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Simulation of g factor for size optimization and coupling in phased array coil design

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Progress in Natural science:Materials International 2006年第2期16卷 120-124页

作者： SONG Xiaoyu, ZHANG Hongjie, WANG Le, BAO Shanglian, SUN Yanrong and ZU Donglin (beijing Key Laboratory of Medical Physics & engineering, peking university,{3., china Physics school, peking university,{3., china) [a]beijing Key Labaratory of Medical Physics & engineering Peking University Beijing China [b]Physics school Peking University Beijing China

The effect of geometric parameters of the coil element in an array on signal-to-notse ratio (SNR) and g factor of parallel imaging are analyzed, and the optimal parameters for the maximal SNR and minimal g factor are also given in this paper. In addition, the effects of coupling on SNR and g factor have been analyzed. The test results indicate that g factor for parallel imaging is greatly increased and SNR is decreased for coupling. According to the optimization, a six-channel parallel coil has been designed for torso imaging.

关键词： MRI phased array coil SENSE parallel imaging.

Morita contexts on the Hopf algebroid

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science china Mathematics 2005年第7期48卷 958-971页

作者： YIN Yanmin school of Mathematical sciences, peking university,{3., china Department of Mathematics, Shandong Institute of Architecture and engineering, Jinan 250101, china 1. school of Mathematical sciences Peking University 100871 Beijing China 2. Department of Mathematics Shandong Institute of Architecture and Engineering 250101 Jinan China

We generalize the Morita theory to the Hopf algebroid and give the characterization of the surjectivity of one of the Morita context maps.

关键词： comodule algebra, generalized smash product, Morita context.

Surface Nanocrystallization of Magnesium Alloy AZ91D by High-Energy Shot Peening

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Journal of Wuhan university of Technology(Materials science) 2009年第4期24卷 515-519页

作者：张津 school of Materials science & engineering University of Science and Technology Beijing College of Materials science & engineering Chongqing University of Technology

High-energy shot peening （HESP）, a method to produce severe plastic deformation by high velocity flying balls, was applied on die cast magnesium alloy AZ91D. Effects of surface nanocrystallization by HESP and heat treatment at different temperatures were investigated. The mi- crostructure evolution was conducted using X-ray diffraction （XRD） and field emission scanning electronic microscopy （FESEM）. The hardness was measured by microhardness tester. The experimental results show that surface nanocrystrallization of AZ91D obtained by HESP would lead to the increase of microhardness. Low temperature heated at 100℃ for 1 h do not change the property obviously. However, both the microstructure and microhardness vary greatly after heat treatment at 400℃ for 1 h.

关键词： AZ91 D surface nanocrystallization HESP microhardnss corrosion resistance

Convergence analysis of the adaptive finite element method with the red-green refinement

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science china Mathematics 2010年第2期53卷 499-512页

作者： ZHAO XuYing 1, 3., HU Jun 2,? & SHI ZhongCi 1 1 State Key Laboratory of Scientific and engineering Computing, Institute of Computational Mathematics and Scientific/engineering Computing, Academy of Mathematics and Systems science, Chinese Academy of sciences, beijing 100190, china 2 Key Laboratory of Mathematics and Applied Mathematics (peking university), Ministry of Education and school of Mathematical sciences, peking university, beijing 100871, china 3.Graduate university of Chinese Academy of sciences, beijing 100190, china 1. State Key Laboratory of Scientific and engineering Computing Institute of Computational Mathematics and Scientific/Engineering Computing Academy of Mathematics and Systems Science Chinese Academy of Sciences Beijing 100190 China3. Graduate University of Chinese Academy of Sciences Beijing 100190 China2. Key Laboratory of Mathematics and Applied Mathematics (Peking University) Ministry of Education and School of Mathematical Sciences Peking University Beijing 100871 China

In this paper, we analyze the convergence of the adaptive conforming P 1 element method with the red-green refinement. Since the mesh after refining is not nested into the one before, the Galerkin-orthogonality does not hold for this case. To overcome such a difficulty, we prove some quasi-orthogonality instead under some mild condition on the initial mesh (Condition A). Consequently, we show convergence of the adaptive method by establishing the reduction of some total error. To weaken the condition on the initial mesh, we propose a modified red-green refinement and prove the convergence of the associated adaptive method under a much weaker condition on the initial mesh (Condition B).

