• Journal of Applied Reliability
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• v.18 no.1
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• pp.1-7
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• 2018

Purpose: Maintaining appropriate operational availability (Ao) is a key element of combat victory, but estimates vary according to estimation methods. The purpose of this study is to improve the accuracy of estimating operational availability by tracing the changes of the weapon system's failure rate, repair rate, and the level of logistic support. Methods: In order to track the change in the operating availability, the MDT (mean down time) is modeled by adding the repair time and the ALDT (administration and logistic delay time) to the service time. Results: Using the field data of the weapon system A operated by the ROKAF, the failure rate follows a non-homogeneous Poisson process that changes with time, and it is modeled considering the changing repair rate and the logistic support time. Conclusion: The accuracy of the analytical results was verified by comparing the actual operating data with the estimated availability. The results of this study can be used to track and evaluate the availability in a realistic situation where the failure rate and maintenance rate continuously change in operating environment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.2
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• pp.157-164
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• 2012

When designing a multifunctional system consisting of many components performing many functions or missions, it is important to determine the reliability, availability, and maintainability (RAM) of the system and components, and we consider system availability to be the optimization criterion. For given intervals of mean time between failure (MTBF) and mean time to repair (MTTR) of the components, we want to determine the values of MTBF and MTTR for all components that satisfy the target availability. A heuristic method is proposed for finding near-optimal solutions through simulation. We also study numerical examples to check effects of model parameters on the optimal solutions.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.264-270
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• 1998

This research broadens the prime concern of nuclear power plant operations from safe performance to both economic and safe performance. First emergency diesel generator is identified as one of main contributors for the lost plant availability through the review of plants forced outage records. The framework of an integrated architecture for performing modern on-line condition for operational availability improvement is configured in this work. For the development of the comprehensive sensor networks for complex target systems, an integrated methodology incorporating a structural hierarchy, a functional hierarchy, and a fault-system matrix is formulated. The second part of our research is development of intelligent diagnosis and maintenance advisory system, which employs Bayesian Belief networks (BBNs) as a high level reasoning tool incorporating inherent uncertainty use in probabilistic inference. Our prototype diagnosis algorithms are represented explicitly through topological symbols and links between them in a causal direction. As new evidence from sensor network development is entered into the model especially, our advisory of system provides operational advice concerning both availability and safety, so that the operator is able to determine the likely modes, diagnose the system state, locate root causes, and take the most advantageous action. Thereby, this advice improves operational availability

• Journal of the Korea Institute of Information Security & Cryptology
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• v.24 no.3
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• pp.547-560
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• 2014

Smart Grid, which maximize the efficiency of energic utilization by applying Information and Communication Technology to Power Grid, requires high availability. Attacks, such as DDoS, which cause suspension of service and lead to social disruptions have recently been increasing so that systematic management over availability becomes more important. In this paper, we presents a new evaluation criteria of Korean Smart Grid by comparing availability assessment items of international standards specified in management system and then overcome the limitations of availability evaluation of existing information security management system.

• Journal of KIISE:Computer Systems and Theory
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• v.30 no.9
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• pp.445-453
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• 2003

As cluster systems used for high performance computing consist of large number of running servers, one has to solve the low availability problems occurred by the high chance of the server failures. To handle the problems, it is necessary to have the precise definition of available performance of cluster systems that represents availability and performability of the systems simultaneously. Previous research results that mention availability issues lack for concerning system performance such as waiting time and response time in their availability definition. In this paper, we propose a new availability metric for (n, k)-way cluster systems which compose of n primary servers and k backup servers. With the metric, the change of system performance according to arrival rates is captured and the waiting time of a request can be kept below to a certain level. Using various system operating parameters, we calculate availability and downtime of cluster systems along with waiting tine deadline.

• Journal of Digital Contents Society
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• v.8 no.4
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• pp.483-489
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• 2007

The high availability of information security system shall be primarily studied in relation to the Next Generation Network(NGN) Information Security infrastructure, because it is very important to maintain availability at each moment as a variety of intrusions occur continuously. The high availability of the security system can be realized with the topology and configuration properly defined to fully utilize the recovery function of the security system in the thoroughly planned optimized method. The active-active high availability on the NGN information security infrastructure system in is assured by letting the failover mechanism operate upon the entire structure through the structural design and the implementation of functions. The proposed method reduces the system overload rating due to trouble packets and improves the status of connection by SNMP polling trap and the ICMP transport factor by ping packet.

• Journal of the Korean Society for Railway
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• v.6 no.2
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• pp.108-113
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• 2003

The safety of staff, customers and of general Public in general viewed as one of the most important requirements in the urban transit. The maintenance computerization system for car of urban transit is a part of standardization and development of urban transit system, and We have been performed the establishment of maintenance computerization system from 2001 to 2005. The RAMS(reliability, availability, maintainability and safety) estimation for maintenance computerization system are utilized in a variety of computerization system for user's convenience and safety in maintenance. Ever since its inception though, the urban transit has searched for ways to improve reliability, availability, maintainability and safety of the railway subsystem. Provision of a reliable maintenance system include RAMS of the vehicles plays a very important role in achieving a safe system.

• Journal of Applied Reliability
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• v.16 no.2
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• pp.110-117
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• 2016

Purpose: Biswas and Sarkar [11] found the availability of a system maintained through several imperfect repairs before a replacement is allowed. However they missed a part of coefficients in the integration. This paper corrects the erratum of Biswas and Sarkar [11] and performs the reliability analysis incorporating the optimal number of imperfect repairs. Methods: To find the singularities and residues of the suitable complex-valued function for the availability, the computer package Matlab is used. Also the performance measures are calculated by defining and assigning costs. Results: The accurate availability functions with respect to the numbers of imperfect repairs and the optimal number of imperfect repairs before a replacement are obtained. Conclusion: The reliability for a system under imperfect repair before a replacement is analyzed using Fourier transform technique.

• Journal of the Korean Society for Railway
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• v.7 no.3
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• pp.245-250
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• 2004

The safety of staff, customers and of general Public in general viewed as one of the most important requirements in the urban transit. The maintenance computerization system for car of urban transit is a part of standardization and development of urban transit system, and We have been performed the establishment of maintenance computerization system from 2001 to 2005. The RAMS (reliability, availability, maintainability and safety) estimation for maintenance computerization system are utilized in a variety of computerization system for user's convenience and safety in maintenance. Ever since its inception though, the urban transit has searched for ways to improve reliability, availability, maintainability and safety of the railway subsystem. Provision of a reliable maintenance system include RAMS of the vehicles plays a very important role in achieving a safe system.

• Journal of Information Processing Systems
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• v.1 no.1 s.1
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• pp.96-101
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• 2005

Spotlighted as an innovative information technology environment, ubiquitous computing has been actively researched on recently. Especially, domestic and global researches focus on the RFID system, which is being eyed to replace the existing bar-code system. As an essential technology for ubiquitous computing, the RFID system can be applied for various purposes. The security issues of the RFID system focus on how the low-priced tag type could have reasonable price competitiveness. The Auto-ID Center in the U.S. is spearheading the research on distribution service and omni-directional security. As for Japan, the researches on omni-directional security and EPC application are necessary in securing the technology for ubiquitous computing with support from the Ministry of Public Management Home Affairs, Posts, and Telecommunication. In this paper, a method of ensuring the availability of the RFID system service will be presented based on the ubiquitous computing environment with the existing omni-directional security and user-friendly interface. While the existing researches focus on the RF reader system and tag-based security, this paper's suggestion also considers the availability of a sen ice to suggest ways of increasing the practical usage of a low-priced RF tag.