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  • *Stars, Celestial  (1)
  • constant-flux layer  (1)
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    Detection of the water reservoir in a forming planetary system (2011)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2011-10-25
    Description: Icy bodies may have delivered the oceans to the early Earth, yet little is known about water in the ice-dominated regions of extrasolar planet-forming disks. The Heterodyne Instrument for the Far-Infrared on board the Herschel Space Observatory has detected emission lines from both spin isomers of cold water vapor from the disk around the young star TW Hydrae. This water vapor likely originates from ice-coated solids near the disk surface, hinting at a water ice reservoir equivalent to several thousand Earth oceans in mass. The water's ortho-to-para ratio falls well below that of solar system comets, suggesting that comets contain heterogeneous ice mixtures collected across the entire solar nebula during the early stages of planetary birth.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hogerheijde, Michiel R -- Bergin, Edwin A -- Brinch, Christian -- Cleeves, L Ilsedore -- Fogel, Jeffrey K J -- Blake, Geoffrey A -- Dominik, Carsten -- Lis, Dariusz C -- Melnick, Gary -- Neufeld, David -- Panic, Olja -- Pearson, John C -- Kristensen, Lars -- Yildiz, Umut A -- van Dishoeck, Ewine F -- New York, N.Y. -- Science. 2011 Oct 21;334(6054):338-40. doi: 10.1126/science.1208931.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Leiden Observatory, Leiden University, Post Office Box 9513, 2300 RA Leiden, Netherlands. michiel@strw.leidenuniv.nl〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22021851" target="_blank"〉PubMed〈/a〉
    Keywords: Evolution, Planetary ; Extraterrestrial Environment ; *Ice ; *Planets ; *Stars, Celestial ; *Steam
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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    Electronic Resource
    Electronic Resource
    First-Order Chemistry in the Surface-Flux Layer (1997)
    Springer
    Journal of atmospheric chemistry 27 (1997), S. 249-269 
    Details
    ISSN: 1573-0662
    Keywords: atmospheric surface layer ; constant-flux layer ; ozone ; nitric oxide ; radon ; thoron ; thoron exhalation ; Damköhler ratio ; eddy diffusivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We have discussed the behavior of a non-conserved scalar in the stationary, horizontally homogeneous, neutral surface-flux layer and, on the basis of conventional second-order closure, derived analytic expressions for flux and for mean concentration of a gas, subjected to a first-order removal process. The analytic flux solution showed a clear deviation from the constant flux, characterizing a conserved scalar in the surface-flux layer. It decreases with height and is reduced by an order of magnitude of the surface flux at a height equal to about the typical mean distance a molecule can travel before destruction. The predicted mean concentration profile, however, shows only a small deviation from the logarithmic behavior of a conserved scalar. The solution is consistent with assuming a flux-gradient relationship with a turbulent diffusivity corrected by the Damköhler ratio, the ratio of a characteristic turbulent time scale and the scalar mean lifetime. We show that if we use only first-order closure and neglect the effect of the Damköhler ratio on the turbulent diffusivity we obtain another analytic solution for the profiles of the flux and the mean concentration which, from an experimental point of view, is indistinguishable from the first analytic solution. We have discussed two cases where the model should apply, namely NO which, by night, is irreversibly destroyed by interaction with mainly O3 and the radioactive 220Rn. Only in the last case was it possible to find data to shed light on the validity of our predictions. The agreement seemed such that a falsification of our model was impossible. It is shown how the model can be used to predict the surface flux of 220Rn from measured concentration profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005800416423
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