• Journal of the Korean Applied Science and Technology
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• v.24 no.4
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• pp.354-361
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• 2007

The distribution of light in a randomly scattering medium can represent problems found in many area. Particularly, in the clinical application of lasers for Photodynamic therapy(PDT) or in the fluorescence spectroscopy for biological tissue, turbidity plays a very important role. The influences of fluorophor, scatterer, and absorber in turbid material by light scattering were interpreted for the scattered fluorescence intensity and wavelength. The molecular properties have been studied by laser induced fluorescence spectroscopy in scattering medium as tissue. It has been found that the effects of optical properties in scattering media could be investigated by the optical $parameters({\mu}_s$, ${\mu}_a$ ,${\mu}t)$. Experimental and Monte Carlo simulation method for modelling light transport in tissue was applied. The experimental results using a randomly distributed scattering medium were discussed and compared with those obtained through Monte Carlo simulation. It'll be also important in designing the best model for oil chemistry, medicine and application of medical engineering.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.816-821
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• 2003

The pumping characteristics of a disk-type drag pump (DTDP) from free molecular flow region to the slip flow region are calculated by the direct simulation Monte Carlo (DSMC) method. In this study, the pumping performance is studied numerically for several channel depths. The interaction between molecules is modeled by variable hard-sphere (VHS). The no time counter method is used as a collision sampling technique. The clearance between rotor and stator is considered an effect on performance. Spiral channels are cut on both upper and lower sides of rotating disks, and stationary disks are planar. A three-dimensional DSMC method for the analysis of steady rarefied flows in a single-stage DTDP has been developed. Velocity and density fields were obtained by the DSMC simulation in the rotor. The present experimental data in the outlet pressure range of $7.5{\times}10^{-3}{\sim}4$ Torr were compared with the DSMC results in the single-stage DTDP. Comparison between the experimental data and DSMC results showed good agreement.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.515-518
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• 2005

In this paper, we report on our theoretical study on the effect of surface anchoring. Molecular dynamics as well as optical characteristics of PVA cell are computer-simulated with 3D-FEM numerical solver, TechWiz $LCD^{(R)}$. Although simulation parameters are the same except for the consideration of surface anchoring, the simulation reveals that optical transmittance is improved by more than 8% for the weak anchoring case with comparison to the strong anchoring case. Moreover, capacitance between pixel and common electrode is 7% lower for the strong anchoring than that for the weak anchoring. This implies that there exists an appreciable difference between the strong anchoring case and the weak anchoring case. It is very important to take the effect of surface anchoring into account in order to figure out the optical characteristics of an LCD cell more accurately.

• Bulletin of the Korean Chemical Society
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• v.28 no.11
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• pp.2069-2074
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• 2007

The 27Al multiple quantum magic angle spinning (MQMAS) nuclear magnetic resonance (NMR) spectra of mordenite zeolites were simulated using the point charge model (PCM). The spectra simulated by the PCM considering nearest neighbor atoms only (PCM-n) or including atoms up to the 3rd layer (PCM-m) were not different from those generated by the Hartree-Fock (HF) molecular orbital calculation method. In contrast to the HF and density functional theory methods, the PCM method is simple and convenient to use and does not require sophisticated and expensive computer programs along with specialists to run them. Thus, our results indicate that the spectral simulation of the 27Al MQMAS NMR spectra obtained with the PCM-n is useful, despite its simplicity, especially for porous samples like zeolites with large unit cells and a high volume density of pores. However, it should be pointed out that this conclusion might apply only for the atomic sites with small quadrupole coupling constants.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.98.1-98.1
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• 2012

We present the results of dust scattering simulations carried out for the Orion-Eridanus Superbubble region by comparing them with observations made in the far-ultraviolet. The albedo and the phase function asymmetry factor (g-factor) of interstellar grains were estimated, as were the distance and thickness of the dust layers. The results are as follows: [0.43]_(-0.04)^(+0.02) for the albedo and [0.43]_(-0.2)^(+0.2) for the g-factor, in good agreement with previous determinations and theoretical predictions. The distance of the assumed single dust layer, modeled for the Orion Molecular Cloud Complex, was estimated to be ~110 pc, and the thickness ranged from ~130 at the core to ~50 pc at the boundary for the region of present interest, implying that the dust cloud is located in front of the superbubble. The simulation result also indicates that a thin (~10 pc) dust shell surrounds the inner X-ray cavities of hot gas at a distance of ~70-90 pc.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.2
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• pp.37-44
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• 2013

