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OXIDATION RESISTANCE OF NANOCRYSTAL ODS ALUMINIDE COATINGS PRODUCED BY PACK ALUMINIzING PROCESS ASSISTED BY BALL PEENING

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Acta Metallurgica Sinica(English Letters) 2006年第3期19卷 215-222页

作者： z.L. zhan Y.D. He W. gao Kunming University of Science and Technology Kunming 650093 China Beijing Key Laboratory for Corrosion Erosion and Surface Technology University of Science and Technology Beijing Beijing 100083 China Engineering School The University of Auckland Auckland 1020 New Zealand

Nanocrystal ODS （oxide dispersion strengthening） aluminide coatings were produced on a stainless steel and nickel-based superalloy by the pock aluminizing process assisted by ball peening, Pure Al powders and 1% of ultra-fine Y2O3 powders were mixed by ball milling. The ultra-fine Y2O3 powders were dispersed in Al particles. Ball peening welded the Al particles onto the substrate and accelerated the formation of aluminide coating. Nanocrystal ODS aluminide coatings were produced by the outward growth at a much low temperature （below 600℃） in a short treatment time. The effects of the operation temperature and treatment time on the formation of the coatings were analyzed. SEM （scanning electron microscope）, AFM （atomic force microscope）, EDS （energy dispersive X-ray spectroscopy）, XRF （X-ray fluorescence spectrometer） and XRD （X-ray diffraction） methods were applied to investigate the microstructure of the coatings. High-temperature oxidation tests were carried out to evaluate the oxidation resistance of the ODS aluminide coatings.

关键词： nano-coating ODS coating aluminide coating ball peening high-temperature oxidation

Finite element simulations on the mechanical properties of MHS materials

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Acta Mechanica Sinica 2007年第1期23卷 65-75页

作者： z. Y. gao T. X. Yu D. Karagiozova Department of Mechanical Engineering Hong Kong University of Science &Technology Clear Water Bay Kowloon Hong Kong China Institute of Mechanics Bulgarian Academy of Sciences Acad. G. Bonchev Street Block 4 Sofia 1113 Bulgaria

Finite element simulations are carried out to examine the mechanical behavior of the metallic hollow sphere （MHS） material during their large plastic deformation and to estimate the energy absorbing capacity of these materials under uniaxial compression. A simplified model is proposed from experimental observations to describe the connection between the neighboring spheres, which greatly improves the computation efficiency. The effects of the governing physical and geometrical parameters are evaluated; whilst a special attention is paid to the plateau stress, which is directly related to the energy absorbing capacity. Finally, the empirical functions of the relative material density are proposed for the elastic modulus, yield strength and plateau stress for FCC packing arrangement of hollow spheres, showing a good agreement with the experimental results obtained in our previous study.

关键词： Cellular material Hollow sphere Large plastic deformation Numerical simulation FEM

CALCULATION OF THE DAMPING OF THE zn-27Al ALLOY BASED ON THE MICRO INTERFACE SLIDING MODEL

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Acta Metallurgica Sinica(English Letters) 2006年第3期19卷 228-234页

作者： Y.z. zhao Q. gao Y.C. Liu School of Civil Engineering Southwest Jiaotong University Chengdu 610031 China Department of Applied Mechanics and Engineering Southwest Jiaotong University Chengdu 610031 China

The microstructures of the zn-27Al alloy after modification, solid-solution treatment, and natural aging were studied. It was clarified why the damping properties of zn-27Al alloys, after treatment, had advanced most on the basis of analyzing the microstructures. Approximate expressions have been educed, which can be used to quantificationally work out the damping of the zn-27Al alloy on the basis of the micro interface sliding model. By comparing the testing damping properties of the foundry zn-27Al alloys and the zn-27Al alloys after modification, solid solution, and natural aging, it was shown that the expressions were rational.

关键词： modification solid solution and aging damping micromechanism micro interface sliding model

Stability analysis of the simplest Takagi-Sugeno fuzzy control system using circle criterion

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Journal of Systems Engineering and Electronics 2007年第2期18卷 311-319页

作者： Lu Hongqian Huang Xianlin gao X. z. Ban Xiaojun Yin Hang Dept. of Control Theory and Engineering Harbin Inst. of Technology Harbin 150001 P. R. China Inst. of Intelligent Power Electronics Helsinki Univ. of Technology Espoo Finland

A frequency-domain-based sufficient condition is derived to guarantee the globally asymptotic stability of the simplest Takagi-Sugeno （T-S） fuzzy control system by using the circle criterion. The analysis is performed in the frequency domain, and hence the condition is of great significance when the frequency-response method, which is widely used in the linear control theory and practice, is employed to synthesize the simplest T-S fuzzy controller. Besides, this sufficient condition is featured by a graphical interpretation, which makes the condition straightforward to be used. Comparisons are drawn between the performance of the simplest T-S fuzzy controller and that of the linear compensator. Two numerical examples are presented to demonstrate how this sufficient condition can be applied to both stable and unstable plants.

