欧空局的多任务地面基础设施(1996-2005)

为了支持欧空局(ESA)下世纪的多项卫星任务,该局正在建设地面多任务基础设施,支持1996-2006年之间预期发射的10多种不同类型的卫星(科学、地球观测、通信、货运飞船)。 该基础设施为不同任务提供公共的地面设施,其中心设在欧洲空间操作中心(ESOC),将延伸至FSA不同的地面站。 该基础设施包括6个主要系统: ·备有相应遥测、遥控处理器,以面向目标法建造的飞行控制系统; ·配有一整套综合性软件以及相关用户接口的飞行动力学系统,用于姿态和轨道的确定及控制; ·地面站监视及控制系统; ·遥测处理系统 ·遥控编码器; ·多用跟踪系统。 本文描述了该基础设施的各个系统,它们的相互接口以及实施计划。论述了该基础设施的设计方案以及采用的基本技术,特别突出了技术及操作上的先进性,以及这种方式的成本效益。     

小卫星的空间操作

CAT空间系统公司(原DSI)在80及90年代的“小卫星”计划中起了重要的作用。传统低轨卫星的设计、制造、发射及操作成本高,时间长。这些问题一直在激励人们去开发新的工艺、技术,以及低成本、毋需严格调整的卫星。这些卫星采用低功率“小卫星”通信设备(TDRSS用于NASA低轨星则要求大功率),通常搭载不需要大量冗余备价系统并且不需要大型地面设备和人员保障的有效载荷/实验设备。这种小型且适应性强的卫星还有研制周期非常短(通常1～2年)的特点。本文介绍了CTA空间系统(CTA/SS)在这些新计划中采用的几种方法和成功的有代表性的例子,并就如何减轻NASA越来越大的降低航天器及其操作成本方面的压力提出建议。重点是在任务操作的主控设施和各种用户终端(UT)中使用适应性强、功能足够、价格低廉的基于PC机的地面设备。这些系统以CTA/SS多种型号的用户终端成功地控制了20多颗USAF、USN、APPA卫星,从而使这些系统得到验证。这些用户终端经同步轨道卫星和低轨道卫星建立了链路,而且在边远地区自动担负起中继任务。由于用户可以很容易安装轻型天线(通常是用小功率马达、PC驱动的全向或螺旋型),低轨卫星的应用特别显示了这些方法的效能。几英尺长的同轴电缆与小型收发模块(小型PC机大小)相连,串行线与相应PC机相连,便     

Combustion modeling in a model combustor

The flow-field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically studied.Results obtained from four combustion models,combined with the re-normalization group(RNG) k-ε turbulence model,discrete ordinates radiation model and enhanced wall treatment are presented and discussed.The results are compared with a comprehensive database obtained from a series of experimental measurements.The flow patterns and the recirculation zone length in the combustion chamber are accurately predicted,and the mean axial velocities are in fairly good agreement with the experimental data,particularly at downstream sections for all four combustion models.The mean temperature profiles are captured fairly well by the eddy dissipation(EDS),probability density function(PDF),and laminar flamelet combustion models.However,the EDS-finite-rate combustion model fails to provide an acceptable temperature field.In general,the flamelet model illustrates little superiority over the PDF model,and to some extent the PDF model shows better performance than the EDS model.      

The origin and early evolution of membrane channels

The origin and early evolution of ion channels are considered from the point of view that the transmembrane segments of membrane proteins are structurally quite simple and do not require specific sequences to fold. We argue that the transport of solute species, especially ions, required an early evolution of efficient transport mechanisms, and that the emergence of simple ion channels was protobiologically plausible. We also argue that, despite their simple structure, such channels could possess properties that, at the first sight, appear to require markedly greater complexity. These properties can be subtly modulated by local modifications to the sequence rather than global changes in molecular architecture. In order to address the evolution and development of ion channels, we focus on identifying those protein domains that are commonly associated with ion channel proteins and are conserved throughout the three main domains of life (Eukarya, Bacteria, and Archaea). We discuss the potassium-sodium-calcium superfamily of voltage-gated ion channels, mechanosensitive channels, porins, and ABC-transporters and argue that these families of membrane channels have sufficiently universal architectures that they can readily adapt to the diverse functional demands arising during evolution.     

Did life begin on the beach?

Water is one of the prerequisites of life. Further requirements are the existence of a system of interacting organic molecules capable of capturing and converting the supply of external energy and elaborating the replicating function that is needed for propagation. None of this would be possible without the existence of some means of concentrating, selecting, and then containing these mutually interacting substances in proximity to one another, i.e., a primitive cell. Starting from this hypothesis we propose a model for the development of life on Earth. Our model embodies the following new features: (1) rapid cycles of catalysis and transport of material, (2) desegregation (separation by tidal action and degradation by catalysis) as well as segregation (by chromatography on tidal beaches), (3) cross-catalysis instead of auto-catalysis, as well as (4) compartmentalization, although the latter idea is of course not new. But our "lipid first" model, in contrast to earlier "peptide first" or "RNA first" models, provides for the compartments needed to act as a cradle for the subsequent development of information- rich molecules like peptides and RNA. If anything, the earliest information-rich molecules were probably membrane-spanning peptides/proteins.     

Microbial diversity of Indian Ocean hydrothermal vent plumes: microbes tolerant of desiccation, peroxide exposure, and ultraviolet and gamma-irradiation

The microbial diversity of Kali chimney plumes, part of a hydrothermal vent field in the Rodriguez Triple Junction, Indian Ocean (depth approximately 2,240 m), was examined in an attempt to discover "extremotolerant" microorganisms that have evolved unique resistance capabilities to this harsh environment. Water and sediment samples were collected from the vent and from sediments located at various distances (2-20 m) away from and surrounding the chimney. Samples were screened for hypertolerant microbes that are able to withstand multiple stresses. A total of 46 isolates were selected for exposure to a number of perturbations, such as heat shock, desiccation, H(2)O(2), and ultraviolet (UV) and gamma-irradiation. The survival of Psychrobacter sp. L0S3S-03b following exposure to >1,000 J/m(2) UV(254) radiation was particularly intriguing amid a background of varying levels of resistance. Vegetative cells of this non-spore-forming microbe not only survived all of the treatments, but also exhibited a 90% lethal dose of 30 s when exposed to simulated martian UV radiation and a 100% lethal dose of 2 min when exposed to full spectrum UV, which is comparable to findings for bacterial endospores.     

CCD互相关粒子图像测速及其在对抗流流场测量中的应用

在常规自相关粒子图像测速（ＰＩＶ）系统的基础上,发展了一个采用ＣＣＤ像机的互相关粒子图像测速系统。用这一新系统测量了对抗流流场的结果表明,这一技术克服了自相关粒子图像测速技术在测量具有滞止点的流场中的困难。实验说明,与自相关粒子图像测速技术相比,这一技术更快捷有效。