• Economic and Environmental Geology
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• v.52 no.6
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• pp.587-593
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• 2019

This study were subjected to accelerated weathering test under freeze-thaw and pressure conditions to observe initiation and propagation of cracks using CLSM. Applied stress was set at 50 MPa, 55 MPa, 70 MPa for 3 samples each by using compressor and freeze-thaw experiment was conducted while samples maintained that condition. In freeze-thaw experiments, a temperature range was set to -20~40℃ which was 1 cycle for 6 hours. The freeze-thaw cycle was composed of time which reached to set temperature for 1 hour and holding time for 2 hours. On the basis of this cycle, surface of samples was observed by CLSM after each 20 freeze-thaw cycle. From this research, according to increase freeze-thaw cycle, there were 7, 10, 19 each cracks and High pressured sample's accumulate length was longer than low pressured sample's. High pressured sample's crack velocities were also faster than low pressured sample's which were calculated by accumulate length and freeze-thaw cycle.

• Digital Contents
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• no.12 s.115
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• pp.74-81
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• 2002

인터넷 서비스의 대명사로 자리잡은 '포탈'이 '제5의 권력'으로 부상하고 있다. '한메일' 서비스로 성장한 다음커뮤니케이션, 검색 사이트 '네이버'로 성장한 NHN, 그리고 야후!코리아 등 TOP3는 각사의 장점을 살리며 영향력을 강화해 나가고 있다. 이제 더 이상 이들 포탈은 정보를 얻을 수 있었던 '인터넷 사이트'에 머물지 않는다. 다음커뮤니케이션, NHN(구 네이버), 야후!코리아 TOP3 포탈사이트의 누적 체류시간 비중이 2000년 11월 55%에서 2002년 5월 65%로 증가하면서 상위 사업자군의 이용시간 지배력이 강화되고 있다. 업계 최고의 인지도를 자랑하는 다음, 최고의 수익률을 자랑하는 NHN, 그리고 3위 자리를 내놓지 않고 승승장구하고 있는 야후!코리아. 한국의 대표적인 인터넷 기업의 현재 서비스와 향후 전략을 비교했다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2013.10a
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• pp.37-39
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• 2013

현재 우리나라는 보유 또는 지배선박이 약 1,000척, 3천만G/T로 노르웨이에 이어 세계 6위의 해운강국으로 성장하였다. 그리고 수많은 사관과 부원들이 다양한 선박에 승선하고 있으며 해운산업이 성장할수록 더 많은 선원들이 선박에 근무할 것으로 예상된다. 그러나 IMO와 ILO 등에서는 선원들의 선박근무환경 및 휴식 등에 관해서 최소한만을 규정하고 있고, 이로 인하여 선원들이 높은 노동 강도에 시달리게 되고 피로와 스트레스가 누적되어 해양사고의 한 원인이 되고 있는 실정이다. 이 연구에서는 각 선박의 고유 특성과 운항환경 등으로 고려한 선박의 근무강도를 평가할 수 있는 요소와 지수를 개발하기 위하여 선박에 장기간 승선한 경험이 있는 응답자로 하여금 각 평가요소에 대하여 주관적으로 인지하는 선박의 근무강도를 평가하도록 하였다. 이 평가요소와 지수를 기반으로 선원들을 각 선원의 특성과 여건에 맞는 선박에 배정함으로서 선원들의 피로와 스트레스를 경감시켜 해양사고의 예방에 기여할 수 있을 것으로 예상된다.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.6
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• pp.100-107
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• 1999

This paper describes a probabilistic remaining life assessment program for the creep crack growth. The probabilistic life assessment program is developed to increase the reliability of life assessment. The probabilistic life assessment involves some uncertainties, such as, initial crack size, material properties, and loading condition, and a triangle distribution function is used for random variable generation. The resulting information provides the engineer with an assessment of the probability of structural failure as a function of operating time given the uncertainties in the input data. This study forms basis of the probabilistic life assessment technique and will be extended to other damage mechanisms.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.10
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• pp.747-752
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• 2019

By using the failure information and the cumulative test execution time obtained by performing the reliability growth test, it is possible to estimate the parameter of the reliability growth model, and the Mean Time Between Failure (MTBF) of the product can be predicted through the parameter estimation. However the failure information could be acquired periodically or the number of sample data of the obtained failure information could be small. Because there are various constraints such as the cost and time of test or the characteristics of the product. This may cause the error of the parameter estimation of the reliability growth model to increase. In this study, the Bayesian method is applied to estimating the parameters of the reliability growth model when the number of sample data for the fault information is small. Simulation results show that the estimation accuracy of Bayesian method is more accurate than that of Maximum Likelihood Estimation (MLE) respectively in estimation the parameters of the reliability growth model.

