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Cross-sectional deformation of H96 brass double-ridged rectangular tube in rotary draw bending process with different yield criteria

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Chinese Journal of Aeronautics 2020年第6期33卷 1788-1798页

作者： Yangyang XIA Yuli liu mengmeng liu Research&Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen 518057China State Key Laboratory Solidification Process School of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi'an 710072China

Different yield criterion has great difference in predicting the deformation of tube with different *** order to improve the prediction accuracy of the cross-sectional deformation of the double-ridged rectangular tube(DRRT)during rotary draw bending(RDB)process,Mises isotropic yield criterion,Hill’48 and Barlat/Lian anisotropic yield criteria commonly used in practical engineering are introduced to simulate RDB of *** inverse method combining uniaxial tensile test of whole tube and response surface methodology was proposed to identify the parameters of Hill’48 and Barlat/Lian yield criteria of small-sized H96 brass extrusion DRRT as *** based on ABAQUS/Explicit platform,the FE models of RDB process of DRRT considering Mises,Hill’48 and Barlat/Lian yield criteria were *** results show that:The variation trend of cross-sectional deformation ratio is same when using different yield *** cross-sectional deformation ratio by using Mises yield criterion is close to that by using Hill’48 yield ***,there is a quite difference between by using Barlat/Lian yield criterion and by using Mises or Hill’48 yield *** prediction values of cross-sectional height deformation by using three yield criteria all underestimate the experiment ones,and the prediction values of cross-sectional width deformation overestimate the experiment *** comparing the simulation results of cross-sectional deformation of the DRRT with different yield criteria and experiment ones,Barlat/Lian yield criterion is found to be suitable for describing the RDB process of DRRT.

关键词： Anisotropy yield criterion Cross-sectional deformation H96 double-ridged rectangular tube H-type rotary draw bending Inverse method

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Relationship between types of urban forest and PM_(2.5) capture at three growth stages of leaves

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Journal of Environmental Sciences 2015年第1期27卷 33-41页

作者： Thithanhthao Nguyen Xinxiao Yu Zhenming Zhang mengmeng liu Xuhui liu College of Soil and Water Conservation Beijing Forestry University Science and Technology Department College of Nature Conservation Beijing Forestry University

Particulate matter diameter ≤ 2.5 μm（PM2.5） causes direct harm to human health. Finding forms of urban forest systems that with the ability to reduce the amount of particulate matter in air effectively is the aim of this study. Five commonly cultivated kinds of urban forest types were studied in Beijing city at three stages of leaf growth. Results show that the urban forest system is capable of storing and capturing dust from the air. The types of shrubs and broadleaf trees that have the ability to capture PM2.5from the air are most effective when leaves have fully developed. In the leafless season, the conifer and mixed tree types are the most effective in removing dust from the air. For all kinds of forest types and stages of leaf growth, the PM2.5concentration is highest in the morning but lower in the afternoon and evening. Grassland cannot control particles suspended in the air,but can reduce dust pollution caused by dust from the ground blown by the wind back into the air.

关键词： Particulate matter PM2.5 Type of urban forest Growth stages of leaves

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Accelerating H^(*)desorption of hollow Mo_(2)C nanoreactor via in-situ grown carbon dots for electrocatalytic hydrogen evolution

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Journal of Energy Chemistry 2024年第9期96卷 464-471页

作者： mengmeng liu Yuanyuan Jiang Zhuwei Cao Lulu liu Hong Chen Sheng Ye School of Materials and Chemistry Anhui Agricultural UniversityHefei 230036AnhuiChina

Molybdenum carbide(Mo_(2)C)is a promising non-noble metal electrocatalyst with electronic structures similar to Pt for hydrogen evolution reaction(HER).However,strong H^(*)adsorption at the Mo sites hinders the improvement of HER ***,we synthesized monodisperse hollow Mo_(2)C nanoreactors,in which the carbon dots(CD)were in situ formed onto the surface of Mo_(2)C through carburization *** to finite element simulation and analysis,the CD@Mo_(2)C possesses better mesoscale diffusion properties than Mo_(2)C *** optimized CD@Mo_(2)C nanoreactor demonstrates superior HER performance in alkaline electrolyte with a low overpotential of 57 mV at 10 mA cm^(−2),which is better than most Mo_(2)C-based ***,CD@Mo_(2)C exhibits excellent electrochemical stability during 240 h,confirmed by operando Raman and X-ray diffraction(XRD).Density functional theory(DFT)calculations show that carbon dots cause the d-band center of CD@Mo_(2)C to shift away from Fermi level,promoting water dissociation and the desorption of H^(*).This study provides a reasonable strategy towards high-activity Mo-based HER eletrocatalysts by modulating the strength of Mo–H bonds.

