Comparative study of productivity of the Rosetta target Comet 67P/Churyumov-Gerasimenko

In an attempt to evaluate correlations between several properties of comets we report the results of a cometary research involving a criterious analysis of gas and dust mass production rates in Comets 67P/Churyumov-Gerasimenko (main target of Rosetta Mission), 1P/Halley, Hyakutake (C/1996 B2), and 46P/Wirtanen and make a comparison between them.     

Composition of the Volatile Material in Halley's Coma from In Situ Measurements

The investigation of the volatile material in the coma of comets is a key to understanding the origin of cometary material, the physical and chemical conditions in the early solar system, the process of comet formation, and the changes that comets have undergone during the last 4.6 billion years. So far, in situ investigations of the volatile constituents have been confined to a single comet, namely P/Halley in 1986. Although, the Giotto mission gave only a few hours of data from the coma, it has yielded a surprising amount of new data and has advanced cometary science by a large step. In the present article the most important results of the measurements of the volatile material of Halley's comet are summarized and an overview of the identified molecules is given. Furthermore, a list of identified radicals and unstable molecules is presented for the first time. At least one of the radicals, namely CH₂, seems to be present as such in the cometary ice. As an outlook to the future we present a list of open questions concerning cometary volatiles and a short preview on the next generation of mass spectrometers that are being built for the International Rosetta Mission to explore the coma of Comet Wirtanen. This revised version was published online in June 2006 with corrections to the Cover Date.     

添加镍粉和二硼化锆防静电涂层的对比研究

对添加镍粉和二硼化锆涂层的导电性进行了对比试验，讨论了添加型防静电涂层的防静电机理。试验结果表明：添加型防静电涂层导电通路的形成是导电粒子的直接接触和隧道效应综合作用的结果。文中还推导了计算涂层中导电粒子间距的近似公式。     

The Coma of Comet 9P/Tempel 1

As comet 9P/Tempel 1 approaches the Sun in 2004–2005, a temporary atmosphere, or “coma,” will form, composed of molecules and dust expelled from the nucleus as its component icy volatiles sublimate. Driven mainly by water ice sublimation at surface temperatures T > 200 K, this coma is a gravitationally unbound atmosphere in free adiabatic expansion. Near the nucleus (≤ 10² km), it is in collisional equilibrium, at larger distances (≥10⁴ km) it is in free molecular flow. Ultimately the coma components are swept into the comet’s plasma and dust tails or simply dissipate into interplanetary space. Clues to the nature of the cometary nucleus are contained in the chemistry and physics of the coma, as well as with its variability with time, orbital position, and heliocentric distance. The DI instrument payload includes CCD cameras with broadband filters covering the optical spectrum, allowing for sensitive measurement of dust in the comet’s coma, and a number of narrowband filters for studying the spatial distribution of several gas species. DI also carries the first near-infrared spectrometer to a comet flyby since the VEGA mission to Halley in 1986. This spectrograph will allow detection of gas emission lines from the coma in unprecedented detail. Here we discuss the current state of understanding of the 9P/Tempel 1 coma, our expectations for the measurements DI will obtain, and the predicted hazards that the coma presents for the spacecraft. An erratum to this article is available at .     

Deep Impact Mission Design

The Deep Impact mission is designed to provide the first opportunity to probe below the surface of a comet nucleus by a high-speed impact. This requires finding a suitable comet with launch and encounter conditions that allow a meaningful scientific experiment. The overall design requires the consideration of many factors ranging from environmental characteristics of the comet (nucleus size, dust levels, etc.), to launch dates fitting within the NASA Discovery program opportunities, to launch vehicle capability for a large impactor, to the observational conditions for the two approaching spacecraft and for telescopes on Earth.     

The History and Dynamics of Comet 9P/Tempel 1

Since its discovery in 1867, periodic comet 9P/Tempel 1 has been observed at 10 returns to perihelion, including all its returns since 1967. The observations for the seven apparitions beginning in 1967 have been fit with an orbit that includes only radial and transverse nongravitational accelerations that model the rocket-like thrusting introduced by the outgassing of the cometary nucleus. The successful nongravitational acceleration model did not assume any change in the comet’s ability to outgas from one apparition to the next and the outgassing was assumed to reach a maximum at perihelion. The success of this model over the 1967–2003 interval suggests that the comet’s spin axis is currently stable. Rough calculations suggest that the collision of the impactor released by the Deep Impact spacecraft will not provide a noticeable perturbation on the comet’s orbit nor will any new vent that is opened as a result of the impact provide a noticeable change in the comet’s nongravitational acceleration history. The observing geometries prior to, and during, the impact will allow extensive Earth based observations to complement the in situ observations from the impactor and flyby spacecraft.     

用急冷Al基活性钎料钎焊Si3N4陶瓷的研究

研制了三种急冷Ａｌ基活性钎料。研究结果表明：急冷Ａｌ基活性钎料的组织明显细化，熔点明显下降，基体硬度升高。在较低的钎焊温度（７５０℃）下，下加Ｎｉ粉的接头的剪切强度较高（２０８．８ＭＰａ）。钎焊温度对接头强度影响较大。当超过一定钎焊温度后，接头强度明显下降；加Ｎｉ粉复合钎焊可明显提高接头的剪切强度，在钎焊温度为８００℃时接头的最高剪切强度为２２５ＭＰａ，加Ｎｉ粉的复合接头在界面两侧形成均匀分布富Ｎｉ带。这是接头强度提高的主要原因。     

填料的表面改性及其对涂层力学性能的影响

研究了填料经硅烷偶联剂和自制的处理剂进行表面改性后对涂层力学性能的影响.借助扫描电镜进一步分析了填料在树脂中的分散情况.结果表明填料经后一种方法处理后,与树脂基体相容性明显改善,涂层力学性能得到了显著提高.     

Newton迭代法的P．C．格式

基于Newton迭代法 ,提出了一种有效的预估校正 (P .C .)迭代格式。本方法把牛顿法中的微分以差商替代 ,因而 ,既可求解具离散根的方程 ,也适用于有重根的方程求解 ,大量的试验结果表明 ,本文算法不仅可有效解决重根问题 ,而且有较高的收敛速度。     

GaInP_2外延薄膜的成份调制与超结构间的关联

用自制的具有极高分辨率的微机控制的三晶体x-射线衍射仪测量了用MOCVD方法生长的Ga_(0.52)In(0.48)P外延薄膜的超结构。我们发现,在Ga_(0.52)In(0.48)P外延薄膜内由In平面和Ga平面交替组成的(?)平面中,存在着交替的In丰与Ga丰平面。对此,我们定义了有序因子,并首先精确地测定了有序因子值。由此导出了成份调制的表达式。这样,我们就可用成份调制表示式来表达GaInP_2外延薄膜中存在的部分有序相的超结构特征。