随着卫星导航系统的快速发展,基于低地球轨道(low earth orbit,LEO)卫星的高精度可信导航已成为当前研究的热点.然而,LEO卫星导航的安全可信问题一直阻碍其大规模应用,基于扩频码和导航电文(spreading code and navigation data based a...随着卫星导航系统的快速发展,基于低地球轨道(low earth orbit,LEO)卫星的高精度可信导航已成为当前研究的热点.然而,LEO卫星导航的安全可信问题一直阻碍其大规模应用,基于扩频码和导航电文(spreading code and navigation data based authentication proposal,SNAP)认证方案在解决上述问题中展现了良好势头.本文的重点是解决SNAP信号的间歇跟踪算法及性能分析,并得到跟踪误差的解析表达式.研究结果表明:由于间歇跟踪导致的误差累积服从高斯分布,其均值与多普勒频移变化率成正比,均方差可等价于载噪比(carrie noise ratio,CNR)的损失,相较载波环,码环受多普勒的影响较小.本文的研究结果为间歇跟踪结构下接收机系统参数设计提供重要理论参考.展开更多
构建了聚光比为2.3的曲柄连杆跟踪式复合抛物面聚光（CPC）太阳能集热器。改进了太阳入射角模型,推导了太阳入射角公式,并建立了集热器的光学效率模型。分析了不同太阳入射角下CPC集热器的聚光行为,考察了春分、夏至、秋分和冬至日的太...构建了聚光比为2.3的曲柄连杆跟踪式复合抛物面聚光（CPC）太阳能集热器。改进了太阳入射角模型,推导了太阳入射角公式,并建立了集热器的光学效率模型。分析了不同太阳入射角下CPC集热器的聚光行为,考察了春分、夏至、秋分和冬至日的太阳入射角变化规律,比较了不同放置方式和跟踪模式下CPC集热器的光学性能。模拟得到横向投影角（θt）是影响CPC集热器光学性能的主要因素,θt为-23.5°～23.5°时,入射角修正因子（IAM）达到0.95～1.14;跟踪可有效缩小θt,使CPC集热器均处于高效聚光状态。采用间歇跟踪即可获得较高的光学性能。对于该CPC集热器在南京地区采用南北放置三点间歇跟踪模式光学性能最佳,日均能量密度最大值约为1.122 k W/m^2,不同节气下的日均能量密度比南北放置连续跟踪时高5%,达到固定模式的1.86～2.37倍。展开更多
Based on an equivalent two-dimensional Fornasini-Marchsini model for a batch process in industry, a closed-loop robust iterative learning fault-tolerant guaranteed cost control scheme is proposed for batch processes w...Based on an equivalent two-dimensional Fornasini-Marchsini model for a batch process in industry, a closed-loop robust iterative learning fault-tolerant guaranteed cost control scheme is proposed for batch processes with actuator failures. This paper introduces relevant concepts of the fault-tolerant guaranteed cost control and formulates the robust iterative learning reliable guaranteed cost controller (ILRGCC). A significant advantage is that the proposed ILRGCC design method can be used for on-line optimization against batch-to-batch process uncertainties to realize robust tracking of set-point trajectory in time and batch-to-batch sequences. For the convenience of implementation, only measured output errors of current and previous cycles are used to design a synthetic controller for iterative learning control, consisting of dynamic output feedback plus feed-forward control. The proposed controller can not only guarantee the closed-loop convergency along time and cycle sequences but also satisfy the H∞performance level and a cost function with upper bounds for all admissible uncertainties and any actuator failures. Sufficient conditions for the controller solution are derived in terms of linear matrix inequalities (LMIs), and design procedures, which formulate a convex optimization problem with LMI constraints, are presented. An example of injection molding is given to illustrate the effectiveness and advantages of the ILRGCC design approach.展开更多
Nowadays, a considerably large number of documents are available over many online news sites (e.g., CNN and NYT). Therefore, the utilization of these online documents, for example, the discovery of a burst topic and i...Nowadays, a considerably large number of documents are available over many online news sites (e.g., CNN and NYT). Therefore, the utilization of these online documents, for example, the discovery of a burst topic and its evolution, is a significant challenge. In this paper, a novel topic model, called intermittent Evolution LDA (iELDA) is proposed. In iELDA, the time-evolving documents are divided into many small epochs. iELDA utilizes the detected global topics as priors to guide the detection of an emerging topic and keep track of its evolution over different epochs. As a natural extension of the traditional Latent Dirichlet Allocation (LDA) and Dynamic Topic Model (DTM), iELDA has an advantage: it can discover the intermittent recurring pattern of a burst topic. We apply iELDA to real-world data from NYT; the results demonstrate that the proposed iELDA can appropriately capture a burst topic and track its intermittent evolution as well as produce a better predictive ability than other related topic models.展开更多
文摘随着卫星导航系统的快速发展,基于低地球轨道(low earth orbit,LEO)卫星的高精度可信导航已成为当前研究的热点.然而,LEO卫星导航的安全可信问题一直阻碍其大规模应用,基于扩频码和导航电文(spreading code and navigation data based authentication proposal,SNAP)认证方案在解决上述问题中展现了良好势头.本文的重点是解决SNAP信号的间歇跟踪算法及性能分析,并得到跟踪误差的解析表达式.研究结果表明:由于间歇跟踪导致的误差累积服从高斯分布,其均值与多普勒频移变化率成正比,均方差可等价于载噪比(carrie noise ratio,CNR)的损失,相较载波环,码环受多普勒的影响较小.本文的研究结果为间歇跟踪结构下接收机系统参数设计提供重要理论参考.
