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New approach to determine the plastic viscosity of self- compacting concrete

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Frontiers of Structural and Civil Engineering 2016年第2期10卷 198-208页

作者： M. BENAICHA x. ROGUIEZ O. JALBAUD Y. BURTSCHELL A. Hafidi ALAOUI Civil Engineering Department IUSTI UMR 7343 Laboratory AMU Marseille 13453 France Civil Engineering Department Abdelmalek Essaadi University Morocco

The rheology of concrete is best measured with the use of a rheometer. The slump flow test gives a good indication of the flowability of the mix.ure and is therefore still used ex.ensively to judge the workability of SCC mix.ures. However, this test presents some defects. The objective of this paper is to develop a new methodology for measuring the workability of a SCC. In this article, we have proposed a correlation between the plastic viscosity of concrete, the time and the characteristics of the flow final profile from the V-funnel coupled to a Plex.glas horizontal channel. The proposed approach, verified by ex.erimental results, represents a simple, economical and usable tool on building site, and it allows to characterize rheologically the SCC from its flow. The comparison between our approach and the ex.erimental values of the plastic viscosity shows that, in a laboratory or on site, instead of using a rheometer we can use our approach to characterize the rheological behavior of a SCC.

关键词： rheology viscosity V-funnel flow profile rheometer behavior

ON HYDRODYNAMIC INSTABILITIES,CHAOS AND PHASE TRANSITION

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Acta Mechanica Sinica 1996年第1期12卷 1-14页

作者： D. Y. Hsieh S. Q. Tang x. P. Wang Department of Mathematics The Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong Institute of Mathematics Chinese Academy of Sciences Beijing 100080 China

Ellipticity as the underlying mechanism for instabilities of physical systems is highlighted in the study of model nonlinear evolution equations with dissipation and the study of phase transition in Van der Waals fluid. Interesting results include spiky solutions, chaotic behavior in the contex. of partial differential equations, as well as the nucleation process due to ellipticity in phase transition.

关键词： ellipticity hydrodynamic instabilities chaos phase transition

ELECTRONIC STRUCTURE OF THE LaNi_(5-x.Ga_x.INTERMETALLIC COMPOUNDS

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Acta Metallurgica Sinica(English Letters) 2008年第3期21卷 157-162页

作者： D. Chen G.x. Li D.L. Zhang T. Gao Department of Physics and Electronic Engineering Xinyang Normal University Xinyang 464000 China College of Science Qingdao Agriculture University Qingdao 266109 China Institute of Atomic and Molecular Physics Sichuan University Chengdu 610065 China

The equilibrium structures and electronic structure of LaNi5-x.ax.（x.0, 0.5, 1.0） compounds have been investigated by all-electron calculations. Based on the full geometry optimization, the densities of states and electron densities of LaNi5-x.ax.are plotted and analyzed. It is clear that the substitution of Ga at the Ni site leads to a progressive filling of the Ni-d bands, the ionic interaction between Ni and Ni, with Ga plays a dominant role in the stability of LaNi5-x.ax.compounds. The smaller the shift of EF toward higher energy region, the more stable the compounds will be. The increased contribution of the Ni-d-Ga-d interactions near EF and the low energy metal-gallium bonding bands indicate that the compounds become more stable. The results are compared with ex.erimental data and discussed in light of previous studies.

关键词： FLAPW and GGA LaNi5-x.ax Intermetallie compound Electronic structure

A quasi-in-situ EBSD study of the thermal stability and grain growth mechanisms of CoCrNi medium entropy alloy with gradient-nanograined structure

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Journal of Materials Science & Technology 2022年第14期109卷 54-63页

作者： P.-C.Zhao B.Guan Y.-G.Tong R.-Z.Wang x.Li x.-C.Zhang S.-T.Tu Key Laboratory of Pressure Systems and Safety Ministry of EducationSchool of Mechanical and Power EngineeringEast China University of Science and TechnologyShanghai 200237China College of Materials Science and Engineering Chongqing UniversityChongqing 400044China College of Automobile and Mechanical Engineering Changsha University of Science and TechnologyChangshaChina

