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Enhanced dielectric properties of polypropylene based composite using Bi2S3 nanorod filler

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Progress in Natural Science:Materials International 2011年第3期21卷 216-220页

作者： Yu DANG,Yao WANG,Yuan DENG,Mao LI,Ye ZHANG,Zhi-wei ZHANG beijing Key Laboratory of Special Functional Materials and Film,School of Chemistry and Environment, Beihang University,beijing 100191,China beijing Key Laboratory of Special Functional Materials and Film School of Chemistry and Environment Beihang University Beijing 100191 China

A novel two-phase composite system using polypropylene(PP) as matrix and semiconductor bismuth sulfide(Bi2S3) as filler,was prepared by a simple *** KH550 was chosen to modify the interface between inorganic fillers and organic PP *** variations of dielectric properties of the Bi2S3/PP composites with the volume fraction of Bi2S3,frequency and temperature were *** results reveal a percolative behavior of the composites with the threshold of *** composite is demonstrated to have good dielectric *** thermal stability of dielectric property and high breakdown strength of the composites show their potential application in film capacitor.

关键词： composite materials dielectric properties interface

Effect of dendrite arm spacing and the γ' phase size on stress rupture properties of Ni_3Al-base single crystal superalloy IC6SX

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Science China(Technological Sciences) 2010年第6期53卷 1460-1465页

作者： JIANG LiWu1,LI ShuSuo1,WU MeiLing1 & HAN YaFang1,2 1 School of Materials Science and Engineering,Beihang University,beijing 100191,China 2 beijing Institute of Aeronautical Materials,beijing 100095,China School of Materials Science and Engineering Beihang University Beijing China beijing Institute of Aeronautical Materials Beijing China

The effect of dendrite arm spacing and the size of γ' phase on stress rupture properties of as-cast Ni3Al-based single crystal superalloy IC6SX was *** has been found that the stress rupture properties were affected by dendrite arm spacing and the size of γ' phase significantly,i.e.,the stress rupture lives of as-cast specimens under the test condition of 1100°C/120 MPa were significantly increased from about 10 h to 31 h with decreasing dendrite arm spacing and the size of γ' phase from 3.0 μm and 1.6 μm to 1.3 μm and 0.8 μm,*** creep cracks generated easily in the brittle Y-NiMo *** the cracks gradually mergered and grew up during creep,and finally led to specimens *** orientated coarsening of γ' phase has been found in the stress ruptured specimens,due to the elements ***,the γ' phase did not form the integrated structure during the short periods of 10-31 h as the creep tests lasted.

关键词： dendrite arm spacing size of γ’ phase Ni3Al-based single crystal stress rupture property

A non-flux-splitting WENO scheme with low numerical dissipation

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Science China(Technological Sciences) 2010年第4期53卷 3365-3378页

作者： KANG Lei & Lee ChunHian National Laboratory for CFD, Beihang University, beijing 100191, China National Laboratory for CFD Beihang University Beijing China

A WENO scheme without implementing the flux-splitting procedure is developed in the present paper. The scheme is deduced by taking the optimized coefficients, originally constant in any flux-splitting WENO scheme, to vary with respect to eigenvalues in the characteristic space. As a result, the weights are associated with both the eigenvalues and the smoothness measurements. The scheme is formulated to avoid the implementing of the flux-splitting procedure via computation of the weighs of WENO stencils, and is capable of reducing the numerical dissipation. Numerical experiments show that the new scheme is less dissipative than the WENO scheme with flux-splitting, and possesses higher resolution using the same grid mesh. Computations of the test cases also demonstrate a comparatively higher computational efficiency of the new scheme. Especially, for problems involving shocks, strong shear and long time evolution, the solutions computed by the presently developed scheme with no flux-splitting and the other existing methods with flux-splitting differ remarkably from each other, and the new scheme is proven to be an effective way for controlling the numerical dissipation and retaining the real effects of the physical viscosity.

