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Table of Content

    30 April 2022, Volume 28 Issue 2
    Invited Review
    Skeleton-based action recognition by manifold assumption
    PENG Yaxin, ZHAO Qian
    2022, 28(2):  179-200.  doi:10.12066/j.issn.1007-2861.2316
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    Skeletal data are obtained by encoding the spatial geometricposition of the action, which can prevent the interference ofredundant background information. It is one of the commonly useddata types in the field of action recognition. The existing reviewof action recognition related to skeletal data is mainly dividedinto the classical skeletal data representation and the applicationof skeletal action recognition based on deep learning. Compared withthe action recognition methods based on the traditional Euclideanmetric, manifolds provide an important mathematical tool for abetter study of nonlinear structures. However, there is still a lackof summaries about action recognition from skeletal data using themanifold assumption. Therefore, starting from the four steps ofskeleton representation -- trajectory temporal alignment, actionsequence characterization, and action classification -- thisarticle systematically summarizes the action recognition work basedon the manifold assumption, and compares the performance of eachwork on the benchmark datasets. Finally, according to the currentdevelopment trend of action recognition, further improvement of themanifold assumption in thedirection of action recognition is prospected.

    Urban Traffic and the Environment
    An equilibrium analysis of commuting considering location of parking slot and walking cost in a two-to-one network
    ANG Tingcai, JIANG Rui
    2022, 28(2):  201-214.  doi:10.12066/j.issn.1007-2861.2363
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    Commuters from two different residence places drive to the same working place through two completely non-overlapping highways with bottlenecks and share a parking space. Based on the classical bottleneck model, we introduced competition for parking spaces between the two groups of commuters, constructed a function about location of parking slot and established the departure time choice model considering walking cost. Based on the start time and end time of the rush hour of the two groups, the equilibrium state can be classified into four situations. Considering the time of on time arrival, the four situations can be further classified into 14 sub-situations. We have derived the departure pattern and arrival pattern of the commuters in these sub-situations. Finally, considering the scenario that two groups of commuters have the same value of time and the bottleneck capacities on the two highways are also the same, numerical examples have been presented to show how the equilibrium state changes with walking speed and commuter numbers.

    Traffic bottleneck induced by vehicles entering residential areas and its effect on road capacity
    SHENG Zhe, ZHOU Wenhai, GAO Qingfei, DONG Liyun
    2022, 28(2):  215-225.  doi:10.12066/j.issn.1007-2861.2292
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    Vehicles decelerate in advance when entering a residential area, forming traffic bottlenecks. Especially in evening peaks, vehicles returning to residential areas will significantly reduce road capacity. This paper introduces anticipation time to reflect the deceleration behavior of vehicles before entering the residential area based on the velocity-dependent randomization (VDR) model. Both the one-way, single-lane system and the two-way, two-lane system are studied in this paper. The simulation results show that there is a critical injection probability when the entry probability is large enough. When the injection probability is greater than the critical value, a traffic platform appears. The critical injection probability and its corresponding flux value decrease with increasing the entry probability. When the injection probability is less than the critical value, the flux in the two-way, two-lane system is greater than that in the one-way, single-lane system. There are three bottlenecks in the two-way, two-lane system: the entrance to the residential area and the upstream and downstream ends of the road. When the entrance to the residential area is not close to the ends of the road, the influence of the entrance location on road capacity is negligible.

    Research Articles
    An algorithm for solving the permutation indeterminacy problem of frequency-domain ICA based on speech energy ratio
    ANG Zhiqiang, WANG Tao, JIN Zhiwen
    2022, 28(2):  226-237.  doi:10.12066/j.issn.1007-2861.2239
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    With the development of artificial intelligence & internet of things (AIoT) and the rapid advancement of hardware technology, an increasing number of smart speakers are becoming a part of people's lives. Human-computer interaction has also witnessed a shift from remote control to voice control. However, the audio signals recorded by the microphone in a device usually contain considerable noise and interfering voices. Therefore, separation needs to be performed on the signals recorded by the microphones. Frequency-domain independent component analysis (ICA) is a commonly used separation technique, but it faces the permutation indeterminacy problem, i.e., the separated components from Source 1 are classified into a channel for Source 2, whereas the separated components from Source 2 are classified into a channel for Source 1, which greatly deteriorates the separation performance. To address this issue, we proposed an algorithm based on the speech energy ratio, which effectively improved the separation performance. The separation performance was tested on the Signal Separation Evaluation Campaign (SiSEC) and Computational Hearing in Multisource Environments (CHiME) datasets. The results showed that the proposed algorithm outperformed existing algorithms, and a good separation performance for mixed signals could be maintained even in an environment with strong reverberations.

