Steady dynamos in finite domains: an integral equation approach

The paper deals with the integral equation approach to steady kinematic dynamo models in finite domains based on Biot‐Savart's law. The role of the electric potential at the boundary is worked out explicitly. As an example, a modified version of the simple spherical α‐effect dynamo model proposed by Krause and Steenbeck is considered in which the α‐coeffcient is no longer constant but may vary with the radial coordinate. In particular, the results for the original model are re‐derived. Possible applications of this integral equation approach for numerical simulations of dynamos in arbitrary geometry and for an “inverse dynamo theory” are sketched.     

基于STM32的地震观测台站通用智能电源控制器的研制

电源是一切电子设备的心脏,是保障电子设备正常运行的关键,但目前针对地震观测台站使用电源的相关研究较少,本文在分析目前台站电源存在问题的基础上,开发设计了适用于台站的通用智能电源控制器,该控制器以STM32F107微处理器为核心,设计了相应的信号采集、电压控制及驱动电路,整机功耗约0.6W、工作电压范围DC7～23V,其通过外接方式即可对台站原有供电系统进行功能扩展和优化,满足低功耗、易操作、高可靠等设计要求,具有较好的推广价值。     

南西天山晚新生代沉积序列磁组构特征及其构造意义

喀什凹陷西部位于塔里木盆地、帕米尔构造带和南西天山构造带的交接处,在新生代以来接受了大量来自于南天山和帕米尔的沉积物,并记录了新生代以来南西天山构造抬升的信息。本文选择了位于南西天山山前的铁热克萨孜晚新生代剖面开展磁组构研究。铁热克萨孜剖面晚新生代沉积序列自下而上为一套整体上粒度逐渐变粗的陆相沉积,由河流湖泊相逐渐变为扇三角洲相,并最终变为冲积扇相和洪积扇相。岩石磁学结果的分析表明剖面晚新生代沉积序列中的主要磁性矿物为赤铁矿,仅在帕卡布拉克组下部为以磁铁矿为主。磁组构结果表明该剖面的磁组构为早期的同沉积弱变形磁组构,指示了当时构造应力的方向和变化。在22.1Ma以来南西天山山前晚新生代磁组构所反映的构造应力整体上为N-S向挤压,这与帕米尔和南天山的南北向持续汇聚作用相一致。在安居安组和西域组时期,应力方向由N-S向挤压变为NNE-SSW向挤压,这一变化可能是由塔拉斯-费尔干纳断裂的活动所导致的。塔拉斯-费尔干纳断裂(Talas-Fergana Fault, TFF)的右行走滑活动可能吸收了南西天山晚新生代的部分应变量,使得南西天山山前的构造应变量相对TFF以东的南天山山前地区要更小,使...     

日球层扰动变化的高纬地磁场响应

本文简要地论述了行星际过程与高纬地磁场扰动的关系,并对高纬极区地磁场变化对行星际过程的响应和地磁变化场的特点进行了分析研究和评述。     

利用核磁共振方法探查岩溶水

核磁共振（ＮＭＲ）找水方法是目前唯一直接找水的物探新方法,该方法可以探查各种类型的地下水。本文仅论述了在岩溶发育区常规电阻率方法找水时遇到的地质干扰。ＮＭＲ找水方法的原理,仪器的组成,并以实例说明了ＮＭＲ找水方法探查岩溶水的效果。     

髓外硬膜下肿瘤磁共振成像诊断(英)

MR检查65例髓外硬膜下肿瘤。所有病例均经手术和病理证实。40例神经鞘瘤,8例神经纤维瘤,17例脊膜瘤。髓外硬膜下肿瘤具有相同的定位MRI表现：1、推移脊髓向对侧移位;2、肿瘤侧上下蛛网膜下腔扩大。本文讨论了每一种肿瘤的信号特征。MRI在评价椎管肿瘤方面显示出世大的优越性：无电离辐射、无创伤性、无骨伪影、多平面成像、不需椎管内注入造影剂、多发病变一次成像,直接显示肿瘤信号及其与周围结构的关系,定位及定性准确率高。尤其是Gd－DTPA的应用,对微小肿瘤的检出及鉴别肿瘤囊变与实体部分都是十分有用的。目前,MRI在很大程度上已经替代椎管造影或CT检查。     

