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641.
642.
L. T. Fan Rekha S. Nadkami Larry E. Erickson 《Journal of the American Water Resources Association》1971,7(6):1210-1220
An analytical solution is developed to predict the BOD and DO profiles in a stream having several outfalls of waste and intakes of water. The model also incorporates continuous addition and removal of BOD and DO along the stream. A steady state one dimensional dispersion model is used to describe the transport of BOD and DO in a stream. Changes in stream properties along the length are considered by dividing the stream into several segments and changing the parameters of the BOD and DO equations as needed in each segment. By applying continuity equations at the boundaries of these segments and equilibrium conditions at either ends of the infinitely long stream, the arbitrary constants in the solutions to the differential equations for BOD and DO can be determined. Some applications of the results in studying water pollution problems are illustrated. 相似文献
643.
ABSTRACT Numerical and analytical solutions are developed for the distribution of a contaminant within an adsorbing porous medium in a unidirectional flow field subject to a step function for input concentration. The medium is considered to be homogeneous, isotropic, and areally finite. As a by-product, solutions are also obtained for the case of a non-absorbing porous medium. An example that demonstrates the applicability of the solutions is presented. 相似文献
644.
L. Van Rensburg T.L. Morgenthal H. van Hamburg M.D. Michael 《The Environmentalist》2003,23(4):285-295
The aim of this paper is to compare the rehabilitation result between two ash disposal sites with regard to its vegetation establishment and soil nutrient status. The study areas were situated in close proximity, in the Mpumalanga coalfield, South Africa. Although both areas received a similar amelioration treatment and were seeded with similar seed mixture the vegetation composition were significantly different. Both areas were poor in essential nutrients, this probably being one of the most limiting factors for vegetation establishment. No serious phytotoxic conditions, as is frequently experience with coal ash, could be identified. A regular monitoring and low level maintenance program is therefore proposed to improve the sustainability of the vegetation. The study proposed that results form such evaluations be used to identify performance standards for rehabilitated derelict land. 相似文献
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647.
D. Vlachogiannis S. Rafailidis J. G. Bartzis S. Andronopoulos A. G. Venetsanos 《Water, Air, & Soil Pollution: Focus》2002,2(5-6):405-417
The wind-driven flow patterns and the dispersion of vehicle exhaust pollutants released at street level has been simulated with the three-dimensional (3-D) dispersion model ADREA-HF (Andronopoulos et al., 1993), for idealised two-dimensional urban fetches occupied by buildings with slanted roofs. The simulation used oncoming atmospheric boundary layer characteristics corresponding to realistic above-town wind characteristics, as measured in reference wind tunnel experiments (Rafailidis, 1997). At that stage, analysis was limited to neutral stability conditions only. Firstly, the quality assurance of the numerical model was investigated in terms of the sensitivity to different grid allocations. The modelling results were corroborated by comparison with wind tunnel measurements in a similar two-dimensional domain (Pavageau et al., 1997). The numerical modelling replicated well the high degree of non-uniformity in the dispersion field in the test street, and the results agreed satisfactorily with the experimental measurements. The reasons for the differences observed have been investigated. With the model thus validated, three different exhaust release scenarios have been tested, keeping the same overall emission rate but different spatial patterns of street-release. The effect of the different street-release scenarios was found to be only marginal, with the dispersion patterns on the sidewalls affected only locally, close to the street level. 相似文献
648.
P. Sahm P. Louka M. Ketzel E. Guilloteau J.-F. Sini 《Water, Air, & Soil Pollution: Focus》2002,2(5-6):587-601
Microscale Computational Fluid Dynamics (CFD) models havebecome an efficient and common simulation tool forassessment and prediction of air quality in urban areas.The proper validation of such a model is a crucialprerequisite for its practical application. Within theframework of the European research network TRAPOS a workinggroup on computational fluid dynamics modelling wasestablished and model intercomparison exercises werelaunched. Different Computational Fluid Dynamics Codes wereapplied for simulating the wind flow and pollutantconcentration patterns in several test cases. The aim ofthe present model intercomparison is (1) to assess andallocate the source of differences that appear whendifferent CFD codes using the same turbulence model areapplied to well defined test cases and (2) to improve theknowledge base for model development and application.Throughout the series of model applications coveringmanifold urban configurations, the overall agreementbetween the various models and experimental data is fair.In spite of quantitative differences between the variousnumerical results, the models are capable of reproducingthe flow patterns and dispersion characteristics observedin urban areas but they show significant differences forthe turbulent kinetic energy field that controls thedispersion of pollutants. 相似文献
649.
发展中国有机食品产业 总被引:7,自引:0,他引:7
本文根据有机食品的概念,中国有机食品发展现状,论述了发展有机食品是时代进步的要求,中国应发展有机食品产业。 相似文献
650.
矿井安全状况的解释结构建模法(ISM)分析 总被引:6,自引:0,他引:6
依据影响矿井安全状况的 13个因素之间存在的逻辑关系 ,运用系统工程中的解释结构建模(ISM)方法进行了定性处理 ,建立了影响矿井安全状况因素的多级递阶结构模型。在该模型中 ,13个因素分为 6个级别 ,即事故和职业病 ;危险因素和有害因素 ;安全技术 ;开采和生产装备 ;矿井自然条件、矿区环境和安全投入 ;生产人员素质、安全管理和发展。通过模型 ,揭示了因素之间的纵向和横向关系 ,明了各因素对矿井安全状况的影响程度 ,为建立和完善矿井安全状况评价结构模型 ,确定模型中各因素的权重值 ,以及制定矿井生产安全对策措施提供了科学依据。 相似文献