• 천문학회보
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• 제44권1호
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• pp.79.4-79.4
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• 2019

We introduce a newly established cosmology research group at the University of Seoul. We also present our recent progress with SDSS Main Galaxy samples and various types of cosmological simulations as follows: (1) A hint for the periodicity of very large-scale structures is found in both SDSS observation and the Horizon Run 4 (HR4) simulation. (2) New galaxy clustering and void finding algorithms, which are thought to be sensitive to the topological shape of galaxy distribution, are developed and tested in both SDSS and HR4 data. (3) Properties such as radial distribution of galaxies or cosmological shock waves are studied in hydrodynamic simulations.

• 한국지반환경공학회 논문집
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• 제16권2호
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• pp.5-13
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• 2015

본 연구에서는 36개의 CFRD에 대한 계측자료(38개 지점)를 통해 댐 축조단계에서 얻어지는 계측자료를 이용하여 담수 후 댐의 정부침하량 및 내부침하량 예측기법을 제안하였다. 전체 데이터에 대한 분석 결과, 댐체의 정부침하량 및 시공 중 최대 내부침하량은 댐체의 높이 및 간극비에 비례하였다. 그러나 내부침하량과 댐 높이에 대한 반대수지 상에서의 선형회귀분석 결과는 간극비에 따른 차이 없이 대단히 유사함을 확인하였다. 또한 CFRD의 시공 중 내부침하량을 통해 정부침하량의 예측이 가능하였으며, 댐체가 조밀할 경우 연직변형계수가 크게 평가됨과 동시에 계곡형상의 영향을 많이 받는 것으로 나타났다. 본 연구결과는 향후 CFRD의 설계, 시공, 장기적 유지관리를 위한 유용한 도구가 될 것으로 사료된다.

• 한국해양공학회지
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• 제21권4호
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• pp.21-27
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• 2007

The multiplication equipment of marine products with artificial upwelling structures could be useful in the fishing grounds near coastal areas. Artificial upwelling structures could move the inorganic nutrients from the bottom to the surface. Artificial upwelling structures have been used to improve the productivity of fishing grounds. Until now, research on artificial upwelling structures has been related to the distribution of the upwelling region, upwelling structures, and the marine environment. However, little work on the optimum design of the rubber-mound artificial upwelling structures has been done to increase the efficiency of drawing up the inorganic nutrients. This study investigated the optimum cross-section of rubber-mound artificial upwelling structures by means of hydraulic experiments. The hydraulic experiments include the falling test of rubber. Based on the results of the falling test, the relationship between the length of the rubber mound and water velocity, and the relationship between the shape of the rubber and the stratification parameter were established. In addition, the effect of the void ratio of various artificial structures on the stratification parameter was studied. From the experiment, it was found that upwelling could be enhanced when the ratio of structure height to water depth was 0.3 and stratification parameter was 3.0. The upwelling was not improved when the void ratio exceeded 0.43. The optimum size of rubber mounds was determined when the incident velocity was influenced by the mean horizontal length rather than size of block.

• 한국정밀공학회지
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• 제16권1호통권94호
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• pp.227-237
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• 1999

As the interface bonding phenomenon between the matrix and the reinforcements has a large effect on the mechanical properties of MMCs, a sugestion of the strength analysis technique considering the residual stress and the interface bonding phenomenon is very important for the design of pans and the estimation of fatigue behavior. In this paper the three dimensional finite element anaysis is performed during the elasto-plastic deformation of the particulate reinforced metal matrix composites. It was analyzed with the volume fractions in view of microscale. Bonding strength. interface separation and matrix void growth between the matrix and the reinforcements will be predicted on deformation under tensile loading. An interface seperation is estimated by the fracture criterion which is a critical value of generalized plastic work per unit volume. The shape of the reinforcement is assumed to be a perfect sphere. And the type of the reinforcement distribution is assumed as FCC array. The thermal residual stress in MMCs is induced by the heat treatment. It is included at the simulation as an initial residual stress. The element birth and death method of the ANSYS program is used for the estimation of the interface bonding strength, void generation and propagation. It is assumed that the fracture in the matrix region begin to occur under the external loading when the plastic work per unit volume is equal to the critical value. The fracture strain will be defined. The experimental data of the extruded $SiC_p$>/606l Al composites are compared with the theoretical results.

