245 research outputs found

    Optimization of replacement policy for a one-component system subject to Poisson shocks

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    In reliability engineering, system failures may occur due to intrinsic or extrinsic factors. For example, drinking water systems may fail due to ageing and deterioration (i.e., intrinsic factors) or flooding (i.e., extrinsic factors). An interesting question is: for such systems, how should preventive maintenance be scheduled? This paper investigates this question. The paper develops a maintenance policy for repairable systems subject to extrinsic shocks. It assumes that a system may fail due to either intrinsic factors or extrinsic factors. Reliability indexes and the expected long run cost rate are then derived. A numerical example is given to illustrate the theoretical results

    Generalized integrated importance measure for system performance evaluation: application to a propeller plane system

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    The integrated importance measure (IIM) evaluates the rate of system performance change due to a component changing from one state to another. The IIM simply considers the scenarios where the transition rate of a component from one state to another is constant. This may contradict the assumption of the degradation, based on which system performance is degrading and therefore the transition rate may be increasing over time. The Weibull distribution describes the life of a component, which has been used in many different engineering applications to model complex data sets. This paper extends the IIM to a new importance measure that considers the scenarios where the transition rate of a component degrading from one state to another is a time-dependent function under the Weibull distribution. It considers the conditional probability distribution of a component sojourning at a state is the Weibull distribution, given the next state that component will jump to. The research on the new importance measure can identify the most important component during three different time periods of the system lifetime, which is corresponding to the characteristics of Weibull distributions. For illustration, the paper then derives some probabilistic properties and applies the extended importance measure to a real-world example (i.e., a propeller plane system)

    Corruption May Worsen in Democratizing Economies: But Don\u27t Let it Erode Our Faith in Democracy

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    This commentary is based on a recent study we conducted on the relationship between regime type, corruption, and economic development. We build a theory that links corruption and regime type to economic growth and test it on 158 countries, using multiple databases including Polity IV, transparency international, the World Bank, and others. We first distinguish three regime types, autocracy (dictatorship), anocracy (countries in early stage of democratization), and mature democracy. We found that when autocratic countries begin democratize, corruption usually gets worse. As the infant democracies mature, corruption decreases