• 한국해양공학회지
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• 제36권5호
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• pp.326-339
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• 2022

Recently, not only Korea but also the world has been suffering from problems related to coastal erosion. The hard defense method has been primarily used as a countermeasure against erosion. However, this method is expensive and has environmental implications. Hence, interest in other alternative methods, such as the eco-friendly vegetation method, is increasing. In this study, we aim to analyze the hydraulic characteristic of submerged rigid vegetation according to the cross-sectional change through a hydraulic experiment and numerical simulation. From the hydraulic experiment, the reflection coefficient, transmission coefficient, and energy dissipation coefficient were analyzed according to the density, width, and multi-row arrangement of the vegetation zone. From numerical simulations, the flow field, vorticity distribution, turbulence distribution, and wave distribution around the vegetation zone were analyzed according to the crest depth, width, density, and multi-row arrangement distance of the vegetation zone. The hydraulic experiment results suggest that the transmission coefficient decreased as the density and width of the vegetation zone increased, and the multi-row arrangement condition did not affect the hydraulic characteristics significantly. Moreover, the numerical simulations showed that as the crest depth decreased, the width and density of vegetation increased along with vorticity and turbulence intensity, resulting in increased wave height attenuation performance. Additionally, there was no significant difference in vorticity, turbulence intensity, and wave height attenuation performance based on the multi-row arrangement distance. Overall, in the case of submerged rigid vegetation, the wave energy attenuation performance increased as the density and width of the vegetation zone increased and crest depth decreased. However, the multi-row arrangement condition did not affect the wave energy attenuation performance significantly.

• 유통과학연구
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• 제14권8호
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• pp.45-50
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• 2016

Purpose - This study aimed to develop a new practical and universally applicable service quality model by improving the service quality measurement model proposed by many previous studies. Research design, data, and methodology - An in-depth analysis on what influences such service quality model had on the improvement effect of service quality, and Service Evaluation Model("SEM"), which was revised from the existing service quality measurement model, was developed. The model is divided into the two integrative categories: First, activity, that is the group of service-related activities. Next is item, the group of service-related objects. The level of service is evaluated for each category via survey questionnaire on service level evaluation. Based on the model, SEM has visibility by structuring the whole service industry. Results - For the application of the new service quality model, this study attempted to examine the appropriateness of the newly proposed service quality model by applying it to retail service field. Conclusions - As a result, the proposed service model would be a useful and applicable service quality measurement model required by many organizations. Service company can set up self check service levels. Through these results, they can look for the ways to provide better services to customers. Service users can ensure the objectivity of business plan based upon SEM.

• 대한수학회지
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• 제59권6호
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• pp.1185-1201
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• 2022

Feller introduced an unfair-fair-game in his famous book [3]. In this game, at each trial, player will win 2^k yuan with probability p_k = 1/2^kk(k + 1), k ∈ ℕ, and zero yuan with probability p₀ = 1 - Σ^∞_k=1 p_k. Because the expected gain is 1, player must pay one yuan as the entrance fee for each trial. Although this game seemed "fair", Feller [2] proved that when the total trial number n is large enough, player will loss n yuan with its probability approximate 1. So it's an "unfair" game. In this paper, we study in depth its convergence in probability, almost sure convergence and convergence in distribution. Furthermore, we try to take 2^k = m to reduce the values of random variables and their corresponding probabilities at the same time, thus a new probability model is introduced, which is called as the related model of Feller's unfair-fair-game. We find out that this new model follows a long-tailed distribution. We obtain its weak law of large numbers, strong law of large numbers and central limit theorem. These results show that their probability limit behaviours of these two models are quite different.

• Ocean Systems Engineering
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• 제6권2호
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• pp.161-189
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• 2016

This paper provides a practical stochastic method by which the maximum equilibrium scour depth around a vertical pile exposed to random waves plus a current on mild slopes can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Battjes and Groenendijk (2000) wave height distribution for mild slopes including the effect of breaking waves, and using the empirical formulas for the scour depth on the horizontal seabed by Sumer and Fredsøe (2002). The present approach is valid for wave-dominant flow conditions. Results for random waves alone and random wave plus currents have been presented and discussed by varying the seabed slope and water depth. An approximate method is also proposed, and comparisons are made with the present stochastic method. For random waves alone it appears that the approximate method can replace the stochastic method, whereas the stochastic method is required for random waves plus currents. Tentative approaches to related random wave-induced scour cases on mild slopes are also suggested.

• Ocean Systems Engineering
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• 제7권3호
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• pp.275-298
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• 2017

This paper provides a practical stochastic method by which the maximum equilibrium scour depth below a pipeline exposed to random waves plus a current on mild slopes can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Battjes and Groenendijk (2000) wave height distribution for mild slopes including the effect of breaking waves, and using the empirical formulas for the scour depth on the horizontal seabed by Sumer and Fredsøe (1996). The present approach is valid for wave-dominant flow conditions. Results for random waves alone and random wave plus currents have been presented and discussed by varying the seabed slope and water depth. An approximate method is also proposed, and comparisons are made with the present stochastic method. For random waves alone it appears that the approximate method can replace the stochastic method, whereas the stochastic method is required for random waves plus currents. Tentative approaches to related random wave-induced scour cases for random waves alone are also suggested.

