• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.169-169
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• 2011

STT-MRAM (수직자화 자기메모리)는 자화반전 현상을 원리로 구동하는 비휘발성 메모리로 기존의 메모리 장치에 비해 빠른 접근 속도와 높은 저장 밀도를 가지며 영구적인 기록이 가능하다. 이러한 장점들에 더해 적은 소모 전력을 지니므로 기존의 SRAM등의 한계를 극복할 대안으로 각광받고 있으며 차세대 메모리 군의 선두주자로 가장 적합한 후보중 하나이다. STT-MRAM의 건식 식각 방식에 있어 가장 큰 이슈는 소자 구동에 핵심적인 역할을 하는 MTJ(Magnetic Tunnel Junction)의 식각이다. MTJ는 free layer, tunnel barrier, pinned layer 3개의 층으로 구성되어 있으며 양 끝 layer에는 강자성체인 CoFeB가 사용되고 tunnel barrier에는 절연층인 MgO가 사용되고 있다. 이러한 물질들은 기존의 반도체 소자에서는 사용되지 않았던 물질들로 기존 공정에서 사용되던 Cl2 based plasma etching에서는 측벽에 비화발성 반응물과 잔류 Cl2에 의해 부식이 발생하는 문제점이 드러나고 있다. 이러한 문제점을 해결하기 위한 새로운 대안으로 CO/NH3/Ar나 CH4/Ar 같은 새로운 가스 조합을 사용하는 연구가 진행되고 있다. 이러한 연구에 의해 기존의 Cl2 plasma를 이용한 식각에서 나타나는 문제점은 해결이 되었으나 또 다른 문제점들이 보고되고 있다. 본 연구에서는 stack MRAM sample을 사용하여 기존의 사용되는 Cl2/Ar plasma와 대안 gas인 CO/NH3, CH4/Ar plasma에서의 식각을 진행하였으며 실험 조건(gas 비율 변화, Bias power 변화, 식각 시간)에 따른 식각 속도의 변화나 식각 후의 profile에 대하여 관찰하였다. 이에 따라 식각후에 어떠한 차이점이 있는 지를 알아보았으며 CO/NH3나 CH4/Ar plasma에서 식각시 나타나는 문제점에 대하여도 조명해 보았다.

• KIEAE Journal
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• v.10 no.5
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• pp.131-137
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• 2010

The building industry must aim at high-durability and sustainability. A holistic life cycle based approach is recommended to reduce the environmental load. In recent years, technical innovations in the construction industry have advanced to a great extent, and caused the active research and development of high-performance and multifunctional construction materials. Nowadays, various polymer powders have been commercialized to manufacture construction materials in the form of prepackaged-type products, which have rapidly been developed for lack of skilled workmen in construction sites. Recently, terpolymer powders of improved quality have been developed and commercialized as cement modifiers. And, hydrocalumite is a material that can adsorb the chloride ions (Cl-) causing the corrosion of reinforcing bars and liberate the nitrite ions (NO2-) inhibiting the corrosion in reinforced concrete, and can provide a self-corrosion inhibition function to the reinforced concrete. The purpose of this study is to ascertain the self-corrosion inhibition function of polymer-modified mortars using redispersible powders with hydrocalumite. Polymer-modified mortars using VA/E/MMA and VAE redispersible powders are prepared with various calumite contents and polymer-binder ratios, and tested for chloride ion penetration depth, corrosion inhibition. As a result, regardless of the polymer-binder ratio, the replacement of ordinary portland cement with hydrocalumite has a marked effect on the corrosion-inhibiting property of the polymer-modified mortars. Anti-corrosion effect of polymer-modified mortars using VA/E/MMA terpolymer powder with hydrocalumite is higher than that of VAE copolymer powder.

• Journal of Intelligence and Information Systems
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• v.9 no.3
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• pp.117-135
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• 2003

This study is to propose a procedure solving scale problem of traditional collaborative filtering (CF) approach. The CF approach generally uses some similarity measures like correlation coefficient. So, as the user of the Website increases, the complexity of computation increases exponentially. To solve the scale problem, this study suggests a clustering model-based approach using Self-Organizing Map (SOM) and RFM (Recency, Frequency, Momentary) method. SOM clusters users into some user groups. The preference score of each item in a group is computed using RFM method. The items are sorted and stored in their preference score order. If an active user logins in the system, SOM determines a user group according to the user's characteristics. And the system recommends items to the user using the stored information for the group. If the user evaluates the recommended items, the system determines whether it will be updated or not. Experimental results applied to MovieLens dataset show that the proposed method outperforms than the traditional CF method comparatively in the recommendation performance and the computation complexity.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.281-281
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• 2010

