With the objective to develop catalysts having application potential for oxidative coupling of methane (OCM) at relatively lower temperature. A series of Ln2Zr2O7 compounds with varied rare earth A sites have been pre...With the objective to develop catalysts having application potential for oxidative coupling of methane (OCM) at relatively lower temperature. A series of Ln2Zr2O7 compounds with varied rare earth A sites have been prepared by a co-precipitation method. XRD and Raman have proved that pure Ln2Zr2O7 compounds have been successfully prepared for all the catalysts. By decreasing the rA/rB ratio, their crystalline structure transform from an ordered pyrochlore (La2Zr2O7) to a less ordered pyrochlore (Pr2Zr2O7 and Sm2Zr2O7) and eventually to a defective cubic fluorite phase (Y2Zr2O7). H2-TPR, O2-TPD and XPS have testified that the amount of surface active O2-species follows the order of La2Zr2O7>Pr2Zr2O7>Sm2Zr2O7 > Y2Zr2O7, which is well consistent with the reaction performance, indicating that the abundance of surface O2- sites is a critical factor influencing the reaction performance. CO2-TPD has demonstrated that a better catalyst generally possesses a larger amount of surface moderate alkaline sites, which is another factor to affect the reaction performance. It is concluded that the concerted interaction between the two types of surface active sites controls the reaction performance of the Ln2Zr2O7 catalysts. In comparison with the state-of-the art Mn/Na2WO4/SiO2, La2Zr2O7, the best catalyst, exhibits much improved reaction performance below 750 ℃.展开更多
The earth’s surface irregularities can substantially affect seismic waves and induce amplifi cations of ground motions. This study investigates whether and how the source characteristics affect the site amplifi catio...The earth’s surface irregularities can substantially affect seismic waves and induce amplifi cations of ground motions. This study investigates whether and how the source characteristics affect the site amplifi cation effects. An analytical model of a line source of cylindrical waves impinging on an alluvial valley is proposed to link the source and site. The analytical solution to this problem proves one aspect of the strong effect of source on site amplifi cation, i.e., the wave curvature effect. It is found that the site amplifi cation depends on the source location, especially under conditions of a small source-to-site distance. Whether the displacement is amplifi ed or reduced and the size of the amplifi cation or reduction may be determined by the location of the source. It is suggested that traditional studies of site responses, which usually ignore the source effect, should be further improved by combining the source with site effects.展开更多
The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins ca...The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins can help to reduce the earthquake hazard. Site effects of Luoyang basin are estimated by the horizontal-to-vertical spectral ratio(HVSR) method using ambient noise records from a short-period dense array. The sites in Luoyang basin are sorted into three types according to the pattern of the HVSR curves. There are cases with a single clear peak, two clear peaks, and an unclear low frequency peak or multiple peaks, which correspond to there being one large impedance contrast interface, two large interfaces, and a moderate one beneath the sites, respectively. The site effects characterized by fundamental frequency from HVSR curves are affected by underlying sedimentary layers and depth of sedimentary basement. According to our results, the existence of thick sediment layer obviously lowers the fundamental frequency to the period range from 2 to 4 s in the downtown area of Luoyang city. The ground motion will amplify when through the sites and the buildings with height of 20–50 floors can resonate at the similar frequency domain. Site effects estimation using HVSR method from a short-period dense array is an effective technique in areas of moderate seismic risk where strong motion recordings are lacking, such as the Luoyang basin.展开更多
基于汶川地震断层距150km内112条水平分量加速度记录,分析断层距、场地类型、地震动持时、上盘和下盘效应、方向性效应对SDOF(single degree of freedom)体系弹性地震输入能的影响。结果表明:近断层断层距30km范围应考虑加速度峰值增大...基于汶川地震断层距150km内112条水平分量加速度记录,分析断层距、场地类型、地震动持时、上盘和下盘效应、方向性效应对SDOF(single degree of freedom)体系弹性地震输入能的影响。结果表明:近断层断层距30km范围应考虑加速度峰值增大对输入能显著提高的影响;场地越软输入能越大,输入能谱的特征周期并不随着场地越软而向右移动;地震动持时对输入能谱峰值相应周期的结构影响显著,持时越长,输入能谱峰值越大。近断层下盘效应和方向性效应对地震输入能有显著影响,断层距大于30km范围内,下盘效应使中、长周期结构的地震输入能显著提高。展开更多
基金the Natural Science Foundation of China (Nos. 21567016, 21566022, 21666020)the Natural Science Foundation of Jiangxi Province (Nos. 20181ACB20005, 20171BAB213013 and 20181BAB203017)+4 种基金the Key Laboratory Foundation of Jiangxi Province for Environment and Energy Catalysis(No. 20181BCD40004) the Education Department of Jiangxi Province (Nos. GJJ150016, GJJ150085 and KJLD14005)the China Postdoctoral Science Foundation(No. 2018M631294)Innovation Fund Designated for Undergraduate Students of Nanchang University of China (No. 201802369)the Graduate Student Creativity Funding of Nanchang University(No. 201802062)