关键词： T-S fuzzy controller, Stability analysis Circle criterion Frequency response method.

Numerical Simulation of Bubble Formation at a Single Orifice in Gas-fluidized Beds with Smoothed Particle Hydrodynamics and Finite Volume Coupled Method

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Computer Modeling in Engineering & Sciences 2015年第1期104卷 41-68页

作者： F.z.Chen H.F.Qiang W.R.gao 601 Staff Room Xi’an Hi–Tech InstituteXi’anShanxiPRCPC 710025

A coupled method describing gas–solid two-phase flow has been proposed to numerically study the bubble formation at a single orifice in gas-fluidized *** particles are traced with smoothed particle hydrodynamics,whereas gas phase is discretized by finite volume *** force,gas pressure gradient,and volume fraction are used to couple the two *** effect of injection velocities,particle sizes,and particle densities on bubble growth is analyzed using the coupled *** simulation results,obtained for two-dimensional geometries,include the shape and diameter size of a bubble as a function of time;such results are compared with experimental data,previous numerical results,and other approximate model predictions reported in the ***,the flow profiles of gas and particle phases and the temperature distribution by the heat transfer model around the forming bubble are also *** results show that the coupled method efficiently describes of the bubble formation in fluidized *** proposed method is applicable for solving gas–solid two-phase flow in fluidization.

关键词： coupled method smoothed particle hydrodynamics finite volumemethod bubble formation heat transfer fluidization

Spatial Distribution of Magnetic Properties and Selected Heavy Metals in Calcareous Soils as Affected by Land Use in the Isfahan Region,Central Iran

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Pedosphere 2012年第1期22卷 33-47页

作者： z. DANKOUB S. AYOUBI H. KHADEMI LU Sheng-gao Department of Soil Science College of Agriculture Isfahan University of Technology Isfahan 84156-83111 （Iran） College of Environmental and Resource Sciences Zhejiang University Hangzhou 310000 （China）

Anthropogenic activities have caused the accumulation of heavy metals in the soil environment. Pollution of the soils significantly reduces environmental quality and affects human health. In many recent studies, magnetic susceptibility ts have been used for pollution monitoring. The objective of this research was to determine the spatial variability of magnetic properties and selected heavy metals and the effect of land use on their variability in the surface soils of the Isfahan region, Central Iran. A total of 158 composite surface （0-5 cm） samples of calcareous soils were collected from an area of about 700 km2, located along a cross-border transect from Isfahan City to a steel plant, covering urban, industrial, agricultural, and uncultivated land uses. Concentrations of copper （Cu）, zinc （zn）, lead （Pb）, manganese （Mn）, iron （Fe）, nickel （Ni）, chromium （Cr）, and cobalt （Co） and magnetic parameters, magnetic susceptibility at low frequency （xlf）, natural remanent magnetization （NRM）, saturation isothermal remanent magnetization （SIRM）, and isothermal remanent magnetization at the field of 100 mT （IRM100mT） and the backfield of 100 mT （IRM-100mT）, were measured in all the soil samples. Results showed that magnetic susceptibility in the urban and industrial land topsoils （0-5 cm） samples was significantly higher than that in the agricultural and uncultivated land soils in the study area. Concentrations of Cu, zn, Pb, Mn, and Fe were positively correlated with magnetic properties （xlf, IRM100mT, SIRM, IRM-100mT, and NRM）, which could be attributed to their inputs from traffic emissions and industrial activities at the study sites. Ni and Cr concentrations showed significant negative correlations with magnetic properties. No significant correlation was found between Co concentration and magnetic parameters. The Tomlinson pollution load index （PLI） showed significant correlation with the magnetic properties （xlf, IRM100mT, SIRM, IRM-100mT, and NRM）. The spatial distri

关键词： anthropogenic activities contaminated soils magnetic susceptibility pollution load index proxy measure

Differential Formulation of Discontinuous Galerkin and Related Methods for the Navier-Stokes Equations

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Communications in Computational Physics 2013年第4期13卷 1013-1044页

