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"Lewis, Ethan"
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North Korea's cyber operations : strategy and responses
North Korea is emerging as a significant actor in cyberspace with both its military and clandestine organizations gaining the ability to conduct cyber operations. However, there is no comprehensive standard literature about North Korea's cyber capabilities that takes an integrated view of the topic. Existing research is fragmented in pockets of strategic, technical, and policy pieces, though no individual study reaches far enough to create a standard reference document about North Korea's cyber capabilities. This report aims to fill this void, integrating Korean and English language information sources, existing work in each respective field, and creating a foundation for future deeper research.
Immigration Restrictions as Active Labor Market Policy
by
Clemens, Michael A.
,
Postel, Hannah M.
,
Lewis, Ethan G.
in
Economic policy
,
Employment
,
Endogenous
2018
An important class of active labor market policy has received little impact evaluation: immigration barriers intended to raise wages and employment by shrinking labor supply. Theories of endogenous technical advance raise the possibility of limited or even perverse impact. We study a natural policy experiment: the exclusion of almost half a million Mexican bracero farm workers from the United States to improve farm labor market conditions. With novel labor market data we measure state-level exposure to exclusion, and model the absent changes in technology or crop mix. We fail to reject zero labor market impact, inconsistent with this model.
Journal Article
Causal mediation analysis for time-varying heritable risk factors with Mendelian randomization
2025
Understanding the causal mechanisms of diseases is crucial in clinical research. When randomized experiments are unavailable, Mendelian Randomization (MR) leverages genetic mutations to mitigate confounding. However, most MR analyses assume static risk factors, oversimplifying dynamic risk factor effects. The framework of life-course MR addresses this but struggles with limited GWAS cohort sizes and correlations across time points. We propose FLOW-MR, a computational approach estimating causal structural equations for temporally ordered traits using only GWAS summary statistics. FLOW-MR enables inference on direct, indirect, and path-wise causal effects, demonstrating superior efficiency and reliability, especially with noisy data. By incorporating a spike-and-slab prior, it mitigates challenges from extreme polygenicity and weak instruments. Applying FLOW-MR, we uncovered a childhood-specific protective effect of BMI on breast cancer and analyzed the evolving impacts of BMI, systolic blood pressure, and cholesterol on stroke risk, revealing their causal relationships.
Here the authors reveal FLOW-MR, a computational tool using genetic data to study how traits across the life course affect disease. It suggests a protective role link between childhood body mass in breast cancer and confirms adult blood pressure as a cause of stroke.
Journal Article
Do male-female wage differentials reflect differences in the return to skill?
2014
Male-female wage gaps declined significantly over the 1980s and 1990s, while returns to education increased. In this papen we use cross-city data to explore whether, like the return to education, the change in the gender wage gap may reflect changes in skill prices induced by the diffusion of information technology. We show that male-female and education-wage differentials moved in opposite directions in response to the adoption of PCs. Our most credible estimates imply that changes in skill prices driven by PC adoption can explain most of the decline in the US male-female wage gap since 1980.
Journal Article
Single-cell RNA sequencing reveals placental response under environmental stress
2024
The placenta is crucial for fetal development, yet the impact of environmental stressors such as arsenic exposure remains poorly understood. We apply single-cell RNA sequencing to analyze the response of the mouse placenta to arsenic, revealing cell-type-specific gene expression, function, and pathological changes. Notably, the Prap1 gene, which encodes proline-rich acidic protein 1 (PRAP1), is significantly upregulated in 26 placental cell types including various trophoblast cells. Our study shows a female-biased increase in PRAP1 in response to arsenic and localizes it in the placenta. In vitro and ex vivo experiments confirm PRAP1 upregulation following arsenic treatment and demonstrate that recombinant PRAP1 protein reduces arsenic-induced cytotoxicity and downregulates cell cycle pathways in human trophoblast cells. Moreover, PRAP1 knockdown differentially affects cell cycle processes, proliferation, and cell death depending on the presence of arsenic. Our findings provide insights into the placental response to environmental stress, offering potential preventative and therapeutic approaches for environment-related adverse outcomes in mothers and children.
Environmental stressors have been associated with placental dysfunction and pregnancy complications. Here, the authors reveal gene expression changes in the mouse placenta exposed to arsenic at single-cell resolution and identify a potential therapeutic target to mitigate its harmful effects on pregnancy and fetal development.
Journal Article
Placenta-derived extracellular vesicles in fetal health: emerging insights into brain development and environmental interactions
2025
Placenta-derived extracellular vesicles (EVs) are emerging as critical regulators of maternal–fetal communication during pregnancy. These lipid bilayer-enclosed particles, primarily secreted by trophoblasts, transport bioactive cargos—including RNAs, proteins, lipids and neurotransmitters—that influence a wide range of developmental and immunological processes. While much attention has been given to their roles in maternal adaptation and health outcomes, recent studies highlight their direct impact on fetal development, particularly fetal brain development. Emerging evidence suggests that placental EVs may traverse both the placental and blood–brain barriers, thereby contributing to signaling processes that influence neurogenesis, cell fate specification and regional brain patterning. Their cargo composition is dynamic, modulated by gestational age and environmental factors such as air pollution, viral infection and chemical toxicants. These stressors can alter EV secretion and molecular content, contributing to adverse fetal outcomes including impaired organogenesis and neurodevelopmental delays. In this review, we synthesize current knowledge on placental EV biology, examine their roles in maternal and fetal health with an emphasis on neurodevelopment and evaluate how environmental exposures reshape EV-mediated signaling. We also discuss emerging technologies and translational opportunities, including EV-based diagnostics and therapeutic delivery systems. Collectively, placenta-derived EVs represent a vital yet underexplored mechanism in fetal programming, offering novel insights into the developmental origins of health and disease.
