Orbit determination by four observations

An elliptic orbit is determined from two short-arc pairs of observations at different oppositions by the angular momentum integral. Other methods for initial orbit determination than the classical do exist.     

双星轨道拟合的研究进展

双星轨道拟合是天文学的一项基础性研究工作。其主要目的是给出双星系统的二体轨道参数,这些参数不仅是高精度、高网格密度星表参考架的必要组成部分,而且也为理解各种有关观测现象提供了必要的动力学基础;更重要的是,双星轨道拟合可以直接估计恒星物理和星系天文学等领域极有应用价值的恒星质量参数。因此,长期以来双星轨道拟合工作一直受到研究者的广泛关注。近年来,随着高精度的恒星运动学观测资料的大量积累,双星轨道拟合更成为天体测量和天体力学的一个共同的热点课题,有关研究也有了长足的进展。综述了双星轨道拟合的历史及现状,其中着重介绍了目前所用的主要观测资料和各种具体的拟合模型、拟合方法;简要描述了几种主要的双星星表;展望了今后双星轨道拟合工作的发展趋势。     

一种载人小行星探测轨道优化设计方法

给出了一种基于变比冲核电推进载人飞船探测小行星的轨道优化设计方法.首先基于双脉冲单圈Lambert轨道转移,对地球出发段和返回段进行搜索剪枝,再从两个可行区域中优选最佳飞行路径.设定"推进-滑行-推进"的分段飞行策略,以工质消耗最少为指标,利用混合法优化核电推进飞行轨迹,最后以分段优化参数为初值,基于整体任务约束将全飞行过程转化为非线性优化问题,将各飞行段进行拼接,获得整体参数优化解,并给出了数值和图形结果.     

The Hill stability of a binary or planetary system during encounters with a third inclined body

The dynamical interaction of a binary or planetary system and a third body moving on a parabolic orbit inclined to the system is discussed in terms of Hill stability for the full three-body problem. The situation arises in binary star disruption and exchange, in extrasolar planetary system disruption, exchange and capture. It is found that increasing the inclination of the third body decreases the Hill regions of stability. This makes exchange or disruption of the component masses more likely as does increasing the eccentricity of the binary.
The stability criteria are applied to determine possible disruption and capture distances for currently known extrasolar planetary systems.     

On the Dynamics of Dust Grains in a Hierarchical Environment

Most main sequence stars are binaries or higher multiplicity Systems and it appears that at birth most stars have circumstellar disks. It is commonly accepted that planetary systems arise from the material of these disks; consequently, binary and multiple systems may have a main role in planet formation. In this paper, we study the stage of planetary formation during which the particulate material is still dispersed as centimetre-to-metre sized primordial aggregates. We investigate the response of the particles, in a protoplanetary disk with radius R_D = 100 AU around a solar-like star, to the gravitational field of bound perturbing companions in a moderately wide (300–1600 AU) orbit. For this purpose, we have carried out a series of simulations of coplanar hierarchical configurations using a direct integration code that models gravitational and viscous forces. The massive protoplanetary disk is around one of the components of the binary. The evolution in time of the dust sub-disk depends mainly on the nature (prograde or retrograde) of the relative revolution of the stellar companion, and on the temperature and mass of the circumstellar disk. Our results show that for binary companions near the limit of tidal truncation of the disk, the perturbation leads to an enhanced accretion rate onto the primary, decreasing the lifetime of the particles in the protoplanetary disk with respect to the case of a single star. As a consequence of an enhanced accretion rate the mass of the disk decreases faster, which leads to a longer resultant lifetime for particles in the disk. On the other hand, binary companions may induce tidal arms in the dust phase of protoplanetary disks. Spiral perturbations with m = 1 may increase in a factor 10 or more the dust surface density in the neighbourhood of the arm, facilitating the growth of the particles. Moreover, in a massive disk (0.01M⊙) the survival time of particles is significantly shorter than in a less massive nebula (0.001M⊙) and the temperature of the disk severely influences the spiral-in time of particles. The rapid evolution of the dust component found in post T Tauri stars can be explained as a result of their binary nature. Binarity may also influence the evolution of circumpulsar disks. This revised version was published online in July 2006 with corrections to the Cover Date.     

