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Dirac Quasinormal modes of Static f(R) de Sitter Black Holes

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Communications in Theoretical Physics 2018年第2期69卷 179-187页

作者： Hong ma Department of Physics Chongqing University Chongqing 401331 China

Quasinormal modes （QNms） for Dirac perturbations off（R） black holes （BHs） are described in this paper, involving two types of f（R） solution： f（R）（Sehwarzschild） BHs and f（R）（maxwell） BHs. With the finite difference method, the stability of the f（R） black holes （BHs） is analysed and the threshold range off（R）（Schwarzschild） BHs and f（R）（maxwell） BHs is defined respectively. The results show that due to the presence of the correction factor Ro, the damping rate of Dirac field decreases. meanwhile, the influence of angular quantum number values [k] on the f（R） BHs is investigated. The results indicate that the QNms oscillation becomes tenser and damping speed slowly decreases with ]k[ increasing. Furthermore, under the Dirac perturbation, the stability off（R） solutions can be reflected in the manner of Dirac QNms. The relationships between the QNms and the parameters （]k], charge Q and mass m） are discussed in massless, and massive cases, by contrast to the classical BHs.

关键词： Dirae perturbation f(R) black holes quasinormal modes (QNms)

Water mass characteristics in the western North Pacific based on a streamfunction projection

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Science China Earth Sciences 2015年第11期58卷 2067-2077页

作者： ma Xiao SUN Che Institute of Oceanology Chinese Academy of Sciences College of Earth Sciences University of Chinese Academy of Sciences

A streamfunction projection method called gravest empirical mode(GEm) is applied to the hydrographic section at 137°E to filter out eddy noises in the western North Pacific and derive quantitative ensemble-average water mass properties in the North Equatorial Current region. The GEm fields capture more than 80% of total property variances in the thermocline layer. The core layer structures of key water masses, including the North Pacific Tropical Water(NPTW) and the North Pacific Intermediate Water(NPIW), are examined with a definition of water mass boundary based on property gradient. It shows that a tongue of maximal root-mean-square(RmS) residual exists in the upper half of NPIW for all water properties. These subsurface RmS tongues appear to be close to sharp property gradients. It is the first time a GEm diagnosis is applied to nutrient data, which reveals a drastic difference of N/P reaction rate ratio above and below the maximal-nutrient core at 1250 m. Additionally, a GEm velocity reconstruction successfully produces the North Equatorial Undercurrent(NEUC), demonstrating the stable thermal-wind nature of this newly-discovered current.

关键词： streamfunction projection gravest empirical mode water masses western North Pacific

Fabrication of large-bulk ultrafine grained 6061 aluminum alloy by rolling and low-heat-input friction stir welding

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Journal of materials Science & Technology 2018年第1期34卷 112-118页

作者： C.Y.Liu B.Qu P.Xue Z.Y.ma K.Luo m.Z.ma R.P.Liu Shenyang National Laboratory for materials Science Institute of Metal Research Chinese Academy of Sciences Key Laboratory of New Processing Technology for Nonferrous metal & materials Ministry of Education Guilin University of Technology Guangxi Key Laboratory of Universities for Clean metallurgy and Comprehensive Utilization of Nonferrous metal Resources Guilin University of Technology State Key Laboratory of metastable materials Science and Technology Yanshan University

In this study, the ultrafine grained （UFG） 6061 Al alloys fabricated by cold rolling were friction stir welded （FSW） with different rotation rates under both air cooling and rapid cooling in water. Low-heat-input parameters of 400 rpm rotation rate in water （400-Water） could effectively inhibit the coarsening of recrystallized grains, reduce the precipitation rate, and retain more dislocations of the UFG 6061 Al parent metal. 400-Water joint showed high lowest-hardness value, narrow low-hardness zone, and high tensile strength, attributing to the effect of dislocation, grain boundary, solid-solution, and precipitation hardening. This work provides an effective strategy to fabricate large-sized bulk UFG AI alloy by cold rolling with large deformation and low-heat-input FSW.

