• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.9 no.5
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• pp.458-464
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• 2016

This paper proposes the compensation method which decreases the radiation pattern distortion caused by the mutual coupling in an array antenna. If the element distance of an array antenna decreases, the radiation pattern could be distorted by the strong mutual coupling, which changes the magnitude and phase of input signals and causes an unwanted radiation pattern. To remove the pattern distortion, compensated input signals are inserted in an array antenna. The magnitude and phase of input signals are determined by Particle Swarm Optimization (PSO) algorithm. A $4{\times}1$ dipole array antenna with omnidirectional elements is used to confirm the validity of the algorithm, where each element is placed in 0.2 wavelength to evoke the strong coupling. After input signals are optimized by PSO, it is found that the compensated radiation results in the same as the ideal case.

• Polymer(Korea)
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• v.28 no.2
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• pp.170-176
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• 2004

The effect of reaction conditions on the size and size distribution of superparamagnetic iron oxide coated with siloxane was big investigated by using dynamic light scattering. The hydrogen bond between the hydroxyl groups on tile surface of the magnetite and silanol was confirmed by FT-IR. The size of nanoparticles increased with the reaction temperature, but decreased with monomer contents and agitation speeds. There was not a big difference in size of nanoparticles, prepared by different reaction conditions, but its distribution was in the range of 14∼41nm. All samples exhibited the superparamagnetic nature. The magnetic susceptibility of the nanoparticles increased with the reaction temperature while it decreased with the monomer content and agitation speed.

• Polymer(Korea)
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• v.36 no.6
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• pp.822-830
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• 2012

We used dipodal type bis[3-(trimethoxysilyl)propyl]amine (BTMA) silane coupling agent to modify silica nanoparticles to introduce secondary amino groups on the silica surface. These N-H groups were reacted with three different molecular weights (M.W. = 258, 575, and 700) of poly(ethylene glycol) diacrylates to introduce different attached layer thicknesses on the silica surface by Michael addition reaction. After Michael addition reaction, we used several analytical techniques such as fourier transform infrared spectroscopy (FTIR), elemental analysis (EA) and solid state $^{13}C$ cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance spectroscopy to characterize introduced structures. We found almost complete Michael addition reaction of both two acrylate groups of PDGDA with N-H groups of BTMA modified silica to form ${\beta}$-amino acid esters. Between equimolar ratio of pure BTMA and pure PEGDA reaction, only one acrylate group of two acrylate groups of PEGDA reacted with N-H groups of pure BTMA to form ${\beta}$-amino acid ester and the other remaining acrylate group can be used to form a polymer later.

• Polymer(Korea)
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• v.33 no.4
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• pp.389-395
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• 2009

To develop the carrier of hydrophobic antifungal agents based on low molecular weight water-soluble chitosan (LMWSC), LMWSC was chemically modified with deoxycholic acid (DA) which is one of the bile acid as a hydrophobic group. The nanoparticles (WSCDA) using DA conjugated LMWSC were characterized using dynamic light scattering (DLS) and transmittance electron microscope (TEM). The particle size of WSCDA ranged from 250 to 350 nm and increased with the number of DA substitution. The loaded itraconazole as an antifungal agent WSCDA nanoparticles (WSCDA-ITCN) were prepared by solvent evaporation method. The drug content and the loading efficiency were investigated approximately $9{\sim}10%$ and $61{\sim}68%$ by UV spectrophotometer, respectively. The release of drug from nanoparticles was slow and showed sustained release characteristics. Based on the results of release study that the higher DA contents in WSCDA, the slower the releasing rate, the WSCDA-ITCN could be used as an excellent antifungal agent.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.3
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• pp.145-151
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• 2003

Using computational fluid dynamics (CFD) method, we investigated three-dimensional fluid flow field and particle movement with respect to the injected gas flow rate variation in typical cyclone separator system. The results of numerical investigation were deduced by coupling the analysis of fluid flow field with Wavier-stokes equation and the tracking of the particle trajectory with Langrangian approach. It was shown that the increasing of injected gas flow rate resulted in the increasing of pressure loss in the separator. This change of inner pressure had an effect on an aspect of the fluid flow in the separator. Particle movement was determined by fluid flow in the separator and was fully depended on a diameter of particles under the fixed flow rate. Increasing of injected gas flow rate was led to an increasing of the trace of particle, so the particles moved to the lower part of the separator. For this reason, the minimum diameters of the particles were decreased and increased the separation rate under the fixed particle diameter. In conclusion, the changes of injected gas flow rate have an important factor to the fluctuation of the fluid flow field and particle trajectory in the separator.

