The behaviour of the hazard rate of the lognormal random variable, as has been reported in some recent publications, is quite misleading. This paper mainly attempts to put forth the true behaviour of the hazard rate of lognormal distribution, after carrying out analytical and numerical investigations. It has been shown, using method of calculus that the hazard rate is a unimodal function with convexity upwards. This typical behaviour is not acceptable in reliability engineering. The true behavior of the hazard rate has been numerically simulated in MATLAB, Version 7.0, with appropriate case studies. The findings of the investigation are discussed and conclusion drawn.
Received on March 27, 2007
References: 08

An interconnection network system consists of layers of switching elements connected together in a predefined topology providing the connectivity between the set of processors and the set of memory modules. Performance analysis of a network system is important as it determines the usability and the efficiency of the network to provide services. A shuffle-exchange network (SEN), a specific type of Multistage Interconnection Network (MIN) that consists of 2x2 switching elements, has been widely considered as a practical interconnection system. This paper presents a network reliability model based on a minimum cut set method for SEN systems. A general equation for large-scale network reliability is derived subsequently to reduce the complexity of the reliability analysis for the interconnection network system.
Received on September 17, 2007
References: 17

A novel structural performance/health assessment method, denoted as GILS-EKF-UI, is under development by the research team at the University of Arizona. The procedure is essentially inverse solution of a system identification-based algorithm in the presence of uncertainty. The unique feature of the algorithm is that it can identify members' properties and in the process access the performance/health of a structural system using only noise-contaminated dynamic response information measured at few locations completely ignoring the excitation information. The experimental and analytical verification of the method is emphasized in this paper. To verify the GILS-EKF-UI method using minimum response information, a substructure is considered. A two-dimensional defect-free steel frame is identified using limited analytical (noise-free and noise-contaminated) and experimental responses. Several defects were then introduced in the frame. Two defects in particular; by removing a member and by reducing the cross sectional area of a member over a finite length, are presented in the paper. In all cases, the GILS-EKF-UI method predicted the health of the frame by correctly identifying the defect and its location, conclusively establishing the viability of the novel concept.
Received on August 02, 2007
References:19

This paper suggests failure analysis of mechanical systems using function cum structure approach. Operational parameters of system function are identified and their relationships are developed. The predicates, which comprise of components of the system and their properties as their attributes, i.e., type of connectivity (fixed or sliding contact) and functions (transmit torque, and transmit force etc.) represent the facts. The facts are modelled in terms of functional-cum-structure graph. By analyzing interaction of a failure function i.e., function of a failed component in the graph with other functions, the failure cause-function is identified. The problem can either be solved by removing the cause-functions or by modifying the failure function. A critical function is also identified from function set on the basis of importance of a function. Appropriate parameters for in-situ design provision for condition monitoring of the system are also identified. Various steps of the methodology are illustrated by means of an example.
Received on April 04, 2007
References: 32

This paper summarizes the state of knowledge and ongoing research on methods and techniques for resilience evaluation, taking into account the resilience-scaling challenges and properties related to the ubiquitous computerized systems. We mainly focus on quantitative evaluation approaches and, in particular, on model-based evaluation techniques that are commonly used to evaluate and compare, from the dependability point of view, different architecture alternatives at the design stage. We outline some of the main modeling techniques aiming at mastering the largeness of analytical dependability models at the construction level. Actually, addressing the model largeness problem is important with respect to the investigation of the scalability of current techniques to meet the complexity challenges of ubiquitous systems. Finally we present two case studies in which some of the presented techniques are applied for modeling web services and General Packet Radio Service (GPRS) mobile telephone networks, as prominent examples of large and evolving systems.
Received on July 26, 2007
References: 47

Equipment deteriorates as it is used and its vibration level usually increases accordingly. As a result, vibration has been used as an indicator of equipment health condition. Effective prediction of equipment deterioration trend can help prevention of equipment breakdown. However, little work has been done in machine degradation forecasting based on vibration data. Support Vector Machines (SVM) is a new tool for solving regression and classification problems. Successful applications of SVM for time series predictions reported in the literature motivates this study to use SVM for vibration trend prediction. This paper describes applications of SVM in vibration trend prediction. We compare the results obtained from time series forecasting methods and SVM.
Received on May 30, 2007
References: 14

In this paper, Hotelling’s T² chart and the DPCA(Dynamic PCA)-based T_A²
and Q charts are applied to real oil data histories obtained from condition monitoring of
heavy hauler truck transmissions. The objective is to evaluate the impending failure
detection capability and the false alarm rate of the control charts in a CBM (conditionbased
maintenance) application. When applied to failure histories, both T² and Q
charts were able to correctly identify the impending failures in more than 50% cases, but
the number of false alarms was considerably higher for the T² chart.
Received on May 24, 2007
References: 08

In this short communication, we have explored and compared the performance of Alternate Phase Return-to-Zero (APRZ) modulation format on both strongly and weakly managed dispersion maps with varying path average dispersion values. Our findings show that, as opposed to 0 or 180 deg APRZ, 90 deg APRZ is more efficient for both strongly and weekly managed dispersion maps in minimizing Intra Channel Four-wave Mixing (IFWM) for reliable 40Gb/s transmission.
Received on October 09, 2007
References: 03

One-way ANOVA (analysis of variance) is widely used in quality engineering for quality characteristics comparison. The basic assumption in applying ANOVA is that the response is normally distributed. However, in life tests, the times to failure usually do not follow this assumption. In this paper, a method similar to the regular one-way ANOVA is proposed for reliability assessment. A generalized linear model together with a likelihood ratio test is developed. The proposed method can be used to compare the reliability of different designs. It also can be applied to study whether a factor has an effect on product life.
Received on November 05, 2007
References: 04