Optimal inspection policy for a parallel redundant system

This paper considers an inspection policy for an n-unit parallel redundant system which is checked at successive times x (k=1, 2,…). The preventive maintenance is made if j units (1<j<n−1) fail at each inspection. The expected cost is derived and the optimum policy to minimize it is discussed. Two modified models are introduced. A numerical example is given when the failure times of each unit have a Weibull distribution.     

Cost-benefit analysis of a system with inspection, replacement and two types of repair

This paper investigates a mathematical model of a system composed of two units—one operative and the other in cold standby. There is a single repair facility which serves the triple role of inspection, repair and replacement of a failed unit. After inspection, the unit goes to minor (major) repair with probability p(q = 1 − p). Whenever the failed unit goes to major repair, an order is immediately placed for a new unit to replace the unit under major repair. Failure, inspection and delivery time distributions are negative exponential, whereas repair time distribution is arbitrary. The system is analysed in detail using the regenerative point technique and several reliability characteristics of interest to system designers and operation managers are obtained. Earlier results are verified in particular cases.     

Optimal replacement policy for a warrantied system with imperfect preventive maintenance operations

This paper determines the optimal replacement time for a system with imperfect preventive maintenance operations under the modified warranty policy. The hazard rate after preventive maintenance lies between the states as good as new and as bad as old. After minimal repair, the hazard rate remains unchanged. Modified warranty policy is a mixed type of free and pro-rata warranty policy. Numerical examples using the Weibull case are presented.     

Optimal inspection when the system is repaired upon detection of failure

In Barlow and Proschan (Mathematical Theory of Reliability, 1965, Section 3.2) a cost model is presented for a system subject to random failure and whose state is known only by inspection. Upon detection of failure repair (or replacement) is performed and the system is then as good as new. A method of determining the inspection schedule which minimizes the long run average (expected) cost per unit time is proposed. In this present paper we look closer into the problem of finding an optimal inspection schedule for this model. Some new results, which are useful in connection with the computation of the optimal inspection schedule, are given.     

Sensitivity analysis of a coherent system

For the purpose of improving the reliability of a system, several methods can be adopted such as “improvement method”, “redundance method” and “standby method”, which are discussed later. An example is given to show that it is probably better to give a redundance to the component which has lower probability importance than to another which has higher probability importance. So, the new concepts of redundancy sensitivity and standby sensitivity are proposed and the simple relation between these and probability importance is revealed. Moreover, some new results are also presented in this paper.     

Cost-benefit analysis of a single server three-unit redundant system with inspection, delayed replacement and two types of repair

This paper deals with a redundant system with two types of spare units—a warm standby unit for instantaneous replacement at the time of failure of the active unit and a cold standby (stock) unit which can be replaced after a random amount of time. The type of the failure of operative or warm standby unit is detected by inspection only. The service facility plays the triple role of replacement, inspection and repair of a unit. Failure time distributions of operative and warm standby units are negative exponential whereas the distributions of replacement time, inspection time and repair times are arbitrary. The system has been studied by using regenerative points.     

相干态相位的最优估计与跟踪方法

在传统量子相位跟踪方法中,通常对输出结果进行线性化处理,这对本振相位和信号相位有严格的限制要求,且并不适用于如干涉法测角等导航系统。为此,本文将零拍输出形式进行等价变换,设计了一种最大似然估计迭代算法,实现了相干态相位跟踪。与传统线性化的量子相位跟踪方法相比,避免引入线性化误差,更加适用于导航系统中信号相位跟踪;通过计算Fisher信息矩阵,证明此方法在理论上能够达到量子克拉美－罗下界,具有最优估计性能。     

MTBF of a complex binary coherent system

It is noted that there has yet been no detailed study of the relationships between the MTBF (mean time between failures) of a system and the sequences of component failures, except for the case of a series system where every component failure causes a system failure. The author defines MTBF anew and derives relationships between the properties of the MTBF of a binary coherent system and the properties of the sequences of component failures, assuming that the lifetime distributions of the components are either new-better-than-used (NBU) exponential or increasing failure rate (IFR). Lower bounds of MTBF that can be used to predict the MTBF and to decide whether the system would satisfy the MTBF requirement are derived     

Towards a coherent optical free-space communication system

A coherent optical communication system based on a diode laser pumped Nd:YAG laser with 620 mW single frequency output power has been developed. Differential phase shift keying at a data rate of 565 Mbit/s has been applied. Bit-error-rates of 10/sup -9/ have been measured at a received light power of -46 dBm.<>     

