• Child Health Nursing Research
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• v.13 no.3
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• pp.318-328
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• 2007

Purpose: Because it is important to prevent adolescents from becoming involved in smoking, this study was done to explore important factors influencing cigarette use and the increase in smoking frequency. Method: For this study the Korea Youth Panel Survey (KYPS) was analyzed. Because the KYPS is longitudinal, a fixed effect regression method was used to control for the effects of time-independent factors. More specifically, a logistic regression was used to explore factors affecting cigarette use, and a Poisson regression was used to explore smoking frequency. Result: As the adolescents got older, the number of male adolescents who tried smoking increased, while the number of female adolescents who tried smoking decreased. Also, the frequency of cigarette use among male and female smokers increased over time. Significant factors affecting cigarette use were friends who smoked, delinquent behavior, and loneliness at schools. Important factors affecting the increase in smoking frequency were grade (e.g., the 2nd- and 3rd-year of middle school), friends who smoked, delinquent behavior, monthly pocket money, expectation for the highest level of education, and attack tendency. Conclusions: To solve the problems linked to adolescent smoking, it is critical to develop intervention programs that target specific homogeneous subgroups of smokers, and that take into consideration gender difference in smoking and factors affecting levels of smoking behavior.

• Journal of Mechanical Science and Technology
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• v.20 no.12
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• pp.2136-2146
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• 2006

A study on a creep-fatigue crack growth behavior has been carried out for a cylindrical structure with weldments by using a structural test and an evaluation according to the assessment procedures. The creep-fatigue crack growth behavior following the creep-fatigue crack initiation has been assessed by using the French A16 procedure and the conservatism for the present structural test has been examined. The structural specimen is a welded cylindrical shell made of 316 L stainless steel (SS) for one half of the cylinder and 304 SS for the other half. In the creep-fatigue test, the hold time under a tensile load which produces the primary nominal stress of 45 MPa was one hour at $600^{\circ}C$ and creep-fatigue loads of 600 cycles were applied. The evaluation results for the creep-fatigue crack propagation were compared with those of the observed images from the structural test. The assessment results for the creep-fatigue crack behavior according to the French Al6 procedure showed that the Al6 is overly conservative for the creep-fatigue crack propagation in the present case with a short hold time of one hour.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2913-2921
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• 1994

In SMA(shape memory alloy), the degradation by fatigue is one of the most important problems to be overcome, when SMA is used for robot-actuator material. The actuator is operated repeatitively for long time and its repeating operation develops the fatigue degradation of SMA. The fatigue degradation changes the transformation temperature and deformation behavior and results in inaccurate operation control of robot. Accordingly, the changing behavior of transformation temperature and deformation which results from repeating operation is to be investigated in advance and the scheme to resolve those problems have to be made for the design of actuator. In this study, the fatigue tests were carried out on SMA specimens prepared to have different condition of aging time and pre-strain with the direct-current heating-cooling method, which was a general method of operation in robot actuators. The behavior of transformation temperature and deformation were examined and analyzed in each specimen and the study was performed to establish the optimistic manufacturing condition of SMA against the fatigue degradation.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.4
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• pp.287-293
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• 1999

Effect of heat-treatment on the microstructure and recrystallization behavior of pure Zr was studied. The specimens were prepared under the various annealing temperatures from $400^{\circ}C$ to $800^{\circ}C$ and times from 300 to 5000 minutes after vacuum arc remelting. The recrystallization behavior was observed by a polarized optical microscope, TEM and micro-vickers hardness tester. With increasing the annealing time, the temperature region of hardness drop moved to the lower temperature region due to the recovery and recrystallization behaviors at the lower temperature. The recrystallization of cold-worked pure Zr was completed between 450 and $600^{\circ}C$. The size of recrystallized grain increased at $700^{\circ}C$ for 600min. Activation energy(Q) of pure Zr measured by the time for constant fraction technique was 78 KJ/mol.

• Journal of Biosystems Engineering
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• v.18 no.3
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• pp.262-269
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• 1993

Stress relaxation behaviors of the cucumber under bending moment were tested with UTM at three levels of loading rate and initial deflection ratio. Sample cucumber was selected from three cultivars of cucumber, Cheongjangmadi, Baekdadagi, and Gyeousalicheongjang, because these cultivars are the most popular grown cultivars in Korea. When the bending moment was applied to the cucumber sample, the effective span between simple supports was held a constant value of 116mm with consideration of the selected sample length. The objectives of this study were to develop the rheological models such as linear and nonlinear models of the stress relaxation for the cucumber samples, and to investigate the effects of loading rate and initial deflection ratio on the stress relaxation behavior of the cucumber. The results of this study may be summarized as follows : 1. Stress relaxation behavior of the cucumber could be well described by the generalized Maxwell model for each level of deflection ratio. But the stress relaxation behavior of the sample was found to be initial deflection ratio and time dependent, and it was represented the nonlinear viscoelastic model as a function of initial deflection ratio and time. 2. Stress relaxation behavior of the cucumber samples was very highly affected by the loading rate and the initial deflection ratio. The more loading rate and initial deflection ratio resulted in the more initial bending stress and after stress relaxation progressed more rapidly. 3. At the same test conditions, it was found that the stress relaxation rate of Cheongjangmadi was faster than that of other cultivars.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.442-445
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• 2006

