Université Gustave Eiffel
  • Champs-sur-Marne, France
Recent publications
This paper presents an inverse Algebraic Wavenumber Identification (AWI) technique for multi-modal 1D-periodic structures, which can extract complex wavenumbers from steady-state vibration measurements under stochastic conditions. These wave dispersion characteristics provide valuable vibroacoustic indicators for model updating, damage monitoring in operational conditions, or metamaterial design. Wavenumber extraction techniques are highly sensitive to noisy measurements, nonuniform sampling points, or geometrical uncertainties. The proposed formulation relies on algebraic parameters identification to enable the extraction of complex wavenumbers in four scenarios: (a) low Signal Noise Ratio; (b) small perturbation caused by uncertainties on sampling points’ coordinates; (c) unknown structural periodicity; (d) nonuniform sampling. This AWI is compared with Inhomogeneous Wave Correlation (IWC) method and INverse COnvolution MEthod (INCOME) to assess the robustness and accuracy of the method.
We study the ground state of the Gross–Pitaevskii energy in a strip, with a phase imprinting condition, motivated by recent experiments on matter waves solitons. We prove that when the width of the strip is small, the ground state is a one dimensional soliton. On the other hand, when the width is large, the ground state is a solitonic vortex. We provide an explicit expression for the limiting phase of the solitonic vortex as the size of the strip is large: it has the same behavior as the soliton in the infinite direction and decays exponentially due to the geometry of the strip, instead of algebraically as vortices in the whole space.
Urban functional zone mapping is essential for providing deeper insights into urban morphology and improving urban planning. The emergence of Volunteered Geographic Information (VGI), which provides abundant semantic data, offers a great opportunity to enrich land use information extracted from remote sensing (RS) images. Taking advantage of very-high-resolution (VHR) images and VGI data, this work proposed a SATL multifeature ensemble learning framework for mapping urban functional zones that integrated 65 features from the shapes of building objects, attributes of points of interest (POIs) tags, locations of cellphone users and textures of VHR images. The dimensionality of SALT features was reduced by the autoencoder, and the compressed features were applied to train the ensemble learning model composed of multiple classifiers for optimizing the urban functional zone classification. The effectiveness of the proposed framework was tested in an urbanized region of Nanchang City. The results indicated that the SALT features considering population dynamics and building shapes are comprehensive and feasible for urban functional zone mapping. The autoencoder has been proven efficient for dimension reduction of the original SALT features as it significantly improves the classification of urban functional zones. Moreover, the ensemble learning outperforms other machine learning models in terms of the accuracy and robustness when dealing with multi-classification tasks.
In order to explore the role of bacteria in the alteration of stained glass windows, and especially on the browning phenomenon, it is necessary to have an overview of the microbial inhabitants likely to be found on this kind of material. In this study, biological samples were collected on stained glass of different colours, both on site and stored in a conservation workshop. Cultivable bacterial communities were identified by 16S rDNA sequencing. Similarity values ranged from 99 to 100% to known bacteria. Sequence analysis showed different bacterial communities depending on the sampling site. The more represented genera were Arthrobacter, Micrococcus, Paenibacillus and Bacillus. Some of the identified bacteria are known for their weathering potential.
In this paper, stochastic planar stick–slip motions are investigated using a slider-on-belt model where the coefficient of friction (COF) of the contact interface is modelled as a random field. New three-variable stick–slip transition criteria are proposed to improve the accuracy and robustness of the algorithm. Stochastic analyses are performed concerning the Peak-to-Valley value of the displacement and friction forces and the time duration of the stick state. It is found that the correlation length of the COF random field is dominantly responsible for the stochastic behaviours of the system. In contrast, the belt velocity and the mean value of the COF have a significant influence on the time duration of the stick state compared with the corresponding deterministic slider-on-belt model.
Friction dampers are classically used in turbomachinery for bladed discs to control the levels of vibrations at resonance and limit the risk of fatigue failure. It consists of small metal components located under the platforms of the blades, which dissipate the vibratory energy through friction when a relative displacement between the blades and the damper appears. It is well known that the shape of such component has a strong influence on the damping properties and should be designed with a particular attention. With the arrival of additive manufacturing, new dedicated shapes for these dampers can be considered, determined with specific numerical methods as topological optimisation (TO). However, the presence of the contact nonlinearity challenges the use of traditional TO methods to minimise the vibration levels at resonance. In this work, the topology of the damper is parametrised with the moving morphable components (MMC) framework and optimised based on meta-modelling techniques: here kriging coupled with the efficient global optimisation (EGO) algorithm. The level of vibration at resonance is computed based on the harmonic balance method augmented with a constraint to aim directly for the resonant solution. It corresponds to the objective function to be minimised. Additionally, a mechanical constraint based on static stress analysis is also considered to propose reliable damper designs. Results demonstrate the efficiency of the method and show that damper geometries that meet the engineers’ requirements can be identified.
