CONTROL OF GULLY EROSION USING STIFF GRASSES

Concentrated flow can cause gully formation on sloping lands and in riparian zones. Current practice for riparian gully erosion control involves blocking the gully with a structure comprised of an earthen embankment and a metal or plastic pipe. Measures involving native vegetation would be more attractive for habitat recovery and economic reasons. To test the hypothesis that switchgrass （Panicum virgatum L.） hedges planted at 0.5-m vertical intervals within a gully would control erosion, a series of hedges was established in four concentrated flow channels. Two of the channels were previously eroded trapezoidal channels cut into compacted fill in an outdoor laboratory. The other two channels were natural gullies located at the edge of floodplain fields adjacent to an incised stream. While vegetation was dormant, artificial runoff events were created in the two laboratory gullies and one of the natural gullies using synthetic trapezoidal-shaped hydrographs with peak discharge rates of approximately 0.03, 0.07, and 0.16 m3/s. During these tests flow depth, velocity, turbidity, and soil pore water pressures were monitored. The fourth gully was subjected to a series of natural runoff events over a five-month period with peaks up to 0.09 m3/s. Flow depths in all tests were generally 〈 0.3 m, and flow velocities varied spatially and exceeded 2.0 m/s at the steepest points of the gullies. Erosion rates were negligible for controlled flow experiments, but natural flows in the fourth gully resulted in 1 m ofthalweg degradation, destroying the central portions of the grass hedges, most likely due to the highly erodible nature of the soils at this site. Geotechnical modeling of soil steps reinforced with switchgrass roots showed factors of safety 〉 1 for step heights 〈 0.5 m, but instability was indicated for step heights 〉1 m, consistent with the experimental observations.     

电磁和电离层监测的短期地震预报系统

最近科学界确定和公认这样一个事实：在大地震（火山喷发）之前的几天或几小时,在强震和火山活动区的地壳和对流层中存在电磁耦合过程,在电离层内存在异常变化。解释这一现象的一批物理模型出现了。其中最可能的模型基于大气边界层地壳发射物（氡、惰性气体和金属气溶胶）的化学反应。这些发射物改变了边界层的电导率,从而改变了活动区域内的大气电场值。根据实验测量,在大地震前几天或几小时,地表的地震感应的垂直电场强度可达到1至几个kV／m,而在无干扰情况下该值为100v／m。异常电场渗透到电离层引起了不同种类的变化（离子成分、电子密度、标高、电子温度等的变化）,这些变化用实验方法可以从地面及人造卫星上测量到。这样的变化被称作地震的电离层前兆。电离层前兆的优点在于电离层把活动区域作为一个整体,而不只是事件在地面上发生的一个点进行测量。这就避免了导致地面测量的物理和地球化学前兆中出现错误的前兆镶嵌式特征。第二个优点是与其他前兆比较电离层前兆的出现有稳定的时间尺度,这使它在短临地震预报中更具实用价值。因为对所有IASPEI需求的响应,我们现有的知识水平使得电离层前兆的短期地震预报成为可能。逼近震中的位置可以从电离层前兆沿磁力线到地面的投影估计出来。要预报的地震震级可以由电离层中被改变区域的大小估计出来。发震时间可以从电离层前兆出现的时间估计出来。考虑到提议的短临预报系统是第一次创建,地震参数测定的精确度将在系统测试阶段加以确定。作为第一步,这些参数可在理论上估计出来。项目任务阐明如下：（1）在墨西哥Guerrem州创建连续的电磁和电离层监测系统包括基于地面的电离层测高仪,IGEF UNAM和INEGI的GPS接收仪网络,电场探测器网络,监测P．H脉冲的高频（HF）接收仪,甚低频（VLF）接收仪,高频（HF）多普勒装置,氧元素的557．7nm和630nm谱线的光学测量法,磁力仪网络。（2）测试系统的质量,用实验的方法确定虚报和错报的概率及地震参数测定的精确度。（3）如果结果没有问题,就在墨西哥Guerrero州和墨西哥的所有地震活动区应用该系统。（4）把该体系推荐给其他遭受地震灾害的国家,使其在他们的地域内应用。部分已创建的体系和所使用的技术受专利保护。     

