检索结果-南通市图书馆

Orbital reference frame estimation with power spectral density constraints for drag-free satellites

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2016年第6期29卷 1721-1729页

作者： Zhang Yonghe Wang Yamin Mao Qingyun liang xuwen Shanghai Institute of Microsystem and Information Technology Chinese Academy of SciencesShanghai 200050China Shanghai Engineering Centre for Microsatellites Shanghai 201210China Joint Key Laboratory of Microsatellite Chinese Academy of SciencesShanghai 201210China

The drag-free satellites are widely used in the field of fundamental science as they enable the high-precision measurement in pure gravity fields. This paper investigates the estimation of local orbital reference frame(LORF) for drag-free satellites. An approach, taking account of the combination of the minimum estimation error and power spectral density(PSD) constraint in frequency domain, is proposed. Firstly, the relationship between eigenvalues of estimator and transfer function is built to analyze the suppression and amplification effect on input signals and obtain the eigenvalue range. Secondly, an optimization model for state estimator design with minimum estimation error in time domain and PSD constraint in frequency domain is established. It is solved by the sequential quadratic programming(SQP) algorithm. Finally, the orbital reference frame estimation of low-earth-orbit satellite is taken as an example, and the estimator of minimum variance with PSD constraint is designed and analyzed using the method proposed in this paper.

关键词： Drag-free satellite Orbital reference frame Power spectral density State estimation Transfer function

A distributed routing algorithm based-on simplified topology in LEO satellite networks

在线全文

学校读者我要写书评

暂无评论

High Technology Letters 2010年第2期16卷 117-123页

作者：曾媛 liang xuwen Li Yong Shanghai Engineering Center for Micro-Satellites Shanghai 200050 P.R. China Shanghai Institute of Microsystem and Information Technology Chinese Academy of Sciences Shanghai 200050 P.R. China

In this paper, a distributed muting strategy based on simplified topology （DRBST） was proposed for LEO satellite networks. The topology of LEO satellite networks was simplified aiming at minimizing intersatellite links handover number. To optimize the route based on the simplified topology, we considered not only the transmission delay but also the queuing delay and the processing delay, which were analyzed using Markov chain and determined using a novel methodology. The DRBST algorithm was simulated in a LEO satellite networks model built using OPNET. The simulation results demonstrate that the low complexity DRBST algorithm can guarantee end-to-end delay bound. Moreover, the muting protocol cost is much less than traditional algorithms.

关键词： LEO satellite networks distributed muting strategy based on simplified topology (DRBST) inter-satellite links handover OPNET simulation delay complexity

Cloning and Characterization of the fecC Gene Necessary for Optimal Growth under Iron-Deficiency Conditions in the Cyanobacterium Anabaena sp. PCC7120

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Wuhan University Journal of Natural Sciences 2004年第4期9卷 498-502页

作者： xuwen-liang LIUYong-ding ZHANGCheng-cai LIJuan CollegeofLifeSciences CentralChinaNormalUniversityWuhan430079HubeiChina InstituteofHydrobiology ChineseAcademyofSciencesWuhan430072HubeiChina CollegeofLifeSciencesandTechnology HuazhongAgriculturalUniversityWuhan430070HubeiChina CollegeofLifeSciences CentralChinaNormalUniversityWuhan430079HubeiChina

ThefecC gene encoding a putative iron (III) dicitrate transporter was cloned from nitrogen-fixing cyanobacteriumAnabaena sp. PCC 7120, and inactivated. The mutant grows normally in medium with NO 3 ? , NH 4 + or without combined nitrogen. But in iron-deficient medium, the mutant grows slowly. Photosynthetic properties were compared between the mutant and the wildtype strain, the content of photosynthetic pigments in the mutant is lower than that of the wild-type. The results of RT-PCR experiments show that thefecC gene is expressed under iron-deficient conditions, but is not expressed under iron-replete conditions. These results revealed thatfecC gene product is required for optimal growth under iron-deficient conditions inAnabaena sp. PCC 7120. Key words Anabaena sp. PCC 7120 - fecC - iron deficiency - photosynthetic properties - expression CLC number Q 933 Foundation item: Supported by the National Natural Sciences Foundation of China (30070154), the Frontier Science Projects Program of the Institute of Hydrobiology, the Chinese Academy of Sciences (220316), State Key Project on Cyanobacterial Bloom Control in Lake Dianchi (K99-05-35-01)Biography: XU Wen-liang (1974-), male, Ph. D, research direction: molecular genetics of cyanobacteria.

