Are Pulsation and Magnetic Axes Aligned in roAp Stars?     

L. Bigot  W.A. Dziembowski 《Astrophysics and Space Science》2003,284(1):217-220

It is commonly assumed that in the rapidly oscillating Ap (roAp) stars the mode axis is aligned or nearly aligned with the magnetic field axis. This would be possible if the field is the only important effect causing departure from spherical symmetry. We show that even though these stars are slow rotators, the centrifugal force cannot be neglected. The consequence is that the modes cannot be in general symmetric about the magnetic field. We argue that such a symmetry is not implied by the observed coincidence between the field and pulsation amplitude maxima.  相似文献   

稻麦轮作农田近地层湍流通量计算方案对比研究     

刘昕晔  李煜斌 《气象科技》2024,52(3):434-445

稻麦轮作农田是我国典型农田类型,其模拟效果对我国农田气候模拟具有重要参考价值。气候中尺度模拟结果对近地层通量极为敏感,选择合适的通量计算方案对模拟效果至关重要。因此,对比分析稻麦轮作农田下不同的通量计算方案具有重要意义。本文选取了8种具有代表性的近地层湍流通量计算方案,采用寿县国家气候观象台实测资料对比分析了各方案在稻麦轮作农田的计算特征和差异。结果表明,在不同稳定度和不同风速情况下,各方案的误差特征各异。本文基于归一化标准差综合评价了各方案的准确度,总体而言,所有方案的动量通量总体平均归一化平均差为0.536,其中SS14(Sharan和Srivastava,2014年)方案最大为0.575,SS20(Sharan和Srivastava等,2020年)方案最小为0.517;所有方案的感热通量总体平均归一化标准差为0.638,其中GLGS20(Gryanik等,2020年)方案最大为0.871,SS14方案最小为0.476。此外,本研究还给出了稻麦轮作农田不同稳定层结和不同风速情况下各通量计算方案的误差特征。本文的研究结论,可为准确计算近地层湍流通量提供支撑。  相似文献   

近年新疆地震围绕塔里木盆地的顺时针迁移与塔里木盆地的顺时针旋转     

周伟  李媛 《地震地磁观测与研究》2021,42(2):188-189

塔里木盆地是我国最大的内陆盆地,作为稳定地块,被周围许多深大断裂所围限.王琪等(2000)基于天山及塔里木地区多年的GPS观测结果,认为塔里木盆地整体上作为刚性块体,相对于稳定的西伯利亚地块作顺时针旋转,其内部变形较小或基本不变形.赵俊猛等(2008)应用人工地震和天然地震等综合地球物理探测方法,获得青藏高原壳幔组成、...  相似文献   

Tides—a modern perspective     

Lakshmi H. Kantha 《Marine Geodesy》2013,36(4):275-297

Progress in tidal science has been rapid in recent years. The advent of precision altimetry has enabled, for the very first time in tidal history, an accurate measurement of tides in most of the global oceans. This has revolutionized our knowledge of tides and tidal processes. Combined with high‐resolution numerical models of tides (and other recent advances in astronomy and geodesy), this increased knowledge is providing valuable assistance in effecting closure on many outstanding problems in this three‐centuries‐old science. For example, we now know the dissipation rate of lunar tides to be 3.17 TW to within 2%. However, there do remain some outstanding issues. While we know the rate at which tidal energy is being dissipated in the global oceans, there is still considerable uncertainty as to the mechanisms, locations, and magnitudes of various tidal energy sinks. Imminent advances in shallow‐water barotropic and deep‐water baroclinic tides hold the prospect of a better understanding of these also. Improved knowledge of oceanic tides and high‐precision satellite measurements of tides are enabling better assessment of some matters of geophysical interest, such as the anelasticity and the length‐of‐day fluctuations of the Earth's mantle. It has been possible to map long‐period lunar tides more accurately and derive their contribution to the Earth's rotation rate fluctuations and its anelasticity at these frequencies. We discuss various aspects related to tides, including tidal dissipation and its consequences, as well as several other topics such as tidal energetics, internal tides, and long‐period tides, where considerable progress has been made in the last decade. Both oceanographic and geophysical implications are mentioned.  相似文献   

1米太阳望远镜光谱仪像旋转及消旋控制     

柳光乾  付玉  程向明 《天文研究与技术》2012,(1):86-92

光谱仪是1 m太阳望远镜的主要终端设备之一,该望远镜采用地平式的机架结构和修正的格里高利光学系统。在望远镜跟踪太阳时,由于地平式望远镜的自身运动特点和光学系统中平面反射镜的存在,其光谱仪狭缝所在平面上的太阳像随时间绕主光轴旋转,因此光谱仪必须进行消旋才能正常工作。首先深入研究了光谱仪狭缝平面上像的旋转变化,分析其旋转范围、速度和加速度随时角变化的特性,然后根据光谱仪消旋精度并结合像的旋转特性提出伺服系统位置检测和驱动电机的主要性能指标,最后给出光谱仪消旋伺服控制方案。  相似文献   

