11-钨硼酸钾的结构和振动光谱研究

标题化合物K₈H(BW₁₁O₃₉)·13H₂O属立方晶系,空间群P43m,a=10.710(1)Å,V=1228.58ų,Z=1;D_O=4.39g·cm^-3,D_c=4.42g·cm^-3。(BW₁₁O₃₉^9-离子属于不饱和α-Keggin型结构,B原子位于O₂四面体的中心。测定并研究了化合物的IR和Raman光谱性质。     

天然水晶与水热法合成水晶的近红外光谱对比分析

水热法合成水晶与天然水晶的物理化学性质相似、内含物少见,常规检测方法无法鉴别。本论文采用德国布鲁克(Bruker)TENSOR27红外光谱仪测试分析,发现合成无色水晶以3585cm~(-1)谱带为特征;烟水晶特征吸收峰在3300~3000cm~(-1)附近,而合成烟水晶位于3600~3300cm~(-1)附近;合成黄水晶仅有5200cm~(-1)吸收峰,黄水晶不具有此特征吸收;紫水晶具有5228cm~(-1)、4450cm~(-1)特征谱带,合成紫水晶在4000~3000cm~(-1)内有特征吸收峰;合成绿水晶仅有5200cm~(-1)吸收峰。     

Quantum chemistry studies of adenosine 2503 methylation by S‐adenosylmethionine‐dependent enzymes

Ribosome methylation is important for life processes and is mainly catalyzed by radical S‐Adenosylmethionine (SAM) enzymes. Two SAM molecules serve as the cofactor by providing the 5 ′‐deoxyadenosyl radical for substrate activation and the methyl. Recently, Booker and coworkers (Science 2011, 332, 604) proposed an alternative mechanism for a pair of radical SAM enzymes, RlmN and Cfr, which respectively methylate the C2 and C8 of adenosine 2503. Their deuterium labeling experiments reveal that methyl group does not transfer directly from SAM to adenosine, instead it passes to Cys³⁵⁵ first, then onto adenosine. In this article, this new reaction mechanism is studied using density functional theory with B3LYP hybrid functional. The reaction system is simulated using small model compounds in the gas phase, and the protein environment is approximated using polarizable continuum model. The structures of the transition states and the intermediates are identified, and their free energies are calculated. The activation barriers indicate that the proposed reaction mechanism is plausible. The formation of a disulfide bond is found to be the rate‐limiting step. © 2012 Wiley Periodicals, Inc.     

天然水晶和水热法合成水晶的拉曼光谱分析

水热法合成水晶是依据天然水晶的物理化学性质并模拟其形成环境制得,常规检测方法无法鉴别。本论文采用法国(HORIBA Jobin Yvon)OLYMPUS BX41激光拉曼仪测试分析,并对天然水晶与水热法合成水晶拉曼谱466 cm~(-1)谱峰进行高斯线性拟合,发现水晶半高宽均大于6.5 cm~(-1),而合成水晶半高宽均小于6.5 cm~(-1)。拉曼光谱半高宽值的差异可对天然水晶和水热法合成水晶的鉴别提供依据。     

与下雨相关的几个力学问题

1 雨滴对伞的压力 雨中行进需撑伞挡雨，雨滴会对伞产生一个持续的压力，压力的大小与雨滴的质量、单位体积内雨滴的数量和雨滴的下落速度（大小和方向）有关．     

光干涉条纹图的中心线提取算法

本文针对光干涉条纹图的特点,以近年来采用的多种方法为基础,找出了提取条纹中心线的“探索数”算法。分析和实验表明,该算法实现速度快,处理精度好,自动化程度高。本文介绍了该算法处理云纹图和全息图的实例。     

显微拉曼光谱在宝石鉴定中的应用

探讨了用显微共焦拉曼光谱仪鉴定宝石的可行性、可靠性。结果表明,根据对宝石本体的拉曼测量很容易识别真假宝石。而用显微共焦系统对微小包裹的测量可提供宝石是天然或人造的信息,甚至可追踪天然宝石的产地。我们还注意到,与拉曼谱同时记录到的光荧光谱也是有关样品的珍贵信息,有时也可据此判明宝石是天然的还是人工合成的     

Correction to: First-principles study on the Jahn-Teller distortion in trigonal bipyramidal coordinated LiFe1−xMxBO3 (M=Mn,Co, and Ni) compounds

The development of new cathode materials with high capacity, good stability, and high safety is important for the future improvement of Li batteries. LiFeBO₃ is considered to be a type of promising electrode materials for Li-ion batteries due to its low cost, high theoretical capacity of 220 mAh/g (about 30% larger than that of LiFePO₄), low toxicity, and small volume change of 2% during the Li⁺ reversible extraction/insertion process. However, its electronic conductivity and rate performance still need further improvement. To optimize the performance of the LiFeBO₃, Mn, Cr, and Ni doping at Fe site have been studied experimentally, while the effect of minor addition of 3d transition metals on the electronic structure of LiFeBO₃ is rarely investigated. Thus, density functional theory calculations corrected by on-site Coulomb interactions have been conducted to study the crystal structure and electronic property of the LiFe_1−xM_xBO₃ (M = Mn, Co, and Ni) electrode systems. The results indicate that the coordination geometry about Fe in LiFeBO₃ is a distorted trigonal bipyramid with a distortion which can be attributed to a Jahn-Teller effect. The band gap energy of LiFeBO₃ is calculated to be 3.40 eV, which is in reasonable agreement with the previously computed values. The doping at Fe site with Mn cannot reduce the distortion of Jahn-Teller effect, whereas Co doping intensifies Jahn-Teller distortion of the FeO₅ trigonal bipyramid in LiFeBO₃. Ni substitution is predicted to be able to introduce impurity levels, and the Jahn-Teller distortion degree of the trigonal bipyramid decreased from 11.9 of the FeO₅ to 8.7% of the NiO₅. Thus, Ni doping is expected to increase stability and the electronic conductivity of the LiFeBO₃ structure.

     

用GeoGebra描述运动

物理教学中经常会分析物体的运动,有些运动比较复杂,可以用GeoGebra模拟物体运动.