EIT: Extreme-ultraviolet Imaging Telescope for the SOHO mission   总被引：10，自引：0，他引：10  

J. -P. Delaboudinière  G. E. Artzner  J. Brunaud  A. H. Gabriel  J. F. Hochedez  F. Millier  X. Y. Song  B. Au  K. P. Dere  R. A. Howard  R. Kreplin  D. J. Michels  J. D. Moses  J. M. Defise  C. Jamar  P. Rochus  J. P. Chauvineau  J. P. Marioge  R. C. Catura  J. R. Lemen  L. Shing  R. A. Stern  J. B. Gurman  W. M. Neupert  A. Maucherat  F. Clette  P. Cugnon  E. L. Van Dessel 《Solar physics》1995,162(1-2):291-312

The Extreme-ultraviolet Imaging Telescope (EIT) will provide wide-field images of the corona and transition region on the solar disc and up to 1.5 R above the solar limb. Its normal incidence multilayer-coated optics will select spectral emission lines from Fe IX (171 ), Fe XII (195 ), Fe XV (284 ), and He II (304 ) to provide sensitive temperature diagnostics in the range from 6 × 10⁴ K to 3 × 10⁶ K. The telescope has a 45 x 45 arcmin field of view and 2.6 arcsec pixels which will provide approximately 5-arcsec spatial resolution. The EIT will probe the coronal plasma on a global scale, as well as the underlying cooler and turbulent atmosphere, providing the basis for comparative analyses with observations from both the ground and other SOHO instruments. This paper presents details of the EIT instrumentation, its performance and operating modes.  相似文献   

A late Precambrian (∼ 710 Ma) high volcanicity rift in the southern Eastern Desert of Egypt     

Robert J. Stern  Alfred Kröner  Abdul A. Rashwan 《International Journal of Earth Sciences》1991,80(1):155-170

The late Precambrian Shadli Metavolcanics of SE Egypt constitute a slightly metamorphosed bimodal sequence that has been previously interpreted as manifesting volcanic activity at an island arc. We report the first Rb-Sr geochronologic, trace element (including REE), and Nd isotopic data for these rocks. Two types of basalt are recognized, the stratigraphically lower suite having compositions like N-MORB ferrobasalt while the overlying basalt is similar to slightly fractionated E-MORB. The two basalt types were derived from melting of a strongly depleted source, most likely within the upper 60–75 km of the upper mantle. The origin of the felsic melts is problematic, and these could either have fractionated from a mafic melt or resulted from melting of juvenile crust. The mafic and felsic lavas yield a Rb-Sr isochron age of 712±24 Ma that probably represents the time of volcanic eruption. The trace element characteristics of both mafic and felsic members of the Shadli Metavolcanics show few of the hallmarks of subduction-related melts, and we reject the hypothesis that these formed at an island arc. Instead, the field and geochemical data are most consistent with the hypothesis that these rocks originated in a magmatic rift, where the eruption of large volumes of lava accompanied large-scale lithospheric extension. This inference suggests that the tectonic setting of the important 700–715 Ma crust-forming event in NE Africa and Arabia needs to be critically reexamined.

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Zusammenfassung Die spätpräkambrischen Shadli-Metavulkanite in der südöstlichen Eastern Desert von Ägypten sind eine schwach metamorphe bimodale Basalt-Rhyodazit-Abfolge, die bisher als Ausdruck eines Inselbogen-Vulkanismus gedeutet wurde. Zwei Basalt-Typen können aufgrund ihrer unterschiedlichen chemischen Zusammensetzung unterschieden werden: der stratigraphisch untere Typ ist ein N-MORB ähnlicher Ferrobasalt, während der überlagernde Typ Charakteristika eines leicht fraktionierten E-MORB aufweist. Die beiden Basaltvarietäten werden von stark an inkompatiblen Elementen verarmten Schmelzen aus den oberen 60–75 km des Mantels abgeleitet. Die Entstehung der sauren Metavulkanite ist nicht eindeutig geklärt; sowohl Fraktionierung aus einer mafischen Schmelze als auch Aufschmelzung juveniler Kruste vom Inselbogen-Typ sind denkbar. Die mafischen und felsischen Gesteine definieren zusammen ein Rb-Sr-Isochronenalter von 712 ± 24 Ma, das wir als den Zeitraum der Eruption deuten. Die Spurenelement-Verteilung der Shadli-Metavulkanite weist keine der charakteristischen Merkmale von Subduktionsmagmatismus auf, und wir sehen daher keinen direkten Zusammenhang mit einer Inselbogen-Entwicklung. Wir interpretieren den Shadli-Vulkanismus als Resultat eines Riftprozesses in junger kontinentaler Kruste, ähnlich dem Rio Grande-Rift oder dem Afar-Dreieck, wo starke Lithosphärendehnung die Förderung großer Lavamengen ermöglichte. Diese Interpretation stellt das einfache Schema einer panafrikanischen Krustenbildung durch Inselbogen-Addition im arabisch-nubischen Schild in Frage und erfordert eine Neubewertung bisheriger Modellvorstellungen.