关键词： Aluminum alloys Ultrafine grained materia Friction stir welding mechanical properties

The dimension split element-free Galerkin method for three-dimensional potential problems

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Acta mechanica Sinica 2018年第3期34卷 462-474页

作者： Z.J.meng H.Cheng L.D.ma Y.m.Cheng Shanghai Institute of Applied mathematics and mechanics Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai University School of Applied Science Taiyuan University of Science and Technology Department of Civil Engineering Shanghai University School of materials Science and Engineering Taiyuan University of Science and Technology

This paper presents the dimension split element-free Galerkin （DSEFG） method for three-dimensional potential problems, and the corresponding formulae are obtained. The main idea of the DSEFG method is that a three-dimensional potential problem can be transformed into a series of two-dimensional problems. For these two-dimensional problems, the improved moving least-squares （ImLS） approximation is applied to construct the shape function, which uses an orthogonal function system with a weight function as the basis functions. The Galerkin weak form is applied to obtain a discretized system equation, and the penalty method is employed to impose the essential boundary condition. The finite difference method is selected in the splitting direction. For the purposes of demonstration, some selected numerical examples are solved using the DSEFG method. The convergence study and error analysis of the DSEFG method are presented. The numerical examples show that the DSEFG method has greater computational precision and computational efficiency than the IEFG method.

关键词： Dimension split method Improved moving least-squares (ImLS) approximation Improved element-free Galerkin (IEFG) method Finite difference method (FDm) Dimension split element-free Galerkin (DSEFG) method Potential problem

Synthesis and Characterization of mesoporous Alumina via a Reverse Precipitation method

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Journal of materials Science & Technology 2012年第6期28卷 572-576页

作者： Y.S.Wu J.ma F.Hu m.C.Li College of materials Science and Engineering Shenyang University of TechnologyShenyang 110870China

mesoporous aluminaΥ-AI203 with high specific surface area and large pore volume is prepared by using a facile reverse precipitation method from sodium aluminate and nitric acid. The effects of terminal pH value, aging time and thermal stability on the characterization of Υ-Al2Oa are studied by means of X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FTIR）, Brunauer-Emmett-Teller （BET） method and scanning electron microscopy （SEm）. The results show that Υ-A1203 with better properties can be obtained by changing the preparation parameters. High BET surface area of 340 m2/g can be obtained by calcining at 500℃ for 4 h with large pore volume of 0.90 cm3/g and average pore size of 7.6 nm. After calcining at 1000°, the surface area is still 86 m2//g and the pore volume is 0.37 cm31/g.

关键词： mesoporous alumina Reverse precipitation Thermal stability

Research on High-Speed Drilling Performances of Austenitic Stainless Steels

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上海交通大学学报 2004年第Z2期38卷 83-88页

作者： J.W.Zhong Y.P.ma F.H.Sun m.Chen School of mechanical Engineering Shanghai Jiaotong University Shanghai200030China School of Mechanical Engineering Shanghai Jiaotong University Shanghai200030China School of Mechanical Engineering Shanghai Jiaotong University Shanghai200030China School of Mechanical Engineering Shanghai Jiaotong University Shanghai200030China

Due to specific properties arising from their structure (high ductility, high toughness,strong tenacious and low heat conductivity), the stainless steels have poor machinability. The drilling of the stainless steels becomes the machining difficulty for their serious work-hardening and abrasion of tools. In this paper, the austenitic stainless steel is used as the work-piece to perform the contrastive experiments with the TiN coated and TiAlN-coated high-speed steel drills. The cutting force, torque, cutting temperature, and the abrasion of drills and tool life are tested and analyzed in the process of high-speed drilling. Experiment results show the effect of drilling speed on cutting force, cutting temperature, and drill wear. TiAlN-coated drills demonstrate better performances in high speed drilling. The research results will be of great benefit in the selection of drills and in the control of tool wear in high speed drilling of stainless steels.

