Une nouvelle méthode pour caractériser une cible radar

- Dans cet article, on propose une méthode généralisant la méthode root-MUSIC à la diversité de polarisation pour caractériser une cible radar. Cette méthode permet d'exploiter pleinement l'information contenue dans les signaux vectoriels, tout en conservant un temps de calcul comparable à celui des méthodes ne tenant pas compte de l'aspect vectoriel des signaux reçus

La polarisation dans les méthodes à haute résolution

Dans cet article, on se propose de généraliser la méthode MUSIC à la diversité de polarisation. La méthode proposée permet d'exploiter pleinement l'information contenue dans les signaux vectoriels, tout en gardant un temps de calcul raisonnable

A duct mapping method using least squares support vector machines

International audienceThis paper introduces a “refractivity from clutter” (RFC) approach with an inversion method based on a pregenerated database. The RFC method exploits the information contained in the radar sea clutter return to estimate the refractive index profile. Whereas initial efforts are based on algorithms giving a good accuracy involving high computational needs, the present method is based on a learning machine algorithm in order to obtain a real-time system. This paper shows the feasibility of a RFC technique based on the least squares support vector machine inversion method by comparing it to a genetic algorithm on simulated and noise-free data, at 1 and 5 GHz. These data are simulated in the presence of ideal trilinear surface-based ducts. The learning machine is based on a pregenerated database computed using Latin hypercube sampling to improve the efficiency of the learning. The results show that little accuracy is lost compared to a genetic algorithm approach. The computational time of a genetic algorithm is very high, whereas the learning machine approach is real time. The advantage of a real-time RFC system is that it could work on several azimuths in near real time

Non circular sources localization using an uncalibrated array

We present in this article a self-calibration method for uncalibrated array of sensors. The proposed algorithm estimates the unknown sensors gain and phase. The originality of our approach is in the consideration of non circularity of the impinging signals. We show that this method works even in the case where the number of sources is larger than the number of sensors. Simulation examples are processed in order to show the behaviour of our algorithm, in terms of convergence speed and estimation accuracy.Cet article présente un algorithme d'autocalibration d'une antenne multicapteur. Cet algorithme permet d'estimer le gain et la phase des capteurs, dont la connaissance précise est nécessaire pour localiser les sources en présence. L'originalité de notre approche réside dans la prise en compte de la non circularité des sources. L'exploitation de cette caractéristique permet d'augmenter la dimension de l'espace des observations, et de localiser des sources en nombre supérieur à celui des capteurs. Des simulations montrent que la performance de cet algorithme en terme de rapidité de convergence et de précision des estimations est satisfaisante

The abundant extrachromosomal DNA content of the Spiroplasma citri GII3-3X genome

<p>Abstract</p> <p>Background</p> <p><it>Spiroplama citri</it>, the causal agent of citrus stubborn disease, is a bacterium of the class <it>Mollicutes </it>and is transmitted by phloem-feeding leafhopper vectors. In order to characterize candidate genes potentially involved in spiroplasma transmission and pathogenicity, the genome of <it>S. citri </it>strain GII3-3X is currently being deciphered.</p> <p>Results</p> <p>Assembling 20,000 sequencing reads generated seven circular contigs, none of which fit the 1.8 Mb chromosome map or carried chromosomal markers. These contigs correspond to seven plasmids: pSci1 to pSci6, with sizes ranging from 12.9 to 35.3 kbp and pSciA of 7.8 kbp. Plasmids pSci were detected as multiple copies in strain GII3-3X. Plasmid copy numbers of pSci1-6, as deduced from sequencing coverage, were estimated at 10 to 14 copies per spiroplasma cell, representing 1.6 Mb of extrachromosomal DNA. Genes encoding proteins of the TrsE-TraE, Mob, TraD-TraG, and Soj-ParA protein families were predicted in most of the pSci sequences, in addition to members of 14 protein families of unknown function. Plasmid pSci6 encodes protein P32, a marker of insect transmissibility. Plasmids pSci1-5 code for eight different <it>S. citri </it>adhesion-related proteins (ScARPs) that are homologous to the previously described protein P89 and the <it>S. kunkelii </it>SkARP1. Conserved signal peptides and C-terminal transmembrane alpha helices were predicted in all ScARPs. The predicted surface-exposed N-terminal region possesses the following elements: (i) 6 to 8 repeats of 39 to 42 amino acids each (sarpin repeats), (ii) a central conserved region of 330 amino acids followed by (iii) a more variable domain of about 110 amino acids. The C-terminus, predicted to be cytoplasmic, consists of a 27 amino acid stretch enriched in arginine and lysine (KR) and an optional 23 amino acid stretch enriched in lysine, aspartate and glutamate (KDE). Plasmids pSci mainly present a linear increase of cumulative GC skew except in regions presenting conserved hairpin structures.</p> <p>Conclusion</p> <p>The genome of <it>S. citri </it>GII3-3X is characterized by abundant extrachromosomal elements. The pSci plasmids could not only be vertically inherited but also horizontally transmitted, as they encode proteins usually involved in DNA element partitioning and cell to cell DNA transfer. Because plasmids pSci1-5 encode surface proteins of the ScARP family and pSci6 was recently shown to confer insect transmissibility, diversity and abundance of <it>S. citri </it>plasmids may essentially aid the rapid adaptation of <it>S. citri </it>to more efficient transmission by different insect vectors and to various plant hosts.</p

Uplift of the Bolivian orocline coastal areas based on geomorphologic evolution of marine terraces and abrasion surfaces: preliminary results

The southern Pacific coast morphology and especially the presence of marine surfaces gives information on the dynamics of Andean forearc evolution from the Neogene. Along most of the Southern Peru and Northern Chilean coasts, discontinuous uplifts are recorded by marine terraces and marine abrasion surfaces; they have thus, preserved a record of eustatic sea level changes and the uplift history of the coastal area in the Andean forearc. One approach to study the tectonic history of the Andean forearc is to identify its effects in marine sedimentation or erosion patterns along the coastal area. To investigate these processes, the Neogene marine formations are studied in various coastal sections either in southern Peru, at Chala (15°50'S) and Ilo (17°32'S-17°48'S), situated above a steep subduction segment and at San Juan de Marcona (15°20'S), situated above the southern part of the Nazca ridge; or in Chile, from Tongoy (30°15'S) to Los Vilos (31°55'S), situated above a flat subduction segment (Fig.1). We chose various sites from each branch of the Arica bend in order to sample possibly different time spans during the Neogene and different response of the continental plate to the subduction process. Various studies were already undertaken on such problems either in Peru or Chile but mainly leaded to the datation of the 5th isotopic stage. So, differential GPS and cosmogenic datations are pursued in order to propose robust ages on these sites and subtract the effects of eustatic sea-level changes from local curves, identifying tectonic uplifts

Localisation des points brillants d'une cible à partir de la puissance diffractée

Nous présentons ici une méthode de traitement de la puissance diffractée par une cible radar dans le cas de l'approximation en zone optique. A partir d'un diagramme de S.E.R. relevé sur un intervalle angulaire |o,π| nous montrons comment il est possible d'extraire les paramètres caractérisant la cible à partir du spectre obtenu dans le plan de Tchebyscheff. De plus, nous mettons en évidence les réflexions d'ordre 2