排序方式: 共有73条查询结果,搜索用时 15 毫秒
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The present work is an analytical study of the influence of geometrical parameters, such as length, thickness and immersion of the plate, on the reflection coefficient of a regular wave for an immersed horizontal plate in the presence of a uniform current with the same direction as the propagation of the incident regular wave. This study was performed using the linearized potential theory with the evanescent modes while searching for complex roots to the dispersion equation that are neither pure real nor pure imaginary. The results show that the effects of the immersion and the relative length on the reflection coefficient of the plate are accentuated by the presence of the current, whereas the plate thickness practically does not have an effect if it is relatively small. 相似文献
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Rob Ivison Ian Smail Andrew Blain Jean-Paul Kneib David Frayer 《Astrophysics and Space Science》1999,266(1-2):285-290
We discuss observations of the submm-selected galaxy,SMM J02399-0136, and what has been learnt about it during the yearfollowing its discovery. SMM J02399-0136 was the first distantgalaxy detected in surveys with the Submm Common-User Bolometer Array(SCUBA). Its association with a massive, gas-rich starburst/AGN atz = 2.8 has lead to suggestions that the prevalence of AGN in theearly Universe may be high (Ivison et al. 1998) and that these AGNmay account for a significant fraction of the far-IR background (e.g.Fixsen et al. 1998). 相似文献
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Structure,composition, and location of organic matter in the enstatite chondrite Sahara 97096 (EH3) 总被引:1,自引:0,他引:1
Laurette PIANI François ROBERT Olivier BEYSSAC Laurent BINET Michèle BOUROT‐DENISE Sylvie DERENNE Corentin LE GUILLOU Yves MARROCCHI Smail MOSTEFAOUI Jean‐Noël ROUZAUD Aurélien THOMEN 《Meteoritics & planetary science》2012,47(1):8-29
Abstract– The insoluble organic matter (IOM) of an unequilibrated enstatite chondrite Sahara (SAH) 97096 has been investigated using a battery of analytical techniques. As the enstatite chondrites are thought to have formed in a reduced environment at higher temperatures than carbonaceous chondrites, they constitute an interesting comparative material to test the heterogeneities of the IOM in the solar system and to constrain the processes that could affect IOM during solar system evolution. The SAH 97096 IOM is found in situ: as submicrometer grains in the network of fine‐grained matrix occurring mostly around chondrules and as inclusions in metallic nodules, where the carbonaceous matter appears to be more graphitized. IOM in these two settings has very similar δ15N and δ13C; this supports the idea that graphitized inclusions in metal could be formed by metal catalytic graphitization of matrix IOM. A detailed comparison between the IOM extracted from a fresh part and a terrestrially weathered part of SAH 97096 shows the similarity between both IOM samples in spite of the high degree of mineral alteration in the latter. The isolated IOM exhibits a heterogeneous polyaromatic macromolecular structure, sometimes highly graphitized, without any detectable free radicals and deuterium‐heterogeneity and having mean H‐ and N‐isotopic compositions in the range of values observed for carbonaceous chondrites. It contains some submicrometer‐sized areas highly enriched in 15N (δ15N up to 1600‰). These observations reinforce the idea that the IOM found in carbonaceous chondrites is a common component widespread in the solar system. Most of the features of SAH 97096 IOM could be explained by the thermal modification of this main component. 相似文献
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We present a multicolour catalogue of faint galaxies situated close to bright stars, V ≲ 15 , with the aim of identifying high-redshift galaxies suitable for study with adaptive optics-equipped near-infrared imagers and spectrographs. The catalogue is constructed from archival calibration observations of the United Kingdom Infrared Telescope (UKIRT) Faint Standard stars with the UKIRT Fast Track Imager (UFTI) camera on UKIRT. We have analysed the deepest 16 fields from the archive to provide a catalogue of galaxies brighter than K ∼ 20.3 lying between 3 and 25 arcsec of the guide stars. We identify 111 objects in a total survey area of 8.7 arcmin2 . Of these, 87 are classified as galaxies based on their light profiles in our ∼0.5 arcsec median seeing K -band images. 12 of the galaxies have ( J − K ) ≥ 2.0 consistent with them lying at high redshifts, z ≳ 2 . These 12 very red galaxies have K -band magnitudes of K = 18.1–20.1 and separations from the guide stars of 4–20 arcsec and hence are very well suited to adaptive optics studies to investigate their morphologies and spectral properties on sub-kpc scales. We provide coordinates and JHK photometry for all catalogued objects. 相似文献
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Anders Meibom Jean-Pierre Cuif Smail Mostefaoui Karin L. Meibom 《Geochimica et cosmochimica acta》2008,72(6):1555-1569
Distributions of Mg and Sr in the skeletons of a deep-sea coral (Caryophyllia ambrosia) and a shallow-water, reef-building coral (Pavona clavus) have been obtained with a spatial resolution of 150 nm, using the NanoSIMS ion microprobe at the Muséum National d’Histoire Naturelle in Paris. These trace element analyses focus on the two primary ultra-structural components in the skeleton: centers of calcification (COC) and fibrous aragonite. In fibrous aragonite, the trace element variations are typically on the order of 10% or more, on length scales on the order of 1-10 μm. Sr/Ca and Mg/Ca variations are not correlated. However, Mg/Ca variations in Pavona are strongly correlated with the layered organization of the skeleton.These data allow for a direct comparison of trace element variations in zooxanthellate and non-zooxanthellate corals. In both corals, all trace elements show variations far beyond what can be attributed to variations in the marine environment. Furthermore, the observed trace element variations in the fibrous (bulk) part of the skeletons are not related to the activity of zooxanthellae, but result from other biological activity in the coral organism. To a large degree, this biological forcing is independent of the ambient marine environment, which is essentially constant on the growth timescales considered here.Finally, we discuss the possible detection of a new high-Mg calcium carbonate phase, which appears to be present in both deep-sea and reef-building corals and is neither aragonite nor calcite. 相似文献
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