Environmental Regulation, Pollution, and Public Health

In the first chapter, I investigate the effects of the Residential Lead Based Paint Hazard Reduction Act. Enacted in 1996, the lead hazard disclosure policy requires sellers and landlords to disclose known lead-based paint hazards to potential buyers or renters. Employing a difference-in-differences approach, I find evidence that the law prompted some families with children to reallocate toward homes without significant lead risks, increased lead mitigation in rental properties, and reduced blood-lead levels among children in rental properties. However, because white families appear to be more responsive to information disclosure than other groups, the information disclosure law might exacerbate racial disparities in lead exposure. In the second chapter, I estimate the spatio-temporal dynamics between wildfire and infant birthweight. Exposure to wildfire smoke is determined using the latitude and longitude coordinates of each infant's home address and a fine-scaled, spatial dataset of wildfire smoke plumes re-constructed in GIS from satellite images of the landscape. Using a difference-in-differences estimation strategy, model estimates show that wildfire smoke leads to a 4% to 6% reduction in birthweight. These effects are most pronounced among mothers exposed during their second and third trimesters of pregnancy and attenuate with respect to distance to a fire. We find no statistically significant relationships between proximity to wildfire and the birthweights of infants located outside the path of wildfire smoke. In the third chapter, I examine the relationship between hurricanes, the salience of flood risk, and residential property investment. Utilizing a difference-in-differences estimation strategy, I find a significant increase in the probability a homeowner invests in a damaged building located in a statutorily designated flood risk area. However, I find no change in the rate of property investment in damaged homes located outside of these areas. Results suggest that a recent storm may elevate households' perceptions of flood risk; however, we show that the primary mechanism driving these changes is a household's exposure to storm damage. We find no evidence of saliency effects in regions less proximate to storm damage. These findings cast doubt on the potential for an information-based regulation to align risk-perceptions with risk-actualities

Modal auxiliaries in learning and teaching Chinese as a second language

Chinese modal auxiliary is one of the most important language elements in the Chinese language. Therefore, to effectively and efficiently fulfil the communicative purpose, learning modal auxiliaries is necessary for second language learners. However, modal auxiliaries are still a) a comparatively weak point in Chinese research as well as b) a challenge for foreign students who learn Chinese as a foreign language. To lay a theoretical foundation for the later empirical study: this study constructs a new definition and categorisations of Chinese modal auxiliaries; 13 Chinese modal auxiliaries are thoroughly studied; a comparison between Chinese modal auxiliaries and English modal verbs is explored; errors that the students made in the application of Chinese modal auxiliaries are analysed, categorised and summarised; the deep reasons behind the errors are explored from a syntactic and pedagogical perspective. The study proves that explicit instructions from the language instructors are a critical countermeasure against CMA application difficulties. Interaction with peers and language partners benefits L2 learners’ acquisition of the second language. After-class exercises and corrective feedback from language instructors are supplementary solutions. And the study points out that language instructors have attached great importance to the unique grammatical structures of the Chinese modal auxiliaries, suggesting that the semantics of different Chinese modal auxiliaries should be the instructional focus in future teaching practice