用轨迹球实现地物化资料三维立体图的旋转     

袁小龙  段新力  毕武  彭仲秋  黄显义  李永华 《物探化探计算技术》2012,34(5):622-624

为了从各个角度观察屏幕上的三维场景,可以通过鼠标的拖动来实现。通常的做法是使场景绕X、Y、Z旋转,但这样操作不方便,旋转效果不理想。有一种更好的方法是:为三维场景建立一个外接球,旋转外接球的同时旋转了球体内的三维场景,这种技术叫轨迹球技术。这里介绍了轨迹球技术的数学原理、计算方法,并用轨迹球技术在OpenGL环境下实现了地物化资料三维立体图的旋转,操作起来方便直观,人机交互体验良好。  相似文献   

Orientations of palaeotectonic features as a key to understanding the neotectonic block rotation of the Kocaeli peninsula,NW Turkey     

《International Geology Review》2012,54(4):329-344

Due to northward subduction of Neotethys, the ?stanbul zone collided with the Sakarya zone in northwest Turkey during the early Eocene. Subsequently, this region was subjected to compressional forces during the late Eocene–early Miocene period. Folds, thrusts and reverse faults developed approximately parallel to long axes of the ?stanbul zone. NNW–SSE oriented conjugate strike‐slip faults developed with continued contraction. In addition to the orientations of palaeotectonic features, the morphotectonic, stratigraphic and seismic characteristics expose differences between the northeastern Marmara peneplain and the southern Black Sea highland. This study reports causes of this diversity reflecting the neotectonic evolution of the ?stanbul zone. The diversity is related to the clockwise rotation of the Kocaeli peninsula between two dextral zone‐bounding faults and two sinistral block‐bounding faults. The principle factors of this process were the development of the North Anatolian fault zone (NAFZ) and the related evolution of the Adapazar?–Karasu fault zone (AKFZ), the Bosphorus fault zone (BFZ) and the Northern Boundary fault (NBF).  相似文献   

塔里木盆地阿瓦提凹陷周缘的晚新生代张扭性断层带   总被引：1，自引：0，他引：1       下载免费PDF全文

李曰俊  孙龙德  杨海军  张光亚  齐英敏  桑洪  刘亚雷  张强  文磊 《地质科学》2013,(1):109-123

塔里木盆地西北部的阿瓦提凹陷周缘发育晚新生代正断层,其中第四纪的正断层活动是塔里木盆地构造地质研究的新发现。这些正断层受先存基底断裂控制,平面上沿沙井子断裂带、阿恰断裂带和吐木休克断裂带右阶式雁列状分布,构成右阶左旋张扭性正断层带。剖面上,向下断达下古生界后不清楚,向上断至第四系上部,构成阶梯状或小型地堑(或负花状构造)构造。生长系数计算结果表明,正断层带形成于新近纪末,第四纪早-中期持续活动,到第四纪晚期停止活动。这些张扭性正断层带的成因是阿瓦提地块相对于周边地质体的顺时针旋转而致,其动力学来源于印度板块与欧亚板块陆-陆碰撞,在晚喜马拉雅山期依然持续作用而导致的远程效应。  相似文献   

South Australian seismicity 1967–1971     

Ian C. F. Stewart  Angela Slade  D. J. Sutton 《Australian Journal of Earth Sciences》2013,60(4):441-452

The South Australian seismograph network has been extended since 1968 so that most earthquakes of Richter magnitude ML ≥ 1.9 within the state are located accurately. Recurrence relations have been derived which define the seismicity of the known active areas. The seismic energy release has also been used to indicate the spatial variation in earthquake activity. Epicentre trends have been noted, and may be related to hypothesized movements on intracontinental plate boundaries.  相似文献   

Paleomagnetic study of the Late Silurian–Early Devonian Mt Daubeny Formation from the Broken Hill area,New South Wales     

C Vérard 《Australian Journal of Earth Sciences》2013,60(5):687-710

The geological map of the Broken Hill area in New South Wales shows a striking feature, the Grasmere Knee Zone, which consists of a major change in structural trend. North of the Grasmere Knee Zone, the analysis of the structure of the Late Silurian–Early Devonian Mt Daubeny Basin coupled with AMS measurements suggests that the basin has undergone two phases of folding. Correction of magnetic data from bedding orientation has consisted in unfolding sequentially fold F2 to obtain a simple syncline and unfolding fold F1. Although the fold tests, conglomerate test and dyke test may be considered to be positive concerning the high-temperature component (DAU-C_H), paleomagnetic results from the Mt Daubeny Formation (locality DAU) are subject to caution, in particular due to the complex unfolding procedure. If component DAU-C_H, carried by hematite, is interpreted to be primary in origin, the corresponding paleopole is consistent with an X-type of apparent polar wander path for Gondwana, in particular if one relies on the proposed optimum bedding correction. South of the Grasmere Knee Zone, the Mt. Daubeny Formation is considered to be rotated clockwise relative to the north. The tentative model presented herein proposes that a block corresponding to the Southwestern Subprovince of Lachlan Orogen indented the Tasmanides between the Central Subprovince of the Lachlan Orogen and the Delamerian Orogen from the mid-Devonian (Tabberabberan event) up to the Early Carboniferous, triggering rotations in the Broken Hill area. A later magmatic event, thought to be Early Cretaceous, may have induced fluid migration and deposition of magnetite leading to the occurrence of an important magnetic overprint (DAU-C_M).  相似文献