Table of Content

30 October 2020, Volume 26 Issue 5

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Invited Review

Mechanism of the accelerated corrosion of Zr-Nb alloys in lithiated water from the viewpoint of β-Nb oxidation

YAO Meiyi, ZHOU Bangxin

2020, 26(5):  681-692.  doi:10.12066/j.issn.1007-2861.2258

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Zr-Nb series zirconium alloys such as E110 and M5 show excellent corrosion resistance in nuclear reactors and static autoclaves with deionised water at 360 °C and 18.6 MPa. However, the alloys exhibit accelerated corrosion in lithiated water with 0.01 mol/L LiOH under identical conditions of temperature and pressure. The oxidation behaviour of β-Nb, which is the main second phase particle in Zr-Nb series zirconium alloys, is overviewed under different corrosive conditions in this study. It is found that β-Nb is quickly oxidised to Nb₂O₅ , which may react with LiOH to form LiNbO₃; it also dissolves into the corrosive environment to leave pores in the oxide films. The mechanism of accele-rated corrosion of Zr-Nb series zirconium alloys in lithiated water with LiOH is proposed from the viewpoint of β-Nb oxidation.



Digital Film and Television Technology

Grain noise restoration algorithm based on sub-regional bilateral filter

XU Min, DING Youdong, DONG Sun, ZHANG Qianqian, LI Fuyuan, CHEN Yu

2020, 26(5):  693-701.  doi:10.12066/j.issn.1007-2861.2120

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Grain noise in film films and their corresponding repair algorithms are numerous, but they usually have defects, such as smooth transition and high complexity. Combined with the correlation of RGB channels, a noise restoration algorithm based on a sub-regional bilateral filter was developed in this study to eliminate common grain noise in film films and ensure quality assurance for subsequent repair work, such as spots, scratches, image stabilisation, and scintillation. The test results showed that the de-noised image captured using the proposed algorithm not only satisfied the visual requirements of the human eye but also significantly improved the peak signal-to-noise ratio and structural similarity index measure values and decreased the running time to almost half of the original time. These benefits will not only improve the commercial value of old films but will also save a large amount of historical data.



Modelling of deep jump and audience perception reaction time in virtual reality images

TIAN Feng, DAI Shuaifan, ZHANG Yan

2020, 26(5):  702-714.  doi:10.12066/j.issn.1007-2861.2177

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A new depth perception model was developed to investigate the effect of deep jump on the human visual system in virtual reality images. In addition, the effect of parallax change on depth perception based on HTC Vive head-mounted display was evaluated, and the variation of the perception with jump parallax was analysed. The experimental results showed that the reaction time was proportional to the absolute value of parallax change. Furthermore, the parallax transition response time of the approaching angle of view was longer, the target depth and depth variations were negatively correlated with the physiological comfort, and the variation in the depth was positively correlated with the emotional influence. The model was applied to the creation and evaluation of actual images, and a pixel-by-pixel reaction time distribution map based on horizontal parallax was obtained.



Research Articles

Staggered-layered pilot aided channel estimation scheme for IEEE 802.11p

FANG Yong, LIU Chang

2020, 26(5):  715-725.  doi:10.12066/j.issn.1007-2861.2069

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Vehicle to vehicle (V2V) communication has a more rigorous requirement for channel estimation performance due to its complex and unfavorable channel environment. In this paper, in view of the fact that the pilots in IEEE 802.11p are too poor to accurately track the frequency selective fading channel, a novel channel estimation and tracking scheme based on staggered-layered pilot has been proposed. On the premise of not changing the data transmission efficiency of IEEE 802.11p, this scheme tracks the V2V channel based on the frequency domain interpolation of the estimated channel obtained from the pilots of adjacent symbols according to the high correlation between the channel of adjacent symbols, which outperforms the channel estimation and the tracking scheme based on original pilot in open and high-speed communication scenarios. In the framework of the proposed staggered-layered pilot scheme, selecting the appropriate channel estimation scheme according to the characteristics of different V2V communication scenarios can greatly improve the performance of IEEE 802.11p.



