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121.
This paper presents a theoretical model for computing the velocity and sediment concentration profiles in a uniform sediment-laden flow carrying all fine, medium and coarse sediments. The proposed model essentially includes the effect of sediment concentration in total turbulent shear stress and eddy diffusivity in addition to the modified mixing length derived by Umeyama and Gerritsen [J. Hydr. Engng., ASCE, 118 (2) (1992) 229–245] applied to Hunt’s diffusion equation. Numerical solution of coupled differential equations for velocity and sediment concentration is carried out. The theoretical results show quite good agreement with the experimental data. 相似文献
122.
A. V. Hirner 《International journal of environmental analytical chemistry》2013,93(1-3):77-85
Abstract Several commonly used sequential chemical extraction procedures of heavy metals in soils and sediments are compared, and their advantages and disadvantages are discussed focusing on selected case studies. In particular, problems caused by handling of anoxic samples, and of specific phases (e.g. organic fractions and sulfides) are addressed. Eventually, recommendations for the improvement of extraction selectivity as well as the reduction of readsorption effects are given. 相似文献
123.
G. Peng J.-U. Sommer A. Blumen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):73-79
We investigate numerically, using the bond-fluctuation model, the adsorption of many random AB-copolymers with excluded volume
interactions at the interface between two solvents. We find two regimes, controlled by the total number of polymers. In the
first (dilute) regime, the copolymers near the interface extend parallel to it, while in the second regime they extend perpendicular
to it. The density at the interface and the density in the bulk depend differently on the total number of copolymers: In the
first regime the density at the interface increases more rapidly than in the bulk, whereas the opposite is true in the second
regime.
Received 4 March 1998 and Received in final form 22 September 1998 相似文献
124.
从分析气体分子的悬浮和静水中Brown微粒的悬浮之机理出发,论述了重力场中粒子(分子、微粒等)的悬浮不一定需要其它外力,粒子本身的任何形式的无规则运动,达到一定强度后都能使粒子弥散悬浮.河流中的泥沙颗粒和气(水)力输送管道中的颗粒的悬浮也主要靠颗粒物的无规则运动.作用于颗粒的升力和其它力可改变颗粒悬浮沿高度的分布,但仅用这些力(若无任何无规则运动)无法解释颗粒的弥散悬浮状态.讨论了颗粒对流动阻力的双重作用:支持颗粒悬浮的湍流脉动因引入颗粒而削弱,这是颗粒的减阻作用;颗粒增阻的一个主要机制是,流体给予颗粒的水平动量在颗粒一壁面碰撞中不断地损失.用悬浮动概念解释颗粒引起的增阻是不正确的. 相似文献
125.
随着核技术的不断发展,核试验、乏燃料后处理及核电站事故等人类核活动向自然界释放了大量的~(129)I。~(129)I在沉积物中的含量与化学形态分布对揭示其迁移规律和沉降信息有着重要的意义。因此,对于研究沉积物中~(129)I不同形态所需要的合理分离及制备流程就尤为重要。结合太湖湖泊沉积物的特点并通过比较众多沉积物中~(129)I形态的分离流程,提出了改进的逐级浸取流程。在温度、时间不同的实验条件下,对沉积物样品分离出沉积物中~(129)I可交换态、有机结合态、金属氧化物态、残余矿物态四种不同形态,并通过高温热解法及125I示踪计算回收率及损失率。改进后的逐级浸取法能达到90%的提取效率,离子可交换态、有机结合态、金属氧化物结合态的适宜浸取时间和温度分别为4.5h、30℃,4.5h、75℃,5.5h、75℃。流程适用于同类湖底沉积物样品分析。 相似文献
126.
127.
