1,720,970 research outputs found
Set covering and network optimization: dynamic and approximation algorithms
No full textThe dissertation concerns design and analysis of set covering and network optimization algorithms.The content of the dissertation consists of three parts: Probabilistic Set Covering, Dynamic GraphAlgorithms, and Network Optimization. For the set covering problem we study the behavior of asimple algorithm in the most general probabilistic model for the problem. We show that this algorithmis asymptotically optimum in expectation with a small variance of the produced solution values. Thisresults are extended for the case of the well known greedy algorithm for set covering. We also studyrobustness of feasible solutions in the same model. In the second part we design algorithms foroptimization problems on dynamic undirected networks with connectivity constraints and develop thefirst dynamic algorithm for the directed minimum spanning tree problem on directed graphs. Finally,we study two representative network optimization problems: we develop a game-theoretic analysisfor the object placement problem over a network, and design approximation algorithms for theSteiner tree problem in the presence of input uncertainty.Η διατριβή αφορά σε σχεδίαση και ανάλυση αλγορίθμων για το πρόβλημα κάλυψης συνόλου και γιαπροβλήματα βελτιστοποίησης δικτύων. Το περιεχόμενο της διατριβής χωρίζεται θεματικά σε τρίαμέρη: Πιθανοτική Κάλυψη Συνόλου, Δυναμικοί Αλγόριθμοι Γράφων, και Βελτιστοποίηση Δικτύων. Γιατο πρόβλημα κάλυψης συνόλου αναλύουμε τη συμπεριφορά ενός απλού αλγορίθμου στο γενικότεροπιθανοτικό μοντέλο για το πρόβλημα. Δείχνουμε ότι ο αλγόριθμος αυτός είναι βέλτιστος κατάαναμενόμενη τιμή με μικρή διασπορά στις τιμές των λύσεων που παράγει. Τα αποτελέσματα αυτάεπεκτείνονται στην περίπτωση του διαδεδομένου άπληστου αλγόριθμου για το πρόβλημα. Επιπλέονμελετούμε την ευρωστία εφικτών λύσεων στο συγκεκριμένο πιθανοτικό μοντέλο. Στο δεύτερο μέροςσχεδιάζουμε αλγορίθμους για προβλήματα βελτιστοποίησης δυναμικών μη κατευθυνόμενων δικτύωνμε περιορισμούς συνδεσιμότητας και αναπτύσσουμε τον πρώτο δυναμικό αλγόριθμο για τοπρόβλημα κατευθυνόμενου επικαλυπτικού δέντρου ελάχιστου κόστους σε κατευθυνόμενουςγράφους. Τέλος, μελετούμε δύο αντιπροσωπευτικά προβλήματα βελτιστοποίησης δικτύων:αναπτύσσουμε μια παιγνιοθεωρητική ανάλυση για το πρόβλημα τοποθέτησης αντικειμένων σε έναδίκτυο, και σχεδιάζουμε προσεγγιστικούς αλγορίθμους για το πρόβλημα Steiner δέντρου ελάχιστουκόστους σε συνθήκες αβεβαιότητας των δεδομένων εισόδου
Item Bidding for Combinatorial Public Projects
No full textWe present and analyze a mechanism for the Combinatorial Public Project Problem (CPPP). The problem asks to select k out of m available items, so as to maximize the social welfare for autonomous agents with combinatorial preferences (valuation functions) over subsets of items. The CPPP constitutes an abstract model for decision making by autonomous agents and has been shown to present severe computational hardness, in the design of truthful approximation mechanisms. We study a non-truthful mechanism that is, however, practically relevant to multi-agent environments, by virtue of its natural simplicity. It employs an Item Bidding interface, wherein every agent issues a separate bid for the inclusion of each distinct item in the outcome; the k items with the highest sums of bids are chosen and agents are charged according to a VCG-based payment rule. For fairly expressive classes of the agents' valuation functions, we establish existence of socially optimal pure Nash and strong equilibria, that are resilient to coordinated deviations of subsets of agents. Subsequently we derive tight worst-case bounds on the approximation of the optimum social welfare achieved in equilibrium. We show that the mechanism's performance improves with the number of agents that can coordinate, and reaches half of the optimum welfare at strong equilibrium
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
Strategic Scheduling Games: Equilibria and Efficiency
No full textin Book series, Springer Optimization and Its Applications, Volume 60Motivated by today’s decentralized operation of interconnected computing platforms, classical task scheduling models are revisited under a game theoretic perspective. Instead of being designed by a central entity which aims at optimizing an aggregate efficiency measure, task allocations emerge through aggregated localized decisions taken by a group of autonomous self-interested agents. The outcome is sought as an equilibrium whose overall social efficiency typically diverges from the optimal group’s choice. This divergence, captured by a measure that came to be known as the Price of Anarchy, can be alleviated by local scheduling policies called Coordination Mechanisms. This chapter reviews standard task scheduling models, dedicated coordination mechanisms and their influence on the price of anarchy. It also exemplifies the design and analysis of coordination mechanisms on a particular scheduling model with setup times, and discusses open research questions.ouinonouirechercheInternationa
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