关键词： propene epoxidation   gold cluster   O-2 activation   hydroperoxyl   water   AIMD  

摘要： We have studied the mechanism of propene epoxidation with O-2-H2O mixture on Au-7/alpha-Al2O3(0001) using global minimum approach, density functional theory (DFT), and ab initio molecular dynamics (AIMD) methods. It is found that water can easily dissociate on coordinatively unsaturated surface Al sites to form a hydroxylated Al2O3 surface. The Au-7 cluster on such a surface prefers anchoring at bare Al sites and transfers from upright to flat structures with a decrease of surface hydroxyl groups. The activation of molecular oxygen via a hydroperoxyl (OOH) intermediate (i.e., O-2 abstracting a hydrogen atom from coadsorbed water) is identified to be a feasible pathway from both AIMD simulations and static DFT calculations. Additional water promotes the H-transfer process by constructing a hydrogen bonding chain with reactants. The resulting OOH turns out to be a key oxidative species for subsequent propene epoxidation. It can either dissociate into atomically oxygen species to epoxide propene or combine with propene directly, forming an important *C3H6OOH species that could be easily transformed to epoxypropane. study reveals the important role of water in propene epoxidation and may stimulate further exploration and the usage of O2-H2O mixture as oxidizing agent in other oxidation reactions.

关键词： computational materials science   mechanical properties   molecular dynamics   monocrystals   superalloys  

摘要： The mechanical properties of Ni/Ni3Al monocrystal of nanophases with varying temperatures, strain rates, and phase sizes have been studied using molecular dynamics simulation. The simulation results show that the primary deformation mechanisms in Ni/Ni3Al monocrystal of nanophases were slip bands and antiphase boundaries at room temperature. The studies on the effects of temperature showed that the yield strain, yield strength, and elastic module decreased as temperature increased. However, the influences of strain rate and phase size on the mechanical properties of Ni/Ni3Al monocrystal of nanophases showed that the high strain rate led to the increase of yield stress, and the phase sizes had no significant influence on the maximum yield stress. In addition, the behavior of crack propagation in the model of Ni/Ni3Al interface was investigated under cyclic loading, and it was found that the interface of Ni/Ni3Al was resistance to the fatigue crack propagation.

关键词： Mechanical stress   Metabolomics   NMR spectroscopy   Populus nigra   Principal component analysis   Root secondary metabolites   Taproot  

摘要： Introduction Molecular factors are differentially observed in various bent sectors of poplar (Populus nigra) woody taproots. Responses to stress are modulated by a complex interplay among different hormones and signal transduction pathways. In recent years, metabolomics has been recognized as a powerful tool to characterize metabolic network regulation, and it has been widely applied to investigate plant responses to biotic and abiotic stresses. Objectives In this paper we used metabolomics to understand if long term-bending stress induces a "spatial" and a "temporal" metabolic reprogramming in woody poplar roots. Methods By NMR spectroscopy and statistical analysis we investigated the unstressed and three portions of stressed root (above-bent, bent, and below-bent) sectors collected at 12 (T-0), 13 (T-1) and 14 (T-2) months after stress induction. Results The data indicate a clear between-class separation of control and stressed regions, based on the metabolites regulation, during both spatial and temporal changes. We found that taproots, as a consequence of the stress, try to restore homeostasis and normal metabolic fluxes thorough the synthesis and/or accumulation of specific compounds related to mechanical forces distribution along the bent taproot. Conclusion The data demonstrate that the impact of mechanical stress on plant biology can efficiently be studied by NMR-based metabolomics.

关键词： Functionally graded cemented carbides   Kinetics   Grain growth   Gradient layer   Mechanical properties  

摘要： Functionally graded cemented carbides (FGCCs) were prepared by pre-sintering and carburizing of carbon deficient WC-Co cemented carbides. Submicron WC powder with different contents was added in FGCCs with coarse grains to study the influences of microstructures, kinetics and mechanical properties. The results show that the addition of submicron WC can increase the thickness of the gradient layer, and improve the carburizing rate in FGCCs. The average grain size becomes finer with the content of submicron WC increasing. The FGCCs with the addition of submicron WC has a higher grain growth rate, and the grain growth kinetics is proposed to be diffusion-controlled. Meanwhile, a simplified equation for estimating the final average grain size of FGCCs is provided. The hardness and the transverse rupture strength of FGCCs can be efficiently improved by the addition of submicron WC due to the fine microstructures and thick gradient layer. (C) 2016 Elsevier Ltd. All rights reserved.

