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排序方式: 共有402条查询结果,搜索用时 15 毫秒
21.
Christopher Packham Keith L. Thompson Almudena Zurita Johan H. Knapen Ian Smail Robert Greimel Daniel F. M. Folha Chris Benn rew Humphrey Rene Rutten David Ciardi Matthieu Bec Richard Bingham Simon Craig Kevin Dee Derek Ives Paul Jolley Peter Moore Marti Pi i Puig Simon Rees Gordon Talbot Sue Worswick 《Monthly notices of the Royal Astronomical Society》2003,345(2):395-405
22.
Yves Marrocchi Emmanuel Jacquet Julia Neukampf Johan Villeneuve Michael E. Zolensky 《Meteoritics & planetary science》2023,58(2):195-206
The ungrouped carbonaceous chondrite (CC) Bells has long been considered petrographically similar to CM chondrites based on its matrix abundance and degree of aqueous alteration, but also shows significant isotopic affinities to CR chondrites. Its taxonomic status is thus important for clarifying the relationship of the CRHB (formerly “CR”) clan with other CCs. In this study, we measured the oxygen isotopic compositions of olivines in type I chondrules and isolated olivine grains in Bells. Bells olivines mostly have ∆17O > −4‰, similar to CR chondrites but unlike other CCs that are rich in refractory inclusions, in which chondrules are generally richer in 16O. Therefore, Bells is a CR chondrite (albeit an anomalous one), most similar to the rare, matrix-rich CRs like Al Rais. These chondrites (i) may not necessarily derive from the same primary parent body as mainstream CRs, (ii) bear witness to significant variations of the matrix/chondrule ratio within the CRHB clan, and (iii) may be a good analog for samples retrieved by the space mission OSIRIS-REx. 相似文献
23.
Spectrophotometric data show that major compositional groups among outer solar system (OSS) surfaces include bright ices and at least two distinct classes of blackish carbonaceous-like materials, called C-type and RD-type. VJHK colorimetry of asteroids, satellites, and laboratory samples shows that these three classes can be distinguished by VJHK colors. We define an “α index” that denotes the position of objects in VJHK color - color diagrams; it empirically increases with albedo and ice/dirt ratio. We use the above data to define color fields that may be useful in interpreting our observations of eight comets (1980–1981). All eight comets have colors generally resembling RD asteroids and are inconsistent with reflection off clean ice surfaces. The observations suggest that these comets' halos contain RD dirt or dirty ice grains colored by RD dirt, supporting J. Gradie and J. Veverka's [Nature283, 840–842 (1980)] prediction of RD, rather than C, material in comets. Remote Comet P/Schwassmann-Wachmann 1 was observed both during outburst and quiescence and had the highest α index of any observed comet. Comet α indices appear to be correlated with solar distance. Further work will be needed to clarify possible coloring effects due to particle size, dispersal, and composition. We suggest a number of physical interpretations based on a single two-component mixing model, which assumes that all OSS planetesimals formed primarily from bright ices and dark carboneceous-like dirt, consistent with condensation theory. We discuss differentiation processes that concentrated one component or the other at the surface. All measured OSS interplanetary bodies have surfaces of dark dirt or dark dirty ice colored by the dirt component. Comets, consistent with the Whipple dirty iceberg model, are such objects close enough to the Sun for volatilization to throw dirty ice grains into the coma. In remote comets, the ice component of the grains remains stable, and we see dirty ice grains; in near comets, the ice component vaporizes, and we see dirt grains. A volatile-depleted dusty regolith on P/Schwassmann-Wachmann 1 and other remote comets could explain their eruptive behavior by means of gas pressure buildup in the porous, weakly bonded dust. 相似文献
24.
A new bird from the early Cretaceous Yixian Formation of Liaoning, China is described. This new species, Grabauornis lingyuanensis, shares several synapomorphies with the Enantiornithes. The specimen is relatively well preserved. The skeletal morphology of Grabauornis bears close resemblance to that of other Chinese members of this clade. The brachial index (the ratio between the lengths of humerus and ulna) is 0.95, which is close to the average for enantiornithine birds. It indicates that Grabauornis was a rather good flyer, and the presence of an alula in the wing further testifies to this. 相似文献
25.
Johan Spross Lars Olsson Håkan Stille 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2018,12(3):183-189
The Swedish Geotechnical Society has adopted a general methodology for risk management in geotechnical engineering projects to reduce the costs related to negative outcomes of geotechnical risks. This technical note highlights the main features of the methodology and strives to inspire the international geotechnical community to apply sensible risk management methods. In the authors’ opinion, a successful geotechnical risk management needs to be structured, be tailored to the project, and permeate the engineers’ everyday work. Then, sufficient quality can be achieved in the project with larger probability. 相似文献
26.
