• Journal of Korean Society of Industrial and Systems Engineering
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• v.21 no.47
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• pp.47-55
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• 1998

This paper proposes a maintenance model considering the Inherent availability of certain requirement and two types of failures, repairable or irrepairable. In this model, the system is replaced in time when it doesn't meet the inherent availability requirement despite of all repairable failures; Otherwise it is replaced by the first irrepairable failure. Assuming that the j-th failure is repairable with probability ${\alpha}_j$, minimal repairs are performed for repairable failures between replacements. We drive the expected cost rate through the application of NHPP(Non-Homogeneous Poisson Process) in order to determine the optimal number $n^*$. The model includes some previous studies as special cases.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.28 no.1
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• pp.97-104
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• 2005

Considered is the concurrent spare part(CSP) requirements problem of new equipment system. In the considered system, when a part fails, the part cannot be repaired and should be replaced. In addition, cannibalization is allowed. It is assumed that the failure of a part follows a Poisson process. The operational availability concept in CSP is defined, and a formula is derived to calculate the operational availability using expected machine operating time during CSP period. The problem is formulated as the operational availability maximization problem with available budget constraint and a heuristic solution search procedure is developed. An illustrative example is shown to explain the solution procedure.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.30 no.1
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• pp.115-121
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• 2007

In this paper, we study flowshop scheduling problems with availability constraints. In such problems, n jobs have to be scheduled on m machines sequentially under assumption that the machines are unavailable during some periods of planning horizon. The objective of the problem is to find a non-permutation schedule which minimizes the makespan. As a solution procedure, we propose an improved genetic algorithm which utilizes a look-ahead schedule generator to find good solutions in a reasonable time Computational experiments show that the proposed genetic algorithm outperforms the existing genetic algorithm.

• Journal of the military operations research society of Korea
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• v.7 no.2
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• pp.43-62
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• 1981

Computational expressions for point availability and average availability of a system of components each of which is subject to random failures and has random restoration times are determined. Each component is assumed to have a fixed number of spares such that where all spares are exhausted no restoration can take place. These expressions are useful in deciding PL and ASL in the military logistic applications. Given a fixed length of mission duration and finite number of spares, a system may not be available at the end of a mission due to lack of spares. The probability distribution of system down time due to lack of spares is determined as a function of number of spares and mission duration.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.4
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• pp.813-818
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• 2015

In this paper, WiMedia Distributed-MAC protocol is adopted for development of a seamless N-screen wireless service. Furthermore, to provide the OSMU (One Source Multi Use) N-screen service through P2P streaming in the seamless D-MAC protocol, a new Multicast-free DRP Availability IE is proposed and analyzed. In this Multicast-free DRP Availability IE, indicating Multicast DRP Owner and Receiver is required. The ACK frame transmissions are not required for Multicast transmissions in P2P N-screen services. Using this property, the Multicast-free DRP Availability IE scheme is proposed to expand the number of time slots available for unicast and multicast DRP reservations. Simulation results show that our Multicast scheme enhances performances in vewpoints of DRP reservation conflict and throughput.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.33 no.3
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• pp.199-207
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• 2010

In this paper considered is the provisioning quantity determination problem of consumable concurrent spare parts (CSP) of a new equipment system to minimize the procurement cost under the operational availability constraint. When a part fails, repair of the failed part is impossible and the part is replaced and cannibalization is allowed. The failure of a part is assumed to follow a Poisson process and the operational availability in CSP is defined. The solution procedure consists of two parts. Firstly, a heuristic algorithm is developed under the assumption that the failure rate is constant during the CSP period. Secondly, proposed is a simulation search procedure which improves the heuristic solution to the near optimal solution in a reasonable amount of time. An illustrative example is shown to explain the solution procedure.

• Journal of the Korea Computer Industry Society
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• v.3 no.2
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• pp.227-234
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• 2002

An cluster web server system, one has the problem that does the low availability occured by the high chance of the server failures and it is not easy to provide high performance and availability occuring software aging. In this paper, running cluster web sewers consists of n primary servers and k backup servers, propose software rejuvenation model on performance and switchover time. Based on the various system operational parameters, we calculate to evaluate the rejuvenation policy such steady-state probabilities, availability, and downtime cost. And we validate the solutions of mathematical model by experiments based on various operation parameters and fud that the software rejuvenation method can be adopted as prventive fault tolerant technique for stability of system.

• Journal of Applied Reliability
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• v.7 no.1
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• pp.13-22
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• 2007

A preventive maintenance model, caller FNBM (${\alpha},{\delta},{\gamma}$) model, is proposed to decide an optimal repair number under achieved availability requirements (r) along with taking two types of failures (repairable or irrepairable) into account. In this model, the current system is replaced by a new one in case when it doesn't meet the achieved availability requirement, even though it is repairable failure; Othewise it is replaced in time of the first irrepairable failure. Assumed that the j-th failure is repairable with probability ${\alpha}_j$ minimal repairs are allowed for repairable failure between replacements. Expected cost rate for preventive maintenance model is developed using NHPP (Non - Homogeneous Poisson Process) in order to de term in the optimal number $n^*$, also numerical examples are shown in order to explain the proposed model. Since the proposed FNBM (${\alpha},{\delta},{\gamma}$) model includes Park FNBM model (1979) and Nakagawa FNBM (p) model (1983) m this proposed model is thought to be better than previous model, especially for weapon system which requires availability as primary parameter.

• Safety and Health at Work
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• v.10 no.2
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• pp.166-171
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• 2019

Objective: This study explored personal protective equipment (PPE) availability and PPE utilization among interventionalists in the catheterization laboratory, which is a highly contextualized workplace. Methods: This is a cross-sectional study using mixed methods. Participants (108) completed a survey. A hyperlink was sent to the participants, or they were asked to complete a paper-based survey. Purposively selected participants (54) were selected for individual (30) or group (six) interviews. The interviews were conducted at conferences, or appointments were made to see the participants. Logistic regression analysis was performed. The qualitative data were analyzed thematically. Results: Lead glasses were consistently used 10.2% and never used 61.1% of the time. All forms of PPE were inconsistently used by 92.6% of participants. Women were 4.3 times more likely to report that PPE was not available. PPE compliance was related to fit and availability. Conclusions: PPE use was inconsistent and not always available. Improving the culture of radiation protection in catheterization laboratories is essential to improve PPE compliance with the aim of protecting patients and operators. This culture of radiation protection must include all those involved including the users of PPE and the administrators and managers who are responsible for supplying sufficient, appropriate, fitting PPE for all workers requiring such protection.

• ETRI Journal
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• v.41 no.4
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• pp.473-482
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• 2019

High availability and reliability have been considered promising requirements for the support of seamless network services such as real-time video streaming, gaming, and virtual and augmented reality. Increased availability can be achieved within a local area network with the use of the virtual router redundancy protocol that utilizes backup routers to provide a backup path in the case of a master router failure. However, the network may still lose a large number of packets during a failover owing to a late failure detections and lazy responses. To achieve an efficient failover, we propose the implementation of fast detection with virtual router redundancy protocol (FDVRRP) in which the backup router quickly detects a link failure and immediately serves as the master router. We implemented the FDVRRP using open neutralized network operating system (OpenN2OS), which is an open-source-based network operating system. Based on the failover performance test of OpenN2OS, we verified that the FDVRRP exhibits a very fast failure detection and a failover with low-overhead packets.