多层隔热组件的制作工艺

介绍了多层隔热组件及影响其隔热性能的主要因素,包括反射屏与间隔层的选材、多层组件的层密度、放气孔等.结合实际工程应用,对于多层隔热组件的材料选择和制作工艺进行了着重说明.     

轴拉载荷下轴棒法C/ C 复合材料的渐进损伤

以渐进损伤方法和双线性内聚力模型为理论基础,结合ABAQUS6.8用户子程序USDFLD对轴向拉伸载荷作用下轴棒法C/C复合材料的破坏模式及载荷进行了预测,对比了试验结果与预测结果.结果表明:本方法可以准确预测轴拉载荷作用下轴棒法C/C复合材料的破坏模式.     

C/ C 复合材料SiC/ SiO2 涂层的制备及其抗氧化性能

为提高C/C复合材料的抗氧化性能,采用包埋法和低压化学气相法制备了SiC/SiO2涂层.借助XRD、SEM和EDS等测试手段分析了复合涂层的微观结构,并研究了其在l273、1773 K静态空气中的抗氧化性能.结果表明,包埋法制备的SiC涂层具有一定的浓度梯度.低压化学气相法制备的非晶Si02外涂层则有效地封堵了SiC内涂层的的裂纹和孔洞,并解决了SiC涂层在中温区(1073～1473 K)无法形成完整SiO2膜的问题.在l 273、1 773 K静态空气中经10h氧化后,涂层试样的质量损失率分别仅有4.97和0.36 mg/cm2,表现出良好的抗氧化性能.     

C/C复合材料密度的CT定量无损检测技术

讨论了利用水模试样和石墨试样标定CT检测过程中影响CT值的因素(系统噪声、产品尺寸、检测参数、摆放位置等)对CT值的影响,然后利用C/C复合材料试样建立CT值和材料密度的拟合曲线和拟合公式.结果表明系统噪声、产品尺寸、检测参数、摆放位置等对CT值的影响很小,C/C复合材料织物和复合物CT值和材料密度的拟合公式分别为P=(T+793)/659和P=(T+100)/860,说明利用CT值可以对C/C复合材料的密度进行定量定义.     

大型不规则椭球回转面的曲面重构与仿真加工

提出了大型不规则椭球回转面的一种新的曲面重构与仿真加工方法。基于GeomagicStudio软件,处理大型不规则椭球回转面的采集数据点云,重构了实测曲面的等距面模型;采用Pro/E对实测曲面的等距面模型进行等距操作,生成实测曲面模型;利用GeomagicQualify软件对实测曲面的等距面模型相对于原始数据点云,以及实测曲面模型相对于理论曲面模型进行误差分析;最后利用Pro/NC模块对实测曲面模型进行数控编程和仿真加工。研究结果表明,该方法提高了大型不规则椭球回转面的曲面重构精度,生成的标准数控加工程序具有可移植性,解决了原加工方法对专用设备的依赖。     

“三明治”型预制体结构对C/C刹车材料CVI工艺的影响

本试验设计了一种三明治型的C/C刹车材料的预制体结构,并研究了这种三明治预制体结构对C/C刹车材料CVI工艺的影响。结果表明,相对一般针刺毡结构,采用三明治预制体结构制备C/C复合材料时,增密速率快,可有效消除CVI瓶颈效应,密度分布更加均匀;且可一次性致密,无需中间热处理等加工步骤,有效缩短了生产周期,降低了生产成本。     

DS/FH混合扩频测速技术研究

由于DS/FH混合扩频信号带宽较宽,传输信道难以保证信号在宽带条件下线性传输,信号会发生群时延畸变,导致载波相位不再连续,影响载波的稳定跟踪,从而使测速精度降低。本文提出了基于跳频图案同步辅助的鉴频方案,可以消除相位跳变对载波跟踪的影响,实现对扩跳信号载波的稳定跟踪,从而提高DS/FH混合扩频测速的精度。     

直升机典型结构件RCMA/MSG-3技术分析与研究

以某民用直升机典型结构件的RCMA/MSG-3技术分析为例,阐述并分析了直升机典型结构件RC-MA/MSG-3技术的分析流程和逻辑决策方法,为今后直升机典型结构件RCMA/MSG-3技术分析提供方法和参考。     

Effects of simulated weightlessness on the intestinal mucosal barrier of rats

This study employed a rat tail-suspension model to investigate the effects of simulated weightlessness on the intestinal mucosal barrier. Twenty-four Wistar rats were randomly divided into control (CON), 14-day tail-suspension (SUS-14d), and 21-day tail-suspension (SUS-21d) groups (n = 8 per group). Expression of occludin and zonula occludins-1 (ZO-1), proteins of the tight junction (TJ), in the intestinal mucosa was measured by immunohistochemical analysis, Western blotting, and mRNA fluorescent quantitation PCR. Plasma concentrations of diamine oxidase (DAO) and d-lactate were determined using an enzymatic spectrophotometric assay. Expression of occludin and ZO-1 was reduced in the SUS-14d and SUS-21d groups as compared to the CON group, with lowest expression observed in the SUS-21d group (P < 0.01). Examination by transmission electron microscopy (TEM) of the jejunal epithelium revealed increased intercellular space, decreased TJ and desmosome densities, and destruction of microvilli in the SUS-14d and SUS-21d groups. Plasma DAO and d-lactate concentrations in the SUS-21d group were higher than those in SUS-14d group and significantly higher than those in the CON group (P < 0.01). In all three groups, the expression of occludin and ZO-1 was found to correlate negatively with DAO (P < 0.01) and d-lactate (P < 0.01) concentrations. It is concluded that simulated weightless results in down-regulation of expression of TJ proteins in the rat intestinal mucosa. Simulated weightlessness is proposed to increase intestinal permeability through damage to the TJ.     

GNSS water vapour tomography – Expected improvements by combining GPS,GLONASS and Galileo observations

The German Research Centre for Geosciences (GFZ) operates a GNSS water vapour tomography system using about 350 German GNSS stations. The GNSS data processing at the GFZ works in near real-time and provides zenith total delays, integrated water vapour and slant delay data operationally. This large data set of more than 50,000 slant delays per hour is used to reconstruct spatially resolved humidity fields by means of tomographic techniques. It can be expected that additional observations from the future Galileo system provide more information with improved quality. A simulation study covering 12 h at 14 July 2009 was therefore started to estimate the impact of GPS, Galileo and GLONASS data on the GNSS tomography. It is shown that the spatial coverage of the atmosphere with slant paths is highly improved by combining observations from two or three satellite systems. Equally important for a reliable tomographic reconstruction is the distribution of slant path intersections as they are required to locate the integrated delay information. The number of intersection points can be increased by a factor of 4 or 8 if two or three systems are combined and their distribution will cover larger regions of the atmosphere. The combined data sets can be used to increase the spatiotemporal resolution of the reconstructed humidity fields up to 30 km horizontally, 300 m vertically and 15 min. The reconstruction quality could not be improved considerably using the currently available techniques.