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33 results on '"Wang, Feicheng"'

3. Catalytic Priors: Using Synthetic Data to Specify Prior Distributions in Bayesian Analysis

Author

Huang, Dongming, Wang, Feicheng, Rubin, Donald B., and Kou, S. C.

Subjects
Statistics - Methodology
Abstract

Catalytic prior distributions provide general, easy-to-use, and interpretable specifications of prior distributions for Bayesian analysis. They are particularly beneficial when the observed data are inadequate to stably estimate a complex target model. A catalytic prior distribution is constructed by augmenting the observed data with synthetic data that are sampled from the predictive distribution of a simpler model estimated from the observed data. We illustrate the usefulness of the catalytic prior approach using an example from labor economics. In the example, the resulting Bayesian inference reflects many important aspects of the observed data, and the estimation accuracy and predictive performance of the inference based on the catalytic prior are superior to, or comparable to, that of other commonly used prior distributions. We further explore the connection between the catalytic prior approach and a few popular regularization methods. We expect the catalytic prior approach to be useful in many applications.

Published
2022

4. Rate-matching the regret lower-bound in the linear quadratic regulator with unknown dynamics

Author

Wang, Feicheng and Janson, Lucas

Subjects
Computer Science - Machine Learning, Electrical Engineering and Systems Science - Systems and Control, Mathematics - Statistics Theory
Abstract

The theory of reinforcement learning currently suffers from a mismatch between its empirical performance and the theoretical characterization of its performance, with consequences for, e.g., the understanding of sample efficiency, safety, and robustness. The linear quadratic regulator with unknown dynamics is a fundamental reinforcement learning setting with significant structure in its dynamics and cost function, yet even in this setting there is a gap between the best known regret lower-bound of $\Omega_p(\sqrt{T})$ and the best known upper-bound of $O_p(\sqrt{T}\,\text{polylog}(T))$. The contribution of this paper is to close that gap by establishing a novel regret upper-bound of $O_p(\sqrt{T})$. Our proof is constructive in that it analyzes the regret of a concrete algorithm, and simultaneously establishes an estimation error bound on the dynamics of $O_p(T^{-1/4})$ which is also the first to match the rate of a known lower-bound. The two keys to our improved proof technique are (1) a more precise upper- and lower-bound on the system Gram matrix and (2) a self-bounding argument for the expected estimation error of the optimal controller.

Published
2022

8. Business as usual? Unraveling the impact of Brexit on UK‐EU business links.

Author

Kone, Zovanga, Wang, Feicheng, Wang, Zheng, and Zhou, Zhuo

Subjects
BUSINESS travel, INTERNATIONAL travel, INTERNATIONAL business enterprises, BRITISH withdrawal from the European Union, 2016-2020, REFERENDUM
Abstract

We present the first systematic evidence on the impact of Brexit on the business links between the United Kingdom (UK) and the European Union (EU) through the lens of international visits. We find important asymmetry in the direction of changes in business visits between the two regions following the referendum. Specifically, we observe a significant drop in EU‐to‐UK trips, while UK‐to‐EU trips increased noticeably after the vote. These results support the claim that Brexit has made the UK less attractive to EU businesses, but also reveal that UK businesses are investing more in their relationships with EU partners to offset the uncertainty. [ABSTRACT FROM AUTHOR]

Published
2024
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9. Adaptive median filter salt and pepper noise suppression approach for common path coherent dispersion spectrometer.

Author

Guan, Shouxin, Liu, Bin, Chen, Shasha, Wu, Yinhua, Wang, Feicheng, Liu, Xuebin, and Wei, Ruyi

