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SOME RESULTS ON GENERALIZED DIFFERENCE SETS

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Journal of Systems science & Complexity 2008年第1期21卷 76-84页

作者： Xiwang CAO school of Mathematical science, Nanjing university of {3. and astronautics, Nanjing 210016, china State Key Lab. of Information Security, beijing 100049, china. school of Mathematical science Nanjing University of Aeronautics astronautics Nanjing 210016 China State Key Lab. of Information Security Beijing 100049 China

Sequences with ideal correlation functions have important applications in communications such as CDMA, FDMA, etc. It has been shown that difference sets can be used to construct such sequences. The author extends Pott and Bradley＇s method to a much broader case by proposing the concept of generalized difference sets. Some necessary conditions for the existence of generalized difference sets are established by means of some Diophantine equations. The author also provides an algorithm to determine the existence of generalized difference sets in the cyclic group Zv. Some examples are presented to illustrate that our method works.

关键词： Correlation functions diophantine equations generalized difference sets.

Modified HDDR Process for Producing Anisotropic NdFeB Powders

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Journal of university of science and Technology beijing 2001年第2期8卷 111-114页

作者： Xubo Liu, Yue Ming, Yaofu Xiao, Qi Zeng, Zhengyi Zhang, Run Wang (material science and engineering {3., university of science and Technology beijing, beijing 1.0083, china) (beijing Institute of Aeronautical materials, beijing 100095, china) Univ Sci & Technol beijing Mat Sci & Engn Sch Beijing 100083 Peoples R China Inst Aeronaut Mat Beijing 100095 Peoples R China

The effect of HDDR (hydrogenation-decomposition-desorption-recombination process) treating conditions on magnetic anisotropy of Nd13.ebalCo17B7Ga1Zr0.1 powders has been studied. It is found that increasing recombination temperature is effective for magnetic anisotropy formation, but at the cost of reducing the coercive force. The microstructure analysis (TEM) indicates that the NdFeB recombination nucleation takes place markedly during the transition range from decomposition stage to recombination stage, in which both temperature and H-2 pressure change sharply. In order to create a more stable treatment condition for recombination nucleation, a modified HDDR process is established in which the conventional continuous transition range is divided into several stages. The experimental results have proved that such a process can effectively enhance the remanence of the magnet powders with high certainty, while only cause a little reduction in coercivity.

关键词： HDDR anisotropy NdFeB

The effect of diffusion on the permanence of Smith population model in a polluted patch

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Communications in Nonlinear science and Numerical Simulation 2001年第4期6卷 217-221页

作者： Zhuoqin YANG, Qishao LU and Zaizhong YANG school of science, beijing university of aeronautics and astronautics,{3., china Department of Mathematics, Inner Mongolia university, Inner Mongolia 010021, china school of science Beijing Univ. of Aero. and Astronautics Beijing 100083 China Department of Mathematics Inner Mongolia University Inner Mongolia 010021 China

The effect of diffusion on the permanence of population in a polluted patch is studied by setting up a single-population diffusive system in two patches. The analysis focuses on the case that the toxicant input in the polluted patch has a limit value. It is shown that when there is no diffusion and the limit value exceeds a certain value, the population in the polluted patch goes extinct; when the diffusion exists and population diffusive coefficients between the two patches satisfy some conditions, the population of the system goes either permanent or extinct.

关键词： population diffusion system pollution permanence extinction

Production of O' -sialon-SiC Composites by Carbon Reduction-Nitridation

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International Journal of Minerals,Metallurgy and materials 1998年第1期12卷 26-30页

作者： Haijun Zhang Wenchao Li Xiangcong Zhong (Applied science school, university of science and Technology beijing, beijing 1 0008 3. china) Applied science school University of Science and Technology Beijing Beijing 100083 China

The effect of temperature, soak times, carbon and addition on composites was discussed in the process ofsynthesizing O'-sialon-SiC by carbonthermal reduction-nitration from nature kaolin. It showed that the fracturestrength (MOR) of composites sintered under certain conditions can be up to 140MPa at room temperature. Thetarget parameter optima regions with good mechanical properties of this material were also indicated by usingcomputer pattern recognition program.

关键词： O'-sialon-SiC compostites carbonthermal reduction-nitration pattern recognition program

Application and Comparison of SST Model in Numerical Simulation of the Axial Compressors

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Journal of Thermal science 2010年第4期19卷 300-309页

作者： YIN Song~1,JIN Donghai~2,GUI Xingmin~3.and ZHU Fang Aero-Engines Simulation Research Center,school of Jet Propulsion,beijing university of {3. and astronautics, beijing,100191,china Aero-Engines Simulation Research Center School of Jet Propulsion Beijing University of Aeronautics and Astronautics Beijing China

The shear-stress transport(SST)turbulence model is incorporated into Navier-Stokes equations to simulate a turbomachinery flowfield.A staggered finite volume method is used to make the mean flow equations and turbulence model equations strongly coupled and enhance the stability of the numerical *** implicit treatment of the source terms is applied to the SST model.A steady state solution is obtained using five-stage Runge-Kutta time-stepping scheme with local time stepping and residual smoothing to accelerate convergence. The wall distance d,a key parameter in the SST model,is solved by a partial differential *** validations of the code are conducted on rotor 3.,wp11 at design and off-design conditions by comparison with measurements and the Spalart-Allmaras(SA)turbulence *** flow within the tip is calculated with a multi-block grid.

