The system of the Milky Way, LMC and SMC     

Adam Ružčka 《Astrophysics and Space Science》2003,284(2):519-522

A simple sticky-particle numerical model has been developed in order to check whether extended structures of gas created due to the dynamical evolution of the Galaxy and the Magellanic Clouds system can be explained as remnants of a tidal interaction. Influence of dissipative nature of gaseous medium has been taken into account. The most remarkable features are: the Magellanic Stream, the common HI envelope surrounding both the LMC and SMC and the bridge extended between the Clouds. In contrast to previous works of Murai and Fujimoto (1980), Gardiner et al. (1994) and H and Rohlfs (1994) no presumptions were done on the actual galactocentric velocities of the Magellanic Clouds. The mean values of the LMC and SMC velocity vectors obtained from the Hipparcos proper motion measurements (Kroupa and Bastian, 1997) were used in order to verify whether they allow to reproduce the observed HI distribution. Numerical simulations showed that tidal forces are really significant for the evolution of extended structures such as the Magellanic Stream but this approach becomes unsufficient for the internal regions of galaxies where self-gravity and dissipative properties of the gas cannot be neglected. More precise proper motion measurements are urgently needed. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Global force balance of region 1 current system     

George L. Siscoe   《Journal of Atmospheric and Solar》2006,68(18):2119-2126

At times of strong solar wind forcing such as those that produce major magnetic storms, the region 1 current system dominates over the Chapman–Ferraro current system in mediating the transfer of force between the solar wind and the terrestrial system. The global force balance can be broken into two components, one involving the high-altitude part of the region 1 current system that is in contact with the solar wind (labeled here the HRS) and the other involving the low-altitude part of the region 1 current system that lies in the ionosphere (the LRS). Both communicate their J×B force to the geomagnetic dipole via a gradient in the magnetic field that they generate. In the HRS case the force acts to push the dipole away from the sun. This is the region 1 analog of the Chapman–Ferraro mechanism for transmitting the solar wind's force to the Earth. However, in the LRS case, the force (which is much stronger than in the HRS case) acts to push the dipole toward the sun, seemingly paradoxically. The LRS balances the ‘paradoxical’ sunward force on the dipole with an opposite force on the atmosphere. This paper uses MHD simulations to demonstrate the presence of both the normal force-transmitting gradient generated by the Chapman–Ferraro and the counter-Chapman–Ferraro gradient in the magnetic field generated by the region 1 current system.  相似文献   

锚索抗滑桩与岩土体相互作用研究     

李凯玲  门玉明 《水文地质工程地质》2006,33(1):20-22,26

就目前锚索抗滑桩的研究现状来看，基本上都是将锚索和抗滑桩分开计算，忽略了锚索与抗滑桩之间存在的相互作用关系。针对这一问题，对锚索-抗滑桩-岩土体相互作用系统的计算方法进行了研究。提出了在锚索抗滑桩设计计算中，除了应考虑锚索的强度外。还应该考虑锚索的伸长量，使其与桩的变形相协调。在此基础上，建立了新的锚索抗滑桩计算理论。本文用该方法进行了工程实例分析，并与其他计算方法所得结果进行了对比。  相似文献   

一次持续性强暴雨过程的平均特征   总被引：4，自引：1，他引：4       下载免费PDF全文

陈忠明闵文彬  高文良何光碧 《应用气象学报》2006,17(3):273-280

2004年9月2—6日四川盆地中东部发生了一次持续性强暴雨过程。利用时间平均合成分析方法对强暴雨维持期间 (9月3日20:00—5日08:00, 北京时) 的探测资料进行合成平均, 再对合成平均资料做诊断分析, 以揭示持续性强暴雨过程持续期的平均特征。诊断分析显示, 台风西进导致稳定的环流以及中低层大量的水汽输送为暴雨持续提供了背景条件。在时间平均流场上, 与暴雨相联系的中尺度系统十分显著, 它在对流层中低层表现为准东西向的中尺度辐合带, 在对流层高层表现为中尺度辐散带, 两者垂直耦合为深厚系统。此外, 在暴雨持续期间, 对流层低层大气运动表现出强烈的非平衡特征, 这种非平衡的动力强迫作用支撑着低层强辐合的维持。  相似文献   

应用低频信号提高高速玄武岩下的成像质量     

佘德平  管路平  徐颖  李佩 《应用地球物理》2006,3(2):112-119

针对高速玄武岩屏蔽层下深层成像困难的实际问题,采用波动方程波场数值模拟技术,根据玄武岩地层的特点,设计三个相应的简单高速玄武岩模型,通过对深层反射地震信号能量的分析,说明了低频地震信号既具有较强的穿透薄高速玄武岩屏蔽层的能力,也具有减弱因粗糙表面所产生的绕射噪音的能力。一个完整的2D玄武岩模型的模拟试验证明了利用低频信号可以提高高速玄武岩屏蔽层下深层成像的质量,实际资料的低通滤波处理也取得了预期的效果。  相似文献   

