Breakdown potential modelling of austenitic stainless steel

The breakdown potential is a crucial factor in the study of pitting corrosion resistance of stainless steel. This work aims to demonstrate the advantage of different chemometric techniques to estimate the breakdown potential of austenitic stainless steel. In order to predict pitting corrosion behaviour of stainless steel, a total of 60 samples of this alloy were subjected to electrochemical tests varying chloride ion concentration, pH and temperature. The experimental values of the breakdown potential, in addition to the tested environmental factors, were used to construct the predictive models based on support vector machines and artificial neural networks. A multiple‐comparison study based on statistic tests was applied to determine the optimal configuration for each technique. According to the results, support vector machines became a suitable and reliable technique to be applied in the modelling of the breakdown potential of austenitic stainless steels. This technique outperformed the models based on artificial neural networks and provided a useful tool to compare the pitting corrosion resistance of stainless steel in different environmental conditions without recourse to polarization tests. Therefore, this model presented a relevant meaning in science and engineering applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Impact of different potentials on the structures and energies of clusters

Cluster studies have attracted much interest in the past decades because of their extraordinary properties. To describe the interaction between atoms or molecules and predict the energies and structures, potential functions are developed. However, different potentials generally produce different structures and energies for a cluster. To study the effect of potentials on the structure of a cluster, He clusters in the size range of 13-140 are investigated by Lennard-Jones (LJ), Pirani, and Hartree-Fock-dispersion individual damping (HFD-ID) potential with dynamic lattice searching (DLS) method. Potential function curves, cluster structures, bonds, and energies of the global minima are compared. The results show that cluster energies decrease with the values of the potential functions, the differences between structures depend upon the disagreements of the potentials, and the preferable motif of a cluster changes from icosahedron to decahedron with the increase of the derivative of the short-range part of the potentials.     

Can Enantioselectivity be Computed in Enthalpic Barrierless Reactions? The Case of CuI‐Catalyzed Cyclopropanation of Alkenes

An extensive computational study has been carried out on different catalytic systems for cyclopropanation reactions based on copper. Most DFT schemes used present drawbacks that preclude the calculation of accurate absolute kinetic properties (energy barriers) of such systems, excepting the M05 and M06 suites of density functionals. On the other hand, there is a wide range of DFT methods capable of reproducing relative energy values, which can be easily translated into selectivities. Most of the theoretical levels used tend to overestimate activation barriers, allowing the location of the transition state (TS) on the potential-energy surface (PES) of the most reactive systems, which are probably artifacts of the method. However, after a thorough analysis of the calculated PES, and the origin of the energy differences obtained for the different alkene approaches in chiral systems, it is found that energy differences are almost constant over a wide range of geometries covering the reaction channel zone in which the true TS on the Gibbs free-energy surface (GFES) lies. Therefore, many computational schemes can still be used confidently to explain and predict enantioselectivities in these systems.     

准经典轨线研究Li+HF(ν=0, j=0)→LiF+H反应动力学

基于Aguado等人拟合的APW势能面(PES), 运用准经典轨线(QCT)方法, 对反应Li+HF(ν=0, j=0)→LiF+H的动力学性质进行了计算. 主要研究了不同碰撞能条件下的反应截面、转动取向、产物散射角分布和竞争反应模式等. 结果表明, 该反应存在直接提取型和间接插入型两种反应模式, 在低能量下反应以间接插入反应模式为主, 能量大于200 meV时则以直接提取反应为主.     

金纳米粒子组装体系中偶联单分子层膜结构的SERS光谱表征与分析

通过分子自组装方法制备4,4′-二硫联吡啶(PySSPy)单分子膜修饰的金电极. 利用所形成的对巯基吡啶自组装单分子膜(SAMs)作为偶联层进行金纳米粒子有序膜的组装. 对该纳米粒子组装体系进行Raman光谱测定, 得到了具有良好信噪比的对巯基吡啶单分子膜的表面增强拉曼散射(SERS)光谱. 在此基础上, 进一步采用电化学现场SERS光谱技术研究了该纳米粒子组装体系的SERS光谱随电位变化的规律. 在该体系稳定的电位范围内表征对巯基吡啶单分子膜的特征谱峰1011与1093 cm^-1、1575与1610 cm^-1以及1206与1215 cm^-1这三对谱峰其强度随着所施加电位的改变呈现出明显的规律性. 分析表明, 偶联单分子层中吡啶环芳香性随着所施加电位的改变而有规律地变化是SERS光谱特征改变的内在原因.     

