关键词： Planar mechanical system   Dynamic behavior   Joint clearance   Flexible links  

摘要： Joint clearance and flexible links are two important factors that affect the dynamic behaviors of planar mechanical system. Traditional dynamics studies of planar mechanism rarely take into account both influence of revolute clearance and flexible links, which results in lower accuracy. And many dynamics studies mainly focus on simple mechanism with clearance, the study of complex mechanism with clearance is a few. In order to study dynamic behaviors of two-degree-of-freedom (DOF) complex planar mechanical system more precisely, the dynamic analyses of the mechanical system with joint clearance and flexibility of links are studied in this work. Nonlinear dynamic model of the 2-DOF nine-bar mechanical system with revolute clearance and flexible links is built by Lagrange and finite element method (FEM). Normal and tangential force of the clearance joint is built by the Lankarani-Nikravesh and modified Coulomb's friction models. The influences of clearance value and driving velocity of the crank on the dynamic behaviors are researched, including motion responses of slider, contact force, driving torques of cranks, penetration depth, shaft center trajectory, Phase diagram, Lyapunov exponents and Poincar, map of clearance joint and slider are both analyzed, respectively. Bifurcation diagrams under different clearance values and different driving velocities of cranks are also investigated. The results show that clearance joint and flexibility of links have a certain impact on dynamic behavior of mechanism, and flexible links can partly decrease dynamic response of the mechanical system with clearance relative to rigid mechanical system with clearance.

关键词： IRON alloys   MOLYBDENUM alloys   CRYSTALLOGRAPHY   ATOMS   SOLID solutions  

摘要： The reaction kinetics of equiatomic Fe-Mo solid solutions produced by mechanical alloying were studied by X-ray diffraction and Mossbauer spectroscopy. The materials were milled with velocities of rotation of 400 and 500 rpm for several milling times to obtain samples of various reaction stages. The X-ray diffraction patterns showed the presence of two bcc phases, corresponding to metallic Fe and Mo, in all samples. Analysis of these diffractograms indicated diffusion of Mo within the Fe matrix and diffusion of Fe within the Mo matrix, as a result of the milling process. While the X-ray diffraction technique did not allow for the identification of a crystallographic phase being clearly transformed, making it difficult to study the reaction kinetics, using Mossbauer spectroscopy, it was possible to identify two magnetic phases that suffer transformation during the course of milling: a ferromagnetic sextet corresponding to metallic Fe and a paramagnetic doublet corresponding to Fe atoms with a majority of Mo neighbors (metallic Mo does not possess a magnetic moment). Both magnetic phases may be present in the bcc Fe matrix or the bcc Mo matrix. The transformation kinetics of the sextet were studied using a method based on a local description of phase volume transformation, depicted by the tribochemical activity parameter. The results were compared to published work on the application of this method to Fe-Cu and Fe-N systems. A behavior similar to that of Fe-N was observed, which, similar to the Fe-Mo system and as opposed to the Fe-Cu system, possesses a positive enthalpy of mixing.

关键词： Boron concentrate   Mechanical activation   Leaching kinetics   Surface area   Surface free energy  

摘要： Mechanical activation is an effective pretreatment method that can change the properties of boron concentrates, thus promoting B2O3 leaching from samples. Four boron concentrate samples were milled for 0, 10, 30, and 60 min and leached in a NaOH solution at various leaching temperatures and initial NaOH concentrations. We investigated the main control steps for leaching and obtained the kinetic parameters. We discuss the influences of the specific surface area and surface free energy on the apparent rate constants. During the early-stage leaching (0-20 min), the leaching process was controlled by a combination of the surface chemical reaction and diffusion through the product layer;however, the surface chemical reaction was the main controlling step with an apparent activation energy of 29.37-39.77 kJ/mol. During the late-stage leaching (> 40 min), the leaching process of the milled samples was controlled by a combination of the surface chemical reaction and diffusion through the product layer;in contrast, that of the unmilled sample was controlled by the surface chemical reaction and showed a high apparent activation energy of 69.14 kJ/mol. With increasing milling time, the apparent activation energy and reaction order decreased, thus reducing the dependence on temperature and NaOH concentration. The leaching rate constants were related to the specific surface area, surface free energy, and other properties, such as crystal amorphization and chemical bonds stability. After milling for 60 min, the surface free energy increased from 26.88 to 33.99 mJ/m(2), and the Lewis acid component increased from 0 to 3.31 mJ/m(2), promoting the absorption of the solvent and OH-in the leaching solution, which also accelerated the leaching rate.

