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Statistical approach to weak signal detection and estimation using Duffing chaotic oscillators

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Science china(Information Sciences) 2011年第11期54卷 2324-2337页

作者： JIN Tian & ZHANG Hua School of electronic Information engineering,beihang university,beijing 100191,china School of electronic Information engineering BeiHang University Beijing China

In this paper,we describe the statistical characteristics of weak signal detection by a chaotic Duffing oscillator,and present a new method for signal detection and estimation using the largest Lyapunov *** research has shown that weak signals can be detected by a chaotic *** researchers use the Lyapunov exponent to flag the detection of a chaotic state,but our research shows that the Lyapunov exponent follows statistical characteristics,and therefore more factors should be considered in flagging chaotic weak ***,we analyze the statistical characteristics inherent in the Lyapunov exponent calculation steps,and build up a statistical model for different chaotic states based on simulation ***,we provide expressions for false-alarm and detection probabilities,selection of driving force threshold and detection of ***,we summarize the method of signal amplitude *** research indicates that the performance of the detection system is related to sampling times and intervals,in accord with the theory of statistical signal detection.

关键词： weak signal detection Lyapunov exponent chaos Duffing oscillation statistical signal process

A Linear Domain System Identification for Small Unmanned Aerial Rotorcraft Based on Adaptive Genetic Algorithm

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Journal of Bionic engineering 2010年第2期7卷 142-149页

作者： Xusheng Lei,Yuhu Du School of the Instrumentation Science and Opto-electronic engineering,beihang university,beijing 100191,P.R.china School of the Instrumentation Science and Opto-electronic engineering Beihang University Beijing P. R. China

This paper proposes a new adaptive linear domain system identification method for small unmanned aerial *** the flash memory integrated into the micro guide navigation control module, system records the data sequences of flighttests as inputs (control signals for servos) and outputs (aircraft’s attitude and velocity information).After data preprocessing, thesystem constructs the horizontal and vertical dynamic model for the small unmanned aerial rotorcraft using adaptive *** identified model is verified by a series of simulations and *** between flight data and the one-stepprediction data obtained from the identification model shows that the dynamic model has a good estimation for real unmannedaerial rotorcraft *** on the proposed dynamic model, the small unmanned aerial rotorcraft can perform hovering,turning, and straight flight tasks in real flight tests.

关键词： small unmanned aerial rotorcraft dynamic space model model identification adaptive genetic algorithm

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A GTD model and state space approach based method for extracting the UWB scattering center of moving target

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Science china(Information Sciences) 2011年第1期54卷 182-196页

作者： WANG Jun,WEI ShaoMing,SUN JinPing & MAO ShiYi School of electronic and Information engineering,beihang university,beijing 100191,china School of electronic and Information engineering Beihang University Beijing China

Movements of the scattering center on the condition of ultra-wideband(UWB)will impact the extraction of *** paper presents an approach for extracting the moving targets’UWB scattering center parameters based on the geometrical theory of diffraction(GTD)model and the state space approach. Firstly,the UWB GTD scattering model is transformed into state-space equations in order to estimate the range and range rate through the singular value ***,the type parameter in the whole bandwidth is indicated dimension-reducedly by orthonormalized basis and estimated by traversal algorithm and minimumnorm ***,the intensity of scattering center is worked out based on the least square *** paper provides the Cramer-Rao bound(CRB)for parameter *** effectiveness of the approach is verified by computer *** approach can estimate range,range rate,reflection intensity and type parameter simultaneously in order to improve the track of scattering centers and the target identification.

关键词： scattering center extraction GTD model state space approach ultra-wideband Doppler processing

Quality evaluation for air plasma spray thermal barrier coatings with pulsed thermography

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Progress in Natural Science:Materials International 2011年第4期21卷 301-306页

作者： Shi-bin ZHAO~1,Cun-lin ZHANG~2,Nai-ming WU~3,Hua-ming WANG~1 1.School of Materials Science and engineering,beihang university,beijing 100191,china 2.department of Physics,Capital Normal university,beijing 100048,china 3.School of Jet Propulsion,beihang university,beijing 100191,china School of Materials Science and engineering Beihang University Beijing 100191 China department of Physics Capital Normal University Beijing 100048 China School of Jet Propulsion Beihang University Beijing 100191 China

Pulsed thermography(PT) as a non-contact non-destructive evaluation(NDE) technique was employed to examine as-sprayed air plasma spray(APS) thermal barrier coatings(TBCs) for quality *** and micro-structural characteristics play a vital role in determining the *** this paper,PT logarithmic peak second-derivative method was adopted to measure the thickness of top *** dependent thermal images were used to characterize the microstructure which was confirmed by scanning electron microscope(SEM).The results showed that there was relationship between the temperature distribution of the surface and microstructure change in *** distribution in thermal images and measurement results of thickness were in fairly good agreement with the microstructure *** can be concluded that it was possible to employ these NDE methods as quality evaluation for as-sprayed TBCs.

关键词： thermal barrier coatings(TBCs) non-destructive evaluation(NDE) pulsed thermography microstructure thickness measurement

An improved constrained steering law for SGCMGs with DPC

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Acta Mechanica Sinica 2009年第5期25卷 713-720页

作者： Lei Jin Shijie Xu department of Guidance, Navigation and Control,School of Astronautics, beihang university, 100191 beijing, china department of Guidance Navigation and Control School of Astronautics Beihang University Beijing China

An improved constrained （IC） steering law for single gimbal control moment gyros （SGCMGs） with deformed pyramid configuration （DPC） is proposed, First of all, the original system with five pyramid configuration （FPC） whose two adjacent gyros are in failure state is reconfigured as a degraded system with DPC. Then, the singular angular momentum hypersurfaces of the original and the degraded systems are plotted via the singular angular momentum equa- tion of SGCMGs. Based on singular surfaces, the differences between FPC and DPC in singularity and momentum envelope are obtained directly, which provide an important reference for steering law design of DPC. Finally, an IC steering law is designed and applied to DPC. The simulation results demonstrate that the IC steering law has advantages in simplicity of calculation, avoidance of singularity and exactness of output torque, which endow the degraded system with fine controllability in a restricted workspace.

