Anisotropic metrics for finite element meshes using a posteriori error estimates: Poisson and Stokes equations

In this paper, metrics derived from a posteriori error estimates for the Poisson problem and for the Stokes system solved by some finite element methods are presented. Numerical examples of mesh adaptation in two dimensions of the space are given and show that these metrics detect the singular behavior of the solution, in particular its anisotropy.     

A URI-based approach for addressing fragments of media resources on the Web

To make media resources a prime citizen on the Web, we have to go beyond simply replicating digital media files. The Web is based on hyperlinks between Web resources, and that includes hyperlinking out of resources (e.g., from a word or an image within a Web page) as well as hyperlinking into resources (e.g., fragment URIs into Web pages). To turn video and audio into hypervideo and hyperaudio, we need to enable hyperlinking into and out of them. The W3C Media Fragments Working Group is taking on the challenge to further embrace W3C??s mission to lead the World Wide Web to its full potential by developing a Media Fragment protocol and guidelines that ensure the long-term growth of the Web. The major contribution of this paper is the introduction of Media Fragments as a media-format independent, standard means of addressing media resources using URIs. Moreover, we explain how the HTTP protocol can be used and extended to serve Media Fragments and what the impact is for current Web-enabled media formats.     

Which types of firm use collaborative innovative spaces?

Collaborative innovation spaces (CIS) can bring together multiple actors to enhance creativity, collaboration and knowledge exchange, sometimes leading to innovation. In this paper, we suggest that CIS can be categorized into three broad types (internal to the firm, external and virtual) and that each type is related to innovation processes, knowledge-sourcing and geographic context in specific ways. Our results, based on an original firm-level survey, reveal that there is heterogeneity with respect to firm attributes and innovation activities associated with different types of CIS. In particular, whilst innovation is associated with the use of CIS in general, radical and technological innovations are more strongly associated with internal CIS, whereas smaller firms tend to use virtual CIS. External CIS, whilst not associated with technological innovation, are associated with high-tech firms. CIS use does not vary across geographic context. These results emphasize the importance of in-person, internal, CIS for radical and technological innovation and the need to distinguish between different types of CIS in order to understand how each is associated with different types of innovation, knowledge-sourcing and firm.     

Similarity based image selection with frame rate adaptation and local event detection in wireless video sensor networks

Wireless Video Sensor Networks (WVSNs7unding environmental information. Those sensor nodes can locally process the information and then wirelessly transmit it to the coordinator and to the sink to be further processed. As a consequence, more abundant video and image data are collected. In such densely deployed networks, the problem of data redundancy arises when information are gathered from neighboring nodes. To overcome this problem, one important enabling technology for WVSN is data aggregation, which is essential to be cost-efficient. In this paper, we propose a new approach for data aggregation in WVSN based on images and shot similarity functions. It is deployed on two levels: the video-sensor node level and the coordinator level. At the sensor node level the proposed algorithms aim at reducing the number of frames sensed by the sensor nodes and sent to the coordinator. At the coordinator level, after receiving shots from different neighbouring sensor nodes, the similarity between these shots is computed to eliminate redundancies and to only send the frames which meet a certain condition to the sink. The similarity between shots is evaluated based on their color, edge and motion information. We evaluate our approach on a live scenario and compare the results with another approach from the literature in terms of data reduction and energy consumption. The results show that the two approaches have a significant data reduction to reduce the energy consumption, thus our approach tends to overcome the other one in terms of reducing the energy consumption related to the sensing process, and to the transmitting process while guaranteeing the detection of all the critical events at the node and the coordinator levels.

     

Détection d’obstacles routiers par stéréovision : l’approche « v-disparité »

This paper presents an innovating real time method for detecting road obstacles by on board stereovision. After having exposed the stakes of the obstacles detection, having presented the state of the art and having identified the problems to be solved, the developed approach is described. It is based on the analysis of the “v-disparity” image, which provides a suitable representation of the geometric content of the road scene. The method is then evaluated with respect to the problems generally affecting stereovision approaches. The theoretical good properties of the “v-disparity” algorithm — genericity, effectiveness, robustness, and computational efficiency — are thus experimentally confirmed. Thanks to the performances obtained, the described algorithm is used for on board driving assistance applications.     

Solving large sparse linear systems in a grid environment: the GREMLINS code versus the PETSc library

Solving large sparse linear systems is essential in numerous scientific domains. Several algorithms, based on direct or iterative methods, have been developed for parallel architectures. On distributed grids consisting of processors located in distant geographical sites, their performance may be unsatisfactory because they suffer from too many synchronizations and communications. The GREMLINS code has been developed for solving large sparse linear systems on distributed grids. It implements the multisplitting method that consists in splitting the original linear system into several subsystems that can be solved independently. In this paper, the performance of the GREMLINS code obtained with several libraries for solving the linear subsystems is analyzed. Its performance is also compared with that of the widely used PETSc library that enables one to develop portable parallel applications. Numerical experiments have been carried out both on local clusters and on distributed grids.     

Model and heuristic for a generalized access network design problem

The generalized access network design problem consists of finding a topology, capacity assignment and routing that minimize the sum of costs to connect every pair of remote unit and its central node specified by the telecommunication company. We consider an integer programming formulation with a partial multicommodity structure. We analyze some aspects and extensions of the proposed model and we introduce a heuristic based on Lagrangian relaxation and the subgradient method. We report computational results for a set of randomly generated test problems. They include networks with up to 300 nodes and show that even problem instances defined in small networks can be extremely difficult problems. The heuristic generates effective and acceptable designs from the practical point of view. We compare our heuristic with a commercial code. This revised version was published online in June 2006 with corrections to the Cover Date.