• Journal of the Korean Magnetics Society
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• v.16 no.6
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• pp.293-299
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• 2006

Magnetic nanoparticles were prepared by thermal decomposition and adsorbed with lecithin by applying ultrasonic. The size and saturation magnetization of magnetic nanoparticles were observed with different lecithin concentration, and the maximum tolerated dose (HTD) and toxicity of magnetic fluid was investigated through a biological test. The thickness of lecithin-adsorption layer increased non-linearly with increasing amounts of added lecithin, and the desirable adsorption amount was observed in the lecithin concentration of 20%(w/v). The dispersibility and magnetic properties of lecithin-adsorbed magnetic nanoparticles were most excellent when the ultrasonic exposure time was 1.5h. Also, the maximum tolerated concentration with best cell viability was $32{\mu}g/ml$ in vitro test, and lecithin-adsorbed magnetic fluids improved the biocompatibility by 1.2 times compared with bare magnetite fluids in vivo.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.191-191
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• 2012

유체 플라즈마 공정(SPP)은 고에너지를 가지는 플라즈마를 유체 내에 발생시키는 공정으로서 나노유체 및 촉매 물질 제조 등 여러 가지 응용분야에 적용할 수 있다. 본 연구에서는 SPP 공정을 이용하여 금 나노입자를 합성하였고 전압과 방전시간의 변화에 따른 금나노 입자의 환원속도를 분석하였다.

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.1
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• pp.29-38
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• 2005

The fluid animation procedure consists of physical simulation and visual rendering. In the physical simulation of fluids, the most frequently used practices are the numerical simulation of fluid particles using particle dynamics equations and the continuum analysis of flow via Wavier-Stokes equation. Particle dynamics method is fast in calculation, but the resulting fluid motion is conditionally unrealistic The method using Wavier-Stokes equation, on the contrary, yields lifelike fluid motion when properly conditioned, yet the complexity of calculation restrains this method from being used in real-time applications. Global illumination is generally successful in producing premium-Duality rendered images, but is also excessively slow for real-time applications. In this paper, we propose a rapid fluid animation method incorporating enhanced particle dynamics simulation method and pre-integrated volume rendering technique. The particle dynamics simulation of fluid flow was conducted in real-time using Lennard-Jones model, and the computation efficiency was enhanced such that a small number of particles can represent a significant volume. For real-time rendering, pre-integrated volume rendering method was used so that fewer slices than ever can construct seamless inter-laminar shades. The proposed method could successfully simulate and render the fluid motion in real time at an acceptable speed and visual quality.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.383.1-383.1
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• 2016

열전달 시스템에서 임계 열유속 발생 시 시스템의 물리적 손상을 야기하기 때문에 비등 열전달에서 임계 열유속은 열전달 시스템의 한계 또는 안전성을 나타낸다. 따라서 열전달 시스템의 안정성을 위해서는 임계 열유속 향상이 필수적이다. 최근에는 나노유체를 열전달 시스템에 적용할 경우 임계 열유속이 증가한다고 보고되었다. 하지만 나노유체는 원전 및 각종 열전달 시스템에 적용 시 나노입자가 열전달 표면에 침착되는 파울링 현상을 발생시킬 수 있으며, 이 때문에 시스템의 열효율이 크게 감소할 수 있다. 따라서 본 연구에서는 열전달 시스템에 나노유체를 적용했을 때, 나노유체의 침착현상이 시스템에 미치는 영향을 분석하였다. 그 결과 유속과 코팅시간이 증가할수록 산화처리된 다중벽 탄소나노튜브 나노유체의 임계 열유속이 크게 증가하고 있음을 확인할 수 있다. 하지만 나노입자 침착정도와 유속이 증가할수록 비등 열전달 표면과 유체의 포화온도의 차이인 과열도가 상당히 크게 증가함을 알 수 있었으며, 열전달 계수는 순수 물의 0 m/s의 비등 열전달 계수와 비교하면 감소하는 것을 확인하였다.

• The Korean Journal of Rheology
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• v.9 no.4
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• pp.183-189
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• 1997

본 연구에서는 고분자용액을 분산매로한 현탁액 내에서 입자의 수력학적확산에 관 한 실험적인 연구를 수행하여다. 입자로는 평균직경 275마이크론의 polymethlmethacrylate (PMMA)구형입자를 사용하였고, 분산매로는 PMMA 입자와 밀도르 맞춘 글리세린과 에틸 렌글리콜의 혼합용액에 고분자를 첨가하여 사용하였다. 고분자로는 분자량 6백만의 시약용 폴리아크릴아마이드를 사용하였다. 입자농도는 50%이었다. 용액의 농도는 0∼700ppm이었으 며 이러한 용액은 전단박화현상을 나타내지 않았다. 확산계수는 쿠엣장치 내에서 입자가 두 원통사이에서 아래쪽의 빈 공간으로 확산할 때 시간에 따른 점도측정결과로부터 예측하여 다. 본 연구의 결과 뉴튼성유체의 경우와는 달리 무차원확산계수(D/2)가 일정하지 않으며 전단율이 증가될수록 점점 감소하는 현상을 나타내었다. 고분자의 농도가 증가하는 경우에 는 무차원 확산계수가 감솨는 것을 볼수있었다. 이러한 무차원 확산계수의 감소는 유동하는 현탁액 내에서 입자간의 상호작용이 뉴튼성유체에 비하여 가역적인 것에 기인하는 것으로 판단된다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.161-161
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• 2013

