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Molecular behaviors in thin film lubrication——Part three: Superlubricity attained by polar and nonpolar molecules

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Friction 2019年第6期7卷 625-636页

作者： xiangyu ge Tobias HALMANS Jinjin LI Jianbin LUO State Key Laboratory of Tribology Tsinghua UniversityBeijing 100084China RWTH Aachen University Aachen 52062Germany

In thin-film lubrication(TFL), generally, the viscosity of the lubricant and its coefficient of friction(Co F) increase. Finding a method to reduce the Co F in TFL is a significant challenge for tribologists. In the present work, we report a robust superlubricity attained by using polyalkylene glycols(PAGs, polar molecules) and poly-α-olefins(PAOs, nonpolar molecules) as lubricants on steel/steel friction pairs that have been pre-treated by wearing-in with polyethylene glycol aqueous solution(PEG(aq)). A steady superlubricity state with a Co F of 0.0045 for PAG100 and 0.006 for PAO6 could be maintained for at least 1 h. Various affecting factors, including the sliding velocity, normal load, and viscosity of the lubricants, were investigated. Element analysis proved that composite tribochemical layers were deposited on the worn region after the treatment with PEG(aq). These layers were formed by the tribochemical reactions between PEG and steel and composed of various substances including oxides, iron oxides, Fe OOH, and Fe(OH)3, which contributed to the superlubricity. In addition to the tribochemical layers, ordered layers and a fluid layer were formed by the PAGs and PAOs during the superlubricity periods. All the three types of layers contributed to the superlubricity, indicating that it was attained in the TFL regime. Accordingly, a mechanism was proposed for the superlubricity of the PAGs and PAOs in the TFL regime in this work. This study will increase the scientific understanding of the superlubricity in the TFL regime and reveal, in the future, the potential for designing superlubricity systems on steel surfaces for industrial applications.

关键词： thin film lubrication superlubricity PEG PAG PAO

Graphene superlubricity:A review

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Friction 2023年第11期11卷 1953-1973页

作者： xiangyu ge Zhiyuan CHAI Qiuyu SHI Yanfei LIU Wenzhong WANG School of Mechanical Engineering Beijing Institute of TechnologyBeijing 100081China State Grid Smart Grid Research Institute Co. Ltd.Beijing 102209China

Superlubricity has drawn substantial attention worldwide while the energy crisis is challenging human ***,numerous endeavors are bestowed to design materials for superlubricity achievement at multiple *** in graphene-family materials,such as graphene,graphene oxide,and graphene quantum dots,initiated an epoch for atomically thin solid ***,superlubricity achieved with graphene-family materials still needs fundamental understanding for being applied in engineering in the *** this review,the fundamental mechanisms for superlubricity that are achieved with graphene-family materials are outlined in detail,and the problems concerning graphene superlubricity and future progress in superlubricity are *** review concludes the fundamental mechanisms for graphene superlubricity and offers guidance for utilizing graphene-family materials in superlubricity systems.

关键词： superlubricity graphene graphene-family materials two-dimensional(2D)materials friction

Conductive grease synthesized using nanometer ATO as an additive

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Friction 2015年第1期3卷 56-64页

作者： xiangyu ge Yanqiu XIA Zongying SHU Xiaopei ZHAO School of Energy Power and Mechanical Engineering North China Electric Power UniversityBeijing 102206China

A new conductive grease was synthesized using a nanometer powder,i.e.,Sb doped SnO2(ATO),as an *** typical properties of this new conductive grease were investigated in *** results indicate that ATO can dramatically improve the dropping point and reduce contact *** tribological properties of the new conductive grease were investigated using the MFT-R4000 reciprocating friction and wear *** tribol-test results indicate that ATO can dramatically improve the tribological properties of the *** the ATO concentration is 0.1wt%,the grease demonstrates the best friction reduction properties;when the concentration is 0.5wt%,the grease demonstrates the best anti-wear *** worn surfaces were observed and analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy,and the friction mechanisms for the new conductive grease are *** excellent tribological properties of the new conductive grease are attributed to the mechanical effect of ATO,and the film formed by Sn and Sb elements or metallic oxide deposited on worn surfaces during the friction process.

