• 소성∙가공
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• 제13권7호
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• pp.600-607
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• 2004

This paper addresses a viscoplastic constitutive model that allows a consistent way of modeling positive and negative rate sensitivities of flow stress concerned with dynamic strain aging. Based on the concept of continuum mechanics, a phenomenological constitutive model includes the use of a yield surface within the framework of unified viscoplasticity theory. To model negative rate sensitivity, rate-dependent back stress is introduced and flow stress in fully developed inelastic deformation regime is thus decomposed into the plastic contribution of rate independency and the viscous one of rate dependency.

• Structural Engineering and Mechanics
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• 제50권1호
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• pp.89-103
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• 2014

According to experimental studies made so far, design formula of shear characteristics suggested by ISO 22762 and JEAG 4614, representative design code for Lead Rubber Bearing(LRB) shows dependence caused by changes in compressive stress. Especially, in the case of atypical special structure, such as a nuclear power structure, placement of seismic isolation bearing is more limited compared to that of existing structures and design compressive stress is various in sizes. As a result, there is a difference between design factor and real behavior with regards to shear characteristics of base isolation device, depending on compressive stress. In this study, a full-scale low hardness device of LRB, representative base isolation device was manufactured, analyzed, and then evaluated through an experiment on shear characteristics related to various compressive stresses. With design compressive stress of the full-scale LRB (13MPa) being a basis, changes in shear characteristics were analyzed for compressive stress of 5 MPa, 10 MPa, 13 MPa, 15 MPa, and 20 MPa based on characteristics test specified by ISO 22762:2010 and based on the test result, a regression analysis was made to offer an empirical formula. With application of proposed design formula which reflected the existing design formula and empirical formula, trend of horizontal characteristics was analyzed.

• 대한간호학회지
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• 제33권6호
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• pp.713-721
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• 2003

Purpose: This study was to determine the mediator or moderator role of social support in the relationship between stress and depression among family caregivers of older adults with dementia. Method: Sixty nine family caregivers were randomly selected from health care centers in P city and a face-to-face interview was conducted using questionnaires from January to May of 2002. Data were analyzed with descriptive statistics, Pearson correlation, and hierarchical multiple regression using SPSS program. Result: Family caregivers of older adults with higher dependency in ADLs and higher problematic behaviors, provided care to the older adults for a longer period of time, and perceived less social support reported higher depression. Social support showed mediating effects between stress and depression, while did not show moderating effects. Elderly dependency on ADLs and caregiving duration decreased perceived social support and decreased social support increased depression. Conclusion: To increase family and social support to the caregivers of more functionally impaired elderly, family education to increase emotional support and physical assistance to the caregivers and broader and flexible application of social support such as increasing accessibility to the elderly daycare service with lower price may prove beneficial.

• Coupled systems mechanics
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• 제11권2호
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• pp.93-106
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• 2022

The total embankment settlement consists of three stages: the initial settlement, the primary consolidation settlement, and the secondary consolidation settlement. The total embankment settlement is largely controlled by the primary consolidation settlement, which is usually computed with numerical models that implement Biot's theory of consolidation. The key parameter that affects the primary consolidation time is the coefficient of permeability. Due to the complex stress and strain states in the foundation soil under the embankment, to be able to predict the consolidation time more precisely, aside from porosity-dependency, the strain-dependency of the coefficient of permeability should be also taken into account in numerical analyses. In this paper, we propose a two-dimensional plane strain numerical model of embankment primary consolidation, which implements Biot's theory of consolidation with both porosity-dependent and strain-dependent coefficient of permeability. We perform several numerical simulations. First, we demonstrate the influence of the strain-dependent coefficient of permeability on the computed results. Next, we validate our numerical model by comparing computed results against in-situ measurements for two road embankments: one near the city of Saga, and the other near the city of Boston. Finally, we give our concluding remarks.

• 터널과지하공간
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• 제23권5호
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• pp.383-391
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• 2013

1960년대 후반 이래로 수행된 여러 진삼축압축시험 결과에 의하면 암석의 파괴강도는 중간주응력의 크기에 상당한 영향을 받는 것으로 나타나고 있다. 이러한 실험적 결과를 바탕으로 지금까지 중간주응력이 파괴에 미치는 영향을 고려할 수 있는 다양한 3차원 파괴조건식들이 제안되고 있다. 그러나 문헌에 보고된 대부분의 3차원 파괴기준식들은 암석의 진삼축압축 강도를 현상학적으로 재현하기 위한 목적으로 개발되었기 때문에 관련된 강도정수들의 역학적 의미가 명확하지 않다. 이 연구에서는 암석강도의 중간주응력 의존성이 암석 내에 포함된 연약면들의 공간적 분포특성과 관련성이 있다는 가능성을 확인하기 위해 평면이방성 암석모델을 대상으로 수치 진삼축압축시험을 수행하였다. 미소구조텐서 개념을 활용하여 이방성 Mohr-Coulomb 파괴기준식을 개발하였으며 이를 강도기준식으로 활용하고 임계면법을 적용하여 평면이방성 암석의 파괴강도 및 파괴면 방향의 중간주응력 의존성을 분석하였다. 분석결과는 암석에 포함된 미시적 연약면들의 주응력 방향에 대한 방향성이 암석강도의 중간주응력 의존성과 밀접한 관련성이 있음을 암시해준다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2012년도 추계학술대회
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• pp.51-52
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• 2012

