• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.2
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• pp.155-164
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• 2014

Carbon-fiber-reinforced plastic (CFRP) composites are increasingly being used in a variety of industry applications, such as aircraft, automobiles, and ships because of their high specific stiffness and high specific strength. Aircraft are exposed to high temperatures and high humidity for a long duration during flights. CFRP materials of the aircraft can absorb water, which could decrease the adhesion strength of these materials and cause their volumes to change with variation in internal stress. Therefore, it is necessary to estimate the characteristics of CFRP composites under actual conditions from the viewpoint of aircraft safety. In this study air-coupled ultrasonic testing (ACUT) was applied to the evaluation of water absorption properties of CFRP composites. CFRP specimens were fabricated and immersed in distilled water at $75^{\circ}C$ for 30, 60, and 120 days, after which their ultrasonic images were obtained by ACUT. The water absorption properties were determined by quantitatively analyzing the changes in ultrasonic signals. Further, shear strength was applied to the specimens to verify the changes in their mechanical properties for water absorption.

• Composites Research
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• v.26 no.5
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• pp.315-321
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• 2013

In this work, pitch-carbonized glass fibers were prepared for reinforcement of composites. The influence of acid functionalization of the fibers on the morphological, mechanical, and thermal properties of fiber-reinforced epoxy matrix composites was investigated. The acid functionalization of the fibers led to 10 and 150% increases in the mechanical and thermal properties, respectively, as compared to carbon fiber-reinforced composites. This can be attributed to the superior orientation of fiber structures and good interfacial interactions between fillers and epoxy matrix, resulting in enhanced degree of dispersion and formation of thermally conductive paths in the functionalized composites.

• The Journal of Korean Academy of Prosthodontics
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• v.58 no.4
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• pp.300-305
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• 2020

Purpose: The purpose of this study is to compare the shear bond strength of 3D printing denture base resin according to surface treatment of artificial teeth. Materials and methods: 3D printing denture base resin was fabricated as specimens using 3D printer. The experimental group divided the surface treatment of artificial teeth into five groups according to the application of sandblasting and primer (n=10). Shear bond strengths between denture base and artificial teeth were measured by universal testing machine. All measurements were analyzed by one-way ANOVA and Turkey test (α=.05). Fracture mode of each specimen was analyzed. Microscopic evaluation was conducted by using a scanning electron microscope. Results: Unsurfaced treated group represented the lowest value. The primer groups had significantly higher result values (P<.05). Most specimens of the primer groups had cohesive failure. Conclusion: In 3D printing denture base resin group, mechanical and chemical surface treatment of artificial teeth has increased the shear bond strength. Therefore, if dentures are produced using 3D printing, proper mechanical and chemical treatment of artificial teeth is necessary for adhesion of dentures and artificial teeth.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.1
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• pp.27-32
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• 2004

The diamond-like carbon (DLC) films were deposited on the Si (100) wafer by a rf-PECVD method as a function of the mixture rate of methane-hydrogen gas and bias voltage. The bonding structure and mechanical properties of these deposited DLC films were investigated using FT-IR, Raman, and nano-indenter. The deposition rates of DLC films increased with increased flow rate of methane in the gas mixtures and increased bias voltage. The $sp^3/sp^2$ bonding ratio of carbon in thin film and the hardness increased with increasing flow rate of hydrogen in the gas mixtures and increasing bias voltage.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.9-14
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• 2022

Silica aerogel is a porous material with a very low density and high specific surface area. Still, its application is limited due to its weak mechanical properties due to structural features. To solve this problem, a method of complexing it with various polymers has been proposed. We synthesized polyimide cross-linked silica aerogel by the sol-gel process to obtain high mechanical properties. Tetraethyl orthosilicate (TEOS) was used as a precursor to make silica aerogel, and 3- aminopropyltriethoxysilane (APTES) was used as a coupling agent for cross-linking polyimide. Polyimide was synthesized using pyromellitic dianhydride and 3,5-diaminobenzoic acid, and mechanical properties were improved by crosslinking polyimide with 10 repeating units in the polyimide chain using the reaction formula ${\frac{n_1}{n_2}}={\frac{n}{n+1}}$ To realize silica aerogel, polyimide having various weight ratios was added before gelation, resulting in a 19-fold or greater increase in maximum compressive strength compared to pure silica aerogel. From this study, an enhancement of silica aerogel could be enhanced through polymer cross-linking bonds.

