• The Journal of Information Systems
• /
• v.31 no.3
• /
• pp.197-220
• /
• 2022

Purpose The purpose of this study is to identifies the demand pattern categorization of repair parts of Automotive After-sales Service(A/S) and proposes a demand prediction model for Auto repair parts using Long Short-Term Memory (LSTM) of artificial neural networks (ANN). The optimal parts inventory quantity prediction model is implemented by applying daily, weekly, and monthly the parts demand data to the LSTM model for the Lumpy demand which is irregularly in a specific period among repair parts of the Automotive A/S service. Design/methodology/approach This study classified the four demand pattern categorization with 2 years demand time-series data of repair parts according to the Average demand interval(ADI) and coefficient of variation (CV²) of demand size. Of the 16,295 parts in the A/S service shop studied, 96.5% had a Lumpy demand pattern that large quantities occurred at a specific period. lumpy demand pattern's repair parts in the last three years is predicted by applying them to the LSTM for daily, weekly, and monthly time-series data. as the model prediction performance evaluation index, MAPE, RMSE, and RMSLE that can measure the error between the predicted value and the actual value were used. Findings As a result of this study, Daily time-series data were excellently predicted as indicators with the lowest MAPE, RMSE, and RMSLE values, followed by Weekly and Monthly time-series data. This is due to the decrease in training data for Weekly and Monthly. even if the demand period is extended to get the training data, the prediction performance is still low due to the discontinuation of current vehicle models and the use of alternative parts that they are contributed to no more demand. Therefore, sufficient training data is important, but the selection of the prediction demand period is also a critical factor.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.11a
• /
• pp.43.1-43.1
• /
• 2010

In the crystalline silicon solar cells, the full area aluminum_back surface field(BSF) is routinely achieved through the screen-printing of aluminum paste and rapid firing. It is widely used in the industrial solar cell because of the simple and cost-effective process to suppress the overall recombination at the back surface. However, it still has limitations such as the relatively higher recombination rate and the low-to-moderate reflectance. In addition, it is difficult to apply it to thinner substrate due to wafer bowing. In the recent years, the dielectric back-passivated cell with local back contacts has been developed and implemented to overcome its disadvantages. Although it is successful to gain a lower value of surface recombination velocity(SRV), the series resistance($R_{series}$) becomes even more important than the conventional solar cell. That is, it is a trade off relationship between the SRV and the $R_{series}$ as a function of the contact size, the contact spacing and the geometry of the opening. Therefore it is essential to find the best compromise between them for the high efficiency solar cell. We have investigated the optimal design for the local back contact by using PC1D simulation.

• Bulletin of the Korean Mathematical Society
• /
• v.49 no.4
• /
• pp.875-883
• /
• 2012

Let $\mathbb{F}_q$ be a finite field with q elements and $\mathbb{F}_q((X^{-1}))$ be the field of all formal Laurent series with coefficients lying in $\mathbb{F}_q$. This paper concerns with the size of the set of points $x{\in}\mathbb{F}_q((X^{-1}))$ with their partial quotients $A_n(x)$ both lying in a given subset $\mathbb{B}$ of polynomials in $\mathbb{F}_q[X]$ ($\mathbb{F}_q[X]$ denotes the ring of polynomials with coefficients in $\mathbb{F}_q$) and deg $A_n(x)$ tends to infinity at least with some given speed. Write $E_{\mathbb{B}}=\{x:A_n(x){\in}\mathbb{B},\;deg\;A_n(x){\rightarrow}{\infty}\;as\;n{\rightarrow}{\infty}\}$. It was shown in [8] that the Hausdorff dimension of $E_{\mathbb{B}}$ is inf{$s:{\sum}_{b{\in}\mathbb{B}}(q^{-2\;deg\;b})^s$ < ${\infty}$}. In this note, we will show that the above result is sharp. Moreover, we also attempt to give conditions under which the above dimensional formula still valid if we require the given speed of deg $A_n(x)$ tends to infinity.

• Journal of the Korean Operations Research and Management Science Society
• /
• v.21 no.3
• /
• pp.197-214
• /
• 1996

Financial analysis of stock data usually involves extensive computation of large amount of time series data sets. To handle the large size of the data sets and complexity of the analyses, database management systems have been increasingly adaopted for efficient management of stock data. Specially, relational database management system is employed more widely due to its simplistic data management approach. However, the normalized two-dimensional tables and the structured query language of the relational system turn out to be less effective than expected in accommodating time series stock data as well as the various computational operations. This paper explores a new data management approach to stock data management on the basis of an object-oriented database management system (ODBMS), and proposes a data model supporting times series data storage and incorporating a set of financial analysis functions. In terms of functional stock data analysis, it specially focuses on a primitive set of operations such as variance of stock data. In accomplishing this, we first point out the problems of a relational approach to the management of stock data and show the strength of the ODBMS. We secondly propose an object model delineating the structural relationships among objects used in the stock data management and behavioral operations involved in the financial analysis. A prototype system is developed using a commercial ODBMS.

