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28 October 2021, Volume 47 Issue 5 Previous Issue    Next Issue

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Materials Science and Engineering

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Effect of heat treatment on the corrosion behavior of 347H stainless steel in molten nitrate salt TANG Meng-lan, WANG Jun, LIU Tian-zeng, LI Jun-chen, FENG Li 2021, 47 (5):  1-9.  Abstract ( 442 )   PDF (11473KB) ( 311 )   Save In this paper, a static molten salt immersion experiment is used to study the corrosion behavior of 347H stainless steel with different grain sizes in mixed nitrate molten salt (60%NaNO3+40%KNO3) at 565 ℃ for up to 120 h. The corrosion kinetic curve is drawn by the weight gain method, the surface corrosion products and phases of 347H stainless steel are studied, and the micro-area composition of the corroded surface is analyzed to explain the corrosion mechanism of 347H stainless steel in nitrate molten salt. The results show that the corrosion rate of 347H stainless steel whose grain size is adjusted by solution treatment decreases during molten salt corrosion, and the corrosion kinetics curve becomes a linear growth trend. Through XRD detection, the corrosion products of 347H stainless steel in molten nitrate salt are mainly Fe2O3 and a small amount of Fe3O4 and NaFeO2. Fe3O4 has a compact structure, which can effectively reduce the corrosion of nitrate molten salt to the steel matrix, resulting in a decrease in the quality loss of 347H stainless steel in the later stage of corrosion. The results of corrosion product morphology and cross section thickness analysis show that the corrosion layer thickness of 347H stainless steel reaches the minimum of 0.661 μm when the grain size of the stainless steel reaches 7 after solution treatment at 1 160 ℃-1 h, and the corrosion resistance of 347H stainless steel in molten nitrate salt reaches the best. References | Related Articles | Metrics

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Metal recovery from spent lithium-ion power batteries by roasting and water leaching method WANG Da-hui, ZHANG Ke, CHEN Huai-jing, LIU Zhen-ning, HU Ping-ping 2021, 47 (5):  10-18.  Abstract ( 414 )   PDF (7625KB) ( 102 )   Save Lithium-ion power batteries have been widely used in new energy vehicles. The clean and efficient recovery of Li, Ni, Co, Mn and other metals after their scrap is of great significance to promote the recycling of non-ferrous metals. Li, Ni, Co, and Mn are recoveringfrom lithium-ion power batteries using LiNi0.5Co0.2Mn0.3O2 as the cathode material, and TG-DSC, XRD, ICP-OES, XPS, and thermodynamics and other studies is used to study the phase evolution law of the recycling process and the main factors which affect the metal recovery rate. The research results show that the mixture composed of LiNi0.5Co0.2Mn0.3O2 and NaHSO4·H2O, the occurrence state of Li, Ni, Co, and Mn after roasting have been changed from the complex metal oxide form which is insoluble in water into the form of water-soluble metal sulfate. After roasting, the roasted product is leached with water under certain conditions, the elements Li, Ni, Co, and Mn are transferred to the aqueous solution in the form of metal ions for recovery. The composition of the mixture and the roasting temperature restrict the occurrence of Li, Ni, Co, and Mn elements in the roasted material, and are also the main factors affecting the recovery rate of Li, Ni, Co, and Mn; the roasting and water leaching process is adopted. References | Related Articles | Metrics

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Research on DR digital imaging automatic detection method of blade air film hole processing defects LIU Tao, SHI Yu, LI Chun-kai, SUN Zhong-chen, MAN Yue-e, LV Jian 2021, 47 (5):  19-23.  Abstract ( 387 )   PDF (3987KB) ( 713 )   Save Air film holes are one of the important cooling structures in turbine blades, it has great significance to improve the cooling efficiency of aircraft engines, reduce the temperature of the combustion chamber and even increase the service life of the engine. However, in the actual course of working, it is easy to have internal defects such as unopened air film holes, deflection, and damage to the inner wall due to external factors. Traditional detection methods mainly use artificial film X-ray method to detect internal defects, but there are problems such as low detection efficiency, high cost and high dependence on the experience and skills of the inspectors. This paper proposes an automatic detection method for air film hole defects based on X-ray digital imaging technology. By studying the equivalence of DR digital images and film images, the law of the effect of the transillumination angle on defect recognition and the optimization of the detection process, key technologies based on deep learning neural network defect self-recognition, high-precision detection and intelligent recognition of blade air film hole processing defects are realized. References | Related Articles | Metrics

