科研成果

An improved indirect scheme for laser positron generation is proposed. The positron yields in high-$Z$ metal targets irradiated by laser produced electrons from near-critical density plasmas and underdense plasma are investigated numerically. It is found that the positron yield is mainly affected by the number of electrons of energies up to several hundreds of MeV. Using near-critical density targets for electron acceleration, the number of high energy electrons can be increased dramatically. Through start-to-end simulations, it is shown that up to $6.78\times10^{10}$ positrons can be generated with state-of-the-art Joule-class femtosecond laser systems.

The past five years have witnessed the significant breakthrough of perovskite solar cells (PSCs). High certificated power conversion efficiency (PCE) of 22.1% was achieved in a short time after the inorganic-organic perovskite was firstly used as the light absorber in the solar cells. It is believed that PSCs now become one of the most promising photovoltaic in the new-generation solar cells, which may rival silicon based solar cells. In this article, simplified planar perovskite solar cells without a hole-blocking layer were fabricated by a two-step spin-coating method, and the highest PCE of 15.1% was achieved with an average PCE of 13.6%. Moreover, it is found that the hysteresis effect is reduced in this kind of devices. The research on improved performance for the PSCs with simplified device architecture is very important both for understanding the working mechanism of cells, and for fabricating low-cost and high-performance PSCs to approach commercial applications. (C) 2017 Published by Elsevier Ltd.

Evergreen broadleaved woody plants (EBWPs) are dominant components in forests and savanna of the global tropic and subtropic regions. Southern China possesses the largest continuous area of subtropical EBWPs distribution, harboring a high proportion of endemic species. Hotspot and gap analyses are effective methods for analyzing the spatial pattern of biodiversity and conservation and were used here for EBWPs in China. Based on a distribution data set of 6,265 EBWPs with a spatial resolution of 50 × 50 km, we measured diversity of EBWPs in China using four indices: species richness, corrected weighted endemism, relative phylogenetic diversity, and phylogenetic endemism. According to the results based on 10% threshold, 15.73% of China’s land area was identified as hotspots using at least one diversity index. Only 2.14% of China’s land area was identified as hotspots for EBWPs by all four metrics simultaneously. Most of the hotspots locate in southern mountains. Moreover, we found substantial conservation gaps for Chinese EBWPs. Only 25.43% of the hotspots are covered by existing nature reserves by more than 10% of their area. We suggest to promote the establishment and management of nature reserve system within the hotspot gaps.

Total OH reactivity measurements were conducted on the Peking University campus (Beijing) in August 2013 and in Heshan (Guangdong province) from October to November 2014. The daily median OH reactivity was 20 +/- 11 s(-1) in Beijing and 31 +/- 20 s(-1) in Heshan, respectively. The data in Beijing showed a distinct diurnal pattern with the maxima over 27 s(-1) in the early morning and minima below 16 s(-1) in the afternoon. The diurnal pattern in Heshan was not as evident as in Beijing. Missing reactivity, defined as the difference between measured and calculated OH reactivity, was observed at both sites, with 21% missing reactivity in Beijing and 32% missing reactivity in Heshan. Unmeasured primary species, such as branched alkenes, could contribute to missing reactivity in Beijing, especially during morning rush hours. An observation-based model with the RACM2 (Regional Atmospheric Chemical Mechanism version 2) was used to understand the daytime missing reactivity in Beijing by adding unmeasured oxygenated volatile organic compounds and simulated intermediates of the degradation from primary volatile organic compounds (VOCs). However, the model could not find a convincing explanation for the missing reactivity in Heshan, where the ambient air was found to be more aged, and the missing reactivity was presumably attributed to oxidized species, such as unmeasured aldehydes, acids and dicarbonyls. The ozone production efficiency was 21% higher in Beijing and 30% higher in Heshan when the model was constrained by the measured reactivity, compared to the calculations with measured and modeled species included, indicating the importance of quantifying the OH reactivity for better understanding ozone chemistry.

