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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.

In recent years, multiple functions traditionally realized by hardware components have been replaced by digital-signal processing, making radar and wireless communication technologies more similar.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.

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.

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.

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.

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.

The upcoming 5G era is considered as a critical answer to future railway communication needs. In this correspondence, we analyze the performance of sliding window time domain (TD) LMMSE channel estimation technique where a generalized development is proposed and analyzed for 5G filter bank multicarrier-offset quadratic-amplitude modulation waveform candidates. In order to enhance performance, the analytical model is extended to exploit multipaths and multiantennas correlation wherever they do exist e.g., tunnels. TD-LMMSE performance for 5G waveforms and achieved enhancements are verified by Monte Carlo simulations.

The aim of this experiment was to investigate the effect of hydrodynamic shockwave (SW) processing on the muscle protein structure and digestibility in vitro. Beef brisket steaks were subjected to hydrodynamic SW (11 kJ/pulse) and were sous-vide cooked at 60°C for 12 hours, followed by in vitro gastric digestion. The protein native α-helix structure of connective tissue and myofibers was modified after SW processing and SW-sous-vide cooking respectively. Acidic gastric digestion was found to have less effect on the molecular structure of myofibers of SW-sous-vide cooked meat in comparison with unprocessed meat. These structural changes may influence the meat protein digestive properties and hence have an impact on the nutritional value of the meat.

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.

IEEE 15th International Conference on ITS Telecommunications, Warsaw, POLOGNE, 29-/05/2017 - 31/05/2017; International audience; In this paper we review the most promising 5G waveform candidates and their robustness to the Railway context and particularly the high speed. We surf in addition the compatibility of these waveforms to the short packet communication and the MIMO technologies which are fundamental components of future wireless communication systems. Interesting solutions to the faced challenges in that regard are explored.

IEEE International Conference on Communications - ICC2017, Paris, France, 21-/05/2017 - 25/05/2017; International audience; In this paper, we present a new and intuitive way to show important green techniques for the future fifth generation of mobile networks such as adaptive beamforming to the general public. We use a new device called the Radio Waves Display, which is a one meter square panel composed of twenty by twenty radio frequency sensors spaced by five cm. The Electromagnetic Field strength measured by each sensor is converted into visible light. This new device enables a direct visualization of the waves that pass through it, in real time. It enables us to show to the general public, which is naturally more concerned about the energy consumption of devices, that the network energy efficiency as well can be improved. Most of the presented demonstrations have been effectively shown to a general public at the Mobile World Congress 2016 and other events.

Acoustics'2017, BOSTON, ETATS-UNIS, 25-/06/2017 - 29/06/2017; In room acoustics, starting from the sound particle concept, it is now well established that the reverberant field can be modeled from a diffusion equation function of the acoustic density and a gradient equation function of the acoustic intensity. The main works on the development of an acoustic diffusion model have highlighted the major role of a coefficient of the model, the so-called diffusion coefficient. Indeed, the main phenomena influencing the reverberant sound field can be modeled by proposing an appropriate expression of this diffusion coefficient. The work presented here deals with the modeling of inhomogeneous reverberant sound fields induced by geometric disproportions, and investigates, in particular, the case of long rooms. Previously, the ability of the acoustic diffusion to model adequately the spatial variations of the sound field along the room has been demonstrated by considering a diffusion coefficient that is spatially dependent. We propose here to extend this work by determining an empirical law of the diffusion coefficient, depending on both the scattering and absorption coefficients of the walls of the room. The approach proposed here is statistical and is based on the least squares method. Several linear models are proposed, for which a rigorous statistical analysis makes it possible to assess their relevance.

The modal analysis of wave problems of unbounded type involves a continuous sum of radiation modes. This continuum is difficult to handle mathematically and physically. It can be approximated by a discrete set of leaky modes, corresponding to improper modes growing to infinity. Perfectly matched layers (PMLs) have been widely applied in numerical methods to efficiently simulate infinite media, most often without considering a modal approach. This letter aims to bring insight into the modal basis computed with PMLs. PMLs actually enable to reveal of the contribution of leaky modes by redefining the continua (two for elastodynamics), discretized after PML truncation.

