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901.
A.S. Brun 《Astronomische Nachrichten》2007,328(10):1137-1141
Using the 3-dimensional ASH code, we have studied numerically the instabilities that occur in stellar radiation zones in presence of large-scale magnetic fields, rotation and large-scale shear. We confirm that some configurations are linearly unstable, as predicted by Tayler and collaborators, and we determine the saturation level of the instability. We find that rotation modifies the peak of the most unstable wave number of the poloidal instability but not its growth rate as much as in the case of the m = 1 toroidal instability for which it is changed to σ = /Ω. Further in the case with rotation and shear, we found no sign of the dynamo mechanism suggested recently by Spruit even though we possess the essential ingredients (Tayler's m = 1 instability and a large scale shear) supposedly at work. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
902.
Coronal holes are regions of dominantly monopolar magnetic field on the Sun where the field is considered to be ‘open’ towards interplanetary space. Magnetic bipoles emerging in proximity to a coronal hole boundary naturally interact with this surrounding open magnetic field. In the case of oppositely aligned polarities between the active region and the coronal hole, we expect interchange reconnection to take place, driven by the coronal expansion of the emerging bipole as well as occasional eruptive events. Using SOHO/EIT and SOHO/MDI data, we present observational evidence of such interchange reconnection by studying AR 10869 which emerged close to a coronal hole. We find closed loops forming between the active region and the coronal hole leading to the retreat of the hole. At the same time, on the far side of the active region, we see dimming of the corona which we interpret as a signature of field line ‘opening’ there, as a consequence of a topological displacement of the ‘open’ field lines of the coronal hole. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
903.
Inspired by a recently observed axisymmetric field in a fully convective star we investigate the influence of an anisotropic diffusivity on the dynamo. We find that with reasonable assumptions for the anisotropy of the diffusivity and the α -effect the preference of axisymmetric modes is achieved. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
904.
905.
龙门山飞仙关断层传播褶皱磁组构特征及构造意义 总被引:3,自引:0,他引:3
沿龙门山南段冲断前锋带飞仙关断层传播褶铍剖面钻取了270个磁组构定向岩芯样品,对其进行了磁性矿物与磁组构分析。通过等温剩磁和三轴热退磁实验确定了样品中的主要载磁矿物为赤铁矿。磁组构测试结果显示27个采样点的磁组构为中间组构与构造组构两种类型。通过对各点磁组构特征及各项磁组构参数进行详细分析,再结合断层传播褶皱运动学模型,得出断层传播褶皱形成过程中岩石应变及磁组构演化:断层扩展前的平行层缩短作用把原始的沉积组构改造成为中问组构;在断层扩展过程中,两翼地层的旋转抬升产生的简单剪切作用对地层磁化率各向异性产生影响,使得校正的磁化率各向异性度Pj值局部升高,以及在剪切变形强烈的区域形成构造磁组构。 相似文献
906.
研究了深水铰接塔平台在波流联合作用下的组合共振特性。将平台顶部工作单元简化为集中质量,塔柱和浮力仓简化为均匀直杆,建立了铰接塔平台运动分析模型。考虑海流和波浪对平台的作用,应用Morison公式计算铰接塔平台瞬时位置所受水动力,依据拉格朗日原理建立了铰接塔平台的强非线性运动方程。分别考虑波浪作用和波流联合作用,采用数值计算方法,计算了高400m、塔柱直径15m的浮力塔平台的多种组合共振响应。研究表明,波浪作用下平台将出现2vm+vn组合共振,波流联合作用下平台将出现vm+vn组合共振、2vm+vn组合共振。 相似文献
907.
908.
909.
研究Winkler地基上材料非线性矩形薄板的参数共振-主共振问题。建立Winkler地基上材料非线性矩形薄板的动力学方程。利用Galerkin方法将其转化为非线性振动方程。应用非线性振动的多尺度法求得系统满足主参数共振-主共振条件的近似解,并进行数值计算。分析激励、调谐值、阻尼系数、非线性参数、几何参数对共振响应曲线的影响。 相似文献
910.
Variability of East Asian Winter Monsoon in Quaternary Climatic Extremes in North China 总被引:1,自引:0,他引:1
Huayu Lu Ko van Huissteden Jie Zhou Jef Vandenberghe Xiaodong Liu Zhisheng An 《Quaternary Research》2000,54(3):321
In order to examine high-frequency variations of East Asian winter monsoon in Quaternary climatic extremes, two typical loess–paleosol sequences in the Chinese Loess Plateau were investigated. Sandy layers in the loess deposits, the “Upper sand” and “Lower sand” (layers L9 and L15, respectively), which represent a high-resolution record of paleomonsoon changes, have been sampled at intervals of 5–6 cm from sections at Luochuan and Xifeng. The grain size and magnetic susceptibility was measured for all samples. The grain-size results (a proxy of winter monsoon strength) indicate that the winter monsoon strength fluctuated on a millennial timescale during cold climatic extremes, with climatic events of a few hundred to a few thousand years. However, the winter monsoon was relatively stable during warm periods. The magnetic susceptibility signal (a proxy of summer monsoon intensity) is practically constant over the same period. This is tentatively explained by the assumption that the summer monsoon intensity was too low to be recorded in the magnetic susceptibility signal. The intensified winter monsoon events show periodicities in a range of 1000 to 2770 yr, with a dominant cycle of approximately 1450 yr. The detection of this oscillation in older glacial stages strongly suggests that it may be a pervasive cycle of the cold climatic phases of the Quaternary. Millennial-scale variations of the winter monsoon may be caused by instability of the westerly jet, which is determined by temperature differences between the polar and the equatorial regions. 相似文献