• Proceedings of the KIEE Conference
• /
• 1998.07a
• /
• pp.319-321
• /
• 1998

Some design technologies of AC traction motor for rolling stocks are presented. AC Traction motors for rolling stocks are operated in worst conditions such as frequent mechanical vibrations, compact design with limited mounting space, severe thermal stress at outside, driven with nonsinusoidal voltage waveform inverters, and so on. Therefore, design procedures must be carefully investigated in the viewpoint of theoritically and practical use. Design procedure contains, the motor size determination, electromagnetic circuit design, insulation system design, vibrations and thermal expansion of rotor bars, temperature rise, as well as output characteristics.

• Proceedings of the KSR Conference
• /
• 2002.05a
• /
• pp.386-391
• /
• 2002

Stainless rolling stocks are usually fabricated by spot welding process without painting. Indentation on the surface of the car body after spot welding injures the beauty of the stainless rolling stocks. In this study, electrode tips to reduce the indentation are developed and applied to the actual spot welding works. The developed tips are composed of head, nut hole far cooling water, body and resistance material. They provide large surface contact area with the base materials during spot welding and enhance the current density by necking. Experimental results using the developed tips show that small indentation and sufficient tensile shear strength is produced due to large contact area and enhanced current density.

• International Journal of Railway
• /
• v.1 no.2
• /
• pp.59-63
• /
• 2008

The maintenance effect is a peculiar factor applied to repairable systems such as rolling stocks. Conventional statistical analysis for failure times takes into account one of the two following extreme assumptions, namely, the state of the system after maintenance is either as "good as new" (GAN, perfect maintenance model) or as "bad as old" (BAO, minimal maintenance model). Most of the papers concerning the stochastic behavior of railroad systems assume two types of maintenance: perfect and minimal maintenance. However, Lee, Kim & Lee (2008) analyzed the failure data of a door system in Metro EMU and the effect of preventive maintenance was imperfect. It is seen that the imperfect maintenance is of great significance in practice. This article describes how to deal with the maintenance effect in reliability studies of rolling stocks. Maintenance policies under imperfect maintenance are described and the method is proposed to evaluate their performance.

• Communications for Statistical Applications and Methods
• /
• v.29 no.6
• /
• pp.695-708
• /
• 2022

Recently, several studies have been conducted using state space model. In this study, a dynamic linear model with state space model form is applied to stock data. The monthly returns for 135 Korean stocks are fitted to a dynamic linear model, to obtain an estimate of the time-varying 𝛽-coefficient time-series. The model formula used for the return is a capital asset pricing model formula explained in economics. In particular, the transition equation of the state space model form is appropriately modified to satisfy the assumptions of the error term. k-shape clustering is performed to classify the 135 estimated 𝛽 time-series into several groups. As a result of the clustering, four clusters are obtained, each consisting of approximately 30 stocks. It is found that the distribution is different for each group, so that it is well grouped to have its own characteristics. In addition, a common pattern is observed for each group, which could be interpreted appropriately.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.17 no.4
• /
• pp.69-85
• /
• 2014

Carbon stocks of NFI plots can be accurately estimated using field survey information. However, an accurate estimation of carbon stocks in other unsurveyed sites is very difficult. In order to fill this gap, various spatial information can be used as an ancillary data. In South Korea, there is the 1:5,000 forest type map that was produced by digital air-photo interpretation and field survey. Because this map contains very detailed forest information, it can be used as the high-quality spatial data for estimating carbon stocks. In this study, we compared three upscaling methods based on the 1:5,000 forest type map and 5th national forest inventory data. Map algebra(method 1), RK(Regression Kriging)(method 2), and GWR(Geographically Weighted Regression)(method 3) were applied to estimate forest carbon stock in Chungcheong-nam Do and Daejeon metropolitan city. The range of carbon stocks from method 2(1.39~138.80 tonC/ha) and method 3(1.28~149.98 tonC/ha) were more similar to that of previous method(1.56~156.40 tonC/ha) than that of method 1(0.00~93.37 tonC/ha). This result shows that RK and GWR considering spatial autocorrelation can show spatial heterogeneity of carbon stocks. We carried out paired t-test for carbon stock data using 186 sample points to assess estimation accuracy. As a result, the average carbon stocks of method 2 and field survey method were not significantly different at p=0.05 using paired t-test. And the result of method 2 showed the lowest RMSE. Therefore regression kriging method is useful to consider spatial variations of carbon stocks distribution in rugged terrain and complex forest stand.

