Abstract:To solve the problem of color distortion existing in low illumination image enhancement method, a novel low illumination image enhancement method based on dark-channel prior with the capability of preserving scene color is presented. First, the intensity of every image pixel with dark-channel prior is estimated directly, and for dealing with wrong dark-channel values in white region, the regions with wrong grey values by calculating the minimum difference value of the RGB channels and correct the dark-channel values of the regions are founded. Then, a linear smoothing method is used to refine the block effect caused by dark-channel prior, and the enhanced image is achieved by scaling up the pixel intensity according to its value in dark-channel image. Finally, by comparing with the existing low illumination image enhancement method, the effectiveness of our method with better color preserving capability and higher PSNR is proved.

Abstract:To solve the problem of transmitter parameter optimization in different communication modes for cognitive radio (CR) systems, a cognitive decision engine based on binary chaotic particle swarm optimization (BCPSO) is proposed. The BCPSO algorithm has both the fast convergence of particle swarm optimization and global ergodic property of chaos. Therefore, the cognitive decision engine based on BCPSO can jump off the local extreme points effectively, which can improve the precision and stability of parameter optimization. The cognitive orthogonal frequency division multiplexing (OFDM) system is used for the performance analysis. And the simulation results show that the proposed cognitive decision engine, which has higher fitness value and stronger robustness for different communication modes, is better than the other existing engines. The proposed engine achieves the objective of parameter optimization effectively.

Abstract:Since the existence of buried targets influences the thermal physical properties of the surrounding area, causing the temperature differences over time in the regional surface, which reflected in the infrared image is the gray value changes over time. To solve the problem, we research on the mathematical model of temperature change of the region containing buried targets, and reveal the relationship between the regional temperature changes and thermal physical properties and buried position of the buried targets. We use real multi-temporal and multi-spectral infrared images to get the temperature distribution of the region surface which compared with the solution of the mathematical model. By continuously changing the value of the thermal model parameters, we can get a solution which consistent with the temperature distribution obtained by the real temporal infrared images, and then we complete the detection of subsurface targets.

Abstract:To research the geometric nonlinear problem of tapered beam with shear deformation, based on Timoshenko theory, the displacement and rotation independent interpolation method was adopted to obtain the shape functions of tapered beam considering shear deformation, whose inertia moment varied quadratic. Then, started from the virtual work increment equation, the geometric nonlinear incremental equilibrium equation of the plane tapered beam element was established, including axial force, shear effect, bending effect and its coupling term, and the large displacement tangential stiffness matrix of the tapered beam was obtained. Finally, the classical examples are calculated, and the results show that the proposed method is accurate and effective.

Abstract:To solve the out-of-plane stability problem of the telescopic boom subjected follower forces, the deflection differential equations of the multi-telescopic boom model which under actions of pull-rope are established. With proper boundary conditions, the recurrence formulas of buckling characteristic equations are presented, and the explicit expressions of the boom in some practical applications are given. The influence on destabilizing critical force of telescopic boom due to the ratio of a／l is discussed in detail, where a is the length of wire projected to telescopic boom, and l is the length of telescopic boom. In comparison with the ANSYS method, the results show that the buckling characteristic equations are completely correct. As the ratio of a／l increases, the capacity of anti buckling reduces and tends to be a constant value.

Abstract:To make the designed rover have self-adaptability and better contact with ground, DOFs required for single suspension system and the whole rover are studied. Three classification ways of self-adaptability are given, and the relationship between self-adaptability and climbing performance, stability, energy consumption is analyzed. Mathematic model of single wheel-suspension system is established and such system’s DOF is obtained. Based on aforementioned analysis, mathematic models of double, three and k wheel-suspension system are established respectively with calculated DOFs for these systems. Two DOF models for wheeled rover are given followed by DOF statistics and analysis of some representative self-adaptive rovers. The analysis shows that self-adaptability is the basis for realizing comprehensive performance of the locomotion mechanism. DOFs for single suspension system and rover are 1 and 3, respectively. The conclusion has universalism and can determine required DOFs for structural synthesis of wheeled rover.

Abstract:To investigate the damage mechanism of TiB2P／2024Al composites in high-cyclic fatigue, axial fatigue experiments were carried out. SEM micrographs of fracture surfaces indicated that fatigue cracks mostly initiated at interior defects of the composites. The dominate damage modes were porous assembling type damage in matrix and interface debonding, scarcely any particle cracking. And coexistences of dimples and fatigue striations were observed in main propagation zone. The intrinsic mechanism governing the enhanced fatigue fracture characteristics are that, since the enforced particulate dimension is between sub-micron and micron level, lesser particles decrease stress concentration, disperse damage initiation sites, and increase the probability of crack deflection and bifurcation, then, the matrix plasticity exerts adequately. Therefore, the composites exhibit high fatigue resistance.

Abstract:To achieve more accurate result and lower computational complexity of range analysis for multiplication in automatic word length optimization, this paper presents a novel refined affine approximation method of multiplication for range analysis in automatic word length optimization, which is named novel affine arithmetic approximation (NAA). In NAA, a new noise term represents the error which is caused by approximation. This error is estimated more accurately without increasing the computational complexity. The computational complexity of NAA is O(M₁), where M₁ denotes the total of the nonzero noise of the two multipliers. In experiments, the accuracy of the range using NAA is 1.47 times of that using trivial range estimation, and the same as that using Chebyshev approximation.