    Time difference of arrival localization based on an improved salp swarm algorithm
    MA Yiming, SHI Zhidong, ZHAO Kang, GONG Changlei, SHAN Lianhai
    2022, 28(2):  238-249.  doi:10.12066/j.issn.1007-2861.2237
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    To address the nonlinear optimization problem of indoor time difference of arrival (TDOA) location estimation, an improved salp swarm algorithm (SSA) is proposed to search target locations. An improved fitness function is constructed by selecting the optimal master base station so that the fitness function can better reflect the quality of the solution, thereby enhancing search accuracy. The approximate solution is introduced into an initial salp population to simplify global exploration, and the convergence speed of the algorithm is accelerated in the early stage. An adaptive following strategy is used to update follower locations to solve the problem of low efficiency in local exploitation, which accelerates the algorithm convergence speed in the later stage. Simulation results show that the TDOA localization technology based on the improved SSA has higher localization accuracy and faster convergence speed than other meta-heuristic algorithms.

    Just-noticeable distortion model based on colour complexity and structure tensor
    WANG Chuang, WANG Yongfang, LIAN Junjie
    2022, 28(2):  250-260.  doi:10.12066/j.issn.1007-2861.2276
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    The just noticeable distortion (JND) threshold refers to the minimum distortion at which eyes can perceive. JND can be used to remove visual redundancy derived from image or video compression. Considering that JND models do not make full use of colour features and structural information, this study proposes a JND model based on colour complexity and structure tensor. First, the colour complexity is estimated and it is used to calculate the visual weight values related to the sensitivity of human eyes. Then the estimated colour complexity is combined with the contrasting masking effect to improve the accuracy of the model. Next, utilising the local structure tensor to represent local features, the modulation factor is established to calculate the visual redundancy of irregular regions. Finally, the colour complexity structure tensor based JND (CSJND) model is estimated by combining the colour-complexity-based JND model and structure tensor modulation factor. Experimental results show that the proposed CSJND model can acquire a noticeably lower peak-signal-to-noise ratio as compared with some existing JND models while also achieving the same subjective perceptual quality. This is more consistent with human visual perception. The proposed CSJND model can also calculate the JND thresholds more accurately.

    Image matting based on deep learning
    WANG Rongrong, XU Shugong, HUANG Jianbo
    2022, 28(2):  261-269.  doi:10.12066/j.issn.1007-2861.2287
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    Image editing technology, which is widely used in the post-production of film and television and in daily life, is based on image matting. In this study, an image matting network based on deep learning which estimates the value of each pixel by inputting the original image and trimap is proposed. Based on the original down- and up-sampling network and to address the problem of slow network convergence caused by the large difference between matting dataset pictures, batch normalisation (BN) is applied after each convolution layer in this study. In the normalisation layer, the input data are normalised to speed up the convergence of the model. This enables the update direction of the parameters to be more consistent with the overall characteristics of the dataset. Because the edge of the object should be carefully considered in the matting task, a deformable convolution layer is used instead of the custom convolution layer. The deformable convolution layer can adaptively learn the shape of the convolution kernel according to different input data, effectively expand the range of the receptive field, and improve the prediction effect in detailed image parts.

    Chinese nested named entity recognition based on hierarchical tagging
    JIN Yanliang, XIE Jinfei, WU Dijia
    2022, 28(2):  270-280.  doi:10.12066/j.issn.1007-2861.2283
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    Chinese named entity recognition plays a critical role in Chinese information processing. In Chinese information text, many named entities contain nested entities. However, most recent studies have focused solely on the recognition of flat entities, which cannot fully capture the boundary information between nested entities. In this study, a hierarchical tagging method is used for nested named entity recognition (NNER), in which each layer of entity recognition is parsed into a separate task, and a gated filtering mechanism is used to promote information exchange between layers. Experiments are conducted on the public NNER corpus of the People's Daily from 1998 to verify the effectiveness of the model. Experimental results show that the F1 value of this method on the People's Daily dataset reach 91.41% without using external resource dictionary information. Thus, the method is shown to improve the recognition of Chinese nested named entities.

