New insights into optimal widely linear array receivers for the demodulation of BPSK, MSK, and GMSK signals corrupted by noncircular interferences-application to SAIC

International audienc

Systeme mixte de goniometrie a haute resolution et de rejection adaptative de brouilleurs dans la gamme HF

Le propos de cet article est de présenter les résultats expérimentaux obtenus, dans la gamme HF, avec un système mixte de goniométrie et de filtrage spatial adaptatif. Une goniométrie à haute-résolution par la méthode MUSIC fournit une estimée des vecteurs directeurs des sources présentes, que le filtrage adaptatif utilise pour mettre en oeuvre le Filtre Adapté Spatial (FAS) à l'une des sources détectées. Après une présentation des techniques utilisées et du système expérimental, les résultats obtenus sont décrits. Ceux-ci sont généralement satisfaisants, aussi bien en ondes de sol qu'en ondes ionosphériques, et dans certains cas approchent même les performances théoriques

Egaliseur multicapteurs à structure DFE : Mise en oeuvre et performances sur un canal radiomobile Brouille

L'augmentation de la capacité des réseaux cellulaires de communications radiomobiles, rendue nécessaire par leur succès croissant auprès des utilisateurs, peut être atteinte en utilisant le principe de l'AMRS (Accès Multiple à Répartition Spatiale), qui consiste à permettre à plusieurs mobiles situés dans la même cellule d'utiliser la même fréquence au même moment. Ce fonctionnement est rendu possible par l'introduction des techniques de traitement d'antenne. L'objet de cet article est précisément de présenter une telle technique, ses performances sur un canal radiomobile brouillé, ainsi que ses conditions de mise en oeuvre (structure, algorithmie, contraintes sur la forme d'onde,...)

Dynamic SIMS for Materials Analysis in Nuclear Science

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Spatial and Space-Time Algorithms for Synchronisation in the Downlink of the UMTS FDD and TDD Modes

This paper presents methods for synchronisation in the downlink of the FDD and TDD modes of a UMTS system. Space-time processing based on multiple receive antennas is used to suppress co-channel interference caused by other base stations. We develop a detection-based synchronisation procedure exploiting the structure of the respective UMTS mode, for which we present two alternative detection algorithms. Simulation results using various propagation environments indicate the good performance of our synchronisation methods in the presence of strong co-channel interference

Thermal diffusion of chlorine in uranium dioxide studied by secondary ion mass spectrometry and X-ray adsorption spectroscopy

In a nuclear reactor, 35Cl present as an impurity in the nuclear fuel is activated by thermal neutron capture. During interim storage or geological disposal of the nuclear fuel, 36Cl may be released from the fuel to the geo/biosphere and contribute significantly to the ‘instant release fraction'. In order to elucidate the diffusion mechanisms, both irradiation and thermal effects must be assessed. This paper deals with the thermal diffusion of chlorine in depleted UO2. For this purpose, sintered UO2 pellets were implanted with 37Cl at an ion fluence of 1013 cm−2 and successively annealed in the 1175–1475 K temperature range. The implanted chlorine is used to simulate the behaviour of the displaced one due to recoil and to interactions with the fission fragments during reactor operation. The behaviour of the pristine and the implanted chlorine was investigated during thermal annealing. SIMS and μ-XAS (at the Cl–K edge) analyses show that: (1) the thermal migration of implanted chlorine becomes significant at 1275 K; this temperature and the calculated activation energy of 4.3 eV points out the great ability of chlorine to migrate in UO2 at relatively low temperatures, (2) the behaviour of the implanted chlorine which aggregates into ‘hot spots' during annealing before its effusion is clearly different from that of the pristine one which remains homogenously distributed after annealing, (3) the ‘hot spot' and the pristine chlorine seem to be in different structural environments. Both types of chlorine are assumed to have a valence state of −I, (4) the comparison between an U2O2Cl5 reference compound and the pristine chlorine environment shows a contribution of the U2O2Cl5 to the pristine chlorine

Molecular dynamics simulations of Mo nanoparticles sputtering under irradiation

International audience$^{99}$Mo is an essential isotope in nuclear medicine, but the nuclear reactors used for their production reaching their end of life, problems of supply arise and new methods of production need to be considered. Here we study the possibility of using gamma and neutron irradiation of Mo nanoparticles (NPs) in suspension and use the separation of the isotopes escaping the nanoparticle by primary recoil to evaluate the efficiency of the process for $^{99}$Mo production. Molecular Dynamics simulations with empirical potential of Ackland and Thetford were used to obtain information about the $^{99}$Mo escape yield from the NPs and the resulting sputtering depending on NPs sizes and recoil energy. Results show that the best yield is obtained for 5 nm NPs irradiated with gamma particles. These results are used to guide accelerator irradiation experiments led in parallel in order to evaluate the possibility of using accelerators instead of nuclear reactors for the production of $^{99}$Mo