When investigating the association between brain tumors and use of mobile telephones, accurate data on tumor position are essential, due to the highly localized absorption of energy in the human brain from the radio-frequency fields emitted. We used a point process model to investigate this association using information that included tumor localization data from the INTERPHONE Study (Australia, Canada, Denmark, Finland, France, Germany, Israel, Italy, Japan, New Zealand, Norway, Sweden, and the United Kingdom). Our main analysis included 792 regular mobile phone users diagnosed with a glioma between 2000 and 2004. Similar to earlier results, we found a statistically significant association between the intracranial distribution of gliomas and the self-reported location of the phone. When we accounted for the preferred side of the head not being exclusively used for all mobile phone calls, the results were similar. The association was independent of the cumulative call time and cumulative number of calls. However, our model used reported side of mobile phone use, which is potentially inuenced by recall bias. The point process method provides an alternative to previously used epidemiologic research designs when one is including localization in the investigation of brain tumors and mobile phone use.; Il s'agit d'explorer la relation entre dose de radiofréquences reçue ds le cerveau lors de l'utilisation de téléphone mobile et la survenue de tumeurs du cerveau.

This paper evaluates several techniques capable of mitigating the impact of low-power radio frequency jammers that interfere with ground-to-train communications. These radio communications are used for railway signaling, and interfering with these signals can have a negative impact on the train operation. Although the commercialization, detention, and use of radiofrequency jammers is strictly forbidden in most countries, they can be easily found on the internet at low cost and unexpectedly switched on by a passenger in a moving train. In this paper, we evaluate and compare the ground-to-train radio communication and intentional electromagnetic interference (IEMI) received signal powers delivered by roof train antennas to the train control command receiver. This comparison is used to deduce the potential zones of interference along the train trajectory and its consequences. Operating at the physical layer, we then propose and evaluate three mitigations techniques that can be used separately or combined to reduce the impact of this type of interference. We show that they can significantly reduce the jamming capability and help us in maintaining railway full operation.; Cet article évalue plusieurs techniques capables d'atténuer l'impact des brouilleurs de fréquence radio de faible puissance qui interfèrent avec les communications sol-train. Ces communications radio sont utilisées pour la signalisation ferroviaire, et l'interférence avec ces signaux peut avoir un impact négatif sur le fonctionnement du train. Bien que la commercialisation, la détention et l'utilisation de brouilleurs radiofréquences soient strictement interdites dans la plupart des pays, elles peuvent facilement être trouvées sur Internet à faible coût et allumées de manière inattendue par un passager dans un train en mouvement. Dans cet article, nous évaluons et comparons les puissances des signaux de communication radio sol-train et interférence électromagnétique intentionnelle (IEMI) fournies par les antennes des trains de toit au récepteur de commande de contrôle des trains. Cette comparaison permet de déduire les zones d'interférence potentielles le long de la trajectoire du train et ses conséquences. Opérant au niveau de la couche physique, nous proposons et évaluons trois techniques d'atténuation qui peuvent être utilisées séparément ou combinées pour réduire l'impact de ce type de brouillage. Nous montrons qu'ils peuvent réduire considérablement la capacité de brouillage et nous aider à maintenir le plein fonctionnement du chemin de fer.

Elastic guided waves are of interest for the non-destructive evaluation of cables. Such structures are usually helical, multiwired and highly prestressed, which greatly complicates the understanding of wave propagation from a theoretical point of view. A remarkable feature is the occurrence of a missing frequency band in experimental time–frequency diagrams, sometimes referred to as notch frequency in the literature. The central frequency of this band increases under tensile loads. Recently, a numerical model has been proposed to compute the dispersion curves of prestressed helical seven-wire waveguides. Results have shown that the notch frequency indeed corresponds to a curve veering phenomenon between two longitudinal-like modes and that the increase of the notch under tensile loads is mainly due to interwire contact mechanisms. The main goal of this paper is to highlight the origin of this curve veering phenomenon, which is still unexplained up to the author׳s knowledge. This paper also provides further results which allow us to clarify the accuracy of numerical solutions as well as the influence of contact assumptions. First, the static part of the model, necessary to compute the prestress state including contact effects, is checked from reference analytical solutions. Owing to the importance of contact, the accuracy of results is discussed both in statics and in dynamics. The influence of slip contact conditions is outlined. Then, some numerical tests are conducted by varying the Poisson coefficient and the helix lay angle. These tests allows us to find out that the radial displacement constraint imposed on peripheral wires by the central one in the contact regions constitutes the main source of curve veering. More precisely, it is shown that a similar curve veering does occur for an uncoupled single peripheral wire when constrained by a radially blocked motion localized in its contact zone. Indeed, such a localized boundary condition completely breaks the circular symmetry of the wire cross-section, yielding coupling between longitudinal, flexural and torsional motion together with curve veering phenomena.