关键词： Anabaena sp. PCC 7120 fecC iron deficiency photosynthetic properties expression

Effect of Iron Deficiency on Heterocyst Differentiation and Physiology of the Filamentous Cyanobacterium Anabaena sp. PCC 7120

在线全文

学校读者我要写书评

暂无评论

Wuhan University Journal of Natural Sciences 2003年第03A期8卷 880-884页

作者： xuwen-liang LiuYong-ding ZhangCheng-cai InstituteofHydrobiology ChineseAcademyofSciencesWuhan430072HubeiChina LaboratoiredeChimieBacterienne(UPR9043) CNRS31CheminJosephAiguier13402Marseillecedex20France

The effect of iron deficiency on heterocyst differentiation and some physiological properties of the filamentous cyanobacterium Anabaena sp. PCC 7120 was investigated. Under moderate iron limitation conditions, achieved by addition of iron chelator 2,2′\|Dipyridyl (<80 μmol/L) led to delayed heterocyst differentiation, no heterocyst differentiation was observed under severe iron limitation conditions, when the concentration of 2,2′\|Dipyridyl in the medium was more than 100 μmol/L . It seemed that there are certain iron\|regulated genes or operons whose function is to control heterocyst development. In addition, iron deficiency impaired the growth. Low\|iron cells had a decrease in the quantities of pigment content (chlorophyll and phycocyanin content),the whole cell in vivo absorbance spectra confirmed the decrease, the protein electrophoretic profiles revealed that iron\|deficient cells had less protein bands, with the increase of 2,2′\|Dipyridyl ,the protein bands was more and more less. And differently, iron deficiency also caused an increase of ROS (Reactive Oxygen Species)and SOD activity, it suggests that iron deficiency led to oxidative stress, which generally occured under high\|iron conditions.

关键词： Anabaena sp. PCC 7120 iron deficiency heterocyst development protein SDS \|PAGE oxidative stress

扩频通信系统PMF-FFT捕获算法检测性能的分析与提高

在线全文

学校读者我要写书评

暂无评论

高技术通讯 2012年第6期22卷 571-575页

作者：丁晟刘会杰梁旭文上海微小卫星工程中心上海200050 中国科学院上海微系统与信息技术研究所上海200050

针对扩频通信系统部分匹配滤波结合快速傅立叶变换（PMF-FFT）捕获算法由于FFTr对频偏补偿不完全而引起相关能量衰减从而导致检测概率降低的问题，研究了检测器的输出特性，利用剩余频偏存在时检测器输出相关能量扩展的特点，提出了将... 详细信息

针对扩频通信系统部分匹配滤波结合快速傅立叶变换（PMF-FFT）捕获算法由于FFTr对频偏补偿不完全而引起相关能量衰减从而导致检测概率降低的问题，研究了检测器的输出特性，利用剩余频偏存在时检测器输出相关能量扩展的特点，提出了将相邻检测单元输出值累加作为检测变量的相邻bin联合检测方案，理论推导了该方案的虚警概率、检测概率。仿真结果表明，与原检测方案相比，该方案不仅能够提高检测概率，而且在不同剩余频偏条件下的检测具有良好的鲁棒性，适用于高动态低信噪比条件下扩频信号的快速捕获。

关键词：捕获部分匹配滤波(PMF) 快速傅立叶变换(FFT) 检测

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

采用三音校准法的星载多波束天线校准系统

江苏大学学报（自然科学版） 2012年第2期33卷 181-186页

作者：赵星惟龚文斌梁旭文上海微小卫星工程中心上海200050 中国科学院上海微系统与信息技术研究所上海200050

为了解决宽带多波束天线系统中常规校准不能兼顾工作频带的低频段和高频段的问题,根据星载多波束天线系统的特点,提出了三音校准法.采用3个单音信号作为校准信号对多波束系统的通道进行测量,以二次拟合得到全工作带宽内的通道幅相特性曲... 详细信息

为了解决宽带多波束天线系统中常规校准不能兼顾工作频带的低频段和高频段的问题,根据星载多波束天线系统的特点,提出了三音校准法.采用3个单音信号作为校准信号对多波束系统的通道进行测量,以二次拟合得到全工作带宽内的通道幅相特性曲线,并采用多次测量形成拟合点,降低了测量误差的影响;再以拟合的特性曲线的逆函数进行通道幅相补偿,使全带宽内通道特性曲线成为水平直线,从而完成了单通道的校准;最后以补偿项补偿通道间幅相差异,从而达到通道间误差校准的目的.并将三音校准法应用到卫星天线的近场校准和内部校准2种校准系统中.结果表明:三音校准法比传统的单点校准和分段式校准更利于通道间误差的校准,能够有效地抑制通道的不一致性.