关键词： Single gimbal control moment gyros (SGCMGs) - Deformed pyramid configuration (DPC) Failure Singularity - Steering law

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Flocking shape analysis of multi-agent systems

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Science china(Technological Sciences) 2010年第3期53卷 741-747页

作者： YANG JiChen,LU QiShao &LANG XiuFeng department of Dynamics and Control,beihang university,beijing 100191,china department of Dynamics and Control Beihang University Beijing China

In this paper,we consider the shape control in flocking behavior of a multi-agent system with a virtual *** the traditional flocking control terms,which include a gradient-based term,a velocity consensus term and a navigational feed-back in general,a new piecewise smooth neighbor-based local controller is added to regulate the configuration to the desired flocking *** agent velocities approach the desired velocity asymptotically,while collisions among agents can be ***,based on the proved stability,we obtain three kinds of flocking shapes,such as those in a single line,vee shape or corner *** numerical simulation results are provided to demonstrate theoretical issues.

关键词： flocking non-smooth control multi-agent system

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A novel spaceborne SAR wide-swath imaging approach based on Poisson disk-like nonuniform sampling and compressive sensing

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Science china(Information Sciences) 2012年第8期55卷 1876-1887页

作者： SUN JinPing,ZHANG YuXi,TIAN JiHua&WANG Jun School of electronic and Information engineering,beihang university,beijing 100191,china School of electronic and Information engineering Beihang University Beijing China

Since the range swath width in the conventional single channel spaceborne synthetic aperture radar(SAR)is restricted by the system parameters,there is a trade-off between the azimuth resolution and the swath width in order to satisfy the Nyquist sampling *** this paper,we propose a novel spaceborne SAR wide-swath imaging scheme based on compressive sensing(CS)for the sparse *** proposed method designs a Poisson disk-like nonuniform sampling pattern in the azimuth direction,which meets the demand of wider swath by restricting the smallest time interval between any two azimuth samples,with the conventional sampling pattern preserved in the range *** a similar way to the processing procedure of spectral analysis(SPECAN)algorithm,the linear range migration correction(RMC)is realized while carrying out range compression,which can meet the demand for focusing with middle level *** reduce the computation load of CS reconstruction,we propose a novel fast reconstruction algorithm based on nonuniform fast Fourier transform(NUFFT),which greatly reduces the computation complexity from O(2M N)to O(4N log N).Experiment results validate the effectiveness of the proposed methods via the point target simulation and the Radarsat-1 raw data processing in F2 mode.

关键词： SAR wide-swath imaging compressive sensing NUFFT

Effects of surface modification on thermal cycling lifetime of thermal barrier coatings with HVOF NiCrAlY bond coat

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Progress in Natural Science:Materials International 2012年第3期22卷 237-243页

作者： Liyong Ni, Chungen Zhou department of Materials Science and engineering, beijing university of Aeronautics and Astronautics, beijing 100191, china department of Materials Science and engineering Beijing University of Aeronautics and Astronautics Beijing 100191 China

NiCrAlY bond coat was prepared by HVOF (high-velocity oxygen fuel) spray on nickel-based superalloy. Surface treatments like grit-blasting, shot-peening and vacuum treatment methods were carried out in order to study the effects of surface modification on thermal cycling lifetime of TBCs. The surface-modified TBCs exhibited better thermal shock resistance. Failure of TBCs with the as-sprayed bond coat occurred within the top coat and at the interface between spinels and the top coat, while that of after shot-peening, grit-blasting and vacuum treatment occurred mainly within the top coat. TGO (thermally grown oxide) formed on as-sprayed bond coat was composed of a Ni(Al,Cr)2O4 spinels outer layer and a Al2O3 inner layer. But, a continuous and uniform Al2O3 formed after surface modification. Formation of the mixed oxides (spinels) on the as-sprayed bond coat accelerated the failure of TBCs.

关键词： Thermal barrier coatings NiCrAlY HVOF Thermally grown oxide (TGO)

Self-Organizing Tunnel Peers

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计算机工程 2002年第S1期28卷 7-12页

作者： CHEN Maoke , LI Xing (department of electronic engineering, Tsinghua university, beijing 100084,china ) department of electronic engineering Tsinghua University Beijing 100084China

Tunneling is an important approach in IPv6 transition techniques. The tunnel broker model provides a way to build virtual IPv6 networks without manual ***, neither it adapts performance variation on the IPv4 infrastructure, norit is a scalable solution for a wide-area IPv6 networking environment. In this paper, a self-organizing tunnel peer (SOTP) model is *** peers are clustered in the SOTP system so that optimization is scalable. Four primitive operations related to --cluster constructionarrest,release,division and deathendow the system with the nature of self-organization. Occurrence and behavior of the operations are decided by criteria on the IPv4 end-to-end performance; hence measurement is an indispensable component of the system. The metabolism of cluster relaxes the requirement to accuracy of measurement and optimization.

关键词： S elf-organizationTunnelingEnd-to-end measurementIPv6