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Résumé Les roches volcaniques faiblement métamorphisées du Précambrien tardif de Shadli dans le Sud-Est de l'Egypte se caractérisent par une séquence bimodale qui était jusqu'ici interprétée comme résultant d'un volcanisme d'arc insulaire. Nous présentons ici les premières données isotopiques (Rb-Sr, Nd) obtenues pour ces roches ainsi que des données d'éléments en trace (y compris les Terres Rares). Deux types principaux de basaltes peuvent être distingués: les basaltes qui se trouvent dans la partie inférieure de la colonne stratigraphique, ont une composition comparable aux ferrobasaltes de type N-MORB, tandis que les roches se trouvant dans la partie supérieure de la séquence s'apparentent plutôt aux E-MORB légèrement fractionnés. Les deux types de basalte proviennent de la fusion partielle d'un manteau fortement appauvri, et ce à une profondeur probable de 60 à 75 km dans le manteau supérieur. L'origine des laves acides pose, quant à elle, quelques problèmes: elles peuvent s'être formées par cristallisation fractionnée à partir d'un liquide basique, ou alors elles sont le produit de la fusion partielle d'une croûte juvénile. La combinaison des données Rb-Sr obtenues pour les roches acides et basiques permet l'obtention d'une isochrone définissant un âge de 712 ± 24 Ma. Cet âge est interprété comme datant les éruptions volcaniques. Les données d'éléments en traces obtenues pour les laves basiques et acides ne présentent aucune des caractéristiques associées au volcanisme d'arc insulaire. Par conséquent, nous rejetons l'hypothèse selon laquelle les roches volcaniques de Shadli se seraient formées dans un contexte d'arc insulaire. Les données géochimiques et de terrain seraient plutôt en accord avec une hypothèse selon laquelle les roches volcaniques métamorphiques de Shadli se seraient formées dans une zone de rift où de très volumineux épanchements de laves auraient succédé à une extension à grande échelle de la lithosphère. Cette interprétation des données nous conduit à suggérer un réexamen critique du contexte tectonique entourant la période de formation crustale se situant entre 700 a 715 Ma, dans le nord-est de l'Afrique ainsi qu'en Arabie.

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External perturbations on distant planetary orbits and objects in the Kuiper disk     

S. Alan Stern 《Celestial Mechanics and Dynamical Astronomy》1989,47(3):267-273

We investigate the potential importance of molecular cloud and stellar perturbations on the orbits of Pluto and more distant (hypothetical) planets up to 500 AU from the Sun. It is found that stellar and molecular cloud-core perturbations are of roughly equal importance. It also is found that the likelihood of substantial perturbations on Pluto is not insignificant, and that numerous substantial stellar and molecular cloud perturbations are likely to have influenced the orbits of any planets beyond 200 AU. These perturbations may contribute to a prevalence of moderate eccentricities and inclinations for planets beyond the orbit of Neptune, and may be a characteristic of distant planetary orbits in other solar systems. Given the recent discovery of chaotic behavior in Pluto's orbit (Sussman and Wisdom 1988), the effects of external perturbations on the long-term stability of Pluto's orbit warrant continued study.  相似文献   

Comment on rotating hydraulics     

Melvin E. Stern 《地球物理与天体物理流体动力学》2013,107(2):127-130

Abstract

Numerical solutions of the axisymmetric flows during the relatively early phase of spin-up from rest of a stratified fluid in a cylinder are presented. Detailed results are given for a cylinder of aspect ratio of O(l) and for a minute Ekman number, showing axisymmetric spin-up for three values of the stratification parameter. As the stratification increases, the meridional circulation is confined to a region closer to the Ekman layers. An axisymmetric shear wave propagates radially inward from the sidewall, but, unlike the strictly vertical front for a homogeneous fluid, the interface which separates rotating from nonrotating fluid is bow-shaped. For a stratified fluid, the axial vorticity distribution is nonuniform both in the vertical and in the radial directions. With increasing stratification, diffusive vorticity production near the sidewall is more pronounced. Axisymmetric flows in the early phase of spin-up of a stratified fluid are controlled by both the inviscid dynamic effect and the viscous diffusion effect. At a location close to the Ekman layers, the inviscid effect outweighs the viscous effect, in much the same way as in a homogeneous fluid. However, at a location close to mid-depth, the viscous diffusion effect, enhanced by substantial flow gradients in that region, is dominant. This points to the necessity of including the direct effect of viscous diffusion in the interior in formulating an analytical model of stratified spin-up problems.  相似文献   

