The primordial excitation and clearing of the asteroid belt—Revisited     

David P. O'Brien  Alessandro Morbidelli 《Icarus》2007,191(2):434-452

We have performed new simulations of two different scenarios for the excitation and depletion of the primordial asteroid belt, assuming Jupiter and Saturn on initially circular orbits as predicted by the Nice Model of the evolution of the outer Solar System [Gomes, R., Levison, H.F., Tsiganis, K., Morbidelli, A., 2005. Nature 435, 466-469; Tsiganis, K., Gomes, R., Morbidelli, A., Levison, H.F., 2005. Nature 435, 459-461; Morbidelli, A., Levison, H.F., Tsiganis, K., Gomes, R., 2005. Nature 435, 462-465]. First, we study the effects of sweeping secular resonances driven by the depletion of the solar nebula. We find that these sweeping secular resonances are incapable of giving sufficient dynamical excitation to the asteroids for nebula depletion timescales consistent with estimates for solar-type stars, and in addition cannot cause significant mass depletion in the asteroid belt or produce the observed radial mixing of different asteroid taxonomic types. Second, we study the effects of planetary embryos embedded in the primordial asteroid belt. These embedded planetary embryos, combined with the action of jovian and saturnian resonances, can lead to dynamical excitation and radial mixing comparable to the current asteroid belt. The mass depletion driven by embedded planetary embryos alone, even in the case of an eccentric Jupiter and Saturn, is roughly 10-20× less than necessary to explain the current mass of the main belt, and thus a secondary depletion event, such as that which occurs naturally in the Nice Model, is required. We discuss the implications of our new simulations for the dynamical and collisional evolution of the main belt.  相似文献   

Thermodynamics of rare events and impulsive relaxation events in the magnetospheric substorm dynamics     

Giuseppe Consolini  Matthieu Kretzschmar 《Planetary and Space Science》2007,55(15):2244-2250

The magnetosphere dynamics shows fast relaxation events following power-law distribution for many observable quantities during magnetic substorms. The emergence of such power-law distributions has been widely discussed in the framework of self-organized criticality and/or turbulence. Here, a different approach to the statistical features of these impulsive dynamical events is proposed in the framework of the thermodynamics of rare events [Lavenda, B.H., Florio, A., 1992. Thermodynamics of rare events, Int. J. Theor. Phys. 31, 1455–1475; Lavenda, B.H., 1995. Thermodynamics of Extremes. Albion]. In detail, an application of such a novel approach to the magnetospheric substorm avalanching dynamics as monitored by the auroral electroject index is discussed.  相似文献   

Iron line profiles and self-shadowing from relativistic thick accretion discs     

Sheng-Miao Wu  Ting-Gui Wang 《Monthly notices of the Royal Astronomical Society》2007,378(3):841-851

We present Fe Kα line profiles from and images of relativistic discs with finite thickness around a rotating black hole using a novel code. The line is thought to be produced by iron fluorescence of a relatively cold X-ray-illuminated material in the innermost parts of the accretion disc and provides an excellent diagnostic of accretion flows in the vicinity of black holes. Previous studies have concentrated on the case of a thin, Keplerian accretion disc. This disc must become thicker and sub-Keplerian with increasing accretion rates. These can affect the line profiles and in turn can influence the estimation of the accretion disc and black hole parameters from the observed line profiles. We here embark on, for the first time, a fully relativistic computation which offers key insights into the effects of geometrical thickness and the sub-Keplerian orbital velocity on the line profiles. We include all relativistic effects such as frame-dragging, Doppler boost, time dilation, gravitational redshift and light bending. We find that the separation and the relative height between the blue and red peaks of the line profile diminish as the thickness of the disc increases. This code is also well suited to produce accretion disc images. We calculate the redshift and flux images of the accretion disc and find that the observed image of the disc strongly depends on the inclination angle. The self-shadowing effect appears remarkable for a high inclination angle, and leads to the black hole shadow being in this case, completely hidden by the disc itself.  相似文献   

A signature of the donor star in the extra-galactic X-ray binary LMC X−2     

R. Cornelisse  D. Steeghs  J. Casares  P. A. Charles  I. C. Shih  R. I. Hynes  K. O'Brien 《Monthly notices of the Royal Astronomical Society》2007,381(1):194-200

