• 대한기계학회논문집A
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• 제39권6호
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• pp.583-588
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• 2015

완전접촉 문제를 이론적으로 해석하기 위해서 점근해법이 많이 사용된다. 점근해로서의 응력장은 특이항 만으로 구성되므로 접촉경계로부터 멀어질수록 정확도가 감소한다. 이에 반해 유한요소해석 방법은 요소크기의 제한으로 인해 완전접촉 문제에서의 응력특이성을 엄밀히 표현할 수 없다. 따라서 본 연구에서는 이론적 해법을 보조하고 또 그와 비교하기 위해 응착접촉 상태에 있는 완전접촉 문제를 이론적으로 해석한 후, 모아레 실험 및 유한요소해석 방법으로 접촉부 부근의 응력장을 분석하였다. 실험은 알루미늄과 구리 합금을 접촉각 $120^{\circ}$, $135^{\circ}C$로 가공하여 수행하였으며 모아레 무늬로부터 얻은 변위장과 유한요소해석을 수행한 결과와 비교하였다. 이로부터 타당성이 확보된 수치적 방법을 이용하여 실험조건에서의 일반화 응력확대계수와 접촉부 응력장을 구하여 이론 해와 비교하였으며, 접촉경계로부터 멀어질 때 나타나는 이론과 수치 해의 차이를 분석하였다.

• Journal of Welding and Joining
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• 제28권5호
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• pp.45-50
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• 2010

The fatigue crack growth characteristics of base metal and weld joint of 9% Ni steel for LNG storage tank was carried out using CT specimen at room temperature and $-162^{\circ}C$. Fatigue crack growth rate of base and weld metals at RT and $-162^{\circ}C$ was coincided with a single line independent of the change of stress ratio and temperature. In the region of lower stress intensity factor range, fatigue crack growth rate at $-162^{\circ}C$ was slower than that at RT, and the slop of fatigue crack growth rate at $-162^{\circ}C$ increased sharply with propagating of fatigue crack, fatigue crack growth rate at RT and $-162^{\circ}C$ was intersected near the region of $2{\times}10-4\;mm$/cycle, and after the intersection region, fatigue crack growth rate at $-162^{\circ}C$ was faster than that at RT. The micro-fracture mechanism using SEM shows the ductile striation in the stable crack growth region. Also the defects of weld specimen after fatigue testing were detected using the A scan of ultrasonic apparatus.

• 대한물리의학회지
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• 제10권3호
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• pp.29-37
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• 2015

PURPOSE: The aim of this study is to investigate the relationship between psychosocial factors and the severity of musculoskeletal pain in veterans with posttraumatic stress disorder (PTSD). METHODS: A total of 60 subjects were recruited from among the veterans with musculoskeletal pain at D Veterans Hospital. PTSD was evaluated by using the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition; severity of pain was measured by using the short-form McGill Pain Questionnaire (SF-MPQ); depression and anxiety were measured by using the Symptom Checklist-90-Revision; and the quality of sleep was measured by using the Pittsburgh Sleep Quality Index. All data were analyzed using SPSS 18.0 software for Windows. RESULTS: The averages cores of pain intensity ($7.48{\pm}1.67$), SF-MPQ-sensory ($13.84{\pm}7.52$), SF-MPQ-affective ($4.41{\pm}3.79$), depression ($19.30{\pm}11.37$), anxiety ($13.39{\pm}7.99$), and quality of sleep ($10.05{\pm}5.89$) were obtained in veterans with PTSD. SF-MPQ-sensory measures sleep quality (r=0.346, p<0.01), SF-MPQ-affective measures depression (r=0.318, p<0.01) and anxiety (r=0.404, p<0.01), and these showed a statistically significant positive correlation in veterans with PTSD. Pain levels were observed to be higher in veterans with PTSD. Moreover, in these subjects, physical pain had a significant influence on the anxiety variable among the psychosocial factors. CONCLUSION: These findings suggest that musculoskeletal pain provides meaningful information about depression, anxiety, and sleep disorder in veterans with PTSD. Our data suggest that musculoskeletal pain may need to be addressed as part of the health management process of veterans.

