Mesure acoustique des sédiments en suspension dans les rivières : impact potentiel des micro-bulles d'air?

Underwater Acoustics Conference and Exhibition 2017, Skiathos, GRC, 03-/09/2017 - 08/09/2017International audienceFollowing the success of Acoustic Doppler Current Profiler (ADCP) technology for measuring river discharge, there has been a growing interest in the last decade in extracting information on river suspended sediment fluxes from acoustic backscatter data. Despite the efforts to find a relationship between suspended sediment concentration (SSC) and backscatter, an inversion technique applicable to vertical river backscatter profiles is still missing. The theoretical and empirical bases of such techniques have been originally developed for ocean bottom suspended sediment monitoring. As a first step in our attempt to adapt these models to rivers, we measured the acoustic response of a usual glass beads suspension in a tank. Unsurprisingly, the acoustic model agrees quite well with the measurements as soon as the effect of air micro-bubbles is limited. As a second step, we deployed an acoustic backscatter profiler in the Rhône River (France) in very clear water conditions (SSC < 10 mg/l). The recorded acoustic intensities were stronger than expected at low frequency, suggesting that other scatters may contribute to the recorded echo. Typical river sediment suspensions are expected to produce weak backscatter signal, especially at common ADCP frequencies, due to small particle sizes (Rayleigh regime) and relatively low concentrations. In such conditions, the impact of air micro-bubbles - generally neglected at the bottom of the ocean - could be relevant in rivers. This preliminary work calls for further investigation to assess the potential impact of nonsediment scatterers on acoustic backscatter when trying to measure SSC with sonar technologies in rivers

On the stability of standing waves of Klein-Gordon equations in a semiclassical regime

We investigate the orbital stability and instability of standing waves for two classes of Klein-Gordon equations in the semi-classical regime.Comment: 9 page

Analytic theory of narrow lattice solitons

The profiles of narrow lattice solitons are calculated analytically using perturbation analysis. A stability analysis shows that solitons centered at a lattice (potential) maximum are unstable, as they drift toward the nearest lattice minimum. This instability can, however, be so weak that the soliton is ``mathematically unstable'' but ``physically stable''. Stability of solitons centered at a lattice minimum depends on the dimension of the problem and on the nonlinearity. In the subcritical and supercritical cases, the lattice does not affect the stability, leaving the solitons stable and unstable, respectively. In contrast, in the critical case (e.g., a cubic nonlinearity in two transverse dimensions), the lattice stabilizes the (previously unstable) solitons. The stability in this case can be so weak, however, that the soliton is ``mathematically stable'' but ``physically unstable''

The Air Microwave Yield (AMY) experiment - A laboratory measurement of the microwave emission from extensive air showers

The AMY experiment aims to measure the microwave bremsstrahlung radiation (MBR) emitted by air-showers secondary electrons accelerating in collisions with neutral molecules of the atmosphere. The measurements are performed using a beam of 510 MeV electrons at the Beam Test Facility (BTF) of Frascati INFN National Laboratories. The goal of the AMY experiment is to measure in laboratory conditions the yield and the spectrum of the GHz emission in the frequency range between 1 and 20 GHz. The final purpose is to characterise the process to be used in a next generation detectors of ultra-high energy cosmic rays. A description of the experimental setup and the first results are presented.Comment: 3 pages -- EPS-HEP'13 European Physical Society Conference on High Energy Physics (July, 18-24, 2013) at Stockholm, Swede

Intruder bands and configuration mixing in the lead isotopes

A three-configuration mixing calculation is performed in the context of the interacting boson model with the aim to describe recently observed collective bands built on low-lying $0^+$ states in neutron-deficient lead isotopes. The configurations that are included correspond to the regular, spherical states as well as two-particle two-hole and four-particle four-hole excitations across the Z=82 shell gap.Comment: 20 pages, 4 figures, accepted by PRC, reference added for section 1 in this revised versio

Collectivity and configuration mixing in 186,188Pb and 194Po

Lifetimes of prolate intruder states in 186Pb and oblate intruder states in 194Po have been determined by employing, for the first time, the recoil-decay tagging technique in recoil distance Doppler-shift lifetime measurements. In addition, lifetime measurements of prolate states in 188Pb up to the 8+ state were carried out using the recoil-gating method. The B(E2) values have been deduced from which deformation parameters |β2|=0.29(5) and |β2|=0.17(3) for the prolate and the oblate bands, respectively, have been extracted. The results also shed new light on the mixing between different shapes

Collectivity and Configuration Mixing in \u3csup\u3e186,188\u3c/sup\u3ePb and \u3csup\u3e194\u3c/sup\u3ePo

Lifetimes of prolate intruder states in 186Pb and oblate intruder states in 194Po have been determined by employing, for the first time, the recoil-decay tagging technique in recoil distance Doppler-shift lifetime measurements. In addition, lifetime measurements of prolate states in 188Pb up to the 8+state were carried out using the recoil-gating method. The B(E2) values have been deduced from which deformation parameters lβ2l = 0.29(5) and lβ2l = 0.17(3) for the prolate and the oblate bands, respectively, have been extracted. The results also shed new light on the mixing between different shapes

Highlights from the Pierre Auger Observatory

The Pierre Auger Observatory is the world's largest cosmic ray observatory. Our current exposure reaches nearly 40,000 km$^2$ str and provides us with an unprecedented quality data set. The performance and stability of the detectors and their enhancements are described. Data analyses have led to a number of major breakthroughs. Among these we discuss the energy spectrum and the searches for large-scale anisotropies. We present analyses of our X$_{max}$ data and show how it can be interpreted in terms of mass composition. We also describe some new analyses that extract mass sensitive parameters from the 100% duty cycle SD data. A coherent interpretation of all these recent results opens new directions. The consequences regarding the cosmic ray composition and the properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray Conference, Rio de Janeiro 201