• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.3
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• pp.2212-2218
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• 2015

In order to find out the load bearing behavior of sand and clay which sustain three types of shallow footing, finite element analyses were performed. Failure zone of sand which sustain strip footing was affected by relative density of sand whereas, failure zone of clay was not affected by soil strength and it was similar to the failure zone which is considered in theory. Considering the shape of load-settlement curves obtained by numerical analyses, punching shear failure can be seen in loose sand and ultimate bearing load can not be seen in dense sand whereas, yielding point can be seen in clay. Ultimate bearing loads for sand predicted by theory were greater than those obtained by numerical analyses and ultimate bearing loads for clay predicted by theory were similar to those of numerical analyses. Ultimate bearing loads determined by 1 inch settlement criteria were slightly less than those of numerical analyses.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.47 no.3
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• pp.161-166
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• 2002

The ultrastructural characteristics of epidermis isolated from healthy and rusty ginseng roots(Panax ginseng) were observed by scanning electron microscopy (SEM), and the distribution profiles of inorganic elements were also examined by energy dispersive X-ray analysis (EDX). The epidermis of rusty ginseng was thick and cell walls were also severely disrupted whereas the epidermal image of healthy ginseng showed relatively thin, clear and rectangular structure. A high amount of rod-shaped bacteria was found in rusty ginseng and cells near bacteria were degraded. The bacterial density in epidermis of rusty ginseng was ranged from 2.9$\times$10$^{6}$ to 3.5 $\times$ 10$^{7}$ CFU/g fresh weight, while that of healthy ones was from 4.7$\times$10$^2$ to 1.2$\times$10$^3$CFU/g. Artificial inoculation of bacteria isolated from rusty ginseng induced similar symptom like rusty ginseng. The mineral contents inculding Al, Si and Fe were Higher in the epidermis of rusty ginseng, but K content was lower compared to healthy ones.

• Journal of the Korean Society for Nondestructive Testing
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• v.7 no.2
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• pp.42-47
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• 1988

The off-axis tensile strength of the unidirectional carbon fiber reinforced plastic and the residual strength of impact damaged CFRP were measured and compared with the stress wave factor (SWF) of the specimens. The SWF values were measured to be decreased with the strength reduction in both cases and found to be useful for the nondestructive strength evaluation of unidirectional CFRP. The failure behaviour of the unidirectional CFRP during off-axis tensile testing was also monitored by acoustic emission(AE) method. The AE energy release showed the characteristic feature depending on the off-axis angle and this result was analyzed to be caused by the difference of the expected failure mode depending on the off-axis angle. The failure mode of CFRP was found to be analyzed by investigation of the peak amplitude distribution of AE.

• Journal of the Korean Wood Science and Technology
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• v.46 no.5
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• pp.425-436
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• 2018

This study was conducted to evaluate the planar (rolling) shear strength of OSB (oriented strand board) panels and domestic plywood through 5 point bending test method in ASTM D2718 standard. The test specimens were prepared in parallel and perpendicular direction to major axis (along the length of panels) and tested up to failure, and failure modes were also examined. From the test results, rolling shear strength were found to be $1.32{\sim}1.94N/mm^2$ in parallel to major axis, and $1.46{\sim}1.99N/mm^2$ in perpendicular to major axis respectively. Little difference was found between parallel and perpendicular direction of rolling shear strength. There were no statistically significant differences in rolling shear strength between Canadian OSB and domestic plywood in the parallel direction, and between Chilean OSB and domestic plywood in the perpendicular direction. The shear failure was observed in all tested OSB panels, whereas shear failure, glue line delamination, and bending combined with shear failure were observed in the domestic plywood.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.135-145
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• 2004

