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28 April 2023, Volume 49 Issue 2 Previous Issue    Next Issue

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Materials Science and Engineering

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Effects of K2ZrF6 and EDTA-Na additives, voltage and their interactions on corrosion resistance of micro-arc oxidation coatings on magnesium alloys WANG Hao, MA Ying, WANG Zhan-ying, AN Ling-yun, LIU Yun-po 2023, 49 (2):  1-8.  Abstract ( 327 )   PDF (2644KB) ( 379 )   Save Micro-arc oxidation (MAO) coatings were prepared on AZ91D magnesium alloys in alkaline phosphate-based electrolyte. The effects of the additives of K2ZrF6 and EDTA-Na, voltage, and their interactions on the coatings were studied based on orthogonal experiment. The thicknesses, morphologies and phase composition of the coatings were examined by using TT260 eddy-current coating thickness gauge, SEM and XRD, respectively. The corrosion resistance of the coatings in acidic media was evaluated by the HNO3 spot test. The results showed that K2ZrF6, EDTA-Na, voltage and their interactions exhibit different effects on the thickness and corrosion resistance of MAO coatings. The effect of the loading voltage on the thickness and corrosion resistance of the coatings is significant. With the voltage increasing, the thickness and the corrosion resistance of the coatings are both improved significantly. The individual factor of K2ZrF6 has little effect on the coating thickness, but it exhibits a certain impact on corrosion resistance of the coatings. The individual factor of EDTA-Na has little effect on the coating thickness and corrosion resistance, While the interaction between K2ZrF6 and voltage is very significant, and the coatings with more excellent comprehensive properties can be obtained when a high concentration of K2ZrF6 and high concentration of EDTA-Na combine with high loading voltage. References | Related Articles | Metrics

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Analysis of the effect of FeCr phase and AlCo phase in the friction process of AlCoCrCuFeNi high entropy alloy coating BIAN Chun-hua, YANG Wei-jie, ZHANG Wei, LI Qiu-da, WEN Jie, FENG Li 2023, 49 (2):  9-16.  Abstract ( 208 )   PDF (4925KB) ( 461 )   Save AlCoCrCuFeNix(x=0.5,1) high-entropy alloy coating was prepared by cold spray-assisted in situ synthesis method, and the microstructure structure and friction and wear performance of the coating were characterized and tested. Then, the friction process of AlCo and FeCr phases in high entropy alloy coating was simulated by molecular dynamics method, and the influence of AlCo and FeCr phases on the friction properties of high entropy alloy coating was simulated and analyzed. The results showed that under the same friction conditions, the friction force exerted by the AlCo phase is greater than that exerted by the FeCr phase, and the wear of the AlCo phase is greater than that of the FeCr phase. The AlCo phase produces adhesion and desorption atoms during friction, resulting in an increase in the total friction force, while during the FeCr phase friction, no obvious adhesion atoms are found. An obvious dislocation structure is produced inside the AlCo phase, the total length of the dislocation continues to increase with the increase of the friction distance, and two mixed dislocation structures are produced in the final stage of friction, but no dislocation structure is found inside the FeCr phase. This shows that the FeCr has a greater contribution to the wear resistance of the AlCoCrCuFeNi high-entropy alloy coating. References | Related Articles | Metrics

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Corrosion behaviors cold spraying Zn-Al composite coating in 3.5 wt.% NaCl solution SUN Yong-jiang, ZHANG Jin-ling, ZHAI Hai-min, WANG Hai-peng, LI Wen-sheng 2023, 49 (2):  17-23.  Abstract ( 218 )   PDF (4883KB) ( 226 )   Save The Zn-Al composite coating with different Al content had been deposited on the surface of Q235 steel by low pressure cold spraying. The corrosion potential, impedance value and corrosion current density of Zn-Al composite coating in 3.5 wt.% NaCl solution were analyzed by means of open-circuit potential and polarization curves. The morphology of the coating and the content of elements in the specific area were characterized by scanning electron microscope with energy dispersive spectrometer, X-ray diffractometer was used to analyze the coating phase after corrosion in 3.5wt.% NaCl solution for 1 440 h. The results showed that the corrosion resistance of the coating is better with the increase of Al content in 3.5 wt.% NaCl solution, and the corrosion resistance of the coating is better when the Al content is greater 35%. Because corrosion of zinc is prior than that of Al element, and the stable oxidation film is formed, at the same time, Al element inhibits the activity of zinc to slow down the corrosion rate, and the higher Al content has the better results. The corrosion mechanism of Zn-Al composite coating in 3.5 wt.% NaCl solution is uniform corrosion, pitting, local pitting and self-sealing of corrosion products. References | Related Articles | Metrics

