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International audience; More connectivity, higher data rates, more reliability, massive network capacity, higher performance and fewer delays are required in the fifth generation (5G) of cellular networks. The last ten years have contained explosive growth in mobile data traffic due to the rapid proliferation of Internet-connected smart devices. For 5G mobile and wireless networks, one of the challenges is to discover how to solve the dilemma between capacity requirements and spectrum shortage. Millimeter-wave communication is therefore a key enabler for 5G technologies. Due to the high path and penetration losses at millimeter wavelengths, antenna beamforming assumes a pivotal role in establishing and maintaining a robust communication link. Recently, codebook-based beamforming has been proposed to achieve a fair balance between complexity and performance and to eliminate the overheads. In this paper, we track the techniques of codebook-based beamforming for millimeter-wave communications in the context of the distinct requirements for low-mobility channel and high-mobility channel scenarios. Subsequently, we will provide a comparison of existing codebook-based beamforming techniques in terms of their respective benefits and shortcomings. Finally, some open directions of research are discussed, and challenges that need to be met are pointed out.

Este trabalho apresenta uma análise dos diferentes usos do item onde em contextos de interação virtual, por meio de postagens do Twitter. A escolha por levantar dados a partir desta rede social se deu em razão de as postagens do Twitter tenderem a se aproximar de contextos de escrita mais informal e, em alguns momentos, até mesmo reproduzir traços da oralidade, o que pode favorecer o uso de formas inovadoras. O objetivo deste trabalho é observar se é possível: a) a partir dos novos usos encontrados para o item em questão, verificar em que medida esses novos usos de onde se destacam daqueles tradicionalmente referidos na tradição gramatical;eb) afirmar se o processo de gramaticalização de onde atestado em trabalhos anteriores obedece à trajetória prototípica desse fenômeno, no qual itens lexicais passam a assumir funções gramaticais em determinados contextos. A presente análise busca mapear os novos usos de onde, sobretudo quando o item é utilizado com valor anafórico-discursivo, de tempo ou marcador discursivo.

International audience; Wireless connections are more and more used in different applications and in public areas for services to consumers but also for handling (sometimes) sensitive communications (for instance in railway systems or for remote video monitoring systems). Such systems can have to face different kind of attacks that target the behind service. Our work aims to detect, as soon as possible and online, attacks that can occur on wireless networks, to be able to react very quickly. In this paper, we present some results of data analysis methods, on Wi-Fi signals, to differentiate the ones with attacks from the ones without. This study focuses on low power jamming attacks with a slight or even no impact on Wi-Fi communications. This is more challenging than detecting high power jamming attacks which have already been addressed in the literature. Being able to detect a low impact attack is a crucial issue in a global security strategy, making it possible to launch countermeasures before the interruption of the communication. The Wi-Fi bands are also in the ISM frequencies, making the environment complicated to analyze. Clustering methods such as Agglomerative Hierarchical Clustering are used to identify some clusters and then to map them to the real classes (with or without attacks). A deep analysis of the clusters obtained in a dataset acquired in uncontrolled conditions is carried out. This is done in order to understand what is responsible of the clustering assignment of the different points and to extract the clusters which can be used to design a detection attack strategy.

IRMMW-THz 2021, 46th International Conference on Infrared, Millimeter and Terahertz Waves, Chengdu, CHINE, 29-/08/2021 - 03/09/2021; In order to be able to use a handled portable terahertz sensor, a solution combining augmented reality and a frequency modulated continuous wave (FMCW) radar is proposed. The achieved architecture ensures simple handling during the acquisition process while the result visualization can be performed in live directly with a smartphone, with a 3D live superimposed augmented reality view.

Zero Group Velocity (ZGV) modes are peculiar guided waves that can exist in elastic plates or cylinders, and have proved to be very sensitive tools in characterizing materials or thickness variations with sub-percent accuracy at space resolutions of about the plate thickness. In this article we show theoretically and experimentally how such a mode can be generated as the sum-frequency interaction of two high amplitude primary waves, and then serve as a local probe of material non-linearity. The solutions to the phase matching condition, i.e. condition for a constructive non-linear effect, are obtained numerically in the mark of classical, quadratic non-linearity. The coupling coefficients that measure the transfer rate of energy as a function of time from primary to secondary modes are derived. Experiments are conducted on an aluminum plate using piezo-electric transducers and a laser interferometer, and explore the interaction for incident symmetric and anti-symmetric fundamental Lamb modes. In an experiment operated without voltage amplifier we demonstrate that the resonant nature of these ZGV modes can be leveraged to accumulate energy from long excitations and produce detectable effects at extraordinarily low input power even in such weakly non-linear material.

