Abstract:A designing method of supersonic nozzle with controllable contour based on B-Spline curve and characteristic line algorithm is proposed. The contour of the nozzle was adjusted by assigning the distribution of Mach number on the nozzle’s axis. The reliability of the designing method was validated by numerical simulation, which shows that the outflow of the nozzle with high quality can be produced and the contour can be adjusted freely. The result also shows that the nozzle designed by the proposed method can produce better flow than the minimal length nozzle(MLN) with the same length.

Abstract:Space electromagnetic docking technology has perfect application for on-orbit servicing, but the electromagnetic and geomagnetic torques it brings create disturbances to the docking attitude. Also, the problems resulted from nonlinearity and coupling properties exist in the attitude controller design of space electromagnetic docking. The combined method of feedback linearization andH_∞, extended state observer andH_∞was proposed to design robust attitude controller for absolute/relative dynamics respectively, and the mentioned problems are better resolved. The advantages and shortages of the two control strategies are compared and researched, and the feasibility of designed controllers is verified by simulation. From theoretical research and simulation verification, it is right to put forward that the two control strategies are feasible and have better robust performance to model parameter change and outer disturbance, and the strategy of relative attitude control design is better for its preferably using measure information and no state estimator needs to be added.

Abstract:A hardware-in-the-loop simulation system for X-ray pulsar navigation was built in order to do some research for the key technologies in X-ray pulsar navigation field. The system consists of an X-ray pulsar source simulation unit, an X-ray photon receive unit and a navigation estimate unit. The system can simulate X-ray pulsar with different intensities, periods and pulse profiles. The TOA of individual X-ray photon was recorded, and the pulse profile was reconstructed with these data. By comparing the measured pulse profile with the standard pulse profile of the X-ray pulsar source generator, the pulse TOA and the navigation estimation were calculated in the DSP chip. This system is proved effective in test some pulsar navigation algorithms, and can provide reference for the test of feasibility, dynamics and the project application for related X-ray pulsar navigation.

Abstract:A theoretical and experimental investigation of the vibration characteristics of fluid-filled tank with internal pressure is presented. The dynamic equations of vibration are based on the elastic mechanics and velocity potential theory. The form related to the difference of pressure inside and outside was given by analysis of its effects on the tank. Also the form related to the solid-fluid interaction was given by analysis of its effects. The classic boundary-value approach was used here to calculate the natural frequencies of the tank. A modal experiment about vibration characteristics of fluid-filled tank with internal pressure was conducted, and the frequencies were measured. Results of theoretical calculation agree with the experimental data, which indicates that the frequencies of the tank decrease when filled with liquid, but they increases with internal pressure, compared with that of the empty tank. Further analysis of the results shows the effects of factors, such as the wave number, internal pressure, fluid density, structural geometric parameters and flexural rigidity of the tank on the dynamical behaviors.

Abstract:A method of hit point forecasting based on “current” statistical model is proposed for maneuvering target attacked by missiles. The method detects the target maneuvering in real time. In addition, it forecasts the hit point. Based on the forecasting, the optimal guidance law for maneuvering target attacking has been studied, while the analytic solution has been obtained. Based on the proposed method, assumption of target maneuvering model is needless. The results of simulations of several hypothetical scenes have proved that the method is effective.

Abstract:The near-space airship provides a unique and promising platform for telecommunication, broadcasting relays, surveillance, and scientific exploration. A key control technical challenge for a near-space airship is station keeping, the ability to remain fixed over a geo-location. A fuzzy variable structure control approach for an airship is proposed. First, problem formulation of an airship’s attitude control was derived. Second, the attitude control system was designed by using the variable structure control theory, and a fuzzy system was used to turn the control gains for better performance of eliminating chattering. Finally, simulation results demonstrate the effectiveness and robustness of the proposed control approach in the presence of parameter uncertainties.

