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Essays in Macroeconomics and Labor Economics
No full textThis dissertation presents three essays.
In the first essay, we study the information advantages that employers hold over employees.
Employers may have private information on impending separation shocks and may choose to withhold it if disclosing the information risks causing workers to leave prematurely.
We examine whether employers have such information advantages by leveraging variations in the coverage of the Worker Adjustment and Retraining Notification (WARN) Act across states.
The WARN Act requires employers to give advance notice of mass layoffs or plant closings to employees, reducing information asymmetry. We test whether there is excessive voluntary quits before WARN-covered mass layoffs or plant closings, as these quits indicate workers' knowledge about impending layoffs.
Using confidential establishment-level labor turnover data, we observe an increase in voluntary quits leading up to WARN-covered plant closings, relative to trends in the control group, but results for mass layoffs are noisy due to a lack of statistical power.
We also find evidence that WARN-covered establishments manipulate layoff scales to avoid triggering the advance notice requirement.
Both findings suggest that employers hold information advantages over workers.
We build an extended search-and-matching model to study the implications of such information advantages for equilibrium labor market outcomes.
The second essay examines the role of social networks in shaping labor mobility, with a particular focus on how the sectoral backgrounds of an individual’s current coworkers influence job-switching decisions.
To identify causal effects, we employ multiple strategies, including distinguishing between current-year and non-current-year coworkers, controlling for time-varying shocks specific to the industry pairs, and using unexpected death or retirement events to isolate idiosyncratic changes in coworker networks.
Using German administrative matched employer-employee longitudinal data, we find a positive causal relationship between the proportion of coworkers from a sector and both the propensity of transitioning to that sector and the sensitivity to sectoral wage changes. To quantify the coworker mechanism's contribution to employment and reallocation, we develop and estimate a multi-sector, multi-firm general equilibrium model where perceived wages and adjustment costs for sector transitions depend on coworker shares.
Our results show that the welfare effect of COVID-induced productivity shocks is higher when considering coworker networks compared to assuming no influence from coworkers. Maintaining worker-employer ties to reduce competition in positively shocked sectors can further increase welfare.
In the third essay, we study the optimal policy for dual-use goods---items such as semiconductors or drones that have both military and civilian applications. We begin by empirically documenting that the regulation and trade flows of dual-use goods respond to changes in the security environment over time. To put structure on the national security externality, we introduce military procurement into a multi-country general equilibrium network model and add a military contest to the national welfare function. In a simple two-country case, optimal export taxes depend on a trade-off between the good's military centrality and its distortion centrality. Military centrality is a network-adjusted sales share to the foreign military; distortion centrality reflects taxation misallocation in the domestic economy from roundabout imports. Using U.S. defense procurement data, we construct a measure of military use across goods, which ranges from zero to one, by scaling the U.S. closed-economy military centrality by import demand elasticities. Our measure effectively evaluates policy restrictions and military content in trade flows. To quantify the macroeconomic magnitude of the consumption-security trade-off, we calibrate our model to a potential U.S.-China conflict. The revealed preference estimate of the value placed on the probability of winning the conflict equals 2.5 times the annual U.S. GDP.Economic
Synaptic connectivity mapping among thousands of neurons via parallelized intracellular recording with a microhole electrode array
No full textMassive parallelization of neuronal intracellular recording, which can measure synaptic signals across a network and thus can enable the mapping and characterization of synaptic connections, is a challenge still open in neuroscience, with the state-of-the-art limited to a mapping of ~300 synaptic connections. Here, we report a 4,096 platinum/platinum-black microhole electrode array fabricated on a complementary metal-oxide semiconductor electronic chip that substantially advances parallel intracellular recording and synaptic connectivity mapping. The microhole-neuron interface, together with current-clamp electronics in the underlying semiconductor chip, allows 90% average intracellular coupling rate with rat neuronal cultures, generating network-wide intracellular recording data that abound with synaptic signals. From these data we extract 70,000+ plausible synaptic connections amongst 2,000+ neurons, and catalogue them into inhibitory, weak/uneventful excitatory, and strong/eventful excitatory chemical synaptic connections, and electrical synaptic connections, with an estimated overall error rate of around 5%. The reported scale of synaptic connection mapping, with the ability to characterize synaptic connections, provides a step toward functional connectivity mapping of a large-scale neuronal network.Chemistry and Chemical BiologyEngineering and Applied SciencesPhysicsAccepted Manuscrip
The Art of Ciphering and the Early Modern Literary Imagination
No full textAbstract
It is well-established, both by scholarship and in the public awareness, that early modern England was replete with secret forms of writing. Scholarly works have extensively investigated the use of so-called substitution systems in the period, which were used to encrypt sensitive political and diplomatic correspondence during the Henrician, Elizabethan, and Jacobean periods; at the same time, public programming, such as a 2014 exhibit at the Folger Shakespeare Library entitled “Codes and Ciphers from the Renaissance to Today,” has made the allure and intrigue of early modern cryptographic objects and methods available to the public.