Spectrally efficient waveforms have been extensively investigated in the last few years for the upcoming 5G systems. Filter Bank Multicarrier (FBMC) and Generalized Frequency Division Multiplexing (GFDM) are two of the best contenders that offer very low out of band emissions. To make better use of the available spectral resources, we propose coupling the 5G waveforms candidates with Cognitive Radio (CR). To perform spectrum sensing, we rely on cyclostationary detection. Although some papers have addressed second order cyclic features of the aforementioned waveforms, they are special cases of the results presented herein. In fact, in the present work, we first derive the explicit theoretical mth order pth conjugate cyclic cumulants of both FBMC and GFDM. Our analysis reveals that FBMC has distinctive cyclostationary properties. GFDM exhibits rich cyclic features as a result of the block filtering, the Cyclic Prefix (CP) insertion and the use of subsymbol guards. The obtained results are then exploited for signal detection purposes. Detection probability of FBMC is the best among the considered waveforms, followed by GFDM, where both outperform OFDM detection, specially if the used CP is low.

In recent years, multiple functions traditionally realized by hardware components have been replaced by digital-signal processing, making radar and wireless communication technologies more similar. A joint radar and communication system, referred to as a RadCom system, was proposed to overcome the drawbacks of the conventional existent radar techniques while using the same system for intervehicular communication. Consequently, this system enhances used spectral resources. Conventional orthogonal frequency division multiplexing (OFDM) was proposed as a RadCom waveform. However, due to OFDM’s multiple shortcomings, we propose universal filtered multicarrier (UFMC), a new 5G waveform candidate, as a RadCom waveform that offers a good trade-off between performance and complexity. In addition to that, we propose multicarrier code division multiple access (MC-CDMA) as a multiple-access (MA) technique that can offer great performance in terms of multiuser detection and power efficiency. Moreover, we study how UFMC filter length and MC-CDMA spreading sequences can impact overall performance on both radar and communication separately under a multipath channel. Analysis of the bit error rate (BER) of the UFMC waveform was performed in order to confirm the experiment results.

We show that the values of certain physical constants verify a geometry of which the Planck length and the Planck time are the central constants. We interpret this property of Planck length and Planck time by a quantum-gravitational conception of the position. This conception contains the relativistic conception as approximation and shows how both a quantum and gravitational nature of the Galilean referential can so far be imperceptibly neglected.; Nous montrons que les valeurs de certaines constantes physiques vérifient une géométrie dont la longueur de Planck et le temps de Planck sont les constantes centrales. Nous interprétons cette propriété de la longueur de Planck et du temps de Planck par une conception quanto-gravitationnelle de la grandeur position. Cette conception contient la conception relativiste comme cas limite et montre comment une nature à la fois quantique et gravitationnelle des référentiels galiléens peut être jusqu'à présent imperceptiblement négligée.

Low Density Signature (LDS) is an emerging non-orthogonal multiple access (NOMA) technique that has never been evaluated under a vehicular channel in order to simulate the environment of a vehicle to everything (V2X) communication. Moreover, the LDS structure has been combined with only Orthogonal Frequency Division Multiplexing (OFDM) and Filter-Bank Multi-Carrier (FBMC) waveforms to improve its performances. In this paper, we propose new schemes where the LDS structure is combined with Universal Filtered Multi-Carrier (UFMC) and Filtered-OFDM waveforms and the Bit Error Rate (BER) is analysed over a frequency selective channel as a reference and over a vehicular channel to analyse the effect of the Doppler shift on the overall performance.

Anglo-French Physical Acoustics Conference, SOUT CROYDON, ROYAUME-UNI, 15-/01/2020 - 17/01/2020; The computation of the eigenmodes of solid spheres is a classical problem in mechanics solved more than a century ago by Lamb. This topic has found many applications in geophysics, composites structures and non-destructive testing. The eigenmodes are the solutions of a dispersion relationship which can be obtained analytically. However, numerical methods are preferred for complex structures such as a multilayered spheres. One-dimensional models can be obtained based on semi-analytical methods, in which the angular directions are described analytically (based on spherical harmonics functions) and the radial direction is discretized. This approach yields a linear eigenproblem which is simple to solve. The existing semi-analytical methods (Heyliger & Jilani, 1992 ; Park, 2002) are not fully satisfactory. Indeed, the related eigenproblems are not given in a closed-form (numerous integrations are required) or are specific to a choice of interpolating functions. We propose a more general formulation. The main issue is to correctly identify the orthogonality relationships of spherical harmonics, used to uncouple the angular and the radial directions. Because the elastodynamics equations are vector wave equations, both vector and tensor spherical harmonics orthogonalities are required. While the orthogonality of vector spherical harmonics is rather well-known and straightforward, the orthogonality of tensor spherical harmonics is much more mathematically involved (Martinec, 2000). In this work, a closed-form eigenproblem is eventually obtained for any interpolating function and favourably compared to literature results (Eringen & Suhubi, 1975). Additionally, the forced response can be calculated explicitly based on the eigenmodes. It can be used to reconstruct surface wave propagation phenomena. We particularly focus on the phenomenon of Rayleigh wave collimation described by Clorennec and Royer (2004): for a line source of specific width, the Rayleigh wave is not diffracted on the surface of the sphere but propagates with a quasi-constant width. We show that this phenomenon is accurately recovered with our numerical model. An analysis based on eigenmodes is proposed. We also study the perturbation induced by the addition of a thin viscoelastic coating. Furthermore, the case of an infinite embedding medium surrounding the sphere is also considered. In that case, the radial direction must be bounded so that the problem can be numerically handled. For that purpose, a radial Perfecty Matched Layer (PML) of finite thickness is applied. The leakage amount (radiative losses) of eigenmodes, of practical interest to select the modes with the highest quality factor, is then evaluated. The existence of a collimating wave with an infinite surrounding medium is also investigated.