Elastic guided waves are of interest for the non-destructive evaluation of cables. Cables are most often multi-wire structures, and understanding wave propagation requires numerical models accounting for the helical geometry of individual wires, the interwire contact mechanisms and the effects of prestress. In this paper, a modal approach based on a so-called semi-analytical finite element method and taking advantage of a biorthogonality relation is proposed in order to calculate the forced response under excitation of a cable, multi-wired, twisted, and prestressed. The main goal of this paper is to investigate how the energy transfers from a given wire, directly excited, to the other wires in order to identify some localization of energy inside the active wire as the waves propagate along the waveguide. The power flow of the excited field is theoretically derived and an energy transfer parameter is proposed to evaluate the level of energy localization inside a given wire. Numerical results obtained for different polarizations of excitation, central and peripheral, highlight how the energy may localize, spread, or strongly change in the cross-section as waves travel along the axis. In particular, a compressional mode localized inside the central wire is found, with little dispersion and significant excitability.

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.

hal-01150611; International audience; Wind waves are responsible for some of the spatio-temporal gradients observed in the biotic and abiotic variables in large shallow lakes. However, their effects on the phytoplankton community composition are still largely unexplored especially in freshwater systems such as lakes. In this paper, using field observations and mesocosm bioassay experiments, we investigated the impact of turbulence generated by wind waves on the phytoplankton community composition (especially on harmful cyanobacteria) in Lake Taihu, a large, shallow eutrophic lake in China. The composition of the phytoplankton community varied with the intensity of wind waves in the different areas of the lake. During summer, when wind waves were strong in the central lake, diatoms and green algae seemed to dominate while harmful cyanobacteria dominated in the weakly influenced Meiliang Bay. Turbulence bioassays also showed that diatoms and green algae were favoured by turbulent mixing. The critical time for the shift of the phytoplankton community composition was approximately 10 days under turbulent conditions. However, short-term (6 days) turbulence is rather beneficial for the dominance of cyanobacteria. This study suggests that the duration of wind events and their associated hydrodynamics are key factors to understanding the temporal and spatial changes of phytoplankton communities.

The chapter 3 is organized in three main sections. The first section is devoted to wireless communications for public transport applications. We first recall some challenges for sustainable mobility and the difficulties encountered to implement on the shelf wireless systems for public transport. Then, we will give a brief overview and some examples of the wireless technologies deployed today: beacons, bifilar communications, radio systems, etc. After this, we present the future trends in the domain of wireless systems for public transport applications and the ongoing research in the railway domain as well as the metro and tramway domains. Particularly, we emphasis the railway applications of Internet of Things. The second section of the chapter is focused on the localization function for public transport applications. The position is the core of every intelligent transportation system, for non-safe as well as safe systems. After a brief description of the principles and the advantages and drawbacks of the systems, we describe the main existing applications and the one foreseen in the future. We then extend to the case where satellites are not available, particularly in the case of tunnels. We describe the more solutions deployed or planned for the future. In the last section, we highlight the problems set up by the specific context of electromagnetic and propagation environments for railways. We show the necessity to develop electromagnetic modeling of some environments, to set up ad'hoc channel models as well as noise distribution. It is also important to cope with non-metallic material of the trains and to find solution for the implementation of multiple antennas at various locations and at very different frequencies (from several kHz to several GHz). Finally we conclude this chapter.

