Table of Content

31 December 2020, Volume 26 Issue 6

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Invited Review

Spatial contrast structure for singular perturbation problems with right end discontinuities

NI Mingkang, PAN Yafei, WU Xiao

2020, 26(6):  853-883.  doi:10.12066/j.issn.1007-2861.2259

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This paper surveys recent developments in spatial contrast structure solutions to singularly perturbed problems with discontinuous right-hand sides. Studies on second-order non-linear singularly perturbed problems, including semi-linear, quasi-linear, and weakly non-linear system Dirichlet problems, are reviewed. In addition, the first-order ordinary differential equations under homogeneous Neumann conditions are discussed. A type of piecewise-continuous second-order Dirichlet problems of the Tikhonov system and boundary value problem of a singularly perturbed parabolic equation with a discontinuous term is also included.

Intelligent Ocean Surface Robot

Hydrodynamic modeling of an eccentric paddle mechanism with rotational paddling gait

LI Xiaomao, PENG Yu, LI Tianbo, CHEN Junjie, XU Jia, CUI Jianxiang

2020, 26(6):  884-895.  doi:10.12066/j.issn.1007-2861.2167

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In previous work, an eccentric paddle (ePaddle) mechanism has been proposed to improve the mobility of amphibious robot under challenging environments, which can execute various terrestrial and aquatic gaits. In this paper, to investigate the hydrodynamic characteristics of rotational paddling gait, a hydrodynamic model is presented based on Morison equation for analyzing the effects on thrust characteristics with different configuration of parameters such as slip ratio, eccentric distance, etc. The accuracy of the model has been verified by the experiments. Based on the theoretical model and experimental results, the reasonable application suggestions for the rotational paddling gait of the ePaddle are presented.



Hierarchical model identification method for unmanned surface vehicle

YUAN Xiaoyu, HUANG Chengyi, PENG Yan, QU Dong, LIU Dongke

2020, 26(6):  896-908.  doi:10.12066/j.issn.1007-2861.2248

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With the developments in science, technology, and military, unmanned surface vehicles (USVs) with unique roles have been rapidly developed in recent years. Considering the large interference of the sea environment, large time delay, and limited computing capability of the onboard computer, it is challenging to obtain an accurate control mode for the USV. As an industry robot, rapid identification of the control model is important for the research, development, and engineering. To address this issue, this paper proposes a hierarchical mode identification method for the USV, with a rudder steering model and heading control model at different speeds. The validity of the model is verified by a simulation and experiment. This method is simple and fast and can be quickly applied to the control system of the USV.



Research Articles

Stitching algorithm of multi-mode fusional vehicle panorama

LIU Chang, XU Meihua, GUO Aiying

2020, 26(6):  909-920.  doi:10.12066/j.issn.1007-2861.2098

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As the traditional driver assistant system provides only one viewpoint, its usage is limited. A panoramic stitching algorithm, which can automatically switch between forward and backward modes, is proposed. This algorithm can provide a more flexible viewpoint for drivers. First, the distortion of images input by fish-eye cameras is corrected. Second, the driving direction is deduced by the displacements of the feature points detected between adjacent images. Third, the viewpoint transformation is chosen according to the driving direction, using cylindrical projection for the forward direction and perspective transformation for the backward direction. Finally, images are matched using piecewise stitching in place of the traditional stitching method and overlapped regions are fused. The model can automatically switch the mode according to the driving direction. The images of the cameras are highly reserved. The time cost for the cylindrical projection of this model is 75% lower than the traditional value.



Low-cost surge-resistant circuit with absorption capacitance

SUN Die, YAN Limin, JIA Shi, GAO Wenkai

2020, 26(6):  921-926.  doi:10.12066/j.issn.1007-2861.2099

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The conventional surge protection circuit requires a high-power level of circuit components, which leads to lower performance and higher hardware costs of the entire circuit structure. This paper presents the design of a low-cost anti-surge circuit with absorbing capacitance. Through theoretical analysis, software simulation, and experimental tests, it is proven that the designed circuit structure can increase the voltage grade and improve circuit stability by reducing the cost of the surge protection circuit with a lower power-level metal-oxide-semiconductor field-effect transistor (MOSFET).