Abstract:The ground forces have to face more and more threat from the space in future operations. The primary threat is coming from reconnaissance satellites. The threat assessment method of optics imaging reconnaissance satellite was studied. The methods to evaluate image quality of remote sensing satellites and the influence factors of image quality were discussed. The ground target discrimination probability model of optics image reconnaissance satellites was formulated, and amended by influence coefficients of illumination, weather and contrast. Taking into account military task, the expressions of threat degree were formulated when target size was given. The threat degree was then divided into several rankings according to the target size to support the military operations decision, and the evaluation method of threat ranking of optics image reconnaissance satellites was presented. Finally, the method was applied to threat evaluation of an optics image reconnaissance satellite, and the result was given.

Abstract:Electrodeposition was used to fill the voids of PS colloidal crystals on silicon wafer with Ni and Ni inverse opal was obtained. The influence of chemical etching of silicon wafer on the electrodeposition of Ni was studied by using cyclic voltammetry scan. The resulted Ni inverse opal was characterized by scanning electron microscopy and X-ray diffraction. It showed that chemical etching of silicon surface is beneficial for the deposition of Ni on silicon wafer. Ni grown in the voids of PS colloidal crystals is the polycrystalline phase and the ordered porous structure of Ni is formed after the removing of the PS template.

Abstract:Various kinds of flame retardants mixed together will improve the flame retardation significantly. Effects of a mixture of microencapsulated red phosphorus/aluminum hydroxides/stibium oxides/methyl phosphoric dimethyl on flame retardant performance and mechanical properties of the matrix resin 9001 were investigated, and a new price-advantages resin system which showed excellent mechanical and flame retardant performance was determined. The test results showed that the properties of resin 9001 with flame retardant system 12%MRP,50%Al(OH)₃,2%Sb₂O₃ is the best of all. Viscosity of the resin system at room temperature is about 100mPa·s, and the gel time of the resin is beyond 80 min, which satisfies the requirement of RTM and VIMP process for large composite parts. The tensile strength and modulus of the glass fabric reinforced the resin composites are 215.4MPa and 13.85GPa, respectively. The bending strength and modulus are 177.15MPa and 13.36GPa, respectively. And the LOI of the composites is 39.7.

Abstract:Compressed Sensing (CS) is a new framework for simultaneous sensing and compression, and how to recover sparse signal form limited measurements is the key problem in CS. A fast and stable method, called Expectation Minimization of approximate norm (abr. EML0), is proposed for sparse signal reconstruction with noisy measurements. The basic idea of the method is that sparse signal is recovered by minimizing the expectation of approximate norm, and then the expectation model by statistical character of noise is simplified so that the expectation model can be solved by the steepest descent method. Simulation results show that the proposed method provides better accuracy than existing methods at lower computational cost.

Abstract:Considering the conditionality of the Polarization Sensitive Array (PSA) in realization, an original Alternate Polarization Array (APA) is proposed. The ultimate filtering performance is presented theoretically and numerically, which is contrasted with that of PSA comprehensively. Compared with the PSA, the filtering performance of APS approaches that of PSA, but the equipments and the degree of freedom is cut by half. The APA overcomes the disadvantages in implementation of PSA. Therefore, APA has great potential to be used in arrayed radar and other fields. 

Abstract:A closed analytical model is developed for the performance analysis of wireless multi-hop path. The research first analyzed the interference within the multi-hop path which is the cause of the intra-flow contention problem and derived the model for its quantitative calculation, and then it modeled the multi-hop path as a queuing network and derived its analytical model for performance analysis based on diffusion approximation method. Finally it calculated the capacity of the multi-hop path under the constraint of network stability. This model can be used to explore the transmission capacity of the multi-hop wireless networks and to analyze its ability to support QoS applications. The accuracy of the proposed model is validated through comparing the numerical results and the simulation results.

Abstract:To integrate multiple location estimates obtained at different time instants by a three-satellite TDOA-based passive location system, a method based on sub-covariance weighting is proposed. Based on the outcomes of the location precision analysis of a single estimate, the algorithm yields an integrated estimate of the spatial location through a two-step process: firstly, by using the inverse of the sub-covariance as the weighting matrix, it estimated two of the three coordinates through weighted least square (WLS); secondly, it calculated the last one coordinate by solving the WGS-84 ellipsoid model function of the earth. Simulations show that the proposed method, compared with the existing methods, can significantly increase the location precision.

