Born-Infeld Black Holes in 4D Einstein-Gauss-Bonnet Gravity

A novel four-dimensional Einstein-Gauss-Bonnet gravity was formulated by D. Glavan and C. Lin [Phys. Rev. Lett. 124, 081301 (2020)], which is intended to bypass the Lovelock's theorem and to yield a non-trivial contribution to the four-dimensional gravitational dynamics. However, the validity and consistency of this theory has been called into question recently. We study a static and spherically symmetric black hole charged by a Born-Infeld electric field in the novel four-dimensional Einstein-Gauss-Bonnet gravity. It is found that the black hole solution still suffers the singularity problem, since particles incident from infinity can reach the singularity. It is also demonstrated that the Born-Infeld charged black hole may be superior to the Maxwell charged black hole to be a charged extension of the Schwarzschild-AdS-like black hole in this new gravitational theory. Some basic thermodynamics of the black hole solution is also analyzed. Besides, we regain the black hole solution in the regularized four-dimensional Einstein-Gauss-Bonnet gravity proposed by H. L\"u and Y. Pang [arXiv:2003.11552].Comment: 13 pages and 18 figures, published versio

Typing Composable Coroutines

Coroutine, as a powerful programming construct, is widely used in asynchronous applications to replace thread-based programming or the callback hell. Using coroutines makes code more readable and maintainable, for its ability to transfer control while keeping the literal scope. However, reasoning about coroutine behavior can be challenging without proper typing. We propose a type notation and calculus for composing asymmetric, first-class, stackless coroutines. Given the types of a list of coroutines, we can compute a composed type matching the collective behavior of the coroutines, so that the input and output can be type-checked by a type system. Our coroutine types can model the data received by or yielded from a coroutine, which be of coroutine types as well. On top of our type calculus, we discuss its soundness and evaluation issues, then provide four application scenarios of our coroutine types. Not only can our types be used in modern programming languages, such as Python, but also model program behaviors in OCaml and even Prolog

CO preferential oxidation in a novel Au@ZrO₂ flow-through catalytic membrane reactor with high stability and efficiency

CO preferential oxidation (CO-PROX) achieves much interest as a strategy to remove trace CO in reformed gases for hydrogen utilization. Herein, we reported a novel Au@ZrO₂ catalytic membrane reactor by embedding gold nano-particles in ZrO₂ hollow fiber membrane for CO-PROX. The flow-through catalytic membrane exhibited high catalytic activity and oxygen selectivity, which gave a turnover frequency of 4.73 s⁻¹ at 60 °C, 2–3 times higher than conventional catalyst pellets. CO conversion of >95% was achieved over the catalytic membrane, which maintained great operational stability during 500-h operation even CO₂ and H₂O were added in the feed stream. The excellent catalytic performance of the flow-through catalytic membrane makes gold catalyst possible for practical application in the removal of CO from hydrogen

Essays in determinants of comparative advantage and welfare implications of trade wars

My main research areas are international trade and empirical microeconomics. In the first and second chapter of my PhD dissertation, I use similar empirical methodology clearly identify and analyzing comparative advantage among aging and female labor supply unbalanced countries. The third chapter focus on the effect of US China trade war on the country welfare with intermediate and non-tradable goods. In the first chapter, we investigate a particular mechanism through which differences in demographic composition across countries affect international trade flows. Some cognitive functions are known to vary across the adult life span, and in particular the ability to update skills and adapt to changes in working conditions. As a country's population is getting older, it becomes increasingly difficult for firms to find workers with up-to-date skills. As a result, countries with aging populations will start losing comparative advantage in industries that rely heavily on workers' ability to adapt to frequent changes in working conditions. We test this hypothesis and find robust empirical evidence for a significant negative effect of population aging on comparative advantage of a country in industries which are intensive in skill adaptability of the labor force, in both the cross-sectional and the dynamic panel data sets. In the second chapter, we study the effect of female labor supply change on China's international trade. In 1979, the one-child policy (OCP) was introduced in China, many more boys than girls have been born, changing the relative female labor supply. Differences in sex ratios across cities, caused by differences in OCP enforcement, affect availability of gender-dependent skills. These regional differences interact with sector-specific differences in intensities in gender-dependent skills. Other things equal, cities with higher female population share specialize in industries which use female labor intensively. We empirically confirm this insight for the sample of 283 Chinese prefecture cities, using spatial variation in OCP stringency as an exogenous female labor supply shifter. We interpret our results as highlighting the importance of labor force gender composition for industry's productivity. Our results imply that the effect of gender imbalances in labor supply on labor market outcomes, observed in many parts of the world, can be mitigated through international trade by utilizing relatively abundant type of labor in export-oriented industries. In the third chapter, we use a quantitative general equilibrium trade model to analyze the effect of the US China trade war on welfare of the main countries affected by it. In 2018, the US introduced a 25% import tariff on certain imports from China in an attempt to reduce US China trade deficits and to nudge the Chinese government to abandon its unfair trade practices. Quantitative results suggest that after three rounds of import tariff increase both China and US suffered welfare reductions, by 0.3 and 0.0075 percentage points respectively. At the same time, some other economies benefited from the trade war, especially the ones that are close trade partners to either US or China. We use this model to simulate the effect of the same additional import tariff imposed on randomly selected industries, and find similar reduction in welfare