Bonding and correlation analysis of various Si2CO isomers on the potential energy surface

At various levels of theory, singlet and triplet potential energy surfaces (PESs) of Si₂CO, which has been studied using matrix isolation infrared spectroscopy, are investigated in detail. A total of 30 isomers and 38 interconversion transition states are obtained at the B3LYP/6‐311G(d) level. At the higher CCSD(T)/6‐311+G(2d)//QCISD/6‐311G(2d)+ZPVE level, the global minimum ¹1 (0.0 kcal/mol) corresponds to a three‐membered ring singlet O‐cCSiSi (¹A′). On the singlet PES, the species ¹2 (0.2 kcal/mol) is a bent SiCSiO structure with a ¹A′ electronic state, followed by a three‐membered ring isomer Si‐cCSiO (¹A′) ¹3 (23.1 kcal/mol) and a linear SiCOSi ¹4 (¹Σ⁺) (38.6 kcal/mol). The isomers ¹1, ¹2, ¹3 , and ¹4 possess not only high thermodynamic stabilities, but also high kinetic stabilities. On the triplet PES, two isomers ³1 (³B₂) (18.8 kcal/mol) and ³7 (³A″) (23.3 kcal/mol) also have high thermodynamic and kinetic stabilities. The bonding natures of the relevant species are analyzed. The similarities and differences between C₃O, C₃S, SiC₂O, and SiC₂S are discussed. The present results are also expected to be useful for understanding the initial growing step of the CO‐doped Si vaporization processes. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Theoretical study on reaction mechanism of isocyanate radical NCO with ethene

The NCO + C₂H₄ reaction is simple and prototype for reaction of the NCO radical with unsaturated hydrocarbons, and it is considered to be important in fuel‐rich combustion. In this article, we for the first time perform detailed theoretical investigations for its reaction mechanism based on Gaussian‐3//B3LYP scheme covering various entrance and decomposition channels. The most favorable channel is firstly the NCO and C₂H₄ approach each other, forming a weakly‐bound complex L1 OCN···C₂H₄, followed by the formation of isomer L2 OCNCH₂CH₂ via a small barrier of 1.3 kcal/mol. Transition states of any decomposable or isomeric channels for L2 in energy are much higher than reactants, which indicate that adduct L2 has stabilization effect in this NCO + C₂H₄ reaction. The direct H‐abstraction channel leading to P1 HNCO + C₂H₃, might have an important contribution to the eventual products in high temperature. These results can well explain available kinetic experiment. Moreover, reaction mechanism for the title reaction is significantly different from the NCO + C₂H₂ reaction which proceeds on most favorably to generate the products HCN + HCCO and OCCHCN + H via a four‐membered ring intermediate. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Effectiveness of Phosphate Groups in Noncovalent Interactions in Binary Adenosine Nucleotides/Phosphoserine Aqueous Systems

Adduct formation in binary systems of O-phospho-L-serine (Ser-P) with adenosine 5′-monophosphate (AMP), adenosine 5′-diphosphate (ADP) and adenosine 5′-triphosphate (ATP), has been investigated. This study was performed in aqueous solutions using a potentiometric method with computer analysis of the data, together with ¹³C and ³¹P NMR spectroscopic measurements. The overall stability constants of the adducts and the equilibrium constants for their formation have been determined. Ion-dipole and ion-ion interactions have been established to occur in the identified noncovalent complexes. An analysis of the equilibrium constants of the reaction has allowed the determination of the effectiveness of the phosphate groups and donor atoms of heterocyclic rings for molecular complex formation. The potential reaction centers are the atoms N(1) and N(7) from the purine base, the phosphate group of the nucleotides, and the phosphate, carboxyl and amine groups from phosphorylated serine. Sites for the interactions in the bioligands have been found on the basis of an equilibrium constant study and an analysis of the changes in the signal positions of their NMR spectra.     

Ferrocenyl pyrazolines: Preparation, structure, redox properties and DFT study on regioselective ring-closure

Cyclocondensation of 1-phenyl-3-ferrocenyl-2-propen-1-one (1) with RNHNH2 hydrazines and the substituent-dependent product distribution were investigated. With methylhydrazine, formation of two regioisomeric pairs of pyrazolines and pyrazoles was observed. The ratio of the products varied with the solvent and temperature. Transformation of 5-ferrocenyl-N-substituted pyrazolines into pyrazoles was systematically studied and DDQ was found to be the most suitable reagent. Mechanism of the cyclization reactions taking place under kinetic- and thermodynamic controls was supported with DFT calculations. The energy-dependence of the transformation of pyrazoline to pyrazole was investigated also by EI MS. Structure determination of the new compounds was performed by IR, MS and NMR methods including 2D-HMQC, 2D-HMBC, DEPT and DIFFNOE measurements. For two compounds structures were also proved by X-ray diffraction.     

