• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.315-321
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• 2012

In this study, a sequential multiscale homogenization method to characterize the effective thermal conductivity of nano particulate polymer nanocomposites is proposed through a molecular dynamics(MD) simulations and a finite element-based homogenization method. The thermal conductivity of the nanocomposites embedding different-sized nanoparticles at a fixed volume fraction of 5.8% are obtained from MD simulations. Due to the Kapitza thermal resistance, the thermal conductivity of the nanocomposites decreases as the size of the embedded nanoparticle decreases. In order to describe the nanoparticle size effect using the homogenization method with accuracy, the Kapitza interface in which the temperature discontinuity condition appears and the effective interphase zone formed by highly densified matrix polymer are modeled as independent phases that constitutes the nanocomposites microstructure, thus, the overall nanocomposites domain is modeled as a four-phase structure consists of the nanoparticle, Kapitza interface, effective interphase, and polymer matrix. The thermal conductivity of the effective interphase is inversely predicted from the thermal conductivity of the nanocomposites through the multiscale homogenization method, then, exponentially fitted to a function of the particle radius. Using the multiscale homogenization method, the thermal conductivities of the nanocomposites at various particle radii and volume fractions are obtained, and parametric studies are conducted to examine the effect of the effective interphase on the overall thermal conductivity of the nanocomposites.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2702-2707
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• 2007

The purpose of this study is to calculate the behavior of molecules for the generation of homogeneous thin-films in the process of spray deposition. The calculation system was composed of a suface molecular region and droplet molecular region. The thin-film was generated when droplet molecules fell to surface molecules. Lennard-Jones potential had been used as intermolecular potential, and only attraction 때 d repulsion had been used for the behavior of the droplet on the solid surface. As results, the behavior of the droplet was so much influenced by the surface temperature in the spray deposition process. High temperature of surface has higher porosity and larger spread area. It was found that simulation results generally agreed well with previous the experimental results. This simulation result will be the foundation for the deposition processes of industry.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.8
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• pp.862-869
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• 2007

The compressive and torsional buckling behavior of carbon nanotube bundles at room temperature is examined with classical molecular dynamics simulation. The critical compressive load and stiffness of a single carbon nanotube in the bundle are found to be similar to those of individual carbon nanotubes. However, the critical torsional moment and stiffness of a single carbon nanotube in the bundle are found to be higher than those of individual carbon nanotubes. In addition, this study demonstrates that van der Waals interactions between the nanotubes in the bundle significantly affect the critical compressive load of the nanotube bundle.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.6
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• pp.454-459
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• 2003

We investigate the structure and properties of SiC (Silicon Carbide) nanotubes using molecular dynamics simulation based on the Tersoff bond-order potential. For small diameter tubes, the Si-C bond distance of SiC nanotubes decreases as the nanotube diameter is decreased, due to curvature of the nanotube surface. We find that Young's modulus of SiC nanotubes is somewhat smaller than that of the other nanotubes considered so far. However, Young's modulus for SiC nanotubes is larger than that of ${\beta}$-SiC and almost equal to the experimental value for SiC nanorod and SiC whisker. The strain energy of the SiC nanotubes is also lower than that of the other nanotubes. The lower strain energy of SiC nanotubes raises the possibility of synthesis of SiC nanotubes.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.4
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• pp.331-334
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• 2009

In this paper, we present a surface relaxation model in atomistic calculations for thin nanofilms. This surface relaxation model is very simple model which have only two degrees of freedoms to determine the atomic positions of nanofilms. Whereas in conventional molecular statics simulations, the same number of degrees of freedoms at all atom positions are used as unknown variables. In order to prove the reliability of the presented model, we present the results of self-equilibrium strain calculations with the surface parameters obtained from this model.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.421-426
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• 2007

A parametric study to investigate the effects of composition variables on the glass transition and mechanical properties of CNT-based nanocomposites was performed using molecular dynamics simulations. In this study, matrix chain length and CNT length were chosen as the candidate characteristic parameters. In order to understand the effect of both parameters in detail, three sample sets having different chain lengths with the same CNT configuration and two sample sets having different CNT lengths with same chain length were prepared. Other parameters such as volume fraction and density were fixed to enable rigorous comparisons. Amorphous polyethylene is used as matrix polymer and (10,0) zigzag CNT is embedded into the matrix to reinforce polymer matrix. As a result, longer polymer chain length of matrix solely increased glass transition temperature but no reinforcing enhancement was observed. CNT length showed similar increase with little enhancement of elastic modulus. In addition to this, nanocomposites showed temperature-dependent elastic modulus jump passing thorough the glass transition region agrees well with experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.6
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• pp.569-577
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• 2010

