Statistical characterization of arsenic contamination in shallow tube wells of western Bangladesh     

Faisal Hossain  Amvrossios C. Bagtzoglou  Nurun Nahar  M. Delawer Hossain 《水文研究》2006,20(7):1497-1510

A regional assessment of the arsenic (As) contamination scenario in shallow tube wells (depth < 150 m) of western Bangladesh is presented. Comparisons are made in light of bulk geological differences (Pleistocene versus Holocene deposits/northwest versus southwest) and As measurement protocols (field kit (FK) versus atomic absorption spectroscopy (AAS)). Our As database comprised the following: (1) the nationwide As survey completed in 1999 by the British Geological Survey in collaboration with the Department of Public Health Engineering (DPHE); and (2) a regional As survey conducted in southwest Bangladesh by the Japan International Cooperation Agency in collaboration with DPHE in 2002. First, we characterize the error structure of the semi‐quantitative FK As measurements using collocated AAS As measurements as reference from a set of 307 wells located in southwest Bangladesh. The depth distribution of As is identified using a very dense cluster of 2963 wells over a 560 km² domain. The probability of the FK method for successful detection of a well sample as unsafe (safe) was found to be 96·9% (34·1%) and 95·2% (80·3%) for the World Health Organization (WHO) and Bangladesh safe limits, respectively. Similarly, the probability of false alarms and false hopes for WHO (Bangladesh) safe limits were found to be 3·1% (4·8%) and 87·5% (19·7%), respectively. The depth at which the highest fraction of wells exceeding a given safe limit occurred could still be inferred correctly by FK measurements. A simple bias adjustment procedure on FK As data did not result in a more accurate characterization of depth distribution of As. This indicated that simple error statistics are inadequate for advancing the utility of FKs; rather, an understanding of the complex and multidimensional error structure is required. Regional anisotropy in the spatial dependence of As for the northwest was found to be stronger than the southwest. The correlation length for As concentration in the east–west direction of northwest Bangladesh (i.e. across major river floodplains) was found to be almost twice (158·80 km) that of the north–south direction (along the major axis of Pleistocene deposits) (78·21 km). For the southwest region, the ratio of east–west to north–south correlation lengths ranged from 1·40 to 1·51. For the northwest region, because it is well known to have the lowest concentrations of As countrywide, knowledge of this anisotropy appears to suggest the need for drilling twice as many remediation deep wells in the proximity of an unsafe shallow well in the north–south direction than in the east–west direction. Findings from this study are potentially useful in setting priority areas for emergency testing, distributing remediation resources equitably and formulating a regional water resources strategy for western Bangladesh. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Spectrophotometric discrimination of river dissolved organic matter     

Andy Baker 《水文研究》2002,16(16):3203-3213

There is a need to be able to differentiate the dissolved organic matter (DOM) fraction in river waters. Research in the 1970s and 1980s has attempted to utilize both absorbance and fluorescence to distinguish between DOM fractions in river waters, but both were limited by the available technology. Total organic carbon content has, therefore, been widely used as a standard method of measuring DOM concentration, although it has little power to differentiate DOM fractions. Recent advances in fluorescence spectrophotometry enable rapid and optically precise analysis of DOM. Here, we show how a combination of both fluorescence and absorbance can be used to discriminate statistically between spatial variations of DOM in tributaries in a small catchment of the Ouseburn, NE England. The results of the discriminant analysis suggest that about 70% of the samples can be correctly classified to its tributary. Discriminant function 1 explains 60·8% of the variance in the data and the fulvic‐like fluorescence intensity has the largest absolute correlation within this function; discriminant function 2 explains a further 21·5% of the variance and the fulvic‐like fluorescence emission wavelength has the largest absolute correlation within this function. The discriminant analysis does not correctly classify all tributaries every time, and successfully discriminates between the different tributaries 70% of the time. Occasions when the tributary waters are less well discriminated are due to either episodic pollution events (at two sites) or due to tributaries that have strong seasonal trends in spectrophotometric parameters, which allows the sites to be misclassified. Results suggest that spectrophotometric techniques have considerable potential in the discrimination of DOM in rivers. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Rayleigh scattering cross-section redward of Lyα by atomic hydrogen     

Hee-Won Lee  Hee Il Kim 《Monthly notices of the Royal Astronomical Society》2004,347(3):802-806

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The detectability of H i 21-cm absorption in damped Lyman α systems     

S. J. Curran  J. K. Webb 《Monthly notices of the Royal Astronomical Society》2006,371(1):356-362

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Atomic oscillator strengths in the spectral domain of Gaia     

