A total of more than 50000 landslides has occurred in Sichuan province since the"5·12"Wenchuan earthquake,resulting in serious damage to the surface vegetation in southwestern China.In this study,we sel...A total of more than 50000 landslides has occurred in Sichuan province since the"5·12"Wenchuan earthquake,resulting in serious damage to the surface vegetation in southwestern China.In this study,we select Yingxiu,the epicenter of Wenchuan earthquake,as the experimental area.The vegetation coverage information of the experimental area is extracted from the remote sensing images collected in the year of 2005,2011 and 2013,respectively.The surface vegetation coverage in different periods is analyzed,and the vegetation recovery rate of the whole area is calculated.The experimental results show that in the first three years after the earthquake,the speed of vegetation restoration is slow,and the vegetation coverage rate is less than 20%better than 0.241,while in 2013,the vegetation coverage increases significantly.展开更多
The properties of a series of imide oligomers were characterized according to their molecular weights, solubility, and thermal and rheological properties. This series of imide oligomers was synthesized via a two-step ...The properties of a series of imide oligomers were characterized according to their molecular weights, solubility, and thermal and rheological properties. This series of imide oligomers was synthesized via a two-step method using 2,2′,3,3′-biphenyltetracarboxylic dianhydride(3,3′-BPDA) and aromatic diamines as the monomers, and 4-phenylethynyl phtlialic anhydride(PEPA) as the end-capping agent. The imide oligomers based on 3,3′-BPDA showed excellent solubility in low boiling point solvents and low melt viscosity, which were attributed to their unique bent architectures. High-performance thermosetting polyimides were produced from these oligomers via thermal crosslinking of the phenylethynyl groups. The mechanical and thermal properties of the thermosets were studied using tensile testing, dynamic mechanical thermal analysis(DMTA), and thermogravimetric analysis(TGA). The 3,3′EPDA-based thermosets exhibited excellent thermal properties, with glass transition temperatures of up to 455℃, and 5% mass loss temperatures of up to 569℃ in air. The thermosets based on 3,3-BPDA showed superior thermal properties compared to those derived from TriA-X series oligomers.展开更多
基金supported by the NationalKey R&D Program of China(2019YFC1510700)the National Natural Science Foundation of China(41602355,41701499)+2 种基金the Sichuan Science and Technology Program(2018GZ0265)Chengdu University of Technology Backbone Teacher Program(2019SJ01-04230)Special earthquake science and technology project of Sichuan Seismological Bureau(LY1814)。
文摘A total of more than 50000 landslides has occurred in Sichuan province since the"5·12"Wenchuan earthquake,resulting in serious damage to the surface vegetation in southwestern China.In this study,we select Yingxiu,the epicenter of Wenchuan earthquake,as the experimental area.The vegetation coverage information of the experimental area is extracted from the remote sensing images collected in the year of 2005,2011 and 2013,respectively.The surface vegetation coverage in different periods is analyzed,and the vegetation recovery rate of the whole area is calculated.The experimental results show that in the first three years after the earthquake,the speed of vegetation restoration is slow,and the vegetation coverage rate is less than 20%better than 0.241,while in 2013,the vegetation coverage increases significantly.
基金the Technology Innovation Fund of Chinese Academy of Sciences(NO.CXJJ-17-M159)the National Natural Science Foundation of China(No.51473157).
文摘The properties of a series of imide oligomers were characterized according to their molecular weights, solubility, and thermal and rheological properties. This series of imide oligomers was synthesized via a two-step method using 2,2′,3,3′-biphenyltetracarboxylic dianhydride(3,3′-BPDA) and aromatic diamines as the monomers, and 4-phenylethynyl phtlialic anhydride(PEPA) as the end-capping agent. The imide oligomers based on 3,3′-BPDA showed excellent solubility in low boiling point solvents and low melt viscosity, which were attributed to their unique bent architectures. High-performance thermosetting polyimides were produced from these oligomers via thermal crosslinking of the phenylethynyl groups. The mechanical and thermal properties of the thermosets were studied using tensile testing, dynamic mechanical thermal analysis(DMTA), and thermogravimetric analysis(TGA). The 3,3′EPDA-based thermosets exhibited excellent thermal properties, with glass transition temperatures of up to 455℃, and 5% mass loss temperatures of up to 569℃ in air. The thermosets based on 3,3-BPDA showed superior thermal properties compared to those derived from TriA-X series oligomers.
