关键词： REACTION mechanisms (Chemistry)   SUBSTITUTION reactions   MACROMOLECULES   PHENOL   NUCLEOPHILIC reactions   QUANTUM theory   MOLECULAR dynamics   SIMULATION methods & models  

摘要： A combination of molecular dynamics simulations and quantum chemistry calculations affords a good understanding of the reaction between [NPCl2](n), and the bifunctional nucleophile aminophenol HO-C6H4-NH2 in THF solution and in the presence of alkali carbonates. This reaction is regiospecific at room temperature favoring the attack by the NH2 group, and only at higher temperatures the attack by the OH is activated. It is also explained why the reaction of HO-C6H4-NH2 with {[NP(O2C12H8)](1-x)[NPCl2](x)}(n) and Cs2CO3 at reflux proceeds exclusively by the OH giving aryloxyphosphazenes with terminal NH2 substituents. Molecular dynamics simulations have been performed on model systems consisting on [NPCl2](n) chains surrounded by aminophenol molecules or ions obtained by deprotonation of either the OH or NH2 groups. Quantum mechanics calculations consisted in density functional theory (DFT) computation of the reaction mechanism of aminophenol with the phosphoranimine (NH2)Cl2P(= NH) as a simple model for the NPCl2 phosphazene units, using B3LYP approximation with 6-31G(d). Our results provide evidence to support that the macromolecular substitution reactions of poly(dichlorophosphazene) with aryloxide ions are diffusion controlled and governed by the atomic charges, while the reaction with amino-arenes are directed by hydrogen interactions between the NH, hydrogens and the phosphazene nitrogen atoms that initiate a lower activation energy stepwise mechanism competing with a concerted mechanism. The combined methodology employed in this work seems to be useful to address the regiochemistry of the macromolecular substitution on polyphosphazenes with heterobifunctional nucleophiles which is a central issue in the design of polymers with predetermined chemical composition and structure.

关键词： OXIDATION   THIOCYANATES   HYDROGEN-ion concentration   CHEMICAL kinetics   CHEMICAL reactors   TEMPERATURE effect   SULFATES   AMMONIUM  

摘要： The wet oxidation of thiocyanate has been investigated in a I-L semibatch reactor at temperatures in the range of 438.15-468.15 K and total pressures between 2.0 x 10(3) kPa and 8.1 x 10(3) kPa. The initial pH value of the reaction media was varied between pH 2 and pH 12 and was found to be a key parameter in the rate of thiocyanate degradation. The evolution of concentration of substrate and products (sulfate and ammonium) were analyzed. Based on the experimental data and bibliography information, a kinetic model was obtained and, here, possible pathways, depending on the initial pH of the media, are suggested for thiocyanate oxidation.

关键词： Foams  

摘要： Heterogeneous materials usually break through a process of microcracking that eventually leads to final rupture after accumulation and coalescence of many microcracks. The statistical properties of microcracking rupture have been known to resemble critical point statistics, with many of the physical quantities obeying power law distributions. However, there is no clear understanding of the origin of these distributions and of the specific values observed for the power law exponents. In this paper, we review the special case of polymeric foams that have the advantage of containing a single material component, the polymer, as opposed to usual heterogeneous materials such as composites. First, we briefly review the typical features of the polymeric foam mechanical response up to rupture that have been widely studied previously. Then, we focus on a less well-known aspect: the rupture dynamics of polymeric foams. We not only show that polymeric foams behave like other heterogeneous materials, i.e. they display power law statistics, but we are also able to test the effect on the power laws of the following properties: the foam heterogeneity by changing its density, the foam mechanical response by changing its temperature and the mechanical history by comparing creep tests and tensile tests.

关键词： 农业劳动力   膳食能量   农业机械化   协整分析   江苏省  

摘要： 本文采用江苏省1983～2007年的数据,运用协整和误差修正模型,对农业劳动力人均膳食能量节省与人均农机动力水平之间的关系进行实证研究。结果表明:农业劳动力人均膳食能量节省与人均农机动力之间存在长期均衡关系,无论是长期还是短期,提高人均农机动力水平对增加人均膳食能量节省都有明显的正效应;短期内人均农机动力变化是人均膳食能量节省的Granger原因;农业机械化水平的提高可能还导致了农民膳食能量结构的变化。

关键词： 高速并联机械手   弹性构件   弹性动力学   动应力   固有频率  

摘要： 采用有限元方法建立了一种新型两自由度平动并联机械手的弹性动力学模型.在该模型的基础上,分析了机械手在工作空间的前四阶固有频率的分布情况,研究了在外力和刚体惯性力激励下机械手动平台的位置误差,给出了构件在各个时刻的最大动应力及其出现的位置.结果表明:系统的固有频率与其位形有关,机械手动平台的位置误差主要由高速运动时的刚体惯性力引起,机械手各个柔性构件的动应力谱是变幅应力谱.

