• Journal of the Korean Operations Research and Management Science Society
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• v.35 no.4
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• pp.33-53
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• 2010

When purchase prices of a raw material fluctuate over time, the total purchasing cost is mainly affected by reordering time. Existing researches focus on deciding the right time when the demand for each period is replenished at the lowest cost. However, the decision is based on expected future prices which usually turn out to include some error. This discrepancy between expected prices and actual prices deteriorates the performance of inventory models dealing with fluctuating purchase prices. In this paper, we propose a new inventory model which incorporates not only cost but also risk into making up a replenishment schedule to meet each period's demand. For each replenishment schedule, the risk is defined to be the variance of its total cost. By introducing the risk into the objective function, the variability of the total cost can be mitigated, and eventually more stable replenishment schedule will be obtained. According to experimental results from crude oil inventory management, the proposed model showed better performance over other models in respect of variability and cost.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.135-143
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• 2009

The majority of development projects fail to meet their target schedule and cost, with the overrun typically between 40 and 200 percent. These overruns happen because the planners underestimate the work or do not consider the need to rework at project planning. Representative schedule planning/management techniques such as Gantt Chart, PERT/CPM etc. that are used in domestic project planning are unable to reflect rework. This paper proposes a method to consider rework to provide more realistic estimates at schedule planning. Additionally, to prevent the underestimation of the work this paper proposes a simulation method that calculates a probabilistic estimated schedule and the associated variance based on the random variable modeling of individual task completion dates.

• Korean Management Science Review
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• v.21 no.1
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• pp.39-55
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• 2004

Efficient crew scheduling for cockpit crew is important in airline industry due to operational safety and cost associated with the flight duty time. Because of complexity of regulations imposed to the cockpit crew. it is complicated to generate an efficient schedule. Schedule of cockpit crew can be generated through two steps; selecting of flight patterns. and scheduling of them to the specific time horizon. Heuristic method is developed and applied with massive data in a limited time of computation. A set of flight patterns is selected from all possible flight patterns. which are generated by composing the flight leg based on regulations. by using the set partitioning problem with objective function of oversea stay cost. The selected set of flight patterns found at the first step is allocated to 4 week crew schedule to minimize the variance of total fight time assigned to each crew. The crew schedules obtained are evaluated and compared with the ones currently used in one of major airline company.

• Korean Journal of Construction Engineering and Management
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• v.10 no.1
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• pp.26-35
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• 2009

Work breakdown structure (WBS) can be used as an information center in earned value management system (EVMS) for the construction project. Because EVMS results, such as schedule variance and cost variance, are analyzed for the selected WBS code, the role of WBS code is important in EVMS. This study suggests a methodology for organizing WBS map with a quadrant. It can represent the project organization collectively by work level in a coordinate system. And the study developed an EVMS tool based on the WBS map and this tool can visualize various attribute indexes of EVMS by color symbols. Those methodologies can be used for improving practical application of EVMS.

• International conference on construction engineering and project management
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• 2013.01a
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• pp.403-411
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• 2013

Horizontal construction projects such as oil and gas pipeline projects typically involve repetitive-work activities with the same crew and equipment from one end of the project to the other. Repetitive scheduling also known as linear scheduling is known to have superior schedule management capabilities specifically for such horizontal construction projects. This study discusses on expanding the capabilities of repetitive scheduling to account for the variance in production rates and visual representation by developing an automated alignment based linear scheduling program for applying temporal and spatial changes in production rates. The study outlines a framework to apply changes in productions rates when and where they will occur along the horizontal alignment of the project and illustrates the complexity of construction through the time-location chart through a new linear scheduling model, Linear Scheduling Model with Varying Production Rates (LSM_VPR). The program uses empirically derived production rate equations with appropriate variables as an input at the appropriate time and location based on actual 750 mile natural gas liquids pipeline project starting in Wyoming and terminating in the center of Kansas. The study showed that the changes in production rates due to time and location resulted in a close approximation of the actual progress of work as compared to the planned progress and can be modeled for use in predicting future linear construction projects. LSM_VPR allows the scheduler to develop schedule durations based on minimal project information. The model also allows the scheduler to analyze the impact of various routes or start dates for construction and the corresponding impact on the schedule. In addition, the graphical format lets the construction team to visualize the obstacles in the project when and where they occur due to a new feature called the Activity Performance Index (API). This index is used to shade the linear scheduling chart by time and location with the variation in color indicating the variance in predicted production rate from the desired production rate.

