Advanced joined materials development and their shear strength evaluation for aerospace, energy and structural applications

L'abstract è presente nell'allegato / the abstract is in the attachmen

Self-consistent inhomogeneous steady states in Hamiltonian mean field dynamics

Long-lived quasistationary states, associated with stationary stable solutions of the Vlasov equation, are found in systems with long-range interactions. Studies of the relaxation time in a model of $N$ globally coupled particles moving on a ring, the Hamiltonian Mean Field model (HMF), have shown that it diverges as $N^\gamma$ for large $N$, with $\gamma \simeq 1.7$ for some initial conditions with homogeneously distributed particles. We propose a method for identifying exact inhomogeneous steady states in the thermodynamic limit, based on analysing models of uncoupled particles moving in an external field. For the HMF model, we show numerically that the relaxation time of these states diverges with $N$ with the exponent $\gamma \simeq 1$. The method, applicable to other models with globally coupled particles, also allows an exact evaluation of the stability limit of homogeneous steady states. In some cases it provides a good approximation for the correspondence between the initial condition and the final steady state.Comment: 5 pages, 4 figures, revised, accepted for publication on Phys. Rev.

Out of equilibrium phase transitions in mean field Hamiltonian dynamics

Systems with long-range interactions display a short-time relaxation towards Quasi-Stationary States (QSSs), whose lifetime increases with system size. With reference to the Hamiltonian Mean Field (HMF) model, we here review Lynden-Bell's theory of ``violent relaxation''. The latter results in a maximum entropy scheme for a water-bag initial profile which predicts the presence of out-of-equilibrium phase transitions} separating homogeneous (zero magnetization) from inhomogeneous (non-zero magnetization) QSSs. Two different parametric representations of the initial condition are analyzed and the features of the phase diagram are discussed. In both representations we find a second order and a first order line of phase transitions that merge at a tricritical point. Particular attention is payed to the condition of existence and stability of the homogenous phase.Comment: Proceedings of the conference "Chaos, Complexity and Transport" (Marseille, 5-9 June 2007

Origin of 60^{60}Fe nuclei in cosmic rays: the contribution of local OB associations

The presence of live $^{60}$Fe nuclei (lifetime of 3.8~Myr) in cosmic rays detected by the ACE/CRIS instrument suggests a nearby nucleosynthesis source. $^{60}$Fe is primarily produced in core-collapse supernovae, and we aim to clarify whether the detected $^{60}$Fe nuclei can be associated with a particular local supernova. We consider 25 OB associations and sub-groups located within 1 kpc of the solar system based on recent $Gaia$ census. A model is developed that combines stellar population synthesis within these OB associations, cosmic-ray acceleration within associated superbubbles, and cosmic-ray transport to the solar system. The most critical model parameter impacting $^{60}$Fe cosmic-ray production is the explodability criterion, which determines if a massive star ends its life as a supernova. Our study points to the Sco-Cen OB association as the most probable origin of the observed $^{60}$Fe nuclei, particularly suggesting they were accelerated in the Sco-Cen superbubble by a young supernova aged $\leq500$ kyr with a progenitor mass of approximately $13-20~M_\odot$. A less likely source is the supernova at the origin of the Geminga pulsar 342 kyr ago, if the progenitor originated in the Orion OB1 association. The contribution of local OB associations to the cosmic-ray density of stable $^{56}$Fe is estimated to be around 20\%, with some sensitivity to cosmic ray acceleration efficiency and diffusion coefficient. These findings shed light on the origins of cosmic-ray nuclei, connecting them to nucleosynthesis events within our local cosmic neighborhood

Study of solutions to optimize the extraction of hemp fibers for composite materials

