Spread Spectrum Modulation with Grassmannian Constellations for Mobile Multiple Access Underwater Acoustic Channels

The objective of this study is to evaluate Grassmannian constellations combined with a spread spectrum multiple access scheme for underwater acoustic mobile multiple access communication systems. These communication systems enable the coordination of a fleet of Autonomous Underwater Vehicles (AUVs) from a surface or bottom control unit, e.g., a boat. Due to its robustness against phase rotation, the demodulator of Grassmannian constellations uses non-coherent detection, and the main advantage of such modulation lies in the spectrum efficiency gain with respect to conventional differential modulation. The communication system under study in this paper consists of (i), at the transmitter side, a Grassmannian modulation used in an orthogonal spread spectrum multiple access scheme called Multiuser Hyperbolic Frequency Modulation (MU-HFM) and (ii), at the receiver side, a non-coherent array decoder. The modulation and demodulation are presented as well as the considered spreading sequences. Finally, performances of the proposed transmission scheme are evaluated over replayed underwater acoustic channel responses collected at sea by a multi-sensor acoustic acquisition system.Spread Spectrum Modulation with Grassmannian Constellations for Mobile Multiple Access Underwater Acoustic ChannelspublishedVersio

La chaîne hercynienne au Pérou et en Bolivie : premiers résultats

The main part of the basement of the Peruvian and Bolivian Andes is formed by the remnants of a Hercynian intracratonic range in which some elements of the Precambrian basement are reworked. The Hercynian sedimentary prism is made of thick detrital Lower Paleozoic sediments, which are partly flysch-like but seem to be never associated with ophiolites. Those sediments were strongly disturbed by the Upper Devonian « Eohercynian » folding ; they display close folds with axial-plane cleavage which result of at least two subphases of deformation, in some areas a greenschist facies metamorphism is associated with the folds. On the whole the range does not show any preferential vergence. The Eohercynian folded complex and its unconformable caver of Carboniferous and Lower and Middle Permian sediments are reworked at the end of the Middle Permian by the Late Hercynian movements which in Peru are in most cases only epirogenetic. The magmatism is mostly post-tectonic, granitic rocks are intruded and andesitic tu rhyolitic breccias and slows are interstratified in the Carboniferous and Upper Permian molasses. The chronology of the Hercynian deformation is difficult to establish in Bolivia because i) of the lack of a Permo-Garboniferous caver in the intensely folded axial part of the chain and ii) of the quite complete hiatus of the Upper Permian, Trias and Jurassic. This chronology is infered from the study of the less deformed adjoining regions where the Permo-Carboniferous is present and from considerations about the style and direction of the structures. The result is that in Bolivia the main folding is due to the Late-Hercynian phase. The Peru-Bolivia Hercynian range runs over more than 2 500 km and is connected « en échelon » to the Chile-Argentina Hercynian branch wellknown in the Frontal Cordillera and the Precordillera of Argentina. This branch is a part of the great Hercynian « Samfrau orogene )) which was bordering the Gondwana before ist breaking up and the other elements of which are found in South Africa, in Antarctide and in Australia

Sample preparation for an optimized extraction of localized metabolites in lichens: Application to Pseudevernia furfuracea

International audienceLichens are symbiotic organisms known for producing unique secondary metabolites with attractive cosmetic and pharmacological properties. In this paper, we investigated three standard methods of preparation of Pseudevernia furfuracea (blender grinding, ball milling, pestle and mortar). The materials obtained were characterized by electronic microscopy, nitrogen adsorption and compared from the point of view of extraction. Their microscopic structure is related to extraction efficiency. In addition, it is shown using thalline reactions and mass spectrometry mapping (TOF-SIMS) that these metabolites are not evenly distributed throughout the organism. Particularly, atranorin (a secondary metabolite of interest) is mainly present in the cortex of Pseudevernia furfuracea. Finally, using microwave assisted extraction (MAE) we obtained evidence that an appropriate preparation can increase the extraction efficiency of atranorin by a factor of fiv

Systematic study of halide-induced ring opening of 2-substituted aziridinium salts and theoretical rationalization of the reaction pathways

The ring-opening reactions of 2-alkyl-substituted 1,1-bis(arylmethyl)- and 1-methyl-1-(1-phenylethyl)aziridinium salts with fluoride, chloride, bromide and iodide in acetonitrile have been evaluated for the first time in a systematic way. The reactions with fluoride afforded regioisomeric mixtures of primary and secondary fluorides, whereas secondary β-chloro, β-bromo and β-iodo amines were obtained as the sole reaction products from the corresponding halides by regiospecific ring opening at the substituted position. Both experimental and computational results revealed that the reaction outcomes in the cases of chloride, bromide and iodide were dictated by product stability through thermodynamic control involving rearrangement of the initially formed primary halides to the more stable secondary halides. The ring opening of the same aziridinium salts with fluoride, however, was shown to be mediated by steric interactions (kinetic control), with the corresponding primary β-fluoro amines being obtained as the main reaction products. Only for 2-acylaziridinium ions was the reaction outcome shown to be under full substrate control, affording secondary β-fluoro, β-chloro, β-bromo and β-iodo amines through exclusive attack at the activated α-carbonyl carbon atom

Les traits géologiques essentiels des Andes centrales (Pérou-Bolivie)

The peruano•bolivian segment of the Andes is about 2500 km long and its direction is NW-SE north of 18° S, submeridian further south. Its frame made of precambrian and hercynian folded material, constitutes a sialic basement for the Andean orogenic belt. From a stratigraphical point of view, the peruano-bolivian Andes appear as an intracratonic chain, where continental or neritic series prevail. The paleogeographic evolution is controlled by a system of two or three basins separated by rises and generally oriented parallel to the future chain; its most internal element is a high zone, where an intense volcanic activity has been remarkably constant in time and. space during the Mesozoic. The chain built up through three brief and homo•axial tectonic phases occurring respectively at the end of the Cretaceous, the end of the Eocene and the mid•Pliocene, that develop a moderate folding accompanied by large faults and by rare and local overthrusts. From one phase to the other, the concerned zone migrates progressively to the east. The magmatic evolution appears to be clearly related to the "liminal" position of the chain, that is to the existence of a subduction zone. During the upper Cretaceous and the Tertiary the intrusion of the granodioritic batholiths takes place. Their age and volume gradually decrease to the east. Then a powerful calc•alkaline volcanism sets up, the emissive centers of which migrate too in an easterly direction through the Tertiary