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排序方式: 共有4175条查询结果,搜索用时 15 毫秒
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R. Wieler Th. Graf P. Signer S. Vogt G. F. Herzog C. Tuniz D. Fink L. K. Fifield J. Klein R. Middleton A. J. T. Jull P. Pellas J. Masarik G. Dreibus 《Meteoritics & planetary science》1996,31(2):265-272
Abstract— We determined He, Ne, Ar, 10Be, 26Al, 36Cl, and 14C concentrations, as well as cosmic-ray track densities and halogen concentrations in different specimens of the H6 chondrite Torino, in order to constrain its exposure history to cosmic radiation. The Torino meteoroid had a radius of ~20 cm and travelled in interplanetary space for 2.5–10 Ma. Earlier, Torino was part of a larger body. The smallest possible precursor had a radius of 55 cm and a journey through space longer than ~65 Ma. If the first-stage exposure took place in a body with a radius of >3 m or in the parent asteroid, then it lasted nearly 300 Ma. The example of Torino shows that it is easy to underestimate first-stage exposure ages when constructing two-stage histories. 相似文献
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The effect of a transverse magnetic field and of the viscosity diffusion on the free-convection flow of an electrically-conducting incompressible fluid past a uniformally accelerated vertical plate is discussed. A finite difference method has been used to obtain a numerical solution. The influence of the various parameters on the flow field is discussed. 相似文献
24.
Yannick Giraud-Héraud Jean Kaplan François De Volnay Martin Charling Tao Sylvaine Turck-Chièze 《Solar physics》1990,128(1):21-33
The Saclay solar evolution code is used to check the effect of WIMPs on solar evolution. In this paper we study the effects of various types of Cosmion-matter interactions, give constraints on the crosssections compatible with the measured neutrino rate of 2 SNU on chlorine, and relate these constraints to ongoing dark matter detection experiments.Unité associée au CNRS UA 280, F-75251 Paris Cedex 05, France.On leave from LPC, Collège de France. 相似文献
25.
Martin M. Roth Thomas Fechner Dieter Wolter Andreas Kelz Thomas Becker 《Experimental Astronomy》2002,14(2):99-105
PMAS, the Potsdam Multi-Aperture Spectrophotometer, is a new integral field spectrograph in the optical, which is optimized
for good transmission and high image quality from 350 nm to 1 μm. We present our plan to implement a CCD charge-shuffle mode
to allow for beam switching with a very high degree of sky subtraction accuracy for faint object 3-D spectroscopy.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
26.
D. H. Morgan Q. A. Parker Martin Cohen 《Monthly notices of the Royal Astronomical Society》2003,346(3):719-730
We report the discovery of the first probable Galactic [WN] central star of a planetary nebula (CSPN). The planetary nebula candidate was found during our systematic scans of the AAO/UKST Hα Survey of the Milky Way. Subsequent confirmatory spectroscopy of the nebula and central star reveals the remarkable nature of this object. The nebular spectrum shows emission lines with large expansion velocities exceeding 150 km s−1 , suggesting that perhaps the object is not a conventional planetary nebula. The central star itself is very red and is identified as being of the [WN] class, which makes it unique in the Galaxy. A large body of supplementary observational data supports the hypothesis that this object is indeed a planetary nebula and not a Population I Wolf–Rayet star with a ring nebula. 相似文献
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Abstract— In the early morning hours of December 13, 2002, a bright Geminid fireball with an absolute magnitude of ?9.2 ± 0.5 was observed from Southern Saskatchewan, Canada. The fireball displayed distinct small‐scale oscillations in brightness, or flickering, indicative of the parent meteoroid being both non‐spherical and rotating. Using the light curve derived from a calibrated radiometer, we determine a photometric mass of 0.429 ± 0.15 kg for the meteoroid, and we estimate from its initial rotation rate of some 6 Hz that the meteoroid was ejected from the parent body (3200) Phaethon some 2500 ± 500 years ago. We find that 70% of Geminid fireballs brighter than magnitude ?3 display distinct flickering effects, a value that is in stark contrast to the 18% flickering rate exhibited by sporadic fireballs. The high coincidence of flickering and the deep atmospheric penetration of Geminid fireballs are suggestive of Geminid meteoroids having a highly resilient structure, a consequence, we suggest, of their having suffered a high degree of thermal processing. The possibility of Gemind material surviving atmospheric ablation and being sampled is briefly discussed, but the likelihood of collecting and identifying any such material is admittedly very small. 相似文献