1,720,978 research outputs found
Self-configuration of IEEE 802.15.4 Wireless PANs for Urban Applications
No full textPervasive sensor devices are expected to flood the urban environments of the future to provide citizens with specific services. Such services will be based on the monitoring of a multiplicity of urban parameters such as the level of the acoustic/environmental pollution, the presence of traffic jams, specific cultural events, etc. Citizens themselves, through their portable digital devices equipped with sensors, can collect images, sounds and environmental parameters and provide a "real time" vision of a portion of a city or of a particular event. The use of IEEE 802.15.4 wireless sensor networks for this data collection seems particularly appropriate thanks to the characteristics of self-configurability, adaptability, scalability and low cost of this wireless Standard. In this work, we present a distributed procedure able to self-configure an IEEE 802.15.4 Wireless Personal Area Network (WPAN) in order to control the resulting network depth by selecting a suitable node that will perform the coordination of the WPAN. Performance evaluation shows that this approach for reconfiguring the WPAN achieves the goal of limiting the network depth. This will result in a reduction of the overall WPAN energy consumption and packets delay that are key performance parameters to be optimized for urban applications. © 2009 EuMA
A case study for evaluating IEEE 802.15.4 wireless sensor network formation with mobile sinks
No full textWireless Sensor Networks are traditionally composed of a multiplicity of sensor nodes that sense given phenomena and deliver the sensed data to specific sink nodes. In the most of the application scenarios, sensor nodes have been considered motionless. On the contrary, interesting possibilities arise if some sensors are embedded in devices carried by mobile agents as people, cars, animals, etc. If sinks move within the considered sensor field, they are able to provide both sparse sensing and collecting of data measured by static sensors placed at fixed locations. The main goal of this work is to evaluate, through simulations, the impact of sinks' mobility in a wireless sensor network created by using the topology formation mechanism provided by the IEEE 802.15.4 Standard. To this aim, as a practical case study, we consider a wireless sensor network deployed in a museum used to monitor the presence, the localization and other parameters of artworks exposed in it. In this context, we analyze how sinks' mobility affects connectivity and energy consumption for network formation and re-configuration. ©2009 IEEE
Performance and Flexibility of Open Source Routing Software
No full textRouting protocols are a critical component in IP networks. Beside dedicated hardware, a great interest on routing systems based on open software is raising among Internet Service Providers. Many open source implementations of this protocol have been developed, among which Quagga and Xorp are the most used in PC-based router. In this paper we evaluate the OSPF performance of Quagga and Xorp routing software according to the test methodologies defined within the Internet Engineering Task Force. Moreover we describe a set of changes made on Quagga code in order to optimize some processes, whose algorithms were not efficient. In order to show the flexibility of an Open Source Routing Software, we have also implemented in Quagga an incremental algorithm for the evaluation of the shortest path. The realized implementation allows the shortest path computation time to be reduced of about the 97 © 2007 Springer
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
Analisi comparata dell'evoluzione del transitorio di rottura da 3" in gamba fredda nell'impianto PWR unificato e nell'impianto in scala SPES, mediante il programma di calcolo RELAP4/mod6
No full textImpianti di teleriscaldamento. Studio di una centrale Diesel per produzione di energia elettrica ed acqua surriscaldata per reti di teleriscaldamento
No full textCalcolo del coefficiente locale di condensazione per "down-flow" in regime "shear-controlled" su file di tubi orizzontali
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