Abstract:TOPSAR (Terrain Observation by Progressive Scans) is a novel spaceborne SAR mode for wide-swath observation, which solves the scalloping problem of ScanSAR though steering antenna beam in azimuth direction. The relationship between azimuth resolution and cycle time of TOPSAR was derived. Furthermore, the constraint of parameters was analyzed and the flow of engineering parameter design was presented. Finally, a TerraSAR-X like sample was provided and a simulation was conducted with the design result in SBRAS (SpaceBorne Radar Advance Simulator). The results show the effectiveness of the design.

Abstract:The arithmetic of decimation and synchronisation of Base-band signal is a key problem in space-based AIS(Automatic Identification System) processing. Aiming at the defect of the Detection of Striding across Zero and the Early-late Gate, a method to decimate and synchronise the base band signal based on energy measurement was proposed. We divided the base-band signal into segments with the same length according the rate of sampling and the rate of code, and then we calculated the measurement of corresponding sampling point of every segment. Finally we chose the sequence number of the maximum energy measurement as the best decimation and synchronisation sampling point, which has the character of maximum SNR. Numerical performance of the proposed methods performs better than the existing ones. 

Abstract:In weak GNSS signal environments, due to navigation data bit, the dynamic of receiver and the quality of receiver’s oscillator, the traditional carrier loop cannot use long coherent integration time to enhance input SNR of the loop. A navigation data bits estimation method based on FFT is proposed, which just needs to calculate the FFT of one combination of data bits’ signs. The FFT of the received signal under any other data bits combination can be obtained through a few additions. The proposed method reduces the calculation complexity of navigation data bits’ signs estimation. Based on the estimation of the signs and bit edges of navigation data bits, the proposed method can adopt short coherent integration time samples over long time and FFT to discriminate doppler frequency error, which can overcome the SNR degradation introduced by receiver’s dynamic and doppler frequency estimation error over long coherent integration time and enhance the output SNR of the loop. Simulation results show that the proposed carrier tracking method can track carrier frequency in weak signal and low dynamic environments.

Abstract:In multiple platform electronic reconnaissance system, time difference of arrival (TDOA) can be used for pulse sorting. A method for TDOA sorting based on recursive extended histogram is proposed to deal with both the problem of misleading TDOA clusters caused by high pulse repetitive frequency (PRF) emitters and the problem of less pulse accumulation caused by ultra-low PRF emitters. TDOA data were formed into an extended histogram structure, which is processed recursively to detect and sort out the pulses of each emitter. By defining the extension operator, the misleading TDOA clusters could be removed, and the histogram noise level decreased step by step as well, so the method improved the performance of TDOA sorting effectively. Simulation results show that the method is applicable and effective.

Abstract:Website topics, describing aggregation and classification of website information, embodying information logic structure, is crucial for website information analysis. Analysis of logical structure is the reverse process of website design. In order to accurately analyze the site topics, the research proposed a topic structure model describing the organizational forms, logic relations and related properties of different website’s topics in a formal way, providing the necessary theoretical basis for the topic oriented web information extraction. On this basis, navigation-based topic structure induction was proposed with algorithm and experimental analysis to automatically construct topic structure of websites. Experimental results show that topic structure model generalizes most of the site’s topic structural characteristics, while the navigation based topic structure induction can correctly establish the site's topic structure, and has a faster running time.

Abstract:The direction-of-arrival (DOA) estimation for target and decoy under the towed radar decoy jamming is the precondition to achieve correct selection of target. The fact that target and decoy both exist within radar beam causes the merging of the radar echoes aliasing and measurement, and leads the regular processing of observation extraction and parameter measurement to fail. Through utilizing the information about the unknown parameter embodying in the covariance matrix of conditional probability distribution of the sum/diff channel echoes, the explicit solution for the DOA estimation of target and decoy was obtained. In order to satisfy the need of relative power ratio (RPR) in the estimation processing, the twice joint estimation algorithm for DOA based on circular estimation of RPR utilizing the information about jamming detection, radar measuring and target tracking was proposed. Simulation results with different conditions proved the performance effectiveness of the proposed method.