• 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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• 2009.06a
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• pp.158-158
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• 2009

기계적 에너지를 전기적 에너지로 변환하는 에너지 변환소자인 압전 세라믹스는 액추에이터, 변압기, 초음파모터 및 각종 센서로 응용되고 있으며, 그 응용분야는 크게 증가하고 있다. 최근에는 이러한 압전 소자를 앞으로 도래하는 ubiquitous, 무선 모바일 시대의 휴대용 전자제품, robotics 등의 분야에 적용하기 위하여 소형화 및 경량화를 구현하고자 다양한 연구가 진행되고 있다. 본 연구에서는 압전 특성이 우수한 PNN-PMN-PZT 삼원계 세라믹을 이용하여 압전 트랜스포머를 제작하고 전기적 특성을 평가하였다. 압전트랜스포머는 전왜-압전효과를 이용한 소전력용 고전압발생소자로서 종래의 권선형 트랜스포머에 비교해서 소형, 경량이면서 승압비가 높고 구조가 간단하므로 직류 고전압전원에 응용되고 있다. 압전트랜스의 이론적인 고찰은 Rosen 이후로 많은 연구자들에 의해서 보고되었다. 그런데 압전세라믹트랜스는 공진 시 강력한 에너지변환을 하기 때문에 재료의 물리적 특성이 매우 중요함에도 불구하고, 이러한 물리적 특성에 관한 연구는 거의 없었다. 따라서 본 연구에서는 물리적 특성과 전기적 특성의 상호 연관성을 고찰하고자 하였다. 압전트랜스용 재료는 전기기계결합계수($k_p$)와 기계적품질계수(Qm)가 높아야 한다. 전기기계결합계수를 높이기 위해서는 상경계 조성의 Pb(Zr,Ti)$O_3$[PZT]계 세라믹스가 가장 우수하다. 본 연구에서는 기계적 품질계수를 향상시키기 위해서 $Pb(Nn_{1/3}Nb_{2/3})_{0.06+x}(Mn_{1/3}Nb_{2/3})_{0.065-x}(Zr_{0.48}Ti_{0.52})_{0.875}0_3$계의 조성을 설계하여 압전특성을 평가하고 미세구조를 분석하였다. 또한 압전트랜스를 제작하여 입출력의 승압비 및 주파수 특성 등도 평가하였다.

• Polymer(Korea)
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• v.36 no.5
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• pp.573-578
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• 2012

In general, most physical properties of wood/polyvinyl chloride (PVC) composites are lower than those of corresponding neat PVC resin because of poor interfacial adhesion between the hydrophilic wood flour and hydrophobic PVC. Therefore, in this study, we treated wood flour with three aminosilanes to improve wood/PVC interfacial adhesion strength, and eco-friendly wood/PVC/nanoclay composites were prepared by melt blending the aminosilane-treated wood flour, a heavy metal free PVC compound, and a type of nanoclay. The effects of treating wood flour with the aminosilanes and adding the nanoclay on the mechanical properties of the composites were investigated. Mechanical properties of the composites were investigated by universal testing machine (UTM), izod impact tester, dynamic mechanical analyzer (DMA), and thermomechanical analyzer (TMA). The tensile properties of the composites with the aminosilane-treated wood flour were considerably higher than those of the composites with neat wood flour. Furthermore, a small amount of the nanoclay improved mechanical properties of the composites. The performance of the wood/PVC composites was considerably improved by using the aminosilane-treated wood flour and the nanoclay.

• Elastomers and Composites
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• v.42 no.2
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• pp.112-118
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• 2007

An HRP immobilized carbon paste electrode, which was bound by EPDM, was newly fabricated and its electrochemical properties were investigated for the purpose of validating the new possibility for the practical use of biosensor. In the experimental range of substrate concentration, Lineweaver-Burk plot of the signal showed a good linearity. This means that HRP was embedded effectively to preserve its identity in the bulk of composite electrode materials and EPDM is a recommendatory binder. When the electrode was run at low operating potential($0.0\sim-1.0$ V vs. Ag/AgCl), it showed a high sensitivity and a good reproducibility. Especially the mechanical stability of the dried rubber was a remarkable breakthrough to get over a difficulty in putting the carbon-paste electrode bound with silicon oil to real use.

• 한국어정보학회:학술대회논문집
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• 2016.10a
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• pp.285-290
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• 2016

한국어는 형태론적으로 굴절어에 속하는 언어로서, 어휘의 형태가 문장 속에서 문법적인 기능을 하게 되고, 형태론적으로 풍부한 언어라는 특징 때문에 조사나 어미와 같은 기능어들이 다양하게 내용어들과 결합한다. 이와 같은 특징들은 한국어를 대상으로 하는 구 기반 통계적 기계번역 시스템에서 데이터 부족문제(Data Sparseness problem)를 더욱 크게 부각시킨다. 하지만, 한국어의 몇몇 조사와 어미는 함께 결합되는 내용어에 따라 의미는 같지만 두 가지의 형태를 가지는 이형태로 존재한다. 따라서 본 논문에서 이러한 이형태들을 하나로 표준화하여 데이터부족 문제를 완화하고, 베트남-한국어 통계적 기계 번역에서 성능이 개선됨을 보였다.