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51.
Geochemical and oxygen isotope perspective of a new R chondrite Dhofar 1671: Affinity with ordinary chondrites 下载免费PDF全文
Arshad Ali Sobhi J. Nasir Iffat Jabeen Ahmed Al Rawas Neil R. Banerjee Gordon R. Osinski 《Meteoritics & planetary science》2017,52(9):1991-2003
Dhofar 1671 is a relatively new meteorite that previous studies suggest belongs to the Rumuruti chondrite class. Major and REE compositions are generally in agreement with average values of the R chondrites (RCs). Moderately volatile elements such as Se and Zn abundances are lower than the R chondrite values that are similar to those in ordinary chondrites (OCs). Porphyritic olivine pyroxene (POP), radial pyroxene (RP), and barred olivine (BO) chondrules are embedded in a proportionately equal volume of matrix, one of the characteristic features of RCs. Microprobe analyses demonstrate compositional zoning in chondrule and matrix olivines showing Fa‐poor interior and Fa‐rich outer zones. Precise oxygen isotope data for chondrules and matrix obtained by laser‐assisted fluorination show a genetic isotopic relationship between OCs and RCs. On the basis of our data, we propose a strong affinity between these groups and suggest that OC chondrule precursors could have interacted with a 17O‐rich matrix to form RC chondrules (i.e., ?17O shifts from ~1‰ to ~3‰). These interactions could have occurred at the same time as “exotic” clasts in brecciated samples formed such as NWA 10214 (LL3–6), Parnallee (LL3), PCA91241 (R3.8–6), and Dhofar 1671 (R3.6). We also infer that the source of the oxidation and 17O enrichment is the matrix, which may have been enriched in 17O‐rich water. The abundance of matrix in RCs relative to OCs, ensured that these rocks would be apparently more oxidized and appreciably 17O‐enriched. In situ analysis of Dhofar 1671 is recommended to further strengthen the link between OCs and RCs. 相似文献
52.
We show that a class of solutions for a vacuum cylindrically symmetric gravitational field with nonvanishing cosmological constant reduce to the welknown Levi-Civita metric close to the axis. All the circular geodesics in this generalized vacuum are time like, null or space like depending on the relative magnitudes of the two parameters appearing in the solutions.For other particles moving inZ=constant plane there are some cases where the trapping of timelike and null trajectories occur, while in other cases some of the particles may orbit round the axis in a fixed zone bounded by two limiting radii. 相似文献
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We consider essential mechanisms for orbit shrinkage or 'hardening' of compact binaries in globular clusters (GCs) to the point of Roche lobe contact and X-ray emission phase, focusing on the process of collisional hardening due to encounters between binaries and single stars in the cluster core. The interplay between this kind of hardening and that due to emission of gravitational radiation produces a characteristic scaling of the orbit-shrinkage time with the single-star binary encounter rate γ in the cluster which we introduce, clarify and explore. We investigate possible effects of this scaling on populations of X-ray binaries in GCs within the framework of a simple 'toy' scheme for describing the evolution of pre-X-ray binaries in GCs. We find the expected qualitative trends sufficiently supported by data on X-ray binaries in Galactic GCs to encourage us towards a more quantitative study. 相似文献
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We present exact solutions of a Bianchi type VI0 viscous fluid cosmological model. It is a generalization of the model proposed by Banerjee and Santos (1983) for Bianchi type I. 相似文献
59.
The diffusion coefficient of neutrinos in the trapping regime in a presupernova star,where the scattering of neutrinos by nuclei is the dominant effect, is calculated within the framework of relativistic kinetic theory in the lowest order Chapman-Enskog approximation. The screening of the nuclei by ion-ion and electron-electron correlations is also taken into account. 相似文献
60.
Petrographic observations of two Vindhyan black shales (Rampur Shale of the Semri Group and Bijaigarh Shale of the Kaimur
Group) revealed the following features:
These features are indirect evidence of microbial mat colonization during the Proterozoic. The microbial mats probably fixed
carbon at the sediment surface, stabilized sediment and recycled organic matter and were the primary producers, unlike during
the Phanerozoic time. 相似文献
– | •general wavy lamination, |
– | •contorted and folded thin shreds of organic matter, |
– | •wavy pyritic laminae, |
– | •‘teeth and socket’ structure. |