Photochemistry of methane-water ices     

Robert Hodyss  Paul V. Johnson  Julie V. Stern  Jay D. Goguen  Isik Kanik 《Icarus》2009,200(1):338-156

We report a study on the broadband ultraviolet photolysis of methane-water ice mixtures, at low methane concentrations and temperatures relevant to the icy satellites of the outer Solar System. The photochemistry of these mixtures is dominated by the action of hydroxyl radicals on methane and the resulting products. This implies that, given sufficient exposure time, the methane will eventually be completely oxidized to carbon dioxide. The presence of methane inhibits the formation of hydrogen peroxide by serving as a trap for hydroxyl radicals. The distribution of photochemical products is broadly similar to that previously conducted using ion and electron sources, with some differences possibly attributable to the difference in radiation source. The results are applicable to a variety of icy bodies in the Solar System. On Enceladus, where methane mixed with water is measured in the plumes, methane in the surface ices is subject to oxidation and will eventually be converted to CO₂. The CH stretch feature detected in the VIMS spectra of the Enceladus surface ice suggests that methane is currently being supplied to the surface ice, likely from re-condensation of the plume gas.  相似文献   

Origin of a late Neoproterozoic (605 ± 13 Ma) intrusive carbonate–albitite complex in Southern Sinai, Egypt     

Mokhles Kamal Azer  Robert J. Stern  Jun-Ichi Kimura 《International Journal of Earth Sciences》2010,99(2):245-267

New geochemical, isotopic, and geochronological data and interpretations are presented for late Neoproterozoic intrusive carbonates and related rocks of southern Sinai, Egypt (northernmost Arabian–Nubian Shield). The Tarr carbonates are coarsely crystalline and related to explosive emplacement of hypabyssal and volcanic albitite at 605 ± 13 Ma. The carbonates associated with the albitites are divisible into two types: primary dolomitite and secondary breunneritite (Fe-rich magnesite). The dolomitite was clearly intrusive but differs from classic igneous carbonatites, containing much lower abundances of incompatible elements, such as REE, U, Th, Rb, Nb, Y, P, Sr, Zr, Ba, and total alkalies. The breunneritite is a secondary replacement of dolomitite, probably marking the roots of a vigorous hydrothermal system. Albitites show pristine abundances of major and trace elements and were not subjected to a major metamorphic overprint. They are relatively more fractionated, alkaline and related to within-plate A-type magmas, were emplaced in an extensional or non-compressive tectonic regime in the cupola of high-level A-type granite. Tarr albitites may represent residual magma remaining after near-total crystallization of an A-type granite pluton at depth, forcibly emplaced into the roof above the cooling pluton. The intrusive dolomitite exsolved from highly differentiated albitite melt, in the apical regions of a still-buried alkaline “A-type” granite pluton that was rich in CO₂; these volatiles migrated upwards and towards the cooler margins of the magma body. Late NNE-SSW extension allowed a shallow-level cupola to form, into which albitite melts and carbonate fluids migrated, culminating in explosive emplacement of albitite breccia and intrusive carbonate. Isotopic compositions of Tarr dolomitite and albitite indicate these are consanguineous and ultimately of mantle origin. Magmatic volatiles fenitized the wall rock, while submarine hydrothermal activity transformed some of the dolomitite into breunneritite. Recognition of Tarr-type should encourage similar hypabyssal complex intrusions to be sought for in association with A-type granitic plutons elsewhere.  相似文献   

Population changes in a growth center region with reference to the Israeli Negev     

Stern E  Sonis M 《GeoJournal》1981,5(3):261-268

The aim of this paper is to present a scheme of relative population changes in a geographic-termed growth center region, with reference to a real problem of development as implemented in the Israeli Negev arid zone. The growth process described in the scheme leads to dynamic steady-states which indicate stable structure and stable relationships between the components of the regional system — the growth center and its urban and rural hinterlands. It was found that the relative population growth process in the Negev during the last thirty years is similar to the process determined by the scheme. Furthermore, geo-political changes in the area due to the peace treaty between Egypt and Israel may alter this process and open a new period of regional growth. An additional thrust of this paper is methodological: to introduce and apply the hexagonal diagram to describe and classify processes of relative population growth.  相似文献   