A. López García E. Blanco González J. I. García Alonso A. Sanz-Medel 《Chromatographia》1992,33(5-6):225-230
Summary Analytical methods for the determination in environmental samples, of some selected Polycyclic Aromatic Hydrocarbons (PAH's), which are included on the EPA Priority Pollutant list, have been developed and evaluated. The methodology involves the extraction of PAH's from water samples by solvent extraction with dichloromethane. Solid samples were ultrasonically extracted with acetone/hexane and the extract was cleaned up on a silica gel/alumina column. The concentrated and cleaned up extracts were analysed by HPLC on a polymeric C18 column using a gradient of acetonitrile/water as the mobile phase and fluorescence detection. Typical detection limits lie in the range of 1–30 ng ml–1 of the analytes, but after sample pretreatment detection limits of 10–300 ng l–1 were obtained. The extraction, clean-up and HPLC methodology was applied to the determination of selected PAH's in coal washings samples and the method was validated by the quantification of PAH's in a natural contaminated and a spiked sediment. 相似文献
128.
A flow-injection analysis atomic absorption spectrometric (FIA-AAS) method was developed for the determination of trace amounts of arsenic, selenium and mercury in a proposed estuarine sediment standard reference material (SRM 1646a). The samples were prepared in two manners: a) A wet digestion procedure with HNO3, H2SO4, and HClO4 using a reflux column and b) A microwave-oven digestion procedure utilizing HNO3, H2SO4, and HCl for As and Se, and HNO3 for Hg. Microwave-oven digestion provides results comparable to those found by reflux column digestion and reduces the sample preparation time by a factor of 10. The proposed method employing the microwave-oven digestion procedure coupled with FIA-AAS for As and Se, and FIA-CVAAS for Hg, has detection limits of 0.15 ng As/ml, O.17 ng Se/ml and 0.15 ng Hg/ml.On leave from the Defense Metallurgical Research Laboratory, Hyderabad, India 相似文献
129.
FENG JingLan WANG GuoLiang SUN JianHui SUN ShengPeng &LIU XiangFu Henan Key Laboratory for Environmental Pollution Control College of Chemistry Environmental Sciences Henan Normal University Xinxiang China State Key Laboratory of Pollution Control Resources Reuse College of Environmental Science Engineering Tongji University Shanghai China 《中国科学:化学》2010,(5)
The concentrations of Cd,Cr,Cu,Ni,Pb and Zn were determined in the water and surface sediments from the Henan reaches of the Yellow River.Twenty-three sampling sites along the Yellow River and its tributaries were selected.Generally,metal concentrations were found to decrease in sequences of Zn>Cu>Pb>Cr>Ni>Cd in water and Zn>Cr>Pb>Ni>Cu>Cd in sediments.High levels of metal concentration were determined at a few stations of the river and its tributaries,such as Yiluo River,Si River and Qin River.The pollutio... 相似文献
130.
An interference-free, fast, and simple method is proposed for Pb determination in environmental solid samples combining slurry sampling and electrothermal atomic absorption spectrometry. Samples were ground to an adequate particle size and slurries were prepared by weighing from 0.05 g to 0.20 g of dry sediment, adding nitric acid, and a solution containing 0.1% Triton X-100. Ultrasonic agitation was employed for slurries homogenization. Analytical variables including acid pre-treatment conditions, particle size, slurry stability, temperature program of the graphite furnace, and type and concentration of the chemical modifier were studied. The undesirable effects of potential non-specific and spectral interferences on Pb signal were also taken into account. Continuum source and self-reversal methods for background correction were evaluated and compared. For calibration, synthetic acid solutions of Pb were employed. Calibration was linear within the range 1-30 μg L−1 and 5-30 μg L−1 when the 217.0 nm and 283.3 nm analytical lines were used. Correlation coefficients of 0.9992 and 0.9997 were obtained. Using optimized conditions, limits of detection (3σ) of 0.025 μg g−1 and 0.1 μg g−1 were achieved for the 217.0 nm and 283.3 nm analytical lines, respectively. The method was successfully applied to the determination of lead in soil, contaminated soil, municipal sludge, and sediment samples. The accuracy was assessed by the analysis of two certified reference materials: municipal sludge (QC MUNICIPAL SLUDGE A) and lake sediment (TRAP-LRM from IJS). 相似文献