文摘With the objective to develop catalysts having application potential for oxidative coupling of methane (OCM) at relatively lower temperature. A series of Ln2Zr2O7 compounds with varied rare earth A sites have been prepared by a co-precipitation method. XRD and Raman have proved that pure Ln2Zr2O7 compounds have been successfully prepared for all the catalysts. By decreasing the rA/rB ratio, their crystalline structure transform from an ordered pyrochlore (La2Zr2O7) to a less ordered pyrochlore (Pr2Zr2O7 and Sm2Zr2O7) and eventually to a defective cubic fluorite phase (Y2Zr2O7). H2-TPR, O2-TPD and XPS have testified that the amount of surface active O2-species follows the order of La2Zr2O7>Pr2Zr2O7>Sm2Zr2O7 > Y2Zr2O7, which is well consistent with the reaction performance, indicating that the abundance of surface O2- sites is a critical factor influencing the reaction performance. CO2-TPD has demonstrated that a better catalyst generally possesses a larger amount of surface moderate alkaline sites, which is another factor to affect the reaction performance. It is concluded that the concerted interaction between the two types of surface active sites controls the reaction performance of the Ln2Zr2O7 catalysts. In comparison with the state-of-the art Mn/Na2WO4/SiO2, La2Zr2O7, the best catalyst, exhibits much improved reaction performance below 750 ℃.
基金National Natural Science Foundation of China under Grant Nos.51479050 and 51338009National Key Basic Research Program of China under Grant No.2015CB057901+2 种基金the Public Service Sector R&D Project of Ministry of Water Resource of China under Grant No.201501035-03the Fundamental Research Funds for the Central Universities under Grant Nos.2013B05814,2014B06814 and 2015B01214the 111 Project under Grant No.B13024
文摘The earth’s surface irregularities can substantially affect seismic waves and induce amplifi cations of ground motions. This study investigates whether and how the source characteristics affect the site amplifi cation effects. An analytical model of a line source of cylindrical waves impinging on an alluvial valley is proposed to link the source and site. The analytical solution to this problem proves one aspect of the strong effect of source on site amplifi cation, i.e., the wave curvature effect. It is found that the site amplifi cation depends on the source location, especially under conditions of a small source-to-site distance. Whether the displacement is amplifi ed or reduced and the size of the amplifi cation or reduction may be determined by the location of the source. It is suggested that traditional studies of site responses, which usually ignore the source effect, should be further improved by combining the source with site effects.
基金funded by the National Key R&D Program of China(No.2017YFC1500202)supported by the National Natural Science Foundation of China(No.41604048)China Earthquake Science Experiment(No.2016CESE0103)
文摘The influence of local site effects on seismic ground motions is an important issue in seismic hazard assessment and earthquake resistant design. Determining site effects in densely populated cities built on basins can help to reduce the earthquake hazard. Site effects of Luoyang basin are estimated by the horizontal-to-vertical spectral ratio(HVSR) method using ambient noise records from a short-period dense array. The sites in Luoyang basin are sorted into three types according to the pattern of the HVSR curves. There are cases with a single clear peak, two clear peaks, and an unclear low frequency peak or multiple peaks, which correspond to there being one large impedance contrast interface, two large interfaces, and a moderate one beneath the sites, respectively. The site effects characterized by fundamental frequency from HVSR curves are affected by underlying sedimentary layers and depth of sedimentary basement. According to our results, the existence of thick sediment layer obviously lowers the fundamental frequency to the period range from 2 to 4 s in the downtown area of Luoyang city. The ground motion will amplify when through the sites and the buildings with height of 20–50 floors can resonate at the similar frequency domain. Site effects estimation using HVSR method from a short-period dense array is an effective technique in areas of moderate seismic risk where strong motion recordings are lacking, such as the Luoyang basin.
文摘基于汶川地震断层距150km内112条水平分量加速度记录,分析断层距、场地类型、地震动持时、上盘和下盘效应、方向性效应对SDOF(single degree of freedom)体系弹性地震输入能的影响。结果表明:近断层断层距30km范围应考虑加速度峰值增大对输入能显著提高的影响;场地越软输入能越大,输入能谱的特征周期并不随着场地越软而向右移动;地震动持时对输入能谱峰值相应周期的结构影响显著,持时越长,输入能谱峰值越大。近断层下盘效应和方向性效应对地震输入能有显著影响,断层距大于30km范围内,下盘效应使中、长周期结构的地震输入能显著提高。
