COHERENT STRUCTURES AND UNIMODALITY

This paper is concerned with the preservation of unimodality under coh erent structures of independent components having a common life distri bution function. This result in a way generalizes a result of Alam [1] , as Alam's result indirectly also deals with preservation of unimodal ity for (n-i+1)-out-of-n systems of independent and identically distri buted components. The usefulness of this property of coherent systems in obtaining sharper upper bounds on the reliability of the concerned system has been illustrated below for a bridge structure with componen ts having a gamma life distribution function.