Search

We investigate the scattering attenuation characteristics of the Martian crust and uppermost mantle to understand the structure of the Martian interior. We examine the energy decay of the spectral envelopes for 21 high-quality Martian seismic events from sols 128 to 500 of InSight operations. We use the model of Dainty, Toksöz, et al. (1974) to approximate the behavior of energy envelopes resulting from scattered wave propagation through a single diffusive layer over an elastic half-space. Using a grid search, we mapped the layer parameters that fit the observed InSight data envelopes. The single diffusive layer model provided better fits to the observed energy envelopes for high-frequency (HF) and very-high-frequency (VF) than for the low-frequency and broadband events. This result is consistent with the suggested source depths (Giardini et al., 2020) for these families of events and their expected interaction with a shallow scattering layer. The shapes of the observed data envelopes do not show a consistent pattern with event distance, suggesting that the diffusivity and scattering layer thickness is nonuniform in the vicinity of InSight at Mars. Given the consistency in the envelope shapes between HF and VF events across epicentral distances and the trade-offs between the parameters that control scattering, the dimensions of the scattering layer remain unconstrained but require that scattering strength decreases with depth and that the rate of decay in scattering strength is the fastest near the surface. This is generally consistent with the processes that would form scattering structures in planetary lithospheres.

International audience; Nonword repetition is a relevant task in clinical phonological assessment. However, few authors have considered the impact of syllable constituency on child performance in such task. In this study, we analyse the contribution of syllable constituency in nonword repetition through the validation of a new test (LITMUS-QU-NWR-EP) adapted to European Portuguese (EP). Two syllable structures were considered: lateral coda (both in word-medial and word-final position) and branching onsets (obstruent + lateral clusters). Results from typically developing children, aged 5 to 8 years, showed generalized difficulties in both structures, although codas were less problematic than branching onsets. Portuguese child performance contrasts with the data obtained for the French version of the instrument (LITMUS-QU-NWR-FR), given the overall lower performance found for EP, and the preference for codas over branching onsets, unlike attested for French children. A comparative analysis shows that nonword repetition difficulties in what concerns syllabic constituency may be language dependent. Clinical implications for EP are discussed.

National audience; In an election, the vote shares by party for a given subdivision of a territory form a compositional vector (positive components adding up to 1). Conventional multiple linear regression models are not adapted to explain this composition due to the constraint on the sum of the components and the potential spatial autocorrelation across territorial units. We develop a simultaneous spatial autoregressive model for compositional data that allows for both spatial correlation and correlations across equations. Using simulations and a data set from the 2015 French departmental election, we illustrate its estimation by two-stage and three-stage least squares methods.

International audience; The biofilm formation on food-contact-surfaces is a serious threat for public health and often results in huge human and economic losses. Thus, it is of importance to develop new strategies that allow the monitoring of the biofilm formation on food-contact-surfaces. Such strategies permit effective and timely countermeasures and, therefore, to avoid the microbiological risk and associated environmental impact due to cleaning processes. Therefore, this work investigated a non-invasive method for monitoring and detection of the biofilm formation using Coda Wave Interferometry (CWI) method. The principle of this method and the calculation of decorrelation coefficient based on the ultrasonic measurements were explained. The results underlined that our developed method is able to detect the early stage of the biofilm formation of Staphylococcus aureus on the stainless steel. Namely, it is shown that the bacterial cell kinetic is well captured by the evolution of the decorrelation coefficient as a function of incubation times. Overall, this work showed that this cost effective CWI method is a promising tool for the detection of early stage biofilm formation on food-contact-surfaces.

International audience; Due to a sharp contrast in elastic properties across the basement rocks of sedimentary basins (SBs), strong reverberations are generated during the passage of seismic waves. Traditional receiver function methods become inadequate for imaging crustal structure due to the existence of these strong reverberations. We investigate the feasibility of an autocorrelation technique to extract vertical component receiver functions from teleseismic earthquake data and the efficiency of the method to image the crustal architecture in presence of a SB. The method involves spectral whitening followed by autocorrelation and stacking in the depth domain. We show promising results when using temporary seismic networks in the eastern United States. Using synthetic and field‐data examples, we demonstrate that vertical autocorrelations are more efficient than classical radial receiver functions for interpretation purposes in an SB context. We also perform a joint analysis of the amplitudes on radial and vertical receiver functions for characterizing the thickness of the Mohorovičić discontinuity (Moho). We find that the Moho in the eastern United States is a transitional layer (up to 5‐km thick) instead of a sharp boundary. Further, we point out that it is challenging to unambiguously pick and interpret reflected phases on autocorrelations because of the effects of reverberations, cross‐mode contaminations, and a narrow frequency band limiting the resolution of velocity gradients. We therefore send a message of caution for future interpretations based on this technique.

International audience; In considering theoretical, methodological, and pedagogical perspectives for preparing language learners and teachers in/for the 21st century, the preceding chapters have sought to highlight how research findings could/should inform curriculum, instruction, and professional development in higher education so as to promote language learning and sustain its link to professionalization in today’s and tomorrow’s society. Language learning and professionalization have been explored here through researches focusing on: university students who need to learn to communicate in one or more foreign languages to both interact as global citizens and increase their chances of employability; professionals who, on their lifelong learning journey, study foreign languages to enrich or develop (new) skills for a variety of reasons, including the need to meet evolving work requirements and adapt to an ever changing society; and (pre-service) language teachers who need to learn how best to meet the needs of learners. In this brief coda, we synthesize the major points from the chapters included in this book and highlight the opportunities that exist and the challenges that must be addressed if we want the opportunities not to remain just that.

International audience

Several seismic experiments were deployed on the Moon by the astronauts during the Apollo missions. The experiments began in 1969 with Apollo 11, and continued with Apollo 12, 14, 15, 16 and 17. Instruments at Apollo 12, 14, 15, 16 and 17 remained operational until the final transmission in 1977. These remarkable experiments provide a valuable resource. Now is a good time to review this resource, since the InSight mission is returning seismic data from Mars, and seismic missions to the Moon and Europa are in development from different space agencies. We present an overview of the seismic data available from four sets of experiments on the Moon: the Passive Seismic Experiments, the Active Seismic Experiments, the Lunar Seismic Profiling Experiment and the Lunar Surface Gravimeter. For each of these, we outline the instrumentation and the data availability. We show examples of the different types of moonquakes, which are: artificial impacts, meteoroid strikes, shallow quakes (less than 200 km depth) and deep quakes (around 900 km depth). Deep quakes often occur in tight spatial clusters, and their seismic signals can therefore be stacked to improve the signal-to-noise ratio. We provide stacked deep moonquake signals from three independent sources in miniSEED format. We provide an arrival-time catalog compiled from six independent sources, as well as estimates of event time and location where available. We show statistics on the consistency between arrival-time picks from different operators. Moonquakes have a characteristic shape, where the energy rises slowly to a maximum, followed by an even longer decay time. We include a table of the times of arrival of the maximum energy 𝑡�max and the coda quality factor 𝑄�𝑐� . Finally, we outline minimum requirements for future lunar missions to the Moon. These requirements are particularly relevant to future missions which intend to share data with other agencies, and set out a path for an International Lunar Network, which can provide simultaneous multi-station observations on the Moon. ISSN:1572-9672 ISSN:0038-6308

