Seismic Design of Symmetric Structures for Accidental Torsion

The paper presents an analytical estimation of the dynamic effects, caused by the shifting of the centre of mass with accidental eccentricity in symmetric structures. The approximate analytical solution proves, that even under small accidental eccentricities the symmetric structures exhibit “irregular behaviour” and the accidental torsional effects cannot be described properly by static application of torsional moments. The prescribed application rule by Eurocode 8 for multimodal analysis underestimates the accidental torsional effects up to 21% for 5% eccentricity for the structures considered in the paper. An expression for the correction of member responses is derived. It is proved by numerical simulations of the dynamic response of three-dimensional models of symmetric structures, that the proposed correction coefficient gives accurate results in cases of single-storey and multi-storey structures. It gives a convenient way for the design practice to estimate accurately the accidental torsional effects on planar and 3-D models of symmetric structures. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于原位激光粒度仪(LISST)的悬浮体平均粒径计算方法对比研究

根据2012年夏季和2016年冬季在南黄海中部利用原位激光粒度仪(laser in situ scattering and transmissometry,LISST)进行调查获得的实测数据,对两种平均粒径计算方法的结果进行比较研究,并对产生差别的原因进行分析。结果表明:无论在夏季和冬季,在温度跃层以上粒度分布以粗颗粒为主,两种计算方法差值较小,可以相互替代。在温盐跃层以下层位,细颗粒组分增加,导致二者计算差值变大。端元分析表明较高的平均粒径值倾向于造成平均粒径差值增大。矩值法强调了粗颗粒组分的贡献,而平均粒级法对细颗粒组分的贡献更加敏感,后者是更适用于将LISST观测数据应用于陆架海区现代沉积环境研究的粒径参数计算方法。本文为使用LISST在陆架海区进行现代沉积过程研究提供了参考。     

Construction of invariant tori for the spin-orbit problem in the mercury-sun system

The stability of spin-orbit resonances, namely commensurabilities between the periods of rotation and revolution of an oblate satellite orbiting around a primary body, is investigated using perturbation theory. We reduce the system to a model described by a one-dimensional, time-dependent Hamiltonian function. By means of KAM theory we rigorously construct bidimensional invariant surfaces, which separate the three dimensional phase space. In particular with a suitable choice of the rotation numbers of the invariant tori we are able to trap the periodic orbit associated with a given resonance in a finite region of the phase space. This technique is applied to the Mercury-Sun system. A connection with the probability of capture in a resonance is also provided.     

Reconstitution des apports en éléments traces métalliques et bilan de leur migration dans un Luvisol sableux soumis à 100 ans d'irrigation massive par des eaux usées brutes

Raw wastewaters were massively spread on sandy luvisols near Paris from 1899 to 2002, leading to high trace metals (TM) pollution of soils. Mass balance calculations were performed on a soil profile to assess vertical migration of TM. The contamination was estimated by subtracting the natural pedo-geochemical background of the horizons. TM inputs were estimated using Cr as an invariant. It is shown that Pb and Cr remained in the surface horizon, while Ni, Cd, Cu and Zn migrated downward, being more or less trapped depending on the physicochemical properties of the horizons. To cite this article: C. Dère et al., C. R. Geoscience 338 (2006).     

Precipitation regional extreme mapping as a tool for ungauged areas and the assessment of climate changes

The spatial‐temporal characteristics of mean annual daily maximum precipitation events in the upper Yangtze River basin in China are examined using a framework termed precipitation regional extreme mapping (PREM). The framework consists of regional analyses and mapping methods, which have the capability to assess the presence or absence of climate change. The findings confirm the homogeneous regions identified by Wang (2002) using a heterogeneity measure, where all three regions have heterogeneity less than 1.0. The Pearson type III (PE3) distribution was found to be acceptable for all three regions, while the generalized extreme‐value distribution performs better than PE3 for Region I (eastern portion of the upper Yangtze basin). Two indices, root mean square error and mean bias, were used to access the performance of the extreme map, and the results show that the map of extreme can predict precipitation for ungauged regions with acceptable accuracy. The regional frequency maps were used in conjunction with the Student's t‐test to identify the statistical significance of changes of extremes in precipitation. Results indicate that there have been no significant changes in maximum daily precipitation magnitudes over the past four decades, a finding that is valuable for the safe planning of major hydraulic projects and the management and planning of water resources in the upper Yangtze River basin. Copyright © 2015 John Wiley & Sons, Ltd.     

基于小波变换和不变矩匹配的快速人体定位

人体定位是指在图片中确定行人位置的过程.为了提高人体定位的正确率和速度,提出了一种结合小波变换和不变矩匹配的定位方法.首先对图像进行小波变换,提取出图像小波系数;再根据行人模板的系数特征提取出不变矩模板;然后在小波域上通过不变矩匹配实现人体定位.该方法减少了待检区域,降低了计算代价.实验结果表明,该算法识别率达78.6%,测试结果比Oren等人提出的匹配方法提高了26.7%.     

基于NSCT和SURF的遥感图像匹配

SURF(Speed Up Robust Features)算法是对尺度不变特征变换SIFT(Scale Invariant Feature Transform)算法的一种改进,应用到遥感图像匹配领域中可以大大提高匹配速度,但是匹配精度略有下降。为此,本文提出一种基于无下采样Contourlet变换NSCT(Nonsubsampled Contourlet Transform)和SURF的遥感图像匹配算法。首先使用NSCT分别分解参考图像和待匹配图像,得到各自对应的低频分量;然后把这两幅低频分量图像作为SURF算法的输入图像进行预匹配,降低高频噪声对匹配结果的影响;最后利用预匹配结果求解变换模型的参数,并采用随机抽样一致RANSAC(Random Sample Consensus)算法剔除误匹配点对,解决了SURF算法存在的错误匹配问题。实验结果表明,与SIFT算法、SURF算法相比,本文算法具有更高的匹配精度和更快的匹配速度,且抗旋转、噪声、亮度变化能力更强。     

不同条件下水文要素重现期的计算方法

重现期在工程规划、设计、运行和管理中已经得到了广泛应用,然而,由于气候变化和人类活动破坏了水文频率分析中的一致性基础,致使基于一致性的重现期计算方法面临挑战,迫切需要研究新的重现期计算方法。以重现期两种不同的定义入手,给出了在水文系列满足独立性假定后重现期在一致性与非一致性条件下各自计算公式,并以广东省东江流域龙川站1956~2009年的年最大洪峰资料系列为例,分析了不同条件下重现期及其变化的特点与原因。     

斜压Ertel-Rossby不变量在梅雨锋降水过程中的研究与应用

绝热无摩擦下,位涡(PV)的守恒性、不可渗透性和可反演性使之非常广泛地应用在中高纬度天气学诊断分析中,但由于其本身不包含力管项,无法描述强烈天气的快速流形等局限性,因此分析了Zdunkowski and Bott(2003)提出的斜压Ertrl-Rossby不变量(ERI),结果表明,绝热无摩擦条件下的ERI在其表达式中就已经明确地包含了螺旋度和PV的表达式,同时也涵盖了斜压大气中的力管项效应,可以描述快速流形的天气系统,具有PV所不能取代的优点,这使得它具有非常广泛的潜在应用价值。在此基础上,还利用ERI诊断了2003年7月3～6日的一次梅雨降水过程,结果表明,ERI完整地刻画了这次降水带南移及降水强度变化的特点,随着24h累积降水带的移动,ERI低值区也随之移动,二者吻合非常好。和PV相比,ERI对降水落区及强度变化的诊断能力更强。