• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.1200-1203
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• 2003

The dielectric breakdown of epoxy composites used for transformers was experimented and then its data were applied to Weibull distribution probability. First of all, speaking of dielectric breakdown properties, the more hardener increased, the stronger breakdown strength became at low temperature because of cross-linked density by the virtue of ester radical. The breakdown strength of specimens with filler was lower than it of non-filler specimens because it is believed that the adding filler forms interface and charge is accumulated in it, therefore the molecular motility is raised and the electric field is concentrated. In the case of filled specimens with treating silane, the breakdown strength become much higher. Finally, according to Weibull distribution analysis, reducing breakdown probability of equipment insulation lower than 0.1% level requires the allowable field allowable field intensity values to be kept under 21.5 MV/cm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.212-217
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• 2002

The dielectric breakdown of epoxy composites used for transformers was experimented and then its data were simulated by Weibull distribution probability. First of all, speaking of dielectric breakdown properties, the more hardener increased the stronger breakdown strength at low temperature because of cross-linked density by the virtue of ester radical. The breakdown strength of specimens with filler was lower than it of non-filler specimens because it is believed that the adding filler forms interface and charge is accumulated in it, therefore the molecular motility is raised and the electric field is concentrated. In the case of filled specimens with treating silane, the breakdown strength become much higher Finally, from the analysis of weibull distribution, it was confirmed that as the allowed breakdown probability was given by 0.1[%], the applied field value needed to be under 21.5 MV/cm.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.5 s.98
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• pp.175-185
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• 1999

Acoustic emission(AE) measurement was carried out to evaluate the fracture behavior of high tension steel. Fracture toughness $K_{AE}$ could be determined reasonably by using the load value corresponding to an abrupt change of the accumulated AE counts AE emitted from the test specimens. AE characteristics of the base metal, the weld metal and the heat-affected zone could be distinguished using a constant value b which represented the AE amplitude distribution, Consequently the structure integrity can be evaluated by variation of the constant b at the load level. In addition it was found that AE signals due to crack growth have high amplitude but low rise time and duration.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05b
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• pp.159-163
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• 2003

In this study, the DC dielectric breakdown of epoxy composites used for PCB material was experimented and then its data were simulated by Weibull distribution equation. The more hardener increased the stronger breakdown strength at low temperature because of cross-linked density by the virtue of ester radical, and the breakdown strength of specimens with filler was lower than it of non-filler specimens because it is believed that the adding filler forms interface and charge is accumulated in it, therefore the molecular motility is raised, the electric field is concentrated, and the acceleration of electron and the growth of electron avalanche are early accomplished. From the analysis of Weibull distribution, it was confirmed that as the allowed breakdown probability was given by 0.1[%], the applied field value needed to be under 21.5[kV/mm].

• Journal of Korean Society for Quality Management
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• v.15 no.2
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• pp.2-9
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• 1987

The Deterioration Factor (DF) for a single pollutant within an engine family is computed as the ratio of two points on a linear regression line describing durability vehicle test results as a function of accumulated mileage. It is inteded to represent the factor by which emissions will increase during the ''useful life" of a vehicle in the engine family. Here are discribed procedures for computing the DF and how consideration of the DF is included in the development for the motor vehicle emission certification process. This paper is aimed to develop the distribution of the DF for three pollutant and to estimate the parameter values for the distribution of the DF.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.579-581
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• 2019

In this paper, dispersion-managed optimal link configuration with the growth/decay distribution of accumlative dispersion as the fiber span is increased, in which optical phase conjugator placed at midway, is proposed. It is confirmed that if net residual dispersion set to be -15 ps/nm or 15 ps/nm in the proposed optical link configuration, the best compensation of the distorted wavelength division multiplexed channels will be obtained.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.123-133
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• 2014

