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During the last two decades, the advent of high-angular resolution imaging techniques on large optical and infrared telescopes has generated an empirical revolution in many aspects of astrophysics. In this contribution, I describe some of the techniques developed in recent years to obtain high-angular resolution images and present their advantages and limitations. I then illustrate the key role played by these techniques by presenting some of the most important results obtained in the study of extrasolar planets and planet-forming disks around stars other than our Sun. 相似文献
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Céline Martin Stéphanie Duchêne Béatrice Luais Philippe Goncalves Etienne Deloule Céline Fournier 《Contributions to Mineralogy and Petrology》2010,159(4):437-458
The geochemical and isotopic characterization of an eclogite and the associated retrogressive amphibolite at Vårdalsneset, WGR, Norwegian Caledonide was undertaken to investigate the mobility of REE and Hf and the behavior of Lu–Hf and Sm–Nd geochronometers during metamorphic dehydration/rehydration. Eclogitic garnets display a distinct core–rim chemical zoning. Thermodynamic modeling indicates that both cores (13–22 kbar, 500–580°C) and rims (>16 kbar, 610–660°C) crystallized under eclogite-facies conditions. The core–rim zoning corresponds to the dehydration of the system. This petrographic disequilibrium is associated with Lu–Hf and Sm–Nd disequilibrium, which prevents dating of the eclogitic stages. At the rock scale, the incoming fluid responsible for eclogite–amphibolite retrogression brought in Sm and Nd, leached Lu, and had no influence on Hf. At the grain scale, mass balance shows that Sm and Nd were stored in clinozoisite since the first eclogitic stage, whereas Lu and Hf, which were more thoroughly redistributed among minerals during retrogression, enable the dating of the amphibolitic facies at 378 ± 17 Ma. 相似文献
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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
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Populus nigra L. establishment and fluvial landform construction: biogeomorphic dynamics within a channelized river 
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下载免费PDF全文 Dov Corenblit Johannes Steiger Gaspard Charrier José Darrozes Virginia Garófano‐Gómez Alexandre Garreau Eduardo González Angela M. Gurnell Borbála Hortobágyi Frédéric Julien Luc Lambs Sébastien Larrue Thierry Otto Erwan Roussel Franck Vautier Olivier Voldoire 《地球表面变化过程与地形》2016,41(9):1276-1292
Populations of the riparian pioneer species Populus nigra L. which establish on alluvial bars within river channels modulate sediment dynamics and fluvial landforms. Dense cohorts of P. nigra have colonized gravel point bars along the channelized River Garonne, France, during the last 20 years and have enhanced the vertical, lateral and longitudinal development of the bars. For this period, the geomorphic characteristics of two wooded point bars on this laterally stable river are closely linked to the spatial distribution and intensity of establishment and resistance of different cohorts of P. nigra. Furthermore, P. nigra colonization dynamics were controlled by engineer effects of this same species. This relationship is illustrated by a significant correlation between key geomorphic and biological variables measured in situ and characterized with a set of four aerial photographs taken between 2000 and 2010. The development of wooded point bars, which are discrete biogeomorphic units, over the studied period, appear to result from a specific biogeomorphic positive feedback of matter aggregation and vegetation establishment related to sediment trapping and stabilization by pioneer engineer plants. We propose a conceptual model of biogeomorphic unit construction for channelized, lateral stable rivers. We consider the resultant biogeomorphic units as functional from an ecological point of view because P. nigra enhances at the cohort scale (i) its own inherent capacity to resist hydrogeomorphic disturbances, and (ii) its resilience capacity as a result of successful colonization, especially downstream of mature poplar stands. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Joyia Chakungal Jaroslav Dostal Djordje Grujic Stéphanie Duchêne Kharka S. Ghalley 《Tectonophysics》2010,480(1-4):198-212
Mafic granulites and amphibolites in the Masang Kang area of NW Bhutan Himalaya have been investigated for their geochemical and isotopic characteristics in order to determine their protolith history. Bulk-rock major and trace element geochemistry indicate that the rocks were originally tholeiitic and alkali basalts with minor ultramafics. U–Pb zircon SIMS data suggest an age of 1742 ± 39 Ma for mafic magmatism. The age-corrected εNd(1742) values of the rocks are highly variable, ranging from high positive (+ 8.4) to negative (? 3.3). The positive value suggests a primitive magma source, similar to that of rift-related tholeiites. We suggest that the rocks of the Masang Kang suite were produced during a major late Paleoproterozoic thermal event that caused the mobilization and enrichment of the sub-continental lithospheric mantle beneath the north Indian margin. The geochemical signature of these rift-related metabasic rocks may have been produced during an earlier episode of oceanic underplating or subduction from which the fluid required to mobilize and enrich the overlying sub-lithospheric mantle may have been derived. Though their occurrence is rare, Paleoproterozoic igneous rocks within the Greater Himalayan Sequence (GHS), in addition to sources identified throughout the LHS, may have contributed to the detrital zircon population that form the 1.7–1.9 Ga peak in the age spectra of the Lesser Himalayan Sequence (LHS). In addition, the coeval Paleoproterozoic magmatism in both LHS and GHS suggests that the two lithotectonic units may have belonged to the same continental plate at that time period. 相似文献
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This article proposes an improvement of automated cartographic generalization using multi‐agent sytems in urban areas. Indeed the AGENT model, whose robustness has been tested and approved through the European project AGENT, gives very good results in generalizing dense urban areas by means of enlargement, removal and displacement of buildings. But this model does not tackle the question of including particular structures like building alignments in the process, which is a crucial issue. The problem is that integrating such structures does not fit into the accurate top‐down hierarchy of urban agents. In order to face this problem, we propose to partly re‐engineer the model by introducing the concept of reactional agents whose behavior is very different from hierarchical agents of the original model as they use bottom‐up activation. In this view, urban alignment is considered to be a reactional agent activated only by its inner buildings, which generalizes the aligned buildings together into one entire structure. Associating reactional alignment behavior with new generalization actions on alignments significantly improves the model and gives better results in dense urban areas. Moreover, the idea could probably be used for other applications. 相似文献