• Journal of the Korea Institute of Building Construction
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• v.10 no.1
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• pp.199-212
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• 2010

To establish an infrastructure for technology and information in the domestic construction industry, several construction regulations pertaining to construction information have been institutionalized. However, there are major problems with the domestic information classification system, earned value management (EVM) and project management information system (PMIS). In particular, the functions of the current PMIS have consisted of a builder-oriented system, and as EVM is not applied to PMIS, the functions of reporting, analysis and forecast for owners are lacking. Moreover, owners cannot confirm information on construction schedule and cost in real time due to the differences between the EVM and PMIS operation systems. The purpose of this study is to provide a framework that is capable of operating PMIS efficiently under an e-business environment, by providing a proposal on how to establish a work breakdown structure (WBS) and an EVM - PMIS integration model, so that PMIS may provide the function of EVM, and stakeholders may have all information in common. At the core of EVM - PMIS integration is the idea that EVM and PMIS have the same operation system, in order to be an activity-based system. The principle of the integration is data integration, in which the information field of an activity is connected with the field of a relational database table consisting of sub-modules for the schedule and cost management function of PMIS using a relational database management system. Therefore, the planned value (PV), cost value (CV), actual cost (AC), schedule variance (SV), schedule performance index (SPI), cost variance (CV) and cost performance index (CPI) of an activity are connected with the field of the relational database table for the schedule and cost sub-modules of PMIS.

• Journal of Construction Engineering and Project Management
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• v.3 no.4
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• pp.5-11
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• 2013

Construction industry is overwhelmed by delay and often has suffered cost and time overrun. In this context, Last Planner System (LPS) has been considered as a very useful tool for the management of the construction process. Many previous studies have reported its effectiveness in construction performance. This study aims to evaluate the level of importance of the Last Planner processes in the Vietnam construction industry (VCI), and analyze the existing barriers when implementing these processes in construction management. These barriers were collected based on previous studies from International Group for Lean Construction (IGLC). A survey was carried out through questionnaire. The respondents are been experienced people in construction project management. There are four processes of LPS that were investigated including master schedule, phase schedule, lookahead plan, and weekly work plan. The results showed that master schedule is the most important item when performing a construction project in the VCI. The highest degree of agreement belongs to 'owner - contractor' pair with 77.1% importance indices; whereas the lowest belongs to 'consultants - contractors' pair with 63.8% importance indices. Eventually, three barrier factors were extracted from factor analysis technique with 62.2% of variance explained.

• International Journal of Contents
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• v.6 no.2
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• pp.10-13
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• 2010

For applications that are grid enabled, the grid can offer a resource balancing effect by scheduling grid jobs on machines with low utilization. When jobs communicate with each other, the internet, or with storage resources, an advanced scheduler could schedule them to minimize communications traffic or minimize the distance of the communications. We propose an intelligent load distribution algorithm to minimize communications traffic and distance of the communications using genetic algorithm. The experiments show the proposed load redistribution algorithm performs efficiently in the variance of load in grid environments.

• Korean Journal of Occupational Health Nursing
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• v.29 no.4
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• pp.306-315
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• 2020

Purpose: This study was conducted to identify the effects of caffeine intake by shift workers on sleep, considering various variable related to the sleep health of shift workers. Methods: A descriptive survey study was conducted with 128 employees who worked shifts. Respondents were surveyed on their of caffeine intake behavior, schedule type, quality of sleep, health promotion behavior, and occupational stress. Differences in their quality of sleep were assessed using the t-test and analysis of variance, while factors influencing the effect of caffeine intake on the quality of sleep were analyzed using hierarchical logistic regression. Results: The average Pittsburgh Sleep Index, Korean Version score of those surveyed was 7.3±3.25, indicating that their quality of sleep was low. On the other hand, their aveage daily intake of caffeine was 1.6±0.99 cups (1 cup =150 mL) and 116.4±77.58 mg/dL of caffeine. When the various variables that could have affected the quality of sleep were corrected, an increase in the amount of caffeine consumed was found to lead to a decrease in the quality of sleep (p=.015). Conclusion: Caffeine intake by shift workers has a significant bearing on their quality of sleep; therefore, such intake should be adjusted to improve their sleep health.

• Journal of Sasang Constitutional Medicine
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• v.24 no.2
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• pp.39-46
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• 2012

1. Objectives : The purpose of this study was to validate the Sasang Personality Questionnaire (SPQ) with Positive And Negative Affection Schedule(PANAS) for emotionality and Body Mass Index (BMI) for body constituents. 2. Methods : The SPQ along with Questionnaire for Sasang Constitution Classification (QSCC) II, PANAS, BMI was measured with 232 College students. The correlation coefficient was measured with Pearson correlation between SPQ and PANAS, BMI. The SPQ, PANAS, and BMI score of each Sasang constitution groups based on QSCCII were compared using analysis of variance and profile analysis. 3. Results : The SPQ score of each Sasang constitution groups was significantly (p<0.01) different. The SPQ showed significant correlation with PANAS Positive Affect (r=0.201, p=0.002), but not with the BMI (r=0.097, p=0.146). The SPQ-Emotionality scale, unlike other SPQ subscales, showed positive correlation with PANAS Negative Affection. 4. Conclusions : We performed the constructive validity of SPQ using PANAS and BMI. The SPQ would be useful for the study on psychophysiological mechanism of the Sasang constitutions.