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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土地管理信息系统建立过程中地图数据质量问题讨论   总被引：1，自引：0，他引：1       下载免费PDF全文

江泓 《山东国土资源》2007,23(4):18-21

地图数据对于土地管理信息系统来说至关重要,地图数据质量的好坏直接影响到信息系统的质量和应用效果乃至信息系统建设的成败。该文对土地管理信息系统建立过程中有关地图数据质量问题进行分析探讨并提出了提高地图数据质量的方法。  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   

Rethinking the N(H₂)/I(CO) conversion factor     

W. F. Wall 《Monthly notices of the Royal Astronomical Society》2007,379(2):674-688

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Newly discovered cataclysmic variables from the INT/WFC photometric Hα survey of the northern Galactic plane     

A. R. Witham  C. Knigge  A. Aungwerojwit  J. E. Drew  B. T. Gänsicke  R. Greimel  P. J. Groot  G. H. A. Roelofs  D. Steeghs  P. A. Woudt 《Monthly notices of the Royal Astronomical Society》2007,382(3):1158-1168

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Timing studies on RXTE observations of SAX J2103.5+4545     

A. Baykal  S. Ç. &#;nam  M. J. Stark  C. M. Heffner  A. E. Erkoca  J. H. Swank 《Monthly notices of the Royal Astronomical Society》2007,374(3):1108-1114

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Outbursts of EX Hydrae revisited     

N. Mhlahlo  D. A. H. Buckley  V. S. Dhillon  S. B. Potter  B. Warner  P. A. Woudt 《Monthly notices of the Royal Astronomical Society》2007,380(1):353-364

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济南地区地下水位观测井固体潮对比研究          下载免费PDF全文

苏道磊  董晓娜  王晓军  刘晨 《山东国土资源》2007,23(4):7-10

收集了济南地区3口地下水位观测井的水位观测数据,分析了水位资料的变化规律与差异,重点针对观测井的固体潮效应,采用维尼迪科夫调和分析法求解出各井孔固体潮效应参数值。对比分析了M2波月序列潮汐因子、相对误差的大小,对井孔的内在质量进行了对比分析及客观评价。  相似文献   

The photoevaporation of discs around young stars in massive clusters     

C. J. Clarke 《Monthly notices of the Royal Astronomical Society》2007,376(3):1350-1356

We present models in which the photoevaporation of discs around young stars by an external ultraviolet source (as computed by Adams et al.) is coupled with the internal viscous evolution of the discs. These models are applied to the case of the Orion Nebula Cluster (ONC), where the presence of a strong ultraviolet field from the central OB stars, together with a detailed census of circumstellar discs and photoevaporative flows, is well established. In particular we investigate the constraints that are placed on the initial disc properties in the ONC by the twin requirement that most stars possess a disc on a scale of a few astronomical unit (au), but that only a minority (<20 per cent) are resolved by Hubble Space Telescope ( HST ) at a scale of 50 au. We find that these requirements place very weak constraints on the initial radius distribution of circumstellar discs: the resulting size distribution readily forgets the initial radius distribution, owing to the strong positive dependence of the photoevaporation rate on disc radius. Instead, the scarcity of large discs reflects the relative scarcity of initially massive discs (with mass  >0.1 M_⊙  ). The ubiquity of discs on a small scale, on the other hand, mainly constrains the time-span over which the discs have been exposed to the ultraviolet field (<2 Myr). We argue that the discs that are resolved by HST represent a population of discs in which self-gravity was important at the time that the dominant central OB star switched on, but that, according to our models, self-gravity is unlikely to be important in these discs at the present time. We discuss the implications of our results for the so-called proplyd lifetime problem.  相似文献