1,721,045 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
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
The Optimal swapping problem during nuclear refueling operations
Full text linkMinimizing the downtime due to refueling is a crucial economic problem in Pressurized Water Nuclear Reactors. Among the unloaded nuclear fuel bundles, some remain in the cooling pool and are replaced by fresh ones when the reactor is reloaded. The fuel bundles are covered by so-called "clusters" which serve different roles during the nuclear reaction: some help regulate the reaction, some are emergency stopping systems, others allow monitoring and some are simple plugs covering the bundle. When the reactor is emptied, bundles are manipulated together with their clusters, but since bundles do not return to the same position in the core after refueling, many clusters need to be swapped between bundles in order to move to their correct position when the core is reloaded. This swapping operation uses different tools to handle the clusters but only one tool at a time can be used on the manipulation crane. Finally, some clusters are interchangeable, making some permutations operations equivalent overall. The global number of cluster permutations leads to a dramatically combinatorial problem when trying to minimize the global operation time, which is a crucial issue since this operation is part of the refueling process' critical path.
We approach this problem as a graph-based shortest path problem between an initial situation and one of the multiple possible desired allocations of clusters on bundles. Our contribution is three-fold. First we analyze the problem symmetries and define an abstract state which groups together equivalent states, making the goal state unique. This first step uses the equivalence between interchangeable clusters and the equivalence between non-reloaded bundles. It allows to reason in terms of equivalent sets rather than in terms of bundles and clusters, and hence reduces the number of equivalent search paths. Secondly, we define an on-the-fly child node generation procedure, that only generates a subgraph of the search graph, which is guaranteed to contain at least one optimal path to the goal state. This pruning procedure exploits the equivalence between sequences of operations. Finally, we experimented a heuristic A* search algorithm in this pruned abstract subgraph and a stochastic depth first search (DFS). The best admissible heuristic for the A* search turned out to be a simple weighted Hamming distance with the goal state. We observed that only the DFS approach was able to tackle industrial size instances of the Optimal Swapping Problem and conjectured that the solution quality was close to optimal, based on comparisons between both approaches on smaller instances. Overall, this study provides insight into a difficult combinatorial problem and introduces efficient methods to address the full planning problem as well as on-the-fly replanning issues
Temporal coordination under uncertainty: initial results for the two agents case
Full text linkWe focus on the problem of decentralized planning and coordination for two
heterogeneous autonomous agents, having a common mission in an uncertain
environment. For example, we consider a helicopter UAV and a ground rover
cooperating in the exploration of a dangerous zone where communication is
limited, which forces decentralization of planning. After proposing a framework for decentralized planning, we underline the need for a planner under uncertainty taking continuous time into account in time-dependent
problems and present initial results on temporal planning under uncertainty
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
Temporal Markov Decision Problems : Formalization and Resolution
Full text linkThis thesis addresses the question of planning under uncertainty within a time-dependent changing environment. Original motivation for this work came from the problem of building an autonomous agent able to coordinate with its
uncertain environment; this environment being composed of other agents communicating their intentions or non-controllable processes for which some discrete-event model is available. We investigate several approaches for modeling continuous time-dependency in the framework of Markov Decision Processes (MDPs), leading us to a definition of Temporal Markov Decision Problems. Then our approach focuses on two separate paradigms. First, we investigate time-dependent problems as \emph{implicit-event} processes and describe them through the formalism of Time-dependent MDPs (TMDPs). We extend the existing results concerning optimality equations and present a new Value Iteration algorithm based on piecewise polynomial function representations in order to solve a more general class of TMDPs. This paves the way to a more general discussion on parametric actions in hybrid state and action spaces MDPs with continuous time. In a second time, we investigate the
option of separately modeling the concurrent contributions of exogenous events. This approach of \emph{explicit-event} modeling leads to the use of Generalized Semi-Markov Decision Processes (GSMDP). We establish a link between the general framework of Discrete Events Systems Specification (DEVS) and the formalism of GSMDP, allowing us to build sound discrete-event compatible simulators. Then we introduce a simulation-based Policy Iteration approach for
explicit-event Temporal Markov Decision Problems. This algorithmic contribution brings together results from simulation theory, forward search in MDPs, and statistical learning theory. The implicit-event approach was tested on a
specific version of the Mars rover planning problem and on a drone patrol mission planning problem while the explicit-event approach was evaluated on a subway network control problem
Towards a hybrid approach for intra-daily recourse strategies
Full text linkThis paper highlights continued work on the question of combining Supervised Learning (SL) and Mixed Integer Programming (MIP) in order to solve intra-daily recourse strategies computation problems, in the field of energy management. Our goal is twofold. On the one hand we wish to share with the research community which are the hot open problems associated with the hybrid method developed in [3]. On the other hand, we highlight and analyze, and introduce solution methods for three key methodological bottlenecks related to the questionof predicting which power units are the most important ones for these recourse strategies, in order to make the optimization process compatible with operational constraints
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