关键词： CREBBP   Bromodomain   Molecular dynamics   Propionylshikonin   MM-PBSA   MM-GBSA   QM/MM  

摘要： The Proteins involved in the chemical modification of lysine residues in histone, is currently being excessively focused as the therapeutic target for the treatment of cell related diseases like cancer. Among these proteins, the epigenetic reader, CREB-binding protein (CREBBP) bromodomain is one of the most prominent targets for effective anticancer drug design, which is responsible for the reorganization of acetylated histone lysine residues. Therefore, this study employed an integrative approach of structure based drug design, in combination with Molecular Dynamics (MD) and QM/MM study to identify as well as to describe the binding mechanism of two shikonin derivatives, acetylshikonin and propionylshikonin as inhibitors of CREBBP bromodomain. Here induced fit docking strategy was employed to explore the important intrinsic interactions of ligands with CREBBP bromodomain, consistently molecular dynamics simulation with two different methods and binding energy calculations by MM-GBSA and MM-PBSA were adopted to determine the stability of intermolecular interactions between protein and ligands. The results showed that both these derivatives made direct contacts with the important conserved residues of the active site, where propionylshikonin demonstrated stronger binding and stability than acetylshikonin, according to molecular dynamics simulation and binding free energy calculations. Further, QM/MM energy calculation was employed to study the chemical reactivity of the propionylshikonin and also to describe the mechanism of non bonded interactions between the propionylshikonin and CREBBP bromodomain. Though this study demands in vitro and in vivo experiments to evaluate the efficiency of the compound, these insights would assist to design more potent CREBBP bromodomain inhibitor, guiding the site of modification of propionylshikonin moiety for designing selective inhibitors. (C) 2018 Elsevier Inc. All rights reserved.

关键词： 船舶动力机械   不锈钢装置   钢丝绳减震   激振力   振动控制  

摘要： 在变载荷影响下,船舶动力系统中的不锈钢钢丝绳,极易因振动波的振幅发生改变,而出现严重振荡现象。为解决上述问题,设计变载荷下船舶动力机械不锈钢钢丝绳减振装置。通过变载荷引起的激振力确定、动力机械减振控制2个步骤,完成新型减振装置应用环境的搭建。通过钢丝绳隔振器选择、船舶隔振垫设计、振荡采集传感器设计3个步骤,完成新型减振装置使用模块的搭建。控制变量因素设计对比实验结果显示,应用变载荷下船舶动力机械不锈钢钢丝绳减振装置后,振动波振幅的变化情况得到有效控制,钢丝绳严重振荡现象的发生几率,也得到一定程度的抑制。

关键词： Dealloying   Dissolution   Kinetics   Porous  

摘要： The mechanism and kinetics of dealloying of mechanically alloyed Ag25Zn75 powder particles was investigated at four different temperatures under free corrosion conditions in freely aerated 2N HCl. The activation energies of 30.65 +/- 2.08 kJ/mole and 41.51 +/- 3.30 kJ/mole, corresponding to the dissolution of Zn and pore coarsening, respectively, were obtained. The pore formation is controlled by Zn dissolution from the alloy and coarsening is controlled by diffusion of Ag atoms on the alloy/electrolyte interface. Ag rearrangement was found to be the rate controlling phenomenon for the overall dealloying.

