Time-domain dynamic analysis of dam–reservoir–foundation interaction including the reservoir bottom absorption

In this paper, time-domain dynamic analysis of dam–reservoir–foundation interaction is presented by coupling the dual reciprocity boundary element method (DRBEM) in the infinite reservoir and foundation domain and the finite element method in the finite dam domain. An efficient coupling procedure is formulated by using the sub-structuring method. The effects of the reservoir bottom absorption are included in the formulations. Sharan's boundary condition for the far-end of the infinite fluid domain is implemented. To verify the proposed scheme, numerical examples are carried out by comparing with the available exact solutions and finite–finite element coupling results for the dam–reservoir interaction. A complete dam–reservoir–foundation interaction is also studied by including the bottom absorption effects. Copyright © 2004 John Wiley & Sons, Ltd.     

Strategies for spatial and temporal extrapolation and interpolation of wet delay

. The excess radio-path delay due to the atmospheric water vapor, the wet delay, can be derived from water vapor radiometer (WVR) measurements. WVR data used for external calibration of space geodetic measurements are not always acquired in the directions of the space geodetic signal sources, thus extrapolation and interpolation methods for the wet delay are needed. We evaluate three different methods using approximately 10 days of WVR measurements. Two methods, the gradient method and turbulence method, use the directional information in the data, while the third method used is linear regression in time regardless of the direction of the observations. The turbulence method yielded at least 10% less RMS estimation error than the errors from the other two methods. Received: 20 May 1997 / Accepted: 15 December 1997     

Estimating regional deformation from a combination of space and terrestrial geodetic data

We discuss an approach for efficiently combining different types of geodetic data to estimate time-dependent motions of stations in a region of active deformation. The primary observations are analyzed separately to produce loosely constrained estimates of station positions and coordinate system parameters which are then combined with appropriate constraints to estimate velocities and coseismic displacements. We define noninteger degrees of freedom to handle the case of finite constraints and stochastic perturbation of parameters and develop statistical tests for determining compatibility between different data sets. With these developments, we show an example of combining space and terrestrial geodetic data to obtain the deformation field in southern California. Received: 23 January 1997 / Accepted: 30 September 1997     

航天雷达图像在1∶5万区调中的应用

利用航天雷达图像不仅可以对不同类型岩石进行识别,而且能够揭示一定埋深的隐伏地质体特征。将该图像应用于１∶５万区调中,能够丰富地质填图内容,提高区调成果质量。     

An experiment to study and control the Langmuir sheath around INTERBALL-2

The satellite INTERBALL-2 has an orbit with high inclination (62.8°), covering the altitude range between a few hundred and about 20000 km. The ambient plasma conditions along this orbit are highly variable, and the interactions of this plasma with the spacecraft body as well as the photo-electron sheath around it are considered to be interesting topics for detailed studies. The electric potential of the spacecraft with respect to the ambient plasma that develops as a result of the current equilibrium reacts sensitively to variations of the boundary conditions. The measurement and eventual control of this potential is a prerequisite for accurate measurements of the thermal plasma. We describe the purpose and technical implementation of an ion emitter instrument on-board INTERBALL-2 utilising ion beams at energies of several thousand electron volts in order to reduce and stabilise the positive spacecraft potential. First results of the active ion beam experiments, and other measures taken on INTERBALL-2 to reduce charging are presented. Furthermore, the approach and initial steps of modelling efforts of the sheath in the vicinity of the INTERBALL-2 spacecraft are described together with some estimates on the resulting spacecraft potential, and effects on thermal ion measurements. It is concluded that even moderate spacecraft potentials as are commonly observed on-board INTERBALL-2 can significantly distort the measurements of ion distribution functions, especially in the presence of strongly aniso-tropic distributions.     