• 펄프종이기술
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• 제44권3호
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• pp.1-8
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• 2012

The effects of several factors including organic pigment blending and calending conditions on the surface and optical properties of coated paper were investigated. When clay and calcium carbonate are blended in the ratio of 7 to 3, highest smoothness and relative sediment volume were obtained. When organic pigments were added to the mixture of clay and calcium carbonate, the relative sediment volume did not changed significantly. However, when organic pigments were added to calcium carbonate, sheet gloss and smoothness were improved, and showed the better results than that obtained from the mixture of organic pigment and clay. When organic pigment is blended with clay, the particles of organic pigment are buried in the packing structure of coating layer. However, the particle shape of calcium carbonate is quite different from that of clay, and the aspect ratio of calcium carbonate is similar to that of organic pigment. Thus organic pigment particles are not buried and improved effectively the physical characteristics of coating layer. When the hollow sphere pigment was blended, opacity and sheet gloss were improved significantly. Even though the coating color applied was reduced, the similar level of opacity was maintained. Also, if particle size and void volume are increased, gloss is improved, because coating layer is easily transformed in calendering. Therefore, even though lower pressure was applied during calendering, the smoothness of surface of coating layer was improved, and the decrease of void volume in coating layer was reduced, and the quality of coated sheet can be improved.

• 한국세라믹학회지
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• 제44권7호
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• pp.362-367
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• 2007

Stent is a tiny structure made with either ceramic coating and/or bare metal. Being approximately $1{\sim}2 mm$ in diameter, it consists of holes, slots, or void space and is designed to cover entire medical lesions. Stent implantation into patients' arteries has been practiced for a little more than a decade in order to widen the blocked artery. The adoption of the stent has significantly improved the efficacy when compared with the previous medical practice by balloon angioplasty alone. Yet better biomedical performance of the stent is being demanded in order to eliminate the still existing problem of artery restenosis, which means the artery becomes narrowed again. Recent literature survey shows researches on ceramic coatings onto the stent surface, or material design to improve the mechanical response of the stent. This study focuses more on the material design and mechanical analysis. The results showed that the void configuration within the stent affects the mechanical response significantly. The rectangular shape was found to yield expansion at a relatively lower pressure than the elliptical slot for a slotted tube stent. The present results, when combined with research on coating at the stent surface, may provide stents with improved bio-medical performance.

• Composites Research
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• 제34권5호
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• pp.296-304
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• 2021

본 연구에서는 유한요소법(FEM)에 기반한 CF/PEKK 열가소성 복합재 고속 열 성형 해석을 수행하였고 제작 공정을 예측 및 검증하였다. 대표적인 L 형 구조물 모델에 대해 트리밍 여유에 따른 성형성을 응력, 두께, 주름분포를 분석하였다. 그 결과, 블랭크의 트리밍 여유가 증가할수록 구조물의 성형성이 향상하는 것을 확인하였다. 특히 두께 및 주름 분포 측면에서 해석 모델과 실험 결과를 비교하여서 고속 열 성형 모델의 타당성을 검증하였다. 제작된 구조물은 시차 주사 열량 분석법 및 이미지 분석법을 통해 결정화도와 기공률이 측정되었다. 제작된 열가소성 구조물의 전 영역 기공률은 평균 0.75%, 결정화도는 약 21%로 항공기에 적용 가능한 수치로 평가되었다. 따라서 본 연구를 토대로 열가소성 복합재 고속 열 성형 공정에 대해 효과적인 예측이 가능할 것으로 판단된다.

• 마이크로전자및패키징학회지
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• 제25권3호
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• pp.13-19
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• 2018