Subjects
ADAPTIVE filters, PIXELS, NOISE, SPECTROMETERS, ALGORITHMS
Abstract

The Common-path Coherent-dispersion Spectrometer (CODES), an exoplanet detection instrument, executes high-precision Radial Velocity (RV) inversions by recording the phase shifts of interference fringes. Salt-and-pepper noise caused by factors such as improper operation of the CCD probe/analog-to-digital converter and strong dark currents may interfere with the phase information of the fringe. This lowers the quality of the interfering fringe image and significantly interferes with the RV's inversion. In this study, an adaptive median filtering algorithm (CODESmF) based on submaximum and subminimum values is designed to eliminate the interference fringe image's salt-and-pepper noise as well as to reduce RV error. This allows the interference fringe image's phase information to be retained more completely. The algorithm consists of two major modules. Pixel Sub-extreme-based Filtered Noise Monitoring Module: discriminates signal pixels and noise pixels based on the submaximum and subminimum values of the pixels in the filtering window. Adaptive Median Filter Noise Suppression Module: the signal pixel is kept at the original value output, the noise pixel serves as the filtering window's center pixel, and the adaptive median filtering procedure is repeated numerous times with various filtering window sizes. According to the experimental findings, the CODESmF outperforms comparable algorithms and works better at recovering interference fringes. More than 90% of the phase/RV error caused by salt-and-pepper noise is typically eliminated by the CODESmF algorithm, and in certain circumstances, it can even remove roughly 98% of the phase error. [ABSTRACT FROM AUTHOR]

Published
2024
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18. Mechanical Properties of Steel Fiber-Reinforced, Recycled, Concrete-Filled Intersecting Nodes in an Oblique Grid.

Author

Zhao, Jun, Wang, Feicheng, Zhu, Yinhong, and Yang, Bai

Subjects
COMPRESSION loads, TENSION loads, STEEL, STEEL tubes, ULTIMATE strength
Abstract

The construction of high-rise oblique grid buildings requires a large amount of concrete. To save resources, an oblique grid of intersecting nodes composed of steel outer tubes and steel fiber, recycled concrete inner tubes (OGSFRCIN) has been proposed. ABAQUS is used to study the mechanical properties of the nodes under axial pressure, accounting for the effects of six parameters: the oblique angle, the thickness of the stiffening ring, the thickness of the connecting plate, the concrete strength, the recycled aggregate replacement rate, and the steel fiber content. The results show that the oblique angle, connecting plate thickness, concrete strength, and steel fiber content significantly affect the ultimate bearing capacity of specimens. The reinforcing ring thickness has a significant effect on the evolution of lateral displacement. It is not advisable to use components with a replacement rate of 100% recycled aggregate in engineering practice because of insufficient lateral stiffness and ultimate strength. The specimen's out-of-plane displacement is tightly restricted when the connecting plate's thickness is greater than or equal to 10 mm. In practical engineering, the connecting plate and reinforcing ring thickness should not be less than 10 mm, and the recommended steel fiber content is 1.0% to 2.0%. Through the analysis of the mechanical properties of the OGSFRCIN under monotonic axial compression and reciprocating axial tension and compression loads, it can be seen that OGSFRCIN have good mechanical properties and can be applied in engineering practice. Here, the modified formulas for calculating the bearing capacity of OGSFRCIN are put forward. [ABSTRACT FROM AUTHOR]

Published
2023
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20. Epidemiology and risk factors for the development of cutaneous toxicities in patients treated with immune-checkpoint inhibitors: A United States population-level analysis

Author

Wongvibulsin, Shannon, primary, Pahalyants, Vartan, additional, Kalinich, Mark, additional, Murphy, William, additional, Yu, Kun-Hsing, additional, Wang, Feicheng, additional, Chen, Steven T., additional, Reynolds, Kerry, additional, Kwatra, Shawn G., additional, and Semenov, Yevgeniy R., additional

Published
2022
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21. Importing Air Pollution? Evidence from China's Plastic Waste Imports

Author

Unfried, Kerstin and Wang, Feicheng

Subjects
F18, China, Q53, air pollution, ddc:330, PM2.5, waste import ban, plastic waste trade, Q56, F64
Abstract

Plastic waste trade has grown considerably in the last decades and has caused severe environmental problems in recipient countries. As the largest recipient, China has permanently banned the imports of plastic waste since 2018. This paper examines the causal effect of plastic waste imports on air pollution by exploiting China's experience of importing plastic waste and the recent import ban. Combining data on plastic waste imports with PM2.5 data at the city level for the years 2000-2011, we find that plastic waste imports increased PM2.5 density significantly. This effect is linked to expanded production in the waste processing sector and an increased number of incineration. To evaluate the impact of the import ban on air quality, we employ daily data on air pollution between 2015 and 2020. Our difference-in-differences results show that affected cities, relative to other cities, experienced a significant improvement in air quality following the ban. These findings suggest potential environmental gains from banning plastic waste imports in other countries.