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Effect of CdBr2 on defect state regulation and photoelectric properties of CsPbBr3 perovskite grain boundary LIU Wen-wu, LIU Yu-cheng, CUI Chong-yang, NIU Sheng-tao RAN Fen, QUE Yu-lun 2021, 47 (5):  24-29.  Abstract ( 258 )   PDF (3619KB) ( 245 )   Save The effects of different concentrations of isopropanol solution of CdBr2 on the photoelectric properties of CsPbBr3perovskite solar cells were studied by passivating CsPbBr3perovskite films with CdBr2. The results show that the introduction of CdBr2 to the surface of CsPbBr3perovskite, can decreases the density of defects at the surface, suppresses nonradiative recombination and promotes the extraction and diffusion of photogenerated electrons and holes. Therefore, the interface recombination loss is reduced. The photoelectric conversion efficiency of all inorganic CsPbBr3perovskite solar cell devices were increased from 6.58% to 8.19%, and the Vocwas increased from 1.368 V to 1.531 V. References | Related Articles | Metrics

Mechanical Engineering and Power Engineering

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Ontology-based heterogeneous knowledge modeling and fusion of steam turbine YAN Chang-feng, ZHANG Yong-ming, AI Ke-yong, LI Yu, WU Li-xiao 2021, 47 (5):  30-37.  Abstract ( 225 )   PDF (4361KB) ( 397 )   Save In view of the problems that the knowledge of steam turbine generator equipment maintenance and fault diagnosis is scattered in different power plant, and there are widespread problems such as multi-source heterogeneity, sharing difficulties and the formation of information islands, the structural characteristics of steam turbine generator equipment are analyzed based on the methods of global ontology and local ontology modeling. The global ontology model and local ontology model of the steam turbine generator sets are established by means of Protégé_4.3. The mapping relationship between global ontology and local ontology is designed. The multi-source heterogeneous knowledge fusion and multi-source knowledge retrieval of turbo generator sets are realized. The SQI mechanical fault simulation test rig is used to simulate the faults generated by the steam turbine generator sets. The results show that they have 98% similarity, two different concept faults have the same fault source, which shows that the multi-source heterogeneous knowledge model and fusion method based on ontology is effective and feasible through the simulation of rotor mass eccentricity and rotor imbalance. References | Related Articles | Metrics

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Rotor fault diagnosis method based on M-WDLS and PCA ZHAO Rong-zhen, CHANG Shu-yuan 2021, 47 (5):  38-44.  Abstract ( 178 )   PDF (2759KB) ( 174 )   Save Based on Manhattan distance as the information measure of similarity between features,a feature selection method based on Manhattan-weighted Discriminative Laplacian Score (M-WDLS) was proposed.It can reduce the difficulty in fault classification identification caused by overlapping interactions of different fault characteristics. In this method, Manhattan distance was used to measure the similarity between high-dimensional feature vectors,and the data sample marker information was integrated into the weight calculation to enhance the discrimination of weight,so as to improve the sensitive feature screening performance of LS algorithm. A rotor fault diagnosis method based on M-WDLS and PCA was proposed by combining M-WDLS with Principal component analysis (PCA). Firstly, the time domain,frequency domain and time frequency domain of the original vibration signal were extracted to construct the feature set of the mixed domain. Then, sensitive features were selected by M-WDLS to form sensitive feature matrix. Finally, the sensitive feature matrix was reduced by PCA and the result was input into k-nearest neighbor classifier (KNN) for pattern recognition. The experimental results showed that this method could effectively extract the vibration signal characteristics of the rotor system and improve the accuracy of fault identification. References | Related Articles | Metrics

