• Journal of computational fluids engineering
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• v.14 no.1
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• pp.86-95
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• 2009

A kinetic theory analysis is used to study the ultra-thin gas flow field in gas bearings. The Boltzmann equation simplified by a collision model is solved by means of a finite difference approximation with the discrete ordinate method. Calculations are made for flows inside micro-channels of backward-facing step, forward-facing step, and slider bearings. The results are compared well with those from the DSMC method. The present method does not suffer from statistical noise which is common in particle based methods and requires less computational effort.

• Journal of The Korean Astronomical Society
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• v.29 no.2
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• pp.195-205
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• 1996

The evolution of the stellar debris after tidal disruption due to the super massive black hole's tidal force is difficult to solve numerically because of the large dynamical range of the problem. We developed an SPH (Smoothed Particle Hydrodynamics) - TVD (Total Variation Diminishing) hybrid code in which the SPH is used to cover a widely spread debris and the TVD is used to compute the stream collision more accurately. While the code in the present form is not sufficient to obtain desired resoultion, it could provide a useful tool in studying the aftermath of the stellar disruption by a massive black hole.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.167-170
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• 2005

The mechanism of striation in the coplanar- and matrix-type plasma display panel (PDP) cells has been studied using the particle-in-cell Monte-Carlo Collision (PIC-MCC) model. The striation formation is related to the ionization energy of neutral atoms and the well-like deformation of space potential by space charge distribution. Negative wall charge accumulation by electrons on the MgO surface of the anode region is also one of the key factors for the formation of striation. The clearness of the striation phenomenon in PIC-MCC code in comparison with fluid code can be explained by using nonlocal electron kinetic effect.

• Journal of the Korean Ceramic Society
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• v.26 no.6
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• pp.836-842
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• 1989

In this study, finely divided vanadium pentoxide was prepared by carrying vapor of vanadyl trichloride into the flame of an C3H8-O2-H2 with a specially designed burner. The flame-synthesized oxide particles had a nonporous spherical shape with nearly constant diameter in the range of 200-600$\AA$. The surface area of these particles depends on the residence time and the concentration of metal chloride vapor in the burner. The experimental results showed that the growth of particles is controlled by fusion rather than collision. The crystal size of finely divided V2O5 particle was increased after calcination at temperature above 50$0^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.8
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• pp.742-747
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• 2007

In 2-dimensional SCBF (Spherically Convergent Beam Fusion) device, the effect on neutron production rate of the grid cathode geometry was simulated. The motion of Particles was tracked using Monte Carlo Method including the atomic and molecular collision processes and potential distribution was calculated by Finite Element Method, Main processes of the discharge were the ionization of $D_2$ by fast $D_2^+\;ion$. As the number of cathode rings was small and the size of grid cathode decreased, the ion current increased and neutron production rate will also increase. The star mode discharge which is a very important characteristic in SCBF device, was confirmed by the ionization position.

• Bulletin of the Korean Chemical Society
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• v.34 no.2
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• pp.574-578
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• 2013

In this work, the friction and diffusion coefficients of a tracer in a mesoscopic solvent are evaluated as a function of the tracer size by a hybrid molecular dynamics simulation where solute molecules evolve by Newton's equations of motion but the solvent evolves through the multi-particle collision dynamics. The friction coefficient is shown to scale linearly with the tracer size for larger tracers in accord with predictions of hydrodynamic theories. The diffusion coefficient of tracer is found to be inversely proportional to tracer size. The behavior of Stokes-Einstein formula is validated as a function of tracer size.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.369-372
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• 1997

Wire Ion Plasma Source (WIPS) is a plasma device which has a thin wire anode, a coaxially-set cylindrical cathode and electrodes located in both ends of the cylinder. The potential between the anode and cathode changes logarithmically by this electrode configuration. This electrode configuration enables high-density plasma to produce even at a low anode voltage. Since the electrode configuration is axially symmetric and long. plasma with axially uniform number density can be produced. Using particle-in-cell(PIC) and Monte Carlo collision(MCC), we investigate the traiectory of electrons and the characteristics of D.C. discharge in Wire ton Plasma Source.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.714-714
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• 2005

This paper presents the modeling and impact analysis for a rotating cantilever beam having a concentrated mass. The concentrated mass takes an impact force during the rotating motion and the transient response of the beam induced by the impact is calculated by applying the Rayleigh-Ritz assumed mode method. The stiffness variation effect caused by the rotating motion is considered in this modeling. The effects of the concentrated mass size, impact position and the angular velocity of the beam on the transient responses are investigated through numerical studies.

• Proceedings of the Korean Society of Computer Information Conference
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• 2023.01a
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• pp.395-398
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• 2023

본 논문에서는 물리 기반 옷감 시뮬레이션과 SPH(Smoothed particle hydrodynamics) 기반의 유체 시뮬레이션 간의 상호작용에서 표현되는 다양한 물리적 효과를 GPU 기반으로 빠르게 표현할 수 있는 프레임워크를 제안한다. 기존 기법과는 다르게 수치적 안정성을 개선하기 위해 CCD(Continuous collision detection)를 활용하였으며, 모든 연산이 GPU에서 동작하기 때문에 매우 빠르게 옷감과 유체의 상호작용 장면인 다공성 재질, 기공 흐름, 흡수, 방사, 확산을 모델링할 수 있다.

• Publications of The Korean Astronomical Society
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• v.7 no.1
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• pp.89-96
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• 1992

Recent spectroscopic observations indicate concentration of dark masses in the nuclei of nearby galaxies. This has been usually interpreted as the presence of massive black holes in these nuclei. Alternative explanations such as the dark cluster composed of low mass stars (brown dwarfs) or dark stellar remnants are possible provided that these systems can be stably maintained for the age of galaxies. For the case of low mass star cluster, mass of individual stars can grow to that of conventional stars in collision time scale. The requirement of collision time scale being shorter than the Hubble time gives the minimum cluster size. For typical conditions of M31 or M32, the half-mass radii of dark clusters can be as small as 0.1 arcsecond. For the case of clusters composed of stellar remnants, core-collapse and post-collapse expansion are required to take place in longer than Hubble time. Simple estimates reveal that the size of these clusters also can be small enough that no contradiction with observational data exists for the clusters made of white dwarfs or neutron stars. We then considered the possible outcomes of interactions between the black hole and the surrounding stellar system. Under typical conditions of M31 or M32, tidal disruption will occur every $10^3$ to $10^4$ years. We present a simple scenario for the evolution of stellar debris based on basic principles. While the accretion of stellar material could produce large amount of radiation so that the mass-to-light ratio can become too small compared to observational values it is too early to rule out the black hole model because the black hole can consume most of the stellar debris in time scale much shorter than mean time between two successive tidal disruptions. Finally we outline recent effort to simulate the process of tidal disruption and subsequent evolution of the stellar debris numerically using Smoothed Particle Hydrodynamics technique.