Rigid‐plastic seismic design of reinforced concrete structures

In this paper a new seismic design procedure for Reinforced Concrete (R/C) structures is proposed—the Rigid‐Plastic Seismic Design (RPSD) method. This is a design procedure based on Non‐Linear Time‐ History Analysis (NLTHA) for systems expected to perform in the non‐linear range during a lifetime earthquake event. The theoretical background is the Theory of Plasticity (Rigid‐Plastic Structures). Firstly, a collapse mechanism is chosen and the corresponding stress field is made safe outside the regions where plastic behaviour takes place. It is shown that this allows the determination of the required structural strength with respect to a pre‐defined performance parameter using a rigid‐plastic response spectrum, which is characteristic of the ground motion alone. The maximum strength demand at any point is solely dependent on the intensity of the ground motion, which facilitates the task of distributing required strength throughout the structure. Any artificial considerations intended to adjust results according to empirical observations are avoided, which, from a conceptual point of view, is considered to be an advantage over other simplified design procedures for seismic design. The procedure is formulated using a step‐by‐step format followed by a design example of a 4‐storey‐R/C‐plane‐frame. Results are compared with refined NLTHA and found to be extremely encouraging. Copyright © 2006 John Wiley & Sons, Ltd.     

2006年全球气候异常，多项纪录被打破

 以世界气象组织发布的2006年全球变化状况的报告为基础，结合全球相关的资料报道，总结了2006年全球的气候变化特征：2006年为近百年来第5个最暖年，全球出现了大范围的气候异常，包括欧洲最暖的秋天、澳大利亚的严重干旱、非洲大角地区的极端干旱和严重洪涝、菲律宾群岛的暴雨，以及北极海冰面积的进一步减少等。     

The Influence of the North Atlantic Oscillation on Rainfall Triggering of Landslides near Lisbon

The majority of landsliding episodes in the area north of Lisbon are associated with rainfall events of short (less than 5 days) medium (5–20 days) or long duration (more than 20 days). The precipitation regime in Portugal is highly irregular, with large differences between wet and dry years. We have assessed the impact of the North Atlantic Oscillation (NAO) on both the winter precipitation and the timing and magnitude of associated landslide events. Results show that the large inter-annual variability of winter precipitation is largely modulated by the NAO mode. The precipitation composite corresponding to high NAO index presents a considerable lower median value (47 mm/month) than the corresponding low NAO index class (134 mm/month). The entire precipitation distribution associated with the low NAO index composite encompasses a wider range of values than the corresponding high NAO index composite. This non-linear behavior is reflected in the probability of occurrence of a very wet month (precipitation above the 90% percentile) that is just 1% for the positive NAO class and 23% for low NAO index months. Results for the low NAO class are crucial because these months are more likely associated with long-lasting rainfall episodes responsible for large landslide events. This is confirmed by the application of a 3-month moving average to both NAO index and precipitation time series. This procedure allowed the identification of many months with landslide activity as being characterized by negative average values of the NAO index and high values of average precipitation (above 100 mm/month). Finally, using daily data we have computed the return periods associated with the entire set of landslide episodes and, based on these results, obtained a strong linear relationship between critical cumulative rainfall and the corresponding critical rainfall event duration.     

Computing periodic orbits of the three-body problem: Effective convergence of Newton’s method on the surface of section

We consider Newton’s method for computing periodic orbits of dynamical systems as fixed points on a surface of section and seek to clarify and evaluate the method’s uncertainty of convergence. Several fixed points of various multiplicities, both stable and unstable are computed in a new version of Hill’s problem. Newton’s method is applied with starting points chosen randomly inside the maximum possible—for any method—circle of convergence. The employment of random starting points is continued until one of them leads to convergence, and the process is repeated a thousand times for each fixed point. The results show that on average convergence occurs with very few starting points and non-converging iterations being wasted.     

随机采样信号重构的快速计算方法

信号的重构有着广泛地应用,探讨和采用有效的方法至关重要。这里讨论了基于神经网络的最大熵信号重构方法和随机采样信号重构常用的两种算法,提出了利用随机采样数据进行信号重构时选点的分条分块方法和映射定点方法。当重构区域为N×M时,分成M条和N块,会使运算量最小;当随机采样点分布不均匀时,先进行点域映射,再进行插值计算,可以克服偏倚效应,得到良好的重构结果。这些方法使得重构效果得到了改善,计算速度提高了几十乃至几百倍,经过实际应用证实,该方法具有一定的先进性和高效率。     

Analysis of a Long Record of Annual Maximum Rainfall in Athens,Greece, and Design Rainfall Inferences