Abstract:To solve the problem that singular-modal image recognition using only the low-level visual features has low accuracy, considering that many images have embedded-in textual information, a collaborative method using the embedded-in text to aid the recognition of images is proposed. The method includes three steps. Firstly, after localization, segmentation, binarization and feature extraction, semantics of text is gotten. Secondly, the collaborative posterior probability is calculated by extracting visual features of images and counting correlation of visual and textual modals. At last, for each class of images, the joint posterior probability is calculated using the previous two items. A new image is recognized to the class with maximal joint posterior probability. Experiments on the self-built data set of sports video frames showed that the proposed method performed better than the singular-modal method on three different visual features and had higher accuracy.

Abstract:The influences of porosity, impact energies and moisture contents on the residual tensile strength and bending strength after impact of CFRP laminates are evaluated. CFRP laminates of three porosity levels were immersed in water for 7、 14 days and moisture saturation. Impact tests on the CFRP laminates of three porosity levels with different immersion time were conducted at five impact energy levels of 3-15J at room temperature, followed by the residual tensile test and bending test performed on the specimens. The experimental results show that the residual tensile strength and bending strength after impact decreased significantly with the increasing impact energy. For the same impact energy, no obvious effects of void contents on the residual tensile strength and bending strength after impact were observed. The delamination induced by the impact would reduce the influence of void on the residual strength of the impacted specimens.

Abstract:Aiming at non-cooperative spacecraft with rectangular structures, a more simple and general relative attitude determination algorithm was deduced by expressing the relative attitude in the form of coordination transformation matrix. To verify the method, the image acquisition and processing system was designed based on MATLAB, and using STK the target simulator was built. Furthermore a ground test system was established, and the tests of flying around in the orbit plane and out of the orbit plane were performed. The results indicate that the relative attitude determination algorithm can derive the relative attitude of non-cooperative spacecraft exactly.

Abstract:Multi-lift system control was researched based on control input inverse solution. In multi-lift system with slung load,every helicopter has different stability and response due to cable forces influence. It is very difficult to directly introduce cable forces feedback in controller design due to lack of explicit physical transformation from forces to actuators control. According to aerodynamics and flight dynamics, a nonlinear model following control scheme is proposed based on control inputs inverse solution. It is desirable to provide a high degree of stability augmentation for the multi-lift system by using direct cable forces feedback. The most significant improvement is that each helicopter in the multi-lift system has the same control structure and control law, which remarkably simplify design of controller and improve control performance. Controller’s performance is demonstrated in a nonlinear robust simulation.

Abstract:For the good performance of DRM／DAB／AM／FM frequency synthesizer, the implementation of a high-speed large division ratio low-power pulse swallow frequency divider is described, which consists of a divided-by-32／33 dual-modulus prescaler (DMP), a 5 bits swallow counter, an 11-bits programmable divider, and a time sequence control circuit. The different modules of pulse swallow frequency divider apply SCL, TSPC, CMOS static flip-flop DFF, and CMOS static flip-flop DFF with preset to realize the low power, large division ratio, and high speed performances. The chip has been fabricated in a 0.18 μm CMOS process of SMIC and the core area is 270 μm×110 μm. Measured results show that its most high operation frequency is 3.4 GHz and the rang of operation frequency is from 0.9 GHz to 3.4 GHz. And when the operating frequency is 3.4 GHz and division ratio is 45 695, the maximum core power consumption is 3.2 mW under 1.8 V power supply. Its performance satisfies the requirement of DRM／DAB／AM／FM frequency synthesizer.

Abstract:To study the characteristics of ship airwake, the simplified frigate ship, SFS1 and SFS2, and actual frigate ship were simulated, and the results were used to analyze the characteristics of flow field around the flight deck by comparing with the experimental data in wind tunnel. The centerline surface pressure coefficient and vortex separation off the top of hangar shed and reattached on the flight deck were found by the simulation of SFS1, and the existence of horseshoe vortex on the surface of the flight deck was verified. An example indicates that the blocking of the ship geometry is an important driving force for the vortex separation and shedding. The actual frigate ship with 0° and 30° starboard winds was simulated, and the results showed that the shape and size of the hangar affected the intensity and location of the vortices around the flight deck. In the 0° wind direction, to open the hangar door could improve the flow field status of the flight deck.

Abstract:To research the friction performance of grease lubricated sliding bearing of the boom in engineering machinery under long-time action of cyclic radial heavy load, a friction torque and coefficient test bench for this kind of bearing has been developed. The test bench can not only simulate the working process of the bearing under the condition of low speed and heavy load approximately, but realize two relative movement forms between bearing and pin shaft. Based on the bench, experiments about the relationship between active torque and friction torque on the sliding bearings in the working process are carried out, and a test calculation method of the friction torque and coefficient is introduced. The wear test shows that the method can be used to accurately obtain the friction coefficient between the bearing and pin shaft. The method provides references for designers to estimate the bearing life and work efficiency, as well as for the optimal design of this type of bearing.

