1,721,066 research outputs found
Hurricane risk to healthcare on the United States Atlantic and Gulf Coasts
No full textData for analysis of hurricane storm surge and sea level rise effects on hospital flooding along the Atlantic and Gulf Coast
Fully dynamic (2 + epsilon) approximate all-pairs shortest paths with fast query and close to linear update time
No full textFor any fixed 1 > [epsilon] > 0 we present a fully dynamic algorithm for maintaining (2 + [epsilon])-approximate all-pairs shortest paths in undirected graphs with positive edge weights. We use a randomized (Las Vegas) update algorithm (but a deterministic query procedure), so the time given is the expected amortized update time. Our query time O(log log log n). The update time is O[over ~](mnO(1/[sqrt](log n)) log (nR)), where R is the ratio between the heaviest and the lightest edge weight in the graph (so R = 1 in unweighted graphs). Unfortunately, the update time does have the drawback of a super-polynomial dependence on e. it grows as (3/[epsilon])[sqrt]log n/log(3/[epsilon]) = n [sqrt]log (3/[epsilon])/log n. Our algorithm has a significantly faster update time than any other algorithm with sub-polynomial query time. For exact distances, the state of the art algorithm has an update time of O[over ~](n[superscript 2]). For approximate distances, the best previous algorithm has a O(kmn[superscript 1/k]) update time and returns (2 k - 1) stretch paths. Thus, it needs an update time of O(m[sqrt](n)) to get close to our approximation, and it has to return O([sqrt](log n)) approximate distances to match our update time
A Nearly Optimal Oracle for Avoiding Failed Vertices and Edges
Full text linkWe present an improved oracle for the distance sensitivity problem. The goal is to preprocess a directed graph G = (V,E) with non-negative edge weights to answer queries of the form: what is the length of the shortest path from x to y that does not go through some failed vertex or edge f. The previous best algorithm produces an oracle of size ~O(n[superscript 2]) that has an O(1) query time, and an ~O(nn[superscript 2]√m) construction time. It was a randomized Monte Carlo algorithm that worked with high probability. Our oracle also has a constant query time and an ~O(n[superscript 2]) space requirement, but it has an improved construction time of ~O(mn), and it is deterministic. Note that O(1) query, O(n[superscript 2]) space, and O(mn) construction time is also the best known bound (up to logarithmic factors) for the simpler problem of finding all pairs shortest paths in a weighted, directed graph. Thus, barring improved solutions to the all pairs shortest path problem, our oracle is optimal up to logarithmic factors
Matchings in evolving graphs
No full textTraditionally, the matching problem has been studied in settings where the entire graph is a priori available to the algorithm. Several practical applications such as internet ad allocation, ride sharing, and task allocation have motivated the study of this problem in models where the graph is revealed in parts or is undergoing modifications. In this thesis, we study the matching problem in such evolving graph models:
1. Online Graphs with Bounded Recourse: In the online model, the graph, while fixed, is revealed to the algorithm adversarially, in the form of requests. The algorithm is required to respond to these requests immediately, and irrevocably. We study a variant of this model where the algorithm can revoke its decisions a bounded number of times. In this setting, we show upper and lower bounds on the recourse when the goal is to maintain an optimal matching.
2. Dynamic Graphs: In the dynamic graph model, the graph is undergoing modifications in the form of edge insertions and deletions. The algorithm must adapt to these changes with the goal of minimizing the work done to reoptimize the solution. We study the matching problem in partially and fully dynamic settings, and obtain efficient algorithms which maintain close to optimal solutions.Ph.D.Includes bibliographical reference
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
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