SUMMARY Coda-Q is used to estimate the attenuation and scattering properties of the Earth. So far focus has been on earthquake data at frequencies above 1 Hz, as the high noise level in the first and second microseismic peak, and possibly lower scattering coefficient, hinder stable measurements at lower frequencies. In this work, we measure and map coda-Q in the period bands 2.5–5 s, 5–10 s and 10–20 s in the greater Alpine region using noise cross-correlations between station pairs, based on data from permanent seismic stations and from the temporary AlpArray experiment. The observed coda-Q for short interstation distances is independent of azimuth so there is no indication of influence of the directivity of the incoming noise field on our measurements. In the 2.5–5 s and 5–10 s period bands, our measurements are self-consistent, and we observe stable geographic patterns of low and high coda-Q in the period bands 2.5–5 s and 5–10 s. In the period band 10–20 s, the dispersion of our measurements increases and geographic patterns become speculative. The coda-Q maps show that major features are observed with high resolution, with a very good geographical resolution of for example low coda-Q in the Po Plain. There is a sharp contrast between the Po Plain and the Alps and Apennines where coda-Q is high, with the exception a small area in the Swiss Alps which may be contaminated by the low coda-Q of the Po Plain. The coda of the correlations is too short to make independent measurements at different times within the coda, so we cannot distinguish between intrinsic and scattering Q. Measurements on more severely selected data sets and longer time-series result in identical geographical patterns but lower numerical values. Therefore, high coda-Q values may be overestimated, but the geographic distribution between high and low coda-Q areas is respected. Our results demonstrate that noise correlations are a promising tool for extending coda-Q measurements to frequencies lower than those analysed with earthquake data.

International audience; A laboratory study was carried out using a vibrating system (SyGAVib) to produce aerosols from four soils collected in the central Tunisian region around Sfax. The aim of this device is to mimic dust emission by natural wind erosion. Using compositional analysis, the dust produced was compared to (i) dust generated in a wind tunnel by the same soils, (ii) fine sieved and (iii) original bulk soils, and (iv) naturally occurring aerosol samples collected in the same area. The relative quartz content strongly decreases from bulk to fine soils, and again from fine soils to both wind tunnel and vibration‐generated aerosols. Compositional data analysis (CoDA) clearly shows (i) a silica dilution effect in bulk soils, and (ii) that if silica is removed from the composition, the elemental compositions of fine soils and generated aerosols are similar but differ from bulk soils. Both aerosol generation methods produce material with chemical compositions that are also close to those measured in field‐sampled aerosols, and the fine soil composition is much closer to that of field and laboratory aerosols than to the parent soil. Aerosols generated from soils in the laboratory, either using a vibrating system or a wind tunnel, can be used as surrogates of the particles collected directly in the field.

In the context of seismic monitoring, recent studies made successful use of seismic coda waves to image the lateral extent of medium changes. Locating the depth of the changes, however, remains a challenge. We use multiply scattered body- and surface-wave 3-D combined sensitivity kernels to address this problem. We show that we can locate velocity perturbations at depth with numerical data from elastic wave-field simulations in 3-D heterogeneous media. This procedure is then applied to assess the extent of the crustal damage due to the $$M_{\mathrm{w}}$$ 7.9, 2008 Wenchuan earthquake. We discuss the potential and limitations of our approach to retrieve the depth information of temporal changes occurring in heterogeneous structures.

International audience; Volcano monitoring and eruption forecasting are based on the observation and joined interpretation of several precursory phenomena. It is thus important to detect new types of precursor and to study their relationship with forthcoming eruptions. In the last years, variations of seismic velocity have been observed in some volcanoes, mainly basaltic, before eruptions. In this paper, we look for velocity variations and waveform decorrelations before the 2014 eruptive sequence of the andesitic Ubinas volcano in Peru. We compute velocity changes by using seismic ambient noise cross-correlation (between pairs of stations) and cross-components correlation (between vertical and horizontal components of single stations), as well as coda wave interferometry of seismic multiplets. With these different approaches, we show that the major explosions that occurred from 13 to 19 April were preceded by a clear velocity decrease and waveform decorrelation. The amplitude of velocity change is generally larger on single-station cross-components correlation than on two-stations cross-correlation in all the frequency ranges tested (between 0.1 and 8 Hz). We highlight an apparent anisotropy of velocity change in single-station cross-components correlation, with larger amplitudes when correlating vertical and tangential components than using vertical and radial components with respect to the crater. The Mw = 8.1 Iquique earthquake on 1 April 2014 produced also a marked co-seismic velocity drop detected in a high frequency range (3-5 Hz) in both single-station cross-components correlation and cross-correlations. We locate in the horizontal plane and in depth the velocity perturbation and the structural change related with decorrelation. During the main phase of eruptive activity, the velocity decrease at low frequency (0.1-1 Hz) appears to affect the whole edifice mainly at depth of about 1 to 3 km below the surface. The structural perturbation is more concentrated on the south flank of the volcano, a zone that corresponds to an ancient collapse. We suggest that the observed velocity variations are due to the dilatation of the edifice and to microfracturation induced by magma pres-surization. The structural change may be locally enhanced by a possible zone of material weakness in the southern sector. The co-seismic velocity perturbation is located mostly in the southeast flank, at depth smaller than 0.5 to 1 km, and may be related to the presence of the hydrothermal system of the volcano.

A variety of studies have shown differences between phonetic features of consonants according to their prosodic and/or syllable (onset vs. coda) positions. However, differences are not always found, and interactions between the various factors involved are complex and not well understood. Our study compares acoustical characteristics of coda consonants in Vietnamese taking into account their position within words. Traditionally described as monosyllabic, Vietnamese is partially polysyllabic at the lexical level. In this language, tautosyllabic consonant sequences are prohibited, and adjacent consonants are only found at syllable boundaries either within polysyllabic words (CVC.CVC) or across monosyllabic words (CVC#CVC). This study is designed to examine whether or not syllable boundary types (interword vs. intraword) have an effect on the acoustic realization of codas. The results show significant acoustic differences in consonant realizations according to syllable boundary type, suggesting different coarticulation patterns between nuclei and codas. In addition, as Vietnamese voiceless stops are generally unreleased in coda position, with no burst to carry consonantal information, our results show that a vowel's second half contains acoustic cues which are available to aid in the discrimination of place of articulation of the vowel's following consonant.

The numerical studies conducted in this paper are based on our previous research (Chen et al., 2017); through use of the spectral element method, parametric sensitivity studies of Nonlinear Coda Wave Interferometry (NCWI) are established here and divided into two parts. In the first part, CWI observables are found to be proportional to the product of the changes in elastic modulus within the Effective Damaged Zone (EDZ) and the EDZ surface area. The modifications to intrinsic properties are quantified via an overall wave velocity variation, as probed by a reverberated coda wave. However, for high-level changes, CWI may fail due to meaningless decorrelation values. In this context, parametric studies are conducted to yield a maximum range for EDZ contrast and area. To further validate these observations using a more realistic numerical model, instead of introducing a homogeneous EDZ model, the second part of this paper adds random cracks with random orientations into the EDZ of a material sample. The influence of a strong pump wave on localized nonlinear damage is reestablished; results show that the cracks added into the EDZ reduce the property changes required to match the previous experimental dataset.