• KDI Journal of Economic Policy
• /
• v.23 no.1_2
• /
• pp.71-147
• /
• 2001

The structural balance is obtained by neutralizing the impact of economic cycles on the actual balance. It is often used as an indicator of the long-term stability of government finance and as a measure of fiscal stance. Many countries nowadays produce and report the estimates of their structural balances regularly, and the IMF recently advised the Korean government to adopt this practice for better fiscal transparency. This paper surveys the methodologies employed by the OECD secretariat and the IMF to estimate structural balances and apply them to the Korean data. It then computes the fiscal impulse indicator (FI) and suggests a decomposition of FI into the changes in structural expenditures and revenues. In addition, primary and operational balances are estimated. The estimated series of structural balances, one by the OECD methodology and the other by the IMF, show no sizable difference from each other. These series also follow the actual series of budget balance quite closely. The latter characteristic stems from two factors, namely the rather small GDP gap and the rather small size of the tax revenue as a share of GDP. The impulse indicator estimated for the last three decades indicates that the fiscal stance in Korea contributed to smoothing the economic cycles in about half of the times. In particular, the fiscal tightening in the early 1980s to reduce inflation resulted in a pro-cyclical movement in fiscal stance as did the expansionary policy in the early 1990s. The overall performance, however, is not bad when compared with those of other countries.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.17 no.1
• /
• pp.77-84
• /
• 2012

This paper describes the process of optimal resonant frequency design with full-bridge series-loaded resonant dc-dc converter in a high efficiency 3.3 kW on-board battery charger application for Electric Vehicles and Plug-in Hybrid Electric Vehicles. The optimal range of resonant frequency and switching frequency used for ZVS are determined by considering trade-off between loss of switching devices and resonant network with size of passive/magnetic devices. In addition, it is defined charging region of battery, the load of on-board charger, as the area of load by deliberating the characteristic of resonant. It is verified the designed frequency band by reflecting the defined area on resonant frequency.

• Proceedings of the Korean Radioactive Waste Society Conference
• /
• 2004.02a
• /
• pp.170-181
• /
• 2004

DUPIC powder and pellets were successfully fabricated in accordance with the quality assurance program described in the Quality Assurance Manual for DUPIC fuel fabrication, which was developed on the basis of the CAN3-Z299.2-85 standard. This manual describes the quality management system applicable to the activities performed for DUPIC fuel fabrication. It covers the work processes, policies and procedures used for planning, executing, and verifying the work carried out for DUPIC fuel fabrication. It is important that a Quality Program is in place before the fabrication of the fuel for irradiation testing. In order to qualify the DUPIC pellet manufacturing processes, 3 series of experiments for the pre-qualification and 3 series for the qualification were performed. In these experiments, the optimum process conditions were established. Then, under the control of the QA program, 8 series of production runs were performed to make the qualified DUPIC pellets in a batch size of 1 kg. In these production runs, DUPIC fuel pellets satisfying the standard CANDU fuel pellet specifications could be successfully produced.

• Journal of Wind Energy
• /
• v.14 no.1
• /
• pp.37-43
• /
• 2023

In this study, synthetic time series wind data was generated numerically using a second-order Markov chain. One year of wind data in 2020 measured by the AWS on Wido Island was used to investigate the statistics for measured wind data. Both the transition probability matrix and the cumulative transition probability matrix for annual hourly mean wind speed were obtained through statistical analysis. Probability density distribution along the wind speed and autocorrelation according to time were compared with the first- and the second-order Markov chains with various lengths of time series wind data. Probability density distributions for measured wind data and synthetic wind data using the first- and the second-order Markov chains were also compared to each other. For the case of the second-order Markov chain, some improvement of the autocorrelation was verified. It turns out that the autocorrelation converges to zero according to increasing the wind speed when the data size is sufficiently large. The generation of artificial wind data is expected to be useful as input data for virtual digital twin wind turbines.

• Proceedings of the KIPE Conference
• /
• 2011.11a
• /
• pp.26-27
• /
• 2011

This paper focuses on the zero-voltage/zero current transition voltage equalization circuit for the series connected battery cell. By adding auxiliary resonant cells at the main switching devices such as MOSFET or IGBT, zero current switching is achieved and turned off loss of switching elements is eliminated and by the voltage/second balancing of the inductor, zero voltage switching can be applied to switching element. Transformer coupling between battery cells and ZVZCT (Zero Voltage Zero Current Transition) switching method allow the fast balancing speed and high frequency operation, which reduces the size and weight of the circuit. The validity of the battery equalization is further verified using simulation involving four lithium-ion battery cell models.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.8
• /
• pp.1191-1199
• /
• 2003

This paper describes to observe the combustion process of only one droplet cluster. In this study, liquid fuel was atomized by ultrasonic wave to form an acoustically levitated droplet cluster. In order to elucidate the detailed structure of burning process of the droplet cluster, laser tomography method was applied. Time-series planar images of fuel droplets were processed and diameter of the each droplet was calculated based on the Mie-scattering theory. Using these data, the modified droplet group combustion number was estimated in time-series. As the result, when the internal droplet group combustion occur, the modified group combustion number dose not decrease monotonically, but show a tow-staged decreasing process. In all case of combustion process, combustion reactions were measured two types that combustion speed was fast and slow. It was casued by difference of concentration degree and droplet size distribution.