Transdural Spinal Cord Herniation: Tips and Tricks

Recognition of transdural spinal cord herniation has increased over the past decade. This condition remains little known, particularly outside the specialized fields of spinal surgery and neuroradiology, leading to a significant delay in clinical diagnosis and treatment. It should be considered among the differential diagnoses in patients with gradual-onset lower-limb weakness of presumed spinal origin. Reaching a diagnosis using magnetic resonance imaging is essential to refer patients for surgery before their myelopathy worsens. We describe our surgical experience to untether the spinal cord by wrapping a dura graft around the spinal cord. Three case reports and a review of the literature are discussed

DISCONTINUOUS GALERKIN DISCRETIZATION AND HP-REFINEMENT FOR THE RESOLUTION OF THE NEUTRON TRANSPORT EQUATION

International audienceThis paper presents a hp−refinement method for a first order scalar transport- reaction equation discretized by a discontinuous Galerkin method. First, the theoretical rates of convergence of h− and p−refinement are recalled and numerically tested. Then, in order to design some meshes, we propose two different estimators of the local error on the spatial domain. These quantities are analysed and compared depending on the regularity of the solution so as to find the best way to lead the refinement process and the best strategy to choose between h− and p−refinement. Finally, the different possible refinement strategies are compared first on analytical examples and then on realistic applications for neutron transport in a nuclear reactor core

Kinematics, topography, shortening, and extrusion in the India-Eurasia collision

Laurent Jolivet est Professeur à l'Université d'Orléans depuis le 1er Septembre 2009International audienceWe examine the problem of partitioning between shortening and extrusion in the India-Asia collision since 45 Ma. We compute the amount of shortening expected from the kinematics of India's motion with respect to Eurasia, using the reconstruction at collision time to put bounds on the possible amounts of surface loss within Greater India and within Eurasia. We then compute the amounts of surface loss corresponding to the thickened crust of Tibet and of the Himalayas, assuming conservation of continental crust. The spatial distribution of the topography reveals a large systematic deficit of crustal thickening distributed rather uniformly west of the eastern syntaxis but an excess of shortening east of it. This distribution indicates an important eastward crustal mass transfer. However, the excess mass east of the eastern syntaxis does not account for more than one third to one half of the deficit west of the eastern syntaxis. The deficit may be accounted either by loss of lower crust into the mantle, for example through massive eclogitization, or by lateral extrusion of nonthickened crust. A mass budget of the crust of the Himalayas indicates that lower crust has not been conserved there, but the deficit is so large that local loss in the mantle is unlikely to be the unique cause of the deficit. Alternatively, following Zhao and Morgan [1985], lower crust may have been transferred below the Tibetan crust. We conclude that a combination of possible transfer of lower crust to the mantle by eclogitization and lateral extrusion has to account for a minimum of one third and a maximum of one half of the total amount of shortening between India and Asia since 45 Ma. This conclusion leaves open the possibility that the partitioning between extrusion and loss of lower crust into the mantle on the one hand and shortening on the other hand has significantly changed during the 45 m.y. history of the collision

Variabilité inter-et intraspécifique de la composition chimique de la phase minérale des ciments utilisés dans la construction du tube de plusieurs polychètes bioconstructeurs

International audienceSeveral species of marine polychaetes reside in individual protective tubes. These tubes may be agglomerated in patches of varied sizes with very high densities, or form massive reef-like mounds which can be stretch over several kilometers. These polychaetes can thus be considered as the most important building organisms after corals in coastal environments. We especially focused on several species belonging to the families of Sabellariidae, Terrebeliidae and Pectinariidae. Tubes grains are glued together with biomineralized cement secreted from a building organ connected to specialized glands. Different methods of micro-analysis were used to analyze the biomineral components of these cements for four varyingly gregarious tube-building polychaetes: Lanice conchilega, Pectinaria koreni, Sabellaria alveolata and Phragmatopoma caudata. The aim of this study is to describe and compare the inter- and the intraspecific variability in the main biomineral components of cement at local, regional and continental scales. Scanning Electron Microscopy confirms an identical structure of the cement within species of Sabellariidae in Europe and America. Electron Probe Micro-Analysis (EPMA) confirms the presence of calcium, phosphorus, and magnesium plus traces of manganese in all cements, with varying concentrations of these elements at different locations for the same species or for different species at the same location. Finally, our dataset is compared with previous studies from literature