Ambient-noise interferometry is an approach to estimate the transient response between two receivers without an active source. The method consists of cross-correlating recordings of ambient vibrations at a pair of passive instruments that act only as receivers. This dissertation contributes to evaluating the robustness and accuracy of Green's function reconstruction by cross-correlation of noise, disentangling the respective roles of ballistic and reverberated ('coda') signals. We focus our study on a strongly reverberating medium. We conduct a suite of experiments on a highly reverberating thin duralumin plate. We find that the coda of the arrivals contribute the most to retrieval of the Green's function. We also develop an analytical model that predicts the dependence of symmetry of the cross-correlations on the number of sources. Next, we focus on a reverberating medium with a scatterer. We passively estimate the scattering strength of the scatterer by implementing ambient-noise interferometry. In the last part, we focus on a reverberating medium with locally resonant scatterers which acts as a metamaterial. Our objective is to assess the behaviour of the cross-correlation in such a medium. We build an example of such materials in the laboratory by attaching an array of rods, arranged in a sub-wavelength order, to the surface of a thin elastic plate. We find different behaviours which are consistent with the regimes that correspond to propagation band and bandgap. We next apply the cross-correlation technique to the real data obtained in METAFORET experiment. Our findings are consistent with the resonating behaviour of trees at the corresponding frequency bands.; L'interférométrie de bruit ambiant est une approche pour estimer la réponse impulsionnelle entre deux récepteurs sans source active. Cette thèse contribue à l'évaluation de la robustesse et de la précision de la reconstruction de la fonction de Green par la corrélation du bruit ambiant dans les milieux réverbérants. Plus précisément, on distingue les rôles respectifs de la partie balistique et coda des signaux dans les corrélations. Ensuite, nous nous concentrons sur un milieu réverbérant incluant un diffuseur. Nous estimons de manière passive la force du diffuseur en utilisant l'interférométrie du bruit ambiant. Dans la dernière partie de ce travail, nous nous concentrons sur un milieu réverbérant contenant les inclusions résonantes. Notre but est d'évaluer le comportement de la corrélation dans ce type de milieu. Nous avons construit un de ces matériaux au laboratoire qui est constitué des tiges verticales à la surface d'une plaque mince élastique. Nous trouvons que les différents comportements sont bien cohérents avec les régimes qui correspondent à la bande de propagation ou interdite. Comme la partie sismique, nous appliquons la technique de corrélation aux données réelles récupérées lors de l'expérience METAFORET. Nos résultats sont sont en accord avec le comportement diffusant des arbres dans les gammes de fréquence correspondante.

Ambient-noise interferometry is an approach to estimate the transient response between two receivers without an active source. The method consists of cross-correlating recordings of ambient vibrations at a pair of passive instruments that act only as receivers. This dissertation contributes to evaluating the robustness and accuracy of Green's function reconstruction by cross-correlation of noise, disentangling the respective roles of ballistic and reverberated ('coda') signals. We focus our study on a strongly reverberating medium. We conduct a suite of experiments on a highly reverberating thin duralumin plate. We find that the coda of the arrivals contribute the most to retrieval of the Green's function. We also develop an analytical model that predicts the dependence of symmetry of the cross-correlations on the number of sources. Next, we focus on a reverberating medium with a scatterer. We passively estimate the scattering strength of the scatterer by implementing ambient-noise interferometry. In the last part, we focus on a reverberating medium with locally resonant scatterers which acts as a metamaterial. Our objective is to assess the behaviour of the cross-correlation in such a medium. We build an example of such materials in the laboratory by attaching an array of rods, arranged in a sub-wavelength order, to the surface of a thin elastic plate. We find different behaviours which are consistent with the regimes that correspond to propagation band and bandgap. We next apply the cross-correlation technique to the real data obtained in METAFORET experiment. Our findings are consistent with the resonating behaviour of trees at the corresponding frequency bands.; L'interférométrie de bruit ambiant est une approche pour estimer la réponse impulsionnelle entre deux récepteurs sans source active. Cette thèse contribue à l'évaluation de la robustesse et de la précision de la reconstruction de la fonction de Green par la corrélation du bruit ambiant dans les milieux réverbérants. Plus précisément, on distingue les rôles respectifs de la partie balistique et coda des signaux dans les corrélations. Ensuite, nous nous concentrons sur un milieu réverbérant incluant un diffuseur. Nous estimons de manière passive la force du diffuseur en utilisant l'interférométrie du bruit ambiant. Dans la dernière partie de ce travail, nous nous concentrons sur un milieu réverbérant contenant les inclusions résonantes. Notre but est d'évaluer le comportement de la corrélation dans ce type de milieu. Nous avons construit un de ces matériaux au laboratoire qui est constitué des tiges verticales à la surface d'une plaque mince élastique. Nous trouvons que les différents comportements sont bien cohérents avec les régimes qui correspondent à la bande de propagation ou interdite. Comme la partie sismique, nous appliquons la technique de corrélation aux données réelles récupérées lors de l'expérience METAFORET. Nos résultats sont sont en accord avec le comportement diffusant des arbres dans les gammes de fréquence correspondante.

International audience

International audience; Large scale studies of temporal reduction are of interest to obtain linguistic knowledge and this understanding can potentially help improve speech technologies. Automatic speech recognition (ASR) supports the processing of very large corpora and can be used to enrich linguistic studies with models of speech production and perception grounded on observed commonly used pronunciations. In return, ASR can benefit from the linguistic findings by including pronunciation variants that reflect the linguistic variability. This study focuses on two temporal reduction phenomena in Peninsular and Latin American varieties of Spanish: lenition of intervocalic voiced stops V/bdg/V and coda-s. First, the two phenomena are investigated via a study of transcription errors produced by a speech recognition system designed for Peninsular Spanish which can be potentially attributed to lenition. In a second step, automatic forced alignment experiments are conducted using specific pronunciation variants with and without lenition to measure the extent of the phenomenon as a function of geographical and stylistic repartition. The results show that the distribution of pronunciation variants across Peninsular and Latin American Spanish varieties is consistent with trends depicted by classical linguistic studies. The speaking style appears to be the main factor affecting the +/-lenition variation. The findings also suggest that including such variants in ASR system's lexicon may improve performance when processing multiple Spanish varieties.

In this work, we map the absorption properties of the French crust by analyzing the decay properties of coda waves. Estimation of the coda quality factor $$Q_{c}$$ in five non-overlapping frequency-bands between 1 and 32 Hz is performed for more than 12,000 high-quality seismograms from about 1700 weak to moderate crustal earthquakes recorded between 1995 and 2013. Based on sensitivity analysis, $$Q_{c}$$ is subsequently approximated as an integral of the intrinsic shear wave quality factor $$Q_{i}$$ along the ray connecting the source to the station. After discretization of the medium on a 2-D Cartesian grid, this yields a linear inverse problem for the spatial distribution of $$Q_{i}$$ . The solution is approximated by redistributing $$Q_{c}$$ in the pixels connecting the source to the station and averaging over all paths. This simple procedure allows to obtain frequency-dependent maps of apparent absorption that show lateral variations of $$50\%$$ at length scales ranging from 50 km to 150 km, in all the frequency bands analyzed. At low frequency, the small-scale geological features of the crust are clearly delineated: the Meso-Cenozoic basins (Aquitaine, Brabant, Southeast) appear as strong absorption regions, while crystalline massifs (Armorican, Central Massif, Alps) appear as low absorption zones. At high frequency, the correlation between the surface geological features and the absorption map disappears, except for the deepest Meso-Cenozoic basins which exhibit a strong absorption signature. Based on the tomographic results, we explore the implications of lateral variations of absorption for the analysis of both instrumental and historical seismicity. The main conclusions are as follows: (1) current local magnitude $$M_{L}$$ can be over(resp. under)-estimated when absorption is weaker(resp. stronger) than the nominal value assumed in the amplitude-distance relation; (2) both the forward prediction of the earthquake macroseismic intensity field and the estimation of historical earthquake seismological parameters using macroseismic intensity data are significantly improved by taking into account a realistic 2-D distribution of absorption. In the future, both $$M_{L}$$ estimations and macroseismic intensity attenuation models should benefit from high-resolution models of frequency-dependent absorption such as the one produced in this study.