The thermal stability and mechanical properties of a gradient-nanograined structure(GNS)CoCrNi medium entropy alloy(MEA)processed by ultrasonic surface rolling were studied by using isothermal/isochronal annealing tests combined with quasi-in-situ electron backscatter diffraction(EBSD)characterization and Vickers micro-hardness(HV)measurements.A layer by layer high-throughput investigation method was used to quantitatively study the grain growth kinetics and grain boundary evolution with different initial grain sizes,which could effectively save specimen and time *** grain nucleation and growth,as well as shrink and disappearance process throughΣ3 coincidence site lattice boundary migration with slightly lattice rotation during annealing were directly *** layer by layer grain growth kinetics and calculated activation energy indicate that the thermal stability of nanograined top surface layer is relatively higher than that of nano-twined subsurface layer for the gradient CoCrNi MEA processed by ultrasonic surface *** analysis show that the grain boundary relax.tion and dynamic recrystallization of the topmost nano-grains led to the decrease of grain boundary energy,thus improving their thermal *** present work provided theoretical basis for the application of CoCrNi MEA at high ***,the high-throughput method on the investigation of grain stability by using gradient structure can be easily ex.ended to other materials and it is of great significance for understanding the microstructural evolution of gradient materials.

关键词： Medium entropy alloy Grain growth Gradient materials Nanostructured materials Annealing High throughput

Deformation kinking and highly localized nanocrystallization in metastableβ-Ti alloys using cold forging

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Journal of Materials Science & Technology 2022年第25期120卷 53-64页

作者： Keer Li W.Chen G.x.Yu J.Y.Zhang S.W.x.n J.x.Liu x.x.Wang J.Sun State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China Northwest Institute for Nonferrous Metal Research Xi’an 710016China Baoji Titanium Industry Co. Ltd.Baoji 721014China

Deformation kinking as an uncommon plastic deformation mechanism has been reported in several materials while the relevant microstructure evolution and grain refinement behavior at a large strain remain unclear so *** this study,the issue was systematically investigated by utilizing cold forging to impose severe plastic deformation(SPD)on Ti-11 V metastableβ-Ti *** is found that the formation of kink bands ex.eriences dislocation gliding,pre-kinking and the ripening of pre-kinks in *** kink bands are subsequently thickened through the coalescence of multiple kink bands in a manner of high *** dislocation slip is developed as a dominant deformation mechanism when deformation kinking is *** resulting grain refinement involves transverse breakdown and longitudinal splitting of dislocation walls and cells,which fragment kink bands into smallβ-*** refinement of theβ-blocks is still governed by dislocation activities,and finally nanograins with a diameter of~15 nm are produced at a large strain of ***,it is revealed that nanocrystallization is highly localized inside kink bands while the outer microstructure maintains original coarse *** localized refinement characterization is ascribed to the intrinsic soft nature of kink bands,shown as low hardness in nanoindentation *** intrinsic softening of kink bands is uncovered to originate from the inner degraded dislocation density evidenced by both ex.erimental measurement and theoretical *** findings enrich fundamental understanding of deformation kinking,and shed some light on ex.loring the deformation accommodation mechanisms for metal materials at large strains.

关键词： Metastableβ-Ti alloys Deformation kinking Microstructural evolution Grain refinement Dislocations

Molecular dynamics simulations of microscopicstructure of ultra strong shock waves in dense helium

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Frontiers of physics 2016年第6期11卷 197-207页

作者： Hao Liu Wei Kang Qi Zhang Yin Zhang Huilin Duan x. T. He HEDPS Center for Applied Physics and Technology Peking University Beijing 100871 China College of Engineering Peking University Beijing 100871 China Department of Mechanics and Engineering Science College of Engineering Peking University Beijing 100871 China Center for Applied Physics and Technology HEDPS and IFSA Collaborative Innovation Center of MoE Peking University Beijing 100871 China Institute of Applied Physics and Computational Mathematics Beijing 100088 China

Hydrodynamic properties and structure of strong shock waves in classical dense helium are simulated using non-equilibrium molecular dynamics methods. The shock speed in the simulation reaches 100 km/s and the Mach number is over 250, which are close to the parameters of shock waves in the implosion process of inertial confinement fusion. The simulations show that the high-Mach-number shock waves in dense media have notable differences from weak shock waves or those in dilute gases. These results will provide useful information on the implosion process, especially the structure of strong shock wave front, which remains an open question in hydrodynamic simulations.

