resulting substitution between home and foreign goods. Expenditure-switching is the main channel through which exchange rates transmit to the real economy. Conventional wisdom holds that this channel's strength is increasing in exchange rate pass-through into prices: assuming the import demand elasticity is independent of pass-through, larger effects of exchange rates on prices yield larger substitution of spending between domestic and foreign goods. In this paper, I show that this conventional wisdom does not hold. Using confidential US micro-data and a panel-data local projection technique, I show that quantity-exchange rate elasticities are similar across high and low pass-through environments. In essence, low pass-through is subject to a larger import demand elasticity than is high pass-through. I then propose an extension of a standard small open economy New Keynesian model by adding a layer of import buying (retail) firms, in which both exporting and importing firms are subject to price rigidities. I show empirically and theoretically that the ``import buyer rigidity" dampens overall adjustment, but less so under low pass-through because in this case the pass-through is more persistent. The model thus accounts for why the quantity-exchange rate elasticities are similar across pricing regimes. I conclude by exploring the implications of this framework for monetary and exchange rate policy, actually finding a stronger expenditure-switching channel under low pass-through.
Chapter 2: The second chapter, joint with Victor Orestes, documents how currency markets and trade flows respond to tariffs imposed by and on the US as related to other countries' macrofinancial position. We show that countries which maintain higher interest rates than the US depreciate much more strongly -- to the point of offsetting the tariffs on impact -- than their low-interest counterparts. However, these effects are not as persistent as the tariff shocks. Our results highlight a US hegemonic asymmetry: tariffs imposed on the US have little effect on currency markets, US demand for high-interest countries' goods is relatively elastic, but the latter's demand for US exports is not. Monetary policy can be an effective tool to target the exchange rate fluctuation as it has a similar incidence as tariffs. Finally, we present evidence that the interest rate analysis could draw from trade-network fundamentals. To rationalize our findings, we modify a baseline model of exchange rate determination using the interest rate as a "sufficient statistic" wedge in fundamentals. Our model indicates that the financial market imperfections we observe in data distort the global response to tariff escalation.
Chapter 3: The third chapter proposes an answer to the question of why there is complete long-run pass-through of both tariffs and exchange rates in US exports, despite evidence of flexible markups. I develop a methodology to leverage tariffs and exchange rates to uncover the structural drivers of pass-through, the markup elasticity and the marginal cost scale elasticity. I derive and quantify the scale channel of pass-through, which can be decomposed into a bilateral scale and the novel "shock span" scale effect. The shock span channel arises because different correlation patterns across customers enters prices via the scale channel. Because exchange rates are correlated across trading partners, compared to tariffs they have greater capacity for shock-span effects of scale economies. Quantifying the bilateral and shock span components of the scale channel, the paper demonstrates that scale economies can rationalize the discrepancy between markup flexibility and observed pass-through.Ph.D
Factorization in additive monoids of evaluation polynomial semirings
No full textFor a positive real α, we can consider the additive submonoid M of the real line that is generated by the nonnegative powers of α. When α is transcendental, M is a unique factorization monoid. However, when α is algebraic, M may not be atomic, and even when M is atomic, it may contain elements having more than one factorization (i.e., decomposition as a sum of irreducibles). The main purpose of this paper is to study the phenomenon of multiple factorizations inside M. When α is algebraic but not rational, the arithmetic of factorizations in M is highly interesting and complex. In order to arrive to that conclusion, we investigate various factorization invariants of M, including the sets of lengths, sets of Betti elements, and catenary degrees. Our investigation gives continuity to recent studies carried out by Chapman et al. in 2020 and by Correa-Morris and Gotti in 2022
Facilitating Creative Learning: Engaging in a Practice of Care
No full textCreative learning is shaped not only by tools and activities, but by relationships. This dissertation explores facilitation in creative learning environments as a relational practice centered on care—not as a set of techniques, but as a deeply human way of being with others, a commitment to creating spaces where people feel supported enough to explore, connected enough to share, and valued enough to express themselves. Grounded in constructionist, socioconstructivist, and humanistic pedagogies, the research draws from my multi-year engagement with Learning Creative Learning (LCL)—an online course and global community for educators—and WeScratch, a series of hands-on, collaborative online workshops introducing educators to creative coding. Through qualitative analysis of small-group facilitation during WeScratch workshops, I explore how volunteer facilitators experience and reflect on their practice. Drawing from three case studies, I examine how care takes shape in the situated, relational work of creative learning facilitation. In particular, I identify three interrelated forms of care: epistemic care, which focuses on what and how people learn; affirming care, which supports what learners value and who they are; and convivial care, which attends to how learners feel and relate to one another in a group. After introducing these three forms of care through the work of individual facilitators, I show how epistemic, affirming, and convivial care are deeply interwoven in practice—at times reinforcing one another, at times pulling in different directions. Facilitators must navigate these tensions in the moment, making situated judgments about when to step in, when to hold back, and how to respond to the evolving needs of individuals and groups. By centering care, this research highlights facilitation as deeply human, relational work that sustains the conditions for creative learning, contributing to the broader and evolving discourse on constructionism. It also makes the case for seeing facilitation as an ethical and political practice. In a time when educational discourse is increasingly shaped by ideals of efficiency and optimization—and the world faces rising authoritarianism and dehumanization—choosing to care is not only pedagogically meaningful, but also politically urgent.Ph.D
