Reliability analysis of a Markovian deteriorating system

The reliability of a complex system passes through a gradual deterioration until at some critical level, the system fails completely. The study of such a system failure requires the application of Markov processes to obtain reliability measures such as mean time of system failure. The Laplace transform of reliability of the system starting from each operating state is employed for solving such a complex system of differential equations. A four-state deteriorating system is considered and various particular cases of the arbitrary repair times distribution are discussed.     

On distribution of cycles in a Markovian queueing system

This paper studies the probability distribution of the number of cycles completed in a single-server queueing system with Poisson arrivals, exponential service times and having a limited capacity. The expressions for the number of cycles completed in the time interval (0, t] and the distribution of the number of busy periods completed in time interval (0, t] are obtained explicitly. These distributions are contemplated through the joint probability distribution of the number of customers in the system at time t and the number of times the system reaches its extreme state in the interval (0, t].     

A two-unit parallel redundant system with bivariate exponential lifetimes

In this paper we discuss a two-unit parallel redundant system with a single repair facility in which the lifetimes of two units obey a bivariate exponential distribution and the repair time of the failed unit obeys an arbitrary distribution. Applying an extended Markov renewal process, we obtain the quantities of interest thoroughly in reliability theory.     

On a vacation queue with instantaneous customer loss

The paper studies an M/M/1 queueing system with variable batch-size arrivals and single exponential departures. The system is subject to time-homogeneous server vacations. In addition, a variable bulk customer loss of j units occurs with probability π_j (j = 0, 1, 2, 3,.. . M) where Σ π_j = 1 , at an instant when a vacation starts. The vacation times follow a general probability distribution. The probability generating functions of the number in the system have been determined and some particular cases of interest have been discussed. Finally some steady state results have been derived.     

On a series parallel system

Expressions for the Laplace transform of the availability of a complex system consisting of two subsystems is obtained by identifying suitable regeneration points.     

N-unit parallel redundant system with multiple correlated failures

This paper deals with mathematical models of an N-unit parallel redundant system with one repair facility and multiple correlated failures. These models are generalized on the basis of the results obtained previously and related to a system subject to a process of single failures and double and N-unit correlated failures. The method of the supplementary variable in two models differing by the repair policy is used. We obtain the following results: for both models the stationary availability, and for the second model the Laplace transform (L.T.) of the system reliability, L.T. of the pointwise a vailability, and the mean time to system failure (MTSF).     

Reliability analysis of a multicomponent system in a multistate Markovian environment

Consider a system which operates in a randomly changing environment. The changes of environmental levels are described by a Markov process with finite states. The system consists of several units and one repair facility, the repair time of a failed unit has an arbitrary distribution. We obtain the system reliability functions, availabilities and failure frequencies.     

一种基于集群的新型并行文件系统研究

首先阐述了基于集群的并行文件系统和并行I／O研究的必要性及其现状。然后提出了一种应用于集群中并行文件访问的新型并行文件系统CLUPFS，介绍了CLUPFS中的数据表示。包括文件分割模型、文件拆分后物理子文件与逻辑视图之间的转换，最后指出了CLUPFS并行文件系统进一步研究与实现的方向。     

并行调度两级轮询控制系统分析研究

为了保证系统公平性不受损害,文中提出中心站点采用门限服务,普通站点采用并行调度完全服务的两级优先级轮询控制系统模型。通过马尔科夫链与概率母函数相结合的方法对模型的平均排队队长、平均等待时间等重要参数进行解析。经仿真得出,模拟仿真值与理论值误差较小,近似相等,表明模型理论分析合理正确。数值结果对比表明,模型区分网络业务高低优先级的性能优良,且普通站点工作效率得以提高,从而保证了系统公平性。     

Cost-benefit analysis of a multi-unit parallel trichotomous system with random shocks

This paper deals with the analysis of profit function of an n-unit parallel trichotomous system subject to random shocks. Failure times are assumed to follow negative exponential distributions with different parameters whereas the repair time distributions are taken to be general. Several reliability characteristics of interest to system engineers/designers as well as operation managers have been evaluated using the supplimentary variable technique.     

连接计算机并口的数据采集系统

针对目前大多数导弹测试数据都从测试计算机并口输出,设计了基于单片机对测试数据进行并口采集的系统,通过介绍打印机的工作模式和工作时序,给出了并口数据采集的原理、系统的接口电路和软件编程的流程图,且给出了中断程序的代码,最后通过用样本数据调试系统,证实该系统数据接收效果令人满意、实时性好。     

On the increase of system reliability by parallel redundancy

Adding parallel redundancy to different components generally yields different system reliability improvements. The effect of such parallel redundancy upon system reliability when applied at various places and in various systems is investigated. The problem of how to choose components for parallel redundancy is studied, and some results are given. Some examples are presented to illustrate the approach     

Markovian source separation

A maximum likelihood (ML) approach is used to separate the instantaneous mixtures of temporally correlated, independent sources with neither preliminary transformation nor a priori assumption about the probability distribution of the sources. A Markov model is used to represent the joint probability density of successive samples of each source. The joint probability density functions are estimated from the observations using a kernel method. For the special case of autoregressive models, the theoretical performance of the algorithm is computed and compared with the performance of second-order algorithms and i.i.d.-based separation algorithms.     

