Reliability Theory

We present a foundational theory of software system re-liability based on components. The theory describes how component developers can design and test their components to produce measurements that are later used by system de-signers to calculate composite system reliability — ...

Based on the nature of the upper- and lower-bound block diagram models of multistage interconnection networks (MINs), a series system consisting of independent subsystems is considered. To model the reliability of such a system with online repair and imperfect coverage, the usual approach is to construct and solve a large, overall Markov model. A two-level hierarchical model is instead proposed in which each subsystem is modeled as a Markov chain and the system reliability is then modeled as a series system of independent Markov components. This technique is extended to compute the instantaneous availability of the system with imperfect coverage and online repair. Extensions to allow for transient faults and phase-type repair time distributions are straightforward. It should be possible to apply this approach to other fault-tolerant MINs and to any system that can be modeled as a series system where each subsystem has a parallel-redundant structure

In this research, it was aimed to develop an instrument for determining problematic
internet usage of university students. Factorial structure of the data collected from
1658 university students revealed three factors. Of these, the first factor is called negative
consequences of the internet and accounted for 25.36% of the variance, the second
factor is called social benefit / social comfort and accounted for 14.62% of the variance,
and the third factor is called excessive usage and explained 8.98 % of the variance.
All three factors consisting of 33 items accounted for the 48.96% of the total
variance. It was found that the scale was able to discriminate problematic internet use
with respect to the time spent on the internet and individuals’ perception of themselves
as the internet addicts. The correlation between the scale and the Davis’s Online
Cognitive Scale-Turkish adaptation (Keser Özcan ve Buzlu, 2005) was found as
0.61. Internal consistency coefficient of the scale (α) was found to be 0.94. Item total
correlations ranged between 0.31 and 0.70 (p<.001). Test-re-test reliability coefficient
was found to be 0.81 and split half reliability coefficient was found to be 0.83. Thus,
the scale called as “the Problematic Internet Usage Scale” was developed.

The aim of the current study was to develop a short form of Coping Styles Scale based on COPE
Inventory. A total of 275 undergraduate students (114 female, and 74 male) were administered in
the first study. In order to test factors structure of Coping Styles Scale Brief Form, principal components
factor analysis and direct oblique rotation was used. Factor analysis Results indicated
that Coping Styles Scale Brief Form had 14 factors with two items. All factors explained 80.37% of
the variance in the scale. In order to test concurrent validity of CSS-BF, the relationship between
coping styles, social desirability, self-esteem, life satisfaction and A type personality were examined.
Cronbach’s alfa coefficient of subscales ranged from 0.39 (Restraint Coping) to 0.92 (Humor)
and test re-tests (two weeks interval) coefficients were ranged from .44 (Restraint Coping) to .90
(Religion).

The intuition of data reliability has recently been incorporated into the main stream of research on ordered weighted averaging (OWA) operators. Instead of relying on human-guided variables, the aggregation behavior is determined in accordance with the underlying characteristics of the data being aggregated. Data-oriented operators such as the dependent OWA (DOWA) utilize centralized data structures to generate reliable weights, however. Despite their simplicity, the approach taken by these operators neglects entirely any local data structure that represents a strong agreement or consensus. To address this issue, the cluster-based OWA (Clus-DOWA) operator has been proposed. It employs a cluster-based reliability measure that is effective to differentiate the accountability of different input arguments. Yet, its actual application is constrained by the high computational requirement. This paper presents a more efficient nearest-neighbor-based reliability assessment for which an expensive clustering process is not required. The proposed measure can be perceived as a stress function, from which the OWA weights and associated decision-support explanations can be generated. To illustrate the potential of this measure, it is applied to both the problem of information aggregation for alias detection and the problem of unsupervised feature selection (in which unreliable features are excluded from an actual learning process). Experimental results demonstrate that these techniques usually outperform their conventional state-of-the-art counterparts.

We consider repairable reliability systems with m components, the lifetimes and repair times of which are independent. The l-th component can be either in the failure state 0 or in the perfect state dl or in one of the degradation states {1, 2,..., dl − 1}. The time of staying in any of these states is a random variable following a discrete distribution not geometric. Thus, the state of every component and consequently of the whole system is described by a discrete-time semi-Markov chain together with the backward recurrence chain. Using recently obtained results concerning the discrete-time semi-Markov chains, we derive basic reliability measures in a general form. Finally, we present some numerical results of our proposed approach in specific reliability systems. 1 The General Model Let us consider a multi-state system (MSS) of order m, which means that it consists of m components which in their run are multi-state. As usually, the states of components determine the state of the s...

The performance of space and frequency diversity techniques at 1800 MHz in an indoor environment are investigated. Three linear signal combining techniques are considered: signal selection (SEL), maximal ratio combining (MRC), and equal gain combining (EGC). The computations of received fading envelopes are performed by means of an analytical model, based on a three-dimensional ray-tracing (RT)/uniform theory of diffraction (UTD) technique; the reliability of the adopted approach is confirmed by comparison with some test measurements. The electromagnetic field components are adequately processed to obtain the single branch and combined signal envelope. The results show the very significant benefits that can be achieved both in terms of diversity gain and diversity advantage for both diversity techniques. Antenna spacings of about 0.75-1λ are nearly sufficient for achieving optimum performance, whereas frequency separation on the order of 10 MHz is needed for sufficiently decorrelated transmission on the two carriers

This paper develops the asymptotic sampling distribution of the inverse of the coefficient of variation (InvCV). This distribution is used for making statistical inference about the population CV (coefficient of variation) or InvCV without making an assumption about the population distribution. It applies to making inferences (point and interval estimation, and hypothesis-testing) about the shape parameter of some popular lifetime distributions like the Gamma, Weibull, and log-normal, when the scale parameter is unknown. The test procedure is used to test exponentiality against a Gamma or a Weibull alternative. The results are compared with those in the literature

An approach to the optimization of software reliability is proposed. The emphasis is put on the software redundancy to achieve fault tolerance, i.e. the results of the optimization process are used to determine the optimal structure of the software to be developed. Two optimization models are formulated covering, respectively, modified recovery block scheme and multiversion programming approaches. Both cases are illustrated by simple examples. The models show that it is possible to formulate and solve some software related reliability optimization problems. They further show that the concept of redundancy to achieve fault tolerance (basic for the traditional theory of reliability) can be used in the field of software reliability optimization