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Static and Vibration Analysis of Two-phase Peridynamic Rods or Strings under General Boundary Conditions — Exact, FDM and FEM Approaches
No full textInternational audienceStatic and dynamic analysis of two-phase peridynamic one-dimensional systems is thoroughly investigated in this paper for various boundary conditions by exact and numerical approaches. Such a nonlocal study concerns the axial or torsional responses of two-phase peridynamic rods or the behavior of a two-phase peridynamic string. For a normalized exponential kernel, the integro-differential equation of the two-phase peridynamic problem can be converted as a linear higher-order differential equation with constant coefficients. Exact static solutions of fixed–fixed and fixed–free two-phase peridynamic axial rod (TPPAR) under uniform distributed loading and concentrated force are analytically derived. It is shown that the pure peridynamic rod problem can be ill-posed due to a conflict between the natural boundary condition and the peridynamic constitutive boundary condition. The two-phase peridynamic problem may be justified from physical arguments, and is also seen as a regularized peridynamic problem. The exact eigen-frequencies of the two-phase peridynamic rods are also analytically obtained for various boundary conditions, including fixed–free, fixed–fixed or free–free boundary conditions. These theoretical approaches are corroborated by numerical investigations based on Finite Difference Method (FDM), Finite Element Method (FEM), exact FEM and variational iterative methods. Two FDM schemes are presented for the statics and the vibration of two-phase peridynamic rods, with convergence orders of 1 and 2, respectively. Moreover, three different FE procedures are proposed as: (1) FEM for direct solving the integro-differential equations of two-phase peridynamic one-dimensional system, (2) FEM for discretizing the pure differential equations, and (3) Exact FEM to obtain both the exact stiffness matrix and exact dynamic stiffness matrix of two-phase peridynamic one-dimensional system, based on Eisenberger’s methodology. The order of convergence for the first and the second proposed FEM is equal to 2 and 4, according to the type of selected finite elements. Moreover, the third proposed FEM based on the exact shape function of the peridynamic problem gives the exact solution from one single FEM element. In addition, the variational iterative method of Stodola–Vianello is successfully applied to the two-phase peridynamic eigenvalue problems
Hyperbolicité orbifolde
No full textIn this thesis, we study the notion of hyperbolicity in the context of orbifolds, by generalizing classical results from complex algebraic geometry to Campana’s orbifolds. In particular, we extend a theorem of Noguchi, which establishes the finiteness of the set of dominant maps to hyperbolic varieties.Our main result shows that the set of surjective orbifold maps between smooth projectiveorbifolds is finite when the target pair is hyperbolic and is either uniformizable or has a pseudo-effective orbifold canonical bundle. We also establish other finiteness results, notably for the orbifold automorphism group of a hyperbolic orbifold and for the set of pointed orbifold morphisms.Furthermore, we study the deformation of orbifold morphisms, focusing on the case of classical morphisms. In doing so, we generalize a theorem of Hwang–Kebekus–Peternell by extending it to the orbifold setting.Dans cette thèse, nous étudions la notion d’hyperbolicité dans le cadre des orbifoldes, en généralisant des résultats classiques de géométrie algébrique complexe aux orbifoldes au sens de Campana. Nous étendons notamment un théorème de Noguchi, qui établit la finitude de l’ensemble des applications dominantes vers des variétés hyperboliques. Notre résultat principal démontre que l’ensemble des applications orbifoldes surjectives entre orbifoldes lisses projectives est fini lorsque la paire d’arrivée est hyperbolique et qu’elle est, soit uniformisable, soit dotée d’un fibre canonique orbifolde pseudo-effectif. Nous établissons aussi d’autres résultats de finitude, notamment pour le groupe d’automorphismes orbifoldes d’une orbifolde hyperbolique et pour l’ensemble des morphismes orbifoldes pointés. Nous étudions également la déformation des morphismes orbifoldes, en nous concentrant sur le cas des morphismes classiques. Nous généralisons ainsi un théorème de Hwang–Kebekus–Peternell, en l’étendant aux orbifoldes
