• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1157-1166
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• 2021

In this study, a numerical sensitivity analysis was performed to determine the fire suppression time for a large number of water mist nozzles in a large fire compartment. Fire simulations were performed using FDS (Fire dynamics simulator) 6.5.2 under the same condition as the test scenario 5 of the International Maritime Organization (IMO) 1165 test protocol. The sensitivities of input parameters including cell size, extinguishing coefficient (EC), droplets per second (DPS), and peak heat release rate (HRR) of fuel were investigated in terms of the normalized HRR and temperature distribution in the compartment. A new method of determining the fire suppression time using FDS simulation was developed, based on the concept of the cut-off time by cut-off value (COV) of the heat release rate per unit volume (HRRPUV) and the cooling time by the HRR cooling time criteria value (CTCV). In addition, a method was developed to determine the average EC value for the simulation input, using the cooling time and cut-off time.

• Journal of Environmental Science International
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• v.18 no.4
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• pp.369-374
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• 2009

To examine the trend on the flowering time in some weather flora including Prunus serrulata var. spontanea, Cosmos bipinnatus, and Robinia pseudo-acacia in Busan, the changes in time series and rate of flowering time of plants were analyzed using the method of time series analysis. According to the correlation between the flowering time and the temperature, changing pattern of flowering time was very similar to the pattern of the temperature, and change rate was gradually risen up as time goes on. Especially, the change rate of flowering time in C. bipinnatus was 0.487 day/year and showed the highest value. In flowering date in 2007, the difference was one day between measurement value and prediction value in C. bipinnatus and R. pseudo-acacia, whereas the difference was 8 days in P. mume showing great difference compared to other plants. Flowering time was highly related with temperature of February and March in the weather flora except for P. mume, R. pseudo-acacia and C. bipinnatus. In most plants, flowering time was highly related with a daily average temperature. However, the correlation between flowering time and a daily minimum temperature was the highest in Rhododendron mucronulatum and P. persica, otherwise the correlation between flowering time and a daily maximum temperature was the highest in Pyrus sp.

• Journal of Korean Society of Transportation
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• v.17 no.5
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• pp.43-55
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• 1999

The value of time in freight transportation describes the importance of goods during transport and shows the direction of efficient logistic management having inventory cost in transporting The value of time differs from class to class in freight transportation. It is due to the differences of shipper's willingness to Pay for time saving. In this research the value of time in intercity freight transportation of manufacturers in Korea was estimated as follows: first, the Perception factors which were the important criteria of shippers for choosing truck were sampled. second, the shippers were classified into three homogeneous classes. third, the value of time of each class was estimated by using multinominal logit model. The results of this research showed that the value of time in freight transportation was different from every class, that the shipper had to Pay 1,680 won for saving one hour Per each shipment, and that the inventory cost in transporting occupied 9.54% in the mean freight Price.

• Journal of Korean Society of Transportation
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• v.20 no.7
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• pp.167-175
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• 2002

The objective of this study is to reveal a shipper's preference for road freight transport according to commodity classification code. The shipper's preference in freight transport can be obtained by using value of travel-time savings. The characteristics of freight are so various that the shipper's preference also appear widely different. In these days, there were few attempts to estimate value of freight travel-time savings in Korea. but most of them included only rail or marine freight transport so it couldn't obtain unique travel-time savings for road freight transport. In this study the value of travel-time savings of road freight transport was estimated according to commodity classification code. Revealed preference method and associated binominal logit models were applied to estimate the value of travel-time savings in transit from a Seoul metropolitan commodity flow survey data in 1998. Data sets were segmented by commodity classification code and nineteen binominal legit models were estimated according to segmented groups. The results of this study showed that the value of freight travel-time savings varied wide ranges from 16,441 won to 66,769 won per hour a vehicle along with commodity classification code.

• Journal of applied mathematics & informatics
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• v.28 no.3_4
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• pp.945-952
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• 2010

In this paper, existence criteria of one solution to a nonlinear first-order periodic boundary value problem of impulsive dynamic equation on time scales are obtained by using the well-known Schaefer fixed-point theorem.