The removal of the non-steroidal anti-inflammatory drug (NSAID) Naproxen (NAX) in water by hydroxyl radicals (•OH) was performed by electrochemical advanced oxidation processes either with Pt or BDD anodes and a 3D carbon felt cathode. The degradation of NAX by (•OH vs. electrolysis time) was well fitted to a pseudo-first-order reaction rate kinetic. The detected reaction intermediates (aromatic compounds and carboxylic acids) were experimentally monitored during the process via LC, while density functional theory (DFT) was applied to uncover undetected intermediates, some for the first time in literature. The formation of toxic intermediates with higher toxicity than NAX were identified, such as IMS4b (6-Methoxy-1-[1-(6-methoxynaphthalen-2-yl) ethyl] naphthalen-2-ol), catechol, and glycolic acid. Based on these data, a detailed oxidation pathway of NAX by •OH was proposed. The evolution of solution toxicity indicated that formed toxic intermediates were subsequently removed during the TOC removal process. Finally, almost complete mineralization of NAX was achieved in simulated urine or wastewater, by the electro-Fenton treatment with an optimized dose of iron as catalyst, showing the EAOPs’ potential to efficiently remove NAX even from challenging matrices. In extension, the strategies developed can be applied to the treatment of other NSAIDs.
The conservation of textile objects has always been a difficult area to asses due to the heterogeneity of the materials used and their fragility. The experimentation and diagnosis of these historical objects remain impossible because of the destructive nature of the existing tools. Numerical modeling offers an excellent alternative for evaluating these materials and predicting their mechanical degradation. For this purpose, a mechanical model is developed based on continuum mechanics together with finite element computations. The macroscopic description of the material requires the use of the shell theory for an orthotropic material together with Hill’s plastic criterion. This modelling should consider simultaneous mechanical phenomena that historical textiles undergo, namely: the mechanical stresses generated by the self-weight; viscosity which causes delayed responses of the material; and plasticity which is the cause of irreversible deformations. This was achieved by using the rheological model implemented in Abaqus; the 2-layers viscoelastic-plasticity consisting of an elasto-plastic network in parallel with a Maxwell-type visco-elastic branch. Then the simulations of different configurations were made, in the objective of optimizing the choices of conservation and exhibition of these rare heritage objects.
A novel theoretical model is developed to describe the whole response of Saccharomyces cerevisiae yeasts. In this contribution, a yeast is represented as a thin-walled, liquid-filled, impermeable, spherical shell structure. Herein, we adopt the quasi-Kirchhoff shell theory that we extend to the range of finite viscoelasticity. The used kinematics is the multiplicative decomposition of the deformation gradient into an elastically relaxing part and a viscous part. Motivated by a generalized Maxwell model, we assume an incompressible hyper-viscoelastic model of N = 1-Ogden-Ogden type. In addition, the cell-wall is regarded as homogeneous and isotropic in a first approach. On another hand, the internal cell-liquid resists to external loads by a normal pressure on the cell-wall. This pressure is represented by using follower loads, the magnitude of which is accounted for via an updated procedure of the Uzawa-type to insure the incompressibility of this inner fluid. Furthermore, adopting a frictionless contact, on one hand, and using intrinsic parameters from the literature, on the other hand, we predict within the finite element method the responses of various compressed cells between flat parallel surfaces and probes of different geometries.
We propose an algebraic approach to investigate K-diagnosability of partially observed labeled Petri nets which can be either bounded or unbounded. Namely, a necessary and sufficient condition for K-diagnosability is established based on the resolution of an Integer Linear Programming (ILP) problem. When the system is K-diagnosable, our approach also yields the minimal value Kmin≤K that ensures Kmin-diagnosability. The value of Kmin is calculated directly, using the same ILP formulation, i.e, without testing 1,…,(Kmin−1)-diagnosability. A second K-diagnosability approach, which is derived from the first one, is also developed on a compacted horizon providing a sufficient condition for K-diagnosability. This second technique allows for reducing the system dimensionality yielding a higher computational efficiency and allowing the characterization of the length of the sequences that lead to the fault occurrence, which is necessary to perform the K-diagnosability test of the first approach.
