科研成果

People often see the origins of communist movements in Southeast Asia and the region’s overseas Chinese community as closely intertwined. This perception is evident in the cases of densely Chinesepopulated areas such as Malaya and Siam (Thailand), as well as places like Vietnam and Cambodia, where China’s influence has been historically strong in both political and cultural domains. Admittedly, it is very convenient to connect many Chinese-involved communist activities in Southeast Asia to the emergence of the communist party in China, but the simplistic argument – that Southeast Asia imports communism from China – is severely problematic. While overseas Chinese...

An unmanned aerial vehicle (UAV) equipped with miniature monitors was used to study the vertical profiles of PM2.5 (particulate matter with a <= 2.5-mu m diameter) and black carbon (BC) in Macau, China, from the surface to 500 m above ground level (AGL). Twelve- and 11-day measurements were conducted during February and March 2018, respectively. In total, 46 flights were conducted between 05:00 and 06:00 AM Local Time (LT). The average concentrations of PM2.5 and BC were significantly lower in March (40.1 +/- 17.9 and 2.3 +/- 2.0 mu g m(-3), respectively) when easterly winds prevailed, compared with those in February (69.8 +/- 35.7 and 3.6 +/- 2.0 mu g m(-3), respectively) when northerly winds dominated. In general, PM2.5 concentrations decreased with height, with a vertical decrement of 0.2 mu g m(-3) per 10 m. BC concentrations exhibited diverse vertical profiles with an overall vertical decrement of 0.1 mu g m(-3) per 10 m. Meteorological analyses including back-trajectory analysis and atmospheric stability categorization revealed that both advection and convection transports may have notable influences on the vertical profiles of PM pollutants. The concentration of PM pollutants above the boundary layer was lower than that within the layer, thus exhibiting a sigmoid profile in some cases. In addition, the lighting of firecrackers and fireworks on February 16 (first day of the Chinese New Year) resulted in the elevated concentrations of PM2.5 and BC within 150 m AGL. The takeoff of a civil flight on February 10 may have resulted in a substantial increase in the PM2.5 concentrations from 80.8 (+/- 2.1) mu g m(-3) at the ground level to 119.2 (+/- 9.3) mu g m(-3) at a height of 330 m. Although the results are confined to a height of 500 mAGL, the current study provides a useful dataset for PM vertical distributions, complementing the spatiotemporal variations by ground-based measurements. (C) 2019 Elsevier B.V. All rights reserved.

Photocatalytic nitrogen fixation represents a green alternative to the conventional Haber–Bosch process in the conversion of nitrogen to ammonia. In this study, a series of Bi5O7Br nanostructures were synthesized via a facile, low-temperature thermal treatment procedure, and their photocatalytic activity toward nitrogen fixation was evaluated and compared. Spectroscopic measurements showed that the tubular Bi5O7Br sample prepared at 40 °C (Bi5O7Br-40) exhibited the highest electron-transfer rate among the series, producing a large number of O2.– radicals and oxygen vacancies under visible-light photoirradiation and reaching a rate of photocatalytic nitrogen fixation of 12.72 mM·g–1·h–1 after 30 min of photoirradiation. The reaction dynamics was also monitored by in situ infrared measurements with a synchrotron radiation light source, where the transient difference between signals in the dark and under photoirradiation was analyzed and the reaction pathway of nitrogen fixation was identified. This was further supported by results from density functional theory calculations. The reaction energy of nitrogen fixation was quantitatively estimated and compared by building oxygen-enriched and anoxic models, where the change in the oxygen vacancy concentration was found to play a critical role in determining the nitrogen fixation performance. Results from this study suggest that Bi5O7Br with rich oxygen vacancies can be used as a high-performance photocatalyst for nitrogen fixation.

Thermionic electron sources are scaled down to the microscale on a chip and batch fabricated on 4-in silicon wafers by utilizing microfabrication technologies and exploiting carbon nanotubes as microscopic filaments of thermionic electron emission. The microfabricated on-chip thermionic electron sources not only satisfy the metrics of compactness and ease of batch fabrication, but also exhibit the advantages of good performance reproducibility (±6.9% variation over 100 test cycles under a driven voltage of 3.5 V) and high emission stability (fluctuation < 5% for emission current level of ≈10−8 A over 900 s) under a relatively low vacuum condition (10−4–10−2 Pa). Furthermore, to extract electrons and tune emission current, an extraction gate with a mesh is monolithically integrated with the thermionic electron sources using anodic bonding technique. The integrated electron sources exhibit a strong gate controllability and a considerable electron transmission ratio of ≈76% through the extraction gate. All these results make our devices a promising type of on-chip electron source in the applications of miniature vacuum electronic devices/systems.

