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Based upon the effect of land-sea interaction on the paleomonsoon variation and the time series of climatic proxy-indicators, the historical Asian monsoon variation over the last 130,000 and 18,000 years has been reconstructed with an emphasis on the basic characteristics of summer monsoon circulation. The monsoon-climatic cycles and associated model of environmental development over the central and eastern China are proposed and the mechanism of paleomonsoon variation of China preliminarily discussed. The variation of East Asian monsoon circulation should be regarded as a regional result of both solar-radiation changes and the global glacial-interglacial cycles. The episodic uplifting of the Qinghai-Xizang Plateau since the late Miocene has to a large extent controlled the forming and evolution of the paleomonsoon circulation of China. 相似文献
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由于对γ射线灵敏度低,而且可在很宽的范围内中子能量响应比较平坦,长计数管在中子产额的测量中得到了广泛的应用。为了提高探测效率,一般用BF3或^3He正比管外包围一定厚度的石蜡或聚乙烯慢化体来构成长计数管探测系统。建立的长计数器主要是针对中子管产生的DD(2.4MeV)或DT(14.1MeV)或两种能量混合的脉冲中子进行测量。为了达到探测系统设计要求,首先详细模拟了慢化体尺寸及结构对探测效率的影响,以便对探测器系统的加工制作提供依据。根据模拟结果建立了探测器,从实验上对探测器的性能进行了测量。 相似文献
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The characteristics of the modern monsoon climate o?China may be used as clues for recognizing the records of paleomonsoon climate. The present paper deals primarily with the various paleomonsoon records of the last 130,000 years in the southeast monsoon area. These records mainly come from the following three fields: (i) the historical, (ii) the geological, including loess-paleosol sequence, deserts, lakes, snowlines, timberlines, the phenomena of continental desertization and so on, and (iii) the biological, presented by vegetation and mammals. Among these records, the loess-paleosol sequence in the Loess Plateau reflects a climatic history characterized by alternation of two different climatic periods when the Asian winter monsoon and summer monsoon showed pronounced effects on environment, respectively. 相似文献
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本文用三点弯曲试件对不同a/W值的高强度钢38CrMoAl的临界应力强度因子K_(Ic)值进行了系列的实验研究,实验结果表明:a/W值减小,则材料的K_(IC)值增大.当a/W=0.1时,其K_(lC)值为a/W=0.5的1.2倍.另外,还对a/W值不同时实验中应注意的一些问题,进行了探讨. 相似文献