• Journal of the Korean Operations Research and Management Science Society
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• v.17 no.2
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• pp.123-130
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• 1992

The model of k-out-of n : G repairable system with identical components is extended to a repairable system with n different components. The objective is to analytically derive the mean time of the busy period for a k-out-of-n : G system with unrestricted repair. Then, the lower and upper bounds on the average time of the busy period of the n-component system with restricted repair are also shown.

• Proceedings of the Safety Management and Science Conference
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• 2000.11a
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• pp.39-52
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• 2000

This paper is concerned with the method of estimating lifetime distribution for field data in warranty period and for a situation where some additional field data can be gathered after the warranty period. Implementing the proposed methods in this paper will result in obtaining the more precise product life time estimation and product improvement.

• Journal of the Korea Safety Management & Science
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• v.3 no.4
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• pp.65-76
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• 2001

Field data have been recorded as the time to failure or the number of failure of systems. We consider the time to failure and covariate variables in some pre-specified follow-up or warranty period. This paper aims to investigate study on the reliability estimation when some additional field data can be collected within-warranty period or after-warranty period. A various likelihood-based methods are outlined and examined for exponential or Weibull distribution.

• Korean Journal of Organic Agriculture
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• v.29 no.4
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• pp.507-521
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• 2021

The livestock farmers are producing under uncertainties such as Foot-and-Mouth Disease (FMD) and Free Trade Agreement (FTA). The purpose of this study is to strengthen the management capabilities of Hanwoo farmers to prepare them for the uncertainties just mentioned. To this end, this study was conducted to find the optimal rearing period in order to reduce the feed cost, which accounts for the largest portion of the operation cost of Hanwoo. Using the universal lattice model, 41,139 of 289,000 Hanwoo slaughter data from 2010 to 2019 were used for the FMD period and 246,605 heads for the general period. The results show that the maximum cutoff price of Hanwoo steer is 6,394,457 won at the 4th week of 27 months of age in general period, where as 6,242,752 won at the 2nd week of 26 months of age in the FMD period. Therefore, it is judged that it will be helpful for Hanwoo farms to maximize their business profits by slaughtering one month and two weeks earlier in the FMD period than in the general period. In addition, Hanwoo farmers need to break away from the conventional rearing method and improve their management efficiency through a more flexible rearing method.

• Korean Journal of Soil Science and Fertilizer
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• v.48 no.6
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• pp.641-647
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• 2015

Monitoring of soil fertility by long-term application of fertilizers is necessary to improve the fertility of soil and the productivity of crop. The objective of this study was conducted to investigate the changes of exchangeable Mg by continuous application of fertilizers from 1969 to 2014. The treatments were no fertilization (No fert.) and fertilization (NPK, NPK+C, NPK+S, and NPK+CS). The concentration of exchangeable Mg in No fert., NPK+C, and NPK+S treatments tended to increase from 1965 to 1975, but decrease gradually from 1976 to 1987, and increase again after 1988. Based on these, the changes of exchangeable Mg were divided into period I ('69 ~'75), period II ('76~'87), and period III ('88~'14). Especially, exchangeable Mg decreased in the period II. This was presumed that a significant amount of Mg from topsoil were leached into subsoil by break of plow pan and some of subsoil was incorporated into topsoil according to change of plowing depth by replacement of tillage machinery. It could be possible that exchangeable Mg in NPK, NPK+S, and NPK+CS was accumulated in the depth of 15~20 cm. For the period III, exchangeable Mg in No fert., NPK, NPK+C, NPK+S, and NPK+CS treatments increased at rates of 0.013, 0.018, 0.015, 0.023, and $0.024cmolckg^{-1}{\cdot}yr^{-1}$ respectively. Exchangeable Mg level in NPK+S was lower than the other treatments in the period I and period II, but higher than in the period III. This result was attributed to replacement of silicate fertilizer type from wollastonite (Mg 0.3%) to silicate fertilizer (Mg 3%). Also, exchangeable Mg level of No fert. treatment increased, which showed that Mg concentration of irrigated water had the greatest impact on Mg accumulation of soil. Recently, Mg level of irrigated water tended to increase, indicating that Mg concentration of water will affect greatly the concentration of exchangeable Mg of soil in the future. Like these, the changes of exchangeable Mg were greatly influenced by agricultural environment such as plowing depth, plow pan, content of fertilizer, and quality of irrigated water. Considering these agricultural environment, the proper management of soil is needed for the improvement of soil fertility and crop productivity.

