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Tribological properties and tribomechanism of nickel nanoparticles in-situ synthesized in rapeseed oil

Friction 2024年第3期12卷 474-489页

作者： Wenya XU Guangbin YANG Shengmao ZHANG Jun XU Yujuan ZHANG Tianhua SUN Ningning SONG Laigui YU Pingyu ZHANG Engineering Research Center for Nanomaterials Henan UniversityKaifeng 475004China State Key laboratory of Tribology in advanced Equipment Tsinghua UniversityBeijing 100084China

Nickel(Ni)nanoparticles can be enriched on the surface of iron-based frictional pairs,which provides the possibility to get rid of the competitive adsorption between the polar species of vegetable oil and the surface-active nano-additives *** this paper,nickel acetylacetonate was used as a precursor to in-situ synthesize nickel nanoparticles with an average diameter of about 12 nm in rapeseed oil(RO)as the reducing agent,surface modifier,and solvent as *** tribological properties of the as-synthesized Ni nanoparticles were evaluated with a four-ball tribometer,and their tribomechanism was investigated based on the characterizations of the tribofilm on rubbed steel surfaces by the scanning electron microscopy(sem),transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS).It was found that the Ni nanoparticles in-situ prepared in the RO with a mass fraction of 0.3%can reduce the wear scar diameter(WSD)of the steel ball by 36%.This is because,on the one hand,the Ni nanoparticles are adsorbed on the rubbed steel surfaces to repair or fill up the micro-pits and grooves *** the other hand,Ni nanoparticles participate in tribochemical reactions with atmospheric O and steel substrate to form the tribochemical reaction film on the rubbed steel surfaces with the assistance of friction-induced heat and applied normal *** addition,an amorphous carbon film is formed on the rubbed surface via the carbonization of base oil under the catalysis of Ni *** adsorbed Ni layer,the tribochemical reaction film,and the carbon layer comprise a composite tribofilm composed of amorphous carbon,polar fatty acid,metallic nickel,iron oxides,and nickel oxides on the rubbed steel surfaces,which contributes to significantly improving the antiwear ability and load-carrying capacity of the RO for the steel-steel sliding pair.

关键词： nickel(Ni)nanoparticles rapeseed oil(RO) in-situ synthesis tribological properties tribomechanism

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An Uncertainty Evaluation on the ΔK_(th) and ΔK_(IC) of Fine-grained Isotropic Graphite

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Acta Mechanica Solida Sinica 2024年第3期37卷 478-486页

作者： Yantian Zhang Lina Zhu Ruiguo Yan Xishu Wang Department of Engineering Mechanics Tsinghua UniversityBeijing100084China Wheel-Rail Center Tianjin Research Institute for Advanced EquipmentTsinghua UniversityTianjin300300China

This paper intensively explores the critical issues related to the quantitative and accurate evaluations of FCG behavior in the early stage,macro fatigue fracture toughness,and the critical crack size for damage tolerance in nuclear *** address these issues,scale-span FCG tests were carried out using two typical specimens,CT and sem in-situ *** results indicate that the FCG threshold and the effective FCG length have a significant correlation with the modified maximum loop stress theory for a mixed I/II *** particular,the effective FCG length(a_(eq))and the applied stress threshold of polycrystalline graphite are important parameters for fatigue damage tolerance design in engineering *** influencing factors of ΔK_(th,eq) and a_(eq) were discussed in detail using the mixed I/II mode,*** addition,the scattered values of ΔK_(IC) for this graphite can be quantitatively estimated using the Weibull distribution *** predicated parameters and experimental results demonstrate a strong correlation.

关键词： Nuclear graphite Mixed I/II mode Fatigue crack Fatigue crack growth threshold Fatigue fracture toughness

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Effect of slow shot speed on externally solidified crystal,porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

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China Foundry 2024年第1期21卷 11-19页

作者： Wen-ning Liu Wei Zhang Peng-yue Wang Yi-xian Liu Xiang-yi Jiao Ao-xiang Wan Cheng-gang Wang Guo-dong Tong Shou-mei Xiong School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China Key laboratory for advanced Materials Processing Technology Tsinghua UniversityBeijing 100084Beijing China FAW Group Co. Ltd.Changchun 130013China China FAW Foundry Co. Ltd.Changchun 130013China

The effect of slow shot speed on externally solidified crystal(ESC),porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy(OM),scanning electron microscopy(sem)and laboratory computed tomography(CT).Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg *** AlSi9MnMoV alloy,which was designed with trace multicomponent additions,displays a notable grain refining effect in comparison to the AlSi10MnMg *** elements Ti,Zr,V,Nb,B promote heterogeneous nucleation and reduce the grain size of primaryα-*** a lower slow shot speed,the large ESCs are easier to form and gather,developing into the dendrite net and *** an increase in slow shot speed,the size and number of ESCs and porosities significantly *** addition,the distribution of ESCs is more dispersed and the net-shrinkage *** tensile property is greatly improved by adopting a higher slow shot *** ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa(increased by 11.52%),and the elongation is enhanced from 3.72%to 6.34%(increased by 70.52%).