This study developed a framework for combining multi-regional input-output analysis and network indicators to assess the interregional CO2 flows in China. The interregional CO2 flows of eight regions were calculated and visualized based on a multiregional input-output (MRIO) model for China. The focus of the research was intermediate use. The results of the network indicators showed that refined petroleum, coke, nuclear fuel and chemical products (07), and basic metals and fabricated metal sectors (09) played key roles in the complex networks. and these sectors in most regions controlled a large share of CO2 transfer by functioning as key hubs and authorities. They along with commerce, transport, storage, and post (16) acted as agents that brokered the CO2 flows within and between regions. The roles of some other industrial sectors were also identified, e.g., construction (15) functioned as the largest authority. The results demonstrated the importance and effectiveness of network indicators for identifying the characteristics of CO2 emissions embedded in the domestic supply chain, and provided new information relevant to policy implementation.

{BACKGROUND: Methylation quantitative trait loci (mQTLs) are the genetic variants that may affect the DNA methylation patterns of CpG sites. However, their roles in influencing the disturbances of smoking-related epigenetic changes have not been well established. This study was conducted to address whether mQTLs exist in the vicinity of smoking-related CpG sites (+/- 50 kb) and to examine their associations with smoking exposure and all-cause mortality in older adults. RESULTS: We obtained DNA methylation profiles in whole blood samples by Illumina Infinium Human Methylation 450 BeadChip array of two independent subsamples of the ESTHER study (discovery set

Fluorotelomer alcohol (6:2 FTOH) is a polyfluoalkyl substance that has been widely used in industry and consumer products in recent years, causing potential harm to the environment. However, currently the impact of 6:2 FTOH and its degradation products on microbial communities in sediment is unclear. The purpose of this study is to explore the impact of the biodegradation of 6:2 FTOH on bacterial community structures in surface sediment based on gene analysis. Surface sediment and river water were collected from Hai river, Tianjin, and a microcosm experiment was performed in the laboratory. The concentration of 6:2 FTOH and its degradation products were analyzed by liquid chromatograph-mass spectrometry/mass spectrometry (LC-MS/MS). The bacterial community structure was analyzed by denaturing gradient gel electrophoresis and high-throughput sequencing. The results showed that 6:2 FTOH could be degraded by microorganisms (half-life was less than 3 d), producing transient products such as 6:2 fluorotelomer carboxylic acid (FTCA) and 6:2 fluorotelomer unsaturated carboxylic acid (FTUCA) and stable products such as 5:2 fluorotelomer (FT) ketone, 5:2 fluorotelomer alcohol (sFTOH), perfluorohexanoic acid(PFHxA), perfluoro-n-pentanoic acid (PFPeA), perfluorobutanoic acid (PFBA) and 5:3 polyfluorinated acid. At different stages of 6:2 FTOH degradation, a change of bacteria and the predominant population became somewhat different. Based on the experimental results for 100 d, at the Phylum level, the biodegradation of 6:2 FTOH greatly increases the abundance of Chloroflexi (+24.8%) and decreases the abundance of Proteobacteria (-17.8%) and Firmicutes (-15.9%). At the Class level, due to the biodegradation of 6:2 FTOH, bacteria with notable increases included Anaerolineae (+19.6%) and δ-Proteobacteria (+4.3%), while bacteria with notable decreases included ε-Proteobacteria (-20.0%), Clostridia (-10.1%), Bacilli (-5.8%) and γ-Proteobacteria (-4.2%). At the Genus level, due to the biodegradation of 6:2 FTOH, bacteria with notable increases included Anaerolineaceae_(uncultured) (+19.1%) and Thioalkalispira (+13.3%), while bacteria with notable decreases included Vibrio (-14.1%), Sulfurimonas (-13.2%), Bacillus (-5.1%), Sulfurovum (-4.2%) and Fusibacter (-4.1%). These results are helpful for predicting the response of bacteria to the contamination of polyfluoalkyl substances and isolating the bacteria capable of the biodegradation of polyfluoalkyl substances. © 2017, Science Press. All right reserved.