Tributyltin determination in marine sediments: A comparative study of methods

Two independent speciation methods have been applied to the determination of tributyltin (TBT) in marine sediments: (1) acetic acid leaching/hydride generation/cold trapping/GC/quartz furnace AA; and (2) toluene–tropolone extraction/HPLC/GFAA. TBT determines in a typically moderately polluted sediment (Porto Vecchio Bay, Corsica, France) are in very good agreement, as also are the determination of total recoverable tin by the first method and by a direct one using strong acid leaching followed by GFAA. These cross-verifications lead one to conclude that both speciation methods are convenient and allow for valid determination of TBT in marine sediments, with no loss of TBT. Method-induced modification of tin speciation has not been observed.     

Emission to air of volatile organotins from tributyltin‐contaminated harbour sediments

An analytical method for determining the presence in air of volatile forms (e.g. chlorides) of tributyltin (TBT) and that of methylbutyltins Me _nBu_(4?n)Sn (n = 1–3) was developed and used to establish whether dredged harbour sediments contaminated with TBT served as sources of air pollution with respect to organotin compounds. The method was based on active sampling of the air being analysed and sorption of analytes onto Poropak‐N. Sorbed methylbutyltins were extracted with dichloromethane and analysed by gas chromatography using flame photometric detection. Other butyltins were converted into butyltin hydrides prior to analysis by gas chromatography. It was shown that TBT‐contaminated sediments from Marsamxett Harbour, Malta, placed in 0.5 l chambers through which air was displaced by continuous pumping for 11 days released mainly methylbutyltins, with concentrations (as tin) reaching maximum 48 h mean values of 8.7 (Me₃BuSn), 22.1 (Me₂Bu₂Sn) and 93.0 ng m^?3(MeBu₃Sn) being measured. Other volatile forms of TBT, dibutyltin and monobutyltin were detected in the headspace air, but very infrequently and at much lower tin concentrations (<2 ng m^?3). It was also shown that methylbutyltins dissolved in sea‐water ([Sn] = 0.2 to 400 ng l^?1) were very difficult to exsolve from this medium, even on prolonged evaporation of the solutions using mechanical agitation and active ventilation. The results suggest that emission of methylbutyltins from contaminated sediments probably occurs only from the surface of the material. The environmental implications of these findings in the management of TBT‐polluted harbour sediments are discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

应用近红外光谱技术重建南极湖泊初级生产力变化的一种新方法

为探求快速、廉价、无损、同步的光谱技术在南极古湖沼研究中的可能性,本文分析了南极中山站附近采集的一根湖泊沉积柱样晶的近红外反射光谱数据,通过主成分(PCA)统计分析方法,发现主成分因子载荷值与反映湖泊生产力变化的环境指标S2(有机质热解烃类化合物指标,指示湖藻类来源有机质)在深度剖面上具有一致的变化趋势,两者表现出显著...     

A lattice Boltzmann model for the eddy–stream equations in two-dimensional incompressible flows

A lattice Boltzmann model for two-dimensional incompressible flows with eddy–stream equations is proposed. By using two kinds of distribution functions and employing several higher-order moments of equilibrium distribution functions, the eddy equation and stream function equation with the second-order truncation error are obtained. In the numerical examples, we compared the numerical results of this scheme with those obtained by other classical method. The numerical results agree well with the classical ones.     

The nonsimilar laminar wall jet along a moving wall,in a free stream and in a free stream/moving wall

The flow of a laminar wall jet along either a moving plate, or in a free stream, or in combined moving plate and free stream is considered. The plate is isothermal and its temperature is different from that of the ambient fluid. The governing boundary-layer equations are converted into non-dimensional form and are solved numerically. Velocity and temperature profiles as well as the variation of wall shear stress and wall heat transfer are presented for all cases considered. For the case of a moving plate new results have been found although this problem has been investigated in the past. For the case of the free stream and the combined moving plate/free stream all the results are new and are presented for the first time in the literature. The three cases have been tackled with a unified way.     

黄河小型清沟封冻过程现场模拟实验与实测数据分析

利用黄河封冻阶段的冰层,开16m2敞流水面模拟清沟,通过雷达测冰厚的方法,观测敞流水面因冰花封冻过程,并测量敞流水面封冻后冰盖厚度分布,并用费氏台观察冰晶体结构.通过将实测冰厚数据绘成等高线图以及冰厚剖面图,证实封河过程中,由周边向中间封冻的清沟除了与冰冻度日有关外,还与清沟下水流速度和方向以及冰花含量有关.水流携带冰花流至清沟时,冰花会漂浮在清沟中.由于水的粘性作用,水流使清沟中的水起动,然后冲击下游冰壁引起涡旋.涡旋场在清沟上游形成较平静区域,可以积累大量冰花;而在下游冰壁处水体运动活跃,冰花无法堆积.经过长时间冻结,上游处冰花被冻结成为较厚的冰花冰,而下游逐渐冻结成较薄的冰花冰.之后,柱状冰在冰花冰下开始生长.最后经过1个月的冻结,形成了敞流水面下游处冰较薄,上游处冰较厚的非对称冻结厚度分布,并在与水流垂直的方向表现为对称冻结厚度分布.     

An approach to the study of multistate insurance contracts

We derive a matrix representation for formulas of moments of cash value of future payment streams arising from multistate insurance contract, where the evolution of the insured risk and the interest rate are random. As an application, we derive formulas for net single and period premiums. The general theory is illustrated with a case where the evolution of the insured risk is modeled by a Markov chain. Copyright © 2012 John Wiley & Sons, Ltd.     

A coupled blade element momentum – Computational fluid dynamics model for evaluating tidal stream turbine performance

A modelling approach based on blade element momentum theory is developed for the prediction of tidal stream turbine performance in the ocean environment. Through the coupling of the blade element momentum method with computational fluid dynamics, the influence of upstream hydrodynamics on rotor performance is accounted for. Incoming flow onto the rotor can vary in speed and direction compared to free-stream conditions due to the presence of obstructions to the flow in the upstream, due to other devices for example, or due to the complexity of natural bathymetries. The relative simplicity of the model leads to short run times and a lower demand on computational resources making it a useful tool for considering more complex engineering problems consisting of multiple tidal stream turbines. Results from the model compare well against both measured data from flume experiments and results obtained using the classical blade element momentum model. A discussion considering the advantages and disadvantages of these different approaches is included.     

Sorption of Europium (III), Cobalt (II) and Cesium (I) by Fresh Water Sediment Fractions Part 2: Effect of Some Environmental Ligands

The sorption behaviour of the radiotracers Eu⁹⁺, Co²⁺ and Cs⁺ by the sediment fractions: sand, coars silt, fine silt and clay was investigated from aqueous solutions containing the complexing agents; humic acid, sodium phosphate or disodium EDTA. The effect of ligand concentration on the sorption of these elements by the sediment fractions was elucidated at varying pH values. The results obtained are interpreted in the light of the complex formation between the ligand and the metal cations beside the interaction between the ligand and the respective sediment fraction investigated.     

流体力学中的总流伯努利方程

文章从宏观上分析流体的平衡和运动规律,着重阐述流体力学中理想流体和压强的概念以及静止流体内压强的分布规律.文章介绍了流体的定常运动及流线、流量和总流的概念,给出了连续性方程,并在此基础上推导了理想流体定常运动的总流伯努利方程.结合工程实际问题,文章还介绍了实际流体的定常流动的总流伯努利方程.