A search for narrow band signals with SERENDIP II: a progress report

Commensal programs for the Search for Extraterrestrial Intelligence (SETI), carried out concurrently with conventional radio astronomical observing programs, can be an attractive and cost-effective means of exploring the large multidimensional search space intrinsic to this effort. Our automated commensal system, SERENDIP II, is a high resolution 131,072 channel spectrometer. It searches for 0.49 Hz signals in sequential 64,700 Hz bands of the IF signal from a radio telescope being used for an astronomical observation. Upon detection of a narrow band signal with power above a preset threshold, the frequency, power, time, and telescope direction are recorded for later study. The system has been tested at the Hat Creek Radio Astronomy Observatory 85 ft telescope and the NASA-JPL Deep Space Station (DSS 14) 64 m telescope. It is currently collecting data at the National Radio Astronomy Observatory 300 ft telescope.     

微波光导纤维展望

预测今后十年中微波系统用光纤的需求,徽波光纤迅速普及的一个主要因素是它的损耗极小;概要介绍光纤在遥控中心、相控阵、频谱分析仪、延迟线信号处理器、导弹制导和模/数转换装置中应用的优越性及使用方式;对各种光纤的性能改进作了展望.     

固体推进剂药柱结构安全裕度预测方法述评

当前,各工业公司用来预测固体推进剂药柱结构安全裕度的方法各不相同。虽然他们所用的计算公式均很相似,但针对具体问题算得的安全裕度值却是有正有负。事实上,这一问题已成为发动机药柱设计结构完整性评定工作产生混乱的根源。本文评论了影响安全裕度计算的各项参数,即破坏准则、结构分析方法、推进剂响应和破坏特性。本文还鉴别和讨论了与上述参数有关的技术问题,提出了今后研究工作中应予关注的问题。     

机载阵列雷达抑制运动杂波的学习算法

一种称为自适应空时处理器(STP)的线性滤波器是一种相对比较新的方法，它使机载阵列天线雷达目标检测概率达到最大。理论上，全自适应STP可以实时获得最优解(一种维恩滤波器)。但是，实际上全自适应STP也存在一些问题。首先，线性滤波器的加权数可能非常大。其次，单一加权矢量的计算复杂度大约为O(MN)^3。再次，STP为线性滤波器但却工作在非线性不稳定的环境中。这些问题导致采用空时处理器传统技术的实时、最佳处理是现行计算技术内所不及的。为使运动杂波对目标检测的影响最小，本文探讨了人工神经网络和几种学习算法的可应用性。人工神经网络是一种自适应、并行、分布式处理系统，可以实时完成复杂计算。学习算法的机理是为了存储新的信息或变更信息，人工神经网络中的长期存储器要不断更新而又不被破坏。由于学习算法既能在系统的使用期内保留信息又能变更信息，所以对雷达系统的计算要求降到了最低，同时还能适应环境的变化。     

二相流的最大推力喷管

本文针对在流场中含有凝态和固态颗粒的最大喷管设计进行了最佳分析。编制一套设计程序,程序中分析一个假定的喷管形状,确定它是否为最大推力喷管,若不是,就用松弛法修正假定的形状,直到获得最大推力喷管为止。参数的研究说明颗粒尺寸、喷管收敛角、喉部曲率半径、颗粒阻力、热传递系数、颗粒与气体质量流量比以及喷管尺寸的影响。     

Supercooled water brines within permafrost-an unknown ecological niche for microorganisms: a model for astrobiology

This study describes brine lenses (cryopegs) found in Siberian permafrost derived from ancient marine sediment layers of the Arctic Ocean. The cryopegs were formed and isolated from sediment ~100,000-120,000 years ago. They remain liquid at the in situ temperature of -10 degrees C as a result of their high salt content (170-300 g/L). [(14)C] Glucose is taken up by the cryopeg biomass at -15 degrees C, indicating microbial metabolism at low temperatures in this habitat. Furthermore, aerobic, anaerobic heterotrophs, sulfate reducers, acetogens, and methanogens were detected by most probable number analysis. Two psychrophilic microbes were isolated from the cryopegs, a Clostridium and a Psychrobacter. The closest relatives of each were previously isolated from Antarctica. The cryopeg econiche might serve as a model for extraterrestrial life, and hence is of particular interest to astrobiology.     

