关键词： Molecular dynamics   Interface thermal conductance   Carbon nanotube   Modulation  

摘要： Classical molecular dynamics (MD) simulations are performed in this work to investigate the interfacial thermal transport across stacked carbon nanotube (CNT) junctions. Various approaches are irnplemented to increase the thermal conductance (G) between CNTs. Effects of crossing angle, contact area, bonding strength, external force and hydrocarbon functionalization on G are investigated. A remarkably increase of thermal conductance is achieved by connecting two CNTs with hydrocarbon chain linkers CH2. The predicted G changes from 229 pW/K without linkers to 4901 pW/K with an optimized linker number, which increases by a factor of 20. Meanwhile, thermal conductance is found to increase monotonically with contact area but decrease inversely with crossing angle. The van der Waals (vdW) bonding strength has similar effects with applied external force on thermal conductance, both of which facilitate the interfacial thermal transport by enhancing the contact pressures. Synthesized relationship of internal coupling strength, external force and final separation distance between CNTs is explored to illustrate the variation of thermal conductance and intermolecular potential energy. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Graphene fracture   Molecular dynamics   Size-scale effects   Size effect law   Multifractal scaling law   Lattice orientation effect  

摘要： In this paper, the combined effect of domain size, lattice orientation and crack length on the mechanical properties of Graphene, namely the yield strength and strain, are studied extensively based on molecular dynamics simulations. Numerical predictions are compared with the continuum- based laws of size effect and multifractal scaling. The yield strength is found to vary with the specimen size as approximate to L-1/3, which is in agreement with the multifractal scaling law, and with the inverse square of the initial crack length as approximate to a(0)(1/2), according to the Griffith's energy criterion for fracture. (C) 2016 Elsevier B.V. All rights reserved.

关键词： material protection   Coating   Intermetallic phases   galvanizing   Kinetics   Mechanical properties   hot dip galvanizing  

摘要： Hot-dip galvanizing process is one of most used techniques to generate coatings for metallic material protection in aggressive environments. In last decades, such a process has been developed in order to obtain coatings with chemical and mechanical properties for specific utilizations. In this work, the influence of high contents of Sn (3% by weight) on the performance of the traditional Zn coatings is experimentally analysed in terms of both microstructure kinetics formation and mechanical properties. Further, a Finite Element model simulates the tested coated specimens under bending. The agreement between experimental and numerical results is satisfactory, especially under plastic regime.

关键词： Portlandite   Crystalline structure   Mechanical properties   Temperature effects   Strain rate   Molecular dynamics  

摘要： The structural, thermal, and mechanical properties of portlandite, the primary solid phase of ordinary hydrated cement paste, are investigated using the molecular dynamics method. To understand the effects of temperature on the structural properties of portlandite, the coefficients of thermal expansion of portlandite are determined in the current study and validated with what reported from the experimental tests. The atomic structure of portlandite equilibrated at various temperatures is then subjected to uniaxial tensile strains in the three orthogonal directions and the stress-strain curves are developed. Based on the obtained results, the effect of the direction of straining on the mechanical properties of portlandite is investigated in detail. Structural damage analysis is performed to reveal the failure mechanisms in different directions. The energies of the fractured surfaces are calculated in different directions and compared to those of the ideal surfaces available in the literature. The key mechanical properties, including tensile strength, Young's modulus, and fracture strain, are extracted from the stress-strain curves. The sensitivity of the obtained mechanical properties to temperature and strain rate is then explored in a systematic way. This leads to valuable information on how the structural and mechanical properties of portlandite are affected under various exposure conditions and loading rates.

关键词： Redox chemistry   Kinetics   Ruthenium   Reduction   Ascorbate   Ascorbyl radical  

摘要： A detailed kinetic study of the reduction of cis-dichloridobispicolinatoruthenate(III) by l-ascorbic acid that leads to the formation of the corresponding Ru-II complex, was carried out spectrophotometrically using the stopped-flow technique. The reaction was studied as a function of [AscH(2)](T), [Ru-III], and pH. The observed kinetic traces could only be fitted to a three-exponential function, characteristic for three parallel reaction paths. However, an earlier study clearly showed that under the selected experimental conditions only a single complex species is present in solution. The observed complication is suggested to arise from the low driving force of the reaction during which the re-oxidation of Ru-II by the semi-oxidized l-ascorbic acid, i.e. ascorbyl radical Asc(-), accounts for the apparent three-exponential behavior of the reaction. A detailed account of different modeling efforts and a comparison with related systems is presented.

