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521.
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Qizhong Wen Suhua Yu Fuqing Sun Yuqi Wang Bingru Chen Shude Tu Jingxin Sun 《中国地球化学学报》1985,4(2):172-180
TheΣ REE in loesses of different ages in the Luochuan section shows a narrow range of variation, indicating the homogeneity of loessic materials in chemical composition. The REEs in loess are concentrated mainly in silt-sized detrital minerals. Loesses and paleosols of different ages all are relatively enriched in rare-earth elements of the Ce family, and show similar REE distribution patterns. The fractionation among various REEs in the loess is different from that in morainic, marine and lacustrine sediments, but is similar to that in sand samples from deserts in Northwest China. The ratios of Ce/Ce* and Eu/Eu* reflect that the provenance of loessic materials and their accumulating area are all in an oxidation environment with weakly basic mediums under arid or semi-arid climate. 相似文献
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A zonal-vertical two-dimensional equatorial model is used to study the possibility that the long period oscillation of the zonal mean flow occurring in the lower equatorial stratosphere (QBO) is caused by local thermal ac-tivities at the tropical tropopause. The model successfully reproduces QBO-like oscillations of the zonal mean flow, suggesting that the local heating or cooling at the tropical tropopause is probably the main reason of QBO’s genera-tion. The analysis of the dependence of the oscillation on the wave fencing indicates that the oscillation is not sensible to the forcing scale. The model can reproduce QBO-like oscillations with any forcing scale if the fencing period and amplitude take appropriate values, proving that the internal gravity waves generated by local thermal source take much important roles in QBO. 相似文献
524.
影响蔬菜周年均衡供应的原因是多方面的,不利的天气气候影响是主要原因之一。广西以广州市为例,剖析了影响蔬菜年供应的原因,并提出缩短淡季实现周年均衡供应的对策。 相似文献
525.
汉南杂岩与金成矿特征 总被引:2,自引:0,他引:2
汉南杂岩区位于扬子地台北缘,围岩为元古界绿片岩 勉县—洋县深大断裂系统在成岩、成矿与盆地形成方面占有重要的地位.杂岩体由斜长花岗岩、二长花岗岩、钾长花岗岩、石英闪长岩和辉长辉绿岩组成.金矿化类型主要有石英脉型和蚀变岩型,与接触带、断裂带、蚀变带有关,蚀变后岩石矿物成分变化.使金重新分布,砂金分布与金源、地貌和新构造运动关系密切. 相似文献
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The probability distributions of field differences x()=x(t+)-x(t), where the variable x(t) may denote any solar wind scalar field or vector field component at time t, have been calculated from time series of Helios data obtained in 1976 at heliocentric distances near 0.3 AU. It is found that for comparatively long time lag , ranging from a few hours to 1 day, the differences are normally distributed according to a Gaussian. For shorter time lags, of less than ten minutes, significant changes in shape are observed. The distributions are often spikier and narrower than the equivalent Gaussian distribution with the same standard deviation, and they are enhanced for large, reduced for intermediate and enhanced for very small values of x. This result is in accordance with fluid observations and numerical simulations. Hence statistical properties are dominated at small scale by large fluctuation amplitudes that are sparsely distributed, which is direct evidence for spatial intermittency of the fluctuations. This is in agreement with results from earlier analyses of the structure functions of x. The non-Gaussian features are differently developed for the various types of fluctuations. The relevance of these observations to the interpretation and understanding of the nature of solar wind magnetohydrodynamic (MHD) turbulence is pointed out, and contact is made with existing theoretical concepts of intermittency in fluid turbulence. 相似文献
529.
应用数学分析方法建立一个地图质量模糊评判的数学模型,并用上述模型对12幅地形图编绘质量进行评判,所得结果令人满意。 相似文献
530.
本文论述了广东冬季气候资源的优势及冬季寒害的两重性,分析了近两年寒害对农业生产的影响,在些基础上,提出了防御寒害的综合对策。 相似文献