• 한국수소및신에너지학회논문집
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• 제21권6호
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• pp.513-518
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• 2010

In the present work the second-order perturbation solutions of the simple physical model for liquid pool spreading is obtained for the case of instantaneous spill. To generalize the solution governing equations are non-dimensionalized, and two dimensionless parameters, dimensionless evaporation rate and aspect ratio of the initial pool, are identified to control the governing equations. The dimensional governing equations have three parameters. The second-order solution improves fairly the first-order solution for the pool volume.

• ETRI Journal
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• 제41권2호
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• pp.207-223
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• 2019

Network function virtualization can significantly improve the flexibility and effectiveness of network appliances via a mapping process called service function chaining. However, the failure of any single virtualized network function causes the breakdown of the entire chain, which results in resource wastage, delays, and significant data loss. Redundancy can be used to protect network appliances; however, when failures occur, it may significantly degrade network efficiency. In addition, it is difficult to efficiently map the primary and backups to optimize the management cost and service reliability without violating the capacity, delay, and reliability constraints, which is referred to as the reliability-aware service chaining mapping problem. In this paper, a mixed integer linear programming formulation is provided to address this problem along with a novel online algorithm that adopts the joint protection redundancy model and novel backup selection scheme. The results show that the proposed algorithm can significantly improve the request acceptance ratio and reduce the consumption of physical resources compared to existing backup algorithms.

• 한국신뢰성학회지:신뢰성응용연구
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• 제15권3호
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• pp.207-215
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• 2015

Safety' can be used in a variety of ways and may also have different meanings when used in theoretical field and routinely used. In this paper, the 'safety' means that human injury, fire or physical accident condition does not occur while used by the end-user. The meaning of safety may be different by era and culture. Even in contemporary era, the meaning can be used differently by country, region and culture. As the rights of consumers are increasingly reinforced, we can expect the acceptable risk or safety level can rise higher. In this paper, the R-map of Japan and the European risk assessment guidelines (RAPEX) were reviewed considering domestic incidents database status and its applicability. Because it is difficult to make a model based on a R-map, a revised model was developed mainly based on European Assessment Model with a combination of the important characteristics of Japan model R-map. Also utilizing this revised model, the availability as a new risk assessment model was confirmed by comparing the test results for the same scenarios to the other risk assessment model (RAPEX/RAG).

• 한국통신학회논문지
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• 제38C권12호
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• pp.1170-1178
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• 2013

최근 항공기, 잠수함, 로봇 등 고도의 신뢰성이 요구되는 군사무기체계 분야에 상용 필드버스의 적용이 활발히 이루어지고 있다. 잠수함 전투체계 역시 대표적인 군사용 전자 장비로서 다양한 컴퓨터와 센서 및 액추에이터들이 실시간 네트워크로 연결되어 있다. 잠수함의 작전수행능력 및 생존성과 직결되는 전투체계용 네트워크는 매우 높은 수준의 신뢰성을 만족해야 된다. 그 결과 잠수함 전투체계의 구성장비들을 제어하기 위한 필드버스로써 표준 CAN(Controller Area Network)을 기반으로 채널과 제어기를 이중화한 이중채널 CAN 버스가 주로 이용되고 있다. 본 논문에서는 Petri Net을 이용하여 이중채널 CAN 버스의 신뢰도 분석 모델을 제시한다. 기존연구에서는 네트워크를 통한 정보전송 성능 분석에 주안점이 주어졌으나, 본 논문에서는 CAN의 다양한 물리적 고장 유형을 반영하여 GSPN(Generalized Stochastic Petri Nets) 모델을 제안한다. 제안된 모델을 기반으로 고장율과 고장복구율을 변경하면서 각 고장 유형이 이중채널 CAN 버스의 신뢰도에 미치는 영향을 분석한다.

• 한국철도학회논문집
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• 제20권3호
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• pp.349-355
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• 2017

철도시스템의 고장은 운행지연 또는 철도사고의 원인이 될 수 있으며, 철도안전을 확보하기 위하여 높은 신뢰성이 요구된다. 철도시스템은 신뢰도 및 가용도를 높이기 위하여 동일 시스템을 다중으로 구성하여 동작 중인 시스템에 고장이 발생한 경우에 대기 시스템이 정상 동작을 수행하도록 설계한다. 일반적으로 시스템의 신뢰도는 시스템을 구성하는 각 요소의 신뢰도를 사용하여 분석하며, 시스템간의 물리적, 기능적, 프로세스적 독립이 보장되지 않는 다중 시스템의 경우는 다중 시스템에 동시에 고장을 유발하는 공통원인고장을 고려하여야 한다. 본 논문에서는 철도 시스템에서 사용되고 있는 대기 이중계 시스템에 대하여 각 시스템이 독립일 경우와 공통원인고장을 고려한 종속일 경우에 대한 신뢰도를 분석하였다. 신뢰도 분석을 위하여 다중계 구조의 다양성과 시스템 상태 전이별로 모델링이 가능한 마코브 모델을 사용하였으며, 공통고장모드의 분석 유무의 차이점 평가를 통해 시스템 신뢰도평가의 정확도 향상 방안을 제시한다.

