基于EEMD的明代北京地区干旱灾害特征分析     

李艳萍  陈昌春  张余庆  毕硕本 《中国沙漠》2014,34(3):835-840

集合经验模态分解（EEMD）是一种适用于非线性、非平稳序列的信号分析方法,将EEMD应用于气候要素时间序列,可提取真实可靠的气候变化信号。根据北京地区历史时期干旱灾害资料,采用EEMD分解方法对明代（1368—1644年）北京地区干旱灾害等级序列进行多时间尺度的分析,获得简洁且平稳性较好的固有模态函数分量,并与所统计的明代北京地区干旱灾害频次多项式拟合曲线进行对比。结果表明：将EEMD应用于干旱灾害等级序列,可以提取干旱灾害中各个尺度的变化,对明代北京地区干旱灾害进行多尺度分析。明代北京地区干旱灾害存在着2.8年、6.3年的年际周期,11.5年、26.6年、53.6年的年代际周期和118.7年、299.5年的世纪周期。北京地区干旱灾害在明代整个时间跨度上呈现着先增加后微减的变化趋势,总体而言明代中期以后旱灾明显增多。  相似文献   

Ground-roll separation of seismic data based on morphological component analysis in two-dimensional domain     

Xiao-Hong Xu  Guang-Zhong Qu  Yang Zhang  Yun-Yun Bi  Jin-Ju Wang 《应用地球物理》2016,13(1):116-126

Ground roll is an interference wave that severely degrades the signal-to-noise ratio of seismic data and affects its subsequent processing and interpretation. In this study, according to differences in morphological characteristics between ground roll and reflected waves, we use morphological component analysis based on two-dimensional dictionaries to separate ground roll and reflected waves. Because ground roll is characterized by low-frequency, low-velocity, and dispersion, we select two-dimensional undecimated discrete wavelet transform as a sparse representation dictionary of ground roll. Because of a strong local correlation of the reflected wave, we select two-dimensional local discrete cosine transform as the sparse representation dictionary of reflected waves. A sparse representation model of seismic data is constructed based on a two-dimensional joint dictionary then a block coordinate relaxation algorithm is used to solve the model and decompose seismic record into reflected wave part and ground roll part.The good effects for the synthetic seismic data and application of real seismic data indicate that when using the model, strong-energy ground roll is considerably suppressed and the waveform of the reflected wave is effectively protected.  相似文献   

Identifying sources and hazardous risks of heavy metals in topsoils of rapidly urbanizing East China   总被引：3，自引：0，他引：3  

Yang Liu  Zongwei Ma  Jianshu Lv  Jun Bi 《地理学报(英文版)》2016,26(6):735-749

With rapid economic and social development, soil contamination arising from heavy metals has become a serious problem in many parts of China. We collected a total of 445 samples (0–20 cm) at the nodes of a 2 km×2 km grid in surface soils of Rizhao city, and analyzed sources and risk pattern of 10 heavy metals (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb and Zn). The combination of Multivariate statistics analysis and Geostatistical methods was applied to identify the sources and hazardous risk of heavy metals in soils. The result indicated that Cr, Ni, Co, Mn, Cu, and As were mainly controlled by parent materials and came from natural sources. Cd and Hg originated from anthropogenic sources. Pb and Zn, belonging to different groups in multivariate analysis, were associated with joint effect of parent materials and human inputs. Ordinary Kriging and Indicator Kriging suggested that single element and elements association from the same principal components had similar spatial distribution. Through comprehensive assessment on all elements, we also found the high risk areas were located in the populated urban areas and western study area, which could be attributed to the higher geological background in the western part and strong human interference in the eastern part.  相似文献   

基于UPFs的珊瑚岛礁场地地震反应分析方法研究          下载免费PDF全文

朱圣华  尹训强  王桂萱 《地震工程学报》2022,44(1):108-118

合理且高效地模拟珊瑚砂非线性动力特性、远场无限地基辐射阻尼以及海域岛礁动水压力的影响是进行珊瑚岛礁抗震安全分析的关键技术问题.以通用有限元软件ANSYS为研究工具,基于UPFs二次开发灵活性的特点,建立了适用于珊瑚砂地基条件下的岛礁场地地震反应分析时域计算模型.通过创建一种新的珊瑚砂等价线性单元描述岛礁场地的非线性动力...  相似文献   

