变质量少体问题及其应用

该文以变质量质点动力学方程（密歇尔斯基方程）为基础,建立了变质量少体问题的运动方程,并利用小参数方法得到了变质量少体问题的分析解。文中还将研究结果应用到彗星运动上,讨论彗星轨道中非引力效应。指出非引力效应会导致某些彗星轨道半长径和偏心率等产生长期和周期变化,这些变化将明显地影响彗星运动的周期以及过近日点的时间和地点。因此在这些彗星精密定轨和探讨其轨道动力演化时应当考虑这种非引力效应。文末还具体计算了恩克彗星轨道中非引力效应。     

Interception of comet Hyakutake's ion tail at a distance of 500 million kilometres

Remote sensing observations and the direct sampling of material from a few comets have established the characteristic composition of cometary gas. This gas is ionized by solar ultraviolet radiation and the solar wind to form 'pick-up' ions, ions in a low ionization state that retain the same compositional signatures as the original gas. The pick-up ions are carried outward by the solar wind, and they could in principle be detected far from the coma (Sampling of pick-up ions has also been used to study interplanetary dust, Venus' tail and the interstellar medium.) Here we report the serendipitous detection of cometary pick-up ions, most probably associated with the tail of comet Hyakutake, at a distance of 3.4 AU from the nucleus. Previous observations have provided a wealth of physical and chemical information about a small sample of comets, but this detection suggests that remote sampling of comet compositions, and the discovery of otherwise invisible comets, may be possible.     

（Ⅲ）m=0类二次系统的极限环问题，（Ⅰ）

彗星的空间探测是当代前沿课题．本文首先概述彗星的主要研究结果．彗星的本体是不大的‘脏雪球’彗核；随着接近太阳，其表面冰升华并带出尘埃而形成彗发，发生复杂的物理-化学过程；太阳辐射压和太阳风推斥彗发的尘埃和离子而形成彗尾；彗星尘散失在轨道附近而成为流星群．虽然地面观测到彗发和彗尾的丰富资料，但对彗核却了解甚少，需要发射飞船进行空间探测；接着，从探测彗核的真实性质、采集彗星样品分析成分、探索彗星活动和机制、彗星的有机物与生命起源、彗星-地球关系、太阳系起源和演化线索几方面阐述彗星的空间探测的科学意义；然后，综述彗星空间探测的一些计划进展情况，总结彗星空间探测的重要成果；最后，讨论未来的彗星空间探测的科学目标，包括高轨卫星采集彗星尘、搜寻近地小彗星、搜寻未知彗星、发射更优秀飞船探测不同彗星．     

Identification of two sources of carbon monoxide in comet Hale-Bopp.

The composition of ices in comets may reflect that of the molecular cloud in which the Sun formed, or it may show evidence of chemical processing in the pre-planetary accretion disk around the proto-Sun. As carbon monoxide (CO) is ubiquitous in molecular clouds, its abundance with respect to water could help to determine the degree to which pre-cometary material was processed, although variations in CO abundance may also be influenced by the distance from the Sun at which comets formed. Observations have not hitherto provided an unambiguous measure of CO in the cometary ice (native CO). Evidence for an extended source of CO associated with comet Halley was provided by the Giotto spacecraft, but alternative interpretations exist. Here we report observations of comet Hale-Bopp which show that about half of the CO in the comet comes directly from ice stored in the nucleus. The abundance of this CO with respect to water (12 per cent) is smaller than in quiescent regions of molecular clouds, but is consistent with that measured in proto-stellar envelopes, suggesting that the ices underwent some processing before their inclusion into Hale-Bopp. The remaining CO arises in the coma, probably through thermal destruction of more complex molecules.     

单细胞凝胶电泳技术在DNA损伤和细胞凋亡检测中的应用

用不同质量浓度的丝裂霉素C(MMC)、卡铂和5-氟尿嘧啶(5- Fu)处理Hela细胞24h,利用单细胞凝胶电泳( SCGE)技术分析这些药物对细胞DNA的损伤情况,结果发现:各药物处理组细胞都出现“彗星”,且随着各药物浓度的增大,彗星率升高,彗尾的荧光强度和长度也随之增大;各剂量组间存在良好的剂量-效应关系,差异显著...     

