Repair limit policy of aircraft component based on extended uncertain random renewal reward process

PurposeThe purpose of this paper is to focus on an optimizing maintenance policy with repair limit time for a new type of aircraft component, in which the lifetime is assumed to be an uncertain variable due to no historical operation data, and the repair time is a random variable that can be described by the experimental data.Design/methodology/approachTo describe this repair limit time policy over an infinite time horizon, an extended uncertain random renewal reward theorem is firstly proposed based on chance theory, involves uncertain random interarrival times and stochastic rewards. Accordingly, the uncertain random programming model, which minimized the expected maintenance cost rate, is formulated to find the optimal repair limit time.FindingsA numerical example with sensitivity analysis is provided to illustrate the utility of the proposed policy. It provides a useful reference and guidance for aircraft optimization. For maintainers, it plays an important guiding role in engineering practice.Originality/valueThe proposed uncertain random renewal reward process proved useful for the optimization of maintenance strategy with maintenance limited time for a new type of aircraft components, which provides scientific support for aircraft maintenance decision-making for civil aviation enterprises.

Self-harm and suicidal content online, harmful or helpful? A systematic review of the recent evidence

Purpose There are calls for greater regulation of online content related to self-harm and suicide, particularly that which is user-generated. However, the online space is a source of support and advice, including an important sharing of experiences. This study aims to explore what it is about such online content, and how people interact with it, that may confer harm or offer benefit. Design/methodology/approach The authors undertook a systematic review of the published evidence, using customised searches up to February 2021 in seven databases. The authors included empirical research on the internet or online use and self-harm or suicide content that had been indexed since 2015. The authors undertook a theoretically driven narrative synthesis. Findings From 4,493 unique records, 87 met our inclusion criteria. The literature is rapidly expanding and not all the evidence is high quality, with very few longitudinal or intervention studies so little evidence to understand possible causal links. Very little content online is classifiable as explicitly harmful or definitively helpful, with responses varying by the individual and immediate context. The authors present a framework that seeks to represent the interplay in online use between the person, the medium, the content and the outcome. Originality/value This review highlights that content should not be considered separately to the person accessing it, so online safety means thinking about all users. Blanket removal or unthinking regulation may be more harmful than helpful. A focus on safe browsing is important and tools that limit time and diversify content would support this.

Améliorer la prévision de température en montagne par des descentes d'échelle

En montagne, la prévision du temps et d'aléas aussi dangereux et localisés que les avalanches requiert une modélisation de l'atmosphère à haute résolution spatiale. Palliant des simulations coûteuses, des méthodes de descente d'échelle ont été appliquées pour produire des champs météorologiques à 500 m de résolution, sur les massifs alpins, à partir des prévisions issues du modèle Arome à 1,3 km. L'évaluation s'est concentrée sur la température à 2 mètres, paramètre météorologique clé pour la physique du manteau neigeux. Une descente d'échelle exploite un profil thermique environnemental. Sa pertinence est démontrée dans certaines configurations météorologiques, mais les erreurs intrinsèques au modèle Arome contraignent son potentiel. In mountain areas, a numerical model with high spatial resolution is necessary to forecast the local meteorological conditions and the natural hazard such as avalanches. To limit time-consuming computations, downscaling methods were used to produce meteorological fields within a grid spacing of 500 m in the Alps from the Météo-France 1.3 km resolution forecast model (Arome). The evaluation focuses on the 2 meters temperature which is a key variable in snowpack changes. One method employs a correction based on a local vertical temperature lapse rate. Its impact is quite positive in some atmospheric conditions but remains limited by the Arome bias.

Quantum speed limit time in the presence of disturbance

Quantum theory sets a bound on the minimal time it takes for a system to evolve from initial state to target state. This bound is called the quantum speed limit (QSL) time. The quantum speed limit time is used to quantify the maximal speed of the quantum evolution. The quantum evolution will be faster if the quantum speed limit time decreases. In this work, we study the quantum speed limit time for an open quantum system in the presence of disturbance in an environment. We use the model which is provided by Ban [Phys. Rev. A 99, 012116 (2019)]. In this model, two quantum systems [Formula: see text] and [Formula: see text] interact with environment sequentially. At first, quantum system [Formula: see text] interacts with the environment [Formula: see text] as an auxiliary system, then quantum system [Formula: see text] starts its interaction with disturbed environment immediately. In this work, we consider the dephasing coupling with two types of environment that has different spectral density: Ohmic and Lorentzian. We observe that, non-Markovian effects will appear in the dynamics of the second quantum system [Formula: see text] due to the interaction of the first quantum system [Formula: see text] with the environment. Given the fact that the quantum speed limit time reduces due to the non-Markovian feature of quantum evolution, we show that disturbance effects will reduce the quantum speed limit time for the dynamics of the second quantum system [Formula: see text].