离子镀机理

离子镀是应用于膜沉积工艺的一个常用术语。在该工艺中,基材表面和/或沉积膜受到高能粒子流的作用,足以导致在界面区域或膜与未经轰击沉积情况相比诸多性质的改变。离子镀正是取代溅射沉积、真空蒸发和电镀的一种涂层新工艺。为了对各种沉积技术恰当地选用,有必要了解有关离子镀的基本机理。该文评述了当采用离子镀时,低能离子轰击对表面、界面的形成以及膜的生长的影响。离子镀的许多问题目前仍不明确,因而希望通过呼吁引起对这些问题的重视,科研工作者和工艺学家们能把较多的精力投向研究和控制离子镀工艺。     

Preservation of martian organic and environmental records: final report of the Mars biosignature working group

The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars. Orbital images confirm that layered rocks achieved kilometer-scale thicknesses in some regions of ancient Mars. Clearly, interplays of sedimentation and erosional processes govern present-day exposures, and our understanding of these processes is incomplete. MSL can document and evaluate patterns of stratigraphic development as well as the sources of layered materials and their subsequent diagenesis. It can also document other potential biosignature repositories such as hydrothermal environments. These capabilities offer an unprecedented opportunity to decipher key aspects of the environmental evolution of Mars' early surface and aspects of the diagenetic processes that have operated since that time. Considering the MSL instrument payload package, we identified the following classes of biosignatures as within the MSL detection window: organism morphologies (cells, body fossils, casts), biofabrics (including microbial mats), diagnostic organic molecules, isotopic signatures, evidence of biomineralization and bioalteration, spatial patterns in chemistry, and biogenic gases. Of these, biogenic organic molecules and biogenic atmospheric gases are considered the most definitive and most readily detectable by MSL.     

悲情铱星:出现在中国天空的闪光

2000年3月17日,铱星公司由于找不到合适的买主终于宣布破产。 铱星座始建初期就引起世人的广泛关注,它以先进的航天技术为依托,在现代通信领域竖立了一座新的里程碑。铱星座的建成,可以使任何人在任何时间任何地点实现与外界任何方式的通信,使我们渴望已久的全球通信成为现实。但是,再高新的技术也要经过市场的检验,铱星手机的高昂收费使使用者望而却步,因而铱星公司到它宣布破产时也只有6.5万用户。再者,铱星设计时系统选择的频率与射电天文学家监视羟基分子的特征频率很接近,对天文工作有很大干扰,因此必须每天提供8个小时的无干扰时间,这无疑造成了铱星电话的又一大弊端。高投入、低回馈的经营使铱星公司不堪重负,最终宣布破产,并计划用两年的时间使卫星离轨,进入大气层烧毁。 但是,也许是铱星的经营者们没有想到的,在天上运行的66颗铱卫星,为世界各地的夜空增加了一道亮丽的风景。它们能发出比天空中最亮的星星都亮得多的闪光。任何人,不论对星空熟悉与否,不论在任何地方,只要朝向正确的方向看,都会看到耀人眼目的铱星闪光。当我们哀叹铱星计划失败时,只有铱星的闪光依然美丽如昔,为此,我们特别刊登美国航宇局约翰逊空间中心的Paui D.Maley特别为中国爱好者撰写的文章。让我们在有限的两年时光里,看     

The Mawrth Vallis region of Mars: A potential landing site for the Mars Science Laboratory (MSL) mission

The primary objective of NASA's Mars Science Laboratory (MSL) mission, which will launch in 2011, is to characterize the habitability of a site on Mars through detailed analyses of the composition and geological context of surface materials. Within the framework of established mission goals, we have evaluated the value of a possible landing site in the Mawrth Vallis region of Mars that is targeted directly on some of the most geologically and astrobiologically enticing materials in the Solar System. The area around Mawrth Vallis contains a vast (>1?×?10? km2) deposit of phyllosilicate-rich, ancient, layered rocks. A thick (>150?m) stratigraphic section that exhibits spectral evidence for nontronite, montmorillonite, amorphous silica, kaolinite, saponite, other smectite clay minerals, ferrous mica, and sulfate minerals indicates a rich geological history that may have included multiple aqueous environments. Because phyllosilicates are strong indicators of ancient aqueous activity, and the preservation potential of biosignatures within sedimentary clay deposits is high, martian phyllosilicate deposits are desirable astrobiological targets. The proposed MSL landing site at Mawrth Vallis is located directly on the largest and most phyllosilicate-rich deposit on Mars and is therefore an excellent place to explore for evidence of life or habitability.     

