关键词： hydroformylation   propene   rhodium   cyclohexyl diphenylphosphine   kinetic modeling  

摘要： Hydroformylation of propene to isobutyraldehyde and n-butyraldehyde was studied in the kinetic regime in a semibatch stainless steel reactor at 85-115 degrees C and 115 bar pressure in 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate solvent with rhodium catalyst cyclohexyl diphenylphosphine as a ligand, which showed lower normal/isometric aldehyde ratio (n/i) than previously studied triphenylphosphine. The rate was pressure and Rh concentration dependent. The regioselectivity was conversion independent;however, dependent on the ligand concentration, as higher ligand concentration promoted isobutyraldehyde formation. The influence of ligand concentration on regioselectivity was investigated. A kinetic model was proposed based on the mechanism of alkene hydroformylation and compared with experimental observations. Numerical data fitting was performed showing good agreement of reaction rates and regioselectivity with experimental data. (C) 2011 American Institute of Chemical Engineers AIChE J, 2012

关键词： Bangham's equation   Endothermic   Film diffusion   Pseudo second-order model  

摘要： Biosorption potential of Cedrus deodara sawdust (CDS) in terms of sorption of Zn(II) ion across liquid phase has been evaluated in the present investigation. The surface of the CDS biomass before the sorption of Zn(II) ions seemed to be more porous, non-crystalline and heterogeneous. The maximum uptake capacity of CDS was 97.39?mg?g-1. Sorption of Zn(II) ion on the surface of CDS sawdust was maximum at pH 5, temperature 45 degrees C, initial concentration of Zn(II) ion 100?mg?L-1, biomass dose 1?g?L-1, contact time 150?min, and agitation rate 160?rpm. Pseudo second-order kinetics with the highest linear regression coefficient (R2?=?0.99), and lowest values of error functions, i.e., chi (?2) and sum of square errors (SSE) against pseudo first-order rate kinetics showed that the sorption of Zn(II) ion on the surface of CDS was mediated by chemosoprtive forces of attraction rather than physical adsorption. Mechanistically, relatively higher proportion of sorption of Zn(II) ion in early phase of contact time was profoundly explained by Bangham's equation and film diffusivity (Df). Intraparticle or pore diffusion (Dp) of Zn(II) ion inside the pores of CDS was rate limiting step at the later stage of contact time. Furthermore, the thermodynamic study on sorption of metal ion delineated the fact that the Zn(II) sorption on the surface of CDS was spontaneous, endothermic together with increased entropy at solid liquid interface.

关键词： proton transport   quanta   Fragments   Molecular Dynamics  

摘要： We show that the hybrid quantum mechanical/effective fragment potential (QM/EFP) can be a very effective and practical quantum mechanical molecular dynamics method, when it is properly combined with well-developed traditional molecular dynamics (MD) techniques. QM/EFP-MD simulations on intra-molecular proton transfer of glycine with 290 EFP waters yielded accurate free energy change and reaction barrier of the zwitterion -> neutral form conversion. Water rearrangements turned out to be the main driving force of the proton transfer. (C) 2012 Elsevier B. V. All rights reserved.

关键词： Microscopy, Atomic Force   Models, Molecular   Molecular Dynamics Simulation   Protein Conformation   Protein Folding   Proteins/chemistry  

摘要： Protein structure is highly diverse when considering a wide range of protein types, helping to give rise to the multitude of functions that proteins perform. In particular, certain proteins are known to adopt a knotted or slipknotted fold. How such proteins undergo mechanical unfolding was investigated utilizing a combination of single molecule atomic force microscopy (AFM), protein engineering, and steered molecular dynamics (SMD) simulations to show the mechanical unfolding mechanism of the slipknotted protein AFV3-109. Our results reveal that the mechanical unfolding of AFV3-109 can proceed via multiple parallel unfolding pathways that all cause the protein slipknot to untie and the polypeptide chain to completely extend. These distinct unfolding pathways proceed via either a two- or three-state unfolding process involving the formation of a well-defined, stable intermediate state. SMD simulations predict the same contour length increments for different unfolding pathways as single molecule AFM results, thus providing a plausible molecular mechanism for the mechanical unfolding of AFV3-109. These SMD simulations also reveal that two-state unfolding is initiated from both the N- and C-termini, while three-state unfolding is initiated only from the C-terminus. In both pathways, the protein slipknot was untied during unfolding, and no tightened slipknot conformation was observed. Detailed analysis revealed that interactions between key structural elements lock the knotting loop in place, preventing it from shrinking and the formation of a tightened slipknot conformation. Our results demonstrate the bifurcation of the mechanical unfolding pathway of AFV3-109 and point to the generality of a kinetic partitioning mechanism for protein folding/unfolding.

