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141.
ABSTRACT: Customarily, it has been assumed that hydraulic conductivity is a stationary, homogeneous stochastic process with a finite variance for stochastic analysis of solute transport in the subsurface. That the distribution of hydraulic conductivity may have a fractal behavior with long range correlations was suggested from field data analyses. This motivates us to further investigate how the fractal behavior of permeability distribution impacts solute transport in porous media. This study provides longitudinal and transverse macrodispersivity coefficients and the variance of the solute concentration. Longitudinal and transverse macrodispersivity coefficients are found to depend strongly on the fractal dimension (D) of logarithmic hydraulic conductivity (logK). The longitudinal and transverse macrodispersivity coefficients are the highest when D = 1, and the values decrease monotonically to zero at D = 2. Both coefficients correspond to the characteristic length scale of the logK distribution, thus are scale dependent parameters. The ratio of the transverse to the longitudinal macrodispersivity coefficient is on the order of 10‐1 to 10‐4. Concentration variance also decreases with the fractal dimension of logK. There is no spatial spreading of solute for D = 2, and the concentration variance reaches zero for this case. 相似文献
142.
Seventeen sediment cores were collected from different coastalecosystems of Tamil Nadu, India that include coastal lagoon (Pulicat), polluted rivers in Chennai (Adyar and Cooum), Coral reef (Gulf of Mannar) and a perennial river (Tamiraparani).Radiometric dating has been used to determine the modern sedimentation rates in these ecosystems. The Pulicat Lake and thepolluted rivers (Adyar and Cooum) yield an average sediment accumulation rate of 12.34 and 7.85 mm yr-1, respectively. Inthe Gulf of Mannar coral reef, the sedimentation rate averages 17.37 mm yr-1, while the rate in Tamiraparani River is 11.00 mm yr-1. In the Tamiraparani River basin, the deposition rates were an order of magnitude higher when compared to the erosion rates, which may be due to bank erosion and the intense human activity. In general high rates of sedimentation observed in the coastal ecosystems not only reflect the capacity of the coastal regions as sinks for trace metals but also denoteincreased input of pollutants into the coastal environments in the recent past. The deposition rates of heavy metals – Fe, Mn,Zn, Cu, Cr and Ni in the depth profiles have been computed using sedimentation rates and their distribution is discussed. It can be seen that the mean deposition rates of all the measured elements in the Tamil Nadu coastal ecosystems are high compared with rates determined for the sediments of the deltaic regions ofIndia and the Bay of Bengal. 相似文献
143.
Antonio Finizio Antonio Di Guardo Lara Cartmale 《Environmental monitoring and assessment》1998,49(2-3):327-336
Atmospheric change comprises many phenomena, namely climate change, acidic deposition, stratospheric ozone depletion, SMOG, increasing trend of suspended particulate matter, and hazardous air pollutants (HAPs). Among HAPs, a particular group of Persistent Organic Pollutants (POPs), such as some organochlorine pesticides, has shown a variety of toxic effects, altering the biodiversity of many ecosystems. Because of their persistence in the environment, and of their long range transport, the study of the global cycle of POPs is important in understanding how they can affect biodiversity. This can be accomplished by coupling different approaches: toxicity and ecological studies, emission estimates, and the use of global models. 相似文献
144.
Resilience engineering (RE) is capable of handling disruptive events and controlling their consequences in process industries such as petrochemical plants. This study aims at analyzing the level of adaptive capacity and identifying effective factors on developing adaptive capacity in the organizational structure of process industries. The data of this study were obtained through direct observation and a structured questionnaire in a petrochemical plant. Managers at all levels participated in the survey. Data envelopment analysis (DEA), which is a mathematical approach, was used to compute and analyze the role of the factors contributing to adaptive capacity. The results indicated that reporting safety issues played a central role in enhancing adaptive capacity at all management levels. Both middle management and low-level management emphasized the importance of management commitment, whereas top-level management considered flexibility as a vital factor in managing disruptions and reducing accidents. The findings of this study could be useful for managers and other decision-makers to improve safety in process industries. 相似文献
145.
一种新的结构可靠度通用计算方法 总被引:1,自引:0,他引:1
根据可靠度指标β的几何定义,运用具有全局优化能力的改进遗传算法,提出一种新的结构可靠度通用计算方法。针对可靠度几何优化模型搜索区域大而可行区域小的特点,在可靠区域和失效区域分别产生初始种群,在两种群之间通过不断迭代的二分法,使二分点不断接近极限状态曲面(线),从而产生可行解。对可行解进行选择、交叉、变异,最后求出全局最优解。该方法不需要使用结构功能函数的偏导数,对于功能函数不能明确表达的可靠度问题尤为适用;对于功能函数可以明确表达但求导复杂的问题,可省去求导过程;可任意设定初始值,且不受结构功能函数凹凸性的限制;通过算例验证,所提方法具有较高的精度和效率。 相似文献
146.
147.
148.
Air Quality in Norwich, UK Multi-Scale Modelling to Assess the Significance of City, County and Regional Pollution Sources 总被引:1,自引:0,他引:1
T. Chatterton S. Dorling A. Lovett M. Stephenson 《Environmental monitoring and assessment》2000,65(1-2):425-433
Norwich is the eastern most city in the United Kingdom. Despite a population of only 100,000 and very little local industry, studies have shown that the city experiences levels of nitrogen dioxide, ozone, particulates and sulphur dioxide exceeding the UK Air Quality Standards. Because of Norwich's situation within a large, predominantly rural area a large non-resident workforce is one factor that contributes to large, often very congested traffic flows. The city's location close to the European mainland also exposes it to polluted airmasses transported from the continent, especially in the case of particulates and ozone. In order to assess the relative contributions of local and regional sources, data from rural and urban monitoring sites are to be used in conjunction with ADMS-Urban and the UK Meteorological Office's NAME model. 相似文献
149.
于2010年5、8和11月,2011年2月,分别采集了金华江支流白沙溪4个断面附生硅藻样品,分析其硅藻群落结构及物种多样性,并利用多样性指数对水质进行了生物学评价;同时,应用典型对应分析揭示白沙溪硅藻群落结构与环境因子之间的关系。结果表明:(1)共鉴定附生硅藻92种(含变型和变种),隶属于2纲19科31属;多样性指数为140~248,总平均为189;均匀度指数为012~038,总平均为023;(2)硅藻群落结构呈现出季节上的变化。在季节变化上,物种丰富度及多样性指数以夏季(8月)最高,而以春季(5月)最低。白沙溪水体总体为α 中污水体;(3)典型对应分析结果表明,氨氮、水温和pH是影响白沙溪附生硅藻群落分布的主要因素,硅藻群落结构随着这些环境因子的变化表现出一定的空间差异 相似文献
150.