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Survey of the mechanisms of power take-off(PTO)devices of wave energy converters

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Acta Mechanica Sinica 2020年第3期36卷 644-658页

作者： z.liu R.zhang H.Xiao X.Wang School of Engineering RMIT UniversityBundooraVIC 3083Australia

Ocean wave energy conversion as one of the renewable clean energy sources is attracting the research interests of many *** review introduces different types of power take-off(PTO)technology of wave energy *** novelty of this paper is to present advantages and disadvantages of the linear direct and indirect drive PTO devices for ocean wave energy *** designs and optimizations of PTO systems of ocean wave energy converters have been studied from reviewing the recently published *** novel mechanical designs of the PTO systems have been compared and investigated in order to increase the energy harvesting efficiency.

关键词： ocean wave energy

Distinct dendritic α phase emerging on the surface of primary α phase in a compressed near-α titanium alloy

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Journal of Materials Science & Technology 2018年第4期34卷 666-669页

作者： z.liu z.B.zhao J.R.liu Q.J.Wang R.Yang Institute of Metal Research Chinese Academy of Sciences School of Materials Science and Engineering University of Science and Technology of China

The characteristic of the surface morphology of primary α phase was studied in a deformed near-α tita- nium alloy. Dendritic α phase emerged on the surfaces of primary α phase when the alloy was air-cooled in α ＋β phase field after deformation. The dendritic α grain has the same orientation with its original primary α grain. The formation of the dendritic α phase could be explained by interface instability in epi- taxial growth process of the primary α phase. The dislocations induced by deformation could facilitate the formation of dendritic α phase leading to the dendritic α phase and more obvious with the increase of strain. The growth of dendritic α phase was finally limited by the nucleation of second α phase with cooling.

关键词： Epitaxial growth Dendritic α phase Microstructure Interface instability Hot deformation

Digital Earth: decadal experiences and some thoughts

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International Journal of Digital Earth 2010年第1期3卷 31-46页

作者： H.D.Guo z.liu L.W.zhu Center for Earth Observation and Digital Earth Chinese Academy of SciencesNo.9 Beiyitiao RoadZhongguancunHaidian DistrictBeijing 100190China

The understanding that mankind should reasonably exploit and utilize earth resources and effectively protect the planet on which we live,is now widely ***,effective actions can only be conducted if we better understand and visualize the *** meet this need,digital earth science and technology have been put forward and *** paper introduces the evolution and development process of digital earth,and presents an overview by reviewing and analyzing the 1999 and 2009 Beijing Declaration on Digital Earth,the scientific and commercial digital earth systems,global and regional digital earth research,and some existing platforms of digital earth *** also presents some thoughts about digital earth’s future development.

关键词： Beijing Declaration digital earth system global change

Analysis of local crystallographic orientation in an annealed Ti60 billet

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Journal of Materials Science & Technology 2019年第4期35卷 591-595页

作者： z.B.zhao z.liu Q.J.Wang J.R.liu R.Yang Institute of Metal Research Chinese Academy of Sciences School of Materials Science and Engineering University of Science and Technology of China

A heterogeneous microstructure in terms of local orientation distribution is often found in near-α titanium alloys. The presence of large regions with similar crystallographic orientation, called ‘macrozones',could drastically decrease the fatigue performance of titanium alloys. The present work reports on the crystallographic orientation of a near-α titanium alloy, Ti60, billet after annealing in an α+β phase *** texture was found to be weak, and no obvious macrozone was found in our measured zone where the variant selection is suppressed. Meanwhile, in-depth electron backscattered diffraction(EBSD) analysis was applied to evaluate the final microstructure, and the mechanisms by which they formed were analyzed.

关键词： Titanium alloys Microstructure Texture Heat treatment EBSD

Microstructural evolution and superelastic properties of ultrafine-graine d NiTi-base d shape memory alloy via sintering of amorphous ribbon precursor

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Journal of Materials Science & Technology 2023年第7期138卷 80-92页

作者： W.S.Cai H.z.Lu H.z.Li z.liu H.B.Ke W.H.Wang C.Yang National Engineering Research Center of Near-net-shape Forming for Metallic Materials Guangdong Provincial Key Laboratory for Processing and Forming of Advanced Metallic MaterialsSouth China University of TechnologyGuangzhou 510640China Songshan Lake Materials Laboratory Dongguan 523808China Institute of Physics Chinese Academy of SciencesBeijing 100190China

NiTi-based shape memory alloys(SMAs)are considered as cutting-edge intelligent functional ***,it remains a great challenge to obtain ultrafine-grained(UFGed)bulk materials with mm-scale size as well as outstanding superelastic ***,UFGed bulk Ti_(35)zr_(15)Ni_(35)Cu_(15)NiTi-based SMA is successfully prepared via spark plasma sintering of amorphous ribbon precursor at different sintering temperatures,and microstructural evolution and superelastic properties are symmetrically *** is found that its grain size ranges from UFG to micro-grain with increased sintering temperature regard-less of the predominant B2 matrix in all bulk ***,the orientation relationships between B2 matrix and nano-scale fcc(Ti,zr)_(2)Ni precipitate evolve from coherent to ***,the UFGed samples exhibit perfect superelasticity with the high recoverable strain of∼5.8%,the stable recov-ery rate above 99%,and the great critical stress inducing martensitic transformation higher than 1 GPa,far superior to the corresponding ones of suction-cast micro-grained TizrNiCu ***,the perfect superelasticity is attributed to the good resistance to dislocation slip or grain boundary slip by residual nano-scale amorphous phase or secondary phase of coherent and semi-coherent fcc(Ti,zr)_(2)Ni *** addition,the gentle superelastic plateau is associated to the favorable transfer stress and the strong ability to accommodate dislocation movement,which is generated by the coherent interface between nano-scale fcc(Ti,zr)_(2)Ni and UFGed B2 *** results suggest that spark plasma sintering of amorphous alloy precursor is a feasible route to obtaining excellent superelasticity in NiTi-based SMAs.

