Tomographie acoustique du Léman

The main objective was to show that the acoustic tomography constitutes a new method to investigate the main hydrodynamical processes of the lake of Geneva. The work is based of the various related fields to the tomography, namely : acoustic wave propagation, signal processing and physical limnology. The development of a tomographic system was carried out so as to study the dynamics of the Great Lake by the analysis of the propagation along its small axis. This work is based on modelling of the sound propagation and its systematic comparison with experimental data. The constitution of a temperature profiles calendar is created starting from four orthogonal empirical functions constituting a fundamental information for the resolution of the tomographic problem. The modelling of the thermal destratification and of internal stationnary waves effects on the propagation validate winter measurements, which are correlated with the weather data. It is established that the qualification of the major processes controlling hydrodynamics (thermal stratification, internal waves) is possible by the analysis of sound travel times between two sites close to the banks. The main part of this work constitutes a reference for the adaptation of oceanic tomography to the case of great lakes. It suggests solutions for a best comprehension of the major processes during their phase of thermal destratification

Sensor array optimization for sources separation and detection in the at-worst determined case

Most of the number of sources estimation techniques use the well-known signal-subspace approach in which the number of dominant sources is deduced regarding the multiplicity of the lowest eigenvalues of the correlation matrix. In the at-worst determined case (number of microphones just equals the maximal number of possible radiating sources) such methods are inoperative because the noise subspace could be inexistant. However, a well chosen sensor array geometry permits to achieve source detection using eigenvalues above conditions to some a priori knowledge on the sources. This paper explores some relation between geometry and eigenvalues in order to achieve optimal sources detection and separation. This study yields analytical formulations of both optimisation problem by working on the simple case of two uncorrelated harmonic sources. Theoretical and experimental measurements are presented and discussed

Active low-frequency modal noise cancellation for room acoustics: an experimental study

Low frequency background noise in rooms generated by numbers of human activities - traf-fic, railway, airport and industrial noise - creates major disturbances from loss of speech in-telligibility to stress and fatigue. To overcome such situations classical solutions generally consist in deploying resonator-like absorbing materials to reduce both the acoustic level and the reverberation time. Unfortunately these traditional acoustic treatments are not efficient enough to attain A-weighted level specifications imposed by regulation laws. In the context of cancellation of low frequencies in rooms, an experiment was performed to qualify and quantify performances of a low-frequency noise cancellation active system. So as to minim-ize and increase performance in noise reduction, active solutions are actually studied to attain and fulfill high expectations in terms of integration with high efficiency in opposite to pas-sive solutions. We propose an experiment based on active sources to counteract modal low frequency noise for quasi-stationary to permanent noise emission. We present some results using a step-by-step approach to understand the global behavior of the room excited in the frequency band of its first modes. Through coherent assumptions and observations we show the efficiency of low-power active system with a priori constraints affecting modal active control

Spatial echogram analysis of a small auditorium with observations on the dispersion of early reflections.

Classical room acoustics are based on the interpretation of different sound attributes such as reverberation time, clarity and spatial decay. Based on echograms calculated from a microphone array, the dispersion of early reflections is measured and the reflections are identified. In small auditoriums, the method delivers some comprehensive information of the acoustic paths between the source and the microphone array qualifying global and local characteristics of the room boundaries. Results validate the process and highlight its contributions, but also the difficulties of implementation

Localisation des premières réflexions dans une salle par chrono-goniométrie acoustique

De plus en plus souvent, les espaces d'écoute sont amenés à accueillir des spectacles autres que ceux pour lesquels ils ont été conçus et dimensionnés. C'est le cas d'un auditorium classique devenant le temps d'un festival une salle de concert pour musique amplifiée, ou d'une cathédrale se prêtant occasionnellement à des concerts de musique chorale. En pareille situation, l'acousticien n'a d'autres alternatives que d'utiliser des abat-sons ou une assistance électroacoustique pour améliorer le confort d'écoute. En créant des réflexions précoces naturelles ou artificielles, ces dispositifs permettent de renforcer le son direct et ainsi de satisfaire auditoire et musiciens. Toutefois, si les outils actuels savent très bien estimer les dispersions temporelles de ces réflexions, il n'existe pas de méthode globale pour veiller à leur bonne répartition dans la salle. Ce contexte particulier a motivé le développement d'un outil de qualification spatio-temporelle des réflexions précoces dans une salle. L'idée générale de l'approche proposée est de combiner l'information temporelle issue de la mesure d'échogrammes spatialement distribués avec un module de localisation angulaire par triangulation. Ce dernier est basé sur l'analyse des différences de temps de propagation qui existent au sein d'un arrangement de capteurs de géométrie connue en présence d'une source située en champ lointain. Par extension, on définit la chrono-goniométrie acoustique comme une méthode de localisation active basée sur l'estimation conjointe des directions et des instants d'arrivée. Après avoir introduit le contexte de l'étude, nous formulerons le problème de localisation dans une salle tout en précisant les hypothèses de travail. Puis, un aperçu réaliste des performances in situ du chrono-goniomètre pour localiser simultanément plusieurs réflexions sera présenté

