关键词： Mechanical systems with impact and friction   Contact detection algorithm   Mechanical toys   Rolling bearing mechanism  

摘要： In this work, some new results are presented on the dynamics of a class of multibody mechanical systems, involving contact and friction. The main contribution refers to the development of a systematic, accurate and efficient method for detecting contact among the components of a system of solid bodies. For some simple geometries, this task is achieved by employing analytical means. For systems possessing components with complex geometric shapes a more involved numerical methodology is developed. In both cases, once a potential contact point is detected, the common tangent plane and normal vector are located and the penetration depth is calculated, leading to determination of the force arising between the contacting bodies. This information is then passed to a solver, providing the full dynamic response of the system. The validity and numerical efficiency of the methodology developed is first demonstrated by considering a number of examples with relatively small geometric complexity but large traditional value and interesting dynamic response. Some new results are obtained and presented on the dynamics of these systems. Finally, the same methodology is also tested in a more complicated and demanding mechanical application. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Carbon nanotube   mechanical properties   molecular dynamics   graphene   thermal conductivity  

摘要： Single layer graphene sheets and carbon nanotubes have resulted in the development of new materials for a variety of applications. Though there are a large number of experimental and numerical studies related to these nanofillers, still there is a lack of understanding of the effect of geometrical characteristics of these nanofillers on their mechanical properties. In this study, molecular dynamics simulation has been used to assess this issue. Two different computational models, single layer graphene sheets-copper and carbon nanotube-copper composites have been examined to study the effect of nanofiller geometry on Young's modulus and thermal conductivity of these nanocomposites. Effect of increase in temperature on Young's modulus has also been predicted using molecular dynamics. The effect of nanofiller volume fraction (V-f) on Young's modulus and thermal conductivity has also been studied. Results of thermal conductivity obtained using molecular dynamics have been compared with theoretical models. Results show that with increase in V-f the Young's modulus as well as thermal conductivity of single layer graphene sheets-Cu composites increases at a faster rate than that for carbon nanotube-Cu composite. For the same V-f, the Young's modulus of single layer graphene sheets-Cu composite is higher than carbon nanotube-Cu composite.

关键词： borides   hardness   molten-salt boriding   pure titanium   wear properties  

摘要： To modify the surface properties of pure titanium, boride layers had been fabricated by the boron molten-salt diffusion on pure titanium surfaces in the temperature range of 900-1100 A degrees C for 5- to 30-h treatments. The results demonstrated that the boride layers were mainly composed of TiB whiskers and TiB2 layers without the rutile titanium oxide TiO2. Two diffusion models were introduced to model the growth kinetics of boride layers. The parabolic growth constants and the boron diffusion coefficients were obtained. The boron activation energies for TiB2 and TiB were 225.617 and 165.266 kJ mol(-1), respectively. The surface microhardness of the borided titanium decreased with the increase in distance from the surface. The results of wear tests indicated that the wear properties had been improved significantly compared to the pure titanium under dry sliding conditions.

关键词： graphene   mechanical properties   molecular dynamics  

摘要： This work reports estimation of mechanical properties, particularly Young's modulus of a single-layered graphene sheet by molecular dynamics (MD) simulation-based four different approaches, viz. tensile modeling, bending modeling, oscillation modeling and equilibrium MD modeling. The Young's modulus is estimated to be of the order of some TPa. The equilibrium MD method has yielded a Young's modulus value lower than the other non-equilibrium methods, due to the absence of any external forcing factor. Among the non-equilibrium MD methods, the bending modeling is found to predict the highest value of Young's modulus. Comparison among different non-equilibrium methods has established the effect of strain rate on the estimated value of the Young's modulus. The MD simulation-based approaches adopted here can be useful for the design of graphene and graphene-based materials in advanced mechanical applications.

关键词： rat   isolated cardiac myocytes   nitric oxide   mechanical stretch   fluorescent detection  

摘要： Discrete mechanical stretch of isolated spontaneously contracting cardiac myocytes was employed to examine the kinetics of NO production in these cells. NO oscillations were detected with fluorescent dye 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate. The mechanisms underlying stretch-induced changes in NO concentration remain unclear and further studies are needed to evaluate the role of NO oscillation in the regulation of cardiomyocyte function.