Public policy and vertical relationships in the healthcare market

In complex, rapidly evolving healthcare markets, vertical relationships play an increasingly important role in pricing and health care delivery, creating or eliminating barriers to market efficiency. Despite their importance, few studies have addressed how vertical relationships affect care coordination and utilization and how public policies affect the market through those relationships. This dissertation focuses on two types of vertical relationships---the price negotiation between insurers and health care providers and the relationship between health care organizations and physicians. Chapter 1 examines the effect of medical loss ratio (MLR) regulation on insurer pricing behavior in light of insurer-provider price negotiation. Such regulation could disincentivize insurers from efficient cost-cutting, resulting in higher health service prices and consumer welfare loss. Using a Nash-in-Nash bargaining model with a regulation constraint, I find that MLR regulation rules out price bargaining equilibria with low health service price. The empirical examination of the Affordable Care Act MLR regulation shows that the regulation significantly increases medical cost for non-compliant insurers. Either restricting health service prices or replacing the regulation with a low-margin public option could keep prices low and improve consumer welfare. Chapter 2 utilizes patient changes of their primary care physicians (PCP) to examine the effect of health care organization boundaries on patient healthcare utilization. We define a visit-based organizational care concentration metric to measure how patient health care utilization spreads across organizations. Applying that metric to Medicare data, we capture the substantial variation of organizational care concentration across physicians and regions. Leveraging on PCP changes due to the exit of original PCPs, we find that patients who switched to PCPs with higher organizational care concentration experience a significant decrease in their total healthcare utilization without significant changes in quality of care. Chapter 3 examines the consequences of vertical integration between hospitals and physician practice groups, which could incentivize physicians to refer more patients to hospitals and induce higher medical spending. Employing an event-study framework and a discrete choice model, we find consistent and robust evidence that vertical integration increases the probability of choosing hospital-based facilities for outpatient surgical procedures, increasing both medical spending and travel distances

Current-Induced Dynamics and Chaos of Antiferromagnetic Bimerons

A magnetic bimeron is a topologically non-trivial spin texture carrying an integer topological charge, which can be regarded as the counterpart of skyrmion in easy-plane magnets. The controllable creation and manipulation of bimerons are crucial for practical applications based on topological spin textures. Here, we analytically and numerically study the dynamics of an antiferromagnetic bimeron driven by a spin current. Numerical simulations demonstrate that the spin current can create an isolated bimeron in the antiferromagnetic thin film via the damping-like spin torque. The spin current can also effectively drive the antiferromagnetic bimeron without a transverse drift. The steady motion of an antiferromagnetic bimeron is analytically derived and is in good agreement with the simulation results. Also, we find that the alternating-current-induced motion of the antiferromagnetic bimeron can be described by the Duffing equation due to the presence of the nonlinear boundary-induced force. The associated chaotic behavior of the bimeron is analyzed in terms of the Lyapunov exponents. Our results demonstrate the inertial dynamics of an antiferromagnetic bimeron, and may provide useful guidelines for building future bimeron-based spintronic devices.Comment: 6 pages, 4 figure

Mapping World Scientific Collaboration on the Research of COVID-19: Authors, Journals, Institutions, and Countries

The COVID-19 (2019 novel Coronavirus) is the most widespread pandemic infectious disease encountered in human history. Its economic losses and the number of countries involved rank first in the history of human viruses. After the outbreak, researchers in the field of medicine quickly carried out scientific research on the virus. Through a visual analysis of relevant scientific research papers from January 1st to April 1st, 2020, we can grasp the worldwide scientific research cooperation situation of 2019-nCoV research and reflect the international collaboration in combating the pandemic. To this end, 415 papers indexed in Thomson Reuters’s Web of Science were studied to provide a visualized description of scientific collaborations across the world by multiple levels, including author level, journal level, institution level and country level

Current-driven skyrmionium in a frustrated magnetic system

Magnetic skyrmionium can be used as a nanometer-scale non-volatile information carrier, which shows no skyrmion Hall effect due to its special structure carrying zero topological charge. Here, we report the static and dynamic properties of an isolated nanoscale skyrmionium in a frustrated magnetic monolayer, where the skyrmionium is stabilized by competing interactions. The frustrated skyrmionium has a size of about $10$ nm, which can be further reduced by tuning perpendicular magnetic anisotropy or magnetic field. It is found that the nanoscale skyrmionium driven by the damping-like spin-orbit torque shows directional motion with a favored Bloch-type helicity. A small driving current or magnetic field can lead to the transformation of an unstable N\'eel-type skyrmionium to a metastable Bloch-type skyrmionium. A large driving current may result in the distortion and collapse of the Bloch-type skyrmionium. Our results are useful for the understanding of frustrated skyrmionium physics, which also provide guidelines for the design of spintronic devices based on topological spin textures.Comment: 5 pages, 5 figure