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Kinematic Calibration of a Six-Legged Walking Machine Tool

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Chinese Journal of Mechanical Engineering 2022年第2期35卷 28-44页

作者： Jimu Liu zhijun Chen Feng gao State Key Laboratory of Mechanical System and Vibration Shanghai Jiao Tong UniversityShanghai 200240China

This paper presents the kinematic calibration of a novel six-legged walking machine tool comprising a six-legged mobile robot integrated with a parallel manipulator on the body.Each leg of the robot is a 2-universal-prismatic-spherical(UPS)and UP parallel mechanism,and the manipulator is a 6-PSU parallel mechanism.The error models of both subsystems are derived according to their inverse kinematics.The objective function for each kinematic limb is formulated as the inverse kinematic residual,i.e.,the deviation between the actual and computed joint coordinates.The hip center of each leg is first identified via sphere fitting,and the other kinematic parameters are identified by solving the objective function for each limb individually using the least-squares method.Thus,the kinematic parameters are partially decoupled,and the complexities of the error models are reduced.A calibration method is proposed for the legged robot to overcome the lack of a fixed base on the ground.A calibration experiment is conducted to validate the proposed method,where a laser tracker is used as the measurement equipment.The kinematic parameters of the entire robot are identified,and the motion accuracy of each leg and that of the manipulator are significantly improved after calibration.Validation experiments are performed to evaluate the positioning and trajectory errors of the six-legged walking machine tool.The results indicate that the kinematic calibration of the legs and manipulator improves not only the motion accuracy of each individual subsystem but also the cooperative motion accuracy among the subsystems.

关键词： Parallel mechanism Legged robot Kinematic calibration

Building Indoor Dangerous Behavior Recognition Based on LSTM-GCN with Attention Mechanism

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Computer Modeling in Engineering & Sciences 2023年第11期137卷 1773-1788页

作者： Qingyue Zhao Qiaoyu Gu Zhijun Gao Shipian Shao Xinyuan Zhang School of Management Shenyang Jianzhu UniversityShenyang110168China School of Information and Communication Engineering North University of ChinaTaiyuan030051China School of Information and Control Engineering Shenyang Jianzhu UniversityShenyang110168China

Building indoor dangerous behavior recognition is a specific application in the field of abnormal human recognition.A human dangerous behavior recognition method based on LSTM-GCN with attention mechanism(GLA)model was proposed aiming at the problem that the existing human skeleton-based action recognition methods cannot fully extract the temporal and spatial features.The network connects GCN and LSTMnetwork in series,and inputs the skeleton sequence extracted by GCN that contains spatial information into the LSTM layer for time sequence feature extraction,which fully excavates the temporal and spatial features of the skeleton sequence.Finally,an attention layer is designed to enhance the features of key bone points,and Softmax is used to classify and identify dangerous behaviors.The dangerous behavior datasets are derived from NTU-RGB+D and Kinetics data sets.Experimental results show that the proposed method can effectively identify some dangerous behaviors in the building,and its accuracy is higher than those of other similar methods.

关键词： Human skeleton building indoor dangerous behaviors recognition graph convolution network long short term memory network attention mechanism

Synthesis of carbon-coated cobalt ferrite core-shell structure composite:A method for enhancing electromagnetic wave absorption properties by adjusting impedance matching

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Chinese Journal of Chemical Engineering 2022年第7期35卷 206-217页

作者： Jing gao zhijun Ma Fuli Liu Cunxin Chen School of Mining Liaoning Technical UniversityFuxin 123000China School of Chemical and Environmental Engineering China University of Mining and TechnologyBeijing 100083China

Cobalt ferrite has problems such as poor impedance matching and high density,which results in unsatisfactory electromagnetic wave(EMW)absorption performance.In this study,the CoFe_(2)O_(4)@C core-shell structure composite was synthesized by a two-step hydrothermal method.X-ray diffraction,transmission electron microscopy,Fourier transform infrared spectroscopy,thermogravimetric analysis,and vector network analysis et al.were used to test the structure and EMW absorption properties of CoFe_(2)O_(4)@C composite.The results show that the reflection loss(RL)of the CoFe_(2)O_(4)@C composite reaches the maximum value of25.66 dB at 13.92 GHz,and the effective absorbing band(EAB)is 4.59 GHz(11.20-15.79 GHz)when the carbon mass content is 6.01%.The RL and EAB of CoFe_(2)O_(4)@C composite are increased by 219.55%and 4.59 GHz respectively,and the density is decreased by 20.78%compared with the cobalt ferrite.Such enhanced EMW absorption properties of CoFe_(2)O_(4)@C composite are attributed to the attenuation caused by the strong natural resonance of the cobalt ferrite,moreover,the carbon coating layer adjusts the impedance matching of the composite,and the introduced dipole polarization and interface polarization can cause multiple Debye relaxation processes.