The goal of this paper is to investigate the propagation of two-dimensional elastic Bloch waves in helical periodic structures, obeying two discrete screw symmetries about the same axis. First, a three-dimensional coordinate system is built from the two helical directions of periodicity of the problem and the radial coordinate originating from the symmetry axis. The existence of Bloch waves in bi-helical structures can be justified owing to the independence of the metric tensor of the coordinate system on both helical coordinates. Considering the elastodynamic equilibrium equations, Bloch theorem is expressed in appropriate bases to project the vector wavefields, namely the covariant/contravariant bases of the bi-helical coordinate system (or, alternatively, the cylindrical basis). From a geometrical point of view, the three-dimensional unit cell is delimited by non-plane boundaries, which must be carefully parametrized. The so-called wave finite element method is then applied to numerically solve the Bloch wave eigenproblem and the implementation of the numerical method in a bi-helical system is detailed. Owing to the cylindrical nature of the geometry, the two-dimensional propagation constants are not independent to each other. The relationship between both constants is established. The calculation of wave mode properties (wavenumbers, group and energy velocities) is performed along the helical propagation directions, as well as the straight axial and circumferential directions. Numerical validations of the overall approach are carried out for cylindrical uniform tubes and a chiral nanotube. Finally, the method is applied to a complex multi-wire structure, often encountered in energy cables, consisting of two layers of helical wires twisted in opposite directions.

In real structures, the proportional damping assumption is never strictly verified. Indexes of non-proportionality are then necessary to determine if this assumption leading to real modes still remains valid. If not, complex modes will appear and moreover, if their corresponding natural frequencies are close, their imaginary part can become large. In this paper, a new non-proportionality index, quantifying the “complexity” of mode shapes, is presented, derived from the notion of optimal complex modes introduced by Adhikari. This new index is designed for experimental results, for which the system’s parameters are not known, and proven to be equal to the previous one up to the first order on damping. Modal identification based on wavelet analysis is considered promising in this study for processing free responses of non-proportionally damped systems, integrated in noise, to directly obtain complex modes. A procedure for choosing an appropriate quality factor for the time-frequency resolution, necessary to get correct identification results in the case of free responses combined with responses to ambient excitation and/or to additive noise, is detailed. The proposed identification technique based on Continuous Wavelet Transform (CWT) is finally applied on different transient responses of a masonry wall specimen during an experimental campaign comprising simultaneous vibrations and shear-compression tests. The results of the CWT method for modal identification are compared with those obtained by a classical modal analysis technique, called Least Squares Complex Frequency method, by means of the Modal Assurance Criterion and the proposed non-proportionality index.

Background and AimsExtracellular ATP governs a range of plant functions, including cell viability, adaptation and cross-kingdom interactions. Key functions of extracellular ATP in leaves and roots may involve an increase in cytosolic free calcium as a second messenger (‘calcium signature’). The main aim here was to determine to what extent leaf and root calcium responses require the DORN1/P2K1 extracellular ATP receptor in Arabidopsis thaliana. The second aim was to test whether extracellular ATP can generate a calcium wave in the root.MethodsLeaf and root responses to extracellular ATP were reviewed for their possible links to calcium signalling and DORN1/P2K1. Leaves and roots of wild type and dorn1 plants were tested for cytosolic calcium increase in response to ATP, using aequorin. The spatial abundance of DORN1/P2K1 in the root was estimated using green fluorescent protein. Wild type roots expressing GCaMP3 were used to determine the spatial variation of cytosolic calcium increase in response to extracellular ATP.Key ResultsLeaf and root ATP-induced calcium signatures differed markedly. The leaf signature was only partially dependent on DORN1/P2K1, while the root signature was fully dependent. The distribution of DORN1/P2K1 in the root supports a key role in the generation of the apical calcium signature. Root apical and sub-apical calcium signatures may operate independently of each other but an apical calcium increase can drive a sub-apical increase, consistent with a calcium wave.ConclusionDORN1 could underpin several calcium-related responses but it may not be the only receptor for extracellular ATP in Arabidopsis. The root has the capacity for a calcium wave, triggered by extracellular ATP at the apex.