关键词： flux-splitting WENO scheme numerical dissipation

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Effects of hydrogen on a tungsten grain boundary:A first-principles computational tensile test

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Progress in Natural Science:Materials International 2011年第3期21卷 240-245页

作者： Hong-bo ZHOU,Shuo JIN,Ying ZHANG,Guang-hong LU Department of Physics,Key Laboratory of Micro-nano Measurement-Manipulation and Physics(Ministry of Education),beijing University of Aeronautics and Astronautics,beijing 100191,China Department of Physics Key Laboratory of Micro-nano Measurement-Manipulation and Physics (Ministry of Education) Beijing University of Aeronautics and Astronautics Beijing 100191 China

A first-principles computational tensile test has been preformed to investigate the effects of hydrogen on a tungsten grain *** has been found that the maximum ideal tensile strength of the tungsten grain boundary with hydrogen atom segregation was 32.85 GPa,which was about 9%lower than that of the clean tungsten grain boundary(36.23 GPa).This indicated that the theoretical strength of the tungsten grain boundary became weaker in the presence of the hydrogen *** configuration analysis showed that the grain boundary fracture was caused by the interfacial bond *** Griffith fracture energy was calculated to be 161 meV/A~2(2.58 J/m~2) and 155 meV/A~2(2.48 J/m~2) for the tungsten grain boundary without and with the hydrogen atom segregation,*** solution energy of the hydrogen atom in a fracture free surface was -0.31 eV,which was 0.08 eV lower than that of the hydrogen atom in a tungsten grain *** indicated that hydrogen was a grain boundary embrittler according to the Rice-Wang thermodynamic *** Bader charge analysis suggested that the physical origin for hydrogen-induced embrittlement was the charge transfer induced by hydrogen in the tungsten grain boundary.

关键词： tungsten hydrogen grain boundary tensile strength first-principles

Bursting of Morris-Lecar neuronal model with current-feedback control

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Science China(Technological Sciences) 2009年第3期52卷 771-781页

作者： DUAN LiXia1, LU QiShao2 & CHENG DaiZhan3 1 College of Science, North China University of Technology, beijing 100144, China 2 School of Science, beijing University of Aeronautics and Astronautics, beijing 100191, China 3 Institute of Systems Science, Chinese Academy of Sciences, beijing 100190, China College of Science North China University of Technology Beijing China School of Science Beijing University of Aeronautics and Astronautics Beijing China Institute of Systems Science Chinese Academy of Sciences Beijing China

The Morris-Lecar (ML) neuronal model with current-feedback control is considered as a typical fast-slow dynamical system to study the combined influences of the reversal potential VCa of Ca2+ and the feedback current I on the generation and transition of different bursting oscillations. Two-parameter bifurcation analysis of the fast subsystem is performed in the parameter (I, VCa)-plane at first. Three important codimension-2 bifurcation points and some codimension-1 bifurcation curves are obtained which enable one to determine the parameter regions for different types of bursting. Next, we further divide the control parameter (V0, VCa)-plane into five different bursting regions, namely, the "fold/fold" bursting region R1, the "fold/Hopf" bursting region R2, the "fold/homoclinic" bursting region R3, the "subHopf/homoclinic" bursting region R4 and the "subHopf/subHopf" bursting region R5, as well as a silence region R6. Codimension-1 and -2 bifurcations are responsible for explanation of transition mechanisms between different types of bursting. The results are instructive for further understanding the dynamical behavior and mechanisms of complex firing activities and information processing in biological nervous systems.

关键词： neuron bursting bifurcation fast-slow dynamics analysis codimension

Displacement residual based DDM matching algorithm

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Science China(Information Sciences) 2012年第9期55卷 2090-2101页

作者： ZHANG Lin 1,2,ZHOU Zhong 1,2,LIU Lin 1,2 & WU Wei 1,2 1 State Key Laboratory of Virtual Reality Technology and Systems,Beihang University,beijing 100191,China 2 School of Computer Science and Engineering,Beihang University,beijing 100191,China State Key Laboratory of Virtual Reality Technology and Systems Beihang University Beijing China School of Computer Science and Engineering Beihang University Beijing China

