Current Issue : July - September Volume : 2016 Issue Number : 3 Articles : 4 Articles
The coefficient of reliability is often estimated from a sample that includes few subjects. It is\ntherefore expected that the precision of this estimate would be low. Measures of precision such as\nbias and variance depend heavily on the assumption of normality, which may not be tenable in\npractice. Expressions for the bias and variance of the reliability coefficient in the one and two way\nrandom effects models using the multivariate Taylor�s expansion have been obtained under the\nassumption of normality of the score (Atenafu et al. [1]). In the present paper we derive analytic\nexpressions for the bias and variance, hence the mean square error when the measured responses\nare not normal under the one-way data layout. Similar expressions are derived in the case of the\ntwo-way data layout. We assess the effect of departure from normality on the sample size requirements\nand on the power of Wald�s test on specified hypotheses. We analyze two data sets, and\ndraw comparisons with results obtained via the Bootstrap methods. It was found that the estimated\nbias and variance based on the bootstrap method are quite close to those obtained by the\nfirst order approximation using the Taylor�s expansion. This is an indication that for the given data\nsets the approximations are quite adequate....
As a reliability quantitative specification, parametric accelerated life testing was used to assess\nthe reliability of a newly designed compressor of a commercial refrigerator subjected to repetitive\nstresses. A generalized life-stress failure model and new sample size equation with a new load\nconcept were derived starting with the basic refrigeration cycle. The sample size equation with\nthe acceleration factor also enabled the parametric accelerated life testing to quickly evaluate the\nexpected lifetime. The design of this testing should help an engineer uncover the design parameters\naffecting reliability during the design process of the compressor system. Consequently, it\nshould help companies improve product reliability and avoid recalls due to the product failures in\nthe field. A newly designed compressor in a commercial refrigerator was used as a test case....
In the present article we study the production of grape molasses. Data drawn from a specified biolaboratory,\nare properly analyzed in order to detect factors that affect significantly the Brix value\nand the volatile acidity of the final product. The ground that is used for planting and a variety of\ngrapes have been taken into account. Off-line statistical quality control techniques have been employed\nand the outcomes are displayed and discussed in detail....
Smart grids have been constructed so as to guarantee the security and stability of the power\ngrid in recent years. Power transformers are a most vital component in the complicated smart grid\nnetwork. Any transformer failure can cause damage of the whole power system, within which the\nfailures caused by overloading cannot be ignored. This research gives a new insight into overload\ncapability assessment of transformers. The hot-spot temperature of the winding is the most critical\nfactor in measuring the overload capacity of power transformers. Thus, the hot-spot temperature\nis calculated to obtain the duration running time of the power transformers under overloading\nconditions. Then the overloading probability is fitted with the mature and widely accepted Weibull\nprobability density function. To guarantee the accuracy of this fitting, a new objective function is\nproposed to obtain the desired parameters in the Weibull distributions. In addition, ten different\nmutation scenarios are adopted in the differential evolutionary algorithm to optimize the parameter\nin the Weibull distribution. The final comprehensive overload capability of the power transformer is\nassessed by the duration running time as well as the overloading probability. Compared with the\nprevious studies that take no account of the overloading probability, the assessment results obtained\nin this research are much more reliable....
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