A conscious fault-tolerant routing algorithm with turn balanced in 3D NoC

LI Jiao, GUO Runlong, CAI Sheng, CHONG Yunfeng, XU Haipeng, RAN Feng

2020, 26(5):  726-734.  doi:10.12066/j.issn.1007-2861.2081

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Aiming at the poor performance of adaptive routing strategy and the imperfect fault tolerant mechanism in 3D NoC, the study proposes a perceptually fault-tolerant routing algorithm with turn balanced. Firstly, the XY, XZ and YZ are divided into the odd and even planes and six different forbidden turn directions are established on the row and column to get a more balanced turn model. Then, the horizontal and vertical boundary and internal link fault classification design fault model and fault-tolerant bypass. Finally, the proposed turn and fault model is applied to the routing algorithm combined with the strategy of “full plane 1 hop look-ahead” to improve network performance and fault tolerance. The experimental results show that the proposed algorithm improves throughput by 16.2% and transmission delay by 3.6% when no link failure occurs, and decreases transmission delay by 11.8% at lower link failure rate. With the link failure rate increased, this algorithm still has advantages.



Positive effect of cognitive reappraisal on low Theta electroencephalogram activity

ZHAO Minjie, LI Yingjie

2020, 26(5):  735-746.  doi:10.12066/j.issn.1007-2861.2084

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Cognitive reappraisal is one of the important strategies for emotional regulation. However, not every implementation of the strategy will succeed. The research on the physiological mechanism behind this phenomenon is still lacking. By analyzing the neural activity of a group who has successfully completed the cognitive reappraisal task and another group failing to complete the task, this study tries to explore the related electrophysiological mechanism. In conducting the research, 29 healthy subjects have been recruited, and they have been asked to complete the task of cognitive reappraisal, watching negative emotional images and neutral images, while their scalp electroencephalogram (EEG)s are collected simultaneously. According to the ratings of valence and arousal to the reappraisal of negative stimuli, the participants have been divided into two groups with cognitive reappraisal of success (15 subjects) and failure (14 subjects) respectively. The event-related spectral perturbation (ERSP) analysis shows that, under the condition of cognitive reappraisal, the low Theta (4.0~6.5 Hz) activity of the successful group is significantly higher than the failure group within 300 to 1 200 ms after the stimulus onset. Within 1 200 to 2 700 ms after the stimulus onset, the frontal lateralization is found only in the successful group, showing that the left frontal ERSP is significantly higher than the right frontal ERSP. Moreover, the left frontal ERSP in the successful group is significantly higher than in the failure group. In addition, in the task of cognitive reappraisal; the left frontal ERSP is significantly higher than the right frontal in both groups within 300 to 1 200 ms after the stimulus onset. In summary, whether or not cognitive reappraisal can be successfully completed is distinguishable in the EEG spectrum. To some extent, the activity of frontal low Theta can reflect the level of a person's cognitive reappraisal ability, which provides a potential objective indicator for evaluating individual's emotion regulation ability.



A graph-based method for multi-feature entity linking

ZHOU Jin, ZHU Yonghua, ZHANG Tienan, XING Yixue, ZHANG Ke

2020, 26(5):  747-755.  doi:10.12066/j.issn.1007-2861.2068

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Entity linking refers to the process of linking entity mentioned in text with knowledge base entity, which is one of the key steps in knowledge graph and knowledge fusion. This paper proposes a graph-based method for multi-feature entity linking. This method first preprocesses the knowledge base and the text, then identifies the named entity references in the text, and then combines the semantic similarity of multiple features such as topics, context, metadata, etc. In the expanded graph model, the probability of restarting random walk is used, and the target candidate entity is selected by joint disambiguation. The results of experiment show that the joint feature-based entity linking method based on graphs effectively improves the effectiveness of entity linking.



Incentive problem of collaborative technology innovation in mega projects considering fairness preference

MA Guanghong, LIU Jiawei

2020, 26(5):  756-768.  doi:10.12066/j.issn.1007-2861.2122

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This study focuses on the incentive mechanism of collaborative technology innovation of mega projects. To analyse the impact of fairness preference on the design of incentive mechanism, this study discusses four situations based on the principal-agent theory: both sides have fairness preference, both sides are self-interested, the agent has fairness preference, and the owner has fairness preference. The results reveal that when the fairness preference of the two sides is not equal, the optimal incentive coefficient is positively correlated with the agent's fairness preference, while negatively correlated with that of the owner. When the fairness preference of the two sides is equal, the fixed payment changes negatively with the fairness preference, and the output contribution rate changes the influence of fairness preference on the incentive coefficient. The final performance is that the output sharing proportion obtained by the side with the lower contribution rate is positively correlated to fairness preference, but not more than 0.5. The numerical modelling shows that the gap between two sides' fairness preference is beneficial to the improvement of the owner's utility, but a wide gap is unfavorable to the total profit.



