动态力学分析——评价二维碳一碳复合材料的一种方法

动态力学分析(DMA)已用于检验由碳基致密碳布制成的复合材料。本文介绍了从环境温度到500℃范围内,其平板和锥体两种结构件的研究,由此法计算求得的拉伸存储模量值,在整个测试温度范围内的任意一点上,其重现性在5%以内。实验证明,这种技术能对样品进行无损分析,确定锥体和平板复合材料力学性能的差别,显示锥体内存在的微弱的各向异性以及沥青基体与化学气相沉积基体的区别,发现了锥体的取向效应。本文还讨论了实验技术的细节和进行力学性能计算时所做的假设。     

瞬态流动条件下固体推进剂的点火

本文的目的主要是测定圆柱形固体推进剂在横向气流中的对流点火模式和位置。使用激波风洞可提供20毫秒时间的加热气流,其压力为1～2.0兆帕,温度为1600～2100K,流速为10～300米/秒。实验气体的组分为100％N_2;10％O_2和90％N_2;50％O_2和50％N_2共三种。测试仪器包括六个辐射探测器、高速摄影机、压力传感器和热流计等。点火为气相过程。相对于三基推进剂来讲,单基和双基推进剂在含氧气流中,点火较为容易。对大Reynolds数(如为16000),低含氧量的自由流气体,火焰会产生分离现象。在高的加热速率、并伴有边界层出现时,点火就会在小于1毫秒的时间内发生。根据流动条件的不同,点火位置可能在气流的前沿区或者在尾流区。     

随机PCM/FM和PSK信号的射频频谱特性

遥测射频(RF)频谱越来越变得拥挤。因此,遥测系统工程师和频率管理人员必须具有更多的关于遥测信号的RF频谱特性方面的知识。本文给出计算随机不归零(NRZ)脉冲编码调制/调频(PCM/FM)和相移键控(PSK)信号RF频谱的方法,讨论码率、峰值频偏、预调滤波和频谱分析的分辨带宽等对频谱特性的影响。这些方法很容易用个人计算机和具有绘图功能的程序完成。计算的频谱同测量的频谱十分吻合。本文根据测出的RF谱给出了随机NRZ PCM/FM未调载波功率及峰值频偏的精确估计式。同时还计算了邻道干扰。     

固体火箭喷管空气动力设计的一般原理

在一定条件的约束下,扩散和两相流效应对喷管空气动力的设计和喷管效率实质上起着支配的作用。为了减少两相流动的损失,提出了一些一般原理。这些原理应用于所介绍的方法中,以便得到一种新的喷管形状。描述了收敛段,喉部和扩散段的结构,通过多项式的起始膨胀区的截短喷管的方法获得了扩散段的形状。所得到喷管的结构对减轻喷管重量比较有利。     

Bacillus subtilis spores on artificial meteorites survive hypervelocity atmospheric entry: implications for Lithopanspermia

An important but untested aspect of the lithopanspermia hypothesis is that microbes situated on or within meteorites could survive hypervelocity entry from space through Earth's atmosphere. The use of high-altitude sounding rockets to test this notion was explored. Granite samples permeated with spores of Bacillus subtilis strain WN511 were attached to the exterior telemetry module of a sounding rocket and launched from White Sands Missile Range, New Mexico into space, reaching maximum atmospheric entry velocity of 1.2 km/s. Maximum recorded temperature during the flight was measured at 145 degrees C. The surfaces of the post-flight granite samples were swabbed and tested for recovery and survival of WN511 spores, using genetic markers and the unique DNA fingerprint of WN511 as recovery criteria. Spore survivors were isolated at high frequency, ranging from 1.2% to 4.4% compared with ground controls, from all surfaces except the forward-facing surface. Sporulation-defective mutants were noted among the spaceflight survivors at high frequency (4%). These experiments constitute the first report of spore survival to hypervelocity atmospheric transit, and indicate that sounding rocket flights can be used to model the high-speed atmospheric entry of bacteria-laden artificial meteorites.     