作者： Haiyang gao z.J.Wang H.T.Huynh Department of Aerospace Engineering and CFD Center Iowa State University2271 Howe Hall AmesIA 50011USA NASA Glenn Research Center MS 5-11ClevelandOH 44135USA

A new approach to high-order accuracy for the numerical solution of conservation laws introduced by Huynh and extended to simplexes by Wang and gao is renamed CPR(correction procedure or collocation penalty via reconstruction).The CPR approach employs the differential form of the equation and accounts for the jumps in flux values at the cell boundaries by a correction *** addition to being simple and economical,it unifies several existing methods including discontinuous Galerkin,staggered grid,spectral volume,and spectral *** discretize the diffusion terms,we use the BR2(Bassi and Rebay),interior penalty,compact DG(CDG),and I-continuous *** first three of these approaches,originally derived using the integral formulation,were recast here in the CPR framework,whereas the I-continuous scheme,originally derived for a quadrilateral mesh,was extended to a triangular *** stability and accuracy analyses for these schemes on quadrilateral and triangular meshes are carried ***,results for the Navier-Stokes equations are shown to compare the various schemes as well as to demonstrate the capability of the CPR approach.

关键词： Discontinuous Galerkin lifting collocation penalty flux reconstruction Navier-Stokes equations correction procedure via reconstruction unstructured hybrid grids

Effect of icosahedral clusters on β-relaxations in metallic glasses

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Chinese Physics B 2017年第1期26卷 86-90页

作者： X Q gao Y T Sun z Wang M z Li H Y Bai Institute of Physics Chinese Academy of Sciences Beijing 100190 China Department of Physics Renmin University of China Beijing 100872 China

The most pronounced β-relaxation was found in the Y-based binary metallic glasses（MGs）. The correlation betweenβ-relaxation and local atomic structure was studied. The dynamic mechanical measurements were performed for three chosen binary systems： zr-, Ti-, and Y-based MGs. The experimental results show that, in each system,the larger negative enthalpy of mixing（？Hm） between the component elements makes β-relaxation become more pronounced. The less negative value of ？Hm facilitates the formation of icosahedral clusters, which have a pinning effect on the excitation of β-relaxations and correspondingly make the β-relaxation become less pronounced. These chemical effects on β-relaxations can only be compared in the same MG system, and it is not suitable for the comparison between different systems due to the different features of the major metallic elements.

关键词： metallic glass β-relaxation enthalpy of mixing icosahedral clusters

Microelectrode Array-evaluation of Neurotoxic Effects of Magnesium as an Implantable Biomaterial

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Journal of Materials Science & Technology 2016年第1期32卷 89-96页

作者： Ting Huang zhonghaiWang Lina Wei Mark Kindy Yufeng zheng Tingfei Xi Bruce z. gao Center for Biomedical Materials and Tissue Engineering Academy for Advanced Interdisciplinary Studies Peking University Beijing 100871 China Department of Bioengineering Clemson University Clemson SC29634 USA Departments of Neurosciences and Regenerative Medicine and Cell Biology Medical University of South Carolina Charleston SC29466 USA Ralph H. Johnson VA Medical Center Charleston SC29403 USA Department of Materials Science and Engineering College of Engineering Peking University Beijing 100871 China Shenzhen Key Laboratory of Human Tissue Regeneration and Repair Shenzhen Institute Peking University Shenzhen 518057 China

Magnesium （Mg）-based biomaterials have shown great potential in clinical applications. However, the cytotoxic effects of excessive Mg2. and the corrosion products from Mg-based biomaterials, particularly their effects on neurons, have been little studied. Although viability tests are most commonly used, a functional evaluation is critically needed. Here, both methyl thiazolyl tetrazolium （MTT） and lactate de- hydrogenase （LDH） assays were used to test the effect of Mg2. and Mg-extract solution on neuronal viability. Microelectrode arrays （MEAs）, which provide long-term, real-time recording of extracellular electro- physiological signals of in vitro neuronal networks, were used to test for toxic effects. The minimum effective concentrations （ECmin） of Mg2. from the MTr and LDH assays were 3 mmol/L and 100 mmol/L respec- tively, while the ECmin obtained from the MEA assay was 0.1 mmol/L MEA data revealed significant loss of neuronal network activity when the culture was exposed to 25% Mg-extract solution, a concentra- tion that did not affect neuronal viability. For evaluating the biocompatibility of Mg-based biomaterials with neurons, MEA electrophysiological testing is a more precise method than basic cell-viability testing.

关键词： Magnesium Microelectrode array Neuroelectrophysiology Neuron viability Neuronal network