Safety at sea continues to be an important topic for research. The factors that contribute to safety issues are often complex and unclear. Lack of non-technical skills in such areas as communication, teamworking, situational awareness, decision making etc. are well documented as directly affecting safety in high risk work settings such as on board merchant vessels. Competence in non-technical skills can be affected by various habits and circumstances that influence a worker and result in either positive thinking and behaviour or negative thinking and behaviour. Negative thinking can cause stress, anger, frustration; loneliness etc. and this can possibly result in behaviour or actions that undermine the safety of crew and ship. Factors that may contribute to these negative thoughts and behaviours are many and varied and this paper will be looking at one aspect: mobile phone use. In the Republic of Korea, dependency on mobile phones is uniquely high. Maritime students are also susceptible to such dependency and this paper will demonstrate that the symptoms associated with mobile phone addiction and dependency, and in particular the symptoms of withdrawal, are important factors that need to be mitigated in order to improve safety at sea. Although the benefits of mobile phones are many it will be suggested that over-reliance, dependency or addiction can result in negative thinking or behaviour that may directly or indirectly contribute to the factors that cause incidents and accidents at sea. It will be suggested that the most appropriate method of dealing with this problem is twofold: firstly, through training at the educational level and secondly, by encouraging the shipping industry and government to invest more into providing seafarers with better access to the communication methods that they are used to on shore in order to improve work conditions.

• 대한가정학회지
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• 제28권4호
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• pp.119-133
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• 1990

This study attempts to expore factors which influence of stress. Date were obtained from structed interview conducted with 373 men and women who were 60 years over and living in Kyungnam. Data were analyzed through X2, ANOVA, T-TEST, FACTOR ANALYSIS, MULTIPLE REGRESSTION techniques. The results are summarized as follow: 1. Stress of old age were showed over middle level. The domains of stress showed that health problem is first, later life problem is second, trouble of communication is third, dependency problem is fourth, alienation is last(p<.001). 2. Of the variables health status, family type, economic status, self-esteem, mastery were significant with stress(p<.001). 3. Of the variables sex, religious, self-esteem, mastery were significant of used method in coping with stress. 4. The most of effective variables of stress were mastery, health status, self-esteem.

• 한국산학기술학회논문지
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• 제19권6호
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• pp.219-230
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• 2018

본 연구는 일부 대학생들의 우울수준에 관련된 요인을 알아보기 위해 D광역시의 남녀 대학생 546명을 대상으로 2015년 10월에 자기기입식 설문지(self-administered questionnaire)를 사용한 설문조사를 실시하였다. 자료의 분석은 우울수준을 종속변수로, 관련변수들을 독립변수로 하여 변수들 간의 단변량 분석, 로지스틱회귀분석 및 다변량 회귀분석을 시행하였다. 연구결과, 조사대상학생들의 우울수준은 개인적인 속성, 가정생활 및 학교생활특성, 건강관련행위특성의 여러 변수에 따라 유의한 차이를 보였다. 조사대상학생들의 우울이 나타날 위험비는 가족 및 친구의 사회적지지가 높은 군에 비해 낮은 군에서, 자기존중감이 높은 군보다 낮은 군에서, 통제신념이 높은 군보다 낮은 군에서, 스트레스가 정상인 군보다 고위험스트레스 군에서 유의하게 증가하였다. 조사대상학생들의 우울수준에 영향을 미치는 요인으로는 종교유무, 가족 및 친구의 사회적 지지, 대인의존행동특성, 통제신념 및 스트레스가 유의한 변수로 선정되었다. 위와 같은 연구결과는 대학생들의 우울수준은 개인적인 속성, 가정생활 및 학교생활특성, 건강관련행위특성 등 다양한 요인이 관여하고 있으며, 특히 사회적 지지와 심리적 행동특성이 낮고, 스트레스가 높을 경우 증가한다는 것을 시사하고 있다. 따라서 대학생들의 우울수준을 감소시키기 위해서는 학생들이 경험하는 우울수준에 관련된 요인을 정확히 파악하고 그 요인들을 감소시키기 위한 노력이 필요하다고 사료된다.

• 대한가정학회지
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• 제39권9호
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• pp.63-78
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• 2001

The purpose of this study is to compare how different the belief, social support, stress, coping and motivation between the Korean and American children. The data was collected from 157 Korean and 114 American students (5·8th grade). The resets were as follows: 1. Korean children's other dependency and pessimism level was significantly higher than those of American children. Also Korean children perceived higher than American children in the control-pressure stress and elf-respect stress. 2. Pessimism was observed the highest effect factor on Korean children's stress. 3. Korean students tried various coping under the relationship stress. 4. Problem oriented coping was found as an effective coping in Korean children. But the pursuit of support was found as an effective coping in American children.

• International Journal of Reliability and Applications
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• 제17권1호
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• pp.21-49
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• 2016

Many mechanical, electrical and electronic products have more than one performance characteristics (PCs). For example the performance degradation of rubidium discharge lamps can be characterized by the rubidium consumption or the decreasing intensity the lamp. The product may degrade due to all the PCs which may be independent or dependent. This paper deals with the design of optimal bivariate step-stress partially accelerated degradation test (PADT) with degradation paths modelled by gamma process. The dependency between PCs has been modelled through Frank copula function. In partial step-stress loading, the unit is tested at usual stress for some time, and then the stress is accelerated. This helps in preventing over-stressing of the test specimens. Failure occurs when the performance characteristic crosses the critical value the first time. Under the constraint of total experimental cost, the optimal test duration and the optimal number of inspections at each intermediate stress level are obtained using variance optimality criterion.