1,720,962 research outputs found
Mathematical models and optimization algorithms for sustainable operations in manufacturing and services
No full textModelli matematici e algoritmi di ottimizzazione per la sostenibilità nel settore manifatturiero e dei servizi
No full textQuesta tesi di dottorato affronta problemi decisionali e gestionali complessi che emergono in contesti reali di imprese manifatturiere e di servizi. La tesi esamina aspetti economici, ambientali e sociali dell’ottimizzazione, con l’obiettivo di sviluppare metodi di risoluzione efficaci per tali problemi e applicarli per risolvere istanze reali. Lo scopo è contribuire all’avanzamento dello stato dell’arte nell’area di ricerca cosiddetta delle “Operazioni Sostenibili”, un recente campo interdisciplinare che impiega metodi quantitativi della Ricerca Operativa per perseguire la sostenibilità economica, ambientale e sociale nelle imprese, risolvendo applicazioni reali di crescente complessità, partendo da problemi mono-obiettivo, passando ai problemi bi-obiettivo e infine a quelli bi-livello.
La prima parte della tesi esplora diverse applicazioni nel contesto tradizionale di un singolo decisore con un singolo obiettivo di ottimizzazione. La Programmazione Lineare Intera Mista (PLIM) è utilizzata per formulare e risolvere in modo esatto due problemi di assegnamento nei settori dell’educazione e della sanità. Inoltre, si applicano algoritmi esatti di decomposizione per risolvere un problema di schedulazione in un laboratorio di testing e metodi di machine learning per prevedere la domanda in un’applicazione di pianificazione della produzione con elevato impatto ambientale. La seconda parte di questa tesi è dedicata all’ottimizzazione bi-obiettivo, che consente di bilanciare obiettivi contrastanti di un singolo decisore. Si studiano problemi di localizzazione di impianti per la gestione dei rifiuti e di sostituzione di veicoli per la transizione energetica nel contesto bi-obiettivo, incorporando obiettivi sia economici che ambientali. Attraverso l’uso iterato di modelli PLIM, si dimostra come i decisori possano considerare contemporaneamente costi ed emissioni di carbonio. Nella terza parte di questa tesi, si esplora l’ottimizzazione bi-livello. L’ottimizzazione bi-livello consente di modellare problemi di ottimizzazione con molteplici decisori coinvolti in una relazione gerarchica a due livelli. Questo si verifica in molte situazioni realistiche, che coinvolgono, ad esempio, entità governative e imprese private, o fornitori e produttori della stessa catena di approvvigionamento. L’obiettivo è esaminare in modo esaustivo la letteratura esistente sull’ottimizzazione bi-livello con prospettive di sostenibilità. Nel complesso, questa tesi mostra il potenziale della Ricerca Operativa nel perseguire la sostenibilità anche in contesti decisionali molto complessi, risolvendo diverse applicazioni reali con una varietà di metodi di ottimizzazione.This PhD thesis addresses complex decision-making and management problems emerging in some real-world manufacturing and service business contexts. It considers economic, environmental, and social aspects of optimization, with the objective to devise effective solution methods for the problems at hand and apply them to solve real-world instances. The aim is to contribute to the advancement of the state of the art in Sustainable Operations, a recent interdisciplinary field that employs quantitative methods from Operations Research to achieve economic, environmental, and social sustainability in business, by solving real-world applications of increasing complexity, starting from mono-objective problems, then moving to bi-objective and finally bilevel problems.
The first part of the thesis explores applications within the traditional setting of a single decision maker with a single optimization goal. Mixed Integer Linear Programming (MILP) is applied to formulate and solve in an exact way two optimization problems in the educational and healthcare sectors. Additionally, exact decomposition approaches are used to solve a scheduling problem in a test laboratory environment, and machine learning methods are employed to forecast demand in an environmentally impactful production planning application. The second part of the thesis is devoted to bi-objective optimization, which allows to make a trade-off between conflicting goals of a single decision maker. Facility location for waste management and equipment replacement problems for energy transition are studied under the bi-objective setting, incorporating both economic and environmental goals. By the iterated use of MILP models, it is
shown how decision makers can simultaneously consider costs and carbon emissions. In the third part of the thesis, bilevel optimization is explored. Bilevel optimization allows to model optimization problems with multiple decision makers in a hierarchical two-level relationship. This appears in many realistic situations involving, for instance, government and private businesses, or suppliers and manufacturers of the same supply chain. We aim to comprehensively review the existing literature on bilevel optimization with sustainable perspectives. Overall, this thesis showcases the potential of Operations Research in achieving sustainability even in very complex decision-making settings, solving several real-world applications with a variety of optimization methods
Exact algorithms for a parallel machine scheduling problem with workforce and contiguity constraints
Full text linkWe address a real-world scheduling problem where the objective is to allocate a set of tasks to a set of machines and to a set of workers in such a way that the total weighted tardiness is minimized. Our case study encompasses four types of constraints: precedence, resource, eligibility, and contiguity. While the first three constraints are common in the scheduling literature, contiguity constraints, which can be defined as a form of precedence constraints that requires both a predecessor and its successor to be processed on the same machine with no intermediate jobs in-between (but idle time is allowed), have never been studied in the literature. We present four exact methods to solve the problem: two methods use integer linear programming, one uses constraint programming, and one uses a combinatorial Benders’ decomposition. We introduce method-specific strategies to model the contiguity constraints for each of the proposed methods. We empirically evaluate, through an extensive set of computational experiments, the performance of the four methods on a heterogeneous dataset composed of real, realistic, and random instances, and outline that every method offers a competitive advantage on a targeted subset of instances. We also show that our algorithms can be generalized to solve related scheduling problems with contiguity constraints
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
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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