2012年4月11日M8.6印度洋地震的深远影响:短期全球触发后为更长期全球阴影

2012年4月11日发生的M8.6印度洋地震是一次不寻常的洋内走滑大地震。在几天中,距离震中很远(数千千米)处的全球M≥4.5和M≥6.5地震活动发生率都有提高。走滑型主震通过其勒夫波触发了全球性的走滑余震,并持续了数天。但在随后的95天中,M≥6.5地震的活动率下降到零,而在此期间M≤6.0的全球地震发生率则与背景接近。在过去的一个世纪中,震后95天的时间内很少不发生M≥6.5的地震,大型主震之后更是没有过。同时在过去的一个世纪中,历次大主震(M≥8)后的静止期或者是非常短,或者是在给定主震后经过很长时间才开始,对于这一点我们无法给出相应的物理解释。2012年主震的独特之处体现在两个方面:短暂的全球地震活动增多和随后很长的静止期。我们认为,这两者之间是有联系的,且可以将这种模式解释为全球断层系动态应力作用的结果。瞬时动态应力可以促进短期的触发,但自相矛盾的是,它也可以暂时抑制破裂,直到背景构造负荷将断层系恢复到主震前的应力水平。     

Damage detection on framed structures: modal curvature evaluation using Stockwell Transform under seismic excitation

The key parameters for damage detection and localization are eigenfrequencies, related equivalent viscous damping factors and mode shapes. The classical approach is based on the evaluation of these structural parameters before and after a seismic event, but by using a modern approach based on time-frequency transformations it is possible to quantify these parameters throughout the ground shaking phase. In particular with the use of the S-Transform, it is possible to follow the temporal evolution of the structural dynamics parameters before, during and after an earthquake. In this paper, a methodology for damage localization on framed structures subjected to strong motion earthquakes is proposed based on monitoring the modal curvature variation in the natural frequency of a structure. Two examples of application are described to illustrate the technique: Computer simulation of the nonlinear response of a model, and several laboratory(shaking table) tests performed at the University of Basilicata(Italy). Damage detected using the proposed approach and damage revealed via visual inspections in the tests are compared.     

Particulate matter geochemistry of a highly industrialized region in the Caribbean:Basis for future toxicological studies

Air pollution has become an important issue,especially in Caribbean urban areas,and,particulate matter(PM)emitted by different natural and anthropogenic sources causes environmental and health issues.In this work,we studied the concentrations of PM₁₀ and PM_2.5 sources in an industrial and port urban area in the Caribbean region of Colombia.PM samples were collected within 48-h periods between April and October 2018 by using a Partisol 2000 i-D sampler.Elemental geochemical characterization was performed by X-ray fluorescence(XRF)analysis.Further,ionic species and black carbon(BC)were quantified by ion chromatography and reflectance spectroscopy,respectively.Using the Positive Matrix Factorization(PMF)receptor model,the contributions of PM sources were quantified.The average concentration of PM₁₀ was 46.6±16.2μg/m³,with high concentrations of Cl and Ca.For PM_2.5,the average concentration was 12.0±3.2μg/m³,and the most abundant components were BC,S,and Cl.The receptor model identified five sources for PM₁₀ and PM_2.5.For both fractions,the contributions of marine sea spray,re-suspended soil,and vehicular traffic were observed.In addition,PM_2.5 included two mixed sources were found to be fuel oil combustion with fertilizer industry emissions,and secondary aerosol sources with building construction emissions.Further,PM₁₀ was found to also include building construction emissions with re-suspended soil,and metallurgical industry emissions.These obtained geochemical atmospheric results are important for the implementation of strategies for the continuous improvement of the air quality of the Caribbean region.     

