• 한국군사과학기술학회지
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• 제23권5호
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• pp.435-443
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• 2020

Thermal barrier coating(TBC) applied to fighter and turbine engines is a technology that improves the durability of core parts by lowering the surface temperature of base material. The thermal stress caused by mis-match of the coefficient of thermal expansion between the top coating and the TGO interface is the main cause of TBC breakage. Since the thermal stress is dependent on the microstructure of the TBC, designing microstructure of TBC can improve the durability as well as lower the thermal stress. In this study, the effect of coating thickness, volume of porosity and vertical cracking on the thermal stress was analyzed through finite element analysis. Through the analysis results, a design range of a microstructure that can improve the durability of thermal barrier coating by lowering thermal stress is proposed.

• 대한화학회지
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• 제48권1호
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• pp.66-76
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• 2004

이 연구는 한국과 일본의 고등학교 화학교육과정을 구성체제, 목표, 내용, 교수${\cdot}$학습방법 및 평가의 관점에서 비교 분석하였다. 이러한 비교분석을 통하여 양국의 화학교육과정에서 나타나는 공통점과 차이점들을 구분하였다. 또한 선택취지를 살린 교육과정 편성과 안내 기능의 충실, 탄력적인 학습지도의 운영, 개인에 따른 지도의 충실, 학습내용의 엄선과 기초기본의 충실, 교육과정도입에 있어서 완충기간의 설정 등과 같이 한국의 교육과정연구에 도움이 되는 시사점을 이끌어 낼 수 있었다.

• Ocean and Polar Research
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• 제39권3호
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• pp.233-244
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• 2017

This study seeks to analyze the needs of biotechnology companies in relation to their entry into the marine biotechnology industry and to discuss the policy implications associated with empirical tasks based on issues raised from empirical results gathered from a survey data of 200 biotechnology companies in Korea. This study made a comparison between marine and non-marine biotechnology companies and analyzed non-marine biotechnology companies' needs related to their entry into the marine biotechnology companies by using Social Network Analysis (SNA). Empirical results indicate that 23.5% of biotechnology companies produce goods using marine bio-resources. Once the utility of marine bio-resources is established, 58.8% of non-marine biotechnology companies intend to enter the marine biotechnology industry. This study also shows that non-marine biotechnology companies need technical support, information sharing, and the acquisition of raw materials to enter the marine biotechnology industry. The findings in this study provide important pointers for the direction of policies and future research in the area of marine biotechnology industry.

• 정보교육학회논문지
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• 제20권5호
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• pp.433-442
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• 2016

본 연구의 목적은 플립러닝이 소프트웨어교육에 있어서의 대학생들의 학습동기에 미치는 영향을 분석하는 것이다. 이를 위해 K교육대학교 1학년 2개 반을 실험집단과 비교집단으로 구성하여 10주간 스크래치를 이용한 소프트웨어 교육을 실시하였다. 실험집단은 SW교육 관련 온라인 강좌 사이트를 동시에 병행하여 플립러닝을 적용하였다. 실험 결과, 실험집단의 사후 학습동기는 사전 학습동기에 비해 유의미하게 놓아졌으며, 사후 학습동기 검사 결과도 실험집단이 비교집단에 비해 학습동기가 유의미하게 높게 나타났다. 이에 향후 소프트웨어교육에서 플립러닝이 대학교에서 뿐 아니라 초중등 교육 현장에서도 효과적인 학습 전략으로 저변 확대되기를 기대한다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2001년도 춘계학술발표대회 논문집
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• pp.126-129
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• 2001

LIPCA (LIghtweight Piezo-composite Curved Actuator) is an actuator device which is lighter than other conventional piezoelectric ceramic type actuator. LIPCA is composed of a piezoelectric ceramic layer and fiber reinforced light composite layers, typically a PZT ceramic layer is sandwiched by a top fiber layer with low CTE (coefficient of thermal expansion) and base layers with high CTE. LIPCA has curved shape like a typical THUNDER (thin-layer composite unimorph feroelectric driver and sensor), but it is lighter an than THUNDER. Since the curved shape of LIPCA is from the thermal deformation during the manufacturing process of unsymmetrically laminated lay-up structure, an analysis for the thermal deformation and residual stresses induced during the manufacturing process is very important for an optimal design to increase the performance of LIPCA. To investigate the thermal deformation behavior and the induced residual stresses of LIPCA at room temperature, the curvatures of LIPCA were measured and compared with those predicted from the analysis using the classical lamination theory. A methodology is being studied to find an optimal stacking sequence and geometry of LIPCA to have larger specific actuating displacement and higher force. The residual stresses induced during the cooling process of the piezo-composite actuators have been calculated. A lay-up geometry for the PZT ceramic layer to have compression stress in the geometrical principal direction has been designed.