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The research of isothermal reduction kinetics for iron-rich nickel slag by coal-based hydrogen metallurgy LI Bin, SUN Ming-xuan, WANG Ming-hua, LEI Peng-fei, WANG Sheng, DU Xue-yan 2023, 49 (2):  24-29.  Abstract ( 136 )   PDF (2416KB) ( 348 )   Save The iron in nickel slag was efficiently reduced by coal-based hydrogen metallurgy method. The variation of metallization rate for coal-containing nickel slag pellets during isothermal reduction at different temperatures was investigated. The kinetic of coal-based hydrogen reduction for nickel slag pellets was analyzed by grain model and unreacted core shrinking model. The control process of different reaction phase was determined with the corresponding kinetic equations established. The results showed that the metallization rate of coal-containing nickel slag pellets for 20 min reduction at 1 300 °C is 90.2%. The reaction kinetics of the initial, middle and final stages are dominated by interfacial chemical reaction control, reaction-diffusion mixed control, and internal diffusion control, and the corresponding apparent activation energies are 174.01 kJ/mol, 124.15 kJ/mol and 83.14 kJ/mol, respectively. References | Related Articles | Metrics

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Numerical simulation and experimental analysis of residual stress of tube sheet joint YIN Xiang, MA Cheng-yan, ZHOU Kai, WANG Xin-min, WANG Yi, WANG Xiao-jun 2023, 49 (2):  30-34.  Abstract ( 199 )   PDF (2483KB) ( 376 )   Save Radial and hoop residual stress value of the welded joint between tube and tube sheet were predicted by the thermal stress analysis module of FEA software ABAQUS. The simulation results showed that the maximum radial stress appears on the heat affected zone (HAZ) between the adjacent welds in the surface of the tube sheet. The maximum value of hoop stress is located in the weld toes, and close to the gaps between tube and tube sheet. The weld toe is directly contacted with heat exchange medium, which is prone to stress corrosion cracking at the connection between the heat exchange tube and the tube plate. The welding residual stress in the heat affected zone of the tube and plate joint are measured by X-ray diffraction method. It is found that the process of expansion before welding reduce the probability of stress corrosion between the tube and tube sheet because not only the gap between the heat exchange tube and tube sheet is reduced, but also welding residual stress value is decreased, even the tensile stress is turned into compressive stress. Comparing the calculated and measured values of the post-weld hoop residual stresses, the trend of both is consistent. References | Related Articles | Metrics

Mechanical Engineering and Power Engineering

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Unsteady numerical simulation of self-priming process of self-priming centrifugal pump ZHAO Wan-yong, CAO Li-jian, WANG Dong-wei, HU Jia-jun 2023, 49 (2):  35-40.  Abstract ( 134 )   PDF (3657KB) ( 352 )   Save In order to study the self-priming process of self-priming centrifugal pump, an externally mixed self-priming centrifugal pump is selected as the research object. Using the VOF multi-phase flow model and the standard k-ε model, the gas-liquid two-phase mixed flow and separation process of this type of self-priming centrifugal pump is studied through simplified boundary conditions. By analyzing the gas content rate, velocity and pressure of each monitoring point, the following conclusions can be drawn: the gas-liquid stratification phenomenon is emerged in self-priming process with the exhaust efficiency reduced. At the small gap between the impeller and the volute, high-intensity gas content rate fluctuations is produced. References | Related Articles | Metrics

