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Rare Metals 2012年第5期31卷 470-473页

作者： SUN wei ZHU Minggang FANG Yikun PAN wei li Jiajie li Yanfeng li wei Division of functional Materials Central Iron and Steel Research Institute Group Beijing 100081 China

The microstructures and magnetic properties of Ce-32.15Co_49.36Cu_9.84Fe_9.65 magnet sintered at the temperatures ranging from 1005 to 1105 °C were investigated. The results on scanning electron microscopy and X-ray diffraction analysis indicate that the remanence B r of the magnets is mainly influenced by the degree of the easy-axis orientation when sintering temperature is less than 1085 °C, the rapidly increasing amount of the secondly phase (5:19 phase) gives rise to the deterioration of the magnetic properties of the magnet above 1085 °C. Moreover, it is found that intrinsic coercivity H ci is strongly related to the content of copper in the matrix of the sintered magnets. The optimal sintering temperature is located in 1025~1055 °C, the corresponding magnetic properties of the magnets are B_r =0.685T, H_(ci) =350kA·m^-1 , and maximum energy product (BH)_m =85.6 kJ·m 3 .

关键词： Ce-Co permanent magnet sintering temperature coercivity

The Optimal Preconditioner of Strictly Diagonally Dominant Z-matrix

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Acta Mathematicae Applicatae Sinica 2008年第2期24卷 305-312页

作者： Ji-cheng li wei li Department of Mathematics Xi'an Jiaotong University Xi'an 710049 China

In this paper, we present a series of new preconditioners with parameters of strictly diagonally dominant Z-matrix, which contain properly two kinds of known preconditioners as special cases. Moreover, we prove the monotonicity of spectral radiuses of iterative matrices with respect to the parameters and some comparison theorems. The results obtained show that the bigger the parameter k is（i.e., we select the more upper right diagonal elements to be the preconditioner）, the less the spectral radius of iterative matrix is. A numerical example generated randomly is provided to illustrate the theoretical results.

关键词： Preconditioned method iteration splitting linear system

Cloning and Expression of Rat liver S-Adenosylmethionine Synthetase

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Chemical Research in Chinese Universities 2006年第2期22卷 236-238页

作者： CUI wei HUANG Lei li wei WANG li-ping College of life Science Jilin University Changchun 130021 P. R. China

The S-adenosylmethionine synthetase（SAM synthetase） is responsible for in vivo synthesis of S-adenosylmethionine（SAM）, which is a kind of biologically active molecules distributed in all body tissues and fluids and involved in a number of biochemical reactions. In this study, a cDNA containing the coding sequence for rat liver SAM synthetase was cloned into the prokaryotic expression vector pQE30 and expressed in E. coli M15. A major band corresponding to a protein of 48 kDa was detected on SDS-PAGE. The protein was distributed in both the soluble fraction and the insoluble fraction. In soluble fractions the protein was fully active.

关键词： SAM SAM synthetase, Cloning Expression HPLC

The Infiltration Process and Texture Transition of 2D C/C Composites

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Journal of Materials Science & Technology 2009年第1期25卷 109-114页

作者： Hejun li Guozhong Xu Kezhi li Chuang Wang wei li Miaoling li Carbon/carbon Composites Research Center Key Laboratory of Ultrahigh Temperature Composites Northwestern Polytechnical University Xi＇an 710072 China

2D needle-punched fiber felt was infiltrated by a kind of rapid isothermal chemical vapor infiltration technique. The infiltration process and texture transition of the infiltrated C/C composites were investigated. The porosity and the variations of the cumulative pore volume were determined by mercury porosimetry. The texture of matrix carbon was studied under a polarized light microscope. The results show that the relative mass gain of the sample increases directly as the infiltration time at the initial stage until 20 h, and subsequently the increasing rate of the relative mass gain decreases gradually with the prolonging of infiltration time. Three layers of pyrocarbon were formed around fibers. Low-textured pyrocarbon was obtained at the initial stage. With the densification going on, high-textured pyrocarbon was formed on the surface of low-textured pyrocarbon. Then, low-textured pyrocarbon was produced again during the final stage of densification. The texture transition is ascribed to the variation of the ratio of cumulative inner surface area to volume of pores and the gas partial pressure in pores.