The fields of applications involving elastic waves propagating in slender structures are numerous. A slender structure can be considered as a waveguide, infinite in one or more directions (plates, bars, tubes ...). Guided waves have the particularity of propagating over long distances with little loss of energy, which can constitute an advantage or a disadvantage depending on the targeted application (non-destructive evaluation vs. reduction of vibrations, for example).One difficulty associated with guided waves is that they are multimodal and dispersive in nature. To determine the behavior of these waves, modeling tools are essential. My research works have been oriented towards the development of generic tools, capable of handling complex geometries. Such modeling tools requires numerical methods. They are based on finite element methods allowing the computation of modes in waveguides with a cross-section, or a unit cell, of arbitrary shape. The developments, theoretical or numerical, take into account various specificities: curvature of waveguides (helical or/and rotational symmetries), excitation, presence of inhomogeneities (local defects), leakage losses (buried waveguides), multi-wire geometry (cables). These five aspects are broken down into different sections that form the outline of the presentation. The overall objective is to take advantage of the modal formalism at every stage: for obtaining the dispersion curves (free response), for the calculation of solutions under excitation (forced response) or for the resolution of diffraction problems (interaction between waves and local inhomogeneities).Among the perspectives of this work, we can cite the development of imaging methods using sensitivity methods. The proposed modeling tools make it possible to exploit the power of modal formalism to quickly calculate solutions to a given excitation (direct and adjoint problems) as well as synthetic data., Les domaines d'applications impliquant des ondes élastiques se propageant dans des structures élancées sont nombreux. Une structure élancée peut être considérée comme un guide d'onde, infini dans une ou plusieurs directions (plaques, barres, tubes...). Les ondes guidées ont la particularité de se propager sur de longues distances avec peu de perte d'énergie, ce qui peut constituer un avantage ou bien un inconvénient suivant l'application visée (évaluation non-destructive vs. réduction des vibrations, par exemple). Une difficulté liée aux ondes guidées est qu'elles sont de nature multimodale et dispersive. Pour déterminer le comportement de ces ondes, des outils de modélisation sont indispensables. Mes travaux se sont orientés vers le développement d'outils généraux, capables de traiter des géométries de guides complexes, ce qui nécessite la mise en oeuvre de méthodes numériques. Les outils mis en place sont basés sur des méthodes d'éléments finis permettant le calcul des modes d'onde. Ils permettent d'étudier des guides ayant une section, ou une cellule unitaire, de forme arbitraire. Les développements, théoriques ou numériques, tiennent compte de diverses spécificités : courbure du guide (symétries hélicoïdales ou/et de rotation), excitation, présence d'inhomogénéités («défauts»), pertes par fuite (enfouissement), géométrie multi-brins (câbles). Ces cinq aspects sont déclinés tour à tour en différentes sections qui forment le plan de l'exposé. L'objectif global est de tirer parti du formalisme modal, que ce soit pour l'obtention des courbes de dispersion (réponses libres), le calcul de solutions sous excitation (réponses forcées) ou pour la résolution de problèmes de diffraction (interaction entre ondes et inhomogénéité locale). Parmi les perspectives envisagées de ces travaux, on peut citer le développement de méthodes d'imagerie par méthodes de sensibilité. Les outils de modélisation proposés permettent en effet d'exploiter la puissance du formalisme modale pour calculer rapidement des solutions à une excitation donnée (problèmes directs et adjoints) ainsi que des données synthétiques.

The fields of applications involving elastic waves propagating in slender structures are numerous. A slender structure can be considered as a waveguide, infinite in one or more directions (plates, bars, tubes ...). Guided waves have the particularity of propagating over long distances with little loss of energy, which can constitute an advantage or a disadvantage depending on the targeted application (non-destructive evaluation vs. reduction of vibrations, for example).One difficulty associated with guided waves is that they are multimodal and dispersive in nature. To determine the behavior of these waves, modeling tools are essential. My research works have been oriented towards the development of generic tools, capable of handling complex geometries. Such modeling tools requires numerical methods. They are based on finite element methods allowing the computation of modes in waveguides with a cross-section, or a unit cell, of arbitrary shape. The developments, theoretical or numerical, take into account various specificities: curvature of waveguides (helical or/and rotational symmetries), excitation, presence of inhomogeneities (local defects), leakage losses (buried waveguides), multi-wire geometry (cables). These five aspects are broken down into different sections that form the outline of the presentation. The overall objective is to take advantage of the modal formalism at every stage: for obtaining the dispersion curves (free response), for the calculation of solutions under excitation (forced response) or for the resolution of diffraction problems (interaction between waves and local inhomogeneities).Among the perspectives of this work, we can cite the development of imaging methods using sensitivity methods. The proposed modeling tools make it possible to exploit the power of modal formalism to quickly calculate solutions to a given excitation (direct and adjoint problems) as well as synthetic data.; Les domaines d'applications impliquant des ondes élastiques se propageant dans des structures élancées sont nombreux. Une structure élancée peut être considérée comme un guide d'onde, infini dans une ou plusieurs directions (plaques, barres, tubes...). Les ondes guidées ont la particularité de se propager sur de longues distances avec peu de perte d'énergie, ce qui peut constituer un avantage ou bien un inconvénient suivant l'application visée (évaluation non-destructive vs. réduction des vibrations, par exemple). Une difficulté liée aux ondes guidées est qu'elles sont de nature multimodale et dispersive. Pour déterminer le comportement de ces ondes, des outils de modélisation sont indispensables. Mes travaux se sont orientés vers le développement d'outils généraux, capables de traiter des géométries de guides complexes, ce qui nécessite la mise en oeuvre de méthodes numériques. Les outils mis en place sont basés sur des méthodes d'éléments finis permettant le calcul des modes d'onde. Ils permettent d'étudier des guides ayant une section, ou une cellule unitaire, de forme arbitraire. Les développements, théoriques ou numériques, tiennent compte de diverses spécificités : courbure du guide (symétries hélicoïdales ou/et de rotation), excitation, présence d'inhomogénéités («défauts»), pertes par fuite (enfouissement), géométrie multi-brins (câbles). Ces cinq aspects sont déclinés tour à tour en différentes sections qui forment le plan de l'exposé. L'objectif global est de tirer parti du formalisme modal, que ce soit pour l'obtention des courbes de dispersion (réponses libres), le calcul de solutions sous excitation (réponses forcées) ou pour la résolution de problèmes de diffraction (interaction entre ondes et inhomogénéité locale). Parmi les perspectives envisagées de ces travaux, on peut citer le développement de méthodes d'imagerie par méthodes de sensibilité. Les outils de modélisation proposés permettent en effet d'exploiter la puissance du formalisme modale pour calculer rapidement des solutions à une excitation donnée (problèmes directs et adjoints) ainsi que des données synthétiques.

