检索结果-南通市图书馆

TARTARIC ACID TEMPLATED SYNTHESIS OF MESOPOROUS Ti-INCORPORATED SILICA AND ITS CATALYTIC ACTIVITY FOR THE RING-OPENING polymerIZATION OF ε-CAPROLACTONE

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of polymer science 2002年第4期20卷 361-368页

作者： Jie-bin Pang Chang-ming Dong Kun-yuan qiu Yen Wei department of polymer {3. and engineering college of chemistry and Molecular engineering peking university beijing 100871, China department of chemistry Drexel university Philadelphia, Pennsylvania 19104, USA peking Univ Coll Chem & Mol Engn Dept Polymer Sci & Engn Beijing 100871 Peoples R China Drexel Univ Dept Chem Philadelphia PA 19104 USA

Ti-incorporated mesoporous silica materials with pore diameters of 3.4 nm have been prepared via the co-hydrolysis and co-condensation reactions, that is the sol-gel reactions, of titanium (IV) tetrabutoxide and tetraethylorthosilicate in the presence of tartaric acid as template, followed by extraction with ethanol to remove the templatemolecules. The materials were characterized in detail by Fourier transform infrared spectroscopy, nitrogen adsorption-desorption test, powder X-ray diffraction, transmission electron microscopy and X-ray energy dispersive spectroscopy. Theresults indicate that the Ti-containing silica materials have large specific surface areas (ca. 1200 m^2 g^(-1)) and pore volumes(ca. 0.900 cm^3.g^(-1)). The mesoporosity arises from disordered interconnecting channels or pores. The Ti-incorporated silicasexhibit catalytic activity for the ring-opening polymerization of ε-caprolactone, otherwise, the pure mesoporous silicamaterial shows no catalytic activity under the identical conditions.

关键词： Mesoporous material Ti-incorporated silica ε-Caprolactone Ring-opening polymerization Sol-gel reactions

New discrete element models for elastoplastic problems

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2009年第5期25卷 629-637页

作者： Ming Cheng Weifu Liu Kaixin Liu LTCS and department of Mechanics and Aerospace engineering,college of engineering, peking university, 100871 beijing, China LTCS and department of Mechanics and Aerospace engineering College of Engineering Peking University 100871 Beijing China

The discrete element method （DEM） has attractive features for problems with severe damages, but lack of theoretical basis for continua behavior especially for nonlinear behavior has seriously restricted its application. The present study proposes a new approach to developing the DEM as a general and robust technique for modeling the elastoplastic behavior of solid materials. New types of connective links between elements are proposed, the interelement parameters are theoretically determined based on the principle of energy equivalence and a yield criterion and a flow rule for DEM are given for describing nonlinear behavior of materials. Moreover, a numerical scheme, which can be applied to modeling the behavior of a continuum as well as the transformation from a continuum to a discontinuum, is obtained by introducing a fracture criterion and a contact model into the DEM. The elastoplastic stress wave propagations and the tensile failure process of a steel plate are simulated, and the numerical results agree well with those obtained from the finite element method （FEM） and corresponding experiment, and thus the accuracy and efficiency of the DEM scheme are demonstrated.

关键词： DEM Continuum Plasticity Fracture

MECHANICAL PERTURBATION INDUCED MOLECULAR ALIGNMENTS IN A SIDE-CHAIN LIQUID CRYSTALLINE POLYACETYLENE, POLY{10-[4-(4'-METHOXYPHENOXY-CARBOML)PHENOXYCARBONYL]-1-DECYNE}

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of polymer science 1999年第3期17卷 289-294页

作者： Ben-zhong Tang Xiang-xing Kong Xin-de feng department of chemistry, Hong Kong {3. of science & Technology, Clear Water Bay, Kowloon, Hong Kong, China department of polymer science & engineering, college of chemistry, peking university, beijing 100871, China Hong Kong Univ Sci & Technol Dept Chem Hong Kong Peoples R China peking Univ Coll Chem Dept Polymer Sci & Engn Beijing 100871 Peoples R China

