SUMMARYThe main purpose of this work is to present a new parallel direct solver: Dissection solver. It is based on LU factorization of the sparse matrix of the linear system and allows to detect automatically and handle properly the zero-energy modes, which are important when dealing with DDM. A performance evaluation and comparisons with other direct solvers (MUMPS, DSCPACK) are also given for both sequential and parallel computations. Results of numerical experiments with a two-level parallelization of large-scale structural analysis problems are also presented: FETI is used for the global problem parallelization and Dissection for the local multithreading. In this framework, the largest problem we have solved is of an elastic solid composed of 400 subdomains running on 400 computation nodes (3200 cores) and containing about 165 millions dof. The computation of one single iteration consumes less than 20 min of CPU time. Several comparisons to MUMPS are given for the numerical computation of large-scale linear systems on a massively parallel cluster: performances and weaknesses of this new solver are highlighted.

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Road traffic accidents (RTAs) are a global burden that particularly affects people in developing countries. According to the World Health Organization, having reliable and precise data is necessary to raise the alert on the scale of road accidents and convince decision-makers of the need to take action. Each year, nearly 700 people lose their lives due to accidents on Senegalese roads. In Senegal, dis-aggregated data related to accidents are rare due to very significant under-recording. Most of these data are in a non-computerized form and their collection methods differ from one side to the other among road safety actors. The task of collecting data is simply considered of secondary importance for certain road safety actors. The disparity between the collection methods as well as collected data and the non computerized collection processes limit the possibility of having a real knowledge of the phenomenon of road accidents. In this work, we present a global solution of a road crash data collection and management system. In particular, we will focus here on the collection component with an application that aims to federate data collection processes of all road safety actors in Senegal. It uses a collection guide designed after a review of road accident data guides in Senegal and in other regions of the world. It also implements a parallel collection methodology, i.e the possibility of several agents working on collecting data for the same accident.

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Free space optical (FSO) communication systems provide wireless line of sight connectivity in the unlicensed spectrum, and wireless optical communication achieves higher data rates compared to their radio frequency (RF) counterparts. FSO systems are particularly attractive for last mile access problem by bridging fiber optic backbone connectivity to RF access networks. To cope with this practical deployment scenario, there has been increasing attention to the so-called dual-hop (RF/FSO) systems where RF transmission is used at a hop followed by FSO transmission to another. In this article, we study the performance of cooperative transmission systems using a mixed RF-FSO DF (decode and forward) relay using error-correcting codes including QC-LDPC codes at the relay level. The FSO link is modeled by the gamma-gamma distribution, and the RF link is modeled by the Additive White Gaussian Noise (AWGN) model. Another innovation in this article is the use of cooperative systems using a mixed FSO/RF DF relay using quasicyclic low-density parity check (QC-LDPC) codes at the relay level. We also use the space-coupled low-density parity check (SC-LDPC) codes on the same scheme to show its importance in cooperative optical transmission but also in hybrid RF/FSO transmission. The latter will be compared with QC-LDPC codes. The use of mixed RF/FSO cooperative transmission systems can improve the reliability and transmission of information in networks. The results demonstrate an improvement in the performance of the cooperative RF/FSO DF system based on QC-LDPC and SC-LDPC codes compared to RF/FSO systems without the use of codes, but also to the DF systems proposed in the existing literature.