International Journal of Reliability, Quality and Safety Engineering

In the literature, median type control charts have been widely investigated as easy and efficient means to monitor the process mean when observations are from a normal distribution. In this work, a Variable Sampling Interval (VSI) Exponentially Weighted Moving Average (EWMA) median control chart is proposed and studied. The Markov chains are used to calculate the average run length to signal (ARL). A performance comparison with the original EWMA median control chart is made. The numerical results show that the proposed chart is considerably more effective as it is faster in detecting process shifts. Finally, the implementation of the proposed chart is illustrated with an example in food production process.

Various open source software (OSS) projects are in action around the world. Many OSS are developed and maintained under these OSS projects. Considering the characteristics of OSS, the operation performance of OSS development will take an irregular fluctuation in the long term of operation, because several developers and many users are closely related to the maintenance of OSS.

This paper focuses on the irregular fluctuation of the operation performance of OSS. We apply the jump diffusion process model to the noisy cases in the operation of OSS. In particular, the maintenance effort is estimated by the stochastic differential equation model in terms of OSS project management. Moreover, we discuss the method of maintenance effort management based on jump diffusion process model considering the irregular fluctuation of performance for OSS projects. In particular, we propose the method of productivity assessment based on the proposed jump diffusion models. Thereby, it is helpful for the OSS development managers to understand the effort status of OSS from the standpoint of OSS project management. Also, we analyze actual data to show numerical examples of the proposed method considering the characteristics of OSS projects.

The random age replacement policies discussed in literatures are helpful to complete the nonstopping works with random working cycles, however, maintenance policies are more easily performed at periodic times in real applications. For such a viewpoint, this paper proposes that age replacement policies are planned at periodic times while considering the random working cycles. Using the modeling approaches of replacement first and last policies, we discuss two models such that the unit is replaced at periodic times $KT$ and working cycles $N$, whichever occurs first and whichever occurs last. The expected cost rate models are obtained and their optimal solutions for $K$ and $N$ are discussed. The comparisons between the policies of $K$ and $N$, and replacement first and last are made from the point of cost. Numerical examples are illustrated when the failure time has a Weibull distribution.

This paper discusses a reliability problem of window flow control scheme with Explicit Congestion Notification (ECN) in the communication system, which is an essential issue in the long-distance transmission such as cloud computing. For example, there is a problem of reduction in transmission efficiency caused by a packet loss from network congestion. In order to solve the problem, recently, High-performance and Flexible Protocol (HpFP) has been proposed and performed a verification of effectiveness by simulation. HpFP provides efficient packet communication by changing a packet transmission interval [T. Murata, T. Mizuhara, A. Takagi, K. Fukushima, K. Yamamoto, Y. Nagaya, K. Muranaga and E. Kimura, HpFP: A new protocol for LFNs with packet-loss based on UDP: A basic concept and detailed design of the protocol, IEICE Technical Report 115(484) IN2015-109, pp. 7–12 (2016)].

We have discussed the reliability model of a window flow control scheme based on a packet transmission interval. We have proposed the model which judges the occurrence of congestion in a network by the number of retransmission [M. Kimura, M. Imaizumi and T. Nakagawa, Reliability modelling of window flow control scheme for a communication system based on packet transmission interval, in Proc. 23rd ISSAT Int. Conf. Reliability and Quality in Design (2017), pp. 171–175]. On the other hand, ECN mechanism for the detection of incipient congestion has been already proposed. ECN mechanism is efficient for the window flow control scheme because ECN bit is set in the packet header as an indication of congestion and is avoided unnecessary packet drops.

We consider a stochastic model of a window flow control scheme based on a packet transmission interval with ECN. If ECN bit has been set during connection, a packet transmission interval is prolonged. We derive the mean time until packet transmissions succeed, and analytically discuss an optimal policy to maximize the amount of packets per unit of time until the transmission succeeds.

Assessing the reliability of a multistate flow network (MFN) has been significantly attractive in recent years. Generally, some assumptions such as budget or time limits are considered in this problem to make it more realistic. Considering the cost constraint, the network reliability at level $(d,c)$ is the probability of transmitting at least $d$ units of product from a source node to a destination node through the network within the cost of $c$, where $d$ is a given demand value. Here, the problem of reliability evaluation of an MFN with cost constraint in terms of minimal cuts is considered. Presenting some techniques to improve the solution, a simple improved algorithm is proposed to address the problem. The complexity results are provided which demonstrate our proposed algorithm to be more efficient than some other existing ones in the literature. Some numerical comparisons between our MATLAB implementation of the proposed algorithm here and a recently proposed one are made. This way, computational comparative results on three benchmarks and a thousand random test problems are provided in the sense of performance profile introduced by Dolan and Moré, which show our proposed algorithm to be more efficient than the other.