Orbital motion of a massive object in a dense stellar system     

Masatoshi Taga  & Masanori Iye 《Monthly notices of the Royal Astronomical Society》1998,299(1):111-117

In this paper we show the positional oscillation of a massive object in a dense stellar system by numerical N -body simulations. We found that the central massive object, which at first is placed at rest at the centre of the surrounding spherical stellar system, promptly departs from the centre and rotates in accordance with the rotation of the stellar system, if the stellar system has an appreciable rotation. This oscillatory motion continues for a long time because of the absence of dynamical friction. Such a long-lasting oscillation may explain the asymmetric structure observed in the centres of M31 and NGC 4486B, may cause the secular flow of gaseous elements distributed in the central regions of galaxies on to the massive object, and may ignite activity in the centres of galaxies.  相似文献   

Non-parametric reconstruction of distribution functions from observed galactic discs     

C. Pichon  & E. Thiébaut 《Monthly notices of the Royal Astronomical Society》1998,301(2):419-434

A general inversion technique for the recovery of the underlying distribution function for observed galactic discs is presented and illustrated. Under the assumption that these discs are axisymmetric and thin, the proposed method yields a unique distribution compatible with all the observables available. The derivation may be carried out from the measurement of the azimuthal velocity distribution arising from positioning the slit of a spectrograph along the major axis of the galaxy. More generally, it may account for the simultaneous measurements of velocity distributions corresponding to slits presenting arbitrary orientations with respect to the major axis. The approach is non-parametric, i.e. it does not rely on a particular algebraic model for the distribution function. Special care is taken to account for the fraction of counter-rotating stars, which strongly affects the stability of the disc. An optimization algorithm is devised — generalizing the work of Skilling &38; Bryan — to carry this truly two-dimensional ill-conditioned inversion efficiently. The performance of the overall inversion technique with respect to the noise level and truncation in the data set is investigated with simulated data. Reliable results are obtained up to a mean signal-to-noise ratio of 5, and when measurements are available up to 4  R _e. A discussion of the residual biases involved in non-parametric inversions is presented. The prospects of application of the algorithm to observed galaxies and other inversion problems are discussed.  相似文献   

Numerical simulations of protostellar encounters — II. Coplanar disc–disc encounters     

S. J. Watkins  A. S. Bhattal  H. M. J. Boffin  N. Francis  & A. P. Whitworth 《Monthly notices of the Royal Astronomical Society》1998,300(4):1205-1213

It is expected that an average protostar will undergo at least one impulsive interaction with a neighbouring protostar whilst a large fraction of its mass is still in a massive, extended disc. Such interactions must have a significant impact upon the evolution of the protostars and their discs.   We have carried out a series of simulations of coplanar encounters between two stars, each possessing a massive circumstellar disc, using an SPH code that models gravitational, hydrodynamic and viscous forces. We find that during a coplanar encounter, disc material is swept up into a shock layer between the two interacting stars, and the layer then fragments to produce new protostellar condensations. The truncated remains of the discs may subsequently fragment; and the outer regions of the discs may be thrown off to form circumbinary disc-like structures around the stars. Thus coplanar disc–disc encounters lead efficiently to the formation of multiple star systems and small- N clusters, including substellar objects.  相似文献   

Automated classification of stellar spectra — II. Two-dimensional classification with neural networks and principal components analysis     

Coryn A. L. Bailer-Jones  Mike Irwin  & Ted von Hippel 《Monthly notices of the Royal Astronomical Society》1998,298(2):361-377

We investigate the application of neural networks to the automation of MK spectral classification. The data set for this project consists of a set of over 5000 optical (3800–5200 Å) spectra obtained from objective prism plates from the Michigan Spectral Survey. These spectra, along with their two-dimensional MK classifications listed in the Michigan Henry Draper Catalogue, were used to develop supervised neural network classifiers. We show that neural networks can give accurate spectral type classifications (σ₆₈= 0.82 subtypes, σ_rms= 1.09 subtypes) across the full range of spectral types present in the data set (B2–M7). We show also that the networks yield correct luminosity classes for over 95 per cent of both dwarfs and giants with a high degree of confidence.   Stellar spectra generally contain a large amount of redundant information. We investigate the application of principal components analysis (PCA) to the optimal compression of spectra. We show that PCA can compress the spectra by a factor of over 30 while retaining essentially all of the useful information in the data set. Furthermore, it is shown that this compression optimally removes noise and can be used to identify unusual spectra.   This paper is a continuation of the work carried out by von Hippel et al. (Paper I).  相似文献   