A multiscale particle simulation technique that can be applied to a multiphase fluid system has been developed. In the boundary region where the macroscopic- and microscopic-scale models overlap each other, three distinctive features are introduced in the simulation. First, a wall is set up between the gas and liquid phases to separate them and match the phases respectively to the macroscopic conditions stably. Secondly, the interfacial profile is obtained near the matching region and the wall translates and rotates to accommodate the change in the liquid-vapor interfacial position in the molecular model. The contact angle thus obtained can be sent to the macroscopic model. Finally, a state of mass and temperature in the region is maintained by inserting and deleting the particles. Good matching results are observed in the cases of the complete and partial wetting fluid systems.

• Korean Journal of Agricultural and Forest Meteorology
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• v.12 no.2
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• pp.122-131
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• 2010

This paper introduces the concept of a virtual ecosystem and reports the following three mathematical approaches that could be widely used to construct such an ecosystem, along with examples: (1) a molecular dynamics simulation approach for animal flocking behavior, (2) a stochastic lattice model approach for termite colony behavior, and (3) a rule-based cellular automata approach for biofilm growth. The ecosystem considered in this study consists of artificial organisms and their environment. Each organism in the ecosystem is an agent that interacts autonomously with the dynamic environment, including the other organisms within it. The three types of model were successful to account for each corresponding ecosystem. In order to accurately mimic a natural ecosystem, a virtual ecosystem needs to take many ecological variables into account. However, doing so is likely to introduce excess complexity and nonlinearity in the analysis of the virtual ecosystem's dynamics. Nonetheless, the development of a virtual ecosystem is important, because it can provide possible explanations for various phenomena such as environmental disturbances and disasters, and can also give insights into ecological functions from an individual to a community level from a synthetic viewpoint. As an example of how lower and higher levels in an ecosystem can be connected, this paper also briefly discusses the application of the second model to the simulation of a termite ecosystem and the influence of climate change on the termite ecosystem.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.48 no.1
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• pp.71-75
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• 2015

Nicotinic acetylcholine receptors (nAChRs) are essential for neurotransmission and important therapeutic targets of diseases related to neurotransmission. A recent experimental study identified three residues (Lys185, Asp187, and Ile188) of the ${\alpha}6$ nAChR subunit as determinants of ${\alpha}$-conotoxin BuIA selectivity, yet how these residues confer toxin selectivity remains unclear. In this study, we performed all-atom molecular dynamics simulations with two toxin-bound ${\alpha}4{\beta}2$ nAChR systems: the wild-type ${\alpha}4{\beta}2$ and one in which we replaced the three ${\alpha}4$ subunit residues with three ${\alpha}6$ subunit residues identified in an experimental study (Tyr185Lys, Thr187Asp, and Arg188Ile). After mutation, Asp199 lost the salt bridge formed with Arg188 in the wild type located around loop C. Then, the loop C conformation changed and became more flexible than that of the wild type. We also detected reduced space between the toxin and the binding site in the mutant simulation, resulting in increased binding affinity to the toxin. Therefore, we propose a new Asp199 mutation that breaks the salt bridge and may produce similar selectivity to that of the Arg188 mutation.

• Membrane Journal
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• v.32 no.6
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• pp.475-485
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• 2022

The continuous excessive consumption of fossil fuels is causing global warming, climate, and environmental crisis. Accordingly, hydrogen energy attracts attention among alternative energies of fossil fuels, because it has the advantage of not emitting pollutants and not having resource restrictions. Therefore, various studies are being conducted on a water electrolysis system for producing hydrogen and a fuel cell system for producing electricity by using hydrogen energy as a fuel. In this study, 3D ionomer models were produced by reflecting the excessive water condition of an anion-conductive ionomer material, which is one of the core materials of water electrolysis systems and fuel cells. Finally, by analyzing the structural stability and performance of the ionomer under an excessively hydrated condition, we suggested a performance improvement factor in the design of an anion conductive ionomer, a key material for water electrolysis systems and fuel cells.