摘要： In adaptation biology of the discovery of the intracellular osmolytes, the osmolytes are found to play a central role in cellular homeostasis and stress response. A number of models using these molecules are now poised to address a wide range of problems in biology. Here, a combination of biophysical measurements and molecular dynamics (MD) simulation method is used to examine the effect of trimethylamine-N-oxide (TMAO) on stem bromelain (BM) structure, stability and function. From the analysis of our results, we found that TMAO destabilizes BM hydrophobic pockets and active site as a result of concerted polar and non-polar interactions which is strongly evidenced by MD simulation carried out for 250 ns. This destabilization is enthalpically favourable at higher concentrations of TMAO while entropically unfavourable. However, to the best of our knowledge, the results constitute first detailed unambiguous proof of destabilizing effect of most commonly addressed TMAO on the interactions governing stability of BM and present plausible mechanism of protein unfolding by TMAO.

关键词： ETHYLENE oxide   MOLECULAR dynamics -- Simulation methods   TENSILE test (Materials)   TETRACHLOROETHYLENE   CRYSTALLINE polymers  

摘要： The tensile response to uniaxial deformation of polyethylene-based (Tetra-PE) and poly(ethylene oxide) based (Tetra-PEO) networks of various strand lengths with idealized diamond connectivity have been studied via atomistic molecular dynamics simulations. Tetra-PE and Tetra-PEO diamond networks with the same strand length show comparable maximum extensibility but the Young's moduli and tensile strength of the former are significantly lower than those of the latter, consistent with stronger intersegmental attractions in the amorphous Tetra-PEO networks. The stress strain curves show that the stress in short-stranded networks increased rapidly and monotonically with strain while for long-stranded networks it increased very little at small strain and then very sharply as the limit of extensibility was approached. The soft response observed at small strains and the strain-induced crystallization that ensues at large strains rendered the deformations largely nonelastic (irreversible). Spontaneous partial crystallization of a long-stranded Tetra-PE diamond network under supercooling was demonstrated, and the resulting system was used to (1) estimate its melting point as the temperature where any crystalline material disappeared abruptly and (2) show that the presence of crystalline material in the undeformed state leads to higher stress responses upon deformation compared to amorphous samples, a result consistent with experimental observations. The spontaneous crystallization of Tetra-PEO networks at large supercooling was unsuccessful due to the slow motions of the network beads and the prohibitively long crystal nucleation times entailed.

关键词： Monod growth kinetics   Methanogens   Hydrogen pool  

摘要： Existing mathematical models to estimate methane production in the rumen are based on calculation of hydrogen balances without considering the presence of methanogens. In this study, a mechanistic model of methane production is proposed that depicts the interaction between hydrogen concentration and methanogens in the rumen. Analytical results show that it meets biological expectations, namely increased fractional passage rate leads to a greater growth rate of methanogens, and a greater steady state hydrogen concentration. This model provides a basis on which to develop a more comprehensive model of methane production in the rumen that includes thermodynamics and feed fermentation pathways. (c) 2016 Elsevier Ltd. All rights reserved.

关键词： Tissues   Elastic moduli   Viscoelasticity   Viscosity   Strain measurement  

摘要： Regeneration of a tissue fragment of freshwater polyp Hydra is accompanied by significant morphological fluctuations, suggesting the generation of active forces. In this study, we utilized a two fingered micro-robotic hand to gain insights into the mechanics of regenerating tissues. Taking advantage of a high force sensitivity (similar to 1 nN) of our micro-hand, we non-invasively acquired the bulk elastic modulus of tissues by keeping the strain levels low (epsilon < 0.15). Moreover, by keeping the strain at a constant level, we monitored the stress relaxation of the Hydra tissue and determined both viscous modulus and elastic modulus simultaneously, following a simple Maxwell model. We further investigated the correlation between the frequency of force fluctuation and that of morphological fluctuation by monitoring one "tweezed" tissue and the other "intact" tissue at the same time. The obtained results clearly indicated that the magnitude and periodicity of the changes in force and shape are directly correlated, confirming that our two fingered micro-hand can precisely quantify the mechanics of soft, dynamic tissue during the regeneration and development in a non-invasive manner. (C) 2016 AIP Publishing LLC.

关键词： 混合动力   液压系统   工程机械   控制策略  

摘要： 针对油液混合动力工程机械能量损失较大、能量回收效率偏低以及控制策略相对单一等问题,从混合动力系统液压原理和控制策略2个方面分析.将油液混合动力工程机械液压系统分为泵控液压系统、二次调节液压系统和复合结构液压系统3种形式,研究液压系统的设计思路和工作原理,将油液混合动力工程机械控制策略分为门限值控制策略、模糊控制策略和优化控制策略3类,分析适用工况,对比油电混合动力汽车控制策略与油液混合动力工程机械控制策略.油液混合动力工程机械的发展方向包括利用泵控系统代替阀控系统、开发储能元件、设计针对工程机械结构特点的控制策略以及控制目标多样化.

关键词： 工程机械   液压系统   动力控制技术  

摘要： 工程机械液压系统动力控制技术主要涉及电力控制、液压系统控制和发动机三个方面,本文将对工程机械液压系统动力控制技术进行分析。