• Proceedings of the KSME Conference
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• 2001.06a
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• pp.274-279
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• 2001

Creep-fatigue crack growth behavior was experimentally measured particularly when a crack was located in the heat affected region of 1Cr-0.5Mo steel. Load hold times of the tests for trapezoidal fatigue waveshapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the $C_t$-parameter. It was found that the crack growth rates were the highest when the crack path was located along the fine-grained heat affected zone(FGHAZ). Cracks located in other heat affected regions had a tendency to change the crack path eventually to FGHAZ. Creep-fatigue crack growth law of the studied case is suggested in terms of $(da/dt)_{avg}$ vs. $(C_t)_{avg}$ for residual life assessment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.12
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• pp.3088-3095
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• 2000

Creep-fatigue crack growth behavior was experimentally measured particularly when a crack was located in the heat affected region of lCr-5Mo steel. Load hold times of the tests for trapezoidal fatigue waveshapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the $C_r$parameter. It was found that the crack growth rates were the highest when the crack path was located along the fine-grained heat affected zone(FGHAZ). Cracks located in other heat affected regions had a tendency to change the crack path eventually to FGHAZ. Creep-fatigue crack growth law of the studied case is suggested in terms of (da/dt)$_{avg}$ vs. ($C_t$)$_{avg}$ for residual life assessment.

• Journal of the Korean Home Economics Association
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• v.36 no.5
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• pp.75-88
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• 1998

The purpose of this study is to investigate (1) the level of childrens' concern and behavior on the environmental preservation, (2) the influential factors related to the two dependent variables above mentioned. The subjects were 286 childrens, in October, 1997, in kwangju. The data obtained were analyzed by Mean, Person's correlation, Stepwise Regression and Path Analysis. The major findings were as follows: 1) The general tendency of the childrens' concern and behavior on the environmental preservation was over the average level. 2) According to the background variables(ie: environment information contracting time, family cohesion and adaptability, biospheric orientation, egoistic orientation), the childrens' concern on the environment was significantly different. 3) According to (1) the background variables(ie: environment information contracting time, family cohesion and adaptability, concern on the environment, biospheric orientation), (2) intermediated variable(ie: concern on the environment), the childrnes' behavior on the environmental preservation was significantly different. 4) The indirect variable of the positive influence for childrnds' behavior on the environment, environment information contracting time. The indirect variable of the negative influence for childrens' the environmental behavior was egoistic orientation.

• Journal of Welding and Joining
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• v.18 no.6
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• pp.89-95
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• 2000

Creep-fatigue crack growth behavior at the heat affected zone of 1Cr-0.5Mo steel weldment has been experimentally studied. Load hold times of the tests for trapezoidal fatigue waveshapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the {TEX}$C_{t}${/TEX} estimated with the equation proposed by the previous finite element analysis work. It was concluded that the {TEX}$C_{t}${/TEX} values calculated from the properties of parent metal were quite comparable to the accurate {TEX}$C_{t}${/TEX} values calculated from both of weld and parent metals. Scatter of data was claimed due to the difference of exact location of the cracks in HAZ. The cracks have a tendency to change their path from the original location eventually to the relatively soft HAZ(ie, near-FGHAZ region, fine grained heat affected zone).

• Journal of The Korean Association For Science Education
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• v.16 no.3
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• pp.249-259
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• 1996

The purpose of this study was to analyze relationships among science achievement, science process skills and affective perception of high school students. The affective perception was included attitude toward science and science anxiety in the study. The instruments were developed HARS and SAMS for this study. The subject was sampled 1,115 students by stratified cluster sampling method. The major findings of this study were as follows: The tendency to affective perception was investigated according to students variables. Atittude toward science was showed a negative perception on female than male, in rural area than city. Science anxiety was percepted highly on female than male, in rural area than city. Attitude toward science showed positive relations to science process skills, science achievement, but which showed negative relation to science anxiety. Science anxiety showed negative relations among science process skills, science achievement and attitude toward science. Structural relationships among affective perception, science process skills and science achievement were analyzed by effect size through the path analysis on the independent and dependent variables. By the results, it was indicated that there have significant direct effect not only affective perception influence on science achievement but also on science process skills in hypothesized model. Prediction of science achievement and science process skills were clarified to characteristics of the affective perception.Therefore, understanding about affective perception will be helpful to make the strategy of science teaching

• Journal of Family Resource Management and Policy Review
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• v.1 no.2
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• pp.1-15
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• 1997