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Energy and exergy analysis of solar energy enhanced two-stage compression heat pump system SHI Jia-meng, LI Feng-lei 2023, 49 (2):  41-48.  Abstract ( 175 )   PDF (3300KB) ( 244 )   Save In order to improve the performance of the heat pump system, a solar energy enhanced two-stage compression heat pump system (SETHP) is proposed. A thermodynamic model of the system is established. The system performance under different working conditions is analyzed, which compared with the traditional two-stage compression heat pump system (TSHP). The results indicate that the coefficient of heating performance COPh and exergy efficiency first increase and then decrease with the increase of the intermediate temperature. As the condensation temperature increases, COPh decreases and exergy efficiency increases. As the evaporation temperature increases and solar irradiance increases, COPh and exergy efficiency both increase. Compared with the TSHP system, the performance of the SETHP system is significantly improved. The research of SETHP system can provide new ideas and methods for the application of solar heat pump heating technology in low temperature environment. References | Related Articles | Metrics

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Analytical solutions for free vibration of functionally graded graphene reinforced beam ZHANG Jing-hua, SI Cheng-long, MA Hao 2023, 49 (2):  49-55.  Abstract ( 167 )   PDF (2252KB) ( 347 )   Save Based on Euler-Bernoulli beam theory, free vibration characteristics of functionally graded beams reinforced by graphene platelets are examined. In the study, it is considered that the graphene platelets are randomly and uniformly distributed in each layer of matrix, and its content varies in three different patterns along the thickness. Firstly, equivalent material properties are obtained according to Halpin-Tsai mechanical model and rule of mixture. And then, dynamic governing differential equations of the graphene platelets reinforced functionally graded beam are derived by Hamiltonian principle. Finally, the analytical expressions of natural frequency and mode are obtained through solving free vibration equations accurately and analytically. Meanwhile, analytic expression between the natural frequencies of this composite beam and that of a uniform beam with the same boundary conditions is given. The influence of the mass fraction, geometry and distribution of the graphene platelets on the natural frequency of the free vibration of the beam is analyzed through parametric research. References | Related Articles | Metrics

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Simulation model of cutting force in helical milling hole of titanium alloy based on material damage evolution LI Wei, ZHOU Lan, WANG Lin-jun, AN Guo-sheng, FENG Li, FENG Zhao-he 2023, 49 (2):  56-64.  Abstract ( 135 )   PDF (5934KB) ( 337 )   Save Cutting force simulation is an effective way to reduce experimental verification costs and optimize process parameters. The material damage process is difficult to describe and the grid distortion is serious in the 3D simulation of helical milling hole. In order to solve this problems, the evolution mode of fracture energy is defined as exponential evolution, the physical separation criterion was adopted and the fracture energy parameter was determined to be 44 350 N/m. Combined with the range of axial and tangential feed in the machining cycle, the meshing parameters were set and the 3D finite element model of unit period of revolution in the stable machining stage of helical milling hole was constructed. The results show that the fracture energy and meshing parameters can effectively improve the accuracy of cutting force simulation model. The average values of axial cutting force and tangential cutting force of helical milling are 91.7% and 92% of the experimental values, respectively, with the maximum error less than 9%. The model also shows strong can also be applied to the simulation of cutting force in helical milling with different cutter teeth (single, two, three and four teeth) and the same geometry of mills. References | Related Articles | Metrics

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Fatigue strength analysis of high-strength bolts for tower flange of wind turbine LIANG Yuan, WANG You-liang, WEI Tai, LIU Jian-hui 2023, 49 (2):  65-69.  Abstract ( 268 )   PDF (1391KB) ( 730 )   Save An analysis method for high-strength bolts of wind turbine tower flange was established by considering the influence of external load on fatigue damage. Firstly, the maximum load section was determined with the aid of the tower equivalent model according to the damage parameters of the stress state on the connection section. Secondly, the external load on any sector of the tower was obtained by Schmidt-Neuper algorithm. Afterwards, the fatigue damage distribution model of high-strength bolts was established and the relationship between the external load and the internal stress of high-strength bolts was explored based on the finite element model. Finally, the optimal bolt pretightening force was determined with comparing the fatigue cumulative damage values with different bolt pretightening forces by considering the influence of pretightening forces. The results show that the positions of the maximum fatigue cumulative damage of flange bolts were －4.17° and 175.87°, and the bolt pretightening force was the most suitable value when the bolt pretightening force ratio was 70%. References | Related Articles | Metrics