关键词： SST model staggered finite volume method turbomachinery simulation multi-block grid

Adhesion of NiCu Films DC Biased Plasma-Sputter-Deposited on MgO (001)

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International Journal of Minerals,Metallurgy and materials 2000年第3期14卷 218-221页

作者： Hong Qiu, Mituru Hashimoto ( beijing Keda-Tianyu Microelectronic material Technology Development Corporation, beijing 1.0083,{3. Applied science school, university of science and Technology beijing, beijing 1.0083,{3. Department of Applied Phys beijing Keda-Tianyu Microelectronic material Technology Development Corporation Beijing 100083 China Applied science school University of Science and Technology Beijing Beijing 100083 China Department of Applied Physics and Chemistry University of Electro-Communications 1-5-1 Chofugaoka Chofu-shi Tokyo 182-8585 Japan

NiCu films about 60nm thick were deposited on MgO (001) substrates at 23.℃ by DC plasma-sputtering at 2.7kV and 8mA in pure Ar gas using a Ni90Cu10 target. A DC bias voltage of 0, 60, 110 or 140V was applied to the substrate during deposition. The adhesion of the film to the substrate was studied using a scratch test as a function of . The application of is very effective in increasing the adhesion of the film to the substrate. In conclusion, the adhesion increases with cleaning the substrate surface by sputtering off impurity admolecules during the film initial formation due to the energetic Ar ion particle bombardment.

关键词： NiCu film plasma-sputter-deposition negative bias voltage adhesion

Formation control for networked spacecraft in deep space:with or without communication delays and with switching topology

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science china(Information sciences) 2011年第3期54卷 469-481页

作者： WANG Nan 1,2, ZHANG TianWu 2 & XU JieQiong 1 1 school of Aeronautic science and engineering,{3., beijing 100191, china 2 Department of Computer science and engineering, Henan Institute of engineering, Zhengzhou 451191, china 1. school of Aeronautic science and engineering Beijing University of Aeronautics and Astronautics Beijing 100191 China2. Department of Computer Science and Engineering Henan Institute of Engineering Zhengzhou 451191 China

In this paper, several formation controllers are developed with constant and variable connected communication topology for six-degree-of-freedom (6-DOF) networked spacecraft flying in deep space with constant and time-varying communication delays considered. In the control algorithm, any explicit leader does not exist in the formation team and it is required that each spacecraft communicate only with its neighbors and therefore the required communication loads of the whole formation is greatly reduced. The proposed control strategies allow that each spacecraft can track its desired position and attitude and simultaneously the whole group moves to the desired formation and obtain its desired relative attitudes with its neighbors. Simulation results demonstrate the effectiveness of the proposed controllers.

关键词： deep space graph theory formation control communication topology delays

Fretting corrosion of surgical 3.6L stainless steel in saline solutions

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International Journal of Minerals,Metallurgy and materials 1997年第3期11卷 18-21页

作者： BAI Zhijun WU Yinshun ZHANG Tiancheng LIU Qiang (material science and engineering {3., university of science and Technology beijing, beijing 1.0083, china)

A new simulation system for the laboratory investigation of fretting wear is developed. It consist of a mechanism device, a electrochemical cell and a datum acqulsition and process software. Fretting of surgical 3.6L stainlesssteel in saline is studied. The results show that electrochemical corrosion is enhanced by fretting and anodic currentdensity under fretting is 100 times than static condition. Fretting corrosion is a mechanic -elec trochemical al Process.

关键词： fretting system 3.6L sninless steel saline solution

Surface Metallurgy of Nickle Base Superalloy

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International Journal of Minerals,Metallurgy and materials 1999年第1期13卷 47-49页

作者： Xu Zhang Zhongmin Yang Jianxin Dong Xishan Xie Yuan Gao Zhong Xu (material science and engineering {3., university of science and Technology beijing, beijing 1.0083, china)(Institute of Surface engineering, Taiyuan university of Technology, Taiyua material science and engineering {3. University of Science and Technology Beijing Beijing 100083 China Institute of Surface engineering Taiyuan University of Technology Taiyuan 030024 China

The Double Glow Plasma Surface Alloying Technique, the Xu-Tee Process, is a new method to produce high quality alloying layer on the surface of less expensive materials. By using thes technique, the surface alloying layer similar to superalloy Inconel 625 has been obtained on the surface of three kinds of melallic materials (low carbon steel, industrial pure iron, stainless steel Cr18Ni9). The results of the composition and microstructure analyzed by Scanning Electron Microscopy (SEM) and X-Ray Uffrachon (XRD) show that the alloying layer consistS of y matrix and several precipitates (Laves intermetallic phase and carbide etc.). The electrochemical corrosion results show that the surface alloying layer formed on the surface of stainless steel and industrial pure iron have better corrosion resistance than that of nickel base alloy inconel 625 and stainless steel Cr18Ni9 in 3.5%NaCl solution. The exper iments indicate that it is an effective way to obtain the gradient surface alloying layer on the surfaces of steels by using Double Glow Plasma Surface Alloying Technique.

关键词： double glow nickel base alloy plasma surface alloying