关键词： hypoeutectic Al-Si alloy high pressure die casting porosity externally solidified crystal tensile property

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Improvement of impact properties of Al-Si-Mg alloy via solution treatment and joint modification with Sr and La

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Rare Metals 2024年第7期43卷 3301-3313页

作者： Xiong-Ling Zheng Shao-Xiang Li Jia-Le Ma Qing-Yan Xu Hai-Dong Zhao Zhi-Qiang Han Key laboratory for advanced Materials Processing Technology Ministry of EducationSchool of Materials Science and EngineeringTsinghua UniversityBeijing 100084China National Engineering Research Center of Near-Net Shape Forming for Metallic Materials South China University of TechnologyGuangzhou 510641China

An effort to obtain superior impact properties for Al-7Si-0.35 Mg alloy is presented,where modification with 0.02 wt% Sr and 0.1 wt% La as well as solution treatment was jointly *** samples were solution treated at 535℃ for 15 min to 12 *** microstructure,fracture mechanism,and their correlation with the impact properties of the alloy were studied in detail mainly through optical microscopy(OM),scanning electron microscopy(sem) and oscillography impact *** results show that the addition of Sr and La refined the eutectic Si particles significantly from~ 2.05 μm(modified with Sr alone) to~ 0.75 μm in as-cast microstructure,leading to a very homogeneous distribution of spheroidized Si particles in the alloy solution treated at 535℃ for 8 *** alloy exhibits excellent impact toughness up to 75 J·cm^(-2),which is much higher than the maximum impact toughness of the alloys modified by Sr alone(~ 46 J·cm^(-2)).The major reason for this remarkable increase in the impact property is the dramatic increase in crack initiation *** dispersoid-free zones(DFZs)near the eutectic regions mainly consist of the ductile Al-matrix,which exhibits excellent *** ductile Al-matrix of the DFZs hinders the crack propagation,resulting in a significant increase in crack propagation energy.

关键词： Aluminum alloys Modification Solution treatment Microstructure Impact properties Fracture mechanism

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Development of wet adhesion of honeybee arolium incorporated polygonal structure with three-phase composite interfaces

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Friction 2024年第2期12卷 215-230页

作者： Lulu LIANG Jieliang ZHAO Qun NIU Li YU Xiangbing WU Wenzhong WANG Shaoze YAN Zhenglei YU School of Mechanical Engineering Beijing Institute of TechnologyBeijing 100081China Division of Intelligent and Biomechanical Systems State Key Laboratory of TribologyDepartment of Mechanical EngineeringTsinghua UniversityBeijing 100084China Key of Bionic Engineering Ministry of EducationJilin UniversityChangchun 130022China

Inspired by the dynamic wet adhesive systems in nature,various artificial adhesive surfaces have been developed but still face different ***,the theoretical mechanics of wet adhesives has never been sufficiently ***,we develop a novel adhesive mechanism for governing wet adhesion and investigate the biological models of honeybee arolium for reproducing the natural wet adhesive ***-nano structures of honeybee arolium and arolium-prints were observed by Cryogenic scanning electron microscopy(Cryo-sem),and the air pockets were found in the contact interface ***,the adhesive models with a three-phase composite interface(including air pockets,liquid secretion,and hexagonal frames of arolium),were formed to analyze the wet adhesion of honeybee *** results of theoretical calculations and experiments indicated an enhanced adhesive mechanism of the honeybee by liquid self-sucking effects and air-embolism *** these effects,normal and shear adhesion can be adjusted by controlling the proportion of liquid secretion and air pockets in the contact ***,the air-embolism effects contribute to the optimal coupling of smaller normal adhesion with greater shear adhesion,which is beneficial for the high stride frequency of *** works can provide a fresh perspective on the development of bio-inspired wet adhesive surfaces.

关键词： honeybee arolium air pockets wet adhesion a three-phase interface self-sucking effects air-embolism effects

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Reconfigurable intelligent surface based hybrid precoding for THz communications

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Intelligent and Converged Networks 2022年第1期3卷 103-118页

作者： Yu Lu Mo Hao Richard Mackenzie Beijing National Research Center for Information Science and Technology(BNRist) and the Department of Electronic EngineeringTsinghua UniversityBeijing 100084China. tsinghua sem advanced ict laboratory Tsinghua UniversityBeijing 100084China. BT Technology Adastral ParkIpswichIP53REUK.

