Semi-analytical solution for one-dimensional consolidation of fractional derivative viscoelastic saturated soils

This paper presents a semi-analytical solution to one-dimensional consolidation equation of fractional derivative Kelvin-Voigt viscoelastic saturated soils subjected to different time-dependent loadings. The theory of fractional calculus is first introduced to Kelvin-Voigt constitutive model to describe consolidation behavior of viscoelastic saturated soils. By applying Laplace transform upon the one-dimensional consolidation equation of saturated soils, the analytical solutions of effective stress and settlement in the Laplace transform domain are obtained. The present solutions are more general and have good agreements with available solutions from the literature, and are degenerated into ones for one-dimensional consolidation of elastic and viscoelastic saturated soils.     

摩擦时间依从的地震活动性细胞自动机模型

设计了一个改进的单断层地震孕育过程细胞自动机（ＣＡ）模型,通过设计外界通过 施加应力与模型间进行的能量交换和模型的细胞之间存在的非线性力学作用,试图理解地震 活动特性的力学机制．与早期细胞自动机模型相比,改进了参数的取值方式,将摩擦时间依 从的理论引进模型,使该细胞自动机模型更接近实际的孕震系统．研究表明参数取值方式对 人工地震序列和各细胞破裂事件的非均匀时间特性有重要影响,较小震级和较大震级范围中 的事件分别遵从明显不同的累积频度一震级关系．     

中国大陆基于BPT模型的时间相依地震危险性分析

概率地震危险性分析是地震区划图编制、重大工程场地地震安全性评估以及地震风险管理等领域的重要依据,地震时间活动性模型则是概率地震危险性分析的主要理论基础.本研究中基于布朗过程时间（Brownian passage time（BPT））模型,计算了不同情况下中国大陆特征地震震源区时间相依的地震发生率,采用概率地震危险性计算方法,选择合适的地震动模型,评估了中国大陆地区时间相依的地震危险性,并与基于泊松模型的地震危险性做了比较.结果表明,时间相依的地震活动特征对概率地震危险性具有显著影响,在那些地震离逝时间相对较长,离逝率较大（大于1）的震源区,时间相依的地震危险性结果相较于基于泊松模型的地震危险性结果显著增大,增大幅度最大可达50%以上.相反,在那些刚发生地震不久,地震离逝时间较短的震源区,时间相依的地震危险性结果相较于泊松模型显著减小,减小幅度最大可达50%左右.地震复发间隔的变异系数对地震危险性结果也有显著影响,选择合适的变异系数对时间相依地震危险性分析十分重要,后续应该加强对地震复发间隔不确定性的研究.研究结果还表明,时间相依的地震活动特征对不同超越概率下的地震危险性结果的影响是一致的,不随超越概率水平的变化而变化.本文研究结果对地震风险管理、地震保险以及相关防震减灾政策的制定等方面具有重要的应用价值.

     

数字处理技术在桩基动测中的应用

目前,国内桩基动测正由模拟记录方式向数字记录方式过渡,本文针对这一时期出现的一些技术问题,从推广应用数字处理技术的角度,系统地阐述了诸如数字滤波、非线性放大,倒频谱、频率细化等技术的应用方法,并以实例说明其效果,最后概要地介绍了笔者编写的实现上述技术的实用软件。     

A method for untriggered time-dependent searches for multiple flares from neutrino point sources

A method for a time-dependent search for flaring astrophysical sources which can be potentially detected by large neutrino experiments is presented. The method uses a time-clustering algorithm combined with an unbinned likelihood procedure. By including in the likelihood function a signal term which describes the contribution of many small clusters of signal-like events, this method provides an effective way for looking for weak neutrino flares over different time-scales. The method is sensitive to an overall excess of events distributed over several flares which are not individually detectable. For standard cases (one flare) the discovery potential of the method is worse than a standard time-dependent point source analysis with unknown duration of the flare by a factor depending on the signal-to-background level. However, for flares sufficiently shorter than the total observation period, the method is more sensitive than a time-integrated analysis.     

Time-dependent analytic solutions of quasi-steady shocks with cooling

The author presents time-dependent analytical solutions of quasi-steady shocks with cooling, where quasi-steady shocks are objects composed of truncated steady-state models of shocks at any intermediate time. These solutions are compared to simulations with a hydrodynamical code and finally quasi-steady shocks are discussed as approximations to time-dependent shocks. Large departure of both the adiabatic and steady-state approximations from the quasi-steady solution emphasise the importance of the cooling history in determining the trajectory of a shock.     

Direct time-domain soil profile reconstruction for one-dimensional semi-infinite domains

We discuss the inverse medium problem associated with the reconstruction of the heterogeneous material profile of a semi-infinite (layered) soil medium, directly in the time domain, based on the complete waveform response of the medium to interrogating waves. To tackle the inversion process, we use a partial-differential-equation-constrained optimization approach, supplemented with a time-dependent regularization scheme. We introduce an absorbing boundary to truncate the semi-infinite extent of the physical domain, and propose two schemes to refine the reconstructed profiles: the first is based on iteratively re-positioning the truncation boundary until convergence, and the second is based on optimizing the observation period, so as to exclude records with information beyond the truncation boundary. We present numerical results that attest to the efficacy of the proposed schemes in reconstructing sharp profiles of semi-infinite soil domains using both noise-free and noisy data, while in the presence of absorbing boundaries.     

论地貌的平衡与演化

地貌的平衡与演化牵涉到地貌学的理论核心,是其他地貌问题研究的前提和基础。但长期以来对此缺乏共识,认识混乱文呈讨论了地貌平衡的基本含义,认为根据剥蚀速率和堆积速率的大小,可把地貌平衡分为稳定平衡、不稳定平衡及动力平衡等３类,除稳定平衡外,其他两类平衡连同不平衡和非平衡都是与时间相关的,因而都是地貌演化的表现形式。即平衡可以伴随地貌演化而存在,把平衡与演化对立起来的错误观点引起了不少混乱。真实地貌作为     

时变三维电离层层析成像重建公式

基于GPS信标观测数据重建电离层电子密度的时变三维电离层层析问题的数学基础，在简化电离层电子密度随时间变化的条件下，导出了三维平行束层析重建公式. 在二维情况下，本文导出的三维平行束层析重建公式与Yeh等给出的二维电离层层析重建公式相同. 文中还讨论了有限视角和有限接收机孔径对重建图像的影响. 根据文中给出的三维平行束层析重建公式，在这些非理想条件下，对一个脉冲源函数进行CT重建的结果表明，基于GPS信标观测数据重建电离层电子密度的时变三维电离层层析是可行的.