This paper addresses the problem of transmitting a given amount of data along a single path from the sending end node to the receiving end node in a directed network so that the performance of transmission is best. The performance of the transmission along a path is described in terms of an expression defined as performance reliability (PR). PR is a function of each link's reliability, capacity, and delay. A path is said to be a best-performing path (BPP) if the performance reliability of this path is maximum among all the available paths between the two specified nodes. The algorithm developed for selecting the best-performing path uses Dijkstra's shortest path algorithm. The proposed algorithm is more suitable for store-and-forward data transmission. The best-performing path selection is an important precomputation in developing routing protocols considering reliability, capacity and delay.
Received on February 28, 2006
References: 16

A Petri net with controller is used to model discrete events in flexible job shop scheduling problem (JSSP). It not only has the modeling capability of a traditional Petri net, but also it can depict system characteristics, such as equipment maintenance, different types of priorities, and so on. It is flexible in responding to unexpected scenario changes and is thus robust to system disturbances. The JSSP is characterized by flexible routings, and flexible machines and labors; and the scheduling results are obtained based on genetic algorithm and simulated annealing algorithm(GASA). Themethod is developed to address the dynamic scheduling problem in manufacturing systems constrained by machines and labors. After using crossover, mutation, probabilistic updating strategy and re-assignment strategy and so on genetic and simulated operation a best or second best scheduling plan can be found. Simulation results based on job shop scheduling show that the method is feasible and efficient.
Received on January 13, 2006
References: 13

We examine the behaviour of maintained systems that deteriorate according to a Non Homogenous Poisson Processes (NHPP). The system failures are selfannouncing; after each failure only a minimal repair is made so that the system failure rate l(t) (corresponding to Weibull failure distribution Weib (a,b)) is not disturbed. We propose a closed-formula for computing Mean Time between Failures as function of Mean Time to First Failure MTTF and the shape parameter b of Weibull failure distribution. This can lead to evaluate better the graceful degradation of complex system (power stations, airplanes, computers, etc.) with a minimal repair maintenance policy between replacements or overhauls.
Received on June 13, 2006
References: 05

The deterministic limit equilibrium methods are widely used for assessing the stability of slopes in geotechnical engineering practice. The input parameters required for the calculations are very often inadequate and imprecise. At times sufficient data may be available to define some of the uncertainties and at others data may be scarce or based on expert judgment. In this case former can be modeled based on probability theory and the latter needs fuzzy set theory for modeling. This is a case where both types of uncertainty are present in the same problem. This paper proposes a method of estimating reliability for fuzzy uncertain parameters, and extends further for combination of uncertainties i.e. when some uncertainties are fuzzy and others are random (Hybrid Approach). Later part is devoted to a comparison of probabilistic, fuzzy set and hybrid methods of reliability analysis with respect to its applicability for practical problems in geotechnical engineering, especially slopes. This article shows the importance of proper modeling of uncertainty. In general, possibilistic method gives the lowest value of reliability index; probabilistic method yields the highest value of reliability index, whereas the hybrid approach accommodates itself in between. This is in agreement with the consistency principles proposed by Zadeh [14].
Received on February 18, 2006
References: 15

This paper proposes an efficient cut set approach to enumerate the subsets cut groups (SCG) from apriori knowledge of minimal cutsets of a network. These SCG block a given amount of flow through the network despite the network being (s, t) connected and are being used to evaluate capacity related reliability (CRR) by employing any sum of disjoint product approach. For each minimal cutset and a given flow requirement, the proposed method enumerates the non-redundant SCG from a cut-matrix, which is constructed from the minimal cutsets information. Two simple equations are proposed to check the validity of a cut for being (i) valid SCG (as a whole) or (ii) used to enumerate its subsets from a certain order onwards to form valid SCG. Thus, an enumeration scheme to enumerate subsets of certain order from a given set is also proposed. The proposed approach is illustrated with an example and implemented using MATLAB. Several examples are solved and their results are also provided along with a comparison with recent algorithms.
Received on February 28, 2006
References: 25