본 연구에서는 백금 나노입자의 크기, 형상, 분포도에 따른 전기 화학적 효율을 평가하기 위해 계면활성제 농도를 달리하여 백금 나노입자를 합성하였다. 계면활성제로는 CTAB(cetyltrimethylammonium bromide)이 사용되었으며, 0.5 mM의 $H_2PtCl_6$의 백금 염을 환원시키기 위하여 유체 플라즈마 공정을 이용하였다. 공정 시간은 UV-vis 스펙트럼 결과를 토대로, 262 nm의 파장대에서 관찰된 LMCT(ligand-to-metal charge transfer) peak이 사라지는 시간을 기준으로 하여 공정을 진행하였다. 합성된 나노입자는 순환 전류-전압곡선(CV), TEM이미지와 XRD 분석을 이용하여 전기화학적 특성, 입자의 평균 크기 및 형상 변화를 비교 분석 하였다. 그 결과 CTAB을 넣지 않은 백금나노입자의 경우, CTAB을 넣고 제조한 백금 나노입자와는 달리 구의 형태로 뭉쳐있음을 관찰하였고, 이러한 백금 나노입자의 구조는 보다 높은 전기화학적 활성 특성을 가짐을 보였다.

• Korean Chemical Engineering Research
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• v.59 no.4
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• pp.639-643
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• 2021

In this study, fluorinated ethylene propylene (FEP) nanoparticle as an adhesive for fabricating a three-dimensional multilayered microfluidic device was studied. The formation of evenly distributed FEP nanoparticles layer with 3 ㎛ in thickness on substrates was achieved by simple spin coating of FEP dispersion solution at 1500 rpm for 30 s. It is confirmed that FEP nanoparticles transformed into a hydrophobic thin film after thermal treatment at 300 ℃ for 1 hour, and fabricated polyimide film-based microfluidic device using FEP nanoparticle was endured pressure up to 2250 psi. Finally, a three-dimensional multilayered microfluidic device composed of 16 microreactors, which are difficult to fabricate with conventional photolithography, was successfully realized by simple one-step alignment of FEP coated nine polyimide films. The developed three-dimensional multilayered microfluidic device has the potential to be a powerful tool such as high-throughput screening, mass production, parallelization, and large-scale microfluidic integration for various applications in chemistry and biology.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.58-64
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• 2019

This study presents a novel method for preparing monodisperse polyethylene glycol diacrylate (PEGDA) microparticles in a dispensing needle based microfluidic device. The microfluidic devices are manufactured by manually assembling various off-the-shelf products without using additional equipment. In this microfluidic device, the volumetric flow rates of the dispersed phase of PEGDA solution and the continuous phase of oil are controlled to generate monodisperse PEGDA droplets. The PEGDA droplet contains photo-initiator thus it is crosslinked to microparticle by photopolymerization at the ends of the device. The particle size is easily controlled by adjusting the volume flow rate and the size of the microfluidic device. The monodispersity of the particles is calculated by a coefficient of variation of 2.57%. To demonstrate the biological applications of PEGDA particles, cells are encapsulated and observed for proliferation and viability.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1438-1449
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• 1988

An analysis of radiative heat transfer has been conducted on axisymmetric finite cylindrical media. It is assumed that the temperature in the media is uniformly distributed and the boundaries are diffusely emitting and reflecting at a constant temperature. The scattering phase function is represented by the delta-Eddington approximation to account for highly forward scattering by particulates just as in the combustion system. Exact numerical solutions are obtained by Gaussian quadrature method and compared with P-1 and P-3 approximation solutions to verify their engineering application limit. The effects of optical thickness, scattering albedo, wall emissivity and aspect ratio are investigated. The results show that P-3 approximation is found to be in good agreement with the exact solution.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.7
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• pp.455-462
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• 2017

The magnetic interaction between elliptic Janus magnetic particles are investigated using a direct simulation method. Each particle is a one-to-one mixture of paramagnetic and nonmagnetic materials. The fluid is assumed to be incompressible Newtonian and nonmagnetic. A uniform magnetic field is applied externally in a horizontal direction. A finite-element-based fictitious domain method is employed to solve the magnetic particulate flow in the creeping flow regime. In the magnetic problem, the magnetic field in the entire domain, including the particles and the fluid, is obtained by solving the governing equation for the magnetic potential. Then, the magnetic forces acting on the particles are calculated via a Maxwell stress tensor formulation. In a single particle problem, it is found that the orientation angle at equilibrium is affected by the aspect ratio of the particle. As for the two-particle interaction, the dynamics and the final conformation of the particles are significantly influenced by the aspect ratio, the orientation, and the spatial positions of the particles. For the given positions of the particles, the fluid flow is also influenced by the orientation of each particle. The self-assembly structure of the particles is not a fixed one, but it varies with the above-mentioned factors.