• 한국산학기술학회논문지
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• 제13권4호
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• pp.1900-1907
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• 2012

일반적으로 활용되고 있는 원통형 단면쉘 구조로 이루어진 타워구조의 대형화에 한계가 있어 다각형 단면쉘 기둥구조의 활용이 대두되고 있다. 현재 대형 다각형 단면쉘 기둥구조의 국부좌굴강도에 대한 자료가 충분치 않고 관련 기준이나 지침이 명확히 제시되고 있지 않은 실정이다. 이에 3차원 유한요소프로그램인 ABAQUS를 이용한 다양한 변수해석 모델을 수립하여 탄성좌굴 및 비선형비탄성 변수해석을 수행하였다. 이 때, 단면제원은 대형 풍력발전타워 기둥구조에 적용하는 것을 가정하여 선정하였고, 다각형의 각형 수, 잔류응력의 크기 및 분포특성, 강재 항복강도 등의 변수를 고려한 해석결과를 토대로 다각형 단면쉘 기둥구조의 국부좌굴 특성을 분석하였다. 본 변수해석 연구결과로부터 세부적인 잔류응력 분포양상 보다는 잔류응력의 최대크기가 축방향 압축을 받는 다각형 쉘의 국부좌굴강도에 중요한 영향인자인 것을 알 수 있다. 다각형 단면 쉘 구조의 국부좌굴강도는 4변 단순지지된 평판구조의 기준을 적용하여 평가할 수 있을 것으로 판단된다.

• 한국지반공학회논문집
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• 제15권3호
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• pp.27-40
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• 1999

사면안정해석을 수행하기 위하여 많이 사용하는 한계평형방법은 일정한 가정을 하여 안전율을 평형에 필요한 응력과 흙의 전단강도의 비로 정의하여 대상사면의 안전율을 구한다. 유한요소법을 이용한 사면안정해석방법은 응력상태를 유한요소법으로 구한 후 원호나 대수나선형등의 일정한 모양의 사면 파괴선을 가정하여 반복적으로 최소안전율을 구한다. 본 연구에서는 유한요소법을 이용한 사면안정해석방법을 개발하여 사면의 가장 취약한 부분을 따라 파괴선이 발생하도록 하였다. 이것은 요소내의 국부안전율과 파괴각을 고려하여 사면파괴선을 자동적으로 구할 수 있도록 함으로써 가능한데 이 방법은 임의의 파괴선을 가정할 필요가 없으며 절편에 작용하는 힘에 대하여 가정을 할 필요가 없고 임의의 모양의 파괴선을 구할 수 있는 장점이 있다. 본 연구에서는 개발된 해석방법을 검증하기 위하여 가상의 사면, 자연사면, 그리고 댐사면에 적용하여 실무에서 많이 사용하는 한계평형방법 프로그램인 STABL5M과 SLOPE/W과 비교 평가하였다.

• 한국의류산업학회지
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• 제2권3호
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• pp.265-271
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• 2000

Heat stress results in fatigue, a decline in strength, alertness., and mental capacity. The problem is compounded when high humidity exists. To help relieve worker heat stress, many types of cooling units are marketed. While workers may experience some cooling, critical body core temperatures often continue to elevate. This study was designed to find the effects of three kinds of cooling vest with portable frozen gel strips on thermophysiological parameters and on temperature and humidity within clothing. The heart rate, rectal, and skin temperature as well as sweat rate and clothing microclimate were measured during 80 min in 5 healthy males. Inquiries were also made into the subjective rating thermal, humidity comfort, and fatigue sensations. The main findings in our experiments are as follows: (a) Physiological parameters such as rectal temperature was the lowest in garb A1, intermediate in garb A, and the highest in garb A2 throughout the experiment. And mean skin temperature was the lowest in garb A, intermediate in garb A1, and the highest in garb A2; (b) Temperature and humidity within clothing (back) were garb in Al, intermediate in garb A, and the highest in garb A2. But the temperature and humidity within clothing (chest) were garb in A, intermediate in garb A1, and the highest in garb A2; (c) Most participants (4 out of 5 persons) answered that they felt more comfortable and fatigueless in garb A1 than in garb A and A2. It is concluded that local cooling in garb A1 of the upper torso could physiological reduce the thermal strain in participants wearing cooling vest.

• Plant Biotechnology Reports
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• 제2권1호
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• pp.41-46
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• 2008

Salinity stress is a major limiting factor in cereal productivity. Many studies report improvements in salt tolerance using model plants, such as Arabidopsis thaliana or standard varieties of rice, e.g., the japonica rice cultivar Nipponbare. However, there are few reports on the enhancement of salt tolerance in local rice cultivars. In this work, we used the indica rice (Oryza sativa) cultivar BR5, which is a local cultivar in Bangladesh. To improve salt tolerance in BR5, we introduced the Escherichia coli catalase gene, katE. We integrated the katE gene into BR5 plants using an Agrobacterium tumefaciens-mediated method. The introduced katE gene was actively expressed in the transgenic BR5 rice plants, and catalase activity in $T_1$ and $T_2$ transgenic rice was approximately 150% higher than in nontransgenic plants. Under NaCl stress conditions, the transgenic rice plants exhibited high tolerance compared with nontransgenic rice plants. $T_2$ transgenic plants survived in a 200 mM NaCl solution for 2 weeks, whereas nontransgenic plants were scorched after 4 days soaking in the same NaCl solution. Our results indicate that the katE gene can confer salt tolerance to BR5 rice plants. Enhancement of salt tolerance in a local rice cultivar, such as BR5, will provide a powerful and useful tool for overcoming food shortage problems.

