Estimation of a multidimensional covariance function in case of anisotropy

A model of a multivariate covariance function with an ellipsoidal directional correlation scale has been developed. The axes of the ellipsoidal scale are related to the eigenvalues and eigenvectors of a matrix B which characterizes the ellipsoid of the range of influence. The matrix B is found to be related to a matrix T which can be estimated directly from sparse sampling data and can be used to determine estimates of the matrix B. The method has been applied to both two-dimensional and three-dimensional cases. The numerical results show that the satisfactory accuracy is obtained with sparse sampling data from an anisotropic random function.     

地电供电系统对地磁观测的影响试验

通过试验，认为地电供电系统对地磁观测的影响主要是来自供电导线产生的磁场，其强与公式Ｈ＝１／１０．２Ｉ／ｒ计算结果基本相符。而地下电流产生的磁场是很弱的，这对避免和减小其影响提供了新思维。     

顾及起始数据误差影响时单位权中误差的估值

本文推导了在附有条件的间接平差和附有未知数的条件平差两种方法中,顾及起始数据误差影响时,计算单位权中误差估值(?)的公式,并以两个实例说明,平差时应该考虑起始数据误差对(?)的影响。     

考虑高振型影响的结构层间位移能力谱分析方法

工程界普遍采用的能力谱分析方法是建立在结构单自由度简化假设基础上，利用结构基本振型来进行能力分析。虽然此简化假设可以为工程界提供一种简便的分析方法，但从其分析效果来看，简化方法并不能很好地反映结构真实地震反应。高振型对结构局部变形的影响在分析结构动力反应特性中是很重要的因素，不应忽略掉。基于上述对现有能力谱分析方法不足之处的考虑，从提高结构能力谱分析方法的准确性出发，本文在Chopra能力谱分析方法的基础之上，根据我国振型分解反应谱思想，在能力谱分析方法中引入了结构高振型的影响分析，并提出了考虑结构高振型影响的结构层间位移能力谱分析方法的一般步骤。通过平面框架结构体系的算例分析，说明上述推荐方法在改进能力谱分析精度上的有效性。     

FD-125测氡仪观测中值得注意的几个问题

论述了FD-125测氡仪在水氡观测中值得注意的几个问题：①仪器的供电系统中不应有线路接触不良；②仪器接地线应避免接触不良；③其他用电器内部线路也不应有接触不良；④引起电场和磁场变化的大功率用电设备不应在测量时间内使用；⑤供电电路中电压尽可能避免大幅度波动等。上述因素对氡测值都有影响，影响幅度可达10％以上。     

Modeling doline populations with logistic growth functions

Initiation and evolution of a large karst depression population consisting of parent and daughter dolines were spatially and temporally modeled using logistic growth functions. Logistic growth models are well suited for analyzing doline population initiation and evolution because they reflect the density‐dependent growth mechanisms present in the evolution of karst depressions. Seven assumptions based upon previous studies were refined into mathematical statements and tested using more than 2000 dolines from a subpopulation of both parent and daughter karst depressions on the Western Highland Rim and Pennyroyal Plain of Tennessee and Kentucky. Logistic growth models quantify the initiation and evolution of doline populations and interface well with recent models describing the evolution of three‐dimensional conduit systems. Logistic growth models should apply to modeling other doline populations in karst terranes with hydraulically efficient, three‐dimensional conduit systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Two different methods of geoidal height determinations using a spherical harmonic representation of the geopotential, topographic corrections and the height anomaly–geoidal height difference

 It is suggested that a spherical harmonic representation of the geoidal heights using global Earth gravity models (EGM) might be accurate enough for many applications, although we know that some short-wavelength signals are missing in a potential coefficient model. A `direct' method of geoidal height determination from a global Earth gravity model coefficient alone and an `indirect' approach of geoidal height determination through height anomaly computed from a global gravity model are investigated. In both methods, suitable correction terms are applied. The results of computations in two test areas show that the direct and indirect approaches of geoid height determination yield good agreement with the classical gravimetric geoidal heights which are determined from Stokes' formula. Surprisingly, the results of the indirect method of geoidal height determination yield better agreement with the global positioning system (GPS)-levelling derived geoid heights, which are used to demonstrate such improvements, than the results of gravimetric geoid heights at to the same GPS stations. It has been demonstrated that the application of correction terms in both methods improves the agreement of geoidal heights at GPS-levelling stations. It is also found that the correction terms in the direct method of geoidal height determination are mostly similar to the correction terms used for the indirect determination of geoidal heights from height anomalies. Received: 26 July 2001 / Accepted: 21 February 2002