The Roche Limit     

I. P. Williams 《Celestial Mechanics and Dynamical Astronomy》2003,87(1-2):13-25

The role of tides in deforming and possibly disrupting a secondary body orbiting about a primary body has been known for a considerable time. This was first inspired by the observations of ocean tides on Earth and then seen as playing an important role in the formation and evolution of the Earth–Moon system. Finally, in the beginning of the 20th century it was generally thought to have a significant role in the formation of the solar system through the tidal disruption of the Sun. Here, an overview of the historical developments of the ideas concerned with tidal disruption of a secondary body that can lead to mass loss is given. Some discussion of possible extensions to consider more realistic situations where the secondary body may not be moving on a circular orbit and may not rotate so as to maintain the phase-on configuration to the primary body is also given.  相似文献   

Gravitational collapse and equilibrium conditions of a toroidal vortex with thermal pressure     

K. Yu. Bliokh  V. M. Kontorovich 《Astronomy Letters》2003,29(11):724-730

We found the equilibrium conditions for a self-gravitating toroidal vortex by taking thermal pressure into account. These conditions are shown to significantly differ from those for a disk or a sphere. The evolution of a thin vortex turns it into a compact vortex that loses mechanical stability for low masses at a polytropic index γ<4/3 but retains stability for sufficiently high masses and densities determined by the velocity circulation in the vortex.  相似文献   

Reliability assessment of serviceability performance of braced retaining walls using a neural network approach     

A. T. C. Goh  F. H. Kulhawy 《国际地质力学数值与分析法杂志》2005,29(6):627-642

In urban environments, one major concern with deep excavations in soft clay is the potentially large ground deformations in and around the excavation. Excessive movements can damage adjacent buildings and utilities. There are many uncertainties associated with the calculation of the ultimate or serviceability performance of a braced excavation system. These include the variabilities of the loadings, geotechnical soil properties, and engineering and geometrical properties of the wall. A risk‐based approach to serviceability performance failure is necessary to incorporate systematically the uncertainties associated with the various design parameters. This paper demonstrates the use of an integrated neural network–reliability method to assess the risk of serviceability failure through the calculation of the reliability index. By first performing a series of parametric studies using the finite element method and then approximating the non‐linear limit state surface (the boundary separating the safe and ‘failure’ domains) through a neural network model, the reliability index can be determined with the aid of a spreadsheet. Two illustrative examples are presented to show how the serviceability performance for braced excavation problems can be assessed using the reliability index. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Geobarometry for Peridotites: Experiments in Simple and Natural Systems from 6 to 10 GPa   总被引：3，自引：0，他引：3  

Brey  Gerhard P.; Bulatov  Vadim K.; Girnis  Andrei V. 《Journal of Petrology》2008,49(1):3-24

Experiments with peridotite minerals in simple (MgO–Al₂O₃–SiO₂,CaO–MgO–SiO₂ and CaO–MgO–Al₂O₃–SiO₂)and natural systems were conducted at 1300–1500°Cand 6–10 GPa using a multi-anvil apparatus. The experimentsin simple systems demonstrated consistency with previous lowerpressure experiments in belt and piston–cylinder set-ups.The analysis of spatial variations in pyroxene compositionswithin experimental samples was used to demonstrate that pressureand temperature variations within the samples were less than0·4 GPa and 50°C. Olivine capsules were used in natural-systemexperiments with two mineral mixtures: SC1 (olivine + high-Alorthopyroxene + high-Al clinopyroxene + spinel) and J4 (olivine+ low-Al orthopyroxene + low-Al clinopyroxene + garnet). Theexperiments produced olivine + orthopyroxene + garnet ±clinopyroxene assemblages, occasionally with magnesite and carbonate-richmelt. Equilibrium compositions were derived by the analysisof grain rims and evaluation of mineral zoning. They were comparedwith our previous experiments with the same starting mixturesat 2·8–6·0 GPa and the results from simplesystems. The compositions of minerals from experiments withnatural mixtures show smooth pressure and temperature dependencesup to a pressure of 8 GPa. The experiments at 9 and 10 GPa producedandradite-rich garnets and pyroxene compositions deviating fromthe trends defined by the lower pressure experiments (e.g. higherAl in orthopyroxene and Ca in clinopyroxene). This discrepancyis attributed to a higher degree of oxidation in the high-pressureexperiments and an orthopyroxene–high-P clinopyroxenephase transition at 9 GPa. Based on new and previous resultsin simple and natural systems, a new version of the Al-in-orthopyroxenebarometer is presented. The new barometer adequately reproducesexperimental pressures up to 8 GPa. KEY WORDS: garnet; mineral equilibrium; multi-anvil apparatus; orthopyroxene; geobarometry  相似文献   

On the Assessment of Failure in Slope Stability Analysis by the Finite Element Method   总被引：3，自引：0，他引：3  