• IE interfaces
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• v.10 no.1
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• pp.119-134
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• 1997

The management of blood inventory is very important within the medical care system. The efficient management of blood supplies and demands for transfusions is of great economic and social importance to both hospitals and patients. For any blood type, there is a complex interaction among the optimal inventory level, daily demand level, daily supply level, transfusion to crossmatch ratio, crossmatch release period, issuing policy and the age of arriving units that determine the shortage and outdate rate. In this paper, we develop an efficient decision rule for blood inventory management in a hospital blood bank which can support efficient hospital blood inventory management using simulation. The primary use of the efficient decision rule will be to establish minimum cost function which consists of inventory levels, period in inventory, outdate and shortage rate for whole blood and various component inventories for a hospital blood bank or a transfusion service. If the administrator compute the mean daily demand for each blood type, the mean daily supply for each blood type, the length of the crossmatch release period and the average transfusion to crossmatch ratio, then it is possible to apply the efficient decision rule to compute the optimal inventory level, inventory period, outdate and shortage rate. This rule can also be used as a decision support system that allows the blood bank administrator to do sensitivity analysis related to controllable blood inventory parameters.

• Atmosphere
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• v.22 no.3
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• pp.381-386
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• 2012

The monthly number of days with rain or snow in Seoul extends backward to 1626 from the present. The number of rain and snow days are from the ancient records and combined with the modern precipitation records from 1907 to the present. There are two distinct and abrupt changes in the time series, which allow us to divide the entire period into three sub-periods of CR-I, CR-II, and MR. For each sub-period, we calculated the basic statistics and the associated distributions. The analysis proves Seoul, which may comprise East Asia when considering the lengthy period of dry condition, had dry climate for the Maunder Minimum when Europe experienced cold climate. We also note relationships between the rain days and sunspot numbers in various frequency bands.

• Korea Journal of Hospital Management
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• v.22 no.1
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• pp.21-39
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• 2017

Purpose : This study was intended to investigate the structural relationship among empowerment, self-efficacy, job motivation, autonomy, critical thinking, job-satisfaction, burnout, and self-achievement. In addition, we tested the moderating effect of the career period on the influence of empowerment. Methodology : The structural equation model was used to test the causal relationship between factors, and t-test, ANOVA, descriptive statistics are applied to analyze the research data. Findings : The result of this study shows that the structural model that is the empowerment encourages the self-efficacy, job motivation, autonomy, and critical thinking, also these factors affect the self-achievement through both the job-satisfaction and burnout is acceptable according to the goodness of fitness indices. In addition, we show that the career period moderates the influence of empowerment on the self-efficacy, job-motivation, and autonomy, but not critical thinking. Usually, the shorter the career period is the higher the influence of empowerment is. This moderating effect means that to give proper empowerment to lower position nurses encourage them, and prevent from burnout. Therefore, they feel job-satisfaction and finally self-achievement. Practical Implications : The empowerment helps the nurse to activate self-efficacy, job motivation, autonomy, critical thinking. Hence, these factors decrease burn-out but increase job satisfaction. Finally a sense of self-perfection increase.

• Journal of Distribution Science
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• v.17 no.4
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• pp.5-16
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• 2019

Purpose - This study examines whether price cartel firms perform downward earnings management to avoid or minimize penalty surcharges levied by the Korea Fair Trade Commission and analyzes such earnings management in distribution industry. Research design, data, and methodology - We use 247 firms from 64 price cartel cases in the period of 2011-2016, and collect data from 3 years before to 3 years after the start of price cartel. Earnings management is measured by discretionary accruals. Three discretionary accrual estimation models are employed; modified Jones model, ROA adjusted modified Jones model and CFO-adjusted modified Jones model. For pre- and post-cartel periods, one year, two year, and three year windows are used. Additional empirical analyses are performed for distribution industry sub-sample of 25 cartel firms. Result - The regression results show that cartel firms' discretionary accruals are significantly lower in the period after the start of price cartel than before. And discretionary accruals are lower in cartel firms than in non-cartel firms during the cartel period. Cartel firms in distribution industry also show the earnings management similar to those in other industries. Conclusions - These two findings lead to the conjecture that managers of cartel firms manage their earnings downward. This behavior is indistinguishable between firms in distribution industry and other industries.

• Smart Media Journal
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• v.12 no.11
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• pp.95-102
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• 2023

Road accidents not only caused loss of human lives but also costed 3% of gross domestic product in most of the countries. The road accidents pose significant challenges to public safety and urban transportation management. There is a need to identify the high-risk area of accidents along with the critical day of week and vulnerable time period in order to implement effective preventive measures and optimizing the resource allocation. We collected 5,012 accident data from 대구교통종합정보. This study identified the high-risk locations, days of week, and time periods for accidents in Daegu and estimated the conditional probabilities of accidents occurring based on combinations of location, day of the week, and time period. The result is visualized in the form of dashboard in Tableau. This study holds substantial practical significance for urban planners, transportation authorities, and policymakers in Daegu to strategically allocate resources for traffic management, law enforcement, and targeted safety campaigns.