检索结果-南通市图书馆

Phase-Sensitive Optical Time-Domain Reflectometry Amplified by Gated Raman Pump

在线全文

学校读者我要写书评

暂无评论

Photonic Sensors 2015年第4期5卷 345-350页

作者： Yi li Yi ZHOU li zhang Mengqiu FAN Jin li Key Laboratory of Optical Fiber Sensing & Communications (Ministry of Education) University of Electronic Scienceand Technology of China Chengdu 611731 China

A long-range phase-sensitive optical time-domain reflectometry is proposed and experimentally demonstrated, based on the gated Raman amplification （RA）. This technique can reduce the amplified spontaneous emissions （ASE） noise of the Raman pump while extend the sensing distance. A direct-detection based phase-sensitive optical time-domain reflectometry （O-OTDR） with an operation range of 50 km and a spatial resolution of 20 m has been demonstrated. The influence of different delay time of the gated Raman pump on the O-OTDR system is also discussed.

关键词： Fiber optic sensors Rayleigh scattering stimulated Raman scattering

A new coupled model for alloy solidification

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Science China Mathematics 2004年第Z1期47卷 41-52页

作者： li Daming li Ruo zhang Pingwen LMAM CCSE & School of Mathematical Sciences Peking University Beijing 100871 China LMAM CCSE & School of Mathematical Sciences Peking University Beijing 100871 China LMAM CCSE & School of Mathematical Sciences Peking University Beijing 100871 China

A new coupled model in the binary alloy solidification has been developed. The model is based on the cellular automaton (CA)technique to calculate the evolution of the interface governed by temperature, solute diffusion and Gibbs-Thomson effect. The diffusion equation of temperature with the release of latent heat on the solid/liquid (S/L) interface is valid in the entire *** temperature diffusion without the release of latent heat and solute diffusion are solved in the entire domain. In the interface cells, the energy and solute conservation, thermodynamic and chemical potential equilibrium are adopted to calculate the temperature, solid concentration, liquid concentration and the increment of solid fraction. Compared with other models where the release of latent heat is solved in implicit or explicit form according to the solid/liquid (S/L) interface velocity, the energy diffusion and the release of latent heat in this model are solved at differentscales, I.e. The macro-scale and micro-scale. The variation ofsolid fraction in this model is solved using several algebraicrelations coming from the chemical potential equilibrium andthermodynamic equilibrium which can be cheaply solved insteadof the calculation of S/L interface velocity. With the assumptionof the solute conservation and energy conservation, the solidfraction can be directly obtained according to the thermodynamicdata. This model is natural to be applied to multiple (>2)spatial dimension case and multiple (>2) component alloy. Themorphologies of equiaxed dendrite are obtained in numericalexperiments.

关键词： alloy solidification, dendritic growth, cellular automaton, segregation.

Theoretical Studies on the Dihydrogen Bonding Between Shortchain Hydrocarbon and Magnesium Hydride

在线全文

学校读者我要写书评

暂无评论

Chemical Research in Chinese Universities 2014年第5期30卷 831-836页

作者： li li BAI Fuquan zhang Hongxing State Key Laboratory of Theoretical and Computational Chemistry Institute of Theoretical Chemistry Jilin University Changchun 130021 P. R. China

The C--H…H dihydrogen-bonded complexes of methane, ethylene, acetylene, and their derivatives with magnesium hydride were systematically investigated at MP2/aug-cc-PVTZ level. The results confirm that the strength of dihydrogen bonding increases in the following order of proton donors： C（sp3）-H〈C（sp2）-H〈C（sp）-H and chlorine substituents enhance the C-H…H interaction. In the majority of the complexes with a cyclic structure, the Mg-H proton-accepting bond is more sensitive to the surroundings than C-H proton-donating bond. The nature of the electrostatic interaction in these C-H…H dihydrogen bonds was also unveiled by means of the atoms in mo- lecules（AIM） analysis. The natural bond orbital（NBO） analysis suggests that the charge transfer in the cyclic com- plexes is characteristic of dual-channel. The direction of the net charge transfer in the cyclic complexes is contrary to that previously found in dihydrogen bonded systems.

