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281.
Michael Schäfer Tanja Schäfer Matthew R. M. Izawa Edward A. Cloutis Stefan E. Schröder Thomas Roatsch Frank Preusker Katrin Stephan Klaus‐Dieter Matz Carol A. Raymond Christopher T. Russell 《Meteoritics & planetary science》2018,53(9):1925-1945
Ceres’ surface has commonly been linked with carbonaceous chondrites (CCs) by ground‐based telescopic observations, because of its low albedo, flat to red‐sloped spectra in the visible and near‐infrared (VIS/NIR) wavelength region, and the absence of distinct absorption bands, though no currently known meteorites provide complete spectral matches to Ceres. Spatially resolved data of the Dawn Framing Camera (FC) reveal a generally dark surface covered with bright spots exhibiting reflectance values several times higher than Ceres’ background. In this work, we investigated FC data from High Altitude Mapping Orbit (HAMO) and Ceres eXtended Juling (CXJ) orbit (~140 m/pixel) for global spectral variations. We found that the cerean surface mainly differs by spectral slope over the whole FC wavelength region (0.4–1.0 μm). Areas exhibiting slopes 10% μm?1 constitute only ~3% of the cerean surface and mainly occur in the bright material in and around young craters, whereas slopes ≥?10% μm?1 occur on more than 90% of the cerean surface; the latter being denoted as Ceres’ background material in this work. FC and Visible and Infrared Spectrometer (VIR) spectra of this background material were compared to the suite of CCs spectrally investigated so far regarding their VIS/NIR region and 2.7 μm absorption, as well as their reflectance at 0.653 μm. This resulted in a good match to heated CI Ivuna (heated to 200–300 °C) and a better match for CM1 meteorites, especially Moapa Valley. This possibly indicates that the alteration of CM2 to CM1 took place on Ceres. 相似文献
282.
We describe our laboratory procedures for precise measurements of lattice surface profile, where Bragg reflection takes place, of bent monocrystal wafers. A comparison of X-ray spectrometer characteristics for perfect and real crystals is presented. The described procedures will be used to measure the properties of the crystals that will be used as the dispersive elements in the future solar X-ray spectrometers SolpeX and ChemiX. 相似文献
283.
John D. Monnier Stefan Kraus Michael J. Ireland Fabien Baron Amelia Bayo Jean-Philippe Berger Michelle Creech-Eakman Ruobing Dong Gaspard Duchêne Catherine Espaillat Chris Haniff Sebastian Hönig Andrea Isella Attila Juhasz Lucas Labadie Sylvestre Lacour Stephanie Leifer Antoine Merand Ernest Michael Stefano Minardi Christoph Mordasini David Mozurkewich Johan Olofsson Claudia Paladini Romain Petrov Jörg-Uwe Pott Stephen Ridgway Stephen Rinehart Keivan Stassun Jean Surdej Theo ten Brummelaar Neal Turner Peter Tuthill Kerry Vahala Gerard van Belle Gautam Vasisht Ed Wishnow John Young Zhaohuan Zhu 《Experimental Astronomy》2018,46(3):517-529
The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H2O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality. 相似文献
284.
Christiane Richter Daniel Wolf Frank Walther Stefan Meng Lilit Sahakyan Hayk Hovakimyan Tilmann Wolpert Markus Fuchs Dominik Faust 《第四纪科学杂志》2020,35(5):634-649
In the present study, we performed gastropod analyses on loess–palaeosol sequences from northeast Armenia (Southern Caucasia) covering at least three glacial–interglacial cycles. The elaborated ecostratigraphy shows significant patterns of species composition related to the succession of pedocomplexes and loess, respectively. Pedocomplexes included species that can be associated with high-grass to forest-steppe biomes, indicating increased humidity for these sections compared to the loess layers. In contrast, loess layers that relate to glacial periods are associated with gastropod species of semidesert environments with shrub- and shortgrass-steppes, indicating semiarid to arid conditions. Furthermore, the loess deposits do not show any evidence for cold-adapted gastropod species. Therefore, we suggest that average July temperatures in the study area were above 10 °C, even during periods of loess deposition. Consequently, we propose that the limiting factor for tree growth during glacial periods was aridity, rather than temperature. In addition, we observe environmental differences between the various glacial times, with our results indicating a trend towards steadily increasing aridity in Southern Caucasia across the Middle to Late Pleistocene. 相似文献
285.