Abstract:Optical components with freeform surface can achieve excellent performance. It is used more and more widely in the modern optical system. Slow Tool Servo (STS) is a new technique to machining freeform surface. Due to the complexity of freeform surface and the particularity of STS, the relative position relationship between tool and work piece must be deeply researched. In this research, STS machining technique was introduced. Two tool geometry selection methods were proposed and researched on. One of the two methods was based on section curves and the other was based on whole surface using NURBS.

Abstract:A trajectory planning problem for a single unmanned combat aerial vehicle (UCAV) performing an air-to-surface multi target attack mission was studied. First, this problem was mathematically formulated as a variant of the traveling salesman problem (TSP), called the dynamic-constrained TSP with Neighborhoods (DCTSPN). A novel planning algorithm based on an updatable probabilistic roadmap (PRM) was then presented to solve the DCTSPN. This algorithm blends the sampling-based motion planning ideas with combinatorial optimization, and can reduce the complicated trajectory planning problem in high-dimensional continuous state space to a routing problem on a finite discrete graph, while maintaining completeness guarantees (in a probabilistic sense). The entire planning procedure was divided into two phases: 1) In offline preprocessing phase, the original problem was converted into a standard ATSP (Asymmetric TSP) by Halton quasirandom number generator and the Noon-Bean transformation algorithm; 2) In online querying phase, a fast heuristic searching algorithm was used to solve the ATSP. To generate dynamically feasible flight trajectories, a trajectory planning algorithm based on the Gauss pseudospectral method (GPM) was developed. Numerical experiments indicate that the algorithm adopted can generate both feasible and near-optimal attack trajectories quickly for online purposes.

Abstract:Based on the principle of gear engaging and tribology theory, by simplifying spiral bevel gear to spur gear, and by considering the impact of gear contact ratio and time-variant factors including meshpoint relative sliding velocity, normal load, and friction coefficient, the computing model of friction power loss for spiral bevel gear was established. According to the model, the friction power loss was calculated and analyzed by taking the spiral bevel gear of a helicopter tail reducer as research object. The results show that the computing model is reasonable, simple and reliable, and has a reference value to calculate the friction power loss for spiral bevel gears.

Abstract:While registering transfer level or even behavioral level, the hardware description language is widely used, and Satisfiability Modulo Theories(SMT) gradually replaces Boolean Satisfiability(SAT), and plays an important role in VLSI formal verification. A minimal unsatisfiable subformula can help automatic tools to rapidly locate the errors. A depth-first-search algorithm is proposed to extract minimal unsatisfiable subformulae in SMT to adopt depth-first searching and incremental solving strategy. The experimental results show that the depth-first-search algorithm effectively derived minimal unsatisfiable subformulae, and is more efficient than the breadth-first-search algorithm, which is the best method for computing the minimal unsatisfiable subformulae in SMT, with the number of variables and clauses in the original formulae increasing.

Abstract:With the help of Technology Computer-Aided Design (TCAD) 3-D simulation, the dependence of process parameters on single event transient (SET) in 25 nm raised source-drain FinFET (Fin Field Effect transistor) was studied. It is found that the fluctuation of some process parameters exert remarkable impact on the charge collection, thus affecting the SET pulse width propagated in circuits. For the best corner process parameters, the amount of charge collected can be reduced by 38%, whereas the charges will increase 79% for the worst corner process, which foumulates a new idea for the SET mitigation and radiation-harden design in FinFET.

Abstract:The security of block cipher Zodiac against impossible differential cryptanalysis was re-evaluated. By analyzing the properties of diffusion layer P, two new 14-round impossible differentials of Zodiac were introduced. Based on the new impossible differential characteristics and combining with the Early-Abort technique, an effective attack was applied to the full 16-round Zodiac, and the data complexity was 285.6 chosen plaintexts and the time complexity is only 232.6 encryptions. Compared with the previous best result, the time complexity in this paper decreases with a factor of 233. The result shows that Zodiac is vulnerable to impossible differential cryptanalysis due to its poor diffusion.

