In this paper, a method of stabilizing electric power by a system which is a combination of wind power generation and pumped storage power generation is proposed. The system operates based on the output predicted valu...In this paper, a method of stabilizing electric power by a system which is a combination of wind power generation and pumped storage power generation is proposed. The system operates based on the output predicted value of the windfarm. When the measured windfarm output is larger than the predicted value, the system is pumping up water with surplus power. When the windfarm output is smaller than the predicted value, the system is filling up lack power by hydro generator. Also, since hydro generator works with a start-up delay time, output shortage occurs at this time. To improve output shortage at the time, we estimate the time below the predicted value by a statistical model. As the result, the system succeeded in stabilizing the power and improving the start-up delay time of the hydro generator.展开更多
We conducted a systematic census of leaf N for 102 plant species at 112 research sites along the North-South Transect of Eastern China （NSTEC） following the same protocol, to explore how plant functional types （PFT...We conducted a systematic census of leaf N for 102 plant species at 112 research sites along the North-South Transect of Eastern China （NSTEC） following the same protocol, to explore how plant functional types （PFTs） and environmental factors affect the spatial pattern of leaf N. The results showed that mean leaf N was 17.7 mg g^-1 for all plant species. The highest and lowest leaf N were found in deciduous-broadleaf and evergreen-conifer species, respectively, and the ranking of leaf N from high to low was： deciduous 〉 evergreen species, broadleaf 〉 coniferous species, shrubs ≈ trees 〉 grasses. For all data pooled, leaf N showed a convex quadratic response to mean annual temperature （MAT）, and a negative linear relationship with mean annual precipitation （MAP）, but a positive linear relationship with soil nitrogen concentration （Nsoil）. These patterns were similar when PFTs were examined individually. Importantly, PFTs, climate and Nsoil, jointly explained 46.1% of the spatial variation in leaf N, of which the independent explanatory powers of PFTs, climate and Nsoil, were 15.6%, 2.3% and 4.7%, respectively. Our findings suggest that leaf N is regulated by climate and Nsoil, mainly via plant species composition. The wide scale empirical relationships developed here are useful for understanding and modeling of the effects of PFTs and environmental factors on leaf N.展开更多
The quantification of the sheltering and exposure effects of non-uniform sediments has been widely achieved through hiding function models. Big challenge exists so far in the model parameter that is highly variable an...The quantification of the sheltering and exposure effects of non-uniform sediments has been widely achieved through hiding function models. Big challenge exists so far in the model parameter that is highly variable and differs greatly between laboratory flumes and field streams. This paper presents an improved surface-based hiding fimction. The force balance for particle inception was formulated and the allocation of the overall bed shear stress into each group of sediments was mimicked. The new hiding function was examined against and agrees well with the documented field and flume data. It was shown that the hiding fimction is closely related to the relative flow depth and the reference elevation in the velocity profile in addition to the bed material gradation. The power law of velocity profile that applies to both flume flows and natural streams can link the flume and field data together. The hiding function with b = 1/6 and b = 1/2 is applicable to natural streams and laboratory flumes, respectively. The value orb = 0.263 also works well for gravel bed rivers. The range of the reference elevation, namely z0 = 0.4Dm-1.4Dm, is recommended for either the flume or field data. The new hiding function contributes to addressing clearer physical meanings and a useful perspective for further improvement.展开更多
文摘In this paper, a method of stabilizing electric power by a system which is a combination of wind power generation and pumped storage power generation is proposed. The system operates based on the output predicted value of the windfarm. When the measured windfarm output is larger than the predicted value, the system is pumping up water with surplus power. When the windfarm output is smaller than the predicted value, the system is filling up lack power by hydro generator. Also, since hydro generator works with a start-up delay time, output shortage occurs at this time. To improve output shortage at the time, we estimate the time below the predicted value by a statistical model. As the result, the system succeeded in stabilizing the power and improving the start-up delay time of the hydro generator.
基金supported by the National Key Research and Development Program (2010CB833504)the CAS Strategic Priority Research Program (XDA05050602)
文摘We conducted a systematic census of leaf N for 102 plant species at 112 research sites along the North-South Transect of Eastern China （NSTEC） following the same protocol, to explore how plant functional types （PFTs） and environmental factors affect the spatial pattern of leaf N. The results showed that mean leaf N was 17.7 mg g^-1 for all plant species. The highest and lowest leaf N were found in deciduous-broadleaf and evergreen-conifer species, respectively, and the ranking of leaf N from high to low was： deciduous 〉 evergreen species, broadleaf 〉 coniferous species, shrubs ≈ trees 〉 grasses. For all data pooled, leaf N showed a convex quadratic response to mean annual temperature （MAT）, and a negative linear relationship with mean annual precipitation （MAP）, but a positive linear relationship with soil nitrogen concentration （Nsoil）. These patterns were similar when PFTs were examined individually. Importantly, PFTs, climate and Nsoil, jointly explained 46.1% of the spatial variation in leaf N, of which the independent explanatory powers of PFTs, climate and Nsoil, were 15.6%, 2.3% and 4.7%, respectively. Our findings suggest that leaf N is regulated by climate and Nsoil, mainly via plant species composition. The wide scale empirical relationships developed here are useful for understanding and modeling of the effects of PFTs and environmental factors on leaf N.
基金the Beijing Municipal Science&Technology Project(Grant No.Z141100003614052)the National Natural Science Foundation of China(Grants No.51525901&51379100)as well as by China Ministry of Science and Technology(Grant No.2011CB409901)
文摘The quantification of the sheltering and exposure effects of non-uniform sediments has been widely achieved through hiding function models. Big challenge exists so far in the model parameter that is highly variable and differs greatly between laboratory flumes and field streams. This paper presents an improved surface-based hiding fimction. The force balance for particle inception was formulated and the allocation of the overall bed shear stress into each group of sediments was mimicked. The new hiding function was examined against and agrees well with the documented field and flume data. It was shown that the hiding fimction is closely related to the relative flow depth and the reference elevation in the velocity profile in addition to the bed material gradation. The power law of velocity profile that applies to both flume flows and natural streams can link the flume and field data together. The hiding function with b = 1/6 and b = 1/2 is applicable to natural streams and laboratory flumes, respectively. The value orb = 0.263 also works well for gravel bed rivers. The range of the reference elevation, namely z0 = 0.4Dm-1.4Dm, is recommended for either the flume or field data. The new hiding function contributes to addressing clearer physical meanings and a useful perspective for further improvement.
