关键词： multilayer network   dynamics   rheological quantities   fluorescence depolarization   generalized Gaussian structures  

摘要： In this paper, we focus on the mechanical relaxation of a multilayer polymer network built by connecting identical layers that have, as underlying topologies, the dual Sierpinski gasket and the regular dendrimer. Additionally, we analyze the dynamics of dipolar energy transfer over a system of chromophores arranged in the form of a multilayer network. Both dynamical processes are studied in the framework of the generalized Gaussian structure (GSS) model. We develop a method whereby the whole eigenvalue spectrum of the connectivity matrix of the multilayer network can be determined iteratively, thereby rendering possible the analysis of the dynamics of networks consisting of a large number of layers. This fact allows us to study in detail the crossover from layer-like behavior to chain-like behavior. Remarkably, we highlight the existence of two bulk-like behaviors. The theoretical findings with respect to the decomposition of the intermediate domain of the relaxation quantities, as well as the chain-like behavior, are well supported by experimental results.

关键词： Nanoindentation   Geopolymer   Molecular dynamics   Indentation size effect  

摘要： Using molecular dynamics simulations, the mechanical response of amorphous geopolymer binder (GB) under spherical nanoindentation was examined as a function of GB composition (Si/Al ratio), indenter size (radius of indenter) and loading rates. The observed hardness values were strongly dependent on the indenter size and loading rates. Specifically, the GB hardness increased with decreasing indenter size and increasing loading-rate. The indenter size effect and the effect of loading rate were related to the ease of rotation of the underlying Si and Al tetrahedra in conjunction with the breaking of bridging Si-O and Al-O bonds. Further, for a given indenter size, increasing the Si/Al ratio increased the hardness and Young's modulus of the GB, which was correlated to higher strength of Si-O bonds as compared to Al-O bonds present in the GB. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Two-dimensional silicon dioxide   Crystalline   Vitreous   Elastic property   Fracture mechanism  

摘要： The recently discovered two-dimensional (2D) silica films can be grown in both crystalline phase and vitreous phase. Using molecular dynamics simulations, we show that these two phases of 2D silica possess vastly different mechanical properties. It is shown that the Young's modulus of crystalline 2D silica is 54% greater than that of its vitreous counterpart. The vitreous 2D silica fails via the ductile fracture with serrated stress-strain curves, while its crystalline counterpart exhibits the abrupt brittle rupture. Both the fracture strength and fracture strain of crystalline 2D silica are significantly larger than those of its vitreous counterpart. Fracture mechanics theory is utilized to give some explanations to the different fracture properties of these two phases. Moreover, 2D silica mixed by crystalline phase and vitreous phase is also studied. Owing to the different mechanical properties of crystalline and vitreous phases, the elastic and fracture properties of this mixed-phase 2D silica are strongly dependent on its crystallinity. Specifically, we find that the Young's modulus of the mixed-phase 2D silica, ranging between the values of its crystalline and vitreous counterparts, increases as the degree of crystallinity increases. Meanwhile, with the increase of the degree of crystallinity the fracture strain of the mixed-phase 2D silica is found to decrease, making its value smaller than that of the purely crystalline and vitreous 2D silica. (C) 2017 Elsevier B.V. All rights reserved.

关键词： Organic-inorganic nanostructures   Self-assembly   Surface assembly  

摘要： Although 'active' surfactants, which are responsive to individual external stimuli such as temperature(1), electric(2,3) or magnetic(4) fields, light(5,6), redox processes(6,7) or chemical agents(8), are well known, it would be interesting to combine several of these properties within one surfactant species. Such multi-responsive surfactants could provide ways of manipulating individual droplets and possibly assembling them into larger systems of dynamic reactors(9,10). Here we describe surfactants based on functionalized nanoparticle dimers that combine all of these and several other characteristics. These surfactants and therefore the droplets that they cover are simultaneously addressable by magnetic, optical and electric fields. As a result, the surfactant-covered droplets can be assembled into various hierarchical structures, including dynamic ones, in which light powers the rapid rotation of the droplets. Such rotating droplets can transfer mechanical torques to their non-nearest neighbours, thus acting like systems of mechanical gears. Furthermore, droplets of different types can be merged by applying electric fields and, owing to interfacial jamming(11,12), can form complex, non-spherical, 'patchy' structures with different surface regions covered with different surfactants. In systems of droplets that carry different chemicals, combinations of multiple stimuli can be used to control the orientations of the droplets, inter-droplet transport, mixing of contents and, ultimately, sequences of chemical reactions. Overall, the multi-responsive active surfactants that we describe provide an unprecedented level of flexibility with which liquid droplets can be manipulated, assembled and reacted.

