• Structural Engineering and Mechanics
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• 제20권6호
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• pp.673-693
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• 2005

A general step-by-step simulation for the time-dependent analysis of segmentally-erected prestressed concrete box-girder bridges is presented. A three dimensional finite-element model for the balanced-cantilever construction of segmental bridges, including effects of the load history, material nonlinearity, creep, shrinkage, and aging of concrete and the relaxation of prestressing steel was developed using ABAQUS software. The models included three-dimensional shell elements to model the box-girder walls and Rebar elements representing the prestressing tendons. The step-by-step procedure allows simulating the construction stages, effects of time-dependent deformations of materials and changes in the structural system of the bridges. The structural responses during construction and throughout the service life were traced. A comparison of the developed computer simulation with available experimental results was conducted and good agreement was found. Deflection of the bridge deck, changes in stresses and strains and the redistribution of internal forces were calculated for different examples of bridges, built by the balanced-cantilever method, over thirty-year duration. Significant time-dependent effects on the bridge deflections and redistribution of internal forces and stresses were observed. The ultimate load carrying capacities of the bridges and the behavior before collapse were also determined. It was observed that the ultimate load carrying capacity of such bridges decreases with time as a result of time-dependent effects.

• 한국지능시스템학회논문지
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• 제25권3호
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• pp.210-216
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• 2015

사람의 의식과 뇌 구조는 복잡계 현상을 가지고 있다고 알려져 있다. 이들은 사람의 감정과 관련이 있다. 사람의 감정은 다양한 종류가 있으며 그 중 하나인 사랑은 사회학과 심리학에서 주된 관심사의 하나로 연구되어 왔다. 본 논문에서는 로미오와 줄리엣의 사랑 방정식에서 동일한 시간 지연과 서로 다른 지연 시간을 고려하여 이들 사이의 사랑 거동을 시계열과 위상 공간으로 나타내고 이들 사이의 차이를 분석하였다.

• Korea-Australia Rheology Journal
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• 제19권4호
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• pp.211-219
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• 2007

Here we demonstrate complex transient behavior of viscoelastic liquid described numerically with the Leonov model in straight and contraction channel flow domains. Finite element and implicit Euler time integration methods are employed for spatial discretization and time marching. In order to stabilize the computational procedure, the tensor-logarithmic formulation of the constitutive equation with SUPG and DEVSS algorithms is implemented. For completeness of numerical formulation, the so called traction boundaries are assigned for flow inlet and outlet boundaries. At the inlet, finite traction force in the flow direction with stress free condition is allocated whereas the traction free boundary is assigned at the outlet. The numerical result has illustrated severe forward-backward fluctuations of overall flow rate in inertial straight channel flow ultimately followed by steady state of forward flow. When the flow reversal occurs, the flow patterns exhibit quite complicated time variation of streamlines. In the inertialess flow, it takes much more time to reach the steady state in the contraction flow than in the straight pipe flow. Even in the inertialess case during startup contraction flow, quite distinctly altering flow patterns with the lapse of time have been observed such as appearing and vanishing of lip vortices, coexistence of multiple vortices at the contraction comer and their merging into one.

• 드라이브 ㆍ 컨트롤
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• 제16권4호
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• pp.38-47
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• 2019

In this paper, a real-time simulation model of an excavator using Amesim was proposed, considered the operation of functional valves with the main control valve (MCV). The hydraulic system models including the pump and MCV have been developed. The kinematic and dynamic models of the manipulator have also been developed, to confirm the behavior of the excavator. The MCV model includes various functional valves such as the regenerative valves, holding valves, swing and boom priority valves, and regen-cut valves so that simulations similar to real excavators can be performed. Additionally, to obtain the real-time calculation performance, the parts with no major influence on the dynamic behavior were simplified, high frequency factors were removed, and parameters were optimized. The models were compared with each other through the numerical analysis with variable time-step and fixed time-step, and the results were verified by comparison with the results of the actual vehicle tests.

• 대한기계학회논문집A
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• 제30권8호
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• pp.976-984
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• 2006

Time-temperature superposition has been studied to determine the long-term fatigue life over millions of cycles for glassy polymers. π le superposition is supposed to make an accelerated lifetime testing (ALT) technique possible. Dog-bone shaped specimens made of carbon filled Polycarbonate (PC) were tested under fatigue, based on the stress-lifetime approach (S-N curve). Fatigue-induced localized yield-like deformation is considered as the defect leading to fatigue and its evolution behavior is characterized by a modified energy activation model in which temperature is considered as fatigue acceleration factor. This model allows the reduced time concept to account for effects of different temperature in short-term fatigue data to determine long-term fatigue life through the use of time-temperature superposition that is applicable under a low frequency and isothermal conditions. The experimental results validated that the proposed technique could be a possible method for accelerated lifetime testing (ALT) of time-dependent polymeric materials.