可用于带耗散力卫星轨道长间隔积分的数值积分方法   总被引：2，自引：0，他引：2  

徐继鸿  黄天衣 《紫金山天文台台刊》1998,17(1):28-37

本文分析了对称方法不适合带耗散力的卫星轨道长间隔积分的缺陷和本质原因,并针对这个问题,采用文所介绍的方法,构造并推荐了一组积分公式。  相似文献   

日冕物质抛射的理想MHD模型研究   总被引：3，自引：0，他引：3  

章振大  林隽 《天文学进展》1998,16(3):195-209

概括了日冕物质抛射的一些观测结果和它们与其它太阳活动现象的相关性。简要回顾了较早期日冕物质抛射的理论研究,着重介绍了最近研究得较多的理论机制,即能量储存机制,以及其中的磁通量绳突变模型与其它理论模型的MHD数值和解析研究以及相应的重要应用．  相似文献   

煤岩对压裂裂缝长期导流能力影响的实验研究   总被引：7，自引：0，他引：7  

张士诚  牟善波  张劲  王雷 《地质学报》2008,82(10):1444-1449

煤层中一般都伴有煤层气,通过压裂可以将煤层气释放出来,一方面能够获得清洁能源,另一方面可以提高煤田的安全开采。煤岩层自身特点决定了其在压裂中应用的实验评价方法及结论应具有特殊性,本文主要针对煤层气井的煤岩层压裂裂缝长期导流能力进行实验评价研究。实验表明,与砂岩地层不同,煤岩的硬度较小,压裂中支撑剂嵌入情况较严重;煤岩易破碎,碎屑颗粒充填到支撑剂中;同时支撑剂存在破碎及吸附伤害等,多种作用导致支撑裂缝的导流能力降低。实验中,以煤岩层闭合压力为一个重要的参数,实验对比分析了在不同闭合压力下,铺砂浓度、支撑剂粒径、支撑剂种类及组合的选择、支撑剂颗粒的破碎与嵌入、压裂液残渣等因素对煤岩层导流能力的影响。本文的实验结论为,嵌入对煤岩层支撑裂缝的导流能力伤害很大,加大铺砂浓度、采用低破碎率支撑剂、降低压裂液伤害能在一定程度上提高煤层裂缝的导流能力,但影响程度随闭合压力的增加而逐渐降低。本文所得出的结论对今后煤层气的开发及设计施工具有一定的指导意义。  相似文献   

某基坑工程土钉支护工作性状试验研究   总被引：1，自引：0，他引：1  

熊勃  刘帅花 《岩土工程技术》2008,22(5):257-259

通过对广州天河荟雅苑基坑工程土钉支护进行试验和研究,分析了土钉支护体系的工作性状,并为同类工程的设计提供了一定的依据。  相似文献   

Numerical simulation of migration–accumulation of oil resources     

Yirang Yuan  Yuji Han 《Computational Geosciences》2008,12(2):153-162

Numerical simulation of oil migration and accumulation is to describe the history of oil migration and accumulation in basin evolution. It is of great value to the evaluation of oil resources and to the determination of the location and amount of oil deposits. This thesis discusses the characteristics of petroleum geology and permeation fluid mechanics. For the three-dimensional problems of Dongying hollow of Shengli Petroleum Oil Field, it puts forward a new model and a kind of modified method of upwind finite difference fractional steps implicit interactive scheme. For the famous hydraulic experiment of secondary migration–accumulation, the numerical simulation test has been done, and both the computational and experimental results are basically identical. For the actual problem of Dongying hollow, the numerical simulation test and the actual conditions are basically coincident. Thus, the well-known problem has been solved.  相似文献   

西藏札达盆地控盆断裂有限元数值模拟   总被引：1，自引：0，他引：1  

段岩  孟宪刚  邵兆刚  朱大岗 《地质通报》2008,27(10)

札达盆地是喜马拉雅构造带中的一个山间断陷盆地,其演化过程与盆地两侧的控盆构造密切相关。对控盆断裂的构造应力场进行模拟计算,将有助于进一步深化对本区构造控盆的认识。因此,在对盆地构造地质进行详细调查的基础上,结合本区的深部地质与地球物理资料,对札达盆地控盆断裂的构造应力场进行了模拟。计算结果表明,札达盆地的演化明显受盆地两侧边界断裂的控制,札达盆地是在整体南北向挤压应力的作用下,不同块体差异隆升作用的结果。其南侧的控盆断裂为北倾的正断层,北侧的控盆断裂为南倾的逆断层,二者共同形成了南降北升的翘板式断陷盆地运动过程,是喜马拉雅地块在陆内汇聚挤压构造环境中构造应力场调整的一种方式。  相似文献