Fibres from hemp stems can be extracted through different mechanical processes following dew or water retting etc. Extraction processes generally have a significant impact on mechanical and morphological properties of the fibres. In this study, hemp fibres are extracted following three different ways. In the first route hemp fibres are extracted from FUTURA 75 variety stems by performing scutching, hackling and microwave degumming. A second batch of fibres of the same variety was extracted by scutching and hackling after an initial microwave degumming treatment. In the third route, the same variety of hemp fibres are extracted from dew retted stems grown at Piacenza (Italy). Finally, the mechanical properties of single fibres as well as the fineness of technical fibres of all types of extracted fibres are evaluated and compared and the interest of the microwave degumming for hemp stem is evaluated

Modelling, additive layer manufacturing and testing of interlocking structures for joined components

Modelling, additive layer manufacturing and testing of interlocking structures for joined component

Interactive Learning-Based Realizability for Heyting Arithmetic with EM1

We apply to the semantics of Arithmetic the idea of ``finite approximation'' used to provide computational interpretations of Herbrand's Theorem, and we interpret classical proofs as constructive proofs (with constructive rules for $\vee, \exists$) over a suitable structure \StructureN for the language of natural numbers and maps of G\"odel's system \SystemT. We introduce a new Realizability semantics we call ``Interactive learning-based Realizability'', for Heyting Arithmetic plus \EM_1 (Excluded middle axiom restricted to $\Sigma^0_1$ formulas). Individuals of \StructureN evolve with time, and realizers may ``interact'' with them, by influencing their evolution. We build our semantics over Avigad's fixed point result, but the same semantics may be defined over different constructive interpretations of classical arithmetic (Berardi and de' Liguoro use continuations). Our notion of realizability extends intuitionistic realizability and differs from it only in the atomic case: we interpret atomic realizers as ``learning agents''

Combination of a Solvent-dispensing and Micro-aspiration Device for Removal of Varnishes on Painted Surfaces

The use of organic solvents in treatments for the removal of varnishes on easel paintings is still a common practice among conservators worldwide. The more polar solvents required for aged, oxidized varnishes may promote leaching of fatty acid components of oil-based paints. The strategy tested in this study to reduce the diffusion of the solvents, in an attempt to minimize interactions, relied on the use of a system composed of two devices: a pump for delivering a precisely controlled amount of solvent to the surface, and a solvent-proof membrane pump to quickly aspirate it. This method was compared with two traditional methods of solvent application, to remove the varnish on two oil paintings on canvas, one from the twentieth century and the other dated 1872: swab-rolling and application through a Japanese paper sheet. The extent of leaching was measured by GC−MS analysis of the paint samples taken from the treated areas. The profiles of the fatty acids before and after varnish removal could thus be compared

Torsion Test vs. Other Methods to Obtain the Shear Strength of Elastic-Plastic Adhesives

Nowadays adhesive joints are more and more used; therefore, a precise and reliable shear strength measurement of these joints is necessary to design and predict a final components’ performance. This work aimed to assess the shear strength value of adhesively joined ceramics (SiC, Si3N4) and steel in the case of an elasto‐plastic (ductile) joining material (Loctite EA 9321 AERO) by an experimental campaign and associated analytical modelling. The joined samples were tested using a single lap offset test in compression (SLO), an asymmetrical 4‐point bending test (A4PB, ASTM C1469), and by torsion on fully joined hourglass shaped samples (THG). A simple model based on the elastic‐plastic response in shear was proposed to fit the torque‐rotation curve measured in the torsion tests. The results showed that, with the adopted test methods and conditions, and by using the model, consistent values of shear strength could be obtained by torsion tests

Plate-forme de prototypage et conception pour les systèmes de radio-logicielle

- Cet article présente la plate-forme radio logicielle utilisée dans le projet PALMYRE, élaboré dans le cadre du Contrat de Plan Etat Région (CPER) pour une durée de 5 ans. La plate-forme hétérogène et commune à plusieurs laboratoires bretons va ainsi permettre le développement et l'évaluation de systèmes radioélectriques pour les futures générations. Pour faciliter le portage de multiples applications sur cette plate-forme, une méthodologie de conception est mise en place, offrant ainsi un couplage algorithme-architecture maximal