• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.5
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• pp.618-622
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• 2011

Specialized large-scale computational finite-element and molecular dynamic models have been used in order to understand and predict how dislocation density emission and contact stress field due to nanoindentation affect inelastic deformation evolution scales that span the molecular to the continuum level in ductile crystalline systems. Dislocation density distributions and local stress fields have been obtained for different crystalline slip-system and grain-boundary orientations. The interrelated effects of grain-boundary interfaces and orientations, dislocation density evolution and crystalline structure on indentation inelastic regions have been investigated.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.2
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• pp.45-50
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• 2008

Molecular flows inside a guide block in the OLED(organic luminescent emitting device) deposition process have been simulated using DSMC(direct simulation Monte Carlo) method. Because the organic materials are evaporated under vacuum, molecules flow at a high Knudsen number of the free molecular regime, where the continuum mechanics is not valid. A guide block is designed as a part of the linear cell source to transport the evaporated materials to a deposition chamber, When solving the flows, the inlet boundary condition is proved to affect significantly the whole flow pattern. Thus, it is proposed that the pressure should be specified at the inlet. From the analysis of the density distributions at the nozzle exit of the guide block, it is shown that the longer nozzle can emit molecules more straightly. Finally, a nondimensionalized mass flow profile is obtained by numerical experiments, where various nozzle widths and inlet pressures are tested.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.4
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• pp.421-427
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• 2015

In this paper, a description is given of finite element method (FEM) simulations of the elastic bending modulus of multi-layered graphene sheets that were carried out to investigate the mechanical behavior of graphene sheets with different gap thicknesses through molecular mechanics theory. The interaction forces between layers with various gap thicknesses were considered based on the van der Waals interaction. A finite element (FE) model of a multi-layered rectangular graphene sheet was proposed with beam elements representing bonded interactions and spring elements representing non-bonded interactions between layers and between diagonally adjacent atoms. As a result, the average elastic bending modulus was predicted to be 1.13 TPa in the armchair direction and 1.18 TPa in the zigzag direction. The simulation results from this work are comparable to both experimental tests and numerical studies from the literature.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.5
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• pp.117-122
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• 2018

3D printing technology and its applications have grown rapidly in academia and industry. We consider a 3D printing system designed for the selective laser sintering (SLS) method, which is one of the powder bed fusion (PBF) techniques to build up the final product by layering sintered powder slices. Thermal distortion of printing products is a critical challenge in 3D printing. This study investigates temperature-dependent conformational behaviors of 3D printed samples of sintered poly-ether-ether-ketone (PEEK) powders using molecular dynamics simulations. The wear and chemical resistance properties of PEEK are understood, as it is a well-known biocompatible material used for implants. However, studies on physical phenomena at nanoscale in PEEK are rarely published in public. We simulate dissipative particle dynamics to elucidate how a cavity regime forms in PEEK at different system temperatures. We demonstrate how PEEK structures deform subject to the system temperature distribution.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.5
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• pp.60-65
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• 2019

Since nanofluids (NFs), which are a mixture of a small amount of nanoparticles and a bulk liquid solvent, were first proposed by Stephen Choi at the Argonne National Lab in 1995, they have been considered for use in many technical studies of power cooling systems and their practical application due to their high thermal conductivity and heat transfer coefficients compared to conventional coolants. Although nanofluids are a well-known form of engineering fluid that show great promise for use in future cooling systems, their underlying physics as demonstrated in experiments remain unclear. One proven method of determining the heat transfer performance of nanofluids is measuring the concentration of nanoparticles in a mixture. However, it is experimentally inefficient to build testbeds to systematically observe particle distributions on a nanoscale. In this paper, we demonstrate the distribution of nanoparticles under a temperature gradient in a solution using molecular dynamics simulations. First, temperature profiles based on substrate temperature are introduced. Following this, the radial pair distribution functions of pairs of nanoparticles, solvents, and substrates are calculated. Finally, the distribution of nanoparticles in different heating regions is determined.

• Journal of Microbiology and Biotechnology
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• v.7 no.3
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• pp.200-203
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• 1997

Bacteria isolated from ultrapure water made by a high-purity water manufacturing system in a semiconductor manufacturing plant were classified into two groups which either grew in diluted nutrient broth medium (oligotrophic bacteria) or could not grow (copiotrophic bacteria). The nutritional flexibility of oligotrophic and copiotrophic bacteria was investigated. The oligotrophic bacteria were shown to be able to utilize a significantly broader range of organic substrates than the copiotrophic bateria. This finding substantiates the hypothesis that nutritional flexibility is adaptive for oligotrophic bacteria.

• International Journal of Advanced Culture Technology
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• v.1 no.1
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• pp.19-22
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• 2013

The basic principle of the product manufacturing technology using the 3D printing technique materializes the material including the high molecular substance or plastic and metallic dust, and etc. the product into the laminate additive manufacturing according to the design diagram gradually. It is applied to the various industrial field including the field of food division, field of home appliances, field of medicine, field of mechanical department and construction, etc.. The global development case of 3D printing technique is the next. This study described global technology and market trends. Afterward, 3D printing technique manages the important role when it exceeds the product manufacturing view just and is grafted with the various technology including the biotechnology, nanotechnology, and etc. and it improves the quality of the human life.

• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.707-710
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• 2012

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2678-2683
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• 2007

The interaction between metal molecules and liquid metal molecules was modeled in the molecular scale and simulated by the molecular dynamics method in order to understand behaviors of the cluster on metallic surface in collision process. Lennard-Jones potential had been used as intermolecular potential, and only attraction 때 d repulsion had been used for the behavior of the cluster on the metal surface. As results, the behavior of the cluster was so much influenced by the cluster of liquid metal temperature and function of molecules forces, such as attraction and repulsion, in the collision progress. These results of simulation will be the foundation for the micro fabrication manufacturing by using spray application technology.

• Journal of the Korean Magnetic Resonance Society
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• v.20 no.1
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• pp.7-12
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• 2016

PTMEG(Polytetramethylene ether glycol) is a polymer compound widely used as a wide range of applications in the textile industry. PTMEG substance carrying various 1,800~2,000 molecular weight are mainly used as the raw material of the spandex production. Molecular weight and degree of polymerization value for 4 different PTMEG samples under pilot plant scale synthetic process were determined by a new quantitative NMR method. In NMR experiments, p-toluenesulfonic acid(TSOH) was used for external standard material of PTMEG quantitative analysis. were measuring The concentration of the primary standard TSOH was measured by UV/Vis spectroscopy. By using NMR peak assignments and the integral values of designated proton NMR peaks, We were able to measure the % composition of the synthetic PTMEG polymers, concentrations, molecular weight and the degree of polymerization that show the synthetic process of each manufacturing pilot plant. By utilizing a newly developed quantitative NMR method were able to obtain the molecular weight of PTMEG samples within 0.08 error % range.