关键词： red-green refinement adaptive finite element method convergence non-nested local refinement

Perfect reconstruction image modulation based on BEMD and quaternionic analytic signals

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science china(Information sciences) 2011年第12期54卷 2622-2634页

作者： QIAO LiHong 1 , NIU KaiFu 2 , WANG Ning 2 & PENG LiZhong 2 1 College of Information science and engineering, Henan university of Technology, Zhengzhou 450001,{3. 2 school of Mathematical sciences, peking university, beijing 100871,{3. 1. College of Information science and engineering Henan University of Technology Zhengzhou 450001 China2. School of Mathematical Sciences Peking University Beijing 100871 China

Image modulation represents image by meaningful characters such as image instantaneous amplitude and instantaneous frequency. A perfect reconstruction image modulation method is proposed. In detail, the bidimensional empirical mode decomposition (BEMD) is first improved to adaptively decompose image into monocomponents. Then by the quaternionic analytic method, suitable analytic signals is acquired. A new polar form is further proposed to modulate images, then seven characters are derived including instantaneous amplitude and instantaneous frequencies. We demonstrate the techniques on both synthetic and natural images, depict the needle program of the estimated frequencies and obtain the reconstructions that are the same with the original images. The applications in image segmentation and separation establish the validity of characterizing images of this type as sums of locally narrow band modulated components.

关键词： perfect reconstruction image modulation AM-FM representation BEMD quaternionic analytic signals

The steady-state solution of dendritic growth from the undercooled binary alloy melt with the far field flow

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science china(Technological sciences) 2009年第8期52卷 2280-2287页

作者： CHEN MingWen1,2, WANG ZiDong2 & XU JianJun2,3.4 1 school of Applied sciences, university of science and Technology beijing, beijing 100083. china 2 school of Materials science and engineering, university of science and Technology beijing, beijing 100083. china 3.school of Mathematical sciences, Nankai university, Tianjin 3.0071, china 4 Department of Mathematics and Statistics, McGill university, Montreal H3. 2K6, Canada school of Applied sciences University of Science and Technology Beijing Beijing 100083 China school of Materials science and engineering University of Science and Technology Beijing Beijing 100083 China school of Mathematical sciences Nankai University Tianjin 300071 China Department of Mathematics and Statistics McGill University Montreal H3A 2K6 Canada

The steady-state dendritic growth from the undercooled binary alloy melt with the far field flow is considered. By neglecting the interface energy, interface kinetics and buoyancy effects in the system, we obtaine the steady-state solution for the case of the large Schmidt number, in terms of the multiple variable expansion method. The changes of the temperature and concentration fields, the morphology of the interface, the normalization parameter and the Peclet number of the system induced by uniform external flow are derived. The results show that, compared with the system of dendritic growth from undercooled pure melt, the convective flow in the system of growth from undercooled binary alloy has stronger effects on the morphology of the interface. Nevertheless, the shape of the interface still remains nearly a paraboloid.

关键词： binary alloy melt convection dendritic growth interfaces steady-state solution multiple variable expansion method

Nonlinear Theory on Dynamic Controlling Interface Patterns DuringSolidification of a Dilute Binary Alloy

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International Journal of Minerals,Metallurgy and Materials 1999年第4期13卷 253-258页

作者： Zidong Wang Hanqi Hu(Material science and engineering school, {3. of science and Technology beijing, beijing 100083. china) Material science and engineering school University of Science and Technology Beijing Beijing 100083 China

In non-equilibrium nonlinear region, the nonlinear equations of time dependence of perturbation amplitude at the solid/liquidinterface during solidification of a dilute binary alloy are established on the base of assuming that there is local equilibrium at the solid/liquid interface and considering that curvature, temperature and composition at the solid/liquid interface which are related to the perturbation amplitude are nonlinear. As a result, patterns at the solid/liquid interface during solidification process, which is from nonsteadystate to steady state can be controlled by these nonlinear equations.

关键词： nonlinearity solidification, dilute binary alloy, dynamic control

Producing Calcium-Bearing Mullite Thermal-Insulating Refractories by Kyanite

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International Journal of Minerals,Metallurgy and Materials 1999年第1期13卷 50-53页

作者： Wen Ni (Resources engineering school, university of {3. and Technology beijing, beijing 100083. china) Resources engineering school University of Science and Technology Beijing Beijing 100083 China

To improve the physical properties, a series of experiments have been camed out to produce calcium-bearing mullite thermal-insulating refractories by using kyanite as major raw materials. The experiments were carried out by a foaming technique and using white cement as a combing agent. The results show that the calcium-bearing mullite refractory has much better physical properhes than traditional clay refractory and high-alumina refractory.

关键词： mullite thermal-insulating refractory kyanite

A New Safety Electric Initiating System

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International Journal of Minerals,Metallurgy and Materials 1999年第4期13卷 306-308页

作者： Daze Lin(Resource engineering school, university of {3. and Technology beijing, beijing 100083. china) Univ of science and Technology Beijing Beijing China

Based on the analysis of weakness on the safety of traditional electric detonators, a BJ-l safety electric detonator initiatingsystem and its corresponding safe examination technique were successfully developed. By leading false foot wires and taking advantageof the transmitting frequency band of Mo-Zn ferrite, detonators in this new system can completely impede the direct induction of outsidecrosstalk that may cause casual firing in the ordinary as well as eleclromagnetic ones. Possible causality by lightning was discussed. Results are presented, of its safety tests on resistance to direct and alternating current, electrostatic, and crosstalk induced by damp leakagein saturated salty water.

关键词： electric detonator blasting engineering, electric initiating system, safety