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DLA based compressed sensing for high resolution MR microscopy of neuronal tissue
No full textInternational audienc
Theoretical Aspects of Computing - ICTAC 2015: 12th International Colloquium, Cali, Colombia, October 29-31, 2015, Proceedings
No full textInternational audienceThis volume contains the papers presented at ICTAC 2015: The 12th InternationalColloquium on Theoretical Aspects of Computing held during October 29–31, 2015, inCali, Colombia.The International Colloquia on Theoretical Aspects of Computing (ICTAC) is aseries of annual events founded in 2003 by the United Nations University InternationalInstitute for Software Technology. Its purpose is to bring together practitioners andresearchers from academia, industry, and government to present research results andexchange experience and ideas. Beyond these scholarly goals, another main purpose isto promote cooperation in research and education between participants and theirinstitutions from developing and industrial regions.The city of Cali, where this year’s ICTAC took place, is the third largest city ofColombia and the seat of six major universities of the country. The UniversidadJaveriana-Cali, host of the colloquium, has built a reputation on theoretical computerscience through the works of Avispa, a research team founded in the Cali-based universitiesof Javeriana and Universidad del Valle, with active members in the universitiesof Cork (Ireland), École Polytechnique-Paris (France), Oxford (UK), andGroningen (The Netherlands). The latter three institutions were co-organizers of thisyear’s colloquium, which was also sponsored by Microsoft Research Center, Inria,CNRS, CLEI, and the Colombian Computation Society.We were honored to have seven distinguished guests as invited speakers:– Jean-Raymond Abrial (consultant, France)– Volker Diekert (University of Stuttgart, Germany)– César Muñoz (NASA Langley, USA)– Catuscia Palamidessi (Inria and École Polytechnique, France)– Davide Sangiorgi (Inria and University of Bologna, Italy)– Moshe Vardi (Rice University, USA)– Glynn Winskel (University of Cambridge, UK)Jean-Raymond Abrial’s talk undertook the study of a proof of a well-known theorem inplanar graphs to motivate the new discipline of mathematical engineering. VolkerDiekert discussed different monitor constructions for checking safety properties ofcomplex systems. César A. Muñoz’s talk concerned the application of formal methodsto the safety analysis of air traffic management systems. He described the detect andavoid (DAA) capability to address the challenge of NASA’s Unmanned AircraftSystems Integration project. Catuscia Palamidessi’s talk discussed the problem ofprotecting the privacy of the user when dealing with location-based services. DavideSangiorgi presented his work on refinements of co-inductive proof methods for functionaland process languages. He discussed the contraction technique that refinesMilner’s unique solution of equations to reason about bisimilarity. Glynn Winskeldiscussed his work on optimal probabilistic strategies for distributed games. MosheVardi’s talk described the rise and fall of mathematical logic in computer science andthen analyzed the quiet revolution in logic that has given rise again to modern applicationsof logic to computing.ICTAC 2015 received 93 submissions from 30 different countries. Each submissionwas reviewed by at least three members of the Program Committee, along with helpfrom external reviewers. Out of these 93 submissions, 25 full-length papers wereaccepted. The committee also accepted two short papers and three tool papers. Thiscorresponds approximately to a 1/3 acceptance ratio.Apart from the paper presentations and invited talks, ICTAC 2015 continued thetradition of previous ICTAC conferences in holding a four-course school on threeimportant topics in theoretical aspects of computing: formal methods and verification,formal models of concurrency, and security in concurrency. These courses were:“Formal Modeling” given by Jean-Raymond Abrial (France), “Formal VerificationTechniques,” by Martin Leucker (University of Lübeck, Germany), “Security andInformation Flow,” by Kostas Chatzikokolakis (CNRS-École Polytechnique, France),and “Models for Concurrency” by Pawel Sobocinski (University of Southampton, UK).In addition, co-located for the first time with ICTAC, we hosted the 11th InternationalWorkshop on Developments in Computational Models (DCM 2015) chaired by CésarA. Muñoz (NASA) and Jorge A. Pérez (University of Groningen).We thank all the authors for submitting their papers to the conference, and theProgram Committee members and external reviewers for their excellent work inthe review, discussion, and selection process. We are indebted to all the members of theOrganizing Committee for their hard work in all phases of the conference. We alsoacknowledge our gratitude to the Steering Committee for their constant support.We are also indebted to EasyChair that greatly simplified the assignment andreviewing of the submissions as well as the production of the material for the proceedings.Finally, we thank Springer for their cooperation in publishing theproceedings
Hungarian Scaling of Polynomial Eigenproblems
