晶体滤波器的目前趋势

本文评述了晶体滤波器最近的和预定的研制情况。主要发展方面是:甚高频(VHF)和超高频(UHF)滤波器、数据传输滤波器、线性度、封装以及降低成本。     

Relationships between orientation, movement and posture in weightlessness: preliminary ethological observations

Weightlessness in man induces changes in astronaut orientations and consequently in his patterns of movements and postures. An ethological method has been used to describe the "overall" spontaneous behaviour of astronauts as seen from video recordings made during Space Flights. The work has consisted in analysing the relationships between orientation, movement and posture as an indication of a motor adaptative reorganization in such a situation. The results obtained lead us to consider three different aspects: (1) Orientation references. The astronaut orientates himself with reference to the Space Shuttle's internal structure; the increase of visual activity confirms the choice of the retinal vertical as frame of reference. (2) Motor coordination. The main data reveals a decrease in motor stereotypes by the diversity of motor acts observed and the importance of the link between orientation and posture described as follows: slightly inclined forward position, with legs flexed at about 135 degrees. (3) Cognitive references. There appears to be a new organization of the cognitive image of the body scheme, the missing vestibular information being supplied by peripheral vision instead which could play a role in the astronaut's perception of his own movement.     

航天飞机固体火箭发动机金属壳体部件制造

简介宇航局马歇尔宇航飞行中心根据 NAS 8—30490号合同,包给锡奥科尔公司华萨奇分公司研制的直径为146时(相当于φ3.7米)航天飞机固体火箭发动机的金属壳体部件已成功地进行了静态试车。设计中的问题是各钢厂、锻件厂、热处理厂和机械加工厂等单位都受到现有经验和条件的限制。锡奥科尔公司以前也没有制造过这样大的和断裂韧性最小为90ksi(in)~(1/2)(相当于315kg/mm~(3/2))的金属部件。为了保证固体火箭发动机能够按规定指标生产出来,有必要对逐一炉料、逐一锻件和逐次热处理过程的全部数据进行协调。本文扼要介绍试制工艺并提     

孔、轮廓和表面(六)

第四章工程定位设备的准则(二) 热膨胀——当温度变化时,不同材料之间膨胀系数的差别是很大的。铝 12.3青铜 9.9钢 6.2铸铁 6.0碳化钨(硬质合金) 3.3因钢 1.5温度每变化华氏一度时,材料每时长度(25.4毫米)的线值膨胀量(以微时计,1微时=0.025微米)。热膨胀的重要性可以通过下面的例子得到验证:一个10时长的钢块规,在温度上升10°F时,其伸长量将大于万分之五时,这说明,这类变化在精密测量中确实是不容忽视的。     

光学动目标的检测算法

本文阐述了一种用于空间非稳态泊松背景和噪声条件下光学运动目标的检测算法。该算法可用于恒星背景下对流星,小行星和卫星目标的光学探测,用最大似然法降低恒星干扰。可以看到:通过选择检测门限来保证恒虚警率,所得到的这种算法与目标的信号强度无关。本文对这种算法进行了分析,给出了在几种虚警率条件下的检测概率。     

卫星激光测距中的大气折射修正

大气折射会使卫星激光测距(SLR)系统产生显著的误差。可用两种方法来修正这些误差。光线轨迹证明了基于地面压力、温度以及相对湿度测量值的大气模型,当仰角大于20°时,可精确到几个厘米以内。此模型中的残差主要是由折射率的水平梯度而产生的。尽管导出了几种模型来预测这种梯度影响,但初步研究表明它们对地形影响很敏感。大气湍流能使折射率产生随机起伏,但在仰角低于10°时仅产生厘米级的误差。双色脉冲系统能直接测量出卫星测距中的大气延迟。该系统需要用锁模多频激光器和基于高速扫描摄影机的接收机,目前可以0.5cm以上的精度测量大气延迟。