Gravity and aeromagnetic constraints on the structure of the Woods Mountains volcanic center, southeastern California

 The Woods Mountain volcanic center is a well-exposed, mildly alkaline volcanic center that formed during the Miocene in southeastern California. Detailed geologic mapping and geochemical studies have distinguished three major volcanic phases: precaldera, caldera forming, and postcaldera. Geologic mapping indicates that caldera formation occurred incrementally during eruptions of three large ignimbrites and continued into a period of voluminous intracaldera lava-flow eruptions. Rhyolitic ignimbrites and lava flows within the caldera are associated with large amplitude, circular gravity, and magnetic minima that are among the most prominent gravity and magnetic anomalies in southeastern California. Analysis of a Bouguer gravity anomaly map, reduced-to-the-pole magnetic intensity map, and three-dimensional gravity and magnetic models indicates that there is a single, funnel- to bowl-shaped caldera approximately 4 km thick and approximately 10 km wide at the surface. This model is consistent with other siliceous, pyroclastic-filled calderas on continental crust, except that most siliceous volcanic centers associated with more than one eruption are characterized by more than one caldera. Received: 20 December 1997 / Accepted: 15 October 1998     

Magnetic zoning and seismic structure of the South China Sea ocean basin

We made a systematic investigation on major structures and tectonic units in the South China Sea basin based on a large magnetic and seismic data set. For enhanced magnetic data interpretation, we carried out various data reduction procedures, including upward continuation, reduction to the pole, 3D analytic signal and power spectrum analyses, and magnetic depth estimation. Magnetic data suggest that the South China Sea basin can be divided into five magnetic zones, each with a unique magnetic pattern. Zone A corresponds roughly to the area between Taiwan Island and a relict transform fault, zone B is roughly a circular feature between the relict transform fault and the northwest sub-basin, and zones C, D, and E are the northwest sub-basin, the east sub-basin, and the southwest sub-basin, respectively. This complexity in basement magnetization suggests that the South China Sea evolved from multiple stages of opening under different tectonic settings. Magnetic reduction also fosters improved interpretation on continental margin structures, such as Mesozoic and Cenozoic sedimentary basins and the offshore south China magnetic anomaly. We also present, for the first time, interpretations of three new 2D reflection seismic traverses, which are of ~2,000 km in total length and across all five magnetic zones. Integration of magnetic and seismic data enables us to gain a better 3D mapping on the basin structures. It is shown that the transition from the southwest sub-basin to the east sub-basin is characterized by a major ridge formed probably along a pre-existing fracture zone, and by a group of primarily west-dipping faults forming an exact magnetic boundary between zones D and E. The northwest sub-basin has the deepest basement among the three main sub-basins (i.e., the northwest sub-basin, the southwest sub-basin, and the east sub-basin). Our seismic data also reveal a strongly faulted continent–ocean transition zone of about 100 km wide, which may become wider and dominated with magmatism or transit to an oceanic crust further to the northeast.     

贵州省麦岗水库沉积物磁性特征及其与粒度的关系

对贵州省麦岗水库沉积物环境磁性特征的研究表明,亚铁磁性矿物主导了沉积物矿物磁性特征,但同时也存在反铁磁性矿物等其他矿物,超顺磁颗粒在沉积物中广泛存在.在所选矿物磁性参数中,χlf、χfd、SOFT与粒度不相关;χARM、SIRM、F300与粒度相关,但相关系数不高;χARM/χlf、χARM/SIRM和粒度显著相关,可以作为粒度的代用指标.研究结果显示,磁性参数确实可以作为粒度的代用指标.但对比研究表明,在不同沉积环境,甚至相似沉积环境的沉积物中,矿物磁性参数和粒度的关系可能不同,在特定沉积环境中,利用磁性参数作为粒度的代用指标应该在充分研究的基础上进行,使研究结果更为可靠.