Two nights of phase-resolved medium-resolution Very Large Telescope spectroscopy of the extra-galactic low-mass X-ray binary LMC X−2 have revealed a 0.32 ± 0.02 d spectroscopic period in the radial velocity curve of the He  ii λ4686 emission line that we interpret as the orbital period. However, similar to previous findings, this radial velocity curve shows a longer term variation that is most likely due to the presence of a precessing accretion disc in LMC X−2. This is strengthened by He  ii λ4686 Doppler maps that show a bright spot that is moving from night to night. Furthermore, we detect narrow emission lines in the Bowen region of LMC X−2, with a velocity of   K _em= 351 ± 28 km s⁻¹  , that we tentatively interpret as coming from the irradiated side of the donor star. Since K _em must be smaller than K ₂, this leads to the first upper limit on the mass function of LMC X−2 of   f ( M ₁) ≥ 0.86  M_⊙  (95 per cent confidence), and the first constraints on its system parameters.  相似文献   

The Galaxy Evolution Explorer UV emission in shell galaxies: tracing galaxy 'rejuvenation' episodes     

R. Rampazzo  A. Marino  R. Tantalo  D. Bettoni  L. M. Buson  C. Chiosi  G. Galletta  R. Grützbauch  R. M. Rich 《Monthly notices of the Royal Astronomical Society》2007,381(1):245-262

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On the origin of the dichotomy of early-type galaxies: the role of dry mergers and active galactic nucleus feedback     

X. Kang  Frank C. van den Bosch  A. Pasquali 《Monthly notices of the Royal Astronomical Society》2007,381(1):389-400

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Disc–jet coupling in black hole accretion systems – I. General relativistic magnetohydrodynamical models     

Jonathan C. McKinney  Ramesh Narayan 《Monthly notices of the Royal Astronomical Society》2007,375(2):513-530

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知识产权贸易下的全球地缘科技格局及其演化   总被引：1，自引：3，他引：1  

段德忠  杜德斌  谌颖 《地理研究》2019,38(9):2115-2128

中国崛起,关键在于科技崛起。在当前技术针对与封锁的国际环境中,探讨建构以中国为核心的全球创新网络和科学制定中国未来科技战略是当前创新地理学和地缘政治学交叉之下研究的重点课题,而明晰全球地缘科技格局及其演变过程则是基础所在。本文基于2001—2015年全球国家（地区）间的知识产权进出口数据,在研究全球知识产权贸易格局和网络结构的基础上,探讨了全球地缘科技体系的时空演化特征,得出以下结论：① 全球知识产权贸易网络两极分化显著,是一典型的小世界网络,以美国为核心的金字塔结构不断夯实;② 基于敏感性和脆弱性模型阐释的全球知识产权贸易的非对称依赖性进一步验证了美国是全球地缘科技格局的核心,且其核心地位不断巩固和加强。  相似文献   

Cometary outbursts – the post-Deep Impact outlook on collisions as possible causes     

P. Gronkowski 《Monthly notices of the Royal Astronomical Society》2007,379(3):1049-1052

The possibility of impacts between comets belonging to the Jupiter Family and other small bodies orbiting in the main asteroid belt, and the consequences in relation to cometary activity are discussed. The probability of such events and the jumps in cometary brightness caused by impacts are examined. The results are compared with the results of the Deep Impact mission to Comet 9P/Tempel 1. The main conclusion of this paper is in agreement with previous findings, namely that an impact mechanism cannot be the main cause of the outburst activity of comets.  相似文献   

Isolated versus common envelope dynamos in planetary nebula progenitors     

J. Nordhaus  E. G. Blackman  A. Frank 《Monthly notices of the Royal Astronomical Society》2007,376(2):599-608

The origin, evolution and role of magnetic fields in the production and shaping of proto-planetary nebulae (PPNe) and planetary nebulae (PNe) are a subject of active research. Most PNe and PPNe are axisymmetric with many exhibiting highly collimated outflows; however, it is important to understand whether such structures can be generated by isolated stars or require the presence of a binary companion. Towards this end, we study a dynamical, large-scale α−Ω interface dynamo operating in a 3.0 M_⊙ Asymptotic Giant Branch (AGB) star in both an isolated setting and a setting in which a low-mass companion is embedded inside the envelope. The back reaction of the fields on the shear is included and differential rotation and rotation deplete via turbulent dissipation and Poynting flux. For the isolated star, the shear must be resupplied in order to sufficiently sustain the dynamo. Furthermore, we investigate the energy requirements that convection must satisfy to accomplish this by analogy to the Sun. For the common envelope case, a robust dynamo results, unbinding the envelope under a range of conditions. Two qualitatively different types of explosion may arise: (i) magnetically induced, possibly resulting in collimated bipolar outflows and (ii) thermally induced from turbulent dissipation, possibly resulting in quasi-spherical outflows. A range of models is presented for a variety of companion masses.  相似文献