A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily 'tunab1e' by simple mechanical perturbation. Thepolymerization of 10- [ 4 - (4' -methoxyphenoxycarbonyl )phenoxycarbonyl] - 1 -decyne (4 ) in itiated by theWCl_6-Ph_4Sn/dioxane complex yields polymer 5 with a M_w of 28400. The molecular structure of 5 ischaracterized by NMR, IR, and UV spectroscopy and its liquid crystalline behavior is investigated by DSC,POM, and XRD analysis. Upon mechanical perturbation, 5 exhibits unusual agitation-induced high-strengthdisclinations, shear-induced inversion walls, and solidification-induced banded textures. Such phenomenahave been observed in the main-chain liquid crystalline polymers with rigid backbones, but have seldom beenreported for the side-chain liquid crystalline polymers with flexible backbones, suggesting that the rigidpolyacetylene backbone of 5 plays a constructive role in inducing the novel molecular alignments.

关键词： Liquid crystals Side-chain liquid crystalline polymers Polyacetylenes High-strength disclinations Inversion walls Banded textures Molecular alignments

SMALL ANGLE LIGHT SCATTERING MEASUREMENT OF THE ISOTROPIC TO NEMATIC TRANSITION OF A SIDE CHAIN NEMATIC POLYMETHACRYLATE

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of polymer science 2002年第5期20卷 431-437页

作者： Zhong-ming Hu Ren-yuan qian Shou-xi Chen Xiao-fang Chen qi-feng Zhou Centre for Molecular {3., Institute of chemistry Chinese Academy of {3.s, beijing 100080, China department of polymer {3. & engineering college of chemistry & Molecular engineering{13. beijing 100871, China Chinese Acad Sci Inst Chem Ctr Mol Sci Beijing 100080 Peoples R China peking Univ Coll Chem & Mol Engn Dept Polymer Sci & Engn Beijing 100871 Peoples R China

The kinetics of I-->N transition of a side chain nematic polymethacrylate has been studied by small angle depolarized light scattering intensity measurements using a charge coupled device linear image sensor. The polymer shows the transition temperatures K52N79I in degreesC, The H-v scattering intensity T(q,t) during the transition I (at 80.2degreesC)-->N (at 75.8degreesC) shows that T(q) is independent of q for all t, and during the initial stage (in 6 s) T(t) increases exponentially with t. In the later stage of the transition T(t) approaches a saturation value in 2 min. This experimental result indicates that the I-->N transition of a liquid crystalline polymer is a spinodal type of phase transition mediated by orientation fluctuation.

关键词： side chain nematic polymer isotropic-nematic transition small angle depolarized light scattering

THE APPLICATION OF DISCRETE ELEMENT METHOD IN SOLVING THREE-DIMENTIONAL IMPACT DYNAMICS PROBLEMS

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2003年第3期16卷 256-261页

作者： Liu Kaixin Gao Lingtian (department of Mechanics and engineering science,{3. university,beijing 100871,China) department of Mechanics and engineering science Peking University Beijing 100871 China

A three-dimensional discrete element model of the connective type is presented. Moreover,a three-dimensional numerical analysis code,which can carry out the transitional pro- cess from connective model(for continuum)to contact model(for non-continuum),is developed for simulating the mechanical process from continuum to *** wave propagation process in a concrete block(as continuum)made of cement grout under impact loading is numer- ically simulated with this *** comparing its numerical results with those by LS-DYNA,the calculation accuracy of the model and algorithm is ***,the failure process of the concrete block under quasi-static loading is demonstrated,showing the basic dynamic tran- sitional process from continuum to *** results of calculation can be displayed by *** damage modes are similar to the experimental *** two numerical examples above prove that our model and its code are powerful and efficient in simulating the dynamic failure problems accompanying the transition from continuum to *** also shows that the discrete element method(DEM)will have broad prospects for development and application.

关键词： discrete element method three-dimensional model impact stress wave dynamic failure

On Catastrophe and Cavitation for SphericalCavity

在线全文

学校读者我要写书评

暂无评论

Communications in Nonlinear science and Numerical Simulation 1999年第4期4卷 249-254页

作者： Ming JIN Kefu HUANG Jike WU(department of Mechanics and engineering science,{3., beijing 100871,China) department of Mechanics and engineering science Peking University Beijing 100871 China

IntroductionInrecelltyears,theresearchesoncavitationandcatastropheofacavitysu***therwithbifllrcationtheory... 详细信息

IntroductionInrecelltyears,theresearchesoncavitationandcatastropheofacavitysu***therwithbifllrcationtheory...