El “cuerpo colectivo” y los cuerpos individuales. Actores, espacios y temporalidades de las exhumaciones: el ejemplo de los 545 “asesinados por el franquismo” (Huesca)
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Du port au monde. Une histoire globale des ports indochinois
No full textInternational audienceEt si l’histoire de l’Indochine et du Việt Nam s’écrivait d’abord depuis les ports ? Interfaces entre terre et mer, entre époques et sociétés, zones de contact (contact zones) et lieux « d’hybridation » par excellence, ils sont au cœur des connexions où se négocient pouvoirs, circulations et « modernités ». Issu d’un programme de recherche et d’un grand colloque international – INDOPORTS – accueilli à Đà Nẵng en octobre 2022, ce volume collectif propose une histoire au long cours, globale, connectée et comparée des ports de l’ancienne Union indochinoise (Việt Nam, Cambodge, Laos, Guangzhouwan). Des chercheurs en histoire, géographie, économie, droit, littérature, anthropologie, architecture et urbanisme y croisent leurs travaux pour explorer non seulement la séquence coloniale, mais aussi ses antécédents et prolongements, et tenter de saisir les territoires et les dynamiques humaines qui les animent. Des ports des royaumes Việts anciens (XVIIe - début XIXe siècles) aux grands ports à conteneurs du XXIe siècle, l’ouvrage explore toutes les échelles (locale, régionale, [trans-]nationale, [trans-]impériale, globale) et toutes les dimensions des mondes portuaires : juridiques et sanitaires ; économiques et logistiques ; militaires et stratégiques ; sociales, culturelles et patrimoniales. En prenant ensemble grands ports et petits ports de cabotage, il restitue la diversité des acteurs, des infrastructures, des systèmes et des circulations – et, peut-être surtout, leur connectivité. Du port au monde – de la voile à la mondialisation logistique –, il articule arrière-pays (hinterland) et avant-pays (foreland), et met en regard données, pratiques, imaginaires et mémoires pour éclairer continuités, bifurcations et ruptures. Plutôt qu’une conclusion fermée, ce livre offre une synthèse ouverte : un nouveau prisme pour penser le Việt Nam et l’Indochine par la mer
Distribution channels – a source of perceived captivity among farmers?
No full textInternational audiencePurpose Given the significant and ongoing decline in the number of farms in France and the growing mistrust of distribution intermediaries among new generations of farmers, it has become imperative to examine these relationships from a farmer's perspective (Bijman and Wijers, 2019). The quantitative research presented here initially focuses on the determinants of farmers' distribution channel choices, and then examines the farmer-distribution intermediary relationship by using the concepts of perceived control, perceived captivity and satisfaction with distribution. It will explore these issues by comparing the various perceptions of the farmer based on the intra- or extra-territorial nature of the distribution channel. Design/methodology/approach The research is based on data collected from 116 French farmers with various distribution strategy profiles, located in the Brittany region of France. Findings Ultimately, we find that some distribution channels generate a stronger sense of captivity than others, lower satisfaction and less perceived control. Originality/value Few studies take an overall view of the different forms of distribution that would allow for comparisons to be made from a farmer's perspective. To bridge this research gap, the present study addresses channel choice from the original perspective of geographical scale, focussing on the extent of distribution localness rather than distribution channel length
Innovations in Core–Shell Electrospinning: A Comprehensive Review in Recent Advances of Core–Shell Electrospun Polylactic Acid Nanocomposite Fibers for Potential Biomedical Applications
No full textInternational audienceThe unique structural and functional properties of polylactic acid (PLA) nanofibers, particularly in core-shell structures, have placed them as a crucial material in biomedical engineering. In addition to its renewable characteristics, biodegradability, and biocompatibility, PLA distinguishes itself and satisfies the increasing demand for environmentally friendly and sustainable materials in medical applications. It is an optimal material for scaffolds, implants, and biomedical devices due to its adjustable mechanical strength, degradation rate, excellent biocompatibility, and capacity to form intricate fiber architectures. The precise manipulation of PLA nanofibers can be made easier