Chemical Industry and Light Industry

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Axial strain characteristics of buried pipeline under landslide debris flow WANG Hui, HU Hai-tao, XIE Yue, MA Hong-qiang 2023, 49 (2):  70-75.  Abstract ( 120 )   PDF (3101KB) ( 197 )   Save In order to ensure the stable operation of pipelines under landslide debris flow disasters, a strain analysis model for buried pipelines under the longitudinal action of landslide debris was established based on the thermal elastic-plastic theory. Meanwhile, the axial strain distribution characteristics were studied for buried pipelines under different lengths, widths and thicknesses of landslide debris flow. The results show that the influence degree of landslide debris flow size on the pipeline axial tensile and compressive strain is landslide thickness, length and width. By analyzing the influence of structural parameters such as diameter to thickness ratio, pipe wall thinning and pipe buried depth on axial tensile strain, it was found that the maximum axial tensile and compressive strain of the pipeline decreases significantly with the increase of slope and buried depth. The wall thickness reduction of the pipeline was positively correlated with the axial tensile and compressive strain of the pipeline, while the buried depth of the pipeline was negatively correlated with it. From the perspective of the influence of pipeline structural parameters on the maximum axial tensile and compressive strain of the pipeline, the order was pipeline buried depth, pipe wall thinning, and diameter thickness ratio. Properly increasing the buried depth of pipelines under the condition of landslide debris flow can reduce. References | Related Articles | Metrics

Automation Technique and Computer Technology

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The calculation method for influence of photovoltaic power generation system on three-phase voltage unbalance degree of distribution network CHEN Wei, NI Yuan-hong, JI Qing-chun, WANG Zhong-fei, HE Feng 2023, 49 (2):  76-82.  Abstract ( 412 )   PDF (1911KB) ( 536 )   Save Aiming at the deficiency of traditional deterministic power flow calculation in the evaluation of three-phase voltage unbalance caused by distributed photovoltaic power stations connected to the distribution network, a method based on multi-point linearization semi-invariant probabilistic power flow and importance sampling was proposed to evaluate the unbalance degree of distribution network. First, given the limitations of the Beta distribution, the adaptive nonparametric kernel density estimation method was adopted to characterize the photovoltaic output and load fluctuation random process to improve the modeling accuracy, and then the method of piecewise linearization semi-invariant was used to perform stochastic trend analysis to reduce the error due to uncertainty. Afterward, the mixed Copulas connect function was constructed to calculate the unbalance of the public connection point. Finally, the sampling method was used to get the mean value of unbalance degree for evaluation. In the end, the effectiveness of the proposed method was verified by the simulation analysis of the IEEE33 node system. References | Related Articles | Metrics

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Study on intelligent algorithm for remaining useful life prediction of relay protection equipment XIE Nan, MA Zhen-guo, TANG Bing, HUANG Yu-ming, ZHANG Ke-qi, CAO Dan-yi 2023, 49 (2):  83-87.  Abstract ( 153 )   PDF (1204KB) ( 448 )   Save Remaining useful life prediction can not only improve the maintenance efficiency of relay protection equipment of the power system but also enrich the full-lifecycle management of power equipment in the state grid. Based on the relay protection equipment of JC city power supply company and its characteristics of data, this paper defines the design life course and actual life course according to the variable installation date, damage date, current date, and design life related to attributes. Support vector regression(SVR), regression tree(RT), and random forest(RF) methods are used to predict the remaining useful life of unmonitored equipment. Case analysis shows that the prediction method of random forest performs best. References | Related Articles | Metrics

