巴基斯坦Bahawalpur黄土岩石磁学特征及磁化率变化机制研究     

何玲珊  刘秀铭  马明明  毛学刚  A.R.Tabrez  吕镔  綦昕瑶  师永辉 《地球物理学报》2021,64(3):925-936

风成黄土是陆地上分布最广泛的沉积物之一,记载了各种古气候演化信息.目前巴基斯坦的黄土研究甚少,磁化率与气候对应的变化机制研究尚未开展.本文对位于巴基斯坦印度河平原Bahaw alpur地区新发现的黄土-古土壤剖面进行系统的岩石磁学研究,结合粒度和漫反射光谱(DRS)数据,讨论巴基斯坦黄土的磁化率变化机制.实验结果显示:...  相似文献   

基于双通道参考技术的磁共振地下水探测电磁噪声分布规律研究          下载免费PDF全文

林婷婷  于思佳  么晓康  韦萌  张扬 《地球物理学报》2021,64(1):355-362

磁共振地下水探测(MRS)技术能直接测量水中氢质子的拉莫尔进动,可表征地下水含水量和介质孔隙度等信息,因而获得了广泛应用.然而,MRS信号微弱,实际探测中电磁噪声强度大,若噪声未被有效去除,会导致后续水文参数解释不准确,采用"8"字形线圈或运用带参考线圈的噪声抵消等方法可抑制噪声干扰,但这些方法消噪效果的好坏取决于电磁...  相似文献   

黔西南"水银洞式"金矿成因研究     

唐波  张敏  黄建国  张竹如  聂爱国 《矿物学报》2007,27(3):450-455

水银洞式金矿受控于上二叠统龙潭组,其沉积环境为同生断裂夹持的泻湖．潮坪．局限台地。矿石宏观及显微组构表现为沉积-成岩特征,硫同位素、稀土元素、金及微量元素组合反映矿石与围岩特征一致,沉积-成岩期是水银洞式金矿主成矿期。  相似文献   

Observations on fabric evolution to a common micromechanical state at the soil-structure interface     

Hua-Xiang Zhu  Wan-Huan Zhou  Xue-Ying Jing  Zhen-Yu Yin 《国际地质力学数值与分析法杂志》2019,43(15):2449-2470

The fabric plays an important role in the mechanical behavior of granular material. The aim of this paper is to investigate the evolution of fabric in a soil-structure interface (SSI) to a large shearing in an effort to clarify whether and how this form of fabric evolution can lead to a common microstructure. Using the discrete element method (DEM), two-dimensional (2D) numerical interface shear tests were carried out, and certain macromechanical and micromechanical properties were exploited. All samples exhibited prominently localized strain in a zone covering the structure's surface (named the localized zone), and much lower density and higher soil fabric anisotropy levels were found inside this zone than outside it. Disregarding different initial void ratios, a common critical state microstructure was observed in large shear deformations of soil samples, with essentially the same fabric arrangement in terms of contact orientation and internal force transmission. Due to the systematic forming, buckling, and collapsing of force chains, an angular zone (called an α -zone), in which contact density was sluggish to varying degrees, appeared and extended around the main direction of the distribution of contact orientation inside the localized zone. The gradual deterioration of the force chains' stability, as a result of an increasing void ratio, seemed to drive the α -zone's extension and lead to the rare variation of microstructures in the critical state.  相似文献   

Localized ionization patches in the nighttime ionosphere of Mars and their electrodynamic consequences     

M.O. Fillingim  L.M. Peticolas  D.A. Brain  D. Lummerzheim 《Icarus》2010,206(1):112-119

Using an electron transport model, we calculate the electron density of the electron impact-produced nighttime ionosphere of Mars and its spatial structure. As input we use Mars Global Surveyor electron measurements, including an interval when accelerated electrons were observed. Our calculations show that regions of enhanced ionization are localized and occur near magnetic cusps. Horizontal gradients in the calculated ionospheric electron density on the night side of Mars can exceed 10⁴ cm⁻³ over a distance of a few tens of km; the largest gradients produced by the model are over 600 cm⁻³ km⁻¹. Such large gradients in the plasma density have several important consequences. These large pressure gradients will lead to localized plasma transport perpendicular to the ambient magnetic field which will generate horizontal currents and electric fields. We calculate the magnitude of these currents to be up to 10 nA/m². Additionally, transport of ionospheric plasma by neutral winds, which vary in strength and direction as a function of local time and season, can generate large (up to 1000 nA/m²) and spatially structured horizontal currents where the ions are collisionally coupled to the neutral atmosphere while electrons are not. These currents may contribute to localized Joule heating. In addition, closure of the horizontal currents and electric fields may require the presence of vertical, field-aligned currents and fields which may play a role in high altitude acceleration processes.  相似文献   

Bifurcation of the tail current sheet in Jovian magnetosphere     

P.L. Israelevich  A.I. Ershkovich  R. Oran 《Planetary and Space Science》2007,55(15):2261-2266

