Global Response of Martian Plasma Environment to an Interplanetary Structure: From Ena and Plasma Observations at Mars

As a part of the global plasma environment study of Mars and its response to the solar wind, we have analyzed a peculiar case of the subsolar energetic neutral atom (ENA) jet observed on June 7, 2004 by the Neutral Particle Detector (NPD) on board the Mars Express satellite. The “subsolar ENA jet” is generated by the interaction between the solar wind and the Martian exosphere, and is one of the most intense sources of ENA flux observed in the vicinity of Mars. On June 7, 2004 (orbit 485 of Mars Express), the NPD observed a very intense subsolar ENA jet, which then abruptly decreased within ∼10 sec followed by quasi-periodic (∼1 min) flux variations. Simultaneously, the plasma sensors detected a solar wind structure, which was most likely an interplanetary shock surface. The abrupt decrease of the ENA flux and the quasi-periodic flux variations can be understood in the framework of the global response of the Martian plasma obstacle to the interplanetary shock. The generation region of the subsolar ENA jet was pushed towards the planet by the interplanetary shock; and therefore, Mars Express went out of the ENA jet region. Associated global vibrations of the Martian plasma obstacle may have been the cause of the quasi-periodic flux variations of the ENA flux at the spacecraft location.     

医疗博弈与医疗资源最优化配置

医疗是与医疗活动相关的各方（医生、药商、病人、与医疗管理相关的政府官员）共同参与的博弈活动,这种活动一般体现为信息不对称。正是由于信息不对称,才导致医疗市场失效,即导致医生、药商运用医疗信息优势,欺诈医疗信息稀缺的消费者（即病人）。于是造成看病难、看病贵,且造成医疗资源大量浪费。改革的根本途径是：在继续坚定地走市场化取向改革之路的同时,政府建立医疗监察机制,克服医疗欺诈,以保障医疗市场在充分有效条件下到达既公平又高效率的最优均衡点,从而实现全社会医疗资源的最优化配置。     

实施精益生产方式的有效性

精益生产方式源于日本丰田公司,它是运用多种管理方法、手段对生产过程中的“人、机、料、法、环”诸要素进行组合,做到以必要的劳动确保必要的时间内,按必要的数量,生产必要的零部件,以期达到杜绝超量生产,消除无效劳动,降低成本,提高质量,用最少的投入实现最大产出的一种先进的生产方式。     

行星采样柔性机械臂运动规划研究

为适应行星表面较大范围的采样要求及系统减重的需求,采样机械臂通常是细长形臂杆加多关节组成的连杆型关节机械臂,这使得抑制柔性振动成为机械臂控制系统的研究重点。针对采样机械臂的工作过程,提出带抛物线过渡的平滑轨迹规划方法,即在运动过程中使加速度连续,避免关节转动的力矩突变,并且最大限度降低峰值。首先建立基于D-H法的机械臂运动学方程,然后在考虑臂杆及关节柔性的动力学模型环境下,进行变加速—匀速—变减速的笛卡尔空间加速度连续平滑轨迹规划运动,达到减小柔性臂振动、提高定位精度的目的。仿真结果表明,在运动规划中引入抛物线过渡的加速度连续环节、降低加速度冲击可以明显改善运动平稳性,对提高动态跟踪精度有直接作用。     

行星轮系动态啮合应力研究

针对行星传动齿轮系的结构特点,建立了行星齿轮和主动齿轮的非线性接触有限元模型,应用AN-SYS软件进行了动态接触分析的研究。基于研究结果,建立了可以体现行星齿轮系在工作过程的啮合应力变化情况的计算模型,可以直观地观察到行星齿轮系从开始啮合到完全脱开整个过程中的应力分布及变化情况。选择20节点六面体单元,模拟齿轮受载情况,迅速、高效地得出整个齿轮系的强度、刚度分布云图,大大提高了设计效率。     

两级星型齿轮传动动态均载特性分析

建立了两级星型齿轮传动系统的动力学均载分析模型,考虑了各构件的制造误差与安装误差。计算了系统的载荷不均匀系数。对由制造误差与安装误差引起的动态不均载特性进行了动力学分析。分析了各误差和载荷不均匀系数的关系,得到了各误差与系统载荷不均匀系数间的变化关系,讨论了各类误差对系统载荷不均载系数的影响。研究结果表明,第一级星轮及其所在轴轴承偏心误差对系统载荷不均匀系数的影响最大;各误差对第一级系统载荷不均匀系数的影响比对第二级的影响大;随着星轮个数增加,系统载荷不均匀系数增大。      