Diffuse ultrasound is highly sensitive to changes in mechanical properties. Based on the coda wave interferometry analysis, we investigate the environmental temperature-induced wave velocity variations in high-manganese steels with plastic deformations by diffuse ultrasound. We observe the velocity changes in the materials at test with [Formula: see text] relative resolution. We propose the temperature-dependent coefficient as the key parameter for damage assessment in the specimens with different plastic deformations. The results show that the early-stage damage caused by plastic deformation in the specimens at test varying from 6% to 14% are successfully characterized by temperature-dependent coefficients in the absence of external mechanical load. The theoretical analysis on the sensitivity of the temperature-dependent coefficient to plastic deformation as well as the potential on-site application is discussed in this article.

International audience; To monitor both the permanent (thermal microcracking) and the nonpermanent (thermo‐elastic) effects of temperature on Westerly Granite, we combine acoustic emission monitoring and ultrasonic velocity measurements at ambient pressure during three heating and cooling cycles to a maximum temperature of 450°C. For the velocity measurements we use both P wave direct traveltime and coda wave interferometry techniques, the latter being more sensitive to changes in S wave velocity. During the first cycle, we observe a high acoustic emission rate and large—and mostly permanent—apparent reductions in velocity with temperature (P wave velocity is reduced by 50% of the initial value at 450°C, and 40% upon cooling). Our measurements are indicative of extensive thermal microcracking during the first cycle, predominantly during the heating phase. During the second cycle we observe further—but reduced—microcracking, and less still during the third cycle, where the apparent decrease in velocity with temperature is near reversible (at 450°C, the P wave velocity is decreased by roughly 10% of the initial velocity). Our results, relevant for thermally dynamic environments such as geothermal reservoirs, highlight the value of performing measurements of rock properties under in situ temperature conditions.

When the aim is to model market-shares, the marketing literature proposes some regression models which can be qualified as attraction models. They are generally derived from an aggregated version of the multinomial logit model. But aggregated multinomial logit models (MNL) and the so-called generalized multiplicative competitive interaction models (GMCI) present some limitations: in their simpler version they do not specify brand-specific and cross-effect parameters. In this paper, we consider alternative models: the Dirichlet model (DIR) and the compositional model (CODA). DIR allows to introduce brand-specific parameters and CODA allows additionally to consider cross-effect parameters. We show that these two models can be written in a similar fashion, called attraction form, as the MNL and the GMCI models. As market-share models are usually interpreted in terms of elasticities, we also use this notion to interpret the DIR and CODA models. We compare the properties of the models in order to explain why CODA and DIR models can outperform traditional market-share models. An application to the automobile market is presented where we model brands market-shares as a function of media investments, controlling for the brands price and scrapping incentive. We compare the quality of the models using measures adapted to shares.; Lorsque l'objectif est de modéliser des parts de marché, la littérature marketing propose des modèles de régression qui peuvent être qualifié de modèles d'attraction. Ils sont généralement dérivés d'une version agrégée du modèle multinomial logit. Mais le logit multinomial agrégé et le modèle d'attraction appelé generalized multiplicative competitive interaction models (GMCI) présentent quelques limitations : dans leur version simple, ils ne spécifient pas de paramètres propres aux marques ni d'effets croisés. Dans ce papier, nous considérons des modèles alternatifs : le modèle de Dirichlet (DIR) et le modèle de composition (CODA). DIR permet d'introduire des paramètres propres aux marques et CODA permet en plus de considérer des effets croisés. Nous montrons que ces deux modèles peuvent être exprimés sous une forme similaire, appelée formulation en attraction, comme les modèles MNL et GMCI. Les modèles de parts de marché étant habituellement interprétés en termes d’élasticités, nous utilisons également cette notion pour interpréter les modèles DIR et CODA. Nous comparons les propriétés des modèles de manière à expliquer pourquoi les modèles CODA et DIR peuvent être plus performants que les modèles de parts de marché traditionnels. Une application au marché automobile est présentée où nous modélisons les parts de marché des marques en fonction des investissements médias, en contrôlant pour le prix des marques et l’existence ou non de prime à la casse. Nous comparons la qualité des modèles en utilisant des mesures adaptées aux données de parts.

Seismic signal windowing is the preliminary step for many analysis procedures in engineering seismology (standard spectral ratio, quality factor, general inversion techniques, etc.). Moreover a noise window is often necessary for the data quality control through the signal-to-noise verification. Selecting the noise window can be challenging when large heterogeneous datasets are considered, especially when they include short pre-event noise signals. This study proposes a fully automatic and configurable (i.e., with default parameters that can also be user-defined) algorithm to windowing the noise and the P, S, coda and full signal once the P-wave (T P ) and S-wave (T S ) first arrivals are known. An application example is given on a KiK-net dataset. A Matlab language implementation of this algorithm is proposed as an online resource.

Multiple scattering of seismic waves is often seen as a nightmare for conventional migration techniques that generally rely on a ballistic or a single scattering assumption. In heterogeneous areas such as volcanoes, the multiple scattering contribution limits the imaging-depth to one scattering mean free path, the mean distance between two successive scattering events for body waves. In this Letter, we propose a matrix approach of passive seismic imaging that pushes back this fundamental limit by making an efficient use of scattered body waves drowned into a noisy seismic coda. As a proof-of-concept, the case of the Erebus volcano in Antarctica is considered. The Green's functions between a set of geophones placed on top of the volcano are first retrieved by the cross-correlation of coda waves induced by multiple icequakes. This set of impulse responses forms a reflection matrix. By combining a matrix discrimination of singly-scattered waves with iterative time reversal, we are able to push back the multiple scattering limit beyond 10 scattering mean free paths. The matrix approach reveals the internal structure of the Erebus volcano: A chimney-shaped structure at shallow depths, a magma reservoir at 2500 m and several cavities at sea level and below it. The matrix approach paves the way towards a greatly improved monitoring of volcanic structures at depth. Beyond this specific case, the matrix approach of seismic imaging can generally be applied to all scales and areas where multiple scattering events undergone by body waves prevent in-depth imaging of the Earth's crust., 14 pages, 7 figures

International audience; A discussion of nondestructive techniques is presented for the investigation of complex media, with a focus on composite samples. Traditionally, one applies ultrasonic C-scans, or polar scans, which are easy to implement and to interpret. However, in many realistic cases, it is important to use more sophisticated approaches as C-scans often do not reveal any useful information. Typically, the early part of received signals is used to extract information, whereas the later part is considered either as noise or as a useless coda wave as in musical acoustics. Nevertheless, it appears that the coda part carries useful information about the medium, and therefore, it is important to explore techniques to extract that information. In addition, it turns out that the coda is very sensitive to material properties and damage as those sound waves interact longer with the material than early arrival waves. First, earlier results will be shown which compare experimental polar scans with numerical simulations, then, for the same samples, coda wave results will be presented to show the effect of damage on the composite samples. The main damage indicator is the change in relative wave velocity which is caused by the damage.

44th Annual Review of Progress in Quantitative Nondestructive Evaluation, PROVO, ETATS-UNIS, 16-/07/2017 - 21/07/2017; Civil engineering is constantly demanding new methods for evaluation and non-destructive testing (NDT), particularly to prevent and monitor serious damage to concrete structures. Tn this work, experimental results are presented on the detection and characterization of cracks using nonlinear modulation of coda waves interferometry (NCWT) [1]. This method consists in mixing high-amplitude low-frequency acoustic waves with multi-scattered probe waves (coda) and analyzing their effects by interferometry. Unlike the classic method of coda analysis (CWT), the NCWT does not require the recording of a coda as a reference before damage to the structure. Tn the framework of the PTA-ENDE project, a 1/3 model of a preconstrained concrete containment (EDF VeRCoRs mock-up) is placed under pressure to study the leakage of the structure. During this evaluation protocol, specific areas are monitored by the NCWT (during 5 days, which correspond to the protocol of nuclear power plant pressurization under maintenance test). The acoustic nonlinear response due to the high amplitude of the acoustic modulation gives pertinent information about the elastic and dissipative nonlinearities of the concrete. Tts effective level is evaluated by two nonlinear observables extracted from the interferometry. The increase of nonlinearities is in agreement with the creation of a crack with a network of microcracks located at its base; however, a change in the dynamics of the evolution of the nonlinearities may indicate the opening of a through crack. Tn addition, as during the experimental campaign, reference codas have been recorded. We used CWT to follow the stress evolution and the gas leaks ratio of the structure. Both CWT and NCWT results are presented in this paper.

