Excitations of amorphous solid helium

We present neutron scattering measurements of the dynamic structure factor, $S(Q,\omega)$, of amorphous solid helium confined in 47 $\AA$ pore diameter MCM-41 at pressure 48.6 bar. At low temperature, $T$ = 0.05 K, we observe $S(Q,\omega)$ of the confined quantum amorphous solid plus the bulk polycrystalline solid between the MCM-41 powder grains. No liquid-like phonon-roton modes, other sharply defined modes at low energy ($\omega<$ 1.0 meV) or modes unique to a quantum amorphous solid that might suggest superflow are observed. Rather the $S(Q,\omega)$ of confined amorphous and bulk polycrystalline solid appear to be very similar. At higher temperature ($T>$ 1 K), the amorphous solid in the MCM-41 pores melts to a liquid which has a broad $S(Q,\omega)$ peaked near $\omega \simeq$ 0 characteristic of normal liquid $^4$He under pressure. Expressions for the $S(Q,\omega)$ of amorphous and polycrystalline solid helium are presented and compared. In previous measurements of liquid $^4$He confined in MCM-41 at lower pressure the intensity in the liquid roton mode decreases with increasing pressure until the roton vanishes at the solidification pressure (38 bars), consistent with no roton in the solid observed here

Design and implementation of a multi-octave-band audio camera for realtime diagnosis

Noise pollution investigation takes advantage of two common methods of diagnosis: measurement using a Sound Level Meter and acoustical imaging. The former enables a detailed analysis of the surrounding noise spectrum whereas the latter is rather used for source localization. Both approaches complete each other, and merging them into a unique system, working in realtime, would offer new possibilities of dynamic diagnosis. This paper describes the design of a complete system for this purpose: imaging in realtime the acoustic field at different octave bands, with a convenient device. The acoustic field is sampled in time and space using an array of MEMS microphones. This recent technology enables a compact and fully digital design of the system. However, performing realtime imaging with resource-intensive algorithm on a large amount of measured data confronts with a technical challenge. This is overcome by executing the whole process on a Graphic Processing Unit, which has recently become an attractive device for parallel computing

Block-sparse approach for the identification of complex sound sources in a room

International audienceGeometrical acoustic softwares are necessary to produce auralizations for specific sound environment. Whether the room impulse response computation require point-source and receiver to be of omnidirectional sensitivity, the influence of their directivity on the resulting virtual audio rendering Is relevant. It is then crucial to account for when simulating accurately a calibrate acoustic model.We treats here the case of the source directivity. The use of a spherical surrounding microphone array remains the most natural way to measure it. The source is located inside the delimiting volume. The radiated pressure is sampled at fixed points. The directivity pattern is then computed in term of spherical harmonics functions. But due to hardware complexity, most of the spherical antennas in the litterature have a few number of microphones. This limits the performance of the antenna in term of resolution and bandwidth. Also, decomposition errors can appear with a possible mismatch between the acoustic center of the source and the origin of the array. An additional optimization task is required which increases the complexity of the process.In this paper, we propose a practical strategy, comprising a dedicated algorithm and an array design, to estimate the directivity pattern of complex sound sources. The study takes place in reverberant rooms.Firstly, we describe a greedy-sparse algorithm called Block Orthogonal Matching Pursuit. By this iterative approach, the identification and characterization tasks can be joint in a unique scheme. This facilitates the acoustic center research. However, under non-anechoic conditions, BlockOMP fails because of the free-field propagation assumption. Considering the first reflections to approximate the room transfer function permits to solve the inverse problem. The notion of virtual microphone arrays, based on an analogy with the Image Source Method, is introduced to extend the validity of BlockOMP. Numerical results supply a proof of the concept in a scenario including multiple acoustic sources.Secondly, a large three-dimensional microphone array is deployed. Largeness concerns here in both its dimensions and the number of microphones. The array consists of five sub-planes which surround the entire room where sources are located. The acquisition system comprises digital MEMS microphones chips. The entire signal processing chain is directly integrated on the captor. The microphones are flush mounted on the walls of the room. The true location of the sensors is known, given by an acoustic geometrical calibration step. The 1024 MEMS record synchronously the pressure signal emitted by the sources. From each harmonic spectral component, a sparse spherical harmonics decomposition of each target can be achieved.An experiment is performed to assert the efficiency of the proposed strategy. The goal is to recover the nature of two prototypes of source. They are build from an unbaffled loudspeaker, arranged to show a dipole and a quadripole behaviour. Their directivity pattern are previously measured under controlled conditions using a semi-circular array of 64 microphones. This database serves here as reference. For the experiment, they emit the same signal simultaneous. The results with our system indicates good correlations. Separating both the sound radiating contribution is well achieved. Our last study case deals with the voice directivity measurements. If the dependence with the frequency has been established, the effect of the phonema variation is rarely identified. We demonstrate here that our apparatus constitutes a powerful tool to examine this aspect

Le Marin – Poterie Boisset

L’intervention archéologique sur le site de l’ancienne Poterie Boisset situé à la Pointe Borgnesse a concerné de manière urgente l’étude d’un four de potier dont la conservation exceptionnelle a été mise à mal par les intempéries qui se sont abattues à la fin du mois d’avril 2013 sur la Martinique, causant l’effondrement de l’angle sud du bâtiment. Les services de l’État (Dac de la Martinique et l’ONF, propriétaire-gestionnaire du site) ont souhaité que soit établi un relevé topographique et ..

Le François – Îlet Oscar

L’opération archéologique qui s’est déroulée sur l’îlet Oscar a concerné l’étude et la fouille d’un petit four à chaux situé au sud-ouest de l’îlet. Le propriétaire-gestionnaire des lieux, l’ONF, souhaitant mettre en valeur le four s’est alors rapproché de la Dac de la Martinique afin d’être informé de l’impact de son projet sur le bâti. Le service régional de l’archéologie a préconisé afin de mieux connaître le site, l’étude et la fouille du four. Le four est implanté sur la roche volcanique..

Le Marin – Petite Poterie

Débutée en novembre 2012, la première campagne de fouille de la poterie Dalençon à Petite Poterie au Marin s’inscrit dans le cadre du Projet Collectif de Recherche dirigé par Henri Amouric (LA3M) et intitulé « Poteries des îles françaises de l’Amérique, productions locales et importées xviie-xxe s. ». L’opération a été soutenue par la Dac Martinique, le Conservatoire du Littoral, le Laboratoire d’archéologie médiévale et moderne en Méditerranée (AMU/CNRS) et l’association Arkaeos. Cette opéra..

Le Marin – Petite Poterie

À l’issue de la troisième année de fouille sur la poterie Dalençon, au lieu-dit Petite Poterie, l’opération archéologique aura contribué à une meilleure connaissance des poteries modernes de la Martinique dont l’étude doit se poursuivre dans le cadre d’une problématique de recherche du LA3M englobant plus largement les Antilles françaises. Les campagnes de fouille de 2012 et de 2013 avaient permis, la première année, de fouiller le four de potier et la partie orientale d’un grand bâtiment de ..