Petrology and geochemistry of alkali basalts and ultramafic inclusions from the palei-aike volcanic field in Southern Chile and the origin of the patagonian plateau lavas     

Milka Alexandra Skewes  Charles R. Stern   《Journal of Volcanology and Geothermal Research》1979,6(1-2)

The Palei-Aike volcanic field, the southernmost unit of the Patagonian plateau lavas, consists of Pleistocene to Recent alkali olivine basalts petrologically and geochemically similar to alkali basalts from diverse tectonic environments. The Palei-Aike basalts have lower SiO₂ and Al₂O₃ and higher TiO₂ and P₂O₃ than published analyses of other Patagonian plateau basalts. Garnet, garnet + spinel-, and phlogopite-peridotites, not reported from other Patagonian plateau lavas or from elsewhere in South America, are common inclusions within Palei-Aike lavas along with spinel-lherzolite, dunite, granulites, and aluminous clinopyroxene megacrysts. The inclusion of these high-pressure assemblages indicates a mantle origin for the Palei-Aike lavas. The Patagonian plateau lavas are located in a tectonic position similar to back-arc basins, and their origin may be a consequence of subduction. The origin and distinct chemical features of the Palei-Aike basalts may be due in part to thermal or mechanical perturbations of the mantle related to changes in plate boundaries and motions in the vicinity of the unstable trench-transform triple junction formed by the South American, Antarctic and Scotia plates.  相似文献   

The Negev continental bridge: a chain in an intermodal transport system     

Eliahu Stern  Yehuda Gradus  Yehuda Hayuth 《Geoforum》1983,14(4):461-469

This paper is a second follow-up discussion concerning the role, economic viability and operational characteristics of the Negev Continental Bridge in the fluid geo-political atmosphere of the Middle East. The two previous papers (Geoforum8, 29–32 and 311–318) discussed the viability of the Israeli Continental Bridge as an alternative to the Suez Canal. Now, two years after the Canal was re-opened for use by Israeli vessels, the annual amount of cargo movement across the Israeli land bridge is still growing, although it is less economical than the Suez Canal. It is thus suggested that there is a need to view the continental bridge as one part of a chain in an intermodal transport system.  相似文献   

X-Ray Emission from Comet McNaught-Hartley (C/1999 T1)     

V.A. KrasnopolskyD.J. Christian  V. KharchenkoA. Dalgarno  S.J. WolkC.M. Lisse  S.A. Stern 《Icarus》2002,160(2):437-447

Comet McNaught-Hartley was observed in five 1-h exposures on January 8-14 2001 using the advanced CCD imaging spectrometer on board the Chandra X-ray Observatory. The X-ray image of the comet does not show a crescent-like shape. The brightest region is offset from the nucleus between the sunward and comet velocity directions. The comet mean X-ray luminosity is equal to 7.8×10¹⁵ erg s⁻¹ for photon energy E>150 eV and aperture ρ=1.5×10⁵ km where the comet X-ray brightness exceeds 20% of the peak value. Gas production rate was 10²⁹ s⁻¹ during the observations, and the efficiency of X-ray excitation was equal to 4×10⁻¹⁴ erg AU^3/2. Day-to-day variations in X-rays reached a factor of 5. The strongest short-term variation was by a factor of 1.75 for 1600 s. This variation may be explained by a decline in the solar-wind flux by the same factor in ≈800 s. The comet and Earth were seeing different faces of the Sun, and time delay in the solar-wind events on the Earth and the comet was long, equal to 6 days. The best correlation between the comet X-ray luminosity and the solar-wind proton density is for the time delay of 5.5 days and may be explained by the higher velocity of heavy ions.Careful background subtraction made it possible to extract the comet spectrum from 150 to 1000 eV. No signal was detected at E>1000 eV, and a 3σ upper limit to any emission with E>1000 eV is 0.3% of the photon emission at 150-1000 eV. The best χ²-fit model to the spectrum consists of nine narrow emission features. The emission energies and intensities are in good agreement with a charge exchange spectrum calculated by us for the slow solar wind. Using this spectrum, we identify the observed emissions as (Ne⁷⁺+Mg⁷⁺+Mg⁸⁺) at 195 eV, (Mg⁸⁺+Mg⁹⁺+Si⁸⁺) at 250 eV, C⁵⁺ at 370 and 460 eV, O⁶⁺ at 560 eV, O⁷⁺ at 650, 780, and 840 eV, and Ne⁸⁺ at 940 eV. X-ray spectroscopy of comets may be used to diagnose the solar-wind composition and its interaction with comets.  相似文献