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Pavle TAN?I? Radovan DIMITRIJEVI? Maja POZNANOVI? Aleksandar PA?EVSKI Slobodanka SUDAR 《《地质学报》英文版》2012,86(6):1524-1538
The crystal structure of ludwigite from Vranovac ore deposit (Boranja Mt., Serbia) was refined using the X-ray powder diffraction (XRPD) Rietveld method in the space group Pbam to a final RB=7.45% and RF=5.26%. It has the unit cell dimensions of: a=9.2515(2) ?; b=12.3109(2) ?; c=3.03712(7) ?; and V=345.91(1) ?3. The calculated distances and angles are mostly in good agreement with the Mg2+-Fe2+ substitutions across the M(1) and M(3) sites, as well as with the Fe3+-Al3+ replacement in the M(4) site. However, the mean observed M(2)-O distance is considerably shorter than prescribed, due to a slight increase of the Fe3+ content in the M(2) site. Such replacement was compensated by slight increase of the Fe2+ content in the M(4) site, resulting in the (Mg1.48Fe2+0.46Fe3+0.05Mn0.02)2.01(Fe3+0.94Fe2+0.04Al0.02)1.00B1.00O5 composition. The formation temperature was estimated to be about 500–600°C. The influences of the various chemical compositions to the crystallographic parameters, M-O distances, M(3) and M(4) sites shift, distortion parameters and estimated valences, were also studied and compared with other reference samples. 相似文献
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PA Franklin 《新西兰海洋与淡水研究杂志》2013,47(1):112-126
Maintenance of suitable conditions in lowland rivers for both fish passage and resident species is crucial to ensuring the long-term sustainability of fish populations. The dissolved oxygen concentration of water is a key factor controlling habitat quality for fish and a critical measure of stream health. Continued land use intensification and greater exploitation of water resources has contributed towards increasing the frequency and duration of low dissolved oxygen events in lowland rivers and the associated risk of adverse effects on fish communities. Revised guidelines are therefore proposed to support setting of biologically relevant dissolved oxygen limits for the protection of New Zealand freshwater fish communities. These guidelines account for both event magnitude and duration, identify different protection levels based on the risk of negative impacts and are based on current scientific knowledge on the tolerances of New Zealand fish species. 相似文献
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Assessment of prediction performances of stochastic models: Monthly groundwater level prediction in Southern Italy 下载免费PDF全文
Stochastic modelling of hydrological time series with insufficient length and data gaps is a serious challenge since these problems significantly affect the reliability of statistical models predicting and forecasting skills. In this paper, we proposed a method for searching the seasonal autoregressive integrated moving average(SARIMA) model parameters to predict the behavior of groundwater time series affected by the issues mentioned. Based on the analysis of statistical indices, 8 stations among 44 available within the Campania region(Italy) have been selected as the highest quality measurements. Different SARIMA models, with different autoregressive, moving average and differentiation orders had been used.By reviewing the criteria used to determine the consistency and goodness-of-fit of the model, it is revealed that the model with specific combination of parameters, SARIMA(0,1,3)(0,1,2) _(12), has a high R~2 value,larger than 92%, for each of the 8 selected stations. The same model has also good performances for what concern the forecasting skills, with an average NSE of about 96%. Therefore, this study has the potential to provide a new horizon for the simulation and reconstruction of groundwater time series within the investigated area. 相似文献
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The dinoflagellate genus Ostreopsis produces palytoxin-like compounds (PLTXs) and the genus Gambierdiscus produces ciguatoxins (CTXs) and maitotoxin (MTX). Human illness has been recorded following the consumption of CTX-contaminated finfish. Their effects on the flora and fauna in the environment are largely unexplored. Toxin profiles of extracts of Ostreopsis and Gambierdiscus isolates from the Pacific region were characterised using liquid chromatography tandem mass spectrometry. Sea urchin (Evechinus chloriticus) fertilisation was unaffected by any algal extracts, but extracts containing maitotoxin-3 (MTX-3, but not MTX or CTXs), or with high concentrations of PLTXs, were toxic to urchin larval development. Gambierdiscus extracts containing CTXs elicited toxic responses in zebrafish (Danio rerio) embryo toxicity assays; extracts containing only MTX-3 elicited a limited response. Ostreopsis extracts containing PLTXs caused no response. The results demonstrate potential impacts of toxic dinoflagellates on larval organisms and the potential of embryonic assays as toxicity screening tools. 相似文献
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