Placental extracellular vesicles influence fetal brain development
Extracellular vesicles (EVs) are tiny particles released by cells that help them communicate. They carry important materials such as proteins and RNA, reflecting the health of the cells they come from. This review focuses on EVs from the placenta, which play a crucial role during pregnancy. These placental EVs help in communication between the mother and fetus, affecting immune responses and fetal development. The study summarized various methods to isolate and analyze these EVs, including advanced techniques such as high-resolution flow cytometry. Researchers stressed that placental EVs can cross barriers between mother and fetus, carrying signals that influence fetal organ development, including the brain. They also emphasized that environmental factors such as pollution can change the content of these EVs, potentially affecting fetal health. The findings suggest that placental EVs are vital for healthy pregnancy outcomes.
This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author.
Journal Article
Systemic Uptake of Rhodamine Tracers Quantified by Fluorescence Imaging: Applications for Enhanced Crop–Weed Detection
2025
Systemic fluorescence tracers introduced into crop plants provide an active signal for crop–weed differentiation that can be exploited for precision weed management. Rhodamine B (RB), a widely used tracer for seeds and seedlings, possesses desirable properties; however, its application as a seed treatment has been limited due to potential phytotoxic effects on seedling growth. Therefore, investigating mitigation strategies or alternative systemic tracers is necessary to fully leverage active signaling for crop–weed differentiation. This study aimed to identify and address the phytotoxicity concerns associated with Rhodamine B and evaluate Rhodamine WT and Sulforhodamine B as potential alternatives. A custom 2D fluorescence imaging system, along with analytical methods, was developed to optimize fluorescence imaging quality and facilitate quantitative characterization of fluorescence intensity and patterns in plant seedlings, individual leaves, and leaf disc samples. Rhodamine compounds were applied as seed treatments or in-furrow (soil application). Rhodamine B phytotoxicity was mitigated by growing in a sand and perlite media due to the adsorption of RB to perlite. Additionally, in-furrow and seed treatment methods were tested for Rhodamine WT and Sulforhodamine B to evaluate their efficacy as non-phytotoxic alternatives. Experimental results demonstrated that Rhodamine B applied via seed pelleting and Rhodamine WT used as a direct seed treatment were the most effective approaches. A case study was conducted to assess fluorescence signal intensity for crop–weed differentiation at a crop–weed seed distance of 2.5 cm (1 inch). Results indicated that fluorescence from both Rhodamine B via seed pelleting and Rhodamine WT as seed treatment was clearly detected in plant tissues and was ~10× higher than that from neighboring weed plant tissues. These findings suggest that RB ap-plied via seed pelleting effectively differentiates plant seedlings from weeds with reduced phytotoxicity, while Rhodamine WT as seed treatment offers a viable, non-phytotoxic alternative. In conclusion, the combination of the developed fluorescence imaging system and RB seed pelleting presents a promising technology for crop–weed differentiation and precision weed management. Additionally, Rhodamine WT, when used as a seed treatment, provides satisfactory efficacy as a non-phytotoxic alternative, further expanding the options for fluorescence-based crop–weed differentiation in weed management.
Journal Article
Immigration, skill mix, and capital skill complementarity
2011
Over the past thirty years, U.S. manufacturing plants invested heavily in automation machinery. This paper shows these investments substituted for the least-skilled workers and complemented middle-skilled workers at equipment and fabricated metal plants. Specifically, it exploits the fact that some metropolitan areas experienced faster growth in the relative supply of less-skilled labor in the 1980s and 1990s due to an immigration wave and the tendency of immigrants to regionally cluster. Plants in these areas adopted significantly less machinery per unit output, despite having similar adoption plans initially. The results imply that fixed rental rates for automation machinery reduce the effect that immigration has on less-skilled relative wages.
Journal Article
Cracks in the Melting Pot: Immigration, School Choice, and Segregation
2012
We examine whether low-skilled immigration to the United States has contributed to immigrants' residential isolation by reducing native demand for public schools. We address endogeneity in school demographics using established Mexican settlement patterns in California and use a comparison group to account for immigration's broader effects. We estimate that between 1970 and 2000, the average California school district lost more than 14 non-Hispanic households with children to other districts in its metropolitan area for every 10 additional households enrolling low-English Hispanics in its public schools. By disproportionately isolating children, the native reaction to immigration may have longer-run consequences than previously thought.
Journal Article
Schooling and the Armed Forces Qualifying Test: Evidence from School-Entry Laws
by
Lewis, Ethan G
,
Cascio, Elizabeth U
in
Academic education
,
Academic testing
,
Achievement Rating
2006
How much can late schooling investments close racial and ethnic skill gaps? We investigate this question by exploiting the large differences in completed schooling that arise among teenagers with birthdays near school-entry cutoff dates. We estimate that an additional year of high school raises the Armed Forces Qualifying Test (AFQT) scores of minorities in the NLSY 79 by 0.31 to 0.32 standard deviations. These estimates imply that closing existing racial and ethnic gaps in schooling could close skill gaps by between 25 and 50 percent. Our approach also uncovers a significant direct effect of season of birth on test scores, suggesting that previous estimates using season of birth as an instrument for schooling are biased.
Journal Article