Current Issue : October - December Volume : 2012 Issue Number : 4 Articles : 4 Articles
A four-parameter family of Weibull distributions is introduced, as an example of a more general class created along the lines\r\nof Marshall and Olkin, 1997. Various properties of the distribution are explored and its usefulness in modelling real data is\r\ndemonstrated using maximum likelihood estimates....
We address the challenge of link estimation and routing over highly dynamic links, thats is, bursty links that rapidly shift between\r\nreliable and unreliable periods of transmissions. Based on significant empirical evidence of over 100,000 transmissions over\r\neach link in 802.15.4 and 802.11 testbeds, we propose two metrics, expected future transmissions (EFT) and MAC3, for runtime\r\nestimation of bursty wireless links.We introduce a bursty link estimator (BLE) that based on these two metrics, accurately estimates\r\nbursty links in the network rendering them available for data transmissions. Finally, we present bursty routing extensions (BRE):\r\nan adaptive routing strategy that uses BLE for forwarding packets over bursty links if they offer better routing progress than longtermstable\r\nlinks. Our evaluation, comprising experimental data from widely used IEEE 802.15.4-based testbeds, reveals an average\r\nof 19% and a maximum of 42% reduction in the number of transmissions when routing over long-range bursty links typically\r\nignored by routing protocols. Additionally, we show that both BLE and BRE are not tied to any specific routing protocol and\r\nintegrate seamlessly with existing routing protocols and link estimators....
In this paper, based on the kinematic accuracy theory and matrix-based system reliability analysis\r\nmethod, a practical method for system reliability analysis of the kinematic performance of planar\r\nlinkages with correlated failure modes is proposed. The Taylor series expansion is utilized to derive\r\na general expression of the kinematic performance errors caused by random variables. A proper\r\nlimit state function performance function for reliability analysis of the kinematic performance of\r\nplanar linkages is established. Through the reliability theory and the linear programming method\r\nthe upper and lower bounds of the system reliability of planar linkages are provided. In the course\r\nof system reliability analysis, the correlation of different failure modes is considered. Finally, the\r\npracticality, efficiency, and accuracy of the proposed method are shown by a numerical example....
In this work, Probabilistic Safety Assessment (PSA) is used to evaluate Allowed Outage Times (AOT) and Surveillance Test Intervals\r\n(STI) extensions for three Angra 1 nuclear power plant safety systems. The interest in such an analysis lies on the fact that\r\nPSA comprises a risk-based tool for safety evaluation and has been increasingly applied to support both the regulatory and the\r\noperational decision-making processes. Regarding Angra 1, among other applications, PSA is meant to be an additional method\r\nthat can be used by the utility to justify Technical Specification relaxation to the Brazilian regulatory body. The risk measure used\r\nin this work is the Core Damage Frequency, obtained from the Angra 1 Level 1 PSA study. AOT and STI extensions are evaluated\r\nfor the Safety Injection, Service Water and Auxiliary Feedwater Systems using the SAPHIRE code. In order to compensate for the\r\nrisk increase caused by the extensions, compensatory measures as (1) test of redundant train prior to entering maintenance and (2)\r\nstaggered test strategy are proposed. Results have shown that the proposed AOT extensions are acceptable for two of the systems\r\nwith the implementation of compensatory measures whereas STI extensions are acceptable for all three systems....
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