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Analysis of flow field and hydraulic characteristics of liquid-ring pump as vacuum pump and compressor ZHANG Ren-hui, YU Hao, WEI Xiao-xiao 2021, 47 (5):  45-52.  Abstract ( 382 )   PDF (6753KB) ( 322 )   Save The inner flow and performance of vacuum pump and compressor conditions of 2BE liquid-ring pump were analyzed by using numerical simulation and experimental method. Analysis results show that the volume flow rate of compressor is less than that of the vacuum pump under the same pressure ratio, and the ratio of volume flow rate and efficiency decrease with the increasing of pressure ratio. The distribution of phase, velocity and pressure field are basically the same under the conditions of vacuum pump and compressor. The secondary flow in the exhaust zone and the transition zone of the compressor are obviously stronger than those in the vacuum pump condition. Under the same variation of pressure ratio, the pressure in the exhaust area of the compressor increases significantly. The frequency characteristics of pressure for the pump casing shows obviously partition characteristics along the circumferential direction. The main frequency characteristic of vacuum pump is the same as that of compressor. Under different pressure ratios condition, the pressure fluctuation amplitude of the inner wall of the pump housing in compressor condition is larger than that of the vacuum pump. With the increase of the pressure ratio, the pressure fluctuation amplitude for the compressor exhaust zone and transition zone increases obviously. References | Related Articles | Metrics

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Optimization design and performance analysis of CNC machine tools composite structure bed based on grey theory GUO Run-lan, DENG Wen-qiang, LI Dian-lun 2021, 47 (5):  53-58.  Abstract ( 254 )   PDF (2882KB) ( 245 )   Save To improve the comprehensive performance of CNC machine tools, a steel-concrete composite structure bed is designed, based on a certain horizontal machining center cast iron bed. The method of orthogonal experiment, grey theory and combination weighting is used to optimize its structure, the optimal parameter combination is obtained. Finally, the finite element simulation analysis of the composite structure bed is carried out, and the results are compared with the prototype cast iron bed. The results show that: when the bed mass is increased by 2.3%, the maximum static stress and the maximum static deformation of the composite structure bed are reduced by 51.3% and 82.9%, respectively. The first three natural frequencies are increased by 143.9%, 156.8% and 148.7%, respectively. The maximum amplitudes of the center nodes of x-axis guide rail and z-axis guide rail in x, y and z directions are decreased by 97.6%, 97.1%, 94.0% and 99.6%, 97.9% 85.4%. When the sliding block of the guide rail continuously rubs on the guide rail surface for 1 800 second, the maximum thermal-structural coupling deformation of the guide rail is reduced by 7.3%. References | Related Articles | Metrics

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General model for kinematic analysis of swash plate axial piston pump WANG Jian-sen, CAO Wei-dong, HE Xin-long, WANG Zheng-rong, ZHANG Zhi-wei 2021, 47 (5):  59-64.  Abstract ( 608 )   PDF (3701KB) ( 824 )   Save Based on the comprehensive consideration of swash plate angle, cross angle and piston inclination angle of the swash plate axial piston pump, the general piston kinematics model is established by coordinate transformation method. The analysis results show that the cross angle of swash plate and the inclination angle of piston will increase the maximum amplitudes of displacement, velocity and acceleration of piston, and then increase the displacement of pump, the maximum transient flow velocity in the piston chamber and the inertia force of piston; the cross angle of swash plate will change the phase of piston movement and make the internal and external dead points deflect, which will change the pre-compression and pre-expansion angle of valve plate; the inclination angle of piston will affect the movement of the piston, the smaller the inclination angle of the plunger, the closer the movement of the plunger is to the simple harmonic motion, on the contrary, the larger the deviation is, the maximum deflection angle of internal and external dead center is 90°, the smaller the absolute value of the cross angle is, the smaller the deflection angle of internal and external dead center changes in the range of big swash plate angle, and the greater the gradient of change when swash plate angle is close to zero displacement. References | Related Articles | Metrics