Identification of comet Hyakutake's extremely long ion tail from magnetic field signatures

Observations of the varying orientations of comet tails led to the suggestion of the existence of the solar wind--a continuous outflow of ionized material from the Sun. It is now well established that gas from comets is ionized by several processes and joins the solar wind, forming an ion (plasma) tail that points away from the Sun. The plasma environments of three comets have been measured in situ, but only in the upstream direction or less than 8,000 km downstream of the nucleus. Here we report a fortuitous crossing by a spacecraft of the plasma tail of comet Hyakutake (C/1996 B2), at a distance of more than 3.8 astronomical units (550 million kilometres) from its nucleus. This surpasses the tail length of 2 AU determined for the Great March Comet of 1843 (C/1843 D1). Our measurements reveal that, at this distance, the tail of comet Hyakutake was a structured entity at least 7 million kilometres in diameter.     

Ocean-like water in the Jupiter-family comet 103P/Hartley 2

For decades, the source of Earth's volatiles, especially water with a deuterium-to-hydrogen ratio (D/H) of (1.558?±?0.001)?×?10(-4), has been a subject of debate. The similarity of Earth's bulk composition to that of meteorites known as enstatite chondrites suggests a dry proto-Earth with subsequent delivery of volatiles by local accretion or impacts of asteroids or comets. Previous measurements in six comets from the Oort cloud yielded a mean D/H ratio of (2.96?±?0.25)?×?10(-4). The D/H value in carbonaceous chondrites, (1.4?±?0.1)?×?10(-4), together with dynamical simulations, led to models in which asteroids were the main source of Earth's water, with ≤10 per cent being delivered by comets. Here we report that the D/H ratio in the Jupiter-family comet 103P/Hartley 2, which originated in the Kuiper belt, is (1.61?±?0.24)?×?10(-4). This result substantially expands the reservoir of Earth ocean-like water to include some comets, and is consistent with the emerging picture of a complex dynamical evolution of the early Solar System.     

Compositional homogeneity in the fragmented comet 73P/Schwassmann-Wachmann 3

The remarkable compositional diversity of volatile ices within comets can plausibly be attributed to several factors, including differences in the chemical, thermal and radiation environments in comet-forming regions, chemical evolution during their long storage in reservoirs far from the Sun, and thermal processing by the Sun after removal from these reservoirs. To determine the relevance of these factors, measurements of the chemistry as a function of depth in cometary nuclei are critical. Fragmenting comets expose formerly buried material, but observational constraints have in the past limited the ability to assess the importance of formative conditions and the effects of evolutionary processes on measured composition. Here we report the chemical composition of two distinct fragments of 73P/Schwassmann-Wachmann 3. The fragments are remarkably similar in composition, in marked contrast to the chemical diversity within the overall comet population and contrary to the expectation that short-period comets should show strong compositional variation with depth in the nucleus owing to evolutionary processing from numerous close passages to the Sun. Comet 73P/Schwassmann-Wachmann 3 is also depleted in the most volatile ices compared to other comets, suggesting that the depleted carbon-chain chemistry seen in some comets from the Kuiper belt reservoir is primordial and not evolutionary.     

暗能量对星体进动的影响

主要研究和探讨暗能量的存在对行星进动角的影响。我们发现对于太阳系水星，暗能量对其进动角的贡献大约为总进动角的万分之一。因此，期望通过对水星进动的精密观测，可以推测暗能量的状态函数，并以此作为检验各种暗能量模型的理论依据。     

