• Journal of Korea Society of Industrial Information Systems
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• v.25 no.6
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• pp.95-107
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• 2020

We analyze the performance of South Korea wholesalers and retailers during the period when COVID-19 emerged and began to spread in South Korea. Specifically, we choose operational efficiency as a proxy variable for reflecting corporate performance and apply stochastic frontier analysis for estimating operational efficiency. Importantly, in order to examine the impact of the COVID-19 period (Q1 to Q2 2020) on operational efficiency, we consider the quarterly fixed effect corresponding to the COVID-19 period. Our findings include: (ⅰ) the average level of operational ffficiency is approximately 0.7138 during the analysis period (Q1 2019 to Q2 2020); (ⅱ) the fixed effect of the COVID-19 period on operational efficiency is not significant; and (ⅲ) operational efficiency is positively correlated with the scale of the company. Moreover, from an academic perspective, we make a contribution by examining the relationship between the operational efficiency as a firm-level variable and the COVID-19 period as a macroeconomic variable.

• The Journal of Korean Association of Computer Education
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• v.13 no.1
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• pp.27-36
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• 2010

Introducing algorithm and programming education to the middle school 'Information' curriculum is appropriate to develop higher thinking skills like problem solving ability and creativity that is the most important ability to the people living in the knowledge and information society. But to providing reduced algorithm and programming contents of higher education increase the cognitive burden on the students in the concrete operational period who is not yet reached to the formal operational period, and moreover transfering principles and strategies learned in the algorithm to the programming for the problem solving is difficult. For this study, student's developmental characteristics in the concrete operational period among cognitive developmental periods was considered, and FAAP(First-Algorithm After-Programming) learning model which can transfer algorithm to programming was developed, and finally the effectiveness of learning motivation and achievement to the concrete operational period's students was verified. Results of the tests showed that learning motivation and achievement of the concrete operational period's students that learned FAAP model were different significantly.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.13 no.22
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• pp.1-6
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• 1990

This paper deals with software Release policy having a Fixed Operational period after a Software System is released. The underlying Software Reliability Growth is described by J-M Model Optimal of Software Release Time minimizing Total Expected Cost is Obtained.

• Journal of Environmental Science International
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• v.2 no.4
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• pp.317-324
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• 1993

Effluent recycling effect on UASB reactor performances is known as an important operational factor. In the present study, the possibility of intermittent recycle in UASB process for saving the power consumption was examined at different organic loading and various operational modes in recycle time period. The organic removal efficiencies of the reactors operated with the intermittent effluent recycle were considerably higher compared to those without the effluent recycle. In the intermittent recycle mode, the organic removal efficiencies slightly decreased as the non-recycle time period in the operational mode increased. Proper ratio of recycle and non-recycle time period in the mode seemed to be required to prevent the produced biogas from accumulation in the sludge bed, which caused dead zone in the reactor and sludge loss when the gas was escaped from the bed at the certain pressure.

• Journal of Korean Institute of Industrial Engineers
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• v.21 no.4
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• pp.507-517
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• 1995

The failure rate of an item depends on operational environment. When an item has a chance failure period and a wearout failure period in sequel, the severity of operational environment causes the increase in the slop of wearout failure rate or the increase in the magnitude of chance failure rate. For such a change of operational environment, this paper concerns the change of optimal preventive replacement time. Two preventive replacement policies, age replacement policy and periodic replacement policy with minimal repair, are considered. Investigated properties are: (a) in age replacement policy, optimal preventive replacement time increases as the chance failure rate increases and optimal preventive replacement time decreases as the slope of wearout failure rate increases, and (b) in periodic replacement policy with minimal repair, optimal preventive replacement time increases as the slope of wearout failure rate increases; however, the change of chance failure rate does not alter the optimal preventive replacement time.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.4
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• pp.471-478
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• 2014

Navy forces of ROK asked for more than 90% operational availability in the requirement document of combat ship. This study proposes the evaluation methodology of operational availability with the evaluation process, calculation formula, analysis of operational test data. As the case study, the developed methodology is proved to apply for 00 batch-I naval ship using the data to be acquired during the operational test period. The operational availability by test data was 90.03%, and it was satisfied with objective value 90%. The paper will contribute not only to establish the evaluation methodology of operational availability for combat ship but also other general weapon system.