Minimizing the cylinder wear and the consumption rate of cylinder oil in a large two-stroke diesel engine is of great economic importance. A motor-driven cylinder lubricator for Sulzer RT-flex large two-stroke diesel engines developed by authors is in need of improving the lubricating system to lubricate cylinder parts optimally by an electronically controlled quill device according to changes of engine load and revolution speed. In order to apply the developed accumulating distributor to an integrated cylinder lubricator by the electronically controlled system as the third research stage, the lubricating system is improved in the electronically controlled quill device with a solenoid valve. In this study, the effects of lubricator revolution speed, driving pressure(or plunger stroke) and cylinder back pressure on oil feed rate and lubrication inequality rate are investigated by using the integrated cylinder lubricator system with an accumulated distribution by the electronic control(I.C.S.), and the oil feed rate and lubrication inequality rate of I.C.S. are compared with those of the motor-driven cylinder lubricator by the electronically controlled quill system equipped with an accumulating distributor(E.D.S.). It is found that the oil feed rate of I.C.S. is smaller than that of E.D.S. due to the reduction of delivery velocity by the higher delivery pressure, and the variances of lubrication inequality rate for I.C.S. have become smaller than those of E.D.S. as the driving pressure in all experimental conditions increases, except for the driving pressure of 26 bar(plunger stroke 2 mm) at the cylinder lubricator speed of 120 rpm.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.11
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• pp.548-556
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• 2005

Reliability evaluation of power distribution system is very important to both power utilities and customers. It present the probabilistic number and duration of interruption such as failure rate, SATDI, SAIFI, and CAIDI. However, it has a fatal weakness at reliability index because of accuracy of failure rate. In this paper, the Time-varying Failure Rate(TFR) of power distribution system equipment is extracted from the recorded failure data of KEPCO(Korea Electric Power Corporation) in Korea. For TFR extraction, it is used that the fault data accumulated by KEPCO during 10 years. The TFR is approximated to bathtub curve using the exponential(random failure) and Weibull(aging failure) distribution function. In addition, Kaplan-Meier estimation is applied to TFR extraction because of incomplete failure data of KEPCO. Finally, Probability plot and regression analysis is applied. It is presented that the extracted TFR is more effective and useful than Mean Failure Rate(MfR) through the comparison between TFR and MFR

• Journal of Fisheries and Marine Sciences Education
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• v.26 no.6
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• pp.1435-1441
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• 2014

The fire took place in the synthetic heat transfer fluid boiler used in production process of medium density fiberboard. This study investigated pressure distribution of the first, second and third passes and the temperature in the fire burner. The boiler's internal fluid is unsteady due to the out of order inverter. As the operation continues, the flame's flow and speed are unsteady. The synthetic heat transfer fluid leak spouted about 120kg/min in the form of vapor in the early period of the fire. The flame extended to the second and third passes. The highest temperature of the second and third pass is $1059^{\circ}C$ and $1007^{\circ}C$, respectively. The synthetic heat transfer fluid spouted through the cracked part of the fire box in the first pass and accumulated on the turn table. Therefore, it is expected that the temperature of the interior of the fire box is above $1200^{\circ}C$. The temperature of the burner rises to a maximum level several times in a short period. On account of that, several explosions occur in the fire burner. Pressure distribution at steady state in combustion furnace is 2~5mAq and pressure distribution at inverter under fault condition in combustion furnace is 10~-53mAq. The decrement of coil thickness measurement for synthetic heat transfer fluid boiler is 0~5mm.

• Journal of Distribution Science
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• v.21 no.4
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• pp.91-101
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• 2023

Purpose: Research on the valuation of the e-commerce distribution companies is necessary because the traditional valuation methodology cannot be easily applied. Considering the valuation and initial public offering (IPO) of Coupang, Korea's leading e-commerce company, this study contributes to the literature by examining various valuation methods applicable to corporate valuation in the e-commerce industry and provides their implications. Research design, data and methodology: This case study investigates research, analyst reports, news articles, and magazines to review the valuation methods for companies in the e-commerce industry and analyzes the case of the Coupang IPO. Results: A valuation method that considers growth potential, which is important for companies in the e-commerce industry, is used for IPOs. This led to Coupang's successful IPO on the New York Stock Exchange despite its accumulated losses. However, the continued price decline since listing suggests that Coupang's valuation should have considered more factors. Conclusions: This study provides guidelines for the valuation of companies in the e-commerce industry, which eventually improves the overall industry. Moreover, this study provides directions for improving the valuation methods for e-commerce firms.