Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance

Particle fluxes were measured 7 m above the sea bottom during the predisturbance, disturbance, and postdisturbance periods by using time series sediment traps attached to seven deep-sea moorings deployed in the INDEX experiment site in the Central Indian Basin. The predisturbance particle fluxes varied between 22.3 to 55.1 mg m -2 day -1 . Increased and variable particle fluxes were recorded by the sediment traps during the disturbance period. The increase observed was 0.5 to 4 times more than the background predisturbance fluxes. The increases in particle fluxes (~4 times) recorded by the sediment trap located in the southwestern direction (DMS-1) were the greatest, which could be the result of preferential movement of resuspended particles generated during the deep-sea benthic disturbance along the general current direction prevailing in this area during the experimental period. Also, the traps located closer to the disturbance area recorded greater fluxes than did the traps far away, across the Deep Sea Sediment Resuspension System path. This variability in recorded particle fluxes by the traps around the disturbance area clearly indicates that physical characteristics such as grain size and density of the resuspended particles produced during the disturbance had an important effect on particle movement. The postdisturbance measurements during ~5 days showed a reduction in particle fluxes of ~50%, indicating rapid particle settlement.     

西北太平洋边缘海区海面变化多尺度解析及空间分异

利用MODWT对西北太平洋边缘海区8站位1965~2005年验潮序列进行多尺度分解,讨论了该区域海面变化多尺度波动特征及空间分异。结果显示年周期组分振幅随纬度增大而逐渐增大,半年周期组分振幅以中国沿岸最大,其余站位相对较小。年际尺度的波动中ENSO信号与1~2年尺度的准周期波动存在模态混叠现象,表现为对序列构形和不同时段的相关关系的影响。利用ICA方法从小波分解的年际尺度和信号中分离出的ENSO信号,表明不同纬度海面对ENSO事件的响应整体上呈现向高纬衰减的变化特征。基于小波相似性的分析结果显示,低纬各站海面对ENSO在各尺度上均呈现出显著的负相关,而中高纬地区则呈现出正相关。1980年之前和之后中高纬地区的海面对ENSO的响应出现了显著的差异,这可能与ENSO自身频率的调整有关。     

System versus component response of a two-span reinforced concrete bridge system

A large-scale 20.5 m long asymmetric two-span reinforced concrete bridge was tested to failure using the shake table system at the University of Nevada Reno. Upon completion of testing, in depth analytical modeling was conducted to evaluate the accuracy of conventional methods in reproducing the bridge model response and to develop a model for further study. Utilizing the experimentally verified computer model, the system effect was investigated, comparing the system and response of individual bents as well as the response of several other bridge models. In comparing computational model of the shake table specimen and models of the individual bents with tributary mass, it was shown that for all of the columns in this study, there was generally not an increase in hysteretic energy or large displacement cycles from system response at given displacement demand. The response of the bents for each high amplitude test motion was also compared. It was shown that there were significant differences in the bent demands for a given excitation due to system effects. In addition to the shake table model, four bridge systems with a constant total lateral stiffness were used in a parametric study to determine the system effect. The symmetric and uniform versions of the bridge specimen were shown to be comparable in nonlinear performance to the bridge specimen for the same high amplitude demand. The failure progression of the bridge model and the analytical comparisons suggested that the reserve capacity from varied column heights could provide a beneficial substructure redundancy.