• KDI Journal of Economic Policy
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• v.34 no.4
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• pp.91-116
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• 2012

This paper analyzes how the adverse impacts of the global financial crisis on Korea's employment could be mitigated in comparison with the Asian crisis period. The results from error-correction models suggest that the less severe impacts during the global financial crisis could be attributed to (i) smaller GDP reduction, (ii) better maintenance of domestic demand despite a sharp fall of export, (iii) less serious over-employment during the run-up to the crisis, and (iv) less severe credit crunch. Analyses of OECD cross-country data provide corroborating evidence. In order to mitigate adverse impacts on employment, therefore, priority should be given to expansionary macroeconomic policies to keep aggregate domestic demand from collapsing once a crisis is triggered. Also crucial, however, is to maintain sound economic structures such as flexible labor market and adequately supervised financial market.

• Nuclear Engineering and Technology
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• v.27 no.2
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• pp.226-233
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• 1995

The wall thickness of a pressure tube is increased in order to reduce the probability of failure in a pressure tube of CANDU type reactor. It is presented here that the variation of wall thickness changes stress, hydrogen concentration and delayed hydride cracking in Zr-2.5Nb pressure tube. When the wall thickness is increased from 4.2 mm to 5.2 mm, the stress exerted on the tube and the deuterium taken up during operation are reduced by 19％. Further, the calculated allowable depth of the surface flaw over which delayed hydride cracking(DHC) is susceptible increases by 50％. DHC initiation is controlled by the stress and by the hydrogen concentration in the pressure tube. The results are therefore very significant in such a respect that increased wall thickness may reduce DHC initiation. Ac the wall thickness increases the hydrostatic tension will increase. Its impact on the acceleration of the crack growth rate of DHC deserves further studies.

• KSBB Journal
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• v.14 no.5
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• pp.543-549
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• 1999

For development of an integrated calorimetric bio-reactor to measure the metabolic heat dissipated during cell growth, a 5 liter jar fermenter was modified to measure the pulse length of automatic temperature control signals to set heater on and off, and the to send them to computer to calculate the cumulative heat supplied. Cumulative heats for the calorimetric reactor in the absence of cell growth, were measured with varying conditions. The heat loss by the aeration was 30.9 kJ/vvm and the loss to ambient air was 10.5 kJ/L/hr/$^{\circ}C$. Cumulative heat was measued within $\pm$0.2% when testing with a small electri heater submerged in the reactor. Metabolic heat was measured to be 0.76 and 0.76 and 11.4kJ per g consumption of glucose during cultivation of S. cerevisiae and E. coli, respectively.

• Journal of the Korean Society for Railway
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• v.13 no.4
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• pp.447-454
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• 2010

The defects of rail head induced by fatigue and deterioration are mainly classified by two types ; one occurred on the surface of rail head the another occurred on the inner rail head. This study performed the surface irregularity measurement of rail head according to the passing tonnage in the urban railway. Also, we carried out microscopic structure test, chemical component test and micro-hardness test for the specimen which is the used rail on metro line by accumulated passing tonnage. As a result of this study, for new rail, it should be performed initial grinding in order to remove 0.3mm of de-carbonized layer. The preventive-cyclic grinding for preventing RCF defects is proposed two options : grinding by the whole line and grinding by specified sections.

• Journal of Korean Society of Environmental Engineers
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• v.34 no.6
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• pp.382-390
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• 2012

Global warming has been hot issue world wide. Korea has been dealing with the global issue under the slogan of low carbon and green-growth such as setting national greenhouse gas (GHG) reduction targets and allocation to each industrial sector. Infrastructure construction, in which enormous social overhead capital (SOC) is input, has great role as one of the actions. Road is one of the representative infrastructure and large amount of resources is utilized in its construction, operation and maintenance stage. The estimation methodology of life cycle carbon emissions was developed and applied to a case study of highway currently under construction in this study. Also, total carbon emissions of all the highway in South Korea at present (2009) and cumulative carbon emissions from 2009 to 2020 were estimated using the results of case study.