Substorm timings and timescales: A new aspect

The magnetospheric substorm is a fundamental element of magnetospheric disturbances. After more than 40 years of intensive studies, various aspects of substorm morphology have been qualitatively established. Observations from the International Solar-Terrestrial Physics (ISTP) mission during the last decade have provided more detailed and complete pictures of substorms than before and, consequently, have provided new insights into substorm mechanisms. From the global auroral imaging it is shown that substorm onsets are locally confined; however, the effects of substorms involve a very large space at different times. Observations relying on in situ techniques can be misleading and can introduce confusion if not properly interpreted. On the other hand, remote sensing techniques such as global auroral imaging not only provide a robust means for studying substorm phenomenology but also yield relatively consistent results. This article reviews and summarizes a number of substorm studies conducted based primarily on global auroral images from NASA's Polar satellite, with a main focus on “quantitative” substorm morphology (i.e., onset timing, locations, energy input, and substorm timescales). These studies conclude that (1) auroral breakups are the most reliable substorm indicator, whereas other commonly used onset proxies may not always be associated with substorms and are subject to a propagation delay; (2) after breakup, the expanded auroral bulge can move either westward (60%) or eastward (40%); and (3) a typical substorm expansion phase lasts ～10 minutes and increases with increasing distances from the onset. A key conclusion from some recent studies seems to suggest that magnetotail reconnection, if it ever exists, is a consequence of substorm expansion onset. These findings provide constraints for substorm models and theories.     

HTPB推进剂宽泛应变率下粘弹性本构模型研究

为研究HTPB推进剂的率相关性力学性能,采用材料万能试验机、液压试验机和分离式霍普金森压杆(SHPB),分别开展了低(1.67×10~(-4)~1.67×10~(-1)s~(-1))、中(1~100 s~(-1))、高(700~2 500 s~(-1))应变率的单轴压缩实验。实验结果表明,HTPB推进剂的压缩力学性能是率相关性,随应变率的升高,给定应变下的应力逐渐增大。采用广义非线性ZWT本构模型描述HTPB推进剂宽泛应变率下的压缩力学行为,模型预测与实验数据对比表明,模型中至少需要4个麦克斯韦元件。     

航空产品运输模拟试验结果的测量不确定度评估

航空产品制造、使用、维护过程中,需要采用公路运输模拟试验台在实验室进行运输试验,以检验产品质量。运输试验严酷等级及试验结果主要由主峰频率、加速度总均方根值及加速度功率谱密度三个参数进行控制。本文介绍了通过监测系统显示的此三个试验参数示值误差测量结果的不确定度评估方法。     

布拉格光栅植入角度对在复合材料中传感检测特性影响

植入到复合材料内部的布拉格光栅可用于监测复合材料内部应力应变及温度变化,但是现有研究里对于光栅植入过程中对光栅传感检测特性造成的影响却未见报道。在植入过程中,植入光栅与碳纤维存在的夹角将会产生内应力,这会对光栅传感检测效果产生影响。为了研究其影响规律,通过将光栅植入到准各向同性复合材料的不同层中,研究光纤与相邻预浸带中碳纤维之间的夹角对温度与应力检测特性影响。研究结果表明:光栅植入角度会对其温度和应变传感检测特性造成较大影响,当光栅与相邻预浸带碳纤维存在夹角时,光栅拉伸应变测量值与应变片测量值出现偏差,发生啁啾现象;同时光栅与相邻预浸带碳纤维的夹角越大,光栅温度检测曲线线性拟合度越差。     

固体火箭发动机喷管扩张段粒子冲刷流场分析

某翼柱形药柱固体火箭发动机喷管扩张段出口部位在试验后出现了与药柱翼槽位置相对应的冲刷痕迹,为了研究Al2O3粒子对喷管扩张段的冲刷规律,对喷管型面改进提供依据,对比了不同湍流模型、颗粒轨道模型对形成冲刷痕迹的影响,分析了发动机喷管扩张段两相流场特征,确定了形成冲刷痕迹的粒径范围,判断了冲刷痕迹的形成时间,提出了喷管型面改进方案。结果表明,喷管扩张段的冲刷痕迹形成于发动机工作的15 s时刻之前,主要由药柱后翼燃烧产物中颗粒粒径分布为10~16μm区间的粒子造成,改进后的喷管型面可有效降低粒子对喷管扩张段的冲刷。     

离子推力器空心阴极分区均布模型研究

为了研究空心阴极结构尺寸和工况参数对放电性能的影响规律，基于发射体区和孔腔区等离子体参数均布假设，建立了一种不依赖试验和经验参数的适用于节流型空心阴极的分区均布数学模型。以LHC-5L空心阴极为算例，仿真结果与空心阴极试验结果对比表明，当输入参数在一定范围之内，计算所得放电电压误差优于20%，发射体温度误差优于15%，放电电压等参数随放电电流、工质流率、关键结构尺寸的变化趋势与试验结果基本一致，证明该模型可以用于预测空心阴极放电性能，为空心阴极结构参数选择和设计优化提供依据。     

Differentiation in microgravity of neural and muscle cells of a vertebrate (amphibian).

The CELIMENE space experiment (CELulles en Impesanteur: Muscle Et Neurone Embryonnaires) was devoted to the study of the influence of gravity on the differentiation, the organisation and the maintenance of the highly specialised nervous system and muscular system. CELIMENE was carried out during the first flight of the IBIS hardware (Instrument for BIology in Space) with the fully automatic space mission PHOTON 10 in February 1995. Using the amphibian Pleurodeles waltl as a vertebrate model, in vitro experiments involved immunocytochemical detection of glial-, neuronal- and muscle-specific markers, and neurotransmitters in cells developed under conditions of microgravity compared with 1g controls, on-board and on the ground. We observed that the altered gravity did not disturb cell morphogenesis or differentiation.     

复合材料壳体弹道侵彻数值模拟

采用LS-DYNA动力有限元软件显式算法,对芳纶纤维/环氧树脂复合材料壳体弹道侵彻进行了有限元数值模拟分析,获得了不同入射角及不同初始速度条件下枪弹在复合材料中的速度变化规律。计算结果表明,在入射角为90°、60°、30°3种状态下,在钨珠弹和穿甲弹垂直于壳体入射时,复合材料吸收能量最低,剩余速度最大;随入射角度的减小,子弹与靶体作用时间增加,动能损失较多,导致其剩余速度变小,减小到一定程度出现跳弹。计算获得了钨珠弹及穿甲弹垂直入射穿透该壳体时的临界速度,该计算结果与实验结果吻合较好。     

基于多智能体系统的飞机舵面故障诊断方法

采用了多智能体系统方法对飞机系统的舵面故障诊断问题进行分析.首先从飞机系统的复杂性角度分析了该方法对其进行故障诊断的适应性,然后提出了对组成飞机舵面故障诊断系统的各智能体进行分类、建模和编码的方法,并在此基础上提出了故障诊断智能体的交互模型.在仿真实例中,采用Simulink建立了F-16飞机的仿真模型,用JADE平台构造了故障识别智能体以通过数据融合来对具体的舵面故障进行诊断,并利用MAC-Sim建立了Simulink与JADE平台之间的信息互通.仿真结果说明,该方法能够通过智能体的交互与协作来实现飞机舵面单故障和组合故障的在线协同诊断.