• Proceedings of the Membrane Society of Korea Conference
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• 1996.04a
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• pp.46-47
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• 1996

막분리 공정의 공업적인 이용을 위해서는 막을 특정 용기에 적재한 모듈의 형태가 요구되는데 모듈의 형태에 따라 평판형(plate and frame), 나권형(spiral wound), 관형(tubular), 중공사형(hollow fiber)모듈 등이 있다. 이 중에서 관형 시스템은 내경이 12.5~25 mm, 길이 0.6~6.4 m에 이르는 비교적 큰 open channel로 되어 있으며 공급액 유로가 일반적으로 커서 전처리를 행하지 않고도 fouling이 적으며, 또한 막 표면의 세정이 약품에 의한 것 이외에 스폰지 볼 등에 의한 물리적 세정도 가능하므로 응용 범위가 넓다는 것이 특징이다. 한외여과 공정의 가장 큰 문제점은 농도분극 및 fouling 현상에 의한 플럭스 감소이다. 농도분극 현상은 경계층에서 용질의 대류,확산적인 전달에 기인하여 막 표면으로 갈수록 진해지는 용액층의 형성을 의미한다. 이 현상은 가역적인 과정으로서 감압함으로 원상태로 회복이 가능하며 조작 압력에서 정상상태가 되면 막투과 플럭스는 일정한 값을 유지한다.

• Electrical & Electronic Materials
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• v.3 no.1
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• pp.9-19
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• 1990

본 연구에서는 산회물 혼합법, 솔-젤법, 공침법등의 세가지 방법으로 PbTiO$_{3}$분말을 제조하여 폴리머와 혼합 O-3 복합재료를 제작한 후, 하이드로폰으로의 응용을 위한 제 특성을 고찰하였다. 비유전상수는 PbTiO$_{3}$의 체적비 증가에 따라 지수함수적으로 증가하였으며 유전손실은 선형적으로 증가하였다. 수정입방체 모델로 부터 계산된 변형계수 n은 M-O, S-G, C-P의 경우 각각 0.724, 0.585, 0.483으로 나타났다. 압전 변형계수 d$_{33}$는 PbTiO$_{3}$의 체적비, 분극전장 및 분극 시간의 증가에 따라 증가하였으며 일정시간 경과후에는 포화값을 나타내었다.다.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.7
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• pp.1-7
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• 1989

For H-polarized incident plane wave, an exact integral expression for the scattered field by an inversely tapered resistive half plane is obtained by using Kontorovich-Lebedev transform. Uniform asymptotic results available for all angles are obtained, and non-uniform asymptotic results which provide the ray-optical interpretation of the calculated scattered field are also obtained. The edge diffraction patterns for several values of inverse proportionality of resistivity are shown. We find out that the results are in agreement with physical reasoning.

• Membrane Journal
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• v.7 no.2
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• pp.84-94
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• 1997

The performances of both module sets made by different methods for helical module were compared. All experiments were conducted simultaneously at the same transmembrane pressure and energy cosumption per membrane area. The effects of Dean vortices for reducing concentration polarization and fouling were low for the first module set. The increase of 115% for permeate flux improvement(permeate flux difference ${\times}100$/pemeate flux of linear module) was measured. The second module set was more effective in reducing concentration polarization and fouling.

• Proceedings of the KIEE Conference
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• 2007.04b
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• pp.55-57
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• 2007

오일 변압기 내부의 절연물은 절연지, 프레스보드, 광유 또는 식물유가 주로 사용되고 있다. 사용 기간과 과부하 조건에 따라 열화정도가 달라질 수 있으며, 내부 절연물의 열분해 및 가수분해로 인해 수분은 자연스럽게 생성될 수 있다. 생성된 수분은 절연을 약하게 하는 주된 요인으로 작용해 기기의 고장 또는 정전을 초래할 수도 있다. 본 논문에서는 변압기 내부 절연물의 주파수응답 특성과 절연상태 값을 바탕으로 변압기 내부를 전기적 소자로 등가화하였다. 그 후 등가화된 회로를 이용해 회복전압법의 원리에 따라 EMTP 프로그램을 활용해 분극특성을 모의하였다. 실제 측정 값과의 비교를 위해 보고된 문헌의 데이터를 활용하였고, RVM을 이용한 실측값과 유사한 결과를 얻게 되었다. 따라서 본 시뮬레이션에 활용된 전기적 소자값을 변경함으로서 내부 절연물의 열화정도에 대한 기대 파형을 예측할 수 있는 유용한 도구로 활용될 수 있음을 확인하였다.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.5
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• pp.313-322
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• 2001

