前视时合成孔径雷达的信号函数

本文研究前视和沿复杂航迹飞行时对机载合成孔径雷达进行信号积累时的信号函数形式和特点。     

MX导弹喷管用先进材料评论 Ⅲ 第二级喷管的先进材料

这是评论MX导弹喷管先进材料的连载第三篇文章。根据空军系统司令部的空间导弹系统组织的F07401—73—C—04223合同,航空喷气固体推进公司进行了本文所述的工作。计划包括喷管设计的选择和要求满足MX ADP(Advanced DeveloPment Program)目的的有关技术。本文概述了材料筛选试验、阐述选择材料的原则、所选择材料的性能、缩比尺寸喷管点火试验的结果和用于全尺寸试验的石墨喷管部件的说明等。     

室内火箭试车台的理论和试验评定

用于固体火箭发动机静态试车的一种新的室内试验设施最近在荷兰全国应用科学研究中心的Prins Maurits实验室建成。本文介绍了试车的概况,气体动力学特性,强度和减声特性,以及验证试验的结果。     

宝美高速高精度铣车复合加工中心的独特性能

目前车铣复合加工中心在机床生产商和高端用户市场是个大热门,能生产出复合加工中心无疑是世界级的机床厂商,拥有它的客户肯定是制造高附加值零件,追求精益制造或生产及创新理念的代表。在瑞     

我国某些球粒陨石及中铁陨石稀有气体的同位素丰度

本文测定了剑阁球粒陨石、岩庄球粒陨石、亳县球粒陨石及渭源中铁陨石和新近降落的东乌珠穆沁中铁陨石的稀有气体同位素丰度，根据He、Ne及Ar的测定结果计算宇宙射线暴露年龄，剑阁、岩庄及亳县球粒陨石的宇宙射线暴露年龄分别为5．8Ma、2．5Ma及38．0Ma，东乌珠穆沁及渭源中铁陨石分别为172Ma及17Ma．     

径向两星库仑编队队形保持自适应控制研究

研究地球同步轨道处径向两星库仑编队队形保持的自适应控制问题.建立了双星库仑编队在地球同步轨道处径向两星库仑编队动力学模型.基于建立的非线性化动力学模型,同时考虑到外部扰动和动力学模型误差等因素,设计径向两星库仑编队在地球同步轨道处的构型保持自适应控制律,并利用Lyapnuov稳定性理论证明系统的闭环稳定性.最后进行数值仿真,并与传统PID控制进行了比较.仿真结果表明提出的自适应控制律响应速度快,稳定性好,编队构型能够收敛到期望值,控制性能明显优于PID控制.     

一种非合作卫星目标立体视觉测量技术

针对空间非合作卫星近距离的相对位置和姿态测量问题,提出一种立体视觉测量技术.使用激光雷达为双目立体视觉提供先验距离信息和粗略姿态,在双目相机左右图像特征提取时增加视差范围约束,限定左右图中同名特征点提取的范围,可避免杂光条件下局部复杂纹理的干扰,有效降低计算复杂度,提高图像处理的速度.通过地面闭环试验对测量技术进行了验证,实验结果表明方法的有效性和先进性.     

基于回归分析的飞轮泄漏预测模型构建研究

为解决飞轮在交付前其壳体存在微漏这一难题,选取飞轮转速和跑合时间的相关关系作为回归分析对象,探索一种飞轮密封泄漏预测模型的构建方法,并针对该模型进行方差分析、统计检验和相关分析,以保证模型精确度和工程实用性.利用本模型构建方法,可以针对不同规格飞轮或者飞轮其他性能参数构建预测模型,确保交付后飞轮的密封可靠性.     

The control of posture and movements during REM sleep: neurophysiological and neurochemical mechanisms

Mammalian sleep is characterized by synchronized sleep, in which high-amplitude, low-frequency waves appear in the electroencephalogram, and desynchronized sleep, characterized by small-amplitude, high-frequency waves, absence of tonic muscle activity, and rapid eye movements (REM), which are associated in humans with dreams. The postural atonia typical of desynchronized sleep is due to postsynaptic inhibition of spinal motoneurons resulting from tonic activation of a bulbospinal inhibitory system. Superimposed on this background of postural atonia, a motor pattern appears, characterized by rapid contractions of the limb musculature synchronous with the REM bursts. Simultaneously one observes phasic inhibition of transmission of somatic afferent volleys to motoneurons and ascending spinal pathways. The bursts of REM depend upon rhythmic discharges of vestibulo-oculomotor neurons, due to extralabyrinthine volleys originating from the brainstem. Ascending and descending vestibular volleys are also able to excite corticospinal and other supraspinal descending neurons responsible for the motor events synchronous with the bursts of REM. Activation of cholinergic neurons located in the brainstem reticular formation reproduces the postural atonia typical of desynchronized sleep, as well as the phasic events characterized by the REM bursts and the related changes in spinal cord activities. Even in this instance the bursts of REM and the related spinal effects depend upon rhythmic changes in the discharge of vestibular nuclear neurons. Experimental evidence indicates that the cholinergic reticular neurons fire asynchronously, thus being able to trigger the bulbospinal inhibitory system responsible for postural atonia. Even the vestibulo-oculomotor neurons are activated by these cholinergic reticular neurons; however, the continuous stream of these extralabyrinthine impulses is transformed into rhythmic changes of discharge of the vestibular nuclear neurons due to the presence of inhibitory neurons interposed with the vestibulo-oculomotor system. Waxing and waning in the activity of these cholinergic reticular neurons accounts for the regular occurrence of the cholinergically induced bursts of REM.