用人工神经网络进行空间不完备数据的插补

在地学研究中,特别是区域性资料处理过程中,常常遇到“不完备数据”的问题,即所谓的“数据不全”。在尽量减小估计误差的条件下对缺失数据进行预测或插补,对于充分利用历史资料和已知信息,提高预测质量具有重要意义。利用径向基人工神经网络(RBF)同时具有自组织神经网络和回归网络的优点,可以对缺失数据进行预测。实际区域地球化学数据处理的结果表明,RBF网络对空间不完备数据的建模和预测具有优异的效果。     

用随机共振理论解释地震孕育过程与地震发生现象中的一个显著特征

地震孕震体是一个非线性双稳整系统,具备发生随机共振的条件。而地震的孕震过程与发生现为有量输入和大功率的能量输出。本用随机共振理论,解释了这一特征。     

基于大气降水的华北地区土壤湿度预测模型

基于引入随机变量的机理性模型方法,利用华北地区2000—2008年气象台站观测数据,以大气降水为随机变量,并考虑其延迟效应,利用回归方法建立了预测时效为1旬的土壤相对湿度预测模型。利用预测率和干旱等级预报精度两个评价指标,结合2009年土壤湿度实际观测数据,验证了预测模型预报率均在90%以上,绝大部分站点的干旱等级预报精度均在70%以上,得出该预测模型在华北地区应用的合理性,从而建立了一套客观、动态的土壤湿度预测方法,有利于及时掌握农田旱情程度和分布,主动采取防旱、抗旱应对措施。     

基于视速度的波场变换的叠前强相干噪音压制技术

针对叠前强横速相干噪音(如多次折射波、声波、面波),提出了基于视速度的波场变换叠前强相干噪音压制技术,该技术由基于视速度的波场变换技术和非线性滤波以及奇异值分解（SVD）滤波技术组成。首先由基于视速度的波场变换技术提供变换波场,然后,在变换波场上进行相应的滤波,最后将经过滤波处理的道集通过逆波场变换得到被压制噪音的叠前数据。着重分析了非线性滤波技术,同时也对基于视速度的波场变换叠前强相干噪音压制技术的原理、实现步骤、应用条件及效果给予了详细描述。     

数字化坐标转换中顾及模型误差的影响

针对数字化坐标转换的模型误差,给出了函数模型优选的标准,提出了衡量误差大小的精确度指标及实用估计方法,讨论了线性和非线性对数字化坐标转换的影响,结果表明采用二阶多项式拟合模型对数字化坐标转换的影响很小,在理论上更为合理,文中通过具体的数字化坐标拟合实例论证了这一点。     

Nonlinear analysis of footings on granular bed–stone column improved soft soil

In this paper, a model for the analysis of footings having finite flexural rigidity resting on a granular bed on top of stone columns improved saturated soft (clayey) soil has been proposed. Soft soil has been modeled as a Kelvin–Voigt body to represent its time dependent behavior. Pasternak shear layer has been used to represent the granular layer and the stone columns have been idealized by means of nonlinear Winkler springs. Nonlinear behavior of granular fill, soft soil and stone columns has been invoked by means of hyperbolic constitutive relationships. Governing differential equations for the soil–foundation system have been obtained and finite difference method has been adopted for solving these, using the Gauss-elimination iterative scheme. Detailed parametric study for a combined footing has been carried out to study the influence of parameters, like magnitude of applied load, flexural rigidity of footing, diameter of stone column, spacing of stone column, ultimate bearing capacity of granular fill, poor foundation soil and stone column, relative stiffness of stone columns and degree of consolidation, on flexural response of the footing.     

一种非线性搜索的Unix目录结构与搜索算法

阐述了一种全新的Hash目录结构,并说明了对这种目录的搜索算法.同时,对现有UMX文件系统进行了简要说明.     

Sediment non-linearity and attenuation of seismic waves: a study of accelerograms from Lefkas, western Greece

We investigate the dependence of the S-wave high-frequency spectral-decay parameter, κ (“kappa”) — a measure of wave attenuation — on ground-motion amplitude. 21 three-component accelerograms from two adjacent sediment sites in the town of Lefkas, western Greece, are used, representing 17 earthquakes with magnitudes M_w 4.7–7.0 and hypocentral distances 12–93 km. Recorded peak horizontal ground accelerations (PGA) and velocities (PGV) are 22–540 cm/s² and 1.3–54.5 cm/s.Fourier amplitude spectra are computed for S-wave windows, and the frequency range is visually determined where the high-frequency spectral decay can be approximated by a straight line on the linear-log plot; its slope (and hence κ) is computed by linear regression. κ is found to depend on hypocentral distance as κ=0.108+0.058R (r=0.518).As PGV increases from 1.3 to 54.5 cm/s, κ₀ (κ at 0 km, characterising inelastic attenuation in the site's subsurface geology) varies between 0.060 and 0.160 s. κ₀ is found to correlate very strongly with log MGA (r=0.645) (MGA — mean horizontal acceleration in the S-wave window) but also with log PGA (r=0.447) and log PGV (r=0.627). We attribute this behaviour to sediment non-linearity (shear-modulus degradation), resulting in the decrease of the site's dominant-resonance frequency (from about 3.5 to 2.4 Hz) and leading to the increase of κ₀. Our results imply that at sediment sites, an important contribution to κ comes from wave attenuation (damping) in the softest sediments and show that κ₀ is amplitude dependent, thus being a measure of sediment non-linearity.     

Error propagation in non-linear delay-time tomography

Delay-time tomography can be either linearized or non-linear. In the case of linearized tomography, an error due to the linearization is introduced. If the tomography is performed in a non-linear fashion, the theory used is more accurate from the physical point of view, but if the data have a statistical error, a noise bias in the model is introduced due to the non-linear propagation of errors. We investigate the error propagation of a weakly non-linear delay-time tomography example using second-order perturbation theory. This enables us to compare the linearization error with the noise bias. We show explicitly that the question of whether a non-linear inversion methods leads to a better estimation of the model parameters than a linearized method is dependent on the signal-to-noisc ratio. We also show that, in cases of poor data quality, a linearized inversion method leads to a better estimation of the model parameters than a non-linear method.     

非线性效应对风浪波面极大值和极小值分布的影响

通过分析实验室风浪观测结果研究非线性效应对波面极大值和极小值分布的影响。波面极大值和极小值累积概率的差异表明 ,与线性理论相比 ,波面极小值在平均波面以下的位置偏高。对实验结果的进一步分析表明 ,非线性效应使波面极大值在平均波面以上总概率高于线性理论结果 ,而概率密度峰值处波面极大值高度略低于线性理论结果。波面极小值在平均波面以上各位置出现的概率均高于线性理论结果 ,在平均波面以下的较低位置 ,波面极小值出现概率明显低于线性理论结果。