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| 1 | Highly efficient NHC-iridium-catalyzedβ-methylation of alcohols with methanol at low catalyst loadings显示文摘The methylation of alcohols is of great importance since a broad number of bioactive and pharmaceutical alcohols contain methyl groups.Here,a highly efficientβ-methylation of primary and secondary alcohols with methanol has been achieved by using bis-N-heterocyclic carbene iridium(bis-NHC-Ir)complexes.Broad substrate scope and up to quantitative yields were achieved at low catalyst loadings with only hydrogen and water as by-products.The protocol was readily extended to theβ-alkylation of alcohols with several primary alcohols.Control experiments,along with DFT calculations and crystallographic studies,revealed that the ligand effect is critical to their excellent catalytic performance,shedding light on more challenging Guerbet reactions with simple alcohols. | Zeye Lu Qingshu Zheng Guangkuo Zeng Yunyan Kuang James H.Clark Tao Tu | 2021 | Science China Chemistry2021，64，8： | 2 |
| 2 | Population migration across the Qinghai-Tibet Plateau:Spatiotemporal patterns and driving factors显示文摘Developing a comprehensive understanding of inter-city interactions is crucial for regional planning.We therefore examined spatiotemporal patterns of population migration across the Qinghai-Tibet Plateau(QTP)using migration big data from Tencent for the period between 2015 and 2019.We initially used decomposition and breakpoint detection methods to examine time-series migration data and to identify the two seasons with the strongest and weakest population migration levels,between June 18th and August 18th and between October 8th and February 15th,respectively.Population migration within the former period was 2.03 times that seen in the latter.We then used a variety of network analysis methods to examine population flow directions as well as the importance of each individual city in migration.The two capital cities on the QTP,Lhasa and Xining,form centers for population migration and are also transfer hubs through which migrants from other cities off the plateau enter and leave this region.Data show that these two cities contribute more than 35%of total population migration.The majority of migrants tend to move within the province,particularly during the weakest migration season.We also utilized interactive relationship force and radiation models to examine the interaction strength and the radiating energy of each individual city.Results show that Lhasa and Xining exhibit the strongest interactions with other cities and have the largest radiating energies.Indeed,the radiating energy of the QTP cities correlates with their gross domestic product(GDP)(Pearson correlation coefficient:0.754 in the weakest migration season,WMS versus 0.737 in the strongest migration season,SMS),while changes in radiating energy correlate with the tourism-related revenue(Pearson correlation coefficient:0.685).These outcomes suggest that level of economic development and level of tourism are the two most important factors driving the QTP population migration.The results of this analysis provide critical clarification guidance regarding huge QTP development differences. | WANG Nan WANG Huimeng DU Yunyan YI Jiawei LIU Zhang TU Wenna | 2021 | Journal of Geographical Sciences2021，31，2： | 1 |
| 3 | Prediction of Forest Stock Volume Based on Neural Network Model显示文摘BP and RBF neural network to predict forest stock volume were studied,but the study in evaluating both networks’ application effects was not conducted.In order to find a higher forecast precision,more strong applicative method,the comprehensive analysis and evaluation on the two methods were carried out in the practical application. By the correlation analysis,crown density,shady-slope and sunny-slope,TM1,TM2,TM3,TM5, TM7,NDVI,TM,(4-3),TM4/3 were selected as input variables,and the forest volume of Miyun County as output variables,RBF and BP neural network models for forecasting the forest volume were established.And the neural network training step length,training time,prediction accuracy and the applicability model of the two methods were comprehensively analyzed.The results show that the RBF neural network model is superior to the BP neural network model. | Tu Yunyan Peng Daoli | 2012 | Chinese Forestry Science and Technology2012，11，3： | 0 |
| 4 | Human’s digital footprints on the Qinghai-Tibet Plateau:Variations during festivals and impacts on nature reserves显示文摘Mobile internet and wireless communication technologies have produced unprecedented location-aware data.Such big geospatial data can be used as a proxy measure of the‘digital footprints’left by us on the planet and provide a valuable opportunity to understand the dynamic and short-term human disturbance on the nature at fine scales.This study investigated the spatiotemporal variations of human’s digital footprints on the Qinghai-Tibet Plateau using smartphone-users-generated Tencent’s location request data.The results showed that human’s digital footprints cover less than 5%of Qinghai and Tibet,exhibiting either a U-shaped or an N-shaped temporal change pattern during the major festivals.Spatial changes of the digital footprints manifested a transition process from dispersion to concentration in Xining and Lhasa.Human disturbance assessment of seven large nature reserves on the plateau showed that the Qinghai Lake is the most disturbed one as shown by 14.6%of its area is stained with human digital footprints and the areal average of footprint intensity is 1.59,and the disturbance was significantly escalated during the National Day holiday.By contrast,the Qangtang and Hoh Xil are the least affected nature reserves with the two indices less than 1%and 0.1,respectively. | DU Yunyan TU Wenna LIANG Fuyuan YI Jiawei | 2021 | Journal of Geographical Sciences2021，31，2： | 0 |
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