Among the numerous techniques of non-destructive evaluation, elastic guided waves are of particular interest to evaluate defects inside industrial and civil elongated structures owing to their ability to propagate over long distances. However for guiding structures buried in large solid media, waves can be strongly attenuated along the guide axis due to the energy radiation into the surrounding medium, usually considered as unbounded. Hence, searching the less attenuated modes becomes necessary in order to maximize the inspection distance. In the numerical modeling of embedded waveguides, the main difficulty is to account for the unbounded section. This paper presents a numerical approach combining a semi-analytical finite element method and a perfectly matched layer (PML) technique to compute the so-called trapped and leaky modes in three-dimensional embedded elastic waveguides of arbitrary cross-section. Two kinds of PML, namely the Cartesian PML and the radial PML, are considered. In order to understand the various spectral objects obtained by the method, the PML parameters effects upon the eigenvalue spectrum are highlighted through analytical studies and numerical experiments. Then, dispersion curves are computed for test cases taken from the literature in order to validate the approach.

12th International conference on mathematical and numerical aspects of wave propagation (WAVES 2015), KARLSRUHE, ALLEMAGNE, 20-/07/2015 - 24/07/2015; Helical multi-wire cables are widely used in bridge construction and can be degraded due to corrosion and fatigue. To reveal defects inside cable structures, elastic guided waves are of interest owing to their ability to propagate over long distances. In practice, cables are often buried into a solid matrix and can be considered as open waveguides. Waves can be leaky and strongly attenuate along the guide axis, which reduces the propagating distance. Maximizing this distance is necessary for non-destructive testing. The goal of this work is to propose a numerical method for computing modes in embedded helical structures, combining the so-called semi-analytical finite element (SAFE) method and a radial perfectly matched layer (PML) technique.

Costas codes are a variant of pulse compression waveforms, largely studied for their attractive time-frequency properties. Their 'thumbtack-like' ambiguity function (AF) makes them highly suitable for delay and Doppler estimation, in radar and sonar applications. However, this behaviour depends heavily on the length of the code: the improvement in delay-Doppler resolutions and AF sidelobes level needs an increase in the size of the code. In this study, designs that allow good performance without increasing the size of the code are proposed. They are based on a modification of Costas codes by widening frequency separation between hops and replacing rectangular pulses by other waveforms. This will lead to a removal of autocorrelation function grating lobes that normally appear when frequency separation is increased. The originality of the work lies in the proposal of diversified pulse waveforms, such as phase codes, Slepian sequences, and other Costas codes, to encode main Costas pulses. A performance comparison of the proposed approaches is supplied. Such waveforms could also be of interest for applications where waveform diversity is desired.

International audience; The Cramer-Rao bound (CRB) gives a lower variance bound that an estimator can achieve. Presented is a mathematical approach to estimate it for specific radar signals, namely Costas signals and their modified versions. The modified versions design consists in widening Costas frequency hops and replacing rectangular pulses with other waveforms (namely linear frequency modulated pulses, phase codes and other Costas codes). The calculation is based on approximations of the ambiguity function (AF) around the mainlobe. The CRBs are then derived based on relationships between the AF and these bounds.

2014 International Symposium on signal, Image, Video and Communications - ISIVC 2014, Marrakech, Maroc, 19-/11/2014 - 22/11/2014; Radar waveforms design is an important step to design a hole radar system. In this paper, several waveforms based on modified Costas codes are used. The properties and performances are tested and compared. We propose a detection based on cross-ambiguity calculation for these waveforms. Indeed, such a processing is interesting when delay and Doppler should be estimated. The performances are evaluated in several scenarios in presence of noise and multiple targets. The waveforms are also tested on real experimentation hardware.

