利用松弛变量度量(slack based measure,SBM)的超效率模型,对污染排放约束下中国2004—2014年23个水稻生产省(市、自治区)的水稻生产用水效率进行测度分析,并通过Tobit模型分析影响水稻生产用水效率的因素。结果表明:在污染排放约束下...利用松弛变量度量(slack based measure,SBM)的超效率模型,对污染排放约束下中国2004—2014年23个水稻生产省(市、自治区)的水稻生产用水效率进行测度分析,并通过Tobit模型分析影响水稻生产用水效率的因素。结果表明:在污染排放约束下很多地区的水稻用水效率没有达到生产的前沿面,各地区的水稻生产用水效率存在很大差异,总体上各地区的水稻用水效率呈不断提升的趋势。从水稻生产区域来看,长江中下游地区的水稻生产用水效率最高,而华北地区的水稻生产用水效率多年来一直最低,东北地区和西南地区的水稻生产用水效率的年度波动幅度较大。农村居民人均纯收入、水稻播种面积占比和水稻机械化水平对水稻生产用水效率有显著的正向影响,而水资源丰裕程度、农田水利设施和节水农业发展水平对水稻用水效率并没有显著影响。展开更多
The full magnetic gradient tensor （MGT） refers to the spatial change rate of the three field components of the geomagnetic field vector along three mutually orthogonal axes. The tensor is of use to geological mappin...The full magnetic gradient tensor （MGT） refers to the spatial change rate of the three field components of the geomagnetic field vector along three mutually orthogonal axes. The tensor is of use to geological mapping, resources exploration, magnetic navigation, and others. However, it is very difficult to measure the full magnetic tensor gradient using existing engineering technology. We present a method to use triaxial aeromagnetic gradient measurements for deriving the full MGT. The method uses the triaxial gradient data and makes full use of the variation of the magnetic anomaly modulus in three dimensions to obtain a self-consistent magnetic tensor gradient. Numerical simulations show that the full MGT data obtained with the proposed method are of high precision and satisfy the requirements of data processing. We selected triaxial aeromagnetic gradient data from the Hebei Province for calculating the full MGT. Data processing shows that using triaxial tensor gradient data allows to take advantage of the spatial rate of change of the total field in three dimensions and suppresses part of the independent noise in the aeromagnetic gradient. The calculated tensor components have improved resolution, and the transformed full tensor gradient satisfies the requirement of geological mapping and interpretation.展开更多
The present status of self-elevating drilling units was analysed. Based on statistics of the main dimensions of self-elevating drilling units, a mathematical model was established using stepwise return procedures and ...The present status of self-elevating drilling units was analysed. Based on statistics of the main dimensions of self-elevating drilling units, a mathematical model was established using stepwise return procedures and a back-propagation neural network. mathematical model is applicable and reliable. The of the main dimensions of self-elevating drilling Analysis of examples of calculations showed that the model is useful for mastering the essential variations units and can be used for technical and economic analysis as well as in conceptual designs of drilling units.展开更多
文摘利用松弛变量度量(slack based measure,SBM)的超效率模型,对污染排放约束下中国2004—2014年23个水稻生产省(市、自治区)的水稻生产用水效率进行测度分析,并通过Tobit模型分析影响水稻生产用水效率的因素。结果表明:在污染排放约束下很多地区的水稻用水效率没有达到生产的前沿面,各地区的水稻生产用水效率存在很大差异,总体上各地区的水稻用水效率呈不断提升的趋势。从水稻生产区域来看,长江中下游地区的水稻生产用水效率最高,而华北地区的水稻生产用水效率多年来一直最低,东北地区和西南地区的水稻生产用水效率的年度波动幅度较大。农村居民人均纯收入、水稻播种面积占比和水稻机械化水平对水稻生产用水效率有显著的正向影响,而水资源丰裕程度、农田水利设施和节水农业发展水平对水稻用水效率并没有显著影响。
基金supported by the National High Technology Research and Development Program of China(863 Program)(No.2013AA063901 and No.2006AA06A201)
文摘The full magnetic gradient tensor （MGT） refers to the spatial change rate of the three field components of the geomagnetic field vector along three mutually orthogonal axes. The tensor is of use to geological mapping, resources exploration, magnetic navigation, and others. However, it is very difficult to measure the full magnetic tensor gradient using existing engineering technology. We present a method to use triaxial aeromagnetic gradient measurements for deriving the full MGT. The method uses the triaxial gradient data and makes full use of the variation of the magnetic anomaly modulus in three dimensions to obtain a self-consistent magnetic tensor gradient. Numerical simulations show that the full MGT data obtained with the proposed method are of high precision and satisfy the requirements of data processing. We selected triaxial aeromagnetic gradient data from the Hebei Province for calculating the full MGT. Data processing shows that using triaxial tensor gradient data allows to take advantage of the spatial rate of change of the total field in three dimensions and suppresses part of the independent noise in the aeromagnetic gradient. The calculated tensor components have improved resolution, and the transformed full tensor gradient satisfies the requirement of geological mapping and interpretation.
基金Supported by the National 863 Plan Foundation under Grant No.2003AA414060
文摘The present status of self-elevating drilling units was analysed. Based on statistics of the main dimensions of self-elevating drilling units, a mathematical model was established using stepwise return procedures and a back-propagation neural network. mathematical model is applicable and reliable. The of the main dimensions of self-elevating drilling Analysis of examples of calculations showed that the model is useful for mastering the essential variations units and can be used for technical and economic analysis as well as in conceptual designs of drilling units.