关键词： Bamboo   Vacuum-assisted   Microwave drying   Mechanical property  

摘要： Round bamboos hold great promise for replacing wood as structural materials due to their easy large-scale cultivation, rapid growth, high strength and high toughness. However, rapid drying of round bamboo with good quality remains a key challenge. Here, vacuum-assisted microwave drying (VMD) technology is firstly applied to dry round bamboo. It only takes similar to 150 min to reduce the moisture content of bamboo to similar to 10%. The resulting dried bamboos not only have a smooth surface, superior gloss, uniform golden color and few striking defects, but also show good mechanical performance. Moreover, few splitting, cracking, even "Firecrackers" occur during the drying process, which could not be avoided by conventional drying method. Thus, VMD technology shows a great potential application in drying round bamboo in industry. (C) 2018 Elsevier B.V. All rights reserved.

关键词： C-S-H   Mechanical properties   Molecular dynamics modeling   Interfaces   Colloidal model   Meso-scale  

摘要： At meso-scale, Calcium Silicate Hydrate (C-S-H) can be considered as randomly packed globules (about 4.2 nm), which forms the basic unit cell, with water molecules and voids. In this paper, the nanostructures for the globules are developed based on some plausible atomic structures of C-S-H. The mechanical properties for the C-S-H globules are determined through molecular dynamics simulation. Interfaces between the C-S-H globules are also simulated with different amount of water molecules. Key material parameters, e.g., Young's modulus, strength and fracture energy, are obtained. It has been found that longer mean chain length of silicate tends to increase the strength of C-S-H and change the fracture behavior from brittle to ductile failure, in the chain length direction. In the other direction, however, silicate chains do not play an important role while interlayer structure matters. Moreover, pores in the C-S-H nanostructures can considerably reduce the strength of the globule structures in the normal direction to silicate chain but the weakening effect becomes substantially less in silicate chain direction. Further, it has been found that for all types of the interfaces between C-S-H globules, the interface with no extra water molecules has the greatest tensile/shear strength. The mechanical properties obtained in this paper for C-S-H nanostructures and interfaces could be necessary inputs to the meso-scale modelling of C-S-H via either granular mechanics, i.e., DEM, or continuum mechanics, i.e., FEM. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Actin filament   G-actin   Molecular dynamic simulation   Biomechanics   Nanomechanics   Young's modulus   Persistence length  

摘要： This paper aims to give a comprehensive atomistic modeling of the nanomechanical behavior of actin monomer. Actin is a ubiquitous and essential component of cytoskeleton which forms many different cellular structures. Despite for several years great effort has been devoted to the investigation of mechanical properties of the actin filament, studies on the nanomechanical behavior of actin monomer are still lacking. These scales are, however, important for a complete understanding of the role of actin as an important component in the cytoskeleton structure. Based on the accuracy of atomistic modeling methods such as molecular dynamics simulations, steered molecular dynamics method is performed to assess tension of monomeric G-actin molecule under different types of mechanical loading including axial and lateral. As a result, stress-strain curves are obtained in aqueous solution, with either ATP or ADP bound in the nucleotide binding pocket. The obtained results yield evaluation of the tensile stiffness of a single actin monomer in lateral and normal direction. In order to compare the behavior of ATP and ADP G-actins, the number of hydrogen bonds and nonbonded interactions between the nucleotide and the protein are analyzed. Moreover, The effect of virtual spring of steered molecular dynamics on the mechanical behavior of actin monomer is investigated. The results reveal increasing the virtual spring constant leads to convergence of the stiffness. Moreover, in this paper, a generalized model is proposed to extend the obtained results for the monomeric G-actin scale to the actin filament. Our modeling estimated a persistence length of actin filament 15.41 pm, close to experimental measurements. Moreover, In this paper, the breaking force actin-actin bond is evaluated using steered molecular dynamics simulation. By applying a tensile force, actin-actin bond ruptured at 4197.5 pN. (C) 2018 Elsevier Ltd. All rights reserved.