关键词： Sb doped SnO2(ATO) conductive grease contact resistance friction and wear wear mechanism

Assessment of ecological quality in Northwest China(2000-2020)using the Google Earth Engine platform:Climate factors and land use/land cover contribute to ecological quality

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Journal of Arid Land 2022年第11期14卷 1196-1211页

作者： WANG Jinjie DING Jianli ge xiangyu QIN Shaofeng ZHANG Zhe College of geography and Remote Sensing Science Xinjiang UniversityUrumqi 800046China Xinjiang Key Laboratory of Oasis Ecology Xinjiang UniversityUrumqi 830046China Key Laboratory of Smart City and Environment Modelling of Higher Education Institute Xinjiang UniversityUrumqi 830046China

The ecological quality of inland areas is an important aspect of the United Nations Sustainable Development Goals(UN SDGs).The ecological environment of Northwest China is vulnerable to changes in climate and land use/land cover,and the changes in ecological quality in this arid region over the last two decades are not well *** makes it more difficult to advance the UN SDGs and develop appropriate measures at the regional *** this study,we used the Moderate Resolution Imaging Spectroradiometer(MODIS)products to generate remote sensing ecological index(RSEI)on the Google Earth Engine(geE)platform to examine the relationship between ecological quality and environment in Xinjiang during the last two decades(from 2000 to 2020).We analyzed a 21-year time series of the trends and spatial characteristics of ecological *** further assessed the importance of different environmental factors affecting ecological quality through the random forest algorithm using data from statistical yearbooks and land use *** results show that the RSEI constructed using the geE platform can accurately reflect the ecological quality information in Xinjiang because the contribution of the first principal component was higher than 90.00%.The ecological quality in Xinjiang has increased significantly over the last two decades,with the northern part of this region having a better ecological quality than the southern *** areas with slightly improved ecological quality accounted for 31.26%of the total land area of Xinjiang,whereas only 3.55%of the land area was classified as having a slightly worsen(3.16%)or worsen(0.39%)ecological *** vast majority of the deterioration in ecological quality mainly occurred in the barren areas Temperature,precipitation,closed shrublands,grasslands and savannas were the top five environmental factors affecting the changes in *** factors were allocated different weights for different RSEI *** genera

关键词： ecological quality land use/land cover spatiotemporal change remote sensing ecological index(RSEI) Google Earth Engine Xinjiang

Effect of Counterparts and Applied Load on the Tribological Behavior of the Graphene–Nickel Matrix Self-Lubricating Composite

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Friction 2023年第2期11卷 187-200页

作者： xiangyu ge Zhiyuan CHAI Qiuyu SHI Jinjin LI Jiawei TANG Yanfei LIU Wenzhong WANG School of Mechanical Engineering Beijing Institute of TechnologyBeijing 100081China State Grid Smart Grid Research Institute Co. Ltd.Beijing 102209China State Key Laboratory of Tribology Tsinghua UniversityBeijing 100084China

Graphene-oxide (GO) has been recognized as an excellent lubrication material owing to its two-dimensional structure and weak interlayer interactions. However, the functional groups of GO that can contribute to anti-friction, anti-wear, and superlubricity are yet to be elucidated. Hence, further improvement in GO-family materials in tribology and superlubricity fields is impeded. In this study, macroscale superlubricity with a coefficient of friction of less than 0.01 is achieved by exploiting the high adhesive force between amino groups within aminated GO (GO–NH_(2)) nanosheets and SiO_(2). It was observed that GO–NH_(2) nanosheets form a robust adsorption layer on the worn surfaces owing to the high adsorption of amino groups. This robust GO–NH_(2) adsorption layer not only protects the contact surfaces and contributes to low wear, but also causes the shearing plane to transform constantly from solid asperities (high friction) into GO–NH_(2) interlayers (weak interlayer interactions), resulting in superlubricity. A SiO_(2)-containing boundary layer formed by tribochemical reactions and a liquid film are conducive to low friction. Such macroscale liquid superlubricity provides further insights into the effect of functional groups within functionalized GO materials and a basis for designing functionalized GO materials with excellent tribological performances.

