The role of capillary forces in steady-state and transient seepage flows

Steady and transient seepage problems were investigated numerically using a dimensionless formulation for water flow in variably saturated, two-dimensional anisotropic and homogenous porous media. The dimensionless formulation combines the aspect ratio and the anisotropy ratio in one dimensionless parameter, M, and accounts for capillarity effects using the ratio of the domain height to the height of capillary fringe as another dimensionless parameter, alpha. Two domain geometries were considered: rectangular and trapezoidal. It was found that M and alpha play major roles in the development and the height of the seepage face. The height of the steady-state seepage face increased with the decreasing value of alpha. The effects of capillarity on the development of the transient seepage face were investigated by lowering the open water level on one side of the domain at various uniform velocities while the other side was kept at a constant value. It was found for most scenarios that decoupling between the water table and the open water level first occurred for domains with large alpha. In other words, the seepage face heights of these systems were larger than those with a small alpha. These results are the opposite of the steady-state results and are due to the fact that drainage of the pores was the major mechanism controlling the drop of the transient water table, especially at earlier times. A criterion for the decoupling of the water table from the falling open water level (i.e., the formation of the transient seepage face) was developed by Dracos (1965). It states that decoupling does not occur as long as the falling speed, VF, of the open water level is less than Vd = K(o) sin2 B/phi where K(o) is the saturated hydraulic conductivity of the soil, phi is the porosity, and beta is the angle of the exit face with the horizontal (i.e., beta = pi/2 implies a vertical face). Our investigation revealed that decoupling occurs for smaller falling velocities than Vd, and is caused by, among others, the fact that the water table is not tangent to the exit face but rather intersects it at a nonzero angle.     

Origin of shallow ground water in an alluvial aquifer as determined by isotopic and chemical procedures

In this study, we identify the origin of shallow ground water that supports regionally unique plant and wildlife habitats in a riparian and reservoir-fringe system using isotopic and chemical procedures. This study was conducted where Little Stony Creek flows into East Park Reservoir on the east front of the Coast Range, northern California. Little Stony Creek water, Hyphus Creek water, Franciscan Complex regional ground water, Great Valley Group regional ground water, and local shallow ground water were collected during wet and dry seasons and were analyzed for deuterium, oxygen-18, temperature, pH, redox potential, conductivity, and major cation and anion concentrations. Turnover in the local flow system is rapid indicating that local shallow ground water is dependent on recent recharge. Local shallow ground water is recharged primarily by Little Stony Creek water and Franciscan Complex ground water. In the wet season, Little Stony Creek is the more prominent source of local shallow ground water, and the ratio of Little Stony Creek water to Franciscan Complex ground water decreases with distance from the channel. In the dry season, Franciscan Complex ground water is the more prominent source of local shallow ground water, and the ratio of Little Stony Creek water to Franciscan Complex ground water decreases with distance down the valley. Franciscan Complex ground water discharges to local shallow ground water throughout the year, primarily because the local flow system is a regional low that lies perpendicular to the Franciscan Complex ground water flowpath. Little Stony Creek is a more prominent source of ground water in the wet season than in the dry season because Little Stony Creek flows continuously through the alluvial reach in the wet season and intermittently through the alluvial reach in the dry season. Extensive ground water withdrawals from the Franciscan Complex flow system could reduce the amount of water available to the local flow system, particularly during the dry season, and could substantially reduce the geographic extent of the regionally unique plant and wildlife habitats.     

Okadaic acid, a causative toxin of diarrhetic shellfish poisoning, in green-lipped mussels Perna viridis from Hong Kong fish culture zones: method development and monitoring

Green-lipped mussels (Perna viridis) were collected from seven fish culture zones (FCZs) in Hong Kong and analyzed for okadaic acid (OA). A conventional HPLC method was modified by incorporating a proteinase K digestion step. Results suggest that a higher recovery (2.5 times higher) of OA was obtained from spiked samples after the addition of 1.08 mg proteinase K in comparison with samples incubated without the proteolytic enzyme. For the hepatopancreas (HP) of individual field-collected mussels, the additional digestion step can enhance OA extraction by 3.1 times. Spatial and temporal variations in OA concentrations in the mussels from various FCZs were investigated. The highest concentration of OA in mussel HP samples was 1164.9 ng/g HP wet wt. With respect to OA concentrations in whole mussel tissues from seven sites and four seasonal samplings, the concentrations were between 70.0 and 131.0 ng/g wet wt., which did not exceed the generally recognized international regulatory criteria (>200 ng/g) for OA.     

