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It is vital to support concurrent applications sharing a wireless sensor network in order to reduce the deployment and administrative costs, thus increasing the usability and efficiency of the network. We describe Melete 1 , a system that supports concurrent applications with efficiency, reliability, flexibility, programmability, and scalability. Our work is based on the Maté virtual machine [1] with significant modifications and enhancements. Melete enables reliable storage and execution of concurrent applications on a single sensor node. Dynamic grouping is used for flexible, on-the-fly deployment of applications based on contemporary status of the sensor nodes. The grouping procedure itself is programmed with the TinyScript language. A group-keyed code dissemination mechanism is also developed for reliable and efficient code distribution among sensor nodes. Both analytical and simulation results are presented to study the impact of several key parameters and optimization techniques on the code dissemination mechanism. Simulation results indicate satisfactory scalability of our techniques to both application code size and node density. The usefulness and effectiveness of Melete is also validated by empirical study.

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This paper studies a Bluetooth-based mobile social network application deployed among a group of 28 participants collected during a computer communication conference. We compare the social graph containing friends, as defined by participants, to the contact graph, that is the temporal network created by opportunistic contacts as owners of devices move and come into communication range. Our contribution is twofold: first, we prove that most properties of nodes, links, and paths correlate among the social and contact graphs. Second, we describe how the structure of the social graph helps build forwarding paths in the contact graph, allowing two nodes to communicate over time using opportunistic contacts and intermediate nodes. Efficient paths can be built using only pairs of nodes that are socially close (i.e. connected through a few pairs of friends). Our results indicate that opportunistic forwarding complies with the requirement of social network application.

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