In this paper, definition of L-R type triangular fuzzy set is extended by L-R type triangular vague set. Also T_w (the weakest t-norm) - based arithmetic operations between two L-R type triangular vague sets and vague success tree are introduced. Further a new approach has been developed for analyzing the fuzzy reliability of a series and parallel system using T_w - based arithmetic operations on L-R type triangular vague sets. For the justification of the proposed approach the fuzzy reliability of the desirable movement of an electric robot has been analyzed using the existing approaches [1, 3, 5] and the proposed approach. Comparing the results of existing approaches and the proposed approach, it has been shown that the uncertainty about the reliability is minimized using the proposed approach and the results are exact. While using the existing approaches the results are approximate due to approximate product of triangular fuzzy sets and triangular vague sets.
Received on April 03, 2006
References: 15

The (s,t) expected-hop-count (EHC) in a wireless communication network (WCN), modeled as a graph with probabilistic node failures, is the expected number of operational nodes that a message must traverse from a node s to reach its destination node t. A typical solution for the problem uses factoring theorem to compute the EHC of WCN. Instead, this paper proposes a 2-step approach that utilizes the sum-of-disjoint-product (SDP) technique. First, we provide an efficient technique to generate all (s,t) simple paths considering only the nodes of the WCN. We also propose an efficient algorithm to enumerate all (s,t) simple paths of an interval-graph. Second, we propose using the SDP technique over the paths to compute the reliability and EHC. We show (conjecture) that our SDP-based technique solves the reliability measures in polynomial time (pseudo-polynomial) for WCN containing all disjoint-paths (forming an interval graph). Simulations on several WCN under various conditions show that the SDP-based technique computes the reliability and EHC in several orders of magnitude faster than the existing factoring-based algorithm. The paper also discusses some application of the reliability measures.
Received on February 21, 2006
References: 16

In most practical cases, during a system failure or downtime, all non-failed components are kept idle. This phenomenon is known as suspended animation (SA). In this paper, we provide a simple and efficient method to compute the availability indices of repairable systems subjected to suspended animation. An important aspect of the proposed method is that it is not restricted to exponential failure and repair distributions. Further, the proposed method can be applied to any system configuration with embedded hierarchical k-out-of-n subsystems subjected to suspended animation.
Received on December 27, 2006
References: 04

Predecessor work introduced the "'Good Enough' to Release" (GETR ) Methodology, a process by which engineering judgment as to the acceptability and importance of disparate evidence is transformed into a system-level assessment as to the overall acceptability of a computer-based system for release to a user community. In this paper, we discuss the adaptation of the base GETR model, shown in Figure 1, for use in the assessment of performance quality of computer-based systems. Sources of appropriate quantitative and qualitative evidence are identified through a review of relevant literature and categorized as sources of either process or product evidence. The two main model branches are accordingly populated. The paper ends with a discussion of future work, including the validation of the new model, whose working name is "'Good Enough' Performance" (GEP), and suitable case studies.
Received on February 4, 2007
References: 06

A component replacement methodology for electricity transmission and distribution systems was developed to solve equipment replacement problems for systems composed of sets of heterogeneous assets subject to annual budgetary constraints over a finite planning horizon. The proposed methodology is based on an integrated dynamic and integer programming approach. First, a dynamic programming algorithm is solved for each individual component in the system. Then, two different integer programming models are applied. The first one is used to check whether a feasible system-level solution can be obtained and it is also used to identify infeasibilities for the original problem. The second integer programming model is used to find the system-level replacement schedule with the minimum cost. The method developed can potentially be applied to any replacement problem composed of sets of heterogeneous assets subject to constraints imposed on the system. However, in this work, the method is demonstrated on the replacement analysis of a common electricity distribution system configuration. The objective is to obtain the minimum cost policy such that the Net Present Value of maintenance, purchase and opportunity costs is minimized.
Received on January 29, 2007
References: 12