Numerical examination of the factors controlling DNAPL migration through a single fracture

The migration of five dense nonaqueous phase liquids (DNAPLs) through a single fracture in a clay aquitard was numerically simulated with the use of a compositional simulator. The effects of fracture aperture, fracture dip, matrix porosity, and matrix organic carbon content on the migration of chlorobenzene, 1,2-dichloroethylene, trichloroethylene, tetra-chloroethylene, and 1,2-dibromoethane were examined. Boundary conditions were chosen such that DNAPL entry into the system was allowed to vary according to the stresses applied. The aperture is the most important factor of those studied controlling the migration rate of DNAPL through a single fracture embedded in a clay matrix. Loss of mass to the matrix through diffusion does not significantly retard the migration rate of the DNAPL, particularly in larger aperture fractures (e.g., 50 microm). With time, the ratio of diffusive loss to the matrix to DNAPL flux into the fracture approaches an asymptotic value lower than unity. The implication is that matrix diffusion cannot arrest the migration of DNAPL in a single fracture. The complex relationships between density, viscosity, and solubility that, to some extent, govern the migration of DNAPL through these systems prevent accurate predictions without the use of numerical models. The contamination potential of the migrating DNAPL is significantly increased through the transfer of mass to the matrix. The occurrence of opposite concentration gradients within the matrix can cause dissolved phase contamination to exist in the system for more than 1000 years after the DNAPL has been completely removed from the fracture.     

我国第一部《地球化学》译著的译者——谭勤余

半个世纪之前,即1935年,我国第一部《地球化学》译著译成出版,这是我国地球化学发展史的重大事件。该书系译者据日译本转译而来。原著作者为苏联学者B·N·维尔纳茨基。译者谭勤余、任梦云。全书分上下两册,32开,7章共462页,重点论述了地球化学的概念;地壳中化学元     

Electrokinetic migration of permanganate through low-permeability media

This research was conducted to evaluate the combination of electromigration and potassium permanganate as a potential remediation method for low-permeability media (e.g., soil and sediment) contaminated with dissolved and sorbed organic contaminants. The experimental procedure was composed of two stages: determination of migration rates of permanganate through homogeneous cores and a primarily qualitative analysis of migration in more heterogeneous, two-dimensional scenarios. Results indicated that transport of permanganate through fine-grained porous media and clays can be undertaken using electromigration, and electromigration rates were found to be at least 400% faster than diffusion alone. In addition, the use of an applied electric field in a flushing scenario was shown to result in almost 100% sweep efficiency of a domain consisting of clay blocks interspersed in a glass bead medium. The results of the study show that there is potential for this method to be able to deliver permanganate and other potential remedial agents to treat contaminated zones within heterogeneous and low-permeability porous media through in situ chemical oxidation or other processes.     

1992年加利福尼亚兰德斯前震序列和地震成核的应用

１９９２年６月２８日的加利福尼亚兰德斯地震（ＭＷ＝７．３）是在至少２８个地震组成的前震序列之后７小时发生的。在本研究中我们利用附近台站记录的波形互相关所得到的高精度定位检验了前震的时空发展过程。利用阵列波形而不是单独波形来得到每个地震的走时记录,我们能很大地改进计时精度和甚至对突然出现的地震也能出走时记录,我们利用改善了走时完成了联合重新定位并降低了相对定位误差,水平方向的误差小于１００ｍ,垂直方     

蔚县草沟堡区下花园组的发现及找煤前景

草沟堡区位于河北省蔚县南山腹地,与蔚县煤田同处于Ⅳ级构造单元——蔚县复向斜内,该区广泛分布下花园组之上覆地层九龙山组、张家口组,并表现为向斜构造,基底为奥陶系和寒武系灰岩.近期在草沟堡区外围李家堡发现了含煤地层中一下侏罗统下花园组露头,推测在草沟堡向斜中部也有下花园组赋存,是有希望的找煤区.     

The role of the Río de la Plata bottom salinity front in accumulating debris

The Río de la Plata, one of the most important South American estuarine environments, is characterized by a bottom salinity front that generates an ecotone between the river and the estuary. Based on bottom trawls and costal sampling we describe the distribution, types, and amount of debris found in the bottom and shoreline across this front. Plastics and plastic bags were the main debris types in both areas. Concentrations of total debris upriver the front were always significantly higher than downriver the front showing that the front acts as a barrier accumulating debris. Moreover, a large part of debris end ups accumulated in the coastal area upriver the frontal position. This area is particularly sensitive because the coastline encompasses an UNESCO Man and the Biosphere Reserve and a Ramsar site, and due to the ecological significance of the front for many valuable species.     

煤矿井下随钻测斜仪误差联合校正方法

为降低煤矿井下随钻测斜仪随钻测量钻孔姿态角参数的误差,建立基于递推最小二乘的误差补偿数学模型,采用椭球拟合法、点积不变法和旋转平面拟合法的联合校正方法对随钻测斜仪进行误差补偿校正。对研发的随钻测斜仪进行数值仿真和双轴转台实验,用联合校正方法对实验数据进行误差补偿校正,校正前俯仰角和方位角的最大绝对误差分别为4.7°和5.1°,校正后为0.8°和0.9°,校正后测量精度满足随钻测斜仪要求。实验结果表明,该方法可以对煤矿井下随钻测斜仪进行有效的误差补偿校正。