关键词： Cobalt ferrite Core-shell structure composite Electromagnetic wave absorption Impedance matching

Advances in machine learning-and artificial intelligence-assisted material design of steels

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International Journal of Minerals,Metallurgy and Materials 2023年第6期30卷 1003-1024页

作者： Guangfei Pan Feiyang Wang Chunlei Shang Honghui Wu Guilin Wu Junheng gao Shuize Wang Zhijun Gao Xiaoye Zhou Xinping Mao Beijing Advanced Innovation Center for Materials Genome Engineering University of Science and Technology BeijingBeijing 100083China Yangjiang Branch Guangdong Laboratory for Materials Science and Technology(Yangjiang Advanced Alloys Laboratory)Yangjiang 529500China Guangdong Province Key Laboratory of Durability for Marine Civil Engineering School of Civil EngineeringShenzhen UniversityShenzhen 518060China

With the rapid development of artificial intelligence technology and increasing material data,machine learning-and artificial intelligence-assisted design of high-performance steel materials is becoming a mainstream paradigm in materials science.Machine learning methods,based on an interdisciplinary discipline between computer science,statistics and material science,are good at discovering correlations between numerous data points.Compared with the traditional physical modeling method in material science,the main advantage of machine learning is that it overcomes the complex physical mechanisms of the material itself and provides a new perspective for the research and development of novel materials.This review starts with data preprocessing and the introduction of different machine learning models,including algorithm selection and model evaluation.Then,some successful cases of applying machine learning methods in the field of steel research are reviewed based on the main theme of optimizing composition,structure,processing,and performance.The application of machine learning methods to the performance-oriented inverse design of material composition and detection of steel defects is also reviewed.Finally,the applicability and limitations of machine learning in the material field are summarized,and future directions and prospects are discussed.

关键词： machine learning data-driven design new research paradigm high-performance steel

What attracts China's contracts to Latin America and the Caribbean?An empirical study of the determinants of Chinese contracts

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Economic and Political Studies 2018年第1期6卷 91-117页

作者： Yi Feng Zhijun Gao Wanjun Jiang Department of International Studies Claremont Graduate UniversitClaremontCAUSA Guanghua School of Management Peking UniversityBeijingChina

As China's economy has reached the stage of'New Normal',Chinese companies are increasingly seeking opportunities overseas.In the context of the slow recovery of world economy,China's outward economic activities have found themselves in many parts of the globe,including the Latin Ameria and the Caribbean(LAC)region,some of the farthest places away from China.While many scholars have conducted extensive studies on China's trade and foreign direct investment(FDI)in Latin America and the Caribbean,this paper focusses on Chinese contracts in the region,a topic that has been rarely studied.Using both random-effects and fixed-effects models covering 30 LAC economies during 1998-2015,the multivariate panel regressions show that among numerous determinants,Chinese companies prefer to undertake projects in the countries that are economically more advanced and more populous.In addition to the level of development and the size of population,those that have natural resources,expansionary economy,and political openness tend to have Chinese contracts completed.The above,however,is true of only the countries with which China has diplomatic relations.For the countries that recognise China's Taiwan‘diplomatically',Chinese contracts do not seem to be as much economically determined as those that recognise People's Republic of China(PRC)diplomatically.Politics appear to interfere with contractual decisions except in the following categories:mineral resources and an expansionary economy.

关键词： International contracts China LatinAmericaand the Caribbean natural resources globalisation

Electronic structures and topological properties in nickelates Lnn+1NinO2n+2

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National Science Review 2021年第8期8卷 208-215页

作者： Jiacheng gao Shiyu Peng zhijun Wang Chen Fang Hongming Weng Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of Sciences School of Physical Sciences University of Chinese Academy of Sciences Songshan Lake Materials Laboratory Kavli Institute for Theoretical Sciences Chinese Academy of Sciences Physical Science Laboratory Huairou National Comprehensive Science Center

After the significant discovery of the hole-doped nickelate compound Nd0.8Sr0.2NiO2, analyses of the electronic structure, orbital components, Fermi surfaces and band topology could be helpful to understand the mechanism of its superconductivity. Based on first-principle calculations, we find that Ni3dx~2-y~2states contribute the largest Fermi surface. The Ln5d3z~2-r2states form an electron pocket at, while 5 dxy states form a relatively bigger electron pocket at A. These Fermi surfaces and symmetry characteristics can be reproduced by our two-band model, which consists of two elementary band representations: B1g@1a⊕A1g@1b. We find that there is a band inversion near A, giving rise to a pair of Dirac points along M-A below the Fermi level upon including spin-orbit coupling. Furthermore,we perform density functional theory based Gutzwiller(DFT+Gutzwiller) calculations to treat the strong correlation effect of Ni 3 d orbitals. In particular, the bandwidth of 3dx~2-y~2has been renormalized largely.After the renormalization of the correlated bands, the Ni 3 dxy states and the Dirac points become very close to the Fermi level. Thus, a hole pocket at A could be introduced by hole doping, which may be related to the observed sign change of the Hall coefficient. By introducing an additional Ni3dxyorbital, the hole-pocket band and the band inversion can be captured in our modified model. Besides, the nontrivial band topology in the ferromagnetic two-layer compound La3Ni2O6is discussed and the band inversion is associated with Ni3dx~2-y~2and La5dxyorbitals.

