The reaction of phenacyl benzoate derivatives with acetamide at about 140°in the presence of BF3 catalyst gave 2-aryl-4-phenyloxazoles. This method can be applied to the preparation of 2-alkyl-4-phenyloxazoles as...The reaction of phenacyl benzoate derivatives with acetamide at about 140°in the presence of BF3 catalyst gave 2-aryl-4-phenyloxazoles. This method can be applied to the preparation of 2-alkyl-4-phenyloxazoles as well.展开更多
双行根数(Two Line Element,TLE)作为一类广泛使用的空间物体编目数据,其预报精度和误差特性是TLE编目在空间碎片研究中所要关注的问题之一.TLE编目需要配合SGP4/SDP4(Simplified General Perturbations 4/Simplified Deep Space 4)模...双行根数(Two Line Element,TLE)作为一类广泛使用的空间物体编目数据,其预报精度和误差特性是TLE编目在空间碎片研究中所要关注的问题之一.TLE编目需要配合SGP4/SDP4(Simplified General Perturbations 4/Simplified Deep Space 4)模型进行轨道预报,对深空物体来说,主要考虑带谐项J_(2)、J_(3)、J_(4)摄动、第三体日月摄动和特殊轨道共振问题修正等.其中,SGP4/SDP4模型第三体摄动计算时,对日月轨道近似采用了长期进动根数和简单平运动的方式,在外推10 d时存在约2◦–3◦的日月位置偏差.日月轨道计算可选用更加精确的方法来改进初始位置估计,并根据日月运动规律的不同,对太阳轨道采用平运动近似,对月球轨道采用计算真近点角近似,在外推10 d时,二者位置偏差可分别减小到约1′–2′和15′–20′范围.采用激光测距卫星Etalon 1、伽利略卫星导航系统Galileo 23卫星作为对比算例,结果分析表明二者原始的TLE编目轨道进行预报时存在明显的位置误差异常变化趋势;采用日月轨道计算改进后,重新定轨得到的“改进”编目具有更加精确的轨道预报结果.展开更多
Two global experiments were carried out to investigate the effects of dynamic vegetation processes on numerical climate simulations from 1948 to 2008.The NCEP Global Forecast System(GFS)was coupled with a biophysical ...Two global experiments were carried out to investigate the effects of dynamic vegetation processes on numerical climate simulations from 1948 to 2008.The NCEP Global Forecast System(GFS)was coupled with a biophysical model,the Simplified Simple Biosphere Model(SSi B)version 2(GFS/SSi B2),and it was also coupled with a biophysical and dynamic vegetation model,SSi B version 4/Top-down Representation of Interactive Foliage and Flora Including Dynamics(TRIFFID)(GFS/SSi B4/TRIFFID).The effects of dynamic vegetation processes on the simulation of precipitation,near-surface temperature,and the surface energy budget were identified on monthly and annual scales by assessing the GFS/SSi B4/TRIFFID and GFS/SSi B2 results against the satellite-derived leaf area index(LAI)and albedo and the observed land surface temperature and precipitation.The results show that compared with the GFS/SSiB2 model,the temporal correlation coefficients between the globally averaged monthly simulated LAI and the Global Inventory Monitoring and Modeling System(GIMMS)/Global Land Surface Satellite(GLASS)LAI in the GFS/SSi B4/TRIFFID simulation increased from 0.31/0.29(SSiB2)to 0.47/0.46(SSiB4).The correlation coefficients between the simulated and observed monthly mean near-surface air temperature increased from 0.50(Africa),0.35(Southeast Asia),and 0.39(South America)to 0.56,0.41,and 0.44,respectively.The correlation coefficients between the simulated and observed monthly mean precipitation increased from 0.19(Africa),0.22(South Asia),and 0.22(East Asia)to 0.25,0.27,and 0.28,respectively.The greatest improvement occurred over arid and semiarid areas.The spatiotemporal variability and changes in vegetation and ground surface albedo modeled by the GFS with a dynamic vegetation model were more consistent with the observations.The dynamic vegetation processes contributed to the surface energy and water balance and in turn,improved the annual variations in the simulated regional temperature and precipitation.The dynamic vegetation processes had the greatest influence on the spatiotemporal changes in the latent heat flux.This study shows that dynamic vegetation processes in earth system models significantly improve simulations of the climate mean status.展开更多
The representations of the Dynkin quivers and the corresponding Euclidean quivers are treated in many books. These notes provide three building blocks for dealing with representations of Dynkin （and Euclidean） quive...The representations of the Dynkin quivers and the corresponding Euclidean quivers are treated in many books. These notes provide three building blocks for dealing with representations of Dynkin （and Euclidean） quivers. They should be helpful as part of a direct approach to study representations of quivers, and they shed some new light on properties of Dynkin and Euclidean quivers.展开更多
文摘The reaction of phenacyl benzoate derivatives with acetamide at about 140°in the presence of BF3 catalyst gave 2-aryl-4-phenyloxazoles. This method can be applied to the preparation of 2-alkyl-4-phenyloxazoles as well.