RADAR 2014, International Radar Conference, Lille, France, 13-/10/2014 - 17/10/2014; International audience; Costas codes are a variant of frequency hopping codes that achieve the «thumbtack» auto-ambiguity function needed in radar applications. However, they may show poor cross- ambiguity properties when selected and assigned randomly which makes them poorly adapted to multiuser radar applications. In this paper, we propose a multiuser adaptation of phase coded Costas signals. In fact, this modified version of Costas signals consists in replacing Costas constant frequency sub-pulses with phase codes. This modification allows to suppress autocorrelation function grating lobes that appears when orthogonality condition of Costas codes is not satisfied. Furthermore, the later design adds a degree of freedom for a possible adaptation of these waveforms to a multiuser context. Indeed, in the current work, the sub- pulse phase codes are used to generate a set of waveforms with good cross-correlation properties. Specific conditions on these codes are stated in order to achieve the needed cross-correlation properties, using a same Costas code. The auto-ambiguity and cross-ambiguity properties are also remarkable but within a bounded Doppler region. Furthermore, the families are expanded using different Costas codes with particular properties. Hence, since the phase codes and Costas codes diversity are used, the number of synthesized waveforms is improved.

Dottorato di Ricerca in Scienze e Tecnologie delle Mesofasi e Materiali Molecolari,XXIII Ciclo,a.a. 2010 Università della Calabria

International audience; Elastic guided waves are of interest for inspecting structures due to their ability to propagate over long distances. In numerous applications, the guiding structure is surrounded by a solid matrix that can be considered as unbounded in the transverse directions. The physics of waves in such an open waveguide significantly differs from a closed waveguide, i.e. for a bounded cross-section. Except for trapped modes, part of the energy is radiated in the surrounding medium, yielding attenuated modes along the axis called leaky modes. These leaky modes have often been considered in non destructive testing applications, which require waves of low attenuation in order to maximize the inspection distance. The main difficulty with numerical modeling of open waveguides lies in the unbounded nature of the geometry in the transverse direction. This difficulty is particularly severe due to the unusual behavior of leaky modes: while attenuating along the axis, such modes exponentially grow along the transverse direction. A simple numerical procedure consists in using absorbing layers of artificially growing viscoelasticity, but large layers may be required. The goal of this paper is to explore another approach for the computation of trapped and leaky modes in open waveguides. The approach combines the so-called semi-analytical finite element method and a perfectly matched layer technique. Such an approach has already been successfully applied in scalar acoustics and electromagnetism. It is extended here to open elastic waveguides, which raises specific difficulties. In this paper, two-dimensional stratified waveguides are considered. As it reveals a rich structure, the numerical eigenvalue spectrum is analyzed in a first step. This allows to clarify the spectral objects calculated with the method, including radiation modes, and their dependency on the perfectly matched layer parameters. In a second step, numerical dispersion curves of trapped and leaky modes are compared to analytical results.

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.

A correct understanding of the interactions between the edge plasma and the ion cyclotron (IC) waves (40-80MHz) is needed to inject reliably large amount of power required for self-sustainable fusion plasmas. These thesis objectives were to model separately, with Comsol Multiphysics, but in compatible approaches the wave coupling and the radio-frequency (RF) sheath formation to anticipate development of a single code combining both. Modelling of fast wave coupling requires a detailed description of the antenna (2D or 3D) and of the plasma environment by a full wave approach for a cold plasma. Absorption of outgoing waves is emulated by perfectly matched layers, rendered compatible with a plasma dielectric tensor. Experimental trends for the coupling resistance of the antennas of Tore Supra are qualitatively reproduced but the coupling efficiency is overestimated. In parallel a novel self-consistent description, including RF sheaths, of the interplay between the cold wave propagation and DC biasing of the magnetized edge plasma of a tokamak was developed with the minimum set of physics ingredients. For Tore Supra antenna cases, the code coupled with TOPICA allowed to unveil qualitatively some unexpected observations on the latest design of Tore Supra Faraday screens whose electrical design was supposed to minimize RF sheaths. From simulations, a DC (Direct Current) current transport appears necessary to explain the radial structures of measurements. Cantilevered bars have been identified as the design element in the antenna structure enhancing the plasma potential; Une bonne compréhension des interactions entre les ondes à la fréquence cyclotronique ionique (FCI) (40-80MHz) et le plasma de bord est nécessaire pour injecter de fortes puissances dans un plasma de fusion en continu. Les objectifs de cette thèse étaient de modéliser séparément, avec Comsol Multiphysics, mais de façon compatible le couplage d'ondes et la formation de gaines radiofréquences (RF), qui rétroagissent sur le couplage, pour aboutir à terme à une modélisation auto-cohérente. Modéliser le couplage de l'onde rapide nécessite une description détaillée de l'antenne émettrice (2D ou 3D) et du plasma environnant par une approche pleine onde en plasma froid. L'absorption des ondes sortant du domaine de simulation est émulée par des couches parfaitement adaptées, rendues compatibles avec un tenseur diélectrique plasma. Les tendances expérimentales des résistances de couplage des antennes de Tore Supra sont qualitativement reproduites mais l'efficacité de couplage est surestimée. Parallèlement une description novatrice auto-cohérente, incluant les effets des gaines RF, de la propagation de l'onde lente et de la polarisation DC (Direct Current) du bord d'un plasma magnétisé a été développée avec le minimum d'ingrédients physiques. Dans le cas des antennes Tore Supra, le couplage du code avec TOPICA a permis d'expliciter qualitativement certaines observations inattendues sur un écran de Faraday dont le schéma électrique visait à minimiser les gaines RF. Un transport de courants DC dans la SOL est apparu nécessaire pour expliquer les structures radiales des mesures. Les barreaux coupés sont les éléments de l'antenne responsable de l'augmentation du potentiel plasma