固体推进剂火箭发动机的性能予示和高膨胀比喷管的应用

提出了予示固体推进剂火箭发动机的比冲和特性速度的分析方法。这个方法强调了二维两相流分析,它是以准确的跨音速解为基础,并且给出金属含量高的推进剂的大部分性能损失。它应用于可忽略燃烧损失和出口锥上无粒子撞击的发动机。以一系列的缩比发动机、全尺寸发动机和5台装有高膨胀比喷管的远地点发动机实验结果为背景,评价了它的有效性。膨胀比在很宽的范围内(从9到92)在予示值和实验结果之间完全一致。从本研究得出结论,提出的这个方法是性能予示的一个很准确工具,并且对高膨胀比喷管的气动力设计和分析很有用,这样的喷管对期待中的未来应用是特别有意义的。     

航天发动机用的低密度绝热层的研制

业已公认,减轻航天发动机的消极重量是十分必要的。其中的一项措施是研制和应用先进的复合材料发动机壳体,如计划于八十年代初期发射的MAGE欧洲远地点发动机所做的那样。但是,通过降低壳体内绝热层材料密度,还可以进一步降低发动机消极重量。由于认识到了这样做的必要性,从而开展了本文所述的新型低密度橡胶复合材料的研制工作。这些橡胶材料,大体上都以三元乙丙橡胶(EPDM)为基体,以石棉为填料,以过氧化物为固化剂,适用于装丁羧推进剂和丁羟推进剂的发动机。所述的研制计划除研究了配方技术,调整热性能、烧蚀性能和力学性能以满足发动机要求外,还研究了加工工艺的最佳化,包括易于固化以及和壳体推进剂的粘接性能。     

Blood volume regulating hormones, fluid and electrolyte modifications during 21 and 198-day space flights (Altair-MIR 1993)

During the Altair MIR' 93 mission we studied several parameters involved in blood volume regulation. The experiment was done on two cosmonauts before (B-60, B-30), during (D6, D12, D18 for French and D7, D12, D17 for Russian) and after the flight (R+1, R+3 and R+7). Space flight durations were different for two cosmonauts: for the Russian the flight duration was 198 days and for the French 21 days. On board the MIR station only urinary (volume and electrolytes, atrial natriuretic peptide (ANP), cyclic guanosine monophosphate (cGMP) and catecholamines) and salivary (cGMP and cortisol) samples were collected, centrifuged and stored in freezer. Lithium was used as a tracer to know exactly the 24 h urine output (CNES urine collection Kit). Before and after flight, blood was drawn with an epicite needle and vacutainer system for hormonal assays (renin, antidiuretic hormone, cGMP, ANP and aldosterone) in two positions: after 30 min rest in upright seated position and after 90 min of supine position. Salivary samples were collected simultaneously. During flight a decrease of diuresis and ANP and an increase of osmolality were found. No modifications of hematocrit, but an increase of salivary cGMP and cortisol were also observed. The decrease of urinary ANP is in favor of hypovolemia as described in previous flights. The postflight examinations revealed changes in fluid-electrolyte metabolism which indicate a hypohydration status and a stimulation of hormonal system responsible for water and electrolyte retention in order to readapt to the normal gravity.     

数字频率合成的新途径

本文介绍了从1Hz到399999Hz以1Hz步进频率合成新技术。合成的波形是对称方波,与晶体管—晶体管逻辑(TTL)相容。它所使用的合成算法为高效率使用系统的数字式仪器创造了条件。整套设备是由一个输入装置、一个BCD/二进制转换器、一个二进制分频器、一个数字式比较器和一个锁相环(PLL)倍频器组成。     

中英将在空间科学与技术领域展开合作

“中英空间科学与技术联合实验室”于2007年11月8日在北京航空航天大学揭牌成立。该实验室由北京航空航天大学航空科学与技术国家实验室与英国卢瑟福一阿普尔顿实验室共同组建。双方将通过该联合实验室，在日地环境、微纳卫星分布式组网探测、深空探测及有效载荷技术等领域开展重点合作。