The 3D structure of N132D in the LMC: a late-stage young supernova remnant     

Frédéric Vogt  Michael A. Dopita 《Astrophysics and Space Science》2011,331(2):521-535

We have used the Wide Field Spectrograph (WiFeS) on the 2.3 m telescope at Siding Spring Observatory to map the [O III] 5007 Å dynamics of the young oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. From the resultant data cube, we have been able to reconstruct the full 3D structure of the system of [O III] filaments. The majority of the ejecta form a ring of ～12 pc in diameter inclined at an angle of ～25 degrees to the line of sight. We conclude that SNR N132D is approaching the end of the reverse shock phase before entering the fully thermalized Sedov phase of evolution. We speculate that the ring of oxygen-rich material comes from ejecta in the equatorial plane of a bipolar explosion, and that the overall shape of the SNR is strongly influenced by the pre-supernova mass loss from the progenitor star. We find tantalizing evidence of a polar jet associated with a very fast oxygen-rich knot, and clear evidence that the central star has interacted with one or more dense clouds in the surrounding ISM.  相似文献   

Factors influencing methane-derived authigenic carbonate formation at cold seep from southwestern Dongsha area in the northern South China Sea     

Shuhong Wang  Wen Yan  Vitor H. Magalhães  Zhong Chen  Luis M. Pinheiro  Nikolaus Gussone 《Environmental Earth Sciences》2014,71(5):2087-2094

This paper carried out mineral and geochemical studies on a profile through a diagenetic methane-derived authigenic carbonate sample that was collected from southwestern Dongsha area of the northern South China Sea. Five samples locating in the cross-sectional middle mainly consist of dolomite and quartz, and two samples close to the surface have a small amount of Mg-calcite. The δ¹³C values of the samples vary between ?30.59 and ?0.30 % VPDB, with δ¹⁸O values ranging from 3.07 to 3.59 % VPDB, δ^44/40Ca values ranging from 1.35 to 1.47 % SRM915a, indicating a contribution of methane to the carbon pool where the precipitation of authigenic carbonates occurred. Based on the isotope values alone, it can not be distinguished if the carbon source is thermogenic gas or a mixture of biogenic methane and marine dissolved inorganic carbon. The δ¹⁸O values are in general consistent with dolomite precipitation from a fluid similar to present seawater. The observed small variation might be related to the oxygen isotope composition of seep fluid. The relative small range in calcium isotope values suggests that relatively constant growth conditions and precipitation from seawater. The central part of the carbonate nodule formed under the strong influence of methane seepage, and the external part is less influenced by methane, either due to reduced methane flux to the surface or caused by erosional exhumation of the carbonate nodule from greater depth to the sediment surface.  相似文献   

Identification of fractions of mercury in water,soil and sediment from a typical Hg mining area in Wanshan,Guizhou province,China   总被引：1，自引：0，他引：1  

Yan Lin  Thorjørn Larssen  Rolf D. Vogt  Xinbin Feng 《Applied Geochemistry》2010

Water, sediment and soil in a region with severe Hg contamination resulting from Hg mining and retorting continue to receive anthropogenic Hg loading from discarded tailings and mine waste calcine piles, even after mining has ended. Crucial for potential long-term mobilization and uptake in biota, however, are chemical forms of Hg in the environment. In order to assess potential mobility and bioavailability of Hg in contaminated areas, a refined sequential extraction technique was used for Hg in soil and sediment, allowing identification of the following conceptual Hg fractions: elemental Hg, exchangeable Hg, strongly-bound Hg and organically-bound Hg.  相似文献   

Chemical and isotopic evidence for the nature of the fluid in CH4-containing sediments of the Håkon Mosby Mud Volcano     

A. Lein  P. Vogt  K. Crane  A. Egorov  M. Ivanov 《Geo-Marine Letters》1999,19(1-2):76-83

The pore waters of CH₄-containing sediments of the Håkon Mosby Mud Volcano were rich in NH⁺ ₄, Br^-, and I^-; exhibited a high total alkalinity; but were poor in Cl^-and SO^2- ₄. The geological evidence and our data suggest that organic matter decomposition in preglacial or early interglacial sediments took place during early diagenesis (bacterial processes) and during metamorphism (thermogenic processes under the 3100-m-thick layer of glacial sediments), accompanied by mud volcano fluid generation. It is argued that the CH₄of the mud volcano sediments has a mixed, biogenic and thermogenic, origin.  相似文献   

SW Barents Sea continental margin heat flow and Håkon Mosby Mud Volcano     

O. Eldholm  E. Sundvor  P. R. Vogt  B. O. Hjelstuen  K. Crane  A. K. Nilsen  T. P. Gladczenko 《Geo-Marine Letters》1999,19(1-2):29-37

The high thermal gradient and heat flow >1000?mW?m^-2 on Håkon Mosby Mud Volcano are ascribed to rapid transport of pore water, mud, and gas in a narrow, deep conduit within a 3.1-km-thick glacial sediment unit. The instability is caused by rapid loading of dense glacial sediments on less dense oozes. Changes in pressure–temperature conditions by sudden, large-scale downslope mass movement may induce structural deformation, opening transient pathways from the base of the glacial sediments to the sea floor. This model may also explain slope maxima elsewhere on the margin.  相似文献   

In Memoriam Gabriel Davidovich Ginsburg, 1935–1999     

Peter R. Vogt 《Geo-Marine Letters》1999,19(1-2):1-1

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pacerman– I. A new algorithm to calculate Faraday rotation maps     

