The maximum rate of carboxylation （Vcax） is a key photosynthetic parameter for gross primary produc- tion （GPP） estimation in terrestrial biosphere models. A set of observation-based Vcax values, which take the ni...The maximum rate of carboxylation （Vcax） is a key photosynthetic parameter for gross primary produc- tion （GPP） estimation in terrestrial biosphere models. A set of observation-based Vcax values, which take the ni- trogen limitation on photosynthetic rates into consideration, are used in version 4.5 of the Community Land Model （CLM4.5）. However, CLM4.5 with carbon-nitrogen （CN） biogeochemistry （CLM4.5-CN） still uses an inde- pendent decay coefficient for nitrogen after the photosyn- thesis calculation. This means that the nitrogen limitation on the carbon cycle is accounted for twice when CN bio- geochemistry is active. Therefore, to avoid this double nitrogen down-regulation in CLM4.5-CN, the original Vcmax scheme is revised with a new one that only accounts for the transition between Vcmax and its potential value （without nitrogen limitation）. Compared to flux tower- based observations, the new Vcmax scheme reduces the root-mean-square error （RMSE） in GPP for China's Mainland by 13.7 g C m-2 yr-1, with a larger decrease over humid areas （39.2 g C m 2 yr-1）. Moreover, net primary production and leaf area index are also improved, with reductions in RMSE by 0.8% and 11.5%, respectively.展开更多
改革开放政策实施以来,流动人口成为我国经济高速增长和城镇化进程的一个重要推动力量,同时,值得关注的是各地区之间呈现出来的差异化发展水平和创业活跃程度。流动人口聚集是如何影响中国城市创业活跃度的?为了回答这一问题,本文将异...改革开放政策实施以来,流动人口成为我国经济高速增长和城镇化进程的一个重要推动力量,同时,值得关注的是各地区之间呈现出来的差异化发展水平和创业活跃程度。流动人口聚集是如何影响中国城市创业活跃度的?为了回答这一问题,本文将异质性社会个体与企业家创业的职业选择假设引入到垂直联系的自由企业家模型(footloose entrepreneur model with vertical linkage,FEVL)中,通过理论模型揭示了流动人口对城市创业活跃度的作用机理。在此基础上,利用2010—2014年全国56个城市的面板数据对这一问题进行了实证分析。研究发现,较大的市场规模、较强的知识溢出效应与较低的中间投入品价格是城市吸引流动人口特别是创业型个体的重要动因,并进而提升了城市的创业活跃度。而基于固定效应模型和D&K方法的实证分析结果也表明,流动人口比例会提高城市创业活跃度,城市流动人口规模越大,创业活跃度越高。本研究从流动人口的视角揭示了中国地区之间创业活跃度的差异之谜,同时也拓展了创业研究的经济地理和制度的分析。展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.91125016 and 41305066)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA05110102)
文摘The maximum rate of carboxylation （Vcax） is a key photosynthetic parameter for gross primary produc- tion （GPP） estimation in terrestrial biosphere models. A set of observation-based Vcax values, which take the ni- trogen limitation on photosynthetic rates into consideration, are used in version 4.5 of the Community Land Model （CLM4.5）. However, CLM4.5 with carbon-nitrogen （CN） biogeochemistry （CLM4.5-CN） still uses an inde- pendent decay coefficient for nitrogen after the photosyn- thesis calculation. This means that the nitrogen limitation on the carbon cycle is accounted for twice when CN bio- geochemistry is active. Therefore, to avoid this double nitrogen down-regulation in CLM4.5-CN, the original Vcmax scheme is revised with a new one that only accounts for the transition between Vcmax and its potential value （without nitrogen limitation）. Compared to flux tower- based observations, the new Vcmax scheme reduces the root-mean-square error （RMSE） in GPP for China's Mainland by 13.7 g C m-2 yr-1, with a larger decrease over humid areas （39.2 g C m 2 yr-1）. Moreover, net primary production and leaf area index are also improved, with reductions in RMSE by 0.8% and 11.5%, respectively.
文摘改革开放政策实施以来,流动人口成为我国经济高速增长和城镇化进程的一个重要推动力量,同时,值得关注的是各地区之间呈现出来的差异化发展水平和创业活跃程度。流动人口聚集是如何影响中国城市创业活跃度的?为了回答这一问题,本文将异质性社会个体与企业家创业的职业选择假设引入到垂直联系的自由企业家模型(footloose entrepreneur model with vertical linkage,FEVL)中,通过理论模型揭示了流动人口对城市创业活跃度的作用机理。在此基础上,利用2010—2014年全国56个城市的面板数据对这一问题进行了实证分析。研究发现,较大的市场规模、较强的知识溢出效应与较低的中间投入品价格是城市吸引流动人口特别是创业型个体的重要动因,并进而提升了城市的创业活跃度。而基于固定效应模型和D&K方法的实证分析结果也表明,流动人口比例会提高城市创业活跃度,城市流动人口规模越大,创业活跃度越高。本研究从流动人口的视角揭示了中国地区之间创业活跃度的差异之谜,同时也拓展了创业研究的经济地理和制度的分析。
