• Steel and Composite Structures
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• 제45권5호
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• pp.641-652
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• 2022

Fluid-conveying tubes are widely used to transport oil and natural gas in industries. As an advanced composite material, functionally graded carbon nanotube-reinforced composites (FG-CNTRC) have great potential to empower the industry. However, nonlinear free vibration of the FG-CNTRC fluid-conveying pipe has not been attempted in thermal environment. In this paper, the nonlinear free vibration characteristic of functionally graded nanocomposite fluid-conveying pipe reinforced by single-walled carbon nanotubes (SWNTs) in thermal environment is investigated. The SWCNTs gradient distributed in the thickness direction of the pipe forms different reinforcement patterns. The material properties of the FG-CNTRC are estimated by rule of mixture. A higher-order shear deformation theory and Hamilton's variational principle are employed to derive the motion equations incorporating the thermal and fluid effects. A two-step perturbation method is implemented to obtain the closed-form asymptotic solutions for these nonlinear partial differential equations. The nonlinear frequencies under several reinforcement patterns are presented and discussed. We conduct a series of studies aimed at revealing the effects of the flow velocity, the environment temperature, the inner-outer diameter ratio, and the carbon nanotube volume fraction on the nature frequency.

• 한국표면공학회지
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• 제32권3호
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• pp.211-213
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• 1999

In the future, restrictions are likely to be imposed on the use of lead in the electronics industry. In dealing with such a move, we have been developing Pb-free Sn-Ag plating process to replace presently available Sn-Pb process. In this paper, the result of a basic comparison test between Sn-Pb plating and Sn-Ag plating is reported.

• 사물인터넷융복합논문지
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• 제9권2호
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• pp.19-31
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• 2023

세계적으로 장애물 없는 생활 환경, 즉 배리어 프리의 중요성이 부각되고 있다. 이에 본 연구는 텍스트 마이닝 기법을 활용하여 배리어 프리 연구 동향을 파악해 봄으로써 배리어 프리 환경 조성을 위한 연구의 방향성, 정책의 방향성 제시에 도움을 주고자 했다. 분석 자료는 배리어 프리 관련 연구가 시작된 1996년부터 2022년 현재까지 국내 전문학술지에 개재된 227편의 논문이다. 연구자는 학술 논문의 제목과 주제어, 초록을 텍스트로 전환한 후 논문의 패턴과 데이터의 의미를 분석했다. 연구결과를 요약하면 다음과 같다. 첫째, 2009년 이후 배리어 프리 연구가 증가하기 시작했고, 연평균 17.1편의 논문이 게재됐다. 이는 2008년 7월 15일에 장애물 없는 생활환경(Barrier Free) 인증제도 시행지침 시행과 관련성을 가진다. 둘째, 배리어 프리 텍스트 마이닝 결과 i) 상위 주요 키워드 단어 빈도분석 결과 배리어 프리, 장애인, 디자인, 유니버설 디자인, 접근, 노인, 인증, 개선, 평가, 공간, 시설, 환경 등이 중요 키워드로 나타났다. ii) TD-IDF 분석결과는 유니버설 디자인, 디자인, 인증, 주택, 접근, 노인, 설치, 장애인, 공원, 평가, 건축물, 공간 등이 주요 키워드로 나타났다. iii) N-Ggam 분석결과 배리어프리+인증, 배리어프리+디자인, 배리어프리+배리어프리, 노인+장애인, 장애인+노약자, 장애인+편의시설, 장애인+노인, 사회+노약자, 편의시설+설치, 인증+평가지표, 물리+환경, 삶+질 등이 주요 연관어로 나타났다. 셋째, CONCOR 분석결과 군집 1은 배리어 프리의 현안과 과제, 군집 2는 유니버설 디자인과 공간 활용, 군집 3은 장애인 활용 가능성 제고, 군집 4는 배리어 프리 인증과 평가로 나타났다. 본 연구는 이상의 분석결과에 기반하여 배리어 프리 연구의 활성화와 바람직한 배리어 프리 환경 구축을 위한 정책적 함의를 제시 하였다.

• 대한안전경영과학회:학술대회논문집
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• 대한안전경영과학회 2002년도 춘계학술대회
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• pp.189-191
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• 2002

A supervisor's role is very important to have accident free environment in a company. In order to take full advantage of safety management system, company safety supervisors require to learn how much responsibility they have in their company. To improve safety supervisor's knowledge, they must spend time to learn the importance accident free environment. To improve the efficiency of safety management, the supervisors need to voluntarily emphasize the importance of safety management.

• 대한안전경영과학회지
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• 제4권1호
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• pp.1-9
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• 2002

A supervisor's role is very important to have accident free environment in a company. In order to take full advantage of safety management system, company safety supervisors require to learn how much responsibility they have in their company. To improve safety supervisor's knowledge, they must spend time to learn the importance accident free environment. To improve the efficiency of safety management, the supervisors need to voluntarily emphasize the importance of safety management.

