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961.
962.
由于天线本身的特性及机械加工等原因,GPS卫星和接收机天线相位中心与其几何中心不重合,从而产生相位中心偏差。某些类型的天线该偏差甚至可达数cm,直接影响高精度GPS测量的精确可靠性[1]。讨论了GAMIT软件在高精度GPS数据处理中进行天线相位中心改正的原理、方法和策略,结合美国IGS观测站及南加州区域站观测数据,对改正方法及策略进行了实验对比与分析。结果表明:对接收机天线相位中心和卫星天线相位中心采用模型改正,而卫星天线相位中心偏移不改正,所得到的基线解算结果较好[2];地面接收机天线方位角的变化对U方向的基线解算结果有较大影响,在高精度GPS测量中,必须进行天线方位角的变化改正。 相似文献
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964.
对采自中国东部亚热带地区的浙江天目山、江西庐山及江苏南京紫金山地区的金钱松(Pseudolarix kaemp feri)、冷杉(Abiesfab ricraib)及马尾松(Pinus massoniana)树轮,分别测定它们不同方位10 a、20 a及3 a树轮δ13C序列,探讨不同树种树轮δ13C存在的方位差异与年际变化普遍性。结果表明,在中国东部亚热带地区,树轮δ13C方位差异与年际变化存在普遍性。表现为3个地区、3个树种之间存在差异;同一地区不同树种及相同树种不同个体之间也存在差异;同一个体在相同年份存在方位差异及相同方位存在年际变化等;表明研究树轮δ13C的方位差异与研究其年际变化同样具有重要价值与意义。 相似文献
965.
利用三河—平谷8.0级大震区实施的深地震反射剖面与宽角反射剖面探测方法获得的结果进行了综合研究和解释. 结果表明:两种探测方法给出的地壳基本分层是一致的,在三河—平谷大震区上地壳的埋深为21~23km,莫霍界面的深度为36~37km;该地区基底结构起伏变化较大,浅部断裂发育,在确定的数条断裂构造带中夏垫断裂是一条特征明显、深浅共存的断裂构造带;震源区周围差异明显的速度异常结构和特殊而复杂的地质构造环境意味着这些部位是发生大地震的有利部位;该地区莫霍界面起伏变化和较厚的反射叠层以及局部复杂的楔形反射带的存在等现象表明,该地区地壳结构发生过强烈的挤压、变形,同时也反映出岩浆活动对下地壳结构进行了物质的和结构的强烈改造,从而构成了该地区复杂的地壳深部结构,可将其视为三河—平谷8.0级大地震孕育和发生的深部要素. 相似文献
966.
967.
Jun Inaoka Ken'ichirou Kosugi Naoya Masaoka Tetsushi Itokazu Kimihito Nakamura 《水文研究》2020,34(26):5567-5579
Clarifying rainfall-runoff responses in mountainous areas is essential for disaster prediction as well as water resource management. Although runoff is considered to be significantly affected by topography, some previous studies have reported that geological structures also have significant effects on rainfall-runoff characteristics. Particularly in headwater catchments located in sedimentary rock mountains, dips and strikes may significantly affect rainwater discharge. In this study, the effects of geological structures on rainfall-runoff characteristics were investigated based on observed discharge hydrographs from 12 catchments, which lie radially from the summit of a sedimentary rock mountain. The results obtained were as follows: (1) Even though the topographic wetness index (TWI) distributions of the 12 catchments were similar, there were significant differences in their runoff characteristics; (2) Catchments with average flow direction oriented towards the strike direction (strike-oriented catchments) are characterized by large baseflows; (3) Catchments with average flow direction oriented towards the opposite dip direction (opposite dip-oriented catchments) are steep, and this results in quick storm runoff generation; (4) Catchments with average flow direction oriented toward the dip direction (dip-oriented catchments) are gentle, and this results in delayed storm runoff generation. It was presumed that in strike-oriented catchments, large quantities of groundwater flowing along the bedding planes owing to hydraulic anisotropy, exfiltrate and sustain the large amount of the observed baseflow, that is, in strike-oriented catchments, runoff is directly controlled by geological structures. Conversely, in opposite dip-oriented and dip-oriented catchments, runoff is indirectly controlled by geological structures, that is, geological structures affect slope gradients, which result in differences in storm runoff generation. Thus, this study clearly illustrates that geological structures significantly affect rainfall-runoff responses in headwater catchments located in sedimentary rock mountains. 相似文献
968.
Cheng Zhao Yimeng Zhou Qingzhao Zhang Chunfeng Zhao Hiroshi Matsuda 《国际地质力学数值与分析法杂志》2020,44(3):353-370
To deeply understand the cracking mechanical behavior of brittle rock materials, numerical simulations of a rock specimen containing a single preexisting crack were carried out by the expanded distinct element method (EDEM). Based on the analysis of crack tips and a comparison between stress- and strain-based methods, the strain strength criterion was adopted in the numerical models to simulate the crack initiation and propagation processes under uniaxial and biaxial compression. The simulation results indicated that the crack inclination angle and confining pressure had a great influence on the tensile and shear properties, peak strength, and failure behaviors, which also showed a good agreement with the experimental results. If the specimen was under uniaxial compression, it was found that the initiation stress and peak strength first decreased and then increased with an increasing inclination angle α. Regardless of the size of α, tensile cracks initiated prior to shear cracks. If α was small (such as α ≤ 30°), the tensile cracks dominated the specimen failure, the wing cracks propagated towards the direction of uniaxial compression, and the propagation of shear cracks was inhibited by the high concentration of tensile stress. In contrast, if α was large (such as α ≥ 45°), mixed cracks dominated the specimen failure, and the external loading favored the further propagation of shear cracks. Analyzing the numerical results of the specimen with a 45° inclination angle under biaxial compression, it was revealed that lateral confinement had a significant influence on the initiation sequence and the mechanical properties of new cracks. 相似文献
969.
970.