1,721,229 research outputs found
Perspectives on model forecasts of the 2014–2015 Ebola epidemic in West Africa: lessons and the way forward
Full text linkThe unprecedented impact and modeling efforts associated with the 2014-2015 Ebola epidemic in West Africa provides a unique opportunity to document the performances and caveats of forecasting approaches used in near-real time for generating evidence and to guide policy. A number of international academic groups have developed and parameterized mathematical models of disease spread to forecast the trajectory of the outbreak. These modeling efforts often relied on limited epidemiological data to derive key transmission and severity parameters, which are needed to calibrate mechanistic models. Here, we provide a perspective on some of the challenges and lessons drawn from these efforts, focusing on (1) data availability and accuracy of early forecasts; (2) the ability of different models to capture the profile of early growth dynamics in local outbreaks and the importance of reactive behavior changes and case clustering; (3) challenges in forecasting the long-term epidemic impact very early in the outbreak; and (4) ways to move forward. We conclude that rapid availability of aggregated population-level data and detailed information on a subset of transmission chains is crucial to characterize transmission patterns, while ensemble-forecasting approaches could limit the uncertainty of any individual model. We believe that coordinated forecasting efforts, combined with rapid dissemination of disease predictions and underlying epidemiological data in shared online platforms, will be critical in optimizing the response to current and future infectious disease emergencies
Renormalization approach to the self-organized critical behavior of sandpile models
Full text linkWe introduce a renormalization scheme of a type that is able to describe the self-organized critical state (SOC) of sandpile models. We have defined a characterization of the phase space that allows us to study the evolution of the dynamics under change of scale. In addition, a stationarity condition provides a feedback mechanism that drives the system to its critical state. We obtain an attractive fixed point in the phase space of the parameters that clarifies the self-organized critical nature of these systems. The universality class of several models is identified by studying the properties of the basin of attraction of this fixed point. We compute analytically the avalanche exponent τ and the dynamical exponent z for sandpile models in d=2. The values obtained are in very good agreement with computer simulations. The renormalization scheme can also be applied to study nonconservative sandpile models. The result is that the introduction of a dissipation parameter destroys the critical properties as suggested from simulations. The present theoretical framework seems particularly suitable for all SOC problems and can be naturally extended to other systems showing a critical nonequilibrium stationary state
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
Algorithmic computation and approximation of semantic similarity
Full text linkAutomatic extraction of semantic information from text and links in Web pages is key to improving the quality of search results. However, the assessment of automatic semantic measures is limited by the coverage of user studies, which do not scale with the size, heterogeneity, and growth of the Web. Here we propose to leverage human-generated metadata—namely topical directories—to measure semantic relationships among massive numbers of pairs of Web pages or topics. The Open Directory Project classifies millions of URLs in a topical ontology, providing a rich source from which semantic relationships between Web pages can be derived. While semantic similarity measures based on taxonomies (trees) are well studied, the design of well-founded similarity measures for objects stored in the nodes of arbitrary ontologies (graphs) is an open problem. This paper defines an information-theoretic measure of semantic similarity that exploits both the hierarchical and non-hierarchical structure of an ontology. An experimental study shows that this measure improves significantly on the traditional taxonomy-based approach. This novel measure allows us to address the general question of how text and link analyses can be combined to derive measures of relevance that are in good agreement with semantic similarity. Surprisingly, the traditional use of text similarity turns out to be ineffective for relevance ranking.Fil: Maguitman, Ana Gabriela. Indiana University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; ArgentinaFil: Menczer, Filippo. Indiana University; Estados UnidosFil: Erdinc, Fulya. Indiana University; Estados UnidosFil: Roinestad, Heather. Indiana University; Estados UnidosFil: Vespignani, Alessandro. Indiana University; Estados Unido
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
Decoding the structure of the WWW: a comparative analysis of web crawls
No full textThe understanding of the immense and intricate topological structure of the World Wide Web (WWW) is a major scientific and technological challenge. This has been recently tackled by char-acterizing the properties of its representative graphs, in which vertices and directed edges areidentified with Web pages and hyperlinks, respectively. Data gathered in large-scale crawls havebeen analyzed by several groups resulting in a general picture of the WWW that encompassesmany of the complex properties typical of rapidly evolving networks. In this article, we report adetailed statistical analysis of the topological properties of four different WWW graphs obtainedwith different crawlers. We find that, despite the very large size of the samples, the statistical mea-sures characterizing these graphs differ quantitatively, and in some cases qualitatively, dependingon the domain analyzed and the crawl used for gathering the data. This spurs the issue of thepresence of sampling biases and structural differences of Web crawls that might induce propertiesnot representative of the actual global underlying graph. In short, the stability of the widely ac-cepted statistical description of the Web is called into question. In order to provide a more accuratecharacterization of the Web graph, we study statistical measures beyond the degree distribution,such as degree-degree correlation functions or the statistics of reciprocal connections. The latterappears to enclose the relevant correlations of the WWW graph and carry most of the topologica.Fil: Serrano, Maria Angeles. Indiana University; Estados Unidos. Institute for Scientific Interchange; ItaliaFil: Maguitman, Ana Gabriela. Universidad Nacional del Sur; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; ArgentinaFil: Boguña, Marian. Universitat de Barcelona; EspañaFil: Fortunato, Santo. Institute for Scientific Interchange; Italia. Indiana University; Estados UnidosFil: Vespignani, Alessandro. Institute for Scientific Interchange; Italia. Indiana University; Estados Unido
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