掺铁铌酸锂晶体的光电导衰减特性研究

利用电化学分析仪对掺铁同成分铌酸锂晶体进行瞬态光电导研究. 以不同掺铁浓度铌酸锂晶体为样品, 在不同强度的纳秒级脉冲光照射下对光电导的研究发现: 铌酸锂晶体的瞬态光电导是由较为复杂的电子迁移过程形成, 其衰减可以用一个指数函数叠加一个扩展指数来拟合. 拟合参数与光强、掺铁浓度存在以下依赖关系: 入射光强增强时, 幅值σ₁^max、σ₂^max、时间常数τ₂和扩展因子β 值增大, 在光强增大到一定时, τ₂和β出现饱和; 晶体的掺铁浓度升高时, σ₁^max、σ₂^max、τ₂ 值增大, 而β值减小. 根据实验结果, 从理论上提出了光电子导带迁移伴随光电子在小极化子上跳跃迁移的复合电荷传输模型. 该模型较好地解释了掺铁同成分铌酸锂晶体的光电导的衰减特点.     

The bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes for polyethylene macromonomers

The synthesis of long‐chain branched polyethylene includes the generation of vinyl‐terminated polyethylene macromonomers and the copolymerization of these macromonomers with ethylene. Four new bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes 1a–b, 2a–b were prepared and showed high activities for ethylene homopolymerization upon the activation of methylaluminoxane. The steric bulk of bridged substituent has a profound effect on the catalytic activity as well as on the molecular weight of resulting polyethylene. Complex 1b showed the highest activity of up to 5.32 × 10⁶ g PE/(mol Zr h) for ethylene homopolymerization at 70 °C, which was higher than that of Cp₂ZrCl₂. The polyethylenes produced with complexes 1a–d/MAO are mostly vinyl‐terminated, possess low molecular weight and fit as macromonomers. The (p‐MePh)₂C‐bridged cyclopentadienyl indenyl zirconocene complex 1a could produce polyethylene macromonomer with selectivity for the vinyl‐terminal as high as 94.9%. Copyright © 2010 John Wiley & Sons, Ltd.     

Construction of 3-aryl-1,2,4-benzotriazines via unprecedented rearrangement of bis(benzotriazol-1-yl)methylarenes

3-Aryl-1,2,4-benzotriazines were formed unexpectedly by the treatment of 1,l-bis(benzotriazol-1-yl)methylarenes with allylsamarium bromide. A radical pathway was proposed involving steps, such as fragmentation, ring-opening, and cyclization.     

线上线下混合式-六环节实验教学实践与探索——以化学生物学实验"基于生物正交反应的蛋白质标记"为例

化学生物学综合实验是针对化学生物学专业高年级本科生开设的一门衔接本科-硕士教学的综合性实验课程。本文以“基于生物正交反应的蛋白质标记”科研融合型实验为例,结合化学生物学学科特点,将实验教学内容模块化,探索设计线上线下混合式-六环节教学方式,应用于本科生综合实验教学。经实践取得良好的教学效果,为综合型实验课程教学提供了参考与借鉴。     

具有智能评阅功能的在线有机化学习题平台:ACE: Organic简介及其在教学中的应用*

ACE: Organic(Achieving Chemistry Excellence: Organic Chemistry)是具有智能反馈功能的在线有机化学习题平台。学生利用系统中的画图软件在线完成每个练习题后,平台会判断学生的回答是否正确,即时给出评价与提示,引导学生找到解决问题的思路。对于复杂的机理与合成题,ACE可以接受多种合理的回答。教师可以通过查看平台的统计数据,随时了解学生对知识点的掌握情况。ACE设有论坛,便于教师和学生互动。教学实践证明,ACE的开放有效地提高了学生对有机化学的学习兴趣,培养了学生严谨的科学态度。     

The precise time-dependent solution of the Fokker–Planck equation with anomalous diffusion

We study the time behavior of the Fokker–Planck equation in Zwanzig’s rule (the backward-Ito’s rule) based on the Langevin equation of Brownian motion with an anomalous diffusion in a complex medium. The diffusion coefficient is a function in momentum space and follows a generalized fluctuation–dissipation relation. We obtain the precise time-dependent analytical solution of the Fokker–Planck equation and at long time the solution approaches to a stationary power-law distribution in nonextensive statistics. As a test, numerically we have demonstrated the accuracy and validity of the time-dependent solution.     

Ti/HfO2/Pt阻变存储单元中的氧空位聚簇分布

为了研究阻变存储器导电细丝的形成位置和分布规律, 使用X射线光电子能谱研究了Ti/HfO₂/Pt阻变存储器件单元中Hf 4f的空间分布, 得到了阻变层的微结构信息. 通过I-V测试, 得到该器件单元具有典型的阻变特性; 通过针对Hf 4f的不同深度测试, 发现处于低阻态时, 随着深度的增加, Hf⁴⁺化学组分单调地减小; 而处于高阻态和未施加电压前, 该组分呈现波动分布; 通过Hf⁴⁺在高阻态和低阻态下组分含量以及电子能损失谱分析, 得到高阻态下Hf⁴⁺组分的平均含量要高于低阻态; 另外, 高阻态和低阻态下的O 1s谱随深度的演变也验证了Hf⁴⁺的变化规律. 根据实验结果, 提出了局域分布的氧空位聚簇可能是造成这一现象的原因. 空位簇间的链接和断裂决定了导电细丝的形成和消失. 由于导电细丝容易在氧空位缺陷聚簇的地方首先形成, 这一研究为导电细丝的发生位置提供了参考.     

过载条件下颗粒在液氧输送管内的加速特性研究

应用固体颗粒在液体介质中的沉降理论及ANSYS Fluent的离散相模型(DPM),开展了过载条件下固体颗粒在长距离液氧输送管内的流速特性分析,数值研究了不同颗粒直径、不同过载条件的颗粒加速特性,得到了以下结论:在过载条件下,固体颗粒在长距离液氧输送管内的流体阻力主要是压差阻力,该压差阻力使得颗粒在输送管内的加速特性并不明显。计算表明:对于5mm直径的固体颗粒,在5g过载条件下,颗粒相对液氧的沉降末速略高于1m/s。     

Nitrogen‐Enriched Fe3O4@Carbon Nanospheres Derived from Fe3O4@3‐Aminophenol/Formaldehyde Resin Nanospheres Based on a Facile Hydrothermal Strategy: Towards a Robust Catalyst Scaffold for Platinum Nanocrystals

Robust nitrogen‐enriched Fe₃O₄@carbon nanospheres have been fabricated as a catalyst scaffold for Pt nanoparticles. In this work, core–shell Fe₃O₄@3‐aminophenol/formaldehyde (APF) nanocomposites were first synthesized by a simple hydrothermal method, and subsequently carbonized to Fe₃O₄@N‐Carbon nanospheres for in situ growth of Pt nanocrystals. Abundant amine groups were distributed uniformly onto Fe₃O₄@N‐Carbon nanospheres, which not only improved the dispersity and stability of the Pt nanocrystals, but also endowed the Pt‐based catalysts with good compatibility in organic solvents. The dense three‐dimensional cross‐linked carbon shell protects the Fe₃O₄ cores against damage from harsh chemical environments, even in aqueous HCl (up to 1.0 m ) or NaOH (up to 1.0 m ) solutions under ultrasonication for 24 hours, which indicates that it can be used as a robust catalyst scaffold. In the reduction of nitrobenzene compounds, the Fe₃O₄@N‐Carbon@Pt nanocatalysts show outstanding catalytic activity, stability, and recoverability.