No full textMinisymposia "Matrix Scaling - Theory and Algorithms"International audienceWe study the behaviour of the eigenvalues of a parametric matrix polynomial P in a neighbourhood of zero. If we suppose that the entries of P have Puiseux series expansions we can build an auxiliary matrix polynomial Q whose entries are the leading exponents of those of P. We show that preconditioning P via a diagonal scaling based on the tropical eigenvalues of Q can improve conditioning and backward error of the eigenvalues
Optimal Design for Purcell Three-link Swimmer
No full textInternational audienceIn this paper we address the question of the optimal design for the Purcell 3-link swimmer. More precisely we investigate the best link length ratio which maximizes its displacement. The dynamics of the swimmer is expressed as an ODE, using the Resistive Force Theory. Among a set of optimal strategies of deformation (strokes), we provide an asymptotic estimate of the displacement for small deformations, from which we derive the optimal link ratio. Numerical simulations are in good agreement with this theoretical estimate, and also cover larger amplitudes of deformation. Compared with the classical design of the Purcell swimmer, we observe a gain in displacement of roughly 60%
Performance Analysis of AlxGa1-xAs/epi-Si(Ge) Tandem Solar Cells: A Simulation Study
No full textInternational audienceA new strategy for the development of III-V/Si tandem solar cells has recently been proposed consisting in low temperature PECVD epitaxy of silicon or silicon-germanium on gallium-arsenide. This paper thus gives first insights about theoretical but realistic maximum performance of such tandem cells by means of full numerical simulations considering perfect layers and interfaces. The consequences of using a thin epi-Si bottom cell instead of a thick silicon substrate are investigated. In case no light trapping scheme is considered, a minimum epi-layer thickness of 20 μm is mandatory for the tandem to exhibit higher conversion efficiencies than a single GaAs solar cell. The epi-Si can yet be advantageously replaced by an epitaxial silicon-germanium alloy to increase the bottom cell optical absorption and thus decrease the minimum required thickness by a factor of ∼4 (∼5 μm). Finally, simulations show that over 33% efficiency can be obtained for AlxGa1-xAs/epi-Si0.63Ge0.27, which confirms that this is a promising new concept
Commande optimale
No full textArticle pour l'encyclopédie des sciences de l'ingénieurThe optimal control theory analyzes how to optimize dynamical systems with various criteria : reach a target in minimal time or minimal energy, maximize the efficiency of an industrial process for instance. This involves the optimization of both time independent parameters, and the control variables that are function of time. The article analyzes the first and second order optimality conditions, and the ways to solve them, by time discretization, the shooting algorithm, or dynamic programming.L'objet de la commande optimale est l'optimisation de systèmes dynamiques suivant différents objectifs : atteinte d'une cible en temps ou énergie minimale, maximisation du rendement d'un processus industriel par exemple. Pour cela on joue à la fois sur des paramètres indépendants du temps et sur les commandes qui, elles, dépendent du temps. L'article analyse les conditions d'optimalité du premier et second ordre, et leur résolution par discrétisation temporelle, algorithme de tir, ou programmation dynamique
Hydrological processes as seen with high resolution distributions of δD derived from IASI/MetOp
No full textInternational audienceThe interest for observations of the water isotopic ratio in the vapor has rapidly increased this last decade. Some of the remote sounders in orbit can be used to derive information on the deuterium isotopic ratio, δD, with the great advantage to be able to provide global data. The Infrared Atmospheric Sounding Interferometer (IASI) operational since 2007 for a 15 to 20 years period can provide δD estimates in the free troposphere at high spatio-temporal resolution, allowing for unprecedented daily analyses of the isotopic variations in the troposphere. After a summary of IASI capabilities to retrieve vertical profile of δD - which is mainly sensitive in the free troposphere - we present newly available δD distributions derived from IASI and explore how they can contribute to improve our understanding of several aspects of the hydrological cycle.Among the different hydrological processes seen with IASI we emphasis on the role of the convection. In the tropics, we noticed that the isotopic composition in the free troposphere is sensitive to the height of convection: regions where the convection is the highest show depleted δD values while regions associated to shallow convection are more enriched. This finding could help to evaluate the representation of deep and shallow convection in GCMs (General Circulation Model) which has been suggested to be in a great part associated with the climate sensitivity uncertainty.The interest of IASI measurements is further illustrated with examples of enriched water vapour above and around the tropical continents that indicate an important contribution of the evapotranspiration on the water budget. We also investigate the differences between the Northern and Southern hemispheres during the water vapour transport poleward
Geostrophic vs magneto-geostrophic adjustment and nonlinear magneto-inertia-gravity waves in rotating shallow water magnetohydrodynamics