Benefiting from the growth of the bandwidth,Terahertz(THz)communication can support the new application with explosive requirements of the ultra-high-speed rates for future 6G wireless *** order to compensate for the path loss of high frequency,massive Multiple-Input Multiple-Output(MIMO)can be utilized for high array gains by ***,the existing THz communication with massive MIMO has remarkably high energy consumption because a large number of analog phase shifters should be used to realize the analog *** solve this problem,a Reconfigurable Intelligent Surface(RIS)based hybrid precoding architecture for THz communication is developed in this paper,where the energy-hungry phased array is replaced by the energy-efficient RIS to realize the analog beamforming of the hybrid ***,based on the proposed RIS-based architecture,a sum-rate maximization problem for hybrid precoding is *** the phase shifts implemented by RIS in practice are often discrete,this sum-rate maximization problem with a non-convex constraint is ***,the sum-rate maximization problem is reformulated as a parallel Deep Neural Network(DNN)based classification problem,which can be solved by the proposed low-complexity Deep Learning based Multiple Discrete Classification(DL-MDC)hybrid precoding ***,we provide numerous simulation results to show that the proposed DL-MDC scheme works well both in the theoretical Saleh-Valenzuela channel model and practical 3GPP channel *** with existing iterative search algorithms,the proposed DL-MDC scheme significantly reduces the runtime with a negligible performance loss.

关键词： Reconfigurable Intelligent Surface(RIS) THz communication massive Multiple-Input Multiple-Output(MIMO) hybrid precoding deep learning

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Synthesis of carbon nitride in potassium hydroxide molten salt for efficient uranium extraction from radioactive wastewater

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Frontiers of Environmental Science & Engineering 2024年第8期18卷 89-99页

作者： Shuang Liu Junhan Luo Daniel-James Maguire Liyuan Zheng Zhe Wang Yuexiang Lu Institute of Nuclear and New Energy Technology Tsinghua UniversityBeijing 100084China Nuclear Research Institute for Future Technology and Policy Seoul National UniversitySeoul 08826Republic of Korea Department of Earth Sciences University of CambridgeCambridge CB23EQUK The MOE Key laboratory of Resources and Environmental System Optimization College of Environmental Science and EngineeringNorth China Electric Power UniversityBeijing 102206China

Photocatalysis-assisted removal of uranium has been proven as an effective method for the elimination of radioactive pollution from *** this work,carbon nitride materials were synthesized in potassium hydroxide(KOH)molten salt and applied to photocatalytic uranyl *** materials were confirmed to possess the triazine-s-heptazine structure by NMR,XPS and UV-Vis characterization,and exhibited a wider visible light absorption than graphitic carbon nitride(g-C_(3)N_(4)).The photocatalytic activity of the carbon nitride materials was tailored by varying the precursor mass *** carbon nitride obtained at 80%melamine as precursor(K-CN-80)exhibited the highest photocatalytic extraction ability and its photocatalytic reaction rate is 6.6 times faster than that of g-C_(3)N_(4).The influence of sacrificial agents was studied and the results showed that triethanolamine inhibited U(Ⅵ)photoreduction,but methanol can accelerate U(Ⅵ)photoreduction by consuming photogenerated *** unary KOH molten salt synthesis method has exceptional potential applications in the preparation of carbon nitrides,and the obtained products showed potential in extracting U(Ⅵ)from aqueous solutions for use in nuclear fuel industry and for U(Ⅵ)environmental pollution cleanup.

关键词： Uranium Carbon nitride Molten salt Photocatalysis Radioactive wastewater

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Relationships Between Meteorological Factors and Mongolian Gerbils and Its Flea Burdens—Xilingol League,Inner Mongolia Autonomous Region,China,2012–2021

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China CDC weekly 2024年第23期6卷 547-552,I0012-I0018页

作者： Ke Li Zhenxu Wang Xiaohui Wei Haoqiang Ji Meng Shang Nan Chang Zihao Wang Chenran Guo Lei Xu Ning Zhao Qiyong Liu National Key laboratory of Intelligent Tracking and Forecasting for Infectious Diseases National Institute for Communicable Disease Control and PreventionChinese Center for Disease Control and PreventionBeijingChina School of Public Health Nanjing Medical UniversityNanjing CityJiangsu ProvinceChina Cheeloo College of Medicine Shandong UniversitySchool of Public HealthJinan CityShandong ProvinceChina Vanke School of Public Health Tsinghua UniversityBeijingChina

