科研成果

This study explores how subjectivity is expressed in coherence relations, by means of a distinctive collocational analysis on two Chinese causal connectives: the specific subjective kejian ‘so’, used in subjective argument-claim relations, and the underspecified suoyi ‘so’, which can be used in both subjective argument-claim and objective cause-consequence relations. On the basis of both Horn’s pragmatic Relation and Quality principles and the Uniform Information Density Theory, we hypothesized that the presence of other linguistic elements expressing subjectivity in a discourse segment should be related to the degree of subjectivity encoded by the connective. In line with this hypothesis, the association scores showed that suoyi is more frequently combined with perspective markers expressing epistemic stance: cognition verbs and modal verbs. Kejian, which already expresses epistemic stance, co-occurred more often with perspective markers related to attitudinal stance, such as markers of expectedness and importance. The paper also pays attention to similarities and differences in collocation patterns across contexts and genres.

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.