Effects of different interfaces on mechanical properties of graphene oxide-carbon fibre/epoxy resin composites

ZHANG Yaping, SHI Lei, GUO Xiaofeng, LIU Liqi

2020, 26(6):  927-936.  doi:10.12066/j.issn.1007-2861.2123

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Graphene oxide (GO)-carbon fibre/epoxy (EP) composites were prepared via different synthesis methods. The three interface bonding mechanisms were discussed. The effects of different interfaces on the interfacial shear strength (IFSS), flexural properties, and interlaminar shear strength (ILSS) of GO-carbon fibre/epoxy composites were compared and analysed. The results show that the role of GO on the interface of the composite is primarily to enhance the mechanical interlocking effect at the interface and the force generated by the formation of a small amount of chemical bonds. The interfacial bonding mode of GO adsorbed on the surface of carbon fibre and subsequently formed with epoxy resin increases the interfacial shear strength of the composite by 66.97%, the bending strength by 31.84%, and the interlaminar shear strength by 10%. The utilisation of GO is the highest, and the process is simple. It is therefore conducive to the realisation of industrial production.



Effects of electron beam irradiation on microstructures and thermoelectric power factors of β-Zn₄Sb₃ thin films

GAO Pengfei, OU Zhenghai, QIN Juan, SHI Weimin, WANG Linjun

2020, 26(6):  937-944.  doi:10.12066/j.issn.1007-2861.2168

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In this study, β-Zn₄Sb₃ thermoelectric thin films were fabricated by radio-frequency magnetron sputtering with subsequent electron beam (EB) irradiation with different doses of 0~800 kGy and thermal annealing. The microstructures and surface morphologies of the films were characterised by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The electrical transport and thermoelectric properties of the films were analysed by Hall effect and Seebeck effect measurements. All samples exhibited p-type conduction characteristics. The phase compositions and average grain sizes of the samples subjected to EB irradiation slightly changed, the film surface was more densely compacted, and the grain growth exhibited a preferred orientation along the (223) crystallographic plane. When the EB irradiation dose was 200 kGy, the power factor of the sample reached 6.90 μW/(cm·K²) as the Seebeck coefficient was effectively increased while the conductivity was slightly reduced. This power factor was increased by 41.7% compared to that of the sample without EB irradiation.



Enhancement of SnO₂/g-C₃N₄ dual two-dimensional materials for formaldehyde gas sensing

ZHANG Wenshuang, YUAN Tongwei, ZHANG Dan, MA Zhiheng, CHENG Zhixuan, XU Jiaqiang

2020, 26(6):  945-953.  doi:10.12066/j.issn.1007-2861.2109

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The ultrathin two-dimensional  SnO₂ nanosheet was synthesized by a solvothermal method, and  g-C₃N₄  with grapheme-like structure was obtained by chemical vapor deposition of high-temperature pyrolytic urea. Both materials were then mixed by grinding, sonication, and drying to fabricate  SnO₂/g-C₃N₄ . X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the compositions, morphology, and structures of  SnO₂/g-C₃N₄ . The results showed that the  SnO₂/g-C₃N₄ nanosheets were distributed evenly on the  g-C₃N₄  support and  SnO₂/g-C₃N₄  materials have higher sensitivity, better selectivity, and faster response than pure  SnO₂ for the detection of formaldehyde vapor. The synthetic approach provides a simple and effective strategy for improving the performance of gas-sensing materials and may find application in formaldehyde detection in indoor environments.



Synthesis of Bi₂WO₆/TiO₂ nanobelts for development of visible-light-driven photocatalysts and their photocatalytic properties

TANG Yan, ZHOU Diwen, ZHU Ying, QIAO Dandan, PU Xianjuan, JIAO Zheng, CHENG Lingli

2020, 26(6):  954-962.  doi:10.12066/j.issn.1007-2861.2103

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TiO₂ P25 nanoparticles were used as raw materials to synthesise TiO₂ nanobelts by the alkaline hydrothermal method. The Bi₂WO₆/TiO₂ nanobelts were successfully synthesised by the hydrothermal method using the TiO₂ nanobelts. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were used to study the morphology and structure of the synthesised hybrid material. The experimental results revealed that the Bi₂WO₆ nanosheets could be successfully loaded onto the surface of the TiO₂ nanobelts (attachment via intermolecular interactions). The photocatalytic performance of the Bi₂WO₆/TiO₂ composite material and the mechanism of catalysis were investigated under visible light irradiation. The results showed that the prepared Bi₂WO₆/TiO₂ hybrid material had excellent photocatalytic properties. The enhanced photocatalytic activity could be attributed to the excellent photogenerated electron-hole pair separation (effective charge separation) and specificity of the composite material. The effective charge separation not only generated abundant active sites for photocatalytic reactions but also effectively promoted the axial mobility of electrons.



