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21.
Static analysis of stiffened shells has been carried out using an eight-noded isoparametric element for the shell and a three-noded curved beam element for the stiffener. A same displacement function is used for the shell and the stiffener elements. A modified technique has been followed to analyse the shell, which is an improvement over the degenerated shell concept. The stiffness matrix of the curved beam element is generated irrespective of its position and orientation within the shell element. The stiffness matrix of the stiffener is then transferred to all the nodes of the shell element. Numerical examples of stiffened shells with concentric and eccentric stiffeners have been analysed and the results presented together with those available in published literature. 相似文献
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Multivariate analyses applied to Pleistocene bivalve assemblages from the Oga Peninsula (northern Japan) discriminate three distinct assemblages. The assemblages and their taphonomy were used to recognize environmental settings and changes. The Astarte–Cyclocardia–Glycymeris assemblage indicates shelf environment (below the storm wave base) where gravels and shells are transported from shallower settings. Supply of the exotic coarse sediment probably enabled epifaunal bivalves to inhabit the sea floor. The Glycymeris assemblage is characterized by dominance of G. yessoensis and represents current-swept shoreface environment (above the storm wave base). The Moerella assemblage is characterized by bivalves inhabiting bay to open-marine conditions and diverse deposit-feeders, indicating a moderately land-locked environment, such as an open bay or a bay mouth. Fine-grained substrata rich in organic matters in the bay were probably suitable for the deposit-feeders. Ordination also shows the assemblages along two environmental gradients, a bathymetrical one and the other related to open-marine and bay conditions. The environmental changes are explained mainly by glacio-eustatic sea-level changes and alternation of coastal geomorphology caused by local crustal movements. This study also suggests that fossil assemblages can be a powerful tool to reconstruct environments and depositional dynamics even in intensely bioturbated sedimentary facies. 相似文献
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牡蛎壳体的同位素贝壳年轮研究 总被引：2，自引：0，他引：2
贝壳年轮学通过研究水生生物骨骼的周期性增长,来解译其生命历史及记录的环境信息。介绍了贝壳年轮研究的对象和方法、回顾了贝壳年轮的发展历程,并以渤海湾地区的现生和埋藏牡蛎壳体为例进行了贝壳年轮与壳体同位素剖面分析研究,首次同时关注牡蛎壳体剖面内的生长层和壳体韧带槽表面的特征层,二者共同指示了准确的生长年轮。结果显示,对应于壳体韧带槽表面凹沟的壳体剖面内灰色半透明生长层,具有一个年生长周期内最重的氧同位素比值,是晚秋至早春季节水温较低、食物来源匮乏时期形成的缓慢致密生长层;对应于壳体韧带槽表面外凸层中部的壳体剖面内灰色半透明生长层,具有较轻的氧同位素比值,是春季牡蛎产卵而形成的缓慢致密生长层;二者均具有良好的季节性指示意义,可以根据这些特征生长层对壳体的生长年龄进行准确的判断。 相似文献
24.
Oil ‘futures’: Shell’s Scenarios and the social constitution of the global oil market 总被引：1，自引：0，他引：1
Anna Zalik 《Geoforum》2010,41(4):553-564
This article explores the relationship between the oil industry’s representation of operating conditions in key sites of extraction and the constitution of oil futures markets. An analysis of Shell Oil’s recent Scenarios publications, the ‘Trilemma Scenarios to 2025’ and subsequent ‘Scramble and Blueprints Scenarios to 2050’, provides insight into both the (global) social construction of oil prices and the oil industry’s reaction to social resistance in its operating environment - whether in the form of movements for resource sovereignty or climate change activism. Examining the implications of these two Scenario publications for key sites of Shell investment, the Nigerian Niger Delta and the Canadian Tar Sands, the article demonstrates that understanding the discursive implications of ‘peak oil’ for the petroleum industry requires contextualizing discussions of ‘scarcity’ within business agents role in shaping oil futures markets, and private industry’s interest in the ongoing development of unconventional fossil fuel sources. While the role of deregulated futures trading receives little attention in the Shell Scenarios, speculative trading - and thus perception concerning supply among business agents - is central to shaping global oil prices and thus the social conditions of the oil market. 相似文献
25.
