Secular variations ing 1 0 component of geomagnetic field and its origin

The secular variations (SV) ing ₁ ⁰ of geomagnetic field, caused by the interaction between the geomagnetic field and the radial fluid-flow of the outer-core, are discussed with both statistical and analytic methods. When the value ofg ₁ ⁰ s ₂ ⁰ is relatively high compared with other terms, SV ing ₁ ⁰ is characterized by exponential change. When the effect of non-dipole field is notable, SV ing ₁ ⁰ shows complex features. Especially when the value of g ₁ ⁰ is close to zero, SV ing ₁ ⁰ is completely determined by the random process of non-dipole fields. Project supported by the National Natural Science Foundation of China (Grant No. 49429405) and by the Chinese Academy of Sciences.     

基于半参数回归的DDM内插方法

提出了一种基于半参数回归的数字水深模型(DDM)内插方法。将原始水深数据误差和内插函数的逼近误差分别视作数字水深模型的偶然误差和系统误差部分,构建DDM内插的半参数回归模型;基于距离法与L曲线法,分别确定正规化矩阵R与平滑因子α;采用按方位取点的加权平均法,估计内插函数在任意节点处的逼近误差。实验结果表明:所提方法提高了DDM的构建质量;海底地形复杂程度越大,所提方法对DDM构建质量的提高程度越大。     

An explicit approximation to the wavelength of nonlinear waves

An explicit and concise approximation to the wavelength in which the effect of nonlinearity is involved and presented in terms of wave height, wave period, water depth and gravitational acceleration. The present approximation is in a rational form of which Fenton and Mckee's (1990, Coastal Engng 14, 499–513) approximation is reserved in the numerator and the wave steepness is involved in the denominator. The rational form of this approximation can be converted to an alternative form of a power-series polynomial which indicates that the wavelength increases with wave height and decreases with water depth. If the determined coefficients in the present approximation are fixed, the approximating formula can provide a good agreement with the wavelengths numerically obtained by Rienecker and Fenton's (1981, J. Fluid Mech. 104, 119–137) Fourier series method, but has large deviations when waves of small amplitude are in deep water or all waves are in shallow water. The present approximation with variable coefficients can provide excellent predictions of the wavelengths for both long and short waves even, for high waves.     

热带大气能量频散波射线的低频动力学特征

首先在非零频波条件下采用有、无辐散两类数学模型 ,讨论热带大气低频波传播动力特征 ,研究结果表明 ,非零频的波频率参数是热带大气低频振荡源能量频散波路径及其波振幅的关键影响因子 ,且热带地区低频振荡的经向传播与其伴随着的强对流云团有显著相关 ,并与热带低纬 β因子等相关。文中还进一步揭示了低纬大气低频振荡经向传播伴随的积云对流现象及向高中纬传播机理 ,描述了 WKB近似方法数学模型及其波射线方程解模态对大气低频动力特性及其水汽分布垂直结构、不稳定层结等因子的响应特征。     

基于GIS的任意发生元Voronoi图逼近方法

许多地理问题的空间分析中需要采用Voronoi图,但是目前我们尚缺乏一些简单的易于实现的构建任意发生元Voronoi图的方法,也缺乏一个能直接生成任意发生元Voronoi图的软件,为此我们提出了一种基于GIS的构建任意发生元的未加权Voronoi图的逼近方法。首先用有限点来逼近原始发生元,然后构建这些点发生元Voronoi图,最后消除那些属于同一发生元的顶点和边,即得到原始发生元的逼近的Voronoi图。在该算法的具体实现过程中,充分利用了现有GIS软件可以生成点发生元Voronoi图的特性和处理空间数据的能力。试验结果表明,这种方法可以生成未加权的任意形状发生元的逼近Voronoi图,能满足地理问题空间分析的需要。如地理客体可以是点状地理客体(城市、县城、交通枢纽、商业中心和金融中心等)、线状地理客体(交通运输线、经济地带和河系等)、面状地理客体(经济区、公园和绿地等)或者它们的组合,它们的空间影响范围或空间服务范围都可以采用Voronoi图来界定。     

长期GPS精密星历分析与轨道参数的函数逼近

以力学模型为基础,只能分析GPS卫星在短时间内的变化规律,而利用IGS提供的精密星历可以分析卫星在长时间段内的变化规律。基于精密星历研究了计算GPS卫星轨道参数的方法,然后对轨道参数在长时间段内的变化情况进行了分析,给出了分析的主要结果,并提出用正弦函数对轨道参数进行逼近,以得到GPS轨道的解析模型。     

非自治微分系统的周期解

本之应用李亚普诺夫变换和数值逼近的方法,研究了几类非自治非线性微分系统周期解的存在性及唯一性,得到了一些新的结果。     

一维波动方程的近似解及其在浅海声场计算中的应用

本文给出一维波动方程的一组近似解,它具有WKB解的简洁性,但又克服了WKB解在反转点附近发散的困难。文中用其结果计算了具有粗糙界面的负声速梯度浅海中的简正波声场。     

Scales of Reservoir Heterogeneities and Impact of Seismic Resolution on Geostatistical Integration

Seismic measurements may be used in geostatistical techniques for estimation and simulation of petrophysical properties such as porosity. The good correlation between seismic and rock properties provides a basis for these techniques. Seismic data have a wide spatial coverage not available in log or core data. However, each seismic measurement has a characteristic response function determined by the source-receiver geometry and signal bandwidth. The image response of the seismic measurement gives a filtered version of the true velocity image. Therefore the seismic image cannot reflect exactly the true seismic velocity at all scales of spatial heterogeneities present in the Earth. The seismic response function can be approximated conveniently in the spatial spectral domain using the Born approximation. How the seismic image response affects the estimation of variogram. and spatial scales and its impact on geostatistical results is the focus of this paper. Limitations of view angles and signal bandwidth not only smooth the seismic image, increasing the variogram range, but also can introduce anisotropic spatial structures into the image. The seismic data are enhanced by better characterizing and quantifying these attributes. As an exercise, examples of seismically assisted cokriging and cosimulation of porosity between wells are presented.     

Synthetic seismograms in heterogeneous media by one-return approximation

When reverberations between heterogeneities or resonance scattering can be neglected but accumulated effects of forward scattering are strong, the Born approximation is not valid but the De Wolf approximation can be applied in such cases. In this paper, renormalized MFSB (multiple-forescattering single-backscattering) equations and the dual-domain expression for scalar, acoustic and elastic waves are derived by a unified approach. Two versions of the one-return method (using MFSB approximation) are given: One is the wide-angle dual-domain formulation (thin-slab approximation); the other is the screen approximation. In the screen approximation, which involves a small-angle approximation for the wave-medium interaction, it can be seen clearly that the forward scattered, or transmitted waves are mainly controlled by velocity perturbations; while the backscattered or reflected waves, by impedance perturbations. The validity of the method and the wide-angle capability of the dual-domain implementation are demonstrated by numerical examples. Reflection coefficients of a plane interface derived from numerical simulations by the wide-angle method match the theoretical curves well up to critical angles. For the reflections of a low-velocity slab, the agreement between theory and synthetics only starts to deteriorate for angles greater than 70°. The accuracy of the wide-angle version of the method could be further improved by optimizing the wave-number filtering for the forward propagation and shrinking the step length along the propagation direction.