High level architecture(HLA) is the prevailing standard for modeling and *** data distribution management(DDM) service of HLA is defined for reducing the delivery of irrelevant *** key in DDM implementation is the region overlap computation,*** matching between update and subscription *** algorithms usually make a compromise between region fidelity and network *** paper takes both the matching algorithm efficiency and bandwidth cost into *** main contributions are:1) illustrating the relationship between region changes and overlap changes,as helps reduce the number of region matching and then improves the total matching efficiency;2) classifying region updates into two types of data expression,snapshot and *** network traffic will be reduced by transmitting only residual data instead of full region representations ***,a region matching algorithm called displacement residual-based DDM matching(DRBM) is proposed in the *** analysis,algorithm implementation and experiment evaluation are *** results show that DRBM provides better matching performance and significant network payload reductions especially when there is a large number of changing regions.

关键词： distributed simulation high level architecture data distribution management region snapshot region residual

R-calculus without the cut rule

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Science China(Information Sciences) 2011年第12期54卷 2550-2563页

作者： LUO Jie & LI Wei State Key Laboratory of Software Development Environment, School of Computer Science and Engineering, Beihang University, beijing 100191, China State Key Laboratory of Software Development Environment School of Computer Science and Engineering Beihang University Beijing China

R-calculus is an inference system for deducing all possible changes when a theory is refuted by the facts. In this paper, we try to eliminate the cut rule in R-calculus by modifying the existing rules and by introducing new rules. The result is the R-calculus without the cut rule, which still preserves the reachability, soundness and completeness as R-calculus does. R-calculus without the cut rule is a formal inference system of logical connective symbols and quantifier symbols solely. It can serve as the theoretical foundation of the automation of revision calculus.

关键词： revision R-calculus cut rule

Ultrasonic Frequency Fast-Convert Pulse Plasma Spraying Power Supply Topology

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稀有金属材料与工程 2011年第S4期40卷 297-301页

作者： Zhang Wei1,Qi Bojin1,Xu Haiying21School of Mechanical Engineering and Automation,BeiHang University,beijing 100191,China2beijing Aeronautical Manufacturing Technology Research Institute,beijing 100024,China BeiHang Univ Sch Mech Engn & Automat Beijing 1000191 Peoples R China beijing Aeronaut Mfg Technol Res Inst Beijing 100024 Peoples R China

Considering the high DC current and high pulse frequency characteristic of ultrasonic frequency fast-convert pulse plasma spraying process,a special power supply topology was proposed,which was composed of the mutual independent base current circuit and peak current *** current circuit was consisted of four parallel direct current power supplies,which was not only to meet the requirements of high power output,but also improved the reliability of power *** on the Boost circuit topology,a peak current circuit was designed,which could reduce effectively the output inductance influence and output ultrasonic frequency pulse high current with fast-convert rising and falling *** on the above techniques,the Ultrasonic frequency fast-convert pulse plasma spraying power supply was *** can output 5-1000A base current,0-250A peak current,and the pulse current frequency band is 20-100kHz,10%～80% duty ratio and pulse current change rate over 50A/μs.

关键词： Ultrasonic frequency pulse Fast-convert Plasma spraying

Numerical simulations of leading-edge vortex core axial velocity for flow over delta wings

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Science China(Technological Sciences) 2009年第7期52卷 2029-2036页

作者： CHEN Lan1, 2 & WANG JinJun1 1 Institute of Fluid Mechanics, beijing University of Aeronautics and Astronautics, beijing 100191, China 2 China Aerodynamic Research and Development Center (CARDC), Mianyang 621000, China Institute of Fluid Mechanics Beijing University of Aeronautics and Astronautics Beijing China China Aerodynamic Research and Development Center (CARDC) Mianyang China

Numerical simulations have been performed to investigate the characteristics of leading-edge vortex core axial velocity over two delta wings with leading edge swept angles Λ =50°and 76°, respectively. It is obtained that Reynolds number has the most important effect on the axial velocity of the primary leading-edge vortex core. At Reynolds numbers larger than 105, the jet-like flow of the vortex core is the most common type for both the large and the moderate swept delta wings. While if Reynolds number decreases to 103―104, the core axial velocity distributions for these two delta wings present the wake-like profile for all angles of attack considered in the present investigation.

关键词： delta wing low Reynolds number vortex flows