Patient-specific anisotropic model of human trunk based on MR data

There are many ways to generate geometrical models for numerical simulation, and most of them start with a segmentation step to extract the boundaries of the regions of interest. This paper presents an algorithm to generate a patient-specific three-dimensional geometric model, based on a tetrahedral mesh, without an initial extraction of contours from the volumetric data. Using the information directly available in the data, such as gray levels, we built a metric to drive a mesh adaptation process. The metric is used to specify the size and orientation of the tetrahedral elements everywhere in the mesh. Our method, which produces anisotropic meshes, gives good results with synthetic and real MRI data. The resulting model quality has been evaluated qualitatively and quantitatively by comparing it with an analytical solution and with a segmentation made by an expert. Results show that our method gives, in 90% of the cases, as good or better meshes as a similar isotropic method, based on the accuracy of the volume reconstruction for a given mesh size. Moreover, a comparison of the Hausdorff distances between adapted meshes of both methods and ground-truth volumes shows that our method decreases reconstruction errors faster. Copyright © 2015 John Wiley & Sons, Ltd.Natural Sciences and Engineering Research Council (NSERC) of Canada and the MEDITIS training program (´Ecole Polytechnique de Montreal and NSERC)

Verified Interval Orbit Propagation in Satellite Collision Avoidance

Verified interval integration methods enclose a solution set corresponding to interval initial values and parameters, and bound integration and rounding errors. Verified methods suffer from overestimation of the solution, i.e., non-solutions are also included in the solution enclosure. Two verified integration methods, interval Taylor-series and Taylor-model based methods and their implementation in VNODE-LP and VSPODE, are used to reduce overestimation in verified satellite orbit propagation. Furthermore, two orbital state models based on integration constants, the modified equinoctial elements (MEE) and unified state model (USM), are used to reduce overestimation. Earth-satellite trajectories propagated using VSPODE have 2-3 times less overestimation than those propagated using VNODE-LP. Using the USM and MEE state models, overestimation is further reduced by a factor 4 to 10, depending on initial and parameter uncertainties. It is demonstrated that verified collision detection is feasible and may contribute to prevent satellite collisions to reduce future space debris.Space EngineeringAerospace Engineerin