This study focused on the influence of high H2O/Na2O ratios (higher than 20) on the properties of metakaolin-based geopolymers in fresh and hardened states while keeping constant Si/Al and Na/Al atomic ratios. The increase in H2O/Na2O ratio from 21 to 34 resulted in a decrease of 7-day compressive strength from 10 to 0.025 MPa. This can be attributed to the influence of water on the reactivity of the precursor, which was demonstrated by nuclear magnetic resonance (NMR) spectroscopy, and porosity evolution as the water is not chemically bound. Increasing H2O/Na2O ratio did not change the geopolymer structure of reaction products. A correlation was observed between the reaction degree deduced from NMR spectral decomposition and the cumulated released heat obtained using isothermal calorimetry. The maximum loss tangent, obtained using dynamic rheology, was linearly related to strength development.
The prevention of crowding inside buses, trams and trains is an important component of on-board passenger comfort and is central to the provision of good public transport services. In light of the COVID-19 pandemic and the associated significant reduction in public transport patronage and, more importantly, in passenger confidence, the avoidance of crowds by passengers and operators alike becomes even more critical. This is where the provision of information on on-board comfort becomes a necessity. The present study, therefore, proposes a new Kalman filter based estimation scheme for on-board comfort levels, employing historical and current (same-day) non-exhaustive Automatic Passenger Counting data, as well as Automatic Vehicle Locating measurements. The accuracy and reliability of the estimation is, then, evaluated through application to the tramway network of the French city of Nantes. The results suggest that the proposed method is able to deliver good estimation accuracy, both in terms of absolute passenger numbers, but also, more crucially, in terms of on-board comfort Levels of Service.
Even if there is an increasing public awareness of biodiversity loss, there still is the need to improve individuals’ behaviours in favour of biodiversity conservation, such as composting or buying pollinator-friendly plants. Why do individuals who know about the risks of biodiversity loss, not change their lifestyles to promote biodiversity? The main aim of this paper is to empirically identify the psychological barriers to biodiversity conservation behaviours, with a specific attention to individuals’ perception of the psychological distance of biodiversity loss. To this purpose, 270 individuals were asked to complete a questionnaire. Data demonstrated that six main psychological barriers prevent behavioural change, depending on individuals’ perceived psychological distance as well as on the specific features of the behaviour considered. Our findings constitute a significant theoretical complement to previous research on behavioural change to respond to environmental threats, as it specifically investigates the psychological barriers resulting in citizens’ inaction with regard to biodiversity loss. Furthermore, our paper offers advice for policy-makers, deciding bodies, and associations involved in biodiversity conservation on the cognitive barriers that they might be confronted to when addressing citizens and promoting their engagement in individual and collective actions in favour of the environment.
Dispersing solid hard particles in an elasto-plastic material leads to important shear-history dependence of the behavior, namely strain hardening and Bauschinger effect. Strain hardening is observed as the progressive strengthening of a material during its plastic deformation and is usually associated with ductility, a property often sought after in composite materials to postpone fractures and failure. In addition, anisotropic mechanical properties are developed, the material resistance being larger in the direction of the imposed flow, which is referred to as the Bauschinger effect. We show that this is related here to shear-history-dependent particle-pair distribution functions. Roughness and interparticle contacts likely play a major role, as replacing hard particles by non-deformable bubbles modifies the suspension microstructure and suppresses strain hardening. Beyond suspensions, our study provides new insight in the understanding and control of strain hardening and Bauschinger effect in composite materials.
Furniture failure generally appears at junctions between wooden parts. Failure prediction is a challenging problem considering the various technologies used for the assembly, the geometric dimensions of the wooden assembled parts and of the assembly components as well as the material properties of the wooden parts. Being able to provide a procedure for failure analysis is of great interest to the furniture industry. This paper proposes a multi-model approach in 3 steps: (i) a simplified global modeling of the whole structure (high loft bed) taking into account the specific geometry of each wooden part (beams or plates), (ii) a three-dimensional local numerical analysis of a through-bolt junction subjected to the mean critical load identified during a series of experimental compression tests to determine the local stresses in such a corner-type junction, and (iii) the application of an ad hoc failure criterion adapted to the anisotropic behavior of wood for failure prediction in through-bolt junctions.
The weathering of rocks, especially the clay-rich rocks submitted to chemical attack or wet/dry cycles, may impact negatively the slopes stability. This study aims to characterize the alteration of a carbonated clay-rich material assimilated to a marl after the infiltration of polluted water as observed on Azazga site (Algeria) identified as a landslide area. The marl alteration was simulated in laboratory by wet/dry cycles and the level of material degradation was estimated using geotechnical tests (direct shear tests and fragmentation test) as well as physico-chemical measurements and microstructural observations by X-ray diffraction, mercury intrusion porosimetry, chemical analysis and scanning electron microscopy. The effect of wet/dry cycles with artificially polluted water was compared to cycles without pollutants. The tested carbonated clay-rich material composed by around 30.6% of quartz, 12.5% of carbonates and 45.1% of clays showed a higher degradation in contact with polluted water considered as an activator of the degradation. The soil porosity was evaluated with wet /dry cycles and it was estimated from 19.2 to 25% after the cycles. The degradability test (fragmentation test) agreed with the shear test results with a decrease of the cohesion c’ from 49.9 to 31.5 kPa (while the friction angle remained close to 20°). Results were confirmed at micro scale with few mineralogical changes and with a higher particle aggregation in presence of pollutants resulting in rough surface while a microporosity around 30 μm appeared after cycles with or without pollutants, probably between disaggregated elongated grains or staked plans observed by SEM. In conclusions, wet/dry cycles with water (without pollutant) were mainly responsible to the disaggregation of carbonated clay-rich soil and pollutants reinforced such effect.