Chemical Industry and Light Industry

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An efficient protocol for the synthesis of 1, 3, 5-triarylpyrazoles YANG Zheng, XIE Heng-shen, DING Wei-hua, ZHAO Ming-zhu 2021, 47 (5):  65-69.  Abstract ( 166 )   PDF (839KB) ( 304 )   Save By using 2, 3-epoxypropan-1-one and arylhydrazine, trimethylamine-promoted in situ ring opening/cyclization reaction at100 ℃ was developed in ethanol under microwave irradiation, affording a series of triarylpyrazoles in good yields. Single crystal X-ray diffraction confirmed the structure of compound 3a. Furthermore, the structures of all products were characterized by infrared, nuclear magnetic, and high-resolution mass spectrometry. References | Related Articles | Metrics

Automation Technique and Computer Technology

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Research on characterization of electricity consumption behavior based on clustering and random matrix theory WU Li-zhen, ZHANG Yong-nian, CHEN Wei, HAO Xiao-hong 2021, 47 (5):  70-75.  Abstract ( 226 )   PDF (1941KB) ( 279 )   Save In order to solve the problem that it is difficult to establish a model to describe the user’s electricity consumption behavior under the background of big data application in distribution network, a method based on clustering and random matrix theory is proposed to describe the user’s electricity consumption behavior. Firstly, the K-means clustering method is used to analyze the power consumption characteristic data of massive users, and the users are divided into groups according to the clustering results under different power consumption modes. Then, the model of user electricity behavior analysis is established based on the random matrix theory, through the analysis of the economic data, climate data and electricity price data of each user group, the factors related to the power consumption of the user group are identified, and describes the power user’s electricity consumption behavior. Finally, the effectiveness and accuracy of the proposed method is verified by the actual power consumption data of Wuwei power grid in Gansu Province, which provides data support for accurate power marketing and power demand side response strategy formulation. References | Related Articles | Metrics

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Gaze prediction algorithm based on hypercomplex wavelet convolutional network LI Ce, ZHU Zi-zhong, XU Da-you, GAO Wei-zhe, JIN Shan-gang 2021, 47 (5):  76-84.  Abstract ( 221 )   PDF (5371KB) ( 310 )   Save Gaze based prediction algorithms has a wide range of applications in object recognition, video compression, object tracking and so on. For existing gaze prediction models, the accuracy of gaze prediction is low due to the lack of feature details, single scale, and serious background information interference. This paper proposes a gaze prediction algorithm based on hypercomplex wavelet convolutional network. Firstly, aiming at the problem of loss of detailed features, the hypercomplex wavelet transform is used to extract the detailed features of the image in the frequency domain and fused with the spatial features extracted by the convolutional network. Then, through the atrous spatial pyramid pooling module, the feature maps obtained from different receptive fields are fused to effectively solve the problem of single feature scale. Finally, the proposed algorithm introduces a residual convolutional attention module, which combines spatial and channel attention mechanisms to effectively suppress the interference of background information and improve the accuracy of gaze prediction. On the SALICON datasets, CC, sAUC and SIM evaluation metrics, the performance of the proposed algorithm reaches 0.884 7, 0.769 3 and 0.778 0. On the CAT2000 datasets, the performance of the proposed algorithm is 0.735 5, 0.870 1, and 0.664 5. The experimental results show that the proposed algorithm has a good ability to predict fixation points. References | Related Articles | Metrics

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Star-convex extended target student’s t filter for heavy tailed noise CHEN Hui, ZHANG Xing-xing, YANG Wen-yu 2021, 47 (5):  85-92.  Abstract ( 247 )   PDF (2273KB) ( 288 )   Save Aiming at the problem of irregular shape extended target tracking with nonlinear non-Gaussian heavy tailed noise, this paper proposes a star-convex extended target nonlinear student’s t filter algorithm based on a random hypersurface model. First, in a system with non-Gaussian heavy tailed process and measurement noise, a robust student’s t based nonlinear filter is given based on the student’s t distribution. Then, random hypersurface model (RHM) is used to describe the measurement source distribution of any star-convex extended target, and star-convex extended target student’s t filter is proposed. Finally, numerical simulation example shows the validity and feasibility of the proposed method. References | Related Articles | Metrics