文摘构建了聚光比为2.3的曲柄连杆跟踪式复合抛物面聚光（CPC）太阳能集热器。改进了太阳入射角模型,推导了太阳入射角公式,并建立了集热器的光学效率模型。分析了不同太阳入射角下CPC集热器的聚光行为,考察了春分、夏至、秋分和冬至日的太阳入射角变化规律,比较了不同放置方式和跟踪模式下CPC集热器的光学性能。模拟得到横向投影角（θt）是影响CPC集热器光学性能的主要因素,θt为-23.5°～23.5°时,入射角修正因子（IAM）达到0.95～1.14;跟踪可有效缩小θt,使CPC集热器均处于高效聚光状态。采用间歇跟踪即可获得较高的光学性能。对于该CPC集热器在南京地区采用南北放置三点间歇跟踪模式光学性能最佳,日均能量密度最大值约为1.122 k W/m^2,不同节气下的日均能量密度比南北放置连续跟踪时高5%,达到固定模式的1.86～2.37倍。
基金Supported in part by NSFC/RGC joint Research Scheme （N-HKUST639/09）, the National Natural Science Foundation of China （61104058, 61273101）, Guangzhou Scientific and Technological Project （2012J5100032）, Nansha district independent innovation project （201103003）, China Postdoctoral Science Foundation （2012M511367, 2012M511368）, and Doctor Scientific Research Foundation of Liaoning Province （20121046）.
文摘Based on an equivalent two-dimensional Fornasini-Marchsini model for a batch process in industry, a closed-loop robust iterative learning fault-tolerant guaranteed cost control scheme is proposed for batch processes with actuator failures. This paper introduces relevant concepts of the fault-tolerant guaranteed cost control and formulates the robust iterative learning reliable guaranteed cost controller (ILRGCC). A significant advantage is that the proposed ILRGCC design method can be used for on-line optimization against batch-to-batch process uncertainties to realize robust tracking of set-point trajectory in time and batch-to-batch sequences. For the convenience of implementation, only measured output errors of current and previous cycles are used to design a synthetic controller for iterative learning control, consisting of dynamic output feedback plus feed-forward control. The proposed controller can not only guarantee the closed-loop convergency along time and cycle sequences but also satisfy the H∞performance level and a cost function with upper bounds for all admissible uncertainties and any actuator failures. Sufficient conditions for the controller solution are derived in terms of linear matrix inequalities (LMIs), and design procedures, which formulate a convex optimization problem with LMI constraints, are presented. An example of injection molding is given to illustrate the effectiveness and advantages of the ILRGCC design approach.
基金supported by the National Basic Research Program of China under Grant No. 2012CB316400the National High Technology Research and Development Program of China under Grant No. 2012AA012505the Fundamental Research Funds for the Central Universities
文摘Nowadays, a considerably large number of documents are available over many online news sites (e.g., CNN and NYT). Therefore, the utilization of these online documents, for example, the discovery of a burst topic and its evolution, is a significant challenge. In this paper, a novel topic model, called intermittent Evolution LDA (iELDA) is proposed. In iELDA, the time-evolving documents are divided into many small epochs. iELDA utilizes the detected global topics as priors to guide the detection of an emerging topic and keep track of its evolution over different epochs. As a natural extension of the traditional Latent Dirichlet Allocation (LDA) and Dynamic Topic Model (DTM), iELDA has an advantage: it can discover the intermittent recurring pattern of a burst topic. We apply iELDA to real-world data from NYT; the results demonstrate that the proposed iELDA can appropriately capture a burst topic and track its intermittent evolution as well as produce a better predictive ability than other related topic models.
