Pyrotechnie : une évaluation des risques

Depuis une dizaine d'années, la pyrotechnie tend à se démocratiser, comme en témoigne le développement du marché des artifices de divertissement pour le grand public en France. Elle touche de même l'ensemble de la population dans des applications comme les équipements de sécurité des véhicules automobiles de type airbags ou prétensionneurs de ceinture de sécurité. En effet, ces équipements mettent en oeuvre des matériaux énergétiques adaptés au temps de réaction, extrêmement court, nécessaire à leur bon fonctionnement

Solving ambiguities in contig assembly of Idiomarina loihiensis L2TR chromosome by in silico analyses

Nucleotide composition analyses of bacterial genomes such as cumulative GC skew highlight the atypical, strongly asymmetric architecture of the recently published chromosome of Idiomarina loihiensis L2TR, suggesting that an inversion of a 600-kb chromosomal segment occurred. The presence of 3.4-kb inverted repeated sequences at the borders of the putative rearrangement supports this hypothesis. Reverting in silico this segment restores (1) a symmetric chromosome architecture; (2) the co-orientation of transcription of all rRNA operons with DNA replication; and (3) a better conservation of gene order between this chromosome and other γ-proteobacterial ones. Finally, long-range PCRs encompassing the ends of the 600-kb segment reveal the existence of the reverted configuration but not of the published one. This demonstrates how cumulative nucleotide-skew analyses can validate genome assemblie

The all-intracellular order Legionellales is unexpectedly diverse, globally distributed and lowly abundant

Legionellales is an order of the Gammaproteobacteria, only composed of host-adapted, intracellular bacteria, including the accidental human pathogens Legionella pneumophila and Coxiella burnetii. Although the diversity in terms of lifestyle is large across the order, only a few genera have been sequenced, owing to the difficulty to grow intracellular bacteria in pure culture. In particular, we know little about their global distribution and abundance. Here, we analyze 16/18S rDNA amplicons both from tens of thousands of published studies and from two separate sampling campaigns in and around ponds and in a silver mine. We demonstrate that the diversity of the order is much larger than previously thought, with over 450 uncultured genera. We show that Legionellales are found in about half of the samples from freshwater, soil and marine environments and quasi-ubiquitous in man-made environments. Their abundance is low, typically 0.1%, with few samples up to 1%. Most Legionellales OTUs are globally distributed, while many do not belong to a previously identified species. This study sheds a new light on the ubiquity and diversity of one major group of host-adapted bacteria. It also emphasizes the need to use metagenomics to better understand the role of host-adapted bacteria in all environments. The all-intracellular bacterial order of Legionellales is much more diverse, prevalent and globally distributed than previously thought

A genomic island present along the bacterial chromosome of the Parachlamydiaceae UWE25, an obligate amoebal endosymbiont, encodes a potentially functional F-like conjugative DNA transfer system

BACKGROUND: The genome of Protochlamydia amoebophila UWE25, a Parachlamydia-related endosymbiont of free-living amoebae, was recently published, providing the opportunity to search for genomic islands (GIs). RESULTS: On the residual cumulative G+C content curve, a G+C-rich 19-kb region was observed. This sequence is part of a 100-kb chromosome region, containing 100 highly co-oriented ORFs, flanked by two 17-bp direct repeats. Two identical gly-tRNA genes in tandem are present at the proximal end of this genetic element. Several mobility genes encoding transposases and bacteriophage-related proteins are located within this chromosome region. Thus, this region largely fulfills the criteria of GIs. The G+C content analysis shows that several modules compose this GI. Surprisingly, one of them encodes all genes essential for F-like conjugative DNA transfer (traF, traG, traH, traN, traU, traW, and trbC), involved in sex pilus retraction and mating pair stabilization, strongly suggesting that, similarly to the other F-like operons, the parachlamydial tra unit is devoted to DNA transfer. A close relatedness of this tra unit to F-like tra operons involved in conjugative transfer is confirmed by phylogenetic analyses performed on concatenated genes and gene order conservation. These analyses and that of gly-tRNA distribution in 140 GIs suggest a proteobacterial origin of the parachlamydial tra unit. CONCLUSIONS: A GI of the UWE25 chromosome encodes a potentially functional F-like DNA conjugative system. This is the first hint of a putative conjugative system in chlamydiae. Conjugation most probably occurs within free-living amoebae, that may contain hundreds of Parachlamydia bacteria tightly packed in vacuoles. Such a conjugative system might be involved in DNA transfer between internalized bacteria. Since this system is absent from the sequenced genomes of Chlamydiaceae, we hypothesize that it was acquired after the divergence between Parachlamydiaceae and Chlamydiaceae, when the Parachlamydia-related symbiont was an intracellular bacteria. It suggests that this heterologous DNA was acquired from a phylogenetically-distant bacteria sharing an amoebal vacuole. Since Parachlamydiaceae are emerging agents of pneumonia, this GI might be involved in pathogenicity. In future, conjugative systems might be developed as genetic tools for Chlamydiales