An analysis of seismic coda phases recorded by five small aperture arrays in Kazakhstan and Russia is performed. The characteristics of the coda phases are obtained using array processing providing estimates of direction of propagation, frequency content, and apparent propagation velocity of coherent arrivals propagating through the arrays. A statistical analysis, using the coda characteristics of the whole dataset (far‐regional earthquakes) recorded by the arrays, is performed leading to a time‐azimuth distribution of the detected waves. Long Lg ‐coda wavetrains clearly dominate the far‐regional seismic records. The later part of an Lg ‐coda wavefield is generally expected to consist of omnidirectional and multiple scattered waves; still, in the present study, preferential propagation directions of scattered waves are identified in seismic signals, even for a lapse time larger than 1200 s. The comparison of the Lg ‐coda characteristics for two different groups of earthquakes and for the different arrays shows that the geometrical configuration of the event array strongly influences the back‐azimuthal distribution of detected waves. More precisely, temporal variations of the Lg ‐coda characteristics are identified: (1) as a transitory regime in the early part of the coda where arrival directions deviate from the epicenter back azimuth (eastward or westward); (2) as a final regime where the later part of the Lg coda observed by the two northern arrays exhibits incoherent phases with random propagation directions; and (3) as a final regime for the three southern arrays, which reveals coherent arrivals propagating from array‐specific back azimuths not related to the epicenter back azimuth. Electronic Supplement: Figures showing frequency content of detections.

The seismic effective quality factor (QC) and its frequently dependences or the frequency parameter (n) and attenuation coefficient (δ) for the Earth’s crust and upper mantle of the North Tanzanian divergence zone (East African rift system) were estimated from an analysis of the earthquake coda waves recorded in the SEISMO-TANZ’07 French-Tanzanian seismic experiment. The QC values increase and the n and δ values decrease with increasing frequency and length of the lapse time window. This behavior of the attenuation parameters may be evidence that the degree of heterogeneity of the lithosphere decreases with depth. Comparison of the depth variations in the attenuation coefficient δ and the frequency parameter n with the velocity structure of the region shows that there is a distinct change in the behavior of seismic wave attenuation at velocity discontinuities. The obtained attenuation parameters were compared with the same parameters obtained in our previous studies for other continental rift systems—the Baikal rift system (Eurasia) and the Basin and Range Province (North America).

International audience; This study contributes to the evaluation of the robustness and accuracy of Green's function reconstruction from cross-correlation of strongly dispersed reverberated signals, with disentangling of the respective roles of ballistic and reverberated (“coda”) contributions. We conduct a suite of experiments on a highly reverberating thin duralumin plate, where an approximately diffuse flexural wave field is generated by taking advantage of the plate reverberation and wave dispersion. A large number of impulsive sources that cover the whole surface of the plate are used to validate ambient-noise theory through comparison of the causal and anticausal (i.e., positive- and negative-time) terms of the cross-correlation to one another and to the directly measured Green's function. To quantify the contribution of the ballistic and coda signals, the cross-correlation integral is defined over different time windows of variable length, and the accuracy of the reconstructed Green's function is studied as a function of the initial and end times of the integral. We show that even cross-correlations measured over limited time windows converge to a significant part of the Green's function. Convergence is achieved over a wide time window, which includes not only direct flexural-wave arrivals, but also the multiply reverberated coda. We propose a model, based on normal-mode analysis, that relates the similarity between the cross-correlation and the Green's function to the statistical properties of the plate. We also determine quantitatively how incoherent noise degrades the estimation of the Green's function.

In this paper, the spectral element method is used to perform a parametric sensitivity study of the nonlinear coda wave interferometry (NCWI) method in a homogeneous or heterogeneous sample with localized damage. The influence of a strong pump wave on localized nonlinear damage is modeled as modifications to the elastic properties of an effective damage zone (EDZ), depending on the pump wave amplitude. These modifications are quantified with coda wave interferometry through an overall wave velocity variation probed by a reverberated or multiple scattered coda wave. Results demonstrate that the NCWI observables are independent of the source/receiver positions. Also, relations between the EDZ parameters and method observables are established, e.g. the relative velocity variation is found to be proportional to the product of the change in elastic modulus and the EDZ area. The numerical results reported constitute another step towards quantification and forecasting of the nonlinear acoustic response of a cracked material, which proves to be necessary for a quantitative non-destructive evaluation. Furthermore, it is shown numerically that NCWI sensitivity and applicability are similar for the cases of reverberated waves in a cavity and multiply scattered waves in a heterogeneous medium.

International audience; We present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of Merapi volcano. For the first time to our knowledge, the technique of coda wave interferometry is applied to both families of similar events (multiplets) and to correlation functions of seismic noise. About half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified, including 120 similar events that occurred in the last 20 hr preceding the eruption onset. Daily noise cross-correlation functions (NCF) were calculated for the six pairs of short-period stations available. Using the stretching method, we estimate time-series of apparent velocity variation (AVV) for each multiplet and each pair of stations. No significant velocity change is detected until September 2010. From 10 October to the beginning of the eruption on 26 October, a complex pattern of AVV is observed with amplitude of up to ±1.5 per cent. Velocity decrease is first observed from families of deep events and then from shallow earthquakes. In the same period, AVV with different signs and chronologies are estimated from NCF calculated for various station pairs. The location in the horizontal plane of the velocity perturbations related with the AVV obtained from NCF is estimated by using an approach based on the radiative transfer approximation. Although their spatial resolution is limited, the resulting maps display velocity decrease in the upper part of the edifice in the period 12–25 October. After the eruption onset, the pattern of velocity perturbations is significantly modified with respect to the previous one. We interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations. The perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks. Thus the detected AVVs can be considered as precursors of volcanic eruptions in andesitic volcanoes, without taking their sign into account.

International audience; Arabic dialects have no standard dialectal spelling systems. Arbitrary transcription of dialect words will display varieties of orthographic forms. This causes problems for natural language processing (NLP). In this paper, we present an automatic process for normalization of spontaneously spelled Tunisian Arabic (TA) into a conventional orthography CODA-TA [1]. We show that rule-based and statistical methods can reduce the transcription errors by 77.73% over this baseline on an unseen test set.

International audience; In this work the non-destructive monitoring of the self-healing progress of cracked mortars is presentedthrough the use of three combined methods: nonlinear Coda Wave Interferometry, 3D microscopy and Xray computed microtomography (CT). The aim of the acoustic method is to compare, at various healingstages, both the ultrasonic velocity variations and decorrelation coefficients between a reference codasignal and a signal perturbed by a high level lower-frequency elastic wave. The decrease in the relativevariation of the extracted nonlinearities demonstrates its ability to accurately monitor global crack filling.3D microscopy also reveals this capability. Measurement results of these two techniques agree for theinfluence of age at cracking on healing potential. In reducing the voxel size to 12 lm, X-ray CT imagesconfirm the creation of localized bridges between crack faces and provide information on their location.