• 한국전산구조공학회논문집
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• 제32권3호
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• pp.183-190
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• 2019

본 논문은 균열선단 그리드 세분화기법을 소개하고 자연요소법을 이용한 균열해석에 이 기법을 적용함으로서 그 유효성을 고찰하였다. 유한요소법에 있어서의 국부적 h-세분화와 같이 높은 응력 특이성을 보이는 균열선단 주위를 따라 자연요소법 그리드를 국부적으로 세분화하였다. 본 논문에서 소개되는 그리드 세분화기법은 2단계로 구성되며, 1단계에서는 그리드 점들이 추가되고 2단계에서는 균열선단 절점을 공유하는 델라우니 삼각형들이 나뉘게 된다. 제안하는 그리드 세분화기법의 타당성과 균열해석에서의 유효성을 입증하기 위해 대칭 엣지 균열을 갖는 평면 변형률 상태의 사각 평판을 해석하였다. 수치해석 결과의 상대비교를 위해 균일한 자연요소 그리드를 이용한 균열해석도 수행하였으며, 균열선단이 세분화된 그리드는 균일한 그리드와는 달리 이론해와 조밀한 그리드와 유사한 균열선단 응력분포를 나타내었다. 또한, 총 그리드 절점수에 대한 해석결과의 전역 상대오차에서도 세분화된 그리드가 균일한 그리드에 비해 높은 수렴율 나타내었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.835-840
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• 2001

The new approach is a kind method of restoring temporary defect. Here, it is important for the defect not to occur problems of both local effect and global system. A basic concept is that it measures remaining prestress of PSC structures during the defect is restored. This study suggested new approach for measurement of remaining prestress. Two important results are obtained. First, safety problems, local stress concentration and global system, are very satisfied. Second, measurement value exists within error bound $\pm$ 1% in comparison with known value.

• 한국직업건강간호학회지
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• 제21권2호
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• pp.134-144
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• 2012

Purpose: The purpose was to investigate the relations among job-stress, self-efficacy, and depression of nurses. Methods: The data were collected from a random sample of 213 nurses working in two general hospitals of a local area. A self-reported questionnaire was used to assess the level of job-stress, self-efficacy, and depression. Results: The mean score of job-stress was 49.1 and the score of job demand was the highest. The mean score of self-efficacy was 3.4, and depression was 18.2. The prevalence of depression was very high. The job-stress and depression were negatively correlated with self-efficacy. Hierarchial multiple regression showed that the self-efficacy and the high job demand, lack of reward, and organizational injustice of job-stress explained 53% of the variance for the nurses' depression. Conclusion: The findings indicated that the self-efficacy and job stress, especially job demand, organizational injustice, and lack of reward contributed to the depression. In order to prevent and decrease the depression, the developing programs to improve self-efficacy are needed.

• 한국공작기계학회논문집
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• 제12권4호
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• pp.63-69
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• 2003

In discontinuous composite mechanics, shear lag theory is one of the most popular model because of its simplicity and accuracy. However, it does not provide sufficiently accurate strengthening predictions in elastic regime then the fiber aspect ratio is small. This is due to its neglect of stress transfer across the fiber ends and the stress concentrations that exist in the matrix regions near the fiber ends. To overcome this shortcoming, a more simplified shear lag model introducing the stress concentration factor which is a function of several variables, such as the modulus ratio, the fiber volume fraction, the fiber aspect ratio, is proposed. It is found that the modulus ratio($E_f$/$E_m$) is the essential variable among them. Thus, the stress concentration factor is expressed as a function of modulus ratio in the derivation. It is found that the proposed model gives a good agreement with finite element results and has the capability to correctly predict the values of interfacial shear stresses and local stress variations in the small fiber aspect ratio regime.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1537-1540
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• 2003

MEMS technology with micro scale is complete system utilized as the sensor. micro electro device. The metallization of MEMS is very important to transfer the power operating the sensor and signal induced from sensor part. But in the MEMS structures local stress concentration and deformation is often happened by geometrical shape and different constraint on the metallization. Therefore. this paper studies the effect of supporting type and thickness ratio about thin film thickness of the substrate thickness for the residual stress variation caused by thermal load in the multi-layer thin film. Specimens were made from materials such as Al, Au and Cu and uniform thermal load was applied, repeatedly. The residual stress was measured by FEA and nano-indentation using AFM. Generally, the specimen made of Al induced the large residual stress and the 1st layer made of Al reduced the residual stress about half percent than 2nd layer. Specimen made of Cu and Au being the lower thermal expansion coefficient induce the minimum residual stress. Similarly the lowest indentation length was measured in the Au_Cu specimen by nano-indentation.

• 부모자녀건강학회지
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• 제19권1호
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• pp.1-8
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• 2016

Purpose: This study was done to investigate the level of family support, job stress in clinical nurses end identify the participant's individual characteristics that influenced each of them. Methods: This study was a descriptive correlational study. The participants were 192 clinical nurses working in local middle range hospitals. The data were collected from May to June, 2013 and analyzed using descriptive statistics, t-test and Pearson's correlation by PASW statistics20. Results: The item mean score for family support was 21.01 and job stress was 98.89. There was a statistically significant negative correlation between family support and job stress (r=-.12). The level of job stress differed according to age (p=.014), duration of career (p=.013), department area (p<.001), position (p=.005), work duty form (p<.001), family member (p=.021), burden (p=.031), marital status (p=.001) and satisfaction (p<.001). Conclusion: Family support is needed to reduce job stress. Also, job satisfaction improvement programs and effective working systems should be developed to decrease the nurse's workplace stress.