1,721,093 research outputs found
Production quality performance of manufacturing systems with in-line product traceability and rework
No full textIn-line product inspection and identification are emerging technologies supporting the observability and traceability of the product state evolution in multi-stage manufacturing systems. These technologies enable the dynamic implementation of defect management actions, such as product rework. However, their impact on the system quality and production logistics performance needs to be assessed in order to justify the related investments. This paper presents a theory and a methodology to predict the effective throughput of manufacturing systems with product traceability and rework, jointly considering the product and system state dynamics. The industrial benefits are validated in a real system in the semiconductor industry
Moments of accumulated reward and completion time in Markovian models with application to unreliable manufacturing systems
Full text linkPerformance evaluation models are used by companies to design, adapt, manage and control their production systems. In the literature, most of the effort has been dedicated to the development of efficient methodologies to estimate the first moment performance measures of production systems, such as the expected production rate, the buffer levels and the mean completion time. However, there is industrial evidence that the higher moments of the production output may drastically impact on the capability of managing the system operations, causing the observed system performance to be highly different from what expected. This paper presents a methodology to analyze the cumulated output and the lot completion time moments of Markovian reward models. Both the discrete and continuous time cases are considered. The technique is applied to unreliable manufacturing systems characterized by general Markovian structures. Numerical results show how the theory developed in this paper can be applied to analyse the dependency of the output variability and the service level on the system parameters. Moreover, they highlight previously uninvestigated features of the system behavior that are useful while operating the system in practical settings
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Lead Time Analysis of Manufacturing Systems with Time-Driven Rework Operations
No full textProducts whose quality features deteriorate with the time they spend in the manufacturing system are common in industry. Usually, they are perishable products that loose their performance or value whenever their sojourn time in the system exceeds a certain threshold. A typical example is the food industry where such products need to be identified and scrapped. In other cases, perishable products can be reworked for restoring their functions when their sojourn exceeds a threshold. For instance, automotive painting processes suffer of dust settling on parts before the drying process and semiconductor wafers risk contamination between the cleaning and heating processes. This work develops an analytical method to evaluate the performance of systems with rework operations triggered by an extended residence time. The approach is based on the exact computation of the lead time distribution in production lines featuring general markovian machines. By exploiting the developed method, specific production policies aiming at minimizing the rework rate and maximizing the effective throughput in such systems are investigated. The method is validated within a real case showing high benefits through industrial applications
A Kronecker Algebra Formulation for Markov Activity Networks with Phase-Type Distributions
Full text linkThe application of theoretical scheduling approaches to the real world quite often crashes into the need to cope with uncertain events and incomplete information. Stochastic scheduling approaches exploiting Markov models have been proposed for this class of problems with the limitation to exponential durations. Phase-type approximations provide a tool to overcome this limitation. This paper proposes a general approach for using phase-type distributions to model the execution of a network of activities with generally distributed durations through a Markov chain. An analytical representation of the infinitesimal generator of the Markov chain in terms of Kronecker algebra is proposed, providing a general formulation for this class of problems and supporting more efficient computation methods. This entails the capability to address stochastic scheduling in terms of the estimation of the distribution of common objective functions (i.e., makespan, lateness), enabling the use of risk measures to address robustness
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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