多分量联合逆时偏移最佳匹配层吸收边界   总被引：3，自引：2，他引：1  

杜启振  秦童  朱钇同  毕丽飞 《应用地球物理》2010,7(2):166-173

有限空间内的波动方程逆时偏移需要利用有效的边界处理技术用以消除人工截断对偏移结果产生的影响。本文以横向各向同性介质弹性波速度-应力方程为基础,依据传统分裂式最佳匹配层（Perfect Matched Layer,PML）吸收边界技术的思想,推导了应用于逆时偏移的完全匹配层波动方程,并给出了其高阶交错网格有限差分格式。针对由边界处向计算区域内传播的＂反射波＂,以及地震记录排列两端地震同相轴突变对计算区域的影响这两方面问题,本文给出了逆时偏移中吸收层的布设方式。模型和实际资料的弹性波叠前多分量联合逆时深度偏移结果表明本文的边界处理方法取得了较好的吸收效果,获得了好的联合偏移成像结果。  相似文献   

Required separation distance between decks and at abutments of a bridge crossing a canyon site to avoid seismic pounding     

Kaiming Bi  Hong Hao  Nawawi Chouw 《地震工程与结构动力学》2010,39(3):303-323

Major earthquakes in the past indicated that pounding between bridge decks may result in significant structural damage or even girder unseating. With conventional expansion joints, it is impossible to completely avoid seismic pounding between bridge decks, because the gap size at expansion joints is usually not big enough in order to ensure smooth traffic flow. With a new development of modular expansion joint (MEJ), which allows a large joint movement and at the same time without impeding the smoothness of traffic flow, completely precluding pounding between adjacent bridge decks becomes possible. This paper investigates the minimum total gap that a MEJ must have to avoid pounding at the abutments and between bridge decks. The considered spatial ground excitations are modelled by a filtered Tajimi‐Kanai power spectral density function and an empirical coherency loss function. Site amplification effect is included by a transfer function derived from the one‐dimensional wave propagation theory. Stochastic response equations of the adjacent bridge decks are formulated. The effects of ground motion spatial variations, dynamic characteristics of the bridge and the depth and stiffness of local soil on the required separation distance are analysed. Soil–structure interaction effect is not included in this study. The bridge response behaviour is assumed to be linear elastic. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Study on the “beachrock field” in Haishan Island,Guangdong Province     

Bi Fuzhi  Yuan Youshen 《中国海洋湖沼学报》1988,6(4):343-357

Beachrocks like those in Haishan Island’s “beachrock field” are rarely found elsewhere. They contain typical cement-aragonite. The assemblages of foraminifera and ostracods show that they are typical littoral sediments, the middle and the lower beds of beachrocks being formed in the desalinized seawater, the upper bed in normal seawater. At least four coastal elevations and subsidences have occurred since Late Holocene. The amplitude of the last three subsidences increased each time and the sea coasts receded. Active elevation has been predominant since 600 years B.P. Periodical coastal elevation and subsidence in Fujian and Guangdong has been occurring for the past several thousand years. Each period was 500 years, 250 years of subsidence, 250 years of elevation. This study was financed by the Department of Science and Technology of the State Seismological Bureau and the Joint Seismological Science Foundation.  相似文献   

Book reviews     

Jiří Bičák  Hans Joachim Haubold 《Astrophysics and Space Science》1989,152(2):351-353

  相似文献   

远距离台风影响陕北突发性暴雨成因分析   总被引：27，自引：1，他引：27       下载免费PDF全文

井喜 贺文彬毕旭  艾丽华 《应用气象学报》2005,16(5):655-662

该文对2002年7月4～5日发生在陕西子长县受远距离台风影响而产生的突发性暴雨进行了诊断分析。结果表明:子长特大暴雨是由于β-中尺度强对流云团在子长重复出现而产生的。中低纬度系统的相互作用形成了有利于中尺度强对流云团在子长生成、发展和重复出现的水汽条件、不稳定条件、动力条件和天气尺度环流背景。湿位涡诊断分析表明:当台风向西北方向行进时, (1)暴雨区对流层低层MPV1负值发展的同时伴随对流高层MPV1正值的发展, 为对流层低层不稳定能量的充分积累创造了条件;(2)暴雨区形成有利于中尺度强对流云团生成发展的湿位涡正压项、斜压项垂直结构配置;(3)850 hPa等压面上MP V2等值线密集区和MPV1=-2 PVU中尺度强对流不稳定核心区形成耦合, 耦合区对下游中尺度强对流云团发生发展指示意义明显。当台风向北偏东方向行进时, 暴雨区对流层低层和高层形成双层不稳定;850 hPaMPV2等值线密集区东移, 暴雨区MPV2正值发展, 积累的对流不稳定能量在子长形成集中猛烈释放。  相似文献   

贵州烤烟气候适宜性分区研究   总被引：10，自引：0，他引：10  

童碧庆  帅士章  徐永灵  杨远恒 《贵州气象》2005,29(Z1):48-50

通过对优质烤烟气候条件和贵州省气候资源的简要分析,对贵州省烤烟气候适宜性进行分区,并对分区进行了评述.  相似文献