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The time-varying formation and tracking control of leader-following multi-agent systems HAN Na-ni, ZHAO Li 2023, 49 (2):  88-95.  Abstract ( 148 )   PDF (1764KB) ( 163 )   Save Considering the time-varying delay, the distributed time-varying formation and tracking control for the high-order leader-following multi-agent systems is investigated. Aiming at the linear multi-agent systems, the observer-based time-varying formation and tracking protocols are designed. By model transformation, the formation and tracking control problem is transformed into the stability problem of error systems. Then, by using graph theory and Lyapunov theory, the sufficient conditions that the system realizes time-varying formation and tracking control are presented in the form of LMI. In addition, it is pointed out that the time-varying delay does not affect the formation reference function. Finally, the simulation results show that the designed protocols can make followers form the desired time-varying formation, and track the leader’s trajectory. References | Related Articles | Metrics

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Research on cascading model and algorithm based on multi-link wireless sensor networks WANG Xun, WANG Fei-ru, SHANG Guo-xu 2023, 49 (2):  96-102.  Abstract ( 166 )   PDF (4936KB) ( 191 )   Save The current research on the cascading failure of wireless sensor networks (WSNs) mainly focuses on single-link networks, and rarely involves multi-link networks. Based on this, a cascading model based on multi-link wireless sensor networks is proposed in this paper, and Memetic Algorithms (MAS) is proposed to optimize the multi-link layout to resist cascading failure. Based on the new network balance metric, which is “multi-directional network entropy”, a local search operation operator is designed. The simulation result shows that the proposed cascade model can characterize the cascade process of multi-link WSN, and can effectively improve the stability of the discussed system. Compared with existing algorithms, MAS can obtain a more stable layout scheme in a short time. References | Related Articles | Metrics

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A secure face recognition scheme based on CKKS homomorphic encryption and neural network SU Yun-xuan, TU Zheng, WANG Xu-an, LIN Chuan 2023, 49 (2):  103-109.  Abstract ( 549 )   PDF (2072KB) ( 431 )   Save As big data technology has been evolving over the years, facial recognition is widely used in different fields. However, users are then troubled by safety problems, such as privacy disclosure and data leakage. A face recognition scheme based on homomorphic encryption and neural network under the cloud server is proposed in this paper. The face image is encrypted through the CKKS homomorphic encryption scheme, and the LFW data set is trained through the ResNet50 model and Arcface Loss function in the cloud server, then the vector correlation between the encrypted images is calculated, followed by the decryption of the ciphertext result and comparison with the threshold to judge whether it is the same person, to realize face recognition. The experiment result shows that on the LFW dataset, the scheme of this paper can recognize the cryptograph with an accuracy rate of 99.398% when the threshold value is about 0.25. This result proves the proposed scheme has high recognition accuracy. References | Related Articles | Metrics

Architectural Sciences

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Research on earthquake active earth pressure of inclined retaining wall ZHOU Yong, DU Hao-nan, WANG Zheng-zhen 2023, 49 (2):  110-116.  Abstract ( 163 )   PDF (2584KB) ( 362 )   Save According to the theory that the internal and external friction angles of the soil are gradually exerted with the displacement of the soil, the displacement mode around the bottom of the wall, and the influence of the seismic force on the earth pressure are comprehensively considered. The horizontal layer analysis method is used to derive the theoretical formula of wall seismic active earth pressure along the wall height distribution, resultant force and joint force height. The effects of the displacement of the wall and the seismic acceleration coefficient on the earth pressure distribution, the most dangerous slip surface inclination angle, the combined force point height and the active side soil are analyzed. The analysis results show that the soil pressure intensity is nonlinearly distributed. After simplifying, the obtained combined force of active earth pressure is the same as the result of the Mononobe-Okabe theory. The slip angle of the slip surface decreases with the increase of the seismic coefficient, as does the combined force of active earth pressure, while the active lateral earth pressure coefficient increases with the wall back inclination angle and seismic coefficient. The finite element simulation proves that the variation trend of the soil pressure distribution curve obtained by the simulation is basically consistent with the calculated results. References | Related Articles | Metrics