International audience; Dispersion analysis of Rayleigh waves is performed to assess the velocity of complex structures such as sedimentary basins. At short periods several modes of the Rayleigh waves are often exited. To perform a reliable inversion of the velocity structure an identification of these modes is thus required. We propose a novel method to identify the modes of surface waves. We use the spectral ratio of the ground velocity for the horizontal components over the vertical component (H/V) measured on seismic coda. We then compare the observed values with the theoretical H/V ratio for velocity models deduced from surface wave dispersion when assuming a particular mode. We first invert the Rayleigh wave measurements retrieved from ambient noise cross-correlation with the assumptions that (1) the fundamental mode and (2) the first overtone are excited. Then we use these different velocity models to predict theoretical spectral ratios of the ground velocity for the horizontal components over the vertical component (H/V). These H/V ratios are computed under the hypothesis of equipartition of a diffuse field in a layered medium. Finally we discriminate between fundamental and higher modes by comparing the theoretical H/V ratio with the H/V ratio measured on seismic coda. In an application, we reconstruct Rayleigh waves from cross-correlations of ambient seismic noise recorded at seven broad-band stations in the Valley of Mexico. For paths within the soft quaternary sediments basin, the maximum energy is observed at velocities higher than expected for the fundamental mode. We identify that the dominant mode is the first higher mode, which suggests the importance of higher modes as the main vectors of energy in such complex structures.

En russe, la palatalisation connaît un fort rendement phonologique puisque chaque consonne possède sa contrepartie palatalisée. Les linguistes observent un manque de données articulatoires dans la littérature, notamment sur la production des palatalisées en russe. Le niveau articulatoire est d’autant plus complexe qu’il faut prendre en compte et observer des stratégies individuelles. Notre travail propose de caractériser le geste palatal impliqué dans la réalisation des différents types de consonnes palatalisées et palatales et d’observer la variation de ce geste selon les différents facteurs tels que le locuteur, l’accent et l’effet de la structure syllabique. Dans ce but, nous avons choisi de décrire et de comparer le contour lingual ainsi que le schéma temporel de quatre points de localisation sur la langue. Nos résultats montrent deux stratégies différentes de réalisation des consonnes palatales et palatalisées. On ne relève pas d’impact clair de l’accent sur la cible consonantique atteinte ainsi que sur le timing du geste lingual dans la phase d’atteinte de la cible. Un contrôle plus global de la langue est observé en syllabe atone et en position de coda tandis qu’une certaine indépendance des parties de la langue est relevée en position d’attaque et en syllabe accentuée.

International audience; We detected several thousand deep englacial icequakes on Glacier d’Argentiere (Mont-Blanc Massif) between 30 March and 3 May 2012. These events have been classified in eight clusters. Inside each cluster, the waveforms are similar for P-waves and S-waves, although the time delay between the P-waves and S-waves vary by up to 0.03 s, indicating an extended source area. Although these events were recorded by a single accelerometer, they were roughly located using a polarization analysis. The deepest events were located at a depth of 130 m, 60 m above the ice/bed interface. The clusters are separated in space. The largest cluster extends over about 100 m. For this cluster, the strike of the rupture plane is nearly parallel to the direction of the open crevasses, and the dip angle is 56◦. Deep icequakes occur in bursts of activity that last for a few hours and are separated by quiet periods. Many events occurred on 28-29 April 2012, during the warmest days, when snow melting was likely important. The distribution of events in time and space obeys a power law, as also observed for earthquakes, but with larger exponents.The polarity of the P-waves for all of the events is consistent with tensile faulting. Finally, between 25 April and 3 May, we observed a gliding harmonic tremor with a fun- damental resonance frequency that varied between 30 Hz and 38 Hz, with additional higher frequency harmonics. During this time we also observed shallow hybrid events with high-frequency onsets and a monochromatic coda. These events might be produced by the propagation of fractures and the subsequent flow of water into the fracture. The strongest resonance was observed just after a strong burst of deep icequakes, and during an un- usually warm period when the snow height decreased by 60 cm in one week. The res- onance frequency shows a succession of several sharp decreases and phases of progressive increases. One of the strongest negative steps of the resonance frequency on 28 April coincides with a burst of deep icequakes. These events appear to be associated with the propagation of fractures, which can explain the decrease in the resonance frequency. Finally, we observed an acceleration of glacier flow on 29 April and suggested that melt-water had reached the ice/bed interface. These observations suggest that deep icequakes are due to hydraulic fracturing, and that they can be used to track fluid flow inside glaciers.

This study focuses on imaging local changes in heterogeneous media. The method employed is demonstrated and validated using numerical experiments of acoustic wave propagation in a multiple scattering medium. Changes are simulated by adding new scatterers of different sizes at various positions in the medium, and the induced decorrelation of the diffuse (coda) waveforms is measured for different pairs of sensors. The spatial and temporal dependences of the decorrelation are modeled through a diffuse sensitivity kernel, based on the intensity transport in the medium. The inverse problem is then solved with a linear least square algorithm, which leads to a map of scattering cross section density of the changes.

This paper presents an ultrasonic method, based on the nonlinear acoustic mixing of coda waves with lower-frequency swept pump waves, for providing an efficient global detection of small cracks in cementitious materials. By simultaneously comparing, forboth uncracked and cracked mortars, the ultrasonic velocity variations and decorrelation coefficients between the unperturbed and perturbed signals with pump amplitude, this method makes it possible to accurately detect cracks with widths of around 20 μm in correlation with velocity variations of approximately 0.01%. The potential influence of certain material parameters such as microscopic damage is also discussed.

International audience; We demonstrate the feasibility of high-resolution seismic array imaging based on teleseismic recordings using full numerical wave simulations. We develop a hybrid method that interfaces a frequency–wavenumber (FK) calculation, which provides analytical solutions to 1-D layered background models with a spectral-element (SEM) numerical solver to calculate synthetic responses of local media to plane-wave incidence.This hybrid method accurately deals with local heterogeneities and discontinuity undulations, and represents an efficient tool for the forward modelling of teleseismic coda (including converted and scattered) waves. We benchmark the accuracy of the SEM-FK hybrid method against FK solutions for 1-D media. We then compute sensitivity kernels for teleseismic coda waves by interacting the forward teleseismic waves with an adjoint wavefield, produced by injecting coda waves as adjoint sources, based on adjoint techniques. These sensitivity kernels provide the basis for mapping variations in subsurface discontinuities, density and velocity structures through non-linear conjugate-gradient methods. We illustrate various synthetic imaging experiments, including discontinuity characterization, volumetric structural inversion for the crust or subduction zones. These tests show that using pre-conditioners based upon the scaled product of sensitivity kernels for different phases, combining finite-frequency traveltime and waveform inversion, and/or adopting hierarchical inversions from long- to short-period waveforms could reduce the non-linearity of the seismic inverse problem and speed up its convergence. The encouraging results of these synthetic examples suggest that inversion of teleseismic coda phases based on the SEM-FK hybrid method and adjoint techniques is a promising tool for structural imaging beneath dense seismic arrays.

A statistical reverberation model based on the average distribution of wave packets propagating in a finite plate is described and it is shown that by fitting experimental data to theoretical expressions, either structural or source-related features can be extracted with very few sensors. An original method to localise an impulse acoustic source in a reverberant plate is proposed and discussed as a possible application of this principle. The reverberated wave packets (coda), which are ordinarily discarded in classical localisation techniques, are used here to estimate an energy-related term characteristic of the source. Thereafter, the energies of the early wave packets measured on three sensors are enough to estimate the source location (whereas a minimum of four sensors is required in classical localisation techniques). After detailing the conditions of application of the method, several examples of experimental source localisation are given.

