ZHANG Cheng
,
WANG Yongzhong
,
JIANG Ming
,
ZENG Dechang
,
TANG Hong
,
LI Zhongrun
,
QIAO Guiwen
,
CHUANG Yuzhi(Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang
,
ChinaManuscript received on 20 April 1995)
金属学报(英文版)
Bi-2212 superconductive oxides with nanometer grains have been prepared by means of crystallization from amorphous materials.The structure and grain-size of samples were examined by.X-ray.diffraction,scanning electron microscopy.and high resolution electron microscopy.The temperature dependence of the resistivity.and a.c.susceptibility was measured by the standard four-probe method and the standard mutual-induction measurement,respectively.With the decrease of temperature,the resistivity of the Bi-2212 phase with grain size in nanometer was found to diminish to zero without sudden drop.No diamagnetic transition was detected from room temperature to 4.2 K.The formation of the nanocrystalline 2212 phase and the effect of grain size on the superconductivity were discussed.
关键词:
:Bi-2212
,
null
,
null
,
null
TANG Hong
,
XIANYU Ze
,
HU Qianli
,
QIAO Guiwen
,
WANG Yongzhong
,
ZHUANG Yuzhi1 1) Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang
,
China 2) Northeastern University
,
Shenyang
,
China Manuscript Received 7 March 1995
金属学报(英文版)
In this study, high-Tc YBaCuO superconductors with high Jc value were prepared using MTG(melting-textured growth) method. These superconductors with high density have Jc value in excess of 1.6×104 A/cm2 (77K, zero field) determined by using a d.c. standard four terminal method with the criterion of lμV/cm. The XRD and fractograph analysis revealed that the texture existed in whole MTG-processed YBaCuO sample which consists of the layered and plate-like grains of matrix phase YBa2Cu3Oy unidirectionally aligned along its (103) planes. The experimental results indicated that the connectivity between superconducting grains has been improved greatly and the weak-link problem has been overcome essentially.
关键词:
: YBaCuO high-Tc superconductor
,
null
,
null
,
null
TANG Hong
,
QIAO Guiwen
,
CHUANG YuchiInstitute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang
,
ChinaXIANYU Ze
,
WANG JinxingNortheastern University
,
Shenyang
,
China
金属学报(英文版)
In present paper, study of magnetization behaviour was carried out for textured bulk YBaCuO polycrystalline superconductors synthesized by MTG process. The magnetization behaviour apparently different from that of sintered samples was observed. Magnetization hysteresis measurements were performed for the textured YBaCuO superconductors at 77K in± 10kOe magnetic field range. Based on the results of magnetization hysteresis, the magnetic field dependence of critical current density (Jc) at 77K was evaluated for the textured YBaCuO samples. The magnetic flux penetration in textured bulk YBaCuO polycrystalline superconductors was investigated at 77K through the magnetization hysteresis measurements under various maximum applied magnetic fields (HM) and reasonable discussion for the phenomena was conducted in terms of Bean's critical state model. The enhancement of magnetic properties for textured hulk YBaCuO polycrystalline superconductors is presumably attributed to the improvement of microstructure in these samples.
关键词:
YBaCuO polycrystalline superconductors
,
null
,
null
,
null
,
null
TANG Hong
,
LI Jingmin
,
YAO Biqiang
,
LIAO Hongfu
,
YAO Jin
钢铁研究学报(英文版)
Blast furnace scheme design is very important, since it directly affects the performance, cost and configuration of the blast furnace. An evaluation approach to furnace scheme design was brought forward based on artificial neural network. Ten independent parameters which determined a scheme design were proposed. The improved threelayer BP network algorithm was used to build the evaluation model in which the 10 independent parameters were taken as input evaluation indexes and the degree to which the scheme design satisfies the requirements of the blast furnace as output. It was trained by the existing samples of the scheme design and the experts′ experience, and then tested by the other samples so as to develop the evaluation model. As an example, it is found that a good scheme design of blast furnace can be chosen by using the evaluation model proposed.
关键词:
blast furnace;artificial neural network;scheme design
Acta Physica Sinica
Molecular dynamics (MD) simulation is performed to study the vacancy-interstitial annihilation in crystalline silicon. We choose the Stillinger-Weber potential, which is commonly used for silicon, to describe the interaction between atoms. The system is relaxed under 300K and 1400K respectively. We have found that < 111 > is the preferred recombination direction and propose the presence of an energy barrier in the < 110 > direction. From the calculated value of energy barrier along < 110 > we give a reasonable explanation for the difference between Tang's and Zawadzki's data.