However, notwithstanding the general fascination with early modern cryptography, scholarship has not yet fully explored the capacious use of ciphers or their influence in early modern England. This work begins to fill this gap in scholarly work.
While the vast majority of scholarship on early modern cryptography focuses on its political forms and uses, the present work seeks to expand that definition by cognizing previously under-recognized forms and uses of early modern ciphers and their literary and intellectual influences. Specifically, it argues that monogram ciphers, steganographic encryption, and even the evolving meanings of the word “cipher” in the period illustrate that ciphers were used to negotiate personal as well as political identities. In addition to being tools of exigent concealment, ciphers were also tools of self-fashioning that operated perversely by often putting hidden information on display, even before the eyes of the readers they sought to exclude. The result is that cryptographic modes of making meaning encompass the defiant as well as the subtle and challenge the humanist assumption that to read is to know.
The implications of this study include broadening the ambit of traditional early modern literary studies to include discovery as well as traditional modes of rereading and reinterpretation. Ciphers provide us both with a new set of texts to interpret, and new ways to read them.Englis
"That Hatred of a Lie": Nat Turner, John Brown, and Revolutionary Love
No full textThis paper explores the lives, theological convictions, and violent insurrections of Nat Turner and John Brown through the lens of political philosopher Joy James's concept of Revolutionary Love. By analyzing Du Bois's invocation of both Turner and Brown at the 1906 Niagara Movement gathering at Harper's Ferry, the paper examines the paradox of rejecting violence while remembering those who used it in the name of justice. It argues that both Turner and Brown exemplify Revolutionary Love—a form of agape-driven political will to organize and struggle, nonviolently or violently, for the dignity and liberation of the oppressed. The study delves into the religious experiences, social contexts, and moral choices of each figure, emphasizing their dedication to their cause, their willingness to sacrifice, and the unresolved ethical tensions arising from their violent actions. While not justifying their violence, nor the suitable analytic for that set of moral conclusions, this framework does help reinterpret their legacies, complicating simplistic portrayals of fanaticism and highlighting the enduring power of spiritually grounded, justice-oriented love in their struggles against systemic oppression.Author's Origina
Spherochromatism in representation theory and arithmetic geometry
No full textThe goal of this thesis is to explain some applications of the perspective of chromatic homotopy theory to geometric representation theory and to arithmetic geometry. In the first half of this thesis, we study how the derived geometric Satake equivalence (due to Bezrukavnikov-Finkelberg, building on work of Ginzburg and Mirkovic-Vilonen) changes when one considers the category of constructible equivariant sheaves of -modules on the affine Grassmannian of a complex (simply-laced) reductive group , where is a commutative ring \textit{spectrum}. We state a conjecture describing the ``spectral side'' in terms of the Langlands dual group \ld{G} and the -dimensional formal group associated to via chromatic homotopy theory, and we make progress towards proving this conjecture. We also explore consequences of our conjecture in relation to the relative Langlands program recently elucidated by Ben-Zvi--Sakellaridis--Venkatesh.