No full textInternational audienceThe evolution of localised jets and periodic nonlinear waves in rotating shallow water magnetohydrodynamics (rotating SWMHD) and standard rotating shallow water model (RSW) is compared within the framework of translationally-invariant 1.5-dimensional configurations, which are traditionally used in geophysical fluid dynamics for studying geostrophic adjustment and frontogenesis. Such configurations also allow for exact nonlinear wave solutions in both models. A theory of the magneto-geostrophic adjustment, i.e. adjustment of an arbitrary initial configuration to a state of magneto-geostrophic equilibrium in RSWMHD, is developed and confirmed by numerical simulations with a finite-volume well-balanced code. The code is resolving all kinds of waves in the model and corresponding weak solutions equally well. It is benchmarked by reproducing exact solutions -- steady essentially nonlinear Alfvèn and mixed magneto-inertia-gravity waves -- and used to demonstrate robustness of these solutions with respect to localised along-wave perturbations. It is also shown how the results on adjustment can be extended to the fully 2-dimensional case
Méthodes qualitative pour les milieux hétérogènes
No full textThis thesis focuses on non destructive testing of concrete using ultrasonic waves, and thus examines imagingin complex heterogeneous media. We assume that measurements are multistatic, which means that we record the totalfield on different points by using several sources. For this type of data we wish to build methods that are able to imageinclusions or defects that contributed to the measured field. We focus in this work on the extension of so called samplingmethods to deal with the over-mentioned application where the main additional difficulty is the lack of knowledge ofthe reference media (media without defects, also referred to as background media). The first part of this thesis consistsof a new theoretical analysis of the Linear Sampling Method leading to new mathematically sound formulation of thismethod. Such analysis is done in the framework of regularization theory, and our main contribution is to provide andanalyze a regularization term that ensures exact characterization of the shape in terms of measured data. We also provethat one is able to reconstruct from regularized solutions a sequence of functions that strongly converges to the solutionof the so-called interior transmission problem. This result gives a central place to the interior transmission problemas it allows describing the asymptotic behaviour of our regularized problem. More importantly it also allows us tocompare solutions coming from two different datasets. Based on the result of this comparison, we manage to producean image of the connected components of the background that contain the defects appearing between two measurementcampaigns and this is regardless of background “microstructure”. This strategy is well suited for applications to concrete-like backgrounds as shown on several numerical examples with realistic concrete-like microstructures. Finally, we extendour theoretical results to the case of limited aperture, anisotropic medium and elastic waves, which correspond to thereal physics of the ultrasounds.Motivée par le contrôle non destructif par ultrasons du béton cette thèse s’intéresse à la problématiquede l’imagerie à l’aide d’ondes dans des milieux hétérogènes. On se place dans un contexte de mesures multistatiques,c’est-à-dire qu’il est possible de disposer du champ total en plusieurs points de mesure excités par des sourcesindépendantes. Il est alors proposé de développer des méthodes pour réaliser une image de l’inclusion ou du défautqui a contribué au champ mesuré. Plus précisément on souhaite étendre les méthodes de sampling pour traiter cetteapplication dans le cas où on manque de connaissance sur le milieu de référence (le milieu sans défaut). La premièrepartie de cette thèse a consisté en une nouvelle analyse théorique de la Linear Sampling Method qui a conduit à unenouvelle formulation plus rigoureuse. Cette analyse est faite dans le cadre de la théorie de la régularisation, notreprincipale contribution est d’avoir proposé et analysé un terme de régularisation qui assure une caractérisation exactede la forme du défaut en fonction des données mesurées. Nous avons également démontré que l’on peut construire àpartir des solutions du problème régularisé une suite de fonction qui converge fortement vers la solution du problèmede transmission intérieure. Cette propriété donne un rôle central au problème de transmission intérieure dans le sensoù il permet de décrire le comportement limite de notre solution régularisé. Plus encore cela permet de comparer lessolutions provenant de deux campagnes de mesure différentes. Pour ce faire, une méthode permettant de construire uneimage de la composante connexe du milieu qui contient le défaut qui est apparu entre deux campagnes de mesure estproposée et ce indépendamment du milieu dans lequel le défaut est apparu. Cette méthode d’imagerie différentielleest particulièrement adaptée aux milieux constitués d’un ensemble d’hétérogénéités disjointes, ce qui correspond au casdu béton. Des résultats numériques illustrent son application sur un milieu constitué d’une microstructure simulant lebéton. Finalement, nous montrons que nos résultats, développés dans un cadre d’ondes acoustiques en milieu isotropeavec une émission/acquisition en ouverture totale, s’étendent aux mesures en ouverture limitée, aux milieux anisotropeset aux ondes élastiques qui correspondent à la physique réelle des ultrasons