大型射电望远镜背架精密安装技术

对65 m射电望远镜的背架安装做了尝试,取得较满意的结果.针对天线背架尺寸大、质量重、焊接变形大、几何精度要求高等特性,采用全站仪工业测量系统实现背架的快速、无接触、高精度定位测量,点位测量精度优于1 mm;采用独特的施工工艺和焊接技术,最大限度控制焊接变形,最终点位偏差优于1.5 cm.提出基于设计坐标系建立安装测量...     

Characterization of the mesospheric sodium layer at La Palma

We present the results of a mesospheric sodium monitoring programme at La Palma carried out through five campaigns of one week each, from 1999 September to 2000 August. The yearly averaged parameters of the layer (the sodium column density and the width) are given. We show that the short time-scale dynamics of the layer are governed by the sporadic layers with an average frequency of one event per night. The influence of the short time-scale dynamics of the layer on an adaptive optics system working on the William Herschel Telescope is quantified. It appears that it is a small effect in terms of defocus error. Finally, we present data obtained during the Perseid meteor shower and show that the dynamics of the sodium layer undergoes a transition with the meteoric activity.     

Intrinsic intraday variability in the gravitational lens system B0218+357

Radio monitoring of the gravitational lens system B0218+357 reveals it to be a highly variable source with variations on time-scales of a few days correlated in both images. This shows that the variability is intrinsic to the background lensed source and suggests that similar variations in other intraday variable sources can also be intrinsic in origin.     

SCATTERING PHASE MATRICES OF ICE CRYSTALS WITH HEXAGONAL PRISM AND TRIANGULAR PYRAMID FORM—A VECTOR RAY TRACING METHOD

The work presented previously by the authors(Cai and Liou,1982)has been extended in this paper.By making use of our improved model the calculations on scattering phase matrices of hexagonal prismice crystals(HPIC)have been conducted for monodisperse and polydisperse systems.Compared with themodel of Cai and Liou,the required computational quantity is decreased by about two orders of magni-tude and the errors of results are less for the new model.Meanwhile,the scattering phase matrices of triangularpyramid ice crystals(TPIC)are also computed in the paper,and the comparison between the scatterings of thetwo forms of ice crystals is performed.     

Scattering of elastic wave by a partially sealed cylindrical shell embedded in poroelastic medium

Scattering of an elastic wave by a cylindrical shell embedded in poroelastic medium is investigated theoretically with the assumption that the shell material is also a porous elastic medium. The porous medium is modellized via Biot's theory and the scattering by cylindrical shell is expressed by the definition of scattering matrix. The normal mode expansion technique is employed for analysing the scattering field, and the asymptotic solutions of displacements, stresses and pore pressure are derived. Two limiting cases‐scattering by a poroelastic cylinder in Biot medium and a elastic cylindrical shell in elastic medium are obtained from the general solutions. The dispersion curves of displacement amplitude at the interface of shell and medium is compared with the case of elastic shell. The scattering amplitude associated with the fast, slow and transverse waves are identified by numerical simulation. Furthermore, the influence of the poroelastic property of shell material on scattering amplitude is analysed. Copyright © 2005 John Wiley & Sons, Ltd.     

逆散射级数法预测层间多次波的算法改进及其策略

波动方程预测层间多次波有两类算法.一是由Berkhout和Verschuur（1998）提出的基于CFP（共聚焦点）延拓的算法,另一是由Weglein（1997）等人提出的基于逆散射级数法的算法.ISS（逆散射级数）算法具有不依赖速度模型的优点,但是其计算成本很高.本文改进了Weglein提出的1-D预测公式,提高了计算效率.从理论方面,改进算法的计算速度提高了大约12倍.实际结果表明其计算速度更快,提高近80倍左右,主要原因在于后者的空间复杂度小.此外,由于时间-空间域比伪深度-波数域的层间多次波预测有更多的优点,本文推导了1.5-D时间-空间域ISS层间多次波预测算法,该算法有计算速度快、预测噪音小、适应观测系统能力强和不依赖地震子波等优点.在实际应用中,计算成本高是ISS预测层间多次波算法的主要障碍.因此,本文还讨论了预测层间多次波的策略.结合本文提出的改进算法和应用策略,能够在实际地震资料处理中较好地应用ISS预测层间多次波.     

基于多种方法联合反演的河床岩性结构特征研究

河床结构探测是研究河水-地下水转化过程的关键,复杂河床结构探测过程中,单一物探方法通常精度不高。本文采用多普勒声学流速仪、地质雷达法、高密度电阻率法相结合,在淮北平原典型工作区进行河床形态和沉积物分布特征探测,构建了完整的联合反演河床岩性结构特征的技术体系,取得了较好的识别效果。结果表明:新汴河节制闸上游呈"蝶形",河床结构均匀,底泥厚度变化范围小;下游河床形态受分水坝影响起伏较大,河床形态不平整,底泥厚度为0.8~1 m;涡河处河道形态呈半椭圆形,且底泥两岸薄中间厚。韩村剖面受抽砂干扰严重,河床出现中间高两侧低的情况,底泥分布不均匀;两河口断面下存在弱透水层(粉质黏土),下方为承压含水层,其潜水含水层分布不均匀。实践证明,多种技术联合反演在河床形态探测上能够相互印证,提高成果解译的可靠性和准确性,为河水-地下水转化研究提供支撑。     

浅层气对下伏地层深度预测影响定量研究及在渤海B油田中的应用

浅层气的存在造成下伏地层地震反射出现假象,使得深度预测不准确,增大了油田开发钻井风险。为提高浅层气下伏地层深度预测精度,利用理论模型分析量化描述浅层气对下伏地层的影响范围和影响程度,同时通过正演模拟手段构建时差定量校正量版,指导储层高精度深度预测。根据研究成果和认识,成功解释了渤海B油田两口已钻井深度误差出现的原因,并进一步利用时差校正量版提高了该油田区目标储层深度预测的精度,成功指导了后续多口开发井的准确钻探。