The Genesis Solar Wind Concentrator Target: Mass Fractionation Characterised by Neon Isotopes

The concentrator on Genesis provided samples of increased fluences of solar wind ions for precise determination of the oxygen isotopic composition. The concentration process caused mass fractionation as a function of the radial target position. This fractionation was measured using Ne released by UV laser ablation and compared with modelled Ne data, obtained from ion-trajectory simulations. Measured data show that the concentrator performed as expected and indicate a radially symmetric concentration process. Measured concentration factors are up to ∼30 at the target centre. The total range of isotopic fractionation along the target radius is 3.8%/amu, with monotonically decreasing ²⁰Ne/²²Ne towards the centre, which differs from model predictions. We discuss potential reasons and propose future attempts to overcome these disagreements.     

The Origin of Mercury

Mercury’s unusually high mean density has always been attributed to special circumstances that occurred during the formation of the planet or shortly thereafter, and due to the planet’s close proximity to the Sun. The nature of these special circumstances is still being debated and several scenarios, all proposed more than 20 years ago, have been suggested. In all scenarios, the high mean density is the result of severe fractionation occurring between silicates and iron. It is the origin of this fractionation that is at the centre of the debate: is it due to differences in condensation temperature and/or in material characteristics (e.g. density, strength)? Is it because of mantle evaporation due to the close proximity to the Sun? Or is it due to the blasting off of the mantle during a giant impact? In this paper we investigate, in some detail, the fractionation induced by a giant impact on a proto-Mercury having roughly chondritic elemental abundances. We have extended the previous work on this hypothesis in two significant directions. First, we have considerably increased the resolution of the simulation of the collision itself. Second, we have addressed the fate of the ejecta following the impact by computing the expected reaccretion timescale and comparing it to the removal timescale from gravitational interactions with other planets (essentially Venus) and the Poynting–Robertson effect. To compute the latter, we have determined the expected size distribution of the condensates formed during the cooling of the expanding vapor cloud generated by the impact. We find that, even though some ejected material will be reaccreted, the removal of the mantle of proto-Mercury following a giant impact can indeed lead to the required long-term fractionation between silicates and iron and therefore account for the anomalously high mean density of the planet. Detailed coupled dynamical–chemical modeling of this formation mechanism should be carried out in such a way as to allow explicit testing of the giant impact hypothesis by forthcoming space missions (e.g. MESSENGER and BepiColombo).     

CFG桩复合地基应力比数值分析

本文采用有限元ANSYS程序对CFG桩复合地基的单桩桩体荷载传递规律、应力比及影响因素进行了分析,得出了减小应力比的方法和措施,对工程可起借鉴的作用。     

Modelling of Ejecta as a Space Debris Source

When a micro-debris or a micrometeoroid impacts a spacecraft surface, a large number of secondary particles, called ejecta, are produced. These particles can contribute to a modification of the debris environment: either locally by the occurrence of secondary impacts on the components of complex and large space structures, or at great distance by the formation of a population of small orbital debris. This paper describes firstly, the ejecta overall production, and secondly, the lifetime and the orbital evolution of the particles. Finally the repartition of ejecta in LEO is computed. Some results describing the population as a function of size and altitude are presented.     

对“ZY-1”FM1整星热平衡、热真空试验中有效载荷被污染情况的分析

介绍了卫星在热平衡试验后所发现的有效载荷的污染情况,通过对污染提取物的分析和试验设备的再次污染监测,找出了污染源,并对以后的防污染工作提供了借鉴.     

液相色谱仪故障分析与处理

简述了液相色谱仪工作原理，对常见故障进行了分析，并给出了处理方法。     

空战机动动作库设计方式研究

具体阐述了两类常见空战动作库的设计 :典型战术动作库和基本操作动作库 ,详细分析了这两类空战机动动作库的不足 ,最后提出了改进动作库设计的具体意见和建议。     

VO2薄膜制备工艺及电阻开关特性研究

用溶胶－凝胶法在非晶玻璃上制备VO2薄膜，经过熔融、涂膜、烘干和热处理等工艺最后得到电阻相变2－3个量级的VO2薄膜。对烘干温度、熔融温度、膜厚和热处理温度对薄膜电阻开关特性的影响进行了研究。通过XRD（X－ray diffraction)和XPS（X－ray photoelectron spectroscopy）对薄膜的结构和价态进行分析，表明用溶胶－凝胶法制图VO2膜工艺简单，重复性好。     

低空突防任务下综合飞行/推进系统的建模与仿真

建立了综合飞行／推进系统的数学模型，介绍了飞机全维非线性数学模型和涡轮风扇发动机非线性部件级数学模型的建模及综合方法。对飞机执行地形中随任务时，飞行员调节飞行速度的方法与基于总能量的调节飞行速度的方法进行了比较。结果表明，基于总能量的方法比飞行员直接控制飞行速度能够减小发动机的燃油消耗，降低发动机的磨损，进而可以增加飞机的航程，延长发动机的使用寿命。     

基于有限元法的隧道荷载模型位移反分析

介绍了一种以荷载模型为求解对象的位移反分析法。它是以通用有限元软件为实验平台，利用隧道位移实测值建立荷载灵敏系数方程，根据最小二乘法原理反求隧道模型的荷载，再将正分析结果和实际值进行对比分析井重新调整隧道荷载模型，最终获得较为符合实际的隧道荷载模型。该方法的优点是既考虑了岩土松动荷载效应又能体现支护结构与周围岩土体的共同作用，且具有较好的操作性。