In order to meet the explosion of connected devices with their heterogeneous applications, the upcoming 5G systems focus on the design of spectrally efficient waveforms. Universal Filtered Multicarrier (UFMC) is one of the major waveforms contenders that offers low out of band emissions, compatibility with the existing Multiple Input Multiple Output techniques as well as multiple services support. In this paper, we propose to couple UFMC with Cognitive Radio (CR) to make better use of the available spectral resources. To perform spectrum sensing for the CR, we rely on cyclostationary detection. UFMC cyclostationarity characteristics have not been researched before. Hence in the present work, we first derive the explicit theoretical m-th order cyclic cumulants of UFMC, considering a multipath channel, frequency and timing offsets. Our analysis reveals that the per-subband filtering used in this waveform produces distinctive cyclostationary signatures. Then we exploit these signatures for signal detection. The obtained results are compared to those of the well studied Orthogonal Frequency Division Multiplexing (OFDM). Detection probability of UFMC outperforms the one of OFDM specially when the used Cyclic Prefix (CP) is low.

This article deals with the dynamic response of laterally unbounded, horizontally layered plates subjected to dynamic sources applied at arbitrary locations, which is ultimately a classical problem. This response is most often obtained via a modal superposition in terms of the complex Lamb modes by casting the equations in the frequency–space domain, followed by a Fourier inversion into the space–time domain. Then again, a much less often used alternative method relies on formulating the problem directly in the time domain in terms of a modal superposition in the wavenumber domain, which is followed by a Fourier inversion into the space–domain, as considered in further detail herein. This alternative can offer powerful advantages in some cases, such as dealing easily with anisotropy, or with slowly propagating waves even in the absence of damping. At the same time, however, it is beset by difficulties associated with the Fourier inversion into the space–domain. As a matter of fact, during forcing, the truncation of the modal series and of the numerical integrals is hindered by poorly convergent behaviors. Here we overcome both of these difficulties by considering the asymptotic, static behavior of the integrands. We find that by introducing a regularizing term, the response can be effectively separated into near and far fields, despite the fact that these frequency-domain concepts are alien to a wavenumber–time formulation. The so-defined far field is free of sharp variations and can then be computed in a numerical grid that is optimized regarding the propagating wavelengths, which only depend on the time-spectral content of the excitation and not on its space-spectrum. Finally, we also propose a hybrid way to compute the remaining near field by combining with a non-modal formulation, expressed in the wavenumber–Laplace domain.

The objective of this paper is twofold: first, to introduce an innovative technique for extracting and exploiting the Electromagnetic (EM) waveguide dispersion of civil engineering materials by means of GPR; and second, to monitor the water ingress front during the absorption process for various concrete mixes. This technique is based on a new inversion procedure that applies the Electromagnetic Waveguide Model (WGM) to invert phase velocity dispersion curves in their modal form. A Parallel homogenization model, derived from the Lichtenecker-Rother equation, has been employed to extend the waveguide from a one-layer to a two-layer medium. The WGM outputs are then used to estimate the geometric parameters of the propagation medium and offer a primary application to water transfer monitoring in concrete through capillarity effects. The initial WGM validation is carried out on FDTD-simulated propagation signals, while the second validation relies on GPR data acquired from homogeneous materials. To achieve the second objective, a broad-based experimental study is conducted for the purpose of correlating electromagnetic waveguide dispersion parameters with both the geometric and hydric characteristics of various concrete mixes. Results obtained using the two-layer WGM serve to monitor the water ingress front during an absorption process. These results are then compared to the moisture gradients generated on cores using gammadensimetry, which is set as the reference. This procedure yields a number of trends, which in turn provide key information on the conditioning state of the studied concretes.