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Speaker recognition algorithm based on multi-featured I-Vector ZHAO Hong, YUE Lu-peng, CHANG Zhao-bin, WANG Wei-jie 2021, 47 (5):  93-98.  Abstract ( 303 )   PDF (897KB) ( 295 )   Save Aiming at the problem of inaccurate and inefficient speaker recognition presented by single acoustic feature, a speaker recognition algorithm was proposed based on multi-featured I-Vector. Firstly,different acoustic feature vectors were extracted and combined into a high-dimensional feature vector.Then principal components analysis (PCA) was used to effectively remove the correlation of these feature vectors, so that the features became orthogonalized. Finally, probabilistic linear discriminant analysis(PLDA) was used for modeling and scoring, which led to reduce the spatial dimension to a certain degree.Experiments were carried out on TIMIT corpus in combination with Kaldi speech recognition toolkit, and the results compared with the single-featured systems including Mel-frequency cepstral coefficients (MFCC) and perceptual linear predictive (PLP) coefficients based on I-Vector, the equal error rate (EER) of the purposed algorithm were increased by 8.18%and 1.71%, respectively;the model training time were decreased respectively by 60.4% and 47.5%,respectively.Therefore, the purposed algorithm has betterspeaker recognition performance and efficiency. References | Related Articles | Metrics

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Investigation of highly-selective tri-passband three-dimensional    frequency selective surface YU Zheng-yong, LU Hua-li, HE Xiao-feng 2021, 47 (5):  99-105.  Abstract ( 215 )   PDF (3881KB) ( 431 )   Save A dual-polarized, highly-selective tri-passband three-dimensional frequency selective surface (3D FSS)is proposed. The unit cell of the proposed 3D FSS consists of four layers of square dielectric tubes, which provides one parallel plate waveguide (PPW) path and three square coaxial waveguide (SCW) paths. Owing to the electromagnetic coupling between two same short SCW resonant elements in each SCW path, original single resonant mode provided by the square slot on the end face of SCW path will split into even- and odd-resonant modes, introducing two transmission poles, and then forming a second-order passband. Thus, three SCW paths can realize three second-order passbands. In addition, the electromagnetic waves in different paths are combined out-of-phase,which can generate multiple transmission zeros and improve the frequency selectivity of this FSS.In order to explain the operating principle of the proposed 3D FSS, the distributions of electric-field vector at the frequencies of the transmission zeros/poles are investigated. The simulated results show that the proposed 3D FSS exhibits stable frequency responses to variations of incident angle from 0° to 60° under both transverse electric (TE) and transverse magnetic (TM) polarizations. Meanwhile,this 3D FSS has small band ratios and relatively compact unit cell size. References | Related Articles | Metrics

Architectural Sciences

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Analysis of deep cutting dualistic structure slope stability considering residual strength of sandstone YE Shuai-hua, FAN Li-ming, SHI Yi-lei 2021, 47 (5):  106-114.  Abstract ( 168 )   PDF (4943KB) ( 353 )   Save A large number of dualistic structure slopes occurred during the construction of highways in western China, but the strength of the rock mass material in the stability analysis of such slopes is still unclear. Taking the slope engineering of Lanyong high way as background, the cause of the damage of adualistic structure slope composed of loess and sandstone in K35+000~150 of Lanyong high way was analyzed.Choosing a typical section of the slope engineering, FEM was usedto compare the stability and the destruction characteristics of the deep cutting slope under two different situations that the sandstone was respectively at peak strength and residual strength. Moreover, based on residual strength, the effects of prestressed anchors on the slope stability was studied. The results show that the result calculated by residual strength is more suitable forthe actual failure of the dualistic structure slope and that if the slope can be supported by prestressed anchors, the slope stability would be effectively improved to preventthe slope instability.The research results can provide references for the stability analysis of loess-sandstone dualistic-structure high slope in Gansu Province. References | Related Articles | Metrics