Shell是各类Unix操作系统与外部最主要的接口,是用户与操作系统之间交互的工具,不同Unix操作系统下缺省使用的Shell各不相同,用户在使用不同计算机时因为Shell的不同产生了许多困扰。文章简述了几种主要的Shell及其历史,介绍了如何选择Shell,比较了常用Unix Shell的异同及不同Shell登录时的初始化过程,最后详细介绍了AIX(Advanced Interactive eXecutive)系统中Korn Shell的启动、初始化文件和一个控制用户登陆的Shell应用实例。 相似文献
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柴达木盆地察尔汗贝壳堤剖面年代学研究* 总被引：9，自引：6，他引：9
利用常规14 C、加速器(AMS)和230 Th等测年方法,对位于青藏高原东北部柴达木盆地察尔汗古湖贝壳堤剖面化石贝壳、湖泊沉积(包括现代沉积)样品有机质(包括碱性残留和胡敏酸组分)、碳酸盐(CaCO3)和剖面顶部石盐(NaCl)晶体在不同实验室进行了系统的实验研究,探讨了不同样品测年结果的可靠性和精确性,并通过与已有研究结果的对比,对柴达木盆地贝壳堤剖面记录的察尔汗古湖高湖面演化历史进行了探讨,得出察尔汗古湖高湖面形成于约39.7~17.5 14 C kaB.P. ; 研究证明柴达木盆地沉积物中有机质含量很低,且主要来源于菌藻类等低等藻类和微生物,受老碳和溶解物质影响强烈,因此必须经过多种方法综合测年才能比较可靠地确定所测样品的形成年代; 测年结果的不确定性不仅来源于样品自身元素(同位素)的特性和沉积过程中再沉积作用的影响,也可能源自于放射性14 C产生过程的不稳定性; 对比发现贝壳化石老于同层位有机质14 C年龄15~18ka,这可能与柴达木盆地所处的特殊地理位置和巨大的古湖泊面积及水体有关; 同时,不平衡铀系测年在确定开放体系矿物晶体年代应用中的可靠性尚须进一步深入分析,其机理也还需要探讨和实验研究。 相似文献
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输气管道作为1种薄壁壳体结构,逆冲断层引起的管道压缩变形容易使其破坏。本文以大北南疆输气管道工程为例,探讨了穿越克孜尔逆冲断层的输气管道地震安全问题。在确定管道穿越处的断层倾角、设防断层位错量、表征管土相互作用的土弹簧参数以及钢管容许应变等参数后,采用壳有限元方法,分析了穿越克孜尔逆冲断层的输气管道变形反应。分析结果显示,管道在逆冲断层作用下以压缩应变为主,管道内的最大轴向压缩应变的幅值随着交角的减小而减小。在通过探槽等方法确定断层活动位置后,该管道若以小于或等于11°的交角通过克孜尔断裂,断层引起的最大轴向压缩应变和拉伸应变均在管道相应的容许应变范围内,满足相关规范的抗震要求。 相似文献
28.
节织纹螺(Nassarius hepaticus)贝壳差异的COⅠ基因分析 总被引：1，自引：0，他引：1
选择在厦门港市场购买的节织纹螺(Nassarius hepaticus),挑选五种典型贝壳形态,每种形态各5个个体,研究其COⅠ基因序列及其分子系统发育。结果表明,节织纹螺五种贝壳类型的齿舌形态基本一致,但个体间齿列数和中央齿上缘小齿数有差异;COⅠ基因序列存在较大的变异,678—679bp的片段上有31个变异位点,其中20个为密码子第三位碱基,6个为密码子第二位碱基,5个为密码子第一位碱基;贝壳、齿舌变异与DNA变异不存在关系,同类型和不同类型的个体在DNA序列上差异较小,根据Kimura 2-parameter法计算25个个体的遗传距离在0.001—0.010之间,平均值为0.007。以COⅠ基因序列计算的遗传距离和构建的系统发育树证实五种贝壳形态的25个个体同属于节织纹螺。 相似文献
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Remobilization, bioavailability, and potential toxicity of chemical contaminants were evaluated at the 4H shell mounds – the site of abandoned offshore oil and gas production platforms in the Santa Barbara Channel region of the Southern California Bight. Evaluations used a weight-of-evidence approach based on results from bulk phase chemical analyses and laboratory toxicity testing of shell mound cores, in situ field bioassays using caged mussels, and surficial sediment chemistry. Shell mound cores contained elevated concentrations of metals associated with drilling wastes (e.g., Ba, Cr, Pb, and Zn), as well as monocyclic and polycyclic aromatic hydrocarbons (PAHs). The highest concentrations along with pockets of free oil were associated with the middle “cuttings” stratum. Sediments composited from all core strata caused significant acute toxicity and bioaccumulation of Ba and PAHs in test organisms during laboratory exposures. In contrast, caged mussels placed at each of the shell mounds for a period of 57–58 days had greater than 90% survival, and there were no significant differences in survival of mussels placed at the shell mounds and corresponding reference sites. While all mussel samples exhibited increases in shell length, whole animal weight, and tissue lipid content, in some cases growth metrics for the shell mound mussels were significantly higher than those for the reference sites. Concentrations of metals, PAHs, and polychlorinated biphenyls (PCBs) in tissues of the shell mound mussels were not significantly different from those at reference sites. The presence of labile aromatic hydrocarbons in shell mound cores and absence of significant contaminant accumulation of tissues of caged mussels indicated that chemical contaminants are not being remobilized from the 4H shell mounds. Surficial bottom sediments near the shell mounds contained elevated Ba concentrations that probably were associated with drilling wastes. However, concentrations did not exhibit clear spatial gradients with distance from the shell mounds. Despite a number of storm events during the mussel exposures, maximum currents were 34 cm s−1 and unlikely to erode materials from the shell mounds. Thus, Ba distributions in bottom sediments probably were due to episodic disturbance such as platform removal or trawling rather than ongoing erosion and dispersion of shell mound solids by near-bottom currents. These results suggest that, in the absence of physical disturbances, contaminants are expected to remain sequestered in the shell mounds. 相似文献