关键词： Mo_(2)C nanoreactor Carbon dots H^(*)desorption Electrocatalytic hydrogen evolution

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Performance analysis of frequency synchronization in MIMO-OFDM systems with ST/MRC scheme

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The Journal of China Universities of Posts and Telecommunications 2016年第5期23卷 10-14,39页

作者： Han Daoqi Zhang Jianhua Yu Hao liu mengmeng Key Laboratory of Universal Wireless Communications Ministry of EducationBeijing University of Posts and Telecommunications

In this paper, the performance of frequency synchronization in a multiple-input multiple-output orthogonal frequency division multiplexing （MIMO-OFDM） system is analyzed for the purpose of carrier frequency offset （CFO） estimation and compensation. Specifically, a joint transmit antenna selection （ST） and receive maximum ratio combining （MRC）（ST/MRC） method is adopted, that is, only one transmit antenna with the highest channel power is selected while MRC is used at the receiver to maximize the sum of frequency synchronization metric of CFO estimation are derived for several antenna configurations validate the theoretical analysis. The mean square error （MSE） closed-form expressions Simulations in both flat and multipath fading channels

关键词： MIMO OFDM frequency synchronization

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Cloning and expression of three thaumatin-like protein genes from Polyporus umbellatus

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Acta Pharmaceutica Sinica B 2017年第3期7卷 373-380页

作者： mengmeng liu Dawei Zhang Yongmei Xing Shunxing Guo Key Laboratory of Bioactive Substances and Resources Utilization of Chinese Herbal Medicine Ministry of Education Institute of Medicinal Plant Development Chinese Academy of Medical Sciences & Peking Union Medical College Institute of Bioinformatics and Medical Engineering School of Electrical and Information Engineering Jiangsu University of Technology

Genes encoding thaumatin-like protein(TLPs) are frequently found in fungal ***, information on TLP genes in Polyporus umbellatus is still limited. In this study, three TLP genes were cloned from P. umbellatus. The full-length coding sequence of PuTLP1, PuTLP2 and PuTLP3 were 768, 759 and 561 bp long, respectively, encoding for 256, 253 and 187 amino acids. Phylogenetic trees showed that P. umbellatus PuTLP1, PuTLP2 and PuTLP3 were clustered with sequences from Gloeophyllum trabeum, Trametes versicolor and Stereum hirsutum, respectively. The expression patterns of the three TLP genes were higher in P. umbellatus with Armillaria mellea infection than in the sclerotia without A. mellea. Furthermore, over-expression of three PuTLPs were carried out in Escherichia coli BL21(DE3) strain, and high quality proteins were obtained using Ni-NTA resin that can be used for preparation of specific antibodies. These results suggest that PuTLP1, PuTLP2 and PuTLP3 in P. umbellatus may be involved in the defense response to A. mellea infections.

关键词： Polyporus umbellatus Thaumatin-like protein Defense Gene cloning Expression

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Study on the microcosmic superlubricity mechanism of PVPA affected by metal cations

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Friction 2023年第7期11卷 1150-1164页

作者： Hongyun CAI Caixia ZHANG Fuping LI mengmeng liu Tao ZHANG Hongyan CHU Zhifeng liu Institute of Advanced Manufacturing and Intelligent Technology Faculty of Materials and ManufacturingBeijing University of TechnologyBeijing 100124China Machinery Industry Key Laboratory of Heavy Machine Tool Digital Design and Testing Technology Faculty of Materials and ManufacturingBeijing University of TechnologyBeijing 100124China Key Laboratory of CNC Equipment Reliability Ministry of EducationSchool of Mechanical and Aerospace EngineeringJilin UniversityChangchun 130025China

Hydrophilic polymer coatings on artificial implants generate excellent tribological *** friction properties of polymer coatings are affected by salt ion ***,the atomic force microscopy(AFM)was used to show that the superlubricity was achieved between poly(vinylphosphonic acid)(PVPA)-modified Ti6Al4V and polystyrene(PS)microsphere probe lubricated with monovalent salt solutions(LiCl,NaCl,KCl,and CsCl).Considering that adhesion is an important cause of friction changes,the AFM was further utilized to obtain adhesion between friction pairs in different salt *** results indicated that the larger the cation radius in the lubricant,the smaller the adhesion,and the lower the friction coefficient of the PVPA *** electrostatic interaction between the PVPA and one-valence cations in lubricants was analyzed by the molecular dynamics(MD)simulation as it was found to be the main influencing factor of the *** analysis results of friction and adhesion indicated that by adjusting the size of cation radius in lubricant,the adhesion between the tribo-pairs can be changed,and eventually the magnitude of friction can be *** study opens up a new avenue for analyzing the friction characteristics of hydrophilic polymer coatings from the perspective of intermolecular forces.

