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排序方式: 共有471条查询结果,搜索用时 31 毫秒
291.
万晓云 《中国民航飞行学院学报》2013,(5):34-37
大气数据系统是飞机重要的机载系统。本文结合系统原理、工程技术资料和自身维护经验,对A320系列飞机大气数据系统日常维护中的一些常见故障和特殊故障进行分析,给出维护建议,并对系统维护中的注意事项进行提示与强调。 相似文献
292.
In aero-engines, mortise-tenon joint structures are often used to connect the blades to the turbine disk. The disadvantages associated with conventional manufacturing techniques mean that a low-cost, high-efficiency, and high-quality nickel-based mortise–tenon joint structure is an urgent requirement in the field of aviation engineering. Electrochemical cutting is a potential machining method for manufacturing these parts, as there is no tool degradation in the cutting process and high-quality s... 相似文献
293.
为实现星载微推进器性能评价中的动态推力测量,基于悬臂梁动力学模型,建立了测量系统的传递函数,分析了系统的输入输出特性,根据悬臂梁响应速度快(振动频率高)、动态分量在较小时间区间内接近等幅振荡(阻尼比小)以及高阶振动可视为基频振动噪声的特性,提出了求解稳态位移的末端均值法。该方法通过消除位移响应中的动态分量,得到了误差带较大时的稳态位移时变值,实现了动态推力测量。依据系统稳态位移与推力为线性关系、线性系数为系统增益值这一特性,提出了参数标定方法。搭建了试验平台,标定得到系统响应时间为156ms,通过对比扭摆系统测量结果,悬臂梁测量得到的冲击力与实际推力相对误差为4.064%,结合冲击力本身的测量误差1.383%,最终得到推力测量误差为4.293%。 相似文献
294.
Induction of vascular endothelial phenotype and cellular proliferation from human cord blood stem cells cultured in simulated microgravity 总被引:5,自引:0,他引:5
Recent studies have demonstrated that stem cells derived from adult hematopoietic tissues are capable of trans-differentiation into non-hematopoietic cells, and that the culture in microgravity (microg) may modulate the proliferation and differentiation. We investigated the application of microg to human umbilical cord blood stem cells (CBSC) in the induction of vascular endothelial phenotype expression and cellular proliferation. CD34+ mononuclear cells were isolated from waste human umbilical cord blood samples and cultured in simulated microg for 14 days. The cells were seeded in rotary wall vessels (RWV) with or without microcarrier beads (MCB) and vascular endothelial growth factor was added during culture. Controls consisted of culture in 1 G. The cell cultures in RWV were examined by inverted microscopy. Cell counts, endothelial cell and leukocyte markers performed by flow cytometry and FACS scan were assayed at days 1, 4, 7 and at the termination of the experiments. Culture in RWV revealed significantly increased cellular proliferation with three-dimensional (3D) tissue-like aggregates. At day 4, CD34+ cells cultured in RWV bioreactor without MCB developed vascular tubular assemblies and exhibited endothelial phenotypic markers. These data suggest that CD34+ human umbilical cord blood progenitors are capable of trans-differentiation into vascular endothelial cell phenotype and assemble into 3D tissue structures. Culture of CBSC in simulated microg may be potentially beneficial in the fields of stem cell biology and somatic cell therapy. 相似文献
295.
本文研究了一个光滑的、理想导电的、凸散射体的轮廓重构问题。主要从物理光学散射场的一阶修正项入手,分析了散射场的共极化和交叉极化信息与目标表面形状之间的关系,获得了散射场的极化特性与散射体表面上镜面点的主曲率密切相关的概念。借助于微分几何中曲面再现问题,重构出目标的外形图象。 相似文献
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反馈结构结构系统的排序原理是在递阶导次结构基础上提出来的,对于元素关系很复杂的系统,可能无法建立递阶层次结构模型,而反馈结构模型就为复杂关系提供了条件。在论述了建立反馈结构模型方法的基础上,对大型工程项目总设计单位的评审这一涉及因素多,关系复决策问题,进行了分析计算,在分析反馈结构模型时,借用了图论分析的方法,并建立了两类结构的运算模型,对反馈结构运算模型和递阶层次结构模型的排序结果进行了对比研究 相似文献
300.
Weixing Wan Libo Liu Hong Yuan Baiqi Ning Shunrong Zhang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2465-2469
This work studies the sudden increases in total electron content of the ionosphere caused by the very intense solar flare on July 14, 2000. Total electron content (TEC) data observed from a Global Positioning System (GPS) network are used to calculate the flare-induced TEC increment, δTECf, and variation rate, dTECf/dt. It is found that both dTECf/dt and δTECf are closely related with the solar zenith angles. To explain the observation results, we derived a simple relationship between the partial derivative of the flare-induced TEC, ∂TECf/∂t, which is a good approximation for dTECf/dt, and the solar zenith angle χ, as well as the effective flare radiation flux If, according to the well-known Chapman theory of ionization. The derived formula predicted that ∂TECf/∂t is proportional to If and inverse proportional to Chapman function ch(χ). This theoretical prediction not only explains the correlation of dTECf/dt and δTECf with χ as shown in our TEC observation, but also gives a way to deduce If from TEC observation of GPS network. Thus, the present work shows that GPS observation is a powerful tool in the observation and investigation of solar flare effects on the ionosphere, i.e., the sudden ionospheric disturbances, which is a significant phenomenon of space weather. 相似文献