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A note for preconditioning nonsymmetric matrices

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Applied Mathematics(A Journal of Chinese Universities) 2010年第1期25卷 93-100页

作者： CHEN Xiao-shan LI Wen School of Mathematics, south china Normal university, Guangzhou 510631, china School of Mathematics South China Normal University Guangzhou China

In this paper, we consider preconditioners for generalized saddle point systems with a nonsymmetric coefficient matrix. A constraint preconditioner for this systems is constructed, and some spectral properties of the ... 详细信息

关键词： Preconditioner saddle point matrix minimal polynomial Schilder's factorization.

Preparation of well-defined polystyrene/silica hybrid nanoparticles by ATRP

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Science china Chemistry 2008年第1期51卷 51-57页

作者： OU BaoLi1,2 LI DuXin2 1 College of Chemistry and Chemical Engineering,Hunan university of Science and Technology,Xiangtan 411201, china 2 State Key Laboratory of Powder Metallurgy,Central south university,Changsha 410083, china 1. College of Chemistry and Chemical Engineering Hunan University of Science and Technology Xiangtan 411201 China 2. State Key Laboratory of Powder Metallurgy Central South University Changsha 410083 China

Immobilization of the atom transfer radical polymerization (ATRP) macroinitiators at the silica nanoparticle surfaces was achieved through surface modification with excess toluene-2,4-diisocynate (TDI), after which the residual isocyanate groups were converted into ATRP macroinitiators. Structurally well-defined polystyrene chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polystyrene by ATRP, which was initiated by the as-synthesized silica-based macroinitiator. FTIR, NMR and gel permeation chro-matography (GPC) were used to characterize the polystyrene/silica hybrid particles.

关键词： silica nanoparticles surface modification atom transfer radical polymerization polystyrene hybrid particle

Preparation of polystyrene/silica nanocomposites by radical copolymerization of styrene with silica macromonomer

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Science china Chemistry 2007年第3期50卷 385-391页

作者： OU BaoLi1,2 & LI DuXin2 1 College of Chemistry and Chemical Engineering, Hunan university of Science and Technology, Xiangtan 411201, china 2 State Key Laboratory of Powder Metallurgy, Central south university, Changsha 410083, china 1. College of Chemistry and Chemical Engineering Hunan University of Science and Technology Xiangtan 411201 China 2. State Key Laboratory of Powder Metallurgy Central South University Changsha 410083 China

A two-stage process has been developed to generate the silica-based macromonomer through surface-modification of silica with polymerizable vinyl groups. The silica surfaces were treated with excess 2,4-toluene diisocynate (TDI), after which the residual isocyanate groups were converted into polymerizable vinyl groups by reaction with hydroxypropylacrylate (HPA). Thus, polystyrene/silica nanocomposites were prepared by conventional radical copolymerization of styrene with silica macromonomer. The main effecting factors, such as ratios of styrene to the macromonomer, together with polymerization time on the copolymerization were studied in detail. FTIR, DSC and TGA were utilized to characterize the nanocomposites. Experimental results revealed that the silica nanoparticles act as cross-linking points in the polystytene/silica nanocomposites, and the glass transition temperatures of the nanocomposites are higher than that of the corresponding pure polystyrene. The glass transition temperatures of nanocomposites increased with the increasing of silica contents, which were further ascertained by DSC.

关键词： silica nanoparticles surface modification styrene radical copolymerization nanocomposites

Phototoxic effect of UVR on wild type, ebony and yellow mutants of Drosophila melanogaster: Life Span, fertility, courtship and biochemical aspects

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Science china(Life Sciences) 2008年第10期51卷 885-893页

作者： WANG ZhePeng1,2, LIU RuiFang2, WANG AnRu3, DU LiLi1 & DENG XueMei1 1 College of Animal Science and Technology, china agricultural university, Beijing 100094, china 2 Vocational and Technologic College, Inner Mongolia Agriculture university, Baotou 014109, china 3 College of Veterinary Medicine, china agricultural university, Beijing 100094, china 1. College of Animal Science and Technology China Agricultural University Beijing 100094 China 2. Vocational and Technologic College Inner Mongolia Agriculture University Baotou 014109 China 3. College of Veterinary Medicine China Agricultural University Beijing 100094 China

