Comparison of the Ku-Band Range Noise Level and the Relative Sea-State Bias of the Jason-1, TOPEX,and Poseidon-1 Radar Altimeters Special Issue: Jason-1 Calibration/Validation

TOPEX/Poseidon is a well known success, with the operational altimeter (TOPEX) and the experimental one (Poseidon-1), providing data of unprecedented quality. However, there are two major differences between the TOPEX and Poseidon-1 radar altimeters on board TOPEX/Poseidon. The first is related to the estimated range noise; the second is linked to the sea-state bias (SSB) model estimates. Since the recent launch of the Jason-1 radar altimeter (also called Poseidon-2), we have been cross-comparing these three systems to better characterize each of them. Analyzing standard user products, we have found that Jason-1 is behaving like Poseidon-1 and thus shows the same observed differences when compared with TOPEX. A comparative analysis of their features was performed, starting from the on-board acquisition of the ocean return and ending with the ground generation of the high level accuracy oceanographic product. The results lead us to believe that the sources for these differences lie in both the waveform tracking processing and the presence or abscence of a retracking procedure whether on-board or on ground. Because Poseidon-1 and Jason-1 waveforms are retracked while TOPEX waveforms are not in the products distributed to the users, we have applied the same ground retracking algorithm to the waveforms of the three radar altimeters to get consistent data sets. The analysis of the outputs has shown that: (a) the noise level for the three radar altimeters is definitively the same, and (b) the source of the relative SSB between Jason-1 and TOPEX lies in the different behavior of the on-board tracking softwares.     

Behavior of Weak Soils Reinforced with End-Bearing Soil-Cement Columns Formed by the Deep Mixing Method

This article reports on a series of small-scale, plane strain, 1 g physical model tests designed to investigate the bearing capacity and failure mechanics of end-bearing soil-cement columns formed via Deep Mixing (DM). Pre-formed soil-cement columns, 24 mm in diameter and 200 mm in length, were installed in a soft clay bed using a replacement method; the columns represented improvement area ratios, a_p, of 17%, 26%, and 35% beneath a rigid foundation of width 100 mm. Particle Image Velocimetry (PIV) was implemented in conjunction with close-range photogrammetry in order to track soil displacement during loading, from which the failure mechanisms were derived. Bearing capacity performance was verified using Ultimate Limit State numerical analysis, with the results comparing favorably to the analytical static and kinematic solutions proposed by previous researchers. A new equation for bearing capacity was derived from this numerical analysis based on the improvement area ratio and cohesion ratio of the soil column and ground model.     

甘肃黄土高边坡可靠度研究

以甘肃省266个黄土自然极限状态坡为研究对象,将其按地形地貌、地层岩性等特征划分为4个亚区,对每个亚区的极限状态坡高与坡宽进行双对数线性模型回归和不同置信度下的统计分析,给出4个亚区不同置信度下坡高与坡宽的相关关系。以1 024组黄土物理力学指标统计结果作为计算参数,用Bishop法的稳定系数计算公式建立极限状态方程,利用 Monte Carlo法对各亚区不同置信度下的边坡进行可靠度模拟,系统分析了坡高、坡度、参数变异性对失效概率的影响,以及失效概率与稳定系数的关系。结果表明,临洮-永靖亚区边坡坡度低于31.5?,失效概率可控制在10%以下;陇东亚区、兰州-定西-会宁亚区和天水-秦安-通渭亚区在强度参数变异系数取当地平均水平,稳定系数为1.3情况下失效概率在10%以内,稳定系数为1.2情况下,失效概率多在20%以内。     

金川三矿地应力测量及应力状态特征研究

金川三矿位于金川矿区F17断层以东,是超基性贫矿。随着选矿和冶炼水平的提高,三矿区逐渐进入开采阶段。了解矿山深部的地应力状态可以为巷道开挖和支护设计提供科学依据。为此在三矿1 200 m水平进行了系统的地应力测量,以了解三矿区的地应力状态特征。现场测量采用改进的空芯包体应力解除法,共获得了7个测点的三维应力数据,并绘出了各测点不同法线方向的截面应力椭圆。测量结果表明,在井下约520 m深度,最大主应力量值约为17～21 MPa,属于中等应力水平。最大主应力方向分为NNW～NNE和NE～WE两组,与区域应力场基本吻合,但又表现出新的趋势方向,其原因可能是受三矿区内两条断裂的影响。部分测点最大主应力倾角超过20°,最大达-49°,以水平应力为主的矿区应力场特征发生改变。研究结果对矿山设计及施工具有重要意义。     