• Bulletin of the Korean Space Science Society
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• 2004.10b
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• pp.376-379
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• 2004

Operational orbit determination (OOD) depends on the capability of generating accurate prediction of spacecraft ephemeris in a short period. The predicted ephemeris is used in the operations such as instrument pointing and orbit maneuvers. In this study the orbit prediction problem consists of the estimating diverse arc length orbit using GPS navigation data, the predicted orbit for the next 48 hours, and the fitted 30-hour arc length orbits of double differenced GPS measurements for the predicted 48-hour period. For 24-hour orbit arc length, the predicted orbit difference from truth orbit was 205 meters due to the along-track error. The main error sources for the orbit prediction of the Low Earth Orbiter (LEO) satellite are solar pressure and atmosphere density.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.43 no.4
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• pp.123-132
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• 2020

Currently, there are two types of trainer in Korea : basic and advanced. Both models have been in operation for more than 10 years, and compared to the early stage of operation, reliability has gradually improved and failure rates have also entered a trend of stabilization. Therefore, it is necessary to extend the maintenance period considering economic feasibility. This study investigates the three maintenance period calculation methods: NAVAIR 00-25-403 [17], DOD, U.S. [4], CERL and US Army [3], with intention to extend the maintenance period of the trainer from current 200 hours to 400 hours. In addition, the maintenance period was calculated by the three methods with actual operational data. Common standards and procedures were established to apply operational data to the existing maintenance period calculation methods, the required reliability indicators were derived, and the maintenance periods was calculated based on the results, additionally, a review on the field applicability of the three maintenance cycles was conducted. An on-site interviews were conducted with the calculation results, and 11 out of the 15 items were expected to be extended by 400 hours. It was suggested that the remaining 4 items could be extended to 400 hours by supplementing the inspection method through additional analysis such as functional analysis, inspection content verification, and site connection.

• Architectural research
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• v.14 no.1
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• pp.35-44
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• 2012

Build-Transfer-Lease (BTL) was introduced to the domestic construction market in 2005. Now, seven years later, the BTL model is most active for educational facilities. In 2011, 93 educational facility projects entered the maintenance stage. Considering the characteristics of today's BTL projects for educational facilities, the main issues are the initial performance and maintenance of educational facilities and the service-providing status for the 20-year operational management period, in relation to providing safety and convenience to students, the facility users. Seeking a solution, local education offices and departments in charge of BTL under the Ministry of Education, Science, and Technology have been exploring various methods of evaluating operational maintenance performance from various perspectives. For educational facility BTL projects, however, the appropriateness of initial operation performance evaluation, rather than considering the 20-year operational management period, is controversial in regards to sustainability. On this account, performance evaluation items in four areas-operational maintenance evaluation, facility performance status evaluation, maintenance subject evaluation, and sustainable change response evaluation-should be extracted. An indicator of facility performance evaluation is presented in this study through an AHP survey targeting experts, as part of establishing an operation performance evaluation system for educational facility BTL projects.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.3
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• pp.403-412
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• 2018

In this study, a three-dimensional variational(3DVAR) data assimilation system was developed for the operational numerical weather prediction(NWP) system at the Republic of Korea Air Force Weather Group. The Air Force NWP system utilizes the Weather Research and Forecasting(WRF) meso-scale regional model to provide weather information for the military service. Thus, the data assimilation system was developed based on the WRF model. Experiments were conducted to identify the nested model domain to assimilate observations and the period appropriate in estimating the background error covariance(BEC) in 3DVAR. The assimilation of observations in domain 2 is beneficial to improve 24-h forecasts in domain 3. The 24-h forecast performance does not change much depending on the estimation period of the BEC in 3DVAR. The results of this study provide a basis to establish the operational data assimilation system for the Republic of Korea Air Force Weather Group.