• Composites Research
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• 제27권4호
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• pp.135-140
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• 2014

발포 폴리우레탄의 변형거동을 설명하기 위해 제안된 구성방정식을 발포 폴리프로필렌에 적용하였다. 이 방정식은 7개의 매개변수를 갖고 있으며, 그중 5개의 변수는 기준 변형률속도에서 준정적 압축시험을 하여 얻은 결과를 커브 피팅하여 구하고, 나머지 두 변수는 변형률 속도를 다르게 한 준정적 압축시험으로부터 얻은 결과를 커브 피팅하여 구한다. 이렇게 구한 응력-변형률 방정식이 높은 변형률속도에서도 유효한지 알기 위해 충격시험으로부터 얻은 결과와 비교하였으며 30배와 40배로 발포된 폴리프로필렌 폼 시편에 대하여 각각 시행하였다.

• 대한기계학회논문집A
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• 제26권11호
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• pp.2383-2389
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• 2002

This paper describes an experimental study on fatigue life extension by using cold working process in fastener hole of aircraft structure. Cold working process was applied for A12024-7351 specimens by considering the effect of edge margin on fatigue life. It is generally recognized that cold working process offers a protective zone around fastener hole of aluminum aircraft structure due to the residual compressive stresses which lead to retardation of crack growth. Thus this process provides the beneficial effect of increasing the fatigue life of the component. there by decreasing maintenance costs. It has also been successfully incorporated into damage tolerance and structural integrity programs. Cold working specimens were tested at constant amplitude peak cyclic stresses. Fatigue life of cold working specimen compared with that of specimen fabricated with base material. The increase of fatigue life for cold working specimen is discussed by both considering the effect of residual compressive stresses measured by X-ray diffraction technique and quantitative effect of edge margin.

• Journal of Welding and Joining
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• 제14권1호
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• pp.57-67
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• 1996

With an expansion in automation of welding processes, emphasis has been shifted from other welding processes to the GMA welding. However, there is a problem with this process that the spatter occurs very frequently. In GMA welding, there are several types in the way of metal transfer from the electrode wire to the weld pool, which have a close relatonship with the spatter genetration. This study was concerned with the spatter occurring in the short-circuiting transfer. In welding with short-circuiting, the electromagnetic force formed by the welding current facilitatics the rupture of the metal bridge between the wire and workpiece and ensures the normal process of the welding process. However, the spatter can be genetrated from the droplet because of the upward magnetic force, when the droplet contacts with the weld pool. The passage of current through the bridge results in the accumulation of the thermal energy, which causes the bridge to explode in the final stage of short-circuiting, thus forming the spatter. Based on the above phenomena in conjunction with other experimental results published, the physical phenomenon related with the occurrence of spatter was modeled and the current waveform was investigated to reduce the spatter. Finally, the fuzzy rule based method was proposed to predict the time of short-circuiting and arcing in the metal transfer.

• Journal of Welding and Joining
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• 제25권1호
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• pp.42-48
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• 2007

For high performance and structural stability, application of high strength steel has continuously increased. However, the change of the base metal gives rise to problems with the accuracy management of the welded structure. It is attributed to the martensite phase transformation of the high strength low alloy steel weldment. The purpose of this study is to establish the predictive equation of transverse shrinkage and residual stress for the HY-100 weldment. In order to do it, high speed quenching dilatometer tests were performed to define a coefficient of thermal expansion(CTE) at the heating and cooling stage of HY-100 with various cooling rates. Uncoupled thermal-mechanical finite element(FE) models with CTE were proposed to evaluate the effect of the martensite phase transformation on transverse shrinkage and residual stresses at the weldment. FEA results were verified by comparing with experimental results. Based on the results of extensive FEA and experiments, the predictive equation of transverse shrinkage and longitudinal shrinkage force at the HY-100 weldment were formulated as the function of welding heat input/in-plane rigidity and welding heat input respectively.

• 방송공학회논문지
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• 제23권3호
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• pp.403-408
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• 2018

딥 러닝의 학습을 위해서 일반적으로 많은 양의 데이터가 필요하다. 그러나 많은 양의 데이터 세트를 만드는 것은 쉽지 않기 때문에, 회전, 반전 (flipping), 필터링 (filtering) 등의 간단한 데이터 확장 (data augmentation) 기법을 통해 작은 데이터 세트를 좀 더 큰 데이터 세트로 만드는 여러 시도들이 있었다. 그러나 이러한 기법들은 이미 보유하고 있는 데이터 세트만을 이용하기 때문에 확장성에 제약을 갖는다. 이런 문제를 해결하기 위해 본고에서는 보유하고 있는 영상 데이터를 이용하여 새로운 영상 데이터를 획득하는 기술을 제안한다. 이는 기존 데이터 세트의 영상 데이터를 CBIR(Contents based image retrieval)의 쿼리로 이용하여 유사 영상들을 검색하여 획득하는 방식으로 이루어진다. 최종적으로 CBIR을 이용해 확장한 데이터를 딥 러닝으로 학습시켜 확장 전후의 성능을 비교하였다.