Melanic color-dependent antipredator behavior strategies in barn owl nestlings

The arms race between predators and prey has led to morphological and behavioral adaptations. Different antipredator strategies can coexist within a population if each strategy is the result of a trade-off with competing demands. Antipredator behavior can be associated with morphological traits, like color patterns, either because in the context of sexual selection, coloration signals the ability to avoid predators or because coloration is a naturally selected trait useful in avoiding predators. Because in the barn owl (Tyto alba), heritable eumelanic plumage coloration is associated with the glucocorticoid-dependent response to stress, we tested whether antipredator behavior is also related to this trait. Compared with small-spotted nestlings, individuals displaying larger black spots hissed more intensely in the presence of humans, feigned death longer, had a lower breathing rate under stress, and were more docile when handled. Cross-fostering experiments showed that the covariation between the spot size and the duration of feigning death was inherited from the biological mother, whereas covariation between spot size and docility was inherited from the biological father. Our results confirm that melanin-based coloration is associated with suites of behavioral traits, which are under both genetic and environmental influence. Coloration can thus evolve as a direct or indirect response to predation, but it can also be a signal of antipredator strategies to potential mate

Observation of Vehicle Axles Through Pass-by Noise: A Strategy of Microphone Array Design

This paper focuses on road traffic monitoring using sounds and proposes, more specifically, a microphone array design methodology for observing vehicle trajectory from acoustic-based correlation functions. In a former work, authors have shown that combining generalized cross correlation (GCC) functions and a particle filter onto the audio signals simultaneously acquired by two sensors placed near the road allows the joint estimation of the speed and the wheelbase length of road vehicles as they pass by. This is mainly due to the broadband nature of the tire/road noise, which makes their spatial dissociation possible by means of an appropriate GCC processor. At the time, nothing has been said about the best distance to chose between the sensors. A methodology is proposed here to find this optimum, which is expected to improve the observation quality and, thus, the tracking performance. Theoretical developments of this paper are partially assessed with preliminary experiments

Adjuvant Effect of Orally Applied Preparations Containing Non-Digestible Polysaccharides on Influenza Vaccination in Healthy Seniors: A Double-Blind, Randomised, Controlled Pilot Trial.

Senior individuals can suffer from immunosenescence and novel strategies to bolster the immune response could contribute to healthy ageing. In this double-blind, randomised, controlled pilot trial, we investigated the ability of non-digestible polysaccharide (NPS) preparations to enhance the immune response in a human vaccination model. In total, 239 subjects (aged 50-79 years) were randomised to consume one of five different NPS (yeast β-glucan (YBG), shiitake β-glucan (SBG), oat β-glucan (OBG), arabinoxylan (AX), bacterial exopolysaccharide (EPS)) or control (CTRL) product daily for five weeks. After two weeks of intervention, subjects were vaccinated with seasonal influenza vaccine. The post-vaccination increases in haemagglutination inhibition antibody titres and seroprotection rate against the influenza strains were non-significantly enhanced in the NPS intervention groups compared to CTRL. Specifically, a trend towards a higher mean log2 fold increase was observed in the AX group (uncorrected p = 0.074) combined with a trend for an increased seroprotection rate, AX group (48.7%) compared to CTRL (25.6%) (uncorrected p = 0.057), for the influenza A H1N1 strain. Subjects consuming AX also had a reduced incidence of common colds compared to CTRL (1 vs. 8; p = 0.029 in Fisher exact test). No adverse effects of NPS consumption were reported. The findings of this pilot study warrant further research to study AX as an oral adjuvant to support vaccine efficacy