关键词：校准误差天线阵列多波束天线卫星天线

在线全文

学校读者我要写书评

暂无评论

星载多波束天线通道误差特性分析及校准

江苏大学学报（自然科学版） 2012年第5期33卷 549-554页

作者：赵星惟龚文斌梁旭文上海微小卫星工程中心上海200050 中国科学院上海微系统与信息技术研究所上海200050

针对星载多波束天线幅相误差对天线性能影响较大的问题,通过对多波束发射天线的射频通道在不同温度下的幅相特性进行试验测定,得到了通道幅相特性与温度的对应关系,发现不同通道的幅相特性与通道温度的关系曲线在给定温度区间内基本呈... 详细信息

针对星载多波束天线幅相误差对天线性能影响较大的问题,通过对多波束发射天线的射频通道在不同温度下的幅相特性进行试验测定,得到了通道幅相特性与温度的对应关系,发现不同通道的幅相特性与通道温度的关系曲线在给定温度区间内基本呈线性关系,且斜率基本一致,从而确定了对不同通道的幅相特性进行固定值补偿的校准策略.通过固定值补偿后,各通道的幅相特性曲线基本重合,从而消除了通道间幅相误差.进一步给出了提升温度一致性的措施,并设计了多波束发射天线的校准原理框图和校准流程图.结果表明:新的星载多波束天线幅相误差校准方法是有效的.

关键词：卫星多波束天线通道误差幅相误差校准

在线全文

学校读者我要写书评

暂无评论

基于扩展卡尔曼滤波的动量轮故障检测方法

航空学报 2010年第8期31卷 1614-1621页

作者：李知周张锐朱振才梁旭文中国科学院上海微系统与信息技术研究所上海200050 中国科学院研究生院北京100049 中国科学院微小卫星联合重点实验室上海200050 上海微小卫星工程中心上海200050

动量轮作为卫星姿态控制系统的关键执行部件,对其故障检测对维持卫星的正常运行具有重要意义。首先对动量轮系统的故障进行分析,在建立动量轮线性离散状态空间模型的基础上,把动量轮的故障检测作为时变参数系统的跟踪来处理,将动量轮的... 详细信息

动量轮作为卫星姿态控制系统的关键执行部件,对其故障检测对维持卫星的正常运行具有重要意义。首先对动量轮系统的故障进行分析,在建立动量轮线性离散状态空间模型的基础上,把动量轮的故障检测作为时变参数系统的跟踪来处理,将动量轮的模型参数作为扩展的状态空间中的状态量,使得动量轮物理模型参数与状态空间中的状态量有对应关系,通过在扩展了的状态空间上采用扩展的卡尔曼滤波,完成时变参数的跟踪。然后,将离散空间的状态量变换回连续空间中,利用物理参数与状态量的对应关系,实现对动量轮物理参数的跟踪。此方法物理意义明确,为系统的物理参数提供了定量的估计值,为进一步诊断故障原因提供了良好的基础。数值仿真表明,此方法能够通过同时检测多个故障参量,实现故障的检测并满足卫星实时性要求。

关键词：系统辨识故障检测扩展卡尔曼滤波动量轮时变系统跟踪离散系统连续化

在线全文

学校读者我要写书评

暂无评论

卫星信号快速捕获在FPGA的实现

微计算机信息 2007年第29期23卷 156-158页

作者：刘翔梁旭文中科院上海微系统与信息技术研究所上海200050

本文给出了用于低轨(LEO)卫星通信的双伪随机码直接序列扩频(DSSS)、QPSK调制下的信号多普勒频偏以及码相位二维捕获的检测策略,并给出了用于FPGA实现的系统结构,并对每个子模块给予了详细的介绍与说明,同时描述了整个算法的流程。

关键词：卫星通信直接序列扩频多普勒频偏信号捕获 FPGA