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On new aging classes based on the reversed mean residual life order

Ahmadi K., Rezaei M.

Control and Cybernetics

2013

Vol. 42, no. 3

727--737

In this paper, we introduce new concepts of aging for lifetime distributions. The main idea is the comparison between reversed mean residual life of the random variables X and (X − t | X > t), for all t > 0. Firstly, with some examples, we highlight the role of the proposed aging classes in reliability and life testing. Then, we try to find the connection between the new aging classes and other aging classes well-known from the literature. Reliability properties of the new classes are studied. Formally, we derive the preservation property under monotonic transformations. Some Rother characterization and implications are studied.

(Bi2Te3)0:25(Sb2Te3)0:75 crystal structure improvements with excess Te as studied by AFM, SEM, EBSD and XRD

Kavei G., Ahmadi K., Shadmehr A. K., Kavei A.

Materials Science Poland

2011

Vol. 29, No. 2

144--151

(Bi2Te3)x(Sb2Te3)1-x solid solutions with x = 0:2, 0.25 and 0.3 - p type thermoelectric compounds with an excess of Tellurium dopant up to 4 wt% were crystallized. By increasing the Bi2Te3 content in the Bi-Sb-Te system, the hole concentration decreased and in consequence caused an optimum Seebeck coefficient and a decrease in electrical conductivity and thermal conductivity, thus resulting in an increase in the figure of merit at x = 0:25. The results showed that optimum thermoelectric properties can be achieved for a mixture of x = 0:25 with 3 wt% Te added. Structural characterizations of this compound in the absence and presence of the dopant were carried out by means of X-Ray diffraction measurement, scanning electron microscopy, electron backscattering diffraction and atomic force microscopy. Detailed analyses confirm that the improvements in thermoelectric parameters due to the intrinsic structure and minimum defects during crystallization of the compounds result from the excess of Te.