灰色优势分析在多雷达低空小目标跟踪中的应用

在多部雷达同时跟踪低空／超低空飞行的机动小目标时，因受低空杂波，电子干扰和雷达自身探测精度等因素影响，易使部分雷达探测的数据不完整，不精确，不可靠，甚至相互矛盾，结果造成融合中心数据处理精度下降，针对这一情况，本文应用灰色系统理论的绝对关联度定义和性质，提出了一种改进的绝对关联度计算方法，并在此基础上将多部雷达经一次融合后的数据作为特征数据进行优势分析，把每时送入融合中心比较差的雷达数据用特征数据替换，再进行二次融合，仿真结构表明，应用改进的绝对关联度对雷达数据进行灰色优势分析和二次融合，可进一步提高雷达系统的跟踪精度和可靠性。     

优秀人才是飞机结构设计创新的源动力

根据未来先进战斗机发展的需要和飞机设计队伍的现状，指出了培养优秀飞机人才的紧迫性。论述了优秀飞机结构设计师应具备的基本素质、知识结构和专业技能。提高了改革人才培养机制，激励人才成长的建议。     

人尽其才才尽其用--论人才资源的优化配置

人才资源已成为第一资源，本文分析了人才资源的特征，指出了人才资源优化配置的必要性，并就如何实现人才资源的优化配置提出一定的见解。     

Formation and Composition of Planetesimals

The composition of planetesimals depends upon the epoch and the location of their formation in the solar nebula. Meteorites produced in the hot inner nebula contain refractory compounds. Volatiles were present in icy planetesimals and cometesimals produced in the cold outer nebula. However, the mechanism responsible for their trapping is still controversial. We argue for a general scenario valid in all regions of the turbulent nebula where water condensed as a crystalline ice (Hersant et al., 2004). Volatiles were trapped in the form of clathrate hydrates in the continuously cooling nebula. The epoch of clathration of a given species depends upon the temperature and the pressure required for the stability of the clathrate hydrate. The efficiency of the mechanism depends upon the local amount of ice available. This scenario is the only one so far which proposes a quantitative interpretation of the non detection of N₂ in several comets of the Oort cloud (Iro et al., 2003). It may explain the large variation of the CO abundance observed in comets and predicts an Ar/O ratio much less than the upper limit of 0.1 times the solar ratio estimated on C/2001 A2 (Weaver et al., 2002). Under the assumption that the amount of water ice present at 5 AU was higher than the value corresponding to the solar O/H ratio by a factor 2.2 at least, the clathration scenario reproduces the quasi uniform enrichment with respect to solar of the Ar, Kr, Xe, C, N and S elements measured in Jupiter by the Galileo probe. The interpretation of the non-uniform enrichment in C, N and S in Saturn requires that ice was less abundant at 10 AU than at 5 AU so that CO and N₂ were not clathrated in the feeding zone of the planet while CH₄, NH₃ and H₂S were. As a result, the 14N/15N ratio in Saturn should be intermediate between that in Jupiter and the terrestrial ratio. Ar and Kr should be solar while Xe should be enriched by a factor 17. The enrichments in C, N and S in Uranus and Neptune suggest that available ice was able to form clathrates of CH₄, CO and the NH₃ hydrate, but not the clathrate of N₂. The enrichment of oxygen by a factor 440 in Neptune inferred by Lodders and Fegley (1994) from the detection of CO in the troposphere of the planet is higher by at least a factor 2.5 than the lower limit of O/H required for the clathration of CO and CH4 and for the hydration of NH₃. If CO detected by Encrenaz et al. (2004) in Uranus originates from the interior of the planet, the O/H ratio in the envelope must be around of order of 260 times the solar ratio, then also consistent with the trapping of detected volatiles by clathration. It is predicted that Ar and Kr are solar in the two planets while Xe would be enriched by a factor 30 to 70. Observational tests of the validity of the clathration scenario are proposed.