关键词： stainless steel TiN-coating TiAlN-coating drilling

High-Temperature Oxidation Behavior of a Ni-Cr-W-Al Alloy

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Journal of materials Science & Technology 2011年第9期27卷 841-845页

作者： Y.C. ma X.J. Zhao m. Gao K. Liu Institute of metal Research Chinese Academy of Sciences Shenyang 110016 China

A study was conducted to examine the isothermal oxidation behavior of a new Ni-Cr-W-AI alloy in air at 1250℃ with different time. Oxidation kinetics was determined from weight-change measurements. The microstructure and composition of the oxide scale were investigated by means of scanning electron microcopy and X-ray diffraction. The results showed that the oxide scales of the alloy were a compact and continuous outer Cr2O3 and NiCr2O4 layer and an inner Al2O3 layer that was in dendrite shape. Oxides scales with good adherence were formed on the surface of the alloy, which made the alloy perform excellent high-temperature oxidation resistance.

关键词： Oxidation kinetics Oxide scale High-temperature oxidation resistance

Plaque herniation after stenting the culprit lesion with myocardial bridging in ST elevation myocardial infarction: A case report

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World Journal of Cardiology 2020年第2期12卷 91-96页

作者： Jeffrey ma Gregory m Gustafson Xuming Dai Division of Cardiology Theresa and Eugene M.Lang Center for Research and Education New York Presbyterian–Queens Hospital

BACKGROUND myocardial bridging(mB)is increasingly recognized to stimulate atherogenesis,which may contribute to an acute coronary *** the coronary segment with mB has been recognized to have an increased risk of in-stent restenosis,stent fracture and coronary *** safety and efficacy of stenting the culprit lesion with overlaying mB in ST elevation myocardial infarction(STEmI)as primary reperfusion therapy has not been *** SUmmaRY We reported a patient who presented with inferior STEmI with a culprit lesion of an acute thrombotic occlusion in the right coronary artery and thrombolysis and thrombin inhibition in myocardial infarction 0 *** the stent placement during primary percutaneous coronary intervention,intravascular ultrasound revealed mB overlying the stented segment where heavy atherosclerotic plaque were *** due to the combination of plaque herniation or prolapse caused by mB,as well as local increased inflammation and thrombogenicity,acute stent thrombosis occurred at this region,which led to acute stent *** patient required an emergent repeated cardiac catheterization and placing a second layer of stent to enhance the radial strength and reduce the inter-strut *** Plaque herniation or prolapse after stenting a mB segment in STEmI is a potential etiology for acute stent failure.

关键词： Case report ST elevation myocardial infarction myocardial bridging Plaque herniation Plaque prolapse Intravascular ultrasound Acute stent thrombosis

mHD from a microscopic Concept and Onset of Turbulence in Hartmann Flow

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Communications in Theoretical Physics 2010年第3期53卷 579-583页

作者： L.Jirkovsky L.ma.Bo-ot C.m.Chiang Department of Informatics and Geo-informatics Fakulta Zivotniho ProstrediUniversity of J.E. Purkyne National Institute of Physics University of the Philippines Department of Architecture National Cheng Kung University Taiwan College of Architecture University of the Philippines

We derive higher order magneto-hydrodynamic (mHD) equations from a microscopic picture using projection and perturbation formalism. In an application to Hartmann flow we find velocity profiles flattening towards the center at the onset of turbulence in hydrodynamic limit. Comparison with the system under the effect of a uniform magnetic field yields difference in the onset of turbulence consistent with observations, showing that the presence of magnetic field inhibits onset of instability or turbulence. The laminar-turbulent transition is demonstrated in a phase transition plot of the development in time of the relative average velocities vs. Reynolds number showing a sharp increase of the relative average velocity at the transition point as determined by the critical Reynolds number.

关键词： projection techniques onset of turbulence mHD Hartmann flow