文摘双行根数(Two Line Element,TLE)作为一类广泛使用的空间物体编目数据,其预报精度和误差特性是TLE编目在空间碎片研究中所要关注的问题之一.TLE编目需要配合SGP4/SDP4(Simplified General Perturbations 4/Simplified Deep Space 4)模型进行轨道预报,对深空物体来说,主要考虑带谐项J_(2)、J_(3)、J_(4)摄动、第三体日月摄动和特殊轨道共振问题修正等.其中,SGP4/SDP4模型第三体摄动计算时,对日月轨道近似采用了长期进动根数和简单平运动的方式,在外推10 d时存在约2◦–3◦的日月位置偏差.日月轨道计算可选用更加精确的方法来改进初始位置估计,并根据日月运动规律的不同,对太阳轨道采用平运动近似,对月球轨道采用计算真近点角近似,在外推10 d时,二者位置偏差可分别减小到约1′–2′和15′–20′范围.采用激光测距卫星Etalon 1、伽利略卫星导航系统Galileo 23卫星作为对比算例,结果分析表明二者原始的TLE编目轨道进行预报时存在明显的位置误差异常变化趋势;采用日月轨道计算改进后,重新定轨得到的“改进”编目具有更加精确的轨道预报结果.
基金Supported by the National Key Research and Development Program of China(2018YFC1507700)National Natural Science Foundation of China(41905083)the United States National Science Foundation(AGS-1419526)。
文摘Two global experiments were carried out to investigate the effects of dynamic vegetation processes on numerical climate simulations from 1948 to 2008.The NCEP Global Forecast System(GFS)was coupled with a biophysical model,the Simplified Simple Biosphere Model(SSi B)version 2(GFS/SSi B2),and it was also coupled with a biophysical and dynamic vegetation model,SSi B version 4/Top-down Representation of Interactive Foliage and Flora Including Dynamics(TRIFFID)(GFS/SSi B4/TRIFFID).The effects of dynamic vegetation processes on the simulation of precipitation,near-surface temperature,and the surface energy budget were identified on monthly and annual scales by assessing the GFS/SSi B4/TRIFFID and GFS/SSi B2 results against the satellite-derived leaf area index(LAI)and albedo and the observed land surface temperature and precipitation.The results show that compared with the GFS/SSiB2 model,the temporal correlation coefficients between the globally averaged monthly simulated LAI and the Global Inventory Monitoring and Modeling System(GIMMS)/Global Land Surface Satellite(GLASS)LAI in the GFS/SSi B4/TRIFFID simulation increased from 0.31/0.29(SSiB2)to 0.47/0.46(SSiB4).The correlation coefficients between the simulated and observed monthly mean near-surface air temperature increased from 0.50(Africa),0.35(Southeast Asia),and 0.39(South America)to 0.56,0.41,and 0.44,respectively.The correlation coefficients between the simulated and observed monthly mean precipitation increased from 0.19(Africa),0.22(South Asia),and 0.22(East Asia)to 0.25,0.27,and 0.28,respectively.The greatest improvement occurred over arid and semiarid areas.The spatiotemporal variability and changes in vegetation and ground surface albedo modeled by the GFS with a dynamic vegetation model were more consistent with the observations.The dynamic vegetation processes contributed to the surface energy and water balance and in turn,improved the annual variations in the simulated regional temperature and precipitation.The dynamic vegetation processes had the greatest influence on the spatiotemporal changes in the latent heat flux.This study shows that dynamic vegetation processes in earth system models significantly improve simulations of the climate mean status.
文摘The representations of the Dynkin quivers and the corresponding Euclidean quivers are treated in many books. These notes provide three building blocks for dealing with representations of Dynkin （and Euclidean） quivers. They should be helpful as part of a direct approach to study representations of quivers, and they shed some new light on properties of Dynkin and Euclidean quivers.