关键词： atomic force microscopy(AFM) superlubricity poly(vinylphosphonic acid)(PVPA) cation adhesion molecular dynamics(MD)simulation

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Regulation mechanism of biomolecule interaction behaviors on the superlubricity of hydrophilic polymer coatings

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Friction 2022年第1期10卷 94-109页

作者： Caixia ZHANG Junmin CHEN mengmeng liu Yuhong liu Zhifeng liu Hongyan CHU Qiang CHENG Jianhua WANG Institute of Advanced Manufacturing and Intelligent Technology.Beijing University of Technology Beijing 100124China Beijing Key Laboratory of Advanced Manufacturing Technology Beijing University of TechnologyBeijing 100124China State Key Laboratory of Tribology.Tsinghua University Beijing 100084China

Hydrophilic polymer coatings can improve the surface characteristics of artificial ***,because they are used in vivo,they inevitably come into contact with biomolecules that affect their interfacial tribological *** this paper,the friction behaviors of poly(vinylphosphonic acid)(PVPA)-modified Ti6Al4V and polytetrafluorethylene balls were analyzed using albumin,globulin,aggrecan,and hyaluronic acid as *** interaction properties and dynamic adsorption characteristics of the biomolecules and PVPA molecules were explored by a quartz crystal microbalance to identify the cause of the friction *** was found that protein molecules disturbed the superlubricity of the PVPA-phosphate-buffered saline system because of the formation of a stable adsorption film,which replaced the interfacial characteristics of the PVPA ***,with their excellent hydration properties and polymer structure,had an unstable dynamic interaction or zero adsorption with PVPA molecules,and hardly changed the superlubricity of the PVPA and phosphate-buffered-saline *** influence mechanism of the specific friction of proteins and polysaccharides was *** were observed among different *** can potentially reduce protein *** result of the synergistic regulation of the friction coefficient for PVPA-modified Ti6Al4V is approximately *** results of this study will provide a theoretical basis for the use of polymer coatings in vivo.

关键词： friction interaction adsorption

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Three new species of Tenthredo Linnaeus,1758(Hymenoptera:Tenthredinidae)from Jiangxi and Zhejiang Provinces,China

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Zoological Systematics 2021年第3期46卷 225-233页

作者： mengmeng liu Zejian Li Meicai Wei College of Ecology Lishui UniversityLishuiZhejiang323000China Postdoctoral Work Station Scientific Research and Management Center of East China Pharmaceutical Botanical GardenLishui Ecological Forestry Development CenterZhejiang323000China College of Life Science Jiangxi Normal UniversityJiangxi330022China

Three new species of Tenthredo Linnaeus,1758 from Jiangxi and Zhejiang Provinces,China are described,namely,*** ***.,*** *** *** ***.,belonging to *** group,*** group,and *** group,respectively.

关键词： Symphyta Tenthredinoidea Tenthredo taxonomy sawflies

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Spatial-temporal Dynamics and Driving Forces of Land Development Intensity in the Western China from 2000 to 2015

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Chinese Geographical Science 2020年第1期30卷 16-29页

作者： HUANG Xin HUANG Xiaojun liu mengmeng WANG Bo ZHAO Yonghua School of Earth Science and Resources Chang'an UniversityXi'an 710054China Shaanxi Key Laboratory of Land Consolidation Xi'an 710054China College of Urban and Environmental Science Northwest UniversityXi'an 710127China Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity Xi'an 710127China

The change in land development intensity is an important perspective to reflect the variation in regional social and economic development and spatial *** this paper,spatial statistical analysis,Ordinary Least Squares(OLS),and Geographically weighted regression(GWR)methods are used to systematically analyse the spatial-temporal characteristics and driving forces of land development intensity for 131 spatial units in the western China from 2000 to *** findings of the study are as follows:1)The land development intensity in the western China has been increasing *** 2000 to 2015,land development intensity increased by 3.4 times on average.2)The hotspot areas have shifted from central Inner Mongolia,northern Shaanxi and the Beibu Gulf of Guangxi to the Guanzhong Plain and the Chengdu-Chongqing urban *** areas of cold spots were mainly concentrated in the Qinghai-Tibet Plateau,Yunnan,and Xinjiang.3)Investment intensity and the natural environment have always been the main drivers of land development intensity in the western *** played a powerful role in promoting land development intensity,while the natural and ecological environment distinctly constrained such *** effect of the economic factors on land development intensity in the western China has changed,which is reflected in the driving factor of construction land development shifting from economic growth in 2000 to economic structure,especially industrial structure,in 2015.

关键词： construction land land development intensity spatial-temporal dynamic driving force the western China

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Efficient production of 2′-fucosyllactose in unconventional yeast Yarrowia lipolytica

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Synthetic and Systems Biotechnology 2023年第4期8卷 716-723页

作者： Yan Zhang Xuejing Zhang Haiyan liu Jin Hou mengmeng liu Qingsheng Qi State Key Laboratory of Microbial Technology Shandong UniversityQingdao266237China

2′-Fucosyllactose(2′-FL)has great application value as a nutritional component and the whole cell biosynthesis of 2′-FL has become the focus of current *** lipolytica has great potential in oligosaccharide synthesis and large-scale *** this study,systematic engineering of *** for efficient 2′-FL production was *** fusing different protein tags,the synthesis of 2′-FL was optimized and the ubiquitin tag was demonstrated to be the best choice to increase the 2′-FL *** iterative integration of the related genes,increasing the precursor supply,and promoting NADPH regeneration,the 2′-FL synthesis was further *** final 2′-FL titer,41.10 g/L,was obtained in the strain *** work reports the highest 2′-FL production in ***,and demonstrates that *** is an efficient microbial chassis for the synthesis of oligosaccharides.

关键词： 2′-Fucosyllactose Yarrowia lipolytica Iterative integration Pathway enhancement NADPH regeneration

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