L. Bigot  F. Thévenin 《Monthly notices of the Royal Astronomical Society》2006,372(2):609-614

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Constraining the reionization history with QSO absorption spectra   总被引：1，自引：0，他引：1  

S. Gallerani  T. Roy Choudhury  A. Ferrara 《Monthly notices of the Royal Astronomical Society》2006,370(3):1401-1421

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Calc-silicate reactions and bedding-controlled isotopic exchange in the Notch Peak aureole, Utah: implications for differential fluid fluxes with metamorphic grade     

P. I. Nabelek 《Journal of Metamorphic Geology》2002,20(4):429-440

Fluid compositions and bedding‐scale patterns of fluid flow during contact metamorphism of the Weeks Formation in the Notch Peak aureole, Utah, were determined from mineralogy and stable isotope compositions. The Weeks Formation contains calc‐silicate and nearly pure carbonate layers that are interbedded on centimetre to decimetre scales. The prograde metamorphic sequence is characterized by the appearance of phlogopite, diopside, and wollastonite. By accounting for the solution properties of Fe, it is shown that the tremolite stability field was very narrow and perhaps absent in the prograde sequence. Unshifted oxygen and carbon isotopic ratios in calcite and silicate minerals at all grades, except above the wollastonite isograd, show that there was little to no infiltration of disequilibrium fluids. The fluid composition is poorly constrained, but X(CO₂)_fluid must have been >0.1, as indicated by the absence of talc, and has probably increased with progress of decarbonation reactions. The occurrence of scapolite and oxidation of graphite in calc‐silicate beds of the upper diopside zone provide the first evidence for limited infiltration of external aqueous fluids. Significantly larger amounts of aqueous fluid infiltrated the wollastonite zone. The aqueous fluids are recorded by the presence of vesuvianite, large decreases in δ¹⁸O values of silicate minerals from c. 16‰ in the diopside zone to c. 10‰ in the wollastonite zone, and extensive oxidation of graphite. The carbonate beds interacted with the fluids only along margins where graphite was destroyed, calcite coarsened, and isotopic ratios shifted. The wollastonite isograd represents a boundary between a high aqueous fluid‐flux region on its higher‐grade side and a low fluid‐flux region on its lower‐grade side. Preferential flow of aqueous fluids within the wollastonite zone was promoted by permeability created by the wollastonite‐forming reaction and the natural tendency of fluids to flow upward and down‐temperature near the intrusion‐wall rock contact.  相似文献   

阳极焙烧炉的燃烧计算与分析   总被引：1，自引：1，他引：0  

姚成军  徐明厚 《广东海洋大学学报》2004,24(1):57-62

采用计算燃烧学的原理和模型以及CFD软件对以重油作为燃料的阳极焙烧炉炉内的流动、燃烧过程进行了模拟计算,讨论了炉内温度场、流场和各组分浓度场的分布规律,分析了这些因素对碳阳极焙烧质量的影响.研究表明,在设计阳极焙烧炉结构时应考虑火道中挡板对气流分布的影响.  相似文献   

Assessing the Clock of Gaia: Design and Implementation of A Clock Framework Simulator     

E. García-Berro  J. Portell  J. Castañeda  J. P. Gordo 《Experimental Astronomy》2004,18(1-3):133-158

A powerful and highly configurable simulator of generic clock frameworks is presented and evaluated. This software tool was initially designed to test the reliability of clock data for the Gaia space mission. However, our application has been developed as much parameterized as possible in order to easily adapt it to any other space mission. The main goals of our software tool are to simulate the real performance of an atomic master clock, including the typical noises present in this kind of devices, and to check the reliability of the generation and distribution of clock sub-products. The latter, which are generated by other devices such as frequency multipliers and dividers, are also implemented in the simulator, as well as the corresponding transmission lines. In our simulator the clock outputs obtained from the several nodes of the framework can be displayed with the appropriate graphical tools, therefore easing the task of validating several design issues. Also, the parameters of the master clock and of all the framework devices, as well as the whole clock framework structure are entered using XML files, which can also be graphically verified. Finally, the accuracy and stability of the atomic clock which is expected to fly on-board of Gaia is assessed. We also discuss in depth the several issues regarding the time data products that Gaia will require and we characterize the most important elements.  相似文献   

Two-dimensional adiabatic flows on to a black hole – I. Fluid accretion     

Roger D. Blandford †  Mitchell C. Begelman ‡ 《Monthly notices of the Royal Astronomical Society》2004,349(1):68-86

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