关键词： nonlinearity bifurcation Hooke material

Simultaneous Recrystallization and Oxidation Behavior of Mn-Containing IF Steel

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Iron and Steel Research International 2012年第8期19卷 67-74页

作者： ZHANG Zuo-tai, ZHANG Ying-yi (department of Energy and Resources engineering, college of engineering, peking university, beijing 100871, China) department of Energy and Resources engineering College of Engineering Peking University Beijing 100871 China

The recrystallization and oxidation of a Mn-containing interstitial free (IF) steel were investigated simultaneously using confocal scanning laser microscope (CSLM) under controlled atmosphere of Ar 95% and H2 5% (in volume percent) at different temperatures. It was found that the grain boundary played a significant role in controlling recrystallization and oxidation in overall oxidation kinetics of the steel. The surface morphology was composed of two networks along the original and new grain boundaries respectively, which did not coexist. The grain boundary moved in different directions with different velocities during annealing process. The recrystallization processes were studied by CSLM motion video through observing the moving grain boundary to estimate the time for 50% recrystallization, and the activation energy for recrystallization was therefore calculated. The oxidation mechanism was discussed through comparison of the fluxes among mass transfer of water vapor, dissociation of water vapor and outward diffusion alloying elements. The results indicated that the oxidation was controlled by the mass transfer from the bulk gas to the surface, or dissociation rate, or outward diffusion of manganese, which depended on the temperature to form a grain boundary ridge or groove.

关键词： IF steel oxidation recrystallization grain boundary

Abrupt climate change and collapse of ancient civilizations at 2200BC-2000BC

在线全文

学校读者我要写书评

暂无评论

Progress in Natural science:Materials International 2005年第10期15卷 46-52页

作者： WANG Shaowu (department of Atmospheric science, School of Physics, peking university,{3., China) department of Atmospheric science School of Physics Peking University Beijing 100871 China

Plentiful evidence of historical, archaeological and palaeoclimatic studies proved that an abrupt change from wetter to drier climate occurred over the Nile Valley,the Mesopotamia, the Indus Valley and Huanghe River Valley at 2200BC-2000BC. The abrupt change was developed based on the general lowering of temperature in the middle latitudes, and was a strong cold event since the beginning of the Megathermal (8.5-3.0 kaBP). Collapse of Nile civilization appeared at the First Intermediate Period (2181BC-2040BC). Civilization of Mesopotamia began collapse following the disintegration of Akkadian Empire. This process lasted to the foundation of Babylon Kingdom from 2200BC to 1900BC. Indus civilization abruptly fell off at 1800BC. A widespread alternation of archaeological cultures happened in China at ca. 2000BC except only in its central part. Longsheng culture was replaced by the Erlitou culture, which is now acknowledged in China as Xia Culture. Foundation of Xia Dynasty at 2070BC opened a new chapter in the development of Chinese civilization. Studies indicated that abrupt climate change may be caused by the weakening of the Thermohaline Circulation (THC).

关键词： 2200BC-2000BC abrupt climate change collapse of ancient civilization.

Photorefractive Effect in Poly(N-vinylcarbazole)-Based Composite Sensitised by C_(60)

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Chinese Chemical Letters 1997年第9期8卷 807-810页

作者： Zhi Jie ZHANG Yi Wang CHEN Yuan Kang HE and Hui Ying CHEN(Institute of polymer science, college of chemistry,{3., beijing, 100871)Zhi Jian CHEN Shu feng WANG and qi Huang GONG(department of Physics, Mesoscopic Physics Laboratory, peking U Institute of polymer science College of Chemistry Peking University Beijing 100871 China department of Physics Mesoscopic Physics Laboratory Peking University Beijing 100871 China

A new PVK-based photorefractive polymer composite sensitized by C60 and doped with a higher content of EO chromophore was prepared. The high optical quality thin-film was formed between two ITOcovered glass electrodes. Two-beam-coupling (2BC) experiment was performed by using a He-Ne laser (at wavelength 63..8nm), and an obvious photorefractive performance was observed. The dependence of two-beamcoupling gain coefficient on the applied poling dc electric field was measured.

关键词： Photorefractive Effect in Poly Based Composite Sensitised by C N-vinylcarbazole Rev