ITER 블랑켓 시험모듈(TBM)의 액체형 증식재 성능 시험용 루프의 설계를 완료하였고 현재시험용 루프를 제작 및 설치중이다. 액체형 증식재 성능 시험용 루프의 핵심 구성 부품인 액체 저장용 탱크, 전자석, EM 펌프들과 이들 장치들의 전원장치 및 제어장치를 제작 완료하였다. 액체형 증식재 성능 시험용 루프 설치를 위한 데크를 제작하였으며, 제작된 실험 데크의 총 지지하중은 10 톤 이상이다. 루프설치대 위에 성능 시험용 루프가 설치되며 루프 설치대는 $3\;m\;{\times}\;2.4\;m$ 의 직사각형으로 제작되었으며, 실험 종료 및 유지 보수 시 액체증식재의 drain을 고려하여 전체 루프는 각도 조절이 가능하도록 제작되었다. 루프내의 유량을 측정하기 위한 유량계, 전자석 자장의 변화에 따른 압력의 변화를 측정하기 위한 차압센서가 전자석의 양단에 설치되며, 시험용 루프에 흐르는 액체금속(PbLi) 및 루프관의 온도를 측정하기 위한 열전대가 설치된다. 루프 설치대를 기울였을 때 루프의 최상부에 액체금속 저장고 및 레벨센서를 설치하여 루프 내에 액체금속이 가득 채워졌는지를 레벨센서로 확인하며 루프 내에 잔존하는 기체가 저장고를 통하여 외부로 배출되게 하였다. 액체형 증식재 성능 시험용 루프 설치 후 실험은 고체 상태의 PbLi를 액체 저장용 탱크에 장착한 후 탱크의 열선의 온도 제어에 의한 PbLi의 용융점 확인, 시험용 루프에서의 전자펌프 성능 평가 등의 시험의 기본적인 실험을 수행한 후 자기장 환경에서 MHD 평가, 증식재의 순도 유지, 구조재의 부식 등의 시험을 수행할 예정이다.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.263-269
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• 2003

Magnetic flux leakage (MFL) signals were used for corrosion inspection of buried oil and gas pipeline. 3D finite element analysis was used to examine the effects of far and near-side pit depth and tensile stress on MFL signals. Anisotropci materials were used, and the effects of simulated tensile stress on MFL were investigated. The axial and radial MFL signals depended on far and near-side single pit depth and on the bulk stress, but the circumferential MFL signal did not depend on them. The axial and radial MFL signals increased with increasing pit depth and the bulk stress, but the circumferential MFL signal was scarcely changed.

• Journal of the Korean GEO-environmental Society
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• v.21 no.9
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• pp.25-32
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• 2020

The underground utilities installed under the ground is an important civil engineering structure, such as water supply and sewerage pipes, underground power lines, various communication lines, and city gas pipes. Such underground utilities can be exposed to risk due to external factors such as concentrated rainfall and vehicle load, and it is important to select and construct an appropriate backfill material. Currently, a method mainly used is to fill the soil around the underground utilities and compact it. But it is difficult to compact the lower part of the buried pipe and the compaction efficiency decreases, reducing the stability of the underground utilities and causing various damages. In addition, there are disadvantages such as a decrease in ground strength due to disturbance of the ground, a complicated construction process, and construction costs increase because the construction period becomes longer, and civil complaints due to traffic restrictions. One way to solve this problem is to use a liquid filler. The liquid filler has advantages such as self-leveling ability, self-compaction, fluidity, artificial strength control, and low strength that can be re-excavated for maintenance. In this study, uniaxial compression strength test and fluidity test were performed to characterize the mixed soil using marine clay, stabilizer, and in-situ soil as backfill material. A freezing-thawing test was performed to understand the strength characteristics of the liquid filler by freezing, and in order to examine the effect of the filling materials on the corrosion of the underground pipe, an electrical resistivity test and a pH test were performed.

