An efficient algorithm for exact computation of system and survival signatures using binary decision diagrams

System and survival signatures are important and popular tools for studying and analysing the reliability of systems. However, it is difficult to compute these signatures for systems with complex reliability structure functions and large numbers of components. This paper presents a new algorithm that is able to compute exact signatures for systems that are far more complex than is feasible using existing approaches. This is based on the use of reduced order binary decision diagrams (ROBDDs), multidimensional arrays and the dynamic programming paradigm. Results comparing the computational efficiency of deriving signatures for some example systems (including complex benchmark systems from the literature) using the new algorithm and a comparison enumerative algorithm are presented and demonstrate a significant reduction in computation time and improvement in scalability with increasing system complexity

Estimating the availability of hydraulic drive systems operating under different functional profiles through simulation

Hydraulic drive systems are widely used in a variety of industrial applications where high torque and low speed rotational power are required. The advantages include maximum torque from zero speed, continuously variable speed within wide limits, high reliability and insensitivity to shock loads. A drive system consists of a hydraulic circuit, electric motors, hydraulic pumps, hydraulic motors and auxiliary components. The stress on the components, and hence wear and failure rate, varies with the torque and speed output by the drive. The reliability of a hydraulic drive system of a particular design can therefore vary significantly between installations operating in applications with different functional requirements. Predicting the availability of a drive system in a particular application is useful for several purposes such as optimising the system design and estimating support costs. This paper describes a simulation model, developed to estimate the availability of a hydraulic drive system in a given functional profile, consisting of output torque and speed time phase requirements. It outputs statistics on system availability and component failure rates. As an example, the simulation model is used to compare these statistics for a drive design operating under two distinct operational profiles

Recommender systems and the amplification of extremist content

Policymakers have recently expressed concerns over the role of recommendation algorithms and their role in forming “filter bubbles.” This is a particularly prescient concern in the context of extremist content online; these algorithms may promote extremist content at the expense of more moderate voices. In this article, we make two contributions to this debate. Firstly, we provide a novel empirical analysis of three platforms’ recommendation systems when interacting with far-right content. We find that one platform – YouTube – does amplify extreme and fringe content, while two – Reddit and Gab – do not. Secondly, we contextualise these findings into the regulatory debate. There are currently few policy instruments for dealing with algorithmic amplification, and those that do exist largely focus on transparency. We argue that policymakers have yet to fully understand the problems inherent in “de-amplifying” legal, borderline content and argue that a co-regulatory approach may offer a route towards tackling many of these challenges

An efficient algorithm for computing exact system and survival signatures of K-terminal network reliability

An efficient algorithm is presented for computing exact system and survival signatures of K-terminal reliability in undirected networks with unreliable edges. K-terminal reliability is defined as the probability that a subset K of the network nodes can communicate with each other. Signatures have several advantages over direct reliability calculation such as enabling certain stochastic comparisons of reliability between competing network topology designs, extremely fast repeat computation of network reliability for different edge reliabilities and computation of network reliability when failures of edges are exchangeable but not independent. Existing methods for computation of signatures for K-terminal network reliability require derivation of cut-sets or path-sets which is only feasible for small networks due to the computational expense. The new algorithm utilises binary decision diagrams, boundary set partition sets and simple array operations to efficiently compute signatures through a factorisation of the network edges. The performance and advantages of the algorithm are demonstrated through application to a set of benchmark networks and a sensor network from an underground mine

Reliability assessment techniques for medical procedures

Healthcare aims to deliver good patient outcomes. However deviations in the application of medical procedures can result in failure to deliver reliable care, variation in patient results, waste of hospital resources and increase of risk to staff and patients. Venepuncture – the act of taking blood samples for laboratory tests – has been practised for centuries and is still one of the most common invasive procedures in healthcare. Each step of the procedure can affect the quality of the sample and is thus important for preventing rejection of blood specimens, patient and staff injury and even death. There is evidence that, despite published guidelines, there is wide variability in terms of the procedure, its duration and success rates. This variability can depend on numerous factors: material factors, such as equipment and tubes used during the drawing of blood, and staff factors, such as tourniquet technique and skill of the individual. If the variability effects on outcomes can be evaluated in terms of process reliability and efficiency, potential changes to the current medical practice can be tested before they are proposed and implemented. In this paper a reliability assessment technique based on engineering reliability modelling methods is proposed. A technique based on Petri nets and simulation is presented which can be used to mimic and analyse the performance of a medical procedure through graphical and probabilistic modelling features. The technique can be used to demonstrate variations in the venepuncture procedure affect the outcomes, such as reliability and the duration of the procedure. Different scenarios of resource allocation can be analysed and the most critical steps of the procedure identified. The proposed technique is illustrated using the information gained from interview and questionnaire responses from doctors and phlebotomists working in UK hospitals