关键词： 滤清器   工程机械   发动机维修   安全   全球气候变暖   排放质量   环境保护   燃油利用率  

摘要： 由于全球气候变暖、环境保护等原因,节能、排放和NVH(噪声、振动与平稳)等日益成为影响汽车工业的主要话题。如何提高燃油利用率,如何提高废气排放质量,如何延长发动机维修和更换周期等等,这些都离不开高质量的滤清器——因为,滤清器就是发动机最近距离的保护神。

关键词： topoisomerase I   molecular dynamics   Go-like model   motional characteristics   stretching  

摘要： A coarse grained molecular dynamics model with an implicit solvent is used to elucidate properties of the human topoisomerase I. The model is defined through the native structure and it allows covering significantly longer time scales than in all atom simulations. Single residue and double residue motional characteristics are studied. The results are consistent with all atom simulations reported in the literature indicating usefulness of the model in further studies of this protein. Novel findings include broadening of the description of the dynamic behavior of the lip and hinge regions and a characterization of the motional properties of the RRM binding site of the enzyme. We also consider mechanical stretching of the protein and identify sources of the force peaks. The elastic properties of topoisomerase I are predicted to be average in comparison to other proteins, yielding a maximum force of resistance to pulling which should be of order 120 pN. The contact unraveling pattern is consistent with the understanding of the structure and function of the protein. We find supporting evidence for the hypothesis that the C-terminal domain acquires an ordered structure upon binding with the core enzyme even though it forms a molten globule when in isolation. Proteins 2009;77:420-431. (C) 2009 Wiley-Liss, Inc.

关键词： 移动机械手   柔性机械手   弹性阻尼悬架   机械动力学   控制策略   轨迹规划  

摘要： 选择合适的悬架系统，可以缓解或削弱不规则路面对机械手在力与位移等方面的影响；移动柔性机械手具有诸多移动刚体机械手无法比拟的优点:构件质量轻巧、节能、小的驱动器尺寸规格、运动灵敏快捷、制作成本低、机械手的额定载荷与自重的比值高等。\n 然而由于弹性阻尼悬架的引入，致使移动机械手运动学与动力学相互耦合，同时构件弹性变形与构件整体参考坐标大范围运动存在动力学耦合及机械手末端执行器存在弹性振动现象等。轮式悬架移动柔性机械手动力学模型是一个多自由度、多变量、多参数耦合、高度非线性的复杂系统，这是由其动力学内在本质上的复杂性所决定。动力学模型的建立是诸多动力学问题中一个极其重要的方面，特别针对轮式悬架移动柔性机械手动力学正、逆模型的准确构造，如何评定系统瞬态动力学稳定性，这些将对移动机械手后续的控制策略的构造、轨迹规划等有着重要的意义。\n 建立在多体系统动力学基础上，综合考虑弹性悬架影响和构件的弹性变形(分别采用了Rayleigh-Ritz近似法和有限元法来表述构件的弹性变形)及构件弹性变形与构件整体参考坐标大范围运动的动力学耦合，对系统完整运动力学、动力学、静力学、动力学瞬态稳定性及部分系统参数的确定进行了系统的研究，并进行了相应的数值仿真。\n 本文的主要创新成果如下：\n 1.建立在多刚体系统动力学的基础上，综合考虑了线弹性阻尼悬架对系统动力学的影响，对2 杆轮式移动刚体机械手运动学、动力学、静力学进行了系统的研究，采用广义笛卡尔坐标，并以矩阵、矢量的形式，构建了系统完整运动学、动力学模型、静力学模型。\n 所构建的动力学、静力学正、逆模型有效的统一于系统完整动力学模型中。最后通过数值仿真，比较给定轨迹与计算轨迹(来自动力学模型的数值解)，验证了动力学模型的正确性；通过比较不同悬架弹簧刚度下的动力学模型数值仿真结果，表明了轮式悬架的功用。\n 2.建立在多柔体系统动力学的基础上，综合考虑了弹性悬架影响和构件的弹性变形及构件弹性变形与构件整体参考坐标大范围运动的动力学耦合，采用笛卡尔坐标变量对移动机械手系统的运动学、动力学、静力学进行了研究，并将相应力学模型以矩阵、矢量的形式形成简洁的表达形式。相对关节变量而言，该方法更具有通用性，对大规模多体系统动力学分析有重要指导作用，同时该动力学模型便于应用计算机进行数值求解。通过与Ansys11.0的计算结果比较，验证了系统静力学模型的正确性与有效性。最后采用数值法给出了该动力学模型的正解仿真结果。\n 3.建立在第2章、第3章、第4章动力学研究的基础上，给出了系统瞬态动力学稳定性评价准则，并针对不同的动力学模型，进行动力学瞬态稳定性评价。在给定既定任务工况(路面)下，以动力学稳定性准则为约束条件，对部分系统参数进行优化，形成多目标规划。最后建立在所得优化参数基础上，针对轮式移动刚体机械手、轮式悬架移动刚体机械手、轮式悬架移动刚-柔体机械手、轮式悬架移动柔体机械手稳定性进行了仿真。仿真结果显示了系统在执行任务时瞬态动力学稳定性分布情况及悬架、构件弹性变形对系统整体稳定性的影响。\n 4.建立在欧拉-伯努力梁理论基础上，采用pin-free 边界条件，并引用Hermit 插值函数作为单元形函数对柔性机械手进行了有限元离散；综合利用虚功原理和牛顿-欧拉方程并在全局坐标系和中间坐标系下，以矩阵、矢量简洁的形式分别构建了移动机械手系统的完整正、逆动力学模型及静力学模型。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。最后进行了数值仿真。该方法适用于对移动柔性轻质机械手末端执行器有高精度定位要求的动力学研究，并对系统开环控制和闭环控制的策略构建有着重要参考意义。