Abstract:Partial differential equation (PDE) is one of the main methods for image processing and its significance is usually shown by the corresponding variable model, according to which the PDE can be optimized further to reach ideal results. Based on the classic Beltrami flow for image processing, a new metric tensor model on the image manifold is proposed for image denoising. The Beltrami flow with this metric tensor has clear geometrical significance, which induces the optimal selection method for parameters in the metric tensor. Meanwhile, this model provides a unified framework for the classic PDE based image denoising methods and the optimal selection method for its parameters makes the Beltrami flow have a better balance between smoothing the noise and preserving the edges. The experiment results show that the image denoising quality is greatly improved, especially for the images with abundant edges.

Abstract:Perfect nonlinear function is the optimal function on finite fields with odd character that can resist differential cryptanalysis. All the six classes of the already known perfect functions currently are 2-1. This study proved that when is Dembowski-Ostrom function or Coulter-Matthews function on , the preimage distribution of the perfect nonlinear function has just two kinds of values, one corresponds to all the elements of quadratic residual on , and the other kind corresponds to all the non quadratic residual on .

Abstract:A color and gradient feature based image segmentation and recognition algorithm is proposed for Mycobacterium Tuberculosis (TB) objects in microscopic images. First, the input color image was pre-segmented based on the HSV color space using the threshold method according to the prior information. Then, the original image was transformed to the CIE L*a*b* color space, and the L component image was segmented using an adaptive threshold method to get finer segmentation result. In order to accommodate the complex variety of image background, all the suspected objects were verified according to the “hue consistence” assumption and the false objects were rejected. To identify the TB bacilli, the algorithm used five shape feature descriptors, including the area, the perimeter, the ratio of width to height, the compactness and the roughness, and two gradient feature descriptors, the gradient magnitude weighted average (GMWA) and the gradient magnitude variance average (GMVA) respectively, and makes the judgment through Bayes classifier. Experimental results show that the proposed algorithm can accommodate the complex variety of specimens and the image background, and a high recognition rate (91%) can been obtained.

Abstract:For detecting review spam in the Internet automatically, an method based on resistance network is proposed. By treating the distance between two reviews as a resistance, we represent the given dataset as a resistance network and the resistance distance between two nodes is a measure of the semantic distance between them. Spam reviews are semantic outliers in this network. An electrical outlier factor (EOF) for each review based on its influence on the power dissipated of the network was used to detect the spam reviews. Experimental results testified that EOF is suitable for detecting review spam, and is efficient and effective．

Abstract:Disjoint paths routing catches special attention in multipath research. Shortest disjoint paths problem has been studied maturely, while the research of widest disjoint paths problem is just under development. In this paper, we presented a problem of finding the widest pair of arc-disjoint paths in a directed graph. It differs from Multipath Flows, which may be transformed into the problem of Maximum Flow and Minimum Cut. Then we propose a polynomial algorithm for it with time complexity O(mnlogn). It is not required to reassign flux at common vertices on the widest pair of paths, and this scheme can be implemented easier in real networks.

Abstract:The reverse H?lder type inequality for A-harmonic equations is a very important tool to discuss the integrability for solutions to these equations. In the present paper we dealt with a kind of generalized homogeneous A-harmonic equations formulated by d^*A(x,κ(u－u_Ω),du)=0.The reverse H?lder type inequality were established for the weak solution u of these equations, very similar to the traditional one. The results obtained here for the special cases of κ=0 can lead to the corresponding situation considered before now, which can be regarded as the foundation for studying the regularity and integrability to this kind of equations.

Abstract:The stochastic non-Newtonian flow driven by Lévy noises was studied. By the tight compactness of distribution of the solution for finite-dimensional approximate in a Hilbert space, and Skorohod embedding theorem and representation of martingale, the existence of the martingale solution was confirmed. 