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该文首先介绍了大面积降水的多普勒天气雷达径向速度PPI图像识别技术, 包括:①冷暖平流与大尺度辐合辐散运动叠加的图像特征; ②由零线的朝向和正负速度面积、径向速度值的大小判断风向风速辐合辐散的图像特征, 然后介绍了利用EVAD技术由雷达基数据定量计算大气平均散度和平均垂直速度的方法, 最后应用图像识别技术和EVAD方法对石家庄2004年冬季的一次大面积降雪过程进行了详细分析, 发现:此次大面积降雪过程有明显的辐合辐散图像特征, 径向速度值小, 辐合辐散弱, 始终存在暖平流。另外, 降雪强度和散度、垂直速度关系密切:辐合层厚度加大, 辐散抬高, 则降雪加强; 辐合、辐散层高度降低, 则降雪减弱。同时, 由EVAD技术定量计算的散度和相同时刻由径向速度图像产品定性分析的辐合、辐散基本一致。 相似文献
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C18 O J = 2–1, C17 O J = 2–1 and [C I ] 3 P1 –3 P0 emission from the dense cold cloud B335 has been observed and modelled in order to determine the C/CO ratio. The observed ratio is compared with a prediction by Tarafdar who assumes a mechanism in which the CO dissociation is caused by photons of energy ∼ 13.8 eV. These were postulated by Sciama to result from the decay of dark matter neutrinos. Our value for the C/CO ratio sets an upper limit to the strength of the neutrino decay dissociation process, thus providing a significant datum for interstellar chemistry theory. 相似文献
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A systematic investigation of the effect of configurations of stochastically distributed fracture networks on hydraulic behaviour for fractured rock masses could provide either quantitative or qualitative correlation between the structural configuration of the fracture network and its corresponding hydraulic behaviour, and enhance our understanding of appropriate application of groundwater flow and contaminant transport modelling in fractured rock masses. In this study, the effect of block sizes, intersection angles of fracture sets, standard deviations of fracture orientation, and fracture densities on directional block hydraulic conductivity and representative elementary volume is systematically investigated in two dimensions by implementing a numerical discrete fracture fluid flow model and incorporating stochastically distributed fracture configurations. It is shown from this investigation that the configuration of a stochastically distributed fracture network has a significant quantitative or qualitative effect on the hydraulic behaviour of fractured rock masses. Compared with the deterministic fracture configurations that have been extensively dealt with in a previous study, this investigation is expected to be more practical and adequate, since fracture geometry parameters are inherently stochastically distributed in the field. Moreover, the methodology and approach presented in this study may be generally applied to any fracture system in investigating the hydraulic behaviours from configurations of the fracture system while establishing a ‘bridge’ from the discrete fracture network flow modelling to equivalent continuum modelling in fractured rock masses. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Maxim Yu.Khlopov 《中国天文和天体物理学报》2010,10(6)
Primordial black holes (PBHs) are a profound signature of primordial cos-mological structures and provide a theoretical tool to study nontrivial physics of the early Universe. The mechanisms of PBH formation are discussed and observational constraints on the PBH spectrum, or effects of PBH evaporation, are shown to re-strict a wide range of particle physics models, predicting an enhancement of the ul-traviolet part of the spectrum of density perturbations, early dust-like stages, first or-der phase transitions and stages of superheavy metastable particle dominance in the early Universe. The mechanism of closed wall contraction can lead, in the inflation-ary Universe, to a new approach to galaxy formation, involving primordial clouds of massive BHs created around the intermediate mass or supermassive BH and playing the role of galactic seeds. 相似文献
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雷州马尾藻Sargassum leizhouense(Fucales,Phaeophyta)形态结构及分类研究 总被引:1,自引:0,他引:1
本研究通过对产于雷州半岛的雷州马尾藻(Sargassum leizhouense)形态结构进行研究,结合形态解剖、分类学特征等观察,比较了与同类组中其他3种马尾藻的特征差异,澄清了其分类地位,并修改了雷州马尾藻的检索表。结果表明,雷州马尾藻属于马尾藻属、真马尾藻亚属、叶托混生组、拟叶托混生亚组;尽管雷州马尾藻与该组的瓦氏马尾藻(S.vachellianum)、鳞茎马尾藻(S.bulbiferum)及滑托组的亨氏马尾藻(S.henslowianum)形态有许多相似之处,但其与上述3种马尾藻的主要差异在于球芽及分裂叶的有无。本研究不仅修改了雷州马尾藻分类地位,也为将来开展该马尾藻的人工繁育及养殖、加工提供帮助。 相似文献
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