Extremely red Kuiper-belt objects in near-circular orbits beyond 40 AU

Kuiper-belt objects (KBOs) are an ancient reservoir of comets beyond Neptune's orbit. Some of these objects were recently found to have the reddest optical colours in the Solar System, but the number of objects for which accurate colours were available was too small for any correlation to be discerned between colour and physical or dynamical properties, which might shed light on the origin of these objects. Here we report that all nine of the KBOs in our survey on near-circular (low-eccentricity) orbits with perihelion distances larger than 40 AU have extremely red surfaces, thereby connecting an observable property with a dynamical class. Of the objects with orbital eccentricities greater than 0.1, about half are also very red, while the rest have colours similar to the Sun, meaning that reflected sunlight is not strongly modified by the objects' surface properties. In addition, of the 13 'classical' KBOs (those with semimajor axis a approximately 45 AU and eccentricity e < 0.15), the ten that are very red are in orbits with small angles of inclination to the ecliptic, whereas the three with solar colours are all in high-inclination orbits. We suggest that these three 'grey' classical KBOs may be part of a dynamical group that is separate from the 'red' classical KBOs.     

基于中心差异度迭代调整机制的 网络社区搜寻算法研究

为解决当前网络社区搜寻算法存在的节点聚类形成困难,搜寻迭代过于复杂,难以实现社区归属的二次更新等不足,提出了一种基于中心差异度迭代调整机制的网络社区搜寻算法。首先,通过领袖节点重叠度来实现初次社区搜寻裁决,有效降低了重复搜寻的概率,且根据加入节点与领袖节点差异度进行聚类匹配;随后,通过待加入节点与领袖节点之间的交互热度方式进行基于热度机制的聚类递归,实现对搜寻误差的二次校正。仿真实验表明,与当前网络社区搜寻算法中常用的差分迭代阈值裁决机制,混沌度一体化成型迭代机制相比,本文算法具有更高的首次成功率,以及更小的搜寻次数与迭代周期,具有很强的实际部署价值。     

第三宇宙速度ν_3及获得ν_3所需的火箭推进剂量与地球在公转轨道上的位置的关系

计算结果表明，从地球在公转轨道上的近日点到远日点，第三宇宙速度的值单调增加，获得相应的速度值所需要的火箭推进剂量的增加幅度约达１０％，从而在理论上指出了这一问题中减轻火箭重量的一个有效途径是尽可能接近近日点发射．     

A topographically forced asymmetry in the martian circulation and climate

Large seasonal and hemispheric asymmetries in the martian climate system are generally ascribed to variations in solar heating associated with orbital eccentricity. As the orbital elements slowly change (over a period of >104 years), characteristics of the climate such as dustiness and the vigour of atmospheric circulation are thought to vary, as should asymmetries in the climate (for example, the deposition of water ice at the northern versus the southern pole). Such orbitally driven climate change might be responsible for the observed layering in Mars' polar deposits by modulating deposition of dust and water ice. Most current theories assume that climate asymmetries completely reverse as the angular distance between equinox and perihelion changes by 180 degrees. Here we describe a major climate mechanism that will not precess in this way. We show that Mars' global north-south elevation difference forces a dominant southern summer Hadley circulation that is independent of perihelion timing. The Hadley circulation, a tropical overturning cell responsible for trade winds, largely controls interhemispheric transport of water and the bulk dustiness of the atmosphere. The topography therefore imprints a strong handedness on climate, with water ice and the active formation of polar layered deposits more likely in the north.     

圆柱度误差虚拟测量仪的设计及OpenGL应用

介绍了虚拟测量仪技术和软件开发平台LabWindows/CVI,讨论了在设计圆柱度误差虚拟测量仪时所涉及到的采样方法、理论基础、数学模型等,采用对置两测头法误差分离技术,从而显著地降低了实际测量时对基准件的精度要求,给出了圆柱度误差虚拟测量仪的设计理念、开发实例以及OpenGL在圆柱度误差虚拟测量仪中的应用方法,所设计的虚拟测量仪的软面板可以显示圆柱度误差的三维误差图形,为分析误差产生原因,控制误差产生提供依据·     

普林格尔治疗仪促进产后乳汁分泌的疗效观察

目的：观察普林格式治疗仪促进产后乳汁分泌的疗效。方法各选取100例产后30 d乳汁量少的产妇，一组接受普林格尔治疗仪治疗，称为观察组，一组只接受传统方法治疗，称为对照组，观察两组产妇乳汁量的变化。结果经过普林格尔治疗仪治疗和指导的观察组效果明显优于只接受传统方法治疗的对照组，差异具有显著性（p〈0.05）。结论普林格尔治疗仪有利于促进产妇产后的乳汁分泌，且操作简单、风险小、无副作用，值得推广。     

