使用雷达资料,运用相关法估测CAPPI(constant altitude plan position indicating,等高平面位置显示)上的TREC(tracking radar echoes by correlation)风,根据雷达在两个观测时间的数据,估算CAPPI上的水平流场,从而外推整个回波场的运...使用雷达资料,运用相关法估测CAPPI(constant altitude plan position indicating,等高平面位置显示)上的TREC(tracking radar echoes by correlation)风,根据雷达在两个观测时间的数据,估算CAPPI上的水平流场,从而外推整个回波场的运动走向。经输入台风、暴雨、晴空边界层的回波个例试验,结果表明有助于短时天气预报。在TREC应用于晴空回波时,根据当地实际情况,通过适当改动相关系数的阈值可以消除杂波产生的对TREC矢量的干扰。展开更多
This study examines the relationship between education and intergenerational income mobility in urban China based on the data of Chinese Urban Household Education and Employment Survey(CHUHEES)—2004”by Institute of ...This study examines the relationship between education and intergenerational income mobility in urban China based on the data of Chinese Urban Household Education and Employment Survey(CHUHEES)—2004”by Institute of Economics of Education of Peking University.It analyzes the characteristics of the intergenerational income mobility of Chinese urban household through such indices as intergenerational income inheritance and mobility,and intergenerational income elasticity,exploring the role of education to promote intergenerational income mobility through pathanalysis and binary logistic regression.It also analyzes the changing tendency along with the progress of the market reform in China and tries to provide theoretical explanations for the empirical results.According to the findings,there is rather obvious intergenerational income transmission in urban China,and most children still resort in the same income group with their fathers.As a kind of important mechanism of intergenerational mobility,education is instrumental to promote children of disadvantage group to upgrade of their economic status,showing its strong functions to promote intergenerational upward mobility.With the improvement of the level of marketization together with appropriate social policy,the role of education to promote the intergenerational income mobility and social equity is getting stronger.展开更多
Cloud cavitating flow is highly turbulent and dominated by coherent large-scale anisotropic vortical structures. For the numer- ical investigation of such a class of flow, large eddy simulation （LES） is a reliable m...Cloud cavitating flow is highly turbulent and dominated by coherent large-scale anisotropic vortical structures. For the numer- ical investigation of such a class of flow, large eddy simulation （LES） is a reliable method but it is computationally extremely costly in engineering applications. An efficient approach to reduce the computational cost is to combine Reynolds-averaged Navier-Stokes （RANS） equations with LES used only in the parts of interest, such as massively separated flow regions. A new hybrid RANS/LES model, the modified filter-based method （FBM）, is proposed in the present study which can perform RANS or LES depending on the numerical resolution. Compared to the original FBM, the new method has three modifications： the state-of-the-art shear stress transport （SST） model replaces the k-c model as a baseline RANS model. A shielding function is introduced to obviate the switch from RANS to LES occurring inside the boundary layer. An appropriate threshold controlling the switch from RANS to LES is added to achieve an optimal predictive accuracy. The new model is assessed for its predictive capability of highly unsteady cavitating flows in a typical case of cloud cavitation around a NACA66 hydrofoil. The new mod- el results are compared with data obtained from the Smagorinsky LES and SST model based on the same homogeneous Zwart cavitation model. It is found that the modified FBM method has significant advantages over SST model in all aspects of pre- dicted instantaneous and mean flow field, and its predictive accuracy is comparable to the Smagorinsky LES model even using a much coarser grid in the simulations.展开更多
文摘使用雷达资料,运用相关法估测CAPPI(constant altitude plan position indicating,等高平面位置显示)上的TREC(tracking radar echoes by correlation)风,根据雷达在两个观测时间的数据,估算CAPPI上的水平流场,从而外推整个回波场的运动走向。经输入台风、暴雨、晴空边界层的回波个例试验,结果表明有助于短时天气预报。在TREC应用于晴空回波时,根据当地实际情况,通过适当改动相关系数的阈值可以消除杂波产生的对TREC矢量的干扰。
文摘This study examines the relationship between education and intergenerational income mobility in urban China based on the data of Chinese Urban Household Education and Employment Survey(CHUHEES)—2004”by Institute of Economics of Education of Peking University.It analyzes the characteristics of the intergenerational income mobility of Chinese urban household through such indices as intergenerational income inheritance and mobility,and intergenerational income elasticity,exploring the role of education to promote intergenerational income mobility through pathanalysis and binary logistic regression.It also analyzes the changing tendency along with the progress of the market reform in China and tries to provide theoretical explanations for the empirical results.According to the findings,there is rather obvious intergenerational income transmission in urban China,and most children still resort in the same income group with their fathers.As a kind of important mechanism of intergenerational mobility,education is instrumental to promote children of disadvantage group to upgrade of their economic status,showing its strong functions to promote intergenerational upward mobility.With the improvement of the level of marketization together with appropriate social policy,the role of education to promote the intergenerational income mobility and social equity is getting stronger.
基金supported by the National Natural Science Foundation of China(Grant No.51579118)
文摘Cloud cavitating flow is highly turbulent and dominated by coherent large-scale anisotropic vortical structures. For the numer- ical investigation of such a class of flow, large eddy simulation （LES） is a reliable method but it is computationally extremely costly in engineering applications. An efficient approach to reduce the computational cost is to combine Reynolds-averaged Navier-Stokes （RANS） equations with LES used only in the parts of interest, such as massively separated flow regions. A new hybrid RANS/LES model, the modified filter-based method （FBM）, is proposed in the present study which can perform RANS or LES depending on the numerical resolution. Compared to the original FBM, the new method has three modifications： the state-of-the-art shear stress transport （SST） model replaces the k-c model as a baseline RANS model. A shielding function is introduced to obviate the switch from RANS to LES occurring inside the boundary layer. An appropriate threshold controlling the switch from RANS to LES is added to achieve an optimal predictive accuracy. The new model is assessed for its predictive capability of highly unsteady cavitating flows in a typical case of cloud cavitation around a NACA66 hydrofoil. The new mod- el results are compared with data obtained from the Smagorinsky LES and SST model based on the same homogeneous Zwart cavitation model. It is found that the modified FBM method has significant advantages over SST model in all aspects of pre- dicted instantaneous and mean flow field, and its predictive accuracy is comparable to the Smagorinsky LES model even using a much coarser grid in the simulations.