Melanin plays an important role in protecting organisms from ultraviolet radiation (UVR). Therefore, it is possible that differently colored strains can show different sensitivities to UVR. In the present work, life span, fertility and courtship behavior of wild type (w), ebony (e) and yellow (y) strains of Drosophila melanogaster were studied to evaluate their sensitivity to ultraviolet (UV). Because a range of photo- toxic effects of UVR are mediated through generation of free radicals, levels of free radicals, lipid per- oxide (malondialdehyde, MDA) and superoxide dismutase (SOD) activity of three strains were examined to indicate their antioxidant defending ability and oxidative status. It was shown that w always had the highest lifespan and fertility not only in the control but also in UV-exposed groups. Moreover, lifespan and fertility of e were significantly higher (P2) effect on the SOD activities. After pooling data from the control and UV-exposed groups, we found that w had a significantly (P0.05). MDA levels were increased in the UV dose-dependent manner (P=0.0495). In con- clusion, our results suggested that UVR can decrease life span and fertility of flies and do harm to courtship, which may be due to oxidative damage to flies tissues (e.g. central nervous system) induced by free radicals. w had the highest tolerance to UVR, which may be ascribed to its advantage of survival under the natural condition and at high level of SOD activity. Then differences of pigment between e and y in absorbing UV, shielding agai

关键词： ultraviolet radiation Drosophila melanogaste free radicals pigment

Cloning and sequencing of nifBHDKENX genes of Paenibacillus massiliensis T7 and its nif promoter analysis

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Science china(Life Sciences) 2006年第2期49卷 115-122页

作者： ZHAO Hongxin1,2,3, XIE Baoen2 & CHEN Sanfeng1,2 1. State Key Laboratory for Agrobiotechnology and Biological School, china agricultural university, Beijing 100094, china 2. Key Laboratory for Agro-Microbial Resource and Application of Agriculture Ministry, china agricultural university, Beijing 100094, china 3. Chemical and Biological School, ShenYang Normal university, Shenyang 110034, china 1. State Key Laboratory for Agrobiotechnology and Biological School China Agricultural University Beijing 100094 China 2. Key Laboratory for Agro-Microbial Resource and Application of Agriculture Ministry China Agricultural University Beijing 100094 China 3. Chemical and Biological School ShenYang Normal University Shenyang 110034 China

A 324 bp of nifH fragment was PCR amplified from Paenibacillus massiliensis T7 using the universal degenerate primers. The PCR-amplified nifH fragment was labeled with DIG; then used as a probe in southern blot analysis. southern blot result showed that there were two positive signals, indicating that there might be two copies of nifH in P. massiliensis T7. A total of 10254 bp DNA sequence containing purD; nifBHDKENX was obtained by five rounds of inverse-PCR amplification. The predicted proteins of nifBHDKENX had high homology with those from other nitrogen-fixing bacteria. Only one putative σ[54]-dependent promoter sequence was detected upstream of the nifB gene; nifBHDKENX were likely to be organized in one operon. Assays of β-galactosidase activity of P. massiliensis T7PB carrying a nifB-lacZ fusion under different concentrations of NH4 [+]; O2 showed that the expression of nifB-lacZ was strongly inhibited by O2.

关键词： Paenibacillus massiliensis T7, nifBHDKENX, nifB-lacZ, inverse-PCR.