关键词： functionalized graphene-oxide aminated graphene-oxide superlubricity anti-friction and anti-wear

Asymmetric Thermally Activated Delayed Fluorescence Materials Rendering High-performance OLEDs Through both Thermal Evaporation and Solution-processing

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Chemical Research in Chinese Universities 2022年第6期38卷 1526-1531页

作者： GAO Shiyuan CHEN Xiaojie ge xiangyu CHEN Zhu ZHAO Juan CHI Zhenguo State Key Laboratory of OEMT School of Materials Science and EngineeringSun Yat-sen UniversityGuangzhou510275P.R.China State Key Laboratory of OEMT School of ChemistrySun Yat-sen UniversityGuangzhou510275P.R.China

Exploring high-efficiency thermally activated delayed fluorescence(TADF)materials is of great importance regarding to organic light-emitting diode(OLED).Herein,we present a design strategy for developing asymmetric TADF materials based on a diphenyl sulfone-phenoxazine structure,resulting in efficient TADF emitters(CzPXZ and t-CzPXZ)with aggregation-induced emission properties,while t-CzPXZ is modified with tert-butyl *** two compounds exhibit high solid-state luminescence,efficient TADF,and significantly impressive device performances by both thermal evaporation and solution *** an instance,CzPXZ and t-CzPXZ enable the thermally-evaporated OLEDs with high external quantum efficiencies(EQEs)of over 20%.Meanwhile,t-CzPXZ allows the solution-processed device with a high EQE of 16.3%with low-efficiency roll-off,attributing to the enhanced molecular solubility and suppressed excitons quenching through tert-butyl modification on *** results reveal that the proposed asymmetric structure is a promising approach for developing high-efficiency TADF materials and OLEDs.

关键词： Thermally activated delayed fluorescence Asymmetric strategy Organic light-emitting diode Thermal evaporation Solution processing

Estimation of soil organic matter in the Ogan-Kuqa River Oasis, Northwest China, based on visible and near-infrared spectroscopy and machine learning

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Journal of Arid Land 2023年第2期15卷 191-204页

作者： ZHOU Qian DING Jianli ge xiangyu LI Ke ZHANG Zipeng GU Yongsheng College of geography and Remote Sensing Science Xinjiang UniversityUrumqi 830046China Xinjiang Key Laboratory of Oasis Ecology Xinjiang UniversityUrumqi 830046China Key Laboratory of Smart City and Environment Modelling of Higher Education Institute Xinjiang UniversityUrumqi 830046China

Visible and near-infrared(vis-NIR)spectroscopy technique allows for fast and efficient determination of soil organic matter(SOM).However,a prior requirement for the vis-NIR spectroscopy technique to predict SOM is the effective removal of redundant ***,this study aims to select three wavelength selection strategies for obtaining the spectral response characteristics of *** SOM content and spectral information of 110 soil samples from the Ogan-Kuqa River Oasis were measured under laboratory conditions in July *** correlation analysis was introduced to preselect spectral wavelengths from the preprocessed spectra that passed the 0.01 level significance *** successive projection algorithm(SPA),competitive adaptive reweighted sampling(CARS),and Boruta algorithm were used to detect the optimal variables from the preselected ***,partial least squares regression(PLSR)and random forest(RF)models combined with the optimal wavelengths were applied to develop a quantitative estimation model of the SOM *** results demonstrate that the optimal variables selected were mainly located near the range of spectral absorption features(i.e.,1400.0,1900.0,and 2200.0 nm),and the CARS and Boruta algorithm also selected a few visible wavelengths located in the range of 480.0–510.0 *** models can achieve a more satisfactory prediction of the SOM content,and the RF model had better accuracy than the PLSR *** SOM content prediction model established by Boruta algorithm combined with the RF model performed best with 23 variables and the model achieved the coefficient of determination(R2)of 0.78 and the residual prediction deviation(RPD)of *** Boruta algorithm effectively removed redundant information and optimized the optimal wavelengths to improve the prediction accuracy of the estimated SOM ***,combining vis-NIR spectroscopy with machine learning to estimate SOM content is an important method to improve th

