稀疏生成矩阵的低编码复杂度非正规LDPC码性能

提出了一种新的基于稀疏生成矩阵的高性能非正规LDPC码的构造方法,并研究了其性能。与传统的由校验矩阵定义的LDPC码相比,在相同的译码复杂度前提下,非正规LDPC码的编码复杂度更低。模拟结果显示,在加性高斯白噪声信道下,非正规LDPC码的性能要显著优于传统LDPC码。     

一种基于图像方式的二维条码快速识别的方法

基于图像方式的PDF417二维条码识别由于识别速度的原因,应用中受到限制,本文提出一种平行边距测量法,对符号中相邻元素的相似边之间的距离的测量来判别字符的逻辑值,可以免去占用大量时间的边缘检测,从而显著提高译码速度。实验表明该方法能显著提高PDF417二维条码的识别速度。     

基于DSM的产品并行开发过程仿真

产品开发是一个复杂的、存在很多不确定因素的过程,几乎不存在一种解析的算法能对它进行完整有效的描述和分析。本文基于设计结构矩阵,提出了产品开发过程的仿真模型,包括仿真模型的时间描述、资源竞争描述、队列描述和任务延期描述,并进一步提出了过程的仿真算法,以分析时间、资源等对产品开发过程的影响。最后,通过具体实例说明了该仿真算法的有效性。     

The impact of error covariance matrix structure of GRACE’s gravity solution on the mass flux estimates of Greenland ice sheet

The error variance-covariance matrices of the monthly GRACE gravity field models are usually well-structured (e.g., order-leading) to contain the error information of the monthly gravity field models, and they are important information to further improve the accuracy of the estimated mass transportation by a post-processing scheme. Intensive studies have been performed to understand the impact of different approximations of the full error variance-covariance matrix on the mass estimates obtained with the conventional GRACE-post processing methods (e.g., the de-striping method). In this study, based on the variants of the mascon approach which treat monthly GRACE solutions as input, we consider four different structures to the error variance-covariance matrix, (i) full matrix, (ii) block diagonal matrix, (iii) diagonal matrix, and (iv) identity matrix, and examine their impact on the mass transport estimates in Greenland. Using both synthetic and real data, we analyze the results at four temporal scales: (i) the long-term decadal scale, (ii) the inter-annual scale, (iii) the seasonal scale, and (iv) the monthly scale. Based on the synthetic study, we find that for the recovery of the long-term trend, the application of the diagonal structure obtains the best estimates. This is caused by the amplification of the model error in the mascon approach when considering the full and block diagonal structures of error variance-covariance matrix, not due to any imperfection of them. Therefore, we emphasize that one should be aware of mascon model deficiency in the mascon approach. Furthermore, the best inter-annual, seasonal and monthly mass estimates are derived by considering the block diagonal and full structures. This is caused by the behavior of the bias and the unique parameterization error in the case of different structures. A similar finding is also presented in the real data case. Finally, our analysis denotes the necessity of releasing the block diagonal structure together with the official monthly gravity field model for the GRACE Follow-On mission, instead of releasing only the diagonal structure as done for the GRACE mission.     

基于浸入与不变理论的航天器姿态跟踪自适应控制

针对惯性参数不确定的航天器姿态跟踪控制问题，基于浸入与不变（I&I）方法设计出了一种新的姿态跟踪控制器。研究结果表明，传统的浸入与不变方法运用到姿态跟踪模型，存在参数回归矩阵不可积进而导致偏微分方程无解析解的问题。针对该问题，提出了一种对回归矩阵改造使其满足可积条件的方法，通过动态放缩技术消除了回归矩阵改造前后的差异对闭环系统稳定性的影响，设计出了一种新的航天器姿态跟踪自适应控制器。通过李雅普诺夫稳定性分析方法证明了所设计的控制器能够保证闭环系统的全局渐近稳定性。相对于已有的基于动态放缩法的浸入与不变控制器，设计了一种全新的缩放因子，使得控制器的执行不需要缩放因子的信息，并且也不需要惯量矩阵的先验信息。最后，仿真对比实验进一步验证了所设计控制器的有效性和优越性。     

纤维/树脂浸润测试仪的研制与应用

针对复合材料成型工艺的特点,依据毛细原理,研制了浸润性能测试仪.该测试仪包括浸润质量测试系统与温度控制系统,能够定量测试在较宽的温度范围内发生浸润的速率和浸润程度.对该测试仪的准确性与稳定性进行了校准与标定,并运用该仪器研究了纤维种类、树脂粘度和纤维体积含量对树脂/纤维浸润性能的影响规律.研究结果表明该设备为研究各类复合材料中增强材料与基体间的浸润性能提供了方便的测试手段,对指导复合材料制备工艺具有较高的参考价值.     

An LMI-based decoupling control for electromagnetic formation flight

Electromagnetic formation flight(EMFF) leverages electromagnetic force to control the relative position of satellites. EMFF offers a promising alternative to traditional propellant-based spacecraft flight formation. This novel strategy is very attractive since it does not consume fuel. Due to the highly coupled nonlinearity of electromagnetic force, it is difficult to individually design a controller for one satellite without considering others, which poses challenges to communications.This paper is devoted to decoupling control of EMFF, including regulations, constraints and controller design. A learning-based adaptive sliding mode decoupling controller is analyzed to illustrate the problem of existing results, and input rate saturation is introduced to guarantee the validity of frequency division technique. Through transformation, the imposed input rate saturation is converted to state and input constraints. A linear matrix inequalities(LMI)-based robust optimal control method can then be used and improved to solve the transformed problem. Simulation results are presented to demonstrate the effectiveness of the proposed decoupling control.     

基于模糊聚类非负矩阵分解的软件缺陷预测

为了进一步提高对不平衡软件缺陷数据的预测精度,提出了一种基于模糊聚类非负矩阵分解的缺陷预测方法。该方法首先选取最近邻算法作为不平衡缺陷数据预测的基分类器,然后将非负矩阵分解算法引入软件缺陷预测领域,并提出利用模糊聚类初始化非负矩阵分解算法的思路。该方法一方面解决了最近邻算法处理多属性缺陷数据时计算量大导致性能降低的问题,另一方面克服了非负矩阵分解的随机初始化导致结果陷入局部最优的不足,提高了不平衡软件缺陷数据的预测精度。最后通过两组算例验证了方法的有效性。     

C/SiC复合材料推力室应用研究

C/SiC复合材料密度低、耐高温、抗氧化、抗烧蚀,并且具有非常好的高温力学性能,是制备高性能液体火箭发动机推力室的理想材料.本文从C/SiC复合材料燃烧室结构计算、无损探伤及C/SiC与金属连接等方面,论述了上海空间研究所在C/SiC复合材料应用于液体火箭发动机推力室方面的基础研究及应用进展.     

高超声速飞行器TPS破损修复涂料

分别采用环氧树脂和呋喃树脂作为基体混合碳化硅粉末与晶须制备了耐高温修复涂料.以氧-乙炔烧蚀试验测试涂料的耐高温烧蚀性能,用扫描电子显微镜分析烧蚀后涂料表面的微观形貌,用X射线衍射、表面能谱分析对涂料烧蚀后成分进行分析表征.结果表明:碳化硅粉末与晶须的质量分数比为8/4的呋喃树脂/碳化硅体系涂料具有良好的耐高温烧蚀性能,...