TWO DIMENSIONAL NUMERICAL SIMULATION OF FLOW AND GEO-MORPHOLOGICAL PROCESSES NEAR HEADLANDS BY USING UNSTRUCTURED GRID

1 INTRODUCTION In recent years, due to the increase in population and industrial developments, mankind has faced manyproblems associated with rivers, coastal waters and reservoirs. Some of these problems are flood control,water supply, power generation, and irrigation. In addition, making new hydraulic structures changesnatural conditions. Prediction of these changes is necessary for designing such constructions. For solutionof these problems usually an assessment of flow pattern, sedim…     

An improved optimal elemental method for updating finite element models

The optimal matrix method and optimal elemental method used to update finite element models may not provide accurate results. This situation occurs when the test modal model is incomplete, as is often the case in practice. An improved optimal elemental method is presented that defines a new objective function, and as a byproduct, circumvents the need for mass normalized modal shapes, which are also not readily available in practice. To solve the group of nonlinear equations created by the improved optimal method, the Lagrange multiplier method and Matlab function fmincon are employed. To deal with actual complex structures, the float-encoding genetic algorithm (FGA) is introduced to enhance the capability of the improved method. Two examples, a 7degree of freedom (DOF) mass-spring system and a 53-DOF planar frame, respectively, are updated using the improved method.The example results demonstrate the advantages of the improved method over existing optimal methods, and show that the genetic algorithm is an effective way to update the models used for actual complex structures.     

断裂长度与最大位移的关系及其影响因素

断裂最大位移与断裂迹长遵循幂律关系 :D =cLn,但幂指数n的大小有很大的变化范围。为探索幂指数n的大小和断裂机制 ,从已发表的文献中收集了 18组数据 ,这些数据的断裂长度具有 8个数量级的跨度。经相关分析 ,我们得到n值的大小变化于 0 5 5和 1 6 5之间 ,平均值为 1 0 839。由于走滑断裂的最大长度在其倾向方向 ,不宜与倾滑断裂一起统计 ,我们去掉一组走向滑动断裂的数据 ,幂指数平均值为 1 10 6 6。用双回归方法得到的幂指数峰值 (nd)是 1 0～ 1 1。这些结果表明断裂最大位移与断裂迹长应该是非常接近线性关系。这种线性关系可以用Dugdale模型加以解释。该模型认为弹塑性物质拉张裂缝端点的变形是非弹性变形。模型的适用范围是单一岩性 ,一次构造力作用。我们认为n值的大小之所以有很大的变化范围 ,有可能受到断裂迹线长度偏差的影响 ,造成长度偏差的因素包括 :不同的观察平面 ,断裂端点的分辨率 ,断裂连接作用 ,岩石力学性质变化 ,断裂多期活动等。     

Relationships between hydrosedimentary processes and occurrence of mercury-resistant bacteria (merA) in estuary mudflats (Seine, France)

The Seine estuary (France) is one of the world's macrotidal systems that is most contaminated with heavy metals. To study the mercury-resistant bacterial community in such an environment, we have developed a molecular tool, based on competitive PCR, enabling the quantification of Gram-negative merA gene abundance. The occurrence of the Gram-negative merA gene in relation with the topology (erosion/deposit periods) and the mercury contamination of three contrasted mudflats was investigated through a multidisciplinary approach and compared with a non-anthropized site (Authie, France). The higher abundance of the Gram-negative merA gene in the Seine estuary mudflats indicates a relationship between the degree of anthropization and the abundance of the merA gene in the mudflat sediments. In the Seine mudflats, the maxima of abundance are always located in fresh sediment deposits. Therefore, the abundance is closely related with the hydrosedimentary processes, which thus seem to be determining factors in the occurrence of the Gram-negative merA gene in the surface sediments of the Seine's mudflat.     

Does Manila clam cultivation affect habitats of the engineer species Lanice conchilega (Pallas, 1766)?

The major French site of Manila clam Ruditapes philippinarum (Adams and Reeves, 1850) cultivation is located in the Chausey Archipelago where the associated practices are highly mechanized: every steps of production are made with tractor-driven machinery. The Manila clam concessions are concentrated on Lanice conchilega (Pallas, 1766) bioherms, which are known to increase alpha-diversity and to locally modify sediment dynamics. This study focus on the impacts of Manila clam cultivation on (i) the natural populations of L. conchilega and on (ii) the structure of the associated benthic assemblages during the different steps of the farming production cycle. We found that the L. conchilega populations are significantly affected within the concessions where their total abundances drastically decrease, their spatial patterns are modified and the associated benthic assemblages are significantly altered. Our results are discussed in a context of a sustainable management of the Manila clam cultivation in coastal areas.