A correct understanding of the interactions between the edge plasma and the ion cyclotron (IC) waves (40-80MHz) is needed to inject reliably large amount of power required for self-sustainable fusion plasmas. These thesis objectives were to model separately, with Comsol Multiphysics, but in compatible approaches the wave coupling and the radio-frequency (RF) sheath formation to anticipate development of a single code combining both. Modelling of fast wave coupling requires a detailed description of the antenna (2D or 3D) and of the plasma environment by a full wave approach for a cold plasma. Absorption of outgoing waves is emulated by perfectly matched layers, rendered compatible with a plasma dielectric tensor. Experimental trends for the coupling resistance of the antennas of Tore Supra are qualitatively reproduced but the coupling efficiency is overestimated. In parallel a novel self-consistent description, including RF sheaths, of the interplay between the cold wave propagation and DC biasing of the magnetized edge plasma of a tokamak was developed with the minimum set of physics ingredients. For Tore Supra antenna cases, the code coupled with TOPICA allowed to unveil qualitatively some unexpected observations on the latest design of Tore Supra Faraday screens whose electrical design was supposed to minimize RF sheaths. From simulations, a DC (Direct Current) current transport appears necessary to explain the radial structures of measurements. Cantilevered bars have been identified as the design element in the antenna structure enhancing the plasma potential, Une bonne compréhension des interactions entre les ondes à la fréquence cyclotronique ionique (FCI) (40-80MHz) et le plasma de bord est nécessaire pour injecter de fortes puissances dans un plasma de fusion en continu. Les objectifs de cette thèse étaient de modéliser séparément, avec Comsol Multiphysics, mais de façon compatible le couplage d'ondes et la formation de gaines radiofréquences (RF), qui rétroagissent sur le couplage, pour aboutir à terme à une modélisation auto-cohérente. Modéliser le couplage de l'onde rapide nécessite une description détaillée de l'antenne émettrice (2D ou 3D) et du plasma environnant par une approche pleine onde en plasma froid. L'absorption des ondes sortant du domaine de simulation est émulée par des couches parfaitement adaptées, rendues compatibles avec un tenseur diélectrique plasma. Les tendances expérimentales des résistances de couplage des antennes de Tore Supra sont qualitativement reproduites mais l'efficacité de couplage est surestimée. Parallèlement une description novatrice auto-cohérente, incluant les effets des gaines RF, de la propagation de l'onde lente et de la polarisation DC (Direct Current) du bord d'un plasma magnétisé a été développée avec le minimum d'ingrédients physiques. Dans le cas des antennes Tore Supra, le couplage du code avec TOPICA a permis d'expliciter qualitativement certaines observations inattendues sur un écran de Faraday dont le schéma électrique visait à minimiser les gaines RF. Un transport de courants DC dans la SOL est apparu nécessaire pour expliquer les structures radiales des mesures. Les barreaux coupés sont les éléments de l'antenne responsable de l'augmentation du potentiel plasma

