Table of Content

30 March 2016, Volume 34 Issue 2

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Signal and Information Processing

Structured Compressed Sensing Image Reconstruction Based on Double-Density Dual-Tree Complex Wavelet Transform

WANG Hai-xu, WU Shao-hua, YANG Jing-ran, DING Chan-juan

2016, 34(2):  115-126.  doi:10.3969/j.issn.0255-8297.2016.02.001

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We propose a new structured compressed sensing recovery algorithm of images based on double-density dual-tree complex wavelet transform (DDDT-CWT). The algorithm combines the structured characteristic of coefficients under DDDT-CWT and compressive sample matching pursuit (CoSaMP) recovery algorithm. It has good reconstructed image performance. Simulation results show advantages of the proposed method as compared with traditional recovery algorithm using DWT basis and without considering structured characteristic of coefficients. With the same compression ratio, PSNR is improved by 2.9~3.2 dB and 0.2~1.2 dB when using the DDDT-CWT basis and considering structured characteristic respectively. The PSNR gain reaches 3.8~4.3 dB when combining these two features together.

High-Resolution Image Based on Exponent Moments

SUN Jing-feng, LIU Hui-ying, JI Chao, GUO Hui-juan

2016, 34(2):  127-134.  doi:10.3969/j.issn.0255-8297.2016.02.002

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Based on the definition and calculation method of exponential moments, this paper describes a high-resolution image using the exponential moment matrix. Combining image segmentation and further treatment of sub-images, we use FFT to calculate the exponential moment matrix of a high-resolution image. Each sub-image is then reconstructed with the obtained exponential moment matrix. The original image is recomposed using the reconstructed sub-images. Meanwhile, based on Itti's visual attention model, SNR of the objectively interested area in the reconstructed image is analyzed. Simulation results show that the reconstructed image block effect caused by segmentation can be reduced, and SNR of the reconstructed image is improved. It is shown that describing a high-resolution image with image moment invariant matrix is feasible.

Perceptually Adaptive Loop Filter Aimed at 3D-HEVC

WANG Yong-fang, WANG Yu-bing, SHI Ya-wen, LUO Li-dong, ZHANG Zhao-yang

2016, 34(2):  135-144.  doi:10.3969/j.issn.0255-8297.2016.02.003

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This work proposes a perceptually fast adaptive loop filter algorithm to reduce coding complexity. The largest coding units (LCUs) are classified into different regions according to the just noticeable distortion (JND) profile and using a Canny operator. Based on the ALF performance assessment and an analysis of different regions, all ALF processes for LCUs in sensitive smooth regions and non-sensitive smooth regions are skipped. Experimental results show that the proposed method can significantly reduce ALF encoding complexity while maintaining video quality. The proposed algorithm can achieve better subjective video quality with similar coding complexity compared with the existing efficient ALF algorithm.

Improved Triangle Mesh Method for Surface Reconstruction from Normal Field

FANG Qiao-yun, LÜ Dong-hui, SUN Jiu-ai

2016, 34(2):  145-153.  doi:10.3969/j.issn.0255-8297.2016.02.004

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Photometric stereo is an important contactless method for obtaining object shape information. It is a key step in surface reconstruction based on surface normal field. By reviewing and analyzing existing methods, we find that performance of the triangle mesh method is unsatisfactory in local computation and vulnerable to noise. To improve reconstruction accuracy, an improved triangle mesh method with global constraints as used in the normal and tangent vector method is proposed. An object with Lambertian surface is used in the experiments to compare reconstruction accuracy and computing time of normal and tangent vector method, Poisson method, triangle mesh method and the improved triangle mesh method. The results show that Poisson method is computationally efficient, the improved triangle mesh method is better in reconstruction accuracy when the image does not contain noise, while the proposed triangle mesh method performs better both in reconstruction accuracy and noise resistance.

Smooth Blending of Trigonometric Bézier Curves and Surfaces

LIU Hua-yong, XIE Xin-ping, LI Lu, ZHANG Da-ming

2016, 34(2):  154-162.  doi:10.3969/j.issn.0255-8297.2016.02.005

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Trigonometric polynomial functions with shape parameters are proposed. The λC-Bézier curve and surface basis can achieve higher order smoothness by joining in relatively simple conditions. Meanwhile, their shape can be adjusted freely without changing control points. Based on the trigonometric Bézier polynomial functions, we define a new λC-Bézier curve determined by four control points and a new λC-Bézier surface determined by sixteen control net.The smooth blending conditions of the new curve and surface are discussed. Under the blending conditions, we define a piecewise combination curve and surface consisting of the λC-Bézier curve and surface. The method automatically ensures continuity of the curve and surface. Experimental results show effectiveness of the method.

Electronic Engineering

Effect of Bending Stress on the Conductive Properties of Two-Dimensional Graphene

FU Kai, XU Rong-qing, CHEN Jing

2016, 34(2):  163-170.  doi:10.3969/j.issn.0255-8297.2016.02.006

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Chemical vapor deposition (CVD) was used to grow high-quality two-dimensional graphene, and graphene/PDMS and graphene/PET flexible transparent conductive film were prepared. These were used to study the relationship between conductivity and curvature of two-dimensional graphene in the context of different materials and different thickness of the substrate. The results show that elastic modulus and thickness of the flexible substrate have little effect on conductivity of the two-dimensional graphene. When thickness of the substrate is the same, graphene resistance increases with the increase of the bending curvature. However, the rate of relative change of graphene resistance is small, indicating that two dimensional graphene conductive films can be used as flexible conductors for bendable touching screen, robot skin, and wearable device.