The purpose of this study is to investigate (1)the level of the urban housewives’behavior and satisfaction of wedding, (2)the influential factors related to the two dependent variables above mentioned. So that provides some fundamental materials to improve the level of sound wedding culture and the whole home living. The subjects were 356 housewives, in April, 1997, Seoul. The data obtained were analyzed by Mean, Pearson’s correlation, Stepwise Multiple Regression and Path Analysis. The major findings were as follows: 1) The general tendency of the housewives’wedding behavior and satisfaction was reasonable. 2) According to the background variables(ie: marital form, the existence of job, the recognition degree of her husband’s family’s living standards, the recognition degree of her parents’home’s living standards, the perception of marital transactions), the housewives’wedding behavior was significantly different. 3) According to (1)the background variables(ie: communication frequency in household, self-acceptance, the adequacy of household income, educational level), (2)intermediated variable(ie: articles essential to a marriage), the housewives’wedding satisfaction was significantly different. 4) The indirect variable of the positive influence for housewives’satisfaction of wedding was marital form, the existence of job. the indirect variable of the negative influence for housewives’satisfaction of wedding was the recognition degree of her husband’s family’s living standards, the recognition degree of her parents’home’s living standards, the perception of marital transfactions.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1182-1182
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• 2001

In this study, the newly constructed optical measurement system, which was mainly composed of a parametric tunable laser and a near infrared photoelectric multiplier, was introduced to clarify the optical characteristics of wood as discontinuous body with anisotropic cellular structure from the viewpoint of the time-of-flight near infrared spectroscopy (TOF-NIRS). The combined effects of the cellular structure of wood sample, the wavelength of the laser beam λ, and the detection position of transmitted light on the time resolved profiles were investigated in detail. The variation of the attenuance of peak maxima At, the time delay of peak maxima Δt and the variation of full width at half maximum Δw were strongly dependent on the feature of cellular structure of a sample and the wavelength of the laser beam. The substantial optical path length became about 30 to 35 times as long as sample thickness except the absorption band of water. Δt ${\times}$ Δw representing the light scattering condition increased exponentially with the sample thickness or the distance between the irradiation point and the end of sample. Around the λ=900-950 nm, there may be considerable light scattering in the lumen of tracheid, which is multiple specular reflection and easy to propagate along the length of wood fiber. Such tendency was remarkable for soft wood with the aggregate of thin layers of cell walls. When we apply TOF-NIRS to the cellular structural materials like wood, it is very important to give attention to the difference in the light scattering within cell wall and the multiple specular-like reflections between cell walls. We tried to express the characteristics of the time resolved profile on the basis of the optical parameters for light propagation determined by the previous studies, which were absorption coefficient K and scattering coefficient S from Kubelka-Munk theory and n from nth power cosine model of radiant intensity. The wavelength dependency of the product of K/S and n, which expressed the light-absorbing and -scattering condition and the degree of anisotropy, respectively, was similar to that of the time delay of peak maxima Δt. The variation of the time resolved profile is governed by the combination of these parameters. So, we can easily find the set of parameters for light propagation synthetically from Δt.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.2
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• pp.109-120
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• 2017

A discounted cost model for preventive maintenance of armor units of rubble-mound breakwaters is mathematically derived by combining the deterioration model based on a discrete-time stochastic process of shock occurrence with the cost model of renewal process together. The discounted cost model of condition-based maintenance proposed in this paper can take into account the nonlinearity of cumulative damage process as well as the discounting effect of cost. By comparing the present results with the previous other results, the verification is carried out satisfactorily. In addition, it is known from the sensitivity analysis on variables related to the model that the more often preventive maintenance should be implemented, the more crucial the level of importance of system is. However, the tendency is shown in reverse as the interest rate is increased. Meanwhile, the present model has been applied to the armor units of rubble-mound breakwaters. The parameters of damage intensity function have been estimated through the time-dependent prediction of the expected cumulative damage level obtained from the sample path method. In particular, it is confirmed that the shock occurrences can be considered to be a discrete-time stochastic process by investigating the effects of uncertainty of the shock occurrences on the expected cumulative damage level with homogeneous Poisson process and doubly stochastic Poisson process that are the continuous-time stochastic processes. It can be also seen that the stochastic process of cumulative damage would depend directly on the design conditions, thus the preventive maintenance would be varied due to those. Finally, the optimal periods and scale for the preventive maintenance of armor units of rubble-mound breakwaters can be quantitatively determined with the failure limits, the levels of importance of structure, and the interest rates.