An annual series of maximum dailyrainfall extending through 1860–1995, i.e., 136 years,was extracted from the archives of a meteorologicalstation in Athens. This is the longest rainfall recordavailable in Greece and its analysis is required forthe prediction of intense rainfall in Athens, wherecurrently major flood protection works are under way.Moreover, the statistical analysis of this long recordcan be useful for investigating more generalisedissues regarding the adequacy of extreme valuedistributions for extreme rainfall analysis and theeffect of sample size on design rainfall inferences.Statistical exploration and tests based on this longrecord indicate no statistically significant climaticchanges in extreme rainfall during the last 136 years.Furthermore, statistical analysis shows that theconventionally employed Extreme Value Type I (EV1 orGumbel) distribution is inappropriate for the examinedrecord (especially in its upper tail), whereas thisdistribution would seem as an appropriate model iffewer years of measurements were available (i.e., partof this sample were used). On the contrary, theGeneral Extreme Value (GEV) distribution appears to besuitable for the examined series and its predictionsfor large return periods agree with the probablemaximum precipitation estimated by the statistical(Hershfield's) method, when the latter is consideredfrom a probabilistic point of view. Thus, the resultsof the analysis of this record agree with a recently(and internationally) expressed scepticism about theEV1 distribution which tends to underestimate thelargest extreme rainfall amounts. It is demonstratedthat the underestimation is quite substantial (e.g.,1 : 2) for large return periods and this fact must beconsidered as a warning against the widespread use ofthe EV1 distribution for rainfall extremes.     

极值分布参数的非线性估计及其工程应用

本文基于高斯—牛顿法,在理论频率与实际频率残差平方和最小这一适线准则下,实现了三种极值分布参数的非线性估计。该算法计算精度高,收敛速度快,对观测数据拟合程度较佳。文中对三种极值分布与P-Ⅲ型分布、对数正态分布进行了适线比较,所做工程算例表明;极值Ⅱ型所得小概率设计参数最大,极值Ⅰ型次之,威布尔分布最小,P-Ⅲ型与对数正态分布居中。本文采用的分布参数拟合方法同样适用于其它线型。     

西北东部极端降水事件及异常旱涝季节变化倾向

利用西北地区东部100个气象观测站1960\_2000年逐日降水资料,对降水、极端降水事件及异常旱涝区域面积的季节变化倾向进行了分析。结果表明:春、秋、冬季,虽然极端降水事件频次的变率小于降水距平百分率的变率,但两者的变化趋势一致,春、秋季呈上升趋势,冬季呈下降趋势,表明极端降水事件出现的多与少,基本决定了季节降水趋势的变化;夏季,暴雨出现的多与少不能完全决定夏季降水量的趋势,而大雨频次的变化趋势与降水距平百分率的变化趋势一致,略呈上升趋势。夏季降水异常偏少的区域面积呈减少趋势,表明干旱发生的区域面积缩小了;秋季降水异常偏少的区域面积从20世纪80年代中期开始明显的扩大,表明干旱发生的区域面积增大了;春、冬季,降水异常偏多、偏少的区域面积是对称变化的,即降水异常偏多的区域面积增多,则异常偏少的区域面积减少;反之亦然。     

GeoTiff中GeoTag域解析

GeoTiff是Tiff格式的一种特殊形式, 1.0版的GeoTiff在Tiff格式的基础上增加了6个GeoTag(地理标志)域来描述栅格影像对应的地理坐标信息和投影信息, 并利用像元比例、结点、投影类型、坐标系统、椭球参数等, 准确地实现了影像栅格坐标与地理坐标之间的相互转换.首先介绍了GeoTiff所支持的3种坐标空间, 并在剖析其六大地理标志域间相互关系的基础上, 详细描述了各个标志域的具体含义及其在影像中的存储组织; 其后根据GeoTiff的影像数据地理编码的原理, 给出了栅格空间与模型空间之间坐标转换的方法和步骤; 结合GeoTiff的应用, 阐述了GeoTiff的优点, 并对它的应用前景做出了展望.      

An Isentropic Mass Circulation View on the Extreme Cold Events in the 2020/21 Winter

Three extreme cold events successively occurred across East Asia and North America in the 2020/21 winter.This study investigates the underlying mechanisms of these record-breaking persistent cold events from the isentropic mass circulation(IMC)perspective.Results show that the midlatitude cold surface temperature anomalies always co-occurred with the high-latitude warm anomalies,and this was closely related to the strengthening of the low-level equatorward cold air branch of the IMC,particularly along the climatological cold air routes over East Asia and North America.Specifically,the two cold surges over East Asia in early winter were results of intensification of cold air transport there,influenced by the Arctic sea ice loss in autumn.The weakened cold air transport over North America associated with warmer northeastern Pacific sea surface temperatures(SSTs)explained the concurrent anomalous warmth there.This enhanced a wavenumber-1 pattern and upward wave propagation,inducing a simultaneous and long-lasting stronger poleward warm air branch(WB)of the IMC in the stratosphere and hence a displacement-type Stratospheric Sudden Warming(SSW)event on 4 January.The WB-induced increase in the air mass transported into the polar stratosphere was followed by intensification of the equatorward cold branch,hence promoting the occurrence of two extreme cold events respectively over East Asia in the beginning of January and over North America in February.Results do not yield a robust direct linkage from La Ni?a to the SSW event,IMC changes,and cold events,though the extratropical warm SSTs are found to contribute to the February cold surge in North America.