• 한국산학기술학회논문지
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• 제21권2호
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• pp.535-541
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• 2020

FCAW는 모든 자세에서 용접이 가능하고 작업여건 변수가 많은 현장에서 우수한 품질을 얻을 수 있는 장점이 있어 탄소강과 합금강의 중판, 후판 용접에 많이 사용되고 있다. 최근 국내에서 진행한 연구논문의 대부분이 피로 강도 평가 방법 연구, 잔류응력 및 변형, 필릿 용접 공정 개발 등의 연구가 시행되었으나 필릿 용접을 대상으로 경도, 매크로, 자분탐상 결과를 토대로 하여 기계적 특성을 나타낸 연구가 부족함에 따라 본 연구에서는 FCAW를 이용하여 상부는 SS400(일반구조용 압연강재) 후판은 SM490A(용접구조용 압연강재)를 이용하여 필릿 용접 후 경도시험, 매크로 시험, 자분탐상시험을 통해 아래와 같은 결론을 도출하였다. 경도시험 결과, 모든 결과 값이 KS B 0893의 규격치 350Hv보다 낮게 나타나 양호한 것으로 판단되었고, 매크로 시험 결과 용접부의 형상별로 균일한 조직 상태를 나타냈으며, 용접부 전 단면에 걸쳐 내부 결함, 기포 또는 불순물 등이 발견되지 않아 lamination의 우려가 없었으며, 자분탐상검사 결과 별도의 문제점이 발견되지 않았다.

• 한국과학교육학회지
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• 제41권2호
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• pp.115-131
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• 2021

전 지구적으로 기후변화 위기 상황이 고조되고 있는 오늘날 사회적 행동을 통해 사회를 변화시킬 수 있는 '기후변화를 주제로 한 사회적 실천지향 SSI 교육'의 필요성이 증가하고 있다. 본 연구는 사회문화적 관점을 바탕으로, 기후변화를 주제로 한 사회적 실천지향 SSI 수업을 실행하는 과정에서 직면하는 교사의 어려움이 무엇인지 탐색하고자 하였다. 이를 위해 46차시 동안 진행된 수업에 대한 질적 단일 사례연구를 진행하였으며, 연구 참여자와의 심층 면담, 교사 성찰일지, 수업 동영상, 학생 면담, 학습 결과물, 참여 관찰일지 등과 같은 질적 자료를 수집하였다. 수집된 자료는 실천적-평가적 차원의 구조를 micro(교실), meso (학교), macro (한국 사회) 장으로 나누어 분석하였다. 연구 결과 micro 장에서 새로운 시도의 수업으로 인해 기후변화에 대한 학생들의 이해나 인식을 파악하기 힘들었으며 특히 학생들이 기후변화를 나의 문제라고 인식하는 주인의식을 가지는 데 어려움이 있어 교사가 원하는 방향으로 수업이 이루어지지 않았다. 또한, 학생들은 스스로를 어린이로 위치 지으며 계획한 사회적 행동의 실현 가능성에 대해 회의적이거나, 사회적 행동을 이해하지 못하고 그 가치에 대해 공감하는 데 어려움을 겪어 학습 목표를 성취시키는 데 어려움이 있었다. meso 장에서는 동학년 교사와 교육과정을 비슷하게 운영해야 하는 학교 문화 속에서 교사만의 교육과정을 운영하는 데 어려움을 겪었다. 또한, 기후변화 수업이라는 낯선 과학 수업 주제에 대한 부담을 드러내는 동료 교사들과 소통이 단절된 채 교육과정을 홀로 운영하는 과정에서 전문성을 키워나가는 데 어려움을 겪었다. 관리자 역시 사회적 행동에 대한 소극적인 지원을 하여 학교 밖으로 사회적 행동을 실행하는 과정에서 갈등 상황에 직면하였다. 마지막으로 macro 장에서는 본 수업의 교수학습을 지원하는 물적 자원이 미흡하였으며, 학생들의 사회적 행동에 대한 사회구성원들의 제한된 시각이 교수학습상황의 거시적 제약조건으로 작용하고 있었다. 분석을 위해 유목화된 각 장의 제약조건들은 실제로는 독립적이고 분절적인 요소가 아닌 상호 간에 영향을 미치며 복합적인 그물망을 형성하며 구조적 제약조건을 형성하고 있었다. 이에 본 연구 결과를 통해 기후변화를 주제로 한 사회적 실천지향 SSI 수업을 실행하는데 교육 공동체 여러 주체의 다층적인 지원과 노력이 필요함을 시사한다.

