Space: a testbed for basic biomedical sciences

In Space many bodily functions adjust to the absence of gravity. Our understanding of these homeostatic processes have depended on studies on man and other animals. The present paper briefly reviews how such studies may benefit some terrestrial medical problems.     

美国快速凝固材料的发展和应用概况

本文简要介绍了美国快速凝固材料的发展和应用情况。     

Deuterium-free water (1H2O) in complex life-support systems of long-term space missions

Heavy water containing deuterium displays toxic property. It is stated that any quantity of a heavy isotope of hydrogen--deuterium--is undesirable to animals and plants. It was earlier shown by us that physical-chemical life support systems on board the "MIR" station fractionate (change) isotopes of hydrogen, oxygen and carbon. Therefore, the problem of regenerative systems in habitable space objects should include removal, from water, of a heavy stable isotope of hydrogen--deuterium. In this article we consider one method of obtaining deuterium-free water--decomposition of distillate water in an electrolyser to hydrogen and oxygen with subsequent synthesis in a catalytic or high-temperature reactor. The influence of deuterium-free water on the growth and development of Arabidopsis thaliana and Japanese quail is investigated. It is shown that with the help of the electrolysis method it is possible to fabricate water containing 80% less deuterium in comparison with SMOW. Experimentally, it is proved on a culture of Arabidopsis thaliana and Japanese quail that water with reduced contents of deuterium (80%) displays positive biological activity.     

Disk-averaged synthetic spectra of Mars

The principal goal of the NASA Terrestrial Planet Finder (TPF) and European Space Agency's Darwin mission concepts is to directly detect and characterize extrasolar terrestrial (Earthsized) planets. This first generation of instruments is expected to provide disk-averaged spectra with modest spectral resolution and signal-to-noise. Here we use a spatially and spectrally resolved model of a Mars-like planet to study the detectability of a planet's surface and atmospheric properties from disk-averaged spectra. We explore the detectability as a function of spectral resolution and wavelength range, for both the proposed visible coronograph (TPFC) and mid-infrared interferometer (TPF-I/Darwin) architectures. At the core of our model is a spectrum-resolving (line-by-line) atmospheric/surface radiative transfer model. This model uses observational data as input to generate a database of spatially resolved synthetic spectra for a range of illumination conditions and viewing geometries. The model was validated against spectra recorded by the Mars Global Surveyor-Thermal Emission Spectrometer and the Mariner 9-Infrared Interferometer Spectrometer. Results presented here include disk-averaged synthetic spectra, light curves, and the spectral variability at visible and mid-infrared wavelengths for Mars as a function of viewing angle, illumination, and season. We also considered the differences in the spectral appearance of an increasingly ice-covered Mars, as a function of spectral resolution, signal-to-noise and integration time for both TPF-C and TPFI/ Darwin.     

电调节砷化镓声表面波谐振器振荡器

已经用砷化镓制作出高 Q 表面波谐振器,并且用来控制振荡器的频率。由于砷化镓既是压电材料,又是半导体材料,因此有可能用来对全单片振荡器进行电调节。曾对半绝缘基片上的表面波谐振器的参数进行了研究。这些器件既有刻槽,又有金属电极反射栅。可调节频率的声表面波谐振器被制作在用肖脱基势垒电极作为谐振器栅的外延砷化镓基片上。调节频率并不显著改变介入损耗。两端对谐振器的介入损耗值典型的在15和20dB 之间,在180兆赫的负载 Q 值高达12000。虽然砷化镓的延迟温度系数为52ppm/℃,但是,可以通过加一层 Au/SiO_2对砷化镓延迟线进行温度补偿。     

实时交互式显示环境——航天飞机飞控人员开发的显示生成工具

NASA的飞控中心(MCC)位于约翰逊航天中心,正逐渐从一个集中式结构演变成一个分布式结构。从STS—29开始,一些由主机驱动的控制台屏幕将由工作站驱动的图形终端取代。这些工作站首先由实时数据系统(RTDS)—一个内部开发的系统—提供实时数据,接着数月后(与RTDS并行)再由飞控中心改造(MCCU)软件包的过渡性和最终版本提供。航天飞机飞控人员建立实时交互式显示环境(RTIDE,以便支持航天飞机任务多种新显示的快速开发。RTIDE是一种显示生成工具,允许非统程人员定义面向目标、事件驱动、可用鼠标选择的显示。特别强调RTIDE版本间的向上兼容性、从不同数据源获取数据的能力、实时性能、模块化更新RTIDE的能力、机器可移植性以及一个清晰而强有力的用户接口。本文介绍了使 RTIDE成为当前形式的操作与组织因素,具体设计方案,仿真与飞行操作性能及其建造过程中得到的经验教训。     

使用有限元技术的冲击和振动分析

有限元技术有两个内容:一个是把连续体分成许多离散元素,第二是在这些离散元素的联结点上假设一些条件。我们把这些联结点称之为接点或节点。有限元技术之所以大量使用,很大程度是由于高性能数字计算机的发展。种类繁多的有限元软件可从各个渠道取得。这些软件中大多数用的是刚度法而不是挠度法。刚度法用的静力分析矩阵方程可写成:{F}=[K]{X}(1)式中:{F}=力矢量列阵.[K]=刚度方阵.{X}=位移矢量列阵若设{X}=1,刚度矩阵就表示引起单位位移的力。     

S玻璃-环氧复合材料在持久拉伸载荷下的寿命估算

设计长期使用的纤维复合材料结构件时,估算其寿命是很重要的。为研究这一课题,在1969年,开始对 S 玻璃、芳香族(1971)纤维和一些石墨纤维制成的简单的环氧复合材料进行了实验研究工作。其办法是将这些经过预浸的纤维束在拉伸状态下进行寿命试验(也称应力破坏或静态疲劳试验)。选取纤维束做试样是因为它们真正代表着复合材料的基本结构坯料。当获得这些数据后,就用不同的方法对它们进行分析,并已在过去10年间陆续予以发表。1980年1月,加利福尼亚州北部的一次大地震破坏了大部份试验试样。因而实际上终