Abstract:The spacecraft on highly elliptic orbits fly over their apogee in the most part of their cycles, so this kind of orbit is usually applied in the satellite communication, the observation of celestial bodies and the exploration of space magnetic fields. The kinematics of multi-spacecraft formation is required to deal with the above space missions. Formulations of the relative motion on highly elliptic orbits are presented by kinematic method. On the basis of them, the necessary condition is given to maintain the long-term and close formations. The influence of relative orbital elements on the precision of this linear simplified formulation is discussed and on the dynamic characteristics of relative trajectories. The simulation results show that the formulations are more precise at the orbit apogee. If the relative orbital elements were selected properly, the design formation orbit would satisfy the requirements of the aforementioned missions.

Abstract:The relay satellite, circulating on the GEO (Geographic Earth Orbit), can view the user spacecraft on the LEO (Low Earth Orbit) and the MEO (Middle Earth Orbit) directly as well, and view the ground station directly. The relay satellite can be seen as the bridge between the user spacecrafts and the ground station. The scheduling problem within TDRSS (Tracking and Data Relay Satellite System) is a very important problem. It analyses the characteristics and the constraints of the relay satellite scheduling, and then builds the CSP (Constraints Satisfaction Problem) model of the problem based on CSP theory. The CSP model is solved with STK (Satellite Tool Kits) and simulation method. Computational experiments indicate that the performance of the CSP model is quite good.

Abstract:The alcogel prepared by sol-gel process of polydiethoxysiloxane (PDEOS) according to the mass ratio of C₂H₅OH∶ PDEOS∶HF∶H₂O=20∶10∶3∶0.5, was modified by methyltriethoxysilane(MTES) and washed with alcohol and n-hexane. The obtained gel was then dried under ambient pressure to prepare hydrophobic SiO₂ aerogel. It is shown that hydrophobic SiO₂ aerogels can be obtained when the mass ratio of MTES/ PDEOS is higher than 1.2. The contact angle between hydrophobic SiO₂ aerogels and water is larger than 110°, the densities and specific surface areas of hydrophobic SiO₂ aerogels are in the range of 125～160kg/m³ and 560～900m²/g respectively.

Abstract:Bi-phenolic methane is synthesized by the reaction of phenol and formaldehyde solution in the presence of acid catalyst. Through orthogonal design experiments, the effective regularities of synthetic conditions on the yield rate and bi-nucleus ratio of bi-phenolic methane are discussed. The properties of bi-phenolic methane, such as molecular weight, melting point and bi-nucleus ratio are analyzed and their characteristics expounded.

Abstract:The polycarbosilane (PCS)，the precursor of SiC fiber，is synthesized at 450℃ for 6h in an autoclave by thermal decomposition of polydimethylsilane (PDMS). The composition and structure of the PCS are characterized by softening point, element analysis, IR, molecular weight distribution, and NMR. Structure model of PCS is therefore proposed. IR and NMR show the presence of SiC₄and SiC₃H structure units containing Si-CH₃, Si-CH₂-Si, and Si-H groups. Elemental analysis provides an empirical formula of SiC_1.87 H_7.13O_0.03. Compared with the PCS with close softening point synthesized at normal pressure, the PCS synthesized in the autoclave has a approximate elemental composition, higher Si-H bond content, higher molecular weight, but lower ratio of SiC3H and SiC₄.

Abstract:Thermal curing process was adopted to improve traditional air-process to reduce the oxygen content of the continuous silican carbide fibers by leading oxygen as less as possible to the fibers during the curing treatment. The polycarbosilane fibers cured by thermal curing are sintered step by step. The condition of sintering process and the element composition, microstructure and properties of the fibers are studied in details by element analysis, SEM,EDX,XRD.

Abstract:It is necessary to analyze the structural characteristics of the engine key components so as to be able to predict the engine life and mitigate the components damage, and extend the engine life for improving the reliability, availability and maintainability of liquid rocket engines. The model of the turbine rotor blade with finite element analysis for the newly developing large-thrust liquid rocket engine is set up. Based on these models, characteristics analysis of structural dynamics such as modal analysis under undamped free vibration, harmonic response under undamped forced vibration and transient response under damped forced vibration, is performed respectively. Meanwhile, natural frequencies and mode shapes, harmonic response and transient response of a single turbine rotor blade, are also obtained.

Abstract:A method named MTMM for classification of the aircraft formation is proposed, followed by studying the narrow-band signal with amplitude and phase. The results based on simulated data and measured data prove that it is a helpful method to classify the number of the airborne targets for low-resolution radar.