The chromophores responsible for light absorption in atmospheric brown carbon (BrC) are not well characterized, which hinders our understanding of BrC chemistry, the links with optical properties, and accurate model representations of BrC to global climate and atmospheric oxidative capacity. In this study, the light absorption properties and chromophore composition of three BrC fractions of different polarities were characterized for urban aerosol collected in Xi'an and Beijing in winter 2013-2014. These three BrC fractions show large differences in light absorption and chromophore composition, but the chromophores responsible for light absorption are similar in Xi'an and Beijing. Water-insoluble BrC (WI-BrC) fraction dominates the total BrC absorption at 365 nm in both Xi'an (51 +/- 5%) and Beijing (62 +/- 13%), followed by a humic-like fraction (HULIS-BrC) and high-polarity water-soluble BrC. The major chromophores identified in HULIS-BrC are nitrophenols and carbonyl oxygenated polycyclic aromatic hydrocarbons (OPAHs) with 2-3 aromatic rings (in total 18 species), accounting for 10% and 14% of the light absorption of HULIS-BrC at 365 nm in Xi'an and Beijing, respectively. In comparison, the major chromophores identified in WI-BrC are PAHs and OPAHs with 4-6 aromatic rings (in total 16 species), contributing 6% and 8% of the light absorption of WI-BrC at 365 nm in Xi'an and Beijing, respectively.

When we are interested in high-dimensional system and focus on classification performance, the $\ell_{1}$-penalized logistic regression is becoming important and popular. However, the Lasso estimates could be problematic when penalties of different coefficients are all the same and not related to the data. We proposed two types of weighted Lasso estimates depending on covariates by the McDiarmid inequality. Given sample size $n$ and dimension of covariates $p$, the finite sample behavior of our proposed methods with a diverging number of predictors is illustrated by non-asymptotic oracle inequalities such as $\ell_{1}$-estimation error and squared prediction error of the unknown parameters. We compare the performance of our methods with former weighted estimates on simulated data, then apply these methods to do real data analysis.

We evaluate a reform of the US tax system switching to consumption taxation instead of income taxation. We do so in an environment that allows for progressivity of consumption taxes through differential tax rates between basic and non-basic consumption goods. The consumption tax system that maximizes aggregate welfare involves a 4% subsidy on basic consumption goods and a 68% tax on non-basic goods. Such a tax scheme generates 10% higher output in the long run, with a small increase in inequality. Nonetheless, the bench- mark with progressive income taxes and mild consumption taxes provides higher welfare on aggregate in the steady state, and even more so if we consider the transition.

Background Some bereaved parents experience a decreasing trajectory of grief, while others fail to adapt over the long term and persistently suffer from negative health consequences. This study investigates the mediating role of social integration in the relationship between losing an only child and parental health in a family-oriented society. Method A sample of 1828 bereaved parents and 4739 non-bereaved parents was drawn from a 10-city survey in China. Regression methods were used to examine the impact of child loss on parental health, and Sobel test was applied to examine the mediating role of social integration. Results Bereaved parents who lost their only child have worse self-rated health and more negative affect than the non-bereaved parents, which lasted for years after the death of the only child. The Sobel test shows that 24.8% of the total effects on self-rated health and 6.7% of the total effects on negative affect can be explained via decreased social integration. The gender of parents and child as well as fertility intentions are important sources of heterogeneity in the Chinese culture. Limitation The results based on cross-sectional data may only reveal correlation rather than causality. The data was retrieved from self-reported questionnaires and there is a lack of objective measures of parental health. Moreover, the detailed mechanisms behind how child loss resulted in less social integration should be further explored. Conclusions Significant disparities in health outcomes and social integration were found for bereaved parents relative to the non-bereaved parents. Future work is needed to assess the health of bereaved parents, identify the vulnerable and disadvantaged groups, and design inclusive intervention programs.

The heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) plays an important role in regulating NOx. The N2O5 uptake coefficient, c(N2O5), was determined using an iterative box model that was constrained to observational data obtained in suburban Beijing from February to March 2016. The box model determined 2289 individual c(N2O5) values that varied from <0.001 to 0.02 with an average value of 0.0046 +/- 0.0039 (and a median value of 0.0032). We found the derived winter c(N2O5) values in Beijing were relatively low as compared to values reported in previous field studies conducted during winter in Hong Kong (average value of 0.014) and the eastern U.S. coast (median value of 0.0143). In our study, field evidence of the suppression of c(N2O5) values due to pNO3 content, organics and the enhancement by aerosol liquid water content (ALWC) is in line with previous laboratory study results. Low ALWC, high pNO3 content, and particle morphology (inorganic core with an organic shell) accounted for the low c (N2O5) values in the North China Plain (NCP) during wintertime. The field-derived c(N2O5) values are well reproduced by a revised parameterization method, which includes the aerosol size distribution, ALWC, nitrate and organic coating, suggesting the feasibility of comprehensive parameterization in the NCP during wintertime. (C) 2020 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.

The diversity of vascular plants in Inner Asia has been researched; the main environmental factors determining the distribution of species belonging to various life forms and having different distribution range sizes have been identified. The key factors determining species diversity in Inner Asia are past climate changes and precipitation parameters. By contrast, the temperature conditions of the current climate do not affect the species richness significantly. The following current climatic parameters are important for woody plants: precipitation seasonality, mean precipitation in winter and spring, and diurnal range of temperature. Quite the opposite, the species richness of herbaceous plants is determined by climate-change velocity from the mid-Holocene and Last Glacial Maximum, the spatial heterogeneity of precipitation, and mean summer temperatures. Over time, distribution ranges of rare plants in the studied region may be reduced due to the increasing aridization.