K. Dolag  C. Vogt  T. A. Enßlin 《Monthly notices of the Royal Astronomical Society》2005,358(3):726-731

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On the Bur Gheluai H5 chondrite and other meteorites with complex exposure histories     

S. K. Vogt  D. Aylmer  G. F. Herzog  R. Wieler  P. Signer  P. Pellas  C. Fini  C. Tuniz  A. J. T. Jull  D. Fink  J. Klein  R. Middleton 《Meteoritics & planetary science》1993,28(1):71-85

Abstract— We present the ¹⁴C, ²⁶Al, ¹⁰Be, ³He, ⁴He, ²⁰Ne, ²¹Ne, ²²Ne, ³⁶Ar, ³⁸Ar, and ⁴⁰Ar concentrations and the track densities measured in up to 13 samples of the Bur Gheluai (H5) meteorite fall. Only a multi-stage exposure history can explain the data in a self-consistent way. Parameters for a model two-stage history obtained by simultaneous, least-squares fitting of the concentrations of ¹⁴C, ²⁶Al, ¹⁰Be, and ²¹Ne were: first stage duration ～10 Ma and radius >2 m; second stage duration ～0.6 Ma and radius 40–100 cm. Nominal one-stage ²¹Ne production rates (P₂₁) inferred from ²⁶Al in Bur Gheluai samples exceed those inferred from ¹⁰Be as expected for a meteorite with a complex history. Nonetheless, data for other meteorites indicate that multi-stage irradiations alone do not account for all the high reported values of P₂₁ based on ²⁶A***l: The equations describing the production of cosmogenic nuclides show that uncorrected shielding effects may also play a role. A compilation of ordinary, solar-gas-poor chondrites for which two-stage histories have been proposed includes many with short second stages but none with unambiguously long first stages (>0.2 Ga).  相似文献   

A cloud mask methodology for high resolution remote sensing data combining information from high and medium resolution optical sensors   总被引：1，自引：0，他引：1  

Fernando Sedano  Pieter KempeneersPeter Strobl  Jan KuceraPeter Vogt  Lucia SeebachJesús San-Miguel-Ayanz 《ISPRS Journal of Photogrammetry and Remote Sensing》2011,66(5):588-596

This study presents a novel cloud masking approach for high resolution remote sensing images in the context of land cover mapping. As an advantage to traditional methods, the approach does not rely on thermal bands and it is applicable to images from most high resolution earth observation remote sensing sensors. The methodology couples pixel-based seed identification and object-based region growing. The seed identification stage relies on pixel value comparison between high resolution images and cloud free composites at lower spatial resolution from almost simultaneously acquired dates. The methodology was tested taking SPOT4-HRVIR, SPOT5-HRG and IRS-LISS III as high resolution images and cloud free MODIS composites as reference images. The selected scenes included a wide range of cloud types and surface features. The resulting cloud masks were evaluated through visual comparison. They were also compared with ad-hoc independently generated cloud masks and with the automatic cloud cover assessment algorithm (ACCA). In general the results showed an agreement in detected clouds higher than 95% for clouds larger than 50 ha. The approach produced consistent results identifying and mapping clouds of different type and size over various land surfaces including natural vegetation, agriculture land, built-up areas, water bodies and snow.  相似文献   

Polycrystalline apatite synthesized by hydrothermal replacement of calcium carbonates     

Argyrios Kasioptas  Thorsten Geisler  Christina Perdikouri  Nikolaus Gussone 《Geochimica et cosmochimica acta》2011,75(12):3486-202

Aragonite and calcite single crystals can be readily transformed into polycrystalline hydroxyapatite pseudomorphs by hydrothermal treatment in a (NH₄)₂HPO₄ solution. Scanning electron microscopy of the reaction products showed that the transformation of aragonite to apatite is characterised by the formation of a sharp interface between the two phases and by the development of intracrystalline porosity in the hydroxyapatite phase. In addition, electron backscattered diffraction (EBSD) imaging showed that the c-axis of apatite is predominantly oriented perpendicular to the reaction front with no crystallographic relationship to the aragonite lattice. However, the Ca isotopic composition of the parent aragonite, measured by thermal ionization mass spectrometry was inherited by the apatite product.Hydrothermal experiments conducted with use of phosphate solutions prepared with water enriched in ¹⁸O (97%) further revealed that the ¹⁸O from the solution is incorporated in the product apatite, as measured by micro-Raman spectroscopy. Monitoring the distribution of ¹⁸O with Raman spectroscopy was possible because the incorporation of ¹⁸O in the PO₄ group of apatite generates four new Raman bands at 945.8, 932, 919.7 and 908.8 cm⁻¹, in addition to the ν₁(PO₄) symmetric stretching band of apatite located at 962 cm⁻¹, which can be assigned to four ¹⁸O-bearing PO₄ species. The relative intensities of these bands reflect the ¹⁸O content in the PO₄ group of the apatite product. By using equilibrated and non-equilibrated solutions, with respect to the ¹⁸O distribution between aqueous phosphate and water, we could show that the concentration of ¹⁸O in the apatite product is linked to the degree of ¹⁸O equilibration in the solution. The textural and chemical observations are indicative of a coupled mechanism of aragonite dissolution and apatite precipitation taking place at a moving reaction interface.  相似文献