• Korean Journal of Materials Research
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• 제30권12호
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• pp.693-700
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• 2020

Direct water quenching technique can be used in hot stamping process to obtain higher cooling rate compared to that of the normal die cooling method. In the direct water quenching process, setting proper water flow rate in consideration of material thickness and the size of the area directly cooled in the component is important to ensure uniform microstructure and mechanical properties. In this study, to derive proper water flow rate conditions that can achieve uniform microstructure and mechanical properties, microstructure and hardness distribution in various water flow rate conditions are measured for 3.2 mm thick boron steel sheet. Hardness distribution is uniform under the flow condition of 1.5 L/min or higher. However, due to the lower cooling rate in that area, the lower flow conditions result in a drastic decrease in hardness in some areas in the hot-stamped part, resulting in low martensite fraction. From these results, it is found that the selection of proper water flow rate is an important factor in hot stamping with direct water quenching process to ensure uniform mechanical properties.

• Corrosion Science and Technology
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• 제20권3호
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• pp.105-111
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• 2021

In oxidizing nitric acid solutions, stainless steel undergoes intergranular corrosion accompanied by grain dropping and changes in the corrosion rate. For the safe operation of reprocessing plants, this mechanism should be understood. In this study, we constructed a three-dimensional computational model using a cellular automata method to simulate the intergranular corrosion propagation of stainless steel. The computational model was constructed of three types of cells: grain (bulk), grain boundary (GB), and solution cells. Model simulations verified the relationship between surface roughness during corrosion and dispersion of the dissolution rate of the GB. The relationship was investigated by simulation applying a constant dissolution rate and a distributed dissolution rate of the GB cells. The distribution of the dissolution rate of the GB cells was derived from the intergranular corrosion depth obtained by corrosion tests. The constant dissolution rate of the GB was derived from the average dissolution rate. Surface roughness calculated by the distributed dissolution rates of the GBs of the model was greater than the constant dissolution rates of the GBs. The cross-sectional images obtained were comparable to the corrosion test results. These results indicate that the surface roughness during corrosion is associated with the distribution of the corrosion rate.

• Journal of The Geomorphological Association of Korea
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• 제27권1호
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• pp.47-60
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• 2020

This study tried to produce an uplift rate map and reveal the spatial distribution of the rate with topographical characteristics and absolute ages on marine terrace in the East Coast of the Korean Peninsula. Based on a total of 57 ages at 26 sites from previous study and 13 ages at 13 sites from this study, the coast showed the rates ranging from 0.145 m/ka to 0.410m/ka with an average of 0.258 m/ka. The highest and lowest rates were found from the Jeongdongjin area in Gangneung and the Goraebul area in Yeongdeok, respectively. However, some areas in the coast showed large differences in the rate among the sites. In addition, areas with only 1 age were also found, indicative of low reliability. This study suggests that a more reliable and precise interpretation on the rate can be made with more ages identified, especially in Goseong to northern part of Gangneung, middle and southern parts of Samcheok and Yeongdeok, southern part of Pohang to northern part of Gyeongju, and Ulsan.

• Korean Journal of Medicinal Crop Science
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• 제23권6호
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• pp.431-438
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• 2015

Background : This study was conducted to determine out the effect of storage temperature on the quality of fresh ginseng (Panax ginseng C. A. Meyer) during distribution. Methods and Results : Fresh ginseng was washed, packed in $30{\mu}m$ low density polyethylene (LDPE) film, then stored at 0, -2 and $-4^{\circ}C$. After 4 weeks of storage, ginseng was then stored at $5^{\circ}C$, as a simulation of the distribution process. Ginseng stored at $-4^{\circ}C$ showed higher respiration rate, ethylene production and electrolyte conductivity during the distribution phase than those stored at 0 and $-2^{\circ}C$. Decay and browning rate rapidly increased following 3 weeks of distribution in samples stored $-4^{\circ}C$. However ginseng stored $-2^{\circ}C$, which is below freezing point, for 4 weeks did not show the physiological change or quality deterioration. Ginsenoside contents decreased during storage for all plant, but did not differ significantly between storage temperatures. Conclusions : Storage at temperatures below $-2^{\circ}C$ can negatively affect respiratory characteristics and electrolyte leakage and increase quality deterioration and decay rates during distribution.

• Computers and Concrete
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• 제9권3호
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• pp.179-193
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• 2012

The hydration of cement contributes to the performance characteristics of concrete, such as strength and durability. In order to improve the utilization efficiency of cement and its early properties, the particle size distribution (PSD) of cement varies considerably, and the effects of the particle size distribution of cement on the hydration process should be considered. In order to evaluate effects of PSD separately, experiments testing the isothermal heat generated during the hydration of cements with different particle size distributions but the same chemical composition have been carried out. The measurable hydration depth for cement hydration was proposed and deduced based on the experimental results, and a PSD hydration model was developed in this paper for simulating the effects of particle size distribution on the hydration process of cement. First, a reference hydration rate was derived from the isothermal heat generated by the hydration of ordinary Portland cement. Then, the model was extended to take into account the effect of water-to-cement ratio, hereinafter which was referred to as PSD hydration model. Finally, the PSD hydration model was applied to simulate experiments measuring the isothermal heat generated by the hydration of cement with different particle size distributions at different water-to-cement ratios. This showed that the PSD hydration model had simulated the effects of particle size distribution and water-to-cement ratio on the hydration process of cement with satisfactory accuracy.

