Homoclinic leaves, Hausdorff limits and homeomorphisms

We show that except for one exceptional case, a lamination on the boundary of a 3-dimensional handlebody H is a Hausdorff limit of meridians if and only if it is commensurable to a lamination with a 'homoclinic leaf'. This is a precise version of a philosophy called Casson's Criterion, which appeared in unpublished notes of A. Casson. Applications include a characterization of when a non-minimal lamination is a Hausdorff limit of meridians, in terms of properties of its minimal components, and a related characterization of which reducible self-homeomorphisms of the boundary of H have powers that extend to subcompressionbodies of H.Comment: 74 page

Convexity of strata in diagonal pants graphs of surfaces

We prove a number of convexity results for strata of the diagonal pants graph of a surface, in analogy with the extrinsic geometric properties of strata in the Weil-Petersson completion. As a consequence, we exhibit convex flat subgraphs of every possible rank inside the diagonal pants graph.Comment: 14 pages, 4 figure

Mixing invariants of hyperbolic 3-manifolds

Let M be a compact hyperbolic 3-manifold with incompressible boundary. Consider a complete hyperbolic metric on int(M). To each geometrically finite end of int(M) are traditionnaly associated 3 different invariants : the hyperbolic metric associated to the conformal structure at infinity, the hyperbolic metric on the boundary of the convex core and the bending measured lamination of the convex core. In this note we show how invariants of different types can be realised in the different ends

Analysing End-to-End Packet Delay and Loss in mobile ad hoc networks for interactive audio applications

Colloque avec actes et comité de lecture. nationale.National audienceInteractive audio applications such as audio conferencing and telephony require high constraints on delay, jitter and loss. The packets of these applications must be received without significant loss, with low delay and jitter. When packet loss rate exceeds 10% and one way delay exceeds 150 ms, speech quality can be quite poor. Human conversation tolerates a maximum end-to-end delay of between 150 and 300 milliseconds. In addition, these packets must have a small delay variation to maintain constant rate for successive audio packets at the destination. In ad hoc networks, many factors such load traffic, codec bit rate, routing protocol configuration and mobility speed have an impact on packet loss rate, delays, and jitter which degrade the quality of the received audio signal. In this paper, we analysed how these factors influence packet delay and loss observed at the reciever side. A best knowledge of this behaviour is important to develop more effective mechanisms for dynamic adjustment of playout delays or throughput, in order to improve the perceptual quality of audio applications running in ad hoc networks. At the receiver side, we distinguish two operating phases of an audio flow, normal phase and reconfiguration phase. During a normal phase the flow reaches the destination from the source on the same route without link breakage, while during a reconfiguration phase, nodes move on the current route and the audio flow transfer is interrupted for delay required from a routing protocol to establish a new route towards the destination

TOMAC-WSN: A new WSN efficient protocol for monitoring big distributed mechanical systems

International audienceThis paper addresses a wireless sensor network dedicated to monitor a large mechanical system. The chosen system for the scenario is a chairlift. In this case the wireless sensor network special feature is the mobility of nodes following an invariant path traveled repeatedly. A sensor node is put on each chair and a sink node is at ground at the upper end of the chairlift. A new protocol called TOMAC-WSN is designed in order to schedule frames transmission using token concept. This avoids collision at the medium access. The second concept used by TOMAC-WSN is frame aggregation. This new protocol has been modelled using Finite State Automata. An experimental implementation on Arduino boards shows the correct operation of the network. Network performance in terms of delivery time and packet loss rate is evaluated using simulation. The results show that the proposed TOMAC-WSN protocol delivers the appropriate quality of service for the monitoring of large physical systems

A Survey on Multimedia-Based Cross-Layer Optimization in Visual Sensor Networks

Visual sensor networks (VSNs) comprised of battery-operated electronic devices endowed with low-resolution cameras have expanded the applicability of a series of monitoring applications. Those types of sensors are interconnected by ad hoc error-prone wireless links, imposing stringent restrictions on available bandwidth, end-to-end delay and packet error rates. In such context, multimedia coding is required for data compression and error-resilience, also ensuring energy preservation over the path(s) toward the sink and improving the end-to-end perceptual quality of the received media. Cross-layer optimization may enhance the expected efficiency of VSNs applications, disrupting the conventional information flow of the protocol layers. When the inner characteristics of the multimedia coding techniques are exploited by cross-layer protocols and architectures, higher efficiency may be obtained in visual sensor networks. This paper surveys recent research on multimedia-based cross-layer optimization, presenting the proposed strategies and mechanisms for transmission rate adjustment, congestion control, multipath selection, energy preservation and error recovery. We note that many multimedia-based cross-layer optimization solutions have been proposed in recent years, each one bringing a wealth of contributions to visual sensor networks