1,720,960 research outputs found
Controlled vs. uncontrolled mobility in wireless sensor networks: Some performance insights
No full textAmong the many ways of improving the performance of a wireless sensor network (WSN) in terms of crucial metrics such as its lifetime and data latency, exploiting the mobility of some of the network components has been recently observed to be among the most promising. In this paper we demonstrate how two very different schemes for WSN mobility leads to different benefits for network performance. More specifically, we consider the data MULEs kind of random, uncontrolled mobility with single-hop data collection and we compare it with the controllable mobility of the data collection point (sink) where sensor-to-sink data routing follows multi-hop paths. Through quite thorough ns2-based simulations we show that data MULEs are to be used in those WSNs deployed for delay tolerant applications. Benefits of this scheme include low energy consumption and easier protocol and nodal design. Data latency, however, can be unbearably high. We therefore show that a good tradeoff between network lifetime gains and data latency increases can be obtained by using those solutions where the mobility of the sink is controlled by the network conditions. © 2007 IEEE
Moving multiple sinks through wireless sensor networks for lifetime maximization
No full textWe propose scalable models and centralized heuristics for the concurrent and coordinated movement of multiple sinks in a wireless sensor network (WSN). The proposed centralized heuristic runs in polynomial time given the solution to the linear program and achieves results that are within 2% of the LP-relaxation-based upper bound. It provides a useful benchmark for evaluating centralized and distributed schemes for controlled sink mobility. © 2008 IEEE
Heuristics for lifetime maximization in wireless sensor networks with multiple mobile sinks
No full textThis paper investigates heuristics to control and coordinate the concurrent movement of multiple sinks for lifetime maximization in a wireless sensor network (WSN). We have developed a centralized heuristic that runs in polynomial time given the solution to the linear program from [1] which provides a provable upper bound to the problem of controlled mobility of multiple sinks. The centralized heuristic solves the sink movement and placement problem obtaining lifetimes that are within 2% of the upper bound. We also define a deployable distributed heuristic for coordinating the motion of multiple sinks through the network. The performance comparison of our heuristics with static sink placement and with random sink mobility shows that our distributed heuristic achieves network lifetimes that are remarkably close to the optimum ones, resulting in significant lifetime improvements over random sink mobility (+77.7%) and statically deployed sinks (+382.4%). ©2009 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
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