    Multi-label label-specific feature selection based on graph Laplacian
    WU Zhejun, HUANG Rui
    2022, 28(2):  281-290.  doi:10.12066/j.issn.1007-2861.2243
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    Multi-label feature selection, which can effectively removeredundant features and improve classification performance, has become an effective solution for the problem of "curse of dimensionality". However, existing multi-label feature selection methods select the same features for all labels without considering the intrinsic relation between labels and features. In fact, each label has label-specific features that reflect the specific attributes of the label. A feature selection method called multi-label label-specific feature selectionbased on graph Laplacian (LSGL) is proposed in this study. LSGL first obtains alow-dimensional embedding of instances for each class label based on Laplacianeigenmaps. Next, it obtains a projection matrix that can project samples from adata space to manifold embedding space through sparse regularization. It thendetermines the label-specific features of the corresponding class label bycoefficient analysis of the matrix. Finally, the label-specific featuresare used for classification. Experimental results of multi-label featureselection andclassification on five public multi-label datasets showed the effectiveness of the proposed algorithm.

    First-principles calculation of defects and mechanical properties of tungsten/graphane/tungsten as a first wall material
    GUO Shun, ZHANG Zhaochun, XIE Yaoping, GUO Haibo
    2022, 28(2):  291-303.  doi:10.12066/j.issn.1007-2861.2240
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    A Tokamak is a primary device used to obtain energy from controlledthermonuclear fusion. The first wall material inside the device isthe key to its stable operation. Tungsten metal is widely used as afirst wall material, but the helium atoms derived from the fusionreaction generate helium bubbles and point defects after they enterthe tungsten crystal, which critically affect the stability of thefirst wall material. Therefore, we designed for the first time atungsten/graphane/tungsten system as a first wall material. Resultsof first-principles calculations showed that the interface of thetungsten/graphane/tungsten system can capture helium atoms andvacancies as well as promote recombination between self-interstitialtungsten atoms and vacancies, thereby reducing the defect density ofthe tungsten metal. An elastic constant calculation showed that thepresence of a graphane layer could increase the Cauchy pressurevalue ($C'$) and anisotropy factor ($A$) of the tungsten metal,indicating that the ductility of the material was improved andcracks were not likely to occur. The mechanical modulus of thetungsten/graphane/tungsten material decreased under the sametemperature. Using the quasi-harmonic Debye model to calculate theGibbs free energy ($G^\ast$), heat capacity at constant volume($C_\mathrm V$), entropy ($S$), and other thermodynamic functionsshowed that the thermodynamic stability of thetungsten/graphane/tungsten material decreasedas compared with that of the pure tungsten metal.

    Controllable synthesis of ZnO with different structures and its effect on gas sensitivity
    LI Shen, ZHOU Diwen, HE Xinhua, LI Fei, NING Zhukai, JIAO Zheng
    2022, 28(2):  304-313.  doi:10.12066/j.issn.1007-2861.2285
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    The micromorphology of a material is the main factor that influencesits gas sensitivity. Applications of low-dimensional structuralmaterials are greatly limited because of agglomeration issues duringreactions. The performance of nanomaterials can be improved bydesigning and synthesising multilevel structures. Materialmorphology was mainly adjusted by controlling the hydrothermal time,the concentration of anionic surfactant citrate ions and hydroxideions. The ZnO nanomaterial synthesised under the controlledhydrothermal conditions had three types of morphologies,pompon-like, flaky-flower-shaped, and buns-like. The pompon-like ZnOshowed good gas sensitivity. At 340 $^\circ$C, itsgas-sensitive response to 100$\times10^{-6}$ n-butanol was 238,which was 2.12 times higher than that in case of ethanol, showinggood selectivity. In addition, by investigating the growth andsensing mechanisms of the multistage structure of ZnO, insights wereprovided for designing high-performance gas sensitive materialsusing multilevelarchitecture of ZnO.

    Improved approach to detect small sample target based on remote sensing image
    LI Chengfan, ZHAO Junjuan
    2022, 28(2):  314-323.  doi:10.12066/j.issn.1007-2861.2352
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    In this study, an improved convolutional neural network (CNN)approach is proposed to detect small sample targets from remotesensing images. The approach is designed to address the two issuesof small target samples and the unbalanced distribution of groundobject samples with respect to target detection of small samples byremote sensors. In the proposed method, first, $K$-nearest neighbor(kNN) regression is adopted to extract the features of each pointand convolution layer to construct the local neighborhood. Second,all local features are aggregated by maximum pooling layer in CNN torepresent global features. Subsequently, the full connection layerand scaled exponential linear unit (SELU) activation function areapplied to calculate the probability corresponding to each categoryfor classification. Finally, the proposed approach is tested andevaluated on hyperspectral imager remote sensing images datasets.Experimental results show that the proposed improvements to the CNNmodel fuse fully local features and result in the effectiverecognition and detection of small sample targets from remotesensing image with high accuracy while maintaining thenonlocal diffusion capabilities of information.

