排序方式: 共有47条查询结果,搜索用时 15 毫秒
1.
Pablo Recabarren Pablo Recabarren Mirta Mosconi Hernán Muriel Hernán Muriel Diego García Lambas Diego García Lambas Marc Sarazin Riccardo Giovanelli 《Astrophysics and Space Science》2004,290(3-4):409-413
We present the preliminary results of the astronomical site testing, which the group IATE of the OAC is developing in northwest of Argentine in collaboration with ESO and the Department of Astronomy of Cornell University. We show the results, which we have obtained from the analysis of GOES 8 satellite images in the 10.7 μm band, which allowed us to configurate a map of clear sky regions in an area between 23° and 28° S, and 66° 30′ and 69° W. We also comment logistical and tectonic aspects, and discuss next steps to follow in the research. 相似文献
2.
3.
4.
Kimmeridgian bituminous laminites from Orbagnoux (France) contain abundant amorphous organic matter (AOM). Previous studies have shown that the vulcanization pathway was the dominant preservation mechanism of AOM in these laminites, and led to its structureless aspect (a process called amorphization) at the nanoscale. In contrast, new observations in scanning electron microscopy and transmission electron microscopy demonstrate that this AOM exhibits typical cyanobacterial structures (exopolymeric substances, filamentous and coccoid bacteria) and ultralaminae. This identification is supported by a comparison with a recent cyanobacterial biofilm considered as an analogue. Moreover, this comparison demonstrates that ultralaminae in the Orbagnoux environment cannot solely be attributed to microalgal cell walls, but also to constituents of cyanobacteria. The microscopic identification of a ubiquitous cyanobacterial imprint demonstrates that the selective preservation pathway has been largely underestimated in Orbagnoux AOM and/or that the vulcanization process does not lead to the amorphization of organic matter automatically. 相似文献
5.
Ashwani Kumar Tiwari Raffaella Ghione Marina De Maio Muriel Lavy 《Arabian Journal of Geosciences》2017,10(12):264
The present study aims to discuss the hydrogeochemical processes in the Aosta Valley region and assess the quality of its groundwater for suitability of drinking and irrigation purposes. One hundred twenty-two samples were collected from the Aosta Valley region in the years 2007 and 2008 (61 per year), and analysed for pH, electrical conductivity, total dissolved solids (TDS), total hardness, major cations and anions. The pH of the samples in both years indicated a near-neutral to alkaline nature of the groundwater. The cation and anion chemistry showed the general ionic abundance as: Ca2+ > Mg2+ > Na+ > K+ and HCO3 ?>SO4 2?>Cl?>NO3 ?>F? in both years. Ca2+-Mg2+-HCO3 ? and Ca2+-Mg2+-Cl?-SO4 2? were the dominant hydrogeochemical facies. The computed saturation indices demonstrated that the groundwater was supersaturated with respect to dolomite and calcite in both years. The groundwater chemistry of the study area was mainly controlled by the dissolution of carbonate, sulphate and silicate minerals, as well as ion exchange processes. A comparison of the groundwater quality in relation to drinking water standards showed that most of the water samples were suitable for drinking and domestic uses. The computed water quality index (WQI) values of the study area groundwater ranged from 24 to 84 in the year 2007 and from 22 to 82 in the year 2008, and all the location fell under the Excellent to Good category. Quality assessment for irrigation uses revealed that the groundwater was good to permissible quality for irrigation; however, locally higher salinity, residual sodium carbonate (RSC) and magnesium hazard (MH) restricted its suitability for irrigation at a few sites. These results will be useful in implementing future measures in groundwater resource management at regional and national level. 相似文献
6.
Interaction of bentonite colloids with Cs, Eu, Th and U in presence of humic acid: A flow field-flow fractionation study 总被引:2,自引:0,他引:2
Muriel Bouby Horst Geckeis Silvia Mihai Thorsten Schäfer 《Geochimica et cosmochimica acta》2011,75(13):3866-3880
The interaction of Cs(I), Eu(III), Th(IV) and U(VI) with montmorillonite colloids was investigated in natural Grimsel Test Site groundwater over a 3 years period. The asymmetric flow field-flow fractionation combined with various detectors was applied to study size variations of colloids and to monitor colloid association of trace metals. The colloids suspended directly in the low ionic strength (I), slightly alkaline granitic groundwater (I = 10−3 mol/L, pH 9.6) showed a gradual agglomeration with a size distribution shift from initially 10-200 nm to 50-400 nm within over 3 years. The Ca2+ concentration of 2.1 × 10−4 mol/L in the ground water is believed to be responsible for the slow agglomeration due to Ca2+ ion exchange against Li+ and Na+ at the permanently charged basal clay planes. Furthermore, the Ca2+ concentration lies close to the critical coagulation concentration (CCC) of 10−3 mol L−1 for clay colloids. Slow destabilization may delimit clay colloid migration in this specific groundwater over long time scales. Eu(III) and Th(IV) are found predominantly bound to clay colloids, while U(VI) prevails as the UO2(OH)3− complex and Cs(I) remains mainly as aquo ion under our experimental conditions. Speciation calculations qualitatively represent the experimental data. A focus was set on the reversibility of metal ion-colloid binding. Addition of humic acid as a competing ligand induces rapid metal ion dissociation from clay colloids in the case of Eu(III) even after previous aging for about 3 years. Interestingly only partial dissociation occurs in the case of Th(IV). Experiments and calculations prove that the humate complexes dominate the speciation of all metal ions under given conditions. The partial irreversibility of clay bound Th(IV) is presently not understood but might play an important role for the colloid-mediated transport of polyvalent actinides over wide distances in natural groundwater. 相似文献
7.
8.
The topic of big-city growth is receiving increasing attention from geographers, economists, planners and environmentalists, particularly in relation to the likely social and economic impact of urban primacy, and the theoretical and practical implications of optimal city size. This short paper examines these issues in the context of Barbados, where Bridgetown, the chief port and capital city houses some 42% of the island's total population. Initially, the recommendations of the Physical Development Plan for Barbados, published in 1970 with United Nations technical assistance, are presented. In essence, the plan advocated the creation of a hierarchy of settlements within the island by the 1980s, in order to counter the perceived supremacy of Bridgetown. Subsequently, recent progress in promoting the decentralization of population and facilities from Bridgetown is reviewed; and in conclusion, the original proposals and recent developments are critically evaluated. 相似文献
9.
10.
Muriel Rocher Marc Cushing Francis Lemeille Stéphane Baize 《Comptes Rendus Geoscience》2004,336(13):1209-1218
The ‘Île Crémieu’, a plateau of Jurassic limestones located in the southern border of the Bresse and at the Jura front, is generally considered as non-deformed. Quaternary ice sheets and drainage have underlined and cleaned out some fracture planes trending NNE and NW–SE that border and crosscut the ‘Île Crémieu’. The analysis of seismic profiles reveals NNE-trending normal faults and NW–SE-trending strike-slip faults, crosscutting the basement to Late Miocene layers. Microtectonic fieldwork shows that these faults exist and were activated during the main Cainozoic tectonic events. To cite this article: M. Rocher et al., C. R. Geoscience 336 (2004). 相似文献