A methodology is proposed to investigate guided waves in curved structures. In a general framework, the existence of guided modes is discussed in curved waveguides. Translational invariance, implicitly used for the analysis of straight waveguides, is redefined for curvilinear coordinate systems. We show that a helical coordinate system fulfills the invariance property for any physics. Then our study focuses on elastic waves. Owing to the difficulty in achieving analytical solutions, a numerical approach based on the so-called semi-analytical finite element is adopted. Civil engineering cables constitute the main application of this work. The basic component of cables is usually a helical structure composed of several wires. This multi-wire characteristics further complicates the analysis of guided waves. We show that a twisting coordinate system allows to satisfy translational invariance in seven-wire strands. A model is also proposed in order to account for prestressing effects. Finally, other complicating effects in cables are briefly discussed (presence of embedment, wave scattering by defects).

We study, both experimentally and numerically, the Anderson localization phenomenon in torsional waves of a disordered elastic rod, which consists of a cylinder with randomly spaced notches. We find that the normal-mode wave amplitudes are exponentially localized as occurs in disordered solids. The localization length, measured using these wave amplitudes, decreases as a function of frequency. The normal-mode spectrum is also measured as well as computed, so its level statistics can be analyzed. From the spectrum, the nearest-neighbor spacing distribution can be obtained. This distribution can be described by a phenomenological expression that depends on a parameter α, related to the level repulsion, which is also a function of the frequency. Therefore, the localization length can be expressed in terms of the parameter α. There exists a range in which the localization length grows linearly with α. However, at low values of this parameter the linear dependence does not hold.

Standard seismic methods are generally not well adapted to provide sharp quantitative images of the first few metres of underground. A two-dimensional full-waveform inversion of land seismic data, based on frequency-domain viscoelastic modelling, offers a promising approach to take advantage of the full complexity of seismograms and to simultaneously build 2D images of P and VS parameters. In order to understand the behaviour of this method in a near-surface context and anticipate the corresponding field applications, we perform this investigation by applying waveform inversion on a simple layered medium. We first use synthetic data obtained from numerical modelling and then we employ laboratory data obtained by small-scale physical modelling. We demonstrate that such a near-surface 2D model can be quantitatively determined even in a realistic situation where the data are dominated by high-amplitude surface waves. A comparison of results derived for the same medium from ideal synthetic data and noisy experimental data allows detecting anomalies in the reconstruction of velocity models due to the experimental nature of the data used.

Infrastructure is subject to continuous ageing. This has given life cycle management of infrastructure an increasingly important role. Reliable inspection and monitoring tools are therefore in demand. A reliable prognosis of the condition and behaviour of a structure is an important basis for an effective service life management. Furthermore, traffic loads and loads due to changing environmental conditions increased during the last years and will increase in the future. Repair and maintenance have to be performed, which requires reliable concepts and measurement of data, which is preferably gained through non-destructive methods. Furthermore, infrastructural constructions often have to be reconditioned when they are in use i. e. they cannot be torn down and rebuilt. Therefore, reliable diagnosis of the state of ‘hot spots’ is required. Within the frame of the Franco-German project FilameNDT steel wires of external tendon ducts and prestressing strands, prestressing rods, and stay cables are investigated. With regards to this field of application, practical relevance can only be gained when easily applicable and long ranging methods are used. The evaluation of extended structural elements using non-contact movable systems {bulk wave and guided wave application [Piezo, electromagnetic acoustic transducers (EMAT)], magnetic flux leakage (MFL), Micromagnetic methods} and those of localized elements based on elastic guided wave propagation—are complementary since they can be applied according to the various accessibility conditions of the tested objects. Inspection and monitoring scenarios were developed, hot spots were identified, and lab tests as well as field tests were carried out. A real cable stayed bridge in the Saarland region is available for monitoring within the frame of the project. Results from local investigations using guided waves and from monitoring field tests with micromagnetic sensors are presented and discussed. The results show the scenarios where the non-destructive methods are applicable and how the results can be used for structural health monitoring and maintenance concepts.