• Journal of Korea Foundry Society
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• v.28 no.6
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• pp.268-272
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• 2008

Interfacial characteristics of aluminum borate whisker reinforced AS52 matrix composite was investigated. Peak hardness of AS52 composite was obtained aging at $170^{\circ}C$ for 15h and the aging process was accelerated by the presence of the aluminium borate whisker. The MgO layer, which was the interfacial reaction product between the reinforcement and the Mg matrix, was produced with 20 nm thickness in as-cast condition. As the aging time increased, the thickness of the interfacial reaction layer increased to 50 nm in peak aged condition. The nano-indentation test results indicated that the strength of interface was improved by the aging but over-aging degraded the reinforcement and decreased the interfacial strength which resulted in the decrease of overall composite strength.

• Korean Journal of Radiology
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• v.22 no.7
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• pp.1194-1202
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• 2021

Objective: To investigate the age-dependent changes in regional cerebral blood flow (CBF) in healthy adults by fitting mathematical models to imaging data. Materials and Methods: In this prospective study, 90 healthy adults underwent pseudo-continuous arterial spin labeling imaging of the brain. Regional CBF values were extracted from the arterial spin labeling images of each subject. Multivariable regression with the Akaike information criterion, link test, and F test (Ramsey's regression equation specification error test) was performed for 7 models in every brain region to determine the best mathematical model for fitting the relationship between CBF and age. Results: Of all 87 brain regions, 68 brain regions were best fitted by cubic models, 9 brain regions were best fitted by quadratic models, and 10 brain regions were best fitted by linear models. In most brain regions (global gray matter and the other 65 brain regions), CBF decreased nonlinearly with aging, and the rate of CBF reduction decreased with aging, gradually approaching 0 after approximately 60. CBF in some regions of the frontal, parietal, and occipital lobes increased nonlinearly with aging before age 30, approximately, and decreased nonlinearly with aging for the rest of life. Conclusion: In adults, the age-related perfusion patterns in most brain regions were best fitted by the cubic models, and age-dependent CBF changes were nonlinear.

• KIEE International Transactions on Power Engineering
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• v.5A no.4
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• pp.322-330
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• 2005

This paper proposes methods to incorporate station related aging failures in composite system reliability assessment. Aging failures of station components, such as circuit breakers and bus bars, are a major concern in composite power system planning and operation as an increasing number of station components approach the wear-out phase. This paper presents probabilistic models for circuit breakers involving aging failures and relevant evaluation techniques to examine the effects of station related aging outages. The technique developed to incorporate station related aging failures are illustrated by application to a small composite test system. The paper illustrates the effects of circuit breaker aging outages on bulk system reliability evaluation and examines the relative effects of variations in component age. System sensitivity analysis is illustrated by varying selected component parameters. The results show the implications of including component aging failure considerations in the overall analysis of a composite system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.27-35
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• 2021

Generally, a proper evaluation method of the aging phenomenon of PV modules is required as the electrical performance and lifespan of PV modules can degrade significantly due to several environmental factors, while they are generally known as devices that are used semi-permanently for more than 20 years. On the other hand, there is a lack of objectivity in the existing evaluation method of the aging phenomenon, which compares the adjusted PV output based on STC with the initial PV module specifications due to the data distortion while adjusting the measured data. Therefore, this study implemented a test device for an aging diagnosis to measure and collect actual data from a PV module section and modeled the data for aging using MATLAB S/W to minimize the variability of the PV output, communication error, and delay. Furthermore, this study confirmed the usefulness of the presented test device for aging diagnosis of the PV modules by diagnosing the total period and yearly-basis degradation rate of aging PV modules as 25.73% and 1.55%, respectively, according to the on-site output characteristics of the PV modules by season.

