• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.6
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• pp.451-464
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• 2022

The high-level nuclear waste repository is a deep geological disposal system exposed to complex environmental conditions such as high temperature, radiation, and ground-water due to handling spent nuclear fuel. Continuous exposure can lead to cracking and deterioration of the structure over time. On the other hand, the high-level nuclear waste repository requires an ultra-long life expectancy. Thus long-term structural health monitoring is essential. Various sensors such as an accelerometer, earth pressure gauge, and displacement meter can be used to monitor the health of a structure, and a piezoelectric sensor is generally used. Therefore, it is necessary to develop a highly durable sensor based on the durability assessment of the piezoelectric sensor. This study designed an accelerated life test for durability assessment and life prediction of the piezoelectric sensor. Based on the literature review, the number of accelerated stress levels for a single stress factor, and the number of samples for each level were selected. The failure mode and mechanism of the piezoelectric sensor that can occur in the environmental conditions of the high-level waste repository were analyzed. In addition, two methods were proposed to investigate the maximum harsh condition for the temperature stress factor. The reliable operating limit of the piezoelectric sensor was derived, and a reasonable accelerated stress level was set for the accelerated life test. The suggested methods contain economical and practical ideas and can be widely used in designing accelerated life tests of piezoelectric sensors.

• International Journal of Highway Engineering
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• v.7 no.3 s.25
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• pp.1-10
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• 2005

In this study, accelerated pavement tester(APT) was performed on long-life asphalt pavements that can save maintenance and user costs by increasing the design life twice longer than conventional asphalt pavements. Basic material testings are first conducted on a high modulus base(HMB) mixture developed in this study. Four different pavement sections including thin and thick conventional and thin and thick HMB courses are constructed to compare the load-carrying capacities and to investigate the fatigue and rutting performances using an accelerated pavement tester. Tensile strain values at the bottom of base courses under the various loading levels are measured. The tensile strain values of the HMB sections are lower than those of the conventional sections. It is observed from the APT performed on the thin pavement sections that no significant cracks are developed up to the 180,000 cycles of a wheel load. In terms of rutting, only 3mm of rutting is developed in the thick HMB section while 5.3mm of rutting is developed in the thick conventional section at the 90,000 cycles of the wheel load. The HMB material developed in this study can be successfully used in the long-life asphalt pavements because of its excellent fatigue and rutting performances. It is estimated from a series of structural analysis that the use of the HMB material instead of the conventional base materials may reduce the asphalt thickness at least 5cm because of its better load-carrying capacity.

• Journal of the Korean Society for Railway
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• v.20 no.5
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• pp.649-657
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• 2017

In this study, fatigue testing was carried out for long-term use of rail according to track type. From S-N curves for 50%~0.01% failure probability, the fatigue life of the long-term use rail for each track type was derived using the weight probability analysis technique on the experimental data. Because the rails used in the fatigue test have different cumulative tonnages, the number of repetitions was modified by averaging the cumulative tonnage. In addition, the bending stresses of rail bottoms, considering rail surface irregularities, track support stiffnesses and train speeds, were evaluated using the predicted rail bending stresses derived from existing studies. As a result, for rail fatigue life evaluation, the fatigue life of rail on the ballast track was found to be more than 200 million tons higher than the standard value for rail replacement. Also, the fatigue life of rail on concrete track is more than 300 million tons higher than that on ballast track. The Haibach rule is adaptable for the fatigue life evaluation of rail for stress range under fatigue limit.

• Korean Journal of Pharmacognosy
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• v.47 no.4
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• pp.374-380
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• 2016

The purpose of this study was to evaluate of quality variation of Sibujeondaebotang according to storage period and temperature (5 and $25^{\circ}C$) Identificaion test, pH, specific gravity, heavy metal, microbial limit test and glycyrrhizic acid, paeoniflorin content of Sibjeondaebotang were performed during 12 months. The significant change was not shown on identificaion test, specific gravity, microbial limit test under long term storage and the result suited a safe level standards of 'Korean National Standard of Traditional Medicinal (Herbal and Botanical) Materials - "Sibjeondaebotang"'. The test of pH showed meaningful changes between two storage temperature (5 and $25^{\circ}C$) according to increasing storage period. The contents of glycyrrhizic acid and paeoniflorin had no relation with storage temperature($5^{\circ}C$, $25^{\circ}C$) but it showed a tendency to decrease according to the length of storage period. We predicted shelf-life of glycyrrhizic acid and paeoniflorin at storgae temperature(5 and $25^{\circ}C$) as about 6 and 3 months, respecttively. Therefore considering glycyrrhizic acid and paeoniflorin, sibjeondaebotang is determined to be in good condition within 3 months, regardless of the room temperature and refrigerated temperature. We were expected to serve as a basis for the guideline of medication counseling sibjeondaebotang.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.24 no.2
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• pp.133-138
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• 2024

Lithium-ion batteries are used in many fields due to their high energy density, fast charging conditions, and long cycle life. However, overcharging, over-discharging, physical damage, and use of lithium-ion batteries at high temperatures can reduce battery life and cause damage to people due to fire or explosion due to damage to the protection circuit. In order to reduce the risk of these batteries and improve battery performance, the characteristics of the charging and discharging process must be analyzed and understood. Therefore, in this paper, we analyze the charging and discharging characteristics of lithium-ion batteries using a battery charger and discharger and simulator to reduce the risk of loss of life due to overcharge and overdischarge, as well as casualties from fire and explosion due to damage to the protection circuit.