Localized Surface Plasmon Enhanced Fluorescence on Silver Nanoclusters

ZHANG Tao, XU Rong-qing, CHEN Jing, DENG Bei

2016, 34(2):  171-176.  doi:10.3969/j.issn.0255-8297.2016.02.007

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Using low energy cluster beam deposition based on magnetron plasma gas aggregation cluster source, we fabricated silver nanoclusters on a quartz substrate and measured its transmittance spectrum. Then we dispersed SiO₂ fluorescent nanospheres separately on bare quartz substrates and quartz substrates with silver nanoclusters. We found that the fluorescence intensity with silver nanoclusters was 5.3 larger than that without silver nanoclusters. Finally, we used the Mie scattering theory to numerically calculate the electric field intensity distributions of a single silver nanosphere where surface plasmon resonance existed. We give a reasonable explanation for the experimental results.

Control and System

Control of Trajectory Tracking of Mobile Robots Based on Disturbance Observer

XU Kun, CHEN Mou

2016, 34(2):  177-189.  doi:10.3969/j.issn.0255-8297.2016.02.008

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Focusing on the trajectory tracking problem of mobile robots, an integral sliding mode controller based on a disturbance observer is designed. By considering the influence of skidding and disturbances, kinematic and dynamic models of the mobile robot are established. An adaptive disturbance observer based on the terminal sliding mode theory is designed to realize finite-time estimation of the compound disturbance. A trajectory tracking controller based on kinematic model is then designed, with which the position tracking error converges asymptotically and the angular tracking error is bounded. Combining the disturbance observer and the integral sliding mode method, a velocity tracking controller is designed based on a dynamic model. Finally, simulation results are given to verify effectiveness of the developed control algorithm.

Cooperative Control off Our-Rotor UAV Based on Multi-sensor Fusion

ZHANG Lei, LU Yu-ping, YIN Ming

2016, 34(2):  190-202.  doi:10.3969/j.issn.0255-8297.2016.02.009

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To deal with hovering control of four-rotor UAV from a practical point of view, a scheme of multi-sensor data fusion and a corresponding law of cooperative control are proposed. Based on the overall hardware frame of the aircraft, and within-depth analysis of each sensor in the measurement system, a Kalman filtering algorithm is developed for attitude measurement and a complementary filtering algorithm developed for height measurement. A dual sensor fusion algorithm is proposed to measure horizontal position. A four-rotor UAV model is established using small perturbation linearization. Based on the model, a corresponding cooperative control algorithm is designed. Simulation is performed to test the practicability. All algorithms are applied to a physical platform to verify effectiveness. The results show that the multi-sensor fusion algorithm combined with a coordination controller is reliable and effective. It can effectively improve accuracy of fixed-point hovering of four-rotor UAVs.

Finite-Time Tracking Control of High-Performance Underactuated USV

LIU Hai-tao, TIAN Xue-hong, WANG Gui

2016, 34(2):  203-214.  doi:10.3969/j.issn.0255-8297.2016.02.010

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Finite-time tracking control is proposed for incomplete symmetrical highperformance underactuated unmanned surface vehicles (USV). Global diffeomorphism transformation is used to obtain the form of nonlinear cascaded systems. Thus tracking control of the original USV system is transformed to stabilization of the cascade system. Based on the finite-time Lyapunov theorem, a finite-time convergent controller is designed to obtain fast response and high tracking-precision. The theoretical analysis and simulations show feasibility and effectiveness of the proposed method.

Guidance and Control of Autonomous Aerial Refueling Rendezvous Trajectory Chasing Based on Sliding Mode Method

GONG Quan-quan, YUAN Suo-zhong, ZHANG Jin

2016, 34(2):  215-226.  doi:10.3969/j.issn.0255-8297.2016.02.011

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Based on the relative position and the line of sight between the receiver and the tanker aircraft, the receiver's normal and lateral flight acceleration command are generated using a sliding mode method to meet the trajectory chasing requirement. A dynamic inversion method is used to transform the desired acceleration to angular rate according to the kinematic relations. The roll angle command is designed to coordinate bank-toturn simultaneously. Tracking control of the angular rate loop is achieved using dynamic inversion. The forward acceleration command is generated according to the relative speed and range between the receiver and tanker. The velocity control law is designed using dynamic inversion. Nonlinear digital simulation results demonstrate that the controller is capable of guiding the receiver to rendezvous with the tanker, and the transient performance is good.

Experimental Study of Micro-jet Impingement Cooling Loop System with Micro/Mini-channels

ZHU Li-yao, DONG Li-ning, WANG Jiang, XU Tao, CAO Jian-guang

2016, 34(2):  227-236.  doi:10.3969/j.issn.0255-8297.2016.02.012

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A liquid cooling loop system with micro-jet arrays and micro/mini-channels was designed for high-heat-flux cooling applications. Flow boiling experiments under different operation conditions were conducted to study flow and heat transfer performance of the heat sink. The effects of micro-jet geometry such as shape, diameter and height of jet hole are analyzed. Good agreement between the experimental data and the predictions has been found.