镁带表面黑灰色薄膜组成分析

对牡丹牌镁带(43 mm×3 mm)表面黑灰色薄膜进行了X射线衍射分析,结果表明牡丹牌镁带表面黑灰色薄膜组成是Mg(OH)2和Mg,并以此实验研究结果为基础,对镁带表面黑灰色薄膜形成、显色机理做了理论分析,模拟实验结果进一步验证了理论分析。     

Experimental analysis of a stochastic model for estimating wind-borne compact debris trajectory in turbulent winds

The impact of flying debris against building envelopes during high winds is a major source of structural damage. For example, damage produced by Hurricanes Katrina and Ike in the United States on the facades of tall buildings, located in urban areas, has been documented. It is therefore of relevance to analyze the vulnerability of tall buildings to debris-induced non-structural damage in the general context of performance-based wind engineering. In order to analyze the random trajectory of debris in highly turbulent winds, a numerical model combined with a probability-based algorithm was recently proposed by the authors (Moghim and Caracoglia, 2013). This model investigates the trajectory of “compact debris”, defined as point-mass objects of negligible mass moments of inertia and for which the aerodynamics is predominantly controlled by the drag force. The model replicates both the inherent randomness in debris properties and the effect of wind shear and atmospheric turbulence to estimate debris trajectory and the likelihood of impact against vertical building facades in a probabilistic setting.This paper describes the comparison between numerical model results and wind tunnel experiments. Tests were carried out in the Northeastern University׳s small scale wind tunnel in both smooth flow and grid-generated turbulent flow. The motion of spheres and cubes, simulating compact debris objects, was investigated in two dimensions (2D) on a vertical plane.The 2D motion of compact objects of various sizes was captured by a high-speed digital camera at different flow speeds. Experimental results showed to be consistent with numerical simulations. They also confirmed that not only mean flow speed but also turbulence features can have a non-negligible effect on the trajectory of compact objects.     

硅桥调控的聚茂钒体系电子结构和输运性质

利用密度泛函理论和非平衡格林函数的方法对硅桥调控后的聚茂钒体系（[V（Cp）₂（SiH₂）_n]_m（n=1（a）,n=2（b）,n=3（c）;m=∞;Cp=环戊二烯基））的电子结构和输运性质进行了研究。研究结果表明：随着硅桥的增长,V-V的铁磁性耦合变弱而反铁磁性耦合增强。a和b证实为铁磁性基态,而c更倾向为反铁磁性基态。a和b的铁磁性基态中的每个钒原子的磁距为3.0μ_B,超过钒-苯络合物或者纯聚茂钒体系的3倍。a-c的输运性质同它们的电子结构相一致,导电性变化规律为c > b > a。对于a和b,自旋向下状态的导电性略强于自旋向上状态。a和c都发生了明显的负微分电阻效应而b却没有,这主要是由于两个二茂钒的排列取向不同：a和c（SiH₂为奇数）中二茂钒呈V-型取向排列,进而导致了类似于离子键的量子点耦合,而b（SiH₂是偶数）中二茂钒是平行-型取向排列,从而导致了类似于共价键的量子点耦合。此外,由于散射区和两个电极之间的不对称耦合,a-c的导电性对电压施加方向较敏感。     

高校公共就业服务个人自愿供给对就业水平影响机理的实证研究

“多中心治理”框架下完善的公共就业服务体系应该是政府供给、市场供给和自愿供给的有效融合,公共就业服务自愿供给机制能否有效弥补政府供给和市场供给的相对不足。文章构建了公共就业服务个人自愿供给影响就业的逻辑回归模型,基于4所高校3336份问卷调查的实际数据进行了实证检验,实证结果表明,无论是基于个体自选择信息还是利用个体志愿者多维行为特征的整合来确定个体志愿者的身份,大学生公共就业服务自愿供给均对就业产生显著正向影响,而且不同类型的公共就业服务自愿供给对就业影响存在显著差异,提供就业信息、传授求职经验、介绍面试技巧3类自愿供给服务对就业影响最显著,而介绍简历制作技巧类自愿供给对提升就业无影响。     

纵向涡发生器强化传热的研究历程及进展

首先简要回顾了纵向涡发生器的发展历程,对前人进行的关于纵向涡发生器的实验研究和数值分析进行了归纳分析,并运用场协同原理对纵向涡强化换热的机理进行了初步分析。最终得出结论,对以后纵向涡发生器的发展和研究给出具体意见,认为系统地了解纵向涡发生器各种各样的几何参数对换热和压降的影响,对于将纵向涡发生器成功地用于紧凑式换热器是非常重要的。