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51.
G. Dreibus H. Palme B. Spettel J. Zipfel H. Wnke 《Meteoritics & planetary science》1995,30(4):439-445
Abstract— We report here new analyses of S and Se in carbonaceous chondrites (2 CIs, 11 CMs, 6 CO3s, 7 CV3s, 2 C4s, 4 CRs, and 1 CH), 2 rumurutiites, ordinary chondrites (2 Hs, 2 Ls, and 1 LL), 3 anomalous chondrites, 3 acapulcoites, 3 lodranites, and in silicate inclusions of the Landes IAB iron meteorite. To avoid problems from inhomogeneous distribution of sulfides, the same samples that had been analysed for Se by INAA were analysed for S using a Leybold Heraeus Carbon and Sulfur Analyser (CSA 2002). With the measured CI contents of 5.41% S and 21.4 ppm Se a CI S/Se ratio of 2540 is obtained. A nearly identical S/Se ratio of 2560 ± 150 is found for carbonaceous chondrites (average of falls). The average ratio of all meteorite falls analysed in this study was 2500 ± 270. These data suggest that the new S content of Orgueil with 5.41% provides a reliable estimate for the average Solar System. The new solar system abundance of S of 4.62 × 105 (atoms/106 Si) is in good agreement with the solar photospheric abundance of 7.21 (log (a(H)) = E12) (Anders and Grevesse, 1989). Among the 50 analysed meteorites, 24 were finds from hot (Australia, Africa) and cold (Antarctica) deserts. Weathering effects in the carbonaceous chondrites and in one lodranite from the hot deserts resulted in losses of S, Se, Na and occasionally Ni. Sulfur is apparently more affected by weathering than Se. No losses were observed in ordinary chondrite finds and in meteorites collected in the Antarctica, except for the obvious loss of Na in the CM-chondrite Y 74662. The low S-content of 0.096% in Gibson, a lodranite, is probably not representative of this group of meteorites. Gibson is a find from the Australian desert and has lost S and also Se by weathering. Two other lodranites, finds from Antarctica, have about 2% S. 相似文献
52.
Phase transitions and associated domains of meteoritic troilite (FeS) have been studied by means of transmission electron microscopy (TEM). Three polymorphs have been found, two of which can be described by superstructures of the NiAs-type structure (A, C subcell). The P \(\overline 6\) 2c (√3A, 2C) polymorph, stable at room temperature, displays antiphase domains with the displacement vector 1/3< \(\overline {\text{1}}\) 10>. In situ heating experiments showed that the P \(\overline 6\) 2c polymorph changes at temperatures of 115°–150° C into an orthorhombic pseudohexagonal transitional phase with the probable space group Pmcn (A,√3A, C). It contains antiphase domains with the displacement vector 1/2 [110] and twins with a threefold twin-axis parallel c. When heated above 210° C the transitional phase transforms into the high-temperature modification with NiAs structure (P6 3/mmc). All observed phase transitions are reversible. The occurrence of antiphase and twin domains, respectively, agrees with the symmetry reductions involved in the subsolidus phase transitions. This is demonstrated by group-subgroup relationships among the space groups P6 3/mmc, Pmcn, and P \(\overline 6\) 2c. 相似文献
53.
Ocean Dynamics - Die 7. Sitzung der Kommission für nachhaltige Entwicklung (Commission on Sustainable Development, CSD) der Vereinten Nationen fand vom 19. bis 30. April 1999 im... 相似文献
54.
Jutta Jahnel Christian Zwiener Thomas J. Gremm Gudrun Abbt‐Braun Fritz H. Frimmel Carola Kussatz Dieter Schudoma Werner Rocker 《洁净——土壤、空气、水》2001,29(4):246-253
Quality Targets for Pesticides and Other Pollutants in Surface Waters Surface waters are not only adversely affected by industrial and municipal wastewaters but also by diffuse sources. For the control of the ecological water quality, so‐called quality targets are set. The quality targets are threshold concentrations for hazardous substances related to the protected goods like water ecosystems, drinking water supply, sediments, or fishing. In this paper, quality targets for the protection of aquatic life in surface waters were derived on the basis of a concept developed by the International Commission for the Protection of the Rhine (Internationale Kommission zum Schutze des Rheins – IKSR). The quality targets for the selected hazardous substances, which mainly belong to the chemical class of pesticides, were calculated using ecotoxicological results for species of bacteria, algae, fish, and small crustaceans, as the four trophic standards of the water ecosystem. In cooperation with the Federal Environmental Agency (Umweltbundesamt – UBA) the effect data were taken from ecotoxicological data bases. According to the concept of the IKSR, the lowest test result for the most sensitive species was multiplied by an assessment factor. This proceeding concerns the difficulty in describing the complex interactions in water ecosystems with toxicity data of single laboratory experiments for a few organisms. For seven pesticides quality targets below 0.1 μg/L were proposed. These results show that the ecotoxicologically based quality targets might be even lower than the limit values for pesticides in drinking water of 0.1 μg/L. But for most of the substances the determined values are significantly higher. The great concentration range of quality targets demonstrates distinctly that one standard concentration for all pesticides could not be given with regard to the different effects on aquatic organisms. 相似文献