Quality of experience model for 3DTV

International audienceModern stereoscopic 3DTV brings new QoE (quality of experience) to viewers, which not only enhances the 3D sensation due to the added binocular depth, but may also induce new problems such as visual discomfort. Subjective quality assessment is the conventional method to assess the QoE. However, the conventional perceived image quality concept is not enough to reveal the advantages and the drawbacks of stereoscopic images in 3DTV. Higher-level concepts such as visual experience were proposed to represent the overall visual QoE for stereoscopic images. In this paper, both the higher-level concept quality indicator, i.e. visual experience and the basic level concepts quality indicators including image quality, depth quantity, and visual comfort are defined. We aim to explore 3D QoE by constructing the visual experience as a weight sum of image quality, depth quantity and visual comfort. Two experiments in which depth quantity and image quality are varied respectively are designed to validate this model. In the first experiment, the stimuli consist of three natural scenes and for each scene, there are four levels of perceived depth variation in terms of depth of focus: 0, 0.1, 0.2 and 0.3 diopters. In the second experiment, five levels of JPEG 2000 compression ratio, 0, 50, 100, 175 and 250 are used to represent the image quality variation. Subjective quality assessments based on the SAMVIQ method are used in both experiments to evaluate the subject's opinion in basic level quality indicators as well as the higher-level indicator. Statistical analysis of result reveals how the perceived depth and image quality variation affect different perceptual scales as well as the relationship between different quality aspects

Etude d'un alliage d'aluminium pour l'aéronautique par les techniques avancées de microscopie électronique en transmission

Le durcissement structural est une voie largement utilisée dans le secteur aéronautique pour répondre aux exigences à la fois d'amélioration des propriétés mécaniques des alliages métalliques et d'allègement de structure. Dans les alliages Al-Li-Cu de la série 2000, le durcissement structural est assuré par la présence des précipités T1 (Al2LiCu) qui modifient localement la matrice cristalline d'aluminium qui les entoure. La compréhension des micromécanismes de déformation, qui nécessite la connaissance des interactions des dislocations avec ces phases durcissantes, impose donc une caractérisation précise des champs de déformation. Dans cet objectif, nous avons développé une approche expérimentale adossée à des modélisations. A partir d'analyses en microscopie électronique en haute résolution (MEHR), couplées à des analyses dites " des phases géométriques " (GPA), une méthode de mesure des champs de déformations suivant trois directions de l'espace est proposée. Nous avons ensuite modélisé les précipités par deux dislocations dissociées parfaitement identifiées de type a/6 qui participent au mécanisme de croissance des phases T1. Par ailleurs, nous avons développé plusieurs modèles basés sur la théorie des dislocations et sur la résolution des équations de la micromécanique dans le réseau réciproque en élasticité linéaire et isotrope, afin de reproduire les champs de déformations induits par les phases durcissantes dans la matrice d'aluminium. Cette approche, couplée à nos observations en MEHR, nous a permis de proposer une description des champs de déformation en extrémité de précipité en accord avec l'expérience.In aeronautics, structural hardening is one of the best ways to improve mechanical properties of metal alloys and to make the structures lighter. The structural hardening of the Al-Li-Cu alloys of the 2000 series is due to T1 precipitates (Al2CuLi) which modify locally the matrix which surround them. To understand the mechanism of deformation at a micro scale, we need to know the interactions between dislocations and hardening phases. Consequently, a precise characterization of strains is required. To do that, experimental techniques, which are supported by models, have been developed. Using high resolution electronic transmission microscopy (HREM) and geometrical phase analysis (GPA), a method is proposed to measure strains in three directions of the space. Then, the precipitates were modeled by two dissociated dislocations which are perfectly identified as a/6. The growth mechanism of T1 phases is based on the presence of these dislocations. Other models have been developed to reproduce the strains created in the matrix by the precipitate. They are based on the dislocation theory and the resolution of the equations of micromechanics in the reciprocal space using isotropic and linear elasticity. By employing those models, we are able to propose a description of the strains near the tips of precipitates which is in agreement with the HREM observations

High-order discrete ordinate transport in hexagonal geometry: A new capability in ERANOS

This paper presents the implementation of an arbitrary order discontinuous Galerkin scheme within the framework of a discrete ordinate solver of the neutron transport equation for nuclear reactor calculations. More precisely, it deals with non-conforming spatial meshes for the 2D and 3D modeling of core geometries based on hexagonal assemblies. This work aims at improving the capabilities of the ERANOS code system dedicated to fast reactor analysis and design. Both the angular quadrature and spatial scheme peculiarities for hexagonal geometries are presented. A particular focus is set on the spatial non-conforming mesh and variable order capabilities of this scheme in anticipation to the development of spatial adaptiveness algorithms. These features are illustrated on a 3D numerical benchmark with comparison to a Monte Carlo reference and a 2D benchmark that shows the potential of this scheme for both h- and p-adaptation