Two‐stage component test plans for testing the reliability of a series system

A system reliability is often evaluated by individual tests of components that constitute the system. These component test plans have advantages over complete system based tests in terms of time and cost. In this paper, we consider the series system with n components, where the lifetime of the i‐th component follows exponential distribution with parameter λ_i. Assuming test costs for the components are different, we develop an efficient algorithm to design a two‐stage component test plan that satisfies the usual probability requirements on the system reliability and in addition minimizes the maximum expected cost. For the case of prior information in the form of upper bounds on λ_i's, we use the genetic algorithm to solve the associated optimization problems which are otherwise difficult to solve using mathematical programming techniques. The two‐stage component test plans are cost effective compared to single‐stage plans developed by Rajgopal and Mazumdar. We demonstrate through several numerical examples that our approach has the potential to reduce the overall testing costs significantly. © 2002 John Wiley & Sons, Inc. Naval Research Logistics, 49: 95–116, 2002; DOI 10.1002/nav.1051     

Looking ahead in India

India and China contain more than 40% of the world's population, yet in India it is painfully clear that the political commitment necessary to tackle India's greatest problem is not there in full measure. India's present per capita income is less than $300, and nearly 65% of the people live below the poverty line. The average Indian woman produces 5 children; even if the Indian government's efforts to reduce family size to 2 children is successful by the year 2040, India will have a population of 2.5 billion. The possibility that India will succeed in reducing average family size to 2 children appears remote. 30 years ago, India became the 1st developing country to formally make family planning a matter of national policy. In the early years of the national family planning programs, practitioners had access mostly to sterilization and condoms. Over the years, theIndian government persuaded the US and other western donors to give $2 billion to population control programs. Still, the population continues to grow annually at the rate of 2.1%. Government statistics reflect the ups and downs of national population control policies; thenumber of new family planning users increased from 4.3 million in 1974-1975 to 12.5 million in 1976-1977, due largely to a dramatic increase in vasectomies. Tge number of new contraceptive users fell to 4.5 million after the "emergency" was lifted in 1977. The present Indian generation is far more receptive culturally as well as sociologically to the concept of population control than most other developing countries. What is needed now is renewed political committment by the Gandhi adminiostration. India cannot afford to replicate the Chinese way of tackling overpopulation without inflicting human abuses and without undermining its painstakingly cultivated democratic system.     

The interactive fixed charge linear programming problem

In many decision-making situations, each activity that can be undertaken may have associated with it both a fixed and a variable cost. Recently, we have encountered serveral practical problems in which the fixed cost of undertaking an activity depends upon which other activities are also undertaken. To our knowledge, no existing optimization model can accomodate such a fixed cost structure. To do so, we have therefore developed a new model called the interactive fixed charge linear programming problem (IFCLP). In this paper we present and motivate problem (IFCLP), study some of its characteristics, and present a finite branch and bound algorithm for solving it. We also discuss the main properties of this algorithm.     

求取鱼雷转角射击转角的实用算法

较为详细地推导了鱼雷转角射击公式,根据分鱼雷转向的不同总结出两类求解公式（各种态好都能用两类公式之一来解算）．最后还讨论了所导出的非线性方程的数值解算方法,该算法具有工程应用价值。     

A finite-range distribution of failure times

Properties of a finite-range failure-time distribution, that includes the exponential as a particular case, have been studied. The distribution is IFR when the shape parameter exceeds unity, but is IFRA always. For a given value of the shape parameter, the distribution is NBUE over a segment of its range. Estimators of parameters have been derived. Distributions of two-component series, parallel, and standby system lives have also been worked out.     

A note on a difficulty inherent in estimating reliability from stress–strength relationships

This note calls attention to a difficulty which arises frequently in the application of stress-strength methods in reliability theory. This difficulty has led to unanticipated catastrophic failures in a number of applications.