远地点发动机的最佳化

本文讨论了远地点发动机的最佳化问题,同时还评述了进行这种分析所需要的计算工具。这一问题是从材料和工作过程参数来入手解决的。论述了现行的工艺技术水平和新工艺及新材料,说明了材料对最佳参数的影响,以及发动机性能对这些参数的敏感性。举出了一个现行发动机系统最佳化的例子作为示范,并说明如何采用较先进的工艺技术来改进产品性能。     

偏置○形圈轴封的弹性流体动力润滑效应

本文针对一种新型轴封的润滑机理和工作性能进行了基本理论研究。光学干涉法已成功地用于研究镜面橡胶密封件的液膜剖面。业已发现,在广泛的工况范围内,存在着弹性流体动力润滑效应。对偏置密封件的其他性能参数的研究证明:其有效应用范围界于填料密封和机械密封之间     

X—射线实时检测系统

推进剂内部和推进剂—包复层界面的裂纹、气泡和脱粘的 X-射线实时显像检测系统的产生是固体推进剂火箭发动机质量控制的重大突破。在此之前,用成本很高的普通胶片 X-射线照相法进行抽样检验,而且对送检的每台发动机只能沿推进剂—包复层界面切线方向每隔60度或120度作局部 X-射线检查。新方法具有自动地连续100%检验能力,其成本低于普通的胶     

美国陆军导弹高级制导系统的新进展

一九七八年,美国陆军导弹司令部开始进行一项艰巨的研究任务——为未来的导弹发展一种高级制导系统。为了对付具有二十世纪九十年代以及更远时期预计特性的目标,满足当时战场环境所强加的严格要求和约束条件,设想该系统要“远远超越”目前正在研制的各种系统。本文对此课题重新作了详细说明,并且介绍了最新的发展研究规划。同时,还对迄今已经取得的各种成果作了评述,特别是在以下各个方面:目前正用来分析和模拟导弹及其制导系统的各种数学模型;空气动力学;推进系统;正在研究与分析的各种导引规律;扰动调节控制的发展状况;定位与跟踪目标的信号处理和数字化设计方法研究。本文最后一节还列举了得到合同承包者支持的各种未来计划。     

液体火箭发动机的热结构复合材料

20多年来,火箭工程设计人员一直在研究耐高温、抗氧化陶瓷材料的应用可能性,但是这些材料的主要缺点是易碎和抗热壅塞性差.目前工业用碳陶瓷和陶瓷-陶瓷结构复合材料具有很好的弹性和很强的抗热壅塞性能,这重新引起了人们制造高温火箭发动机复合材料部件的兴趣.这类新材料目前正由欧洲动力装备公司(SEP)生产,其名为SEPCARB和CERASEP,它们具有独特的热和机械性能,可以取代难熔金属而应用于可贮存二元推进剂火箭发动机的整体式喷管和推力室.装有这些部件的工艺发动机已经试验成功,从而为下一代火箭发动机的生产铺平了道路.     

Autonomic regulation of circulation and cardiac contractility during a 14-month space flight

The space flight of physician cosmonaut V.V. Polyakov, the longest to date (438 days), has yielded new data about human adaptation to long-term weightlessness. Autonomic regulation of circulation and cardiac contractility were evaluated in three experiments entitled Pulstrans, Night, and Holter. In the Pulstrans experiment electrocardiographic (ECG), ballistocardiographic (BCG), seismocardiographic (SCG), and some other parameters were recorded. In the Night experiment, only the ballistocardiogram was recorded, but a special feature of this experiment is that the BCG records were obtained with a contactless method. This method has several advantages, the most important of which are the possibility of studying slow-wave variations in physiologic parameters (ultradian rhythms) on the basis of recordings made under standard conditions over a prolonged period. The Holter experiment (24-hour electrocardiographic monitoring) used a portable cardiorecorder (Spacelab, USA). The obtained electrocardiographic data were used to analyze heart rate variability. In the first 6 months of the 14-month flight, the dynamics of cardiovascular parameters in V.V. Polyakov was virtually the same as in the other cosmonauts. The data obtained after the first 6 months of Polyakov's sojourn in space are unique and mention should be made of at least three important aspects: (1) activation of a new, additional adaptive mechanism in the 8th-9th months of flight, as is evidenced by alterations in the periodicity and power of superslow wave oscillations (ultradian rhythms) reflecting the activity of the subcortical cardiovascular centers and of the higher levels of autonomic regulation; (2) growth of cardiac contractility accompanied by a decrease in heart rate during the last few months of flight; (3) a considerable increase in the daily average values of absolute power of heart rate's variability MF component, which reflects the activity of the vasomotor center. Specific mechanisms of adaptation to weightless conditions appear to be associated with activation of higher autonomic centers. The hypothesis that central levels of circulation regulation are activated in a long-term space flight was investigated by analyzing of ultradian rhythms in nighttime. The data, received during the flight of V. V. Polyakov, show, that the process of human adaptation to long influence of weightlessness consists of a number of consecutive stages, during which the activation of more and more high levels of control system of physiological functions occurs.     