土体疲劳对打桩分析的影响

在动力沉桩过程中,桩长时间连续运动导致桩侧土体强度的降低,使土体产生疲劳效应。结合一维应力波动理论,桩土相互作用模型和土体疲劳的不同计算方法,编制计算软件,对渤海某油田采油平台的桩基工程进行打桩分析,预测沉桩过程所需的锤击数、桩周土静阻力以及桩的极限承载力。比较不同的桩侧土体疲劳计算模式的分析结果,并用工程实测数据验证计算值。为工程设计和施工提供参考。     

渭河流域东部全新世黄土-古土壤剖面光释光测年及其记录的土壤侵蚀事件

在渭河流域东部老官台(LGT)全新世黄土-古土壤剖面中,系统采集了15个黄土释光测年样品,应用单片再生剂量法(SAR)对这些样品的细颗粒混合矿物进行了光释光(OSL)测年,测定结果表明:红外之后蓝光释光([post-IR]OSL)的年龄偏大,红外释光(IRSL)的年龄偏小或与蓝光释光(BLSL)的年龄基本一致,应用IRSL和BLSL信号测定的OSL年龄整体偏小可能与测定样品中长石矿物的异常衰退有关,而[post-IR]OSL信号由于很少发生异常衰退问题,使得其年龄可靠性更高。基于测定的[post-IR]OSL年龄,结合该剖面的磁化率和粒度指标,进一步探讨了渭河流域东部自全新世以来发生的两期土壤侵蚀事件,第1期土壤侵蚀事件发生在约12.40~9.34kaBP,即全新世大暖期来临之前的气候转暖期间;第2期土壤侵蚀事件发生在约4.60~3.76kaBP,即全新世大暖期即将结束、气候开始出现恶化、黄河中游地区夏文化发展的时期,这为深入探索夏代发生的大洪水事件及其气候背景提供了科学依据,本区两期显著的土壤侵蚀事件的发现,揭示了东亚季风系统的不稳定性,表现为千年到百年尺度上的快速变化。     

The Characteristics and Related Problems of the Orbits Around the Earth-Moon Libration Points

Due to the specific dynamics, the probes located at the halo orbits or Lissajous orbits around the Earth-Moon collinear libration point L₁ or L₂ are always studied in the synodic system to understand their trajectories. In fact, they are also orbiting the Earth in a distant Keplerian ellipse. Because of their intrinsic orbital instability, in the orbit prediction the initial errors propagate more prominently than those of the normal orbiting satellites, this requires special attention in the orbit design, maneuver, and control. Despite of all this, they are similar to the normal orbiting satellites in orbit determination and hardly require other special attentions. In this paper, the quantitative results of error propagation under the unstable dynamics, together with the theoretical analysis are presented. The results of precise orbit determination and short-arc orbit predictions are also shown, and compared with the results from the Beijing Aerospace Control Center.     

水和土壤环境非水溶相污染物的表面活性剂增效修复机制

分析了表面活性剂和非水溶相有机污染物在水和土壤环境中的相互作用,以及表面活性的特性,解释了表面活性剂增效修复水和土壤环境中非水溶相污染物的机制。表面活性剂溶液通过增溶作用和增流作用,驱除地下水含水层中的非水相液体以及吸附于土壤颗粒物上的污染物,提高地下水和土壤中憎水性有机污染物的现场修复速率。增效修复效果依赖于临界胶束浓度(CMC)、污染物和表面活性剂的吸附特性、污染物的溶解性和土壤类型等。表面活性剂能增加化合物的溶解度,降低与水的界面张力,并形成乳液。     

深层水泥搅拌法在土体加固中的应用

介绍了在某护岸改造工程利用CDM加固体作为临时挡土墙的施工工艺。结果表明该工艺具有理想的效果,开创了CDM加固护岸坡脚土体的新工艺。