• Journal of Nutrition and Health
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• 제55권4호
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• pp.430-440
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• 2022

셀레늄은 산화스트레스 방어 기능으로 인체의 면역기능 유지에 필수적 역할을 하고, 세포의 항산화기능, 면역기능, 갑상선호르몬 조절, 약물이나 중금속 위해에 대한 방어, 만성질환의 위험 감소에 필수 역할을 하는 미량무기질이다. 셀레늄 섭취의 부족은 암, 심혈관질환, 당뇨병, 신경질환, 골관절 및 근육괴사와 약화, 갑상선질환, 염증성 질환 등 다양한 만성적 질환의 위험을 높인다. 본 논문은 2020 한국인 영양소 섭취기준에서 셀레늄의 제정과 개정 근거 기준에 대해 설명하고, 셀레늄 데이터베이스의 현황과 향후 2025 한국인 영양소 섭취기준 설정을 위한 필요 연구에 대해 논의하였다. 셀레늄의 2020 한국인 영양소 섭취기준은 2015년에 이어 혈장 셀레노프로테인 P 수준이 최대가 되는 셀레늄의 평균필요량을 지표로 사용하였고, 중국인 대상의 보고치에 한국인의 기준체중과 변이계수를 적용하는 방법이 적용되었으며, 2015년에 비해 참고체중치의 변경에 따라 성별, 연령별 셀레늄 섭취기준에서 약간의 개정이 있었다. 향후 셀레늄 섭취기준 설정의 발전을 위해서는 1) 한국인 대상의 혈장 셀레노프로테인 P의 최대수준을 나타내는 셀레늄 섭취량을 파악하기 위한 셀레늄 중재연구가 필요하고, 2) 셀레늄 섭취량 판정의 정확성을 높이기 위한 영양평가 프로그램내 식품 셀레늄 데이터베이스의 검토와 식품의 셀레늄 함량 분석을 확대해야 하며, 3) 국민의 셀레늄 섭취와 체내 생물학적 지표와의 관계를 건강한 일반인뿐만 아니라 질환자 및 운동선수와 같은 특수 환경의 대상자들로 확대하는 연구가 요구된다.

• 터널과지하공간
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• 제31권4호
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• pp.221-242
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• 2021

기존의 한국형 기준 처분시스템의 처분 효율을 높인 향상된 한국형 기준 처분시스템(Improved Korean Reference Disposal System, KRS⁺)의 열-수리-역학적 복합거동 성능평가를 위해 TOUGH2-MP/FLAC3D를 이용한 수치모델링 연구가 수행되었다. 사용후핵연료 처분 이후 방사성 붕괴열에 의해 처분시스템의 온도가 상승하고, 방사성 붕괴열이 빠르게 감소함에 따라 온도가 감소하여 최대 온도가 설계기준 온도인 100℃를 넘지 않는 것으로 나타났다. 완충재의 초기 포화도는 온도 상승으로 인한 공극수의 증발로 인해 감소하였다가 주변 암반으로부터 지하수가 유입되어 처분 약 250년 후 포화 상태에 이르렀다. 암반에서는 완충재와 암반의 흡입력의 차이로 인해 암반에서 완충재로 지하수가 유입되어 처분 직후 포화도가 감소하다가 이후 원계 암반으로부터 지하수가 유입되어 포화 상태에 도달했다. 처분시스템 내 열응력과 팽윤압 발생에 의한 주변 암반의 파괴 가능성을 평가하고자 모어-쿨롱 파괴기준식과 스폴링 강도를 사용하였다. KRS⁺ 처분시스템의 처분공의 간격을 감소시키면서 처분시스템의 열적 거동 변화를 확인하였는데, 처분공 간격이 5.5 m 이하에서는 완충재의 설계 기준 온도를 초과하게 된다. 다만, 벤토나이트 완충재 부피의 56.1%의 온도는 90℃ 이하로 유지되었다. 본 연구에서 사용한 수치해석 기법은 향후 응력 모델, 지온 경사 및 입력 물성을 변화시킨 다양한 조건에서의 처분시스템의 THM 복합거동 성능평가에 활용할 수 있을 것으로 판단된다.

• 대한족부족관절학회지
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• 제12권1호
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• pp.36-40
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• 2008

Purpose: The purpose of this study is to find out the normal results in ankle on varus stress, valgus stress, and anterior draw stress in young men in korea. This would be helpful as the basic data of measuring of ankle instability for operational indication. Materials and Methods: Varus and Valgus stress anteroposterior radiographs and Anterior drawing stress lateral radiographs of 600 normal ankles were reviewed. First, A line parallel was drawn parallel to the articular surface of the distal tibia, and another line was drawn parallel to the articular surface of the talus on anteroposterior radiographs. The interior angle that subtended by these two lines was measured. Second, the reference point is located at the posterior border of the tibia, and the shortest distance from this point to the proximal posterior articular surface of the talus is measured. Results: There were 300 males and 600 ankles. The mean age overall was 21 years (19-22 years) old. The mean length of ankle on anterior draw stress was $5.54{\pm}3.33\;mm$. The mean a interior angle of ankle on varus stress was $0^{\circ}-8.93^{\circ}$, and on valgus stress $0^{\circ}-7.78^{\circ}$. Conclusion: We can consider for operational indication at over the 8.87 mm on anterior draw stress, over the $8.93^{\circ}$ on varus stress, and over the $7.78^{\circ}$ on valgus.