关键词： THERMAL analysis   AMINO acids   CHEMICAL kinetics  

摘要： Using initial rate data, the mechanistic investigation for the thermal degradation kinetics of 2-amino-2-methyl-1-propanol (AMP) to 4,4-dimethyl-1,3-oxazolidin-2-one (DMOZD) as a function of amine and CO2 concentration in the solution was performed. Activation energies of different reaction steps in introduced mechanisms imply that the reaction between AMP and CO2 to produce carbamate will happen dose to equilibrium conditions, while the carbamate will tends to revert back to initial amine rather than convert to the DMOZD at lower temperatures. Investigation of different forms of reaction pathways and various reaction orders for reactants including AMP and CO2 demonstrates that the actual reaction mechanism is complex. The closest and simplest mechanism to fit the experimental data provides noninteger reaction order with respect to AMP and CO2 concentration in the rate equation, which indicated more complexity of the reaction mechanism. Through the degradation rate data, the activation energy and reaction rate constant for the reaction of AMP and CO2 to form a zwitterion were also calculated. The obtained reaction parameters through a zwitterion mechanism were consistent with reported literature values, which were calculated through different approaches. However, the zwitterion formation in the degradation mechanism displayed no improvement in the experimental rate prediction ability of the model equation compared to more simplified pathways. Employing the long-term experimental concentration vs time data, the overall reaction between amine and CO2 to produce DMOZD was analyzed. The DMOZD and reactant concentrations at the steady state were calculated through an apparent reaction rate model. The results show that, depending on the AMP concentrations, CO2 loading, and solution temperature, at steady state conditions the percentage ratio of DMOZD concentration over AMP is between 0.5 and 7.

关键词： Magnesium   Hydrogen storage   Graphite   Electrochemical kinetics  

摘要： Magnesium nickel alloy (Mg2Ni) which used as the negative electrode material in the nickel-metal hydride (Ni/MH) secondary battery is modified by graphite via mechanical milling. The effects of graphite on the Mg2Ni are systematically investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and a series of electrochemical tests. The results show that the cycle stability of the Mg2Ni alloy is improved with the addition of 10 wt.% graphite and the discharge capacity at the 20th cycle increase from 116.9 mA g(-1) to 178.5 mA g(-1) The Tafel polarization test indicates better corrosion resistance of the Mg2Ni/graphite composite. Meanwhile, the results of electrochemical tests indicate that both the charge-transfer reaction rate on the surface of the alloy and the hydrogen diffusion rate inside the bulk of alloy are boosted with the introduction of graphite. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： dissipative particle dynamics   rotating nanoparticles   membrane rupture   nanoparticle-membrane interaction   cell apoptosis  

摘要： The effects of binding mode, shape, binding strength, and rotational speed of actively rotating nanoparticles on the integrity of cell membranes have been systematically studied using dissipative particle dynamics simulations. With theoretical analyses of lipid density, surface tension, stress distribution, and water permeation, we demonstrate that the rotation of nanoparticles can provide a strong driving force for membrane rupture. The results show that nanoparticles embedded inside a cell membrane via endocytosis are more capable of producing large membrane deformations under active rotation than nanoparticles attached on the cell membrane surface. Nanoparticles with anisotropic shapes produce larger deformation and have a higher rupture efficiency than those with symmetric shapes. Our findings provide useful design guidelines for a general strategy based on utilizing mechanical forces to rupture cell membranes and therefore destroy the integrity of cells.

关键词： Multibody system dynamics   transfer matrix method for multibody systems   visualized simulation and design   pre-processor   transfer matrix method for multibody system solver   post-processor   software  

摘要： The transfer matrix method for multibody systems is a new method with very high computational speed developed in recent 20 years for studying multibody system dynamics. By combining transfer matrix method for multibody systems, computer graphics, and open-source software, this article puts forward an approach and software MSTMMSim for visualized simulation and design of mechanical system dynamics. The approach includes the following procedures in sequence: design of functional model, design of three-dimensional solid model, design of dynamics model, automated formation of dynamics equations, and software MSTMMSim for visualized simulation and design of mechanical system dynamics. The proposed method and software provide a platform to realize the simulation and design of complex mechanical systems with the following characteristics: (1) automatic deduction of the overall transfer equation, (2) high computational speed, and (3) high visualization and programming of dynamics simulation and design process. The proposed method and software are verified by the practical example of simulation and design of a tank system dynamics using this platform.