PdCl_2-catalyzed heterocyclotrimerization in MeOH/scCO_2:A versatile approach to dimethyl pyridine-3,5-dicarboxylate from methyl acrylate and urea

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Science china Chemistry 2008年第5期51卷 447-451页

作者： ZOU Bo,JIANG HuanFeng College of Chemistry,south china university of Technology,Guangzhou 510640,china 1. College of Chemistry South China University of Technology Guangzhou 510640 China

A novel and green method for the synthesis of dimethyl pyridine-3,5-dicarboxylate has been developed. It is PdCl2-catalyzed heterocyclotrimerization of methyl acrylate with urea in methanol/supercritical carbon dioxid... 详细信息

关键词： PdCl2 heterocyclotrimerization dimethyl pyridine-3 5-dicarboxylate scCO2

SYNTHESIS AND OPTICAL PROPERTIES OF A NOVEL ORGANIC/INORGANIC HYBRID NONLINEAR OPTICAL POLYMER VIA SOL-GEL PROCESS

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Chinese Journal of Polymer Science 2001年第4期19卷 421-427页

作者： Hong-xia Xi Zhong Li Zhao-xi Liang The Institute of Chemical Engineering south china university Guangzhou 510640 china The Institute of Polymer Science, Zhongshan university Guangzhou 510275, china S china Univ Inst Chem Engn Canton 510640 Peoples R China Zhongshan Univ Inst Polymer Sci Canton 510275 Peoples R China

A new organic/inorganic hybrid nonlinear optical (NLO) material was developed by the sol-gel process of an alkoxysilane dye with tetraethoxysilane. A NLO moiety based on 4-nitro-4 ' -hydroxy azobenzene was covalently bonded to the triethoxysilane derivative, i.e, gamma -isocyanatopropyl triethoxysilane. The preparation process and properties of the sol-gel derived NLO polymer were studied and characterized by SEM, FTIR,H-1-NMR, UV-Vis, DSC and second harmonic generation (SHG) measurement. The results indicated that the chemical bonding of the chromophores to the inorganic SiO2 networks induces low dipole alignment relaxation and preferable orientational stability. The SHG measurements also showed that the bonded polymer film containing 75 wt% of the akoxysilane dye has a high electro-optic coefficient (r(33)) of 7.1 pm/V at 1.1 mum wavelength, and exhibit good SHG stability, the r(33) values can maintain about 92.7% of its initial value at room temperature for 90 days, and can maintain about 59.3% at 100 degreesC for 300 min.

关键词： sol-gel process nonlinear optical material alkoxysilane dye dipole alignment relaxation chromophore

Dimension and measure theoretic entropy of a subshift in symbolic space

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Chinese Science Bulletin 1997年第14期42卷 1193-1196页

作者： CHEN Ercai and XIONG Jincheng1. Department of Astronomy, Nanjing university, Nangjing 210093, china 2. Department of Mathematics, south china Normal university, Guangzhou 510631, china Department of Astronomy Nanjing University Nangjing China Department of Mathematics South China Normal University Guangzhou China

1 Definitions and resultsWITH the development of the theory of dynamical systems and fractal geometry, one provedthat symbolic dynamics is a powerful tool to study chaos and fractals. It is useful to study thefractal characteristics of symbolic dynamics. In the present note we shall point out the relationbetween the dimension and measure theoretic entropy of any subshift in symbolic space. Weprove here that the Bowen’s formula for Hausdorff dimension holds without Markov struc-ture. A variational principle for dimension is obtained.

关键词： symbolic space subshift measure theoretic entropy dimension.

H~m convergence rates of solutions of GBBM equations in multi-dimensional spaces

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Progress in Natural Science:Materials International 2009年第9期19卷 1053-1057页

作者： Shaomei Fang a,*, Boling Guo b a Department of Mathematics, south china agricultural university, Guangzhou 510642, china b Institute of Applied Physics and Computational Mathematics, Beijing 100088, china [a]Department of Mathematics South China Agricultural University Guangzhou 510642 China [b]Institute of Applied Physics and Computational Mathematics Beijing 100088 China

In this paper, we study the decay rates of the generalized Benjamin-Bona-Mahony equations in n-dimensional space. By using Fourier analysis for long wave and by applying the energy method for short wave, we obtain the Hm convergence rates of the solutions when the initial data are in the bounded subset of the phase space HmeRnTen P 3T. The optimal decay rates are obtained in our results and are found to be the same as the Heat equation.

关键词： Generalized Benjamin–Bona–Mahony equations Fourier analysis Energy method Optimal convergence rates