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Quality assessment on rural construction of human settlements in loess plateau LIU Ben-teng, ZHANG Jie-ru, YANG Cheng, DONG Jian-hong 2023, 49 (2):  117-124.  Abstract ( 131 )   PDF (948KB) ( 149 )   Save As the main line of the rural revitalization strategy, it has great practical significance to conduct quality assessment research in the Loess Plateau. Firstly, supported by the theory of human settlements, based on the regional characteristics of the Loess Plateau, the indicator system was constructed from five dimensions, namely, production, life, style, customs and governance. Secondly, AHP and the entropy value law were used to determine the weight, and the fuzzy comprehensive assessment method was used to establish the evaluation model. Finally, taking Zhuanglang County, a typical agricultural county in the Loess Plateau, as an example, an empirical study was carried out. The research shows that: (1) the quality assessment value of rural construction in the Loess Plateau represented by Zhuanglang County is in a good grade. (2) Among the five dimensions weights of rural construction quality assessment based on the theory of human settlements, the scores of the custom dimension and the governance dimension are high, and the satisfaction of the production dimension and the life dimension need to be improved. (3) Through the analysis of the IPA quadrantal diagram, it was found that the importance and satisfaction of different dimensions of each indicator are significantly different, and the improvement of food production capacity and housing condition is the key to promote the current rural construction level. In summary, affected by the natural environment and socio-economic conditions, the achievement and problem of rural construction in the Loess Plateau reveal an obvious regional characteristic. References | Related Articles | Metrics

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Experimental study on the mechanical properties of lime-fly ash-cement stabilized macadam JIA Liang, LIAN Shang-cheng 2023, 49 (2):  125-129.  Abstract ( 224 )   PDF (3126KB) ( 441 )   Save Lime-fly ash-ordinary portland cement stabilized macadam is a common pavement base material, but its early strength is low. So, it cannot be used for the opened traffic swiftly. In order to enhance the early strength of stabilized macadam, ordinary Portland cement is substituted by sulfoaluminate cement with equal quality. The unconfined compressive strength (UCS) and split tensile strength (STS) of two kinds of cement stabilized macadam were compared by unconfined compressive strength test (UCT) and split tensile strength test (STS). At the same time, experimental research on the influence of inorganic binder content, cement content and grade-pairing strength of the macadam was carried out. The results show that the UCS and STS of stabilized macadam increase with the increase of cement content and curing age. The UCS of lime-fly ash-sulfoaluminate cement stabilized gravel in the curing period of 1 day can reach to 2.28 MPa, which meets the requirements of the road base open traffic with the strength not decreasing in the later period.A new material for quick maintenance of pavement base course is provided here. References | Related Articles | Metrics

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Study on influence factors of uplift pile bearing capacity under unloading of foundation pit excavation RAO Kai, LIU Yan-hui, WANG Ji-kai, HUANG Zhan-jun, LUO Ru-ping, SHI Yu-feng 2023, 49 (2):  130-137.  Abstract ( 214 )   PDF (5932KB) ( 253 )   Save At present, the research on uplift pile mainly uses pile side friction to reflect the bearing behavior of pile, and there is little research on the normal pressure of pile-soil interface. In view of this, through the PLAXIS 3D, the changes of pile ultimate uplift bearing capacity, pile side friction, pile shaft axial force and pile normal stress after foundation pit excavation were studied. The results show that: for the bearing capacity of pile, the influence of cohesion and friction angle of soil around pile is great; the excavation range has little impact on the bearing capacity characteristics of the pile, for silty clay, when the width of the foundation pit excavation is greater than 37.5 times the pile diameter, compared with the non excavation, the loss ratio of bearing capacity is 10.82%~17.83%; for sandy soil, when the width of the foundation pit excavation is greater than 40 times the pile diameter, compared with no excavation, the bearing capacity loss ratio is 15.37%~33.01%. Linear fitting on the normal pressure curve of the pile soil interface and normalization analysis on the slope in the unexcavated state were performed and the ratio of the slope after excavation to the slope in the unexcavated state was obtained, which is 9.18 for silty clay and 34.92~40.94 for sandy soil. References | Related Articles | Metrics

