A model comparison to predict heat transfer during spot GTA welding

The present work deals with the estimation of the time evolution of the weld fusion boundary. This moving boundary is the result of a spot GTA welding process on a 316L stainless steel disk. The estimation is based on the iterative regularization method. Indeed, the three problems: direct, in variation and adjoint, classically associated with this method, are solved by the finite element method in a two-dimensional axisymmetric domain. The originality of this work is to treat an experimental estimation of a front motion using a model with a geometry including only the solid phase. In this model, the evolution of this solid domain during the fusion is set with the ALE moving mesh method (Arbitrary Lagrangian Eulerian). The numerical developments are realized with the commercial code Comsol Multiphysics® coupled with the software Matlab®. The estimation method has been validated in a previous work using theoretical data ([1]). The experimental data, used here for this identification are, temperatures measured by thermocouples in the solid phase, the temporal evolution of the melt pool boundary observed at the surface by a fast camera and the maximal dimensions of the melted zone measured on macrographs. These experimental data are also compared with numerical results obtained from a heat and fluid flow model taking into account surface tension effects, Lorentz forces and the deformation of the melt pool surface under arc pressure

The effect of ambipolar diffusion on low-density molecular ISM filaments

The filamentary structure of the molecular interstellar medium and the potential link of this morphology to star formation have been brought into focus recently by high resolution observational surveys. An especially puzzling matter is that local interstellar filaments appear to have the same thickness, independent of their column density. This requires a theoretical understanding of their formation process and the physics that governs their evolution. In this work we explore a scenario in which filaments are dissipative structures of the large-scale interstellar turbulence cascade and ion-neutral friction (also called ambipolar diffusion) is affecting their sizes by preventing small-scale compressions. We employ high-resolution, 3D MHD simulations, performed with the grid code RAMSES, to investigate non-ideal MHD turbulence as a filament formation mechanism. We focus the analysis on the mass and thickness distributions of the resulting filamentary structures. Simulations of both driven and decaying MHD turbulence show that the morphologies of the density and the magnetic field are different when ambipolar diffusion is included in the models. In particular, the densest structures are broader and more massive as an effect of ion-neutral friction and the power spectra of both the velocity and the density steepen at a smaller wavenumber. The comparison between ideal and non-ideal MHD simulations shows that ambipolar diffusion causes a shift of the filament thickness distribution towards higher values. However, none of the distributions exhibit the pronounced peak found in the observed local filaments. Limitations in dynamical range and the absence of self-gravity in these numerical experiments do not allow us to conclude at this time whether this is due to the different filament selection or due to the physics inherent of the filament formation.Comment: A&A accepte

Aerosol deposition and origin in French mountains estimated with soil inventories of 210Pb and artificial radionuclides

Radionuclide inventories were measured in soils from different French mountainous areas: Chaîne des Puys (Massif Central), Eastern Corsica, Jura, Montagne Noire, Savoie, Vosges and Rhine Valley. 210Pb soil inventories were used to estimate long-term (>75 yr) deposition of submicron aerosols. Whereas 210Pb total deposition is explained partly by wet deposition, as demonstrated by increase of 210Pb inventory with annual rainfall; a part of 210Pb in the soils of higher altitude is caused by orographic depositions. Using measurements of radionuclides coming from nuclear aerial weapon tests (137Cs and Pu isotopes), we were able to estimate the origin of aerosols deposited in high-altitude sites and to confirm the importance of occult deposition and feeder–seeder mechanism. Using a simple mass balance model, we estimate that occult deposition and feeder–seeder mechanisms account to more than 50% of total deposition of 210Pb and associated submicron aerosols in French altitude sites

Systèmes de production mixtes agriculture pluviale et élevage en zones humide et sub-humide d'Afrique

Ce travail s'inscrit dans une étude générale sur les interactions entre les systèmes de production d'élevage et l'environnement. L'évolution récente des systèmes pastoraux traditionnels africains, vers des systèmes mixtes agriculture et élevage, a des conséquences nouvelles pour l'environnement qui sont d'autant plus profitables que l'association entre l'élevage et l'agriculture est bien maîtrisée