  相似文献   

Modeling of the magnetosphere of Mercury at the time of the first MESSENGER flyby     

Mehdi Benna  Brian J. Anderson  Scott A. Boardsen  Robert E. Gold  Rosemary M. Killen  Stamatios M. Krimigis  Ralph L. McNutt Jr.  William E. McClintock  James A. Slavin  Thomas H. Zurbuchen 《Icarus》2010,209(1):3-10

The MESSENGER spacecraft flyby of Mercury on 14 January 2008 provided a new opportunity to study the intrinsic magnetic field of the innermost planet and its interaction with the solar wind. The model presented in this paper is based on the solution of the three-dimensional, bi-fluid equations for solar wind protons and electrons in the absence of mass loading. In this study we provide new estimates of Mercury’s intrinsic magnetic field and the solar wind conditions that prevailed at the time of the flyby. We show that the location of the boundary layers and the strength of the magnetic field along the spacecraft trajectory can be reproduced with a solar wind ram pressure P_sw = 6.8 nPa and a planetary magnetic dipole having a magnitude of 210 R_M³ − nT and an offset of 0.18 R_M to the north of the equator, where R_M is Mercury’s radius. Analysis of the plasma flow reveals the existence of a stable drift belt around the planet; such a belt can account for the locations of diamagnetic decreases observed by the MESSENGER Magnetometer. Moreover, we determine that the ion impact rate at the northern cusp was four times higher than at the southern cusp, a result that provides a possible explanation for the observed north-south asymmetry in exospheric sodium in the neutral tail.  相似文献   

Jovian plasma torus interaction with Europa: 3D hybrid kinetic simulation. First results     

A.S. Lipatov  J.F. Cooper  E.C. Sittler  D.G. Simpson 《Planetary and Space Science》2010,58(13):1681-1691

The hybrid kinetic model supports comprehensive simulation of the interaction between different spatial and energetic elements of the Europa moon-magnetosphere system with respect to variable upstream magnetic field and flux or density distributions of plasma and energetic ions, electrons, and neutral atoms. This capability is critical for improving the interpretation of the existing Europa flyby measurements from the Galileo orbiter mission, and for planning flyby and orbital measurements (including the surface and atmospheric compositions) for future missions. The simulations are based on recent models of the atmosphere of Europa ( [Cassidy et al., 2007] and [Shematovich et al., 2005]). In contrast to previous approaches with MHD simulations, the hybrid model allows us to fully take into account the finite gyroradius effect and electron pressure, and to correctly estimate the ion velocity distribution and the fluxes along the magnetic field (assuming an initial Maxwellian velocity distribution for upstream background ions). Non-thermal distributions of upstream plasma will be addressed in future work. Photoionization, electron-impact ionization, charge exchange and collisions between the ions and neutrals are also included in our model. We consider two models for background plasma: (a) with O⁺⁺ ions; (b) with O⁺⁺ and S⁺⁺ ions. The majority of O₂ atmosphere is thermal with an extended cold population (Cassidy et al., 2007). A few first simulations already include an induced magnetic dipole; however, several important effects of induced magnetic fields arising from oceanic shell conductivity will be addressed in later work.  相似文献   

Magnetic field investigations during ROSETTA's 2867 Šteins flyby     

H.U. Auster  I. Richter  G. Berghofer  U. Motschmann 《Planetary and Space Science》2010,58(9):1124-1128

During the 2867 Šteins flyby of the ROSETTA spacecraft on September 5, 2008 magnetic field measurements have been made with both the RPC orbiter magnetometer and the ROMAP lander magnetometer. These combined magnetic field measurements allow a detailed examination of any magnetic signatures caused either directly by the asteroid or indirectly by Šteins’ different modes of interaction with the solar wind. Comparing measurements with simulation results show that Šteins does not posses a significant remanent magnetization. The magnetization is estimated at less than 10⁻³ A m²/kg. This is significantly different from results at 9969 Braille and 951 Gaspra.  相似文献   

行星际磁通量绳尺度的幂律谱分布     

冯恒强  曹行健 《天文研究与技术》2010,7(1)

利用最小二乘法拟合了1995年1月至2001年9月Wind卫星观测到的行星际磁通量绳。根据拟合所得磁通量绳的直径,分析了行星际磁通量绳在这段时间内的发生率随磁通量绳直径D变化的关系,发现磁通量绳的发生率P(D)随直径D的变化可近似以幂律形式表示为:P(D)≈64D-0.768。行星际磁通量绳的发生率相对其直径的幂律分布表明所有行星际磁通量绳很可能是同一类现象且有共同的源,即它们都是太阳上日冕物质抛射的行星际对应物,只不过小尺度的磁通量绳对应较小的日冕物质抛射。最后,对行星际磁通量绳、日冕物质抛射和太阳耀斑的可能关系做了讨论。  相似文献