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Cohesion-damage-friction constitutive model of the frozen soil-structure interface CHEN Xiao, HE Peng-fei, DONG Jian-hua, REN Xin, WU Xiao-lei 2021, 47 (5):  115-121.  Abstract ( 278 )   PDF (2507KB) ( 252 )   Save The constitutive model of the interface between frozen soil and structure is very important to the design, analysis and numerical simulation of engineering practice in cold regions. A one-dimensional constitutive model of the interface between frozen soil and structure was established by coupling the cohesive damage model and the friction model. Based on the meso-mechanical assumption, the mechanical response of cemented ice at the interface and the friction mobilization, the representative elementary area of the interface was divided into damaged part and non-damaged part. During the shearing of the interface, the non-damaged part of the representative elementary area was assumed to be elastic deformation. The friction effect was mobilized during the representative elementary area transform from the initial undamaged state to the fully damaged state. The damage evolution equation and the friction evolution process of the representative elementary area were established based on the basic kinematics hypotheses of the interface, and the constitutive relationship of the interface was established according to the homogenization method. The parameters in the model have clear physical meanings and are easy to obtain from the test data. The numerical results show that the model has a good fitting effect on the both strain softening curve and strain hardening curve of the interface, and the key parameters in the test curve can be reflected in the model. References | Related Articles | Metrics

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Low-cycle fatigue test of Q345B steel frame beam-column connection weld LI Wan-run, LIU Yu-fei, DU Yong-feng 2021, 47 (5):  122-129.  Abstract ( 200 )   PDF (4607KB) ( 256 )   Save In order to study the low cycle fatigue of steel frame beam-column connections under different amplitude regimes, the low-cycle fatigue test of six full-scale all-welded beam-column connections were designed and finished, and the fatigue crack initiation and expansion of welds was studied.The influence of cyclic amplitude and loading history on the fatigue performance of the connections was analyzed, and the cumulative degree of fatigue damage during normal amplitude, variable amplitude and random load was compared. The results show that under the three amplitude regimes, the welding toe of the flange welding hole isprone to fatigue cracking, and the final fracture path is the oblique development of the welding holes weld toe crack, which merges with the edge weld of the flange weld to cause full-section fracture. It is disadvantageous for the fatigue performance of connections to directly experience large deformation with equal amplitude. The loading process from small deformation to large deformation can give full play to the energy dissipation capacity. The larger the amplitude of loading, the faster the cumulative damage rate of connections, and the earlier the fatigue damage occurs. References | Related Articles | Metrics

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Fire resistance behavior of earthquake-damaged tubular T-joint reinforced with square doubler plate under fire XU Ji-xiang, YANG Long-long, HAN Jian-ping, TONG Yi-ge 2021, 47 (5):  130-137.  Abstract ( 185 )   PDF (4384KB) ( 246 )   Save Based on the numerical analysis model of tubular T-joint reinforced with square doubler plate verified by existing experimental tests, by introducing damage variable and considering the parameters, such asdiameter ratio, diameter-to- thickness ratio,wall thickness ratio, doubler plate length-to-brace diameter and doubler plate thickness-to-chord thickness, fire resistance of tubular T-joint reinforced with square doubler plate was analyzed under post-earthquake fire. The results show that the critical temperature of tubular T-joint reinforced with square doubler plate is affected by the damage variable, and the critical temperature decreases linearly with the increase of the damage variable; diameter ratio, diameter-to- thickness ratio, wall thickness ratio and doubler plate thickness-to-chord have little influence on the critical temperature of the tubular T-joint reinforced with square doubler plate; doubler plate length-to-brace diameter has a great influence on the critical temperature of the tubular T-joint reinforced with square doubler plate, and the critical temperature of the tubular T-joint reinforced with square doubler plate decreases with the increase of this ratio. References | Related Articles | Metrics