Penser autrement les carrières scolaires

À la suite d’un numéro récent de la Revue française de pédagogie (no 175), l’auteur examine d’autres orientations possibles pour l’étude des « choix scolaires ». Il souligne les conséquences pratiques qui découlent de l’usage de cette terminologie et propose de lui substituer la notion de « carrière scolaire » qui permet d’élargir la recherche à d’autres situations de choix scolaires souvent peu étudiées. Il présente un cadre d’analyse pour l’étude des carrières scolaires et les pistes de recherche qui pourraient en découler.Further to a recent issue of the Revue française de pédagogie (No. 175), the author analyses alternative oirentations for the study of “school options”. He emphasises the practical effects of the use of this term and suggests replacing “school options” by “school paths” as it enables scholars to broaden research to other situations of school options that have often been little studied. He presents an analysis framework for the study of school paths and research topics that might derive from it.Consiguiente a un reciente número de la Revue française de pédagogie (no 175), el autor examina otras posibles orientaciones para el estudio de las « elecciones escolares ». Pone de manifiesto las consecuencias prácticas que resultan del uso de esa terminología y propone substituirla por la noción de « carrera escolar » que permite ampliar la investigación hacia otras situaciones de elecciones escolares a menudo poco estudiadas. Presenta un marco de análisis para el estudio de las carreras escolares y las pistas de investigación que podrían emanar de él.In Folge der neulichen Ausgabe der Revue française de pédagogie (Nr. 175), beobachtet der Autor andere Möglichkeiten zur Analyse der „schulischen Wahl“. Er hebt die praktischen Konsequenzen hervor, die aus der Benutzung dieser Wortwahl hervorgehen und schlägt vor, sie durch den Begriff der „Schulkarriere“ zu ersetzen, weil er erlaubt, die Forschung auf andere oft wenig erforschten Situationen der Schulwahl zu erweitern. Er stellt einen Analyserahmen für die Forschung über Schulkarrieren und daraus folgende Forschungsansätze vor

Efficient handling of synchronization in three vehicle routing problems

International audienceThis paper presents a synthesis of contributions to the solving of three vehicle routing problemsinvolving synchronization constraints. These problems are: the Pickup and Delivery Problem withTransfers (PDPT), studied during the PhD of Renaud Masson, co-advised with Olivier Péton [4], theTwo-Echelon Multiple-Trip Vehicle Routing Problem with Satellite Synchronization (2E-MTVRPSS),studied by Philippe Grangier during his PhD, co-advised with Michel Gendreau and Louis-Martin Rousseau [2], and the Heterogeneous Full Truckload Pickup and Delivery Problem with TimeWindows and Resource Synchronization(HFTPDPTW-RS), under study by Axel Grimault in hisPhD and co-advised with Nathalie Bostel [3]. All these problems have been solved with an AdaptiveLarge Neighborhood Search (ALNS).A special focus is given to the temporal feasibility evaluation of an insertion which has beenproposed for the PDPT [5] and extended to the other problems. The concept of forward time slack[6] is extended to provide a constant time feasibility test of temporal constraints. Experimentsconfirm the solving time reduction provided by the implementation of this test in a meta-heuristic

Influence of a pulsed laser regime on surface finish induced by thedirect metal deposition process on a Ti64 alloy

tThe direct metal deposition (DMD) laser technique is a free-form metal deposition process, which allowsgenerating a prototype or small series of near net-shape structures. Despite numerous advantages, oneof the most critical issues of the technique is that produced pieces have a deleterious surface finish whichrequires post machining steps. Following recent investigations where the use of laser pulses instead of acontinuous regime was successful to obtain smoother DMD structures, this paper relates investigationson the influence of a pulsed laser regime on the surface finish induced by DMD on a widely used titaniumalloy (Ti64). Findings confirm that using high mean powers improves surface finish but also indicate aspecific effect of the laser operating mode: using a quasi-continuous pulsed mode instead of fully-cw laserheating is an efficient way for surface finish improvement. For similar average powers, the use of a pulsedmode with large duty cycles is clearly shown to provide smoothening effects. The formation of larger andstable melt pools having less pronounced lateral curvatures, and the reduction of thermal gradients andMarangoni flow in the external side of the fusion zone were assumed to be the main reasons for surfacefinish improvement. Additional results indicate that combining the benefits from a pulsed regime and auniform laser irradiation does not provide further reduction of surface roughness