1,721,044 research outputs found
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
Efficient Algorithms for Routing Problems with Specific Constraints
No full textCette thèse se concentre sur la conception algorithmique de trois problèmes d’optimisation combinatoire liés à la recherche en transport, logistique et production avec des types spécifiques de contraintes industrielles. Tout d’abord, nous considérons le problème du voyageur de commerce généralisé à contraintes de priorité (PCGTSP). Ce problème est une extension de deux problèmes d’optimisation combinatoire bien connus : le problème généralisé du voyageur de commerce (GTSP) et le problème du voyageur de commerce asymétrique à contrainte de préséance (PCATSP), dont la version de chemin est connue sous le nom de problème de commande séquentielle (SOP).Semblable au GTSP classique, le but du PCGTSP est de trouver pour un digraphe d’entrée donné et une partition de son ensemble de nœuds en clusters un itinéraire cyclique (tour) à coût minimum visitant chaque cluster dans un seul nœud. De plus, comme dans le PCATSP, les visites réalisables sont limitées à la visite des clusters dans le respect de l’ordre partiel donné. Contrairement au GTSP et au SOP, à notre connaissance, lePCGTSP reste encore peu étudié tant en termes de théorie polyédrique que d’algorithmes. Dans cette thèse, pour la première fois pour le PCGTSP, nous proposons plusieurs familles d’inégalités valides, établissons la dimension du polytope PCGTS et prouvons des conditions suffisantes garantissant que les inégalités π et σ étendues de Balas deviennent des facettes -induisant. En nous appuyant sur ces résultats théoriques et les approches algorithmiques existantes pour le PCATSP et le SOP, nous introduisons une famille de modèles MILP et plusieurs variantes de l’algorithme branch-and-cut pour le PCGTSP. Nous étudions leurs performances sur les instances de la bibliothèque publique de benchmark PCGTSPLIB, une adaptation connue du SOPLIB classique au problème en question. Les résultats obtenus montrent l’efficacité de l’algorithme.Notre deuxième sujet de recherche est lié à une application industrielle spécifique du PCGTSP - le problème du chemin de coupe discret (CPP). Dans ce problème, nous avons cherché à trouver une trajectoire optimale pour un outil de coupe, afin de minimiser le coût total de traitement, y compris la découpe, le mouvement de l’air, le perçage et autres dépenses, soumis aux contraintes induites par les restrictions de découpe industrielle. Ilivest pratique de considérer ces restrictions en termes de contraintes de préséance. Nous introduisons un cadre de solution général pour le RPC qui comprend : (i) l’approche de réduction universelle pour de nombreuses variantes de ce problème au problème du voyageur de commerce généralisé avec contraintes de préséance ; (ii) un support méthodologique pour trouver des solutions (sous-) optimales à ce problème sur la base de l’algorithme de branchement et de coupe et de la méta-heuristique PCGLNS. Les résultats des expériences informatiques montrent l’efficacité du cadre proposé pour résoudre les instances industrielles du problème.Enfin, nous abordons le problème de routage de véhicules capacitaires (CVRP). CVRP est fortement NP-difficile (même sur le plan euclidien), difficile à approximer dans le cas général et APX-complet pour une métrique arbitraire. Cependant, pour les paramètres géométriques du problème, il existe un certain nombre de schémas d’approximation temporelle quasi-polynomiale et même polynomiale connus. Parmi ces résultats, le célèbre système d’approximation temporelle quasi-polynomiale (QPTAS) proposé par A. Das et C. Mathieu semble être le plus général. Dans cette thèse, nous proposons la première extension de ce schéma à une classe plus large d’espaces métriques. En fait, nous montrons que la métrique CVRP a un QPTAS à tout moment lorsque le problème est installé dans l’espace métrique de toute dimension de doublement fixe d > 1 et que la capacité ne dépasse pas polylog(n).This thesis focuses on algorithmic design for three combinatorial optimization problems related to transportation, logistics and production research with specific types of indus- trial constraints. First, we consider the Precedence Constrained Generalized Traveling Salesman Problem (PCGTSP). This problem is an extension of two well-known combina- torial optimization problems — the Generalized Traveling Salesman Problem (GTSP) and the Precedence Constrained Asymmetric Traveling Salesman Problem (PCATSP), whose path version is known as the Sequential Ordering Problem (SOP).Similarly to the classic GTSP, the goal of the PCGTSP is to find for a given input digraph and partition of its node set into clusters a minimum cost cyclic route (tour) visiting each cluster in a single node. In addition, as in the PCATSP, feasible tours are restricted to visit the clusters with respect to the given partial