Introduction:Plague is a significant global infectious disease,its spread is linked to host and flea *** conditions can impact flea populations and host densities,hence influencing plague *** the connection between meteorological factors,flea populations,and rodent densities in Inner Mongolia’s natural plague foci can aid in predicting and managing plague ***:Monthly data on flea index,rodent density,meteorological factors,and normalized difference vegetation index(NDVI)were collected for the study *** additive modeling(GAM)was used to analyze the non-linear and lag effects of meteorological factors on flea index and rodent *** equation modeling(sem)was employed to investigate the relationships among meteorological factors,NDVI,flea index,and rodent ***:GAM analysis revealed that temperature,precipitation,relative humidity,and NDVI had significant linear,non-linear,and time-lagged impacts on the density of Mongolian gerbils and the flea *** analysis indicated that meteorological factors could directly influence the density and flea index of Mongolian gerbils,or indirectly impact NDVI,subsequently influencing gerbil density and the flea ***:Meteorological factors primarily influence gerbil density and flea index indirectly by affecting NDVI and the relationship between flea index and gerbil *** study offers additional support for the significance of meteorological factors and NDVI in influencing the vector-rodent system,offering valuable insights for predicting and managing plague outbreaks.

关键词： meteorological offering humidity

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Screening-current-induced magnetic fields and strains in a compact REBCO coil in self field and background field

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Superconductivity 2024年第1期9卷 35-49页

作者： Yufan Yan Donghui Jiang Peng Song Jeonghwan Park Seungyong Hahn Yunfei Tan Timing Qu Department of Electrical and Computer Engineering Seoul National UniversitySeoul 08826Republic of Korea State Key laboratory of Clean and Efficient Turbomachinery Power Equipment Department of Mechanical EngineeringTsinghua UniversityBeijing 100084China High Magnetic Field laboratory Hefei Institutes of Physical ScienceChinese Academy of SciencesHefei 230031China Wuhan National High Magnetic Field Center Huazhong University of Science and TechnologyWuhan 430074China

REBa_(2)Cu_(3)O_(7−x)(REBCO)coated conductors,owing to its high tensile strength and current‐carrying ability in a background field,are widely regarded a promising candidate in high‐field *** the great potentials,recent studies have highlighted the challenges posed by screening currents,which are featured by a highly nonuniform current distribution in the superconducting *** this paper,we report a comprehensive study on the behaviors of screening currents in a compact REBCO coil,specifically the screeningcurrent‐induced magnetic fields and *** were carried out in the self‐generated magnetic field and a background field,*** the self‐field condition,the full hysteresis of the magnetic field was obtained by applying current sweeps with repeatedly reversed polarity,as the nominal center field reached 9.17 T with a maximum peak current of 350 *** a background field of 23.15 T,the insert coil generated a center field of 4.17 T with an applied current of 170 ***,a total center field of 32.58 T was achieved before *** the sequential model and the coupled model considering the perpendicular field modification due to conductor deformation are *** comparative study shows that,for this coil,the electromagnetic–mechanical coupling plays a trivial role in self‐field conditions up to 9 *** contrast,with a high axial field dominated by the background field,the coupling effect has a stronger influence on the predicted current and strain *** discussions regarding the role of background field on the strains in the insert suggest potential design strategies to maximize the total center field.

关键词： Electromagnetic-mechanical analysis High‐field insert coil REBCO coated conductor Screening‐current‐induced magnetic field Screening‐current‐induced stress

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Reconfigurable intelligent surface-aided wireless communications: An overview

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Intelligent and Converged Networks 2022年第1期3卷 33-63页

作者： Muhammad Zain Siddiqi Talha Mir Department of Electronic Engineering Tsinghua UniversityBeijing 100084China Department of Electronic Engineering Faculty of ICTBUITEMSQuetta 87300Pakistan

The reconfigurable intelligent surface(RIS)is an emerging technology,which will hopefully bring a new revolution in wireless *** RIS technology can be deployed in an indoor/outdoor environment to dynamically manipulate the propagation *** RIS consists of a large number of independently controllable passive elements,and these elements are involved in realizing high passive beamforming *** from the conventional active phased antenna array,there is no dedicated radio-frequency(RF)chain installed at the RIS to perform complex signal processing ***,it does not incur additional noise while retransmitting the incident wave,which is substantially a unique feature from the conventional wireless communication *** advantage of its working principle,RIS has been deployed in various practical *** this tutorial,at first we will review the latest advances in RIS,including the application scenarios such as the system and channel model,the information theoretic analysis,the physical realization and design,key signal processing techniques such as precoding and channel estimation,and ***,we discuss interesting future research problems for the RIS-aided communications.

关键词： reconfigurable intelligent surface(RIS) wireless communications new paradigm

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