• Investigative Magnetic Resonance Imaging
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• v.7 no.2
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• pp.137-143
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• 2003

Purpose : B1 field of birdcage RF (radiofrequency) coil that is used most for brain imaging in magnetic resonance imaging (MRI) decreases toward endring from the coil center. We investigated how much RE B1 homogeneity effect the endcap shield brings form the coil center as it towards to endcap region. Materials and Methods : We compared RF B1 field distribution by each finite difference time domain (EDTD) simulations for lowpass, highpass and hybrid birdcage RF coils. We selected the highpass birdcage RF coil that was the highest RF B1 field condition as simulation result, and studied how much RF B1 homogeneity effect was occurred when endcap shield was applied to endring area. Results : B1 field of the highpass birdcage RF coil was higher than other birdcage RF coil types as simulation result. However, the RF B1 homogeneity was lower than other coil types. RE B1 field of highpass birdcage RF coil with endcap shield is similar with RF B1 field of hybrid birdcage RF coil and the overall RE B1 homogeneity in sagittal direction was better. Conclusion In this paper, proposed method can apply improving RF B1 homogeneity of RF coil in clinical examination.

• Journal of the Korea Institute of Building Construction
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• v.12 no.3
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• pp.275-283
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• 2012

Nitrite-type hydrocalumite (calumite) is a material that can adsorb the chloride ions ($Cl^-$)that cause the corrosion of reinforcing bars and liberate the nitrite ions ($NO_2{^-}$) that inhibit corrosion in reinforced concrete, and can provide a self-corrosion inhibition function to the reinforced concrete. In this study, VA/E/MMA-modified mortars with calumite were prepared with various calumite contents and polymer binder-ratios, and tested for corrosion inhibition, chloride ion penetration, carbonation and drying shrinkage. As a result, regardless of polymer-binder ratio, the replacement of ordinary Portland cement with hydrocalumite has a marked effect on the corrosion inhibiting property of the polymer-modified mortars. However, chloride ion penetration and carbonation depths are somewhat increased with higher calumite content, but can be remarkably decreased depending on the polymer-binder ratios. The 28-d drying shrinkage shows a tendency to increase with the polymer-binder ratio and calumite content. VA/E/MMA-Modified mortars with 10 % calumite did not satisfy KS requirements. Accordingly, a calumite content of 5 % is recommended for the VA/E/MMA-modified mortars with calumite.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.4
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• pp.393-400
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• 2012

In recent years, nano-structured thin film systems are often applied in industries such as MEMS/NEMS device, optical coating, semiconductor or like this. Thin films are used for many and varied purpose to provide resistance to abrasion, erosion, corrosion, or high temperature oxidation and also to provide special magnetic or dielectric properties. Quite a number of articles to evaluate the characterization of thin film structure such as film density, film grain size, film elastic properties, and film/substrate interface condition were reported. Among them, the evaluation of film adhesive to substrate has been of great interest. In this study, we fabricated the polymeric thin film system with different adhesive conditions to evaluate the adhesive condition of the thin film. The nano-structured thin film system was fabricated by spin coating method. And then V(z) curve technique was applied to evaluate adhesive condition of the interface by measuring the surface acoustic wave(SAW) velocity by scanning acoustic microscope(SAM). Furthermore, a nano-scratch technique was applied to the systems to obtain correlations between the velocity of the SAW propagating within the system including the interface and the shear adhesive force. The results show a good correlation between the SAW velocities measured by acoustic spectroscope and the critical load measured by the nano-scratch test. Consequently, V(z) curve method showed potentials for characterizing the adhesive conditions at the interface by acoustic microscope.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.641-650
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• 2010

The concrete cracking from the restrained stress caused by the shrinkage may play significant cause of deterioration of concrete structures by allowing the permeation of sulphate and chloride ions which in turn triggers corrosion of steel reinforcement. In particular, the cracking becomes more critical as water binder ratio (W/B) is reduced and concrete strength increases. Therefore, it needs to evaluate correctly the comprehensive shrinkage behavior of concrete with high strength: high-strength concrete (HSC), ultra-highstrength concrete (UHSC). The unrestrained shrinkage tests, however, cannot estimate the net shrinkage effectively which affects cracking after full development of strength and stiffness because it does not consider the degree of restraint, strength development, stress relaxation, and so on. Therefore, in this study, both free and restrained shrinkage tests with variables of W/B (W/B of 30, 25 and 16%) and admixtures (fly ash (FA) and granulated blast-furnace slag (BFS)) for HSC, very-high-strength concrete (VHSC) and UHSC were performed. The test results indicated that the autogenous shrinkage and total shrinkage at drying condition were reduced as W/B increased and FA, BFS were added, and the cracking behavior was suppressed as W/B increased and FA was added.