关键词： nickelate superconductors band representations topological Dirac points DFT+Gutzwiller calculations

Density functional theory and kinetic Monte Carlo simulation study the strong metal-support interaction of dry reforming of methane reaction over Ni based catalysts

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Chinese Journal of Chemical Engineering 2021年第1期34卷 176-182页

作者： Xueyan Zou Xiaodong Li Xiaoyu gao Zhihua gao zhijun Zuo Wei Huang Key Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province Taiyuan University of TechnologyTaiyuan 030024China College of Chemistry and Chemical Engineering Jinzhong UniversityJinzhong 030619China

Oxide supports modify electronic structures of supported metal nanoparticles,and then affect the catalytic activity associated with the so-called strong metal-support interaction(SMSI).We herein report the strong influence of SMSI employing Ni_(4)/α-MoC(111) and defective Ni_(4)/MgO(100) catalysts used for dry reforming of methane(DRM,CO_(2)+CH_4→2 CO+2 H_(2)) by using density functional theory(DFT) and kinetic Monte Carlo simulation(KMC).The results show that α-MoC(111) and MgO(100) surface have converse electron and structural effect for Ni_(4) cluster.The electrons transfer from a-MoC(111) surface to Ni atoms,but electrons transfer from Ni atoms to MgO(100) surface;an extensive tensile strain is greatly released in the Ni lattice by MgO,but the extensive tensile strain is introduced in the Ni lattice by α-MoC.As a result,although both catalysts show good stability,H_(2)/CO ratio on Ni_(4)/α-MoC(111) is obviously larger than that on Ni_(4)/MgO(100).The result shows that Ni/α-MoC is a good catalyst for DRM reaction comparing with Ni/MgO catalyst.

关键词： DRM MgO Ni α-MoC SMSI

Spatial gradient distributions of thermal shock-induced damage to granite

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第5期12卷 917-926页

作者： Lifeng Fan Jingwei gao Xiuli Du zhijun Wu College of Architecture and Civil Engineering Beijing University of TechnologyBeijing100124China School of Civil Engineering Wuhan UniversityWuhan430072China

In this study,we attempted to investigate the spatial gradient distributions of thermal shock-induced damage to granite with respect to associated deterioration mechanisms.First,thermal shock experiments were conducted on granite specimens by slowly preheating the specimens to high temperatures,followed by rapid cooling in tap water.Then,the spatial gradient distributions of thermal shock-induced damage were investigated by computed tomography(CT)and image analysis techniques.Finally,the influence of the preheating temperature on the spatial gradients of the damage was discussed.The results show that the thermal shock induced by rapid cooling can cause more damage to granite than that induced by slow cooling.The thermal shock induced by rapid cooling can cause spatial gradient distributions of the damage to granite.The damage near the specimen surface was at a maximum,while the damage inside the specimen was at a minimum.In addition,the preheating temperature can significantly influence the spatial gradient distributions of the thermal shock-induced damage.The spatial gradient distribution of damage increased as the preheating temperature increased and then decreased significantly over 600C.When the preheating temperature was sufficiently high(e.g.800C),the gradient can be ignored.

关键词： Rock properties Thermal shock High temperature Thermally induced damage Computed tomography(CT)technique

Egocentric Action Anticipation Based on Unsupervised Gaze Estimation

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Wuhan University Journal of Natural Sciences 2021年第3期26卷 207-214页

作者： ZHONG Cengsi FANG zhijun gao Yongbin HUANG Bo School of Electronic and Electrical Engineering Shanghai University of Engineering ScienceShanghai 201620China

Gaze information is important for finding region of interest(ROI)which implies where the next action will happen.Supervised gaze estimation does not work on EPIC-Kitchens for lack of ground truth.In this paper,we develop an unsupervised gaze estimation method that helps with egocentric action anticipation.We adopt gaze map as a feature representation,and input it into a multiple modality network jointly with red-green-blue(RGB),optical flow and object features.We explore the method on EGTEA dataset.The estimated gaze map is further optimized with dilation and Gaussian filter,masked onto the original RGB frame and encoded as the important gaze modality.Our results outperform the strong baseline Rolling-Unrolling LSTMs(RULSTM),with top-5 accuracy achieving 34.31%on the seen test set(S1)and 22.07%on unseen test set(S2).The accuracy is improved by 0.58%and 0.87%,respectively.

关键词： egocentric video action anticipation gaze estimation