Several cryptotephra layers that originate from Icelandic volcanic eruptions with a volcanic explosivity index (VEI) of ≤ 4 and tephra volumes of < 1 km3 have previously been identified in Northern Europe, albeit within a restricted geographical area. One of these is the Hekla 1947 tephra that formed a visible fall-out in southern Finland. We searched for the Hekla 1947 tephra from peat archives within the previously inferred fall-out zone but found no evidence of its presence. Instead, we report the first identification of Hekla 1845 and Hekla 1510 cryptotephra layers outside of Iceland, the Faroe Islands, Ireland and the UK. Additionally, Hekla 1158 tephra was found in Finland for the first time. Our results confirm that Icelandic eruptions of moderate size can form cryptotephra deposits that are extensive enough to be used in inter-regional correlations of environmental archives and carry a great potential for refining regional tephrochronological frameworks. Our results also reveal that Icelandic tephra has been dispersed into Finnish airspace at least seven times during the past millennium and in addition to a direct eastward route the ash clouds can travel either via a northerly or a southerly transport pathway. 相似文献
286.
Stefan H. Doerr 《地球表面变化过程与地形》1998,23(7):663-668
Two common methods to assess soil hydrophobicity are the ‘Water Drop Penetration Time’ and ‘Molarity of an Ethanol Droplet’ techniques. For these, uncertainty exists regarding the representativeness of laboratory tests reflecting field conditions, their replicability, and the comparability of results between the two techniques. Using air-dried soils with a broad particle size and hydrophobicity range, this study shows that a high representativeness and replicability of results can be achieved. A close relationship between the two tests was found for highly, but not for moderately hydrophobic soils. Guidelines are suggested to increase representativeness, replicability and comparability of results in future studies. © 1998 John Wiley & Sons, Ltd. 相似文献
287.
Andrés Marín Stefan Gelcich Gonzalo Araya Gonzalo Olea Miguel Espíndola Juan C. Castilla 《Marine Policy》2010
In 2010, a tsunami generated by a magnitude 8.8 earthquake struck the central-south zone of Chile. This short communication reports the direct impacts on the small-scale artisanal fishing capacity and coastal livelihoods along approximately 600 km of the coastline. Despite the magnitude of the catastrophe, the absence of official warnings, and the failure of telecommunication networks only 8 fisher victims were reported out of a total death toll of more than 170. Results show that this trend is explained by socio-cultural assets and a natural hazard subculture. This highlights the need to integrate contextual and behavioural approaches in disaster management and rehabilitation policies. 相似文献
288.
Mussel farming is considered a viable means for reducing coastal eutrophication. This study assessed the importance of bioturbation by recolonizing fauna for benthic solute fluxes and porewater distributions in manipulated mussel farm sediments. Three consecutive time-series flux incubations were performed during an experimental period of three weeks in sieved farm sediment treated with the brittle star Amphiura filiformis and the polychaete Nephtys sp. The functional behavior of Nephtys sp. and interactions between Nephtys sp. and the spontaneously colonizing spionid Malacoceros fuliginosus determined the biogeochemical response in the Nephtys sp. treatment. For example, the oxic zone was restricted and benthic nitrate and silicate fluxes were reduced compared to the brittle star treatment. A. filiformis seemed to enhance the bioadvective solute transport, although an increased supply of oxygen was due to the highly reducing conditions of the sediment mainly seen as secondary effects related to porewater distributions and benthic nutrient fluxes. 相似文献
289.
Tidal exchange between a freshwater tidal marsh and an impacted estuary: the Scheldt estuary, Belgium 总被引:1,自引:0,他引:1
Stefan Van Damme Dehairs Frank Tackx Micky Beauchard Olivier Struyf Eric Gribsholt Britta Van Cleemput Oswald Meire Patrick 《Estuarine, Coastal and Shelf Science》2009,85(2):197-207
Tidal marsh exchange studies are relatively simple tools to investigate the interaction between tidal marshes and estuaries. They have mostly been confined to only a few elements and to saltwater or brackish systems. This study presents mass-balance results of an integrated one year campaign in a freshwater tidal marsh along the Scheldt estuary (Belgium), covering oxygen, nutrients (N, P and Si), carbon, chlorophyll, suspended matter, chloride and sulfate. The role of seepage from the marsh was also investigated. A ranking between the parameters revealed that oxygenation was the strongest effect of the marsh on the estuarine water. Particulate parameters showed overall import. Export of dissolved silica (DSi) was more important than exchange of any other nutrient form. Export of DSi and import of total dissolved nitrogen (DIN) nevertheless contributed about equally to the increase of the Si:N ratio in the seepage water. The marsh had a counteracting effect on the long term trend of nutrient ratios in the estuary. 相似文献
290.
A new federal administration, alongside initiatives proposed by the President's US Commission on Ocean Policy, provides a timely and critical opportunity for maritime archaeologists and cultural resource managers to re-consider management frameworks for maritime cultural heritage in the USA. Policy is urgently needed that defines governments’ roles and responsibilities in protecting and managing maritime cultural heritage in federal waters. Implementation of a regional governance structure based on the tenets of ecosystem-based management is proposed in this paper to manage and develop these resources effectively. Through regional governance, the maritime heritage of the USA can be conserved for future generations, keeping its citizens connected to deep-rooted maritime traditions and contribute to the well-being, economic growth and development of coastal communities. 相似文献