High-performance Li-ion hybrid capacitor with metal organic framework-derived porous carbon nanomaterial and lithium titanate

YAO Weiwei, MAO Jian, ZHANG Chen, LI Zhen, WU Minghong

2020, 26(6):  963-971.  doi:10.12066/j.issn.1007-2861.2143

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Li-ion hybrid capacitors, which combine the high energy densities of Li-ion batteries and high power densities of super capacitors, are a new type of energy storage device with large application potentials. In this study, a porous carbon nanomaterial (carbonized zeolitic imidazolate framework-8 (cZIF-8)) derived from metal organic frameworks (MOFs) was synthesised by pyrolysis of a MOF precursor at a high temperature. This carbon material had a large specific surface area, excellent porosity, good thermal stability, and high conductivity. A new type of Li-ion hybrid capacitor (cZIF-8//lithium titanate (LTO)) was constructed using a capacitor electrode based on cZIF-8 as a positive electrode and battery electrode based on LTO as a negative electrode. The assembled device had highest energy density of 44 W·h·kg^-1 and power density of 5387 W$\cdot$kg$^{-1}$, significantly higher than that of a cZIF-8//cZIF-8 supercapacitor (16.6 W·h·kg^-1). The Li-ion hybrid capacitor (cZIF-8//LTO) also exhibited a good cyclic performance (85.4% of the initial value after 10000 cycles) at a high current density of 2 A·g^-1. This MOF-based Li-ion hybrid capacitor enables to effectively increase the energy density of the electrochemical energy storage device without reducing the power capability.



Composite of covalent organic framework-derived nitrogen-doped carbon with carbon nanotubes for lithium-storage

TANG Xuxu, YANG Qingsi, YANG Jianwei, SUN Weiwei

2020, 26(6):  972-979.  doi:10.12066/j.issn.1007-2861.2111

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The covalent organic framework, obtained by the facile room-temperature method, was selected as the precursor for fabricating the nitrogen-doped carbon/carbon nanotube composite (N-C-CNT), in with the nitrogen-doped carbon was derived directly from the covalent organic framework, while the carbon nanotubes were formed in situ from acetylene under catalysis by metallic cobalt. Due to N-doping, the carbon layer provides more active sites for lithium storage; therefore, the N-C-CNT composite exhibits high specific capacity and excellent cycle stability (reversible capacity of 652 mA·h·g^-1 after300 cycles) as an anode material for lithium ion batteries.



Quantification of dominant algal species in water reservoir by measuring two-dimensional projection characteristic values of algal clusters

SU Qingqing, LI Chunrong, WANG Xianyun, ZHANG Dong, HUANG Xin

2020, 26(6):  980-988.  doi:10.12066/j.issn.1007-2861.2102

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From March to July 2015, a microscopic survey on species, density, and two-dimensional projection characteristic values of algal clusters showed the obvious seasonal succession pattern of algal species distribution in the reservoir. Tribonema (Xanthophyta) was the dominant algae in spring, accounting for 78.9% to 92.6% of algal clusters, with high correlation between two-dimensional projection area and cell density (R²=0.712). Classification and regression tree (CART) method was used to identify Tribonema, Cyclotella, and Pseudanabaena, with effective recognition rates of 83%, 68%, and 86%, respectively. The two-dimensional projection and image recognition technology were expected to realize rapid identification and characterization of algal clusters in water.