The study of the ultrasonic CODA, already explored in the domain of civil engineering, is applied to composite materials. The damages' evolution is studied using piezoelectric sensors. The method presented here is based on the delay of an acoustic waveinvolved by colliding with defects within the structure. We focus at the end of the signal which contains the sum of all these multi-scattered waves compared to a reference. This data can beregarded to the health of materials (damage and/or strain).; L'étude de la CODA ultrasonore, déjà explorée dans le cadre de la surveillance d'ouvrage d'art, est ici appliquée à des matériaux composites à matrice organique. Un suivi des endommagements est réalisé en employant des capteurs piézoélectriques. La méthode sebase sur le retard que prend une onde acoustique en se heurtant aux différents défauts internes à la structure. On se focalise sur la fin du signal, qui contient la somme de tous ces trajets multidiffusés, par rapport à une référence. Cet observable est mis en relation avec l'état de santé du matériau (endommagement et/ou déformation).

During my thesis, I worked on different aspects of monitoring the elastic properties of the crust, with both numerical analysis and applications with ambient noise. The main body of my thesis consists of two main parts: 1. Properties of coda waves A very important parameter that we continuously encounter in the different parts of my thesis work is the scattering mean free path. I present an original way to determine the scattering mean free path from phase statistics that was successfully tested on a volcano in Auvergne. Then I discuss an intensive numerical analysis of the depth sensitivity of coda waves. This work allowed us to relate the depth sensitivity of coda waves to a combination of bulk wave sensitivity and surface wave sensitivity that depends on the time in the coda and on the scattering mean free path of the medium. We were able to show a time dependence of the relative velocity change in the coda that allows us to discriminate a change that occurs at the surface from a change that occurs at depth. 2. Locating changes in multiply scattering media We developed an inversion method based on probabilistic approaches of the wave propagation to locate changes in the medium. As an additional aspect to seismic noise monitoring techniques that are based on the evaluation of time delays in the coda, we also study the waveform decoherence. Within this thesis, we apply and refine the inversion method with three case studies. We study pre-and co-eruptive changes at Piton de la Fournaise volcano in La Réunion Island. The challenge here is to correctly locate forthcoming eruptions. A second data set comes from the Mw7.9 Wenchuan earthquake in China. In this study, we take the time evolution of the coda into account and jointly invert the data at different times in the coda to study changes in the crust during and after the earthquake. From the results, we can clearly see that waveform decoherence and velocity variations are not sensitive to the same physical properties. In the third study, we test the inversion procedure with a 3D sensitivity kernel to study the fracturing of concrete blocks under increased tension.; Durant mes trois années de thèse, j'ai été amenée à travailler sur différents aspects de la surveillance des propriétés élastiques de la croûte, à la fois par analyses numériques, mais aussi par des applications d'utilisation du bruit ambiant. Ma thèse s'articule autour de deux parties principales: Les propriétés des ondes de la coda Le libre parcours moyen est un paramètre crucial rencontré continuellement dans les différentes parties de mon travail. Dans cette partie, je présente une nouvelle façon de déterminer ce libre parcours moyen à partir des statistiques de phase. Cette méthode a été testée avec succès dans l'étude d'un volcan situé en Auvergne (France). Je présente ensuite une analyse numérique de la sensibilité que les ondes de la coda manifestent en fonction de la profondeur. Ce travail nous a permis de relier cette sensibilité à la profondeur observée dans les ondes de la coda, à une combinaison de la sensibilité des ondes de volume et de celle des ondes de surface. En effet, cette sensibilité des ondes de volume et de surface dépend directement du temps considéré dans la coda et du libre parcours moyen du milieu étudié. Nous avons été capable de montrer que le changement de vitesse relatif dans la coda était lié à une dépendance en temps. Cette importante observation nous permet de pouvoir établir une distinction entre un changement qui se produit en surface et un changement ayant lieu en profondeur. Localisation des changements dans un milieu diffusif Nous avons développé une méthode d'inversion basée sur des approches probabilistes de la propagation des ondes, afin de pouvoir localiser les changements dans le milieu. Nous avons également étudié la décohérence de la forme d'onde, ce qui constitue un aspect additionnel des techniques de surveillance du bruit sismique, qui traditionnellement sont basés sur l'évaluation du temps de retard dans la coda. Au cours de cette thèse, nous avons affiné notre méthode d'inversion en l'appliquant à trois cas d'études. Dans un premier cas, nous avons étudié les changements ayant eu lieu avant et pendant l'éruption du volcan du Piton de la Fournaise situé sur l'Ile de la Réunion. Le challenge ici est de parvenir à localiser correctement la prochaine éruption. La seconde application a concerné le séisme de Mw7,9 de Wenchuan (Chine), sur lequel nous avons obtenu de nombreuses données. Dans ce cas, nous avons pris en compte l'évolution de la coda au cours du temps et nous avons conjointement inversé les données à différents temps dans la coda pour étudier les changements induits dans la croûte, avant et pendant le séisme. A partir de ces résultats, nous avons pu clairement voir que la décohérence de la forme d'onde et les variations de vitesse n'étaient pas sensibles aux mêmes propriétés physiques. Dans le troisième cas d'étude, nous avons testé la procédure d'inversion avec un noyau 3D pour étudier la fracturation dans un bloc de béton soumis à une contrainte croissante.

In highly heterogeneous media, waves don't propagate ballistically. They can interact several times with the heterogeneities of the medium and enter the multiple scattering regime. In this regime, classical imaging techniques, based on direct or singly scattered waves fail. Multiply scattered waveforms (coda) are too complex for being exactly modeled but are perfectly reproducible and very sensitive to small variations of the medium. Recent works demonstrated the possibility of measuring small velocity variations with diffuse waves, either at the geophysical scale (seismic coda) or at the material scale (ultrasonic coda). These works are mainly focused in monitoring global or regional changes of the medium. The present thesis deals with the possibility of using coda waves to study local changes of the medium. Two complementary studies are developed: The forward problem addresses the modeling of the coda variations generated by a local change. We distinguish the case of a structural change (strong impedance contrast) from the case of a velocity change (small impedance contrast). The inverse problem consists in using the coda variations measurements to locate and characterize the changes that occurred. Potential applications may concern, among others, monitoring of geological structures and non-destructive testing of heterogeneous materials. This in mind, we illustrate the different studies with numerical simulations of acoustic and seismic waves and with ultrasound experiments in concrete blocks., Dans les milieux fortement hétérogènes, les ondes ne se propagent pas de façon balistique. Elles peuvent interagir de nombreuses fois avec les hétérogénéités du milieu et entrer ainsi dans le régime de diffusion multiple. Dans ce régime, les méthodes classiques d'imagerie basées sur les trajets des ondes directes ou simplement diffusées sont inefficaces. Les formes d'ondes multiplement diffusées (coda) sont trop complexes pour être modélisées exactement mais elles sont parfaitement reproductibles et très sensibles aux variations du milieu de propagation. Des travaux récents ont démontré la possibilité de mesurer de faibles changements de vitesse d'un milieu grâce aux ondes diffuses, à l'échelle de la croûte terrestre (coda sismique) comme à l'échelle des matériaux (coda ultrasonore). Ces travaux s'intéressent majoritairement à des changements globaux ou régionaux des différents milieux. La problématique de cette thèse concerne la possibilité d'utiliser la coda pour étudier des changements locaux du milieu. Deux études complémentaires sont développées : Le problème direct consiste à modéliser les variations de la coda engendrées par un changement local. Nous distinguons le cas d'un changement local de structure (fort contraste d'impédance) du cas d'un changement local de vitesse (faible contraste d'impédance). Le problème inverse consiste à utiliser les mesures de variations de la coda pour tenter de localiser et de caractériser les changements survenus. Les applications potentielles de ces travaux concernent entre autres le suivi temporel de structures géologiques ainsi que le contrôle non destructif de matériaux hétérogènes. Avec cet objectif, les différentes méthodes développées sont illustrées par des simulations numériques d'ondes acoustiques et sismiques ainsi que par des expériences en ultrasons dans des éléments en béton.