Bayesian shrinkage estimation of reliability in parallel system with exponential failure of the components

The paper presents a Bayesian shrinkage method of estimating the reliability of a parallel system with identical exponential distribution of failure times. Data is available from type II censored samples. Thompson (J. Am. Statist. Ass.63, 113–123, 1968) proposed the ordinary shrunken estimator ?θ + (1-?)θ₀, with ? a constant (0 ? ? ? 1) and θ₀ the prior or guess value of θ, which is more efficient than the unbiased estimator θ if θ is close to θ₀ and is less efficient otherwise. Here we postulate a prior distribution of θ around θ₀ and use an ordinary Bayes estimator of θ instead of θ₀ in the ordinary shrunken estimator. The Bayesian shrinkage estimator of parallel system reliability has thus been obtained and Monte Carlo study of its efficiency with respect to unbiased and maximum likelihood estimators (mles) was conducted. It was found that the proposed estimator is better.     

An approximation analysis for the availability of a parallel redundant system with general distributions

This paper presents an approximation method for deriving the availability of a parallel redundant system with general distributions. The system discussed is composed of two identical units. A single service facility is available for the performance of preventive maintenance(PM) and repair. The failure times, repair times and PM times are assumed to be arbitrarily distributed. The presented method formulates the problem of the availability analysis of a parallel redundant system as a semi-Markov process which represents the state transitions of one specified unit in the system. This method derives the availability easily and accurately. Further, when all the distributions are exponential, the availability obtained by this method is exact.     

Heterogeneous coexistence between cognitive radio networks: a Markovian jump system method

With the increasing demand of wireless spectrum, different unlicensed wireless communication technologies have been applied in the television white space (TVWS). It is vital to understand that the mutual interference over TVWS due to incompatible protocol designs heavily degrades the quality of service of coexisting heterogeneous cognitive radio networks. In this paper, taking the activity of primary users into consideration, we formulate the heterogeneous coexistence problem over TVWS as a nonlinear Markovian jump system (NMJS) based on the Lotka–Volterra competition model. By using the local linearization method, we first obtain a linear Markovian jump system model (which approximates the NMJS linearly at the desired spectrum share) to the NMJS. Further, we obtain an effective feedback controller to the equilibrium assignment of the NMJS via solving a sufficient condition in the form of linear matrix inequalities. Third, we propose an IEEE 802.19.1-compatible spectrum sharing algorithm which enables the NMJS to converge to the assigned spectrum share. Finally, extensive simulations are conducted to validate the effectiveness of our proposals.     

A reliability physics model for parallel system

Reliability analysis of a nonrepairable 2-unit parallel system is carried out using the stress-strength model of failure physics. The analysis is carried out for correlated strengths and altered stress distribution depending upon the number of components surviving. The analysis includes both the cases of deterministic and random cycle times. In the case of random cycle times, Poisson distributed stress cycle occurrences have been considered. Various system characteristics, such as failure time distribution, reliability and moments of time to failure of the system, have been evaluated for both deterministic and random cycle times. Two particular cases, namely (i) bivariate exponential distribution for strength variables and univariate exponential distributions for stress variables and (ii) bivariate normal distribution for strength variables and univariate normal distributions for stress variables, have also been considered.     

Inspection policy for two-unit parallel redundant system

This paper deals with a single-server two-unit parallel redundant system with non-negligible inspection time. We shall assume that a failure of a unit or the system failure is detected by inspection only. We consider two inspection policies and under each inspection policy the stationary availability is derived by applying Piecewise Markov Process. Optimum inspection schedule is discussed to maximize the stationary availability of the system. A numerical example is presented.     

Moment analysis for traffic associated with Markovian queueingsystems

A study is made of various traffic processes associated with Markovian queuing systems, and the moments of the traffic processes are analyzed. The purpose of the study is to develop a means of computing the moments efficiently so as to extend the conventional method of representing the traffic processes to a larger class of queuing systems. As an outcome of the analysis, the recurrence formulae for computing the moments including cross-covariances between multiple traffic processes are derived and expressed in terms of the infinitesimal generator, steady-state probability vector of the Markovian queuing system and a matrix describing traffic rate. The main feature of the analysis is in the utilization of the special block-partitioned structure of the matrices involved. The results are of wide application for the study of various telecommunication networks. Two examples of applications for the Markovian queuing model with batch arrivals and a multislot integrated services system are presented     

A study of a time dependent queueing system with two parallel channels

A time dependent queueing system is studied by obtaining the probabilities of the exact number of arrivals and departures by a given time. The service is accomplished through two parallel channels, each channel having a different service rate. The marginal probability of exactly i arrivals and the mean number of i arrivals are obtained.