In this study, the behavior of unpropped diaphragm walls on decomposed granite soil was investigated through centrifugal and numerical modelling. Centrifuge model tests were performed by changing the interval distance of surcharge. Excavation was simulated during the centrifuge tests by operating a solenoid valve that allowed the zinc chloride solution to drain from the excavation. In these tests, ground deformation, wall displacement and bending moment induced by excavation were measured. FLAC program which can be able to apply far most geotechnical problems was used in the numerical analysis. In numerical simulation, Mohr-Coulomb model fur the ground model, an elastic model for diaphragm wall were used for two dimensional plane strain condition. From the results of model tests, failure surface was straight line type, the ground of retained side inside failure line had downward displacement to the direction of the wall, and finally the failure was made by the rotation of the wall. The angle of failure line was about 67 ∼ 74$^{\circ}$, greater than calculated value. The locations of the maximum ground settlement obtained from model tests and analysis results are in good agreements. The displacement of wall and the change of the embedment depth is likely to have linear relationship.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.89-96
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• 2008

The purpose of this study is to investigate the flexural strengthening effectiveness for the beams reinforced with NSM CFRP strips. To accomplish this objective, concrete T beams were made and tested. From this study, it is found that the flexural stiffness and strength of the beams reinforced with NSM strips were significantly improved compared to the beams without CFRP strip. The maximum increase of flexural strength was 247%. Failure of the beam reinforced with NSM was initiated by a part of separation of NSM strips along the longitudinal direction, and the second failure of strips was investigated. After the first rupture of the NSM strips, the load dropped suddenly and the second rupture was succeeded. This result shows that a perfect composite reaction with NSM strips and concrete is possible in the beam reinforced with NSM CFRP strips the NSM strips and Near surface mounted(NSM) is one of the most recent and promising strengthening techniques for reinforced concrete structures.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.6
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• pp.87-94
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• 2007

Reuse of recycled aggregate from demolished concrete structure is beneficial and necessary from the viewpoint of environmental preservation and effective utilization of resources. The most important mechanical properties of recycled aggregate concrete (RAC) are the compressive strength, the tensile and the flexural strengths, the bond strength and the elastic modulus of such concrete. In particular, the stress-strain relation and fracture process of RAC in compression is especially important in theoretical and numerical analysis as well as engineering design of RAC structures. In this paper, to clarify the characteristics of fracture process in RAC, acoustic emission(AE) method is applied to detect micro-cracking in concrete under compression. From AE parameters, it is found that cracking and fracture behaviors in recycled aggregate concrete fairly differ from that of normal and recycled sand concrete.

• Journal of Periodontal and Implant Science
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• v.36 no.2
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• pp.397-408
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• 2006

치주질환은 치아 지지조직의 파괴로 튿정 지어지는 감염성 질환으로서 이것은 주로 조직의 교원질 성분을 분해시키는 MMP(matrix metalloproteinase)에 의해 이루어진다. 한편, 여러 연구에서 당뇨병과 치주질환의 심도와의 관계에 대한 논의가 있어왔으며 당뇨병이 치주염을 포함한 구강 감염에 대한 감수성을 증가시키며 역으로 만성 치주염의 염증성 매개물질에 의해 인슐린 작용이 방해받을 수 있음을 보고하였다. 본 연구의 목적은 만성 치주염 환자와 제 2형 당뇨병을 동반한 만성 치주염 환자의 치은조직에서 MMP-13과 elastase의 발현 양상을 비교하여 병리 기전의 차이점을 규명하고, 두 단백질간의 상호관계를 알아보기 위한 것이다. 경북대 병원 치주과에 내원한 환자의 비당뇨 환자의 정상 치은 부위, 비당뇨 환자의 만성 치주염 부위, 제 2형 당뇨병 환자의 만성 치주염 부위에서 각각 8개의 변연 치은을 채득하여 액화 질소에 급속 동결시켰다. 모든 조직 샘플에서 동량의 단백질을 western blotting을 통해 분석하여였고, densitometer를 이용하여 정량한 후 ANOVA 분석으로 통계처리 하였다. 결과분석에서 MMP-13은 제 2형 당뇨를 가진 환자의 염증성 조직에서 가장 높게 발현되었고 전신적으로 건강한 환자의 염증성 조직과 정상 조직에서는 유사한 양상을 보였으며 그 차이는 통계적으로 유의하였다. 또한 elastas는 그룹간에 유의한 차이 없이 유사한 양상으로 발현되었고, 염증성 조직에서도 당뇨병의 유무에 관계없이 유사하게 나타났다. 한편 조직내 MMP-13과 elastase의 발현 양상간에 유의한 상관관계는 보이지 않았다. 결론적으로 MMP-13은 당뇨병을 동반한 환자의 치은 염증초직에서 유의하게 증가되어 나타났으며, 전신적으로 건강한 환자의 염증조직과 당뇨를 동반한 환자의 염증조직에서 MMP-13과 elastase의 발현양상은 큰 상관관계가 발견되지 않았다.