• 품질경영학회지
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• 제44권1호
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• pp.121-138
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• 2016

Purpose: Financial institute employees have various education programs for enhancing customer satisfaction. The purpose of this study is to explore critical factors that affect the service commitment in the financial institution and to propose the implication for employee's service involvement. Methods: This study is intended to identify how service quality of education, servicescape, and learning motivation affect the service commitment. The research model proposed in this study is tested via a survey of 322 employees for financial institution employees. Results: This study shows that tangibles, reliability, assurance and ambient condition, physical structure, symbolic artifacts and internal motivation, extrinsic motivation significantly influence education satisfaction. Tangibles, reliability and ambient condition, physical structure, symbolic artifacts and internal motivation significantly influence affective service orientation and that tangibles, reliability, assurance and extrinsic motivation significantly influence altruistic service orientation. It also verifies that education satisfaction affective service orientation, and altruistic service orientation positively affect service commitment. Conclusion: This study suggests critical factors to promote service commitment in the financial institute. It has focused on not only the service quality of education program, but also servicescape and learning motivation as the meaningful factors for increasing the employee's service involvement.

• Physical Therapy Rehabilitation Science
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• 제12권3호
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• pp.346-354
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• 2023

Objective: The objective of this study is to provide medical institutions with theoretical basis by analyzing the effect of service quality-related factors. It will be helpful for hospitals to enhance service quality which will be of use to attain customer satisfaction and ultimately competitive advantage. Design: An empirical study. Methods: To verify the model, I conducted a questionnaire survey analysis. Items for measurement have been extracted from several related studies on medical industry. The survey target has been set by convenience sampling method and consists of citizens reside in Seoul and Gyeonggi-do Province, and total number of 161 samples have been analyzed. To verify validity and reliability, I conducted factor analysis and reliability analysis, and for hypotheses verification, multiple regression analyses have been performed. Results: This study aims to investigate the relation between service quality factors and customer satisfaction, and also those factors and customer loyalty. Service quality factors consist of Tangibles(X1), Reliability(X2), Assurance(X3), Responsiveness(X4), and Empathy(X5). According to the results of regression analyses, X1, X2, X3, and X5 have been proved to have positive relations with customer satisfaction and loyalty, whereas hypothesis related X4 has not been supported. Finally, customer satisfaction has been founded to affects positively to customer loyalty. Conclusions: Service quality factors are significantly related to customer satisfaction and loyalty. So medical institutions should aware of this and try to enhance service quality for attaining competitive advantage.

• 대한기계학회논문집A
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• 제33권10호
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• pp.1163-1170
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• 2009

Reliability analysis is of great importance in the advanced product design, which is to evaluate reliability due to the associated uncertainties. There are three types of uncertainties: the first is the aleatory uncertainty which is related with inherent physical randomness that is completely described by a suitable probability model. The second is the epistemic uncertainty, which results from the lack of knowledge due to the insufficient data. These two uncertainties are encountered in the input variables such as dimensional tolerances, material properties and loading conditions. The third is the metamodel uncertainty which arises from the approximation of the response function. In this study, an integrated method for the reliability analysis is proposed that can address all these uncertainties in a single Bayesian framework. Markov Chain Monte Carlo (MCMC) method is employed to facilitate the simulation of the posterior distribution. Mathematical and engineering examples are used to demonstrate the proposed method.

• International Journal of Internet, Broadcasting and Communication
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• 제12권3호
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• pp.156-162
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• 2020

Wireless Sensor Network (WSN) field is mainly studied to monitor and characterize large-scale physical environments to track various environmental or physical conditions, such as temperature, pressure, wind speed and humidity. WSN can be used in various applications such as wild surveillance, military target tracking and monitoring, dangerous environmental exploration and natural disaster relief. We design probabilistic mobile models that apply to mobile ad hoc network mobile environments. A probabilistic shift model proposed by dividing the number of moving nodes and the distance of travel into two categories to express node movement characteristics. The proposed model of movement through simulation was compared with the existing random movement model, ensuring that the width and variation rate of the first node node node node (FND) was stable regardless of the node movement rate. In addition, when the proposed mobile model is applied to the routing protocol, the superiority of network life can be verified from measured FND values. We overcame the limitations of the existing random movement model, showing excellent characteristics in terms of energy efficiency and stable in terms of changes in node movement.

• International Journal of Reliability and Applications
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• 제2권3호
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• pp.189-197
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• 2001

The estimation of mean lifetimes in presence of interval censoring with mixed replacement procedure is examined when the distributions of lifetimes are exponential. It is assumed that, due to physical restrictions and/or economic constraints, the number of failures is investigated only at several inspection times during the lifetime test; thus there is interval censoring. The maximum likelihood estimator is found in an implicit form. The Cramor-Rao lower bound, which is the asymptotic variance of the estimator, is derived. The estimation of mean lifetimes for competing failures model has been expanded.