H. Zheng  D. F. Liu  C. G. Li 《Rock Mechanics and Rock Engineering》2008,41(4):629-639

  相似文献   

运用3DEEMs及荧光偏振方法研究pH、离子强度及浓度效应对腐殖酸荧光光谱特性的影响   总被引：6，自引：0，他引：6  

梅毅  吴丰昌  王立英  白英臣 《地球化学》2008,37(2):165-173

利用三维荧光激发.发射光谱(3DEEMs)及荧光偏振法研究了3例腐殖酸和1例湖泊溶解有机物(DOM)在不同腐殖酸浓度、离子强度和pH条件下的荧光光谱特性.实验结果表明,随着浓度增大,各腐殖酸样的荧光强度增大,其中垃圾渗滤液腐殖酸和Pahokee泥炭腐殖酸的荧光峰出现红移.随着浓度进一步增大,腐殖酸的荧光偏振值增大,由此推断在此浓度范围内腐殖酸由于分子间的排斥作用使其构型出现伸展.离子强度增大导致腐殖酸及阿哈湖DOM的荧光强度降低.随着氯化钾(KCI)浓度增大,Fluka腐殖酸的荧光峰A蓝移,荧光峰B的荧光偏振值出现减小,推测是由于静电中和作用使其荧光基团发生卷曲造成的.离子强度对其余腐殖酸样和阿哈湖DOM的其他荧光特性没有明显的影响.总的来说,pH值的变化对腐殖酸和湖泊DOM的荧光特征的影响是很明显的.随着pH值增大,腐殖酸和湖泊DOM的荧光强度增强.而pH值减小时,Fluka腐殖酸和Pahokee泥炭腐殖酸的荧光峰(A峰)蓝移,当pH值降到5时,Fhka腐殖酸的荧光峰突然红移到最大,随后又继续蓝移;垃圾渗滤液腐殖酸和阿哈湖DOM的荧光峰位无明显的漂移.所有样品的荧光偏振值都减小(但阿哈湖DOM的A峰变化不大),但在pHi≤5时又增大,这种现象表明随着pH值降低,腐殖酸和湖泊DOM中有机大分子发生卷曲,但在pH≤5时由于羧基的质子化又以平面伸展构型出现在溶液中.  相似文献   

An improved multiple-frequency method for measuring in situ target strengths     

Conti  Stephane G.; Demer  David A.; Soule  Michael A.; Conti  Jean H.E. 《ICES Journal of Marine Science》2005,62(8):1636-1646

  相似文献   

三维斜压模式对冬季南海环流的数值计算   总被引：7，自引：0，他引：7  

游小宝  李荣凤  张铭  曾庆存 《海洋学报》2001,23(6):1-10

用一个三维、自由表面、原始方程模式对南海环流进行了计算.计算结果表明:黑潮在巴士海峡以西呈一反气旋弯曲流动路径,有一相对高温高盐的水舌从巴士海峡伸入南海,表明有部分黑潮水侵入南海.冬季南海的一些观测事实在模式结果里得到了很好的反映,像冬季逆风向东北方向流动的“南海暖流”和一些中尺度涡旋.同时还分析了巴士海峡沿120.75°E断面的流速和盐度的垂直结构,并同观测结果进行了比较.根据模式结果,我们还进一步讨论了“南海暖流”的形成和驱动机制.  相似文献   

Sensitivity to stress of the estuarine bivalve Macoma balthica from areas between the Netherlands and its southern limits (Gironde)     

H. Hummel  C. Amiard-Triquet  G. Bachelet  M. Desprez  J. Marchand  B. Sylvand  J.C. Amiard  H. Rybarczyk  R.H. Bogaards  J. Sinke  Y. De Wit  L. De Wolf 《Journal of Sea Research》1996,35(4):315-321

Variation in the sensitivity to stress of Macoma balthica was measured in several French and Dutch estuaries. For adult and juvenile Macoma balthica exposed to copper under conditions of starvation, differences in mortality rate, condition, glycogen, burrowing rate and copper content were assessed. No significant differences were observed between adults and juveniles; the influence of treatment and origin was always evident. Animals from the most southern estuaries, Loire and Gironde, near to the species's southern limit of distribution, showed, in the field, the strongest deviations for the ecophysiological traits measured, and were in the experiments the most sensitive to stress.  相似文献   

北部湾三维潮流场数值研究(英文)     

刘学刚  叶安乐 《中国海洋大学学报(自然科学版)》1988,(4)

本文对北部湾三维潮波进行了数值研究,并将所得结果与现有观测资料作了比较。通过比较发现两者相当一致。文中还绘制了M_2和K_1分潮的同潮图,并对其作了讨论。可以断定,北部湾的日潮优势是由日潮共振所引起的。M_2和K_1分潮流的水平分布表明,强流区位于它们各自的蜕化无潮点附近。还讨论了分潮流的铅直结构,可以看出这种结构十分接近实际分潮流场的特征。  相似文献