| 3 | 太古代科马提岩和硅质高镁玄武岩的化学和同位素组成:地球早期历史及大陆地壳形成的制约条件显示文摘对太古代科马提岩(AK)和硅质高镁玄武岩的研究能够提供地球形成过程的模型,热力学条件和证实假定的太古代地幔中岩浆海的存在以及早期太古代地壳的岩石成因和太古代镁铁质和超镁铁质杂岩的成矿作用(PGE)等方面的约束机制。 AK一般轻稀土元素(LREE)亏损并具有∈Nd的正初始值(3.5Ga时为+2、2.7Ga时为+4),说明其来源于长期LREE亏损的地幔源(John等,1988)。表明在3.8Ma之前广泛的长英质地壳存在的证据很少,因此需要有另一种导致这种亏损的地壳形成机制(Galen和Galdstein,1988)。极低的Ti Zr和Y丰度值以及Ti-Cu-Pd比率与富尖晶石的Iherzohte捕虏体(来自原始地幔)的相似性,说明AK是由单阶段地幔大规模熔融形成的(Sun,1987)。形成AK的高温(≥2000℃)热源可能来自约670km。 | S.S.Sun 张立辉 | 1991 | 世界地质1991，10，1： | 0 |
| 5 | B3 0749+460A: A New Repeat “Changing-look” Active Galactic Nucleus Associated with X-Ray Spectral Slope Variations显示文摘Here we report an identification of B3 0749+460 A as a new double-peaked local 'changing-look' active galactic nucleus(CL-AGN) in terms of our multi-epoch spectroscopic analysis. By comparing our new spectra taken in 2021 with the ones taken by the Sloan Digital Sky Survey in 2004, BOSS in 2013 and Ma NGA in 2016, we reveal type transitions of Seyfert(Sy) 1.9 → Sy1.8 → Sy1.9. In the transitions, the classical broad Hα emission fades away after 2013 and disappears in our 2021 spectrum, although the absence of broad Hβ can be traced back to at least 2016. A follow-up observation in X-rays by the Swift/XRT reveals that(1) the X-ray emission level gradually decreased since 2005;and(2)the X-ray spectrum is soft in the optical 'turn-off' state and hard in the 'turn-on' state. We argue that the disappearance of the classical broad Hα emission can be likely explained by the disk-wind broad-line-region model, in which the CL phenomenon is sensitive to luminosity in individual AGNs. | J.Wang W.K.Zheng D.W.Xu T.G.Brink A.V.Filippenko C.Gao S.S.Sun J.Y.Wei | 2022 | Research in Astronomy and Astrophysics2022，22，1： | 0 |
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