CASH 2021: commercial access and space habitation

Issues about commercialization of space have been a growing concern in the past decade for the space community. This paper focuses on the work from a team of 51 students attending the Summer Session Program of the International Space University in Bremen, Germany. CASH 2021 (Commercial Access and Space Habitation) documents a plan that identifies commercial opportunities for space utilization that will extend human presence in space, and will chart the way forward for the next 20 years. The group selected four commercial sectors that show the most promise for the future: tourism, entertainment, space system service, assembly and debris removal, and research and development/production. The content of this document presents the results of their research. Historical activities in each of the commercial sectors are reviewed along with the current market situation. To provide a coherent background for future commercialization possibilities a scenario has been developed. This scenario includes a postulated upon ideal future and includes social, political and economic factors that may affect the space industry over the timeline of the study. The study also presents a roadmap, within the limited optimistic scenario developed, for the successful commercialization of space leading to future human presence in space. A broad range of commercially viable opportunities, not only within the current limits of the International Space Station, but also among the many new developments that are expected by 2021 are discussed.     

Evaluation of bleomycin-induced chromosome aberrations under simulated microgravity conditions in human lymphocytes using "FISH" techniques

In the present investigation we report the effects of simulated microgravity conditions (clinostat) on the induction of chromosomal aberrations in human lymphocytes in vitro by (R) Bleomycin. Chromosomal aberrations have been analysed by means of fluorescent in situ hybridisation (FISH) and chromosome-specific composite DNA probes (chromosome painting). The results obtained show that, under simulated microgravity conditions, the levels of both symmetrical and asymmetrical (dicentrics, rings), the number of cells bearing "complex" aberrations and hence the total numbers of aberrations were significantly elevated at any of the dose-levels assayed, compared to the parallel treatments performed as 1g control ("ground"). Furthermore, the ratio symmetrical:asymmetrical translocations was markedly elevated under simulated microgravity conditions, compared to the findings usually observed under "normal" 1g conditions. On these bases, we are much inclined to believe that simulated microgravity, rather than limiting the resealing of DNA double strand breaks (DSB's) induced by genotoxic agents is influencing in terms of enhancement the misrejoining of DSB's which is actually responsible for the fixation of the original lesions to DNA into chromosomal aberrations. In addition, the possible different misrepair processes leading to the formation of symmetrical and asymmetrical translocations might be differentially influenced by microgravity being the symmetrical translocations significantly more represented.     

数据处理软件与机载数据采集软件的连接

由于飞行测试数据采集和遥测系统引用了能提供动态控制能力的微型计算机,所以软件正日益成为机载数据系统的一个不可缺少的组成部分。通常,软件的重要性总是被机载系统的许多用户所低估,甚至迄今,他们还在担心能否把PCM数据循环图编程到电可编程序只读存储器(EPROM)并将它们插入机载硬件中去。由于较新的可编程序系统使用带有电可擦可编程序只读存储器(E~2PROM)和随机存储器(RAM)的微型计算机来提供实时工程单位(EU)显示和控制能力,因而机载软件就成为整个系统计划的一个中心环节。在这些数据采集系统中,实时数据显示和控制所提出的程序设计要求,使地面站的数据处理软件和飞机上的数据采集软件之间要有软件结构控制和一种软件(固件)连接变得非常重要。本文介绍飞行测试过程中新出现的这类问题的一种解决办法。     

军用精密声表面波振荡器的研制

近年来,美国雷声公司已经有研制300～600MHz可军用的声表面波振荡器的课题;此种振荡器在频率调节能力和稳定性两方面均达当代最高水平。本文不讨论这种振荡器的详细用途。对它的要求一般为:(1)噪声本底必需至少为-160dBc/Hz;(2)振动灵敏度至少应与AT切体波器件一样好;(3)振荡器频率应能在大致±10ppm频率窗内进行调节并加以保持。在某些情况还要求加热时间小于3分钟。在满足这些要求方面,雷声公司已取得明显进展。本文将对这种进展加以讨论。在频谱纯度方面,文中讨论了二个题目:其一是低噪声放大器。实验证明,当它与310MHz声表面波谐振器联用时,噪声本底可达-176dBc/Hz。其二主要讨论了外部振动对噪声边带的影响。研制声表面波振荡器最重要的方面之一就是它的频率调节能力。利用金衬微调技术被证实既适用于延迟线也适用于谐振器。文中给出了实验结果,也讨论了在焊封过程中产生频移(约100ppm数量级)这一复杂情况。但已提出一种外部牵引频率技术来重调频率。在很多应用场合要求用恒溫箱以保持常温,于是就要求快速加热,而给出的数据要能显示出3分钟加热周期的频率稳定度。最后,除上述要求外,还要求声表面波振荡器的长稳保持在～1ppm/年的水平。利用提供的数据来确定冷焊密封在TO-8型外壳中的器件的基本老化率,同时也示出微调器件以及低振动灵敏度器件的变化率。