• The Korean Journal of Community Living Science
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• v.24 no.4
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• pp.485-495
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• 2013

As rural life has shifted with the long term changes in the internal and external conditions of rural communities, this study aims to investigate the living conditions and life satisfaction of rural women. 70 questionnaires in health, clothing, food, shelter, economic conditions and child-rearing fields were used for a survey of 393 rural women from five rural areas in the northern region of Gyeongsangbuk-Do. Statistical techniques of frequency analysis, descriptive statistics, ANOVA, t-test and regression analysis were employed through 'SPSS Statistics 21'. Participants were divided into 3 groups, with Group A with income less than 15 million won, Group B with income of at least 15 million won and less than 30 million won, and Group C with at least 30 million won. For the life satisfaction and health conditions, Group C showed higher scores than Group A. The food security status of rural women in the research area was worse than that in the Korea National Health and Nutrition Examination Survey, and food consumption by Group C was higher than that of Group A and Group B. For the satisfaction of kitchen, bathroom facilities and heating system, the income of 15 million won seemed to be the divisive value where richer groups were more satisfied. Job satisfaction seemed more related with the income amount rather than with the job itself. The parenting efficacy and child-rearing satisfaction were higher for Group C than for Group A. Determinants of life satisfaction turned out to be health conditions, heat susceptibility, fruit consumption, kitchen unit satisfaction, job satisfaction and parenting efficacy.

• Journal of Families and Better Life
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• v.26 no.6
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• pp.35-50
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• 2008

The purpose of this study was to analyze the characteristics and financial status of credit delinquents utilizing the debt management program of the Credit Counseling and Recovery Service between January-June in 2007. Total sample of 41,355 cases was analyzed using the statistical program SPSS(Version 12.0). For analysis, descriptive statistics, F-test, Scheffe test, t-test, logit analysis and regression analysis were employed. People in the age range of 30-40s, males, high-school graduates, married couples, part-time employees, costfree residents and residents in other regions were relatively high users of the debt management program. Reasons of credit delinquency were diverse and was combined to credit default. However, increases in expenses and income reductions were found to be the most frequent reasons. Financial conditions of delinquents were worse than those of average persons shown on the national statistics. It was also found that age, sex, educational level, occupation, region of residence, home-ownership, reason of delinquency, income and total outstandings of debt were significant determinants of short-term debt burden which was measured by the ratio of monthly payment to income and long-term debt burden which was measured by repayment period.

• Proceedings of the Korea Contents Association Conference
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• 2015.05a
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• pp.15-16
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• 2015

Measuring sensor, equipment, ICT facilities and their software have relatively short life time comparing to constructional structure so that we should exchange or fix them continuously in the process of maintenance and management. In this paper, we propose a novel design of integrated maintenance, management, and measuring monitoring system applying the concept of mobile cloud. For the sake of disaster prevention for constructional structures such as bridge, tunnel, and other traditional buildings in the village of local heritage, we analyze status of these structures in the long term or short term period as well as disaster situations. Collecting data based on mobile cloud and analyzing future expectations based on probabilistic and statistical techniques, we implement our integrated monitoring system for constructional structures to solve these existing problems. Final results of this design and implementation are basically applied to the monitoring system for more than 10,000 structures spread over national land in Korea. In addition, we can specifically apply the monitoring system presented here to a bridge of timber structure in Asan Oeam Village and a traditional house in Andong Hahoe Village to watch them from possible disasters. Total procedure of system design and implementation as well as development of the platform LinkSaaS and application services of monitoring functions implemented on the platform. We prove a good performance of our system by fulfilling TTA authentication test, web accommodation test, and operation test using real measuring data.

• Journal of Biosystems Engineering
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• v.30 no.2 s.109
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• pp.89-94
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• 2005

The compression strength of corrugated fiberboard container for packaging the agricultural products rapidly decreases because of various environmental conditions during distribution of unitized products. Among various environmental conditions, the main factors affecting the compression strength of corrugated fiberboard are absorption of moisture, long-term accumulative load, and fatigue caused by shock and vibration. An estimated rate of damage for fruit during distribution is about from 30 to 40 percent owing to the shock and vibration. This study was carried out to characterize the durability of corrugated fiberboard container for packaging the fruit and vegetables under simulated transportation environment. The vibration test system was constructed to simulate the land transportation using truck. After the package with corrugated fiberboard container was vibrated by vibration test system at various experimental conditions, the compression test for the package was performed. The compression strength of corrugated fiberboard container decreased with loading weight and vibrating time. The multiple nonlinear regression equation for predicting the decreasing rate of compression strength of corrugated fiberboard containers were developed using four independent variables such as input acceleration level, input frequency, loading weight and vibrating time. The influence of loading weight on the decreasing rate of corrugated fiberboard container was larger than other variables.

• Design & Manufacturing
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• v.12 no.3
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• pp.36-41
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• 2018

Metal 3D printing is very useful for making the injection molds containing complex conformal cooling channels. The most important issue of the 3D printed molds is cost and life cycle. However, powder bed fusion (PBF) methods are vulnerable to fatigue loading because of the presence of pores and rough surfaces. In the present study, the fatigue test was performed to obtain fatigue analysis input data for predicting the durability of a 3D printed injection mold core. The metal 3D printer used to manufacture the specimen was OPM250L from Sodick, and the metal powder material was maraging steel. The ultrasonic fatigue testing method was adopted for the fatigue test. A key advantage of the ultrasonic fatigue method is that $10^8{\sim}10^9$ long cycle test data or more could be obtained within a relatively short period. Based on the results of the experiment, the effect of heat treatment was negligible. However, there was an apparent difference in durability depending on the presence or absence of the surface treatment.