• Asian-Australasian Journal of Animal Sciences
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• 제15권5호
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• pp.745-750
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• 2002

The effects of recording interval (1, 2, 3, 4, 5, 10, 15, 20 and 30 min) on the estimation of some grazing behavior variables in beef cows and calves (<4 months old) were investigated in a daytime grazing (7 h) system utilizing a bahiagrass (Paspalum notatum Flugge) pasture (a 1.1 ha paddock and a 0.4 ha resting area). Recording intervals of 10-30 min tended to underestimate the time spent grazing and ruminating and overestimate the time spent resting by animals, whereas intervals of 1-5 min resulted in almost constant estimates. In all grazing activities, the errors of estimation became larger when the recording interval exceeded 5 min. The accuracy of estimation was higher for grazing time>rumination time>resting time. An increase in recording interval always decreased estimates of the distance walked by animals. It was concluded that recording intervals of 1-5 min provide reliable estimates of the time spent grazing, ruminating and resting. It was also concluded that positioning of animals at 1 min intervals may provide estimates of walking distance with acceptable bias toward underestimation.

• 대한교통학회:학술대회논문집
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• 대한교통학회 1998년도 Proceedings The 4th International Transport Symposium
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• pp.160-167
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• 1998

Recent world-wide interest in activity-based travel behavior modeling has generated an entirely new perspective on how the profession views the travel demand process. This paper seeks to further promote the case of activity-based travel behavior models by providing some empirical evidence of relationship between travel time and activity duration decision for worker with transportation panel data. The travel time from home to work and from work to home, without activity involvement, is estimated by the Ordinary Least Squares (OLS) method. And, the travel time to and from the selected activity and the activity duration are modeled simultaneously by the Three Stage Least Squares (3SLS) method due to the endogenous relationship between travel time and activity duration. Two kinds of models, OLS and 3SLS, include selectivity bias corrections in a discrete/continuous framework, because of the inter-relationship between the choice of activity type/travel mode (discrete) and the travel time/activity duration (continuous). Estimation is undertaken using a sample of over 1300 household two-day trip diaries collected from the same travelers in the Seattle area in 1989. The behavioral consequences of these models provide interesting and provocative findings that should be of value to transportation policy formulation and analysis.

• 한국생활과학회지
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• 제22권5호
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• pp.407-417
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• 2013

The purpose of this study was to investigate and analyze how teachers' recognition of professionalism and the child's gender and term care affect child's social interaction behavior. Participants were three-year-old 61 children and their 20 teachers. Each child was observed by the time sampling method of 20 sec-observation followed by 10 sec-recording for a total of 14 minutes. The teachers completed the rating scales to measure the teachers' recognition of professionalism. The study results show that, children engaged more frequently in individual behavior than in interactions with peers or with teachers in day care centers. And those children had more interaction behavior with their teachers than with their peers. Correlation between teachers' recognition of professionalism and children's social interaction behavior were as following: the more the teachers recognized professionalism, the more the children showed positive interaction behavior toward their teachers. Also, the more the teachers recognized the professionalism related to the job satisfaction, the more the children showed positive interaction behavior toward their peers. Boys interacted more negatively with peers and teachers than girls did. Children who attended the day care center more than two years showed less individual behaviors than others.

• 대한간호학회지
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• 제43권6호
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• pp.714-725
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• 2013

Purpose: This study was done to provide fundamental data for the development of competency reinforcement programs to prevent addictive behavior in adolescents through the construction and examination of an addiction prevention core competency model. Methods: In this study core competencies for preventing addictive behavior in adolescents through competency modeling were identified, and the addiction prevention core competency model was developed. It was validated methodologically. Results: Competencies for preventing addictive behavior in adolescents as defined by the addiction prevention core competency model are as follows: positive self-worth, self-control skill, time management skill, reality perception skill, risk coping skill, and positive communication with parents and with peers or social group. After construction, concurrent cross validation of the addiction prevention core competency model showed that this model was appropriate. Conclusion: The study results indicate that the addiction prevention core competency model for the prevention of addictive behavior in adolescents through competency modeling can be used as a foundation for an integral approach to enhance adolescent is used as an adjective and prevent addictive behavior. This approach can be a school-centered, cost-efficient strategy which not only reduces addictive behavior in adolescents, but also improves the quality of their resources.

• 지역사회간호학회지
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• 제21권2호
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• pp.169-177
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• 2010

Purpose: The purposes of this study were to examine the relations among depression, life satisfaction and health promoting behavior, and to find factors related with health promoting behavior. Methods: The subjects were 198 elderly people of over 65 living in K City and S City. Data were collected through a structured questionnaire and analyzed by SPSS/WIN 13.0. Results: Health promoting behavior was significantly different according to religion, education level, living with family, previous job, pocket money, subjectively economic level, and leisure activities. Depression was significantly different according to education level, living with family, pocket money, economic level, and leisure activities. And life satisfaction was significantly different according to religion, living with family, and pocket money. The variables that affected the degree of health promoting behavior were depression, life satisfaction and living with family, and they represented 29.7% of health promoting behavior. Conclusion: The health promoting behavior of the subjects was better than average and, at the same time, the lower depression in the health promoting behavior was the higher life satisfaction was. Therefore, in order to decrease depression and to increase life satisfaction, the development of advanced health promoting programs will be helpful to lead health life for the elderly people.