Effects of unilateral selective hypergravity stimulation on gait

The purpose of this work is to analyse the neural mechanisms of human motor perturbations induced by dynamic changes in gravity. A unilateral selective hypergravity stimulation (USHS) was produced by stretching an elastic band between the right shoulder and foot. The consequences of the extensor muscle tone change due to the positioning (increased muscular loading) and to its removal (decreased muscular loading) by the elastic band were observed on motor gait skill. Gait spatio-temporal parameters (horizontal displacement of both feet) and lower limb functional length variations (efficiency of flexion and extension movements of the lower limbs) were measured. The latter measure was performed using a device specially designed for that purpose. The main results were: (1) during and after USHS, gait perturbations appeared on the left--the body side not directly stimulated, (2) just after the end of USHS, perturbations were present on the right (homolateral) side evidencing a post treatment effect which caused a decrease in functional shortening of the lower limb during extension and an increase of functional shortening of the lower limb during stance (opposite in sense to the modification observed during swing). Such results afford evidence that, in addition to vestibular receptors, the mechanoreceptors of extensor muscles are involved in determining the changes in motor skills observed at the beginning and at the end of space flights.     

Titan and exobiological aspects of the Cassini-Huygens mission

Titan, the largest satellite of Saturn, has a dense N2-CH4 atmosphere rich in organic compounds, both in gas and in aerosol phases. Its surface is probably covered by oceans of liquid methane-ethane mixtures, with many dissolved organics. This quasi planet appears as a natural laboratory to study chemical evolution toward complex organic systems in a planetary environment over a long time scale. With the Cassini-Huygens mission NASA and ESA will jointly send an orbiter (Cassini) around Saturn and a probe (Huygens) in the atmosphere of Titan. This mission, currently planned to be launched in 1996-1997 for a Saturn - Titan arrival in 2004, offers a unique opportunity to study in detail extra-terrestrial organic processes. Consequently, it has important implications in the field of exobiology and the origins of life.     

Aspects of Global Magnetospheric Processes

Magnetospheric global modeling is a method to link observations from distant regions via physical laws and has long played a unique and crucial role in space physics. It, different from computer simulations, represents the highest level of abstraction of the physical understanding of the processes that cause observed phenomena. It results in various specific models. While it appears in the form of cartoons, it is based on and has to be qualitatively consistent with physical laws. With the advancement of computer simulations, clues to the connection between physical laws and observation can be perceived much more easily than as ever before. However, computer simulation results are highly dependent on the used boundary conditions and numerical methods which may or may not represent the reality, even if the initial conditions are properly set. Therefore, simulations can easily mislead the investigations. Furthermore, a simulation result needs to be examined using diagnostic tools, such as field line tracing and streamline tracing programs. There are uncertainties in these diagnostic methods. The errors can be very large in certain areas under certain conditions. For example, a small error may link two different field lines or stream lines. The interpretations of the simulation results can be misled by these errors. The knowledge of global modeling can be useful in identifying the inconsistencies in the simulations and the flaws in the theoretical interpretation from the simulations. This review-tutorial article outlines the principles of the global modeling and discusses the successes and flaws of several global models.     

斜拉桥钢索的抗蚀保护

预应力砼结构技术的发展,推动了斜拉桥的广泛应用,且具有结构形式经济的虎性。拉索和锚具的高强度和抗疲劳特性以及抗蚀保护成为设计工程师设计的关键。该文着重介绍了近几年 来美国斜拉钢索的防抗蚀方面的新方法、新材料。