关键词： shock structure high Mach number dense media

Machine learning guided automatic recognition of crystal boundaries in bainitic/martensitic alloy and relationship between boundary types and ductile-to-brittle transition behavior

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Journal of Materials Science & Technology 2021年第25期84卷 49-58页

作者： x.C.Li J.x.Zhao J.H.Cong R.D.K.Misra x.M.Wang x.L.Wang C.J.Shang Collaborative Innovation Center of Steel Technology University of Science and Technology BeijingBeijing 100083China Department of Metallurgical Materials and Biomedical EngineeringUniversity of Texas at El Paso500 W.University AvenueEl PasoTX 79968USA

Gradient boosting decision tree(GBDT)machine learning(ML)method was adopted for the first time to automatically recognize and conduct quantitative statistical analysis of boundaries in bainitic microstructure using electron back-scatter diffraction(EBSD)*** spite of lack of large sets of EBSD data,we were successful in achieving the desired accuracy and accomplishing the objective of recognizing the *** with a low model accuracy ofx.s-angle pair as characteristic features,the accuracy of the model was significantly enhanced to about 88%when the Euler angle was converted to overall misorientation angle(OMA)and specific misorientation angle(SMA)and considered as important *** this model,the recall score of prior austenite grain(PAG)boundary was~93%,high angle packet boundary(OMA>40°)was~97%,and block boundary was~96%.The derived outcomes of ML were used to obtain insights into the ductile-to-brittle transition(DBTT)***,ML modeling approach suggested that DBTT was not determined by the density of high angle grain boundaries,but significantly influenced by the density of PAG and packet *** study underscores that ML has a great potential in detailed recognition of complex.multi-hierarchical microstructure such as bainite and martensite and relates to material performance.

关键词： Machine learning Feature engineering Automatic recognition Lath structure Crystallography

Recent progress in the single-cell C4 photosynthesis in terrestrial plants

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Frontiers in Biology 2012年第6期7卷 539-547页

作者： Shiu-Cheung LUNG Makoto YANAGISAWA Simon D. x. CHUONG Department of Biology University of Waterloo Waterloo Ontario N2L 3G1 Canada Agronomy Department Purdue University West Lafayette IN 47907-2054 USA

Currently, single-cell C4 photosynthesis has been reported in four terrestrial plant species, Bienertia cycloptera, B. sinuspersici, B. kavirense and Suaeda aralocaspica, of family Chenopodiaceae. These species possess novel mechanisms of C4 photosynthesis through spatial partitioning of organelles and key enzymes in distinct cytoplasmic domains within single chlorenchyma cells. Anatomical and biochemical studies have shown that the three Bienertia species and S. aralocaspica utilize biochemical and organellar compartmentation to achieve the equivalent spatial separation of Kranz anatomy but within a single photosynthetic cell. These discoveries have challenged the paradigm for C4 photosynthesis in terrestrial plants which had suggested for more than 40 years that the Kranz feature was indispensably required for its C4 function. In this review, we focus on the recent progress in understanding the cellular and molecular mechanisms that control the spatial relationship of organelles in these unique single-cell C4 systems. The demonstrated interaction of dimorphic chloroplasts with microtubules and actin filaments has shed light on the importance of these cytoskeleton components in the intracellular partitioning of organelles. Future perspectives on the potential function of the cytoskeleton in targeting gene products to specific subcellular compartments are discussed.

关键词： C4 plants single-cell C4 photosynthesis Chenopodiaceae dimorphic chloroplasts organelle compartmentation,photosynthetic enzymes cytoskeleton protein targeting

Fast　Ignition　and　Stable　Combustion　of　Coarse　Coal　Particles　in　a　Nonslagging　Cyclone　Combustor

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Journal of Thermal Science 1995年第2期4卷 136-140页

作者： Biao Zhou x. L.Wang R. x. Li Lix.ng Zhou(Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China) Department of Engineering Mechanics Tsinghua University Beijing China

A combustion set-up of an innovative nonslagging cyclone combustor called 'Spouting-Cyclone Combustor (SCC)' ) with two-stage combustion, organized in orthogonal vortex.flows, was established and the ex.erimental studies on the fast ignition and stable combustion of coarse coal particles in this combustor were carried out. The flame temperature versus ignition time and the practical faSt ignition procedure were obtained; The stable coal combustion can be achieved after a short period ignition, and the temperature fields in SCC were obtained. These results show that it is possible to obtain highly efficient and clean combustion of unground coal particles by using this technology.

关键词： coal combustion coal ignition cyclone combustor.