1,721,049 research outputs found
A combinatorial flow-based formulation for temporal bin packing problems
Get PDFWe consider two neighboring generalizations of the classical bin packing problem: the temporal bin packing problem (TBPP) and the temporal bin packing problem with fire-ups (TBPP-FU). In both cases, the task
is to arrange a set of given jobs, characterized by a resource consumption and an activity window, on homogeneous servers of limited capacity. To keep operational costs but also energy consumption low, TBPP
is concerned with minimizing the number of servers in use, whereas TBPP-FU additionally takes into account the switch-on processes required for their operation. Either way, challenging integer optimization
problems are obtained, which can differ significantly from each other despite the seemingly only marginal
variation of the problems. In the literature, a branch-and-price method enriched with many preprocessing
steps (for TBPP) and compact formulations (for TBPP-FU), benefiting from numerous reduction methods,
have emerged as, currently, the most promising solution methods. In this paper, we introduce, in a sense,
a unified solution framework for both problems (and, in fact, a wide variety of further interval scheduling
applications) based on graph theory. Any scientific contributions in this direction failed so far because of
the exponential size of the associated networks. The approach we present in this article does not change
the theoretical exponentiality itself, but it can make it controllable by clever construction of the resulting
graphs. In particular, for the first time all classical benchmark instances (and even larger ones) for the
two problems can be solved – in times that significantly improve those of the previous approaches
Variable and constraint reduction techniques for the temporal bin packing problem with fire-ups
Get PDFThe aim of this letter is to design and computationally test several improvements for the
compact integer linear programming (ILP) formulations of the temporal bin packing
problem with fire-ups (TBPP-FU). This problem is a challenging generalization of
the classical bin packing problem in which the items, interpreted as jobs of given
weight, are active only during an associated time window. The TBPP-FU objective
function asks for the minimization of the weighted sum of the number of bins, viewed
as servers of given capacity, to execute all the jobs and the total number of fire-ups.
The fire-ups count the number of times the servers are activated due to the presence of
assigned active jobs. Our contributions are effective procedures to reduce the number
of variables and constraints of the ILP formulations proposed in the literature as well
as the introduction of new valid inequalities. By extensive computational tests we
show that substantial improvements can be achieved and several instances from the
literature can be solved to proven optimality for the first time
Improved flow-based formulations for the skiving stock problem
Get PDFThanks to the rapidly advancing development of (commercial) MILP software and hardware components, pseudo-polynomial formulations have been established as a powerful tool for solving cutting and packing problems in recent years. In this paper, we focus on the one-dimensional skiving stock problem (SSP), where a given inventory of small items has to be recomposed to obtain a maximum number of larger objects, each satisfying a minimum threshold length. In the literature, different modeling approaches for the SSP have been proposed, and the standard flow-based formulation has turned out to lead to the best trade-off between efficiency and solution time. However, especially for instances of practically meaningful sizes, the resulting models involve very large numbers of variables and constraints, so that appropriate reduction techniques are required to decrease the numerical efforts. For that reason, this paper introduces two improved flow-based formulations for the skiving stock problem that are able to cope with much larger problem sizes. By means of extensive experiments, these new models are shown to possess significantly fewer variables as well as an average better computational performance compared to the standard arcflow formulation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
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