2008年汶川地震前震源区的异常应力状态

我们收集了紫坪铺水库区域台网记录到的2004年8月16日至2008年5月12日汶川地震前发生在震中区及附近区域的486个小震震源机制资料,运用碎裂分析法对这些震源机制数据进行分析,获得了汶川地震前3年多时间内震源区应力水平随时间的演化过程.结果显示,强震发生前震源及附近区域约在2007年6月发生了应力突变,出现了2个应力异常高值区,其形成过程同时伴随着龙门山中央断裂的应力水平降低,最终强震发生在高应力区和低应力区之间的应力梯度带上.汶川地震前应力状态的演化过程,类似于实验研究中出现的非均匀断层失稳前的地震成核现象,符合地震成核的宏观表现.巴颜喀拉块体的南边界-鲜水河断裂的短基线测量也显示出,在同一时间段鲜水河断裂南段由左旋滑动转为异常的右旋错动,反映了汶川强震前整个巴颜喀拉块体有向东加速运动的异常过程.     

青藏块体强震活动状态分析

强震活动状态分析与研究是地震形势跟踪分析的重要基础,以频次的角度分析和探讨青藏块体的强震状态特征,研究表明,青藏块体存在强震平静与活跃交替活动的状态特征,已经历5个平静与活跃交替活动的状态过程.2008年3月21日于田7.3级地震、5月12日汶川8.0级地震和2010年4月14日玉树7.1级地震的发生表明青藏块体强震活动已处于活跃状态.     

基于H∞理论的磁流变阻尼器半主动容错控制

建筑结构的半主动控制系统中的传感器,在强震作用下可能因出现故障而影响控制效果。以磁流变阻尼器为例,研究半主动容错控制系统的设计方法。首先,研究了基于状态观测器的半主动H∞控制器设计方法,并将之应用到建筑结构采用磁流变阻尼器的减振控制中;运用改进Bouc-Wen模型,计算磁流变阻尼器的阻尼力,通过求解一个代数Riccati方程和一个状态观测方程,得出了基于状态观测器的H∞主动控制律;再对其采用Clipped-optimal方法实施半主动控制策略。然后,针对传感器故障,利用观测器组的输出残差对故障进行在线诊断,并通过几个观测器状态值的比较得到故障的大小,并据此对传感器的测量值进行修正,从而消除故障对闭环系统的影响,最终实现半主动H∞容错控制。仿真结果表明,该方法具有很好的容错控制效果。     

Studies of TLP dynamic response under wind, waves and current

Investigated is the coupled response of a tension leg platform (TLP) for random waves. Inferred are the mass matrix, coupling stiffness matrix, damping matrix in the vibration differential equation and external load of TLP in moving coordinating system. Infinitesimal method is applied to divide columns and pontoons into small parts. Time domain motion equation is solved by Runge-Kutta integration scheme. Jonswap spectrum is simulated in the random wave, current is simulated by linear interpolation, and NPD spectrum is applied as wind spectrum. The Monte Carlo method is used to simulate random waves and fluctuated wind. Coupling dynamic response, change of tendon tension and riser tension in different sea conditions are analyzed by power spectral density (PSD). The influence of approach angle on dynamic response of TLP and tendon tension is compared.     

Enhanced resistance of Portunus trituberculatus to Vibrio alginolyticus by selective breeding

We established a line (screened) of Portunus trituberculatus by selectively breeding individuals that survived from challenge with Vibrio alginolyticus, and compared the response of screened and unscreened (control) P. trituberculatus challenged with V. alginolyticus. We measured superoxide dismutase, catalase, acid phosphatase, alkaline phosphatase, and peroxidase activity and the content of hemocyanin in the plasma and phenoloxidase activity in serum. The cumulative survival rate after 24-h challenge with V. alginolyticus was significantly higher in the screened crabs than in the unscreened crabs (P<0.05). T-SOD and PO activity were significantly lower in the screened stock than in the unscreened stock (P<0.05). POD, CAT, and ACP activity and hemocyanin content were significantly higher in the screened stock than in the unscreened stock. Our results suggest that the screened stock was more resistant to infection. Furthermore, the indices we measured may be used to evaluate the health state of P. trituberculatus.     

基于模糊分类的UBGM(1,1)-Markov模型在露天矿边坡沉降预测中的应用

针对UBGM(1,1)-Markov模型中存在2个邻近值可能被归属到不同状态,导致预测值产生偏差的问题,结合模糊分类理论,构建基于模糊分类的无偏灰色-马尔科夫模型(unbiased gray-Markov model based on fuzzy classification, FC-UBGM(1,1)-Markov)。首先对UBGM(1,1)模型进行残差修正,然后将修正后拟合值的相对残差序列作为Markov链进行区间划分,再结合模糊分类的隶属度函数,计算相对残差的模糊向量,根据隶属度确定其所属的状态。实际算例表明,该模型比传统UBGM(1,1)-Markov模型的预测效果更好。