by advanced electrospinning techniques, which maintain the structural integrity of the PLA nanofibers while allowing for the encapsulation with controlled release of bioactive compounds. The core-shell architectures enhance mechanical performance, cellular adhesion, and proliferation, making them suitable for various advanced biomedical applications. Moreover, PLA degradation products have a much lower environmental effect compared to other synthetic nondegradable polymers, signifying a substantial advantage. The review article covers the techniques used for the fabrication of coaxial electrospun PLA nanofibers, their benefits, and potential uses in innovative healthcare products and sustainable biomedical practice
The effect of microstructural inertia on plastic localization and void growth in porous solids
No full textInternational audienceThis paper investigates the impact of microinertia on plastic localization, void growth, and coalescence in ductile porous materials subjected to high strain rates. For that purpose, we have performed finite element calculations on a flat double-notched specimen subjected to dynamic plane strain tension. The simulations employ three distinct approaches to model the mechanical behavior of the porous aggregate: (1) discrete voids within a matrix material governed by von Mises plasticity; (2) homogenized porosity represented using standard quasi-static Gurson-Tvergaard plasticity; and (3) homogenized porosity described with Gurson-Tvergaard plasticity extended by Molinari and Mercier (2001) to account for microinertia effects. The porous microstructures used in the simulations are representative of additive manufactured metals, featuring initial void volume fractions varying between 0.5% and 4%, and pore diameters ranging from 30 μm to 150 μm (Marvi-Mashhadi et al., 2021, Nieto-Fuentes et al., 2023). The applied tensile velocities ranged from 100 m∕s to 1000 m∕s, producing strain rates between 10 5 s -1 and 10 6 s -1 , and stress triaxiality values spanning from 4 to 30. The simulations with discrete voids validate the calculations performed using homogenized porosity and microinertia effects, demonstrating that higher strain rates and larger pore sizes lead to slower void growth and a delayed, regularized plastic localization. Conversely, the standard Gurson-Tvergaard model shows notable mesh sensitivity and fails to describe the influence of the loading rate on plastic localization. Ultimately, the comparison between finite element models with discrete voids and those with homogenized porosity illustrates the stabilizing effects of porous microstructure and multiscale inertia on dynamic plastic flow, while also highlighting the strengths of the constitutive model introduced by Molinari and Mercier (2001) for simulating engineering problems involving porous ductile materials subjected to high-velocity impacts.</div
Tailored nanoarchitectonics of PPy/g-C3N4/MnO2 hybrid on NiCo LDH for enhanced energy storage in supercapacitors
No full textInternational audienceThe growing demand for efficient energy storage devices holding high specific energy has accelerated the search for advanced electrode materials. Transition metal-based layered double hydroxides (LDHs), particularly those containing nickel (Ni) and cobalt (Co), have emerged as promising candidates due to their tunable layered structure and chemical composition. In this study, LDH and its hybrids were prepared using a simple hydrothermal technique. In addition, X-ray diffraction (XRD) measurements approve the presence of H2O molecules and carbonate anions in the interlamellar space due to their extended interlayer spacing. The quaternary NiCo LDH/manganese dioxide (MnO₂)/polypyrrole (PPy)/graphitic carbon nitride (g-C₃N₄) hybrid nanocomposite exhibits a specific capacitance of 2389 F/g at 1 A/g, with 88 % retention after 5000 cycles at a higher current density of 10 A/g. The superior electrochemical performance is accredited to reduced aggregation and enhanced electronic conductivity. Charge storage kinetics were analysed using Dunn's method and power law, reveals increased diffusive contribution in the quaternary nanocomposite. A hybrid supercapacitor device was fabricated using quaternary hybrid as cathode and activated carbon (AC) as anode delivers a high specific capacitance of 260 F/g at 1 A/g, with 95 % cyclic stability after 10,000 cycles. The assembled device achieves a specific energy of 82 Wh/kg at a specific power of 750 W/kg and a coulombic efficiency of 99 %, demonstrating excellent potential for energy storage applications