Swelling characteristics and hydraulic conductivities of bentonite and sand mixtures saturated with landfill leachate

RUAN Kunlin, SUN Dean, FU Xianlei

2020, 26(6):  989-1000.  doi:10.12066/j.issn.1007-2861.2105

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A series of swelling tests were carried out on bentonite and sand mixtures saturated by pure water and landfill leachate; the mixtures sported different sand mixing rates. The tests were carried out under various temperatures and a vertical pressure of50 kPa. Furthermore, the swelling tests were followed by consolidation and falling head tests to measure hydraulic conductivity. The following test results were obtained. (1) The liquid used for saturating the unsaturated soils significantly influenced the swelling characteristics of the bentonite and sand mixture. The final swelling rate of the mixtures saturated by the leachate was less than that of the mixtures saturated by pure water. (2) When the sand mixing rate was low, the swelling pressure of the mixture saturated by the leachate was smaller than that of the mixture saturated by water. When the sand mixing rate was 50%, the swelling pressures of the mixtures saturated by leachate and water were nearly identical. Moreover, the swelling pressures and final swelling rates of the mixtures increased with decreasing temperature. (3) For similar void ratios, the hydraulic conductivity of the mixtures saturated using water was slightly higher than that of the mixtures saturated using leachate. Furthermore, the hydraulic conductivities increased with increasing temperature. (4) For similar void ratios, the hydraulic conductivity measured via consolidation tests was lower than that measured using the falling head test.



Mixed traffic flow signal optimisation based on multi-population coevolutionary algorithm

CHEN Juan, JING Hao, FANG Yujie

2020, 26(6):  1001-1014.  doi:10.12066/j.issn.1007-2861.2100

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To address the traffic signal timing plan optimisation problem of mixed traffic flow at adjacent intersections under dynamic traffic demand, the vehicle delay, nonmotor vehicle delay, and pedestrian waiting time are used as optimisation objectives, a dynamic multi-objective optimisation model is constructed, and a multi-population coevolutionary dynamic-multi-objective genetic algorithm (MPCED-MOGA) is proposed, where the population is divided into search and tracking populations. The optimal solution is searched by the search population, while the changes in the environment are tracked by the tracking population. To obtain an algorithm quickly responding to the environment variations, the information is exchanged constantly between the two populations during the evolution. The proposed algorithm is tested under three classical test functions in FDA series of dynamic multi-objective optimisation function. The result is compared to those obtained by three existing dynamic multi-objective optimisation algorithms. The proposed algorithm is advantageous in terms of convergence and distribution. The effectiveness of the proposed algorithm for the signal optimisation problem is evaluated under a simulation environment based on a real adjacent intersection in Shanghai. The proposed MPCED-MOGA reduces the vehicle delay, nonmotor vehicle delay, and pedestrian waiting time compared to those of the three existing dynamic multi-objective optimisation algorithms and dynamic fixed time control method (TRRL).



Cooperative efficiency measurement of China's provincial science financial system based on network data envelopment analysis and its time-spatial differences

SHI Mingkang, YU Liying

2020, 26(6):  1015-1025.  doi:10.12066/j.issn.1007-2861.2101

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Based on the provincial panel data from 2009 to 2015, using network data envelopment analysis (DEA), this study measures the input-output efficiency of the financial and technology systems and their cooperative efficiency. The Moran index is used to test the spatial correlation of cooperative efficiency. The results revealed that there is a large promotion space for the cooperative efficiency of China's technology and financial systems. There are significant differences among regions, and only Beijing, Shanghai, and Jiangsu reach DEA efficiency. In terms of the time dimension, the cooperative efficiency shows an upward trend year by year and increases by 15% in seven years. In terms of the space dimension, the efficiency of each system shows good spatial correlation, and the correlation increases year by year. The cooperative efficiency of neighboring provinces of Guangdong and Chongqing needs to be improved. Based on the research results, this study puts forward some suggestions for improving the coordination of China's science financial and technology systems.



Parametric greedy randomized Kaczmarz algorithm for solving large sparse linear systems

LIU Yong, $\fbox{GU Chuanqing}$ , CUI Rongrong

2020, 26(6):  1026-1034.  doi:10.12066/j.issn.1007-2861.2151

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To solve large sparse linear systems, a relaxation parameter in introduced in the involved iterative formula of greedy randomized Kaczmarz (GRK) algorithm, and obtain a parametric greedy randomizedKaczmarzalgorithm is obtained. The convergence of this algorithm is proved when the linear system is consistent, and it is showed that it can be more efficient than the greedy randomized Kaczmarz algorithm if the relaxation parameter is chosen appropriately.