关键词： Dihydrogen bond Atom in molecule(AIM) theory Bond critical point Natural bond orbital(NBO) Chargetransfer

Influence of copper element distribution and speciation on the color of Chinese underglaze copper-red porcelain in the Yuan dynasty

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Nuclear Science and Techniques 2019年第7期30卷 83-90页

作者： Mao-lin zhang li-Hua Wang li-li zhang Hai-Sheng Yu Institute of Ancient Ceramics Jingdezhen Ceramic Institute Jingdezhen 333403 China Shanghai Synchrotron Radiation Facility Shanghai Advanced Research Institute Chinese Academy of Sciences Shanghai 201210 China Shanghai Institute of Applied Physics Chinese Academy of Sciences Shanghai 201204 China

A shard of Chinese underglaze copper-red porcelain from the Yuan dynasty (AD 1271–1368) made in the Jingdezhen kiln was measured by synchrotron radiation- induced X-ray fluorescence mapping and X-ray absorption near-edge spectroscopy to investigate the influence of copper element distribution and speciation on the color of porcelain. In black-colored region, copper accumulates at the interface between the body and glaze layers with metallic copper particles as the main speciation. In contrast, Cu is irregularly distributed in the red-colored region with multi-valence speciation. The differences in Cu distribution and speciation in black- and red-colored regions indicate that they are the main factors influencing the different colors of copper-red underglaze porcelain.

关键词： Copper distribution and speciation Chinese underglaze copper-red porcelain Synchrotron techniques

Study on the breakup length of circular impinging jet

在线全文

学校读者我要写书评

暂无评论

Journal of University of Science and Technology Beijing 2007年第6期14卷 585-588页

作者： Shengyong li Mouwei li Shaojun zhang Bangwen Wang Mechanical Engineering School University of Science and Technology Beijing Beijing 100083 China

Circular impinging jet, which is widely used in accelerated control cooling （ACC） equipment to accelerate the cooling of hot rolled plates, is subject to breakup, and may result in undesirable cooling effect. Therefore, the jet breakup should be avoided as possible in industrial production. The objective of this study is to find the relation of the processing parameters of the ACC equipment versus the breakup length of jet with weaker turbulence. To obtain quantitative findings, not only relative experimental study but also numerical simulation was carded out. For a weaker turbulent water jet, the breakup length increases with the increase of jet diameter, as well as with the jet velocity; jet diameter has a significant effect on the breakup length for a certain flow rate when compared with jet velocity; finally a suggested correlation of the jet breakup length versus jet Weber number is presented in this study.

关键词： hot rolled plate circular impinging jet breakup length numerical simulation

Grassmannian precoding MU-MIMO scheme

在线全文

学校读者我要写书评

暂无评论

The Journal of China Universities of Posts and Telecommunications 2008年第3期15卷 105-109,117页

作者： FANG Shu li li-hua zhang Ping Key Laboratory of Universal Wireless Communications Ministry of Education Beijing University of Posts and Telecommunications Beijing 100876 China

In this article, a Grassmannian precoding multiuser multiple-input multiple-output （MU-MIMO） scheme for downlink transmission is proposed. The proposed MU-MIMO scheme will perform scheduling and precoding simultaneously at the base station, to obtain both the multiuser diversity gain and the precoding gain, to maximize the system capacity. The precoding method is related to Grassmannian precoding, which extends the point-to-point single-user Grassmannian precoding to point-to-multipoint multiuser Grassmannian precoding. It provides further significant system capacity enhancement than the single user MIMO （SU-MIMO） system and also outperforms the block dia^onalization （BD） algorithm under the same simulation environment.