A nonlinear acoustic method to assess the damage level of a complex medium is discussed herein. Thanks to the highly nonlinear elastic signatures of cracks or, more generally, internal solid contacts, this method is able to distinguish between contributions from linear wave scattering by a heterogeneity and contributions from nonlinear scattering by a crack or unbounded interface. The coda wave interferometry (CWI) technique is applied to reverberated and scattered waves in glass plate samples featuring various levels of damage. The ultrasonic coda signals are recorded in both the absence and presence of an independent and lower-frequency elastic “pump” wave, before being analyzed by CWI. The monitored CWI parameters quantifying changes in these coda signals, which therefore quantify the nonlinear wave-mixing effects between the coda and pump waves, are found to be dependent on the damage level in the sample. A parametric study is also performed to analyze the influence of sensor positions and average temperature on the method’s output. The reported results could be applied to the non-destructive testing and evaluation of complex-shape materials and multiple scattering samples, for which conventional ultrasonic methods show strong limitations.

Shockwave processing and sous vide cooking improve sensorial and nutritional qualities of beef. Food Structure Digestion and Health congres

CFRAC 2019, 6th International Conference on Computational Modeling of Fracture and Failure of Materials and Structures, Braunschweig, ALLEMAGNE, 12-/06/2019 - 14/06/2019

WTS 2019, Wireless Telecommunications Symposium, New-York, ETATS-UNIS, 09-/04/2019 - 12/04/2019; In this paper, a cyclostationarity based algorithm is proposed for the estimation of key parameters of Universal Filtered Multicarrier (UFMC) waveform. They include the symbol duration, the filter length, the number of subbands and their size as well as the number of subcarriers. The performance of the proposed algorithm under low Signal to Noise Ratio (SNR) in multipath channel is assessed through simulations. Furthermore, the performance under different processing time using different parameters are also compared. The proposed algorithm require no a priori knowledge of the received signal, making it very suitable in the context of cognitive radio, either for spectrum monitoring or communication signal demodulation. To the best of the authors knowledge, this paper is the first work proposing an algorithm for blind estimation of UFMC parameters.

Nonorthogonal multiple access (NOMA) techniques represent a key feature for 5G systems in order to increase multiple users' systems' capacity. In particular, we propose, for study, a pattern division multiple access (PDMA) technique, which defines a pattern matrix used for mapping the users to a group of resource elements that might be shared by multiple users. The contribution of this paper is the analysis of the performances, in terms of bit error rate (BER), of 5G candidate waveforms, such as orthogonal frequency division multiplexing (OFDM), filter bank multi-carrier (FBMC), and generalized frequency division multiplexing (GFDM), in the PDMA scheme. Regarding the detection of different users' data, the successive interference cancellation algorithm is performed at the receiver side. The simulation results, consolidated by the analytic study, exhibit that OFDM and FBMC could be used in the NOMA context, while the BER related to GFDM is very high.

Cette thèse est consacrée à la modélisation de la propagation des ondes planes dans les plaques multicouches infinies, dans le cadre de l'élasticité linéaire. L'objet du travail est de trouver une approximation analytique ou semi-analytique des relations de dispersion des ondes lorsque le rapport de l'épaisseur de la plaque sur la longueur d'onde est petit. Ces relations de dispersion, liant la fréquence angulaire et le nombre d'onde, fournissent des informations clés sur les caractéristiques de propagation des différents modes. On propose dans cette thèse deux modélisations : le modèle du Bending-Gradient et la méthode des développements asymptotiques. La pertinence de ces méthodes est testée en comparant leurs prédictions à celles des théories de plaques bien connues, et à des résultats de référence obtenus par la méthode des éléments finis. Au préalable, dans la première partie de la thèse, une justification mathématique de la théorie du Bending-Gradient dans le cadre statique est réalisée à l'aide des méthodes variationnelles. Il s'agit d'abord d'identifier les espaces mathématiques dans lesquels les problèmes variationnels du Bending-Gradient sont bien posés. Puis, des théorèmes d'existence et d'unicité des solutions correspondantes sont ensuite formulés et prouvés. La deuxième partie est consacrée à la formulation des équations du mouvement du Bending-Gradient. Des simulations numériques sont effectuées pour plusieurs types d'empilements, permettant ainsi de tester la validité du modèle pour la modélisation de la propagation des ondes de flexion. La troisième partie est dédiée à l'analyse asymptotique des équations tridimensionnelles du mouvement, menée à bien grâce à la méthode des développements asymptotiques, le petit paramètre étant le rapport de l'épaisseur sur la longueur d'onde. En supposant que les champs tridimensionnels s'écrivent comme des séries en puissance du petit paramètre, on obtient une succession de problèmes à résoudre en cascade. La validité de cette méthode est évaluée par comparaison avec la méthode des éléments finis.

This work concerns the characterization of the impact sound level in wood constructions from in situ measurements. Two global acoustic indices have been estimated and compared with each other, one associated with the excitation source that is the tapping machine, the other related to the excitation source that is the impact ball, likely to better characterize footsteps. These global acoustic indices were estimated over the frequency range [100 Hz: 3150 Hz] and over the frequency range [50 Hz: 3150 Hz], A-weighted or A-unweighted. A statistical study was then carried out on the di_erence between the global acoustic indice related to the tapping machine and that related to the impact ball. According to the choice of the frequency range and the use of the A-weighting, this statistical study made it possible to conclude on the sensitivity of these global acoustic indices with respect to the correction term normalizing the influence of the reception room and, with respect to the low frequencies [50 Hz: 100 Hz]. Finally, this statistical study concludes on the relevance of the use of a global acoustic indice compared to the other in order to characterize the impact sound level in these wood constructions.