A generation mechanism for chorus emission

A chorus generation mechanism is discussed, which is based on interrelation of ELF/VLF noise-like and discrete emissions under the cyclotron wave-particle interactions. A natural ELF/VLF noise radiation is excited by the cyclotron instability mechanism in ducts with enhanced cold plasma density or at the plasmapause. This process is accompanied by a step-like deformation of the energetic electron distribution function in the velocity space, which is situated at the boundary between resonant and nonresonant particles. The step leads to the strong phase correlation of interacting particles and waves and to a new backward wave oscillator (BWO) regime of wave generation, when an absolute cyclotron instability arises at the central cross section of the geomagnetic trap, in the form of a succession of discrete signals with growing frequency inside each element. The dynamical spectrum of a separate element is formed similar to triggered ELF/VLF emission, when the strong wavelet starts from the equatorial plane. The comparison is given of the model developed using some satellite and ground-based data. In particular, the appearance of separate groups of chorus signals with a duration 2–10 s can be connected with the preliminary stage of the step formation. BWO regime gives a succession period smaller than the bounce period of energetic electrons between the magnetic mirrors and can explain the observed intervals between chorus elements.     

X-CT机空间分辨率测试规范的探讨

空间分辨率有四种测试方法：分辨成排圆孔模型测极限分辨率;分辨成排条形模型测极限分辨率;扫描针模计算ＭＴＦ曲线;扫描条形模型计算ＭＴＦ曲线。前二种方法直观、简单,但模体重、体积大,且测量结果有一定主观因素,这两种方法用于日常质量控制为宜。第三种方法能得到完整的ＭＴＦ曲线,但计算过程复杂,本文推荐使用最后一种方法,并简述其原理,认为该方法测量ＭＴＦ曲线简便易行。     

Spatial and temporal study of nitrate concentration in groundwater by means of coregionalization

 Spatial and temporal behavior of hydrochemical parameters in groundwater can be studied using tools provided by geostatistics. The cross-variogram can be used to measure the spatial increments between observations at two given times as a function of distance (spatial structure). Taking into account the existence of such a spatial structure, two different data sets (sampled at two different times), representing concentrations of the same hydrochemical parameter, can be analyzed by cokriging in order to reduce the uncertainty of the estimation. In particular, if one of the two data sets is a subset of the other (that is, an undersampled set), cokriging allows us to study the spatial distribution of the hydrochemical parameter at that time, while also considering the statistical characteristics of the full data set established at a different time. This paper presents an application of cokriging by using temporal subsets to study the spatial distribution of nitrate concentration in the aquifer of the Lucca Plain, central Italy. Three data sets of nitrate concentration in groundwater were collected during three different periods in 1991. The first set was from 47 wells, but the second and the third are undersampled and represent 28 and 27 wells, respectively. Comparing the result of cokriging with ordinary kriging showed an improvement of the uncertainty in terms of reducing the estimation variance. The application of cokriging to the undersampled data sets reduced the uncertainty in estimating nitrate concentration and at the same time decreased the cost of the field sampling and laboratory analysis. Received: 23 July 1997 · Accepted: 31 March 1998     

空间VLBI与天文地球动力学

介绍了空间VLBI的精密定轨及其在天文地球动力学应用研究中的最新进展．指出因为空间VLBI的时延和时延率观测量同时涉及到射电参考系、动力学参考系和地固参考系,所以特别适合于参考系的直接连接工作．对为评价参考系连接的精度而发展的协方差分析理论也作了介绍,还分析了将时延和时延率资料用于精密定轨时遇到的困难及其解决办法．     

An analysis of the Hubble Space Telescope Fine Guidance Sensor Coarse Track mode

There are two guiding modes of the Hubble Space Telescope used for the acquisition of astronomical data by one of its six scientific instruments. The nominally more precise one is called Fine Lock and the other is known as Coarse Track. Two of the three Fine Guidance Sensors are locked onto Guide Stars, in one of these two modes, thus maintaining the spacecraft's line of sight to a few milli-arc seconds (nominally 7 milli-arc seconds for Fine Lock and 17 milli-arc seconds for Coarse Track). In this paper I report on the most realistic and extensive simulations to date of the Coarse Track guidance mode. These simulations clearly show that the precision of Coarse Track is influenced by one adjustable parameter and that for default operating conditions its precision is 12 milli-arc seconds. A factor of two improvement should be possible by modifying the key parameter which governs the precision of Coarse Track. The importance of this for the scientific mission on the Hubble Space Telescope is that the use of Coarse Track in place of Fine Lock will result in a 1/3 reduction of engineering overhead per scientific target acquisition.See text for a full explanation.