The lightning-induced-damages in the mid-latitude regions are usually caused during severe thunderstorms. But the discharge parameters of natural lightning are difficult to be measured. Five lightning flashes have bee...The lightning-induced-damages in the mid-latitude regions are usually caused during severe thunderstorms. But the discharge parameters of natural lightning are difficult to be measured. Five lightning flashes have been artificially triggered with the rocket-wire technique during the passage of two severe thunderstorms. The discharge current and close electric field of return stroke in artificially triggered lightning have been obtained in microsecond time resolution by using current measuring systems and electric field change sensors. The results show that the five triggered lightning flashes include 1 to 10 return strokes, and the average return stroke current is 11.9 kA with a maximum of 21.0 kA and a minimum of 6.6 kA, similar to the subsequent return strokes in natural lightning. The half peak width of the current waveform is 39 us, which is much larger than the usual result. The peak current of stroke I_p(kA) and the neutralized charge Q(C) has a relationship of I_p = 18.5Q^(0.65). The radiation field of return stroke is 5.9 kV ? m^(-1) and 0.39 kV ? m^(-1) at 60 m and 550 m, respectively. The radiation field decreases as r^(-1.119) with increase of horizontal distance r from the discharge channel. Based on the well-accepted transmission line model, the speed of return stroke is estimated to be about 1.4 × 10~8m·s^(-1), with a variation range of (1.1-1.6)×10~8m·s^(-1). Because of the similarities of the triggered lightning and natural lightning, the results in this article can be used in the protection design of natural lightning.展开更多
文摘设计了基于"落球法"的电热式变温液体黏度测量装置.借助该装置,通过改变2个侧加热板的间距,在室温下研究了侧加热板以及容器壁对蓖麻油中小球下落速度的影响,并以此为基础,利用对称测量原理,对蓖麻油在不同温度下的黏度进行了测量,揭示出蓖麻油的黏度与温度的关系近似满足阿伦尼乌斯公式,活化能约为9.213×10-20 J.
基金the National Natural Science Foundation of China (Grant Nos. 40135010 and 40325013) the Ministry of Science and Technology of China (Grant No. 2004DEA71070)
文摘The lightning-induced-damages in the mid-latitude regions are usually caused during severe thunderstorms. But the discharge parameters of natural lightning are difficult to be measured. Five lightning flashes have been artificially triggered with the rocket-wire technique during the passage of two severe thunderstorms. The discharge current and close electric field of return stroke in artificially triggered lightning have been obtained in microsecond time resolution by using current measuring systems and electric field change sensors. The results show that the five triggered lightning flashes include 1 to 10 return strokes, and the average return stroke current is 11.9 kA with a maximum of 21.0 kA and a minimum of 6.6 kA, similar to the subsequent return strokes in natural lightning. The half peak width of the current waveform is 39 us, which is much larger than the usual result. The peak current of stroke I_p(kA) and the neutralized charge Q(C) has a relationship of I_p = 18.5Q^(0.65). The radiation field of return stroke is 5.9 kV ? m^(-1) and 0.39 kV ? m^(-1) at 60 m and 550 m, respectively. The radiation field decreases as r^(-1.119) with increase of horizontal distance r from the discharge channel. Based on the well-accepted transmission line model, the speed of return stroke is estimated to be about 1.4 × 10~8m·s^(-1), with a variation range of (1.1-1.6)×10~8m·s^(-1). Because of the similarities of the triggered lightning and natural lightning, the results in this article can be used in the protection design of natural lightning.