• Journal of Korean Society of Forest Science
• /
• v.96 no.6
• /
• pp.644-651
• /
• 2007

This study compared and estimated the changes in carbon stocks and emissions of harvested wood products (HWP) by applying FAO statistics and domestic statistics for Korean HWP production, import, and export volume, which is almost always supposed to be included in the carbon emissions and removals inventory by country in negotiations since the 2nd commitment period (2013~2017) of the Kyoto Protocol, for assessing the changes in carbon stocks and emissions of HWP. As a result, when applying FAO statistics to the changes in carbon stocks of HWP as of 2005, stock-change approach (SCA) was estimated at 1.434 Tg C, atmospheric-flow approach (AFA) -1.330 Tg C, and production approach (PA) 0.597 Tg C. When applying Korean statistics, SCA was estimated at 1.246 Tg C, AFA -11.520 Tg C, and PA 0.444 Tg C. When applying FAO statistics to $CO_2$ emissions and removals from HWP, SCA showed a decrease of $-5,258Gg\;CO_2$ (removals), AFA showed an increase of $4,877Gg\;CO_2$ (emissions), and PA showed a decrease of $-2,189Gg\;CO_2$ (removals). When applying Korean statistics, SCA showed a decrease of $-4,569Gg\;CO_2$ (removals), AFA showed an increase of $5,573Gg\;CO_2$ (emissions), and PA showed a decrease of $-1,628Gg\;CO_2$, (removals). Therefore, the application of FAO statistics was shown to be more beneficial for the estimation of both the changes in carbon stocks and emissions of HWP by all methods other than that of Korean statistics.

• Journal of Industrial Convergence
• /
• v.19 no.5
• /
• pp.21-34
• /
• 2021

The purpose of this study is to find out what the investment efficiency of BW is from an investor's point of view and to suggest an efficient investment plan to investors. The research method is to investigate the coupon interest rate, maturity interest rate, issuance date, right exercise start and end date, maturity date, exercise price, etc. for BW issued from 2014 to July 2021. By connecting them, it was attempted to quantitatively understand the efficiency of investment in BW and the effect of new stock acquisitions. As a result of the study, the ratio of the number of days in excess of the exercise price was 41.3% of the available days for new stocks, so it was analyzed that the investment efficiency of bonds with warrants was not high. The return on the exercise start date was 24.8% on average and the return on the end date was 52.6% on average, showing a positive return on average, so it was derived in line with investor expectations. The number of stocks with negative returns on the exercise start date was 1.47 times higher than the number of stocks with positive returns, and the number of stocks with negative returns on the end date was 1.16 times higher than the number of positive stocks.

• Journal of Korean Society of Forest Science
• /
• v.110 no.2
• /
• pp.233-243
• /
• 2021

Considering worldwide efforts to mitigate repercussions of climate change, the South Korean government has declared to reach net zero by 2050 to achieve a carbon-neutral sustainable society. For full implementation of NDCs, the government has actively reflected its forestry sector into these strategies. Since coarse woody debris (CWD) in forests represents an enduring carbon storage, it is of particular significance to determine characteristics of changes in carbon stocks of CWD by utilizing data on dead trees monitored in permanent sample plots within national forest inventories (NFIs). In this study, therefore, both occurrence and carbon stocks of CWD were estimated in such plots using data on CWD from the 5^th, 6^th, and 7^th NFIs. Subsequently, characteristics of changes in carbon stocks over time were analyzed. Based on the analysis of 2,021 plots available for monitoring in each NFI of Gangwon Province, the volume of CWD (m³ ha^-1) was found to be 4.71 in the 5^th NFI and 4.09 in the 6^th NFI. However, the volume of CWD declined to 3.09 in the 7^th NFI. Moreover, the annual carbon stocks of CWD (ton C ha^-1) were estimated to be 0.67 in 2009, 0.64 in 2014, and 0.41 in 2019, showing a downward trend over time. This study provides a basis for future research to investigate long-term changes and estimate carbon stocks of CWD in South Korea forests.

• Proceedings of the Safety Management and Science Conference
• /
• 2006.04a
• /
• pp.421-428
• /
• 2006

It is an hot issue to reduce vibration for improving quality, reliability and safety in railway vehicles including magnetic levitation, monorail way, surface car etc. This paper aims at literature survey in rolling stocks vibration standards. Firstly, we investigate literature concerned vibration test standards and compare these standards. Secondly, we give some suggestions for future study and developing new test standards.

• Proceedings of the Korea Technology Innovation Society Conference
• /
• 2003.05a
• /
• pp.5-17
• /
• 2003

This paper examines the effects of IT technology capital and R&D stock's variation on the growth of Korea's industries with the empirical approaches. We analyze the Granger causality and Impulse response function analysis among the Korea's industrial real output, IT technology capital, and R&D stocks. When it comes to this research conclusion, we know that IT technology capital and R&D stock's shocks affect the growth of Korea's industrial sector in terms of increasing in the real output growth rate.