• The Korean Journal of Physiology and Pharmacology
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• 제15권3호
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• pp.137-142
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• 2011

Extremely low frequency magnetic fields (ELF-MF) have the ability to produce a variety of behavioral and physiological changes in animals. The stomach, as the most sensitive part of the neuroendocrine organ of the gastrointestinal tract, is crucial for the initiation of a full stress response against all harmful stress. Thus, the purpose of this study was to examine whether ELF-MF stimuli induce changes in the activity of neuroendocrine cells, considering their involvement in endocrine or paracrine effect on surrounding cells. The exposure to ELF-MF (durations of 24 h and 1 or 2 weeks, 60 Hz frequency, 0.1 mT intensity) altered the distribution and occurrence of gastrin, ghrelin and somatostatinpositive endocrine cells in the stomach of rats. The change, however, in the secretion of those hormones into blood from endocrine cells did not appear significantly with ELF-MF exposure. Comparing with sham control, ELF-MF exposure for 1 and 2 week induced an increase in $BaSO_4$ suspension propelling ratio of gastrointestinal tract, indicating that ELF-MF affects gastrointestinal motility. Our study revealed that ELF-MF exposure might influence the activity of endocrine cells, an important element of the intrinsic regulatory system in the digestive tract. The pathophysiological character of these changes and the mechanism responsible for neuroendocrine cell are still unclear and require further studies.

• Journal of Oral Medicine and Pain
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• 제45권2호
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• pp.23-28
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• 2020

Purpose: Temporomadibular disorders (TMDs) can result in chronic pain, which is often associated with psychological and sleep disturbance. Increased levels of psychological and sleep impairments are often related with poor treatment outcomes. The purpose of the present study was to evaluate clinical features, psychological profiles and the prevalence of clinical insomnia in TMD patients with chronic pain and to suggest an effective treatment approach. Methods: A total of 200 TMD patients who had visited the Pusan National University Hospital dental clinic for treatment of their pain were recruited from June 2018 through December 2019. TMD patients were classified into an acute (n=100) and chronic (n=100) group and compared the clinical symptoms. The primary diagnosis of TMD were categorized as TMD with joint pain group (TMD_J), TMD with muscle pain group (TMD_M) and TMD with joint-muscle mixed pain group (TMD_JM). Self- report measures of sleep quality and psychological profiles were evaluated via the Insomnia Severity Index (ISI) and the Korean Stress Response Inventory (SRI). Independent t-tests, Mann-Whitney U-tests, and chisquared test were used for the statistical analysis. Results: Chronic TMD patients showed higher pain intensity, as well as higher prevalence of related symptoms (headache, musculoskeletal pain) and myogenous pain. They also had significantly higher scores in all SRI parameters and a higher percentage of clinical insomnia than acute TMD patients. Conclusions: Based on the above results, psychological profiles and sleep quality assessments are necessary to provide essential data that will allow for improved treatment of chronic TMD patients.

• Nuclear Engineering and Technology
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• 제48권6호
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• pp.1423-1432
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• 2016

The integrity of a reactor pressure vessel (RPV) related to pressurized thermal shocks (PTSs) has been extensively studied. This paper introduces an integrity assessment of an RPV subjected to a PTS transient based on the French codes. In the USA, the "screening criterion" for maximum allowable embrittlement of RPV material is developed based on the probabilistic fracture mechanics. However, in the French RCC-M and RSE-M codes, which are developed based on the deterministic fracture mechanics, there is no "screening criterion". In this paper, the methodology in the RCC-M and RSE-M codes, which are used for PTS analysis, are firstly discussed. The bases of the French codes are compared with ASME and FAVOR codes. A case study is also presented. The results show that the method in the RCC-M code that accounts for the influence of cladding on the stress intensity factor (SIF) may be nonconservative. The SIF almost doubles if the weld residual stress is considered. The approaches included in the codes differ in many aspects, which may result in significant differences in the assessment results. Therefore, homogenization of the codes in the long time operation of nuclear power plants is needed.

