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191.
Lifang Zhang Zhenzhong Wang Junwen Wang Yan Wang Chunling Liu 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(6):528-532
An unsymmetrical N-heterocyclic carbene, namely 1-isopropyl-3-benzylimidazol-2-ylidene, is a highly active catalyst for ring-opening polymerization of ?-caprolactone (CL) to give polycaprolactone (PCL) with number average molecular weight (Mn) as high as 2.66 × 104 at 0°C in 100 min in tetrahydrofuran (THF). The effects of monomer/initiator molar ratio ([M]/[I]), catalyst/initiator molar ratio ([C]/[I]), monomer concentration, as well as polymerization temperature and time have been investigated. The kinetic studies of CL polymerization have indicated that the polymerization rate is first-order with respect to both monomer and catalyst concentrations. The apparent activation energy amounts to 56.04 kJ/mol. The proposed mechanism is a monomer-activated process. 相似文献
192.
193.
Bimetallic NiCo Functional Graphene: An Efficient Catalyst for Hydrogen‐Storage Properties of MgH2 下载免费PDF全文
Ying Wang Guang Liu Cuihua An Li Li Fangyuan Qiu Prof. Yijing Wang Lifang Jiao Prof. Huatang Yuan 《化学:亚洲杂志》2014,9(9):2576-2583
Bimetallic NiCo functional graphene (NiCo/rGO) was synthesized by a facile one‐pot method. During the coreduction process, the as‐synthesized ultrafine NiCo nanoparticles (NPs), with a typical size of 4–6 nm, were uniformly anchored onto the surface of reduced graphene oxide (rGO). The NiCo bimetal‐supported graphene was found to be more efficient than their single metals. Synergetic catalysis of NiCo NPs and rGO was confirmed, which can significantly improve the hydrogen‐storage properties of MgH2. The apparent activation energy (Ea) of the MgH2? NiCo/rGO sample decreases to 105 kJ mol?1, which is 40.7 % lower than that of pure MgH2. More importantly, the as‐prepared MgH2? NiCo/rGO sample can absorb 5.5 and 6.1 wt % hydrogen within 100 and 350 s, respectively, at 300 °C under 0.9 MPa H2 pressure. Further cyclic kinetics investigation indicates that MgH2? NiCo/rGO nanocomposites have excellent cycle stability. 相似文献
194.
Hao Chen Yongchang Liu Zesheng Yan Yanli Li Lifang Zhang 《Applied Physics A: Materials Science & Processing》2010,98(1):211-217
The three cooling rates of 10, 100, 200 K/min dilatometry experiments are used to investigate the kinetics of the isochronal
austenite (γ) to ferrite (α) transformation of Fe–0.0036wt.%C alloy. “Normal transformation” and “abnormal transformation” have both been observed for
transformations at different cooling rates. In accordance with the thermodynamic characteristics of the γ→α transformation investigated here and previous kinetic considerations, a JMAK-like approach for the kinetics of isochronal
phase transformations was developed that incorporates three overlapping processes: site saturation nucleation, alternate growth
modes (from interface-controlled to diffusion-controlled to interface-controlled growth), as well as impingement for random
distribution nuclei. The JMAK-like approach has been employed to fit the experimental results, and the fitting results show
that for the γ→α transformation of the Fe–C alloy at all applied cooling rates, the growth mode evolves in the corresponding order: from interface-controlled
to diffusion-controlled growth; from interface-controlled to diffusion-controlled to interface-controlled growth; and interface-controlled
growth. 相似文献
195.
Jianguo Liu Tee Hiang Cheng Yong kee Yeo Yixin Wang Lifang Xue Dawei Wang Xiaojun Yu 《Optics Communications》2008,281(21):5415-5419
The idler is separated from the co-propagating pump in a degenerate four-wave mixing (DFWM) with a symmetrical parametric loop mirror (PALM), which is composed of two identical SOAs and a 70 m highly-nonlinear photonic crystal fiber (HN-PCF). The signal and pump are coupled into the symmetrical PALM from different ports, respectively. After the DFWM based wavelength conversion (WC) in the clockwise and anticlockwise, the idler exits from the signal port, while the pump outputs from its input port. Therefore, the pump is effectively suppressed in the idler channel without a high-speed tunable filter. Contrast to a traditional PALM, the DFWM based conversion efficiency is increased greatly, and the functions of the amplification and the WC are integrated in the smart SOA and HN-PCF PALM. 相似文献
196.
根据矩阵分解性质及原子间的乘积关系,首先探究了单位上三角非负矩阵的原子因式分解性质,然后给出了任意单位上三角非负矩阵A的最小原子因式分解长度l(A)的计算公式,并得到了A具有最小的原子因式分解长度的其中一种分解,从而完善了相关文献中的结果. 相似文献
197.
In this paper, the authors study the boundedness of the operator [μΩ, b], the commutator generated by a function b ∈ Lipβ(Rn)(0 <β≤ 1) and the Marcinkiewicz integrals μΩ, on the classical Hardy spaces and the Herz-type Hardy spaces in the case Ω∈ Lipα(Sn-1)(0 <α≤ 1). 相似文献
198.
铽-钛铁试剂络合物荧光猝灭法测定磷酸盐 总被引:4,自引:0,他引:4
研究Tb3 + 钛铁试剂 (TR)络合物荧光猝灭法测定无机磷酸盐的新方法 ,并讨论采用荧光光谱法测定时的最佳条件 :pH 6 .9六次甲基四胺 HCl缓冲溶液 ,1.2× 10 -6mol/LTb3 + ,4 .0× 10 -6mol/LTiron ,λex=317nm ,λem=5 4 6nm。该方法简便 ,灵敏度高 ,线性范围为 0 .0 0 5~ 30mg/L ,检测限为 4 .1μg/L。直接用于尿样中无机磷酸盐的加入回收测定 ,标准加入回收率为 93%~ 98% ,相对标准偏差为 3.5 %。 相似文献
199.
Fujun Zhang Zheng Xu Xiaojun Liu Suling Zhao Lifang Lu Yongsheng Wang Xurong Xu 《Superlattices and Microstructures》2009,45(6):612-617
Pentacene (C22H14) thin films with different thicknesses were fabricated to study the dynamic growth process and morphology of pentacene on different substrates. A discontinuous monomolecular layer was observed when a pentacene thin film is about 0.5 nm thick on native oxide silicon wafer. The terraced islands and dendritic structure gradually formed with increasing pentacene thin film thickness. The height of each layer is about 1.4 nm which corresponds well with the length of the long axis of the pentacene molecule at 1.45 nm. Experimental results show that the pentacene molecule is perpendicular to the silicon wafer surface with a slight tilted angle. However, the pentacene molecular orientation on a polymer pre-covered indium tin oxide coated substrate could not give any indication on the scale of nanometers. The surface roughness of substrates strongly influences pentacene molecular diffusion and the morphology of pentacene thin films. 相似文献
200.