• Restorative Dentistry and Endodontics
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• v.33 no.2
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• pp.148-161
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• 2008

The purpose of this study was to evaluate the effect of chlorhexidine (CHX) on microtensile bond strength (${\mu}TBS$) of dentin bonding systems. Dentin collagenolytic and gelatinolytic activities can be suppressed by protease inhibitors, indicating that MMPs (Matrix metalloproteinases) inhibition could be beneficial in the preservation of hybrid layers. Chlorhexidine (CHX) is known as an inhibitor of MMPs activity in vitro. The experiment was proceeded as follows: At first, flat occlusal surfaces were prepared on mid-coronal dentin of extracted third molars. GI (Glass Ionomer) group was treated with dentin conditioner, and then, applied with 2 % CHX. Both SM (Scotchbond Multipurpose) and SB (Single Bond) group were applied with CHX after acid-etched with 37% phosphoric acid. TS (Clearfil Tri-S) group was applied with CHX, and then, with adhesives. Hybrid composite Z-250 and resin-modified glass ionomer Fuji-II LC was built up on experimental dentin surfaces. Half of them were subjected to 10,000 thermocycle, while the others were tested immediately. With the resulting data, statistically two-way ANOVA was performed to assess the ${\mu}TBS$ before and after thermo cycling and the effect of CHX. All statistical tests were carried out at the 95 % level of confidence. The failure mode of the testing samples was observed under a scanning electron microscopy (SEM). Within limited results, the results of this study were as follows; 1. In all experimental groups applied with 2 % chlorhexidine, the microtensile bond strength increased, and thermo cycling decreased the micro tensile bond strength (P > 0.05). 2. Compared to the thermocycling groups without chlorhexidine, those with both thermocycling and chlorhexidine showed higher microtensile bond strength, and there was significant difference especially in GI and TS groups. 3. SEM analysis of failure mode distribution revealed the adhesive failure at hybrid layer in most of the specimen. and the shift of the failure site from bottom to top of the hybrid layer with chlorhexidine groups. 2 % chlorhexidine application after acid-etching proved to preserve the durability of the hybrid layer and microtensile bond strength of dentin bonding systems.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.130-130
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• 2015

플라즈마를 이용한 cleaning, etching, sputtering 공정에서 발생하는 마이크로아크방전이나 turn-off후의 잔류정전기는 공정대상물의 절연파괴나 전자소자에 전기적 손상을 유발함으로서 공정의 불량률을 증가시키는 중요한 요인이 된다. 본 연구에서는 잔류정전기를 관찰하기위하여 실린더형 챔버구조의 평행평판 전극구조를 지닌 용량결합형 플라즈마에서 powered electrode에 부착된 유전체 기판 표면의 잔류 정전기의 변화 양상을 planar type probe로 측정해보았다. 300mtorr 압력에서 아르곤가스로 발생시킨 플라즈마가 존재할 때 낮은 음전위 평균값을 가지던 기판표면 전위가 전력인가가 중지되었을때 20V 가량의 양전위를 가질 수 있음을 측정 하였고, 이것을 COMSOL MULTIPHYSICS TOOL을 활용한 시뮬레이션과 비교하였다. 이 현상이 파워인가 전극이 플라즈마 영역에 노출되느냐에 따라 발생할 수 있음을 알게 되었고, 그 크기와 지속시간은 입력전력 및 블로킹 커패시터와 유전체 기판의 정전용량에 의존함을 확인 하였다.