Abstract:For solving the problem of finding suitable robot configurations to meet the specific tasks in the application of reconfigurable modular robot, a task-oriented multi-objective configuration optimization method is discussed. At beginning, the basic structure of the modular robot system is introduced, including the main modules and components of the control system. Then, based on the description of the task, an optimization model of modular robot configuration design is represented. Finally, for the specific tasks of climbing and manipulating, the configuration optimal design of modular robot is processed. The feasibility and effectiveness of the method have been well verified by the optimization simulation. The method is task-oriented and multi-objective, and it includes the performance optimization of degrees-of-freedom, reach-ability, energy consumption, and so on.

Abstract:To obtain excellent comprehensive performance for mechanical product, it’s necessary to select the best one from multiple design schemes. Scheme criteria evaluation matrix was standardized and criteria weight vector of every design scheme was optimized. According to the principle of minimum offset of design scheme evaluation, scheme evaluation problem was linearly programmed. Uncertainty factors of criteria weight were analyzed, and entropy was introduced to describe the uncertainties. According to the maximum entropy theory, design scheme evaluation model was built, which was solved by building Lagrange function and forming nonlinear equations. Finally, these design schemes could be sorted to obtain the best one. The example demonstrated validity of the proposed evaluation method.

Abstract:To accurately and real-time reproduce complex electromagnetic space environment of aeronautical communications system data link, the dynamic interference was simulated. A semi-physical simulation system is designed to simulate the real flight’s anti-interference in static microwave chamber, then the characteristics of aeronautical communications system’s data chain is analyzed, when reproducing the dynamic interference in the anechoic chamber, the electromagnetic space environment’s dynamic interference mapping is achieved through the control of microwave instruments. The corresponding dynamic interference model is built in real-time by using the parametric model characterization techniques, and its matching output switching interference algorithm is designed by using the least mean square method. Thus, the function of simulating the dynamic interference through a static radio trumpet in the microwave chamber is realized by the method of combining static and dynamic simulation. Finally, the verification for anti-interference performance shows that the dynamic interference’s impact on the aircraft can be realistically reflected by the method of simulating dynamic interference in the anechoic chamber based on the microwave switch. The study of the simulation system can greatly improve the anti-interference performance of aeronautical communications system data chain.

Abstract:Aiming at the timing synchronization difficulty of LDPC-coded system on GF(q) in deep space communication, a new soft timing synchronization algorithm is proposed. Firstly one cost function using the soft decoding information of LDPC on GF(q) is introduced for coarse timing synchronization, then the Expectation-Maximum algorithm is used for fine timing synchronization based on the maximum likelihood criterion. Conducting the joint iteration of timing synchronizer, demodulator and decoder, the soft information provided by LDPC decoder is used to aid the timing estimation, and the timing estimation close to the modified Cramer-Rao bound can be obtained by interpolation of the over-sampled data. Simulation results show that, at low SNRs, the efficient timing synchronization can be achieved with large timing offset, and almost ideal performance is obtained with low system complexity.

Abstract:In this paper, the structure of the active disturbance rejection control technique is described in detail, including the tracking differentiator, extended state observer and nonlinear state error feedback. Typical algorithms of each part are given as well. In order to control the attitude of the quad-rotor robot as we desired, we design two kinds of ADRC, including the continuous ADRC and the discrete ADRC. Simulations were carried out based on Simulink. After parameter adjustment, the simulation results show that the ADRC can meet the need of control accuracy and swiftness of response. It also indicates that the controller has strong robustness and anti-disturbance performance, which can control the nonlinear coupling systems effectively.

Abstract:To solve the non-differentiable problem of original frictionmodel, an exponential function containing speed variables is introduced to design the continuous differentiable LuGre steady-state friction model for dual-motor driving servo systems. The proposed model captures the main characteristics of friction including Stribeck effect, coulomb and viscous friction.Based on the continuous differentiable model, a nonlinear variable coefficient characterizing the synchronization rate is used for fast terminal sliding mode, such that the system is proved to achieve synchronization and tracking control for the reference signal with prescribed performance by Lyapunov function.The simulations are included to verify fast convergence speed and high tracking precision of the proposed algorithm.

Abstract:To improve the temperature uniformity of the wafer and better the device performance, a combined conduction and radiation heat transfer model was used to simulate the heat transfer within wafer during Rapid Thermal Process, and the effects of the ratio of gate width to the pattern period (lG／lP=0.5,0.0,0.25) on the temperature distribution were investigated, under three fixed doped silicon gate widths (lT=0,0, 60μm). The results show that, under the same doped silicon gate width, the temperature level of wafer decreases, the temperature difference reduces and the temperature uniformity of the wafer surface increases with the increase of the pattern arrangement density. Under the same doped silicon gate arrangement density, the temperature level enhances but the temperature uniformity changes little with the increase of the doped silicon gate width. This is because the wafer pattern structure changes the surface absorptance, adjusts the absorbing and distributing level of incident radiation energy, and transforms the temperature level and uniformity.