关键词： multiuser MIMO cochannel interference Grassmannian precoding

Synthesis,Structure and Biological Activities of 2-(1H- 1,2,3-Benzotriazol-1-yl)-1-(4-methylphenyl)-2- (1H-1,2,4-triazol-1-yl)-1-ethanone

在线全文

学校读者我要写书评

暂无评论

Chemical Research in Chinese Universities 2006年第4期22卷 465-467页

作者： WAN Jun li Chun-li li Xue-mei zhang Shu-sheng College of Chemistry and Molecular Engineering Qingdao University of Science and Technology Qingdao 266042 P. R. China

The title compound was synthesized and characterized by IR, ^1H NMR, elemental analysis and single crystal X-ray diffraction analysis. Its biological activities were also tested. The results show that the title compound reveals inhibiting activities towards wheat gibberellin, apple ringspot, tomato early blight, peanut cercospora arachidicola and stem wilt of asparagus.

关键词： Triazole derivative Biological activity Crystal structure

Monoterpene and tetrahydronaphthene derivatives from Senecio argunensis

在线全文

学校读者我要写书评

暂无评论

Chinese Chemical Letters 2009年第5期20卷 598-600页

作者： Chao Feng zhang Ning li lin li Mian zhang Research Department of Pharmacognosy China Pharmaceutical University Nanjing 210038 China

Two new compounds, senarguines A and B, were isolated from Senecio argunensis. They were respectively identified as （Z）-3- ethylidene-9-hydroxyl-9-methyl-6,7-dioxaspiro [4.4] nonane-5,8-dione （1） and 3,6,6-trimeth... 详细信息

关键词： Compositae Senecio argunensis Senarguine A Senarguine B

Effects of Temperature and Catalyst to Oil Weight Ratio on the Catalytic Conversion of Heavy Oil to Propylene Using ZSM-5 and USY Catalysts

在线全文

学校读者我要写书评

暂无评论

Journal of Natural Gas Chemistry 2007年第1期16卷 92-99页

作者： Xiaohong li Chunyi li Jianfang zhang Chaohe Yang Honghong Shan State Key Laboratory of Heavy Oil Processing China University of Petroleum （Huadong） Dongying 257061 Shandong China

It is useful for practical operation to study the rules of production of propylene by the catalytic conversion of heavy oil in FCC （fluid catalytic cracking）. The effects of temperature and C/O ratio （catalyst to oil weight ratio） on the distribution of the product and the yield of propylene were investigated on a micro reactor unit with two model catalysts, namely ZSM-5/Al2O3 and USY/Al2O3, and Fushun vacuum gas oil （VGO） was used as the feedstock. The conversion of heavy oil over ZSM-5 catalyst can be comparable to that of USY catalyst at high temperature and high C/O ratio. The rate of conversion of heavy oil using the ZSM-5 equilibrium catalyst is lower compared with the USY equilibrium catalyst under the general FCC conditions and this can be attributed to the poor steam ability of the ZSM-5 equilibrium catalyst. The difference in pore topologies of USY and ZSM-5 is the reason why the principal products for the above two catalysts is different, namely gasoline and liquid petroleum gas （LPG）, repspectively. So the LPG selectivity, especially the propylene selectivity, may decline if USY is added into the FCC catalyst for maximizing the production of propylene. Increasing the C/O ratio is the most economical method for the increase of LPG yield than the increase of the temperature of the two model catalysts, because the loss of light oil is less in the former case. There is an inverse correlation between HTC （hydrogen transfer coefficient） and the yield of propylene, and restricting the hydrogen transfer reaction is the more important measure in increasing the yield of propylene of the ZSM-5 catalyst. The ethylene yield of ZSM-5/A1203 is higher, but the gaseous side products with low value are not enhanced when ZSM-5 catalyst is used. Moreover, for LPG and the end products, dry gas and coke, their ranges of reaction conditions to which their yields are dependent are different, and that of end products is more severe than that of LPG. So it is clear that maximizin

关键词： fluid catalytic cracking heavy oil propylene temperature catalyst to oil weight ratio ZSM-5 USY