为火星探测寻找最佳着陆地点

行星科学家们正在为下一代火星车寻找既安全又有科学价值的着陆地点，但是资料显示恐怕鱼和熊掌不可得兼。     

Influence of Fast Global Variations of Solar Magnetic Fields on Space Weather in Cycle 23

It is established that the large-scale and global magnetic fields in the Sun's atmosphere do not change smoothly, and long-lasting periods of gradual variations are superseded by fast structural changes of the global magnetic field. Periods of fast global changes on the Sun are accompanied by anomalous manifestations in the interplanetary space and in the geomagnetic field. There is a regular recurrence of these periods in each cycle of solar activity, and the periods are characterized by enhanced flaring activity that reflects fast changes in magnetic structures. Is demonstrated, that the fast changes have essential influencing on a condition of space weather, as most strong geophysical disturbances are connected to sporadic phenomena on the Sun. An explanation has been offered for the origin of anomalous geomagnetic disturbances that are unidentifiable in traditionally used solar activity indices. Is shown, main physical mechanism that leads to fast variations of the magnetic fields in the Sun's atmosphere is the reconnection process.     

翼型在自适应壁风洞中试验时的侧壁边界层三元效应研究

二元翼型试验时模型安装于侧壁转盘上会引起侧壁边界层三元效应，中国航空研究院西北工业大学和德国宇航院哥廷根流体力学研究所合作用计算和试验方法进行了研究。作者介绍了1995～1998年的研究，包含研究目的，方案，计算方法，在德国路德维希管风洞中的验证试验，结果分析和初步结论。     

一个包括气相和亚表面反应的过氯酸铵复合推进剂的点火模型

本文提出了 Ap 基复合推进剂点火的一个综合模型及其数值解。这一分析模拟位于滞止区的推进剂试样在快速加压条件下的点火过程。本模型的特点包括:a)考虑了 Ap 基复合推进剂点火的详细的化学动力学资料;b)推进剂几何形状是二维(轴对称)的;c)考虑了气相中压力迅速增加对点燃过程的影响。使用隐式有限差分格式求解瞬态二阶联立、非齐次、非线性偏微分控制方程组。数值解揭示在点火阶段顺序发生的一系列重要事件,包括:点火器气体流入接近样品表面的区域;压缩波到达处未燃成份的燃烧;向推进剂传热;氧化剂和燃烧剂的高温分解;气相反应导致点燃。这个模型正确地预测了实验观察到的现象:随着增压速率提高,点火延迟时间缩短。采用文中考虑的不同点火准则都得到和试验一样的趋势。     

通用数据压缩方法

通用和自适应的数据压缩技术具有压缩各类意据而不丢失信息的能力。但是!这种技术复杂且计算速度慢。由硬件速度的提高及计算成本的下降,使通用数据压缩的应用成为可能。该文对自适应Huffman和Lempel一Ziv压缩算法进行了性能评估,对大小不同的意据文件的压缩比和运行时问关系作了图示并进行了讨论,大体给出了些算法为获得相对于理论上可实现的极限的最佳:峰能所需的调整。     

高级合成孔径雷达(SAR)的几种方案简介

未来的SAR设备需要满足苛刻的性能指标,而现行系统ERS-1(地球资源卫星-1)的发展还不足以满足这些要求。需要设计一个灵活的能够重新组合成不同操作模式的SAR,它能提供宽扫描带覆盖(500km,15°到50°入射角)和高分辨率(10m空间)覆盖。文章对一些各具特点的不同操作模式的系统方案进行了讨论和比较。确定了一些SAR的设计要点,并提出了一个综合的系统选择。     

一种测量浇注弹性体材料导热系数的改性方法

最近,威尔金斯和阿什报导了一种用来测量浇注弹性体材料(如橡胶)导热系数的装置。从己进行的少量试验来看,数据的重现性很好(标准偏差为2.5%)但测得的导热系数比报导的标准值大约高出5%。他们指出,末端热损失是造成误差的原因。所以,为了确定末端损失修正系数,对试验装置作了改进。随后,用改进的装置进行了试验,测得了新的导热系数值,并把它和报导的标准值进行了比较。从本文报导的试验结果和介绍的装置,可以看出,本装置是测量橡胶绝热层或固体推进剂这类浇注弹性体材料导热系数的一种实用而经济的方法。     

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。     

Electrophysiological, histochemical, and hormonal adaptation of rat muscle after prolonged hindlimb suspension

The perspective of long-duration flights for future exploration, imply more research in the field of human adaptation. Previous studies in rat muscles hindlimb suspension (HLS), indicated muscle atrophy and a change of fibre composition from slow-to-fast twitch types. However, the contractile responses to long-term unloading is still unclear. Fifteen adult Wistar rats were studied in 45 and 70 days of muscle unweighting and soleus (SOL) muscle as well as extensor digitorum longus (EDL) were prepared for electrophysiological recordings (single, twitch, tetanic contraction and fatigue) and histochemical stainings. The loss of muscle mass observed was greater in the soleus muscle. The analysis of electrophysiological properties of both EDL and SOL showed significant main effects of group, of number of unweighting days and fatigue properties. Single contraction for soleus muscle remained unchanged but there was statistically significant difference for tetanic contraction and fatigue. Fatigue index showed a decrease for the control rats, but increase for the HLS rats. According to the histochemical findings there was a shift from oxidative to glycolytic metabolism during HLS. The data suggested that muscles atrophied, but they presented an adaptation pattern, while their endurance in fatigue was decreased.