变压器中性点运行方式分析

通过对景性点不接地系统防止系统过电压措施、景性点接地对电力系统的影响进行分析,特别对操作、断线、单相接地、雷击等不同情况下景性点处出现的过电压进行分析,同时结合零序通路问题,总结出变压器景性点接地方式的选择应考虑系统零序阻抗、零序电流的分布、N-1对系统运行方式的影响等因素,做到不使接地点数目过多,以避免零序网络过于复杂、零序保护的定值不好整定、零序保护的各段保护之间不易配合,也不能因为接地点太少而使电网接地不可靠。

Quantitative Geography Analysis on Spatial Structure of A-grade Tourist Attractions in China

Tourist attraction is a very important carrier of tourism activities. A-grade tourist attraction is a national standard of comprehensive evaluation about tourist attractions quality and grade in China. In this paper, spatial structure of 2424 national A-grade tourist attractions are investigated by using GIS and quantitative analysis methods, such as nearest neighbor index （NNI）, quadrat analysis, Gini coefifcient and hot spot clustering. Spatial accessibility of all A-grade tourist attractions was calculated using cost weighted distance method and ArcGIS software. Service range of each tourist attraction at 4A grade and above in China was delimitated based on the cost allocation method. Results show that China’s A-grade tourist attractions present aggregate distribution characteristics on the whole, and cultural attractions aggregate distribution is higher than of natural tourist attractions. Above-4A grade quality attractions aggregate distribution is lower than the Below-4A grade tourist attractions; cultural Above-4A grade are signiifcantly greater than the cultural Below-4A grade tourist attractions. A-grade tourist attractions in China’s eight districts are aggregate. The spatial distribution uniformity is low. Affected by the degree of economic development and tourism resources endowment, the service range of Above-4A grade attractions is big in West, smal in East, big in North, and smal in South. First-order hot spots areas were mainly concentrated in the east side of the line formed by Deqen-Alxa Left Banner. The second-order hot spot areas were composed of 11 regions, while the third-order hot spot areas include Beijing, Tianjin, Central Plains and the Yangtze River Delta.

Influences of electro-acupuncture at related Jing-well Points in rats with vascular dementia

OBJECTIVE:To observe the effects of electro-acupuncture(EA) at related Jing-well Points(HT 9,PC 9,KI 1 and LU 11) in rats with vascular dementia(VD) and discuss the relative mechanism.METHODS:A randomized controlled animal experiment was designed.A total of 104 rats were involved in the present study and divided randomly into 4 groups:sham-operation group,model group,Jing-well Points group,and medication group.The VD model was established according to the modified 4-vessel occlusion(4-VO) method.VD rats in the Jing-well Points group were treated by EA at the related Jing-well Points(HT 9,PC 9,KI 1 and LU 11) while those in the medication group were treated with nimotop.The step-down avoidance test was performed before and after treatment in all rats.Latency and error frequency indexed memory function were recorded.Nitric oxide(NO) levels and superoxide dismutase(SOD) activity in both cerebral tissue and serum were detected after the treatment course.RESULTS:A total of 42 rats were included in the final analysis.Compared with the model group,the latency in the Jing-well Points group was significantly prolonged(P<0.01) and the error frequency was significantly decreased(P<0.05) after therapy;the decrease in NO levels in both brain tissue and serum was significant(P<0.05 and P<0.01,respectively);and the increase in SOD activity was also significant(P<0.01).There was no significant difference in latency,error frequency,NO levels and SOD activity between the Jing-well Points group and medication group.CONCLUSION:EA at related Jing-well Points can remarkably improve memory impairment in VD rats.Moreover,decreasing the overproduction of NO and strengthening the ability of eliminating free radicals may provide therapeutic potential for the treatment of VD.