International audience; For vibro-acoustic applications, a turbulent wall pressure fluctuations model was derived. The model is based on the resolution of the Poisson equation. The pressure is characterized in time and space through its spectrum in the pulsation wave-number domain. The developed model follows trends commonly observed using Corcos model in a large pulsation range but also shows new behaviours for low and high pulsations. The radiated noise due to turbulent wall pressure fluctuations is then computed in accordance with the form of the turbulent wall pressure spectrum. A specific computational methodology is proposed to perform the calculation without introducing limiting hypothesis on the radiated impedance.

GdR Mecawave, FREJUS, FRANCE, 06-/11/2018 - 09/11/2018; De nombreux éléments de structures de génie civil sont élancés, et partiellement ou totalement enfouis dans un milieu solide. Pour le contrôle non-destructif par ondes guidées de tels éléments, un enjeu important est de développer une méthode d'imagerie tenant compte à la fois de la complexité de la propagation des ondes guidées - dispersives, multimodales, atténuées par fuite dans le milieu environnant - et de l'accès souvent limité à la structure. En pratique, ceci restreint la configuration de mesure envisageable. Nous appliquons aux guides d'ondes la méthode dite de l'imagerie topologique. Cette méthode repose sur l'évaluation, en tout point du guide d'onde sain (sans défaut), d'une fonction d'imagerie appelée gradient topologique. La représentation spatiale du gradient révèle naturellement l'emplacement des défauts réels. Le calcul du gradient topologique nécessite la simulation de deux champs en guide sain, les champs direct et adjoint, ainsi que la mesure du champ diffracté dans le guide endommagé. Notons qu'en pratique, l'expression du gradient est simplifiée afin d'obtenir rapidement une image, si bien que le gradient n'est plus topologique à proprement parler.L'objectif de cette contribution est de quantifier l'influence sur la qualité de l'image du type de champ émis et des configurations de mesure. Dans un premier temps, nous simulons l'endommagement d'un guide d'onde axisymétrique fermé et viscoélastique (sans milieu environnant), à l'aide de méthodes éléments finis basées sur un formalisme modal. Ce formalisme permet un calcul rapide en tout point du guide sain des champs direct et adjoint. Les données observables sont limitées au champ réfléchi par le défaut mesuré ponctuellement à la surface du guide. La source émettrice considérée est d'abord monomodale puis multimodale. Avec un champ monomodal, le défaut n'est localisé que suivant l'axe du guide. Un champ multimodal permet de localiser le défaut dans la section du guide. Dans ce dernier cas, nous montrons toutefois que des artefacts apparaissent dans l'image en raison des conversions modales dans les champs générés par les sources primaires (excitation) et secondaires (défaut). L'influence de la configuration de mesure sur les artefacts est étudiée. Pour pallier simplement le phénomène, nous proposons de construire une nouvelle image, combinant une image multimodale (2D) avec une image monomodale (1D). Dans un deuxième temps, le cas d'un guide d'onde ouvert (enfoui dans un milieu environnant) est considéré. Nous montrons l'effet de l'atténuation des ondes sur l'image obtenue, ainsi que l'intérêt du formalisme modal utilisé pour un traitement a priori de l'image.

2nd Franco-Chinese Acoustic Conference, Le Mans, France, 29-/10/2018 - 31/10/2018; Elastic guided waves can be used for the inspection of elongated structures. Since these waves are multi-modal and dispersive, numerical modeling tools are often needed for the design and the optimization of inspection systems. Here we are interested in waves propagating in bi-helical periodic media. Such structures can be encountered in cables used for electricity transportation. One considers a multi-wire structure composed by two layers of helical wires. The layers are twisted in opposite directions yielding a periodic structure along two helical directions. In our work, we want to take advantage of the periodicity properties of this structure by reducing the problem to a single unit cell through the use of the Floquet-Bloch theorem in order to deduce the wave propagation characteristics. However the difficulty lies in that the periodicity occurs along two curved directions, so that the definition of the unit cell becomes complex. Besides, the periodic boundary conditions have to be carefully written.. In this work, we propose a bi-helical coordinate system. First, we prove the existence of Bloch waves in this non-trivial coordinate system. Second, the curved boundaries of the unit cell are defined. The unit cell is then discretized by the finite element method using three-dimensional tetrahedra. Third, the wave finite element method is applied to solve the wave modes of the structure. It is shown that the components of vector fields, initially Cartesian, have to be projected in appropriate bases, namely the covariant and contravariant bases associated with the bi-helical coordinate system. The results are post-processed to find the dispersion relation as well as the group velocity of modes propagating along the straight axial direction of the structure. Numerical validations are carried out on a one-dimensional periodic single wire and on a two-dimensional periodic cylindrical shell before investigating the bi-layered multi-wire structures.