摘要： In the current paper, we report the kinetics of bifunctional dinuclear platinum(II) complexes viz., 1,2-N, N '-di-(2,2-dipyridylamine)ethanetetraaquaplatinum(II), PtL2, 1,3-N, N '-di-(2,2-dipyridylamine) propanetetraaquaplatinum(II), PtL3, 1,4-N, N '-di-(2,2-dipyridylamine) butanetetraaquaplatinum(II), PtL4, 1,5-N, N ' di-(2,2-dipyridylamine) pentanetetraaquaplatinum(II), PtL5 and 1,6-N, N '-di-(2,2-dipyridylamine) hexanetetraaquaplatinum(II), PtL6. The substitution reactions were carried out on tetraaqua complexes with thiourea nucleophiles under pseudo-first-order conditions as a function of nucleophile concentration and temperature by stopped-flow and UV-vis spectrophotometric techniques. An experimental study was conducted with the aim of determining the influence of alkyl chains on the steric and electronic structure of dinuclear platinum(II) complexes. The reactivity of these complexes was dependent on the length of the alkyl spacer. The results obtained herein demonstrate the intriguing odd-even effects induced by the alkyl chain on the complexes. Artificial constraints imposed by the alkyl chain significantly affect their conformational structure to be either synperiplanar (syn-) or antiperiplanar (anti-) characterized by the odd and even effect. The kinetic, mechanistic and conformational behaviour was influenced by the size of the alkyl chain in accordance with odd-even alterations of the spacer. Computational modeling using density functional theory (DFT) calculations supplemented experimental findings that structural features and the reactivity pattern of these organometallic complexes are governed by both steric and electronic effects arising from the flexibility and inductive nature of the alkyl spacer. The strong s-donicity of longer alkyl chains favours sufficient accumulation of electron density at the metal centre and stabilizes a 14-electron intermediate. The study shows the HOMO-LUMO energy (DE) is affected by the length of the spacer. Kinetic an

关键词： Nucleic acids   Central nervous system   Electrodes   Membranes   Electrodeposition  

摘要： Hydrogen peroxide (H2O2) is an endogenous molecule that plays several important roles in brain function: it is generated in cellular respiration, serves as a modulator of dopaminergic signaling, and its presence can indicate the upstream production of more aggressive reactive oxygen species (ROS). H2O2 has been implicated in, several neurodegenerative diseases, including Parkinson's disease (PD), creating a critical need to identify mechanisms by which H2O2 modulates cellular processes in general and how it affects the dopaminergic nigrostriatal pathway, in particular. Furthermore, there is broad interest in selective electrochemical quantification of H2O2, because it is often enzymatically generated at biosensors as a reporter for the presence of nonelectroactive target molecules. H2O2 fluctuations can be monitored in real time using fast-scan cyclic voltammetry (FSCV) coupled with carbon-fiber microelectrodes. However, selective identification is a critical issue when working in the presence of other molecules that generate similar voltammograms, such as adenosine and histamine. We have addressed this problem by fabricating a robust, H2O2-selective electrode. 1,3-Phenylenediamine (mPD) was electrodeposited on a carbon-fiber microelectrode to create a size-exclusion membrane, rendering the electrode sensitive to H2O2 fluctuations and pH shifts but not to other commonly studied neurochemicals. The electrodes are described and characterized herein. The data demonstrate that this technology can be used to ensure the selective detection of H2O2, enabling confident characterization of the role this molecule plays in normal physiological function as well as in the progression of PD and other neuropathies involving oxidative stress.