• Journal of Korean Society of Rural Planning
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• v.18 no.4
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• pp.69-78
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• 2012

Korean population has been rapidly aging. Most of people regard the aging population as future crisis due to the rate of change and agree to prepare for a soft-landing on aging society in South Korea. Particularly, the aging population growth in rural areas is much faster than urban areas. Also rural areas relatively have poorer social and economic conditions so the countermeasures for population aging considering related social and economic indices are required. Moreover, each rural region has the different preparedness level for rural aging based on regional socio-economic characteristics. In this study, we analyzed correlations of the rural aging rate and local characteristics and developed an evaluation index to show the regional preparedness status for rural aging. To test the applicability of developed indicators, we applied them to 161 rural regions and assessed regional preparedness level for rural aging. This study would provide basic data for establishing policies for rural aging.

• Journal of Korean Society of societal Security
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• v.2 no.4
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• pp.59-65
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• 2009

The rebound test using Schmidt hammer is most popular method to estimate strength of concrete. However, this method is inappropriate for Seoul Metro underground structures due to unsuitable aging effects. Consequently, the strength presumption equation of underground structures is proposed according to the correlation of uniaxial compressive strength, rebound test results and age of concrete. To achieve this, the results of in-depth inspection of Seoul Metro underground structures performed annually for last 8 years was anlayed.

• Journal of Korean Society for Quality Management
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• v.35 no.2
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• pp.45-52
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• 2007

The danger of self-ignition of single base propellants will increase with time. Therefore, a good prediction of the safe storage time is very important. In order to determine the remaining shelf-life of the propellants, the content of stabilizer is determined. The propellants stored under normal storage conditions about 10 to 18 years were investigated and accelerated aging test was carried out by storing propellant sample at higher temperature. Finally, we analyzed the results by various methods in order to show the best way to predict the realistic shelf-life. The safe storage life of the propellants will be 24 years, at least 15 years. In case of applying Arrhenius's law, using the reaction rate constant at 28$^{\circ}C$ to 30$^{\circ}C$ to predict the shelf-life by accelerated aging test is reasonable for a good prediction.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.10
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• pp.141-150
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• 2006

In this study we developed accelerated aging test cycle and equipment which can simulate domestic weather condition. And we proposed long term reliability assessment method for polymer housed distribution surge arresters. We carried out electrical and chemical analysis of the arresters which are used for accelerated aging test and outdoor exposure test. Through the analysis we verified the capability of the proposed method and we presented characteristic data for maintenance of domestic arresters.

• Journal of the Korean Society of Safety
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• v.15 no.1
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• pp.28-35
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• 2000

As huge energy transfer systems like a nuclear power plant, steam power plant and petrochemical plant are operated for a long time, mechanical properties are changed by degradation. The life time of the systems can be affected by the mechanical properties. So determination of the integrity of the metallic structure is required either to en4sure that failure will not occur during the service life of the components or to evaluate the lifetime extension of the structure. An automated ball indentation(ABI) method was developed as a non-destructive technique for evaluating the integrity of such metallic components. In this paper, we would like to present the aging evaluation technique by the ABI method. The five classes of the thermally aged CF8M specimens were prepared using an artificially accelerated aging method. After holding 100, 300, 900, 1800 and 3600 hours at 43$0^{\circ}C$, the specimens were cooled down using water to room temperature respectively. The tensile test, hardness test, charpy impact test, ABI test were performed. The results of the fracture test were compared with those of ABI test and the new evaluation technique of the integrity of metallic structures was developed.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.2
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• pp.43-51
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• 2020

After the accelerated aging, the bulkhead initiator using high explosives was carried out to verify aging characteristics. The Thru-Bulkhead Initiator operates by transmitting shock-wave generated from micro-initiator to the acceptor and the ignition explosives through the bulkhead. In order to evaluate the life-time of the product, the accelerated aging condition was set according to the life-time, and the ignition performance of the sample was measured every 10 cycles by measuring the delay time and the maximum pressure through the 10cc closed bomb test. In addition, variance analysis was used to determine aging.