Reliability Theory

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).

Mathematical education is essential for the study of psychology, and is especially important for individuals who will engage themselves in research work in this field of social sciences. The variance and covariance are statistical concepts which are important primarily in the analysis of variance, regression analysis, calculating reliability coefficients, as well as determining the extent of variation in the raw scores of the tasks and the overall test. Psychology students often have difficulties in understanding these concepts, which can be improved by providing practical examples in the form of carefully selected problems for exercise and for testing their knowledge. In this paper, it has also been given a short discussion about statistical reasoning.

Improvement factors in hazard rate and age for a sequential preventative maintenance (PM) policy are introduced. Two imperfect PM models are analyzed: (1) PM reduces the hazard rate while it increases with the number of PMs, and (2) PM reduces the age. The PM is done at intervals xk (k=1,2, . . . , N) and is imperfect. The optimal

Reliability analysis has been supporting
energy operations planning studies in a very significant way,
specially to obtain predictive indexes of peak load supply.
During the last couple of years, due to high growth rates of
peak load, Brazilian organism for Coordination of the
Interconnected Operation (GCOI) decided to implement
reliability studies in the short-term operations planning. The
multi-area methodology that has been used in the long-term
planning was extended and now, important information to the
short-term planning, like probability distribution function of
the EPNS, is available.

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

The characterizations described use relations between the failure rate function and conditional expectation. The theorems proved here extend the results of some authors and can be used in the context of the renewal process. The utility of these results is demonstrated by using them to characterize some common distributions

Since the late 90's IP telephony, commonly referred to as Voice over IP (VoIP), has been presented as a revolution on communications enabling the possibility to converge historically separated voice and data networks, reducing costs, and integrating voice, data and video on applications. This paper presents a study over the standard VoIP protocols H.323, session initiation protocol (SIP), media gateway control protocol (MGCP), and H.248/Megaco. Given the fact that H.323 and SIP are more widespread than the others, we focus our study on them. For each of these protocols we describe and discuss its main capabilities, architecture, stack protocol, and characteristics. We also briefly point their technical limitations. Furthermore, we present the advanced multimedia system (AMS) project, a new system that aims to operate on Next Generation Networks (NGN) taking the advantage of its features, and it is viewed as the successor to H.323 and SIP.

Summary form only given. This work presents a methodology for calculating the optimal generation capacity reserve and siting in power systems planning. The proposed methodology is based on a least-cost planning approach which considers along the planning horizon, the capacity reserve investment costs and the operational expected costs, comprising thermal generation and interruption costs. This problem is solved by using the Benders decomposition technique in which investment and operation subproblems solutions are obtained iteratively and separately thus allowing the use of tailor-made algorithms for each subproblem. The operation subproblem corresponds to a probabilistic evaluation of the minimum operation cost in composite generation/transmission systems, in which the system states are selected through Monte Carlo simulation or state enumeration and the system performance is analysed by a nonlinear optimal power flow solved by an interior point algorithm. The proposed methodology is illustrated in a case study with a modification of the IEEE Reliability Test System (MRTS).

A National Aeronautics and Space Administration (NASA) supported Reliability, Maintainability, and Availability (RMA) analysis team developed a RMA analysis me thodology that uses cut set and importance measure analyses to compare model proposed avionics computing architectures. In this paper we will present an effective and efficient application of the RMA analysis methodology for importance measures that includes Reliability Block Diagram (RBD) Analysis, Comparison modeling, Cut Set Analysis, and Importance Measure Analysis. In addition, we will also demonstrate that integrating RMA early in the system design process is a key and fundamental decision metric that supports design selection. The RMA analysis methodology presented in this paper and applied to the avionics architectures enhances the usual way of predicting the need for redundancy based on failure rat es or subject matter expert opinion. Typically, RBDs and minimal cut sets along with the Fussell-Vesely (FV) method is used to calculate importance measures are calculated for each functional element in the architecture [1]. This paper presents an application of the FV importance measures and presents it as a methodology for using importance measures in success space to compare architectures. These importance measures are used to identify which functional element is most likely to cause a system failure, thus, quickly identifying the path to increase the overall system reliability by either procuring more reliable functional elements or adding redundancy [2]. This methodology that used RBD analysis, cut set analysis, and the FV importance measures allowed the avionics design team to better understand and compare the vulnerabilities in each scenario of the architectures. It also enabled the design team to address the deficiencies in the design architectures more efficiently, while balancing the need to design for optimum weight and space allocations.

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

The redundancy allocation problem (RAP) has been studied for many different system structures, objective functions, and distribution assumptions. In this paper, we present a problem formulation and a solution methodology to maximize the system steady-state availability and minimize the system cost for the repairable series-parallel system designs. In the proposed approach, the components’ time-to-failure (TTF) and time-to-repair (TTR) can follow any distribution such as the Gamma, Normal, Weibull, etc. We estimate an approximation of the steady-state availability of each subsystem in the series-parallel system with an individual meta-model. Design of experiment (DOE), simulation and the stepwise regression are used to build these meta-models. Face centred design, which is a type of central composite design is used to design experiments. According to a max–min approach, obtained meta-models are utilized for modelling the problem alongside the cost function of the system. We use the augmented ε-constraint method to reformulate the problem and solve the model. An illustrative example which uses the Gamma distribution for TTF and TTR is explained to represent the performance of the proposed approach. The results of the example show that the proposed approach has a good performance to obtain Pareto (near-Pareto) optimal solutions (system configurations).

This paper proposes a novel virtual Content-Aware Network (CAN) layer as a part of a full layered architecture, focused, but not limited to, on multimedia distribution with Quality of Services (QoS) assurance. The overall system is based on a flexible cooperation between providers, operators and end-users, enabling users to access the offered multimedia services in various contexts and also to become private content providers. The paper introduces the main concepts and architecture for the main virtual network layer (i.e., CAN), exposing its role and interfaces among overall system layers. This work is a part of the starting effort inside of a new European FP7 ICT research project, ALICANTE.

In this paper we propose an improved BDD approach to the network reliability analysis, that allows the user to compute an exact solution or an approximation based on reliability bounds when network complexity makes the former solution practically impossible. To this purpose, a new algorithm for encoding the connectivity graph on a Binary Decision Diagram (BDD) has been developed; it reduces the computation memory peak with respect to previous approaches based on the same type of data structure without increasing the execution time, and allows us also to derive from a subset of the minpaths/mincuts a lower/upper bound of the network reliability, so that the quality of the obtained approximation can be estimated. Finally, a fair and detailed comparison between our approach and another state of the art approach presented in the literature is documented through a set of benchmarks.

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