Optimal replacement of improving and deteriorating repairablesystems

System improvement and deterioration are defined in terms of partial orderings between life distributions. The effects of ageing of `the distribution of time to first failure' on improvement and deterioration of a repairable system subject to minimal repairs, are investigated. Under various types of life distributions we derive explicitly the times at which the system should be condemned (replaced by a new one) to minimize the total cost of maintenance and replacement in terms of parameters of the distribution and of the cost function     

Optical amplification in a multichannel FSK coherent system

Reports the crosstalk degradation caused by an optical amplifier in a densely spaced four-channel heterodyne FSK system. A maximum receiver sensitivity of 250 photons/bit is obtained for an optimum input signal level. This result is 5 dB poorer than the sensitivity obtained in the absence of an optical amplifier     

Reliability analysis of a two-unit cold standby system with inspection, replacement, proviso of rest, two types of repair and preparation time

This paper deals with a two-unit standby system-one operative and the other in cold standby. Single repair facility which acts the inspection, replacement, preparation and repair. We wait the serverman for some maximum time or until the other unit fails. The analysis is carried out on the supposition that all time distributions are general except failure, delivery, replacement and inspection time distributions are exponentials. Stochastic behavior of the system has been studied by the regeneration point technique and several parameters of interest are obtained. Numerical results pertaining to some special cases are also added.     

A closed-loop coherent PN acquisition system with a pre-loopestimator

We propose a closed-loop system with a pre-loop code phase estimator (PLE) for acquisition of the pseudonoise (PN) signal in direct-sequence spread-spectrum systems. It consists of two major parts: a PLE and a closed-loop acquisition subsystem. The system uses an auxiliary signal, as opposed to the PN signal itself, to correlate with the incoming signal. The PLE uses the correlation result to obtain an estimate of the incoming code phase. Then, starting with this initial estimate, the closed-loop subsystem will acquire the code phase of the incoming PN signal. With coherent carrier demodulation, mean and variance of the acquisition time of the proposed scheme are obtained and compared to those of the conventional serial-search acquisition receiver and the closed-loop system without the pre-loop estimator. Results show that, with proper choices of parameters, the proposed system acquires the PN phase significantly faster than the other two systems     

Reliability analysis : Optimal inspection and maintenance schedules of failing systems

Inspection and maintenance schedules involve planned and unplanned actions carried out to retain a system in, or restore it to an acceptable condition. Optimal maintenance schedules aim to minimize downtime, while providing for the most effective use of systems in order to secure the desired results at the lowest possible costs. This paper is a state-of-the-art review of the literature related to optimal inspection and maintenance schedules of failing systems.     

Optimal continuous-wear limit replacement under periodicinspections

An item breaks down when it wears continuously beyond a certain threshold. The item is preventively replaced as the wear at periodic inspections exceeds a certain wear limit; on failure, it is replaced immediately. The optimal wear limit for preventive replacement that minimizes the long-run total average-cost rate is derived. A numerical example demonstrates its computability     

Optimal wear-limit replacement with wear-dependent failures

The optimal wear-limit for preventive replacement for an item with wear-dependent failure rate is derived by minimizing the long-run total mean cost rate. The generic term wear connotes any type of degradation that accumulates through use and is observed continuously in time. The optimal strategy has the same form as the age replacement policy     

Optimal number of major failures before replacement

When the repair cost of a failed system is random, it is no longer meaningful to expend more than the replacement cost on a catastrophic failure. This paper presents a mathematical model that uses two cost limits to combine and extend the replacement models based on minor-failure number[8] and constant repair cost limit[5] for general time-to-failure distributions. When the failed system requires repair, it is first inspected and the repair cost is estimated. Minimal repair is only then undertaken if the estimated cost is less than the minor repair-cost limit; or if the estimated cost is less than the replacement cost and the predetermined major-failure number is not reached. An example with a Weibull time-to-failure distribution and a negative exponential distribution of estimated repair cost is given to illustrate the computational results.     

Optimal replacement policy (N, n) for a parallel system with common cause failure and geometric repair time

The purpose of this article is to present an improved replacement model for a parallel system of N identical units, by bringing in common cause failure (CCF), maintenance cost and repair cost per unit time additionally, and to develop a procedure to obtain the optimal redundant units N^* and optimal number of repairs n^* with the conditions that the system is allowed to undergo at most a prefixed number of repairs before to be replaced and the successive reapir times after failures constitute a non-decreasing Geometric process. Several conditions for the existence of the optimal N^* and n^* is stated and the results are illustrated by a numerical example.