Seismic quantification of the explosions that destroyed the dome of Volcán de Colima, Mexico, in July–August 2003     

Vyacheslav M. Zobin  Carlos J. Navarro-Ochoa  Gabriel A. Reyes-Dávila 《Bulletin of Volcanology》2006,69(2):141-147

In July–August 2003, the andesitic lava dome at Volcán de Colima, México, was destroyed by a sequence of explosions that replaced the 2×10⁶ m³ dome with a crater 200 m across and 30 m deep. The two strongest explosions occurred on July 17 and August 28. The initial low-frequency impulses that they produced, which were recorded on broadband seismic records, allowed an estimation of the counter forces of the initiating process as being equal to 0.3×10¹¹ N and 1×10¹¹ N for the July and August events, respectively. The seismic characteristics follow the Nishimura-Hamaguchi scaling law for volcanic explosions, reflecting self-similarity in the processes initiating explosive events. The results also show that counter forces can discriminate between the sizes of explosive eruptions that are assigned the same magnitude by conventional methods of classification such as the Volcanic Explosivity Index. The increasing use of broadband seismometers may therefore provide the basis for using counter forces to determine the magnitude of explosive eruptions.  相似文献   

中国石油大厦复合土钉支护现场监测与分析   总被引：4，自引：1，他引：4  

杨耀辉  马昕  周予启 《岩土工程技术》2006,20(1):9-12

桩锚与土钉复合支护在国内得到广泛地应用,但其分析理论和设计方法尚欠不足,实践远超过理论。结合北京中国石油大厦深基坑支护工程,介绍了桩锚-土钉复合支护内力的监测方案。通过对复合土钉支护中桩、锚杆、土钉受力的现场测试和分析,研究了桩锚-土钉复合支护各部分的受力机理,对深入认识桩锚-土钉复合支护的受力机理和桩锚-土钉复合支护结构的优化设计提供参考。  相似文献   

对新型螺杆灌注桩的受力特征与破坏性状的探讨   总被引：1，自引：0，他引：1  

方崇  张信贵  彭桂皎 《岩土工程技术》2006,20(6):316-319

螺杆灌注桩是一种承载力高、造价低、施工方便、无环境污染的新桩型。根据螺杆桩的静荷载试验资料,深入分析了螺杆桩竖向荷载的传递机理,探讨了螺杆桩的受力特征和破坏性状,为今后螺杆桩的设计和施工提供可靠的依据。  相似文献   

A Combined-Power Model for the Distribution of Axial Force in Shaft Anchor along Its Length   总被引：1，自引：0，他引：1  

卫军  周锡武朱玉 罗昕 《中国地质大学学报(英文版)》2006,17(1):89-94

INTRODUCTIONThe anchorage of geomaterial , including shaftanchors and prestressed tendons ,is usually used ingeotechnical engineering. Owing to various advanta-ges ,these two anchorage types are widely used instructures in China ( Cao et al ., 2003 ; Fu et al .,1999 ;Lu et al .,1998 ; Li et al .,1995) . Shaft an-chors can be classifiedinto three kinds by the forceinthe shaft and cement grout :tensile ,press ,and sheartype (Lu et al .,1998) . The tensile type is the mostpopular in China…  相似文献   

塔克拉玛干沙漠腹地沙尘暴发生条件分析   总被引：4，自引：0，他引：4       下载免费PDF全文

李生宇雷加强  徐新文 《应用气象学报》2007,18(4):490-496

利用塔中气象站1997—2002年的气象资料, 从沙尘源丰富程度、风动力条件和空气稳定度等方面分析了塔克拉玛干沙漠腹地沙尘暴的成因。结果表明:在塔克拉玛干沙漠腹地, 沙尘源极为丰富, 为沙尘暴发生提供了必要条件, 降水基本不能改变沙面的湿润状况, 沙尘源丰富度不是沙尘暴发生的限制因子; 风动力是沙尘暴发生的重要条件, 而月平均风速和大风日数是风动力的重要定量表征指标; 空气稳定性也是沙尘暴发生的重要条件, 温度和天气过程是其重要标志, 沙尘暴发生与温度呈正相关, 沙尘暴多发生在夏季和午后; 降水是沙漠腹地天气过程的重要指标, 月降水日数和降水总量与沙尘暴日数呈正相关; 20世纪90年代以来沙尘暴逐年减少, 这种变化趋势可能与全球气候变化有关。  相似文献