基于粗粒化模型对有机溶剂的分子动力学模拟

在基于Boltzmann分布对四种基本构象进行Monte Carlo取样后, 通过与全原子模型的范德华势比较得到了Gay-Berne (GB)参数. 又在对用量化计算得到的分子体系的电势进行电荷、偶极矩和四极矩的拟合后, 得到了电多极展开势(EMP)参数. 利用得到的粗粒化参数, 基于粗粒化模型, 对CHCl₃及四氢呋喃(THF)两种有机溶剂进行了分子动力学模拟(MDS), 并将结果同全原子模拟进行了比较. 计算结果表明用粗粒化模型从整体上能重复全原子模型的模拟结果, 但在某些细节的计算与全原子模型有偏差, 其原因可能是目前工作仅考虑了单位点情况, 为此今后在对具有复杂结构的分子进行粗粒化模拟时还应考虑合理放置及增加相互作用位点.     

不同粒径尿微晶的ζ电位、自相关曲线和聚集状态

采用纳米粒度仪和透射电子显微镜(TEM)比较研究了10例尿石症患者和10例健康对照者的尿液经不同孔径滤膜(0.22、0.45、1.2、3.0、10μm)过滤后,尿微晶平均粒径(d)、粒度分布、自相关曲线、ζ电位和聚集状态的变化。随着滤膜孔径由0.22μm增至10μm,患者尿微晶的d值由162 nm增至3 227 nm,自相关曲线平滑性变差,自相关时间(Ta)由1.92 ms增至2100 ms,ζ由-2.65 mV减小至-9.21 mV,TEM显示尿微晶尺寸差异大,部分尿微晶处于聚集状态。而对照者尿微晶的d值仅由187 nm增加至1 010 nm,自相关曲线平滑,Ta由1.40 ms增加至6.67 ms,ζ平均值由-5.22 mV减小至-6.89 mV,TEM显示尿微晶均匀分散,尺寸较小。上述结果表明:尿石患者的尿液体系不稳定,其尿微晶聚集程度高,导致尿石症形成的危险性增加。     

Ab initio Study of Mechanism of Cycloaddition Reaction between Germylene Silylene (H2GeSi:) and Acetone

The mechanism of the cycloaddition reaction between singlet germylene silylene (H₂GeSi:) and acetone has been investigated with CCSD(T)/6‐31G*//MP2/6‐31G* method. From the potential energy profile, we could predict that the reaction has two competitive dominant reaction channels. The present rule of this reaction is that the [2+2] cycloaddition reaction of the two (‐bonds in germylene silylene and acetone generates a four‐membered ring silylene with Ge. Because of the unsaturated property of Si atom in the four‐membered ring silylene with Ge, it could further react with acetone, resulting in the generation of a bis‐heterocyclic compound with Si and Ge. Simultaneously, the ring strain of the four‐membered ring silylene with Ge makes it isomerize to a twisted four‐membered ring product.     

丙烯腈废水中有机物的高压放电法降解机理

利用气相色谱-质谱探讨了丙烯腈废水中有机物的高压放电法降解机理.结果表明:丙烯腈的氰基首先被破坏生成丙烯酸,丙烯酸进一步被氧化生成乙酸,乙酸降解为甲酸,最后生成CO2.丁二腈首先降解为丁二酸,丁二酸再生成丙酸,并逐步降解为乙酸、甲酸,最后生成CO2.二氰乙基胺在降解过程中依次生成丙腈、丙酸、乙酸和甲酸,最后生成CO2....