• Journal of Ecology and Environment
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• 제37권4호
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• pp.185-194
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• 2014

Seasonal monitoring was implemented to understand the influence of macrophyte bed structure on the composition and trophic interaction of aquatic organisms (algae, zooplankton, macro-invertebrate, and fish) in a shallow wetland (Upo Wetland, South Korea). Distinct division of the plant assemblage (reed zone and mixed plant zone) was observed. The reed zone was composed solely of Phragmites communis, whereas the mixed plant zone comprised a diverse macrophyte assemblage (Salvinia natans, Spirodela polyrhiza, Trapa japonica, Ceratophyllum demersum, and Hydrilla verticillata). Most of the aquatic organisms were more abundant in the mixed plant zone than in the reed zone, and this was positively associated with the seasonal development of macrophyte cover. Stable isotope analysis showed seasonal interactions among aquatic organisms. The majority of aquatic animal (zooplankton, Odonata, and Ephemeroptera) were dependent on epiphytic particulate organic matter (EPOM), and the dependence on EPOM gradually increased toward autumn. Interestingly, Lepomis macrochirus consumed Ephemeroptera and zooplankton in both macrophyte zones, but Micropterus salmoides depended on different food items in the reed zone and the mixed plant zone. Although, M. salmoides in the reed zone showed food utilization similar to L. macrochirus, it consumed Odonata or small L. macrochirus in the mixed plant zone. Based on these results, it appears that differences in the structure of the two macrophyte zones support different assemblages of aquatic organisms, strongly influencing the trophic interactions between the aquatic organisms.

• 한국전기전자재료학회논문지
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• 제23권9호
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• pp.741-746
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• 2010

Three-dimensionally ordered macro-porous Sn-C composites were prepared by using polystyrene microsphere as a template. The Sn-C composites were composed of well-interconnected pore with circular shape and wall structure with wall thickness of a few tens of nano-meters. This porous three-dimensional structure is readily and uniformly accessible to the electrolyte, which facilitates lithium ion diffusion during charge-discharge reactions. The wall thickness of the composites was increased as the increase of Sn content of the composite. From EDS analysis, it is confirmed that the Sn was dispersed uniformly in Sn-C composites. The capacity was increased as the Sn content increased, which is due to Sn anode with high capacity. The Sn-C composites with high Sn content showed superior cyclic performances. Such enhancement is ascribed to the thick wall thickness and small pore size of the sample with high Sn content. The Sn-C composite with Sn 30 wt% showed relatively high capacity and stable cycle life, however, the stability of the 3-dimensional structure should be enhanced by further work.

• 기술혁신연구
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• 제15권1호
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• pp.203-233
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• 2007

This study investigates how characteristics in the value-chain industrial cluster affect the R&D investment and the output of firms in each industries. For this, we try to extract the inter-industrial networking structure from the input-output table in which 17 manufacturing sectors are included. In particular, we will give shape to the "unit structure" which shows the intermediary flows of goods and services between industries in order to get an unit of final demand in a certain industry. Using this "unit structure", we can try the inter-industrial networking analysis and get some indices of centrality and centralization related to the characteristics of each industries in the value-chain industrial cluster. The results show that the centrality in the value-chain industrial cluster does not have any consequence for the R&D investment and the output in each industries. However, there is a correlation between the centralization in the value-chain industrial cluster and the R&D investment and the output of firms in each industries. These results may be very suggestive in bringing up a new frame of industrial cluster policy in a macro level.

• 대한기계학회논문집A
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• 제27권1호
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• pp.109-118
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• 2003

The recent trend towards miniaturization causes an increased demand for parts with very small dimensions. Milli-structure components are classified as a component group whose size is between macro- and micro-scale. The manufacturing process of these components of thin sheet metal forming has a microscopic properties in addition to a typical phenomenon of bulk deformation because of the forming size. Also, the material properties and the deformation behavior change with miniaturization, which means that, a coarse grained materials show a higher resistance against deformation, when the grain size is in the range of the sheet thickness. In this study, a new numerical approach is proposed to simulate intergranular milli-structure in forming by the finite element method. The grain element and grain boundary element are introduced to simulate the milli-structure in the bending. The grain element is used to analyze the deformation of individual grain while the grain boundary element is for the investigation on the movement of the grain boundary. Also, the result of the finite element analysis is confirmed by a series of milli-sized forming experiments.

