Développement d'un code éléments finis pour simuler le soudage par ultrasons de matériaux composites = Development of a Finite element code for simulating the ultrasonic welding of composite materials

National audienceLe développement récent des matériaux composites à matrices thermoplastiques c'est accompagné de nouveaux moyens d'assemblages. Nous nous concentrons ici sur le soudage par ultrasons. Afin d'étudier l'influence des paramètres procédé sur la qualité d'une soudure, nous proposons une modélisation puis une simulation du procédé. La modélisation se fait à l'aide de deux problèmes mécaniques et d'un problème thermique. Un code de simulation multiphysique a été développé afin de résoudre ces trois problèmes. L'évolution que subit l'interface est simulé à l'aide d'une méthode de level-set et de contact unilatéral par pénalité. Les simulations en 2D sans modélisation du contact montrent que des porosités sont piégées à l'interface. Ceci est confirmé par les essais de soudage statique (sans mouvement de l'outil). Les simulations avec modélisation du contact permettent de mieux décrire l'écrasement à l'interface mais montrent des lacunes physiques. Le soudage dynamique avec avance de l'outil est un variant du procédé permettant de limiter les porosités à l'interface. La simulation de l'écoulement tridimensionnel qui en résulte est en cours. Elle devrait permettre d'expliquer la meilleure qualité de la soudure

Practical 3D frame field generation

International audienceFigure 1: Our algorithm produces smooth frame fields in volumes. Frames (a) are represented by spherical harmonic functions (b), attached to each vertex of a tetrahedral mesh. Streamlines and singularities of the field are shown in yellow and red, respectively. Abstract Given a tetrahedral mesh, the algorithm described in this article produces a smooth 3D frame field, i.e. a set of three orthogonal directions associated with each vertex of the input mesh. The field varies smoothly inside the volume, and matches the normals of the volume boundary. Such a 3D frame field is a key component for some hexahedral meshing algorithms, where it is used to steer the placement of the generated elements. We improve the state-of-the art in terms of quality, efficiency and reproducibility. Our main contribution is a non-trivial extension in 3D of the existing least-squares approach used for optimizing a 2D frame field. Our algorithm is inspired by the method proposed by Huang et al. [2011], improved with an initialization that directly enforces boundary conditions. Our initialization alone is a fast and easy way to generate frames fields that are suitable for remeshing applications. For better robustness and quality, the field can be further optimized using nonlinear optimization as in Li et al [2012]. We make the remark that sampling the field on vertices instead of tetrahedra significantly improves both performance and quality

Automatic and Interactive Mesh to T-Spline Conversion

In Geometry Processing, and more specifically in surface approximation, one of the most important issues is the automatic generation of a quad-dominant control mesh from an arbitrary shape (e.g. a scanned mesh). One of the first fully automatic solutions was proposed by Eck and Hoppe in 1996. However, in the industry, designers still use manual tools (see e.g. cyslice). The main difference between a control mesh constructed by an automatic method and the one designed by a human user is that in the second case, the control mesh follows the features of the model. More precisely, it is well known from approximation theory that aligning the edges with the principal directions of curvature improves the smoothness of the reconstructed surface, and this is what designers intuitively do. In this paper, our goal is to automatically construct a control mesh driven by the anisotropy of the shape, mimicking the mesh that a designer would create manually. The control mesh generated by our method can be used by a wide variety of representations (splines, subdivision surfaces...). We demonstrate our method applied to the automatic conversion from a mesh of arbitrary topology into a T-Spline surface. Our method first extracts an initial mesh from a PGP (Periodic Global Parameterization). To facilitate user-interaction, we extend the PGP method to take into account optional user-defined information. This makes it possible to locally tune the orientation and the density of the control mesh. The user can also interactively remove edges or sketch additional ones. Then, from this initial control mesh, our algorithm generates a valid T-Spline control mesh by enforcing some validity constraints. The valid T-Spline control mesh is finally fitted to the original surface, using a classic regularized optimization procedure. To reduce the L-infinity approximation error below a user-defined threshold, we iteratively use the T-Spline adaptive local refinement

An overview of new translational, clinical and therapeutic perspectives in laminopathies and other nuclear envelope-related diseases.

International audienc

XRCC1 is phosphorylated by DNA-dependent protein kinase in response to DNA damage

The two BRCT domains (BRCT1 and BRCT2) of XRCC1 mediate a network of protein–protein interactions with several key factors of the DNA single-strand breaks (SSBs) and base damage repair pathways. BRCT1 is required for the immediate poly(ADP–ribose)-dependent recruitment of XRCC1 to DNA breaks and is essential for survival after DNA damage. To better understand the biological role of XRCC1 in the processing of DNA ends, a search for the BRCT1 domain-associated proteins was performed by mass spectrometry of GST-BRCT1 pulled-down proteins from HeLa cell extracts. Here, we report that the double-strand break (DSB) repair heterotrimeric complex DNA-PK interacts with the BRCT1 domain of XRCC1 and phosphorylates this domain at serine 371 after ionizing irradiation. This caused XRCC1 dimer dissociation. The XRCC1 R399Q variant allele did not affect this phosphorylation. We also show that XRCC1 strongly stimulates the phosphorylation of p53-Ser15 by DNA-PK. The pseudo phosphorylated S371D mutant was a much weaker stimulator of DNA-PK activity whereas the non-phosphorylable mutant S371L endowed with a DNA-PK stimulating capacity failed to fully rescue the DSB repair defect of XRCC1-deficient EM9 rodent cells. The functional association between XRCC1 and DNA-PK in response to IR provides the first evidence for their involvement in a common DSB repair pathway

