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981.
Roman V. Baluev 《Celestial Mechanics and Dynamical Astronomy》2008,102(4):297-325
The full set of published radial velocity data (52 measurements from Keck + 58 ones from ELODIE + 17 ones from CORALIE) for
the star HD37124 is analysed. Two families of dynamically stable high-eccentricity orbital solutions for the planetary system
are found. In the first one, the outer planets c and d are trapped in the 2/1 mean-motion resonance. The second family of
solutions corresponds to the 5/2 mean-motion resonance between these planets. In both families, the planets are locked in
(or close to) an apsidal corotation resonance. In the case of the 2/1 MMR, it is an asymmetric apsidal corotation (with the
difference between the longitudes of periastra Δω ~ 60°), whereas in the case of the 5/2 MMR it is a symmetric antialigned one (Δω = 180°). It remains also possible that the two outer planets are not trapped in an orbital resonance. Then their orbital
eccentricities should be relatively small (less than, say, 0.15) and the ratio of their orbital periods is unlikely to exceed
2.3 − 2.5. 相似文献
982.
P. S. Soulis K. E. Papadakis T. Bountis 《Celestial Mechanics and Dynamical Astronomy》2008,100(4):251-266
We study the existence, linear stability and bifurcations of what we call the Sitnikov family of straight line periodic orbits
in the case of the restricted four-body problem, where the three equal mass primary bodies are rotating on a circle and the
fourth (small body) is moving in the direction vertical to the center mass of the other three. In contrast to the restricted
three-body Sitnikov problem, where the Sitnikov family has infinitely many stability intervals (hence infinitely many Sitnikov critical orbits), as the “family parameter” ż0 varies within a finite interval (while z
0 tends to infinity), in the four-body problem this family has only one stability interval and only twelve 3-dimensional (3D) families of symmetric periodic orbits exist which bifurcate from twelve
corresponding critical Sitnikov periodic orbits. We also calculate the evolution of the characteristic curves of these 3D
branch-families and determine their stability. More importantly, we study the phase space dynamics in the vicinity of these
orbits in two ways: First, we use the SALI index to investigate the extent of bounded motion of the small particle off the
z-axis along its interval of stable Sitnikov orbits, and secondly, through suitably chosen Poincaré maps, we chart the motion
near one of the 3D families of plane-symmetric periodic orbits. Our study reveals in both cases a fascinating structure of
ordered motion surrounded by “sticky” and chaotic orbits as well as orbits which rapidly escape to infinity. 相似文献
983.
I review the implications of our recent numerical simulations of the hydrodynamics of Roche lobe overflow in double white dwarf binaries, with special emphasis on the stability and survival of such systems after the onset of dynamically unstable mass transfer. We find that some of these systems may survive and enter a secular phase of orbital expansion, driven by gravitational radiation, undergoing slow and decreasing mass transfer, and be observable as AM Canum Venaticorum binaries. 相似文献
984.
985.
The excavated height of the left bank slope of the diversion power system intake in Jinchuan hydropower station is about 16o m. The stability and safety of the slope during construction and its operation/utilization become one of the most important geological engineering problems. At the same time, it is also crucial to select a safe and economic excavation gradient for the construction. We studied the problem of how to select a safe and economic slope ratio by analyzing the geological condition of the high slope, including the lithology, slope structure, structural surface and their combinations, rock weathering and unloading, hydrology, and the natural gradient. The study results showed that the use of an excavation gradient larger than the gradient observed during site investigation and the gradient recommended in standards and field practice manuals is feasible. Then, we used the finite element method and rigid limit equilibrium method to evaluate the stability of the excavation slope under natural, rainstorm and earthquake conditions. The calculated results showed that the excavated slope only has limited failure, but its stability is greatly satisfactory. The research findings can be useful in excavation and slope stabilization projects. 相似文献
986.