关键词： C/C composites Isothermal chemical vapor infiltration (ICVI) Pyrocarbon Mercury porosimetry Polarized light microscope

Theoretical Study on the Structural and Electronic Properties of the Reduced SnO_2 (110) Surface

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Chinese Journal of Structural Chemistry 2007年第5期26卷 606-612页

作者： ZHANG Yong-Fan liN wei WANG Qi-wei li Yi li Jun-Qian Department of Chemistry Fuzhou University Fuzhou Fujian 350002 China State Key Laboratory of Structural Chemistry Fujian Institute of Research on the Structure of Matter The Chinese Academy of Sciences Fuzhou Fujian 350002 China

The reduced SnO2（110） surface has been investigated by using first-principles method with a slab model. By examining the vacancy formation energy of three kinds of reduced SnO2（110） surfaces, the most energetically favorable defect surface is confirmed to be the surface with the coexistence of bridging and in-plane oxygen vacancies, which is different with the traditional model by only removing bridging oxygen. The results of band structure calculations indicate that the electronic structure of this defect surface is similar to the SnO surface.

关键词： SnO2(110) surface band structure defect state

Statistical study of EUV and X-ray transient brightenings

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Research in Astronomy and Astrophysics 2010年第7期10卷 696-706页

作者： Jing-wei li Hui li Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 China

Using the visual inspection and base difference method and data from the X-ray Telescope （XRT） onboard Hinode and TRACE with improved spatial and temporal resolution, we selected 48 X-ray transient brightenings （XTBs） and 237 EUV transient brightenings （ETBs） to study the connection between these two types of transient brightenings （TBs）. These ETBs and XTBs have smaller areas （8.42 Mm^2 and 36.3 Mm^2, respectively, on average） and shorter durations （9.0 min and 6.9 min, respectively, on average） than previous studies. These XTBs show three types of morphological structure： point-like, single-loop and multiple-loop. We find only 20% of the ETBs have corresponding XTBs while the other 80% have no X-ray signatures at all. This is presumably due to the small amount of released energy, which is not enough to heat the plasma to coronal temperatures which produce X-ray emission rather than being due to the limitation of spatial resolution and temperature sensitivity of the X-ray instrument. These small ETBs may significantly contribute to the coronal heating.

关键词： Sun X-rays, gamma rays -- Sun UV radiation -- Sun corona

Defect engineering of rutile TiO_(2) ceramics:Route to high voltage stability of colossal permittivity

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Journal of Materials Science & Technology 2021年第25期84卷 10-15页

作者： Yang Yu Yu Zhao Yu-Long Qiao Yu Feng wei-li li wei-Dong Fei School of Electrical and Electronic Engineering Harbin University of Science and TechnologyHarbin 150080China State Key Laboratory of Advanced Welding and Joining Harbin Institute of TechnologyHarbin 150001China Research Center of Basic Space Science Harbin Institute of TechnologyHarbin 150001China National Key Laboratory of Science and Technology on Precision Heat Processing of Metals Harbin Institute of TechnologyHarbin 150001China

Donor-acceptor co-doped rutile TiO_(2) ceramics with colossal permittivity(CP)have been extensively investigated in recent years due to their potential applications in modern *** addition to CP and low dielectric loss,voltage stability is an essential property for CP materials utilized in high-power and high-energy density storage ***,the voltage stability of CP materials based on codoped TiO_(2) does not catch enough ***,we propose a strategy to enhance the voltage stability of co-doped TiO_(2),where different ionic defect clusters are formed by two acceptor ions with different radii to localize free carriers and result in high performance CP ***(Ta+Al+La)co-doped TiO_(2) ceramic with suitable La/Al ratio exhibits colossal permittivity with excellent temperature stability as well as outstanding dc bias *** density functional theory analysis suggests that La^(3+)Al^(3+)V_(0)Ti^(3+)defect clusters and Ta^(5+)-Al^(3+)pairs are responsible for the excellent dielectric properties in(Ta+Al+La)co-doped TiO_(2).The results and mechanisms presented in this work open up a feasible route to design high performance CP materials via defect engineering.

