烧结温度对氧化铝基陶瓷型壳显微组织及力学行为的影响

采用选择性激光烧结(selective laser sintering,SLS)快速制备高温合金叶片用氧化铝基陶瓷型壳初坯,并结合高温烧结(high-temperature sintering)进一步提高陶瓷型壳的力学性能。研究不同烧结温度(1450～1600℃)对氧化铝基陶瓷型壳的抗弯强度的影响,采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)分析型壳的物相组成、断口微观形貌。结果表明:采用选择性激光烧结+高温烧结技术可快速高效地制备力学性能满足要求的陶瓷型壳,随着烧结温度从1450℃升高到1600℃,型壳的室温平均抗弯强度增大,并在1600℃时达到38.03 MPa;型壳的主要强化相为柱状莫来石相,且随烧结温度升高,型壳中莫来石相含量增加,石英相含量降低,方石英相含量先增加后有所降低;裂纹扩展形式从缓慢扩展转变为迅速扩展并引发瞬断,断口由撕裂状演变为平齐小断面,断裂方式由主要沿晶断裂向穿晶断裂转变,裂纹倾向于向晶内莫来石扩展。     

大力矩、低脉动交流永磁力矩电机设计

为满足超精加工等领域对高精度驱动控制系统的需要,交流永磁力矩电机正逐渐向大力矩、低脉动方向发展,但国内相关领域的研究相比于国外仍有很大的差距。根据实际需要,分析研究了大力矩、低脉动交流永磁力矩电机的结构,并根据技术要求对电机加以设计。最后利用有限元分析方法对提出的交流永磁力矩电动机进行分析,用以验证所设计的电机在过载能力、定位力矩及波动力矩的抑制等方面的性能。仿真分析结果显示所设计的电机具有优良性能。     

基于高轨航天器的GNSS接收机技术

全球导航卫星系统（GlobalNavigationSatelliteSystem,GNSS）应用于高轨航天器时,因轨道高于导航卫星,可见星数量急剧减少,空间信号功率微弱,信号的快速捕获和跟踪十分困难。文章对高轨地球同步轨道（GeosynchronousEarthOrbit,GEO）接收技术进行了研究。以中国实践十七号卫星为研究对象,采用官方正式发布的发射天线方向图对GEO下GNSS信号特征及可用性开展研究分析,并针对高轨道航天器GNSS信号微弱的特点,采用长时间积分处理的梳状滤波方法、差分相干累加比特同步算法和基于动力学模型补偿的扩展卡尔曼滤波自主定轨算法设计GNSS接收机,并在半物理仿真平台进行了测试验证。试验结果表明：GNSS接收机捕获灵敏度优于-173dBW,跟踪灵敏度优于-175dBW,定轨位置精度优于50m,速度精度优于0.01m/s。     

Trends in the Neutral and Ionized Upper Atmosphere

This article reviews our knowledge of long-term changes and trends in the upper atmosphere and ionosphere. These changes are part of complex and comprehensive pattern of long-term trends in the Earth’s atmosphere. They also have practical impact. For example, decreasing thermospheric density causes the lifetime of orbiting space debris to increase, which is becoming a significant threat to important satellite technologies. Since the first paper on upper atmosphere trends was published in 1989, our knowledge has progressed considerably. Anthropogenic emissions of greenhouse gases affect the whole atmosphere, not only the troposphere. They cause warming in the troposphere but cooling in the upper atmosphere. Greenhouse gases such as carbon dioxide are not the only driver of long-term changes and trends in the upper atmosphere and ionosphere. Anthropogenic changes of stratospheric ozone, long-term changes of geomagnetic and solar activity, and other drivers play a role as well, although greenhouse gases appear to be the main driver of long-term trends. This makes the pattern of trends more complex and variable. A?consistent, although incomplete, scenario of trends in the upper atmosphere and ionosphere is presented. Trends in F2-region ionosphere parameters, in mesosphere-lower thermosphere dynamics, and in noctilucent or polar mesospheric clouds, are discussed in more detail. Advances in observational and theoretical analysis have explained some previous discrepancies in this global trend scenario. An important role in trend investigations is played by model simulations, which facilitate understanding of the mechanisms behind the observed trends.     

基于引导线的涡轮气冷叶片伸根建模方法

发动机涡轮气冷叶片伸根段是复杂的过渡曲面,设计过程繁琐.针对伸根段的几何结构特征,提出了基于引导线的伸根过渡曲面建模方法,由伸根段边界条件生成引导线,使用最小能量法优化引导线,以此为基础完成伸根段的建模,实现了指定高度截面面积修改.开发了伸根段参数化建模模块,提高了叶片设计效率,并为航空发动机复杂过渡曲面参数化建模提供参考.     

激光引致激波传播规律的数值研究

空气光学击穿的激波流场结构的研究是激光与物质相互作用研究领域中的重要组成部分。利用光线追踪法,采用解耦的辐射输运方程,数值求解含能量源项的流体控制方程,对空气光学击穿诱导激波的传播过程和随时间演化规律进行了研究。通过线形拟合,给出了激波传播的后期阶段激波半径随时间的变化关系。流场中的超压波形有几个峰值,由多列压缩-稀疏波组成,并且强度越来越弱。研究结果可为激光应用技术提供一定的理论支持。     

广义Hilbert变换及其滤波器的设计

广义Hilbert变换将传统的Hilbert变换由整数阶向分数阶的推广,其应用领域也得到了扩展。文章主要研究设计广义Hilbert滤波器时,窗函数的选择问题以及对滤波器的误差进行分析,并给出了分析结果。     

基于部件特性未知的航空发动机故障诊断技术

以航空发动机部件通用特性为基础运用单纯形优化方法,发展了一种预测发动机部件特性的自适应模型方法。并以此为基础运用气路分析原理,选取表征发动机性能参数变化的症兆变量和测量参数,建立了发动机故障诊断小偏差方程。诊断结果表明:症兆变量的选取和相对变化值大小对故障诊断误差有决定性的影响,其值的选取应以门限值1/3为最佳;故障诊断模型症兆变量与实际故障症兆变量变化值相对误差控制在5%内,且不会对故障类型的判断产生影响;故障诊断模型在已知的检验结果内无误诊现象。      

BP网络进行0-9十个数字图像的识别

在BP算法和数字图像处理技术的基础上,本文在MATLAB软件环境下提取Word文档中26种字体的0-9十个数字的图像,使用MATLAB神经网络工具箱及图像处理工具箱进行数字的识别,给出了较详细的处理步骤及相关程序,并比较了各种识别算法的收敛速度和识别率。     

Three-Dimentional Surface Light Irradiance Reconstruction in Bioluminescence Tomography

Reconstruction of 3D surface irradiance distribution using multiple views captured by charged coupled device(CCD)camera is the basis of solving the light source in bioluminescence tomography(BLT).A simple and convenient mapping technique based on the pin-hole imaging model and Lambert′s cosine law was presented to establish the relationship between gray levels and irradiance intensities.Compared with previous integrating sphere camera calibration used in BLT,the proposed method can effectively avoid heavy burden of simulation experiment to obtain the corresponding relationship of gray levels and irradiance intensities.The accuracy and feasibility of the proposed method are validated with no more than 1mm location error by different types of phantom experiments.The mapping approach is also applicable to other noncontact optical imaging system.