• Clean Technology
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• v.10 no.4
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• pp.195-201
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• 2004

Cellulase was modified with copolymer with polyethylene(PE)/polypropylene(PP) oxide and maleic anhydride(MA) by maleylation reaction, and modified cellulase was applied to the reprocessing of old newsprint (ONP). Cellulase of modified cellulase enhanced the detachment of ink particles by fibrillation of fiber. The copolymer, which acted as the surfactant formed bubbles and removed the ink particles in the floatation process. Modified cellulase showed the same deinking ability without excess dosage compared with the conventional method. And, it improved the physical properties including tensile strength, brightness, and whiteness compared with the conventional deinking process. The bond between the ink and fiber got stronger as the storage time increased, and it became very difficult to remove the ink particle. But, modified cellulase increased the deinking ability by 41% compared with the conventional process at the experiment of the ONP for 1 year storage time. It removed the yellowing and increased the whiteness and brightness as well as tensile strength and internal bond strength.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.239-244
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• 2019

Two hydrogenation surface modifications, namely hydrogen atmosphere heat treatment and hydrogen plasma treatment, were found to lead to improved dispersion of nanodiamond (ND) seed particles and enhanced nucleation density for deposition of smooth ultrananocrystalline diamond (UNCD) film. After hydrogenation, the C-O and O-H surface functionalities on the surface of nanodiamond particles were converted to the C-H surface functionalities, and the Zeta potential was increased. As the degree of dispersion was improved, the size of nanodiamond aggregates decreased significantly and nucleation density increased dramatically. After hydrogen heat treatment at 600℃, average size of ND particles was greatly reduced from 3.5 ㎛ to 34.5 nm and a very high nucleation of ~3.9 × 10¹¹ nuclei/㎠ was obtained for the seeded Si surface.

• Journal of the Korean Vacuum Society
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• v.4 no.2
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• pp.210-216
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• 1995

최근에 연구되고 있는 저온, 저압 플라즈마를 이용한 식각기술 중 차세대 반도체 metallization 공정에 응용될 수 있는 가장 적합한 기술이라 사료되는 유도 결합형 플라즈마(Inductively Coupled Plasma : ICP)를 이용한 RF 스퍼터 식각 반응로를 제작하고 이에 대한 특성을 조사하였다. 유도용 주파수로서 13.56 MHz를 사용하였으며 유도결합을 일으키기 위해 3.5회의 나선형 평판형 코일을 사용함으로써 비교적 대면적에 균일한 고밀도 플라즈마를 얻을 수 있었다. 또한 기판에 독립적인 13.56MHz RF power를 가해 DC 바이어스를 인가함으로써 기판으로 입사하는 하전입자들의 에너지를 조절하여 기판에의 손상을 최소화하며 SiO2의 스퍼터 식각 속도를 극대화할 수 있었다. 따라서 이러한 특성을 갖는 유도 결합형 플라즈마 식각장치를 차세대 반도체의 RF스퍼터 식각 공정에 응용할 수 있으리라 사료된다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.324-325
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• 2012

다이아몬드 마이크로 블레이드의 절삭 효율을 향상시키고 소결 공정 중 윤활제의 유동성과 젖음성이 다이아몬드 마이크로 블레이드의 물성에 미치는 영향을 연구하기 위해 Cu/Sn 금속 결합재에 표면을 부식시킨 $WS_2$와 부식을 시키지 않은 $WS_2$ 윤활제를 각각 동일한 체적 분율로 첨가하였다. 윤활제의 표면 개질에 따른 마이크로 블레이드 결합재의 내마모성과 굽힘 강도 시험을 행하였고, 실착 절삭 시험을 위한 마이크로 블레이드 시편을 제작하여 수명 및 효율을 평가하였다. Cu/Sn 금속 결합재 파면에서의 $WS_2$ 입자 방향 분석을 통해 표면 개질 과정을 거친 $WS_2$가 압축소결 공정 중 압축 방향에 수직하게 위치하려는 경향이 크게 나타났으며, 이는 소결체의 강도와 경도를 향상시켰다. 마이크로 블레이드의 절삭 효율 및 수명을 평가하기 위한 실착 절삭 시험 결과, 윤활제 표면 부식처리는 처리하지 않은 경우에 비하여 절삭성능은 비슷하게 관찰되었으나 결합재와의 계면 결함을 줄이므로써 블레이드의 수명을 연장시킬 수 있었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.991-994
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• 2003

Electronic Paper용 무기소재로 $TiO_2$ 나노입자를 적용하기 위해서는 분산시 침전문제, 입자의 전기영동 속도향상을 위한 충분한 $\xi-potential$확보, 분산제 첨가시 안정적 결합을 위한 acidic site의 확보등의 문제가 해결되어야 한다. 이를 위해 저온균일침전법으로 $TiO_2$ 나노입자를 제조하였고, 폴리머 체인을 통하여 encapsulation하여 최적의 분산과 전기영동조건 확보를 위한 공정조건에 대해 연구하였다. 실험결과 다양한 분산매에 계면활성제를 1.0wt% 첨가시 유전율상수가 2.5인 분산매에서 가장 좋은 $\xi-potential$을 얻을 수 있었으며 이를 바탕으로 acidic site에 따른 폴리머 체인의 흡착실험 결과 pH $1{\sim}2$의 조건에서 제조된 $TiO_2$ 나노입자의 경우가 체인과의 흡착정도가 가장 좋아 분산특성을 향상시킬 수 있었다.