• Structural Engineering and Mechanics
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• 제19권4호
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• pp.425-440
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• 2005

In this paper, the behavior of a crack between two half-planes of functionally graded materials subjected to arbitrary tractions is resolved using a somewhat different approach, named the Schmidt method. To make the analysis tractable, it is assumed that the Poisson's ratios of the mediums are constants and the shear modulus vary exponentially with coordinate parallel to the crack. By use of the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations in which the unknown variables are the jumps of the displacements across the crack surfaces. To solve the dual integral equations, the jumps of the displacements across the crack surfaces are expanded in a series of Jacobi polynomials. This process is quite different from those adopted in previous works. Numerical examples are provided to show the effect of the crack length and the parameters describing the functionally graded materials upon the stress intensity factor of the crack. It can be shown that the results of the present paper are the same as ones of the same problem that was solved by the singular integral equation method. As a special case, when the material properties are not continuous through the crack line, an approximate solution of the interface crack problem is also given under the assumption that the effect of the crack surface interference very near the crack tips is negligible. It is found that the stress singularities of the present interface crack solution are the same as ones of the ordinary crack in homogenous materials.

• 한국농공학회논문집
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• 제63권3호
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• pp.47-57
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• 2021

Drought monitoring over paddy field area is an important role as the frequency and intensity of drought due to climate change increases. This study analyzed the applicability of drought monitoring on paddy crops using MODIS-based field surveys. As a satellite-based drought index using evapotranspiration for quantitative drought determination, ESI (Evaporative Stress Index), was applied and calculated through the ratio of MODIS- based actual and potential evapotranspiration. For the irrigated areas of Idong, Gosam, Geumgwang, and Madun reservoirs the availability of irrigation water supply, ponding depth, precipitation, paddy growth were investigated for the paddy field within one grid of MODIS. In addition, the percentile-based ESI drought severity was calculated to compare the growth process of paddy and changes in the drought category of ESI. The Idong area was irrigated about a week later than other reservoirs for the period of water supply, transplanting, and water drainage and the ESI drought category tended to be different. The Gosam, Geumgwang, and Madun area expressed moderate drought prior to the farming season, and indicated normal as the water was supplied. During the water drainage, the drought category intensified, indicating that the water available on land was decreasing. These results demonstrated that the MODIS-based ESI could be an effective tool for agricultural drought monitoring over paddy field area.

• 한국융합학회논문지
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• 제9권12호
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• pp.313-319
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• 2018

본 연구의 목적은 우리나라 만 65세 이상 노인의 연령별 신체활동 및 식생활과 정신건강의 관련정도와 영향요인을 파악하여 노인의 정신건강에 긍정적으로 대처할 수 있는 요인을 확인하고, 노인건강프로그램 개발의 기초자료로 활용하기 위함이다. 본 연구는 2015년도 국민건강영양조사결과를 기초자료로 한 이차자료 분석연구이며, 우리나라 만 65세 이상의 노인 1,484명을 대상으로 하였다. 자료분석은 IBM 23 ver. SPSS를 이용하였다. 본 연구 결과 전기노인은 정신건강변수의 세부항목 중에서 우울감과 스트레스 인지가 높았으며. 후기노인은 자살생각이 높았다. 식생활형편은 전기노인보다 후기노인에서 '음식섭취 부족' 이 높았다. 회귀분석 결과 노인의 식생활 형편, 중강도 신체활동이 노인의 정신건강과 관련성이 있는 것으로 보고되었다. 연구결과를 토대로 세분화된 연령대에 적합한 차별화된 간호중재 프로그램개발이 필요하다.

• 터널과지하공간
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• 제29권2호
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• pp.124-134
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• 2019

암석에서의 임계하 균열성장은 단조 및 반복하중 하에서 일어날 수 있다. 임계하 균열 성장은 암반에 건설되는 지하구조물의 장기 안정성의 평가에 큰 영향을 미친다. 본 연구에서는 모사 암석 시료를 사용하여 단조 및 반복하중 하에서의 임계하 균열성장 지수를 구하였다. 단조하중 조건에서는 일정 응력 속도법이 적용되었으며, 반복하중에 의한 임계하 균열성장 지수는 반복에 의한 균열성장 속도와 응력확대계 수폭의 관계를 이용하였다. 연구에 사용된 시험편은 $45^{\circ}$와 $60^{\circ}$의 균열 경사각을 가지고 있으며, 균열의 간격 및 연속성에 변화를 주어 전단 또는 인장에 의한 균열성장이 가능하도록 하여 전단 또는 인장에 의한 임계하 균열성장 지수도 구하였다. 그 결과, 임계하 균열성장 지수 n은 작용하는 하중 조건, 즉 단조 및 반복하중, 혹은 전단 및 인장에 관계없이 거의 일정한 값을 나타내었다.