Determining the ages of comets from the fraction of crystalline dust

The timescale for the accretion of bodies in the disk surrounding a young star depends upon a number of assumptions, but there are few observational constraints. In our own Solar System, measurements of meteoritic components can provide information about the inner regions of the nebula, but not the outer parts. Observations of the evolution of more massive protostellar systems (Herbig Ae/Be stars) imply that significant changes occur in the physical properties of their dust with time. The simplest explanation is that thermal annealing of the original, amorphous grains in the hot inner nebula slowly increases the fractional abundance of crystalline material over time. Crystalline dust is then transported outward, where it is incorporated into comets that serve as a long-term reservoir for dust disks, such as that surrounding Beta Pictoris. Here we show that when applied to our own Solar System, this process can explain observed variations in both the volatile and dusty components of comets, while also providing a natural indicator of a comet's mean formation age. Studies of comets with different dust contents can therefore be used to investigate the timescales of the early Solar System.     

Rapid collisional evolution of comets during the formation of the Oort cloud

The Oort cloud of comets was formed by the ejection of icy planetesimals from the region of giant planets--Jupiter, Saturn, Uranus and Neptune--during their formation. Dynamical simulations have previously shown that comets reach the Oort cloud only after being perturbed into eccentric orbits that result in close encounters with the giant planets, which then eject them to distant orbits about 10(4) to 10(5) AU from the Sun (1 AU is the average Earth-Sun distance). All of the Oort cloud models constructed until now simulate its formation using only gravitational effects; these include the influence of the Sun, the planets and external perturbers such as passing stars and Galactic tides. Here we show that physical collisions between comets and small debris play a fundamental and hitherto unexplored role throughout most of the ejection process. For standard models of the protosolar nebula (starting with a minimum-mass nebula) we find that collisional evolution of comets is so severe that their erosional lifetimes are much shorter than the timescale for dynamical ejection. It therefore appears that collisions will prevent most comets escaping from most locations in the region of the giant planets until the disk mass there declines sufficiently that the dynamical ejection timescale is shorter than the collisional lifetime. One consequence is that the total mass of comets in the Oort cloud may be less than currently believed.     

网格环境下基于局部性原理的资源发现方法

在现有网格资源发现方法基础上,提出了一种分层网格资源发现模型,用户的查找请求先在底层虚拟组织内进行,若不能满足再转发到由超级节点组成的上层社区层.局部性原理的引入,降低了用户节点对超级节点的查询次数,基于类别的虚拟社区划分,使得对资源请求的查找限定在所属虚拟社区内进行,从而可缩小搜索空间,提高资源的发现速度.     

The evolution of comets in the Oort cloud and Kuiper belt

Comets are remnants from the time when the outer planets formed, approximately 4-4.5 billion years ago. They have been in storage since then in the Oort cloud and Kuiper belt-distant regions that are so cold and sparsely populated that it was long thought that comets approaching the Sun were pristine samples from the time of Solar System formation. It is now recognized, however, that a variety of subtle but important evolutionary mechanisms operate on comets during their long storage, so they can no longer be regarded as wholly pristine.     

一种改进的Rough集属性约简启发式遗传算法

属性约简是知识发现中的关键问题之一 .为了能够有效地获取决策表中属性最小相对约简 ,提出了一种在优化初始群体基础上提高算法性能的启发式遗传算法 .首先 ,通过构造一个新的算子 ,将信息论角度定义的属性重要性度量作为启发式信息 ,来描述所选择的属性子集对论域中确定分类子集的影响 ;接着 ,以此为基础并结合遗传算法 ,选择一些经过优化的染色体作为初始群体 ,在加强局部搜索能力的同时保持了该算法全局寻优的特性 .最后 ,从理论上对算法做了分析 ,证明了新算子所选择的属性子集对原有属性分类能力保持不变 .试验分析表明 ,该算法能有效地对决策表属性进行约简