order. Unlike the GTSP and SOP, to the best of our knowledge, the PCGTSP still remain to be weakly studied both in terms of polyhedral theory and algorithms. In this thesis, for the first time for the PCGTSP, we propose several families of valid inequalities, establish dimension of the PCGTS polytope and prove sufficient conditions ensuring that the extended Balas’ π- and σ-inequalities become facet-inducing. Relying on these theoretical results and existing algorithmic approaches for the PCATSP and SOP, we introduce a family of MILP-models and several variants of the branch-and-cut algorithm for the PCGTSP. We study their performance on the instances of the public benchmark library PCGTSPLIB, a known adaptation of the classic SOPLIB to the problem in question. The obtained results show the efficiency of the algorithm. The paper was published in European Journal of Operational Research.Our second research topic is related to a specific industrial application of the PCGTSP - the discrete Cutting Path Problem (CPP). In this problem, we aimed to find an optimal path for a cutting tool, in order to minimize the total processing cost including cutting, air-motion, piercing, and other expenses, subject to constraints induced by industrial cutting restrictions. It is convenient to consider such restrictions in terms of precedenceconstraints. We introduce a general solution framework for CPP that includes: (i) the universal reduction approach for numerous variants of this problem to the theviPrecedence Constrained Generalized Traveling Salesman Problem; (ii) methodological support for finding (sub-) optimal solutions of this problem on the basis of branch-and-cut algorithm and PCGLNS meta-heuristic. The results of computational experiments show the efficiency of the proposed framework for solving industrial instances of the problem. The paper was submitted to International Journal of Production Research.Finally, we tackle the Capacitated Vehicle Routing Problem (CVRP). CVRP is strongly NP-hard (even on the Euclidean plane), hard to approximate in general case and APX-complete for an arbitrary metric. However, for the geometric settings of the problem, there is a number of known quasi-polynomial and even polynomial time approximation schemes. Among these results, the well-known Quasi-Polynomial Time Approximation Scheme (QPTAS) proposed by A. Das and C. Mathieu appears to be the most general. In this thesis, we propose the first extension of this scheme to a more wide class of metric spaces. Actually, we show that the metric CVRP has a QPTAS any time when the problem is set up in the metric space of any fixed doubling dimension d > 1 and the capacity does not exceed polylog(n). The paper was published in Journal of Global Optimization
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
Extended formulations for robust maintenance planning at power plants
No full textNational audienceWe consider the large-scale power plant maintenance scheduling and production planning problem submitted by EDF to the 2010 Euro/Roadef Challenge. Electricity demand must be met by the combined production of nuclear power plants and thermic plants. The latter can operate continuously while the former have to be shut down regularly for refuelling and maintenance, and cannot produce during outage periods. In this model, we introduce uncertainty about the duration of maintenance operations: we assume that the durations of outages can be extended beyond their normal durations. The objective is to minimize the worst-case total power production cost.In the context of a rolling horizon approach, we investigate the impact of different hypotheses on the uncertainty set on the cost ofthe solutions and on the difficulty to obtain good solutions. Our solver uses an extended formulation of the problem, which is solved by column generation
A Mixed Integer Linear Programming approach to minimize the number of late jobs with and without machine availability constraints
No full textInternational audienceThis study investigates scheduling problems that occur when the weighted number of late jobs that are subject to deterministic machine availability constraints have to be minimized. These problems can be modeled as a more general job selection problem. Cases with resumable, non-resumable, and semi-resumable jobs as well as cases without availability constraints are investigated. The proposed efficient mixed integer linear programming approach includes possible improvements to the model, notably specialized lifted knapsack cover cuts. The method proves to be competitive compared with existing dedicated methods: numerical experiments on randomly generated instances show that all 350-job instances of the test bed are closed for the well-known problem . For all investigated problem types, 98.4% of -job instances can be solved to optimality within one hour
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