Managed water levels and the expansion of emergent vegetation along a lakeshore

Water-level fluctuations may be used to promote the expansion of emergent vegetation along lakeshores. We present the case of the lake Volkerak-Zoommeer in the Netherlands, a fresh-water lake created in 1987 after the enclosure of an estuary. Using an experimental area in which the water level could be manipulated, it was shown that partial summer drawdown of the shoreline created suitable conditions for germination and growth of tall emergent species (in particular Phragmites australis). Plant survival and growth depended on subsequent water-level fluctuations and grazing by waterbirds. Based on the experiment and empirical data, a model was developed to predict the effects of the water-level regime on potential reed bed development. The model was applied for four hydrological scenarios that have been considered for the water-level management of the lake.     

Research on the effect estimation of seismic safety evaluation

IntroductionItisdefinitelystipulatedintheLawofthePeople'sRepublicofChinaonProtectingagainstandMitigatingEarthquakeDisastersthattheseismicsafetyevaluationmustbemadeformajorprojects(includinglifelineprojects)and,accordingtotheresultsobtained,theseismicresistancerequirementsshouldbedetermined.Thenecessityofseismicsafetyevaluationhasbeenrecog-nizedgradually,butthetopicontheeffectofsafetyevaluationhasnotbeenreferredmuch.Gener-allyspeaking,althoughmostpeopleapprovethesocialeffectofsafetyevaluatio…     

Investigation of upper crust anisotropy in Ghaen-Birjand region, east-central Iran

IntroductionWhenpropagatingthroughananisotropicmedium,ashearwavesplitsintotwo(quasi)shearwaveswithdifferentpropagationspeedsandpolarizedorthogonally.Owingtotherecentdevel-opmentofseismicobservationsystem,detectionofshearwavessplittingwithverysmalldelaytimesbetweenfasterandslowershearwavesbecameavailableandprovidedpowerfulapproachfordetectionofcrustalanisotropy.Crampin(1978)emphasizedtheroleofalignedmicrocracksasacauseofcrustalanisotropyandpointedoutthatforverticallyalignedmicrocracksthedirecti…     

3-D finite element modeling for evolution of stress field and interaction among strong earthquakes in Sichuan-Yunnan region

Introduction Sichuan-Yunnan region is a major area with frequent strong earthquakes in Chinese mainland, especially the middle-southern segment of South-North Seismic Zone, where many strong earth-quakes occurred in history. In the past 30 years, Sichuan-Yunnan region has two seismically active periods: one is from Tonghai earthquake in 1970 to Longling-Songpan earthquake in 1976, the other is from Lancang earthquake in 1988 to now. During this two periods, the M=7.7 Tonghai, M=7.1 Dagua…     

Dynamic performance of twin curved cable‐stayed bridges

The dynamic behaviour of two curved cable‐stayed bridges, recently constructed in northern Italy, has been investigated by full‐scale testing and theoretical models. Two different excitation techniques were employed in the dynamic tests: traffic‐induced ambient vibrations and free vibrations. Since the modal behaviour identified from the two types of test are very well correlated and a greater number of normal modes was detected during ambient vibration tests, the validity of the ambient vibration survey is assessed in view of future monitoring. For both bridges, 11 vibration modes were identified in the frequency range of 0ndash;10Hz, being a one‐to‐one correspondence between the observed modes of the two bridges. Successively, the information obtained from the field tests was used to validate and improve 3D finite elements so that the dynamic performance of the two systems were assessed and compared based on both the experimental results and the updated theoretical models. Copyright © 2003 John Wiley & Sons, Ltd.     

Approximate modal decomposition of inelastic dynamic responses of wall buildings

Two approximate methods for decomposing complicated inelastic dynamic responses of wall buildings into simple modal responses are presented. Both methods are based on the equivalent linear concept, where a non‐linear structure is represented by a set of equivalent linear models. One linear model is used for representing only one vibration mode of the non‐linear structure, and its equivalent linear parameters are identified from the inelastic response time histories by using a numerical optimizer. Several theoretical relations essential for the modal decomposition are derived under the framework of complex modal analysis. Various numerical examinations have been carried out to check the validity of the proposed modal decomposition methods, and the results are quite satisfactory in all cases. Fluctuating bending moment and shear at any location along the wall height contributed by each individual vibration mode can be obtained. Modal contributions to shear and flexural strength demands, as well as the corresponding modal properties, under various seismic loading conditions can also be identified and examined in detail. Furthermore, the effects of higher vibration modes on seismic demands of wall buildings are investigated by using the modal decomposition methods. Several new insights into the complicated inelastic dynamics of multi‐story wall buildings are presented. Copyright © 2004 John Wiley & Sons, Ltd.     

一次强风暴的垂直环境特征数值模拟分析

应用MM 5模式对东北冷涡诱发的 2 0 0 2年 7月 1 2日强风暴进行了数值模拟 ,较成功地模拟出中尺度强对流风暴。发现冷涡后部中层干冷空气绝热下沉是东北冷涡 70 0hPa附近干暖盖形成和维持的重要机制 ,而低层暖湿气流爬升及干暖盖的抑制作用是东北冷涡强对流不稳定能量积累的重要机制。风暴发生前持续的低层西南风到中层西北风的风垂直切变产生的差动平流 ,加剧了层结不稳定 ,而风暴临近风垂直切变方向的快速逆转使热成风不平衡 ,必须通过激发垂直环流以适应其变化 ,对风暴发展有重要作用。     

山西省主要河流流域面雨量预报业务流程

以T213、HLAFS模式、MM5中尺度模式输出的格点资料以及日本降水量格点资料为基础，将影响山西降水的天气动力模型归纳为诊断模型，从中引出多个能够全面反映降水模型特征的综合物理因子；根据各种数值模式输出的降水量预报性能和质量优劣特点，依据数值模式的形势场预报优于要素场预报的现实，构造在不同环流形势背景下，启动不同预报方程的面雨量预报业务流程，有效地遏止了在环流形势调整时预报输出不能快速响应的弱点，提高了点和面雨量预报的准确度。     

一种新型降水预报评分方法

在目前已有的降水评分办法的基础上，对原有办法存在的弊端进行了有效的改进，使得降水的预报评估与预报服务业务结合更紧密，也更贴近公众的感受。主要介绍了新方法的基本思路、关键技术、实现方法等。评分系统已投入业务运行，成为考核预报员业务水平的重要依据。