关键词： Thermoelectric materials   Molecular dynamics   Mechanical properties   Skutterudites   Vacancy defect  

摘要： The present work has investigated the tensile mechanical behavior of the skutterudite CoSb3 single-crystal in the presence of antimony vacancies, since the antimony atoms in CoSb3 are active and are usually easy to lose in practice. The molecular dynamics simulation method is employed. The vacancy atoms, whose fraction is limited up to 5%, are chosen randomly. The virtual uniaxial tension is carried out by strain controlling along a principal crystallographic direction at 300 K. The specimens with vacancies show similar stress-strain response features to there of the perfect crystal. However, the effective Young's modulus decreases linearly with the increase of the vacancy content, and the ultimate strength drops substantially from no vacancy to even a small vacancy fraction. Temperature dependence of the simulation results is also considered. Both Young's modulus and the ultimate strength exhibit an approximately linear reduction with increasing temperature for a specific vacancy fraction, and moreover, the reduction rate is comparable for different vacancy fractions. The Vacancy distribution effect is briefly discussed as well. As the vacancy concentration becomes uniform, the ultimate strength of the material would be promoted significantly. (C) 2012 Elsevier B.V. All rights reserved.

关键词： force microscopy   Markov models   RNA folding  

摘要： An RNA kissing loop from the Moloney murine leukemia virus (MMLV) exhibits unusual mechanical stability despite having only two intermolecular base pairs. Mutations at this junction have been shown to destabilize genome dimerization, with concomitant reductions in viral packaging efficiency and infectivity. Optical tweezers experiments have shown that it requires as much force to break the MMLV kissing-loop complex as is required to unfold an 11-bp RNA hairpin [Li PTX, Bustamante C, Tinoco I (2006) Proc Natl Acad Sci USA 103:15847-15852]. Using nonequilibrium all-atom molecular dynamics simulations, we have developed a detailed model for the kinetic intermediates of the force-induced dissociation of the MMLV dimerization initiation site kissing loop. Two hundred and eight dissociation events were simulated (approximately 16 mu s total simulation time) under conditions of constant applied external force, which we use to construct a Markov state model for kissing-loop dissociation. We find that the complex undergoes a conformational rearrangement, which allows for equal distribution of the applied force among all of the intermolecular hydrogen bonds, which is intrinsically more stable than the sequential unzipping of an ordinary hairpin. Stacking interactions with adjacent, unpaired loop adenines further stabilize the complex by increasing the repair rate of partially broken H-bonds. These stacking interactions are prominently featured in the transition state, which requires additional coordinates orthogonal to the end-to-end extension to be uniquely identified. We propose that these stabilizing features explain the unusual stability of other retroviral kissing-loop complexes such as the HIV dimerization site.

关键词： 间苯二酚缩水甘油醚   间苯二甲胺   热机械性能   固化动力学  

摘要： 利用热分析技术对具有高温快速固化性能的间苯二酚缩水甘油醚/间苯二甲胺体系的热机械性能和表观固化反应动力学进行了研究。热机械性能分析(DMA和TMA)结果表明,间苯二酚缩水甘油醚/间苯二甲胺固化产物的玻璃化转变温度为83℃,室温下储能模量为2600 MPa,玻璃态热膨胀系数(α1)为54.9×10-6℃-1,橡胶态的线性热膨胀系数(α2)为177.9×10-6℃-1。通过恒温和非恒温模式差示扫描量热(DSC)测试得到体系的表观反应活化能为62.7 kJ/mol,由此估算出固化反应在160℃时仅需数秒即可完成。

关键词： 路面机械   高等级   固定资产投资   项目总投资   建筑面积   江苏省  

摘要： 日前，江苏华通动力重工有限公司申报的高等级路面机械项目，经江苏省发改委工业发（2012）47号文批复核准建设。该项目总投资15560万美元，其中固定资产投资12585万美元；企业注册资本5188．8万美元．其中增资3820万美元，新增建筑面积15．8万平方米。

关键词： 农机总动力   BP神经网络   预测   农业机械  

摘要： 农业机械总动力是衡量农业机械化水平的一项重要指标。对河南省农业机械总动力进行预测,将为农业机械化部门制定合理的发展规划提供一定的理论支持,同时也为农机企业了解未来市场需求状况提供一定的参考。以1991-2010年间的河南省农业机械总动力统计数据为基础,利用BP神经网络建立了河南省农业机械总动力的预测模型。该模型采用3层BP神经网络,输入层、隐含层和输出层的神经元数目分别为5,13和1。隐含层和输出层的激励函数分别为正切型与对数型Sigmoid函数。采用分步预测的思想,利用自适应学习速率训练方法对该网络进行了训练,获得了该模型中各层之间的连接权值和各层神经元的阈值。利用该模型对现有数据进行了仿真预测,结果表明,该模型具有较高的预测精度。在此基础上,对河南省"十二五"期间的农业机械总动力进行了预测,并给出了预测数据。

关键词： 轮式移动2杆刚-柔机械手   逆动力学   有限元   频域   累计误差  

摘要： 针对轮式2杆刚-柔平面移动机械手逆动力学问题进行了系统研究。采用Pin-free边界条件,对机械手柔性构件进行了离散,采用有限元法分别构建了该移动机械手系统的完整正、逆动力学模型。在频域下,求解了系统驱动力(矩)和弹性构型变量,并在时域内对驱动力矩进行了修正,并对修正力矩和构型变量进行了累计误差分析。为了验证建模方法的有效,进行了大量数值仿真工作,仿真结果显示了其有效性和可行性。