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.     

Application of the mechanical oscillator technique to the investigation of EVA decompression

The ultrasonic bubble detection technique has been used as a versatile tool in the investigation of hypobaric decompression procedures for the last two decades. However, this method can only detect relatively large bubbles > 30-50 micrometers (usually in venous blood) and not the very first stages of bubble formation. Recently, the mechanical oscillator technique has been applied in air diving trials in order to detect small blood density changes due to hypothetical fluid shifts. However, sharp density drops were found in the decompression process, and these have been attributed to gas bubble formation. In this study, this method was applied together with Doppler controls to a series of altitude decompressions to 300 and 500 hPa, which represents the range of EVA operational pressures currently used or planned. Six subjects participated in both series; the oscillator sample tube could be pressurized. By the application of pressure on a blood sample containing questionable gas bubbles, these are reduced in volume, like in recompression therapy, and thus the density of the sample is increased. This effect has been shown in all 6 subjects undergoing decompression to 300 hPa, whereas in the 500 hPa series only 3 out of 6 subjects corresponded with gas phase formation immediately after decompression. Typically, Doppler bubbles appeared only after some latency time between 20 and 60 min; after this time, the density effect had nearly vanished. It is concluded that the mechanical oscillator technique represents a complementary research instrument to the Doppler method, because it is able to deliver a quantitative resolution of the early stage of gas phase formation.     

小型、低成本、P波段机载双极化合成孔径雷达的设计

Wageningen大学和婆罗洲猩猩生存基金会（BOS）希望用一种小型、低成本、P波段机载双极化合成孔径雷达监视印度尼西亚森林的生物群。本文介绍了一台此种雷达设计方面的初步研究情况。确定应用要求，并根据要求得到主要的雷达参数。本文还介绍了基于商用货架元件的系统的初步设计。系统的几点新颖之处是：采用直接数字合成进行调制、采用双极化微带方形贴片（patch）天线以及系统的尺寸和功耗都降低了等。为了有助于SAR系统的计算和比较，开发了基于通用Matlab的SARCAL程序。本文还将阐述其原理和主要功能。     

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.     

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。     

关于无源铷频标中光漂移和缓冲气体漂移问题

本文报道了无源铷频标中光漂移和缓冲气体漂移的计算和测量结果。光漂移是以两种接法,即分立滤光器法和集成滤光器法进行测量的。文章介绍一种能够恰如其份地描述所得结果的唯象分析方法,报道了不同的纯净缓冲气体或混合缓冲气体引起的频率漂移的测量结果,评述了频率与温度的非线性关系,将所得结果跟从前发表的数据做了比较,并且利用二次温度方程式进行简明分析,以进一步对这些结果加以说明。     

Detection of the Earth with the SETI microwave observing system assumed to be operating out in the galaxy

This paper estimates the maximum range at which radar signals from the Earth could be detected by a search system similar to the NASA Search for Extraterrestrial Intelligence Microwave Observing Project (SETI MOP) assumed to be operating out in the galaxy. Figures are calculated for the Targeted Search, and for the Sky Survey parts of the MOP, both operating, as currently planned, in the second half of the decade of the 1990s. Only the most powerful terrestrial transmitters are considered, namely, the planetary radar at Arecibo in Puerto Rico, and the ballistic missile early warning systems (BMEWS). In each case the probabilities of detection over the life of the MOP are also calculated. The calculation assumes that we are only in the eavesdropping mode. Transmissions intended to be detected by SETI systems are likely to be much stronger and would of course be found with higher probability to a greater range. Also, it is assumed that the transmitting civilization is at the same level of technological evolution as ours on Earth. This is very improbable. If we were to detect another technological civilization, it would, on statistical grounds, be much older than we are and might well have much more powerful transmitters. Both factors would make detection by the NASA MOP a much more likely outcome.     

航电软件的升级

航空公司正努力通过升级软件提升航电设备的功能。随着新的空域政策的临近实施以及数字化技术带来的产品功能提升,越来越多的航空公司开始考虑通过升级软件提升其航电设备的功能。美国无线电公司(Arinc)对此也表示认同,认为在提升产品功能方面,现在的航电OEM更愿意采取软件升级的方