Meshless Voronoi on the GPU

International audienceWe propose a GPU algorithm that computes a 3D Voronoi diagram. Our algorithm is tailored for applications that solely make use of the geometry of the Voronoi cells, such as Lloyd's relaxation used in meshing, or some numerical schemes used in fluid simulations and astrophysics. Since these applications only require the geometry of the Voronoi cells, they do not need the combinatorial mesh data structure computed by the classical algorithms (Bowyer-Watson). Thus, by exploiting the specific spatial distribution of the point-sets used in this type of applications, our algorithm computes each cell independently, in parallel, based on its nearest neighbors. In addition, we show how to compute integrals over the Voronoi cells by decomposing them on the fly into tetrahedra, without needing to compute any global combinatorial information. The advantages of our algorithm is that it is fast, very simple to implement, has constant memory usage per thread and does not need any synchronization primitive.These specificities make it particularly efficient on the GPU: it gains one order of magnitude as compared to the fastest state-of-the-art multi-core CPU implementations. To ease the reproducibility of our results, the full documented source code is included in the supplemental material

Hexahedral-dominant meshing

This article introduces a method that generates a hexahedral-dominant mesh from an input tetrahedral mesh.It follows a three-steps pipeline similar to the one proposed by Carrier-Baudoin et al.:(1) generate a frame field; (2) generate a pointset P that is mostly organized on a regulargrid locally aligned with the frame field; and (3) generate thehexahedral-dominant mesh by recombining the tetrahedra obtained from the constrained Delaunay triangulation of P.For step (1), we use a state of the art algorithm to generate a smooth frame field. For step (2), weintroduce an extension of Periodic Global Parameterization to the volumetric case. As compared withother global parameterization methods (such as CubeCover), our method relaxes some global constraintsand avoids creating degenerate elements, at the expense of introducing some singularities that aremeshed using non-hexahedral elements. For step (3), we build on the formalism introduced byMeshkat and Talmor, fill-in a gap in their proof and provide a complete enumeration of all thepossible recombinations, as well as an algorithm that efficiently detects all the matches in a tetrahedral mesh.The method is evaluated and compared with the state of the art on adatabase of examples with various mesh complexities, varying fromacademic examples to real industrial cases. Compared with the methodof Carrier-Baudoin et al., the method results in better scoresfor classical quality criteria of hexahedral-dominant meshes(hexahedral proportion, scaled Jacobian, etc.). The methodalso shows better robustness than CubeCover and its derivativeswhen applied to complicated industrial models

Primary laminopathy fibroblasts display altered genome organization and apoptosis

A number of diseases associated with specific tissue degeneration and premature aging have mutations in the nuclear envelope proteins A-type lamins or emerin. Those diseases with A-type lamin mutation are inclusively termed laminopathies. Due to various hypothetical roles of nuclear envelope proteins in genome function we investigated whether alterations to normal genomic behaviour are apparent in cells with mutations in A-type lamins and emerin. Even though the distributions of these proteins in proliferating laminopathy fibroblasts appear normal, there is abnormal nuclear positioning of both chromosome 18 and 13 territories, from the nuclear periphery to the interior. This genomic organization mimics that found in normal nonproliferating quiescent or senescent cells. This finding is supported by distributions of modified pRb in the laminopathy cells. All laminopathy cell lines tested and an X-linked Emery-Dreifuss muscular dystrophy cell line also demonstrate increased incidences of apoptosis. The most extreme cases of apoptosis occur in cells derived from diseases with mutations in the tail region of the LMNA gene, such as Dunningan-type familial partial lipodystrophy and mandibuloacral dysplasia, and this correlates with a significant level of micronucleation in these cells

A perspective from extinct radionuclides on a Young Stellar Object: The Sun and its accretion disk

Meteorites, which are remnants of solar system formation, provide a direct glimpse into the dynamics and evolution of a young stellar object (YSO), namely our Sun. Much of our knowledge about the astrophysical context of the birth of the Sun, the chronology of planetary growth from micrometer-sized dust to terrestrial planets, and the activity of the young Sun comes from the study of extinct radionuclides such as 26Al (t1/2 = 0.717 Myr). Here we review how the signatures of extinct radionuclides (short-lived isotopes that were present when the solar system formed and that have now decayed below detection level) in planetary materials influence the current paradigm of solar system formation. Particular attention is given to tying meteorite measurements to remote astronomical observations of YSOs and modeling efforts. Some extinct radionuclides were inherited from the long-term chemical evolution of the Galaxy, others were injected into the solar system by a nearby supernova, and some were produced by particle irradiation from the T-Tauri Sun. The chronology inferred from extinct radionuclides reveals that dust agglomeration to form centimeter-sized particles in the inner part of the disk was very rapid (<50 kyr), planetesimal formation started early and spanned several million years, planetary embryos (possibly like Mars) were formed in a few million years, and terrestrial planets (like Earth) completed their growths several tens of million years after the birth of the Sun.Comment: 49 pages, 9 figures, 1 table. Uncorrected preprin

Dihedral angle-based maps of tetrahedral meshes

International audienceWe present a geometric representation of a tetrahedral mesh that is solely based on dihedral angles. We first show that the shape of a tetrahedral mesh is completely defined by its dihedral angles. This proof leads to a set of angular constraints that must be satisfied for an immersion to exist in R 3. This formulation lets us easily specify conditions to avoid inverted tetrahedra and multiply-covered vertices, thus leading to locally injective maps. We then present a constrained optimization method that modifies input angles when they do not satisfy constraints. Additionally, we develop a fast spectral reconstruction method to robustly recover positions from dihedral angles. We demonstrate the applicability of our representation with examples of volume parameterization, shape interpolation, mesh optimization, connectivity shapes, and mesh compression