关键词： soil organic matter content vis-NIR spectroscopy random forest Boruta algorithm machine learning

新型免疫抑制剂brasilicardin A的研究进展

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生物工程学报 2023年第9期39卷 3605-3614页

作者：葛祥宇史社坡王娟北京中医药大学中药现代研究中心北京100029

Brasilicardin A(BraA)是从致病性放线菌巴西诺卡菌(Nocardia brasiliensis)IFM 0406中发现的具有显著免疫抑制作用(IC_(50)=0.057μg/mL)的二萜糖苷类化合物。BraA发挥免疫抑制活性的作用机制与现有临床常用的免疫抑制剂不同,BraA通过... 详细信息

Brasilicardin A(BraA)是从致病性放线菌巴西诺卡菌(Nocardia brasiliensis)IFM 0406中发现的具有显著免疫抑制作用(IC_(50)=0.057μg/mL)的二萜糖苷类化合物。BraA发挥免疫抑制活性的作用机制与现有临床常用的免疫抑制剂不同,BraA通过抑制氨基酸转运体L系统的转运进而影响T-淋巴细胞对氨基酸的摄入而发挥免疫抑制作用。相比目前已知的免疫抑制剂环孢菌素A、子囊霉素和他克莫司等,BraA在小鼠混合淋巴细胞反应中显示低毒、高效的优势。因此,BraA作为新型的免疫抑制剂,极具开发潜力,已成为全球免疫抑制剂发现新领域。但其结构复杂、合成困难,原菌种产率低且具有致病性,BraA及其类似物的获得已成为此类新型免疫抑制剂研究的瓶颈。本文综述了BraA的分子特征、药理活性、作用机制、目前获得的BraA类似物和衍生化方面的研究进展,以期为BraA及其类似物的高效生产提供参考。

关键词： brasilicardin A 分子特征免疫抑制活性生物合成机制化学合成

交通基础设施投资与经济增长——基于准自然实验的证据

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系统工程理论与实践 2019年第4期39卷 922-934页

作者：葛翔宇黄永强周艳丽中南财经政法大学统计与数学学院武汉430073 赣南师范大学商学院赣州341000 中南财经政法大学金融学院武汉430073

基于京九铁路构建的准自然实验样本并运用非参数匹配估计方法,本文探讨了交通基础设施投资与经济增长的关系.利用1991-2010年中部地区50个县数据检验了京九铁路投资对途经县市经济增长的短期效应,中长期效应及滞后效应.实证检验结论表明... 详细信息

基于京九铁路构建的准自然实验样本并运用非参数匹配估计方法,本文探讨了交通基础设施投资与经济增长的关系.利用1991-2010年中部地区50个县数据检验了京九铁路投资对途经县市经济增长的短期效应,中长期效应及滞后效应.实证检验结论表明:第一,京九铁路投资对途经县市经济增长的影响总体上是显著的.短期内京九铁路投资对途经县市人均GDP的增长显著,且平均增加值达220元左右,中长期的平均增加值达1100元左右.第二,京九铁路投资存在明显的溢出效应,京九铁路沿线主要站点附近县市的经济增长均受益.第三,京九铁路投资对途经县市的经济增长存在滞后效应并呈现倒U型结构,表现为经济增长会逐步增大至10年左右后呈逐步减弱的特点.

关键词：基础设施京九铁路经济增长倾向值匹配