The key area of the first eigenvector of eof for summer precipitation decadal change in china allots in south and north of changjiang river which vary contrary ; the second one ' s allots in middle valley of changjiang river and jianghuai valley ; the third one ' s allots almost in total china . ( 3 ) tropic and north pacific summer ssta ' s decadal change has good correlation with china summer precipitation ' s decadal change 中国年平均与汛期平均降水eof分析的前三个特征向量基本一致，第一特征向量表现为长江南北反向的形态，第二特征向量表现为中部为正，其余为负的分布形态，第三特征向量表现为长江中游、江淮流域为正，其南北两侧为负的分布形态。
2 . the pre - flashover phenomena of alumina insulators in vacuum have been investigated . according to the experimental results , a reversed pre - flashover current was observed repetitively , which often occurs at the tail of pulse voltage close to zero ( sometimes after the applied pulse voltage ) 首次发现了大量的、重复性的反向预闪络现象，即在冲击电压波尾附近电压幅值已经接近零、甚至在冲击电压作用完后（已没有电压）的情况下仍然存在试样表面发光现象，同时伴有反向的电流脉冲。