Laboratory Detection of a Molecular Band at lambda4429

This Letter presents infrared spectra taken with the newly commissioned near-infrared spectrometer (NIRSPEC) on the Keck II telescope of the high-redshift radio galaxy MRC 2025-218 (z=2.63). These observations represent the deepest infrared spectra of a radio galaxy to date and have allowed for the detection of Hbeta, [O iii] lambdalambda4959, 5007, [O i] lambda6300, Halpha, [N ii] lambdalambda6548, 6583, and [S ii] lambdalambda6716, 6713. The Halpha emission is very broad (FWHM=9300 km s-1) and luminous (2.6x1044 ergs s-1), and it is very comparable to the line widths and strengths of radio-loud quasars at the same redshift. This strongly supports active galactic nucleus unification models linking radio galaxies and quasars, although we discuss some of the outstanding differences. The line [O iii] lambda5007 is extremely strong and has extended emission with large relative velocities toward the nucleus. We also derive that if the extended emission is due to star formation, each knot has a star formation rate comparable to a Lyman-break galaxy at the same redshift.     

Preliminary results of biomarker responses in zooplankton of brackish environments

Zooplankton is an essential component of the food chains of marine and brackish environments. Ecotoxicological risk to zooplankton, evaluated by the biomarker approach, can be used as an early warning signal of risk to the health of marine ecosystems. The aim of this project is to evaluate the application of certain biomarkers in zooplankton. In the present paper, laboratory and field studies were performed with the copepods Acartia margalefi, Acartia latisetosa and the mysid Siriella clausi. Acetylcholinesterase activity (AChE) was determined in homogenates of whole organisms. Mean AChE activity was 10.05 micromol min g(-1) for A. margalefi, 3.30 micromol min g(-1) for A. latisetosa and 79.70 micromol min g(-1) for S. clausi. A. margalefi and S. clausi also showed a linear increase in enzyme activity with increasing concentrations of samples. Preliminary laboratory work was also carried out with specimens of A. latisetosa, which were exposed to an organophosphorus insecticide (parathion). Moderate inhibition of AChE (19%) with respect to controls was observed. AChE activities were two orders of magnitude higher in the zooplankton than in hemolymph samples of the decapod Carcinus aestuarii (Fossi et al., 1996) indicating that these species have a high metabolic rate, which makes them suitable for biomarker studies.     

地下流体前兆数据库的质量监控系统研制及其开发技术

质量监控系统, 作为地下流体学科中心技术系统的重要组成部分之一, 监控着全国地下流体前兆数据库管理的所有台站观测数据的质量。该系统具有定时自动监控和运行速度较快的特点, 体系结构为客户/服务器。详细阐述了本系统服务器和客户端应用开发的结构、功能及其主要实现技术。     

基于CNN的地震前兆台网观测数据异常图像识别方法

地震前兆台网观测数据异常图像识别方法一直是地震监测预报人员研究的重要课题.为提高异常图像识别的工作效率,充分利用已有的异常图像识别经验知识,开展基于卷积神经网络(CNN)的快速异常识别方法探索性研究.结果表明:基于CNN的异常图像识别方法准确率较高,实现了异常图像的快速识别.整个台网的异常图像丰富多样,影响较多.由于特...     

基于数据挖掘的甘肃武都殿沟泉氡异常与地震活动统计关系研究

殿沟泉气氡浓度在汶川地震后经常出现成簇高频震荡异常。应用数据挖掘方法，采用正规化、聚类、特征值计算等方法对氡观测数据和地震目录进行预处理，提取气氡异常、震级、震源深度和地震分区等参数，在此基础上采用贝叶斯网络模型开展殿沟泉氡异常与周边区域地震活动统计关系研究。利用聚类开展的地震分区结果显示与构造分区基本吻合，反映出不同构造单元地震活动的丛集性特征；贝叶斯网络模型结果表明泉点气氡异常与周边地震活动有关，特别是与汶川地震主震区龙门山断裂中段和临近区青川断裂区域的地震活动有关。研究结果有助于了解泉点气氡对周边地震响应的差异性特征，对未来该泉点气氡异常的判断与地震预测有参考意义。为地震前兆异常分析和地震活动分区提供了一种新的技术思路和方法。