Published
2022

22. China's aid exports to Africa and the COVID-19 pandemic: How much? Where? What?

Author

Fuchs, Andreas, Kaplan, Lennart, Kis-Katos, Krisztina, Schmidt, Sebastian S., Turbanisch, Felix, and Wang, Feicheng

Subjects
ddc:330
Abstract

China's aid to Africa receives significant attention from policymakers, development practitioners, and observers worldwide. This is even more the case since the outbreak of the coronavirus pandemic, given China's importance as a donor of vaccines, ventilators, face masks, disinfectants, and other medical supplies. This PEGNet Policy Brief describes the general patterns of Beijing's so-called 'mask diplomacy' and 'vaccine diplomacy' compared to China's pre-pandemic aid exports. First, we find that China's average monthly aid exports to Africa did not increase after the pandemic outbreak (in contrast to those to the rest of the world). Second, we observe a shift towards medical aid at the expense of other aid goods after the pandemic outbreak. Chinese non-medical aid to Africa was 26.6% below its prepandemic (2017-2019) level. Third, we find significant shifts in the cross-country distribution of Chinese aid exports, creating both so-called aid darlings (e.g., Ethiopia) and aid orphans (e.g., Côte d'Ivoire) across the African continent.

Published
2022

23. Tracking Chinese aid through China customs: Darlings and orphans after the COVID-19 outbreak

Author

Fuchs, Andreas, Kaplan, Lennart, Kis-Katos, Krisztina, Schmidt, Sebastian S., Turbanisch, Felix, and Wang, Feicheng

Subjects
I15, China, vaccine diplomacy, I18, P33, H12, F59, aid exports, COVID-19, mask diplomacy, Health Silk Road, ddc:330, official development assistance, F35, H84
Abstract

Since the outbreak of the COVID-19 pandemic, China's mask and vaccine diplomacy have been widely discussed, but the debate relies on a few stylized data points. This article introduces a systematic way to measure China's foreign aid in almost real-time through official customs records of exported aid goods. Our results show significant shifts in China's aid after the outbreak of the COVID-19 pandemic. First, medical aid skyrocketed after the outbreak. It was initially dominated by face masks and other protective equipment and later by vaccines. This came at the expense of non-medical aid, which was 16.3 percent below its pre-pandemic level. Second, China's aid became global, clearly extending beyond the Global South. Third, in the aftermath of the initial outbreak in March 2020, China's aid became less responsive to both recipient need and political friendship, which can be mainly attributed to the rise of aid through non-government sources. However, in the vaccine diplomacy period of 2021, economic needs and political factors have regained their original importance.

Published
2022

30. Exact Asymptotics of Linear Quadratic Adaptive Control and Population-level Comorbidity Analysis

Author

Wang, Feicheng

Subjects
Statistics
Abstract

We present two self-contained topics in this thesis: exact asymptotics of linear quadratic adaptive control (LQAC) and population-level comorbidity analysis. LQAC is perhaps the simplest non-bandit reinforcement learning problem. Existing work on LQAC is focused almost exclusively on characterizing rates of regret and their ability to learn the underlying system dynamics, with little attention paid to the constants multiplying those rates that can be critically important in practice. By carefully combining recent finite-sample performance bounds for the LQAC problem with a particular (less-recent) martingale central limit theorem, we are able to derive asymptotically-exact expressions for the regret, estimation error, and prediction error of a rate-optimal stepwise-updating LQAC algorithm. In simulations on both stable and unstable systems, we find that our asymptotic theory also describes the algorithm’s finite-sample behavior remarkably well. In the same LQAC setting, we closes a log(T) rate gap between regret upper bound and lower bound by establishing a novel regret upper-bound of Op(√T). Population-level comorbidity analysis can be conducted with Electronic health records (EHRs), which have more data, lower cost, and less ethical concern comparing with clinical trials. With nationwide insurance claims data of 85.97 million enrollees across 8 years, our study quantifies the bi-directional causal effect: getting one of cancers and autoimmune diseases could increase the risk of getting the other. We identified a significantly increased risk of developing autoimmune diseases among patients receiving immunotherapy agents in all seven cancer types commonly treated with immunotherapy. On the reversal direction, we suggested that the underlying immune system dysregulation of rheumatoid arthritis (a common autoimmune disease), rather than its treatments, implicates the development of subsequent cancers. We applied the matching methods to balance the treatment and control group patients by sex, race, age, and inferred health and economic status. Our method is extensible to investigating the connections among drugs, diseases, and comorbidities at scale.

Published
2022

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