Economic policy uncertainty, investor's sentiment and stock price synchronicity: a time-varying analysis based on TVP-VAR model

REN Yongping, LI Wei

2020, 26(5):  769-781.  doi:10.12066/j.issn.1007-2861.2080

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Based on the time-varying parameter-vector auto regression (TVP-VAR) model, a time-varying correlation between economic policy uncertainty, investor's sentiment and stock price synchronicity has been examined. The results show that the economic policy uncertainty has the positive effect on stock price synchronicity with obvious volatility in the short and medium term, and the long-term effect is relatively weak and has the stable performance. The investor's sentiment has a negative impact on the stock price synchronicity, and the short-term impact is the most obvious and the long-term impact is weak. The results of the time-point impulse function show that the stock price synchronicity has the positive response to the impact of the economic policy uncertainty and the negative response to the impact of the investor's sentiment at different time points. And there are differences in terms of response degree and response time at different time points. The conclusion sheds new light on how to further improve the policy control system, regulate and guide investors' behavior, and promote market rationalization.



Optically-induced electropolymerization of IgG/PEGDA hydrogel microstructures

SUN Yuyang, LUO Jun, LIU Na, YANG Yang, SUN Yi

2020, 26(5):  782-789.  doi:10.12066/j.issn.1007-2861.2082

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Encapsulating proteins in hydrogels has wide applications in drug release and tissue scaffolds modifications. In this paper, an optically-induced electropolymerization technique for patterning immunoglobulin G/polyethylene glycol diacrylate (IgG/PEGDA) hydrogels is reported. First the mechanism of optically-induced electropolymerization of PEGDA hydrogels is investigated. Then the electropolymerization of pure PEGDA and IgG/PEGDA hydrogels are experimentally verified respectively. The experimental results indicate that the reported technique can manufacture protein-encapsulated hydrogels with different geometry shapes, through using optical images designed by computer, alternating electrical field, and solution with hydrogel molecules and proteins. The cross-section shapes of the hydrogels are controlled by the optical images, the height of the hydrogels becomes increased with the increase of the deposition time. The smallest size of the manufactured structures is 3~4 μm. This technique makes possible the manufacture of tubular and high depth/width-ratio hydrogel microstructures, which is hard to imagine with the traditional manufacture methods.



Modelling solids with fluid-filled pores using eigenstrain formulation of boundary integral equations

ZHOU Jicheng, HE Donghong, MA Hang

2020, 26(5):  790-801.  doi:10.12066/j.issn.1007-2861.2090

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In view of the fact that elastic solids contain fluid-filled pores, Eshelby's idea of eigenstrain and equivalent inclusion has been incorporated into the boundary integral equations (BIE), and as a result, the computational model of eigenstrain boundary integral equations and the corresponding iterative solution procedures are presented in the paper for the numerical simulation of solids with fluid-filled pores in great number. In order to guarantee the convergence of iteration sufficiently, the local Eshelby matrix has been proposed and constructed from the BIE combined with Eshelby's idea. The feasibility and effectiveness of the proposed computational model are verified in comparison with the results of the analytical solution in the case of a single circular fluid-filled pore in full space and of the subdomain BIE in other cases. The overall mechanical properties of solids are computed using a representative volume element (RVE) with more than one thousand fluid-filled pores distributed either regularly or randomly with the proposed computational model, showing the feasibility and high efficiency of the present model and the solution procedures.



Interfacial instability and particle dispersion of explosion-driven fuel cloud

SHEN Yang, DING Jue, WENG Peifen

2020, 26(5):  802-815.  doi:10.12066/j.issn.1007-2861.2094

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In industrial explosion disaster area and the military area, the unsteady two- phase combustion detonation of the fuel cloud composed of gas and fuel particles can have a destructive effect on the surrounding medium, which is closely related to fuel motion characteristics and mass spatial distribution. In this paper, a two-dimensional gas-liquid (two-phase) flow model is established. Based on the finite volume method and the two-order accuracy monotonic upwind scheme for conservation laws (MUSCL) difference scheme, the numerical study on propagation of the shock waves in a two-phase medium, instability evolution of the fuel cloud interface, the mechanism of shock induced vortices and the initial motion of fuel cloud are conducted based on $n$-heptanes as the fuel. The research results show that the interaction between shock wave and fuel is a transfer process of momentum and energy. When the shock wave sweeps through the two-phase medium, the pressure attenuates and the relation with the proportional distance satisfies the power law. Moreover, the reflected wave and refraction wave are generated in the cloud and the wave front in the gas-liquid medium is bent. The liquid fuel obtains the same propagation direction of wave. For the initial particle size 60 $\mu $m, the fuel cloud will increase up to 22.8 m/s during the period of 112 μs. In the meantime, when the shock wave acts on the fuel cloud, then the flow field at the gas-liquid interface is disturbed. During the wave passing around the fuel cloud, large-scale vortices will be generated around the outer edge of cloud, which enhances the turbulence intensity of the original undisturbed flow field. Furthermore, the vorticity is induced by the density and pressure gradient of the flow field near the interface, and the development of Richtmyer-Meshkov instability (RMI) makes the interface generate a series of small-scale vortices. Large and small-scale vortices promote the development of turbulence, which also enhances the movement of fuel cloud and the dispersion of particles. It provides important conditions for the expansion of the cloud and subsequent two-phase detonation.