关键词:
molecular dynamics;vacancy and interstitial;diffusion;point-defects;diffusion;mechanisms
陈修帅
,
侯传金
,
李晴
,
刘彦军
,
杨瑞丰
,
胡向平
催化学报
doi:10.1016/S1872-2067(16)62488-9
手性2,3-二氢呋喃衍生物是一类重要的杂环化合物,广泛存在于天然产物和生物活性分子中.它们也经常被用于手性四氢呋喃化合物的不对称合成.因此,人们发展了很多合成手性2,3-二氢呋喃化合物的方法,如有机小分子催化的多米诺迈克尔-烷基化反应、“中断的”Feist-Bénary反应或改进的 Feist-Bénary反应.此外,过渡金属催化的手性2,3-二氢呋喃的不对称合成在近些年引起了人们的极大关注. Ozawa等通过 Pd-催化2,3-二氢呋喃的动力拆分方法获得了手性2-芳基-2,3-二氢呋喃. Evans发展了一种 Sc-催化联烯硅和乙醛酸乙酯的[3+2]环加成反应合成手性2,3-二氢呋喃的方法.最近, Fu和 Tang等发展了 Cu催化烯酮和重氮化合物的[4+1]环加成反应合成手性2,3-二氢呋喃的方法.在 Nishibayashi和 van Maarseveen的开创性工作之后, Cu催化的不对称炔丙基转化反应取得了很大的进展.最近,我们发展了一类新的三齿手性 P,N,N-配体,在 Cu催化不对称炔丙基取代、脱羧炔丙基取代、[3+2]、[3+3]和[4+2]环加成反应中表现出优秀的对映和非对映选择性.其中,我们发现采用 Cu催化炔丙醇酯和β-酮酯的[3+2]环加成反应,能高对映选择性地获得手性2,3-二氢呋喃.我们设想,采用β-羰基膦酸酯代替β-酮酯,通过这种 Cu催化[3+2]环加成反应,将可以合成一类具有重要生物活性的手性膦酰化2,3-二氢呋喃化合物.基于这种设想,本文使用手性 P,N,N-配体,通过 Cu催化炔丙醇酯与β-羰基膦酸酯的不对称[3+2]环加成反应,以很好的收率和最高92% ee的对映选择性获得了一系列光学活性的膦酰化2,3-二氢呋喃化合物.我们以炔丙醇酯1a与β-羰基膦酸酯2a为标准底物,优化了反应条件,考察了配体、Cu盐、碱和反应温度等对反应收率和对映选择性的影响.我们确定了最佳的反应条件：以4b为配体,以 Cu(OTf)2为铜盐,以t-BuOK为碱,以 MeOH为溶剂,–20oC反应24 h.在此条件下,我们对β-羰基磷酸酯2的适用范围进行了考察.结果表明,各种苯基取代的β-羰膦磷酸酯均能得到很好的收率和对映选择性.苯环上取代基的空间效应对反应的对映选择性影响不大,但对反应收率影响较大,与相应3-取代或4-取代底物相比较,2-取代的底物获得的收率较低.苯环对位取代基的电子效应对反应的影响不大,给电子基或吸电子基的底物,均得到了较好的收率和对映选择性.杂环取代的底物同样适用于该反应,以90%的收率和89% ee的对映选择性获得了相应的[3+2]环加成产物.对于烷基底物,虽然反应的产率略低,但是得到了高达92% ee的产物.此外,我们对炔丙醇酯底物的适用范围也进行了考察.结果表明,该体系对于各种取代的炔丙醇酯底物均可以获得较高的收率和良好的对映选择性.总之,本文发展了一种铜催化炔丙醇酯与β-羰基膦酸酯的不对称[3+2]环加成反应的方法,成功合成了手性膦酰化2,3-二氢呋喃化合物.通过使用一个结构刚性的酮亚胺三齿 P,N,N-配体,以很好的收率和最高92% ee的对映选择性获得了一系列光学活性的膦酰化2,3-二氢呋喃化合物.
关键词:
铜
,
不对称合成
,
3+2环加成
,
β-羰基膦酸酯
,
膦酰化 2,3-二氢呋喃