• 한국해양환경ㆍ에너지학회지
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• 제8권3호
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• pp.116-121
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• 2005

본 연구에서는 자유표면을 갖는 대규모의 환경유동의 해를 구하는데 있어 비정수압의 효과를 고려하는 새로운 계산 기법을 제시하였다. Sigma 좌표계에서 시간은 전진차분으로, 공간은 중간차분 및 풍상차분을 혼합하여 2단계 해법을 도입하였다. 계산기법의 타당성과 유효성을 검증하기 위하여, 자유표면을 갖는 정상유동과 비정상유동에 대한 전형적인 예를 설정하여 정수압 계산과 비정수압 계산을 수행하고 이들을 비교하였다. 계산결과 복잡한 해저지형을 갖는 자유표면 유동에 있어, 지정수압효과가 무시할 수 없는 유동영역이 존재함이 입증되었으며, MAC기법과 같은 3차원 유체동역학적 기법을 적용하기에는 비경제적인 문제에 대해 본 계산기법이 매우 유효하게 적용될 수 있다는 가능성이 입증되었다.

• 동아시아식생활학회지
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• 제11권1호
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• pp.1-10
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• 2001

Since the Industrial Revolution, people have enjoyed an abundant life, owing to the technological innovations of science. However, because of changes in the environment or polution to the environment, it has brought on many chronic diseases. Especially, even though it may be a small amount, if cadmium gets into a human body, because its biological half life is long, it fatally causes a kidney disease and damage to human organisms. It was reported that Metallothioneins(MT), a substance that is closely related with a free radical that comes from environmental pollution and the course of which cadmium, which causes chronic addition in the body, is formed, along with harmful metals, make the toxicity reduce. MT compound led into the body by cadmium indirectly functions as an antioxidation, supplied adequate amount of vitamin E, and suppresses the accumulation of cadmium in heart, liver and blood. Cadmium content found in Korean soil according to the test conducted from 1992 to 1996 was 0.02~0.03mg/kg in cereals, pulses, and potatoes. Free radical scavenger, finding solution for metal substance that comes from environmental pollution from food and natural substances implicates a better future for the study of food science.

• Smart Structures and Systems
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• 제29권3호
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• pp.395-420
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• 2022

A new hybrid quasi-3D and 2D high-order shear deformation theory is studied in this mathematical formulation, for an investigation of the bending, free vibrations and buckling influences on a functionally graded material plate. The theoretical formulation has been begun by a displacement field of five unknowns, governing the transverse displacement across the thickness of the plate by bending, shearing and stretching. The transverse shear deformation effect has been taken into consideration, satisfying the stress-free boundary conditions, especially on plate free surfaces as parabolic variation through its thickness. Thus, the mechanical properties of the functionally graded plate vary across the plate thickness, following three distributions forms: the power law, exponential form and the Mori-Tanaka scheme. The mechanical properties are used to develop the equations of motion, obtained from the Hamilton principle, and solved by applying the Navier-type solution for simply supported boundary conditions. The results obtained are compared with other solutions of 2D, 3D and quasi-3D plate theories have been found in the literature.

• 인간식물환경학회지
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• 제22권3호
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• pp.289-298
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• 2019

As part of the free semester program, the 'Gardener for a day' program in the Korea National Arboretum was newly developed in 2018. The program was developed as a free semester program reflecting the works of a 'gardener' who performs the planning, preparation, maintenance and management of exhibition gardens. This 'Gardener for a day' program was applied to a total of 106 middle school students in October 2018. Educational elements were extracted from Korea National Arboretum exhibition gardens and career exploration of gardeners. The program was designed to provide education on theory and practices, including watching the gardener video, visiting the gardener booth, meeting with actual gardeners at Korea National Arboretum, visiting two exhibition gardens, and participating in three types of practical training as a gardener. A survey about program satisfaction and education was conducted after the program to analyze the students' satisfaction with the program (contents, management, instructor), free semester program (career planning, occupational attitude, independence), and education (awareness of forest biospecies, preservation will). The analysis showed that the following results: satisfaction with the program (score 4.0), free semester program (score 3.8), and education (score 4.0). Comparative analysis of the pretest-posttest questionnaires showed that there were significant educational effects in career planning, occupational attitude, and awareness of forest biospecies.

• 한국물환경학회지
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• 제26권5호
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• pp.781-788
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• 2010

A pilot study was performed to examine the feasibility of multiple stage of constructed wetland (CW) for nutrient removal. The system is composed of six wetland cells connected with water-ways. The hydraulic of wetland cells is designed as free water surface flow. The treatment capacity was $25m^3d^{-1}$ at HRT of about one day for each cell. The magnitude of nutrient removal was related with the length of wetlands and plant density. Total N and P removal rates were 1353 and $246mg\;m^{-2}d^{-1}$ respectively. The pilot-scale reactor was model as continuous flow system containing contribution of CSTR and PFR typed-reactors. The $k-C^*$ model equation was applied to predict N and P reduction. The result indicated the equation was well guided to estimate reduction of $NO_3-N$ and $PO_4-P$.