• Journal of Distribution Science
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• 제16권7호
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• pp.47-56
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• 2018

Purpose - This study aims to not only investigate spatial pattern of immigrants' residence and crime occurrences in South Korea, but shed light on how geographic distribution of immigrants and immigrant segregation affect crime rates. Research design, data, and methodology - Th unit of analysis is Si-Gun-Gu municipal level entities of South Korea. The crime data was obtained by Korea National Police Agency and two major types(violence and property) of crime were measured. Most demographic, social, and economic variables were derived from Korean Census Data in 2015. In order to examine spatial patterns of immigrants' distribution and crime rates in South Korea, the present study utilized GIS mapping technique and Exploratory Spatial Data Analysis(ESDA) tools. The causal linkage was investigated by a series of regression models using STATA. Results - Spatial inequality between urban metropolitan vs rural areas was visualized by mapping. Assuming large Moran's I value, spatial autocorrelation appeared to be quite strong. Several neighborhood characteristics such as residential stability and economic prosperity were found to be important factors leading to crime rate change. Residential distribution and segregation for immigrants were negatively significant in the regression models. Conclusions - Unlike the traditional arguments of social disorganization theory, immigrant segregation appeared to reduce violent crime rate and the high proportion of immigrants also turned out to be a crime prevention factor.

• Journal of Environmental Science International
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• 제28권6호
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• pp.535-544
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• 2019

We computed parameters that affect velocity distribution by applying Chiu's two-dimensional velocity distribution equation based on the theory of entropy probability and acoustic doppler current profiler (ADCP) of Jungmun-stream, Akgeun-stream, and Yeonoe-stream among the nine streams in Jeju Province between July 2011 and June 2015. In addition, velocity and flow were calculated using a surface image velocimeter to evaluate the parameters estimated in the velocity observation section of the streams. The mean error rate of flow based on ADCP velocity data was 16.01% with flow calculated using the conventional depth-averaged velocity conversion factor (0.85), 6.02% with flow calculated using the surface velocity and mean velocity regression factor, and 4.58% with flow calculated using Chiu's two-dimensional velocity distribution equation. If surface velocity by a non-contact velocimeter is calculated as mean velocity, the error rate increases for large streams in the inland areas of Korea. Therefore, flow can be calculated precisely by utilizing the velocity distribution equation that accounts for stream flow characteristics and velocity distribution, instead of the conventional depth-averaged conversion factor (0.85).

• Journal of Distribution Science
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• 제21권3호
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• pp.93-100
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• 2023

Purpose: The purpose of this paper is to confirm whether stocks belonging to the distribution industry in Korea have reversals, following large daily stock price changes accompanied by large trading volumes. Research design, data, and methodology: We examined whether there were reversals after the event date when large-scale stock price changes appeared for the entire sample of distribution-related companies listed on the Korea Composite Stock Price Index from January 2004 to July 2022. In addition, we reviewed whether the reversals differed depending on abnormal trading volume on the event date. Using multiple regression analysis, we tested whether high trading volume had a significant effect on the cumulative rate of return after the event date. Results: Reversals were confirmed after the stock price shock in the Korean distribution industry and the return after the event date varied depending on the size of the trading volume on the event day. In addition, even after considering both company-specific and event-specific factors, the trading volume on the event day was found to have significant explanatory power on the cumulative rate of return after the event date. Conclusions: Reversals identified in this paper can be used as a useful tool for establishing a trading strategy.

• Journal of Distribution Science
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• 제21권5호
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• pp.101-111
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• 2023

Purpose: The purpose of this paper is to examine the effect of the VKOSPI index on short-term stock returns after a large-scale stock price shock of individual stocks of firms in the distribution industry in Korea. Research design, data, and methodology: This study investigates the effect of the change of the VKOSPI index or investor mood on abnormal returns after the event date from January 2004 to July 2022. The significance of the abnormal return, which is obtained by subtracting the rate of return estimated by the market model from the rate of actual return on each trading day after the event date, is determined based on T-test and multifactor regression analysis. Results: In Korea's distribution industry, the simultaneous occurrence of a bad investor mood and a large stock price decline, leads to stock price reversals. Conversely, the simultaneous occurrence of a good investor mood and a large-scale stock price rise leads to stock price drifts. We found that the VKOSPI index has strong explanatory power for these reversals and drifts even after considering both company-specific and event-specific factors. Conclusions: In Korea's distribution industry-related stock market, investors show an asymmetrical behavioral characteristic of overreacting to negative moods and underreacting to positive moods.

• Water Engineering Research
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• 제3권1호
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• pp.63-74
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• 2002