1,720,959 research outputs found
Decomposition algorithms for a class of nonlinear multicommodity network design problems
No full textThis paper discusses problems in the context of multicommodity network design where the additional constraints (such as capacity), rather than being imposed in a strict manner, are allowed to be violated at the expense of additional penalty costs. Such penalized cost structures allow these constraints to be treated as utilization targets and provide a better modelling framework in terms of strategic or tactical level planning of network design, especially in freight transportation systems. However, due to penalized costs, these problems are generally in the form of a nonlinear integer multicommodity network problem. This paper presents two algorithms based on Lagrangean relaxation and decomposition for the solution of such problems. The first is through relaxing flow constraints that results in an arc decomposition, and the second relies upon dualizing the capacity constraints that result in a flow decomposition. It is shown that nonlinearities in the decomposed substructures can be handled in a very efficient manner. Arc decomposition is shown, through computational experiments, to have better convergence properties. Through the proposed algorithms, reasonably good solutions can be obtained for these problems where publicly available state-of-the-art nonlinear optimization codes fail to identify feasible solutions
Lagrangean-based decomposition algorithms for multicommodity network design problems with penalized constraints
No full textLagrangean-based decomposition algorithms for multicommodity network design problems with penalized constraints
No full textThis paper discusses problems in the context of multicommodity network design where the additional constraints (such as capacity), rather than being imposed in a strict manner, are allowed to be violated at the expense of additional penalty costs. Such penalized cost structures allow these constraints to be treated as utilization targets and provide a better modelling framework in terms of strategic or tactical level planning of network design, especially in freight transportation systems. However, due to penalized costs, these problems are generally in the form of a nonlinear integer multicommodity network problem. This paper presents two algorithms based on Lagrangean relaxation and decomposition for the solution of such problems. The first is through relaxing flow constraints that results in an arc decomposition, and the second relies upon dualizing the capacity constraints that result in a flow decomposition. It is shown that nonlinearities in the decomposed substructures can be handled in a very efficient manner. Arc decomposition is shown, through computational experiments, to have better convergence properties. Through the proposed algorithms, reasonably good solutions can be obtained for these problems where publicly available state-of-the-art nonlinear optimization codes fail to identify feasible solutions
Effect of captopril on aldosterone response to potassium infusion in primary aldosteronism
No full textA novel defense mechanism against SYN flooding attacks in IP networks
No full textSYN flooding exploits the TCP three-way handshake process by sending many connection requests with spoofed source IP addresses to the victim. This keeps the victim from handling legitimate requests by causing it to populate its backlog queue with forged TCP connections. In this paper we propose a novel defense mechanism that makes use of the edge routers of the spoofed IP addresses networks. These edge routers determine whether the incoming SYN-ACK segment is valid or not by maintaining a matching table of the outgoing SYNs and incoming SYN-ACKs and also by using the ARP protocol. If the incoming SYN-ACK segment is not valid, the edge router resets the connection at the victim's machine freeing up an entry in the victim's backlog queue and enabling it to accept other legitimate incoming connection requests. The proposed mechanism introduces also a collaborative model to encourage various networks to protect each other. Implementation and test trials have shown the efficiency of the proposed mechanism. © 2005 IEEE.
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
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