在两个水平主应力随深度呈线性增加的前提下,通过数学推导,建立了侧压系数、水平最大与水平最小主应力之比(σH/σh)以及剪应力相对大小μm等应力参数随深度变化的关系式.在此基础上,依据中国大陆1780条二维水压致裂和应力解除的原地应力测量数据,对多个应力参数随深度的变化进行了回归分析.结果显示,中国大陆地壳浅部的侧压系数随深度的变化呈完整的双曲线形态,通过稳定性检验说明,即使缺少较深的原地应力实测数据,只要有一定数量的测试深度超过1500 m的数据,仍然可以得到比较可信的侧压系数回归分析结果,在整个脆性上地壳的物性参数没有本质变化的前提下,可以利用地壳浅部的侧压系数回归分析结果推断脆性上地壳的2个水平主应力的取值范围;相对于侧压系数,在中国大陆地表以下几千米深度范围内,σHH/σ和μm的变化不大,更接近线性分布,σH/σh的拟合值在1.5左右,μm的拟合值在0.2左右,并且μm的线性集中程度更好.利用μm的大小来判断活动断裂的地震危险性具有一定合理性. 相似文献
987.
根系生物量是准确评估森林生态系统碳储量及碳汇功能的一个重要数据。采用标准木全收获法研究了新疆3种主要森林树种根系生物量,并分析了其在垂直梯度上的分配规律和随年龄的变化特点。结果表明:(1)新疆杨、西伯利亚落叶松和阿勒泰冷杉根系总生物量分别为43.409、42.152 t/hm2和16.19 t/hm2;(2)根系生物量随土壤深度增加迅速减少,约88.37%以上的根系生物量集中分布在0~40 cm土层中,在超过40 cm土层中,根系生物量降至较低水平(约为8.3%);(3)随林分年龄的增长,各林分根系总生物量呈递增趋势,在中龄林根系生物量增长速率达到最大。各级根系中粗根、中根及细根生物量随年龄的增长所占比例呈现递减规律,而其根桩和毛细根生物量差异较大,所占比例随年龄的增大基本呈增大趋势;(4)在表层土壤中各林分在林木的幼龄及中龄阶段根系生物量都处于较高比例,之后呈下降趋势后维持在一定水平基本不变,而深层土壤中各林分在幼龄阶段都处于一个较低的水平,后以一定比例逐渐增长;(5)新疆杨、西伯利亚落叶松和阿勒泰冷杉根系年平均生产力分别为:1.070 8 t·hm-2·a-1、1.014 4 t·hm-2·a-1和0.910 7 t·hm-2·a-1。 相似文献
988.
989.
以甘肃省西和县西山Ⅲ号滑坡为例分析了地震与降雨耦合作用对滑坡稳定性的影响。采用GEOSTUDIO软件对其进行了天然及地震降雨耦合作用两种条件下的数值模拟。通过计算结果对比可知,西山Ⅲ号滑坡在天然状态下处于稳定状态;地震降雨耦合作用对西山Ⅲ号滑坡的稳定会起到很强的削弱作用,滑坡将处于失稳状态。在此处采用的计算条件下,相同降雨量下地震与不同降雨强度的耦合作用显示,降雨强度越小雨水入渗相对越多,地震作用下超孔隙水压力影响区域越大,滑坡越不稳定。 相似文献
990.
欧美国家绅士化问题的城市地理学研究进展 总被引:2,自引:0,他引:2
欧洲和北美地区的绅士化研究代表着世界绅士化研究的主流与方向。在介绍绅士化的传统与衍生概念的基础上,对绅士化概念问世以来的主要理论解释派系进行分析总结,特别是从生产端和消费端进行解释的两大阵营。本文对欧美绅士化的三波发展浪潮进行介绍,并将半个世纪以来的绅士化研究划分为4 个发展阶段:绅士化现象描述阶段、两大阵营的激烈论战阶段、两种理论的相互融合阶段与绅士化政策应对研究阶段。在对绅士化作为全球城市发展战略和绅士化的主要社会空间效应做出简单评价以后,展望了世界范围内绅士化问题的研究前景;绅士化研究虽然已经走过了很长的一段路,但依然存在着巨大的研究空间。 相似文献