关键词： Activated carbon   Rhodamine B (RDB)   Adsorption isotherm   Equilibrium   Kinetic and Thermodynamic parameters   Intraparticle diffusion  

摘要： Adsorption of rhodamine B from aqueous solution on the surface of Moringa oliefera bark carbon was accomplished under the optimize conditions of temperature, concentration, pH, contact time and quantity of adsorbent. Spectrometric technique was used for the measurements of concentration of dye before and after adsorption. The percentage removal of rhodamine B was calculated. The values of % adsorption data for Moringa oliefera bark carbon system show better adsorption capacity. The experimental data are fitted to the Langmuir and Freundlich isotherm equations. The values of their corresponding constant were determined from the slope and intercepts of their respective plots. Thermodynamic parameters like Delta G(0), Delta H-0 and Delta S-0 were calculated. Rhodamine B-Moringa oliefera bark carbon system shows spontaneous and endothermic behaviour. The results of these investigations suggested that natural adsorbents can be utilized as adsorbent materials, because of their selectivity's for the removal of dyes.

关键词： Zinc-beta-lactamases   Molecular dynamics   PM3   Density functional   Linear-scaling methods  

摘要： Zinc-beta-lactamases exhibit important differences in their mode of action that hamper the development of effective inhibitors. This fact has prompted a considerable theoretical interest in these metalloenzymes in order to increase our knowledge at the molecular level. Herein, we present results from molecular dynamics (MD) simulations of the mononuclear Bcll enzyme and its Michaelis complex with imipenem. Four protonation patterns of the active site were modeled in aqueous solution and their relative stability was estimated by means of linear-scaling semiempirical quantum mechanical (QM) energy calculations. Two binding modes of the imipenem substrate were examined: (a) the substrate interacts only with protein residues: (b) the beta-lactam carbonyl group becomes a fifth ligand around the Zn ion. For the free enzyme, the energetically most stable configurations present a Zn-OH moiety, a neutral Asp(120) and a neutral His(263) residue. In contrast, for the complex formed between the Bcll enzyme and imipenem, the energetic analyses predict that the configuration with a Zn-OH fragment and a doubly protonated His(263) residue becomes stabilized. Moreover, the MD simulations and energy calculations reveal that binding of the beta-lactam carbonyl group to the Zn ion results in a proper enzyme/imipenem orientation for catalysis. (C) 2009 Elsevier B.V. All rights reserved.