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101.
Influence of sedimentary setting on the use of magnetic susceptibility: examples from the Devonian of Belgium 总被引:1,自引:0,他引:1
Bulk magnetic susceptibility measurements on sedimentological samples from all geological periods have been used widely in the last two decades for correlations and as a proxy for sea‐level variations. This paper explores the link between magnetic susceptibility, depositional setting and environmental parameters. These environmental parameters include distal–proximal transects, microfacies successions and fourth‐order trends on different carbonate platform types (platform, ramp, carbonate mound or atoll) during different Devonian stages (Eifelian, Givetian and Frasnian). Average magnetic susceptibility values over a distal–proximal‐trending facies succession vary markedly with depositional setting. On carbonate platforms, average magnetic susceptibility generally increases towards the top of shallowing‐upward sequences. On a distal–proximal transect, average magnetic susceptibility is intermediate for the deepest facies, decreases for the reef belts and increases to a maximum in the back‐reef zone. In ramps and atolls, magnetic susceptibility trends clearly differ; average magnetic susceptibility generally decreases towards the top of shallowing‐upward sequences and is highest in the deepest facies. The strong relationship between magnetic susceptibility, facies and sequences implies a strong environmental influence. However, the different responses in the different platform types suggest that sea‐level changes leading to variation in detrital input is not the only parameter controlling average magnetic susceptibility values. Other primary or secondary processes also probably influenced magnetic mineral distribution. Primary processes such as carbonate production and water agitation during deposition are probably key factors. When carbonate production is high, the proportion of magnetic minerals is diluted and the magnetic susceptibility signal decreases. High water agitation during deposition will also selectively remove magnetic minerals and will lead to low average magnetic susceptibility values. These parameters explain the lowest values observed on the reef platform, inner ramp and atoll crown, which are all in areas characterized by higher carbonate production and greater water agitation during deposition. The lowest values observed in the lagoon inside the atoll crown can be related to detrital isolation by the atoll crown. However, other parameters such as biogenic magnetite production or diagenesis can also influence the magnetic signal. Diagenesis can change magnetism by creating or destroying magnetic minerals. However, the influence of diagenesis probably is linked strongly to the primary facies (permeability, amount of clay or organic matter) and probably enhanced the primary signal. The complexity of the signal gives rise to correlation problems between different depositional settings. Thus, while magnetic susceptibility has the potential to be an important correlation tool, the results of this investigation indicate that it cannot be used without consideration of sedimentary processes and depositional environments and without strong biostratigraphical control. 相似文献
102.
Marco Sabatini Giovanni B. Palmerini 《Celestial Mechanics and Dynamical Astronomy》2009,105(1-3):229-244
Swarms are characterized in nature by a dynamic behaviour which is quite appealing for researchers involved in numerous fields of study, like robotics, computer science, pure mathematics and space sciences. Global group organization acquired in absence of centralized control is the feature of natural swarms which is most interesting to reproduce. This study proposes to make use of some evolutionary robotics findings in order to obtain the autonomous group organization in the framework of a deeper knowledge of the astrodynamics. The main task which will be accomplished is the implementation of the control laws for the single satellite. A careful tuning of the parameters at member level is necessary in order to gain an autonomously evolving global behaviour in a number of space missions of immediate interest. In remote sensing missions, for example, trains of a small number of satellites are already orbiting and integrating their collected data: in near future entire swarms of agents could accomplish this task, and should be controlled in order to acquire and maintain the desired leader-follower configuration. Another example can be seen in deep space exploration of unknown celestial bodies, where the migration of the entire swarm from a reference orbit to a (previously unknown) targeted one is an issue; the same group migration is of interest in Earth orbit, when transferring from parking to operational orbit. Finally, self-assembly of rigid-like virtual structures is also simulated. This paper shows that all these cases are autonomously performed by the swarm by correctly implementing four simple rules at individual level, which assess the primal needs for any satellite: avoid collision, remain grouped, align to the neighbor, reach a goal. 相似文献
103.
珊瑚混凝土在海洋环境中氯离子扩散实验 总被引:1,自引:1,他引:0
采用自然扩散法研究了珊瑚混凝土在海水环境中的氯离子扩散特性,探讨了养护龄期、暴露时间和环境差异性对珊瑚混凝土表观氯离子扩散系数的影响。结果表明:随着暴露时间的延长,珊瑚混凝土的表观氯离子扩散系数呈幂指数衰减规律;且延长养护龄期可降低珊瑚混凝土的表观氯离子扩散系数;随着强度等级增加,混凝土的表观氯离子扩散系数降低。我国实际海洋工程中珊瑚混凝土结构的表观氯离子扩散系数比实验室条件要提高3个数量级。因此,适当延长养护时间、提高强度等级有助于延长珊瑚混凝土结构在海洋环境的服役寿命。 相似文献
104.
利用2000-2014年MOD10A2积雪产品和数字高程模型DEM数据,以积雪覆盖率为指标,在分析西藏高原积雪空间分布特点的基础上,定量研究了高程、坡度和坡向等地形要素对高原积雪时空分布的影响。主要结论有:① 西藏高原积雪的空间分布差异显著,具有中东部念青唐古拉山和周边高山积雪丰富,覆盖率高,而南部河谷和羌塘高原中西部积雪少,覆盖率低的特点。② 海拔越高积雪覆盖率越高,积雪持续时间越长,年内变化越稳定。海拔2 km以下积雪覆盖率不足4%,海拔6 km以上覆盖率达75%。海拔4 km以下年内积雪覆盖呈单峰型分布特点,海拔越高,单峰型越明显;而海拔4 km以上则为双峰型,海拔越高,双峰型越明显。海拔6 km以下积雪覆盖率最低值出现在夏季,而6 km以上则出现在冬季。③ 总体上,高原地形坡度越高积雪覆盖率越高。不同坡向中,北坡积雪覆盖率最高,南坡最低,年内分布呈双峰型,而无坡向的平地积雪覆盖率要小于有坡向的山地,其年内变化呈单峰型分布特点。 相似文献
105.
315国道依吞布拉克—若羌段水毁灾害问题十分突出,为配合公路改建工程的勘察计,通过对水毁路段野外勘测,在获取沿线主要河流的历史洪水信息基础上,分3种方案分析计算了既定控制节点历史洪水洪峰流量,并确定了历史洪水重现期。在此基础上,采用多种方法计算了控制节点设计洪峰流量和设计洪水位,经分析论证后推荐选用其合理的计算成果作为公路设计的基础依据。本次研究所提出的小汇水区设计洪水计算技术路线和方法为公路、铁路、水利等部门开展类似流域设计洪水分析计算提供了有益的借鉴。 相似文献
106.
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109.
Effect of consolidation on strain localization of soft clays 总被引:4,自引:0,他引:4
A finite element formulation developed by Belytschko and his coworkers [1] is used to examine localized deformation as it exists for laboratory specimens of compressible Chicago clays. The element is based on an assumed strain formulation wherein localized and non-localized zones are embedded into an element when material based bifurcation is detected. A plane strain compression test of a natural clay specimen in which deformations localized into a single shear band during undrained shear is simulated using this element. Localization is initiated by imposing a non-uniform applied displacement consistent with that measured experimentally. Results indicate that to insure localization to a single band, considerations must be made for non-uniformities developed during the consolidation phase. 相似文献
110.
R. C. Knox D. A. Sabatini J. H. Harwell R. E. Brown C. C. West F. Blaha C. Griffin 《Ground water》1997,35(6):948-953