关键词： Shape memory alloy Amorphous alloy Microstructure Superelasticity

A dissolution-diffusion sliding model for soft rock grains with hydro-mechanical effect

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Journal of Rock Mechanics and Geotechnical Engineering 2018年第3期10卷 457-467页

作者： z.liu C.Y.zhou B.T.Li Y.Q.Lu X.Yang Guangdong Engineering Research Center for Major Infrastructure Safety School of Civil Engineering Sun Yat-sen University

The deformation and failure of soft rock affected by hydro-mechanical（HM） effect are one of the most concerns in geotechnical engineering, which are basically attributed to the grain sliding of soft rock. This study tried to develop a dissolution-diffusion sliding model for the typical red bed soft rock in South China. Based on hydration film, mineral dissolution and diffusion theory, and geochemical thermodynamics, a dissolution-diffusion sliding model with the HM effect was established to account for the sliding rate. Combined with the digital image processing technology, the relationship between the grain size of soft rock and the amplitude of sliding surface was presented. An equation for the strain rate of soft rocks under steady state was also derived. The reliability of the dissolution-diffusion sliding model was verified by triaxial creep tests on the soft rock with the HM coupling effect and by the relationship between the inversion average disjoining pressure and the average thickness of the hydration film. The results showed that the sliding rate of the soft rock grains was affected significantly by the waviness of sliding surface, the shear stress, and the average thickness of hydration film. The average grain size is essential for controlling the steady-state creep rate of soft rock. This study provides a new idea for investigating the deformation and failure of soft rock with the HM effect.

关键词： Soft rock Hydro-mechanical (HM) effect Mineral dissolution-diffusion Grain sliding model

A COVID-19 epidemic model with latency period

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Infectious Disease Modelling 2020年第1期5卷 323-337页

作者： z.liu P.Magal O.Seydi G.Webb School of Mathematical Sciences Beijing Normal UniversityBeijing100875People's Republic of China Univ.Bordeaux France CNRSIMBUMR 5251F-33400TalenceFrance Département Tronc Commun École Polytechnique de ThiésSenegal Mathematics Department Vanderbilt UniversityNashvilleTNUSA

At the beginning of a COVID-19 infection,there is a period of time known as the exposed or latency period,before an infected person is capable of transmitting the infection to another *** develop two differential equations models to account for this *** first is a model that incorporates infected persons in the exposed class,before transmission is *** second is a model that incorporates a time delay in infected persons,before transmission is *** apply both models to the COVID-19 epidemic in *** estimate the epidemiological parameters in the models,such as the transmission rate and the basic reproductive number,using data of reported *** thus evaluate the role of the exposed or latency period in the dynamics of a COVID-19 epidemic.

关键词： Corona virus Reported and unreported cases Isolation Quarantine Public closings Epidemic mathematical model

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主动施加时滞的振动控制

北京邮电大学学报 2000年第3期23卷 25-29页

作者：刘晓平 B.Yang z.liu 北京邮电大学自动化学院北京100876 UniversityofSouthernCalifornia

研究了主动引入时滞的结构振动输出反馈控制方法 .该方法能有效地解决结构振动非对位控制中常易出现的控制失稳问题 ,并取得较好的振动控制效果 .通过悬臂梁结构振动控制算例深入分析了该方法的有效性 .

关键词：地动主动控制时滞悬臂梁

语义矢量空间模式（SVSM）及其试验评价——自然语言处理与文献自动标引

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情报学报 1996年第6期15卷 402-413页

作者： Geofrey z.liu 美国加利福尼亚州圣何塞州立大学图书情报学院

本文介绍一种基于句法分析和格式语义结构，被称为“语义矢量空间模式”的文献自动标引／检索技术。在此模式中，自然语言文献和检索提问均表示为语义矩阵。通过计算语义矩阵的相似值，检索系统可以预测文献与给定提问之间的相关度，从... 详细信息

本文介绍一种基于句法分析和格式语义结构，被称为“语义矢量空间模式”的文献自动标引／检索技术。在此模式中，自然语言文献和检索提问均表示为语义矩阵。通过计算语义矩阵的相似值，检索系统可以预测文献与给定提问之间的相关度，从而达到检索相关文献的目的。初步试验结果表明，若文献及检索提问较长，特别是以原文献作为提问样本时，此检索技术与康奈尔大学的ＳＭＡＲＴ系统相比，在检全率。

关键词：情报检索自动标引矢量空间模式自然语言处理