• 대한기계학회논문집A
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• 제31권5호
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• pp.562-569
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• 2007

This paper presents plastic limit loads and approximate J estimates for axial through-wall cracked pipe bends under internal pressure and in-plane bending. Geometric variables associated with a crack and pipe bend are systematically varied, and three possible crack locations (intrados, extrados and crown) in pipe bends are considered. Based on small strain finite element limit analyses using elastic-perfectly plastic materials, effect of bend and crack geometries on plastic limit loads for axial through-wall cracked pipe bends under internal pressure and in-plane bending are quantified, and closed-form limit solutions are given. Based on proposed limit load solutions, a J estimation scheme for axial through-wall cracked pipe bends under internal pressure and in-plane bending is proposed based on reference stress approach.

• 한국압력기기공학회 논문집
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• 제15권2호
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• pp.1-8
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• 2019

The integrity of the Reactor Pressure Vessel (RPV) is affected by the neutrons bombarding the vessel wall leading to embrittlement. This irradiation-induced embrittlement leads to reduction in the fracture toughness of RPV materials. This paper presents a comparative study of typical Optimized Power Reactor (OPR)1000 reactor pressure-temperature (P-T) limit curves using the pre-2006 American Society of Mechanical Engineers (ASME) editions used in the power plant and the current ASME edition of 2010. The current ASME Code utilizes critical reference stress intensity factor based on the lower bound of static, while the Pre-2006 ASME editions are based the critical reference stress intensity factor based on the lower bound of static, dynamic and crack arrest. Model-Based Systems Engineering approach was used to evaluate ASME Code Section XI Appendix G for generating the P-T limit curves. The results obtained from this analysis indicate decrease in conservatism in P-T limit curves constructed using the current 2017 ASME code, which can potentially increase operational flexibility and plant safety. Hence it is recommended to use ASME code edition after 2006 be used in all operating nuclear power plants (NPPs) to establish P-T limit curve.

• 대한기계학회논문집A
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• 제25권9호
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• pp.1325-1333
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• 2001

Critical defects in pressure vessels and pipes are generally found in the form of a semi-elliptical surface crack, and the analysis of which is consequently an important problem in engineering fracture mechanics. Furthermore, in addition to the traditional single parameter K or J-integral, the second parameter like T-stress should be measured to quantify the constraint effect. In this work, the validity of the line-spring finite element is investigated by comparing line-spring J-T solutions to the reference 3D finite element J-T solutions. A full 3D-mesh generating program for semi-elliptical surface cracks is employed to provide such reference 3D solutions. Then some structural characteristics of the surface-cracked T and L-joints are studied by mixed mode line-spring finite element. Negative T-stresses observed in T and L-joints indicate the necessity of J-T two parameter approach for analyses of surface-cracked T and L-joints.

• 대한기계학회논문집A
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• 제31권6호
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• pp.710-717
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• 2007

This paper presents plastic limit loads and approximate J-integral estimates for circumferential part-through surface crack at the interface between elbows and pipes. Based on finite element limit analyses using elastic-perfectly plastic materials, plastic limit moments under in-plane bending are obtained and it is found that they are similar those for circumferential part-through surface cracks in the center of elbow. Based on present FE results, closed-form limit load solutions are proposed. Welds are not explicitly considered and all materials are assumed to be homogeneous. And the method to estimate the elastic-plastic J-integral for circumferential part-through surface cracks at the interface between elbows and straight pipes is proposed based on the reference stress approach, which was compared with corresponding solutions fur straight pipes.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2550-2563
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• 2022

This study performed a precise dynamic finite element time history elastic-plastic seismic analysis considering the welds, which have been not considered in design stage, on the nuclear components subjected to severe seismic loadings such as beyond-design basis earthquakes for sustainable nuclear power plants. First, the dynamic finite element elastic-plastic seismic analysis was performed for a general design practice that does not take into account the welds of the pressurizer surge line system, one of safety class I components in nuclear power plants, and then the reference values for the accumulated equivalent plastic strain, equivalent plastic strain, and von Mises effective stress were set. Second, the dynamic finite element elastic-plastic seismic analyses were performed for the case of considering only the mechanical strength over-mismatch of the welds as well as for the case of considering both the strength over-mismatch and welding residual strain. Third, the effects of the strength over-mismatch and welding residual strain were analyzed by comparing the finite element analysis results with the reference values. As a result of the comparison, it was found that not considering the strength over-mismatch may lead to conservative assessment results, whereas not considering the welding residual strain may be non-conservative.

• 대한기계학회논문집
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• 제19권4호
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• pp.981-989
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• 1995

A new weight function approach to determine SIF(stress intensity factor) using single-layer potential has been presented. The crack surface displacement field was represented by one boundary integral term whose kernel was modified from Kelvin's fundamental solution. The proposed method enables the calculation of SIF using only one SIF solution without any modification for the crack geometries symmetric in two-dimensional plane such as a center crack in a plate with or without an internal hole, double edge cracks, circumferential crack or radial cracks in a pipe. The application procedure to those crack problems is very simple and straightforward with only one SIF solution. The necessary information in the analysis is two reference SIFs. The analysis results using present closed-form solution were in good agreement with those of the literature.

• 대한기계학회논문집
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• 제15권2호
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• pp.596-603
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• 1991

Fatigue life prediction of pressure vessel is studied analytically using cumulative damage models and linear elastic fracture mechanics method. The stresses are analyzed by finite element method. During operation, the maximum stress occurs at the outside of neck region while fatigue analysis indicates that the bottom of nozzle part has the shortest fatigue life. Previously proposed fatigue life prediction equation and cumulative damage model are modified successfully by introducing reference fatigue modulus. It is found that the modified life prediction equation and damage model are useful for lower stress level application.