ITST 2018, 16th International Conference on Intelligent Transport Systems Telecommunications, Lisbonne, PORTUGAL, 15-/10/2018 - 17/10/2018; International audience; Filter Bank Multi Carrier (FBMC) based waveforms received recently a lot of interest due to their high frequency localization and hence their suitability to the fragmented spectrum utilization. In this paper, we analyze the doubly selective channel estimation aspect of the FBMC-OQAM waveform. We perform a frequency domain channel estimation using the Linear Minimum Mean Square Error (LMMSE) estimtator. In addition, we study the spreading effects of the FBMC filtering operation and the channel selectivity on the received symbol. This study is exploited later to offer a trade off between the complexity level of the LMMSE estimator and its performance accuracy. An analytical analysis of this study is provided and verified by Monte Carlo simulations.

International audience; In this paper, a high data rate modulation scheme for impulse radio ultra-wideband (IR-UWB) communication system using orthogonal waveforms is presented. The proposed M-state Orthogonal Amplitude Modulation (M-OAM) is evaluated under additive White Gaussian noise and indoor multipath channels IEEE.802.15. The simulation results show that the proposed system performance, in term of bit error rate (BER), is of the same order as that of the traditional UWB modulation. In addition, the M-OAM modulations provide a high data rate for short range wireless applications. Nevertheless, the multipath effect reduces the quality of transmission. Thus, the performances of three receiver architectures, that employ different pulse combining schemes, are investigated. Namely, a conventional matched filter receiver, a RAKE receiver and a minimum mean square error equalizer are considered. This study shows that the proposed M-OAM communication system offers good performances in term of quality of services, channel capacity and BER.

International audience; In this paper, we describe how we can finely adjust the electromagnetic losses inside a mode-stirred reverberation chamber (MSRC) using a device containing a variable quantity of conductive liquid. This device can be used for several applications such as decreasing the lowest usable frequency in MSRCs for electromagnetic compatibility (EMC) tests or controlling the root-mean-square (rms) delay spread inside a configured MSRC to reproduce the wireless multipath channel of different electromagnetic (EM) environments such as those inside vehicles. In this study, we will focus on wireless environment simulation applications. The rms delay spread is determined inside a cavity provided with apertures and a stirrer and loaded with a conductive liquid. It is compared to that obtained inside an automotive vehicle for different positions of a couple of wireless communication antennas. The comparisons show that, in our case, the static wireless multipath channel of a complex EM environment of a vehicle may be simulated inside such a cavity.; Les constructeurs automobiles souhaitent réduire le plus possible le temps de développement nécessaire à la mise sur le marché de nouveaux Îhicules. Ces Îhicules abritent de plus en plus d'équipements de première monte et nomades exploitant des communications radio échangeant des données à l'intérieur du Îhicule ainsi que vers l'extérieur. Ces systèmes opèrent le plus souvent à des fréquences comprises entre 1 et 6 GHz. A ces fréquences, les habitacles s'apparentent à des cavités métalliques dont les caractéristiques en termes de radio propagation dépendent de facteurs tels que la forme, le volume, les surfaces et répartitions d'ouvertures...Cet article propose un nouveau moyen de mesure opérationnel dans cette bande de fréquence, fondé sur l'utilisation d'une cavité spécifique chargée de façon variable en continu à l'aide d'un liquide conducteur. Celle-ci s'aÏre en mesure de reproduire différents environnements de propagation intra-Îhicules. Ce dispositif permet de modifier, à la demande, certaines des caractéristiques du canal de propagation nécessaires à l'évaluation de protocoles de radio communication et ceci, dès la phase de conception du Îhicule, avant que toute réalisation physique ne soit effectuée. De premiers essais corroborent les résultats obtenus préalablement en simulation numérique, notamment en termes de profil d'étalement des retards de propagation.

A numerical method is proposed to compute high-frequency low-leakage modes in structural waveguides surrounded by infinite solid media. In order to model arbitrary shape structures, a waveguide formulation is used, which consists of applying to the elastodynamic equilibrium equations a space Fourier transform along the waveguide axis and then a discretization method to the cross-section coordinates. However several numerical issues must be faced related to the unbounded nature of the cross-section, the number of degrees of freedom required to achieve an acceptable error in the high-frequency regime as well as the number of modes to compute. In this paper, these issues are circumvented by applying perfectly matched layers (PML) along the cross-section directions, a high-order spectral element method for the discretization of the cross-section, and an eigensolver shift suited for the computation of low-leakage modes. First, computations are performed for an embedded cylindrical bar, for which literature results are available. The proposed PML waveguide formulation yields good agreement with literature results, even in the case of weak impedance contrast. Its performance with high-order spectral elements is assessed in terms of convergence and accuracy and compared to traditional low-order finite elements. Then, computations are performed for an embedded square bar. Dispersion curves exhibit strong similarities with cylinders. These results show that the properties of low-leakage modes observed in cylindrical bars can also occur in other types of geometry.