Home  About us  Contact
 

System Lifetimes (system + lifetime)

Distribution by Scientific Domains
Information Science and Computing40%

Selected Abstracts

Behavioural modelling of long-lived evolution processes,some issues and an example

JOURNAL OF SOFTWARE MAINTENANCE AND EVOLUTION: RESEARCH AND PRACTICE, Issue 5 2002
M. M. Lehman
Abstract For reasons now well understood, application software that is regularly used for real-world problem solving must be continually adapted and enhanced to maintain its fitness to an ever-changing real world, its applications and application domains. This type of activity is termed progressive. As evolution continues, the complexity (functional, structural) of the evolving system is likely to increase unless work, termed anti-regressive, is undertaken to control and even reduce it. However, with progressive and anti-regressive work naturally competing for the same pool of resources, management requires means to estimate the amount of work and resources to be applied to each of the two types. After providing a necessary background, the paper describes a systems dynamics model that can serve as the core of a tool to support decision making regarding the optimal personnel allocation over the system lifetime. The model is provided as an example of the use of formalisms in modelling the behaviour of the evolution process. Copyright © 2002 John Wiley & Sons, Ltd. [source]

A general model of heterogeneous system lifetimes and conditions for system burn-in

NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2003
Kyungmee O. Kim
Abstract Burn-in is a technique to enhance reliability by eliminating weak items from a population of items having heterogeneous lifetimes. System burn-in can improve system reliability, but the conditions for system burn-in to be performed after component burn-in remain a little understood mathematical challenge. To derive such conditions, we first introduce a general model of heterogeneous system lifetimes, in which the component burn-in information and assembly problems are related to the prediction of system burn-in. Many existing system burn-in models become special cases and two important results are identified. First, heterogeneous system lifetimes can be understood naturally as a consequence of heterogeneous component lifetimes and heterogeneous assembly quality. Second, system burn-in is effective if assembly quality variation in the components and connections which are arranged in series is greater than a threshold, where the threshold depends on the system structure and component failure rates. © 2003 Wiley Periodicals, Inc. Naval Research Logistics 50: 364,380, 2003. [source]

Performance analysis and improvement for BitTorrent-like file sharing systems

CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 13 2007
Ye Tian
Abstract In this paper, we present a simple mathematical model for studying the performance of the BitTorrent (http://www.bittorrent.com) file sharing system. We are especially interested in the distribution of peers in different states of the download job progress. With the model we find that the distribution of the download peers follows an asymmetric U-shaped curve under the stable state, due to BitTorrent's unchoking strategies. In addition, we find that the seeds' departure rate and the download peers' abort rate will influence the peer distribution in different ways notably. We also analyze the content availability under the dying process of the BitTorrent file sharing system. We find that the system's stability deteriorates with decreasing and unevenly distributed online peers, and BitTorrent's built-in ,tit-for-tat' unchoking strategy could not help to preserve the integrity of the file among the download peers. We propose an innovative ,tit-for-tat' unchoking strategy which enables more peers to finish the download job and prolongs the system's lifetime. By playing our innovative strategy, download peers could cooperate to improve the stability of the system by making a trade-off between the current downloading rate and the future service availability. Finally, experimental results are presented to validate our analytical results and support our proposals. Copyright © 2007 John Wiley & Sons, Ltd. [source]

On the application and extension of system signatures in engineering reliability

NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2008
Jorge Navarro
Abstract Following a review of the basic ideas in structural reliability, including signature-based representation and preservation theorems for systems whose components have independent and identically distributed (i.i.d.) lifetimes, extensions that apply to the comparison of coherent systems of different sizes, and stochastic mixtures of them, are obtained. It is then shown that these results may be extended to vectors of exchangeable random lifetimes. In particular, for arbitrary systems of sizes m < n with exchangeable component lifetimes, it is shown that the distribution of an m -component system's lifetime can be written as a mixture of the distributions of k -out-of- n systems. When the system has n components, the vector of coefficients in this mixture representation is precisely the signature of the system defined in Samaniego, IEEE Trans Reliabil R,34 (1985) 69,72. These mixture representations are then used to obtain new stochastic ordering properties for coherent or mixed systems of different sizes. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008 [source]