In the second half of this thesis, we describe some joint work with Arpon Raksit, in which we refine work of B\"okstedt-Madsen to provide a complete description of the topological Hochschild homology of the ring of -adic integers in terms of the classical image of J spectrum. This result has several applications, both to homotopy theory and to arithmetic geometry, which we outline. We also describe some joint work with Jeremy Hahn, Arpon Raksit, and Allen Yuan, which aims to extend the theory of prismatization recently developed by Bhatt-Lurie-Drinfeld to the setting of ring spectra. This is tightly related to the theory of equivariant formal groups, and we provide some explicit calculations of these objects by generalizing rudiments of -deformed calculus. The constructions we describe also have applications to classical arithmetic geometry; for example, we explain how our work can be used to provide a higher-dimensional refinement of Drinfeld's recent reinterpretation of Deligne-Illusie's work on Hodge theory in characteristic .Mathematic
Three Revisionist Viewpoints on the Nineteenth Century Cholera Epidemics: Applicable Perspectives for the COVID Crisis
No full textAuthor's Origina
Odors as ''natural language'': sparse neural networks in mammalian olfactory systems and large language models
No full textThe studies of physics, neuroscience, and artificial intelligence (AI) have a long intertwined history. Particularly, sparse connectivity is a common feature of the brain neural networks and a key focus in AI for efficient computation; notably, pruning trained networks for sparse connectivity has a long history, partially inspired by neuroscience. This thesis explores sparse neural networks through two linked research topics: one focused on the brain (bilateral alignment in olfactory systems), and the other on AI (pruning large language models for on-device AI assistants).
For the first topic, inspired by mammalian dual nostrils creating two cortical neural representations of odors, in Chapter 1, we studied how to construct the inter-hemispheric projections aligning these representations. We hypothesized that this construction originates from online learning since mammals are constantly breathing. With a local Hebbian rule, we found that sparse inter-hemispheric projections suffice for bilateral alignment and discovered an inverse scaling that more cortical neurons allow sparser projections. Also, the local Hebbian rule was found to approximate the global stochastic gradient descent (SGD) rule since their update vectors align, suggesting that biologically plausible learning rules can approximate global learning rules if they contain the gradient information of the latter.
The next chapter extends Chapter 1 from four perspectives: an analysis of the update vector alignment between Hebbian and SGD rules and how it depends on the network parameters; a simple theory that recurrent connections in olfactory cortex may improve the bilateral alignment, inspired by the Hopfield Networks (associative memory) and similar to the design of Google Titans model that combines recurrent neural networks with Transformers; the dynamical properties of Hebbian learning; and finally, the geometric landscape of Hebbian learning.
A similar inverse scaling has been discovered in the Transformer attention matrices used in large language models (LLMs), which motivated the second topic. Concretely, we pruned pretrained Meta Llama-2 and Llama-3 models to obtain models with fewer parameters and develop on-device AI assistants, explored their sparsity limits, and compared their performance at the limits. We found that more than 50% of the
parameters in both models could be pruned, and Llama-3 produced fewer factual errors at the sparsity limit but required more parameters presumably due to its training settings and dataset.
In summary, by studying sparsity in both biological and artificial neural networks, this thesis may provide valuable insights into the general bilateral alignment problem in neuroscience (across different modalities and brain regions such as the frontal cortex responsible for short-term and motor response and the medial entorhinal cortex for spatial memory), open the door to interesting theoretical questions, and inspire more efficient AI algorithms or applications.Biology, Molecular and Cellula
Elegance With a Purpose: Assessing the Environmental and Social Efficacy of a High-End Clothing and Bag Rental Model in Jakarta
No full textMy research analyzed the environmental and social efficacy of the high-end fashion rental business model in Jakarta. With fashion waste contributing 10% of global greenhouse gas (GHG) emissions, the fast fashion industry has exacerbated this issue by lowering the average fashion goods utilization rate, with items on average discarded after only seven wears (McKinsey and Company, 2023; Shank & Bédat, 2016). Despite its economic benefits, the industry's environmental harm necessitated exploring circular fashion business models, such as fashion rental, to mitigate waste and emissions.
Experts have advocated for reuse with maintenance over recycling due to higher utilization rates. The rental model reduced new production and landfill waste. While previous research focused on fashion recycling and resale, studies on rental models, particularly in developing countries with weaker environmental regulations, were lacking (Farfetch, 2019; Herold & Prokop, 2023; Semba et al., 2020). Additionally, garment factories had high accident rates due to unethical labor practices. A rental business model allowing workers to repair items from home could improve livelihoods. Thus, my research examined both the environmental and social efficacy of implementing this model in Jakarta, using Luxeloop, a peer-to-peer high-end fashion rental platform, as a case study.
To address my research questions, I analyzed Luxeloop’s customer and employee data from June 2024 to February 2025. First, I measured displacement rates by surveying customers who had rented during this period, estimating how rentals reduced new
purchases. The findings confirmed that high-end fashion rentals mitigated the need to buy new items. Second, using Luxeloop’s transaction history database, I estimated the carbon dioxide (COExtension Studie