Generally, a reduced chemical mechanism of n-heptane is used as chemical fuel of a 3-D diesel engine simulation because diesel fuel consists of hundreds of chemical components and various chemical classes so that it is very complex and large to use for the calculation. However, the importance of fuel in a 3-D simulation increases because detailed fuel characteristics are the key factor in the recent engine research such as homogeneous charged compression ignition engine. In this study, normal paraffin, iso paraffin and aromatics were selected to represent diesel characteristics and n-dodecane was used as a representative normal paraffin to describe the heavy molecular weight of diesel oil (C10~C20). Reduced kinetics of iso-octane and toluene which are representative species of iso paraffin and aromatics respectively were developed in the previous study. Some species were selected based on the sensitivity analysis and a mechanism was developed based on the general oxidation scheme. The ignition delay times, maximum pressure and temperature of the new reduced n-dodecane chemical mechanisms were well matched to the detailed mechanism data.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.359-359
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• 2010

Self-organized nanostructures of dots, holes or ripples produced by energetic ion bombardment have been reported in a wide variety of substrates. Ion bombardment on an alloy or compound also draws much attention because it can induce a surface composition modulation with a topographical surface structure evolution. V. B. Shenoy et al. further suggested that, in the case of alloy surfaces, the differences in the sputtering yields and surface diffusivities of the alloy components will lead to a lateral surface composition modulation [1]. In the present work, the classical molecular dynamics simulation of Ar bombardment on metallic alloys at room temperature revealed that this bombardment induces a surface composition modulation in layer-by-layer mode. In both the $Co_{0.5}Cu_{0.5}$ alloy and the CoAl B2 phase, the element of higher-sputtering yield is accumulated on the top surface layer, whereas it is depleted in lower layers. A kinetic model considering both the rearrangement and the sputtering of the substrate atoms agrees with the puzzling simulation results, which revealed that the rearrangement of the substrate atoms plays a significant role in the observed composition modulation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.649-652
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• 2005

It is reported that semi-solid forming process takes many advantages over the conventional forming process, such as long die lift, good mechanical properties and energy saves. Rheology material has a thixotropic, pseudo-plastic and shear-thinning characteristic. Therefore, general plastic or fluid dynamic analysis is not suitable for the behavior of rheology material. So it is difficult for a numerical simulation of the rheology process to be performed because complicated processes such as the filling to include the state of the free surface and solidification in the phase transformation must be considered. Moreover, it is important to predict the deformation behavior for optimization of net shape forging process with semi-solid materials and to control liquid segregation for mechanical properties of materials. In this study, so, molecular dynamics simulation was performed for the control of liquid segregation in compression experiment as a part of study on analysis of rheology forming process.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.150-156
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• 2008

A program based on a 2-D CFD code has been developed to simulate a gas turbine engine. 2-D Navier-Stokes implicit code with $k-\omega$ turbulent model is used in compressor and turbine. Lumped method chemical equilibrium code with 10 species of molecular is applied to combustor with assuming perfect mixture and 100% combustion efficiency at constant pressure state. Fluid properties are shared on interfaces between engine components. Compressor supplies outlet temperature and pressure to combustor. At the same time, combustor also carries temperature and pressure to turbine. The back pressure of compressor outlet is transferred by inlet pressure of turbine. Unsteady phenomena in rotor-stator are covered by mixing-plane method. The running condition of engine can be determined only by given the inlet condition of compressor, the outlet condition of turbine, equivalence ratio and rotating speed.

• Nuclear Engineering and Technology
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• v.47 no.7
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• pp.827-837
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• 2015

Following a severe accident in a nuclear power plant, iodine is a major contributor to the potential health risks for the public. Because the amount of iodine released largely depends on its volatility, iodine's behavior in containment has been extensively studied in international programs such as International Source Term Programme-Experimental Program on Iodine Chemistry under Radiation (EPICUR), Organization for Economic Co-operation and Development (OECD)-Behaviour of Iodine Project, and OECD-Source Term Evaluation and Mitigation. Korea Institute of Nuclear Safety (KINS) has joined these programs and is developing a simplified, stand-alone iodine chemistry model, RAIM (Radio-Active Iodine chemistry Model), based on the IMOD methodology and other previous studies. This model deals with chemical reactions associated with the formation and destruction of iodine species and surface reactions in the containment atmosphere and the sump in a simple manner. RAIM was applied to a simulation of four EPICUR tests and one Radioiodine Test Facility test, which were carried out in aqueous or gaseous phases. After analysis, the results show a trend of underestimation of organic and molecular iodine for the gas-phase experiments, the opposite of that for the aqueous-phase ones, whereas the total amount of volatile iodine species agrees well between the experiment and the analysis result.