• Korea Trade Review
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• v.46 no.6
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• pp.191-209
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• 2021

In this paper, various time series analysis models and machine learning models are presented for long-term prediction of export growth rate, and the prediction performance is compared and reviewed by RMSE and MAE. Export growth rate is one of the major economic indicators to evaluate the economic status. And It is also used to predict economic forecast. The export growth rate may have a negative (-) value as well as a positive (+) value. Therefore, Instead of using the ReLU function, which is often used for time series prediction of deep learning models, the PReLU function, which can have a negative (-) value as an output value, was used as the activation function of deep learning models. The time series prediction performance of each model for three types of data was compared and reviewed. The forecast data of long-term prediction of export growth rate was deduced by three forecast methods such as a fixed forecast method, a recursive forecast method and a rolling forecast method. As a result of the forecast, the traditional time series analysis model, ARDL, showed excellent performance, but as the time period of learning data increases, the performance of machine learning models including LSTM was relatively improved.

• Culinary science and hospitality research
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• v.24 no.3
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• pp.35-46
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• 2018

This study investigated the quality characteristics of makpyeon made of dry milled rice powder according to soaking time. Makpyeon samples made of dry milled rice powder were analyzied with various soacking time, the moisture content, pH, Hunter's color value texture characteristics, attribute difference test and acceptance test. The moisture content of makpyeon did not indicate difference among samples. pH resulted in MS90 showed the lowest moisture content. The L-value (lightness) and a-value (greenness) result in that MS0 showed the highest and decreased according to soaking time. The b-value (yellowness) increased according to soaking time, MS90 showed the highest. TPA resulted in that MS90 indicated the highest hardness, chewiness, gumminess and the lowest adhesiveness. Hardness of makpyeon samples was higher than sulgitteok samples, adhesiveness was lower than those of sulgitteok in each soaking time. Based on attribute difference test, the score of brightness, moistness, glossy, particle size were decreased and firmness were increased according to soaking times. Flavor, taste and mouth feel attribute was stronger in makpyeon samples with the longer soaking time. Acceptance results showed that MS0 and MS30 (soaking for 30 min) were preferred the most. Also limitations and future research directions of this study were discussed.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.8
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• pp.69-76
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• 2020

The study examines lagged economic effects of research and development (R&D) investment on the market value of manufacturing firms listed on the Shanghai Stock Exchange or the Shenzhen Stock Exchange in China. This study applies panel data analysis methods to address the following issues: 1) There might be an adjustment lag in the impact of R&D investment on corporate market value, and 2) Unobserved firm effects must be taken into account. The balanced panel data includes a total of 1,462 observations with 34 cross-sections of manufacturing firms listed on Chinese stock markets and with 27 time-specific quarterly periods from 2007 to 2017. The results indicate that the R&D investment of Chinese manufacturing firms tends to yield favorable market value of the firm with some adjustments to time. The results show that R&D investment exhibits a strong positive impact on their market value of manufacturing firms in Chinese stock markets. Moreover, R&D investment has a positive time-lag effect on the market value of the firm. Interestingly, the R&D investment of Chinese manufacturing firms generate a relatively constant positive effect on their market value, supporting the notion that the corresponding returns of R&D investment for such firms yield lagged but added market values.

• Journal of Families and Better Life
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• v.21 no.1
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• pp.61-72
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• 2003

This study examines the problematic fact that most housewives are excluded from receiving the benefits of the National Pension Plan in South Korea. The National Pension Plan assigns no value to housework or household production, which in turn discourages full-time housewives from participating voluntarily in the Plan. In this article, I propose to utilize Credit Splitting and Pension Sharing in order to take into account full-time housewives' economic contribution in the National Pension Plan. In this article, I also discuss the ranges and application methods of the Credit Splitting and Pension Sharing. For this study, I have analyzed the data of 11,967 unemployed married women living with spouses published in“Research Data on Everyday Life Time Usage”by the Korea National Statistical Office in 1999. The value of the full-time housewives' labor varies depending on the methods of estimation. However, all estimated values exceed the average value assigned to the housewives by the National Pension Corporation. It is clear that full-time housewives' unpaid labor contributes a great deal to the formation of household property and wealth, which is a valid reason for Pension Sharing and Credit Splitting. This article also provides logical factors to consider in the process of Pension Sharing and Credit Splitting, which can be used for developing computerized software to determine a full-time housewives' labor value at the time of divorce or for any other purpose.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1475-1477
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• 1998

In this paper, breakdown strength and time to breakdown are experimented under semiconducting layer/needle electrode in XLPE which is used for power cable insulator. Shape and scale parameters of obtained data are estimated using 2-parameters Weibull distribution. Life-time coefficient(n-value) using shape parameters for breakdown strength and time to breakdown tests is estimated. n-value of 1000 hour aged XLPE showed higher value than that of virgin XLPE. Increase of n-value is estimated by the stability due to removal of by-product and residue gas in XLPE by heating.