본 연구에서는 태양광 접속함 모듈 적용을 위한 유연 솔더(Sn-Pb) 및 무연 솔더(Sn-3.0Ag-0.5Cu 및 Sn-1.0Ag-0.7Cu-1.6Bi-0.2In)의 특성을 비교 평가하였다. 접속함 내에는 전압 및 전류 검출용 모듈, 고내압용 다이오드가 실장된 정류모듈 등 다양한 모듈이 내장되어있다. 본 연구에서는 솔더링특성, 인쇄성, 솔더형상 검사, X-ray를 이용한 솔더 내 void 검사 및 접합강도를 측정하였고, 무연 솔더 합금의 공정최적화는 step 1과 step 2로 구분하여 검토를 실시하였다. Step 1은 유연 솔더와 무연 솔더 페이스트 인쇄 검사 시험을 1차와 2차로 나누어 실험을 진행하였고 printability는 void 함량 및 접합강도의 상관관계로 검토하였다. 전체적으로 유연 솔더의 특성은 무연 솔더에 비하여 상대적으로 우수하였다. Step 2는 리플로우 공정의 최고점 온도 변화에 따른 접합부 특성 변화를 관찰하였다. 리플로우 최고 온도가 증가할수록 접합부 내의 void 함량이 2~4% 정도 감소하였고, 접합강도는 약 0.5 kgf 범위내에서 큰 차이 없이 나타났다. 기판 표면처리종류에 있어서는 ENIG 표면처리가 OSP 및 Pb-free 솔더 표면처리보다 우수한 접합강도를 나타내었다. 1종류의 무연솔더와 OSP 표면처리로 접합된 태양광 접속함 모듈의 500 싸이클 열충격 신뢰성시험 전후에 전기적 특성변화는 0.3% 내의 범위에서 안정적으로 작동함을 확인하였다.

• 한국건축시공학회지
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• 제20권2호
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• pp.155-162
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• 2020

본 연구에서는 비정형 패널 제작 기술력 향상을 위한 기초적인 연구로 비정형 패널의 오차율을 분석하였다. 이에 본 연구에서는 우선적으로 비정형 패널 제작시 매끄러운 형상을 표현하기 위해 콘크리트 대신 혼합모르타르를 사용하여 적정 배합비를 도출하였다. 그 후 도출한 배합비를 적용하여 비정형 패널을 CNC장비를 통해 제작하였으며 패널의 오차율을 분석하였다. 본 연구에서는 두 가지의 배합을 선정하였으며 선정한 첫 번째 배합은 혼합시멘트 페이스트 배합, 두 번째 배합은 혼합모르타르 배합이었다. 실험결과 두 배합모두 품질적 측면에서 만족하는 정량적 수치를 보였다. 하지만 두 배합모두 양생하는 방법에 차이를 두었고 이로 인해 오차가 발생했다. 이를 통해 오차율은 사용재료의 특성과 재료 간 화학반응의 문제보다는 패널을 양생하는 방법에 따라 더 많은 영향을 끼치는 것으로 판단하였다. 본 연구는 현재 기초적인 연구수행으로 추후 본 연구를 토대로 추가적인 연구를 진행한다면 콘크리트 타설시 흘러내림을 방지하는 방안과 오차율을 줄일 수 있는 양생방법을 찾는 연구가 함께 병행되어야 한다. 위와 같은 연구수행을 통해 비정형 패널 제작에 대한 연구 및 개발에 기여할 수 있으며 나아가 비정형 건축시장에서 경쟁력을 확보할 수 있다.

• 한국조경학회지
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• 제31권2호
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• pp.1-11
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• 2003

The purpose of this study is to investigate how five winning design proposals for the Seoul City Hall Plaza Design Competition have shown the spatial characteristics by comparing and reviewing them. Each design proposal shown different approaches that reveal the spatial characteristics. Through scrutinizing these design proposals, some similar and different aspects among them were identified. In order to examine these aspects, the winning design proposals were analysed and compared based on five categories such as design concepts, main facilities, representation of historical images, spatial connection, and event programs. Gilles Deleuze explained the spatial characteristics as striated space and smooth space. Striated space could be defined as sedentary space. It is distant vision-optical space that has dimensional, metric, and centered characteristics, whereas smooth space is defined as nomadic, close vision-haptic space that has directional and acentered characteristics. This study focused on the analysis of spatial characteristics according to smooth space and striated space. Based on the analysis of the spatial characteristics according to the smooth and striated space, some design proposals shown more characteristics of striated space while other proposals shown more characteristics of smooth space. Those design proposals that shown more characteristics of smooth space reveal flexible or changeable shape and void space, whereas the others that shown more characteristics of striated space try to suggest apparent guidelines for the future use by retaining the idea of a plaza through the concrete shape. This study, which analyzed the winning design proposals based on the spatial characteristics according to the smooth and striated space, can be used to analyze the designs and could help to develop a new methodology with a different perspective. furthermore, it could provide practical and creative design strategies for landscape design.