Abstract:The efficient motion estimation algorithms are the important research hotspot in the real-time video coding-decoding technology. In order to reduce the high computational complexity of motion estimation in the video-coding, a fast adaptive motion estimation algorithm based on the context is proposed. The novel algorithm uses a kind of parallelogram pattern to search directionally, and imports secondary minimum distortion point. The basic idea of the novel algorithm is: In the process of block-matching, this novel fast algorithm uses the former search step's motion vector and the relative location between the minimum distortion point and secondary minimum point to select adaptively one parallelogram model and decide the search direction of next step, and then keeps on searching for more accurate motion vector. Experimental results show that the proposed algorithm reduced the computational complexity of the motion estimation in video-coding effectively.

Abstract:The fast multipole method is applied for calculating the radar cross section of a groove in a perfectly conducting plane. The coupled integral equations for the induced currents of a groove in a perfect conducting plane are obtained in terms of equivalent principle, and solved by using CGM and current iteration method, FMM is employed to speed up the matrix-vector multiplication. After FMM acceleration, both the computing time and memory needs are reduced from O(N²) to O(N^1.5) without increasing the complexity of implementation. Some examples are calculated, the numerical results are in perfect agreement with the MOM result.

Abstract:Some problems in the application of spatial information, such as distributed enormous data, heterogeneous format, complexity of processing and intensive computing have been obstacles to realize wide sharing and integration of spatial information. By taking grid technology and web services as its technical core, spatial information grid (SIG) shares and aggregates the distributed enormous spatial information resources to implement dynamic integration and collaboration. Based on building open seven-layer application architecture of SIG, we put, in the research, emphasis on SIG service composition. A novel service composition model named service/resource net (SRN) is proposed based on Petri net and graph theory. Moreover, an innovative service selection model (SISM) is presented to implement the dynamic service selection in the process of SIG service composition. In accordance with the application requirements of the national geological survey, an application example of ground water evaluation is given and the validity and usability of SIG are verified.

Abstract:This paper describes an approach to elimination of inference channels in the database based on rough set theory. The approach builds an incomplete decision table on all data in the database, then analyzes and discovers all the relations between non-sensitive and sensitive data with rough set theory. According to these relations, rules of inference control are generated and used to modify the data queried by generic users dynamically and most parsimoniously so as to eliminate inference channels. Experimental result shows that the approach is scalable and preserves security of inference control while improving availability of the data in the database.

Abstract:A new ranging method based on quadric difference frequency is presented. The principle of ranging is deduced in details. The rules for frequency selection are proposed，which make convenient the design of transmitter and later signal processing. The need for SNR is analyzed when solving ambiguity correctly. Compared with the uneven ranging method, its advantages are proved. Simulation results verify the validity of the method.

Abstract:An unsupervised hyperspectral image classification method simultaneously realizing the mixture of probabilistic PCA and clustering under the frame of EM algorithm is proposed. It is based on the fact that different class should have its own representative feature set, and it realizes feature extraction and classification in one step while preserving as much separability. It also possesses the advantages of PPCA model, which is more effective to high dimensional data processing. Applying the method to simulated data and real data shows that it can achieve better results compared with the method that applies PCA to all data without differentiation among classes.

Abstract:Multi-polarization, low frequency ultra-wideband synthetic aperture radar (UWB SAR) is one of the most important aspects of the radar technology. The low frequency, UWB and large processing angle result that the common SAR polarimetric calibration cannot be used. In this paper, with the system echo model, considered the electromagnetic scattering characteristics of the reference calibrator, the polarimetric calibration for the system is proposed. The computer simulation is used to validate the method.

Abstract:A new method for tracking the maneuver of a mobile vehicle by fusing the information of network-based positioning and the local sensors equipped on the vehicle is proposed. We employ the positioning system of the commercial mobile communication network as the network based positioning. The local sensors used here are internal sensors, such as position and velocity sensors of the vehicle. In order to reject random noises in the global and local position sensing, the variable-dimension Kalman filter is employed to fuse the information from different sources and estimate the position of the vehicle. The performance of this new method has been verified by simulations on the tracking of maneuvering vehicles.

Abstract:The general-purpose computer, supported by all kinds of compatible standard hardware and plenty of application softwares, has been most wildly used in the world. However, the operating system running on it is always the multi-tasks OSs, such as windows 9x/2000 and Linux, which cannot meet the need of the real-time simulation in a general way. Firstly ,the acquiring of high-resolution real-time clock is discussed. Secondly, the stability of frame time under the general-purpose OS environment is studied at length. Several methods used to carry out the real-time simulation on the general-purpose computer has been presented, and an actual general-purpose simulation system also established. The experiment results show that the real-time simulation based on the general computer is feasible.

Abstract:With the development of fabricate technology for digital signal processor(DSP), the power dissipation of the bus is the main part of the whole power dissipation in DSP. This paper researches the power saving ways for address bus、data bus、internal bus in LS-DSP . Bus coding technology has been used for that purpose. The experimental results show that the LS-DSP bus power can reduce effectively when it uses the power saving ways discussed in this paper are used.