The PROCESS experiment: an astrochemistry laboratory for solid and gaseous organic samples in low-earth orbit

The PROCESS (PRebiotic Organic ChEmistry on the Space Station) experiment was part of the EXPOSE-E payload outside the European Columbus module of the International Space Station from February 2008 to August 2009. During this interval, organic samples were exposed to space conditions to simulate their evolution in various astrophysical environments. The samples used represent organic species related to the evolution of organic matter on the small bodies of the Solar System (carbonaceous asteroids and comets), the photolysis of methane in the atmosphere of Titan, and the search for organic matter at the surface of Mars. This paper describes the hardware developed for this experiment as well as the results for the glycine solid-phase samples and the gas-phase samples that were used with regard to the atmosphere of Titan. Lessons learned from this experiment are also presented for future low-Earth orbit astrochemistry investigations.     

A sulfur-based survival strategy for putative phototrophic life in the venusian atmosphere

Several observations indicate that the cloud deck of the venusian atmosphere may provide a plausible refuge for microbial life. Having originated in a hot proto-ocean or been brought in by meteorites from Earth (or Mars), early life on Venus could have adapted to a dry, acidic atmospheric niche as the warming planet lost its oceans. The greatest obstacle for the survival of any organism in this niche may be high doses of ultraviolet (UV) radiation. Here we make the argument that such an organism may utilize sulfur allotropes present in the venusian atmosphere, particularly S(8), as a UV sunscreen, as an energy-converting pigment, or as a means for converting UV light to lower frequencies that can be used for photosynthesis. Thus, life could exist today in the clouds of Venus.     

再入制导和弹道跟踪误差分析

新一代可重复使用运载器对再入制导提出了更高地要求。目前的空间运输系统证明基于阻力加速度的制导方法是行之有效的。其基本概念是跟踪基准阻力加速度包线，在飞行过程中可根据需要更新这个包线。跟踪适当的阻力加速度包线保证了飞行器可以飞行准确的距离达到目标，同时满足弹道约束。在横向上，我们可采用类似于美国航天飞机的倾斜反转逻辑或航向角跟踪技术。本文推导出了基于反馈线性化的控制算法，并将其应用于可重复使用运载器纵向和横向的制导。最后，我们分析了阻力加速度跟踪的误差。     

The Suess-Urey mission (return of solar matter to Earth)

The Suess-Urey (S-U) mission has been proposed as a NASA Discovery mission to return samples of matter from the Sun to the Earth for isotopic and chemical analyses in terrestrial laboratories to provide a major improvement in our knowledge of the average chemical and isotopic composition of the solar system. The S-U spacecraft and sample return capsule will be placed in a halo orbit around the L1 Sun-Earth libration point for two years to collect solar wind ions which implant into large passive collectors made of ultra-pure materials. Constant Spacecraft-Sun-Earth geometries enable simple spin stabilized attitude control, simple passive thermal control, and a fixed medium gain antenna. Low data requirements and the safety of a Sun-pointed spinner, result in extremely low mission operations costs.     

在电解高纯石英谐振器中辐照引起的频率和电阻的变化

本文描述了由电解高纯石英制造的高精密5兆赫AT切石英谐振器中辐照引起的频率和电阻的变化。文中介绍了辐照测量方法、瞬态和稳态数据,以及热模拟结果。依嗦尔研究成果中的光学级和超Q石英可以像生长的晶体一样足够纯,得出的结论是:1)没有观察到通常与频率时间相关的t~(-1/2)恢复特性;2)如果未经电解,杂质含量仍然很高,足以在离子辐照脉冲后的一个短时间内使品质因数明显下降;3)由于电解能够进一步降低辐照响应,所以,杂质的影响不再很明显;4)电解石英的瞬时辐照响应实际上主要是热造成的。