关键词： acute myocardial infarction   left ventricular assist device   percutaneous mechanical circulatory support   ventricular unloading  

摘要： OBJECTIVES The aim of this study was to directly compare the hemodynamic effects of 2 contemporary percutaneous mechanical circulatory support devices in a porcine model of acute myocardial infarction. BACKGROUND Percutaneous support devices offer the ability to unload the ischemic left ventricle, but the comparative hemodynamic effects of contemporary platforms are unclear. METHODS Yorkshire swine (mean weight 76 +/- 2 kg;n = 7) were instrumented with a left ventricular (LV) pressure-volume (PV) catheter and subjected to a 2-h coronary occlusion. Hemodynamic parameters and PV-derived indexes of LV performance were assessed 30 min after reperfusion and during LV support with Impella CP (ICP) and TandemHeart devices (in randomized order) at comparable flow rates. RESULTS Myocardial infarction produced a rightward shift of the PV loop and increased LV end-diastolic pressure (from 9 +/- 2 mm Hg to 15 +/- 2 mm Hg;p = 0.04). After reperfusion, both devices maintained aortic pressure, shifted the PV loop to the left, and decreased LV end-diastolic pressure (ICP vs. TandemHeart;11 +/- 1 mm Hg vs. 7 +/- 4 mm Hg;p = 0.04). However, only TandemHeart elicited significant reductions in native LV stroke volume (from 75 +/- 7 ml to 39 +/- 7 ml;p < 0.01), dP/dtmax (from 988 +/- 77 mm Hg/s to 626 +/- 42 mm Hg/s;p < 0.01), stroke work (from 0.70 +/- 0.03 J to 0.26 +/- 0.05 J;p < 0.01), PV area (from 0.95 +/- 0.11 J to 0.47 +/- 0.10 J;p < 0.01), and pre-load-recruitable stroke work slope (from 41.7 +/- 2.8 J/ml to 30.6 +/- 3.9 J/ml;p = 0.05). CONCLUSIONS At comparable device flow rates, TandemHeart decreased LV pre-load, native LV stroke volume, and myocardial contractility to a greater degree than ICP. Reductions in load-independent indexes of LV performance indicate favorable effects on myocardial oxygen balance and support further study of TandemHeart in clinical scenarios requiring mechanical support in the setting of acute myocardial ischemia. (C) 2016 by the American College of

关键词： Dynamics of hydrogen bonds   Mechanical behaviors   Supramolecular elastomer  

摘要： Here our special consideration is devoted to the relationship between dynamics and mechanical behaviours of supramolecular elastomer (SE) based on 2-ureido-4[1H]-pyrimidinone (UPy) groups. We find that SE exhibits a new relaxation mode (alpha' relaxation) which differs from segmental relaxation mode (alpha relaxation) and normal relaxation mode (NM). Calculated by Arrhenius model, supramolecular interactions are much lower than the bonds energy of covalent bonds;this enables high energy dissipation as the elastomer is subjected to deformation. Moreover, unlike covalent bonds, the hydrogen bonds of UPy groups are dynamic and longer waiting time leads to better re-association efficiency, as evidenced by recovery of hysteresis loop during cyclic tensile tests. This work on the relationship between dynamics and mechanical properties will not only improve the understanding of reversible bonds relaxation, but also provide an idea on preparing mechanically robust SE for us. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Molecular dynamics simulation   Bimodal structures  

摘要： Molecular dynamics simulation (MD) was performed on the polycrystalline copper with bimodal structures. As our special grain size distribution based on the inverse Hall-Petch relation, the small grain region and large grain region play different roles in the uniaxial tensile tests. The large grain region imparts the bimodal Cu samples high strength for the lattice dislocations activation. The large grain size effect was studied in this paper. Through our MD simulations, an atomic scale view of the interactions between two regions is also presented with the deformation progress. (C) 2016 Elsevier B.V. All rights reserved.

关键词： Ribonucleoproteins   Environmental conditions   PICs   Stressing   Steam generators   Intrinsically Disordered Proteins   condensation   Amino Acid Motifs   disassemble  

摘要： The accumulation of stalled translation preinitiation complexes (PICs) mediates the condensation of stress granules (SGs). Interactions between prion-related domains and intrinsically disordered protein regions found in SG nucleating proteins promote the condensation of ribonucleoproteins into SGs. We propose that PIC components, especially 405 ribosomes and mRNA, recruit nucleators that trigger SG condensation. With resolution of stress, translation reinitiation reverses this process and SGs disassemble. By cooperatively modulating the assembly and disassembly of SGs, ribonucleoprotein condensation can influence the survival and recovery of cells exposed to unfavorable environmental conditions.

关键词： boron   molecular dynamics   mechanical properties   2D materials  

摘要： The most recent experimental advances could provide ways for the fabrication of several atomic thick and planar forms of boron atoms. For the first time, we explore the mechanical properties of five types of boron films with various vacancy ratios ranging from 0.1-0.15, using molecular dynamics simulations with ReaxFF force field. It is found that the Young's modulus and tensile strength decrease with increasing the temperature. We found that boron sheets exhibit an anisotropic mechanical response due to the different arrangement of atoms along the armchair and zigzag directions. At room temperature, 2D Young's modulus and fracture stress of these five sheets appear in the range 63-136 N m(-1) and 12-19 N m(-1), respectively. In addition, the strains at tensile strength are in the ranges of 9%-14%, 11%-19%, and 10%-16% at 1, 300, and 600 K, respectively. This investigation not only reveals the remarkable. stiffness of 2D boron, but establishes relations between the mechanical properties of the boron sheets to the loading direction, temperature and atomic structures.