Abstract:The linear characteristics of the ship wakes in SAR image is analyzed. Due to the fact that there are many factors which can generate the linear features, so aiming at the problem of the uncertainty in detecting the ship wake peaks in the Radon transform domain, an algorithm based on the peak morphological information to detect the ship wakes in SAR ocean imagery is proposed. The algorithm extracts all possible peaks by thresholding the Radon coefficients, and perform the continuous wavelet transform to the peak match for all these 1-dimensional local peak sections, and makes decision in the feature space finally using the decision vectors formed by the extracted parameters. The simulation and real data processing results show that the algorithm is reliable and can efficiently improve the accuracy of detection.

Abstract:Feature selection and parameters optimization of the fault classifier can enhance the fault diagnosis accuracy. Using the interdependent relationship between the feature selection and classifier parameter, a method of joint optimization of feature selection and classifier parameters is proposed to improve the diagnosis accuracy. By using the method we adopt the support vector machine (SVM) as a fault classifier, take into account of the radius-margin bounds for the accuracy evaluation of SVM classifier, and applies genetic algorithm (GA) to solve the joint optimization problem. In the gear fault diagnosis experiment, the joint optimization method guarantees better diagnosis accuracy and the optimization process has a higher rate than the single optimization of features or SVM parameters. So the joint optimization of fault features and classifier can fast achieve the better diagnosis accuracy in fault diagnosis.

Abstract:The technology of magnetic suspension control is one of the key technologies of EMS maglev train. Aiming at the nonlinearity of the magnetic suspension system, a nonlinear controller was designed. Firstly a nonlinear mathematical model of the magnetic suspension system was derived under some reasonable assumptions. Then the model was linearized exactly by means of feedback linearization, and an equivalent linear model was developed. Finally the design of a nonlinear suspension controller was presented using state feedback based on the linear model. Results of the simulation show that the controller works better than the traditional controller based on the local approximate linearization, and has robustness against the disturbance of the gap and load.

Abstract:The space-borne rubidium atomic frequency standards(RAFS) play a critical role in many space systems. Their performance and reliability will greatly influence the functions of these systems. The failure mode and effects analysis (FMEA) is applied in the space-borne RAFS to identify and rectify the failures during its development and design stages. The basic principle of the space-borne RAFS and its framework diagram are introduced. A certain space-borne RAFS is divided into six subsystems and its reliability block diagram is depicted. Each subsystem is analyzed by FMEA and a part of the FMEA table of physics package subsystem is presented as an example.

Abstract:The sensor system, especially the sensor placement, plays an importance part in the research of the health monitoring system of large-span cable-stayed bridge. The various optimum algorithms for the sensor placement at present are classified and discussed. Genetic algorithm is introduced and applied to determining the optimal position of the sensors of the monitoring system of the single-tower cable-stayed bridge of the Zhaobaoshan in Ningbo. Numerical simulation results indicates that this algorithm has a good convergence and ability to get the stable and reliable solution.

Abstract:In the battlefields of the information age, the flatting and networking organizations are the primary mode of the military organizations for network centric warfare. To explore the methodology of designing the mode of the military force, the model of PCANS is used to characterize the military organization in the traditional battlefields, on which its shortages are analyzed for organizations in the information age. Importing the information into PCANS, We advance a new approach to describe the organizations. And the essence, objective and methodology of designing the organization are presented on the organizational description in the information age.

Abstract:To solve the problem of the store and transmission of vast DEM data, an efficient compression algorithm for DEM data is presented. A technique based on the lifting scheme is designed to construct the compactly supported wavelets whose coefficients are composed of free variables. By properly selecting the coefficients of the 9-7 wavelet filter and being associated with the lifting scheme, an efficient approach via wavelet for DEM data compression is developed. The integer wavelets based on the lifting scheme only used integral addition, integral multiplication and shift, so it can be fast and easily realized via the hardware. When t=1, the integral wavelet filters approximately have the same complexity as integer wavelets 5-3, but preserve approximate quality of the compressed DEM data with the well-known CDF9-7 wavelet filters. The experiments show that the method can compress DEM data very well. Provided that the terrain figure and hypsography are maintained, the DEM data's compression ratio is 4096 and PSNR>34DB.

Abstract:The prior distribution parameters of the falling points are obtained by using the construction simulation, then the credibility of the prior information is acquired by consistent test. The bayesian estimations of the mean and variance of the falling points are obtained by considering the credibility of the prior information. An example validates that it is successful to use the simulation information, and Bayesian estimation on considering the credibility has a better confidence level.

Abstract:Genetic algorithm is altered to solve the problems restricted by the implicit formula on the basis of the research on schema theorem and canonical genetic algorithm theorem.The simulation results show that its performance of searching the global optimal solution and rapid convergence is better than that of some other GAs. It is a good way in numerical computing.