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821.
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We simulated quartz-type GeO2 and investigated its high-pressure transformation using the molecular dynamics (MD) simulation method with a model potential. The calculated results under hydrostatic compression indicated that a pressure-induced amorphization of quartz-type GeO2 originated from the mechanical instability of the quartz lattice as, in previous theoretical studies of SiO2. Furthermore, quartz-type GeO2 directly transformed to a rutile-like structure with only subtle displacements of ions under σ
x
y
imposed shear stressed decompression. This is the first reproduction of the quartz-to-rutile transformation. A possible pathway
of this transition is proposed in this study.
Received: 14 April 1999 / Revised, accepted: 11 August 1999 相似文献
824.
Behaviour of industrially added boron in the well mixed Ambika river estuary of South Gujarat, India has been studied along with that of calcium and magnesium. The ratios of Ca : Cl and Mg : Cl at varying chlorinities were always within the normal ranges found in river water at one end and seawater at the other end. B : Cl exceeded the river water end limit at the ebb tide at an upstream station. Percentage addition or removal of boron, calcium and magnesium was calculated using the concept of the theoretical dilution line. The external input raised the boron concentration by 263% in the vicinity of the industrial discharge. A correlation coefficient of ?0·82 between chlorinity and percentage addition or removal of boron supports the theory of boron incorporation in sediments in amounts proportional to salinity. Inverse relationship between percentage addition or removal of boron and suspended solids was observed. Behaviour of calcium and magnesium was in line with the replacement of Ca2+ ions occupying the majority of ion-exchange sites in riverine clays by Mg2+, Na+ and K+ during their first encounter with seawater. 相似文献
825.
本文阐述了嫩江公路大桥原型及模型动力试验,通过实测数据分析,给出了该桥的动态特性及振动响应。 相似文献
826.
用偏微分方程组特征理论研究层状并以垂直轴为对称轴的横向各向同性(TIV)介质的参数反演问题,首先从弹性波运动方程与TIV介质的应力-应变关系导出了平面波耦合方程组的特征型.根据奇性分析与特征积分法给出了连续情形下的特征线边界条件,连续清形下的波场延拓方程即平面波耦合方程组的特征型与特征线边界条件组成了层状TIV平滑介质、弱间断介质参数反演问题的基本方程组.并导出了间断情形下的波场延拓方程与特征线边界条件,这些方程组可用于层状介质(间断情况)的参数反演.基于这些基本方程组,探讨了利用地面多分量地震资料反演层状TIV介质多个弹性参数的问题. 相似文献
827.
Geotechnical site conditions that can be very different due to changes in thickness and properties of soil layers, depth of bedrock and water table are among the main factors controlling earthquake characteristics on the ground surface. Soil layers subjected to cyclic stresses may lead to degradation of stress–strain and shear strength properties. The laboratory tests were conducted to evaluate the changes in the stress–strain and shear strength characteristics in terms of threshold cyclic shear stresses and cyclic yield stress. The effects of local site conditions are assessed based on geotechnical site conditions and earthquake source characteristics. 相似文献
828.
In this work, a hybrid boundary integral equation method (BIEM) is developed, based on both displacement and hypersingular traction formulations, for the analysis of time-harmonic seismic waves propagating through cracked, multi-layered geological regions with surface topography and under plane strain conditions. Specifically, the displacement-based BIEM is used for a multi-layered deposit with interface cracks, while the regularized, traction-based BIEM is used when internal cracks are present within the layers. The standard uni-dimensional boundary element with parabolic shape functions is employed for discretizing the free surface and the layer interfaces, while special discontinuous boundary elements are placed near the crack tips to model the asymptotic behaviour of both displacements and tractions. This formulation yields displacement amplitudes and phase angles on the free surface of a geological deposit, as well as stress intensity factors near the tips of the cracks. Finally, in the companion paper, numerical results are presented which show that both scattered wave and stress concentration fields are sensitive to the incidence seismic wave parameters and to specific site conditions such as surface topography, layering, the presence of cracks and crack interaction. 相似文献
829.
830.