    Frequency characteristics of magnetic coupling resonance superconducting wireless power transmission
    DAI Peng, HAN Shulun, ZHOU Difan, GUO Yanqun, CAI Chuanbing
    2022, 28(2):  324-332.  doi:10.12066/j.issn.1007-2861.2320
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    Traditional wireless power transmission systems have lowtransmission efficiency under low-frequency conditions, limitingtheir application in low-frequency and high-power wireless powertransmission scenarios, such as electric vehicles and underwatersubmarines. In this study, a solution was developed to solve thisproblem using high-temperature superconducting coils instead ofcopper coils. The transmission characteristics of the wireless powertransmission systems with superconducting and copper coils atdifferent operating frequencies were investigated throughtheoretical analysis and experimental verification. The resultsshowed that the superconducting coils had a lower resistance and ahigher quality factor than the copper coils. In addition, thesuperconducting coils had unique advantages under low-frequencyconditions. It was demonstrated that the use of superconductingcoils in wireless power transmission systems operating at lowfrequencies could significantly improve the output power andtransmission efficiency of the system.

    Implementation of charge qubits in ultra-strong coupling regime and quantum-state transfer
    YU Jing, ZHOU Mo, HUANG Tangyou, HAO Minjia, CHEN Xi
    2022, 28(2):  333-346.  doi:10.12066/j.issn.1007-2861.2345
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    The Cooper-pair box (CPB) capacitively coupled to an LC resonatorwas considered in a superconducting quantum circuit that permittedthe high adjustability of light-matter interactions. The deep-strongcoupling (DSC) and ultra-strong coupling (USC) regimes could beobtained by increasing the impedance of the LC resonator anddecreasing the Josephson energy of the qubit. In this regard, atwo-qubit circuit, as a coherent mediator with a promising degree ofnoise immunity, was used to transfer quantum states between pairs ofTransmon qubits. This study provided new insights into USC regimesin light-matter interaction systems. Furthermore, it contributed tothe fields of quantum control, quantum simulation, and quantuminformation processing with superconducting quantum circuits.

    Strong decay of ${\Lambda}_{\bf c}\textbf{(2880)}^{+}$ as 2D-wave excitations
    LI Yang, ZHANG Ailin
    2022, 28(2):  347-356.  doi:10.12066/j.issn.1007-2861.2324
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    The strong decay of $\Lambda _{c} (2880)^+$ in the $^3P_0 $model was investigated. The decay widths and the ratio of branchingfractions of $\Lambda _{c} (2880)^+$ were calculated. Thenumerical results showed that $\Lambda _{c} (2880)^+$ may be a2D-excited $\Lambda _{{c}2}\big(\frac{3}{2}^+\big)$ with$J^P\!=\!\frac{3}{2}^+$. $n_\rho \!=\!1$ and $l_\lambda\!=\!2$belonged to the radial $\rho $-mode excitation and the orbital$\lambda $-mode excitation, respectively. The ratio of branchingfractions was $R={\it\Gamma} (\Lambda _{c} (2880)^+\to \Sigma_{c} (2520)\pi )$/${\it\Gamma} (\Lambda _{c} (2880)^+\to\Sigma _{c} (2455)\pi )=0.16$. The total decay width was${\it\Gamma} _{total} = 18.53$ MeV. $\Lambda _{c} (2880)^+$could also be a 2D-excited $\Lambda _{{c}2}^{'}\big(\frac{3}{2}^+\big)$ with $J^P=\frac{3}{2}^+$,$n_\lambda =1$ and $l_\lambda=2$, indicating the radial $\lambda$-mode excitation and the orbital $\lambda $-mode excitation. Inthis study, ${\it\Gamma} _{total} =1.69$ MeV, and $R={\it\Gamma}(\Lambda _{c} (2880)^+\to \Sigma _{c} (2520)\pi)$/${\it\Gamma} (\Lambda _{c} (2880)^+\to \Sigma _{c}(2455)\pi )=0.10$.