关键词： Colossal permittivity Co-doped TiO_(2) Defect cluster Voltage stability

Photoactivity of titanium dioxide/carbon felt composites prepared with the assistance of supercritical carbon dioxide: Effects of calcination temperature and supercritical conditions

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Science China Chemistry 2011年第3期54卷 497-505页

作者： li YouJi CHEN wei li LeiYong MA MingYuan College of Chemistry and Chemical Engineering Jishou University Jishou 416000 China

TiO2-coated carbon felt(TCF)composite catalysts have been prepared via a supercritical treatment of titanium tetraisopropoxide(TTIP)as the *** physical properties of the catalysts were characterized by means of thermogravimetric and differential thermal analysis(TG–DTA),X-ray diffraction(XRD),fluorescence spectroscopy,scanning electron microscopy (SEM),and BET surface areas *** photocatalytic activities of the materials were evaluated using the degradation of Congo red(CR)as a probe *** the composites showed much higher photocatalytic activity than commercial P25 due to significant synergistic *** TCF retained high photocatalytic activity for degradation of *** photocatalytic efficiency in CR degradation was found to be strongly dependent on the TiO2-coating ratio and calcination temperature.A possible mechanism for the enhanced reactivity involves shuttling of electrons from TiO2 particles to the carbon felt(CF)as a result of an optimal arrangement in TCF that stabilizes charge separation and reduces charge *** addition to the significant synergistic effects,the abundant spaces between adjacent carbon fibers allow UV light to penetrate into the felt-like photocatalyst to a considerable depth,so that a three-dimensional environment is available for the photocatalytic reaction.

关键词： titanium dioxide carbon felt supercritical calcination photocatalysis

Study on Assessment of Mine Environments

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Acta Geologica Sinica(English Edition) 2008年第5期82卷 1027-1034页

作者： WU Qiang li wei li Ruijun China University of Mining and Technology Beijing 100083 China

Mine environmental evaluation is the key to mine environmental study. On the basis of the characteristics of the mine environmental problems, they are classified into （1） three wastes problem, （2） ground distortion, （3） contradiction among mine drainage, water supply, ecological environment, （4） desertification, and （5） soil erosion. The evaluation is the basis of mine environmental problem classification and investigation, mine environmental rehabilitation, and the information system constructed can be used for subsequent research of evaluation techniques. A synthetic assessment of the 5 kinds of mine environmental problems can be divided into single-factor or multi-factor synthetic assessments; while by the viewpoint of time, the mine environmental assessment can be classified as the historical assessment, the current status assessment and the forecasting assessment.

关键词： single-factor assessment multi-factor synthetic assessment historical assessment current status assessment

Silicon assistant carbothermal reduction for SiC powders

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Journal of University of Science and Technology Beijing 2008年第4期15卷 484-488页

作者： Kezhi li Jian wei Hejun li Chuang Wang Gengsheng Jiao National Key Laboratory of Thermostructure Composite Materials Northwestern Polytechnical University Xi＇an 710072 China

The silicon assistant method to increase the reaction yield of carbothermal reduction of silica at a lower temperature is reported. The effect of silicon on the carbothermal reduction process has been investigated in detail. Compared with traditional reduction, the introduction of silicon can change the reaction path and further increase the conversion of silicon carbide at a lower temperature. It is considered that the assistant reduction consists of three steps： vaporizing and melting of silicon, formation of silicon monoxide, and synthesis of silicon carbide. The morphology of the synthesized SiC powders through the silicon assistant method can be affected apparently by the experimental temperature.

关键词： carbide powders solid state reaction electron microscopy X-ray diffraction