X射线脉冲星导航系统的闭环校正滤波器设计

X射线脉冲星导航(XNAV)系统对脉冲到达时间或相位的在轨测量存在星载钟计时误差问题. 本文提出将钟差与卫星三维位置参数一起作未知量处理, 采用4颗以上脉冲星的观测信息解算出卫星位置; 将该位置信息与轨道动力学预报的位置信息的差值作为量测信息, 结合卫星轨道动力学模型, 设计闭环校正卡尔曼滤波器. 仿真表明, 设计的闭环校正滤波器能够对卫星轨道状态进行最优估计, 解决了XNAV系统中的钟差问题.     

中轨道Walker导航星座备份策略分析SS设计北大核心

针对中轨道Walker导航星座的备份策略问题,设计与实现了中轨道Walker导航星座备份策略分析仿真软件。软件由卫星可靠性分析模块、星座备份策略分析模块以及在轨备份星轨位设计模块组成。详细介绍了软件各组成模块的功能特性和关键技术,并给出了软件的应用实例。该软件能有效模拟卫星部件随机故障的动态行为,可为导航星座备份策略分析提供更为准确的卫星可靠性模型,支持对不同备份策略进行评估分析,从而获得不同条件下的最优备份策略,同时可对备份策略中在轨备份星轨位进行优化设计,可推广应用于其它卫星星座备份策略分析评估。     

GPS广播星历误差及其对导航定位精度的影响

利用国际GPS地球动力学服务(International GPS service (IGS)for geodynamics)提供的广播星历和精密星历数据，全面分析GPS卫星轨道及其钟差修正量误差的变化规律。前者具有6h的短周期正弦波动和1个GPS周的长周期线性递增特性；后者以12h为周期作正弦波动变化，这对用户导航定位精度将产生周期性影响。若使用IGS预报星历代替广播星历数据进行导航定位计算，可以使定位精度提高5m。     

基于Fuzzy ART聚类的卫星在轨姿态监测系统设计

针对传统卫星在轨姿态监测系统无法确定在轨姿态向量与正常向量匹配度,导致姿态角度监测结果不精准的问题,提出基于Fuzzy ART聚类的卫星在轨姿态监测系统设计;系统硬件根据GPS解算方位角和俯仰角,隔离载体扰动;使用MSP430数字/模拟信号转换器,统一CPU指令和寻址模式;使用AS5145B磁角位置编码器输出脉冲信号;通过双轴磁传感器HMC6352的电磁罗盘电路得出卫星在轨姿态大致方向;软件部分利用Fuzzy ART聚类卫星在轨姿态监测数据,确定聚类中心,判定卫星在轨姿态向量与正常向量匹配度,根据匹配结果,开辟新的记忆节点,给出报警信息,完成姿态监测;实验结果表明,所设计系统在轨道圈数为1圈时施加控制力矩,能够迅速使姿态达到稳定;轨道圈数为2圈时,z轴方向的俯仰角与实际三维角度相差1°,表明该系统对卫星在轨姿态监测准确率较高.     

捷联惯导在轨标定算法研究

为了保证长期在轨工作的捷联惯性导航系统的精度,设计了一种捷联惯导在轨标定算法.通过分析捷联惯导的主要误差源,建立了标定误差模型和导航误差模型.用加速度计的零位漂移、陀螺仪的零位漂移、陀螺仪的标度因数误差和安装误差构造系统状态方程,利用卫星导航系统提供的速度、位置信息和星敏感器提供的姿态信息构造量测方程,经过滤波运算得到各项误差估计值.算法解决了捷联惯导与星敏感器坐标轴不重合的问题,提高了嵌入式计算机的计算能力.最后对算法进行了数学仿真,仿真结果证明了算法的有效性.     

北京一号小卫星MTF在轨测量与图像复原

卫星调制传递函数(MTF)的在轨测试是监测卫星平台及其遥感器在轨运行情况和性能衰减程度的有效手段。本文针对北京一号小卫星多光谱相机,研究利用边缘地物法进行MTF在轨监测,并基于MTF测试结果,采用维纳滤波法对北京一号小卫星多光谱图像进行复原。结果表明NW向和NE向两个方向的MTF差别不大,在这两个方向上LSF的半带宽分别为3.75和4.35个像元。根据所计算得到的MTF值对图像进行复原可以明显提高北京一号小卫星图像清晰度以及边界信息。     

导航卫星上行注入与测距性能测试系统设计

导航卫星的上行注入与测距性能是卫星导航系统服务精度一个重要保证,设计了一种导航卫星的上行注入与测距性能测试系统;该系统以控制处理计算机为核心,并结合了专用设计的基准频率发生器模块、基准时间发生器模块、注入信号发生器模块和通用商业化仪器,能实时动态地模拟导航卫星在轨期间接收地面注入信号的情形,完成导航卫星上行注入性能测试中电文信息的生成和比对以及上行测距性能测试;该测试系统稳定、灵活,测量精度高,而且可以通过修改测试软件参数来满足新的测试要求,便于测试系统的升级改造。     

卫星导航接收设备健康管理技术研究

针对卫星导航接收设备的技术特点和维护需求,基于故障检测与健康管理技术,提出了一种从射频前端、数字信号处理到算法实现全流程的预测与健康管理方案,搭建了卫星导航接收设备预测与健康管理系统体系结构。基于检测信息设置,完成信号处理与状态监测,开展卫星导航接收设备实时健康评估与寿命预测研究,根据评估与预测结果制定维护方案,实现卫星导航接收设备的健康管理。通过开展仿真试验与实际工程应用,验证了所设计的卫星导航接收设备健康管理方案的正确性与有效性,具有一定的工程推广价值。     

自校正滤波器在卫星定位中的应用

设计了一种新的基于ARMA模型的自校正卡尔曼滤波器,对卫星定位误差模型参数进行分段在线估计,根据误差模型估计参数直接求取滤波增益阵.并提出了一种直接计算滤波误差方差阵的方法,对两个不同的定位系统进行信息融合.仿真结果表明,在未知噪声统计特性的情况下,自校正卡尔曼滤波器能有效过滤观测噪声,基于它的信息融合规则能够有效提高定位精度.计算过程简单,并可以在线建模.     

基于单神经元PID控制器的压电陶瓷控制方法

卫星地面综合测试是卫星研制过程中的重要环节,对系统功能验证及性能评估具有重要作用。传统的卫星地面综合测试系统存在研制周期长、投入较大、自动化流程不够完整、可重用性较差等不足。而北斗导航卫星地面综合测试系统采用分布式、高实时性、可配置、多主机的集成体系结构,是集计算机通讯、实时控制、实时数据处理、事后分析等功能于一体的测试系统,适用于从卫星总装集成到发射各个阶段的电气测试。通过卫星系统级的各项接口、功能、性能指标测试,表明该系统满足支持系统论证、状态确认、问题排查等测试需求,有力支撑了北斗导航卫星的成功发射和在轨运行。     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.