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881.
The behaviors of granular material and influencing factors under complex dynamic loading are studied by more and more researchers with particle flow method. Only the strain-controlled loading has been generally used in the current study, although this method was not consistent with the practice of engineering in many situations. In this article, stress-controlled dynamic simulation tests were carried out with particle flow method, which were used to study the collapse characteristics of silt under mutation of principal stress orientation. The tests were performed by PFC2D. The simulation results and the laboratory real tests’ results had a high degree of similarity, particularly in the collapse strain and vibration times. It was very useful to forecast the silt's critical failure state. Based on the verification data, the effects of confining pressure and cyclic shear stress ratio on the collapse characteristics of silt were studied further. With the increase of cyclic shear stress ratio, the deviator strain amplitude increased and the required vibration times gradually reduced to achieve the same strain level. Under the same dynamic shear stress ratio and vibration times, the initial dynamic elastic modulus slightly increased with the increase of initial confining pressure, and the variation range of final collapse deviator strain was small. In the analysis of micro-structural evolution, the redistribution of internal stress of sample was revealed during cyclic loading. With the increase of vibration times, the development of distribution gradually stabilized, and then the high shear stress appeared in some connected regions. On that stage, the particle system developed to instability and failure. The PFC simulation results confirmed that the collapse state was the critical stage to trigger the liquefaction of silt. 相似文献
882.
提出一种利用POS辅助多视角倾斜影像匹配的算法。首先,利用POS数据对倾斜影像进行近似核线纠正;然后,用SIFTGPU算法对纠正影像进行特征匹配,根据匹配结果计算出两张影像的水平和垂直方向视差进而求得其近似重叠区域;将重叠区域进行分块特征匹配,采用比值提纯法、视差约束和RANSAC算法等约束条件剔除误匹配;最后,将匹配结果通过POS数据反算回到原始影像上。试验结果表明,将POS数据应用到多视角倾斜影像匹配中,可快速获得比常规影像匹配方法数量更多、分布更均匀的匹配点。 相似文献
883.
884.
针对点云与图像信息快速融合的问题,该文研究并实现了一种基于单目相机姿态估计的点云与图像融合方法。首先利用视觉导航中单目相机姿态估计方法估算小型无人机的姿态信息,然后与无人机导航系统中的姿态信息匹配来准确获得相机曝光时间点,最后结合图像曝光时间点的外方位元素和已知的内方位元素完成点云与图像融合。该方法直接利用图像信息进行融合,省去了相机时间检校步骤,避免了由此带来的误差,提高了时间匹配的准确性以及数据融合的自动化水平。实验结果表明,该方法能够准确地获得时间匹配信息,融合效果良好。 相似文献
885.
Understanding the orientation distribution of structural discontinuities using the limited information afforded by their trace in outcrop has considerable application, with such analysis often providing the basis for geological modelling. However, eigen analysis of 3D structural lineaments mapped at decimetre to regional scales indicates that discontinuity best fit plane estimates from such datasets tend to be unreliable. Here, the relationship between digitised lineament vertex geometry (coplanarity/collinearity) and the reliability of their estimated best fitting plane is investigated using Monte Carlo experiments. Lineaments are modelled as the intersection curve between two orthonormally oriented fractional Brownian surfaces representing the outcrop and discontinuity plane. Commensurate to increasing lineament vertex collinearity (K), systematic decay in estimated pole vector precision is observed from these experiments. Pole vector distributions are circumferentially constrained around the axis of rotation set by the end nodes of the synthetic lineaments, reducing the rotational degrees of freedom of the vertex set from three to one. Vectors on the unit circle formed perpendicular to this arbitrary axis of rotation conform to von Mises (circular normal) distributions tending towards uniform at extreme values of K. This latter observation suggests that whilst intrinsically unreliable, confidence limits can be placed upon orientation estimates from 3D structural lineaments digitised from remotely sensed data. A probabilistic framework is introduced which draws upon the statistical constraints obtained from our experiments to provide robust best fit plane estimates from digitised 3D structural lineaments. 相似文献
886.
Climate change denial is motivated in part by ideology, with research showing that a greater tolerance of social inequality is consistently linked to lower pro-environmentalism. We report findings from two mixed-methods studies. In Study One, we provide insight into how individuals with varying levels of social dominance orientation discuss environmental issues by analyzing 59 interviews. These analyses revealed that many individuals were concerned about the causes, consequences, and potential solutions to climate change; however, many were also armed with justifications excusing their and others’ inaction on the problem. To establish further how the ideas shared in the interviews related to social dominance, we reworked the ideas into statements for survey-based research in Study Two. Social dominance orientation and its composite dimensions related to most interview-based statements, with those scoring higher on dominance attitudes more opposed to top-down action on climate change, and those more tolerant of inequality more opposed to individual action. We discuss implications for climate change communication. 相似文献
887.
888.
以浙江省铀成矿地质背景为基础,按成因分类法结合赋矿围岩特征对铀资源类型进行了划分,论述了不同铀资源类型的分布特征及相互关系。通过分析浙江省铀资源的形成条件和成矿潜力,提出了浙江省寻找火山岩型铀矿的目标和方向,认为浙江省火山岩型铀矿资源丰富,具有良好的找矿前景。 相似文献
889.
详细介绍了在立井平面联系测量中连接三角形法一井定向的测量和解算方法,特别提出了不同连接三角形解算适用不同的计算公式。并结合实践经验,阐述了一井定向连接三角形法和瞄直法的使用范围和测量注意事项。 相似文献
890.
《The Journal of geography》2012,111(3):134-135
Abstract Bibliographic instruction is aneglected component of undergraduate education in many geography curricula. Significant research problems are difficult to formulate and self-education cannot be achieved without the ability to use reference materials effectively. The research methods course is a logical vehicle for providing bibliographic instruction at the undergraduate level. Library training can be incorporated in this course through a series of instructional modules that requires students to work with a wide variety of bibliographic materials. Students should be allowed to focus on publications pertaining to topics of individual interest in all phases of their work. This paper outlines a methods course that emphasizes bibliographic instruction and gives suggestions for incorporating selected developmental materials. 相似文献