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Excavation deformation of deep foundationpit of subway station in coastal marsh area REN Xiao-min, LIU Jun-jie, LIU Jun-wei, WANG Chen 2023, 49 (2):  138-143.  Abstract ( 132 )   PDF (3286KB) ( 252 )   Save There are not many deep foundation pits in long and narrow subway stations in coastal marsh area, which are difficult to excavate due to the effect of upper silt soil and rich underground water. The deep foundation pit excavation of the subway station under this condition in the Qingdao area is selected for real-time monitoring, and a three-dimensional numerical model is established by using Midas GTS NX software for analysis. The analysis shows that the deep horizontal displacement-depth deformation curve of the pile is in the shape of a bow, and the maximum horizontal displacement of retaining pile appears at 0.55H(H is the excavation depth of foundation pit). The surface settlement around the foundation pit is a parabola with a small settlement, and the maximum settlement is about 0.058%H, which is 0.6H away from the foundation pit. There is a relationship between the maximum horizontal displacement δhmax of the retaining wall and the maximum settlement δvmax of the surface, which is δvmax=0.88 δhmax. In addition, compared with the deep foundation pit engineering under the working conditions in other areas, the excavation deformation of the water-rich deep foundation pit in the marsh area shows a similar change law. References | Related Articles | Metrics

Scientific

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Pattern avoiding problems on the hybrid d-trees YANG Sheng-liang, JIANG Mei-yang 2023, 49 (2):  144-150.  Abstract ( 170 )   PDF (741KB) ( 163 )   Save The counting problem of avoiding some patterns in the set of hybrid d-ary trees are discussed in this paper, and the corresponding counting formula and generation function is obtained. Finally, the bijection between hybrid d-ary trees for avoiding one pattern and d-Schröder paths is established. References | Related Articles | Metrics

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Gorenstein flat-cotorsion objects in categories of rooted quiver representations WU De-jun, LI Dan 2023, 49 (2):  151-156.  Abstract ( 138 )   PDF (511KB) ( 193 )   Save Let R be an associative ring with identity and Q=(Q0,Q1,s,t) be a quiver. The definition and equivalent characterizations of Gorenstein flat-cotorsion objects in categories of rooted quiver representations are given, and the related properties of Gorenstein flat-cotorsion objects are studied. References | Related Articles | Metrics

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Dynamics of a Cholera model with environmental transmission and physiological age structure KANG Yue-nan, GUO Wen-dan, NIE Lin-fei 2023, 49 (2):  157-164.  Abstract ( 177 )   PDF (1904KB) ( 249 )   Save Based on the rules of Cholera transmission between humans and environment, as well as individual differences between humans, a Cholera model with environmental transmission and physiological age structure is proposed, and the existence and uniqueness of the global positive solution of this model are proved by semigroup theory. Furthermore, the expression of basic reproduction number R0 is derived by linear approximation method, it is concluded that if R0<1, the disease-free steady state is globally asymptotically stable; if R0>1, the disease-free steady state is unstable, and the model has a unique endemic steady state and is locally asymptotically stable under certain conditions. The main theoretical results are explained by numerical simulation. References | Related Articles | Metrics

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Molecular dynamics study on the effect of interior hydrophilicity/hydrophobicity of dendrimers on their interaction with lipid membrane XIE Li-qiang, LIANG Sheng-de, ZHU Kai-li 2023, 49 (2):  165-172.  Abstract ( 152 )   PDF (3354KB) ( 207 )   Save Coarse-grained molecular dynamics simulations were adopted to investigate the interaction between dendrimers with different hydrophobic cores and lipid membranes. The results show that the polyamidoamine dendrimer can be wrapped by lipid bilayer. In contrast, the polypropyleneimine dendrimer with a strong hydrophobic core can penetrate through the membrane, and lipid-dendrimer micelle structure forms. The results point out the electrostatic interaction between dendrimers and membranes helps the dendrimer anchor on the membrane, while the hydrophobic interaction between the dendrimer and lipid membrane drives further interactions. The results are helpful to elucidate the mechanism of interaction between dendrimers and lipid membranes at the molecular level, which is of great theoretical significance for dendrimer synthesis and medical application. References | Related Articles | Metrics