• Corrosion Science and Technology
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• 제3권3호
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• pp.87-97
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• 2004

This paper presents a new approach with meso scale structure models to express mechanical property, such as stress - strain relationships, of concrete. This approach is successful to represent both uniaxial tension and uniaxial compression stress - strain relationship, which is in macro scale. The meso scale approach is also applied to predict degraded mechanical properties of frost-damaged concrete. The degradation of mechanical properties with frost-damaged concrete was carefully observed. Strength and stiffness in both tension and compression decrease with freezing and thawing cycles (FTC), while stress-free crack opening in tension softening increases. First attempt shows that the numerical simulation can express the experimentally observed degradation by introducing changes in the meso scale structure in concrete, which are assumed based on observed damages in the concrete subjected to FTC. At the end applicability of the meso scale approach to prediction of the degradation by combined effects of salt attack and FTC is discussed. It is shown that clarification of effects of frost damage in concrete on corrosion progress and on crack development in the damaged cover concrete due to corrosion is one of the issues for which the meso scale approach is useful.

• 대한기계학회논문집B
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• 제33권12호
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• pp.992-999
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• 2009

The focus of this study is placed on the behavior characteristics of gasoline spray under condition field of room temperature and pressure. To analyze the behavior and flow characteristics of injected fuel spray is important in speculation of mixture formation process. Also the exhausted emissions from actual engines can be controlled by the analyzed results. The ${\varphi}$(degree of freedom) and K(energy ratio of particle motion) are selected as the simulation parameter. The factors affect characteristics of spray structure, and the factors are included in the sub-program of the KIVA-II code. In this study, the simulation study by modified KIVA-II code was conducted and the calculated results obtained by the modified KIVA-II code show good agreements with experimental results. As a result, applying the improved TAB model with ${\varphi}$=8 and K=2 to simulation analysis of the KIVA-II code is sufficiently useful for analyzing the macro characteristics in spray structure, such as the spray tip penetration of injected fuel spray.

• Ocean and Polar Research
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• 제25권4호
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• pp.519-528
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• 2003

Species composition and community structure of marine benthic community were studied in the intertidal zone of Jijindo Island, Gwangyang Bay. A total of 85 species of benthic marine plants including the 5 Cyanophyta, 9 Chlorophyta, 13 Phaeophyta, 56 Rhodophyta and 2 Magnoliophyta that were listed. The community structure was represented by Gelidium divaricatum in the upper zone, Celidium divalicatum and Ulva pertusa in the middle, and Ulva pertusa, Chondria crassicaulis, Chondracanthus intermedia and Sargassum thunbergii in the lower intertidal zone. The dominant species in the rnscro-zoobenthic community were Chthamalux challengeri in the upper and middle, Littorina brevicula between the upper and middle, and Mytilus edulis and Crassostrea gigas in the middle and lower intertidal zones. The economic benthic organisms such as Undaria pinnatifida, Mytilus edulis, and Crassostrea gigas found in the lower intertidal zone were frequently disturbed due to their collection by local resident. Therefore, it is necessary to record the correct information pertaining to these cases. The species diversity indices estimated kom different sources were quite different. They were 2.22 derived from frequency, 1.67 based on coverage, 2.17 based on sum of frequency and coverage and 2.04 derived from importance value. Species diversity and number of algal species in Gwangyang Bay have noticeably decreased, compared with their previously reported status. It is estimated that their decreases were caused by changes in the marine environment, especially pertaining to the polychaete community resulting from reclamation and dredging activity undertaken for the industrial development.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2006년도 춘계학술논문 발표대회 제6권1호
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• pp.167-171
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• 2006

In this study, for the establishment of the performance evaluation methods of repair material and method for reinforced concrete structure and the quality control standards of durability recovery method, the quantitative exposure data by exposure experiment under the coastal and normal atmosphere environment is accumulated and analyzed. Investigating and evaluating the result of exposure experiment during 30 months of exposure age under the coastal and normal atmosphere environment, carbonation depth and chlorideion penetration depth very little penetrated than cover depth. It seems reasonable to conclude that main cause of corrosion of reinforcing bar are inner chloride-ion and macro cell from the result of corrosion area and corrosion velocity. Accordingly, it is considered that fundamental data on the performance evaluation and quality control standards of repair material and method could be presented through continuous exposure test in the future.