• 한국물환경학회지
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• 제33권3호
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• pp.311-325
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• 2017

Habitat suitability index (HSI) of 17 benthic macroinvertebrate taxa, which were lotic insects of generic category except Potamanthidae in mayfly, was developed for three physical habitat factors (current velocity, water depth and substrate) based on an ecological monitoring in a Korean stream (Gapyeong). Weibull model was used as a probability density function to analyze the distribution of individual abundance related with physical factors, which showed it was so available. Number of species and total individual abundance increased along with the increase of current velocity and the mean diameter of substrate, and decreased along with the increase of water depth. Most taxa showed a clear preference for a fast current velocity, shallow water depth and coarse substrate except Ephemera, Potamanthidae (mayfly), and Plectrocnemia (caddisfly) which were rheophobic, potamophilic and lithophobious. Based on the canonical correspondence analysis, the relative importance of each factor was determined as follows: current velocity > substrate > water depth.

• 산경연구논집
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• 제12권7호
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• pp.15-25
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• 2021

Purpose: The greatest asset to all organizations is the employees and they should be guarded against factors hindering their work ability. Nevertheless, most organizations are always more concerned about making profits to the extent of forgetting their employee's welfare. On this point, this study aims to examine employee's work-related stress and its relationship with work ability. Research design, data and methodology: This study focused on obtaining mostly peer-reviewed works to suggest research findings, assuming that qualitative literature approach allows researchers to explore in-depth information concerning complex issues in a standard life setting. Numerous prior researchers applied their research design in content analysis, especially where various concepts are present for analysis. Results: Based on numerous qualitative textual resources, this study found that human resource practitioners should plan stress management strategies for their employees to apply five kinds of solutions that the current study suggests because it is vital to ensure their wellbeing towards sustaining their performance. Conclusions: All in all, based on the findings, this study concludes that employee's work stress negatively impacts their work ability with affecting their mental health. As a result, there is little doubt that practitioners should regularly monitor the working environment for stress-related factors besides creating a healthy working environment for all employees.

• 한국재료학회지
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• 제20권11호
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• pp.581-585
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• 2010

High strength sheet steels for automobile are seriously compromised by hydrogen embrittlement. This issue has been continuously studied, but the field of interest, which lies between microstructural characteristics and hydrogen behavior with hydrogen charging, has not yet been thoroughly investigated. This study was done to investigate the behavior of hydrogen according to the hydrogen volume fraction on 590MPa grade DP steels, which are developed under hydrogen charging conditions as high strength sheet steels for automobiles. The penetration depths and the mechanical properties, according to charging conditions, were investigated through the distribution of micro-hardness and the microstructural observation of the subsurface zone. It was found that the amount of hydrogen trapping in 590MPa DP steels was related to the austenite volume fraction. It was confirmed that the distribution of micro-hardnesses according to the depth of the subsurface zone under the free surface showed the relationship of the depth of the hydrogen saturation between the charging conditions.

• 유통과학연구
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• 제18권12호
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• pp.45-54
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• 2020

Purpose: Indonesia's maritime logistics and distribution system is currently faced with several challenges, some of which include prolonged export and import time for goods handling as well as the high logistics cost. This study further analyzes the existing business processes in maritime logistics in East Java Province in order to provide solutions to the challenges. Research design, data and methodology: This research was carried out in East Java Province, Indonesia, with data collected through field observations, documentation, and in-depth interviews with all the stakeholders involved. Results: The study showed that the number of stakeholders and activities involved in the flow of goods movement ultimately impacted the length of time. These factors can be classified into the following five: 1) export and import regulations, 2) third party logistics competencies, 3) transportation infrastructure and facilities, 4) adoption of information systems and technology, and 5) maritime line connectivity. Conclusion: Analyzing the three supply chain flows in the maritime logistics and distribution industry called for the need for improvement to increase coordination among related institutions, improve the flexibility of dwelling time to the conditions of each port, enhance service levels, improve transportation infrastructure and facilities, implement information system and technology, and develop shipping routes and networks. Therefore, a collaborative supply chain management system can be realized.

• 유통과학연구
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• 제22권7호
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• pp.23-32
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• 2024

Purpose: Increasingly limited environmental resources encourage all sectors to implement robust distribution systems, including Logistics Service Provider (LSP) as a company that manages customer logistics activities. However, efforts to achieve a robust distribution system have many challenges. To overcome these challenges, as a first step, LSP needsto classify and analyze the challenges faced and find solutions. Knowledge of the challengesin managing robust logisticsisstill not widely researched in developing countries. This paper explores existing research gaps in the region. Research design, data and methodology: The research enquiries used are a questionnaire and in-depth interviews. In the field study, surveys, observations, interviews related to robust logistics implementation in the LSP were carried out. Results: The results of the study show that although robust logistics is recognized as very important, understanding among LSPs is still very diverse. The main challengesfound in this study come from the economic aspect and the internal conditions of the organization. Conclusion: LSP is advised to carry out internal strengthening of the company, especially for economic and organizational aspects therefore they can implement robust and sustainability practices more intensively. LSP needs to have good financial support in order to implement the aspects on an ongoing basis.