The objective of this paper is to present a MATLAB-based toolbox called CSA-T-TDS (acronym for Complete Stability Analysis Toolbox for Time-Delay Systems). By using this toolbox, one can easily find the whole stability delay-set for a linear system with commensurate delays. For a better understanding of the methodology at the origin of the software, the theoretical core of CSA-T-TDS (the frequency-sweeping approach together with the auxiliary characteristic function) is discussed. Then, this application of the toolbox will be demonstrated along with some numerical examples.
A solution is given to a conjecture proposed recently by Y. Wigderson and A. Wigderson concerning a “Heisenberg-like” uncertainty principle. That conjecture is about the image of the map f↦fqf⌢qf2f⌢2,f∈ℓℝ\0,\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ f\mapsto \frac{{\left\Vert f\right\Vert}_q{\left\Vert \overset{\frown }{f}\right\Vert}_q}{{\left\Vert f\right\Vert}_2{\left\Vert \overset{\frown }{f}\right\Vert}_2},f\in \ell \left(\mathbb{R}\right)\backslash \left\{0\right\}, $$\end{document} where ℓ(ℝ) stands for the Schwartz class of functions on the real line. Also, a more general question is answered, where the L2 norm is replaced by the Lp norm in the denominator.
Porous media containing voids which can be filled with gas and/or liquids are ubiquitous in our everyday life: soils, wood, bricks, concrete, sponges, and textiles. It is of major interest to identify how a liquid, pushing another fluid or transporting particles, ions, or nutriments, can penetrate or be extracted from the porous medium. High-resolution X-ray microtomography, neutron imaging, and magnetic resonance imaging are techniques allowing us to obtain, in a nondestructive way, a view of the internal processes in nontransparent porous media. Here we review the possibilities of a simple though powerful technique which provides various direct quantitative information on the liquid distribution inside the porous structure and its variations over time due to fluid transport and/or phase changes. It relies on the analysis of the details of the NMR (nuclear magnetic resonance) relaxation of the proton spins of the liquid molecules and its evolution during some process such as the imbibition, drying, or phase change of the sample. This rather cheap technique then allows us to distinguish how the liquid is distributed in the different pore sizes or pore types and how this evolves over time; since the NMR relaxation time depends on the fraction of time spent by the molecule along the solid surface, this technique can also be used to determine the specific surface of some pore classes in the material. The principles of the technique and its contribution to the physical understanding of the processes are illustrated through examples: imbibition, drying or fluid transfers in a nanoporous silica glass, large pores dispersed in a fine polymeric porous matrix, a pile of cellulose fibers partially saturated with bound water, a softwood, and a simple porous inclusion in a cement paste. We thus show the efficiency of the technique to quantify the transfers with a good temporal resolution.
The offshore Campos Basin, located in Southeastern Brazil represents an important area in theBrazilian economy as it is one of the most prolific oil-producing basins in the country. With thedevelopment of offshore infrastructures in this region, structural design and location must con-sider different geohazards. This paper addresses the seismic response of gentle submarine slopessubjected to small-to-moderate-sized earthquakes, representative of the Brazilian seismic condi-tions. The seismic analyses employed numerical modeling, with a nonlinear constitutive model. Aset of bedrock ground motions representative of the offshore Campos Basin seismicity wasobtained, employing a Uniform Hazard Response spectrum for the region and earthquakes fromthe Pacific Earthquake Engineering Research (PEER) database. Numerical modelling results showedthat, even for small slope angles and moderate earthquakes, there is an accumulation of perman-ent displacements and shear strains in the downslope direction can affect the stability and per-formance of existing offshore infrastructures. The findings of this research provide a valuablereference for the prediction of seismic displacements, shear strains and seabed amplification orattenuation of earthquakes on gentle slopes in deep-water deposits similar to those found in theoffshore Campos Basin.
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Mahdi Zargayouna
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Champs-sur-Marne, France
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https://www.univ-gustave-eiffel.fr/