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Gray correlation analysis of the influence of particle size distribution of steel slag on hydraulic activity of steel slag cement NAN Xue-li, YANG Lan-lan, TANG Wei-bin, HAN Bo, WANG Chao-jie 2021, 47 (5):  138-143.  Abstract ( 259 )   PDF (1955KB) ( 308 )   Save Based on the principle of mechanical activation, the effects of particle size distribution and specific surface area of steel slag powderfor different grinding time on the hydration properties of steel slag cement mortar were studied from two aspects of strength and Ca(OH)2 content. And the influence of particle size of steel slag on the strength and hydration performance of steel slag cement mortar was researched by the gray relational analysis method. The results show that the specific surface area of steel slag and its activity increase with the grinding time; DTG thermal analysis shows that the specific surface area of steel slag affects the crystallization and crystal growth rate of Ca(OH)2; Slag powder particles with the sizes of 10~20 μm have the greatest effect on the strength of steel slag cementand those with the sizes of 5~10 μm play a catalytic role in the content of Ca(OH)2 at the 28th day. Therefore, increasing the content of steel slag particles in the range of 5~20 μm is beneficial to the activity of steel slag. References | Related Articles | Metrics

Scientific

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Cotorsion pair and Cotilting module WU De-jun, YI Chen-gang 2021, 47 (5):  144-149.  Abstract ( 156 )   PDF (861KB) ( 235 )   Save Some sufficient conditions when the kernel of a complete hereditary cotorsion pair is the closure under products of a cotilting module are given by studying the properties of the cotorsion pair and cotilting modules. References | Related Articles | Metrics

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Existence of positive solution for a class of m-point boundary value problems    with conformable fractional differential derivatives ZHAO Wei 2021, 47 (5):  150-154.  Abstract ( 194 )   PDF (794KB) ( 328 )   Save The existence of positive solution for a class of m-point boundary value problem with conformable fractional differential derivatives is studied. By using different functionals which are satisfied with a new defined functional to compute the fixed point index, the existence of positive solution is obtained. An example is given to illustrate the application of the theorem. References | Related Articles | Metrics

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New criteria based H-tensors for identifying the positive definiteness of multivariate homogeneous forms SUN De-shu, BAI Dong-jian, WANG Feng 2021, 47 (5):  155-161.  Abstract ( 175 )   PDF (833KB) ( 170 )   Save Some practical conditions for H-tensors are provided by constructing different positive diagonal matrices and applying some techniques of inequalities. As applications, new methods for the positive definiteness of even-order homogeneous multivariate polynomial are presented. Numerical examples are given to illustrate the feasibility of the new method. References | Related Articles | Metrics

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Study on preparation of NiCo2O4/RGO composite material and its electrochemical performance WANG Qing, GENG Wen-bo, DAI Jian-feng , LI Wei-xue, GAO Shan-shan 2021, 47 (5):  162-166.  Abstract ( 218 )   PDF (2927KB) ( 208 )   Save The NiCo2O4/RGO composite material was prepared by a two-step hydrothermal method and its electrochemical performance was studied. The research results showed that when the current density was 1 A/g, the specific capacitance of NiCo2O4/RGO composite material was as high as2 332.40 F/g, which was about three times that of NiCo2O4 material. When the current density was increased to 10 A/g, its specific capacitance could be maintained 1 127.22 F/g, showing excellent rate performance. Due to the special porous and fluffy structure of the composite material, the specific surface area of the material is effectively increased. The specific surface area of NiCo2O4 is 56.488 0 cm2/g, while the specific surface area of NiCo2O4/RGO composite material is as high as 188.604 2 cm2/g, which can provide more reactive sites, at the same time, RGO can effectively improve the conductivity of the material, thereby, the electrochemical performance is greatly improve. References | Related Articles | Metrics

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Elastoplastic buckling of functionally graded cylindrical shells ZHANG Jing-hua, ZHENG Wu 2021, 47 (5):  167-172.  Abstract ( 212 )   PDF (1345KB) ( 240 )   Save The elastoplastic buckling behaviors of functionally graded materials (FGM)cylindrical shells under uniform axial compression are investigated. Based on the linear mixed enhanced elastoplastic model, material properties and elastoplastic constitutive equations of the FGM are given. Then, Hamilton principle is introduced, and the elastoplastic buckling is simultaneously transformed into solving eigenvalue in symplectic space. Furthermore, critical buckling loads corresponding to generalized eigenvalues of canonical equation are calculated by the bifurcation condition,and locations of the elastoplastic interface are obtained by combining the yield condition. The effects of material gradient parameters and structural geometry parameters on the critical loads and the elastoplastic interfaces are discussed. References | Related Articles | Metrics