Security enhancements for FPGA-based MPSoCs: a boot-to-runtime protection flow for an embedded Linux-based system

International audienceNowadays, embedded systems become more and more complex: the hardware/software codesign approach is a method to create such systems in a single chip which can be based on reconfigurable technologies such as FPGAs (Field-Programmable Gate Arrays). In such systems, data exchanges are a key point as they convey critical and confidential information and data are transmitted between several hardware modules and software layers. In case of an FPGA development life cycle, OS (Operating System) / data updates as runtime communications can be done through an insecure link: attackers can use this medium to make the system misbehave (malicious injection) or retrieve bitstream-related information (eavesdropping). Recent works propose solutions to securely boot a bitstream and the associated OS while runtime transactions are not protected. This work proposes a full boot-to-runtime protection flow of an embedded Linux kernel during boot and confidentiality/integrity protection of the external memory containing the kernel and the main application code/data. This work shows that such a solution with hardware components induces an area occupancy of 10% of a xc6vlx240t Virtex-6 FPGA while having an improved throughput for Linux booting and lowlatency security for runtime protection

Genometrics as an essential tool for the assembly of whole genome sequences: the example of the chromosome of Bifidobacterium longum NCC2705

BACKGROUND: Analysis of the first reported complete genome sequence of Bifidobacterium longum NCC2705, an actinobacterium colonizing the gastrointestinal tract, uncovered its proteomic relatedness to Streptomyces coelicolor and Mycobacterium tuberculosis. However, a rapid scrutiny by genometric methods revealed a genome organization totally different from all so far sequenced high-GC Gram-positive chromosomes. RESULTS: Generally, the cumulative GC- and ORF orientation skew curves of prokaryotic genomes consist of two linear segments of opposite slope: the minimum and the maximum of the curves correspond to the origin and the terminus of chromosome replication, respectively. However, analyses of the B. longum NCC2705 chromosome yielded six, instead of two, linear segments, while its dnaA locus, usually associated with the origin of replication, was not located at the minimum of the curves. Furthermore, the coorientation of gene transcription with replication was very low. Comparison with closely related actinobacteria strongly suggested that the chromosome of B. longum was misassembled, and the identification of two pairs of relatively long homologous DNA sequences offers the possibility for an alternative genome assembly proposed here below. By genometric criteria, this configuration displays all of the characters common to bacteria, in particular to related high-GC Gram-positives. In addition, it is compatible with the partially sequenced genome of DJO10A B. longum strain. Recently, a corrected sequence of B. longum NCC2705, with a configuration similar to the one proposed here below, has been deposited in GenBank, confirming our predictions. CONCLUSION: Genometric analyses, in conjunction with standard bioinformatic tools and knowledge of bacterial chromosome architecture, represent fast and straightforward methods for the evaluation of chromosome assembly

Identification of Lamination Stack Properties: Application to High Speed Induction Motors

International audienceIn order to predict the lateral rotordynamics of a high-speed induction motor, an optimization procedure is used for identifying the dynamic behavior of the magnetic core made of a lamination stack, tie rods, and short-circuit rods. Modal parameters predicted by a finite-element model based on beam elements and measured on induction motors are included in modal error functions contained in a functional. The minimization of this functional by using the Levenberg-Marquardt algorithm permits extracting the equivalent constitutive properties of the lamination stack for several rotors of different sizes. Finally, the size effect on the constitutive properties identified is discussed

Remark on an example by R.Schoen concerning the scalar curvature

soumis à Differential Geometry and its ApplicationsGeneralization of an example by R.Schoen of multiple solutions for the Yamabe Problem on Manifolds with positive scalar curvature