The effects of thermal conduction on the ADAF with a toroidal magnetic field     

S. Abbassi  J. Ghanbari  S. Najjar 《Monthly notices of the Royal Astronomical Society》2008,388(2):663-668

The observation of the hot gas surrounding Sgr A * and a few other nearby galactic nuclei imply that electron and proton mean free paths are comparable to the gas capture radius. So, the hot accretion flows are likely to proceed under week-collision conditions. Hence, thermal conduction has been suggested as a possible mechanism by which the sufficient extra heating is provided in hot advection-dominated accretion flow (ADAF) accretion discs. We consider the effects of thermal conduction in the presence of a toroidal magnetic field in an ADAF around a compact object. For a steady-state structure of such accretion flows, a set of self-similar solutions are presented. We find two types of solutions which represent high and slow accretion rate. They have different behaviours with saturated thermal conduction parameter, φ.  相似文献   

Lateglacial varve chronology and biostratigraphy of lakes Holzmaar and Meerfelder Maar, Germany     

ACHIM BRAUER  THOMAS LITT  JÖRG F. W. NEGENDANK  BERND ZOLITSCHKA 《Boreas: An International Journal of Quaternary Research》2001,30(1):83-88

In this paper we briefly compare previously published data on four lateglacial sediment profiles from lakes Holzmaar and Meerfelder Maar in the Eifel region. Two of these profiles (one from each lake) are varvedated, whereas the other two pollen profiles are on depth scales. In general, the palynological signal in all profiles compares well, proving the regional validity of the individual data sets. There are some discrepancies between Holzmaar and Meerfelder Maar, however, mainly concerning varve dating of major lateglacial features, and these are explained after detailed correlation using a combination of varve dating and palynological signals. The result is a consistent varve-dated biostratigraphy for the Lateglacial in the Eifel region. Moreover, it is demonstrated that a combination of varve chronology and high resolution palynostratigraphy in several lake profiles enables even gaps of a few decades up to a few centuries to be detected, thus providing a valuable tool for precise regional palaeoenvironmental study. This multi-core study on two lakes from the same region demonstrates the likelihood of undetected errors in single-core studies on non-varved sediments.  相似文献   

The diatom flora in the Fram Strait. A comparison with the Pleistocene/Holocene boundary flora in the Norwegian Sea     

BJØRG STABELL 《Polar research》1987,5(3):321-322

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