关键词： 有创机械通气   无创机械通气   慢性阻塞性肺疾病   II型呼吸衰竭   血流动力学  

摘要： 目的探讨有创无创序贯机械通气对慢性阻塞性肺疾病(COPD)合并Ⅱ型呼吸衰竭患者血流动力学的影响。方法将100例COPD合并Ⅱ型呼吸衰竭患者分为观察组和对照组,各50例。两组患者均进行有创机械通气治疗,观察组在出现肺部感染控制窗时改用压力支持通气,比较两组患者机械通气前和撤机时血流动力学指标的变化[心输出量(SV)、心排血指数(CI)、左室射血分数(LVEF)、动态肺顺应性(C_(RS))、乳酸、系统血管阻力(SVR)、中心静脉压(CVP)、平均动脉压(MAP)、动脉血氧分压(PaO_2)、动脉血二氧化碳分压(PaCO_2)]。结果两组有创通气撤机时和无创通气撤机时SV、CI、LVEF、CRS、PaO_2均较治疗前高,乳酸、SVR、CVP、PaCO_2均较治疗前低(均P<0.05)。且观察组无创通气撤机时CI、CRS、乳酸、CVP、PaO_2、PaCO_2的改善程度均优于对照组有创通气撤机时(均P<0.05)。结论有创无创序贯机械通气能明显改善COPD合并Ⅱ型呼吸衰竭患者的血流动力学指标及心功能。

关键词： 机械化水平   农业从业人员   统计分析   劳动力转移  

摘要： 耕地机械化水平的提高和农村劳动力的有序转移是土地规模化经营的基础。以河南省为研究区域,采用经典的统计学方法对农用机械动力、农业从业人员的变化趋势进行分析,并对河南省耕地机械化程度和富裕劳动力之间的关系进行初步分析。结果表明:1978~2008年河南省农用机械总动力、单位面积农用机械动力和人均农用机械动力均呈指数型增长;农林牧渔业从业人员在1978~2000年缓慢增长,2001~2008年快速减少,其占总人口比重也快速下降;农业机械化水平与劳动力转移二者之间相互影响。机械化水平的提高促进劳动生产效率提高,推动富裕劳动力的产生,富裕劳动力的转移又进而促进机械化水平的提高。

关键词： Reactivity   Rigidity   Flexibility   Methylene   Associative  

摘要： This paper reports on a mechanistic interaction between mononuclear and polynuclear platinum(II) complexes viz;phenyl-dichlorido-2,2'-dipyridinylaminediaquaplatinum(II) (PtC1);di-2-pyridy-laminomethylbenzenediaquaplatinum( II) (PtC2);1,3,5-tris(2,2'dipyridylamino)-benzenehexaquaplatinum( II) (PtC3);1,3,5-tris(2,2'dipyridylmethylamino) benzenehexaquaplatinum(II) (PtC4);and 2,4,6-tris (2,2'-dipyridylamino)-1,3,5-triazinehexaquaplatinum(II) (PtC5) with thiourea nucleophiles under pseudo-first-order conditions as a function of nucleophile concentration and temperature using stopped-flow and UV-Vis spectrophotometric techniques. The reactivity of the complexes followed the order PtC5 > PtC1 > PtC3 > PtC2 > PtC4 with thiourea (TU) as the entering nucleophile. The study demonstrates that both rigidity and flexibility has an influence on the kinetics of the complexes and governs by both steric and electronic effects. Introduction of methylene groups destroys conjugacy and lowers the acidity of the complexes. Kinetic and DFT data concur and illustrates that electron donation by methylene bridge leads to stabilization of the complexes. The study further shows that replacement of the methyne (= CH-) groups with nitrogen atoms enhances reactivity. The small positive enthalpy of activation and large negative values of entropy of activation indicate an associative mode of activation for aqua ligand substitutions and dechelation processes. (C) 2017 Elsevier B.V. All rights reserved.

关键词： 动力学   掘进机   钻孔机械手   仿真  

摘要： 针对掘进机机载钻孔机械手在开采过程中的负载变化特性,依据多刚体动力学和多柔体动力学理论建立其刚柔耦合动力学方程,利用有限元分析软件ANSYS、Recur Dyn来进行模拟。通过分析模拟结果,可知机械手各关节驱动力相近,在开采过程中钻杆和伸缩臂的变形对钻孔机械手的力学特性影响较小,但是对钻头的运动精度影响很大,对钻头运转速度影响较弱。