Structural and electronic properties of nitrogen and boron substitutions of C$_{64}$-graphyne: the first-principle calculations

LI Hui, XIN Zihua

2020, 26(5):  816-823.  doi:10.12066/j.issn.1007-2861.2091

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By using the first-principles calculations based on density functional theory, the nitrogen and boron substitutions of a novel monolayer planar structure named C₆₄-graphyne are studied. By substituting one nitrogen atom for a carbon atom in the hexatomic ring or tetratomic ring, two planar structures are obtained, which are named B_4ringC-C₆₄and B_6ringC-C₆₄ with the lattice parameter of 9.378×10^-10 m and 9.383×10^-10 m, respectively. Further investigation shows that a new structure named (BN)_chain-C₆₄ can be obtained by alternating substitution of boron and nitrogen atoms for carbon atoms in tetratomic ring and carbon chain. The doping with single boron atom induces the metal properties of two monolayer structures. The alternating substitution of boron and nitrogen atoms makes it act as semiconductor with band gap of 2.56 eV.



Two-dimensional material band gap prediction based on machine learning method

YOU Yang, DU Wan, LI Weiju, CHEN Jingzhe

2020, 26(5):  824-833.  doi:10.12066/j.issn.1007-2861.2089

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Machine learning (ML) algorithm and the traditional density functional theory (DFT) are combined to study the band gap of two-dimensional metal compounds, and as a result, a simple and effective model which is more cost-effective than the traditional quantum calculation method is established. Results of general gradient approximation-Perdew-Burke-Ernzerhof (GGA-PBE) and  G₀W₀ are taken as reference and a two-dimensional material data set with chemical formula MX₂ is investigated. Least absolute shrinkage and selection operator (LASSO), support vector machine regression (SVR) and gradient boosting regressor (GBR) and other machine learning methods are used to build a band gap prediction model. Among these models, it is found that the SVR model based on linear kernel function and LASSO model both can give a good prediction result, the mean absolute error (MAE) of training model is 0.34 eV and MAE of testing set is 0.5 eV. Thus, for the prediction of two-dimensional material band gap, the feature parameter set adopted by us has a certain completeness and rationality, which has a certain reference value for the preliminary prediction for the band gap of new materials.



Extremal representations of polar set and ${M}$-addition

LIU Chang, LENG Gangsong

2020, 26(5):  834-841.  doi:10.12066/j.issn.1007-2861.2092

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The extremal representations of the polar set and M-addition are studied. If K is a compact and convex subset of  Rⁿ, then we have K° = (ext K)°. It is proved that M-sum of K and L is equal to the (bd M)-sum, if K and $L$ are convex bodies containing the origin and M is a convex body in the first quadrant of  R². Moreover, by the counter-examples given in section 3, all these conditions cannot be removed.

Application of CFD-DEM coupling method in seepage-induced ground subsidence

LI Xiaojiao, LU Ye, WU Yajun

2020, 26(5):  842-852.  doi:10.12066/j.issn.1007-2861.2093

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One of the main causes of urban ground subsidence is groundwater seepage. Finite element method is not an ideal method to reveal the microscopic mechanism of ground settlement. With discrete element method, the microscopic mechanism may be revealed, but it doesn't help with the building of a flow filed model with complex shape. Based on discrete element method (DEM) and computational fluid dynamics (CFD) coupling principle, a fluid-solid coupling method is proposed. This method uses PFC to simulate the solid phase and Fluent to simulate the liquid phase. It achieves fluid-solid coupling calculation based on particle microscopic view. Then this method is applied to the study of ground settlement caused by seepage. The effectiveness and feasibility of this method are verified by three examples. It is found that the PFC-Fluent method can show the whole dynamic process of ground settlement caused by seepage from a microscopic perspective, and can also realize the simulation and calculation of various complex shape conditions. The stability of soil was changed under the influence of seepage, and the soil migration lead to ground subsidence. Land subsidence increases with the rise of hydraulic gradient. This study reveals the whole process of ground subsidence under the action of hydraulic gradient, which provides a basis for the prevention and control of urban geological hazards.