Measurement of charged hadron multiplicity in Au+Au collisions at s NN = 200 GeV with the sPHENIX detector
No full textThe pseudorapidity distribution of charged hadrons produced in Au+Au collisions at a center-of-mass energy of s NN = 200 GeV is measured using data collected by the sPHENIX detector. Charged hadron yields are extracted by counting cluster pairs in the inner and outer layers of the Intermediate Silicon Tracker, with corrections applied for detector acceptance, reconstruction efficiency, combinatorial pairs, and contributions from secondary decays. The measured distributions cover |η| < 1.1 across various centralities, and the average pseudorapidity density of charged hadrons at mid-rapidity is compared to predictions from Monte Carlo heavy-ion event generators. This result, featuring full azimuthal coverage at mid-rapidity, is consistent with previous experimental measurements at the Relativistic Heavy Ion Collider, thereby supporting the broader sPHENIX physics program
MEDS: Building Models and Tools in a Reproducible Health AI Ecosystem
No full textKDD ’25, Toronto, ON, CanadaHealth AI suffers from a systemic reproducibility crisis that irreparably hinders research in this space across academia and industry. To combat this and empower researchers in the health AI space, we propose a comprehensive interactive tutorial introducing the ''Medical Event Data Standard'' (MEDS) and its growing open-source ecosystem. Working in MEDS allows you to more easily build AI models over public or private longitudinal EHR datasets and to readily benchmark existing, published models against contributions on local datasets and tasks. MEDS simplifies the construction of AI models on longitudinal Electronic Health Record (EHR) datasets and enables straightforward benchmarking against established models. Reflecting its growing adoption, MEDS is utilized at over 15 institutions across 8 countries, features 7+ open-source tools, supports 10+ published models, and provides publicly available Extract-Transform-Load (ETL) pipelines for major public EHR datasets. A KDD tutorial offering practical experience with MEDS will significantly enhance reproducibility and comparability in health AI research.
In this tutorial, we will teach attendees how to (1) transform datasets into the MEDS format(2) pre-process MEDS data for modeling needs(3) build highly effective, efficient, AI models for diverse predictive tasks on their datasets, and (4) contribute their results to MEDS-DEV, a decentralized benchmark enabling robust evaluation against meaningful baselines. Participants will engage in collaborative, minimal-dependency Jupyter notebook exercises, guided through each step by structured instruction and practical coding sessions. Attendees will leave equipped with practical knowledge to build reproducible, state-of-the-art AI models within the MEDS ecosystem
Sensitivity analysis of aromatic chemistry to gas-phase kinetics in a dark molecular cloud model
No full textThe increasingly large number of complex organic molecules detected in the interstellar medium necessitates robust kinetic models that can be relied upon for investigating the involved chemical processes. Such models require rate coefficients for each of the thousands of reactions; the values of these are often estimated or extrapolated, leading to large uncertainties that are rarely quantified. We have performed a global Monte Carlo and a more local one-at-a-time sensitivity analysis on the gas-phase rate coefficients in a 3-phase dark cloud model. Time-dependent sensitivities have been calculated using four metrics to determine key reactions for the overall network as well as for the cyanonaphthalene molecule in particular, an important interstellar species that is severely under-produced by current models. All four metrics find that reactions involving small, reactive species that initiate hydrocarbon growth have large effects on the overall network. Cyanonaphthalene is most sensitive to a number of these reactions as well as ring-formation of the phenyl cation (C6H5+) and aromatic growth from benzene to naphthalene. Future efforts should prioritize constraining rate coefficients of key reactions and expanding the network surrounding these processes. These results highlight the strength of sensitivity analysis techniques to identify critical processes in complex chemical networks, such as those often used in astrochemical modeling
Thrust Density in Porous Electrospray Thrusters
No full text39th International Electric Propulsion Conference, Imperial College London, London, United Kingdom 14-19 September 2025A path for increasing thrust density in electrospray thrusters is through fabrication of
denser arrays of emitters. Conventional arguments assume thrust to scale linearly with the
emitter number, but there has not been a critical analysis to examine the behavior of this
trend at very high densities. Here, we describe a model for thruster current as a function
of array density which considers how hydraulic losses change as density increases, and we
find that the ideal scaling is a poor approximation. In the optimistic cases, the current
increases monotonically with density but with diminishing returns. In the worst cases,
packing more emitters into the same space is detrimental as hydraulic losses dominate over
gains in the number of emitters. Under certain conditions there is an optimum density
which maximizes the net output. We also describe the fabrication and testing of a family
of porous electrospray emitters featuring pore sizes in the 10 nm to 100 nm range, with
the purpose of leveraging the high precision and uniformity afforded by these materials
to develop a platform suitable for experimentally validating the density models. A set
of test results from two of these thrusters is presented, both having a 450 µm pitch but
with different pore sizes. The 100 nm pore thruster shows characteristics similar to other
porous electrosprays, emitting in the pure-ion mode at currents up to 400 µA and exhibiting
current-temperature behavior commensurate with the liquid viscosity. The 10 nm pore
thruster appears to be greatly flow-restricted, producing about an order of magnitude less
current at analogous conditions and showing negligible response to changes in temperature.National Aeronautics and Space Administration (NASA)National Science Foundation (NSF
Angle-strained sila-cycloalkynes
No full textSecond row elements in small- and medium-rings modulate strain. Herein we report the synthesis of two novel oligosilyl-containing cycloalkynes that exhibit angle-strain, as observed by X-ray crystallography. However, the angle-strained sila-cyclooctynes are sluggish participants in cycloadditions with benzyl azide. A distortion-interaction model analysis based on density functional theory calculations was performed