International audience; In this study, we demonstrate that cross-correlation gathers of multi-channel and multi-shot configurations provide accurate estimations of shear wave velocity (Vs) perturbations from Rayleigh wave data for the reconstruction of two-dimensional (2D), high-resolution velocity distributions without requiring the systematic calculation of surface wave dispersion, as in the spectral analysis of surface waves (SASW). Data acquisition for cross-correlation analysis is similar to that for a 2D seismic common midpoint reflection survey. The data processing involved is similar to the coda wave interferometry used for seismological data but differs in the sense that the cross-correlation of the original waveform is calculated for active source seismic data. Data processing in cross-correlation analysis consists of the following three steps: First, cross-correlations are calculated for every trace in each shot gather with the same offset trace as a reference shot to flatten the linearly sloping events of surface waves. A common receiver location stack section can then be obtained, which allows for the assessment of lateral variations in the elastic properties of the medium. Second, the maxima of the time-shifted cross-correlation gathers and the maxima of the shot gathers' envelope traces are picked for different frequencies, and trace values having the same receiver location are averaged to calculate Vs perturbations, as described in the theory of coda wave interferometry. Finally, a 2D Vs profile is reconstructed by applying the lateral Vs perturbation to a homogeneous Vs velocity profile obtained by inversion of the surface wave dispersion of the reference shot gather. Analyses of waveform data from numerical modelling and field observations indicate that this new method is valid and greatly improves the accuracy and resolution of near-surface imagery using surface waves and reconstructed subsurface velocity distributions compared with a conventional SASW or multi-channel application.

International audience; We present an imaging technique allowing to locate a weak perturbation appearing in a multiple scattering environment. This technique is based on the direct dependence in space and time of the coda (diffuse waves) decorrelation resulting from the apparition of an extra scatterer, which one wishes to image. The inverse problem solution – the location and scattering cross section of the defect – is obtained using a maximum likelihood computation. The LOCADIFF technique has been applied to locate a millimeter change in concrete using ultrasounds with a precision of the order of one centimeter. The size of the defect is comparable to the size of the heterogeneities constituting the sample.

Approximately one billion users have access to mobile broadband, through which they intend to obtain the same data they can reach using a wired connection. Because of the cost of transmitting data over a mobile-broadband connection and given that 3G networks are quickly reaching their data-transfer capacity, some researchers envision the inter-connection of mobile devices using Wi-Fi, forming a challenged network. Such networks suffer from high latency, low data rates, and frequent disconnections; because end to end paths between pairs of nodes may not always exist, a mobile device must store content before delivering it to the intended receivers. We designed the content-optimal delivery algorithm (CODA) for distributing named data over a delay-tolerant network (DTN), which is a network of challenged networks. Current content-dissemination techniques for DTNs consist mainly of the following items: a content store, for caching and indexing retrieved content, and a query and response mechanism to search the network for matching content. Some algorithms attempt to optimize an objective function, such as the total delivery-delay. While disseminating content, CODA maximizes the network throughput by computing the utility of each item published: a device with a full buffer drops content in order of increasing utility and transmits content in order de- creasing utility. We implemented CODA over the CCNx protocol, which provides the basic tools for querying, caching, and transmitting content.

International audience; In this paper, we describe an experimental study of concrete behavior under a uniaxial tensile load by use of the thermally-compensated Coda Wave Interferometry (CWI) analysis. Under laboratory conditions, uniaxial tensile load cycles are imposed on a cylindrical concrete specimen, with continuous ultrasonic measurements being recorded within the scope of bias control protocols. A thermally-compensated CWI analysis of multiple scattering waves is performed in order to evaluate the stress-induced velocity variation. Concrete behavior under a tensile load can then be studied, along with CWI results from both its elastic performance (acoustoelasticity) and plastic performance (microcracking corresponding to the Kaiser effect). This work program includes a creep test with a sustained, high tensile load; the acoustoelastic coefficients are estimated before and after conducting the creep test and then used to demonstrate the effect of creep load. Concrete’s behaviors under direct tensile load are studied using ultrasonic method. Thermally-compensated CWI provides accurate stress-induced velocity variation (αF). With αF, we have clear observations of Kaiser effect and acoustoelastic effect.Effective acoustoelastic coefficient β is estimated as a nonlinear parameter. β shows a higher sensitivity to the creep damage of concrete than αF.

International audience; Correlations of ambient seismic noise are now widely used to retrieve the Earth response between two points. In this study, we reconstruct the surface-wave Green's function by iterating the correlation process over the tail of the noise-based correlation function. It has been demonstrated that the so-called C 3 function shows the surface-wave part of the Green's function. Using data from 150 continuously recording stations in Europe, the C 3 results help in the extraction of the travel-times from noise-based measurements, especially through the suppression of effects caused by non-isotropic source distributions. We present the results of the next iterative step (i.e. C 5), which show that some coherent signal is still present in the coda of the C 3 function, and we investigate the evolution of the reconstruction of the Green's function throughout the iteration process. Finally, we discuss the interest of combining information from the different correlation functions to improve noise-based tomography analysis.

Background During meiosis, homologous chromosomes exchange segments via the formation of crossovers. This phenomenon is highly regulated; in particular, crossovers are distributed heterogeneously along the physical map and rarely arise in close proximity, a property referred to as "interference". Crossover positions form patterns that give clues about how crossovers are formed. In several organisms including yeast, tomato, Arabidopsis, and mouse, it is believed that crossovers form via at least two pathways, one interfering, the other not. Results We have developed a software package - "CODA", for CrossOver Distribution Analyzer - which allows one to quantitatively characterize crossover patterns by fitting interference models to experimental data. Two families of interfering models are provided: the "gamma" model and the "beam-film" model. The user can specify single or two-pathways modeling, and the software package infers the model's parameters and their confidence intervals. CODA can handle data produced from measurements on bivalents or gametes, in the form of continuous crossover positions or marker genotyping. We illustrate the possibilities on data from Wheat, corn and mouse. Conclusions CODA extends the kind of crossover data that could be analyzed so far to include gametic data (rather than only bivalents/tetrads) when using two-pathways modeling. It will also enable users to perform analyses based on the beam-film model. CODA implements that model's complex physics and mathematics, and uses a summary statistic to overcomes the lack of a computable likelihood which has hampered its use till now.

The use of Coda Wave Interferometry (CWI) to Non Destructively assess concrete structures is an emerging topic. CWI has recently been proposed to determine the stress level of in situ pre-stressed concrete structure as well as to monitor damage of concrete material. The idea is using ultrasonic waves with a wavelength similar to the aggregate size to be in the diffusive regime, and so to probe very small changes of the material. The velocity change is of the order of 0.1% for classical concrete under a 10MPa strain which can be measured with CWI. This velocity variation can be linked to the stress level modification by Murnaghan’s theory. While CODA theory and experiments are emerging in the civil engineering NDT laboratory, it becomes relevant in parallel to know what is actually the investigated zone for, in fine, relating the velocity changes to a given distribution of stress or damage as a function of depth in in situ condition. In this paper we show an experiment that illustrates the existence of an investigated zone in a concrete beam of 0.8 m x 0.2 m x 0.1 m.