The effects of Zr/Ti concentration ratio in PLZT (10/y/z) thin films prepared by sol-gel method are investigated for the NVFRAM application. Rosette and pyrochlore phase are observed in PLZT (10/40/60) thin film and the (100) orientation, the grain size, and the surface roughness of PLZT thin films increase due to the increase of Ti amount in Zr/Ti concentration ratio. As Ti amount of Zr/Ti concentration ratio increases, the dielectric constants at 10KHz decrease from 600 to 400, while the loss tangents increase from 0.028 to 0.053 and the leakage current densities at 170 kY/cm decrease from 1.64$\times$10$^{-6}$ to 1.26$\times$10$^{-7}$ A/$\textrm{cm}^2$. In the results of hysteresis loops measured at $\pm$ 170 ㎸/cm, the remanent polarization and the coercive field increase from 6.62 to 12.86 $\mu$C/$\textrm{cm}^2$ and from 32.15 to 56.45 ㎸/cm, respectively, according to the change from 40/60 to 0/100 in Zr/Ti concentration ratio. Fatigue and retention properties also improve much as the Zr/Ti concentration ratio change from 40/60 to 0/100. After applying 10$^{9}$ square pulses with $\pm$5V, the remanent polarization of the PLZT (10/40/60) thin film decreases 50％ from the initial state while that of the PLZT (10/0/100) thin film decreases 30％. In the results of retention measurements of 10$^{5}$ s, the remanent polarization of the PLZT (10/0/100) thin film decreases only 11％ from the initial state, while that of the PLZT (10/40/60) thin film decreases 40%.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.3
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• pp.609-615
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• 2005

The effects of Zr/Ti concentration ratio in PLZT (10/y/z) thin films prepared by sol-gel method are investigated for the NVFRAM application. As Ti amount of Zr/Ti concentration ratio increases, the dielectric constants at 10 kHz decrease from 550 to 400, while the loss tangents increase from 0.028 to 0.053 and the leakage current densities at 170 kV/cm decrease from $1.64\times10^{-6}$ to $1.26\times10^{-7}\;A/cm^2$. In the results of hysteresis loops measured at $\pm170kV/cm$, the remanent polarization and the coercive field increase from 6.62 to $12.86{\mu}C/cm^2$ and from 32.15 to 56.45 kV/cm, respectively, according to the change from 40/60 to 0/100 in Zr/Ti concentration ratio. Fatigue and retention properties also improve much as the Zr/Ti concentration ratio change from 40/60 to 0/100. After applying $10^9$ square pulses with $\pm5V$, the remanent polarization of the PLZT (10/40/60) thin film decreases $50\%$ from the initial state while that of the PLZT (10/0/100) thin film decreases $28\%$. In the results of retention measurements of 10s s, the remanent polarization of the PLZT (10/0/100) thin film dec.eases only $10\%$ from the initial state, while that of the PLZT (10/40/60) thin film decreases $40\%$.

• Geophysics and Geophysical Exploration
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• v.12 no.3
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• pp.246-254
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• 2009

We developed a novel polarization filter to separate linearly polarized waves from elliptically polarized waves in an infinite homogeneous medium and at the free surface using methods of multicomponent complex trace analysis. Sensitivity to filter parameters were examined using synthetic data simulating particle motions in a homogeneous medium. For known amplitude ratios of horizontal-to-vertical components of P and Rayleigh waves $C_L$ and $C_R$, respectively, the polarization filter precisely removes Rayleigh waves. Errors in the vertical and horizontal components of the filtered results increase with the ratio $C_R$/$C_L$ and the product $C_R$.$C_L$, respectively. The vertical component errors also increase rapidly as the ratios of applied-to-modeled values of $C_L$ and $C_R$ ($C_L'$/$C_L$ and $C_R'$/$C_R$) decrease, and are sensitive to $C_R'$/$C_R$ and $C_L'$/$C_L$ for small and large incidence angles, respectively. Errors of the filter are exactly the same for shear waves when the incidence angle is the supplementary of P-wave incidence angle.

• Korean Journal of Optics and Photonics
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• v.19 no.3
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• pp.199-207
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• 2008

Wavelength converting devices with a ridge-type waveguide in periodically poled $MgO:LiNbO_3$ are made and characterized. The experimental results are compared with theoretical analysis on the effects of waveguide dimension and duty ratio of the periodically poled structure. To show the relationship of the conversion efficiency to those factors, a new measurement system is configured. That experimental results show that the center wavelength, normalized conversion efficiency and full width half maximum of the conversion efficiency curve are 1067.45 nm, 90.7%/$Wcm^2$ and 0.17 nm, respectively. Also, the estimated results of the duty period and full width half maximum of the conversion efficiency from theoretical calculations agreed well with experimental results with the errors of 0.016 ${\mu}m$ and 0.01 nm.

• Journal of the Korean Vacuum Society
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• v.11 no.4
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• pp.230-234
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• 2002

Metal-ferroelectric-semiconductor(MFS) capacitors by using rapid thermal annealed $LiNbO_3$/Si structures were successfully fabricated and demonstrated nonvolatile memory operations of the MFS capacitors. The C-V characteristics of MFS capacitors showed a hysteresis loop due to the ferroelectric nature of the $LiNbO_3$thin film. The dielectric constant of the $LiNbO_3$film calculated from the capacitance in the accumulation region in the capacitance-voltage(C-V) curve was about 25. The gate leakage current density of MFS capacitor using a platinum electrode showed the least value of $1{\times}10^{-8}\textrm{A/cm}^2$ order at the electric field of 500 kV/cm. The minimum interface trap density around midgap was estimated to be about $10^{11}/cm^2$.eV. The typical measured remnant polarization(2Pr) value was about 1.2 $\mu\textrm{C/cm}^2$, in an applied electric field of $\pm$ 300 kv/cm. The ferroelectric capacitors showed no polarization degradation up to about $10^{10}$ switching cycles when subjected to symmetric bipolar voltage pulse in the 500 kHz.