This paper presents an analytical prediction of nonlinear characteristics and behavior characteristics PSC structures with un-bonded tendon system. In this paper, a numerical model for un-bonded tendon is proposed based on the finite element method, which can represent straight or curved un-bonded tendon behavior. this model and time-dependent material model used to investigate the time-dependent behavior of un-bonded prestressed concrete structures. The accuracy and objectivity of the assessment process may be enhanced by the use of sophisticated nonlinear finite element analysis program. A computer program, named RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology), for the analysis of concrete structures and steel plate was used. The material nonlinearities are taken into account by comprising the tension, compression, and shear models of cracked concrete and models for reinforcements and tendons in the concrete. The smeared crack approach is incorporated. It accounts for the aging, creep and shrinkage of concrete and the stress relaxation of prestressed steel. The proposed un-bonded tendon model and numerical method of un-bonded prestressed concrete structures is verified by comparison with reliable experimental results.

• Journal of the Korean Home Economics Association
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• v.40 no.6
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• pp.69-83
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• 2002

This study examined the effects of demographic variables on buying behavior, and investigated buyers'perceived value and risk perception of the internet shopping mall. The sample was collected by a department store in Daegu, and it included 1,732 individuals using the Cyber Mall. Research methods used in this study were simple statistics, t-test and ANOVA. The buyers perceived values through the internet shopping mall were classified into five categories-price, time, convenience, intrinsic attributes, reliability and the risk perception also was classified such as the overall purchasing process, quality of products, exposure of the personal information, delivery system, refund and exchange. The major findings of this study were 1) most important categories affecting their buying behavior were the value of convenience and following values in order were time, price, reliability, intrinsic attributes. 2) the risk perception were overall purchasing behavior, quality of products, exposure of personal information, delivery, and refund & exchange in order. 3) age of buyers, buying experience on the internet shopping mall, and gender were the important factors affecting the buyers'perceived value and risk. 4) the study also, showed that according to the variety of products, buyers perceived the value and risk differently, for example, the price was the most important perceived value in case of food product. The implication of the study is to strategically suggest how to enhance the buyers'perceived value and diminish perceived risk of different products.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.8
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• pp.856-863
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• 2008

High-rise apartments of shear wall system are governed by flexural behavior like a cantilever beam. Installation of the damper-brace system in a structure governed by flexural behavior is not suitable. Because of relatively high lateral stiffness of the shear wall, a load is not concentrate on the brace and the brace cannot perform a role as a damping device. In this paper, a friction damper applying flexibility of shear wall is proposed in order to reduce the deformation of a structure. To evaluate performance of the proposed friction damper, nonlinear time history analysis is executed by SeismoStruct analysis program and MVLEM(multi vertical linear element model) be used for simulating flexural behavior of the shear wall. It is found that control performance of the proposed friction damper is superior to one of a coupled wall with rigid beam. In conclusion, this study verified that the optimal control performance of the proposed friction damper is equal to 45 % of the maximum shear force inducing in middle-floor beam with rigid beam.

• Journal of the Ergonomics Society of Korea
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• v.29 no.1
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• pp.17-24
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• 2010

There has been recent interest in intelligent vehicle technologies, such as advanced driver assistance systems (ADASs) or in-vehicle information systems (IVISs) that offer a significant enhancement of safety and convenience to drivers and passengers. However, unsuitable design of HMI (Human Machine Interface) must increase driver distraction and workload, which in turn increase the chance of traffic accidents. Distraction in particular often occurs under a heavy driving workload due to multitasking with various electronic devices like a cell phone or a navigation system while driving. According to the 2005 road traffic accidents in Korea report published by the ROad Traffic Authority (ROTA), more than 60% of the traffic accidents are related to driver error caused by distraction. This paper suggests the structure of vehicle environment for real-time driving behavior monitoring system while driving which is can be used the driver workload management systems (DWMS). On-road experiment results showed the feasibility of the suggested vehicle environment for driving behavior monitoring system.

• Korean Journal of Child Studies
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• v.32 no.6
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• pp.157-185
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• 2011

The purpose of this study was to explore the factors influencing preschoolers' emergent English as a second language literacy skills in terms of maternal language behavior in Korean and English picture book reading. This study was also conducted in order to identify the pathways of each factor. The subjects consisted of 201 mothers and their 3~5 year-old children from middle income families living in Seoul, Incheon, Gyyounggi-do, and Chungcheongbuk-do. The results indicated that the factors influencing preschoolers' emergent English as a second language literacy skills acquisition were as follows : maternal beliefs about the value of picture book reading, the child's level of interest in picture book reading, the time spent on picture book reading and maternal language behavior during picture book reading activities. The results further indicate that it is important that the mother shares desirable language interaction with her children in their native language while reading not only Korean but also English picture books when aiming to improve preschoolers' emergent English literacy skills.