The spatial-temporal patterns of grain production and consumption have an important influence on the effective national grain supply on condition of tight balance in the total grain amount in China. In this paper, we ...The spatial-temporal patterns of grain production and consumption have an important influence on the effective national grain supply on condition of tight balance in the total grain amount in China. In this paper, we analyze the spatial-temporal pattems of grain production, consumption and the driving mechanism for their evolution processes in China. The results indicate that both gravity centers of grain production and consumption in China moved toward the northern and eastern regions, almost in the same direction. The coordination of grain production and consumption increased slightly from 1995 to 2007 but decreased from 2000 to 2007. There is a spatial difference between the major districts of output increase and the strong growth potential in grain consumption, which indicates an increasing difficulty in improving the regional coordination of grain production and consumption. The movement of the gravity center of grain production is significantly correlated with regional differences in grain production policy, different economic development models, and spatial disparity of land and water resource use. For grain consumption, the main driving factors include rapid urbanization, the upgrade of food consumption structure, and distribution of food industries.展开更多
In the design theory of scroll profiles for refrigeration scroll compressor,a mechanism principle of scroll profiles based on the center of natural temporal involutes and meshing region is presented,by which the perfo...In the design theory of scroll profiles for refrigeration scroll compressor,a mechanism principle of scroll profiles based on the center of natural temporal involutes and meshing region is presented,by which the performance characteristics of the various involutes are studied. Profiles type selection is very important for scroll compressor. Through analyzing the characteristic geometry,natural meshing mechanism is discovered in the study of scrolls. And a novel method for scroll profiles based on natural meshing mechanism is proposed. The result shows that the meshing region angle of odd regular polygon involutes is half of the characteristic-geometry exterior angle,and that of even regular polygon involutes is equal to the exterior angle to the moment. The corresponding meshing region angle is reduced increasingly with the increase of the edge number of characteristic geometry. The performance characteristics of scroll compressor tend towards the best correspondingly. Aiming at the existing problems of profile design for scrolls,we developed a novel methodology to study scroll profile. Originality research was done for the further study of scroll profile. It is the fundamentality factor representing essence character of scroll profiles function itself.展开更多
基金supported by the Key Technologies R&D Program of China during the 12th Five-Year Plan period(2012BAH20B04)the National Natural Science Foundation of China(41201599, 41001108)+1 种基金the Natural Science Foundation of Shandong Province,China(ZR2009DL011)the Social Science Foundation of China(08BJY113)
文摘The spatial-temporal patterns of grain production and consumption have an important influence on the effective national grain supply on condition of tight balance in the total grain amount in China. In this paper, we analyze the spatial-temporal pattems of grain production, consumption and the driving mechanism for their evolution processes in China. The results indicate that both gravity centers of grain production and consumption in China moved toward the northern and eastern regions, almost in the same direction. The coordination of grain production and consumption increased slightly from 1995 to 2007 but decreased from 2000 to 2007. There is a spatial difference between the major districts of output increase and the strong growth potential in grain consumption, which indicates an increasing difficulty in improving the regional coordination of grain production and consumption. The movement of the gravity center of grain production is significantly correlated with regional differences in grain production policy, different economic development models, and spatial disparity of land and water resource use. For grain consumption, the main driving factors include rapid urbanization, the upgrade of food consumption structure, and distribution of food industries.
基金supported by the National Natural Science Foundation of China(Grant No.50805149)China Postdoctoral Science Foundation(Grant No.20090450166)the Open Foundation of State Key Lab of Mechanical Transmission.
文摘In the design theory of scroll profiles for refrigeration scroll compressor,a mechanism principle of scroll profiles based on the center of natural temporal involutes and meshing region is presented,by which the performance characteristics of the various involutes are studied. Profiles type selection is very important for scroll compressor. Through analyzing the characteristic geometry,natural meshing mechanism is discovered in the study of scrolls. And a novel method for scroll profiles based on natural meshing mechanism is proposed. The result shows that the meshing region angle of odd regular polygon involutes is half of the characteristic-geometry exterior angle,and that of even regular polygon involutes is equal to the exterior angle to the moment. The corresponding meshing region angle is reduced increasingly with the increase of the edge number of characteristic geometry. The performance characteristics of scroll compressor tend towards the best correspondingly. Aiming at the existing problems of profile design for scrolls,we developed a novel methodology to study scroll profile. Originality research was done for the further study of scroll profile. It is the fundamentality factor representing essence character of scroll profiles function itself.