Piotr Wojda Serge Brouyère Johan Derouane Alain Dassargues 《Hydrogeology Journal》2010,18(8):1953-1962
Managing, handling and accessing hydrogeological information depends heavily on the applied hydrogeological data models, which differ between institutions and countries. The effective dissemination of hydrogeological information requires the convergence of such models to make hydrogeological information accessible to multiple users such as universities, water suppliers, and administration and research organisations. Furthermore, because hydrogeological studies are complex, they require a wide variety of high-quality hydrogeological data with appropriate metadata in clearly designed and coherent structures. A need exists, therefore, to develop and implement hydrogeological data models that cover, as much as possible, the full hydrogeological domain. A new data model, called HydroCube, was developed for the Walloon Region in Belgium in 2005. The HydroCube model presents an innovative holistic project-based approach which covers a full set of hydrogeological concepts and features, allowing for effective hydrogeological project management. The model stores data relating to the project locality, hydrogeological equipment, and related observations and measurements. In particular, it focuses on specialized hydrogeological field experiments such as pumping and tracer tests. This logical data model uses entity-relationship diagrams and it has been implemented in the Microsoft Access environment. It has been enriched with a fully functional user interface. 相似文献
27.
This study assesses the origin and pollution of trace metals in surface soils in a region with contrasting land uses (urban
vs. rural). Principal component analysis (PCA) reveals that Cr and Ni are predominantly of geogenic origin. These two trace
metals are also the only ones with statistically significant correlations with soil particle size and organic matter content.
Copper, Pb and Zn, and possibly Hg, are of anthropogenic origin, but their concentrations rarely reach levels described as
strongly polluted by pollution indexes. The concentrations of these anthropogenic trace metals are statistically not different
in urban and rural areas, except for Pb that is higher in the urban area. This general lack of a difference between the two
land uses indicates that the influence of this small urban area on trace metal concentrations in soils is minor. Lead and
Zn have the most, but still a modest number, of strongly polluted sites, mainly in an industrial part of the city. GIS analysis
shows that, based on the pollution load index (PLI), overall concentrations of trace metals also reach their highest levels
in that industrial area. These observations indicate that the influence of industry on trace metal pollution in soil exceeds
that of other urban activities in the region. Local background concentrations were found to be very different from general
crustal background concentrations. This demonstrates the importance of the careful selection of a background type in studies
like this. 相似文献
28.
29.
We present a complete set of stability constants (SO4β1) for the monosulfato-complexes of yttrium and the rare earth elements (YREE), except Pm, at I = 0.66 m and t = 25°C, where SO4β1 = [MSO4+] × [M3+]−1[SO42−]−1 (M ≡ YREE and brackets indicate free ion concentrations on the molal scale). Stability constants were determined by investigating the solubility of BaSO4 in concentrated aqueous solutions of MCl3. This is the first complete set to be published in more than 30 years.The resulting SO4β1 pattern is very similar in shape to one reported by de Carvalho and Choppin (1967a) (I = 2 mol/L; t = 25°C) that has been largely ignored. Stability constants vary little between La and Sm, but display a weak maximum at Eu. Between Eu and Lu, SO4β1 decreases by 0.2 log units, substantially exceeding the ±0.02 log unit average analytical precision. The stability constant for Y is approximately equal to that for Er. Our SO4β1 pattern is consequently distinctly different from the consensus pattern, based on a single data set from 1954, which is essentially flat, with a range of only 0.07 log units between the lowest and highest SO4β1 values within the lanthanide series (excluding Y).Values of SO4β1 obtained in this work, in conjunction with the ion-pairing model of Millero and Schreiber (1982), allow prediction of SO4β1 between 0 and 1 m ionic strength. These results are used to assess both the absolute and relative extent of YREE sulfate complexation in acidic, sulfate-rich waters. 相似文献
30.
Wim Kellens Tijs Neutens Pieter Deckers Johan Reyns Philippe De Maeyer 《Natural Hazards》2012,60(3):1211-1229
Since coastal tourism is one of the fastest growing sectors of tourism industry, coastal areas have become increasingly vulnerable
in the case of flooding. While in recent years a number of different methods have been put forward to map coastal flood risks,
the implications of tourism dynamics for the assessment of human casualties has remained largely overlooked in these models.
This chapter examines to what extent the ignorance of (residential) coastal tourism may bias the calculations of human casualties.
To this end, a case study has been conducted on the Belgian coast. Both the dynamic nature of coastal tourism and the behaviour
of residential tourists in storm surge scenarios are considered. The results of this study show that including tourism dynamics
in flood risk management is justified and appropriate, depending on the tourist attractiveness of the flood-prone area and
its temporal fluctuations. 相似文献